JPH09178947A - Light transmission body for back light of liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a light transmission body which has high luminance and is free from unequal luminance over the entire part by consisting the light transmission body of a transparent resin contg. a specific ratio of hollow crosslinked resin particles having a specific grain size. SOLUTION: This light transmission body consists of the transparent resin contg. the hollow crosslinked resin particles. The particle size of the hollow crosslinked resin particles is required to be within a range of 0.5 to 100μm. The content of the hollow crosslinked resin particles in the transparent resin is 0.01 to 0.1wt.%. A methacrylic resin is optimum as the transparent resin for its high ray transmittance and excellent heat resistance, dynamic characteristic and moldability. The methacrylic resin is a resin consisting essentially of methyl methacrylate and the content of the methyl methacrylate is preferably >=80wt.%. An acrylic crosslinked resin is preferable as the hollow crosslinked resin particles for its small light absorption in a visible light region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide for a backlight of a liquid crystal display device used in a computer, a liquid crystal television or the like, and more specifically,
The present invention relates to a light guide for a backlight, which can provide a uniform backlight with high brightness and no brightness unevenness.

[0002]

2. Description of the Related Art In recent years, portable notebook personal computers having a liquid crystal display device, portable liquid crystal TVs, video integrated liquid crystal TVs,
In a car navigation system or the like, a high-quality image as high as a CRT (cathode ray tube) is required, and a high-luminance and uniform backlight is required. Also,
Since the power consumption of liquid crystal display devices increases the battery driving time, it is important to keep the power consumption of the backlight, which has a large percentage of power consumption, as low as possible, to increase the battery driving time and increase the practical value of the above products. It has been. However, if the brightness of the backlight is reduced by suppressing the power consumption of the backlight, it is not preferable because the liquid crystal display becomes difficult to see. Therefore, it is desired to improve the optical efficiency of the backlight in order to suppress the power consumption without sacrificing the brightness of the backlight.

[0003]

As a structure of such a backlight, there is a direct type in which a light source such as a fluorescent lamp is arranged below a liquid crystal panel, and an edge using a light guide body in which the light source is arranged in a side surface. It is roughly divided into the light system. Among them, the edge light method has the feature that the backlight can be made compact, but has the disadvantage that the brightness is lower than that of the direct light method, and the problem of high image quality and power saving of the liquid crystal display device. Was not enough.

On the other hand, it has been practiced to add inorganic particles or organic particles having a refractive index different from that of the transparent resin to the transparent resin forming the light guide to impart light diffusing property to the light guide. .
However, when the inorganic particles or the organic particles are added as described above, since the diffusing particles themselves absorb light in the visible light region, there is a problem that the light transmittance is lowered and high luminance cannot be obtained. Was. Further, although the light diffusivity of the light guide is improved, it was not possible to obtain a sufficiently high light diffusivity. The present invention provides a light guide body which has a high brightness and can constitute a backlight of a liquid crystal display device which has high brightness and has no brightness unevenness over the entire surface in an edge light system which makes the best use of the feature of making the backlight compact. To aim.

[0005]

In view of such circumstances, the inventors of the present invention have arrived at the present invention as a result of earnestly studying a resin material forming a light guide for a backlight. That is, the light guide for a backlight of the liquid crystal display device of the present invention is characterized by comprising a transparent resin containing 0.01 to 0.1% by weight of hollow crosslinked resin particles having a particle diameter of 0.5 to 100 μm. To do.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION As the transparent resin constituting the light guide of the present invention, various highly transparent synthetic resins such as methacrylic resin, acrylic resin and polycarbonate resin can be used. In particular, the methacrylic resin is excellent in its high light transmittance, heat resistance, mechanical properties, and moldability, and is most suitable as a material for a light guide.

In the present invention, the methacrylic resin means
It is a resin containing methyl methacrylate as a main component, and methyl methacrylate is preferably 80% by weight or more.
Copolymerization components other than methyl methacrylate include methyl acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate,
2-ethylhexyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, glycidyl (meth) acrylate, diethylaminoethyl (meth) acrylate and the like ( (Meth) acrylic acid esters, (meth) acrylic acids, ethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, allyl (meth) acrylate, neopentyl glycol di (meth) acrylate, and other polyfunctional (meth) acrylates. ) Acrylates, aromatic vinyl monomers such as styrene and α-methylstyrene, maleimides such as phenylmaleimide and cyclohexylmaleimide, and maleic anhydride. In addition, for the purpose of improving the impact resistance of methacrylic resin, a rubber-like copolymer containing acrylate as a main component and a copolymer containing a copolymer containing methacrylate as a main component grafted are also used. it can.

In the present invention, it is important to blend the hollow crosslinked resin particles with the transparent resin represented by the methacrylic resin as described above in order to achieve the object of the present invention. The hollow crosslinked resin particles used are not particularly limited, and hollow particles composed of various highly transparent crosslinked resins such as methacrylic resin, acrylic resin, and polycarbonate resin should be used. For example, the methacrylic cross-linking resin constituting the above-mentioned light guide, the acrylic cross-linking resin containing acrylate as a main component, and the like can be mentioned. Among them, acrylic cross-linked resins are preferable because they have small light absorption in the visible light region. In particular, hollow particles made of an acrylic cross-linked resin are excellent in dispersibility in a methacrylic resin when the light guide is made of a methacrylic resin, and when the light guide is molded by a method such as injection molding. Moreover, the heat does not cause partial melting and collapse of the particle shape.

The hollow crosslinked resin particles used preferably have a refractive index relatively close to that of the transparent resin forming the light guide. This is because when the refractive index difference between the two is large, the light-guiding body tends to have a high concealing property and the light transmittance tends to decrease. For example, when using a methacrylic resin as the transparent resin forming the light guide,
The refractive index of the hollow crosslinked resin particles is preferably in the range of 1.39 to 1.49. It has a refractive index (n _d ) of 1.
When it is less than 39, the difference in the refractive index with the transparent resin becomes large and the concealing property comes out, and when it exceeds 1.49, the difference in the refractive index with the transparent resin becomes small and a sufficient light transmittance is obtained. This is because it cannot be obtained, and more preferably 1.42
The range is 1.46.

The hollow crosslinked resin particles used in the present invention need to have a particle size in the range of 0.5 to 100 μm. This is because when the particle diameter of the hollow crosslinked resin particles is less than 0.5 μm, the light loss on the short wavelength side in the visible light region becomes large, and the light emitted from the light guide becomes reddish. This is because if it exceeds 100 μm, the light transmittance is lowered, the difference in brightness depending on the distance from the light source becomes large, and brightness unevenness occurs, and the range of 5 to 30 μm is preferable.

The content of the hollow crosslinked resin particles in the transparent resin is 0.01 to 10% by weight, preferably 0.05.
２2% by weight. This is because when the content of the hollow crosslinked resin particles is less than 0.01% by weight, sufficient light diffusibility cannot be obtained and the brightness cannot be sufficiently improved. When it exceeds 10% by weight, the light transmittance is increased. Is decreased, and the difference in brightness depending on the distance from the light source is increased, resulting in uneven brightness. The content of the hollow crosslinked resin particles is preferably appropriately set within this range according to the shape of the light guide body and the like.

The method for adding the silicone particles to the transparent resin is not particularly limited. For example, the pellet-like or bead-like transparent resin and the hollow crosslinked resin particles are mixed and kneaded by using an extruder. As a result, the hollow crosslinked resin particles can be uniformly dispersed in the transparent resin. In particular, it is preferable to perform kneading using a twin-screw extruder from the viewpoint of uniform diffusion of the hollow crosslinked resin particles. When the hollow crosslinked resin particles are not uniformly dispersed, brightness unevenness is likely to occur as a backlight.

The light guide for a backlight of the present invention is produced by melt-kneading a mixture of transparent resin and hollow crosslinked resin particles and molding the mixture by injection molding or extrusion molding which is generally used. be able to. In the present invention, the backlight light guide has a sheet shape with a uniform thickness, a wedge shape with a gradually decreasing thickness from the one-lamp type light source side, and a two-lamp type light source side. It is possible to use various shapes such as those having a gradually decreasing wall thickness toward the central portion. In addition, in order to make the distribution of the light emitted from the light guide more uniform, a dot pattern is printed on the emission surface of the light guide using an ink such as white or translucent color, or a texture such as a grain or a dot is formed. Unevenness processing can be performed.

[0014]

The present invention will be described below in detail with reference to examples. Example 1 A methacrylic resin (Acrypet VH # manufactured by Mitsubishi Rayon Co., Ltd.)
001) 99.5% by weight and 0.5% by weight of hollow crosslinked acrylic resin particles (Matsumoto Yushi-Seiyaku Co., Ltd. Matsumoto Microspheres M-610) having a particle size distribution of 5 to 25 μm in Henschel. After stirring and mixing for 2 minutes,
Charged into an extruder (PCM45 manufactured by Ikegai Co., Ltd.) and barrel temperature 2
40 ° C, die temperature 240 ° C, screw speed 200
The mixture was kneaded and extruded at rpm, and the extruded strand was pelletized using a pelletizer. The obtained pellets are
The hollow crosslinked acrylic resin particles were uniformly dispersed in the methacrylic resin.

The methacrylic resin pellets containing the hollow crosslinked acrylic resin particles thus obtained were 180 mm at a cylinder temperature of 240 ° C. and a mold temperature of 70 ° C. using an injection molding machine (IS80FA3-2A manufactured by Toshiba Machine Co., Ltd.). × 90m
m, a wedge-shaped light guide having one end face having a thickness of 3 mm and the other end face having a thickness of 1.5 mm was formed. Then
A V-shaped groove was formed on one surface of the light guide by machining. As shown in FIG. 1, a reflective film was laminated on the surface of the obtained light guide having the V-shaped groove, and a diffusion film was laminated on the opposite surface, and a fluorescent lamp was installed on the thick end face. A backlight with a simple structure was constructed. The brightness of the light emitted from the surface of the diffusion film of the obtained backlight was measured at five points A to E shown in FIG. 1, and the average value was taken as the average brightness.
The minimum brightness / maximum brightness is shown in Table 1 as brightness unevenness. The average brightness is shown as 100 in Example 1 for the purpose of relative comparison with Comparative Example 1.

Comparative Example 1 A light guide was obtained in the same manner as in Example 1 except that hollow crosslinked acrylic resin particles were not used. A backlight was constructed in the same manner as in Example 1 using the obtained light guide, and the luminance was measured. The average luminance (value with respect to the average luminance of 100 in Example 1) and the luminance unevenness are shown in Table 1.

Example 2 Methacrylic resin (Acrypet TF-produced by Mitsubishi Rayon Co., Ltd.)
5 # 000) 99.95% by weight, particle size 5-25μ
Hollow crosslinked acrylic resin particles having a distribution of m (Matsumoto Microsphere M-610 manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.)
0.05% by weight was mixed by stirring in Henschel for 2 minutes, then charged into an extruder (PCM45 manufactured by Ikegai Co., Ltd.), and kneaded and extruded at a barrel temperature of 220 ° C., a die temperature of 220 ° C., and a screw rotation speed of 200 rpm. The extruded strand was pelletized using a pelletizer. In the obtained pellets, hollow crosslinked acrylic resin particles were uniformly dispersed in the methacrylic resin.

The resulting methacrylic resin pellets containing hollow crosslinked acrylic resin particles were heated to a cylinder temperature of 210 ° C. and a mold temperature of 60 ° C. using an injection molding machine (M-200-DM manufactured by Meiki Seisakusho Co., Ltd.). 200 mm x 180 m
A plate-shaped light guide having a thickness of 4 mm and a thickness of 4 mm was formed. A dot pattern is printed using white ink on one surface of the obtained light guide, a reflective film is laminated on the printed surface, and a diffusion film is laminated on the opposite surface, and a fluorescent lamp is mounted on the thick end face. After installation, a backlight having a structure as shown in FIG. 2 was constructed. The brightness of the light emitted from the surface of the diffusion film of the obtained backlight is shown in FIG.
Measured at a point, the average value is taken as the average brightness, and the minimum brightness /
The maximum luminance is shown in Table 1 as luminance unevenness. The average luminance is shown as 100 in Example 2 for the purpose of relative comparison with Comparative Example 2.

Comparative Example 2 A light guide was obtained in the same manner as in Example 2 except that hollow crosslinked acrylic resin particles were not used. Using the obtained light guide, a backlight was constructed in the same manner as in Example 2, and the luminance was measured. The average luminance (value with respect to the average luminance of 100 in Example 2) and the luminance unevenness are shown in Table 1.

Comparative Example 3 Instead of hollow crosslinked acrylic resin particles, an average particle diameter of 20
A light guide was obtained in the same manner as in Example 2 except that polypropylene particles of μm were used. Using the obtained light guide, a backlight was constructed in the same manner as in Example 2, and the luminance was measured. The average luminance (value with respect to the average luminance of 100 in Example 2) and the luminance unevenness are shown in Table 1.

[0021]

[Table 1]

[0022]

EFFECTS OF THE INVENTION The present invention provides a uniform backlight with high brightness and less brightness unevenness by constructing a light guide using a transparent resin containing a specific amount of hollow crosslinked resin particles having a specific particle size. Therefore, high image quality and power saving of the liquid crystal display device can be achieved.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a configuration of a backlight according to a first exemplary embodiment.

FIG. 2 is a perspective view showing a configuration of a backlight according to a second exemplary embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light guide 2 ... Fluorescent lamp 3 ... Reflective film 4 ... Diffusion film

Claims (1)

[Claims] 1. A light guide for a backlight of a liquid crystal display device, comprising a transparent resin containing 0.01 to 0.1% by weight of hollow crosslinked resin particles having a particle diameter of 0.5 to 100 μm.