Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified... – Alignment layer of specified composition
Reexamination Certificate
1999-06-07
2001-04-24
Thomas, Alexander S. (Department: 1772)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
Alignment layer of specified composition
C428S001200, C428S001270
Reexamination Certificate
active
06221444
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a liquid crystal device used as a display for personal computers, etc.
In recent years, liquid crystal devices have been frequently used, and most of them are TN (twisted nematic)-mode liquid crystal devices using a liquid crystal cell comprising a pair of substrates provided with alignment films having rubbing directions which are deviated from each other by 90 deg. and a nematic liquid crystal disposed between the substrates. There is also known a liquid crystal device wherein a nematic liquid crystal is placed in a splay alignment state between a pair of substrates provided with alignment films having identical rubbing directions. Further, a type of cell (&pgr;-cell) wherein the above-mentioned liquid crystal placed in a splay alignment is re-aligned into a bend alignment by applying a voltage thereto so as to provide an improved response speed, was disclosed by U.S. Pat. No. 4,582,396 to P. J. Bos, et al. Further, a system (OCB cell) wherein such a bend alignment cell is combined with phase compensation to provide an improved viewing angle characteristic was disclosed by Miyashita et al., Preprint for L. C. Forum (1993) 2B13.
In such a bend alignment-type nematic liquid crystal device aims at suppressing a back-flow phenomenon in response of liquid crystal to provide improved and high-speed responsiveness, but has involved several problems for its commercialization.
One of such problems is that an electric field treatment is required for transforming the splay alignment into the bend alignment. The splay-bend alignment transformation is not continuous, and a disclination line is present between the two alignment states, so that a process including nucleation and its growth is necessary. In such a process, it is difficult to cause nucleation in all the regions and the control of the nucleation threshold is difficult, so that a high voltage application is required for the electric field treatment. Further, the velocity of growth of the bend alignment regions formed by the nucleation is larger at a higher voltage application, and a time of several seconds to several minutes is required at a low voltage. Another problem is that, in an actual matrix-structured cell, the bend region does not readily grow between pixel electrodes. Several studies have been made regarding manners of voltage application in active matrix-type cells using TFTs (thin film transistors) (e.g., IBM, IDW 1996, p. 133, Initialization of Optically Compensated Bend-mode LCDs”, and Japanese Laid-Open Patent Application (JP-A) 9-185032). A further problem is that the bend alignment is restored to splay alignment if the bending voltage is removed, so that a bending treatment is required anew for re-use.
A type of cell (&pgr;-cell) having a pretilt angle of 50-51 deg. was disclosed by P. J. Bos, et al., at SID in 1998, as a cell not requiring a bending treatment before use. A bend alignment cell having a large pretilt angle from the initial stage of cell formation was also disclosed by a group of Kogakuin University at Japan 5th Liquid Crystal Forum in 1979 (Preprint, page 166-) and also in JP-A 55-142316.
However, as means for providing such high pretilt angles are very unstable except for oblique evaporation, satisfactory realization has been unsuccessful. Further, at least one time of voltage application has been required after the injection of a liquid crystal into a liquid crystal cell.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a liquid crystal device utilizing a bend alignment, which requires no electric field treatment for transforming splay alignment into bend alignment, no additional bending treatment for re-use, or no holding voltage for bend alignment.
Another object of the present invention is to provide a cell structure capable of providing stable bend alignment, realizing bend alignment from an initial stage after liquid crystal injection, or unnecessitating a bending treatment from splay alignment.
According to the present invention, there is provided a liquid crystal device, comprising: a pair of substrates each having thereon an electrode and an alignment film, and a nematic liquid crystal disposed between the substrates,
wherein said alignment film is provided with an alignment power of aligning liquid crystal molecules of the nematic liquid crystal in a bend alignment state under no voltage application and providing a retardation R (nm) of the liquid crystal device under application of a prescribed voltage relative to a refractive index anisotropy &Dgr;n of the liquid crystal and a cell thickness d (nm) of the liquid crystal device, providing a retardation factor R/&Dgr;n·d of at most 0.3.
In the liquid crystal device according to the present invention, the liquid crystal can assume a stable bend alignment from an initial stage immediately after the injection of the liquid crystal into the cell, so that it becomes unnecessary to apply an electric field treatment for the bending or a holding voltage for retaining the bend alignment.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
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Mizutani Hidemasa
Munakata Hirohide
Okada Shinjiro
Sato Koichi
Tsuboyama Akira
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Thomas Alexander S.
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