Optical styrene resin composition, light guide plate, edge-light type surface light source unit, light diffusion plate, and direct type surface light source unit

Abstract

Provided is an optical styrene-based resin composition which is excellent in terms of transparency, hue, and dimensional stability and of stability to the light from LED light sources in long-term use.　This optical styrene-based resin composition comprises: a styrene-based resin (A) which is a copolymer comprising units of a styrene-based monomer and units of a (meth)acrylic ester monomer; and a hindered-amine light stabilizer (B). The copolymer comprises 95-20 mass% the units of a styrene-based monomer and 5-80 mass% the units of a (meth)acrylic ester monomer, the copolymer being taken as 100 mass%. The hindered-amine light stabilizer (B) is contained in an amount of 0.001-1.0 parts by mass per 100 parts by mass of the styrene-based resin (A).

Description

[Technical field]

[0001] The present invention relates to an optical styrene-based resin composition, 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 technology]

[0002] There are two types of backlights for liquid crystal display devices: direct-light types, in which the light source is placed in front of the display device, and edge-light types, in which the light source is placed on the side. Edge-light backlights use a component called a light guide plate, which guides light from a light source placed on the side to the front of the display device. They are used in a wide range of applications, including televisions, monitors for desktop personal computers, notebook personal computers, mobile phones, and monitors for car navigation systems. Backlights that use light guide plates are also used as lighting devices, signs, etc.

[0003] Light guide plates are required to have a particularly high light transmittance because the light transmission distance is relatively long and the light loss in the optical path length is large. For this reason, acrylic resins such as polymethyl methacrylate (PMMA) are used as the material for light guide plates. However, PMMA has high water absorption, and water absorption may cause warping or dimensional changes in the light guide plate. In addition, PMMA is prone to thermal decomposition during molding, so there is a problem that molding at high temperatures is likely to cause poor appearance of the molded product. To solve these problems, for example, Patent Document 1 proposes using a styrene-methyl (meth)acrylate copolymer as the material for the light guide plate.

[0004] On the other hand, molded products of styrene-methyl (meth)acrylate copolymers have poorer hue than PMMA, and may cause color unevenness when used as a backlight. In order to solve this problem, Patent Document 2 proposes a technology for improving the hue of styrene-methyl (meth)acrylate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-075648 A [Patent Document 2] International Publication No. 2016-129675 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, as the resolution of backlight units in televisions and monitors has increased, high-brightness LEDs are often used as edge light sources. However, depending on the usage environment, conventional light guide plates made of styrene-methyl (meth)acrylate copolymers can experience deterioration (carbonization) on the edge surfaces of the light guide plate after being turned on for long periods of time.

[0007] The present invention has been made in consideration of such problems, and provides an optical styrene-based resin composition that is excellent in transparency, hue, and dimensional stability, and also has excellent light stability against long-term use of an LED light source. [Means for solving the problem]

[0008] According to the present invention, there is provided an optical styrene-based resin composition containing a styrene-based resin (A) which is a copolymer containing a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit, and a hindered amine light stabilizer (B), wherein the copolymer contains 95 to 20 mass % of the styrene-based monomer unit and 5 to 80 mass % of the (meth)acrylic acid ester-based monomer unit in 100 mass % of the copolymer, and contains 0.001 to 1.0 part by mass of the hindered amine light stabilizer (B) per 100 parts by mass of the styrene-based resin (A).

[0009] Means for Solving the Problems The present inventors have conducted intensive research and have found that an optical styrene-based resin composition comprising a styrene-based resin having a content of styrene-based monomer units and (meth)acrylic acid ester-based monomer units within a specific range, and a hindered amine light stabilizer within a specific range, simultaneously satisfies the transparency, hue, dimensional stability, and light stability against long-term use of an LED light source, thereby completing the present invention.

[0010] Various embodiments of the present invention will be described below. The embodiments described below can be combined with each other. [1] An optical styrenic resin composition comprising a styrenic resin (A) which is a copolymer containing a styrenic monomer unit and a (meth)acrylic acid ester monomer unit, and a hindered amine light stabilizer (B), wherein the copolymer contains 95 to 20 mass % of the styrenic monomer unit and 5 to 80 mass % of the (meth)acrylic acid ester monomer unit in 100 mass % of the copolymer, and contains 0.001 to 1.0 part by mass of the hindered amine light stabilizer (B) per 100 parts by mass of the styrenic resin (A). [2] The optical styrene-based resin composition according to [1], wherein the hindered amine light stabilizer (B) is an NH-type hindered amine light stabilizer and / or an NR-type hindered amine light stabilizer. [3] The NH-type hindered amine light stabilizer is bis(2,2,6,6-tetramethylpiperidin-4-yl) sebacate, 2,2,6,6-tetramethyl-4-piperidyl hexadecanoate, 2,2,6,6-tetramethyl-4-piperidyl octadecanoate, Tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, Polycondensation product of N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine and 4-morpholino 2,6-dichloro-1,3,5-triazine, Polycondensation 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, Polycondensation product of N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine, 2,4,6-trichloro-1,3,5-triazine, N-butyl-1-butanamine and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine, 1,6,11-tris[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidyl)amino)-s-triazin-6-yl]aminoundecane, Polycondensation product of 1,2,3,4-butanetetracarboxylic acid, 2,2,6,6-tetramethyl-4-piperidinol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5,5]undecane-3,9-diethanol, The optical styrene-based resin composition according to [2], wherein the optical styrene-based resin composition is at least one selected from the following: [4] The NR-type hindered amine light stabilizer is methyl(1,2,2,6,6-pentamethylpiperidin-4-yl)sebacate, Bis(1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate, Bis(1,2,2,6,6-pentamethylpiperidin-4-yl) n-butyl 3,5-di-tert-butyl 4-hydroxybenzyl malonate, Polycondensation product of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol and succinic acid dimethyl ester, 1,5,8,12-tetrakis[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, Polycondensation product 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, A mixture of a polycondensate of succinic acid and (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)ethanol and N,N',N'',N'''-tetrakis-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine, The optical styrene-based resin composition according to [2] or [3], wherein the optical styrene-based resin composition is at least one selected from the following: [5] The optical styrene-based resin composition according to any one of [1] to [4], further comprising 0.001 to 0.5 parts by mass of a phosphorus-based antioxidant (C-1) relative to 100 parts by mass of the styrene-based resin (A). [6] The optical styrene-based resin composition according to [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-1-phenyloxy)(2-ethylhexyloxy)phosphorus, 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, tetrakis(2,4-di-tert-butylphenyl)[1,1biphenyl]-4,4'-diylbisphosphonite, and bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite. [7] A light guide plate obtained by molding the optical styrene-based resin composition according to any one of [1] to [6]. [8] An edge-light type surface light source unit having the light guide plate described in [7] and a light source that supplies LED light to an end surface of the light guide plate. [9] A light diffusion plate obtained by molding the optical styrene-based resin composition according to any one of [1] to [6].

[10] A direct-type surface light source unit having the light diffusion plate according to [9] and a light source that supplies LED light to the light diffusion plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described. Various features shown in the following embodiments can be combined with each other. Also, each feature can be an invention independently.

[0012] 1. Optical styrene resin composition An optical styrene-based resin composition according to one embodiment of the present invention is an optical styrene-based resin composition containing a styrene-based resin (A) and a hindered amine light stabilizer (B).

[0013] <Styrene-based resin (A)> The styrene-based resin (A) is a resin obtained by copolymerizing a monomer including a styrene-based monomer and a (meth)acrylic acid ester-based monomer. The styrene-based resin (A) is a copolymer including a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit. The copolymer contains 95-20% by mass of a styrene-based monomer unit and 5-80% by mass of a (meth)acrylic acid ester-based monomer unit in 100% by mass of the copolymer, preferably 90-25% by mass of a styrene-based monomer unit and 10-75% by mass of a (meth)acrylic acid ester-based monomer unit, more preferably 80-30% by mass of a styrene-based monomer unit and 20-70% by mass of a (meth)acrylic acid ester-based monomer unit, and even more preferably 60-40% by mass of a styrene-based monomer unit and 40-60% by mass of a (meth)acrylic acid ester-based monomer unit. By setting the content in such a range, transparency, hue, and dimensional stability can be simultaneously satisfied. By making the styrene monomer 90% by mass or less, a light guide plate excellent in transparency and hue can be obtained, and by making the styrene monomer 20% or more, a light guide plate excellent in dimensional stability can be obtained. The content of the (meth)acrylic acid ester monomer unit in the styrene 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, or 80% by mass, and may be within a range between any two of the numerical values ​​exemplified here.

[0014] Examples of the styrene monomer include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, ethylstyrene, and pt-butylstyrene. These can be used alone or in combination of two or more. The styrene monomer is preferably styrene.

[0015] Examples of the (meth)acrylic acid ester monomer include (meth)acrylic acid alkyl esters such as 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, and lauryl (meth)acrylate; and (meth)acrylic acid aryl esters such as phenyl (meth)acrylate and benzyl (meth)acrylate. esters; (meth)acrylic acid cycloalkyl esters such as cyclohexyl (meth)acrylate, 4-t-butylcyclohexyl (meth)acrylate, 2-norbornyl (meth)acrylate, isobornyl (meth)acrylate, adamantan-1-yl (meth)acrylate, 2-methyladamantan-2-yl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, and tricyclodecanyl (meth)acrylate; glycidyl (meth)acrylate; and dicyclopentanyl (meth)acrylate. These may be used alone or in combination of two or more. The (meth)acrylic acid ester monomer is preferably an alkyl (meth)acrylate, and more preferably methyl methacrylate.

[0016] The styrene-based resin (A) may be a copolymer obtained by copolymerizing a styrene-based monomer and a (meth)acrylic acid ester-based monomer with a monomer copolymerizable therewith. Examples of the copolymerizable monomer include (meth)acrylic acids such as acrylic acid and methacrylic acid; vinyl cyanides such as acrylonitrile and methacrylonitrile; α,β-ethylenically unsaturated carboxylic acids such as maleic anhydride and fumaric acid; and imides such as phenylmaleimide and cyclohexylmaleimide. These may be used alone or in combination of two or more.

[0017] The weight average molecular weight (Mw) of the styrene resin (A) is preferably 50,000 to 400,000, more preferably 100,000 to 350,000. The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the styrene resin (A) is preferably 1.0 to 3.5, more preferably 1.5 to 3.0. By setting it in such a range, both moldability and strength of the light guide plate can be achieved. If the weight average molecular weight (Mw) is less than 50,000, the strength of the molded product may be insufficient, and if it exceeds 400,000, the moldability may decrease. If the number average molecular weight (Mn) ratio (Mw / Mn) is less than 1.0, the moldability may decrease, and if it exceeds 3.5, the strength of the molded product may decrease.

[0018] <Hindered amine light stabilizer (B)> The optical styrene-based resin composition contains 0.001 to 1.0 parts by mass of the hindered amine light stabilizer (B) relative to 100 parts by mass of the styrene-based resin (A), preferably 0.01 to 0.3 parts by mass. By setting the content in such a range, the transparency, hue, and light stability against an LED light source can be improved. The content of the hindered amine light stabilizer (B) relative 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, or 1.0 parts by mass, and may be within a range between any two of the numerical values ​​exemplified here. The hindered amine light stabilizer (B) may be used alone or in combination of two or more kinds.

[0019] The hindered amine light stabilizer (B) is a compound having a structural unit represented by the following general formula (1).

[0020] [ka]

[0021] In 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 R includes a hydrogen atom, a linear or branched alkyl group having 1 to 10 carbon atoms, a methylene group and an alkoxy group. Here, when R is a hydrogen atom, it is referred to as an NH-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 referred to as an NR-type hindered amine light stabilizer, and when R is an alkoxy group, it is referred to as an N-OR hindered amine light stabilizer.

[0022] Specific examples of NH-type hindered amine light stabilizers include bis(2,2,6,6-tetramethylpiperidin-4-yl)sebacate (TINUVIN770DF manufactured by BASF), 2,2,6,6-tetramethyl-4-piperidylhexadecanoate, 2,2,6,6-tetramethyl-4-piperidyloctadecanoate (SABOSTAB UV91 manufactured by SONGWON), tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate (ADK STAB LA-57 manufactured by ADEKA), polycondensate of N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine and 4-morpholino 2,6-dichloro-1,3,5-triazine (SABOSTAB manufactured by SONGWON), UV79), polycondensation 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 (BASF Chimass®b944FDL), polycondensation product of N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine, 2,4,6-trichloro-1,3,5-triazine, N-butyl-1-butanamine and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine (SONGWON SABOSTAB UV40), 1,6,11-tris[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidyl)amino)-s-triazin-6-yl]aminoundecane (BASF Chimass®rb2020FDL), 1,2,3,4-butanetetracarboxylic acid, 2,2,6,6-tetramethyl-4-piperidinol, and β,β,β′,β′-tetramethyl-2,4,8,10-tetraoxaspiro[5,5]undecane-3,9-diethanol polycondensate (ADEKA ADKSTAB LA-68), dodecyl 3-(2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazadispiro(5.1.11.2)henicosan-20-yl)propionate, tetradecyl 3-(2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazadispiro(5.1.11.2) Henicosane-20-yl)propionate (HOSTAVIN 3030 manufactured by CLARIANT), and polycondensate of 2,2,4,4-tetramethyl-7-oxa-3,20-diazadispiro-(5.1.11.2)henicosan-21-one and epichlorohydrin (HOSTAVIN N30P manufactured by CLARIANT).

[0023] Specific examples of NR-type hindered amine light stabilizers include methyl (1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate, bis(1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate (BASF's TINUVIN 292, TINUVIN 765), bis(1,2,2,6,6-pentamethylpiperidin-4-yl) n-butyl 3,5-di-tert-butyl 4-hydroxybenzyl malonate (BASF's TINUVIN 144), and polycondensate of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol and dimethyl succinate (BASF's TINUVIN 622SF), 1,5,8,12-tetrakis [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 (BASF Chimass® rb119), polycondensate 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 (ADEKA ADKSTAB LA-63P), a polycondensate of succinic acid and (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)ethanol, and a mixture of N,N',N'',N'''-tetrakis-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine (TINUVIN111FDL, manufactured by BASF).

[0024] Specific examples of N-OR type hindered amine light stabilizers include bis(1-octyloxy-2,2,6,6-tetramethylpiperidyl)sebacate (TINUVIN123 manufactured by BASF) and bis(1-undecanoxy-2,2,6,6-tetramethylpiperidin-4-yl)carbonate (ADKSTAB LA-81 manufactured by ADEKA).

[0025] Among them, the hindered amine light stabilizer (B) is preferably an NH-type hindered amine light stabilizer and / or an NR-type hindered amine light stabilizer, and more preferably an NR-type hindered amine light stabilizer, in terms of having little effect on the transparency and hue of the optical styrene-based resin composition. It is generally known that the hindered amine light stabilizer (B) is oxidized by oxygen, ultraviolet light, and peroxide to generate nitroxy radicals. In this embodiment, the mechanism by which the hindered amine light stabilizer (B) can improve the light stability of an LED light source for long-term use is still being elucidated, but the present invention has revealed the effectiveness of the hindered amine light stabilizer (B).

[0026] <Antioxidants (C)> The optical styrene-based resin composition preferably contains 0.001 to 0.5 parts by mass of the phosphorus-based antioxidant (C-1) relative to 100 parts by mass of the styrene-based resin (A), more preferably 0.002 to 0.4 parts by mass, and particularly preferably 0.005 to 0.3 parts by mass. By setting the content in such a range, the 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, or 0.5 parts by mass, and may be within a range between any two of the numerical values ​​exemplified here.

[0027] The phosphorus-based antioxidant (C-1) is a phosphorous (or phosphite) ester having no phenolic hydroxyl group in the basic skeleton, and is preferably a phosphorous (or phosphite) ester, which is a trivalent phosphorus compound. Specific examples of phosphorus-based antioxidants (C-1) include 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus, bis-(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, tris(2,4-di-tert-butylphenyl)phosphite, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]undecane, tetrakis(2,4-di-tert-butylphenyl)[1,1biphenyl]-4,4'-diylbisphosphonite, bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite, and the like. These may be used alone or in combination of two or more.

[0028] The optical styrene resin composition may contain 0 to 0.5 parts by mass of a phenolic antioxidant (C-2) relative to 100 parts by mass of the styrene resin (A). If the content of the phenolic antioxidant (C-2) exceeds 0.5 parts by mass, the hue deteriorates, which is not preferable. The content of the phenolic antioxidant (C-2) 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, or 0.5 parts by mass relative to 100 parts by mass of the styrene resin (A), and may be within a range between any two of the numerical values ​​exemplified here.

[0029] The phenol-based antioxidant (C-2) is an antioxidant that has a phenolic hydroxyl group in the basic skeleton and is not a phosphorous ester. Specific examples of the phenol-based antioxidant (C-2) include octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, ethylene bis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], and pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which can be used alone or in combination of two or more.

[0030] The antioxidant includes phosphorus-phenol-based compounds 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]dioxaphosphepine. In the case of such compounds, the optical styrene-based resin composition is considered to contain both a phosphorus-based antioxidant and a phenol-based antioxidant, and for example, when the optical styrene-based resin composition contains 0.1 part by mass of a phosphorus-phenol-based compound relative to 100 parts by mass of the styrene-based resin (A), the optical styrene-based resin composition is considered to contain 0.1 part by mass of a phosphorus-based antioxidant and 0.1 part by mass of a phenol-based antioxidant.

[0031] <Other ingredients> The content of t-butylcatechol (TBC) in the optical styrene resin composition is preferably 10 ppm or less, more preferably 5 ppm or less. By setting the content in this 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, and may be within any two of the values ​​exemplified here.

[0032] The content of 6-tert-butyl-2,4-xylenol (TBX) in the optical styrene resin composition is preferably 10 ppm or less, more preferably 5 ppm or less. By setting the content in this 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, and may be within the range between any two of the values ​​exemplified here.

[0033] The optical styrene-based resin composition may contain release agents such as sulfur-based antioxidants, lactone-based antioxidants, ultraviolet absorbers, antistatic agents, hydrophilic additives, liquid paraffin (mineral oil), polyethylene wax, microcrystalline wax, bluing agents, higher fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid, higher fatty acid amides such as stearic acid amide, erucic acid amide, and ethylene bisstearic acid amide, higher fatty acid glycerides such as lauric acid monoglyceride, palmitic acid monoglyceride, stearic acid monoglyceride, and behenic acid monoglyceride, and higher alcohols such as myristyl alcohol, cetyl alcohol, and stearyl alcohol, provided that the properties of the present invention are not impaired.

[0034] The melt mass flow rate (MFR) of the optical styrene resin composition is preferably 0.5 to 5.0 g / 10 min, and more preferably 1.0 to 4.0 g / 10 min, at a temperature of 200° C. and a load of 49 N. If the MFR is less than 0.5 g / 10 min, molding stability decreases, and if the MFR exceeds 5.0 g / 10 min, strength becomes insufficient.

[0035] The Vicat softening temperature of the optical styrene-based 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 may be deformed depending on the usage environment.

[0036] <Method of producing optical styrene-based resin composition> The polymerization method of the styrene-based resin (A) may be a known styrene polymerization method such as bulk polymerization, solution polymerization, suspension polymerization, or emulsion polymerization. In terms of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization is preferred. As the solvent, for example, alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane can be used.

[0037] During polymerization of the styrene-based resin (A), polymerization aids such as polymerization initiators, chain transfer agents, crosslinking agents, and other polymerization aids may be used as necessary. As the polymerization initiator, a radical polymerization initiator is preferred, and examples of the polymerization initiator include peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butylperoxy)butane, 2,2-di(4,4-di-t-butylperoxycyclohexyl)propane, and 1,1-di(t-amylperoxy)cyclohexane, hydroperoxides such as cumene hydroperoxide and t-butyl hydroperoxide, alkyl peroxides such as t-amylperoxyisononanoate, and dialkyl peroxides such as t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, and di-t-hexyl peroxide. Examples of the peroxides include peroxyesters such as t-butyl peroxyacetate, t-butyl peroxybenzoate, and t-butyl peroxyisopropyl monocarbonate; peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyether tetrakis(t-butyl peroxycarbonate); N,N'-azobis(cyclohexane-1-carbonitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile), and N,N'-azobis[2-(hydroxymethyl)propionitrile]; and the like. These may be used alone or in combination of two or more. Examples of the chain transfer agent include aliphatic mercaptans such as n-dodecyl mercaptan and tert-dodecyl mercaptan, aromatic mercaptans, thiocarboxylic acids such as thioglycolic acid and mercaptopropionic acid, polyfunctional mercaptans obtained by esterifying the hydroxyl groups of polyhydric alcohols such as ethylene glycol, tetraethylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, and sorbitol with thioglycolic acid or mercaptopropionic acid, pentaphenylethane, α-methylstyrene dimer, and terpinolene. Among these, aliphatic mercaptans, aromatic mercaptans, thiocarboxylic acids, and polyfunctional mercaptans are preferred from the viewpoint of ease of molecular weight adjustment.

[0038] In the case of continuous polymerization, the styrene-based resin (A) can be produced by a method including a polymerization step, a devolatilization step, and a granulation step.

[0039] First, in the polymerization step, a known complete mixing tank type stirring tank or tower type reactor is used, and the polymerization reaction is controlled by adjusting the polymerization temperature, etc., so as to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate.

[0040] The polymer solution containing the polymer that has left the polymerization process is transferred to the devolatilization process, where unreacted monomers and polymerization solvent are removed. The devolatilization process is comprised of a vacuum devolatilization tank with a heater and a devolatilization extruder with a vent. The molten polymer that has left the devolatilization process is transferred to the granulation process. In the granulation process, the molten resin is extruded in the form of strands from a multi-hole die, and processed into pellets by the cold cut method, the air hot cut method, or the underwater hot cut method.

[0041] The optical styrene-based resin composition can be produced by adding a hindered amine light stabilizer (B), a phosphorus-based antioxidant (C-1), and a phenol-based antioxidant (C-2) to a styrene-based resin (A). The hindered amine light stabilizer (B), the phosphorus-based antioxidant (C-1), and the phenol-based antioxidant (C-2) may be added to the raw material solution before the polymerization of the styrene-based resin (A), or may be mixed in an extruder or a static mixer installed before granulation after the polymerization of the styrene-based resin (A). In addition, the styrene-based resin (A) may be produced by dry blending the pellets after granulation with the hindered amine light stabilizer (B), the phosphorus-based antioxidant (C-1), and the phenol-based antioxidant (C-2) and melt-kneading. Alternatively, the hindered amine light stabilizer (B), the phosphorus-based antioxidant (C-1), and the phenol-based antioxidant (C-2) may be melt-kneaded in advance with a small amount of a styrene-based resin to prepare a pellet-shaped master batch, which may then be dry-blended with the styrene-based resin (A) and then melt-kneaded to prepare the composition.

[0042] The content of t-butylcatechol or 6-tert-butyl-2,4-xylenol in the optical styrene-based resin composition can be adjusted at the start of polymerization of the styrene-based resin (A) and in the subsequent devolatilization step or the like.

[0043] 2.Light guide plate A light guide plate according to one embodiment of the present invention is a molded product obtained by molding the optical styrene-based resin composition. The light guide plate is a light guide plate that can be used in an edge-light type surface light source unit.

[0044] <Shape of light guide plate> The light guide plate may have an uneven shape on the surface of the light guide plate. More specifically, the light guide plate may have a plurality of lenticular-shaped and / or prism-shaped convex portions 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 are particularly provided on one surface which is the front surface (light-emitting surface) of the light guide plate. They may also be provided on other surfaces if necessary, but it is more preferable that they are provided only on the front surface (light-emitting surface) of the light guide plate.

[0045] Here, the lenticular-shaped convex portion is an arc-shaped convex portion, and is a protrusion having an arc-shaped cross-sectional edge. The prism-shaped convex portion is an arc-shaped convex portion, and is a protrusion having a triangular mountain-shaped cross-sectional edge. The convex portion may be formed in a plurality of stripes parallel to each other. The convex portion may be formed integrally with the light guide plate.

[0046] 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. Within such a range, it is easy to produce a light guide plate having excellent moldability, such as excellent extrusion stability, and strength, in molding the optical styrene-based resin composition.

[0047] <Optical properties> The light guide plate has an average transmittance of 85% or more, more preferably 86% or more, for wavelengths of 380 to 780 nm when the light path length is 115 mm.

[0048] The YI value of the light guide plate when the optical path length is 115 mm is preferably 6.0 or less, and more preferably 4.0 or less.

[0049] <Method of manufacturing light guide plate> The light guide plate according to one embodiment of the present invention is obtained by molding the optical styrene-based resin composition described above, and the molding method can be a known method such as sheet extrusion molding, injection molding, compression molding, etc., but in terms of productivity and ease of making large-sized molded products, continuous sheet extrusion molding equipped with a surface shape transfer mold is preferable. An example of the sheet extrusion molding is a continuous sheet extrusion molding method having an extrusion process in which a resin is supplied to a feed block in a heated and molten state and an extrusion sheet is continuously produced from a die, a pressing process in which the resin sheet is sandwiched between a pressure roll and a cooling roll, and a conveying process in which the resin sheet is conveyed while being in close contact with the cooling roll after the pressing process, and a transfer mold is provided on the surface of the cooling roll, and any uneven shape can be transferred to the sheet surface by changing the shape of the transfer mold.

[0050] The light guide plate may have an uneven surface on the front surface (light-emitting surface), and the rear surface may be subjected to a reflective treatment for diffusely reflecting light. Examples of the reflective treatment include silk screen printing and inkjet printing, as well as a method of applying dot-shaped unevenness by laser irradiation, and ink having fine particles that diffuse light can be used for printing the dot pattern.

[0051] 3. Edge-light type surface light source unit An edge-light type surface light source unit according to one embodiment of the present invention is an edge-light type surface light source unit having the above-mentioned light guide plate and a light source that supplies LED light to an end face of the light guide plate. The edge-light type surface light source unit is suitably used as a surface light source device for a liquid crystal display device.

[0052] 4. Light diffusion plate A light diffusion plate according to one embodiment of the present invention is a molded product obtained by molding the above-mentioned optical styrene-based resin composition. The light diffusion plate is a light diffusion plate that can be used in a direct type surface light source unit.

[0053] <Shape of light diffusion plate> The thickness of the light diffusion plate according to one embodiment of the present invention is not limited, but is, for example, 1 to 3 mm. The light diffusion plate may have an antistatic agent applied to its surface. By applying the antistatic agent, adhesion of dust and the like due to static electricity is suppressed after the light diffusion plate is attached to a backlight device, so that the light diffusion plate can be used for a long period of time without a decrease in brightness. In addition, the light diffusion plate of the present invention may have a fine uneven shape such as embossing on both sides or one side, or a lenticular shape or prism shape on both sides or one side.

[0054] The light diffusion plate may contain 0.1 to 1.0 parts by mass of a light diffusing agent relative to 100 parts by weight of the optical styrene-based resin composition. The light diffusing agent may be particles having a different refractive index from that of the optical styrene-based resin composition and having the effect of diffusing incident light, and may be, for example, organic particles such as styrene-based polymer particles, acrylic polymer particles, and siloxane-based polymer particles, or inorganic particles such as glass beads, silica particles, aluminum hydroxide particles, calcium carbonate particles, barium sulfate particles, titanium oxide particles, and talc. Among these, at least one selected from acrylic polymer particles, styrene-based polymer particles, and siloxane-based polymer particles is preferred.

[0055] <Method of manufacturing light diffusion plate> The light diffusion plate according to one embodiment of the present invention can be manufactured by molding the optical styrene resin composition by various methods such as extrusion molding and injection molding, but is preferably manufactured by extrusion molding. An example of extrusion molding is a method in which the optical styrene resin composition is melt-kneaded using a single-screw extruder or a twin-screw extruder, continuously extruded from a T-die, and then cooled and solidified by a cooling roll unit. When forming an uneven shape on the surface of the light diffusion plate, a transfer mold is provided on the surface of the cooling roll, and any uneven shape can be formed by changing the shape of the transfer mold. In addition, when a surface layer is laminated on both sides or one side of the light diffusion plate, methods such as a co-extrusion method, a bonding method, a thermal adhesion method, a solvent adhesion method, a casting method, and a surface coating method can be adopted.

[0056] 5. Direct-type surface light source unit A direct-type surface light source unit according to one embodiment of the present invention includes the light diffusion plate and a light source that supplies LED light to the light diffusion plate. The direct-type surface light source unit is preferably used as a surface light source device for a liquid crystal display device. EXAMPLES

[0057] The present invention will be described in more detail below with reference to examples. Note that these are merely illustrative and do not limit the scope of the present invention.

[0058] 1. Production of optical styrene resin compositions [Example 1] The polymerization process was performed by connecting the first reactor, which was a complete mixing type stirring tank, and the second reactor, which was a plug flow type reactor with a static mixer, in series, to produce a styrene-based resin. The capacity of each reactor was 30 liters for the first reactor and 12 liters for the second reactor. The raw material composition was 51 mass% styrene (TBC concentration 11 μg / g), 39 mass% methyl methacrylate (TBX concentration 7 μg / g), and 10 mass% ethylbenzene. At the inlet of the first reactor, the polymerization initiator was adjusted to 150 ppm of t-butylperoxyisopropyl monocarbonate (manufactured by NOF Corporation: Perbutyl I) and the chain transfer agent was adjusted to 500 ppm of n-dodecyl mercaptan (manufactured by Arkema Co., Ltd.) (both concentrations are based on the mass of the entire monomer), and the raw material solution was continuously supplied to the first reactor set at 128 ° C. at 8.0 kg / h. The obtained polymerization solution was continuously fed to the second reactor to complete the polymerization. The polymerization rate of the monomer was 70%. In the second reactor, a temperature gradient was applied along the flow direction, and the temperature was adjusted to 130°C at the middle part and 145°C at the outlet part. Subsequently, the solution containing the polymer continuously taken out from the second reactor was introduced into a vacuum volatilization tank equipped with a preheater composed of two stages in series, the temperature of the preheater was adjusted so that the resin temperature was 220°C, and unreacted styrene and ethylbenzene were separated at a pressure of 0.8 kPa. The obtained molten polymer was continuously fed into an extruder, and 0.1 parts by mass of a hindered amine light stabilizer (770) was added from an additive feed port to 100 parts by mass of the polymer, and the mixture was mixed at a set temperature of 220°C, extruded into a strand shape from a multi-hole die, and the strand was cooled and cut by a cold cut method to pelletize. The TBC concentration in the obtained optical styrene-based resin composition was 1.5 μg / g, and the TBX concentration was 0.2 μg / g. The weight average molecular weight (Mw) was 170,000, and the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) was 2.0.

[0059] [Examples 2 to 17 and Comparative Examples 1 to 6] An optical styrene-based resin composition and a light guide plate were produced in the same manner as in Example 1, except that the composition of the raw material solution and the polymerization conditions were changed as shown in Table 1, and the blending 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 as shown in Table 2 (Tables 2-1 and 2-2) to Table 3. Various measurement and evaluation results are shown in Table 2 (Tables 2-1 and 2-2) to Table 3.

[0060] [Table 1]

[0061] [Table 2-1]

[0062] [Table 2-2]

[0063] [Table 3]

[0064] The hindered amine light stabilizer (B), phosphorus-based antioxidant (C-1), phenol-based antioxidant (C-2), and ultraviolet absorber (D) in Tables 2 (Tables 2-1 and 2-2) to 3 are as follows:

[0065] (Hindered amine light stabilizer (B)) 770: Bis(2,2,6,6-tetramethylpiperidin-4-yl)sebacate (BASF TINUVIN770DF) 944: Polycondensation 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 (BASF Chimass®b944FDL) 292: A mixture of 25% methyl (1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate and 75% bis(1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate (TINUVIN 292, manufactured by BASF) 123: Bis(1-octyloxy-2,2,6,6-tetramethylpiperidyl) sebacate (BASF TINUVIN123)

[0066] (Phosphorus-based antioxidant (C-1)) 168: Tris(2,4-di-tert-butylphenyl)phosphite (Irgafos 168, manufactured by BASF) HP-10: 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus (ADEKA ADKSTAB HP-10) 126: Bis-(2,4-di-tert-butylphenyl)pentaerythritol diphosphite (Irgafos 126, manufactured by BASF)

[0067] (Phenol-based antioxidant (C-2)) 1076: Octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (BASF Irganox 1076)

[0068] (Ultraviolet absorber (D)) P: 2-(2-hydroxy-5-methylphenyl)benzotriazole (TINUVIN P manufactured by BASF)

[0069] 2. Evaluation The optical styrene-based resin compositions shown in Tables 2 (Tables 2-1 and 2-2) to 3 were evaluated by the following methods.

[0070] <Melt Mass Flow Rate (MFR)> The melt mass flow rate was measured in accordance with JIS K 7210 under conditions of a temperature of 200° C. and a load of 49 N.

[0071] <Vicat softening temperature> The Vicat softening temperature was measured in accordance with JIS K 7206 at a temperature rise rate of 50° C. / hr and a test load of 50 N.

[0072] <Contents of TBC and TBX in optical styrene resin compositions> 0.2 g of the optical styrene resin composition was dissolved in a small amount of THF, and then 200 μL of BSTFA (M,O-bis(trimethylsilyl)trifluoroacetamide) was added to carry out trimethylsilyl derivatization treatment. The volume was adjusted to 10 mL with THF, and the supernatant separated by centrifugation was measured by gas chromatography mass spectrometry (GC / MS) under the following conditions. A calibration curve prepared in advance was used to determine the concentration. GC device: Agilent 7890A Column: Agilent DB-5ms (0.25 mm id x 30 m) Liquid phase film thickness: 0.25 μm Column temperature: 50℃ (1 min) → (20℃ / min temperature increase) → 320℃ (6.5 min) Total 20 min Injection port: 300℃, 1.5mL / min, (split ratio 1:5) Injection volume: 1μL MS device: Agilent 5975C Interface temperature: 320℃ MS detection conditions: SIM measurement TBC (m / z 295 for quantification, m / z 310 for confirmation)

[0073] <Contents of hindered amine light stabilizer (B), phosphorus-based antioxidant (B-1), and phenol-based antioxidant (B-2) in optical styrene-based resin composition> After 1.0 g of the optical styrene resin composition was completely dissolved in 20 mL of THF, 5 mL of methanol was added dropwise and stirred for 20 minutes. The mixture was centrifuged at 4000 rpm for 10 minutes, and the separated supernatant was measured by gas chromatography (GC) under the following conditions. The concentration was determined using a calibration curve prepared in advance. GC equipment: Shimadzu GC2010 Plus Column: DB-1 (30m x 0.25mm id, df = 0.10μm) Column temperature: 240℃ (1min) → (10℃ / min temperature increase) → 320℃ (15min) Injection port: 320℃, 1.02mL / min (split ratio 1:5) Injection volume: 1μL

[0074] <Weight average molecular weight (Mw)> The weight average molecular weight (Mw), Z average molecular weight (Mz), and number average molecular weight (Mn) were measured by gel permeation chromatography (GPC) under the following conditions. GPC model: Showa Denko Co., Ltd. Shodex GPC-101 Column: Polymer Laboratories PLgel 10μm MIXED-B Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass Temperature: oven 40℃, injection port 35℃, detector 35℃ Detector: Differential refractometer The molecular weight was calculated as a polystyrene-equivalent molecular weight by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.

[0075] 3. Manufacturing and evaluation of light guide plates <Manufacture of light guide plates> The optical styrene-based resin composition was fed into a single-screw vented extruder with a screw diameter of 90 mm and L / D=32, melt-kneaded at 200 to 235°C, and then extruded through a T-die with a lip width of 1000 mm and a lip opening of 3.0 mm at a T-die temperature of 245 to 250°C. After cooling and solidifying with three vertical cooling rolls, the end faces were trimmed to obtain a light guide plate with a width of 800 mm and a thickness of 2.0 mm.

[0076] <Evaluation of light guide plates> The average transmittance, YI value, dimensional stability (deformation due to moisture absorption), and LED durability of the light guide plates in Tables 2 and 3 were evaluated as follows.

[0077] <Average transmittance and YI value of light guide plate> The average transmittance and YI value were measured according to the following procedure. A test piece of 115 mm × 85 mm was cut out from the light guide plate obtained above, and the end face was polished by buffing to create a plate-shaped molded product having a mirror surface on the end face. For the plate-shaped molded product after polishing, using a UV-visible spectrophotometer V-670 manufactured by JASCO Corporation, the spectral transmittance at a wavelength of 350 nm to 800 nm with an optical path length of 115 mm was measured for incident light with a size of 20 × 1.6 mm and a spread angle of 0°, and the YI value at a viewing angle of 2° under a C light source was calculated according to JIS K7105. The average transmittance (total light transmittance) was calculated as the average of the spectral transmittances at wavelengths of 380 to 780 nm.

[0078] <Dimensional stability (moisture absorption deformation)> A test piece of 200 mm × 300 mm was cut out from the light guide plate obtained above, and the test piece was stored for 500 hours under the conditions of a temperature of 60°C and a relative humidity of 90%. The dimensional change of the long side before and after storage was measured, and the deformation rate was calculated by the following formula. Deformation rate = ((long side length after storage) - (long side length before storage)) ÷ (long side length before storage) × 100 (%) The dimensional stability (moisture absorption change) of the light guide plate was evaluated as ○ for those with a change rate of less than 0.10%, △ for those with a change rate of 0.10 to 0.15%, and × for those with a change rate of more than 0.15%.

[0079] <LED durability> A test piece of 115 mm × 85 mm was cut out from the light guide plate obtained above, and the end face was polished using an end face polishing machine (GCPB-500 manufactured by Megatechnique Co., Ltd.) with a diamond blade rotating at a speed of 8000 rpm at a feed rate of 2.0 m / min by 0.2 mm to create a plate-shaped molded product having a mirror surface on the end face. For the plate-shaped molded product after polishing, a flat-type blue LED light source for TV (peak wavelength 445 nm) was placed at a position 0.5 mm from the end face, and in an environment of 80°C, 0.05 W / mm 2The LED light was irradiated for 500 hours with an input current of 1.0 mA. For the plate-shaped molded product after the test, the spectral transmittance was measured at a wavelength of 350 nm to 800 nm with an optical path length of 115 mm for incident light with a size of 20 × 1.6 mm and a spread angle of 0° using a UV-visible spectrophotometer V-670 manufactured by JASCO Corporation, and the YI value at a field of view of 2° with a C light source was calculated according to JIS K7105. The value obtained by subtracting the YI value before the test from the YI value after the test was defined as ΔYI. In addition, the LED light entrance part of the plate-shaped molded product after the test was visually checked, and LED durability was evaluated by marking those that did not change as ◯ and those that carbonized as ×.

[0080] In Examples 1 to 17, the transparency, hue, and dimensional stability were good, no carbonization occurred after exposure to LED, and the hue stability was excellent.

Claims

1. An optical styrene-based resin composition comprising: (A) a styrene-based resin which is a copolymer containing a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit; and (B) a hindered amine light stabilizer, The copolymer contains, based on 100 mass% of the copolymer, 85 to 20 mass% of the styrene-based monomer unit and 15 to 80 mass% of the (meth)acrylic acid ester-based monomer unit, The styrene-based resin (A) contains 0.001 to 1.0 part by mass of the hindered amine light stabilizer (B) relative to 100 parts by mass of the styrene-based resin (A), The hindered amine light stabilizer (B) contains an N-R type hindered amine light stabilizer (however, excluding those containing 10 to 60 parts by mass of a graft copolymer obtained by graft copolymerizing a monomer mixture containing at least a styrene-based monomer and a (meth)acrylic acid ester-based monomer in the presence of a rubber polymer, and 40 to 90 parts by mass of the styrene-based resin (A).

2. An optical styrene-based resin composition comprising: (A) a styrene-based resin which is a copolymer containing a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit; and (B) a hindered amine light stabilizer, The copolymer contains, based on 100 mass% of the copolymer, 85 to 45 mass% of the styrene-based monomer unit and 15 to 55 mass% of the (meth)acrylic acid ester-based monomer unit, The styrene-based resin (A) contains 0.001 to 1.0 part by mass of the hindered amine light stabilizer (B) relative to 100 parts by mass of the styrene-based resin (A), The optical styrene-based resin composition, wherein the hindered amine light stabilizer (B) comprises an N-R type hindered amine light stabilizer.

3. 3. The optical styrene-based resin composition according to claim 1, wherein the hindered amine light stabilizer (B) is an N-R type hindered amine light stabilizer.

4. The N-R type hindered amine light stabilizer is methyl(1,2,2,6,6-pentamethylpiperidin-4-yl)sebacate, bis(1,2,2,6,6-pentamethylpiperidin-4-yl)sebacate, Bis(1,2,2,6,6-pentamethylpiperidin-4-yl) n-butyl 3,5-di-tert-butyl 4-hydroxybenzyl malonate, Polycondensation product of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol and dimethyl succinate, 1,5,8,12-tetrakis[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, Polycondensation product 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]undencane-3,9-diethanol, a mixture of a polycondensate of succinic acid and (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)ethanol and N,N',N",N'"-tetrakis-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine, The optical styrene-based resin composition according to claim 1 or 2, which is at least one selected from the following:

5. 3. The optical styrene-based resin composition according to claim 1, further comprising 0.001 to 0.5 parts by mass of a phosphorus-based antioxidant (C-1) relative to 100 parts by mass of the styrene-based resin (A).

6. The optical styrene-based resin composition according to claim 5, wherein the phosphorus-based antioxidant (C-1) is at least one selected from tris(2,4-di-tert-butylphenyl)phosphite, 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus, 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, tetrakis(2,4-di-tert-butylphenyl)[1,1biphenyl]-4,4'-diylbisphosphonite, and bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite.

7. The optical styrene-based resin composition according to claim 1 or 2, wherein the optical styrene-based resin composition has a melt mass flow rate of 0.5 to 5.0 g / 10 min under conditions of 200° C. and a load of 49 N.

8. The optical styrene-based resin composition according to claim 1 or claim 2, wherein the optical styrene-based resin composition has a Vicat softening temperature of 95 to 104°C, as measured in accordance with JIS K 7206 at a heating rate of 50°C / hr and a test load of 50N.

9. A light guide plate obtained by molding the optical styrene-based resin composition according to claim 1 or 2.

10. A light guide plate obtained by molding an optical styrene-based resin composition, The optical styrene-based resin composition contains a styrene-based resin (A) which is a copolymer containing a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit, and a hindered amine light stabilizer (B), The copolymer contains, based on 100 mass% of the copolymer, 85 to 20 mass% of the styrene-based monomer unit and 15 to 80 mass% of the (meth)acrylic acid ester-based monomer unit, The optical styrene-based resin composition contains 0.001 to 1.0 part by mass of the hindered amine light stabilizer (B) relative to 100 parts by mass of the styrene-based resin (A), The optical styrene-based resin composition has a melt mass flow rate of 0.5 to 5.0 g / 10 min under conditions of 200° C. and a load of 49 N. A light guide plate (excluding those in which the optical styrene-based resin composition contains 10 to 60 parts by mass of a graft copolymer obtained by graft copolymerizing a monomer mixture containing at least a styrene-based monomer and a (meth)acrylic acid ester-based monomer in the presence of a rubber polymer, and 40 to 90 parts by mass of the styrene-based resin (A).

11. A light guide plate obtained by molding an optical styrene-based resin composition, The optical styrene-based resin composition contains a styrene-based resin (A) which is a copolymer containing a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit, and a hindered amine light stabilizer (B), The copolymer contains, based on 100 mass% of the copolymer, 85 to 45 mass% of the styrene-based monomer unit and 15 to 55 mass% of the (meth)acrylic acid ester-based monomer unit, The optical styrene-based resin composition contains 0.001 to 1.0 part by mass of the hindered amine light stabilizer (B) relative to 100 parts by mass of the styrene-based resin (A), The optical styrene-based resin composition has a melt mass flow rate of 0.5 to 5.0 g / 10 min under conditions of 200° C. and a load of 49 N. light guide plate.

12. An edge-light type surface light source unit comprising 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 a light guide plate as described in claim 10 or claim 11 and a light source that supplies LED light to an end surface of the light guide plate.

14. A light diffusion plate obtained by molding the optical styrene-based resin composition according to claim 1 or 2.

15. A light diffusion plate formed from an optical styrene-based resin composition, comprising: The optical styrene-based resin composition contains a styrene-based resin (A) which is a copolymer containing a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit, and a hindered amine light stabilizer (B), The copolymer contains, based on 100 mass% of the copolymer, 85 to 20 mass% of the styrene-based monomer unit and 15 to 80 mass% of the (meth)acrylic acid ester-based monomer unit, The optical styrene-based resin composition contains 0.001 to 1.0 part by mass of the hindered amine light stabilizer (B) relative to 100 parts by mass of the styrene-based resin (A), The optical styrene-based resin composition has a melt mass flow rate of 0.5 to 5.0 g / 10 min under conditions of 200° C. and a load of 49 N. A light diffusion plate (excluding those in which the optical styrene-based resin composition contains 10 to 60 parts by mass of a graft copolymer obtained by graft copolymerizing a monomer mixture containing at least a styrene-based monomer and a (meth)acrylic acid ester-based monomer in the presence of a rubber polymer, and 40 to 90 parts by mass of the styrene-based resin (A)).

16. A light diffusion plate formed by molding an optical styrene-based resin composition, The optical styrene-based resin composition contains a styrene-based resin (A) which is a copolymer containing a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit, and a hindered amine light stabilizer (B), The copolymer contains, based on 100 mass% of the copolymer, 85 to 45 mass% of the styrene-based monomer unit and 15 to 55 mass% of the (meth)acrylic acid ester-based monomer unit, The optical styrene-based resin composition contains 0.001 to 1.0 part by mass of the hindered amine light stabilizer (B) relative to 100 parts by mass of the styrene-based resin (A), The optical styrene-based resin composition has a melt mass flow rate of 0.5 to 5.0 g / 10 min under conditions of 200° C. and a load of 49 N. Light diffuser.

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

18. A direct-type surface light source unit having a light diffusion plate as described in claim 15 or claim 16 and a light source that supplies LED light to the light diffusion plate.

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