JP2000305088A - Liquid crystal aligning agent and liquid crystal alignment film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain good aligning property of a liquid crystal with low surface tension by preparing a polyimide having a specified recurring unit by imide of a polyimide precursor and forming an alignment film having crystallinity on a substrate. SOLUTION: The polyimide prepared by imidization of a polyimide precursor has the recurring unit expressed by the formula, and the alignment film formed on a substrate has crystallinity. In the formula, n is any integer. The polyimide precursor is preferably obtd. by polymerizing 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 1,3-bis(4-aminophenoxy)benzene in a solvent. As for the solvent used for the polymn., an org. solvent can be used, and for example, N,N-dimethylformamide and N,N-dimethylacetoamide can be used. The liquid crystal aligning agent is prepared from the polymn. liquid containing the polyimide precursor as it is, or preferably prepared by adding an org. solvent or a poor solvent to the polymn. liquid to control the viscosity of the solvent to 0.1 to 10 poise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel liquid crystal aligning agent and a liquid crystal aligning film using the same. More specifically, a polyimide-based liquid crystal alignment agent capable of forming a liquid crystal alignment film having a low surface tension, good liquid crystal alignment properties, and a high pretilt angle retention after annealing treatment, and a liquid crystal using the same. It relates to an alignment film.

[0002]

2. Description of the Related Art Hitherto, various polyimide-based liquid crystal aligning agents have been proposed, for example, a liquid crystal aligning agent described in JP-A-9-258229, which can form a liquid crystal alignment film which is hard to be rubbed. JP-A-9-2581
No. 58, a liquid crystal aligning agent which does not require a flattening treatment of a base, or a liquid crystal display element described in Japanese Patent Application Laid-Open No. 9-241646, which erases an afterimage after releasing the application of voltage. Liquid crystal alignment agents capable of forming a liquid crystal alignment film having a short time to complete are known. And
The lower the surface tension of the liquid crystal aligning agent, the higher the pretilt angle of the liquid crystal alignment film, and the pretilt angle needs to be 2 ° or more.

However, the liquid crystal aligning agent described in JP-A-9-258158 requires the reaction of a polycyclic aromatic tetracarboxylic dianhydride having three or more rings as a tetracarboxylic acid component. The liquid crystal aligning agent described in Japanese Unexamined Patent Publication No. 9-258158 requires a combination use of a polyamic acid and a phenol resin.
The liquid crystal aligning agent described in JP-A No. 46 needs to react an alicyclic polycyclic diamine as a diamine compound, and none of them is practical. In addition, even if the pretilt angle of the liquid crystal alignment film is large, the pretilt angle after annealing is often greatly reduced.

[0004]

SUMMARY OF THE INVENTION The present invention provides a liquid crystal aligning agent capable of forming a liquid crystal alignment film having a low surface tension and a good liquid crystal alignment, and having a high pretilt angle retention after annealing. And to provide a liquid crystal alignment film using the same.

[Means for Solving the Problems]

According to the present invention, a polyimide precursor obtained by polymerizing 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and 1,3-bis (4-aminophenoxy) benzene is used as an organic solvent. Contained in the polyimide, the polyimide obtained by imidizing the polyimide precursor is represented by the following formula (1)

[0006]

Embedded image (In the formula, n represents an arbitrary integer.) The present invention relates to a liquid crystal alignment agent having an alignment film formed on a substrate and having crystallinity. Further, according to the present invention, the alignment film formed on the substrate has crystallinity, the pretilt angle after the annealing treatment is 2 ° or more on average, and the retention (the ratio to the pretilt angle before the annealing treatment) On average) is 70 on average
%, And the present invention further relates to a liquid crystal alignment film obtained using the above liquid crystal alignment agent.

The polyimide precursor in the present invention is preferably prepared by polymerizing 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and 1,3-bis (4-aminophenoxy) benzene in a solvent. It is obtained by doing.

[0008] A part of the 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, preferably less than 50 mol%, especially 20 mol% or less, and especially 10 mol% or less, It may be replaced with another tetracarboxylic dianhydride such as an aromatic tetracarboxylic dianhydride or an alicyclic tetracarboxylic dianhydride. Also, part of the above-mentioned 1,3-bis (4-aminophenoxy) benzene, preferably 5
Less than 0 mol%, especially 20 mol% or less, and especially 1
0 mol% or less may be replaced with another diamine such as another aromatic diamine or alicyclic diamine.

The other tetracarboxylic dianhydrides include 2,3,3 ', 4'-biphenyltetracarboxylic dianhydride and 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride. Anhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4-
Dicarboxyphenyl) ether dianhydride, bis (2,
3-dicarboxyphenyl) ether dianhydride, 3,
3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 2,2 ′, 3,3′-benzophenonetetracarboxylic dianhydride, 4,4- (p-phenylenedioxy)
Diphthalic dianhydride, 4,4- (m-phenylenedioxy) diphthalic dianhydride, pyromellitic dianhydride,
1,2,5,6-naphthalenedicarboxylic dianhydride,
1,4,5,8-naphthalenedicarboxylic dianhydride,
2,3,6,7-naphthalenedicarboxylic dianhydride,
1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1 , 2,7,8-phenanthrenetetracarboxylic dianhydride, ethylene tetracarboxylic dianhydride, butanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, cyclohexanetetracarboxylic dianhydride, 1, 1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride and the like can be mentioned. . These tetracarboxylic dianhydrides can be used alone or in combination of two or more.

The other diamines include diaminocyclohexane, bis (aminomethyl) cyclohexane,
Bicyclohexyldiamine, 2,2-bis (3-aminocyclohexyl) propane, 2,2-bis (4-aminocyclohexyl) propane, bis (3-methyl-4-aminocyclohexyl) methane, xylylenediamine,
Diaminodiphenyl ether, diaminobenzophenone, diaminodiphenylmethane, 2,2-bis (3-aminophenyl) propane, 2,2-bis (4-aminophenyl) propane, 2,2-bis [4- (3-amino Phenoxy) phenyl] propane, 2,2-bis [4-
(4-aminophenoxy) phenyl] propane, 2,2
-Bis [4- (3-aminophenoxy) phenyl]-
1,1,1,3,3,3-hexafluoropropane,
2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 1,4-bis (3-aminophenoxy) benzene,
1,4-bis (4-aminophenoxy) benzene, 1,
3-bis (3-aminophenoxy) benzene, 4,4 ′
-Bis (3-aminophenoxy) biphenyl, 4,4 '
-Bis (4-aminophenoxy) biphenyl, bis [4
-(3-aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) ) Phenyl] ether and the like. These diamines can be used alone or in combination of two or more. In particular, in the liquid crystal aligning agent of the present invention, in order to improve the adhesion between the liquid crystal aligning film and the substrate surface as long as the effect of the present invention is not impaired, diaminodiamine such as bis (γ-aminopropyl) tetramethyldisiloxane is used. Siloxane in diamine 1-1
You may make it contain about 0 mol%.

The ratio of the tetracarboxylic dianhydride component to the diamine component is such that the diamine component is used in a molar ratio of 0.9 to 1.1 with respect to the tetracarboxylic dianhydride component. it can. When a polyimide precursor is produced outside this range, the mechanical strength of the resulting polyimide is significantly reduced. In particular, it is desirable to use within the range of 0.95 to 1.05. At this time, the logarithmic viscosity (ηinh) of the obtained polyimide is in the range of 0.1 to 2.0.

In the above polymerization, substituted or unsubstituted imidazole, pyrazole, benzimidazole, pyridine, quinoline, pyrimidine, pyrazine, p-hydroxybenzoic acid, m-hydroxybenzoic acid, p-hydroxyphenyl Addition of additives such as acetic acid and p-hydroxybenzenesulfonic acid can increase the degree of polymerization. The use amount of these additives is 0.01 to 4.0 mol, preferably 0.02 to 2.0 mol, per 1 mol of the aromatic tetracarboxylic dianhydride.

As the solvent used in the above polymerization,
The organic solvent used in the present invention can be used. As the organic solvent used in the present invention,
N, N-dimethylformamide, N, N-dimethylacetamide, N, N-dimethylmethoxyacetamide, N
-Methyl-2-pyrrolidone and the like. These solvents can be used alone or in combination of two or more. The amount of the organic solvent used is not particularly limited, but the content of the produced polyimide precursor is preferably about 3 to 20% by weight. Further, in order to improve the uniformity of the liquid crystal alignment film, a poor solvent such as γ-butyrolactone, butyl cellosolve, propylene glycol alkyl ethers, diglyme, triglyme, tetralin, xylylene, carbitol, etc. You may make it contain about 30%.

The liquid crystal aligning agent of the present invention has a viscosity of about 0.1 to 10 poise when the polymerization solution containing the polyimide precursor is used as it is or when one of the organic solvents or a poor solvent is added to the polymerization solution. Preferably, it is obtained as

The above-mentioned liquid crystal aligning agent is preferably such that the alignment film formed on the substrate has crystallinity, and after the annealing treatment, the conditions are as follows:
After the annealing treatment at 120 ° C. for 30 minutes, the pretilt angle is 2 ° or more on average and the retention is 70% or more on average.

In order to obtain a liquid crystal alignment film and a liquid crystal display element using the liquid crystal alignment agent of the present invention, for example, the following method can be used. (1) The liquid crystal aligning agent of the present invention is applied to one surface of a substrate such as a glass substrate provided with a transparent conductive film such as an ITO electrode by, for example, a spinner method, and then the organic solvent is removed by heating the coating. Then, it is imidized to form a polyimide film. For the purpose of improving the adhesiveness of the polyimide film to the substrate surface and the transparent conductive film, a coupling agent such as an aminosilane-based coupling agent can be applied in advance. (2) A rubbing process is performed on the surface of the polyimide film formed on the substrate surface by rotating a roll around which a cloth such as nylon or polyester is wound. In addition to the rubbing method, the liquid crystal alignment film can be formed by a uniaxial stretching method, a Langmuir-Blodgett method, or the like. (3) The substrate on which the liquid crystal alignment film was formed as described above
Two substrates are prepared and, for example, two substrates are arranged to face each other with a gap (cell gap) therebetween so that the respective alignment processing directions are orthogonal to each other. A peripheral portion of the two substrates is sealed with a sealing agent such as an epoxy resin, and a liquid crystal is injected and filled in a cell gap to manufacture a liquid crystal display element.

The above coating film is heated to remove the organic solvent,
50-10 when imidizing to form a polyimide film
1-30 minutes at 0 ° C, then 1-30 minutes at 150-200 ° C
It is preferable to perform the heating by multi-stage heating at 250-300 ° C. for about 1-30 minutes.

[0018]

The present invention will be described below in detail with reference to examples. Synthesis Example 1 In a 500 ml three-necked flask equipped with a stirrer and purged with nitrogen, 8.7708 g (0.03 mol) of 1,3-bis (4-aminophenoxy) benzene and N-methyl-2 were added.
313 g of pyrrolidone (final solid content of 5% by weight)
Was added and stirred and dissolved at room temperature. To this,
8.8266 g (0.03 mol) of 3 ', 4,4'-biphenyltetracarboxylic dianhydride was gradually added, and stirring was continued at room temperature for 5 hours. During this time, the viscosity of the polyamic acid reaction liquid increased with the elapse of the reaction time, and the viscosity of the polymerization liquid when stirring for 5 hours reached 0.4 poise (room temperature). This polymerization liquid is referred to as a liquid crystal aligning agent 1.

Synthesis Example 2 In place of 1,3-bis (4-aminophenoxy) benzene, 12.2156 g (0.03 mol) of 2,2-bis [4- (4-aminophenoxy) phenyl] propane was used. A polymerization liquid having a viscosity of 0.4 poise was obtained in the same manner as in Synthesis Example 1 except that the amount of N-methyl-2-pyrrolidone was changed to 380 g. This polymerization liquid is used as a liquid crystal aligning agent 2.

Example 1 The liquid crystal aligning agent 1 obtained in Synthesis Example 1 was applied on an ITO glass substrate by spin coating at 4000 rpm for 30 seconds to form a film, and the film was formed in a hot air drier at 80 ° C. From 2
The temperature was raised stepwise to 50 ° C. and heat treatment was performed. Then, a rubbing treatment [E. H. C. RM-300H, Stage 200 rpm (0.5 cm / sec), Roller 500 rpm
m] to form a liquid crystal alignment film. Next, liquid crystal (K15, manufactured by Merck) was dropped on the rubbed surface. The time required for the liquid crystal to develop into a thin film was measured to be 15 minutes. Separately, a polyimide film was formed on a glass plate by the same operation as the orientation formation, and it was confirmed by X-ray diffraction that the polyimide had crystallinity.

Example 2 The liquid crystal aligning agent 1 obtained in Synthesis Example 1 was applied on an ITO glass substrate by spin coating at 4000 rpm for 30 seconds to form a film, and the film was formed at 80 ° C. in a hot air drier. From 2
The temperature was raised stepwise to 50 ° C. and heat treatment was performed. Then, a rubbing treatment [E. H. C. RM-300H, Stage 200 rpm (0.5 cm / sec), Roller 500 rpm
m] to form a liquid crystal alignment film. Similarly, another IT
A liquid crystal alignment film was formed on an O glass substrate. These two substrates are stacked in the anti-parallel direction, and a mixture of a UV-curable resin (NOA65, manufactured by Norland) and a spacer (25 μm in diameter, manufactured by Sumita Optical Glass Co., Ltd.) is applied to the four corners of the substrate, And cured. A liquid crystal (K15, manufactured by Merck) was heated to 40 ° C., phase-transformed, and injected by capillary action to form a cell (liquid crystal display element). A similar process was performed to create five cells. These 5
Pretilt angle for one cell
As a result, the average was 3.1 °.
Furthermore, the pretilt angle after annealing the five cells at 120 ° C. for 30 minutes was an average of 2.5 °.

Example 3 Of the rubbing treatment conditions, the condition of the roller was set to 500 rpm.
m to 100rpm, 300rpm or 700r
A liquid crystal alignment film and a cell (liquid crystal display element) were prepared in the same manner as in Example 2 except that the value was changed to pm. In each case, the pretilt angle of the cell was 3.1 ° or more.

Comparative Example 1 A cell was prepared in the same manner as in Example 2 except that the liquid crystal aligning agent 2 obtained in Synthesis Example 2 was used instead of the liquid crystal aligning agent 1. It was 45 minutes when the time required for the liquid crystal to develop into a thin film was measured. When the pretilt angles of the five cells were determined by the crystal rotation method,
The average was 6.8 °. In addition, the cell was heated
After observing the alignment state after annealing for 5 minutes,
It was in a non-oriented state, and the oriented state at the time of cell preparation was not maintained. The average pretilt angle after annealing the five cells at 120 ° C. for 30 minutes was 0.7 °. Separately, a polyimide film was formed on a glass plate by the same operation as the formation of the orientation, and it was confirmed by X-ray diffraction that the polyimide did not show crystallinity.

Comparative Example 2 A cell was prepared in the same manner as in Example 2 except that a commercially available polyimide-based liquid crystal aligning agent was used instead of the liquid crystal aligning agent 1. When the pretilt angles of the five cells were determined by the crystal rotation method, the average was 4.1 °. Furthermore, five cells were annealed at 120 ° C. for 30 minutes.
The pretilt angle after the pre-tilting process is 2.1 ° on average,
Significantly lower than before annealing.

[0025]

Since the present invention is configured as described above, it has the following effects. According to the present invention, a polyimide-based liquid crystal aligning agent having low surface tension and good liquid crystal alignment can be obtained. Further, according to the present invention, a practical liquid crystal alignment film having stable alignment characteristics can be obtained.

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 2H090 HB08Y JB02 MA10 MB01 4J043 PA02 QB26 QB31 RA35 SA06 SB01 TA14 TA22 TB01 UA132 UA141 UB131 VA021 ZA09 ZB23

Claims (3)

[Claims] 1. A polyimide precursor obtained by polymerizing 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 1,3-bis (4-aminophenoxy) benzene in an organic solvent. A polyimide obtained by imidizing the polyimide precursor is represented by the following formula (1): (In the formula, n represents an arbitrary integer.) A liquid crystal alignment agent having a repeating unit represented by the following formula, wherein the alignment film formed on the substrate has crystallinity. 2. An alignment film formed on a substrate has crystallinity,
A liquid crystal aligning agent having a pretilt angle after annealing of 2 ° or more on average and a retention of 70% or more on average. 3. A liquid crystal alignment film obtained by using the liquid crystal alignment agent according to claim 1.