JP2001183662A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of suffiently visualizing an image while improving contrast when the image on a liquid crystal panel is visualized by an user. SOLUTION: The liquid crystal display device D comprises a liquid crystal panel 1, a transparent light guide plate 2 disposed on the front face of the liquid crystal panel 1 and having a rugged pattern formed on at least one surface so as to allow the light entering the light guide plate from a light source 3 to outgo to the liquid crystal panel 1, and a reflection plate 5 disposed on the back face of the liquid crystal panel 1 to reflect the light passing from the light guide plate 2 through the liquid crystal panel 1 in the direction to the liquid crystal panel 1 and the light guide plate 2. An absorption layer 19 to absorb external light is formed on a part of the rugged surface of the light guide plate 2.

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 employing a front light system.

[0002]

2. Description of the Related Art Conventionally, there is a transflective liquid crystal display device having a backlight in a liquid crystal display device. Light from a backlight disposed on a rear surface of a liquid crystal panel is transmitted through a transflective reflector. From the liquid crystal panel.

In recent years, a reflection type liquid crystal display device having a front light has been proposed. FIG. 6 is a diagram showing an example of a reflection type liquid crystal display device having the above-mentioned front light. The liquid crystal display device Dc includes a liquid crystal panel 3 having a liquid crystal C sealed between a pair of transparent substrates 30a and 30b.
1, a light guide plate 32 and a polarizing plate 33a are provided on the front surface (the upper surface in the figure) of the liquid crystal panel 31 so as to overlap each other. On the rear surface of the liquid crystal panel 31, a polarizing plate 33b and a reflecting plate 34 are provided so as to overlap with each other.

[0004] The light guide plate 32 is formed in a transparent and substantially flat plate shape, and has a plurality of convex portions 35 formed on one surface thereof. Each convex part 3
5 is a triangular shape in side view having two types of inclined surfaces 35a and 35b having different inclination directions and inclination angles, and has a form which is continuous in a certain direction and extends in the depth direction of the light guide plate 32. I have. A light source 36 composed of a point light source is provided on the side of the light guide plate 32.

According to this liquid crystal display device, when the light source 36 is turned on, the light from the light source 36 travels inside the light guide plate 32 and is totally reflected on the inner surface of the light guide plate 32. The light is reflected on the inner surface of each convex portion 35 of the light guide plate 32, and the light is emitted downward, and is irradiated on the polarizing plate 33 a and the liquid crystal panel 31. The light transmitted through the liquid crystal panel 31 is thereafter transmitted through the polarizing plate 33b and then reflected upward by the reflecting plate 34.
After passing through the polarizing plate 33a again, the light passes through the light guide plate 32. Then, the light transmitted through the light guide plate 32 is emitted to the front surface of the liquid crystal display device Dc.

On the other hand, when external light such as sunlight or indoor lighting is incident without driving the light source 36, the external light is transmitted through the light guide plate 32, the polarizing plate 33a, and the liquid crystal panel 3.
After sequentially transmitting the light 1 and the polarizing plate 33b downward, the light is reflected upward by the reflection plate 34, so that the light is transmitted through the respective parts in the opposite direction to the above, and is emitted to the front surface of the liquid crystal display device Dc.

[0007]

However, in the liquid crystal display device Dc in which the convex portions 35 are formed on the surface of the light guide plate 32 as described above, the visibility may vary depending on the direction in which the user views the liquid crystal panel 31. May be inhibited. That is, for example, when the user visually recognizes the liquid crystal panel 31 from the diagonally upper right direction in FIG. 6 (see arrow C), when external light is incident, a part of the external light incident on the light guide plate 32 is on the inclined surface 35b. Reflected and inclined surface 35a
, The reflected light travels in the direction of the line of sight visually recognized by the user. Light source 3
6, the light from the light source 36 enters the light guide plate 32 and is totally reflected in the light guide plate 32. Of those lights, the light radiated in the direction perpendicular to the inclined surface 35b becomes the inclined surface 35b.
In this case, the light may be emitted to the outside of the light guide plate 32 without being totally reflected, and may proceed in a direction in which the user visually recognizes the light. Therefore, the contrast in the liquid crystal panel 31 is reduced, and visibility is impaired. Such a problem is caused by the liquid crystal display device Dc in which the convex portions 35 are formed on the surface of the light guide plate 32 described above.
This phenomenon is unique to.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been conceived under the circumstances described above, and when a user visually recognizes an image on a liquid crystal panel, the user can view the image satisfactorily by improving the contrast. It is an object of the present invention to provide a liquid crystal display device capable of performing such operations.

In order to solve the above problems, the present invention takes the following technical measures.

According to the liquid crystal display device provided by the present invention, a liquid crystal panel and at least one surface arranged on the front surface of the liquid crystal panel and emitting light incident inside from a light source toward the liquid crystal panel are emitted. A liquid crystal display comprising: a transparent light guide plate formed in an uneven shape; and a reflector disposed on a rear surface of the liquid crystal panel and reflecting light passing through the liquid crystal panel from the light guide plate toward the liquid crystal panel and the light guide plate. The device is characterized in that an absorption layer for absorbing external light and / or light from a light source is formed on a part of the uneven surface of the light guide plate.

According to this structure, since the absorption layer for absorbing the external light and / or the light from the light source is formed on a part of the surface of the light guide plate, the external light or the light incident on the light guide plate is formed. Of the light from the light source, the light that reaches the absorption layer is
It is not reflected and absorbed by this absorbing layer. For this reason, in the related art, depending on the direction in which the user visually recognizes, the light is reflected and the contrast is reduced due to the absence of the absorption layer. However, the absorption layer can suppress the decrease in contrast. Therefore, the display quality of the liquid crystal display device can be improved.

According to a preferred embodiment of the present invention,
On the surface of the light guide plate, a plurality of triangular convex portions in side view having two types of inclined surfaces having different inclination directions, inclination angles, and inclined areas are formed continuously in a fixed direction, and the absorption layer is Of the two types of inclined surfaces, the inclined surface has a smaller inclined area. As described above, if the absorbing layer is formed on an inclined surface having a very small area as compared with an inclined surface having a small inclined area, for example, an inclined surface having a large inclined area, a user can visually recognize the liquid crystal panel. Since there is no effect on the operation, the image on the liquid crystal panel can be visually recognized without any trouble.

According to another preferred embodiment of the present invention, the absorbing layer is formed by applying a black paint. Thus, if the absorbing layer is formed to be black, the light absorbing effect can be further enhanced.

According to another preferred embodiment of the present invention, the inclination direction and the inclination angle of the inclined surface are set so that an appropriate contrast can be obtained in the effective viewing angle range of the liquid crystal panel. . Here, the effective viewing angle refers to an angle at which the user can view the liquid crystal panel well when viewing it. With the above configuration, if the user views the liquid crystal panel from a predetermined direction within the range of the effective viewing angle, the user can view the liquid crystal panel in a state where an appropriate contrast is obtained.

[0015] Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a liquid crystal display device according to the present invention. This liquid crystal display device D employs a so-called front light system, and has a liquid crystal panel 1
And a polarizing plate 4a provided on the front surface (the upper surface in the figure) of the liquid crystal panel 1, and a light guide plate 2 provided on the front surface of the polarizing plate 4a.
And a light source 3 for making light incident on the light guide plate 2, a polarizing plate 4b provided on the rear surface of the liquid crystal panel 1, and a reflecting plate 5 provided further on the rear surface of the polarizing plate 4b. .

The liquid crystal panel 1 has a liquid crystal C sealed in a region surrounded by a pair of transparent substrates 6a and 6b made of glass and a sealing member 7. The liquid crystal panel 1 is configured to be capable of, for example, color display, and a color filter 8 (8) of each of R, G, and B is provided on the transparent substrate 6a.
R, 8G, and 8B) are provided in a matrix, and a black matrix 9 is provided between the color filters 8.

The transparent substrates 6a and 6b are provided with alignment films 11a and 11b for imparting a twist to liquid crystal molecules and transparent electrodes 12a and 12b, respectively. The liquid crystal panel 1 employs, for example, an active matrix driving method, and one liquid crystal cell is provided with a not-shown thin film transistor (TFT) for holding a voltage applied to the liquid crystal cell.

The light guide plate 2 is in the form of a transparent, substantially flat plate, and is made of polycarbonate or polycarbonate having excellent transparency.
MMA (polymethyl methacrylate (methacrylic resin))
Are preferably used. In the present embodiment, the thickness of each part of the light guide plate 2 is made substantially uniform. However, for example, the thickness may become thinner as the distance from the light source 3 increases.

The back surface (lower surface) of the light guide plate 2 is smooth and flat, while the upper surface (upper surface) is uneven. More specifically, as shown in FIG. 2, the surface of the light guide plate 2 has a plurality of triangular side-view surfaces having two types of inclined surfaces 16 a and 16 b having different inclination directions, inclination angles, and inclination areas. Is formed in a concavo-convex shape formed continuously in a certain direction. Each protrusion 16 extends uniformly in the depth direction of the light guide plate 2 (direction of arrow A), and the pitch of the plurality of protrusions 16 is set to, for example, about one hundred and several tens of μm.

One of the inclined surfaces 16a of each convex portion 16 corresponds to the one shown in FIG.
And the other inclined surface 16b is formed so as to face substantially diagonally right upward in FIG. Also, the inclination angle θa of one inclined surface 16a (see FIG. 3) is different from that of the other inclined surface 1a.
6b is smaller than the inclination angle θb (see FIG. 6). Further, one inclined surface 16a is connected to the other inclined surface 16a.
The slope area is larger than b.

Here, the inclination direction and the inclination angle θa of the convex portion 16 on the inclined surface 16 a are set so that an appropriate contrast can be obtained in the range of the effective viewing angle of the user on the liquid crystal panel 1. . The effective viewing angle refers to an angle at which the user can view the liquid crystal panel 1 well when viewing it.

Usually, in a liquid crystal display device, since the refractive index of light is different between the major axis direction and the minor axis direction of the liquid crystal molecules, the liquid crystal panel 1 is more visible than when the liquid crystal panel 1 is viewed almost from the front.
Is seen from an oblique direction, the contrast in the liquid crystal panel 1 is reduced. That is, the liquid crystal display device has a characteristic such as the effective viewing angle described above. In the present embodiment, if the user views the liquid crystal panel 1 from a predetermined direction within the range of the effective viewing angle, an appropriate contrast is obtained. The inclination direction and the inclination angle of the inclined surface 16a are set so that the inclined surface 16a is inclined. Specifically, the inclination angle of the inclined surface 16a is set in a range of, for example, 1 to 10 °, and the inclination direction is formed so as to be substantially diagonally upward to the left in FIG. 1 as described above. . As described above, since the inclination angle of the inclined surface 16a is set in consideration of the range of the effective viewing angle of the user, the user can visually recognize the liquid crystal panel 1 in a state where an appropriate contrast is obtained. it can.

The projection 16 has one inclined surface 16.
a may be formed such that the inclined area is smaller and the inclination angle is larger than that of the other inclined surface 16b. In this case, the absorption layer 19 is formed on one inclined surface 16a. Further, the convex portion 16 may be formed so as to be inclined in the depth direction of the light guide plate 2 (the direction of arrow A in FIG. 2).

The light source 3 is a so-called point light source such as an LED light source, and has one side surface 17 extending in the depth direction of the light guide plate 2.
An appropriate number is provided adjacent to a. In addition, this LED
Instead of the light source, a cold cathode tube or the like extending along one side surface 17a of the light guide plate 2 may be used, and the specific type of the light source is not limited in the present embodiment.

When the light source 3 is lighted and driven by combining the light source 3 and the light guide plate 2, light emitted from the light source 3 is transmitted to the light guide plate 2 via one side surface 17 a of the light guide plate 2. After being incident, the inside of the light guide plate 2 is changed to the other side surface 1 while repeating total reflection by the front and back surfaces of the light guide plate 2.
7b. When light traveling inside the light guide plate 2 reaches the inclined surface 16a on the surface of the light guide plate 2, the angle of incidence of light on the inclined surface 16a is reduced by the amount that the inclined surface 16a is inclined in a predetermined direction. Therefore, the possibility that the incident angle becomes smaller than a predetermined total reflection critical angle determined by the refractive index of the light guide plate 2 increases. Therefore, the ratio of the light totally reflected by the inclined surface 16a can be increased, and the light can be prevented from being emitted upward from various points on the surface of the light guide plate 2.

The feature of this embodiment is that an absorption layer 19 for absorbing external light and / or light from the light source 3 is formed on a part of the surface of the light guide plate 2. More specifically, as shown in FIG. 2, in the uneven front surface of the light guide plate 2, the slope area is one slope surface 1.
On the other inclined surface 16b, which is smaller than 6a, a black paint is applied so as to extend in the depth direction of the light guide plate 2, and an absorbing layer 19 is formed.

With this configuration, when light reaches the absorption layer 19 formed on the inclined surface 16b, the light that has reached is absorbed by the absorption layer 19 without being reflected. Therefore, unlike the related art, external light reflected on the inclined surface 16b is less likely to be emitted in the direction of the line of sight of the user who visually recognizes the liquid crystal panel 1, and a decrease in contrast in the liquid crystal panel 1 can be suppressed. Therefore, the liquid crystal display device D
Display quality can be improved.

As the above-mentioned black paint, for example, inorganic pigments such as carbon black, iron black and titanium black, organic pigments and the like are preferably used. The above-mentioned absorbing layer 19 is formed by dissolving these in an appropriate organic solvent or resin. After that, it is formed by drying. In addition, as a black paint,
The pigment is not limited to the above-mentioned pigment, and the color is not limited to black. The point is that any material that can absorb incident light may be used. Further, instead of the method of applying the black paint, a method of blackening the inclined surface 16b by modulating the intensity of a laser beam using a laser may be adopted.

Further, the portion to which the black paint is applied does not have to be applied to the entire inclined surface 16b of the light guide plate 2, and the portion to be applied may be selected as needed. .

Next, the operation of the liquid crystal display device D having the above-described configuration when displaying an image on the liquid crystal panel 1 will be described. First, when an image is displayed using external light, when external light such as sunlight or indoor lighting enters the light guide plate 2, most of the light passes through the light guide plate 2, and Light is emitted downward from the back surface, and is irradiated on the polarizing plate 4a and the liquid crystal panel 1. On the other hand, of the external light that has entered the light guide plate 2, the light that has reached the inclined surface 16 b of the light guide plate 2 is
It is directly absorbed by the absorbing layer 19 on the inclined surface 16b and is not reflected or transmitted.

The light transmitted through the liquid crystal panel 1 is thereafter transmitted through the polarizing plate 4b and then reflected upward by the reflecting plate 5, and transmitted again through the polarizing plate 4b, the liquid crystal panel 1 and the polarizing plate 4a, and then transmitted through the light guide plate. 2 is transmitted. When the light passes through the light guide plate 2, part of the light reflected by the reflection plate 5 is further absorbed by the absorption layer 19 of the light guide plate 2. Then, most of the light transmitted through the light guide plate 2 is emitted to the front surface of the liquid crystal display device D.

When the user views the liquid crystal panel 1 of the liquid crystal display device D, for example, viewing the liquid crystal panel 1 from an obliquely upper right direction in FIG. Since external light is not reflected, light that has been reflected and traveled toward the user in the past is not emitted in the present embodiment. For this reason, a decrease in contrast is suppressed, and the user can surely visually recognize an image on the liquid crystal panel 1 without any trouble.

On the other hand, when the light source 3 is driven to turn on,
The light emitted from the light source 3 enters the light guide plate 2 and travels inside the light guide plate 2 while being totally reflected by the outer surface of the light guide plate 2. During this progress, the light is reflected by the inclined surface 16a of each convex portion 16 of the light guide plate 2, light is emitted downward from the back surface of the light guide plate 2, and the light is applied to the polarizing plate 4a and the liquid crystal panel 1. . The inclined surface 16a of each protrusion 16 is
Light that travels inside the light guide plate 2 plays a role in facilitating emission toward the liquid crystal panel 1. Further, the light proceeds from the light source 3 to the inside of the light guide plate 2, and the inclined surface 16 of each convex portion 16 of the light guide plate 2.
The light reaching b is absorbed by the absorption layer 19 and is not reflected.

The light transmitted through the light guide plate 2 is sequentially transmitted downward through the polarizing plate 4a, the liquid crystal panel 1 and the polarizing plate 4b, and then reflected upward by the reflecting plate 5, whereby
The light is transmitted through the respective parts in the opposite manner to the above, and is emitted to the front surface of the liquid crystal display device D. Even in this case,
When the light reflected by the reflection plate 5 passes through the light guide plate 2 and reaches the inclined surface 16 b of the light guide plate 2, the absorption layer 19 is formed.
Is absorbed by

As described above, even when the light source 3 is driven to be turned on, a part of the light from the light source 3 is transmitted through the light guide plate 2 and is absorbed by the absorption layer 19. Therefore, even when the light source 3 is used, the slope 16
b, reflection can be prevented, and good visibility can be realized.

FIG. 3 is a sectional view of a liquid crystal display device showing a modification of the present invention. In this liquid crystal display device Da, the back surface of the light guide plate is made uneven, instead of the surface of the light guide plate being made uneven. That is, the light guide plate 21
Has a smooth planar surface (upper surface), but has an uneven rear surface (lower surface). That is, the front and rear surfaces of the light guide plate are opposite to those of the above-described embodiment. The polarizing plate 4 a is provided on the surface of the light guide plate 21. Note that, as in the above-described embodiment, the concavo-convex configuration differs in the direction of inclination, the angle of inclination, and the area of inclination.
A plurality of convex portions 16 having a triangular shape in side view having various types of inclined surfaces 16a and 16b are formed continuously in a certain direction.

As the light source 22, a cold cathode tube extending along one side surface 17a of the light guide plate 21 is used instead of a point light source such as an LED light source. A reflector 23 that reflects light emitted from the cold cathode tube toward the light guide plate 21 is provided around the cold cathode tube. Other configurations are substantially the same as the configurations shown in the above embodiment.

Also in this configuration, the absorbing layer 19 is formed by applying black paint on the inclined surface 16b of the convex portion 16 formed on the back surface of the light guide plate 21. Therefore, the same operation and effect as the above embodiment can be obtained.

FIG. 4 is a sectional view of a liquid crystal display device showing another modification of the present invention. FIG. 5 is a schematic external view of the light guide plate 25 shown in FIG. In the liquid crystal display device Db, a plurality of substantially columnar projections 26 are formed on the surface of the light guide plate 25 to form the unevenness instead of forming the protrusions on the surface of the light guide plate and forming the unevenness. I have. Then, a black paint is applied to the peripheral side surface 26 a of the projection 26 to form the absorbing layer 19. Other configurations are substantially the same as the configurations shown in the above embodiment.

In this configuration, the same operation and effect as the above embodiment can be obtained. In particular, in this modification, the projections 26 are scattered to every corner in the plane of the liquid crystal panel 1, and the projections 26 are formed in a substantially columnar shape, and the absorbing layer 19 is provided on the peripheral side surface 26a. Is formed. Therefore, the possibility that external light incident from all directions can be absorbed is increased, and as compared with the case where the absorbing layer 19 is formed on the inclined surface 16b as in the above-described embodiment, the factor of lowering the contrast is reduced. There is an advantage that the property can be further improved.

The shape of the projection 26 can be various shapes such as a substantially conical shape and a substantially pyramid shape, instead of the substantially cylindrical shape. In short, the absorption layer 19 may be formed in a portion that does not affect the visual recognition of the user.

Of course, the scope of the present invention is not limited to the above embodiment. For example, in the above-described embodiment, the type of liquid crystal display device capable of color display has been described, but the configuration of the absorption layer 19 can be applied to a monochrome type liquid crystal display device.

[Brief description of the drawings]

FIG. 1 is a sectional view of a liquid crystal display device according to the present invention.

FIG. 2 is an external view of a main part showing a light guide plate of the liquid crystal display device shown in FIG.

FIG. 3 is a diagram showing a modification of the liquid crystal display device shown in FIG.

FIG. 4 is a diagram showing another modification of the liquid crystal display device shown in FIG.

5 is a schematic external view of the light guide plate shown in FIG.

FIG. 6 is a sectional view of a conventional liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 2 Light guide plate 3 Light source 5 Reflector 16 Convex part 16a, 16b Inclined surface 19 Absorption layer D, Da, Db Liquid crystal display device

Continued from the front page F-term (reference) 2H091 FA08X FA08Z FA16Z FA23X FA34X FA41X FD06 LA17 LA30 5G435 AA00 AA02 BB12 BB16 CC09 CC12 DD14 EE23 EE33 FF00 FF03 FF05 FF08 FF14 GG12 GG23 GG24

Claims (4)

[Claims] 1. A liquid crystal panel, and a transparent light guide plate disposed on a front surface of the liquid crystal panel and having at least one surface formed in a concavo-convex shape so that light incident from a light source to the inside is emitted toward the liquid crystal panel. A liquid crystal display device, comprising: a reflector disposed on the rear surface of the liquid crystal panel, and reflecting light passing through the liquid crystal panel from the light guide plate toward the liquid crystal panel and the light guide plate. A liquid crystal display device, characterized in that an absorption layer for absorbing external light and / or light from a light source is formed on a part of the uneven surface of the light guide plate. 2. The surface of the light guide plate has a plurality of triangular projections in a side view having two types of inclined surfaces having different inclination directions, inclination angles, and inclination areas, which are continuously formed in a predetermined direction. The liquid crystal display device according to claim 1, wherein the absorbing layer is formed on an inclined surface having a small inclined area among the two types of inclined surfaces. 3. The liquid crystal display device according to claim 1, wherein the absorbing layer is formed by applying a black paint. 4. The liquid crystal panel according to claim 1, wherein the inclination direction and the inclination angle of the inclined surface are set so that an appropriate contrast is obtained in a range of an effective viewing angle of the liquid crystal panel. The liquid crystal display device as described in the above.