JP5715830B2 - Styrenic resin composition for light guide plate and light guide plate - Google Patents

Description

The present invention relates to hue and excellent in transparency for light guide plate styrenic resin composition Contact and light guide plate.

There are two types of backlights for liquid crystal displays: a direct type backlight in which a light source is disposed in front of the display device and an edge light type backlight in which a light source is disposed on a side surface. The light guide plate is incorporated in the edge-light type backlight and plays the role of guiding the light from the side to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, car navigation systems. The An acrylic resin typified by PMMA (polymethylmethacrylate) is used for the light guide plate. However, since the water absorption is high, there may be a problem that the molded product is warped or a change in dimensions.
Therefore, it has been proposed to use MS resin which is a copolymer of styrene and methyl (meth) acrylate with improved properties. Patent Document 1 has been proposed as an improvement technique of MS resin such as water absorption and reduction of discoloration during molding.
However, Patent Document 1 discloses a light guide plate having a weight average molecular weight (Mw) of styrene- (meth) acrylic ester copolymer resin of 60 to 170,000, a residual monomer amount of 3000 ppm or less, and an oligomer amount of 2% or less. However, the water-absorbing property and the dimensional stability tend to be worse than those of the styrene resin using a styrene monomer as a raw material.
On the other hand, although a styrene resin using a styrene monomer as a raw material has low water absorption, there is a problem that it is easily colored by heating due to high-temperature heat history such as molding. When the molded product is colored and yellowed, when the optical path length is long like a light guide plate, there is a problem that the light transmittance is reduced due to light absorption loss and the luminance of the display is lowered.

Japanese Patent Laid-Open No. 2003-075648

  An object of the present invention is to provide a styrenic resin composition excellent in colorless transparency, which is suitable for optical applications such as a light guide plate and prevents heating and coloring due to a high temperature heat history such as molding.

（式中、Ｒ_１は炭素原子数１〜９のアルキル基を示し、Ｒ_２は水素原子または炭素原子数１〜４のアルキル基を示し、Ｒ_３は炭素原子数１〜３０のアルキル基を示す。）

前記ホスファイト化合物は、例えば、２，２メチレンビス（４，６−ジ−ｔ−ブチルフェニル）オクチルホスファイトである。
また、前記ヒンダードフェノール系酸化防止剤は、例えば、オクタデシル−３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート及び／又はエチレンビス（オキシエチレン）ビス〔３−（５−ｔｅｒｔ−ブチル−４−ヒドロキシ−ｍ−トリル）プロピオネート〕である。
そして、本発明に係る導光板は、前述したスチレン系樹脂組成物からなるものである。 The styrene resin composition for a light guide plate according to the present invention is a styrene resin composition processed into a light guide plate, and the resin component is styrene, α-methyl styrene, o-methyl styrene, and p-methyl styrene. Among them , a phosphite compound obtained by polymerizing one or two or more monomers, consisting of a styrene resin having a weight average molecular weight of 150,000 to 700,000 and represented by the following general formula (I) : It contains 08 to 0.40% by mass and hindered phenol antioxidant : 0.02 to 0.40% by mass.

(In the formula, R ₁ represents an alkyl group having 1 to 9 carbon atoms, R ₂ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ₃ represents an alkyl group having 1 to 30 carbon atoms. Show.)

The phosphite compound is, for example, 2,2 methylene bis (4,6-di-t-butylphenyl) octyl phosphite.
The hindered phenol-based antioxidant is, for example, octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate and / or ethylenebis (oxyethylene) bis [3- (5 -Tert-butyl-4-hydroxy-m-tolyl) propionate].
And the light-guide plate which concerns on this invention consists of a styrene-type resin composition mentioned above.

  The styrenic resin composition of the present invention has low water absorption and is cheaper than PMMA and MS resin, and is excellent in heat coloring prevention due to high-temperature heat history such as molding processing. The molded product is excellent in colorless transparency and can be suitably used for optical applications such as a light guide plate.

  The styrene resin of the present invention can be obtained by polymerizing a styrene monomer. The styrene monomer is an aromatic vinyl monomer, such as styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, or a mixture of two or more, preferably styrene.

  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 terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. 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.

  A polymerization initiator and a chain transfer agent can be used as needed during the polymerization of the styrene resin. As polymerization initiators, organic peroxides such as benzoyl peroxide, t-butylperoxybenzoate, 1,1-di (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy)- 3,3,5-trimethylcyclohexane, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, t-butylperoxyisopropyl carbonate, dicumyl peroxide, t-butylcumyl peroxide, t-butyl peroxyacetate, t-butylperoxy-2-ethylhexanoate, polyether tetrakis (t-butylperoxycarbonate), ethyl-3,3-di (t-butylperoxy) butyrate, t- Examples include butyl peroxyisobutyrate. Examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like.

  In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate using a well-known complete mixing tank type stirring tank or tower reactor in the polymerization process. Is done. The polymerization solution containing the polymer exiting the polymerization step is transferred to the devolatilization step, and unreacted monomers and polymerization solvent are removed. The devolatilization process includes a vacuum devolatilization tank with a heater, a vented devolatilization extruder, and the like. The polymer in the molten state that has exited the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in a strand form from a porous die and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.

The styrene resin of the present invention has a weight average molecular weight of 150,000 to 700,000, preferably 180,000 to 500,000. If it is less than 150,000, the strength of the molded product becomes insufficient, and if it exceeds 700,000, the moldability is remarkably lowered. The weight average molecular weight of the styrenic resin should be controlled by the reaction temperature of the polymerization process, the residence time, the type and amount of polymerization initiator, the type and amount of chain transfer agent, the type and amount of solvent used during polymerization, etc. Can do.
The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer The molecular weight of the present invention is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.

（式中、Ｒ１は炭素原子数１〜９のアルキル基を示し、Ｒ２は水素原子または炭素原子数１〜４のアルキル基を示し、Ｒ３は炭素原子数１〜３０のアルキル基を示す。） The styrene resin composition of the present invention comprises a styrene resin, a specific phosphite compound represented by the following general formula (I), and a hindered phenol antioxidant.

(In the formula, R 1 represents an alkyl group having 1 to 9 carbon atoms, R 2 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R 3 represents an alkyl group having 1 to 30 carbon atoms.)

  Examples of the phosphite compound of the present invention include 2,2 methylenebis (4,6-di-t-butylphenyl) octyl phosphite, which is preferably used.

  The phosphite compound content in the styrenic resin composition of the present invention is 0.08 to 0.40 mass%, preferably 0.08 to 0.25 mass%. When the content of the phosphite compound is less than 0.08% by mass, the heat coloring prevention property due to the high-temperature heat history such as during molding is not sufficient, and the yellowness of the obtained molded product becomes strong. Moreover, when content exceeds 0.40 mass%, the effect only corresponding to content will not be acquired, but the hue of a molded article will deteriorate rather.

  In the present invention, it is necessary to use a hindered phenol antioxidant together with the phosphite compound. Only the phosphite compound or the hindered phenol antioxidant alone does not provide sufficient heat coloration prevention property, and the combined use of the phosphite compound and the hindered phenol antioxidant exhibits the heat coloration prevention property.

  Examples of the hindered phenol-based antioxidant of the present invention include octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, ethylenebis (oxyethylene) bis [3- (5-tert -Butyl-4-hydroxy-m-tolyl) propionate], 4,6-bis (octylthiomethyl) -o-cresol, 4,6-bis [(dodecylthio) methyl] -o-cresol, 2,4-dimethyl -6- (1-methylpentadecyl) phenol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, DL-α-tocopherol, 2-t-butyl- 6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-H Roxy-3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4′-thiobis (6-t-butyl-3-methylphenol), 1,1 , 3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4′-butylidenebis (3-methyl-6-t-butylphenol), and the like. -(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and / or ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] are preferred. .

  The hindered phenol antioxidant content in the styrene resin composition of the present invention is preferably 0.02 to 0.40 mass%, more preferably 0.04 to 0.20 mass%. Moreover, it is preferable that the sum total of content of a phosphite compound and a hindered phenolic antioxidant is 0.10-0.50 mass%, More preferably, it is 0.17-0.35 mass%.

  As a method of adding the phosphite compound and hindered phenolic antioxidant of the present invention, addition and mixing in a polymerization process, a devolatilization process, a granulation process of a styrenic resin, an extruder at the time of molding, etc. The method of doing is mentioned, It is not specifically limited.

  The styrenic resin composition of the present invention may contain mineral oil as long as the colorless transparency of the present invention is not impaired. Further, additives such as an internal lubricant such as stearic acid and ethylene bisstearylamide, a sulfur-based antioxidant, a lactone-based antioxidant, an ultraviolet absorber, a light stabilizer, and an antistatic agent may be contained. As the external lubricant, ethylene bisstearylamide is suitable, and the content is preferably 30 to 200 ppm in the resin composition.

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

  The styrenic resin composition of the present invention can be molded into a plate-shaped product by a molding method according to the purpose such as injection molding, extrusion molding, compression molding, etc., and used as a light guide plate. At that time, a reflection pattern such as a dot pattern can be provided on the back surface (opposite side of the light emitting surface) of the plate-shaped molded product, and used as a light guide plate. When processing from the resin plate to the light guide plate, it is preferable to polish the light incident surface or the entire end surface of the resin plate to make a mirror surface. In addition, in order to improve the uniformity of the emitted light, a prism pattern can be provided on the surface (surface from which light is emitted) of the plate-shaped molded product. The pattern on the front surface or the back surface of the plate-shaped molded product can be formed at the time of molding the plate-shaped molded product. For example, the pattern can be formed by a mold shape in injection molding or roll transfer in extrusion molding.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.

(Production of styrene resin PS-1)
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A mixed solution of 84.0% by mass of styrene and 16.0% by mass of ethylbenzene was prepared, and 400 ppm of 2,2-bis (4,4-t-butylperoxycyclohexyl) propane was mixed on the basis of styrene, A raw material solution was obtained. As 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, Pertetra A manufactured by NOF Corporation was used. This raw material solution was continuously supplied to the first reactor at a rate of 11.2 kg / hour. The reaction temperature of each reactor is 116 ° C. in the first reactor, 120 ° C. in the second reactor, and in the third reactor, a temperature gradient is created along the direction of flow, 140 ° C. in the middle portion, and in the outlet portion. The temperature was adjusted to 150 ° C. Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted of two stages in series, and after separating unreacted styrene and ethylbenzene, a strand shape After being extruded and cooled, it was cut into pellets. The resin temperature in the first stage devolatilization tank is set to 160 ° C., the pressure in the vacuum devolatilization tank is set to 65 kPa, the resin temperature in the second stage devolatilization layer is set to 235 ° C. The pressure in the volatilization tank was 0.4 kPa.
The obtained styrene resin had a weight average molecular weight (Mw) of 367,000, a Z average molecular weight (Mz) of 771,000, and a number average molecular weight (Mn) of 101,000. The amount of residual styrene in the styrene resin was 350 ppm, the amount of residual ethylbenzene was 100 ppm, the amount of styrene dimer was 100 ppm, and the amount of styrene trimer was 3400 ppm. The melt mass flow rate was 1.2 g / 10 min, and the Vicat softening temperature was 103 ° C. (The melt mass flow rate was in accordance with JIS K-7210, under the conditions of 200 ° C. and 49 N load, and the Vicat softening temperature was In accordance with JIS K 7206, the test was performed at a heating rate of 50 ° C./hr and a test load of 50 N).

(Examples 1-6, Comparative Examples 1-7)
In the formulation shown in Table 1, styrene resin PS-1, phosphite compound and hindered phenol antioxidant were melted at a cylinder temperature of 230 ° C. and a screw rotation speed of 100 rpm using a single screw extruder with a screw diameter of 40 mm. Kneading gave pellets.
The phosphite compounds and hindered phenolic antioxidants used in Table 1 are shown below.
(Phosphite compound)
A-1: 2,2 methylene bis (4,6-di-t-butylphenyl) octyl phosphite (Adeka Corporation Adeka Stub HP-10)
A-2: Tris (2,4-di-tert-butylphenyl) phosphite (Irgafos 168 manufactured by BASF Japan Ltd.)
A-3: Bis [2,4-bis (1,1-dimethylethyl) -6-methylphenyl] ethyl ester phosphorous acid (Irgafos 38 manufactured by BASF Japan Ltd.)
(Hindered phenolic antioxidant)
B-1: Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076 manufactured by BASF Japan Ltd.)
B-2: Ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate] (Irganox 245 manufactured by BASF Japan Ltd.)
Using the obtained pellets, injection molding was performed 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. A test piece of 115 × 115 mm was cut out from the obtained plate-shaped product, and the end surface was polished by buffing to obtain a plate-shaped product having a mirror surface on the end surface.
About the obtained plate-shaped molded article, the parallel light transmittance and b value of 115 mm light guide were implemented using Nippon Denshoku Industries Co., Ltd. ASA-300A. Table 1 shows the characteristics of each resin composition. The wavelength range was 400 to 700 nm, and a C light source was used as the light source.

  The molded product of the example is a molded product having a low b value and a small yellowness, and has a high parallel light transmittance and excellent transparency.

  The styrenic resin composition of the present invention is excellent in hue and transparency due to improved heat coloring during molding, such as televisions, desktop personal computers, notebook personal computers, mobile phones, car navigation systems, etc. It can be suitably used for light guide plate applications.

Claims (4)

A styrenic resin composition processed into a light guide plate,
The resin component is obtained by polymerizing one or more monomers of styrene, α-methylstyrene, o-methylstyrene, and p-methylstyrene, and has a weight average molecular weight of 150,000 to 700,000. Made of styrene resin ,
A styrenic resin composition for a light guide plate containing a phosphite compound represented by the following general formula (I) : 0.08 to 0.40% by mass and a hindered phenol antioxidant : 0.02 to 0.40% by mass object.

(In the formula, R ₁ represents an alkyl group having 1 to 9 carbon atoms, R ₂ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ₃ represents an alkyl group having 1 to 30 carbon atoms. Show.) The styrenic resin composition for a light guide plate according to claim 1, wherein the phosphite compound is 2,2methylenebis (4,6-di-t-butylphenyl) octyl phosphite. The hindered phenol antioxidant is octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate and / or ethylenebis (oxyethylene) bis [3- (5-tert-butyl). -4-hydroxy-m-tolyl) propionate]. The styrene-based resin composition for a light guide plate according to claim 1 or 2. The light-guide plate which consists of a styrene-type resin composition of any one of Claims 1-3.