JPH02282224A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain oriented films the pretilt angle of which is >=5 deg. with an org. thin film system to uniformly orient a liquid crystal by using films consisting of a graft-polymerized vinyl compd. by a redox polymn. using persulfate. CONSTITUTION:The films consisting of the graft-polymerized vinyl compd. by the redox polymn. using the persulfate are used as the oriented films of the liquid crystal display element formed by disposing two sheets of transparent electrode substrates provided with the oriented films on transparent electrodes so as to face each other with the oriented films positioned on an inner side and sealing the liquid crystal between the substrates. The vinyl compd. can be easily grafted on the substrates by using any of persulfate + lithium halogenide, persulfate + acidic sulfurous acid or persulfuric acid + Ag system in the redox polymn. using the persulfate as the oriented films. The persulfate is usually used in the range of 1 to 0.005mol per 1mol vinyl compd. and heating is not particularly required for the graft polymn. reaction.

Description

[Detailed description of the invention] [Field of invention] The present invention relates to an alignment film for a liquid crystal display element.

More specifically, the present invention relates to an alignment film used in a ferroelectric liquid crystal display element.

[Technical background of the invention and prior art]

BACKGROUND ART Conventionally, liquid crystal display elements used in watches, computers, bupros, etc. have mainly displayed in a leisted nematic (TN) mode or a swerved twisted nematic (STN) mode in which nematic liquid crystal has a twisted structure. However, these liquid crystal display elements have a slow response speed, currently limited to 20 milliseconds, which is a major problem when used in television panels and other applications that require high-speed response. ing.

In contrast, recently, ferroelectric liquid crystals with high-speed response are expected to open up a new field of displays.
being researched. In a display element using this ferroelectric liquid crystal material, it is important to uniformly orient the liquid crystal molecules in a certain direction.

Some known methods for aligning ferroelectric liquid crystals utilize file stress applied with a strong magnetic field, but these methods cannot be said to be practical in terms of production processes. In addition, orientation from spacer edges has been proposed (``Nature'', July 1983 issue, pp. 36-46, ``OPTRONI'').
C3), September 1983 issue, pages 64 to 70), the region where -like orientation can be achieved is 10 from the edge.
The diameter is as narrow as 0 μm, which is still insufficient for practical use.

On the other hand, a method of rubbing polyimide, polyvinylidene fluoride, etc. used in conventional nematic liquid crystals with a cloth in a specific direction (Japanese Patent Application Laid-open Nos. 61-1869 and 63-200124) is known. However, these methods do not necessarily align the ferroelectric liquid crystal uniformly, and so-called zigzag defects occur.

Furthermore, methods in which polyimide resin is vapor-deposited and polymerized in vacuum (Japanese Unexamined Patent Publication No. 61-138924) or a polyimide film formed by glow discharge (Japanese Unexamined Patent Publication No. 61219029) are used as an alignment film, the alignment is not necessarily sufficient. However, a decrease in contrast becomes a problem.

Recently, it has been reported that if SiO is deposited from an oblique direction and the liquid crystal molecules are tilted at a certain angle from the substrate (pretilt), they will be uniformly aligned (for example, Nakano, Hiroshima;
Proceedings of the LCD Symposium, page 150 (198B))
. However, when considering industrial production, oblique vapor deposition of inorganic oxides is extremely unprofitable and difficult to increase in size.

Therefore, it is desirable to obtain a pretilt angle of the same degree (5° to 35°) as that of the SiO obliquely deposited film using an industrially profitable rubbing method for an organic alignment film.

There is a report that a pretilt angle of 10 to 20 degrees can be obtained by adding a long-chain alkylamine to an acid anhydride, which is a monomer component of polyimide, during polymerization (IEICE technical report, ED8B-34-42) , page 1
9). However, this method varies greatly depending on the temperature during heat treatment, heating time, rubbing intensity, etc., and it is quite difficult to control the angle to a constant value.

[Summary of the invention]

An object of the present invention is to provide an alignment film for uniformly aligning liquid crystals.

More specifically, it relates to an alignment film in a liquid crystal display element in which two transparent electrode substrates each having an alignment film provided on a transparent electrode are arranged with the alignment films facing inside, and a liquid crystal is sealed between them.

The first object of the present invention is to use an organic thin film system with a pretilt of 5°.
The second is to provide an alignment film with good reproducibility, the third is to provide an alignment film that is stable over time, and the fourth is to provide a large size alignment film. It is an object of the present invention to provide an alignment film that can be easily applied to a substrate and has little variation within the substrate.

It has been found that the above object can be achieved by using, as the alignment film, a film in which a vinyl compound is graft-polymerized by redox polymerization using a persulfate.

[Structure of the Invention] The grafting reaction by redox polymerization using persulfate is described in detail in "Graft Polymerization and Its Applications" (written by Fumio Ide, Shin Kobunshi Bunko).

In this method, hydroxyl groups, amino groups, imino groups, cyano groups, aldehyde groups, etc. can be easily grafted onto a substrate with

As a substrate, a transparent conductive layer made of indium tin oxide or the like is provided on a glass or plastic film, and a polymer film is further applied. At this time, a polymer having functional groups such as a hydroxyl group, an amino group, an imino group, or a cyano group may be applied, or after the polymer film is applied, corona treatment, glow treatment, fire treatment, or chemical oxidation treatment may be applied. may be applied.

However, since the reaction is carried out in an aqueous medium, it is desirable that these polymer films do not dissolve in water. Furthermore, the above polymer film does not dissolve in liquid crystal and has a glass transition temperature of approximately 80°C.
or more, or preferably a crystalline polymer with a melting point of about 80°C or more. Specifically, polyimide, nylon, cellulose acetate, cyanoethylcellulose, ethylcellulose, nitrocellulose, polyacrylonitrile, polymethylmethacrylate, polybendelmethacrylate, polyvinylidene fluoride, crystalline polystyrene epoxy resin, crosslinked gelatin, polyphenylene, polyphenylene oxide. , polyacrylate resin,
Examples include polysulfone and polyether siphon.

Corona treatment and glow treatment may be performed in an oxygen atmosphere or in a nitrogen atmosphere.

Any vinyl compound to be reacted may be used as long as it is soluble in water even in a very small amount. For example, alkyl methacrylate (alkyl group is 01-C1), alkyl acrylate (alkyl group is Cl-C4), N N'-dialkylaminomethylmethacrylamide (alkyl group C
0~C,L N,N'-dialkylaminoethyl methacrylamide (alkyl group 01~C,), N-alkylaminoethyl methacrylamide (alkyl group c+
-C3), N N'-alkylaminoethyl acrylamide (alkyl group 01-C3), N,N'-alkylaminomethylacrylamide (alkyl group C0-C
ff), N-alkylaminoethyl acrylamide (alkyl group C, -C3), N-alkylaminomethylacrylamide (alkyl group 01-C3), N, N'-alkylmethacrylamide (alkyl group C3-C,), N
, N'-alkylacrylamide (alkyl group 01-C
3), 1) N-methylaminostyrene, N-vinyl-dialkylamine (alkyl group C1 to C3), hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylonitrile, hydroxystyrene, styrene, vinylpyridine, vinylpyrrolidone, vinyl acetate, etc. can be raised. Also, divinyl compounds, such as C
H=CHC00(CHz-Ct(z)nOcOcH=c
H (n is 1 to 3), CH=CCHsCOO(CHz
−CHz)nOcOccH:+=CH (n is 1 to 3), etc. can also be used.

The concentration of the vinyl compound during the reaction depends on the molecular weight of the vinyl compound, but the concentration of the vinyl compound in the reaction solution ranges from 0.05 weight fraction (%) to 1.
A weight fraction (%) of 0 is preferred.

The persulfate is usually used in an amount of 1 to 0.005 mol per mol of the vinyl compound to be grafted. Especially 0
．． It is preferable to use it within the range of 5 to 0.01 mol.

The graft polymerization reaction of a vinyl compound onto a polymer surface, which is carried out in the presence of a persulfate, does not particularly require heating. Therefore, the reaction can be carried out at room temperature or by heating. The reaction time is usually 0.1 to 5 hours.

Note that the presence of oxygen in the reaction system may reduce reactivity, so it is preferable to conduct the reaction in a closed container and while introducing an inert gas such as nitrogen gas into the aqueous medium. .

By performing graft polymerization in this way, the vinyl compound is usually graft-polymerized onto groups such as hydroxyl groups, aldehyde groups, amino groups, cyano groups, or imino groups on the surface of the polymer film on the substrate surface. .

The vinyl compound is not three-dimensionally polymerized but chain-likely graft-polymerized. It is thought that the graft-polymerized chain polymer is bonded to the above-mentioned group at one end, and the other end is a free end.

After the graft reaction, it is desirable to wash with water, further wash with an organic solvent such as propatool, acetone, methyl ethyl ketone, etc., and dry. Drying at 80-150°C
It takes about 30 to 90 minutes.

The alignment film obtained by graft polymerization can be made of synthetic fibers such as nylon, polyester, polyacrylonitrile, cotton,
Rubbing with natural fibers such as wool is preferred.

Rubbing may be performed on only one of the alignment films of the two substrates, or both alignment films may be rubbed.

In the case of weak rubbing, it is preferable to apply it to both alignment films.

Specifically, the liquid crystal having ferroelectricity used in the liquid crystal display element of the present invention is chiral smectic C phase (SmC").
, H phase (SmH”), I phase (Sm I”), J phase (
SmJ''), K phase (SmK''), G phase (SmG'')
) or F phase (SmF'').

For example, the following molecules are used as ferroelectric liquid crystals.

Cl5 (here, R-n-Alkyl, n-Alkoxy
) or I N l-13 1l CH.

(Here, R=CFh, C2H4) As a specific liquid crystal composition, C3-10 manufactured by Chisso ■
11, C5-1013, C5-1015, ZLI-3488, ZLI-3489 manufactured by Merck, Teikoku Kagaku Sangyo ■
H3-98P, H3-78, P (all product names) manufactured by
Examples include, but are not limited to, the following. There is no problem in adding dichroic dyes, thickeners, etc. that dissolve in the liquid crystals to these liquid crystals.

In liquid crystal display elements, the cell thickness ranges from 0.5μ to 15μ.
μ is good, more preferably 1 μ to 10 μ. There is no problem even if a spacer that defines the cell thickness of a liquid crystal display element is sprinkled on the alignment film formed by graft polymerization.

When a ferroelectric liquid crystal is used, the alignment can be further improved by injecting the liquid crystal into the cell, heating it until it becomes an isotropic liquid, and then slowly cooling it. There is no problem in applying a temperature difference between the upper and lower substrates during slow cooling.

Of course, the liquid crystal display element of the present invention can be provided with structures provided in conventional liquid crystal display elements, such as a polarizing plate, an electrical insulating layer, and a color filter, depending on the purpose of use.

Next, Examples and Comparative Examples of the present invention will be described.

However, the present invention is not limited to this example.

Example 1 Sunever 130 (polyimide type) manufactured by Nissan Chemical was coated on the electrode surface of a 1.1M thick glass substrate having a transparent electrode made of indium and tin oxides, and heated at 170°C for 10 minutes.
Dry for an hour.

This polyimide surface was subjected to glow discharge treatment at 100 W for 2 minutes in an oxygen atmosphere of 150 mmHg.

This substrate was immersed in a solution having the following formulation, stirred for 30 minutes while blowing nitrogen gas into the solution, and then taken out.

Distilled water 600g KzSzOs O, 7g NaH5
O* o, 22 g Hydroxymethyl methacrylate 3 g The removed substrate was washed with water, then with propatool, and washed with 1
It was dried at 20°C for 1 hour.

This pair of substrates was rubbed three times with a nylon napkin, and the cell gap was 1. A cell of 8μ was created.

After injecting nematic liquid crystal into this cell, the pretilt angle was measured by the crystal rotation method and was found to be 30°.

Another mole prepared under the same conditions as above was heated to 100° and heated to ZLI-36, a ferroelectric liquid crystal manufactured by Merck & Co.
No. 54 was injected and showed uniform orientation when slowly cooled to room temperature.

Example 2 A substrate treated with glow discharge in the same manner as in Example 1 was placed in the following solution to cause a graft reaction.

Distilled water 450g K2520B 0.9gNallSO
30.3g Glycidyl methacrylate 3g After grafting reaction, after washing with water, after washing with propatool, 120″
It was dried at C for 1 hour.

A rubbed cell similar to that in Example 1 was prepared, and the pretilt angle was measured using nematic liquid crystal and found to be 25''.

When this cell was heated to 100° C., ZLI-3489, a ferroelectric liquid crystal manufactured by Merck & Co., Ltd. was injected and slowly cooled to room temperature, a uniform orientation was observed.

On the other hand, I applied Sunever 130 manufactured by Kankaku Kagaku Co., Ltd. and applied 17
Using a substrate that had been dried for just one hour at 0° C., the same rubbing treatment as above was performed, a cell was prepared, and the pretilt angle of the nematic liquid crystal was measured and found to be almost zero.

Claims (1)

[Claims] In a liquid crystal display element in which two transparent electrode substrates each having an alignment film on a transparent electrode are arranged with the alignment film inside, and a liquid crystal is sealed between them, at least one of the alignment films uses persulfate. A liquid crystal display element characterized in that it is a film obtained by graft polymerizing a vinyl compound through a redox reaction.