JP2844768B2 - Liquid crystal display - Google Patents

Description

The present invention relates to a liquid crystal display device used as a liquid crystal television or the like.

[Conventional technology]

In recent years, liquid crystal display devices are lightweight and thin,
It is drawing attention as a portable display,
Widely used for LCD TVs and laptop computers.

Hereinafter, an example of a conventional liquid crystal display device will be described with reference to the drawings. FIG. 2 is a cross-sectional view of a conventional liquid crystal display device. This liquid crystal display device has an illumination unit 12 composed of a light source 1, a reflection plate 2, and a diffusion plate 3, and two transparent electrode films 6, 8. A liquid crystal cell 13 in which a liquid crystal 7 is sealed between a plurality of substrates 5, 9; a polarizer 4 disposed on the front and back of the liquid crystal cell 13; an analyzer 10; and a liquid crystal drive for controlling a voltage applied to the liquid crystal 7. And a control circuit 14.

The operation of the liquid crystal display device configured as described above will be described below. The light emitted from the light source 1 is partially reflected by the reflection plate 2 and then illuminates the liquid crystal cell 13 as illumination light 20 having a uniform illumination distribution by the diffusion plate 3. Polarizer 4 is illumination light
It is used to transmit only 20 specific polarization components and obtain linearly polarized light. As the liquid crystal 7, twisted nematic (TN) liquid crystal is used, and although not explicitly shown in the figure, an alignment process is applied to the boundary surfaces between the transparent electrode films 6, 8 and the liquid crystal 7. The TN liquid crystal has a function of rotating incident linearly polarized light, and the optical rotation changes depending on the applied voltage. Therefore, the use of the analyzer 10 can control the amount of emitted light 21. Therefore, image display is performed by controlling the voltage applied to the liquid crystal 7 by the liquid crystal drive control circuit 14.

Such a conventional liquid crystal display device is shown in FIG.
When the illuminating light 20 from the light source 1 is linearly polarized by the polarizer 4, more than half the amount of light is absorbed, so that the light intensity of the resulting outgoing light 21 is weak, resulting in a dark display screen.
Therefore, when observed in a bright environment such as outdoors or near a window, there is a problem that reflected light 25 of external light 23 is generated on the surface 24 of the liquid crystal display device, making the screen difficult to see. Further, since the analyzer 10 on the surface 24 of the liquid crystal display device is made of plastic, it is difficult to apply an antireflection film. Such a problem of surface reflection occurs not only in a conventional liquid crystal display device but also in a general display device such as a cathode ray tube, and is particularly regarded as a cause of fatigue of a video display terminal (VDT) operator. . To solve this problem, an antireflection filter has been devised as a VDT filter.

Hereinafter, an example of a conventional antireflection filter will be described with reference to the drawings. FIG. 3 is a cross-sectional view for explaining a conventional antireflection filter 19. The anti-reflection filter 19 includes a polarizing plate 16 on a transparent substrate 17 on which an anti-reflection film 18 is applied.
And the quarter-wave plate 15 are sequentially bonded, and the angle between the polarization axis of the polarizing plate 16 and the optical axis of the quarter-wave plate 15 is particularly 45 °.
It is arranged to become. External light 23 incident on the anti-reflection filter passes through the transparent substrate 17 without generating reflected light due to the anti-reflection film 18 applied to the transparent substrate 17, and the polarizing plate 16
Thereby becomes linearly polarized light, and further becomes a circularly polarized light by the quarter-wave plate 15. The circularly polarized transmitted light 26 is
Partially reflected at the surface 34 of the light-emitting device, thereby producing reflected light 25. The reflected light 25, which is circularly polarized light, becomes linearly polarized light again incident on the quarter-wave plate, and its polarization direction is orthogonal to the polarization direction of the linearly polarized light when the external light 23 passes through the polarizing plate 16. Direction. Therefore, the reflected light 25 is absorbed by the polarizing plate 16, so that the reflection preventing filter is used.
19 cannot be transmitted. On the other hand, the output light 31 obtained as the display screen of the display device 30 has a light amount of about half in the polarizing plate 16, but passes through the antireflection filter and becomes the output light. Therefore, the observer can observe the display screen without being affected by the external light 23 although the display screen becomes dark.

[Problems to be Solved by the Invention] However, when the above-described conventional antireflection filter is used in a conventional liquid crystal display device, the following problems occur. Light emitted from a conventional liquid crystal display device is linearly polarized light transmitted through an analyzer, and when incident on a conventional anti-reflection filter, depends on the angle between the polarization direction of the linearly polarized light and the optical axis of the quarter-wave plate. The polarization state of the light passing through the quarter-wave plate changes, and when the angle formed is 0 ° or 90 °, the light becomes linearly polarized light, when 45 °, circularly polarized light, and at other times, elliptically polarized light. When this light passes through the polarizing plate of the anti-reflection filter, in the case of linearly polarized light, the angle between the polarization direction and the polarizing plate is 45 °, so that the amount of light is reduced by half. In the case of circularly polarized light, the amount of light is reduced by half, and in the case of elliptically polarized light, the amount of light is reduced and the hue of transmitted light is also changed. As described above, the display screen of the conventional liquid crystal display device, which is not inherently bright, is further darkened, which poses a practical problem.

As an example of another anti-reflection filter, fine grooves are periodically formed on the surface of the transparent substrate, and in particular, by processing the cross-sectional shape of the grooves into a saw-tooth shape, the surface reflected light is reflected in a direction other than the direction of the observer's eyes. There is a filter. However, since the pixels of the conventional liquid crystal display device are formed in a matrix, the period of the groove of the antireflection filter does not match the period of the pixel,
Moire fringes are generated due to the misalignment and the direction, and the front screen becomes difficult to see.

An object of the present invention is to provide a liquid crystal display device having a filter for preventing surface reflection without extremely lowering the brightness and visibility of a display screen.

[Means for solving the problem]

In order to achieve the above object, a liquid crystal display device of the present invention includes a liquid crystal cell in which liquid crystal is sealed between two substrates, a polarizer provided on the surface of the liquid crystal cell, and a polarizer provided on the back surface of the liquid crystal cell. A liquid crystal display device configured to display an image by controlling a voltage applied to the liquid crystal, at least comprising an analyzer;
A first quarter-wave plate is attached to the analyzer so that the linearly polarized light transmitted through the polarizer, the liquid crystal cell, and the analyzer becomes circularly polarized light, and one surface of a transparent substrate An anti-reflection filter formed by sequentially attaching at least a polarizing plate and a second quarter-wave plate to the other surface of the first quarter-wave plate and the second quarter-wave plate. It is characterized in that it is arranged so as to face a quarter-wave plate.

[Action]

According to the above configuration of the present invention, an anti-reflection film formed on one side and an anti-reflection filter formed by sequentially bonding at least a polarizing plate and a quarter-wave plate to a transparent substrate on the other side have the same anti-reflection effect as in the past Is obtained, and the emitted light of the display screen becomes a circularly polarized light by the 1/4 wavelength plate bonded to the analyzer, and becomes a linearly polarized light transmitted through the polarizing plate by the 1/4 wavelength plate of the antireflection filter. A liquid crystal display device that does not extremely reduce the brightness of the display screen and the visibility is obtained.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a liquid crystal display device showing an embodiment of the present invention.

This liquid crystal display device comprises an illuminating unit 12 composed of a light source 1, a reflecting plate 2, and a diffusing plate 3, and a liquid crystal 7 sealed between two substrates 5, 9 provided with transparent electrode films 6, 8, respectively. Liquid crystal cell 13
A polarizer 4 and an analyzer 10 arranged on the front and back of the liquid crystal cell 13, and a quarter-wave plate 11 arranged on the surface of the analyzer 10,
A liquid crystal drive circuit 14 for controlling the voltage applied to the liquid crystal 7, and a polarizing plate 16 and a quarter-wave plate 1 on a transparent substrate 17 provided with an antireflection film 18.
5 are sequentially bonded to each other.

In the above configuration, the illumination unit 12, the polarizer 4, the liquid crystal cell 13, the analyzer 10, and the liquid crystal drive circuit 14 are the same as those of the conventional liquid crystal display device, and an image is displayed by controlling the voltage applied to the liquid crystal. . Here, glass substrates were used as the substrates 5 and 9. The polarizer 4 and the analyzer 10 used a polarizing film in which iodine or the like was oriented and adsorbed on a polyvinyl alcohol filter, and adhered to the front and back of the liquid crystal cell 13, respectively. Although the driving method for controlling the voltage applied to the liquid crystal 7 and displaying an image uses the simple matrix method, an active matrix method in which a switching transistor or a switching diode is provided for each image may be used. Although the TN liquid crystal is used as the liquid crystal 7, a ferroelectric liquid crystal, a birefringence control type liquid crystal, or the like can also be used. As the display image, a television display, a character display of a personal computer, a graphic display, and other information display images such as a clock are used. In addition, 1/4 bonded to analyzer 10
The wave plate 11 is formed by stretching a polyvinyl alcohol film so as to have a birefringent property. In particular, the analyzer 10 and the quarter-wave plate 11 are adhered to each other with matching refractive indexes, and The angle between the polarization axis of photon 10 and the optical axis of quarter-wave plate 11 is 45
°.

The anti-reflection film 19 is provided with an anti-reflection film 18 that does not generate reflected light due to the interference effect of the dielectric multilayer film on one surface of a transparent substrate 17 that is a glass substrate, and a polarizing plate that is the above-described polarizing film on the other surface. 16 and a quarter-wave plate 15 were sequentially bonded.

When the external light 23 is incident on the liquid crystal display device described above, the reflected light 25 of the external light 23 generated on the surface 24 of the quarter-wave plate 11 bonded to the analyzer 10 by the action of the antireflection filter 18 described above. The light is absorbed by the polarizing plate 16 and is not emitted from the liquid crystal display device. On the other hand, the illumination light 20 is transmitted through the polarizer 4, the liquid crystal cell 13, the analyzer 10, and the quarter-wave plate 11, and the emitted light 21 of the display screen obtained is the analyzer 10
To a linearly polarized light, and a quarter-wave plate 1
By passing through 1, it becomes circularly polarized light. Where 1
When the optical axis of the quarter-wave plate 11 is set so that the rotation directions of the circularly polarized light of the reflected light 25 and the circularly polarized light of the output light 21 are opposite, the output light
The polarization direction of the linearly polarized light obtained by passing through the quarter-wave plate of the antireflection filter 19 is parallel to the polarization axis of the polarizing plate 16. Therefore, the outgoing light 21 of the display screen is
At 19, the light can be transmitted without being absorbed and becomes the outgoing light 22, so that the observer can see a bright display screen.

In the above description, the quarter-wave plate 11 bonded to the analyzer 10 does not affect the brightness only by changing the polarization state of the emitted light 21. Therefore, in an environment where the reflected light 25 due to the external light 23 does not occur, the display screen can be observed in the same manner even if the antireflection filter 19 is removed, so that the antireflection filter 19 may be configured to be removable.

〔The invention's effect〕

As described above, according to the present invention, a liquid crystal display device including a filter for preventing surface reflection without reducing the brightness of a display screen can be obtained. The brightness is twice as high as that in the case where the conventional liquid crystal display device and the antireflection filter are combined, and the device can be used even in a bright environment without a change in the hue of the display screen.

[Brief description of the drawings]

FIG. 1 is a sectional view of a liquid crystal display device showing an embodiment of the present invention. FIG. 2 is a sectional view of a conventional liquid crystal display device. FIG. 3 is a sectional view of a conventional antireflection filter. 4 ... Polarizer, 10 ... Analyzer, 11 ... Quarter wave plate, 12 ...
... illumination unit, 13 ... liquid crystal cell, 14 ... liquid crystal drive control circuit,
19 ... Anti-reflection filter.

Claims (1)

(57) [Claims] 1. A liquid crystal cell comprising a liquid crystal sealed between two substrates, a polarizer provided on the front and back surfaces of the liquid crystal cell, and an analyzer, wherein a voltage applied to the liquid crystal is controlled. In a liquid crystal display device for controlling and displaying an image, a first polarized light is transmitted to the polarizer, the liquid crystal cell, and the analyzer in order so that the linearly polarized light is circularly polarized light.
Of the transparent substrate, an antireflection film is applied to one surface of the transparent substrate, and at least a polarizing plate and a second
An anti-reflection filter formed by sequentially bonding a quarter-wave plate to the first quarter-wave plate is disposed so that the first quarter-wave plate and the second quarter-wave plate face each other. Liquid crystal display.