JPS62918A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain a liq. crystal orienting film having uniform orienting properties at a low temp. by using polyamide having repeating units represented by a prescribed structural formula. CONSTITUTION:Dicarboxylic acid chloride is reacted with diamine to produce polyamide having repeating units represented by the formula [where X is -(CH2)-m (m=1, 2 or 3), -O- or -S- and n is an integer of 1-8]. The polyamide has high solubility in solvents and a stable soln. is prepd. by dissolving the polyamide in an aprotic solvent such as dimethylformamide. The polyamide shows superior solubility especially when at least one of amide groups bonding to benzene rings bonds at the m-positions with respect to X. The polyamide is dissolved in N,N-dimethylformamide to prepare a soln. having 0.5-5wt% concn., and this soln. is spin-coated on a substrate and dried at 120-150 deg.C or at 50 deg.C under reduced pressure. The drying rate is regulated by adding a high b.p. solvent such as N-methylpyrrolidone. The preferred mol. wt. of the polyamide is >=0.3 (expressed in terms of logarithmic viscosity number) and the thickness of the resulting film is about 500-3,000Angstrom . Thus, a heat and weather resistant liq. crystal orienting film having superior orienting properties is obtd. The film is easily patterned by etching.

Description

[Detailed description of the invention] Cunning! TECHNICAL FIELD The present invention relates to a liquid crystal display element, and particularly to improvements in its liquid crystal alignment film.

A variety of transparent conductive substrates with alignment films are used in liquid crystal display devices manufactured by Jōmei Engineering.Since the alignment film has a large effect on the display quality of the liquid crystal display device, much effort has been put into its development. It is directed towards.

Conventionally, as an alignment film material for horizontally aligning liquid crystals,
It is known to use polymeric coatings such as polyimide - for example polypyromellitimide and polyimide isoindoquinazolinedione.

However, since polyimide as mentioned above is insoluble in solvents, in order to form a film on a substrate, its precursor, polyamic acid (a ring-opened form of polyimide), is applied in the form of a solution and then heated and cyclized. A polyimide structure is required.

In this case, heating cyclization requires a high temperature of 250 to 300° C. or higher, which causes problems such as deformation of the glass substrate and the need for special heating equipment. In recent years, active matrix liquid crystal display devices using thin film transistor arrays have been attracting attention in order to increase display capacity. However, since thin film transistor arrays are susceptible to deterioration at high temperatures, it is difficult to use the polyimide as an alignment film. It is. In addition, liquid crystal display elements using plastic substrates have also been developed, but in the case of plastic substrates, the heat resistance is poor, so it is difficult to apply the above-mentioned polyimide as an alignment film. In this case, the precursor polyamic acid is unstable, so it has a short pot life.

The present invention provides a liquid crystal display element in which a liquid crystal alignment film can be formed at low temperatures.

The liquid crystal display element of the present invention has a liquid crystal alignment film on a substrate, wherein the liquid crystal alignment film has a general formula (I).
It is characterized by having a polyamide as a main component having a repeating unit represented by:

(In the formula, X and n represent the following:
〇- or -S- n: an integer of 1 to 8) The present invention will be described in more detail below.

The polyamide of the present invention can be synthesized, for example, by reacting a corresponding dicarboxylic acid chloride with a diamine.

Unlike conventional polyimides, the polyamide represented by the general formula (1) itself has high solvent solubility, such as aprotic polar solvents such as N-methyl-2-pyrrolidone, dimethylformamide, dimethylsulfoxide, and dimethylacetamide. to give a stable solution.

In general formula (1), a polyimide in which at least one of the amide groups bonded to the benzene ring is bonded to the meta position with respect to X exhibits even better solubility.

The polyamide used in the present invention has high film-forming properties, and this solution is applied onto a substrate by methods such as blade coating, spin cord, gravure coating, and screen printing.
By heating and distilling off the solvent, a uniform alignment film can be formed. The solvent used, solution concentration, drying conditions, etc.
Although it depends on the coating method, for example, in the case of spin code, the concentration is 0.5 to 5 wt%, and the solvent is N, N-
Dimethylformamide and dimethylacetamide are preferred, and the drying temperature is preferably 120-150°C. Also,
Drying at a temperature of 50° C. or lower is also possible by performing vacuum drying, and the alignment film can be formed at a significantly lower temperature than conventional polyimide alignment films. In order to adjust the drying rate, a high boiling point solvent such as N-methylpyrrolidone may be added as appropriate.

The molecular weight of the polyamide represented by the general formula (1) is preferably 0.3 or more in terms of logarithmic viscosity (η1nh).

If it is less than 0.3, alignment defects such as reverse domains are likely to occur.

The thickness of the polyamide alignment film is preferably about 500 to 3,000. When the film thickness is less than 500, alignment defects are likely to occur, and when it exceeds 3,000, the operating voltage of the liquid crystal display element becomes high.

This alignment film can be subjected to alignment treatment by rubbing with cotton cloth, nylon flocked fabric, polyester flocked fabric, or the like.

The type of liquid crystal substrate used in the present invention is not limited, and can include glass substrates, polyester, polyether sulfone,
Plastic films such as polysulfone and acetyl cellulose, substrates on which semiconductor elements such as thin film transistor arrays are formed, silicon wafers, etc. can be advantageously used.

The polyamide alignment film of the present invention has excellent homogeneous alignment with respect to liquid crystal. For example, as a liquid crystal,
Schiff base liquid crystal, azoxy liquid crystal, biphenyl liquid crystal, phenylcyclohexane liquid crystal, ester liquid crystal,
Examples include pyrimidine liquid crystal, terphenyl liquid crystal, and biphenylcyclohexane liquid crystal. These liquid crystals are
Used alone or usually as a mixture. Furthermore, for these liquid crystals, cholesteric liquid crystals such as cholesteryl chloride, cholesteryl nonaate, and cholesteryl carbonate, and chiral nematic liquid crystals such as those sold under the trade names C-15 and CB-15 by British Drug House Ltd. You may also attach
Ionic dopants such as tetraalkylammonium salts can also be added.

The liquid crystal display element of the present invention has excellent alignment performance and reliability because its alignment film is formed mainly from polyamide of general formula (1), which has excellent heat resistance and weather resistance. It has a high value. In addition, the alignment film can be easily formed at low temperatures and has excellent productivity.

Furthermore, the polyamide alignment film used in the present invention can be eluted using a normal organic solvent when performing etching to form required parts such as electrode lead-out parts and seal formation parts on the substrate, so it can be eluted using photolithography, etc. By a simple method,
Required etching can be performed safely.

Synthesis Example 1 Adipic acid 2.92g (0.02mol), 3,4'-
Diaminodiphenyl ether 4. Og (0.02mol
), 2 g of lithium chloride, 10 mA of pyridine and 12.4 g of triphenylphosphine were mixed with 4 g of N-methylpyrrolidone.
0 mm, and reacted at 100° C. for 3 hours under a nitrogen stream.

The reaction solution was poured into a large amount of methanol, and the resulting precipitate was collected by filtration, washed, and dried to obtain a polyamide.

This polyamide was purified by repeating the procedure of redissolving it in N,N-dimethylformamide and then pouring it into methanol.

Infrared absorption spectrum: 3290, 1660, 121
0c+s-1 Thermal decomposition start temperature = 360°C Logarithmic viscosity ηinh: 1.12 (N, N-dimethylformamide, 5 g/d12, 30°C) Example 1 The polyamide obtained in Synthesis Example 1 was treated with N.

It was dissolved in N-dimethylformamide to obtain a lipolyamide solution with a concentration of 2% by weight. This solution was coated on a glass substrate having a transparent conductive film of isodium oxide-tin oxide by a spin code method, and then heated at 120°C for 15 minutes and at 150°C for 3 hours.
A uniform polyamide coating was obtained by heating for 0 minutes to evaporate the solvent.

Next, this polyamide film was subjected to a rubbing treatment to form an alignment film, and then subjected to a heat resistance test at 150°C for 24 hours and a 60°C-
A moisture resistance test was conducted at 90% RH for 100 hours. The two substrates obtained in this way were placed in a 10μ
They were stacked with a spacer of
) to create a twisted nematic liquid crystal-filled cell. The liquid crystal filled cell obtained in this way is
It showed good alignment with no alignment defects such as reverse domains, and no difference was observed in the alignment when compared with a liquid crystal-filled cell similarly prepared without conducting a heat resistance test or moisture resistance test. It was confirmed that the material exhibited excellent high-temperature durability and high-humidity durability.

Further, when the liquid crystal-filled cell was subjected to a high temperature storage test at 80° C. for 1000 hours and a high temperature storage test at 60° C. and 90% RH for 1000 hours, it was confirmed that the alignment properties did not change.

Example 2 A liquid crystal-filled cell was produced in the same manner as in Example 1, except that phenylcyclohexane liquid crystal (manufactured by E-Merck, ZLI-1285) was used as the liquid crystal. This product also showed excellent orientation similar to Example 1.

Example 3 A liquid crystal-filled cell was produced in the same manner as in Example 1 except that a polyester film with a transparent conductive film was used as the substrate. This cell also showed excellent orientation similar to Example 1.

Claims (1)

[Claims] 1. In a liquid crystal display element having a liquid crystal alignment film on a substrate, the liquid crystal alignment film has a general formula (I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) (wherein, X, n indicates the following
, 1O- or -S-n: an integer of 1 to 8) A liquid crystal display element characterized in that the main component thereof is a polyamide having a repeating unit represented by