JPH11295508A - Optical reflector and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strong emitted light quantity, to reduce the diffusion degree of emitted light, to further improve emitted light intensity in front and to improve an execution reflectance by turning a diffusion member to a light transmission type mainly for forward scattering and combining it with a specular surface. SOLUTION: This optical reflector is provided with a light diffusion plate 1 and a specular metallic reflector 2 arranged behind the diffusion plate 1. The diffusion plate 1 is turned to the light diffusion plate of mainly the transmission of large forward scattering and small backward scattering. The diffusion plate 1 is turned to the diffusion plate of mainly the transmission provided with a property for which the reflectance along the normal direction of the optical reflector becomes higher than the reflectance in a larger polar angle direction. Further, as for intensity distribution by the direction of the emitted light for which the light made incident and transmitted along the normal direction of the surface of the diffusion plate 1 is reflected by the specular metallic reflector 2, transmitted through the diffusion plate 1 again and emitted from the surface of the diffusion plate 1, the diffusion plate 1 is designed so as to make the emitted light intensity to the vicinity of the normal direction substantially stronger than the emitted light intensity in the direction for forming a larger polar angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light reflecting device for reflecting incident light in a wide range of angles, and more particularly to a light reflecting device and a reflecting type suitable for use in a reflection type liquid crystal display device. The present invention relates to a novel structure of a liquid crystal display device.

[0002]

2. Description of the Related Art A reflection type liquid crystal display device does not have a light-emitting light source itself, and uses ambient light (external light) as a display light source. In a reflection type liquid crystal display device, a light reflection device is arranged on the back side of the liquid crystal cell (the side opposite to the display surface). In order to efficiently use ambient light and obtain a bright screen, the higher the light reflectance of the light reflecting device, the better.

[0003] The mirror-finished metal surface provides a reflective surface with high light reflectivity and forms reflected light that is the inverse of the optical rotation of the incident light.
However, when a mirror surface is used, the same reflection as a normal mirror occurs, and the brightness of the screen easily changes depending on the position of the user.

[0004] As a light reflection device of a reflection type liquid crystal display device, a reflection type scattering plate mainly composed of back scattering having a reflection characteristic close to that of a standard white plate has been used. Backscattering has a light traveling direction of 9
Scattering that changes by 0 degrees or more.

[0005] Forward scattering is scattering that changes the traveling direction of light by less than 90 degrees. The scattered light spreads within a certain solid angle range. By scattering the light, reflection can be prevented, and a change in brightness depending on the position of the user can be reduced.

[0006]

In a reflection type liquid crystal display device using a conventional light reflection device, an effective light reflectance is low, and a brighter display screen with a higher reflectance has been desired.

An object of the present invention is to provide a light reflection device having a high effective light reflectance and a light diffusion function, and a reflection type liquid crystal display device using the reflection device.

[0008]

According to the present invention, there is provided a diffusing member for diffusing transmitted light, and a mirror surface for reflecting light passing through the diffusing member in the direction of the diffusing member. Is greater than forward scattering, which changes the traveling direction of the incident light by less than 90 degrees, than back scattering, which changes the angle by more than 90 degrees.

[0009]

The light incident on the light reflecting device is reflected by a mirror surface, the scattering angle of the reflected light is narrowed, and the effective reflectance in the direction important for the display is increased.

[0010]

FIG. 1 is a sectional view of a light reflecting device according to an embodiment of the present invention. The light reflection device includes a diffusion plate 1,
A specular metal reflector 2 disposed behind the diffuser 1.
The diffusion plate 1 is a light diffusion plate mainly composed of a transmission, which has a large forward scattering and a small back scattering.

The mirror-surface metal reflector 2 inverts clockwise or counterclockwise polarized light with respect to circular (elliptical) polarized light, but changes the polarization state uniformly, and depolarization substantially occurs. Not something. Such a property is obtained by a normal mirror surface.

When a refractive index distribution is formed in a transparent material, light is transmitted and refracted and changes its traveling direction. in this case,
The polarization state of the light is maintained. When a large number of reflecting surfaces having various directions are used, the traveling direction of light can be changed at a larger angle. However, when a reflecting surface having various directions is used, the state of polarization changes, and the emission light obtained as a sum becomes close to natural light containing various polarization components. That is, the reflection type light scattering member has a strong tendency to cause depolarization.

A light diffusion plate mainly composed of a transmissive refraction element has a small polar angle (spreading angle) and is suitable for forming a light beam while maintaining a polarization component.

The diffusion plate 1 is formed as a transmission-dominant diffusion plate having such a property that the reflectivity in the vicinity of the normal direction of the light reflecting device is higher than the reflectivity in the larger polar angle direction. That is, the diffusion plate 1 is not a perfect scatterer such as standard white paper, but forms outgoing light while maintaining the incident direction component.

Further, light incident and transmitted along the normal direction of the surface of the diffusion plate 1 is reflected by the specular reflection plate 2, transmitted through the diffusion plate 1 again, and emitted from the surface of the diffusion plate 1. Is designed so that the intensity of the emitted light in the vicinity of the normal direction is much higher than the intensity of the emitted light in the direction forming a larger polar angle from the normal direction.

Such an intensity distribution characteristic of the reflected light can be obtained, for example, by using a diffusion plate having a microlens structure as shown in FIG. In FIG. 2A, a diffusion plate 1 is formed by distributing a large number of microlenses 11 on a transparent base film 10 and embedding the periphery of the microlenses 11 with a polymer 12.
I support.

The micro lens 11 is, for example, a gra
dede refractive index (GRAI
N), which forms a lens with a concentric structure in which the refractive index varies depending on the radial position and is distributed.

FIG. 2 (B) shows that the refractive index at the center is increased,
The case where the refractive index is lowered toward the outside in the radial direction to form a convex lens is shown. FIG. 2C shows a case where the refractive index of the central portion is reduced and the refractive index is increased toward the outside in the radial direction to form a concave lens. Either lens can diverge a parallel light beam, and the degree of divergence can be changed by the profile of the refractive index distribution. Hereinafter, the case of a convex lens will be described. FIG. 2D is a schematic top view of a diffusion plate using microlenses. A large number of microlenses 11 are embedded in the polymer support layer 12 and randomly distributed.

In the microlens of FIG. 2A, the lens effect is enhanced by having a structure having a curved surface called surface relief lenses on the upper surface. The degree of divergence can also be changed by the radius of curvature of this curved surface. The diameter of one lens is, for example, about 5 μm. As such a micro lens, for example, a micro lens M manufactured by Nashua
microsharp® can be used.

If a diffusion plate that diverges a light beam by such a transmission refraction function is used, basically no backscattering occurs,
Only forward scatter occurs. The extent of the forward scattering may be small as long as reflection can be prevented.

The reflection characteristics of the light reflecting device of this embodiment will be described in more detail with reference to the characteristic diagrams of FIGS. FIG. 3 shows the reflection characteristics of a light reflection device using a conventional perfect diffusion plate (standard white plate), FIG. 4 shows the reflection characteristics of the light reflection device according to the embodiment, and FIG. 5 shows the reflection characteristics of FIGS. It is the figure which superimposed the reflection characteristic.

Here, the reflection characteristic is an intensity distribution characteristic with respect to the emission direction of the emitted light that enters the reflection device along the normal direction of the surface of the diffuser plate, and is reflected and emitted. That is, the intensity distribution indicates in which direction and how much light of the reference intensity incident in the normal direction is reflected and diffused.

3 to 5, the horizontal axis is the incident surface, the point A is the incident point, the vertical axis is the normal direction, and the vector length from the incident point A to the intensity curves 20 and 30 is It shows the intensity of the reflected diffused light in the direction. θ indicates the angle from the normal line.

FIG. 3 shows the intensity characteristics of the reflected light with respect to the vertically incident light of the perfect diffusion plate (standard white plate). The intensity distribution is shown by a circle 20 in contact with the incident point A.

FIG. 4 shows the reflection characteristics of the light reflection device of this embodiment, which has an intensity distribution of an elliptical shape 30 having a long axis in the normal direction. The length of the major axis of the ellipse 30 (the intensity of the reflected light) is longer than the diameter of the circle 20 of the perfect diffusion plate in FIG. That is, it is shown that the intensity of the reflected light of the light reflecting device according to the present embodiment is higher than that of the conventional perfect diffusion plate in the normal direction and the direction near the normal direction.

Referring to FIG. 5, the relationship between FIGS. 3 and 4 will be described in more detail. The angle formed by a straight line L connecting the intersection point B of the circle 20 and the ellipse 30 and the incident point A and the normal line is defined as θ. As the value of θ increases, the characteristic of the ellipse 30 approaches the characteristic of the circle 20. As the value of θ becomes smaller, the major axis of the ellipse 30 becomes longer, and the spread of the reflected diffused light becomes narrower. In an angle region smaller than the angle θ, the light reflecting device of the present embodiment has a higher reflectivity than the conventional reflecting device using a perfect diffusion plate.

According to an experiment conducted by the present inventor, when the angle θ is smaller than 30 °, the directivity of reflected light is too strong, and
It was found that when the angle was larger than 5 °, the effect of improving the reflectance could not be obtained. Further, the optimum condition for not feeling the directivity and obtaining the effect of improving the reflectance is that the angle θ is from 40 ° to 45 °.
° range. Such different characteristics of θ were obtained by using microlenses having various focal lengths or various packing densities.

FIGS. 9 and 10 schematically show the difference in diffusion characteristics between the conventional transmission type diffusion plate and the diffusion plate according to the present embodiment for easy understanding. In the conventional example of FIG. 9, light entering the diffusion plate 60 in the vertical direction is diffused equally in all directions.
In the diffusion plate 70 of this embodiment shown in FIG. 10, the intensity of diffused light in the normal direction is large, and the intensity of diffused light decreases as the direction deviates from the normal line.

FIG. 6 is a sectional view showing the structure of a guest-host-phase change (GH-PC) type liquid crystal display device (embodiment 1) using a light reflecting device. On the back side (opposite to the display surface) of the 240 ° twisted GH-PC liquid crystal cell 40, the above-mentioned transmissive diffusion plate (microlens) 1 made by Nashua and a mirror reflection plate 2 having silver evaporated on its surface are arranged. Is done. The diffusion plate 1 has a value of 42 shown in FIG.

When the electro-optical characteristics of the liquid crystal display device were measured, the results shown in Table 1 were obtained. For comparison,
The results when a conventional light reflecting device (Peachcoat manufactured by Kimoto Co., Ltd.) is combined are also shown. According to the results in Table 1, the reflectance and the contrast are improved.
Particularly, the improvement of the reflectance is remarkable.

[0031]

[Table 1]

FIG. 7 is a sectional view showing the structure of an STN type liquid crystal display device (Example 2) using a light reflecting device. 2
Polarizing plates 51 and 52 are arranged on both sides of a 40 ° twisted STN type liquid crystal cell 50, and the first embodiment is provided outside the polarizing plate 52.
A diffusing plate (microlens) 1 mainly composed of a transparent material and a specular reflecting plate 2 having silver deposited on its surface are arranged.

When the electro-optical characteristics of the liquid crystal display device were measured, the results shown in Table 2 were obtained. For comparison,
The results when the conventional light reflecting device is combined are also shown. Also in this embodiment, the reflectance is improved.

[0034]

[Table 2]

FIG. 8 shows another STN using a light reflecting device.
FIG. 5 is a cross-sectional view showing a structure of a liquid crystal display device (Example 3). In this embodiment, only one polarizing plate 51 is arranged above the liquid crystal cell 50 in order to improve the amount of emitted light. Below the liquid crystal cell 50, a diffusion plate (microlens) 1 mainly composed of a transmission, similar to that of the first embodiment, and a reflection plate 2 having silver deposited on the surface thereof
Are arranged.

When the electro-optical characteristics of the liquid crystal display device were measured, the results shown in Table 3 were obtained. For comparison,
The results when the conventional light reflecting device is combined are also shown. In this embodiment, the reflectance and the contrast are improved.

[0037]

[Table 3]

In an STN type liquid crystal display device using only one polarizing plate, depolarization of returning polarized light to natural light upon reflection must not be caused. When a reflection plate such as a metal plate having a specular reflection condition is used, depolarization does not occur, but reflection occurs. The surface is made uneven to prevent reflection. The diffusion plate of the present embodiment basically causes diffusion by the lens action of a large number of microlenses. Unlike a conventional diffusion plate, light is mixed without depolarizing transmitted light. Therefore, no reflection occurs and processing of the mirror surface is not required.

In the embodiment described above, a mirror-finished metal reflector provided separately from the diffuser is used as the reflector, but a metal material is deposited or vapor-deposited on one surface of the diffuser (the side opposite to the liquid crystal cell). It can also be plated to form a reflective mirror surface.

In addition, although a description has been given of a case in which a cylindrical microlens is used as a diffusion plate mainly composed of a transmissive material, the scattering of which is larger than that of backscattering, a material in which beads are embedded or a transparent member having irregularities on the surface is used. Can also.

The above-described light reflection device is not limited to a guest-host type liquid crystal display device or an STN type liquid crystal display device, but may be a TN type, ETN type liquid crystal display device.
It is clear that the present invention is effective for all types of reflective liquid crystal display devices such as CB type and FLC (ferroelectric) type.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example,
It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0043]

According to the light reflecting device of the present invention, the diffusing member is of a light transmission type mainly for forward scattering, and a strong outgoing light quantity can be obtained by combining with a mirror surface. Further, by reducing the degree of diffusion of the emitted light, the intensity of the emitted light in the front can be further increased. Since the effective reflectance can be increased, a bright and high-contrast display device can be provided when used in a reflective liquid crystal display device.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of a light reflection device according to the present invention.

FIG. 2 is a sectional view and a graph showing a structure of a diffusion plate.

FIG. 3 is a graph showing a reflection characteristic of a light reflecting device using a conventional perfect diffusion plate.

FIG. 4 is a graph showing reflection characteristics of the light reflecting device according to the embodiment of the present invention.

FIG. 5 is a graph in which the reflection characteristics of the conventional light reflection device and the reflection characteristics of the light reflection device according to the embodiment of the present invention are superimposed.

FIG. 6 shows G using a light reflecting device according to an embodiment of the present invention.
It is sectional drawing which shows the structure of an H-PC type liquid crystal display device.

FIG. 7 illustrates an example of an S using a light reflecting device according to an embodiment of the present invention.
It is sectional drawing which shows the structure of a TN liquid crystal display device.

FIG. 8 illustrates an example of an S using a light reflecting device according to an embodiment of the present invention.
It is sectional drawing which shows the structure of a TN liquid crystal display device.

FIG. 9 is a schematic diagram showing diffusion characteristics of a conventional transmission type perfect diffusion plate.

FIG. 10 is a schematic diagram showing diffusion characteristics of a diffusion plate used in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diffusion plate 2 Mirror-surface metal reflection plate 10 Base film 11 Micro lens 20 Conventional characteristic curve 30 Characteristic curve of the example of the present invention 40 GH-PC type liquid crystal cell 50 STN type liquid crystal cell

Claims (13)

[Claims] 1. A diffusing member for diffusing transmitted light, and a mirror surface for reflecting light passing through the diffusing member in a direction of the diffusing member, wherein the diffusing member has a traveling direction of incident light of 90 degrees or more. Instead of changing backscattering, the direction of travel of incident light is 9
A light reflecting device having a large forward scatter that is changed by less than 0 degrees. 2. The light reflection device according to claim 1, wherein the light reflectance in the vicinity of the normal direction of the surface of the light reflection device is higher than the reflectance in the larger polar angle direction. 3. The light diffusing member has an intensity distribution in which, for the light incident along the surface normal direction and transmitted and diffused, the outgoing light in the vicinity of the normal direction is stronger than the outgoing light in the larger polar angle direction. The light reflecting device according to claim 1, comprising: 4. An intensity distribution characteristic curve relating to an emission direction of an outgoing light that enters the reflecting device along a normal direction of a surface of the diffusing member and is reflected and emitted is a standard intensity of an outgoing light of a standard diffusion plate. 2. The light reflecting device according to claim 1, wherein an angle from a normal line of a straight line connecting an intersection point of the distribution characteristic curve and the incident point of the incident light beam is in a range of 30 ° to 85 °. 5. An intensity distribution characteristic curve relating to an emission direction of outgoing light which enters the reflecting device along a normal direction of a surface of the diffusing member and is reflected and emitted is a standard intensity of outgoing light of a standard diffusion plate. 2. The light reflecting device according to claim 1, wherein an angle from a normal line of a straight line connecting an intersection of the distribution characteristic curve and the incident point of the incident light ray is in a range of 40 ° to 45 °. 6. The light reflecting device according to claim 3, wherein the diffusion member is a diffusion plate having a structure in which a plurality of microlenses are arranged on a light transmitting member. 7. The light reflection device according to claim 1, wherein the diffusion member mainly has a function of changing a traveling direction of a light beam by transmission and refraction, and has little depolarization. 8. The light reflection device according to claim 1, wherein the mirror surface is a reflection plate having a metal reflection surface arranged independently of the diffusion member. 9. The light reflection device according to claim 1, wherein the mirror surface is a metal reflection surface formed on one surface of the diffusion member. 10. A reflection type liquid crystal display device comprising: the light reflection device according to claim 1; and a liquid crystal cell using light reflected from the reflection device as a light source. 11. The reflection type liquid crystal display device according to claim 10, further comprising two polarizing plates sandwiching said liquid crystal cell. 12. The reflection type liquid crystal display device according to claim 10, wherein a polarizing plate for polarizing light incident on the liquid crystal cell is arranged on a display surface side. 13. The reflection type liquid crystal display device according to claim 10, wherein said liquid crystal cell is a guest-host phase change type liquid crystal display cell.