TW202346381A - Optical styrene-based resin composition, light guide plate, edge-light system flat-surface light source unit, light diffusion plate, and direct under-light system flat-surface light source unit - Google Patents

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

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

The present invention relates to an optical styrene resin composition, a light guide plate, an edge light surface light source unit, a light diffusion plate, and a direct type surface light source unit.

The backlight of the liquid crystal display device includes a direct type in which the light source is arranged on the front of the display device and an edge light type in which the light source is arranged on the side. Edge-light backlights use a component called a light guide plate that guides light from light sources arranged on the side to the front of the display device. It is used in a wide range of applications such as televisions, desktop PC monitors, notebook PCs, mobile phones, and car navigation monitors. In addition, backlights using light guide plates are also used as lighting devices or signage.

The light transmission distance of the light guide plate is relatively long, and the light loss in the optical path length is large, so it requires a particularly high light transmittance. Therefore, acrylic resin represented by polymethylmethacrylate (PMMA) is used as the material of the light guide plate. However, PMMA has high water absorption, so water absorption may cause the light guide plate to warp or change dimensions. In addition, it is easily thermally decomposed during molding, so if molded at high temperatures, there is a problem that the appearance of the molded product is likely to be poor. In order to improve these problems, for example, in Patent Document 1, it is proposed to use a styrene-methyl (meth)acrylate copolymer as a material for a light guide plate.

On the other hand, the molded body of styrene-methyl (meth)acrylate copolymer has a poorer hue than PMMA, and when used as a backlight, color unevenness may occur. In order to improve this problem, Patent Document 2 is proposed as a hue improvement technology of styrene-methyl (meth)acrylate. [Prior technical literature] [Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 2003-075648 [Patent Document 2] International Publication No. 2016-129675

[Problem to be solved by the invention]

In recent years, as the resolution of backlight units such as televisions and monitors has increased, high-brightness LEDs (light-emitting diodes) have sometimes been used as edge light sources. However, previously, styrene-(methyl) Depending on the usage environment, the end surface of the light guide plate made of methyl acrylate copolymer may deteriorate (carbonate) after being lit for a long time.

The present invention was made in view of such problems, and provides an optical styrene-based resin composition that is excellent in transparency, hue, and dimensional stability, and has excellent light stability for long-term use of an LED light source. [Technical means to solve problems]

According to the present invention, there is provided an optical styrene-based resin composition containing a styrene-based resin (A) that is a copolymer containing a styrene-based monomer unit and a (meth)acrylate-based monomer unit, and a hindered Amine light stabilizer (B), and the above-mentioned copolymer contains 95 to 20 mass% of the above-mentioned styrene monomer units and 5 to 80 mass% of the above-mentioned (meth)acrylate monomer units in 100 mass% of the above-mentioned copolymer. The optical styrenic resin composition contains 0.001 to 1.0 parts by mass of the hindered amine light stabilizer (B) based on 100 parts by mass of the styrenic resin (A).

The present inventors conducted intensive research and found that a styrene-based resin containing a styrene-based monomer unit and a (meth)acrylate-based monomer unit content within a specific range, and a hindered amine light stabilizer within a specific range The present invention was completed by developing an optical styrenic resin composition that simultaneously satisfies transparency, hue, dimensional stability, and light stability for long-term use of an LED light source.

Various embodiments of the present invention are illustrated below. The embodiments shown below can be combined with each other. [1] An optical styrene-based resin composition containing a styrene-based resin (A) that is a copolymer containing a styrene-based monomer unit and a (meth)acrylate-based monomer unit, and a hindered amine light Stabilizer (B), and the above-mentioned copolymer contains 95 to 20 mass% of the above-mentioned styrene-based monomer units and 5-80 mass% of the above-mentioned (meth)acrylate-based monomer units in 100 mass% of the above-mentioned copolymer, and the above-mentioned The optical styrene-based resin composition contains 0.001 to 1.0 parts by mass of the hindered amine light stabilizer (B) based on 100 parts by mass of the styrene-based resin (A). [2] The optical styrenic resin composition according to [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. [3] The optical styrenic resin composition according to [2], wherein the N-H type hindered amine light stabilizer is selected from Bis(2,2,6,6-tetramethylpiperidin-4-yl) sebacate, 2,2,6,6-tetramethyl-4-piperidinyl hexadecanoate, 2,2,6,6-tetramethyl-4-piperidinyl octadecanoate, 1,2,3,4-butanetetracarboxylic acid quaternary (2,2,6,6-tetramethyl-4-piperidinyl) ester, N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine and 4-𠰌linyl 2,6-dichloro-1,3,5- Three condensation polymers, 2,4-Dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-trichloro-N,N'-bis(2,2,6,6 -Condensation polymer of tetramethyl-4-piperidinyl)hexamethylenediamine, N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine and 2,4,6-trichloro-1,3,5-trichloro-1,3,5-trimethyldiamine and Condensation polymer of N-butyl-1-butanamine and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine, 1,6,11-Shen[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidinyl)amine) symmetric tris-6-yl ]Amino undecane, 1,2,3,4-butanetetracarboxylic acid and 2,2,6,6-tetramethyl-4-piperidinol and β,β,β',β'-tetramethyl-2,4, Condensation polymer of 8,10-tetraoxasspiro[5,5]undecane-3,9-diethanol At least 1 of them. [4] The optical styrenic resin composition according to [2] or [3], wherein the N-R type hindered amine light stabilizer is selected from Methyl sebacate (1,2,2,6,6-pentamethylpiperidin-4-yl) ester, Bis(1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate, n-Butyl 3,5-di-tert-butyl 4-hydroxybenzylmalonate bis(1,2,2,6,6-pentamethylpiperidin-4-yl) ester, Condensation polymer of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol and dimethyl succinate, 1,5,8,12-bis[4,6-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidinyl)amino)-1, 3,5-Tris-2-yl]-1,5,8,12-tetraazadodecane, 1,2,3,4-butanetetracarboxylic acid and 1,2,2,6,6-pentamethyl-4-piperidinol and β,β,β',β'-tetramethyl-2, Condensation polymer of 4,8,10-tetraoxasspiro[5,5]undecane-3,9-diethanol, Condensation polymer of succinic acid and (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)ethanol and N,N',N'',N'''-4-(4, 6-Bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-tris-2-yl)-4,7-diazo Mixture of heterodecane-1,10-diamines At least 1 of them. [5] The optical styrene-based resin composition according to any one of [1] to [4], which contains a phosphorus-based antioxidant (C-1) based on 100 parts by mass of the styrene-based resin (A). )0.001～0.5 parts by mass. [6] The optical styrene-based resin composition according to [5], wherein the phosphorus-based antioxidant (C-1) is selected from the group consisting of ginseng (2,4-di-tert-butylphenyl) phosphite , 2,2'-methylenebis(4,6-di-tert-butyl-1-phenoxy)(2-ethylhexyloxy)phosphorus, bis-(2,4-di-tert-butyl) Phenyl) pentaerythritol diphosphite, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9- Diphosphaspiro[5,5]undecane, 4(2,4-di-tert-butylphenyl)[1,1biphenyl]-4,4'-diyl bisphosphonite, phosphorous acid At least one kind of bis(2,4-di-tert-butyl-6-methylphenyl) ethyl ester. [7] A light guide plate formed by molding the optical styrene-based resin composition according to any one of [1] to [6]. [8] An edge light surface light source unit having the light guide plate as described in [7], and a light source that supplies LED light to the end surface of the light guide plate. [9] A light diffusion plate formed 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 as described in [9], and a light source that supplies LED light to the light diffusion plate.

Hereinafter, embodiments of the present invention will be described. Various features shown in the embodiments shown below can be combined with each other. Furthermore, each characteristic matter independently establishes the invention.

1. Styrenic resin composition for optical use An optical styrene resin composition according to one embodiment of the present invention is an optical styrene resin composition containing a styrenic resin (A) and a hindered amine light stabilizer (B).

＜Styrenic resin (A)＞ The styrene-based resin (A) is a resin obtained by copolymerizing a monomer including a styrene-based monomer and a (meth)acrylate-based monomer. The styrene-based resin (A) is a copolymer containing a styrene-based monomer unit and a (meth)acrylate-based monomer unit. The copolymer contains 95 to 20 mass % of styrene monomer units and 5 to 80 mass % of (meth)acrylate monomer units in 100 mass % of the copolymer, and preferably contains 90 to 80 mass % of styrene monomer units. 25% by mass and 10% to 75% by mass of (meth)acrylate monomer units, more preferably 80% to 30% by mass of styrene monomer units and 20% to 70% by mass of (meth)acrylate monomer units. %, and further preferably contains 60 to 40 mass% of styrene monomer units and 40 to 60 mass% of (meth)acrylate monomer units. By setting it within this range, transparency, hue, and dimensional stability can be satisfied at the same time. By setting the styrene-based monomer content to 90% by mass or less, a light guide plate excellent in transparency and hue can be obtained, and by setting the styrene monomer content to 20% or more, a light guide plate excellent in dimensional stability can be obtained. The content of the (meth)acrylate monomer unit in the styrenic 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 within the range between any two of the numerical values illustrated here.

Examples of styrenic monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, ethylstyrene, and p-tert-butylstyrene. wait. These can be used individually by 1 type or in combination of 2 or more types. The styrenic monomer is preferably styrene.

Examples of (meth)acrylate monomers include: (meth)acrylate methyl ester, (meth)ethyl acrylate, (meth)acrylate n-propyl ester, (meth)acrylate isopropyl ester, (meth)acrylate n-butyl acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, isopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (meth)acrylate )(meth)alkyl acrylates such as lauryl acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; cyclohexyl (meth)acrylate, (meth)acrylate 4-tert-butylcyclohexyl acrylate, 2-norpropyl (meth)acrylate, isopropyl (meth)acrylate, (meth)adamantane-1-yl acrylate, (meth)acrylate (Meth)acrylic acid cycloalkyl esters such as 2-methyladamant-2-yl acrylate, 2-ethyl-2-adamantyl (meth)acrylate, tricyclodecyl (meth)acrylate; Glycidyl (meth)acrylate; dicyclopentyl (meth)acrylate, etc. These can be used individually by 1 type or in combination of 2 or more types. The (meth)acrylate-based monomer is preferably alkyl (meth)acrylate, more preferably methyl methacrylate.

Moreover, the styrene-based resin (A) may be a copolymer obtained by copolymerizing a styrene-based monomer and a (meth)acrylate-based monomer with a copolymerizable monomer. Examples of copolymerizable monomers include (meth)acrylic acid such as acrylic acid and methacrylic acid; acrylonitrile such as acrylonitrile and methacrylonitrile; α,β-ethylenically unsaturated such as maleic anhydride and fumaric acid. Carboxylic acids; phenylmaleimide, cyclohexylmaleimide and other imines. These can be used individually by 1 type or in combination of 2 or more types.

The weight average molecular weight (Mw) of the styrenic resin (A) is preferably 50,000 to 400,000, more preferably 100,000 to 350,000. Moreover, the ratio (Mw/Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the styrenic resin (A) is preferably 1.0 to 3.5, more preferably 1.5 to 3.0. By setting it in this range, it is possible to achieve both formability and strength of the light guide plate. If the weight average molecular weight (Mw) is less than 50,000, the strength of the molded article may become insufficient, and if it exceeds 400,000, the formability may decrease. In addition, if the number average molecular weight (Mn) ratio (Mw/Mn) is less than 1.0, the formability decreases, and if it exceeds 3.5, the strength of the molded article may decrease.

＜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), preferably 0.01 to 0.3 parts by mass, based on 100 parts by mass of the styrene-based resin (A). By setting it within such a range, transparency, hue, and light stability with respect to LED light sources can be improved. The content of the hindered amine light stabilizer (B) relative to the styrenic resin (A) is, 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, or within the range between any two of the numerical values illustrated here. Moreover, the hindered amine light stabilizer (B) can be used individually by 1 type or in combination of 2 or more types.

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

[Chemical 1]

In the general formula (1), Chain or branched alkyl, methylene, alkoxy. Here, when R is a hydrogen atom, it is an N-H type hindered amine light stabilizer, and when R is a linear or branched alkyl group or methylene group having 1 to 10 carbon atoms, it is an N-R type hindered amine. The light stabilizer is an N-OR hindered amine type light stabilizer when R is an alkoxy group.

Specific examples of the N-H type hindered amine light stabilizer include bis(2,2,6,6-tetramethylpiperidin-4-yl) sebacate (TINUVIN770DF manufactured by BASF), 2,2,6,6-tetramethyl-4-piperidinyl alkanoate, 2,2,6,6-tetramethyl-4-piperidinyl octadecanoate (SABOSTAB UV91 manufactured by SONGWON Corporation), 1,2,3,4-butanetetracarboxylic acid quaternary (2,2,6,6-tetramethyl-4-piperidinyl) ester (ADK STAB LA-57 manufactured by ADEKA), N,N' -Condensation polymerization of bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine and 4-𠰌linyl 2,6-dichloro-1,3,5-tri𠯤 (SABOSTAB UV79 manufactured by SONGWON Co., Ltd.), 2,4-dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-trichloro-N,N' -Condensation polymer of bis(2,2,6,6-tetramethyl-4-piperidinyl)hexamethylenediamine (Chimassorb 944FDL manufactured by BASF), N,N'-bis(2,2,6 ,6-Tetramethylpiperidin-4-yl)hexamethylenediamine and 2,4,6-trichloro-1,3,5-trichloro-1,3,5-trichloro-N-butyl-1-butanamine and N -Condensation polymer of butyl-2,2,6,6-tetramethyl-4-piperidinamine (SABOSTAB UV40 manufactured by SONGWON Co., Ltd.), 1,6,11-bis(N-butyl -N-(2,2,6,6-Tetramethyl-4-piperidinyl)amino)symmetric tris-6-yl]aminoundecane (Chimassorb 2020FDL manufactured by BASF), 1,2 ,3,4-butanetetracarboxylic acid and 2,2,6,6-tetramethyl-4-piperidinol and β,β,β',β'-tetramethyl-2,4,8,10 -Condensation polymer of tetraoxasspiro[5,5]undecane-3,9-diethanol (ADKSTAB LA-68 manufactured by ADEKA), 3-(2,2,4,4-tetramethyl-21 -Oxo-7-oxa-3,20-diazabispiro(5.1.11.2)ecosan-20-yl)propionic acid dodecyl ester, 3-(2,2,4,4 -Tetramethyl-21-oxo-7-oxa-3,20-diazabispiro(5.1.11.2)necosyl-20-yl)tetradecyl propionate (manufactured by CLARIANT Corporation HOSTAVIN3030), condensation polymer of 2,2,4,4-tetramethyl-7-oxa-3,20-diazabispiro-(5.1.11.2) henosan-21-one and epichlorohydrin (HOSTAVIN N30P manufactured by CLARIANT).

Specific examples of N-R type hindered amine light stabilizers include: methyl sebacate (1,2,2,6,6-pentamethylpiperidin-4-yl) ester, bis(1) sebacate , 2,2,6,6-pentamethylpiperidin-4-yl) ester (TINUVIN292, TINUVIN765 manufactured by BASF), n-butyl 3,5-di-tert-butyl 4-hydroxybenzylmalonic acid Bis(1,2,2,6,6-pentamethylpiperidin-4-yl) ester (TINUVIN144 manufactured by BASF), 4-hydroxy-2,2,6,6-tetramethyl-1-piperidin The condensation polymer of ethanol and dimethyl succinate (TINUVIN622SF manufactured by BASF), 1,5,8,12-4[4,6-bis(N-butyl-N-(1,2,2,6 ,6-pentamethyl-4-piperidinyl)amino)-1,3,5-tris-2-yl]-1,5,8,12-tetraazadodecane (manufactured by BASF Corporation Chimassоrb119), 1,2,3,4-butanetetracarboxylic acid and 1,2,2,6,6-pentamethyl-4-piperidinol and β,β,β',β'-tetramethyl -Condensation polymer of 2,4,8,10-tetraoxasspiro[5,5]undecan-3,9-diethanol (ADKSTAB LA-63P manufactured by ADEKA), succinic acid and (4-hydroxy- Condensation polymer of 2,2,6,6-tetramethylpiperidin-1-yl)ethanol and N,N',N'',N'''-4-(4,6-bis-(butyl- (N-Methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-tris-2-yl)-4,7-diazadecane-1,10- A mixture of diamines (TINUVIN111FDL manufactured by BASF).

Specific examples of the N-OR type hindered amine light stabilizer include: bis(1-octyloxy-2,2,6,6-tetramethylpiperidinyl) sebacate (manufactured by BASF Corporation) TINUVIN123), bis(1-undecyloxy-2,2,6,6-tetramethylpiperidin-4-yl)carbonate (ADKSTAB LA-81 manufactured by ADEKA).

Among them, 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 in terms of having less influence on the transparency and hue of the optical styrenic resin composition. Amine light stabilizer, preferably N-R type hindered amine light stabilizer. It is known that hindered amine light stabilizer (B) is generally oxidized by oxygen, ultraviolet rays and peroxides to generate nitroxide radicals. In this embodiment, although the mechanism by which the hindered amine light stabilizer (B) can improve the light stability of the LED light source for long-term use has not yet been elucidated, the present invention discovered the effectiveness of the hindered amine light stabilizer (B).

＜Antioxidant (C)＞ The styrene-based resin composition for optical use preferably contains 0.001 to 0.5 parts by mass of the phosphorus-based antioxidant (C-1), more preferably 0.002 to 0.4 parts by mass, based on 100 parts by mass of the styrene-based resin (A). Preferably, it is 0.005 to 0.3 parts by mass. By setting it to this range, transparency and hue can be improved. Specifically, the content of the phosphorus antioxidant (C-1) is, for example, 0.001, 0.002, 0.003, 0.004, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, based on 100 parts by mass of the styrenic resin (A). 0.4 and 0.5 parts by mass may also be within the range between any two of the numerical values illustrated here.

The phosphorus-based antioxidant (C-1) is a ()phosphite ester having no phenolic hydroxyl group in its basic skeleton, and is preferably a phosphite ester which is a trivalent phosphorus compound. Specific examples of the phosphorus antioxidant (C-1) include 2,2'-methylenebis(4,6-di-tert-butyl-1-phenoxy)(2-ethylhexyloxy) base) phosphorus, bis-(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, phosphite (2,4-di-tert-butylphenyl) ester, 3,9-bis(2 ,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]undecane, 4(2 ,4-di-tert-butylphenyl)[1,1biphenyl]-4,4'-diyl bisphosphonite, bis(2,4-di-tert-butyl-6-methyl phosphite) Phenyl) ester ethyl ester, etc., these can be used individually by 1 type or in combination of 2 or more types.

Furthermore, the optical styrene-based resin composition may contain 0 to 0.5 parts by mass of the phenolic antioxidant (C-2) based on 100 parts by mass of the styrene-based resin (A). If the content of the phenolic antioxidant (C-2) exceeds 0.5 parts by mass, the hue will deteriorate, which is undesirable. Specifically, the content of the phenolic antioxidant (C-2) is, for example, 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, based on 100 parts by mass of the styrenic resin (A). 0.3, 0.4, and 0.5 parts by mass may also be within the range between any two of the numerical values illustrated here.

The so-called phenolic antioxidant (C-2) is an antioxidant that has a phenolic hydroxyl group in the basic skeleton and is not a ()phosphite ester. Specific examples of the phenolic antioxidant (C-2) include octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, ethylidene bis( Oxyethylidene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxybenzene base) propionate], these may be used singly or in combination of two or more.

Antioxidants such as 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetratert-butyldibenzo[d ,f][1,3,2]dioxaphosphene is a phosphorus-phenol compound that has both a phosphite structure and a phenol structure in the same molecule. In the case of such a compound, it is considered that the optical styrene-based resin composition contains each of a phosphorus-based antioxidant and a phenol-based antioxidant. For example, it contains phosphorus- based on 100 parts by mass of the styrene-based resin (A). In the case of 0.1 parts by mass of the phenolic compound, it is considered that 0.1 parts by mass of the phosphorus-based antioxidant and 0.1 part by mass of the phenolic antioxidant are included.

＜Other ingredients＞ The tert-butylcatechol (TBC) in the optical styrene-based resin composition is preferably 10 ppm or less, more preferably 5 ppm or less. By setting it within such a range, a light guide plate excellent in hue and transmittance can be obtained. Specifically, the content of TBC is, 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 it can be Within the range between any two of the numerical values illustrated here.

The content of 6-tert-butyl-2,4-xylenol (TBX) in the optical styrene-based resin composition is preferably 10 ppm or less, more preferably 5 ppm or less. By setting it within such a range, a light guide plate excellent in hue and transmittance can be obtained. Specifically, the content of TBX is, 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 within the range between any two of the values illustrated here.

Within the scope that does not impair the characteristics of the present invention, the optical styrene-based resin composition may also contain sulfur-based antioxidants, lactone-based antioxidants, ultraviolet absorbers, antistatic agents, hydrophilic additives, liquid paraffin ( Mineral oil), polyethylene wax, microcrystalline wax, bluing agent, lauric acid, myristic acid, palmitic acid, stearic acid and other higher fatty acids, stearamide, erucamide, ethyl distearamide and other high-grade fatty acid glycerides, high-grade fatty acid glycerides such as glyceryl monolaurate, glyceryl monopalmitate, glyceryl monostearate, and glyceryl monobehenate, myristyl alcohol, cetyl alcohol, stearyl alcohol, etc. Alcohol release agent.

The melt mass flow rate (MFR) of the optical styrenic resin composition under the conditions of a temperature of 200°C and a load of 49 N is preferably 0.5 to 5.0 g/10 minutes, 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.

The Vickers softening temperature of the optical styrene-based resin composition is preferably 95 to 104°C, more preferably 100 to 104°C. If the Vickers 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.

<Production method of styrenic resin composition for optical use> Examples of the polymerization method of the styrenic resin (A) include known styrene polymerization methods such as block polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. In terms of quality or productivity, block polymerization and solution polymerization are preferred, and continuous polymerization is preferred. Examples of solvents that can be used include benzene, toluene, alkylbenzenes such as ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.

When polymerizing the styrenic resin (A), polymerization auxiliaries such as a polymerization initiator, a chain transfer agent, and a cross-linking agent, and other polymerization auxiliaries may be used as necessary. The polymerization initiator is preferably a radical polymerization initiator, and examples of the well-known and commonly used ones include 1,1-bis(tert-butylperoxy)cyclohexane, 2,2-bis(tert-butylperoxy)cyclohexane, peroxy)butane, 2,2-di(4,4-di-tert-butylperoxycyclohexyl)propane, 1,1-di(tert-pentylperoxy)cyclohexane, etc. Hydroperoxides such as oxyketals, cumene hydroperoxide, tert-butyl hydroperoxide, alkyl peroxides such as tert-amyl peroxyisononanoate, tert-butylcumyl peroxide Oxide, di-tert-butyl peroxide, dicumyl peroxide, di-tert-hexyl peroxide and other dialkyl peroxides, tert-butyl peroxyacetate, tert-butyl peroxybenzoate Peroxy esters such as butyl ester, tert-butyl peroxy isopropyl monocarbonate, tert-butyl peroxy isopropyl carbonate, polyether tetrakis (tert-butyl peroxycarbonate), etc. Carbonates, N,N'-Azobis(cyclohexane-1-carbonitrile), N,N'-Azobis(2-methylbutyronitrile), N,N'-Azobis(2 , 4-dimethylvaleronitrile), N,N'-azobis[2-(hydroxymethyl)propionitrile], etc., one of these can be used or two or more of them can be used in combination. Examples of chain transfer agents include aliphatic mercaptans such as n-dodecyl mercaptan and tertiary dodecyl mercaptan, aromatic mercaptans, sulfur carboxylic acids such as thioglycolic acid and mercaptopropionic acid, and ethanol. Polyfunctional thiols obtained by esterifying the hydroxyl groups of polyols such as glycol, tetraethylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, and sorbitol with thioglycolic acid or mercaptopropionic acid. , pentaphenylethane, α-methylstyrene dimer and terpinolene, etc. Among these, aliphatic thiols, aromatic thiols, sulfur carboxylic acids, and polyfunctional thiols are preferable from the viewpoint of easy adjustment of molecular weight.

In the case of continuous polymerization, the styrenic resin (A) can be produced by a method including a polymerization step, a devolatization step, and a granulation step.

First, in the polymerization step, a well-known complete mixing tank-type stirred tank or tower-type reactor is used, and the polymerization reaction is controlled by adjusting the polymerization temperature and the like to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate.

The polymerization solution containing the polymer that has completed the polymerization step is transferred to a devolatization step to remove unreacted monomers and polymerization solvent. The devolatilization step includes a vacuum devolatilization tank with a heater or a devolatilization extruder with a vent, etc. The molten polymer that has completed the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded from the porous mold in a linear shape and processed into a granular shape by cold cutting, aerial thermal cutting, or underwater thermal cutting.

The optical styrene-based resin composition can be prepared by adding a hindered amine light stabilizer (B), a phosphorus-based antioxidant (C-1), and a phenol-based antioxidant (C-2) to the styrene-based resin (A). manufacturing. The hindered amine light stabilizer (B), phosphorus antioxidant (C-1), and phenolic antioxidant (C-2) can be added to the raw material solution before the polymerization of the styrene resin (A), or by The extruder or static mixing device installed after the polymerization of the styrenic resin (A) and before the pelletization is used for mixing. Alternatively, the granulated styrenic resin (A) may be dry-blended with the hindered amine light stabilizer (B), phosphorus antioxidant (C-1), and phenolic antioxidant (C-2). Made by melting and kneading. Alternatively, the hindered amine light stabilizer (B), phosphorus antioxidant (C-1), and phenol antioxidant (C-2) may be melt-kneaded together with a small amount of styrene resin in advance. The granular masterbatch is prepared by dry blending the styrenic resin (A) and the masterbatch, and then melting and kneading the masterbatch.

The content of tert-butylcatechol or 6-tert-butyl-2,4-xylenol in the optical styrene resin composition can be equal to the content at the start of polymerization of the styrene resin (A) Adjustment and adjustment of content in subsequent devolatilization steps, etc.

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 resin composition. The light guide plate is a light guide plate that can be used for edge light surface light source units.

＜Shape of light guide plate＞ The light guide plate may have a concave and convex shape on the surface of the light guide plate. More specifically, the surface of the light guide plate may have a plurality of lens-shaped and/or lens-shaped convex portions. The convex portion is preferably provided on at least one surface of the light guide plate, particularly on one surface serving as the front surface (light-emitting surface) of the light guide plate. Other surfaces can also be provided if necessary, but it is better to be provided only on the front surface (light-emitting surface) of the light guide plate.

Here, the so-called lens-shaped convex portion is an arc-shaped convex portion, and the cross-sectional edge shape is an arc-shaped protrusion. Moreover, the shape of the so-called ridge is an arc-shaped convex part, and the edge shape of the cross section is a triangular mountain-shaped protrusion. Moreover, a plurality of convex portions may be formed in a parallel relationship with each other. Moreover, the convex part may be integrally formed with the light guide plate.

The thickness of the light guide plate is 0.2~3.0 mm, preferably 0.3~2.5 mm, more preferably 0.4~2.4 mm. If it is within this range, it is easy to produce a light guide plate with excellent moldability such as excellent extrusion stability and strength during the molding of the optical styrene-based resin composition.

＜Optical characteristics＞ The average transmittance of the light guide plate at a wavelength of 380 to 780 nm under an optical path length of 115 mm is preferably more than 85%, and more preferably more than 86%.

The YI (Yellowness Index, yellowness index) value of the light guide plate when the optical path length is 115 mm is preferably below 6.0, and more preferably below 4.0.

＜Manufacturing method of light guide plate＞ The light guide plate according to one embodiment of the present invention is obtained by molding the above-mentioned optical styrene-based resin composition. As a molding method, known methods such as sheet extrusion molding, injection molding, and compression molding can be used. In order to facilitate the enlargement of molded products, continuous sheet extrusion molding with a surface shape transfer mold is preferred. An example of this sheet extrusion molding is a continuous sheet extrusion molding method, which has an extrusion step of supplying resin in a heated and molten state to a feed block (feed block), and continuously extruding it from the die. Extruding to form a sheet; a pressing step, which uses a pressure roller and a cooling roller to clamp the above-mentioned resin sheet; and a conveying step, which after the pressing step, conveys the resin sheet while being in close contact with the cooling roller; Furthermore, a transfer mold is provided on the surface of the cooling roller; by changing the shape of the transfer mold, any uneven shape can be transferred to the surface of the sheet.

In addition, the light guide plate may have an uneven shape on the front surface (light-emitting surface), and the back surface may be subjected to reflection processing to diffuse light. Examples of reflective processing include a method of providing dot-shaped irregularities by laser irradiation in addition to screen printing or inkjet printing. Ink containing fine particles that diffuse light can be used for dot pattern printing.

3. Edge light surface light source unit An edge light surface light source unit according to one embodiment of the present invention is an edge light surface light source unit having the above-mentioned light guide plate and a light source that supplies LED light to an 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.

4.Light diffusion plate A light diffusion plate according to one embodiment of the present invention is a molded product obtained by molding the optical styrene resin composition. The light diffusion plate is a light diffusion plate that can be used for direct type surface light source units.

＜Shape of light diffusion plate＞ The thickness of the light diffusion plate according to an embodiment of the present invention is not limited, but is, for example, 1 to 3 mm. An antistatic agent can also be coated on the surface of the light diffusion plate. By coating the antistatic agent, after the light diffusion plate is installed on the backlight device, adhesion of dust and the like caused by static electricity can be suppressed, so that the light diffusion plate can be used without any decrease in brightness for a long time. In addition, the light diffusion plate of the present invention may be formed with minute uneven shapes such as embossing on both sides or one side thereof, or may be formed with a lens shape or a lens shape on both sides or one side.

The light diffusing plate may contain 0.1 to 1.0 parts by mass of a light diffusing agent based on 100 parts by weight of the optical styrene-based resin composition. The light diffusing agent can be used as long as it is particles with a different refractive index from that of the optical styrene-based resin composition and has the effect of diffusing incident light. For example, styrene-based polymer particles, acrylic polymer particles, and silicone can be used. Organic particles such as oxyalkane 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 them, at least one type selected from the group consisting of acrylic polymer particles, styrene polymer particles, and siloxane polymer particles is preferred.

＜Manufacturing method of light diffusion plate＞ The light diffusion plate according to one embodiment of the present invention can be produced by molding the optical styrene-based resin composition using various methods such as extrusion molding and injection molding, and is preferably produced by extrusion molding. As an example of extrusion molding, there is a method in which an optical styrene-based resin composition is melt-kneaded using a single-screw extruder or a twin-screw extruder, and is continuously extruded from a T-die, and then cooled. The roller unit cools and solidifies. When forming an uneven shape on the surface of the light diffusion plate, any uneven shape can be formed by providing a transfer mold on the surface of the cooling roller and changing the shape of the transfer mold. When the surface layer is laminated on both sides or one side of the light diffusion plate, methods such as co-extrusion, adhesion, heat bonding, solvent bonding, casting, and surface coating can be used.

5. Direct type surface light source unit A direct type surface light source unit according to one embodiment of the present invention is a direct type surface light source unit including the above-mentioned 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. [Example]

Hereinafter, an Example is given and this invention is demonstrated in further detail. In addition, these are examples and do not limit the content of the present invention.

1. Production of styrenic resin composition for optical use [Example 1] A first reactor, which is a complete mixing type stirred tank, and a second reactor, which is a plug flow type reactor with a static mixer, are connected in series to form a polymerization step and produce a styrene-based resin. The capacity of each reactor is 30 liters for the 1st reactor, and 12 liters for the 2nd reactor. The raw material composition is 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 , adjusted so that the addition concentration of tert-butyl peroxyisopropyl monocarbonate (manufactured by NOF Co., Ltd.: PERBUTYL I) as the polymerization initiator is 150 ppm, and n-dodecyl as the chain transfer agent. After mercaptan (manufactured by Arkema Co., Ltd.) reached an added concentration of 500 ppm (both concentrations are based on the mass of the entire monomer), the raw material solution was continuously supplied to the first reaction set at 128°C at 8.0 kg/h. device. Furthermore, the obtained polymerization solution was continuously supplied to the second reactor to complete the polymerization. At this time, the polymerization rate of the monomer is 70%. Furthermore, in the second reactor, a temperature gradient was set along the flow direction, and the temperature gradient was adjusted so that the middle part became 130°C and the outlet part became 145°C. Then, the solution containing the polymer continuously taken out from the second reactor was introduced into a two-stage vacuum devolatization tank with a preheater in series, and the temperature of the preheater was adjusted so that the resin temperature became 220°C. Under a pressure of 0.8 kPa, separate unreacted styrene and ethylbenzene. The obtained molten polymer was continuously supplied to the extruder, and 0.1 parts by mass of hindered amine light stabilizer (770) was added from the additive inlet relative to 100 parts by mass of the polymer, and mixed at a set temperature of 220°C. Finally, it is extruded from the porous die in a linear shape, and the strand is cooled and cut by cold cutting to pelletize it. The TBC concentration and the TBX concentration in the obtained optical styrene-based resin composition were 1.5 μg/g and 0.2 μg/g, respectively. Moreover, 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.

[Examples 2 to 17 and Comparative Examples 1 to 6] In addition to changing the composition and polymerization conditions of the raw material solution to those shown in Table 1, the hindered amine light stabilizer (B), phosphorus antioxidant (C-1), phenolic antioxidant (C-2), and ultraviolet absorber An optical styrene-based resin composition and a light guide plate were manufactured in the same manner as in Example 1, except that the composition of (D) was changed to that in Table 2 (Table 2-1 and Table 2-2) to Table 3. Various measurement and evaluation results are shown in Table 2 (Table 2-1 and Table 2-2) to Table 3.

[Table 1] Table 1 Condition 1 Condition 2 Condition 3 Condition 4 Condition 5 Condition 6 Resin name A-1 A-2 A-3 A-4 A-5 A-6 Raw material supply flow kg/hr 8.0 8.0 8.0 8.0 8.0 8.0 Raw material composition Styrene methyl methacrylate ethylbenzene mass % mass % mass % 51.0 39.0 10.0 65.5 24.5 10.0 79.0 11.0 10.0 27.0 63.0 10.0 90.0 0.0 10.0 10.0 80.0 10.0 polymerization initiator ppm*1 150 150 150 100 250 100 chain transfer agent ppm*1 500 300 100 2800 - 4000 reaction temperature Reactor 1 Reactor 2 (middle) Reactor 2 (outlet) ℃ ℃ ℃ 128 130 145 140 130 150 140 140 165 130 130 145 130 135 150 125 130 145 Go to volatilization tank resin temperature pressure ℃ kPa 220 0.8 220 0.8 220 0.8 220 0.8 220 0.8 220 0.8 Addition of stabilizer Add method -*2 EXT EXT EXT EXT EXT EXT resin temperature - 220 220 220 220 220 220 *1 Concentration relative to the mass basis of the entire monomer Polymerization initiator: tert-butyl peroxyisopropyl monocarbonate Chain transfer agent: n-dodecyl mercaptan *2 EXT: Extruder

[table 2-1] table 2-1 unit Example 1 2 3 4 5 6 7 8 9 Resin composition composition Styrenic resin (A) Kind - Α-1 Α-1 Α-1 Α-1 Α-1 Α-1 Α-1 Α-1 Α-1 PMMA amount mass % 47 47 47 47 47 47 47 47 47 Adding amount parts by mass 100 100 100 100 100 100 100 100 100 Hindered Amine Light Stabilizer (B) Kind - 770 944 292 292 292 123 944 292 292 Adding amount parts by mass 0.1 0.1 0.01 0.05 0.1 0.1 0.1 0.05 0.1 Antioxidants (C) Phosphorus antioxidant (C-1) Kind - - - - - - - 168 168 168 Adding amount parts by mass - - - - - - 0.05 0.2 0.05 Phenolic antioxidant (C-2) Kind - - - - - - - - - - Adding amount parts by mass - - - - - - - - - Resin properties Melt mass flow rate g/10 min 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 Vickers softening temperature ℃ 101 101 101 101 101 101 101 101 101 Mw ×10 ⁴ 17 17 17 17 17 17 17 17 17 Mw/Mn - 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 TBC content μ/g 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 TBX content μ/g 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Characteristics of light guide plate Optical characteristics of optical path length 115 mm average transmittance - 88 88 89 89 89 85 90 90 90 YI value - 3.8 4.0 2.4 2.5 2.8 6.0 3.8 2.3 2.5 Dimensional stability (hygroscopic deformation) - ○ ○ ○ ○ ○ ○ ○ ○ ○ LED durability (500 hr) ΔYI - 0.9 0.9 0.8 0.8 0.6 2.0 0.7 0.7 0.5 Whether there is carbonization - ○ ○ ○ ○ ○ ○ ○ ○ ○

[Table 2-2] Table 2-2 unit Example 10 11 12 13 14 15 16 17 Resin composition composition Styrenic resin (A) Kind - Α-1 Α-1 Α-1 Α-1 Α-1 Α-2 Α-3 Alpha-4 PMMA amount mass % 47 47 47 47 47 32 15 70 Adding amount parts by mass 100 100 100 100 100 100 100 100 Hindered Amine Light Stabilizer (B) Kind - 292 292 292 292 944 292 292 292 Adding amount parts by mass 0.1 0.1 0.1 0.1 0.3 0.1 0.1 0.1 Antioxidants (C) Phosphorus antioxidant (C-1) Kind - HP-10 126 168 HP-10 168 168 168 168 Adding amount parts by mass 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Phenolic antioxidant (C-2) Kind - - - 1076 1076 - - - - Adding amount parts by mass - - 0.05 0.05 - - - - Resin properties Melt mass flow rate g/10 min 1.7 1.7 1.7 1.7 1.9 2.5 3.5 1.7 Vickers softening temperature ℃ 101 101 101 101 100 100 99 103 Mw ×10 ⁴ 17 17 17 17 17 18 twenty one 11 Mw/Mn - 2.0 2.0 2.0 2.0 2.0 1.9 2.2 2.1 TBC content μ/g 1.5 1.5 1.5 1.5 1.5 1.9 2.3 0.8 TBX content μ/g 0.2 0.2 0.2 0.2 0.2 0.1 0.1 0.3 Characteristics of light guide plate Optical characteristics of optical path length 115 mm average transmittance - 90 90 90 90 87 89 88 91 YI value - 2.3 2.5 2.5 2.5 4.5 2.5 3.0 1.2 Dimensional stability (hygroscopic deformation) - ○ ○ ○ ○ ○ ○ ○ △ LED durability (500 hr) ΔYI - 0.2 0.5 1.0 1.0 0.7 1.0 2.1 0.2 Whether there is carbonization - ○ ○ ○ ○ ○ ○ ○ ○

[table 3] table 3 unit Comparative example 1 2 3 4 5 6 Resin composition composition Styrenic resin (A) Kind - Α-5 Α-1 Α-1 Α-1 Α-6 Α-1 PMMA amount mass % 0 47 47 47 89 47 Adding amount parts by mass 100 100 100 100 100 100 Hindered Amine Light Stabilizer (B) Kind - - - - 944 944 - Adding amount parts by mass 0 0 0 1.2 0.1 0 Antioxidants(C) Phosphorus antioxidant (C-1) Kind - 168 - 168 - 168 - Adding amount parts by mass 0.05 - 0.015 - 0.05 - Phenolic antioxidant (C-2) Kind - 1076 - 1076 - - - Adding amount parts by mass 0.05 - 0.05 - - - UV absorber(D) Kind - - - - - - P Adding amount parts by mass - - - - - 0.1 Resin properties Melt mass flow rate g/10 min 1.7 1.7 1.7 2.1 1.3 1.3 Vickers softening temperature ℃ 99 101 101 99 104 104 Mw ×10 ⁴ 32 17 17 17 8 17 Mw/Mn - 2.2 2.0 2.0 2.0 1.9 2.0 TBC content μ/g 2.6 1.5 1.5 1.5 0.4 1.5 TBX content μ/g 0.0 0.2 0.2 0.2 0.4 0.2 Characteristics of light guide plate Optical characteristics of optical path length 115 mm average transmittance - 85 84 88 82 86 85 YI value - 5.5 6.0 4.0 8.2 4.6 5.0 Dimensional stability (hygroscopic deformation) - ○ ○ ○ ○ × ○ LED durability (500 hr) ΔYI - - - - 0.7 0.2 - Whether there is carbonization - × × × ○ ○ ×

Furthermore, regarding the hindered amine light stabilizer (B), phosphorus antioxidant (C-1), and phenolic antioxidant (C-2) in Table 2 (Table 2-1 and Table 2-2) to Table 3 , ultraviolet absorber (D), respectively as follows.

(Hindered Amine Light Stabilizer (B)) 770: Bis(2,2,6,6-tetramethylpiperidin-4-yl) sebacate (TINUVIN770DF manufactured by BASF) 944: 2,4-Dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-tris-N,N'-bis(2,2,6 , 6-tetramethyl-4-piperidinyl) condensation polymer of hexamethylenediamine (Chimassоrb944FDL manufactured by BASF) 292: Methyl sebacate (1,2,2,6,6-pentamethylpiperidin-4-yl) ester: 25% and bis(1,2,2,6,6-pentamethyl sebacate Piperidin-4-yl) ester: 75% mixture (TINUVIN 292 manufactured by BASF) 123: Bis(1-octyloxy-2,2,6,6-tetramethylpiperidinyl) sebacate (TINUVIN 123 manufactured by BASF)

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

(Phenolic antioxidant (C-2)) 1076: 3-(3,5-di-tert-butyl-4-hydroxyphenyl)octadecylpropionate (Irganox 1076 manufactured by BASF)

(UV absorber (D)) P: 2-(2-hydroxy-5-methylphenyl)benzotriazole (TINUVIN P manufactured by BASF)

2.Evaluation The evaluation of the optical styrene-based resin compositions described in Tables 2 (Table 2-1 and Table 2-2) to 3 was performed according to the following method.

＜Melt mass flow rate (MFR)＞ The melt mass flow rate was measured in accordance with JIS K 7210 at a temperature of 200°C and a load of 49 N.

＜Vickers Softening Temperature＞ The Vickers softening temperature is measured in accordance with JIS K 7206 at a heating rate of 50°C/hr and a test load of 50 N.

<Content of TBC and TBX in styrenic resin composition for optical use> After dissolving 0.2 g of the optical styrene-based resin composition in a small amount of THF, 200 μL of BSTFA (M,O-bis(trimethylsilyl)trifluoroacetamide) was added to perform trimethylsilyl derivatization. After physical and chemical treatment, the volume was adjusted to 10 mL with THF (tetrahydrofuran), and the supernatant liquid was separated by centrifugation and measured by gas chromatography mass analysis (GC/MS) under the following conditions. Furthermore, the concentration is determined using a pre-made calibration curve. GC device: 7890A manufactured by Agilent Column: DB-5ms (0.25 mm i.d.×30 m) manufactured by Agilent Company, liquid phase film thickness 0.25 μm Column temperature: 50℃(1 min)→(20℃/min temperature rise)→320℃(6.5 min) for a total of 20 minutes Injection port: 300℃, 1.5 mL/min, (split ratio 1:5) Injection volume: 1 μL MS device: 5975C manufactured by Agilent Interface temperature: 320℃ MS detection conditions: SIM determination of TBC (m/z 295 for quantification, m/z 310 for confirmation)

<Contents of hindered amine light stabilizer (B), phosphorus antioxidant (B-1), and phenolic antioxidant (B-2) in the optical styrene resin composition> After completely dissolving 1.0 g of the optical styrene-based resin composition in 20 mL of THF, 5 mL of methanol was added dropwise and stirred for 20 minutes. Centrifuge at 4000 rpm for 10 minutes, and the separated supernatant is measured by gas chromatography (GC) under the following conditions. Furthermore, the concentration is determined using a pre-made calibration curve. GC device: GC2010 Plus manufactured by Shimadzu Corporation Column: DB-1 (30 m×0.25 mm i.d., df=0.10 μm) Column temperature: 240℃(1 min)→(10℃/min temperature rise)→320℃(15 min) Injection port: 320℃, 1.02 mL/min (split ratio 1:5) Injection volume: 1 μL

<Weight average molecular weight (Mw)> The weight average molecular weight (Mw), Z average molecular weight (Mz), and number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions. GPC model: Shodex GPC-101 manufactured by Showa Denko Co., Ltd. Column: PLgel 10 μm MIXED-B manufactured by Polymer Laboratories Mobile phase: tetrahydrofuran Sample concentration: 0.2 mass% Temperature: oven 40℃, injection port 35℃, detector 35℃ Detector: Differential Refractometer The molecular weight is calculated by calculating the molecular weight at each dissolution time based on the dissolution curve of monodisperse polystyrene, and calculating it in the form of polystyrene-converted molecular weight.

3. Manufacturing and evaluation of light guide plates ＜Manufacturing of light guide plate＞ The above optical styrene-based resin composition is supplied to a single-axis vented extruder with a screw diameter of 90 mm and L/D=32, and after melting and kneading at 200 to 235°C, a die lip width of 1000 mm is used. . A T-mold with a die lip opening of 3.0 mm is flowed out at a T-mold temperature of 245 to 250°C. After cooling and solidification using a vertical three-roller cooling roller, the end face is trimmed to obtain a light guide plate with a width of 800 mm and a thickness of 2.0 mm.

＜Evaluation of light guide plate＞ The average transmittance, YI value, dimensional stability (hygroscopic deformation), and LED durability of the light guide plates in Tables 2 and 3 were evaluated as follows.

＜Average transmittance and YI value of light guide plate＞ The average transmittance and YI value are measured by the following steps. A test piece of 115 mm × 85 mm was cut from the light guide plate obtained above, and the end surface was ground by polishing to produce a plate-shaped molded product with a mirror surface on the end surface. For the plate-shaped molded product after grinding, the ultraviolet-visible spectrophotometer V-670 manufactured by Nippon ASCO Co., Ltd. was used to measure the incident light with a size of 20×1.6 mm, a diffusion angle of 0°, and an optical path length of 115 mm. The spectral transmittance of wavelengths 350 nm to 800 nm is calculated according to JIS K7105 and the YI value under the visual field of 2° in C light source. The average transmittance (total light transmittance) is calculated as the average of the spectral transmittance at a wavelength of 380 to 780 nm.

＜Dimensional stability (hygroscopic deformation)＞ Cut a 200 mm × 300 mm test piece from the light guide plate obtained above, store the test piece for 500 hours at a temperature of 60°C and a relative humidity of 90%, and measure the dimensional change of the long side before and after storage. According to the following Calculate the deformation rate with the formula. Deformation rate = ((length of the long side after storage) - (length of the long side before storage)) ÷ (length of the long side before storage) × 100 (%) The change rate of less than 0.10% was marked as 0, the change rate of 0.10 to 0.15% was marked as △, and the change rate of more than 0.15% was marked as ×. The dimensional stability (hygroscopic change) of the light guide plate was evaluated.

<LED durability> A test piece of 115 mm x 85 mm was cut out from the light guide plate obtained above, and an end grinder (GCPB-500 manufactured by Megaro Technology Co., Ltd.) was used, using a diamond rotating at a speed of 8000 rpm. The end surface of the knife is ground to 0.2 mm at a feed speed of 2.0 m/min to produce a plate-shaped molded product with a mirror surface on the end surface. For the plate-shaped molded product after grinding, a flat-panel blue LED light source (peak wavelength 445 nm) for TV (television) is placed 0.5 mm away from the end surface, and the temperature is 0.05 W/mm ² in an environment of 80°C. Under the input current, the LED light is irradiated for 500 hours. For the plate-shaped molded product after the test, the ultraviolet-visible spectrophotometer V-670 manufactured by Japan ASCO Co., Ltd. was used to measure the incident light with a size of 20×1.6 mm, a diffusion angle of 0°, and an optical path length of 115 mm. The spectral transmittance of wavelengths 350 nm to 800 nm is calculated according to JIS K7105, and the YI value under the visual field of 2° in C light source is calculated. The value obtained by subtracting the YI value before the test from the YI value after the test is set as ΔYI. In addition, the LED light-incident part of the plate-shaped molded product after the test was visually confirmed, and those with no change were marked as 0, and those with carbonization were marked as ×, and the LED durability was evaluated.

In Examples 1 to 17, the transparency, hue, and dimensional stability are good, no carbonization occurs after the LED is exposed, and the hue stability is excellent.

Claims (10)

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)acrylate-based monomer unit, and a hindered amine light stabilizer ( B), and The above-mentioned copolymer contains 95 to 20 mass% of the above-mentioned styrene-based monomer units and 5-80 mass% of the above-mentioned (meth)acrylate-based monomer units in 100% by mass of the above-mentioned copolymer, The optical styrene-based resin composition contains 0.001 to 1.0 parts by mass of the hindered amine light stabilizer (B) based on 100 parts by mass of the styrene-based resin (A). The optical styrene resin composition of claim 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. The optical styrenic resin composition of claim 2, wherein the N-H type hindered amine light stabilizer is selected from Bis(2,2,6,6-tetramethylpiperidin-4-yl) sebacate, 2,2,6,6-tetramethyl-4-piperidinyl hexadecanoate, 2,2,6,6-tetramethyl-4-piperidinyl octadecanoate, 1,2,3,4-butanetetracarboxylic acid quaternary (2,2,6,6-tetramethyl-4-piperidinyl) ester, N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine and 4-𠰌linyl 2,6-dichloro-1,3,5- Three condensation polymers, 2,4-Dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-trichloro-N,N'-bis(2,2,6,6 -Condensation polymer of tetramethyl-4-piperidinyl)hexamethylenediamine, N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine and 2,4,6-trichloro-1,3,5-trichloro-1,3,5-trimethyldiamine and Condensation polymer of N-butyl-1-butanamine and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine, 1,6,11-Shen[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidinyl)amine) symmetric tris-6-yl ]Amino undecane, 1,2,3,4-butanetetracarboxylic acid and 2,2,6,6-tetramethyl-4-piperidinol and β,β,β',β'-tetramethyl-2,4, Condensation polymer of 8,10-tetraoxasspiro[5,5]undecane-3,9-diethanol At least 1 of them. The optical styrenic resin composition of claim 2 or 3, wherein the above-mentioned N-R hindered amine light stabilizer is selected from Methyl sebacate (1,2,2,6,6-pentamethylpiperidin-4-yl) ester, Bis(1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate, n-Butyl 3,5-di-tert-butyl 4-hydroxybenzylmalonate bis(1,2,2,6,6-pentamethylpiperidin-4-yl) ester, Condensation polymer of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol and dimethyl succinate, 1,5,8,12-bis[4,6-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidinyl)amino)-1, 3,5-Tris-2-yl]-1,5,8,12-tetraazadodecane, 1,2,3,4-butanetetracarboxylic acid and 1,2,2,6,6-pentamethyl-4-piperidinol and β,β,β',β'-tetramethyl-2, Condensation polymer of 4,8,10-tetraoxasspiro[5,5]undecane-3,9-diethanol, Condensation polymer of succinic acid and (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)ethanol and N,N',N'',N'''-4-(4, 6-Bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-tris-2-yl)-4,7-diazo Mixture of heterodecane-1,10-diamines At least 1 of them. The optical styrene-based resin composition according to any one of claims 1 to 3, which contains 0.001 to 0.5 parts by mass of the phosphorus-based antioxidant (C-1) based on 100 parts by mass of the styrene-based resin (A). The optical styrene-based resin composition of claim 5, wherein the phosphorus-based antioxidant (C-1) is selected from the group consisting of ginseng (2,4-di-tert-butylphenyl) phosphite, 2,2' -Methylenebis(4,6-di-tert-butyl-1-phenoxy)(2-ethylhexyloxy)phosphorus, bis-(2,4-di-tert-butylphenyl)pentaerythritol di Phosphite, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[ 5,5]Undecane, 4(2,4-di-tert-butylphenyl)[1,1biphenyl]-4,4'-diylbisphosphonite, phosphite bis(2,4 -At least one kind of di-tert-butyl-6-methylphenyl) ethyl ester. A light guide plate formed by molding the optical styrene-based resin composition according to any one of claims 1 to 3. An edge light type surface light source unit has a light guide plate as claimed in claim 7, and a light source that supplies LED light to the end surface of the light guide plate. A light diffusion plate formed by molding the optical styrene-based resin composition according to any one of claims 1 to 3. A direct type surface light source unit has a light diffusion plate as claimed in claim 9, and a light source that supplies LED light to the light diffusion plate.