KR20140107474A - Styrene-based optical resin composition - Google Patents

Abstract

An object of the present invention is to provide a transparent styrenic resin composition capable of suppressing the problem (whitening phenomenon) that the molded article becomes opaque due to environmental changes such as temperature, humidity and hot water immersion, which are shortcomings of the styrenic resin. According to the present invention, there is provided a styrenic resin composition comprising a styrenic resin having a weight average molecular weight of 150,000 to 700,000 and a hydrophilic additive, wherein the hydrophilic additive is a polyoxyethylene surfactant having an average addition mole number of ethylene oxide of 3 to 150 And polyethylene glycol having an average molecular weight of 200 to 10000, an HLB value of 5 to 20, and a content of the styrene type resin composition in 100 mass% of 0.4 to 2.0 mass% Styrene-based resin composition.

Description

STYRENE-BASED OPTICAL RESIN COMPOSITION [0002]

The present invention relates to a transparent styrene resin composition in which whitening due to environmental changes is suppressed.

The styrenic resin has excellent properties such as transparency, rigidity, low water absorption and dimensional stability, and is excellent in molding processability. Therefore, the styrenic resin can be produced by various molding methods such as injection molding, extrusion molding, blow molding, Packaging containers, miscellaneous goods, and the like. Further, it is used for an optical member such as a light guide plate as an application utilizing transparency.

A backlight of a liquid crystal monitor has a direct light type backlight in which a light source is disposed on the front surface of a display device and an edge light type backlight disposed on a side surface. The light guide plate is assembled in an edge light type backlight and serves to guide light from the side to the liquid crystal panel and is used for a wide range of purposes such as a television, a desktop personal computer monitor, a notebook personal computer, a mobile phone, and a car navigation do. An acrylic resin typified by PMMA (polymethylmethacrylate) is used for the light guide plate, however, since the absorbency is high, warpage may occur in the molded article or a change may occur in dimensions.

Therefore, it has been proposed to use an MS resin which is a copolymer of styrene and methyl (meth) acrylate, which has improved these properties. Patent Document 1 has been proposed as an improvement technique such as absorbency of MS resin and discoloration at the time of formation.

However, Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of 6-17,000, a residual monomer content of 3,000 ppm or less, and an oligomer content of 2% or less in the styrene- (meth) acrylic acid ester copolymer resin. It is high and the dimensional stability tends to be worse than that of the styrene type resin using the styrene-based monomer as a raw material.

On the other hand, the styrene type resin having the styrene-based monomer as a raw material has a low water absorption property. However, the styrene type resin is contaminated with white turbidity due to environmental changes such as temperature, humidity and hot water immersion (non-patent document 1) ) (Whitening phenomenon), and transparency, which is advantageous depending on applications, may be impaired. Specifically, when the molded article is exposed to a change in environment to a room temperature environment or a change in environment to a low-temperature environment under a high-temperature and high-humidity environment, the water uniformly present in the styrene-based resin becomes unstable, And defects in a disk shape are generated, and as a result, the inside of the molded article is cloudy. Further, after a molded article of a styrenic resin is immersed in hot water for a certain period of time or more, the molded article may be whitened by taking it out, which is also a phenomenon caused by the same mechanism.

When the molded article becomes opaque, when the optical path length is long like the light guide plate, the light transmittance is significantly lowered due to light scattering, and the brightness of the display is lowered.

[Patent Document 0001] Japanese Unexamined Patent Publication No. 2003-075648

[Non-Patent Document 0001] Textile Journal, Vol. 34, No. 6, pp. 245-253, 1978

Disclosure of the Invention It is an object of the present invention to provide a transparent styrene resin composition which suppresses whitening due to environmental changes.

According to the present invention, there is provided a styrenic resin composition comprising a styrenic resin having a weight average molecular weight of 150,000 to 700,000 and a hydrophilic additive, wherein the hydrophilic additive is a polyoxyethylene surfactant having an average addition mole number of ethylene oxide of 3 to 150 And polyethylene glycol having an average molecular weight of 200 to 10000, an HLB value of 5 to 20, and a content of the styrene type resin composition in 100 mass% of 0.4 to 2.0 mass%. Styrene-based resin composition.

The inventors of the present invention have made extensive studies in order to suppress whitening due to environmental changes, and it has been found that the addition of a hydrophilic additive first is effective in suppressing the whitening phenomenon. However, as a result of further investigation, it has been found that the addition of only a hydrophilic additive may not be sufficient. Thus, the present inventors have further investigated whether the hydrophilic additive has a characteristic configuration, (2) its HLB value is within a specified range, and (3) its content is in a specified range, The heat resistance of the resin composition is maintained, the effect of suppressing the whitening phenomenon is remarkably enhanced, and the transparency of the styrene resin is not impaired. Although the effect of obtaining such an effect is not disclosed at all, it is believed that the effect is exerted only when the above-mentioned three conditions are coincident with each other.

Hereinafter, various embodiments of the present invention will be exemplified.

Preferably, the hydrophilic additive is a polyoxyethylene type surfactant having an average addition mole number of ethylene oxide of 10 to 60, and a content of the surfactant in 100 mass% of the styrene type resin composition is 0.6 to 1.4 mass%.

Preferably, the hydrophilic additive is a polyoxyethylene type surfactant having an average addition mole number of ethylene oxide of 13 to 35, and a content of the surfactant in 100 mass% of the styrene type resin composition is 0.6 to 0.9 mass%.

Preferably, the hydrophilic additive has an HLB value of 10 to 18.

Preferably, the polyoxyethylene type surfactant is a polyoxyethylene type nonionic surfactant.

Preferably, the polyoxyethylene type nonionic surfactant is at least one kind selected from the group consisting of polyoxyethylene alkyl ethers represented by the following general formula (1) and / or polyoxyethylene fatty acid esters represented by the following general formula (2) to be.

(Wherein R represents an alkyl group having 8 to 20 carbon atoms), polyvalent polyoxyethylene alkyl ether having a maximum of six polyvalent polyoxyethylene alkyl ether skeletons, polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent polyvalent poly N is an integer, and represents the number of moles of ethylene oxide units added.)

Preferably, the hydrophilic additive is a polyethylene glycol having an average molecular weight of 200 to 10,000, and the content of the hydrophilic additive in 100% by mass of the styrene-based resin composition is 0.6 to 1.4% by mass.

Preferably, the hydrophilic additive is a polyethylene glycol having an average molecular weight of 200 to 1800.

Preferably, the hydrophilic additive has a content of 0.6 to 0.9% by mass in 100% by mass of the styrene resin composition.

(Meth) acrylic acid copolymer resin obtained by copolymerizing a styrene type monomer with (meth) acrylic acid, wherein the content of the styrene type monomer unit in the styrene type resin is 90.0 to 99.9 mass%, the content of the (meth) acrylic acid Unit content is 0.1 to 10.0 mass%. However, the total content of the styrene-based monomer unit and the (meth) acrylic acid unit in the styrene-based resin is set at 100% by mass.

The styrene-based (meth) acrylic ester copolymer resin obtained by copolymerizing a styrene type monomer with a (meth) acrylic acid ester is preferably a styrene type resin having a content of styrene type monomer units of 40.0 to 99.0 mass% ) Acrylate unit content is 1.0 to 60.0 mass%. However, the total content of the styrene-based monomer unit and the (meth) acrylate unit of the styrene-based resin is 100% by mass.

Further, it is also possible to synthesize 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra- , 3, 2] dioxaphosphpine.

Further, it includes a phosphorus antioxidant and / or a hindered phenol antioxidant.

Further, it is a molded article comprising the optical styrene resin composition.

Further, it is a light guide plate made of the above molded article.

INDUSTRIAL APPLICABILITY The styrenic resin composition of the present invention is low in absorbability and inexpensiveness as compared with PMMA and MS resins and does not cause whitening due to environmental changes which are defects of styrenic resins and has excellent colorless transparency. Can be suitably used for applications taking advantage of transparency.

Hereinafter, embodiments of the present invention will be described in detail.

 << Styrene resin >>

The styrene resin of the present invention can be obtained by polymerizing a styrene-based monomer. The styrene-based monomer is an aromatic vinyl-based monomer such as styrene,? -Methylstyrene, o-methylstyrene, p-methylstyrene, or a mixture of two or more thereof, preferably styrene. In addition, it may be copolymerized with a styrenic monomer within the range not impairing the characteristics of the present invention. Examples of the monomer include acrylic acid monomers such as acrylic acid and methacrylic acid, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, Acrylic monomers such as ethyl acrylate, methyl acrylate and methyl methacrylate, and imide-based monomers such as α, β-ethylenically unsaturated carboxylic acids such as maleic anhydride and fumaric acid, phenylmaleimide and cyclohexylmaleimide.

The styrene resin composition is preferably composed of a styrene resin and various additives, and the proportion of the styrene resin in 100 mass% of the styrene resin composition is, for example, 90 to 99.6 mass% and 95 to 99.6 mass% desirable. Specifically, the ratio of the styrene resin is, for example, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.6 mass% It may be in the range.

(Meth) acrylic acid copolymer resin obtained by copolymerizing a styrene type monomer with (meth) acrylic acid, the content of the styrene type monomer unit in the styrene type resin is 90.0 to 99.9 mass%, the content of the (meth) acrylic acid unit The content is preferably 0.1 to 10.0 mass%. However, the total content of the styrene-based monomer unit and the (meth) acrylic acid unit is set at 100% by mass. (Meth) acrylic acid is acrylic acid, methacrylic acid, etc., and methacrylic acid is preferable.

The content of the (meth) acrylic acid unit in the styrene resin is measured at room temperature. 0.5 g of the styrene resin was weighed, dissolved in a mixed solution of toluene / ethanol = 8/2 (volume ratio), neutralized and titrated with a 0.1 mol / L ethanol solution of potassium hydroxide and the end point was detected. The amount of the potassium hydroxide ethanol solution , The content based on the mass of the (meth) acrylic acid unit is calculated. On the other hand, a potentiometric automatic titrator can be used and can be measured by AT-510 manufactured by Kyoto Electronics Industry Co., Ltd. The content of the (meth) acrylic acid unit in the styrene-based resin can be adjusted by the composition ratio of the styrene-based monomer and the (meth) acrylic acid monomer as raw materials in the polymerization of the styrene-based resin, (Meth) acrylic acid unit and a styrene-based resin containing no (meth) acrylic acid unit may be mixed and adjusted.

(Meth) acrylic ester copolymer resin obtained by copolymerizing a styrene type monomer with a (meth) acrylic acid ester, the content of the styrene type monomer unit in the styrene type resin is 40.0 to 99.0 mass%, the content of the (meth) acrylic acid It is preferable that the ester unit content is 1.0 to 60.0 mass%. However, the total content of the styrene-based monomer unit and the (meth) acrylate unit is 100% by mass. (Meth) acrylic acid esters include methacrylic acid esters such as methyl methacrylate and ethyl methacrylate; and acrylic esters such as methyl acrylate and ethyl acrylate.

The content of the (meth) acrylic acid ester unit in the styrene resin can be measured by pyrolysis gas chromatography under the following conditions.

Pyrolysis furnace: PYR-2A (manufactured by Shimadzu Corporation, manufactured by Shimadzu Corporation)

Pyrolysis furnace temperature setting: 525 ℃

Gas chromatograph: GC-14A (manufactured by Shimazu Seisakusho Co., Ltd.)

Column: Glass 3mm diameter × 3m

Filler: FFAP Chromsorb WAW 10%

Injection, detector Temperature: 250 ° C

Column temperature: 120 DEG C

Carrier gas: nitrogen

As the polymerization method of the styrene type resin, known styrene polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization can be mentioned. From the viewpoints of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization is preferred. As the solvent, for example, alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane can be used.

In the polymerization of the styrenic resin, a polymerization initiator and a chain transfer agent may be used if necessary. As the polymerization initiator, a radical polymerization initiator is preferable, and examples of known generators include 1,1-di (t-butylperoxy) cyclohexane, 2,2- Propane, 1,1-di (t-amylperoxy) cyclohexane and the like, cumene hydroperoxide, t-butyl hydroperoxide, Hydroperoxides such as peroxide, peroxide, and the like, alkyl peroxides such as t-butyl peroxyacetate and t-amylperoxy isononanoate, tertiary butyl peroxides such as t-butyl cumyl peroxide, Di-t-hexyl peroxide, peroxy esters such as t-butyl peroxyacetate, t-butyl peroxybenzoate and t-butyl peroxyisopropyl monocarbonate, t- Butyl peroxy isopropyl carbonate, polyether tetrakis (t-butyl peroxycarbonate), and other peroxycarbone Azo compounds such as N, N'-azobis (cyclohexane-1-carbonitrile), N, N'-azobis (2-methylbutyronitrile) Nitrile), and N, N'-azobis [2- (hydroxymethyl) propionitrile]. These may be used alone or in combination of two or more. Examples of the chain transfer agent include aliphatic mercaptans, aromatic mercaptans, pentaphenyl ethane, alpha -methylstyrene dimer, and terpinolene.

In the case of continuous polymerization, the polymerization reaction is controlled by adjusting the polymerization temperature so as to achieve the target molecular weight, the molecular weight distribution, and the conversion conversion, using a fully mixed molding (mixing tank type) stirring tank or a tower reactor known in the polymerization process. The polymerization solution containing the polymer subjected to the polymerization process is transferred to a devolatilization process, and the unreacted monomer and the polymerization solvent are removed. The devolatilization process consists of a vacuum devitrification vessel equipped with a heater or a devolatilization extruder equipped with a vent. The molten polymer undergoing the devolatilization process is transferred to a granulation process. In the assembling step, a molten resin is extruded from a porous die into a strand shape, and processed into a pellet shape by a cold-cut method, an aerial hot-cut method, or an underwater hot-cut method.

The weight average molecular weight of the styrenic resin of the present invention is preferably 150,000 to 700,000, and preferably 180,000 to 500,000. When it is less than 150,000, the strength of the molded product is insufficient, and when it exceeds 70,000, the moldability remarkably decreases. The weight average molecular weight of the styrene resin can be controlled by the reaction temperature of the polymerization process, the residence time, the kind and amount of the polymerization initiator, the kind and amount of the chain transfer agent, the kind and amount of the solvent used in polymerization, and the like.

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

 GPC model: Shodex GPC-101 made by Showa Denko K.K.

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

Mobile phase (mobile phase): tetrahydrofuran

Sample concentration: 0.2 mass%

Temperature: oven 40 ° C, inlet 35 ° C, detector 35 ° C

Detector: differential refractometer

The molecular weight of the present invention is calculated from the elution curve of the monodispersed polystyrene by calculating the molecular weight at each elution time and calculating the molecular weight in terms of polystyrene.

<< Hydrophilic Additives >>

A hydrophilic additive is a compound having a hydrophilic group capable of interacting with water (hydrogen bonding). The hydrophilic group is preferably a polyether chain. The polyether chain is a skeleton structure in which ether bonds are continuous. For example, the polyether chain is a poly (oxyalkylene) group synthesized by an addition reaction of an alkylene oxide such as ethylene oxide (hereinafter sometimes referred to as "EO"), propylene oxide, Oxyethylene chain, polyoxypropylene chain, polyoxybutylene chain, polyglycerol chain synthesized by dehydration condensation of glycerin, etc., but polyoxyethylene chain is preferable. The polyether chain may have not only one group in one molecule but also a plurality of groups.

Of these various hydrophilic additives, in the present invention, at least one selected from a polyoxyethylene type surfactant having an average addition mole number of ethylene oxide of 3 to 150 and a polyethylene glycol having an average molecular weight of 200 to 10000 is added. This is because it has been experimentally found that it is necessary to use a hydrophilic additive having such a specific constitution in order to enhance the suppression effect of the whitening phenomenon.

The HLB value of the hydrophilic additive is 5 to 20. This is because it has been experimentally found that it is necessary to use a hydrophilic additive having such a specific HLB value to enhance the suppression effect of the whitening phenomenon. The HLB value is preferably 8 to 20, more preferably 10 to 20, and even more preferably 10 to 18. The HLB (Hydrophilic-lipophilic blance) value is a value indicating the hydrophilicity of the additive. When the HLB value is in the range of 8 to 10, it is stably dispersed in water. When the HLB value is more than 10, the dispersed state is transparent and completely dissolved. In a nonionic surfactant having a polyether chain, HLB value = (molecular weight of hydrophilic moiety) / (molecular weight of additive) x 20, such as paraffin which does not contain a hydrophilic group, has an HLB value of 0, For glycols, the HLB value is 20; for nonionic surfactants, the HLB value is between 0 and 20.

The hydrophilic additive is added so that the content of the hydrophilic additive in 100 mass% of the styrene resin composition becomes 0.4 to 2.0 mass%. This is because it has been experimentally found that it is necessary to add such a content in order to enhance the effect of suppressing the whitening phenomenon while maintaining the heat resistance of the styrenic resin composition. The content of the hydrophilic additive in 100 mass% of the styrene resin composition is preferably 0.7 to 1.6 mass% or 0.6 to 1.4 mass%, and more preferably 0.6 to 0.9 mass%.

It is preferable that the hydrophilic additive has a heating loss (loss on heating) of not more than 10% by mass at a temperature of 200 캜 under a nitrogen atmosphere. The heating loss at a temperature of 200 占 폚 under a nitrogen atmosphere can be determined by thermogravimetric analysis (TGA) and can be obtained from a weight reduction amount at a temperature of 200 占 폚 by heating from a room temperature state at a heating rate of 10 占 폚 / min in a nitrogen atmosphere . An additive having a heating loss of more than 10 mass% at a temperature of 200 占 폚 and a nitrogen atmosphere is highly volatile and gas may be generated during the molding of the styrene resin, so that the mold or the roll may become dirty.

Examples of the method of adding the hydrophilic additive include a method of adding and mixing in a polymerization process of a styrene resin, a devolatilization process, a granulation process, a method of adding and mixing by means of an extruder or the like during molding, a method of adding a hydrophilic additive to a resin composition And a method of diluting and mixing to the desired content by a styrene-based resin which is not added, and the like, and the method is not particularly limited.

For example, a styrenic resin composition containing 0.5 to 50.0 mass% of a hydrophilic additive and a styrenic resin without additives may be mixed by using an extruder or an injection molding machine to obtain a styrenic resin composition, a molded article and a light guide plate of a desired concentration Method.

&Lt; Polyoxyethylene type surfactant >

Examples of the polyoxyethylene type surfactant include a polyoxyethylene type nonionic surfactant, a polyoxyethylene type anionic surfactant, a polyoxyethylene type cationic surfactant, and a polyoxyethylene type amphoteric surfactant. , And polyoxyethylene type nonionic surfactants are preferable.

The polyoxyethylene type nonionic surfactant is a polyoxyethylene alkyl ether represented by the following general formula (1) or a polyoxyethylene fatty acid ester represented by the following general formula (2), polyoxyethylene hydrogenated castor oil, polyoxyethylene sorbitan Fatty acid esters and polyoxyethylene sorbitol fatty acid esters, but they are preferably at least one selected from the group of polyoxyethylene alkyl ethers and / or polyoxyethylene fatty acid esters. Further, it is also possible to use a polyoxyethylene alkyl ether having a plurality of polyoxyethylene alkyl ether skeletons in a molecule or a polyoxyethylene fatty acid ester having a plurality of polyoxyethylene fatty acid ester skeletons in one molecule to achieve the object of the present invention can do. The polyoxyethylene alkyl ether or the polyoxyethylene fatty acid ester has a valence of 2 or more, and refers to the number of polyoxyethylene alkyl ether skeleton or polyoxyethylene fatty acid ester skeleton present in one molecule.

(Wherein R represents an alkyl group having from 8 to 20 carbon atoms), a polyglycidyl polyoxyethylene alkyl ether having a plurality of polyoxyethylene alkyl ether skeletons and a polyglycidyl polyoxyethylene alkyl ether having a plurality of polyoxyethylene fatty acid ester skeletons, N is an integer and indicates an addition mole number of the ethylene oxide unit.)

The polyoxyethylene alkyl ether is prepared by adding ethylene oxide to an alcohol. The polyoxyethylene fatty acid ester is produced by adding ethylene oxide to a fatty acid or by directly esterifying a fatty acid and polyethylene glycol. The average addition mole number of ethylene oxide 3 ~ 150. It is experimentally found that, in order to enhance the suppression effect of the whitening phenomenon, it is necessary that the average addition mole number be within this specified range. The average addition mole number is preferably 7 to 100, more preferably 10 to 60, still more preferably 10 to 50, still more preferably 13 to 35.

Specific examples of the polyoxyethylene type surfactant of the present invention include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene octyldodecyl ether, polyoxyethylene Polyoxyethylene alkyl ethers such as myristyl ether and polyoxyethylene 2-ethylhexyl ether, polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate and polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan fatty acid esters such as tetraoleic acid poly Polyoxyethylene sorbitol fatty acid esters such as polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, and polyethylene glycol monooleate; polyoxyethylene hydrogenated castor oil such as polyoxyethylene hydrogenated castor oil Free, polyoxyethylene monomethyl ether, polyoxyethylene dimethyl ether, polyoxyethylene glyceryl ether, polyoxyethylene tetraoleic acid, polyoxyethylene triisostearic acid, polyoxyethylene coconut fatty acid glyceryl and the like.

<Polyethylene Glycol>

The average molecular weight of the polyethylene glycol employed in the present invention is 200 to 10,000. More preferably 200 to 4000, more preferably 200 to 1800, and still more preferably 300 to 1,000. When the average molecular weight of the polyethylene glycol is less than 200, gas is generated during the molding process, and the mold or the roll is soiled, which is not preferable. On the other hand, if the molecular weight exceeds 10000, there is a tendency that the effect of preventing the whitening phenomenon is lowered. In addition, the compatibility with the styrene-based resin is lowered and the styrene-based resin composition or the molded article thereof may be clouded. The average molecular weight is calculated from the concentration of hydroxyl groups (in accordance with JIS K1557) measured by pyridine phthalic anhydride method.

<< Additives · Antioxidants >>

The styrene resin composition of the present invention may contain a mineral oil within the range not impairing the colorless transparency of the present invention. Further, it is also possible to use a lubricant such as an internal lubricant such as stearic acid and ethylene bisstearic acid amide, a hindered phenol antioxidant, a phosphorus antioxidant, a sulfur antioxidant, a lactone antioxidant, a hindered amine stabilizer, an ultraviolet absorber, Additives may be included. As the external lubricant, ethylenebisstearic acid amide is preferred, and the content thereof is preferably 30 to 200 ppm in the resin composition.

The styrene-based resin composition of the present invention can be suitably used for optical applications as an optical material, for example, in the field of transparency because deterioration of optical properties such as transmittance, hue and transparency characteristic of a styrenic resin is small . Examples of optical applications include a lens, a light guide plate, a film, an optical fiber, and an optical waveguide (optical waveguide).

To the styrenic resin composition of the present invention, (c) 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra- (D) a phosphorus-based antioxidant, and (e) a hindered phenol-based antioxidant are added to a solution of the dibenzo [d, f] [1,3] And can provide long-term thermal stability. For long-term applications such as optical applications, long term thermal stability is one of the important characteristics. Long-term thermal stability indicates changes in color and transmittance due to heat in long-term use, and excellent thermal stability results in small changes in color and transmittance. The long-term thermal stability is an acceleration test. The molded article can be stored at a high-temperature condition (60 to 90 ° C) to such an extent that the resin is not deformed, and the color and the transmittance can be evaluated with a change over time.

Compound X is a processing stabilizer having a skeleton of a hindered phenol-based antioxidant and a skeleton of a phosphorus-based antioxidant in the same molecule.

The content of the compound X in 100% by mass of the styrene resin composition is preferably 0.02 to 0.40% by mass, more preferably 0.05 to 0.20% by mass. When the content of the compound X is less than 0.02 mass%, the long-term thermal stability is poor, and the initial color and transmittance are also poor. In addition, if it exceeds 0.40 mass%, the long-term thermal stability deteriorates. The long-term thermal stability indicates changes in hue and transmittance due to heat in long-term use, and excellent thermal stability shows little change in hue and transmittance. The long-term thermal stability is an acceleration test. The molded article can be stored at a high-temperature condition (60 to 90 ° C) to such an extent that the resin is not deformed, and the color and transmittance can be evaluated with a change over time. The content of the compound X in 100% by mass of the styrene-based resin composition is, for example, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.15, 0.20, 0.25, %, And may be in the range between any two of the values exemplified herein.

Addition of the compound X to the styrene resin composition of the present invention can impart long-term thermal stability, and addition of a phosphorus-based antioxidant and / or hindered phenol-based antioxidant can provide long-term thermal stability.

The phosphorus antioxidant is preferably contained in an amount of 0.02 to 0.50 mass%, more preferably 0.05 to 0.40 mass%, and more preferably 0.05 to 0.30 mass% in 100 mass% of the styrene resin composition. When the content is less than 0.02% by mass, the long-term thermal stability is poor, and the initial color and transmittance are also poor. If it exceeds 0.50% by mass, long-term thermal stability deteriorates. The content of the phosphorus-based antioxidant in 100% by mass of the styrene-based resin composition is specifically 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.15, 0.20, 0.25, 0.40, 0.45, and 0.50% by mass, and may be in a range between any two of the values exemplified herein.

The hindered phenolic antioxidant is preferably contained in an amount of 0.02 to 0.50 mass%, more preferably 0.02 to 0.30 mass%, and more preferably 0.05 to 0.30 mass% in 100 mass% of the styrene resin composition. When the content is less than 0.02% by mass, the long-term thermal stability is poor, and the initial color and transmittance are also poor. If it exceeds 0.50% by mass, long-term thermal stability deteriorates. The content of the hindered phenol-based antioxidant in 100% by mass of the styrene-based resin composition is specifically 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.15, 0.20, 0.25, , 0.35, 0.40, 0.45, 0.50% by mass, and may be in a range between any two of the values exemplified herein.

The phosphorus antioxidant is a phosphorous acid ester which is a trivalent phosphorus compound. Examples of the phosphorus antioxidant include tris (2,4-di-tert-butylphenyl) phosphite, 2,2'-methylenebis (4,6- (2,4-dicumylphenyl) pentaerythritol diphosphite, 4,4'-biphenylene diphosphinic acid tetrakis (2,4-di-tert-butylphenyl), 3 (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane, cyclic neopentane (2,4-di-t-butylphenyl phosphite), distearyl pentaerythritol diphosphite, bis (nonylphenyl) pentaerythritol diphosphite, bis- [ - (1,1-dimethylethyl) phenyl] ethylphosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, tetrakis (2,4- 5-methylphenyl) -4,4'-biphenylene diphosphonite, and the like. As the phosphorus-based antioxidant, it is preferable to have excellent hydrolysis resistance, and tris (2,4-di-tert-butylphenyl) phosphite, 2,2'-methylenebis (4,6- (2-ethylhexyloxy) phosphorus, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, 3,9-bis ) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane. Particularly preferably, it is tris (2,4-di-tert-butylphenyl) phosphite. The phosphorus antioxidant may be used singly or in combination of two or more kinds.

The hindered phenolic antioxidant is an antioxidant having a phenolic hydroxyl group in the basic skeleton. The hindered phenolic antioxidant may be, for example, octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- 5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis Bis (octylthiomethyl) -o-cresol, 4,6-bis [(tert-butyl-4-hydroxy-m-tolyl) propionate] Methyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) silanetriol ) Propionate] methane, DL- alpha -tocopherol, 2-t-butyl-6- (3-t-butyl- (2-hydroxy-3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenylacrylate, 4,4'- Phenol), 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4'-butylidenebis Phenol) and bis- [3,3-bis- (4'-hydroxy-3'-tert-butylphenyl) -butanoic acid] -glycol ester. 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- [3- (3- (5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, ethylenebis (oxyethylene) -tert-butyl-4-hydroxy-m-tolyl) propionate]. The hindered phenol-based antioxidant may be used alone or in combination of two or more.

Examples of the method for adding the compound X, the phosphorus-based antioxidant and the hindered phenol-based antioxidant include a method of adding and mixing in the polymerization step of the styrene-based resin, the devolatilization step and the granulation step, a method of adding and mixing by means of an extruder or an injection molding machine , And a method of diluting and mixing a resin composition prepared by adjusting these additives at a high concentration to a desired content by a styrenic resin without additives and the like, and the like are not particularly limited.

The ultraviolet absorber has a function of suppressing deterioration or coloration due to ultraviolet rays. Examples of the ultraviolet absorber include benzophenone, benzotriazole, triazine, benzoate, salicylate, cyanoacrylate, , Malonic acid ester type, formamidine type and the like. These may be used alone or in combination of two or more, and a light stabilizer such as hindered amine may be used in combination.

<< Styrene resin composition >>

The styrene resin composition of the present invention can be obtained by various molding methods for purposes such as injection molding, extrusion molding, blow molding, compression molding and the like. The shape of the molded article can be a shape according to the purpose, and is not limited. For example, if it is a plate-shaped molded article, it can be used as a light guide plate. As a method of using a light guide plate, it is known to provide a reflection pattern such as a dot pattern on the back surface (the side opposite to the light output surface) of the plate-like molded article. It is preferable to polish the incident surface of the light or the entire end surface of the resin plate to form a mirror surface when processing the resin plate to the light guide plate. Further, in order to increase the uniformity of the emitted light, a prism pattern may be provided on the surface (surface on which light is emitted) of the plate-like molded article. The pattern on the surface or the back surface of the plate-like molded article can be formed at the time of molding the plate-like molded article, and for example, the pattern can be formed by a die in injection molding or by roll transfer in extrusion molding.

The softening temperature of the styrene-based resin composition of the present invention is preferably 95 to 104 占 폚, and more preferably 97 to 104 占 폚. When the Vicat softening temperature is less than 95 캜, heat resistance is insufficient and the molded article may be deformed depending on the use environment.

The haze of the styrene-based resin composition of the present invention is preferably 5% or less, more preferably 1% or less, as a molded article having a thickness of 4 mm.

Example

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

<< Test 1 >>

(Production of styrene series resin A-1 to A-3)

A third reactor, which is a plug flow type reactor having a first reactor, a second reactor and a static mixer, which are a complete mixing type stirrer, was connected in series to form a polymerization process. By the conditions shown in Table 1, . The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. The raw material solution was prepared in the raw material composition shown in Table 1, and the raw material solution was continuously supplied to the first reactor at the flow rate shown in Table 1. The polymerization initiator was added to the raw material solution at the inlet of the first reactor so that the addition concentration (concentration based on the mass basis of the total amount of raw styrene and methacrylic acid) described in Table 1 was uniformly mixed. The polymerization initiators shown in Table 1 are as follows.

Polymerization initiator-1: 2,2-di (4,4-t-butylperoxycyclohexyl) propane (PERTETRA A manufactured by Nichiyu Corporation) was used.

Polymerization initiator-2: 1,1-di (t-butylperoxy) cyclohexane (PERHEXA C manufactured by Nichiyu K.K.) was used.

On the other hand, in the third reactor, a temperature gradient was given according to the flow direction, and the temperature was adjusted to be the temperature shown in Table 1 at the middle portion and the outlet portion.

Subsequently, a solution containing the polymer continuously withdrawn from the third reactor was introduced into a vacuum evacuation tank equipped with a preheater (two-stage stage) in series, and the temperature of the preheater was adjusted to the resin temperature shown in Table 1 And unreacted styrene and ethylbenzene were separated by adjusting the pressure as shown in Table 1, extruded into a strand shape with a porous die, and the strands were cooled and cut by a cold cut method to form pellets.

(Examples 1-1 to 1-33 and Comparative Examples 1-1 to 1-9)

Styrene resins A-1 to A-3 and additives were melt-kneaded at a cylinder temperature of 230 DEG C and a screw rotation speed of 100 rpm using a single screw extruder having a screw diameter of 40 mm to obtain pellets. The additives used in Table 2 are shown below.

B-1: polyoxyethylene ethylene lauryl ether ethylene oxide average addition number of moles = 25 (Emulgen 123P, manufactured by Kao Corporation)

B-2: polyoxyethylene ethylene stearyl ether ethylene oxide average addition number of moles = 12 (Emulgen 320 P manufactured by Kao Corporation)

B-3: polyoxyethylene ethylene lauryl ether ethylene oxide average addition number of moles = 9 (Emulgen 109P, manufactured by Kao Corporation)

B-4: polyoxyethylene ethylene cetyl ether ethylene oxide average addition mole number = 7 (Emulgen 210P, manufactured by Kao Corporation)

B-5: polyoxyethylene ethylene lauryl ether ethylene oxide average addition number of moles = 30 (Emulgen 130K, manufactured by Kao Corporation)

B-6: polyoxyethylene ethylene lauryl ether ethylene oxide average addition number of moles = 47 (Emulgen 150 manufactured by Kao Corporation)

B-7: polyoxyethylene ethylene myristyl ether ethylene oxide average addition mole number = 85 (Emulgen 4085, manufactured by Kao Corporation)

B-8: polyethylene glycol monolauratoethylene oxide average addition number of moles = 12 (Emanon 1112, manufactured by Kao Corporation)

B-9: polyoxyethylene ethylene stearyl ether ethylene oxide average addition number of moles = 6 (Emulgen 306P, manufactured by Kao Corporation)

B-10: Polyoxyethylene hardened castor oil (EMANON CH-40, manufactured by Kao Corporation)

B-11: Polyethylene glycol having an average molecular weight of 400 (PEG # 400 manufactured by Nichiyu K.K.)

B-12: Polyethylene glycol having an average molecular weight of 300 (PEG # 300 made by Nichiyu K.K.)

B-13: Polyethylene glycol having an average molecular weight of 600 (PEG # 600 made by Nichiyu K.K.)

B-14: Polyethylene glycol having an average molecular weight of 1000 (PEG # 1000 made by Nichiyu K.K.)

B-15: Polyethylene glycol having an average molecular weight of 2000 (PEG # 2000 made by Nichiyu K.K.)

B-16: Polyethylene glycol having an average molecular weight of 3100 (PEG # 4000, manufactured by Nichiyu K.K.)

B-17: Polyethylene glycol having an average molecular weight of 8800 (PEG # 6000, manufactured by Nichiyu K.K.)

B-18: Polyoxyethylene monomethyl ether (Uniox M-550 manufactured by Nichiyu K.K.)

B-19: Polyoxyethylene triisostearic acid (Uniox GT-20IS manufactured by Nichiyu K.K.)

B-20: Polyoxyethylene octyldodecyl ether (Emulgen 2025G, manufactured by Kao Corporation)

B-21: Polyoxyethylene glyceryl ether (Uniox G-750 manufactured by Nichiyu K.K.)

B-22: Polyoxyethylene tetraoleic acid (Uniox ST-30E manufactured by Nichiyu K.K.)

B-23: Stearyl alcohol (Cal. Cole 8098 manufactured by Kao Corporation)

B-24: stearic acid monoglyceride (EXCELS-95 made by Kao Corporation)

B-25: Polyethylene glycol having an average molecular weight of 60,000 (ALKOX L-6 manufactured by Meisei Kagaku Kogyo K.K.)

B-26: Polyglycerin having an average molecular weight of 500 (polyglycerin # 500 manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.)

Using the obtained pellets, injection molding was carried out at a cylinder temperature of 230 캜 and a mold temperature of 50 캜 to form a plate-like molded article having a thickness of 127 x 27 x 3 mm.

In Example 1-33, the styrene-based resin A-1 and the additive B-1 were melt-kneaded using a single screw extruder having a screw diameter of 40 mm at a cylinder temperature of 230 ° C and a screw rotation speed of 100 rpm, This pellet is obtained by once obtaining pellets having a concentration of 20% by mass, mixing the pellets with the styrene-based resin A-1 in a ratio of 1:24, and injection-molding.

<MFR>

The MFR (melt flow rate) of the styrene-based resin composition was measured at 200 占 폚 under a load of 49 N, based on JIS K 7210.

<Initial color evaluation>

A test piece having a thickness of 115 x 5 x 3 mm was cut out of the obtained plate-like molded product and polished by buffing to obtain a plate-like molded product having a mirror-finished surface in cross-section. The resulting plate-like molded product was measured for an ultraviolet-visible spectrophotometer V-670 manufactured by Nihon Bunko K.K. under the conditions of a size of 20 × 1.6 mm and a wavelength of 350 nm to 800 nm at an optical path length of 115 mm, The spectral transmittance was measured, and in the C light source, the YI value at a visual field of 2 DEG was calculated in accordance with JIS K7105. The obtained value is "YI 115 mm" in Table 2. The "transmittance of 115 mm" shown in Table 2 indicates an average transmittance of a wavelength of 380 nm to 780 nm.

Further, the "haze 4 mm" in Table 2 was obtained by injection molding the pellets obtained in the above process at a cylinder temperature of 220 ° C. and a mold temperature of 40 ° C. to obtain a test piece having a thickness of 55 × 50 × 4 mm , And NDH5000 (manufactured by Nippon Denshoku Kogyo K.K.), the value measured based on JIS K-7105, and the value of "YI 4 mm" in Table 2 was obtained by using the above-mentioned test piece and measuring the colorimetric colorimeter NDJ4000 (Manufactured by Nippon Denshoku Kogyo K.K.) and measured by a reflection method.

&Lt; Bleaching inhibition effect >

Further, in order to check the whitening phenomenon caused by environmental changes, the test piece was taken out at 23 DEG C and 50% relative humidity environment, exposed to a 60 DEG C, 90% relative humidity environment for 150 hours, The whitening phenomenon generated inside was observed and the whitening inhibition effect was determined as follows.

A: No whitening occurs completely.

○: It is partially whitened after 1 hour, but disappears after 24 hours.

B: It is whitened after 1 hour of taking out, but most of it disappears after 24 hours.

X: remarkably whitened after 1 hour from being taken out, and not disappearing after 24 hours.

<Vicat softening temperature>

The Vicat softening temperature was determined according to JIS K-7206 at a heating rate of 50 ° C / hr and a test load of 50 N

<Overall evaluation>

We performed comprehensive evaluation according to the following criteria.

S: a whitening inhibiting effect is?, A Vicat softening temperature is 100 占 폚 or higher

The A: S condition is not satisfied, the whitening inhibition effect is ⊚, the Vicat softening temperature is 98 캜 or higher, the whitening inhibition effect is ◯, and the Vicat softening temperature is 100 ° C or higher

B: the condition of A is not satisfied, the whitening inhibition effect is ⊚, the Vicat softening temperature is 95 ° C or higher, the whitening inhibition effect is ◯, the Vicat softening temperature is 98 ° C or higher, DELTA and the Vicat softening temperature was 100 DEG C or higher

C: Any of the above conditions is not met.

Table 2 shows the properties and evaluation results of each resin composition.

The molded article of the Example is excellent in whitening inhibition effect, and has neither transparency nor YI value deterioration, and is also excellent in transparency and color. In Comparative Examples 1-1, 1-2, and 1-4 in which the hydrophilic additive was not added or the addition amount was too small, inhibition of the whitening phenomenon was insufficient. In Comparative Examples 1-3 and 1-5 in which the hydrophilic additive was added in excess, the heat resistance was excessively lowered. Further, in Comparative Examples 1-6 and 1-7, the test was conducted by adding stearyl alcohol and stearic acid monoglyceride, which are hydrophilic additives, respectively, but the whitening inhibition effect was insufficient. In addition, in Comparative Examples 1-8 and 1-9, polyethylene glycol and polyglycerin having a large molecular weight were added and tested, but the hydrophilic additive was not compatible with the styrene resin and the molded article was opaque.

From the above results, it was found that (1) the hydrophilic additive has the characteristic composition, (2) the HLB value is within the specified range, and (3) It is essential to maintain the heat resistance and transparency of the styrene-based resin composition while suppressing the whitening phenomenon. Referring to Examples 1-20 to 1-21, it has been found that the same result can be obtained even when the styrene type resin is a copolymer of a styrene type monomer and (meth) acrylic acid or (meth) acrylic acid ester.

<< Test 2 >>

(Examples 2-1 to 2-46)

A third reactor as a plug flow type reactor having a first reactor, a second reactor and a static mixer as a complete mixing type stirrer was connected in series to constitute a polymerization process, and a styrene type resin was produced under the conditions shown in Table 1 . The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. The raw material solution was prepared by using the raw material composition shown in Table 1, and the raw material solution was continuously supplied to the first reactor at the flow rate shown in Table 1.

A hydrophilic additive having a polyether chain was added to the inlet of the third reactor so as to have the kind and content shown in Table 3. The types of additives and polyethylene glycols used are as follows.

B-1: Polyethylene glycol having an average molecular weight of 400 (PEG # 400 made by Nichiyu K.K.)

B-2: Polyethylene glycol having an average molecular weight of 1000 (PEG # 1000 manufactured by Nichiyu K.K.)

B-3: Polyethylene glycol having an average molecular weight of 2000 (PEG # 2000 manufactured by Nichiyu K.K.)

B-4: polyoxyethylene ethylene lauryl ether ethylene oxide average addition number of moles = 25 (Emulgen 123P, manufactured by Kao Corporation)

B-5: polyoxyethylene ethylene lauryl ether ethylene oxide average addition number of moles = 12 (Emulgen 320P, manufactured by Kao Corporation)

B-6: polyoxyethylene ethylene lauryl ether ethylene oxide average addition number of moles = 9 (Emulgen 109P manufactured by Kao Corporation)

B-7: polyoxyethylene ethylene lauryl ether ethylene oxide average addition mole number = 30 (Emulgen 130K, manufactured by Kao Corporation)

B-8: polyethylene glycol monolauratoethylene oxide average addition number of moles = 12 (Emanon 1112, manufactured by Kao Corporation)

Subsequently, a solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum evacuation tank equipped with a preheater composed of two stages in series, unreacted styrene and ethylbenzene were separated, and then extruded into a strand shape and cooled , And cut into pellets. On the other hand, the resin temperature in the first stage degreasing was set to 160 DEG C, the pressure of the vacuum evacuation tank was set to 65 kPa, the temperature of the resin in the second stage degreased layer was set to 235 DEG C, and the pressure of the vacuum evacuation tank was set to 0.8 kPa .

Next, the pellets of the styrene resin obtained above and the compound X, the additive D and the additive E were used as the pellets of the styrene-based resin obtained above as the additives shown in Table 3, using a single screw extruder having a screw diameter of 40 mm, And melt-kneaded at a number of 100 rpm to obtain pellets. Compounds X, D and E used in Table 3 are shown below. On the other hand, Compound X can be obtained by reacting 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra- ] [1, 3, 2] dioxaphosphper, additive D is phosphorus antioxidant, and additive E is hindered phenol antioxidant.

Compound X: 6- [3- (tert-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-tert- butyldibenzo [d, 1,3,2] dioxaphosphperin (Sumilizer GP manufactured by Sumitomo Chemical Co., Ltd.)

D-1: Tris (2,4-di-tert-butylphenyl) phosphite (Irgafos 168 manufactured by BASF Japan K.K.)

D-2: 2,2'-methylenebis (4,6-di-tert-butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus (ADEKASTOP HP-10 manufactured by ADEKA,

D-3: Bis (2,4-dicumylphenyl) pentaerythritol diphosphite (Doverphos S-9228, Dover Chemical Corporation)

D-4: 3,9-bis (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphospaspiro [5.5] undecane (Adekastop PEP-36 manufactured by ADEKA Corporation)

E-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076, BASF Japan)

E-2: 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] , 10-tetraoxaspiro [5.5] undecane (ADEKA STOP AO-80 manufactured by ADEKA)

E-3: Ethylene bis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (BASF Japan Irganox 245)

The melt flow rate (MFR) was measured in accordance with JIS K 7210 at 200 ° C under a load of 49N, and the Vicat softening temperature was measured at a temperature rising rate of 50 ° C / hr and a test load of 50N in accordance with JIS K 7206.

The obtained pellets were injection molded at a cylinder temperature of 230 DEG C and a mold temperature of 50 DEG C to form a plate-like molded article having a thickness of 127 x 127 x 3 mm. In order to evaluate the long-term thermal stability, the obtained molded article was stored in an oven at 80 DEG C for 1000 hours. In order to evaluate the optical properties of the initial molded article before storage and the stored article after storage, a test piece having a thickness of 115 x 85 x 3 mm was cut out from the plate shaped article and the end surface was polished by buff polishing to obtain a plate- A molded article was prepared. For the plate-shaped molded product after polishing, a UV-visible spectrophotometer V-670 manufactured by Nihon Bunko K.K. was used, and with a size of 20 x 1.6 mm and a spread angle of 0 占 incident light, a wavelength of 350 nm- The spectral transmittance at 800 nm was measured, and the visual field 2 占 YI value in the C light source was calculated according to JIS K7105. The transmittance shown in Table 3 indicates an average transmittance at a wavelength of 380 nm to 780 nm.

Next, the DELTA YI difference was calculated based on the following equation.

YI difference = (YI difference from the beginning in the embodiment in which additional additives are present) - (YI difference from the initial in the embodiment in which no additional additive is present)

In Example 2-2 in which the additional additive is present, since the YI difference from the initial value is 1.1 and the YI difference from the initial value in Example 2-1 in which no additional additive is present is 5.1, The? YI difference of 2-2 is -4.0. This value shows a long-term improvement in thermal stability by the additive (Compound X, phosphorus D, hindered phenol series E), and the smaller the value, the greater the long-term improvement in thermal stability.

Further, in order to check the whitening phenomenon caused by environmental changes, the plate-shaped molded article having a mirror surface in cross section was exposed to an environment at 60 ° C and 90% relative humidity for 150 hours, and the test piece was taken out at an environment of 23 ° C and 50% relative humidity , Whitening phenomenon occurring inside the molded product was observed, and the whitening inhibition effect was determined as follows.

A: No whitening occurs completely.

○: It is partially whitened after 1 hour, but disappears after 24 hours.

B: It is whitened after 1 hour of taking out, but most of it disappears after 24 hours.

X: remarkably whitened after 1 hour from being taken out, and not disappearing after 24 hours.

<Overall evaluation>

The results of evaluation of the whitening inhibition effect,? YI difference, and Vicat softening temperature were numerically expressed in accordance with the following criteria.

The score of the whitening inhibition effect (? -? 3,? -> 2,? 1,? 0)

A score of the YI difference (-4.0 or less → 4, -3.5 or less → 3, -2.5 or less → 2, -1.5 or less → 1 or other 0)

Vicat softening temperature score (99 ° C or higher → 3, 97 ° C or higher → 2, 95 ° C or higher → 1, other → 0)

The total score obtained according to the above criteria was subjected to comprehensive evaluation according to the following criteria.

S: 10, A: 9, B: 8, C: 7, D: 6 or less.

Table 3 shows the properties and evaluation results of each resin composition. Styrene resin A-1 prepared in accordance with Condition 1 was used in Examples 2-1 to 2-42, styrene resin A-2 prepared in accordance with Condition 2 in Examples 2-43 to 2-44, In Examples 2-45 to 2-46, styrene-based resin A-3 prepared according to Condition 3 was used.

Referring to Table 3, it can be seen that the whitening inhibiting effect of all the examples is good. Comparing Examples 2-1 to 2-35 with Examples 2-36 to 2-42, it can be seen that long-term thermal stability is particularly good when the content of compound X is 0.02 to 0.40 mass% . Further, in Examples 2-43 to 2-46, it was found that the same result can be obtained even when the styrene type resin is a copolymer of a styrene type monomer and (meth) acrylic acid or (meth) acrylic acid ester.

<< Test 3 >>

(Examples 3-1 to 3-36)

In Test 3, evaluation was carried out in the same manner as in Test 2 except that Compound X was not added. In Examples 3-1 to 3-32, the styrene type resin A-1 prepared according to Condition 1 was used, while in Examples 3-33 to 3-34, the styrene type resin A-2 prepared according to Condition 2 was used In Examples 3-35 to 3-36, styrene resin A-3 prepared according to Condition 3 was used.

The results are shown in Table 4.

Referring to Table 4, it can be seen that the whitening inhibiting effect of all the examples is good. Comparing the examples 3-1 to 3-24 and the examples 3-25 to 3-32, it is understood that the content of the phosphorus D is 0.05 to 0.40 mass% and the content of the phenol E is 0.02 to 0.30 mass% , It can be seen that the long-term thermal stability is particularly excellent. Further, it was found that the same results can be obtained when the styrene-based resin is a copolymer of a styrene-based monomer and (meth) acrylic acid or (meth) acrylic acid ester, referring to Examples 3-33 to 3-36.

The styrene-based resin composition of the present invention is capable of maintaining transparency, which is an advantage of the styrene-based resin, even in applications where whitening has conventionally occurred due to environmental changes since the whitening phenomenon due to environmental changes is prevented, There is, and can be used as a family register.

In addition, the styrene resin composition excellent in long-term thermal stability can be used while maintaining the transparency and hue for a longer period than the conventional ones because the color change is small.

For example, the use of a light guide plate such as a television, a desk-top PC, a notebook PC, a mobile phone, and a car navigation system.

Claims (15)

Wherein the hydrophilic additive has a polyoxyethylene type surfactant with an average addition mole number of ethylene oxide of 3 to 150 and a polyoxyethylene type surfactant with an average molecular weight of 200 to 200. The styrenic resin composition according to claim 1, To 10,000, and an HLB value of 5 to 20, and a content of the styrene-based resin composition in 100 mass% of the styrene-based resin composition is 0.4 to 2.0 mass%.
The method according to claim 1,
Wherein the hydrophilic additive is a polyoxyethylene type surfactant having an average addition mole number of ethylene oxide of 10 to 60 and a content of the polyoxyethylene type surfactant in 100 mass% of the styrene type resin composition is 0.6 to 1.4 mass%.
3. The method according to claim 1 or 2,
Wherein the hydrophilic additive is a polyoxyethylene type surfactant having an average addition mole number of ethylene oxide of 13 to 35, and a content of the polyoxyethylene type surfactant in the styrene type resin composition is from 0.6 to 0.9 mass%.
The method of claim 3,
Wherein the hydrophilic additive has an HLB value of 10 to 18.
5. The method according to any one of claims 1 to 4,
Wherein the polyoxyethylene type surfactant is a polyoxyethylene type nonionic surfactant.
6. The method according to any one of claims 1 to 5,
Wherein the polyoxyethylene type nonionic surfactant is at least one selected from the group consisting of a polyoxyethylene alkyl ether represented by the following general formula (1) and / or a polyoxyethylene fatty acid ester represented by the following general formula (2) Styrene resin composition for optical use.

(Wherein R represents an alkyl group having 8 to 20 carbon atoms), a polyoxyalkylene alkyl ether having 6 polyoxyethylene alkyl ethers having 6 or more polyoxyethylene alkyl ether skeletons, a polyoxyethylene alkyl ether having 6 polyoxyethylene fatty acid ester skeletons Polyoxyethylene fatty acid ester, n is an integer and indicates the number of moles of ethylene oxide units added.
The method according to claim 1,
Wherein the hydrophilic additive is polyethylene glycol having an average molecular weight of 200 to 10000, and the content of the hydrophilic additive in 100% by mass of the styrene resin composition is 0.6 to 1.4% by mass.
8. The method of claim 7,
Wherein the hydrophilic additive is a polyethylene glycol having an average molecular weight of 200 to 1800. The styrene-
9. The method of claim 8,
Wherein the hydrophilic additive has a content of 0.6 to 0.9% by mass in 100% by mass of the styrene-based resin composition.
10. A process according to any one of claims 1 to 9
(Meth) acrylic acid copolymer resin obtained by copolymerizing a styrene type monomer with (meth) acrylic acid, wherein the content of the styrene type monomer unit in the styrene type resin is 90.0 to 99.9 mass%, the content of the (meth) acrylic acid unit Wherein the content of the styrene-based monomer unit and the (meth) acrylic acid unit in the styrene-based resin is 0.1 to 10.0% by mass, and the content of the styrene-based monomer unit and the (meth) acrylic acid unit in the styrene-based resin is 100%
10. The method according to any one of claims 1 to 9,
(Meth) acrylic ester copolymer resin obtained by copolymerizing a styrene type monomer with a (meth) acrylic acid ester, wherein the content of the styrene type monomer unit in the styrene type resin is 40.0 to 99.0 mass%, the content of the (meth) acrylic acid Wherein the content of the ester unit is 1.0 to 60.0 mass% and the total content of the styrene-based monomer unit and the (meth) acrylic ester unit of the styrene-based resin is 100 mass%.
The method according to any one of claims 1 to 11,
Propyl] -2,4,8,10-tetra-tert-butyldibenzo [d, f] [1, 3-dihydroxy- , 2] dioxaphosphpine. &Lt; / RTI &gt;
13. The method according to any one of claims 1 to 12,
Wherein the resin composition comprises a phosphorus-based antioxidant and / or a hindered phenol-based antioxidant.
A molded article comprising the optical styrene resin composition according to any one of claims 1 to 13.
A light guide plate comprising the molded article according to claim 14.