JP2003075648A - Light guide plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lightweight light guide plate having low moisture absorption, high strength and high transparency. SOLUTION: The light guide plate is made of a styrene (meth)acrylate copolymer resin which is a styrene (meth)acrylate copolymer consisting of styrene monomers, (meth)acrylate monomers and vinyl monomers copolymerizable with these monomers. In the copolymer, the proportions of the styrene monomers and the (meth)acrylate monomers are 80 to 20 mass% of the styrene monomers and 20 to 80 mass% (meth)acrylate monomers, the weight average molecular weight (Mw) of the styrene (meth)acrylate copolymer ranges from 60,000 to 170,000, the amount of the residual monomers in the styrene (meth)acrylate copolymer is <=3,000 ppm, and the amount of oligomers is <=2 mass%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide plate used for a back light of an OA equipment such as a personal computer and a liquid crystal display device used for various monitors of image signals.

[0002]

2. Description of the Related Art Recently, a light guide for a backlight of a liquid crystal display device having an illumination lamp has been used. As a backlight system, there are generally used two types, a so-called direct type in which a light guide is sandwiched between a light source and a liquid crystal unit, and an edge light system in which a light source is attached to an edge of a light guide plate. The edge light method is mainly used, in which a light source is arranged on a side surface of a light guide body, and light incident on the light guide body from the light source is scattered at a bottom surface portion facing a light emitting surface. Many such techniques have been disclosed so far.

For example, Japanese Utility Model Laid-Open Nos. 61-157986, 62-87315 and 63-43.
Japanese Patent Application Publication No. 186, Japanese Utility Model Laid-Open No. 5-47922, and the like disclose a technique of using a light guide body provided with unevenness so that the amount of light scattering increases as the distance from the light source increases. In Japanese Patent Laid-Open No. 165504/1990, a groove is devised so that the light from the light source can be efficiently emitted to the observation side. The groove is formed on the bottom surface portion facing the light emitting surface of the light guide, and the groove is formed as the distance from the light source increases. There is disclosed a technique of increasing the amount of light scattering by widening the gap and forming a deep groove. Further, in Japanese Utility Model Application Laid-Open No. 60-94605, a groove shape for scattering light is formed on the bottom surface portion facing the light emitting surface of the light guide,
A technique is disclosed in which the light guide is formed in a wedge shape in which the thickness decreases as the distance from the light source increases, thereby achieving thinning and weight reduction and high brightness.

[0004]

As described above, various techniques relating to the light guide are disclosed. As the resin used for the light guide plate, polystyrene or acrylic resin,
Among them, acrylic resin has been mainly studied, but acrylic resin has high hygroscopicity, and therefore the dimension of the light guide plate is likely to change, and the demand for ultra-lightening of recent OA equipment is sufficient. There was a problem that I could not respond.

As a result of various studies to solve the above-mentioned problems, the present inventors have found that a styrene-based monomer, a (meth) acrylic acid ester-based monomer, and a vinyl-based copolymerizable with these monomers. Styrene- (meth) acrylic acid ester-based copolymer resin composed of monomers, which can be copolymerized with a specific ratio of styrene-based monomer, (meth) acrylic acid ester-based monomer, and these monomers Which is a vinyl-based monomer having a weight average molecular weight (Mw) of the styrene- (meth) acrylic acid ester-based copolymer resin, the amount of residual monomers, and the amount of oligomers controlled within specific ranges, has a hygroscopic property. The present invention has been completed based on the knowledge that it is small, has high strength, high transparency, is lighter, and is suitable for a light guide plate.

[0006]

Means for Solving the Problems That is, the present invention provides (1)
A styrene- (meth) acrylic acid ester-based copolymer resin comprising a styrene-based monomer, a (meth) acrylic acid ester-based monomer, and a vinyl-based monomer copolymerizable with these monomers, , Styrene-based monomer 80 to 20 mass%,
20 to 80% by mass of (meth) acrylic acid ester-based monomer and 0 to 10% by mass of vinylic monomer copolymerizable with these monomers, wherein the styrene- (meth) acrylic acid ester-based monomer The weight average molecular weight (Mw) of the copolymer resin is 6
10,000 to 170,000, the residual monomer amount of the styrene- (meth) acrylic acid ester-based copolymer resin is 3000 ppm or less, and the oligomer amount is 2%.
The light guide plate comprising the following styrene- (meth) acrylic acid ester-based copolymer resin, (2) Furthermore, the light guide plate according to (1), wherein the alkaline earth metal content is 10 ppm or less.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
Examples of the styrene-based monomer used in the present invention include styrene, α-methylstyrene, p-methylstyrene, o-methylstyrene, m-methylstyrene, ethylstyrene,
Pt-butyl styrene and the like can be mentioned, but styrene is preferable. These styrenic monomers may be used alone or in combination of two or more.

Examples of the (meth) acrylic acid ester-based monomer used in the present invention include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and methacrylic acid ester of 2-ethylhexyl (meth) acrylate. , Methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate,
An acrylic acid ester such as decyl acrylate may be mentioned, but methyl (meth) acrylate or n-butyl acrylate is preferable, and methyl (meth) acrylate is particularly preferable. These (meth) acrylic acid ester-based monomers may be used alone or in combination of two or more.

Further, vinyl monomers copolymerizable with these monomers, if necessary, include acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile,
Examples thereof include N-phenylmaleimide and N-cyclohexylmaleimide.

The method for producing the vinyl copolymer used in the present invention is not particularly limited, and for example, a polymerization method such as an emulsion polymerization method, a suspension polymerization method, a bulk polymerization method or a solution polymerization method can be adopted.

A styrene-based monomer of the styrene- (meth) acrylic acid ester-based copolymer resin used in the present invention,
The (meth) acrylic acid ester-based monomer and the vinyl-based monomer copolymerizable with these monomers include styrene-based monomers 80 to 20% by mass, (meth) acrylic acid ester-based monomers. 20 to 80% by mass, and 0 to 10% by mass of a vinyl-based monomer copolymerizable with these monomers (however, a styrene-based monomer, a (meth) acrylic acid ester-based monomer, and these The total number of vinyl monomers that can be copolymerized with the monomer is 1
It is preferably 100% by mass). Particularly, if the (meth) acrylic acid ester-based monomer is less than 20% by mass, the bending strength and the total light transmittance are lowered, which is not preferable, and if the (meth) acrylic acid ester-based monomer exceeds 80% by mass. It is not preferable because the hygroscopicity and the specific gravity increase.

The characteristics of the styrene- (meth) acrylate copolymer resin used in the present invention are 200 ° C., 5
It is preferable that the MFR under a load of kg is MFR ≧ 1.0 g / 10 minutes and the VSP under a load of 5 kg is VSP ≧ 95 ° C.

The styrene- (meth) acrylic acid ester copolymer resin used in the present invention has a weight average molecular weight (M
w) is preferably 60,000 to 170,000. If the weight average molecular weight (Mw) is less than 60,000, the bending strength will be decreased, which is not preferable.
If it exceeds 00, the flow is lowered, which is not preferable.

The amount of residual monomer of the styrene- (meth) acrylic acid ester copolymer resin used in the present invention is 3
It is preferably 000 ppm or less. If the amount of residual monomer exceeds 3000 ppm, molding defects and heat resistance decrease may occur, which is not preferable.

The amount of oligomer of the styrene- (meth) acrylic acid ester copolymer resin used in the present invention is preferably 2% or less. If the amount of the oligomer exceeds 2%, the heat resistance decreases, which is not preferable. In the present invention, the amount of oligomer is determined by evaporating and drying the extract obtained by refluxing n-hexane for 6 hours or more using a Soxhlet extractor for a freeze-ground sample (Xg). An extract (denoted as Yg) is obtained by the following formula, and calculated by the following formula. Oligomer amount (%) = Y / X × 100 From the above, it can be said that the oligomer amount (%) is equivalent to the n-hexane extracted portion (%).

Further, the styrene- (meth) acrylic acid ester-based copolymer resin used in the present invention can be suspension-polymerized by using an alkaline earth metal salt as a dispersant. The content of the earth metal is preferably 10 ppm or less in order to further improve the transparency.

In the light guide plate of the present invention, organic light diffusing agents such as crosslinked acrylic particles and crosslinked styrene particles, barium sulfate, calcium carbonate and titanium oxide are used as other components within a range not impairing the object of the present invention. Inorganic light diffusing agents, colorants, heat stabilizers, antioxidants, ultraviolet absorbers and the like can be added.

The method for obtaining the light guide plate of the present invention is not particularly limited. If necessary, after mixing any additive within the range not impairing the object of the present invention with a Henschel mixer or a blender, a method or a heat press molding machine to obtain a sheet-shaped molded article by extruding with a sheet molding extruder, or It is possible to use a method of obtaining a molded product having an arbitrary shape by filling a resin in a mold or a mold with an injection molding machine or the like.

EXAMPLES Detailed contents will be described below with reference to examples, but the present invention is not limited to the following examples.

[0019]   Evaluation methods   Measured at 200 ° C and 5kg load according to MFR JIS K-6874                   Decided   It was measured under a load of 5 kg according to VSP JIS K-7206.   Bending strength Measured according to ASTM D790.   Total light transmittance Measured according to ASTM D1003.   It was measured according to HaZe ASTM D1003.

Example 1 100 k of pure water was put in an autoclave having a capacity of 250 liters.
0.5 g of sodium dodecylbenzene sulfonate
g, tricalcium phosphate 250 g, styrene 40 k
g, 60 kg of methyl methacrylate, and 100 t-butylperoxyisobutyrate as a polymerization initiator.
220 g of g, t-dodecyl mercaptan was added, and the mixture was dispersed under stirring at a rotation speed of 150 rpm. Then, the mixed solution is heated at 100 ° C. for 8 hours and at 130 ° C. for 2.5 hours.
Heat polymerization was carried out for a period of time. After completion of the reaction, washing, dehydration and drying were performed to obtain a bead-shaped copolymer resin. This is a copolymer resin M
It was set to S (1). Next, this MS (1) was pelletized at a temperature of 230 ° C. using a 40 mm single screw extruder. Next, the obtained pellets were used as an electric injection molding machine J3 manufactured by Japan Steel Works, Ltd.
50ELIII, molding temperature of 270 ℃ vertical 292.5
A light guide plate having a size of mm, a width of 220 mm, and a thickness of 2 mm was obtained. Then, the characteristics of the obtained light guide plate were evaluated. The results are shown in Tables 1 and 2.

Example 2 100 k of pure water was placed in an autoclave having a capacity of 250 liters.
0.5 g of sodium dodecylbenzene sulfonate
g, tricalcium phosphate 250 g, styrene 40 k
g, 60 kg of methyl methacrylate, and 100 t-butylperoxyisobutyrate as a polymerization initiator.
180 g of g, t-dodecyl mercaptan was added, and the mixture was dispersed under stirring at a rotation speed of 150 rpm. Then, the mixed solution is heated at 100 ° C. for 8 hours and at 130 ° C. for 2.5 hours.
Heat polymerization was carried out for a period of time. After completion of the reaction, washing, dehydration and drying were performed to obtain a bead-shaped copolymer resin. This is a copolymer resin M
It is S (2). Next, a light guide plate was obtained in the same manner as in Example 1. Then, the characteristics of the obtained light guide plate were evaluated. The results are shown in Tables 1 and 2.

Example 3 A fully mixed reactor having a volume of about 15 liters, a tower plug flow reactor having a volume of about 40 liters, a first devolatilization tank equipped with a preheater, a static mixer, a first equipped with a preheater. Two
It was constructed by connecting devolatilization tanks in series. 15 parts by mass of ethylbenzene, 0.03 parts by mass of t-butylperoxyisopropylmonocarbonate (1 hour half-life temperature: 118 ° C.), with respect to a monomer solution composed of 40 parts by mass of styrene and 60 parts by mass of methyl methacrylate. Octadecyl-3-
(3,5-di-t-butyl-4-hydroxyphenyl)
0.1 parts by mass of propionate (antioxidant) and 0.05 parts by mass of t-dodecyl mercaptan were mixed to prepare a raw material solution. This raw material solution was fed at 6.9 kg / hr to a completely mixed reactor controlled at a temperature of 120 ° C. Further, this polymerization liquid was introduced into a column plug flow type reactor adjusted so that a gradient of 120 ° C. to 150 ° C. was formed in the flow direction. While heating this polymerization liquid with a preheater, 10.6k
The mixture was introduced into the first devolatilization tank whose pressure was reduced to Pa, and a part of the unreacted monomer was removed at the first devolatilization tank temperature of 230 ° C. Further, while extracting this liquid with a gear pump, 18 g of water (0.3 parts by mass relative to 100 parts by mass of total amount of monomers) was added to the static mixer every hour and mixed, and then while being heated by a preheater, 1 Introduced into the second devolatilization tank depressurized to 0.3 kPa,
Unreacted monomers were removed at a temperature in the second devolatilization tank of 230 ° C. This was extracted with a gear pump, and extruded into a strand shape and cut to obtain a pellet-shaped copolymer resin. This was designated as a copolymer resin MS (3). Next, Example 1
A light guide plate was obtained in the same manner as. Then, the characteristics of the obtained light guide plate were evaluated. The results are shown in Tables 1 and 2.

Example 4 15 parts by mass of ethylbenzene and t-butylperoxyisopropylmonocarbonate (1 hour half-life temperature: 118 ° C.) with respect to a monomer solution composed of 55 parts by mass of styrene and 45 parts by mass of methyl methacrylate. 0.03 parts by mass of octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (antioxidant) was added.
The same procedure as in Example 3 was performed except that 1 part by mass and 0.05 part by mass of t-dodecyl mercaptan were mixed to prepare a raw material solution.
The copolymer resin thus obtained was designated as MS (4). Next, Example 1
A light guide plate was obtained in the same manner as. Then, the characteristics of the obtained light guide plate were evaluated. The results are shown in Tables 1 and 2.

Comparative Example 1 100 k of pure water was placed in an autoclave having a capacity of 250 liters.
0.5 g of sodium dodecylbenzene sulfonate
g, tricalcium phosphate 250 g, styrene 60 k
g, 40 kg of methyl methacrylate, and 100 t-butylperoxyisobutyrate as a polymerization initiator.
g, t-dodecyl mercaptan (320 g) was added, and the mixture was dispersed under stirring at a rotation speed of 150 rpm. Then, the mixed solution is heated at 100 ° C. for 8 hours and at 130 ° C. for 2.5 hours.
Heat polymerization was carried out for a period of time. After completion of the reaction, washing, dehydration and drying were performed to obtain a bead-shaped copolymer resin. This is a copolymer resin M
It was S (5). Next, a light guide plate was obtained in the same manner as in Example 1. Then, the characteristics of the obtained light guide plate were evaluated. The results are shown in Tables 1 and 2.

Comparative Example 2 100 k of pure water was placed in an autoclave having a capacity of 250 liters.
0.5 g of sodium dodecylbenzene sulfonate
g, tricalcium phosphate 250 g, styrene 40 k
g, 60 kg of methyl methacrylate, and 100 t-butylperoxyisobutyrate as a polymerization initiator.
220 g of g, t-dodecyl mercaptan was added, and the mixture was dispersed under stirring at a rotation speed of 150 rpm. Then, this mixed solution is heated at 100 ° C. for 8 hours and at 120 ° C. for 2.5 hours.
Heat polymerization was carried out for a period of time. After completion of the reaction, washing, dehydration and drying were performed to obtain a bead-shaped copolymer resin. This is a copolymer resin M
It was S (6). Next, a light guide plate was obtained in the same manner as in Example 1. Then, the characteristics of the obtained light guide plate were evaluated. The results are shown in Tables 1 and 2.

Comparative Example 3 Example 3 was repeated except that t-butylperoxyisopropyl monocarbonate was not added to the raw material solution. The copolymer resin thus obtained was designated as MS (7). Next, a light guide plate was obtained in the same manner as in Example 1. Then, the characteristics of the obtained light guide plate were evaluated. The results are shown in Tables 1 and 2.

Comparative Example 4 100 k of pure water was placed in an autoclave having a capacity of 250 liters.
0.5 g of sodium dodecylbenzene sulfonate
g, tricalcium phosphate 250 g, styrene 90 k
g, 10 kg of methyl methacrylate, and 100 t-butylperoxyisobutyrate as a polymerization initiator.
220 g of g, t-dodecyl mercaptan was added, and the mixture was dispersed under stirring at a rotation speed of 150 rpm. Then, the mixed solution is heated at 100 ° C. for 8 hours and at 130 ° C. for 2.5 hours.
Heat polymerization was carried out for a period of time. After completion of the reaction, washing, dehydration and drying were performed to obtain a bead-shaped copolymer resin. This is a copolymer resin M
It was set to S (8). Next, a light guide plate was obtained in the same manner as in Example 1. Then, the characteristics of the obtained light guide plate were evaluated. The results are shown in Tables 1 and 2.

Comparative Example 5 100 k of pure water was placed in an autoclave having a capacity of 250 liters.
0.5 g of sodium dodecylbenzene sulfonate
g, tricalcium phosphate 250 g, styrene 10 k
g, 90 kg of methyl methacrylate, and 100 t-butylperoxyisobutyrate as a polymerization initiator.
220 g of g, t-dodecyl mercaptan was added, and the mixture was dispersed under stirring at a rotation speed of 150 rpm. Then, the mixed solution is heated at 100 ° C. for 8 hours and at 130 ° C. for 2.5 hours.
Heat polymerization was carried out for a period of time. After completion of the reaction, washing, dehydration and drying were performed to obtain a bead-shaped copolymer resin. This is a copolymer resin M
It was S (9). Next, a light guide plate was obtained in the same manner as in Example 1. Then, the characteristics of the obtained light guide plate were evaluated. The results are shown in Tables 1 and 2.

Comparative Example 6 100 k of pure water was placed in an autoclave having a capacity of 250 liters.
0.5 g of sodium dodecylbenzene sulfonate
g, tricalcium phosphate 250 g, styrene 100 k
g, 100 g of t-butyl peroxyisobutyrate as a polymerization initiator, t-dodecyl mercaptan 22
0 g was added, and the mixed solution was dispersed under stirring at a rotation speed of 150 rpm. Then, this mixed solution was heated and polymerized at a temperature of 100 ° C. for 8 hours and at 130 ° C. for 2.5 hours. After completion of the reaction, washing, dehydration and drying were performed to obtain a white bead-shaped copolymer resin. This was designated as a copolymer resin PS (1). Next, a light guide plate was obtained in the same manner as in Example 1. Then, the characteristics of the obtained light guide plate were evaluated. The results are shown in Tables 1 and 2.

Comparative Example 7 An acrylic resin (trade name: Sumipex MG-SG manufactured by Sumitomo Chemical Co., Ltd.) was used in place of the copolymer resin used in the examples. This was designated as PMMA (1). Next, a light guide plate was obtained in the same manner as in Example 1. Then, the characteristics of the obtained light guide plate were evaluated. The results are shown in Tables 1 and 2.

[0031]

[Table 1]

[0032]

[Table 2]

From Table 1, the experiment No. Nos. 12 to 15 have excellent properties as a light guide plate such as bending strength, total light transmittance, HaZe, weight change, and size change. Experiment Nos. 16 to 22 are Nos. Compared to 12-15
It can be seen that the characteristics of the light guide plate are inferior.

[0034]

According to the present invention, a light guide plate having low hygroscopicity, high strength, high transparency and light weight can be provided. Further, according to the present invention, the manufacturing cost can be reduced, and a light guide plate having a good appearance can be easily obtained, which is extremely useful industrially.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuyoshi Ebe             6 Goi Minami Coast, Ichihara City, Chiba Electrochemical             Industrial Co., Ltd. Chiba factory F-term (reference) 2H038 AA55 BA06                 2H091 FA23Z FB02 FC01 LA11                 4J100 AB02P AB03P AB04P AJ02R                       AL03Q AL04Q AL05Q AM02R                       CA04 CA05 JA32

Claims (2)

[Claims] 1. A styrene- (meth) acrylic acid ester-based copolymer comprising a styrene-based monomer, a (meth) acrylic acid ester-based monomer, and a vinyl-based monomer copolymerizable with these monomers. Polymerized resin, styrene monomer 80
˜20% by mass, (meth) acrylic acid ester-based monomer 2
0 to 80% by mass, and 0 to 10% by mass of a vinyl-based monomer copolymerizable with these monomers, and the weight average molecular weight (Mw) of the styrene- (meth) acrylic acid ester-based copolymer resin. Is 60,000 to 170,000, the amount of residual monomer of the styrene- (meth) acrylic acid ester-based copolymer resin is 3000 ppm or less, and the amount of oligomer is 2% or less, styrene- (meth) acrylic acid. A light guide plate made of ester copolymer resin. 2. The light guide plate according to claim 1, further comprising 10 ppm or less of alkaline earth metal.