JPH0882715A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To improve luminance of a back light and to reduce power consumption by increasing tube surface luminance of a cold cathode fluorescent lamp without accompanying with a local temp. rise of a liquid crystal display element. CONSTITUTION: In a liquid crystal display device provided with at least a light transmission body 5 constituted of a transparent plate, a reflection plate 4, a diffusion plate 6, a surface light source constituted of a linear light source 1 arranged along the vicinity of at least one side surface of the light transmission plate 5 and a reflection sheet 3 set up opened and surrounding the linear light source 1 on the side surface of the light transmission body 5, and the liquid crystal display element 8 laminated on the diffusion plate 6 side, at least a slit 13 formed along the extending direction of the linear light source 1 of the light transmission body 5 is provided on the vicinity of the linear light source l of the light transmission body 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device,
In particular, the present invention relates to a liquid crystal display device provided with a thin, high-brightness back light source (so-called backlight).

[0002]

2. Description of the Related Art A conventional liquid crystal display device uses a nematic liquid crystal having a positive dielectric anisotropy between two electrode substrates.
It has a twisted spiral structure, and a polarizing plate is arranged outside each electrode substrate so that its polarization axis (or absorption axis) is orthogonal or parallel to the liquid crystal molecules adjacent to the electrode substrate, and the back surface is formed. A backlight is arranged at the electrode, and the orientation of liquid crystal molecules is changed by applying a potential difference to the electrodes to control the transmission of light from the backlight so that an image or the like is displayed (for example, (See Japanese Examined Patent Publication No. 51-13666).

In such a liquid crystal display device having a twist angle (α) of 90 degrees, there are problems in terms of the steepness (γ) of the change in the transmittance of the liquid crystal layer versus the voltage applied to the liquid crystal layer and the viewing angle characteristic. ,
The number of time divisions (corresponding to the number of scanning electrodes) was 64, which was a practical limit.

However, in order to cope with the recent demands for improving the image quality and increasing the display information amount for liquid crystal display elements, the twist angle α of the liquid crystal molecules is set to be larger than 180 degrees, and the birefringence effect is utilized to make time-division driving characteristics. To improve the number of time divisions and improve the applied physics letters 45, N
o.10,1021 1984 (Applied Physics Letter, TJScheffe
r, J.Nehring: "A new, highly multiplexable liquidcrys
tal display ") and a super twisted birefringence effect (SBE) liquid crystal display device has been proposed.

A surface light source (backlight) used in this type of liquid crystal display device is a light guide made of a transparent plate, a reflector,
It is composed of a diffusion plate and a surface light source having a linear light source made of a cold cathode fluorescent lamp arranged along at least one side surface of the light guide.

The light guide is made of a transparent resin plate or the like, and propagates light from the linear light source from one end of the light guide to the other end, and a reflection plate (installed on the lower surface (back surface) of the light guide ( Alternatively, a reflection sheet) and a diffusion plate (or
A diffuser sheet) and a prism sheet installed as necessary illuminate the liquid crystal display element laminated above the diffuser sheet as a uniform surface light source.

A reflective sheet is provided around the linear light source except for a region facing the light guide, and the light of the linear light source is efficiently introduced into the light guide.

FIG. 5 is a cross-sectional view of an essential part for explaining the structure of a liquid crystal display device according to the prior art. Reference numeral 1 is a cold cathode fluorescent lamp, 2
Is a power supply cable for a cold cathode fluorescent lamp, 3 is a reflection sheet, 4 is a reflection plate, 5 is a light guide, 6 is a diffusion plate, 7 is a prism sheet, 8 is a liquid crystal display element, 9 is a lower frame, and 10 is an upper frame. , 11 is a printed circuit board, and 12 is a drive IC mounted on the printed circuit board.

In the figure, a cold cathode fluorescent lamp (CFL)
1, cable 2, reflection sheet 3, reflection plate 4, light guide 5,
A backlight (light source unit) is configured by the diffusion plate 6 and the prism sheet 7.

A liquid crystal display element 8 is laminated above the backlight which is the light source unit, and a lower frame 9 and an upper frame 10 are integrated with a printed circuit board 11 on which a drive IC 12 is mounted to form a liquid crystal display device.

The heat generated by driving the cold cathode fluorescent lamp 1 propagates through the light guide 5 as shown by the arrow in the figure, and is conducted in the direction of the liquid crystal display element 8 so that the liquid crystal display element 8 is exposed from the rear surface. To heat.

[0012]

The luminous efficiency that determines the brightness and power consumption of the cold cathode fluorescent lamp, which is a linear light source that constitutes the backlight, is restricted by the tube surface temperature of the cold cathode fluorescent lamp.

FIG. 6 is a characteristic diagram showing the tube surface temperature dependence of the tube surface brightness of a cold cathode fluorescent lamp. In the backlight used in the conventional liquid crystal display device, the tube surface temperature is about 50. °.

Generally, in this type of cold cathode fluorescent lamp, the tube surface temperature at which the tube surface brightness becomes maximum is 10 ° C.
15 ° C higher than 60 °.

It is conceivable to improve the brightness of the tube surface by devising the light source section. However, if the tube surface temperature of the cold cathode fluorescent lamp is raised, the temperature of the liquid crystal cell section near the cold cathode fluorescent lamp of the liquid crystal display element rises. However, there is a problem in that the transmittance of the liquid crystal cell portion in the dark is increased and display unevenness occurs, and it is not possible to simply raise the tube surface temperature.

The object of the present invention is to solve the above-mentioned problems of the prior art, to raise the tube brightness of the cold cathode fluorescent lamp and to improve the brightness of the backlight without causing a local temperature rise of the liquid crystal display element. An object of the present invention is to provide a liquid crystal display device with reduced power consumption.

[0017]

In order to achieve the above object, a first invention according to claim 1 is at least a light guide body, a reflection plate, a diffusion plate, and a light guide body which are made of a transparent plate. A surface light source composed of a linear light source arranged along the vicinity of one side surface and a reflection sheet installed on the side surface of the light guide body to surround the linear light source, and a liquid crystal laminated on the diffusion plate side. A liquid crystal display device including at least a display element, comprising at least one slit formed along the extending method of the linear light source in the vicinity of the linear light source of the light guide body. And

[0018]

The heat from the cold cathode fluorescent lamp mainly reaches the liquid crystal display element through the light guide.

However, according to the structure of the first invention, even if the temperature of the tube surface of the cold cathode fluorescent lamp is increased, the heat is blocked by the air in the slit formed in the light guide body, and the liquid crystal cell of the liquid crystal display element. It does not reach the point of heating.

As described above, the slit formed in the vicinity of the cold cathode fluorescent lamp of the light guide has a function of increasing the thermal resistance of the heat conduction path from the cold cathode fluorescent lamp to the liquid crystal display element. Even if the tube surface temperature is increased, the heat does not adversely affect the display characteristics of the liquid crystal display element.

[0021]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a sectional view of an essential part for explaining the structure of a first embodiment of a liquid crystal display device according to the present invention. As in FIG. 5, 1 is a cold cathode fluorescent lamp and 2 is a cold cathode fluorescent lamp. Power feeding cable, 3 a reflection sheet, 4 a reflection plate, 5 a light guide made of an acrylic plate, 6 a diffusion plate, 7 a prism sheet, 8
Is a liquid crystal display element, 9 is a lower frame, 10 is an upper frame,
Reference numeral 11 is a printed circuit board, and 12 is a drive IC mounted on the printed circuit board. Reference numeral 13 is a slit formed in the vicinity of the linear light source of the light guide 5 along the extension method of the linear light source.

In the figure, a cold cathode fluorescent lamp (CFL)
1, cable 2, reflection sheet 3, reflection plate 4, slit 1
The light guide 5, the diffuser plate 6, and the prism sheet 7 on which the light source 3 is formed constitute a backlight (light source unit).

A liquid crystal display element 8 is laminated above the backlight which is the light source section, and the lower frame 9 and the upper frame 10 are integrated with the printed circuit board 11 on which the driving IC 12 is mounted to form a liquid crystal display device.

The light from the cold cathode fluorescent lamp 1 is emitted toward the liquid crystal display element 8 while propagating through the light guide 5 as shown by the arrow in the figure, and illuminates the liquid crystal display element 8 from the rear surface.

Since the cold cathode fluorescent lamp 1 is thermally shielded from the display area by the presence of the slits 13 formed in the light guide body 5, display unevenness occurs even if the tube surface temperature is raised to about 60 °. do not do.

That is, the light from the cold cathode fluorescent lamp 1 is directed toward the light guide 5 by the reflection sheet 3 and introduced into the light guide 5. Further, the heat radiated by the heat generation of the cold cathode fluorescent lamp 1 is
Although it is transmitted to the light guide 5 as shown by the arrow in the figure, it is blocked by the air layer in the slit 13 and the conduction is suppressed in the direction of the liquid crystal display element as described in FIG.

As described above, according to this embodiment, the temperature of the surface of the cold cathode fluorescent lamp is increased to improve the brightness of the surface of the fluorescent lamp.
Since the display of the liquid crystal display device can be brightened, the luminous efficiency of the cold cathode fluorescent lamp is improved and the power consumption can be reduced.

FIG. 2 is a plan view of an essential part of a backlight portion for explaining the structure of the second embodiment of the liquid crystal display device according to the present invention. 13a and 13b are slits, and the same reference numerals as those in FIG. 1 correspond to the same portions. To do.

In this embodiment, the slits formed in the light guide 5 are two parallel thin slits 13a and 13b.

FIG. 3 is a plan view of an essential part of a backlight portion for explaining the structure of the third embodiment of the liquid crystal display device according to the present invention. 13c and 13d are slits, and the same reference numerals as those in FIG. 2 are the same portions. Corresponding to.

In this embodiment, as in the second embodiment, the number of slits formed in the light guide 5 is two, and the widths of the two slits 13c and 13d are different.

Also according to the embodiment of the diffuser plate shown in FIGS. 2 and 3, as in the first embodiment, the tube surface temperature of the cold cathode fluorescent lamp is increased and the tube surface brightness is suppressed while suppressing the display unevenness. Since the liquid crystal display device can be improved and the display of the liquid crystal display device can be brightened, the luminous efficiency of the cold cathode fluorescent lamp is improved and the power consumption can be reduced.

The number and width of the slits may be selected according to the heat generation characteristics of the cold cathode fluorescent lamp 1 and the light propagation characteristics of the light guide 5, and these slits penetrate the light guide. It is not limited to the one formed, but may have a bottom portion or a ceiling portion having an appropriate thickness.

FIG. 4 is an exploded perspective view for explaining an example of the overall constitution of the liquid crystal display device according to the present invention. Reference numerals 1 to 13 correspond to the same parts as in the above embodiment, 14 is a spacer, 15 is a light shielding frame, Reference numeral 16 is a lamp cover, and 17 is an intermediate frame.

In the figure, the structure of the backlight is the same as in the above-mentioned embodiment, the cold cathode fluorescent lamp 1, the reflection sheet 3,
It is composed of a reflection plate 4, a light guide body 5, a diffusion plate 6, and a prism sheet 7.

A printed circuit board 1 is provided above the backlight.
1, the liquid crystal display element 8 integrated with 1 is laminated, and the backlight and the liquid crystal display element 8 are held by the intermediate frame 17, and are sandwiched between the lower frame 9 and the upper frame 10 together with the spacer 14 and the light shielding frame 15. The liquid crystal display device is fixed and configured.

Any of the slits described in each of the above-described embodiments is formed in the light guide 5 which constitutes the above-mentioned backlight.

According to the structure of this liquid crystal display device, it is possible to obtain a bright display by increasing the tube surface brightness of the cold cathode fluorescent lamp which constitutes the backlight.

[0040]

As described above, according to the present invention,
The cold cathode fluorescent lamp that constitutes the backlight can be driven with a luminous efficiency close to its theoretical value, and a good image quality without display unevenness of the liquid crystal display element due to heat generation of the cold cathode fluorescent lamp can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part for explaining the structure of a first embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is a plan view of a principal part of a backlight portion for explaining the structure of a second embodiment of the liquid crystal display device according to the present invention.

FIG. 3 is a plan view of an essential part of a backlight portion for explaining the structure of a third embodiment of the liquid crystal display device according to the present invention.

FIG. 4 is a developed perspective view illustrating an example of the overall configuration of a liquid crystal display device according to the present invention.

FIG. 5 is a cross-sectional view of relevant parts for explaining the structure of a liquid crystal display device according to a conventional technique.

FIG. 6 is a characteristic diagram showing tube surface temperature dependence of tube surface brightness of a cold cathode fluorescent lamp.

[Explanation of symbols]

 1 Cold Cathode Fluorescent Lamp 2 Power Supply Cable for Cold Cathode Fluorescent Lamp 3 Reflective Sheet 4 Reflector 5 Light Guide 6 Diffuser 7 Prism Sheet 8 Liquid Crystal Display Element 9 Lower Frame 10 Upper Frame 11 Printed Circuit Board 12 Drive IC 13 Slit 14 Spacer 15 Shading frame 16 Lamp cover 17 Intermediate frame.

Claims (1)

[Claims] 1. A light guide comprising a transparent plate, a reflection plate, a diffusion plate,
And a surface light source composed of a linear light source arranged along at least one side surface of the light guide body and a reflection sheet opened to a side surface of the light guide body and surrounding the linear light source, In a liquid crystal display device including at least a liquid crystal display element laminated on a diffuser plate side, at least one slit formed in the vicinity of the linear light source of the light guide along the extension method of the linear light source. A liquid crystal display device comprising.