JP3771407B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reflective liquid crystal display device employing a front light system.
[0002]
[Prior art]
Conventionally, a liquid crystal display device includes a transflective liquid crystal display device having a backlight, and light from a backlight disposed on the rear surface of the liquid crystal panel is transmitted through the transflective reflector and then incident on the liquid crystal panel. Is configured to do.
[0003]
In recent years, a reflective liquid crystal display device having a front light has been proposed. FIG. 6 is a diagram showing an example of a reflective liquid crystal display device having the front light. In this liquid crystal display device Dc, a liquid crystal panel 31 in which liquid crystal C is sealed is provided between a pair of transparent substrates 30a and 30b, and a light guide plate 32 and a polarizing plate are provided on the front surface (upper surface in the figure) of the liquid crystal panel 31. 33a is provided so as to overlap. A polarizing plate 33b and a reflecting plate 34 are provided on the rear surface of the liquid crystal panel 31 so as to overlap each other.
[0004]
The light guide plate 32 has a transparent substantially flat plate shape, and a plurality of convex portions 35 are formed on one surface thereof. Each convex portion 35 has a triangular shape in side view having two types of inclined surfaces 35 a and 35 b having different inclination directions and inclination angles, and is continuous in a certain direction and extends in the depth direction of the light guide plate 32. Have. A light source 36 including a point light source is provided on the side of the light guide plate 32.
[0005]
According to this liquid crystal display device, when the light source 36 is driven to turn 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 of the convex portions 35, the light is emitted downward, and is applied to the polarizing plate 33 a and the liquid crystal panel 31. The light transmitted through the liquid crystal panel 31 is then transmitted through the polarizing plate 33b and then reflected upward by the reflecting plate 34. The light passes through the polarizing plate 33b, the liquid crystal panel 31 and the polarizing plate 33a again, and then passes through the light guide plate 32. To do. The light transmitted through the light guide plate 32 is emitted to the front surface of the liquid crystal display device Dc.
[0006]
On the other hand, when external light such as sunlight or indoor lighting is incident without driving the light source 36 to be lit, the external light sequentially faces the light guide plate 32, the polarizing plate 33a, the liquid crystal panel 31, and the polarizing plate 33b downward. Then, the light is reflected upward by the reflecting plate 34, so that the light is transmitted through the respective parts in reverse to the above and emitted to the front surface of the liquid crystal display device Dc.
[0007]
[Problems to be solved by the invention]
However, in the liquid crystal display device Dc in which the convex portion 35 is formed on the surface of the light guide plate 32 as described above, the visibility may be hindered depending on the direction in which the user visually recognizes the liquid crystal panel 31. That is, for example, when the user visually recognizes the liquid crystal panel 31 from the 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 reflected on the inclined surface 35b. By reflecting and further reflecting on the inclined surface 35a, the reflected light travels in the direction of the line of sight visually recognized by the user. When the light source 36 is driven, the light from the light source 36 enters the light guide plate 32 and is totally reflected in the light guide plate 32, and the light irradiated in the direction orthogonal to the inclined surface 35b is inclined. The light may be emitted to the outside of the light guide plate 32 without being totally reflected by the surface 35b, and may be traveled in the direction visually recognized by the user. Therefore, the contrast in the liquid crystal panel 31 is lowered, and visibility is hindered. Such a defect is a phenomenon peculiar to the liquid crystal display device Dc in which the convex portion 35 is formed on the surface of the light guide plate 32 described above.
[0008]
DISCLOSURE OF THE INVENTION
The present invention has been conceived under the circumstances described above, and a liquid crystal that allows a user to visually recognize an image by improving contrast when visually recognizing an image on a liquid crystal panel. An object is to provide a display device.
[0009]
In order to solve the above problems, the present invention takes the following technical means.
[0010]
According to the liquid crystal display device provided by the first aspect of the present invention, at least the liquid crystal panel and at least the light disposed on the front surface of the liquid crystal panel and incident inside from the light source are emitted toward the liquid crystal panel. A transparent light guide plate with one surface formed in an uneven shape, and a reflector that is disposed on the rear surface of the liquid crystal panel and reflects light that has passed through the liquid crystal panel from the light guide plate toward the liquid crystal panel and the light guide plate In the liquid crystal display device, the concavo-convex surface of the light guide plate faces the liquid crystal panel, and a part of the concavo-convex surface of the light guide plate is exposed to external light and / or a light source. An absorption layer for absorbing light is formed.
[0011]
According to this configuration, since the absorption layer for absorbing external light and / or light from the light source is formed on a part of the surface of the light guide plate, the light from the external light or light source incident on the light guide plate is formed. Of the light, the light that reaches the absorption layer is absorbed by the absorption layer and is not reflected. Therefore, conventionally, depending on the direction in which the user visually recognizes, the light is reflected and the contrast is lowered because the absorbing layer is not present, but the contrast can be suppressed by the absorbing layer. Therefore, the display quality of the liquid crystal display device can be improved.
[0012]
According to a preferred embodiment of the present invention, the surface of the light guide plate has a plurality of convex portions having a triangular shape in a side view having two types of inclined surfaces having different inclination directions, inclination angles, and inclined areas in a certain direction. It is formed continuously, and the absorption layer is formed on an inclined surface having a small inclined area among the two types of inclined surfaces. As described above, if the absorbing layer is formed on an inclined surface having a very small area compared with an inclined surface having a small inclined area, for example, an inclined surface having a large inclined area, the user can visually recognize the liquid crystal panel. Therefore, the image on the liquid crystal panel can be viewed without any trouble.
[0013]
According to another preferred embodiment of the present invention, the absorbing layer is formed by applying a black paint. Thus, if the absorption layer is formed to be black, the light absorption effect can be further enhanced.
[0014]
According to the liquid crystal display device provided by the second aspect of the present invention, the liquid crystal panel and light disposed on the front surface of the liquid crystal panel and incident from the light source to the inside are emitted toward the liquid crystal panel. A transparent light guide plate having at least one surface formed in a concavo-convex shape, and light that is disposed on the rear surface of the liquid crystal panel and that has passed through the liquid crystal panel from the light guide plate is reflected toward the liquid crystal panel and the light guide plate. A liquid crystal display device including a reflector, wherein the one-sided uneven surface is a surface on which a plurality of protrusions are formed, and external light and / or light from a light source is applied to a peripheral side surface of the protrusions. It is characterized in that an absorption layer for absorption is formed. According to this configuration, it is possible to suppress a decrease in contrast, and the display quality of the liquid crystal display device can be improved. The plurality of protrusions can be scattered all over the light guide plate, and the absorbing layer is formed on the peripheral side surface. Therefore, since the possibility that external light incident from all directions can be absorbed increases, the visibility of the liquid crystal display device can be further improved.
[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 INVENTION
Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the accompanying drawings.
[0017]
Figure 1 is a sectional view showing a reference example of a liquid crystal display device. This liquid crystal display device D employs a so-called front light system, and includes a liquid crystal panel 1, a polarizing plate 4a provided on the front surface (upper surface in the figure) of the liquid crystal panel 1, and a front surface of the polarizing plate 4a. A light guide plate 2 provided, a light source 3 for allowing light to enter 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 on the rear surface of the polarizing plate 4b. It is prepared for.
[0018]
The liquid crystal panel 1 has a liquid crystal C sealed in a region surrounded by a pair of glass transparent substrates 6 a and 6 b and a seal member 7. The liquid crystal panel 1 is configured to be capable of color display, for example, and the transparent substrate 6a is provided with color filters 8 (8R, 8G, 8B) of R, G, B colors in a matrix. A black matrix 9 is provided between the color filters 8.
[0019]
The transparent substrates 6a and 6b are provided with alignment films 11a and 11b and transparent electrodes 12a and 12b for twisting the liquid crystal molecules, respectively. The liquid crystal panel 1 employs, for example, an active matrix driving method, and a thin film transistor (TFT) (not shown) for holding a voltage applied to the liquid crystal cell is disposed in one liquid crystal cell.
[0020]
The light guide plate 2 has a transparent substantially flat plate shape, and the material thereof is preferably polycarbonate or PMMA (polymethyl methacrylate (methacrylic resin)) having excellent transparency. In this reference example , the thickness of each part of the light guide plate 2 is made substantially uniform. However, the thickness may be reduced as the distance from the light source 3 increases, for example.
[0021]
The light guide plate 2 has a smooth flat surface on the back surface (lower surface), whereas the surface (upper surface) has an uneven shape. More specifically, as shown in FIG. 2, the surface of the light guide plate 2 has a plurality of triangular shapes in side view having two types of inclined surfaces 16a and 16b having different inclination directions, inclination angles, and inclination areas. The convex portion 16 is formed in a concavo-convex shape formed continuously in a certain direction. Each convex part 16 is extended uniformly in the depth direction (arrow A direction) of the light-guide plate 2, and the pitch of the some convex part 16 is set to about several hundred tens of micrometers, for example.
[0022]
One inclined surface 16a of each convex portion 16 is formed so as to face substantially diagonally upward left in FIG. 1, and the other inclined surface 16b is opposed substantially diagonally upward to the right in FIG. Is formed. Further, the inclination angle θa (see the same figure) of one inclined surface 16a is made smaller than the inclination angle θb (see the same figure) of the other inclined surface 16b. Furthermore, one inclined surface 16a has a larger inclined area than the other inclined surface 16b.
[0023]
Here, the inclination direction and the inclination angle θa on the inclined surface 16a of the convex portion 16 are set so that appropriate contrast can be obtained in the range of the effective viewing angle of the user in the liquid crystal panel 1. The effective viewing angle refers to an angle at which the user can visually recognize the liquid crystal panel 1 well.
[0024]
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 viewed from an oblique direction as compared with the case where the liquid crystal panel 1 is viewed from the front. In this case, the contrast in the liquid crystal panel 1 is lowered. That is, the liquid crystal display device has a characteristic such as the above-described effective viewing angle. In this reference example , if the user visually recognizes the liquid crystal panel 1 from a predetermined direction within the range of the effective viewing angle, an appropriate contrast can be obtained. As described above, the inclination direction and the inclination angle of the inclined surface 16a are set. Specifically, the inclination angle of the inclined surface 16a is set, for example, in a range of 1 to 10 °, and the inclination direction is formed so as to face the substantially upper left direction in FIG. 1 as described above. . Thus, 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.
[0025]
The convex portion 16 may be formed such that one inclined surface 16a has a smaller inclination area and a larger inclination angle than the other inclined surface 16b. The absorption layer 19 is formed on the surface 16a. Moreover, the said convex part 16 may be formed so that it may incline in the depth direction (arrow A direction of FIG. 2) of the light-guide plate 2. As shown in FIG.
[0026]
The light source 3 is a so-called point light source such as an LED light source, and is provided in an appropriate number adjacent to one side surface 17 a extending in the depth direction of the light guide plate 2. In addition, you may make it use the cold cathode tube etc. which extend along the one side surface 17a of the light-guide plate 2 instead of this LED light source.
[0027]
When the light source 3 is driven to turn on by combining such a light source 3 and the light guide plate 2, the light emitted from the light source 3 is incident on the light guide plate 2 through one side surface 17 a of the light guide plate 2. The inside of the light guide plate 2 is sequentially advanced toward the other side surface 17b while repeating total reflection by the front and back surfaces of the light guide plate 2. When the light traveling in the light guide plate 2 reaches the inclined surface 16a on the surface of the light guide plate 2, the incident angle of light with respect to the inclined surface 16a is reduced by the amount that the inclined surface 16a is inclined in a predetermined direction. Therefore, there is a high possibility that the incident angle is smaller than a predetermined total reflection critical angle determined by the refractive index of the light guide plate 2. Therefore, the ratio of the light totally reflected by the inclined surface 16a can be increased, and light can be prevented from being emitted upward from various places on the surface of the light guide plate 2.
[0028]
Here, the feature of this reference example 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, on the front surface of the light guide plate 2 that is uneven, the other inclined surface 16 b having a smaller inclined area than the one inclined surface 16 a is arranged in the depth direction of the light guide plate 2. The absorbing layer 19 is formed by extending and applying black paint.
[0029]
With this configuration, when light reaches the absorption layer 19 formed on the inclined surface 16b, the reached light is not reflected by the absorption layer 19 but absorbed. Therefore, unlike in the past, external light reflected by the inclined surface 16b is less likely to be emitted in the direction of the line of sight of the user viewing the liquid crystal panel 1, and a decrease in contrast in the liquid crystal panel 1 can be suppressed. Therefore, the display quality of the liquid crystal display device D can be improved.
[0030]
As the black paint, for example, inorganic pigments and organic pigments such as carbon black, iron black and titanium black are preferably used. After the absorption layer 19 is dissolved in an appropriate organic solvent or resin and applied, It is formed by drying. The black paint is not limited to the above-described pigment, and the color is not limited to black. The point is that it can absorb incident light. Further, instead of applying the black paint, a method of blackening the inclined surface 16b by using a laser to modulate the intensity of the laser beam may be adopted.
[0031]
Further, the portion to which the black paint is applied does not have to be applied to all the inclined surfaces 16b of the light guide plate 2 described above, and the portion to be applied may be selected as necessary.
[0032]
Next, an operation when displaying an image on the liquid crystal panel 1 in the liquid crystal display device D having the above-described configuration will be described. First, when displaying an image using external light, when external light such as sunlight or indoor lighting is incident on the light guide plate 2, most of the light is transmitted through the light guide plate 2, and Light is emitted downward from the back surface and is applied to the polarizing plate 4 a and the liquid crystal panel 1. On the other hand, the light that has reached the inclined surface 16b of the light guide plate 2 out of the external light incident on the light guide plate 2 is directly absorbed by the absorption layer 19 of the inclined surface 16b and is not reflected or transmitted.
[0033]
The light transmitted through the liquid crystal panel 1 is then transmitted through the polarizing plate 4b and then reflected upward by the reflecting plate 5, and is transmitted through the polarizing plate 4b, the liquid crystal panel 1 and the polarizing plate 4a again and then transmitted through the light guide plate 2. To do. When transmitting 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.
[0034]
When the user visually recognizes the liquid crystal panel 1 of the liquid crystal display device D, even if the user visually recognizes the liquid crystal panel 1 from the upper right direction in FIG. Since the light is not reflected, the light that has been reflected and traveled toward the user in the past is not emitted in the present reference example . Therefore, a decrease in contrast is suppressed, and the user can surely view the image on the liquid crystal panel 1 without hindrance.
[0035]
On the other hand, when the light source 3 is driven to turn on, light emitted from the light source 3 enters the light guide plate 2 and travels through the light guide plate 2 while being totally reflected by the outer surface of the light guide plate 2. To do. During this progression, 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 light is irradiated to the polarizing plate 4a and the liquid crystal panel 1. . The inclined surface 16 a of each convex portion 16 plays a role of facilitating emission of light traveling inside the light guide plate 2 in the direction of the liquid crystal panel 1. Further, the light traveling from the light source 3 to the inside of the light guide plate 2 and reaching the inclined surface 16b of each convex portion 16 of the light guide plate 2 is absorbed by the absorption layer 19 and is not reflected.
[0036]
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 is reflected upward by the reflecting plate 5, so that the light passes through each of the above parts. 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, it reaches the inclined surface 16 b of the light guide plate 2 and is absorbed by the absorption layer 19.
[0037]
Thus, even when the light source 3 is driven to turn on, a part of the light from the light source 3 passes through the light guide plate 2 and is absorbed by the absorption layer 19. Therefore, even when the light source 3 is used, reflection on the inclined surface 16b can be prevented and good visibility can be realized.
[0038]
FIG. 3 is a cross-sectional view showing an example of a liquid crystal display device according to the present invention. In this liquid crystal display device Da, instead of the surface of the light guide plate being uneven, the back surface of the light guide plate is uneven. That is, the light guiding plate 21, whereas the surface (upper surface) is smooth planar, the rear surface (lower surface) is the uneven, i.e., the reference example described above, the front and back surfaces of the light guide plate opposite The polarizing plate 4 a is provided on the surface of the light guide plate 21. As in the above-described reference example , the concavo-convex configuration has a plurality of triangular convex portions 16 having two types of inclined surfaces 16a and 16b having different inclination directions, inclination angles, and inclination areas. It is the structure formed continuously in a fixed direction.
[0039]
Further, as the light source 22, a cold cathode tube extending along the 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 reference example .
[0040]
Also in this configuration, the black paint is applied to the inclined surface 16 b of the convex portion 16 formed on the back surface of the light guide plate 21 to form the absorption layer 19. Therefore, the same operational effects as those of the reference example can be achieved.
[0041]
FIG. 4 is a cross-sectional view showing another example of the liquid crystal display device according to the present invention. FIG. 5 is a schematic external view of the light guide plate 25 shown in FIG. In this liquid crystal display device Db, a plurality of substantially cylindrical protrusions 26 are formed on the surface of the light guide plate 25 to make it uneven, instead of forming the protrusions on the surface of the light guide plate. Yes. A black paint is applied to the peripheral side surface 26 a of the protrusion 26 to form the absorption layer 19. Other configurations are substantially the same as the configurations shown in the above embodiment.
[0042]
Even in this configuration, the same effects as those of the above-described embodiment can be achieved. In particular, in this modification, the protrusions 26 are scattered all over the plane of the liquid crystal panel 1, and the protrusions 26 are formed in a substantially cylindrical shape, and the absorbing layer 19 is formed on the peripheral side surface 26a. Is formed. Therefore, since the possibility that external light incident from all directions can be absorbed is increased, the factor of lowering the contrast is reduced as compared with the case where the absorption layer 19 is formed on the inclined surface 16b as in the above-described embodiment. There is an advantage that the sex can be further enhanced.
[0043]
The shape of the projection 26 may alternatively substantially cylindrical, substantially conical, substantially pyramidal shape, Ru can be applied a variety of shapes.
[0044]
Of course, the scope of the present invention is not limited to the embodiment described above. For example, in the above embodiment, a liquid crystal display device capable of color display has been described. However, the structure of the absorption layer 19 can also be applied to a monochrome liquid crystal display device.
[Brief description of the drawings]
It is a sectional view showing a reference example of FIG. 1 liquid crystal display device.
FIG. 2 is a main part external view showing a light guide plate of the liquid crystal display device shown in FIG. 1;
FIG. 3 is a diagram showing an example of a liquid crystal display device according to the present invention .
FIG. 4 is a diagram showing another example of a liquid crystal display device according to the present invention .
5 is a schematic external view of the light guide plate shown in FIG. 4. FIG.
FIG. 6 is a cross-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 Absorbing layer D, Da, Db Liquid crystal display device

Claims (4)

LCD panel,
A transparent light guide plate which is arranged on the front surface of the liquid crystal panel and has at least one surface formed in a concavo-convex shape so that light incident inside from a light source 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 that has passed through the liquid crystal panel from the light guide plate toward the liquid crystal panel and the light guide plate,
The uneven surface of the light guide plate faces the liquid crystal panel,
A liquid crystal display device, wherein 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. On the surface of the light guide plate, a plurality of convex portions having a triangular shape in a side view having two types of inclined surfaces having different inclination directions, inclination angles, and inclination areas are continuously formed in a certain direction,
The liquid crystal display device according to claim 1, wherein the absorption layer is formed on an inclined surface having a small inclination area among the two types of inclined surfaces.   The liquid crystal display device according to claim 1, wherein the absorption layer is formed by applying a black paint. LCD panel,
A transparent light guide plate which is arranged on the front surface of the liquid crystal panel and has at least one surface formed in a concavo-convex shape so that light incident inside from a light source 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 that has passed through the liquid crystal panel from the light guide plate toward the liquid crystal panel and the light guide plate,
The one-sided surface having the concavo-convex shape is a surface on which a plurality of protrusions are formed,
A liquid crystal display device , wherein an absorption layer for absorbing external light and / or light from a light source is formed on a peripheral side surface of the protrusion .

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