Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Reexamination Certificate
2000-06-19
2003-09-16
Gupta, Yogendra N. (Department: 1751)
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
C252S299010, C252S299680, 48, 48, 48, 48, 48, 48
Reexamination Certificate
active
06620339
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polyimide aligning film which excels in electrical properties and reliability for the field of electronic materials, in particular for a liquid crystal aligning film; to a polyamic acid composition for providing such an aligning film; and to a liquid crystal display element produced from such an aligning film.
BACKGROUND ART
The present mainstream of liquid crystal display elements is that utilizing nemetic liquid crystals. Liquid crystal display elements presently in practical use include a matrix TN element twisted by 90°, an STN element usually twisted by 180° or more, and a TFT liquid crystal display element utilizing thin film transistors. In addition to these, IPS (In Plane Switching) mode having improved viewing angle properties has been developed. The progress of liquid crystal display elements is not limited to only these modes, but active efforts to improve peripheral materials have been made toward improvement of the properties of liquid crystal display elements.
With the wider use of liquid crystal display elements in various fields, liquid crystal display elements having improved properties have been demanded. Such demands include better display performance and higher reliability in long-time use. In particular, important factors for TFT liquid crystal display elements are electrical properties, especially the voltage holding ratio and the residual voltage. If the voltage holding ratio is low, the voltage applied to liquid crystals during the field period lowers, causing the problem of lowered contrast. Therefore, a higher voltage holding ratio is desired, and ideally, the voltage holding ratio should be 100%.
On the other hand, if the residual voltage is large, it will remain even after the electric field has been turned off after being once turned on. In such a case, images to be erased will remain as residual images. Therefore, it is desired that the residual voltage approach zero infinitesimally. This residual image phenomenon is one of the most important issues in liquid crystal display elements.
Another problem in liquid crystal display element is an increase in the electric current of the display element occurring during long-term use. The increase in the electric current lowers the voltage applied to the liquid crystal itself and raises liquid crystal molecules insufficiently, thus lowering contrast, and in some cases failing to display images.
Furthermore, in manufacturing processes for liquid crystal display elements, the stability of properties of the display elements is an important factor to achieve process margin. For example, if the pre-tilt angle of liquid crystals changes significantly with solvent evaporation conditions after coating of an alignment material, with imidizing (normally heating) conditions of a polyamic acid, or with annealing conditions after injection of liquid crystals, elements having a stable pre-tilt angle cannot be manufactured unless the process conditions are strictly controlled for each process.
When TFT elements were first marketed, the pre-tilt angle of liquid crystals for a TFT element was required to be nearly 0 degrees. In recent years, however, liquid crystals have been required to have some pre-tilt angle (3 to 12 degrees) in order to inhibit the occurrence of domains.
An object of the present invention is to provide a liquid crystal aligning film for producing a liquid display element having a pre-tilt angle required for TFT display elements, small manufacturing process dependence of the pre-tilt angle, little residual voltage of the liquid crystal display element, and high voltage holding ratio, as well as high reliability.
The prior art for producing an element having a small residual voltage and a high voltage holding ratio suited for TFT display elements is disclosed in, for example, Japanese Patent Application Laid-open No. 8-106097. In this reference, a tetracarboxylic dianhydride having aromatic groups, aliphatic groups, or a combination of aromatic and aliphatic groups is used as a tetracarboxylic acid component, and a diamine having ether groups is used as a main diamine component, but a large effect cannot be obtained. The pre-tilt angle is as small as 1.3 to 3.6 degrees.
In Japanese Patent Application Laid-open No. 7-120768 is disclosed an alignment material containing a polyamic acid having an aliphatic tetracarboxylic dianhydride as its essential component and a polyamic acid having an aromatic tetracarboxylic dianhydride as its essential component. Although this reference describes that siloxane-based diamines have particularly excellent properties, experiments conducted by the present inventors show that the residual voltage is small but alignment is poor. Also, no diamine components that increase the tilt angle are described.
DISCLOSURE OF INVENTION
The inventors of the present invention conducted repeated examinations for solving the above problems, and found that the above object was achieved by a polyimide film used as a polymer component of a liquid crystal aligning film used in liquid crystal elements, which film is formed by heat-curing a polyamic acid composition comprising a polyamic acid that provides a polyimide resin giving a small residual voltage and a high voltage holding ratio, and a polyamic acid that provides a polyimide resin giving a large pre-tilt angle.
According to a first aspect of the present invention, there is provided a polyamic acid composition comprising a polyamic acid providing a polyimide resin giving a small residual voltage and a high voltage holding ratio, and a polyamic acid providing a polyimide resin giving a large pre-tilt angle, the ratio (weight ratio) of the former to the latter being 50/50 to 95/5.
According to a second aspect of the present invention, there is provided a polyamic acid composition comprising a polyamic acid A and a polyamic acid B, wherein the essential acid component of the polyamic acid A is an alicyclic tetracarboxylic dianhydride, the diamine component of the polyamic acid A is a diamine having at least one of the aromatic diamines represented by the following formula (1), the acid component of the polyamic acid B contains 50 mole % or more aromatic tetracarboxylic dianhydride, and the essential diamine component of the polyamic acid B is a diamine having a group enabling the pre-tilt angle of a liquid crystal to be increased on the side chain thereof, the ratio A/B of the polyamic acid A to the polyamic acid B being 50/50 to 95/5 (by weight).
where, X is a divalent aliphatic group, each R is independently a hydrogen atom or CH
3
, and a and b are 1 or 2.
According to a third aspect of the present invention, there is provided a polyamic acid composition according to the second aspect, wherein the acid component of the polyamic acid A comprises an alicyclic tetracarboxylic dianhydride and an aromatic tetracarboxylic dianhydride.
According to a fourth aspect of the present invention, there is provided a polyamic acid composition according to the second aspect, wherein the diamine component of the polyamic acid B comprises at least one diamine having a group enabling the pre-tilt angle of a liquid crystal to be increased on the side chain thereof, and a diamine represented by the formula (1).
According to a fifth aspect of the present invention, there is provided a polyamic acid composition according to the second aspect, wherein the essential diamine component of the polyamic acid B comprises at least one of the diamines represented by the following formulas (2) and (3).
where R is a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, Y is a CH
2
group, m is an integer from 0 to 2, A is a benzene ring or a cyclohexane ring, p is 0 or 1, z is an oxygen atom or a CH
2
group, and n is 0 or 1.
where, X1 is a CH
2
group or an oxygen atom, each of R1 and R2 are individually a hydrogen atom, an alkyl group or a perfluoroalkyl group having 1 to 12 carbon atoms; at least one of R1 and R2 being an alkyl group or a perfluoroalkyl group having 3 or more carbon atoms; and n1 is 0 or 1.
Hara Kumiko
Kato Haruo
Murata Shizuo
Shimizu Itsuo
Tanioka Satoshi
Chisso Corporation
Gupta Yogendra N.
Hamlin Derrick G.
McDermott & Will & Emery
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