JP6248169B2 - Styrenic resin composition for optics - Google Patents

Description

The present invention relates to a transparent styrenic resin composition in which whitening due to environmental changes is suppressed.

  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.

  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, the styrene resin has a problem that a molded product becomes cloudy due to environmental changes such as temperature, humidity, and warm water immersion (Non-Patent Document 1). There is a whitening phenomenon), and the transparency, which is an advantage, may be impaired depending on the application. 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.

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

Journal of Textile Society, 34, No. 6, pp. 245-253, 1978

  An object of the present invention is to provide a transparent styrenic resin composition in which whitening due to environmental changes is suppressed.

  According to the present invention, 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 hydrophilic additive is an average added mole number of ethylene oxide. Is at least one selected from a polyoxyethylene surfactant having an average molecular weight of 200 to 10,000, an HLB value of 5 to 20, and 100 masses of the styrenic resin composition. The content in% is 0.4 to 2.0% by mass, and an optical styrene resin composition is provided.

  The present inventors have intensively studied to suppress the whitening phenomenon due to environmental changes, and have found that the addition of a hydrophilic additive is effective in suppressing the whitening phenomenon. However, further investigations have revealed that simply adding a hydrophilic additive may not work. Therefore, when further investigation was made, (1) the hydrophilic additive has a characteristic configuration, (2) its HLB value is within a specific range, and (3) its content is When the amount is in a specific range, the heat resistance of the styrene resin composition is maintained, and the whitening phenomenon suppressing effect is extremely high, and the transparency of the styrene resin is not impaired. It was. Although the operational effect for obtaining such an effect is not necessarily clarified, it is considered to be due to the synergistic effect of these three conditions because it is exhibited effectively only when the above three conditions are met.

Hereinafter, various embodiments of the present invention will be exemplified.
Preferably, the hydrophilic additive is a polyoxyethylene surfactant having an average addition mole number of ethylene oxide of 10 to 60, and the content in 100% by mass of the styrene resin composition is 0.00. It is 6-1.4 mass%.
Preferably, the hydrophilic additive is a polyoxyethylene surfactant having an average addition mole number of ethylene oxide of 13 to 35, and the content in 100% by mass of the styrene resin composition is 0.00. It is 6-0.9 mass%.
Preferably, the hydrophilic additive has an HLB value of 10-18.
Preferably, the polyoxyethylene type surfactant is a polyoxyethylene type nonionic surfactant.
Preferably, the polyoxyethylene type nonionic surfactant is 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). One or more types.
(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.)
Preferably, the hydrophilic additive is polyethylene glycol having an average molecular weight of 200 to 10,000, and the content in 100% by mass of the styrenic resin composition is 0.6 to 1.4% by mass.
Preferably, the hydrophilic additive is polyethylene glycol having an average molecular weight of 200 to 1800.
Preferably, the hydrophilic additive has a content in 100% by mass of the styrene resin composition of 0.6 to 0.9% by mass.
Further, 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.
The styrenic resin is a styrene- (meth) acrylic acid ester copolymer resin obtained by copolymerizing a styrene 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.
In addition, 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3, 2] Including dioxaphosphine.
Moreover, a phosphorus antioxidant and / or a hindered phenol antioxidant are included.
Moreover, it is a molded article which consists of said styrene resin composition for optics.
Moreover, it is a light-guide plate which consists of said molded article.

The styrenic resin composition of the present invention has low water absorption and is inexpensive compared to PMMA and MS resins, and does not cause whitening due to environmental changes, which is a drawback of styrenic resins, and is excellent in colorless transparency. Therefore, it can be suitably used for applications utilizing the original transparency of the styrene resin.

  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. 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. .
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 99.6% by mass. And 95 to 99.6 mass% is preferable. Specifically, the ratio of the styrenic resin is, for example, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.6% by mass, and any one 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 The amount is preferably 90.0 to 99.9% by mass, and the content of (meth) acrylic acid units is preferably 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 Is preferably 40.0 to 99.0% by mass, and (meth) acrylic acid ester unit content is preferably 1.0 to 60.0% 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.

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 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 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 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.

<< Hydrophilic additive >>
The hydrophilic additive is a compound having a hydrophilic group capable of interacting with water (hydrogen bonding). The hydrophilic group is preferably a polyether chain. The polyether chain is a skeleton structure in which ether bonds are linked. For example, a polyoxyethylene chain synthesized by an addition reaction of alkylene oxide such as ethylene oxide (hereinafter sometimes referred to as EO), propylene oxide, butylene oxide, A polyglycerol chain synthesized by dehydration condensation of a polyoxypropylene chain, a polyoxybutylene chain or glycerin can be mentioned, and a polyoxyethylene chain is preferable. The polyether chain may have not only one set per molecule but also a plurality of sets.

  Among such various hydrophilic additives, the present invention is selected from polyoxyethylene surfactants having an average added mole number of ethylene oxide of 3 to 150 and polyethylene glycol having an average molecular weight of 200 to 10,000. Add at least one. This is because it has been experimentally found that it is essential to use a hydrophilic additive having such a specific configuration in order to enhance the effect of suppressing the whitening phenomenon.

  Moreover, the HLB value of a hydrophilic additive is 5-20. This is because it has been experimentally found that it is essential to use a hydrophilic additive having such a specific HLB value in order to enhance the whitening phenomenon suppressing effect. HLB value becomes like this. Preferably it is 8-20, More preferably, it is 10-20, More preferably, it is 10-18. HLB (Hydrophilic-lipophilic balance) value is a value that represents the hydrophilicity of the additive. If the HLB value is 8 to 10, it is stably dispersed in water, and if it exceeds 10, it completely dissolves transparently from a transparent dispersion state. It becomes a state to do. For nonionic surfactants having a polyether chain, the HLB value = (molecular weight of hydrophilic group part) / (molecular weight of additive) × 20. For paraffins that do not contain a hydrophilic group, the HLB value = In the case of 0, polyethylene glycol having only a hydrophilic group has an HLB value = 20, and a nonionic surfactant has an HLB value of 0-20.

A hydrophilic additive is added so that content in 100 mass% of styrene resin compositions may be 0.4-2.0 mass%. This is because it has been experimentally found that it is essential to add such a content in order to increase the whitening phenomenon suppressing effect while maintaining the heat resistance of the styrene-based resin composition. The content of the hydrophilic additive in 100% by mass of the styrenic resin composition is preferably 0.7 to 1.6% by mass or 0.6 to 1.4% by mass, more preferably 0.6. It is -0.9 mass%.

  The heating loss of the hydrophilic additive 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.

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.

<Polyoxyethylene type surfactant>
Polyoxyethylene type surfactants include polyoxyethylene type nonionic surfactants, polyoxyethylene type anionic surfactants, polyoxyethylene type cationic surfactants, polyoxyethylene type amphoteric surfactants And a polyoxyethylene type nonionic surfactant is preferable.

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 3 to 150. This is because it has been experimentally found that it is essential that the average added mole number is within such a specific range in order to enhance the whitening phenomenon suppressing effect. The average added mole number is preferably 7 to 100, more preferably 10 to 60, further preferably 10 to 50, and further preferably 13 to 35.

  Specific examples of the polyoxyethylene surfactant of the present invention include, for example, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene octyl decyl ether, polyoxyethylene myristyl ether Polyoxyethylene alkyl ethers such as polyoxyethylene 2-ethylhexyl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan tristearate, and polyoxyethylene sorbitan tetraoleate Oxyethylene sorbitol fatty acid ester, polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene Polyoxyethylene fatty acid esters such as recall distearate, polyethylene glycol monooleate, polyoxyethylene hydrogenated castor oil, polyoxyethylene monomethyl ether, polyoxyethylene dimethyl ether, polyoxyethylene glyceryl ether, polyoxyethylene tetraoleic acid, poly Examples thereof include oxyethylene triisostearic acid and polyoxyethylene coconut fatty acid glyceryl.

<Polyethylene glycol>
The average molecular weight of polyethylene glycol used in the present invention is 200 to 10,000. It is preferable that it is 200-4000, It is more preferable that it is 200-1800, It is more preferable that it is 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.

<< Additives / Antioxidants >>
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 styrenic resin composition of the present invention is suitable for optical applications as a field utilizing transparency, for example, an optical material, because the deterioration of optical properties such as transmittance, hue, and transparency, which are characteristics of the styrene resin, is small. Can be used. Examples of optical applications include lenses, light guide plates, films, optical fibers, and optical waveguides.

  In the styrene resin composition of the present invention, (c) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyl is added. Dibenzo [d, f] [1,3,2] dioxaphosphine (hereinafter referred to as “compound X”), (d) phosphorus antioxidant, (e) hindered phenol antioxidant By adding at least one of them, long-term thermal stability can be imparted. In fields that are used for a long period of time, such as optical applications, long-term thermal stability is an important characteristic. 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.

  Compound X is a processing stabilizer having a hindered phenol antioxidant skeleton and a phosphorus antioxidant skeleton in the same molecule.

  The content of the compound X in 100% by mass of the styrene-based resin composition is preferably 0.02 to 0.40% by mass, and more preferably 0.05 to 0.20% by mass. If the content of the compound X 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 compound X in 100% by mass of the styrene resin composition is, for example, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08. 0.09, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40 mass%, and the range between any two of the numerical values exemplified here It may be within.

In addition to adding compound X to the styrenic resin composition of the present invention, long-term thermal stability can be imparted, and long-term thermal stability can also be achieved by adding phosphorus-based antioxidants and / or hindered phenol-based antioxidants. Can be granted.

  The phosphorus-based antioxidant is preferably contained in 0.02 to 0.50% by mass in 100% by mass of the styrene-based resin composition, more preferably 0.05 to 0.40% by mass, and 0.05 to More preferably, the content is 0.30% by mass. If it is less than 0.02% by mass, the long-term thermal stability is poor, and the initial hue and transmittance are also poor. Even if it exceeds 0.50 mass%, long-term thermal stability will deteriorate. Specifically, the content of the phosphorus antioxidant in 100% by mass of the styrene resin composition is, for example, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50 mass%, where It may be within a range between any two of the exemplified numerical values.

  The hindered phenolic antioxidant is preferably contained in 0.02 to 0.50% by mass, more preferably 0.02 to 0.30% by mass in 100% by mass of the styrene resin composition. More preferably, the content is from 0.5 to 0.30% by mass. If it is less than 0.02% by mass, the long-term thermal stability is poor, and the initial hue and transmittance are also poor. Even if it exceeds 0.50 mass%, long-term thermal stability will deteriorate. Specifically, the content of the hindered phenol-based antioxidant in 100% by mass of the styrene-based resin composition is, for example, 0.02, 0.03, 0.04, 0.05, 0.06, 0.0. 07, 0.08, 0.09, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50% by mass, It may be within 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, 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.

  Compound X, phosphorus antioxidant and hindered phenol antioxidant can be added by adding and mixing in the polymerization process, devolatilization process and granulation process of styrene resin, and extruders and injections during molding. A method of adding and mixing with a molding machine, etc., a method of diluting and mixing a resin composition prepared by adding these additives to a high concentration with an additive-free styrenic resin, etc. Absent.

  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.

<< Styrenic resin composition >>
The styrenic resin composition of the present invention can obtain a molded product by various molding methods according to purposes such as injection molding, extrusion molding, blow molding, compression molding and the like. The shape of the molded product can be a shape according to the purpose, and is not limited. For example, if it is a plate-shaped molded article, it can be used as a light guide plate. As a method of forming a light guide plate, it is known to provide a reflection pattern such as a dot pattern on the back surface of the plate-shaped molded product (opposite the surface from which light is emitted). 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.

  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.

  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 A-1 to A-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 1-33, Comparative Examples 1-1 to 1-9)
With the contents shown in Table 2, the styrene resins A-1 to A-3 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. Pellets were obtained. The additives used in Table 2 are shown below.
B-1: Polyoxyethylene ethylene lauryl ether Ethylene oxide average added mole number = 25 (Emalgen 123P manufactured by Kao Corporation)
B-2: Polyoxyethylene ethylene stearyl ether ethylene oxide average addition mole number = 12 (Emulgen 320P manufactured by Kao Corporation)
B-3: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 9 (Emulgen 109P manufactured by Kao Corporation)
B-4: Polyoxyethylene ethylene cetyl ether Ethylene oxide average added mole number = 7 (Emalgen 210P manufactured by Kao Corporation)
B-5: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 30 (Emulgen 130K manufactured by Kao Corporation)
B-6: Polyoxyethylene ethylene lauryl ether Average addition mole number of ethylene oxide = 47 (Emulgen 150 manufactured by Kao Corporation)
B-7: Polyoxyethylene ethylene myristyl ether Average addition mole number of ethylene oxide = 85 (Emulgen 4085 manufactured by Kao Corporation)
B-8: Polyethylene glycol monolaurate Ethylene oxide average addition mole number = 12 (Emanon 1112 manufactured by Kao Corporation)
B-9: Polyoxyethylene ethylene stearyl ether ethylene oxide average addition mole number = 6 (Emulgen 306P manufactured by Kao Corporation)
B-10: Polyoxyethylene hydrogenated castor oil (Emanon CH-40 manufactured by Kao Corporation)
B-11: Polyethylene glycol having an average molecular weight of 400 (PEG # 400 manufactured by NOF Corporation)
B-12: Polyethylene glycol having an average molecular weight of 300 (PEG # 300 manufactured by NOF Corporation)
B-13: Polyethylene glycol having an average molecular weight of 600 (PEG # 600 manufactured by NOF Corporation)
B-14: Polyethylene glycol having an average molecular weight of 1000 (PEG # 1000 manufactured by NOF Corporation)
B-15: Polyethylene glycol having an average molecular weight of 2000 (PEG # 2000 manufactured by NOF Corporation)
B-16: Polyethylene glycol having an average molecular weight of 3100 (PEG # 4000 manufactured by NOF Corporation)
B-17: Polyethylene glycol having an average molecular weight of 8800 (PEG # 6000 manufactured by NOF Corporation)
B-18: Polyoxyethylene monomethyl ether (UNIOX M-550 manufactured by NOF Corporation)
B-19: Polyoxyethylene triisostearic acid (UNIOX GT-20IS manufactured by NOF Corporation)
B-20: Polyoxyethylene octyldodecyl ether (Emulgen 2025G manufactured by Kao Corporation)
B-21: Polyoxyethylene glyceryl ether (UNIOX G-750, NOF Corporation)
B-22: Polyoxyethylene tetraoleic acid (Niox ST-30E manufactured by NOF Corporation)
B-23: Stearyl alcohol (Calcoal 8098 manufactured by Kao Corporation)
B-24: Stearic acid monoglyceride (Excel S-95 manufactured by Kao Corporation)
B-25: Polyethylene glycol having an average molecular weight of 60000 (Alcox L-6 manufactured by Meisei Chemical Co., Ltd.)
B-26: Polyglycerin having an average molecular weight of 500 (polyglycerin # 500 manufactured by Sakamoto Pharmaceutical Co., Ltd.)

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 Example 1-33, styrene resin A-1 and additive B-1 were melt-kneaded at a cylinder temperature of 230 ° C. and a screw rotation speed of 100 rpm using a single screw extruder having a screw diameter of 40 mm, and added. This is a molded product obtained by once obtaining pellets having a concentration of 20% by mass of the agent B-1 and then mixing the pellets and the styrene resin A-1 so as to have a ratio of 1:24, followed by injection molding. .

<MFR>
The MFR (melt mass flow rate) of the styrene-based resin composition was measured based on JIS K 7210 under the conditions of 200 ° C. and 49 N load.

<Early hue evaluation>
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 obtained value is “YI 115 mm” in Table 2. In addition, “transmittance 115 mm” shown in Table 2 represents an average transmittance of wavelengths 380 nm to 780 nm.
Furthermore, “Haze 4 mm” in Table 2 is a plate-shaped molded article having a thickness of 55 × 50 × 4 mm by performing injection molding at a cylinder temperature of 220 ° C. and a mold temperature of 40 ° C. using the pellets obtained in the above process. Is a value obtained by performing measurement in accordance with JIS K-7105 using NDH5000 (manufactured by Nippon Denshoku Industries Co., Ltd.), using a test piece obtained by molding YY 4 mm in Table 2. "Is a value obtained by performing a measurement by a reflection method using a colorimetric color difference meter NDJ4000 (manufactured by Nippon Denshoku Industries Co., Ltd.) using this test piece.

<Whitening suppression effect>
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. , Will not disappear after 24 hours

<Vicat softening temperature>
The Vicat softening temperature was determined according to JIS K-7206 at a heating rate of 50 ° C./hr and a test load of 50 N.

<Comprehensive evaluation>
Comprehensive evaluation was performed according to the following criteria.
S: The whitening suppression effect is ◎ and the Vicat softening temperature is 100 ° C or higher. A: The condition of S is not satisfied, the whitening suppression effect is ◎ and the Vicat softening temperature is 98 ° C or higher, or the whitening suppression effect is ○. Yes and the Vicat softening temperature is 100 ° C. or higher B: The condition of A is not satisfied, the whitening suppression effect is ◎ and the Vicat softening temperature is 95 ° C. or higher, or the whitening suppression effect is ○ and the Vicat softening temperature is 98 ° C. Above, or whitening suppression effect is Δ and Vicat softening temperature is 100 ° C. or higher C: None of the above conditions is satisfied

  Table 2 shows the characteristics and evaluation results of each resin composition.

The molded articles of the examples were excellent in the whitening suppressing effect, were excellent in transparency and hue without deterioration in transmittance and YI value. In Comparative Examples 1-1, 1-2, and 1-4 in which the hydrophilic additive was not added or the addition amount was too small, the suppression of the whitening state was insufficient. In Comparative Examples 1-3 and 1-5 in which the hydrophilic additive was excessively added, the heat resistance was excessively lowered. Moreover, in Comparative Examples 1-6 and 1-7, the test was performed by adding stearyl alcohol and stearic acid monoglyceride, which are hydrophilic additives, respectively, but the whitening suppressing effect was insufficient. Further, in Comparative Examples 1-8 and 1-9, tests were performed by adding polyethylene glycol and polyglycerin having a large molecular weight, but the hydrophilic additive was not compatible with the styrene resin, and the molded product became cloudy. .
From the above results, (1) the hydrophilic additive has a characteristic configuration, (2) its HLB value is within a specific range, and (3) its content is within a specific range. It has been found that satisfying the three conditions of the amount is essential for suppressing the whitening phenomenon while maintaining the heat resistance and transparency of the styrene resin composition. Referring to Examples 1-20 to 1-21, the same result was obtained when the styrene resin was a copolymer of a styrene monomer and (meth) acrylic acid or (meth) acrylic acid ester. Was found to be obtained.

<< Test 2 >>
(Examples 2-1 to 2-46)
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.

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 3. 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.

Next, using the single-screw extruder with a screw diameter of 40 mm, compound X, additive D, and additive E as pellets of the styrenic resin obtained as described above and additive E are added so as to have the contents shown in Table 3. The mixture was melt kneaded at a cylinder temperature of 230 ° C. and a screw rotation speed of 100 rpm to obtain pellets. The compounds X, D and E used in Table 3 are shown below. Compound X is 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [ 1,3,2] dioxaphosphepine, additive D represents a phosphorus-based antioxidant, and additive E represents a hindered phenol-based antioxidant.
Compound X: 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 3 represents an average transmittance at a wavelength of 380 nm to 780 nm.

Next, the ΔYI difference was calculated based on the following formula.
ΔYI difference = (YI difference from initial in Example with additional additive) − (YI difference from initial in Example without additional additive)
In one example, in Example 2-2 with an additional additive, the value of the YI difference from the initial value is 1.1, and the YI difference from the initial value in Example 2-1 without the additional additive is 5.1. Therefore, the ΔYI difference in Example 2-2 is −4.0. This value represents the long-term thermal stability improvement effect of the additive (compound X, phosphorus-based D, hindered phenol-based E), and the smaller the value, the greater the long-term thermal stability improvement effect. I mean.

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. , Will not disappear after 24 hours

<Comprehensive evaluation>
According to the following criteria, the evaluation results of the whitening suppression effect, the ΔYI difference, and the Vicat softening temperature were quantified.
Whitening suppression effect score ◎ → 3, ○ → 2, △ → 1, × → 0)
ΔYI difference score (−4.0 or lower → 4, −3.5 or lower → 3, −2.5 or lower → 2, −1.5 or lower → 1, otherwise → 0)
Vicat softening temperature score (99 ° C or higher → 3, 97 ° C or higher → 2, 95 ° C or higher → 1, otherwise → 0)

The total score obtained according to the above criteria was comprehensively evaluated according to the following criteria.
S: 10, A: 9, B: 8, C: 7, D: 6 or less

Table 3 shows the characteristics and evaluation results of each resin composition. In Examples 2-1 to 2-42, the styrene resin A-1 prepared according to Condition 1 was used, and in Examples 2-43 to 2-44, the styrene resin A-2 prepared according to Condition 2 was used. In Examples 2-45 to 2-46, styrene resin A-3 prepared according to Condition 3 was used.

  When Table 3 is referred, it turns out that the whitening suppression effect of all the examples is excellent. Further, when Examples 2-1 to 2-35 and Examples 2-36 to 2-42 are compared, long-term thermal stability is obtained when the content of Compound X is 0.02 to 0.40 mass%. Can be seen to be particularly excellent. Further, referring to Examples 2-43 to 2-46, the same applies to the case where the styrene resin is a copolymer of a styrene monomer and (meth) acrylic acid or (meth) acrylic acid ester. It turned out that the result of is obtained.

<< Test 3 >>
(Examples 3-1 to 3-36)
In Test 3, the evaluation was performed in the same manner as in Test 2, except that Compound X was not added. In Examples 3-1 to 3-32, styrene resin A-1 prepared according to Condition 1 was used, and in Examples 3-33 to 3-34, styrene resin A-2 prepared according to Condition 2 was used. In Examples 3-35 to 3-36, styrene resin A-3 produced according to Condition 3 was used.
The results are shown in Table 4.

  When Table 4 is referred, it turns out that the whitening suppression effect of all the examples is excellent. Further, when Examples 3-1 to 3-24 and Examples 3-25 to 3-32 are compared, the content of phosphorus D is 0.05 to 0.40 mass%, and phenol E It can be seen that the long-term thermal stability is particularly excellent when the content is 0.02 to 0.30 mass%. Further, referring to Examples 3-33 to 3-36, the same applies to the case where the styrene resin is a copolymer of a styrene monomer and (meth) acrylic acid or (meth) acrylic acid ester. It turned out that the result of is obtained.

The styrenic resin composition of the present invention prevents the whitening phenomenon due to environmental changes and is excellent in transparency and hue, so that it is an advantage of the styrenic resin even in applications where the whitening phenomenon has conventionally occurred due to environmental changes. It can maintain transparency and can be used suitably.
Furthermore, since the styrenic resin composition having excellent long-term thermal stability has a small hue change, it can be used while maintaining transparency and hue for a long period of time.
For example, light guide plate applications such as a television, a desktop personal computer, a notebook personal computer, a mobile phone, and a car navigation can be used.

Claims (14)

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 hydrophilic additive has an average added mole number of ethylene oxide of 10 to 150. or polyoxyethylene type surfactant, or both of the polyoxyethylene type surfactant and the average of polyethylene glycol of molecular weight 200 to 10,000, an HLB value of 5-20, and the styrene resin composition optical styrene resin composition content of the object 100 mass% is characterized in that it is a 0.6 to 0.9 mass%. Said polyoxyethylene type surfactant is the average number of moles of added ethylene oxide is 10 to 60, optical styrenic resin composition according to claim 1. It said polyoxyethylene type surfactant is the average number of moles of added ethylene oxide is 13 to 35, claim 1 or optical styrenic resin composition according to claim 2. The hydrophilic additive, HLB value of 10 to 18, optical styrenic resin composition according to any one of claims 1 to 3. The optical styrene-based resin composition according to any one of claims 1 to 4, wherein the polyoxyethylene-type surfactant is a polyoxyethylene-type nonionic surfactant. The polyoxyethylene type nonionic surfactant is selected from the group of polyoxyethylene alkyl ethers represented by the following general formula (1) and / or polyoxyethylene fatty acid esters represented by the following general formula (2) It is the above, The styrenic resin composition for optics of Claim 5 characterized by the above-mentioned.
(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.) The optical hydrophilic styrenic resin composition according to any one of claims 1 to 6, wherein the hydrophilic additive is both the polyoxyethylene-type surfactant and the polyethylene glycol . The polyethylene glycol has an average molecular weight of from 200 to 180 0, optical styrenic resin composition according to claim 7. The styrene resin is a styrene- (meth) acrylic acid copolymer resin obtained by copolymerizing a styrene monomer and (meth) acrylic acid, and is a styrene monomer unit of the styrene resin. Content is 90.0-99.9 mass%, Content of a (meth) acrylic acid unit is 0.1-10.0 mass%, Any 1 of Claims 1-8 characterized by the above-mentioned. A styrenic resin composition for optics as 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 styrenic resin is a styrene- (meth) acrylic acid ester copolymer resin obtained by copolymerizing a styrenic monomer and a (meth) acrylic acid ester, and is a styrenic monomer of a styrenic resin content of 40.0 to 99.0% by weight of units, of claims 1 to 8, wherein the content of (meth) acrylic acid ester unit is 1.0 to 60.0 wt% The optical styrenic resin composition 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. 6- [3- (3-tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1,3,2] The styrene resin composition for optics according to any one of claims 1 to 10 , comprising dioxaphosphepine. The optical styrenic resin composition according to any one of claims 1 to 11 , comprising a phosphorus-based antioxidant and / or a hindered phenol-based antioxidant. A molded article comprising the optical styrenic resin composition according to any one of claims 1 to 12 . A light guide plate comprising the molded product according to claim 13 .