JPH06148434A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the efficiency of light utilization in the case of thinning the device by providing a condensing body condensing parallel beams or divergent light from a tubular light source on the light incident tip part of a light transmission plate in a nearly straight line between the light incident tip part of the light transmission plate and the tubular light source. CONSTITUTION:The condensing body 16 condensing the parallel beams or the divergent light from the tubular light source 14 on the light incident tip part 13 of the light transmission plate 12 in the nearly straight line is provided between the light incident tip part 13 of the light transmission plate 12 and the tubular light source 14. A slab lens having a one direction refractive index distribution function refracting light only in the back-and-forth direction of a liquid crystal display device is used as the condensing body 16. The parallel beams or the divergent light radiated from the tubular light source 14 is made incident on the slab lens as the condensing body 16. The light is condensed in the back-and-forth direction in the slab lens, and the light is condensed in the nearly straight line in the case of being projected from the slab lens and reaching the light incident tip part 13 of the light transmission plate 12. As a result, even though the light transmission plate 12 is thinned to make the area of the light incident tip part 13 small, the light incidence is sufficiently secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light receiving type liquid crystal display device having back lighting.

[0002]

2. Description of the Related Art As a back lighting device (backlight system) mounted on a conventional liquid crystal display device, a light guide plate (light guide) type device is apt to become the mainstream as the market needs to be thinner. It is in.

Generally, in the back lighting device, as shown in FIG. 4, the light guide plate 1 is made of polymethylmethacrylate (PMMA).
Is used to provide a diffusion film 2 for uniformly diffusing light on the front surface of the light guide plate 1 (the upper surface in FIG. 4), and for the light scattering reflection on the rear surface of the light guide plate 1 (the lower surface in FIG. 4). The dot pattern 7 is formed, and the reflection film 3 for efficiently scattering and reflecting the light is provided.

As the light source 4, a tubular light source such as a cold cathode tube or a hot cathode tube is mainly used. A light source reflector (lamp reflector) 5 that efficiently reflects light toward the light guide plate 1 is provided around the tubular light source 4.

In FIG. 4, 6 is a liquid crystal display panel.

[0006]

In a conventional light guide plate (light guide) type back lighting device, the thickness of the light guide plate 1 is made thin in order to meet the demand for thinner liquid crystal display devices. However, as the thickness of the light guide plate 1 becomes thinner, the area of the light incident end face of the light guide plate 1 decreases, so that the light emitted from the tubular light source 4 is not efficiently incident on the light incident end face of the light guide plate 1, As a result, the surface luminance of the back lighting device is reduced, which is a serious problem to be solved in display quality. Further, due to a strong demand from the market, it is necessary to realize low power consumption as well, and further improvement in light utilization efficiency is desired regardless of future monochrome or color liquid crystal display devices. .

In view of the above problems, it is an object of the present invention to provide a liquid crystal display device capable of improving light utilization efficiency when it is made thin.

[0008]

The means for solving the problems according to the first and second aspects of the present invention are, as shown in FIG. 1, arranged in parallel with the liquid crystal display plate 11 and behind the liquid crystal display plate 11 to illuminate it. In the liquid crystal display device including the light guide plate 12 and the tubular light source 14 arranged at the light incident end portion 13 of the light guide plate 12, between the light incident end portion 13 of the light guide plate 12 and the tubular light source 14,
A light collector 16 for collecting parallel light or divergent light from the tubular light source 14 on the light incident end portion 13 of the light guide plate 12 in a substantially straight line is provided. A slab lens having a unidirectional refractive index distribution function of refracting light only in the vertical direction in FIG. 1) is used.

[0009]

In the means for solving the problems according to the first and second aspects, the parallel light or the divergent light emitted from the tubular light source 14 enters the slab lens as the condenser 16. In the slab lens, the light is condensed in the front-rear direction, and when the light is emitted from the slab lens and reaches the light incident end 13 of the light guide plate 12, the light is condensed on a substantially straight line.

As a result, even if the light guide plate 12 is made thin to reduce the area of the light incident end portion 13, the light incident can be sufficiently ensured. Therefore, it is possible to realize an ultra-thin liquid crystal display device.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a liquid crystal display device according to an embodiment of the present invention includes a liquid crystal display plate 11, a light guide plate 12 which is arranged in parallel behind the liquid crystal display plate 11 and illuminates the liquid crystal display plate 11. Light guide plate 1
2, a tubular light source 14 disposed at the light incident end portion 13, a light source reflector 15 that reflects light around the tubular light source 14 toward the light guide plate 12, a light incident end portion 13 of the light guide plate 12, and a tubular shape. The light incident end 1 of the light guide plate 12 is arranged between the light source 14 and the parallel light (collimated light) or divergent light from the tubular light source 14.
3 is provided with a light collector 16 that collects light substantially linearly.

As shown in FIG. 1, the light guide plate 12 is made of polymethylmethacrylate (PMMA), quartz glass, or the like, and has a length of 200 mm, a width of 160 mm, and a thickness of 4 mm, for example.
It is formed in the following flat plate shape.

An existing diffusion film 17 for diffusing the light from the light guide plate 12 toward the liquid crystal display plate 11 is attached to the front surface (the upper surface in FIG. 1) of the light guide plate 12.

The tubular light source 14 is, as shown in FIG. 1, a cold cathode tube (C) in which filaments and electrodes are housed inside a glass tube.
CFT) or hot cathode tube (HCFT) is used, for example, the diameter is 4 mm, the tube surface brightness is 18000 nt, and it is arranged at the light incident end 13 of the light guide plate 12.

As the light source reflector 15, as in the conventional case, a silver vapor deposition film or a resin molded product having a high efficiency reflectance is used.

As the light collector 16, a known rectangular parallelepiped slab lens is used.

In the slab lens, a translucent material such as a polycarbonate resin is divided into layers in the front-rear direction of the liquid crystal display device (vertical direction in FIG. 1), and layers having different refractive indexes are provided between the respective layers. The translucent resin is applied to the liquid crystal display device as shown in FIGS.
It has a unidirectional refractive index distribution function that refracts light only in the vertical direction.

Here, FIG. 2 is a diagram showing the focusing operation of the slab lens when the light from the tubular light source 14 is parallel light (collimated light) and FIG. 3 is divergent light. However, in reality, the light from the tubular light source 14 is a mixture of parallel light and divergent light.

It can be said that the slab lens has an optical function similar to that of a semi-cylindrical cylindrical lens, but from the viewpoint of the mechanism when it is attached to and supported by the back lighting device, a rectangular parallelepiped is used. It is different from the cylindrical lens in that it is formed in a shape.

Regarding the unidirectional refractive index distribution of the slab lens in the front-back direction (vertical direction in FIG. 1), the distance between the tubular light source 14 and the light incident end portion 13 of the light guide plate 12, the tubular light source 1
4, the positional relationship between the center of 4 and the center of the light guide plate 12, the tubular light source 14
Is adjusted according to design factors such as the diameter of the light guide plate 12 and the thickness of the light guide plate 12.

As shown in FIG. 1, the front and rear surfaces of the slab lens are in close contact with the light source reflector 15 to prevent light leakage, and the location of the slab lens is such that the focal point of the lens is the light incident end portion 1.
3 is included in the plane.

In FIG. 1, reference numeral 21 is a white reflecting sheet that reflects the backward light in the light guide plate 12 toward the diffusion film 17 side. Further, 22 is a white light scattering material such as TiO ₂ printed and applied on the front surface of the reflection sheet 21.

In the above structure, when the tubular light source 14 is caused to emit light, the emitted light enters the condenser 16 as parallel light or divergent light.

Since the condenser 16 is composed of a slab lens formed by dividing it into a plurality of layers, the condenser 1
The light that has entered the inside 6 is repeatedly refracted every time it enters and exits each layer adjacent to each other in the front-back direction (vertical direction in FIG. 1) of the liquid crystal display device.

When the light is emitted from the condenser 16 and reaches the light incident end 13 of the light guide plate 12, the light is condensed on a substantially straight line.

As a result, even if the light guide plate 12 is made thin to reduce the area of the light incident end portion 13, the light incident can be sufficiently secured and the light utilization efficiency can be improved. Therefore, regardless of whether it is a monochrome or color liquid crystal display device, it is possible to improve the brightness characteristics of the liquid crystal display device while realizing the ultra-thin light guide plate 16.

The present invention is not limited to the above embodiment, and it goes without saying that many modifications and changes can be made to the above embodiment within the scope of the present invention.

[0028]

As is apparent from the above description, according to the present invention, the light from the tubular light source is refracted only between the light incident end of the light guide plate and the tubular light source in the front-back direction of the liquid crystal display device. Since a condensing body that collects parallel light or divergent light on the light incident end of the light guide plate is provided almost linearly, even if the light guide plate is made thin and the area of the light incident end is small, A sufficient incidence can be secured. Therefore, there is an excellent effect that the liquid crystal display device can be made extremely thin.

[Brief description of drawings]

FIG. 1 is a sectional view of a liquid crystal display device showing an embodiment of the present invention.

FIG. 2 is a diagram showing a light collecting operation of a light collector when light from a tubular light source is parallel light.

FIG. 3 is a diagram showing a light collecting operation of a light collector when light from a tubular light source is divergent light.

FIG. 4 is a sectional view of a conventional liquid crystal display device.

[Explanation of symbols]

 11 liquid crystal display plate 12 light guide plate 13 light incident end 14 tubular light source 15 light source reflector 16 light collector

Claims (2)

[Claims] 1. A liquid crystal display comprising a liquid crystal display plate, a light guide plate arranged in parallel behind the liquid crystal display plate to illuminate the liquid crystal display plate, and a tubular light source arranged at a light incident end of the light guide plate. In the device, a light collector is provided between the light incident end portion of the light guide plate and the tubular light source, and collects parallel light or divergent light from the tubular light source substantially linearly at the light incident end portion of the light guide plate. A liquid crystal display device characterized by the above. 2. The liquid crystal display device according to claim 1, wherein a slab lens having a unidirectional refractive index distribution function of refracting light only in the front-back direction of the liquid crystal display device is used.