Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-01-19
2003-10-14
Chowdhury, Tarifur (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S112000, C349S062000, C359S619000
Reexamination Certificate
active
06633351
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical sheet that has a function of improving a directivity of light rays—that is, an optical functionality sheet composed of a microlens array and a reflective film or light-blocking film—and a planar light source, and liquid crystal display apparatus using this sheet.
Recently, image display apparatuses, of which liquid crystal display panels are representative examples, have come into wide general use as display means for personal computers, workstations, and so forth. In terms of the quality of the images displayed using such display apparatuses, the characteristics demanded are high brightness and high display contrast, together with a wide angle of visibility.
In order to realize the above described image quality, an installation of a light-diffusing plate between a liquid crystal display panel and a back light source has been disclosed in JP-A-6-95099 specification. Also, a method has been disclosed for enlarging an angle of visibility by installing a sheet that has a microlens array and a light-blocking layer on a liquid crystal image display surface.
Moreover, in JP-A-10-39769 specification, a screen that coordinates array patterns of microlenses and light-blocking film has been disclosed as the screen of a rear-projection type projection apparatus.
When the above described wide-angle-of-visibility sheet is used in a liquid crystal display apparatus, characteristics required of the light source are high directivity and nearly collimated light rays (parallel light rays). The reason for this is that, if the light rays were not parallel, the rays would not be converged sufficiently by the microlenses, and would be projected onto areas where the light should be blocked. This would cause light loss and reduce the brightness of the image display apparatus.
General planar light sources (backlights) for the above described use employ various kinds of diffusion plates that diffuse light beams randomly, in order to achieve uniformity of brightness of the light emitting surface, and the beams emitted from this light emitting surface do not have directivity.
Furthermore, a so-called louver sheet, comprising many rows of light-blocking walls aligned with the direction of travel of the beams, is known as a light source that has directivity. By means of a louver sheet, it is possible to obtain a planar light source that has arbitrary directivity, by taking emitted light with a spread of 120 degrees or more in an emitting surface, for example, and cutting off beams traveling in other than the required direction by means of light-blocking walls. However, this sheet has low light usage efficiency, and is not suitable for the image display apparatus which is an objective of the present invention.
As another method, a method has been disclosed whereby a prism sheet arrayed with a large number of minute triangular prisms is placed on the surface of a photoconductive plate. This is achieved by controlling to some extent the direction of emission of the beams. This prism sheet enables directivity of the order of ±30 degrees to be obtained, but does not meet the requirements of the image display apparatus which is an objective of the present invention.
A light ray directivity sheet that eliminates the above described problems, has high light directivity and light usage efficiency, is moreover of thin shape, and enables a uniform planar light source to be obtained, and a directional planar light source using this, have been disclosed in JP-A-9-1675133 specification and JP-A-10-241434 specification.
This method consists of a light ray directivity sheet, one surface of which comprises a group of microlenses in which unit lenses are arrayed, and on the other surface of which a light ray blocking film (reflective film) is formed, wherein, at least, areas in the vicinity of the focal points of light rays entering from the microlens group side of the above described light ray blocking film are made apertures. By positioning the surface of this light ray directivity sheet on which the light ray blocking film is formed on the light source side, and positioning the microlens surface on the viewing side (liquid crystal display element side), a planar light source is obtained that is given directivity by the operation of the microlenses.
SUMMARY OF THE INVENTION
By using a planar light source fitted with the above described light ray directivity sheet using microlenses, and an angle of visibility enlargement sheet using similar microlenses, it is possible to realize an image display apparatus with high brightness and a wide field of view.
However, with any sheet, there are many problems that need to be solved in the actual construction process.
First of all, there are major limitations in the construction of an angle of visibility enlargement sheet. That is to say, when a microlens array and a light-blocking layer (black matrix) for suppressing the re-reflection of external light reflected by the surface of this microlens array are combined, it is essential for the layout patterns of the microlenses and light-blocking layer to be precisely positioned relative to each other, since a slight misalignment will halve their function.
Known common methods for forming a light-blocking layer include forming as a thin metal film, and a method whereby a photosensitive resin film, in which a pigment such as carbon black has been dispersed or in which a black or other dye has been dissolved, is formed on a substrate, and is patterned by means of photolithography
However, if the light-blocking layer and the microlenses are formed by totally independent processes, and the two are combined later, it can be said that it is difficult to align the two accurately within several &mgr;m. When the size of the microlenses is very small (several tens of &mgr;m), in particular, accurate alignment is extremely difficult.
On the other hand, as a solution to the problems relating to an angle of visibility enlargement sheet, sensitization of a photosensitive layer by energy ray irradiation via optical elements (for example, a microlens array) corresponding to a black matrix pattern, and forming a black matrix of the desired pattern, has been disclosed in JP-A-10-246804 specification.
As the microlenses and the transparent parts of the light-blocking layer are formed by means of self-alignment, an advantage of this method is that it is easy to coordinate the respective pattern positions precisely, but the following problem arises in realizing this.
Namely, with the above described method, from the viewpoint of the work processes, a positive-type resist is generally used whereby the parts irradiated with energy rays are sensitized and become soluble in a solvent. However, in order for the light-blocking layer to be formed simultaneously by this method, the use of a non-transparent material containing carbon black, or a black dye or pigment, etc., in the above described resist is assumed. Therefore, the transmittivity of the energy rays, and especially the light rays used for pattern forming, is decreased, and it is difficult to obtain a prescribed pattern.
Therefore, the problem arises of it being necessary to spend a long time on energy ray irradiation, or to make the resist film thin, in order to compensate for the fact that the photo-transmittivity is low. Thus, the exposure process is time-consuming, and it is difficult to obtain a light-blocking film with a high optical density (high light-blocking capability).
Another method is one in which, after a layer constituting the light-blocking layer has been formed using a negative-type resist, the light-blocking layer is patterned by means of photolithography. However, the problem with this method is that the work processes are even more complex, making it impractical.
On the other hand, the same kind of problems as described above also arise with regard to a light ray directivity sheet using microlenses. That is to say, the array patterns of the microlenses and the light-blocking layer must be accurately aligned
Ariyoshi Toshihiko
Hira Yasuo
Chowdhury Tarifur
Nguyen Hoan
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