JP2591564B2 - Alignment film for liquid crystal display device - Google Patents

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.

[0002]

2. Description of the Related Art Conventionally, there has been known a method of using an organic polymer film such as polyvinyl alcohol, polyamide resin, or polyimide resin as an alignment film of a liquid crystal display. In particular, polyimide resins are widely used as liquid crystal alignment films because they have a function of aligning various liquid crystals and have excellent heat resistance and the like. Polyimide resins currently generally used as liquid crystal alignment films can be classified into the following two types. One is insoluble in a solvent in the state of polyimide, so that it is applied to a substrate in the state of a polyamic acid solution and then imidized by heating and sintering to form a polyimide alignment film. After applying a solution in which a soluble polyimide resin is dissolved in a solvent to a substrate, the solvent is removed by heating to form a polyimide alignment film.

However, the former type, in which a polyamic acid solution is applied, generally requires a temperature of 250 ° C. or more in order to completely imidize it, which causes a reduction in productivity in a liquid crystal display device manufacturing process. It has become. Furthermore, if firing at 250 ° C. or higher is not possible due to the heat resistance of the color filter, etc., firing must be performed at a temperature lower than this temperature. As a result, the imidation ratio of the alignment film becomes insufficient and the production of display elements becomes insufficient. Yield is significantly reduced. On the other hand, in the latter case, a solution obtained by dissolving a polyimide resin soluble in a solvent in a solvent is applied to a substrate, and then the solvent is removed by heating to form a polyimide alignment film. Although possible, since the polyimide resin itself is basically soluble in a solvent, it does not have sufficient resistance to liquid crystals and does not have long-term stability.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks of the conventional alignment film and provides an alignment film for a liquid crystal display element which is stable at a low firing temperature.

[0005]

The present invention is characterized in that a polymer solution containing an isoimide structure in a molecule is coated on a transparent electrode substrate and then heat-treated at a temperature of 100 ° C. or more. This is an alignment film for a liquid crystal display element.

[0006]

The polymer containing the isoimide structure shown in the present invention in a molecule is generally synthesized by reacting a polyamic acid solution with dicyclohexylcarbodiimide (DCC) or a condensing agent such as acetic anhydride and pyridine.

The raw material of the polyamic acid is not particularly limited, and the acid anhydride and the diamine are converted to N-methyl-2-pyrrolidone (NM
The reaction is performed in a solvent such as P), N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), γ-butyrolactone, and m-cresol.

[0008] Acid anhydrides include 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 2,2', 3,3'-benzophenone tetracarboxylic dianhydride, 2,3,3 ', 4'-benzophenone tetracarboxylic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 2 , 2 ', 3,3'-Biphenyltetracarboxylic dianhydride, aromatic compounds such as 1,4,5,8-naphthalenetetracarboxylic dianhydride, or cyclopentanetetracarboxylic dianhydride, cyclobutane Examples thereof include aliphatic compounds such as tetracarboxylic dianhydride, and these can be used alone or in combination of two or more.

The diamine compounds include m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenyl ether, and 3,3'-diamino Diphenylmethane, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 2,4-diaminotoluene, 1,3-bis (3-aminophenoxybenzene), 1,4-
Bis (3-aminophenoxybenzene), 1,3-bis (4-aminophenoxybenzene), 2,2-bis (4- (4-aminophenoxy) phenyl) propane, 2,2-bis (4- (4 Aromatic compounds such as (-aminophenoxy) phenyl) hexafluoropropane; aliphatic compounds such as 4,4'-diaminodicyclohexylmethane and 1,4-diaminocyclohexane; and silicone diamine compounds represented by the formula (1) These can be used alone or in combination of two or more.

[0010]

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(R ₁ is a divalent aliphatic group having 1 to 5 carbon atoms or an aromatic group having 6 or more carbon atoms, and R ₂ and R ₃ are a monovalent aliphatic group or an aromatic group. And m may be the same or different, and m is an amino equivalent or ¹ to 50 as an average value determined from ¹ H-NMR spectrum.)

When a condensing agent such as DCC is added to a polyamic acid solution obtained from an acid anhydride compound and a diamine compound as described above, imidization may occur partially, but an isoimide structure is selectively formed. Generally, it is soluble in the solvent even in this state. Furthermore, if stored for a long time in the state of amic acid, hydrolysis of the main chain is likely to occur,
This lowers the molecular weight and solution viscosity, but the isoimide structure is extremely stable even at room temperature, and exhibits stable solution properties for a long period of time. Furthermore, the isoimide group is 100 ° C
To a imide group at a temperature of from 220 ° C. to 220 ° C., so that a stable polyimide resin is finally formed and exhibits excellent properties as an alignment film.

The thus obtained polymer solution containing a polyisoimide structure is applied on a transparent electrode substrate by spin coating or printing, and then heat-treated at a temperature of 100 ° C. or more, preferably 150 ° C. or more. , The isoimide structure is converted to an imide structure. Due to the heat resistance of other materials, the upper limit of the heat treatment temperature is generally 22
Although it is about 0 ° C., firing at a higher temperature is possible if there is no limitation on the firing temperature. After baking as described above, a rubbing treatment is performed, if necessary, as in the case of a conventional polyimide alignment film, and used as an alignment film for a liquid crystal display element.

[0014]

The present invention will now be described in detail with reference to Examples.
The present invention is not limited by these examples.

Example 1 2,2-bis (4- (4-aminophenoxy) phenyl) was placed in a 1000 ml four-neck separable flask equipped with a thermometer, a stirrer, a raw material inlet and a dry nitrogen gas inlet. 58.11 g (0.1416 mol) of propane, dehydrated N-methyl-2
-Add 550 g of pyrrolidone and adjust the system temperature under a stream of dry nitrogen.
30.89 g of pyromellitic dianhydride (0.1
416 mol) and reacted for 5 hours to obtain a viscous liquid. Here, 58.60 g of dicyclohexylcarbodiimide
(0.142 mol) was added and the mixture was stirred at room temperature for 5 hours. A precipitate of dicyclohexylurea was formed. Therefore, dicyclohexylurea was separated by filtration, and the polymer solution was reprecipitated in methanol to isolate the polymer. Further, the operation of dissolving the obtained polymer in N-methyl-2-pyrrolidone and reprecipitating it in ion-exchanged water was repeated three times. When the IR spectrum of the polymer finally obtained was measured, no absorption due to the amic acid structure was detected, and the isoimide structure was about 80% and the imide structure was about 20%.

The polymer obtained above is diluted with N-methyl-2-pyrrolidone until the viscosity becomes 30 mPa · s, and applied to the transparent electrode surface of a glass substrate with a transparent electrode by a spin coater, at 180 ° C. for 1 hour It was fired to form a film of about 800 Å. When the IR spectrum of this coating film was measured, the isoimide group was completely converted to an imide group.
Subsequently, the surface of the coating film was rubbed with a rubbing machine, the two substrates were bonded together with a gap of 20 μm, and a liquid crystal (ZLI-1132 manufactured by Merck) was injected to prepare a liquid crystal cell. When the orientation of the cell was evaluated with a microscope,
It was uniform over the entire surface, and the pretilt angle measured by the crystal rotation method was 5 degrees. Furthermore, this cell was heated at 100 ° C. and 60% RH for 1 hour.
After the treatment for one month, the liquid crystal orientation and the pretilt angle were measured, but no change was observed compared to before the treatment.

Example 2 38.02 g (0.174 g) of pyromellitic dianhydride was placed in a 1000 ml four-neck separable flask equipped with a thermometer, a stirrer, a raw material inlet and a dry nitrogen gas inlet.
3 mol) and 544.4 g of dehydrated N-methyl-2-pyrrolidone.
The mixture was stirred under a stream of dry nitrogen. While maintaining the temperature of the reaction system at 20 ° C., bisaminopropyl polydimethylsiloxane (in the formula (1), R ₁ = (CH ₂ ) ₃ , R ₂ = R ₃ = CH ₃ , m = 7.6) 24.03
g (0.0327 mol) was reacted, and 2,2-bis (4-
58.11 g of (4-aminophenoxy) phenyl) propane (0.14
16 mol) and 100 g of dehydrated N-methyl-2-pyrrolidone, and further stirred for 180 minutes to obtain a yellow-brown viscous polyamic acid solution. Here, in the same manner as in Example 1, dicyclohexylcarbodiimide was added in an equimolar amount to the amide acid bond to carry out isoimidization. The polymer was isolated in the same manner as in Example 1. When the IR spectrum of the polymer finally obtained was measured, no amic acid was detected, and the isoimide structure was about 75% and the imide structure was about 25%.

The polymer is treated with N until the viscosity becomes 30 mPa · s.
When diluted with -methyl-2-pyrrolidone, applied to a glass substrate with a transparent electrode in the same manner as in Example 1, and baked at 160 ° C. for 1 hour, the isoimide group was completely converted to an imide group. Further, an alignment film was formed in the same manner as in Example 1, and a liquid crystal cell was prepared to evaluate the alignment. As a result, a completely uniform alignment state was exhibited, and the pretilt angle was 9 degrees. After the cell was treated for one month under the conditions of 100 ° C. and 60% RH, the liquid crystal alignment and the pretilt angle were measured.

(Comparative Example 1) Polyamic acid was synthesized by the same raw material and reaction method as in Example 1, without isoimidization with dicyclohexylcarbodiimide, and in the state of a polyamic acid solution, a transparent electrode surface of a glass substrate with a transparent electrode. Was applied by a spin coater and baked at 180 ° C. for 1 hour to form a coating film of about 800 Å. Further, after rubbing treatment as in Example 1, liquid crystal was injected to prepare a liquid crystal cell, and the liquid crystal alignment state and pretilt angle were evaluated and measured. The pretilt angle was 4 degrees. Was good, but 10
When evaluated and measured after treatment for one month at 0 ° C. and 60% RH, the pretilt angle was 6 ° C. and the stability was insufficient. Also, some disclinations occurred.

Comparative Example 2 A Dean-Stark reflux condenser was attached to the same reactor as in Example 1, and 2,2-bis (4- (4
-Aminophenoxy) phenyl) propane 58.11 g (0.1416
Mol), and 550 g of dehydrated N-methyl-2-pyrrolidone, and while maintaining the temperature of the system at 20 ° C under a stream of dry nitrogen, 5- (2,5-dioxotetrahydro-3-furanyl) -3-methyl- 37.44 g (0.1416 mol) of 3-cyclohexene-1,2-dicarboxylic anhydride
Was added and the mixture was stirred and reacted for 2 hours. To this system, 30 g of toluene was added, the temperature of the system was raised to 170 ° C. by removing the dry nitrogen gas inlet, and the system was refluxed for 3 hours to perform imidization. The resulting solution was dropped into methanol to precipitate and isolate the polymer. The operation of dissolving the obtained polymer again in N-methyl-2-pyrrolidone and reprecipitating it in ion-exchanged water was repeated three times.

The polymer obtained above was diluted with N-methyl-2-pyrrolidone until the viscosity became 30 mPa · s, and a liquid crystal cell was prepared in exactly the same manner as in Example 1 to determine the liquid crystal alignment state and pretilt angle. Evaluation and measurement showed that the pretilt angle was
It was 3 degrees, indicating a good orientation immediately after cell fabrication. However, after one month of treatment at 100 ° C. and 60% RH, unevenness of the entire cell due to poor orientation occurred. The angles could not be clearly measured.

[0022]

By using a liquid crystal alignment film formed by applying and baking a polymer solution containing a polyisoimide structure shown in the present invention for a liquid crystal display element, the alignment characteristics of the liquid crystal can be stabilized for a long time, and the contrast can be improved. In addition, a display element having excellent visual characteristics can be obtained.

Claims (1)

(57) [Claims] 1. An alignment film for a liquid crystal display element, which is formed by applying a polymer solution containing an isoimide structure in a molecule on a transparent electrode substrate and then heat-treating the same at a temperature of 100 ° C. or higher.