JPH0784265A - Orienting film for liquid crystal display element and liquid crystal display element using that - Google Patents

Abstract

PURPOSE:To obtain an orienting film for a liquid crystal display element and a liquid crystal display element showing a stable high pretilt angle and good electro-optic characteristics by incorporating a specified polymer. CONSTITUTION:A polymer having a repeating unit expressed by formula is incorporated. In formula, R1-R4 are hydrogen atoms or univalent org. groups and may be different from one another. Ar1 is a quadrivalent aromatic group and Ar2 is a bivalent org. group including aromatic groups. When the polymer expressed by this formula is to be used for the orienting film for a liquid crystal display element, the polyimide polymer of the formula is dissolved in a solvent and the obtd. soln. is applied and baked. Or, a soln. of an polyamide acid as the precursor of the polyimide polymer of the formula is applied and baked to form the polyimide polymer of the formula. When an orienting film for a liquid crystal is formed by using this polymer, a soln. of the liquid crystal orienting agent is applied on a substrate and baked by heating The soln. is applied by spin coating, printing, or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment film for a liquid crystal display device and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art Conventionally, there has been known a method of using an organic polymer such as polyvinyl alcohol, polyamide resin or polyimide resin as an alignment film of a liquid crystal display. In particular, the polyimide resin is widely used as a liquid crystal alignment film because it has the function of aligning various liquid crystals and is excellent in heat resistance and the like.

However, with the recent improvement in the characteristics of liquid crystal displays, it has become necessary for the alignment film material to have better characteristics than ever before. Specifically, it exhibits good liquid crystal alignment characteristics such as stably giving a high pretilt angle, and has excellent electro-optical characteristics such as high voltage holding ratio and low current consumption. Among these, the pretilt angle of the liquid crystal is a characteristic that directly affects the visual characteristics of the liquid crystal display, and particularly the STN method, the TFT method,
Further, it is very important to provide a stable high pretilt angle in some displays such as a ferroelectric type, but it cannot be said that the current alignment film sufficiently meets the demand. In addition, regarding the voltage holding characteristics that are particularly required in the TFT method, even if the characteristics that are almost satisfactory when using the conventional liquid crystal are used, the deterioration occurs when the liquid crystal has a lower driving voltage. There is a problem of doing it.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks and provides an alignment film for a liquid crystal display device which stably gives a high pretilt angle and good electro-optical characteristics, and a liquid crystal display device using the same. It is provided.

[0005]

The present invention provides an alignment film for a liquid crystal display device, which comprises a polymer having a repeating unit represented by the formula (1), and a liquid crystal display device using the same. is there.

[0006]

[Chemical 1]

When the polymer represented by the formula (1) is used as an alignment film for a liquid crystal display device, a method of coating and baking a solution prepared by dissolving the polyimide polymer of the formula (1) in a solvent, A solution of polyamic acid that is a precursor of the polyimide polymer of (1) is applied and baked to obtain the polyimide polymer of formula (1).

The method for synthesizing the polymer for liquid crystal alignment film of the present invention is not particularly limited, but the following method is generally used. First, a tetracarboxylic dianhydride represented by the formula (2) is synthesized by a Diels-Alder reaction of aryldicyclobutene such as benzodicyclobutene and naphthodicyclobutene with maleic anhydride, and the acid anhydride and diamine N-methyl-2-pyrrolidone (NMP), N, N
-Dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), γ-butyrolactone (GB
L) and the like are reacted to synthesize a polyamic acid.

[0009]

[Chemical 2]

When the imidization reaction is further carried out, a method of adding acetic anhydride, pyridine or the like for chemical imidization, or a method of heating imidization at a temperature of 150 ° C. or higher is used. In the case of heat imidization, a solvent such as toluene or xylene that forms an azeotropic mixture with water may be added to the reaction system, or pyridine or isoquinoline may be added as an imidization catalyst. The polymer thus obtained can be used as it is as a liquid crystal aligning agent, but the reaction solution of the polymer is put in a poor solvent which does not dissolve the polymer such as methanol, the polymer is purified and isolated, and after drying, It may be dissolved in a solvent to prepare a liquid crystal aligning agent solution. The solvent is not particularly limited as long as the obtained polymer can be uniformly dissolved, and examples thereof include NMP, DMF, DMAc, γ-butyrolactone, butyl cellosolve, ethyl cellosolve, diglyme and ethyl carbitol. Alone,
Alternatively, it is used as a mixed system of two or more kinds.

When a liquid crystal aligning film is formed using the polymer obtained above, a method of applying a liquid crystal aligning agent solution to a substrate and then baking it by heating is used. The substrate is coated by a method such as spin coating or printing, and the baking conditions generally depend on the solvent used, but the temperature is generally 100 ° C.
It is performed at the above temperature.

[0012]

EXAMPLES Examples of the present invention will be described in detail below.
The invention is in no way limited by these examples.

Synthesis Example 1 14.87 g (0.075 mol) of diaminodidiphenylmethane was added to a 300 ml four-neck separable flask equipped with a thermometer, a stirrer, a raw material charging port, and a dry nitrogen gas inlet.
200 g of MP was added, and 24.45 g (0.075 mol) of tetracarboxylic acid dianhydride of the formula (3) was added thereto and reacted at 20 ° C. for 5 hours to obtain a viscous solution of polyamic acid.

[0014]

[Chemical 3]

Synthetic Example 2 Using the same apparatus as in Synthetic Example 1, 24.45 g (0.075) of the formula (3) as the starting tetracarboxylic dianhydride was used.
Mol), diaminodidiphenylmethane as diamine 9.91 g (0.050 mol), and bisaminopropyltetramethyldisiloxane 6.21 g (0.025 mol) were used to synthesize a polyamic acid to obtain a viscous solution. .

Synthetic Example 3 Using the same apparatus as in Synthetic Example 1, 24.45 g (0.075) of the formula (3) as the starting tetracarboxylic dianhydride was used.
Mol), and 30.75 g (0.02) of 2,2-bis (4- (4-aminophenoxy) phenyl) propane as a diamine.
(75 mol) to synthesize a polyamic acid to obtain a viscous solution.

Synthesis Example 4 1 part by weight of the polyamic acid solution obtained in Synthesis Example 3 was added.
Toluene (0%) was added, and the mixture was refluxed at 170 ° C. for 5 hours to remove water generated by imidization from the outside of the system to obtain a polyimide. This polyimide solution was reprecipitated in methanol to isolate the polymer.

Example 1 NMP was added to the polyamic acid solution obtained in Synthesis Example 1 so that the polymer concentration was 6%, and the pore size was 0.5 μm.
After filtering with a membrane filter of, a spin coater was applied to the transparent electrode surface of the glass substrate with a transparent electrode,
It was heated at 180 ° C. for 1 hour to form a coating film of about 800 Å. Subsequently, the coating film surface was rubbed by a rubbing machine, two substrates were bonded together with a gap of 20 μm, and liquid crystal (ZLI-5081 manufactured by Merck & Co., Inc.) was injected to prepare a liquid crystal cell. When the orientation of the liquid crystal was evaluated by a microscope, it was uniform over the entire surface, and the pretilt angle was measured by the crystal rotation method. As a result, the pretilt angle was 3.1 degrees. Further, the voltage holding ratio was measured and found to be 99.8% at room temperature and 99.0% at 80 ° C. Furthermore, this cell is kept at 120 ° C for 6
After 1 month of treatment under 0% RH conditions, the liquid crystal alignment, pretilt angle and voltage holding ratio were measured, and there was no change compared to before treatment.

Examples 2 and 3 Liquid crystal cells were prepared in the same manner as in Example 1 using the polyamic acid solutions obtained in Synthetic Examples 2 and 3, and the alignment state of liquid crystal, pretilt angle and voltage holding ratio were measured. The results are shown in Table 1.
Shown in. Also, in both examples, the cell was placed at 120 ° C and 60% RH.
After treatment for 1 month under the conditions, the liquid crystal orientation and the pretilt angle were measured, but there was no change compared to before treatment.

Example 4 The polyimide obtained in Synthesis Example 4 was dissolved in a mixed solvent of NMP / butyl cellosolve = 8/2 (weight ratio) so as to have a concentration of 6%, and filtered through a membrane filter having a pore size of 0.5 μm. After that, a liquid crystal cell was prepared in the same manner as in Example 1, and the results of measuring the alignment state of the liquid crystal, the pretilt angle, and the voltage holding ratio are shown in Table 1. In each example, 12 cells are used.
After treatment for 1 month at 0 ° C. and 60% RH, the liquid crystal alignment and pretilt angle were measured, but there was no change compared to before treatment.

[0021]

[Table 1]

[0022]

Since the liquid crystal alignment film of the present invention can exhibit good liquid crystal alignment, stable liquid crystal pretilt angle, and good electro-optical characteristics, a liquid crystal display device of TFT type, STN type or ferroelectric type is provided. It is preferably used for.

Claims (2)

[Claims] 1. An alignment film for a liquid crystal display device, which contains a polymer having a repeating unit represented by the formula (1). [Chemical 1] 2. A liquid crystal display device using the liquid crystal alignment film according to claim 1.