JPH11326898A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a display picture which is bright, easy-to-see, and excellent in display quality and also small in size, light in weight and low in power consumption even under an environment dark in lighting by preventing the transmission light of a light emitting device, with which a reflection type liquid crystal display element is irradiated from the front side, from being shaded, refracted, and dispersed by transmission dots provided on a light guide plate. SOLUTION: On a 1st emitting surface 24a of a light guide plate 24 of a front light device 21, a pillar-like transmission dot 26 is formed, of which a side face 26a vertical to the 1st emitting surface 24a and a top flat plane 26b parallel with the 1st emitting surface 24a are mirror-finished for total reflection of light. The light L3 in the light guide plate 24 is made to exit from the side face 26a, and the light L3 reflected from a reflecting plate 16 is efficiently transmitted through the light guide plate 24 without being refracted and scattered on the top plane 26b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device, and more particularly to a reflection type liquid crystal display device having an auxiliary light source arranged on a display surface side.

[0002]

2. Description of the Related Art In recent years, it has been thin and lightweight and has low power consumption.
Among liquid crystal display devices that are often used as display devices for personal OA equipment and video display devices such as televisions, the display is performed by reflecting external light without a built-in backlight, thereby reducing the weight and reducing the weight. Reflection type liquid crystal display devices for reducing power consumption have been developed. Since this reflection type liquid crystal display device is basically supposed to be used under bright illumination where sufficient external light can be obtained, it has been impossible to display and read in a dark place and cannot be used. Therefore, in order to enable use in such a dark place, a transmissive light irradiation device (hereinafter referred to as a front light device) that weakly and auxiliaryly illuminates the front surface, which is the display surface of the reflective liquid crystal display element, as necessary. Abbreviations) have also been developed.

Conventionally, a front light device 1 as shown in FIG. 8 has been used as a device for irradiating the display surface of such a reflection type liquid crystal display device from the front side. That is, a light source 4 whose rear surface is surrounded by a reflecting mirror 3 is disposed close to at least one side of a light guide plate 2 made of an acrylic resin or the like having a high light transmittance,
Light incident on the light guide plate 2 from the light source 4 propagates in a direction away from the light source 4 while repeating total reflection at the interface between the light guide plate 2 and air. During this time, due to the irregular reflection caused by the plurality of scattering dots 6 arranged on the light guide plate 2, a part thereof is emitted to the outside from the light guide plate 2 to illuminate the liquid crystal display element 7 from the front, and the reflection plate after passing through the liquid crystal composition 7a. The reflected light 10 reflected by 8 was incident on the light guide plate 2 and emitted in the display direction.

The scattering dots 6 are made of titanium oxide (Ti).
O) or other ink containing a pigment is applied to the surface of the light guide plate 2 by silk printing, or random irregularities or fine irregularities having a height sufficiently higher than the wavelength of light propagated on the surface of the light guide plate 2 during molding of the light guide plate. It is formed by forming a hemisphere or a prism shape.

[0005]

However, in the above-mentioned conventional front light device used for the reflection type liquid crystal display device, when the scattering dots are made by silk-printing ink containing pigment, the scattering dots are opaque thin films. Therefore, when the reflected light from the reflecting plate passes through the light guide plate and exits in the display direction, the reflected light is blocked by the scattering dots and appears as a black dot on the display image, thereby deteriorating the display quality. Had the problem of coming. On the other hand, if the scattering dots have an uneven pattern, the reflected light from the reflector is not blocked, but the reflected light is also scattered when the reflected light is emitted from the light guide plate. There has been a problem that a display image by the device is difficult to see, resulting in a decrease in display quality.

Accordingly, the present invention has been made to solve the above-mentioned problems, and prevents a light guide plate from blocking, refracting, or scattering light reflected from a reflection plate of a liquid crystal display element, so that illumination is dark and external light is insufficient. It is an object of the present invention to provide a light irradiation device and a reflection type liquid crystal display device which can obtain a bright display even under an unfavorable environment and can easily view an image without deteriorating the display quality.

[0007]

According to the present invention, as a means for solving the above problems, a liquid crystal layer sandwiched between a pair of substrates opposed to each other, and one of the pair of substrates has a reflector. A liquid crystal display element, comprising a flat light guide plate disposed on the other main surface of the pair of substrates, and a light source disposed adjacent to one side surface of the light guide plate; A plurality of transmissive dots are formed on the main surface adjacent to the liquid crystal display element in a three-dimensional manner and have a top surface formed of a mirror surface parallel to the main surface.

According to the present invention, the liquid crystal cell is irradiated with light from the side of the transmission dot. In addition, when viewed from an observation direction substantially perpendicular to the liquid crystal cell, since reflected light from the liquid crystal cell is transmitted through the top plane of the transmission dot, the transmission dot is almost invisible and a good display image is obtained. Can be done. As the side surface of the transmission dot is closer to being perpendicular to the main surface of the light guide plate, the transmission dot becomes less visible. Further, since the transmission dots do not scatter light, higher display quality can be obtained as compared with the case where a conventional light guide plate having scattering dots is used.

[0009]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described with reference to FIGS. Reflective liquid crystal display device 1
The second liquid crystal display element 13 includes an array substrate 17 having a pixel electrode 14 and a reflection plate 16 driven by a driving element,
A liquid crystal composition 20 is sealed between a counter substrate 19 having a counter electrode 18. On the front side of the liquid crystal display element 13, a front light device 21 which is a light irradiating means for illuminating the liquid crystal display element 13 from the front side is provided.

The front light device 21 has a light guide plate 24 for transmitting light from a light source 23 formed of a bar-shaped cold cathode tube condensed by a reflecting mirror 22 and emitting the light in a planar shape. The light guide plate 24 is made of a pair of flat transparent acrylic resins having a higher refractive index and a higher light transmittance than air, and its outer surface is mirror-finished so as to totally reflect light from the light source 23. The first light exit surface 24a of the light guide plate 24 adjacent to the liquid crystal display element 13 has a side surface 2 perpendicular to the first light exit surface 24a.
A transmission dot 26 is formed as a mirror-like and column-shaped projection on the top surface 26b parallel to the first emission surface 24a and 6a.

As shown in FIG. 2, the transmission dot 26 is
3 is formed on the first exit surface 24a so that the arrangement density is low and the arrangement density increases as the distance from the light source increases. For the production of transmission dots, protrusions are formed in the mold in advance by machining or etching process,
Next, light irradiation of the liquid crystal display element 13 by the front light device 21 obtained by injection molding using the mold will be described. Light source 23 when used in a dark environment
Is turned on, the light emitted from the light source 23 is efficiently condensed by the reflecting mirror 22 and enters the light guide plate 24. Light incident on the light guide plate 24 having a higher refractive index than air is propagated in a direction away from the light source 23 while repeating total reflection at the interface. This principle is the same as the principle of light propagation in an optical fiber.

When a part of the light propagating in the light guide plate 24 enters the transmission dot 26 in this manner, as shown in FIG. 3, the light L1 incident on the top plane 26b parallel to the first exit surface 24a is formed. Are totally reflected similarly to the light L2 incident on the first emission surface 24a and propagate through the light guide plate 24. On the other hand, FIG.
As shown in the figure, since the light L3 incident on the side surface 26a of the transmission dot 26 cannot satisfy the condition of total reflection, the transmission dot 2
6 from the side surface 26a of the liquid crystal display element 13 outside the light guide plate 24.
And irradiates the liquid crystal display element 13 from the front side. The light L3 applied to the liquid crystal display element 13 transmits through the counter substrate 19 and the liquid crystal composition 20, and is reflected by the reflection plate 16, and then transmits through the liquid crystal composition 20 and the counter substrate 19 through the reverse path. Out of the liquid crystal display element 13.

The light L3 emitted to the front side of the liquid crystal display element 13 passes through the light guide plate 24 and displays an image on the front side, which is the image display side of the liquid crystal display device 12. The light L3 emitted from the front side of the liquid crystal display element 13 is
4 can be transmitted almost at a right angle, and can be transmitted efficiently at the position of the transmission dot 26 without being scattered on the top plane 26b. Thereby, the observer can see a good display image of the liquid crystal display device 12 which is not affected by the transmission dots 26.

With this configuration, the light L3 emitted from the side surface 26a of the transmission dot 26 and reflected by the reflector 16 is
At the position of the transmission dot 26, it is formed in a mirror surface in parallel with the first emission surface 24a of the light guide plate 24, and is shielded by the top plane 26b of the transmission dot 26 which is substantially the same as the first emission surface 24a. Alternatively, the light is incident on the light guide plate 24 without being refracted or scattered by the top plane 26b, and is efficiently emitted to the front side of the liquid crystal display device 12. Therefore, the liquid crystal display device 1
2 is a transmission dot 26 formed on the first emission surface 24a.
It can be used in a bright environment without losing the display quality and without losing the small size, light weight and low power consumption even in an environment where the lighting is dark and the external light is insufficient. In this case, a bright and easy-to-view display image with good display quality can be easily obtained.

The transmission dots 2 formed on the light guide plate 24
Since the arrangement density of 6 increases as the distance from the light source 23 increases, a display image of good display quality with uniform illumination luminance over the entire surface of the liquid crystal display device 12 can be obtained.

The present invention is not limited to the above-described embodiment, and can be changed without departing from the spirit of the present invention. For example, the shape of the projected transmission dot is not a column but a square column. Optional.

Further, the front light device does not form projecting transmission dots for emitting light from the light guide plate, but instead forms the first light guide plate 24 as shown in the modified examples shown in FIGS.
Side surface 2 perpendicular to the first emission surface 24a
A front light device 28 may be formed by forming a hole-shaped transmission dot 27 having a circular or square cross section formed by polishing a bottom surface 27b parallel to the first emission surface 24a to the mirror 7a. By doing so, similar to the above embodiment,
A part of the light propagating in the light guide plate 24 is a hole-shaped transmission dot 2.
7, the light L4 incident on the bottom surface 27b parallel to the first light exit surface 24a as shown in FIG.
The light is totally reflected in the same manner as the light L2 incident on the light guide a and propagates through the light guide plate 24.

On the other hand, as shown in FIG.
Since the light L5 incident on the side surface 27a of the LED 7 cannot satisfy the condition of total reflection, the light L5 is emitted from the side surface 27a of the hole-shaped transmission dot 27 to the outside of the light guide plate 24, irradiates the liquid crystal display element 13, and is reflected by the reflection plate 16. After reflection, the light is transmitted through the light guide plate 24 and an image is displayed on the front side of the liquid crystal display device 12. In this modification, similarly to the above-described embodiment, the light L5 reflected from the reflection plate 16 is not blocked or refracted or scattered by the hole-shaped transmission dots 27, and the light guide plate is not. The light is efficiently emitted from 24 to the image display side of the liquid crystal display device 12.
Therefore, the liquid crystal display device 12 can be controlled by the front light device 28 even in an environment where the illumination is dark and the external light is insufficient.
A bright and easy-to-view display image with good display quality can be easily obtained as in the case of using in a bright environment without impairing compactness and lightness and low power consumption.

Further, a projection-shaped transmission dot or a hole-shaped transmission dot having a top plane may be formed by vapor-depositing a dielectric on a light guide plate through a predetermined mask.

The light source of the front light device is not limited, and a plurality of light emitting diodes may be linearly arranged on one side. Furthermore, in order to make the illumination brightness of the liquid crystal display device by the front light device constant over the entire surface, the arrangement density of the transmission dots is made uniform, and the height of the projection-like transmission dots is increased as the distance from the light source is increased, or a hole-like shape is formed. The depth of the transmission dot may be increased as the distance from the light source increases.
Further, in order to prevent reflection of an external light source on the surface of the front light device, it is optional to apply a non-reflection coating to the surface of the light guide plate. Further, instead of the reflection plate of the liquid crystal cell, the pixel electrode may have a reflection function.

[0021]

As described above, according to the present invention, when the reflected light from the reflective liquid crystal display element passes through the light irradiation device on the front side of the liquid crystal display element, the reflected light is blocked by the transmission dots. Or scattering can be prevented. Therefore, the reflected light from the liquid crystal display element can be satisfactorily incident on the light guide plate and can be transmitted to the front side of the liquid crystal display device, and the display quality is not impaired by the scattering dots of the light guide plate as in the related art, and is sufficient. Brightness is good, even in an environment where the lighting is dark and the external light is insufficient, and the display quality is bright and easy to see as well as in a bright environment, without compromising compactness, lightness and low power consumption. A simple display image can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a plan view showing an arrangement density of transmission dots on a first emission surface of the light guide plate according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing propagation of light L1 on a top plane of a transmission dot of the light guide plate according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing emission of light L3 on a side surface of a transmission dot of the light guide plate according to the embodiment of the present invention.

FIG. 5 is a schematic explanatory view showing a liquid crystal display device according to a modified example of the invention.

FIG. 6 is an explanatory diagram showing propagation of light L4 on the bottom surface of a hole-shaped transmission dot of a light guide plate according to a modification of the present invention.

FIG. 7 is an explanatory diagram showing emission of light L5 on a side surface of a hole-shaped transmission dot of a light guide plate according to a modification of the present invention.

FIG. 8 is a schematic explanatory view showing a liquid crystal display device of a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 ... Liquid crystal display device 13 ... Liquid crystal display element 16 ... Reflection plate 17 ... Array substrate 19 ... Counter substrate 20 ... Liquid crystal composition 21 ... Front light device 22 ... Reflection mirror 23 ... Light source 24 ... Light guide plate 24a ... First emission surface 26: transmission dot 26a: side surface 26b: top plane

Claims (9)

[Claims] 1. A liquid crystal layer sandwiched in a gap between a pair of substrates facing each other, a liquid crystal display element in which one of the pair of substrates has a reflection plate, and a liquid crystal display element disposed on the other main surface of the pair of substrates. And a light source disposed adjacent to one side surface of the light guide plate. The light guide plate is formed three-dimensionally on a main surface of the light guide plate adjacent to the liquid crystal display element. A reflective liquid crystal display device having a plurality of transmission dots whose planes are mirror surfaces parallel to the main surface. 2. The reflection type liquid crystal display device according to claim 1, wherein a side surface of the transmission dot is perpendicular to a main surface of the light guide plate. 3. The reflection type liquid crystal display device according to claim 1, wherein the transmission dots have a projection shape. 4. The reflection type liquid crystal display device according to claim 1, wherein the transmission dots have a hole shape. 5. The reflection type liquid crystal display device according to claim 1, wherein a top plane shape of the transmission dot is circular. 6. The reflection type liquid crystal display device according to claim 1, wherein the top plane shape of the transmission dot is quadrangular. 7. The reflection type liquid crystal display device according to claim 1, wherein the arrangement density of the transmission dots is lower on the light source side and increases as the distance from the light source increases. 8. The height of the transmission dots from the main surface of the light guide plate is:
7. The reflection type liquid crystal display device according to claim 1, wherein the reflection type liquid crystal display device has a lower value on a light source side and a higher value as the distance from the light source increases. 9. The reflection type liquid crystal display device according to claim 3, wherein the transmission dots are dielectrics deposited on the main surface of the light guide plate.