KR20090054913A - Resin composition for light diffusing plate and light diffusing plate - Google Patents

Abstract

A resin composition for a light diffusing plate is provided to realize properties such as high thermal resistance, low absorption, high brightness, and high light diffusion by using a methyl methacrylate/methacrylic acid/styrene terpolymer and a diffusing agent. A resin composition for a light diffusing plate is prepared by mixing a terpolymer 100.0 parts by weight and a light-diffusing agent 0.1~10.0 parts by weight. The terpolymer comprises a methyl methacrylate unit 10~40 weight%, a methacrylic acid unit 2~20 weight% and a styrene unit 40~88 weight%. The range of the average molecular weight is 80000~300000. The light-diffusing agent is at least one selected form partially crosslinked siloxane-based polymer particles, acrylic polymer particles or calcium carbonate.

Description

RESIN COMPOSITION FOR LIGHT DIFFUSING PLATE AND LIGHT DIFFUSING PLATE}

The present invention relates to a light diffusion plate having high light resistance, high heat resistance, low absorption, high brightness, and high light diffusion, and a resin composition used therein.

The light-diffusion plate which has a light-diffusion transmittance which uses resin as a main material can obtain a uniform brightness surface. For this reason, light diffusing plates are widely used for applications such as lighting covers, internally illuminated signboards, transmissive displays, and the like. In recent years, the demand for the light-diffusion plate as a surface light source for the direct type backlight of a liquid crystal display or a liquid crystal television is increasing.

In order to achieve the above functions optimally, the light diffusing plate is required to scatter light rays without going straight as much as possible and to suppress light transmission loss due to scattering as much as possible.

In order to obtain a light diffusing plate expressing these required characteristics, a method of adding inorganic particles such as calcium carbonate, barium sulfate, titanium oxide, silicon oxide, talc, mica, aluminum hydroxide, magnesium oxide, styrene polymer particles By the method of adding partially crosslinked polymer microparticles | fine-particles, such as an acryl-type polymer particle and a siloxane-type polymer particle, or a method of using them together, the method of scattering light by an additive has been employ | adopted (for example, a patent document 1 ~ 3).

Examples of the transparent resin used in the light diffusion plate include acrylic resins, polycarbonates, and methyl methacrylate-styrene copolymer resins, which do not have satisfactory physical properties in terms of heat resistance, hardness, and water absorption. In addition, Patent Documents 4 and 5 disclose a method of blending a diffusing agent into a copolymer resin of styrene and methacrylic acid, and the improvement of heat resistance has been improved. However, since styrene-based resin is a main component, light resistance is inferior and separate ultraviolet rays. Techniques, such as providing an absorbing layer, are used together.

[Patent Document 1] Japanese Patent Publication No. 3195543

[Patent Document 2] Japanese Patent Publication No. 3195544

[Patent Document 3] Japanese Patent Publication 2512544

[Patent Document 4] Japanese Unexamined Patent Publication No. 2006-124522

[Patent Document 5] Japanese Unexamined Patent Publication No. 2007-219456

In recent years, while the improvement of the member characteristics of a liquid crystal display or a liquid crystal television is being planned, the light diffusion plate using acrylic resin has high absorbency.

In addition, since the backlight generates heat during use of the display, the light diffusion plate directly above it also requires heat resistance. However, conventional acrylic resins do not satisfy the characteristics.

In addition, the heat resistant styrene resin is effective for improving absorbency and heat resistance. However, the light resistance is inferior, and coloration and mechanical properties are deteriorated by long-term irradiation of the backlight, resulting in color variation and cracking when the display is used.

As described above, the conventional light diffusion plate does not sufficiently satisfy the function of the light diffusion plate requiring high light, high brightness, high light diffusion, and low absorption.

The present invention has been made in view of the above problems, and an object thereof is to provide a light diffusion plate having high light resistance, high heat resistance, high low absorption, high brightness, and high light diffusion.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining, the present inventors discovered that the light-diffusion plate shape | molded by using the resin composition for light-diffusion plates which consists of methyl methacrylate / methacrylic acid / styrene copolymer resin and a diffusing agent which have a specific composition can achieve the said objective. Thus, the present invention has been completed.

The resin composition for a light diffusion plate according to the present invention is composed of a ratio of 10 to 40% by weight of methyl methacrylate units, 2 to 20% by weight of methacrylic acid units and 40 to 92% by weight of styrene units, and has a weight average molecular weight of 80000. It is characterized by consisting of 0.1 to 10.0 parts by weight of the light diffusing agent based on 100 parts by weight of the copolymer resin of ~ 300000.

The present invention also relates to a light diffusion plate molded into a plate having a thickness of 0.5 to 3 mm by melt extrusion molding or injection molding.

The copolymer resin used in the resin composition for the light diffusion plate of the present invention is preferably a continuous bulk polymerization method or a continuous solution polymerization method using a completely mixed reactor in order to maintain uniformity of composition and molecular weight and good appearance. It is also possible in batch-type mass or solution polymerization. It is preferable to exist an initiator at the time of superposition | polymerization, As a initiator, the peroxide and / or azo compound used for normal radical polymerization can be used. In addition, an appropriate amount of a chain transfer agent such as alkyl mercaptan may be added to adjust the molecular weight. After the completion of the polymerization, a process such as volatilization and pelletization may be performed by a conventional method to obtain a copolymer resin for use in the resin composition for a light diffusion plate of the present invention.

10 to 40% by weight of methyl methacrylate unit, preferably 10 to 25% by weight, and 2 to 20% by weight of methacrylic acid unit, preferably 4 to 15% by weight as a unit constituting the copolymer resin. , 40 to 88% by weight, preferably 55 to 60% by weight of styrene units. If the ratio of the methyl methacrylate unit is less than 10% by weight, the light resistance is lowered. If the ratio of the methyl methacrylate unit is more than 40% by weight, the material has a high hygroscopic property, and thus the material easily bends. If the ratio of the methacrylic acid unit is less than 2% by weight, the heat resistance is too low. If the ratio of the methacrylic acid unit is more than 20% by weight, the amount of gel generated by crosslinking during polymerization is excessive and the surface becomes uneven. Further, if the ratio of styrene units is less than 40% by weight, the material has high hygroscopicity, and thus warp is likely to occur, and if it exceeds 88% by weight, heat resistance is lowered.

The molecular weight of the copolymer resin is in the range of 80000 to 300000 as the weight average molecular weight. If a weight average molecular weight is less than 80000, fluidity will become high too much and will become a sheet with a thickness deviation. In addition, when the weight average molecular weight exceeds 300,000, molding becomes difficult because the fluidity becomes too low.

The melt flow rate of the copolymer resin is preferably in the range of 0.5 to 3.0 g / 10 min. Preferably it is 1.0-2.5 g / 10min. If the melt flow rate is higher than 3.0 g / 10 min, the sheet may have a thickness variation. If the melt flow rate is less than 0.5 g / 10 min, molding becomes difficult because the fluidity is too low.

In addition, the Vicat softening temperature of this copolymer resin is 103 degreeC or more, Preferably it is 105-130 degreeC. If the non-cat softening temperature is less than 103 ° C, the heat resistance to heat generation of the backlight is low, so that deformation of the substrate is likely to occur.

In addition, the copolymer resin has a water absorption of 0.30% or less, preferably 0.25% or less. When the water absorption exceeds 0.30%, the problem of warping due to absorption is likely to occur.

As a raw material monomer, the raw material containing methyl methacrylate, methacrylic acid, and styrene is used. These ratios are used while considering the polymerizability so that the copolymer resin in which the methyl methacrylate unit, the methacrylic acid unit, and the styrene unit become the above ratios is obtained. In addition, the copolymer resin is prepared to increase the transparency. The use ratio of this raw material monomer and the ratio of each structural unit in copolymerization resin correspond substantially.

In addition, a small amount of other structural units can be present in the copolymer resin without departing from the object of the present invention. As a monomer which gives such a structural unit, you may use combining one or more types of substituted styrene other than styrene. As said substituted styrene, halogenated styrene, such as chloro styrene and bromostyrene, alkyl styrene, such as vinyltoluene, (alpha) -methylstyrene, etc. are mentioned, for example. Moreover, you may use combining one or more types of (meth) acrylic acid esters other than methyl methacrylate. As (meth) acrylic acid ester, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, octadecyl methacrylate, phenyl methacrylate, benzyl methacrylate, octadecyl methacrylate, methacrylic acid 2- Methacrylic acid ester, such as ethylhexyl, methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, acrylic ester, such as 2-ethylhexyl acrylate, etc. are mentioned.

The resin composition for light diffusing plates according to the present invention is obtained by blending the light diffusing agent in an amount of 0.1 to 10.0 parts, preferably 0.2 to 5.0 parts, based on 100 parts (parts by weight) of the copolymer resin. If the blending amount is less than 0.1 part, since the concealment of the light source is lacking, the luminance deviation resulting from the image of the backlight light source becomes noticeable light diffusion plate. If it exceeds 10.0 parts, the amount of transmitted light will be insufficient, resulting in a light diffusion plate lacking brightness.

Known fine particles can be used as the light diffusing agent, and preferably, partially crosslinked siloxane polymer particles, acrylic polymer particles or calcium carbonate having a particle diameter of 1 to 10 µm. These diffusing agents may use only one type or several types. As other diffusing agents, inorganic particles such as barium sulfate, titanium oxide, silicon oxide, talc, mica, aluminum hydroxide, and magnesium oxide or styrene polymer particles may be used in combination, but it may be less than 50% by weight of the light diffusing agent. good.

The mixing of the copolymer resin and the light diffusing agent can be performed so as to form a homogeneous mixture by a known method. The resin composition for light diffusing plates thus obtained is advantageously molded by extrusion or injection molding into a plate having a thickness of 0.5 to 3 mm. If the thickness is less than 0.5 mm, it is difficult to secure the strength of the backlight diffusion plate. If the thickness exceeds 3 mm, the weight of the diffusion plate becomes large, so that it becomes difficult to cope with the increase in size and thickness. The light diffusing plate according to the present invention is obtained by cutting or surface treatment, etc. as it is or with a predetermined size. However, the production method is not particularly limited as long as the object of the present invention can be satisfied.

If the light-diffusion plate of this invention is comprised with the said resin composition for light-diffusion plates, it may be comprised by a single layer, and may be comprised by the multilayer of two or more layers.

The light diffusing plate of the present invention uses a ternary copolymer resin of methyl methacrylate / methacrylic acid / styrene and a diffusing agent, thereby obtaining physical properties such as high light resistance, high heat resistance, high low absorption, high brightness, and high light diffusion. However, various additives such as an antistatic agent, an antioxidant, a flame retardant, a light stabilizer, an ultraviolet absorber, and a fluorescent brightener may be used as necessary so long as it does not significantly impair this object.

The light diffusing plate of the present invention is used as a diffuser plate for direct backlight of liquid crystal display or liquid crystal television, which is required for the balance of light diffusivity and light transmittance, and in particular, high light resistance, heat resistance and high hardness with large size and thinness. It is suitable for the required use. The light diffusing plate obtained from the resin composition for light diffusing plate according to the present invention has high heat resistance and low absorption, and is excellent in light resistance.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

The physical property of the copolymer resin used for the resin composition for light-diffusion plates was measured by the following method.

(1) molecular weight

Gel permeation chromatography was used to determine the weight average molecular weight in terms of polystyrene.

(2) each unit composition in the copolymer

The methyl methacrylate unit and the styrene unit composition of the copolymer were titrated from the area ratio of the monomers in the pyrolysis gas chromatography, and the methacrylic acid unit was titrated with an automatic potentiometric titration device to calculate each monomer unit composition.

(3) Melt flow rate (MFR)

It carried out by 200 degreeC and a 5 kg load based on JISK-7210.

(4) Vicat softening temperature (VST)

It carried out based on JISK-7206.

(5) Absorption rate

It measured based on JISK-7209.

The physical property evaluation of the light-diffusion plate was performed by the following method.

(1) total light transmittance

It carried out based on the B method of JISK7105.

(2) light diffusivity

Four cold cathode tubes were arranged at 2 cm intervals, and the light-diffusion plate samples were fixed in parallel on 10 mm, and visually, it was represented by (circle) that the cold cathode tube which is a light source was not reflected, and was shown by x.

(3) luminance deviation

Four cold cathode tubes were arranged at intervals of 2 cm, and the light-diffusion plate samples were fixed in parallel on 10 mm, and visually, those with uniform luminance on the screen were indicated by ○ and those with luminance deviation as x.

(4) light resistance

Filter: KF-1 (transmission wavelength range; 295 ~ 780nm), operation mode: continuous irradiation, UV illuminance: 75㎽ / ㎠, BP temperature: 80 ℃, tank (using accelerated light resistance tester using metal halide lamp as light source) I) Humidity: 50% RH, spray: none, test time: 24 hours, sample thickness was used 2mm sheet. The sample after the light resistance test was evaluated by ΔE of transmitted light using a spectrophotometer.

In addition, the symbol used in an Example and a comparative example has the following meaning.

MMA: methyl methacrylate

MAA: methacrylic acid

St: Styrene

Initiator: Parkadox 12-EB20

(Reference Examples 1-9)

The raw material monomer and the polymerization initiator were added so as to have the copolymerization resin composition of Table 1, and the continuous bulk polymerization was carried out by using a facility in which a solar-type complete mixing reactor and a volatilization tank were connected under a reaction temperature of 120 ° C. and 5 hours residence condition. Volatilization and pelletization yielded the target transparent copolymer resin. The resin was injection molded at a resin temperature of 240 ° C. with a 75t molding machine (manufactured by Mitsubishi Juko Co., Ltd.), a plate for absorptivity measurement having a length of 50 × width 75mm × thickness 4mm, a length of 10 × width 10mm × thickness 4mm The test piece for VST measurement of was obtained. Table 1 shows the composition of the obtained copolymerized resin. In Table 1, the copolymer resin composition is MMA unit / MAA unit / St unit.

Table 1 shows the results of measurement of the molecular weight and various physical properties of the obtained resin.

<Example>

(Examples 1-3 and Comparative Examples 1-3)

The copolymer resin produced in the reference example and the diffusing agent shown in Table 2 were mixed and kneaded with a twin screw extruder to obtain a pelletized resin composition. This resin composition was extruded at a resin temperature of 220 deg. C to prepare a light diffusion plate having a thickness of 2 mm. Table 2 shows the total light transmittance, light diffusivity, and luminance deviation of the obtained light diffusion plate. The siloxane polymer particles used herein have an average particle diameter of 2 µm, the acrylic polymer particles have an average particle diameter of 10 µm, and the calcium carbonate has an average particle diameter of 1.8 µm. In addition, in Table 2, a siloxane type polymer particle, an acrylic type polymer particle, and a calcium carbonate are abbreviated as siloxane type, an acryl type, and a tankal, respectively.

Claims (3)

10 to 40% by weight of methyl methacrylate unit, 2 to 20% by weight of methacrylic acid unit, and 40 to 88% by weight of styrene unit, and the weight average molecular weight is in the range of 80000 to 300000 copolymer resin 0.1-10.0 weight part of light diffusing agents are mix | blended with respect to the resin composition for light-diffusion plates characterized by the above-mentioned. The method of claim 1, At least 1 sort (s) chosen from the siloxane type polymer particle, acrylic type polymer particle, or calcium carbonate which the light-diffusion agent partially bridged, The particle composition is 1-10 micrometers, The resin composition for light-diffusion plate. A light diffusing plate according to claim 1 or 2, wherein the resin composition for light diffusing plate is molded into a plate having a thickness of 0.5 to 3 mm by melt extrusion molding or injection molding.