JPH02223918A - Formation of oriented film - Google Patents

Abstract

PURPOSE:To optimize the angle with a substrate in correspondence to the kind of a liquid crystal and the helix angle of the liquid crystal and to improve the contrast of a liquid crystal display body to an optimum state by applying a soln. prepd. by dissolving specific two kinds of polyamide acids on the substrate with transparent electrodes, then subjecting the coating to drying, calcining and rubbing treatments. CONSTITUTION:The soln. contg. the polyamide acid having the constitutional formula expressed by formula I and the polyamide acid which is the precursor of the polyimide oriented film having a low angle, preferably <=5 deg. angle with the substrate is applied on the substrate and thereafter, the coating is subjected to the drying and calcining, then to the rubbing. In the formula I, n denotes a positive integer; R denotes hydrogen or alkyl group. Since the oriented film consists of a polyimide resin, the film has the excellent heat resistance which is the characteristic of the polyimide. The angle of the liquid crystal molecules with the substrate can be changed as desired from 0 to 5 deg. up to 22 deg. by changing the mixing ratio of the polyamide acid of the two components and the need for preparing orienting agents to meet with the kind, helix angle, etc., of the liquid crystal is eliminated. Dealing with all cases is possible in this way by preparing two kinds of the polyamide acid.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an alignment film for a liquid crystal cell for a liquid crystal display.

[Conventional technology]

In recent years, the development of liquid crystal display technology has been remarkable, and it has become possible to apply it to liquid crystal televisions and the like. As shown in Fig. 1, this liquid crystal display consists of a substrate (11) with two transparent electrodes (12) and a liquid crystal (
14) and an alignment film (13).

In the case of active matrix drive used in LCD televisions, the pixels are driven independently, so there was no problem with conventional alignment technology. However, in this case, there is a drawback that the yield is low and the cost is high.

On the other hand, the simple matrix drive method is considered to be an alternative to the active method because it may be cheaper.

These alternative technologies are called SBE method, NTN method, etc.

The important point of this technology is that the liquid crystal molecules in conventional liquid crystal displays are twisted at 90 degrees, but are twisted at more than 180 degrees.

For this reason, it is necessary to make the liquid crystal molecules tilt at an angle of 5 degrees or more with respect to the substrate to release distortion caused by excessive twisting. One of the methods to make the angle 5 degrees or more is to use an alignment film.

The conventional method for creating an alignment film that twists liquid crystal molecules by 180 degrees or more is to apply a single-component polyimide resin.

[Problem to be solved by the invention]

In order to achieve the best contrast in a liquid crystal display, the angle between the liquid crystal molecules and the substrate must be optimized depending on the type of liquid crystal, the twist angle of the liquid crystal, etc.

However, since a single component was used, it was not possible to arbitrarily change the angle with the substrate.

Furthermore, even if attempts were made to change the angle by using multiple components, it was impossible to widely change the angle because there was no single component that could significantly change the angle with the substrate.

[Means for Solving the Problems] The present invention was made to improve the above-mentioned drawbacks of conventional alignment films. The method is characterized by applying a solution containing polyamic acid, which is a precursor of a polyimide alignment film, preferably at a temperature of 5 degrees or less, followed by drying and baking, and then rubbing.

(However, n represents a positive integer, and R represents hydrogen or an alkyl group.) The following compounds can be considered as polyamic acids that are precursors of polyimide alignment films that form a low angle with the substrate.

lh (wherein n indicates a positive integer) Such polyamic acid compounds can be made by reacting tetracarboxylic acid anhydride and diamine compounds as raw materials, and various other raw materials can be considered in addition to the raw materials for the above compounds. .

For example, the tetracarboxylic anhydride is hexafluoropropylidene cyphthalic anhydride, biphenyltetracarboxylic anhydride, and the diamine compound is m-phenylenediamine, M, (Mikata Petrochemical), B15
-P (manufactured by Mikata Petrochemical) and various other options are possible.

As for drying, firing conditions, rubbing conditions, etc., conventional conditions for producing a polyimide alignment film can be applied as they are.

Coating methods (2) Although spin-coding, dipping, casting, brushing, and other methods are all possible, the spin-coding method is superior.

[For production]

According to the method for producing an alignment film of the present invention, since the alignment film is made of polyimide resin, it has excellent heat resistance, which is a characteristic of polyamic acid.

The angle of the liquid crystal molecules with respect to the substrate can be changed from several degrees (0 to 5 degrees) to 2 degrees by changing the mixing ratio of the two components of polyamic acid.
You can freely change it up to 2 times.

There is almost additivity between the angle between the liquid crystal molecules and the substrate achieved by mixing and the angle achieved by the two components before mixing.

Hereinafter, the present invention will be explained in detail with reference to Examples.

[Example 1] A 10 weight percent N-methylpyrrolidone solution was prepared by mixing two types of polyamic acids having the following structural formulas in the proportions shown in Table 1, and was used as alignment agent 1-5.

Note that the numerical values in the table indicate weight percentages.

Polyamic acid 1 Polyamic acid 2 C4Hg n Assemble a liquid crystal cell through a 12 micron swathe, fill it with liquid crystal (ZI, I2214 manufactured by Merck fL), and connect the liquid crystal molecules and substrate using the magnetic field alignment method. When the angle was measured, the results shown in Table 2 were obtained.

Table 2 Table 1 These alignment agents were rotated at a rotation speed of 150O using the spin code method.
The transparent electrode was coated on a primed substrate at r.p.m.

This substrate was dried at 90 degrees Celsius for 2 hours and then fired at 200 degrees Celsius for 2 hours.

After firing, this substrate was transferred under a rotary body with a diameter of 80 mm whose surface was flocked with nylon fibers, rotating at a speed of 400 rpm at a feed rate of 0.6 m/min, and subjected to a rubbing treatment. did.

The substrate thus obtained was subjected to the same treatment using a 10 weight percent N-methylpyrrolidone solution containing only polyamic acid 1 and polyamic acid 2, with a rubbing direction of 220, and the measurement result was 22.5. It was 1.2 degrees.

[Example 2] A 10% by weight dimethylbormamide solution was prepared by mixing two types of polyamic acids having the following structural formulas in the proportions shown in Table 3, and used as alignment agent 6-10.

Note that the numerical values in the table indicate weight percentages.

A liquid crystal cell was assembled using polyamic acid 1 and polyamic acid 3, filled with liquid crystal (ZLI2214 manufactured by Merck & Co.), and the angle between the liquid crystal molecules and the substrate was measured by a magnetic field alignment method, and the results shown in Table 4 were obtained.

Table 4 Table 3 These alignment agents were rotated at a rotation speed of 2000 using the spin code method.
It was applied onto a substrate with a transparent electrode at rpm.

This substrate was dried at 90 degrees Celsius for 2 hours and then fired at 200 degrees Celsius for 2 hours.

After firing, this substrate was transferred at a feed rate of 0.6 m/min under a rotary body with a diameter of 80 mm that was rotating at a rotation speed of 40 rpm and whose surface was flocked with nylon fibers, and was subjected to a rubbing treatment. did.

The thus obtained substrate was rubbed in a direction of 220 degrees, and the 12 micron spacers were subjected to the same treatment using a 10% by weight dimethylformamide solution containing only polyamic acid 1 and polyamic acid 2. However, the results of aP1 determination were 22.3 degrees and 0.2 degrees.

Although the embodiments have been described above, the present invention is not limited to the above embodiments, but can be broadly applied to other raw materials, solvents, coating conditions, drying, and firing conditions.

〔Effect of the invention〕

As described above, according to the present invention, there is no need to prepare an alignment agent according to the type of liquid crystal, the twist angle, etc., and it is possible to deal with all types of liquid crystal by preparing two types of polyamic acids.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of a liquid crystal display. 11・ 12Φ 13・ 14 @ ·substrate ·electrode ・Alignment film ·liquid crystal that's all Applicant: Seiko Epson Corporation

Claims (1)

[Claims] 1) A liquid crystal cell for a liquid crystal display comprising a substrate with a transparent electrode, an alignment film coated on the substrate, a spacer, and a liquid crystal, which comprises a polyamic acid having the following structural formula and an initial alignment of the liquid crystal. Creation of an alignment film characterized by applying a solution containing polyamic acid, which is a precursor of a polyimide alignment film that forms a low angle to the substrate, onto a substrate with transparent electrodes, followed by drying, baking, and rubbing treatment. Method. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (However, n is a positive integer, and R means hydrogen or an alkyl group.) 2) A claim characterized in that the low angle is 5 degrees or less. 1. The method for creating an alignment film according to 1.