Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-06-25
2001-06-26
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S187000, C428S001400
Reexamination Certificate
active
06252642
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique of optical alignment and more particularly a technique for aligning a polymer film, a method for aligning a liquid crystal with a controllable pretilt angle by using the polymer aligned-film and a liquid crystal display(LCD) employing the above techniques.
2. Related Art
A flat panel display is an important device in a television having a small size and a large scale screen and a portable terminal. Specially, an LCD is widely used as information display device in view of low addressing voltage, high contrast ratio, cheap cost, high reliability to the solar light and good interface to an integrated circuit.
So as to manufacture the LCD having an uniform brightness and high contrast ratio, the liquid crystal inserted between a pair of substrates in the LCD should be arranged in one direction. Generally, alignment films are formed on the opposite surfaces of a upper substrate and a lower substrate, thereby aligning the liquid crystal in one direction.
A general method for aligning the liquid crystal molecules is a surface treatment, specifically rubbing. A polyimide resin is coated on a surface of the substrate and then rubbed with a fabric, thereby forming a straight groove. The liquid crystal is aligned along the groove.
However, since rubbing is performed after forming the polyimide on the glass substrate having a color filter or a thin film transistor(TFT) array, the color filter or the TFT array beneath the substrate can be subjected to mechanical or electrical damage. Accordingly, reproduction of the process is not good. Also, the LCD manufactured by the rubbing method has a narrow viewing angle. In order to solve the narrow viewing angle, there is a technique for forming multi-domain. The process for forming the multi-domain using the rubbing method is complicated.
In the LCD, by using the rubbing method, it is not easy to control a pretilt angle of the liquid crystal which is an important factor for the response time and the contrast ratio of the LCD. Therefore, recently, a method for adjusting the pretilt angle, without rubbing, has been actively studied.
SUMMARY OF THE INVENTION
Accordingly, an aim of the present invention is to optically align a polymer without a rubbing method.
Another aim of the present invention is to control a pretilt angle of a liquid crystal without the rubbing method.
Still another aim of the present invention is to provide a method for optically aligning an alignment film having a good reproduction.
In order to realize a spirit of the present invention, a liquid crystal display has a first substrate, a second substrate opposite the first substrate, a high molecular thin film including an azo-dye and formed on an opposite surface of the first substrate, an alignment film formed on an opposite surface of the second substrate, and a liquid crystal layer formed between the polymer film and the alignment film. Here, the polymer film is a polyvinyl alcohol including a methyl orange as azo-dye.
Referring to a method for forming the above mentioned polymer film as an alignment film, first, a substrate is provided. The polymer film including azo-dye is formed on the substrate. A pump beam having a predetermined polarization state is applied to the polymer film, thereby modifying an arrangement of molecules of the polymer. The polymer film is a polyvinyl alcohol including a methyl orange as azo-dye. The predetermined polarization state is one of a circular polarization, an ellipse polarization and a linear polarization. As to the arrangement of the polymer film, a number of the polymer film arranged in a first direction parallel to a propagation direction of the pump beam and a number of the polymer film arranged in a second direction perpendicular to the propagation direction of the pump beam are controlled according to an intensity scale of electric fields of major axis and minor axis of the pump beam. That is, as a ratio of the electric field scale of the major axis to that of the minor axis approaches 1, the number of the polymer film arranged in the first direction is exponetially increased. Also, as a ratio of the electric field scale of the major axis and that of the minor axis approaches 1, the number of the polymer film arranged in the second direction is exponetially decreased. Further, a birefringence of the polymer film is exponentially increased as a ratio of the electric field scale of the major axis and that of the minor axis approaches 1.
Referring to a method for aligning a liquid crystal with an easily controllable pretilt angle, first, a first substrate and a second substrate opposite the first substrate are provided. The polymer film including azo-dye is formed on an opposite surface of the first substrate. A pump beam having a predetermined polarization state is applied to the polymer film, modifying an arrangement of molecules of the polymer film. A liquid crystal layer is formed between the first substrate and the second substrate. Here, the polymer film is a polyvinyl alcohol including a methyl orange as azo-dye. The predetermined polarization state is one of a circular polarization, an ellipse polarization and a linear polarization. A pretilt angle in a liquid crystal of the liquid crystal layer is controlled according to the polarization state of the pump beam. In detail, a pretilt angle in a liquid crystal is exponentially increased as a ratio of the electric field scale of the major axis and that of the minor axis approaches 1. Also, a pretilt angle in a liquid crystal of the liquid crystal layer is exponentially increased as the molecular number of the polymer arranged in the first direction is increased. Further, a pretilt angle in a liquid crystal of the liquid crystal layer is exponentially decreased as the molecular number of the polymer arranged in the second direction is increased. A pretilt angle in a liquid crystal of the liquid crystal layer is increased as a birefringence of the polymer film is increased.
As described above, the arrangement of molecules of the polymer is controlled and a pretilt angle of molecules of the liquid crystal is easily adjusted, by using polyvinyl alcohol as the polymer including methyl orange as azo-dye.
REFERENCES:
patent: 5032009 (1991-07-01), Gibbons et al.
patent: 5438421 (1995-08-01), Sugawara et al.
patent: 5731405 (1998-03-01), Gibbons et al.
patent: 5889571 (1999-03-01), Kim et al.
patent: 6294959 (1994-10-01), None
Choi Sang Un
Kim Tae Kwon
Hyundai Electronics Industries Co,. Ltd.
Selitto Behr & Kim
Ton Toan
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