JP2729618B2 - Liquid crystal element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal device having an improved alignment control method in a liquid crystal device having an alignment control film. (Prior art) Liquid crystal display elements used in conventional watches and calculators are:
The mainstream is a twisted nematic (hereinafter abbreviated as TN) mode in which the arrangement direction of nematic liquid crystal molecules is twisted at 90 degrees on the surfaces of a pair of upper and lower electrode substrates. However, in this display mode, the contrast is low and the viewing angle is narrow, so that it is not enough to improve the display quality and the display area. Recently, a liquid crystal display device using a super twisted nematic (hereinafter abbreviated as STN) mode in which the alignment direction of nematic liquid crystal molecules between the upper and lower electrodes is twisted at 180 to 270 degrees has been developed. These STN modes make use of the fact that the interference color generated by the retardation based on the birefringence of liquid crystal molecules changes steeply in response to the application of a voltage. Good quality (for example, contrast ratio, viewing angle dependency, etc.) can be obtained. However, in this STN mode, a pretilt angle of 5 degrees or more (hereinafter abbreviated as θ ₀ ) is required between the long axis of the liquid crystal molecules and the substrate surface, and when θ ₀ is 5 degrees or less, the element has a threshold. When a voltage near the value is applied, a failure mode in which liquid crystal molecules rise in a direction opposite to the initially determined twisting direction often occurs. For this reason, a liquid crystal alignment control film having good orientation and capable of controlling the pretilt angle to a uniform value at 5 ° or more becomes important. At present, the best way to reliably obtain a pretilt angle of 5 degrees or more is to use a thin film obtained by vacuum-depositing SiO or SiO ₂ or the like from an oblique direction to a substrate surface as an alignment control film. However, this method requires a large-sized facility to uniformly control the incident direction of the evaporated particles on a large-sized substrate, and has a drawback that the productivity is inferior because a vacuum is used. On the other hand, the method conventionally used for manufacturing an alignment control film of a TN mode liquid crystal element is a rubbing method, in which a substrate coated with an organic thin film (liquid crystal alignment control film) such as polyvinyl alcohol, polyamide, or polyimide as the alignment control film. Is rubbed (rubbed) in one direction to give orientation to the liquid crystal and control the alignment.
By performing these operations on the TN mode liquid crystal alignment control film, a pretilt angle can also be obtained,
With them, only a pretilt angle of less than 5 degrees can be obtained,
It is insufficient for use in STN mode liquid crystal devices. However, from the viewpoint of the productivity of the liquid crystal element, it is desirable to perform the alignment treatment by the rubbing method as in the case of the TN mode liquid crystal element in the production of the STN mode liquid crystal element. There is a need for a membrane. (Problems to be solved by the invention) As is clear from the above, the object of the present invention is to
An object of the present invention is to provide a liquid crystal element provided with an alignment control film capable of realizing good orientation and a high pretilt angle by rubbing. (Means for Solving the Problems) The present invention relates to a liquid crystal element having good liquid crystal orientation and a high pretilt angle, and includes a substrate, a voltage applying means,
In a liquid crystal device including an alignment control film and a liquid crystal layer, the alignment control film has the following general formula I: (Wherein, the R ₁ is an alkyl group having 6 to 22 carbon atoms, R ₂ represents respectively hydrogen or an alkyl group having 1 to 22 carbon atoms, R ₃ to R
_{10 represents the} same or different hydrogen or an alkyl group having 1 to 4 carbon atoms, respectively, and Ar represents a tetravalent aromatic group. ) Is characterized by including a polyimide-based polymer substance having a structural unit represented by the following formula: The liquid crystal device of the present invention includes a liquid crystal light modulation device and a liquid crystal display device. Hereinafter, the present invention will be described in more detail. Since the polyimide-based polymer used for the alignment control film of the liquid crystal element of the present invention has an imide bond and is generally insoluble in a solvent, in order to provide a uniform polyimide-based polymer film on a substrate, a precursor thereof is required. Usually, polyamic acid obtained by condensation of tetracarboxylic dianhydride and diamino compound is converted to N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), etc. Dissolve in the solvent of this, the brush coating method, dipping method, spin coating method, spray method,
It is preferable to apply a method such as a printing method to a substrate and then heat-treat at 100 to 450 ° C., preferably 150 to 300 ° C. to dehydrate and close the ring to have an imide bond. Polyamic acid, a precursor of the above polyimide, is usually synthesized by condensation of a tetracarboxylic dianhydride with a diamino compound. These condensation reactions are carried out under anhydrous conditions under N-
Methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethyl sulfate, sulfolane, butyrolactone, cresol, phenol, halogenated phenol, cyclohexanone, dioxane, tetrahydrofuran, and the like are preferable. Is carried out in a solvent of N-methyl-2-pyrrolidone (NMP) at a temperature of 50 ° C. or lower. However, when the polyimide polymer has no problem in solubility in a solvent, it may be reacted at a high temperature in a stage before coating on a substrate and used as a polyimide varnish. Formula II as a diamino compound: (Wherein, the R ₁ is an alkyl group having 6 to 22 carbon atoms, R ₂ represents respectively hydrogen or an alkyl group having 1 to 22 carbon atoms, R ₃ to R
_{10 represents the} same or different hydrogen or an alkyl group having 1 to 4 carbon atoms, respectively. ) Is used. When this compound is used as a raw material of a polyimide for a liquid crystal alignment control film, R _{1 in the} formula (II) has 6 to 12 carbon atoms.
And a diamino compound wherein R ₂ is an alkyl group having 1 to 12 carbon atoms. Among them, compounds in which R ₂ is a methyl group or an ethyl group and R ₁ is a straight-chain alkyl group having 6 to 12 carbon atoms are preferable. When the alkyl chain length of R ₁ and R ₂ is 3 or less in total, the pretilt angle of a liquid crystal element using the obtained polyimide alignment control film cannot be increased, which is not preferable. Examples of the tetracarboxylic dianhydride include the following compounds. 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, 2,3,
3 ', 4'-benzophenonetetracarboxylic dianhydride,
2,2 ', 3,3'-benzophenonetetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride Products, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride and the like. Further, in order to enhance the adhesion of the polyimide alignment control film to the substrate, it is possible to introduce an aminosilicon compound or a diaminosilicon compound for modification. Examples of the aminosilicon compound include the following compounds. When these aminosilicon compounds are introduced into the polyimide-based polymer substance used in the present invention, the content thereof can be used within a range that satisfies the following relationship between the polyimide raw materials. In the above formula, A, B and C are each a tetracarboxylic dianhydride which is a polyimide raw material, and the above-mentioned general formula (II)
And the number of moles of the diamino compound and the aminosilicon compound represented by Also, as the diamino silicon compound, (In the formula, 1 represents an integer of 0 to 4.) When the compound is introduced into polyimide, 50 mol% or less, preferably 30 mol% or less of the diamino compound represented by the formula (II) is used. Can be replaced with a diaminosilicon compound. The polyimide-based polymer used for the alignment control film of the liquid crystal element of the present invention can be modified by introducing an aromatic diamino compound, an alicyclic diamino compound and a derivative thereof in addition to the above components. Specific examples include 4,4'-diaminophenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfide, 4,4'-di (meth-aminophenoxy)
Diphenylsulfone, 4,4'-di (para-aminophenoxy) diphenylsulfone, ortho-phenylenediamine, meta-phenylenediamine, para-phenylenediamine, benzidine, 2,2'-diaminobenzophenone,
4,4'-diaminobenzophenone, 4,4'-diaminodiphenyl-2,2'-propane, 1,5-diaminonaphthalene,
Aromatic diamino compounds such as 1,8-diaminonaphthalene,
There are alicyclic diamino compounds such as 1,4-diaminocyclohexane. To coat polyamic acid on a substrate, the polyamic acid is coated with N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DM
F), dissolved in a solvent such as dimethyl sulfoxide (DMSO), and adjusted to a 0.1 to 30% by weight solution (preferably a 1 to 10% by weight solution). This solution is brushed, dipped, spin-coated, sprayed It is applied by a coating method or a printing method to form a coating film on the substrate. After application, 100-450 ° C (preferably 150-
(Up to 300 ° C.), and a dehydration ring-closing reaction is performed to provide a polyimide polymer film. If the obtained polyimide polymer film does not have good adhesiveness to the substrate, the surface should be treated with a silane coupling agent on the substrate surface in advance, and then the polyimide polymer film should be formed. Is improved. Thereafter, the coated surface is rubbed in one direction with a cloth or the like to obtain a liquid crystal alignment control film. Next, an example of a method for measuring the pretilt angle θ ₀ will be described. The polyimide polymer film provided on the liquid crystal element substrate is rubbed in one direction by a rubbing device (for example, a liquid crystal cell rubbing device manufactured by Kyoei Semiconductor) by the above-mentioned method in a rubbing direction having a cell thickness of about 10 μm. The liquid crystal elements are assembled such that are parallel and face each other. A nematic liquid crystal having a known dielectric constant (ε) in a liquid crystal molecule long axis direction and a dielectric constant (ε⊥) in a direction perpendicular to the molecule long axis is sealed in this liquid crystal element for which θ ₀ is to be measured, and is sufficiently higher than a threshold voltage. Dielectric constant (ε) by applying low voltage to
Is measured, θ ₀ is obtained according to the following equation. The value of ε = ε sin ² θ ₀ + ε⊥cos ² θ ₀ ε is given by the homeotropically oriented cell:
Ε⊥ can be determined by applying a voltage sufficiently lower than the threshold voltage of the Freedericksz transition using a homogeneously oriented cell. (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 A polyimide-based polymer film was prepared as follows. Ten
A 0 ml flask was equipped with a stirrer, a thermometer, a condenser, and a nitrogen purging apparatus. After the inside of the flask was replaced with nitrogen gas, dehydrated and purified N-methyl-2-pyrrolidone 50 was added.
ml was added. Then, 2.53 g (5.27 mmol) of 2,2-bis [4- (4-aminophenoxy) phenyl] octane was charged and dissolved by stirring, followed by cooling to 5 ° C. with an ice bath. Next, 1.15 g (5.27 mmol) of pyromellitic dianhydride was added at a time, and the mixture was stirred and reacted while cooling. After the reaction for 2 hours, a clear solution of polyamic acid having a molar ratio of 1,2-bis [4- (4-aminophenoxy) phenyl] octane to pyromellitic dianhydride of 1: 1 was obtained at 6.67% by weight. 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., Ltd.)
It was 6.4 centipoise. This solution was provided on one side with an indium oxide-based transparent conductive film (ITO film) as an electrode, and a silane coupling agent APS-E (Chisso Corporation) was previously prepared.
Co., Ltd.), and the surface was treated by a spin coating method (spinner method). The application condition is 3,00 revolutions
It was 0 rpm for 10 seconds. After coating, heat treatment was performed at 200 ° C. for 1 hour to obtain a polyimide polymer film. When the thickness of the obtained polyimide-based polymer film was measured with a stylus-type film thickness meter, the thickness of the coating film was about 1,200 mm. Subsequently, the coating surfaces of the two substrates were each rubbed 30 times with a rubbing device, and a liquid crystal cell having a cell thickness of 10 μm was assembled so that the rubbing directions were parallel and opposed to each other. YY-4006 was enclosed. After enclosing,
A liquid crystal element was obtained by heating to an isotropic liquid temperature and gradually cooling. The orientation of the liquid crystal element was good, and the pretilt angle of the liquid crystal element obtained by the above-described method of measuring the pretilt angle was 19 degrees. Example 2 A polyimide-based polymer film was produced by the following method. 30
A 0 ml flask was equipped with a stirrer, a thermometer, a condenser, and a nitrogen purging apparatus. After the inside of the flask was replaced with nitrogen gas, dehydrated and purified N-methyl-2-pyrrolidone 15 was added.
0.71 ml was added. Next, 5.00 g (10.4 mmol) of 2,2-bis [4- (4-aminophenoxy) phenyl] octane was charged and dissolved by stirring, followed by cooling to 5 ° C. with an ice bath. Next, 2.60 g (11.9 mmol) of pyromellitic dianhydride was added at a time, and the mixture was stirred and reacted while cooling.
The reaction system exothermed to 10 ° C. while the viscosity gradually increased.
After reacting for 1 hour, p-aminophenyltrimethoxysilane
0.57 g (2.67 mmol) was added, and the mixture was stirred at 10 ° C. for 1 hour to give 5% by weight of pyromellitic dianhydride, 2,2- [4-
(4-aminophenoxy) phenyl] octane and para-aminophenyltrimethoxysilane
A clear solution of polyamic acid consisting of 8: 7: 1.8 was obtained.
The viscosity of this solution at 25 ° C. was 17.3 centipoise.
This solution was diluted with butyl cellosolve to remove polyamic acid.
After making a 4.5% solution, it was applied by a spin coating method (spinner method) on a transparent glass substrate provided with an indium oxide-based transparent conductive film (ITO film) on one surface as an electrode. The application conditions were 3,000 rpm for 10 seconds. After the application, a heat treatment was performed at 200 ° C. for 1 hour to obtain a polyimide polymer film having a thickness of about 1,000 mm. Subsequently, by the same operation as in Example 1, the cell thickness was 10 μm.
Was obtained. The orientation of the liquid crystal element was good, and the pretilt angle of the liquid crystal element obtained by the above-described method of measuring the pretilt angle was 13 degrees. Example 3 N-methyl-2-pyrrolidone 194.61 ml, 2,2-bis [4- (4-aminophenoxy) phenyl] decane 6.60
g (13.0 mmol), pyromellitic dianhydride 3.24 g (1
4.9 mmol) and 0.71 g (3.33 mmol) of para-aminophenyltrimethoxysilane were used in the same manner as in Example 2 to give 5% by weight of pyromellitic dianhydride, 2,2-bis [4- ( A clear solution of polyamic acid having a molar ratio of 4-aminophenoxy) phenyl] decane and para-aminophenyltrimethoxysilane of 8: 7: 1.8 was obtained. The viscosity of this solution at 25 ° C. was 13.5 centipoise. This solution was diluted with butyl cellosolve to form a solution having a polyamic acid concentration of 4.5%.
A polyimide-based polymer film having a thickness of about 1,000 mm was formed in the same manner as described above to obtain a liquid crystal device having a cell thickness of 10 μm. The orientation of this liquid crystal element was good, and the obtained pretilt angle was 18 degrees. Reference Example 1 235.19 ml of N-methyl-2-pyrrolidone, 2,2-bis [4- (4-aminophenoxy) phenyl] hexane 7.
60 g (16.9 mmol), pyromellitic dianhydride 4.22 g
(19.3 mmol) and 0.93 g (4.36 mmol) of para-aminophenyltrimethoxysilane were used in exactly the same manner as in Example 2, and 5% by weight of pyromellitic dianhydride, 2,2-bis [4 A clear solution of polyamic acid having a molar ratio of-(4-aminophenoxy) phenyl] hexane and para-aminophenyltrimethoxysilane of 8: 7: 1.8 was obtained. The viscosity of this solution at 25 ° C. was 38.4 centipoise. This solution was diluted with a mixed solvent of N-methyl-2-pyrrolidone and butyl cellosolve 1: 1 to obtain a 4.0 solution of polyamic acid. A film was formed, and a liquid crystal element having a cell thickness of 10 μm was obtained. The orientation of the liquid crystal element was good, and the obtained pretilt angle was 7 degrees. Example 5 151.7 ml of N-methyl-2-pyrrolidone, 2,2-bis [4
-(4-Aminophenoxy) phenyl] octane 4.34 g
(9.04 mmol), 2.63 g of pyromellitic dianhydride (12.
Example 2 except that 1.28 g (6.01 mmol) of paraaminophenyltrimethoxysilane was used.
In the same manner as above, 5% by weight of pyromellitic dianhydride,
2,2-bis [4- (4-aminophenoxy) phenyl]
A clear solution of polyamic acid having a molar ratio of octane and para-aminophenyltrimethoxysilane of 8: 6: 4 was obtained. The viscosity of this solution at 25 ° C. was 21 centipoise. After diluting this solution with butyl cellosolve to obtain a 4.5% solution of polyamic acid, a polyimide polymer film having a thickness of about 860 ° was formed in the same manner as in Example 1 to obtain a liquid crystal device having a cell thickness of 10 μm. . The orientation of the liquid crystal element was good, and the obtained pretilt angle was 7 degrees. Comparative Example 1 N-methyl-2-pyrrolidone 61 ml, 2,2-bis [4-
(4-aminophenoxy) phenyl] propane 2.16 g
(5.27 mmol), pyromellitic dianhydride 1.15 g (5.2
7 mmol), and the molar ratio of 2,2-bis [4- (4-aminophenoxy) phenyl] propane and pyromellitic dianhydride was 5% by weight. : 1 resulted in a clear polyamic acid solution. The viscosity of this solution at 25 ° C. was 203 centipoise. After diluting this solution with butyl cellosolve to obtain a 2.5% solution of polyamic acid, a polyimide-based polymer film having a thickness of about 1,000 mm was prepared in the same manner as in Example 1.
A liquid crystal element having a cell thickness of 10 μm was obtained. The orientation of the liquid crystal element was good, and the obtained pretilt angle was 5 degrees. (Operation and Effect) According to the present invention, a liquid crystal element having a high pretilt angle can be easily obtained. A high pretilt angle can be achieved by using a liquid crystal alignment control film obtained by rubbing a polyimide polymer film having the structural unit of the formula (I). It is believed that the high pretilt angle is effectively provided by the linear alkyl of R ₁ and R ₂ in formula (I). It can be seen that the chain length of from Example 2 to 4 (I) formula R ₁ becomes longer in a range pretilt angle is increased. By using the liquid crystal element of the present invention, an STN mode liquid crystal display with good display quality can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1, FIG. 2 and FIG. 3 are infrared absorption spectra of the polyimide polymer films prepared in Examples 2, 3 and Reference Example 1, respectively.

   ────────────────────────────────────────────────── ─── Continuation of front page                   (56) References JP-A-61-240223 (JP, A)                 JP-A-58-91430 (JP, A)

Claims (1)

(57) [Claims] In a liquid crystal device including a substrate, a voltage applying means, an alignment control film and a liquid crystal layer, the alignment control film has the following general formula I: (Wherein, the R ₁ is an alkyl group having 6 to 22 carbon atoms, R ₂ represents respectively hydrogen or an alkyl group having 1 to 22 carbon atoms, R ₃ to R
₁₀ represents the same or different hydrogen or an alkyl group having 1 to 4 carbon atoms, and Ar represents a tetravalent aromatic group. )
A liquid crystal device comprising a polyimide polymer having a structural unit represented by the formula: 2. 2. A liquid crystal device according to claim 1, wherein said liquid crystal device is a liquid crystal light modulation device. 3. 2. The liquid crystal device according to claim 1, wherein said liquid crystal device is a liquid crystal display device.