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

Abstract

Provided is an optical styrene-based resin composition having excellent light stability for long-term use of a semiconductor light source such as an LED light source. According to the present invention, provided is an optical styrene-based resin composition containing a styrene-based resin, the content of a styrene-based monomer being 1000 [mu] g or less and the total of the content of a linear dimer of the styrene-based monomer and the content of a linear trimer of the styrene-based monomer being 10-500 [mu] g per 1 g of the optical styrene-based resin composition.

Description

Technical Field

[0001] This invention relates to an optical styrene-based resin composition, a molded body, a light guide plate, and an edge-beam light source unit. Background Technology

[0002] Backlights for liquid crystal displays (LCDs) include types where the light source is positioned directly below the front of the display and edge-lit types where the light source is positioned on the side. Edge-lit backlights use a component called a light guide plate, which guides the light from the side-lit source to the front of the display. These backlights are widely used in televisions, desktop computer monitors, laptops, mobile phones, car navigation displays, and more. Additionally, backlights using light guide plates are also used in lighting devices and billboards.

[0003] Light guide plates, due to their relatively long light transmission distance and significant light loss along the optical path, require exceptionally high light transmittance. Therefore, acrylic resins, such as polymethyl methacrylate (PMMA), are commonly used as materials for light guide plates. However, PMMA has high water absorption, which can lead to warping or dimensional changes in the light guide plate. Furthermore, its susceptibility to thermal decomposition during molding can result in poor appearance if molded at high temperatures. To address these issues, for example, Patent Document 1 proposes using styrene-(methyl)methacrylate copolymer as the material for light guide plates.

[0004] On the other hand, compared to PMMA, the hue of molded styrene-(meth)acrylate copolymers is poor, which can lead to uneven color when used as backlights. To improve this problem, Patent Document 2 discloses a hue improvement technique for styrene-(meth)acrylate.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2003-075648

[0008] Patent Document 2: International Publication No. 2016 / 129675 Summary of the Invention

[0009] In recent years, with the increasing resolution of backlight units in televisions and monitors, high-brightness LEDs (Light Emitting Diodes) have been used as edge light sources. However, traditional styrene-(meth)acrylate copolymer light guides suffer from the following: depending on the usage environment, the end face of the light guide deteriorates (yellowing) after prolonged use. Furthermore, in recent years, displays using higher-energy blue mini-LEDs as light sources and utilizing QD (quantum dots) for color conversion have been introduced, placing increasingly higher demands on the light stability of the light guide.

[0010] The present invention was made in view of the following problem, and aims to provide an optical styrene-based resin composition that exhibits excellent photostability for long-term use with semiconductor light sources such as LED light sources.

[0011] The inventors conducted intensive research to solve the above-mentioned problems and found that by keeping the content of styrene monomers, the content of styrene monomer linear dimers, and the content of styrene monomer linear trimers in the styrene-based resin composition within a specific range, the above-mentioned problems can be solved, thereby completing the present invention.

[0012] The present invention provides the following invention.

[0013] [1] An optical styrene-based resin composition comprising a styrene-based resin.

[0014] Compared to 1g of the above-mentioned styrene-based resin composition for optical applications,

[0015] The content of styrene monomers is less than 1000 μg.

[0016] The total content of styrene monomer linear dimers and styrene monomer linear trimers is 10–500 μg.

[0017] [2] The optical styrene-based resin composition as described in [1], wherein the styrene-based resin is a copolymer comprising 95 to 20% by mass of styrene monomer units and 5 to 80% by mass of (meth)acrylate monomer units.

[0018] [3] The optical styrene resin composition as described in [1] or [2], wherein the content of phosphorus atoms is 50 μg or less relative to 1 g of the optical styrene resin composition.

[0019] [4] An optical styrene-based resin composition as described in any of [1] to [3], wherein,

[0020] Compared to 1g of the aforementioned styrene-based resin composition for optical applications, when the content of the aforementioned styrene monomer is set to Mμg, the content of the aforementioned styrene monomer linear dimer is set to Dμg, the content of the aforementioned styrene monomer linear trimer is set to Tμg, and the content of phosphorus atoms is set to Pμg,

[0021] Satisfy the following equation (1):

[0022] (M+D+T)×P≦20000(1).

[0023] [5] The optical styrene-based resin composition described in any one of [1] to [4] contains 0.001 to 0.5 parts by weight of hindered amine light stabilizer relative to 100 parts by weight of the styrene-based resin.

[0024] [6] An optical styrene-based resin composition as described in any of [1] to [5], used for transmitting light from an LED light source having maximum radiant intensity in the wavelength region of 400 nm to 500 nm.

[0025] [7] A molded article comprising an optical styrene-based resin composition as described in any one of [1] to [6].

[0026] [8] A light guide plate having a molded body of [7].

[0027] [9] An edge-lit surface light source unit having a light guide plate as described in [8] and a light source that provides LED light to the end face of the light guide plate. Attached Figure Description

[0028] Figure 1 This is a diagram illustrating the shape of the plate-shaped test piece 1. Detailed Implementation

[0029] The embodiments of the present invention will now be described. The various features shown in the embodiments described below can be combined with each other. Furthermore, each feature independently enables the invention to be realized.

[0030] 1. Optical styrene-based resin composition

[0031] An optical styrene-based resin composition according to one embodiment of the present invention comprises a styrene-based resin (A).

[0032] <Styrene-based resins (A)>

[0033] Styrene-based resin (A) is a resin obtained by polymerizing raw material monomers containing styrene monomers. Styrene-based resin (A) is preferably a resin obtained by copolymerizing monomers containing styrene monomers and (meth)acrylate monomers. Styrene-based resin (A) is preferably a copolymer containing styrene monomer units and (meth)acrylate monomer units (styrene-acrylate copolymer). For the styrene-acrylate copolymer, it contains 95-20% by mass of styrene monomer units and 5-80% by mass of (meth)acrylate monomer units per 100% by mass; preferably, it contains 90-25% by mass of styrene monomer units and 10-75% by mass of (meth)acrylate monomer units; more preferably, it contains 80-30% by mass of styrene monomer units and 20-70% by mass of (meth)acrylate monomer units; and even more preferably, it contains 60-40% by mass of styrene monomer units and 40-60% by mass of (meth)acrylate monomer units. By setting these ranges, transparency, hue, and dimensional stability can be simultaneously satisfied. By setting the styrene monomer content to 90% by mass or less, molded bodies with excellent transparency and hue (such as light guide plates) can be obtained; by setting the styrene monomer content to 20% or more, molded bodies with excellent dimensional stability can be obtained. Specifically, the content of the (meth)acrylate monomer units in the styrene resin (A) is, for example, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, or 80% by mass, or within any range between any two values ​​exemplified herein.

[0034] Examples of styrene monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, ethylstyrene, and p-tert-butylstyrene. They can be used alone or in combination of two or more. Styrene is the preferred styrene monomer.

[0035] Examples of (meth)acrylate monomers include: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isoamyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, etc. (meth)alkyl acrylates; phenyl methacrylate, benzyl methacrylate, etc. (meth)aryl acrylates; cyclohexyl methacrylate, 4-tert-butylcyclohexyl methacrylate, 2-norbornyl methacrylate, isobornyl methacrylate, adamantane-1-yl methacrylate, 2-methyladamantane-2-yl methacrylate, 2-ethyl-2-adamantyl methacrylate, tricyclodecyl methacrylate, etc. (meth)cycloalkyl acrylates; glycidyl methacrylate; dicyclopentyl methacrylate, etc. They can be used alone or in combination of two or more. The (meth)acrylate monomers are preferably alkyl (meth)acrylates, and more preferably methyl methacrylate.

[0036] In addition, styrene-based resins (A) can also be copolymers obtained by copolymerizing with other monomers that can copolymerize with styrene-based monomers and (meth)acrylate-based monomers. Examples of other monomers that can copolymerize include: acrylic acid, methacrylic acid, and other (meth)acrylic acids; vinyl cyanides such as acrylonitrile and methacrylonitrile; α,β-vinyl unsaturated carboxylic acids such as maleic anhydride and fumaric acid; and imides such as phenylmaleimide and cyclohexylmaleimide. They can be used alone or in combination of two or more.

[0037] 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. Furthermore, the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the styrene-based resin (A) (Mw / Mn) is preferably 3.5 or less, more preferably 1.0 to 3.5, and even more preferably 1.5 to 3.0. By setting it within this range, both moldability and the strength of the light guide plate can be balanced. If the weight-average molecular weight (Mw) is less than 50,000, the strength of the molded article may be insufficient; if it exceeds 400,000, the moldability may decrease. Additionally, if the number-average molecular weight (Mn) ratio (Mw / Mn) exceeds 3.5, the strength of the molded article may decrease.

[0038] Hindered amine light stabilizers

[0039] The styrene-based resin composition for optical applications preferably contains 0.001 to 1.0 parts by weight of hindered amine light stabilizer (B) relative to 100 parts by weight of styrene-based resin (A), more preferably 0.001 to 0.5 parts by weight, and even more preferably 0.05 to 0.3 parts by weight. By setting it within this range, photostability can be improved. Specifically, the content of hindered amine light stabilizer (B) relative to 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 parts by weight, or may fall within the range of any two values ​​exemplified herein. Furthermore, hindered amine light stabilizer (B) can be used alone or in combination of two or more types.

[0040] Hindered amine light stabilizers (B) are compounds having the structural units represented by the following general formula (1).

[0041] [Chemistry 1]

[0042]

[0043] In general formula (1), X is an organic group bonded to the 4-position of a piperidinium group via a carbon atom, an oxygen atom, and a nitrogen atom. R can be a hydrogen atom, a straight-chain or branched alkyl group with 1 to 10 carbon atoms, a methylene group, or an alkoxy group. When R is a hydrogen atom, it is designated as an NH-type hindered amine light stabilizer; when R is a straight-chain or branched alkyl group with 1 to 10 carbon atoms or a methylene group, it is designated as an NR-type hindered amine light stabilizer; and when R is an alkoxy group, it is designated as an N-OR-type hindered amine light stabilizer.

[0044] Specific examples of NH-type hindered amine light stabilizers include: bis(2,2,6,6-tetramethylpiperidin-4-yl) sebacate (BASF TINUVIN770DF), 2,2,6,6-tetramethyl-4-piperidinyl hexadecanoate, 2,2,6,6-tetramethyl-4-piperidinyl octadecanoate (SONGWON SABOSTAB UV91), tetra(2,2,6,6-tetramethyl-4-piperidinyl)-1,2,3,4-butanetetracarboxylate (ADEKA ADK STAB LA-57), and the condensation polymer of N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine and 4-morpholino-2,6-dichloro-1,3,5-triazine (SONGWON SABOSTAB). UV79), condensation polymers of 2,4-dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-triazine·N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)hexamethylenediamine (manufactured by BASF, Chimassorb 944FDL), and condensation polymers of N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine with 2,4,6-trichloro-1,3,5-triazine, N-butyl-1-butaneamine, and N-butyl-2,2,6,6-tetramethyl-4-piperidinylamine (manufactured by SONGWON, SABOSTAB). UV40), 1,6,11-tris[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidinyl)amino)symmetric triazine-6-yl]aminoundecane (manufactured by BASF, Chimassorb 2020FDL), condensate of 1,2,3,4-butanetetracarboxylic acid with 2,2,6,6-tetramethyl-4-piperidinol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5,5]undecane-3,9-diethanol (manufactured by ADEKA, ADKSTAB) LA-68), dodecyl 3-(2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazabispiro(5.1.11.2)octadec-20-yl)propionate, tetradecyl 3-(2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazabispiro(5.1.11.2)octadec-20-yl)propionate (HOSTAVIN 3030 manufactured by CLARIANT), and condensation polymer of 2,2,4,4-tetramethyl-7-oxa-3,20-diazabispiro(5.1.11.2)octadec-21-one with epichlorohydrin (HOSTAVIN N30P manufactured by CLARIANT).

[0045] Specific examples of NR-type hindered amine light stabilizers include: methyl (1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate, bis(1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate (BASF TINUVIN 292, TINUVIN 765), bis(1,2,2,6,6-pentamethylpiperidin-4-yl) n-butyl 3,5-di-tert-butyl 4-hydroxybenzyl malonate (BASF TINUVIN 144), and the condensation polymer of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol and dimethyl succinate (BASF). The condensation polymers of TINUVIN622SF, 1,5,8,12-tetra[4,6-bis(n-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidinyl)amino)-1,3,5-triazin-2-yl]-1,5,8,12-tetraazadodecane (manufactured by BASF, Chimassorb119), 1,2,3,4-butanetetracarboxylic acid with 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 (manufactured by ADEKA, ADKSTAB) A mixture of LA-63P), succinic acid and (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)ethanol, and N,N',N”,N”'-tetra-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine (manufactured by BASF, TINUVIN111FDL).

[0046] Specific examples of N-OR type hindered amine light stabilizers include: bis(1-octyloxy-2,2,6,6-tetramethylpiperidinyl) sebacate (BASF TINUVIN123) and bis(1-undecyloxy-2,2,6,6-tetramethylpiperidin-4-yl) carbonate (ADEKA ADKSTAB LA-81).

[0047] <Antioxidant (C)>

[0048] The styrene-based resin composition for optical applications preferably contains 0.001 to 0.5 parts by weight of a phosphorus-based antioxidant (C-1) relative to 100 parts by weight of the styrene-based resin (A), more preferably 0.002 to 0.4 parts by weight, and even more preferably 0.005 to 0.3 parts by weight. By setting it within such ranges, good transparency and hue can be obtained. The content of phosphorus-based antioxidant (C-1) relative to 100 parts by weight of styrene-based resin (A) is specifically, 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 weight, or within any range between any two values ​​exemplified herein.

[0049] Phosphorus-based antioxidants (C-1) are (phosphite) esters that do not have phenolic hydroxyl groups in their basic skeleton, and are preferably phosphite esters that are ternary phosphorus compounds. Specific examples of phosphorus-based antioxidants (C-1) include 2,2'-methylenebis(4,6-di-tert-butyl-1-phenoxy)(2-ethylhexyloxy)phosphine, 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, tetra(2,4-di-tert-butylphenyl)[1,1biphenyl]-4,4'-diylbisphosphonite, and bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite. They can be used alone or in combination of two or more.

[0050] Furthermore, the styrene-based resin composition for optical applications preferably contains 0.001 to 0.5 parts by weight of a phenolic antioxidant (C-2) relative to 100 parts by weight of the styrene-based resin (A), more preferably 0.002 to 0.4 parts by weight, and even more preferably 0.005 to 0.3 parts by weight. If the content of the phenolic antioxidant (C-2) exceeds 0.5 parts by weight, the color deteriorates, and therefore it is not preferred. The content of phenolic antioxidant (C-2) relative to 100 parts by weight of styrene resin (A) is specifically, 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 weight, or within any range between any two values ​​exemplified herein.

[0051] Phenolic antioxidants (C-2) are antioxidants that have phenolic hydroxyl groups in their basic skeleton and are not (phosphite) esters. Specific examples of phenolic antioxidants (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 tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. They can be used alone or in combination of two or more.

[0052] Antioxidants include phosphorus-phenolic compounds, such as 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosphazene, which possess both phosphite and phenolic structures within the same molecule. It is believed that such compounds are present in optical styrene-based resin compositions containing both phosphorus-based and phenolic antioxidants. For example, when 0.1 parts by mass of a phosphorus-phenolic compound is present relative to 100 parts by mass of styrene-based resin (A), it is believed that the composition contains both 0.1 parts by mass of a phosphorus-phenolic antioxidant and 0.1 parts by mass of a phenolic antioxidant.

[0053] <Monomers, Dimers, Trimers, and Phosphorus>

[0054] In the optical styrene-based resin composition, the content of styrene monomers relative to 1g of the optical styrene-based resin composition is 1000μg or less, preferably 700μg or less, and more preferably 500μg or less. There is no particular limitation on the lower limit of the styrene monomer content, for example, it is 1μg or more. Specifically, the content of styrene monomers relative to 1g of the optical styrene-based resin composition is, for example, 0, 1, 10, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000μg, or may be within the range of any two values ​​exemplified herein. By setting such a range, the optical styrene-based resin composition exhibits excellent photostability.

[0055] In the optical styrene-based resin composition, the total content (D+T) of the straight-chain dimer and the straight-chain trimer of the styrene monomers relative to 1 g 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, this total (D+T) relative to 1 g 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, or may be within any two values ​​exemplified herein. By setting it within such a range, the optical styrene-based resin composition exhibits excellent photostability.

[0056] In the styrene-based resin composition for optical applications, the content of styrene monomer linear dimers relative to 1 g of the styrene-based resin composition is preferably 500 μg or less, more preferably 100 μg or less, and even more preferably 50 μg or less. There is no particular limitation on the lower limit of the content of styrene monomer linear dimers relative to 1 g of the styrene-based resin composition for optical applications, for example, it is 1 μg or more. Specifically, the content of styrene monomer linear dimers relative to 1 g of the styrene-based resin composition for optical applications is, for example, 0, 1, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, or 500 μg, or may be within the range of any two values ​​exemplified herein. By setting such a range, the styrene-based resin composition for optical applications exhibits excellent photostability.

[0057] In the styrene-based resin composition for optical applications, the content of styrene monomer linear trimers relative to 1 g of the styrene-based resin composition is preferably 500 μg or less, more preferably 300 μg or less, and more preferably 200 μg or less. There is no particular limitation on the lower limit of the content of styrene monomer linear trimers relative to 1 g of the styrene-based resin composition for optical applications, for example, it is 10 μg or more. The content of the styrene-based monomer linear trimer relative to 1g of the optical styrene-based 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, or within any two values ​​exemplified herein. By setting such a range, the optical styrene-based resin composition exhibits excellent photostability.

[0058] In the optical styrene-based resin composition, the phosphorus atom content relative to 1g of the optical styrene-based resin composition is preferably 100μg or less, more preferably 50μg or less, and even more preferably 20μg or less. There is no particular limitation on the lower limit of the phosphorus atom content relative to 1g of the optical styrene-based resin composition, for example, it can be 0μg or more. Specifically, the phosphorus atom content relative to 1g of the optical styrene-based resin composition is, for example, 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, or 100μg, or may be within the range of any two values ​​exemplified herein. By setting such a range, the photostability of the optical styrene-based resin composition is excellent. It should be noted that the phosphorus atom content can be adjusted, for example, by the amount of phosphorus-based antioxidant (C-1) added.

[0059] The optical styrene-based resin composition preferably satisfies the following formula (1) when, relative to 1 g of the optical styrene-based resin composition, the content of styrene monomers is set to M μg, the content of styrene monomer linear dimers is set to D μg, the content of styrene monomer linear trimers is set to T μg, and the content of phosphorus atoms is set to P μg. "(M+D+T)×P" is more preferably 15000 or less, and even more preferably 10000 or less. By setting it within such a range, the optical styrene-based resin composition exhibits excellent photostability.

[0060] (M+D+T)×P≦20000(1)

[0061] There are no particular limitations on the methods for determining the content of styrene monomers, styrene monomer linear dimers, and styrene monomer linear trimers in optical styrene resin compositions; for example, gas chromatography can be used for determination.

[0062] In one example, when using the synthesized styrene-based resin (A), the weight of the styrene-based resin (A) before composition preparation is accurately weighed, dissolved in tetrahydrofuran (THF) along with an internal standard (e.g., p-diethylbenzene), and the content of the styrene monomer is determined using capillary gas chromatography. The content of the styrene monomer relative to the styrene-based resin (A) is calculated and converted into the content (μg) in 1g of an optical styrene-based resin composition using the styrene monomer. It should be noted that a calibration curve related to the styrene monomer is prepared beforehand for quantification.

[0063] In another example, the weight of an optical styrene-based resin composition was accurately weighed and dissolved in tetrahydrofuran (THF) along with an internal standard (e.g., p-diethylbenzene). The content of styrene monomers was determined using capillary gas chromatography. It should be noted that a calibration curve related to the styrene monomers was prepared beforehand for quantification.

[0064] In one example, when using the synthesized styrene-based resin (A), the following assay solution can be prepared to determine the content of styrene monomer linear dimers and styrene monomer linear trimers in the styrene-based resin (A) before the composition is prepared. The assay solution is prepared by adding THF to the styrene-based resin (A) and extracting by sonication, followed by adding hexane to precipitate the polymer, allowing it to stand, and then concentrating the supernatant. The assay solution is then measured using capillary gas chromatography to calculate the content of the styrene monomers relative to the styrene-based resin (A), which is then converted to the content (μg) per 1g of the optical styrene-based resin composition using them. It should be noted that styrene monomer linear dimers and styrene monomer linear trimers, or commercially available products, should be synthesized beforehand, and calibration curves related to them should be prepared for quantification.

[0065] In another example, the following assay solution can be prepared to determine the content of styrene monomer linear dimers and styrene monomer linear trimers in an optical styrene resin composition. The assay solution is prepared by adding THF to the optical styrene resin composition and extracting it by sonication, followed by adding hexane to precipitate the polymer, allowing it to stand, and then concentrating the supernatant. The assay solution is then measured using a capillary gas chromatograph. It should be noted that styrene monomer linear dimers and trimers can be synthesized or obtained commercially available products, and calibration curves associated with them can be prepared in advance for quantification.

[0066] The styrene-based monomer linear-chain dimers and trimers are dimers and trimers of styrene-based monomers. These dimers and trimers are, for example, derived from styrene-based monomers (byproducts, etc.) used in the synthesis of styrene-based resins (A). As dimers and trimers of styrene-based monomers, they can exist as dimers and trimers formed by bonding in a linear form (linear dimers / linear trimers), and as dimers and trimers formed by bonding in a non-linear form (e.g., cyclic) (non-linear dimers / non-linear trimers). In this invention, the content of linear styrene-based monomer linear-chain dimers and trimers is specified.

[0067] In addition, regarding styrene-based monomer linear dimers and styrene-based monomer linear trimers, when using multiple styrene-based monomers, in addition to styrene-based monomer linear dimers and styrene-based monomer linear trimers formed by dimerizing or trimerizing the same type of styrene-based monomers, it may also include styrene-based monomer linear dimers and styrene-based monomer linear trimers formed by bonding two or three different types of styrene-based monomers.

[0068] When styrene is used as a styrene monomer in the synthesis of styrene-based resin (A), 2,4-diphenyl-1-butene can be generated as a linear dimer of the styrene monomer, and 2,4,6-triphenyl-1-hexene can be generated as a linear trimer of the styrene monomer. In one embodiment using styrene as a styrene monomer, the styrene-based resin composition for optical applications preferably contains 1000 μg or less of styrene per 1 g of the optical styrene-based resin composition, and the total content of 2,4-diphenyl-1-butene and 2,4,6-triphenyl-1-hexene is 10 to 500 μg. In one embodiment where styrene is used as a styrene monomer, the numerical ranges relating to the content of styrene monomer, the total content of styrene monomer linear dimers and styrene monomer linear trimers, the content of each, and the relationship of the above formula (1) can be set as preferred numerical ranges relating to styrene, 2,4-diphenyl-1-butene, and 2,4,6-triphenyl-1-hexene.

[0069] The phosphorus atom content can be calculated, for example, based on the amount of phosphorus-containing additives (such as phosphorus-based antioxidants) added to the optical styrene-based resin composition. Alternatively, the phosphorus atom content can 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.

[0070] <Other Ingredients>

[0071] The tert-butylcatechol (TBC) content in the styrene-based resin composition for optical applications is preferably 10 ppm or less, more preferably 5 ppm or less. By setting it within such a range, a light guide plate with excellent hue and transmittance can be obtained. Specifically, the TBC content 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, or 10 ppm, or may be within the range of any two values ​​exemplified herein.

[0072] 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 it within such a range, a light guide plate with excellent hue and transmittance can be obtained. Specifically, the TBX content 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, or 10 ppm, or may be within the range of any two values ​​exemplified herein.

[0073] The styrene-based resin composition for optical applications may, within a range that does not impair the properties of the present invention, contain sulfur-based antioxidants, lactone-based antioxidants, ultraviolet absorbers, antistatic agents, hydrophilic additives, liquid paraffin (mineral oil), polyethylene wax, microcrystalline wax, bluing agents, higher fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid, higher fatty acid amides such as octadecylamide, erucamide, and ethylene bis-stearamide, higher fatty acid glycerides such as laurate monoglyceride, palmitate monoglyceride, stearate monoglyceride, and betaine monoglyceride, and release agents such as myristol, cetyl alcohol, and stearyl alcohol.

[0074] <Characteristics of Styrene-based Resin Compositions for Optical Applications>

[0075] The melt mass flow rate (MFR) of the styrene-based resin composition for optical applications under conditions of 200°C and 49N load is preferably 0.5 to 5.0 g / 10 min, more preferably 1.0 to 4.0 g / 10 min. If the MFR is below 0.5 g / 10 min, the molding stability decreases; if the MFR exceeds 5.0 g / 10 min, the strength is insufficient. Specifically, the MFR is, for example, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0 g / 10 min, or may be within the range of any two values ​​exemplified herein.

[0076] The Vickers softening temperature of the styrene-based resin composition for optical applications is preferably 95–104°C, more preferably 100–104°C. If the Vickers softening temperature is below 95°C, the heat resistance is insufficient, which may cause deformation of the light guide plate depending on the application environment. Specifically, this Vickers softening temperature is, for example, 95, 96, 97, 98, 99, 100, 101, 102, 103, or 104°C, or may be within the range of any two values ​​exemplified herein.

[0077] The average transmittance of the molded article of the styrene-based resin composition for optical applications at a wavelength of 380-780 nm with an optical path length of 115 mm is preferably 85% or more, and more preferably 86% or more.

[0078] The molded article of the styrene-based resin composition for optical use preferably has a YI (Yellowness Index) value of 6.0 or less, more preferably 4.0 or less, at an optical path length of 115 mm.

[0079] The molded body of the styrene-based resin composition for optical applications is stored at a temperature of 60°C and a relative humidity of 90% for 500 hours. The change rate of the long side before and after storage, calculated by the following formula, is preferably less than 0.15%, and more preferably less than 0.10%.

[0080] Regarding the styrene-based resin composition for optical applications, the time required for the yellowness YI of the molded article to exceed 20 by irradiation with a blue LD (Laser Diode) is preferably 150 hours or more, more preferably 400 hours or more, and even more preferably 600 hours or more. Detailed conditions for blue LD irradiation will be described in the examples described later.

[0081] <Method for manufacturing styrene-based resin compositions for optical applications>

[0082] Examples of known styrene polymerization methods for styrene-based resins (A) include bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. From the perspectives of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization is even more desirable. Solvents that can be used include, for example, alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene; ketones such as acetone and methyl ethyl ketone; or aliphatic hydrocarbons such as hexane or cyclohexane.

[0083] During the polymerization of styrene-based resins (A), polymerization initiators, chain transfer agents, crosslinking agents, and other polymerization aids may be used as needed. Free radical polymerization initiators are preferred, and commonly known examples include: peroxy ketals such as 1,1-di(tert-butylperoxy)cyclohexane, 2,2-di(tert-butylperoxy)butane, 2,2-di(4,4-di-tert-butylperoxycyclohexyl)propane, and 1,1-di(tert-pentylperoxy)cyclohexane; hydroperoxides such as cumene hydroperoxide and tert-butyl hydroperoxide; peroxides such as alkyl peroxides such as tert-pentylperoxyisononanoate; tert-butyl peroxide; di-tert-butyl peroxide; and peroxides such as cumene hydroperoxide. Dialkyl peroxides such as di-tert-hexyl, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, tert-butyl peroxyisopropyl monocarbonate and other peroxy esters, tert-butyl peroxyisopropyl carbonate, polyether tetra(tert-butyl peroxycarbonate) and other peroxy carbonates, N,N'-azobis(cyclohexane-1-carboxynitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylpentanonitrile), N,N'-azobis[2-(hydroxymethyl)propionitrile], etc.; one of them may be used, or a combination of two or more. Examples of chain transfer agents include: aliphatic thiols such as n-dodecyl mercaptan and tert-dodecyl mercaptan; aromatic thiols; thioglycolic acids such as thioglycolic acid and mercaptopropionic acid; polyfunctional thiols obtained by esterifying the hydroxyl groups of polyols such as ethylene glycol, tetraethylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, and sorbitol using thioglycolic acid or mercaptopropionic acid; pentaphenyl ethane; α-methylstyrene dimers; and terpinene oils. Among these, aliphatic thiols, aromatic thiols, thiocarboxylic acids, and polyfunctional thiols are preferred in terms of ease of molecular weight adjustment.

[0084] In continuous polymerization, styrene-based resins (A) can be manufactured by a method that includes a polymerization process, a devolatilization process, and a granulation process.

[0085] First, in the polymerization process, known stirred tanks or tower reactors are used to control the polymerization reaction by adjusting the polymerization temperature in order to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate.

[0086] The polymer solution containing the polymer, after the polymerization process has been completed, is transferred to a devolatilization process to remove unreacted monomers and polymerization solvent. The devolatilization process includes a vacuum devolatilization tank equipped with a heater. Alternatively, the devolatilization process can be carried out, for example, by continuously introducing the polymer-containing solution taken from the reactor into a vacuum devolatilization tank equipped with a preheater, configured in series in two stages. In the first devolatilization tank of the first stage, the temperature can be set to, for example, 160–200°C, and the pressure to be set to 0.8–1.2 kPa. In the second devolatilization tank of the second stage, the temperature can be set to, for example, 201–250°C, and the pressure to be set to 0.5–0.9 kPa. The molten polymer, after the devolatilization process has been completed, is transferred to a granulation process. In the granulation process, the molten resin is extruded into a filament from a porous die and processed into granules by cold cutting, air hot cutting, or underwater hot cutting. It should be noted that, in order to suppress the formation of dimers and trimers (depolymerization caused by thermal processes), it is preferable not to perform devolatilization or add additives during the mixing process using an extruder.

[0087] In optical styrene-based resin compositions, hindered amine light stabilizer (B), phosphorus-based antioxidant (C-1), and phenolic antioxidant (C-2) may be added to the styrene-based resin (A) as needed. The hindered amine light stabilizer (B), phosphorus-based antioxidant (C-1), and phenolic antioxidant (C-2) may be added to the raw material solution before the polymerization of the styrene-based resin (A), or they may be mixed using a static mixing device after the polymerization of the styrene-based resin (A).

[0088] The content of tert-butylcatechol or 6-tert-butyl-2,4-dimethylphenol in the styrene-based resin composition for optical applications can be adjusted at the beginning of the polymerization of the styrene-based resin (A), and can also be adjusted in subsequent devolatilization processes, etc.

[0089] 2. Molded body, light guide plate

[0090] The aforementioned optical styrene-based resin composition can be used to transmit light from LED light sources that have maximum radiant intensity in the wavelength region of 400 nm to 500 nm. One embodiment of the present invention has a molded body made of the aforementioned optical styrene-based resin composition, which can be obtained by molding the aforementioned optical styrene-based resin composition. Another embodiment of the present invention has a light guide plate comprising a molded body made of the aforementioned optical styrene-based resin composition, which can be obtained by molding the aforementioned optical styrene-based resin composition. The light guide plate can be used in edge-lit surface light source units.

[0091] <Shape of the light guide plate>

[0092] The light guide plate may have an uneven surface. More specifically, the surface of the light guide plate may have multiple biconvex and / or prismatic protrusions. The protrusions are preferably provided on at least one side of the light guide plate, particularly on the side that serves as the front surface (light-emitting surface) of the light guide plate. Other sides may also be provided if necessary, but it is more preferable that they are provided only on the front surface (light-emitting surface) of the light guide plate.

[0093] Among them, the double-convex shaped convex part is an arc-shaped convex part, which is a protruding strip with an arc-shaped edge in cross-section. Additionally, the prism-shaped convex part is an arc-shaped convex strip with a triangular mountain-shaped edge in cross-section. Furthermore, multiple convex parts can be formed in a parallel manner. Moreover, the convex parts can be integrally formed on the light guide plate.

[0094] 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 this range, it is easy to manufacture a light guide plate with excellent extrusion stability or other formability and strength in the molding of optical styrene-based resin compositions.

[0095] <Optical Properties>

[0096] The average transmittance of the light guide plate at a wavelength of 380-780nm with an optical path length of 115mm is preferably 85% or more, and more preferably 86% or more.

[0097] The YI value of the light guide plate at an optical path length of 115 mm is preferably 6.0 or less, and more preferably 4.0 or less.

[0098] <Manufacturing Method of Light Guide Plate>

[0099] One embodiment of the light guide plate 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 pressure molding can be used. In terms of ease of production and large-scale production of molded products, continuous sheet extrusion molding with a surface shape transfer mold is preferred. As an example of this sheet extrusion molding, a continuous sheet extrusion molding method having the following steps and having a transfer mold on the surface of the cooling roller is listed: an extrusion step in which resin is supplied to the feeding module in a heated and molten state and continuously extruded from the die to produce a sheet; an extrusion step in which the resin sheet is clamped by a pressure roller and a cooling roller; and a conveying step in which the resin sheet is conveyed while being sealed to the cooling roller after the extrusion step; by changing the shape of the transfer mold, any concave or convex shape can be transferred onto the surface of the sheet.

[0100] Furthermore, the light guide plate may have an uneven shape on its front surface (light-emitting surface), allowing for a reflective processing that diffuses light onto the back surface. As a reflective processing method, in addition to screen printing or inkjet printing, methods such as laser irradiation to impart a dotted shape with unevenness can be cited. In the printing of the dotted pattern, ink containing particles that diffuse light can be used. That is, the light guide plate may have a light-guiding layer (light-guiding part) made of the aforementioned optical styrene-based resin composition, and a reflective processing layer (reflective processing part) for reflection.

[0101] 3. Edge-shaped surface light source unit

[0102] One embodiment of the present invention is an edge-type surface light source unit having the aforementioned light guide plate and a light source that provides LED light to the end face of the light guide plate. The edge-type surface light source unit can be suitably used as a surface light source device for a liquid crystal display device.

[0103] Example

[0104] The present invention will be described in more detail below with examples. These are merely illustrative and do not limit the scope of the invention.

[0105] 1. Preparation of styrene-based resin compositions for optical applications

[0106] [Example 1]

[0107] A polymerization process is performed by connecting a first reactor, which is a fully mixed stirred tank, and a second reactor, which is a plug flow reactor with an attached static mixer, in series to manufacture styrene-based resin (A). The capacity of each reactor is set to 30 liters for the first reactor and 12 liters for the second reactor. As shown in Table 1, for a raw material composition of 51% by mass of styrene, 39% by mass of methyl methacrylate, and 10% by mass of ethylbenzene, the raw material solution is adjusted at the inlet of the first reactor to an addition concentration of 150 ppm of tert-butyl peroxide monocarbonate (manufactured by Nippon Oil Co., Ltd.: PERBUTYL I) as a polymerization initiator and 500 ppm of n-dodecyl mercaptan (manufactured by Arkema Co., Ltd.) as a chain transfer agent (both concentrations relative to the mass basis of the raw material feed (total raw material monomers) [*1 in Table 1]). The raw material solution is then continuously supplied to the first reactor, which is set at 128°C, at a rate of 8.0 kg / h. The resulting polymerization solution is then continuously supplied to the second reactor to complete the polymerization. At this point, the polymerization rate of the monomer is 70%. It should be noted that in the second reactor, a temperature gradient is set along the flow direction, adjusted so that the middle section is 130°C and the outlet section is 145°C.

[0108] Subsequently, the polymer-containing solution continuously extracted from the second reactor is introduced into a vacuum devolatilization tank with a preheater, which is configured in series in two stages. The temperature and pressure are adjusted as shown in Table 2 to separate unreacted monomers and ethylbenzene. Various additives are melt-added to the resulting molten polymer in the amounts shown in Table 2. The polymer is then extruded into filaments through a porous die via an SMX (static mixer). The filaments are cooled, cut, and granulated by cold cutting.

[0109] <Monomer content in styrene-based resin compositions for optical applications>

[0110] The amount of styrene monomer (styrene) in the styrene-based resin (A) was determined by accurately weighing 0.2 g of the styrene-based resin (A) before the addition of various additives, dissolving it in 10 mL of tetrahydrofuran (THF) containing p-diethylbenzene as an internal standard, and measuring it using capillary gas chromatography under the following conditions. In the table, the results are expressed as a percentage (μg) relative to 1 g of the optical styrene-based resin composition.

[0111] Capillary gas chromatograph: GC-4000 (manufactured by GL Science, Inc.)

[0112] Column: InertCap WAX, manufactured by GS Science, Inc., 0.25 mm inner diameter, 30 m length, 50 μm film thickness.

[0113] Injection temperature: 180℃

[0114] Column temperature: 60℃~170℃

[0115] Detector temperature: 210℃

[0116] Flow split ratio: 5 / 1

[0117] <Content of dimers and trimers in styrene-based resin compositions for optical applications>

[0118] The contents of styrene-based linear dimer (2,4-diphenyl-1-butene) and styrene-based linear trimer (2,4,6-triphenyl-1-hexene) of styrene monomer (styrene) in styrene-based resin (A) were determined according to the following conditions and order.

[0119] • Sample preparation: 5 mL of THF was added to 0.1 g of styrene-based resin (A) and the mixture was ultrasonically extracted. Hexane was then added in increments of 50 mL to precipitate the polymer. After standing, the supernatant (total volume) was concentrated to 2 mL as the test solution. The test results are shown in Tables 2-4, converted to the content (μg) per 1 g of the optical styrene-based resin composition.

[0120] • Measurement conditions

[0121] Gas chromatograph: JEOL K9 (Japan Electronics Corporation)

[0122] Chromatographic column: ZB-5MS 0.25mm × 30m, film thickness 0.25μm

[0123] Injection temperature: 200℃

[0124] Column temperature: 40-320℃

[0125] Detector temperature: 300℃

[0126] Flow split ratio: 10 / 1

[0127] Ionization method: EI

[0128] Mass range: m / z = 29~600

[0129] Carrier gas: Nitrogen

[0130] It should be noted that 2,4-diphenyl-1-butene and 2,4,6-triphenyl-1-hexene were purchased from Fujifilm and Kojin Chemical Co., Ltd., and calibration curves were prepared for quantification.

[0131] <Mel mass flow rate (MFR)>

[0132] The melt mass flow rate of the styrene-based resin composition for optical applications was determined according to JIS K 7210 at a temperature of 200°C and a load of 49 N.

[0133] <Vickers softening temperature>

[0134] The Vickers softening temperature of the styrene-based resin composition for optical applications was determined according to JIS K 7206 at a heating rate of 50°C / hr and a test load of 50 N.

[0135] <Molecular weight>

[0136] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of styrene-based resin (A) were determined using gel permeation chromatography (GPC) under the following conditions.

[0137] GPC Model: Shodex GPC-101 manufactured by Showa Denko K.K.

[0138] Chromatographic Column: PLgel 10μm MIXED-B manufactured by Polymer Laboratories

[0139] Mobile Phase: Tetrahydrofuran

[0140] Sample Concentration: 0.2% by mass

[0141] Temperature: Oven 40°C, Injection Port 35°C, Detector 35°C

[0142] Detector: Differential Refractometer

[0143] The molecular weight is calculated as the molecular weight at each elution time based on the elution curve of monodisperse polystyrene and is calculated as the molecular weight in terms of polystyrene.

[0144] Hereinafter, a plate-like test piece 1 is produced as a molded body assumed to be a light guide plate, and the characteristics of the molded body are evaluated.

[0145] <Evaluation of Optical Properties of Resin Composition>

[0146] Using the obtained particles of the optical styrene-based resin composition, injection molding is carried out at a cylinder temperature of 230°C and a mold temperature of 60°C. Using a mold with the end face #3 polished to a mirror finish as shown in Figure 1 , a molded body (plate-like test piece 1) with dimensions of 115 mm × 80 mm × 3 mm (length × width × thickness) is molded (the opposite faces of each face shown in the end face #3 are also mirror-finished). Using a UV-visible spectrophotometer V-670 manufactured by JASCO Corporation, the spectral transmittance at wavelengths from 350 nm to 800 nm with an optical path length of 115 mm is measured under incident light with a size of 20 × 1.6 mm and a diffusion angle of 0°. The YI value under a 2° field of view of a C light source is calculated according to JIS K7105. The average transmittance shown in Tables 2 to 4 represents the average transmittance at wavelengths from 380 nm to 780 nm.

[0147] <Dimensional Stability>

[0148] The plate-like test piece 1 is stored for 500 hours under the 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 is measured. The deformation rate is calculated according to the following formula.

[0149] [[ID=3�]]Deformation Rate = ((Length of the long side after storage) - (Length of the long side before storage)) ÷ (Length of the long side before storage) × 100 (%)

[0150] The dimensional stability (moisture absorption deformation) of the molded body is evaluated by setting the change rate below 0.10%, setting it to △ for 0.10 to 0.15%, and setting it to × for more than 0.15%.

[0151] <Durability Evaluation of Blue LD of Resin Composition>

[0152] An irradiated portion was positioned near the center of surface 5 of the plate-shaped test piece 1. An optical fiber (450±10nm) from PRECISE GAUGES PLS-1000S was placed 0.5mm directly above the irradiated portion. A blue LD was then applied to the plate-shaped test piece 1 at room temperature. Illuminance was measured using a lux meter (Hamamatsu Photonics Co., Ltd. sensor head H12684-385, controller C12144), and the illuminance was determined to be 12W / cm². 2 Subsequently, every 50 hours, the plate-shaped test piece 1 was removed, and the yellowness YI of the irradiated area was measured using a colorimeter COLOR-7e2 (manufactured by Kurashiki Boshoku Co., Ltd.). The time when the value exceeded 20 was recorded in the table. It should be noted that a yellowness YI value exceeding 20 for more than 100 hours is considered acceptable.

[0153] [Examples 2-22 and Comparative Examples 1-4]

[0154] The composition of the raw material solution and polymerization conditions were modified as shown in Table 1. The formulations of the styrene-based resin (A), the hindered amine light stabilizer (B), the phosphorus-based antioxidant (C-1), and the phenolic antioxidant (C-2) were modified as shown in Tables 2 to 4. Otherwise, the optical styrene-based resin composition and molded article (plate test piece 1) were manufactured in the same manner as in Example 1. Various measurement and evaluation results are shown in Tables 2 to 4. It should be noted that "ND" in the tables indicates that phosphorus atoms were not detected.

[0155] [Table 1]

[0156]

[0157] [Table 2]

[0158]

[0159] [Table 3]

[0160]

[0161] [Table 4]

[0162]

[0163] It should be noted that the hindered amine light stabilizer (B), phosphorus-based antioxidant (C-1), and phenolic antioxidant (C-2) in Tables 2 to 4 are described below.

[0164] (Hindered amine light stabilizer (B))

[0165] 944: A condensation polymer of 2,4-dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-triazine-N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)hexamethylenediamine (Chimassorb 944FDL manufactured by BASF).

[0166] 292: A mixture of 25% methyl (1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate and 75% bis(1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate (TINUVIN 292 manufactured by BASF).

[0167] (Phosphorus-based antioxidants (C-1))

[0168] 168: Tris(2,4-di-tert-butylphenyl) phosphite (manufactured by BASF, Irgafos 168)

[0169] HP-10: 2,2'-Methylenebis(4,6-di-tert-butyl-1-phenoxy)(2-ethylhexyloxy)phosphine (ADKSTAB HP-10 manufactured by ADEKA)

[0170] PEP-36: 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (ADKSTAB PEP-36 manufactured by ADEKA Inc.)

[0171] (Phenolic antioxidants (C-2))

[0172] 1076: Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (manufactured by BASF, Irganox 1076)

[0173] In Examples 1 to 22, the transparency (average transmittance), hue (YI value), and dimensional stability were good, and the LD durability was excellent.

[0174] Symbol Explanation

[0175] 1: Molded product

[0176] 3: End face (mirror finish)

[0177] 5: Face

Claims

1. An optical styrene-based resin composition comprising a styrene-based resin, Relative to 1g of the aforementioned styrene-based optical resin composition, The content of styrene monomers is less than 1000 μg. The total content of styrene monomer linear dimers and styrene monomer linear trimers is 10–500 μg.

2. The styrene-based resin composition for optical applications according to claim 1, wherein, The styrene-based resin is a copolymer comprising 95-20% by mass of styrene monomer units and 5-80% by mass of (meth)acrylate monomer units.

3. The styrene-based resin composition for optical applications according to claim 1, wherein, The phosphorus content is less than 50 μg relative to 1g of the optical styrene-based resin composition.

4. The styrene-based resin composition for optical applications according to claim 1, wherein, When, relative to 1 g of the optical styrene-based resin composition, the content of the styrene monomer is set to M μg, the content of the styrene monomer linear dimer is set to D μg, the content of the styrene monomer linear trimer is set to T μg, and the content of phosphorus atoms is set to P μg, then... Satisfy the following equation (1): (M+D+T)×P≦20000(1).

5. The styrene-based resin composition for optical applications according to claim 1, wherein, relative to 100 parts by weight of the styrene-based resin, it contains 0.001 to 0.5 parts by weight of a hindered amine light stabilizer.

6. The styrene-based resin composition for optical applications according to claim 1, used for transmitting light from an LED light source having maximum radiant intensity in the wavelength region of 400 nm to 500 nm.

7. A molded article comprising an optical styrene-based resin composition according to any one of claims 1 to 6.

8. A light guide plate comprising the molded body as described in claim 7.

9. An edge-lit surface light source unit, comprising a light guide plate as described in claim 8, and a light source for providing LED light to the end face of the light guide plate.

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