JPH08120078A - Novel polyimide - Google Patents

Abstract

PURPOSE: To obtain a polyimide excellent in liquid-crystal alignment, etc., and suited for use as a liquid-crystal alignment film by reacting two specific diamino compounds with a specific tetracarboxylic dianhydride and heating the resultant poly(amic acid). CONSTITUTION: A diamino compound represented by formula I (wherein R<1> is a 1-20C alkyl) (e.g. ethyl 3,5-diaminobenozate) is reacted with a diamino compound represented by formula II (wherein (m) is 1-20; (n) is 1-2; and R<2> is a 1-20C alkyl or alkoxy) e.g. 4-(trans-4-ethylcyclohexyl)phenoxypropyl)3,5 diaminobenzoate} and the tetracarboxylic dianhydride represented by formula III in a solvent to yield a polyamic acid. This acid is heated to obtain a polyimide comprising 5-95mol% structural units represented by formula IV and 95-5mol% structural units represented by formula V.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel polyimide copolymer having an alkyl ester and a liquid crystal group in a side chain.

[0002]

2. Description of the Related Art Polyimide has the highest heat resistance among commercially available plastics, and its characteristics do not change significantly with temperature.
It is an excellent plastic with good impact resistance, dimensional stability, electrical characteristics and wear 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 liquid crystal 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 Unexamined Patent Publication (Kokai) No. 4-100020 discloses a diamino compound having a linear alkyl ester in a side chain,
A polyimide alignment film comprising 3 ', 4,4'-biphenyltetracarboxylic dianhydride and having the structural unit of the above formula [1], and a liquid crystal display device using the same are disclosed. However, there is no specific description about the pretilt angle of this alignment film. On the other hand, JP-A-3-179322, JP-A-3-179323, and JP-A-5-2724.
Japanese Patent Publication No. 4 discloses a polyimide-based liquid crystal alignment film containing a diamine component having a liquid crystal group in a side chain as a monomer. However, when these polyimides are manufactured
Firing at 0 ° C. for 1 to 2 hours is required, and when a dye color filter having low heat resistance is attached, there is a risk of causing fading deterioration.

The present inventor has a spacer composed of a flexible alkyl chain in the side chain, and a diamine component having a liquid crystal group such as a phenylcyclohexyl group or a phenylbicyclohexyl group at the tip thereof and 2,2-bis (4 -Aminophenoxyphenyl) -propane was used as a monomer and was invented as a polyimide having excellent low-temperature curability, and a patent application was filed as Japanese Patent Application No. 6-173269. When this polyimide was used as a liquid crystal alignment film, The pretilt angle was a relatively low value of about 8 degrees. As a result of further studies, a diamine component and a tetracarboxylic 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 When a polyimide alignment film having the structural unit of the above formula [2] obtained by the reaction with was produced, it was discovered that it had a high pretilt angle of 30 degrees or more, and a patent application was filed as Japanese Patent Application No. 6-234162. went. However, since this polymer is a homopolymer, it was difficult to freely control the pretilt angle according to the purpose.

[0007]

As described above, in the conventional polyimide-based alignment film, there is a risk of fading deterioration of the color filter during manufacture, and it is difficult to freely control the pretilt angle. Met. The object of the present invention is for electrical and electronic materials that can be produced by firing at a lower temperature for a shorter time, and in particular, it has excellent liquid crystal orientation without causing discoloration of a color filter or the like during the production of liquid crystal cells.
It is to provide a novel polyimide useful as a liquid crystal alignment film capable of freely controlling the pretilt angle in a wide range of 5 degrees.

[0008]

The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, a diamine component having a flexible alkyl chain as a side chain can be obtained as a monomer. And a diamine component having a liquid crystal group such as a phenylcyclohexyl group or a phenylbicyclohexyl group in its side chain as a monomer, a polyimide comprising a copolymer of the structural unit of the above formula [2] Since it can be manufactured at a relatively low temperature and for a short time, it does not cause discoloration of color filters etc. during liquid crystal cell manufacturing, and has excellent film-forming properties, adhesion to glass substrates and thermal stability. And the liquid crystal alignment was good. Further, by changing the composition ratio of the compound of formula [1] and the compound of formula [2],
The inventors have found that the pretilt angle can be freely controlled in a wide range of degrees and completed the present invention.

That is, the constitution of the present invention is as follows. (1) A structural unit represented by the formula [1] and a structural unit represented by the formula [2], wherein the molar ratio of the structural unit of the formula [1] is 5
~ 95 mol% polyimide.

[Chemical 6] (However, R ¹ represents an alkyl group having 1 to 20 carbon atoms.)

[Chemical 7] (However, m is an integer of 1 to 20, n is 1 to 2, and R ² is an alkyl group or an alkoxy group having 1 to 20 carbon atoms.) (2) Diamino represented by the formula [3] and the formula [4] A polyimide obtained by reacting a compound with a tetracarboxylic acid dianhydride represented by the formula [5] in a solvent to produce a polyamic acid, and heating the polyamic acid.

Embedded image (However, R ¹ represents an alkyl group having 1 to 20 carbon atoms.)

[Chemical 9] (However, m is an integer of 1 to 20, n is 1 to 2, and R ² is an alkyl group or an alkoxy group having 1 to 20 carbon atoms.)

[Chemical 10] (3) A liquid crystal alignment film using the polyimide described in any one of the above items (1) to (2). (4) A liquid crystal display device including the liquid crystal alignment film described in the above item (3).

In the present invention, as the amine component of the polyimide, 3,5-diaminobenzoic acid alkyl ester represented by the formula [3] and 3,5-diaminobenzoic acid [4- (trans-4 -Alkyl-cyclohexyl) phenoxyalkyl] ester is used.

[Chemical 11] (However, R ¹ represents an alkyl group having 1 to 20 carbon atoms.)

[Chemical 12] (However, m is an integer of 1 to 20, n is 1 to 2, and R ² is an alkyl group or an alkoxy group having 1 to 20 carbon atoms.)

The 3,5-diaminobenzoic acid alkyl ester represented by the above formula [3] is produced according to the following chemical formula 13. That is, alcohol in the presence of triethylamine,
Condensed with 3,5-dinitrobenzoyl chloride to give 3,5
-Dinitrobenzoic acid alkyl ester is obtained, and this compound is catalytically reduced in the presence of a palladium-carbon catalyst to produce 3,5-diaminobenzoic acid alkyl ester.

[Chemical 13] (However, R ¹ represents an alkyl group having 1 to 20 carbon atoms.)

The 3,5-diaminobenzoic acid [4- (trans-4-alkyl-cyclohexyl) phenoxyalkyl] ester represented by the above formula [4] is produced according to the following Chemical Formula 14. That is, first, 4- (trans-4-alkyl-cyclohexyl) phenol and α, ω-alkylenehalohydrin were added in the presence of excess potassium carbonate to dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP). ) Or in a solvent such as dimethylformamide (DMF) at 100 to 150 ° C. to obtain an alcohol. Subsequently, this compound was condensed with 3,5-dinitrobenzoyl chloride in the presence of triethylamine,
3,5-Dinitrobenzoic acid [4- (trans-4-alkyl-cyclohexyl) phenoxyalkyl] ester is obtained. Finally, this compound is catalytically reduced in the presence of a palladium-carbon catalyst to produce 3,5-diaminobenzoic acid [4- (trans-4-alkyl-cyclohexyl) phenoxyalkyl] ester.

[0013]

Embedded image (However, m is an integer of 1 to 20, n is 1 to 2, and R ² is an alkyl group or an alkoxy group having 1 to 20 carbon atoms.)

The tetracarboxylic dianhydride used in the present invention is 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (BPDA) represented by the formula [5].

[Chemical 15]

The molar ratio of each structural unit in the polyimide molecule consisting of the structural units represented by the formulas [1] and [2] is 5 to 95 mol% in the formula [1] and 95 in the formula [2].
Is preferably 5 to 5 mol%, more preferably 30 to 70 mol% in the formula [1] and 70 to 30 mol% in the formula [2]. When the ratio of the formula [1] is 5 mol% or less, there is a problem that the pretilt angle of the obtained polyimide alignment film is lowered.

The length of the alkyl group in the structural unit represented by the formula [1] in the polyimide molecule is preferably 3 or more carbon atoms, more preferably 6 or more carbon atoms. When the number of carbon atoms is 3 or less, the flexibility in the side chain direction becomes low and the low temperature curability deteriorates.

The m in the structural unit represented by the formula [2] in the polyimide molecule is preferably 3 or more, and more preferably 6 or more. When m is 3 or less, flexibility in the side chain direction is reduced, and therefore, high temperature firing is required during production.

The above diamine and tetracarboxylic dianhydride are subjected to a condensation reaction to obtain a polyamic acid. These reactions are carried out under anhydrous conditions in a solvent such as DMAc, NMP, DMF, dimethyl sulfoxide (DMSO), sulfolane, butyrolactone, cresol, phenol, halogenated phenol, cyclohexanone, dioxane and tetrahydrofuran, preferably in NMP solvent-10. ~ 30
Perform at a temperature of ° C.

In order to form the polyimide and the liquid crystal alignment film of the present invention on the substrate, the above-mentioned polyamic acid is applied on the substrate, heat-treated and dehydrated to form a polyimide polymer film on the substrate. The method is preferred. More specifically, the above polyamic acid is added to NMP and DMA.
Dissolve in a solvent such as c, DMF, DMSO, butyl cellosolve, ethyl carbitol and adjust to a solution of 0.1 to 30% by weight, and use this solution for brush coating, dipping, spin coating, spraying and printing. And the like on the substrate.

After coating, 100 to 450 ° C., preferably 1
Heat treatment is performed at 80 to 220 ° C., and a dehydration ring closure reaction is performed to provide a polyimide-based polymer film. If the surface of the substrate is treated with a silane coupling agent before coating and a polymer 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 the liquid crystal display element is usually a glass substrate, and an electrode, specifically, a substrate having a transparent electrode of ITO (indium oxide-tin oxide) or tin oxide formed thereon. 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 substrate and the substrate, and the insulating film, the color filter film or the like may be overlaid on the electrode. A coat film may be provided. In addition, TFT (Thin film transistor Th
in-Film-Transistor) element, MIM
(Metal Insulator Metal Metal-Ins
An active element such as an ulator-metal 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.

The substrate with electrodes formed as described above is assembled into a cell, liquid crystal is injected, and the injection port is sealed to form 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 5 to 45 degrees by selecting the monomer ratio.

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 5 to 45 degrees, that is, a liquid crystal alignment film according to the present invention. Is a feature, usually a substrate with electrodes,
It is composed of a voltage applying means, a liquid crystal alignment film, a liquid crystal layer and the like.

[0024]

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 application method.

[0026]

【Example】

Example 1 Production of Polyimide Comprising Structural Units Represented by Formula [1] and Formula [2]: 1) 3,5-Diaminobenzoic acid stearyl ester represented by Formula [3] (R ¹ = C ₁₈ H ₃₇ ). Manufacturing of. 200 ml of tetrahydrofuran (THF) was placed in a 500 ml three-necked flask equipped with a stirrer, 13.5 g (0.050 mol) of stearyl alcohol and 8.4 ml of triethylamine were added thereto, and the mixture was stirred at 0 ° C. To this, 11.5 g (0.05) of 3,5-dinitrobenzoyl chloride was added.
A solution prepared by dissolving 50 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. Subsequently, the organic layer was washed 3 times with 3N hydrochloric acid and then with saturated aqueous sodium hydrogen carbonate.
Washed once and then 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 3,5-dinitrobenzoic acid stearyl ester 18.1 g ( 0.039m
ol) was obtained. The melting point was 75.9-76.7 ° C. After confirming the structure of this compound by IR and NMR, the compound was subjected to catalytic reduction.

That is, 8.0 g (0.017 mol) of 3,5-dinitrobenzoic acid stearyl ester was dissolved in 300 ml of ethyl acetate to prepare 1.0 g of 5% palladium-carbon.
Was added to carry out catalytic reduction under normal temperature and pressure. After completion of the reaction, the catalyst was filtered off, the solvent was distilled off under reduced pressure, and the obtained crystals were recrystallized twice with n-heptane / ethyl acetate to give 4,5-diaminobenzoic acid stearyl ester 4.48 g (0 0.011m
ol) was obtained. The melting point of this compound is 81.8-82.6 ° C.
Met.

2) 3,5-diaminobenzoic acid [4- (trans-4-ethyl-cyclohexyl) phenoxypropyl] ester represented by the formula [4] (where m = 3, n
= 1 and R ² = C ₂ H ₅ ). In a 1 L three-necked flask equipped with a condenser and a stirrer, 500 ml of dimethylformamide and 20.4 g (0.10 g) of 4- (trans-4-ethyl-cyclohexyl) phenol.
mol) and 41.4 g (0.30 mol) of potassium carbonate were added and stirred at room temperature. 18.1 g (0.13 mol) of 3-bromo-1-propanol was added thereto, and the mixture was vigorously stirred at 100 ° C. After reacting for 10 hours, this solution was added to 2 L of water and extracted with 1.5 L of ethyl acetate. Then, the organic layer was washed 3 times with 3N hydrochloric acid and 3 times with 2N aqueous sodium hydroxide solution.
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 4- (trans-
17.6 g (0.067 mol) of 4-ethyl-cyclohexyl) phenoxypropanol was obtained. Melting point is 68.5
It was ~ 69.9 ° C.

Subsequently, 300 ml of THF was placed in a 500 ml three-necked flask equipped with a stirrer, and 18.0 g (0.068 mol) of 4- (trans-4-ethyl-cyclohexyl) phenoxypropanol and 11.4 ml of triethylamine were added thereto. The mixture was stirred at 0 ° C. 3,5 to this
-Dinitrobenzoyl chloride 15.7 g (0.068 m
ol) was dissolved in 50 ml of THF, and the solution was added dropwise over 30 minutes, and the reaction was performed for 6 hours. After completion of the reaction, this liquid was added to 1 L of water and extracted with 1.5 L of ethyl acetate. Subsequently, the organic layer was washed with 3N hydrochloric acid three times, saturated aqueous sodium hydrogen carbonate 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 ethyl acetate to give 3,5-dinitrobenzoic acid [4- (trans- 4-ethyl-cyclohexyl)
Phenoxypropyl] ester 23.3 g (0.051 m
ol) was obtained. The melting point was 108.0-109.4 ° C. After confirming the structure of this compound by IR and NMR, the compound was subjected to catalytic reduction.

That is, 3,5-dinitrobenzoic acid [4
1-5.0 g (0.033 mol) of-(trans-4-ethyl-cyclohexyl) phenoxypropyl] ester was dissolved in 300 ml of ethyl acetate, 1.50 g of 5% palladium-carbon was added, and catalytic reduction was performed at room temperature and atmospheric pressure. After completion of the reaction, the catalyst was filtered off, the solvent was distilled off under reduced pressure, and the obtained crystals were recrystallized twice with n-heptane / ethyl acetate to give 3,
5-diaminobenzoic acid [4- (trans-4-ethyl-
Cyclohexyl) phenoxypropyl] ester 11.
1 g (0.028 mol) was obtained. The melting point of this compound was 91.5 to 92.4 ° C.

3) Polymerization reaction In a three-necked 50 ml flask, 0.0606 g (0.15 mmo) of 3,5-diaminobenzoic acid stearyl ester was obtained.
l), 3,5-diaminobenzoic acid [4- (trans-4
-Ethyl-cyclohexyl) phenoxypropyl] ester 0.5348 g (1.35 mmol), NMP 3.0 m
l was added and the mixture was stirred and dissolved at room temperature under a nitrogen stream. Next, this solution was kept at 10 ° C. and 0.4413 g (1.5%) of BPDA was added.
0 mmol) was added. NMP the BPDA on the vessel wall
It was washed off with 3 ml and reacted for 3 hours as it was. The obtained reaction liquid was diluted to 4.0 wt% with NMP / butyl cellosolve = 1/1 solvent, and then applied on a glass substrate with a transparent electrode of ITO by spin coating (spinner method). After coating, it was baked at 200 ° C. for 30 minutes to obtain a substrate provided with a polyimide film having a film thickness of 600 angstrom. This polyimide had a decomposition temperature of 360.3 ° C. and had good adhesion to the substrate. The remaining reaction liquid is methanol 30
It was poured into 0 ml and the deposited precipitate was filtered. This filtered material was dried under reduced pressure at room temperature to obtain a polyamic acid. The intrinsic viscosity of this polyamic acid is 0.51 (30 ° C, 0.5 g /
dl, NMP solution).

4) Preparation of Cell and Measurement of Pretilt Angle Rubbing treatment was applied to each film surface of the substrate provided with two polyimide films, and a liquid crystal cell having a cell thickness of 20 μm was assembled so that the rubbing directions were anti-parallel, and the chisso ( Liquid crystal FB-01 manufactured by K.K. Then, the enclosed cell was heat-treated at 120 ° C. for 30 minutes. After the heat treatment, it was allowed to cool and the pretilt angle was determined to be 29.2 degrees. Further, when the cell was observed with a microscope, the orientation was not disturbed, and excellent orientation was exhibited.

Examples 2 to 5, except that the component ratios of 3,5-diaminobenzoic acid stearyl ester and 3,5-diaminobenzoic acid [4- (trans-4-ethyl-cyclohexyl) phenoxypropyl] ester were changed. Polymerization reaction, cell preparation and pretilt angle measurement were carried out according to 3) and 4) of Example 1. Table 1 shows the component ratios and 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. A liquid crystal alignment film using this polyimide is excellent in adhesion to a glass substrate and liquid crystal alignment. Further, by changing the copolymerization ratio, the pretilt angle can be freely controlled in a wide range of about 5 to 45 degrees, and thus it is useful as a material for an alignment film of a liquid crystal cell for TN, STN and SBE.

[Brief description of drawings]

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

Claims (4)

[Claims] 1. A polyimide comprising a structural unit represented by the formula [1] and a structural unit represented by the formula [2], wherein the molar ratio of the structural unit of the formula [1] is 5 to 95 mol%. Embedded image (However, R ¹ represents an alkyl group having 1 to 20 carbon atoms.) (However, m is an integer of 1 to 20, n is 1 to 2, and R ² is an alkyl group or an alkoxy group having 1 to 20 carbon atoms.) 2. A diamino compound represented by the formula [3] or [4] and a tetracarboxylic acid dianhydride represented by the formula [5] are reacted in a solvent to produce a polyamic acid,
A polyimide obtained by heating the polyamic acid. Embedded image (However, R ¹ represents an alkyl group having 1 to 20 carbon atoms.) (However, m is an integer of 1 to 20, n is 1 to 2, and R ² is an alkyl group or an alkoxy group having 1 to 20 carbon atoms.) 3. A liquid crystal alignment film comprising the polyimide according to any one of claims 1 and 2. 4. A liquid crystal display device comprising the liquid crystal alignment film according to claim 3.