TW201402680A - Styrene-based resin composition for optical applications, molded product, and light guide plate - Google Patents

Abstract

The problem addressed by the present invention lies in providing a styrene-based resin composition for optical applications that has excellent long-term thermal stability, shows little change in color or transmittance, and has excellent colorless transparency, as well as a molded product and a light guide plate. The present invention provides a styrene-based resin composition for optical applications, which is characterized in being a styrene-based resin composition formed from (a) a styrene-based resin having a weight-average molecular weight of 150,000 to 700,000, (b) a phosphorus-based antioxidant having a specific structure, and (c) a hindered phenol-based antioxidant having a specific structure, wherein in terms of 100 mass% of styrene-based resin composition, the content of (b) is 0.03 to 0.40 mass% and the content of (c) is 0.02 to 0.30 mass%.

Description

Optical styrene resin composition, molded article and light guide plate

The present invention relates to a styrene resin composition, a molded article and a light guide plate which have excellent hue and transparency, and long-term heat stability.

As a backlight module of a liquid crystal display, there is a direct type backlight module in which a light source is disposed on a front surface of a display device, and a light edge type backlight module in which a light source is disposed on a side surface. The light guide plate is assembled on the edge light type backlight module, and the light from the side is guided to the liquid crystal panel to function, and can be used in a television, a desktop personal computer display, a notebook personal computer, a mobile phone, a car navigation, etc. Used in a wide range of applications. Moreover, the backlight module having a light guide plate can also be used for illumination. The light guide plate has always used an acrylic resin represented by PMMA (polymethyl methacrylate), but has high water absorption, and thus has a problem or a size in which the molded article is bent. A change has occurred.

For this reason, an MS resin which is a copolymer of styrene and methyl (meth) acrylate which has improved these characteristics has been proposed. Patent Document 1 proposes an improved technique such as water absorption of an MS resin and reduction in discoloration during molding.

Patent Document 1 discloses a light guide plate in which a weight average molecular weight (Mw) of a styrene-(meth)acrylate polymer resin is 6 ^to 170,000, a residual monomer amount is 3000 ppm or less, and an amount of oligomer is 2% or less. The water absorbing property is high and the dimensional stability is not as good as the styrene resin which uses a styrene monomer as a raw material.

On the other hand, the styrene-based resin using a styrene-based monomer as a raw material has a low water absorption property, but undergoes thermal discoloration during long-term use, and the molded article is yellowed, resulting in a decrease in transmittance. As a result, the brightness of the backlight module is lowered, and the chromaticity may vary.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-075648

An object of the present invention is to provide a styrene resin composition, a molded article and a light guide plate which have excellent hue and transparency and which have little change in hue and transmittance during long-term use.

The styrene resin composition for optical use according to the present invention, wherein the styrene resin composition is a) a styrene resin having a weight average molecular weight of 150,000 ^to 700,000; and is selected from (B-1) ^to (B-4). (b) a phosphorus-based antioxidant; and (c) a hindered phenol-based antioxidant selected from at least one of (C-1) ^to (C-4), wherein benzene The content of (b) in 100% by mass of the ethylene resin composition is 0.03 ^to 0.40% by mass, and the content of (c) is 0.02 ^to 0.30% by mass.

(B-1) tris(2,4-di-tertiary butylphenyl) phosphite

(B-2) 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus

(B-3) bis(2,4-dicumylphenyl)pentaerythritol diphosphite

(B-4) 3,9-bis(2,6-di-tri-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphospha Snail [5.5] undecane

(C-1) octadecyl-3-(3,5-di-tri-butyl-4-hydroxyphenyl)propionate

(C-2) 3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propanoxy]-1,1-dimethylethyl ]-2,4,8,10-tetraoxaspiro[5.5]undecane

(C-3) ethylene bis(oxyethylene) bis[3-(5-tris-butyl-4-hydroxy-m-tolyl)propionate]

(C-4) pentaerythritol tetrakis[3-(3,5-di-tri-butyl-4-hydroxyphenyl)propionate]

The inventors of the present invention have conducted intensive review to suppress discoloration occurring in long-term use, and it has been found that the use of a phosphorus-based antioxidant and a hindered phenol-based antioxidant can effectively suppress discoloration. However, further research found that the combination of these two antioxidants did not achieve the goal.

Therefore, further studies have found that (1) the phosphorus-based antioxidant has a specific structure, (2) its content is within a specific range, (3) the hindered phenol-based antioxidant has a specific structure, and (4) the content thereof is within a specific range. The styrene resin composition has an extremely high discoloration suppressing effect. The effect of obtaining such an effect is not clear, but the effect can be exerted only when the above four conditions are satisfied at the same time, and therefore it can be considered that these four conditions have a multiplication effect.

Various embodiments of the invention are exemplified below. The various embodiments shown below can be combined with each other.

Preferably, the combination of the (b) phosphorus-based antioxidant and the (c) hindered phenol-based antioxidant is selected from the group consisting of (B-1) and (C-1), (B-1) and (C-2). , (B-1) and (C-3), (B-1) and (C-4), (B-2) and (C-1), (B-2) and (C-4), ( B-3) and (C-1), (B-3) and (C-2), (B-3) and (C-3), (B-3) and (C-4), (B- 4) at least one of (C-1), (B-4) and (C-2), (B-4) and (C-3), (B-4) and (C-4) combinations More preferably, it is selected from (B-1) and (C-1), (B-1) and (C-2), (B-1) and (C-3), (B-1) and ( At least one of C-4), (B-2), and (C-1), (B-2), and (C-4).

Further, the styrene resin is a styrene-(meth)acrylic copolymer resin obtained by copolymerizing a styrene monomer and (meth)acrylic acid, and the content of the styrene monomer unit of the styrene resin 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. Here, the total content of the styrene monomer unit and the (meth)acrylic unit of the styrene resin is 100% by mass.

Further, the styrene resin is a styrene-(meth)acrylate copolymer resin obtained by copolymerizing a styrene monomer and a (meth) acrylate, and a styrene monomer unit of a styrene resin The content is 40.0 ^to 99.0% by mass, and the content of the (meth) acrylate unit is 1.0 ^to 60.0% by mass. Here, the total content of the styrene monomer unit and the (meth) acrylate unit of the styrene resin is 100% by mass.

Further, the content of the hydrophilic additive having a polyether chain is 0.4 ^to 2.0% by mass.

Further, a molded article is composed of the above-mentioned optical styrene resin composition.

Further, a light guide plate is composed of the above-mentioned molded article.

The water absorbing property of the styrene resin composition and molded article of the present invention compared to PMMA or MS resin It is low and inexpensive, has a small change in hue and transmittance during long-term use, and has excellent colorless transparency, and is suitable for optical applications such as a light guide plate. Further, the coloring prevention effect in a high-temperature heat environment such as forming processing is high.

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

<<Styrene resin>>

The styrene resin of the present invention can be obtained by polymerizing a styrene monomer. The styrene monomer refers to styrene, α -methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, ethylstyrene as an aromatic vinyl monomer. Separately, a mixture of two or more kinds of p-tertiary butyl styrene or the like is preferably styrene. Further, the styrene-based monomer may be copolymerized in a range that does not impair the characteristics of the present invention, and examples thereof include an acrylic monomer such as acrylic acid or methacrylic acid, a vinyl cyanide monomer such as acrylonitrile or methacrylonitrile, and acrylic acid. Acrylic monomers such as butyl ester, ethyl acrylate, methyl acrylate, methyl methacrylate, or α ,β-ethylenically unsaturated carboxylic acids such as maleic anhydride and fumaric acid, phenylmaleimide, cyclohexyl A quinone imine monomer such as 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 may be 90 to 99.95% by mass. Selected as 95~99.95 mass%. Specifically, the ratio of the styrene-based resin is, for example, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, and 99.95 mass%, and may be any of the numerical values exemplified herein. Within a range of values.

When a styrene-based (meth)acrylic copolymer resin obtained by copolymerizing a styrene-based monomer and (meth)acrylic acid as a styrene-based resin, it was experimentally confirmed that a styrene-based monomer of a styrene-based resin The content of the unit is from 90.0 to 99.9% by mass, and the content of the (meth)acrylic unit is from 0.1 to 10.0% by mass. Here, the total content of the styrene monomer unit and the (meth)acrylic unit is 100% by mass. (Meth)acrylic acid means acrylic acid, methacrylic acid, etc., and methacrylic acid is preferable here.

The measurement of the (meth)acrylic acid unit content in the styrene resin was carried out at room temperature. 0.5 g of a styrene-based resin was weighed and dissolved in a mixed solution of toluene/ethanol = 8/2 (volume ratio), and then neutralized and titrated with a 0.1 mol/L potassium hydroxide ethanol solution to detect the end point, according to hydrogen. The amount of the potassium oxide ethanol solution used was calculated from the mass basis of the (meth)acrylic acid unit. Here, the measurement can be performed by using an electric potential automatic titrator and using AT-510 manufactured by Kyoto Electronics Industry Co., Ltd. The content of the (meth)acrylic acid unit in the styrene resin can be adjusted by the composition ratio of the styrene monomer and the (meth)acrylic monomer which are raw materials in the polymerization of the styrene resin, but it is also compatible. The styrene resin containing a (meth)acrylic acid unit and the styrene-based resin containing no (meth)acrylic acid unit were mixed in the range of adjustment.

As a styrene resin, a styrene monomer and a (meth) acrylate are copolymerized. In the case of the olefin-(meth) acrylate copolymer resin, it was confirmed by experiments that the content of the styrene monomer unit of the styrene resin was 40.0 to 99.0% by mass, and the content of the (meth) acrylate unit was 1.0~. The object of the present invention can also be attained at 60.0% by mass. Here, the total content of the styrene monomer unit and the (meth) acrylate unit is 100% by mass. The (meth) acrylate is a methacrylate such as methyl methacrylate or ethyl methacrylate, or an acrylate such as methyl acrylate or ethyl acrylate.

The content of the (meth) acrylate unit in the styrene resin can be measured by a pyrolysis gas chromatograph under the following conditions.

Pyrolysis furnace: PYR-2A (made by Shimadzu Corporation)

Pyrolysis furnace temperature setting: 525 ° C

Gas Chromatograph: GC-14A (made by Shimadzu Corporation)

Column: 3mm diameter × 3m made of glass

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 view of quality and productivity, a bulk polymerization method or a solution polymerization method is preferred, and continuous polymerization is preferred. 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.

When the styrene resin is polymerized, a polymerization initiator or a chain transfer agent may be used as needed. As the polymerization initiator, a radical polymerization initiator is preferred, and a conventionally known one may be mentioned, for example, 1,1-di(tri-butylperoxy)cyclohexane (1,1-di(t-butylperoxy). Cyclohexane), 2,2-di(t-butylperoxy)butane, 2,2-di(4,4-di-tertiary butyl) 1,2-di(4,4-di-t-butyl peroxy cyclohexylpropane), 1,1-di(tert-amylperoxy)cyclohexane (1,1- Hydroperoxides such as di(t-amyl peroxy)cyclohexane), hydroperoxides such as Cumene hydroperoxide and t-butyl hydroperoxide, Alkyl peroxides such as t-Butyl peroxyacetate and t-amyl (peroxy isononanoate), tertiary butyl peroxide T-butyl cumyl peroxide, Di-t-butyl peroxide, Dicumyl peroxide, Di-t-hexyl peroxide Such as dialkyl peroxides, t-butylperoxy acetate, tertiary butyl peroxygen Peroxy esters such as t-butyl peroxybenzoate, t-butyl peroxyisopropylmonocarbonate, t-butylperoxy isopropyl Peroxycarbonate such as carbonate, polyether tetrakis (t-butyl peroxy carbonate), N,N'-azobis(cyclohexane-1- N,N'-azobis(cyclohexane-1-carbonitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile), N,N'-azobis[2-(hydroxyl) Alkylonitrile] (N, N'-azobis [2-(hydroxymethyl)propionitrile]), etc., may be used alone or in combination of two or more. The chain transfer agent may, for example, be an aliphatic thiol, an aromatic thiol, pentaphenylethane, an α-methylstyrene dimer or a terpinolene.

In the case of the continuous polymerization, the polymerization reaction is first controlled by a polymerization step by adjusting the polymerization temperature or the like in order to achieve the target molecular weight, the molecular weight distribution, and the reaction conversion rate by using a known fully mixed tank type stirred tank or a column type reactor. The polymerization solution containing the polymer of the polymerization step is transferred to a devolatilization step to remove unreacted monomers and a polymerization solvent. The devolatilization step is constituted by a vacuum devolatilization tank with a heater, a devolatilizing extruder with a vent hole, and the like. The molten state polymer in the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded into a strand shape from a porous die, and processed into a pellet shape by a cold solution method, an air thermal cutting method, or an underwater hot cutting method.

The styrene resin of the present invention has a weight average molecular weight of 150,000 to 700,000, preferably 160,000 to 700,000, and preferably 160,000 to 400,000 or 180,000 to 500,000. If it is less than 150,000, the strength of the molded article becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin can be controlled by the reaction temperature in the polymerization step, the residence time, the type and amount of the polymerization initiator, the type and amount of the chain transfer agent, the type and amount of the solvent used in the polymerization, and the like.

The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured by gel permeation chromatography (GPC) under the following conditions.

GPC type: Shodex GPC-101, manufactured by Showa Denko Co., Ltd.

Column: PLgel 10μm MIXED-B manufactured by Polymer Labs

Mobile phase: tetrahydrofuran

Sample concentration: 0.2% by mass

Temperature: furnace temperature 40 ° C, injection port 35 ° C, detector 35 ° C

Detector: differential refractometer

The molecular weight is a value calculated by calculating the molecular weight of each elution time based on the elution curve of monodisperse polystyrene and calculating the molecular weight in terms of polystyrene.

<<Phosphorus antioxidants. Hindered Phenolic Antioxidants >>

The styrene resin composition contains (b) a phosphorus-based antioxidant and/or (c) a hindered phenol-based antioxidant, and the content of (b) in 100% by mass of the styrene resin composition is 0.03 to 0.40% by mass. The content of (c) is 0.02 to 0.30% by mass. Preferably, the content of (b) is 0.05 to 0.40% by mass, and the content of (c) is 0.02 to 0.20% by mass. More preferably, the content of (b) is from 0.10 to 0.25 mass%, and the content of (c) is from 0.05 to 0.15 mass%. When the content of (b) and (c) is outside the above range, long-term heat stability is deteriorated. The long-term thermal stability shows a change in color tone and transmittance due to heat during long-term use, and a change in color tone and transmittance of the styrene-based resin composition excellent in thermal stability is small. The long thermal stability can be evaluated by accelerating the test, and the molded article is stored under high temperature conditions (60 to 90 ° C) in which the resin is not deformed, and the change in color tone and transmittance is measured with time. The content of the phosphorus-based antioxidant in 100% by mass of the styrene resin composition is specifically 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. The mass % may be a value within any two of the numerical values exemplified herein. The content of the hindered phenol-based antioxidant in 100% by mass of the styrene resin composition is specifically 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, for example. % may also be a value within any two of the numerical values exemplified herein.

The phosphorus-based antioxidant refers to a phosphite of a trivalent phosphorus compound, and the hindered phenol-based antioxidant refers to an antioxidant having a phenolic hydroxyl group in the basic skeleton. There are many compounds which can be used as a phosphorus-based antioxidant or a hindered phenol-based antioxidant. However, the inventors of the present invention have experimentally found that at least one selected from the group consisting of (B-1) ^to (B-4) shown below is used. When the phosphorus-based antioxidant is combined with at least one of the hindered phenol-based antioxidants selected from the following (C-1) ^to (C-4), the discoloration preventing performance of the styrene-based resin composition is particularly effective.

(B-1) tris(2,4-di-tertiary butylphenyl) phosphite

(B-2) 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus

(B-3) bis(2,4-dicumylphenyl)pentaerythritol diphosphite

(B-4) 3,9-bis(2,6-di-tri-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphospha Snail [5.5] undecane

(C-1) octadecyl-3-(3,5-di-tri-butyl-4-hydroxyphenyl)propionate

(C-2) 3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propanoxy]-1,1-dimethylethyl ]-2,4,8,10-tetraoxaspiro[5.5]undecane

(C-3) ethylene bis(oxyethylene) bis[3-(5-tris-butyl-4-hydroxy-m-tolyl)propionate]

(C-4) pentaerythritol tetrakis[3-(3,5-di-tri-butyl-4-hydroxyphenyl)propionate]

The method of adding the phosphorus-based antioxidant and the hindered phenol-based antioxidant is not particularly limited, and a method of adding and mixing by a polymerization step, a devolatilization step, or a granulation step using a styrene resin; A method of adding and mixing an extruder or the like during molding, and a method of diluting and mixing a resin composition adjusted to a high concentration of a hydrophilic additive into a target content by a styrene-based resin which is not added.

<<Other additives>>

In the styrene resin composition, mineral oil may be contained in a range that does not affect the colorless transparency of the present invention. Further, it may contain an internal lubricant such as stearic acid or ethylene bis-stearate, a sulfur-based antioxidant, a lactone-based antioxidant, a hindered amine-based stabilizer, an ultraviolet absorber, an antistatic agent, and external lubrication. Additives such as agents. Further, as the external lubricant, ethylene bis-stearate is preferred, and it is preferably 30 to 200 ppm in the resin composition.

The ultraviolet absorber is a UV absorber having a function of suppressing deterioration or coloration by ultraviolet rays, and examples thereof include a benzophenone type, a benzotriazole type, a triazine type, a benzoate type, and a salicylate. A UV absorber such as a cyanoacrylate, an oxalic acid aniline, a malonate or a formazan. These may be used alone or in combination of two or more kinds, or a light stabilizer such as a hindered amine may be used in combination.

The styrene-based resin obtained by polymerizing a styrene-based monomer may have white turbidity in an environmental change such as temperature, humidity, or warm water immersion, but copolymerization of a styrene monomer and (meth)acrylic acid The obtained styrene-(meth)acrylic copolymer resin or the styrene-(meth)acrylate copolymer resin obtained by copolymerizing a styrene monomer and a (meth) acrylate can prevent white turbidity. Further, in the case where the styrene resin composition contains a hydrophilic additive having a polyether chain, it is possible to prevent white turbidity. Here, a method of changing the kind of the styrene resin and a method of adding the hydrophilic additive may be used in combination.

The styrene resin has a problem of white turbidity (whitening phenomenon) of the molded article due to environmental changes such as temperature or humidity and warm water immersion (Journal of Fiber Society, Vol. 34, No. 6, pp. 245-253, 1978). The transparency is damaged depending on the application. Specifically, when the molded article is exposed to a high temperature and high humidity environment to a room temperature environment, or when the temperature changes from a room temperature environment to a low temperature environment, the water uniformly present in the styrene resin becomes unstable and phase separation occurs. As a result, a disk-shaped defect is generated, and as a result, white turbidity appears inside the molded article. In addition, when the molded article of the styrene resin is immersed in hot water for a predetermined period of time or more, whitening occurs when the molded article is taken out, which is also caused by the above mechanism.

Benzene-(meth)acrylic copolymer resin obtained by copolymerizing a styrene-based monomer and (meth)acrylic acid as a styrene-based resin as a method of preventing the turbidity of the molded product due to environmental changes The content of the styrene monomer unit of the vinyl resin is from 90.0 ^to 99.2% by mass, the content of the (meth)acrylic acid unit is preferably from 0.8 ^to 10.0% by mass, and the content of the (meth)acrylic unit is from 0.8 ^to 4.5% by mass. For better, 1.8 ^to 3.0% by mass is the best. Here, the total content of the styrene monomer unit and the (meth)acrylic unit is 100% by mass. (Meth)acrylic acid means acrylic acid, methacrylic acid, etc., and methacrylic acid is preferable here. If the content of the (meth)acrylic acid unit is less than 0.8% by mass, the whitening suppressing effect is insufficient. When the ratio exceeds 10.0% by mass, the initial hue and transmittance are likely to deteriorate.

When a styrene-based (meth) acrylate copolymer resin obtained by copolymerizing a styrene-based monomer and a (meth) acrylate is used as a styrene-based resin as a method for preventing the turbidity of the molded product due to environmental changes, The styrene resin has a styrene monomer unit content of 40 ^to 96% by mass, the (meth) acrylate unit content of 4 ^to 60% by mass, and the (meth) acrylate unit content of 4 ^~ 15% by mass is more preferable, 6 ^to 12% by mass is more preferable, and 7 ^to 9% by mass is more preferable. Here, the total content of the styrene monomer unit and the (meth) acrylate unit is 100% by mass. The (meth) acrylate is a methacrylate such as methyl methacrylate or ethyl methacrylate, or an acrylate such as methyl acrylate or ethyl acrylate. If the content of the (meth) acrylate unit is less than 4% by mass, the whitening suppressing effect is insufficient. Further, when it exceeds 60.0% by mass, the water absorbability is likely to deteriorate. Further, an increase in the content of the (meth) acrylate unit tends to lower the fluidity, and in applications requiring high fluidity such as injection molding, the moldability is likely to be lowered.

The hydrophilic additive refers to a compound having a hydrophilic group capable of interacting (hydrogen bonding) with water. The hydrophilic group is preferably a polyether chain. The polyether chain is a skeleton structure in which an ether bond is bonded, and examples thereof include a polyoxyethylene chain and a polyoxypropylene synthesized by an addition reaction of an alkylene oxide such as ethylene oxide, propylene oxide or butylene oxide. A chain, a polyoxybutylene chain, or a polyglycerol chain synthesized by dehydration condensation of glycerin or the like, preferably a polyoxyethylene chain. The polyether chain may have one group or more groups in one molecule.

Examples of the hydrophilic additive having a polyether chain include a polyoxyethylene type nonionic surfactant, a polyoxyethylene type anionic surfactant, a polyoxyethylene type cationic surfactant, and a polyoxyethylene type amphiphilic. A polyoxyethylene surfactant such as a surfactant or polyethylene glycol. The polyoxyethylene type surfactant is preferably a polyoxyethylene type nonionic surfactant.

The polyoxyethylene type nonionic surfactant may, for example, be a polyoxyethylene alkyl ether represented by the following formula (1) or a polyoxyethylene fatty acid ester represented by the following formula (2) or a polyoxyethylene cured product. Sesame oil, polyoxyethylene The sorbitan fatty acid ester and the polyoxyethylene sorbitan fatty acid ester are preferably one or more selected from the group consisting of polyoxyethylene alkyl ethers and/or polyoxyethylene fatty acid esters. Further, even a polyvalent polyoxyethylene alkyl ether having a plurality of polyoxyethylene alkyl ether skeletons in one molecule or a polyvalent polyoxyethylene fatty acid having a plurality of polyoxyethylene fatty acid ester skeletons in one molecule is used. Esters can also achieve the objects of the present invention. The valence of the polyoxyethylene alkyl ether and the polyoxyethylene fatty acid ester means the number of the polyoxyethylene alkyl ether skeleton or the polyoxyethylene fatty acid ester skeleton present in one molecule.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms. Further, it may be a polyvalent polyoxyethylene alkyl ether having a plurality of polyoxyethylene alkyl ether skeletons having a hexavalent number, or may have a plurality of A polyvalent polyoxyethylene fatty acid ester of a polyoxyethylene fatty acid ester skeleton having a valence of six. N is an integer and represents the number of moles of addition of an ethylene oxide unit.

Polyoxyethylene alkyl ether is obtained by adding ethylene oxide and alcohol, and polyoxyethylene fatty acid ester is obtained by adding ethylene oxide with fatty acid or directly esterifying fatty acid and polyethylene glycol. The average addition mole number of oxyethane is preferably from 7 to 100, more preferably from 10 to 50.

The average molecular weight of polyethylene glycol is preferably from 200 to 10,000. 200~4000 is better, 300~1000 is the best. If the average molecular weight of the polyethylene glycol is less than 200, gas is generated during the molding process, and the mold or the roll is contaminated, which is not preferable. In addition, when it is more than 10,000, the effect of preventing the whitening phenomenon tends to be lowered, and the compatibility with the styrene resin is lowered, and the styrene resin composition and the molded article thereof are reduced. It produces white turbidity. The average molecular weight is a value calculated based on the concentration of a hydroxyl group (based on JIS K1557) measured by a phthalic anhydride pyridine method.

Examples of the hydrophilic additive having a polyether chain include dodecyl polyoxyethylene ether, hexadecyl polyoxyethylene ether, octadecyl polyoxyethylene ether, and octyldodecyl polyoxyl. Alkyl polyoxyethylene ether such as vinyl ether, tetradecyl polyoxyethylene ether or 2-ethylhexyl polyoxyethylene ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan tri-hard Polyoxyethylene sorbitan fatty acid ester such as fatty acid, polyoxyethylene sorbitan fatty acid ester such as polyoxyethylene sorbitol tetraoleate, polyethylene glycol monolaurate, polyethylene glycol Polyoxyethylene fatty acid esters such as monostearate, polyethylene glycol distearate, polyethylene glycol monooleate, polyoxyethylene cured castor oil, polyethylene glycol, polyoxyethylene monomethyl Ether, polyoxyethylene dimethyl ether, polyoxyethylene glyceryl ether, polyoxyethylene tetraoleate, polyoxyethylene triisostearate, polyoxyethylene coconut fatty acid glyceride, diglycerin, polyglycerol, poly Oxyethylene glyceryl ether, polyglycerin fatty acid ester, and the like.

The hydrophilic additive having a polyether chain preferably has an HLB value of 8 or more, more preferably 10 to 20. The HLB (Hydrophilic-lipophilic blance) value is a value indicating the hydrophilicity of the additive, and if the HLB value is 8 to 10, it is stably dispersed in water, and if it exceeds 10, it is changed from a dispersed state having a transparent feeling to a state of being completely transparent and transparent. . In the nonionic surfactant having a polyether chain, the HLB value = (molecular weight of the hydrophilic group portion) / (molecular weight of the additive) × 20 is calculated, and the hydrophilic additive HLB such as an alkane having no hydrophilic group is calculated. The value is 0. For polyethylene glycol having only a hydrophilic group, the HLB value is 20, and for the nonionic surfactant, the HLB value is between 0 and 20.

The hydrophilic additive having a polyether chain preferably has a heating loss of 10% by mass or less at a temperature of 200 ° C in a nitrogen atmosphere. The heating loss at a temperature of 200 ° C under a nitrogen atmosphere can be obtained by thermogravimetric analysis (TGA), and is heated from a room temperature state at a temperature increase rate of 10 ° C / min under a nitrogen atmosphere, and a weight loss at a temperature of 200 ° C. Seek. The additive having a heating loss of more than 10% by mass in a nitrogen atmosphere at a temperature of 200 ° C has high volatility and generates gas during molding processing of the styrene resin, which may contaminate the mold and the roll.

The content of the hydrophilic additive having a polyether chain in 100% by mass of the styrene resin composition is 0.4 to 2.0% by mass, preferably 0.7 to 1.6% by mass. When the content of the hydrophilic additive having a polyether chain is less than 0.4% by mass, it is difficult to prevent whitening caused by environmental changes, and the heat resistance of the styrene resin composition is lowered beyond 2.0% by mass.

The method of adding the hydrophilic additive having a polyether chain is not particularly limited, and examples thereof include a method of adding and mixing by a polymerization step, a devolatilization step, and a granulation step of a styrene resin, and an extruder using a molding process. A method of adding a mixture; a method of diluting and mixing a resin composition adjusted to a high concentration of a hydrophilic additive into a target content by a styrene-based resin which is not added.

For example, a styrene resin composition containing 0.5 to 50.0% by mass of a hydrophilic additive and a non-added styrene resin are mixed by an extruder or an injection molding machine to obtain a styrene system having a target concentration. A method of a resin composition, a molded article, and a light guide plate.

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

When the molded article having a thickness of 4 mm is formed as the haze of the styrene resin composition of the present invention, 5% or less is preferable, and 1% or less is more preferable.

The styrene resin composition of the present invention can be obtained by various molding methods such as injection molding, extrusion molding, compression molding, and blow molding according to the purpose, and the shape thereof is not limited. For example, when a plate-shaped molded article is used, it can be processed into a light guide plate or the like. The obtained molded article can be used as an optical member that transmits light to the inside of a molded article such as a light guide plate. An optical member such as a light guide plate has a long light transmission distance (optical path length), and therefore a material having a high transmittance and an excellent hue is suitably used. The initial transmittance of the optical path length of 115 mm is 84% or more, and the YI value of 7.0 or less is preferable. Further, after storage for 1000 hours at a temperature of 80 ° C, the difference between the value and the initial value is preferably 3.0 or less, and more preferably 1.5 or less.

The transmittance and YI value of the optical path length of 115 mm were measured by the following procedure. Using pellets of a styrene resin composition, injection molding was carried out 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 for evaluating long-term heat stability was stored in an oven temperature of 80 ° C for 1,000 hours. Next, a test piece having a thickness of 115 × 85 × 3 mm was cut out from the plate-shaped molded article, and the end surface was polished by polishing to obtain a plate-shaped molded article having a mirror surface on the end surface. For the plate-shaped molded product after polishing, an ultraviolet visible spectrophotometer V-670 manufactured by JASCO Corporation was used to measure a wavelength of 350 nm at an optical path length of 115 mm under incident light having a size of 20 × 1.6 mm and a diffusion angle of 0°. The spectral transmittance at 800 nm was calculated according to JIS K7105, and the YI value at a viewing angle of 2° of the C light source was calculated. Here, the transmittance indicates an average transmittance of a wavelength of 380 nm to 780 nm.

The light guide plate receives light from an end surface (side surface) of the plate-shaped molded article, and guides the light to the front surface (light-emitting surface) of the molded article according to a reflection pattern formed on the rear surface of the molded article (non-light-emitting surface), and causes the surface to emit light. Parts. The reflection pattern can be formed by a method such as a screen printing method, an injection molding method, a laser method, or an inkjet method. When the plate-shaped molded article is processed into a light guide plate, it is preferable to polish the incident surface or the entire end surface of the light to form a mirror surface. Further, in order to improve the uniformity of the emitted light, a prism pattern or the like may be provided on the front surface (light emitting surface) of the plate-shaped molded article. The front or rear pattern of the plate-shaped molded article can be formed at the time of forming a plate-shaped molded article, for example, a mold shape if it is injection-molded, and a pattern by roll transfer or the like if it is extrusion molding.

[Examples]

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

<<Test 1>> (Manufacture of styrene resin PS-1 ^~ PS-3)

The first reactor and the second reactor as a completely mixed agitation tank and the third reactor as a piston type flow reactor with a static mixer are connected in series to form a polymerization step, as shown in Table 1. The production of the styrene resin was carried out under the conditions shown. The capacities of the respective reactors were 39 liters in the first reactor, 39 liters in the second reactor, and 16 liters in the third reactor. The raw material solution was prepared using the raw material compositions described in Table 1, and the raw material solution was continuously supplied to the first reactor at the flow rate shown in Table 1. At the inlet of the first reactor, a polymerization initiator was added to the raw material solution so as to have an additive concentration (concentration based on the total amount of the raw material styrene and methacrylic acid) described in Table 1, and uniformly mixed. The polymerization initiator described in Table 1 is as follows: polymerization initiator-1: 2,2-bis(4,4-tributylperoxycyclohexyl)propane (PATORA A manufactured by Nippon Oil Co., Ltd.).

Polymerization initiator-2: 1,1-di(tri-butylperoxy)cyclohexane (using PERHEXA C manufactured by Nippon Oil Co., Ltd.)

Here, in the third reactor, a temperature gradient is generated along the flow direction, and the intermediate portion and the outlet portion are adjusted so as to have the temperature of Table 1.

Next, the polymer-containing solution continuously taken out by the third reactor was introduced into a vacuum devolatilization tank having a preheater consisting of two stages connected in series, and the preheating was adjusted so as to have the resin temperature shown in Table 1. The temperature of the heat exchanger was adjusted according to the pressure shown in Table 1, and the unreacted styrene and ethylbenzene were separated, and then extruded into a strand shape by a porous die, and the strands were cooled and cut by a cold solution method. , granulation.

(Examples 1-1 ^to 1-30, Comparative Examples 1-1 ^to 1-10)

Using a uniaxial extruder having a screw diameter of 40 mm, the styrene resins PS-1, PS-2, PS-3 and B and C as additives were at a cylinder temperature of 230 ° C at a content shown in Table 2, Screw speed 100rpm The mixture is melted and melted to obtain granules. The additives B and C used in Table 2 are shown below. Here, the additive B represents (b) a phosphorus-based antioxidant, and the additive C represents (c) a hindered phenol-based antioxidant.

B-1: Tris(2,4-di-tertiary butylphenyl) phosphite (Irgafos 168, manufactured by BASF Japan Co., Ltd.)

B-2: 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus (ADKSTAB HP-10, manufactured by ADEKA) )

B-3: bis(2,4-dicumylphenyl)pentaerythritol diphosphite (Doverphos S-9228, manufactured by Dover Chemical Corporation)

B-4: 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphorane [5.5] Undecane (ADKSTAB PEP-36 manufactured by ADEKA Co., Ltd.)

B-5: tetrakis(2,4-di-tert-butylphenyl)[1,1'-biphenyl]-4,4 diphosphonate (Hostanox P- by Clariant Co. Ltd.) EPQ)

B-6: ethyl bis(2,4-di-tertiarybutyl-6-methylphenyl)phosphite, (Irgafos 38, manufactured by BASF Japan Co., Ltd.)

B-7: Diphenyl-2-ethylhexyl phosphite (ADKSTAB C manufactured by ADEKA Co., Ltd.)

B-8: Triisodecyl phosphite (ADKSTAB 3010, manufactured by ADEKA Co., Ltd.)

B-9: cyclopentane tetrakis(bis(2,4-di-tert-butylphenylphosphite) (ADKSTAB PEP-8, manufactured by ADEKA)

C-1: octadecyl-3-(3,5-di-tri-butyl-4-hydroxyphenyl)propionate (Irganox 1076, manufactured by BASF Japan Co., Ltd.)

C-2: 3,9-bis[2-[3-(3-tri-butyl-4-hydroxy-5-methylphenyl)propanoxy]-1,1- Dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane (ADKSTAB AO-80, manufactured by ADEKA)

C-3: ethylenebis(oxyethylene)bis[3-(5-tris-butyl-4-hydroxy-m-tolyl)propionate] (Irganox 245, manufactured by BASF Japan Co., Ltd.)

C-4: pentaerythritol tetrakis[3-(3,5-di-tri-butyl-4-hydroxyphenyl)propionate] (Irganox 1010, manufactured by BASF Japan Co., Ltd.)

C-5: 1,1,3-tris(2-methyl-4-hydroxy-5-tributylphenyl)butane (ADKSTAB AO-30, manufactured by ADEKA Co., Ltd.)

C-6: 4,4'-butylene bis(3-methyl-6-tertiary butylphenol) (ADKSTAB AO-40, manufactured by ADEKA Co., Ltd.)

C-7: 2-methyl-4,6-bis(dodecylthiomethyl)phenol (Irganox 1726, manufactured by BASF Japan Co., Ltd.)

Further, using the obtained pellets, injection molding was carried out 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 heat stability, the obtained molded article was stored in an oven temperature of 80 ° C for 1,000 hours. In order to evaluate the optical properties of the initial molded product before storage and the molded product after storage, 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 polishing to prepare a plate having a mirror surface at the end surface. Shaped product. For the plate-shaped molded product after polishing, an ultraviolet visible spectrophotometer V-670 manufactured by JASCO Corporation was used to measure a wavelength of 350 nm at an optical path length of 115 mm under incident light having a size of 20 × 1.6 mm and a diffusion angle of 0°. The spectral transmittance at 800 nm was calculated according to JIS K7105, and the YI value at a viewing angle of 2° of the C light source was calculated. The transmittance shown in Table 2 is an average transmittance indicating a wavelength of 380 nm to 780 nm.

Next, the ΔYI difference is calculated based on the following formula. In the following formula, "without an additive" means a case where neither the additive B nor the additive C is added, and "the additive" means a case where at least one of the additive B and the additive C is added. Here, the examples, comparative examples, and reference examples are collectively referred to as "test examples."

△ YI value after heating = ("YI value after 80 ° C * 1000 hours" in the test example with additives") - "YI value after 80 ° C * 1000 hours in the test example without additives")

In one example, in Example 1-1 having an additive, the YI value after 80 ° C * 1000 hours was 7.0, and in Reference Example 1-1 in which the type of the styrene resin composition was the same, after 80 ° C * 1000 hours The YI value was 11.6. Therefore, the "YI value after Δ heating" of Example 1-1 was -4.6. This value indicates the degree of the discoloration preventing effect after the addition of the additive B and the additive C, and the smaller the value, the larger the effect.

Further, based on the YI value after Δ heating, and according to the following criteria, the examples. The comparative example was ranked.

S: △ YI value after heating -4.0

A:-4.0 △YI value after heating -3.5

B:-3.5 △YI value after heating -2.5

C:-2.5 △YI value after heating

Table 2 shows the characteristics and evaluation results of the respective resin compositions.

【Table 2】

In the molded article of the example, the initial transmittance and the YI value were excellent, and the amount of change in YI after storage at 80 ° C for 1,000 hours was small, and the long-term thermal stability was also excellent. Further, (1) the phosphorus-based antioxidant has a specific structure, (2) the content thereof is within a specific range, (3) the hindered phenol-based antioxidant has a specific structure, and (4) the content thereof is within a specific range, the styrene system The discoloration suppressing effect of the resin composition is extremely high. Further, from Examples 1-13 and 1-14, it is understood that the styrene-based resin can be obtained in the same manner as the styrene-(meth)acrylic copolymer resin or the styrene-(meth)acrylate copolymer resin. effect.

<<Test 2>> (Example 2-1 ^~ 2-26)

The first reactor and the second reactor as a completely mixed agitation tank and the third reactor as a piston type flow reactor with a static mixer are connected in series to form a polymerization step, as shown in Table 1. The conditions 1 shown are the manufacture of a styrene resin. The capacities of the respective reactors were 39 liters in the first reactor, 39 liters in the second reactor, and 16 liters in the third reactor. The raw material solution was prepared using the raw material composition described in Condition 1 of Table 1, and the raw material solution was continuously supplied to the first reactor at the flow rate shown in Table 1.

Further, at the inlet of the third reactor, the hydrophilic additive D having a polyether chain was added so as to have the kind and content shown in Table 3. The types of additives and polyethylene glycols used are as follows.

D-1: polyethylene glycol having an average molecular weight of 400 (PEG#400 manufactured by Nippon Oil Co., Ltd.)

D-2: polyethylene glycol having an average molecular weight of 1000 (PEG#1000 manufactured by Nippon Oil Co., Ltd.)

D-3: polyethylene glycol having an average molecular weight of 2,000 (PEG#2000 manufactured by Nippon Oil Co., Ltd.)

D-4: vinyl dodecyl polyoxyethylene ether ethylene oxide average addition mole number = 25 (Kao EMULGEN 123P)

D-5: vinyl dodecyl polyoxyethylene ether, ethylene oxide average addition mole number = 12 (EMULGEN 320P, manufactured by Kao Corporation)

D-6: Vinyl lauryl polyoxyethylene ether, ethylene oxide average addition mole number = 9 (EMULGEN 109P, manufactured by Kao Corporation)

D-7: Ethylene lauryl polyoxyethylene ether, ethylene oxide, average addition mole number = 30 (EMULGEN 130K, manufactured by Kao Corporation)

D-8: Polyethylene glycol monolaurate Ethylene oxide average addition mole number = 12 (Malay Co., Ltd. EMANON 1112)

Next, the polymer-containing solution continuously taken out to the third reactor is introduced into a vacuum devolatilization tank having a preheater consisting of two stages connected in series, and the unreacted styrene and ethylbenzene are separated and then extruded. After being stranded and cooled, the cut was made to form pellets. Here, the resin temperature in the devolatilization tank of the first stage is set to 160 ° C, the pressure of the vacuum devolatilization tank is 65 kPa, and the resin temperature in the devolatilization layer of the second stage is set to 235 ° C, and the pressure of the vacuum devolatilization tank It is 0.8 kPa.

The weight average molecular weight (Mw) of the obtained styrene resin was 370,000.

Next, the styrene resin pellets and the additives B and C obtained by the above-described contents shown in Table 3 were melt-blended at a cylinder temperature of 230 ° C and a screw rotation speed of 100 rpm using a single-axis extruder having a screw diameter of 40 mm. Refining to obtain granules. The labels of the additives B and C used in Table 3 were the same as those shown in Test 1.

In addition, the melt mass flow rate (MFR) is measured according to JIS K 7210 under the conditions of 200 ° C and 49 N load, and the Vicat softening temperature is according to JIS K 7206, at a heating rate of 50 ° C / hr, and a test load of 50 N. The measurement was carried out. The transmittance and YI values were measured by the method as in Test 1.

Further, in order to confirm the whitening phenomenon caused by the environmental change, the plate-shaped molded article having the mirror surface on the end surface was exposed to an environment of 60° C. and 90% relative humidity for 150 hours, and the test piece was taken out at 23° C. and 50% relative humidity. The whitening phenomenon generated inside the molded article was observed, and the whitening suppression effect was determined as follows.

◎: no whitening at all

○: A little whitening after taking out for 1 hour, but disappearing after 24 hours

△: whitening after taking out for 1 hour, but almost disappeared after 24 hours

×: Significantly whitened after taking out for 1 hour, even if it does not disappear after 24 hours

Table 3 shows the characteristics and evaluation results of the respective resin compositions.

The molded articles of Examples 2-1 ^to 2-23 have an excellent whitening suppressing effect, and the initial transmittance and YI value are also excellent, and the amount of change in YI after storage at 80 ° C for 1000 hours is small, and long-term heat stability is also outstanding. On the other hand, Examples 2-24 ^to 2-25 may be because the hydrophilic additive D was not added, or the amount added was too small, so whitening occurred. Further, in Examples 2 to 26, since the amount of the hydrophilic additive D added was too large, the heat resistance was lowered.

<<Trial 3>> (Production Example of Styrene Resin A-1 ^to 7)

The first reactor and the second reactor as a complete mixing type agitation tank and the third reactor as a piston type flow reactor with a static mixer are connected in series to form a polymerization step, as shown in Table 4. The production of the styrene resin was carried out under the conditions shown. The capacities of the respective reactors were 39 liters in the first reactor, 39 liters in the second reactor, and 16 liters in the third reactor. The raw material solution was prepared using the raw material compositions described in Table 4, and the raw material solution was continuously supplied to the first reactor at the flow rate shown in Table 4. At the inlet of the first reactor, a polymerization initiator was added to the raw material solution so as to have an additive concentration (concentration based on the total amount of the raw material styrene and methacrylic acid) described in Table 4, and uniformly mixed. The polymerization initiator described in Table 4 is as follows: a polymerization initiator - 1:1, 1-di(tertiary butylperoxy)cyclohexane (using PERHEXA C manufactured by Nippon Oil Co., Ltd.).

Here, in the third reactor, a temperature gradient is generated along the flow direction, and the intermediate portion and the outlet portion are adjusted so as to have temperatures of Table 4.

Next, the polymer-containing solution continuously taken out by the third reactor was introduced into a vacuum devolatilization tank equipped with a preheater consisting of two stages connected in series, and the preheating was adjusted so as to become the resin temperature shown in Table 4. The temperature of the heat exchanger was adjusted according to the pressures shown in Table 4, and the unreacted styrene and ethylbenzene were separated, and then extruded into a strand shape by a porous die, and the strands were cooled by a cold solution method. And cut and granulated.

The content (PMMA amount) of the methyl (meth) acrylate unit in the styrene resin can be measured by a pyrolysis gas chromatograph under the following conditions.

Pyrolysis furnace: PYR-2A (made by Shimadzu Corporation)

Pyrolysis furnace temperature setting: 525 ° C

Gas Chromatograph: GC-14A (made by Shimadzu Corporation)

Column: 3mm diameter × 3m made of glass

Filler: FFAP Chromsorb WAW 10%

Injection, detector temperature: 250 ° C

Column temperature: 120 ° C

Carrier gas: nitrogen

The melt mass flow rate (MFR) is measured according to JIS K 7210 under the conditions of 200 ° C and 49 N load. The Vicat softening temperature is measured according to JIS K 7206 at a heating rate of 50 ° C / hr and a test load of 50 N. .

When the water absorption amount is measured, the mass W1 after drying at a temperature of 80 ° C for 24 hours is measured by the above-mentioned plate-shaped molded article, and then the plate-shaped molded article is stored in an environment of 40 ° C and a temperature of 80% relative humidity, after each lapse of a certain period of time. The weight was taken out and measured immediately, and the mass W2 when the weight did not change (saturated state) was measured, and the water absorption amount = (W2-W1) / W2 × 1000000 (ppm). Table 4 shows the characteristics of each styrene resin.

(Examples 3-1 ^to 3-18)

Next, styrene resin A and B and C as additives were melted at a cylinder temperature of 230 ° C and a screw rotation speed of 100 rpm using a uniaxial extruder having a screw diameter of 40 mm as shown in Table 5. Mixing to obtain granules. The labels of B and C of the additives used in Table 5 are the same as those in Test 1.

The transmittance, the YI value, and the whitening suppression effect were measured and evaluated by the method as in Test 2.

Table 5 shows the characteristics and evaluation results of the respective resin compositions.

The molded articles related ^to Examples 3-1 ^to 3-16 having a relatively large content of (meth) acrylate units have an excellent whitening inhibitory effect, and the initial transmittance and YI value are also excellent, and storage is 80 ° C * 1000 hours. The amount of YI change is small and the long-term thermal stability is excellent. On the other hand, Examples 3-17 ^to 3-18 which do not contain a (meth) acrylate unit or have a small content show that the whitening inhibitory effect is insufficient.

[Industrial use possibilities]

The styrene resin composition for optical use and the molded article of the present invention have excellent hue and transparency, and are excellent in long-term thermal stability. In addition, since the whitening phenomenon caused by the environmental change is excellent in transparency and hue, the transparency which is an advantage of the styrene-based resin can be maintained in the use of the whitening phenomenon due to environmental changes, and it can be suitably used. For example, it can be applied to a light guide plate of a television, a desktop personal computer, a notebook personal computer, a mobile phone, a car navigation, or the like.

Claims (8)

A styrene resin composition for optical use comprising a) a styrene resin having a weight average molecular weight of 150,000 ^to 700,000; and at least one selected from the group consisting of (B-1) ^to (B-4) below. (b) a phosphorus-based antioxidant; and (c) a hindered phenol-based antioxidant selected from at least one of the following (C-1) ^to (C-4), (B-1) three (2, 4) -di-tertiary butylphenyl)phosphite, (B-2) 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy) (2-B (hexyloxy)phosphorus, (B-3) bis(2,4-dicumylphenyl)pentaerythritol diphosphite, (B-4) 3,9-bis(2,6-di-tridecyl) (4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, (C-1)octadecyl-3- (3,5-di-tri-butyl-4-hydroxyphenyl)propionate, (C-2)3,9-bis[2-[3-(3-tri-butyl-4-hydroxy-) 5-methylphenyl)propanoxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane, (C-3) Bis(oxyethylene) bis[3-(5-tris-butyl-4-hydroxy-m-tolyl)propionate], (C-4) pentaerythritol tetra[3-(3,5-di-tris) Butyl-4-hydroxyphenyl)propionate], wherein the styrene resin composition is 100% by mass (B) in an amount of 0.03 ^to 0.40 mass%, (c) in an amount of from 0.02 ^to 0.30% by mass. The styrene resin composition for optical use according to the first aspect of the invention, wherein the combination of the (b) phosphorus-based antioxidant and the (c) hindered phenol-based antioxidant is selected from the group consisting of (B-1) and ( C-1), (B-1) and (C-2), (B-1) and (C-3), (B-1) and (C-4), (B-2) and (C-1), (B-2) and (C -4), (B-3) and (C-1), (B-3) and (C-2), (B-3) and (C-3), (B-3) and (C-4 ), (B-4) and (C-1), (B-4) and (C-2), (B-4) and (C-3), (B-4) and (C-4) combinations At least one of the groups. The styrene resin composition for optical use according to the first or second aspect of the invention, wherein the combination of (b) the phosphorus-based antioxidant and the (c) hindered phenol-based antioxidant is selected from (B-1) And (C-1), (B-1) and (C-2), (B-1) and (C-3), (B-1) and (C-4), (B-2) and At least one of C-1), (B-2), and (C-4). The styrene-based resin composition for optical use according to any one of claims 1 to 3, wherein the styrene-based resin is obtained by copolymerizing a styrene-based monomer and (meth)acrylic acid. The styrene-(meth)acrylic copolymer resin, the content of the styrene monomer unit of the styrene resin 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, wherein benzene The total content of the styrene monomer unit and the (meth)acrylic unit of the ethylene resin is 100% by mass. The styrene-based resin composition for optical use according to any one of claims 1 to 3, wherein the styrene resin is obtained by copolymerizing a styrene monomer and a (meth) acrylate. The obtained styrene-(meth)acrylate copolymer resin, the content of the styrene monomer unit of the styrene resin is 40.0 to 99.0% by mass, and the content of the (meth) acrylate unit is 1.0 to 60.0% by mass. The total content of the styrene monomer unit and the (meth) acrylate unit of the styrene resin is 100% by mass. The styrene-based resin composition for optical use according to any one of claims 1 to 3, which contains 0.4 ^to 2.0% by mass of a hydrophilic additive having a polyether chain. A molded article characterized by any one of claims 1 to 6 The optical structure described above is composed of a styrene resin composition. A light guide plate comprising the molded article according to item 7 of the patent application.