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

Abstract

A styrene-based resin composition is provided that has excellent transparency, color, and dimensional stability, as well as excellent long-term durability against LED light sources. According to the present invention, a styrene resin composition is provided comprising a styrene resin (A) which is a copolymer comprising a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit, an antioxidant (B), and an anthraquinone-based coloring agent (C), wherein the antioxidant (B) comprises either one or both of a phosphorus-based antioxidant (B-1) and a phosphorus-phenol-based antioxidant (B-2), and the phosphorus-based antioxidant (B-1) and the phosphorus-phenol-based antioxidant (B-2) are contained in a total of 0.001 to 0.5 parts by mass per 100 parts by mass of the styrene resin (A), and the anthraquinone-based coloring agent (C) is contained in a total of 0.1 to 150 ppb per styrene resin (A).

Description

Technology Field

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

[0002] Liquid crystal display (LCD) backlights are classified into direct-lit types, where the light source is placed in front of the display, and edge-lit types, where it is placed on the side. Edge-lit backlights utilize a component called a light guide plate that directs the light from the side-mounted source to the front of the display. They are used in a wide range of applications, including televisions, desktop personal computer monitors, laptop computers, mobile phones, and in-car navigation monitors. Additionally, backlights utilizing light guide plates are also used in lighting devices and signage.

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

[0004] Meanwhile, molded bodies of styrene-(meth)acrylate copolymer have poor color compared to PMMA, so color stains may occur when used as a backlight. To improve this problem, Patent Document 2 proposes a specific amount of blue dye mixed into styrene-(meth)acrylate methyl. Prior art literature

[0005] Japanese Patent Publication No. 2003-075648 Japanese Patent Publication No. 2013-082800 The problem to be solved

[0006] Recently, as energy saving measures are being implemented for backlight units such as televisions, monitors, and lighting, there is a need to increase brightness with fewer LEDs, so high-brightness type LEDs are sometimes used as edge light sources. However, conventional styrene-(meth)methyl acrylate copolymer light guide plates may turn yellow after being lit for a long time depending on the usage environment. When yellowing occurs, it becomes visible as color stains on televisions or monitors, and in lighting, the color temperature changes, which causes a problem in that the initial lighting design cannot be maintained.

[0007] The present invention was made in consideration of these problems, and aims to provide a styrene-based resin composition that has excellent transparency, color, and dimensional stability, as well as excellent long-term durability against LED light sources. means of solving the problem

[0008] According to the present invention, a styrene resin composition is provided comprising a styrene resin (A) which is a copolymer comprising a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit, an antioxidant (B), and an anthraquinone-based coloring agent (C), wherein the antioxidant (B) comprises either one or both of a phosphorus-based antioxidant (B-1) and a phosphorus-phenol-based antioxidant (B-2), and the phosphorus-based antioxidant (B-1) and the phosphorus-phenol-based antioxidant (B-2) are contained in a total of 0.001 to 0.5 parts by mass per 100 parts by mass of the styrene resin (A), and the anthraquinone-based coloring agent (C) is contained in a total of 0.1 to 150 ppb per styrene resin (A).

[0009] As a result of careful examination by the inventors, it was discovered that a styrene resin composition comprising a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit, an antioxidant within a predetermined range, and an anthraquinone-based colorant simultaneously satisfies transparency, color, dimensional stability, and long-term durability for LED light sources, and thus the present invention was completed.

[0010] Various embodiments of the present invention are illustrated below. The embodiments described below can be combined with one another.

[0011] [1] A styrene resin composition comprising a copolymer of styrene-based monomer units and (meth)acrylic acid ester-based monomer units, an antioxidant (B), and an anthraquinone-based coloring agent (C),

[0012] The above antioxidant (B) comprises either one or both of a phosphorus-based antioxidant (B-1) and a phosphorus-phenol-based antioxidant (B-2).

[0013] With respect to 100 parts by mass of the above styrene-based resin (A), the phosphorus-based antioxidant (B-1) and the phosphorus-phenol-based antioxidant (B-2) are contained in a total of 0.001 to 0.5 parts by mass.

[0014] A styrene-based resin composition containing 0.1 to 150 ppb of the anthraquinone-based coloring agent (C) with respect to the styrene-based resin (A).

[0015] [2] A styrene resin composition described in [1], wherein the styrene resin (A) contains 20 to 95 mass% of the styrene monomer unit and 5 to 80 mass% of the (meth)acrylic acid ester monomer unit in 100 mass% of the styrene resin (A).

[0016] [3] The above phosphorus-based antioxidant (B-1) is selected from at least 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)[1,1-biphenyl]-4,4'-diylbisphosphonite, and bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite ester. A styrene-based resin composition of type 1, as described in either [1] or [2].

[0017] [4] A styrene-based resin composition described in any one of claims [1] to [3], wherein the phosphorus-phenol-based antioxidant (B-2) is 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosperpine.

[0018] [5] A styrene-based resin composition described in any one of [1] to [4], wherein the average transmittance of a wavelength of 380 to 780 nm at an optical path length of 115 mm, measured using a test specimen made by molding the above styrene-based resin composition to a thickness of 115 mm x 80 mm x 3 mm, is 85% or more.

[0019] [6] A styrene-based resin composition described in any one of [1] to [5], wherein the YI value at an optical path length of 115 mm measured using a test specimen made by molding the above styrene-based resin composition to a thickness of 115 mm x 80 mm x 3 mm is 4.0 or less.

[0020] [7] An edge-light type light guide plate that is a molded body of a styrene-based resin composition as described in any one of [1] to [6].

[0021] [8] An edge-light type light guide plate as described in [7] and an edge-light type surface light source unit having a light source that supplies light to the cross-section of the light guide plate.

[0022] [9] An edge-light type surface light source unit for lighting as described in [7]. Specific details for implementing the invention

[0023] Embodiments of the present invention are described below. The various feature details presented in the embodiments described below may be combined with one another. Furthermore, an invention is established independently for each feature detail. Moreover, elements not specified in the claims of the embodiments below may be omitted as they are optional elements. Any number of '0's (e.g., one or two) may be added to the last digit of the numbers disclosed in the description below. For example, one or two '0's may be added after '1.4' to make it '1.40' or '1.400'.

[0024] 1. Styrene-based resin composition

[0025] A styrene-based resin composition according to one embodiment of the present invention is a styrene-based resin composition containing a styrene-based resin (A), an antioxidant (B), and an anthraquinone-based coloring agent (C).

[0026] The styrene-based resin composition comprises, for example, 95.000 to 99.999 mass% of styrene-based resin (A) in 100 mass% of the styrene-based resin composition, preferably 98.000 to 99.999 mass%, and more preferably 99.000 to 99.999 mass%.

[0027] <Styrene-based resin (A)>

[0028] The styrene-based resin (A) is a resin obtained by copolymerizing a monomer including a styrene-based monomer and a (meth)acrylic acid ester-based monomer, and is a copolymer including a styrene-based monomer unit which is a constituent unit derived from the styrene-based monomer and a (meth)acrylic acid ester-based monomer unit which is a constituent unit derived from the (meth)acrylic acid ester-based monomer. The styrene-based resin (A) is preferably a copolymer comprising 20 to 95 mass% of styrene-based monomer units and 5 to 80 mass% of (meth)acrylic acid ester-based monomer units in 100 mass% of the styrene-based resin (A), more preferably a copolymer comprising 25 to 90 mass% of styrene-based monomer units and 10 to 75 mass% of (meth)acrylic acid ester-based monomer units, and even more preferably a copolymer comprising 30 to 85 mass% of styrene-based monomer units and 15 to 70 mass% of (meth)acrylic acid ester-based monomer units. By setting the ranges to these values, transparency, color, and dimensional stability can be satisfied simultaneously. By making the styrene-based monomer 95 mass% or less, a light guide plate with excellent transparency and color can be obtained, and by making the styrene-based monomer unit (styrene monomer unit) 20 mass% or more, a light guide plate with excellent dimensional stability can be obtained. The content of the (meth)acrylic acid ester-based monomer unit of the styrene-based resin (A) is, specifically, for example, 5, 6, 7, 8, 9, 10, 15, 18, 20, 25, 30, 35, 40, 45, 47, 50, 55, 60, 65, 70, 75, 80 mass%, and may be within a range between any two of the values ​​exemplified herein.

[0029] The styrene-based resin (A) comprises, in 100 mass% of the styrene-based resin (A), a total of styrene-based monomer units and (meth)acrylic acid ester-based monomer units, for example, 80 to 100 mass%, preferably 90 to 100 mass%, more preferably 99 to 100 mass%, and particularly preferably (substantially) 100 mass%. The total content of styrene-based monomer units and (meth)acrylic acid ester-based monomer units in 100 mass% of styrene-based resin (A) is, specifically, for example, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100 mass%, and may be within a range between any two of the figures exemplified here.

[0030] Examples of styrene-based monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, ethylstyrene, pt-butylstyrene, etc. These may be used individually or in combination of two or more types. The styrene-based monomer is preferably styrene.

[0031] (Metha)acrylic acid ester monomers (acrylic acid ester monomers or methacrylic acid ester monomers) are, for example, (meth)acrylic acid alkyl esters such as (meth)acrylate methyl, (meth)acrylate ethyl, (meth)acrylate n-propyl, (meth)acrylate isopropyl, (meth)acrylate n-butyl, (meth)acrylate isobutyl, (meth)acrylate t-butyl, (meth)acrylate isoamyl, (meth)acrylate 2-ethylhexyl, (meth)acrylate lauryl, etc.; (meth)acrylic acid aryl esters such as (meth)acrylate phenyl, (meth)acrylate benzyl, (meth)acrylate; Examples include (meth)acrylate cycloalkyl esters such as (meth)acrylate cyclohexyl, (meth)acrylate 4-t-butylcyclohexyl, (meth)acrylate tricyclodecanyl, and (meth)acrylate adamantyl; (meth)acrylate glycidyl; and (meth)acrylate dicyclopentadienyl. These may be used individually or in combination of two or more. The (meth)acrylate ester monomer is preferably an (meth)acrylate alkyl ester, more preferably an alkyl methacrylate ester, and even more preferably methyl methacrylate.

[0032] In addition, the styrene-based resin (A) may be a copolymer obtained by copolymerizing a styrene-based monomer and a monomer capable of copolymerizing with a (meth)acrylic acid ester-based monomer. Examples of copolymerizable monomers include (meth)acrylic acids such as acrylic acid and methacrylic acid; vinyl cyanide such as acrylonitrile and methacrylonitrile; α,β-ethylene unsaturated carboxylic acids such as maleic anhydride and fumaric acid; and imides such as phenylmaleimide and cyclohexylmaleimide. These may be used individually or in combination of two or more types.

[0033] The weight average molecular weight (Mw) of the styrene-based resin (A) is preferably 50,000 to 400,000, and more preferably 100,000 to 350,000. Specifically, the weight average molecular weight (Mw) of the styrene-based resin (A) is, for example, 50,000, 100,000, 150,000, 160,000, 170,000, 180,000, 190,000, 200,000, 210,000, 220,000, 230,000, 240,000, 250,000, 300,000, 350,000, and 400,000, and may be within a range between any two of the figures exemplified herein. In addition, the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the styrene-based resin (A) is preferably 1.0 to 3.5, and more preferably 1.5 to 3.0. The ratio (Mw / Mn) is, specifically, for example, 1.0, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 3.0, 3.5, and may be within a range between any two of the values ​​exemplified here. By using this range, formability and the 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 becomes insufficient, and if it exceeds 400,000, the formability may decrease. Additionally, if the ratio (Mw / Mn) of the number average molecular weight (Mn) is less than 1.0, the formability decreases, and if it exceeds 3.5, the strength of the molded product may decrease.

[0034] <Antioxidant (B)>

[0035] The antioxidant (B) includes either one or both of the phosphorus-based antioxidant (B-1) and the phosphorus-phenol-based antioxidant (B-2).

[0036] The styrene-based resin composition contains, with respect to 100 parts by mass of styrene-based resin (A), a total of 0.001 to 0.5 parts by mass, preferably 0.002 to 0.4 parts by mass, and more preferably 0.005 to 0.3 parts by mass of a phosphorus-based antioxidant (B-1) and a phosphorus-phenol-based antioxidant (B-2). By setting the composition within this range, transparency and color can be improved. The total content of the phosphorus-based antioxidant (B-1) and the phosphorus-phenol-based antioxidant (B-2) is, specifically, 0.001, 0.002, 0.003, 0.004, 0.005, 0.01, 0.02, 0.025, 0.05, 0.075, 0.1, 0.15, 0.2, 0.3, 0.4, and 0.5 parts by mass with respect to 100 parts by mass of the styrene-based resin (A), and may be within a range between any two of the values ​​exemplified here.

[0037] Phosphorus-based antioxidant (B-1) refers to (hypo)phosphoric acid esters that do not have phenolic hydroxyl groups in their basic framework, and preferably hypophosphoric acid esters that are trivalent phosphorus compounds. Specific examples of phosphorus-based antioxidants (B-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-di-phosphaspiro[5,5]undecane, tetrakis(2,4-di-tert-butylphenyl)[1,1-biphenyl]-4,4'-diylbisphosphonite, bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite ester, etc. One type can be used alone or in combination of two or more types.

[0038] The phosphorus-phenol antioxidant (B-2) is a (hypo)phosphoric acid ester having a phenolic hydroxyl group in its basic framework, preferably a hypophosphoric acid ester that is a trivalent phosphorus compound having a phenolic hydroxyl group in its basic framework. The phosphorus-phenol antioxidant (B-2) is, for example, 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphospherine, etc.

[0039] In addition, the styrene-based resin composition may contain 0 to 0.5 parts by mass of a phenolic antioxidant (B-3) per 100 parts by mass of the styrene-based resin (A). If the content of the phenolic antioxidant (C-3) exceeds 0.5 parts by mass, it is undesirable because the color deteriorates. The content of the phenolic antioxidant (C-3) per 100 parts by mass of the styrene-based resin (A) is, specifically, for example, 0.001, 0.002, 0.003, 0.004, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, or 0.5 parts by mass, and may be within a range between any two of the values ​​exemplified herein.

[0040] Phenolic antioxidants (B-3) are antioxidants that have phenolic hydroxyl groups in their basic framework and are not (hy)phosphoric acid esters. The phenolic antioxidant (B-2) is, for example, at least one selected from octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, ethylenebis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], pentaerythritoltetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxasspiro[5,5]undecane. These can be used alone or in combination of two or more.

[0041] <Anthraquinone-based coloring agent (C)>

[0042] The styrene-based resin composition contains an anthraquinone-based coloring agent (C) in an amount of 0.1 to 150 ppb, preferably 0.5 to 100 ppb, and more preferably 1 ppb or more and less than 75 ppb with respect to the styrene-based resin (A). By setting the range to this, a styrene-based resin composition with good average transmittance and color, and excellent long-term stability for an LED light source can be obtained. The content of the anthraquinone-based coloring agent (B) with respect to the styrene-based resin (A) is, specifically, for example, 0.1, 0.5, 1, 5, 10, 15, 20, 35, 30, 35, 40, 45, 47, 50, 55, 60, 65, 70, 74, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150 ppb, and may be within a range between any two of the values ​​exemplified herein. In addition, the anthraquinone-based coloring agent (C) may be used as a single type or in combination of two or more types.

[0043] Anthraquinone-based coloring agent (C) is a compound having a structural unit represented by the following general formula (1).

[0044]

[0045] In general formula (1), R1 is a hydrogen atom, a group selected from the group consisting of a C1 to C10 alkyl group, a C3 to C10 cycloalkyl group, an aryl group, and an alkoxy group. R2 to R8 are each independently a hydrogen atom, a C1 to C10 alkyl group, a C3 to C10 cycloalkyl group, an aryl group, an alkoxy group, a hydroxyl group, a halogen group, an amino group, a sulfo group, a carboxyl group, a cyano group, a nitro group, -COR9, -COOR9, -NR9R 10 , -NR9COR 10 , -NR9SO2R 10 , -CONR9R 10 , -SO3R9, -CONHSO2R9, -SO2NR9R 10, and is a group selected from the -SO2NHCOR9 group, and R9 and R 10 It is a group independently selected from the group consisting of hydrogen atoms, or aliphatic groups, aromatic groups, and heterocyclic groups. For reference, if the structure has -SO3H and / or -CO2H, they may form salts such as sodium salts or potassium salts.

[0046] Examples of alkyl groups having 1 to 10 carbon atoms in R1 to R8 include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, 2-ethylhexyl, etc., and these alkyl groups may have substituents such as hydroxyl, halogen, amino, sulfo, carboxyl, cyano, nitro, or nitrile groups.

[0047] Examples of cycloalkyl groups having 3 to 10 carbon atoms in R1 to R8 include cyclopropyl groups, cyclopentyl groups, cyclohexyl groups, cycloheptyl groups, cyclooctyl groups, tricyclodecyl groups, etc., and these cycloalkyl groups may have substituents such as hydroxyl groups, halogen groups, amino groups, sulfonate groups, carboxyl groups, cyano groups, nitro groups, nitrile groups, etc.

[0048] Examples of aryl groups in R1 to R8 include phenyl groups, o-tolyl groups, m-tolyl groups, p-tolyl groups, cumyl groups, xylyl groups, propylphenyl groups, n-butylphenyl groups, 4-tert-butylphenyl groups, etc., and these aryl groups may have substituents such as hydroxyl groups, halogen groups, amino groups, sulfonate groups, carboxyl groups, cyano groups, nitro groups, nitrile groups, etc.

[0049] Examples of alkoxy groups in R1 to R8 include methoxy groups, ethoxy groups, propoxy groups, butoxy groups, tert-butoxy groups, phenoxy groups, naphthoxy groups, etc., and these alkoxy groups may have substituents such as hydroxyl groups, halogen groups, amino groups, sulfonate groups, carboxyl groups, cyano groups, nitro groups, nitrile groups, etc.

[0050] 안트라퀴논계 착색제의 구체적인 예로는 아래의 것을 들 수 있다. 참고로 이하에 나열한 명칭은 컬러 인덱스명이다. Disperse Violet4, Disperse Violet8, Disperse Violet17, Disperse Violet26, Disperse Violet28, Disperse Violet31, Disperse Blue3, Disperse Blue14, Disperse Blue60, Disperse Blue72, Disperse Blue134, Disperse Blue181, Disperse Blue197, Solvent Violet11, Solvent Violet12, Solvent Violet13, Solvent Violet26, Solvent Violet31, Solvent Violet33, Solvent Violet34, Solvent Violet36, Solvent Violet37, Solvent Violet38, Solvent Violet48, Solvent Violet51, Solvent Violet59, Solvent Violet60, Solvent Blue11, Solvent Blue12, Solvent Blue13, Solvent Blue14, Solvent Blue16, Solvent Blue18, Solvent Blue35, Solvent Blue36, Solvent Blue45, Solvent Blue58, Solvent Blue59, Solvent Blue59:1, Solvent Blue63, Solvent Blue67, Solvent Blue68, Solvent Blue74, Solvent Blue76, Solvent Blue78, Solvent Blue79, Solvent Blue83, Solvent Blue90, Solvent Blue94, Solvent Blue95, Solvent Blue97, Solvent Blue98, Solvent Blue101, Solvent Blue102, Solvent Blue104,Solvent Blue105, Solvent Blue111, Solvent Blue112, Solvent Blue122, Solvent Blue128, Solvent Blue132, Solvent Blue136, Solvent Blue146, Acid Blue27, Acid Blue43, Acid Blue47, Acid Blue49, Acid Blue51, Acid Blue55, Acid Blue145, Mordant Blue23, Mordant Blue27, Disperse Green6:1, Solvent Green3, Solvent Green20, Solvent Green28, Solvent Green33, Acid Green25.,

[0051] <Hindered amine-based light stabilizer (D)>

[0052] The styrene-based resin composition may contain a hindered amine-based light stabilizer (D). The styrene-based resin composition preferably contains 0.001 to 1.0 parts by mass of the hindered amine-based light stabilizer (D) per 100 parts by mass of the styrene-based resin (A), more preferably 0.001 to 0.5 parts by mass, and even more preferably 0.05 to 0.3 parts by mass. By setting the composition within these ranges, light stability can be improved. The content of the hindered amine-based light stabilizer (D) with respect to the styrene-based resin (A) is, specifically, for example, 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 parts by mass, and may be within a range between any two of the values ​​exemplified herein. In addition, the hindered amine-based light stabilizer (D) may be used as a single type or in combination of two or more types.

[0053] Hindered amine-based light stabilizer (D) is a compound having a structural unit represented by the following general formula (2).

[0054]

[0055] In general formula (2), X is an organic group that is bonded to the 4-position of a piperidyl group via a carbon atom, an oxygen atom, or a nitrogen atom, and R is a hydrogen atom, a straight-chain or branched alkyl group having 1 to 10 carbon atoms, a methylene group, or an alkoxy group. Here, when R is a hydrogen atom, it is called an NH-type hindered amine-based light stabilizer; when R is a straight-chain or branched alkyl group having 1 to 10 carbon atoms or a methylene group, it is called an NR-type hindered amine-based light stabilizer; and when R is an alkoxy group, it is called an N-OR-type hindered amine-based light stabilizer.

[0056] Specific examples of NH-type hindered amine-based light stabilizers include bis(2,2,6,6-tetramethylpiperidine-4-yl)sebacate (BASF TINUVIN 770 DF), 2,2,6,6-tetramethyl-4-piperidylhexadecanoate, 2,2,6,6-tetramethyl-4-piperidyloctadecanoate (SONGWON SABOSTAB UV91), tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate (ADEKA ADK STAB LA-57), N,N'-bis(2,2,6,6-tetramethylpiperidine-4-yl)hexamethylenediamine and 4-morpholino 2, Polycondensate with 6-dichloro-1,3,5-triazine (SABOSTAB UV79 manufactured by SONGWON), polycondensate with 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 (Chimasorb 944 FDL manufactured by BASF), polycondensate with N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylenediamine and 2,4,6-trichloro-1,3,5-triazine and N-butyl-1-butanamine and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine (SABOSTAB UV40 manufactured by SONGWON), 1,6,11-tris[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidyl)amino)-s-triazine-6-yl]aminoundecane (BASF Chimassorb 2020 FDL), 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]undecane-3,9-diethanol (ADEKA ADKSTAB LA-68), dodecyl 3-(2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazadisspiro(5.1.11.Examples include 2)henicosan-20-yl)propionate, tetradecyl 3-(2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazadisspiro(5.1.11.2)henicosan-20-yl)propionate (HOSTAVIN 3030 manufactured by CLARIANT), and a polycondensate of 2,2,4,4-tetramethyl-7-oxa-3,20-diazadisspiro-(5.1.11.2)henicosan-21-one and epichlorohydrin (HOSTAVIN N 30P manufactured by CLARIANT).

[0057] Specific examples of NR-type hindered amine light stabilizers include methyl(1,2,2,6,6-pentamethylpiperidine-4-yl)sebacate, bis(1,2,2,6,6-pentamethylpiperidine-4-yl)sebacate (BASF TINUVIN 292, TINUVIN 765), bis(1,2,2,6,6-pentamethylpiperidine-4-yl)n-butyl 3,5-di-tert-butyl 4-hydroxybenzyl malonate (BASF TINUVIN 144), and a polycondensate of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol and dimethyl succinate ester (BASF TINUVIN 622 SF). 1,5,8,12-tetrakis[4,6-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino)-1,3,5-triazine-2-yl]-1,5,8,12-tetraazadodecane (Chimasorb 119 manufactured by BASF), 1,2,3,4-butanetetracarboxylic acid and 1,2,2,6,6-pentamethyl-4-piperidinol and , , ', Examples include a polycondensate of succinic acid with 2,4,8,10-tetraoxaspiro[5,5]undecane-3,9-diethanol (ADKSTAB LA-63P manufactured by ADEKA), a polycondensate of succinic acid with (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)-triazine-2-yl)-4,7-diazadecane-1,10-diamine (TINUVIN 111 FDL manufactured by BASF).

[0058] Specific examples of N-OR type hindered amine-based light stabilizers include bis(1-octyloxy-2,2,6,6-tetramethylpiperidyl)sebacate (TINUVIN 123 manufactured by BASF) and bis(1-undecanoxy-2,2,6,6-tetramethylpiperidine-4-yl)carbonate (ADKSTAB LA-81 manufactured by ADEKA).

[0059] Other ingredients

[0060] The t-butylcatechol (TBC) in the styrene-based resin composition is preferably 10 ppm or less, and more preferably 5 ppm or less. By setting it to this range, a light guide plate with excellent color and transmittance can be obtained. Specifically, the content of TBC is, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ppm, and may be within a range between any two of the values ​​exemplified herein.

[0061] The 6-tert-butyl-2,4-xylenol (TBX) in the styrene-based resin composition is preferably 10 ppm or less, and more preferably 5 ppm or less. By setting it to this range, a light guide plate with excellent color and transmittance can be obtained. Specifically, the content of TBX is, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 ppm, and may be within a range between any two of the values ​​exemplified herein.

[0062] The styrene-based resin composition may include, to the extent that it does not impair the characteristics of the present invention, sulfur-based antioxidants, lactone-based antioxidants, ultraviolet absorbers, antistatic agents, hydrophilic additives, liquid paraffin (mineral oil), polyethylene wax, microcrystalline wax, bluing agents, higher fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid, higher fatty acid amides such as stearic acid amide, erucic acid amide, and ethylenebisstearic acid amide, higher fatty acid glycerides such as lauric acid monoglyceride, palmitic acid monoglyceride, stearic acid monoglyceride, and behenic acid monoglyceride, and release agents such as higher alcohols such as myristyl alcohol, cetyl alcohol, and stearyl alcohol.

[0063] The melt mass flow rate (MFR) of the styrene-based resin composition under conditions of a temperature of 200°C and a load of 49 N is preferably 0.5 to 5.0 g / 10 min, more preferably 1.0 to 4.5 g / 10 min, and even more preferably 1.2 to 4.0 g / 10 min. Specifically, the MFR is, for example, 0.5, 1.0, 1.2, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.5, 4.0, 4.5, 5.0, and may be within a range between any two of the values ​​exemplified herein. If the MFR is less than 0.5 g / 10 min, the molding (extrusion) stability is reduced, and if the MFR exceeds 5.0 g / 10 min, the strength becomes insufficient.

[0064] The Vicat softening temperature of the styrene-based resin composition (measured at a heating rate of 50°C / hr and a test load of 50N) is preferably 95°C or higher, and more preferably 98°C or higher. If the Vicat softening temperature is less than 95°C, the heat resistance is insufficient, and there is a possibility that the light guide plate may deform depending on the usage environment. For reference, the upper limit of the Vicat softening temperature may be, for example, 130°C or 104°C.

[0065] The average transmittance of a wavelength of 380 to 780 nm at an optical path length of 115 mm, measured using a test specimen made by molding a styrene-based resin composition to a thickness of 115 mm x 80 mm x 3 mm, is preferably 85% or higher, and more preferably 86% or higher. The said average transmittance (before long-term durability test) is, specifically, for example, 85, 86, 87, 88, 89, 90, 95%, and may be within a range between any two of the values ​​exemplified herein. In addition, the average transmittance of a wavelength of 380 to 780 nm at an optical path length of 115 mm, measured using the said test specimen after a long-term durability test (stored in an oven at 80°C for 1000 hours), is preferably 85% or higher. The corresponding average transmittance (after long-term durability test) is, specifically, for example, 85, 86, 87, 88, 89, 90, 95%, and may be within a range between any two of the values ​​exemplified here.

[0066] The YI value (YI1) at an optical path length of 115 mm, measured using a test specimen made by molding a styrene-based resin composition to a thickness of 115 mm x 80 mm x 3 mm, is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less. Specifically, the YI value (YI1) is, for example, 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, and may be within a range between any two of the values ​​exemplified herein. In addition, the YI value (YI2) at an optical path length of 115 mm, measured using the test specimen after a long-term durability test (stored in an oven at 80°C for 1000 hours), is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.5 or less. The corresponding YI value (YI2) is, specifically, for example, 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, and may be within a range between any two of the values ​​exemplified here. Also, YI(YI2-YI1) is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less.

[0067] Method for manufacturing a styrene-based resin composition

[0068] As a polymerization method for the styrene-based resin (A), known styrene polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be used. In terms of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization is preferred. As a solvent, examples of 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.

[0069] When polymerizing a 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 needed. Radical polymerization initiators are preferred as polymerization initiators, and known and commonly used examples 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-butylperoxyacetate and t-amylperoxyisonanoate; dialkyl peroxides such as t-butylcumyl peroxide, di-t-butylperoxide, dicumyl peroxide, and di-t-hexyl peroxide; and t-butylperoxyacetate and t-butylperoxybenzoate. Examples include peroxyesters such as t-butylperoxyisopropyl monocarbonate, peroxycarbonates such as t-butylperoxyisopropyl carbonate and polyethertetrakis(t-butylperoxycarbonate), N,N'-azobis(cyclohexane-1-carbonitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile), N,N'-azobis[2-(hydroxymethyl)propionitrile], etc., and one or more of these may be used in combination. 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 groups of polyhydric alcohols such as ethylene glycol, tetraethylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, and sorbitol are 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 due to the ease of controlling molecular weight.

[0070] In the case of continuous polymerization, a styrene-based resin (A) can be manufactured through a method comprising a polymerization process, a degassing process, and an assembly process.

[0071] First, the polymerization reaction is controlled by controlling the polymerization temperature, etc., using a fully mixed stirring tank or a tower-type reactor known in the polymerization process to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate.

[0072] The polymerization solution containing the polymer obtained from the polymerization process is transferred to the degassing process to remove unreacted monomers and polymerization solvents. The degassing process consists of a vacuum degassing tank equipped with a heater or a degassing extruder with a vent. The molten polymer obtained from the degassing process is transferred to the assembly process. In the assembly process, the molten resin is extruded in the form of strands through a porous die and processed into pellets using a cold cut, an air hot cut, or an underwater hot cut method.

[0073] A styrene-based resin composition can be prepared by adding an antioxidant (B) and an anthraquinone-based colorant (C) to a styrene-based resin (A). The antioxidant (B) and anthraquinone-based colorant (C) may be added to the raw material solution before polymerization of the styrene-based resin (A), or they may be mixed using an extruder or static mixing device installed before granulation after polymerization of the styrene-based resin (A). Alternatively, the composition may be prepared by dry blending the pellets with the antioxidant (B) and anthraquinone-based colorant (C) and then melt-kneading them after granulation of the styrene-based resin (A). In addition, a pellet-type masterbatch may be prepared by first melt-kneading the antioxidant (B) and anthraquinone-based colorant (C) together with a small amount of styrene-based resin to produce a pellet-type masterbatch, and then dry-blending the styrene-based resin (A) with the said masterbatch and then melt-kneading it.

[0074] t-butylcatechol or 6-tert-butyl in a styrene-based resin composition The content of 2,4-xylenol can be adjusted during the polymerization of the styrene-based resin (A), the content at the start of the polymerization, and the content during the subsequent degassing process.

[0075] 2. Light guide plate

[0076] A light guide plate according to one embodiment of the present invention is a molded article formed by molding the styrene-based resin composition. The light guide plate can be used for various purposes, but is particularly suitable for use in an edge-light type surface light source unit. The edge-light type surface light source unit may be, for example, a lighting unit, and the light guide plate may be a lighting light guide plate used in the unit.

[0077] Shape of the light guide plate

[0078] The light guide plate may have an uneven surface. More specifically, the surface of the light guide plate may have a plurality of convex portions having a lenticular shape and / or a prism shape. It is preferable that the convex portions be provided on at least one side of the light guide plate, and in particular, on the front surface (light-emitting surface) of the light guide plate. They may be provided on other sides as well if necessary, but it is more preferable that they be provided only on the front surface (light-emitting surface) of the light guide plate.

[0079] Here, the lenticular-shaped convex portion refers to an arc-shaped convex portion, which is a projection with an arc-shaped edge on the cross-section. Additionally, the prism-shaped portion refers to a convex portion with a triangular peak-shaped edge on the cross-section. Furthermore, the convex portion can be formed as multiple strands arranged in a parallel relationship with each other. Additionally, the convex portion can be formed integrally with the light guide plate.

[0080] 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, when molding a styrene-based resin composition, it is easy to manufacture a light guide plate with excellent moldability, such as extrusion stability, and excellent strength.

[0081] Optical properties

[0082] The average transmittance of the light guide plate at a wavelength of 380 to 780 nm at an optical path length of 115 mm is preferably 85% or more, and more preferably 86% or more. In addition, the average transmittance of the light guide plate at a wavelength of 380 to 780 nm at an optical path length of 115 mm after a long-term durability test (stored in an oven at 80°C for 1000 hours) is preferably 85% or more.

[0083] The YI value (YI1) at an optical path length of 115 mm of the light guide plate is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less. Specifically, the YI value (YI1) is, for example, 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, and may be within a range between any two of the values ​​exemplified herein. In addition, the YI value (YI2) at an optical path length of 115 mm of the light guide plate after a long-term durability test (stored in an oven at 80°C for 1000 hours) is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.5 or less. The corresponding YI value (YI2) is, specifically, for example, 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, and may be within a range between any two of the values ​​exemplified here. In addition, △YI(YI2-YI1) is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less.

[0084] Method for manufacturing a light guide plate

[0085] A light guide plate according to one embodiment of the present invention is obtained by molding the styrene-based resin composition. Known methods such as sheet extrusion molding, injection molding, or compression molding may be used as molding methods, but continuous sheet extrusion molding equipped with a surface shape transfer mold is preferred in terms of productivity and ease of increasing the size of the molded product. Examples of such sheet extrusion molding include an extrusion process in which a resin is supplied to a feed block in a heated molten state and an extrusion sheet is continuously formed in a die, a compression process in which the resin sheet is fed into a compression roll and a cooling roll, and a conveying process in which the resin sheet is conveyed while being pressed against the cooling roll after the compression process, and a continuous sheet extrusion molding method equipped with a transfer mold on the surface of the cooling roll. By changing the shape of the transfer mold, any uneven shape can be transferred to the surface of the sheet.

[0086] In addition, the light guide plate may have an uneven surface on the front (light-emitting surface) and may undergo a reflective process on the back to diffusely reflect light. Examples of reflective processes include silk screen printing or inkjet printing, as well as methods to impart dot-shaped unevenness through laser irradiation; for dot pattern printing, ink containing fine particles that diffuse light may be used.

[0087] 3. Edge-light type surface light source unit

[0088] An edge-light type surface light source unit according to one embodiment of the present invention is an edge-light type surface light source unit having a light guide plate and a light source that supplies light to the end surface of the light guide plate. The edge-light type surface light source unit is suitably used as a surface light source device, such as for lighting or for a liquid crystal display device.

[0089] Examples

[0090] The present invention will be explained in more detail below with reference to examples. Furthermore, these are merely illustrative and do not limit the scope of the invention.

[0091] 1. Preparation of styrene-based resin composition

[0092] [Example 1]

[0093] A polymerization process was configured by connecting a first reactor, which is a completely mixed stirring tank, and a second reactor, which is a plug flow type reactor equipped with a static mixer, in series, and a styrene-based resin was manufactured. The capacity of each reactor was set to 30 liters for the first reactor and 12 liters for the second reactor. With a raw material composition of 65 mass% of styrene (TBC concentration 11 μg / g), 25 mass% of methyl methacrylate (TBX concentration 7 μg / g), and 10 mass% of ethylbenzene, the addition concentrations were adjusted at the inlet of the first reactor to 100 ppm of t-butylperoxyisopropyl monocarbonate (manufactured by Nichiyu Co., Ltd.: Perbutyl I) as a polymerization initiator and 150 ppm of n-dodecyl mercaptan (manufactured by Arkema Co., Ltd.) as a chain transfer agent (both concentrations based on mass relative to the raw material styrene), and the raw material solution was continuously supplied at a rate of 8.0 kg / h to the first reactor set at 135°C. Furthermore, the obtained polymerization solution was continuously supplied to the second reactor to complete the polymerization. At this time, the monomer polymerization rate was 70%. For reference, in the second reactor, a temperature gradient was set along the flow direction to adjust the temperature to 135°C in the middle section and 145°C at the outlet section.

[0094] Next, a solution containing the polymer continuously extracted from the second reactor was introduced into a vacuum degassing tank equipped with a preheater configured in two stages in series, the temperature of the preheater was adjusted so that the resin temperature became 240°C, and unreacted styrene and ethylbenzene were separated at a pressure of 0.8 kPa. The obtained molten polymer was continuously fed into an extruder, and through an additive inlet, 0.2 parts by mass of a phosphorus-based antioxidant (168) and 0.1 parts by mass of a phosphorus-phenol-based antioxidant (GP) were added to 100 parts by mass of the polymer, and an anthraquinone-based coloring agent (SV13) was added to the polymer at a concentration of 47 ppb. After mixing at a set temperature of 220°C, the mixture was extruded in the form of a strand through a porous die, and the strand was cooled and cut by a cold cut method to form pellets.

[0095] [Examples 2 to 18 and Comparative Examples 1 to 8]

[0096] A styrene-based resin composition and a light guide plate were prepared in the same manner as in Example 1, except that the composition of the raw material solution and the polymerization conditions were changed as shown in Table 1, and the formulations of the phosphorus-based antioxidant (B-1), phosphorus-phenol-based antioxidant (B-2), phenol-based antioxidant (B-3), anthraquinone-based colorant (C), and hindered amine-based light stabilizer (D) were changed as shown in Tables 2 to 4. The content of the phosphorus-based antioxidant (B-1), phosphorus-phenol-based antioxidant (B-2), phenol-based antioxidant (B-3), and hindered amine-based light stabilizer (D) is the content per 100 parts by mass of the polymer (styrene-based resin), and the content of the anthraquinone-based colorant (C) is the ratio to the polymer (styrene-based resin). Various measurement and evaluation results are shown in Tables 2 to 4.

[0097]

[0098]

[0099]

[0100]

[0101] For reference, the phosphorus-based antioxidant (B-1), phosphorus-phenol-based antioxidant (B-2), anthraquinone-based coloring agent (C), and hindered amine-based light stabilizer (D) in Tables 2 and 3 are as follows.

[0102] (Phosphorus-based antioxidant (B-1))

[0103] 168: Tris(2,4-di-tert-butylphenyl)phosphite (Irgafos 168 manufactured by BASF)

[0104] 6260: Bis-(2,4-di-tert-butylphenyl)pentaerythritol diphosphite (Songnox 6260 manufactured by SONGWON)

[0105] HP-10: 2,2'-Methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus (ADEKA ADKSTAB HP-10)

[0106] (Phosphorus-phenolic antioxidant (B-2))

[0107] GP: 6-〔3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy〕-2,4,8,10-tetra-tert-butyldibenzo〔d, f〕〔1,3,2〕dioxaphospherine(Sumiriser GP manufactured by Sumitomo Chemical Corporation)

[0108] (Phenolic antioxidant (B-3))

[0109] 245: Ethylenebis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate](Irganox 245 manufactured by BASF Japan Co., Ltd.)

[0110] 1010: Pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate](Irganox 1010 manufactured by BASF Japan Co., Ltd.)

[0111] 1076: Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Irganox 1076 manufactured by BASF)

[0112] (Anthraquinone-based coloring agent(C))

[0113] SV13 (Solvent Violet 13): 1-hydroxy-4-(4-methylphenylamino)anthracene-9,10-dione (Macrolex Violet B Gran manufactured by LANXESS)

[0114] SV33(Solvent Violet33): (Diaresin Blue J manufactured by Mitsubishi Chemical Corporation)

[0115] SB45(Solvent Blue45): 3, 3'-[(9, 10-dihydro-9, 10-dioxo-1, 4-anthracene)diimino]bis[N-cyclohexyl-2,4,6-trimethylbenzenesulfonamide] (Transparent Blue S-RLS manufactured by EPSILON)

[0116] (Hindered amine-based light stabilizer (D))

[0117] 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 (BASF TINUVIN292)

[0118] 2. Evaluation

[0119] The measurement and evaluation of the resin characteristics of Table 1 and the characteristics of the styrene-based resin compositions described in Tables 2 to 4 were performed according to the following method.

[0120] <Molten Mass Flow Rate (MFR)>

[0121] The molten mass flow rate was measured according to JIS K 7210 under conditions of a temperature of 200℃ and a load of 49N.

[0122] Vicat softening temperature

[0123] The Vicat softening temperature was measured according to JIS K 7206 at a heating rate of 50℃ / hr and a test load of 50N.

[0124] Content of TBC and TBX in Styrene-based Resin (Copolymer)

[0125] 0.2 g of styrene-based resin was dissolved in a small amount of THF, 200 μL of BSTFA (M, O-bis(trimethylsilyl)trifluoroacetamide) was added, and trimethylsilyl derivatization treatment was performed. After dissolving the mixture in 10 mL of THF, the supernatant separated by centrifugation was measured by gas chromatography-mass spectrometry (GC / MS) under the following conditions. For reference, a calibration curve prepared in advance was used to determine the concentration. For reference, TBC and TBX contained in the styrene-based resin composition can be calculated from the mixing ratio of the resins used. In addition, the same measurement is possible for the styrene-based resin composition.

[0126] GC Device: Agilent 7890A

[0127] Column: Manufactured by Agilent DB-5ms (0.25mm id x 30m) Liquid film thickness 0.25μm

[0128] Column temperature: 50℃ (1 min) → (heating increase at 20℃ / min) → 320℃ (6.5 min) Total 20 min

[0129] Injection port: 300℃, 1.5mL / min, (Split ratio 1:5)

[0130] Injection volume: 1μL

[0131] MS Device: Agilent 5975C

[0132] Interface temperature: 320℃

[0133] MS Detection Conditions: SIM Measurement TBC (M / z 295 for quantification, M / z 310 for verification)

[0134] <Content of phosphorus-based antioxidant (B-1) and phosphorus-phenol-based antioxidant (B-2) in styrene-based resin composition>

[0135] 1.0 g of a styrene-based resin composition was completely dissolved in 20 mL of THF, 5 mL of methanol was added dropwise, and the mixture was stirred for 20 minutes. Centrifugation was performed at 4000 rpm for 10 minutes, and the separated supernatant was measured by gas chromatography (GC) under the following conditions. For reference, a calibration curve prepared in advance was used to determine the concentration.

[0136] GC Device: Shimadzu Corporation GC2010 Plus

[0137] Column : DB-1(30m×0.25mm id, df=0.10μm)

[0138] Column temperature: 240℃ → (heating increase of 10℃ / min) → 320℃(15min)

[0139] Injection port: 320℃, 1.02 mL / min (split ratio 1:5)

[0140] Injection volume: 1μL

[0141] Weight Average Molecular Weight (Mw)

[0142] The weight-average molecular weight (Mw), Z-average molecular weight (Mz), and number-average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.

[0143] GPC Model: Shodex GPC-101 manufactured by Showa Denko Co., Ltd.

[0144] Column: PLgel 10μm MIXED-B manufactured by Polymer Laboratories

[0145] Mobile phase: Tetrahydrofuran

[0146] Sample concentration: 0.2 mass%

[0147] Temperature: Oven 40℃, Inlet 35℃, Detector 35℃

[0148] Detector: Parallax Refractometer

[0149] The molecular weight was calculated as the polystyrene equivalent molecular weight by determining the molecular weight at each elution time from the monodisperse polystyrene elution curve.

[0150] <Average transmittance and YI value of styrene-based resin composition>

[0151] Average transmittance and YI values ​​were measured in the following order.

[0152] Using styrene-based resin composition pellets, injection molding was performed at a cylinder temperature of 190°C and a mold temperature of 40°C to form a plate-shaped molded product with a thickness of 115 mm x 80 mm x 3 mm.

[0153] Next, for the obtained molded product, the spectral transmittance at wavelengths from 350 nm to 800 nm at an optical path length of 115 mm was measured using a UV-visible spectrophotometer V-670 manufactured by Nihon Bunko Co., Ltd. under incident light conditions of size 20 x 1.6 mm and a diffusion angle of 0°, and the YI value under a viewing angle of 2° from a C light source was calculated in accordance with JIS K7105. The average transmittance (total light transmittance) was calculated as the average of the spectral transmittance at wavelengths from 380 to 780 nm.

[0154] In addition, to evaluate long-term thermal stability, the obtained molded product was stored in an 80°C oven for 1,000 hours. The one before storage was designated as the initial test light guide plate, and the one after storage was designated as the test light guide plate after the long-term durability test. Test specimens were cut out in the same manner from the test light guide plate after the long-term durability test, and the YI value and average transmittance were calculated.

[0155] 3. Manufacturing and Evaluation of Light Guide Plates

[0156] Manufacture of light guide plates

[0157] A styrene-based resin composition was fed into a single-ended vented extruder with a screw diameter of 90 mm and L / D=32, melt-kneaded at 200 to 235°C, discharged through a T-die with a lip width of 800 mm and a lip opening of 3.0 mm at a T-die temperature of 245 to 250°C and a screw rotation speed of 75 rpm, cooled and solidified using a vertical 3-line cooling roll, and then the end surface was trimmed to obtain a test light guide plate with a width of 600 mm and a thickness of 2.0 mm.

[0158] Light Guide Plate Evaluation

[0159] In Tables 2 to 4, the extrusion stability (surging), color temperature change, and dimensional stability (moisture absorption deformation) of the test light guide plates were evaluated as follows.

[0160] Extrusion Stability (Surging)

[0161] In the manufacture of test light guide plates, the screw rotation speed of the extruder was gradually increased to determine the screw rotation speed at which surging (discharge defects such as plate thickness variation) occurred, and extrusion stability was evaluated based on the following criteria.

[0162] ◎: Stable manufacturing possible at screw rotation speeds exceeding 150 rpm.

[0163] ○: Stable manufacturing is possible within a screw rotation speed range of 100 to 150 rpm.

[0164] △: Stable manufacturing possible at screw rotation speeds of less than 100 rpm.

[0165] Color Temperature Change (Long-term durability for LED light sources)

[0166] A test light guide plate was assembled into a 600mm x 600mm edge-light type lighting unit, and after turning on a 5700K white LED, the color temperature at the center of the surface was measured at a measurement distance of 1m using a Konica Minolta CL-200A colorimeter (initial color temperature). Next, the lighting was turned on continuously for 5,000 hours, and the color temperature was measured in the same way (color temperature after 5,000 hours), and the change in color temperature was evaluated according to the following criteria.

[0167] Color temperature change (%) = [Initial color temperature (K) - Color temperature after 5,000 hr (K)] / Initial color temperature (K) × 100

[0168] ○: Color temperature change less than 1%

[0169] △: Color temperature change ranges from 1 to 5%

[0170] Х: Color temperature change exceeds 5%

[0171] Dimensional stability (moisture absorption deformation)

[0172] A 200mm x 300mm test specimen was cut from a test light guide plate, the specimen was stored for 500 hours under conditions of 60℃ temperature and 90% relative humidity, the change in dimensions of the longer side before and after storage was measured, and the strain was calculated by the following formula.

[0173] Strain = ((Length of the longer side after storage) - (Length of the longer side before storage)) χ (Length of the longer side before storage) × 100 (%)

[0174] The dimensional stability (moisture absorption change) of the light guide plate was evaluated by assigning ○ for strain less than 0.10%, △ for strain between 0.10% and 0.15%, and Х for strain greater than 0.15%.

[0175] In Examples 1 to 18, transparency, color, extrusion stability, long-term color stability, and dimensional stability were good, and in Examples 1 to 16, extrusion stability and dimensional stability were particularly excellent. In addition, Example 3, which had a hindered amine-based light stabilizer (D) added, had a color temperature change of 0.2% less than Example 2, which did not have the stabilizer added, and thus had better long-term durability for the LED light source.

Claims

Claim 1 A styrene resin composition comprising a styrene resin (A) which is a copolymer comprising a styrene-based monomer unit and a (meth)acrylic acid ester-based monomer unit, an antioxidant (B), and an anthraquinone-based coloring agent (C), wherein the antioxidant (B) comprises either one or both of a phosphorus-based antioxidant (B-1) and a phosphorus-phenol-based antioxidant (B-2), and the composition contains a total of 0.001 to 0.5 parts by mass of the phosphorus-based antioxidant (B-1) and the phosphorus-phenol-based antioxidant (B-2) per 100 parts by mass of the styrene resin (A), and contains 0.1 to 150 ppb of the anthraquinone-based coloring agent (C) relative to the styrene resin (A). Claim 2 A styrene resin composition according to claim 1, wherein the styrene resin (A) contains 20 to 95 mass% of the styrene monomer unit and 5 to 80 mass% of the (meth)acrylic acid ester monomer unit in 100 mass% of the styrene resin (A). Claim 3 In claim 1, the phosphorus-based antioxidant (B-1) is selected from 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-di-phosphaspiro[5,5]undecane, tetrakis(2,4-di-tert-butylphenyl)[1,1-biphenyl]-4,4'-diylbisphosphonite, and bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite ester. A styrene-based resin composition comprising at least one type. Claim 4 A styrene-based resin composition according to claim 1, wherein the phosphorus-phenol-based antioxidant (B-2) is 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d, f][1,3,2]dioxaphosperpine. Claim 5 A styrene-based resin composition according to claim 1, wherein the average transmittance of a wavelength of 380 to 780 nm at an optical path length of 115 mm, measured using a test specimen manufactured by molding the styrene-based resin composition to a thickness of 115 mm x 80 mm x 3 mm, is 85% or higher. Claim 6 A styrene-based resin composition according to claim 1, wherein the YI value at an optical path length of 115 mm, measured using a test specimen manufactured by molding the styrene-based resin composition to a thickness of 115 mm x 80 mm x 3 mm, is 4.0 or less. Claim 7 An edge-light type light guide plate that is a molded body of a styrene-based resin composition as described in any one of claims 1 to 6. Claim 8 An edge-light type surface light source unit having an edge-light type light guide plate described in claim 7 and a light source that supplies light to the end surface of the light guide plate. Claim 9 An edge-light type surface light source unit for lighting as described in Paragraph 7.

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