TWI738639B - Styrene resin composition for optics - Google Patents

Abstract

The object of the present invention is to provide a styrene-(meth)acrylate copolymer with excellent transparency and hue, low water absorption, and excellent warpage resistance or dimensional stability caused by moisture absorption.

The present invention is a styrenic resin composition for optics, which comprises 20 to 80% by mass of styrene monomer units and 80 to 20% by mass of (meth)acrylate monomer units of styrene-(methyl) )Acrylate copolymer (A), hindered phenol antioxidant (B), and phosphorus antioxidant (C), relative to the total amount of (A) to (C), the content of (B) is 0.01~0.3 The content of mass% and (C) is 0.001 to 0.3 mass%.

Description

Styrene resin composition for optics

The present invention relates to an optical styrene resin composition with excellent hue and transparency, its molded article, and light guide plate.

As the backlight of the liquid crystal display device, there are a direct type in which the light source is arranged on the front of the display device and an edge light type in which the light source is arranged on the side. The light guide plate plays a role of guiding the light of the light source used for the side-light type backlight and arranged on the side to the front. Edge-lit backlights have been used in applications requiring thinness in TVs, personal computer displays, mobile phones, car navigation, etc., to expand their use. Previously, the proportion of edge-lit backlights used in TVs with large screen sizes (for example, 32 inches or more) where direct type occupies the majority has also increased.

Acrylic resin represented by PMMA (polymethyl methacrylate) is used in the light guide plate, but because of its high water absorption, the molded product may warp or change in size. In addition, since the thermal decomposition during molding is high, there is a problem that the molded body tends to have poor appearance during high-temperature molding.

Therefore, it has been proposed to use styrene-methyl (meth)acrylate copolymers with improved properties. As a technique for improving the water absorption of styrene-methyl (meth)acrylate copolymer, Patent Document 1 is proposed.

On the other hand, the styrene-methyl (meth)acrylate copolymer has a poorer color (yellow) than the PMMA molded body, and when used as a backlight, uneven color may occur on the surface of the liquid crystal display device. Therefore, Patent Document 2 is proposed as a technique for improving the hue of a styrene-methyl (meth)acrylate copolymer.

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2003-075648

[Patent Document 2] Japanese Patent Laid-Open No. 2013-082800

The present invention provides a novel optical styrene resin composition with good transparency and hue, and low water absorption, and a molded product thereof. It can be preferably used in molded products, especially light guide plates for liquid crystal display devices and the like.

That is, the present invention is as follows.

(1) A styrenic resin composition for optics, characterized in that it contains 20 to 80% by mass of styrene monomer units and 80 to 20% by mass of (meth)acrylate monomer units. (Meth)acrylate-based copolymer (A), hindered phenol-based antioxidant (B), and phosphorus-based antioxidant (C), relative to the total amount of (A) ~ (C), the content of (B) is 0.01~0.3% by mass, the content of (C) is 0.001~0.3% by mass, and the styrene-(meth)acrylate copolymer (A) is the content of the residual polymerization inhibitor less than 10ppm.

(2) The optical styrenic resin composition according to (1), wherein the weight average molecular weight of the styrene (meth)acrylate copolymer is 50,000 to 200,000.

(3) The styrenic resin composition for optics as in (1) or (2), wherein the styrene-(meth)acrylate copolymer (A) is made to contain 0.1-20 ppm of 4-tert-butyl It is obtained by copolymerizing styrene-based monomer of catechol and (meth)acrylate-based monomer containing 0.1-20 ppm of 6-tert-butyl-2,4-xylenol.

(4) A molded article comprising the styrene-based resin composition according to any one of (1) to (3).

(5) A light guide plate comprising the molded product as in (4).

The optical styrenic resin composition and molded article of the present invention have excellent transparency and hue, low water absorption, and excellent warpage resistance or dimensional stability caused by moisture absorption, so they can be preferably used for guiding Optical applications such as light boards.

Hereinafter, embodiments of the present invention will be described in detail. In addition, in the specification of this case, for example, the description of "A~B" means more than A and less than B.

The styrene-based resin composition of the present invention is a composition comprising a styrene-(meth)acrylate-based copolymer (A), a hindered phenol-based antioxidant (B), and a phosphorus-based antioxidant (C).

Styrene-(meth)acrylate-based copolymer (A) is a copolymer having styrene-based monomer units and (meth)acrylate-based monomer units, such as styrene-methyl (meth)acrylate copolymer Things.

Styrene-based single-system aromatic vinyl monomer. It is styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, ethylstyrene, p-tert-butylstyrene, etc. alone or a mixture of two or more, preferably styrene.

(Meth) acrylate series single-system methacrylate of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate , Methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl methacrylate, 2-ethylhexyl acrylate, decyl acrylate, etc. alone or a mixture of two or more, preferably (methyl )Methyl acrylate.

The content of the styrene monomer unit in the styrene-(meth)acrylate copolymer is 20 to 80% by mass, and the content of the (meth)acrylate monomer unit is 80 to 20% by mass. More preferably, the content of the styrene-based monomer unit is 30-60% by mass, and the content of the (meth)acrylate monomer unit is 70-40% by mass. More preferably, it is one of the styrene-based monomer units The content is 45 to 55% by mass, and the content of the (meth)acrylate monomer unit is 55 to 45% by mass. If the content of the styrene-based monomer unit is small, due to moisture absorption, warpage and dimensional deformation will increase. If the content of the styrene-based monomer unit is too large, the hue will be deteriorated or the surface hardness will be reduced, and it will be easy to be injured.

In the styrene-(meth)acrylate-based copolymer, those having a small amount of other unit structures can be used. The other unit structure is preferably 5% by mass or less. As another unit structure, there is a unit structure derived from a vinyl monomer copolymerizable with a styrene-based monomer and a (meth)acrylate-based monomer. Examples of the copolymerizable monomers include acrylonitrile, methacrylic acid, acrylic acid, maleic anhydride, and the like.

The content of the styrene-based monomer unit and the (meth)acrylate-based monomer unit of the styrene-(meth)acrylate-based copolymer is measured by thermal decomposition gas chromatography under the following conditions.

Thermal decomposition furnace: PYR-2A (manufactured by Shimadzu Corporation)

Thermal decomposition furnace temperature setting: 525℃

Gas chromatograph: GC-14A (manufactured by Shimadzu Corporation)

Column: 3mm diameter × 3m made of glass

Filler: FFAP Chromsorb WAW 10%

Column temperature: 120℃

Carrier gas: Nitrogen

As a method for producing the styrene-(meth)acrylate copolymer, a well-known method can be used. It can be manufactured by, for example, block polymerization, solution polymerization, suspension polymerization, emulsion polymerization, and the like. As the operating method of the reaction device, any of continuous, batch (batch), and semi-batch can be applied. In terms of quality or productivity, such as transparency, bulk polymerization or solution polymerization is preferred, and continuous type is preferred. As the solvent for bulk polymerization or solution polymerization, there are, for example, alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone or methyl ethyl ketone, and aliphatic hydrocarbons such as hexane or cyclohexane. .

As the polymerization method of the styrene-(meth)acrylate copolymer, a well-known method can be used. In terms of simplicity of the process and excellent productivity, the radical polymerization method is preferred.

In the bulk polymerization or solution polymerization of the styrene-(meth)acrylate copolymer, a polymerization initiator and a chain transfer agent can be used, and the polymerization temperature is preferably in the range of 110 to 170°C. In the case of continuous block polymerization or solution polymerization, from the viewpoint of productivity, it is preferable to use the conversion rate of styrene monomer and (meth)acrylate monomer at the exit of the polymerization step Polymerize in a way that reaches more than 60%.

As the polymerization initiator, for example, benzyl peroxide, tert-butylperoxybenzoate, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis( Tertiary butyl peroxide)-3,3,5-trimethylcyclohexane, 1,1-bis(tertiary butyl peroxide)-3,3,5-trimethylcyclohexane, 2, 2-bis(4,4-di-tert Butyl peroxyacetate, tertiary butyl peroxy-2-ethylhexanoate, polyether tetra (tertiary butyl peroxycarbonate), ethyl-3,3-bis (tertiary peroxide) (Butyl) butyrate, tert-butyl peroxide-2-ethylhexanoate and other organic peroxides.

The addition amount of the polymerization initiator is preferably 0.001 to 0.2% by mass relative to the total 100% by mass of the monomers. More preferably, it is 0.001 to 0.05% by mass. If the addition amount of the polymerization initiator is too large, the hue will deteriorate.

Examples of the chain transfer agent include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, and terpinolene.

The addition amount of the chain transfer agent is preferably 0.001 to 0.5% by mass relative to the total 100% by mass of the monomers, more preferably 0.005 to 0.2% by mass. If the addition amount of the chain transfer agent is 0.001 to 0.5% by mass, the thermal stability is good.

From the solution after the polymerization of the styrene-(meth)acrylate copolymer is completed, it is a devolatization method to remove unreacted monomers or solvents used in solution polymerization and other volatile components. Enough to use well-known methods. It is possible to use, for example, a vacuum devolatization tank with a preheater or a devolatization extruder with a vent. The temperature of the styrene-(meth)acrylate copolymer in the devolatization step is preferably 200°C to 300°C, more preferably 220°C to 260°C. If the temperature of the styrene-(meth)acrylate copolymer in the devolatization step is too high, the hue will deteriorate. The styrene-(meth)acrylate copolymer in the molten state after being devolatized is transferred to the pelletizing step, which can be extruded through a porous die linearly, cold cutting, air thermal cutting, or underwater thermal cutting The method is processed into a particle shape.

The unreacted monomers removed in the devolatization step and the solvent used for solution polymerization are preferably recovered and purified and used as a mixture of fresh raw materials after refining and removing impurities such as polymerization inhibitors. Since the recycled raw materials do not contain polymerization inhibitors, they can be mixed with fresh raw materials to reduce the content of polymerization inhibitors in the raw materials supplied to the polymerization step. The content of the polymerization inhibitor in the raw material supplied to the polymerization step is preferably less than 12 ppm, more preferably less than 9 ppm, still more preferably less than 6 ppm, and most preferably less than 4 ppm. If the content of the polymerization inhibitor in the raw material supplied to the polymerization step is less than 12 ppm, the transmittance and transparency are good. Among them, the fresh raw material is the raw material newly supplied to the production step of the styrene-(meth)acrylate-based copolymer, and it is so called in order to distinguish it from the recycled raw material.

The recovery and purification method of the unreacted monomer removed in the devolatization step and the solvent used in the solution polymerization can be a well-known method. For example, the following method can be cited: the unreacted monomer and solvent gas removed in the devolatization step are condensed and liquefied by a condenser, and high boiling point components are separated and removed by purification by a flash distillation column. In addition, the following method can be cited: from the unreacted monomer and solvent gas removed in the devolatization step, first use a condenser or spray tower to condense and separate only the high boiling point components, and use the condenser to make the remaining The total amount of gas is condensed. As a polymerization inhibitor, for example, 4-tert-butylcatechol has a boiling point of 285°C, and 6-tert-butyl-2,4-xylenol has a boiling point of 249°C. It can be used as a high-boiling component from monomers and Separation and removal from the solvent (the boiling point of styrene is 145℃, (meth)acrylic acid The boiling point of methyl ester is 101°C, and the boiling point of ethylbenzene is 136°C).

The weight average molecular weight (Mw) of the styrene (meth)acrylate copolymer is preferably 50,000 to 200,000. It is more preferably 70,000 to 180,000, further preferably 75,000 to 160,000, and most preferably 80,000 to 150,000. If the weight average molecular weight (Mw) is less than 50,000, the strength of the light guide plate may decrease. If the weight average molecular weight (Mw) exceeds 200,000, the fluidity will decrease, and the moldability will deteriorate. The weight average molecular weight (Mw) can be controlled by the reaction temperature of the polymerization step, the residence time, the type and amount of polymerization initiator, the type and amount of chain transfer agent, and the type and amount of solvent used during polymerization. .

The weight average molecular weight (Mw) is measured using gel permeation chromatography (GPC) under the following conditions.

GPC model: Shodex GPC-101 manufactured by Showa Denko Co., Ltd.

Column: PLgel 10μm MIXED-B manufactured by Polymer Laboratories Ltd

Mobile phase: Tetrahydrofuran

Sample concentration: 0.2% by mass

Temperature: oven 40℃, injection port 35℃, detector 35℃

Detector: Differential refractometer

The molecular weight of the present invention is calculated by calculating the molecular weight in each elution time from the elution curve of monodisperse polystyrene, and it is calculated as the molecular weight in terms of polystyrene.

The total amount of the residual monomer in the styrene-(meth)acrylate copolymer and the polymerization solvent is preferably 0.5% by mass or less, more preferably 0.2% by mass or less. If the total amount of the residual monomer and the polymerization solvent exceeds 0.5% by mass, the heat resistance is insufficient.

Residual monomer and polymerization solvent The amount of the remaining monomer and polymerization solvent in the styrene-(meth)acrylate copolymer includes, for example, styrene, methyl (meth)acrylate, and ethylbenzene. The amount of residual monomer and polymerization solvent can be adjusted under the composition of the devolatization step or the conditions of the devolatization step.

The amount of residual monomer and polymerization solvent is accurately weighed 0.2g of styrene-(meth)propylene The acid ester copolymer was dissolved as an internal standard substance in 10 ml of tetrahydrofuran containing p-diethylbenzene, and measured under the following conditions using a capillary gas chromatograph.

Capillary gas chromatograph: GC-4000 (manufactured by GL Science Co., Ltd.)

Column: InertCap WAX manufactured by GL Science Co., Ltd., inner diameter 0.25mm, length 30m, film thickness 50μm

Injection temperature: 180℃

Column temperature: 60℃~170℃

Detector temperature: 210℃

Split ratio: 5/1

The total amount of 2-mer or 3-mer (hereinafter referred to as oligomer) of styrene-based monomers and (meth)acrylate-based monomers in the styrene-(meth)acrylate-based copolymer, preferably It is 2% by mass or less, more preferably 1% by mass or less. If the total amount of oligomers exceeds 1% by mass, the heat resistance as a light guide plate is insufficient.

The oligomer is measured by dissolving 200 mg of styrene-(meth)acrylate copolymer in 2 mL of 1,2-dichloromethane, adding 2 mL of methanol to precipitate the copolymer and letting it stand. Measured by gas chromatograph under the following conditions.

Gas chromatograph: HP-5890 (manufactured by Hewlett-Packard Company)

Column: DB-1(ht) 0.25mm×30m, film thickness 0.1μm

Injection temperature: 250℃

Column temperature: 100-300℃

Detector temperature: 300℃

Split ratio: 50/1

Internal standard substance: n-eicosane

Carrier gas: Nitrogen

The Vicat softening point of the styrene-(meth)acrylate copolymer is preferably 95°C or higher, more preferably 98°C or higher. If the Vicat softening point does not reach 95°C, the heat resistance is insufficient, and it is successful. Possibility of the shape product to deform according to the use environment. (The Vicat softening temperature is based on JIS K 7206, the heating rate is 50°C/hr, and the test is carried out under a test load of 50N)

The content of the hindered phenol antioxidant (B) in the styrene resin composition is 0.01 to 0.3% by mass relative to the total amount of (A) to (C). It is preferably 0.02 to 0.2% by mass, more preferably 0.03 to 0.15% by mass, and still more preferably 0.04 to 0.1% by mass. If the content of the hindered phenol antioxidant (B) is too small, there will be no hue improving effect, and too much will result in poor hue.

The hindered phenol antioxidant (B) is an antioxidant having a phenolic hydroxyl group in the basic skeleton. As hindered phenol-based antioxidants, for example, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, ethylene bis(oxyethylene) bis[3 -(5-tert-butyl-4-hydroxy-m-tolyl)propionate], 3,9-bis[2-〔3-(3-tert-butyl-4-hydroxy-5-methylbenzene Yl)propionyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane, pentaerythritol tetra[3-(3,5- Di-tert-butyl-4-hydroxyphenyl) propionate), 4,6-bis(octylthiomethyl)-o-cresol, 4,6-bis((dodecylthio)methyl Base]-o-cresol, 2,4-dimethyl-6-(1-methylpentadecyl)phenol, tetrakis(methylene-3-(3,5-di-tert-butyl-4) -Hydroxyphenyl)propionate) methane, 4,4'-thiobis(6-tertiarybutyl-3-methylphenol), 1,1,3-tris(2-methyl-4-hydroxyl -5-tert-butylphenyl)butane, 4,4'-butylene bis(3-methyl-6-tert-butylphenol), bis-[3,3-bis-(4'-hydroxy -3'-tert-butylphenyl)-butanoic acid)-diol ester, 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)- 4-methylphenyl acrylate, 2-[1-(2-hydroxy-3,5-di-tertiary pentyl phenyl) ethyl]-4,6-di-tertiary pentyl phenyl acrylate Wait. Preferably octadecyl-3-(3,5-di-tertiary butyl-4-hydroxyphenyl) propionate, ethylene bis(oxyethylene) bis (3-(5-tertiary butyl) 4-hydroxy-m-tolyl)propionate], pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. More preferred is octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. The hindered phenol-based antioxidant can be used alone or in combination of two or more kinds.

The content of the phosphorus antioxidant (C) in the styrene resin composition is 0.001 to 0.3% by mass relative to the total amount of (A) to (C). Preferably it is 0.001~0.1% by mass, more preferably 0.001 to 0.05 mass%, more preferably 0.001 to 0.02 mass%. If the content of the phosphorus antioxidant (C) is too much, the hue may deteriorate. In addition, mold contamination may occur during injection molding, or roll contamination may occur during extrusion of plate-shaped molded products.

Phosphorus antioxidants (C) are phosphites of trivalent phosphorus compounds. Examples of phosphorus antioxidants include 6-[3-(3-tertiarybutyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-third Butylbenzo[d,f][1,3,2]dioxaphosphole, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-Tetraoxa-3,9-Diphosphaspiro[5.5]undecane, bis(2,4-dicumylphenyl) pentaerythritol diphosphite, 2, 2'-methylenebis(4,6-di-tert-butyl-1-phenoxy)(2-ethylhexyloxy)phosphorus, tris(2,4-di-tert-butylphenyl) ) Phosphite, bis(2,4-bis(1,1-dimethylethyl)-6-methylphenyl] ethyl phosphite, bis(2,4-di-tert-butylphenyl) ) Pentaerythritol diphosphite, cyclic neopentanetetrayl bis(octadecyl phosphite), bis(nonylphenyl) pentaerythritol diphosphite, 4,4'-biphenyl diphosphine Tetrakis(2,4-di-tert-butylphenyl) ester, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, tetrakis(2,4-di-th Tributyl-5-methylphenyl)-4,4'-biphenyl diphosphonite and the like. Preferably 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butylbenzo(d ,f]〔1,3,2]dioxaphosphorine, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8 ,10-Tetraoxa-3,9-diphosphaspiro[5.5]undecane, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, 2,2'-methylene Bis (4,6-di-tertiary butyl-1-phenoxy) (2-ethylhexyloxy) phosphorus, tris (2,4-di-tertiary butyl phenyl) phosphite, bis (2,4-Di-tert-butylphenyl) pentaerythritol diphosphite. More preferably 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butylbenzo(d ,f) [1,3,2] dioxaphosphorene, bis(2,4-dicumylphenyl) pentaerythritol diphosphite, tris(2,4-di-tertiary butyl) Phenyl) phosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, more preferably 6-[3-(3-tert-butyl-4-hydroxy- 5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butylbenzo[d,f][1,3,2]dioxaphosphepene, bis (2,4-Dicumylphenyl) pentaerythritol Phosphate, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite. Phosphorus antioxidants can be used alone or in combination of two or more kinds.

The sum of the content of hindered phenol antioxidant (B) and the content of phosphorus antioxidant (C) in the styrene resin composition {(B)+(C)}, relative to (A)~(C) The total amount is 0.011 to 0.6% by mass. It is preferably 0.021 to 0.25% by mass, more preferably 0.031 to 0.2% by mass, and still more preferably 0.041 to 0.12% by mass. If the sum {(B)+(C)} of the content of the hindered phenol-based antioxidant (B) and the content of the phosphorus-based antioxidant (C) is too small, there will be no hue improvement effect, and if too much, the hue will deteriorate.

The method for producing the styrene resin composition containing the styrene-(meth)acrylate copolymer (A), hindered phenol antioxidant (B), and phosphorus antioxidant (C) can be a well-known method. It is preferable to add a hindered phenol-based antioxidant (B) and a phosphorus-based antioxidant (C) in the manufacturing steps such as the polymerization step, devolatization step, and granulation step of (A). After the reacted monomer and solvent are removed, the styrene-(meth)acrylate copolymer is added. For example, when a vacuum devolatization tank is used, the styrene-(meth)acrylate-based copolymer that can be extracted from the devolatization tank is added with the hindered phenol-based antioxidant (B) and phosphorus-based antioxidant ( C) When using a static mixer mixing method or a devolatizing extruder with vent holes, the hindered phenol antioxidant (B) and phosphorus antioxidant (C) can be added and mixed within the vent area. In addition, it can be directly added when the styrene-(meth)acrylate copolymer (A) is molded, and it can also be added as a master batch.

The styrene-based resin composition may contain mineral oil within a range that does not impair transparency. In addition, internal lubricants such as stearic acid and ethylene bisstearyl amide, or sulfur-based antioxidants, lactone-based antioxidants, ultraviolet absorbers, hindered amine-based stabilizers, antistatic agents, and external lubricants may also be included. Agents and other additives. Furthermore, as the external lubricant, ethylene bisstearyl amide is preferred.

系、苯甲酸酯系、水 楊酸酯系、氰基丙烯酸酯系、丙二酸酯系、甲醛系等紫外線吸收劑。該等能夠單獨使用，亦能夠將2種以上組合使用，能夠將受阻胺等光穩定劑併用。 The ultraviolet absorber has the function of inhibiting the deterioration or coloring caused by ultraviolet rays, such as benzophenone series, benzotriazole series, triazole

UV absorbers such as benzoate, benzoate, salicylate, cyanoacrylate, malonate, and formaldehyde. These can be used alone or in combination of two or more, and light stabilizers such as hindered amines can be used in combination.

The polymerization inhibitor is added to the monomer in order to prevent unexpected polymerization during the storage of the monomer. Examples of the types of polymerization inhibitors include catechols such as 4-tert-butylcatechol, phenols such as 6-tert-butyl-2,4-xylenol and p-methoxyphenol, Hydroquinone, 2,2,6,6-tetramethylpiperidinyl-1-hydrocarbyloxy group, 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-hydrocarbyloxy group Wait.

The content of the polymerization inhibitor remaining in the styrene-(meth)acrylate copolymer is preferably less than 10 ppm, more preferably less than 5 ppm, and still more preferably less than 3 ppm. The polymerization inhibitor is derived from 4-tert-butylcatechol and 6 -Tertiary butyl-2,4-xylenol, etc. The content of 6-tert-butyl-2,4-xylenol remaining in the styrene-(meth)acrylate copolymer is preferably less than 4 ppm, more preferably less than 2 ppm. If the content of the polymerization inhibitor is too large, the polymerization inhibitor itself will be denatured during the polymerization reaction or during the molding process, and become a colored substance, thereby deteriorating transparency or hue. The content of the polymerization inhibitor remaining in the copolymer can be controlled according to the content of the polymerization inhibitor in the monomer used in the copolymerization. In addition, in the continuous bulk polymerization or solution polymerization method, the unreacted monomer can be recovered and purified by reuse, effectively reducing the content of the polymerization inhibitor remaining in the copolymer.

The concentration of 4-tert-butylcatechol and 6-tert-butyl-2,4-xylenol in the styrene-(meth)acrylate copolymer are first dissolved in tetrahydrofuran (adjust to After 50mg/ml), use BSTFA (N,O-bis(trimethylsilyl)trifluoroacetamide) to carry out trimethylsilyl derivatization treatment, and the supernatant liquid will be separated by centrifugal separation. GC/MS is measured under the following conditions. Use a pre-made standard curve to determine the concentration.

GC/MS measurement conditions:

GC device: Agilent 6890

Column: DB-1 (0.25mm i.d.×30m) liquid phase thickness 0.25mm

Column temperature: 40°C (hold for 5min)→(heat up at a rate of 20°C/min)→320°C (hold for 6min) for a total of 25min

Note inlet temperature: 320℃

Injection method: split method (split ratio 1:5)

Sample volume: 2μl

MS device: Agilent MSD5973

Ion source temperature: 230℃

Interface temperature: 320℃

Ionization method: electron ionization (EI) method

Measuring method: SCAN method (scanning range m/z 10~800)

As a polymerization inhibitor, the styrene-based monomer preferably contains 0.1-20 ppm of 4-tert-butylcatechol, more preferably 0.1-12 ppm, and still more preferably 0.1-7 ppm. If the concentration of 4-tert-butylcatechol in the styrene-based monomer exceeds 20 ppm, the 4-tert-butylcatechol itself will be denatured and become a coloring substance. Therefore, the styrene-(meth)acrylate-based The transparency and hue of the copolymer have deteriorated.

As a polymerization inhibitor, a (meth)acrylate-based monomer preferably contains 0.1-20 ppm of 6-tert-butyl-2,4-xylenol, more preferably 0.1-12 ppm, and still more preferably 0.1~ 7ppm. If the concentration of 6-tert-butyl-2,4-xylenol in the (meth)acrylate monomer exceeds 20 ppm, the body of 6-tert-butyl-2,4-xylenol will be denatured and become As a coloring substance, the transparency and hue of the styrene-(meth)acrylate copolymer are deteriorated.

The polymerization inhibitor of styrene-based monomers or (meth)acrylate-based monomers can be removed or reduced by the adsorption and removal of activated alumina.

The concentration of 4-tert-butylcatechol in styrene-based monomers and 6-tert-butyl-2,4-xylenol in (meth)acrylate-based monomers After mixing with tetrahydrofuran to reach 50mg/ml, use BSTFA (N,O-bis(trimethylsilyl)trifluoroacetamide) to carry out trimethylsilyl derivatization treatment, using gas chromatography mass spectrometry ( GC/MS), measured under the same conditions as the measurement of styrene-(meth)acrylate copolymer. Use a pre-made standard curve to determine the concentration.

The styrene-based resin composition can be formed into a molded product by well-known methods such as extrusion molding, injection molding, compression molding, and blow molding. For example, it can be used by extrusion molding to produce a plate-shaped molded product and process it into a light guide plate.

The styrene-based resin composition of the present invention has excellent thermal stability, so it is possible to recover and pulverize non-productive parts such as sheet end materials during extrusion molding or rolls or runners during injection molding, and mix them with raw materials Used in.

The light guide plate is a member that has the following function: the reflection pattern formed on one surface of the plate-shaped molded product guides the light incident from the end surface of the plate-shaped molded product to the side of the plate-shaped molded product and makes it emit light . The reflective pattern can be formed by a method such as a screen printing method, a laser processing method, and an inkjet method. In addition, it is possible to provide a pattern or the like on the opposite surface (light emitting surface) of the surface on which the reflection pattern is formed. The reflection pattern or the pattern of the plate-shaped molded product can be formed when the plate-shaped molded product is formed. For example, in injection molding, mold shape, extrusion molding, it can be formed by roll transfer or the like.

The term "optical use" refers to products supplied to structural members that contain light sources such as LED (Light Emitting Diode), fluorescent lamps, and incandescent lamps. Examples of products include televisions, desktop personal computers, notebook personal computers, mobile phones, car navigation, indoor lighting, etc., for example, the use of light guide plates.

The styrene-based resin composition for optics preferably has an average spectral transmittance at a wavelength of 350nm~800nm measured with an optical path length of 115mm of 87.0% or more, more preferably 87.5% or more, and even more preferably 88.0% or more, The best is above 88.5%. Also, preferably The YI value at 2° of the field of view in the C light source measured based on JIS K7105 is 3.5 or less, more preferably 3.0 or less, still more preferably 2.5 or less, and most preferably 2.0 or less.

[Example]

Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited to these examples.

<Production example of styrene-(meth)acrylate copolymer A-1>

The styrene-(meth)acrylate copolymer is produced by continuous solution polymerization by a radical polymerization method. A complete mixing tank type stirring tank was used as the first reactor, and a plug flow type reactor with static mixer was used as the second reactor, connected in series to form a polymerization step. The capacity of the first reactor is set to 30L, and the capacity of the second reactor is set to 12L. Prepare methyl (meth)acrylate (hereinafter referred to as fresh MMA) used in industry as a (meth)acrylate monomer, so 6-tert-butyl-2,4-xylenol (hereinafter referred to as The concentration of TBX) is 4.9 ppm. The styrene (hereinafter referred to as fresh Sty) used in industry is prepared as a styrene-based monomer, so the concentration of 4-tert-butylcatechol (hereinafter referred to as TBC) is 10.2 ppm. Prepare ethylbenzene (hereinafter referred to as fresh EB) used in industry as a polymerization solvent. In addition, the monomer and polymerization solvent gas separated in the vacuum devolatization tank described later are condensed in a condenser and purified in a flash distillation column to be used as a recovered raw material. The concentration of TBX and TBC in the recovered raw materials is below the lower limit of detection. Using fresh MMA, fresh Sty, and recycled raw materials, a raw material solution was prepared so as to become the raw material composition in Table 1, and the feed flow rate shown in Table 1 was continuously supplied to the polymerization step. The use ratio of the recycled raw materials is shown in Table 1, which is in balance with the amount of separation and purification in the devolatization tank. In addition, relative to the raw material solution, isopropyl monocarbonate tert-butyl peroxide was used as the polymerization initiator so that the concentration reached 150 ppm, and n-dodecyl mercaptan was used as the chain transfer agent so that the concentration reached 500 ppm. It is continuously added to the supply line of the raw material solution. Adjust the temperature of the first reactor to 135°C, set a temperature gradient along the flow direction in the second reactor, adjust the middle part to 130°C, and the outlet part to 145°C. Polymer concentration at the exit of the polymerization step It is 65%, and the conversion rate of methyl (meth)acrylate and styrene is 72%. The polymer solution continuously taken out from the reactor is supplied to a vacuum devolatization tank with a preheater to separate unreacted methyl (meth)acrylate, styrene, ethylbenzene, etc. Adjust the temperature of the preheater so that the polymer temperature in the devolatization tank reaches 240°C, and set the pressure in the devolatization tank to 1kPa. A gear pump was used to extract the polymer from the vacuum devolatization tank, extruded linearly, cooled with cooling water, and cut to obtain a pelletized styrene-(meth)acrylate copolymer A-1. Table 1 shows the composition of A-1 and the content of the polymerization inhibitor. In Table 1, Sty is the abbreviation for styrene, MMA is the abbreviation for methyl (meth)acrylate, and EB is the abbreviation for ethylbenzene. In addition, the weight average molecular weight of A-1 was 145,000, the total amount of residual monomers and polymerization solvent was 0.07% by mass, and the total amount of residual oligomers was 0.35% by mass.

<Production example of styrene-(meth)acrylate copolymer A-2>

Except that the TBX concentration of 11.2 ppm was used as the fresh MMA used in industry, the same procedure was performed as in A-1. Table 1 shows the composition of A-2 and the content of the polymerization inhibitor. In addition, the weight average molecular weight of A-2 is 145,000, the total amount of residual monomers and polymerization solvent is 0.07% by mass, and the total amount of residual oligomers is 0.36% by mass.

<Production example of styrene-(meth)acrylate copolymer A-3>

Except that the recovered raw material was not used, the same was performed as in A-1. The composition of A-3 and the content of the polymerization inhibitor are shown in Table 1. In addition, the weight average molecular weight of A-3 was 145,000, the total amount of residual monomers and polymerization solvent was 0.06% by mass, and the total amount of residual oligomers was 0.35% by mass.

<Production example of styrene-(meth)acrylate copolymer A-4>

Except that activated alumina was added to fresh MMA and fresh Sty, and the TBX and TBC concentrations were each less than 0.1 ppm, the same procedure was performed as in A-1. Table 1 shows the composition of A-4 and the content of the polymerization inhibitor. In addition, the weight average molecular weight of A-4 is 145,000, the total amount of residual monomers and polymerization solvent is 0.07% by mass, and the total amount of residual oligomers The amount is 0.36 mass%.

<Production example of styrene-(meth)acrylate copolymer A-5>

Except that the composition of the raw materials was changed to the contents of Table 1, and the concentration of n-dodecyl mercaptan was 1000 ppm, it was carried out in the same manner as in A-1. Table 1 shows the composition of A-5 and the content of polymerization inhibitor. In addition, the weight average molecular weight of A-5 is 120,000, the total amount of residual monomers and polymerization solvent is 0.06% by mass, and the total amount of residual oligomers is 0.34% by mass.

<Production example of styrene-(meth)acrylate copolymer A-6>

In addition to changing the composition of the raw materials to the content in Table 1, the feed flow rate is set to 5.7 kg/h, the concentration of t-butyl peroxide isopropyl monocarbonate is set to 100 ppm, and the concentration of n-dodecyl mercaptan is set It was set to 3000 ppm, and the temperature of the 1st reactor was set to 130 degreeC, and it carried out similarly to A-1. Table 1 shows the composition of A-6 and the content of the polymerization inhibitor. In addition, the weight average molecular weight of A-6 is 80,000, the total amount of residual monomers and polymerization solvent is 0.05% by mass, and the total amount of residual oligomers is 0.32% by mass.

<Production example of styrene-(meth)acrylate copolymer A-7>

In addition to changing the composition of the raw materials to the content in Table 1, the feed flow rate is set to 5.7 kg/h, the concentration of t-butyl peroxide isopropyl monocarbonate is set to 100 ppm, and the concentration of n-dodecyl mercaptan is set Set to 3000 ppm, set the temperature of the first reactor to 122°C, set the temperature of the middle part of the second reactor to 140°C, and set the temperature of the outlet part to 150°C, and proceed in the same way as A-1 . The composition of A-7 and the content of the polymerization inhibitor are shown in Table 1. In addition, the weight average molecular weight of A-7 is 80,000, the total amount of residual monomers and polymerization solvent is 0.06% by mass, and the total amount of residual oligomers is 0.34% by mass.

<Production example of styrene-(meth)acrylate copolymer A-8>

Except for changing the composition of the raw materials to the content in Table 1, stop adding n-dodecyl mercaptan, set the temperature of the first reactor to 140°C, set the temperature of the middle part of the second reactor to 140°C, and set the outlet The temperature of the part is other than 160 degreeC, and it implements similarly to A-1. The composition of A-8 and the content of the polymerization inhibitor are shown in Table 1. In addition, the weight average molecular weight of A-8 is 240,000, the total amount of residual monomers and polymerization solvent is 0.06% by mass, and the total amount of residual oligomers is 0.33% by mass.

<Production example of styrene-(meth)acrylate copolymer A-9>

Except that the industrially used TBX with a concentration of 13.6 ppm was used as fresh MMA, and the TBC with a concentration of 12.2 ppm as fresh Sty, and no recycled raw material was used, the same procedure was performed as in A-1. Table 1 shows the composition of A-9 and the content of the polymerization inhibitor. In addition, the weight average molecular weight of A-9 was 145,000, the total amount of residual monomers and polymerization solvent was 0.06% by mass, and the total amount of residual oligomers was 0.35% by mass.

<Production example of styrene-(meth)acrylate copolymer A-10>

Except that n-dodecyl mercaptan was continuously added as a chain transfer agent to the supply line of the raw material solution so that the concentration reached 450 ppm, it was carried out in the same manner as in A-1. Table 1 shows the composition of A-10 and the content of polymerization inhibitor. In addition, the weight average molecular weight of A-10 is 150,000, the total amount of residual monomers and polymerization solvent is 0.06% by mass, and the total amount of residual oligomers is 0.36% by mass.

<Examples 1-22, Comparative Examples 1-7>

單軸擠出機及T模具、3根鏡面，於單軸擠出機之汽缸溫度為225℃、螺桿轉速為120rpm之條件下進行薄片擠出。T模具之寬度為450mm，開度設為3mm。 The hindered phenol-based antioxidants (B-1)~(B-3) and phosphorus-based antioxidants (C-1)~(C-6) shown below are mixed in the production example with the content shown in Table 2. Among the styrene-methyl (meth)acrylate copolymers, the sheet extruder manufactured by LEADER is used for repeated melting and kneading with antioxidants, and a sheet molded product of 450mm×500mm×2mm is obtained. Sheet extruder contains 50mm

Single-screw extruder, T-die, 3 mirrors, and extrude sheet under the conditions of the cylinder temperature of the single-screw extruder is 225℃ and the screw speed is 120rpm. The width of the T mold is 450mm, and the opening is set to 3mm.

(B-1) Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Co., Ltd.)

(B-2) Ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate] (Irganox 245 manufactured by BASF Japan Co., Ltd.)

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

(C-1)6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldiphenyl And [d,f][1,3,2] dioxaphosphorene (Sumilizer GP manufactured by Sumitomo Chemical Co., Ltd.)

(C-2) Tris(2,4-di-tert-butylphenyl) phosphite (Irgafos 168 manufactured by BASF Japan Co., Ltd.)

(C-3) Bis(2,4-dicumylphenyl) pentaerythritol diphosphite (Doverphos S-9228 manufactured by Dover Chemical Corporation)

(C-4)3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphorous acid Ester[5,5]undecane (Adekastab PEP-36 manufactured by ADEKA Co., Ltd.)

(C-5) 2,2'-methylenebis(4,6-di-tert-butyl-1-phenoxy)(2-ethylhexyloxy)phosphorus (Adekastab manufactured by ADEKA Co., Ltd.) HP-10)

(C-6) bis(2,4-di-tertiary butylphenyl) pentaerythritol diphosphite (Songwon Songnox 6260 manufactured by International Japan Co., Ltd.)

(Water absorption)

Cut the obtained sheet molded product to obtain a molded product with a size of 200mm×300mm. The molded product was stored for 500 hours under the conditions of a temperature of 60°C and a humidity of 90%, the mass before and after storage and the dimensional changes of the long sides were measured, and the water absorption and deformation rate were calculated according to the following formula as an index of water absorption.

(Water Absorption)=((Quality after Storage)-(Quality Before Storage))÷(Quality Before Storage)×100(%)

(Deformation rate)=((Long side length after storage)-(Long side length before storage))÷(Long side length before storage)×100(%)

Table 2 shows the evaluation results.

(Optical characteristics under 115mm optical path length)

A test piece with a thickness of 115mm×85mm×2mm was cut out from the obtained sheet molded product, and the end surface was polished by buffing to prepare a plate-shaped molded product with a mirror surface on the end surface. Regarding the plate-shaped molded product after grinding, the UV-Vis Spectrophotometer V-670 manufactured by JASCO Corporation was used to measure the wavelength under the light path length of 115mm under incident light with a size of 20×1.6mm and a widening angle of 0°. The spectral transmittance of 350nm~800nm is based on JIS K7105 to calculate the YI value under 2° of the field of view in the C light source. The transmittance shown in Table 1 represents the average transmittance at a wavelength of 380nm~780nm. Table 2 shows the evaluation results.

As shown in Table 2, it can be seen that by adding hindered phenol-based antioxidants and phosphorus-based antioxidants, styrene-(meth)acrylic acid with superior transparency and hue compared to Comparative Example 1 without these additions can be produced Methyl ester copolymer. Although only hindered phenol-based antioxidants or phosphorus-based antioxidants were added in Comparative Examples 2 and 3, they resulted in poorer transparency and color compared to Example 1 in which hindered phenol-based antioxidants and phosphorus-based antioxidants were used in combination. . Although only 0.5% by mass of hindered phenol-based antioxidant was added in Comparative Example 4, it was inferior in transparency and color compared with Example 1. It can be considered that it is because the hindered phenol antioxidant is extruded into the sheet. It is deformed due to heat, etc., and becomes a colored substance. Although 0.5% by mass of phosphorus antioxidant was added in Comparative Example 5, not only the transparency and hue were deteriorated, but also roll contamination occurred during the extrusion molding of the sheet, which impaired the surface smoothness of the sheet. In Comparative Example 6, a copolymer with a higher composition of methyl (meth)acrylate was used. The transparency and hue are good, on the other hand, the water absorption is high, and the dimensional stability is poor compared with the examples. Although a copolymer with a higher styrene composition was used in Comparative Example 7, it resulted in inferior transparency and color phase compared with the examples. In addition, in Examples 1, 16, 17, 18, and 21, it has been confirmed that as the amount of polymerization inhibitor in the copolymer increases, the transparency and hue tend to gradually deteriorate.

[Industrial availability]

The styrene-(meth)acrylate copolymer and styrene resin composition of the present invention and molded products thereof have low water absorption, excellent transparency and hue under long light paths, and can be preferably used for, for example, televisions. , Desktop personal computers, notebook personal computers, mobile phones, car navigation, indoor lighting and other light guide applications.

Claims (4)

A styrenic resin composition for optics, characterized in that it contains styrene-(methyl) with 20 to 80% by mass of styrene monomer units and 80 to 20% by mass of (meth)acrylate monomer units. )Acrylate copolymer (A), hindered phenol antioxidant (B), and phosphorus antioxidant (C), relative to the total amount of (A) to (C), the content of (B) is 0.01 to 0.3 Mass%, the content of (C) is 0.001~0.3% by mass, the above-mentioned styrene-(meth)acrylate copolymer (A) is the content of the residual polymerization inhibitor less than 10ppm, the above-mentioned styrene-(former) The weight average molecular weight of the base) acrylate copolymer (A) is 80,000 to 200,000, and the average value of the spectral transmittance at a wavelength of 350 nm to 800 nm measured with an optical path length of 115 mm is 87.0% or more. The optical styrene resin composition of claim 1, wherein the styrene-(meth)acrylate copolymer (A) is a styrene containing 0.1-20 ppm of 4-tert-butylcatechol It is obtained by copolymerization of a monomer and a (meth)acrylate monomer containing 0.1-20 ppm of 6-tert-butyl-2,4-xylenol. A molded article comprising the styrene-based resin composition of claim 1 or 2. A light guide plate comprising the molded product as claimed in claim 3.