JP2014031491A - Styrene-based resin composition, planar molded article and light guide plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a styrene-based resin composition excellent in colorless transparency, which prevents a whitening phenomenon by environmental changes and is particularly suitable for an optical use such as a light guide plate.SOLUTION: The styrene-based resin composition comprises a styrene-based resin having a weight average molecular weight of 150000 to 700000 and a polyoxyethylene type nonionic surfactant, in which the content of the polyoxyethylene type nonionic surfactant is 0.4 to 2.0 mass% in 100 mass% of the styrene-based resin composition.

Description

  The present invention relates to a styrene-based resin composition, a plate-shaped molded article, and a light guide plate, which do not cause a whitening phenomenon due to environmental changes, have excellent hue and transparency, and are suitable for light guide plate applications.

There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The An acrylic resin typified by PMMA (polymethylmethacrylate) is used for the light guide plate. However, since the water absorption is high, there may be a problem that the molded product is warped or a change in dimensions.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
However, Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylic ester copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water-absorbing property and the dimensional stability tend to be worse than those of the styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, there is a problem (whitening phenomenon) that a molded product becomes cloudy due to environmental changes such as temperature and humidity. Specifically, when a molded product is exposed to an environmental change from a high-temperature and high-humidity environment to a room temperature environment or an environmental change from a room temperature environment to a low-temperature environment, moisture that was present uniformly in the molded product. Becomes unstable and phase-separates to form a disk-like defect. As a result, the inside of the molded product becomes cloudy. When the molded product becomes cloudy, when the optical path length is long as in the light guide plate, there is a problem that the transmittance is greatly reduced due to light scattering and the luminance of the display is lowered.

Japanese Patent Laid-Open No. 2003-075648

  An object of the present invention is to provide a styrenic resin composition that prevents whitening due to environmental changes, has excellent colorless transparency, and is particularly suitable for optical applications such as a light guide plate and has heat resistance.

（式中、Ｒは炭素数８〜２０のアルキル基を示し、ｎは整数でエチレンオキサイド単位の付加モル数を表す）
（３）（１）又は（２）に記載のスチレン系樹脂組成物を成形してなる板状成形品。
（４）（３）に記載の板状成形品からなる導光板。 The present invention is (1) a styrene resin composition comprising a styrene resin having a weight average molecular weight of 150,000 to 700,000 and a polyoxyethylene type nonionic surfactant, which is 100% by mass of the styrene resin composition. The content of the polyoxyethylene type nonionic surfactant in the content is 0.4 to 2.0% by mass.
(2) The polyoxyethylene type nonionic surfactant is at least one selected from the group of polyoxyethylene alkyl ether represented by the following general formula 1 and / or polyoxyethylene fatty acid ester represented by the following general formula 2. The styrenic resin composition according to claim 1, wherein the ethylene oxide has an average added mole number of 7 to 100.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms, and n is an integer representing the number of added moles of ethylene oxide units)
(3) A plate-like molded product obtained by molding the styrene resin composition according to (1) or (2).
(4) A light guide plate comprising the plate-like molded product according to (3).

  The styrene resin composition of the present invention has low water absorption and is inexpensive compared to PMMA and MS resin, and does not cause whitening due to environmental changes, which is a disadvantage of PS resin, and is excellent in colorless transparency. It can be suitably used for optical applications such as a light guide plate.

  The styrene resin of the present invention can be obtained by polymerizing a styrene monomer. The styrene monomer is an aromatic vinyl monomer, such as styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, or a mixture of two or more, preferably styrene.

  Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.

  A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.

  In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.

The styrene resin of the present invention has a weight average molecular weight of 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer The molecular weight of the present invention is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.

  The styrene resin composition of the present invention contains (c) a polyoxyethylene type nonionic surfactant (also referred to as a polyethylene glycol type nonionic surfactant) in 100% by mass of the styrene resin composition, Content is 0.4-2.0 mass%, and it is preferable that it is 0.7-1.6 mass%. If the content of the polyoxyethylene type nonionic surfactant is less than 0.4% by mass, it is difficult to prevent the whitening phenomenon due to environmental changes. If the content exceeds 2.0% by mass, the heat resistance of the styrene-based resin composition is reduced. descend.

（式中、Ｒは炭素数８〜２０のアルキル基を示し、ｎは整数でエチレンオキサイド単位の付加モル数を表す） Polyoxyethylene type nonionic surfactants include polyoxyethylene alkyl ether represented by the following general formula (1), polyoxyethylene fatty acid ester represented by the following general formula (2), polyoxyethylene hydrogenated castor oil, polyoxy Ethylene sorbitan fatty acid ester and polyoxyethylene sorbitol fatty acid ester are exemplified, but one or more selected from the group of polyoxyethylene alkyl ether and / or polyoxyethylene fatty acid ester are preferable.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms, and n is an integer representing the number of added moles of ethylene oxide units)

  Polyoxyethylene alkyl ether is made by adding ethylene oxide to alcohol, and polyoxyethylene fatty acid ester is made by adding ethylene oxide to fatty acid or directly esterifying fatty acid and polyethylene glycol. The number is preferably 7 to 100, and more preferably 10 to 50.

  Examples of the polyoxyethylene alkyl ether include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene octyl decyl ether, polyoxyethylene myristyl ether, polyoxyethylene-2-ethylhexyl ether and the like. Is mentioned.

  Examples of the polyoxyethylene fatty acid ester include polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, and the like.

  As a method for adding the polyoxyethylene type nonionic surfactant of the present invention, it is added and mixed by a method of adding and mixing in a polymerization step, a devolatilization step, and a granulation step of a styrenic resin, an extruder at the time of molding, or the like. Examples of the method include, but are not limited to.

  The Vicat softening temperature of the styrene-based resin composition of the present invention is preferably 95 to 104 ° C, and more preferably 97 to 104 ° C. When the Vicat softening temperature is less than 95 ° C., the heat resistance is insufficient, and the molded product may be deformed depending on the use environment.

  The styrenic resin composition of the present invention may contain mineral oil as long as the colorless transparency of the present invention is not impaired. In addition, internal lubricants such as stearic acid and ethylenebisstearic acid amide, hindered phenol antioxidants, phosphorus antioxidants, sulfur antioxidants, lactone antioxidants, hindered amine stabilizers, UV absorbers In addition, additives such as an antistatic agent may be contained. As the external lubricant, ethylene bis stearamide is preferable, and the content is preferably 30 to 200 ppm in the resin composition.

  The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. For example, benzophenone, benzotriazole, triazine, benzoate, salicylate, cyanoacrylate, oxalic anilide, malonic ester UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.

  The styrenic resin composition of the present invention can be molded into a plate-shaped product by a molding method according to the purpose such as injection molding, extrusion molding, compression molding, etc., and used as a light guide plate. At that time, a reflection pattern such as a dot pattern can be provided on the back surface (opposite side of the light emitting surface) of the plate-shaped molded product, and used as a light guide plate. When processing from the resin plate to the light guide plate, it is preferable to polish the light incident surface or the entire end surface of the resin plate to make a mirror surface. In addition, in order to improve the uniformity of the emitted light, a prism pattern can be provided on the surface (surface from which light is emitted) of the plate-shaped molded product. The pattern on the front surface or the back surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.

(Examples 1-13, Comparative Examples 1-3)
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A mixed solution of 84.0% by mass of styrene and 16.0% by mass of ethylbenzene was prepared, and 400 ppm of 2,2-bis (4,4-t-butylperoxycyclohexyl) propane was mixed on the basis of styrene, A raw material solution was obtained. As 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, Pertetra A manufactured by NOF Corporation was used. This raw material solution was continuously supplied to the first reactor at a rate of 11.2 kg / hour. The reaction temperature of each reactor is 116 ° C. in the first reactor, 120 ° C. in the second reactor, and in the third reactor, a temperature gradient is created along the direction of flow, 140 ° C. in the middle portion, and in the outlet portion. The temperature was adjusted to 150 ° C.
Further, a polyoxyethylene type nonionic surfactant was added to the inlet of the third reactor so as to have the types and contents shown in Table 1. The types of polyoxyethylene type nonionic surfactants are as follows.
P-1: Polyoxyethylene ethylene lauryl ether Ethylene oxide average added mole number = 25 (Emalgen 123P manufactured by Kao Corporation)
P-2: Polyoxyethylene ethylene stearyl ether ethylene oxide average added mole number = 12 (Emulgen 320P manufactured by Kao Corporation)
P-3: Polyoxyethylene ethylene lauryl ether Ethylene oxide average addition mole number = 9 (Emulgen 109P manufactured by Kao Corporation)
P-4: Polyoxyethylene ethylene cetyl ether Average number of moles of ethylene oxide added = 7 (Emulgen 210P manufactured by Kao Corporation)
P-5: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 30 (Emulgen 130K manufactured by Kao Corporation)
P-6: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 47 (Emulgen 150 manufactured by Kao Corporation)
P-7: Polyoxyethylene ethylene myristyl ether Ethylene oxide average addition mole number = 85 (Emulgen 4085 manufactured by Kao Corporation)
P-8: Polyethylene glycol monolaurate Ethylene oxide average added mole number = 12 (Emanon 1112 manufactured by Kao Corporation)
P-9: polyoxyethylene ethylene stearyl ether ethylene oxide average addition mole number = 6 (Emulgen 306P manufactured by Kao Corporation)
Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted of two stages in series, and after separating unreacted styrene and ethylbenzene, a strand shape After being extruded and cooled, it was cut into pellets. The resin temperature in the first stage devolatilization tank is set to 160 ° C., the pressure in the vacuum devolatilization tank is set to 65 kPa, the resin temperature in the second stage devolatilization layer is set to 235 ° C. The pressure in the volatilization tank was 0.8 kPa.

The weight average molecular weights (Mw) of the obtained styrene resin compositions were all 370,000. In addition, the melt mass flow rate (MFR) is in accordance with JIS K-7210, under conditions of 200 ° C. and 49 N load, the Vicat softening temperature is in accordance with JIS K 7206, the heating rate is 50 ° C./hr, and the test load is 50 N. Measured with
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. A test piece having a thickness of 115 × 85 × 3 mm was cut out from the obtained plate-shaped product, and the end surface was polished by buffing to obtain a plate-shaped product having a mirror surface on the end surface. About the obtained plate-shaped molded article, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a spread angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance shown in Table 1 represents an average transmittance at a wavelength of 380 nm to 780 nm.
Furthermore, in order to confirm the whitening phenomenon due to environmental changes, a plate-like molded article having a mirror surface on the end face is exposed to an environment of 60 ° C. and 90% relative humidity for 150 hours, and the test piece is placed in an environment of 23 ° C. and 50% relative humidity. Taking out and observing the whitening phenomenon occurring inside the molded product, the following judgment was made as a whitening suppression effect.
A: No whitening occurs. O: Whitening occurs slightly after 1 hour, but disappears after 24 hours. Δ: Whitening occurs after 1 hour, but almost disappears after 24 hours. X: Remarkably whitening after 1 hour. Table 1 shows the properties of each resin composition.

  The molded articles of the examples are excellent in whitening suppression effect, are excellent in transparency and hue without deterioration in transmittance and YI value.

  The styrenic resin composition of the present invention prevents lightening due to environmental changes and is excellent in transparency and hue, so that it can be used for light guide plates in televisions, desktop personal computers, notebook personal computers, mobile phones, car navigation systems, etc. Can be suitably used.

[００２３]
実施例の成形品は、白化抑制効果に優れ、透過率とＹＩ値の悪化もなく透明性と色相にも優れている。
[産業上の利用可能性]
[００２４]
本発明のスチレン系樹脂組成物は、環境変化による白化現象が防止され、透明性と色相に優れることから、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 1)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
A styrene resin composition comprising a styrene resin having a weight average molecular weight of 150,000 to 700,000 and polyethylene glycol, wherein the content of polyethylene glycol in 100% by mass of the styrene resin composition is 0.4 to 2.0. A styrenic resin composition, characterized in that the content is% by mass.
[Claim 2]
Vicat softening temperature is 95-104 degreeC, The styrene resin composition of Claim 1 characterized by the above-mentioned.
[Claim 3]
A plate-like molded article formed by molding the styrene-based resin composition according to claim 1 or 2.
[Claim 4]
A light guide plate comprising the plate-like molded product according to claim 3.
[Document Name] Statement
[Title of Invention] Styrenic resin composition, plate-shaped molded article and light guide plate
[Technical field]
[0001]
The present invention relates to a styrene-based resin composition, a plate-shaped molded article, and a light guide plate, which do not cause a whitening phenomenon due to environmental changes, have excellent hue and transparency, and are suitable for light guide plate applications.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The An acrylic resin typified by PMMA (polymethylmethacrylate) is used for the light guide plate. However, since the water absorption is high, there may be a problem that the molded product is warped or a change in dimensions.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
However, Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylic ester copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water-absorbing property and the dimensional stability tend to be worse than those of the styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, there is a problem (whitening phenomenon) that a molded product becomes cloudy due to environmental changes such as temperature and humidity. Specifically, when a molded product is exposed to an environmental change from a high temperature and high humidity environment to a room temperature environment or an environmental change from a room temperature environment to a low temperature environment, moisture present uniformly in the molded product is not present. It becomes stable and phase-separates, and a disk-like defect is generated. As a result, the inside of the molded product becomes cloudy. When the molded product becomes cloudy, when the optical path length is long as in the light guide plate, there is a problem that the transmittance is greatly reduced due to light scattering and the luminance of the display is lowered.
[Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
An object of the present invention is to provide a styrenic resin composition that prevents whitening due to environmental changes, is particularly suitable for optical applications such as a light guide plate, has excellent colorless transparency, and also has heat resistance.
[Means for solving problems]
[0005]
The present invention is (1) a styrene resin composition comprising a styrene resin having a weight average molecular weight of 150,000 to 700,000 and polyethylene glycol, wherein the content of polyethylene glycol in 100% by mass of the styrene resin composition is A styrene-based resin composition, which is 0.4 to 2.0% by mass.
(2) The styrenic resin composition according to (1), wherein the Vicat softening temperature is 95 to 103 ° C.
(3) A plate-like molded product obtained by molding the styrene resin composition according to (1) or (2).
(4) A light guide plate comprising the plate-like molded product according to (3).
[Effect of the invention]
[0006]
The styrene resin composition of the present invention has low water absorption and is inexpensive compared to PMMA and MS resin, and does not cause whitening due to environmental changes, which is a disadvantage of PS resin, and is excellent in colorless transparency. It can be suitably used for optical applications such as a light guide plate.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin of the present invention can be obtained by polymerizing a styrene monomer. The styrene monomer is an aromatic vinyl monomer, such as styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, or a mixture of two or more, preferably styrene.
[0008]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0009]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0010]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0011]
The styrene resin of the present invention has a weight average molecular weight of 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer The molecular weight of the present invention is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0012]
The styrenic resin composition of the present invention comprises a styrenic resin and polyethylene glycol. In 100% by mass of the styrene-based resin composition, the content of polyethylene glycol is 0.4 to 2.0% by mass, preferably 0.6 to 1.6% by mass, and 0.6 to 1.2%. More preferably, it is mass%. If the polyethylene glycol content is less than 0.4% by mass, it is difficult to prevent the whitening phenomenon due to environmental changes, and if it exceeds 2.0% by mass, the heat resistance of the styrene-based resin composition decreases.
[0013]
The average molecular weight of the polyethylene glycol used in the present invention is preferably 200 to 4000, and more preferably 300 to 1000. If the average molecular weight of polyethylene glycol is less than 200, gas is generated during the molding process, and the mold and roll are soiled, which is not preferable. On the other hand, if it exceeds 4000, the effect of preventing the whitening phenomenon tends to decrease. The average molecular weight is calculated from the hydroxyl group concentration (based on JIS K1557) measured by the pyridine phthalic anhydride method.
[0014]
Examples of the method for adding the polyethylene glycol of the present invention include a method of adding and mixing in the polymerization step, devolatilization step, and granulating step of the styrene resin, and a method of adding and mixing with an extruder at the time of molding, and the method is particularly limited. Is not.
[0015]
The Vicat softening temperature of the styrene-based resin composition of the present invention is preferably 95 to 104 ° C, and more preferably 97 to 104 ° C. When the Vicat softening temperature is less than 95 ° C., the heat resistance is insufficient, and the molded product may be deformed depending on the use environment.
[0016]
The styrenic resin composition of the present invention may contain mineral oil as long as the colorless transparency of the present invention is not impaired. In addition, internal lubricants such as stearic acid and ethylenebisstearic acid amide, hindered phenol antioxidants, phosphorus antioxidants, sulfur antioxidants, lactone antioxidants, hindered amine stabilizers, UV absorbers In addition, additives such as an antistatic agent may be contained. As the external lubricant, ethylene bis stearamide is preferable, and the content is preferably 30 to 200 ppm in the resin composition.
[0017]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0018]
The styrenic resin composition of the present invention can be molded into a plate-shaped product by a molding method according to the purpose such as injection molding, extrusion molding, compression molding, etc., and used as a light guide plate. At that time, a reflection pattern such as a dot pattern can be provided on the back surface (opposite side of the light emitting surface) of the plate-shaped molded product, and used as a light guide plate. When processing from the resin plate to the light guide plate, it is preferable to polish the light incident surface or the entire end surface of the resin plate to make a mirror surface. In addition, in order to improve the uniformity of the emitted light, a prism pattern can be provided on the surface (surface from which light is emitted) of the plate-shaped molded product. The pattern on the front surface or the back surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0019]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0020]
(Examples 1-11, Comparative Examples 1-3)
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A mixed solution of 84.0% by mass of styrene and 16.0% by mass of ethylbenzene was prepared, and 400 ppm of 2,2-bis (4,4-t-butylperoxycyclohexyl) propane was mixed on the basis of styrene, A raw material solution was obtained. As 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, Pertetra A manufactured by NOF Corporation was used. This raw material solution was continuously supplied to the first reactor at a rate of 11.2 kg / hour. The reaction temperature of each reactor is 116 ° C. in the first reactor, 120 ° C. in the second reactor, and in the third reactor, a temperature gradient is created along the direction of flow, 140 ° C. in the middle portion, and in the outlet portion. The temperature was adjusted to 150 ° C.
In addition, polyethylene glycol was added to the inlet of the third reactor so as to have the types and contents shown in Table 1-1. The types of polyethylene glycol are as follows.
P-1: Polyethylene glycol having an average molecular weight of 400 (PEG # 400 manufactured by NOF Corporation)
P-2: Polyethylene glycol having an average molecular weight of 300 (PEG # 300 manufactured by NOF Corporation)
P-3: Polyethylene glycol having a weight average molecular weight of 600 (PEG # 600 manufactured by NOF Corporation)
P-4: Polyethylene glycol having a weight average molecular weight of 1000 (PEG # 1000 manufactured by NOF Corporation)
P-5: Polyethylene glycol having a weight average molecular weight of 2000 (PEG # 2000 manufactured by NOF Corporation)
P-6: Polyethylene glycol having a weight average molecular weight of 3100 (PEG # 4000 manufactured by NOF Corporation)
P-7: Polyethylene glycol having a weight average molecular weight of 8800 (PEG # 6000 manufactured by NOF Corporation)
Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted of two stages in series, and after separating unreacted styrene and ethylbenzene, a strand shape After being extruded and cooled, it was cut into pellets. The resin temperature in the first stage devolatilization tank is set to 160 ° C., the pressure in the vacuum devolatilization tank is set to 65 kPa, the resin temperature in the second stage devolatilization layer is set to 235 ° C. The pressure in the volatilization tank was 0.8 kPa.
[0021]
All of the obtained styrene resins had a weight average molecular weight (Mw) of 370,000. In addition, the melt mass flow rate (MFR) is in accordance with JIS K-7210, under conditions of 200 ° C. and 49 N load, the Vicat softening temperature is in accordance with JIS K 7206, the heating rate is 50 ° C./hr, and the test load is 50 N. Measured with
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. A test piece having a thickness of 115 × 85 × 3 mm was cut out from the obtained plate-shaped product, and the end surface was polished by buffing to obtain a plate-shaped product having a mirror surface on the end surface. About the obtained plate-shaped molded article, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a spread angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance shown in Table 1-1 represents the average transmittance at a wavelength of 380 nm to 780 nm.
Furthermore, in order to confirm the whitening phenomenon due to environmental changes, a plate-like molded article having a mirror surface on the end face is exposed to an environment of 60 ° C. and 90% relative humidity for 150 hours, and the test piece is placed in an environment of 23 ° C. and 50% relative humidity. Taking out and observing the whitening phenomenon occurring inside the molded product, the following judgment was made as a whitening suppression effect.
A: No whitening occurs. O: Whitening occurs slightly after 1 hour, but disappears after 24 hours. Δ: Whitening occurs after 1 hour, but almost disappears after 24 hours. X: Remarkably whitening after 1 hour. Table 1-1 shows the characteristics of each resin composition.
[0022]
[Table 1-1]

[0023]
The molded articles of the examples are excellent in whitening suppression effect, are excellent in transparency and hue without deterioration in transmittance and YI value.
[Industrial applicability]
[0024]
The styrenic resin composition of the present invention prevents lightening due to environmental changes and is excellent in transparency and hue, so that it can be used for light guide plates such as TVs, desktop personal computers, notebook personal computers, mobile phones, car navigation systems Can be suitably used.

[００２７]
実施例の成形品は、白化抑制効果に優れ、ヘーズとＹＩ値の悪化もなく透明性と色相にも優れている。
[産業上の利用可能性]
[００２８]
本発明のスチレン系樹脂組成物は、従来では環境変化によって白化現象が発生していた用途でも、スチレン系樹脂の長所である透明性を維持することができ、好適に用いることができる。 (Appendix 2)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
A styrene resin composition comprising a styrene resin having a weight average molecular weight of 150,000 to 700,000 and a hydrophilic additive, wherein the content of the hydrophilic additive in 100% by mass of the styrene resin composition is 0.4. Styrenic resin composition characterized by being -2.0 mass%.
[Claim 2]
The styrenic resin composition according to claim 1, which is transparent and suppresses a whitening phenomenon.
[Claim 3]
The styrenic resin composition according to claim 1 or 2, wherein the hydrophilic additive has a polyether chain.
[Claim 4]
The styrene resin composition according to any one of claims 1 to 3, wherein the hydrophilic additive has an HLB value of 10 to 20.
[Document Name] Statement
[Title of the Invention] Styrenic Resin Composition
[Technical field]
[0001]
The present invention relates to a transparent styrenic resin composition in which whitening due to environmental changes is suppressed.
[Background]
[0002]
Styrenic resins have excellent properties such as transparency, rigidity, low water absorption, and dimensional stability, and are excellent in molding processability. Therefore, various types of molding methods such as injection molding, extrusion molding, blow molding, etc. Widely used as industrial materials, food packaging containers, miscellaneous goods and the like. Moreover, it is used also for optical members, such as a light-guide plate, as an application using transparency.
However, the styrene resin has a problem that the molded product becomes clouded due to environmental changes such as temperature, humidity, and warm water immersion (Non-patent Document 1), and the transparency, which is an advantage, may be impaired depending on the application. there were. Specifically, when a molded product was exposed to an environmental change from a high-temperature and high-humidity environment to a room temperature environment or an environment change from a room temperature environment to a low-temperature environment, it was uniformly present in the styrene resin. This is a phenomenon in which moisture becomes unstable and phase separation occurs to form a disk-like defect, and as a result, the inside of the molded product becomes cloudy. In addition, when a molded product of a styrene resin is immersed in warm water for a certain period of time or more and then the molded product is taken out, whitening may occur. This is also a phenomenon caused by the same mechanism.
[Prior art documents]
[Non-patent literature]
[0003]
[Non-Patent Document 1] Journal of Textile Society, Vol. 34, No. 6, pp. 245-253, 1978
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
An object of the present invention is to provide a transparent styrenic resin composition that prevents whitening due to environmental changes.
[Means for solving problems]
[0005]
The present invention is (1) a styrene resin composition comprising a styrene resin having a weight average molecular weight of 150,000 to 700,000 and a hydrophilic additive, the hydrophilic additive in 100% by mass of the styrene resin composition The styrene-based resin composition is characterized by having a content of 0.4 to 2.0% by mass.
(2) The styrenic resin composition according to (2), which is transparent and suppresses the whitening phenomenon.
(3) The styrenic resin composition according to (1) or (2), wherein the hydrophilic additive has a polyether chain.
(4) The styrene resin composition according to any one of (1) to (3), wherein the hydrophilic additive has an HLB value of 10 to 20.
[Effect of the invention]
[0006]
The styrenic resin composition of the present invention does not generate a whitening phenomenon due to environmental changes, which is a drawback of styrenic resins, and therefore can be suitably used for applications that make use of the original transparency.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin of the present invention can be obtained by polymerizing a styrene monomer. The styrene monomer is an aromatic vinyl monomer, such as styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, or a mixture of two or more, preferably styrene. Further, it may be copolymerized with a styrene monomer within the range not impairing the characteristics of the present invention, acrylic acid monomers such as acrylic acid and methacrylic acid, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, and butyl acrylate. , Acrylic monomers such as ethyl acrylate, methyl acrylate, and methyl methacrylate; and α, β-ethylenically unsaturated carboxylic acids such as maleic anhydride and fumaric acid; and imide monomers such as phenyl maleimide and cyclohexyl maleimide. .
[0008]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0009]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0010]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0011]
The styrene resin of the present invention has a weight average molecular weight of 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) are measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer The molecular weight of the present invention is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0012]
The styrene resin composition of the present invention contains a hydrophilic additive in 100% by mass of the styrene resin composition, the content thereof is 0.4 to 2.0% by mass, and 0.7 to 1.6. It is preferable that it is mass%. If the content of the hydrophilic additive is less than 0.4% by mass, it is difficult to prevent the whitening phenomenon due to environmental changes, and if it exceeds 2.0% by mass, the heat resistance of the styrene-based resin composition decreases.
[0013]
The hydrophilic additive of the present invention is a compound having a hydrophilic group capable of interacting with water (hydrogen bonding), and preferably has a polyether chain. A polyether chain is a compound in which ether bonds are linked. For example, a polyoxyethylene chain, a polyoxypropylene chain, a polyoxybutylene chain or glycerin synthesized by an addition reaction of an alkylene oxide such as ethylene oxide, propylene oxide, or butylene oxide. A polyglycerol chain synthesized by dehydration condensation of a polyoxyethylene chain is preferable, and a polyoxyethylene chain is preferable.
[0014]
Examples of the hydrophilic additive of the present invention include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene octyl esyl ether, polyoxyethylene myristyl ether, polyoxyethylene 2-ethylhexyl. Polyoxyethylene alkyl ether such as ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan fatty acid ester such as polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitol fatty acid ester such as polyoxyethylene sorbitol tetraoleate, polyethylene Glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene Polyoxyethylene fatty acid esters such as ethylene glycol monooleate, polyoxyethylene hydrogenated castor oil, polyethylene glycol, polyoxyethylene monomethyl ether, polyoxyethylene dimethyl ether, polyoxyethylene glyceryl ether, polyoxyethylene tetraoleic acid, polyoxyethylene Examples include triisostearic acid, polyoxyethylene coconut fatty acid glyceryl, diglycerin, polyglycerin, polyoxyethylene polyglyceryl ether, and polyglycerin fatty acid ester.
[0015]
The HLB value of the hydrophilic additive of the present invention is preferably 8 or more, and more preferably 10-20. HLB (Hydrophilic-lipophilic balance) is a value representing the hydrophilicity of the additive. When the HLB value is 8 to 10, it is stably dispersed in water, and when it exceeds 10, it completely dissolves transparently from a transparent dispersion state. It becomes a state. For nonionic surfactants having a polyether chain, HLB = (molecular weight of hydrophilic group part) / (molecular weight of additive) × 20, and paraffins that do not contain a hydrophilic group are HLB = 0. In the case of polyethylene glycol having only a hydrophilic group, HLB = 20, and in the case of a nonionic surfactant, HLB is between 0 and 20.
[0016]
The heating loss of the hydrophilic additive of the present invention at a temperature of 200 ° C. and in a nitrogen atmosphere is preferably 10% by mass or less. Heat loss in a nitrogen atmosphere at a temperature of 200 ° C. can be determined by thermogravimetric analysis (TGA). Heating is performed at a temperature increase rate of 10 ° C./min from a room temperature in a nitrogen atmosphere, and the weight loss at a temperature of 200 ° C. It can be determined from the quantity. An additive having a temperature loss of 200 ° C. and a heating loss of more than 10% by mass in a nitrogen atmosphere has high volatility, and gas is generated during the molding process of the styrene-based resin, which may cause mold or roll contamination.
[0017]
Examples of the method of adding the hydrophilic additive of the present invention include a method of adding and mixing in the polymerization step, devolatilization step, and granulating step of the styrenic resin, and a method of adding and mixing with an extruder at the time of molding. It is not limited.
[0018]
The Vicat softening temperature of the styrene-based resin composition of the present invention is preferably 95 to 104 ° C, and more preferably 97 to 104 ° C. When the Vicat softening temperature is less than 95 ° C., the heat resistance is insufficient, and the molded product may be deformed depending on the use environment.
[0019]
The haze of the styrenic resin composition of the present invention is preferably 5% or less, more preferably 1% or less in a molded product having a thickness of 4 mm.
[0020]
The styrenic resin composition of the present invention may contain mineral oil. Also, lubricants (internal lubricant and / or external lubricant) such as stearic acid, fatty acid metal salts, ethylene bis stearamide, hindered phenol antioxidants, phosphorus antioxidants, sulfur antioxidants, lactones Additives such as system antioxidants, hindered amine stabilizers, ultraviolet absorbers and antistatic agents may be included.
[0021]
The styrenic resin composition of the present invention can be used in various molding methods depending on purposes such as injection molding, extrusion molding, blow molding and the like.
[Example]
[0022]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0023]
(Production of styrene resin PS-1)
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A mixed solution of 84.0% by mass of styrene and 16.0% by mass of ethylbenzene was prepared, and 400 ppm of 2,2-bis (4,4-t-butylperoxycyclohexyl) propane was mixed on the basis of styrene, A raw material solution was obtained. As 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, Pertetra A manufactured by NOF Corporation was used. This raw material solution was continuously supplied to the first reactor at a rate of 11.2 kg / hour. The reaction temperature of each reactor is 116 ° C. in the first reactor, 120 ° C. in the second reactor, and in the third reactor, a temperature gradient is created along the direction of flow, 140 ° C. in the middle portion, and in the outlet portion. The temperature was adjusted to 150 ° C. Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted of two stages in series, and after separating unreacted styrene and ethylbenzene, a strand shape After being extruded and cooled, it was cut into pellets. The resin temperature in the first stage devolatilization tank is set to 160 ° C., the pressure in the vacuum devolatilization tank is set to 65 kPa, the resin temperature in the second stage devolatilization layer is set to 235 ° C. The pressure in the volatilization tank was 0.4 kPa.
The obtained styrene resin PS-1 had a weight average molecular weight (Mw) of 370,000, a Z average molecular weight (Mz) of 770,000, and a number average molecular weight (Mn) of 110,000. The amount of residual styrene in the styrene resin was 350 ppm, the amount of residual ethylbenzene was 100 ppm, the amount of styrene dimer was 100 ppm, and the amount of styrene trimer was 3400 ppm.
[0024]
(Examples 1-17, Comparative Examples 1-5)
Using the content shown in Table 2-1, the styrene resin PS-1 and additives were melt kneaded at a cylinder temperature of 230 ° C. and a screw rotation speed of 100 rpm using a single screw extruder with a screw diameter of 40 mm. Obtained. The additives used in Table 2-1 are shown below.
P-1: Polyethylene glycol having an average molecular weight of 400 (PEG # 400 manufactured by NOF Corporation)
P-2: Polyoxyethylene ethylene lauryl ether Ethylene oxide average added mole number = 25 (Emalgen 123P manufactured by Kao Corporation)
P-3: Polyoxyethylene ethylene lauryl ether Ethylene oxide average added mole number = 30 (Emulgen 130K manufactured by Kao Corporation)
P-4: Polyethylene glycol monolaurate Ethylene oxide average added mole number = 12 (Emanon 1112 manufactured by Kao Corporation)
P-5: Polyoxyethylene ethylene cetyl ether Ethylene oxide average addition mole number = 7 (Emalgen 210P manufactured by Kao Corporation)
P-6: Polyoxyethylene ethylene stearyl ether ethylene oxide average addition mole number = 6 (Emulgen 306P manufactured by Kao Corporation)
P-7: Polyoxyethylene hydrogenated castor oil (Emanon CH-40 manufactured by Kao Corporation)
P-8: Polyethylene glycol having a weight average molecular weight of 1000 (PEG # 1000 manufactured by NOF Corporation)
P-9: Polyoxyethylene monomethyl ether (UNIOX M-550 manufactured by NOF Corporation)
P-10: Polyoxyethylene triisostearic acid (Niox GT-20IS manufactured by NOF Corporation)
P-11: Stearyl alcohol (Calcoal 8098 manufactured by Kao Corporation)
P-12: Stearic acid monoglyceride (Excel S-95 manufactured by Kao Corporation)
[0025]
In order to confirm the whitening phenomenon due to environmental changes, injection molding is performed at a cylinder temperature of 220 ° C. and a mold temperature of 40 ° C. using the obtained pellets to form a 55 × 50 × 4 mm thick plate-like molded product. After exposure to an environment of 60 ° C. and 90% relative humidity for 150 hours, the test piece was taken out in an environment of 23 ° C. and 50% relative humidity, and the whitening phenomenon occurring inside the molded product was observed. Judgment was performed.
A: No whitening occurs. O: Whitening occurs slightly after 1 hour, but disappears after 24 hours. Δ: Whitening occurs after 1 hour, but almost disappears after 24 hours. X: Remarkably whitening after 1 hour. In addition, the haze (cloudiness value) was measured according to JIS K-7105 using the same test piece and using NDH5000 (manufactured by Nippon Denshoku Industries Co., Ltd.). Similarly, YI (yellowness) was measured by a reflection method using a colorimetric color difference meter NDJ4000 (manufactured by Nippon Denshoku Industries Co., Ltd.).
Melt mass flow rate is in accordance with JIS K-7210, temperature is 200 ° C. under a load of 49N, and Vicat softening temperature is in accordance with JIS K 7206, with a heating rate of 50 ° C./hr and a test load of 50N. Table 2-1 shows the characteristics of each resin composition.
[0026]
[Table 2-1]

[0027]
The molded articles of the examples are excellent in whitening suppression effect, are excellent in transparency and hue without deterioration of haze and YI value.
[Industrial applicability]
[0028]
The styrenic resin composition of the present invention can maintain transparency, which is an advantage of the styrenic resin, even in applications where a whitening phenomenon has conventionally occurred due to environmental changes.

[００２３]
実施例の成形品は、初期の透過率とＹＩ値に優れており、長期の熱安定性にも優れている。
[産業上の利用可能性]
[００２４]
本発明のスチレン系樹脂組成物からなる板状成形品は、色相および透明性に優れ、長期の熱安定性に優れることから、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 3)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8, A styrene resin composition comprising 10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, wherein (b) in 100% by mass of the styrene resin composition A transparent plate-shaped molded article comprising a styrenic resin composition, wherein the content is 0.05 to 0.40 mass%.
[Claim 2]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8, A styrenic resin composition comprising 10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (c) a hindered phenol antioxidant, the styrenic resin composition The content of (b) in 100% by mass of the product is 0.05 to 0.40% by mass, and the content of (c) is 0.02 to 0.50% by mass. Transparent plate-shaped molded product made of objects.
[Claim 3]
A light guide plate comprising the plate-like molded product according to claim 1.
[Document Name] Statement
[Title of Invention] Plate-shaped molded article and light guide plate made of styrene resin composition
[Technical field]
[0001]
The present invention relates to a plate-shaped molded article and a light guide plate made of a styrenic resin composition having excellent hue and transparency and excellent long-term thermal stability.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The An acrylic resin typified by PMMA (polymethylmethacrylate) is used for the light guide plate. However, since the water absorption is high, there may be a problem that the molded product is warped or a change in dimensions.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
However, Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylic ester copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water-absorbing property and the dimensional stability tend to be worse than those of the styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, there is a problem in that discoloration due to heat occurs during long-term use, the molded product turns yellow, and the transmittance decreases. As a result, there is a problem that the luminance of the display is lowered or the chromaticity is changed.
[Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
It is an object of the present invention to provide a plate-like molded article and a light guide plate made of a styrene resin composition that have small changes in hue and transmittance even after long-term use and are excellent in colorless transparency.
[Means for solving problems]
[0005]
The present invention relates to (1) (a) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy]. A styrene resin composition comprising -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, and having a styrene resin composition of 100 mass % Of (b) is 0.05-0.40 mass%, The transparent plate-shaped molded article which consists of a styrene-type resin composition characterized by the above-mentioned.
(2) (a) Styrenic resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4 , 8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (c) a styrene resin composition comprising a hindered phenol antioxidant, The content of (b) in 100% by mass of the resin-based resin composition is 0.05 to 0.40% by mass, and the content of (c) is 0.02 to 0.50% by mass. A transparent plate-shaped molded article made of a resin composition.
(3) A light guide plate comprising the plate-like molded product according to (1) or (2).
[Effect of the invention]
[0006]
The plate-shaped molded article made of the styrene resin composition of the present invention has low water absorption and is cheaper than PMMA and MS resin, and changes in hue and transmittance over a long period of time, which are disadvantages of PS resin. Since it is small and excellent in colorless transparency, it can be suitably used for optical applications such as a light guide plate. Moreover, the coloring prevention effect with respect to high temperature heat history, such as a shaping | molding process, is also high.
[Mode for Carrying Out the Invention]
[0007]
The styrenic resin used in the present invention can be obtained by polymerizing a styrenic monomer. The styrene monomer is an aromatic vinyl monomer, such as styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, or a mixture of two or more, preferably styrene.
[0008]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0009]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0010]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0011]
The styrene resin used in the present invention has a weight average molecular weight of 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer The molecular weight of the present invention is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0012]
The styrene resin composition of the present invention comprises (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4, in 100% by mass of the styrene resin composition. It contains 8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, and its content is 0.05 to 0.40% by mass. When the content of (b) is less than 0.05% by mass, the long-term thermal stability is inferior, and the initial hue and transmittance are also inferior. Moreover, even if it exceeds 0.40 mass%, long-term thermal stability will deteriorate.
[0013]
The styrene resin composition used in the present invention preferably contains 0.02 to 0.50 mass% of (c) hindered phenol antioxidant in 100 mass% of the styrene resin composition. It is more preferable to contain -0.30 mass%. 6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Long-term thermal stability, initial hue, and transmittance are improved as compared with the case of using dioxaphosphepine alone.
[0014]
Examples of the hindered phenol antioxidant used in the present invention include octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, ethylenebis (oxyethylene) bis [3- (5 -Tert-butyl-4-hydroxy-m-tolyl) propionate], 4,6-bis (octylthiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -o-cresol, 2,4 -Dimethyl-6- (1-methylpentadecyl) phenol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, DL-α-tocopherol, 2-t- Butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1 (2-hydroxy-3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4′-thiobis (6-t-butyl-3-methylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-tert-butylphenol) Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate and / or ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate ] Is preferable.
[0015]
6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3 of the present invention , 2] Dioxaphosphine and hindered phenol antioxidants can be added by adding and mixing in the polymerization process, devolatilization process, granulation process of styrene resin, and extruders and injections during molding. A method of adding and mixing with a molding machine or the like can be mentioned, and it is not particularly limited.
[0016]
The styrenic resin composition used in the present invention may contain mineral oil as long as the colorless transparency of the present invention is not impaired. Additives such as internal lubricants such as stearic acid and ethylene bisstearylamide, phosphorus antioxidants, sulfur antioxidants, lactone antioxidants, UV absorbers, hindered amine stabilizers, antistatic agents, etc. It may be included. As the external lubricant, ethylene bisstearylamide is suitable, and the content is preferably 30 to 200 ppm in the resin composition.
[0017]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0018]
A transparent plate-shaped molded article made of the styrene resin composition of the present invention can be molded by a molding method according to the purpose such as injection molding, extrusion molding, compression molding or the like. Further, a reflection pattern such as a dot pattern can be provided on the back surface (opposite side of the light emitting surface) of the plate-shaped molded product, and used as a light guide plate. When processing the plate-shaped molded article into the light guide plate, it is preferable to polish the light incident surface or the entire end surface of the resin plate to give a mirror surface. In addition, in order to improve the uniformity of the emitted light, a prism pattern can be provided on the surface (surface from which light is emitted) of the plate-shaped molded product. The pattern on the front surface or the back surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0019]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0020]
(Production of styrene resin PS-1)
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A mixed solution of 84.0% by mass of styrene and 16.0% by mass of ethylbenzene was prepared, and 400 ppm of 2,2-bis (4,4-t-butylperoxycyclohexyl) propane was mixed on the basis of styrene, A raw material solution was obtained. As 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, Pertetra A manufactured by NOF Corporation was used. This raw material solution was continuously supplied to the first reactor at a rate of 11.2 kg / hour. The reaction temperature of each reactor is 116 ° C. in the first reactor, 120 ° C. in the second reactor, and in the third reactor, a temperature gradient is created along the direction of flow, 140 ° C. in the middle portion, and in the outlet portion. The temperature was adjusted to 150 ° C. Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted of two stages in series, and after separating unreacted styrene and ethylbenzene, a strand shape After being extruded and cooled, it was cut into pellets. The resin temperature in the first stage devolatilization tank is set to 160 ° C., the pressure in the vacuum devolatilization tank is set to 65 kPa, the resin temperature in the second stage devolatilization layer is set to 235 ° C. The pressure in the volatilization tank was 0.4 kPa.
The obtained styrene resin PS-1 had a weight average molecular weight (Mw) of 370,000, a Z average molecular weight (Mz) of 770,000, and a number average molecular weight (Mn) of 110,000. The amount of residual styrene in the styrene resin was 350 ppm, the amount of residual ethylbenzene was 100 ppm, the amount of styrene dimer was 100 ppm, and the amount of styrene trimer was 3400 ppm. The melt mass flow rate was 1.2 g / 10 min, and the Vicat softening temperature was 103 ° C. (The melt mass flow rate was in accordance with JIS K-7210, under the conditions of 200 ° C. and 49 N load, and the Vicat softening temperature was In accordance with JIS K 7206, the test was performed at a heating rate of 50 ° C./hr and a test load of 50 N).
[0021]
(Examples 1-9, Comparative Examples 1-3)
With the contents shown in Table 3-1, styrene resin PS-1 and A and B as additives were melt kneaded at a cylinder temperature of 230 ° C. and a screw speed of 100 rpm using a single screw extruder with a screw diameter of 40 mm. To obtain pellets. Additives A and B used in Table 3-1 are shown below. In addition, additive A is (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, additive B represents (c) a hindered phenolic antioxidant.
A-1: 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3,2] Dioxaphosphepin (Sumitomo GP, manufactured by Sumitomo Chemical Co., Ltd.)
B-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
B-2: Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. In order to evaluate long-term thermal stability, the obtained plate-shaped molded article was stored in an 80 ° C. oven for 500 hours. In order to evaluate the optical properties before and after storage, a 115 × 85 × 3 mm thickness test piece was cut out from the plate-shaped molded product, the end surface was polished by buffing, and a plate-shaped molded product having a mirror surface on the end surface was created. Using an ultraviolet-visible spectrophotometer V-670 manufactured by Co., Ltd., measuring the spectral transmittance at a wavelength of 350 nm to 800 nm at an optical path length of 115 mm in incident light having a size of 20 × 1.6 mm and a spread angle of 0 °, The YI value at a visual field of 2 ° for the C light source was calculated according to JIS K7105. The transmittance shown in Table 3-1 represents the average transmittance at a wavelength of 380 nm to 780 nm.
Table 3-1 shows the characteristics of each resin composition.
[0022]
[Table 3-1]

[0023]
The molded articles of the examples are excellent in initial transmittance and YI value, and are also excellent in long-term thermal stability.
[Industrial applicability]
[0024]
The plate-shaped molded article comprising the styrene resin composition of the present invention is excellent in hue and transparency, and excellent in long-term thermal stability. Therefore, a television, a desktop personal computer, a notebook personal computer, a mobile phone, a car navigation system It can use suitably for light-guide plate uses, such as.

[００２７]
実施例の成形品は、初期の透過率とＹＩ値に優れ、８０℃×１０００時間での保管におけるＹＩ変化量が小さく、長期の熱安定性にも優れている。
[産業上の利用可能性]
[００２８]
本発明の光学用スチレン系樹脂組成物は、色相および透明性に優れ、長期の熱安定性に優れることから、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 4)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8, A styrene resin composition comprising 10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, wherein (b) in 100% by mass of the styrene resin composition Content is 0.02-0.40 mass%, The styrenic resin composition for optics characterized by the above-mentioned.
[Claim 2]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8, A styrene resin composition comprising 10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (c) a phosphorus-based antioxidant, the styrene resin composition 100 The content of (b) in the mass% is 0.02 to 0.40 mass%, and the content of (c) is 0.02 to 0.50 mass%. object.
[Claim 3]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8, A styrene resin composition comprising 10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (d) a hindered phenolic antioxidant, wherein the styrene resin composition The content of (b) in 100% by mass of the product is 0.02 to 0.40% by mass, and the content of (d) is 0.02 to 0.50% by mass. Resin composition.
[Claim 4]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8, Styrene resin composition comprising 10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, (c) phosphorus antioxidant and (d) hindered phenol antioxidant The content of (b) in 100% by mass of the styrene-based resin composition is 0.02 to 0.40% by mass, the content of (c) is 0.02 to 0.50% by mass, ( Content of d) is 0.02-0.50 mass%, The styrene resin composition for optics characterized by the above-mentioned.
[Claim 5]
The molded article using the styrene resin composition for optics of any one of Claims 1-4.
[Claim 6]
A light guide plate using the molded product according to claim 5.
[Document Name] Statement
[Title of the Invention] Optical Styrenic Resin Composition, Molded Product, and Light Guide Plate
[Technical field]
[0001]
The present invention relates to an optical styrenic resin composition excellent in hue and transparency, a molded article, and a light guide plate.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The A backlight using a light guide plate is also used for illumination. An acrylic resin typified by PMMA (polymethyl methacrylate) is used for the light guide plate. However, since the water absorption is high, the molded product may be warped or dimensional changes may occur.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylate copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water absorption is high and the dimensional stability tends to be worse than that of a styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, discoloration due to heat may occur during long-term use, and the molded product may turn yellow to lower the transmittance. As a result, the luminance of the backlight may decrease and the chromaticity may change.
[Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
An object of the present invention is to provide a styrenic resin composition for optics, a molded article, and a light guide plate that are excellent in long-term thermal stability and excellent in colorless transparency.
[Means for solving problems]
[0005]
(1) (a) Styrenic resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4 , 8,10-Tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, a styrene resin composition comprising ( An optical styrene-based resin composition, wherein the content of b) is 0.02 to 0.40 mass%.
(2) (a) Styrenic resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4 , 8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (c) a phosphorous antioxidant comprising a styrene resin The optical styrene, wherein the content of (b) in 100% by mass of the composition is 0.02 to 0.40% by mass, and the content of (c) is 0.02 to 0.50% by mass. -Based resin composition.
(3) (a) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4 , 8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (d) a hindered phenol antioxidant, The optical system characterized in that the content of (b) in 100% by mass of the resin-based resin composition is 0.02 to 0.40% by mass, and the content of (d) is 0.02 to 0.50% by mass. Styrenic resin composition.
(4) (a) Styrenic resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4 , 8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, (c) phosphorus antioxidant and (d) hindered phenol antioxidant The content of (b) in 100% by mass of the styrene resin composition is 0.02 to 0.40% by mass, and the content of (c) is 0.02 to 0.50 mass. %, The content of (d) is 0.02 to 0.50% by mass, an optical styrene resin composition.
(5) A molded product using the optical styrenic resin composition according to any one of (1) to (4).
(6) A light guide plate using the molded product according to (5).
[Effect of the invention]
[0006]
The styrenic resin composition and molded product of the present invention are low in water absorption and inexpensive compared to PMMA and MS resin, excellent in long-term thermal stability, and excellent in colorless transparency. It can be suitably used for optical applications. Moreover, the coloring prevention effect with respect to high temperature heat history, such as a shaping | molding process, is also high.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin is a polymer having a unit structure derived from a styrene monomer. The styrene resin can be obtained by polymerizing a styrene monomer. Examples of the styrene monomer include styrene, α-methyl styrene, p-methyl styrene, o-methyl styrene, m-methyl styrene, ethyl styrene, pt-butyl styrene, and preferably styrene. Styrenic monomers may be used alone or in combination of two or more. As the styrenic resin, those having a small amount of other unit structures can also be used. The other unit structure is preferably 5% or less. Other unit structures include unit structures derived from vinyl monomers copolymerizable with styrene monomers. Examples of copolymerizable vinyl monomers include acrylic acid monomers such as acrylic acid and methacrylic acid, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, acrylic monomers such as butyl acrylate and methyl methacrylate, and maleic anhydride. Examples include α, β-ethylenically unsaturated carboxylic acids such as acid and fumaric acid, and imide monomers such as N-phenylmaleimide and N-cyclohexylmaleimide.
[0008]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0009]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0010]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0011]
The weight average molecular weight of the styrene resin is 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: differential refractometer The molecular weight is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0012]
The styrene-based resin composition is (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10 in 100% by mass of the styrene-based resin composition. -Tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine is contained, the content thereof is 0.02 to 0.40% by mass, 0.05 to 0. 0. It is preferably 20% by mass. When the content of (b) is less than 0.02% by mass, the long-term thermal stability is inferior, and the initial hue and transmittance are also inferior. Moreover, even if it exceeds 0.40 mass%, long-term thermal stability will deteriorate. Long-term thermal stability represents changes in hue and transmittance due to heat in long-term use, and those having excellent thermal stability have small changes in hue and transmittance. Long-term thermal stability can be evaluated as an accelerated test by storing a molded product under a high temperature condition (60 to 90 ° C.) such that the resin does not deform, and changing the hue and transmittance over time.
[0013]
The styrenic resin composition preferably contains 0.02 to 0.50% by mass of (c) phosphorus antioxidant in 100% by mass of the styrene resin composition, and 0.05 to 0.30% by mass. More preferably. 6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Long-term thermal stability is improved as compared with the case of using dioxaphosphepine alone.
[0014]
The styrene resin composition used in the present invention preferably contains 0.02 to 0.50 mass% of (d) a hindered phenolic antioxidant in 100 mass% of the styrene resin composition. It is more preferable to contain -0.25 mass%. 6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Compared to the case where dioxaphosphepine is used alone, the initial hue and transmittance are improved, and the long-term thermal stability tends to be improved.
[0015]
6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Dioxaphosphepine is a processing stabilizer having a hindered phenol antioxidant skeleton and a phosphorus antioxidant skeleton in the same molecule.
[0016]
Phosphorous antioxidants are phosphites that are trivalent phosphorus compounds. Phosphorus antioxidants include, for example, tris (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2- Ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 4,4′-biphenylenediphosphinic acid tetrakis (2,4-di-tert-butylphenyl), 3,9-bis (2 , 6-Di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane, cyclic neopentanetetraylbis (2,4-di -T-butylphenyl phosphite), distearyl pentaerythritol diphosphite, bis (nonylphenyl) pe Taerythritol diphosphite, bis- [2-methyl-4,6-bis- (1,1-dimethylethyl) phenyl] ethyl phosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10 -Oxide, tetrakis (2,4-di-tert-butyl-5-methylphenyl) -4,4'-biphenylenediphosphonite and the like. As the phosphorus-based antioxidant, those excellent in hydrolysis resistance are preferred, such as tris (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert-). Butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 3,9-bis (2,6-di-tert-butyl-4-methyl) Phenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane is preferred. Particularly preferred is tris (2,4-di-tert-butylphenyl) phosphite. Phosphorous antioxidants may be used alone or in combination of two or more.
[0017]
The hindered phenol antioxidant is an antioxidant having a phenolic hydroxyl group in the basic skeleton. Examples of hindered phenol antioxidants include octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3-tert-butyl). -4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate], 4,6-bis (octylthiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -o-cresol, 2, , 4-Dimethyl-6- (1-methylpentadecyl) phenol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) Propionate] methane, DL-α-tocopherol, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy -3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4'-thiobis (6-t-butyl-3-methylphenol), 1,1, 3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-t-butylphenol), bis- [3,3-bis- (4 And '-hydroxy-3'-tert-butylphenyl) -butanoic acid] -glycol ester. Preferably, octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methyl) Phenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4 -Hydroxy-m-tolyl) propionate]. Hindered phenolic antioxidants may be used alone or in combination of two or more.
[0018]
6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Dioxaphosfepine, phosphorus antioxidants and hindered phenol antioxidants can be added by adding and mixing in the styrene resin polymerization process, devolatilization process, granulation process or extrusion during molding. A method of adding and mixing with a machine, an injection molding machine or the like can be mentioned, and it is not particularly limited.
[0019]
The styrenic resin composition may contain mineral oil as long as the colorless transparency of the present invention is not impaired. Also includes additives such as internal lubricants such as stearic acid and ethylenebisstearylamide, sulfur antioxidants, lactone antioxidants, UV absorbers, hindered amine stabilizers, antistatic agents, external lubricants, etc. It may be. As the external lubricant, ethylene bisstearylamide is suitable, and the content is preferably 30 to 200 ppm in the resin composition.
[0020]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0021]
The styrenic resin composition of the present invention can be molded by a molding method according to the purpose, such as injection molding, extrusion molding, or compression molding. The obtained molded product is used as an optical member that functions by transmitting light into the molded product such as a light guide plate. An optical member such as a light guide plate is preferably a material having a high transmittance and an excellent hue because of a long light transmission distance (optical path length). It is preferable that the initial transmittance at an optical path length of 115 mm is 85% or more and the YI value is 6.5 or less. Further, the YI difference after storage for 1000 hours at 80 ° C. is preferably 3.0 or less, and more preferably 1.5 or less.
The transmittance and YI value for an optical path length of 115 mm were measured by the following procedure. Using pellets of the styrene-based resin composition, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. Here, the sample to be evaluated for long-term thermal stability was stored in an oven at 80 ° C. for 1000 hours. Next, a test piece having a thickness of 115 × 85 × 3 mm was cut out from the plate-shaped molded product, and the end surface was polished by buffing to produce a plate-shaped molded product having a mirror surface on the end surface. About the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a divergence angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance is an average transmittance at a wavelength of 380 nm to 780 nm.
[0022]
The light guide plate receives light from the end surface (side surface) of the plate-shaped molded product, and guides light to the front surface (light emitting surface) of the molded product by a reflection pattern formed on the rear surface (non-light emitting surface) of the molded product. It is a member that has the function of emitting surface light. The reflective pattern can be formed by a method such as a screen printing method, an injection molding method, a laser method, or an ink jet method. When processing the plate-shaped molded product into the light guide plate, it is preferable to polish the light incident surface or the entire end surface to a mirror surface. Moreover, in order to improve the uniformity of the emitted light, a prism pattern or the like can be provided on the front surface (light emitting surface) of the plate-shaped molded product. The pattern on the front surface or the rear surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0023]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0024]
(Production of styrene resin PS-1)
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A mixed solution of 84.0% by mass of styrene and 16.0% by mass of ethylbenzene was prepared, and 400 ppm of 2,2-bis (4,4-t-butylperoxycyclohexyl) propane was mixed on the basis of styrene, A raw material solution was obtained. As 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, Pertetra A manufactured by NOF Corporation was used. This raw material solution was continuously supplied to the first reactor at a rate of 11.2 kg / hour. The reaction temperature of each reactor is 116 ° C. in the first reactor, 120 ° C. in the second reactor, and in the third reactor, a temperature gradient is created along the direction of flow, 140 ° C. in the middle portion, and in the outlet portion. The temperature was adjusted to 150 ° C. Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted of two stages in series, and after separating unreacted styrene and ethylbenzene, a strand shape After being extruded and cooled, it was cut into pellets. The resin temperature in the first stage devolatilization tank is set to 160 ° C., the pressure in the vacuum devolatilization tank is set to 65 kPa, the resin temperature in the second stage devolatilization layer is set to 235 ° C. The pressure in the volatilization tank was 0.4 kPa.
The obtained styrene resin PS-1 had a weight average molecular weight (Mw) of 370,000, a Z average molecular weight (Mz) of 770,000, and a number average molecular weight (Mn) of 110,000. The amount of residual styrene in the styrene resin was 350 ppm, the amount of residual ethylbenzene was 100 ppm, the amount of styrene dimer was 100 ppm, and the amount of styrene trimer was 3400 ppm. The melt mass flow rate was 1.2 g / 10 min and the Vicat softening temperature was 103 ° C. (The melt mass flow rate was in accordance with JIS K 7210, under the conditions of 200 ° C. and 49 N load, and the Vicat softening temperature was JIS K 7210. The test was conducted in accordance with K 7206 at a heating rate of 50 ° C./hr and a test load of 50 N).
[0025]
(Examples 1-26, Comparative Examples 1-8)
With the contents shown in Table 4-1, styrene resin PS-1 and B, C, and D as additives were melted at a cylinder temperature of 230 ° C. and a screw rotation speed of 100 rpm using a single screw extruder with a screw diameter of 40 mm. Kneading gave pellets. Additives B, C and D used in Table 4-1 are shown below. The additive B was (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, additive C represents (c) phosphorus antioxidant, and additive D represents (d) hindered phenol antioxidant.
B-1: 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3,2] Dioxaphosphepine (Sumitomo Chemical Co., Ltd. Sumilizer GP)
C-1: Tris (2,4-di-tert-butylphenyl) phosphite (Irgafos 168 manufactured by BASF Japan Ltd.)
C-2: 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus (Adeka Corporation HP ADEKA STAB HP-10)
C-3: Bis (2,4-dicumylphenyl) pentaerythritol diphosphite (Doverphos S-9228 manufactured by Dober Chemical Corporation)
C-4: 3,9-bis (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane ADEKA ADK STAB PEP-36)
D-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
D-2: 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10 -Tetraoxaspiro [5.5] undecane (Adeka Corporation Adeka Stub AO-80)
D-3: Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. In order to evaluate long-term thermal stability, the obtained molded product was stored in an oven at 80 ° C. for 1000 hours. In order to evaluate the optical properties of the initial molded product before storage and the molded product after storage, a 115 × 85 × 3 mm thickness test piece was cut out from the plate-shaped molded product, the end surface was polished by buffing, and a mirror surface was formed on the end surface. A plate-shaped molded article having the same was prepared. About the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a divergence angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance shown in Table 4-1 represents the average transmittance at a wavelength of 380 nm to 780 nm.
Table 4-1 shows the characteristics of each resin composition.
[0026]
[Table 4-1]

[0027]
The molded articles of the examples are excellent in the initial transmittance and YI value, have a small amount of YI change during storage at 80 ° C. × 1000 hours, and are excellent in long-term thermal stability.
[Industrial applicability]
[0028]
The optical styrenic resin composition of the present invention is excellent in hue and transparency and excellent in long-term thermal stability, so that it is a light guide plate for televisions, desktop personal computers, notebook personal computers, mobile phones, car navigation systems, etc. It can be suitably used in applications.

[００２４]
実施例の成形品は、初期の透過率とＹＩ値に優れ、８０℃×１０００時間での保管におけるＹＩ変化量が小さく、長期の熱安定性にも優れている。
[産業上の利用可能性]
[００２５]
本発明の光学用スチレン系樹脂組成物は、色相および透明性に優れ、長期の熱安定性に優れることから、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 5)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
A styrene resin composition comprising (a) a styrene resin having a weight average molecular weight of 150,000 to 700,000, (b) a hindered phenol antioxidant, and (c) a phosphorus antioxidant, the styrene resin Content of (b) in 100% by mass of composition is 0.02 to 0.30% by mass, and content of (c) is 0.03 to 0.40% by mass. -Based resin composition.
[Claim 2]
A molded article using the optical styrenic resin composition according to claim 1.
[Claim 3]
A light guide plate using the molded product according to claim 2.
[Document Name] Statement
[Title of the Invention] Optical Styrenic Resin Composition, Molded Product, and Light Guide Plate
[Technical field]
[0001]
The present invention relates to an optical styrenic resin composition excellent in hue and transparency, a molded article, and a light guide plate.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The A backlight using a light guide plate is also used for illumination. An acrylic resin typified by PMMA (polymethyl methacrylate) is used for the light guide plate. However, since the water absorption is high, the molded product may be warped or dimensional changes may occur.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylate copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water absorption is high and the dimensional stability tends to be worse than that of a styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, discoloration due to heat may occur during long-term use, and the molded product may turn yellow to lower the transmittance. As a result, the luminance of the backlight may decrease and the chromaticity may change.
[Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
An object of the present invention is to provide a styrenic resin composition for optics, a molded article, and a light guide plate that are excellent in long-term thermal stability and excellent in colorless transparency.
[Means for solving problems]
[0005]
(1) A styrene resin composition comprising (a) a styrene resin having a weight average molecular weight of 150,000 to 700,000, (b) a hindered phenol antioxidant, and (c) a phosphorus antioxidant, The content of (b) in 100% by mass of the styrene-based resin composition is 0.02 to 0.30% by mass, and the content of (c) is 0.03 to 0.40% by mass. Styrenic resin composition for optics.
(2) A molded article using the optical styrenic resin composition according to (1).
(3) A light guide plate using the molded product according to (2).
[Effect of the invention]
[0006]
The styrenic resin composition and molded product of the present invention are low in water absorption and inexpensive compared to PMMA and MS resin, excellent in long-term thermal stability, and excellent in colorless transparency. It can be suitably used for optical applications. Moreover, the coloring prevention effect with respect to high temperature heat history, such as a shaping | molding process, is also high.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin is a polymer having a unit structure derived from a styrene monomer. The styrene resin can be obtained by polymerizing a styrene monomer. Examples of the styrene monomer include styrene, α-methyl styrene, p-methyl styrene, o-methyl styrene, m-methyl styrene, ethyl styrene, pt-butyl styrene, and preferably styrene. Styrenic monomers may be used alone or in combination of two or more. As the styrenic resin, those having a small amount of other unit structures can also be used. The other unit structure is preferably 5% or less. Other unit structures include unit structures derived from vinyl monomers copolymerizable with styrene monomers. Examples of copolymerizable vinyl monomers include acrylic acid monomers such as acrylic acid and methacrylic acid, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, acrylic monomers such as butyl acrylate and methyl methacrylate, and maleic anhydride. Examples include α, β-ethylenically unsaturated carboxylic acids such as acid and fumaric acid, and imide monomers such as N-phenylmaleimide and N-cyclohexylmaleimide.
[0008]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0009]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0010]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0011]
The weight average molecular weight of the styrene resin is 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: differential refractometer The molecular weight is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0012]
The styrene-based resin composition contains (b) a hindered phenol-based antioxidant and (c) a phosphorus-based antioxidant in 100% by mass of the styrene-based resin composition, and the content of (b) is 0.02 to 0.02%. The content of 0.30% by mass and (c) is 0.03 to 0.40% by mass. Preferably, the content of (b) is 0.02 to 0.20 mass%, and the content of (c) is 0.05 to 0.30 mass%. More preferably, the content of (b) is 0.05 to 0.15% by mass, and the content of (c) is 0.10 to 0.25% by mass. When the contents of (b) and (c) are outside the above ranges, the long-term thermal stability is poor. Long-term thermal stability represents changes in hue and transmittance due to heat in long-term use, and those having excellent thermal stability have small changes in hue and transmittance. Long-term thermal stability can be evaluated as an accelerated test by storing a molded product under a high temperature condition (60 to 90 ° C.) such that the resin does not deform, and changing the hue and transmittance over time.
[0013]
The hindered phenol antioxidant is an antioxidant having a phenolic hydroxyl group in the basic skeleton. Examples of hindered phenol antioxidants include octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3-tert-butyl). -4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate], 4,6-bis (octylthiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -o-cresol, 2, , 4-Dimethyl-6- (1-methylpentadecyl) phenol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) Propionate] methane, DL-α-tocopherol, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy -3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4'-thiobis (6-t-butyl-3-methylphenol), 1,1, 3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-t-butylphenol), bis- [3,3-bis- (4 And '-hydroxy-3'-tert-butylphenyl) -butanoic acid] -glycol ester. Preferably, octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methyl) Phenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4 -Hydroxy-m-tolyl) propionate]. Hindered phenolic antioxidants may be used alone or in combination of two or more.
[0014]
Phosphorous antioxidants are phosphites that are trivalent phosphorus compounds. Phosphorus antioxidants include, for example, tris (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2- Ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 4,4′-biphenylenediphosphinic acid tetrakis (2,4-di-tert-butylphenyl), 3,9-bis (2 , 6-Di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane, cyclic neopentanetetraylbis (2,4-di -T-butylphenyl phosphite), distearyl pentaerythritol diphosphite, bis (nonylphenyl) pe Taerythritol diphosphite, bis- [2-methyl-4,6-bis- (1,1-dimethylethyl) phenyl] ethyl phosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10 -Oxide, tetrakis (2,4-di-tert-butyl-5-methylphenyl) -4,4'-biphenylenediphosphonite and the like. As the phosphorus-based antioxidant, those excellent in hydrolysis resistance are preferred, such as tris (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert-). Butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 3,9-bis (2,6-di-tert-butyl-4-methyl) Phenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane is preferred. Particularly preferred is tris (2,4-di-tert-butylphenyl) phosphite. Phosphorous antioxidants may be used alone or in combination of two or more.
[0015]
Methods for adding hindered phenolic antioxidants and phosphorus antioxidants include addition and mixing in the polymerization process, devolatilization process, and granulation process of styrenic resins, extruders and injection molding machines during molding, etc. The method of adding and mixing is mentioned, but it is not particularly limited.
[0016]
The styrenic resin composition may contain mineral oil as long as the colorless transparency of the present invention is not impaired. Also includes additives such as internal lubricants such as stearic acid and ethylenebisstearylamide, sulfur antioxidants, lactone antioxidants, UV absorbers, hindered amine stabilizers, antistatic agents, external lubricants, etc. It may be. As the external lubricant, ethylene bisstearylamide is suitable, and the content is preferably 30 to 200 ppm in the resin composition.
[0017]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0018]
The styrenic resin composition of the present invention can be molded by a molding method according to the purpose, such as injection molding, extrusion molding, or compression molding. The obtained molded product is used as an optical member that functions by transmitting light into the molded product such as a light guide plate. An optical member such as a light guide plate is preferably a material having a high transmittance and an excellent hue because of a long light transmission distance (optical path length). The initial transmittance at an optical path length of 115 mm is preferably 84% or more and the YI value is 7.0 or less. The YI difference after storage at 80 ° C. for 1000 hours and the initial YI is preferably 2.0 or less, and more preferably 1.0 or less.
The transmittance and YI value for an optical path length of 115 mm were measured by the following procedure. Using pellets of the styrene-based resin composition, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. Here, the sample to be evaluated for long-term thermal stability was stored in an oven at 80 ° C. for 1000 hours. Next, a test piece having a thickness of 115 × 85 × 3 mm was cut out from the plate-shaped molded product, and the end surface was polished by buffing to produce a plate-shaped molded product having a mirror surface on the end surface. About the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a divergence angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance is an average transmittance at a wavelength of 380 nm to 780 nm.
[0019]
The light guide plate receives light from the end surface (side surface) of the plate-shaped molded product, and guides light to the front surface (light emitting surface) of the molded product by a reflection pattern formed on the rear surface (non-light emitting surface) of the molded product. It is a member that has the function of emitting surface light. The reflective pattern can be formed by a method such as a screen printing method, an injection molding method, a laser method, or an ink jet method. When processing the plate-shaped molded product into the light guide plate, it is preferable to polish the light incident surface or the entire end surface to a mirror surface. Moreover, in order to improve the uniformity of the emitted light, a prism pattern or the like can be provided on the front surface (light emitting surface) of the plate-shaped molded product. The pattern on the front surface or the rear surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0020]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0021]
(Production of styrene resin PS-1)
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A mixed solution of 84.0% by mass of styrene and 16.0% by mass of ethylbenzene was prepared, and 400 ppm of 2,2-bis (4,4-t-butylperoxycyclohexyl) propane was mixed on the basis of styrene, A raw material solution was obtained. As 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, Pertetra A manufactured by NOF Corporation was used. This raw material solution was continuously supplied to the first reactor at a rate of 11.2 kg / hour. The reaction temperature of each reactor is 116 ° C. in the first reactor, 120 ° C. in the second reactor, and in the third reactor, a temperature gradient is created along the direction of flow, 140 ° C. in the middle portion, and in the outlet portion. The temperature was adjusted to 150 ° C. Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted of two stages in series, and after separating unreacted styrene and ethylbenzene, a strand shape After being extruded and cooled, it was cut into pellets. The resin temperature in the first stage devolatilization tank is set to 160 ° C., the pressure in the vacuum devolatilization tank is set to 65 kPa, the resin temperature in the second stage devolatilization layer is set to 235 ° C. The pressure in the volatilization tank was 0.4 kPa.
The obtained styrene resin PS-1 had a weight average molecular weight (Mw) of 370,000, a Z average molecular weight (Mz) of 770,000, and a number average molecular weight (Mn) of 110,000. The amount of residual styrene in the styrene resin was 350 ppm, the amount of residual ethylbenzene was 100 ppm, the amount of styrene dimer was 100 ppm, and the amount of styrene trimer was 3400 ppm. The melt mass flow rate was 1.2 g / 10 min and the Vicat softening temperature was 103 ° C. (The melt mass flow rate was in accordance with JIS K 7210, under the conditions of 200 ° C. and 49 N load, and the Vicat softening temperature was JIS K 7210. The test was conducted in accordance with K 7206 at a heating rate of 50 ° C./hr and a test load of 50 N).
[0022]
(Examples 1-12, Comparative Examples 1-9)
Using the content shown in Table 5-1, styrene resin PS-1 and additives B, C and D were melted at a cylinder temperature of 230 ° C. and a screw rotation speed of 100 rpm using a single screw extruder with a screw diameter of 40 mm. Kneading gave pellets. Additives B and C used in Table 5-1 are shown below. Additive B represents (b) a hindered phenol-based antioxidant, and additive C represents (c) a phosphorus-based antioxidant.
B-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
B-2: 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10 -Tetraoxaspiro [5.5] undecane (Adeka Corporation Adeka Stub AO-80)
B-3: Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
C-1: Tris (2,4-di-tert-butylphenyl) phosphite (Irgafos 168 manufactured by BASF Japan Ltd.)
C-2: 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus (Adeka Corporation HP ADEKA STAB HP-10)
C-3: Bis (2,4-dicumylphenyl) pentaerythritol diphosphite (Doverphos S-9228 manufactured by Dober Chemical Corporation)
C-4: 3,9-bis (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane ADEKA ADK STAB PEP-36)
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. In order to evaluate long-term thermal stability, the obtained molded product was stored in an oven at 80 ° C. for 1000 hours. In order to evaluate the optical properties of the initial molded product before storage and the molded product after storage, a 115 × 85 × 3 mm thickness test piece was cut out from the plate-shaped molded product, the end surface was polished by buffing, and a mirror surface was formed on the end surface. A plate-shaped molded article having the same was prepared. About the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a divergence angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance shown in Table 5-1 represents the average transmittance at a wavelength of 380 nm to 780 nm.
Table 5-1 shows the characteristics of each resin composition.
[0023]
[Table 5-1]

[0024]
The molded articles of the examples are excellent in the initial transmittance and YI value, have a small amount of YI change during storage at 80 ° C. × 1000 hours, and are excellent in long-term thermal stability.
[Industrial applicability]
[0025]
The optical styrenic resin composition of the present invention is excellent in hue and transparency and excellent in long-term thermal stability, so that it is a light guide plate for televisions, desktop personal computers, notebook personal computers, mobile phones, car navigation systems, etc. It can be suitably used in applications.

（式中、Ｒは炭素数８〜２０のアルキル基を示し、ｎは整数でエチレンオキサイド単位の付加モル数を表す）
[請求項４]
請求項１〜３のいずれか１項に記載のスチレン系樹脂組成物を成形してなる板状成形品。
[請求項５]
請求項４に記載の板状成形品からなる導光板。
[書類名]明細書
[発明の名称]スチレン系樹脂組成物、板状成形品および導光板
[技術分野]
[０００１]
本発明は、色相と透明性に優れ、環境変化による白化現象が発生せず、長期の熱安定性に優れた導光板用途に適したスチレン系樹脂組成物、板状成形品および導光板に関するものである。
[背景技術]
[０００２]
液晶ディスプレイのバックライトには光源を表示装置の正面に配置する直下型バックライトと側面に配置するエッジライト型バックライトがある。導光板はエッジライト型バックライトに組み込まれ、側面からの光を液晶パネルに導く役割を果たし、テレビ、デスクトップ型パーソナルコンピューターのモニター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなど幅広い用途で使用される。導光板にはＰＭＭＡ（ポリメチルメタクリレート）に代表されるアクリル樹脂が使用されているが、吸水性が高いため、成形品に反りが発生する問題や寸法の変化が発生する場合がある。
そのため、これら特性を改善したスチレンと（メタ）アクリル酸メチルとの共重合体であるＭＳ樹脂を用いることが提案されている。ＭＳ樹脂の、吸水性や成形時の変色低減等の改良技術としては特許文献１が提案されている。
しかしながら、特許文献１では、スチレン−（メタ）アクリル酸エステル系共重合体樹脂の重量平均分子量（Ｍｗ）６〜１７万、残存モノマー量３０００ｐｐｍ以下、更にオリゴマー量が２％以下の導光板が開示されているが、吸水性が高く寸法安定性がスチレン系単量体を原料とするスチレン系樹脂よりも悪い傾向にあった。
一方、スチレン系単量体を原料とするスチレン系樹脂は吸水性が低いものの、温度や湿度などの環境変化により成形品が白濁する問題（白化現象）があった。具体的には、高温高湿環境下から室温環境下への環境変化や室温環境下から低温環境下への環境変化に成形品が曝された場合、成形品中に均一に存在する水分が不安定となって相分離し、円盤状の欠陥が生成し、その結果、成形品の内部が白濁する。成形品が白濁すると、導光板のように光路長が長い場合、光散乱により透過率が大きく低下して、ディスプレイの輝度が低下する問題がある。
さらに、スチレン系樹脂は長期間の使用において熱による変色が発生し、成形品が黄変して透過率が低下する問題がある。その結果、ディスプレイの輝度が低下したり、色度が変化する問題がある。
[先行技術文献]
[特許文献]
[０００３]
[特許文献１]特開２００３−０７５６４８号公報
[発明の概要]
[発明が解決しようとする課題]
[０００４]
本発明は、環境変化による白化現象を防止し、長期間の使用においても色相および透過率の変化が小さく、特に導光板等の光学用途に適した、無色透明性に優れ、耐熱性も供えたスチレン系樹脂組成物を提供することを課題とする。
[課題を解決するための手段]
[０００５]
本発明は、（１）（ａ）重量平均分子量が１５万〜７０万のスチレン系樹脂と（ｂ）６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンと（ｃ）ポリオキシエチレン型非イオン性界面活性剤からなるスチレン系樹脂組成物であって、スチレン系樹脂組成物１００質量％中の（ｂ）の含有量が０．０５〜０．４０質量％、（ｃ）の含有量が０．４〜２．０質量％であることを特徴とするスチレン系樹脂組成物。
（２）（ａ）重量平均分子量が１５万〜７０万のスチレン系樹脂と（ｂ）６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンと（ｃ）ポリオキシエチレン型非イオン性界面活性剤と（ｄ）ヒンダードフェノール系酸化防止剤からなるスチレン系樹脂組成物であって、スチレン系樹脂組成物１００質量％中の（ｂ）の含有量が０．０５〜０．４０質量％、（ｃ）の含有量が０．４〜２．０質量％、（ｄ）の含有量が０．０２〜０．５０質量％であることを特徴とするスチレン系樹脂組成物。
（３）（ｃ）ポリオキシエチレン型非イオン性界面活性剤が下記一般式１で示されるポリオキシエチレンアルキルエーテル及び／又は下記一般式２で示されるポリオキシエチレン脂肪酸エステルの郡から選ばれる１種類以上であり、かつエチレンオキサイドの平均付加モル数が７〜１００であることを特徴とする（１）又は（２）に記載のスチレン系樹脂組成物。

（式中、Ｒは炭素数８〜２０のアルキル基を示し、ｎは整数でエチレンオキサイド単位の付加モル数を表す）
（４）（１）〜（３）のいずれかに記載のスチレン系樹脂組成物を成形してなる板状成形品。
（５）（４）に記載の板状成形品からなる導光板。
[発明の効果]
[０００６]
本発明のスチレン系樹脂組成物は、ＰＭＭＡやＭＳ樹脂と比較して、吸水性が低く安価であり、ＰＳ樹脂の欠点である環境変化による白化現象が発生せず、また、長期間の使用における色相および透過率の変化が小さく、無色透明性に優れることから、導光板等の光学用途に好適に用いることが出来る。また、成形加工などの高温熱履歴に対する着色防止効果も高い。
[発明を実施するための形態]
[０００７]
本発明のスチレン系樹脂は、スチレン系単量体を重合して得ることができる。スチレン系単量体とは、芳香族ビニル系モノマーである、スチレン、α−メチルスチレン、ｏ−メチルスチレン、ｐ−メチルスチレン等の単独または２種以上の混合物であり、好ましくはスチレンである。
[０００８]
スチレン系樹脂の重合方法としては、塊状重合法、溶液重合法、懸濁重合法、乳化重合法等公知のスチレン重合方法が挙げられる。品質面や生産性の面では、塊状重合法、溶液重合法が好ましく、連続重合であることが好ましい。溶媒として例えばベンゼン、トルエン、エチルベンゼン及びキシレン等のアルキルベンゼン類やアセトンやメチルエチルケトン等のケトン類、ヘキサンやシクロヘキサン等の脂肪族炭化水素等が使用できる。
[０００９]
スチレン系樹脂の重合時に、必要に応じて重合開始剤、連鎖移動剤を使用することができる。重合開始剤としては、ラジカル重合開始剤が好ましく、公知慣用の例えば、１，１−ジ（ｔ−ブチルパーオキシ）シクロヘキサン、２，２−ジ（ｔ−ブチルパーオキシ）ブタン、２，２−ジ（４，４−ジ−ｔ−ブチルパーオキシシクロヘキシル）プロパン、１，１−ジ（ｔ−アミルパーオキシ）シクロヘキサン等のパーオキシケタール類、クメンハイドロパーオキサイド、ｔ−ブチルハイドロパーオキサイド等のハイドロパーオキサイド類、ｔ−ブチルパーオキシアセテート、ｔ−アミルパーオキシイソノナノエート等のアルキルパーオキサイド類、ｔ−ブチルクミルパーオキサイド、ジ−ｔ−ブチルパーオキサイド、ジクミルパーオキサイド、ジ−ｔ−ヘキシルパーオキサイド等のジアルキルパーオキサイド類、ｔ−ブチルパーオキシアセテート、ｔ−ブチルパーオキシベンゾエート、ｔ−ブチルパーオキシイソプロピルモノカーボネート等のパーオキシエステル類、ｔ−ブチルパーオキシイソプロピルカーボネート、ポリエーテルテトラキス（ｔ-ブチルパーオキシカーボネート）等のパーオキシカーボネート類、Ｎ，Ｎ'−アゾビス（シクロヘキサン−１−カルボニトリル）、Ｎ，Ｎ'−アゾビス（２−メチルブチロニトリル）、Ｎ，Ｎ'−アゾビス（２，４−ジメチルバレロニトリル）、Ｎ，Ｎ'−アゾビス［２−（ヒドロキシメチル）プロピオニトリル］等が挙げられ、これらの１種あるいは２種以上を組み合わせて使用することができる。連鎖移動剤としては、脂肪族メルカプタン、芳香族メルカプタン、ペンタフェニルエタン、α−メチルスチレンダイマー及びテルピノーレン等が挙げられる。
[００１０]
連続重合の場合、まず重合工程にて公知の完全混合槽型攪拌槽や塔型反応器等を用い、目標の分子量、分子量分布、反応転化率となるよう、重合温度調整等により重合反応が制御される。重合工程を出た重合体を含む重合溶液は、脱揮工程に移送され、未反応の単量体及び重合溶媒が除去される。脱揮工程は加熱器付きの真空脱揮槽やベント付き脱揮押出機などで構成される。脱揮工程を出た溶融状態の重合体は造粒工程へ移送される。造粒工程では、多孔ダイよりストランド状に溶融樹脂を押出し、コールドカット方式や空中ホットカット方式、水中ホットカット方式にてペレット形状に加工される。
[００１１]
本発明のスチレン系樹脂の重量平均分子量は１５万〜７０万であり、１８万〜５０万であることが好ましい。１５万未満では成形品の強度が不十分となり、７０万を超えると成形性が著しく低下する。スチレン系樹脂の重量平均分子量は、重合工程の反応温度、滞留時間、重合開始剤の種類及び添加量、連鎖移動剤の種類及び添加量、重合時に使用する溶媒の種類及び量等によって制御することができる。
重量平均分子量（Ｍｗ）及びＺ平均分子量（Ｍｚ）、数平均分子量（Ｍｎ）は、ゲルパーミエイションクロマトグラフィー（ＧＰＣ）を用いて、次の条件で測定した。
ＧＰＣ機種：昭和電工株式会社製Ｓｈｏｄｅｘ ＧＰＣ−１０１
カラム：ポリマーラボラトリーズ社製 ＰＬｇｅｌ １０μｍ ＭＩＸＥＤ−Ｂ
移動相：テトラヒドロフラン
試料濃度：０．２質量％
温度：オーブン４０℃、注入口３５℃、検出器３５℃
検出器：示差屈折計
本発明の分子量は単分散ポリスチレンの溶出曲線より各溶出時間における分子量を算出し、ポリスチレン換算の分子量として算出したものである。
[００１２]
本発明のスチレン系樹脂組成物は、スチレン系樹脂組成物１００質量％中（ｂ）６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンを含有し、その含有量が０．０５〜０．４０質量％である。（ｂ）の含有量が０．０５質量％未満では長期の熱安定性に劣り、初期の色相および透過率にも劣る。また、０．４０質量％を超えても長期の熱安定性が悪化する。
[００１３]
本発明のスチレン系樹脂組成物は、スチレン系樹脂組成物１００質量％中（ｄ）ヒンダードフェノール系酸化防止剤を０．０２〜０．５０質量％含有することが好ましく、０．０５〜０．３０質量％含有することがより好ましい。６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンを単独で使用した場合よりも長期の熱安定性および初期の色相、透過率が向上する。
[００１４]
本発明に用いられるヒンダードフェノール系酸化防止剤は、例えば、オクタデシル−３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート、エチレンビス（オキシエチレン）ビス〔３−（５−ｔｅｒｔ−ブチル−４−ヒドロキシ−ｍ−トリル）プロピオネート〕、４，６−ビス（オクチルチオメチル）−ｏ−クレゾール、４，６−ビス〔（ドデシルチオ）メチル〕−ｏ−クレゾール、２，４−ジメチル−６−（１−メチルペンタデシル）フェノール、テトラキス〔メチレン−３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート〕メタン、ＤＬ−α−トコフェロール、２−ｔ−ブチル−６−（３−ｔ−ブチル−２−ヒドロキシ−５−メチルベンジル）−４−メチルフェニルアクリレート、２−〔１−（２−ヒドロキシ−３，５−ジ−ｔ−ペンチルフェニル）エチル〕−４，６−ジ−ｔ−ペンチルフェニルアクリレート、４，４’−チオビス（６−ｔ−ブチル−３−メチルフェノール）、１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン、４，４’−ブチリデンビス（３−メチル−６−ｔ−ブチルフェノール）等を挙げることができるが、オクタデシル−３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート及び／又はエチレンビス（オキシエチレン）ビス〔３−（５−ｔｅｒｔ−ブチル−４−ヒドロキシ−ｍ−トリル）プロピオネート〕が好ましい。
[００１５]
本発明のスチレン系樹脂組成物は、スチレン系樹脂組成物１００質量％中（ｃ）ポリオキシエチレン型非イオン性界面活性剤（ポリエチレングリコール型非イオン性界面活性剤ともいう）を含有し、その含有量は０．４〜２．０質量％であり、０．７〜１．６質量％であることが好ましい。ポリオキシエチレン型非イオン性界面活性剤の含有量が０．４質量％未満では環境変化による白化現象の防止が困難であり、２．０質量％を超えるとスチレン系樹脂組成物の耐熱性が低下する。
[００１６]
ポリオキシエチレン型非イオン性界面活性剤は、下記一般式（１）で示されるポリオキシエチレンアルキルエーテルや下記一般式（２）で示されるポリオキシエチレン脂肪酸エステル、ポリオキシエチレン硬化ひまし油、ポリオキシエチレンソルビタン脂肪酸エステル、ポリオキシエチレンソルビトール脂肪酸エステルが挙げられるがポリオキシエチレンアルキルエーテル及び／又はポリオキシエチレン脂肪酸エステルの郡から選ばれる１種類以上であることが好ましい。

（式中、Ｒは炭素数８〜２０のアルキル基を示し、ｎは整数でエチレンオキサイド単位の付加モル数を表す）
[００１７]
ポリオキシエチレンアルキルエーテルはアルコールにエチレンオキサイドを付加させて作られ、ポリオキシエチレン脂肪酸エステルは脂肪酸にエチレンオキサイドを付加させるか脂肪酸とポリエチレングリコールを直接エステル化させて作られ、エチレンオキサイドの平均付加モル数は７〜１００であることが好ましく、１０〜５０であることがより好ましい。
[００１８]
ポリオキシエチレンアルキルエーテルとしては、例えば、ポリオキシエチレンラウリルエーテル、ポリオキシエチレンセチルエーテル、ポリオキシエチレンステアリルエーテル、ポリオキシエチレンオクチルドデシルエーテル、ポリオキシエチレンミリスチルエーテル、ポリオキシエチレン−２−エチルヘキシルエーテル等が挙げられる。
[００１９]
ポリオキシエチレン脂肪酸エステルとしては、例えば、ポリエチレングリコールモノラウレート、ポリエチレングリコールモノステアレート、ポリエチレングリコールジステアレート等が挙げられる。
[００２０]
本発明の６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンおよびヒンダードフェノール系酸化防止剤、ポリエチレングリコールの添加方法としては、スチレン系樹脂の重合工程、脱揮工程、造粒工程で添加混合する方法や成形加工時の押出機などで添加混合する方法が挙げられ、特に限定されることではない。
[００２１]
本発明のスチレン系樹脂組成物のビカット軟化温度は９５〜１０４℃であることが好ましく、９７〜１０４℃であることがより好ましい。ビカット軟化温度が９５℃未満では耐熱性が不足し、使用環境によっては成形品が変形する可能性がある。
[００２２]
本発明のスチレン系樹脂組成物には、本発明の無色透明性を損なわない範囲でミネラルオイルを含有しても良い。また、ステアリン酸、エチレンビスステアリン酸アミド等の内部潤滑剤やリン系酸化防止剤、イオウ系酸化防止剤、ラクトン系酸化防止剤、ヒンダードアミン系安定剤、紫外線吸収剤、帯電防止剤等の添加剤が含まれていても良い。また、外部潤滑剤としては、エチレンビスステアリン酸アミドが好適であり、含有量としては樹脂組成物中に３０〜２００ｐｐｍであることが好ましい。
[００２３]
紫外線吸収剤は、紫外線による劣化や着色を抑制する機能を有するものであって、例えば、ベンゾフェノン系、ベンゾトリアゾール系、トリアジン系、ベンゾエート系、サリシレート系、シアノアクリレート系、蓚酸アニリド系、マロン酸エステル系、ホルムアミジン系などの紫外線吸収剤が挙げられる。これらは、単独又は２種以上組み合わせて用いることができ、ヒンダートアミン等の光安定剤を併用してもよい。
[００２４]
本発明のスチレン系樹脂組成物は、射出成形、押出成形、圧縮成形等、目的に応じた成形方法で板状成形品に成形し、導光板として用いることができる。その際、板状成形品の背面（光を出射する面の反対側）にドットパターンなどの反射パターンを設けて、導光板として用いることができる。樹脂板から導光板に加工する際、光の入射面あるいは樹脂板の端面全面を研磨処理して、鏡面とすることが好ましい。また、出射光の均一性を高めるために、板状成形品の表面（光が出射される面）にプリズムパターンを設けることができる。板状成形品の表面あるいは背面のパターンは、板状成形品の成形時に形成させることができ、例えば射出成形では金型形状、押出成形ではロール転写などによって、パターン形成させることができる。
[実施例]
[００２５]
以下、実施例を挙げて本発明を具体的に説明するが、本発明はこれら実施例に限定されるものではない。
[００２６]
（実施例１〜１９、比較例１〜７）
完全混合型撹拌槽である第１反応器と第２反応器及び静的混合器付プラグフロー型反応器である第３反応器を直列に接続して重合工程を構成した。各反応器の容量は、第１反応器を３９リットル、第２反応器を３９リットル、第３反応器を１６リットルとした。スチレン８４．０質量％、エチルベンゼン１６．０質量％の混合溶液を作成し、スチレンに対して２，２−ビス（４，４−ｔ−ブチルパーオキシシクロヘキシル）プロパンを質量基準で４００ｐｐｍ混合し、原料溶液とした。２，２−ビス（４，４−ｔ−ブチルパーオキシシクロヘキシル）プロパンは、日油株式会社製パーテトラＡを使用した。この原料溶液を毎時１１．２ｋｇの割合で第１反応器へ連続的に供給した。各反応器の反応温度は、第１反応器で１１６℃、第２反応器で１２０℃、第３反応器では、流れの方向に沿って温度勾配をつけ、中間部分で１４０℃、出口部分で１５０℃となるよう調整した。
また、第３反応器の入口に、ポリオキシエチレン型非イオン性界面活性剤を表６−１に示す種類と含有量になるよう添加した。ポリオキシエチレン型非イオン性界面活性剤の種類は次の通り。
Ｐ−１：ポリオキシエチレンエチレンラウリルエーテル エチレンオキサイド平均付加モル数＝２５（花王株式会社製エマルゲン１２３Ｐ）
Ｐ−２：ポリオキシエチレンエチレンステアリルエーテル エチレンオキサイド平均付加モル数＝１２（花王株式会社製エマルゲン３２０Ｐ）
Ｐ−３：ポリオキシエチレンエチレンラウリルエーテル エチレンオキサイド平均付加モル数＝９（花王株式会社製エマルゲン１０９Ｐ）
Ｐ−４：ポリオキシエチレンエチレンセチルエーテル エチレンオキサイド平均付加モル数＝７（花王株式会社製エマルゲン２１０Ｐ）
Ｐ−５：ポリオキシエチレンエチレンラウリルエーテル エチレンオキサイド平均付加モル数＝３０（花王株式会社製エマルゲン１３０Ｋ）
Ｐ−６：ポリオキシエチレンエチレンラウリルエーテル エチレンオキサイド平均付加モル数＝４７（花王株式会社製エマルゲン１５０）
Ｐ−７：ポリオキシエチレンエチレンミリスチルエーテル エチレンオキサイド平均付加モル数＝８５（花王株式会社製エマルゲン４０８５）
Ｐ−８：ポリエチレングリコールモノラウレート エチレンオキサイド平均付加モル数＝１２（花王株式会社製エマノーン１１１２）
Ｐ−９：ポリオキシエチレンエチレンステアリルエーテル エチレンオキサイド平均付加モル数＝６（花王株式会社製エマルゲン３０６Ｐ）
続いて、第３反応器より連続的に取り出した重合体を含む溶液を直列に２段より構成される予熱器付き真空脱揮槽に導入し、未反応スチレン及びエチルベンゼンを分離した後、ストランド状に押し出しして冷却した後、切断してペレットとした。なお、１段目の脱揮槽内の樹脂温度は１６０℃に設定し、真空脱揮槽の圧力は６５ｋＰａとし、２段目の脱揮層内の樹脂温度は２３５℃に設定し、真空脱揮槽の圧力は０．８ｋＰａとした。
得られたスチレン系樹脂の重量平均分子量（Ｍｗ）はすべて３７万であった。
[００２７]
次に、表６−１に示す含有量となるよう、上記で得られたスチレン系樹脂のペレットと添加剤ＡおよびＢをスクリュー径４０ｍｍの単軸押出機を用いて、シリンダー温度２３０℃、スクリュー回転数１００ｒｐｍで溶融混錬してペレットを得た。表６−１で用いた添加剤ＡおよびＢを次に示す。なお、添加剤Ａは（ｂ）６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンを、添加剤Ｂは（ｄ）ヒンダードフェノール系酸化防止剤を表す。
Ａ−１：６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピン（住友化学株式会社製 スミライザーＧＰ）
Ｂ−１：オクタデシル−３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート（ＢＡＳＦジャパン株式会社製 Ｉｒｇａｎｏｘ １０７６）
Ｂ−２：エチレンビス（オキシエチレン）ビス〔３−（５−ｔｅｒｔ−ブチル−４−ヒドロキシ−ｍ−トリル）プロピオネート〕（ＢＡＳＦジャパン株式会社製 Ｉｒｇａｎｏｘ ２４５）
メルトマスフローレート（ＭＦＲ）は、ＪＩＳ Ｋ−７２１０に準拠し、２００℃、４９Ｎ荷重の条件で、ビカット軟化温度は、ＪＩＳ Ｋ ７２０６に準拠し、昇温速度５０℃／ｈｒ、試験荷重５０Ｎで測定した。
また、得られたペレットを用いて、シリンダー温度２３０℃、金型温度５０℃にて射出成形を行い、１２７×１２７×３ｍｍ厚みの板状成形品を成形した。長期の熱安定性を評価するため、得られた板状成形品を８０℃オーブン内で５００時間保管した。保管前後の光学特性と評価するため、板状成形品から１１５×８５×３ｍｍ厚みの試験片を切り出し、端面をバフ研磨によって研磨し、端面に鏡面を有する板状成形品を作成し、日本分光株式会社製の紫外線可視分光光度計Ｖ−６７０を用いて、大きさ２０×１．６ｍｍ、広がり角度０°の入射光において、光路長１１５ｍｍでの波長３５０ｎｍ〜８００ｎｍの分光透過率を測定し、Ｃ光源における、視野２°でのＹＩ値をＪＩＳ Ｋ７１０５に倣い算出した。表６−１に示す透過率とは、波長３８０ｎｍ〜７８０ｎｍの平均透過率を表す。
さらに、環境変化による白化現象を確認するため、端面に鏡面を有する板状成形品を６０℃、９０％相対湿度の環境に１５０時間暴露し、２３℃、５０％相対湿度の環境に試験片を取出し、成形品内部に発生する白化現象を観察し、白化抑制効果として下記の通り判定を行った。
◎：全く白化が発生しない
○：取出し１時間後にやや白化するが、２４時間後には消失する
△：取出し１時間後に白化するが、２４時間後にはほとんど消失する
×：取出し１時間後に著しく白化し、２４時間経っても消失しない
表６−１に各樹脂組成物の特性を示す。
[００２８]
[表６−１]

[００２９]
実施例の成形品は、白化抑制効果に優れ、初期の透過率とＹＩ値に優れており、長期の熱安定性にも優れている。
[産業上の利用可能性]
[００３０]
本発明のスチレン系樹脂組成物は、環境変化による白化現象が防止され、長期の熱安定性に優れることから透明性と色相に優れており、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 6)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8, A styrene-based resin composition comprising 10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (c) a polyoxyethylene-type nonionic surfactant, comprising styrene The content of (b) in 100% by mass of the resin-based resin composition is 0.05 to 0.40% by mass, and the content of (c) is 0.4 to 2.0% by mass. -Based resin composition.
[Claim 2]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8, From 10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, (c) a polyoxyethylene-type nonionic surfactant, and (d) a hindered phenolic antioxidant. The content of (b) in 100% by mass of the styrene resin composition is 0.05 to 0.40% by mass, and the content of (c) is 0.4 to 2. A styrenic resin composition characterized in that the content of 0% by mass and (d) is 0.02 to 0.50% by mass.
[Claim 3]
(C) The polyoxyethylene type nonionic surfactant is selected from the group of the polyoxyethylene alkyl ether represented by the following general formula (1) and / or the polyoxyethylene fatty acid ester represented by the following general formula (2). The styrenic resin composition according to claim 1, wherein the styrene-based resin composition is one or more types, and an average added mole number of ethylene oxide is 7 to 100.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms, and n is an integer representing the number of added moles of ethylene oxide units)
[Claim 4]
The plate-shaped molded article formed by shape | molding the styrene resin composition of any one of Claims 1-3.
[Claim 5]
A light guide plate comprising the plate-like molded product according to claim 4.
[Document Name] Statement
[Title of Invention] Styrenic resin composition, plate-shaped molded article and light guide plate
[Technical field]
[0001]
The present invention relates to a styrene-based resin composition, a plate-shaped molded article, and a light guide plate that are excellent in hue and transparency, do not cause whitening due to environmental changes, and have excellent long-term thermal stability, and are suitable for light guide plate applications. It is.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The An acrylic resin typified by PMMA (polymethylmethacrylate) is used for the light guide plate. However, since the water absorption is high, there may be a problem that the molded product is warped or a change in dimensions.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
However, Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylic ester copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water-absorbing property and the dimensional stability tend to be worse than those of the styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, there is a problem (whitening phenomenon) that a molded product becomes cloudy due to environmental changes such as temperature and humidity. Specifically, when a molded product is exposed to an environmental change from a high temperature and high humidity environment to a room temperature environment or an environmental change from a room temperature environment to a low temperature environment, moisture present uniformly in the molded product is not present. It becomes stable and phase-separates, and a disk-like defect is generated. As a result, the inside of the molded product becomes cloudy. When the molded product becomes cloudy, when the optical path length is long as in the light guide plate, there is a problem that the transmittance is greatly reduced due to light scattering and the luminance of the display is lowered.
Furthermore, the styrenic resin undergoes discoloration due to heat during long-term use, and there is a problem that the molded product turns yellow and the transmittance decreases. As a result, there is a problem that the luminance of the display is lowered or the chromaticity is changed.
[Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
The present invention prevents whitening due to environmental changes, has little change in hue and transmittance even after long-term use, and is particularly suitable for optical applications such as a light guide plate, and has excellent colorless transparency and heat resistance. It is an object to provide a styrene-based resin composition.
[Means for solving problems]
[0005]
The present invention relates to (1) (a) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy]. Styrenic resin comprising -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (c) polyoxyethylene type nonionic surfactant The content of (b) in 100% by mass of the styrene-based resin composition is 0.05 to 0.40% by mass, and the content of (c) is 0.4 to 2.0% by mass. A styrene-based resin composition characterized by being.
(2) (a) Styrenic resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4 , 8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, (c) polyoxyethylene type nonionic surfactant, and (d) hindered phenol oxidation A styrene resin composition comprising an inhibitor, wherein the content of (b) in 100% by mass of the styrene resin composition is 0.05 to 0.40% by mass, and the content of (c) is 0.4. A styrenic resin composition characterized in that the content of -2.0% by mass and (d) is 0.02-0.50% by mass.
(3) (c) 1 selected from the group of polyoxyethylene fatty acid esters represented by the following polyoxyethylene alkyl ether represented by the following general formula 1 and / or polyoxyethylene fatty acid ester represented by the following general formula 2: The styrenic resin composition as described in (1) or (2), wherein the styrene resin composition is one or more types and the average added mole number of ethylene oxide is 7 to 100.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms, and n is an integer representing the number of added moles of ethylene oxide units)
(4) A plate-like molded product obtained by molding the styrene resin composition according to any one of (1) to (3).
(5) A light guide plate comprising the plate-like molded product according to (4).
[Effect of the invention]
[0006]
The styrenic resin composition of the present invention is less expensive and less water-absorbing compared to PMMA and MS resin, does not cause the whitening phenomenon due to environmental changes, which is a disadvantage of PS resin, and in long-term use Since changes in hue and transmittance are small and excellent in colorless transparency, it can be suitably used for optical applications such as a light guide plate. Moreover, the coloring prevention effect with respect to high temperature heat history, such as a shaping | molding process, is also high.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin of the present invention can be obtained by polymerizing a styrene monomer. The styrene monomer is an aromatic vinyl monomer, such as styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, or a mixture of two or more, preferably styrene.
[0008]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0009]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0010]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0011]
The styrene resin of the present invention has a weight average molecular weight of 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer The molecular weight of the present invention is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0012]
The styrene resin composition of the present invention comprises (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4, in 100% by mass of the styrene resin composition. It contains 8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, and its content is 0.05 to 0.40% by mass. When the content of (b) is less than 0.05% by mass, the long-term thermal stability is inferior, and the initial hue and transmittance are also inferior. Moreover, even if it exceeds 0.40 mass%, long-term thermal stability will deteriorate.
[0013]
The styrene resin composition of the present invention preferably contains 0.02 to 0.50 mass% of (d) a hindered phenol antioxidant in 100 mass% of the styrene resin composition, and 0.05 to 0 More preferably, the content is 30% by mass. 6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Long-term thermal stability, initial hue, and transmittance are improved as compared with the case of using dioxaphosphepine alone.
[0014]
Examples of the hindered phenol antioxidant used in the present invention include octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, ethylenebis (oxyethylene) bis [3- (5 -Tert-butyl-4-hydroxy-m-tolyl) propionate], 4,6-bis (octylthiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -o-cresol, 2,4 -Dimethyl-6- (1-methylpentadecyl) phenol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, DL-α-tocopherol, 2-t- Butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1 (2-hydroxy-3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4′-thiobis (6-t-butyl-3-methylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-tert-butylphenol) Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate and / or ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate ] Is preferable.
[0015]
The styrene resin composition of the present invention contains (c) a polyoxyethylene type nonionic surfactant (also referred to as a polyethylene glycol type nonionic surfactant) in 100% by mass of the styrene resin composition, Content is 0.4-2.0 mass%, and it is preferable that it is 0.7-1.6 mass%. If the content of the polyoxyethylene-type nonionic surfactant is less than 0.4% by mass, it is difficult to prevent the whitening phenomenon due to environmental changes. descend.
[0016]
Polyoxyethylene type nonionic surfactants include polyoxyethylene alkyl ether represented by the following general formula (1), polyoxyethylene fatty acid ester represented by the following general formula (2), polyoxyethylene hydrogenated castor oil, polyoxy Ethylene sorbitan fatty acid ester and polyoxyethylene sorbitol fatty acid ester are exemplified, but one or more selected from the group of polyoxyethylene alkyl ether and / or polyoxyethylene fatty acid ester are preferable.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms, and n is an integer representing the number of added moles of ethylene oxide units)
[0017]
Polyoxyethylene alkyl ether is made by adding ethylene oxide to alcohol, and polyoxyethylene fatty acid ester is made by adding ethylene oxide to fatty acid or directly esterifying fatty acid and polyethylene glycol. The number is preferably 7 to 100, and more preferably 10 to 50.
[0018]
Examples of the polyoxyethylene alkyl ether include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene octyl decyl ether, polyoxyethylene myristyl ether, polyoxyethylene-2-ethylhexyl ether and the like. Is mentioned.
[0019]
Examples of the polyoxyethylene fatty acid ester include polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, and the like.
[0020]
6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3 of the present invention , 2] Dioxaphosphepine, hindered phenolic antioxidant and polyethylene glycol can be added by adding and mixing in the polymerization process, devolatilization process, granulation process of styrene resin, and extrusion during molding process. There is a method of adding and mixing with a machine or the like, and there is no particular limitation.
[0021]
The Vicat softening temperature of the styrene-based resin composition of the present invention is preferably 95 to 104 ° C, and more preferably 97 to 104 ° C. When the Vicat softening temperature is less than 95 ° C., the heat resistance is insufficient, and the molded product may be deformed depending on the use environment.
[0022]
The styrenic resin composition of the present invention may contain mineral oil as long as the colorless transparency of the present invention is not impaired. Additives such as internal lubricants such as stearic acid and ethylene bis stearamide, phosphorus antioxidants, sulfur antioxidants, lactone antioxidants, hindered amine stabilizers, UV absorbers, antistatic agents, etc. May be included. As the external lubricant, ethylene bis stearamide is preferable, and the content is preferably 30 to 200 ppm in the resin composition.
[0023]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0024]
The styrenic resin composition of the present invention can be molded into a plate-shaped product by a molding method according to the purpose such as injection molding, extrusion molding, compression molding, etc., and used as a light guide plate. At that time, a reflection pattern such as a dot pattern can be provided on the back surface (opposite side of the light emitting surface) of the plate-shaped molded product, and used as a light guide plate. When processing from the resin plate to the light guide plate, it is preferable to polish the light incident surface or the entire end surface of the resin plate to make a mirror surface. In addition, in order to improve the uniformity of the emitted light, a prism pattern can be provided on the surface (surface from which light is emitted) of the plate-shaped molded product. The pattern on the front surface or the back surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0025]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0026]
(Examples 1-19, Comparative Examples 1-7)
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A mixed solution of 84.0% by mass of styrene and 16.0% by mass of ethylbenzene was prepared, and 400 ppm of 2,2-bis (4,4-t-butylperoxycyclohexyl) propane was mixed on the basis of styrene, A raw material solution was obtained. As 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, Pertetra A manufactured by NOF Corporation was used. This raw material solution was continuously supplied to the first reactor at a rate of 11.2 kg / hour. The reaction temperature of each reactor is 116 ° C. in the first reactor, 120 ° C. in the second reactor, and in the third reactor, a temperature gradient is created along the direction of flow, 140 ° C. in the middle portion, and in the outlet portion. The temperature was adjusted to 150 ° C.
Moreover, the polyoxyethylene type nonionic surfactant was added to the inlet of the 3rd reactor so that it might become a kind and content shown in Table 6-1. The types of polyoxyethylene type nonionic surfactants are as follows.
P-1: Polyoxyethylene ethylene lauryl ether Ethylene oxide average added mole number = 25 (Emalgen 123P manufactured by Kao Corporation)
P-2: Polyoxyethylene ethylene stearyl ether ethylene oxide average added mole number = 12 (Emulgen 320P manufactured by Kao Corporation)
P-3: Polyoxyethylene ethylene lauryl ether Ethylene oxide average addition mole number = 9 (Emulgen 109P manufactured by Kao Corporation)
P-4: Polyoxyethylene ethylene cetyl ether Average number of moles of ethylene oxide added = 7 (Emulgen 210P manufactured by Kao Corporation)
P-5: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 30 (Emulgen 130K manufactured by Kao Corporation)
P-6: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 47 (Emulgen 150 manufactured by Kao Corporation)
P-7: Polyoxyethylene ethylene myristyl ether Ethylene oxide average addition mole number = 85 (Emulgen 4085 manufactured by Kao Corporation)
P-8: Polyethylene glycol monolaurate Ethylene oxide average added mole number = 12 (Emanon 1112 manufactured by Kao Corporation)
P-9: polyoxyethylene ethylene stearyl ether ethylene oxide average addition mole number = 6 (Emulgen 306P manufactured by Kao Corporation)
Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted of two stages in series, and after separating unreacted styrene and ethylbenzene, a strand shape After being extruded and cooled, it was cut into pellets. The resin temperature in the first stage devolatilization tank is set to 160 ° C., the pressure in the vacuum devolatilization tank is set to 65 kPa, the resin temperature in the second stage devolatilization layer is set to 235 ° C. The pressure in the volatilization tank was 0.8 kPa.
All of the obtained styrene resins had a weight average molecular weight (Mw) of 370,000.
[0027]
Next, using a single screw extruder having a screw diameter of 40 mm, the pellets of the styrenic resin and the additives A and B obtained above were used so that the content shown in Table 6-1 was obtained. Pellets were obtained by melt-kneading at a rotation speed of 100 rpm. Additives A and B used in Table 6-1 are shown below. In addition, additive A is (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3, 2] dioxaphosphepine, additive B represents (d) a hindered phenol antioxidant.
A-1: 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3,2] Dioxaphosphepin (Sumitomo GP, manufactured by Sumitomo Chemical Co., Ltd.)
B-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
B-2: Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
Melt mass flow rate (MFR) is measured in accordance with JIS K-7210 under the conditions of 200 ° C. and 49 N load, Vicat softening temperature is measured in accordance with JIS K 7206 at a heating rate of 50 ° C./hr and a test load of 50 N. did.
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. In order to evaluate long-term thermal stability, the obtained plate-shaped molded article was stored in an 80 ° C. oven for 500 hours. In order to evaluate the optical properties before and after storage, a 115 × 85 × 3 mm thickness test piece was cut out from the plate-shaped molded product, the end surface was polished by buffing, and a plate-shaped molded product having a mirror surface on the end surface was created. Using an ultraviolet-visible spectrophotometer V-670 manufactured by Co., Ltd., measuring the spectral transmittance at a wavelength of 350 nm to 800 nm at an optical path length of 115 mm in incident light having a size of 20 × 1.6 mm and a spread angle of 0 °, The YI value at a visual field of 2 ° for the C light source was calculated according to JIS K7105. The transmittance shown in Table 6-1 represents the average transmittance at a wavelength of 380 nm to 780 nm.
Furthermore, in order to confirm the whitening phenomenon due to environmental changes, a plate-like molded article having a mirror surface on the end face is exposed to an environment of 60 ° C. and 90% relative humidity for 150 hours, and the test piece is placed in an environment of 23 ° C. and 50% relative humidity. Taking out and observing the whitening phenomenon occurring inside the molded product, the following judgment was made as a whitening suppression effect.
A: No whitening occurs. O: Whitening occurs slightly after 1 hour, but disappears after 24 hours. Δ: Whitening occurs after 1 hour, but almost disappears after 24 hours. X: Remarkably whitening after 1 hour. Table 6-1 shows the characteristics of each resin composition.
[0028]
[Table 6-1]

[0029]
The molded articles of the examples are excellent in whitening suppression effect, excellent in initial transmittance and YI value, and excellent in long-term thermal stability.
[Industrial applicability]
[0030]
The styrenic resin composition of the present invention prevents whitening due to environmental changes and is excellent in transparency and hue because of excellent long-term thermal stability, and is used in televisions, desktop personal computers, notebook personal computers, mobile phones. It can be suitably used for light guide plate applications such as telephones and car navigation systems.

[００２６]
実施例の成形品は、白化抑制効果に優れ、初期の透過率とＹＩ値に優れており、長期の熱安定性にも優れている。
[産業上の利用可能性]
[００２７]
本発明のスチレン系樹脂組成物は、環境変化による白化現象が防止され、長期の熱安定性に優れることから透明性と色相に優れており、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 7)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8, A styrene-based resin composition comprising 10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (c) polyethylene glycol, in 100% by mass of the styrene-based resin composition The content of (b) is 0.05 to 0.40% by mass, and the content of (c) is 0.4 to 2.0% by mass.
[Claim 2]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8, A styrene resin composition comprising 10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, (c) polyethylene glycol, and (d) a hindered phenol antioxidant. The content of (b) in 100% by mass of the styrene-based resin composition is 0.05 to 0.40% by mass, the content of (c) is 0.4 to 2.0% by mass, and (d) Content is 0.02-0.50 mass%, Styrenic resin composition characterized by the above-mentioned.
[Claim 3]
Vicat softening temperature is 95-103 degreeC, The styrenic resin composition of Claim 1 or 2 characterized by the above-mentioned.
[Claim 4]
The plate-shaped molded article formed by shape | molding the styrene resin composition of any one of Claims 1-3.
[Claim 5]
A light guide plate comprising the plate-like molded product according to claim 4.
[Document Name] Statement
[Title of Invention] Styrenic resin composition, plate-shaped molded article and light guide plate
[Technical field]
[0001]
The present invention relates to a styrene-based resin composition, a plate-shaped molded article, and a light guide plate that are excellent in hue and transparency, do not cause whitening due to environmental changes, and have excellent long-term thermal stability, and are suitable for light guide plate applications. It is.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The An acrylic resin typified by PMMA (polymethylmethacrylate) is used for the light guide plate. However, since the water absorption is high, there may be a problem that the molded product is warped or a change in dimensions.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
However, Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylic ester copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water-absorbing property and the dimensional stability tend to be worse than those of the styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, there is a problem (whitening phenomenon) that a molded product becomes cloudy due to environmental changes such as temperature and humidity. Specifically, when a molded product is exposed to an environmental change from a high temperature and high humidity environment to a room temperature environment or an environmental change from a room temperature environment to a low temperature environment, moisture present uniformly in the molded product is not present. It becomes stable and phase-separates, and a disk-like defect is generated. As a result, the inside of the molded product becomes cloudy. When the molded product becomes cloudy, when the optical path length is long as in the light guide plate, there is a problem that the transmittance is greatly reduced due to light scattering and the luminance of the display is lowered.
Furthermore, the styrenic resin undergoes discoloration due to heat during long-term use, and there is a problem that the molded product turns yellow and the transmittance decreases. As a result, there is a problem that the luminance of the display is lowered or the chromaticity is changed.
[Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
The present invention prevents whitening due to environmental changes, has little change in hue and transmittance even after long-term use, has excellent colorless transparency suitable for optical applications such as a light guide plate, and provided heat resistance. It is an object to provide a styrene-based resin composition.
[Means for solving problems]
[0005]
The present invention relates to (1) (a) a styrene resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy]. A styrene resin composition comprising -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (c) polyethylene glycol, The styrene-based resin is characterized in that the content of (b) in 100% by mass of the resin composition is 0.05 to 0.40% by mass and the content of (c) is 0.4 to 2.0% by mass. Resin composition.
(2) (a) Styrenic resin having a weight average molecular weight of 150,000 to 700,000 and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4 , 8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, (c) polyethylene glycol and (d) a hindered phenol antioxidant The content of (b) in 100% by mass of the styrene-based resin composition is 0.05 to 0.40% by mass, the content of (c) is 0.4 to 2.0% by mass, ( A styrenic resin composition, wherein the content of d) is 0.02 to 0.50 mass%.
(3) The styrenic resin composition according to (1) or (2), wherein the Vicat softening temperature is 95 to 103 ° C.
(4) A plate-shaped molded article obtained by molding the styrene-based resin composition according to any one of (1) to (3).
(5) A light guide plate comprising the plate-like molded product according to (4).
[Effect of the invention]
[0006]
The styrenic resin composition of the present invention is less expensive and less water-absorbing compared to PMMA and MS resin, does not cause the whitening phenomenon due to environmental changes, which is a disadvantage of PS resin, and in long-term use Since changes in hue and transmittance are small and excellent in colorless transparency, it can be suitably used for optical applications such as a light guide plate. Moreover, the coloring prevention effect with respect to high temperature heat history, such as a shaping | molding process, is also high.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin of the present invention can be obtained by polymerizing a styrene monomer. The styrene monomer is an aromatic vinyl monomer, such as styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, or a mixture of two or more, preferably styrene.
[0008]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0009]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0010]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0011]
The styrene resin of the present invention has a weight average molecular weight of 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer The molecular weight of the present invention is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0012]
The styrene resin composition of the present invention comprises (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4, in 100% by mass of the styrene resin composition. It contains 8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, and its content is 0.05 to 0.40% by mass. When the content of (b) is less than 0.05% by mass, the long-term thermal stability is inferior, and the initial hue and transmittance are also inferior. Moreover, even if it exceeds 0.40 mass%, long-term thermal stability will deteriorate.
[0013]
The styrene resin composition of the present invention preferably contains 0.02 to 0.50 mass% of (d) a hindered phenol antioxidant in 100 mass% of the styrene resin composition, and 0.05 to 0 More preferably, the content is 30% by mass. 6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Long-term thermal stability, initial hue, and transmittance are improved as compared with the case of using dioxaphosphepine alone.
[0014]
Examples of the hindered phenol antioxidant used in the present invention include octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, ethylenebis (oxyethylene) bis [3- (5 -Tert-butyl-4-hydroxy-m-tolyl) propionate], 4,6-bis (octylthiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -o-cresol, 2,4 -Dimethyl-6- (1-methylpentadecyl) phenol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, DL-α-tocopherol, 2-t- Butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1 (2-hydroxy-3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4′-thiobis (6-t-butyl-3-methylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-tert-butylphenol) Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate and / or ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate ] Is preferable.
[0015]
In the styrene resin composition of the present invention, the content of polyethylene glycol is 0.4 to 2.0% by mass, preferably 0.6 to 1.6% by mass, and 0.6 to 1.2. More preferably, it is mass%. If the polyethylene glycol content is less than 0.4% by mass, it is difficult to prevent the whitening phenomenon due to environmental changes, and if it exceeds 2.0% by mass, the heat resistance of the styrene-based resin composition decreases.
[0016]
The average molecular weight of the polyethylene glycol used in the present invention is preferably 200 to 4000, and more preferably 300 to 1000. If the average molecular weight of polyethylene glycol is less than 200, gas is generated during the molding process, and the mold and roll are soiled, which is not preferable. On the other hand, if it exceeds 4000, the effect of preventing the whitening phenomenon tends to decrease. The average molecular weight is calculated from the hydroxyl group concentration (based on JIS K1557) measured by the pyridine phthalic anhydride method.
[0017]
6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3 of the present invention , 2] Dioxaphosphepine, hindered phenolic antioxidant and polyethylene glycol can be added by adding and mixing in the polymerization process, devolatilization process, granulation process of styrene resin, and extrusion during molding process. There is a method of adding and mixing with a machine or the like, and there is no particular limitation.
[0018]
The Vicat softening temperature of the styrene-based resin composition of the present invention is preferably 95 to 104 ° C, and more preferably 97 to 104 ° C. When the Vicat softening temperature is less than 95 ° C., the heat resistance is insufficient, and the molded product may be deformed depending on the use environment.
[0019]
The styrenic resin composition of the present invention may contain mineral oil as long as the colorless transparency of the present invention is not impaired. Additives such as internal lubricants such as stearic acid and ethylene bis stearamide, phosphorus antioxidants, sulfur antioxidants, lactone antioxidants, hindered amine stabilizers, UV absorbers, antistatic agents, etc. May be included. As the external lubricant, ethylene bis stearamide is preferable, and the content is preferably 30 to 200 ppm in the resin composition.
[0020]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0021]
The styrenic resin composition of the present invention can be molded into a plate-shaped product by a molding method according to the purpose such as injection molding, extrusion molding, compression molding, etc., and used as a light guide plate. At that time, a reflection pattern such as a dot pattern can be provided on the back surface (opposite side of the light emitting surface) of the plate-shaped molded product, and used as a light guide plate. When processing from the resin plate to the light guide plate, it is preferable to polish the light incident surface or the entire end surface of the resin plate to make a mirror surface. In addition, in order to improve the uniformity of the emitted light, a prism pattern can be provided on the surface (surface from which light is emitted) of the plate-shaped molded product. The pattern on the front surface or the back surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0022]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0023]
(Examples 1-17, Comparative Examples 1-7)
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A mixed solution of 84.0% by mass of styrene and 16.0% by mass of ethylbenzene was prepared, and 400 ppm of 2,2-bis (4,4-t-butylperoxycyclohexyl) propane was mixed on the basis of styrene, A raw material solution was obtained. As 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, Pertetra A manufactured by NOF Corporation was used. This raw material solution was continuously supplied to the first reactor at a rate of 11.2 kg / hour. The reaction temperature of each reactor is 116 ° C. in the first reactor, 120 ° C. in the second reactor, and in the third reactor, a temperature gradient is created along the direction of flow, 140 ° C. in the middle portion, and in the outlet portion. The temperature was adjusted to 150 ° C.
Further, polyethylene glycol was added to the inlet of the third reactor so as to have the types and contents shown in Table 7-1. The types of additives and polyethylene glycol used are as follows.
P-1: Polyethylene glycol having an average molecular weight of 400 (PEG # 400 manufactured by NOF Corporation)
P-2: Polyethylene glycol having an average molecular weight of 300 (PEG # 300 manufactured by NOF Corporation)
P-3: Polyethylene glycol having a weight average molecular weight of 600 (PEG # 600 manufactured by NOF Corporation)
P-4: Polyethylene glycol having a weight average molecular weight of 1000 (PEG # 1000 manufactured by NOF Corporation)
P-5: Polyethylene glycol having a weight average molecular weight of 2000 (PEG # 2000 manufactured by NOF Corporation)
P-6: Polyethylene glycol having a weight average molecular weight of 3100 (PEG # 4000 manufactured by NOF Corporation)
P-7: Polyethylene glycol having a weight average molecular weight of 8800 (PEG # 6000 manufactured by NOF Corporation)
Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted of two stages in series, and after separating unreacted styrene and ethylbenzene, a strand shape After being extruded and cooled, it was cut into pellets. The resin temperature in the first stage devolatilization tank is set to 160 ° C., the pressure in the vacuum devolatilization tank is set to 65 kPa, the resin temperature in the second stage devolatilization layer is set to 235 ° C. The pressure in the volatilization tank was 0.8 kPa.
All of the obtained styrene resins had a weight average molecular weight (Mw) of 370,000.
[0024]
Next, using a single screw extruder with a screw diameter of 40 mm, the pellets of the styrenic resin and the additives A and B obtained above were used at a cylinder temperature of 230 ° C. and a screw so that the content shown in Table 7-1 was obtained. Pellets were obtained by melt-kneading at a rotation speed of 100 rpm. Additives A and B used in Table 7-1 are shown below. In addition, additive A is (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3, 2] dioxaphosphepine, additive B represents (d) a hindered phenol antioxidant.
A-1: 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3,2] Dioxaphosphepin (Sumitomo GP, manufactured by Sumitomo Chemical Co., Ltd.)
B-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
B-2: Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
In addition, the melt mass flow rate (MFR) is in accordance with JIS K-7210, under conditions of 200 ° C. and 49 N load, the Vicat softening temperature is in accordance with JIS K 7206, the heating rate is 50 ° C./hr, and the test load is 50 N. Measured with
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. In order to evaluate long-term thermal stability, the obtained plate-shaped molded article was stored in an 80 ° C. oven for 500 hours. In order to evaluate the optical properties before and after storage, a 115 × 85 × 3 mm thickness test piece was cut out from the plate-shaped molded product, the end surface was polished by buffing, and a plate-shaped molded product having a mirror surface on the end surface was created. Using an ultraviolet-visible spectrophotometer V-670 manufactured by Co., Ltd., measuring the spectral transmittance at a wavelength of 350 nm to 800 nm at an optical path length of 115 mm in incident light having a size of 20 × 1.6 mm and a spread angle of 0 °, The YI value at a visual field of 2 ° for the C light source was calculated according to JIS K7105. The transmittance shown in Table 7-1 represents the average transmittance at a wavelength of 380 nm to 780 nm.
Furthermore, in order to confirm the whitening phenomenon due to environmental changes, a plate-like molded article having a mirror surface on the end face is exposed to an environment of 60 ° C. and 90% relative humidity for 150 hours, and the test piece is placed in an environment of 23 ° C. and 50% relative humidity. Taking out and observing the whitening phenomenon occurring inside the molded product, the following judgment was made as a whitening suppression effect.
A: No whitening occurs. O: Whitening occurs slightly after 1 hour, but disappears after 24 hours. Δ: Whitening occurs after 1 hour, but almost disappears after 24 hours. X: Remarkably whitening after 1 hour. Table 7-1 shows the characteristics of each resin composition.
[0025]
[Table 7-1]

[0026]
The molded articles of the examples are excellent in whitening suppression effect, excellent in initial transmittance and YI value, and excellent in long-term thermal stability.
[Industrial applicability]
[0027]
The styrenic resin composition of the present invention prevents whitening due to environmental changes and is excellent in transparency and hue because of excellent long-term thermal stability, and is used in televisions, desktop personal computers, notebook personal computers, mobile phones. It can be suitably used for light guide plate applications such as telephones and car navigation systems.

[００３５]
実施例の成形品は、白化抑制効果に優れ、初期の透過率とＹＩ値に優れており、８０℃×１０００時間での保管におけるＹＩ変化量が小さく、長期の熱安定性にも優れている。
[産業上の利用可能性]
[００３６]
本発明の光学用スチレン系樹脂組成物は、色相および透明性に優れ、長期の熱安定性に優れることから、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 8)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000, (b) a hydrophilic additive having a polyether chain, and (c) 6- [3- (3-tert-butyl-4-hydroxy-5) -Methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, a styrene resin composition comprising styrene The optical system characterized in that the content of (b) in 100% by mass of the resin composition is 0.4 to 2.0% by mass and the content of (c) is 0.02 to 0.40% by mass. Styrenic resin composition.
[Claim 2]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000, (b) a hydrophilic additive having a polyether chain, and (c) 6- [3- (3-tert-butyl-4-hydroxy-5) -Methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (d) a phosphorus-based antioxidant It is a resin composition, Comprising: Content of (b) in 100 mass% of styrenic resin compositions is 0.4-2.0 mass%, Content of (c) is 0.02-0.40 mass% (D) content is 0.02-0.50 mass%, The optical styrene resin composition characterized by the above-mentioned.
[Claim 3]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000, (b) a hydrophilic additive having a polyether chain, and (c) 6- [3- (3-tert-butyl-4-hydroxy-5) -Methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (e) a hindered phenolic antioxidant. The content of (b) in 100% by mass of the styrene resin composition is 0.4 to 2.0% by mass, and the content of (c) is 0.02 to 0.40. A styrenic resin composition for optical use, wherein the content of (e) is 0.02 to 0.50% by mass.
[Claim 4]
(A) a styrene resin having a weight average molecular weight of 150,000 to 700,000, (b) a hydrophilic additive having a polyether chain, and (c) 6- [3- (3-tert-butyl-4-hydroxy-5) -Methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, (d) phosphorus antioxidants and (e) A styrene resin composition comprising a hindered phenol-based antioxidant, wherein the content of (b) in 100% by mass of the styrene resin composition is 0.4 to 2.0% by mass, the content of (c) The amount is 0.02 to 0.40% by mass, the content of (d) is 0.02 to 0.50% by mass, and the content of (e) is 0.02 to 0.50% by mass. An optical styrene resin composition.
[Claim 5]
The molded article using the styrene resin composition for optics of any one of Claims 1-4.
[Claim 6]
A light guide plate using the molded product according to claim 5.
[Document Name] Statement
[Title of the Invention] Optical Styrenic Resin Composition, Molded Product, and Light Guide Plate
[Technical field]
[0001]
The present invention relates to an optical styrenic resin composition excellent in hue and transparency, a molded article, and a light guide plate.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The A backlight using a light guide plate is also used for illumination. An acrylic resin typified by PMMA (polymethyl methacrylate) is used for the light guide plate. However, since the water absorption is high, the molded product may be warped or dimensional changes may occur.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylate copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water absorption is high and the dimensional stability tends to be worse than that of a styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, discoloration due to heat may occur during long-term use, and the molded product may turn yellow to lower the transmittance. As a result, the luminance of the backlight may decrease and the chromaticity may change.
In addition, a styrene resin using a styrene monomer as a raw material has low water absorption, but the molded product may become cloudy due to environmental changes such as temperature and humidity (whitening phenomenon). Specifically, when a molded product is exposed to an environmental change from a high temperature and high humidity environment to a room temperature environment or an environmental change from a room temperature environment to a low temperature environment, moisture present uniformly in the molded product is not present. It becomes stable and phase-separates, and a disk-like defect is generated. As a result, the inside of the molded product becomes cloudy. When the molded product becomes cloudy, when the optical path length is long like a light guide plate, the transmittance is greatly reduced due to light scattering, and the luminance of the display is lowered.
[Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
An object of the present invention is to provide a styrenic resin composition for optical use, a molded article, and a light guide plate that prevent whitening due to environmental changes, is excellent in long-term thermal stability, and is excellent in colorless transparency.
[Means for solving problems]
[0005]
(1) (a) a styrene resin having a weight average molecular weight of 150,000 to 700,000, (b) a hydrophilic additive having a polyether chain, and (c) 6- [3- (3-tert-butyl-4- Hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine is a styrenic resin composition. The content of (b) in 100% by mass of the styrene-based resin composition is 0.4 to 2.0% by mass, and the content of (c) is 0.02 to 0.40% by mass. An optical styrene resin composition.
(2) (a) a styrene resin having a weight average molecular weight of 150,000 to 700,000, (b) a hydrophilic additive having a polyether chain, and (c) 6- [3- (3-tert-butyl-4- Hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (d) phosphorus antioxidant The content of (b) in 100% by mass of the styrene-based resin composition is 0.4 to 2.0% by mass, and the content of (c) is 0.02 to 0.00%. An optical styrene resin composition, wherein the content of 40% by mass and (d) is 0.02 to 0.50% by mass.
(3) (a) a styrene resin having a weight average molecular weight of 150,000 to 700,000, (b) a hydrophilic additive having a polyether chain, and (c) 6- [3- (3-tert-butyl-4- Hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (e) hindered phenolic antioxidants A styrene resin composition comprising an agent, wherein the content of (b) in 100% by mass of the styrene resin composition is 0.4 to 2.0% by mass, and the content of (c) is 0.02 to 0.02%. An optical styrene-based resin composition having a content of 0.40% by mass and (e) of 0.02 to 0.50% by mass.
(4) (a) a styrene resin having a weight average molecular weight of 150,000 to 700,000, (b) a hydrophilic additive having a polyether chain, and (c) 6- [3- (3-tert-butyl-4- Hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (d) a phosphorus-based antioxidant (E) A styrene resin composition comprising a hindered phenol antioxidant, wherein the content of (b) in 100% by mass of the styrene resin composition is 0.4 to 2.0% by mass, (c ) Content of 0.02 to 0.40 mass%, (d) content of 0.02 to 0.50 mass%, and (e) content of 0.02 to 0.50 mass%. A styrenic resin composition for optics.
(5) A molded product using the optical styrenic resin composition according to any one of (1) to (4).
(6) A light guide plate using the molded product according to (5).
[Effect of the invention]
[0006]
The optical styrenic resin composition and molded product of the present invention have low water absorption, excellent dimensional stability and are inexpensive compared to PMMA and MS resin. Moreover, since the whitening phenomenon by the environmental change which is a fault of PS resin does not generate | occur | produce, it is excellent in long-term thermal stability and colorless transparency, Therefore It can use suitably for optical uses, such as a light-guide plate. Moreover, the coloring prevention effect with respect to high temperature heat history, such as a shaping | molding process, is also high.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin is a polymer having a unit structure derived from a styrene monomer. The styrene resin can be obtained by polymerizing a styrene monomer. Examples of the styrene monomer include styrene, α-methyl styrene, p-methyl styrene, o-methyl styrene, m-methyl styrene, ethyl styrene, pt-butyl styrene, and preferably styrene. Styrenic monomers may be used alone or in combination of two or more. As the styrenic resin, those having a small amount of other unit structures can also be used. The other unit structure is preferably 5% or less. Other unit structures include unit structures derived from vinyl monomers copolymerizable with styrene monomers. Examples of copolymerizable vinyl monomers include acrylic acid monomers such as acrylic acid and methacrylic acid, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, acrylic monomers such as butyl acrylate and methyl methacrylate, and maleic anhydride. Examples include α, β-ethylenically unsaturated carboxylic acids such as acid and fumaric acid, and imide monomers such as N-phenylmaleimide and N-cyclohexylmaleimide.
[0008]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0009]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0010]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0011]
The weight average molecular weight of the styrene resin is 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: differential refractometer The molecular weight is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0012]
The styrene-based resin composition contains a hydrophilic additive having a polyether chain in 100% by mass of the styrene-based resin composition, the content is 0.4 to 2.0% by mass, and 0.6 to 1 It is preferably 6% by mass. If the content of the hydrophilic additive having a polyether chain is less than 0.4% by mass, it is difficult to prevent the whitening phenomenon due to environmental changes, and if it exceeds 2.0% by mass, the heat resistance of the styrene resin composition is lowered. To do.
[0013]
The hydrophilic additive having a polyether chain is an additive having a polyether chain in the molecule. A polyether chain is a compound in which ether bonds are linked. For example, a polyoxyethylene chain, a polyoxypropylene chain, a polyoxybutylene chain or glycerin synthesized by an addition reaction of an alkylene oxide such as ethylene oxide, propylene oxide, or butylene oxide. A polyglycerol chain synthesized by dehydration condensation of a polyoxyethylene chain is preferable, and a polyoxyethylene chain is preferable.
[0014]
Examples of the hydrophilic additive having a polyether chain include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene octyl decyl ether, polyoxyethylene myristyl ether, polyoxyethylene 2 -Polyoxyethylene alkyl ethers such as ethylhexyl ether, polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitol fatty acid esters such as polyoxyethylene sorbitol tetraoleate , Polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol dis Polyoxyethylene fatty acid esters such as allate, polyethylene glycol monooleate, polyoxyethylene hydrogenated castor oil, polyethylene glycol, polyoxyethylene monomethyl ether, polyoxyethylene dimethyl ether, polyoxyethylene glyceryl ether, polyoxyethylene tetraoleic acid, poly Oxyethylene triisostearic acid, polyoxyethylene coconut fatty acid glyceryl, polypropylene glycol, polyoxypropylene glyceryl ether, polyoxypropylene diglyceryl ether, polyoxypropylene sorbitol, polybutylene glycol, diglycerin, polyglycerin, polyoxyethylene polyglyceryl ether , Polyoxypropylene polyglyceryl ether, polyglyceryl And fatty acid esters. Among these, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester and polyethylene glycol are preferable, and the effect of preventing whitening phenomenon is high.
[0015]
Polyoxyethylene alkyl ether is made by adding ethylene oxide to alcohol, and polyoxyethylene fatty acid ester is made by adding ethylene oxide to fatty acid or directly esterifying fatty acid and polyethylene glycol. The average added mole number of ethylene oxide is preferably 7 to 100, and more preferably 10 to 50.
[0016]
The average molecular weight of polyethylene glycol is preferably 200 to 4000, and more preferably 300 to 1000. If the average molecular weight of polyethylene glycol is less than 200, gas is generated during the molding process, and the mold and roll are soiled, which is not preferable. On the other hand, if it exceeds 4000, the effect of preventing the whitening phenomenon tends to decrease. The average molecular weight is calculated from the hydroxyl group concentration (based on JIS K1557) measured by the pyridine phthalic anhydride method.
[0017]
The heat loss of the hydrophilic additive having a polyether chain at a temperature of 200 ° C. and in a nitrogen atmosphere is preferably 10% by mass or less. Heat loss in a nitrogen atmosphere at a temperature of 200 ° C. can be determined by thermogravimetric analysis (TGA). Heating is performed at a temperature increase rate of 10 ° C./min from a room temperature in a nitrogen atmosphere, and the weight loss at a temperature of 200 ° C. It can be determined from the quantity. Additives whose weight loss on heating at a temperature of 200 ° C. and under a nitrogen atmosphere exceeds 10% by mass have high volatility, and gas is generated during the molding process of the styrene resin composition, which may cause mold or roll contamination.
[0018]
Examples of the method for adding a hydrophilic additive having a polyether chain include a method of adding and mixing in a polymerization step, a devolatilization step and a granulation step of a styrenic resin, and a method of adding and mixing with an extruder during molding processing. There is no particular limitation.
[0019]
The Vicat softening temperature of the styrene resin composition is preferably 95 to 104 ° C, and more preferably 97 to 104 ° C. When the Vicat softening temperature is less than 95 ° C., the heat resistance is insufficient, and the molded product may be deformed depending on the use environment. The Vicat softening temperature was measured according to JIS K 7206 at a heating rate of 50 ° C./hr and a test load of 50 N.
[0020]
The styrene resin composition is composed of (c) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10 in 100% by mass of the styrene resin composition. -Tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine is contained, the content thereof is 0.02 to 0.40% by mass, 0.05 to 0. 0. It is preferably 20% by mass. When the content of (c) is less than 0.02% by mass, the long-term thermal stability is inferior, and the initial hue and transmittance are also inferior. Moreover, even if it exceeds 0.40 mass%, long-term thermal stability will deteriorate. Long-term thermal stability represents changes in hue and transmittance due to heat in long-term use, and those having excellent thermal stability have small changes in hue and transmittance. Long-term thermal stability can be evaluated as an accelerated test by storing a molded product under a high temperature condition (60 to 90 ° C.) such that the resin does not deform, and changing the hue and transmittance over time.
[0021]
The styrene resin composition preferably contains 0.02 to 0.50 mass% of (d) phosphorus antioxidant in 100 mass% of the styrene resin composition, and 0.05 to 0.30 mass%. More preferably. 6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Long-term thermal stability is improved as compared with the case of using dioxaphosphepine alone.
[0022]
The styrene resin composition used in the present invention preferably contains 0.02 to 0.50 mass% of (e) a hindered phenol antioxidant in 100 mass% of the styrene resin composition. It is more preferable to contain -0.25 mass%. 6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Compared to the case where dioxaphosphepine is used alone, the initial hue and transmittance are improved, and the long-term thermal stability tends to be improved.
[0023]
6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Dioxaphosphepine is a processing stabilizer having a hindered phenol antioxidant skeleton and a phosphorus antioxidant skeleton in the same molecule.
[0024]
Phosphorous antioxidants are phosphites that are trivalent phosphorus compounds. Phosphorus antioxidants include, for example, tris (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2- Ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 4,4′-biphenylenediphosphinic acid tetrakis (2,4-di-tert-butylphenyl), 3,9-bis (2 , 6-Di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane, cyclic neopentanetetraylbis (2,4-di -T-butylphenyl phosphite), distearyl pentaerythritol diphosphite, bis (nonylphenyl) pe Taerythritol diphosphite, bis- [2-methyl-4,6-bis- (1,1-dimethylethyl) phenyl] ethyl phosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10 -Oxide, tetrakis (2,4-di-tert-butyl-5-methylphenyl) -4,4'-biphenylenediphosphonite and the like. As the phosphorus-based antioxidant, those excellent in hydrolysis resistance are preferred, such as tris (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert-). Butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 3,9-bis (2,6-di-tert-butyl-4-methyl) Phenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane is preferred. Particularly preferred is tris (2,4-di-tert-butylphenyl) phosphite. Phosphorous antioxidants may be used alone or in combination of two or more.
[0025]
The hindered phenol antioxidant is an antioxidant having a phenolic hydroxyl group in the basic skeleton. Examples of hindered phenol antioxidants include octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3-tert-butyl). -4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate], 4,6-bis (octylthiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -o-cresol, 2, , 4-Dimethyl-6- (1-methylpentadecyl) phenol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) Propionate] methane, DL-α-tocopherol, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy -3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4'-thiobis (6-t-butyl-3-methylphenol), 1,1, 3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-t-butylphenol), bis- [3,3-bis- (4 And '-hydroxy-3'-tert-butylphenyl) -butanoic acid] -glycol ester. Preferably, octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methyl) Phenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4 -Hydroxy-m-tolyl) propionate]. Hindered phenolic antioxidants may be used alone or in combination of two or more.
[0026]
6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Dioxaphosfepine, phosphorus antioxidants and hindered phenol antioxidants can be added by adding and mixing in the styrene resin polymerization process, devolatilization process, granulation process or extrusion during molding. A method of adding and mixing with a machine, an injection molding machine or the like can be mentioned, and it is not particularly limited.
[0027]
The styrenic resin composition may contain mineral oil as long as the colorless transparency of the present invention is not impaired. Also includes additives such as internal lubricants such as stearic acid and ethylenebisstearylamide, sulfur antioxidants, lactone antioxidants, UV absorbers, hindered amine stabilizers, antistatic agents, external lubricants, etc. It may be. As the external lubricant, ethylene bisstearylamide is suitable, and the content is preferably 30 to 200 ppm in the resin composition.
[0028]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0029]
The styrenic resin composition of the present invention can be molded by a molding method according to the purpose, such as injection molding, extrusion molding, or compression molding. The obtained molded product is used as an optical member that functions by transmitting light into the molded product such as a light guide plate. An optical member such as a light guide plate is preferably a material having a high transmittance and an excellent hue because of a long light transmission distance (optical path length). It is preferable that the initial transmittance at an optical path length of 115 mm is 85% or more and the YI value is 6.5 or less. Further, the YI difference after storage for 1000 hours at 80 ° C. is preferably 3.0 or less, and more preferably 1.5 or less.
The transmittance and YI value for an optical path length of 115 mm were measured by the following procedure. Using pellets of the styrene-based resin composition, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. Here, the sample to be evaluated for long-term thermal stability was stored in an oven at 80 ° C. for 1000 hours. Next, a test piece having a thickness of 115 × 85 × 3 mm was cut out from the plate-shaped molded product, and the end surface was polished by buffing to produce a plate-shaped molded product having a mirror surface on the end surface. About the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a divergence angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance is an average transmittance at a wavelength of 380 nm to 780 nm.
[0030]
The light guide plate receives light from the end surface (side surface) of the plate-shaped molded product, and guides light to the front surface (light emitting surface) of the molded product by a reflection pattern formed on the rear surface (non-light emitting surface) of the molded product. It is a member that has the function of emitting surface light. The reflective pattern can be formed by a method such as a screen printing method, an injection molding method, a laser method, or an ink jet method. When processing the plate-shaped molded product into the light guide plate, it is preferable to polish the light incident surface or the entire end surface to a mirror surface. Moreover, in order to improve the uniformity of the emitted light, a prism pattern or the like can be provided on the front surface (light emitting surface) of the plate-shaped molded product. The pattern on the front surface or the rear surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0031]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0032]
(Examples 1-34, Comparative Examples 1-12)
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A mixed solution of 84.0% by mass of styrene and 16.0% by mass of ethylbenzene was prepared, and 400 ppm of 2,2-bis (4,4-t-butylperoxycyclohexyl) propane was mixed on the basis of styrene, A raw material solution was obtained. As 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, Pertetra A manufactured by NOF Corporation was used. This raw material solution was continuously supplied to the first reactor at a rate of 11.2 kg / hour. The reaction temperature of each reactor is 116 ° C. in the first reactor, 120 ° C. in the second reactor, and in the third reactor, a temperature gradient is created along the direction of flow, 140 ° C. in the middle portion, and in the outlet portion. The temperature was adjusted to 150 ° C.
Moreover, the hydrophilic additive which has a polyether chain | strand was added to the inlet_port | entrance of a 3rd reactor so that it might become a kind and content shown in Table 8-1. The types of additives and polyethylene glycol used are as follows.
B-1: Polyethylene glycol having an average molecular weight of 400 (PEG # 400 manufactured by NOF Corporation)
B-2: Polyethylene glycol having an average molecular weight of 1000 (PEG # 1000 manufactured by NOF Corporation)
B-3: Polyethylene glycol having an average molecular weight of 2000 (PEG # 2000 manufactured by NOF Corporation)
B-4: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 25 (Emalgen 123P manufactured by Kao Corporation)
B-5: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 12 (Emulgen 320P manufactured by Kao Corporation)
B-6: Polyoxyethylene ethylene lauryl ether Ethylene oxide average addition mole number = 9 (Emulgen 109P manufactured by Kao Corporation)
B-7: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 30 (Emulgen 130K manufactured by Kao Corporation)
B-8: Polyethylene glycol monolaurate Ethylene oxide average addition mole number = 12 (Emanon 1112 manufactured by Kao Corporation)
Subsequently, a solution containing a polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted by two stages in series, and after separating unreacted styrene and ethylbenzene, strands were formed. After being extruded and cooled, it was cut into pellets. The resin temperature in the first stage devolatilization tank is set to 160 ° C., the pressure in the vacuum devolatilization tank is set to 65 kPa, the resin temperature in the second stage devolatilization layer is set to 235 ° C. The pressure in the volatilization tank was 0.8 kPa.
All of the obtained styrene resins had a weight average molecular weight (Mw) of 370,000.
[0033]
Next, using the single-screw extruder with a screw diameter of 40 mm, the cylinder temperature of 230 ° C. was used for the pellets of the styrenic resin obtained above and the additives C, D, and E so that the contents shown in Table 8-1 were obtained. The mixture was melt-kneaded at a screw speed of 100 rpm to obtain pellets. Additives C, D and E used in Table 8-1 are shown below. The additive C was (c) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3, 2] dioxaphosphine, additive D represents (d) phosphorus antioxidant, and additive E represents (e) hindered phenol antioxidant.
C-1: 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3,2] Dioxaphosphepine (Sumitomo Chemical Co., Ltd., Sumitizer GP)
D-1: Tris (2,4-di-tert-butylphenyl) phosphite (Irgafos 168 manufactured by BASF Japan Ltd.)
D-2: 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus (ADEKA STAB HP-10 manufactured by ADEKA Corporation)
D-3: Bis (2,4-dicumylphenyl) pentaerythritol diphosphite (Doverphos S-9228 manufactured by Dober Chemical Corporation)
D-4: 3,9-bis (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane ADEKA ADK STAB PEP-36)
E-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
E-2: 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10 -Tetraoxaspiro [5.5] undecane (Adeka Corporation Adeka Stub AO-80)
E-3: Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
The melt mass flow rate (MFR) is in accordance with JIS K 7210, under conditions of 200 ° C. and a load of 49 N, and the Vicat softening temperature is in accordance with JIS K 7206, with a heating rate of 50 ° C./hr and a test load of 50 N. It was measured.
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. In order to evaluate long-term thermal stability, the obtained molded product was stored in an oven at 80 ° C. for 1000 hours. In order to evaluate the optical properties of the initial molded product before storage and the molded product after storage, a 115 × 85 × 3 mm thickness test piece was cut out from the plate-shaped molded product, the end surface was polished by buffing, and a mirror surface was formed on the end surface. A plate-shaped molded article having the same was prepared. About the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a divergence angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance shown in Table 8-1 represents the average transmittance at a wavelength of 380 nm to 780 nm.
Furthermore, in order to confirm the whitening phenomenon due to environmental changes, a plate-like molded article having a mirror surface on the end face is exposed to an environment of 60 ° C. and 90% relative humidity for 150 hours, and the test piece is placed in an environment of 23 ° C. and 50% relative humidity. Taking out and observing the whitening phenomenon occurring inside the molded product, the following judgment was made as a whitening suppression effect.
A: No whitening occurs. O: Whitening occurs slightly after 1 hour, but disappears after 24 hours. Δ: Whitening occurs after 1 hour, but almost disappears after 24 hours. X: Remarkably whitening after 1 hour. Table 8-1 shows the characteristics of each resin composition.
[0034]
[Table 8-1]

[0035]
The molded articles of the examples are excellent in whitening suppression effect, excellent in initial transmittance and YI value, small in change in YI during storage at 80 ° C. × 1000 hours, and excellent in long-term thermal stability. .
[Industrial applicability]
[0036]
The optical styrenic resin composition of the present invention is excellent in hue and transparency and excellent in long-term thermal stability, so that it is a light guide plate for televisions, desktop personal computers, notebook personal computers, mobile phones, car navigation systems, etc. It can be suitably used in applications.

[００３２]
実施例の成形品は、白化抑制効果に優れ、初期の透過率とＹＩ値に優れており、８０℃×１０００時間での保管におけるＹＩ変化量が小さく、長期の熱安定性にも優れている。
[産業上の利用可能性]
[００３３]
本発明の光学用スチレン系樹脂組成物は、色相および透明性に優れ、長期の熱安定性に優れることから、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 9)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
(A) From a styrene resin having a weight average molecular weight of 150,000 to 700,000, (b) a hydrophilic additive having a polyether chain, (c) a hindered phenol antioxidant, and (d) a phosphorus antioxidant. The content of (b) in 100% by mass of the styrene-based resin composition is 0.4 to 2.0% by mass, and the content of (c) is 0.02 to 0.00%. 30% by mass, and the content of (d) is 0.03 to 0.40% by mass. An optical styrene-based resin composition.
[Claim 2]
A molded article using the optical styrenic resin composition according to claim 1.
[Claim 3]
A light guide plate using the molded product according to claim 2.
[Document Name] Statement
[Title of the Invention] Optical Styrenic Resin Composition, Molded Product, and Light Guide Plate
[Technical field]
[0001]
The present invention relates to an optical styrenic resin composition excellent in hue and transparency, a molded article, and a light guide plate.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The A backlight using a light guide plate is also used for illumination. An acrylic resin typified by PMMA (polymethyl methacrylate) is used for the light guide plate. However, since the water absorption is high, the molded product may be warped or dimensional changes may occur.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylate copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water absorption is high and the dimensional stability tends to be worse than that of a styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, discoloration due to heat may occur during long-term use, and the molded product may turn yellow to lower the transmittance. As a result, the luminance of the backlight may decrease and the chromaticity may change.
In addition, a styrene resin using a styrene monomer as a raw material has low water absorption, but the molded product may become cloudy due to environmental changes such as temperature and humidity (whitening phenomenon). Specifically, when a molded product is exposed to an environmental change from a high temperature and high humidity environment to a room temperature environment or an environmental change from a room temperature environment to a low temperature environment, moisture present uniformly in the molded product is not present. It becomes stable and phase-separates, and a disk-like defect is generated. As a result, the inside of the molded product becomes cloudy. When the molded product becomes cloudy, when the optical path length is long like a light guide plate, the transmittance is greatly reduced due to light scattering, and the luminance of the display is lowered.
[Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
An object of the present invention is to provide a styrenic resin composition for optical use, a molded article, and a light guide plate that prevent whitening due to environmental changes, is excellent in long-term thermal stability, and is excellent in colorless transparency.
[Means for solving problems]
[0005]
(1) (a) a styrene resin having a weight average molecular weight of 150,000 to 700,000, (b) a hydrophilic additive having a polyether chain, (c) a hindered phenol antioxidant, and (d) a phosphorous oxidation. A styrene resin composition comprising an inhibitor, wherein the content of (b) in 100% by mass of the styrene resin composition is 0.4 to 2.0% by mass, and the content of (c) is 0.02. An optical styrene-based resin composition having a content of ˜0.30 mass% and a content of (d) of 0.03 to 0.40 mass%.
(2) A molded article using the optical styrenic resin composition according to (1).
(3) A light guide plate using the molded product according to (2).
[Effect of the invention]
[0006]
The optical styrenic resin composition and molded product of the present invention have low water absorption, excellent dimensional stability and are inexpensive compared to PMMA and MS resin. Moreover, since the whitening phenomenon by the environmental change which is a fault of PS resin does not generate | occur | produce, it is excellent in long-term thermal stability and colorless transparency, Therefore It can use suitably for optical uses, such as a light-guide plate. Moreover, the coloring prevention effect with respect to high temperature heat history, such as a shaping | molding process, is also high.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin is a polymer having a unit structure derived from a styrene monomer. The styrene resin can be obtained by polymerizing a styrene monomer. Examples of the styrene monomer include styrene, α-methyl styrene, p-methyl styrene, o-methyl styrene, m-methyl styrene, ethyl styrene, pt-butyl styrene, and preferably styrene. Styrenic monomers may be used alone or in combination of two or more. As the styrenic resin, those having a small amount of other unit structures can also be used. The other unit structure is preferably 5% or less. Other unit structures include unit structures derived from vinyl monomers copolymerizable with styrene monomers. Examples of copolymerizable vinyl monomers include acrylic acid monomers such as acrylic acid and methacrylic acid, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, acrylic monomers such as butyl acrylate and methyl methacrylate, and maleic anhydride. Examples include α, β-ethylenically unsaturated carboxylic acids such as acid and fumaric acid, and imide monomers such as N-phenylmaleimide and N-cyclohexylmaleimide.
[0008]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0009]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0010]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0011]
The weight average molecular weight of the styrene resin is 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: differential refractometer The molecular weight is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0012]
The styrene-based resin composition contains a hydrophilic additive having a polyether chain in 100% by mass of the styrene-based resin composition, the content is 0.4 to 2.0% by mass, and 0.6 to 1 It is preferably 6% by mass. If the content of the hydrophilic additive having a polyether chain is less than 0.4% by mass, it is difficult to prevent the whitening phenomenon due to environmental changes, and if it exceeds 2.0% by mass, the heat resistance of the styrene resin composition is lowered. To do.
[0013]
The hydrophilic additive having a polyether chain is an additive having a polyether chain in the molecule. A polyether chain is a compound in which ether bonds are linked. For example, a polyoxyethylene chain, a polyoxypropylene chain, a polyoxybutylene chain or glycerin synthesized by an addition reaction of an alkylene oxide such as ethylene oxide, propylene oxide, or butylene oxide. A polyglycerol chain synthesized by dehydration condensation of a polyoxyethylene chain is preferable, and a polyoxyethylene chain is preferable.
[0014]
Examples of the hydrophilic additive having a polyether chain include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene octyl decyl ether, polyoxyethylene myristyl ether, polyoxyethylene 2 -Polyoxyethylene alkyl ethers such as ethylhexyl ether, polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitol fatty acid esters such as polyoxyethylene sorbitol tetraoleate , Polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol dis Polyoxyethylene fatty acid esters such as allate, polyethylene glycol monooleate, polyoxyethylene hydrogenated castor oil, polyethylene glycol, polyoxyethylene monomethyl ether, polyoxyethylene dimethyl ether, polyoxyethylene glyceryl ether, polyoxyethylene tetraoleic acid, poly Oxyethylene triisostearic acid, polyoxyethylene coconut fatty acid glyceryl, polypropylene glycol, polyoxypropylene glyceryl ether, polyoxypropylene diglyceryl ether, polyoxypropylene sorbitol, polybutylene glycol, diglycerin, polyglycerin, polyoxyethylene polyglyceryl ether , Polyoxypropylene polyglyceryl ether, polyglyceryl And fatty acid esters. Among these, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester and polyethylene glycol are preferable, and the effect of preventing whitening phenomenon is high.
[0015]
Polyoxyethylene alkyl ether is made by adding ethylene oxide to alcohol, and polyoxyethylene fatty acid ester is made by adding ethylene oxide to fatty acid or directly esterifying fatty acid and polyethylene glycol. The average added mole number of ethylene oxide is preferably 7 to 100, and more preferably 10 to 50.
[0016]
The average molecular weight of polyethylene glycol is preferably 200 to 4000, and more preferably 300 to 1000. If the average molecular weight of polyethylene glycol is less than 200, gas is generated during the molding process, and the mold and roll are soiled, which is not preferable. On the other hand, if it exceeds 4000, the effect of preventing the whitening phenomenon tends to decrease. The average molecular weight is calculated from the hydroxyl group concentration (based on JIS K1557) measured by the pyridine phthalic anhydride method.
[0017]
The heat loss of the hydrophilic additive having a polyether chain at a temperature of 200 ° C. and in a nitrogen atmosphere is preferably 10% by mass or less. Heat loss in a nitrogen atmosphere at a temperature of 200 ° C. can be determined by thermogravimetric analysis (TGA). Heating is performed at a temperature increase rate of 10 ° C./min from a room temperature in a nitrogen atmosphere, and the weight loss at a temperature of 200 ° C. It can be determined from the quantity. Additives whose weight loss on heating at a temperature of 200 ° C. and under a nitrogen atmosphere exceeds 10% by mass have high volatility, and gas is generated during the molding process of the styrene resin composition, which may cause mold or roll contamination.
[0018]
Examples of the method for adding a hydrophilic additive having a polyether chain include a method of adding and mixing in a polymerization step, a devolatilization step and a granulation step of a styrenic resin, and a method of adding and mixing with an extruder during molding processing. There is no particular limitation.
[0019]
The Vicat softening temperature of the styrene resin composition is preferably 95 to 104 ° C, and more preferably 97 to 104 ° C. When the Vicat softening temperature is less than 95 ° C., the heat resistance is insufficient, and the molded product may be deformed depending on the use environment. The Vicat softening temperature was measured according to JIS K 7206 at a heating rate of 50 ° C./hr and a test load of 50 N.
[0020]
The styrene resin composition contains (c) a hindered phenol antioxidant and (d) a phosphorus antioxidant in 100% by mass of the styrene resin composition, and the content of (c) is 0.02 to 0.02%. The content of 0.30% by mass and (d) is 0.03 to 0.40% by mass. Preferably, the content of (c) is 0.02 to 0.20 mass%, and the content of (d) is 0.05 to 0.30 mass%. More preferably, the content of (c) is 0.05 to 0.15% by mass, and the content of (d) is 0.10 to 0.25% by mass. When the contents of (c) and (d) are outside the above range, the long-term thermal stability is poor. Long-term thermal stability represents changes in hue and transmittance due to heat in long-term use, and those having excellent thermal stability have small changes in hue and transmittance. Long-term thermal stability can be evaluated as an accelerated test by storing a molded product under a high temperature condition (60 to 90 ° C.) such that the resin does not deform, and changing the hue and transmittance over time.
[0021]
The hindered phenol antioxidant is an antioxidant having a phenolic hydroxyl group in the basic skeleton. Examples of hindered phenol antioxidants include octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3-tert-butyl). -4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate], 4,6-bis (octylthiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -o-cresol, 2, , 4-Dimethyl-6- (1-methylpentadecyl) phenol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) Propionate] methane, DL-α-tocopherol, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy -3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4'-thiobis (6-t-butyl-3-methylphenol), 1,1, 3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-t-butylphenol), bis- [3,3-bis- (4 And '-hydroxy-3'-tert-butylphenyl) -butanoic acid] -glycol ester. Preferably, octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methyl) Phenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4 -Hydroxy-m-tolyl) propionate]. Hindered phenolic antioxidants may be used alone or in combination of two or more.
[0022]
Phosphorous antioxidants are phosphites that are trivalent phosphorus compounds. Phosphorus antioxidants include, for example, tris (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2- Ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 4,4′-biphenylenediphosphinic acid tetrakis (2,4-di-tert-butylphenyl), 3,9-bis (2 , 6-Di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane, cyclic neopentanetetraylbis (2,4-di -T-butylphenyl phosphite), distearyl pentaerythritol diphosphite, bis (nonylphenyl) pe Taerythritol diphosphite, bis- [2-methyl-4,6-bis- (1,1-dimethylethyl) phenyl] ethyl phosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10 -Oxide, tetrakis (2,4-di-tert-butyl-5-methylphenyl) -4,4'-biphenylenediphosphonite and the like. As the phosphorus-based antioxidant, those excellent in hydrolysis resistance are preferred, such as tris (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert-). Butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 3,9-bis (2,6-di-tert-butyl-4-methyl) Phenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane is preferred. Particularly preferred is tris (2,4-di-tert-butylphenyl) phosphite. Phosphorous antioxidants may be used alone or in combination of two or more.
[0023]
Methods for adding hindered phenolic antioxidants and phosphorus antioxidants include addition and mixing in the polymerization process, devolatilization process, and granulation process of styrenic resins, extruders and injection molding machines during molding, etc. The method of adding and mixing is mentioned, but it is not particularly limited.
[0024]
The styrenic resin composition may contain mineral oil as long as the colorless transparency of the present invention is not impaired. Also includes additives such as internal lubricants such as stearic acid and ethylenebisstearylamide, sulfur antioxidants, lactone antioxidants, UV absorbers, hindered amine stabilizers, antistatic agents, external lubricants, etc. It may be. As the external lubricant, ethylene bisstearylamide is suitable, and the content is preferably 30 to 200 ppm in the resin composition.
[0025]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0026]
The styrenic resin composition of the present invention can be molded by a molding method according to the purpose, such as injection molding, extrusion molding, or compression molding. The obtained molded product is used as an optical member that functions by transmitting light into the molded product such as a light guide plate. An optical member such as a light guide plate is preferably a material having a high transmittance and an excellent hue because of a long light transmission distance (optical path length). The initial transmittance at an optical path length of 115 mm is preferably 84% or more and the YI value is 7.0 or less. The YI difference after storage at 80 ° C. for 1000 hours and the initial YI is preferably 2.0 or less, and more preferably 1.0 or less.
The transmittance and YI value for an optical path length of 115 mm were measured by the following procedure. Using pellets of the styrene-based resin composition, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. Here, the sample to be evaluated for long-term thermal stability was stored in an oven at 80 ° C. for 1000 hours. Next, a test piece having a thickness of 115 × 85 × 3 mm was cut out from the plate-shaped molded product, and the end surface was polished by buffing to produce a plate-shaped molded product having a mirror surface on the end surface. About the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a divergence angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance is an average transmittance at a wavelength of 380 nm to 780 nm.
[0027]
The light guide plate receives light from the end surface (side surface) of the plate-shaped molded product, and guides light to the front surface (light emitting surface) of the molded product by a reflection pattern formed on the rear surface (non-light emitting surface) of the molded product. It is a member that has the function of emitting surface light. The reflective pattern can be formed by a method such as a screen printing method, an injection molding method, a laser method, or an ink jet method. When processing the plate-shaped molded product into the light guide plate, it is preferable to polish the light incident surface or the entire end surface to a mirror surface. Moreover, in order to improve the uniformity of the emitted light, a prism pattern or the like can be provided on the front surface (light emitting surface) of the plate-shaped molded product. The pattern on the front surface or the rear surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0028]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0029]
(Examples 1-23, Comparative Examples 1-13)
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A mixed solution of 84.0% by mass of styrene and 16.0% by mass of ethylbenzene was prepared, and 400 ppm of 2,2-bis (4,4-t-butylperoxycyclohexyl) propane was mixed on the basis of styrene, A raw material solution was obtained. As 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, Pertetra A manufactured by NOF Corporation was used. This raw material solution was continuously supplied to the first reactor at a rate of 11.2 kg / hour. The reaction temperature of each reactor is 116 ° C. in the first reactor, 120 ° C. in the second reactor, and in the third reactor, a temperature gradient is created along the direction of flow, 140 ° C. in the middle portion, and in the outlet portion. The temperature was adjusted to 150 ° C.
Moreover, the hydrophilic additive which has a polyether chain | strand was added to the inlet_port | entrance of a 3rd reactor so that it might become a kind and content shown in Table 9-1. The types of additives and polyethylene glycol used are as follows.
B-1: Polyethylene glycol having an average molecular weight of 400 (PEG # 400 manufactured by NOF Corporation)
B-2: Polyethylene glycol having an average molecular weight of 1000 (PEG # 1000 manufactured by NOF Corporation)
B-3: Polyethylene glycol having an average molecular weight of 2000 (PEG # 2000 manufactured by NOF Corporation)
B-4: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 25 (Emalgen 123P manufactured by Kao Corporation)
B-5: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 12 (Emulgen 320P manufactured by Kao Corporation)
B-6: Polyoxyethylene ethylene lauryl ether Ethylene oxide average addition mole number = 9 (Emulgen 109P manufactured by Kao Corporation)
B-7: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 30 (Emulgen 130K manufactured by Kao Corporation)
B-8: Polyethylene glycol monolaurate Ethylene oxide average addition mole number = 12 (Emanon 1112 manufactured by Kao Corporation)
Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted of two stages in series, and after separating unreacted styrene and ethylbenzene, a strand shape After being extruded and cooled, it was cut into pellets. The resin temperature in the first stage devolatilization tank is set to 160 ° C., the pressure in the vacuum devolatilization tank is set to 65 kPa, the resin temperature in the second stage devolatilization layer is set to 235 ° C. The pressure in the volatilization tank was 0.8 kPa.
All of the obtained styrene resins had a weight average molecular weight (Mw) of 370,000.
[0030]
Next, using a single screw extruder having a screw diameter of 40 mm, the pellets of the styrenic resin and the additives C and D obtained above were used so that the content shown in Table 9-1 was used. Pellets were obtained by melt-kneading at a rotation speed of 100 rpm. Additives C, D and E used in Table 9-1 are shown below. The additive C represents (c) a hindered phenol antioxidant, and the additive D represents (d) a phosphorus antioxidant.
C-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
C-2: 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10 -Tetraoxaspiro [5.5] undecane (Adeka Corporation Adeka Stub AO-80)
C-3: Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
D-1: Tris (2,4-di-tert-butylphenyl) phosphite (Irgafos 168 manufactured by BASF Japan Ltd.)
D-2: 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus (ADEKA STAB HP-10 manufactured by ADEKA Corporation)
D-3: Bis (2,4-dicumylphenyl) pentaerythritol diphosphite (Doverphos S-9228 manufactured by Dober Chemical Corporation)
D-4: 3,9-bis (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane ADEKA ADK STAB PEP-36)
In addition, the melt mass flow rate (MFR) is in accordance with JIS K-7210, under conditions of 200 ° C. and 49 N load, the Vicat softening temperature is in accordance with JIS K 7206, the heating rate is 50 ° C./hr, and the test load is 50 N. Measured with
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. In order to evaluate long-term thermal stability, the obtained molded product was stored in an oven at 80 ° C. for 1000 hours. In order to evaluate the optical properties of the initial molded product before storage and the molded product after storage, a 115 × 85 × 3 mm thickness test piece was cut out from the plate-shaped molded product, the end surface was polished by buffing, and a mirror surface was formed on the end surface. A plate-shaped molded article having the same was prepared. About the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a divergence angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance shown in Table 9-1 represents the average transmittance at a wavelength of 380 nm to 780 nm.
Furthermore, in order to confirm the whitening phenomenon due to environmental changes, a plate-like molded article having a mirror surface on the end face is exposed to an environment of 60 ° C. and 90% relative humidity for 150 hours, and the test piece is placed in an environment of 23 ° C. and 50% relative humidity. Taking out and observing the whitening phenomenon occurring inside the molded product, the following judgment was made as a whitening suppression effect.
A: No whitening occurs. O: Whitening occurs slightly after 1 hour, but disappears after 24 hours. Δ: Whitening occurs after 1 hour, but almost disappears after 24 hours. X: Remarkably whitening after 1 hour. Table 9-1 shows the characteristics of each resin composition.
[0031]
[Table 9-1]

[0032]
The molded articles of the examples are excellent in whitening suppression effect, excellent in initial transmittance and YI value, small in change in YI during storage at 80 ° C. × 1000 hours, and excellent in long-term thermal stability. .
[Industrial applicability]
[0033]
The optical styrenic resin composition of the present invention is excellent in hue and transparency and excellent in long-term thermal stability, so that it is a light guide plate for televisions, desktop personal computers, notebook personal computers, mobile phones, car navigation systems, etc. It can be suitably used in applications.

（式中、Ｒは炭素数８〜２０のアルキル基を示し、ｎは整数でエチレンオキサイド単位の付加モル数を表す）
[請求項３]
請求項１〜２のいずれか１項に記載のスチレン系樹脂組成物を成形してなる板状成形品。
[請求項４]
請求項３に記載の板状成形品からなる導光板。
[書類名]明細書
[発明の名称]スチレン系樹脂組成物、板状成形品および導光板
[技術分野]
[０００１]
本発明は、環境変化による白化現象が発生せず、耐熱性に優れ、色相と透明性に優れ、導光板用途に適したスチレン系樹脂組成物、板状成形品および導光板に関するものである。
[背景技術]
[０００２]
液晶ディスプレイのバックライトには光源を表示装置の正面に配置する直下型バックライトと側面に配置するエッジライト型バックライトがある。導光板はエッジライト型バックライトに組み込まれ、側面からの光を液晶パネルに導く役割を果たし、テレビ、デスクトップ型パーソナルコンピューターのモニター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなど幅広い用途で使用される。導光板にはＰＭＭＡ（ポリメチルメタクリレート）に代表されるアクリル樹脂が使用されているが、吸水性が高いため、成形品に反りが発生する問題や寸法の変化が発生する場合がある。
そのため、これら特性を改善したスチレンと（メタ）アクリル酸メチルとの共重合体であるＭＳ樹脂を用いることが提案されている。ＭＳ樹脂の、吸水性や成形時の変色低減等の改良技術としては特許文献１が提案されている。
しかしながら、特許文献１では、スチレン−（メタ）アクリル酸エステル系共重合体樹脂の重量平均分子量（Ｍｗ）６〜１７万、残存モノマー量３０００ｐｐｍ以下、更にオリゴマー量が２％以下の導光板が開示されているが、吸水性が高く寸法安定性がスチレン系単量体を原料とするスチレン系樹脂よりも悪い傾向にあった。
一方、スチレン系単量体を原料とするスチレン系樹脂は吸水性が低いものの、温度や湿度などの環境変化により成形品が白濁する問題（白化現象）があった。具体的には、高温高湿環境下から室温環境下への環境変化や室温環境下から低温環境下への環境変化に成形品が曝された場合、成形品中に均一に存在する水分が不安定となって相分離し、円盤状の欠陥が生成し、その結果、成形品の内部が白濁する。成形品が白濁すると、導光板のように光路長が長い場合、光散乱により透過率が大きく低下して、ディスプレイの輝度が低下する問題がある。
また、バックライトの内部は使用環境によっては高温となり、温度による導光板の変形を防止するためには耐熱性が要求される。
[先行技術文献]
[特許文献]
[０００３]
[特許文献１]特開２００３−０７５６４８号公報
[発明の概要]
[発明が解決しようとする課題]
[０００４]
本発明は、耐熱性を供え、環境変化による白化現象を防止し、特に導光板等の光学用途に適した、無色透明性に優れたスチレン系樹脂組成物を提供することを課題とする。
[課題を解決するための手段]
[０００５]
本発明は、（１）（ａ）スチレン系単量体と（メタ）アクリル酸とを共重合して得られる重量平均分子量が１５万〜７０万で、（メタ）アクリル酸単位の含有量が０．３〜２．０質量％であるスチレン系樹脂と（ｂ）ポリオキシエチレン型非イオン性界面活性剤からなるスチレン系樹脂組成物であって、スチレン系樹脂組成物１００質量％中の（ｂ）の含有量が０．１〜１．０質量％であることを特徴とするスチレン系樹脂組成物。
（２）（ｂ）ポリオキシエチレン型非イオン性界面活性剤が下記一般式１で示されるポリオキシエチレンアルキルエーテル及び／又は下記一般式２で示されるポリオキシエチレン脂肪酸エステルの郡から選ばれる１種類以上であり、かつエチレンオキサイドの平均付加モル数が７〜１００であることを特徴とする請求項１に記載のスチレン系樹脂組成物。

（式中、Ｒは炭素数８〜２０のアルキル基を示し、ｎは整数でエチレンオキサイド単位の付加モル数を表す）
（３）（１）〜（２）のいずれか１項に記載のスチレン系樹脂組成物を成形してなる板状成形品。
（４）（３）に記載の板状成形品からなる導光板。
[発明の効果]
[０００６]
本発明のスチレン系樹脂組成物は、ＰＭＭＡやＭＳ樹脂と比較して、吸水性が低く安価であり、ＰＳ樹脂の欠点である環境変化による白化現象が発生せず、耐熱性を供え、無色透明性に優れることから、導光板等の光学用途に好適に用いることが出来る。
[発明を実施するための形態]
[０００７]
本発明のスチレン系樹脂は、スチレン系単量体と（メタ）アクリル酸系単量体とを重合して得ることができる。スチレン系単量体とは、芳香族ビニル系モノマーである、スチレン、α−メチルスチレン、ｏ−メチルスチレン、ｐ−メチルスチレン等の単独または２種以上の混合物であり、好ましくはスチレンである。（メタ）アクリル酸系単量体は、アクリル酸、メタクリル酸等であり、メタクリル酸が好ましい。
[０００８]
スチレン系樹脂の重合方法としては、塊状重合法、溶液重合法、懸濁重合法、乳化重合法等公知のスチレン重合方法が挙げられる。品質面や生産性の面では、塊状重合法、溶液重合法が好ましく、連続重合であることが好ましい。溶媒として例えばベンゼン、トルエン、エチルベンゼン及びキシレン等のアルキルベンゼン類やアセトンやメチルエチルケトン等のケトン類、ヘキサンやシクロヘキサン等の脂肪族炭化水素等が使用できる。
[０００９]
スチレン系樹脂の重合時に、必要に応じて重合開始剤、連鎖移動剤を使用することができる。重合開始剤としては、ラジカル重合開始剤が好ましく、公知慣用の例えば、１，１−ジ（ｔ−ブチルパーオキシ）シクロヘキサン、２，２−ジ（ｔ−ブチルパーオキシ）ブタン、２，２−ジ（４，４−ジ−ｔ−ブチルパーオキシシクロヘキシル）プロパン、１，１−ジ（ｔ−アミルパーオキシ）シクロヘキサン等のパーオキシケタール類、クメンハイドロパーオキサイド、ｔ−ブチルハイドロパーオキサイド等のハイドロパーオキサイド類、ｔ−ブチルパーオキシアセテート、ｔ−アミルパーオキシイソノナノエート等のアルキルパーオキサイド類、ｔ−ブチルクミルパーオキサイド、ジ−ｔ−ブチルパーオキサイド、ジクミルパーオキサイド、ジ−ｔ−ヘキシルパーオキサイド等のジアルキルパーオキサイド類、ｔ−ブチルパーオキシアセテート、ｔ−ブチルパーオキシベンゾエート、ｔ−ブチルパーオキシイソプロピルモノカーボネート等のパーオキシエステル類、ｔ−ブチルパーオキシイソプロピルカーボネート、ポリエーテルテトラキス（ｔ-ブチルパーオキシカーボネート）等のパーオキシカーボネート類、Ｎ，Ｎ'−アゾビス（シクロヘキサン−１−カルボニトリル）、Ｎ，Ｎ'−アゾビス（２−メチルブチロニトリル）、Ｎ，Ｎ'−アゾビス（２，４−ジメチルバレロニトリル）、Ｎ，Ｎ'−アゾビス［２−（ヒドロキシメチル）プロピオニトリル］等が挙げられ、これらの１種あるいは２種以上を組み合わせて使用することができる。連鎖移動剤としては、脂肪族メルカプタン、芳香族メルカプタン、ペンタフェニルエタン、α−メチルスチレンダイマー及びテルピノーレン等が挙げられる。
[００１０]
連続重合の場合、まず重合工程にて公知の完全混合槽型攪拌槽や塔型反応器等を用い、目標の分子量、分子量分布、反応転化率となるよう、重合温度調整等により重合反応が制御される。重合工程を出た重合体を含む重合溶液は、脱揮工程に移送され、未反応の単量体及び重合溶媒が除去される。脱揮工程は加熱器付きの真空脱揮槽やベント付き脱揮押出機などで構成される。脱揮工程を出た溶融状態の重合体は造粒工程へ移送される。造粒工程では、多孔ダイよりストランド状に溶融樹脂を押出し、コールドカット方式や空中ホットカット方式、水中ホットカット方式にてペレット形状に加工される。
[００１１]
本発明のスチレン系樹脂の重量平均分子量は１５万〜７０万であり、１８万〜５０万であることが好ましい。１５万未満では成形品の強度が不十分となり、７０万を超えると成形性が著しく低下する。スチレン系樹脂の重量平均分子量は、重合工程の反応温度、滞留時間、重合開始剤の種類及び添加量、連鎖移動剤の種類及び添加量、重合時に使用する溶媒の種類及び量等によって制御することができる。
重量平均分子量（Ｍｗ）及びＺ平均分子量（Ｍｚ）、数平均分子量（Ｍｎ）は、ゲルパーミエイションクロマトグラフィー（ＧＰＣ）を用いて、次の条件で測定した。
ＧＰＣ機種：昭和電工株式会社製Ｓｈｏｄｅｘ ＧＰＣ−１０１
カラム：ポリマーラボラトリーズ社製 ＰＬｇｅｌ １０μｍ ＭＩＸＥＤ−Ｂ
移動相：テトラヒドロフラン
試料濃度：０．２質量％
温度：オーブン４０℃、注入口３５℃、検出器３５℃
検出器：示差屈折計
本発明の分子量は単分散ポリスチレンの溶出曲線より各溶出時間における分子量を算出し、ポリスチレン換算の分子量として算出したものである。
[００１２]
本発明のスチレン系樹脂は、スチレン系樹脂１００質量％中に（メタ）アクリル酸単位を含有し、その含有量が０．３〜２．０質量％であり、０．８〜１．６質量％であることが好ましい。（メタ）アクリル酸単位の含有量が０．３質量％未満では、白化抑制効果と耐熱性のバランスが取れない。また、２．０質量％を超えると、初期の色相および透過率が悪化する。
[００１３]
スチレン系樹脂中の（メタ）アクリル酸単位含有量の測定は室温で実施した。スチレン系樹脂０．５ｇを秤量し、トルエン／エタノール＝８／２（体積比）の混合溶液に溶解後、水酸化カリウム０．１ｍｏｌ／Ｌエタノール溶液にて中和滴定を行い、終点を検出し、水酸化カリウムエタノール溶液の使用量より、（メタ）アクリル酸単位の質量基準の含有量を算出した。なお、電位差自動滴定装置を使用することができ、京都電子工業株式会社製ＡＴ−５１０により測定を行った。スチレン系樹脂中の（メタ）アクリル酸単位の含有量は、スチレン系樹脂の重合時における原料のスチレン系単量体と（メタ）アクリル酸単量体の組成によって調整することができるが、相溶する範囲において（メタ）アクリル酸単位を含有するスチレン系樹脂と（メタ）アクリル酸単位を含有しないスチレン系樹脂をブレンドして調整することもできる。
[００１４]
本発明のスチレン系樹脂組成物は、スチレン系樹脂組成物１００質量％中（ｃ）ポリオキシエチレン型非イオン性界面活性剤（ポリエチレングリコール型非イオン性界面活性剤ともいう）を含有し、その含有量は０．１〜１．０質量％であり、０．３〜０．６質量％であることが好ましい。ポリオキシエチレン型非イオン性界面活性剤の含有量が０．１質量％未満では環境変化による白化現象の防止が困難であり、１．０質量％を超えるとスチレン系樹脂組成物の耐熱性が低下する。
[００１５]
ポリオキシエチレン型非イオン性界面活性剤は、下記一般式（１）で示されるポリオキシエチレンアルキルエーテルや下記一般式（２）で示されるポリオキシエチレン脂肪酸エステル、ポリオキシエチレン硬化ひまし油、ポリオキシエチレンソルビタン脂肪酸エステル、ポリオキシエチレンソルビトール脂肪酸エステルが挙げられるがポリオキシエチレンアルキルエーテル及び／又はポリオキシエチレン脂肪酸エステルの郡から選ばれる１種類以上であることが好ましい。

（式中、Ｒは炭素数８〜２０のアルキル基を示し、ｎは整数でエチレンオキサイド単位の付加モル数を表す）
[００１６]
ポリオキシエチレンアルキルエーテルはアルコールにエチレンオキサイドを付加させて作られ、ポリオキシエチレン脂肪酸エステルは脂肪酸にエチレンオキサイドを付加させるか脂肪酸とポリエチレングリコールを直接エステル化させて作られ、エチレンオキサイドの平均付加モル数は７〜１００であることが好ましく、１０〜５０であることがより好ましい。
[００１７]
ポリオキシエチレンアルキルエーテルとしては、例えば、ポリオキシエチレンラウリルエーテル、ポリオキシエチレンセチルエーテル、ポリオキシエチレンステアリルエーテル、ポリオキシエチレンオクチルドデシルエーテル、ポリオキシエチレンミリスチルエーテル、ポリオキシエチレン−２−エチルヘキシルエーテル等が挙げられる。
[００１８]
ポリオキシエチレン脂肪酸エステルとしては、例えば、ポリエチレングリコールモノラウレート、ポリエチレングリコールモノステアレート、ポリエチレングリコールジステアレート等が挙げられる。
[００１９]
本発明の６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンおよびヒンダードフェノール系酸化防止剤、ポリエチレングリコールの添加方法としては、スチレン系樹脂の重合工程、脱揮工程、造粒工程で添加混合する方法や成形加工時の押出機などで添加混合する方法が挙げられ、特に限定されることではない。
[００２０]
本発明のスチレン系樹脂組成物のビカット軟化温度は１０１℃以上であることが好ましく、１０２℃であることがより好ましい。ビカット軟化温度が１０１℃未満では耐熱性が不足し、使用環境によっては成形品が変形する可能性がある。
[００２１]
本発明のスチレン系樹脂組成物には、本発明の無色透明性を損なわない範囲でミネラルオイルを含有しても良い。また、ステアリン酸、エチレンビスステアリン酸アミド等の内部潤滑剤やヒンダードフェノール系酸化防止剤、リン系酸化防止剤、イオウ系酸化防止剤、ラクトン系酸化防止剤、ヒンダードアミン系安定剤、紫外線吸収剤、帯電防止剤等の添加剤が含まれていても良い。また、外部潤滑剤としては、エチレンビスステアリン酸アミドが好適であり、含有量としては樹脂組成物中に３０〜２００ｐｐｍであることが好ましい。
[００２２]
紫外線吸収剤は、紫外線による劣化や着色を抑制する機能を有するものであって、例えば、ベンゾフェノン系、ベンゾトリアゾール系、トリアジン系、ベンゾエート系、サリシレート系、シアノアクリレート系、蓚酸アニリド系、マロン酸エステル系、ホルムアミジン系などの紫外線吸収剤が挙げられる。これらは、単独又は２種以上組み合わせて用いることができ、ヒンダートアミン等の光安定剤を併用してもよい。
[００２３]
本発明のスチレン系樹脂組成物は、射出成形、押出成形、圧縮成形等、目的に応じた成形方法で板状成形品に成形し、導光板として用いることができる。その際、板状成形品の背面（光を出射する面の反対側）にドットパターンなどの反射パターンを設けて、導光板として用いることができる。樹脂板から導光板に加工する際、光の入射面あるいは樹脂板の端面全面を研磨処理して、鏡面とすることが好ましい。また、出射光の均一性を高めるために、板状成形品の表面（光が出射される面）にプリズムパターンを設けることができる。板状成形品の表面あるいは背面のパターンは、板状成形品の成形時に形成させることができ、例えば射出成形では金型形状、押出成形ではロール転写などによって、パターン形成させることができる。
[実施例]
[００２４]
以下、実施例を挙げて本発明を具体的に説明するが、本発明はこれら実施例に限定されるものではない。
[００２５]
（実施例１〜１０、比較例１〜８）
完全混合型撹拌槽である第１反応器と第２反応器及び静的混合器付プラグフロー型反応器である第３反応器を直列に接続して重合工程を構成し、表１０−１に示す条件によりスチレン系樹脂の製造を実施した。各反応器の容量は、第１反応器を３９リットル、第２反応器を３９リットル、第３反応器を１６リットルとした。表１０−１に記載の原料組成にて、原料溶液を作成し、第１反応器に原料溶液を表１０−１に記載の流量にて連続的に供給した。重合開始剤は、第１反応器の入口で表１０−１に記載の添加濃度（原料スチレン及びメタクリル酸の合計量に対する質量基準の濃度）となるように原料溶液に添加し、均一混合した。表１０−１に記載の重合開始剤は次の通り
重合開始剤−１ ：２，２−ジ（４，４−ｔ−ブチルパーオキシシクロヘキシル）プロパン（日油株式会社製パーテトラＡを使用した。）
なお、第３反応器では、流れの方向に沿って温度勾配をつけ、中間部分、出口部分で表１０−１の温度となるよう調整した。
また、第３反応器の入口に、ポリオキシエチレン型非イオン性界面活性剤を表１０−２に示す種類と含有量になるよう添加した。ポリオキシエチレン型非イオン性界面活性剤の種類は次の通り。
Ｐ−１：ポリオキシエチレンエチレンラウリルエーテル エチレンオキサイド平均付加モル数＝２５（花王株式会社製エマルゲン１２３Ｐ）
Ｐ−２：ポリオキシエチレンエチレンステアリルエーテル エチレンオキサイド平均付加モル数＝１２（花王株式会社製エマルゲン３２０Ｐ）
Ｐ−３：ポリオキシエチレンエチレンラウリルエーテル エチレンオキサイド平均付加モル数＝９（花王株式会社製エマルゲン１０９Ｐ）
Ｐ−４：ポリオキシエチレンエチレンセチルエーテル エチレンオキサイド平均付加モル数＝７（花王株式会社製エマルゲン２１０Ｐ）
Ｐ−５：ポリオキシエチレンエチレンラウリルエーテル エチレンオキサイド平均付加モル数＝４７（花王株式会社製エマルゲン１５０）
Ｐ−６：ポリオキシエチレンエチレンミリスチルエーテル エチレンオキサイド平均付加モル数＝８５（花王株式会社製エマルゲン４０８５）
Ｐ−７：ポリエチレングリコールモノラウレート エチレンオキサイド平均付加モル数＝１２（花王株式会社製エマノーン１１１２）
続いて、第３反応器より連続的に取り出した重合体を含む溶液を直列に２段より構成される予熱器付き真空脱揮槽に導入し、表１０−１に記載の樹脂温度となるよう予熱器の温度を調整し、表１０−１に記載の圧力に調整することで、未反応スチレン及びエチルベンゼンを分離した後、多孔ダイよりストランド状に押し出しして、コールドカット方式にて、ストランドを冷却および切断しペレット化した。
[００２６]
メルトマスフローレート（ＭＦＲ）は、ＪＩＳ Ｋ−７２１０に準拠し、２００℃、４９Ｎ荷重の条件で、ビカット軟化温度は、ＪＩＳ Ｋ ７２０６に準拠し、昇温速度５０℃／ｈｒ、試験荷重５０Ｎで測定した。
また、得られたペレットを用いて、シリンダー温度２３０℃、金型温度５０℃にて射出成形を行い、１２７×１２７×３ｍｍ厚みの板状成形品を成形した。得られた板状成形品から１１５×８５×３ｍｍ厚みの試験片を切り出し、端面をバフ研磨によって研磨し、端面に鏡面を有する板状成形品を得た。得られた板状成形品について、日本分光株式会社製の紫外線可視分光光度計Ｖ−６７０を用いて、大きさ２０×１．６ｍｍ、広がり角度０°の入射光において、光路長１１５ｍｍでの波長３５０ｎｍ〜８００ｎｍの分光透過率を測定し、Ｃ光源における、視野２°でのＹＩ値をＪＩＳ Ｋ７１０５に倣い算出した。表１０−２に示す透過率とは、波長３８０ｎｍ〜７８０ｎｍの平均透過率を表す。
さらに、環境変化による白化現象を確認するため、端面に鏡面を有する板状成形品を６０℃、９０％相対湿度の環境に１５０時間暴露し、２３℃、５０％相対湿度の環境に試験片を取出し、成形品内部に発生する白化現象を観察し、白化抑制効果として下記の通り判定を行った。
◎：全く白化が発生しない
○：取出し１時間後にやや白化するが、２４時間後には消失する
△：取出し１時間後に白化するが、２４時間後にはほとんど消失する
×：取出し１時間後に著しく白化し、２４時間経っても消失しない
表１０−１に各樹脂組成物の特性を示す。
[００２７]
[表１０−１]

[００２８]
[表１０−２]

[００２９]
実施例の成形品は、耐熱性に優れ、白化抑制効果に優れ、初期の透過率とＹＩ値に優れている。
[産業上の利用可能性]
[００３０]
本発明のスチレン系樹脂組成物は、耐熱性に優れ、環境変化による白化現象が防止され、透明性と色相に優れており、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 10)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
(A) The weight average molecular weight obtained by copolymerizing a styrene monomer and (meth) acrylic acid is 150,000 to 700,000, and the content of (meth) acrylic acid units is 0.3 to 2.0. A styrene-based resin composition comprising a styrene-based resin having a mass% and (b) a polyoxyethylene-type nonionic surfactant, wherein the content of (b) in 100% by mass of the styrene-based resin composition is 0. A styrenic resin composition characterized by having a content of 1 to 1.0% by mass.
[Claim 2]
(B) The polyoxyethylene type nonionic surfactant is selected from the group of the polyoxyethylene alkyl ether represented by the following general formula (1) and / or the polyoxyethylene fatty acid ester represented by the following general formula (2). The styrenic resin composition according to claim 1, wherein the styrene resin composition is one or more types and an average added mole number of ethylene oxide is 7 to 100.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms, and n is an integer representing the number of added moles of ethylene oxide units)
[Claim 3]
The plate-shaped molded article formed by shape | molding the styrene resin composition of any one of Claims 1-2.
[Claim 4]
A light guide plate comprising the plate-like molded product according to claim 3.
[Document Name] Statement
[Title of Invention] Styrenic resin composition, plate-shaped molded article and light guide plate
[Technical field]
[0001]
The present invention relates to a styrenic resin composition, a plate-shaped molded article, and a light guide plate that are free from whitening due to environmental changes, have excellent heat resistance, excellent hue and transparency, and are suitable for light guide plate applications.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The An acrylic resin typified by PMMA (polymethylmethacrylate) is used for the light guide plate. However, since the water absorption is high, there may be a problem that the molded product is warped or a change in dimensions.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
However, Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylic ester copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water-absorbing property and the dimensional stability tend to be worse than those of the styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, there is a problem (whitening phenomenon) that a molded product becomes cloudy due to environmental changes such as temperature and humidity. Specifically, when a molded product is exposed to an environmental change from a high temperature and high humidity environment to a room temperature environment or an environmental change from a room temperature environment to a low temperature environment, moisture present uniformly in the molded product is not present. It becomes stable and phase-separates, and a disk-like defect is generated. As a result, the inside of the molded product becomes cloudy. When the molded product becomes cloudy, when the optical path length is long as in the light guide plate, there is a problem that the transmittance is greatly reduced due to light scattering and the luminance of the display is lowered.
Further, the inside of the backlight becomes high temperature depending on the use environment, and heat resistance is required to prevent the deformation of the light guide plate due to the temperature.
[Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
An object of the present invention is to provide a styrenic resin composition excellent in colorless transparency that provides heat resistance, prevents whitening due to environmental changes, and is particularly suitable for optical applications such as a light guide plate.
[Means for solving problems]
[0005]
In the present invention, the weight average molecular weight obtained by copolymerizing (1) (a) a styrene monomer and (meth) acrylic acid is 150,000 to 700,000, and the content of (meth) acrylic acid units is A styrene resin composition comprising 0.3 to 2.0 mass% of a styrene resin and (b) a polyoxyethylene-type nonionic surfactant, wherein (in 100 mass% of the styrene resin composition ( A styrenic resin composition, wherein the content of b) is 0.1 to 1.0% by mass.
(2) (b) The polyoxyethylene type nonionic surfactant is selected from the group of the polyoxyethylene alkyl ether represented by the following general formula 1 and / or the polyoxyethylene fatty acid ester represented by the following general formula 2. The styrenic resin composition according to claim 1, wherein the styrene resin composition is of more than one type and has an average addition mole number of ethylene oxide of 7 to 100.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms, and n is an integer representing the number of added moles of ethylene oxide units)
(3) A plate-shaped molded article obtained by molding the styrene resin composition according to any one of (1) to (2).
(4) A light guide plate comprising the plate-like molded product according to (3).
[Effect of the invention]
[0006]
The styrenic resin composition of the present invention has low water absorption and is inexpensive compared to PMMA and MS resins, does not cause whitening due to environmental changes, which is a disadvantage of PS resin, provides heat resistance, and is colorless and transparent Because of its excellent properties, it can be suitably used for optical applications such as a light guide plate.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin of the present invention can be obtained by polymerizing a styrene monomer and a (meth) acrylic acid monomer. The styrene monomer is an aromatic vinyl monomer, such as styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, or a mixture of two or more, preferably styrene. The (meth) acrylic acid monomer is acrylic acid, methacrylic acid or the like, and methacrylic acid is preferable.
[0008]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0009]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0010]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0011]
The styrene resin of the present invention has a weight average molecular weight of 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer The molecular weight of the present invention is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0012]
The styrene resin of the present invention contains a (meth) acrylic acid unit in 100% by mass of the styrene resin, the content is 0.3 to 2.0% by mass, and 0.8 to 1.6% by mass. % Is preferred. When the content of the (meth) acrylic acid unit is less than 0.3% by mass, the whitening suppression effect and the heat resistance cannot be balanced. Moreover, when it exceeds 2.0 mass%, an initial hue and the transmittance | permeability will deteriorate.
[0013]
The (meth) acrylic acid unit content in the styrene resin was measured at room temperature. Weigh 0.5 g of styrene resin, dissolve in toluene / ethanol = 8/2 (volume ratio) mixed solution, then perform neutralization titration with potassium hydroxide 0.1 mol / L ethanol solution to detect the end point. From the usage amount of the potassium hydroxide ethanol solution, the mass-based content of (meth) acrylic acid units was calculated. An automatic potentiometric titration apparatus can be used, and measurement was performed with AT-510 manufactured by Kyoto Electronics Industry Co., Ltd. The content of the (meth) acrylic acid unit in the styrene resin can be adjusted by the composition of the raw styrene monomer and the (meth) acrylic monomer during the polymerization of the styrene resin. In the range to melt | dissolve, the styrene resin containing a (meth) acrylic acid unit and the styrene resin which does not contain a (meth) acrylic acid unit can also be blended and adjusted.
[0014]
The styrene resin composition of the present invention contains (c) a polyoxyethylene type nonionic surfactant (also referred to as a polyethylene glycol type nonionic surfactant) in 100% by mass of the styrene resin composition, Content is 0.1-1.0 mass%, and it is preferable that it is 0.3-0.6 mass%. If the content of the polyoxyethylene type nonionic surfactant is less than 0.1% by mass, it is difficult to prevent the whitening phenomenon due to environmental changes. If the content exceeds 1.0% by mass, the heat resistance of the styrene-based resin composition is reduced. descend.
[0015]
Polyoxyethylene type nonionic surfactants include polyoxyethylene alkyl ether represented by the following general formula (1), polyoxyethylene fatty acid ester represented by the following general formula (2), polyoxyethylene hydrogenated castor oil, polyoxy Ethylene sorbitan fatty acid ester and polyoxyethylene sorbitol fatty acid ester are exemplified, but one or more selected from the group of polyoxyethylene alkyl ether and / or polyoxyethylene fatty acid ester are preferable.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms, and n is an integer representing the number of added moles of ethylene oxide units)
[0016]
Polyoxyethylene alkyl ether is made by adding ethylene oxide to alcohol, and polyoxyethylene fatty acid ester is made by adding ethylene oxide to fatty acid or directly esterifying fatty acid and polyethylene glycol. The number is preferably 7 to 100, and more preferably 10 to 50.
[0017]
Examples of the polyoxyethylene alkyl ether include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene octyl decyl ether, polyoxyethylene myristyl ether, polyoxyethylene-2-ethylhexyl ether and the like. Is mentioned.
[0018]
Examples of the polyoxyethylene fatty acid ester include polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, and the like.
[0019]
6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3 of the present invention , 2] Dioxaphosphepine, hindered phenolic antioxidant and polyethylene glycol can be added by adding and mixing in the polymerization process, devolatilization process, granulation process of styrene resin, and extrusion during molding process. There is a method of adding and mixing with a machine or the like, and there is no particular limitation.
[0020]
The Vicat softening temperature of the styrene resin composition of the present invention is preferably 101 ° C. or higher, and more preferably 102 ° C. When the Vicat softening temperature is less than 101 ° C., the heat resistance is insufficient, and the molded product may be deformed depending on the use environment.
[0021]
The styrenic resin composition of the present invention may contain mineral oil as long as the colorless transparency of the present invention is not impaired. In addition, internal lubricants such as stearic acid and ethylenebisstearic acid amide, hindered phenol antioxidants, phosphorus antioxidants, sulfur antioxidants, lactone antioxidants, hindered amine stabilizers, UV absorbers In addition, additives such as an antistatic agent may be contained. As the external lubricant, ethylene bis stearamide is preferable, and the content is preferably 30 to 200 ppm in the resin composition.
[0022]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0023]
The styrenic resin composition of the present invention can be molded into a plate-shaped product by a molding method according to the purpose such as injection molding, extrusion molding, compression molding, etc., and used as a light guide plate. At that time, a reflection pattern such as a dot pattern can be provided on the back surface (opposite side of the light emitting surface) of the plate-shaped molded product, and used as a light guide plate. When processing from the resin plate to the light guide plate, it is preferable to polish the light incident surface or the entire end surface of the resin plate to make a mirror surface. In addition, in order to improve the uniformity of the emitted light, a prism pattern can be provided on the surface (surface from which light is emitted) of the plate-shaped molded product. The pattern on the front surface or the back surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0024]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0025]
(Examples 1-10, Comparative Examples 1-8)
A polymerization process is configured by connecting a first reactor, which is a complete mixing tank, a second reactor, and a third reactor, which is a plug flow reactor with a static mixer, in series. Table 10-1 A styrene resin was produced under the conditions shown. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A raw material solution was prepared with the raw material composition described in Table 10-1, and the raw material solution was continuously supplied to the first reactor at a flow rate described in Table 10-1. The polymerization initiator was added to the raw material solution at the inlet of the first reactor so as to have the addition concentration shown in Table 10-1 (concentration on the mass basis with respect to the total amount of raw styrene and methacrylic acid), and mixed uniformly. The polymerization initiator described in Table 10-1 was polymerization initiator-1: 2,2-di (4,4-t-butylperoxycyclohexyl) propane (Pertetra A manufactured by NOF Corporation) as follows. )
In the third reactor, a temperature gradient was provided along the direction of flow, and the temperature was adjusted so that the temperature shown in Table 10-1 was obtained at the intermediate part and the outlet part.
Moreover, the polyoxyethylene type nonionic surfactant was added to the inlet of the 3rd reactor so that it might become the kind and content which are shown in Table 10-2. The types of polyoxyethylene type nonionic surfactants are as follows.
P-1: Polyoxyethylene ethylene lauryl ether Ethylene oxide average added mole number = 25 (Emalgen 123P manufactured by Kao Corporation)
P-2: Polyoxyethylene ethylene stearyl ether ethylene oxide average added mole number = 12 (Emulgen 320P manufactured by Kao Corporation)
P-3: Polyoxyethylene ethylene lauryl ether Ethylene oxide average addition mole number = 9 (Emulgen 109P manufactured by Kao Corporation)
P-4: Polyoxyethylene ethylene cetyl ether Average number of moles of ethylene oxide added = 7 (Emulgen 210P manufactured by Kao Corporation)
P-5: Polyoxyethylene ethylene lauryl ether Ethylene oxide average added mole number = 47 (Emalgen 150 manufactured by Kao Corporation)
P-6: Polyoxyethylene ethylene myristyl ether Ethylene oxide average added mole number = 85 (Emalgen 4085 manufactured by Kao Corporation)
P-7: Polyethylene glycol monolaurate Ethylene oxide average added mole number = 12 (Emanon 1112 manufactured by Kao Corporation)
Subsequently, the solution containing the polymer continuously taken out from the third reactor is introduced into a vacuum devolatilization tank with a preheater constituted by two stages in series, so that the resin temperatures shown in Table 10-1 are obtained. After adjusting the temperature of the preheater and adjusting to the pressure shown in Table 10-1, unreacted styrene and ethylbenzene are separated, and then extruded into a strand shape from a perforated die. Cooled and cut and pelletized.
[0026]
Melt mass flow rate (MFR) is measured in accordance with JIS K-7210 under the conditions of 200 ° C. and 49 N load, Vicat softening temperature is measured in accordance with JIS K 7206 at a heating rate of 50 ° C./hr and a test load of 50 N. did.
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. A test piece having a thickness of 115 × 85 × 3 mm was cut out from the obtained plate-shaped product, and the end surface was polished by buffing to obtain a plate-shaped product having a mirror surface on the end surface. About the obtained plate-shaped molded article, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a spread angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance shown in Table 10-2 represents an average transmittance at a wavelength of 380 nm to 780 nm.
Furthermore, in order to confirm the whitening phenomenon due to environmental changes, a plate-like molded article having a mirror surface on the end face is exposed to an environment of 60 ° C. and 90% relative humidity for 150 hours, and the test piece is placed in an environment of 23 ° C. and 50% relative humidity. Taking out and observing the whitening phenomenon occurring inside the molded product, the following judgment was made as a whitening suppression effect.
◎: No whitening occurs. ○: Whitening occurs slightly after 1 hour after removal, but disappears after 24 hours. Table 10-1 shows the characteristics of each resin composition.
[0027]
[Table 10-1]

[0028]
[Table 10-2]

[0029]
The molded articles of the examples are excellent in heat resistance, excellent in whitening suppression effect, and excellent in initial transmittance and YI value.
[Industrial applicability]
[0030]
The styrenic resin composition of the present invention has excellent heat resistance, prevents whitening due to environmental changes, has excellent transparency and hue, and is used in televisions, desktop personal computers, notebook personal computers, mobile phones, car navigation systems. It can use suitably for light-guide plate uses, such as.

[００２５]
[表１１−２]

[００２６]
実施例の成形品は、耐熱性に優れ、白化抑制効果に優れ、初期の透過率とＹＩ値に優れており、長期の熱安定性にも優れている。
[産業上の利用可能性]
[００２７]
本発明のスチレン系樹脂組成物は、耐熱性に優れ、環境変化による白化現象が防止され、長期の熱安定性に優れることから透明性と色相に優れており、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 11)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
(A) The weight average molecular weight obtained by copolymerizing a styrene monomer and (meth) acrylic acid is 150,000 to 700,000, and the content of (meth) acrylic acid units is 0.8 to 4.5. And (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [ d, f] [1, 3, 2] dioxaphosphine, and the content of (b) in 100% by mass of the styrene resin composition is 0.05 to 0.40 mass. % Styrenic resin composition, wherein
[Claim 2]
(A) The weight average molecular weight obtained by copolymerizing a styrene monomer and (meth) acrylic acid is 150,000 to 700,000, and the content of (meth) acrylic acid units is 0.8 to 4.5. And (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [ d, f] [1,3,2] dioxaphosphin and (c) a styrene resin composition comprising a hindered phenol antioxidant, the content of (b) in 100% by mass of the styrene resin composition A styrenic resin composition characterized in that the amount is 0.05 to 0.40% by mass and the content of (c) is 0.02 to 0.50% by mass.
[Claim 3]
The plate-shaped molded article formed by shape | molding the styrene resin composition of any one of Claims 1-2.
[Claim 4]
A light guide plate comprising the plate-like molded product according to claim 3.
[Document Name] Statement
[Title of Invention] Styrenic resin composition, plate-shaped molded article and light guide plate
[Technical field]
[0001]
The present invention has excellent heat resistance, excellent hue and transparency, does not cause whitening due to environmental changes, and has excellent long-term thermal stability. And a light guide plate.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The An acrylic resin typified by PMMA (polymethylmethacrylate) is used for the light guide plate. However, since the water absorption is high, there may be a problem that the molded product is warped or a change in dimensions.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
However, Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylic ester copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water-absorbing property and the dimensional stability tend to be worse than those of the styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, there is a problem (whitening phenomenon) that a molded product becomes cloudy due to environmental changes such as temperature and humidity. Specifically, when a molded product is exposed to an environmental change from a high temperature and high humidity environment to a room temperature environment or an environmental change from a room temperature environment to a low temperature environment, moisture present uniformly in the molded product is not present. It becomes stable and phase-separates, and a disk-like defect is generated. As a result, the inside of the molded product becomes cloudy. When the molded product becomes cloudy, when the optical path length is long as in the light guide plate, there is a problem that the transmittance is greatly reduced due to light scattering and the luminance of the display is lowered.
Furthermore, the styrenic resin undergoes discoloration due to heat during long-term use, and there is a problem that the molded product turns yellow and the transmittance decreases. As a result, there is a problem that the luminance of the display is lowered or the chromaticity is changed.
Further, the inside of the backlight becomes high temperature depending on the use environment, and heat resistance is required to prevent the deformation of the light guide plate due to the temperature.
[Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
The present invention provides heat resistance, prevents whitening due to environmental changes, has little change in hue and transmittance even during long-term use, and is excellent in colorless transparency, particularly suitable for optical applications such as a light guide plate It is an object to provide a styrene-based resin composition.
[Means for solving problems]
[0005]
In the present invention, the weight average molecular weight obtained by copolymerizing (1) (a) a styrene monomer and (meth) acrylic acid is 150,000 to 700,000, and the content of (meth) acrylic acid units is 0.8-4.5% by mass of a styrenic resin and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10- A styrene-based resin composition comprising tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, and the content of (b) in 100% by mass of the styrene-based resin composition is 0. A styrenic resin composition, characterized by being from 0.05 to 0.40 mass%.
(2) (a) The weight average molecular weight obtained by copolymerizing a styrene monomer and (meth) acrylic acid is 150,000 to 700,000, and the content of (meth) acrylic acid units is 0.8 to 4.5% by mass of a styrene resin and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert- A styrene resin composition comprising butyldibenzo [d, f] [1,3,2] dioxaphosphine and (c) a hindered phenolic antioxidant, wherein (b ) Is 0.05 to 0.40% by mass, and (c) is 0.02 to 0.50% by mass.
(3) A plate-shaped molded article obtained by molding the styrene resin composition according to any one of (1) to (2).
(4) A light guide plate comprising the plate-like molded product according to (3).
[Effect of the invention]
[0006]
The styrenic resin composition of the present invention is less expensive and less water-absorbing compared to PMMA and MS resin, does not cause the whitening phenomenon due to environmental changes, which is a disadvantage of PS resin, and in long-term use Since changes in hue and transmittance are small, heat resistance is provided, and colorless transparency is excellent, it can be suitably used for optical applications such as a light guide plate. Moreover, the coloring prevention effect with respect to high temperature heat history, such as a shaping | molding process, is also high.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin of the present invention can be obtained by polymerizing a styrene monomer and a (meth) acrylic acid monomer. The styrene monomer is an aromatic vinyl monomer, such as styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, or a mixture of two or more, preferably styrene. The (meth) acrylic acid monomer is acrylic acid, methacrylic acid or the like, and methacrylic acid is preferable.
[0008]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0009]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0010]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0011]
The styrene resin of the present invention has a weight average molecular weight of 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer The molecular weight of the present invention is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0012]
The styrene resin of the present invention contains a (meth) acrylic acid unit in 100% by mass of the styrene resin, the content thereof is 0.8 to 4.5% by mass, and 1.8 to 3.0% by mass. % Is preferred. When the content of the (meth) acrylic acid unit is less than 0.8% by mass, the whitening suppression effect is insufficient. On the other hand, if it exceeds 4.5% by mass, the initial hue and transmittance deteriorate.
[0013]
The (meth) acrylic acid unit content in the styrene resin was measured at room temperature. Weigh 0.5 g of styrene resin, dissolve in toluene / ethanol = 8/2 (volume ratio) mixed solution, then perform neutralization titration with potassium hydroxide 0.1 mol / L ethanol solution to detect the end point. From the usage amount of the potassium hydroxide ethanol solution, the mass-based content of (meth) acrylic acid units was calculated. An automatic potentiometric titration apparatus can be used, and measurement was performed with AT-510 manufactured by Kyoto Electronics Industry Co., Ltd. The content of the (meth) acrylic acid unit in the styrenic resin can be adjusted by the composition ratio of the raw styrene monomer and the (meth) acrylic acid monomer during the polymerization of the styrene resin. In a compatible range, a styrene resin containing a (meth) acrylic acid unit and a styrene resin not containing a (meth) acrylic acid unit can be blended and adjusted.
[0014]
The styrene resin composition of the present invention comprises (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4, in 100% by mass of the styrene resin composition. It contains 8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, and its content is 0.05 to 0.40% by mass. When the content of (b) is less than 0.05% by mass, the long-term thermal stability is inferior, and the initial hue and transmittance are also inferior. Moreover, even if it exceeds 0.40 mass%, long-term thermal stability will deteriorate.
[0015]
The styrene resin composition of the present invention preferably contains 0.02 to 0.50 mass% of (c) hindered phenol antioxidant in 100 mass% of the styrene resin composition, and 0.05 to 0 More preferably, the content is 30% by mass. 6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Long-term thermal stability, initial hue, and transmittance are improved as compared with the case of using dioxaphosphepine alone.
[0016]
Examples of the hindered phenol antioxidant used in the present invention include octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, ethylenebis (oxyethylene) bis [3- (5 -Tert-butyl-4-hydroxy-m-tolyl) propionate], 4,6-bis (octylthiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -o-cresol, 2,4 -Dimethyl-6- (1-methylpentadecyl) phenol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, DL-α-tocopherol, 2-t- Butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1 (2-hydroxy-3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4′-thiobis (6-t-butyl-3-methylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-tert-butylphenol) Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate and / or ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate ] Is preferable.
[0017]
The Vicat softening temperature of the styrene resin composition of the present invention is preferably 104 ° C. or higher, more preferably 106 ° C. If the Vicat softening temperature is less than 104 ° C, the heat resistance is insufficient, and the molded product may be deformed depending on the use environment.
[0018]
The styrenic resin composition of the present invention may contain mineral oil as long as the colorless transparency of the present invention is not impaired. Additives such as internal lubricants such as stearic acid and ethylene bis stearamide, phosphorus antioxidants, sulfur antioxidants, lactone antioxidants, hindered amine stabilizers, UV absorbers, antistatic agents, etc. May be included. As the external lubricant, ethylene bis stearamide is preferable, and the content is preferably 30 to 200 ppm in the resin composition.
[0019]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0020]
The styrenic resin composition of the present invention can be molded into a plate-shaped product by a molding method according to the purpose such as injection molding, extrusion molding, compression molding, etc., and used as a light guide plate. At that time, a reflection pattern such as a dot pattern can be provided on the back surface (opposite side of the light emitting surface) of the plate-shaped molded product, and used as a light guide plate. When processing from the resin plate to the light guide plate, it is preferable to polish the light incident surface or the entire end surface of the resin plate to make a mirror surface. In addition, in order to improve the uniformity of the emitted light, a prism pattern can be provided on the surface (surface from which light is emitted) of the plate-shaped molded product. The pattern on the front surface or the back surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0021]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0022]
(Examples 1-11, Comparative Examples 1-6)
A polymerization process is configured by connecting a first reactor that is a complete mixing tank, a second reactor, and a third reactor that is a plug flow reactor with a static mixer in series, and Table 11-1 A styrene resin was produced under the conditions shown. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A raw material solution was prepared with the raw material composition described in Table 11-1, and the raw material solution was continuously supplied to the first reactor at a flow rate described in Table 11-1. The polymerization initiator was added to the raw material solution at the inlet of the first reactor so as to have the addition concentration shown in Table 11-1 (concentration on a mass basis with respect to the total amount of raw styrene and methacrylic acid), and mixed uniformly. The polymerization initiator described in Table 11-1 was polymerization initiator-1: 2,2-di (4,4-t-butylperoxycyclohexyl) propane (Pertetra A manufactured by NOF Corporation) as follows. )
Polymerization initiator-2: 1,1-di (t-butylperoxy) cyclohexane (Perhexa C manufactured by NOF Corporation was used.)
In the third reactor, a temperature gradient was provided along the flow direction, and the temperature was adjusted so that the temperature shown in Table 11-1 was obtained at the intermediate part and the outlet part.
Then, the solution containing the polymer continuously taken out from the third reactor is introduced into a vacuum devolatilization tank with a preheater constituted by two stages in series, so that the resin temperatures shown in Table 11-1 are obtained. By adjusting the temperature of the preheater and adjusting to the pressure shown in Table 11-1, unreacted styrene and ethylbenzene are separated, and then extruded into a strand shape from a perforated die. Cooled and cut and pelletized.
[0023]
Next, using the single-screw extruder with a screw diameter of 40 mm, the pellets obtained above and additives A and B at a cylinder temperature of 230 ° C. and a screw rotation speed of 100 rpm so that the contents shown in Table 11-2 are obtained. Pellets were obtained by melt kneading. Additives A and B used in Table 11-1 are shown below. In addition, additive A is (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, additive B represents (c) a hindered phenolic antioxidant.
A-1: 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3,2] Dioxaphosphepin (Sumitomo GP, manufactured by Sumitomo Chemical Co., Ltd.)
B-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
B-2: Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
Melt mass flow rate (MFR) is measured in accordance with JIS K-7210 under the conditions of 200 ° C. and 49 N load, Vicat softening temperature is measured in accordance with JIS K 7206 at a heating rate of 50 ° C./hr and a test load of 50 N. did.
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. In order to evaluate long-term thermal stability, the obtained plate-shaped molded article was stored in an 80 ° C. oven for 500 hours. In order to evaluate the optical properties before and after storage, a 115 × 85 × 3 mm thickness test piece was cut out from the plate-shaped molded product, the end surface was polished by buffing, and a plate-shaped molded product having a mirror surface on the end surface was created. Using an ultraviolet-visible spectrophotometer V-670 manufactured by Co., Ltd., measuring the spectral transmittance at a wavelength of 350 nm to 800 nm at an optical path length of 115 mm in incident light having a size of 20 × 1.6 mm and a spread angle of 0 °, The YI value at a visual field of 2 ° for the C light source was calculated according to JIS K7105. The transmittance shown in Table 11-2 represents the average transmittance at a wavelength of 380 nm to 780 nm.
Furthermore, in order to confirm the whitening phenomenon due to environmental changes, a plate-like molded article having a mirror surface on the end face is exposed to an environment of 60 ° C. and 90% relative humidity for 150 hours, and the test piece is placed in an environment of 23 ° C. and 50% relative humidity. Taking out and observing the whitening phenomenon occurring inside the molded product, the following judgment was made as a whitening suppression effect.
A: No whitening occurs. O: Whitening occurs slightly after 1 hour, but disappears after 24 hours. Δ: Whitening occurs after 1 hour, but almost disappears after 24 hours. X: Remarkably whitening after 1 hour. Table 11-1 shows the characteristics of each resin composition.
[0024]
[Table 11-1]

[0025]
[Table 11-2]

[0026]
The molded articles of the examples are excellent in heat resistance, excellent in whitening suppression effect, excellent in initial transmittance and YI value, and excellent in long-term thermal stability.
[Industrial applicability]
[0027]
The styrenic resin composition of the present invention has excellent heat resistance, prevents whitening due to environmental changes, and has excellent long-term thermal stability, so it has excellent transparency and hue, such as televisions, desktop personal computers, notebooks. It can be suitably used for light guide plate applications such as portable personal computers, mobile phones, and car navigation systems.

（式中、Ｒは炭素数８〜２０のアルキル基を示し、ｎは整数でエチレンオキサイド単位の付加モル数を表す）
[請求項４]
請求項１〜３のいずれか１項に記載のスチレン系樹脂組成物を成形してなる板状成形品。
[請求項５]
請求項４に記載の板状成形品からなる導光板。
[書類名]明細書
[発明の名称]スチレン系樹脂組成物、板状成形品および導光板
[技術分野]
[０００１]
本発明は、耐熱性に優れ、色相と透明性に優れ、環境変化による白化現象が発生せず、長期の熱安定性に優れた導光板用途に適したスチレン系樹脂組成物、板状成形品および導光板に関するものである。
[背景技術]
[０００２]
液晶ディスプレイのバックライトには光源を表示装置の正面に配置する直下型バックライトと側面に配置するエッジライト型バックライトがある。導光板はエッジライト型バックライトに組み込まれ、側面からの光を液晶パネルに導く役割を果たし、テレビ、デスクトップ型パーソナルコンピューターのモニター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなど幅広い用途で使用される。導光板にはＰＭＭＡ（ポリメチルメタクリレート）に代表されるアクリル樹脂が使用されているが、吸水性が高いため、成形品に反りが発生する問題や寸法の変化が発生する場合がある。
そのため、これら特性を改善したスチレンと（メタ）アクリル酸メチルとの共重合体であるＭＳ樹脂を用いることが提案されている。ＭＳ樹脂の、吸水性や成形時の変色低減等の改良技術としては特許文献１が提案されている。
しかしながら、特許文献１では、スチレン−（メタ）アクリル酸エステル系共重合体樹脂の重量平均分子量（Ｍｗ）６〜１７万、残存モノマー量３０００ｐｐｍ以下、更にオリゴマー量が２％以下の導光板が開示されているが、吸水性が高く寸法安定性がスチレン系単量体を原料とするスチレン系樹脂よりも悪い傾向にあった。
一方、スチレン系単量体を原料とするスチレン系樹脂は吸水性が低いものの、温度や湿度などの環境変化により成形品が白濁する問題（白化現象）があった。具体的には、高温高湿環境下から室温環境下への環境変化や室温環境下から低温環境下への環境変化に成形品が曝された場合、成形品中に均一に存在する水分が不安定となって相分離し、円盤状の欠陥が生成し、その結果、成形品の内部が白濁する。成形品が白濁すると、導光板のように光路長が長い場合、光散乱により透過率が大きく低下して、ディスプレイの輝度が低下する問題がある。
さらに、スチレン系樹脂は長期間の使用において熱による変色が発生し、成形品が黄変して透過率が低下する問題がある。その結果、ディスプレイの輝度が低下したり、色度が変化する問題がある。
また、バックライトの内部は使用環境によっては高温となり、温度による導光板の変形を防止するためには耐熱性が要求される。
[先行技術文献]
[特許文献]
[０００３]
[特許文献１]特開２００３−０７５６４８号公報
[発明の概要]
[発明が解決しようとする課題]
[０００４]
本発明は、耐熱性を供え、環境変化による白化現象を防止し、長期間の使用においても色相および透過率の変化が小さく、特に導光板等の光学用途に適した、無色透明性に優れたスチレン系樹脂組成物を提供することを課題とする。
[課題を解決するための手段]
[０００５]
本発明は、（１）（ａ）スチレン系単量体と（メタ）アクリル酸とを共重合して得られる重量平均分子量が１５万〜７０万で、（メタ）アクリル酸単位の含有量が０．３〜２．０質量％であるスチレン系樹脂と（ｂ）６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンと（ｃ）ポリオキシエチレン型非イオン性界面活性剤からなるスチレン系樹脂組成物であって、スチレン系樹脂組成物１００質量％中の（ｂ）の含有量が０．０５〜０．４０質量％、（ｃ）の含有量が０．１〜１．０質量％であることを特徴とするスチレン系樹脂組成物。
（２）（ａ）スチレン系単量体と（メタ）アクリル酸とを共重合して得られる重量平均分子量が１５万〜７０万で、（メタ）アクリル酸単位の含有量が０．３〜２．０質量％であるスチレン系樹脂と（ｂ）６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンと（ｃ）ポリオキシエチレン型非イオン性界面活性剤と（ｄ）ヒンダードフェノール系酸化防止剤からなるスチレン系樹脂組成物であって、スチレン系樹脂組成物１００質量％中の（ｂ）の含有量が０．０５〜０．４０質量％、（ｃ）の含有量が０．１〜１．０質量％、（ｄ）の含有量が０．０２〜０．５０質量％であることを特徴とするスチレン系樹脂組成物。
（３）（ｃ）ポリオキシエチレン型非イオン性界面活性剤が下記一般式１で示されるポリオキシエチレンアルキルエーテル及び／又は下記一般式２で示されるポリオキシエチレン脂肪酸エステルの郡から選ばれる１種類以上であり、かつエチレンオキサイドの平均付加モル数が７〜１００であることを特徴とする（１）又は（２）に記載のスチレン系樹脂組成物。

（式中、Ｒは炭素数８〜２０のアルキル基を示し、ｎは整数でエチレンオキサイド単位の付加モル数を表す）
（４）（１）〜（３）のいずれか１項に記載のスチレン系樹脂組成物を成形してなる板状成形品。
（５）（４）に記載の板状成形品からなる導光板。
[発明の効果]
[０００６]
本発明のスチレン系樹脂組成物は、ＰＭＭＡやＭＳ樹脂と比較して、吸水性が低く安価であり、ＰＳ樹脂の欠点である環境変化による白化現象が発生せず、また、長期間の使用における色相および透過率の変化が小さく、耐熱性を供え、無色透明性に優れることから、導光板等の光学用途に好適に用いることが出来る。また、成形加工などの高温熱履歴に対する着色防止効果も高い。
[発明を実施するための形態]
[０００７]
本発明のスチレン系樹脂は、スチレン系単量体と（メタ）アクリル酸系単量体とを重合して得ることができる。スチレン系単量体とは、芳香族ビニル系モノマーである、スチレン、α−メチルスチレン、ｏ−メチルスチレン、ｐ−メチルスチレン等の単独または２種以上の混合物であり、好ましくはスチレンである。（メタ）アクリル酸系単量体は、アクリル酸、メタクリル酸等であり、メタクリル酸が好ましい。
[０００８]
スチレン系樹脂の重合方法としては、塊状重合法、溶液重合法、懸濁重合法、乳化重合法等公知のスチレン重合方法が挙げられる。品質面や生産性の面では、塊状重合法、溶液重合法が好ましく、連続重合であることが好ましい。溶媒として例えばベンゼン、トルエン、エチルベンゼン及びキシレン等のアルキルベンゼン類やアセトンやメチルエチルケトン等のケトン類、ヘキサンやシクロヘキサン等の脂肪族炭化水素等が使用できる。
[０００９]
スチレン系樹脂の重合時に、必要に応じて重合開始剤、連鎖移動剤を使用することができる。重合開始剤としては、ラジカル重合開始剤が好ましく、公知慣用の例えば、１，１−ジ（ｔ−ブチルパーオキシ）シクロヘキサン、２，２−ジ（ｔ−ブチルパーオキシ）ブタン、２，２−ジ（４，４−ジ−ｔ−ブチルパーオキシシクロヘキシル）プロパン、１，１−ジ（ｔ−アミルパーオキシ）シクロヘキサン等のパーオキシケタール類、クメンハイドロパーオキサイド、ｔ−ブチルハイドロパーオキサイド等のハイドロパーオキサイド類、ｔ−ブチルパーオキシアセテート、ｔ−アミルパーオキシイソノナノエート等のアルキルパーオキサイド類、ｔ−ブチルクミルパーオキサイド、ジ−ｔ−ブチルパーオキサイド、ジクミルパーオキサイド、ジ−ｔ−ヘキシルパーオキサイド等のジアルキルパーオキサイド類、ｔ−ブチルパーオキシアセテート、ｔ−ブチルパーオキシベンゾエート、ｔ−ブチルパーオキシイソプロピルモノカーボネート等のパーオキシエステル類、ｔ−ブチルパーオキシイソプロピルカーボネート、ポリエーテルテトラキス（ｔ-ブチルパーオキシカーボネート）等のパーオキシカーボネート類、Ｎ，Ｎ'−アゾビス（シクロヘキサン−１−カルボニトリル）、Ｎ，Ｎ'−アゾビス（２−メチルブチロニトリル）、Ｎ，Ｎ'−アゾビス（２，４−ジメチルバレロニトリル）、Ｎ，Ｎ'−アゾビス［２−（ヒドロキシメチル）プロピオニトリル］等が挙げられ、これらの１種あるいは２種以上を組み合わせて使用することができる。連鎖移動剤としては、脂肪族メルカプタン、芳香族メルカプタン、ペンタフェニルエタン、α−メチルスチレンダイマー及びテルピノーレン等が挙げられる。
[００１０]
連続重合の場合、まず重合工程にて公知の完全混合槽型攪拌槽や塔型反応器等を用い、目標の分子量、分子量分布、反応転化率となるよう、重合温度調整等により重合反応が制御される。重合工程を出た重合体を含む重合溶液は、脱揮工程に移送され、未反応の単量体及び重合溶媒が除去される。脱揮工程は加熱器付きの真空脱揮槽やベント付き脱揮押出機などで構成される。脱揮工程を出た溶融状態の重合体は造粒工程へ移送される。造粒工程では、多孔ダイよりストランド状に溶融樹脂を押出し、コールドカット方式や空中ホットカット方式、水中ホットカット方式にてペレット形状に加工される。
[００１１]
本発明のスチレン系樹脂の重量平均分子量は１５万〜７０万であり、１８万〜５０万であることが好ましい。１５万未満では成形品の強度が不十分となり、７０万を超えると成形性が著しく低下する。スチレン系樹脂の重量平均分子量は、重合工程の反応温度、滞留時間、重合開始剤の種類及び添加量、連鎖移動剤の種類及び添加量、重合時に使用する溶媒の種類及び量等によって制御することができる。
重量平均分子量（Ｍｗ）及びＺ平均分子量（Ｍｚ）、数平均分子量（Ｍｎ）は、ゲルパーミエイションクロマトグラフィー（ＧＰＣ）を用いて、次の条件で測定した。
ＧＰＣ機種：昭和電工株式会社製Ｓｈｏｄｅｘ ＧＰＣ−１０１
カラム：ポリマーラボラトリーズ社製 ＰＬｇｅｌ １０μｍ ＭＩＸＥＤ−Ｂ
移動相：テトラヒドロフラン
試料濃度：０．２質量％
温度：オーブン４０℃、注入口３５℃、検出器３５℃
検出器：示差屈折計
本発明の分子量は単分散ポリスチレンの溶出曲線より各溶出時間における分子量を算出し、ポリスチレン換算の分子量として算出したものである。
[００１２]
本発明のスチレン系樹脂は、スチレン系樹脂１００質量％中に（メタ）アクリル酸単位を含有し、その含有量が０．３〜２．０質量％であり、０．８〜１．６質量％であることが好ましい。（メタ）アクリル酸単位の含有量が０．３質量％未満では、白化抑制効果と耐熱性のバランスが取れない。また、２．０質量％を超えると、初期の色相および透過率が悪化する。
[００１３]
スチレン系樹脂中の（メタ）アクリル酸単位含有量の測定は室温で実施した。スチレン系樹脂０．５ｇを秤量し、トルエン／エタノール＝８／２（体積比）の混合溶液に溶解後、水酸化カリウム０．１ｍｏｌ／Ｌエタノール溶液にて中和滴定を行い、終点を検出し、水酸化カリウムエタノール溶液の使用量より、（メタ）アクリル酸単位の質量基準の含有量を算出した。なお、電位差自動滴定装置を使用することができ、京都電子工業株式会社製ＡＴ−５１０により測定を行った。スチレン系樹脂中の（メタ）アクリル酸単位の含有量は、スチレン系樹脂の重合時における原料のスチレン系単量体と（メタ）アクリル酸単量体の組成によって調整することができるが、相溶する範囲において（メタ）アクリル酸単位を含有するスチレン系樹脂と（メタ）アクリル酸単位を含有しないスチレン系樹脂をブレンドして調整することもできる。
[００１４]
本発明のスチレン系樹脂組成物は、スチレン系樹脂組成物１００質量％中（ｂ）６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンを含有し、その含有量が０．０５〜０．４０質量％である。（ｂ）の含有量が０．０５質量％未満では長期の熱安定性に劣り、初期の色相および透過率にも劣る。また、０．４０質量％を超えても長期の熱安定性が悪化する。
[００１５]
本発明のスチレン系樹脂組成物は、スチレン系樹脂組成物１００質量％中（ｄ）ヒンダードフェノール系酸化防止剤を０．０２〜０．５０質量％含有することが好ましく、０．０５〜０．３０質量％含有することがより好ましい。６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンを単独で使用した場合よりも長期の熱安定性および初期の色相、透過率が向上する。
[００１６]
本発明に用いられるヒンダードフェノール系酸化防止剤は、例えば、オクタデシル−３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート、エチレンビス（オキシエチレン）ビス〔３−（５−ｔｅｒｔ−ブチル−４−ヒドロキシ−ｍ−トリル）プロピオネート〕、４，６−ビス（オクチルチオメチル）−ｏ−クレゾール、４，６−ビス〔（ドデシルチオ）メチル〕−ｏ−クレゾール、２，４−ジメチル−６−（１−メチルペンタデシル）フェノール、テトラキス〔メチレン−３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート〕メタン、ＤＬ−α−トコフェロール、２−ｔ−ブチル−６−（３−ｔ−ブチル−２−ヒドロキシ−５−メチルベンジル）−４−メチルフェニルアクリレート、２−〔１−（２−ヒドロキシ−３，５−ジ−ｔ−ペンチルフェニル）エチル〕−４，６−ジ−ｔ−ペンチルフェニルアクリレート、４，４’−チオビス（６−ｔ−ブチル−３−メチルフェノール）、１，１，３−トリス（２−メチル−４−ヒドロキシ−５−ｔ−ブチルフェニル）ブタン、４，４’−ブチリデンビス（３−メチル−６−ｔ−ブチルフェノール）等を挙げることができるが、オクタデシル−３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート及び／又はエチレンビス（オキシエチレン）ビス〔３−（５−ｔｅｒｔ−ブチル−４−ヒドロキシ−ｍ−トリル）プロピオネート〕が好ましい。
[００１７]
本発明のスチレン系樹脂組成物は、スチレン系樹脂組成物１００質量％中（ｃ）ポリオキシエチレン型非イオン性界面活性剤（ポリエチレングリコール型非イオン性界面活性剤ともいう）を含有し、その含有量は０．１〜１．０質量％であり、０．３〜０．６質量％であることが好ましい。ポリオキシエチレン型非イオン性界面活性剤の含有量が０．１質量％未満では環境変化による白化現象の防止が困難であり、１．０質量％を超えるとスチレン系樹脂組成物の耐熱性が低下する。
[００１８]
ポリオキシエチレン型非イオン性界面活性剤は、下記一般式（１）で示されるポリオキシエチレンアルキルエーテルや下記一般式（２）で示されるポリオキシエチレン脂肪酸エステル、ポリオキシエチレン硬化ひまし油、ポリオキシエチレンソルビタン脂肪酸エステル、ポリオキシエチレンソルビトール脂肪酸エステルが挙げられるがポリオキシエチレンアルキルエーテル及び／又はポリオキシエチレン脂肪酸エステルの郡から選ばれる１種類以上であることが好ましい。

（式中、Ｒは炭素数８〜２０のアルキル基を示し、ｎは整数でエチレンオキサイド単位の付加モル数を表す）
[００１９]
ポリオキシエチレンアルキルエーテルはアルコールにエチレンオキサイドを付加させて作られ、ポリオキシエチレン脂肪酸エステルは脂肪酸にエチレンオキサイドを付加させるか脂肪酸とポリエチレングリコールを直接エステル化させて作られ、エチレンオキサイドの平均付加モル数は７〜１００であることが好ましく、１０〜５０であることがより好ましい。
[００２０]
ポリオキシエチレンアルキルエーテルとしては、例えば、ポリオキシエチレンラウリルエーテル、ポリオキシエチレンセチルエーテル、ポリオキシエチレンステアリルエーテル、ポリオキシエチレンオクチルドデシルエーテル、ポリオキシエチレンミリスチルエーテル、ポリオキシエチレン−２−エチルヘキシルエーテル等が挙げられる。
[００２１]
ポリオキシエチレン脂肪酸エステルとしては、例えば、ポリエチレングリコールモノラウレート、ポリエチレングリコールモノステアレート、ポリエチレングリコールジステアレート等が挙げられる。
[００２２]
本発明の６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンおよびヒンダードフェノール系酸化防止剤、ポリエチレングリコールの添加方法としては、スチレン系樹脂の重合工程、脱揮工程、造粒工程で添加混合する方法や成形加工時の押出機などで添加混合する方法が挙げられ、特に限定されることではない。
[００２３]
本発明のスチレン系樹脂組成物のビカット軟化温度は１０１℃以上であることが好ましく、１０２℃であることがより好ましい。ビカット軟化温度が１０１℃未満では耐熱性が不足し、使用環境によっては成形品が変形する可能性がある。
[００２４]
本発明のスチレン系樹脂組成物には、本発明の無色透明性を損なわない範囲でミネラルオイルを含有しても良い。また、ステアリン酸、エチレンビスステアリン酸アミド等の内部潤滑剤やリン系酸化防止剤、イオウ系酸化防止剤、ラクトン系酸化防止剤、ヒンダードアミン系安定剤、紫外線吸収剤、帯電防止剤等の添加剤が含まれていても良い。また、外部潤滑剤としては、エチレンビスステアリン酸アミドが好適であり、含有量としては樹脂組成物中に３０〜２００ｐｐｍであることが好ましい。
[００２５]
紫外線吸収剤は、紫外線による劣化や着色を抑制する機能を有するものであって、例えば、ベンゾフェノン系、ベンゾトリアゾール系、トリアジン系、ベンゾエート系、サリシレート系、シアノアクリレート系、蓚酸アニリド系、マロン酸エステル系、ホルムアミジン系などの紫外線吸収剤が挙げられる。これらは、単独又は２種以上組み合わせて用いることができ、ヒンダートアミン等の光安定剤を併用してもよい。
[００２６]
本発明のスチレン系樹脂組成物は、射出成形、押出成形、圧縮成形等、目的に応じた成形方法で板状成形品に成形し、導光板として用いることができる。その際、板状成形品の背面（光を出射する面の反対側）にドットパターンなどの反射パターンを設けて、導光板として用いることができる。樹脂板から導光板に加工する際、光の入射面あるいは樹脂板の端面全面を研磨処理して、鏡面とすることが好ましい。また、出射光の均一性を高めるために、板状成形品の表面（光が出射される面）にプリズムパターンを設けることができる。板状成形品の表面あるいは背面のパターンは、板状成形品の成形時に形成させることができ、例えば射出成形では金型形状、押出成形ではロール転写などによって、パターン形成させることができる。
[実施例]
[００２７]
以下、実施例を挙げて本発明を具体的に説明するが、本発明はこれら実施例に限定されるものではない。
[００２８]
（実施例１〜１６、比較例１〜１２）
完全混合型撹拌槽である第１反応器と第２反応器及び静的混合器付プラグフロー型反応器である第３反応器を直列に接続して重合工程を構成し、表１２−１に示す条件によりスチレン系樹脂の製造を実施した。各反応器の容量は、第１反応器を３９リットル、第２反応器を３９リットル、第３反応器を１６リットルとした。表１２−１に記載の原料組成にて、原料溶液を作成し、第１反応器に原料溶液を表１２−１に記載の流量にて連続的に供給した。重合開始剤は、第１反応器の入口で表１２−１に記載の添加濃度（原料スチレン及びメタクリル酸の合計量に対する質量基準の濃度）となるように原料溶液に添加し、均一混合した。表１２−１に記載の重合開始剤は次の通り
重合開始剤−１ ：２，２−ジ（４，４−ｔ−ブチルパーオキシシクロヘキシル）プロパン（日油株式会社製パーテトラＡを使用した。）
なお、第３反応器では、流れの方向に沿って温度勾配をつけ、中間部分、出口部分で表１２−１の温度となるよう調整した。
また、第３反応器の入口に、ポリオキシエチレン型非イオン性界面活性剤を表１２−２に示す種類と含有量になるよう添加した。ポリオキシエチレン型非イオン性界面活性剤の種類は次の通り。
Ｐ−１：ポリオキシエチレンエチレンラウリルエーテル エチレンオキサイド平均付加モル数＝２５（花王株式会社製エマルゲン１２３Ｐ）
Ｐ−２：ポリオキシエチレンエチレンステアリルエーテル エチレンオキサイド平均付加モル数＝１２（花王株式会社製エマルゲン３２０Ｐ）
Ｐ−３：ポリオキシエチレンエチレンラウリルエーテル エチレンオキサイド平均付加モル数＝９（花王株式会社製エマルゲン１０９Ｐ）
Ｐ−４：ポリオキシエチレンエチレンセチルエーテル エチレンオキサイド平均付加モル数＝７（花王株式会社製エマルゲン２１０Ｐ）
Ｐ−５：ポリオキシエチレンエチレンラウリルエーテル エチレンオキサイド平均付加モル数＝４７（花王株式会社製エマルゲン１５０）
Ｐ−６：ポリオキシエチレンエチレンミリスチルエーテル エチレンオキサイド平均付加モル数＝８５（花王株式会社製エマルゲン４０８５）
Ｐ−７：ポリエチレングリコールモノラウレート エチレンオキサイド平均付加モル数＝１２（花王株式会社製エマノーン１１１２）
続いて、第３反応器より連続的に取り出した重合体を含む溶液を直列に２段より構成される予熱器付き真空脱揮槽に導入し、表１２−１に記載の樹脂温度となるよう予熱器の温度を調整し、表１２−１に記載の圧力に調整することで、未反応スチレン及びエチルベンゼンを分離した後、多孔ダイよりストランド状に押し出しして、コールドカット方式にて、ストランドを冷却および切断しペレット化した。
[００２９]
次に、表１２−２に示す含有量となるよう、上記で得られたスチレン系樹脂のペレットと添加剤ＡおよびＢをスクリュー径４０ｍｍの単軸押出機を用いて、シリンダー温度２３０℃、スクリュー回転数１００ｒｐｍで溶融混錬してペレットを得た。表１２−１で用いた添加剤ＡおよびＢを次に示す。なお、添加剤Ａは（ｂ）６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピンを、添加剤Ｂは（ｄ）ヒンダードフェノール系酸化防止剤を表す。
Ａ−１：６−〔３−（３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロポキシ〕−２，４，８，１０−テトラ−ｔｅｒｔ−ブチルジベンゾ〔ｄ，ｆ〕〔１，３，２〕ジオキサホスフェピン（住友化学株式会社製 スミライザーＧＰ）
Ｂ−１：オクタデシル−３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート（ＢＡＳＦジャパン株式会社製 Ｉｒｇａｎｏｘ １０７６）
Ｂ−２：エチレンビス（オキシエチレン）ビス〔３−（５−ｔｅｒｔ−ブチル−４−ヒドロキシ−ｍ−トリル）プロピオネート〕（ＢＡＳＦジャパン株式会社製 Ｉｒｇａｎｏｘ ２４５）
メルトマスフローレート（ＭＦＲ）は、ＪＩＳ Ｋ−７２１０に準拠し、２００℃、４９Ｎ荷重の条件で、ビカット軟化温度は、ＪＩＳ Ｋ ７２０６に準拠し、昇温速度５０℃／ｈｒ、試験荷重５０Ｎで測定した。
また、得られたペレットを用いて、シリンダー温度２３０℃、金型温度５０℃にて射出成形を行い、１２７×１２７×３ｍｍ厚みの板状成形品を成形した。長期の熱安定性を評価するため、得られた板状成形品を８０℃オーブン内で５００時間保管した。保管前後の光学特性と評価するため、板状成形品から１１５×８５×３ｍｍ厚みの試験片を切り出し、端面をバフ研磨によって研磨し、端面に鏡面を有する板状成形品を作成し、日本分光株式会社製の紫外線可視分光光度計Ｖ−６７０を用いて、大きさ２０×１．６ｍｍ、広がり角度０°の入射光において、光路長１１５ｍｍでの波長３５０ｎｍ〜８００ｎｍの分光透過率を測定し、Ｃ光源における、視野２°でのＹＩ値をＪＩＳ Ｋ７１０５に倣い算出した。表１２−２に示す透過率とは、波長３８０ｎｍ〜７８０ｎｍの平均透過率を表す。
さらに、環境変化による白化現象を確認するため、端面に鏡面を有する板状成形品を６０℃、９０％相対湿度の環境に１５０時間暴露し、２３℃、５０％相対湿度の環境に試験片を取出し、成形品内部に発生する白化現象を観察し、白化抑制効果として下記の通り判定を行った。
◎：全く白化が発生しない
○：取出し１時間後にやや白化するが、２４時間後には消失する
△：取出し１時間後に白化するが、２４時間後にはほとんど消失する
×：取出し１時間後に著しく白化し、２４時間経っても消失しない
表１２−１に各樹脂組成物の特性を示す。
[００３０]
[表１２−１]

[００３１]
[表１２−２]

[００３２]
実施例の成形品は、耐熱性に優れ、白化抑制効果に優れ、初期の透過率とＹＩ値に優れており、長期の熱安定性にも優れている。
[産業上の利用可能性]
[００３３]
本発明のスチレン系樹脂組成物は、耐熱性に優れ、環境変化による白化現象が防止され、長期の熱安定性に優れることから透明性と色相に優れており、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 12)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
(A) The weight average molecular weight obtained by copolymerizing a styrene monomer and (meth) acrylic acid is 150,000 to 700,000, and the content of (meth) acrylic acid units is 0.3 to 2.0. And (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [ d, f] [1,3,2] dioxaphosphepine and (c) a styrene-based resin composition comprising a polyoxyethylene-type nonionic surfactant, in 100% by mass of the styrene-based resin composition The content of (b) is 0.05 to 0.40% by mass, and the content of (c) is 0.1 to 1.0% by mass.
[Claim 2]
(A) The weight average molecular weight obtained by copolymerizing a styrene monomer and (meth) acrylic acid is 150,000 to 700,000, and the content of (meth) acrylic acid units is 0.3 to 2.0. And (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [ a styrenic resin composition comprising d, f] [1,3,2] dioxaphosphin, (c) a polyoxyethylene nonionic surfactant, and (d) a hindered phenolic antioxidant. The content of (b) in 100% by mass of the styrene-based resin composition is 0.05 to 0.40% by mass, the content of (c) is 0.1 to 1.0% by mass, and the content of (d) The amount is 0.02-0.50% by mass System resin composition.
[Claim 3]
(C) The polyoxyethylene type nonionic surfactant is selected from the group of the polyoxyethylene alkyl ether represented by the following general formula (1) and / or the polyoxyethylene fatty acid ester represented by the following general formula (2). The styrenic resin composition according to claim 1, wherein the styrene-based resin composition is one or more types, and an average added mole number of ethylene oxide is 7 to 100.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms, and n is an integer representing the number of added moles of ethylene oxide units)
[Claim 4]
The plate-shaped molded article formed by shape | molding the styrene resin composition of any one of Claims 1-3.
[Claim 5]
A light guide plate comprising the plate-like molded product according to claim 4.
[Document Name] Statement
[Title of Invention] Styrenic resin composition, plate-shaped molded article and light guide plate
[Technical field]
[0001]
The present invention has excellent heat resistance, excellent hue and transparency, does not cause whitening due to environmental changes, and has excellent long-term thermal stability. And a light guide plate.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The An acrylic resin typified by PMMA (polymethylmethacrylate) is used for the light guide plate. However, since the water absorption is high, there may be a problem that the molded product is warped or a change in dimensions.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
However, Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylic ester copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water-absorbing property and the dimensional stability tend to be worse than those of the styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, there is a problem (whitening phenomenon) that a molded product becomes cloudy due to environmental changes such as temperature and humidity. Specifically, when a molded product is exposed to an environmental change from a high temperature and high humidity environment to a room temperature environment or an environmental change from a room temperature environment to a low temperature environment, moisture present uniformly in the molded product is not present. It becomes stable and phase-separates, and a disk-like defect is generated. As a result, the inside of the molded product becomes cloudy. When the molded product becomes cloudy, when the optical path length is long as in the light guide plate, there is a problem that the transmittance is greatly reduced due to light scattering and the luminance of the display is lowered.
Furthermore, the styrenic resin undergoes discoloration due to heat during long-term use, and there is a problem that the molded product turns yellow and the transmittance decreases. As a result, there is a problem that the luminance of the display is lowered or the chromaticity is changed.
Further, the inside of the backlight becomes high temperature depending on the use environment, and heat resistance is required to prevent the deformation of the light guide plate due to the temperature.
[Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
The present invention provides heat resistance, prevents whitening due to environmental changes, has little change in hue and transmittance even during long-term use, and is excellent in colorless transparency, particularly suitable for optical applications such as a light guide plate It is an object to provide a styrene-based resin composition.
[Means for solving problems]
[0005]
In the present invention, the weight average molecular weight obtained by copolymerizing (1) (a) a styrene monomer and (meth) acrylic acid is 150,000 to 700,000, and the content of (meth) acrylic acid units is Styrenic resin in an amount of 0.3 to 2.0% by mass and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10- A styrenic resin composition comprising tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (c) a polyoxyethylene type nonionic surfactant, comprising a styrenic resin Content of (b) in 100 mass% of composition is 0.05 to 0.40 mass%, and content of (c) is 0.1 to 1.0 mass%. Composition.
(2) (a) The weight average molecular weight obtained by copolymerizing a styrene monomer and (meth) acrylic acid is 150,000 to 700,000, and the content of (meth) acrylic acid units is 0.3 to 2.0% by mass of a styrene resin and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert- Styrenic resin composition comprising butyldibenzo [d, f] [1,3,2] dioxaphosphine, (c) polyoxyethylene type nonionic surfactant, and (d) hindered phenol antioxidant And the content of (b) in 100% by mass of the styrene-based resin composition is 0.05 to 0.40% by mass, the content of (c) is 0.1 to 1.0% by mass, (d ) Content of 0.02 to 0.50 mass% Styrene-based resin composition.
(3) (c) 1 selected from the group of polyoxyethylene fatty acid esters represented by the following polyoxyethylene alkyl ether represented by the following general formula 1 and / or polyoxyethylene fatty acid ester represented by the following general formula 2: The styrenic resin composition as described in (1) or (2), wherein the styrene resin composition is one or more types and the average added mole number of ethylene oxide is 7 to 100.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms, and n is an integer representing the number of added moles of ethylene oxide units)
(4) A plate-shaped molded article obtained by molding the styrene resin composition according to any one of (1) to (3).
(5) A light guide plate comprising the plate-like molded product according to (4).
[Effect of the invention]
[0006]
The styrenic resin composition of the present invention is less expensive and less water-absorbing compared to PMMA and MS resin, does not cause the whitening phenomenon due to environmental changes, which is a disadvantage of PS resin, and in long-term use Since changes in hue and transmittance are small, heat resistance is provided, and colorless transparency is excellent, it can be suitably used for optical applications such as a light guide plate. Moreover, the coloring prevention effect with respect to high temperature heat history, such as a shaping | molding process, is also high.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin of the present invention can be obtained by polymerizing a styrene monomer and a (meth) acrylic acid monomer. The styrene monomer is an aromatic vinyl monomer, such as styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, or a mixture of two or more, preferably styrene. The (meth) acrylic acid monomer is acrylic acid, methacrylic acid or the like, and methacrylic acid is preferable.
[0008]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0009]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0010]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0011]
The styrene resin of the present invention has a weight average molecular weight of 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer The molecular weight of the present invention is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0012]
The styrene resin of the present invention contains a (meth) acrylic acid unit in 100% by mass of the styrene resin, the content is 0.3 to 2.0% by mass, and 0.8 to 1.6% by mass. % Is preferred. When the content of the (meth) acrylic acid unit is less than 0.3% by mass, the whitening suppression effect and the heat resistance cannot be balanced. Moreover, when it exceeds 2.0 mass%, an initial hue and the transmittance | permeability will deteriorate.
[0013]
The (meth) acrylic acid unit content in the styrene resin was measured at room temperature. Weigh 0.5 g of styrene resin, dissolve in toluene / ethanol = 8/2 (volume ratio) mixed solution, then perform neutralization titration with potassium hydroxide 0.1 mol / L ethanol solution to detect the end point. From the usage amount of the potassium hydroxide ethanol solution, the mass-based content of (meth) acrylic acid units was calculated. An automatic potentiometric titration apparatus can be used, and measurement was performed with AT-510 manufactured by Kyoto Electronics Industry Co., Ltd. The content of the (meth) acrylic acid unit in the styrene resin can be adjusted by the composition of the raw styrene monomer and the (meth) acrylic monomer during the polymerization of the styrene resin. In the range to melt | dissolve, the styrene resin containing a (meth) acrylic acid unit and the styrene resin which does not contain a (meth) acrylic acid unit can also be blended and adjusted.
[0014]
The styrene resin composition of the present invention comprises (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4, in 100% by mass of the styrene resin composition. It contains 8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, and its content is 0.05 to 0.40% by mass. When the content of (b) is less than 0.05% by mass, the long-term thermal stability is inferior, and the initial hue and transmittance are also inferior. Moreover, even if it exceeds 0.40 mass%, long-term thermal stability will deteriorate.
[0015]
The styrene resin composition of the present invention preferably contains 0.02 to 0.50 mass% of (d) a hindered phenol antioxidant in 100 mass% of the styrene resin composition, and 0.05 to 0 More preferably, the content is 30% by mass. 6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Long-term thermal stability, initial hue, and transmittance are improved as compared with the case of using dioxaphosphepine alone.
[0016]
Examples of the hindered phenol antioxidant used in the present invention include octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, ethylenebis (oxyethylene) bis [3- (5 -Tert-butyl-4-hydroxy-m-tolyl) propionate], 4,6-bis (octylthiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -o-cresol, 2,4 -Dimethyl-6- (1-methylpentadecyl) phenol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, DL-α-tocopherol, 2-t- Butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1 (2-hydroxy-3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4′-thiobis (6-t-butyl-3-methylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-tert-butylphenol) Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate and / or ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate ] Is preferable.
[0017]
The styrene resin composition of the present invention contains (c) a polyoxyethylene type nonionic surfactant (also referred to as a polyethylene glycol type nonionic surfactant) in 100% by mass of the styrene resin composition, Content is 0.1-1.0 mass%, and it is preferable that it is 0.3-0.6 mass%. If the content of the polyoxyethylene type nonionic surfactant is less than 0.1% by mass, it is difficult to prevent the whitening phenomenon due to environmental changes. If the content exceeds 1.0% by mass, the heat resistance of the styrene-based resin composition is reduced. descend.
[0018]
Polyoxyethylene type nonionic surfactants include polyoxyethylene alkyl ether represented by the following general formula (1), polyoxyethylene fatty acid ester represented by the following general formula (2), polyoxyethylene hydrogenated castor oil, polyoxy Ethylene sorbitan fatty acid ester and polyoxyethylene sorbitol fatty acid ester are exemplified, but one or more selected from the group of polyoxyethylene alkyl ether and / or polyoxyethylene fatty acid ester are preferable.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms, and n is an integer representing the number of added moles of ethylene oxide units)
[0019]
Polyoxyethylene alkyl ether is made by adding ethylene oxide to alcohol, and polyoxyethylene fatty acid ester is made by adding ethylene oxide to fatty acid or directly esterifying fatty acid and polyethylene glycol. The number is preferably 7 to 100, and more preferably 10 to 50.
[0020]
Examples of the polyoxyethylene alkyl ether include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene octyl decyl ether, polyoxyethylene myristyl ether, polyoxyethylene-2-ethylhexyl ether and the like. Is mentioned.
[0021]
Examples of the polyoxyethylene fatty acid ester include polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, and the like.
[0022]
6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3 of the present invention , 2] Dioxaphosphepine, hindered phenolic antioxidant and polyethylene glycol can be added by adding and mixing in the polymerization process, devolatilization process, granulation process of styrene resin, and extrusion during molding process. There is a method of adding and mixing with a machine or the like, and there is no particular limitation.
[0023]
The Vicat softening temperature of the styrene resin composition of the present invention is preferably 101 ° C. or higher, and more preferably 102 ° C. When the Vicat softening temperature is less than 101 ° C., the heat resistance is insufficient, and the molded product may be deformed depending on the use environment.
[0024]
The styrenic resin composition of the present invention may contain mineral oil as long as the colorless transparency of the present invention is not impaired. Additives such as internal lubricants such as stearic acid and ethylene bis stearamide, phosphorus antioxidants, sulfur antioxidants, lactone antioxidants, hindered amine stabilizers, UV absorbers, antistatic agents, etc. May be included. As the external lubricant, ethylene bis stearamide is preferable, and the content is preferably 30 to 200 ppm in the resin composition.
[0025]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0026]
The styrenic resin composition of the present invention can be molded into a plate-shaped product by a molding method according to the purpose such as injection molding, extrusion molding, compression molding, etc., and used as a light guide plate. At that time, a reflection pattern such as a dot pattern can be provided on the back surface (opposite side of the light emitting surface) of the plate-shaped molded product, and used as a light guide plate. When processing from the resin plate to the light guide plate, it is preferable to polish the light incident surface or the entire end surface of the resin plate to make a mirror surface. In addition, in order to improve the uniformity of the emitted light, a prism pattern can be provided on the surface (surface from which light is emitted) of the plate-shaped molded product. The pattern on the front surface or the back surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0027]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0028]
(Examples 1-16, Comparative Examples 1-12)
A polymerization process is configured by connecting a first reactor, which is a complete mixing tank, a second reactor, and a third reactor, which is a plug flow reactor with a static mixer, in series. Table 12-1 A styrene resin was produced under the conditions shown. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A raw material solution was prepared with the raw material composition described in Table 12-1, and the raw material solution was continuously supplied to the first reactor at a flow rate described in Table 12-1. The polymerization initiator was added to the raw material solution at the inlet of the first reactor so as to have the addition concentration shown in Table 12-1 (concentration based on the mass with respect to the total amount of raw styrene and methacrylic acid), and mixed uniformly. The polymerization initiator described in Table 12-1 was polymerization initiator-1: 2,2-di (4,4-t-butylperoxycyclohexyl) propane (Pertetra A manufactured by NOF Corporation) as follows. )
In the third reactor, a temperature gradient was provided along the flow direction, and the temperature was adjusted so that the temperature shown in Table 12-1 was obtained at the intermediate portion and the outlet portion.
Moreover, the polyoxyethylene type nonionic surfactant was added to the inlet of the 3rd reactor so that it might become a kind and content shown in Table 12-2. The types of polyoxyethylene type nonionic surfactants are as follows.
P-1: Polyoxyethylene ethylene lauryl ether Ethylene oxide average added mole number = 25 (Emalgen 123P manufactured by Kao Corporation)
P-2: Polyoxyethylene ethylene stearyl ether ethylene oxide average added mole number = 12 (Emulgen 320P manufactured by Kao Corporation)
P-3: Polyoxyethylene ethylene lauryl ether Ethylene oxide average addition mole number = 9 (Emulgen 109P manufactured by Kao Corporation)
P-4: Polyoxyethylene ethylene cetyl ether Average number of moles of ethylene oxide added = 7 (Emulgen 210P manufactured by Kao Corporation)
P-5: Polyoxyethylene ethylene lauryl ether Ethylene oxide average added mole number = 47 (Emalgen 150 manufactured by Kao Corporation)
P-6: Polyoxyethylene ethylene myristyl ether Ethylene oxide average added mole number = 85 (Emalgen 4085 manufactured by Kao Corporation)
P-7: Polyethylene glycol monolaurate Ethylene oxide average added mole number = 12 (Emanon 1112 manufactured by Kao Corporation)
Subsequently, the solution containing the polymer continuously taken out from the third reactor is introduced into a vacuum devolatilization tank with a preheater constituted by two stages in series, so that the resin temperatures shown in Table 12-1 are obtained. By adjusting the temperature of the preheater and adjusting to the pressure described in Table 12-1, unreacted styrene and ethylbenzene are separated, and then extruded into a strand form from a perforated die. Cooled and cut and pelletized.
[0029]
Next, using a single screw extruder with a screw diameter of 40 mm, the pellets of the styrenic resin and the additives A and B obtained above were used so that the contents shown in Table 12-2 were used. Pellets were obtained by melt-kneading at a rotation speed of 100 rpm. Additives A and B used in Table 12-1 are shown below. In addition, additive A is (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3, 2] dioxaphosphepine, additive B represents (d) a hindered phenol antioxidant.
A-1: 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3,2] Dioxaphosphepin (Sumitomo GP, manufactured by Sumitomo Chemical Co., Ltd.)
B-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
B-2: Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
Melt mass flow rate (MFR) is measured in accordance with JIS K-7210 under the conditions of 200 ° C. and 49 N load, Vicat softening temperature is measured in accordance with JIS K 7206 at a heating rate of 50 ° C./hr and a test load of 50 N. did.
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. In order to evaluate long-term thermal stability, the obtained plate-shaped molded article was stored in an 80 ° C. oven for 500 hours. In order to evaluate the optical properties before and after storage, a 115 × 85 × 3 mm thickness test piece was cut out from the plate-shaped molded product, the end surface was polished by buffing, and a plate-shaped molded product having a mirror surface on the end surface was created. Using an ultraviolet-visible spectrophotometer V-670 manufactured by Co., Ltd., measuring the spectral transmittance at a wavelength of 350 nm to 800 nm at an optical path length of 115 mm in incident light having a size of 20 × 1.6 mm and a spread angle of 0 °, The YI value at a visual field of 2 ° for the C light source was calculated according to JIS K7105. The transmittance shown in Table 12-2 represents the average transmittance at a wavelength of 380 nm to 780 nm.
Furthermore, in order to confirm the whitening phenomenon due to environmental changes, a plate-like molded article having a mirror surface on the end face is exposed to an environment of 60 ° C. and 90% relative humidity for 150 hours, and the test piece is placed in an environment of 23 ° C. and 50% relative humidity. Taking out and observing the whitening phenomenon occurring inside the molded product, the following judgment was made as a whitening suppression effect.
◎: No whitening occurs. ○: Whitening occurs slightly after 1 hour after removal, but disappears after 24 hours. Table 12-1 shows the characteristics of each resin composition.
[0030]
[Table 12-1]

[0031]
[Table 12-2]

[0032]
The molded articles of the examples are excellent in heat resistance, excellent in whitening suppression effect, excellent in initial transmittance and YI value, and excellent in long-term thermal stability.
[Industrial applicability]
[0033]
The styrenic resin composition of the present invention has excellent heat resistance, prevents whitening due to environmental changes, and has excellent long-term thermal stability, so it has excellent transparency and hue, such as televisions, desktop personal computers, notebooks. It can be suitably used for light guide plate applications such as portable personal computers, mobile phones, and car navigation systems.

[００３０]
[表１３−２]

[００３１]
実施例の成形品は、白化抑制効果に優れ、初期の透過率とＹＩ値に優れており、８０℃×１０００時間での保管におけるＹＩ変化量が小さく、長期の熱安定性にも優れている。
[産業上の利用可能性]
[００３２]
本発明の光学用スチレン系樹脂組成物は、色相および透明性に優れ、長期の熱安定性に優れることから、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 13)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
(A) The weight average molecular weight obtained by copolymerizing a styrene monomer and a (meth) acrylic acid ester monomer is 160,000 to 700,000, and the content of (meth) acrylic acid ester units is 4 Styrenic resin and ˜15% by mass and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyl A styrene resin composition comprising dibenzo [d, f] [1,3,2] dioxaphosphine, wherein the content of (b) in 100% by mass of the styrene resin composition is 0.02 to 0.02%. An optical styrene-based resin composition, which is 0.40% by mass.
[Claim 2]
(A) The weight average molecular weight obtained by copolymerizing a styrene monomer and a (meth) acrylic acid ester monomer is 160,000 to 700,000, and the content of (meth) acrylic acid ester units is 4 Styrenic resin and ˜15% by mass and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyl A styrene resin composition comprising dibenzo [d, f] [1,3,2] dioxaphosphine and (c) a phosphorus antioxidant, wherein (b) in 100% by mass of the styrene resin composition The optical styrene resin composition is characterized in that the content of is 0.02 to 0.40 mass% and the content of (c) is 0.02 to 0.50 mass%.
[Claim 3]
(A) The weight average molecular weight obtained by copolymerizing a styrene monomer and a (meth) acrylic acid ester monomer is 160,000 to 700,000, and the content of (meth) acrylic acid ester units is 4 Styrenic resin and ˜15% by mass and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyl A styrene resin composition comprising dibenzo [d, f] [1,3,2] dioxaphosphine and (d) a hindered phenol antioxidant, wherein 100% by mass of the styrene resin composition ( An optical styrene-based resin composition, wherein the content of b) is 0.02 to 0.40 mass%, and the content of (d) is 0.02 to 0.50 mass%.
[Claim 4]
(A) The weight average molecular weight obtained by copolymerizing a styrene monomer and a (meth) acrylic acid ester monomer is 160,000 to 700,000, and the content of (meth) acrylic acid ester units is 4 Styrenic resin and ˜15% by mass and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyl A styrene resin composition comprising dibenzo [d, f] [1,3,2] dioxaphosphine, (c) a phosphorus antioxidant, and (d) a hindered phenol antioxidant, The content of (b) in 100% by mass of the resin composition is 0.02 to 0.40% by mass, the content of (c) is 0.02 to 0.50% by mass, and the content of (d) is 0. 0.02 to 0.50% by mass Ren resin composition.
[Claim 5]
The molded article using the styrene resin composition for optics of any one of Claims 1-4.
[Claim 6]
A light guide plate using the molded product according to claim 5.
[Document Name] Statement
[Title of the Invention] Optical Styrenic Resin Composition, Molded Product, and Light Guide Plate
[Technical field]
[0001]
The present invention relates to an optical styrenic resin composition excellent in hue and transparency, a molded article, and a light guide plate.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The A backlight using a light guide plate is also used for illumination. An acrylic resin typified by PMMA (polymethyl methacrylate) is used for the light guide plate. However, since the water absorption is high, the molded product may be warped or dimensional changes may occur.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylate copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water absorption is high and the dimensional stability tends to be worse than that of a styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, discoloration due to heat may occur during long-term use, and the molded product may turn yellow to lower the transmittance. As a result, the luminance of the backlight may decrease and the chromaticity may change.
In addition, a styrene resin using a styrene monomer as a raw material has low water absorption, but the molded product may become cloudy due to environmental changes such as temperature and humidity (whitening phenomenon). Specifically, when a molded product is exposed to an environmental change from a high temperature and high humidity environment to a room temperature environment or an environmental change from a room temperature environment to a low temperature environment, moisture present uniformly in the molded product is not present. It becomes stable and phase-separates, and a disk-like defect is generated. As a result, the inside of the molded product becomes cloudy. When the molded product becomes cloudy, when the optical path length is long like a light guide plate, the transmittance is greatly reduced due to light scattering, and the luminance of the display is lowered. [Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
An object of the present invention is to provide a styrenic resin composition for optical use, a molded article, and a light guide plate that prevent whitening due to environmental changes, is excellent in long-term thermal stability, and is excellent in colorless transparency.
[Means for solving problems]
[0005]
(1) (a) The weight average molecular weight obtained by copolymerizing a styrene monomer and a (meth) acrylate monomer is 160,000 to 700,000, and contains a (meth) acrylate unit Styrenic resin having an amount of 4 to 15% by mass and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra- A styrene-based resin composition comprising tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, wherein the content of (b) in 100% by mass of the styrene-based resin composition is 0. An optical styrenic resin composition, characterized in that the content is 0.02 to 0.40% by mass.
(2) (a) The weight average molecular weight obtained by copolymerizing a styrene monomer and a (meth) acrylate monomer is 160,000 to 700,000, and contains a (meth) acrylate unit Styrenic resin having an amount of 4 to 15% by mass and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra- A styrene-based resin composition comprising tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (c) a phosphorus-based antioxidant, wherein 100% by mass of the styrene-based resin composition A content of (b) is 0.02 to 0.40% by mass, and a content of (c) is 0.02 to 0.50% by mass.
(3) (a) The weight average molecular weight obtained by copolymerizing a styrene monomer and a (meth) acrylate monomer is 160,000 to 700,000, and contains a (meth) acrylate unit Styrenic resin having an amount of 4 to 15% by mass and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra- A styrenic resin composition comprising tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (d) a hindered phenolic antioxidant, the styrenic resin composition being 100% by mass An optical styrene resin composition, wherein the content of (b) is 0.02 to 0.40% by mass, and the content of (d) is 0.02 to 0.50% by mass.
(4) (a) The weight average molecular weight obtained by copolymerizing a styrene monomer and a (meth) acrylate monomer is 160,000 to 700,000, and contains a (meth) acrylate unit. Styrenic resin having an amount of 4 to 15% by mass and (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra- A styrene-based resin composition comprising tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, (c) a phosphorus-based antioxidant, and (d) a hindered phenol-based antioxidant. The content of (b) in 100% by mass of the styrene-based resin composition is 0.02 to 0.40% by mass, the content of (c) is 0.02 to 0.50% by mass, and the content of (d) Light characterized in that the amount is 0.02 to 0.50 mass% Use styrenic resin composition.
(5) A molded article using the optical styrenic resin composition according to any one of (1) to (4).
(6) A light guide plate using the molded product according to (5).
[Effect of the invention]
[0006]
The optical styrenic resin composition and molded product of the present invention have low water absorption, excellent dimensional stability and are inexpensive compared to PMMA and MS resin. Moreover, since the whitening phenomenon by the environmental change which is a fault of PS resin does not generate | occur | produce, it is excellent in long-term thermal stability and colorless transparency, Therefore It can use suitably for optical uses, such as a light-guide plate. Moreover, the coloring prevention effect with respect to high temperature heat history, such as a shaping | molding process, is also high.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin of the present invention is a polymer having a unit structure derived from a styrene monomer and a (meth) acrylate monomer. The styrene resin can be obtained by copolymerizing a styrene monomer and a (meth) acrylic acid ester monomer. Examples of the styrene monomer include styrene, α-methyl styrene, p-methyl styrene, o-methyl styrene, m-methyl styrene, ethyl styrene, pt-butyl styrene, and preferably styrene. Styrenic monomers may be used alone or in combination of two or more. The (meth) acrylic acid ester monomer is a methacrylic acid ester such as methyl methacrylate or ethyl methacrylate, or an acrylic acid ester such as methyl acrylate or ethyl acrylate. Methyl methacrylate and methyl acrylate are preferable because they have a whitening suppression effect in a small amount. The (meth) acrylic acid ester monomer may be used alone or in combination of two or more. As the styrenic resin, those having a small amount of other unit structures can also be used. The other unit structure is preferably 5% or less. Other unit structures include unit structures derived from vinyl monomers copolymerizable with styrene monomers. Examples of copolymerizable vinyl monomers include acrylic acid monomers such as acrylic acid and methacrylic acid, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, and α, β-ethylenically unsaturated monomers such as maleic anhydride and fumaric acid. Examples thereof include imide monomers such as carboxylic acids, N-phenylmaleimide, and N-cyclohexylmaleimide.
[0008]
The content of the (meth) acrylic acid ester unit in 100% by mass of the styrenic resin is 4 to 15% by mass, preferably 6 to 12% by mass, and more preferably 7 to 9% by mass. When the content of the (meth) acrylic acid ester unit is less than 4% by mass, the whitening suppression effect is insufficient. Moreover, when it exceeds 15 mass%, water absorption will deteriorate. Further, when the content of the (meth) acrylic acid ester unit is increased, the fluidity tends to be lowered, and the moldability is lowered in an application requiring high fluidity such as injection molding.
[0009]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0010]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0011]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0012]
The styrene resin has a weight average molecular weight of 160,000 to 700,000, preferably 160,000 to 400,000. If it is less than 160,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: differential refractometer The molecular weight is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0013]
The styrene-based resin preferably has a water absorption of less than 2000 ppm at a temperature of 40 ° C. and 80% humidity, more preferably less than 1600 ppm.
[0014]
The styrene-based resin composition is (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10 in 100% by mass of the styrene-based resin composition. -Tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine is contained, the content thereof is 0.02 to 0.40% by mass, 0.05 to 0. 0. It is preferably 20% by mass. When the content of (b) is less than 0.02% by mass, the long-term thermal stability is inferior, and the initial hue and transmittance are also inferior. Moreover, even if it exceeds 0.40 mass%, long-term thermal stability will deteriorate. Long-term thermal stability represents changes in hue and transmittance due to heat in long-term use, and those having excellent thermal stability have small changes in hue and transmittance. Long-term thermal stability can be evaluated as an accelerated test by storing a molded product under a high temperature condition (60 to 90 ° C.) such that the resin does not deform, and changing the hue and transmittance over time.
[0015]
The styrenic resin composition preferably contains 0.02 to 0.50% by mass of (c) phosphorus antioxidant in 100% by mass of the styrene resin composition, and 0.05 to 0.30% by mass. More preferably. 6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Long-term thermal stability is improved as compared with the case of using dioxaphosphepine alone.
[0016]
The styrene resin composition used in the present invention preferably contains 0.02 to 0.50 mass% of (d) a hindered phenolic antioxidant in 100 mass% of the styrene resin composition. It is more preferable to contain -0.25 mass%. 6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Compared to the case where dioxaphosphepine is used alone, the initial hue and transmittance are improved, and the long-term thermal stability tends to be improved.
[0017]
6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Dioxaphosphepine is a processing stabilizer having a hindered phenol antioxidant skeleton and a phosphorus antioxidant skeleton in the same molecule.
[0018]
Phosphorous antioxidants are phosphites that are trivalent phosphorus compounds. Phosphorus antioxidants include, for example, tris (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2- Ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 4,4′-biphenylenediphosphinic acid tetrakis (2,4-di-tert-butylphenyl), 3,9-bis (2 , 6-Di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane, cyclic neopentanetetraylbis (2,4-di -T-butylphenyl phosphite), distearyl pentaerythritol diphosphite, bis (nonylphenyl) pe Taerythritol diphosphite, bis- [2-methyl-4,6-bis- (1,1-dimethylethyl) phenyl] ethyl phosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10 -Oxide, tetrakis (2,4-di-tert-butyl-5-methylphenyl) -4,4'-biphenylenediphosphonite and the like. As the phosphorus-based antioxidant, those excellent in hydrolysis resistance are preferred, such as tris (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert-). Butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 3,9-bis (2,6-di-tert-butyl-4-methyl) Phenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane is preferred. Particularly preferred is tris (2,4-di-tert-butylphenyl) phosphite. Phosphorous antioxidants may be used alone or in combination of two or more.
[0019]
The hindered phenol antioxidant is an antioxidant having a phenolic hydroxyl group in the basic skeleton. Examples of hindered phenol antioxidants include octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3-tert-butyl). -4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate], 4,6-bis (octylthiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -o-cresol, 2, , 4-Dimethyl-6- (1-methylpentadecyl) phenol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) Propionate] methane, DL-α-tocopherol, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy -3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4'-thiobis (6-t-butyl-3-methylphenol), 1,1, 3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-t-butylphenol), bis- [3,3-bis- (4 And '-hydroxy-3'-tert-butylphenyl) -butanoic acid] -glycol ester. Preferably, octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methyl) Phenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4 -Hydroxy-m-tolyl) propionate]. Hindered phenolic antioxidants may be used alone or in combination of two or more.
[0020]
6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] Dioxaphosfepine, phosphorus antioxidants and hindered phenol antioxidants can be added by adding and mixing in the styrene resin polymerization process, devolatilization process, granulation process or extrusion during molding. A method of adding and mixing with a machine, an injection molding machine or the like can be mentioned, and it is not particularly limited.
[0021]
The styrenic resin composition may contain mineral oil as long as the colorless transparency of the present invention is not impaired. Also includes additives such as internal lubricants such as stearic acid and ethylenebisstearylamide, sulfur antioxidants, lactone antioxidants, UV absorbers, hindered amine stabilizers, antistatic agents, external lubricants, etc. It may be. As the external lubricant, ethylene bisstearylamide is suitable, and the content is preferably 30 to 200 ppm in the resin composition.
[0022]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0023]
The styrenic resin composition of the present invention can be molded by a molding method according to the purpose, such as injection molding, extrusion molding, or compression molding. The obtained molded product is used as an optical member that functions by transmitting light into the molded product such as a light guide plate. An optical member such as a light guide plate is preferably a material having a high transmittance and an excellent hue because of a long light transmission distance (optical path length). It is preferable that the initial transmittance at an optical path length of 115 mm is 85% or more and the YI value is 6.5 or less. Further, the YI difference after storage for 1000 hours at 80 ° C. is preferably 3.0 or less, and more preferably 1.5 or less.
The transmittance and YI value for an optical path length of 115 mm were measured by the following procedure. Using pellets of the styrene-based resin composition, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. Here, the sample to be evaluated for long-term thermal stability was stored in an oven at 80 ° C. for 1000 hours. Next, a test piece having a thickness of 115 × 85 × 3 mm was cut out from the plate-shaped molded product, and the end surface was polished by buffing to produce a plate-shaped molded product having a mirror surface on the end surface. About the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a divergence angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance is an average transmittance at a wavelength of 380 nm to 780 nm.
[0024]
The light guide plate receives light from the end surface (side surface) of the plate-shaped molded product, and guides light to the front surface (light emitting surface) of the molded product by a reflection pattern formed on the rear surface (non-light emitting surface) of the molded product. It is a member that has the function of emitting surface light. The reflective pattern can be formed by a method such as a screen printing method, an injection molding method, a laser method, or an ink jet method. When processing the plate-shaped molded product into the light guide plate, it is preferable to polish the light incident surface or the entire end surface to a mirror surface. Moreover, in order to improve the uniformity of the emitted light, a prism pattern or the like can be provided on the front surface (light emitting surface) of the plate-shaped molded product. The pattern on the front surface or the rear surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0025]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0026]
(Production Example of Styrenic Resin A-1 to 7)
A polymerization process is configured by connecting a first reactor, which is a complete mixing tank, a second reactor, and a third reactor, which is a plug flow reactor with a static mixer, in series. Table 13-1 A styrene resin was produced under the conditions shown. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A raw material solution was prepared with the raw material composition described in Table 13-1, and the raw material solution was continuously supplied to the first reactor at a flow rate described in Table 13-1. The polymerization initiator was added to the raw material solution at the inlet of the first reactor so as to have the addition concentration shown in Table 13-1 (concentration based on mass with respect to the total amount of raw material styrene and methyl methacrylate) and mixed uniformly. . The polymerization initiators described in Table 13-1 were as follows: Polymerization initiator-1: 1,1-di (t-butylperoxy) cyclohexane (Perhexa C manufactured by NOF Corporation was used.)
In the third reactor, a temperature gradient was provided along the flow direction, and the temperature was adjusted so that the temperature shown in Table 13-1 was obtained at the intermediate part and the outlet part.
Subsequently, the solution containing the polymer continuously taken out from the third reactor is introduced into a vacuum devolatilization tank with a preheater constituted by two stages in series, so that the resin temperatures shown in Table 13-1 are obtained. After adjusting the temperature of the preheater and adjusting to the pressure shown in Table 13-1, unreacted styrene and ethylbenzene are separated, and then extruded into a strand shape from a perforated die. Cooled and cut and pelletized.
[0027]
The content of methyl methacrylate units (PMMA amount) in the styrene resin was measured by pyrolysis gas chromatography under the following conditions.
Pyrolysis furnace: PYR-2A (manufactured by Shimadzu Corporation)
Pyrolysis furnace temperature setting: 525 ° C
Gas chromatograph: GC-14A (manufactured by Shimadzu Corporation)
Column: Glass 3mm diameter x 3m
Filler: FFAP Chromsorb WAW 10%
Injection, detector temperature: 250 ° C
Column temperature: 120 ° C
Carrier gas: Nitrogen Melt mass flow rate (MFR) conforms to JIS K 7210, temperature 200 ° C, 49N load, Vicat softening temperature conforms to JIS K 7206, heating rate 50 ° C / hr, test Measurement was performed at a load of 50N.
The amount of water absorption was measured using the above-mentioned plate-shaped molded product, and after measuring the mass W1 after drying for 24 hours at a temperature of 80 ° C., the plate-shaped molded product was stored in an environment of 80% relative humidity at a temperature of 40 ° C. for a certain period of time. The weight immediately after taking out was measured every time, and it calculated | required as water absorption = (W2-W1) / W2 * 1000000 (ppm) from mass W2 when the weight change was lost (saturated state). Table 13-1 shows the characteristics of each styrene resin, including MS resin (Denka TX Polymer TX800LF, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a reference.
[0028]
(Examples 1-27, Comparative Examples 1-12)
Next, with the contents shown in Table 13-2, styrene resin A and MS resin (Denka TX Polymer TX800LF, manufactured by Denki Kagaku Kogyo Co., Ltd.) and B, C, and D as additives as single screw extrusion with a screw diameter of 40 mm Using a machine, the mixture was melt kneaded at a cylinder temperature of 230 ° C. and a screw rotation speed of 100 rpm to obtain pellets. Additives B, C and D used in Table 13-1 are shown below. The additive B was (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine, additive C represents (c) phosphorus antioxidant, and additive D represents (d) hindered phenol antioxidant.
B-1: 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3,2] Dioxaphosphepine (Sumitomo Chemical Co., Ltd. Sumilizer GP)
C-1: Tris (2,4-di-tert-butylphenyl) phosphite (Irgafos 168 manufactured by BASF Japan Ltd.)
C-2: 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus (Adeka Corporation HP ADEKA STAB HP-10)
C-3: Bis (2,4-dicumylphenyl) pentaerythritol diphosphite (Doverphos S-9228 manufactured by Dober Chemical Corporation)
C-4: 3,9-bis (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane ADEKA ADK STAB PEP-36)
D-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
D-2: 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10 -Tetraoxaspiro [5.5] undecane (Adeka Corporation Adeka Stub AO-80)
D-3: Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. In order to evaluate long-term thermal stability, the obtained molded product was stored in an oven at 80 ° C. for 1000 hours. In order to evaluate the optical properties of the initial molded product before storage and the molded product after storage, a 115 × 85 × 3 mm thickness test piece was cut out from the plate-shaped molded product, the end surface was polished by buffing, and a mirror surface was formed on the end surface. A plate-shaped molded article having the same was prepared. About the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a divergence angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance shown in Table 13-2 represents an average transmittance at a wavelength of 380 nm to 780 nm.
Furthermore, in order to confirm the whitening phenomenon due to environmental changes, a plate-like molded article having a mirror surface on the end face is exposed to an environment of 60 ° C. and 90% relative humidity for 150 hours, and the test piece is placed in an environment of 23 ° C. and 50% relative humidity. Taking out and observing the whitening phenomenon occurring inside the molded product, the following judgment was made as a whitening suppression effect.
A: No whitening occurs. O: Whitening occurs slightly after 1 hour, but disappears after 24 hours. Δ: Whitening occurs after 1 hour, but almost disappears after 24 hours. X: Remarkably whitening after 1 hour. Table 13-2 shows the properties of each resin composition.
[0029]
[Table 13-1]

[0030]
[Table 13-2]

[0031]
The molded articles of the examples are excellent in whitening suppression effect, excellent in initial transmittance and YI value, small in change in YI during storage at 80 ° C. × 1000 hours, and excellent in long-term thermal stability. .
[Industrial applicability]
[0032]
The optical styrenic resin composition of the present invention is excellent in hue and transparency and excellent in long-term thermal stability, so that it is a light guide plate for televisions, desktop personal computers, notebook personal computers, mobile phones, car navigation systems, etc. It can be suitably used in applications.

[００２７]
[表１４−２]

[００２８]
実施例の成形品は、白化抑制効果に優れ、初期の透過率とＹＩ値に優れており、８０℃×１０００時間での保管におけるＹＩ変化量が小さく、長期の熱安定性にも優れている。
[産業上の利用可能性]
[００２９]
本発明の光学用スチレン系樹脂組成物は、色相および透明性に優れ、長期の熱安定性に優れることから、テレビ、デスクトップ型パーソナルコンピューター、ノート型パーソナルコンピューター、携帯電話機、カーナビゲーションなどの導光板用途で好適に用いることができる。 (Appendix 14)
Hereinafter, another embodiment of the present invention will be additionally described. The following contents are interpreted independently of the contents described so far.
[Document Name] Claims
[Claim 1]
(A) The weight average molecular weight obtained by copolymerizing a styrene monomer and a (meth) acrylic acid ester monomer is 160,000 to 700,000, and the content of (meth) acrylic acid ester units is 4 A styrene resin composition comprising styrene resin of ˜15 mass%, (b) a hindered phenol antioxidant, and (c) a phosphorus antioxidant, in 100 mass% of the styrene resin composition A content of (b) is 0.02 to 0.30% by mass, and a content of (c) is 0.03 to 0.40% by mass.
[Claim 2]
A molded article using the optical styrenic resin composition according to claim 1.
[Claim 3]
A light guide plate using the molded product according to claim 2.
[Document Name] Statement
[Title of the Invention] Optical Styrenic Resin Composition, Molded Product, and Light Guide Plate
[Technical field]
[0001]
The present invention relates to an optical styrenic resin composition excellent in hue and transparency, a molded article, and a light guide plate.
[Background]
[0002]
There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The A backlight using a light guide plate is also used for illumination. An acrylic resin typified by PMMA (polymethyl methacrylate) is used for the light guide plate. However, since the water absorption is high, the molded product may be warped or dimensional changes may occur.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylate copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water absorption is high and the dimensional stability tends to be worse than that of a styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, discoloration due to heat may occur during long-term use, and the molded product may turn yellow to lower the transmittance. As a result, the luminance of the backlight may decrease and the chromaticity may change.
In addition, a styrene resin using a styrene monomer as a raw material has low water absorption, but the molded product may become cloudy due to environmental changes such as temperature and humidity (whitening phenomenon). Specifically, when a molded product is exposed to an environmental change from a high temperature and high humidity environment to a room temperature environment or an environmental change from a room temperature environment to a low temperature environment, moisture present uniformly in the molded product is not present. It becomes stable and phase-separates, and a disk-like defect is generated. As a result, the inside of the molded product becomes cloudy. When the molded product becomes cloudy, when the optical path length is long like a light guide plate, the transmittance is greatly reduced due to light scattering, and the luminance of the display is lowered. [Prior art documents]
[Patent Literature]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-075648
[Summary of Invention]
[Problems to be solved by the invention]
[0004]
An object of the present invention is to provide a styrenic resin composition for optical use, a molded article, and a light guide plate that prevent whitening due to environmental changes, is excellent in long-term thermal stability, and is excellent in colorless transparency.
[Means for solving problems]
[0005]
(1) (a) The weight average molecular weight obtained by copolymerizing a styrene monomer and a (meth) acrylate monomer is 160,000 to 700,000, and contains a (meth) acrylate unit A styrene-based resin composition comprising a styrene-based resin having an amount of 4 to 15% by mass, (b) a hindered phenol-based antioxidant, and (c) a phosphorus-based antioxidant, and having a styrene-based resin composition of 100 mass % Styrene-based resin composition, wherein the content of (b) is 0.02 to 0.30 mass% and the content of (c) is 0.03 to 0.40 mass% .
(2) A molded article using the optical styrenic resin composition according to (1).
(3) A light guide plate using the molded product according to (2).
[Effect of the invention]
[0006]
The optical styrenic resin composition and molded product of the present invention have low water absorption, excellent dimensional stability and are inexpensive compared to PMMA and MS resin. Moreover, since the whitening phenomenon by the environmental change which is a fault of PS resin does not generate | occur | produce, it is excellent in long-term thermal stability and colorless transparency, Therefore It can use suitably for optical uses, such as a light-guide plate. Moreover, the coloring prevention effect with respect to high temperature heat history, such as a shaping | molding process, is also high.
[Mode for Carrying Out the Invention]
[0007]
The styrene resin of the present invention is a polymer having a unit structure derived from a styrene monomer and a (meth) acrylate monomer. The styrene resin can be obtained by copolymerizing a styrene monomer and a (meth) acrylic acid ester monomer. Examples of the styrene monomer include styrene, α-methyl styrene, p-methyl styrene, o-methyl styrene, m-methyl styrene, ethyl styrene, pt-butyl styrene, and preferably styrene. Styrenic monomers may be used alone or in combination of two or more. The (meth) acrylic acid ester monomer is a methacrylic acid ester such as methyl methacrylate or ethyl methacrylate, or an acrylic acid ester such as methyl acrylate or ethyl acrylate. Methyl methacrylate and methyl acrylate are preferable because they have a whitening suppression effect in a small amount. The (meth) acrylic acid ester monomer may be used alone or in combination of two or more. As the styrenic resin, those having a small amount of other unit structures can also be used. The other unit structure is preferably 5% or less. Other unit structures include unit structures derived from vinyl monomers copolymerizable with styrene monomers. Examples of copolymerizable vinyl monomers include acrylic acid monomers such as acrylic acid and methacrylic acid, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, and α, β-ethylenically unsaturated monomers such as maleic anhydride and fumaric acid. Examples thereof include imide monomers such as carboxylic acids, N-phenylmaleimide, and N-cyclohexylmaleimide.
[0008]
The content of the (meth) acrylic acid ester unit in 100% by mass of the styrenic resin is 4 to 15% by mass, preferably 6 to 12% by mass, and more preferably 7 to 9% by mass. When the content of the (meth) acrylic acid ester unit is less than 4% by mass, the whitening suppression effect is insufficient. Moreover, when it exceeds 15 mass%, water absorption will deteriorate. Further, when the content of the (meth) acrylic acid ester unit is increased, the fluidity tends to be lowered, and the moldability is lowered in an application requiring high fluidity such as injection molding.
[0009]
Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.
[0010]
A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As the polymerization initiator, a radical polymerization initiator is preferable. For example, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, 2,2- Peroxyketals such as di (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-di (t-amylperoxy) cyclohexane, cumene hydroperoxide, t-butyl hydroperoxide, etc. Alkyl peroxides such as hydroperoxides, t-butylperoxyacetate, t-amylperoxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t -Dialkyl peroxides such as hexyl peroxide, t-butylperoxyacetate Peroxyesters such as t-butyl peroxybenzoate and t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis (t-butyl peroxycarbonate) N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis (2,4-dimethylvaleronitrile), N, N '-Azobis [2- (hydroxymethyl) propionitrile] and the like can be mentioned, and these can be used alone or in combination. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.
[0011]
In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.
[0012]
The styrene resin has a weight average molecular weight of 160,000 to 700,000, preferably 160,000 to 400,000. If it is less than 160,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: differential refractometer The molecular weight is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
[0013]
The styrene-based resin preferably has a water absorption of less than 2000 ppm at a temperature of 40 ° C. and 80% humidity, more preferably less than 1600 ppm.
[0014]
The styrene-based resin composition contains (b) a hindered phenol-based antioxidant and (c) a phosphorus-based antioxidant in 100% by mass of the styrene-based resin composition, and the content of (b) is 0.02 to 0.02%. The content of 0.30% by mass and (c) is 0.03 to 0.40% by mass. Preferably, the content of (b) is 0.02 to 0.20 mass%, and the content of (c) is 0.05 to 0.30 mass%. More preferably, the content of (b) is 0.05 to 0.15% by mass, and the content of (c) is 0.10 to 0.25% by mass. When the contents of (b) and (c) are outside the above ranges, the long-term thermal stability is poor. Long-term thermal stability represents changes in hue and transmittance due to heat in long-term use, and those having excellent thermal stability have small changes in hue and transmittance. Long-term thermal stability can be evaluated as an accelerated test by storing a molded product under a high temperature condition (60 to 90 ° C.) such that the resin does not deform, and changing the hue and transmittance over time.
[0015]
The hindered phenol antioxidant is an antioxidant having a phenolic hydroxyl group in the basic skeleton. Examples of hindered phenol antioxidants include octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3-tert-butyl). -4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate], 4,6-bis (octylthiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -o-cresol, 2, , 4-Dimethyl-6- (1-methylpentadecyl) phenol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) Propionate] methane, DL-α-tocopherol, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy -3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4'-thiobis (6-t-butyl-3-methylphenol), 1,1, 3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-t-butylphenol), bis- [3,3-bis- (4 And '-hydroxy-3'-tert-butylphenyl) -butanoic acid] -glycol ester. Preferably, octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methyl) Phenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4 -Hydroxy-m-tolyl) propionate]. Hindered phenolic antioxidants may be used alone or in combination of two or more.
[0016]
Phosphorous antioxidants are phosphites that are trivalent phosphorus compounds. Phosphorus antioxidants include, for example, tris (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2- Ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 4,4′-biphenylenediphosphinic acid tetrakis (2,4-di-tert-butylphenyl), 3,9-bis (2 , 6-Di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane, cyclic neopentanetetraylbis (2,4-di -T-butylphenyl phosphite), distearyl pentaerythritol diphosphite, bis (nonylphenyl) pe Taerythritol diphosphite, bis- [2-methyl-4,6-bis- (1,1-dimethylethyl) phenyl] ethyl phosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10 -Oxide, tetrakis (2,4-di-tert-butyl-5-methylphenyl) -4,4'-biphenylenediphosphonite and the like. As the phosphorus-based antioxidant, those excellent in hydrolysis resistance are preferred, such as tris (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert-). Butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 3,9-bis (2,6-di-tert-butyl-4-methyl) Phenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane is preferred. Particularly preferred is tris (2,4-di-tert-butylphenyl) phosphite. Phosphorous antioxidants may be used alone or in combination of two or more.
[0017]
Methods for adding hindered phenolic antioxidants and phosphorus antioxidants include addition and mixing in the polymerization process, devolatilization process, and granulation process of styrenic resins, extruders and injection molding machines during molding, etc. The method of adding and mixing is mentioned, but it is not particularly limited.
[0018]
The styrenic resin composition may contain mineral oil as long as the colorless transparency of the present invention is not impaired. Also includes additives such as internal lubricants such as stearic acid and ethylenebisstearylamide, sulfur antioxidants, lactone antioxidants, UV absorbers, hindered amine stabilizers, antistatic agents, external lubricants, etc. It may be. As the external lubricant, ethylene bisstearylamide is suitable, and the content is preferably 30 to 200 ppm in the resin composition.
[0019]
The ultraviolet absorber has a function of suppressing deterioration and coloring caused by ultraviolet rays. UV absorbers such as those of formaldehyde and formamidine. These can be used alone or in combination of two or more thereof, and a light stabilizer such as hindered amine may be used in combination.
[0020]
The styrenic resin composition of the present invention can be molded by a molding method according to the purpose, such as injection molding, extrusion molding, or compression molding. The obtained molded product is used as an optical member that functions by transmitting light into the molded product such as a light guide plate. An optical member such as a light guide plate is preferably a material having a high transmittance and an excellent hue because of a long light transmission distance (optical path length). The initial transmittance at an optical path length of 115 mm is preferably 84% or more and the YI value is 7.0 or less. The YI difference after storage at 80 ° C. for 1000 hours and the initial YI is preferably 2.0 or less, and more preferably 1.0 or less.
The transmittance and YI value for an optical path length of 115 mm were measured by the following procedure. Using pellets of the styrene-based resin composition, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. Here, the sample to be evaluated for long-term thermal stability was stored in an oven at 80 ° C. for 1000 hours. Next, a test piece having a thickness of 115 × 85 × 3 mm was cut out from the plate-shaped molded product, and the end surface was polished by buffing to produce a plate-shaped molded product having a mirror surface on the end surface. About the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a divergence angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance is an average transmittance at a wavelength of 380 nm to 780 nm.
[0021]
The light guide plate receives light from the end surface (side surface) of the plate-shaped molded product, and guides light to the front surface (light emitting surface) of the molded product by a reflection pattern formed on the rear surface (non-light emitting surface) of the molded product. It is a member that has the function of emitting surface light. The reflective pattern can be formed by a method such as a screen printing method, an injection molding method, a laser method, or an ink jet method. When processing the plate-shaped molded product into the light guide plate, it is preferable to polish the light incident surface or the entire end surface to a mirror surface. Moreover, in order to improve the uniformity of the emitted light, a prism pattern or the like can be provided on the front surface (light emitting surface) of the plate-shaped molded product. The pattern on the front surface or the rear surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.
[Example]
[0022]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0023]
(Production Example of Styrenic Resin A-1 to 7)
A polymerization process is configured by connecting a first reactor, which is a complete mixing tank, a second reactor, and a third reactor, which is a plug flow reactor with a static mixer, in series. Table 14-1 A styrene resin was produced under the conditions shown. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A raw material solution was prepared with the raw material composition described in Table 14-1, and the raw material solution was continuously supplied to the first reactor at a flow rate described in Table 14-1. The polymerization initiator was added to the raw material solution at the inlet of the first reactor so as to have the addition concentration shown in Table 14-1 (concentration based on mass relative to the total amount of raw material styrene and methyl methacrylate), and mixed uniformly. . The polymerization initiators described in Table 14-1 were as follows: Polymerization initiator-1: 1,1-di (t-butylperoxy) cyclohexane (Perhexa C manufactured by NOF Corporation was used.)
In the third reactor, a temperature gradient was provided along the flow direction, and the temperature was adjusted so that the temperature shown in Table 14-1 was obtained at the intermediate part and the outlet part.
Subsequently, the solution containing the polymer continuously taken out from the third reactor is introduced into a vacuum devolatilization tank with a preheater constituted by two stages in series, so that the resin temperatures shown in Table 14-1 are obtained. By adjusting the temperature of the preheater and adjusting to the pressure shown in Table 14-1, unreacted styrene and ethylbenzene are separated, and then extruded into a strand shape from a perforated die. Cooled and cut and pelletized.
[0024]
The content of methyl methacrylate units (PMMA amount) in the styrene resin was measured by pyrolysis gas chromatography under the following conditions.
Pyrolysis furnace: PYR-2A (manufactured by Shimadzu Corporation)
Pyrolysis furnace temperature setting: 525 ° C
Gas chromatograph: GC-14A (manufactured by Shimadzu Corporation)
Column: Glass 3mm diameter x 3m
Filler: FFAP Chromsorb WAW 10%
Injection, detector temperature: 250 ° C
Column temperature: 120 ° C
Carrier gas: Nitrogen Melt mass flow rate (MFR) conforms to JIS K 7210, temperature 200 ° C, 49N load, Vicat softening temperature conforms to JIS K 7206, heating rate 50 ° C / hr, test Measurement was performed at a load of 50N.
The amount of water absorption was measured using the above-mentioned plate-shaped molded product, and after measuring the mass W1 after drying for 24 hours at a temperature of 80 ° C., the plate-shaped molded product was stored in an environment of 80% relative humidity at a temperature of 40 ° C. for a certain period of time. The weight immediately after taking out was measured every time, and the water absorption amount = (W2−W1) / W2 × 1000000 (ppm) was obtained from the mass W2 when the weight change disappeared (saturated state). Table 14-1 shows the characteristics of each styrenic resin, including MS resin (Denka TX Polymer TX800LF, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a reference.
[0025]
(Examples 1-15, Comparative Examples 1-13)
Next, with the contents shown in Table 14-2, styrene resin A and MS resin (Denka TX Polymer TX800LF, manufactured by Denki Kagaku Kogyo Co., Ltd.) and B, C, and D as additives as single screw extrusion with a screw diameter of 40 mm Using a machine, the mixture was melt kneaded at a cylinder temperature of 230 ° C. and a screw rotation speed of 100 rpm to obtain pellets. Additives B and C used in Table 14-1 are shown below. Additive B represents (b) a hindered phenol-based antioxidant, and additive C represents (c) a phosphorus-based antioxidant.
B-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
B-2: 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10 -Tetraoxaspiro [5.5] undecane (Adeka Corporation Adeka Stub AO-80)
B-3: Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
C-1: Tris (2,4-di-tert-butylphenyl) phosphite (Irgafos 168 manufactured by BASF Japan Ltd.)
C-2: 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus (Adeka Corporation HP ADEKA STAB HP-10)
C-3: Bis (2,4-dicumylphenyl) pentaerythritol diphosphite (Doverphos S-9228 manufactured by Dober Chemical Corporation)
C-4: 3,9-bis (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane ADEKA ADK STAB PEP-36)
Further, by using the obtained pellets, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C. to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. In order to evaluate long-term thermal stability, the obtained molded product was stored in an oven at 80 ° C. for 1000 hours. In order to evaluate the optical properties of the initial molded product before storage and the molded product after storage, a 115 × 85 × 3 mm thickness test piece was cut out from the plate-shaped molded product, the end surface was polished by buffing, and a mirror surface was formed on the end surface. A plate-shaped molded article having the same was prepared. About the plate-shaped molded product after polishing, using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, the incident light having a size of 20 × 1.6 mm and a divergence angle of 0 ° has a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance shown in Table 14-2 represents the average transmittance at a wavelength of 380 nm to 780 nm.
Furthermore, in order to confirm the whitening phenomenon due to environmental changes, a plate-like molded article having a mirror surface on the end face is exposed to an environment of 60 ° C. and 90% relative humidity for 150 hours, and the test piece is placed in an environment of 23 ° C. and 50% relative humidity. Taking out and observing the whitening phenomenon occurring inside the molded product, the following judgment was made as a whitening suppression effect.
◎: No whitening occurs. ○: Whitening occurs slightly after 1 hour after removal, but disappears after 24 hours. Table 14-2 shows the characteristics of each resin composition.
[0026]
[Table 14-1]

[0027]
[Table 14-2]

[0028]
The molded articles of the examples are excellent in whitening suppression effect, excellent in initial transmittance and YI value, small in change in YI during storage at 80 ° C. × 1000 hours, and excellent in long-term thermal stability. .
[Industrial applicability]
[0029]
The optical styrenic resin composition of the present invention is excellent in hue and transparency and excellent in long-term thermal stability, so that it is a light guide plate for televisions, desktop personal computers, notebook personal computers, mobile phones, car navigation systems, etc. It can be suitably used in applications.

Claims (4)

  A styrene-based resin composition comprising a styrene-based resin having a weight average molecular weight of 150,000 to 700,000 and a polyoxyethylene-type nonionic surfactant, wherein the polyoxyethylene-type non-polymer in 100% by mass of the styrene-based resin composition A styrene resin composition, wherein the content of the ionic surfactant is 0.4 to 2.0 mass%. One or more polyoxyethylene type nonionic surfactants selected from the group of polyoxyethylene alkyl ether represented by the following general formula (1) and / or polyoxyethylene fatty acid ester represented by the following general formula (2) The styrene resin composition according to claim 1, wherein the ethylene oxide has an average added mole number of 7 to 100.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms, and n is an integer representing the number of added moles of ethylene oxide units)   A plate-like molded article formed by molding the styrene-based resin composition according to claim 1 or 2.   A light guide plate comprising the plate-like molded product according to claim 3.