JP3396964B2 - Polyimide with liquid crystal group - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel polyimide having a liquid crystal group, a liquid crystal alignment film using the same, and a liquid crystal display device.

[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. In addition, in a liquid crystal display element, generally, a liquid crystal alignment film using a polyimide polymer film is formed on the surface of a transparent electrode on the inner surface of a transparent substrate which is arranged to face each other with a predetermined gap. In recent years, a polyimide resin has attracted attention as a material for a liquid crystal alignment film of the liquid crystal display element, and many polyimide-based alignment films have been developed.

In a liquid crystal display element used in a timepiece or a calculator, a pair of upper and lower sheets are paired with each other. The nematic liquid crystal molecules are aligned 90 degrees between the substrates on which the liquid crystal alignment film using the polyimide polymer film is formed.
The twisted nematic (hereinafter abbreviated as TN) mode with a twisted structure is mainly adopted. In addition, a super twisted nematic (hereinafter abbreviated as STN) mode in which the twist angle of the liquid crystal is 180 to 270 degrees has become common now, and is mass-produced for large displays such as word processors and personal computers. The liquid crystal alignment film used in such a liquid crystal display device is not enough to simply arrange the liquid crystal molecules, and in order to improve the response and ensure the bistability, the liquid crystal alignment film is provided between the substrate surface and the liquid crystal molecules. 1-4 in TN mode
, The STN mode must have a pretilt angle of 4 to 8 degrees.

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. This is a system in which a color filter is provided on the transparent electrode of a liquid crystal cell, and is widely used in liquid crystal color televisions and personal computer displays. However, since the dye type color filter is relatively inferior in heat resistance, there is a possibility that the filter may be discolored and degraded by firing. Therefore, when a color filter is attached, it is preferable to bake at a temperature as low as possible when manufacturing a liquid crystal cell.

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. at 1-2 times.
It is necessary to bake for a time to form a polyimide, and when a dye color filter having low heat resistance is attached to the substrate, there is a risk of causing deterioration of color fading of the filter.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, the object of the present invention is to produce polyimides for electric and electronic materials which can be produced by firing at a lower temperature for a shorter time, especially color filters for producing liquid crystal cells. Without causing the fading of
It is an object of the present invention to provide a novel polyimide resin which is excellent in liquid crystal alignment and is useful as a liquid crystal alignment film capable of having a pretilt angle of about 1 to 8 degrees.

[0007]

SUMMARY OF THE INVENTION The inventors of the present invention have developed a high polyimide film which has excellent adhesion to a substrate, a pretilt angle of 1 to 8 degrees, can be manufactured by firing at low temperature for a short time, and is excellent in heat resistance. We have made extensive studies on the molecular film. As a result, it has a spacer consisting of a flexible alkyl chain in the side chain,
A diamine component having a liquid crystal group such as a phenylcyclohexyl group or a phenylbicyclohexyl group at its tip,
Polyimides having the structural units of the above formulas [1] and [2], which are obtained by firing a polyamic acid obtained by using 2,2-bis (4-aminophenoxyphenyl) -propane as a monomer, have a relatively low temperature and are short. Since it can be manufactured by baking for a long time, it does not cause deterioration of discoloration such as color filters at the time of manufacturing a liquid crystal cell, does not adversely affect rubbing treatment, and further improves film forming property and adhesion to a glass substrate. The inventors have found that they have excellent thermal stability, good liquid crystal alignment, and a pretilt angle of 1 to 8 degrees, and completed the present invention.

That is, the constitution of the present invention is as follows. (1) A polyimide comprising a structural unit represented by the formula [1] and a structural unit represented by the formula [2].

[Chemical 6] (However, m = 1 to integer 20, n = 1 to 2, R is 1 carbon atom
To 20 alkyl groups or alkoxy groups, and A represents a phenyl group or a 3,3 ′, 4,4′-biphenyl group. )

[Chemical 7] (However, A represents a phenyl group or a 3,3 ′, 4,4′-biphenyl group.) (2) A diamino compound represented by the formula [3] and the formula [4] and a formula [5] A polyimide obtained by reacting a tetracarboxylic acid dianhydride in a solvent to produce a polyamic acid and heating the polyamic acid.

[Chemical 8] (However, m = 1 to integer 20, n = 1 to 2, R is 1 carbon atom
To 20 alkyl groups or alkoxy groups. )

[Chemical 9]

[Chemical 10] (However, A represents a phenyl group or a 3,3 ′, 4,4′-biphenyl group.) (3) Use of the polyimide described in any one of the above items (1) and (2). Characteristic liquid crystal alignment film. (4) A liquid crystal display device including the liquid crystal alignment film described in the above item (3).

In the polyimide of the present invention, a polyimide precursor polyamic acid obtained by a condensation reaction of a diamine and a tetracarboxylic dianhydride is coated on a substrate and heat-treated for dehydration reaction to form a polyimide film on the substrate. It is manufactured by forming. That is, in the present invention, 2,4-diaminophenol [4- (trans-4-alkyl-cyclohexyl) represented by the formula [3] is used as the diamine.
The phenoxyalkyl] ether is used alone, or the compound represented by the formula [3] is mixed with 2,2-bis (4-aminophenoxyphenyl) -propane represented by the formula [4].

2,4-Diaminophenol [4- (trans-4-alkyl-cyclohexyl) phenoxyalkyl] ether represented by the above formula [3] can be produced according to the reaction formula of the following Chemical formula 11.

[Chemical 11] (However, m = 1 to integer 20, n = 1 to 2, R is 1 carbon atom
To 20 alkyl groups or alkoxy groups. )

That is, first, 4- (trans-4-alkyl-cyclohexyl) phenol and α, ω-alkylenehalohydrin are added in the presence of excess potassium carbonate, dimethylacetamide (DMAc), N-methyl-2- The alcohol compound is obtained by condensation in a solvent such as pyrrolidone (NMP) or dimethylformamide (DMF) at a temperature of 100 to 150 ° C. At this time, the number of moles of α, ω-alkylenehalohydrin is preferably equal to or more than the number of moles of 4- (trans-4-alkyl-cyclohexyl) phenol. Subsequently, the alcohol compound was dissolved in a solvent such as toluene, ether, hexane, or heptane, or with no solvent.
The hydroxyl group was chlorinated by treatment with thionyl chloride in an equimolar amount or more with the alcohol at a temperature of 10 ° C to the boiling point of the solvent. Subsequently, this compound and 2,4-dinitrophenol were treated with DMAc, NMP, D in the presence of excess potassium carbonate.
Condensation in a solvent such as MF at a temperature of 100 to 150 ° C.,
2,4-Dinitrophenol [4- (trans-4-alkyl-cyclohexyl) phenoxyalkyl] ether is obtained. Finally, this compound is produced by catalytic reduction in the presence of 10 to 50% by weight of the compound in the presence of a palladium-carbon catalyst in a solvent such as ethyl acetate, toluene, THF, or an alcohol system.

The tetracarboxylic dianhydride used in the present invention is a compound represented by the formula [5], for example, pyromellitic dianhydride (PMDA), 3,3 ', 4,4'-biphenyltetracarboxylic acid. Acid dianhydride (BPDA).

The polyamic acid is obtained by the condensation reaction of diamine and tetracarboxylic dianhydride. These reactions are carried out under anhydrous conditions in a solvent such as DMAc, NMP, DMF, dimethylsulfoxide (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 film or the liquid crystal alignment film of the present invention on the substrate, the polyamic acid obtained by the above method is added to NMP, DMAc, DMF, DMS.
It is dissolved in a solvent such as O, butyl cellosolve, ethyl carbitol, and adjusted to a 0.1 to 30 wt% solution, and this solution is applied on a substrate by a brush coating method, a dipping method, a spin coating method, a spray method, a printing method, or the like. And the coated substrate at 200 ° C
Thereafter, heat treatment is performed within 30 minutes to cause dehydration ring closure reaction to form a polyimide-based polymer film. The heat treatment conditions at this time are preferably 180 to 200 ° C. and 30 minutes or less, but may be 100 to 450 ° C. and 30 minutes to 2 hours.

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 molar ratio of each structural unit in the polyimide molecule composed of the structural units represented by the formulas [1] and [2] is 10 to 90 mol% in the formula [1] and in the formula [2]. It is preferably 90 to 10 mol%, more preferably 30 to 70 mol% in the formula [1] and 70 to 30 in the formula [2].
Mol%. When the ratio of the formula [1] is 10 mol% or less, there arises a problem that the liquid crystal alignment property of the obtained polyimide alignment film is deteriorated.

A glass substrate is usually used as a substrate used as a liquid crystal display element, and electrodes, specifically, transparent electrodes made of ITO (indium oxide-tin oxide) or tin oxide are formed on the substrate. 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 an insulating film, a color filter film or the like may be provided on the electrode. An overcoat film may be provided.
In addition, a thin film transistor (TFT) element, a metal insulator metal (Metal-Insulator) on the electrode.
An active element such as an or-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 on which the liquid crystal alignment film is thus formed is used to form 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 to which a dichroic dye is added can be used. The liquid crystal alignment film of the present invention has good liquid crystal alignment and can have a pretilt angle of 1 to 8 degrees.

The liquid crystal display device of the present invention is characterized in that it has a liquid crystal alignment film having a good liquid crystal alignment property and a pretilt angle of 1 to 8 degrees, that is, the liquid crystal alignment film of the present invention. Yes, it is usually composed of a substrate, a voltage applying means, a liquid crystal alignment film, a liquid crystal layer, and the like.

[0020]

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 the crystal rotation method.

[0022]

【Example】

Example 1 Production of Polyimide Comprising Structural Units Represented by Formula [1] and Formula [2]: 1) 2,4-Diaminophenol [4- (trans-4-alkyl-cyclohexyl) phenoxy Represented by Formula [3] Alkyl] ether (where m = 3, n = 1,
Production of R = C ₂ H ₅ ). In a 1 L three-necked flask equipped with a cooling tube and a stirrer, 500 ml of dimethylformamide and 40.8 g (0.20) of 4- (trans-4-ethyl-cyclohexyl) phenol.
mol) and 55.2 g (0.40 mol) of potassium carbonate were added and stirred at room temperature. 3-Bromo-1-propanol (33.4 g, 0.14 mol) 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-
37.2 g (0.142 mol) of 4-ethyl-cyclohexyl) phenoxypropanol was obtained. Melting point is 68.5
Was ~ 69.9 ° C.

Then, in a 200 ml round-bottomed flask equipped with a cooling tube, 4- (trans-4-ethyl-cyclohexyl) phenoxypropanol (20.0 g, 0.076 mo) was used.
1) and tetrahydrofuran (10.0 ml) were taken, thionyl chloride (10.0 ml) was added, and the mixture was reacted at 70 ° C. for 1 hour. After the reaction was completed, the solvent was distilled off under reduced pressure to obtain a residue,
Silica gel column (n-heptane: ethyl acetate = 2:
Purification in 1) gave 4- (trans-4-ethyl-cyclohexyl) phenoxypropyl chloride. This compound was used for the next reaction after confirming the structure by IR and NMR.

In a 500 ml three-necked flask equipped with a condenser and a stirrer, 300 ml of dimethylformamide, 2,
4-dinitrophenol 9.20g (0.050mo
1) and 13.8 g (0.10 mol) of potassium carbonate were added and stirred at room temperature. 4- (trans-4-ethyl-
Cyclohexyl) phenoxypropyl chloride 14.0
g (0.050 mol) 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 extracted with 1.5 L of ethyl acetate. Subsequently, the organic layer was washed 3 times with 3N hydrochloric acid, 3 times with 2N aqueous sodium hydroxide solution, and further washed with water. The obtained ethyl acetate layer was dried over anhydrous sodium sulfate, and the solvent was distilled off under reduced pressure to obtain a crystal.
Recrystallized twice from heptane / ethyl acetate to give 2,4-dinitrophenol [4- (trans-4-ethyl-cyclohexyl) phenoxypropyl] ether 12.4 g
(0.029 mol) was obtained. Melting point is 91.5-92.4
It was ℃.

Subsequently, 2,4-dinitrophenol [4
7.00 g (0.016 mol) of-(trans-4-ethyl-cyclohexyl) phenoxypropyl] ether was dissolved in 300 ml of ethyl acetate, 1.0 g of 5% palladium-carbon was added, and catalytic reduction was carried out under normal 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 crystals were recrystallized twice with n-heptane / ethyl acetate to give 2,4
-Diaminophenol [4- (trans-4-ethyl-
Cyclohexyl) phenoxypropyl] ether 4.4
2 g (0.012 mol) was obtained. The melting point of this compound was 98.4 to 100.degree.

2) Polymerization reaction In a 50 ml three-necked flask, 0.3869 g (1.05 m) of 2,4-diaminophenol [4- (trans-4-ethyl-cyclohexyl) phenoxypropyl] ether was added.
mol), 2,2-bis (4-aminophenoxyphenyl) -propane 0.1847 g (0.45 mmol), N
-Methyl-2-pyrrolidone (hereinafter abbreviated as NMP) 3.0 m
l was added and the mixture was stirred and dissolved at room temperature under a nitrogen stream. Next, this liquid was kept at 10 ° C., and 0.4413 g (1.50 mm) of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride.
ol) was added. The vessel wall was rinsed with 3 ml of NMP, and the reaction was continued for 3 hours. The obtained reaction liquid was diluted to 4.0 wt% with N-methyl-2-pyrrolidone / butyl cellosolve = 1/1 solvent, and then applied on an ITO glass substrate by spin coating (spinner method). 3 at 200 ° C after coating
It was baked for 0 minutes to obtain a substrate on which a polyimide film having a film thickness of 600 angstrom was formed. This polyimide had a decomposition temperature of 438.1 ° C. The remaining reaction solution was poured into 300 ml of methanol and the deposited precipitate was filtered. The filtered material was dried under reduced pressure at room temperature to obtain a polyamic acid. The intrinsic viscosity of this polyamic acid is 0.43 (30
C., 0.5 g / dl, NMP solution).

3) Cell preparation and pretilt angle measurement The film surfaces of the two polyimide film-formed substrates were each rubbed, and a liquid crystal cell having a cell thickness of 20 μm was assembled so that the rubbing directions were anti-parallel, and Merck ( Liquid crystal ZLI-1132 manufactured by K.K. Then, the liquid crystal was heat-treated at 120 ° C. for 30 minutes. After the heat treatment, it was allowed to cool and the pretilt angle was calculated to be 1.83 degrees.

Examples 2-3 Different composition ratios of 2,4-diaminophenol [4- (trans-4-ethyl-cyclohexyl) phenoxypropyl] ether and 2,2-bis (4-aminophenoxyphenyl) -propane. Except for the above, the procedure was carried out in accordance with 2) of Example 1. Table 1 shows the component ratios and the physical properties of the obtained polyimide.

Example 4 Except that the tetracarboxylic dianhydride was changed to pyromellitic dianhydride (0.3272 g, 1.50 mmol).
It was carried out in accordance with 2) of Example 1. Table 1 shows the physical properties of the obtained polyimide.

Example 5 1) 2,4-Diaminophenol [4- (trans-4-ethyl-cyclohexyl) phenoxyhexyl] ether represented by the formula [3] (provided that m = 6, n = 1, R =
Production of C ₂ H ₅ ). 6-chloro-instead of 3-bromo-1-propanol
It was manufactured according to 1) of Example 1 except that 1-hexanol was used. The melting point of this compound is 119.6-12.
It was 1.6 ° C.

2) Polymerization reaction As a diamine component, 2,4-diaminophenol [4
-(Trans-4-ethyl-cyclohexyl) phenoxyhexyl] ether 0.4311 g (1.05 mmo
The procedure was carried out in accordance with 2) of Example 1 except that 1) was used. The physical properties of the obtained polyimide are shown in Table 1. The pretilt angle was measured in accordance with 3) of Example 1 and found to be 1.25 degrees.

Example 7 Except that the tetracarboxylic dianhydride was changed to pyromellitic dianhydride (0.3272 g, 1.50 mmol).
It was carried out in accordance with 2) of Example 1. Table 1 shows the physical properties of the obtained polyimide.

[0033]

[Table 1]

[0034]

The polyimide obtained according to the present invention can be produced by baking at low temperature for a short time and has a high decomposition temperature of 400 ° C. or higher and can be used at high temperature. In addition, since the liquid crystal alignment film using the present polyimide is excellent in adhesion to a glass substrate and liquid crystal alignment, and has a large pretilt angle of about 1 to 8 degrees, it is suitable for ordinary liquid crystal cells (for TN and STN). It is useful as a material for an alignment film.

[Brief description of drawings]

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

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C08G 73/00-73/26 CAPLUS (STN) REGISTRY (STN)

Claims (5)

(57) [Claims] 1. A structural unit represented by the formula [1] and a formula [2]
A polyimide comprising a structural unit represented by. [Chemical 1] (However, m is an integer of 1 to 20, n is 1 to 2, R is an alkyl group or an alkoxy group having 1 to 20 carbon atoms, and A is a phenyl group or a 3,3 ', 4,4'-biphenyl group. ) [Chemical 2] (However, A represents a phenyl group or a 3,3 ′, 4,4′-biphenyl group.) 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. [Chemical 3] (However, m is an integer of 1 to 20, n is 1 to 2, and R is an alkyl group or an alkoxy group having 1 to 20 carbon atoms.) [Chemical 5] (However, A represents a phenyl group or a 3,3 ′, 4,4′-biphenyl group.) 3. A liquid crystal alignment film using the polyimide according to claim 1. 4. A liquid crystal display device comprising the liquid crystal alignment film according to claim 3. 5. A 2,4-diaminophm of the formula [3]
Enol [4- (trans-4-alkyl-cyclohexene
Sil) phenoxyalkyl] ether. [Chemical 13] (However, m = 1 to 20 is an integer, n = 1 to 2 and R is the number of carbon atoms.
1 to 20 alkyl or alkoxy groups are shown. )