TW201712064A - Styrene-based optical resin composition - Google Patents

Abstract

The present invention addresses the problem of providing a transparent styrene-based optical resin composition that minimizes a shortcoming of styrene-based resins, namely that environmental changes such as changes in temperature or humidity, or immersion in water cause the clouding (bleaching) of molded products thereof. The present invention provides a styrene-based optical resin composition that contains a styrene-based resin having a weight-average molecular weight of 150,000-700,000 and a hydrophilic additive, and is characterized in that the hydrophilic additive: is at least one substance selected from among polyoxyethylene surfactants having an average added mole number of ethylene oxide of 3-150 and/or polyethylene glycols having an average molecular weight of 200-10,000; has an HLB value of 5-20; and composes 0.4-2.0 mass% of the 100 mass% of the styrene-based resin composition.

Description

Optical styrene resin composition

The present invention relates to a transparent styrene resin composition capable of suppressing whitening caused by environmental changes.

The styrene-based resin has excellent properties such as transparency, rigidity, low water absorbability, dimensional stability, and excellent moldability. Therefore, various molding methods such as injection molding, extrusion molding, and blow molding can be used. Widely used as electrical products and various industrial materials, food packaging containers, groceries, etc. Moreover, it can also be used for optical components, such as a light guide plate, as the use which exhibits transparency.

As a backlight of a liquid crystal display, there is a direct type backlight module in which a light source is disposed on a front surface of a display device, and a light edge type backlight module in which a light source is disposed on a side surface. The light guide plate is assembled on the edge light type backlight module, and the light from the side is guided to the liquid crystal panel to function, and can be used in a television, a desktop personal computer display, a notebook personal computer, a mobile phone, a car navigation, etc. Used in a wide range of applications. The propylene resin typified by PMMA (polymethyl methacrylate) has been used for the light guide plate, but the water absorbing property is high, so that the molded article may be bent or the size may be changed.

For this reason, an MS resin which is a copolymer of styrene and methyl (meth) acrylate which has improved these characteristics has been proposed. Patent Document 1 proposes an improved technique such as water absorption of an MS resin and reduction in discoloration during molding.

However, Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of 6 to 170,000, a residual monomer amount of 3,000 ppm or less, and an oligomer content of 2% or less of a styrene-(meth)acrylate polymer resin. However, it has high water absorbability and is inferior in dimensional stability to a styrene-based resin using a styrene-based monomer as a raw material.

On the other hand, the styrene-based resin having a styrene-based monomer as a raw material has a low water absorption property, but the styrene-based resin has a molded product due to environmental changes such as temperature, humidity, and warm water immersion (Non-Patent Document 1). The problem of white turbidity (whitening phenomenon) occurs, and the transparency as an advantage is damaged depending on the use. Specifically, when the molded article is exposed to a high temperature and high humidity environment to a room temperature environment, or when the temperature changes from a room temperature environment to a low temperature environment, the water uniformly present in the styrene resin becomes unstable and phase separation occurs. As a result, a disk-shaped defect is generated, and as a result, white turbidity appears inside the molded article. In addition, when the molded article of the styrene resin is immersed in hot water for a predetermined period of time or more, whitening occurs when the molded article is taken out, which is also caused by the above mechanism.

When the molded article is white turbid, if the optical path is long such as a light guide plate, there is a problem that the transmittance is largely lowered by light scattering, and the brightness of the display is lowered.

[Prior Art Literature] [Patent Literature]

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

[Non-patent literature]

[Non-Patent Document 1] Journal of the Fiber Society, Vol. 34, No. 6, pp. 245-253, 1978

An object of the present invention is to provide a transparent styrene resin composition that suppresses whitening caused by environmental changes.

According to the present invention, there is provided a styrene resin composition for optical use comprising a styrene resin having a weight average molecular weight of 150,000 to 700,000 and a hydrophilic additive, wherein the hydrophilic additive is selected from the group consisting of ethylene oxide. (ethylene oxide) having an average addition mole number of 3 to 150 polyoxyethylene surfactants and at least one of polyethylene glycol having an average molecular weight of 200 to 10,000, and an HLB value of 5 to 20, and The content in 100% by mass of the styrene resin composition is 0.4 to 2.0% by mass.

The inventors of the present invention have conducted intensive studies to suppress the whitening phenomenon caused by environmental changes. First, it has been found that the addition of a hydrophilic additive is effective for suppressing the whitening phenomenon. However, further research It was found that the addition of only hydrophilicity did not effectively inhibit whitening. Therefore, further studies have revealed that (1) the hydrophilic additive has a characteristic configuration, (2) the HLB value is a value within a specific range, and (3) the content is a specific range, and benzene can be maintained. The effect of suppressing the whitening phenomenon of the heat resistance of the ethylene-based resin composition is extremely high, and the transparency of the styrene-based resin is not impaired. The effect of obtaining such an effect is not clear, but it can be effectively exerted only when the above three conditions are complete, and therefore it can be considered that the multiplication effect due to these three conditions.

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 the content in the 100% by mass of the styrene resin composition is 0.6. ~1.4% by mass.

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

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

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

Preferably, the polyoxyethylene type nonionic surfactant is selected from the group consisting of polyoxyethylene alkyl ethers represented by the following formula (1) and/or polyoxyethylene fatty acid esters represented by the following formula (2). One or more.

(wherein R represents an alkyl group having 8 to 20 carbon atoms. Further, it may have a plurality of polyoxyethylene oxides A polyvalent polyoxyethylene alkyl ether having a valence of about 6 valences of a group ether skeleton, and a valence polyvalent polyoxyethylene fatty acid ester having a plurality of polyoxyethylene fatty acid ester skeletons. n is an integer and represents the number of moles of addition of the ethylene oxide unit. )

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

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

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

Further, the styrene resin is a styrene-(meth)acrylic copolymer resin obtained by copolymerizing a styrene monomer and (meth)acrylic acid, and the content of the styrene monomer unit of the styrene resin is The content of the (meth)acrylic acid unit is from 0.10 to 99.9% by mass and the content of the (meth)acrylic acid unit is from 0.1 to 10.0% by mass. The total content of the styrene monomer unit and the (meth)acrylic acid unit of the styrene resin is 100% by mass.

Further, the styrene resin is a styrene-(meth)acrylic copolymer resin obtained by copolymerizing a styrene monomer and (meth)acrylic acid, and the content of the styrene monomer unit of the styrene resin is 40.0 to 99.0% by mass and the content of the (meth)acrylic acid unit is 1.0 to 60.0% by mass. The total content of the styrene monomer unit and the (meth)acrylic acid unit of the styrene resin is 100% by mass.

In addition, it also contains 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butylbenzo[ d,f][1,3,2]6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10- Tetra-tert-butyl-dibenzo[d,f][1,3,2]dioxaphosphepin).

Further, it contains a phosphorus-based antioxidant and/or a hindered phenol-based antioxidant.

Further, a molded article is composed of the above-mentioned optical styrene resin composition.

Further, a light guide plate is composed of the above-mentioned molded article.

The styrene resin composition of the present invention has low water absorption and low cost compared to PMMA or MS resin, and does not cause whitening due to environmental changes as a disadvantage of the styrene resin, and is excellent in colorless transparency. It is suitable for use in the transparency of the styrene resin itself.

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 monomer. The styrene-based monomer is preferably a single or a mixture of two or more of styrene, α-methylstyrene, o-methylstyrene, and p-methylstyrene as the aromatic vinyl monomer. Styrene. Further, the styrene-based monomer may be copolymerized in a range that does not impair the characteristics of the present invention, and examples thereof include an acrylic monomer such as acrylic acid or methacrylic acid, a vinyl cyanide monomer such as acrylonitrile or methacrylonitrile, and acrylic acid. Acrylic monomer such as butyl ester, ethyl acrylate, methyl acrylate or methyl methacrylate; α,β-ethylene unsaturated carboxylic acid such as maleic anhydride or fumaric acid, phenyl maleimide or cyclohexyl A quinone imine monomer such as maleimide.

The styrene resin composition is preferably composed of a styrene resin and various additives, and the ratio of the styrene resin in 100% by mass of the styrene resin composition may be 90 to 99.6% by mass, preferably 95 to 99.6. %. Specifically, the ratio of the styrene-based resin is, for example, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, and 99.6 mass%, and may be any of the numerical values exemplified herein. Within a range of values.

When the styrene-based (meth)acrylic copolymer resin obtained by copolymerizing a styrene-based monomer and (meth)acrylic acid is used as the styrene-based resin, the content of the styrene-based monomer unit of the styrene-based resin is 90.0~ The content of the (meth)acrylic acid unit is preferably from 0.1 to 10.0% by mass based on 99.9% by mass. Here, the total content of the styrene monomer unit and the (meth)acrylic unit is 100% by mass. (Meth)acrylic acid means acrylic acid, methacrylic acid, etc., and methacrylic acid is preferable here.

The measurement of the (meth)acrylic acid unit content in the styrene resin was carried out at room temperature. 0.5 g of a styrene-based resin was weighed and dissolved in a mixed solution of toluene/ethanol = 8/2 (volume ratio), and then neutralized and titrated with a 0.1 mol/L potassium hydroxide ethanol solution to determine the end point, according to hydrogen. The amount of the potassium oxide ethanol solution used was calculated from the mass basis of the (meth)acrylic acid unit. Here, the measurement can be performed by using an electric potential automatic titrator and using AT-510 manufactured by Kyoto Electronics Industry Co., Ltd. The content of the (meth)acrylic acid unit in the styrene resin can be adjusted by the composition ratio of the styrene monomer and the (meth)acrylic monomer which are raw materials in the polymerization of the styrene resin, but it is also compatible. The styrene resin containing a (meth)acrylic acid unit and the styrene-based resin containing no (meth)acrylic acid unit were mixed in the range of adjustment.

When a styrene-based (meth) acrylate copolymer resin obtained by copolymerizing a styrene-based monomer and a (meth) acrylate is used as the styrene-based resin, a styrene-based monomer unit of a styrene-based resin is preferable. The content is 40.0 to 99.0% by mass, and the content of the (meth) acrylate unit is 1.0 to 60.0% by mass. Here, the total content of the styrene monomer unit and the (meth) acrylate unit is 100% by mass. The (meth) acrylate is a methacrylate such as methyl methacrylate or ethyl methacrylate, or an acrylate such as methyl acrylate or ethyl acrylate.

The content of the (meth) acrylate unit in the styrene resin can be measured by a pyrolysis gas chromatograph under the following conditions.

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

Pyrolysis furnace temperature setting: 525 ° C

Gas Chromatograph: GC-14A (made by Shimadzu Corporation)

Column: 3mm diameter × 3m made of glass

Filler: FFAP Chromsorb WAW 10%

Injection, detector temperature: 250 ° C

Column temperature: 120 ° C

Carrier gas: nitrogen

Examples of the polymerization method of the styrene resin include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. In view of quality and productivity, a bulk polymerization method or a solution polymerization method is preferred, and continuous polymerization is preferred. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene; ketones such as acetone and methyl ethyl ketone; and aliphatic hydrocarbons such as hexane and cyclohexane. Wait.

When the styrene resin is polymerized, a polymerization initiator or a chain transfer agent may be used as needed. As the polymerization initiator, a radical polymerization initiator is preferred, and a conventionally known one may be mentioned, for example, 1,1-di(tri-butylperoxy)cyclohexane (1,1-di(t-butylperoxy). Cyclohexane), 2,2-di(t-butylperoxy)butane, 2,2-di(4,4-di-tertiary butyl) 1,2-di(4,4-di-t-butyl peroxy cyclohexylpropane), 1,1-di(tert-amylperoxy)cyclohexane (1,1- Hydroperoxides such as di(t-amyl peroxy)cyclohexane), hydroperoxides such as Cumene hydroperoxide and t-butyl hydroperoxide, Alkyl peroxides such as t-Butyl peroxyacetate and t-amyl (peroxy isononanoate), tertiary butyl peroxide T-butyl cumyl peroxide, Di-t-butyl peroxide, Dicumyl peroxide, Di-t-hexyl peroxide Such as dialkyl peroxides, t-butylperoxy acetate, tertiary butyl peroxygen Peroxy esters such as t-butyl peroxybenzoate, t-butyl peroxyisopropylmonocarbonate, t-butylperoxy isopropyl Peroxycarbonate such as carbonate, polyether tetrakis (t-butyl peroxy carbonate), N,N'-azobis(cyclohexane-1- N,N'-azobis(cyclohexane-1-carbonitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile) (N,N'-azobis(2,4- Dimethyl valeronitrile)), N,N'-azobis[2-(hydroxymethyl)propionitrile], etc., one of these or Two or more types are used in combination. The chain transfer agent may, for example, be an aliphatic thiol, an aromatic thiol, pentaphenylethane, an α-methylstyrene dimer or a terpinolene.

In the case of the continuous polymerization, the polymerization reaction is first controlled by a polymerization step by adjusting the polymerization temperature or the like in order to achieve the target molecular weight, the molecular weight distribution, and the reaction conversion rate by using a known fully mixed tank type stirred tank or a column type reactor. The polymerization solution containing the polymer of the polymerization step is transferred to a devolatilization step to remove unreacted monomers and a polymerization solvent. The devolatilization step is constituted by a vacuum devolatilization tank with a heater, a devolatilizing extruder with a vent hole, and the like. The molten state polymer in the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded into a strand shape from a porous die, and processed into a pellet shape by a cold solution method, an air thermal cutting method, or an underwater hot cutting method.

The styrene resin of the present invention has a weight average molecular weight of 150,000 to 700,000 and preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded article becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrene resin can be controlled by the reaction temperature in the polymerization step, the residence time, the type and amount of the polymerization initiator, the type and amount of the chain transfer agent, the type and amount of the solvent used in the 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 type: Shodex GPC-101, manufactured by Showa Denko Co., Ltd.

Column: PLgel 10μm MIXED-B manufactured by Polymer Labs

Mobile phase: tetrahydrofuran

Sample concentration: 0.2% by mass

Temperature: furnace temperature 40 ° C, injection port 35 ° C, detector 35 ° C

Detector: differential refractometer

The molecular weight of the present invention is a value calculated by calculating the molecular weight of each elution time based on the dissolution profile of monodisperse polystyrene and calculating the molecular weight in terms of polystyrene.

<<Hydrophilic additive>>

The hydrophilic additive refers to a compound having a hydrophilic group capable of interacting (hydrogen bonding) with water. The hydrophilic group is preferably a polyether chain. The polyether chain is a skeleton structure in which an ether bond is bonded, and is, for example, synthesized by an addition reaction of an alkylene oxide such as ethylene oxide (hereinafter sometimes referred to as E0), propylene oxide or butylene oxide. A polyoxyethylene chain, a polyoxypropylene chain, a polyoxybutylene chain, or a polyglycerol chain synthesized by dehydration condensation of glycerin or the like, preferably a polyoxyethylene chain. The polyether chain may have one group or more groups in one molecule.

Among the various hydrophilic additives, in the present invention, a polyoxyethylene surfactant selected from the group consisting of ethylene oxide having an average addition mole number of 3 to 150 and a polyethylene glycol having an average molecular weight of 200 to 10,000 are added. At least one of them. In order to improve the inhibitory effect of the whitening phenomenon, it has been found that such a specific composition of a hydrophilic additive must be used in the test.

Further, the hydrophilic additive has an HLB value of 5 to 20. In order to enhance the inhibitory effect of the whitening phenomenon, it was found that such a hydrophilic additive having a specific HLB value must be used in the test. The HLB value is preferably 8 ~20, more preferably 10-20, most preferably 10-18. The HLB (Hydrophilic-lipophilic blance) value is a value indicating the hydrophilicity of the additive, and if the HLB value is 8 to 10, it is stably dispersed in water, and if it exceeds 10, it is changed from a dispersed state having a transparent feeling to a state of being completely transparent and transparent. . In the nonionic surfactant having a polyether chain, the HLB value = (molecular weight of the hydrophilic group portion) / (molecular weight of the additive) × 20 is calculated, and the hydrophilic additive HLB such as an alkane having no hydrophilic group is calculated. The value is 0. For polyethylene glycol having only a hydrophilic group, the HLB value is 20, and for the nonionic surfactant, the HLB value is between 0 and 20.

The hydrophilic additive is added so that the content in the 100% by mass of the styrene resin composition is 0.4 to 2.0% by mass. In order to maintain the heat resistance of the styrene resin composition and to suppress the whitening phenomenon, it has been found that the laboratory needs to be added in such a manner. The content of the hydrophilic additive in 100% by mass of the styrene resin composition is preferably 0.7 to 1.6% by mass or 0.6 to 1.4% by mass, and more preferably 0.6 to 0.9% by mass.

The heat loss of the hydrophilic additive at a temperature of 200 ° C and a nitrogen atmosphere is preferably 10% by mass or less. The heating loss at a temperature of 200 ° C under a nitrogen atmosphere can be obtained by thermogravimetric analysis (TGA), and is heated from a room temperature state at a temperature increase rate of 10 ° C / min under a nitrogen atmosphere, and a weight loss at a temperature of 200 ° C. Seek. The additive having a heating loss of more than 10% by mass in a nitrogen atmosphere at a temperature of 200 ° C has high volatility and generates gas during molding processing of the styrene resin, which may contaminate the mold and the roll.

The method of adding the hydrophilic additive is not particularly limited, and examples thereof include styrene resin. a polymerization step, a devolatilization step, a granulation step, a method of adding a mixture; a method of adding and mixing by an extruder or the like at the time of molding processing; and a resin composition adjusted to a high concentration of a hydrophilic additive by a styrene-based resin without addition A method in which the substance is diluted and mixed into a target content.

For example, a styrene resin composition containing 0.5 to 50.0% by mass of a hydrophilic additive and a non-added styrene resin are mixed by an extruder or an injection molding machine to obtain a styrene resin having a target concentration. The method of the object, the molded article, and the light guide plate.

<Polyoxyethylene 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 surface active agent. A polyoxyethylene type nonionic surfactant is preferred as the agent.

The polyoxyethylene type nonionic surfactant may, for example, be a polyoxyethylene alkyl ether represented by the following formula (1) or a polyoxyethylene fatty acid ester represented by the following formula (2) or a polyoxyethylene cured product. The sesame oil, the polyoxyethylene sorbitan fatty acid ester, and the polyoxyethylene sorbitan fatty acid ester are preferably one or more selected from the group consisting of polyoxyethylene alkyl ethers and/or polyoxyethylene fatty acid esters. Further, even a polyvalent polyoxyethylene alkyl ether having a plurality of polyoxyethylene alkyl ether skeletons in one molecule or a polyvalent polyoxyethylene fatty acid having a plurality of polyoxyethylene fatty acid ester skeletons in one molecule is used. Esters can also achieve the objects of the present invention. The valence of the polyoxyethylene alkyl ether and the polyoxyethylene fatty acid ester means the number of the polyoxyethylene alkyl ether skeleton or the polyoxyethylene fatty acid ester skeleton present in one molecule.

(In the formula, R represents an alkyl group having 8 to 20 carbon atoms. Further, it may be a polyvalent polyoxyethylene alkyl ether having a plurality of polyoxyethylene alkyl ether skeletons having a hexavalent number, or may have a plurality of A polyvalent polyoxyethylene fatty acid ester of a polyoxyethylene fatty acid ester skeleton having a valence of six. N is an integer and represents the number of moles of addition of an ethylene oxide unit.

Polyoxyethylene alkyl ether is obtained by adding ethylene oxide and alcohol, and polyoxyethylene fatty acid ester is obtained by adding ethylene oxide with fatty acid or directly esterifying fatty acid and polyethylene glycol. The average addition mole number of oxyethane is from 3 to 150. In order to improve the inhibitory effect of the whitening phenomenon, it is understood from the experimental results that the average addition mole number is required to be within such a specific range. The average addition mole number is preferably from 7 to 100, more preferably from 10 to 60, still more preferably from 10 to 50, most preferably from 13 to 35.

Specific examples of the polyoxyethylene surfactant of the present invention include dodecyl polyoxyethylene ether, hexadecyl polyoxyethylene ether, octadecyl polyoxyethylene ether, and octyl ten. Alkyl polyoxyethylene ether such as dialkyl polyoxyethylene ether, tetradecyl polyoxyethylene ether or 2-ethylhexyl polyoxyethylene ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbent Polyoxyethylene sorbitan fatty acid ester such as sugar anhydride tristearic acid, polyoxyethylene sorbitan fatty acid ester such as polyoxyethylene sorbitol tetraoleate, polyethylene glycol monolaurate Polyethylene glycol fatty acid esters such as polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate, polyoxyethylene cured castor oil, polyoxyethylene monomethyl Ethyl ether, polyoxyethylene dimethyl ether, polyoxyethylene glyceryl ether, polyoxyethylene tetraoleate, polyoxyethylene triisostearate, polyoxyethylene coconut fatty acid glyceride, and the like.

<polyethylene glycol>

The polyethylene glycol used in the present invention has an average molecular weight of 200 to 10,000, preferably 200 to 4,000, more preferably 200 to 1800, and most preferably 300 to 1,000. If 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 contaminated, which is not preferable. In addition, when it is more than 10,000, the effect of preventing the whitening phenomenon tends to be lowered, and the compatibility with the styrene resin is lowered, and the styrene resin composition and the molded article thereof are white turbid. The average molecular weight is a value calculated based on the concentration of a hydroxyl group (based on JIS K1557) measured by a phthalic anhydride pyridine method.

<<Additives ‧ Antioxidants>>

The styrene resin composition of the present invention may contain mineral oil insofar as it does not affect the colorless transparency of the present invention. Further, it may contain an internal lubricant such as stearic acid or ethylene bis-stearate, a hindered phenol-based antioxidant, a phosphorus-based antioxidant, a sulfur-based antioxidant, a lactone-based antioxidant, or a hindered amine-based stabilizer. Additives such as ultraviolet absorbers and antistatic agents. Further, as the external lubricant, ethylene bis-stearate is preferred, and it is preferably 30 to 200 ppm in the resin composition.

In the styrene-based resin composition of the present invention, since the deterioration of optical characteristics such as transmittance, color tone, and transparency as a characteristic of the styrene-based resin is small, it is possible to exhibit transparency, for example, as an optical material. It is preferably used in optical applications. Examples of the optical use include a lens, a light guide plate, a film, an optical fiber, and an optical waveguide.

By adding (c) 6-[3-(3-tertiary butyl-4-) to the styrene resin composition of the present invention Hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxane (6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyl-dibenzo[d,f][1,3,2 At least one of dioxaphosphepin (hereinafter referred to as "compound X"), (d) a phosphorus-based antioxidant, and (e) a hindered phenol-based antioxidant can impart long-term thermal stability. Long-term thermal stability is one of the important characteristics in fields that are used for a long period of time like optical applications. The long-term thermal stability shows a change in color tone and transmittance due to heat during long-term use, and a change in color tone and transmittance of the styrene-based resin composition excellent in thermal stability is small. For the long-term thermal stability, the molded article can be stored under high temperature conditions (60 to 90 ° C) to the extent that the resin is not deformed by an accelerated test, and the color tone and the transmittance are evaluated over time.

The 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. If the content of the compound X is less than 0.02% by mass, the long-term thermal stability is poor, and the initial color tone and transmittance are also deteriorated. In addition, even if it exceeds 0.40 mass%, long-term thermal stability deteriorates. The long-term thermal stability shows a change in color tone and transmittance due to heat during long-term use, and a change in color tone and transmittance of the styrene-based resin composition excellent in thermal stability is small. The long thermal stability can be evaluated by accelerating the test, and the molded article is stored under high temperature conditions (60 to 90 ° C) in which the resin is not deformed, and the change in color tone and transmittance is measured with time. The content of the compound X in 100% by mass of the styrene resin composition is specifically 0.02, 0.03, 0.04, for example. 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40% by mass, and may be a value within any two of the numerical values exemplified herein.

By adding the compound X to the styrene resin composition of the present invention, long-term heat stability can be imparted, and even if a phosphorus-based antioxidant and/or a hindered phenol-based antioxidant is added, long-term heat stability can be imparted.

The phosphorus-based antioxidant is preferably contained in an amount of 0.02 to 0.50% by mass, more preferably 0.05 to 0.40% by mass, even more preferably 0.05 to 0.30% by mass, based on 100% by mass of the styrene resin composition. If it is less than 0.02% by mass, the long-term thermal stability is poor, and the initial color tone and transmittance are also inferior. Even if it exceeds 0.50 mass%, long-term thermal stability deteriorates. The content of the phosphorus-based antioxidant in 100% by mass of the styrene 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, 0.30, 0.35, for example. 0.40, 0.45, and 0.50% by mass, and may be values in any two of the numerical values exemplified herein.

The hindered phenol-based antioxidant is preferably contained in an amount of 0.02 to 0.50% by mass, more preferably 0.02 to 0.30% by mass, even more preferably 0.05 to 0.30% by mass, based on 100% by mass of the styrene resin composition. If it is less than 0.02% by mass, the long-term thermal stability is poor, and the initial color tone and transmittance are also inferior. Even if it exceeds 0.50 mass%, long-term thermal stability deteriorates. The content of the hindered phenol-based antioxidant in 100% by mass of the styrene 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, 0.30, for example. 0.35, 0.40, 0.45, and 0.50% by mass, and may be values in any two of the numerical values exemplified herein.

The phosphorus-based antioxidant refers to a phosphite of a trivalent phosphorus compound. Examples of the phosphorus-based antioxidant include tris(2,4-di-tertiary butylphenyl)phosphite and 2,2'-methylenebis(4,6-di-tertiarybutyl- 1-phenyloxy)(2-ethylhexyloxy)phosphorus, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, 4,4'-biphenyldiphosphonic acid tetrakis(2, 4-di-tertiary butylphenyl), 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa- 3,9-diphosphorus [5.5]undecane, cyclopentane tetrakis(2,4-di-tert-butylphenylphosphite), dioctadecylpentaerythritol diphosphite , bis(nonylphenyl)pentaerythritol diphosphite, bis-[2-methyl-4,6-bis-(1,1-dimethylethyl)phenyl]ethyl phosphite, 9, 10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, tetrakis(2,4-di-tert-butyl-5-methylphenyl)-4,4'-biphenyl Diphosphonite and the like. As the phosphorus-based antioxidant, a phosphorus-based antioxidant excellent in hydrolysis resistance is preferable, and tris(2,4-di-tri-butylphenyl)phosphite and 2,2'-methylenebis (4, 6-di-tertiary butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, 3,9-double (2 , 6-di-tertiary butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane. Particularly preferred is tris(2,4-di-tertiary butylphenyl) phosphite. The phosphorus-based antioxidants may be used singly or in combination of two or more.

The hindered phenol-based antioxidant refers to an antioxidant having a phenolic hydroxyl group in the basic skeleton. The hindered phenol-based antioxidant may, for example, be octadecyl-3-(3,5-di-tri-butyl-4-hydroxyphenyl)propionate or 3,9-bis[2-[3 -(3-tert-butyl-4-hydroxy-5-methylphenyl)propanoxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[ 5.5] undecane, ethylene bis(oxyethylene) bis[3-(5-tris-butyl-4-hydroxy-m-tolyl)propionate], 4,6-bis (octyl) Thiomethyl)-o-cresol, 4,6-bis[(dodecylthio)methyl]-o-cresol, 2,4-dimethyl-6-(1-methylpentadecane Phenol, Tetrakis[methylene-3-(3,5-di-tri-butyl-4-hydroxyphenyl)propionate]methane, DL-α-tocopherol, 2-tris-butyl-6-(3 -tertiary butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2-[1-(2-hydroxy-3,5-di-tert-amylphenyl) 4-,6-di-tert-amylphenyl acrylate, 4,4'-thiobis(6-tri-butyl-3-methylphenol), 1,1,3-tris(2- Methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-butylene bis(3-methyl-6-tertiary butylphenol), bis-[3,3-double -(4'-Hydroxy-3'-tris-butylphenyl)-butyric acid]-ethylene glycol ester or the like. Preferred is octadecyl-3-(3,5-di-tertiarybutyl-4-hydroxyphenyl)propionate, 3,9-bis[2-[3-(3-tri-butyl)- 4-hydroxy-5-methylphenyl)propenyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane, ethylene Bis(oxyethylene)bis[3-(5-tris-butyl-4-hydroxy-m-tolyl)propionate]. The hindered phenol antioxidant may be used singly or in combination of two or more.

The method of adding the compound X, the phosphorus-based antioxidant, and the hindered phenol-based antioxidant is not particularly limited, and examples thereof include a method of adding and mixing by a polymerization step, a devolatilization step, and a granulation step of a styrene resin; A method of adding and mixing by an extruder, an injection molding machine, or the like; a method of diluting and mixing a resin composition adjusted to a high concentration of these additives into a target content by a styrene-based resin which is not added.

The ultraviolet absorber is a UV absorber having a function of suppressing deterioration or coloration by ultraviolet rays, and examples thereof include a benzophenone type, a benzotriazole type, a triazine type, a benzoate type, and a salicylate. A UV absorber such as a cyanoacrylate, an oxalic acid aniline, a malonate or a formazan. These may be used alone or in combination of two or more kinds, or a light stabilizer such as a 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 such as injection molding, extrusion molding, blow molding, and compression molding according to the purpose. The shape of the molded article may be a shape formed 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 forming the light guide plate, it is known to provide a reflection pattern such as a dot pattern on the back surface of the plate-shaped molded article (on the side opposite to the surface on which the light is emitted). When the resin sheet is processed into a light guide plate, it is preferable to polish the light incident surface or the entire surface of the resin sheet to form a mirror surface. Further, in order to improve the uniformity of the emitted light, a prism pattern may be provided on the surface of the plate-shaped molded article (the surface on which light can be emitted). The pattern on the front surface or the back surface of the plate-shaped molded article can be formed at the time of molding the plate-shaped molded article. For example, if it is injection-molded, it is a mold shape, and if it is extrusion-molded, a pattern is formed by roll transfer or the like.

The styrene resin composition of the present invention preferably has a Vicat softening temperature of 95 to 104 ° C and more preferably 97 to 104 ° C. If the Vicat softening temperature is less than 95 ° C, the heat resistance is insufficient, and the molded article may be deformed depending on the use environment.

When the molded article having a thickness of 4 mm is formed as the haze of the styrene resin composition of the present invention, 5% or less is preferable, and 1% or less is more preferable.

[Examples]

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

<<Test 1>>

(Manufacture of styrene resin A-1 to A-3)

The first reactor and the second reactor as a completely mixed agitation tank and the third reactor as a piston type flow reactor with a static mixer are connected in series to form a polymerization step, as shown in Table 1. The production of the styrene resin was carried out under the conditions shown. The capacities of the respective reactors were 39 liters in the first reactor, 39 liters in the second reactor, and 16 liters in the third reactor. The raw material solution was prepared using the raw material compositions described in Table 1, and the raw material solution was continuously supplied to the first reactor at the flow rate shown in Table 1. At the inlet of the first reactor, a polymerization initiator was added to the raw material solution so as to have an additive concentration (concentration based on the total amount of the raw material styrene and methacrylic acid) described in Table 1, and uniformly mixed. The polymerization initiators shown in Table 1 are as follows:

Polymerization Initiator-1: 2,2-bis(4,4-tri-butylperoxycyclohexyl)propane (PATORA A manufactured by Nippon Oil Co., Ltd.)

Polymerization initiator-2: 1,1-di(tri-butylperoxy)cyclohexane (using PERHEXA C manufactured by Nippon Oil Co., Ltd.)

Here, in the third reactor, a temperature gradient is generated along the flow direction, and the intermediate portion and the outlet portion are adjusted so as to have the temperature of Table 1.

Next, the polymer-containing solution continuously taken out by the third reactor was introduced into a vacuum devolatilization tank having a preheater consisting of two stages connected in series, and the preheating was adjusted so as to have the resin temperature shown in Table 1. The temperature of the heat exchanger was adjusted according to the pressures shown in Table 1, and the unreacted styrene and ethylbenzene were separated, and then extruded into a strand shape by a porous die, and the strands were cooled by a cold solution method. And cut and granulated.

【Table 1】

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

The styrene resin A-1 to A-3 and the additive were melt-kneaded at a cylinder temperature of 230 ° C and a screw rotation speed of 100 rpm using a single-screw extruder having a screw diameter of 40 mm as shown in Table 2. One grain. The additives used in Table 2 are as follows.

B-1: Ethylene lauryl polyoxyethylene ether, ethylene oxide, average addition mole number = 25 (EMULGEN 123P, manufactured by Kao Corporation)

B-2: Vinyl octadecyl polyoxyethylene ether Ethylene oxide average addition mole number = 12 (EMULGEN 320P manufactured by Kao Corporation)

B-3: Ethylene lauryl polyoxyethylene ether, ethylene oxide, average addition mole number = 9 (EMULGEN 109P, manufactured by Kao Corporation)

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

B-5: Ethylene lauryl polyoxyethylene ether, ethylene oxide, average addition mole number = 30 (EMULGEN 130K, manufactured by Kao Corporation)

B-6: Vinyl lauryl polyoxyethylene ether, ethylene oxide average addition mole number = 47 (EMULGEN 150, manufactured by Kao Corporation)

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

B-8: Polyethylene glycol monolaurate Ethylene oxide average addition mole number = 12 (Malay Co., Ltd. EMANON 1112)

B-9: Vinyl octadecyl polyoxyethylene ether Ethylene oxide average addition mole number = 6 (EMULGEN 306P, manufactured by Kao Corporation)

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

B-11: Polyethylene glycol having an average molecular weight of 400 (PEG#400 manufactured by Nippon Oil Co., Ltd.)

B-12: Polyethylene glycol having an average molecular weight of 300 (PEG#300 manufactured by Nippon Oil Co., Ltd.)

B-13: Polyethylene glycol having an average molecular weight of 600 (PEG#600 manufactured by Nippon Oil Co., Ltd.)

B-14: Polyethylene glycol having an average molecular weight of 1000 (PEG#1000 manufactured by Nippon Oil Co., Ltd.)

B-15: Polyethylene glycol having an average molecular weight of 2000 (PEG#2000 manufactured by Nippon Oil Co., Ltd.)

B-16: Polyethylene glycol having an average molecular weight of 3,100 (PEG #4000, manufactured by Nippon Oil Co., Ltd.)

B-17: Polyethylene glycol having an average molecular weight of 8800 (PEG#6000 manufactured by Nippon Oil Co., Ltd.)

B-18: Polyoxyethylene monomethyl ether (UNIOX M-550 by Nippon Oil Co., Ltd.)

B-19: Polyoxyethylene triisostearic acid (UNIOX GT-20IS manufactured by Nippon Oil Co., Ltd.)

B-20: Octyldodecyl polyoxyethylene ether (EMULGEN 2025G, manufactured by Kao Corporation)

B-21: Polyoxyethylene glyceryl ether (UNIOX G-750, manufactured by Nippon Oil Co., Ltd.)

B-22: Polyoxyethylene tetraoleic acid (UNIOX ST-30E, manufactured by Nippon Oil Co., Ltd.)

B-23: octadecyl alcohol (KALCOL 8098, manufactured by Kao Corporation)

B-24: Stearic acid monoglyceride (EXCEL S-95, manufactured by Kao Corporation)

B-25: Polyethylene glycol having an average molecular weight of 60,000 (ALKOX L-6, manufactured by Mingcheng Chemical Industry Co., Ltd.)

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

Using the obtained pellets, injection molding was carried out at a cylinder temperature of 230 ° C and a mold temperature of 50 ° C to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm.

Further, in Examples 1-33, the styrene resin A-1 and the additive B-1 were melt-kneaded at a cylinder temperature of 230 ° C and a screw rotation speed of 100 rpm using a single-axis extruder having a screw diameter of 40 mm, once the additive B was obtained. After the concentration of -1 is 20% by mass of the particles, the particles and the styrene resin A-1 are made into 1: A molded article obtained by mixing and molding by a ratio of 24 ratio.

<MFR>

The MFR (melt mass flow rate) of the styrene resin composition was measured based on JIS K 7210 under the conditions of a load of 49 ° C and 49 N.

<Initial tone evaluation>

A test piece having a thickness of 115 × 85 × 3 mm was cut out from the obtained plate-shaped molded article, and the end surface was polished by polishing to obtain a plate-shaped molded article having a mirror surface on the end surface. For the obtained plate-shaped molded product, an ultraviolet visible spectrophotometer V-670 manufactured by JASCO Corporation was used, and a wavelength of 350 nm to 800 nm at an optical path length of 115 mm was measured under incident light having a size of 20 × 1.6 mm and a diffusion angle of 0°. The spectral transmittance is calculated according to JIS K7105, and the YI value at a viewing angle of 2° of the C light source is calculated. The value obtained is "YI 115 mm" of Table 2. Further, "transmittance 115 mm" shown in Table 2 indicates an average transmittance of a wavelength of 380 nm to 780 nm.

Further, "haze 4 mm" in Table 2 was obtained in the following manner, that is, using the pellets obtained in the above steps, injection molding was carried out at a cylinder temperature of 220 ° C and a mold temperature of 40 ° C to make a thickness of 55 × 50 × 4 mm. The test piece obtained by the use of the test piece obtained by the NDH5000 (manufactured by Nippon Denshoku Industries Co., Ltd.) was measured by JIS K-7105 to obtain a value, and the test piece was used for "YI 4 mm" in Table 2. A value obtained by measurement using a colorimetric color difference meter NDJ4000 (manufactured by Nippon Denshoku Industries Co., Ltd.) by a reflection method.

<Whitening inhibition effect>

In addition, in order to confirm the whitening phenomenon caused by environmental changes, the plate-shaped molded article having a mirror surface on the end surface was exposed to an environment of 60 ° C and 90% relative humidity for 150 hours, and the test piece was taken out at 23 ° C and 50% relative humidity. The whitening phenomenon generated inside the molded article was observed, and the whitening suppression effect was determined as follows.

◎: no whitening at all

○: A little whitening after taking out for 1 hour, but disappearing after 24 hours

△: whitening after taking out for 1 hour, but almost disappeared after 24 hours

×: Significantly whitened after taking out for 1 hour, even if it does not disappear after 24 hours

<Vicat Softening Temperature>

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

<Comprehensive evaluation>

Comprehensive evaluation was carried out based on the following criteria.

S: The whitening inhibition effect is ◎ and the Vicat softening temperature is 100 ° C or higher.

A: The condition of S cannot be sufficiently satisfied, the whitening suppression effect is ◎ and the Vicat softening temperature is 98° C. or higher, or the whitening suppression effect is ○ and the Vicat softening temperature is 100° C. or higher.

B: The condition of A cannot be sufficiently satisfied, the whitening suppression effect is ◎ and the Vicat softening temperature is 95° C. or higher, or the whitening suppression effect is ○ and the Vicat softening temperature is 98° C. or higher, or the whitening suppression effect is Δ and Vicat softening Temperature is above 100 °C

C: cannot fully satisfy any of the above conditions

The characteristics and evaluation results of the respective resin compositions are shown in Table 2.

The molded article according to the examples is excellent in the whitening suppressing effect, and the transmittance and the YI value are not deteriorated, and the transparency and the color tone are also excellent. In the comparative examples 1-1, 1-2, and 1-4 in which the hydrophilic additive was not added or the amount of addition was too small, the suppression of the whitening status was insufficient. In Comparative Examples 1-3 and 1-5 in which the hydrophilic additive was excessively added, the heat resistance was excessively lowered. Further, in Comparative Examples 1-6 and 1-7, octadecyl alcohol or stearic acid monoglyceride as a hydrophilic additive was separately added and tested, but the whitening inhibitory effect was insufficient. Further, 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 cloudy.

From the above results, in order to maintain the heat resistance and transparency of the styrene resin composition and to suppress the whitening phenomenon, it is necessary to satisfy the following three conditions: (1) the hydrophilic additive has a characteristic configuration, and (2) the HLB value is specific. A value within the range, and (3) an amount whose content is a specific range. Referring to Examples 1-20 to 1-21, the same results were obtained even when the styrene resin was a copolymer of a styrene monomer and (meth)acrylic acid or (meth)acrylate.

<<Test 2>>

(Examples 2-1 to 2-46)

The first reactor and the second reactor as a completely mixed agitation tank and the third reactor as a piston type flow reactor with a static mixer are connected in series to form a polymerization step, as shown in Table 1. The production of the styrene resin was carried out under the conditions shown. The capacities of the respective reactors were 39 liters in the first reactor, 39 liters in the second reactor, and 16 liters in the third reactor. The raw material solution was prepared using the raw material compositions described in Table 1, and the raw material solution was continuously supplied to the first reactor at the flow rate shown in Table 1.

Further, at the inlet of the third reactor, a hydrophilic additive having a polyether chain was added 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 manufactured by Nippon Oil Co., Ltd.)

B-2: Polyethylene glycol having an average molecular weight of 1000 (PEG#1000 manufactured by Nippon Oil Co., Ltd.)

B-3: Polyethylene glycol having an average molecular weight of 2,000 (PEG#2000 manufactured by Nippon Oil Co., Ltd.)

B-4: Ethylene lauryl polyoxyethylene ether, ethylene oxide, average addition mole number = 25 (EMULGEN 123P, manufactured by Kao Corporation)

B-5: Vinyl lauryl polyoxyethylene ether, ethylene oxide average addition mole number = 12 (EMULGEN 320P, manufactured by Kao Corporation)

B-6: Ethylene lauryl polyoxyethylene ether Ethylene oxide average addition mole number = 9 (EMULGEN 109P, manufactured by Kao Corporation)

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

B-8: Polyethylene glycol monolaurate Ethylene oxide average addition mole number = 12 (Malay Co., Ltd. EMANON 1112)

Next, the polymer-containing solution continuously taken out to the third reactor is introduced into a vacuum devolatilization tank having a preheater consisting of two stages connected in series, and the unreacted styrene and ethylbenzene are separated and then extruded. After being stranded and cooled, the cut was made to form pellets. Here, the resin temperature in the devolatilization tank of the first stage is set to 160 ° C, the pressure of the vacuum devolatilization tank is 65 kPa, and the resin temperature in the devolatilization layer of the second stage is set to 235 ° C, and the pressure of the vacuum devolatilization tank It is 0.8 kPa.

Next, the pellets of the styrene-based resin and the compound X, the additive D and the additive E as additional additives were obtained at a cylinder temperature of 230 using a uniaxial extruder having a screw diameter of 40 mm as shown in Table 3. The mixture was melt-kneaded at ° C and a screw rotation speed of 100 rpm to obtain pellets. The compounds X, D and E used in Table 3 are shown below. Here, the compound X represents 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tertiary butyl Benzo[d,f][1,3,2]dioxepane, additive D represents a phosphorus-based antioxidant, and additive E represents a hindered phenol-based antioxidant.

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

D-1: tris(2,4-di-tertiary butylphenyl) phosphite (Irgafos 168, manufactured by BASF Japan Co., Ltd.)

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

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

D-4: 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphorane [5.5] Undecane (ADKSTAB PEP-36 manufactured by ADEKA Co., Ltd.)

E-1: octadecyl-3-(3,5-di-tri-butyl-4-hydroxyphenyl)propionate (Irganox 1076, manufactured by BASF Japan Co., Ltd.)

E-2: 3,9-bis[2-[3-(3-tri-butyl-4-hydroxy-5-methylphenyl)propanoxy]-1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro[5.5]undecane (made by ADEKA Co., Ltd.) ADKSTABAO-80)

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

In addition, the melt mass flow rate (MFR) is measured according to JIS K 7210 under the conditions of 200 ° C and 49 N load, and the Vicat softening temperature is according to JIS K 7206, at a heating rate of 50 ° C / hr, and a test load of 50 N. The measurement was carried out.

Further, using the obtained pellets, injection molding was carried out at a cylinder temperature of 230 ° C and a mold temperature of 50 ° C to form a plate-shaped molded article having a thickness of 127 × 127 × 3 mm. In order to evaluate long-term heat stability, the obtained molded article was stored in an oven temperature of 80 ° C for 1,000 hours. In order to evaluate the optical properties of the initial molded product before storage and the molded product after storage, a test piece having a thickness of 115 × 85 × 3 mm was cut out from the plate-shaped molded product, and the end surface was polished by polishing to prepare a plate having a mirror surface at the end surface. Shaped product. For the plate-shaped molded product after polishing, an ultraviolet visible spectrophotometer V-670 manufactured by JASCO Corporation was used to measure a wavelength of 350 nm at an optical path length of 115 mm under incident light having a size of 20 × 1.6 mm and a diffusion angle of 0°. The spectral transmittance at 800 nm was calculated according to JIS K7105, and the YI value at a viewing angle of 2° of the C light source was calculated. The transmittance shown in Table 3 is an average transmittance indicating a wavelength of 380 nm to 780 nm.

Next, the ΔYI difference is calculated based on the following formula.

ΔYI difference = (the difference in the example in which the additive is added is compared with the initial YI) - (in the example without the additive, the phase difference is compared with the initial YI)

In an example, in Example 2-2 in which an additive was added, the value compared with the initial YI difference was 1.1. In Example 2-1 without additional additives, the difference in YI from the initial stage was 5.1, so the difference in ΔYI of Example 2-2 was -4.0. This value indicates an effect of improving the long-term thermal stability caused by the additional additive (compound X, phosphorus-based D, and hindered phenol-based E), and the smaller the value, the greater the effect of improving the long-term thermal stability.

In addition, in order to confirm the whitening phenomenon due to environmental changes, the plate-shaped molded article having a mirror surface on the end surface was exposed to an environment of 60 ° C and 90% relative humidity for 150 hours, and the test piece was taken out at 23 ° C and 50% relative humidity. The whitening phenomenon generated inside the molded article was observed, and the whitening suppression effect was determined as follows.

◎: no whitening at all

○: A little whitening after taking out for 1 hour, but disappearing after 24 hours

△: whitening after taking out for 1 hour, but almost disappeared after 24 hours

×: Significantly whitened after taking out for 1 hour, even if it does not disappear after 24 hours

<Comprehensive evaluation>

The evaluation results of the whitening suppression effect, the ΔYI difference, and the Vicat softening temperature were numerically calculated based on the following criteria.

The fractional value of the whitening inhibition effect (◎→3; ○→2; △→1; ×→0)

ΔYI difference score value (-4.0 or less→4; -3.5 or less→3; -2.5 or less→2; -1.5 or less→1; otherwise →0)

The value of the Vicat softening temperature (99 °C or more → 3; 97 ° C or more → 2; 95 ° C or more → 1; other than → 0)

The total of the score values obtained based on the above criteria was comprehensively evaluated based on the following criteria. S: 10; A: 9; B: 8; C: 7; D: 6 or less

Table 3 shows the characteristics and evaluation results of the respective resin compositions. In Examples 2-1 to 2-42, styrene resin A-1 prepared according to Condition 1 was used, and styrene resin A-2 prepared according to Condition 2 was used in Examples 2-43 to 2-44. In the examples 2-45 to 2-46, the styrene resin A-3 prepared according to Condition 3 was used.

Referring to Table 3, it was found that all of the examples had excellent whitening inhibitory effects. Further, in Comparative Examples 2-1 to 2-35 and Examples 2-36 to 2-42, it is understood that when the content of the compound X is 0.02 to 0.40% by mass, the long-term thermal stability is particularly excellent. Further, referring to Examples 2-43 to 2-46, the same results were obtained when the styrene resin was a copolymer of a styrene monomer and (meth)acrylic acid or (meth)acrylic acid ester.

<<Trial 3>>

(Examples 3-1 to 3-36)

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

The results are shown in Table 4.

Referring to Table 4, all of the examples were excellent in whitening suppression effects. Further, in Comparative Examples 3-1 to 3-24 and Examples 3-25 to 3-32, it is understood that when the content of the phosphorus-based D is 0.05 to 0.40% by mass and the content of the phenol-based E is 0.02 to 0.30% by mass, the long-term The thermal stability is particularly excellent. Further, referring to Examples 3-33 to 3-36, the same results were obtained even when the styrene resin was a copolymer of a styrene monomer and (meth)acrylic acid or (meth)acrylic acid ester.

[Industrial availability]

The styrene-based resin composition of the present invention can prevent the whitening phenomenon due to environmental changes, and is excellent in transparency and color tone. Therefore, it is possible to maintain the advantage of being a styrene-based resin in applications in which whitening has been caused by environmental changes. The transparency can be preferably used.

In addition, since the styrene resin composition having excellent long-term thermal stability has a small change in color tone, it can be used while maintaining long-term transparency and color tone as compared with the related art.

For example, it can be applied to a light guide plate of a television, a desktop personal computer, a notebook personal computer, a mobile phone, a car navigation, or the like.

Claims (15)

A styrene resin composition for optical use comprising a styrene resin having a weight average molecular weight of 150,000 to 700,000 and a hydrophilic additive, wherein the styrene resin composition for optical use is characterized in that the hydrophilic additive is a polyoxyethylene surfactant selected from the group consisting of ethylene oxide having an average addition mole number of 3 to 150 and at least one of polyethylene glycol having an average molecular weight of 200 to 10,000, and an HLB value of 5 to 20, and The content in 100% by mass of the styrene resin composition is 0.4 to 2.0% by mass. The styrene-based resin composition for optical use according to the first aspect of the invention, wherein the hydrophilic additive is a polyoxyethylene surfactant having an average addition mole number of ethylene oxide of 10 to 60. The content in the 100% by mass of the styrene resin composition is 0.6 to 1.4% by mass. The styrene-based resin composition for optical use according to claim 1 or 2, wherein the hydrophilic additive is a polyoxyethylene type surface active having an average addition mole number of ethylene oxide of 13 to 35. The content of the agent in 100% by mass of the styrene resin composition is 0.6 to 0.9% by mass. The styrene-based resin composition for optical use according to claim 3, wherein the hydrophilic additive has an HLB value of 10 to 18. The styrene-based resin composition for optical use according to any one of claims 1 to 4, wherein the polyoxyethylene-type surfactant is a polyoxyethylene-type nonionic surfactant. The styrene-based resin composition for optical use according to any one of claims 1 to 5, wherein the polyoxyethylene-type nonionic surfactant is selected from the following formula (1) One or more of the polyoxyethylene alkyl ethers represented by the polyoxyethylene alkyl ethers and/or the polyoxyethylene fatty acid esters represented by the following formula (2), In the formula, R represents an alkyl group having 8 to 20 carbon atoms; and may be a polyvalent polyoxyethylene alkyl ether having a valence of 6 or more having a plurality of polyoxyethylene alkyl ether skeletons, and having a plurality of polyoxyethylene fats The polyvalent polyoxyethylene fatty acid ester having a valence of from hexavalent to the acid ester skeleton, n being an integer and indicating the number of moles of addition of the ethylene oxide unit. The styrene resin composition for optical use according to claim 1, wherein the hydrophilic additive is polyethylene glycol having an average molecular weight of 200 to 10,000, and the styrene resin composition is 100 mass. The content in % is 0.6 to 1.4% by mass. The styrene-based resin composition for optical use according to claim 7, wherein the hydrophilic additive is polyethylene glycol having an average molecular weight of 200 to 1800. The styrene-based resin composition for optical use according to the invention, wherein the content of the hydrophilic additive in 100% by mass of the styrene resin composition is 0.6 to 0.9% by mass. The styrene resin composition for optical use according to any one of claims 1 to 9, wherein the styrene resin is a copolymer of a styrene monomer and (meth)acrylic acid. The content of the styrene-(meth)acrylic copolymer resin, the styrene monomer unit of the styrene resin is 90.0 to 99.9% by mass, and the content of the (meth)acrylic acid unit is 0.1 to 10.0% by mass. The total content of the styrene monomer unit and the (meth)acrylic unit of the styrene resin was 100% by mass. The styrene resin composition for optical use according to any one of claims 1 to 9, wherein the styrene resin is a styrene monomer and a (meth) acrylate. Styrene-(meth)acrylate copolymer resin obtained by copolymerization, styrene series of styrene resin The content of the bulk unit is 40.0 to 99.0% by mass, and the content of the (meth) acrylate unit is 1.0 to 60.0% by mass, wherein the content of the styrene monomer unit and the (meth) acrylate unit of the styrene resin The total amount is 100% by mass. The styrene resin composition for optical use according to any one of claims 1 to 11, which further contains 6-[3-(3-tert-butyl-4-hydroxy-5) -Methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxane. The styrene-based resin composition for optical use according to any one of claims 1 to 12, which contains a phosphorus-based antioxidant and/or a hindered phenol-based antioxidant. A molded article of the styrene resin composition for optical use according to any one of claims 1 to 13. A light guide plate comprising the molded article according to item 14 of the patent application.