JPH05341284A - Light transmission plate for illumination of liquid crystal display device and its production - Google Patents

Abstract

PURPOSE:To obtain the light transmission plate for illumination of the liquid crystal display device which is bright in display, small in the number of parts and excellent in production stability. CONSTITUTION:The light transmission plate for illumination of the liquid crystal display device is composed of a compsn. formed by homogeneously dispersing oxide particulates 12 for light scattering into a transparent polymer 11 which is the essentially component of the light transmission plate. The shape of the light transmission plate is molded by melting, kneading and dispersing oxide particulates 12 subjected to a lipophilic surface treatment into the transparent polymer 11 as the essential component or solvent dissolving and dispersing the particulates therein to form raw material pellets, then injection molding or extrusion molding the mixture.

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 for illuminating a liquid crystal display device which has a bright display and a small number of parts and is excellent in manufacturing stability.

[0002]

2. Description of the Related Art Generally, a liquid crystal display device has a structure in which a cold cathode fluorescent discharge lamp is placed on a side surface, a light guide plate guides light to the back surface, and the liquid crystal display panel is irradiated with the light through a reflection plate and a diffusion plate. Is. To ensure in-plane uniformity of brightness, a reflective pattern with a density distribution is printed on the back surface of the light guide plate, and at least three parts other than the illumination lamp are used to achieve low power, high brightness, and in-plane homogeneity. It was possible to achieve a good balance of thinness and lightness. In order to increase the light utilization efficiency and reduce the number of parts, a method of forming a total reflection layer on the lower surface by incorporating transparent fine particles for light scattering in the light guide plate in a distributed manner (Sho 58-46447) has been proposed. Has been presented. Also, a method using a milky white light scatterer (Japanese Patent Publication No. 3-729).
68) is also presented.

Recently, a milky-white high-brightness light-scattering transmitter capable of controlling a scattering angle by forming a microphase-separated structure with a copolymer having a heterogeneous structure and a blended polymer has been reported (Proceedings of the Polymer Society of Japan, Vol. 41, No. 3 (1992) IL27).

[0004]

In the illumination of the conventional liquid crystal display device, it is necessary to use at least three parts of a light guide plate, a reflection plate, and a diffusion plate in addition to the illumination lamp, and the light utilization efficiency cannot be increased so much. There were challenges. Ideally, all the functions should be integrated into the light guide plate in order to increase the light utilization efficiency and to reduce the manufacturing cost.

The previously proposed method of mixing transparent fine particles for light scattering in a light guide plate so as to have a distribution is extremely difficult to control in manufacturing. In addition, the method of forming a micro phase-separated structure with a copolymer having a non-uniform structure and a blended polymer easily changes the phase structure when heated to obtain the shape of the light guide plate, and thus, the light guide plate can be used in a mass production process. It was impossible to guarantee the function.

Therefore, the present invention solves such a problem, and an object thereof is to provide a light guide plate for illumination of a liquid crystal display device which is excellent in brightness and homogeneity and has a small number of parts, and its manufacturing stability. It provides a manufacturing method.

[0007]

The above object is to provide a light guide plate for illumination of a liquid crystal display device equipped with an illumination lamp, wherein the light guide plate is made of a transparent polymer whose main component is homogeneously dispersed with oxide fine particles for light scattering. This is achieved by having a dispersed composition. Further, the light guide plate for illumination of the liquid crystal display device, melt-kneading dispersion of the oxide fine particles subjected to lipophilic surface treatment in the transparent polymer of the main component, or solvent dissolution dispersion to prepare raw material pellets, injection molding or It can be manufactured by molding the shape of the light guide plate by extrusion molding.

[0008]

【Example】

Example 1 Spherical silica having an average particle size of 0.3 μm was prepared by a wet method using alkoxysilane as a raw material, and heat-treated. By reacting with trimethylchlorosilane, the hydroxyl group on the surface was changed to a trimethylsilyl group so that it had lipophilicity. Pellets containing PMMA as a main component were prepared by dissolving 80% by weight of polymethylmethacrylate (PMMA) in butyl acetate, stirring and dispersing 20% by weight of the surface-treated fine silica particles, and removing the solvent. A light guide plate was formed by extrusion into a flat plate, and aluminum was deposited on the back surface to form a reflective layer. A schematic cross-sectional view of the light guide plate thus manufactured is shown in FIG. Average particle size 0.3 μm
The fine silica particles were uniformly dispersed in the same state as in the raw material pellets.

The scattering angle of the light emitted from the light guide plate and the in-plane brightness distribution can be controlled by the refractive index of the fine particles, the particle size distribution, the density distribution and the like. If the composition of the raw material pellets is maintained after molding as in this embodiment, the material design can be facilitated and the characteristics of the light guide plate can be managed as designed. The light incident on the side surface of the light guide plate from the illumination lamp causes almost no absorption loss, and is emitted almost vertically from the surface due to diffraction at the particle interface. The brightness uniformity on the surface was 90% or more.

FIG. 2 shows a schematic sectional view of a liquid crystal display device using the light guide plate thus manufactured. In FIG. 2, 21 is a liquid crystal panel, 22 is a light guide plate, and 23 is an illumination lamp. The brightness on the display surface was improved from 60 candelas to 80 candelas as compared with the conventional backlight using the same illumination lamp. We were able to achieve a bright and easy-to-see display with little variation between individuals. Also, the reliability of heat, humidity, light resistance, etc. was sufficient.

Example 2 Spherical titania having an average particle size of 0.8 μm was produced by a wet method using alkoxy titanium as a raw material and heat-treated. By reacting with 3-aminopropyltriethoxysilane, the hydroxyl groups on the surface were replaced and lipophilicity was imparted. Polymethyl acrylate (PM
A) 70% by weight and 30% by weight of surface-treated titania fine particles were melt-kneaded and dispersed to prepare pellets containing PMA as a main component. A light guide plate was formed by injection molding into a wedge shape having fine uneven surfaces, and aluminum was deposited on the back surface to form a reflective layer. A schematic cross-sectional view of the light guide plate thus manufactured is shown in FIG. The titania fine particles having an average particle diameter of 0.8 μm were uniformly dispersed in the same state as in the raw material pellets.

The scattering angle of the light emitted from the light guide plate and the in-plane brightness distribution can be controlled by the refractive index, particle size distribution, density distribution and the like of the fine particles. Light incident on the thick side surface of the wedge-shaped light guide plate from the illumination lamp is emitted with an angular distribution having a maximum value in the vertical direction due to diffraction at the particle interface and diffuse reflection by the surface. The brightness uniformity on the surface is 9
It was 0% or more.

In the liquid crystal display device using the light guide plate thus manufactured, the brightness on the display surface is improved from 50 candela to 70 candela, as compared with the conventional backlight using the same illumination lamp. We were able to achieve a bright and easy-to-see display with little variation between individuals. Also, the reliability of heat, humidity, light resistance, etc. was sufficient.

(Example 3) Spherical tin oxide fine particles having an average particle diameter of 0.15 µm were reacted with vinyltrimethoxysilane to substitute the hydroxyl groups on the surface so as to have affinity with the polymer. 90% by weight of polycarbonate (PC) was dissolved in methyl ethyl ketone, 10% by weight of the surface-treated fine tin oxide particles were stirred and dispersed, and the solvent was removed to prepare pellets containing PC as a main component. A light guide plate was formed into a U shape by injection molding, and aluminum was deposited on the back surface to form a reflective layer. A schematic cross-sectional view of the light guide plate thus manufactured is shown in FIG. Average particle size 0.15μ
The tin oxide fine particles of m were uniformly dispersed in the same state as in the raw material pellets.

The scattering angle of the light emitted from the light guide plate and the in-plane brightness distribution can be controlled by the refractive index, particle size distribution, density distribution and the like of the fine particles. The light incident on the thick side surface of the U-shaped light guide plate from the two illumination lamps arranged on both sides is emitted from the surface in a substantially vertical direction due to diffraction at the particle interface. The brightness uniformity on the surface was 90% or more.

In the liquid crystal display device using the light guide plate thus manufactured, the brightness on the display surface is improved from 70 candela to 90 candela, as compared with the conventional backlight using the same illumination lamp. We were able to achieve a bright and easy-to-see display with little variation between individuals. Also, the reliability of heat, humidity, light resistance, etc. was sufficient.

[0017]

As described above, according to the present invention, in the light guide plate for illumination of the liquid crystal display device provided with the illumination lamp, the light guide plate is contained in the transparent polymer as the main component, and the oxide fine particles for light scattering are used. By using a composition in which is uniformly dispersed, it is possible to illuminate a liquid crystal display device that has excellent brightness and homogeneity and has a small number of parts.

In the light guide plate for illumination of the liquid crystal display device, fine particles of oxide having a lipophilic surface treatment are melt-kneaded or dispersed in a transparent polymer as a main component to prepare raw material pellets, which are then injected. By molding the shape of the light guide plate by molding or extrusion molding, stable manufacturing became possible. Since it was possible to reduce the number of components of the lighting, it was possible to improve the utilization efficiency of light and reduce the manufacturing cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing the concept of a light guide plate in Example 1 of the present invention.

FIG. 2 is a cross-sectional view schematically showing the concept of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 3 is a sectional view schematically showing the concept of a light guide plate in Example 2 of the present invention.

FIG. 4 is a sectional view schematically showing the concept of a light guide plate in Example 3 of the present invention.

[Explanation of symbols]

 11 ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 31 ‥‥‥‥‥

Claims (5)

[Claims] 1. A light guide plate for illumination of a liquid crystal display device provided with an illumination lamp, wherein the light guide plate has a composition in which fine oxide particles for light scattering are homogeneously dispersed in a transparent polymer as a main component. A light guide plate for illumination of a characteristic liquid crystal display device. 2. The illumination light guide plate of a liquid crystal display device according to claim 1, wherein the illumination light guide plate of the liquid crystal display device has a wedge shape or a U shape. 3. The light guide plate for illumination of a liquid crystal display device according to claim 1, wherein a metal layer for total reflection is formed on the back surface of the light guide plate for illumination of the liquid crystal display device. 4. The light guide plate for illumination of a liquid crystal display device according to claim 1, wherein the light guide plate for illumination of the liquid crystal display device is provided with a fine uneven surface for scattering light. 5. In the manufacture of a light guide plate for illumination of a liquid crystal display device provided with an illumination lamp, raw material is prepared by melt-kneading dispersion or solvent-dispersion of oxide fine particles subjected to lipophilic surface treatment in a transparent polymer as a main component. A method for manufacturing a light guide plate for illumination of a liquid crystal display device, which comprises forming a pellet and molding the light guide plate by injection molding or extrusion molding.