Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-12-21
2003-06-17
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S112000
Reexamination Certificate
active
06580483
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to reflection-type liquid crystal display devices, and provides those which are made bright and highly visible by arranging therein a cholesteric liquid crystal film having specific optical parameters.
Liquid crystal displays have widened the range of their practical application from displays for pocket- or desk-top-calculators to those for word processors and personal computers, due to their remarkably improved displaying performance. Furthermore, the liquid crystal displays have been expected to widen their markets as displays for portable information terminal devices where the displays can make the best use of their peculiar characteristics, i.e., thin in size and light in weight. When used for portable devices, the liquid crystal displays are usually battery-driven and thus are required to reduce the electricity consumption. Therefore, reflection-type liquid crystal displays, which can dispense with an electricity-consuming back light, particularly those having a reflection plate with high contrast and high display quality level have attracted a great deal of attention because they make it possible to reduce the electricity consumption, width, and weight.
The reflection-type liquid crystal displays with no back light can display the information with the light coming from the user such as an indoor-lighting or a sun light, and thus are required to be enhanced in brightness. In recent years, there have been developed various techniques in order to solve the problems, for which instance, the loss of light is restrained by decreasing the number of polarizers, the number of which normally used is two, to one, the incident light is focused by providing microscopic structures on the reflector surface, a mirror reflector is combined with a diffuser film, and a reflection hologram with a focusing function is used.
However, the methods of reducing the number of polarizers and using the mirror reflector in combination with the diffuser film can enhance the brightness to some extent but are not sufficient, while the methods of providing microscopic structures on the reflector surface and using the reflection hologram have problems in increased production cost and decreased productivity, compared with cases using the conventional reflectors.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to solve the foregoing problems. The present invention was achieved based on the finding that the use of a cholesteric liquid crystal film with specific optical parameters can easily produce a reflection-type liquid crystal display device with a high visibility at low cost.
According to a first aspect of the present invention, there is provided a reflection-type liquid crystal display device comprising a liquid crystal cell where a liquid crystal layer is provided between two opposed electrode substrates, a reflecting layer, and a cholesteric liquid crystal film wherein the ratio (SCE/SCI) of the specular component excluded-reflectance (SCE) to the specular component included-reflectance (SCI) of the cholesteric liquid crystal film is 15% or more, the wavelength bandwidth of the cholesteric selective reflection ranges from 30 nm to 150 nm, and the center wavelength of the cholesteric selective reflection is in the visible range of 380 to 780 nm or in the near-infrared range of 800 to 2000 nm.
According to a second aspect of the present invention, there is provided the reflection-type liquid crystal display device according to the first aspect of the invention wherein the cholesteric liquid crystal film is so orientated that the helical axes are not homogeneously parallel with each other in the direction of the thickness.
According to a third aspect of the present invention, there is provided the reflection-type liquid crystal display device according to the first aspect of the invention wherein the cholesteric liquid crystal film has on a part thereof a region exhibiting a diffractivity.
According to a forth aspect of the present invention, there is provided the reflection-type liquid crystal display device according to the third aspect of the invention wherein the cholesteric liquid crystal film has an orientation in which the helical axes are not homogeneously parallel with each other in the direction of the thickness and the helical pitch lengths are not homogeneously equal in the direction of the thickness.
According to a fifth aspect of the present invention, there is provided the reflection-type liquid crystal display device according to the first through forth aspects of the invention further comprising one or more polarizers.
According to a sixth aspect of the present invention, there is provided the reflection-type liquid crystal display device according to the first through fifth aspects of the invention further comprising one or more optical compensation layers.
DETAILED DESCRIPTION OF THE INVENTION
The reflection-type liquid crystal display device of the present invention comprises a liquid crystal cell where a liquid crystal layer is formed between two opposing electric substrates, a reflection layer, and a specific cholesteric liquid crystal film.
No particular limitation is imposed on the electric substrate as long as the purpose of the invention can be achieved. There may be used known electric substrates for controlling a liquid crystal material exhibiting a liquid crystallinity when it displays.
The liquid crystal layer may be formed by filling and disposing a material exhibiting a liquid crystallinity between the electric substrates. No particular limitation is imposed on the material exhibiting liquid crystallinity. There may be used various monomeric liquid crystals and polymeric liquid crystals which have usually been used as liquid crystal materials constituting various liquid crystal cells, and mixtures thereof. Dyes and chiral agents may be added to the material.
Other than the above-described electric substrates and the material exhibiting a liquid crystallinity, the liquid crystal cell may contain various components which are required to make the cell work in various modes of liquid crystal cell described hereinafter.
No particular limitation is imposed on the mode of a liquid crystal cell. For example, there may be exemplified GH (Guest Host) mode, TN (Twisted Nematic) mode, STN (Super Twisted Nematic) mode, ECB (Electrically Controlled Birefringence) mode, IPS (In-Plane Switching) mode, VA (Vertical Alignment) mode, OCB (Optically Compensated Birefringence) mode, HAN (Hybrid Aligned Nematic) mode, halftone gray scale mode, domain dividing mode, and display modes using a ferrodielectric liquid crystal and an antiferrodielectric liquid crystal.
No particular limitation is imposed on the mode of driving the liquid crystal cell. Therefore, it may be simple matrix mode used in STN-LCD, active matrix mode using active electrodes such as TFT (Thin Film Transistor) electrodes, MIM (Metal Insulator Metal) electrodes and TFD (Thin Film Diode) electrodes, and plasma address mode.
No particular limitation is imposed on the reflection layer arranged in the reflection-type liquid crystal display device as long as it has a sufficiently high reflectivity. For example, the reflection layer may be a metal such as aluminum, silver, gold, chromium, and platinum, an oxide such as magnesium oxide, a laminate of films of dielectrics, a liquid crystal film exhibiting a selective reflectivity, and combinations thereof. These reflection layers may be flat or curved and may have a function as the electrode on the electrode substrate located on the side opposite to the viewing side. The reflection layer may not be only ones which do not transmit but reflect light but also semi-transmissive ones which transmit part of light.
No particular limitation is imposed on the location of the reflection layer in the reflection-type liquid crystal display device as long as it is arranged on the side opposite to the viewing side of the liquid crystal layer.
The cholesteric liquid crystal film of the reflection-type liquid crystal display dev
Komatsu Shin-ichi
Nishimura Suzushi
Suzuki Shinichiro
Akin Gump Strauss Hauer & Feld L.L.P.
Akkapeddi P. R.
Nippon Mitsubishi Oil Corporation
Ton Toan
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