JP6000978B2 - Styrenic resin composition for optics, molded product and light guide plate - Google Patents

Description

  The present invention relates to a styrene resin composition, a molded article, and a light guide plate that are excellent in hue and transparency and excellent in long-term thermal stability.

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.
Patent Document 2 reports that an aromatic monovinyl resin composition containing a specific phosphite ester in an aromatic monovinyl resin is excellent in thermal decomposition resistance.
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.

Japanese Patent Laid-Open No. 2003-075648 Patent 3994495

  An object of the present invention is to provide a styrenic resin composition, a molded article, and a light guide plate that are excellent in hue and transparency, and have small changes in hue and transmittance even after long-term use.

  According to the present invention, 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 (hereinafter also referred to as “additive B”) and (c) phosphorus antioxidant And / or (d) a styrene resin composition comprising a hindered phenolic antioxidant, wherein the content of (b) in 100% by mass of the styrene resin composition is 0.02 to 0.40 mass. %, The content of (c) is 0.02 to 0.50% by mass, and the content of (d) is 0.02 to 0.50% by mass. Provided.

The present inventors have intensively studied to suppress discoloration that occurs during long-term use, and it is effective to suppress discoloration by first using additive B and a phosphorus-based and / or hindered phenol-based antioxidant in combination. It turns out that. However, further investigations have revealed that simply adding additive B and the above antioxidant may not work.
Then, when further examination was advanced, the content of (1) additive B is in a specific range, and (2) the content of phosphorus-based and / or hindered phenol-based antioxidant is in a specific range. It was found that the discoloration suppressing effect of the styrenic resin composition becomes extremely high when the amount is. Although the operational effect for obtaining such an effect is not necessarily clarified, it is considered to be due to a synergistic effect by these two conditions because it is effectively exhibited only when the above two conditions are met.

Hereinafter, various embodiments of the present invention will be exemplified. The various embodiments described below can be combined with each other.
Preferably, the styrene resin composition includes a phosphorus antioxidant which is at least one selected from (C-1) to (C-4). Preferably, the phosphorus antioxidant is at least one selected from (C-1) to (C-3).
(C-1) Tris (2,4-di-tert-butylphenyl) phosphite (C-2) 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2- Ethylhexyloxy) phosphorus (C-3) bis (2,4-dicumylphenyl) pentaerythritol diphosphite (C-4) 3,9-bis (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane Preferably, the styrenic resin composition is at least selected from (D-1) to (D-4) 1 type of hindered phenolic antioxidant is included. Preferably, the hindered phenol-based antioxidant is at least one selected from (D-1) and (D-4).
(D-1) Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (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 (D-3) ethylenebis (oxyethylene) bis [ 3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate]
(D-4) Pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate]
Preferably, the styrene resin is a styrene- (meth) acrylic acid copolymer resin obtained by copolymerizing a styrene monomer and (meth) acrylic acid, and the styrene resin is a styrene resin. The unit content is 90.0 to 99.9% by mass, and the (meth) acrylic acid unit content is 0.1 to 10.0% by mass. However, the total content of styrene monomer units and (meth) acrylic acid units in the styrene resin is 100% by mass.
Preferably, the styrenic resin is a styrene- (meth) acrylic acid ester copolymer resin obtained by copolymerizing a styrenic monomer and a (meth) acrylic acid ester, The content of the monomer unit is 40.0 to 99.0% by mass, and the content of the (meth) acrylic acid ester unit is 1.0 to 60.0% by mass. However, the total content of styrene monomer units and (meth) acrylic acid ester units in the styrene resin is 100% by mass.
Preferably, the hydrophilic additive having a polyether chain is contained in an amount of 0.4 to 2.0% by mass.
Preferably, it is a molded article made of the above-mentioned optical styrenic resin composition.
Preferably, it is a light-guide plate which consists of said molded article.

  The styrenic resin composition and molded article of the present invention have low water absorption and are inexpensive compared to PMMA and MS resin, have small changes in hue and transmittance during long-term use, and are excellent in colorless transparency. Therefore, 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.

  Hereinafter, embodiments of the present invention will be described in detail.

<< Styrenic resin >>
The styrene resin of the present invention can be obtained by polymerizing a styrene monomer. Styrene monomers are aromatic vinyl monomers such as styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, m-methyl styrene, ethyl styrene, pt-butyl styrene, etc. Or it is 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. .
The styrene resin composition is preferably composed of a styrene resin and various additives, and the ratio of the styrene resin in 100% by mass of the styrene resin composition is, for example, 90 to 99.96% by mass. And 95 to 99.96 mass% is preferable. Specifically, the ratio of the styrenic resin is, for example, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.96% by mass, and any of the numerical values exemplified here is 2 It may be within a range between the two.

  When the styrene resin is a styrene- (meth) acrylic acid copolymer resin obtained by copolymerizing a styrene monomer and (meth) acrylic acid, the content of the styrene monomer unit of the styrene resin It has been experimentally confirmed that the object of the present invention can be achieved even when the amount is 90.0 to 99.9% by mass and the content of the (meth) acrylic acid unit is 0.1 to 10.0% by mass. However, the total content of styrene monomer units and (meth) acrylic acid units is 100% by mass. (Meth) acrylic acid is acrylic acid, methacrylic acid or the like, with methacrylic acid being preferred.

  The measurement of the (meth) acrylic acid unit content in the styrene resin is carried out 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 amount of potassium hydroxide ethanol solution used, the mass-based content of (meth) acrylic acid units is calculated. In addition, a potentiometric automatic titration apparatus can be used and it can measure by AT-510 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.

  When the styrene resin is a styrene- (meth) acrylate copolymer resin obtained by copolymerizing a styrene monomer and a (meth) acrylate, a styrene monomer unit of the styrene resin It has been experimentally confirmed that the object of the present invention can be achieved even when the content of styrene is 40.0 to 99.0% by mass and the content of the (meth) acrylic acid ester unit is 1.0 to 60.0% by mass. It was. However, the total content of the styrene monomer unit and the (meth) acrylate unit is 100% by mass. The (meth) acrylic acid ester is a methacrylic acid ester such as methyl methacrylate or ethyl methacrylate, or an acrylic acid ester such as methyl acrylate or ethyl acrylate.

The content of the (meth) acrylic acid ester unit in the styrene resin can be measured under the following conditions by pyrolysis gas chromatography.
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

  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 weight average molecular weight of the styrenic resin is 150,000 to 700,000, preferably 160,000 to 700,000, and more preferably 160,000 to 400,000 or 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 styrenic resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and amount of polymerization initiator, the type and amount of chain transfer agent, the type and amount of solvent used during 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.

<< Additive B >>
The styrenic resin composition of the present invention comprises (b) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyl. Dibenzo [d, f] [1, 3, 2] dioxaphosphine (also referred to as “additive B”) is contained as an essential component. The additive B is a processing stabilizer having a hindered phenol antioxidant skeleton and a phosphorus antioxidant skeleton in the same molecule.

  Content of the additive B is 0.02-0.40 mass% in 100 mass% of styrene resin compositions, and it is preferable that it is 0.05-0.20 mass%. When the content of the additive 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. Specifically, the content of the additive B in 100% by mass of the styrene-based resin composition is, for example, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.0. 08, 0.09, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40 mass%, and between any two of the numerical values exemplified here It may be within the range.

<< Phosphorus antioxidants and hindered phenol antioxidants >>
The styrene resin composition of the present invention contains at least one of a phosphorus antioxidant and a hindered phenol antioxidant as an essential component in addition to the above-mentioned amount of additive B. This is because long-term thermal stability, initial hue, and transmittance are improved as compared with the case where the additive B is used alone.

The phosphorus-based antioxidant is preferably contained in 0.02 to 0.50 mass%, more preferably 0.05 to 0.30 mass%, in 100 mass% of the styrene resin composition. Moreover, it is preferable to contain 0.02 to 0.50 mass% of hindered phenolic antioxidant in 100 mass% of styrene resin compositions, and it is more preferable to contain 0.05 to 0.30 mass%. . This is because when the phosphorus-based or hindered phenol-based antioxidant is added at the above-mentioned content, the discoloration suppressing effect is particularly enhanced by the synergistic effect with the additive B. Specifically, the content of the phosphorus antioxidant and the hindered phenol antioxidant in 100% by mass of the styrene resin composition is, for example, 0.02, 0.03, 0.04, 0.0. 05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40,. 45 and 0.50 mass%, and may be in a range between any two of the numerical values exemplified here.

  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.

  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, pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydride Xylphenyl) propionate], 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-tert-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-tert-butylphenol), bis- [3,3-bis- ( 4′-hydroxy-3′-tert-butylphenyl) -butanoic acid] -glycol ester and the like. 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], pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate]. Hindered phenolic antioxidants may be used alone or in combination of two or more.

  As described above, among the phosphorus-based antioxidants and hindered phenol-based antioxidants, among them, a phosphorus-based antioxidant includes the following (C-1) to (C-4). It is particularly preferable that the hindered phenol-based antioxidant is at least one selected from among (D-1) to (D-4) shown below. Moreover, phosphorus antioxidant is at least 1 sort (s) chosen from (C-1)-(C-3), (d) hindered phenolic antioxidant is (D-1), ( More preferably, it is at least one selected from D-4). This is because, in such a specific combination, it has been experimentally confirmed that discoloration is particularly effectively suppressed.

(C-1) Tris (2,4-di-tert-butylphenyl) phosphite (C-2) 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2- Ethylhexyloxy) phosphorus (C-3) bis (2,4-dicumylphenyl) pentaerythritol diphosphite (C-4) 3,9-bis (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane

(D-1) Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (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 (D-3) ethylenebis (oxyethylene) bis [ 3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate]
(D-4) Pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate]

  As a method for adding the additive B, phosphorus antioxidant and hindered phenol antioxidant, a method of adding and mixing in the polymerization step, devolatilization step, granulation step of styrene resin, an extruder during molding processing, Examples include, but are not limited to, a method of adding and mixing with an injection molding machine, a method of diluting and mixing a resin composition adjusted to a high concentration with a hydrophilic additive to a desired content with an additive-free styrenic resin, and the like. is not.

<< Other additives >>
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.

  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 that can be obtained by polymerizing styrenic monomers may cause the molded product to become cloudy due to environmental changes such as temperature, humidity, and hot water immersion. ) Styrene- (meth) acrylic acid copolymer resin obtained by copolymerizing acrylic acid, or styrene- (meth) acrylic acid obtained by copolymerizing styrene monomer and (meth) acrylic acid ester Cloudiness can be prevented by using an ester copolymer resin. Further, white turbidity can be prevented even when a hydrophilic additive having a polyether chain is contained in the styrene resin composition. Moreover, the method of changing the kind of styrene resin and the method of adding a hydrophilic additive can also be used together.

  Styrenic resins have the problem of white turbidity (whitening phenomenon) due to environmental changes such as temperature, humidity, and warm water immersion (Journal of the Fiber Science Society, Vol. 34, No. 6, pp. 245-253, 1978). The transparency, which is an advantage, may be impaired. 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.

  As a method to prevent white turbidity of molded products due to environmental changes, when the styrene resin is a styrene- (meth) acrylic acid copolymer resin obtained by copolymerizing a styrene monomer and (meth) acrylic acid The styrene monomer unit content of the styrene resin is preferably 90.0 to 99.2% by mass, and the (meth) acrylic acid unit content is preferably 0.8 to 10.0% by mass, The content of the (meth) acrylic acid unit is more preferably 0.8 to 4.5% by mass, and further preferably 1.8 to 3.0% by mass. However, the total content of styrene monomer units and (meth) acrylic acid units is 100% by mass. (Meth) acrylic acid is acrylic acid, methacrylic acid or the like, with methacrylic acid being preferred. When the content of the (meth) acrylic acid unit is less than 0.8% by mass, the whitening suppression effect tends to be insufficient. Moreover, when it exceeds 10.0 mass%, an initial hue and the transmittance | permeability will deteriorate easily.

  As a method for preventing white turbidity of a molded product due to environmental changes, a styrene- (meth) acrylate copolymer resin obtained by copolymerizing a styrene resin with a styrene monomer and a (meth) acrylate ester, In this case, the content of the styrene monomer unit in the styrene resin is preferably 40 to 96% by mass, the content of the (meth) acrylic acid ester unit is preferably 4 to 60% by mass, and (meth) acrylic acid. The content of the ester unit is more preferably 4 to 15% by mass, further preferably 6 to 12% by mass, and further preferably 7 to 9% by mass. However, the total content of the styrene monomer unit and the (meth) acrylate unit is 100% by mass. The (meth) acrylic acid ester is a methacrylic acid ester such as methyl methacrylate or ethyl methacrylate, or an acrylic acid ester such as methyl acrylate or ethyl acrylate. When the content of the (meth) acrylic acid ester unit is less than 4% by mass, the whitening suppression effect tends to be insufficient. Moreover, when it exceeds 60.0 mass%, water absorption will deteriorate easily. Further, when the content of the (meth) acrylic acid ester unit increases, the fluidity tends to decrease, and the moldability tends to decrease in applications where high fluidity is required such as injection molding.

  Polyoxyethylene type nonionic surfactant, polyoxyethylene type anionic surfactant, polyoxyethylene type cationic surfactant, polyoxyethylene type amphoteric as hydrophilic additive having polyoxyethylene chain Examples thereof include polyoxyethylene type surfactants such as surfactants and polyethylene glycol. Of the polyoxyethylene type surfactants, polyoxyethylene type nonionic surfactants are preferred.

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 addition, polyvalent polyoxyethylene alkyl ethers having a plurality of polyoxyethylene alkyl ether skeletons in one molecule and polyvalent polyoxyethylene fatty acid esters having a plurality of polyoxyethylene fatty acid ester skeletons in one molecule are used. Can also achieve the object of the present invention. The valence of polyoxyethylene alkyl ether or polyoxyethylene fatty acid ester means the number of polyoxyethylene alkyl ether skeleton or polyoxyethylene fatty acid ester skeleton present in one molecule.
(In the formula, R represents an alkyl group having 8 to 20 carbon atoms. In addition, a polyvalent polyoxyethylene alkyl ether up to hexavalent having a plurality of polyoxyethylene alkyl ether skeletons and a plurality of polyoxyethylene fatty acid ester skeletons (It may be a polyvalent polyoxyethylene fatty acid ester having up to 6 valences, where n is an integer and represents 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.

  The average molecular weight of polyethylene glycol is preferably 200 to 10,000. More preferably, it is 200-4000, and still more preferably 300-1000. 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. In addition, if it exceeds 10,000, the effect of preventing the whitening phenomenon tends to be reduced, and the compatibility with the styrene resin is reduced, and the styrene resin composition and the molded product thereof may become cloudy. The average molecular weight is calculated from the hydroxyl group concentration (based on JIS K1557) measured by the pyridine phthalic anhydride method.

  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 Examples thereof include oxyethylene triisostearic acid, polyoxyethylene coconut fatty acid glyceryl, diglycerin, polyglycerin, polyoxyethylene polyglyceryl ether, and polyglycerin fatty acid ester.

  The HLB value of the hydrophilic additive having a polyether chain 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.

  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. 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.

  In the hydrophilic additive having a polyether chain, the content in 100% by mass of the styrene resin composition is 0.4 to 2.0% by mass, and preferably 0.7 to 1.6% 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-based resin composition decreases. To do.

  As a method for adding a hydrophilic additive, a method of adding and mixing in a polymerization process of a styrene resin, a devolatilization process, a granulation process, a method of adding and mixing with an extruder or the like at the time of molding, a high concentration of hydrophilic additive A method of diluting and mixing the resin composition adjusted to the desired content with an additive-free styrenic resin can be mentioned, and is not particularly limited.

  For example, a styrenic resin composition containing 0.5 to 50.0% by mass of a hydrophilic additive and an additive-free styrenic resin are mixed using an extruder or an injection molding machine, and the styrenic resin having a target concentration is mixed. Examples of the method include obtaining a resin composition, a molded product, and a light guide plate.

  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 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.

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, compression molding, blow molding, and the shape thereof is not limited. For example, if it is a plate-shaped molded product, it can be processed into a light guide plate or the like. 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. 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.

  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.

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

<< Test 1 >>
(Production of styrene resins PS-1 to PS-3)
The polymerization reactor 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. The styrene resin was manufactured by the above. 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 1, and the raw material solution was continuously supplied to the first reactor at a flow rate described in Table 1. The polymerization initiator was added to the raw material solution at the inlet of the first reactor so that the addition concentration shown in Table 1 (concentration based on mass with respect to the total amount of raw styrene and methacrylic acid) was mixed. The polymerization initiators listed in Table 1 are as follows: polymerization initiator-1: 2,2-di (4,4-t-butylperoxycyclohexyl) propane (Pertetra A manufactured by NOF Corporation was used).
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 in Table 1 was adjusted at the intermediate part and the outlet part.
Subsequently, the solution containing the 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 the preheater was adjusted to the resin temperature shown in Table 1. By adjusting the temperature and adjusting to the pressure shown in Table 1, unreacted styrene and ethylbenzene are separated and then extruded into a strand form from a perforated die, and the strand is cooled and cut by a cold cut method. Pelletized.

(Examples 1-1 to 1-25, Comparative Examples 1-1 to 1-8, Reference Examples 1-1 to 1-9)
With the contents shown in Table 2, styrene resins PS-1, PS-2, PS-3 and B, C and D as additives using a single screw extruder with a screw diameter of 40 mm, a cylinder temperature of 230 ° C., Pellets were obtained by melt-kneading at a screw speed of 100 rpm. Additives B, C and D used in Table 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) a phosphorus antioxidant, and additive D represents (d) a hindered phenol antioxidant.
B: 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3 2] Dioxaphosphepine (Sumitomo GP manufactured by Sumitomo Chemical Co., 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)
C-5: Tetrakis (2,4-di-tert-butylphenyl) [1,1biphenyl] -4,4 diylbiphosphonite (manufactured by Clariant Co. Ltd., Hostanox P-EPQ)
C-6: Bis (2,4-di-tert-butyl-6-methylphenyl) ethyl phosphite (Irgafos 38 manufactured by BASF Japan Ltd.)
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.)
D-4: Pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (Irganox 1010 manufactured by BASF Japan Ltd.)
D-5: 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane (ADEKA STAB AO-30 manufactured by ADEKA Corporation)
D-6: 1,1-bis (2-methyl-4-hydroxy-5-tert-butylphenyl) butane (ADEKA STAB AO-40 manufactured by ADEKA Corporation)

  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 2 represents the average transmittance at a wavelength of 380 nm to 780 nm.

Next, a YI value after Δheating and a ΔYI difference were calculated based on the following formula. In the following formula, “without additional additive” means that only additive B is added, and “with additional additive” means that additive C and additive D are added to additive B. It means the case where at least one is further added. In addition, examples, comparative examples, and reference examples are collectively referred to as “test examples”.
ΔI after heating YI value = (“YI value after 80 ° C. × 1000 hours” of test example with additional additive) − (“YI value after 80 ° C. × 1000 hours” of test example without additional additive)
ΔYI difference = (“YI difference from initial stage” in test example with additional additive) − (“YI difference from initial stage” in test example without additional additive)

For example, in Example 1-1 with an additional additive, the YI value after 7.0 hours at 80 ° C. is 7.0, and the amount of additive B added is the same as that of Example 1-1. Then, since the YI value after 80 ° C. × 1000 hours is 8.5, the “YI value after Δ heating” in Example 1-1 is −1.5. This value indicates the degree of synergistic effect between the additive B and the additives C and D, and the smaller the value, the greater the synergistic effect.
In Example 1-1 with additional additive, the “YI difference from the initial value” was 1.2, and in Reference Example 1-1, the amount of additive B added was the same as in Example 1-1. Since the “YI difference from the initial” is 2.6, the “ΔYI difference” in Example 1-1 is −1.4. The “YI difference from the initial value” indicates the degree of discoloration due to heating, and a smaller value is a preferable value. The ΔYI difference indicates the degree to which the “YI difference from the initial stage” has changed due to the synergistic effect between the additive B and the additives C and D, and the smaller the value, the greater the synergistic effect.

Furthermore, based on the YI value after Δ heating and the ΔYI difference, the examples and comparative examples were ranked according to the following criteria.
S: YI value after Δ heating ≦ −0.5 and ΔYI difference <−0.5
A: YI value after Δ heating ≦ −0.5, and −0.5 ≦ ΔYI difference B: −0.5 <ΔYI value after heating <0
C: 0 ≦ Δ after heating YI value Table 2 shows the characteristics of each resin composition and the evaluation results of the combined effect.

  The molded articles of the examples were 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. Further, when (1) the content of additive B is in a specific range, and (2) the content of phosphorus-based and / or hindered phenol-based antioxidant is in a specific range, It turned out that the discoloration inhibitory effect of a styrene resin composition becomes very high. Furthermore, in Examples 1-20 to 1-23, although the conditions (1) and (2) were satisfied, the degree of synergistic effect was slightly lower than in the other Examples. From these results, among the phosphorus-based and / or hindered phenol-based antioxidants, (C-1) to (C-4) or (D-1) to (D-4) having a specific configuration defined by It has been found that the degree of synergistic effect is particularly high when using one. Further, from Examples 1-24 and 1-25, the same effect can be obtained even when the type of styrene resin is a styrene- (meth) acrylic acid copolymer resin or a styrene- (meth) acrylic acid ester copolymer resin. It turns out that it is obtained.

<< Test 2 >>
(Examples 2-1 to 2-34)
A polymerization process is configured by connecting in series 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. The styrene resin was manufactured by the above. 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 Condition 1 in Table 1, and the raw material solution was continuously supplied to the first reactor at the flow rate described in Table 1. Also, at the inlet of the third reactor, Hydrophilic additive E having a polyether chain was added so as to have the types and contents shown in Table 3. The types of additives and polyethylene glycol used are as follows.
E-1: Polyethylene glycol having an average molecular weight of 400 (PEG # 400 manufactured by NOF Corporation)
E-2: Polyethylene glycol having an average molecular weight of 1000 (PEG # 1000 manufactured by NOF Corporation)
E-3: Polyethylene glycol having an average molecular weight of 2000 (PEG # 2000 manufactured by NOF Corporation)
E-4: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 25 (Emalgen 123P manufactured by Kao Corporation)
E-5: Polyoxyethylene ethylene lauryl ether Ethylene oxide average added mole number = 12 (Emulgen 320P manufactured by Kao Corporation)
E-6: Polyoxyethylene ethylene lauryl ether Ethylene oxide average addition mole number = 9 (Emulgen 109P manufactured by Kao Corporation)
E-7: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 30 (Emulgen 130K manufactured by Kao Corporation)
E-8: Polyethylene glycol monolaurate Ethylene oxide average added 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.

Next, using a single screw extruder having a screw diameter of 40 mm, the pellets of the styrenic resin and the additives B, C, and D obtained above were used at a cylinder temperature of 230 ° C. so that the contents shown in Table 3 were obtained. Pellets were obtained by melt-kneading at a screw speed of 100 rpm. The symbols for Additives C and D used in Table 3 are the same as those shown in Test 1.
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. The transmittance and YI value were measured in the same manner as in Test 1.
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 3 shows the characteristics and evaluation results of each resin composition.

  The molded products of Examples 2-1 to 2-31 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 long-term heat. Excellent stability. On the other hand, in Examples 2-32 to 2-33, the whitening phenomenon occurred because the hydrophilic additive E was not added or the addition amount was too small. Furthermore, in Example 2-34, since the addition amount of the hydrophilic additive E was too much, heat resistance fell.

<< Test 3 >>
(Examples 3-1 to 3-10)
The polymerization reactor 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, to form a polymerization process, and the conditions shown in Table 4 The styrene resin was manufactured by the above. 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 4, and the raw material solution was continuously supplied to the first reactor at a flow rate described in Table 4. 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 4 (concentration based on mass with respect to the total amount of raw styrene and methacrylic acid), and mixed uniformly. The polymerization initiators listed in Table 4 are as follows: Polymerization initiator-1: 2,2-di (4,4-t-butylperoxycyclohexyl) propane (Pertetra A manufactured by NOF Corporation was used).
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 in Table 4 was adjusted at the intermediate part and the outlet part.
Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater composed of two stages in series, and the preheater was adjusted to the resin temperature shown in Table 4. By adjusting the temperature of and adjusting to the pressure shown in Table 4, unreacted styrene and ethylbenzene are separated and then extruded into a strand shape from a perforated die, and the strand is cooled and cut by a cold cut method. Pelletized.

Next, the pellets obtained above and additives B and D were melt-mixed 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 so as to have the contents shown in Table 5. Pellet was obtained by smelting.
D-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
D-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), Vicat softening temperature, transmittance, YI value, and whitening suppression effect were measured or evaluated in the same manner as in Test 2.
Table 5 shows the characteristics and evaluation results of each resin composition.

  The molded article of the styrene resin composition containing methacrylic acid units other than Example 3-9 is excellent in heat resistance, excellent in whitening suppression effect, excellent in initial transmittance and YI value, and long-term Excellent thermal stability. On the other hand, whitening occurred in the styrene resin composition of Example 3-9.

<< Test 4 >>
(Production Example of Styrenic Resin A-1 to 7)
The polymerization reactor 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. The styrene resin was manufactured by the above. 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 6, and the raw material solution was continuously supplied to the first reactor at a flow rate described in Table 6. 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 6 (concentration based on mass relative to the total amount of raw material styrene and methyl methacrylate) and mixed uniformly. The polymerization initiators listed in Table 6 are 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 in Table 6 was adjusted at the intermediate part and the outlet part.
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 the preheater was adjusted to the resin temperature shown in Table 6. After adjusting the temperature of and adjusting to the pressure shown in Table 6, unreacted styrene and ethylbenzene were separated and then extruded into a strand shape from a perforated die, and the strand was cooled and cut by a cold cut method. Pelletized.

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 6 shows the characteristics of each styrene resin.

(Examples 4-1 to 4-26)
Next, with the contents shown in Table 7, the styrene resin A, B, C and D as additives were melt mixed 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. Pellet was obtained by smelting.
The transmittance, YI value, and whitening suppression effect were measured or evaluated in the same manner as in Test 2.
Table 7 shows the characteristics and evaluation results of each resin composition.

  The molded articles of Examples 4-1 to 4-24 having a relatively high content of (meth) acrylic acid ester units are excellent in whitening suppression effect, excellent in initial transmittance and YI value, and are 80 ° C. × 1000. The amount of change in YI during storage over time was small, and long-term thermal stability was also excellent. On the other hand, in Examples 4-25 to 4-26 in which the (meth) acrylic acid ester unit was not included or the content thereof was relatively small, the whitening suppression effect was not sufficient.

  The optical styrenic resin composition and molded article of the present invention are excellent in hue and transparency and excellent in long-term thermal stability. In addition, since the whitening phenomenon due to environmental changes is prevented and the transparency and hue are excellent, transparency, which is an advantage of styrenic resins, can be maintained even in applications where the whitening phenomenon has conventionally occurred due to environmental changes. Can be preferably used. For example, it can be suitably used for light guide plate applications such as televisions, desktop personal computers, notebook personal computers, mobile phones, and car navigation systems.

Claims (10)

(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 containing 10-tetra-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphine and (c) a phosphorus-based antioxidant, the styrene-based resin composition 100 content of 0.02 to 0.40 wt% of (b) in mass%, Ri content of 0.02 to 0.50% by mass of (c), the phosphorus-based antioxidant, ( An optical styrene resin composition , which is at least one selected from C-1) to (C-4) .
(C-1) Tris (2,4-di-tert-butylphenyl) phosphite
(C-2) 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus
(C-3) Bis (2,4-dicumylphenyl) pentaerythritol diphosphite
(C-4) 3,9-bis (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane The optical phosphorus styrenic resin composition according to claim 1, wherein the phosphorus antioxidant is at least one selected from the above (C-1) to (C-3). The said styrenic resin composition contains (d) hindered phenolic antioxidant, and content of (d) is 0.02-0.50 mass%, The claim 1 or Claim 2 characterized by the above-mentioned. Styrenic resin composition for optics. The hindered phenolic antioxidant, (D-1) Ru least 1 Tanedea selected from among ~ (D-4), optical styrenic resin composition according to claim 3.
(D-1) Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (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 (D-3) ethylenebis (oxyethylene) bis [ 3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate]
(D-4) Pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] 5. The optical styrene resin composition according to claim 4, wherein the hindered phenol-based antioxidant is at least one selected from the above (D-1) and (D-4). The styrene resin is a styrene- (meth) acrylic acid copolymer resin obtained by copolymerizing a styrene monomer and (meth) acrylic acid, and contains a styrene monomer unit of the styrene resin. The amount is 90.0 to 99.9% by mass, and the content of (meth) acrylic acid units is 0.1 to 10.0% by mass. The styrenic resin composition for optics described in 1. However, the total content of styrene monomer units and (meth) acrylic acid units in the styrene resin is 100% by mass. The styrene resin is a styrene- (meth) acrylate copolymer resin obtained by copolymerizing a styrene monomer and a (meth) acrylate ester, and is a styrene monomer unit of the styrene resin. The content of is from 40.0 to 99.0% by mass, and the content of (meth) acrylic acid ester units is from 1.0 to 60.0% by mass. The styrene resin composition for optical use according to any one of the above. However, the total content of styrene monomer units and (meth) acrylic acid ester units in the styrene resin is 100% by mass. The optical additive styrenic resin composition according to any one of claims 1 to 7, wherein the hydrophilic additive having a polyether chain is contained in an amount of 0.4 to 2.0% by mass. A molded article comprising the optical styrenic resin composition according to any one of claims 1 to 8. A light guide plate comprising the molded product according to claim 9.