Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-11-04
2003-11-18
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06650393
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based on Japanese Patent Application No. 10-320959 filed on Nov. 11, 1998, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal light modulating device using a liquid crystal material interposed between a pair of substrates, and a method for manufacturing same.
2. Description of Related Art
Conventional light modulating devices are widely known which interpose a liquid crystal material between two substrates and use the liquid crystal material as a light shutter. This type of light modulating device is used, for example, as a display device. This type of display device is used as a display in various devices, foremostly, for example, in notebook style personal computer displays and portable telephone displays. Liquid crystal display devices characteristically are thin in design and have low power consumption, and are widely used in portable devices having a small surface area. In recent years, however, such displays have been developed for large screen displays used in built-in in-wall televisions and as replacements for CRT monitors.
Maintaining a uniform gap between substrates has become more important in conjunction with achieving higher quality and larger surface area liquid crystals. Heretofore, it has been difficult to regulate sufficient uniformity of the inter substrate gap within a light modulation range, with resultant disadvantages including display defects which make it difficult to achieve high quality displays. Management of the flatness of the inter substrate gap is directly concerning with a parameter which defines the display quality particularly in liquid crystal display devices using ferrodielectric liquid crystals, and reflective type liquid crystal display devices using liquid crystals which exhibits a cholesteric phase (i.e., chiral nematic liquid crystals). In ferrodielectric liquid crystals, irregularities in the inter substrate gap cause irregularities in the orientation of the liquid crystals which reduces the display quality. When driving an element which has a memory such as cholesteric liquid crystals, the display irregularities become pronounced due to the reduced threshold characteristics.
Art related to controlling the inter substrate gap is known, e.g., U.S. Pat. No. 4,249,800. This United States patent discloses a liquid crystal display which uses glass beads coated with a thermoplastic resin as spacers. Specifically, the glass beads are dispersed in a photosensitive lacquer, and applied on a substrate, then the glass beads are arranged on the substrate by a so-called photolithographic method which includes masked light exposure and developing.
In the method described in this United States patent, first, manufacturing or preparation of the resin-coated glass beads which requires a labor is necessary. Furthermore, a large amount of the spacers are wastefully removed from the substrate during the photolithographic method. In addition, productivity is low due to the extreme complexity of the various processes such as the required developing process. Since only part of the surface coating layer of the spacers comes into contact with the substrate, adequate adhesion cannot be obtained. Since the spacers themselves are small it is difficult to accurately arrange these spacers at optional positions, essentially making it difficult to eliminate display irregularities.
U.S. Pat. No. 5,285,304 discloses a ferroelectric liquid crystal display in which two substrates, on which adhesive thermosetting polymer particles and nonadhesive thermoplastic polymer particles having a diameter approximately 1.5~5 times the thickness of the liquid crystal layer are dispersed, are pressed each other. Japanese Laid-Open Patent Application No. 8-110524 discloses a method wherein a gap control member which is not deformable even when heated and a gap control member supplying adhesive force to both substrates when hardened after being melted or softened by heating are applied on substrates, and the latter gap controller adheres to both substrates when melted or heated above the softening temperature.
In the methods disclosed in the aforesaid two publications, it is essentially impossible to arrange the gap controller or polymer particles adhering to the substrate at a desired position because, the polymer particles or gap controller are arranged dispersion. Accordingly, when dispersing these materials, the polymer particles or gap controllers easily start to flocculate. As a result, the locations of such flocculation readily produce defects in the orientation of the liquid crystal, and produce regions where light is unmodulated such that a display of sufficiently high quality cannot be obtained.
In contrast, Japanese Laid-Open Patent Application No. 9-258233 proposes a liquid crystal display device wherein spacers are adhered to a pair of substrates by an ultraviolet-curing resin. The arrangement of the spacers on the substrates is accomplished by a silkscreen printing method wherein the spacers are mixed in an ultraviolet-curing resin beforehand. Thereafter, the opposite substrate is overlaid and the ultraviolet-curing resin is hardened by exposure to ultraviolet light. However, sufficient adhesion force is not obtained even when both substrates are adhered inasmuch as the cross section area of the spacers is too small. Furthermore, in general, ultraviolet-curing resin is soft when in an uncured state, such that when the two substrates are overlaid, even a slight dislocation of the substrates may move the oriented spacers and the ultraviolet-curing resin. At this time the ultraviolet-curing resin broadens the interface between the liquid crystal and the substrates so as to cause orientation defects of the liquid crystal in the regions of the broadened ultraviolet-curing resin.
Japanese Laid-Open Patent Application No. 62-203123 discloses a liquid crystal display device using high polymer resin dams continuously arrayed in a matrix across the entire surface of a transparent flexible substrate rather than the particle-like spacers of the conventional art. The purpose of forming resin dams described in this publication is to adhere the resin dams to as long flexible substrate, and cut them to an optional size. According to this publication, an adhesion force is generated between the substrates and the resin damns under light pressure; specifically, an example is given wherein the resin dams are formed by an offset printing method using ultraviolet-curing resin, or photolithographic method using a photoresist, and adhered to the substrates under light pressure at approximately 80° C.
Even when the resin dams are formed in a matrix pattern, for example, it is difficult to realize an accurate inter substrate gap only by the resin dams. In the aforesaid example, since the formed resin structure itself comprises UV-curing resin, sufficient adhesion is not achieved by light pressure on the substrates at approximately 80° C. Accordingly, there is high concern of inter substrate gap fluctuation due to rapid temperature change or external pressure, which will disadvantageously prevent proper light modulation by the liquid crystal layer.
From the perspective of imparting adhesion to the resin structure, a method is proposed wherein the resin structure is formed which is in contact with a pair of substrates using a photopolymerizable material. For example, U.S. Pat. No. 5,473,450 discloses a liquid crystal display device wherein a resin wall is formed by photopolymerization phase separation using a photomask. U.S. Pat. No. 5,682,218 discloses resin columns formed by separating the liquid crystal and uncured resin by cooling a mixture of liquid crystal in isotropic phase and resin (monomer), and thereafter heating or UV-curing the uncured resin.
In methods using photopolymerizable materials, uncured monomer and polymerization initiator may remain within the liquid crystal even after polymerization, thereby disadvantageously af
Dudek James
Minolta Co. , Ltd.
Sidley Austin Brown & Wood LLP
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