JPH05196939A - Beam paralleling device and liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the beam paralleling device for scattered beams which is satisfactorily made thin, and the liquid crystal display device having the wide angle of view visual in a satisfactory display state. CONSTITUTION:This beam paralleling device is provided with ability for condensing the reflected beams of incidental parallel beams and equipped with a transparent slope 4 for full reflecting the scattered beams toward a reflection plane at the front face of a fresnel reflection plane 5 with the optical axis positioned out of the plane, and the liquid crystal display device is provided with a scattered beam source 6 on the condensing optical path of the reflected beams of the incidental parallel beams passed through the fresnel reflection plane 5 and the transparent slope 4 at the beam paralleling device. Therefore, the beam paralleling device converts the scattered beams to planar parallel beams, and the converted parallel beams are not shielded by the light source. The liquid crystal display device enables observation in the satisfactory display state from almost all the directions of the front face of the device by adding a beam scattering plate.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as a device for converting diffused light into parallel light rays to form plane parallel light rays, 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. The two-dimensional arrangement was known. However, the former single-source optical system requires a depth of 1/2 or more of the diagonal line of the target area in order to project parallel rays on the entire surface of a predetermined area such as a screen. There is a problem that the parallel light rays converted by the light source arranged in the light collecting path such as a light spot are blocked. Further, in the latter arrangement system of a large number of independent light sources, there is a problem that a defect of each individual independent light source causes a dark spot such as a partial omission of a screen and lacks reliability.

On the other hand, as shown in FIG. 3, a diffused light source is provided behind a liquid crystal panel 3 in which a retardation 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 having a transparent electrode. A liquid crystal display device having a backlight system 7 including the above is known. However, when viewing a large screen at a short distance or when a large number of people look at one screen from another direction, the visibility greatly varies depending on the viewing angle, the contrast decreases, the display reverses, or the hue changes. Occurs, and there is a problem that the viewing angle that can be viewed in a good display state is narrow. It is said that such a variation in visibility is essentially caused by the liquid crystal itself, which cannot be solved even if the composition of the liquid crystal, the polarizing plate, and the retardation plate are changed.

[0004]

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

[0005]

SUMMARY OF THE INVENTION The present invention has the ability to collect reflected light of incident parallel rays, and diffused light is provided on the front surface of a Fresnel type reflecting surface whose optical axis is located out of the plane. It is intended to provide a light beam collimating device having a transparent inclined surface that totally reflects toward a reflecting surface. Further, the present invention has the above-mentioned light beam collimating device on one side of the liquid crystal panel, and collects reflected light of incident parallel light beams through a Fresnel type reflecting surface and a transparent inclined surface in the light beam collimating device. The present invention provides a liquid crystal display device having a diffused light source on the road.

[0006]

By using a Fresnel type reflecting surface whose optical axis is located out of the plane, it is possible to make it thin even in the case of a parabolic system having the ability to collect reflected light of incident parallel rays. A diffused light source can be arranged in the condensing light path outside of, and the shield of the converted parallel rays by the light source can be avoided. Further, by providing a transparent inclined surface for total reflection of diffused light on the front surface of such a reflecting surface, it is possible to make the device thinner while realizing transmission of parallel rays. The parallel light rays are obtained by arranging a diffused light source in the converging light path, totally reflecting the diffused light on the inclined surface, and making the diffused light incident on the Fresnel type reflection surface to be reflected.

On the other hand, when the plane parallel rays formed as described above are incident on the liquid crystal panel at a constant angle, especially at an angle as vertical as possible, the optical characteristics of the liquid crystal depend on the light incident angle. Based on this, that is, variation in visibility due to difference in incident angle of light is prevented. As a result, only the light showing a good display state is emitted, and the deterioration of the contrast due to the viewing angle, the inversion of the display, the change of the hue, etc. are suppressed, and the viewing angle of the good display or the visibility is improved. Then, by scattering the emitted light by the light diffusing plate, the transmission area of the image can be expanded due to the scattering of the emitted light, and a good visual recognition area can be expanded.

[0008]

FIG. 1 shows an embodiment of a liquid crystal display device having a light collimating device of 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 diffuse light source. The liquid crystal panel 3 comprises a liquid crystal cell 34 and polarizing plates 31 attached to both sides of the liquid crystal cell 34.
Is composed of a liquid crystal 33 sealed with a glass plate 32 having a transparent electrode. Reference numeral 2 is a brightness homogenizing mask.

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

In the present invention, for example, a transparent inclined surface is formed by a sheet or a substrate, and a Fresnel type reflecting surface is also formed by a separate sheet or substrate so that the transparent inclined surface and the Fresnel type reflecting surface are separate bodies. It is also possible to use a 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 the range in which the reflected light of the parallel rays incident on the Fresnel-type reflecting surface can be totally reflected. Is smaller, the more preferable. The transparent inclined surface can be formed of a suitable transparent material such as glass or plastic.

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

The Fresnel type reflecting surface is supposed to have the ability to collect the reflected light of incident parallel rays, which is shown in FIG.
It is not always necessary to form the paraboloidal mirror 52 with the divided body 51 as illustrated in FIG. 1, and it is possible to approximate it with a conical divided body as illustrated 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, it is possible to obtain a satisfactory light converging property by reducing the division size (concavo-convex interval in Fresnel formation: FIG. 2d).

When the Fresnel type reflecting surface is formed, the above-mentioned division size (d) of the parabolic surface or the conical surface should be such that the image forming light rays from the respective pixels are not mixed with each other and the image does not crosstalk. Is preferred. Its size (d)
Is appropriately determined by the size and spacing of pixels in the liquid crystal panel and the spread of the image forming light beam based on the distance from the liquid crystal surface to the light diffusion plate surface.

In the present invention, the Fresnel type reflecting surface is formed so that the optical axis is located out of the plane. That is, when parallel rays are incident on the Fresnel-type reflecting surface, the condensing points of the reflected light are located outside the parallel plates arranged at the upper and lower ends of the reflecting surface. Thus, when a diffused light source is arranged on the condensing light path of the reflected light of the incident parallel rays that passes through the Fresnel type reflection surface and the transparent inclined surface, it is possible to prevent the converted parallel rays from being blocked by the light source. .. The Fresnel-type reflecting surface can be formed, for example, by Fresnelizing with a divided body corresponding to the peripheral portion not including the central portion of the parabolic mirror.

The liquid crystal panel or liquid crystal cell used in the present invention is not particularly limited, and any known one can be used. Examples of general liquid crystal panels and the like include twisted nematic type, super twisted nematic type, homogeneous type, thin film transistor type, active matrix driven type and simple matrix driven type.

As a general polarizing plate attached to a liquid crystal cell, a film made of a hydrophilic polymer such as polyvinyl alcohol is treated with a dichroic dye such as iodine and stretched, or polyvinyl chloride. Examples of the polarizing film include those obtained by treating a plastic film as described in (1) above to orient polyene, and those covered with a protective film. The polarizing plate is arranged on one side or both sides of the liquid crystal cell.

The retardation plate is used as necessary for the purpose of compensating the birefringent light due to 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. The retardation plate can also be arranged on one side or both sides of the liquid crystal cell.

The light diffusion plate 1 provided on the viewing side surface of the liquid crystal display device is for scattering the image light and expanding the viewing angle. Therefore, the light diffusing plate to be used may be any one as long as it scatters the image light, and the material and structure thereof are not particularly limited. Examples thereof include those in which organic or inorganic fine particles or fillers are dispersed in a transparent resin sheet, those in which a high-molecular or low-molecular domain is expressed in a sheet-shaped resin, a polymer film or a glass plate. Examples thereof include those 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.

An appropriate diffuser light source 6 may be used as the diffused light source 6 arranged on the light collecting path of the reflected light of the incident parallel light rays through the Fresnel type reflecting surface and the transparent inclined surface in the light beam collimating device. Examples thereof 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, but in the present invention, for example, a method in which light from the light source is incident through an optical fiber, a reflection plate or the like may be used.

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

The brightness homogenizing mask used as necessary is for compensating for a change in brightness (unevenness in brightness) due to absorption loss or the like due to a difference in distance from the light source.
For example, it can be formed as a sheet having a changed light transmittance. The brightness homogenizing mask can be arranged at any position between the light diffusion plate and the beam collimator. The above-described compensation of the brightness change can be achieved by a method of controlling the reflectance of each divided portion of the Fresnel type reflection plate, for example, and an appropriate method can be adopted.

In the present invention, the liquid crystal panel, the light diffusing plate and the like are fixed to each other as needed. In general, it is preferable to fix the film in terms of suppressing deterioration of display quality due to interface reflection. The fixing can be performed by using, for example, a transparent adhesive or a pressure-sensitive adhesive, and the kind of the adhesive or the like is not particularly limited. Above all, it is preferable that the adherend has the same or similar refractive index. Further, from the viewpoint of preventing changes in the optical properties of the adherend, those that do not require a high temperature process during curing or drying are preferable, and those that do not require a long curing process or drying time are desirable.

[0023]

According to the present invention, it is possible to obtain a light beam collimator capable of converting diffused light into a plane parallel light beam, the converted parallel light beam being not blocked by a light source, and being excellent in thinness. Further, the liquid crystal display device of the present invention using it, the change in contrast and hue depending on the viewing angle is prevented,
Excellent visibility The viewing angle and visibility that can be seen in a good display state are excellent. Further, the addition of the light diffusing plate can further widen the viewing angle, and the liquid crystal display device can be viewed in a good display state from almost all directions on the front surface.

[Brief description of drawings]

FIG. 1 is a sectional view of an example.

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

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

[Explanation of symbols]

 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 type reflecting surface 6: Diffuse light source

Claims (4)

[Claims] 1. A diffused light is totally reflected on the front surface of a Fresnel type reflection surface having an ability to collect reflected light of incident parallel rays and an optical axis of which is located out of the plane. A ray collimator having a transparent inclined surface. 2. The light beam collimating device according to claim 1, wherein the Fresnel type reflecting surface and the transparent inclined surface are integrally formed on opposite surfaces. 3. A light collimating device according to claim 1 on one side of a liquid crystal panel, and reflected light of incident parallel light rays through a Fresnel type reflecting surface and a transparent inclined surface in the light collimating device. A liquid crystal display device having a diffused light source on the light collecting path. 4. The liquid crystal display device according to claim 3, further comprising a light diffusing plate on the surface on the viewing side.