WO2016129675A1

WO2016129675A1 - Styrene-based optical resin composition

Info

Publication number: WO2016129675A1
Application number: PCT/JP2016/054138
Authority: WO
Inventors: 桂輔井上; 智輝小林; 広平西野; 黒川　欽也
Original assignee: デンカ株式会社
Priority date: 2015-02-12
Filing date: 2016-02-12
Publication date: 2016-08-18
Also published as: TWI738639B; JP6725431B2; JPWO2016129675A1; KR102457996B1; CN107250255B; CN107250255A; KR20170117105A; TW201638190A

Abstract

The purpose of the present invention is to provide a styrene-(meth)acrylic ester copolymer having excellent transparency and hue, low water absorption, and excellent dimensional stability or resistance to warping due to moisture absorption. A styrene-based optical resin composition comprising (A) a styrene-(meth)acrylic ester copolymer having 20-80% by mass of styrene-based monomer units and 80-20% by mass of (meth)acrylic-ester-based monomer units, (B) a hindered-phenol-based antioxidant, and (C) a phosphorus-based antioxidant, the content of component (B) with respect to the total content of components (A) through (C) being 0.01-0.3% by mass, and the content of component (C) with respect to the total content of components (A) through (C) being 0.001-0.3% by mass.

Description

Styrenic resin composition for optics

The present invention relates to an optical styrenic resin composition excellent in hue and transparency, a molded product thereof, and a light guide plate.

There are two types of backlights for liquid crystal display devices: a direct type in which a light source is disposed in front of the display device and an edge light type in which a light source is disposed on a side surface. The light guide plate is used for an edge light type backlight and plays a role of guiding light from a light source disposed on a side surface to the front. Edge-light type backlights are used in TVs, personal computer monitors, mobile phones, car navigation systems, and other applications where thinness is required. Even in televisions (for example, 32 inches or more), the rate at which edge-light type backlights are used is increasing.
An acrylic resin typified by PMMA (polymethyl methacrylate) is used for the light guide plate. However, since the water absorption is high, the molded product may be warped or dimensional change may occur. Moreover, since the thermal decomposability at the time of shaping | molding is high, when shape | molding at high temperature, there exists a problem that an external appearance defect tends to arise in a molded object.
Therefore, it has been proposed to use a styrene-methyl (meth) acrylate copolymer with improved properties. Patent Document 1 has been proposed as a technique for improving water absorption of a styrene-methyl (meth) acrylate copolymer.
On the other hand, the styrene-methyl (meth) acrylate copolymer has a molded article having a poor hue (yellowish) as compared with PMMA, and when used as a backlight, color unevenness may occur on the surface of the liquid crystal display device. . Therefore, Patent Document 2 has been proposed as a technique for improving the hue of styrene-methyl (meth) acrylate copolymer.

Japanese Patent Laid-Open No. 2003-075648 Japanese Unexamined Patent Publication No. 2013-082800

An object of the present invention is to provide a novel optical styrenic resin composition having good transparency and hue and low water absorption, and a molded product thereof. Among the molded products, it can be suitably used particularly for a light guide plate used in a liquid crystal display device or the like.

That is, the present invention is as follows.
(1) a styrene- (meth) acrylate copolymer (A) having 20 to 80% by mass of a styrene monomer unit and 80 to 20% by mass of a (meth) acrylate monomer unit; It consists of a hindered phenol antioxidant (B) and a phosphorus antioxidant (C), and the content of (B) is 0.01 to 0. 0 relative to the total amount of (A) to (C). 3% by mass, the content of (C) is 0.001 to 0.3% by mass, and the styrene- (meth) acrylic acid ester copolymer (A) has a residual polymerization inhibitor content of 10 ppm. A styrenic resin composition for optical use, wherein
(2) The optical styrene resin composition according to (1), wherein the styrene (meth) acrylic acid ester copolymer has a weight average molecular weight of 50,000 to 200,000.
(3) The styrene- (meth) acrylic acid ester copolymer (A) contains a styrene monomer containing 0.1 to 20 ppm of 4-tert-butylcatechol, and 6-tert-butyl-2,4. -Optical styrene as described in (1) or (2), which is obtained by copolymerizing a (meth) acrylic acid ester monomer containing 0.1-20 ppm of xylenol -Based resin composition.
(4) A molded article comprising the styrenic resin composition according to any one of (1) to (3).
(5) A light guide plate comprising the molded product according to (4).

The optical styrenic resin composition and molded article of the present invention are excellent in transparency and hue, low in water absorption and excellent in warpage resistance and dimensional stability due to moisture absorption, and are therefore suitably used for optical applications such as light guide plates. I can do it.

Hereinafter, embodiments of the present invention will be described in detail. In the present specification, for example, the description “A to B” means not less than A but not more than B.

The styrene resin composition of the present invention comprises a styrene- (meth) acrylic acid ester copolymer (A), a hindered phenol antioxidant (B), and a phosphorus antioxidant (C). It is a composition.

The styrene- (meth) acrylate copolymer (A) is a copolymer having a styrene monomer unit and a (meth) acrylate monomer unit. For example, styrene-methyl ( There are (meth) acrylate copolymers.

The styrene monomer is an aromatic vinyl monomer. Styrene, α-methyl styrene, o-methyl styrene, m-methyl styrene, ethyl styrene, pt-butyl styrene and the like are used alone or as a mixture of two or more thereof, and styrene is preferred.

(Meth) acrylic acid ester monomers are methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, methacrylic acid ester of 2-ethylhexyl (meth) acrylate, methyl acrylate, ethyl acrylate, n -Butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, decyl acrylate or the like alone or a mixture of two or more thereof, preferably methyl (meth) acrylate.

The content of the styrene monomer unit in the styrene- (meth) acrylic acid ester copolymer is 20 to 80% by mass, and the content of the (meth) acrylic acid ester monomer unit is 80 to 20% by mass. is there. More preferably, the content of styrene monomer units is 30 to 60% by mass, and the content of (meth) acrylic acid ester monomer units is 70 to 40% by mass. More preferably, the content of the styrene monomer unit 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 monomer unit is small, warpage and dimensional deformation may increase due to moisture absorption. When there is too much content of a styrene-type monomer unit, the deterioration of a hue or surface hardness may fall, and it may become easy to be damaged.

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

The content of styrene monomer units and (meth) acrylate monomer units in the styrene- (meth) acrylate copolymer was measured by pyrolysis gas chromatography under the following conditions.
Pyrolysis furnace: PYR-2A (manufactured by Shimadzu Corporation)
Pyrolysis furnace temperature setting: 525 ° C
Gas chromatograph: GC-14A (manufactured by Shimadzu Corporation)
Column: Glass 3mm diameter x 3m
Filler: FFAP Chromsorb WAW 10%
Column temperature: 120 ° C
Carrier gas: Nitrogen

As a method for producing a styrene- (meth) acrylic ester copolymer, a known method can be employed. For example, it can be produced by bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization and the like. As a method for operating the reactor, any of a continuous type, a batch type (batch type), and a semibatch type can be applied. In view of quality such as transparency and productivity, bulk polymerization or solution polymerization is preferable, and continuous polymerization is preferable. Examples of the bulk polymerization or solution polymerization solvent include alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.

As a polymerization method of the styrene- (meth) acrylic acid ester copolymer, a known method can be adopted. The radical polymerization method is preferable because it is a simple process and excellent in productivity.

In bulk polymerization or solution polymerization of a 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. When performing bulk polymerization or solution polymerization in a continuous manner, the conversion rate of the styrene monomer and the (meth) acrylate monomer is 60% or more at the exit of the polymerization step from the viewpoint of productivity. It is preferable to perform polymerization.

Examples of the polymerization initiator include benzoyl peroxide, t-butylperoxybenzoate, 1,1-di (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) -3,3,5. -Trimethylcyclohexane, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, t-butyl Peroxyisopropyl carbonate, dicumyl peroxide, t-butylcumyl peroxide, t-butylperoxyacetate, t-butylperoxy-2-ethylhexanoate, polyether tetrakis (t-butylperoxycarbonate), ethyl -3,3-di (t-butylperoxy) butyrate, t-butylperoxy Organic peroxides such as Sobuchireto the like.

The addition amount of the polymerization initiator is preferably 0.001 to 0.2% by mass with respect to 100% by mass of the total amount of monomers. More preferably, the content is 0.001 to 0.05% by mass. If the addition amount of the polymerization initiator is too large, the hue may 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, more preferably 0.005 to 0.2% by mass with respect to 100% by mass in total of the monomers. When the addition amount of the chain transfer agent is 0.001 to 0.5% by mass, the thermal stability becomes good.

As a devolatilization method for removing volatile components such as unreacted monomers and a solvent used for solution polymerization from the solution after the completion of polymerization of the styrene- (meth) acrylate copolymer, a known method can be adopted. . For example, a vacuum devolatilization tank with a preheater or a vented devolatilization extruder can be used. The temperature of the styrene- (meth) acrylic ester copolymer in the devolatilization step is preferably 200 ° C. to 300 ° C., more preferably 220 ° C. to 260 ° C. If the temperature of the styrene- (meth) acrylic acid ester copolymer in the devolatilization process is too high, the hue may deteriorate. The devolatilized molten styrene- (meth) acrylic acid ester copolymer is transferred to the granulation process and extruded into a strand shape from a porous die for cold cut method, air hot cut method, and underwater hot cut method. Can be processed into a pellet shape.

Unreacted monomers removed in the devolatilization process and the solvent used for solution polymerization are recovered and purified to remove impurities such as polymerization inhibitors, and then mixed with fresh raw materials for recovery. It is preferable. Since the recovered raw material does not contain a polymerization inhibitor, it is possible to reduce the content of the polymerization inhibitor in the raw material supplied to the polymerization step by using it by mixing it with a fresh raw material. 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, even more preferably less than 6 ppm, and most preferably less than 4 ppm. When 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. Here, the fresh raw material is a raw material newly supplied to the production process of the styrene- (meth) acrylic acid ester copolymer, and is referred to as such in order to distinguish it from the recovered raw material.

A known method can be adopted as a method for recovering and purifying the unreacted monomer removed in the devolatilization step and the solvent used in the solution polymerization. For example, there may be mentioned a method in which unreacted monomer and solvent gas removed in the devolatilization step is condensed and liquefied by a condenser and purified by a flash distillation column to separate and remove high-boiling components. In addition, from the unreacted monomer and solvent gases removed in the devolatilization process, only the high-boiling components are first condensed using a condenser or spray tower, etc., and the remaining gas is completely removed by the condenser. The method of condensing is mentioned. 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., and is separated and removed from the monomer and solvent as a high-boiling component. (Boiling point of styrene is 145 ° C, boiling point of methyl (meth) acrylate is 101 ° C, boiling point of ethylbenzene is 136 ° C).

The weight average molecular weight (Mw) of the styrene (meth) acrylic acid ester copolymer is preferably 50,000 to 200,000. More preferably, it is 70,000 to 180,000, more preferably 75,000 to 160,000, and most preferably 80 to 150,000. When the weight average molecular weight (Mw) is less than 50,000, the strength of the light guide plate may decrease. When the weight average molecular weight (Mw) exceeds 200,000, the fluidity may be lowered and the molding processability may be deteriorated. The weight average molecular weight (Mw) can be controlled by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, the type and amount of the solvent used during the polymerization, and the like. it can.

The weight average molecular weight (Mw) was measured under the following conditions using gel permeation chromatography (GPC).
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: PLgel 10 μm MIXED-B manufactured by Polymer Laboratories
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer The molecular weight of the present invention is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.

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

The residual monomer and polymerization solvent are the amount of monomer and polymerization solvent remaining in the styrene- (meth) acrylic acid ester copolymer, and examples thereof include styrene, methyl (meth) acrylate, and ethylbenzene. . The amount of the residual monomer and the polymerization solvent can be adjusted by the constitution of the devolatilization process and the conditions of the devolatilization process.

The amount of the residual monomer and the polymerization solvent was determined by accurately weighing 0.2 g of a styrene- (meth) acrylate copolymer and dissolving it in 10 ml of tetrahydrofuran containing p-hour ethylbenzene as an internal standard substance. Was measured under the following conditions.
Capillary gas chromatograph: GC-4000 (manufactured by GL Sciences Inc.)
Column: GS Science Co., Ltd. InertCap WAX, inner diameter 0.25 mm, length 30 m, film thickness 50 μm
Injection temperature: 180 ° C
Column temperature: 60 ° C-170 ° C
Detector temperature: 210 ° C
Split ratio: 5/1

The total amount of dimer or trimer (hereinafter referred to as oligomer) of styrene monomer and (meth) acrylate monomer in the styrene- (meth) acrylate copolymer is 2% by mass. The following is preferable. More preferably, it is 1 mass% or less. When the total amount of oligomers exceeds 1% by mass, heat resistance as a light guide plate may be insufficient.

The oligomer was measured by dissolving 200 mg of a styrene- (meth) acrylic acid ester copolymer in 2 mL of 1,2-dichloromethane, adding 2 mL of methanol to precipitate the copolymer, allowing it to stand, The liquid was measured under the following conditions using a gas chromatograph.
Gas chromatograph: HP-5890 (manufactured by Hewlett-Packard Company)
Column: DB-1 (ht) 0.25 mm × 30 m, film thickness 0.1 μm
Injection temperature: 250 ° C
Column temperature: 100-300 ° C
Detector temperature: 300 ° C
Split ratio: 50/1
Internal reference material: n-eicosane Carrier gas: Nitrogen

The Vicat softening point of the styrene- (meth) acrylic acid ester copolymer is preferably 95 ° C. or higher, and more preferably 98 ° C. or higher. If the Vicat softening point is less than 95 ° C., the heat resistance is insufficient, and the molded product may be deformed depending on the use environment. (The Vicat softening temperature was tested in accordance with JIS K 7206 at a heating rate of 50 ° C./hr and a test load of 50 N.)

The content of the hindered phenol antioxidant (B) in the styrene resin composition is 0.01 to 0.3% by mass with respect to the total amount of (A) to (C). The amount 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-based antioxidant (B) is too small, the hue improving effect is not obtained, and if it is too much, the hue may be deteriorated.

The hindered phenol antioxidant (B) is an antioxidant having a phenolic hydroxyl group in the basic skeleton. Examples of the hindered phenol antioxidant include octadecyl-3- (3,5-di-t-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-methylphenyl) propionyloxy] -1,1-dimethylethyl]- 2,4,8,10-tetraoxaspiro [5.5] undecane, pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 4,6-bis (octyl) Thiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -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-tert-butyl-3- Methylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-tert-butylphenol), bis- [ 3,3-bis- (4′-hydroxy-3′-tert-butylphenyl) -butanoic acid] -glycol ester, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methyl Benzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy-3,5-di-tert-pentylphenyl) ethyl] -4,6-di-tert-pentylphenylacrylate Over doors and the like. Preferably, octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, ethylene bis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) Propionate], pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate]. More preferred is octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate. Hindered phenolic antioxidants may be used alone or in combination of two or more.

The content of the phosphorus-based antioxidant (C) in the styrene-based resin composition is 0.001 to 0.3% by mass with respect to the total amount of (A) to (C). The content is preferably 0.001 to 0.1% by mass, more preferably 0.001 to 0.05% by mass, and still more preferably 0.001 to 0.02% by mass. When there is too much content of phosphorus antioxidant (C), a hue may deteriorate. In addition, mold contamination may occur during injection molding or roll contamination may occur during extrusion of a plate-shaped molded product.

Phosphorous antioxidant (C) is a phosphite that is a trivalent phosphorus compound. Phosphorous antioxidants include, for example, 6- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-t-butylbenz [d, f ] [1,3,2] dioxaphosphine, 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-phenyloxy) (2-ethylhexyl) Oxy) phosphorus, tris (2,4-di-tert-butylphenyl) phosphite, bis [2,4-bis (1,1-dimethylethyl) -6-methylphenyl] ethyl ester Acid, bis (2,4-di-tert-butylphenyl) pentaerythritol diphosphite, cyclic neopentanetetraylbis (octadecyl phosphite), bis (nonylphenyl) pentaerythritol diphosphite, 4,4 ′ -Biphenylenediphosphinic acid tetrakis (2,4-di-tert-butylphenyl), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, tetrakis (2,4-di-tert-butyl- 5-methylphenyl) -4,4′-biphenylenediphosphonite and the like. Preferably, 6- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-t-butylbenz [d, f] [1,3 2] Dioxaphosphepine, 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-phenyloxy) (2-ethylhexyloxy) phosphorus, tris ( 2,4-di-tert-butylphenyl) phosphite, bis (2,4-di-tert-butylphenyl) pentaerythritol diphosphite. More preferably, 6- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-t-butylbenz [d, f] [1,3 , 2] dioxaphosphepine, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, tris (2,4-di-tert-butylphenyl) phosphite, bis (2,4-di-tert) -Butylphenyl) pentaerythritol diphosphite, more preferably 6- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-t -Butylbenz [d, f] [1,3,2] dioxaphosphine, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, bis (2,4-di- ert- butyl phenyl) pentaerythritol diphosphite. Phosphorous antioxidants may be used alone or in combination of two or more.

The total {(B) + (C)} of the content of the hindered phenolic antioxidant (B) and the content of the phosphorus antioxidant (C) in the styrene resin composition is (A) to ( It is 0.011 to 0.6% by mass relative to the total amount of C). The content 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 total amount of the content of the hindered phenolic antioxidant (B) and the content of the phosphorus antioxidant (C) {(B) + (C)} is too small, there will be no effect of improving the hue. Hue may deteriorate.

A method for producing a styrene resin composition from a styrene- (meth) acrylic acid ester copolymer (A), a hindered phenol antioxidant (B) and a phosphorus antioxidant (C) is known. The method can be adopted. A styrene- (meth) acrylic acid ester copolymer is used in the production step (A) such as polymerization step, devolatilization step, granulation step, etc. in the hindered phenolic antioxidant (B) and phosphorus antioxidant ( There is a method of adding C), which is preferably added after the unreacted monomer and solvent are removed in the devolatilization step. For example, when a vacuum devolatilization tank is used, a hindered phenol antioxidant (B) and a phosphorus antioxidant (C) in a molten state are added to a styrene- (meth) acrylate ester copolymer extracted from the devolatilization tank. ) And mixing with a static mixer, or when using a vented devolatilizing extruder, add a hindered phenolic antioxidant (B) and a phosphorus antioxidant (C) after the venting zone. Can be mixed. Further, it can be added directly at the time of molding the styrene- (meth) acrylic acid ester copolymer (A), or it can be added by preparing a master batch.

The styrene resin composition may contain mineral oil as long as the transparency is not impaired. Also includes additives such as internal lubricants such as stearic acid and ethylene bisstearylamide, sulfur antioxidants, lactone antioxidants, UV absorbers, hindered amine stabilizers, antistatic agents, external lubricants, etc. It may be. As the external lubricant, ethylene bisstearylamide is suitable.

The ultraviolet absorber has a function of suppressing deterioration and coloring due to ultraviolet rays. For example, benzophenone, benzotriazole, triazine, benzoate, salicylate, cyanoacrylate, malonic ester, formamidine UV absorbers such as those of the system. These can be used alone or in combination of two or more thereof, and a light stabilizer such as a hindered amine may be used in combination.

The polymerization inhibitor is added to the monomer in order to prevent unintended polymerization from occurring during storage of the monomer. Examples of the polymerization inhibitor include catechols such as 4-tert-butylcatechol, phenols such as 6-tert-butyl-2,4-xylenol and paramethoxyphenol, hydroquinone, 2,2,6,6, and the like. -Tetramethylpiperidinyl-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl and the like.

The content of the polymerization inhibitor remaining in the styrene- (meth) acrylic acid ester copolymer is preferably less than 10 ppm, more preferably less than 5 ppm, and even more preferably less than 3 ppm. The polymerization inhibitor includes a styrene monomer used for copolymerization of a styrene- (meth) acrylate ester copolymer, 4-tert-butylcatechol derived from a (meth) acrylate ester monomer, and 6- tert-butyl-2,4-xylenol and the like. The content of 6-tert-butyl-2,4-xylenol remaining in the styrene- (meth) acrylic acid ester 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 may be modified during the polymerization reaction or molding process, becoming a colored substance and deteriorating transparency and hue. The content of the polymerization inhibitor remaining in the copolymer can be controlled by the content of the polymerization inhibitor in the monomer used for the copolymerization. Also, in continuous bulk polymerization or solution polymerization, the content of the polymerization inhibitor remaining in the copolymer is efficiently reduced by reusing the recovered and purified unreacted monomer. can do.

The 4-tert-butylcatechol concentration and 6-tert-butyl-2,4-xylenol concentration in the styrene- (meth) acrylic acid ester copolymer were first dissolved in tetrahydrofuran (adjusted to 50 mg / ml). ) After that, trimethylsilyl derivatization treatment was performed using BSTFA (N, O-bis (trimethylsilyl) trifluoroacetamide), and the supernatant separated by centrifugation was analyzed by gas chromatography mass spectrometry (GC / MS). The measurement was performed under the following conditions. A calibration curve prepared in advance was used to determine the concentration.
GC / MS measurement conditions:
GC device: Agilent 6890
Column: DB-1 (0.25 mm id x 30 m)
Liquid phase thickness 0.25mm
Column temperature: 40 ° C. (5 min hold) → (20 ° C./min temperature increase) →
320 ° C (6 min hold) 25 min total
Inlet temperature: 320 ° C
Injection method: Split method (split ratio 1: 5)
Sample volume: 2 μl
MS equipment: Agilent MSD5973
Ion source temperature: 230 ° C
Interface temperature: 320 ° C
Ionization method: Electron ionization (EI) method Measurement method: SCAN method (scan range m / z 10 to 800)

The styrenic monomer preferably contains 0.1 to 20 ppm of 4-tert-butylcatechol as a polymerization inhibitor, more preferably 0.1 to 12 ppm, and even more preferably 0.1 to 7 ppm. It is. When the concentration of 4-tert-butylcatechol in the styrene monomer exceeds 20 ppm, the 4-tert-butylcatechol itself is modified and becomes a colored substance. Therefore, a styrene- (meth) acrylate ester copolymer Transparency and hue may deteriorate.

The (meth) acrylic acid ester monomer preferably contains 0.1 to 20 ppm, more preferably 0.1 to 12 ppm of 6-tert-butyl-2,4-xylenol as a polymerization inhibitor. More preferably, it is 0.1 to 7 ppm. When the concentration of 6-tert-butyl-2,4-xylenol in the (meth) acrylic acid ester monomer exceeds 20 ppm, 6-tert-butyl-2,4-xylenol itself is denatured, Therefore, the transparency and hue of the styrene- (meth) acrylic acid ester copolymer may be deteriorated.

The polymerization inhibitor of styrene monomer or (meth) acrylic acid ester monomer can be removed or reduced by adsorption removal with activated alumina.

The 4-tert-butylcatechol in the styrene monomer and the 6-tert-butyl-2,4-xylenol concentration in the (meth) acrylic acid ester monomer were first set to 50 mg / ml for each monomer. After being mixed with tetrahydrofuran so as to be, trimethylsilyl derivatization treatment was performed using BSTFA (N, O-bis (trimethylsilyl) trifluoroacetamide), and gas chromatography / mass spectrometry (GC / MS) was used. It measured on the same conditions as the measurement of a (meth) acrylic acid ester-type copolymer. A calibration curve prepared in advance was used to determine the concentration.

The styrene resin composition can be formed into a molded product by a known method such as extrusion molding, injection molding, compression molding, or blow molding. For example, a plate-shaped molded product can be produced by extrusion molding and processed into a light guide plate or the like.

Since the styrenic resin composition of the present invention is excellent in thermal stability, it collects and grinds unfinished parts such as sheet end materials during extrusion molding and spools and runners during injection molding, and mixes them with virgin raw materials. Can be used.

The light guide plate is a member having a function of guiding light incident from the end face of the plate-shaped molded product to the surface side of the plate-shaped molded product by a reflection pattern formed on one surface of the plate-shaped molded product and emitting light. The reflection pattern can be formed by a method such as a screen printing method, a laser processing method, or an ink jet method. Further, a prism pattern or the like can be provided on the opposite surface (light emitting surface) of the surface on which the reflection pattern is formed. The reflection pattern and prism pattern of the plate-shaped molded product can be formed when the plate-shaped molded product is molded. For example, it can be formed by a mold shape in injection molding, or by roll transfer in extrusion molding.

“Optical use” refers to use in products in which components include light sources such as LEDs, fluorescent lamps, and incandescent lamps. Examples of the product include a television, a desktop personal computer, a notebook personal computer, a mobile phone, a car navigation, indoor lighting, and the like.

The optical styrene resin composition preferably has an average value of spectral transmittance at a wavelength of 350 nm to 800 nm measured at an optical path length of 115 mm of 87.0% or more, more preferably 87.5% or more, More preferably, it is 88.0% or more, and most preferably 88.5% or more. Moreover, it is preferable that the YI value measured in accordance with JIS K7105 at a visual field of 2 ° with a C light source is 3.5 or less, more preferably 3.0 or less, and even more preferably 2.5 or less. And most preferably 2.0 or less.

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

<Production example of styrene- (meth) acrylic ester copolymer A-1>
The styrene- (meth) acrylic acid ester copolymer was produced by continuous solution polymerization by a radical polymerization method. A complete mixing tank type stirring tank was used as the first reactor, a plug flow type reactor with a static mixer was used as the second reactor, and the polymerization process was configured by connecting in series. The capacity of the first reactor was 30L, and the capacity of the second reactor was 12L. As a (meth) acrylic acid ester monomer, industrially used methyl (meth) acrylate (hereinafter referred to as fresh MMA) was prepared, and 6-tert-butyl-2,4-xylenol (hereinafter, referred to as “fresh MMA”) was prepared. The concentration of (referred to as TBX) was 4.9 ppm. As styrene monomer, industrially used styrene (hereinafter referred to as “Fresh Sty”) was prepared, and the concentration of 4-tert-butylcatechol (hereinafter referred to as “TBC”) was 10.2 ppm. As a polymerization solvent, industrially used ethylbenzene (hereinafter referred to as fresh EB) was prepared. In addition, gases such as a monomer and a polymerization solvent separated from a vacuum devolatilizer described later were condensed by a condenser and purified by a flash distillation column as a recovered raw material. The concentrations of TBX and TBC in the recovered raw material were below the lower limit of detection. Using fresh MMA, fresh Sty and the recovered raw material, a raw material solution was prepared so as to have the raw material composition shown in Table 1, and continuously supplied to the polymerization step at a feed flow rate shown in Table 1. The use ratio of the recovered raw materials is as shown in Table 1, and is balanced with the amount separated and purified in the devolatilization tank. In addition, t-butylperoxyisopropyl monocarbonate as a polymerization initiator was continuously added to the raw material solution supply line to a concentration of 150 ppm and n-dodecyl mercaptan as a chain transfer agent to a concentration of 500 ppm. . The temperature of the first reactor was adjusted to 135 ° C., and the second reactor was adjusted to have a temperature gradient along the flow direction and adjusted to 130 ° C. at the middle portion and 145 ° C. at the outlet portion. The polymer concentration at the outlet of the polymerization process was 65%, and the conversion ratio of methyl (meth) acrylate and styrene was 72%. The polymer solution continuously taken out from the reactor was supplied to a vacuum devolatilization tank equipped with a preheater to separate unreacted methyl (meth) acrylate, styrene, ethylbenzene and the like. The temperature of the preheater was adjusted so that the polymer temperature in the devolatilization tank was 240 ° C., and the pressure in the devolatilization tank was 1 kPa. The polymer was extracted from the vacuum devolatilization tank using a gear pump, extruded into a strand, cooled with cooling water, and then cut to obtain a pellet-shaped 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 an abbreviation for styrene, MMA for methyl (meth) acrylate, and EB for ethylbenzene. The weight average molecular weight of A-1 was 145,000, the total amount of residual monomer and polymerization solvent was 0.07% by mass, and the total amount of residual oligomer was 0.35% by mass.

<Production example of styrene- (meth) acrylic ester copolymer A-2>
It was carried out in the same manner as A-1 except that a fresh MMA used industrially had a TBX concentration of 11.2 ppm. Table 1 shows the composition of A-2 and the content of the polymerization inhibitor. The weight average molecular weight of A-2 was 145,000, the total amount of residual monomer and polymerization solvent was 0.07% by mass, and the total amount of residual oligomer was 0.36% by mass.

<Production example of styrene- (meth) acrylic ester copolymer A-3>
The same procedure as A-1 was performed except that the recovered raw material was not used. Table 1 shows the composition of A-3 and the content of the polymerization inhibitor. The weight average molecular weight of A-3 was 145,000, the total amount of residual monomer and polymerization solvent was 0.06% by mass, and the total amount of residual oligomer was 0.35% by mass.

<Production example of styrene- (meth) acrylic ester copolymer A-4>
It was carried out in the same manner as A-1 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. Table 1 shows the composition of A-4 and the content of the polymerization inhibitor. The weight average molecular weight of A-4 was 145,000, the total amount of residual monomer and polymerization solvent was 0.07% by mass, and the total amount of residual oligomer was 0.36% by mass.

<Production example of styrene- (meth) acrylic ester copolymer A-5>
The same procedure as in A-1 was carried out except that the raw material composition was changed to the contents shown in Table 1 and the concentration of n-dodecyl mercaptan was changed to 1000 ppm. Table 1 shows the composition of A-5 and the content of the polymerization inhibitor. The weight average molecular weight of A-5 was 120,000, the total amount of residual monomer and polymerization solvent was 0.06% by mass, and the total amount of residual oligomer was 0.34% by mass.

<Production example of styrene- (meth) acrylic ester copolymer A-6>
The raw material composition was changed to the contents shown in Table 1, the feed flow rate was 5.7 kg / h, the concentration of t-butylperoxyisopropyl monocarbonate was 100 ppm, the concentration of n-dodecyl mercaptan was 3000 ppm, and the temperature of the first reactor Was carried out in the same manner as A-1, except that the temperature was 130 ° C. Table 1 shows the composition of A-6 and the content of the polymerization inhibitor. The weight average molecular weight of A-6 was 80,000, the total amount of residual monomer and polymerization solvent was 0.05% by mass, and the total amount of residual oligomer was 0.32% by mass.

<Production example of styrene- (meth) acrylic ester copolymer A-7>
The raw material composition was changed to the contents shown in Table 1, the feed flow rate was 5.7 kg / h, the concentration of t-butylperoxyisopropyl monocarbonate was 100 ppm, the concentration of n-dodecyl mercaptan was 3000 ppm, and the temperature of the first reactor Was carried out in the same manner as A-1, except that the temperature of the intermediate part of the second reactor was 140 ° C. and the temperature of the outlet part was 150 ° C. Table 1 shows the composition of A-7 and the content of the polymerization inhibitor. The weight average molecular weight of A-7 was 80,000, the total amount of residual monomer and polymerization solvent was 0.06% by mass, and the total amount of residual oligomer was 0.34% by mass.

<Production example of styrene- (meth) acrylic ester copolymer A-8>
The raw material composition was changed to the contents shown in Table 1, the addition of n-dodecyl mercaptan was stopped, the temperature of the first reactor was 140 ° C, the temperature of the intermediate portion of the second reactor was 140 ° C, and the temperature of the outlet portion was The procedure was the same as A-1, except that the temperature was 160 ° C. Table 1 shows the composition of A-8 and the content of the polymerization inhibitor. The weight average molecular weight of A-8 was 240,000, the total amount of the residual monomer and the polymerization solvent was 0.06% by mass, and the total amount of the residual oligomer was 0.33% by mass.

<Production example of styrene- (meth) acrylic ester copolymer A-9>
Except that the concentration of TBX is 13.6 ppm as fresh MMA used in the industry, and the one where the concentration of TBC is 12.2 ppm as fresh Styl is not used. It carried out like A-1. Table 1 shows the composition of A-9 and the content of the polymerization inhibitor. The weight average molecular weight of A-9 was 145,000, the total amount of residual monomer and polymerization solvent was 0.06% by mass, and the total amount of residual oligomer was 0.35% by mass.

<Production example of styrene- (meth) acrylic ester copolymer A-10>
The same procedure as in A-1 was performed except that n-dodecyl mercaptan as a chain transfer agent was continuously added to the feed line of the raw material solution to a concentration of 450 ppm. Table 1 shows the composition of A-10 and the content of the polymerization inhibitor. The weight average molecular weight of A-10 was 150,000, the total amount of residual monomer and polymerization solvent was 0.06% by mass, and the total amount of residual oligomer was 0.36% by mass.

<Examples 1 to 22 and Comparative Examples 1 to 7>
The hindered phenolic antioxidants (B-1) to (B-3) and phosphorus antioxidants (C-1) shown below are added to the styrene-methyl (meth) acrylate copolymers obtained in the production examples. (C-6) was mixed at the content shown in Table 2, and a sheet molded product of 450 mm × 500 mm × 2 mm was obtained while melt-kneading the antioxidant using a sheet extruder manufactured by LEADER. The sheet extruder was composed of a 50 mmφ single-screw extruder, a T die, and three mirror rolls, and sheet extrusion was performed at a cylinder temperature of 225 ° C. and a screw rotation speed of 120 rpm. The width of the T die was 450 mm and the opening was 3 mm.
(B-1) Octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
(B-2) Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
(B-3) Pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (Irganox 1010 manufactured by BASF Japan Ltd.)
(C-1) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1 , 3,2] dioxaphosphepine (Sumitomo Chemical Co., Ltd. Sumilizer GP)
(C-2) Tris (2,4-di-tert-butylphenyl) phosphite (Irgafos 168 manufactured by BASF Japan Ltd.)
(C-3) Bis (2,4-dicumylphenyl) pentaerythritol diphosphite (Doverphos S-9228 manufactured by Dober Chemical Corporation)
(C-4) 3,9-bis (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5,5] undecane (stock) Adeka Stub made by company ADEKA PEP-36)
(C-5) 2,2′-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus (ADEKA STAB HP-10, manufactured by ADEKA Corporation)
(C-6) Bis (2,4-di-tert-butylphenyl) pentaerythritol diphosphite (Songnox 6260 manufactured by Songwon International Japan Co., Ltd.)

(Water absorption)
The obtained sheet molded product was cut to obtain a molded product having a size of 200 mm × 300 mm. This molded product is stored for 500 hours at a temperature of 60 ° C. and a humidity of 90%. The mass and long-side dimensional changes before and after storage are measured, and the water absorption rate and deformation rate are calculated by the following formulas as a water absorption index. did.
(Water absorption) = ((Mass after storage)-(Mass before storage)) ÷ (Mass before storage) x 100 (%)
(Deformation rate) = ((Long side length after storage)-(Long side length before storage)) ÷ (Long side length before storage) x 100 (%)
Table 2 shows the evaluation results.

(Optical characteristics at an optical path length of 115 mm)
A test piece having a thickness of 115 mm × 85 mm × 2 mm was cut out from the obtained sheet molded product, and the end surface was polished by buffing to produce a plate-shaped molded product having a mirror surface on the end surface. The polished plate-like molded product was measured using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, with an incident light having a size of 20 × 1.6 mm and a spread angle of 0 °, and a wavelength at an optical path length of 115 mm. Spectral transmittances from 350 nm to 800 nm were measured, and the YI value at a visual field of 2 ° with a C light source was calculated according to JIS K7105. The transmittance shown in Table 1 indicates an average transmittance at a wavelength of 380 nm to 780 nm. Table 2 shows the evaluation results.

As shown in Table 2, by adding a hindered phenolic antioxidant and a phosphorus antioxidant, styrene-methyl (meth) acrylate is superior in transparency and hue as compared with Comparative Example 1 in which they are not added. It can be seen that a copolymer can be produced. In Comparative Examples 2 and 3, only the hindered phenol antioxidant or the phosphorus antioxidant was added, but the transparency was higher than that in Example 1 in which the hindered phenol antioxidant and the phosphorus antioxidant were used in combination. And the hue was inferior. In Comparative Example 4, 0.5% by mass of a hindered phenol-based antioxidant was added, but the transparency and hue were inferior to those of Example 1. This is presumably because the hindered phenolic antioxidant itself was modified by heat during sheet extrusion to become a colored substance. In Comparative Example 5, 0.5 mass% of the phosphorus-based antioxidant was added, but in addition to deterioration of transparency and hue, roll contamination occurred during the extrusion of the sheet, and the surface smoothness of the sheet was impaired. In Comparative Example 6, a copolymer having a high methyl (meth) acrylate composition was used. While the transparency and hue were good, the water absorption was high and the dimensional stability was inferior compared to the examples. In Comparative Example 7, a copolymer having a high styrene composition was used, but the results were inferior in transparency and hue as compared with Examples. In Examples 1, 16, 17, 18, and 21, it was confirmed that the transparency and hue tend to deteriorate as the amount of the polymerization inhibitor in the copolymer increases.

The styrene- (meth) acrylic acid ester copolymer and the styrene resin composition of the present invention and the molded product thereof have low water absorption and excellent transparency and hue in a long optical path. For example, televisions, desktop personal computers It can be suitably used for light guide plate applications such as notebook personal computers, mobile phones, car navigation systems, and indoor lighting.

Claims

Styrene- (meth) acrylate copolymer (A) having 20 to 80% by mass of styrene monomer units and 80 to 20% by mass of (meth) acrylate monomer units, and hindered phenol A antioxidant (B) and a phosphorus antioxidant (C), and the content of (B) is 0.01 to 0.3% by mass with respect to the total amount of (A) to (C) The content of (C) is 0.001 to 0.3% by mass, and the content of the polymerization inhibitor remaining in the styrene- (meth) acrylic ester copolymer (A) is less than 10 ppm. A styrenic resin composition for optics.
The optical styrene resin composition according to claim 1, wherein the styrene (meth) acrylic acid ester copolymer has a weight average molecular weight of 50,000 to 200,000.
A styrene- (meth) acrylic acid ester copolymer (A) comprises a styrene monomer containing 0.1 to 20 ppm of 4-tert-butylcatechol, and 6-tert-butyl-2,4-xylenol. 3. The optical styrenic resin composition according to claim 1, which is obtained by copolymerization with a (meth) acrylic acid ester monomer containing 0.1 to 20 ppm.
A molded article comprising the styrenic resin composition according to any one of claims 1 to 3.
A light guide plate comprising the molded product according to claim 4.