JPS5962833A - Substrate for liquid crystal display device and manufacturing method thereof - Google Patents

Abstract

PURPOSE:To provide long-term stability and to improve the orientability to be provided to a liquid crystal by using polyacrylonitrile as a material for orienting the liquid crystal. CONSTITUTION:A film of a polymer consisting of polyacrylonitrile is adapted and provided as a film for orienting a liquid crystal on the surface of a substrate for a liquid crystal display device in contact with the liquid crystal. Such film is disposed on the substrate in the form of a film by applying a soln. prepd. by dissolving the polyacrylonitrile in a solvent which can be easily removed when dried afterward on the a substrate by suitable method of dipping the substrate in said soln. or coating the soln. thereon then drying the soln. The above- mentioned polyacrylonitrile is adequate as a material for orienting the liquid crystal of the substrate for the liquid crystal display device without heat treatment under temp. conditions required for PVA.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a substrate for a liquid crystal display device having a coating for liquid crystal alignment.

A liquid crystal display device generally has two substrates sandwiching a liquid crystal, and at least one of the substrates has a liquid crystal alignment material applied to the surface thereof that comes into contact with the liquid crystal.

Here, the term "substrate" includes the electrode film if the electrode 11α is applied. Therefore, when an electrode film is present on a part of the substrate, a part of the surface of the substrate that comes into contact with the liquid crystal is the electrode film surface. Conventionally, as a method for achieving uniform parallel alignment with a small tilt angle, a method is known in which the surface of the substrate is coated with a material having good parallel alignment properties and the surface is rubbed. Organic substances such as silane, which have a structure close to a monomolecular film, are known as such substances, but they lack long-term stability and require a separate decoy film such as SIO. On the other hand, if there is a good polymer membrane, it is considered to be advantageous in terms of stability. Therefore, one object of the present invention is to have a long-term stable alternative to silane,
The objective is to provide a liquid crystal aligning substance with good alignment properties to the liquid crystal.

It has been found that the above object of the present invention can be achieved by using polyacrylonitrile as a liquid crystal alignment material. Polyacrylonitrile can be applied to a substrate as a solution in a solvent that can be easily removed by subsequent drying by an appropriate method such as dipping the substrate or coating the solution, and then dried to form a film. In the following, the present invention will be described in more detail with reference to embodiments.

Table 1 shows various polymer materials used in the experiments. The substrate used was soda glass partially covered with an In203 transparent electrode, which was immersed in a solution of polymeric phase material and dried to form a 4Jυ film with a thickness of about 100mm (IX). After rubbing the two substrates with a case, using a polyimide film around the periphery as a spacer, they were thermocompressed, and the liquid crystal was vacuum-sealed between the two substrates.The cell thickness was 12μ, and the electrode area was approx. 2.24 cd.The resistance of the cell was measured using a universal bridge manufactured by Yokogawa Electric Corporation.The 1 voltage of the Yokogawa fixed lightning is I KJ (z, 5
"flmV".

47n)'7j (-FTr CH2+t.

Polyheal methyl elapre (pvyr>) -
0C,H,H2O11 polyvinylpyrrolidone (pvp)
-NOn, a l l.

Polyacrylamide (PAAm) -CONH
,H2o l l,.

Polyacrylic 1NEf (PAAcJ,
-COOFI cH,orIl ID polyacrylonitrile! (PAN) ' -cN
r+coN(cn,)2” II,.

Dinner: N,N dimethylformamide (1) Ml
') 11n: Uniform parallel orientation Ill: Parallel orientation 1 where many microdomains exist
1: Ununiform parallel alignment table 2 Liquid crystal sample Cn1T
2n+1J G CN (n = 5.7) cm2
n+No-Q-/@-cN<n=5,7)C
nH2n+1-@-CH=NG-CN (o = 4
, 6) Cnl12n, O-@-CT (-'=N-@
-CN (n=2・4)cnr+2o+,o-o-
CH=N-o-C4I-1, (n = +, 2)
CnH2n+1'Q>'-NJ-o-Cr'IHzn+
t (II = 4.5) Table 1 shows the orientation of biphenyl-based mixed liquid crystal GR-41 (manufactured by Chisso Corporation) for each polymer material. It can be seen that good parallel alignment can be obtained with PAN along with PVA and PAAm. Next, we investigated the alignment of the liquid crystals shown in Table 2 with respect to these three types of polymer films, and as a result, it was confirmed that all liquid crystals were aligned parallel to these polymer films with good uniformity.

Next, we investigated the change in resistance over time when an AC voltage of 20 V at 5 fl Hz was applied to a liquid crystal cell whose alignment was controlled using PAN, PVA, and PAAm films. The results are shown in FIG. The liquid crystal used here is a biphenyl-based mixed liquid crystal GR-481 (manufactured by Chisso Corporation) for TN cells. The figure also shows the characteristics of the cell with a polymer membrane attached for comparison. From the figure, it can be seen that the resistance of the cell using PVA decreases over time, while the resistance of the cell without a polymer film and the cell using PAN hardly changes with time. Also PAA
Although there was no change in resistance for 600 hours, the orientation deteriorated after that and the resistance suddenly decreased. For comparison, we also investigated the change in resistance over time when an alkoxysilane, γ-morpholinopropyltrimethoxysilane (MOMS), was used. There wasn't.

It is thought that the decrease in resistance in PVA is due to ionic impurities being dissolved into the liquid crystal from the PVA film. Therefore, we created a cell by subjecting it to a heat treatment known as a hardening treatment for PVA fibers for 10 minutes. Figure 2 shows the change in resistance over time in this case. It can be seen from the figure that when the process is performed at a temperature of 220° C. or higher, the resistance of the cell changes more rapidly.

220° C. corresponds to the melting point of the PVA used, and it is known that heat treatment at a temperature higher than this promotes crystallization of the PVA film and makes the structure denser.

As a result of examination by X-ray diffraction for PVA membrane, 220
It was confirmed that crystallization was promoted at temperatures above ℃. It is thought that the reason why the film is stabilized by heat treatment is that such a change in the film prevents the elution of ionic impurities. However, if the heat treatment is carried out at a temperature higher than 220°C, the coloring of the film will become noticeable, so it is better not to heat it too high, and 220°C is the optimum temperature.

Since the melting point of PVA changes depending on the number of n in the structural formula shown in Table 1, it can be said that the unnecessary heat treatment in this application is generally in the range of temperatures around or slightly higher than the melting point of PVA. From the results of the above-mentioned experiment, it is understood that polyacrylonitrile is suitable as a liquid crystal aligning material for a substrate for a liquid crystal display fFf without being heat-treated under the above-mentioned temperature conditions like PVA.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the resistance of a liquid crystal cell with 7tf and the change in resistance value with respect to the pressure application time of a liquid crystal cell to which various small combined films are applied as a liquid crystal aligning material. FIG. 2 is a diagram showing the change over time in the resistance of a liquid crystal cell using a PVA film as a liquid crystal alignment material when the heat treatment temperature is changed. Patent applicant: Sukunley Electric Co., Ltd. Agent:
Patent Attorney Yasu Kaizu: Patent Attorney Hirayama - Happy Figure 2. @LSr+Rra7 (Hr)
8 Procedural Amendment (Method) % Formula %) Invention tD Name Relationship with the person who amends the substrate for liquid crystal display device and its manufacturing method 711l] Patent applicant j'111i 2-9-13 Nakameguro, Meguro-ku, Tokyo No.+'CYl('(+I?+・)(230) Stanley Electric Co., Ltd. Representative Contents of drawing amendments

Claims (1)

[Scope of Claims] (Li) A substrate for a liquid crystal display device, characterized in that a polymer film made of polyacrylonitrile is applied as a liquid crystal alignment film to the surface of the substrate in contact with liquid crystal. 2) Applying a solvent solution of a polymer made of polyacrylonitrile to the surface of the substrate for an i-crystal display device that is in contact with the liquid crystal, and forming a film of the polymer by volatilizing and removing the solvent. A method for manufacturing a substrate for a liquid crystal display device having a liquid crystal aligning film. (3) The method described in 4!F Claims No. 2m, wherein the solvent is N,N-dimethylformamide.