Optical waveguides – Noncyclindrical or nonplanar shaped waveguide
Reexamination Certificate
2000-10-27
2003-10-14
Feild, Lynn (Department: 2839)
Optical waveguides
Noncyclindrical or nonplanar shaped waveguide
Reexamination Certificate
active
06633722
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light guide plate as a component of a plane light source apparatus used as a back-light of a variety of display devices.
2. Description of the Related Art
A light guide plate is one of optical members used in a plane light source apparatus installed in a variety of display devices, for example in a plane light source apparatus of an edge light mode, it plays a role of emitting a light from a light source introduced into the light guide plate while guiding the light in a perpendicular direction with respect to the direction in which the light is incident. In such a light guide plate, its overall emission surface serves as a direct light source of a variety of display devices, so it is required to be comprised of members having a high transparency to attain higher luminance, and to have less luminance spots on the luminescence surface to attain a unified distribution of a light emission amount.
Therefore, in the related art, materials, such as a polymethyl methacrylate (PMMA) and polycarbonate (PC) are used as materials of light guide plates, on the light reflection surface (reflector surface) of the light guide plate is devised to be formed recesses having a variety of shapes as a reflection means for attaining higher luminance, for example, it is known to form grooves causing less light losses when molding the light guide plate (The Japanese Unexamined Patent Publication 1990-165504). Also, there are known means for arranging grooves so that density of an arrangement pattern increases along with the distance from the light source, and for arranging to be a check pattern for further higher luminance (The Japanese Unexamined patent Publication 1994-250025 and 1993-216030).
However, with the materials of the related art, such as PMMA and PC, sufficient front luminance has not yet obtained even if the groove arrangement patterns as above are provided due to reasons of optical characteristics of a refractive index, transparency, etc. which the materials themselves have.
Further, in the PMMA, melting viscosity is high and fluidity is deteriorated at the time of injection molding, while in the PC, when a resin temperature is raised for promoting fluidity, it is liable that the resin hydrolyzes and bubbles. There have been harmful influences, such as generation of luminance spots, deterioration of the front face luminance, which are caused because transferability of a preferable groove shape cannot be obtained actually in a range where the arrangement of the reflection pattern is dense (being distant from the light source).
Furthermore, in recent years, as back-light units becoming thinner and lighter each year, the trend in the light guide plate is also shifting to be thinner and wider in area, and in terms of the shape, instead of a flat plate having a constant thickness, light guide plates of a wedge shape wherein the thickness becomes thinner as becoming distant from the light source are often in use in terms of higher luminance by an effective use of a light and a lighter weight. Thus, the PMMA and PC having a disadvantage in moldability have been coming to face a difficult situation in being used as a thin and wide light guide plate.
In addition to the above, in a wedge shaped light guide plate as above, since a region where the arrangement density of the grooves is increased is a region where the thickness of the plate becomes thinner, the PMMA, etc. are concerned about disadvantages that the plate strength declines due to provision of grooves and deformation while in use as a light guide plate (warps of the plate caused by shrink in the direction to the light emission surface having a small surface) becomes remarkable. There have been demands for a light guide plate material capable of overcoming such size deformation, fulfilling the strength, moldability, high luminance and low luminance spots and attaining to be thin and wide area.
Note that, as disclosed in the Japanese Unexamined Patent Publication 1995-43710, study on making the light guide plate thinner, improving luminance balance on the light emission surface, and reducing the luminance spots along with a luminance line by forming a plurality of grooves of an inversed V shape having projections protruding to outside on both sides of a V-shaped groove. It is also studied to form as one body a pattern of recesses and projections for reflection on the light reflection surface of the light guide plate and recesses and projections for light convergence on the surface of the light guide plate (The Japanese Unexamined Patent Publication 1996-179322).
SUMMARY OF THE INVENTION
An object of the present invention is to provide a light guide plate capable of solving the disadvantages of the related art, being superior in moldability, suppressing hygroscopic deformation little while in use, having sufficient strength, and being made thin and wide, and attaining high luminance and low luminance spots.
The present inventors studied diligently to attain the above objects and found that a light guide plate formed by using a polymeric resin having an alicyclic structure, wherein a reflection surface is formed as a reflection pattern recesses arranged so that the density increases along with the distance from a light source, has preferable moldability, transferability, size stability and strength even in the case of being thin and wide, and able to attain high luminance and low luminance spots, and the present invention was completed.
Namely, a light guide plate of the present invention is comprised of a polymeric resin having an alicyclic structure and has recesses for reflection formed on a light reflecting surface, the recesses being so arranged that the density of the recesses increases with the distance from a light source.
A light guide plate of the present invention is comprised of a polymeric resin having an alicyclic structure comprising recesses for reflection formed on a light reflection surface and projections formed respectively near edges of said recesses.
A light guide plate of the present invention is comprised of a polymeric resin having an alicyclic structure, wherein concave portions and convex portions for light convergence are formed integrally on the light emission surface.
The recesses may be formed for example in dots shape (concaves on a certain part) and may be continuously formed for example in a groove shape (concave on a continuous line). The sectional shape of the recesses may be for example V-shape, U-shape, square shape, etc. among them, the recesses is preferably a groove, more preferably a V-shaped groove. In this case, it is preferable that the V-shaped groove has an angle (&thgr;) of 70° to 150° and a depth (H
1
) of 1 &mgr;m to 1000 &mgr;m.
In the case that the recesses are grooves, the direction of the grooves is not particularly limited, and may be formed to extend in the direction of approximately parallel direction with respect to a direction in which a light is incident, or extend in the direction of approximately vertical direction with respect to the same. It is preferably formed in the approximately vertical direction with respect to a direction in which a light is incident with respect to at any position on the light reflection surface. In this case, a length of the groove is preferably formed over the full width in the direction on the light reflection surface of the light guide plate.
It is preferable that projections formed respectively near edges of said recesses is further provided. And the ratio of the cross sectional areas of the recesses and the projections in this case is preferably 10:1 to 10:10. In the present invention, the cross sectional area of the recesses and the projection is calculated based on the light reflection surface of the light guide plate on which the recesses and projections are not formed. Also, the ratio is a ratio of a cross sectional area of the recess and that of the projection when one projection is formed near the edge of one recess. While, when a plurality of projecti
Ishimaru Issei
Kohara Teiji
Konishi Yuichiro
Maruyama Junko
Minami Koji
Armstrong Westerman & Hattori, LLP
Feild Lynn
Hyeon Hae Moon
Nippon Zeon Co. Ltd.
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