Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-04-26
2004-05-11
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S156000
Reexamination Certificate
active
06734944
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display, and more specifically, to a spacer for a liquid crystal display.
BACKGROUND OF THE INVENTION
A liquid crystal cell of a liquid crystal display is formed by sealing a liquid crystal between 2 substrates. The thickness of this sealed liquid crystal layer, that is, a space between the substrates, is called a cell gap. Display unevenness is caused by partial thickness differentials of the liquid crystal layer when cell gaps are not uniform. Accordingly, spherical spacers called pearl spacers and the like or cylindrical spacers are used for providing uniform cell gaps between the substrates.
Since spacers are not fixed to substrates, but they are dispersed between two substrates, variations in the distribution (density) of spacers may result. As a result, small cell gaps where the spacers are less densely distributed may cause display unevenness. Further, it is not desirable that screen flickering can be observed when watching liquid crystal cells on a large screen on the whole. Furthermore, although these spacers are invisible, they cause a problem that the spacers are in shadow when they are on the surface of the pixels, for example, in a case where the pixels represent black, and a black contrast sharply deteriorates due to the appearance of the spacers as white dots on the screen.
Therefore, various techniques for forming pillar-like spacers in predetermined positions by using a photosensitive resin have been suggested to improve the conventional method for manufacturing a liquid crystal display with spherical spacers dispersed. However, all of these techniques have some problems and none of them has been actually used.
For example, the Japanese Laid-Open Patent Publication No. 54-12066 discloses a method for regulating a cell gap by scattering lots of first spacers formed of materials having a high melting point and by adding second spacer portions formed of materials having a relatively low melting point on the first spacers to fuse the second spacer portions with opposing panels. In this method, two kinds of spacers made of different materials are used, and each of them serves as a spacer and an adhesive to the opposing panel as well, but this method requires double deposition, which has turned out to be no good from both aspects of the cost and the productivity.
Further, the Japanese Laid-Open Patent Publication No. 60-164723 discloses a method for providing cell gaps by forming pillars made of electrical insulator on a liquid crystal driving element. Furthermore, the Japanese Laid-Open Patent Publication No. 56-25777 discloses a method for forming a cell gap by providing a spacer function to a portion where a semiconductor is provided. Since these methods are for further forming pillars on a thin film transistor (TFT) having protrusions on it or the like, the level differences of a foundation and positioning accuracy, which exerts an effect on the formation of gaps, made it difficult to form uniform cell gaps.
Further, the Japanese Laid-Open Patent Publication No. 56-38008 discloses a method for forming cell gaps by providing a plurality of spacer materials on an image non-display portion of pixels, which are thicker than semiconductor driving elements. The spacer materials disclosed in this patent publication are highly hard inorganic matters such as metallic oxide, and in addition, a plurality of spacers per pixel are arranged in a liquid crystal display. For this reason, especially, in the case of a cell of 10 inches or more, the spacer having too high strength on the whole causes low-temperature bubbles. Specifically, when a liquid crystal display manufactured at room temperature is cooled down to an extreme low temperature during transportation or the like, cavities (vacuum babble) are created inside the cell gaps because spacers in cell gaps do not shrink, even if the liquid crystals shrink. Because of this problem, this display cell is not suitable for a practical use.
Moreover, the Japanese Laid-Open Patent Publication No. 7-281195 discloses that about 5 &mgr;m-cell gaps are achieved by forming 2 to 3 &mgr;m of plural multi-layered second protrusion parts on the side of the color filter substrate (CF), forming 2 to 3 &mgr;m of plural first protrusion parts on the side of an array substrate by using a pigment dispersion resist, and then superimposing one substrate on another with their protrusions facing each other. In this method, desired cell gaps can be obtained according to the height of the protrusion parts of both array and CF-type substrates. However, the optical density gets higher because the first protrusion parts on the array substrate side also serve as a black matrix (BM). When a photosensitive pigment dispersion resin is used, there is an upper limit of height due to the use of a photo process. On the other hand, since the color filter of the CF laminate on the CF substrate side gets thinner, the second protrusion parts of the CF substrate side have an upper limit to their film thickness and there is also a limit to uniformity of heights obtained by the laminate.
An object of the present invention is to solve problems of unstable positioning of spherical spacers, etc. Another object of the present invention is to provide a liquid crystal display which can inhibit the generation of low-temperature bubbles and serve as a spacer formed of photosensitive resin materials which are resistive to local load.
SUMMARY OF THE INVENTION
As a result of intensive studies to achieve these objects, the inventors have attained this invention. In the liquid crystal display according to the present invention, since spacers, which regulate cell gaps between the first and the second substrates facing each other, are formed on a predetermined position except a non-display region, or a pixel surface by using photosensitive resin, the spacers do not get behind the pixels. As a result, especially a black contrast can be improved. In addition, since a density of the spacers is substantially constant, uniform cell gaps can be provided, so that unevenness and flickering of the liquid crystal screen from both microcosmic and macrocosmic points of view. In the liquid crystal display of the present invention, characteristics and forms of spacers are set within a predetermined range. Therefore, spacers are shrinked when the liquid crystal display is cooled to a low temperature to shrink liquid crystals and then both substrates are bent convexly in an inward direction, so that no vacuum portions or low temperature bubbles are generated inside the cell gaps. Spacers can be elastically deformed when the liquid crystal screen is locally pressed by a finger or the like, and plastic deformation appears on the spacers when the liquid crystal screen is further strongly pressed. However, in the liquid crystal display of the present invention, the dimensions of the spacers can return to approximately original dimensions and the spaces between the cell gaps in the pressed portion can recover to constant spaces by preventing the spacer from being easily crashed by the pushing pressure and minimizing the residual distortion in plastic hysteresis when the pressing force is released.
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Hasumi Taro
Johnai Tomohito
Koseki Toshihiko
Momoi Yuichi
Shohmitsu Yoshinori
Dougherty Anne V.
Parker Kenneth
Trepp Robert M.
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