JP3071538B2 - Light collimation device and liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for collimating a diffused light beam which is excellent in thinness, and a liquid crystal display apparatus which is formed using the same and which has a wide viewing angle for good display.

[0002]

2. Description of the Related Art Conventionally, as a device for converting a diffused light into a parallel light to form a plane parallel light, a single light source optical system using a collimator or a parabolic mirror, or a large number of independent light sources as light sources is used. Two-dimensional arrangements were known. However, in the former single light source optical system, in order to project a parallel ray on the entire surface of a predetermined area such as a screen, a depth of 1/2 or more of a diagonal line of a target area is required. There has been a problem that a parallel light beam converted by a light source disposed in a condensing optical path such as a light spot is blocked. Further, in the latter arrangement system of a large number of independent light sources, there is a problem in that a defect of each individual light source causes a dark spot such as a partial omission of a screen and thus lacks reliability.

On the other hand, as illustrated in FIG. 3, a diffusion light source is provided behind a liquid crystal panel 3 in which a phase difference plate 35 and a polarizing plate 31 are bonded to a liquid crystal cell 34 in which a liquid crystal 33 is sealed with a glass plate 32 with a transparent electrode. There is known a liquid crystal display device having a backlight system 7 comprising. However, when viewing a large screen at a short distance or when viewing a single screen from multiple directions with many people, the visibility varies greatly depending on the screen viewing angle, such as a decrease in contrast, inversion of the display, or a change in hue. And the viewing angle that can be seen in a good display state is narrow. It is considered that such a variation in visibility is essentially caused by the liquid crystal itself which cannot be solved even by variously changing the composition of the liquid crystal, the polarizing plate, and the retardation plate.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to develop a device for collimating diffused light, which is excellent in thinness, and a liquid crystal display device having a wide viewing angle which can be viewed in a good display state.

[0005]

SUMMARY OF THE INVENTION The present invention has the ability to converge reflected light of an incident parallel light beam, and the diffused light is applied to the front surface of a Fresnel-type reflecting surface whose optical axis is located out of the plane. will be have a transparent inclined surface totally reflected toward the reflecting surface, said anti
When a diffused light source is placed on the
An object of the present invention is to provide a light beam collimating device, wherein diffused light from a light source is emitted from the inclined surface as parallel light beams . Also, the present invention has the above-mentioned light beam collimating device on one side of a liquid crystal panel, and the condensed light of the reflected light of the incident parallel light beam through the Fresnel type reflection surface and the transparent inclined surface in the light beam collimating device. An object of the present invention is to provide a liquid crystal display device having a diffusion light source on a road.

[0006]

[Function] By using a Fresnel type reflecting surface whose optical axis is located outside the plane, it can be made thin even in the case of a parabolic system having the ability to collect reflected light of incident parallel light rays, and the reflecting surface. The diffused light source can be arranged in the condensing light path outside the light source, so that the light source can avoid blocking the converted parallel light beam. Furthermore, by providing a transparent inclined surface for total reflection of diffused light on the front surface of such a reflecting surface, the device can be made thinner while realizing the transmission of parallel rays. The parallel light beam is obtained by disposing a diffused light source in the condensing light path, totally reflecting the diffused light on the inclined surface, and making the incident light incident on the Fresnel-type reflective surface and reflecting the light.

On the other hand, when the planar parallel rays formed as described above are made to enter the liquid crystal panel at a constant angle, particularly as much as possible, the optical characteristics of the liquid crystal depend on the light incident angle. That is, variation in visibility due to a difference in the incident angle of light is prevented. As a result, only light indicating a good display state is emitted, and a decrease in contrast, a reversal of display, or a change in hue due to a viewing angle is suppressed, and the viewing angle or visibility of good display is improved. Then, by scattering the emitted light by the light diffusion plate, the transmission area of the image can be expanded by the scattering of the emitted light, so that a good visual recognition area can be expanded.

[0008]

FIG. 1 shows an embodiment of a liquid crystal display device having a light beam collimating device according to the present invention. 1 is a light diffusion plate, 3 is a liquid crystal panel, 4 is a transparent inclined surface, 5 is a Fresnel type reflection surface, 6
Is a diffusion light source. The liquid crystal panel 3 is composed of a liquid crystal cell 34 with polarizing plates 31 adhered to both sides thereof.
Consists of a liquid crystal 33 sealed with a glass plate 32 with a transparent electrode. Reference numeral 2 denotes a luminance homogenization mask.

As is apparent from FIG. 1, the transparent inclined surface 4 and the Fresnel-type reflecting surface 5 are formed on opposing surfaces of a substrate having a substantially triangular cross section. It is formed as. The Fresnel-type reflection surface was formed by grinding a substrate made of a methacrylic resin with an NC lathe to form concentric grooves, and depositing aluminum on the surface.

In the present invention, for example, the transparent inclined surface is formed by a sheet or a substrate, and the Fresnel-type reflecting surface is formed by a separate sheet or substrate, so that the transparent inclined surface and the Fresnel-type reflecting surface are separated. The beam collimating device formed in the above. The angle of inclination of the transparent inclined surface with respect to the Fresnel-type reflecting surface may be appropriately determined within a range in which the reflected light of the parallel rays incident on the Fresnel-type reflecting surface can be totally reflected. Is preferably smaller. The transparent inclined surface can be formed of a suitable transparent material such as glass or plastic, for example.

The reflection surface of the Fresnel type can also be formed by a resin molding method or the like via a mold, and may be formed by an appropriate method. When a Fresnel reflective surface is provided separately from the transparent inclined surface, the reflective surface may be formed of a highly reflective material such as a metal plate and the reflective surface forming process such as metal deposition may be omitted.

The Fresnel-type reflecting surface is said to have the ability to converge the reflected light of the incident parallel rays, as shown in FIG.
It is not always necessary to form it with the divided body 51 of the parabolic mirror 52 as shown in FIG. 1, but it can be approximated by a divided body with a conical surface as shown in FIG. The conical approximation has the advantage of being easier to manufacture than forming a paraboloid. Even in the case of forming a conical shape, a satisfactory light-collecting property can be obtained by reducing the division size (interval of irregularities in Fresnel formation: FIG. 2d).

When forming the Fresnel type reflection surface, the above-mentioned division size (d) of the paraboloid or the conical surface is set to a width such that the image forming rays from each pixel are mixed with each other and the image does not crosstalk. Is preferred. Its size (d)
Is appropriately determined by the spread of image forming light rays based on the size and interval of pixels in the liquid crystal panel and the distance from the liquid crystal surface to the light diffusion plate surface.

In the present invention, the Fresnel-type reflection surface is formed such that the optical axis is located outside the plane. That is, when a parallel light beam is made incident on the Fresnel-type reflection surface, the converging point of the reflected light is formed outside the parallel plate disposed at the upper and lower ends of the reflection surface. Thereby, when the diffused light source is arranged on the converging optical path of the reflected light of the incident parallel light beam via the Fresnel type reflection surface and the transparent inclined surface, it is possible to prevent the converted light beam from being blocked by the light source. . The formation of such a Fresnel-type reflection surface can be performed by, for example, forming a Fresnel by a divided body corresponding to a peripheral portion not including the center of the parabolic mirror.

There is no particular limitation on the liquid crystal panel or liquid crystal cell used in the present invention, and any known materials can be used. Examples of general liquid crystal panels include a twisted nematic type, a super twisted nematic type, a homogeneous type, a thin film transistor type, an active matrix driven type and a simple matrix driven type.

As a general polarizing plate to be attached to a liquid crystal cell, a film made of a hydrophilic polymer such as polyvinyl alcohol, which is treated with a dichroic dye such as iodine and stretched, or a polyvinyl chloride film is used. And a polarizing film formed by treating a plastic film and orienting the polyene, or a polarizing film covered with a protective film. Note that the polarizing plate is disposed on one side or both sides of the liquid crystal cell.

The retardation plate is used as needed for the purpose of compensating for birefringent light by the liquid crystal cell. The retardation plate can be obtained, for example, as a birefringent film obtained by stretching a polymer film uniaxially or biaxially, or a laminate thereof. A retardation plate can also be arranged on one side or both sides of the liquid crystal cell.

The light diffusing plate 1 provided on the viewing side surface of the liquid crystal display device scatters image light to increase the viewing angle. Therefore, the light diffusing plate to be used only needs to scatter such image light, and there is no particular limitation on the material, structure, and the like. Examples thereof include those in which organic or inorganic fine particles or fillers are dispersed in a transparent resin sheet, those in which polymer or low-molecular domains are expressed in a sheet-like resin, those on a polymer film or a glass plate. Provided with a resin layer in which inorganic or organic fine particles or fibers are dispersed, and those obtained by physically or chemically roughening the surface of a polymer film or a glass plate.

As the diffused light source 6 disposed on the converging optical path of the reflected light of the incident parallel light beam through the Fresnel-type reflecting surface and the transparent inclined surface in the light beam collimating device, an appropriate one may be used. Examples include cold cathode tubes, hot cathode tubes, tungsten lamps, metal halide lamps, xenon lamps, and the like. Usually, a low-temperature light source such as a cold-cathode tube is preferably used. In the present invention, for example, a method in which light from the light source is made incident via an optical fiber, a reflector, or the like may be used.

Although the number of light sources to be used is arbitrary, in the present invention, irregular diffused light from a single light source is introduced into a transparent inclined surface and totally reflected, and is incident on a Fresnel type reflector to form a planar light. The method of taking out the light source as a parallel light source is preferable from the viewpoint of thinning and reliability of the light source, and further from the viewpoint of thinning and weight reduction of a liquid crystal display device and the like. The light beam collimating device of the present invention can be preferably used for various purposes.

The luminance homogenization mask used as needed is for compensating for a luminance change (brightness unevenness) due to absorption loss or the like due to a distance difference from a light source.
For example, it can be formed as a sheet or the like in which light transmittance is changed. The brightness homogenization mask can be arranged at any position between the light diffusing plate and the beam collimating device. Note that the above-described compensation of the luminance change can also be achieved by, for example, a method of controlling the reflectance of each divided portion of the Fresnel type reflector, and an appropriate method can be adopted.

In the present invention, the space between the liquid crystal panel and the light diffusing plate is fixed as required. It is generally preferable to fix the display rather than to suppress a decrease in display quality due to interface reflection. The fixation can be performed using, for example, a transparent adhesive or a pressure-sensitive adhesive, and the kind of the adhesive or the like is not particularly limited. In particular, it is preferable that the refractive index is the same as or close to that of the object to be fixed. Further, from the viewpoint of preventing a change in the optical properties of the adherend, a material that does not require a high-temperature process for curing and drying is preferable, and a material that does not require a long curing treatment or drying time is desirable.

[0023]

According to the present invention, it is possible to convert diffused light into planar parallel light and emit it as parallel light from an inclined surface.
As a result, it is possible to obtain a light beam collimating device in which the converted parallel light beam is not blocked by the light source and which is excellent in thinness.
Further, the liquid crystal display device of the present invention using the same is prevented from changing the contrast and hue depending on the viewing angle, and is excellent in the viewing angle, or visibility, which can be viewed in a good display state with excellent clarity. . Also, by adding a light diffusion plate,
The viewing angle can be further widened, and the liquid crystal display can be viewed in a favorable display state from almost all directions on the front surface of the liquid crystal display device.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment.

FIG. 2 is an explanatory sectional view of a Fresnel type reflection surface.

FIG. 3 is an explanatory view of a conventional example.

[Explanation of Signs] 1: Light diffusing plate 3: Liquid crystal panel 31: Polarizing plate 34: Liquid crystal cell 32: Glass plate with transparent electrode 33: Liquid crystal 4: Transparent inclined surface 5: Fresnel reflective surface 6: Diffusion light source

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-33703 (JP, A) JP-A-64-11203 (JP, A) JP-A-61-34583 (JP, A) JP-A-2- 72388 (JP, A) JP-A-4-234729 (JP, A) JP-A-4-168418 (JP, A) JP-A-4-136977 (JP, A) JP-A-5-142422 (JP, A) 60-187406 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/13357

Claims (4)

(57) [Claims] 1. A reflecting light having an ability to collect incident parallel rays of reflected light, the diffused light being totally reflected toward the front surface of a Fresnel-type reflecting surface whose optical axis is located outside the surface. It will be have a transparent inclined surface, expanding the condensed light path by the reflecting surface
When a diffused light source is placed, the diffused light from that
A light beam collimating device that emits a parallel light beam from a slope . 2. The light beam collimating device according to claim 1, wherein the Fresnel-type reflecting surface and the transparent inclined surface are formed as a single body formed on opposing surfaces. 3. A light beam collimating device according to claim 1, provided on one side of a liquid crystal panel, and reflected light of an incident parallel light beam through a Fresnel-type reflecting surface and a transparent inclined surface in the light beam collimating device. A liquid crystal display device having a diffusion light source on a condensing optical path of the present invention. 4. The liquid crystal display device according to claim 3, further comprising a light diffusing plate on the surface on the viewing side.