JP2015195151A - light guide plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide plate that uses, as a raw material, polystyrene advantage of dimension stability of moldability because of low water absorption, is used as a surface light source of an edge light type liquid crystal display device, and solves the problem that white turbidity occurs due to sudden change of humidity and temperature.SOLUTION: A light guide plate comprises a styrene resin composition that contains any two or more kinds of 0.1-0.5 pt.mass of polyethylene glycol having an average molecular weight 200-1000, 0.1-0.5 pt.mass of styrene block copolymer rubber, 1.0-5.0 pts.mass of terpene phenol resin having hydroxyl value of 150 or more, based on 100 pts.mass of styrene resin.

Description

  The present invention relates to a light guide plate made of a polystyrene resin composition that suppresses the occurrence of white turbidity caused by fine crazes generated by rapid changes in temperature and humidity.

  There are two types of backlights for liquid crystal display devices: a direct type in which a light source is disposed in front of the display device and an edge light type in which a light source is disposed on a side surface. The light guide plate is used for an edge light type backlight and plays a role of guiding light from a light source disposed on a side surface to the front. Edge-light type backlights are used in applications that require thinner thickness, such as monitors for TVs, personal computers (for example, for desktops and notebooks), monitors for car navigation systems, mobile phones, PDAs, etc. In many cases, the use of edge-lit backlights is increasing in large-screen TVs (32-inch or larger) TVs, which were mostly direct type, and are now the mainstream of backlights.

In the edge light system, since the light transmission distance in the light guide plate is relatively long, the light loss in the light guide plate is large, and in order to prevent the light loss, the material is required to have a high light transmittance. For this reason, acrylic resin such as methyl methacrylate is often used for the light guide plate, but due to the high water absorption of the acrylic resin, warping of the molded product when water is absorbed from one side or when water is absorbed from the entire surface. There is a problem that a dimensional change occurs, and this problem becomes more noticeable when the screen size is large.
On the other hand, the styrene resin has a low water absorption rate (about 0.05%), so there is no problem of warping or dimensional change of the molded product. Although it is a styrenic resin that is excellent in terms of dimensional stability due to water absorption, there is a problem that white turbidity may occur when exposed to a rapid environmental change (from high temperature / high humidity to room temperature, etc.). This phenomenon is caused by the fact that water that was uniformly present in the styrene resin is rapidly cooled and phase-separated in the resin, resulting in the formation of fine disc-shaped crazes. Due to water absorption.

As means for preventing the occurrence of white turbidity, it is possible to give water absorption by copolymerizing methyl methacrylate or the like (MS resin), but the warpage or dimensional change of the molded product is worsened.
Moreover, as means for improving the white turbidity of the light guide plate made of styrene resin at the time of a sudden environmental change, the following Patent Document 1 includes a styrene resin containing 0.4 to 2.0% by mass of a hydrophilic additive. Although a method of using a composition has been proposed, the generation of white turbidity is improved, and the low water absorption characteristic of a styrene resin is impaired. As a result, the light guide plate particularly for a large screen liquid crystal TV is used. In addition, there is a significant influence on the dimensional stability of a large-sized molded product.

International Publication No. 2013/094641

  In view of the above-described state of the art, the problem to be solved by the present invention is to provide a light guide plate made of a styrene-based resin composition that suppresses white turbidity due to rapid changes in temperature and humidity.

  As a result of intensive investigations and repeated experiments to solve the above problems, the present inventors have determined that a predetermined amount of polyethylene glycols, a predetermined amount of styrene block copolymer rubber, and a predetermined amount of styrene resin. It finds that the said subject is solved by manufacturing a light-guide plate using the styrenic resin composition obtained by adding any two or more of three types of terpene resins, and completes this invention. Has been reached.

That is, the present invention is as follows.
[1] 0.1 to 0.5 parts by mass of polyethylene glycol having an average molecular weight of 200 to 1000, 0.1 to 0.5 parts by mass of styrene block copolymer rubber, and hydroxyl group with respect to 100 parts by mass of styrene resin A light guide plate comprising a styrenic resin composition, containing any two or more of 1.0 to 5.0 parts by mass of a terpene phenol resin having a valence of 150 or more.

  [2] In the above [1], the styrene resin further contains 0.02 to 0.2 parts by mass of a phosphorus antioxidant and 0.02 to 0.2 parts by mass of a phenolic antioxidant. The light guide plate described.

  The light guide plate made of the styrene-based resin composition according to the present invention has low water absorption, thereby suppressing warpage or dimensional change of the molded product and suppressing white turbidity due to rapid changes in temperature and humidity. It can be compatible.

Hereinafter, embodiments of the present invention will be described in detail.
<Styrenic resin composition>
As described above, the styrene resin composition according to the embodiment of the present invention has an average molecular weight of 200 to 1000 polyethylene glycol of 0.1 to 0.5 parts by mass and a styrene block with respect to 100 parts by mass of the styrene resin. It is characterized by containing any two or more of three types of copolymer rubber 0.1 to 0.5 parts by mass and 1.0 to 5.0 parts by mass of a terpene phenol resin having a hydroxyl value of 150 or more. If necessary, various additives are included in a specific ratio.

<Styrene resin>
The styrene resin is a resin containing a styrene monomer as a main component (specifically, more than 50% by mass). Examples of the styrene monomer used to form the styrene resin include styrene, α-methyl styrene, paramethyl styrene, ethyl styrene, propyl styrene, butyl styrene, chlorostyrene, bromostyrene, and the like. . Of these, styrene is preferred. Further, as the styrene resin, a comonomer copolymerizable with styrene may be used. Examples of comonomer copolymerizable with styrene include (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate; α-methylstyrene, o-, aromatic vinyl monomers other than styrene such as m-, p-methylstyrene, bromostyrene, dibromostyrene, chlorostyrene, dichlorostyrene; unsaturated fatty acids such as (meth) acrylic acid, maleic acid, fumaric acid; And unsaturated difatty acid anhydrides such as maleic anhydride and itaconic anhydride; unsaturated difatty acid imides such as N-phenylmaleimide and the like. These monomers can be used individually by 1 type or in combination of 2 or more types.

  The styrenic resin according to the embodiment of the present invention is obtained by thermally polymerizing a monomer component containing a styrenic monomer or by polymerizing by using one or more organic peroxides as a polymerization initiator. Can be obtained. Specific examples of the organic peroxide include peroxyketals such as 1,1-bis (t-butylperoxy) cyclohexane; di-t-butyl peroxide, 2,5-dimethyl-2,5-di ( dialkyl peroxides such as tert-butylperoxy) hexane; diacyl peroxides such as benzoyl peroxide and m-toluoyl peroxide; peroxyesters such as dimyristylperoxydicarbonate; ketones such as cyclohexanone peroxide Peroxides; hydroperoxides such as p-mentahydroperoxide; 2,2-bis (4,4-ditertiarybutylperoxycyclohexyl) propane, 2,2-bis (4,4-ditertiary amylper) Oxycyclohexyl) propane, 2,2-bis (4 4 ditertiary butyl peroxy cyclohexyl) butane, 2,2-bis (4,4-dicumyl oxycyclohexyl) can be exemplified polyfunctional peroxides such as propane.

These organic peroxides are added to the polymerization system (polymerization raw material solution or solution during polymerization) in any step of the polymerization of the monomer component containing the styrene monomer. These organic peroxides may be added to the polymerization raw material solution or may be added to the solution in the middle of polymerization divided into a plurality of times as necessary. The addition amount of the organic peroxide is preferably 0.0005 parts by mass to 0.2 parts by mass, more preferably 0.01 parts by mass to 0.1 parts by mass, with respect to 100 parts by mass of the polymerization raw material solution. More preferably, it is 0.03 mass part-0.08 mass part. If the amount of the organic peroxide added is 0.0005 parts by mass or more, the desired effect of addition of the polymerization initiator can be obtained. On the other hand, if it is 0.2 parts by mass or less, the reaction heat during polymerization Is preferable because it is less likely to occur and the control of polymerization becomes easy.
In the embodiment of the present invention, 4-t-butylcatechol is preferably used as a polymerization inhibitor during storage of the styrene monomer.

Examples of the polymerization method of the monomer component containing the styrene monomer include bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these, bulk polymerization or solution polymerization is preferable, and continuous bulk polymerization or continuous solution polymerization is particularly preferable in terms of both productivity and economy. That is, a monomer component containing a styrene-based monomer, or a polymerization solvent such as ethylbenzene, toluene, xylene as necessary, an organic peroxide as a radical initiator, a chain transfer agent, a stabilizer, liquid paraffin (mineral oil) The raw material solution in which additives such as) are mixed and dissolved is supplied to a reactor equipped with a stirrer, and a monomer component containing a styrene monomer can be polymerized. When organic peroxide is used as the radical initiator, the polymerization temperature takes into account the decomposition temperature of organic peroxide, productivity, heat removal capability of the reactor, fluidity of the target styrene polymer, etc. And can be set using a known technique. The polymerization solution exiting the polymerization reactor is guided to a recovery device as a degassing step, and the solvent and unreacted monomers are removed by heating and vacuum devolatilization. As the recovery device, a device commonly used in the production of a styrene resin, for example, a flash tank system, a multistage vented extruder, or the like can be used.
As the polymerization apparatus for the polymerization raw material containing the styrene monomer, any of a complete mixing type, a plug flow type, a plug flow type equipped with a circulation device, and the like can be suitably used. Among these, a complete mixing type polymerization apparatus is preferable from the uniformity of composition distribution.

<Polyethylene glycol>
In the styrene resin composition constituting the light guide plate according to the present invention, 0.1 to 0.5 parts by mass of polyethylene glycol having an average molecular weight of 200 to 1000 with respect to 100 parts by mass of the styrene resin, It can contain as any 2 or more types of components.
The average molecular weight of the polyethylene glycol used in the embodiment of the present invention is 200 to 1000, preferably 200 to 500, more preferably 300 to 400. When the average molecular weight is less than 200, there is a problem that gas is generated when heated such as during molding to contaminate a roll or a mold. Further, when the average molecular weight exceeds 1000, there is a problem in that the light transmittance is lowered due to a decrease in compatibility with the styrene resin.
As content of polyethyleneglycol, it is 0.1-0.5 mass part with respect to 100 mass parts of styrene resin, Preferably it is 0.1-0.4 mass part. If the content of polyethylene glycol is less than 0.1 parts by mass, the clouding phenomenon due to a rapid change in temperature and humidity may not be improved. If the content exceeds 0.5 parts by mass, the molded product is formed by water absorption of polystyrene glycol. There is a possibility that the dimensional stability of the glass is impaired.

<Styrenic block copolymer rubber>
Styrenic resin composition is 0.1 to 0.5 parts by mass of styrene block copolymer rubber with respect to 100 parts by mass of styrene resin, as any two or more of the above three types, Can be contained.
The styrene block copolymer rubber used in the present invention is a block comprising one or more polymer blocks composed of styrene monomers and one or more polymer blocks composed of conjugated diene monomers. As a general copolymer, a block copolymer composed of styrene and 1,3-butadiene, which is called SBS, and tufprene manufactured by Asahi Kasei Chemical Corporation are listed. The content of the styrene block copolymer rubber is 0.1 to 0.5 parts by mass, preferably 0.1 to 0.4 parts by mass with respect to 100 parts by mass of the styrene resin. If the content of the styrene block copolymer rubber is less than 0.1 parts by mass, the cloudiness phenomenon due to a rapid change in temperature and humidity may not be improved. If the content exceeds 0.5 parts by mass, The total light transmittance may be impaired.

で表されるヤスハラケミカル株式会社製ＹＳ ポリスターシリーズ（Ｎ１２５、Ｋ１２５、Ｋ１４０）等が挙げられる。テルペンフェノール樹脂の含有量は、スチレン系樹脂１００質量部に対して、１．０〜５．０質量部、好ましくは１．０〜４．０質量部である。テルペンフェノール樹脂の含有量が１．０質量部未満であると、温度、湿度の急激な変化による白濁現象が改善しない虞があり、５．０質量部を超えると、ビカット軟化温度など耐熱性が低下する虞がある。 <Terpene resin>
Styrenic resin composition is 1.0-5.0 parts by mass of terpene phenol resin having a hydroxyl value of 150 or more with respect to 100 parts by mass of styrene resin, as any two or more of the above three types. Can be contained.
The terpene phenol resin used in the present invention is a resin obtained by copolymerizing a monomer comprising (A) a terpene monomer and (B) a phenolic monomer.
(A) The terpene monomer is a compound represented by the molecular formula (C ₅ H ₈ ) _n , and preferred terpene monomers include α-pinene, β-pinene, dipentene and the like.
(B) Preferable examples of the phenolic monomer include phenol and cresol.
The terpene phenol resin according to the present invention has a hydroxyl value measured by the method described in JIS K0070-1992 of 150 (KOHmg / g) or more, preferably 200 (KOHmg / g). (I):

YS polystar series (N125, K125, K140) manufactured by Yasuhara Chemical Co., Ltd. The content of the terpene phenol resin is 1.0 to 5.0 parts by mass, preferably 1.0 to 4.0 parts by mass with respect to 100 parts by mass of the styrene resin. If the content of the terpene phenol resin is less than 1.0 part by mass, the cloudiness phenomenon due to a rapid change in temperature and humidity may not be improved. If the content exceeds 5.0 parts by mass, heat resistance such as Vicat softening temperature is obtained. May decrease.

<Additives>
In the embodiment of the present invention, it is necessary at an arbitrary stage before and after the styrene resin recovery process at the time of production of the styrene resin, or at a stage of performing extrusion processing, molding processing, etc. using the styrene resin composition. Depending on the situation, various additives may be added to the system in addition to polyethylene glycol, styrene block copolymer rubber, and terpene phenol resin. In a preferred embodiment, the styrenic resin composition comprises a phosphorus antioxidant, a phenolic antioxidant, a higher fatty acid, a higher aliphatic alcohol, an ultraviolet absorber, a light stabilizer, a lubricant, an antistatic agent, a flame retardant, a dye or At least one additive selected from the group consisting of pigments, optical brighteners, and selective wavelength absorbers may be included. In a more preferred embodiment, the styrenic resin composition is at least one selected from the group consisting of polyethylene glycol, styrenic block copolymer rubber, terpene phenol resin, phosphorus antioxidant, and phenolic antioxidant. One additive can be included.

で表される亜リン酸トリス(2,4-ジ-t-ブチルフェニル）であるアデカスタブ２１１２が薄黄色着色の低減という観点から好ましい。 Specific examples of suitable additives are described below.
<Phosphorus antioxidant>
The phosphorus antioxidant is an antioxidant containing a compound having a phosphorus atom in the molecule. The phosphorus-based antioxidant is stabilized by reducing the hydroperoxide that causes deterioration at a high temperature, thereby contributing to an improvement in the transmittance of light having a relatively short wavelength (for example, a wavelength of 420 to 500 nm), In particular, it contributes to the reduction of light yellow coloring. Examples of phosphorus antioxidants include alkyl phosphites, alkylaryl phosphites, and aryl phosphites. Industrially, Adeka Stab PEP-8 and Adeka Stab PEP-36 manufactured by ADEKA Corporation are available. , ADK STAB HP-10, ADK STAB 2112 and the like are available. Among these, the following structural formula (II):

From the viewpoint of reducing pale yellow coloring, Adekastab 2112 which is tris (2,4-di-t-butylphenyl) phosphite represented by

  Content of the phosphorus antioxidant in a styrene resin composition is 0.02 mass part-0.2 mass part per 100 mass parts of styrene resin. When this content is 0.02 parts by mass or more, a decrease in light transmittance due to deterioration at a high temperature such that the resin melts during molding can be suppressed, and it is 0.2 parts by mass or less. This is advantageous in that mold deposits do not occur or in terms of cost. As this content, 0.03 mass part-0.15 mass part are preferable, and 0.04 mass part-0.12 mass part are more preferable.

で表される3-(3,5-ジ-t-ブチル-4-ヒドロキシフェニル)プロピオン酸ステアリルであるイルガノックス１０７６が高温環境での使用時の薄黄色着色の低減という観点から好ましい。
また、同一分子内にフォスファイト構造も併せ持つフェノール系酸化防止剤として、住友化学（株）製スミライザーＧＰ（6-[3-(3-t-ブチル-4-ヒドロキシ-5-メチルフェニル)プロポキシ]-2,4,8,10-テトラ-t-ブチルベンズ[d,f][1,3,2]ジオキサフォスフェピン）も好適に用いることができる。 <Phenolic antioxidant>
A phenolic antioxidant is an antioxidant containing a hindered phenol structure in the molecule. The phenol-based antioxidant captures peroxy radicals generated in auto-oxidation to form a metastable hydroperoxide, thereby suppressing the progression of chain degradation. Furthermore, the hydroperoxide is reduced and stabilized by a phosphorus antioxidant. This contributes to an improvement in light transmittance retention when exposed to high temperatures, and in particular to a reduction in light yellow coloration when used in high temperature environments. Industrially available as a phenolic antioxidant, Irganox 1010, Irganox 1076, etc., manufactured by BASF Japan Ltd. are available. Among these, the following structural formula (III):

Irganox 1076, which is stearyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate represented by the formula, is preferred from the viewpoint of reducing pale yellow coloring when used in a high temperature environment.
Moreover, as a phenolic antioxidant having a phosphite structure in the same molecule, Sumitizer GP (6- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propoxy] manufactured by Sumitomo Chemical Co., Ltd. -2,4,8,10-tetra-t-butylbenz [d, f] [1,3,2] dioxaphosphine) can also be suitably used.

  Content of the phenolic antioxidant in a styrene resin composition is 0.02 mass part-0.2 mass part per 100 mass parts of styrene resin. When the content is 0.02 parts by mass or more, a decrease in light transmittance due to deterioration at an ambient temperature (room temperature to about 70 ° C.) used as a light guide plate can be suppressed, and 0.2 mass. When the amount is less than or equal to parts, it is advantageous in terms of cost reduction in light transmittance caused by the phenolic antioxidant itself or in terms of cost. As this content, 0.03 mass part-0.15 mass part are preferable, and 0.04 mass part-0.12 mass part are more preferable.

A compound that acts as both a phosphorus-based antioxidant and a phenol-based antioxidant (for example, a compound containing both a phosphite structure and a hindered phenol structure in its molecule, more specifically, for example, the aforementioned Sumitomo Chemical ( In the case of using Sumilyzer GP, etc. (hereinafter also referred to as phosphorus-phenol-antioxidant), the phosphorus-based antioxidant and phenol are used in the content of phosphorus-phenol-antioxidant. It is considered that each of the antioxidants is contained. For example, when 0.1 part by mass of a phosphorus-phenol-antioxidant is included with respect to 100 parts by mass of the styrene-based resin, the phosphorus-based antioxidant 0 with respect to 100 parts by mass of the styrene-based resin. .1 part by mass and 0.1 part by mass of phenolic antioxidant are considered to be contained.
In addition, content of the phosphorus antioxidant and phenolic antioxidant in a styrene resin composition is measured using a gas chromatography.

<Higher fatty acid>
Examples of higher fatty acids include fatty acids having 12 to 20 carbon atoms, and specific examples include lauric acid, myristic acid, palmitic acid, and stearic acid.

<Higher aliphatic alcohol>
Examples of the higher aliphatic alcohol include monohydric alcohols having 6 to 20 carbon atoms, and specific examples include octyl alcohol, decyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol and the like.

<Ultraviolet absorber and / or light stabilizer>
The styrenic resin composition suitable for the light guide plate may contain an ultraviolet absorber and / or a light stabilizer for the purpose of preventing coloring due to ultraviolet rays generated from the light source. Examples of the ultraviolet absorber include 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5bis (α, α′-dimethylbenzyl) phenyl] benzotriazole, 2- Benzotriazole ultraviolet absorbers such as (3,5-di-t-amyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2- Benzophenone ultraviolet absorbers such as hydroxy-4-n-octoxybenzophenone, salicylic acid ultraviolet absorbers such as phenyl salicylate and 4-t-butylphenyl salicylate, 2- (1-arylalkidene) malonic ester ultraviolet absorbers Agents, oxalanilide ultraviolet absorbers and the like. Examples of the light stabilizer include hindered amine light stabilizers. Examples of hindered amine light stabilizers include bis (2,2,6,6-tetramethyl-4-piperidyl) separate, N, N′-bis (3-aminopropyl) ethylenediamine, 2,4-bis. And [N-butyl-N- (1,2,2,6,6-pentamethyl-4-piperidyl) amino] -6-chloro-1,3,5-triazine condensate. The ultraviolet absorber and the light stabilizer can be used alone or in combination, and the amount added is 0.02 with respect to 100 parts by mass of the styrene resin as the total of the ultraviolet absorber and the light stabilizer. It is preferable that it is mass part-2.0 mass parts, and it is more preferable that it is 0.1 mass part-1.5 mass parts.

<Lubricant>
Examples of the lubricant include aliphatic hydrocarbon lubricants such as liquid paraffin. The content of the lubricant is preferably 0.05 to 5 parts by mass with respect to 100 parts by mass of the styrene resin.

<Antistatic agent>
Examples of the antistatic agent include nonionic surfactants such as glycerin fatty acid esters and polymer surfactants such as aromatic sulfonic acid formalin condensates. The content of the antistatic agent is preferably 0.5 to 25 parts by mass with respect to 100 parts by mass of the styrene resin.

<Masking agent>
Furthermore, a masking agent such as a fluorescent brightening agent and a bluing agent can be optionally used in the styrene resin composition suitable for the light guide plate, if necessary.

(Light guide plate)
In the embodiment of the present invention, the light guide plate is obtained by molding the above-mentioned styrenic resin composition. As a molding method, a known method can be used, a method of obtaining a sheet-like molded body by molding with a sheet molding extruder, a method of obtaining a molded body of a desired shape by compression molding, injection molding, etc. Is mentioned.

Hereinafter, the present invention will be specifically described. However, the present invention is not limited to these examples. The evaluations and test methods used in each example and comparative example are as follows.
(1) Measuring method of concentration of polyethylene glycol, phosphorus antioxidant and phenolic antioxidant:
After 1 g of a composition (pellet, molded product, etc.) was sufficiently dissolved in 20 ml of methyl ethyl ketone, 5 ml of methanol was added dropwise and stirred for about 20 minutes. The supernatant liquid separated by centrifugation was measured by gas chromatography (GC). For determination of the concentration, a calibration curve prepared in advance for stearic acid, stearyl alcohol, and each antioxidant was used.
<GC measurement conditions>:
GC device: Shimadzu Corporation GC-2010
Column: DB-1 (0.25 mm id × 30 m) Liquid phase thickness 0.10 mm
Column temperature: 240 ° C. (1 min hold) → (10 ° C./min temperature rise) → 320 ° C. (5 min hold) Total 14 min
Inlet temperature: 320 ° C
Injection method: Split method (split ratio 1: 5)
Sample volume: 1 μL

(2) Evaluation of total light transmittance, haze, and cloudiness occurrence:
Using the obtained pellets, injection molding was performed at a cylinder set temperature of 220 ° C. and a mold temperature of 45 ° C. to obtain a molded piece having a length of 120 mm, a width of 50 mm, and a thickness of 2 mm. Using this molded piece, the occurrence of white turbidity due to rapid changes in temperature and humidity was evaluated.
The test piece was exposed for 100 hours in a constant temperature and humidity chamber set to a temperature of 60 ° C. and a humidity of 95% RH, then taken out to an environment of a temperature of 23 ° C. and a humidity of 50% RH, immediately after removal, 1 hour, and 24 hours. The subsequent total light transmittance (conforming to JIS K7361-1), haze (conforming to JIS K7136) and the occurrence of white turbidity were visually observed. The occurrence of white turbidity was judged by the following three evaluation criteria.
○: Not cloudy △: Slightly cloudy ×: Cloudy

(3) Evaluation of water absorption rate Immediately after molding of the above test piece, it was weighed and designated as W1. Furthermore, after being immersed in distilled water at 23 ° C. for 100 hours, it was taken out from the distilled water, and after removing water droplets on the surface, it was weighed to obtain W2.
The water absorption was calculated using the following formula.
Water absorption rate = (W2-W1) / W1 × 100 (%)

(4) Vicat softening temperature Measured according to JIS K7206.

[Example 1]
5.4 liters of a completely mixed type polymer solution in which 0.05 parts by mass of 1,1-bis (t-butylperoxy) cyclohexane is added to 100 parts by mass of a mixture of 85% by mass of styrene and 15% by mass of ethylbenzene. The reactor was continuously charged at 0.70 liter / hr, and the temperature was adjusted to 101 ° C. The resulting solution was continuously charged into a 3.0 liter laminar flow reactor equipped with a stirrer and temperature controlled in 3 zones. The temperature of the laminar flow reactor was adjusted to 113 ° C / 121 ° C / 128 ° C. Thus, a polymer solution was obtained.
The obtained polymer solution is continuously supplied to a devolatilizing extruder with a two-stage vent, and unreacted monomers and solvents are recovered at an extruder temperature of 225 ° C., a one-stage vent and a two-stage vent with a degree of vacuum of 15 torr. After that, phosphorus antioxidant (Tris phosphite (2,4-di-t-butylphenyl, trade name: ADK STAB 2112)), phenol antioxidant (3- (3,5- Di-t-butyl-4-hydroxyphenyl) stearyl propionate, trade name: Irganox 1076), polyethylene glycol 300 (trade name, average molecular weight 300, manufactured by Wako Pure Chemical Industries, Ltd.) in 100 parts by weight of polymer On the other hand, it added so that it might become a density | concentration of 0.05, 0.05, and 0.15 mass part, respectively, and the styrene-type resin composition was obtained.
The polymerization rate of the monomer was calculated as 68% from the mass yield.
The styrene block copolymer rubber (manufactured by Asahi Kasei Chemicals Corporation, trade name: Toughprene 125) is 0.30 part by mass with respect to 100 parts by mass of the polymer in the obtained styrene resin composition. And melt kneading at a cylinder temperature of 230 ° C. using a twin screw extruder having a screw diameter of 20 mm to obtain a styrene resin composition.

[Example 2]
A styrene resin composition was obtained in the same manner as in Example 1 except that the styrene block copolymer rubber was added to a concentration of 0.50 parts by mass.

[Example 3]
Example except that terpene phenol resin (manufactured by Yasuhara Chemical Co., Ltd., trade name: YS polymer K125, hydroxyl value 200) was added to a concentration of 2.00 parts by mass instead of styrene block copolymer rubber. A styrenic resin composition was obtained in the same manner as in 1.

[Example 4]
Example except that terpene phenol resin (manufactured by Yasuhara Chemical Co., Ltd., trade name: YS polymer K125, hydroxyl value 200) was added to a concentration of 3.00 parts by mass instead of styrene block copolymer rubber. A styrenic resin composition was obtained in the same manner as in 1.

[Example 5]
A styrene resin composition was obtained in the same manner as in Example 1 except that 0.30 part by mass of polyethylene glycol 300 and 0.15 part by mass of styrene block copolymer rubber were used.

[Example 6]
A styrene resin composition was obtained in the same manner as in Example 1 except that 0.30 parts by mass of polyethylene glycol 300 was used.

[Example 7]
Styrene resin as in Example 1 except that polyethylene glycol 300 was added in an amount of 0.3 parts by mass, and terpene phenol resin was added to a concentration of 1.00 parts by mass instead of styrene block copolymer rubber. A composition was obtained.

[Example 8]
Styrene resin as in Example 1 except that polyethylene glycol 300 was added in an amount of 0.30 parts by mass, and terpene phenol resin was added to a concentration of 2.00 parts by mass instead of styrene block copolymer rubber. A composition was obtained.

[Example 9]
A styrene resin composition was obtained in the same manner as in Example 1 except that 0.40 part by mass of polyethylene glycol 300 and 0.15 part by mass of styrene block copolymer rubber were used.

[Example 10]
Styrene resin as in Example 1 except that polyethylene glycol 300 was added in an amount of 0.40 parts by mass, and terpene phenol resin was added to a concentration of 1.00 parts by mass instead of styrene block copolymer rubber. A composition was obtained.

[Example 11]
Styrenic resin as in Example 1 except that polyethylene glycol 300 was not used and styrene block copolymer rubber was added to a concentration of 0.15 parts by mass and terpene phenol resin to a concentration of 1.00 parts by mass. A composition was obtained.

[Example 12]
Styrenic resin as in Example 1 except that polyethylene glycol 300 was not used and styrene block copolymer rubber was added to a concentration of 0.15 parts by mass and terpene phenol resin to a concentration of 2.00 parts by mass. A composition was obtained.

[Example 13]
A styrene resin composition was prepared in the same manner as in Example 1 except that terpene phenol resin was added to a concentration of 1.00 parts by mass in combination with the styrene block copolymer rubber without using polyethylene glycol 300. Obtained.

[Example 14]
A styrene resin composition was prepared in the same manner as in Example 1 except that terpene phenol resin was added to a concentration of 2.00 parts by mass together with styrene block copolymer rubber without using polyethylene glycol 300. Obtained.

[Example 15]
Styrenic resin as in Example 1 except that polyethylene glycol 300 was not used and styrene block copolymer rubber was added to a concentration of 0.50 parts by mass and terpene phenol resin to a concentration of 1.00 parts by mass. A composition was obtained.

[Example 16]
Styrenic resin as in Example 1 except that polyethylene glycol 300 was not used and styrene block copolymer rubber was added to a concentration of 0.50 parts by mass and terpene phenol resin to a concentration of 2.00 parts by mass. A composition was obtained.

[Example 17]
A styrene resin composition was obtained in the same manner as in Example 1 except that styrene block copolymer rubber was added to a concentration of 0.10 parts by mass, and terpene phenol resin was added to a concentration of 1.00 parts by mass. .

[Example 18]
A styrene resin composition was obtained in the same manner as in Example 1 except that the phosphorus antioxidant and the phenol antioxidant were not added.

[Comparative Example 1]
A styrene resin composition was obtained in the same manner as in Example 1 except that 0.30 part by mass of polyethylene glycol 300 and no styrene block copolymer rubber were used.

[Comparative Example 2]
A styrene resin composition was obtained in the same manner as in Example 1 except that 0.30 part by mass of polyethylene glycol 300 and 1.00 part by mass of styrene block copolymer rubber were used.

[Comparative Example 3]
Styrene resin as in Example 1 except that polyethylene glycol 300 was added in an amount of 0.30 parts by mass, and terpene phenol resin was added to a concentration of 6.00 parts by mass instead of styrene block copolymer rubber. A composition was obtained.

[Comparative Example 4]
A styrene resin composition was obtained in the same manner as in Example 1 except that polyethylene glycol 300 was not used.

[Comparative Example 5]
A styrene resin composition was obtained in the same manner as in Example 1 except that 1.00 part by mass of polyethylene glycol 300 was used.

[Comparative Example 6]
A styrene resin composition was prepared in the same manner as in Example 1 except that terpene phenol resin was added to a concentration of 6.00 parts by mass in combination with the styrene block copolymer rubber without using polyethylene glycol 300. Obtained.

[Comparative Example 7]
A styrene resin composition was used in the same manner as in Example 1 except that polyethylene glycol 300 was not used and terpene phenol resin was added to a concentration of 3.00 parts by mass instead of styrene block copolymer rubber. Obtained.

[Comparative Example 8]
Styrene resin as in Example 1 except that polyethylene glycol 300 was added at a concentration of 1.00 parts by mass, and terpene phenol resin was added to a concentration of 3.00 parts by mass instead of styrene block copolymer rubber. A composition was obtained.

[Comparative Example 9]
Styrenic resin as in Example 1 except that polyethylene glycol 300 was not used and styrene block copolymer rubber was added to a concentration of 1.0 part by mass and terpene phenol resin to a concentration of 3.00 parts by mass. A composition was obtained.

  The evaluation results are summarized in Tables 1 and 2 below.

  The light guide plate according to the present invention has a small amount of warpage of the molded product due to low water absorption, and less white turbidity due to a sudden change in temperature and humidity. It can be suitably used in a wide range of applications such as a display device used for a notebook), a car navigation system monitor, a mobile phone, a lighting device for indoor and outdoor spaces, and a signboard.

Claims (2)

  0.1 to 0.5 parts by mass of polyethylene glycol having an average molecular weight of 200 to 1000, 0.1 to 0.5 parts by mass of styrene block copolymer rubber, and a hydroxyl value of 150 or more with respect to 100 parts by mass of styrene resin A light guide plate comprising a styrene-based resin composition, containing any two or more of 1.0 to 5.0 parts by mass of the terpene phenol resin.   The light guide plate according to claim 1, further comprising 0.02 to 0.2 parts by mass of a phosphorus-based antioxidant and 0.02 to 0.2 parts by mass of a phenol-based antioxidant in the styrene-based resin. .