Styrene resin composition for optical use, light guide plate, edge light type surface light source unit, light diffusion plate, and direct down type surface light source unit

Abstract

Provided is an optical styrene-based resin composition having excellent transparency, hue, and dimensional stability, and having excellent light stability for long-term use of an LED light source. The present invention provides an optical styrene-based resin composition containing a styrene-based resin (A), which is a copolymer comprising a styrene-based monomer unit and a (meth) acrylic acid ester-based monomer unit, and a hindered amine light stabilizer (B), the copolymer contains 95-20% by mass of the styrene monomer unit and 5-80% by mass of the (meth) acrylic acid ester monomer unit per 100% by mass of the copolymer, and the optical styrene resin composition contains 0.001-1.0 part by mass of the hindered amine light stabilizer (B) per 100 parts by mass of the styrene resin (A).

Description

[0001] This application is a divisional application of the application with the application date of April 27, 2023, the application number of 202380036124.2, and the invention name of "Styrene resin composition for optical use, light guide plate, edge light type surface light source unit, light diffusion plate, and direct type surface light source unit". TECHNICAL FIELD

[0002] The present application relates to a styrene resin composition for optical use, a light guide plate, an edge light type surface light source unit, a light diffusion plate, and a direct type surface light source unit. BACKGROUND

[0003] The backlight of a liquid crystal display device is of a direct type in which a light source is disposed on the front surface of the display device, and an edge light type in which a light source is disposed on the side surface. The edge light type backlight uses a member called a light guide plate that guides light from a light source disposed on the side surface to the front surface of the display device. It is widely used in displays for televisions, desktop personal computers, notebook personal computers, mobile telephones, car navigation systems, and the like. In addition, the backlight using the light guide plate is also used as an illuminating device or a billboard, and the like.

[0004] The light guide plate has a relatively long light transmission distance, and a large light loss in the optical path length, and thus requires a particularly high light transmittance. Therefore, the material of the light guide plate uses an acrylic resin represented by polymethyl methacrylate (PMMA). However, PMMA has a high water absorption, and thus there are cases where the light guide plate warps or changes in size due to water absorption. In addition, it is easily thermally decomposed at the time of molding, and thus if it is molded at a high temperature, there is a problem that the molded body is easily deteriorated in appearance. In order to improve these problems, for example, Patent Literature 1 proposes to use a styrene-(meth) methyl acrylate copolymer as the material of the light guide plate.

[0005] On the other hand, the molded body of the styrene-(meth) methyl acrylate copolymer has a poor color tone compared to PMMA, and when used as a backlight, color unevenness sometimes occurs. In order to improve this problem, as a color tone improvement technique for styrene-(meth) methyl acrylate, Patent Literature 2 is proposed.

[0006] [Related Art Documents]

[0007] [Patent Literature]

[0008] [Patent Literature 1] Japanese Patent Application Laid-Open No. 2003-075648

[0009] [Patent Literature 2] International Publication No. 2016-129675 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] In recent years, with the high resolution of a backlight unit of a television or a display, a high-brightness LED (light-emitting diode) is sometimes used as an edge light source, but the previous styrene-(meth) methyl methacrylate copolymer light guide plate has a problem that the end surface of the light guide plate is deteriorated (carbonized) after a long time of lighting depending on the use environment.

[0012] The present application has been achieved in view of such a problem, and aims to provide a styrene resin composition for optical use which is excellent in transparency, hue, dimensional stability, and light stability for long-term use of an LED light source.

[0013] Solution to the problem

[0014] According to the present application, a styrene resin composition for optical use is provided, which contains a styrene resin (A) that is a copolymer containing a styrene monomer unit and a (meth) acrylate monomer unit, and a hindered amine light stabilizer (B), and the copolymer contains 95 to 20 mass% of the styrene monomer unit and 5 to 80 mass% of the (meth) acrylate monomer unit in 100 mass% of the copolymer, and the styrene resin composition for optical use contains 0.001 to 1.0 mass% of the hindered amine light stabilizer (B) with respect to 100 mass% of the styrene resin (A).

[0015] The present inventors have made intensive studies, and as a result, have found that a styrene resin composition for optical use containing a styrene resin having a content of a styrene monomer unit and a (meth) acrylate monomer unit within a specific range, and a hindered amine light stabilizer within a specific range, simultaneously satisfies transparency, hue, dimensional stability, and light stability for long-term use of an LED light source, thereby completing the present application.

[0016] Hereinafter, various embodiments of the present application will be illustrated. The embodiments shown below can be combined with each other.

[0017] [1] A styrene resin composition for optical use, which contains a styrene resin (A) that is a copolymer containing a styrene monomer unit and a (meth) acrylate monomer unit, and a hindered amine light stabilizer (B), and the copolymer contains 95 to 20 mass% of the styrene monomer unit and 5 to 80 mass% of the (meth) acrylate monomer unit in 100 mass% of the copolymer, and the styrene resin composition for optical use contains 0.001 to 1.0 mass% of the hindered amine light stabilizer (B) with respect to 100 mass% of the styrene resin (A).

[0018] [2] The styrenic resin composition for optical use as claimed in [1], wherein the hindered amine light stabilizer (B) is an N-H type hindered amine light stabilizer and / or an N-R type hindered amine light stabilizer.

[0019] [3] The styrenic resin composition for optical use as claimed in [2], wherein the N-H type hindered amine light stabilizer is at least one selected from the group consisting of

[0020] bis(2,2,6,6-tetramethylpiperidin-4-yl) sebacate,

[0021] 2,2,6,6-tetramethyl-4-piperidinyl ester of hexadecanoic acid, 2,2,6,6-tetramethyl-4-piperidinyl ester of octadecanoic acid,

[0022] 1,2,3,4-butanetetracarboxylic acid tetra(2,2,6,6-tetramethyl-4-piperidinyl) ester,

[0023] a condensation product of N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine and 4-morpholinyl 2,6-dichloro-1,3,5-triazine,

[0024] a condensation product of 2,4-dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-triazine and N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)hexamethylenediamine,

[0025] a condensation product of N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine and 2,4,6-trichloro-1,3,5-triazine and N-butyl-1-butylamine and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine,

[0026] 1,6,11-tris[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidinyl)amino)perinaphthyl-6-yl]aminoundecane,

[0027] a condensation product of 1,2,3,4-butanetetracarboxylic acid and 2,2,6,6-tetramethyl-4-piperidinol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5,5]undecane-3,9-diethanol

[0028]

[0029] [4] The styrenic resin composition for optical use as claimed in [2] or [3], wherein the N-R type hindered amine light stabilizer is at least one selected from the group consisting of

[0030] methyl sebacate (1,2,2,6,6-pentamethylpiperidin-4-yl) ester,

[0031] ​bis(1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate

[0032] bis(1,2,2,6,6-pentamethylpiperidin-4-yl) ester of n-butyl 3,5-di-tert-butyl-4-hydroxybenzyl malonate

[0033] Condensation polymer of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol and dimethyl succinate,

[0034] 1,5,8,12-Tetra[4,6-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidinyl)amino)-1,3,5-triazin-2-yl]-1,5,8,12-tetraazadodecane,

[0035] A condensation polymer of 1,2,3,4-butanetetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinol, and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5,5]undecane-3,9-diethanol.

[0036] A mixture of succinic acid and (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)ethanol and N,N',N'',N'''-tetra-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine.

[0037] At least one of them.

[0038] [5] The optical styrene-based resin composition described in any one of [1] to [4] contains 0.001 to 0.5 parts by weight of phosphorus-based antioxidant (C-1) relative to 100 parts by weight of the styrene-based resin (A).

[0039] [6] The optical styrene-based resin composition described in [5], wherein the phosphorus antioxidant (C-1) is selected from at least one of the following: tris(2,4-di-tert-butylphenyl) phosphite, 2,2'-methylene bis(4,6-di-tert-butyl-1-phenoxy)(2-ethylhexyloxy)phosphite, bis-(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]undecane, tetra(2,4-di-tert-butylphenyl)[1,1-biphenyl]-4,4'-diylbisphosphonite, and ethyl bis(2,4-di-tert-butyl-6-methylphenyl) phosphite.

[0040] [7] A light guide plate, which is formed by molding an optical styrene resin composition as described in any one of [1] to [6].

[0041] [8] An edge light type surface light source unit having the light guide plate as recited in [7], and a light source that supplies LED light to an end surface of the light guide plate.

[0042] [9] A light diffusion plate that is molded from the optical styrene-based resin composition as recited in any one of [1] to [6].

[0043]

[10] A direct type surface light source unit having the light diffusion plate as recited in [9], and a light source that supplies LED light to the light diffusion plate. DETAILED DESCRIPTION

[0044] Hereinafter, embodiments of the present application will be described. The various features exemplified in the embodiments shown below can be combined with each other. Furthermore, each feature independently makes the application stand.

[0045] 1. Optical styrene-based resin composition

[0046] The optical styrene-based resin composition of one embodiment of the present application is an optical styrene-based resin composition containing a styrene-based resin (A) and a hindered amine light stabilizer (B).

[0047] [Styrene-based resin (A)]

[0048] The styrene-based resin (A) is a resin obtained by copolymerizing monomers including a styrene-based monomer and a (meth)acrylate-based monomer. The styrene-based resin (A) is a copolymer including a styrene-based monomer unit and a (meth)acrylate-based monomer unit. The copolymer contains 95 to 20% by mass of the styrene-based monomer unit and 5 to 80% by mass of the (meth)acrylate-based monomer unit in 100% by mass of the copolymer, preferably 90 to 25% by mass of the styrene-based monomer unit and 10 to 75% by mass of the (meth)acrylate-based monomer unit, more preferably 80 to 30% by mass of the styrene-based monomer unit and 20 to 70% by mass of the (meth)acrylate-based monomer unit, and further preferably 60 to 40% by mass of the styrene-based monomer unit and 40 to 60% by mass of the (meth)acrylate-based monomer unit. By being in such a range, transparency, color tone, and dimensional stability can be satisfied at the same time. By being 90% by mass or less of the styrene-based monomer, a light guide plate with excellent transparency and color tone can be obtained, and by being 20% or more of the styrene-based monomer, a light guide plate with excellent dimensional stability can be obtained. The content of the (meth)acrylate-based monomer unit in the styrene-based resin (A) is specifically, for example, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80% by mass, or a range between any two of the values exemplified here.

[0049] Styrene-based monomers can be exemplified by styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, ethylstyrene, p-tert-butylstyrene, and the like. One of these can be used alone or two or more of these can be used in combination. The styrene-based monomer is preferably styrene.

[0050] (Meth)acrylate-based monomers can be exemplified by methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isoamyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and the like alkyl (meth)acrylates; phenyl (meth)acrylate, benzyl (meth)acrylate, and the like aryl (meth)acrylates; cyclohexyl (meth)acrylate, 4-t-butylcyclohexyl (meth)acrylate, 2-norbornyl (meth)acrylate, isobornyl (meth)acrylate, adamantane-1-yl (meth)acrylate, 2-methyladamantane-2-yl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, tricyclodecanyl (meth)acrylate, and the like cycloalkyl (meth)acrylates; glycidyl (meth)acrylate; dicyclopentyl (meth)acrylate, and the like. One of these can be used alone or two or more of these can be used in combination. The (meth)acrylate-based monomer is preferably an alkyl (meth)acrylate, and more preferably methyl methacrylate.

[0051] In addition, the styrene-based resin (A) can also be a copolymer obtained by copolymerizing a styrene-based monomer and a (meth)acrylate-based monomer with a copolymerizable monomer. As the copolymerizable monomer, for example, (meth)acrylic acid, methacrylic acid, and the like (meth)acrylic acids; acrylonitrile, methacrylonitrile, and the like vinyl cyanides; maleic anhydride, fumaric acid, and the like α,β-ethylenically unsaturated carboxylic acids; phenylmaleimide, cyclohexylmaleimide, and the like imides can be exemplified. One of these can be used alone or two or more of these can be used in combination.

[0052] The weight average molecular weight (Mw) of the styrene-based resin (A) is preferably from 5 x 105 to 4 x 105, and more preferably from 1 x 105 to 3.5 x 105. In addition, the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the styrene-based resin (A) is preferably from 1.0 to 3.5, and more preferably from 1.5 to 3.0. By being within this range, both moldability and the strength of the light guide plate can be balanced. If the weight average molecular weight (Mw) is less than 5 x 105, there is a case where the strength of the molded product becomes insufficient, and if it exceeds 4 x 105, there is a case where moldability decreases. In addition, if the ratio (Mw / Mn) of the number average molecular weight (Mn) is less than 1.0, there is a case where moldability decreases, and if it exceeds 3.5, there is a case where the strength of the molded product decreases.

[0053] <Light stabilizer (B)>

[0054] In the styrene-based resin composition for optical use, 0.001 to 1.0 parts by mass of the hindered amine light stabilizer (B) is contained with respect to 100 parts by mass of the styrene-based resin (A), and preferably 0.01 to 0.3 parts by mass is contained. By being set to such a range, transparency, color tone, and light stability against LED light sources can be improved. The content of the hindered amine light stabilizer (B) with respect to the styrene-based resin (A) is specifically, for example, 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 parts by mass, and can also be within a range between any two of the values exemplified here. Furthermore, the hindered amine light stabilizer (B) can be used alone or in combination with two or more.

[0055] The hindered amine light stabilizer (B) is a compound having a structural unit represented by the following general formula (1).

[0056] [Chemical Formula 1]

[0057]

[0058] In the general formula (1), X is an organic group bonded to the 4-position of the piperidyl group via a carbon atom, an oxygen atom, or a nitrogen atom, and as R, a hydrogen atom, a linear or branched alkyl group having 1 to 10 carbon atoms, a methylene group, or an alkoxy group can be exemplified. Here, when R is a hydrogen atom, it is an N-H type hindered amine light stabilizer, when R is a linear or branched alkyl group having 1 to 10 carbon atoms or a methylene group, it is an N-R type hindered amine light stabilizer, and when R is an alkoxy group, it is an N-OR type hindered amine light stabilizer.

[0059] As specific examples of the hindered amine light stabilizer of the N-H type, there can be mentioned bis(2,2,6,6-tetramethylpiperidin-4-yl) sebacate (TINUVIN 770DF manufactured by BASF Corporation), 2,2,6,6-tetramethyl-4-piperidinyl ester of hexadecanoic acid, 2,2,6,6-tetramethyl-4-piperidinyl ester of octadecanoic acid (SABOSTAB UV91 manufactured by SONGWON Corporation), tetra(2,2,6,6-tetramethyl-4-piperidinyl) ester of 1,2,3,4-butanetetracarboxylic acid (ADK STAB LA-57 manufactured by ADEKA Corporation), polycondensate of N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl) hexamethylenediamine and 4-morpholinyl 2,6-dichloro-1,3,5-triazine (SABOSTAB UV79 manufactured by SONGWON Corporation), polycondensate of 2,4-dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-triazine-N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl) hexamethylenediamine (Chimassorb 944FDL manufactured by BASF Corporation), polycondensate of N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl) hexamethylenediamine and 2,4,6-trichloro-1,3,5-triazine and N-butyl-1-butylamine and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine (SABOSTAB UV40 manufactured by SONGWON Corporation), 1,6,11-tris[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidinyl)amino) sym-triazine-6-yl]aminoundecane (Chimassorb 2020FDL manufactured by BASF Corporation), polycondensate of 1,2,3,4-butanetetracarboxylic acid and 2,2,6,6-tetramethyl-4-piperidinol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5,5]undecane-3,9-diethanol (ADK STAB LA-68 manufactured by ADEKA Corporation), dodecyl 3-(2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazabiso(5.1.11.2)heneicosan-20-yl)propionate, tetradecyl 3-(2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazabiso(5.1.11.2)heneicosan-20-yl)propionate (HOSTAVIN 3030 manufactured by CLARIANT Corporation), polycondensate of 2,2,4,4-tetramethyl-7-oxa-3,20-diazabiso(5.1.11.2)heneicosan-21-one and epichlorohydrin (HOSTAVIN N30P manufactured by CLARIANT Corporation).

[0060] As specific examples of the N-R type hindered amine light stabilizer, there can be mentioned: decanedioic acid methyl ester (1,2,2,6,6-pentamethylpiperidin-4-yl) ester, decanedioic acid bis (1,2,2,6,6-pentamethylpiperidin-4-yl) ester (TINUVIN 292, TINUVIN 765 manufactured by BASF Corporation), n-butyl 3,5-di-tert-butyl-4-hydroxybenzylmalonic acid bis (1,2,2,6,6-pentamethylpiperidin-4-yl) ester (TINUVIN 144 manufactured by BASF Corporation), polycondensate of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol and dimethyl succinate (TINUVIN 622SF manufactured by BASF Corporation), 1,5,8,12-tetra[4,6-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino)-1,3,5-triazin-2-yl]-1,5,8,12-tetraazadodecane (Chimassorb 119 manufactured by BASF Corporation), polycondensate of 1,2,3,4-butanetetracarboxylic acid and 1,2,2,6,6-pentamethyl-4-piperidinol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5,5]undecane-3,9-diethanol (ADKSTAB LA-63P manufactured by ADEKA Corporation), mixture of polycondensate of succinic acid and (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)ethanol and N,N',N",N"'-tetra-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine (TINUVIN 111 FDL manufactured by BASF Corporation).

[0061] As specific examples of the N-OR type hindered amine light stabilizer, there can be mentioned: decanedioic acid bis (1-octyloxy-2,2,6,6-tetramethylpiperidinyl) ester (TINUVIN 123 manufactured by BASF Corporation), carbonic acid bis (1-undecyloxy-2,2,6,6-tetramethylpiperidin-4-yl) ester (ADKSTAB LA-81 manufactured by ADEKA Corporation).

[0062] Among them, from the viewpoint of less influence on the transparency and hue of the styrene resin composition for optical use, the hindered amine light stabilizer (B) is preferably an N-H type hindered amine light stabilizer and / or an N-R type hindered amine light stabilizer, more preferably an N-R type hindered amine light stabilizer. It is known that the hindered amine light stabilizer (B) is generally oxidized by oxygen, ultraviolet rays and peroxide to generate a nitroxyl radical. In the present embodiment, although the mechanism by which the hindered amine light stabilizer (B) can improve the light stability for long-term use of the LED light source has not been elucidated, the present application has found the effectiveness of the hindered amine light stabilizer (B).

[0063] <Antioxidant (C)>

[0064] In the styrene-based resin composition for optical use, 0.001 to 0.5 parts by mass, further preferably 0.002 to 0.4 parts by mass, particularly preferably 0.005 to 0.3 parts by mass of the phosphorus-based antioxidant (C-1) is preferably contained relative to 100 parts by mass of the styrene-based resin (A). By being in this range, transparency and hue can be improved. The content of the phosphorus-based antioxidant (C-1) relative to 100 parts by mass of the styrene-based resin (A) is specifically, for example, 0.001, 0.002, 0.003, 0.004, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 parts by mass, or a range between any two of the values exemplified here.

[0065] The phosphorus-based antioxidant (C-1) is a (sub)phosphoric acid ester having no phenolic hydroxyl group in the basic skeleton, and is preferably a phosphite as a trivalent phosphorus compound. Specific examples of the phosphorus-based antioxidant (C-1) include 2,2'-methylenebis(4,6-di-t-butyl-l-phenoxy)(2-ethylhexyloxy) phosphine, bis-(2,4-di-t-butylphenyl) pentaerythritol diphosphite, tris(2,4-di-t-butylphenyl) phosphite, 3,9-bis(2,6-di-t-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphospha- spiro[5,5]undecane, tetrakis(2,4-di-t-butylphenyl)[l,l-biphenyl]-4,4'-diyl bisphosphinite, bis(2,4-di-t-butyl-6-methylphenyl) ethyl phosphite, and the like, which can be used alone or in combination of two or more.

[0066] In addition, the styrene-based resin composition for optical use can contain 0 to 0.5 parts by mass of a phenol-based antioxidant (C-2) relative to 100 parts by mass of the styrene-based resin (A). If the content of the phenol-based antioxidant (C-2) exceeds 0.5 parts by mass, the hue will deteriorate, and thus is not preferred. The content of the phenol-based antioxidant (C-2) relative to 100 parts by mass of the styrene-based resin (A) is specifically, for example, 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 parts by mass, or a range between any two of the values exemplified here.

[0067] The so-called phenol-based antioxidant (C-2) is an antioxidant having a phenolic hydroxyl group in the basic skeleton and not being a (sub)phosphoric acid ester. As specific examples of the phenol-based antioxidant (C-2), for example, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid octadecyl ester, ethylene bis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] can be listed, which can be used alone or in combination of two or more.

[0068] The antioxidant is, for example, a phosphorus-phenol compound having both a phosphite structure and a phenol structure in the same molecule, such as 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosphepin. In the case of this compound, it is considered that the styrene-based resin composition for optical use contains both a phosphorus-based antioxidant and a phenol-based antioxidant, for example, in the case of containing the phosphorus-phenol compound 0.1 parts by mass with respect to 100 parts by mass of the styrene-based resin (A), it is considered that the phosphorus-based antioxidant is contained 0.1 parts by mass and the phenol-based antioxidant is contained 0.1 parts by mass.

[0069] <Other components>

[0070] The tert-butylcatechol (TBC) in the styrene-based resin composition for optical use is preferably 10 ppm or less, more preferably 5 ppm or less. By being set to such a range, a light guide plate excellent in hue and transmittance can be obtained. The content of TBC is specifically, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ppm, or a range between any two of the values exemplified here.

[0071] The 6-tert-butyl-2,4-dimethylphenol (TBX) in the styrene-based resin composition for optical use is preferably 10 ppm or less, more preferably 5 ppm or less. By being set to such a range, a light guide plate excellent in hue and transmittance can be obtained. The content of TBX is specifically, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 ppm, or a range between any two of the values exemplified here.

[0072] In the optical styrenic resin composition, a sulfur-based antioxidant, a lactone-based antioxidant, a UV absorber, an antistatic agent, a hydrophilic additive, liquid paraffin (mineral oil), a polyethylene wax, a microcrystalline wax, a bluing agent, a higher fatty acid such as lauric acid, myristic acid, palmitic acid, stearic acid, a higher fatty amide such as stearamide, erucamide, ethylene bis-stearamide, a higher fatty acid glyceride such as lauric acid monoglyceride, palmitic acid monoglyceride, stearic acid monoglyceride, behenic acid monoglyceride, a higher alcohol such as myristyl alcohol, cetyl alcohol, stearyl alcohol, and the like can be contained, as long as the characteristics of the present application are not impaired.

[0073] The melt mass flow rate (MFR) of the optical styrenic resin composition under a load of 49 N at a temperature of 200°C is preferably 0.5 to 5.0 g / 10 minutes, and more preferably 1.0 to 4.0 g / 10 minutes. If the MFR is less than 0.5 g / 10 minutes, the molding stability decreases, and if the MFR exceeds 5.0 g / 10 minutes, the strength becomes insufficient.

[0074] The Vicat softening temperature of the optical styrenic resin composition is preferably 95 to 104°C, and more preferably 100 to 104°C. If the Vicat softening temperature is less than 95°C, the heat resistance is insufficient, and the light guide plate can be deformed depending on the use environment.

[0075] <Method for producing the optical styrenic resin composition>

[0076] As the polymerization method of the styrenic resin (A), known polymerization methods of styrene such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be mentioned. In terms of quality or productivity, bulk polymerization or solution polymerization is preferred, and continuous polymerization is preferred. As the solvent, for example, an alkylbenzene such as benzene, toluene, ethylbenzene, or xylene, or a ketone such as acetone or methyl ethyl ketone, an aliphatic hydrocarbon such as hexane or cyclohexane, or the like can be used.

[0077] At the time of polymerization of the styrene resin (A), a polymerization initiator, a chain transfer agent, a crosslinking agent, and the like, other polymerization aids can be used as needed. As the polymerization initiator, a radical polymerization initiator is preferred, and peroxide ketones such as 1,1-di(tert-butylperoxy)cyclohexane, 2,2-di(tert-butylperoxy)butane, 2,2-di(4,4-di-tert-butylperoxy cyclohexyl)propane, 1,1-di(tert-amylperoxy)cyclohexane, cumene hydroperoxide, tert-butyl hydroperoxide, alkyl peroxides such as tert-amyl peroxyisononanoate, di-alkyl peroxides such as tert-butyl cumyl peroxide, di-tert-butyl peroxide, diisopropylbenzene peroxide, di-tert-hexyl peroxide, peroxide esters such as tert-butyl peroxyisopropylmonocarbonate, tert-butyl peroxyisopropyl carbonate, peroxide carbonates such as polyether tetra(tert-butylperoxy carbonate), 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 used, and one or a combination of two or more of them can be used. As the chain transfer agent, aliphatic mercaptans such as n-dodecyl mercaptan and tert-dodecyl mercaptan, aromatic mercaptans, thioglycolic acid, mercaptopropionic acid, and the like, sulfur carboxylic acids, polyfunctional mercaptans obtained by esterification of polyhydric alcohol hydroxyl groups of ethylene glycol, tetraethylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tri-pentaerythritol, sorbitol, and the like with thioglycolic acid or mercaptopropionic acid, pentaphenyl ethane, a-methylstyrene dimer, terpinolene, and the like can be used. Of these, from the viewpoint of easy adjustment of the molecular weight, aliphatic mercaptans, aromatic mercaptans, sulfur carboxylic acids, and polyfunctional mercaptans are preferred.

[0078] In the case of continuous polymerization, the styrene resin (A) can be produced by a method including a polymerization step, a devolatilization step, and a pelletization step.

[0079] First, in the polymerization step, a known complete mixing tank type stirring tank or a column type reactor or the like is used, and the polymerization reaction is controlled to be the target molecular weight, molecular weight distribution, and reaction conversion rate by adjusting the polymerization temperature and the like.

[0080] The polymerization solution containing the polymer for which the polymerization step is completed is transferred to the devolatilization step, and unreacted monomers and polymerization solvents are removed. The devolatilization step includes a vacuum devolatilization tank with a heater or a devolatilization extruder with a vent hole or the like. The polymer in a molten state for which the devolatilization step is completed is transferred to the pelletization step. In the pelletization step, the molten resin is extruded in a linear shape from a porous die, and is processed into a pellet shape by a cold cutting method or an in-air hot cutting method, a water hot cutting method.

[0081] The optical styrenic resin composition can be produced by adding the hindered amine light stabilizer (B), the phosphorus-based antioxidant (C-1), and the phenol-based antioxidant (C-2) to the styrenic resin (A). The hindered amine light stabilizer (B), the phosphorus-based antioxidant (C-1), and the phenol-based antioxidant (C-2) can be added to a raw material solution before polymerization of the styrenic resin (A), or can be mixed by an extruder or a static mixer provided after polymerization of the styrenic resin (A) and before pelletization. Alternatively, the hindered amine light stabilizer (B), the phosphorus-based antioxidant (C-1), and the phenol-based antioxidant (C-2) can be dry-mixed with the pellets of the styrenic resin (A) after pelletization of the styrenic resin (A) and then melt-kneaded. Alternatively, a granular master batch obtained by melt-kneading the hindered amine light stabilizer (B), the phosphorus-based antioxidant (C-1), and the phenol-based antioxidant (C-2) together with a small amount of the styrenic resin can be dry-mixed with the styrenic resin (A) and then melt-kneaded.

[0082] The content of the tert-butylcatechol or 6-tert-butyl-2,4-dimethylphenol in the optical styrenic resin composition can be adjusted at the start of polymerization of the styrenic resin (A) and in the content adjustment step after devolatilization.

[0083] 2. Light guide plate

[0084] The light guide plate according to an embodiment of the present application is a molded product molded from the above-described optical styrenic resin composition. The light guide plate is a light guide plate that can be used for an edge light type surface light source unit.

[0085] <Shape of light guide plate>

[0086] The light guide plate can have a concave-convex shape on the surface of the light guide plate. More specifically, the light guide plate can have a plurality of convex portions in the shape of a lens and / or a prism on the surface of the light guide plate. The convex portions are preferably provided on at least one surface of the light guide plate, and particularly preferably on the surface that is the front surface (light emitting surface) of the light guide plate. The convex portions can be provided on the other surfaces if necessary, but are more preferably provided only on the front surface (light emitting surface) of the light guide plate.

[0087] Here, the convex portion in the shape of a lens is a convex portion in the shape of a circular arc, and the edge shape of the cross section is a circular arc-shaped ridge. Further, the convex portion in the shape of a prism is a convex portion in the shape of a circular arc, and the edge shape of the cross section is a triangular mountain-shaped ridge. Further, the convex portions can be formed in a plurality of lines in a parallel relationship with each other. Further, the convex portions can be integrally formed on the light guide plate.

[0088] The thickness of the light guide plate is 0.2 to 3.0 mm, preferably 0.3 to 2.5 mm, and more preferably 0.4 to 2.4 mm. If the thickness falls within this range, the optical styrenic resin composition is easily molded, and a light guide plate having excellent moldability such as excellent extrusion stability or excellent strength can be easily produced.

[0089] <Optical properties>

[0090] The average transmittance of the light guide plate at a wavelength of 380 to 780 nm at an optical path length of 115 mm is preferably 85% or greater, more preferably 86% or greater.

[0091] The Yellowness Index (YI) value of the light guide plate at an optical path length of 115 mm is preferably 6.0 or less, more preferably 4.0 or less.

[0092] <Method for manufacturing light guide plate>

[0093] The light guide plate of an embodiment of the present application is obtained by molding the above-described optical styrenic resin composition, and as a molding method, known methods such as sheet extrusion molding, or injection molding, compression molding, etc. can be used, and from the viewpoint of productivity and easy realization of large-scale of the molded product, continuous sheet extrusion molding with a surface shape transfer mold is preferable. As an example of this sheet extrusion molding, a continuous sheet extrusion molding method having an extrusion step in which a resin is supplied to a feed block in a heated molten state and continuously extruded from a die to produce a sheet, a pressing step in which the above-described resin sheet is sandwiched by a press roller and a cooling roller, and a conveying step in which the resin sheet is conveyed after the pressing step while being in contact with the cooling roller, and a transfer mold is provided on the surface of the cooling roller, can be cited, and by changing the shape of the transfer mold, an arbitrary concave-convex shape can be transferred to the surface of the sheet.

[0094] Further, the light guide plate can have a concave-convex shape on the front surface (light emitting surface), and the back surface can be subjected to reflection processing for diffusely reflecting light. As the reflection processing, for example, a method of imparting a concave-convex of a dot shape by laser irradiation can be cited in addition to by screen printing or inkjet printing, and the printing of the dot pattern can use ink having particles that diffuse light.

[0095] 3. Edge light type surface light source unit

[0096] The edge light type surface light source unit of an embodiment of the present application is an edge light type surface light source unit having the above-described light guide plate, and a light source that supplies LED light to the end surface of the light guide plate. The edge light type surface light source unit can be suitably used as a surface light source device for a liquid crystal display device.

[0097] 4. Light diffusion plate

[0098] The light diffusion plate of an embodiment of the present application is a molded product obtained by molding the above-described optical styrenic resin composition. The light diffusion plate is a light diffusion plate that can be used for a direct type surface light source unit.

[0099] <Shape of light diffusion plate>

[0100] The thickness of the light diffusion plate of one embodiment of the present application is not limited, and is, for example, 1 to 3 mm. An antistatic agent can be applied to the surface of the light diffusion plate. By applying an antistatic agent, the attachment of dust or the like due to static electricity can be inhibited after the light diffusion plate is attached to a backlight device, and thus the light diffusion plate can be used for a long time without a decrease in luminance. Furthermore, a minute concavo-convex shape such as an embossing process can be formed on both surfaces or one surface of the light diffusion plate of the present application, and a lens shape or a prism shape can be formed on both surfaces or one surface.

[0101] In the light diffusion plate, 0.1 to 1.0 parts by mass of a light diffusion agent can be contained with respect to 100 parts by weight of the optical styrenic resin composition. The light diffusion agent can be used as long as it is a particle having a refractive index different from that of the optical styrenic resin composition and has an effect of diffusing incident light, and for example, an organic particle such as a styrenic polymer particle, an acrylic polymer particle, or a silicone polymer particle, or an inorganic particle such as a glass bead, a silica particle, an aluminum hydroxide particle, a calcium carbonate particle, a barium sulfate particle, a titanium oxide particle, or talc can be used. Of these, at least one selected from an acrylic polymer particle, a styrenic polymer particle, and a silicone polymer particle is preferable.

[0102] <Method for manufacturing light diffusion plate>

[0103] The light diffusion plate of one embodiment of the present application can be manufactured by molding the above-described optical styrenic resin composition by various methods such as extrusion molding or injection molding, and is preferably manufactured by extrusion molding. As an example of extrusion molding, a method in which an optical styrenic resin composition is melt-kneaded using a single-screw extruder or a twin-screw extruder, continuously extruded from a T die, and then solidified by a chill roll unit can be given. In the case where a concavo-convex shape is formed on the surface of the light diffusion plate, an arbitrary concavo-convex shape can be formed by providing a transfer mold on the surface of the chill roll and changing the shape of the transfer mold. Furthermore, in the case where a surface layer is stacked on both surfaces or one surface of the light diffusion plate, a method such as a co-extrusion method, a lamination method, a thermal bonding method, a solvent bonding method, a casting method, or a surface coating method can be used.

[0104] 5. Direct type surface light source unit

[0105] The direct type surface light source unit of one embodiment of the present application is a direct type surface light source unit including the above-described light diffusion plate and a light source that supplies LED light to the light diffusion plate. The direct type surface light source unit can be suitably used as a surface light source device for a liquid crystal display device.

[0106] [Examples]

[0107] Examples are given below to further illustrate the present application. Note that these are examples only and are not intended to limit the present application.

[0108] 1. Manufacture of an optical styrenic resin composition

[0109] [Example 1]

[0110] The first reactor as a complete mixing type stirred tank and the second reactor as a plug flow type reactor with an attached static mixer were connected in series to constitute a polymerization step, and the manufacture of a styrenic resin was carried out. The capacity of each reactor was: 30 liters for the first reactor and 12 liters for the second reactor. With respect to the raw material composition of 51 mass% of styrene (TBC concentration 11 μg / g), 39 mass% of methyl methacrylate (TBX concentration 7 μg / g), and 10 mass% of ethylbenzene, at the inlet of the first reactor, the addition concentration of t-butylperoxy isopropyl monocarbonate (manufactured by Nippon Shokubai Co., Ltd.: PERBUTYL I) as a polymerization initiator was adjusted to 150 ppm, and the addition concentration of n-dodecyl mercaptan (manufactured by Arkema Co., Ltd.) as a chain transfer agent was adjusted to 500 ppm (both concentrations were based on the mass of the entire monomers), and then the raw material solution was continuously supplied to the first reactor set to 128°C at 8.0 kg / h. Further, the obtained polymerization solution was continuously supplied to the second reactor, and the polymerization was completed. The polymerization rate of the monomers at this time was 70%. Furthermore, in the second reactor, a temperature gradient was provided along the flow direction, and the middle portion was adjusted to 130°C and the outlet portion was adjusted to 145°C.

[0111] Subsequently, the solution containing the polymer continuously taken out from the second reactor was introduced into a vacuum devolatilization tank with an attached preheater consisting of two stages in series, the temperature of the preheater was adjusted so that the resin temperature became 220°C, and unreacted styrene and ethylbenzene were separated at a pressure of 0.8 kPa. The obtained molten polymer was continuously supplied to an extruder, 0.1 parts by mass of a hindered amine light stabilizer (HOSTAVIN® 770) was added with respect to 100 parts by mass of the polymer from the additive feeding port, and after mixing at a set temperature of 220°C, the line was extruded from a porous die, and the line was cooled and cut by a cold cutting method to pelletize it. The TBC concentration in the obtained optical styrenic resin composition was 1.5 μg / g, and the TBX concentration was 0.2 μg / g. In addition, the weight average molecular weight (Mw) was 170,000, and the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (Mw / Mn) was 2.0.

[0112] [Examples 2 to 17 and Comparative Examples 1 to 6]

[0113] The composition of the raw material solution and the polymerization conditions were changed to those shown in Table 1, and the composition of the hindered amine light stabilizer (B), the phosphorus-based antioxidant (C-1), the phenol-based antioxidant (C-2), and the ultraviolet absorber (D) was changed to those shown in Tables 2 (Table 2-1 and Table 2-2) to Table 3, and otherwise, optical styrene resin compositions and light guide plates were produced in the same manner as in Example 1. The results of various measurements and evaluations are shown in Tables 2 (Table 2-1 and Table 2-2) to Table 3.

[0114] [Table 1]

[0115]

[0116] [Table 2-1]

[0117]

[0118] [Table 2-2]

[0119]

[0120] [Table 3]

[0121]

[0122] Further, regarding the hindered amine light stabilizer (B), the phosphorus-based antioxidant (C-1), the phenol-based antioxidant (C-2), and the ultraviolet absorber (D) in Tables 2 (Table 2-1 and Table 2-2) to Table 3, each is described below.

[0123] (Hindered amine light stabilizer (B))

[0124] 770: Bis(2,2,6,6-tetramethylpiperidine-4-yl) sebacate (TINUVIN 770DF manufactured by BASF Corporation)

[0125] 944: Condensation product of 2,4-dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-triazine, N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine (Chimassorb 944FDL manufactured by BASF Corporation)

[0126] 292: Methyl sebacate (1,2,2,6,6-pentamethylpiperidin-4-yl) ester: 25% and bis(1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate: 75% mixture (TINUVIN 292 manufactured by BASF Corporation)

[0127] 123: Bis(1-octyloxy-2,2,6,6-tetramethylpiperidyl) sebacate (TINUVIN 123 manufactured by BASF Corporation)

[0128] (Phosphorus antioxidant (C-1))

[0129] 168: Tris(2,4-di-tert-butylphenyl) phosphite (Irgafos 168 manufactured by BASF Corporation)

[0130] HP-10: 2,2'-Methylenebis(4,6-di-tert-butyl-1-phenoxy)(2-ethylhexyloxy) phosphine (ADKSTAB HP-10 manufactured by ADEKA Corporation)

[0131] 126: Bis-(2,4-di-tert-butylphenyl) pentaerythrityl diphosphite (Irgafos 126 manufactured by BASF Corporation)

[0132] (Polyphenol antioxidant (C-2))

[0133] 1076: Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Corporation)

[0134] (Ultraviolet absorber (D))

[0135] P: 2-(2-Hydroxy-5-methylphenyl) benzotriazole (TINUVIN P manufactured by BASF Corporation)

[0136] 2. Evaluation

[0137] The evaluation of the optical styrenic resin composition described in Tables 2 (Table 2-1 and Table 2-2) to 3 was performed according to the following methods.

[0138] <Mass flow rate of melt (MFR)>

[0139] The mass flow rate of melt was measured according to JIS K 7210 under the conditions of a temperature of 200°C and a load of 49 N.

[0140] <Vickers softening temperature>

[0141] The Vickers softening temperature was measured according to JIS K 7206 at a temperature increase rate of 50°C / hr and a test load of 50 N.

[0142] <Content of TBC and TBX in the optical styrenic resin composition>

[0143] After 0.2 g of the styrene-based resin composition for optical use was dissolved in a small amount of THF, 200 μL of BSTFA (M, O-bis(trimethylsilyl)trifluoroacetamide) was added, and trimethylsilyl derivatization treatment was performed. After the volume was made 10 mL with THF (tetrahydrofuran), the supernatant separated by centrifugation was measured by gas chromatography mass spectrometry (GC / MS) under the following conditions. Furthermore, the concentration was determined using a calibration curve prepared in advance.

[0144] GC device: 7890A manufactured by Agilent

[0145] Column: DB-5ms (0.25 mm i.d. x 30 m) liquid phase film thickness 0.25 μm manufactured by Agilent

[0146] Column temperature: 50°C (1 min) → (20°C / min temperature increase) → 320°C (6.5 min) for a total of 20 min

[0147] Injection port: 300°C, 1.5 mL / min, (split ratio 1:5)

[0148] Injection amount: 1 μL

[0149] MS device: 5975C manufactured by Agilent

[0150] Interface temperature: 320°C

[0151] MS measurement conditions: SIM measurement TBC (m / z 295 for quantification, m / z 310 for confirmation)

[0152] <Contents of hindered amine light stabilizer (B), phosphorus-based antioxidant (C-1), and phenol-based antioxidant (C-2) in styrene-based resin composition for optical use>

[0153] After 1.0 g of the styrene-based resin composition for optical use was completely dissolved in 20 mL of THF, 5 mL of methanol was added dropwise, and stirring was performed for 20 minutes. Centrifugation was performed at 4000 rpm for 10 minutes, and the separated supernatant was measured by gas chromatography (GC) under the following conditions. Furthermore, the concentration was determined using a calibration curve prepared in advance.

[0154] GC device: GC2010 Plus manufactured by Shimadzu Corporation

[0155] Column: DB-1 (30 m x 0.25 mm i.d., df = 0.10 μm)

[0156] Column temperature: 240°C (1 min) → (10°C / min temperature increase) → 320°C (15 min)

[0157] Injection port: 320°C, 1.02 mL / min (split ratio 1 :5)

[0158] Injection volume: 1 μL

[0159] <Weight average molecular weight (Mw)>

[0160] The weight average molecular weight (Mw) and Z average molecular weight (Mz), number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.

[0161] GPC machine: Shodex GPC-101 manufactured by Showa Denko K.K.

[0162] Chromatographic column: PLgel 10 μm MIXED-B manufactured by Polymer Laboratories, Inc.

[0163] Mobile phase: Tetrahydrofuran

[0164] Sample concentration: 0.2 mass %

[0165] Temperature: Oven 40°C, injection port 35°C, detector 35°C

[0166] Detector: Differential refractometer

[0167] The molecular weight was calculated from the elution curve of monodisperse polystyrene, and the molecular weight at each elution time was calculated as the molecular weight converted to polystyrene.

[0168] 3. Manufacture and evaluation of light guide plates

[0169] <Manufacture of light guide plates>

[0170] The above-mentioned optical styrenic resin composition was supplied to an extruder with a single shaft with a screw diameter of 90 mm and L / D = 32, and with a vent hole, and was melt-kneaded at 200 to 235°C, and was discharged using a T die with a die lip width of 1000 mm and a die lip opening of 3.0 mm at a T die temperature of 245 to 250°C, and was cooled and solidified using a longitudinal three-roll cooling roll, and the end face was trimmed to obtain a light guide plate with a width of 800 mm and a thickness of 2.0 mm.

[0171] <Evaluation of light guide plates>

[0172] The average transmittance, YI value, dimensional stability (hygroscopic deformation), and LED durability of the light guide plates in Tables 2 to 3 were evaluated as described below.

[0173] <Average transmittance and YI value of light guide plates>

[0174] The average transmittance and YI value were measured by the following procedure.

[0175] A test piece of 115 mm x 85 mm was cut from the light guide plate obtained above, and the end face was polished and ground to produce a plate-shaped molded product having a mirror surface on the end face. With respect to the plate-shaped molded product after grinding, a UV-visible spectrophotometer brightness meter V-670 manufactured by Shimadzu Corporation was used to measure the spectral transmittance at a wavelength of 350 nm to 800 nm at an optical path length of 115 mm under incident light of 20 x 1.6 mm in size and a diffusion angle of 0°, and the YI value in the field of view of 2° under a C light source was calculated in accordance with JIS K7105. The average transmittance (total light transmittance) was calculated as the average of the spectral transmittance at a wavelength of 380 to 780 nm.

[0176] <Dimensional stability (hygroscopic deformation)>

[0177] A test piece of 200 mm x 300 mm was cut from the light guide plate obtained above, and the test piece was stored under conditions of a temperature of 60°C and a relative humidity of 90% for 500 hours, and the dimensional change in the long side before and after storage was measured, and the deformation rate was calculated in accordance with the following formula.

[0178] Deformation rate = ((long side length after storage) - (long side length before storage)) ÷ (length of long side before storage) x 100 (%)

[0179] A rate of less than 0.10% was recorded as O, a rate of 0.10 to 0.15% was recorded as Δ, and a rate exceeding 0.15% was recorded as X, and the dimensional stability (hygroscopic change) of the light guide plate was evaluated.

[0180] <LED durability>

[0181] A test piece of 115 mm x 85 mm was cut from the light guide plate obtained above, and the end face was polished and ground to produce a plate-shaped molded product having a mirror surface on the end face using an end face grinder (GCPB-500 manufactured by MIGAKU Corporation) with a diamond cutter rotating at a speed of 8000 rpm at a feed rate of 2.0 m / min for 0.2 mm. With respect to the plate-shaped molded product after grinding, a flat plate type blue LED light source (peak wavelength 445 nm) for a TV (television) was disposed at a position 0.5 mm from the end face, and the light source was irradiated with 0.05 W / mm2for 100 hours in an environment at 80°C, and the change in the color of the light source was evaluated. 2The LED light was irradiated for 500 h under an input current of 20 mA. The YI value under a visual field of 2° in a C light source was calculated from the spectral transmittance at a wavelength of 350 to 800 nm under an incident light of 20 x 1.6 mm in size, a diffusion angle of 0°, and an optical path length of 115 mm, using a UV-Vis spectrophotometer luminance meter V-670 manufactured by Japan Spectroscopic Co., Ltd. after the test. The value obtained by subtracting the YI value before the test from the YI value after the test was set as ΔYI. In addition, the LED light-incident portion of the plate-shaped molded article after the test was visually confirmed, and those with no change were marked as O, and those with carbonization were marked as X, and the LED durability was evaluated.

[0182] In Examples 1 to 17, the transparency, hue, dimensional stability were good, carbonization did not occur after LED exposure, and the hue stability was excellent.

Claims

1. An optical styrenic resin composition comprising a styrenic resin (A) which is a copolymer containing a styrenic monomer unit and a (meth)acrylate monomer unit, and a hindered amine light stabilizer (B), wherein, The optical styrenic resin composition does not include a composition containing 40 to 90 parts by mass of the styrenic resin (A) and 10 to 60 parts by mass of a graft copolymer obtained by graft copolymerization of a monomer mixture containing at least a styrenic monomer and a (meth)acrylate monomer in the presence of a rubbery polymer, The copolymer contains 85 to 20 mass% of the styrenic monomer unit and 15 to 80 mass% of the (meth)acrylate monomer unit in 100 mass% of the copolymer, The optical styrenic resin composition contains 0.001 to 1.0 parts by mass of the hindered amine light stabilizer (B) with respect to 100 parts by mass of the styrenic resin (A), The hindered amine light stabilizer (B) contains an N-R type hindered amine light stabilizer.

2. An optical styrenic resin composition containing a styrenic resin (A) which is a copolymer containing a styrenic monomer unit and a (meth)acrylate monomer unit, and a hindered amine light stabilizer (B), The copolymer contains 85 to 45 mass% of the styrenic monomer unit and 15 to 55 mass% of the (meth)acrylate monomer unit in 100 mass% of the copolymer, The optical styrenic resin composition contains 0.001 to 1.0 parts by mass of the hindered amine light stabilizer (B) with respect to 100 parts by mass of the styrenic resin (A), The hindered amine light stabilizer (B) contains an N-R type hindered amine light stabilizer.

3. The styrenic resin composition for optical use according to claim 1 or 2, wherein, The hindered amine light stabilizer (B) is the N-R type hindered amine light stabilizer.

4. The styrenic resin composition for optical use according to claim 1 or 2, wherein, The N-R type hindered amine light stabilizer is at least one selected from Methyl decanedioate (1,2,2,6,6-pentamethylpiperidin-4-yl) ester, Bis(1,2,2,6,6-pentamethylpiperidin-4-yl) decanedioate, N-Butyl 3,5-di-tert-butyl 4-hydroxybenzylmalonate bis(1,2,2,6,6-pentamethylpiperidin-4-yl) ester, Polycondensate of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinethanol and dimethyl succinate, 1,5,8,12-tetra[4,6-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino)-1,3,5-triazin-2-yl]-1,5,8,12-tetraazadodecane, Polycondensate of 1,2,3,4-butanetetracarboxylic acid and 1,2,2,6,6-pentamethyl-4-piperidinol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5,5]undecane-3,9-diethanol, Polycondensate of succinic acid and (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)ethanol and mixture of N,N',N'',N'''-tetra-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine ​ 5. The optical styrenic resin composition according to claim 1 or 2, which contains 0.001 to 0.5 parts by mass of the phosphorus-based antioxidant (C-1) with respect to 100 parts by mass of the styrenic resin (A).

6. The styrenic resin composition for optical use according to claim 5, wherein, The phosphorus-based antioxidant (C-1) is at least one selected from the group consisting of tris(2,4-di-tert-butylphenyl) phosphite, 2,2'-methylenebis(4,6-di-tert-butyl-l- phenoxy)(2-ethylhexyloxy) phosphine, bis-(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9- diazaspiro[5,5]undecane, tetrakis(2,4-di-tert-butylphenyl)[l,l-biphenyl]-4,4'- diylbisphosphonite, bis(2,4-di-tert-butyl-6-methylphenyl) ethyl phosphite.

7. The styrenic resin composition for optical use according to claim 1 or 2, wherein, The optical styrenic resin composition has a melt mass flow rate of 0.5 to 5.0 g / 10 min under a temperature of 200°C and a load of 49 N.

8. The styrenic resin composition for optical use according to claim 1 or 2, wherein, The optical styrenic resin composition has a Vicat softening temperature of 95 to 104°C as measured according to JIS K 7206 at a temperature increase rate of 50°C / hr and a test load of 50 N.

9. A light guide plate molded from the optical styrenic resin composition according to claim 1 or 2.

10. A light guide plate molded from an optical styrenic resin composition, The optical styrenic resin composition contains a styrenic resin (A) which is a copolymer containing styrenic monomer units and (meth)acrylate monomer units, and a hindered amine light stabilizer (B), wherein The optical styrenic resin composition does not include a composition containing 40 to 90 parts by mass of the styrenic resin (A), and 10 to 60 parts by mass of a graft copolymer obtained by graft copolymerization of a monomer mixture containing at least a styrenic monomer and a (meth)acrylate monomer in the presence of a rubbery polymer, The copolymer contains 85 to 20 mass% of the styrenic monomer unit and 15 to 80 mass% of the (meth)acrylate monomer unit in 100 mass% of the copolymer, The optical styrenic resin composition contains 0.001 to 1.0 parts by mass of the hindered amine light stabilizer (B) with respect to 100 parts by mass of the styrenic resin (A), The optical styrenic resin composition has a melt mass flow rate of 0.5 to 5.0 g / 10 min under a temperature of 200°C and a load of 49 N.

11. A light guide plate molded from an optical styrenic resin composition, The optical styrenic resin composition contains a styrenic resin (A) which is a copolymer containing a styrenic monomer unit and a (meth)acrylate monomer unit, and a hindered amine light stabilizer (B), The copolymer contains 85 to 45 mass% of the styrenic monomer unit and 15 to 55 mass% of the (meth)acrylate monomer unit in 100 mass% of the copolymer, The optical styrenic resin composition contains 0.001 to 1.0 parts by mass of the hindered amine light stabilizer (B) with respect to 100 parts by mass of the styrenic resin (A), The optical styrenic resin composition has a melt mass flow rate of 0.5 to 5.0 g / 10 min under a temperature of 200°C and a load of 49 N.

12. An edge light type surface light source unit having the light guide plate according to claim 9, and a light source that supplies LED light to an end surface of the light guide plate.

13. An edge light type surface light source unit having the light guide plate according to claim 10 or 11, and a light source that supplies LED light to an end surface of the light guide plate.

14. A light diffusion plate that is molded from the optical styrenic resin composition according to claim 1 or 2.

15. A light diffusion plate that is molded from an optical styrenic resin composition, The optical styrenic resin composition contains a styrenic resin (A) which is a copolymer containing styrenic monomer units and (meth)acrylate monomer units, and a hindered amine light stabilizer (B), wherein The optical styrenic resin composition excludes a composition containing 40 to 90 parts by mass of the styrenic resin (A) and 10 to 60 parts by mass of a graft copolymer obtained by graft copolymerization of a monomer mixture containing at least a styrenic monomer, a (meth)acrylate monomer in the presence of a rubbery polymer, The copolymer contains 85 to 20% by mass of the styrenic monomer unit and 15 to 80% by mass of the (meth)acrylate monomer unit in 100% by mass of the copolymer, The optical styrenic resin composition contains 0.001 to 1.0 parts by mass of the hindered amine light stabilizer (B) with respect to 100 parts by mass of the styrenic resin (A), The optical styrenic resin composition has a melt mass flow rate of 0.5 to 5.0 g / 10 min under a temperature of 200°C and a load of 49 N.

16. A light diffusion plate that is molded from an optical styrenic resin composition, The optical styrenic resin composition contains a styrenic resin (A) that is a copolymer containing a styrenic monomer unit and a (meth)acrylate monomer unit, and a hindered amine light stabilizer (B), The copolymer contains 85 to 45% by mass of the styrenic monomer unit and 15 to 55% by mass of the (meth)acrylate monomer unit in 100% by mass of the copolymer, The optical styrenic resin composition contains 0.001 to 1.0 parts by mass of the hindered amine light stabilizer (B) with respect to 100 parts by mass of the styrenic resin (A), The optical styrenic resin composition has a melt mass flow rate of 0.5 to 5.0 g / 10 min under a temperature of 200°C and a load of 49 N.

17. A direct light type surface light source unit having the light diffusion plate according to claim 11, and a light source that supplies LED light to the light diffusion plate.

18. A direct light type surface light source unit having the light diffusion plate according to claim 15 or 16, and a light source that supplies LED light to the light diffusion plate.

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