Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2000-07-18
2001-11-06
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S440000, C564S443000
Reexamination Certificate
active
06313348
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to materials for aligning liquid crystals, and liquid crystal optical elements.
Current liquid crystal display elements include a product that utilize a twisted nematic mode, i.e. having a structure wherein the aligning direction of nematic liquid crystal molecules is twisted by 90° between a pair of upper and lower electrode substrates, a product utilizing a supertwisted nematic mode, utilizing a birefringent effect, i.e. having a structure wherein the aligning direction of nematic liquid crystal molecules is twisted by 180° to 300° an in-plane-switching mode wherein both electrodes controlling the liquid crystal alignment are present on one substrate and the direction of the liquid crystal orientation in the plane of the substrate changes upon application of an electric field, and a product utilizing a ferroelectric liquid crystal substance or an antiferroelectric liquid crystal substance. Common to each of these products is a liquid crystal layer disposed between a pair of substrates coated with a polymeric alignment layer. The polymeric alignment layer controls the direction of alignment of the liquid crystal medium in the absence of an electric field. Usually the direction of alignment of the liquid crystal medium is established in a mechanical buffing process wherein the polymer layer is buffed with a cloth or other fiberous material. The liquid crystal medium contacting the buffed surface typically aligns parallel to the mechanical buffing direction. Alternatively, an alignment layer comprising anisotropically absorbing molecules can be exposed to polarized light to align a liquid crystal medium as disclosed in U.S. Pat. Nos. 5,032,009 and 4,974,941 “Process of Aligning and Realigning Liquid Crystal Media” which are hereby incorporated by reference.
The process for aligning liquid crystal media with polarized light can be a noncontact method of alignment that has the potential to reduce dust and static charge buildup on alignment layers. Other advantages of the optical alignment process include high resolution control of alignment direction and high quality of alignment.
Requirements of optical alignment layers for liquid crystal displays include low energy threshold for alignment, transparency to visible light (no color), good dielectric properties and voltage holding ratios, long-term thermal and optical stability and in many applications a controlled uniform pre-tilt angle. Most liquid crystal devices, including displays, have a finite pre-tilt angle, controlled, for instance, by the mechanical buffing of selected polymeric alignment layers. The liquid crystal molecules in contact with such a layer aligns parallel to the buffing direction, but is not exactly parallel to the substrate. The liquid crystal molecules are slightly tilted from the substrate, for instance by about 2-15 degrees. For optimum performance in most display applications a finite and uniform pre-tilt angle of the liquid crystal is desirable.
Continuing effort has been directed to the development of processes and compositions for optical alignment of liquid crystals and liquid crystal displays. Through diligent effort and intensive experiments we have found that the alignment quality and electrical properties, specifically the voltage holding ratio, of polyimide alignment layers derived from polyamic acids containing the novel crosslinking diamines disclosed herein are significantly improved over those lacking such crosslinking capability.
SUMMARY OF INVENTION
The present invention provides a polyamic acid for inducing alignment of a liquid crystal medium adjacent to a surface of an optical alignment layer comprising a polyamic acid of structure I
wherein R
1
is selected from the group of C
3
-C
20
linear or branched chain alkyl groups containing 1 to 4 sites of unsaturation; X is a divalent moiety selected from the group —O—, —S—and —NR—, wherein R is selected from H, R
1
, and C
1
-C
4
hydrocarbon chain; X
1
is independently selected from the group H, Cl, F, and Br; m is 1 or 0; Z is selected from the group —S—, —O—, —SO
2
—, —CH
2
—, —C(CF
3
)
2
—, —C(O)—, —CH
2
CH
2
—, —NR
2
— and a covalent bond wherein R
2
is selected from H and C
1
-C
4
hydrocarbon chain; and the carboxylic acid groups are ortho to the amide linkages.
REFERENCES:
patent: 4974941 (1990-12-01), Gibbons et al.
patent: 5276132 (1994-01-01), Nishikawa et al.
patent: 5731405 (1998-03-01), Gibbons et al.
patent: 6066696 (2000-05-01), Yu et al.
patent: 9915576 (1999-04-01), None
Database CAPLUS on STN, Acc. No. 1994:484187, Furuya et al., ‘Diaminophenyl propargyl or allyl ethers and their manufacture.’ JP 05331116 A2 (abstract), 1994.
Gibbons Wayne M.
Shannon Paul Joseph
Zheng Hanxing
Davis Brian J.
Richter Johann
Shannon Paul J.
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