JP2001067920A - Polarized back light and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce electric power consumption of a light source according to the realization of high luminance of a device by emitting the light entering a light guide body from the light source by changing an angle so as to be close to the vertical direction of an emitting surface, and emitting the polarized light being the almost parallel light, being transmissible through an incident surface of a transmission type display unit and being in the same direction as the polarizing direction. SOLUTION: Light from a light source 2 enters a light guide body 3. Among the light impinging on a reflection type polarizing plate 4, an S wave 14 is reflected and returns to the light conductor 3. Among the light from the light conductor 3 striking on the reflection type polarizing plate 4, a P wave passes through the reflection type polarizing plate 4 a P wave 13 impinging on a part where a microprism 10 is brought into close contact with the light guide body 3 enters the microprism 10 to be emitted from an emitting surface by passing through a base 11 and a microlens array 12, and an angle is changed so as to be drawn nearer to the vertical direction of the emitting surface by a curved surface of the microlens array 12. Thus, the P wave 13 of the almost parallel light is obtained. This P wave is irradiated to a transmission type liquid crystal panel 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device having a backlight unit and a transmissive display unit, and more particularly to a display device requiring high luminance and low power consumption.

[0002]

2. Description of the Related Art With the progress of computerization, OA applications and CAD
When a display device is used for an application or an advertising purpose, the display device needs to be large in size so that more information such as the entire paper can be displayed, high brightness is required for easy viewing, and low power consumption is required due to environmental problems. I have.

As a method for enlarging the screen, there is a projection system as disclosed in Japanese Patent Application Laid-Open No. 5-188340, for example. Hereinafter, this method will be described with reference to FIGS. FIG. 2 is a front view of the projection type apparatus.
The display units 51 are lined up without gaps, and a housing 52
There is. FIG. 3 is a configuration diagram of this device as viewed from the AA 'section. Backlight unit 53, transmissive liquid crystal panel 5
4. It is composed of an image forming means 55, an enlarging means 56 and a screen 57. The light from the backlight unit 53 is applied to the transmissive liquid crystal panel 54, and the image displayed on the transmissive liquid crystal panel 54 is formed on the screen 57 by the image forming unit 55. At this time, the image is enlarged by the enlargement means 56 and projected on the screen 57. In this example, four transmissive liquid crystal panels 54 are used, but by this enlargement processing, the gap between the four transmissive liquid crystal panels 54 arranged is eliminated on the screen 57, and a continuous large screen is obtained. I can do it.

As the backlight unit used here, one that emits substantially parallel light is required because of the visual characteristics of the transmissive liquid crystal panel.
A backlight unit that emits substantially parallel light using the technology of No. 574 will be described with reference to FIGS.
FIG. 4 is a perspective view of the backlight unit, and FIG. 5 is a cross-sectional view. A light source 61, a light guide 62, a plurality of microprisms 63 arranged in an array, a base 65, and a microlens 64 arranged corresponding to the microprism 63, the light guide 62, the microprism 63, the base 65, the micro lens 64 is in optical contact.
The light guide 62, the micro prism 63, the base 6
5. The microlenses 64 are made of the same material or a material having the same or similar refractive index. The microprism 63 has a shape in which the apex of the quadrangular pyramid is flattened, and the flattened portion is in close contact with the light guide 62.

A part of the light emitted from the light source 61 is
to go into. The light guide 62 is made of acrylic (refractive index: 1.49),
If the outside is air (refractive index: 1), the critical angle of total reflection when this incident light hits the boundary between the light guide 62 and the outside is 42.15 degrees, and the thickness of the light guide 62 is reduced. By making it thin, most of the light hitting the boundary between the light guide 62 and the outside is reflected. Therefore, most of the light incident on the light guide 62 travels in the light guide 62 toward the surface opposite to the incident surface by reflection or straight traveling.

[0006] Of the light that has traveled by reflection in the light guide 62, the light that hits the portion where the microprism 63 is in close contact with the light guide 62 is not reflected, and
Enter 3. The side wall of the microprism 63 has an angle, and light having an angle with respect to the direction perpendicular to the emission surface of the backlight unit is bent and reflected when hitting the side wall of the microprism 63, and is reflected in the direction perpendicular to the emission surface. It is a close angle. The light that has entered the microprism 63 further passes through the base 65 and the microlens 64. The exit surface 66 of the microlens 64 is curved so that light passing therethrough has an angle closer to a direction perpendicular to the exit surface.

[0007] Micro prism 63, micro lens 6
Reference numerals 4 are arranged in an array on the backlight unit emission surface 66, and substantially parallel light is emitted from the emission surface 66 of the backlight unit.

The transmission type liquid crystal panel has a polarizing plate on an incident surface, and when a light beam (hereinafter referred to as general light) mixed with light having a random polarization direction is incident, a polarized light which matches the polarizing plate on the incident surface. Only light having a direction is transmitted, and light having another polarization direction is absorbed. (Hereinafter, the light in the polarization direction that passes therethrough will be described as a P-wave, and the light in the polarization direction that will be absorbed will be described as an S-wave.) For this reason, about half of the light is absorbed and wasted. As a method of effectively using this light, for example, a backlight that emits polarized light as disclosed in Japanese Patent Application Laid-Open No. 8-146416 has been proposed. An example of this backlight is shown in FIG. It comprises a reflector 74, a light guide 73 having a light source 71 and a reflector 72 on its side, a circular polarizer 77 made of a cholesteric liquid crystal layer that selectively reflects light in the range of 400 to 700 nm, a quarter-wave plate 78, and a diffuser 75. Have been. Light source 7
The light exiting from 1 enters the light guide plate 73, and the light that strikes the reflection plate 74 travels in the direction of the emission surface. Next, the light whose polarization direction does not match that of the cholesteric liquid crystal layer is reflected and returns to the light guide plate 73, and the matching light passes through the circular polarizing plate 77 and becomes circularly polarized light. The light that has passed through the circularly polarizing plate 77 becomes linearly polarized light by the １ ／ wavelength plate 78. Finally, the viewing angle is widened by the diffusion plate 75, and the polarized light is emitted. This cholesteric liquid crystal layer and 1 /
The reflective polarizer using a 4-wavelength plate is Asia Display 9
5 As shown in Digest pp735, SID92 Digest pp427
A method of using a reflective polarizing plate in which dielectric films having different refractive indices are stacked in multiple layers on a prism array shown in FIG.

[0009]

The backlight unit of the projection system described in the prior art emits substantially parallel light. However, since the light is ordinary light, the S-wave is incident on the incident surface of the transmissive liquid crystal panel. Has been absorbed, which has been a problem with respect to demands for higher luminance and lower power consumption.

Further, Japanese Patent Application Laid-Open No. Hei 8-1 described in the prior art
In a backlight that emits polarized light as disclosed in Japanese Patent No. 46416, it is possible to eliminate waste on the incident surface of the transmission type liquid crystal panel. Substantially parallelization of the emitted light beam has not been specifically solved.

[0011]

According to the present invention, there is provided a transmission type display unit having a polarization means on an entrance surface and an exit surface, and a rotation means for rotating a polarization direction therein, and a backlight unit. A display device comprising: an optical system unit for processing an image displayed on a transmission type display unit; a light source, a light guide, a reflective polarizer, and a micropusm installed in an array on the surface of the light guide. And a backlight unit, the light entering the light guide from the light source is passed only in one direction by the reflective polarizing plate in the direction of the emission surface, and the connection between the reflective polarizing plate and the microprism The light is extracted from the light guide only at the inclined side wall of the microprism, and is reflected and emitted so as to change the angle so as to be closer to the vertical direction of the emission surface, is substantially parallel light, and is of the transmission type. The incident surface of the Display Unit to emit polarized light in a transmissive polarization direction in the same direction.

Further, according to the present invention, a transmission type display unit having a polarization means on an entrance surface and an emission surface and internally having a polarization direction rotating means, a backlight unit, and, if necessary, the transmission type display unit A light source, a light guide, a reflective polarizer, a micropusm arranged in an array on the surface of the light guide, and the microprism. A backlight unit is configured with a microlens corresponding to the above, the light entering the light guide from the light source, only the polarized light in one direction passes through the reflective polarizing plate in the direction of the emission surface, and the reflective polarizing plate and Light is extracted from the light guide only at the connection with the microprism, and reflected by the inclined side wall of the microprism so as to change the angle so as to be closer to the direction perpendicular to the exit surface. The micro-lens emits the light at a different angle so as to be closer to the vertical direction of the light exit surface, and emits a substantially parallel light and a polarized light in the same direction as the polarization direction that can be transmitted through the light incident surface of the transmission type display unit. I do.

[0013] Further, the position of the reflection type polarizing plate may be set between the light source and the light guide, and only the polarized light that matches the polarization direction of the emitted light may be put into the light guide to make effective use of the light.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings by using examples. FIG. 7 is a configuration diagram of a projection display device to which the backlight unit of the present invention is applied. This figure is a cross-sectional view as seen from the side of the image display surface. This device is one form of the projection type display device described in the related art, and the front surface is the same as that of FIG. From the rear side, a backlight unit 1, a transmissive liquid crystal panel 9, a pair of microlens arrays 5, a Fresnel concave lens 6, a Fresnel convex lens 7, and a lenticular sheet 8 are provided.

The microlens array 5 is formed by arranging fine double-sided convex lenses in an array. Two microlens arrays correspond to individual lenses and have their optical axes aligned. As a result, the two microlens arrays have a function of forming, on the lenticular sheet 8, an erect real-size real image of the image displayed on the transmissive liquid crystal panel 9. Further, since an image is formed by a fine lens, the working distance can be reduced, and an image can be formed with a short projection distance.

The incident surface Fresnel concave lens 6 has its optical axis aligned with the center of the image display section of the transmission type liquid crystal panel 9 and bends light rays gradually outward from the center toward the outer circumference. A function of enlarging an image displayed on the transmissive liquid crystal panel 9 when projecting the image on the lenticular sheet 8. The enlargement ratio is set so that when an image is projected on the lenticular sheet 8, the size of the image is such that there is no gap between adjacent images. In general, the non-display portion of the transmissive liquid crystal panel 9 has a smaller area than the image display portion, and thus has a magnification of 1.03 to 1.3 times.

The Fresnel convex lens 7 has a function of returning the light beam bent for enlargement to the original parallel state.

The lenticular sheet 8 has the function of a screen that diffuses the image formed here and widens the viewing angle of the device.

The backlight unit 1 illuminates the transmission type liquid crystal panel 9 with light. The transmissive liquid crystal panel 9 has visual characteristics, and has a problem that the contrast is inverted with respect to a light beam that passes obliquely beyond a predetermined angle. Also,
The microlens has a take-in angle, and light exceeding the take-in angle does not form an image at a desired position, causing a drop in contrast. For these reasons, in order to increase the contrast, it is necessary to reduce the light emitted from the transmissive liquid crystal panel 9 that exceeds a predetermined angle. The one that emits substantially parallel light is used. The predetermined angle is ± 10 ° to ± 20 due to the visual characteristics of the transmission type liquid crystal panel 9, the limitation of the take-in angle due to the manufacturing technology of the microlens array 5, the feasibility of the backlight unit 1, and the like.
° is considered reasonable. Further, in order to effectively use the light, the light whose polarization direction matches the incident surface of the transmission type liquid crystal panel 9 is emitted.

Using these, and displaying one image divided for each liquid crystal panel, a large screen image can be obtained on the lenticular sheet 8. Here, in the example of FIG. 2, four 2 × 2 transmissive liquid crystal panels 9
Are arranged in a plane, but this can also be realized by arranging an arbitrary number of m × n transmissive liquid crystal panels 9 in a plane.

FIG. 1 is a sectional view of a backlight unit according to an embodiment of the present invention. Light source 2 on the side of light guide 3
A reflector 16 for reflecting light from the light source and the like into the light guide 3 surrounds the light source. The light guide 3 includes a reflective polarizing plate 4, a microprism 10, and a base 1.
1. The micro-lens array 12 is arranged in this order in the direction of the light exit surface so as to be in close optical contact with each other. The light guide 3, the reflective polarizer 4, the microprism 10, the base 11, and the microlens 12 are made of the same material or a material having the same or similar refractive index. The outside is air, and the space between the microprisms 10 is also air. FIG.
Is a pair of micro prism 10 and micro lens 12
FIG.

Light from the light source 2 enters the light guide 3. Of the light that has entered the light guide 3, light that has hit the boundary between the light guide 3 and air is reflected. By reducing the thickness of the light guide 3, most of the light hitting the boundary between the light guide 3 and the air is totally reflected. Of the light that has hit the reflective polarizer 4 from the light guide 3, the S-wave 14 is reflected and returns to the light guide 3. Of the light that has impinged on the reflective polarizing plate 4 from the light guide 3, the P wave is transmitted through the reflective polarizing plate 4.
The light 13 hitting the portion where 0 is in close contact enters the microprism 10, but the light not hitting the portion where the microprism 10 is in close contact is reflected and returns to the light guide 3. The light 13 entering the microprism 10 hits the inclined side wall of the microprism 10 and is reflected and changed its angle so as to be closer to the direction perpendicular to the exit surface. The light 13 passes through the base 11 and the microlens array 12 and is emitted from the emission surface. The angle of the light 13 can be changed by the curved surface of the microlens array 12 so as to be closer to the direction perpendicular to the emission surface. In this way, a substantially parallel P wave is obtained. The light 13 is applied to the transmission type liquid crystal panel 9.

Here, the light which has not entered the microprism 10 while traveling inside the light guide 3 while being reflected or traveling straight ahead is emitted from the side opposite to the incident side, but is reflected by the reflector 16 to be guided. It is returned to the light body 3 and reused. Here, the light emitted from the opposite side contains a lot of S-waves, but by forming the reflector 16 with a white body, it is possible to use the reflector 16 as the general light 15 with a random polarization plane mixed at the time of reflection.

FIG. 8 is a sectional view of a backlight unit according to another embodiment of the present invention. The micro lens 12 is eliminated as compared with the embodiment of FIG. In this case, it is conceivable that the diffusion angle distribution of the emitted light is widened.

FIG. 9 is a sectional view of a backlight unit according to another embodiment of the present invention. Compared to the embodiment of FIG.
The position of the reflective polarizing plate 4 is between the light source 2 and the light guide 3. The S wave 14 is reflected at the stage of entering the light guide plate 3, and only the P wave enters the light guide 3. Thereby, the light emitted from the backlight unit is limited to the P wave. The S-wave 14 reflected by the reflective polarizing plate 4
When the light is reflected by the reflector 16 made of a white body, it becomes general light 15 and returns to the reflective polarizing plate 4 again.

In another embodiment of the present invention, the reflective polarizer can be provided at both the position of the reflective polarizer in FIG. 1 and the position of the reflective polarizer in FIG. .

Further, in another embodiment of the present invention, the polarization direction of the reflection type polarizing plate 4 is adjusted to the polarization direction of the incident surface of the transmission type liquid crystal panel 9 in the form of FIG. 1, FIG. 8 or FIG. Instead, it is set to the direction in which the light is well reflected by the side wall of the microprism 10. Then, the polarization direction of the incident surface of the transmission type liquid crystal panel 9 is adjusted to the emitted polarized light.

[0028]

According to the present invention, the transmission type display is achieved by emitting substantially parallel light from the backlight unit and polarized light in the same direction as the polarization direction that can be transmitted through the incident surface of the transmission type display unit. Light absorption at the entrance surface of the unit is reduced, and high luminance can be realized by reusing the conventionally absorbed light. Further, by reducing the power of the light source with the increase in luminance, low power consumption can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one embodiment of a backlight unit according to the present invention.

FIG. 2 is a front view of a conventional projection display device.

FIG. 3 is a cross-sectional view of a conventional projection display device.

FIG. 4 is a perspective view of a conventional backlight unit.

FIG. 5 is a sectional view of a conventional backlight unit.

FIG. 6 is a cross-sectional view of a conventional backlight unit.

FIG. 7 is a configuration diagram of a display device to which the present invention is applied.

FIG. 8 is a sectional view of an embodiment of the backlight unit according to the present invention.

FIG. 9 is a cross-sectional view of one embodiment of the backlight unit of the present invention.

FIG. 10 is a three-view drawing of a pair of microprisms and microlenses.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 backlight unit 2 light source 3 light guide 4 reflective polarizer 5 microlens array 6 Fresnel concave lens 7 Fresnel convex lens 8 lenticular sheet 9 transmissive liquid crystal panel 10 microprism 11 base 12 microlens 13 microprism adheres to lightguide plate P wave 14 S wave 15 General light 16 Reflector 51 Image display unit 52 of conventional device 52 Housing 53 Backlight 54 Transmissive liquid crystal panel 55 Image forming means 56 Magnifying means 57 Screen 61 Light source 62 Light guide 63 Microprism 64 Microlens 65 Base 66 Emission surface 71 Light source 72 Reflector 73 Light guide 74 Reflector 75 Diffuser 76 Reflector cover 77 Circular polarizer 78 Quarter wave plate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroki Yoshikawa 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Digital Media Development Division, Hitachi, Ltd. (72) Inventor Naohisa Koizumi 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Address Digital Media System Division, Hitachi, Ltd. (72) Inventor Hitoshi Suzuki 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture F-term, Digital Media System Division, Hitachi, Ltd. 2H091 FA08Z FA14Z FA21Z FA23Z FA29Z FA41Z LA03 LA17 MA10 5G435 AA03 BB12 DD06 EE27 FF03 FF05 FF08 GG02 GG03 GG24 LL15

Claims (3)

[Claims] 1. A transmission type display unit having polarization means on an entrance surface and an exit surface and a rotation means for rotating a polarization direction inside, a backlight unit, and an image displayed on the transmission type display unit which is added as necessary. In a display device including an optical system unit for processing an image, a light source, a light guide,
It is composed of a reflective polarizing plate, and microprisms arranged in an array on the surface of the light guide, and the light entering the light guide from the light source is emitted only in one direction by the reflective polarizing plate in the direction of the emission surface. The light is extracted from the light guide only at the connection between the reflective polarizing plate and the microprism, and is reflected by the inclined side wall of the microprism so as to change the angle so that it is close to the direction perpendicular to the exit surface. And a backlight unit that emits polarized light that is substantially parallel light, and that is polarized in the same direction as the polarization direction that can be transmitted through the incident surface of the transmissive display unit, and the backlight. Display device using unit. 2. A transmission type display unit having a polarization means on an entrance surface and an exit surface and having a polarization direction rotating means therein, a backlight unit, and an image displayed on the transmission type display unit which is added as necessary. In a display device including an optical system unit for processing an image, a light source, a light guide,
A reflective polarizing plate, comprising: a reflective polarizing plate; microprisms arranged in an array on the surface of the light guide; and microlenses corresponding to the microprisms. Only the polarized light in one direction passes in the direction of the exit surface, and the light is extracted from the light guide only at the connection between the reflective polarizing plate and the microprism, and the exit surface is perpendicular to the side wall with the inclination of the microprism. The light is reflected so as to change the angle so as to be closer to the direction, and the light is emitted by changing the angle so as to be closer to the vertical direction of the light-emitting surface with a microlens. A backlight unit that emits polarized light in the same direction as a polarization direction that can be transmitted, and a display device using the backlight unit. 3. The light guide according to claim 1, wherein the position of the reflection type polarizing plate is set between the light source and the light guide, and only the polarized light that matches the polarization direction of the emitted light is introduced into the light guide. 3. The backlight unit according to 2, and a display device using the backlight unit.