JP3138348B2 - Manufacturing method of liquid crystal alignment film and 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 a liquid crystal alignment film and a liquid crystal device, and more particularly to a liquid crystal alignment film and a liquid crystal device in which the alignment film is hardly damaged by rubbing.

[0002]

2. Description of the Related Art Currently used liquid crystal display elements are twisted nematic (hereinafter abbreviated as TN) having a structure in which the arrangement direction of nematic liquid crystal molecules is twisted at 90 degrees on the surface of a pair of upper and lower electrode substrates. ) The mode utilizing the arrangement of the nematic molecules between the upper and lower electrode substrates by 180 to 3
Twisted to 00 degrees, there is a type using a super twist nematic (hereinafter abbreviated as STN) mode using a birefringence effect, a type using a ferroelectric liquid crystal, and the like. For the alignment, an alignment film is formed on the electrode substrate, and the alignment film is rubbed (rubbed in one direction) with a cloth or the like to utilize the property that the liquid crystal is aligned in the rubbing direction.

[0003] However, in this method, since a process of mechanical rubbing is performed, scratches are generated due to the shaping of the alignment film. These flaws appear as flaw-like defects when the liquid crystal element is turned on, and are a major obstacle to a reduction in the defect rate of products. Usually, a polyimide polymer film is used as an alignment film used in these liquid crystal elements.
In general, a polyimide is obtained by applying a polyamic acid, which is a precursor of polyimide, to a substrate with electrodes, and then heating it at 180 ° C. or higher, preferably 200 ° C. or higher. In this process, the coating film shrinks due to a ring-closing reaction accompanied by dehydration reaction due to heating.However, if the imidization proceeds gradually, the stress in the film due to the shrinkage is relaxed and the alignment film is formed. A film having high strength and less likely to cause scratches due to rubbing can be obtained. However, when the imidization is rapidly advanced, the stress in the film is accumulated without being relaxed, so that an alignment film which is inferior in mechanical properties and easily damaged during rubbing can be obtained. That is, the rate of occurrence of scratches due to rubbing is greatly affected by the method of firing the film. Therefore, there is a strong demand for an alignment film in which the occurrence of scratches due to rubbing hardly depends on the firing conditions.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal alignment film in which the occurrence of scratches due to rubbing hardly depends on the firing conditions.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, when producing a polyamic acid which is a precursor of polyimide, several kinds of tetracarboxylic acid dianhydrides having different skeletons are produced. It has been found that the above problem can be solved by using a product and copolymerizing it. In addition, it has been found that a further improvement is possible particularly by using an acid anhydride having an alicyclic skeleton. The details will be described below.

[0006] The method for producing the liquid crystal alignment film of the present invention comprises a divalent aromatic compound.
Diamino compound having an aromatic group or a group having an alicyclic structure
And a tetracarboxylic acid having a group having an aromatic group
Tetracarbons having groups having hydrates and alicyclic structures
Polyamic acid obtained by copolymerizing acid dianhydride
After coating on a substrate with a transparent electrode, heat to dehydrate the ring closure reaction
And the general formula

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And

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[0008] (In the above formulas, X is a group having a divalent aromatic group or alicyclic structure, Y ₁ and Y ₂ is is a group having a different tetravalent aromatic or alicyclic structure together, Y ₁ and
And at least one of Y ₂ is a group having an alicyclic structure.
And m and n are integers) to form a liquid crystal alignment film containing polyimide as a main component having a structural unit represented by
Characterized in that that.

The acid anhydrides of the above general formulas (I) and (II) exemplify two or more different compounds.
_In addition to ₁ and Y ₂ , a structural unit having a different group such as Y ₃ or Y ₄ may be included. The composition ratio of the structural units of the formulas (I) and (II) in the polyimide is 3% to 50% with respect to the structural unit of the formula (I) or the formula (II) as the main component. Preferably 5% to 45%
It is preferable that the weight average molecular weight of the polyamic acid which is a precursor of the polyimide is 5000 to 1,000,000.

[0010] Since the polyimide polymer used as the liquid crystal alignment film of the present invention is generally insoluble in a solvent, a tetracarboxylic dianhydride is usually used as a precursor to provide a uniform polyimide polymer film on a substrate. Polyamic acid obtained by condensation of a product and a diamino compound with N-methyl-2-
Pyrrolidone (NMP), dimethylacetamide (DMA
c), dissolved in a solvent such as dimethylformamide (DMF), dimethylsulfoxide (DMSO), and the solution is applied to a substrate by a method such as brushing, dipping, spin coating, spraying, or printing. A method in which heat treatment is performed at 100 to 450 ° C., preferably 150 to 300 ° C., and a dehydration ring-closing reaction is performed to have an imide bond is preferable.

The polyamic acid as a precursor of the polyimide is usually synthesized by condensation of a tetracarboxylic dianhydride with a diamino compound. These condensation reactions are carried out under anhydrous conditions under the conditions of N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylsulfolane sulfate, butyrolactone, cresol, phenol, Halogenated phenol, cyclohexanone,
Dioxane, tetrahydrofuran and the like, preferably N-
The reaction is performed at a temperature of 50 ° C. or lower in a solvent of methyl-2-pyrrolidone (NMP).

Specific examples of the diamino compound include the following compounds. 1,1-bis [4- (4-
Aminophenoxy) phenyl] cyclohexane, 1,1
-Bis [4- (4-aminophenoxy) phenyl] -4
-Methylcyclohexane, 1,1-bis [4- (4-aminophenoxy) phenyl] -4-ethylcyclohexane, 1,1-bis [4- (4-aminophenoxy) phenyl] -4-npropylcyclohexane, 1,1-bis [4- (4-aminophenoxy) phenyl] -4-nbutylcyclohexane, 1,1-bis [4- (4-aminophenoxy) phenyl] -4-npentylcyclohexane, 1,1-bis [4- (4-aminophenoxy) phenyl] -4-nhexylcyclohexane, 1,1-bis [4- (4-aminophenoxy) phenyl] -4-nheptylcyclohexane, 1,1-bis [4- ( 4-aminophenoxy) phenyl] -4-noctylcyclohexane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane 2,2-bis [4- (4-aminophenoxy) phenyl] butane, 2,2-bis [4- (4
-Aminophenoxy) phenyl] pentane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexane, 2,2-bis [4- (4-aminophenoxy) phenyl] heptane, 2,2-bis [ 4- (4-aminophenoxy) phenyl] octane, 2,2-bis [4- (4
-Aminophenoxy) phenyl] nonane, 2,2-bis [4- (4-aminophenoxy) phenyl] decane,
2,2-bis [4- (4-aminophenoxy) phenyl] dodecane, 4,4'-diaminophenyl ether,
4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfide, 4,4'-di (meth-aminophenoxy) diphenylsulfone, 4,4 '-(para-amino Phenoxy) diphenyl sulfone, ortho-phenylenediamine, meta-phenylenediamine, para-phenylenediamine, benzidine, 2,2'-diaminobenzophenone, 4,4'-diaminobenzophenone, 4,4'-
Diaminodiphenyl-2,2'-propane, 1,5-diaminonaphthalene, 1,8-diaminonaphthalene, 2,
Aromatic diamino compounds such as 2-bis [4- (4-aminophenoxy) phenyl] hexamethylpropane;
Alicyclic diamino compounds such as diaminocyclohexane and 4,4'-diaminodicyclohexylmethane;

The diamino compound used in the present invention is not limited to these. Further, two or more diamino compounds can be used in combination. On the other hand, the tetracarboxylic dianhydride used for bonding to the diamino compound includes, specifically, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ', 3,3'-biphenyltetracarboxylic dianhydride, 2,3,3', 4'-biphenyltetracarboxylic dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride Anhydrous, 2,3,3 ', 4'
-Benzophenonetetracarboxylic dianhydride, 2,
2 ', 3,3'-benzophenonetetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, 5,6-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride and the like, and as alicyclic tetracarboxylic dianhydride,

[0014]

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And the like. Some of these compounds contain isomers, but a mixture thereof may be used. Further, the tetracarboxylic dianhydride used in the present invention is not limited to the above. In the liquid crystal alignment film of the present invention, by introducing an aminosilicon compound or a diaminosilicon compound into polyimide, the adhesiveness to the substrate can be increased.

Specific examples of the aminosilicon compound for the liquid crystal alignment film of the present invention include the following compounds. NH ₂ ─ (CH ₂ ) ₃ ─Si (OCH ₃ ) ₃ ,
NH ₂ ─ (CH ₂ ) ₃ ─Si (OC ₂ H ₅ ) ₃ , NH ₂
{(CH ₂ ) ₃ } Si (CH ₂ ) (OCH ₃ ) ₂ , NH
₂ ─ (CH ₂ ) ₃ ─Si (CH ₃ ) (OC ₂ H ₅ ) ₂ ,
NH ₂ ─ (CH ₂ ) ₃ ─Si (C ₂ H ₅ ) (O _n ─C ₃
H ₇ ) ₂ , NH ₂ ─ (CH ₂ ) ₂ ─Si (OC
H ₃ ) ₂ , NH ₂ ─ (CH ₂ ) ₂ ─Si (OC ₂ H ₅ )
₃ , NH ₂ ─ (CH ₂ ) ₄ ─Si (CH ₃ ) (OC ₂ H
₅ ) ₂ ,

[0017]

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When these aminosilicon compounds are introduced into a polyimide polymer, the content thereof is preferably 50 mol% or less, more preferably 30 mol% or less, based on the polyimide raw material. Also, as the diamino silicon compound,

[0019]

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(Wherein, l represents an integer of 0 to 4) (Wherein, l represents an integer of 0 to 4). When introduced into a polyimide polymer, the content thereof can be replaced with a diamonosilicon compound in an amount of 50 mol% or less, preferably 30 mol% or less of the diamino compound as a polyimide raw material.

In order to provide the liquid crystal alignment film of the present invention on a substrate, a polyamic acid obtained by condensation of a tetracarboxylic dianhydride, which is a precursor of polyimide, with a diamino compound is applied to the substrate, followed by heat treatment. Then, a method of forming a polyimide-based polymer film on a substrate by performing a dehydration reaction is preferable. Specifically, the polyamic acid is N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), butyl cellosolve,
Dissolve in a solvent such as ethyl carbitol, 0.1 to 30
Weight% solution, and apply this solution by brushing, dipping,
Coating is performed by a spin coating method, a spray method, a printing method, or the like to form a coating film on a substrate. After the application, a heat treatment is performed at 100 to 450 ° C., preferably 180 to 290 ° C., and a dehydration ring-closing reaction is performed to provide a liquid crystal alignment film made of a polyimide-based polymer film. If the obtained polymer film does not have good adhesion to the substrate, it can be improved by performing a surface treatment on the substrate surface with a silane coupling agent in advance and then forming the polymer film. Thereafter, the coated surface is rubbed in one direction with a cloth, so that a liquid crystal alignment film is obtained.

In this substrate, an electrode, specifically, a transparent electrode of ITO (indium tin oxide) or tin oxide is formed on the substrate. Under the electrode, an insulating film for the purpose of preventing alkali elution from the substrate, an undercoat film such as a color filter and a color filter overcoat may be formed. An overcoat film such as a filter film may be formed, or an active element such as a TFT or a non-linear resistance element may be formed. The configuration of these electrodes, undercoat, and other components in the cell can be the same as the configuration of the conventional liquid crystal element.

After rubbing the coated surface of the substrate formed as described above with a cloth or the like, cells are formed, liquid crystal is injected, and the injection port is sealed. As the liquid crystal to be enclosed, various liquid crystals such as a liquid crystal to which a dichroic dye is added can be used in addition to a normal nematic liquid crystal. The liquid crystal alignment film of the present invention has such a characteristic that the occurrence of scratches due to rubbing can be reduced even if the firing conditions are changed, while maintaining good alignment in the above-mentioned use.

FIG. 1 is a sectional view of a liquid crystal display device manufactured as described above. This apparatus uses a glass substrate 11
Spacer and seal resin 1 between transparent electrode 12 and liquid crystal alignment film 13 formed thereon and glass substrate 11.
4 and a liquid crystal 15 enclosed by the liquid crystal. The transparent electrode 12 is connected to voltage applying means (not shown), and a liquid crystal display device operates by applying a predetermined device between the electrodes.

[0025]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. Example 1 200 g of dehydrated and purified N-methyl-2-pyrrolidone was added to an 11 four-necked flask equipped with a stirrer, a thermometer, a condenser and a nitrogen purge device, and then 1,1-bis [4-
(4-Aminophenoxy) phenyl] -4-ethylcyclohexane (27.1 g) was charged and dissolved by stirring. This is 2
After cooling to 0 ° C., 9.4 g of pyromellitic dianhydride and 3.1 g of a mixture of alicyclic acid dianhydrides having an average of 1.2 in the above-mentioned general formula (III) are added at once, The mixture was stirred while cooling. Two hours later, 0.4 g of paraaminophenyltrimethoxysilane was added, and the mixture was stirred and reacted at room temperature for 3 hours. Thereafter, the reaction solution was diluted with 133.3 g of N-methyl-2-pyrrolidone and 333.4 g of butyl cellosolve to obtain a clear solution of 6% by weight of polyamic acid. The viscosity of this solution at 25 ° C. (a value measured at a temperature of 25 ± 0.1 ° C. using an E-type viscometer manufactured by Tokyo Keiki Co., Ltd .; the same applies hereinafter) was 50 centipoise. Using this solution, it was applied by printing on a transparent glass substrate provided with an ITO transparent electrode. After the application, the coating was heated and dried on a hot plate, and then heat-treated on a hot plate or oven at 240 ° C. to obtain a polyimide film having a coating thickness of about 600 °. The coating surfaces of the two substrates on which the polyimide film was formed were rubbed with a predetermined strength, and a liquid crystal cell having a twist angle of 240 degrees was assembled to enclose the liquid crystal. After sealing, the liquid crystal element was heated to the temperature of the isotropic liquid and then cooled to obtain a liquid crystal element.

The alignment of these liquid crystal elements is good,
No flaw-like defect generated from rubbing was generated by either of the heating methods. Comparative Example 1 The same operation as in Example 1 was carried out except that pyromellitic acid alone was used without using the alicyclic acid dianhydride represented by the structural formula (III) , and a 6% by weight transparent solution was obtained. Obtained.
The viscosity of this solution at 25 ° C. (measured at a temperature of 25 ± 0.1 ° C. using an E-type viscometer manufactured by Tokyo Keiki Co.) was 60
It was centipoise. Using this solution, it was applied by printing on a transparent glass substrate provided with an ITO transparent electrode.
After application, after heating and drying on a hot plate, 240 ° C
Was performed on a hot plate or oven to obtain a polyimide film having a coating film thickness of about 600 °. The coating surfaces of the two substrates on which the polyimide film was formed were rubbed with a predetermined strength, and a liquid crystal cell having a twist angle of 240 degrees was assembled to enclose the liquid crystal. After sealing, the liquid crystal element was heated to the temperature of the isotropic liquid and then cooled to obtain a liquid crystal element.

The orientation of these liquid crystal devices was good. No rubbing damage was observed in the liquid crystal element obtained by heat treatment in the oven, but rubbing damage was generated in the liquid crystal element heat-treated by the hot plate. The degree of scratching caused by the nucleus is different.

[0028]

According to the present invention, the orientation is good,
An alignment film in which the occurrence of rubbing scratches does not depend on the firing conditions can be obtained. Further, according to the liquid crystal display device using the liquid crystal alignment film of the present invention, it is possible to realize a liquid crystal display having good display quality without rubbing damage.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display device to which the present invention is applied.

[Explanation of symbols]

11: glass substrate, 12: transparent electrode, 13: alignment film, 1
4: spacer and seal resin, 15: liquid crystal.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Katsuhiko Kumakawa, Inventor 302, 94-1 Midoricho, Neyagawa-shi, Osaka (56) References JP-A-4-13724 (JP, A) JP-A-4-194909 (JP, A) JP-A-3-197927 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1337 C08G 73/10

Claims (4)

(57) [Claims] 1. A compound having a divalent aromatic group or an alicyclic structure
A diamino compound having a group and a group having an aromatic group.
Having a tetracarboxylic dianhydride and an alicyclic structure
Copolymerized with a tetracarboxylic dianhydride having a group
The resulting polyamic acid was applied to a substrate with a transparent electrode
Then, the mixture is heated to cause a dehydration ring-closing reaction, and the general formula And (In the above formulas, X is a group having a divalent aromatic group or alicyclic structure, Y ₁ and Y ₂ is is a group having a different tetravalent aromatic or alicyclic structure together, Y ₁ and Y ₂ small
At least one type is a group having an alicyclic structure, m and n
Wherein an integer represents an integer) . A method for producing a liquid crystal alignment film, comprising: forming a liquid crystal alignment film containing a polyimide having a structural unit represented by the following formula: 2. A tetracarboxylic acid having an aromatic group.
Water is pyromellitic dianhydride, 3,3 ', 4,4'-
Biphenyltetracarboxylic dianhydride, 2,2 ', 3
3′-biphenyltetracarboxylic dianhydride, 2,3
3 ′, 4′-biphenyltetracarboxylic dianhydride,
3,3 ', 4,4'-benzophenonetetracarboxylic acid
Dianhydride, 2,3,3 ', 4'-benzophenonetetra
Carboxylic dianhydride, 2,2 ', 3,3'-benzophene
Non-tetracarboxylic dianhydride, bis (3,4-dical
Boxyphenyl) ether dianhydride, bis (3,4-di
Carboxyphenyl) sulfone dianhydride, 1,2,5
6-naphthalenetetracarboxylic dianhydride and 2,
3,6,7, -naphthalenetetracarboxylic dianhydride
Is a compound selected from the group consisting of
The boronic dianhydride has the formula The method according to claim 1 , wherein the compound is a compound selected from the group consisting of: 3. A tetracarboxylic acid having an alicyclic structure.
The composition ratio of the structural unit composed of water is 3% to 97%;
A method for producing a liquid crystal alignment film according to claim 1 . 4. The method according to claim 1, wherein
That the liquid crystal alignment film produced by the method of
Liquid crystal display element.