Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-11-23
2004-09-07
Niebling, John (Department: 2812)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S086000
Reexamination Certificate
active
06788368
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a transmittable light-scattering sheet (or film) useful for assuring a high-luminance display of images in a liquid crystal display device (in particular, reflective liquid crystal display device), a method of producing the same, and a reflective liquid crystal display device utilizing the light-scattering sheet.
BACKGROUND ART
The liquid crystal display device (LCD) is utilized broadly in the display segments of personal computers, word processors, LC televisions, chronometers, desktop calculators and other electrical and electronic products. Since the liquid crystal by itself does not emit light, a backlight for illuminating the liquid crystal cell from the back side is used to the exclusion of low-luminance applications such as watches and desktop calculators.
Recent years have witnessed advances in the construction of infrastructures for telecommunications systems such as internets and in the network consolidation of information through the computer-communications equipment integration. By network consolidation, the access to information is freed from restrictions as to time and place. For an efficient utilization of such networks, currently, portable information terminals such as PDA (personal digital assistance) have been developed. Moreover, in lieu of notebook-sized personal computers, further-downsized mobile personal computers of reduced thickness and weight are now under development.
Since portability is required of these portable telecommunications equipment, it is necessary to reconcile the need for a longer battery operating time with the need for reduced thickness and downsizing of communications devices. Therefore, displays for use in such portable telecommunications equipment must be of reduced thickness, reduced weight and low power consumption. Particularly for attaining the low power consumption goal, replacing the conventional liquid crystal display device using a backlight, a reflecting type liquid crystal display device is considered to be most promising as a display for brightening the display screen by exploiting natural light. Further, to keep abreast with the increasing versatility of data accompanying the ever-continuing advances in multimedia, there is a demand for reflecting-mode liquid crystal display apparatus not only capable of color display and high image-quality (high-definition) display in large screen but also of low production cost.
As a reflective liquid crystal display elements constituting the reflecting liquid crystal display device, there is known a variety of elements such as TN (Twisted Nematic) and STN (Super Twisted Nematic) elements, but elements utilizing a polarizer (one polarizing plate type) is preferred for color display and high-definition display. For example, the R-OCB mode in which the liquid crystal layer is of the HAN (hybrid aligned nematic) alignment has excellent characteristics such as low voltage, wider viewing angle, high-speed response, middle color rendition and high contrast.
In order to insure the uniform brightness of the screen as accompanied with getting a display screen of portable equipment larger, the scattering function is an important factor. That is, in the reflective liquid crystal display device, the brightness of the screen is insured in such manner that the light incident on the liquid crystal layer (natural light, ambient light) is efficiently taken in and reflected with a reflector, and the reflected light is scattered to an extent not deteriorating visibility for the prevention of total reflection. When the polarizer and light-scattering sheet are combined, the reflection efficiency can be further improved. Incidentally, as the reflecting plate (reflector), a light-reflecting back electrode system in which an electrode functions as the reflecting plate and a reflecting plate which is disposed on the outside of a support substrate of an electrode can be employed.
For example, concerning reflective liquid crystal display devices, in Japanese Patent Application Laid-Open No. 228887/1988 (JP-63-228887A) and Photofabrication Symposium '92 sponsored by the Japanese Society of Printing, the fundamental technology about liquid crystal display device and the liquid crystal display device given an enlarged viewing angle of the display screen through the prevention of total reflection by means of a surface-corrugated metal thin film as the back electrode (lower electrode) were introduced.
However, when the reflective liquid crystal display device is to be a color display, a color filter is used in addition to the polarizer. In case where a color filter is used, the proportion of loss of reflected light is increased and the above diffusion reflecting plate (scattering plate) system cannot impart enough brightness to the display screen. Particularly, in color display devices, it is important that high luminance is imparted by directed-type scattering in which the scattered light is directed in a given direction. However, in order to enhance the directionality by scattering and reflecting plate system, it is necessary that configuration and distribution of uneven part of the reflecting plate is accurately controlled, and it requires a high cost.
For the purpose of insuring a high luminance by scattering reflected light, there is also known a liquid crystal display device with a transmittable light-scattering sheet in lieu of the diffuse reflecting plate. For example, Japanese Patent Publication No. 8430/1986 (JP-61-8430B) discloses a liquid crystal display device comprising a polarizing layer formed on the front side of a liquid crystal cell and, as formed thereon, a light-scattering layer. Moreover, there is also known a resin sheet polymerized utilizing holography to impart directionality to a transmitting type light-scattering sheet (The synopsis of Lectures at Japanese Society of Liquid Crystal Science, 1998). However, in order to impart directionality to a transmitting type light-scattering sheet by polymerization with utilizing the above holography, complicated method of producing, and as a result, raises the production cost is required.
Meanwhile, known as a light-scattering sheet of low production cost is a particle scattering type sheet comprised of plastic beads and a transparent resin constituting a islands-in-an ocean structure. For example, Japanese Patent Application Laid-Open No. 261171/1995 (JP-7-261171A) discloses a display device having a light-scattering layer externally of a liquid cell, specifically a display device comprising a polarizing film on the outer surface of an electrode plate and, as formed on the surface of the polarizing film, a light-scattering layer comprising a phase separated dispersion of two or more kinds of resins varying in refractive index. Japanese Patent Application Laid-Open No. 27904/1995 (JP-7-27904A) and 113902/1997 (JP-9-113902A) disclose a transmittable liquid crystal display device in which a particulate-scattering sheet having an islands-in-an ocean structure composed of a plastic bead and a transparent resin is disposed between a backlight and a liquid crystal cell. As an example of the display device having a light-scattering layer within the liquid crystal cell, Japanese Patent Application Laid-Open No. 98452/1995 (JP-7-98452A) discloses a display device comprising a transparent resin layer containing a dispersed fine particle (the light scattering layer) between an electrode and a substrate (electrode support substrate) of an electrode plate.
However, in these islands-in-an ocean structure sheets, since the resin beads are dispersed randomly in a transparent resin matrix, the scattering light intensity distributes according to Gaussian distribution in principle. Thus, the directionality can not be imparted to the scattered light, and it is difficult that brightness of the display surface is advanced. Particularly, in respect to the particle dispersed sheet, the brightness of the reflected light from a reflector is increased in the reflective liquid crystal display device having a large display sc
Nakatsuka Shuji
Nishida Yoshiyuki
Omura Masaya
Takahashi Hiroshi
Birch & Stewart Kolasch & Birch, LLP
Daicel Chemical Industries Ltd.
Niebling John
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