JPH04350821A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the device which is free from the unequal contrast of a liquid crystal screen in spite of a reduction in thickness by using sheet glass coated with a light diffusing agent as a diffusion plate of a back light. CONSTITUTION:The sheet glass 11 coated with the light diffusing agent 10 is used as the diffusion plate 6 of the back light unit constituting the liquid crystal display device. The light diffusing agent 10 may be deposited only on the front surface of the sheet glass 11 or on both front and rear surfaces thereof. This component is an org. or inorg. coating material and pigments may be incorporated therein. The light diffusing agent 10 may also be deposited on the sheet glass 11 at a high temp. The sheet glass 11 has the higher thermal conductivity than the thermal conductivity of acryl, polycarbonate, etc., which are the components of the conventional light diffusion plate 6, the heat generated from a cold cathode tube diffuses rapidly and uniformly to the surface of the diffusion plate 6 if such a glass plate coated with the light diffusing agent 10 is as the diffusion plate 6. Then the unequalness of the heat diffusion on the surface of the diffusion plate 6 is lessened and the unequal temp. distribution of the liquid crystal is eventually suppressed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a liquid crystal display device having a backlight unit used in portable electronic devices such as portable personal computers and word processors.

0002

2. Description of the Related Art As an example of the prior art, a liquid crystal display device having a commonly used FL (cold cathode fluorescent lamp) backlight unit will be described. FIG. 1 is an exploded perspective view of a conventionally known liquid crystal display device. The liquid crystal display device is roughly divided into two parts: a liquid crystal display element 1 and a flexible substrate 2 that connects the liquid crystal display element 1 to
There are two components: a liquid crystal display section consisting of a printed circuit board 3 connected to the LCD panel, and an FL backlight unit 4. Figure 2 shows a completed diagram of this. In FIG. 2, the FL backlight unit 4 includes, in order from the top, a diffusion plate 6 and a diffusion sheet 7.
, FL tube 8, and lamp housing 9.
A liquid crystal display element 1 connected to a printed circuit board via a flexible substrate 2 is installed on top of this.

Next, the function of the FL backlight unit of a liquid crystal display device will be explained based on FIG. The FL backlight unit 4, which is a part of the liquid crystal display device, reflects the light generated from the FL tube toward the upper surface with the lamp housing 9.
The light is uniformly diffused by the diffusion sheet 7 and the diffusion plate 6 to form a surface light source, and this arrangement itself is well known. This diffuser plate 6
The material is made of acrylic, heat-resistant resin, polycarbonate, etc., and the distance between the diffuser plate 6 and the FL tube 8 is generally about 2.0 to 2.5 mm. This structure enables uniform surface light emission using the FL tube as a light source.
L backlight unit is realized.

0004

With the recent trend towards miniaturization of electronic equipment, there has been a demand for backlight units for lighting to be made thinner. In order to meet this demand, it is necessary to reduce the total thickness, that is, to reduce the diameter of the FL tube and to reduce the distance between the diffuser plate and the FL tube. However, if we simply try to satisfy this condition without changing the brightness, the heat generated from the FL tube will increase and the distance between it and the diffuser plate will become smaller, causing the heat to be emitted on the FL backlight unit surface. Heat distribution becomes uneven.

[0005] As a result of this, the heat absorbed by the liquid crystal element surface on the top surface of the FL backlight unit becomes uneven, which causes uneven temperature distribution on the element surface, and furthermore, changes and unevenness in the contrast of the liquid crystal display screen. It turns out. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to realize a liquid crystal display device with no contrast unevenness on a liquid crystal screen even when the device is made thinner.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the means adopted by the present invention is to use a plate glass coated with a light diffusing agent as a diffusion plate of a backlight unit constituting a liquid crystal display device. It is at the point where it was.

[0007]

[Function] When plate glass coated with a light diffusing agent is used as a diffuser plate as in the present invention, plate glass has higher thermal conductivity than acrylic, polycarbonate, etc., which are the components of conventional diffuser plates, so FL tube The generated heat quickly and uniformly diffuses to the surface of the diffuser plate. Therefore, unevenness in heat dissipation on the surface of the diffuser plate is reduced, and as a result, unevenness in temperature distribution of the liquid crystal element can be suppressed.

[0008] Therefore, the contrast unevenness of the liquid crystal display screen that accompanies this unevenness does not occur.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is characterized by the material of the diffusion plate 6. Table 1 is a list of thermal conductivity by material. It can be seen from this table that the thermal conductivity of glass is higher than that of other conventional materials.

0010

[Table 1]

FIG. 4 is a cross-sectional model diagram of the diffusion plate of the present invention, and as shown in FIG. It is in. Figure 4 shows that on the surface of a glass diffuser plate material,
It shows the light diffusing agent 10 being applied. In this example, the light diffusing agent 10 is applied only to the upper surface of the glass plate 11, but it may be applied to both the upper and lower surfaces. Further, the component is an organic or inorganic coating agent, and a pigment may be mixed therein. Furthermore, the light diffusing agent may be applied to a plate glass at a high temperature.

Since glass has a higher thermal conductivity than acrylic, a diffusion plate using glass has a higher thermal diffusion rate than a conventional diffusion plate. However, glass has higher light transmittance than acrylic resin, so use a light diffusing agent with low transmittance to prevent the light transmittance of the diffuser plate from becoming excessively high. .

FIG. 3 shows a conventional diffuser plate made of the following materials:
Made of acrylic, heat-resistant resin, polycarbonate, etc. The diagonal line shown here represents the transmittance of this diffuser plate by its linear density. The diagonal line in Figure 4 also indicates the transmittance, but this is the transmittance of the board before the light diffusing agent is applied, and the linear density is shown to be higher because the transmittance is higher than in Figure 3. There is. By applying a light diffusing agent to this, the light transmittance is adjusted to be approximately the same as that in FIG. 3.

[0014]

[Effects of the Invention] As explained above, according to the present invention,
Even when the space between the diffuser plate and the FL tube is shortened and the diameter of the FL tube is reduced in response to the demand for a thinner overall thickness of the backlight, the heat diffusion of the diffuser plate is rapid, so the FL Local heating of the liquid crystal display element due to heat generation of the tube can be prevented. Therefore, it is possible to obtain a thin liquid crystal display device without uneven temperature distribution of the liquid crystal display element and with no uneven contrast on the screen.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view of a conventionally known liquid crystal display device.

FIG. 2 is an assembled sectional view of the liquid crystal display device of FIG. 1;

FIG. 3 is a cross-sectional model diagram of a conventional diffuser plate.

FIG. 4 is a cross-sectional model diagram of the diffuser plate of the present invention.

[Explanation of symbols]

1 Liquid crystal display element 4 FL backlight unit 6 Diffusion plate 8 FL tube 9 Lamp housing 10 Light diffusing agent 11 Plate glass

Claims (1)

[Claims] 1. A liquid crystal element, a printed circuit board on which an IC chip for driving the liquid crystal element is mounted and connected to the liquid crystal element by a flexible board, and a backlight arranged on the back side of the liquid crystal element to illuminate the same. A liquid crystal display device comprising a unit, characterized in that a plate glass coated with a light diffusing agent is used as a diffusion plate of the backlight unit.