KR20190102083A - Light-guiding plate made of styrenic resin - Google Patents

Abstract

This invention provides the light guide plate which consists of styrene resin which used the styrene-type monomer as a raw material which is excellent in heat resistance and few yellowing at the time of shaping | molding. It is a light-guide plate which consists of styrene resin whose methanol soluble content is 1.5 mass% or less and whose weight average molecular weight (Mw) is 150,000-450,000.

Description

Styrene-based light guide plate {LIGHT-GUIDING PLATE MADE OF STYRENIC RESIN}

This invention relates to the light-guide plate which consists of styrene resin which uses a styrene monomer as a raw material.

The backlight of a liquid crystal display includes a direct type backlight which arranges a light source in the front of a display apparatus, and the edge light type backlight which arrange | positions at the side surface. The light guide plate is inserted into the edge light type backlight, and serves to guide light from the side surface to the liquid crystal panel, and is used in a wide range of applications such as televisions, desktop personal computers, notebook personal computers, mobile phones, and car navigation systems.

In the light guide plate, acrylic resins represented by PMMA (polymethyl methacrylate) are mainly used, but they are excellent in optical properties such as transparency, but tend to have high absorbency, and cause problems of warpage and dimensional changes of molded products. There is.

For this reason, it is proposed that MS resin which is a copolymer of styrene and methyl (meth) acrylate which improved these characteristics is used. Patent document 1 is proposed as an improvement technique, such as water absorptivity and the discoloration reduction at the time of shaping | molding of MS resin.

In Patent Literature 1, a light guide plate having a weight average molecular weight (Mw) of 6 to 170,000, a residual monomer amount of 3000 μg / g or less, and an oligomer amount of 2% or less is disclosed. However, there exists a tendency which is high in water absorption and dimensional stability is worse than styrene resin which uses a styrene monomer as a raw material.

On the other hand, Patent Document 2 proposes a styrene monomer- (meth) acrylic acid monomer copolymer as an example of heat resistance improvement of a light guide plate using a resin made of a styrene monomer.

In patent document 2, it consists of a styrene-type monomer- (meth) acrylic-type monomer copolymer which consists of 95.5 to 99 weight% of styrene-type monomers, and 1 to 4.5 weight% of (meth) acrylic-acid monomers. Although the light guide plate is disclosed, the absorbency is high and the amount of the warpage is larger than that of the styrene resin using the styrene monomer.

Japanese Patent Publication No. 2003-075648 Japanese Patent Publication No. 2007-204536

Conventionally, when a cold cathode tube is used as a light source for a liquid crystal display, PMMA or MS resin with relatively small yellowing due to ultraviolet rays and relatively good optical characteristics is used as the light guide plate material.

On the other hand, from the recent trend of power saving, conversion from a cold cathode tube of a light source to an LED is in progress, and when using a white LED having almost no emission spectrum in the ultraviolet region causing yellowing of the light guide plate, a styrene-based monomer is used as a raw material. A light guide plate made of a styrene resin is also expected to be inexpensive and useful.

However, conventional light guide plates have not always been sufficiently compatible with heat resistance and suppression of yellowing during molding.

An object of this invention is to provide the light-guide plate which consists of styrene resin which used the styrene-type monomer as a raw material which is excellent in heat resistance and has little yellowing at the time of shaping | molding.

MEANS TO SOLVE THE PROBLEM This inventor reached | attained this invention which makes the following a summary as a result of repeating research in order to solve the said subject.

(1) A light guide plate comprising a styrene resin having a methanol soluble content of 1.5 mass% or less and a weight average molecular weight (Mw) of 150,000 to 450,000.

(2) The light guide plate of Claim 1 whose vicat softening temperature which the said styrene resin measured by 50N load is 100 degreeC or more.

(3) The above (1) or (3) wherein the styrene resin is a total amount of the remaining styrene monomer and the residual polymerization solvent in the styrene resin is 500 μg / g or less, and the total amount of the styrene dimer and the trimer is 5000 μg / g or less. The light guide plate of 2).

(4) The light guide plate according to any one of (1) to (3), wherein the styrene resin is a resin obtained by polymerizing a styrene monomer having a 4-t-butylcatechol concentration of less than 10 µg / g.

(5) The light guide plate according to any one of (1) to (4), wherein the styrene resin has a methanol soluble content of 1.0% by mass or less and a weight average molecular weight (Mw) of 200,000 to 400,000.

(6) The light guide plate according to any one of (1) to (5), wherein the styrene-based resin has a Vicat softening temperature measured at 50 N load of 103 ° C or higher.

(7) The light guide plate according to any one of (1) to (6), wherein the styrene resin has a bending strength of 90 MPa or more.

(8) The light guide plate according to any one of (1) to (7), wherein the styrene resin has a total light transmittance of 90% or more.

(9) The light guide plate according to any one of (1) to (8), wherein the styrene resin has a haze of less than 0.5%.

(10) The light guide plate according to any one of (1) to (9), wherein the styrene resin has YI of 0.3 or less.

Since the light guide plate of this invention has high heat resistance, it can suppress the heat deformation at the time of use, and can prevent the yellowing at the time of shaping | molding. Moreover, compared with PMMA and MS resin, water absorption is low and inexpensive.

The light guide plate of this invention can obtain the composition which added the light diffusing agent, an ultraviolet absorber, antioxidant, etc. with respect to styrene resin or styrene resin by molding methods, such as injection molding and extrusion molding, as needed.

A styrene resin can be obtained by superposing | polymerizing a styrene monomer. Styrene-based monomers are styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, or the like or a mixture of two or more thereof, which are aromatic vinyl monomers, preferably styrene.

As a polymerization method of a styrene monomer, well-known styrene polymerization methods, such as a block polymerization method, a solution polymerization method, and suspension polymerization method, are mentioned. In terms of quality and productivity, the bulk polymerization method or the solution polymerization method is preferable, and the continuous polymerization is preferable. As a solvent of a solution polymerization method, alkylbenzenes, such as benzene, toluene, ethylbenzene, and xylene, ketones, such as acetone and methyl ethyl ketone, aliphatic hydrocarbons, such as hexane and cyclohexane, can be used, for example.

At the time of superposition | polymerization of styrene resin, a polymerization initiator and a chain transfer agent can be used as needed. As the polymerization initiator, 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-butylperoxyisopropylcarbonate, dicumylperoxide, t-butylcumylperox Seed, t-butylperoxy acetate, t-butylperoxy-2-ethylhexanoate, polyether tetrakis (t-butylperoxycarbonate), ethyl-3,3-di (t-butylperoxy) butyrate and t-butylperoxy isobutyrate. Examples of the chain transfer agent include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimers, and terpinolene.

In the polymerization step, it is preferable to use a well-known complete mixing tank stirring tank, a tower reactor, or the like, and to control the reaction by adjusting the polymerization temperature or the like so that the resin has a target molecular weight distribution.

The polymerization solution containing the polymer that has undergone the polymerization step is transferred to a devolatilization step to remove unreacted monomers and polymerization solvent. The devolatilization process consists of a vacuum devolatilization tank with a heater, a devolatilizing extruder with a vent, and the like. The polymer in the molten state after the devolatilization process is transferred to the granulation process. In the granulation step, the molten resin is extruded from the porous die into a strand shape and processed into a pellet shape by a cold cut method, an air hot cut method, or an underwater hot cut method.

The methanol soluble content in styrene resin is 1.5 mass% or less, More preferably, it is 1.0 mass% or less, More preferably, it is 0.8 mass% or less. When methanol soluble content exceeds 1.5 mass%, the heat resistance of a light guide plate may become inadequate and may thermally deform.

The methanol soluble component is an amount of a component soluble in methanol in the resin, and for example, various additives such as white oil and silicone oil, in addition to styrene oligomers (styrene dimers and styrene trimers) generated in the polymerization process and devolatilization process. And low molecular weight components such as remaining monomers and remaining polymerization solvents.

Methanol solubles can be reduced by suppressing the amount of styrene oligomers (styrene dimers, styrene trimers) generated by the polymerization process, adjusting the amount of various additives such as white oil, and controlling the amount of residual styrene monomer and remaining polymerization solvent. Can be.

The measurement of the methanol soluble component in the present invention was performed by the following method. Styrene-type resin P (g) is named, 50 mL of tetrahydrofuran is added, and it melt | dissolves at room temperature (25 degreeC) for 1 hour. After dissolution, 5 mL of ethanol is added and mixed well. Next, the said dissolved liquid is put into the beaker which put 400 mL of methanol, and the insoluble component (resin component) is precipitated in methanol, stirring at room temperature. After stirring for 15 minutes, 1 drop of hydrochloric acid is added, followed by stirring at room temperature for 10 minutes. After stirring was stopped and allowed to stand for 10 minutes, the mixture was gradually filtered through a glass filter to separate methanol insoluble content, dried under reduced pressure for 2 hours in a vacuum dryer at 150 ° C, and allowed to cool for 25 minutes in a desiccator, and dried methanol insoluble. Measure the mass N (g) of the minute. The methanol soluble content was computed by the following formula.

Methanol Soluble (mass%) = ((P-N) / P) × 100

The weight average molecular weight (Mw) of styrene resin is 150,000-450,000, More preferably, it is 200,000-400,000. When weight average molecular weight (Mw) becomes less than 150,000, the intensity | strength of a light guide plate will fall. When the weight average molecular weight (Mw) exceeds 450,000, melt mass flow rate may fall, and moldability may deteriorate. The weight average molecular weight (Mw) can be controlled by the reaction temperature of 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), Z average molecular weight (Mz), and number average molecular weight (Mn) were measured on the following conditions using gel permeation chromatography (GPC).

GPC models: Shodex GPC-101 manufactured by Showa Denko Corporation

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

Mobile phase: tetrahydrofuran

Sample concentration: 0.2% by mass

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

Detector: parallax refractometer

The molecular weight in this invention calculates the molecular weight in each elution time from the elution curve of monodisperse polystyrene, and calculates it as molecular weight of polystyrene conversion.

It is preferable that the Vicat softening temperature of styrene resin is 100 degreeC or more, More preferably, it is 103 degreeC or more. If it is less than 100 degreeC, when used as a light guide plate, heat resistance may become inadequate and may thermally deform.

Vicat softening temperature was measured at the temperature increase rate of 50 degree-C / hr, and test load 50N based on JISK7206.

It is preferable that the sum total (remaining volatile matter) of the residual monomer and residual polymerization solvent in a styrene polymer is 500 micrograms / g or less, More preferably, it is 350 micrograms / g or less. When the total of the remaining monomer and the remaining polymerization solvent exceeds 500 µg / g, the heat resistance of the light guide plate may be insufficient. The remaining monomers and the remaining polymerization solvents are part of the methanol soluble component but the components are small in molecular weight and have a large influence on the heat resistance.

 In addition, since the remaining monomer and the remaining polymerization solvent have high volatility, for example, when extruding the light guide plate by extrusion molding, it may be volatilized at the die outlet and condensed in the die, resulting in debris. If the residue adheres to the extruded light guide plate, the appearance is poor. In addition, even in the case of injection molding, gas may be generated at the time of injection molding, which may cause molding failure.

The remaining monomer and the remaining polymerization solvent are the amounts of the monomer remaining in the resin and the remaining polymerization solvent, and examples thereof include styrene, ethylbenzene and toluene. The quantity of the residual monomer and the residual polymerization solvent can be adjusted on the conditions of the structure of a devolatilization process, the temperature, vacuum degree, etc. in a devolatilization process.

The amount of the residual monomer and the residual polymerization solvent is exactly 0.2 g of styrene-based resin, dissolved in 10 ml of tetrahydrofuran containing p-diethylbenzene as an internal standard, under the following conditions using a capillary gas chromatograph. Measured.

Capillary gas chromatograph: GC-4000 (manufactured by GI Science)

Column: InertCap WAX, manufactured by DS Science, Inc. 0.25 mm, length 30 m, film thickness 50 μm

Injection temperature: 180 ℃

Column temperature: 60 ° C to 170 ° C

Detector temperature: 210 ℃

Split ratio: 5/1

The total amount of the dimer and trimer of the styrene monomer in the styrene resin is preferably 5000 μg / g or less, and more preferably 4000 μg / g or less. When the total amount of the dimer and trimer of the styrene monomer exceeds 5000 µg / g, the methanol soluble content increases, and the heat resistance of the light guide plate becomes insufficient.

The dimer and trimer of a styrene-based monomer are those produced by-products during the polymerization reaction in the polymerization step and those produced by thermal decomposition in the devolatilization step. As a method of suppressing dimers and trimers of styrene-based monomers by-produced in the polymerization process, a reactor of a completely mixed tank is used in the initial stage of polymerization to reduce the concentration of styrene-based monomers in the reactor and to use a polymerization initiator. The method of superposing | polymerizing at low temperature is mentioned. As a method of suppressing the dimer and trimer of the styrene monomer produced in a devolatilization process, the method of reducing the resin temperature in a devolatilization process and shortening a residence time is mentioned.

The dimer and trimer of the styrene monomer was measured by dissolving 200 mg of styrene resin in 2 mL of 1,2-dichloromethane, adding 2 mL of methanol to precipitate the copolymer, and allowing the mixture to stand. It measured using gas chromatography (HP-5890, Hewlett-Packard Co.). In addition, detailed conditions are described below.

(A) Column: DB-1 (ht) 0.25 mm × 30 m film thickness 0.1 μm

(B) Injection temperature: 250 ℃

(C) column temperature: 100-300 ° C

(D) Detector temperature: 300 ° C

(E) Split ratio: 50/1

(F) Internal standard: n-eichoic acid

When manufacturing styrene resin, it is preferable that the 4-t- butylcatechol concentration in the styrene monomer supplied to a superposition | polymerization process is less than 10 micrograms / g, More preferably, it is less than 3 micrograms / g. When 4-t-butyl catechol concentration becomes 10 micrograms / g or more, the yellow taste of a light guide plate may become strong. Styrene-based monomers available on the market include 10 to 30 µg / g of 4-t-butylcatechol as a polymerization inhibitor. The 4-t-butylcatechol concentration in the styrene monomer can be reduced by using activated alumina as the adsorbent.

The 4-t-butyl catechol concentration in the styrene monomer was measured by the following method. 50 mL of styrene monomer was added to the separating lot, and 10 ml of 1 N sodium hydroxide was added thereto, followed by shaking for about 2 minutes. After standing separation into two layers, the liquid of the lower layer was extracted, the absorbance (wavelength 486 nm) was measured using the spectrophotometer, and the density | concentration was computed from the calibration curve prepared previously.

70 MPa or more is preferable and, as for the bending strength of styrene resin, 90 MPa or more is more preferable. When it is less than 70 MPa, the light guide plate becomes brittle due to lack of strength.

As the optical properties of the styrene-based resin, the total light transmittance and the haze are measured by injection molding test piece (thickness 2) at a cylinder temperature of 230 ° C. and a mold temperature of 40 ° C. of an injection molding machine (IS130FII-3A) manufactured by Toshiba Kikai. mm and dimensions 40 mm x 40 mm) were measured in accordance with JIS K-7105.

In terms of transparency, the total light transmittance of the styrene resin is preferably 90% or more, and the haze of the styrene resin is preferably 1.0% or less, and more preferably less than 0.5%.

In the present invention, YI (yellowness) was used as a criterion for determining the color, and the sample was measured by a reflection method using a colorimetric colorimeter (NDJ4000, manufactured by Nippon Denshoku Kogyo Co., Ltd.). When YI exceeds 0.7, the yellowishness of a molded article is strong and color falls, which is unpreferable. It determined by YI making 0.7 or less pass. As for YI of styrene resin, it is more preferable that it is 0.3 or less.

A ultraviolet absorber has a function which suppresses deterioration and coloring by ultraviolet-ray, For example, a benzophenone series, a benzotriazole type, a triazine type, a benzoate type, a salicylate type, a cyanoacrylate type, an oxalic acid anhydride And ultraviolet absorbers such as malonic ester and formamidine. These can be used individually or in combination of 2 or more types, and can also use together light stabilizers, such as a hindered amine.

The light guide plate of styrene resin can be shape | molded by the shaping | molding method according to the objective, such as injection molding, extrusion molding, compression molding. 0.1-8.0 mm is preferable and, as for the thickness of the light-guide plate of styrene resin, 0.2-4.0 mm is more preferable.

Example

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

Reference Example, Adjustment of 4-t-Butyl Catechol (hereinafter referred to as TBC) Concentration

Commercially available styrene includes 10 to 30 µg / g TBC as a polymerization inhibitor. 1 part by mass of activated alumina is added to 100 parts by weight of commercially available styrene having a TBC concentration of 12 μg / g, mixed to adsorb the TBC, and the activated alumina is removed by a filter paper. Got it. TBC concentration in styrene supplied to the polymerization process was adjusted by adding TBC to styrene.

(Method for producing styrene resin PS-1 to PS-14)

The polymerization process was constructed by connecting the 1st reactor which is a fully mixing type stirring tank, the 3rd reactor which is a plug flow type reactor with a 2nd reactor, and a static mixer in series. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. The raw material solution was manufactured with the raw material composition of Table 1.

The raw material solution was continuously fed at a flow rate shown in Table 1 for the first reactor. The polymerization initiator was added and mixed to the raw material solution so that the addition concentration (the concentration on the basis of mass relative to the raw material styrene) shown in Table 1 was at the inlet of the first reactor. The polymerization initiator of Table 1 is as follows, respectively. In addition, white oil was supplied to the outlet of the 3rd reactor using Christol N352 by ExxonMobil.

Polymerization Initiator-1: 2,2-bis (4,4-t-butylperoxycyclohexyl) propane (Pertetra A manufactured by Nippon Yushi Co., Ltd. was used.)

Polymerization initiator-2: 1,1-bis (t-butylperoxy) cyclohexane (Perhexa C manufactured by Nippon Yushi Co., Ltd. was used.)

Polymerization initiator-3: t-amyl peroxy isononanoate (Luperox 570 by Arkema Yoshitomi Co., Ltd. was used.)

Chain transfer agent-1: (alpha) -methylstyrene dimer (Novma MSD by Nippon Yushi Co., Ltd. was used.)

In addition, in the 3rd reactor, temperature gradient was given along the flow direction, and it adjusted so that it might become the temperature of Table 1 in an intermediate part and an exit part.

Then, the solution containing the polymer continuously taken out from the 3rd reactor was introduced into the vacuum devolatilization tank with the preheater comprised in two stages in series, and the temperature of the preheater was adjusted so that it might become the resin temperature of Table 1. Further, unreacted styrene and ethylbenzene were separated by adjusting to the pressure shown in Table 1, and then extruded into a strand form from a porous die, and the strand was cooled and cut in a cold cut manner to pelletize. In addition, ethylene bis stearylamide was added to the obtained pellets as an external lubricant at a concentration of 100 µg / g, followed by dry blending.

The bending strength was tested in accordance with JIS K 7171.

Melt mass flow rate was measured as a flow characteristic. Melt mass flow rate was measured on 200 degreeC and the conditions of 49 N load based on JISK-7210.

(Examples 1-12, Comparative Examples 1-4)

Table 2 shows the characteristics of each resin.

In the Example, the light-guide plate which consists of styrene resin which used the styrene-type monomer as a raw material which is excellent in heat resistance and little yellowing at the time of shaping | molding is obtained.

The light guide plate of this invention can be used suitably for a wide range of uses, such as a television, a desktop type personal computer, a notebook type personal computer, a mobile telephone, and car navigation.

In addition, the JP Patent application 2010-143339, the claim, and all the content of the abstract for which it applied on June 24, 2010 are referred here, and it introduces as an indication of the specification of this invention.

Claims (1)

Methanol soluble content is 1.0 mass% or less, the total amount of styrene dimer and trimer is 5000 microgram / g or less, the weight average molecular weight (Mw) is 150,000-450,000, YI (yellowness) is 0.2 or less, and haze Use of a light guide plate for edge light type white LED backlight having a thickness of 0.1 mm to 8.0 mm, characterized in that less than 0.5%, the total light transmittance is 90% or more, and the bending strength is 90 MPa or more.