JPH02223920A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain a polymer oriented film which has >=5 deg. pretilt angle and is stable with age by using a copolymer contg. at least styrene halide and divinyl benzene in the oriented film for a liquid crystal to be used for the liquid crystal display element. CONSTITUTION:The oriented film for the liquid crystal is formed of the copolymer contg. at least the styrene halide and the divinyl benzene. The preferable range of the compsn. thereof contains 98 to 50mol% styrene halide and 2 to 20mol% divinyl benzene and contains the styrene halide and divinyl benzene at >=52% of the entire part. The pretilt angle is determined by the content of the styrene halide and rubbing conditions; the pretilt angle is larger as the content of the styrene halide is higher. The tilt angle is smaller as the pressure of rubbing and the number of rubbing times increase. The content of the styrene halide in the copolymer compsn. is, therefore, adjusted or the rubbing conditions are determined according to the required pretilt angle. The ferroelectric liquid crystal is sufficiently oriented in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the 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, computer word processors, and the like have mainly displayed in a leistid nematic (TN) mode or a superlite 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 a few milliseconds, which is a major problem when used in television panels, etc., which require high-speed response. It becomes.

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.

Known methods for aligning ferroelectric liquid crystals include applying a strong magnetic field and utilizing shear stress, but these methods are not practical in terms of production processes. Orientation has also been proposed from ``Nature''/ReIr3, July issue, pages 3 to 6, ``Optronics (OPT 0)
NIC8) J/RIlr 3rd year February issue No. t4L pages - No. 7
However, the region in which -like orientation can be achieved is narrow, from the edge to ioo .mu.m, and it is also difficult to put it into practical use.

On the other hand, there is a method in which polyimide, polyvinyl fluoride, etc. used in conventional nematic liquid crystals is coated and then rubbed with a cloth in a specific direction (%Kasho 67-/1&?,%Kasho 111[j-200/ 24k)-1)E Although these methods do not necessarily align the ferroelectric liquid crystal uniformly, so-called zigzag defects occur. In addition, #
) (Japanese Unexamined Patent Publication No. 61/1983/3t Octopus No.), and the method of using a polyimide film formed by glow discharge (Japanese Unexamined Patent Application No. 4/2/0-22) as an alignment film is not always sufficient. The problem is that there is no alignment and the contrast decreases.

Method of using polystyrene as an alignment film (Unexamined Japanese Patent Publication No. 7-3t
jλt] has also been disclosed, but polystyrene has a glass transition point of approximately to''c, and if the theory is raised to around lOO''C, the rubbing effect disappears, resulting in poor orientation.

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), uniform alignment can be achieved (for example, Nakano, Hiroshima: No. 74
Proceedings of the 2011 LCD Symposium Conference Page/! 0). However, oblique vapor deposition of inorganic oxides is extremely unprofitable when considering industrial production.

Therefore, it is desired to produce a pretilt angle of the same degree (j~300) as that of the SiO vapor-deposited film using an industrially profitable rubbing method for organic alignment films. However, in the commonly used alignment film rubbing method, the pretilt angle is limited to -3°, and the material that provides a relatively large pretilt angle is initially relatively large, but changes over time. The pretilt angle fluctuates greatly due to small differences in drying conditions.

[Summary of the invention]

An object of the present invention is to provide a polymer alignment film that has a pretilt angle of J@ or more even in the two-pin method in order to uniformly align a ferroelectric liquid crystal, and is stable over time.

The above object is to provide an alignment film for a liquid crystal, which is provided in a liquid crystal display device according to the present invention, in which a liquid crystal is sealed between two transparent electrode substrates, and which contains at least styrene denogenide and divinylbenzene. This is achieved by using a copolymer that

Since the liquid crystal alignment film of the present invention can be formed by a conventional coating method, there is no need to add any new special steps to the production process. 1 more
The liquid crystal alignment film of the present invention can be applied over a wide range with relative ease, so it can be said to be practical.

(Structure of the Invention) The liquid crystal alignment film of the present invention is a copolymer containing at least halogenated styrene and divinylbenzene, and the preferable range of its composition is 2 IP-40 mol of halogenated styrene and 2 IP-40 mol of divinylbenzene. It is composed of a copolymer containing 1 to 20 moles of halogenated styrene and divinylbenzene in an amount of j or more moles of the total amount.

If it is in the form of a general formula, it will be as shown in formula (1).

General formula (I) where p is IP-JO q is 1^-O r is O^4t7 Chlorine or bromine is preferred, and chlorine is preferred because of its good stability. The substitution position may be either the Hiro position or the 3 position.

The vinyl monomer may be one or more, for example, styrene, tri- or dimethylstyrene, methoxystyrene/, hydroxystyrene/, methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, butyl acrylate, Examples include acrylic acid, vinyl acetate, vinyl chloride, vinylidene chloride, itaconic acid, acrylonitrile, vinylpyrrolidone, and vinylpyridine.

Divinylbe/ze/ is a crosslinking component for imparting heat resistance, and has a good range of 1.2 to 2θ mole, preferably 3 to 1 mole. If there is too much, it will completely gel and become impossible to apply.

The alignment film can be installed by a conventionally known method, for example, a coating method.

The solvent for coating may be any solvent that dissolves the above copolymer, such as benzene, toluene, xylene,
- Monomethyl-pyrrolidone, dimethylformamide, diethylformamide, acetamide, acetone, methyl ethyl ketone, methyl isobutyl keto/, methyl cellosolve, ethyl cellosolve, selon rub acetate, carbon tetrachloride, chloroform, methylene dichlorite, ethylene dichloride, butyl acetate, etc. It may be used alone or in a mixed solvent system.

The alignment film may be provided directly on the transparent electrode, or the alignment film may be provided directly on the transparent electrode. A film having other functions, such as electrical insulation J-, may be provided on top of this layer. Further, depending on the purpose of use, functions provided in conventional liquid crystal display elements, such as polarizing plates and color filters, can be provided. However, the thickness of the alignment film is preferably -ooA to λ0ooh.

The alignment film formed under pressure is preferably rubbed with synthetic fibers such as nylon, polyester, and polyacrylonitrile, and natural fibers such as cotton and wool.

The pretilt angle is determined by the content of halogenated styrene in the copolymer and the rubbing conditions. Halogenated styrene/
The pretilt angle becomes larger as the number increases. Furthermore, the tilt angle becomes smaller as the rubbing pressure and number of rubbing increases. Therefore, it is preferable to adjust the content of halogenated styrene in the copolymer composition or to determine the rubbing conditions depending on the required tilt angle.

Ferroelectric liquid crystals can be well aligned by using the alignment film for liquid crystals that provides a pretilt angle according to the present invention.

Specifically, liquid crystals having ferroelectricity include chiral smectic C phase (SmC"), H phase (S m H"), ■ phase (8 mI), J phase (8 mJ), and K phase (SmK").
), G phase (5r11G") 1rtuFa (StnF")
It is a liquid crystal with Specific liquid crystal compositions include C8-10//, C8-10/J, and O8-/ manufactured by Chisso ■.
0/j, Merck & Co., Ltd. 0ZLI-34111, ZL
Examples include, but are not limited to, I-J4#F, ZLI-j4j4'1 Teikoku Kagaku Sangyo H8-5PzP, I(S7jrP (both trade names)). There is no problem in adding dichroic dyes, viscosity reducers, etc. that dissolve in the liquid crystal.

Further, in the liquid crystal hydrogen element using the liquid crystal alignment film of the present invention, it is preferable that spacers are dispersed between both transparent electrode substrates in order to ensure the thickness of the liquid crystal layer.

As the spacer, Nippon Shokubai's Eposter Catalyst Kasei's X-Rinkyu, Tansui Fine Chemical's Micro/Nur, Nippon Electric Glass' glass fiber, etc. can be used alone or in combination.

A transparent conductive layer of indium tin oxide (ITO; surface resistivity: 100Ω) was provided on a glass substrate (thickness: 1 mm), and a coating solution with the following composition was spun on six sides of this layer. Coated with code.

Copolymer copolymer Co,,tX Itobe xylene 30 λ-methylpyrrolid 7 70 After coating, it was heat-treated at /rOoc for 7 hours. Next, this film was subjected to a three-way rubbing treatment with a nylon napkin to form an alignment film. The two transparent sheets obtained in this way? ! The polar substrates were bonded together so that the rubbing directions were antiparallel. As a sweater, a 1μ cotton ball (
(Catalytic Chemicals), Mikata Toatsu's Structbond was used as the peripheral sealing material, and ljO'' was used to harden the sealing material.
A cell was prepared by heat treatment at C for up to minutes.

ZLI, a nematic liquid crystal manufactured by Merck, is used in this cell.
-Ko≠! - was injected. When the pretilt angle was measured using this cell using a polarizing microscope equipped with a universal stage (manufactured by Kon), it was found to be to.

Another cell prepared under the same conditions was injected with C31O/l, a ferroelectric liquid crystal manufactured by Chisso Corporation, heated to too''c, and then slowly cooled to J0C.

When the ferroelectric liquid crystal cell thus obtained was observed under crossed nicol conditions, it was found to have a -like orientation with no defects and excellent bistability.

Example 2 A coating liquid having the following composition was applied onto the same transparent conductive layer as in Example 7 using a spin coater. The rotation speed of the spin coater is J
It was OOOrpm.

Copolymer of co, j! Part 1 Kisilef
30 N comethylpyrrolidone 70 Heat treatment and rubbing treatment were performed in the same manner as in Example. When measuring the pretilt angle using the same nematic liquid crystal with the same device as in Example/, the result is 0.
Met. When ZLI-36117, a ferroelectric liquid crystal manufactured by Merck & Co., Ltd., was injected into a cell prepared under the same conditions and treated in the same manner as in Example 91/, uniform alignment was achieved and no zigzag defects were observed.

Comparative Example 2. Poly(-≠-chlorostyrene) with a mixed solvent of xylene and co-methylpyrrolidone (mixing ratio 3 near) was placed on the same transparent conductive layer as in Example/Comparative Example. J-solution was applied with a spin cord and heat-treated at /10"Cj.A cell was prepared under the same conditions as in Example/, and nematic liquid crystal was injected. However, the alignment of the liquid crystal was insufficient and the exact pretilt angle was determined. I couldn't ask for it.

ZLI-74ja manufactured by Merck & Co., Ltd. was injected as a ferroelectric liquid crystal, but even with this, the alignment of the liquid crystal was not uniform and there were many zigzag defects.

It is clear from Examples 1 and 2 that the liquid crystal alignment film of the present invention can align ferroelectric liquid crystal sufficiently well.

Claims (1)

[Claims] In a liquid crystal display element in which two transparent electrode substrates each having an alignment film provided on a transparent conductive layer are arranged with the alignment film inside, and a liquid crystal is sealed between them, the alignment film contains at least styrene halide and divinyl. A liquid crystal display element characterized by being made of a copolymer containing benzene.