Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1998-01-15
1999-10-19
Nutter, Nathan M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525425, 525428, 525430, 2522994, G02F 11337, G02F 113, C09K 1956
Patent
active
059690550
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a liquid crystal alignment agent. More specifically, the present invention relates to a liquid crystal alignment agent which can give a liquid crystal alignment film having good liquid crystal alignability and can provide a liquid crystal display device with a high pretilt angle and excellent stuck image-free properties.
BACKGROUND ART
There have heretofore been known TN type liquid crystal display devices having a TN (twisted nematic) type liquid crystal cell which comprises two substrates each having, on the surface, a liquid crystal alignment film via a transparent electroconductive film and a nematic liquid crystal layer having a positive dielectric anisotropy, the nematic liquid crystal layer being interposed between the two substrates so as to form a sandwich structure, in which liquid crystal cell the major axes of liquid crystal molecules are continuously twisted by 90.degree. in the direction extending from one of the substrates to the other substrate. The alignment of liquid crystal in the TN type liquid crystal devices is made generally by a liquid crystal alignment film imparted with an alignability for liquid crystal molecules by a rubbing treatment. As the material for the liquid crystal alignment film, there are hitherto known resins such as polyimide, polyamide, polyester and the like. Polyimides, in particular, are used in many liquid crystal display devices because of the excellency in heat resistance, compatibility with liquid crystal, mechanical strengths, etc.
When a TN type liquid crystal display device is produced using a liquid crystal alignment film formed of conventionally used polyimide or the like, however, the liquid crystal display device has problems in that it gives defective display due to its low pretilt angle or an image sticking is caused owing to its a large residual voltage. Hence, it has been desired to develop a liquid crystal alignment agent capable of giving a liquid crystal display device which has a liquid crystal alignment film of good liquid crystal alignability and a high pretilt angle and is excellent in low image retention properties.
DISCLOSURE OF THE INVENTION
The present invention has been completed in view of the above situation. The first object of the present invention is to provide a liquid crystal alignment agent capable of giving a liquid crystal alignment film superior in liquid crystal alignability.
The second object of the present invention is to provide a liquid crystal alignment agent capable of providing a high pretilt angle.
The third object of the present invention is to provide a liquid crystal alignment agent giving a liquid crystal alignment film for a liquid crystal display device having excellent image retention properties.
The other objects and advantages of the present invention will become apparent from the following description.
The above-mentioned objects and advantages of the present invention can be achieved by a liquid crystal alignment agent containing at least two kinds of polymers selected from the group consisting of polyamic acids and imidized polymers having a structure obtained by dehydration and ring closure of polyamic acid, wherein in the at least two kinds of polymers contained in the liquid crystal alignment agent, the polymer of higher imidization degree has a smaller surface free energy.
The liquid crystal alignment agent of the invention may further contain an epoxy compound as an additive. In this case, it is preferable that the at least two kinds of the polymers have an average imidization degree of 5 to 40%. The liquid crystal alignment agent containing an epoxy compound possesses an effect of giving an excellent long-term stability to the resulting liquid crystal display device.
The present invention is hereinafter described in detail.
Each polymer used in the liquid crystal alignment agent of the present invention can be obtained by reacting at least one tetracarboxylic acid dianhydride and at least one diamine compound both mentioned below in an organic
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patent: 5478682 (1995-12-01), Nishikawa et al.
patent: 5612450 (1997-03-01), Mizushima et al.
patent: 5698135 (1997-12-01), Nishikawa et al.
patent: 5700860 (1997-12-01), Nishikawa et al.
Kawamura Shigeo
Matsuki Yasuo
Nishikawa Michinori
Toyoshima Tsukasa
Wakabayashi Kengo
JSR Corporation
Nutter Nathan M.
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