JPH02309322A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To enable imide ring closure at a low temp. and to obtain a liq. crystal display device fitted with polyimide-based orienting films having superior orienting property and not causing bleeding or sticking by using polymer films based on polyimide having a specified structure as orienting films. CONSTITUTION:Heat-treated films based on polyimide consisting of diamine components including arom. diamine compds. separately having structural units represented by formulae I, II and tetracarboxylic acid dianhydride are formed as orienting films on substrates each having an electrode. The amt. of the arom. diamine compds. used is not especially limited but the compds. are preferably used by >=70 mol% of the total amt. of the diamine components. When a copolymer contg. <70 mol% of the arom. diamine compds. is used, bleeding and sticking are liable to occur. The ratio between the diamine components and the tetracarboxylic acid dianhydride is not especially limited but the pref. molar ratio is 1.0:(0.9-1.1).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display element, and more particularly to a liquid crystal display element using a specific polyimide polymer film as an alignment film.

[Prior Art] Conventionally, the structure of a liquid crystal display element is usually to provide segment electrodes made of a transparent conductive film such as indium oxide or tin oxide on two glass or film substrates, and to apply a liquid crystal alignment film thereon by a conventional method. A structure is known in which a liquid crystal is sandwiched between the two, the peripheral portion is sealed with a sealant, and polarizing plates are arranged on both sides.

As alignment films for such liquid crystal display elements, polyimide polymer films are widely used because of their excellent rubbing performance, heat resistance required when sealing liquid crystal display elements, and good durability during use. .

However, many polyimides, such as polyimides obtained from pyromellitic dianhydride and diaminodiphenyl ether, require an imide ring-closing temperature of 300°C to 350°C, and this heat treatment process destroys the substrate (glass). Problems include problems such as damage due to thermal strain and poor product yield, the formed polyimide film becoming brownish and darkening the field of view, and restrictions on the materials used for the equipment used for imide ring closure. there were.

In addition, to prevent damage to the substrate, the imide ring-closing temperature was set to 2.
If the temperature is lowered to 50°C, not only will the heat resistance of the obtained alignment film decrease, but due to the disordered alignment, "bleeding" will occur around the segment electrodes that display characters, etc. when the liquid crystal display element is turned on.
appears, or lights up between adjacent segments.
There was a drawback that "sticking" occurred.

For this reason, in the industry, even when the imide ring is closed by heating at a temperature lower than 250°C, the orientation is excellent and there is no "bleeding" or "
There has been a strong desire for a polyimide polymer film that does not cause "sticking".

In view of the current state of the prior art, the inventors of the present invention have conducted extensive studies on the causes of the above-mentioned "bleeding" and "sticking", and have found that these drawbacks occur when liquid crystal display elements are stored in a high-humidity atmosphere. We found that this was due to a decrease in the resistance value between the segment electrodes due to some chemical change in the alignment film made of polyimide polymer film due to the moisture generated, and we continued to investigate solutions to this problem. As a result, the inventors found that the above-mentioned problems can be solved at the same time when a polyimide-based polymer film having a specific structure as described below is used as an alignment film, and the present invention has been achieved.

[Problems to be Solved by the Invention] Therefore, an object of the present invention is to provide a liquid crystal display element equipped with a polyimide alignment film that can perform imide ring closure at low temperatures, has excellent alignment properties, and does not cause "bleeding" or "sticking". Our goal is to provide the following.

1. Means for Solving the Problem] An object of the present invention is to provide a liquid crystal display element having a liquid crystal alignment film on a substrate having electrodes, in which a diamine component containing an aromatic diamine compound having structural units each represented by the alignment is provided. This is achieved by a liquid crystal display element formed of a heat-treated polyimide film consisting of and tetracarboxylic dianhydride.

Examples of the aromatic diamine compound having the structural unit represented by the formula include the following. These can be used alone or in combination of two or more.
Examples of aromatic diamine compounds having a structural unit represented by O1NH2 include the following, and the tetracarboxylic dianhydrides used in the present invention are represented by the following general formula.

(R is a tetravalent organic group) Specifically, pyromellitic dianhydride, 2. 3゜6.
7-Naphthalene tetracarboxylic dianhydride, 3.4.3
', 4'-biphenyltetracarboxylic dianhydride,
2.3.2', 3'-biphenyltetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(3, 4-dicarboxyphenyl)sulfonic anhydride, 2.2-bis(3,4-dicarboxyphenyl)purpannianhydride, 3.4.3', 4
'-benzophenonetetracarboxylic dianhydride, ethylenetetracarboxylic dianhydride, 1,2,3゜4-butanetetracarboxylic dianhydride, cyclobutane-1,2,3
, 4-tetracarboxylic dianhydride, decahydronaphthalene-1,4,5,8-tetracarboxylic dianhydride, etc., and one type or a mixture of two or more types may be used.

The polyamic acid, which is a precursor compound of the polyimide polymer according to the present invention, is prepared by combining a diamine component containing an aromatic diamine having structural units represented by the general formulas I and (2), respectively, and a tetracarboxylic dianhydride by a known method. It can be produced by reacting in an organic solvent.

The composition ratio of the diamine component and the tetracarboxylic dianhydride is not particularly limited, but preferably diamine component:tetracarboxylic dianhydride=1.0:0°9 to 1.1 (molar ratio)
A range of is preferred.

The blending amount of the aromatic diamine compound having the structural units of general formulas 1 and (2) is not particularly limited, but it is preferably blended in an amount of 70 mol % or more based on the total diamine components. In the case of copolymers containing less than 70 mol% of aromatic diamine compounds having structural units of general formulas I and H, "bleeding" occurs.
and ``<tsutsuki'' are more likely to occur.

The copolymerization ratio of aromatic diamine compounds having the structural units of general formulas 1 and (2) is not particularly limited, but from the viewpoint of orientation and prevention of "bleeding" and "sticking" during storage in a high humidity atmosphere, The diamine compound of formula I to the diamine compound of general formula (I) is preferably in the range of 2 to 8:8 to 2 (mole ratio).

Examples of diamine compounds other than aromatic diamine compounds having structural units represented by general formulas I and 2 include 3,3'- or 4,4'-diaminodiphenylmethane, 3,3'- or 4,4' -diaminodiphenylethane, 3,3'- or 4,4'-diaminodiphenylpropane, 3°3'- or 4,4' -diaminodiphenylsulfone, 3,3'- or 4,4'
-diaminodiphenyl sulfide, bis-(3-aminopropyl)tetramethylsiloxane, bis-(4-aminophenyl)diethylsilane, hexamethylenediamine, etc., and these can be copolymerized if necessary.

As a polymerization method, for example, the concentration of polyamic acid is 1 to 5.
A method of reacting in an organic solvent at a temperature of 5 to 100° C. for 1 to 24 hours so that the amount becomes 0% by weight can be mentioned.

Examples of organic solvents used in this reaction include N-methyl-2-pyrrolidone, N,N'-dimethylacetamide, N,N'-dimethylformamide, dimethylsulfoxide, and tetramethylurea, which are good solvents for polyamic acids. However, other solvents such as toluene, xylene, tetrahydrofuran, dioxane, diglyme, methyl cellosolve, ethyl cellosolve, methanol, and ethanol may be mixed for the purpose of improving coating properties and drying speed. good.

Next, a polyamic acid solution of a predetermined concentration is applied onto a glass substrate provided with segment electrodes made of a transparent conductive film by a method such as dipping, spin coating, or printing, and then heat-treated to form a polyimide-based A polymer film is formed. It is usually coated to a thickness of 50 to 2,000 people and heat treated at a temperature of 150°C to 250°C for 30 minutes to 6 hours.

The alignment film can be obtained by lightly rubbing the heat-treated film with a cotton cloth or the like. The two substrates obtained in this way are combined by a conventional method to create a cell.

It should be noted that an adhesion improver component with an electrode substrate, a sealant, etc., an orientation control agent, a coloring agent, etc. may be added to the polyamic acid solution within a range that does not impair orientation.

As the liquid crystal sealed in the liquid crystal display element, any known liquid crystal may be appropriately selected. It may be a nematic type liquid crystal or a smectic type liquid crystal with enhanced conductivity.

In the manner described above, the liquid crystal display element of the present invention can be obtained.

[Examples] The present invention will be described below based on Examples, but the present invention is not limited thereto.

Example 1 64.9 g (0.6 mol) and 218.1 g (1.0 mol) of pyromellitic dianhydride were dissolved in 2932.6 g of N-methyl-2-pyrrolidone and reacted at 50°C for 8 hours. As a result, a polyamic acid solution having a concentration of 12% by weight was obtained. This solution was mixed with N-methyl-
It was diluted to 5% by weight with 2-pyrrolidone to give a coating solution with a viscosity of 1.10 voids at 25°C.

This coating solution was printed on a glass substrate on which a transparent electrode made of an indium tin oxide film was formed using an offset printing machine, and then heated in a hot air oven at 200°C for 1 hour to form a polyimide film with a thickness of 800 mm. I got it. Next, the coating was rubbed with a nylon flocked cloth to form an alignment film. A cell was assembled by sandwiching the two glass substrates obtained in this way with a spacer in such a manner that the rubbing direction was 90 degrees between the upper and lower substrates, and then nematic liquid crystal (biphenyl liquid crystal) was injected to produce a liquid crystal display element. Note that epoxy resin was used as the sealant.

After this liquid crystal display element was stored in an atmosphere of 85° C. and relative humidity of 85% for 168 hours, it was turned on and examined for the presence of "bleeding" and "sticking". As a result, no such phenomena were observed. In addition, the resistance between the segment electrodes before and after storage is DC2.
As a result of measurement at 5V, it was 4.0XIO12Ω before storage, whereas it was 1°5X1012 after storage, which was only a slight decrease.

Example 2 60.1g (0.3 mol), 73.7g (0.4 mol), pyromellitic dianhydride 130.9g (0.6 mol) 3.4.3',4'-biphenyltetra Example 1 117.7 g (0.4 mol) of carboxylic dianhydride
Polymerization was carried out under the same conditions as above, and then diluted to obtain a polyamic acid solution having a viscosity of 0.96 poise at 25°C. Using this solution, a liquid crystal display element was created in the same manner as in Example 1,
When a storage test was carried out, there was no occurrence of "bleeding" or "sticking", and the resistance between the segment electrodes was only reduced from 2X 10 i 3Ω to 9X10''.

Example 3 87.7g (0.3 mol), 32°4g (0.3 mol), 3.4.3',4'-biphenyltetracarboxylic dianhydride 294.2g (1.0 mol) After polymerization under the same conditions as in Example 1, the solution was diluted to obtain a polyamic acid solution having a viscosity of 0.89 voids at 25°C. A liquid crystal display element was prepared using this solution in the same manner as in Example 1, and a storage test was conducted. There was no occurrence of "bleeding J" or "sticking J", and the resistance between the segment electrodes was 3 x 1013Ω. , it decreased only to 1×10 13 .

Example 4 78.1g (0.3 mol), 49.6g (0.2 mol), 3.4.3',4'-benzophenonetetracarboxylic dianhydride 322.2g (1°0 mol) Polymerization was carried out under the same conditions as in Example 1, further diluted and heated at 25°C.
A polyamic acid solution having a viscosity of 1.06 poise was obtained. Using this solution, a liquid crystal display element was prepared in the same manner as in Example 1, and a storage test was performed. No "bleeding" or "sticking" occurred at all, and the resistance between the segment electrodes was 6x l. Q 12Ω is 2X101
It only decreased to 2.

Comparative Example 1 g (1.0 mol) and pyromellitic dianhydride 218.1
g (1.0 mol) was polymerized under the same conditions as in Example 1, and then diluted to obtain a polyamic acid solution having a viscosity of 0° and 73 voids at 25°C. When a liquid crystal display element was created using this solution in the same manner as in Example 1 and a storage test was performed, "bleeding" and "sticking" occurred.
Also, the resistance between the segment electrodes is 5×1013Ω, but 1
It had decreased to ×1011.

Comparative Example 2 mol) and pyromellitic dianhydride 218.1g (1,0
mol) was polymerized under the same conditions as in Example 1, and further diluted to obtain a polyamic acid solution with a viscosity of 0.89 poise. When a liquid crystal display element was prepared using this solution in the same manner as in Example 1 and a storage test was performed, "bleeding" and "sticking" occurred, and the resistance between the segment electrodes was 3 x 1013Ω. , it had decreased to 1×101U.

1 g (0.5 mol) and 3. 4. 3', 4
' -benzophenone tetracarboxylic dianhydride 322
゜2g (1.0 mol) was polymerized under the same conditions as in Example 1,
Further dilution was performed to obtain a polyamic acid solution having a viscosity of 0.79 voids at 25°C. A liquid crystal display element was prepared using this solution in the same manner as in Example 1, and a storage test was performed. Although no "sticking" occurred, "bleeding" did occur, and the resistance between the segment electrodes is 4
X10"Ω had decreased to lXl0".

[Effect of the invention] Since the present invention is constructed as described above, the imide ring closure is
It can be carried out at a low temperature of 50°C and has excellent orientation.
It is possible to reliably obtain a liquid crystal display element equipped with a polyimide alignment film that does not cause "bleeding" or "sticking".

Claims (1)

[Claims] 1. In a liquid crystal display element having a liquid crystal alignment film on a substrate having electrodes, the alignment film has the following general formula (I) and (
A liquid crystal display element formed of a heat-treated polyimide film comprising a diamine component containing an aromatic diamine compound having the structural units represented by II) and a tetracarboxylic dianhydride. ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) (However, m is 0, 1, or 2.) ▲There are mathematical formulas, chemical formulas, tables, etc.▼(II) (However, n is 1, 2, or 3. )