Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Patent
1993-01-12
1995-04-18
Acquah, Samuel A.
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
528176, 528193, 528194, 528271, 528272, 264319, 359 78, 359 79, 359100, H02H 326
Patent
active
054083478
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INDUSTRIAL UTILITY
The present invention relates to a liquid-crystal display device carrying alignment films that have a high capability for aligning the molecules of a liquid crystal. More particularly, the present invention relates to a liquid-crystal display device having high contrast and quality that uses a wholly aromatic polyester as the material of alignment films.
PRIOR ART
Conventional liquid-crystal alignment films are produced by a process that comprises the steps of forming a thin film of a polymer such as polyimide, polyvinyl alcohol or polyamide by a suitable method such as spin-coating, printing or dipping, curing the thin film and rubbing the cured film in one direction with a cloth or by some other suitable means. The thus produced alignment films have the ability to line up the molecules of a liquid crystal in one direction. Among the polymers mentioned above, polyvinyl alcohol is not used commercially because of its low resistance to heat and moisture. Polyimide and polyamide are commercially used in general because these polymers satisfy the following conditions: carrying alignment films can be heat-sealed together; crystal to be used;
However, polyimide and polyamide have their own disadvantages as materials for alignment films. To produce polyimide films, however, polyamic acid is usually coated as a solution on a substrate and then heated to carry out a cyclizing reaction, but during heating, the applied film can develop a color to impair the appearance of the final device or the lightfastness of the alignment film. Furthermore, in order to perform a cyclizing reaction, heating to a temperature of at least 250.degree. C. is necessary but then, plastic substrates or color filters can potentially deteriorate. In addition, polyimide usually does not have good adhesion to glass substrates and the common practice to deal with this problem has been to improve the adhesion to the substrate by using a silane coupling agent or a silane-containing diamine compound as described in Japanese Patent Publication (Kokai) No. 72924/1983. However, the use of a silane coupling agent suffers from the problem of low solution stability whereas the use of a silane-containing diamine compound is not economical since it involves the separate synthesis of a monomer. Polyamide also has the poor adhesion problem and has suffered from similar problems to polyimide. Attempts have also been made to use liquid-crystal polymers as materials for alignment films (Japanese Patent Publication (Kokai) Nos. 42818/1988 and 164922/1989). However, the polyester-based liquid-crystal polymers described in those laid-open patents have little solubility in common solvents and hence are not suitable for practical use.
SUMMARY OF THE INVENTION
An object, therefore, of the present invention is to provide a new alignment film having enhanced capability for aligning the molecules of a liquid crystal.
Another object of the present invention is to provide a liquid-crystal display device of high contrast and quality using the new alignment film.
The present invention has been accomplished on the basis of the following two findings: a polyester having the composition specified below and being soluble in common solvents has a high capability for aligning the molecules of a liquid crystal; and the polyester also has good adhesion to substrates.
The liquid-crystal display device of the present invention is characterized by using an alignment film that is formed of an aromatic polyester that comprises: ##STR3## a recurring unit II which is a dioxyaryl represented by the following formula: contain at least one substituent selected from the group consisting of a C.sub.1-4 alkyl group, a C.sub.1-4 alkoxy group, a halogen, a phenyl and a substituted phenyl); and formula: ##STR4## (where Ar' has the same meaning as Ar and may be the same as or different from Ar).
The liquid-crystal display device of the present invention uses as an alignment film a polyester comprising at least the three recurring units defined above. The polyest
REFERENCES:
patent: 3884876 (1975-05-01), Cottis et al.
patent: 4377681 (1983-03-01), Deex
patent: 4796979 (1989-01-01), Tsuboyama
B. Bahadur (ed.), Liquid Crystals, World Scientific Publishing Co., pp. 183-185 (1990).
Patent Abstracts of Japan vol. 12 No. 194 (P-713) [3041] Jun. 7, 1988.
Harada Takamasa
Murakami Mikio
Acquah Samuel A.
Hoechst Aktiengesellschaft
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