JPH10153777A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type liquid crystal display device which can light up an image display surface uniformly by irradiating a liquid crystal display panel from the front. SOLUTION: A wedgelike light guide plate 11 is arranged in front of a reflection type liquid crystal display panel 10. A light source 12 faces the end surface (light incidence surface 11a) of the light guide plate 11 on the thick side and the light projection surface of the light guide 11 faces the liquid crystal panel 10. Then, the light projected from the light projection surface 11c of the light guide plate 11 irradiates the liquid crystal display panel 10 and an image of the liquid crystal display panel 10 is transmitted through the light guide plate 11 and viewed from the front.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a liquid crystal display device. In particular, the present invention relates to an illumination system and its configuration in a reflective LCD (liquid crystal display).

[0002]

[Prior art]

(First Conventional Example) For example, a liquid crystal display device of a PC-GH mode (cholesteric / nematic phase transition type guest host mode) has a reflection type liquid crystal display panel and uses sunlight or indoor light, and has a special feature. Since a simple light source is not required, the structure is simple, and it is inexpensive.

As shown in FIG. 1, a liquid crystal display panel has a structure in which a pixel structure is formed between a pair of upper and lower glass substrates 1 and 2 opposed to each other. Each pixel has a metal electrode (reflector) 3 formed on the upper surface of the lower glass substrate 2.
And a liquid crystal 4 sealed thereon, a transparent electrode 5 covering the upper part of the liquid crystal 4, and R (red), G (green), and B (blue) colors formed on the bottom surface of the upper glass substrate 1. Filter 6,
And each metal electrode 3 and R (red), G
The (green) and B (blue) color filters 6 are opposed to each other with their positions aligned.

[0006] Ambient light (sunlight or room light) incident from the light incident side (the glass substrate 1 side) passes through the color filter 6 and the transparent electrode 5 of each pixel. Since the liquid crystal 4 is oriented and transparent between the transparent electrode 5 and the metal electrode 3 to which a voltage is applied (signal is turned on), the ambient light that has passed through the color filter 6 and is colored The light passes through, is reflected by the metal electrode 3, passes through the liquid crystal 4 again, and is emitted to the outside of the glass substrate 1, and the pixel becomes bright. On the other hand, both electrodes 5 to which no voltage is applied (signal off)
Since the liquid crystal 4 is not oriented between the glass substrates 1, the glass substrate 1
The light incident from the side is absorbed by the liquid crystal 4 and does not go out of the liquid crystal display panel, and the pixel becomes dark. Thus, by directly viewing the light emitted from each pixel to the outside of the glass substrate 1, a color image can be visually recognized.

(Conventional example of a reflection type liquid crystal display device provided with a light source) Since the above-mentioned reflection type liquid crystal display device uses ambient light as a light source, sufficient ambient light cannot be obtained. Difficult to see in dark places.

Therefore, a light source is disposed diagonally to the side of the reflection type liquid crystal display panel, and the display surface of the liquid crystal display panel is illuminated with light from the light source as necessary, so that the visibility of the reflection type liquid crystal display device in a dark place is improved. There are also proposals for improving the quality (not shown).

However, in a reflective liquid crystal display device having a light source, pixels closer to the light source are illuminated more brightly.
There is a problem in that the brightness is not uniform over the entire display surface. In particular, it is difficult to make the brightness uniform when the display surface is large.

An electrode material having half translucency as a metal electrode of a reflection type liquid crystal display panel (half mirror electrode)
A backlight is disposed on the back surface of the liquid crystal display panel by using a liquid crystal display panel, and light emitted from the backlight is transmitted through a metal electrode to illuminate the liquid crystal display panel (not shown).

However, in a liquid crystal display device having such a backlight, since the transmittance of the transparent electrode is very low, sufficient brightness cannot be obtained, and the display surface of the liquid crystal display device is dark.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the conventional example, and an object of the present invention is to provide a liquid crystal display device using a so-called reflective liquid crystal display panel. An object of the present invention is to improve visibility in a dark place and improve uniformity of brightness on a display surface.

[0011]

DISCLOSURE OF THE INVENTION In the liquid crystal display device according to the first aspect of the present invention, a light source, a light guide plate for confining light guided from the light source and emitting the light from a light exit surface, and reflecting incident light to a light incident side. A liquid crystal display panel that generates an image by the light guide plate, the light exit surface of the light guide plate and the light incident side of the liquid crystal display panel are arranged to face each other, and the light source is arranged on the outer periphery of the light guide plate. The image of the liquid crystal display panel can be recognized through the light guide plate.

When the light source is turned on, light enters the light guide plate from the outer periphery of the light guide plate. A part of the light reaching the surface of the light guide plate is totally reflected, and the light is guided inside the light guide plate while repeating this. On the other hand, of the light that reaches the light exit surface of the light guide plate, light that is not totally reflected exits from the light exit surface, and the light exiting from the light exit surface illuminates the entire display surface of the liquid crystal display panel from the front side.

Thus, a reflection type liquid crystal display device having a high brightness display surface can be manufactured, and an image can be clearly displayed even in a dark place. Therefore, the visibility of the reflective liquid crystal display device can be improved, and in particular, even with a liquid crystal display device having a large display surface, the entire display surface can be brightly illuminated.

According to a second aspect of the present invention, in the liquid crystal display device according to the first aspect, the light guide plate is thicker on a side closer to the light source and thinner on a side farther from the light source. It is characterized in that the light exit surface of the light guide plate is arranged substantially parallel to the liquid crystal display panel.

In the liquid crystal display device according to the present invention, the light guide plate is thicker on the side closer to the light source and thinner on the side farther from the light source. Is emitted from the light guide plate not only near the light source but also far from the light source. Therefore, light can be emitted from the entire light guide plate toward the liquid crystal display panel, and the liquid crystal display panel can be illuminated with uniform brightness.

In addition, since the light exit surface of the light guide plate faces substantially parallel to the liquid crystal display panel and is inclined on the other surface,
The coupling efficiency between the light emitted from the light exit surface of the light guide plate and the liquid crystal display panel can be increased. In addition, since light can be emitted from the side opposite to the light exit surface in a direction that is difficult to see, light emitted from the side opposite to the light exit surface is less likely to enter the eyes, and the visibility of the liquid crystal display device is reduced. Can be good.

According to a third aspect of the present invention, in the liquid crystal display device according to the first aspect, an uneven pattern is provided on a light emitting surface of the light guide plate.

In the liquid crystal display device according to the third aspect, since the light emitting surface of the light guide plate is provided with an uneven pattern, the light is emitted from the light emitting surface rather than the amount of light leaking from the side opposite to the light emitting surface. The amount of light can be increased, and light can be collected to the liquid crystal display panel side, and the optical coupling efficiency between the light guide plate and the liquid crystal display panel can be increased.

Further, in the liquid crystal display device according to the third aspect, since the thickness of the light guide plate can be made constant, assembly can be facilitated. Further, the light guide plate can be easily formed.

Preferably, the concavo-convex pattern has a sawtooth cross section. At this time, all the light emitted from the liquid crystal display panel is refracted in the same direction, so that the image of the liquid crystal display panel is less disturbed by the uneven pattern of the light guide plate.

According to a fourth aspect of the present invention, in the liquid crystal display device according to the first aspect, the period of the concave / convex pattern is equal to or less than the pixel period of the liquid crystal display panel.

In the liquid crystal display device according to the fourth aspect, since the period of the uneven pattern is set to be equal to or less than the pixel period of the liquid crystal display panel, the shadow of the uneven pattern can be made inconspicuous from the front of the liquid crystal display device. .

According to a fifth aspect of the present invention, in the liquid crystal display device according to the first aspect, a layer having a lower refractive index than the refractive index of the light guide plate between the light emitting surface of the light guide plate and the liquid crystal display panel. It is characterized by having provided.

In the liquid crystal display device according to the fourth aspect, the critical angle of total reflection on the light exit surface of the light guide plate is larger than the critical angle of total reflection on the surface opposite to the light exit surface. The amount of light emitted from the emission surface toward the liquid crystal display panel can be made larger than the amount of light leaking from the opposite surface. Therefore, the effective use of light can be improved, and the brightness of the liquid crystal display device can be improved.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 2 shows a reflection type liquid crystal display device A according to one embodiment of the present invention. This liquid crystal display device A
A reflection type liquid crystal display panel 10, a light guide plate 11 disposed opposite to a display surface of the liquid crystal display panel 10, and a light source 12 for causing light r to enter the light guide plate 11 from an end face (hereinafter, referred to as a light incident surface) 11 a. Consists of

The light guide plate 11 has a wedge shape with a large thickness on the light incident side and a small thickness on the side far from the light source 12, and a lower surface (hereinafter referred to as a light emission surface) 11c of the liquid crystal display panel 10. The liquid crystal display panel 10 is arranged so that it is parallel to the display surface and the upper surface (hereinafter, referred to as an image display surface) 11 b is inclined with respect to the liquid crystal display panel 10.

The light source 12 is a light incident surface 11a of the light guide plate 11.
And a cold cathode ray tube 13 that is driven to emit light by an inverter circuit. The cold cathode ray tube 13 is surrounded by a white lamp cover 15, and the emitted light r
Are collected on the light incident surface 11a of the light guide plate 11 and are efficiently incident.

Further, a reflecting plate 14 is provided on three outer peripheral surfaces of the light guide plate 11 other than the light incident surface 11a.
This prevents the light r from leaking from the outer peripheral surface of the light emitting element 1 and causing a light amount loss.

The illustrated liquid crystal display panel 10 is a PC-GH.
A mode liquid crystal display panel having a structure in which a number of pixels are arranged between an upper glass substrate 1 and a lower glass substrate 2. The pixel is composed of a transparent electrode 5 formed on the lower surface of the glass substrate 1, a liquid crystal 4, and a metal electrode 3 having a diffuse reflection property formed on the upper surface of the glass substrate 2. Note that the type of the liquid crystal display panel 10 is not limited to the monochrome type, but may be a color display type in which a color filter is provided between the glass substrate 1 and the transparent electrode 5 (see FIG. 1).

When the cold cathode ray tube 13 is turned on by the inverter circuit, the light r emitted from the cold cathode ray tube 13 is collected by the white lamp cover 15 on the light incident surface 11a of the light guide plate 11, and the light r from the light incident surface 11a. Light guide plate 11
Guided inside. The light r incident on the light guide plate 11 is divided into an upper surface (image display surface 11b) and a lower surface (light emission surface 11) of the light guide plate 11.
Light is guided inside the light guide plate 11 while repeating total reflection with c).

Here, when the upper surface and the lower surface of the light guide plate 11 are in a flat plate shape parallel to each other, the light r emitted from the light source 12 has an angle smaller than the critical angle of total reflection near the light source 12. Incident on the upper and lower surfaces of the light guide plate 11,
However, at a position distant from the light source 12, the light is incident on the upper and lower surfaces of the light guide plate 11 at an angle larger than the critical angle of total reflection. Therefore, the light emitting surface 11c is bright near the light source 12 and dark at a position distant from the light source 12, and cannot uniformly emit the light r.

On the other hand, since the light guide plate 11 of the present invention has a wedge shape, the light guide plate 11 is moved from the light incident surface 11a.
The angle of incidence of the light r incident on the light exit surface 11c becomes smaller each time the light r is reflected on the upper surface of the light guide plate 11,
The light r is emitted from the light emitting surface 11c even at a position distant from the light source 12, and the light r can be emitted from the entire light emitting surface 11c.

In addition, the amount of light transmitted through the light guide plate 11 is
2, the light guide plate 11 gradually decreases as the distance from the light guide plate 11 increases.
Is gradually reduced as the distance from the light source 12 increases, so that the frequency at which the light r is reflected by the image display surface 11b and the light emission surface 11c of the light guide plate 11 as the distance from the light source 12 increases (the number of reflections per unit length) Becomes larger. As a result, it is possible to prevent the luminance of the light emitting surface 11c from being reduced at a position distant from the light source 12, and the liquid crystal display panel 10
Can be illuminated with uniform brightness.

In this way, the liquid crystal display panel 10 is
Is uniformly illuminated by the light r emitted from the liquid crystal display panel 10, the light r entering the liquid crystal display panel 10 from the light emitting surface 11 c enters the liquid crystal 4, is diffused and reflected by the metal electrode 3, and passes through the liquid crystal 4 again. I do. At this time, in a pixel in which the electrodes 3 and 5 are on, the light r is transmitted and becomes a bright pixel, and in a pixel in which the electrodes 3 and 5 are off, the light r is not transmitted and the pixel becomes a dark pixel. As a whole, a bright and dark image is formed. Since this image is generated by the light r of the light source 12, a bright image with high contrast can be obtained.

The light exit surface 11c of the light guide plate 11 is parallel to the liquid crystal display panel 10, and the image display surface 11b
Is inclined, the light r emitted from the light exit surface 11c
Is efficiently coupled to the liquid crystal display panel 10, but the light r leaking from the image display surface 11b is, as shown in FIG. Direction almost parallel to surface 11b)
Emitted to For this reason, there is no adverse effect that the visible image becomes difficult to see due to being mixed with the light r serving as the visible image. Even when the liquid crystal display device A is directly viewed from the front, the visibility is reduced by the light r leaking from the image display surface 11b. It does not drop.

FIG. 3 is a partially enlarged sectional view showing a pixel of the liquid crystal display panel 10. As shown in FIG. The pixel size b of the liquid crystal display panel 10 is about 100 μm, and each pixel is arranged at a pixel pitch 2b = about 200 μm. Glass substrate 1
The cell gap a of the liquid crystal 4 sandwiched between the metal electrode 3 and the
It is about 0 μm. Thus, the cell gap a
Is about 10 μm, so that even if light r is obliquely incident on the metal electrode 3 at a large angle φ as shown in FIG. 3, interference between adjacent pixels can be avoided. For example,
Considering the maximum incident angle φ as the incident angle φ, that is, about 42 ° which is a critical angle of total reflection in the liquid crystal 4, the horizontal shift c of the light r in the liquid crystal 4 is c = a · tanφ = 9 μm, which is much smaller than the pixel size b = about 100 μm. Therefore, even when the light r is incident on the liquid crystal display panel 10 from the light guide plate 11 at a large angle, adjacent pixels do not interfere with each other and the resolution of an image is not impaired.

(Second Embodiment) FIG. 4 shows a liquid crystal display device B according to another embodiment of the present invention. The liquid crystal display B has a lower surface (a light emitting surface 11) of a light guide plate 11 having a wedge shape.
The low refractive index layer 20 is provided in close contact with c). The low refractive index layer 20 is a transparent thin film or an adhesive layer whose refractive index is smaller than the refractive index of the light guide plate 11 and larger than the refractive index of air.

The image display surface 11b of the light guide plate 11 is in contact with air.
The light exit surface 11c is in contact with the low refractive index layer 20.
Therefore, the criticality of total reflection at the light exit surface 11c of the light guide plate 11
Angle θ 1 is a critical angle θ of total reflection on the image display surface 11b._TwoThan
growing. For example, as shown in FIG.
A low refractive index of 1.38 relative to a light guide plate 11 of 1.5
When the layer 20 is in close contact with the light emitting surface 11c,
Critical angle θ of surface 11c 1 and image display surface in contact with air
11b critical angle θ_TwoIs θ₁= 68 ゜, θ_Two= 4
2 ゜.

Therefore, even if the light r is totally reflected on the image display surface 11b like the light having the incident angle θ ₂ shown in FIG. The light can be incident on the liquid crystal display panel 10. As a result, the amount of light r guided through the light guide plate 11 emitted from the light exit surface 11c becomes larger than the amount leaked from the image display surface 11b.
And the optical coupling efficiency with the light source is improved. Therefore, in the liquid crystal display device B of the present embodiment, the light r is efficiently emitted from the light emission surface 11c, and the effective use of the light r is improved.

(Third Embodiment) FIG. 6 is a sectional view showing a liquid crystal display device C according to still another embodiment of the present invention. In the liquid crystal display device C, the light exit surface 1 of the light guide plate 11
1c, a prism array 30 is formed.

The prism array 30 is formed on the light emitting surface 11c, and each prism 30a constituting the prism array 30 extends in a direction parallel to the light incident surface 11a. Each prism 30a has a right triangle in cross section,
They are arranged at a constant pitch p. The pitch p of the prism 30a is several times smaller than the pixel pitch 2b, so that the shadow of the prism array 30 is not noticeable from the front of the liquid crystal display device C.

Since the image has "roughness" of the size of the pixel pitch 2b, it is desirable that the pitch p of the prism 30a has at least a period smaller than this. Preferably, the pitch p of the prism 30a is equal to or less than 1/4 of the pixel pitch 2b.

The prism 30a gradually becomes deeper as the distance from the light source 12 increases, and the inclination of the slope becomes gradually larger. The light r in the light guide plate 11 is gradually transmitted through the light guide plate 11 by total reflection, and the light exit surface 11c is gradually increased.
And the amount of light decreases, but at a position distant from the light source 12 as shown in FIG. 7, the angle of the prism 30a is large, and the light r is easily emitted from the light emission surface 11c. The light exit surface 11c of the light guide plate 11
Can uniformly emit light r, illuminate the liquid crystal display panel 10 with uniform luminance, and can uniformly brighten the image of the liquid crystal display device C to improve visibility.

(Others) The liquid crystal display device of the present invention can be applied to a reflection type liquid crystal display device of any operation mode, and has a wide range of use. That is, the operation mode of the liquid crystal display device is an external field around the liquid crystal, or
It depends on the characteristics of the liquid crystal such as optical change, phase, dielectric anisotropy, alignment state, etc., and as is generally known, TN mode (twisted nematic mode), F-STN mode (phase difference film compensation mode) , ECB mode (electric field induced birefringence mode), GH mode (guest-host mode), PC-GH mode (cholesteric nematic phase transition type guest-host mode), and the like.

The TN mode is a method widely used for a liquid crystal display device in which liquid crystal molecules are twisted by 90 degrees. The F-STN mode is a method used for a direct matrix type liquid crystal display device in which the twist of liquid crystal molecules is about 240 degrees.

FIG. 8A shows the TN mode or the F-ST mode.
1 shows a configuration of an N-mode liquid crystal display device. The liquid crystal display device of the TN mode or the F-STN mode includes a polarizer 7, a glass substrate 1, a liquid crystal 4, a glass substrate 2,
It has a six-layer structure of a polarizer 7 and a scattering reflector 3a.
Since it is only necessary to place the scattering reflector 3a behind the panel of the conventional TN cell or STN cell, it is used for a mono-color display.

The ECB mode is a system in which the phase difference between extraordinary light and ordinary light caused by the refractive index anisotropy of liquid crystal is controlled by an electric field. FIG. 8B shows a configuration of an ECB mode liquid crystal display device. The ECB mode liquid crystal display device has a five-layer structure of a polarizer 7, a glass substrate 1, a liquid crystal 4, a scattering reflector 3a, and a glass substrate 2 in this order from the front side.

The two-layer type GH mode is used for a liquid crystal display device in which two liquid crystal layers of a Heilmeier type GH mode (Heilmeier type guest / host mode) are stacked, and a method capable of bright display without requiring a polarizing plate. It is. Where Heilme
The ier-type GH mode is a method in which the orientation of a dichroic dye in a nematic liquid crystal is changed by the liquid crystal to control light absorption characteristics.

The PC-GH mode is used for a liquid crystal display by adding a dichroic dye to PDLC mode (polymer dispersion type liquid crystal mode) and PC mode (cholesteric nematic phase transition mode) liquid crystal. This is a method that does not require a polarizing plate and enables bright display.

FIG. 8C shows a two-layer GH mode or P
1 shows a configuration of a C-GH mode liquid crystal display device. Double layer type G
H mode or PC-GH mode liquid crystal display devices
It has a four-layer structure of a glass substrate 1, a liquid crystal 4, a scattering reflector 3a, and a glass substrate 2.

The PC mode is a method used for a liquid crystal display device having a nematic liquid crystal in which a spontaneous twisting structure is induced by adding a chiral agent. The phenomenon of vertical orientation is used.

In the PDLC mode, a liquid crystal is sealed in a polymer network or a fine hole, and is a system utilizing a change in a scattering effect due to an electric field.

FIG. 8D shows the PC mode or PDLC.
1 shows a configuration of a liquid crystal display device in a mode. The liquid crystal display device of the PC mode or PDLC mode has a four-layer structure of a glass substrate 1, a liquid crystal 4, a specular reflector 3b, and a glass substrate 2.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a conventional liquid crystal display device.

FIG. 2 is a cross-sectional view illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 3 is a partially broken sectional view showing a pixel of the liquid crystal display device.

FIG. 4 is a sectional view showing a liquid crystal display according to another embodiment of the present invention.

FIG. 5 is a partially broken cross-sectional view showing a state in which the total reflection angle of a light exit surface is increased by a low refractive index layer.

FIG. 6 is a cross-sectional view illustrating a liquid crystal display according to yet another embodiment of the present invention.

FIG. 7 is a partially broken sectional view showing a state in which light guided by the action of a prism is emitted toward a pixel.

8A is a cross-sectional view illustrating a configuration of a TN mode or F-STN mode liquid crystal display device, and FIG.
FIG. 3 is a cross-sectional view illustrating a configuration of a CB mode liquid crystal display device.
(C) is a sectional view showing a configuration of a liquid crystal display device of a two-layer GH mode or a PC-GH mode, and (d) is a PC.
FIG. 3 is a cross-sectional view illustrating a configuration of a liquid crystal display device in a mode or a PDLC mode.

[Explanation of symbols]

 Reference Signs List 4 liquid crystal 10 liquid crystal display panel 11 light guide plate 11b image display surface 11c light emission surface 11c 12 light source 20 low refractive index layer 30 prism array 30a prism

Claims (5)

[Claims] A light guide plate for confining light guided from the light source and emitting the light from a light exit surface; and a liquid crystal display panel for generating an image by reflecting incident light to a light incident side. The light emitting surface of the light guide plate and the light incident side of the liquid crystal display panel are arranged facing each other, the light source is arranged on the outer periphery of the light guide plate, and the image of the liquid crystal display panel can be recognized through the light guide plate. A liquid crystal display device characterized by the above-mentioned. 2. The light guide plate according to claim 1, wherein the light guide plate is thicker on a side closer to the light source and thinner on a side farther from the light source, and a light exit surface of the light guide plate is arranged substantially parallel to the liquid crystal display panel. The liquid crystal display device according to claim 1, wherein: 3. The liquid crystal display device according to claim 1, wherein an uneven pattern is provided on a light emitting surface of the light guide plate. 4. The liquid crystal display device according to claim 1, wherein a period of the concave and convex pattern is equal to or less than a pixel period of the liquid crystal display panel. 5. The liquid crystal display device according to claim 1, wherein a layer having a refractive index lower than that of the light guide plate is provided between the light exit surface of the light guide plate and the liquid crystal display panel.