JPS59142526A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To use a film substrate which is weak at a high temperature, and also to obtain a liquid crystal display element having a steep gamma characteristic by using as an oriented film a polyimide-polyamide acid coexistent film which is burned at 140 deg.C+ or -5 deg.C about 30min and whose imidized ring closure reaction advances by 50%. CONSTITUTION:Deflecting plates 3, 4 are stuck to the outside surface of a pair of substrates 1, 2 made of glass or plastic, and transparent conductive films 5, 6 and oriented films 7, 8 are formed on the inside surface. A liquid crystal 11 is packed between the films 7, 8 and seal parts 9, 10. The films 7, 8 are constituted of a polyimide-polyamide acid coexistent film whose imidized ring closure reaction advances by about 50% by being burned at a temperature of a range of 140 deg.C+ or - 5 deg.C about 30min. Accordingly, the film substrate 1, 2 which are weak at a high temperature are used, and as for the coexistent film, its R is 10<3> order and small, and even if the impedance drops due to impurities in the liquid crystal, the contrast does not drop. Also, the coexistent film can obtained a steep gamma characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a liquid crystal display element comprising an alignment film made of an organic material.

Description of the Prior Art Conventionally, polyimide films have been used as alignment films for liquid crystal display elements. The polyimide film is obtained, for example, by baking a polyamic acid consisting of bi-D-mellitic anhydride and 4,4-diaminodiphenyl ether at a temperature of 280°C to 310°C for about 30 minutes to 2 hours ti+. Ta. That is, a polyamic acid represented by the structural formula 1 was subjected to an imidization ring-closing reaction of almost 100% to obtain a ballimide film represented by the structural formula (2).

Incidentally, the firing of the polyamic acid is performed after the polyamic acid is applied to the substrate of the liquid crystal display element. Therefore, it cannot be used in a liquid crystal display device using a substrate made of a material that cannot withstand high temperatures of 280° C. to 310° C.

Therefore, it has the disadvantage that it is difficult to use it in film cell type liquid crystal display elements using plastic substrates, which have been attracting attention in recent years.

Further, a complete polyimide group that has undergone 100% imidization ring-closing reaction exhibits a resistance characteristic of the order of 10M.

Therefore, when the resistance value of the liquid crystal (usually on the order of 10 B) is reduced by ionic impurities present in the liquid crystal, the resistance value of the alignment film and the resistance value of the liquid crystal become approximately the same. Therefore, the ratio of the voltage effect due to the alignment film becomes large, resulting in an increase in the threshold voltage Vat and a disadvantage in that the contrast decreases. This drawback was noticeable in highly polar liquid crystals such as metadioxic acid liquid crystals used in 1°5 volt liquid crystal display elements.

Liquid crystals with high polarity are difficult to purify, so
This is because it is thought that there are relatively many ionic impurities.

Furthermore, in conventional alignment films, it is known that the Pre-Tllt angle of the liquid crystal is relatively large (26 or more), and therefore, it is not suitable for high-duty liquid crystal display elements that require steep γ characteristics. It also had the disadvantage of being unsuitable. “Object of the invention Therefore, the object of the invention is to overcome the above-mentioned disadvantages and to
It is an object of the present invention to provide a liquid crystal display element that can use a film substrate, effectively prevents a decrease in contrast due to impurities in the liquid crystal, and has steep γ characteristics.

In summary, the present invention is capable of reducing the imidization ring-closing reaction by firing at a temperature in the range of 140°C ± 5°C for about 30 minutes.
This is a liquid crystal display element in which a polyimide-polyamic acid coexisting film with about 0% progress is used as an alignment film.

Other objects and features of the invention will become more apparent from the following description of the embodiments.

The explanatory drawing of the embodiment is a side sectional view showing a mulberry-type liquid crystal display element to which the present invention can be used. On the outer surface of a pair of substrates 1.2 made of glass or plastic, respectively,
Deflection plates 3 and 4 are attached. On the other hand, Moto! ? 1.2
A transparent conductive IM5.6 is formed on the inner surface. The conductive films 5 and 6 are for applying voltage to the liquid crystal. Furthermore, an alignment film 7.8 is formed on the inner surface of the substrate 1.2 together with the conductive films 5 and 6. Liquid crystal 11 is filled between this orientation m7.8 and seal portion 9.10. The feature of this example is that the orientation IM7.8 is 140°C.
The film is composed of a polyimide-polyamic acid coexistence film in which the imidization ring-closing reaction has progressed by about 50% by firing at a temperature in the range of ±5° C. for about 30 minutes. The rest of the structure is the same as that of a known liquid crystal display element, so a description thereof will be omitted.

As described above, the oriented IM 7.8 is formed by applying the material constituting the alignment film onto the substrate 1.2 and then firing it. The firing conditions of 140° C.±5° C. are based on experiments at various temperatures.

The table shows experimental results at various firing conditions.

As is clear from the table, when fired at a temperature in the range of 140° C.±5° C., it is possible to realize adhesion of the alignment film to the substrate, prevention of contrast deterioration phenomenon, and steep γ characteristics.

Effects of the Invention As described above, according to the present invention, since the alignment film is formed by adjusting the temperature in the range of 140°C ± 5°C, it can be applied not only to glass substrates but also to high humidity substrates. It becomes possible to realize a liquid crystal display element using a film substrate that is susceptible to damage. Moreover, the polyimide obtained by this invention
The resistance value of the polyamic acid coexisting film is on the order of 10 3 , which is relatively small, so even if the impedance of the liquid crystal decreases due to impurities in the liquid crystal, no contrast reduction phenomenon occurs. This is also considered to be based on the fact that impurities in the liquid crystal are trapped in the openings of the polyamic acid (see Structural Formula I above), thereby preventing a drop in liquid crystal impedance. In this way, clear contrast can be obtained despite the drop in impedance of the liquid crystal, making it possible to realize a liquid crystal display element using a highly polar liquid crystal such as metadioxic acid liquid crystal. Therefore, a liquid crystal display element for 1.5 volts can be realized using six liquid crystals with thick polarity. Furthermore, since the polyimide-polyamic acid coexisting film of the present invention has a small pre-tilt angle of about 1° to 5°,
It is possible to obtain a steep γ characteristic, and therefore it is also possible to obtain a high-duty liquid crystal display element.

[Brief explanation of the drawing]

The drawing is a side sectional view showing a typical liquid crystal display element to which the present invention is applied. In the figure, 7 and 8 indicate alignment films. (2 others)

Claims (1)

[Claims] In a liquid crystal display element comprising an organic alignment film, the organic alignment film is a polyimide-polyamic acid coexisting film in which the imidization ring-closing reaction has progressed to about 50% by baking the organic alignment film at a temperature in the range of 140°C ± 5°C for about 30 minutes. A liquid crystal display element characterized by: