Optical waveguides – Noncyclindrical or nonplanar shaped waveguide
Reexamination Certificate
1999-01-29
2001-07-10
Ngo, Hung N. (Department: 2874)
Optical waveguides
Noncyclindrical or nonplanar shaped waveguide
C385S901000, C362S035000
Reexamination Certificate
active
06259854
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a lightguide for a surface light source for use in a liquid crystal display and the like. The present inventive lightguide may be used effectively as a back illuminator of a liquid crystal display of a word-processor, a personal computer, a thin television set and the like.
BACKGROUND OF THE INVENTION
A surface light source device fitted with a so-called edge-light type lightguide arranged so as to illuminate by inputting light from a side end plane of a transparent plate and by emitting the light from the other plane thereof (light emitting surface) is used as a back illuminator of a liquid crystal display of a word-processor, a personal computer, a thin television set and the like. Such surface light source device is constructed such that a tubular light source is disposed at one side end plane, two side end planes perpendicular to each other or two side end planes opposing to each other of the lightguide in general and the remaining planes of the lightguide, except of the incident side end plane and the light emitting surface, and the back side of the tubular light source are covered by a light reflector.
In order to emit primary light inputted from the side end plane of the lightguide uniformly and efficiently from the whole light emitting surface of the lightguide, it is necessary to arrange the lightguide such that its scattering-reflecting capability is low around a light source and its light diffusing-reflecting capability is high at the region farthest from the light source and to distribute the light such that the most of the inputted primary light is emitted from the emitting surface in scattering and reflecting the light guided to the lightguide in the direction perpendicular to its traveling direction. Then, a variety of principles and processing methods for giving such scattering and reflecting capability have been proposed as described below and part of them have been put into practical use.
(1) Those Characterized Mainly by Rough Surface:
There are ones in which the whole light emitting surface or the surface facing thereto is roughened (See JP-A-3-118593, JP-A-118248, etc.), in which the roughness of the rough surface is changed (See JP-A-63-168604, etc.) or in which speckled or linear rough surface patterns are disposed and formed by changing its a real density (See JP-A-4-162002). The surface is roughened by sand-blasting or chemically etching a die and the surface rough patterns are formed by combining photo-etching and sand-blasting (See JP-A-4-52286).
(2) Those in Which Scattering Reflector is Applied:
Those in which a scattering-reflecting substance containing white paint or particles is applied in a meshed dot or linear pattern on the rear surface facing to the light emitting surface by means of screen printing or the like (See JP-A-57-12838, JP-A-1-245220, etc.). Its manufacturing process includes two steps of forming a specular plate having no pattern and of printing the patterns.
(3) Those Characterized Mainly by Diffusion of Bulk:
There have been disclosed ones in which lightguide bulk resin itself is adopted as a light diffusing-scattering substance by mixing light scattering particles, by blending non-compatible polymer or by co-polymerization (See JP-A-1-172801, JP-A-2-221924, JP-A-5-249319, JP-A-6-186560, etc.).
(4) Those Caused by Protruding or Concave Patterns:
These are divided roughly into the following three types. These are fabricated by machining a lightguide itself or a molding die by machine cutting, laser processing, die etching or the like.
1) Concave Patterns:
There are ones in which concave patterns are disposed on a light emitting surface or on a surface facing thereto on the datum plane. There are, for example, ones having one-dimensional linear triangle grooves (See JP-A-2-165504, JP-A-6-3526), rectangular grooves (See JP-A-6-123810, JP-A-6-265731, etc.), semi-circular grooves (See JP-A-5-79537U), broken-line shaped triangular grooves (See JP-A-5-196936, JP-A-5-216030, etc.) and others. There are also those having two-dimensional conical or pyramid engraving (See JP-A-4-278922), semispherical engraving (See JP-A-6-289393, etc.) and cylindrical engraving (See JP-A-1-145902U). There have been also proposed one in which the inner surface of a concave portion of the pattern is roughened (See JP-A-4-355408, JP-A-5-94802U, etc.).
2) Protruding Patterns:
There are ones in which protruding patterns are disposed on a light emitting surface or on a surface facing thereto on the datum plane. There are, for example, ones having one-dimensional linear triangle protrusions (See JP-A-5-313163, JP-A-6-75123), rectangular protrusions (See JP-A-5-79537U) and semi-circular protrusions (See JP-A-6-281928). There is also one having two-dimensional semispherical protrusions (See JP-A-5-79537U, JP-A-6-281929, etc.). There are also ones in which those protruding parts are roughened (See JP-A-5-94802U, JP-A-6-186562, etc.).
3) Concave and Protruding Patterns:
There are ones which have no flat plane on a light emitting surface or on a surface facing thereto and in which one-dimensional saw-tooth patterns or two-dimensional grid patterns are disposed. There are, for example, ones having the one-dimensional saw-tooth patterns (See JP-A-64-11203, JP-A-6-250024, etc.) and the two-dimensional grid patterns (See JP-A-62-278505, JP-A-3-189679, etc.) and ones whose surface is roughened as a whole (See JP-A-6-342159, JP-A-6-123885, etc.).
In addition to the demands on high luminance and high uniformity ratio of illuminance of the past, the demand on a large screen, thin-type, light-weight and low power consumption display is growing more and more lately. The trend is now shifting from a plate-like lightguide which has been put into practical use mainly by the printed patterns of (2) of the past to a tapered (wedge) type lightguide which is thinner and lighter. Then, the pattern printing step which has been required in the technology of (2) described above has become unnecessary and injection molding which allows scattering reflection patterns to be formed in the same time is considered to be desirable in terms of the cost.
From this aspect, the above-mentioned methods (1) through (4) have had the following various problems, respectively.
Although those having the uniform rough surface by the method (1) can be mass-produced by injection molding by using a die, it has had problems that the die is complicated because the die must be formed into a complicated curved wedge shape such that region where primary light enters is fully thickened and the region distant from the light source is thinned in order to attain uniform luminance as a surface light source, the degree of freedom of the shape of the lightguide is restricted and there is a limitation in increasing the area and thinning of the lightguide in principle. Further, although there has been a proposal of changing the surface roughness, it is very difficult to realize that. Meanwhile, although the method of distributing the rough surface as speckle or linear patterns is a relatively excellent method which allows the shape of the lightguide to be freely formed and the luminance to be uniformed in the pattern design, it is risky because of unstable elements in the die fabrication process such as variation between accuracy of photo-etching in forming the patterns and the surface roughening process such as blast in the next step in creating the die.
Although the printing method (2) has been the method put into the practical use most for the conventional plate type lightguides, it has had a problem, as a first problem, that it does not have a merit in terms of the cost as compared to the method of forming patterns in the same time by injection molding because the pattern printing step is a separate step. Further, it has had a problem that the pitch of dots of the scattering reflection patterns cannot be made smaller than around 1 mm (see JP-A-5-100118) due to the limit of the printing accuracy (see JP-A-4-289822). Further, due to this problem of the printing accuracy,
Kunisawa Toshitaka
Shinji Osamu
Yasuda Kozo
Yoshikawa Toshiyuki
Kuraray Co. Ltd.
Ngo Hung N.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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