JPH06265911A - Liquid crystal oriented film and liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide a liquid crystal oriented film which does not cause afterimage or uneven contrast, and to provide a liquid crystal display element equipped with this oriented film. CONSTITUTION:The liquid crystal oriented film essentially consists of polyimide having the repeating unit expressed by formula, and the liquid crystal display element is equipped with this liquid crystal oriented film. In formula, R is hydrogen or an alkyl group of 1-8 carbon number, X, Y, Z are hydrogen, fluorine, or alkyl groups of 1-3 carbon number and these may be the same or partly or wholly different. These substitutents may be introduced to any of ortho or meta positions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal alignment film having a polyimide skeleton and a liquid crystal display device provided with the liquid crystal alignment film, and more specifically to the cause of an afterimage phenomenon of an image when the liquid crystal display device is driven. The present invention relates to a liquid crystal alignment film having an excellent effect of suppressing charge accumulation between upper and lower substrates of a liquid crystal display device, and a liquid crystal display device including the liquid crystal alignment film.

[0002]

2. Description of the Related Art A liquid crystal display element used in a clock or a calculator has a twisted nematic structure in which an arrangement direction of nematic liquid crystal molecules is twisted by 90 degrees between a pair of upper and lower electrode substrates. Hereinafter, abbreviated as TN) mode is mainly adopted. In addition, a super twisted nematic with a large twist angle of 180 to 300 degrees (hereinafter referred to as S
Abbreviated as TN. ) Mode has also been developed, and it has become possible to obtain liquid crystal display elements with good display quality even on a large screen. Furthermore, in recent years, since matrix display and color display have come to be performed, a large number of pixel electrodes and their ON-
BACKGROUND ART Development of MIM (metal-insulation phase-metal) elements and TFT (field effect thin film transistor) elements that employ an active twisted nematic mode that can be turned off has become active.

A problem common to all of these modes is that when the same screen is displayed for a long time and then moved to another screen, the previous image remains as an afterimage, and a fine pattern is formed between the upper and lower substrates of the liquid crystal display device. For example, such foreign matter may be mixed in to cause unevenness in contrast on the display screen around the foreign matter. In particular, in order to obtain a high quality liquid crystal display device, it is a very important problem to improve the afterimage phenomenon. The cause of the afterimage phenomenon and the unevenness of contrast is DC when an ionic component of impurities contained in the liquid crystal or a foreign substance or an ionic component attached to the foreign substance is applied to the liquid crystal display element.
It is considered that this is because an electric double layer is generated on the alignment film due to the component, and a bias of charges is generated between the upper and lower substrates, and the bias is stably maintained, so that a potential difference occurs in the liquid crystal. . In particular, in the TFT element, since the DC component cannot be removed due to the characteristics of the element, the afterimage phenomenon and the contrast unevenness are more noticeable and more serious than those of the TN and STN.

As an alignment film conventionally used for such a liquid crystal display device, an organic film such as polyimide or polyamide is mainly used.
In the 960 publication,

[0005]

[Chemical 4]

A liquid crystal display device provided with a liquid crystal alignment film using a polyimide having a repeating unit represented by: However, such a liquid crystal display device including a liquid crystal alignment film using a polyimide having an ether bond has a drawback that an afterimage phenomenon is likely to occur.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to provide a liquid crystal alignment film having no residual image phenomenon and uneven contrast, and a liquid crystal display device having the liquid crystal alignment film. That is.

[0008]

As a result of intensive studies, the present inventors have confirmed that the afterimage phenomenon and the contrast unevenness are correlated with the polarity of the alignment film surface. And
By using a polymer obtained from a diamino compound having a specific structure having a small polarity and tetracarboxylic dianhydride as a polymer used as an alignment film, a liquid crystal alignment film and a liquid crystal display device free from an afterimage phenomenon and uneven contrast The present invention has been completed, and the present invention has been completed.

The contents of the present invention will be described in more detail as follows: 1) General formula

[0010]

[Chemical 5]

A liquid crystal alignment film containing polyimide as a main component having a structural unit represented by:

2) General formula

[0013]

[Chemical 6]

A polyimide having a repeating unit represented by the formula: 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic anhydride

[0015]

[Chemical 7]

The liquid crystal alignment film according to 1), which is obtained by further dehydrating and ring-closing a polyamic acid obtained by reacting a diamino compound represented by the following in a solvent.

3) A liquid crystal display device provided with the liquid crystal alignment film as described in any one of 1) and 2).

The diamino compound used in the liquid crystal alignment film of the present invention does not have polar atoms such as --O-- and --SO _2- , and the proportion of imide groups is relatively reduced by increasing the molecular weight of amine. The ratio of polar components is made as small as possible, and specific examples are 1,1-bis [4- (4-aminobenzyl) phenyl]
Cyclohexane, 1,1-bis [4- (4-aminobenzyl) phenyl] -4-methylcyclohexane, 1,1
-Bis [4- (4-aminobenzyl) phenyl] -4-
Ethylcyclohexane, 1,1-bis [4- (4-aminobenzyl) phenyl] -4-propylcyclohexane, 1,1-bis [4- (4-aminobenzyl) phenyl] -4-butylcyclohexane, 1,1 -Bis [4-
(4-Aminobenzyl) phenyl] -4-pentylcyclohexane, 1,1-bis [4- (4-aminobenzyl) phenyl] -4-hexylcyclohexane, 1,1
-Bis [4- (4-aminobenzyl) phenyl] -4-
Heptylcyclohexane, 1,1-bis [4- (4-aminobenzyl) phenyl] -4-octylcyclohexane,

1,1-bis [4- (4-amino-3-methylbenzyl) phenyl] -4-methylcyclohexane, 1,1-bis [4- (4-amino-3-methylbenzyl) phenyl]- 4-ethylcyclohexane, 1,1
-Bis [4- (4-amino-3-methylbenzyl) phenyl] -4-propylcyclohexane, 1,1-bis [4- (4-amino-3-methylbenzyl) phenyl]
-4-Butylcyclohexane, 1,1-bis [4- (4
-Amino-3-methylbenzyl) phenyl] -4-pentylcyclohexane, 1,1-bis [4- (4-amino-3-methylbenzyl) phenyl] -4-hexylcyclohexane, 1,1-bis [4- (4-amino-3-methylbenzyl) phenyl] -4-heptylcyclohexane, 1,1-bis [4- (4-amino-3-methylbenzyl) phenyl] -4-octylcyclohexane,

1,1-bis [4- (4-aminobenzyl) -3-methylphenyl] -4-methylcyclohexane, 1,1-bis [4- (4-aminobenzyl) -3-
Methylphenyl] -4-ethylcyclohexane, 1,1
-Bis [4- (4-aminobenzyl) -3-methylphenyl] -4-propylcyclohexane, 1,1-bis [4- (4-aminobenzyl) -3-methylphenyl]
-4-Butylcyclohexane, 1,1-bis [4- (4
-Aminobenzyl) -3-methylphenyl] -4-pentylcyclohexane, 1,1-bis [4- (4-aminobenzyl) -3-methylphenyl] -4-hexylcyclohexane, 1,1-bis [4- (4-Aminobenzyl) -3-methylphenyl] -4-heptylcyclohexane, 1,1-bis [4- (4-aminobenzyl) -3
-Methylphenyl] -4-octylcyclohexane,

1,1-bis [4- (4-aminobenzyl) -2-methylphenyl] -4-methylcyclohexane, 1,1-bis [4- (4-aminobenzyl) -2-
Methylphenyl] -4-ethylcyclohexane, 1,1
-Bis [4- (4-aminobenzyl) -2-methylphenyl] -4-propylcyclohexane, 1,1-bis [4- (4-aminobenzyl) -2-methylphenyl]
-4-Butylcyclohexane, 1,1-bis [4- (4
-Aminobenzyl) -2-methylphenyl] -4-pentylcyclohexane, 1,1-bis [4- (4-aminobenzyl) -2-methylphenyl] -4-hexylcyclohexane, 1,1-bis [4- (4-Aminobenzyl) -2-methylphenyl] -4-heptylcyclohexane, 1,1-bis [4- (4-aminobenzyl) -2
-Methylphenyl] -4-octylcyclohexane,

1,1-bis [4- (4-amino-3-methylbenzyl) phenyl] cyclohexane, 1,1-bis [4- (4-amino-3-ethylbenzyl) phenyl] cyclohexane, 1,1 -Bis [4- (4-amino-3-propylbenzyl) phenyl] cyclohexane,
1,1-bis [4- (4-amino-3-fluorobenzyl) phenyl] cyclohexane, 1,1-bis [4-
(4-Aminobenzyl) -3-methylphenyl] cyclohexane, 1,1-bis [4- (4-aminobenzyl)
-3-Ethylphenyl] cyclohexane, 1,1-bis [4- (4-aminobenzyl) -3-propylphenyl] cyclohexane, 1,1-bis [4- (4-aminobenzyl) -3-fluorophenyl] Cyclohexane,

1,1-bis [4- (4-amino-3-ethylbenzyl) phenyl] -4-methylcyclohexane, 1,1-bis [4- (4-amino-3-propylbenzyl) phenyl]- 4-methylcyclohexane, 1,
1-bis [4- (4-amino-3-fluorobenzyl)
Phenyl] -4-methylcyclohexane,

1,1-bis [4- (4-aminobenzyl) -3-ethylphenyl] -4-methylcyclohexane, 1,1-bis [4- (4-aminobenzyl) -3-
Propylphenyl] -4-methylcyclohexane, 1,
1-bis [4- (4-aminobenzyl) -3-fluorophenyl] -4-methylcyclohexane,

1,1-bis [4- (4-amino-3-ethylbenzyl) phenyl] -4-ethylcyclohexane, 1,1-bis [4- (4-amino-3-propylbenzyl) phenyl]- 4-ethylcyclohexane, 1,
1-bis [4- (4-amino-3-fluorobenzyl)
Phenyl] -4-ethylcyclohexane,

1,1-bis [4- (4-aminobenzyl) -3-ethylphenyl] -4-ethylcyclohexane, 1,1-bis [4- (4-aminobenzyl) -3-
Propylphenyl] -4-ethylcyclohexane, 1,
1-bis [4- (4-aminobenzyl) -3-fluorophenyl] -4-ethylcyclohexane,

1,1-bis [4- (4-amino-3-ethylbenzyl) phenyl] -4-propylcyclohexane, 1,1-bis [4- (4-amino-3-propylbenzyl) phenyl]- 4-propylcyclohexane,
1,1-bis [4- (4-amino-3-fluorobenzyl) phenyl] -4-propylcyclohexane,

1,1-bis [4- (4-aminobenzyl) -3-ethylphenyl] -4-propylcyclohexane, 1,1-bis [4- (4-aminobenzyl) -3
-Propylphenyl] -4-propylcyclohexane,
1,1-bis [4- (4-aminobenzyl) -3-fluorophenyl] -4-propylcyclohexane and the like can be mentioned.

The diamino compound used in the liquid crystal alignment film of the present invention can be produced by the method described in Japanese Patent Application No. 4-351340. And such a diamino compound is
It did not exist in the past.

The tetracarboxylic acid dianhydride used in the liquid crystal alignment film of the present invention is 3,4-dicarboxy-1,2,2.
3,4-Tetrahydro-1-naphthalene succinic anhydride is preferable, and the anhydride can be supplied as a commercial product.

By introducing an aminosilicon compound or a diaminosilicon compound into the liquid crystal alignment film of the present invention, the adhesiveness between the alignment film and the substrate can be improved. Specific examples of the aminosilicon compound include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, and 3-aminopropyltrimethoxysilane.
Aminopropyltris (2-methoxyethoxy) silane, 2-aminoethyltrimethoxysilane, 2-aminoethyltriethoxysilane, 2-aminoethylmethyldimethoxysilane, 2-aminoethylmethyldiethoxysilane, 4-aminobutyltrimethoxy Silane, 4-aminophenyltrimethoxysilane, 4-aminophenyltriethoxysilane, 4-aminophenylmethyldimethoxysilane, 4-aminophenylmethyldiethoxysilane, 4-aminophenyltris (2-methoxyethoxy) silane, 3- (4-Aminophenyl) propyltrimethoxysilane, 3- (4-aminophenyl) propyltriethoxysilane, 3-aminophenyltrimethoxysilane, 3-aminophenyltriethoxysilane, 3-
Examples thereof include (4-aminophenyl) propylmethyldimethoxysilane, 3- (4-aminophenyl) propylmethyldiethoxysilane, 3-aminophenylmethyldimethoxysilane, and 3-aminophenylmethyldiethoxysilane. When these aminosilicon compounds are introduced into the polyimide-based polymer, the content thereof is preferably 50 mol% with respect to the polyimide raw material, preferably 30 mol% or less.

As the diaminosilicon compound,

[0033]

[Chemical 8]

The following may be mentioned. When the diaminosilicon compound is introduced into the polyimide-based polymer, its content is preferably 50 mol% of the diamino compound, which is the raw material for the polyimide, and preferably 30 mol% or less.

In order to provide the liquid crystal alignment film of the present invention on a substrate, a polyamic acid obtained by condensation of a tetracarboxylic dianhydride which is a precursor of polyimide and a diamino compound is coated on the substrate and heat-treated. A method of forming a polyimide-based polymer film on a substrate by a dehydration reaction is preferable. Further, the polyimide of the present invention has a property of being dissolved in a solvent, and thus the obtained polyamic acid precursor is chemically ring-closed using a known dehydration ring-closing catalyst in a solution to obtain a polyimide solution, It is also possible to apply the solution onto a substrate and evaporate the solvent to form a polyimide-based polymer film. More specifically, the former method uses polyamic acid as N-methyl-2-pyrrolidone (NMP),
Dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO),
It is dissolved in a solvent such as butyl cellosolve or ethyl carbitol and adjusted to a 0.1-30 wt% solution, preferably 1-10 wt% solution, and this solution is applied by a brush coating method, a dipping method, a spin coating method, a spray method, A coating film is formed by coating on the substrate by a printing method or the like. After coating, after evaporating the solvent at 50 to 150 ° C, preferably 80 to 120 ° C, 150 ° C
To 400 ° C., preferably 180 ° C. to 280 ° C., and a dehydration ring closure reaction is performed to provide a polybenzylimide polymer film. In the latter method, a polyimide solution obtained by chemically dehydrating and ring-closing is applied by the above method, and the solvent is evaporated to form a polybenzylimide polymer film. Before coating, if the surface of the substrate is treated with a silane coupling agent and a polymer film is formed thereon, the adhesion between the polymer film and the substrate can be improved. Thereafter, 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 device is usually
An electrode, specifically a transparent electrode made of ITO (indium oxide-tin oxide) or tin oxide, is formed on the substrate. Furthermore, alkali elution from the substrate is prevented between this electrode and the substrate. Insulation film, color filter,
An undercoat film such as a color filter overcoat may be provided, and an overcoat film such as an insulating film or a color filter film may be provided on the electrode. 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 formed using the substrate thus formed, liquid crystal is injected, and the injection port is sealed to produce a liquid crystal display element. Alternatively, the liquid crystal may be sprayed on the substrate, the substrates may be overlapped with each other, and the liquid crystal may be sealed so that the liquid crystal does not leak 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 display device of the present invention is characterized in that it has an array control film with less afterimage phenomenon and uneven contrast, and also has good liquid crystal orientation.

[0038]

EXAMPLES In the application examples and application comparative examples shown below, the degree of the afterimage phenomenon was measured using the CV curve method. The C-V curve method uses a liquid crystal cell of 25 mV and 1 kHz.
Is applied, and a direct current triangular wave (hereinafter, referred to as DC voltage) having a frequency of 0.0036 Hz is further overlapped, and D
It is a method of recording the capacitance C which changes by sweeping the C voltage in the range of -10V to 10V. When the DC voltage is swept to the positive side (0 → 10V), the capacity increases. Next, the capacitance is reduced by sweeping to the negative side (10 → 0V). Similarly, when the voltage is swept from 0 to the negative side (0 → -10V), the capacitance increases, and when the voltage is swept to the positive side (-10 → 0V), the capacitance decreases. By repeating this for several cycles, a waveform as shown in FIG. 1 is obtained. When the bias of the charges is generated on the surface of the liquid crystal alignment film and the bias is stabilized, a hysteresis curve as shown in FIG. 1 is drawn on both the positive side and the negative side of the voltage. This Figure 1
A tangent line is drawn to each CV curve based on the above, and a straight line showing the capacitance (C ₀ ) when the DC voltage is 0 is obtained, and the intersections (α _{1 to} α ₄ ) of each of them are obtained. , The positive side is | α
₁ −α ₂ |, the negative side is | α ₃ −α ₄ | After calculating the voltage difference between each two points, the average voltage difference between these two points, that is, (| α ₁ −α ₂ |
_{| + | Α 3 -α 4 |} ) / 2 The calculated, the obtained value was defined as residual charge. If the thickness of the liquid crystal cell and the thickness of the alignment film are the same, the residual charge can be used as a parameter indicating the bias of the charge and its stabilization. That is, it can be understood that the afterimage phenomenon of the liquid crystal display element can be alleviated by using the alignment film having a small residual charge.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. Example 1 50 g of dehydrated and purified N-methyl-2-pyrrolidone was added to a 200 ml four-necked flask equipped with a stirrer, a thermometer, a condenser and a nitrogen purging device, and then 1,1-bis [4- (4 7.43 g of -aminobenzyl) phenyl] cyclohexane was charged and dissolved with stirring. This is 13 ℃
Chilled to 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic anhydride 5.00
g at once and stir reaction while cooling, 20
The mixture was stirred at 4 ° C for 4 hours. Then, the reaction solution was diluted with 61.9 g of N-methyl-2-pyrrolidone (NMP) to obtain a transparent solution containing 10% by weight of polyamic acid. The viscosity of this solution at 25 ° C. was 900 centipoise. A 1: 1 mixed solution of butyl cellosolve and NMP was added to the solution to dilute it to 3% by weight, and then the solution was applied by spin coating (spinner method) onto a transparent glass substrate having an ITO electrode on one surface. Rotation condition is 2000 rpm
, 15 seconds. After the coating film is dried at 100 ° C. for 10 minutes, the temperature is raised to 200 ° C. in an oven for 1 hour, and heat treatment is performed at 200 ° C. for 90 minutes to obtain a film thickness of about 600.
An angstrom polyimide was obtained. Rubbing treatment is performed on the coating surfaces of the two substrates on which the polyimide film is formed to form a liquid crystal alignment film, and a liquid crystal cell having a cell thickness of 6 microns is assembled so that the rubbing directions are parallel and face each other. Liquid crystal FB01 was enclosed. After encapsulation, isotropic treatment was performed at 120 ° C. for 30 minutes, and the liquid crystal element was obtained by gradually cooling to room temperature. The alignment of this liquid crystal element was good, and the residual charge of this cell was 0 V at 25 ° C.

Comparative Example 1 1,1-bis [4- (4-aminobenzyl) phenyl]
7.42-g cyclohexane was added to 2,2-bis [4- (4
6.57 g of -aminophenoxy) phenyl] propane
In place of 5.00 g of 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic anhydride
A polyamic acid solution was obtained in the same manner as in Example 1 except that the amount was changed to 4.80 g. A 1: 1 mixed solution of butyl cellosolve and NMP was added to the obtained solution to give 3
After diluting to a weight percentage, it was applied by a spin coating method (spinner method) on a transparent glass substrate having an ITO electrode on one surface.
The rotation conditions were 2500 rpm and 15 seconds. 10 after coating
After drying at 0 degrees for 10 minutes, 2 hours in the oven
The temperature was raised to 00 ° C., and heat treatment was performed at 200 ° C. for 90 minutes to obtain a polyimide having a film thickness of about 600 Å. The coating surfaces of the two substrates on which the polyimide film is formed are rubbed to form liquid crystal alignment films, and a liquid crystal cell with a cell thickness of 6 microns is assembled so that the rubbing directions are parallel and face each other. LCD FB0
1 was enclosed. After encapsulation, isotropic treatment was performed at 120 ° C. for 30 minutes, and the liquid crystal element was obtained by gradually cooling to room temperature. The residual charge of this cell was 0.50 V at 25 ° C.

Comparative Example 2 1,1-bis [4- (4-aminobenzyl) phenyl]
7.42-g cyclohexane was added to 2,2-bis [4- (4
7.39 g of -aminophenoxy) phenyl] propane
In place of 5.00 g of 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic anhydride
A polyamic acid solution was obtained in the same manner as in Example 1 except that the compound was replaced with 3.93 g of pyromellitic dianhydride. A 1: 1 mixed solution of butyl cellosolve and NMP was added to the obtained solution to dilute it to 3% by weight, and then it was applied by spin coating (spinner method) on a transparent glass substrate having an ITO electrode on one side. . Rotation condition is 5000 rpm
, 15 seconds. After the coating film is dried at 100 ° C. for 10 minutes, the temperature is raised to 200 ° C. in an oven for 1 hour, and heat treatment is performed at 200 ° C. for 90 minutes to obtain a film thickness of about 600.
An angstrom polyimide was obtained. The coating surfaces of the two substrates on which the polyimide film is formed are rubbed to form liquid crystal alignment films, and a liquid crystal cell with a cell thickness of 6 microns is assembled so that the rubbing directions are parallel and face each other. Liquid crystal FB01 was enclosed. After encapsulation, isotropic treatment was performed at 120 ° C. for 30 minutes, and the liquid crystal element was obtained by gradually cooling to room temperature. The residual charge of this cell was 0.90 V at 25 ° C.

[0042]

INDUSTRIAL APPLICABILITY The liquid crystal alignment film of the present invention can uniformly align the liquid crystal over the entire substrate having a wide display area by the ordinary rubbing treatment. Further, the liquid crystal display device using the liquid crystal alignment film is of high quality without occurrence of an afterimage phenomenon.

[0043]

[Brief description of drawings]

FIG. 1 is a diagram showing a CV hysteresis curve.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukino Abe 756-9 Yamadabashi, Ichihara-shi, Chiba Bellheim Kokubunjidai 402

Claims (3)

[Claims] 1. A general formula: A liquid crystal alignment film mainly composed of a polyimide having a repeating unit represented by: 2. A general formula: A polyimide having a repeating unit represented by
-Dicarboxy-1,2,3,4-tetrahydro-1-
Naphthalene succinic anhydride and general formula The liquid crystal alignment film according to claim 1, which is obtained by further dehydrating and ring-closing a polyamic acid obtained by reacting the diamino compound represented by: with a solvent. 3. A liquid crystal display device provided with the liquid crystal alignment film according to claim 1.