Styrene-based resin composition for optical use, molded body, light guide plate, and edge-light type planar light source unit

Abstract

The present invention provides a styrene-based resin composition for optical use, said composition excelling in light stability over long-term use in a semiconductor light source such as an LED light source.　According to the present invention, provided is a styrene-based resin composition for optical use, said composition containing a styrene-based resin, the styrene-based monomer content being 1000 µg or less per 1 g of the styrene-based resin composition for optical use, and the total of the styrene-based monomer linear dimer content and the styrene-based monomer linear trimer content being 10-500 μg.

Description

Optical styrene resin composition, molded body, light guide plate, and edge-light type surface light source unit

[0001] The present invention relates to an optical styrene-based resin composition, a molded article, a light guide plate, and an edge-light type surface light source unit.

[0002] There are two types of backlights for LCD displays: direct-type, in which the light source is placed in front of the display device, and edge-lit, in which the light source is placed on the side. Edge-lit backlights use a component called a light guide plate that 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, desktop personal computer monitors, notebook personal computers, mobile phones, and car navigation monitors. Backlights that use light guide plates are also used in lighting devices, signs, etc.

[0003] Light guide plates are required to have particularly high light transmittance because the light transmission distance is relatively long and the light loss over 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, which can cause warping and dimensional changes in the light guide plate. Furthermore, PMMA is prone to thermal decomposition during molding, which can lead to poor appearance of the molded product when molded at high temperatures. To address these issues, Patent Document 1, for example, proposes using a styrene-methyl (meth)acrylate copolymer as the material for the light guide plate.

[0004] On the other hand, molded articles of styrene-methyl (meth)acrylate copolymers have poorer hue than PMMA, and when used as a backlight, color unevenness may occur. To solve this problem, Patent Document 2 proposes a technology for improving the hue of styrene-methyl (meth)acrylate.

[0005] JP 2003-075648 A International Publication No. 2016 / 129675 A

[0006] In recent years, with the increasing resolution of backlight units for televisions, monitors, etc., high-brightness LEDs are often used as edge light sources, but conventional styrene-methyl (meth)acrylate copolymer light guide plates can sometimes deteriorate (yellowing) at the edge of the light guide plate after being turned on for a long time, depending on the usage environment.In addition, in recent years, displays have emerged that use mini LEDs that emit blue light with higher energy as a light source and perform color conversion using QDs (quantum dots), which means that the light stability required of light guide plates is becoming more advanced.

[0007] The present invention has been made in view of the above problems, and provides an optical styrene-based resin composition that has excellent light stability for long-term use of semiconductor light sources such as LED light sources.

[0008] As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by controlling the content of the styrene-based monomer, the content of the linear styrene-based monomer dimer, and the content of the linear styrene-based monomer trimer in the styrene-based resin composition to fall within predetermined ranges, and have thus completed the present invention.

[0009] The following inventions are provided. [1] An optical styrenic resin composition containing a styrenic resin, wherein the content of a styrenic monomer is 1,000 μg or less per 1 g of the optical styrenic resin composition, and the total content of a linear dimer of a styrenic monomer and a linear trimer of a styrenic monomer is 10 to 500 μg. [2] The optical styrenic resin composition according to [1], wherein the styrenic resin is a copolymer containing 95 to 20 mass% of styrenic monomer units and 5 to 80 mass% of (meth)acrylic acid ester monomer units. [3] The optical styrenic resin composition according to [1] or [2], wherein the content of phosphorus atoms is 50 μg or less per 1 g of the optical styrenic resin composition. [4] The optical styrenic resin composition according to any one of [1] to [3], wherein, relative to 1 g of the optical styrenic resin composition, the content of the styrenic monomer is M μg, the content of the styrenic monomer linear dimer is D μg, the content of the styrenic monomer linear trimer is T μg, and the content of phosphorus atoms is P μg, satisfies the following formula (1): (M + D + T) × P ≦ 20000 (1) [5] The optical styrenic resin composition according to any one of [1] to [4], which contains 0.001 to 0.5 parts by mass of a hindered amine light stabilizer relative to 100 parts by mass of the styrenic resin. [6] The optical styrenic resin composition according to any one of [1] to [5], which is used to transmit light from an LED light source having a maximum radiant intensity in the wavelength region of 400 nm to 500 nm. [7] A molded article made of the optical styrene-based resin composition according to any one of [1] to [6]. [8] A light guide plate comprising the molded article according to [7]. [9] An edge-light type surface light source unit having the light guide plate according to [8] and a light source that supplies LED light to an end face of the light guide plate.

[0010] FIG. 1 is a diagram illustrating the shape of a plate-shaped test piece 1.

[0011] The following describes embodiments of the present invention. The various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an invention independently.

[0012] 1. Optical styrene-based resin composition The optical styrene-based resin composition according to one embodiment of the present invention contains a styrene-based resin (A). <Styrene-based resin (A)> The styrene-based resin (A) is a resin obtained by polymerizing raw material monomers containing a styrene-based monomer. The styrene-based resin (A) is preferably a resin obtained by copolymerizing a styrene-based monomer and a monomer containing a (meth)acrylic acid ester-based monomer. The styrene-based resin (A) is preferably a copolymer containing a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit (styrene-acrylic acid ester-based copolymer). The styrene-acrylic acid ester copolymer contains, per 100% by mass of the styrene-acrylic acid ester copolymer, 95 to 20% by mass of styrene-based monomer units and 5 to 80% by mass of (meth)acrylic acid ester-based monomer units, preferably 90 to 25% by mass of styrene-based monomer units and 10 to 75% by mass of (meth)acrylic acid ester-based monomer units, more preferably 80 to 30% by mass of styrene-based monomer units and 20 to 70% by mass of (meth)acrylic acid ester-based monomer units, and even more preferably 60 to 40% by mass of styrene-based monomer units and 40 to 60% by mass of (meth)acrylic acid ester-based monomer units. By setting the content within these ranges, transparency, hue, and dimensional stability can be simultaneously satisfied. By setting the styrene-based monomer content to 90% by mass or less, a molded article (such as a light guide plate) with excellent transparency and hue can be obtained, and by setting the styrene monomer content to 20% or more, a molded article with excellent dimensional stability can be obtained. The content of the (meth)acrylic acid ester-based monomer unit in the styrene-based resin (A) is specifically, for example, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, or 80 mass%, and may be within a range between any two of the numerical values ​​exemplified here.

[0013] Examples of styrene-based monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, ethylstyrene, and p-t-butylstyrene. These can be used alone or in combination of two or more. The preferred styrene-based monomer is styrene.

[0014] 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. (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.

[0015] The styrene-based resin (A) may also be a copolymer obtained by copolymerizing another monomer copolymerizable with the styrene-based monomer and the (meth)acrylic acid ester-based monomer. Examples of the other 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.

[0016] The weight-average molecular weight (Mw) of the styrene-based 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-based resin (A) is preferably 3.5 or less, more preferably 1.0 to 3.5, and even more preferably 1.5 to 3.0. By adjusting the ratio within these ranges, 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, while if it exceeds 400,000, moldability may decrease. If the number-average molecular weight (Mn) ratio (Mw / Mn) exceeds 3.5, the strength of the molded product may decrease.

[0017] <Hindered Amine Light Stabilizer> The optical styrene-based resin composition preferably contains 0.001 to 1.0 part by mass, more preferably 0.001 to 0.5 part by mass, and even more preferably 0.05 to 0.3 part by mass of the hindered amine light stabilizer (B) relative to 100 parts by mass of the styrene-based resin (A). By adjusting the content within such a range, light stability can be improved. The content of the hindered amine light stabilizer (B) relative to the styrene-based 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, or 1.0 part by mass, and may be within a range between any two of the values ​​exemplified here. The hindered amine light stabilizer (B) may be used alone or in combination of two or more.

[0018] The hindered amine light stabilizer (B) is a compound having a structural unit represented by the following general formula (1).

[0019]

[0020] In general formula (1), X represents an organic group bonded to the 4-position of the piperidyl group via a carbon atom, an oxygen atom, or a nitrogen atom, and examples of R include 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 represents a hydrogen atom, it is referred to as an N-H hindered amine light stabilizer, when R represents a linear or branched alkyl group having 1 to 10 carbon atoms or a methylene group, it is referred to as an N-R hindered amine light stabilizer, and when R represents an alkoxy group, it is referred to as an N-OR hindered amine light stabilizer.

[0021] 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-piperidyl hexadecanoate, 2,2,6,6-tetramethyl-4-piperidyl octadecanoate (SABOSTAB UV91 manufactured by SONGWON), and tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate (ADK STAB manufactured by ADEKA). LA-57), polycondensate of N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine and 4-morpholino 2,6-dichloro-1,3,5-triazine (SABOSTAB UV79, manufactured by SONGWON), polycondensate of 2,4-dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-triazine.N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine (manufactured by BASF), Chimassorb 944FDL), polycondensate 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 (manufactured by 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 (manufactured by BASF) Chimassorb2020FDL), polycondensate 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]undencane-3,9-diethanol (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)henicosan-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).

[0022] Specific examples of the N-R type hindered amine light stabilizer include methyl(1,2,2,6,6-pentamethylpiperidin-4-yl)sebacate, bis(1,2,2,6,6-pentamethylpiperidin-4-yl)sebacate (TINUVIN 292, TINUVIN 765, manufactured by BASF), bis(1,2,2,6,6-pentamethylpiperidin-4-yl)n-butyl 3,5-di-tert-butyl 4-hydroxybenzyl malonate (TINUVIN 144, manufactured by BASF), and polycondensate of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol and succinic acid dimethyl ester (manufactured by BASF). TINUVIN622SF), 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 (CHIMASSORB119 manufactured by BASF), 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 (ADKSTAB manufactured by ADEKA Corporation). 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).

[0023] Specific examples of the N-OR type hindered amine light stabilizer 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).

[0024] <Antioxidant (C)> The optical styrene-based resin composition preferably contains 0.001 to 0.5 parts by mass, more preferably 0.002 to 0.4 parts by mass, and even more preferably 0.005 to 0.3 parts by mass of a phosphorus-based antioxidant (C-1) per 100 parts by mass of the styrene-based resin (A). By containing the antioxidant in such a range, good transparency and hue can be obtained. The content of the phosphorus-based antioxidant (C-1) is, for example, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 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, or 0.5 parts by mass relative to 100 parts by mass of the styrene-based resin (A), and may be within a range between any two of the numerical values ​​exemplified here.

[0025] The phosphorus-based antioxidant (C-1) is a phosphite ester having no phenolic hydroxyl group in the basic skeleton, and is preferably a phosphite ester which is a trivalent phosphorus compound. Specific examples of the phosphorus-based antioxidant (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.

[0026] The optical styrene-based resin composition preferably contains 0.001 to 0.5 parts by mass, more preferably 0.002 to 0.4 parts by mass, and even more preferably 0.005 to 0.3 parts by mass of the phenol-based antioxidant (C-2) relative to 100 parts by mass of the styrene-based resin (A). If the content of the phenol-based antioxidant (C-2) exceeds 0.5 parts by mass, the color tone deteriorates, which is not preferred. The content of the phenolic antioxidant (C-2) is, for example, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 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, 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.

[0027] The phenolic antioxidant (C-2) is an antioxidant that has a phenolic hydroxyl group in its basic skeleton and is not a phosphate ester. Specific examples of the phenolic 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 may be used alone or in combination of two or more.

[0028] The antioxidant includes a phosphorus-phenolic compound having both a phosphite structure and a phenolic 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 a compound, the optical styrene-based resin composition is considered to contain both a phosphorus-based antioxidant and a phenol-based antioxidant. For example, when the optical styrene-based resin composition contains 0.1 part by mass of the phosphorus-phenolic compound per 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 the phosphorus-based antioxidant and 0.1 part by mass of the phenol-based antioxidant.

[0029] <Monomer, Dimer, Trimer, and Phosphorus> In the optical styrene-based resin composition, the content of the styrene-based monomer per 1 g of the optical styrene-based resin composition is 1000 μg or less, preferably 700 μg or less, and more preferably 500 μg or less. The lower limit of the content of the styrene-based monomer is not particularly limited, but is, for example, 1 μg or more. Specific examples of the content of the styrene-based monomer per 1 g of the optical styrene-based resin composition include 0, 1, 10, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, and 1000 μg, and may be within a range between any two of the values ​​exemplified here. By setting the content within such a range, the optical styrene-based resin composition has excellent light stability.

[0030] In the optical styrene-based resin composition, the total content (D + T) of the styrene-based monomer linear dimer and the styrene-based monomer linear trimer per gram of the optical styrene-based resin composition is 10 to 500 μg, preferably 400 μg or less, and more preferably 300 μg or less. Specifically, the total (D + T) per gram of the optical styrene-based resin composition is, for example, 10, 50, 100, 150, 200, 250, 300, 330, 350, 400, 420, 450, or 500 μg, and may be within a range between any two of the values ​​exemplified here. By setting the total in this range, the optical styrene-based resin composition has excellent light stability.

[0031] In the optical styrene-based resin composition, the content of the styrene-based monomer linear dimer per 1 g of the optical styrene-based resin composition is preferably 500 μg or less, preferably 100 μg or less, and more preferably 50 μg or less. The lower limit of the content of the styrene-based monomer linear dimer per 1 g of the optical styrene-based resin composition is not particularly limited, but is, for example, 1 μg or more. Specific examples of the content of the styrene-based monomer linear dimer per 1 g of the optical styrene-based resin composition include 0, 1, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, and 500 μg, and may be within a range between any two of the values ​​exemplified here. By setting the content within such a range, the optical styrene-based resin composition has excellent light stability.

[0032] In the optical styrene-based resin composition, the content of the linear trimer of a styrene-based monomer per 1 g of the optical styrene-based resin composition is preferably 500 μg or less, preferably 300 μg or less, and more preferably 200 μg or less. The lower limit of the content of the linear trimer of a styrene-based monomer per 1 g of the optical styrene-based resin composition is not particularly limited, but is, for example, 10 μg or more. The content of the styrene monomer linear trimer per gram of the optical styrene resin composition is, for example, 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 350, 400, or 500 μg, and may be within a range between any two of the values ​​exemplified here. By setting the content within such a range, the optical styrene resin composition has excellent light stability.

[0033] In the optical styrene-based resin composition, the content of phosphorus atoms per 1 g of the optical styrene-based resin composition is preferably 100 μg or less, more preferably 50 μg or less, and even more preferably 20 μg or less. The lower limit of the content of phosphorus atoms per 1 g of the optical styrene-based resin composition is not particularly limited, but is, for example, 0 μg or more. Specific examples of the content of phosphorus atoms per 1 g of the optical styrene-based resin composition include 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 40, 50, 60, 70, 80, 90, and 100 μg, and may be within a range between any two of the values ​​exemplified here. By setting the content in such a range, the optical styrene-based resin composition has excellent light stability. The content of phosphorus atoms can be adjusted, for example, by the amount of phosphorus-based antioxidant (C-1) added.

[0034] The optical styrene-based resin composition preferably satisfies the following formula (1), where the content of the styrene-based monomer per 1 g of the optical styrene-based resin composition is M μg, the content of the linear dimer of the styrene-based monomer is D μg, the content of the linear trimer of the styrene-based monomer is T μg, and the content of phosphorus atoms is P μg. "(M+D+T)×P" is more preferably 15,000 or less, and even more preferably 10,000 or less. By setting it in such a range, the optical styrene-based resin composition has excellent light stability. (M+D+T)×P≦20,000 (1)

[0035] The method for measuring the contents of the styrene-based monomer, the linear dimer of a styrene-based monomer, and the linear trimer of a styrene-based monomer in the optical styrene-based resin composition is not particularly limited, and for example, they can be measured using a gas chromatograph.

[0036] In one example, when a synthesized styrene-based resin (A) is used, the weight of the styrene-based resin (A) before preparation of the composition is precisely weighed, and dissolved in tetrahydrofuran (THF) together with an internal standard substance (e.g., p-diethylbenzene), the content of the styrene-based monomer is measured using a capillary gas chromatograph, the content of the styrene-based monomer relative to the styrene-based resin (A) is calculated, and this is converted into the content (μg) per 1 g of the optical styrene-based resin composition used. Note that a calibration curve for the styrene-based monomer is prepared in advance and used for quantification.

[0037] In another example, the weight of an optical styrene-based resin composition is precisely weighed, dissolved in tetrahydrofuran (THF) together with an internal standard (e.g., p-diethylbenzene), and the content of the styrene-based monomer is measured using a capillary gas chromatograph. A calibration curve for the styrene-based monomer is prepared in advance and used for quantification.

[0038] In one example, when a synthesized styrene-based resin (A) is used, the contents of the styrene-based monomer linear dimer and styrene-based monomer linear trimer in the styrene-based resin (A) before the composition is prepared can be measured by preparing the following measurement solution. The measurement solution is prepared by adding THF to the styrene-based resin (A) and extracting it by ultrasonic treatment, then adding hexane to precipitate the polymer, allowing it to stand, and concentrating the supernatant. The measurement solution is then measured using a capillary gas chromatograph, and the content of the styrene-based monomer relative to the styrene-based resin (A) is calculated, and this is converted into the content (μg) per 1 g of the optical styrene-based resin composition used. Synthetic or commercially available styrene-based monomer linear dimer and styrene-based monomer linear trimer are obtained, and calibration curves for them are prepared in advance and used for quantification.

[0039] In another example, the contents of styrene-based monomer linear dimer and styrene-based monomer linear trimer in an optical styrene-based resin composition can be measured by preparing the following measurement solution. The measurement solution is prepared by adding THF to the optical styrene-based resin composition, extracting by ultrasonic treatment, then adding hexane to precipitate the polymer, allowing it to stand, and concentrating the supernatant. The measurement solution is then measured using a capillary gas chromatograph. Synthetic or commercially available styrene-based monomer linear dimer and styrene-based monomer linear trimer are obtained, and calibration curves for them are prepared in advance and used for quantification.

[0040] Here, the styrene-based monomer linear dimer and the styrene-based monomer linear trimer refer to dimers and trimers of styrene-based monomers. These dimers and trimers are, for example, those derived from the styrene-based monomer used in the synthesis of the styrene-based resin (A) (by-products, etc.). The dimers and trimers of the styrene-based monomer may include those formed by bonding to form a linear chain (linear dimer / linear trimer) and those formed by bonding to form a non-linear chain (e.g., cyclic) (non-linear dimer / non-linear trimer). In the present invention, the content of the linear styrene-based monomer linear dimer and linear styrene-based monomer trimer is specified.

[0041] Furthermore, when a plurality of types of styrene-based monomers are used, the styrene-based monomer linear dimer and the styrene-based monomer linear trimer may include not only dimerized or trimerized styrene-based monomers of the same type, but also those in which two or three different types of styrene-based monomers are bonded together.

[0042] In the synthesis of the styrene-based resin (A), when styrene is used as the styrene-based monomer, 2,4-diphenyl-1-butene may be produced as the styrene-based monomer linear dimer, and 2,4,6-triphenyl-1-hexene may be produced as the styrene-based monomer linear trimer. In one embodiment in which styrene is used as the styrene-based monomer, the optical styrene-based resin composition preferably has a styrene content of 1000 μg or less and a total content of 2,4-diphenyl-1-butene and 2,4,6-triphenyl-1-hexene of 10 to 500 μg per 1 g of the optical styrene-based resin composition. In one embodiment in which styrene is used as the styrene-based monomer, the above-mentioned numerical ranges for the content of the styrene monomer, the total content of the styrene-based monomer linear dimer and the styrene-based monomer linear trimer, the respective contents, and the relationship of the above formula (1) can be set as preferred numerical ranges for styrene, 2,4-diphenyl-1-butene, and 2,4,6-triphenyl-1-hexene.

[0043] The content of phosphorus atoms can be obtained, for example, by calculation from the amount of an additive containing phosphorus atoms (such as a phosphorus-based antioxidant) added to the optical styrene-based resin composition. The content of phosphorus atoms may be obtained by elemental analysis or ICP-AES (inductively coupled plasma atomic emission spectrometry) of the optical styrene-based resin composition, or by other analytical methods.

[0044] <Other Components> The content of t-butylcatechol (TBC) in the optical styrene-based 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 with excellent hue and transmittance can be obtained. Specific examples of the TBC content are 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, and 10 ppm, and may be within a range between any two of the values ​​exemplified here.

[0045] The 6-tert-butyl-2,4-xylenol (TBX) content in the optical styrene-based resin composition is preferably 10 ppm or less, more preferably 5 ppm or less. By setting the content within this range, a light guide plate with excellent hue and transmittance can be obtained. Specific examples of the TBX content include 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, and 10 ppm, and may be within a range between any two of the values ​​exemplified here.

[0046] The optical styrene-based resin composition may contain, within the scope that does not impair the properties of the present invention, a release agent such as a sulfur-based antioxidant, a lactone-based antioxidant, an ultraviolet absorber, an antistatic agent, a hydrophilic additive, liquid paraffin (mineral oil), polyethylene wax, microcrystalline wax, a bluing agent, a higher fatty acid such as lauric acid, myristic acid, palmitic acid, or stearic acid, a higher fatty acid amide such as stearic acid amide, erucic acid amide, or ethylene bisstearic acid amide, a higher fatty acid glyceride such as lauric acid monoglyceride, palmitic acid monoglyceride, stearic acid monoglyceride, or behenic acid monoglyceride, or a higher alcohol such as myristyl alcohol, cetyl alcohol, or stearyl alcohol.

[0047] <Characteristics of Optical Styrenic Resin Composition> The melt mass flow rate (MFR) of the optical styrene resin composition at a temperature of 200°C and a load of 49 N is preferably 0.5 to 5.0 g / 10 min, and more preferably 1.0 to 4.0 g / 10 min. 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. Specific examples of the MFR are 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 g / 10 min, and may be within a range between any two of the values ​​exemplified here.

[0048] The Vicat softening temperature of the optical styrene-based resin composition is preferably 95 to 104°C, more preferably 100 to 104°C. If the Vicat softening temperature is less than 95°C, heat resistance is insufficient, and the light guide plate may be deformed depending on the usage environment. Specific examples of the Vicat softening temperature include 95, 96, 97, 98, 99, 100, 101, 102, 103, and 104°C, and may be within a range between any two of the values ​​exemplified here.

[0049] The optical styrene resin composition preferably has an average transmittance of 85% or more, more preferably 86% or more, at wavelengths of 380 to 780 nm when the molded article has an optical path length of 115 mm.

[0050] The optical styrene resin composition preferably has a YI value of 6.0 or less, more preferably 4.0 or less, when the molded article has an optical path length of 115 mm.

[0051] When the optical styrene-based resin composition is stored for 500 hours under conditions of a temperature of 60°C and a relative humidity of 90%, the dimensional change in the long side before and after storage, calculated by the following formula, is preferably 0.15% or less, and more preferably less than 0.10%.

[0052] The time required for the yellowness index YI of a molded article of the optical styrene-based resin composition to exceed 20 after blue LD irradiation is preferably 150 hours or more, more preferably 400 hours or more, and even more preferably 600 hours or more. The detailed conditions for blue LD irradiation will be described later in the Examples.

[0053] <Method for producing optical styrene-based resin composition> Examples of the polymerization method for the styrene-based resin (A) include known styrene polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and 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.

[0054] During polymerization of the styrene-based resin (A), polymerization aids such as a polymerization initiator, a chain transfer agent, a crosslinking agent, and other polymerization aids may be used as necessary. The polymerization initiator is preferably a radical polymerization initiator, 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-butylperoxyacetate, t-butylperoxybenzoate, and t-butylperoxyisopropyl monocarbonate; peroxycarbonates such as t-butylperoxyisopropyl carbonate and polyether tetrakis(t-butylperoxycarbonate); 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 these may be used alone or in combination of two or more. Examples of chain transfer agents 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 in which the hydroxyl group of a polyhydric alcohol such as ethylene glycol, tetraethylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, or sorbitol is esterified 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.

[0055] 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.

[0056] First, in the polymerization step, a known complete mixing tank type agitation 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.

[0057] The polymer solution containing the polymer that has left the polymerization step is transferred to a devolatilization step, where unreacted monomers and polymerization solvent are removed. The devolatilization step is performed using a vacuum devolatilization tank equipped with a heater. The devolatilization step may be performed, for example, by introducing the polymer solution continuously removed from the reactor into a vacuum devolatilization tank equipped with a preheater, which is configured in series with two stages. In the first devolatilization tank, the temperature can be set to 160 to 200°C and the pressure to 0.8 to 1.2 kPa, for example. In the second devolatilization tank, the temperature can be set to 201 to 250°C and the pressure to 0.5 to 0.9 kPa, for example. The molten polymer that has left the devolatilization step is transferred to a granulation step. In the granulation step, the molten resin is extruded in the form of strands through a multi-hole die and processed into pellets by a cold cut method, an in-air hot cut method, or an underwater hot cut method. It is preferable not to carry out the devolatilization or addition of additives while kneading with an extruder in order to prevent the generation of dimers and trimers (depolymerization due to thermal history).

[0058] In the optical styrene-based resin composition, a hindered amine light stabilizer (B), a phosphorus-based antioxidant (C-1), and a phenol-based antioxidant (C-2) can be added to the styrene-based resin (A) as needed. 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 polymerization of the styrene-based resin (A), or may be mixed in a static mixer after polymerization of the styrene-based resin (A).

[0059] The content of t-butylcatechol or 6-tert-butyl-2,4-xylenol in the optical styrene resin composition can be adjusted by adjusting the content at the start of polymerization of the styrene resin (A) and the content in the subsequent devolatilization step or the like.

[0060] 2. Molded Article / Light Guide Plate The optical styrene-based resin composition can be used in applications that transmit light from an LED light source having a maximum radiation intensity in the wavelength region of 400 nm to 500 nm. A molded article according to one embodiment of the present invention is a molded article made from the optical styrene-based resin composition, and can be obtained by molding the optical styrene-based resin composition. Furthermore, a light guide plate according to one embodiment of the present invention is a light guide plate comprising a molded article made from the optical styrene-based resin composition, and can be 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.

[0061] <Shape of Light Guide Plate> The light guide plate may have an uneven surface. More specifically, the light guide plate may have a plurality of lenticular and / or prism-shaped convex portions on the surface. The convex portions are preferably provided on at least one surface of the light guide plate, and are particularly provided on one surface that 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.

[0062] Here, the lenticular-shaped convex portions are arc-shaped convex portions, and are protrusions with an arc-shaped cross-sectional edge. Furthermore, the prism-shaped convex portions are arc-shaped convex portions, and are protrusions with a triangular mountain-shaped cross-sectional edge. Furthermore, multiple convex portions can be formed in parallel to each other. Furthermore, the convex portions can be formed integrally with the light guide plate.

[0063] 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 that is excellent in moldability, such as excellent extrusion stability, and strength, when molding the optical styrene-based resin composition.

[0064] <Optical Properties> The average transmittance of the light guide plate at wavelengths of 380 to 780 nm when the light path length is 115 mm is preferably 85% or more, and more preferably 86% or more.

[0065] 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.

[0066] <Method for Manufacturing Light Guide Plate> A light guide plate according to one embodiment of the present invention is obtained by molding the optical styrene-based resin composition described above. Known molding methods such as sheet extrusion, injection molding, and compression molding can be used as the molding method. However, continuous sheet extrusion molding equipped with a surface shape transfer mold is preferred in terms of productivity and ease of producing large molded products. An example of such sheet extrusion molding is a continuous sheet extrusion molding method that includes an extrusion step in which a resin is supplied in a heated and molten state to a feed block and continuously extruded from a die to produce an extrusion sheet, a pressing step in which the resin sheet is sandwiched between a pressure roll and a cooling roll, and a conveying step in which, after the pressing step, the resin sheet is conveyed while being in close contact with the cooling roll, and the cooling roll is equipped with a transfer mold on its surface. By changing the shape of the transfer mold, any desired uneven shape can be transferred to the sheet surface.

[0067] The light guide plate may have a textured front surface (light-emitting surface), and the back surface may be subjected to a reflective treatment for diffused reflection of light. Examples of reflective treatment include silk printing, inkjet printing, and a method for imparting dot-shaped texture by laser irradiation, and ink containing fine particles that diffuse light can be used for printing the dot pattern. That is, the light guide plate may include a light guide layer (light guide portion) composed of the optical styrene-based resin composition and a reflective layer (reflective portion) for reflection.

[0068] 3. Edge-lit surface light source unit An edge-lit surface light source unit according to one embodiment of the present invention is an edge-lit surface light source unit having the above-described light guide plate and a light source that supplies LED light to the end surface of the light guide plate. The edge-lit surface light source unit is suitably used as a surface light source device for a liquid crystal display device.

[0069] The present invention will be described in more detail below with reference to examples, but these examples are merely illustrative and are not intended to limit the scope of the present invention.

[0070] 1. Production of Optical Styrenic Resin Composition [Example 1] A polymerization process was performed by connecting a first reactor, which was a complete mixing type agitation tank, and a second reactor, which was a plug flow reactor equipped with a static mixer, in series, to produce a styrene-based resin (A). The volumes of the first reactor and the second reactor were 30 liters and 12 liters, respectively. As shown in Table 1, the raw material composition was 51% by mass of styrene, 39% by mass of methyl methacrylate, and 10% by mass of ethylbenzene. At the inlet of the first reactor, the added concentrations of 150 ppm of t-butylperoxyisopropyl monocarbonate (Perbutyl I, manufactured by NOF Corporation) as a polymerization initiator and 500 ppm of n-dodecyl mercaptan (manufactured by Arkema Inc.) as a chain transfer agent (both concentrations are based on the mass of the raw material feed (total raw material monomers) [*1 in Table 1]) were adjusted. The raw material solution was then continuously supplied to the first reactor, which was set at 128°C, at a rate of 8.0 kg / h. The resulting polymerization solution was then continuously fed to a second reactor, where the polymerization was completed. The monomer conversion at this time was 70%. A temperature gradient was applied to the second reactor along the flow direction, adjusting the temperature to 130°C at the middle and 145°C at the outlet. The polymer-containing solution continuously withdrawn from the second reactor was then introduced into a two-stage preheater-equipped vacuum devolatilizer tank in series, where the temperature and pressure were adjusted to the values ​​shown in Table 2, and unreacted monomers and ethylbenzene were separated. Various additives were melt-added to the resulting molten polymer in the amounts shown in Table 2, and the polymer was extruded into strands through a multi-hole die via an SMX (static mixer). The strands were cooled, cut, and pelletized by a cold-cut method.

[0071] <Monomer Amount in Optical Styrenic Resin Composition> The amount of styrene monomer (styrene) in the styrene resin (A) was measured using a capillary gas chromatograph under the following conditions: 0.2 g of the styrene resin (A) taken before the various additives were melted and added was precisely weighed, dissolved in 10 mL of tetrahydrofuran (THF) containing p-diethylbenzene as an internal standard, and the amount was measured using a capillary gas chromatograph under the following conditions. In the table, the measurement results are converted into the content (μg) per 1 g of the optical styrene resin composition. Capillary gas chromatograph: GC-4000 (manufactured by GL Sciences Inc.) Column: InertCap WAX manufactured by GS Sciences Inc., inner diameter 0.25 mm, length 30 m, film thickness 50 μm Injection temperature: 180°C Column temperature: 60°C to 170°C Detector temperature: 210°C Split ratio: 5 / 1

[0072] <Content of Dimers and Trimers in Optical Styrenic Resin Compositions> The contents of the styrene-based linear dimer (2,4-diphenyl-1-butene) and the styrene-based linear trimer (2,4,6-triphenyl-1-hexene) of the styrene-based monomer (styrene) in the styrene-based resin (A) were measured under the following conditions and procedures. Sample preparation: 5 mL of THF was added to 0.1 g of the styrene-based resin (A), and the mixture was subjected to ultrasonic treatment to extract. Then, hexane was added to bring the solution volume to 50 mL to precipitate the polymer component. After allowing the mixture to stand, the supernatant (total amount) was concentrated to 2 mL to prepare a measurement solution. In Tables 2 to 4, the measurement results are shown converted into the content (μg) per 1 g of the optical styrene-based resin composition. Measurement conditions Gas chromatograph: JEOL K9 (JEOL Ltd.) Column: ZB-5MS 0.25 mm × 30 m film thickness 0.25 μm Injection temperature: 200°C Column temperature: 40-320°C Detector temperature: 300°C Split ratio: 10 / 1 Ionization method: EI Mass range: m / z = 29 to 600 Carrier gas: nitrogen Note that 2,4-diphenyl-1-butene and 2,4,6-triphenyl-1-hexene were purchased from Fujifilm Wako Pure Chemical Industries, Ltd., and quantification was performed by creating a calibration curve.

[0073] <Melt Mass Flow Rate (MFR)> The melt mass flow rate of the optical styrene resin composition was measured in accordance with JIS K 7210 under conditions of a temperature of 200°C and a load of 49N.

[0074] <Vicat Softening Temperature> The Vicat softening temperature of the optical styrene-based resin composition was measured in accordance with JIS K 7206 at a temperature rise rate of 50° C. / hr and a test load of 50 N.

[0075] <Molecular Weight> The weight average molecular weight (Mw) and number average molecular weight (Mn) of the styrene-based resin (A) were measured using gel permeation chromatography (GPC) under the following conditions: GPC model: Shodex GPC-101 manufactured by Showa Denko K.K. Column: PLgel 10 μm MIXED-B manufactured by Polymer Laboratories, Inc. Mobile phase: tetrahydrofuran Sample concentration: 0.2 mass% Temperature: oven 40°C, injection port 35°C, detector 35°C 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.

[0076] Hereinafter, a plate-shaped test piece 1 was prepared as a molded article intended to be a light guide plate, and the properties of the molded article were evaluated.

[0077] <Evaluation of Optical Properties of Resin Composition> Using pellets of the obtained optical styrene-based resin composition, injection molding was performed at a cylinder temperature of 230 ° C. and a mold temperature of 60 ° C., and a mold polished so that the end surface 3 was a mirror surface as shown in FIG. 1 was used to mold a molded body (plate-shaped test piece 1) of 115 mm × 80 mm × 3 mm (length × width × thickness) (the opposite side of each side shown as end surface 3 is also a mirror surface). Using a UV-visible spectrophotometer V-670 manufactured by JASCO Corporation, the spectral transmittance was measured at wavelengths of 350 nm to 800 nm with an optical path length of 115 mm for incident light of 20 × 1.6 mm and a spread angle of 0 °, and the YI value at a field of view of 2 ° with a C light source was calculated according to JIS K7105. The average transmittance shown in Tables 2 to 4 indicates the average transmittance at wavelengths of 380 nm to 780 nm.

[0078] <Dimensional Stability> Plate-shaped test piece 1 was stored for 500 hours under conditions of a temperature of 60°C and a relative humidity of 90%, and the dimensional change of the long side before and after storage was measured, and the deformation rate was calculated using the following formula: Deformation rate = ((Long side length after storage) - (Long side length before storage)) ÷ (Long side length before storage) x 100 (%) The dimensional stability (deformation due to moisture absorption) of the molded article was evaluated with a change rate of less than 0.10% being ◯, a change rate of 0.10 to 0.15% being △, and a change rate of more than 0.15% being ×.

[0079] <Evaluation of Blue LD Durability of Resin Composition> An irradiated area was set near the center of surface 5 of plate-shaped test piece 1, and a Presize Gauge PLS-1000S optical fiber (450±10 nm) was placed 0.5 mm from directly above the irradiated area, and blue LD was irradiated onto plate-shaped test piece 1 at room temperature. When the illuminance was measured using an illuminance meter (Hamamatsu Photonics K.K., sensor head H12684-385, controller C12144), the illuminance was 12 W / cm ２ Thereafter, the plate-shaped test piece 1 was taken out every 50 hours, and the yellowness index YI of the irradiated portion was measured using a color difference meter COLOR-7e2 (manufactured by Kurabo Industries Co., Ltd.), and the time at which the value exceeded 20 was recorded in the table. Note that a test piece that exceeded the yellowness index YI of 20 for more than 100 hours was deemed to have passed the test.

[0080] Examples 2 to 22 and Comparative Examples 1 to 4 Optical styrene-based resin compositions and molded articles (plate-shaped test pieces 1) were produced in the same manner as in Example 1, except that the compositions of the raw material solutions and polymerization conditions were changed as shown in Table 1, and the blending ratios of the styrene-based resin (A), resin hindered amine light stabilizer (B), phosphorus-based antioxidant (C-1), and phenol-based antioxidant (C-2) were changed as shown in Tables 2 to 4. The results of various measurements and evaluations are shown in Tables 2 to 4. In the tables, "ND" indicates that no phosphorus atoms were detected.

[0081]

[0082]

[0083]

[0084]

[0085] The hindered amine light stabilizer (B), phosphorus-based antioxidant (C-1), and phenol-based antioxidant (C-2) in Tables 2 to 4 are as follows:

[0086] (Hindered amine light stabilizer (B)) 944: Polycondensate of 2,4-dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-triazine.N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine (manufactured by BASF, Chimassorb 944FDL) 292: 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 (manufactured by BASF, TINUVIN 292)

[0087] (Phosphorus-based antioxidants (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 (ADKSTAB HP-10, manufactured by ADEKA) PEP-36: 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (ADEKA STAB PEP-36, manufactured by ADEKA Corporation)

[0088] (Phenol-based antioxidant (C-2)) 1076: Octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (Irganox 1076, manufactured by BASF)

[0089] In Examples 1 to 22, the transparency (average transmittance), hue (YI value), and dimensional stability were good, and the LD durability was excellent.

[0090] 1: Molded product 3: End surface (mirror surface) 5: Surface

Claims

1. An optical styrene-based resin composition containing a styrene-based resin, For 1 g of the optical styrene-based resin composition, The content of styrene-based monomers is 1000 μg or less, the total content of the styrene-based monomer linear dimer and the styrene-based monomer linear trimer is 10 to 500 μg; The styrene-based resin contains a hindered amine light stabilizer in an amount of 0.001 to 0.5 parts by mass relative to 100 parts by mass of the styrene-based resin. Optical styrene resin composition.

2. An optical styrene-based resin composition containing a styrene-based resin, For 1 g of the optical styrene-based resin composition, The content of styrene-based monomers is 1000 μg or less, the total content of the styrene-based monomer linear dimer and the styrene-based monomer linear trimer is 10 to 500 μg; It is used to transmit light from an LED light source having a maximum radiation intensity in the wavelength range of 400 nm to 500 nm. Optical styrene resin composition.

3. 3. The optical styrene-based resin composition according to claim 1, wherein the styrene-based resin is a copolymer containing 95 to 20% by mass of styrene-based monomer units and 5 to 80% by mass of (meth)acrylic acid ester-based monomer units.

4. 3. The optical styrene resin composition according to claim 1, wherein the content of phosphorus atoms per gram of the optical styrene resin composition is 50 μg or less.

5. When the content of the styrene-based monomer per 1 g of the optical styrene-based resin composition is M μg, the content of the styrene-based monomer linear dimer is D μg, the content of the styrene-based monomer linear trimer is T μg, and the content of phosphorus atoms is P μg, The optical styrene-based resin composition according to claim 1 or 2, which satisfies the following formula (1): (M+D+T)×P≦20000 (1)

6. A molded article made from the optical styrene-based resin composition according to claim 1 or 2.

7. A light guide plate comprising the molded article according to claim 6.

8. An edge-light type surface light source unit comprising the light guide plate according to claim 7 and a light source that supplies LED light to an end face of the light guide plate.