JPH0651307A - Thin lighting device for liquid crystal display devices - Google Patents

Abstract

(57) [Summary] [Purpose] The display quality is improved by improving the temperature distribution of the liquid crystal material due to the heat generation of the light source. [Structure] A heat conduction layer 13 made of a material having excellent heat conduction is provided on the outer surface of the linear light source 2 and the back surface of the light guide plate 1. [Effect] Since the heat generated in the linear light source is diffused through the heat conductive layer, the temperature distribution of the liquid crystal material is improved and the display unevenness is reduced. In particular, the birefringence of the liquid crystal material is used.
The effect is great in improving the display quality of the TN type liquid crystal display element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a thin illuminating device which illuminates a transmissive or semi-transmissive liquid crystal display device from the back side.

[0002]

2. Description of the Related Art FIG. 2 is an exploded perspective view showing a general structure of a thin illuminating device for transmissive and semi-transmissive liquid crystal display elements. A transparent light guide plate 1 made of acrylic resin or the like, and this light guide plate. 1. A linear light source 2, such as a cold cathode tube or a hot cathode tube, which is arranged on at least one side edge of 1, a light guide plate reflection plate 3 which is arranged on the back surface of the light guide plate 1, and which is arranged outside the light source 2. The light source reflection plate 4 and the diffusion plate 5 arranged on the front surface of the light guide plate 1 are integrally housed in an upper surface outer case 6 and a lower surface outer case 7. Each of the reflectors 3 and 4 is a resin film or a metal plate on which a thin film of a metal having a high reflectance such as aluminum or silver is vapor-deposited to form a mirror-like reflection surface. The light is guided to the front surface through the light guide plate 1, and the light is appropriately scattered by the diffusion plate 5 so that the luminance distribution is made uniform.

However, if the size of the liquid crystal display device becomes large, it becomes difficult to make the brightness of the display surface uniform, and the display quality tends to deteriorate. Therefore, various methods have been proposed to solve this problem. For example, JP-A-64-
According to Japanese Patent No. 57240, it is proposed that the reflection plate for a light guide plate has a curved surface inclined toward the front side at a portion far from the light source to enhance reflection efficiency at a portion far from the light source. All of these proposals are mainly related to the improvement of the reflection plate and the diffusion plate for making the emitted light uniform, but the display quality of the liquid crystal display device is the uniform brightness obtained by the reflection plate and the diffusion plate. Not only the characteristics but also the temperature distribution due to the heat generation of the light source. That is, the birefringence of the liquid crystal material is lowered due to the temperature rise in the heat generating portion such as the electrode portion of the light source and the vicinity thereof. At the same time, there is a problem that the display quality is significantly deteriorated due to display unevenness caused by the difference in birefringence.

[0004]

The present invention has been made in view of such a temperature rise due to heat generation of a light source, and an object thereof is to improve the temperature rise and improve display quality.

[0005]

In order to solve the above-mentioned problems, according to the present invention, the light of a linear light source arranged on at least one side edge of a light guide plate made of a translucent material is directed to the front face of the light guide plate. In a thin lighting device for a liquid crystal display device, which is configured to be led out and illuminate the liquid crystal display device from the back surface, a heat conduction layer made of a material having excellent heat conduction is provided on the outer surface of the linear light source and the back surface of the light guide plate. There is.

[0006]

The heat generated in the electrode portion of the linear light source is diffused through the heat conductive layer to make the temperature distribution of the liquid crystal material uniform, and display unevenness due to the temperature difference does not occur, thereby improving the display quality. In addition, since the heat dissipation is promoted by the heat conductive layer, the temperature rise of the thin lighting device and the liquid crystal display element is generally reduced.

[0007]

EXAMPLE Next, one example shown in FIG. 1 will be described. The same parts as those of the above-mentioned conventional example are indicated by the same reference numerals, and the different points will be mainly described. In the figure, 11
Is a thin illumination device of the embodiment, 12 is a liquid crystal display element,
Although the drawing shows the thickness direction in an enlarged manner, as is well known, the both are closely arranged and integrally arranged. Reference numeral 13 denotes a heat conductive layer provided by the present invention, which is a thin plate made of a material having excellent heat conductivity such as aluminum or copper.
From the outer side to the back surface of the light guide plate 1, they are wound and wound so as to be in close contact with the reflection plates 3 and 4. The upper and lower outer cases of the thin lighting device 11 are not shown.

The following Table 1 shows the relationship between the continuous lighting time and the temperature difference (difference between the maximum temperature and the minimum temperature) on the surface of the light guide plate 1 as compared with the conventional product and the aluminum plate having a thickness of 1 mm as the heat conduction layer 13. 2 shows an example in which is used.

[Table 1]

Table 2 below shows the relationship between the plate thickness and the temperature difference when the plate thickness of the aluminum plate is changed in the embodiment of Table 1 (lighting time is 30 minutes).

[Table 2]

The following Table 3 shows the thickness 1 as the plate heat conduction layer 13.
The relationship between the continuous lighting time and the temperature difference on the surface of the light guide plate 1 is shown for the example of Table 1 using an aluminum plate of 1 mm and the example using a copper plate of 1 mm thickness.

[Table 3]

From these results, according to the present invention, the temperature difference on the surface of the light guide plate 1 is reduced, and the temperature distribution in the display surface of the liquid crystal display element 12 arranged close to it is also improved. It can be seen that the temperature difference becomes small, and the display unevenness due to the temperature difference of the liquid crystal material hardly occurs. Further, as shown in Table 2, the thicker the heat conduction layer 13, the smaller the temperature difference becomes.
Although the temperature difference between copper and aluminum is smaller than that between aluminum and aluminum, the difference between aluminum and copper is relatively small, so the cost,
Considering weight, workability, etc., practically, the plate thickness is 1.0 to
It seems desirable to use an aluminum plate of about 2.0 mm. Although a metal plate is used as the heat conductive layer 13 in the above-described embodiments, a material such as an organic resin or ceramic can be used as long as it exhibits excellent heat conductivity. Further, the heat conducting layer 13 is not separated from the reflecting plates 3 and 4, but a reflecting surface is formed on the heat conducting layer 13 to form the reflecting plates 3 and 4.
It can also be combined with 4.

[0012]

As is apparent from the above-described embodiments, the present invention provides a heat conduction layer made of a material having excellent heat conduction on the outer surface of a linear light source and the back surface of a light guide plate in a thin lighting device for a liquid crystal display device. Is provided. Therefore, by diffusing the heat generated in the electrode portion of the linear light source through the heat conduction layer, the temperature distribution of the liquid crystal material due to long-time lighting can be improved and the display unevenness due to the temperature difference can be reduced. Especially, it is effective in improving the display quality of the STN type liquid crystal display element utilizing the birefringence of the liquid crystal material.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the present invention.

FIG. 2 is a schematic exploded perspective view of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light guide plate 2 Linear light source 3 Reflector for light guide plate 4 Reflector for light source 5 Diffusion plate 11 Thin lighting device 12 Liquid crystal display element 13 Heat conduction layer

Claims (1)

[Claims] 1. A liquid crystal configured to guide light from a linear light source disposed at at least one side edge of a light guide plate made of a translucent material to the front surface of the light guide plate to illuminate the liquid crystal display element from the back surface. A thin illuminating device for a liquid crystal display element, comprising: a thin conductive illuminating device for a display element, wherein a heat conductive layer made of a material having excellent thermal conductivity is provided on the outer surface of the linear light source and the back surface of the light guide plate.