JPH08239472A - Aligned polyimide film - Google Patents

Abstract

PURPOSE: To obtain an oriented polyimide film useful as an electric and electronic material, especially as a liquid crystal film which can be produced by short-time low-temperature firing by reacting a diamino compound with a tetracarboxylic acid dianhydride and heating the formed polyamic acid. CONSTITUTION: This polyimide comprises structural units represented by the formula (wherein L is 1-20; M is 1-3; N is 0-2; R is 1-20C alkyl or alkoxy; and A is a tetravalent organic group). This polyimide is produced desirably by a process comprising applying a polyamic acid, as a polyimide precursor, obtained by condensing a diamine with a tetracarboxylic acid dianhydride to a substrate, and thermally dehydrating the applied polyamic acid to form a polyimide film on the substrate. In the formula, L is 1-20, desirably 3 or above. When L is 3 or below, the flexibility in the direction of side chains decreases, and therefore high-temperature firing is required in the production. Further, a problem that the main chain interferes with the alignment of side chain liquid crystal groups in the obtained oriented polyimide film arises.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel polyimide alignment film having a liquid crystal group in its side chain.

[0002]

2. Description of the Related Art Polyimide resin is an excellent plastic that has the highest heat resistance among commercially available plastics, has little change in characteristics with temperature, and has good impact resistance, dimensional stability, electrical characteristics, and abrasion resistance. . Utilizing these characteristics, it is used as a material for aerospace and machinery, including electrical and electronic fields such as insulation and sealing materials and printed circuit boards. Further, in recent years, attention has been paid as a material for an alignment film of a liquid crystal display element, and many polyimide-based alignment films have been developed.

In a liquid crystal display element used in a clock or a calculator, a twisted nematic (hereinafter abbreviated as TN) having a structure in which the arrangement direction of nematic liquid crystal molecules is twisted 90 degrees between a pair of upper and lower electrode substrates. ) Mode is mainly adopted. Also, a super twisted nematic (hereinafter abbreviated as STN) in which the twist angle of the liquid crystal is 180 to 270 degrees.
Modes are also now commonplace, and are being produced in large quantities for large displays such as word processors and personal computers. The alignment film used in such a liquid crystal display device is not enough to simply align the liquid crystal molecules, and in order to improve the responsiveness and ensure the bistability, the alignment film is not provided between the substrate surface and the liquid crystal molecules. A pretilt angle of 1 to 4 degrees in the TN mode and 4 to 8 degrees in the STN mode must be provided. Further, in recent years, a super-twist birefringence effect (hereinafter abbreviated as SBE) mode has been developed as a display element having more excellent contrast and viewing angle dependency. In this method, a high pretilt angle of 20 to 30 degrees is required. .

Further, although it is desired to color the liquid crystal display element, there is a color filter method as one of the color display methods which are widely used at present, and its use for liquid crystal color televisions and personal computer displays is expanding. . This method is a method in which a color filter is provided between the substrate and the transparent electrode. In this method, a polyimide film is prepared by applying a polyamic acid to a substrate provided with a transparent electrode and a color filter, followed by drying and firing, but since the dye-type color filter is relatively inferior in heat resistance, the filter is fired. There is a possibility of fading and deterioration. Therefore, when attaching a color filter, it is preferable to bake at a temperature as low as possible.

Japanese Patent Laid-Open Nos. 3-179322 and 3
JP-A-179323 and JP-A-5-27244 disclose a polyimide-based liquid crystal alignment film containing a diamine having a liquid crystal group in a side chain as a monomer. However, these polyimides are produced at 200 to 250 ° C.
Firing for 2 hours is required, and when a dye color filter having low heat resistance is attached, there is a possibility that the color fading of the filter may be deteriorated by firing.

Diamine and pyromellitic dianhydride having a spacer composed of a flexible alkyl chain at the side chain and having a liquid crystal group such as phenylcyclohexyl group or phenylbicyclohexyl group at the tip thereof, 3,3 ',
A polyimide alignment film obtained by reaction with 4,4′-biphenyltetracarboxylic dianhydride or 1,1,1,3,3,3, -hexafluoroisopropylidene-2,2-bisphthalic dianhydride As a result of manufacturing, it was found that it has a high pretilt angle of about 15 degrees or more. However, it does not disclose a polyimide using an acid anhydride component other than the above. Moreover, since these polyimides are homopolymers, it is difficult to control the pretilt angle according to the purpose.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, that is, in the production of polyimide, for electrical and electronic materials which can be produced by firing at a lower temperature and a shorter time, particularly liquid crystals. Provided is a novel polyimide which is excellent in liquid crystal alignment property without causing fading of a color filter or the like during cell production, and is useful as a liquid crystal alignment film capable of freely controlling a pretilt angle in a wide range of about 10 to 50 degrees. That is.

[0008]

Therefore, as a result of intensive studies, the present inventors have found that a diamine component having a liquid crystal group such as a phenylcyclohexyl group or a phenylbicyclohexyl group in its side chain and a tetracarboxylic dianhydride. The polyimide alignment film comprising the structural unit of the formula [1] and the alignment film of the polyimide copolymer comprising the structural unit of the formulas [1] and [4] obtained by the polycondensation reaction of Since it can be manufactured by baking for a long time, it does not cause discoloration of color filters when manufacturing liquid crystal cells, has excellent film-forming properties, adhesion to glass substrates and thermal stability, and liquid crystal alignment. The property was also good. Furthermore, the formula [1]
The present invention has been completed by finding that the pretilt angle can be freely controlled in a wide range of about 10 to 50 degrees by changing the molar ratio of the structural unit of 1 to the structural unit of the formula [4].

That is, the constitution of the present invention is as follows. (1) A polyimide comprising a structural unit represented by the formula [1].

[Chemical 6] (However, L = 1 to 20, M = 1 to 3, N = 0 to 2 are integers, R is an alkyl group or an alkoxy group having 1 to 20 carbon atoms, and A is a tetravalent organic group.) (2) A diamino compound represented by the formula [2] and a formula [3]
A polyimide obtained by reacting a tetracarboxylic acid dianhydride represented by the following in a solvent to produce a polyamic acid and heating the polyamic acid.

[Chemical 7] (However, L = 1 to 20, M = 1 to 3, N = 0 to 2 are integers, and R represents an alkyl group or an alkoxy group having 1 to 20 carbon atoms.)

Embedded image (However, A represents a tetravalent organic group.) (3) A polyimide comprising a structural unit represented by the formula [1] and the formula [4].

[Chemical 9] (However, A represents a tetravalent organic group and B represents a divalent organic group.) (4) A diamino compound represented by the formula [2] or the formula [5] and a formula [3] A polyimide obtained by reacting a tetracarboxylic acid dianhydride in a solvent to produce a polyamic acid, and heating the polyamic acid.

[Chemical 10] (However, B represents a divalent organic group.) (5) A liquid crystal alignment film using the polyimide described in any one of the above items (1) to (4). (6) A liquid crystal display device including the liquid crystal alignment film according to the item (5).

In order to produce the polyimide of the present invention, the polyimide precursor polyamic acid obtained by the condensation reaction of diamine and tetracarboxylic dianhydride is coated on a substrate and heat-treated to dehydrate the polyimide. The method of forming the film on the substrate is preferred.

A detailed description will be given below. Formula [2] as the diamine (where L = 1 to 20, M = 1 to 3 and N = 0
~ 2, R represents an alkyl or alkoxy group having 1 to 20 carbon atoms. ) Compounds represented by
(Trans-4-alkylcyclohexyl) phenoxyalkyl = 3,5-diaminobenzoate, and ω-
(4-Alkylbiphenyl) oxyalkyl = 3,5-
Diaminobenzoate is used. Ω- (trans-4-alkylcyclohexyl) phenoxyalkyl = 3,5-diaminobenzoate represented by the above formula [2], and ω- (4-alkylbiphenyl) oxyalkyl =
3,5-Diaminobenzoate can be produced according to the reaction formula.

[Chemical 11] (However, L = 1 to 20, M = 1 to 3, N = 0 to 2 are integers, R is an alkyl or alkoxy group having 1 to 20 carbon atoms, and X is a halogen.)

That is, first, trans-4-alkylcyclohexylphenol or 4-alkylbiphenol and α, ω-alkylenehalohydrin are added to dimethylacetamide (DMA) in the presence of excess potassium carbonate.
c), N-methyl-2-pyrrolidone (NMP), or dimethylformamide (DMF) in a solvent such as 100 to
Condensation is performed at 150 ° C. to obtain an alcohol compound. Subsequently, this compound was condensed with 3,5-dinitrobenzoyl chloride in the presence of triethylamine to give ω- (trans-4-alkylcyclohexyl) phenoxyalkyl = 3,5-dinitrobenzoate, or ω- (4-alkyl). Biphenyl) oxyalkyl = 3,5-diaminobenzoate is obtained. Finally, this compound is produced by catalytic reduction in the presence of a palladium-carbon catalyst.

As the tetracarboxylic dianhydride, all compounds represented by the formula [3] can be used.
Specifically, 4,4'-oxydiphthalic dianhydride (OD
PA), aromatic tetracarboxylic dianhydrides such as 3,3′4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and 4,4′-sulfonyldiphthalic dianhydride (SDPA), and Aliphatic tetracarboxylic dianhydrides such as cyclobutane tetracarboxylic dianhydride can be mentioned.

As the diamine used when producing the copolymer, all compounds represented by the formula [5] can be used. Specifically, phenylenediamines,
Examples thereof include aromatic diamine compounds such as substituted benzidines and aliphatic diamine compounds such as alkylenediamines and cycloalkylenediamines.

The above polyamic acid is used under the anhydrous condition D
In a solvent such as MAc, NMP, DMF, DMSO, sulfolane, butyrolactone, cresol, phenol, halogenated phenol, cyclohexanone, dioxane, tetrahydrofuran, etc., preferably in NMP solvent -10
It is obtained by a condensation reaction of the above diamine and the above tetracarboxylic dianhydride at a temperature of 30 ° C.

In the polyimide molecule composed of the structural unit represented by the formula [1], L is from 1 to 20, preferably L is 3 or more, and more preferably L is 6 or more. L
When it is 3 or less, flexibility in the side chain direction is lowered, and therefore, high temperature firing is required at the time of production. Further, in the obtained polyimide alignment film, there arises a problem that the alignment of the side chain liquid crystal groups is disturbed by the main chain.

The molar ratio of each structural unit in the copolymer of the structural units represented by the formulas [1] and [4] is represented by the formula [1]
Is preferably 5 to 95 mol%, the formula [4] is preferably 95 to 5 mol%, more preferably the formula [1] is 40 to 95 mol%, and the formula [4] is 60 to 5 mol%. When the ratio of the formula [1] or the formula [4] is 5 mol% or less, the effect of copolymerization is lost. If the ratio of the formula [1] is set to 40 mol% or less, the pretilt angle may decrease.

In order to form the polyimide alignment film and the liquid crystal alignment film of the present invention on the substrate, the above polyamic acid is used as N 2
MP, DMAc, DMF, dimethyl sulfoxide (DM
SO), butyl cellosolve, ethyl carbitol and the like to prepare a 0.1 to 30% by weight solution, and this solution is applied by brushing, dipping, spin coating, spraying,
It is applied on a substrate by a printing method or the like and heat-treated at 100 to 450 ° C., preferably 180 to 220 ° C., and a dehydration ring closure reaction is performed to provide a polyimide alignment film. If the surface of the substrate is treated with a silane coupling agent before coating and a polyimide alignment film is formed thereon, the adhesion between the film and the substrate can be improved. Then, the coated surface is rubbed in one direction with a cloth or the like to obtain a liquid crystal alignment film.

The substrate used as a liquid crystal display element is usually one on which electrodes, specifically, ITO (indium oxide-tin oxide) or tin oxide transparent electrodes are formed.
Further, an insulating film for preventing alkali elution from the substrate, an undercoat film such as a color filter or a color filter overcoat may be provided between the electrode and the substrate, and the insulating film or the color filter film may be provided on the electrode. You may provide an overcoat film, such as. TFT on the electrode
(Thin-Film-Transistor) element,
MIM (Metal-Insulator-Meta)
l) An active element such as an element may be formed. For these electrodes, undercoat, and other internal structure of the liquid crystal cell, the structure of a conventional liquid crystal display element can be used.

A cell is manufactured using a liquid crystal display substrate, liquid crystal is injected, and the injection port is sealed to manufacture a liquid crystal display element. As the liquid crystal to be enclosed, various liquid crystals such as a normal nematic liquid crystal and a liquid crystal added with a dichroic dye can be used. The liquid crystal alignment film of the present invention has good liquid crystal alignment and the pretilt angle can be freely controlled in a wide range of about 10 to 50 degrees by changing the ratio of two kinds of diamines.

The liquid crystal display device of the present invention is provided with a liquid crystal alignment film having a good liquid crystal alignment property and capable of freely controlling the pretilt angle in a wide range of about 10 to 50 degrees, that is, the liquid crystal alignment film of the present invention. And is usually composed of a substrate, a voltage applying means, a liquid crystal alignment film, a liquid crystal layer and the like.

[0022]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

The physical properties of the polyimide or polyamic acid obtained in the examples were measured by the following methods. Decomposition temperature (Td): A differential thermogravimetric simultaneous measurement device (TG / DTA-220 manufactured by Seiko Denshi Kogyo Co., Ltd.) was used to measure the temperature at a temperature rising rate of 10 ° C./min. Logarithmic viscosity: 3 in NMP solvent using Ubbelohde viscometer
It was measured at a concentration of 0.5 g / dl at 0 ° C. Pretilt angle: Measured using a magnetic field capacitance method.

[0024]

【Example】

Example 1 Production of Polyimide Comprising Structural Units Shown by Formula [1]: 1) 3- (trans-4-ethylcyclohexyl) phenoxypropyl = 3,5-diaminobenzoate (shown by formula [2] However, L = 3, M = 1, N = 1, R = C
₂ H ₅ ) production. DM in a 1 L three-necked flask equipped with a condenser and a stirrer.
F500 ml, trans-4-ethylcyclohexylphenol 20.4 g (0.10 mol), potassium carbonate 4
1.4 g (0.30 mol) was added and the mixture was stirred at room temperature. 3-Bromo-1-propanol 18.1 g (0.13 m)
ol) was added and the mixture was vigorously stirred at 100 ° C. After reacting for 10 hours, this solution was added to 2 L of water, and 1.5 L of ethyl acetate was added.
It was extracted with.

Subsequently, the organic layer was washed with 3N hydrochloric acid three times, a 2N sodium hydroxide aqueous solution three times, and further washed with water. The obtained ethyl acetate layer was dried over anhydrous sodium sulfate, the solvent was distilled off under reduced pressure, and the obtained crystal was recrystallized twice with n-heptane to give 3- (trans-4-ethylcyclohexyl) phenoxypropanol 17 0.6g (0.067mo
l) was obtained. The melting point was 68.5-69.9 ° C.

Subsequently, 300 ml of tetrahydrofuran (THF) was placed in a 500 ml three-necked flask equipped with a stirrer.
And 3- (trans-4-ethylcyclohexyl) phenoxypropanol 18.0 g (0.068 m)
ol) and 11.4 ml of triethylamine were added, and the mixture was stirred at 0 ° C. Add to this 3,5-dinitrobenzoyl chloride 1
A solution prepared by dissolving 5.7 g (0.068 mol) in 50 ml of THF was added dropwise over 30 minutes, and the reaction was performed for 6 hours as it was. After completion of the reaction, this liquid was added to 1 L of water and extracted with 1.5 L of ethyl acetate. Then, the organic layer was washed with 3N hydrochloric acid three times,
The extract was washed 3 times with saturated aqueous sodium hydrogen carbonate and further with water. The obtained ethyl acetate layer was dried over anhydrous sodium sulfate, the solvent was distilled off under reduced pressure, and the obtained crystal was recrystallized twice with ethyl acetate to give 3- (trans-4-ethylcyclohexyl) phenoxypropyl = 2,3-dinitrobenzoate 23.3g
(0.051 mol) was obtained. Melting point is 108.0-10
It was 9.4 ° C. After confirming the structure of this compound by IR and NMR, catalytic reduction of this compound was performed.

That is, 3- (trans-4-ethylcyclohexyl) phenoxypropyl = 3,5-dinitrobenzoate (15.0 g, 0.033 mol) was dissolved in 300 ml of ethyl acetate, and 5% palladium-carbon (1.50) was added.
g was added and catalytic reduction was performed at room temperature and normal pressure. After completion of the reaction, the catalyst was filtered off, the solvent was distilled off under reduced pressure, and the obtained crystal was n-
Recrystallize twice from heptane / ethyl acetate to give 3- (trans-4-ethylcyclohexyl) phenoxypropyl =
3,5-diaminobenzoate 11.1 g (0.028 m
ol) was obtained. The melting point of this compound is 91.5 to 92.4 ° C.
Met.

2) Polymerization reaction In a 50 ml three-necked flask, 3- (trans-4-ethylcyclohexyl) phenoxypropyl = 3,5-diaminobenzoate 0.5942 g (1.50 mmol),
NMP (3.0 ml) was added, and the mixture was dissolved with stirring under a nitrogen stream at room temperature. Next, this solution was kept at 10 ° C. and ODPA was 0.46.
53 g (1.50 mmol) was added. NMP 3.0 ml
The vessel wall was rinsed with and the reaction was continued for 3 hours. The obtained reaction liquid was diluted to 4.0 wt% with NMP / butyl cellosolve = 1/1 solvent and then applied on an ITO glass substrate by spin coating (spinner method). 2 coated substrates
It was baked at 00 ° C. for 30 minutes to obtain a substrate on which a polyimide film having a film thickness of about 600 angstrom was formed. The decomposition temperature of this polyimide was 357.9 ° C. The remaining reaction solution was poured into 300 ml of methanol and the deposited precipitate was filtered. The filtered product was dried under reduced pressure at room temperature to obtain a polyamic acid. The intrinsic viscosity of this polyamic acid is 0.55
(30 ° C., 0.5 g / dl, NMP solution).

3) Preparation of Cell and Measurement of Pretilt Angle Rubbing treatment was performed on the film surfaces of two substrates having polyimide films formed thereon, and a liquid crystal cell having a cell thickness of 20 μm was assembled so that the rubbing directions were anti-parallel. Liquid crystal LIXON-5048 manufactured by K.K. Then, the cell in which the liquid crystal was sealed was subjected to heat treatment at 120 ° C. for 30 minutes. After the heat treatment, let it cool down and obtain the pretilt angle.
It was 8.0 degrees.

Example 2 0.433 g (1.50 mmol) BTDA was added to BTDA.
Polymerization reaction and cell preparation were carried out in accordance with 2) and 3) of Example 1 except that Table 1 shows the physical properties of the obtained polyimide.

Example 3 0.5373 g (1.50 mmol) of SDPA was added to SDPA.
Polymerization reaction and cell preparation were carried out in accordance with 2) and 3) of Example 1 except that Table 1 shows the physical properties of the obtained polyimide.

Example 4 Preparation of Polyimide Comprising Structural Unit of Formula [1]: 1) 3- (4-Hexylbiphenyl) oxypropyl = 3,5-diaminobenzoate of Formula [2] (However, L = 3, M = 2, N = 0, R = C ₆ H ₁₃ ) Trans-4-ethylcyclohexylphenol 4-
1) of Example 1 except that it is changed to hexyl biphenol.
Manufactured according to. The melting point of the obtained 3- (4-hexylbiphenyl) oxypropyl = 3,5-diaminobenzoate was 91.5-93.1 ° C.

2) Polymerization reaction and pretilt angle measurement 3- (4-hexylbiphenyl) oxypropyl = 3
5-Diaminobenzoate 0.6691 g (1.50 m
mol), 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride 0.4413 g (1.50 mmol) was used as the monomer, but the polymerization reaction was carried out according to 2) and 3) of Example 1. And the cell was created. Table 1 shows the physical properties of the obtained polyimide.

[0034]

[Table 1]

[0035]

The polyimide obtained by the present invention can be produced by firing at low temperature for a short time, and has a high decomposition temperature of 350 ° C. or higher and can be used at high temperature. Further, the liquid crystal alignment film using the present polyimide is excellent in adhesion to a glass substrate and liquid crystal alignment. Furthermore, since the pretilt angle can be freely controlled in a wide range of about 10 to 50 degrees, TN,
It is useful as a material for the alignment film of liquid crystal cells for STN and SBE.

[Brief description of drawings]

1 is the IR of the polyimide film obtained in Example 4.
It is a spectrum figure.

Claims (6)

[Claims] 1. A polyimide comprising a structural unit represented by the formula [1]. Embedded image (However, L = 1 to 20, M = 1 to 3, N = 0 to 2 are integers, R is an alkyl group or an alkoxy group having 1 to 20 carbon atoms, and A is a tetravalent organic group.) 2. A diamino compound represented by the formula [2] is reacted with a tetracarboxylic dianhydride represented by the formula [3] in a solvent to produce a polyamic acid, and the polyamic acid is heated. A polyimide obtained by Embedded image (However, L = 1 to 20, M = 1 to 3, N = 0 to 2 are integers, and R is an alkyl group or an alkoxy group having 1 to 20 carbon atoms.) (However, A represents a tetravalent organic group.) 3. A polyimide comprising structural units represented by formula [1] and formula [4]. [Chemical 4] (However, A represents a tetravalent organic group and B represents a divalent organic group.) 4. A diamino compound represented by the formula [2] or [5] and a tetracarboxylic acid dianhydride represented by the formula [3] are reacted in a solvent to produce a polyamic acid. A polyimide obtained by heating the polyamic acid. Embedded image (However, B represents a divalent organic group.) 5. A liquid crystal alignment film comprising the polyimide according to any one of claims 1 to 4. 6. A liquid crystal display device comprising the liquid crystal alignment film according to claim 5.