JPH0982123A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the display characteristics of a liquid crystal display device. SOLUTION: For improving the brightness of a liquid crystal display device by using plural linear light sources as a light guide body type backlight and covering the same by a light reflector, when two linear light source tubes 10A, 10B are used, two linear light source axes are parallel arranged in a vertical direction to the light incident surface of the light guide body. When three linear light source tubes are used, the linear light source axes are arranged at the vertex of a triangle, and one of the vertexes of the triangle is faced to the light incident surface of the light guide body.

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 with a surface light source, and more particularly to a surface light source structure which has a thin shape and can efficiently obtain high brightness.

[0002]

2. Description of the Related Art Liquid crystal display devices are used in various fields such as personal computers and word processors as display devices for displaying various images.

Liquid crystal display devices are classified into a simple matrix type and an active matrix type, depending on the pixel selection method.

A simple matrix type liquid crystal display device is one in which liquid crystal is sealed between two sets of intersecting electrodes and pixels are formed at the intersections of the electrodes.

On the other hand, an active matrix type liquid crystal display device has a nonlinear element (switching element) corresponding to each of a plurality of pixel electrodes arranged in a matrix.
Is provided. Since the liquid crystal in each pixel is theoretically always driven (duty ratio 1/1), the active method has a better contrast than the simple matrix method which adopts the time-division driving method. It is becoming an indispensable technology for equipment. A typical switching element is a thin film transistor (TFT).

However, even the recent simple matrix type liquid crystal display device can display a high quality color image by improving its driving system or liquid crystal structure.

Generally, these liquid crystal display devices incorporate a so-called backlight, which irradiates light from the back surface of a liquid crystal panel constituted by the liquid crystal display elements.

As shown in FIG. 14, this backlight is formed by laminating a light diffusion plate 50, a rectangular resin plate (light guide plate) 30 made of a transparent material such as an acrylic plate, a reflection plate 40, etc. A linear light source 10 made of a thin tube arranged along at least one side of the light guide plate 30. Light from the thin tube light source 10 is roughened on the upper and lower surfaces of the light guide plate 30, or printed on the lower surface. The light incident on the light guide plate 30 is gradually added from the other surface (upper surface) directly or to the diffuser plate 50 by applying the processing described above.
A so-called side edge light source light guide (side edge type) surface light source that emits light upward through the light source is used.

For the above-mentioned surface light source, it is important that a large amount of light emitted from the thin tube light source is incident on the end surface of the transparent resin plate for high brightness and high efficiency, that is, power saving.

Further, the liquid crystal display device has a viewing angle characteristic,
In the conventional liquid crystal display device having a narrow viewing angle characteristic, the brightness of the backlight is improved by narrowing the light emission angle θ by the prism sheet 70.

[0011]

However, in order to increase the brightness of the backlight by the side edge method, when the number of thin tube light sources is increased, depending on the arrangement of the thin tube light sources, the rear side of the thin tube light source (the light guide The back side when the side facing the incident light end face of the body is the front side) The emitted light hits the thin tube that is the light source, is not blocked by the thin tube and is not incident on the light guide body, and it becomes an ineffective component and reduces efficiency. I will end up.

An example of providing a plurality of light sources to improve the brightness of the backlight is described in JP-A-64-57240, but the reflected light by the reflector was not considered.

The present invention solves the above-mentioned conventional problems and reduces the light amount loss due to the light source itself of a light guide type liquid crystal display device with a surface light source, thereby reducing the brightness, efficiency, or saving. An object is to provide a liquid crystal display device with a surface light source of electric power.

[0014]

In order to achieve the above object, the present invention uses two linear light source tubes to improve the brightness of a backlight. Two of them are arranged side by side in the direction perpendicular to the incident surface and covered with a light reflector.

Further, according to the present invention, when the brightness of the backlight is improved by using three tubes of the linear light source, the axis of the linear light source is arranged at the apex of the triangle, and one of the apexes of the triangle is guided. It is characterized in that three linear light sources are covered with light reflectors so as to face the light incident surface of the body.

[0016]

In the liquid crystal display device of the present invention, the light from the portion of the plurality of light sources corresponding to the back side of the light guide entrance side becomes the reflected light by the light source reflector and the amount of light blocked by the light source itself is reduced. . Further, since light from a large area of the light source can be incident on the light guide body by being reflected by the light source reflector, high brightness and efficiency can be improved.

[0017]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

Embodiment 1 FIG. 3 is an exploded perspective view of a liquid crystal display device to which the present invention is applied.

In the figure, MCA is a light guide 30, a light source 10A,
10B is a lower case, 40 is a light guide lower reflector, 20 is a reflector, LPC is a cable for supplying power to the light sources 10A and 10B, and GB is light sources 10A and 10B.
Is a rubber bush for holding. 50 is a diffusion plate, 7
Reference numeral 0 is a prism sheet, GC is a rubber cushion, and ILS is a light-shielding spacer. 60 is a liquid crystal display panel, TCP1
Is a semiconductor integrated circuit that drives the video signal lines of the liquid crystal display panel, and TCP2 is a semiconductor integrated circuit that drives the scanning signal lines of the liquid crystal display panel. PCB1 is a video signal side drive circuit board, PCB2 is a scanning signal side drive circuit board, PCB3 is a power supply circuit board, and a flat cable JN1 is provided between the boards.
It is electrically connected by JN2 and JN3. SHD is a metal shield case, and insulating sheets INS1, INS2 and I are provided between SHD and PCB1, PCB2 and PCB3.
NS3 is provided. SHD is TCP1, TCP
2, a function of shielding harmful electric waves emitted from electronic circuits that handle high frequencies such as PCB1, PCB2, and PCB3, and a function of holding the backlight and the liquid crystal display panel 60 together with the lower case MCA. BAT is a double-sided adhesive tape that fixes the liquid crystal display panel 60 to the SHD.

FIG. 4 shows the liquid crystal display device shown in FIG.
It is a figure which shows an example which mounts several linear light sources.

In the figure, the two linear light sources 10A and 10B are held at both ends by rubber bushes GB1 and GB2.
Further, the rubber bushes GB1 and GB2 are the lower case MCA.
Then, the linear light sources 10A and 10B are fixed by being fitted in.
Inside the rubber bushes GB1 and GB2, the electrodes of the respective light sources are connected as shown by the dotted lines in the figure. GB1 is the light source 10
Hold the low-voltage electrode side (cold side) of A and 10B, and connect the low-voltage electrode of 10A and 10B inside the ground cable LP.
It is connected to C1. GB2 holds the high-voltage electrode side (hot side) of the light sources 10A and 10B, and internally holds 10A, 1
The high voltage electrodes of 0B are connected to the high voltage cables LPC2 and LPC3, respectively. Therefore, the rubber bushes GB1, GB
Reference numeral 2 not only serves as a cushion for the light sources 10A and 10B, but also serves as insulation between the electrodes and the cables. In this way, by holding a plurality of linear light sources using the rubber bush and connecting the circuits within the rubber bush, it is possible to achieve compact mounting with good insulation.

LPC1, LPC2, and LPC3 are connected to the cold terminal and the hot terminal of the inverter power supply IV, respectively, via connectors as shown in FIG. LP in this embodiment
The reason for making LPC1 longer than C2 and LPC3 is
Since the current flowing through each cable is high frequency, it leaks cheaply and the LP on the high voltage side is reduced to reduce the leakage current.
The reason is that the lengths of C2 and LPC3 are shortened. Further, the reason why the LPC1 is mounted through the outside of the reflector 20 is that if the LPC1 is provided inside the reflector 20, the reflection efficiency is lowered and the brightness of the backlight is lowered.

FIG. 5 is a plan view of a pixel of the liquid crystal display panel 60. The figure shows an example of a pixel configuration of the active matrix system. The liquid crystal display panel 60 may have a simple matrix system configuration.

FIG. 6 is a sectional view taken along line 5A-5B of the pixel shown in FIG.

5 and 6, ITO1 is a pixel electrode made of a transparent conductive film d1, DL is a video signal line made of metal films d2 and d3, GL is a scanning signal line made of a metal film g2, and TFT.
1, TFT2 is a thin film transistor, and Cadd is a storage capacitor. SUB1 is a glass substrate. TFT1, TF
T2 includes semiconductor films AS and d0, insulating films SiN and AOF, source / drain electrodes SD1 and SD2, and a gate electrode GT. Since the ITO1 is electrically connected to the SD1, the DL is electrically connected to the SD2, and the GL is electrically connected to the GT, the video signal line D
A voltage can be applied to an arbitrary pixel electrode ITO1 by L and the scanning signal line GL. Further, since the storage capacitor Cadd is provided between the pixel electrode ITO1 and the adjacent scanning signal line DL, the voltage applied to the ITO1 can be held until the next voltage is applied.

Unlike the simple matrix method, the active matrix method has a liquid crystal driving duty of 1 regardless of the number of scanning signal lines. Therefore, as shown in FIG. 3, the video signal side driving circuit board PCB1 should be mounted on only one side. Can be done.

The TFT1 and TFT2 are covered with a protective film PAS, and the alignment film ORI1 is provided on the PAS. Each pixel has an R, G, or B color filter FIL on the counter substrate SUB.
2 (not shown) to enable color display.

BM is a light-shielding film (black matrix) for covering the edge of the pixel electrode ITO1 and increasing the display contrast.

In the embodiment shown in FIGS. 5 and 6, in order to improve the viewing angle characteristics of the liquid crystal display panel 60, the pretilt angle of the liquid crystal is changed in the areas A and B.

FIG. 7 is a diagram showing a state in which the pretilt angle of the liquid crystal is divided within a unit pixel in order to improve the viewing angle characteristics of the liquid crystal display panel 60. A general liquid crystal display device has a polarizing plate P.
The deflection direction of the deflected light L passing through the OL1 is controlled by the liquid crystal layer LC, and the light L whose deflection direction is controlled is emitted through the polarizing plate POL2 to perform a display operation. Such a liquid crystal display device has a so-called viewing angle characteristic in which the contrast and contrast of the image change depending on the viewing direction of the viewer. This viewing angle characteristic depends on the pretilt angles α, β, and γ of the liquid crystal molecules MOL, which are determined by the alignment treatment of the alignment films ORI1 and ORI2.

The pretilt angles α and γ are set to A in one pixel,
By changing it in the region B, the viewing angle characteristics of the entire liquid crystal display device can be improved. Pretilt angles α and γ are A,
The method of changing the area B is described in Japanese Patent Application Laid-Open No. 6-222366 and therefore omitted here. According to the embodiment shown in FIG. 7, it is possible to further widen the viewing angle characteristic which was conventionally 30 ° or less in the vertical direction.

The method of improving the viewing angle characteristics is not limited to the embodiment shown in FIG.

FIG. 1 is a side sectional view showing an essential part of a first embodiment of the present invention.

In the figure, 60 is a liquid crystal display panel, and 30 is
Is a light guide body which is disposed below the liquid crystal display panel 60 and is configured to uniformly irradiate the liquid crystal display panel 60 with the light L emitted from the light source. Reference numerals 10A and 10B are cold cathode fluorescent tubes which are linear light sources arranged in the vicinity of at least one side surface of the light guide 30 and along the side surface and having a length substantially the same as the side surface. Reference numeral 20 is a reflector which covers the outside of the cold cathode fluorescent tubes 10A and 10B and focuses the light of the cold cathode fluorescent tubes 10A and 10B to the light guide 30 side, the inner surface of which is silver or the like. Four
Reference numeral 0 is a lower surface reflection plate of white or the like arranged on the lower surface of the light guide body 30 for returning the light from the light guide body 30 to the upper surface to make it bright. Reference numeral 50 denotes a diffusion sheet which is disposed on the upper surface of the light guide body 30 and which diffuses and blurs minute uneven brightness from the light guide body 30 to make it inconspicuous.

In the first embodiment, the linear light source 10 is used to improve the brightness of the backlight by using two linear light source tubes.
Two axes A and 10B were arranged side by side in the direction perpendicular to the light incident surface S of the light guide body 30 and covered with the light reflector 20.

As a result, in the first embodiment, the linear light sources 10A and 1A are arranged parallel to the light incident surface S of the light guide 30 shown in FIG.
It was possible to improve the brightness by 6% as compared with the case where the 0B axes were arranged.

It is considered that the reason why the luminance is improved by the first embodiment is that the amount of light blocked by the tube of the linear light source is small.

In the vertical arrangement of the light sources shown in FIG. 8, the two light sources seem to be bright at first glance because they are close to the light guide, but considering the light reflected by the reflector 20, they are surrounded by a, o, o ', and b. The light L in the blocked region is blocked by the light source tubes 10A and 10B and hardly reaches the light guide. On the other hand, in Example 1, FIG.
As shown in, light other than the area surrounded by a, o ′, and b is guided to the light guide by the reflector. Example 1 has a smaller area that shields the reflected light, so that the brightness is improved. 1 and 8
Where o and o ′ are central axes of the light sources 10A and 10B, and a and b are points where a straight line passing through o and o ′ intersects the reflector 20 at right angles.

Further, in the liquid crystal display device having improved viewing angle characteristics as in the first embodiment, it is meaningless unless the light emission angle of the prism sheet is widened, so that the amount of light entering the light guide from the light source is increased accordingly. A good display screen cannot be obtained unless the number is increased.

Therefore, the present invention has the effect of improving the display characteristics of a liquid crystal display device having a wide viewing angle.

Further, another effect of horizontally placing the light source is thinning. As is clear from FIG. 1 of the first embodiment of the present invention and FIG. 8 of the comparative example, the first embodiment of the present invention
Since the light sources 10A and 10B are arranged side by side, the thickness does not change. However, in Example 1, the width of one light source is increased. However, as shown in FIG. 1, since it is necessary to dispose the liquid crystal driving substrate PCB, the liquid crystal driving integrated circuit TCP, and the like on the linear light sources 10A and 10B, the frame region that does not contribute to the display is not enlarged.

Further, as shown in FIG. 3, the linear light source 10 is used.
A, 10B, the liquid crystal driving substrate PCB, and the liquid crystal driving integrated circuit TCP are mounted close to each other on one side of the liquid crystal display panel, so that the frame area of the liquid crystal display device has the same size and thickness as when there is one light source. , The brightness can be made even brighter. Since the increase in the frame area must be suppressed as much as possible from the design and usability requirements of personal computers and word processors in which the liquid crystal display device is used, the mounting configuration shown in FIG. Has excellent effect.

Example 2 FIG. 2 is a diagram showing Example 2 of the present invention, in which the brightness of the backlight is improved by using three linear light sources.

In FIG. 2, the axis of the linear light source is arranged at the apex of the triangle, and one of the apexes of the triangle is opposed to the light incident surface of the light guide. As a result, as compared with the case where three linear light sources are arranged parallel to the light incident surface of the light guide as shown in FIG.
The brightness could be improved by 4%.

It is considered that the reason why the luminance is improved by the second embodiment is that the amount of light blocked by the tube of the linear light source is small.

The vertical arrangement of the light sources shown in FIG. 9 also looks bright because the three light sources are close to the light guide, but considering the light reflected by the reflector 20, a, o, o ', o'', The light L in the region surrounded by b is blocked by the light source tubes 10A, 10B, and 10C and hardly reaches the light guide. On the other hand, in the second embodiment, as shown in FIG. 2, light other than the area surrounded by a, o, o ′, and b is guided to the light guide by the reflector. The luminance is improved in Example 2 in which the area for blocking the reflected light is small.

As shown in FIG. 10, if three linear light sources are used and arranged side by side, the light source reflector becomes too long, and the effect of the light source reflector decreases.

However, the horizontal arrangement shown in FIG. 10 was able to improve the brightness by 43% as compared with the vertical arrangement shown in FIG.

Also, when three linear light sources are used, they can be mounted in the same manner as shown in FIGS. 3 and 4, and the mounting density can be improved.

When this embodiment is applied to a liquid crystal display device with further improved viewing angle characteristics, a liquid crystal display device of excellent display quality with little reduction in brightness can be obtained even if the light emission angle is maximized.

In any of the above embodiments, the gap between the light source tube surface closest to the light guide and the end surface of the light guide is 0.5 to.
4 mm is preferable, and the maximum brightness is obtained at 2 ± 0.5 mm as shown in FIG. Further, as shown in FIG. 12, in the light source reflector, it is better to make the gap between the light guide and the tube surface of the light source farthest away as small as possible, and 0.5 ± 0.5 mm just before contact reaches the maximum brightness.

The light source according to the present invention is a light source having an end face 1
It is possible to obtain higher brightness by arranging not only on the side but also on the other side as shown in FIG.

[0053]

As described above, according to the present invention, when a plurality of light sources are used to improve the brightness, the light from the light sources is effectively incident on the light guide by the light source reflector, so that the brightness is high. An efficient surface light source can be manufactured with a reduced thickness.

The brightness of the backlight obtained as a result of each example is shown in FIG.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a backlight used in a first embodiment of the present invention.

FIG. 2 is a sectional view of a main part of a backlight used in a second embodiment of the present invention.

FIG. 3 is an exploded perspective view of a liquid crystal display device to which the present invention is applied.

FIG. 4 is a diagram showing an example of mounting a plurality of linear light sources in the present invention.

5 is a plan view of a pixel of the liquid crystal display panel 60. FIG.

6 is a cross-sectional view of the pixel shown in FIG.

FIG. 7 is a diagram showing a state in which the alignment direction is divided within a unit pixel in order to improve the viewing angle characteristics of the liquid crystal display panel 60.

FIG. 8 is a side sectional view of a backlight when two linear light sources are arranged vertically.

FIG. 9 is a cross-sectional side view of a backlight when three linear light sources are arranged vertically.

FIG. 10 is a side sectional view of a backlight when three linear light sources are arranged side by side.

FIG. 11 is a graph showing the relationship between the brightness of the backlight and the gap between the light source tube surface and the end surface of the light guide.

FIG. 12 is a graph showing the relationship between the light source tube surface, the reflective surface gap of the reflector, and the brightness of the backlight.

FIG. 13 shows a modified example of the present invention in which two light sources arranged side by side are arranged not only on one side of the end surface of the light guide but also on the other side.

FIG. 14 shows a structure of a conventional side edge light source light guide type backlight.

FIG. 15 is a diagram comparing the brightness of the backlight obtained as a result of each example.

[Explanation of symbols]

10, 10A, 10B, 10C, 10D ... Light source, 20,
20A, 20B ... Reflector, 30 ... Light guide, 40 ... Reflector, 50 ... Diffuser, 60 ... Liquid crystal display panel, 70 ... Prism sheet, POL1, POL2 ... Polarizing plate, MOL ... Liquid crystal molecule, L ... Light

Claims (2)

[Claims] 1. A light guide, a linear light source disposed on at least one end surface of the light guide, a light reflector, a reflector laminated on a lower surface of the light guide, and the light guide. A liquid crystal display device including at least a liquid crystal display element disposed on the upper surface of the linear light source, two linear light sources are arranged side by side in a direction perpendicular to a light incident surface of the light guide, and the two linear light sources are arranged. A liquid crystal display device, which is covered with the light reflector. 2. A light guide, a linear light source arranged on at least one end surface of the light guide, a light reflector, a reflector laminated on a lower surface of the light guide, and the light guide. A liquid crystal display device including at least a liquid crystal display element disposed on the upper surface of the triangular light source, wherein three linear light sources are used, the axes of the linear light sources are arranged at the vertices of a triangle, and one of the vertices of the triangle is A liquid crystal display device, wherein the three linear light sources are covered with the light reflector so as to face the light incident surface of the light guide.