Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified... – With viewing layer of specified composition
Reexamination Certificate
2002-04-10
2004-11-16
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
With viewing layer of specified composition
C252S299010, C252S299500, C349S106000, C430S007000
Reexamination Certificate
active
06818261
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal composition, a color filter produced using the liquid crystal composition, and a display device including the color filter.
2. Description of the Related Art
Applications of color filters are increasingly extending such as to include mobile information terminals, personal computers, word processors, amusement machines, televisions, and the like, as well as display panels used in various electric and electronic apparatuses.
These apparatuses are conventionally provided with liquid crystal display devices. Advantages of a liquid crystal display device are that electric power consumption thereof is small and that it is thin. The liquid crystal display devices are generally divided into two groups: transmission display devices including a backlight light source and frontlight reflection display devices which do not include a light source or use an optical waveguide on the entire surface thereof. For a full-color display, usually a color filter is used. For example, a color filter used in a color liquid crystal display, and the like, generally includes red (R), green (G) and blue (B) pixels, and a black matrix formed therebetween for improving display contrast.
Majority of this type of color filters has conventionally been produced using pigment dispersion or staining. The pigment dispersion involves dispersing pigments in a photoresist, coating the photoresist on a glass substrate, and then exposing a pattern and developing. This method is excellent in patterning edge, resolution, evenness of film, and the like. However, this method has problems such that it requires a photoresist process, and that, since pigments are used, adjustment of colors is not as easy as when dyes are used. In addition, when the photoresist is applied on the substrate using spin coating, there will be a large loss of materials, and unevenness of the coating will be large when the area of the substrate is large. In the staining, a transparent resin pattern provided with photosensitivity is stained later onto a gelatin, or the like. Advantages of this method is that it produces a color filter which has a high light transmittance because of transparency of dyes, and that adjustment of colors are easy because there are wide variety of types of dyes. However, the method also has drawbacks such that the number of required steps such as a photoresist step is larger than that for the pigment dispersion.
Other known methods for producing a color filter include printing, electrodeposition, ink jet, and the like. The printing has drawbacks such that, since it prints patterns of respective colors one by one, registration of the patterns is difficult, and that, because of low pixel resolution and uneven film thickness of the resulting color filter, it is difficult to use the color filter produced by the printing method to form a highly detailed image pattern. While, an advantage of the printing method is that it uses materials efficiently. The electrodeposition can provide a color filter which has a relatively high resolution and low unevenness in colored layers, however, it has difficulties such that production steps thereof are complicated and handling of fluids is difficult. The ink jet method has had problems regarding resolution, and that colors of mutually adjacent pixels may be mixed.
The color filters (produced by the methods) described above are light-absorbing color filters, which, in theory, can transmit only one third of the light from the light source, and therefore do not have sufficient brightness. In order to compensate this drawback, for example, in the case of a transmission display device, it can be considered to increase brightness of the backlight. However, this will lead to an increase in power consumption, and will impair the advantage of the liquid crystal display device.
In order to solve these problems, U.S. Pat. No. 00/5,668,614 and WO 00/34,808 have proposed color filters employing a cholesteric polarizer, which do not require a liquid development step. The cholesteric polarizer selectively reflects circularly polarized light having predetermined wavelengths and transmits circularly polarized light having the other wavelengths. Therefore, different from the above-described color filters made of colored resins, the color filter comprising the cholesteric polarizer can reuse the once transmitted light to improve light efficiency, thereby forming a substantially bright color filter. Therefore, this type of color filter is suitable for use in a reflection liquid crystal display. Further, since the production of the color filter comprising the cholesteric polarizer does not require a developing step, and patterns having different selective reflection wavelengths can be formed in a single layer, it is also preferable in view of production costs.
As a method for forming this type of color filter which utilizes the selective reflection by the cholesteric liquid crystal layer, the applicant of this patent application has made a patent application on a method for forming a color filter layer, wherein ink comprising a polymerizing liquid crystal compound is deposited by ink jet (Japanese Patent Application No. 11-343666).
Further, the applicant has made patent application on method for forming color filter, wherein the color filter is formed by irradiating light onto a layer comprising a polymerizing liquid crystal compound and a photo-reactive chiral agent having a certain structure (Japanese Patent Application Laid-Open Nos. 2002-080851 ,2002-080478, and the like). The photo-reactive chiral agent includes chiral sites and sites whose structures change when exposed to light. Since a helical twisting power (HTP) of the liquid crystal is largely altered depending, for example, on an amount of irradiated light, selective reflection over a wide wavelength range including the three primary colors: blue (B), green (G) and red (R) can be accomplished.
When a color filter is produced as described above, first, a solution containing the polymerizing liquid crystal compound and the photo-reactive chiral agent and/or a polymerizing monomer, and the like, dissolved in an organic solvent is coated on a glass substrate. However, it has been found that, if the solution is coated in this state, the resulting color filter will have various minute defects including protrusions, white dots in a colored area, black dots on a white background (black defect), deposition of foreign substances, and the like. The major cause of these defects is existence of very minute foreign substances in the solution. It has been found that, if the foreign substances, although very minute, exist in the solution, they interfere orientation of the liquid crystal layer during production of the color filter over wide areas surrounding the foreign substances, and this leads to the above-described defects. Since quality requirements for color filters are becoming increasingly severe, it is desired to eliminate these defects and to produce high quality color filters.
Another problem is a limit in contents of the liquid crystal compound in the solution, because the polymerizing liquid crystal compound does not easily dissolve in organic solvents. Therefore, a viscosity of the solution is low, and this solution cannot form an even and thick layer.
In order to solve this problem, it is considerable to add a small amount of polymer into the solution. However, the added polymer interferes the orientation of the liquid crystal, and therefore it is impossible to produce a high performance color filter in this approach.
Japanese Patent Application Laid-Open (JP-A) No. 2000-154168 discloses a cross-linking liquid crystal composition which comprises a particular macromolecular acrylic photoisomerizing chiral compound and a liquid crystal polymer, which composition can be coated in a solution state. A viscosity of this composition can be adjusted by changing a ratio of a solvent, however, the composition has a drawback that reorientation of the liquid cr
Fuji Photo Film Co. , Ltd.
Sughrue & Mion, PLLC
Wu Shean C.
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