JP2000122067A - Liquid crystal aligning layer and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal aligning layer which ensures good liquid crystal aligning property and very low residual DC voltage by using a polyoxazole as a base. SOLUTION: This liquid crystal aligning layer is based on a polyoxazole preferably having a structure of formula I, wherein X is a tetravalent organic group and R is a non-aromatic divalent organic group, preferably an organic group of formula II or III. In the formula II, (n) is an integer of 4-12. Since the polyoxazole has no high polarity carbonyl group unlike a polyimide or polyamide, low residual DC voltage is ensured. The liquid crystal aligning layer ensures good aligning property and 0.08-0.12 V residual DC voltage, has high voltage retentivity and is particularly suitable for use in an active matrix type liquid crystal display device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal alignment film capable of obtaining good liquid crystal alignment and an extremely low residual DC voltage, and a liquid crystal display device using the same. Things.

[0002]

2. Description of the Related Art At present, liquid crystal display devices have been widely used as thin displays. Commonly used liquid crystal display devices include twisted nematic
There are a (TN) liquid crystal display element, a super twisted nematic (STN) liquid crystal display element, a ferroelectric liquid crystal display element, and the like. When these liquid crystal display elements are manufactured, as described in JP-B-62-38689. In addition, it is necessary to provide a liquid crystal alignment film for aligning liquid crystal sandwiched between substrates with a transparent electrode in a certain direction with respect to the substrate. Examples of such a liquid crystal alignment film include polyimide, polyamide, and polyamide imide. Among them, the case where polyimide is used as the liquid crystal alignment film is the most common at present.

However, in a liquid crystal display device manufactured using these liquid crystal aligning agents, when a certain pattern is continuously displayed on a screen, a phenomenon that the pattern is difficult to be erased (hereinafter, referred to as burn-in phenomenon) occurs. And has become a problem. The burn-in phenomenon occurs when a drive waveform applied to a liquid crystal display element contains a DC component, which accumulates and becomes a DC voltage (residual DC voltage) that remains between the electrodes of the liquid crystal display element even when the voltage is removed. In order to solve this problem, there is a need for a liquid crystal alignment film having a low residual DC voltage.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the liquid crystal alignment film, and provides a liquid crystal alignment film capable of obtaining good liquid crystal alignment and an extremely low residual DC voltage. It is intended to provide a liquid crystal display element.

[0005]

That is, the present invention relates to a liquid crystal alignment film containing polyoxazole as a main component.
The polyoxazole has a structure represented by the general formula (1), and R is a liquid crystal alignment film comprising an organic group represented by the general formula (2) or (3). Furthermore, a liquid crystal display device using these liquid crystal alignment films is provided.

[0006]

Embedded image In the formula, X represents a tetravalent organic group, and R represents a divalent organic group that is not aromatic.

[0007]

Embedded image In the formula, n represents an integer of 4 or more and 12 or less.

[0008]

Embedded image

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a residual DC voltage is caused by polarization of an alignment film or the like at a display portion because the same electric field is continuously applied, and the polarity of the alignment film is low. It is made by examining a polymer which is considered to be less likely to be generated and which is considered to have a lower polarity than polyimide or the like, and which can well align a liquid crystal similarly to polyimide or the like. The polyoxazole used for the liquid crystal alignment film of the present invention does not have a carbonyl group having a high polarity unlike polyimide and polyamide used for the conventional liquid crystal alignment film, and for the above-mentioned reason, when a low residual DC voltage is applied, Conceivable. Further, the liquid crystal can be favorably aligned.

The liquid crystal alignment film of the present invention can be formed by applying a solution of polyoxazole or a polyoxazole precursor on a substrate by printing or spin coating, and then firing. The polyoxazole precursor can be obtained by polycondensing a bis (hydroxyamino) compound and a dicarboxylic acid compound in a polar solvent. Polyoxazole can be obtained by subjecting the obtained precursor polyhydroxyamide to dehydration and ring closure with a heating or dehydrating agent.

Examples of the bis (hydroxyamino) compound used in the present invention include 3,3'-dihydroxy-
4,4'-diaminobiphenyl, 2,2-bis (3-amino-4
-Hydroxyphenyl) propane, 2,2-bis (3-amino
-4-hydroxyphenyl) hexafluoropropane, but is not limited thereto.

Further, examples of the dicarboxylic acid compound include:
Succinic acid, adipic acid, 1,6-hexanedicarboxylic acid,
1,8-octanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,3-cyclobutanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, 2,5- Dimethylphenyldicarboxylic acid, 4,4′-biphenyldicarboxylic acid,
3,3'-biphenyl dicarboxylic acid, 4,4'-benzophenone dicarboxylic acid, 2,2-bis (4-carboxyphenyl)
Examples include, but are not limited to, dicarboxylic acids such as hexafluoropropane and their acid chlorides.

Among these, succinic acid, adipic acid,
1,6-hexanedicarboxylic acid, 1,8-octanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,3-cyclobutanedicarboxylic acid,
Those having a non-aromatic structure, such as 4-cyclohexanedicarboxylic acid, can provide a liquid crystal display element having a high voltage holding ratio, and are preferable as a liquid crystal alignment film for an active matrix LCD. 1,6-hexanedicarboxylic acid, 1,8-octanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, etc., having a methylene number of 4 to 12, or 1,4-cyclohexanedicarboxylic acid It is particularly preferred to use an acid.

Examples of a polar organic solvent for polymerization for obtaining a polyoxazole precursor include N-methyl-2-
Examples include, but are not limited to, pyrrolidone, dimethylformamide, dimethylacetamide, γ-butyrolactone, and the like.

The liquid crystal alignment film of the present invention may contain another polymer as long as the effect of polyoxazole is not impaired. Examples of polymers that can be used in combination include polyimide, polyamide, polyamideimide, and the like, but are not limited thereto. Further, in order to further improve the adhesion to the substrate, a small amount of a silane coupling agent or a titanium-based coupling agent may be added.

A liquid crystal aligning agent is prepared by adding a solvent component to the resin component. Preferred examples of the solvent component used in the present invention include a mixed solvent of N-methyl-2-pyrrolidone (NMP) and butyl cellosolve. A mixed solvent of NMP and ethyl carbitol, a mixed solvent of NMP and propylene glycol mono-n-butyl ether, a mixed solvent of NMP and propylene glycol diacetate, a mixed solvent of γ-butyrolactone and butyl cellosolve, and the like, but are not limited thereto. Not something. Also, three or more solvents may be used in combination.

[0017]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited thereto.

(Synthesis Example 1) In a four-neck separable flask equipped with a thermometer, a stirrer, and a dry nitrogen gas introducing tube, 21.62 g of 3,3'-dihydroxy-4,4'-diaminobiphenyl ( 0.1 mol) and triethylamine 20.24
g (0.2 mol) is converted to N-methyl-2-pyrrolidone (hereinafter referred to as N
Dissolve in 300 g). The separable flask was cooled to maintain the temperature of the system at −10 ° C., and while stirring under nitrogen flow, 20.30 g of terephthaloyl chloride was added.
(0.1 mol), and stirring was continued for 5 hours while maintaining the temperature of the system at -10 ° C. The temperature of the system was returned to room temperature, and after suction filtration, the solution was dropped into a 20-fold amount of ion-exchanged water to precipitate a resin component. After filtering the resin component, it was dried in a vacuum dryer at 50 ° C. for 24 hours to obtain polyhydroxyamide. By NMP and butyl cellosolve, the concentration of the resin component is 5%, and the ratio of NMP to butyl cellosolve is 8: 2.
To obtain a liquid crystal aligning agent (1).

Synthesis Example 2 1,4-hexanedicarboxylic acid 17.4 in a four-neck separable flask equipped with a thermometer, a stirrer, a dropping funnel, and a dry nitrogen gas inlet tube.
2 g (0.1 mol) and 27.03 g (0.2 mol) of 1-hydroxybenzotriazole are dissolved in 200 g of NMP. The separable flask was cooled to maintain the temperature of the system at 0 ° C., and 41.27 g (0.2%) of dicyclohexylcarbodiimide was added from the dropping funnel while stirring under nitrogen flow.
(Mol) in 100 g of NMP is added dropwise and stirred at room temperature for 24 hours. The dropping funnel was removed, and 21.62 g of 3,3'-dihydroxy-4,4'-diaminobiphenyl (0.6%) was added.
1 mol), the temperature is raised to 75 ° C., and the reaction is carried out for 24 hours. The temperature of the system is returned to room temperature, and filtration is performed to remove dicyclohexylcarbodiurea produced by the reaction from the system. The filtrate was dropped into 5 liters of methanol to precipitate a solid content, which was collected by filtration, and dried under vacuum at 50 ° C. for 72 hours to obtain polyhydroxyamide. The liquid crystal aligning agent (2) was diluted with NMP and butyl cellosolve so that the concentration of the resin component was 5% and the ratio of NMP and butyl cellosolve was 8: 2.
I got

(Synthesis Example 3) 17.42 g (0.1 mol) of 1,6-hexanedicarboxylic acid was replaced with 17.22 g (0.1 mol) of 1,4-cyclohexanedicarboxylic acid.
By operating in the same manner as in Synthesis Example 2, a liquid crystal aligning agent (3) was obtained.

(Synthesis Example 4) 17.42 g (0.1 mol) of 1,6-hexanedicarboxylic acid was added to 14.61 g of adipic acid.
(0.1 mol) and 3,3′-dihydroxy-4,4′-
21.62 g (0.1 mol) of diaminobiphenyl was
-Bis (3-amino-4-hydroxyphenyl) propane 2
A liquid crystal aligning agent (4) was obtained in the same manner as in Synthesis Example 2 except that the amount was changed to 5.83 g (0.1 mol).

Synthesis Example 5 17.42 g (0.1 mol) of 1,6-hexanedicarboxylic acid was added to 25.82 g (0.1 mol) of 4,4′-dicarboxydiphenyl ether, and
3'-dihydroxy-4,4'-diaminobiphenyl 21.6
2 g (0.1 mol) of 36.63 g of 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane
(0.1 mol) to obtain a liquid crystal aligning agent (5) in the same manner as in Synthesis Example 2.

(Embodiment 1) 1 cm × 1 cm ITO in the center
A liquid crystal aligning agent (1) by flexographic printing on a 5 cm x 5 cm low alkali glass substrate on which a 1 mm wide electrode is formed so that a transparent electrode can be connected to the outside.
Was printed and pre-dried on a hot plate at 80 ° C. for 2 minutes, and then baked in a clean oven at 220 ° C. for 60 minutes to form a liquid crystal alignment film on the substrate. When the IR spectrum of this alignment film was measured, it was 1060 cm ^-1 and 1
A peak derived from oxazole was strongly observed at 625 cm ^-1 , confirming that polyhydroxyamide was dehydrated and ring-closed, and that polyoxazole was the main component.

On the other hand, the substrate on which the alignment film was formed was subjected to a rubbing treatment so that the rubbing directions were perpendicular to the upper and lower substrates, and a cell having a cell gap of 5 μm was prepared using an epoxy resin sealing material. After injecting a liquid crystal composition ZLI-4792 manufactured by Merck into the cell and sealing the injection port with a UV-curable sealing agent, a polarizing plate is attached to both sides of the cell so as to match the rubbing direction. An element was manufactured. Observation of the liquid crystal display device on a light box (white light source) showed that light was transmitted uniformly and no display defects such as uneven alignment were observed. Further, when a rectangular wave of ± 5 V, 30 Hz was applied to the liquid crystal display element, a portion of 1 cm × 1 cm having the transparent electrode was shielded from light, and good display was obtained. After the liquid crystal display element was left at 90 ° C. for 1000 hours and observed in the same manner, the orientation was good.

Applying DC 10 V for 240 hours to a liquid crystal display element which has not been treated at 90 ° C. for 1000 hours,
Once the electrodes on both sides of the liquid crystal display element are short-circuited, the potential difference becomes zero.
After setting to V, the potential difference between the electrodes was measured with an electrometer. The voltage after 10 minutes of connecting the electrometer
When evaluated as a residual DC voltage, the residual DC voltage was 0.12V. Further, the voltage holding ratio at 25 ° C. of the liquid crystal display element not subjected to the DC 10 V application treatment was measured and found to be 91%.

Example 2 A liquid crystal alignment film was formed in the same manner as in Example 1 using the liquid crystal alignment agent (2) obtained in Synthesis Example 2. The obtained liquid crystal alignment film was mainly composed of polyoxazole as in Example 1. Also, the orientation was as good as in Example 1, and the residual DC voltage was 0.09V.
And the voltage holding ratio was 98%.

Example 3 Using the liquid crystal aligning agent (3) obtained in Synthesis Example 3, a liquid crystal alignment film was formed in the same manner as in Example 1. The obtained liquid crystal alignment film was mainly composed of polyoxazole as in Example 1. Also, the orientation was as good as in Example 1, and the residual DC voltage was 0.08V.
, And the voltage holding ratio was 99%.

Example 4 A liquid crystal alignment film was formed in the same manner as in Example 1 using the liquid crystal alignment agent (4) obtained in Synthesis Example 4. The obtained liquid crystal alignment film was mainly composed of polyoxazole as in Example 1. Also, the orientation was as good as in Example 1, the residual DC voltage was 0.10 V,
The voltage holding ratio was 98%.

Example 5 A liquid crystal alignment film was formed in the same manner as in Example 1 using the liquid crystal alignment agent (5) obtained in Synthesis Example 5. The obtained liquid crystal alignment film was mainly composed of polyoxazole as in Example 1. Also, the orientation was as good as in Example 1, and the residual DC voltage was 0.10 V
The voltage holding ratio was 87%.

Comparative Example 1 In a four-neck separable flask equipped with a thermometer, a stirrer, and a dry nitrogen gas inlet tube, 2,2-bis [4,4 '-(4-aminophenoxy) phenyl was used. ] 41.06 g (0.1 mol) of propane are added to NMP 30
Dissolve in 0 g. While maintaining the temperature of the system at 10 ° C. and stirring under nitrogen flow, 21.81 g (0.1 mol) of pyromellitic dianhydride was charged from the raw material inlet, and the temperature of the system was maintained at 10 ° C. Stirring was continued for 5 hours. The temperature of the system was returned to room temperature to obtain a polyamic acid NMP solution.
This solution was treated with NMP and butyl cellosolve to give a resin component concentration of 5% and a ratio of NMP to butyl cellosolve of 8:
The mixture was diluted to 2 to obtain a liquid crystal aligning agent (6).

[0031] Using the liquid crystal aligning agent (6), in the same manner as in Example 1 to form a liquid crystal alignment film was measured for IR spectrum of the alignment film, the peak derived from imide 1730 cm ^-1 and 1780 cm ^-1 Thus, it was confirmed that a polyimide obtained by dehydration and ring closure of a polyamic acid was a main component. The orientation was as good as in Example 1, but the residual DC was 1.2 V.

Comparative Example 2 In a four-neck separable flask equipped with a thermometer, a stirrer, and a dry nitrogen gas inlet tube, 2,2-bis [4,4 '-(4-aminophenoxy) phenyl was used. 41.06 g (0.1 mol) of propane and 20.24 g (0.2 mol) of triethylamine are dissolved in 400 g of NMP. While maintaining the system at 10 ° C., 20.30 g (0.1 mol) of terephthaloyl chloride was charged from the raw material inlet.
Stirring was continued for 5 hours. The resulting suspension was subjected to suction filtration, and the filtrate was dropped into 10-fold amount of methanol, and the solid content (polyamide) was separated by filtration. This solid was repeatedly dissolved / reprecipitated three times in an NMP / methanol system, and then dried under reduced pressure at 80 ° C. for 24 hours. 5 g of the solid content after drying was dissolved in 95 g of a 8: 2 mixed solvent of NMP and butyl cellosolve to obtain a liquid crystal aligning agent (7).

When a liquid crystal alignment film was formed using the liquid crystal alignment agent (7) in the same manner as in Example 1, the alignment was as good as in Example 1, but the residual DC was 1.9 V. Met

Each of the liquid crystal alignment films obtained in Examples 1 to 5 had good alignment and low residual D of 0.08 to 0.12 V.
C, and the voltage holding ratio was also high.
In No. 4, the voltage holding ratio is as high as 98% or more, which is particularly suitable for an active matrix type liquid crystal display device.

On the other hand, in Comparative Example 1, since the liquid crystal aligning agent containing polyimide as a main component was used, the alignment was good, but the residual DC voltage was as high as 1.2 V. Since the liquid crystal aligning agent was mainly composed of polyamide, the alignment was good, but the residual DC voltage was 1.9.
It was high with V.

[0023]

The liquid crystal alignment film of the present invention and the liquid crystal display device using the same can provide good alignment and a low residual DC voltage, and contribute to the improvement of display quality.

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Claims (4)

[Claims] 1. A liquid crystal alignment film containing polyoxazole as a main component. 2. The liquid crystal alignment film according to claim 1, wherein the polyoxazole has a structure represented by the general formula (1). Embedded image In the formula, X represents a tetravalent organic group, and R represents a divalent organic group that is not aromatic. 3. The method according to claim 1, wherein R in the general formula (1) is an organic group represented by the general formula (2) or the formula (3).
The liquid crystal alignment film according to claim 2. Embedded image In the formula, n represents an integer of 4 or more and 12 or less. Embedded image 4. A liquid crystal display device comprising the liquid crystal alignment film according to claim 1.