TW202041548A - Styrene resin composition, molded article, and light guide plate - Google Patents

Abstract

Provided are a styrene resin composition and a molded article thereof having excellent moist-heat resistance, and a light guide plate. Through the present invention, there is provided a styrene resin composition in which t1 - t2 is 20 minutes or less, where t1 is the oxidation induction time measured in an oxygen atmosphere at 200 DEG C, and t2 is the oxidation induction time measured in an oxygen atmosphere at 200 DEG C after 500 hours of moist heat treatment in an air atmosphere at 80 DEG C and 90% humidity.

Description

Styrene resin composition, molded product, and light guide plate

The invention relates to a styrene resin composition, its molded product and a light guide plate.

The backlight of the liquid crystal display device includes a direct type in which the light source is arranged on the front surface of the display device and an edge light type in which the light source is arranged on the side surface. In the edge light type, a member called a light guide plate that guides the light of a light source arranged on the side to the front of the display device is used. The material of the light guide plate uses acrylic resin represented by polymethyl methacrylate (PMMA). However, due to the high water absorption of PMMA, the light guide plate may warp or change in size due to water absorption. In addition, since it is easily thermally decomposed during molding, when molding at high temperature, the appearance of the molded body is likely to be poor. In order to improve these problems, it is proposed to use styrene-methyl (meth)acrylate copolymer as the material of the light guide plate (for example, refer to Patent Document 1). [Prior Art Literature] [Patent Document]

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

[Problems to be Solved by Invention]

The subject of the present invention is to provide a styrene-based resin composition having excellent moisture and heat resistance, a molded product thereof, and a light guide plate. [Technical means to solve the problem]

That is, the present invention is as follows: (1) A styrene-based resin composition, set the oxidation induction time measured in an oxygen atmosphere at 200°C as t1, set at 80°C and 90% humidity in an air atmosphere for 500 hours after wet heat treatment, and then at 200°C The oxidation induction time measured under an oxygen atmosphere is t2, and t1-t2 is less than 20 minutes. (2) The styrene resin composition according to (1), wherein the t1 is 50 minutes or more. (3) The styrene-based resin composition according to (1) or (2), which contains a hindered phenol-based antioxidant (B) and a phosphorus-based antioxidant (C2) that does not have a phenolic hydroxyl group. (4) The styrene resin composition according to any one of (1) to (3), which contains a styrene resin having a styrene monomer unit and a (meth)acrylate monomer unit ( A). (5) The styrene-based resin composition according to any one of (1) to (4), which contains a phosphorus-based antioxidant (C1) having a phenol-based hydroxyl group. (6) The styrene-based resin composition according to (3), wherein the hindered phenol-based antioxidant (B) is selected from octadecyl-3-(3.5-and -tert-butyl-4- Hydroxyphenyl) propionate, ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl) propionate], pentaerythritol tetra[3-(3,5) -Di-tert-butyl-4-hydroxyphenyl) propionate] at least one compound. (7) The styrene resin composition according to (3), wherein the phosphorus antioxidant (C2) is selected from 2,2'-methylenebis(4,6-di-tert-butyl Phenyl) at least one compound of 2-ethylhexyl phosphite and tris(2,4-di-tert-butylphenyl) phosphite. (8) The styrene-based resin composition described in (5), wherein the phosphorus-based antioxidant (C1) is 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl) ) Propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2] dioxaphosphepin. (9) The styrene-based resin composition according to any one of (1) to (8), wherein the YI value at an initial optical path length of 115 mm is 2.5 or less. (10) A molded article using the styrene resin composition described in any one of (1) to (9). (11) The light guide plate of the molded product described in (10) is used. [Effects of the invention]

According to the present invention, a styrene-based resin composition having excellent moisture and heat resistance, a molded product thereof, and a light guide plate are obtained.

"A-B" in this application specification means more than A and less than B.

The styrenic resin composition of the present invention has an oxidation induction time of t1 measured in an oxygen atmosphere at 200°C. It is subjected to wet heat treatment for 500 hours in an air atmosphere at 80°C and 90% humidity, and then measured in an oxygen atmosphere at 200°C. When the oxidation induction time is t2, t1-t2 is 20 minutes or less, preferably 15 minutes or less, and more preferably 10 minutes or less. If t1-t2 is in this range, the hue deterioration during storage in a high temperature and high humidity environment can be suppressed. In addition, although increasing the amount of antioxidant added helps to maintain the oxidation induction time, on the other hand, it will also adversely affect the hue. Therefore, when considering the balance, t1-t2 is preferably 1 minute or more, more preferably 2 minutes Above, more preferably 4 minutes or more. t1-t2 is, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 minutes. It can be a range between any two of the numerical values exemplified here.

t1 is preferably 50 minutes or more, more preferably 70 minutes or more, and still more preferably 90 minutes or more. When t1 is in this range, yellowing in a high temperature environment can be suppressed. Although increasing the amount of antioxidants can prolong the oxidation induction time, on the other hand it will also adversely affect the hue. Therefore, considering the balance, t1 is preferably 500 minutes or less, and more preferably 200 minutes or less.

The oxidation induction time is a value measured by the chemiluminescence method. Use the following conditions to measure the time change of the luminous amount of the styrene resin composition, and calculate the focal point between the straight line before the change in the luminous amount and the increase in the luminous amount as shown in Figure 1 by measuring the relationship between the time and the luminous amount time. The styrene resin composition is gradually oxidized after being heated in the presence of oxygen. When antioxidants are present in the sample, the antioxidants are gradually consumed due to oxidation, and a certain amount of luminescence is shown in the presence of antioxidants. When the antioxidants disappear, the resin itself is oxidized, and the luminescence will increase for a while. That is, the oxidation induction time means the time when the antioxidant is consumed and the oxidation of the resin composition progresses rapidly. Chemiluminescence analyzer: CLA-FS4 (manufactured by Tohoku Electronics Industry Co., Ltd.) Measuring temperature: 200℃ Oxygen flow rate: 100mL/min

The styrene resin composition of the present invention preferably contains a styrene resin (A), which is a copolymer of a styrene monomer and a (meth)acrylate monomer.

Styrenic monomers refer to aromatic vinyl monomers, which are styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, ethylstyrene, and p-tert-butyl Styrene alone or a mixture of two or more. Among these monomers, styrene is preferably used from the viewpoint of good hue.

(Meth)acrylate-based monomers refer to methacrylic acid of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate Ester, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, and decyl acrylate alone or a mixture of two or more. From the viewpoint of excellent hue and heat resistance, methyl (meth)acrylate is preferably used.

The styrene-based resin (A) preferably has a styrene-based monomer unit content of 20 to 80% by mass, and a (meth)acrylate ester-based monomer unit content of 80-20% by mass. The content is 30-60% by mass, and the content of (meth)acrylate monomer units is 70-40% by mass. If the content of the monomer unit is within this range, the water absorption rate and the deformation rate (water absorption) are low, and the warpage and dimensional change caused by moisture absorption can be suppressed, and the deterioration of the hue or the decrease of the surface hardness can be suppressed. Scratches.

The styrene-based resin (A) can be copolymerized with monomers other than (meth)acrylate-based monomers in a range of 5% by mass or less. The monomer to be copolymerized is a vinyl monomer copolymerizable with a styrene-based monomer and a (meth)acrylate-based monomer, which is 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-based resin can be measured under the following conditions by thermal decomposition gas chromatography. Pyrolysis furnace: PYR-2A (manufactured by Shimadzu Corporation) Pyrolysis furnace temperature setting: 525℃ Gas chromatograph: GC-14A (manufactured by Shimadzu Corporation) Column: 3mm×3m in diameter made of glass Filler: FFAP "Chromsorb" WAW Column temperature: 120℃ Carrier gas: nitrogen

As a manufacturing method of the styrene-based resin, it can be manufactured by known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. As the operation method of the reaction device, any one of continuous type, batch type (batch type), and batch type can be applied. From the viewpoint of quality aspects such as transparency and productivity, bulk polymerization or solution polymerization is preferable, and continuous type is preferable. As a solvent for bulk polymerization or solution polymerization, alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.

The polymerization method of styrene resin can adopt a well-known method. The radical polymerization method is preferred because of its simple process and excellent productivity.

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

The polymerization initiator is benzoyl peroxide, tert-butyl peroxybenzoate, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)-3,3 ,5-Trimethylcyclohexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,2-bis(4,4-di-tert-butyl Peroxycyclohexyl) propane, tert-butylperoxyisopropyl carbonate, dicumyl peroxide, tert-butylcumyl peroxide, tert-butyl peroxyacetate, tert-butylperoxy-2-ethyl Organic peroxides such as hexanoate, polyether tetra(tert-butyl peroxycarbonate), 3,3-bis(tert-butylperoxy) ethyl butyrate, tert-butyl peroxyisobutyrate.

The addition amount of the polymerization initiator is preferably 0.0001 to 0.2% by mass, and more preferably 0.0001 to 0.05% by mass relative to 100% by mass of the total monomers. When the addition amount of the polymerization initiator is too large, the hue deteriorates.

Chain transfer agents are aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer and terpinolene.

The addition amount of the chain transfer agent is preferably 0.0001 to 0.5% by mass relative to 100% by mass of the total monomers, more preferably 0.005 to 0.2% by mass. When the addition amount of the chain transfer agent is 0.001 to 0.5% by mass, the thermal stability becomes good.

The devolatilization method for removing volatile components such as unreacted monomers and solvents suitable for solution polymerization from the solution after the polymerization of the styrene-based resin can be performed by a known method. For example, a vacuum devolatilization tank equipped with a preheater or Devolatilization extruder with vent. The temperature of the styrene-based resin in the devolatilization step is preferably 200°C to 300°C, and more preferably 220°C to 260°C. When the temperature of the styrene-based resin in the devolatilization step is too high, the hue may be deteriorated. The styrenic resin in the molten state after devolatilization is transferred to the granulation process, and extruded into strands with a porous mold, and processed into pellets by cold cutting, air cutting, and water cutting.

Preferably, the unreacted monomers removed in the devolatilization step and the solvent used in the solution polymerization are recovered, and after purification and removal of impurities such as polymerization inhibitors, they are mixed and used as recovered raw materials with fresh raw materials. By mixing recycled raw materials with fresh raw materials that do not contain polymerization inhibitors, the content of polymerization inhibitors in the raw materials supplied to the polymerization step can be reduced. 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. When the content of the polymerization inhibitor in the raw material supplied to the polymerization step is less than 12 ppm, the light transmittance and transparency become good. It should be noted that it is difficult to remove all polymerization inhibitors and usually contains more than 0.01 ppm. In order to distinguish it from recycled raw materials, the raw materials newly supplied to the production process of the styrene-(meth)acrylate copolymer are referred to as fresh raw materials here.

The removal of unreacted monomers in the devolatilization step and the recovery and purification of the solvent used in the solution polymerization can be performed by known methods. For example, the unreacted monomers and solvent gases removed in the devolatilization step can be condensed. It is a method of compressing and liquefying by machine and using a flash tower to refine and separate high-boiling components. In addition, it is also possible to first condense and separate only the high boiling point components from the unreacted monomer and solvent gas removed in the devolatilization step with a condenser or spray tower, and then condense the remaining gas as a whole with a condenser . The boiling point of 4-tert-butyl diphenol, which is a polymerization inhibitor, is 285°C, and the boiling point of 6-tert-butyl-2,4-xylenol is 249°C, so it can be extracted from monomers and solvents that are high boiling point components. Separate and remove (the boiling point of styrene is 145°C, the boiling point of methyl (meth)acrylate is 101°C, and the boiling point of ethylbenzene is 136°C).

The weight average molecular weight (Mw) of the styrene resin is preferably 50,000 to 450,000, more preferably 70,000 to 300,000, and still more preferably 70,000 to 200,000. 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 decreases and the molding processability deteriorates. The weight average molecular weight (Mw) can be controlled according to the reaction temperature, residence time, type and amount of polymerization initiator in the polymerization process, type and amount of chain transfer agent, and type and amount of solvent used during polymerization.

The weight average molecular weight (Mw) can be measured using gel permeation chromatography (GPC) under the following conditions. GPC model: Shodex from Showa Denko Co., Ltd. GPC-01 Column: "PLGel" 10μm" MIXED-B made by Polymer" Labatories 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 at each elution time from the elution curve of monodisperse polystyrene, which is calculated by the molecular weight in terms of polystyrene.

The total amount of the residual monomers of the styrene resin and the polymerization solvent is preferably 0.5% by mass or less, and more preferably 0.2% by mass. When the total amount of residual monomers and polymerization solvent exceeds 0.5% by mass, heat resistance is insufficient.

Residual monomer and polymerization solvent are the amounts of monomer and polymerization solvent remaining in the styrene-based resin, which are styrene, methyl (meth)acrylate, ethylbenzene, and the like. The amount of the residual monomer and the polymerization solvent can be adjusted by the configuration of the devolatilization step or the conditions of the devolatilization step.

The amount of residual monomer and polymerization solvent was accurately weighed 0.2g of styrene-based resin, and dissolved in 10mL of tetrahydrofuran containing p-diethylbenzene as an internal standard substance, and then used capillary gas chromatograph under the following conditions Determination. Capillary gas chromatograph: GC-4000 (manufactured by GL "Sciences" Inc.) Column: GL 　 Sciences 　 Inc. The manufactured InertCap "WAX, the inner diameter is 0.25mm, the length is "30m, and the film thickness is "50μm Injection temperature: 180℃ Column temperature: 60℃～170℃ Detector temperature: 210℃ Split ratio: 5/1

Dimers or trimers of styrene-based monomers and (meth)acrylate-based monomers (hereinafter referred to as oligomers) of styrene resin %the following. 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-based resin in 2 mL of 1,2-dichloromethane, adding 2 mL of methanol to precipitate the copolymer and letting it stand, and then measure the supernatant with a gas chromatograph under the following conditions Liquid obtained. 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 styrene-based resin composition of the present invention preferably contains a hindered phenol-based antioxidant (B). The hindered phenolic antioxidant (B) contained in the styrene resin composition is an antioxidant having a phenolic hydroxyl group in the basic skeleton. The hindered phenol antioxidants are 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-methylphenyl)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]-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'-butylene bis(3-methyl-6-tert-butylphenol), bis-[3,3-bis-(4'-hydroxy-3'-tert-butylphenol)-butane Acid]-ethylene glycol ester, 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2-[1-( 2-hydroxy-3,5-di-tert-butylphenyl) ethyl]-4,6-di-tert-amyl phenyl acrylate, etc. The hindered phenol antioxidants can be used alone or in combination of two or more.

The content of the hindered phenol-based antioxidant (B) is preferably 0.0001 to 0.3 parts by mass relative to 100 parts by mass of the styrene resin (A), more preferably 0.03 to 0.09 parts by mass. By adjusting the content of the hindered phenol-based antioxidant (B) within this range, a styrene-based resin composition having an excellent hue can be obtained.

The styrene resin composition of the present invention preferably contains a phosphorus antioxidant (C1) having a phenolic hydroxyl group. The phosphorus antioxidant (C1) contained in the styrene resin composition is a trivalent phosphorus compound having a phenolic hydroxyl group in the basic skeleton. Phosphorus antioxidant (C1) has the property of being easily hydrolyzed compared with other phosphorus antioxidants, so the obtained styrene resin composition has a high hue improvement effect. Phosphorus antioxidant (C1) is 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyl two Benzo [d, f] [1, 3, 2] dioxaphosphorane etc.

The content of the phosphorus antioxidant (C1) is preferably 0.0001 to 0.3 parts by mass relative to 100 parts by mass of the styrene resin (A), more preferably 0.03 to 0.09 parts by mass, and still more preferably 0. .05～0.08 parts by mass. By adjusting the content of the phosphorus antioxidant (C1) within this range, a styrene resin composition with excellent hue can be obtained.

The styrene resin composition of the present invention preferably contains a phosphorus antioxidant (C2) other than the phosphorus antioxidant (C1) having a phenolic hydroxyl group. The phosphorus antioxidant (C2) contained in the styrene resin composition is a trivalent phosphorus compound without a phenolic hydroxyl group in the basic skeleton. Phosphorus antioxidant (C2) is more difficult to hydrolyze than phosphorus antioxidant (C1), but it can maintain the effect of improving the color of the styrene resin composition for a long time. In other words, it contributes particularly to heat and humidity resistance. Phosphorus antioxidant (C2) is 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxazole-3,9-bis Phosaspiro[5.5]undecane, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, 2,2'-methylenebis(4,6-di-tert-butylbenzene) Base) 2-ethylhexyl phosphite, tris(2,4-di-tert-butylphenyl) phosphite, bis[2,4-bis(1,1-dimethylethyl)- 6-methylphenyl] ethyl ester, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, cycloneopentane tetrayl bis(octadecyl phosphite), bis(nonane) (Phenyl) pentaerythritol diphosphite, 4,4'-biphenyl diphosphite tetrakis (2,4-di-tert-butyl phenyl ester), 9,10-dihydro-9-oxa-10-phosphorus Phenanthrene-10-oxide, tetrakis(2,4-di-tert-butyl-5-methylphenyl)-4,4'-biphenyl diphosphonite, etc., from the viewpoint of continuous improvement of hue effect Preferably, 2,2'-methylene bis(4,6-di-tert-butylphenyl) 2-phosphite and tris(2,4-di-tert-butylphenyl) phosphite are used. Phosphorus antioxidants (C2) can be used alone or in combination of two or more.

The content of the phosphorus antioxidant (C2) is preferably 0.0001 to 0.3 parts by mass relative to 100 parts by mass of the styrene resin (A), more preferably 0.03 to 0.09 parts by mass, and still more preferably 0. .05～0.08 parts by mass. By adjusting the content of the phosphorus antioxidant (C2) within this range, a styrene resin composition having an excellent hue from the initial stage to the long term can be obtained.

The mixing ratio of the phosphorus antioxidant (C1) and the phosphorus antioxidant (C2) is preferably in the range of 3:1 to 1:3, and more preferably 2:1 to 1:2. By adjusting to this range, the balance between the hue and durability of the obtained styrene-based resin composition becomes better.

A known method can be adopted for the method of manufacturing the styrene resin composition. Hindered phenol antioxidants (B), phosphorus antioxidants (C1), and phosphorus antioxidants (C2) are added to the production processes such as the polymerization process, devolatilization process, and granulation process of the styrene resin. In the volatilization step, unreacted monomer and solvent are removed and then added. When using a vacuum devolatilizer, add molten hindered phenol antioxidant (B), phosphorus antioxidant (C1) and phosphorus antioxidant (C2) to the styrene resin extracted from the devolatilizer. And use a static mixer to mix, when using a devolatilization extruder with a vent, add hindered phenol antioxidant (B), phosphorus antioxidant (C1) and phosphorus antioxidant (C2) behind the vent ) And make it mixed. Using an extruder, it is possible to melt-mix hindered phenol-based antioxidants (B), phosphorus-based antioxidants (C) and phosphorus-based antioxidants (C2) into the pelletized styrene-based resin (A).

As long as the transparency is not impaired, mineral oil may be added to the styrene resin composition. In addition, internal lubricants such as stearic acid and ethylene bis-hard amide can be added; sulfur-based antioxidants, lactone-based antioxidants, ultraviolet absorbers, hindered amine-based stabilizers, antistatic agents, and ethylene double External lubricants such as stearylamine.

Ultraviolet absorbers are additives that have the function of inhibiting deterioration or coloring caused by ultraviolet rays, and are benzophenone series, benzotriazole series, triazine series, benzoate series, salicylate series, and cyanoacrylic acid Ester-based, malonate-based, and formamidine-based ultraviolet absorbers. These can be used alone or in combination of two or more, and can also be used in combination with light stabilizers such as hindered amines.

The Vicat softening point of the styrene resin is preferably 95°C or higher, and more preferably 98°C or higher. When the Vicat softening point is lower than 95°C, the heat resistance is insufficient, and the molded product may be deformed depending on the use environment. (The Vicat softening temperature is tested according to JIS "K" 7206 with a heating rate of 50°C/hr and a test load of 50N.)

The styrene-based resin composition can be used by producing a plate-shaped molded product by a known method such as extrusion molding, injection molding, compression molding, and blow molding, and processing it into a light guide plate.

The styrene-based resin composition of the present invention has excellent thermal stability, so non-product parts such as chips during extrusion molding, bobbins and runners during injection molding can be collected and crushed, and then mixed with original materials use.

The light guide plate is a member that guides the light incident from the end surface of the plate-shaped molded product to the surface side of the plate-shaped molded product by forming a reflective pattern on one side surface of the plate-shaped molded product and makes it have light-emitting performance. The reflective pattern can be formed by methods such as screen printing, laser processing, and inkjet. In addition, a prism pattern or the like may be provided on the surface (light emitting surface) opposite to 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, can be formed by a mold shape during injection molding, or formed by roll transfer during extrusion molding.

The YI value measured at an optical path length of 115 mm at the initial stage of the styrene-based resin composition is preferably 2.5 or less, and more preferably 2.0 or less. The so-called "initial stage" here refers to the state before the wet heat treatment is performed for 500 hours in an air atmosphere of 80°C and 90% humidity. The measurement is performed by measuring the spectral transmittance at the wavelength of 350nm～800nm under the light path length of 115mm, and the YI value in the 2° field of view of the C light source is calculated according to JIS 　 K7105. When the YI value measured with the optical path length of 115mm is higher than 2.5, the color changes with the optical path length, so when used as a backlight, color unevenness may occur on the surface of the liquid crystal display device. In addition, it is preferable that the average value of the spectral transmittance at a wavelength of 350 nm to 800 nm measured at an optical path length of 115 mm is 87% or more, more preferably 88% or more, and still more preferably 89% or more. [Example]

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

<Production example of styrene resin A-1> Styrenic resins are produced by continuous solution polymerization and the free radical method. A complete mixing tank type stirring tank is used as the first reactor, and a plug flow type reactor equipped with a static mixer is used as the second reactor, which are connected in series to form the polymerization process. The capacity of the first reactor is 30L, and the capacity of the second reactor is 12L. As a styrene-based monomer, when preparing styrene for industrial use (hereinafter referred to as fresh Sty), the concentration of 4-tert-butylcatechol (hereinafter referred to as TBC) is 10.2 ppm. As a (meth)acrylate-based monomer, when preparing methyl (meth)acrylate for industrial use (hereinafter referred to as fresh MMA), 6-tert-butyl-2,4-xylenol (hereinafter referred to as The concentration of TBX) is 4.9 ppm. As a polymerization solvent, ethylbenzene (hereinafter referred to as fresh EB) used in industry is prepared. In addition, gases such as monomers and polymerization solvents separated from a vacuum devolatilization tank to be described later are condensed by a condenser and purified by a flash tower or the like to be used as recycled raw materials. The concentration of TBX and TBC in the recycled raw materials is lower than the detection limit. Using fresh Sty, fresh MMA, and recycled raw materials, a raw material solution was prepared in accordance with the composition of Sty: 49% by mass, MMA: 41% by mass, and EB: 10% by mass, and was supplied to the polymerization process at a flow rate of 8.0 kg/h. The use ratio of recycled raw materials in the raw material solution is 33% by mass. In addition, the raw material solution was continuously added to the raw material solution supply line so that the concentration of tert-butylperoxyisopropyl monocarbonate as the polymerization initiator was 150 ppm, and the concentration of n-dodecyl mercaptan as the chain transfer agent The concentration is 500 ppm. Adjust the temperature of the first reactor to 135°C, form a temperature gradient along the flow direction in the second reactor, and adjust the middle part to 130°C and the outlet part to 145°C. The polymer concentration at the exit of the polymerization process is 65%, and the conversion rate of styrene to methyl (meth)acrylate is 72%. The polymer solution continuously extracted from the reactor is supplied to a vacuum devolatilizer equipped with a preheater, and unreacted styrene, methyl (meth)acrylate, ethylbenzene, etc. are separated. Adjust the temperature of the preheater so that the polymer temperature in the devolatilization tank is 240°C and the pressure in the devolatilization tank is 1kPa. The polymer was extracted from the vacuum devolatilization tank by a gear pump, extruded into strands, cooled with cooling water, and cut to obtain pelletized styrene resin A-1. The composition of A-1 is Style: 50% by mass and MMA: 50% by mass. In addition, the weight average molecular weight of A-1 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 0.35% by mass.

<Production example of styrene resin A-2> The composition of the raw materials was changed to Type: 77% by mass, MMA: 13% by mass, and EB: 10% by mass, the addition of n-dodecyl mercaptan was stopped, and the temperature of the first reactor was set to 140°C, and the second reactor The temperature of the middle part of the A-1 is set to 140°C, and the temperature of the outlet part is set to 160°C, which is implemented in the same manner as A-1. The use ratio of recycled raw materials in the raw material solution is 33% by mass. The composition of A-2 is Style: 82% by mass and MMA: 18% by mass. In addition, the weight average molecular weight of A-2 was 240,000, the total amount of residual monomers and polymerization solvent was 0.06% by mass, and the total amount of residual oligomers was 0.33% by mass.

<Production example of styrene resin A-3> The composition of the raw materials was changed to Type: 8% by mass, MMA: 79% by mass, and EB: 13% by mass, and the feed flow rate was set to 5.7 kg/h, and the concentration of peroxyisopropyl tert-butyl monocarbonate was set The concentration of n-dodecyl mercaptan is set to 3,000 ppm, the temperature of the first reactor is set to 122°C, the temperature of the middle part of the second reactor is set to 140°C, and the temperature of the outlet part is set to other than 150°C , Implement in the same way as A-1. The use ratio of recycled raw materials in the raw material solution is 34% by mass. The composition of A-3 is System: 10% by mass and MMA: 90% by mass. In addition, the weight average molecular weight of A-3 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.

<Examples 1 to 10, Comparative Example 1, Reference Examples 1 to 2> The styrene-based resins A-1 to A-3 obtained in the production example were reduced in content as shown in Table 1. The hindered phenol-based antioxidant (B), phosphorus-based antioxidant (C1), and phosphorus-based antioxidant ( C2-1), (C2-2), and use a sheet extruder manufactured by LEADER to melt and knead antioxidants to obtain a sheet-like molded product of 450mm×500mm×2mm. The sheet extruder is composed of a 50mmφ single-screw extruder, a T-die, and 3 mirror rollers. The sheet extruder is carried out under the condition that the barrel temperature of the single-screw extruder is 225℃ and the number of screw rotations is 120 rpm. The width of the T-die is 450mm and the opening is 3mm. (B) Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate" (Irganox 1076 manufactured by BASF Japan) (C1) 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d, f] [1, 3, 2] Dioxaphos heptacyclic (Sumilizer GP manufactured by Sumitomo Chemical Co., Ltd.) (C2-1) 2,2'-methylenebis(4,6-di-tert-butylphenyl) 2-ethylhexyl phosphite (Adekastab, HP-10 manufactured by ADEKA Co., Ltd.) (C2-2) (2,4-Di-tert-butylphenyl) phosphite ("Irgafos" 168 manufactured by BASF Japan)

(Oxidation induction time) A 30mm×30mm×2mm thick test piece was cut out of the obtained sheet-like molded product, and the luminescence was measured using a chemiluminescence analyzer CLA-FS4 manufactured by Tohoku Electronics Industry Co., Ltd. at 200°C and an oxygen flow rate of 100 mL/min. According to the relationship between the measurement time and the amount of luminescence, use the method shown in Figure 1 to obtain the oxidation induction time. The oxidation induction time (t1) of the sheet-shaped molded product just extruded and the oxidation induction time (t2) of the sheet-shaped molded product after being heat-treated for 500 hours in an air atmosphere at 80°C and 90% humidity are shown in Table 1. Shown. It should be noted that the amount of luminescence continued to increase immediately after the start of the measurement in Reference Example 1 and Reference Example 2, so the oxidation induction time cannot be measured.

(Optical characteristics under the light path length of 115mm) A 115mm×85mm×2mm thick test piece was cut out from the obtained sheet-shaped molded product, and the end surface was polished to produce a plate-shaped molded product with a mirror surface on the end surface. Using the UV-Vis spectrophotometer V-670 manufactured by JASCO Corporation, the polished plate-shaped molded product has a size of 20×1.6mm, an incident light diffusion angle of 0°, and a wavelength of 350nm under the light path length of 115mm. The spectral transmittance was measured in the range of 800 nm, and the YI value was calculated according to the JIS 　 K 7373 within the 2° field of view at the C light source. The light transmittance shown in Table 1 represents the average light transmittance at a wavelength between 380nm and 780nm. Sheet-shaped molded products that have just been extruded (initial stage), sheet-shaped molded products that have been heat-treated for 500 hours in an air atmosphere of 80°C and 90% humidity, and sheets that have been stored for 1,000 hours at 80°C The measurement results of shaped molded products are shown in Table 1.

(Water absorption) The obtained sheet-shaped molded product was cut 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 change of the long sides were measured as an index of water absorption, and the water absorption and deformation rate were calculated using the following formula. (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 (%) The evaluation results are shown in Table 1. The case where the water absorption rate is 1.0 or less is judged as good, and the case where the deformation rate is less than 0.30 is judged as good.

[產業上的可利用性][Table 1]

[Industrial availability]

The styrene-based resin composition of the present invention and its molded article have excellent heat and humidity resistance, and the hue and transparency are not easily deteriorated, so it can be applied to televisions, desktop computers, notebook computers, mobile phones, car navigation systems, and indoor lighting Light guide plate.

[Figure 1] A conceptual diagram of a method for determining the oxidation induction time by chemiluminescence (Chemiluminencescence 　method).

Claims (11)

A styrene resin composition, Suppose the oxidation induction time measured under an oxygen atmosphere at 200°C is t1, After 500 hours of wet heat treatment is performed in an air atmosphere of 80°C and 90% humidity, the oxidation induction time measured in an oxygen atmosphere of 200°C is t2, and t1-t2 is less than 20 minutes. The styrene resin composition according to claim 1, wherein The t1 is more than 50 minutes. According to the styrene resin composition described in claim 1 or 2, Contains hindered phenolic antioxidant (B) and phosphorus antioxidant (C2) without phenolic hydroxyl. According to the styrene resin composition described in claim 1 or 2, Contains styrene resin (A) having styrene monomer units and (meth)acrylate monomer units. According to the styrene resin composition described in claim 1 or 2, Contains phosphorus antioxidants (C1) with phenolic hydroxyl groups. According to the styrene resin composition described in claim 3, The hindered phenol-based antioxidant (B) is selected from octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, ethylenebis(oxyethylene) Bis[3-(5-tert-butyl-4-hydroxy-m-tolyl) propionate], pentaerythritol tetra[3-(3.5-di-tert-butyl-4-hydroxyphenyl) propionate] At least one compound in. The styrene resin composition according to claim 3, wherein The phosphorus antioxidant (C2) is selected from 2,2'-methylene bis(4,6-di-tert-butylphenyl) 2-ethylhexyl phosphite, tris(2,4-di -At least one compound of tert-butyl phenyl) phosphite. The styrene resin composition according to claim 5, wherein The phosphorus antioxidant (C1) is 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyl Base dibenzo [d, f] [1, 3, 2] dioxaphosphorane. According to the styrene resin composition described in claim 1 or 2, The YI value under the initial light path length of 115mm is 2.5 or less. A molded article using the styrene resin composition described in any one of claims 1 to 9. A light guide plate using the molded product described in claim 10.

Images