JP2006078954A - Diffusion plate for direct backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffusion plate which does not discolor even when exposed to UV light emitted from a backlight. <P>SOLUTION: Discoloring in the diffusion plate is significantly decreased by coating the surface of the diffusion plate with a resin layer in which a UV absorbent having the maximum absorption at a specified wavelength is combined. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a diffusion plate for a direct backlight for a liquid crystal television.

In recent years, a liquid crystal television has attracted attention as a television that replaces a cathode ray tube television.
Unlike liquid crystal tubes, the liquid crystal is not self-luminous, so a light source device called a backlight is required.
There are two types of backlights, called edge light type backlights and direct type backlights, but liquid crystal televisions often use direct type backlights that can achieve large size and high brightness.
The direct type backlight has a structure (cross-sectional view) as shown in FIG. 1 and includes a reflector, a lamp, a diffuser, an optical film, and a liquid crystal panel.

The diffuser plate is a milky white resin plate in which light scattering particles are blended, and has a role of scattering the light of the lamp and preventing the lamp from being seen through.
Further, the optical film in contact with the diffusion plate has a role of collecting light scattered by the diffusion plate and increasing the light emission efficiency.
In recent years when LCD televisions are attracting attention, various research and development have been conducted on diffusion plates. (For example, see Patent Documents 1 to 5)
However, the diffusion plate has a problem of light resistance. As can be seen from FIG. 1, the lamp and the diffuser are close to each other, and the diffuser is discolored by the ultraviolet rays emitted from the lamp. The discoloration of the diffuser causes a decrease in brightness and the light through the lamp. Improvement of the property is desired.
JP 2004-191698 A JP 2004-90626 A Japanese Patent Laid-Open No. 2004-50607 JP 2004-29091 A Japanese Patent Laid-Open No. 11-179856

  An object of the present invention is to provide a diffusion plate that does not change color even when exposed to ultraviolet rays emitted from a backlight.

As a result of intensive studies to solve the above problems, the present inventor has found that the color change of the diffusion plate is due to the surface of the light diffusing agent to be blended being colored with ultraviolet rays having a specific wavelength. The present inventors have found that the discoloration of the diffusion plate can be significantly improved by coating the surface of the diffusion plate with a resin layer containing an ultraviolet absorber having the maximum absorption.
That is, the present invention
(1) 100 parts by weight of a polycarbonate resin is blended with 0.5 to 5 parts by weight of a benzotriazole ultraviolet absorber (A), and 100 parts by weight of a polycarbonate resin is blended with 0.5 to 5 parts by weight of organic crosslinked fine particles. A diffusion plate for direct type backlights laminated on one or both sides of the resin (B) formed,
(2) The diffusion plate for a direct backlight according to (1), wherein the organic crosslinked fine particles are acrylic resin fine particles, styrene resin fine particles, and silicone crosslinked fine particles;
(3) The diffusion plate for direct type backlight according to (1) or (2) above, wherein the layer containing the ultraviolet absorber has a thickness of 10 to 100 μm,
(4) The diffusion plate for direct type backlight according to the above (1) to (3) obtained by coextrusion of the resin (A) and the resin (B),
It is.

  The diffusing plate of the present invention has an effect of not discoloring even when exposed to ultraviolet rays emitted from a backlight.

The present invention will be specifically described below.
The polycarbonate resin used in the present invention is obtained by reacting a dihydric phenol and a carbonate precursor. The production method is not particularly limited, but the interfacial polycondensation method or the melting method is preferably used. Representative examples of the dihydric phenol include 2,2-bis (4-hydroxyphenyl) propane [commonly known as bisphenol A], 1,1-bis (4-hydroxyphenyl) ethane, and 1,1-bis (4-hydroxy). Phenyl) cyclohexane, 2,2-bis (3-methyl-4-hydroxyphenyl) propane, 2,2-bis (3,5-dimethyl-4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfide, bis (4-Hydroxyphenyl) sulfone and the like can be mentioned, and among them, bisphenol A is preferable. These dihydric phenols can be used alone or in admixture of two or more.

As the carbonate precursor, carbonyl halide, carbonate ester, haloformate or the like is used, and specific examples include phosgene, diphenyl carbonate, dihaloformate of dihydric phenol, and the like.
When producing polycarbonate resin by reacting the above dihydric phenol and carbonate precursor by interfacial polycondensation method or melting method, use catalyst, terminal terminator, dihydric phenol antioxidant, etc. as necessary May be. The polycarbonate resin may be a branched polycarbonate resin copolymerized with a trifunctional or higher polyfunctional aromatic compound, or may be a polyester carbonate resin copolymerized with an aromatic or aliphatic difunctional carboxylic acid, Moreover, the mixture which mixed 2 or more types of the obtained polycarbonate resin may be sufficient.
The polycarbonate resin used in the present invention is preferably a resin having a total light transmittance of 80% or more and less dust and foreign matter.
A polycarbonate resin having a molecular weight of Mw of 15,000 to 40,000 is usually used, and a polycarbonate resin having a molecular weight Mw of 20000 to 40,000 is preferable because it is extruded into a sheet shape as a diffusion plate.

There are various light scattering agents blended in the diffusion plate, such as those in the prior art, such as calcium carbonate, barium sulfate, titanium oxide, aluminum hydroxide, silica, glass, talc, mica, Inorganic particles such as white carbon, magnesium oxide, zinc oxide and the like, those subjected to surface treatment, crosslinked or high molecular weight styrene resin particles, crosslinked or high molecular weight acrylic resin particles, crosslinked siloxane resin particles, etc. A resin particle is mentioned. Among these, the light scattering agent used in the present invention is preferably organic fine particles, and more preferably crosslinked organic cross-linked fine particles. By using the organic crosslinked fine particles, it is possible to design a resin plate that has less dispersion unevenness of the light scattering agent in the polycarbonate resin as a matrix, has high light transmittance, and high light scattering properties.
Particularly preferred as organic crosslinked fine particles are acrylic resin crosslinked fine particles, styrene resin crosslinked fine particles, and silicone crosslinked fine particles.

  Examples of the styrene resin fine particles include styrene as a monomer, halogenated styrene such as chlorostyrene and bromostyrene, alkyl styrene such as vinyltoluene and α-methylstyrene, and the like. Two or more of them can also be used. Examples of monomers other than styrenic monomers include methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate. Methacrylic esters such as: methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, etc. Acrylonitrile and the like, and two or more of them can be used as necessary.

  In addition, in order to obtain crosslinked styrenic resin fine particles, a monomer having at least two double bonds in the molecule is introduced. For example, 1,4-butanediol dimethacrylate, neopentyl glycol dimethacrylate, ethylene Di- or higher methacrylates of polyhydric alcohols such as glycol dimethacrylate, diethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, propylene glycol dimethacrylate, tetrapropylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate 1,4-butanediol diacrylate, neopentyl glycol diacrylate, ethylene glycol diacrylate, diethylene glycol Di- or higher acrylates of polyhydric alcohols such as diol diacrylate, tetraethylene glycol diacrylate, propylene glycol diacrylate, tetrapropylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate; , Aromatic polyfunctional monomers such as diallyl phthalate, and the like, and two or more of them can be used as necessary.

As a polymerization method for obtaining these styrene polymer particles, a suspension polymerization method, a micro suspension polymerization method, an emulsion polymerization method, a dispersion polymerization method and the like are usually employed.
Examples of the acrylic monofunctional monomer in the acrylic resin fine particles include, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, methacrylic acid 2 -Methacrylic acid esters such as hydroxyethyl; such as methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate Acrylic acid esters; methacrylic acid, acrylic acid and the like can be mentioned, and two or more of them can be used as necessary.

Examples of the monomer other than the acrylic monomer include those similar to the styrene resin monomer in the styrene polymer particles, acrylonitrile, and the like, and two or more of them are used as necessary. You can also.
In order to obtain acrylic resin crosslinked fine particles, a monomer having at least two double bonds in the molecule is introduced, and examples thereof include the same polyfunctional monomers in the styrene resin fine particles. Two or more of them can be used as necessary.

  As the silicone-based crosslinked fine particles, those generally called silicone rubber and those called silicone resin, which are solid at room temperature, are used. Siloxane polymers can be produced by hydrolyzing and condensing chlorosilanes such as dimethyldichlorosilane, diphenyldichlorosilane, phenylmethyldichlorosilane, methyltrichlorosilane, and phenyltrichlorosilane. The polymer thus obtained is further obtained from benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-chlorobenzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, 2,5 -Alkoxysilanes may be cross-linked by acting a peroxide such as dimethyl-2,5-di (t-butylperoxy) hexane, or have a silanol group at the terminal And may be subjected to condensation crosslinking. The polymer is preferably a crosslinked polymer in which 2 to 3 organic groups are bonded per silicon atom.

The siloxane polymer particles may be obtained, for example, by mechanically pulverizing the siloxane polymer, and in the production thereof, as described in JP-A-59-68333, a line is used. The curable polymer having the organosiloxane block or a composition thereof may be cured in a spray state to obtain spherical particles, or as described in JP-A-60-13813, The alkoxysilane or its partially hydrolyzed condensate may be obtained as spherical particles by hydrolysis and condensation in an aqueous solution of ammonia or amines.
The transmittance of the resin plate can be changed depending on the blending amount of these organic crosslinked fine particles. The transmittance required for the diffusion plate is 40 to 85%, and the blending amount of the organic crosslinked fine particles is preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the polycarbonate resin. When the blending amount is 0.5 parts by weight or more, the transmittance is sufficient and an appropriate light scattering effect is obtained. When the blending amount is 5 parts by weight or less, the transmittance is sufficient, and an appropriate amount of light is used as a direct backlight mounted on a liquid crystal television. Become.

The direct type backlight for a liquid crystal television used as the diffusion plate of the present invention has the structure shown in FIG. 1, and the diffusion plate is arranged in the form of being close to the lamp.
The wavelength of light emitted from the lamp is the strongest of the three wavelengths of red (R), green (G), and blue (B), but it is also known that it contains ultraviolet light of 250 to 380 nm although it is weak.
Usually, the polycarbonate resin is blended with 0.01 to 0.3% of an ultraviolet absorber, and the resin itself is not discolored by the ultraviolet rays emitted from the lamp.
However, there is a problem of discoloration (yellowing) when the liquid crystal television is turned on for a long time in the conventionally used diffusion plates. When the diffuser plate is discolored, there are many problems such as a decrease in brightness and darkening, and a visible lamp.

As a result of intensive studies, the present inventor has found that the surface of the organic crosslinked fine particles blended as a light scattering agent is colored at a specific ultraviolet wavelength as a result of discoloration of the diffusion plate.
The organic crosslinked fine particles have a molecular structure such as a methyl group on the surface of the fine particles in order to improve the adhesion with the resin as a matrix, and this surface molecular structure is particularly a light having a wavelength of 340 to 350 nm out of the ultraviolet rays emitted from the lamp. They found that it was colored.
There are various types of ultraviolet absorbers blended in the polycarbonate resin, such as benzophenone, benzotriazole, triazine, malonic ester, cyanoacrylate, salicylate, and oxalic anilide.

  The maximum absorption wavelength of benzophenone series is approximately 290 to 300 nm, the maximum absorption wavelength of benzotriazole series UV absorber is 340 to 350 nm, the maximum absorption wavelength of triazine series UV absorbent is 270 to 280 nm, and the maximum of malonic ester UV absorbent The absorption wavelength is 300 to 310 nm, the maximum absorption wavelength of the cyanoacrylate UV absorber is 300 to 310 nm, and the maximum absorption wavelength of the salicylate UV absorber is 300 to 310 nm. It was found that it is particularly preferable to use a benzotriazole ultraviolet absorber having a maximum absorption wavelength of 340 to 350 nm.

  Examples of the benzotriazole ultraviolet absorber include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-bis (α, α-dimethylbenzyl). Phenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) benzotriazole, 2- (2′-hydroxy-3′-t-butyl-5′-methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 ', 5'-di-t-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3', 5'-di -T-amylphenyl) benzotriazole, 2- (2'-hydroxy-5'-t-octylphenyl) benzotriazole, 2,2'-methylenebis (4- (1,1 , 3,3-tetramethylbutyl) -6- (2N-benzotriazol-2-yl) phenol, 2- (2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ′) And '-tetrahydrophthalimidomethyl) -5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-5'-methacryloxyphenyl) -2H-benzotriazole.

Since the organic cross-linked fine particles blended in the diffusion plate are dispersed throughout the plate, all organic cross-linked fine particles can be protected even if this benzotriazole UV absorber is blended in the polycarbonate resin as the matrix. I can't.
Therefore, the present inventor has found that the polycarbonate resin containing the organic crosslinked fine particles is protected by coating with a polycarbonate resin containing a large amount of a benzotriazole-based ultraviolet absorber.
That is, the amount of the benzotriazole-based UV absorber blended in the resin laminated as a film is preferably 0.5 to 5 parts by weight, more preferably 1 to 3 parts by weight with respect to 100 parts by weight of the polycarbonate resin as a matrix.

When the blending amount of the benzotriazole ultraviolet absorber is 0.5 parts by weight or more, the ultraviolet wavelength of 340 to 350 nm is sufficiently absorbed, and coloring of the organic crosslinked fine particles can be prevented. It is not sticky with the absorbent and does not adhere to the optical film disposed immediately above.
The combined use of an ultraviolet absorber and another stabilizer is effective, and the combined use with a hindered amine light stabilizer (HALS) is preferable.
Other additives may be added as long as they do not interfere with the effects of the present invention, such as heat stabilizers, antioxidants, various stabilizers, plasticizers, flame retardants, lubricants, antistatic agents, antifungal agents, crystal nuclei. Agents, pigments and dyes.

The resin plate of the present invention is a laminated resin plate, and its production method may be any of press lamination method, coextrusion method, and film lamination method, but the coextrusion method is preferred as a simple and continuous lamination method.
In the coextrusion method, molten resin extruded from different extruders is stacked and widened in a sheet die (die), discharged as a laminated molten resin layer, and then sheet thickness is adjusted and cooled by a polishing roll. In this method, a continuously uniform laminated sheet can be manufactured.
The total thickness of the resin plate as the diffusion plate is preferably 1 to 5 mm, and the coating resin layer containing a large amount of the laminated benzotriazole-based ultraviolet absorber is preferably 10 to 100 μm. When the film is thicker than 10 μm, the UV absorption effect is sufficient, and the discoloration of the diffusion plate can be prevented by suppressing the coloring of the organic crosslinked fine particles. When the film is less than 100 μm, it is easy to form a uniform film layer. The transmittance is uniform.

The present invention will be described based on examples.
[Example 1]
0.7 parts by weight of 100 parts by weight of polycarbonate resin (Teijin Kasei Panlite L1250 (registered trademark)) and benzotriazole ultraviolet absorber (Tinbin 234 (registered trademark) by Ciba Geigy Co., Ltd.) having a maximum absorption wavelength of 346 nm The blended resin (A) is added to 100 parts by weight of a polycarbonate resin (Panlite L1250 (registered trademark) manufactured by Teijin Chemicals Ltd.) and acrylic crosslinked fine particles (Tech Polymer MBX (registered by Sekisui Chemicals Co., Ltd.) as a light diffusing agent. (Trademark)) is co-extruded on both sides of resin (B) containing 1 part by weight of a combination of a screw diameter 60 mm, 30 mm two extruders adjusted to 250 to 270 ° C. and a die for a multi-manifold laminated sheet The molten resin that came out of the die is taken up by three polishing rolls adjusted to 120 ° C. It was formed to Jo.
At this time, the thickness of the resin plate was 2.0 mm, and the thickness of the resin (A) laminated on both sides was about 20 μm.
The produced resin plate was mounted as a diffusion plate of a commercially available 20-inch liquid crystal television, and after 2000 hours of continuous use (lamp continuous lighting), the resin plate was taken out, and the color change from the initial stage was evaluated.
For the color, the yellowness was measured according to JIS K7105, and the difference between the initial yellowness and the yellowness after mounting for 2000 hours was shown as the yellowing degree (ΔYI).
The results are shown in Table 1 together with comparative examples.

[Example 2]
The same procedure as in Example 1 was carried out except that the organic crosslinked fine particles blended in the resin (B) were changed to silicone crosslinked fine particles (Tospearl 120 (registered trademark) manufactured by GE Toshiba Silicone Co., Ltd.).

[Examples 3 and 4]
The same procedure as in Example 1 was carried out except that the blending amount of the benzotriazole-based ultraviolet absorber blended in the resin (A) was changed to 2 parts by weight or 4 parts by weight.

[Examples 5 and 6]
The same procedure as in Example 1 was performed except that the amount of the organic crosslinked fine particles blended in the resin (B) was changed to 2 parts by weight or 4 parts by weight.

[Comparative Examples 1 and 2]
The ultraviolet absorber to be blended with the resin (A) is a benzophenone ultraviolet absorber having a maximum absorption wavelength of 290 nm (Sumisorb 110 (registered trademark) manufactured by Sumitomo Chemical Co., Ltd.) or a triazine ultraviolet absorber having a maximum absorption wavelength of 274 nm (Ciba Geigy Corp.) The same procedure as in Example 1 was performed except that the product was changed to Tinuvin 1577FF (registered trademark). The results are shown in Table 1 together with examples.

[Comparative Example 3]
The same procedure as in Example 1 was conducted except that the amount of the benzotriazole-based ultraviolet absorber blended in the resin (A) was reduced to 0.3 parts by weight.

[Comparative Example 4]
Without using the resin (A), 100 parts by weight of polycarbonate resin (Panlite L1250 (registered trademark) manufactured by Teijin Chemicals Ltd.) and acrylic cross-linked fine particles (Techpolymer MBX manufactured by Sekisui Chemicals Co., Ltd. as a light diffusing agent) Only the resin (B) containing 1 part by weight of the trademark)) was formed into a sheet by extrusion. The plate thickness at this time was adjusted to 2 mm as in Example 1.
The diffusion plate was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Reference example]
A polycarbonate resin (Panlite L1250 (registered trademark) manufactured by Teijin Chemicals Limited) alone was formed into a sheet having a thickness of 2 mm by extrusion to produce a so-called transparent PC sheet.
The resin plate was evaluated in the same manner as in Example 1. The results are shown in Table 1 together with examples and comparative examples.

  The diffusion plate of the present invention can be suitably used as a diffusion plate for a direct backlight for a liquid crystal TV.

The structure (sectional drawing) of the direct type backlight for liquid crystal televisions using the diffuser plate of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 2 Optical film 3 Diffusing plate 4 Lamp 5 Reflecting plate 6 Case

Claims (4)

  A resin (A) prepared by blending 0.5 to 5 parts by weight of a benzotriazole-based UV absorber with 100 parts by weight of a polycarbonate resin, and 0.5 to 5 parts by weight of organic crosslinked fine particles is blended with 100 parts by weight of a polycarbonate resin. A direct-type backlight diffusion plate laminated on one or both sides of the resin (B).   The diffusion plate for a direct backlight according to claim 1, wherein the organic crosslinked fine particles are acrylic resin fine particles, styrene resin fine particles, and silicone-based crosslinked fine particles.   The thickness of the layer containing an ultraviolet absorber is 10-100 micrometers, The diffusion plate for direct type | mold backlights of Claim 1 or 2 characterized by the above-mentioned.   The diffusion plate for direct type backlights according to claim 1, which is obtained by co-extrusion of the resin (A) and the resin (B).

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