JPH05313170A - Liquid crystal oriented film - Google Patents

Abstract

PURPOSE:To provide a uniformly oriented liq. crystal oriented film capable of providing a highly transparent liq. crystal element without need for high-temp. heat treatment by forming the film with a specified polysilane. CONSTITUTION:The oriented film is formed of a polysilane shown by the formula. In the formula, R1 and R2 are independently a group selected from a group consisting of alkyl, aryl and aralkyl, and (n) is a natural number. Besides, 1-4C alkyls are preferably used as the alkyl, and straight-chain alkyls such as methyl, n-propyl, isopropyl, sec-amyl, etc., are exemplified. A monovalent aryl having at least one aromatic ring is used as the aryl, and phenyl, naphthyl, etc., are exemplified. A monovalent aralkyl with at least one aromatic ring substituted by an aliphatic hydrocarbon is used as the aralkyl, and benzyl, phenethyl, etc., are exemplifed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal alignment film material.

[0002]

2. Description of the Related Art Conventionally, a method of orienting liquid crystal molecules in a homeotropic or focal conic state is to apply a surfactant or the like such as lecithin or hexadecyltrimethylammonium bromide to a substrate or to mix it with a liquid crystal material. Are known. However, in this method, since the alignment treatment agent is easily released, there is a problem in terms of high temperature stability of liquid crystal alignment and energization life of the device, and the practicability is insufficient.

There is also known a method in which a silane coupling agent, an organic chromium complex or the like is applied to a substrate and reacted to cause liquid crystal molecules to have homeotropic or focal conic orientation. This method is more advantageous than the method using the surfactant in terms of stability as an element,
There are the following drawbacks (1) and (2). (1) In order to obtain a good liquid crystal alignment, it is necessary to adhere the above-mentioned treatment agent only to the substrate surface in a single layer, and there are many restrictions on the coating conditions and the reproducibility is poor. Will decrease). (2) The chromium complex has a problem of pollution. Among these drawbacks, as a method that seems to be a solution to the problem (1), a method of adding tetraalkoxysilane to a silane coupling agent is proposed. However, even if this method is used, the reproducibility of the liquid crystal alignment is not good.

In addition to the above method, a method using a calcium fluoride vapor deposition film or a cerium oxide vapor deposition film is known.
There is a major drawback in poor mass productivity.

As a method for homogeneously aligning liquid crystals, there is known a method in which polyvinyl alcohol, polyimide or the like is applied to the surface of a substrate and lapping is performed. Further, the method of giving a pretilt to the liquid crystal also uses polyimide. However, when polyimide is used, it is difficult to give uniform pre-tilt and uniform pre-tilt to all liquid crystal phases, and alignment unevenness occurs and display performance is deteriorated, and the process for heat treatment at high temperature is complicated. However, it is difficult to obtain a precise element due to expansion and contraction due to heating and cooling, and there is a problem that transparency is poor.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal alignment film which does not require heat treatment at high temperature, has good transparency, and has little alignment unevenness.

[0007]

[Means for Solving the Problems] The above-mentioned problems are solved by the formula (1).

[Chemical 2] (Wherein R ₁ and R ₂ each independently represents a group selected from the group consisting of an alkyl group, an aryl group and an aralkyl group, n is a natural number), and the solution is achieved by a liquid crystal alignment film made of polysilane.

The polysilane used in the present invention is represented by the formula (1). In the formula, R ₁ and R ₂ each independently represent a group selected from the group consisting of an alkyl group, an aryl group and an aralkyl group.

The alkyl group preferably has 1 to 10 carbon atoms, and particularly preferably 1 to 6 carbon atoms. The alkyl group may be linear or branched. Specific examples of such an alkyl group include linear alkyl groups such as methyl group, ethyl group, n-propyl group and n-butyl group; isopropyl group, sec-butyl group, sec-amyl group and the like. Secondary alkyl group; tertiary alkyl groups such as tert-butyl group and tert-amyl group can be exemplified.

The aryl group may be a monovalent aryl group having at least one aromatic ring. This aromatic ring may have a substituent. Specific examples of such an aryl group include, for example, a phenyl group,
Examples thereof include naphthyl group, tolyl group and xylyl group.

The aralkyl group may be a monovalent aralkyl group in which an aliphatic hydrocarbon is substituted with at least one aromatic ring. This aromatic ring may have a substituent. Specific examples of such an aralkyl group include a benzyl group, a phenethyl group, an α-methylbenzyl group, and a tolylmethyl group.

The number n of repeating units is 10 to 100,00.
0 is preferable, and 100 to 10,000 is particularly preferable. If n is less than 10, there is a drawback that sufficient heat resistance cannot be obtained.

Polysilane is soluble in organic solvents such as aromatic hydrocarbons, saturated hydrocarbons, and ethers, and thus a solution dissolved in an organic solvent is easily applied onto a substrate by spin coating or transfer printing. When the solvent is removed by drying, a liquid crystal alignment film having excellent smoothness can be formed.

Considering the liquid crystal device production conditions and the reliability of the device, it is desirable that the liquid crystal alignment treatment is performed only on the substrate surface excluding the seal portion, and the organic solvent solution of polysilane has excellent printing characteristics. An alignment film can be easily formed on a specific portion of the substrate by a printing method.

The coating film thus formed is stable over time by heat treatment at 100 to 200 ° C. after the coating film is formed by printing, and it can withstand heating at 200 ° C. for about 2 hours and has good reproducibility. Gives orientation.

It is considered that the influence on the alignment of the liquid crystal is related to the molecular structure at the interface of the alignment film and the difference in the surface tension between the substrate and the liquid crystal. The critical surface tension γ _S is one of the physical properties indicating the surface state of a solid. The alignment pattern of the liquid crystal molecules can be predicted from the relative magnitude relationship between the substrate surface γ _S and the liquid crystal surface tension γ _L. When Δγ represented by Δγ = γ _L −γ _S is positive, homogeneous orientation is achieved. γ
_This is because in the case of _L > γ _S , the intermolecular force between the liquid crystals becomes larger than the interaction between the substrate surface and the liquid crystal molecules, and the vertical alignment of the liquid crystal molecules is advantageous in terms of surface energy. When polysilane is applied to the substrate and used as the alignment film, it is considered that Δγ <0.

Therefore, when polysilane is used as the alignment film, usually homeotropic alignment occurs. However, depending on the conditions, a homogeneous state can be obtained, and thus the homeotropic orientation is not always the only option.

The liquid crystal of the present invention is a nematic liquid crystal of the Schiff base liquid crystal, the biphenyl liquid crystal, the azooxy liquid crystal, the azo liquid crystal, the ester liquid crystal, the phenylcyclohexane liquid crystal, the phenylpyrimidine liquid crystal or the like, or a mixture thereof and the above nematic liquid crystal. A cholesteric liquid crystal in which an optically active substance is added to, and a mixed liquid crystal in which a substance that is not a liquid crystal such as a dichroic dye is added is also included. These liquid crystals include both positive and negative dielectric anisotropies, but both of them are included.

[0019]

EXAMPLES The present invention will now be described in more detail with reference to examples. Example 1 n-ethyl, n-butyl polysilane having a solid content of 2%
To a solvent of ethanol and butanol (1: 1) to obtain a solution having a viscosity of 250 cps. By using this liquid, an alignment treatment film can be formed on a specific region of a glass substrate by a transfer printing method. After heating this substrate for 1 hour at 100 ° C., various nematic liquid crystals were injected between the two substrates to prepare a liquid crystal element. The obtained device had a good homeotropic orientation, and this orientation effect was maintained unchanged before and after the device assembly process at 200 ° C. for 1 hour using a one-pack type epoxy adhesive. Further, it was an excellent liquid crystal element with no alignment unevenness and good transparency.

[0020]

EFFECT OF THE INVENTION A liquid crystal alignment film which gives a liquid crystal element having no alignment unevenness, heat treatment at high temperature and good transparency was obtained. This printable liquid crystal alignment film makes it possible to reliably produce a device having good display quality such as contrast in a guest-host type two-color liquid crystal display device at low cost and with high reliability.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoko Motohashi 2-24-25 Tamagawa, Ota-ku, Tokyo Within Showa Denko KK Biochemistry Laboratory (72) Inventor Chozo Inoue 2-24 Tamagawa, Ota-ku, Tokyo No.25 Showa Denko Co., Ltd.

Claims (1)

[Claims] 1. Formula (1): (In the formula, R ₁ and R ₂ each independently represent a group selected from the group consisting of an alkyl group, an aryl group and an aralkyl group. N is a natural number).