JPH09281500A - Liquid crystal orienting film and liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal orienting film having an excellent voltage holding rate and liquid crystal orienting property and good transparency by forming a specified polymonomethyl paraxylilene produced by vapor phase thermal decomposition and polymn. of pdimethylcyclophane on a liquid crystal display element substrate and then subjecting the film to orientation by rubbing or other method. SOLUTION: This liquid crystal orienting film is composed of a polymonomethyl paraxylilene having a structural unit expressed by formula I. The polymonomethyl paraxylilene is obtd. by vapor phase thermal decomposition and polymn. of p- dimethylcyclophane expressed by formula II. As for the method to form the liquid crystal orienting film on a substrate, p-dimethylcyclophane is thermally decomposed in a vapor phase and then vapor deposited and polymerized to form a film at normal temp. For example, a polymer film is formed on the surface of the substrate without pretreatment or preliminarily treated with a silane coupling agent. Then the film is subjected to orientation treatment to give a fine texture by rubbing the film surface in one direction with a cloth or the like or by other method to obtain the liquid crystal orienting film.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a liquid crystal alignment film having a polymonomethylparaxylylene skeleton and a liquid crystal display device having the liquid crystal alignment film.

[0002]

2. Description of the Related Art In recent years, MIM (metal-insulating layer-metal) elements and TFTs (field-effect type elements) capable of colorizing a display screen and turning on and off a large number of pixel electrodes have been developed to improve the functionality of liquid crystal display elements. Active type elements such as thin film transistor elements are used. When carrying out a display device having these colors and a large number of pixel electrodes, especially a color display, an alignment film is formed on the color filter in the production of the display device, but the heat resistance of the color filter used is Therefore, the forming temperature of the alignment film is required to be as low as possible.

Further, regarding a display element using a plastic substrate due to cost reduction, it is required to lower the formation temperature of the alignment film to be used due to the heat resistance of the substrate itself. Further, in the case of an active type element such as a MIM element or a TFT element, an alignment film having a high voltage holding ratio is required in order to prevent flicker of a screen and display nonuniformity due to a voltage drop of a signal voltage applied to the element. To be done.

As the alignment film used in such a display device, a polyimide-based alignment film is mainly used, but when it is used at a firing temperature in consideration of the heat resistance of the color filter and the plastic substrate, it is 200 ° C. or less. The imidization becomes insufficient because it is imidized. It is known that the use of a polyimide alignment film with insufficient imidization adversely affects the characteristics of the display device such as contrast unevenness due to a decrease in voltage holding ratio. In addition, since the polyimide-based alignment film is colored, it affects the brightness of the screen of the obtained liquid crystal display device.

In addition, liquid crystal alignment of polyparaxylylene or its derivatives such as polymonochloroparaxylylene or polymonoethylparaxylylene described in JP-A-51-45547 and JP-A-57-53730 is performed. When used as a film, it is more colorless and transparent than a polyimide-based alignment film, and a liquid crystal display device using the alignment film can obtain a bright screen. However, the polyparaxylylene and its derivatives described in the above publication cannot be an alignment film having both a high voltage holding ratio and a good alignment property.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and it is possible to form a film on a substrate under mild conditions, that is, at room temperature, which is excellent in transparency and has a voltage holding ratio. Another object of the present invention is to provide a liquid crystal alignment film having excellent liquid crystal alignment properties and a liquid crystal display device including the liquid crystal alignment film.

[0007]

As a result of intensive studies, the inventors of the present invention have formed polymonomethylparaxylylene obtained by vapor phase thermal decomposition polymerization of p-dimethylcyclophane on a liquid crystal display device substrate. It has been found that a liquid crystal alignment film and a liquid crystal display device having excellent voltage holding ratio and liquid crystal alignment property and good transparency can be obtained by performing an alignment treatment by a rubbing method or another method, and the present invention is obtained. Completed

The details of the present invention will be described below. (1) General formula

[0009]

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A liquid crystal alignment film comprising polymonomethylparaxylylene having a structural unit represented by:

(2) Polymonomethylparaxylylene has the general formula

[0012]

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A compound obtained by a gas phase thermal decomposition polymerization reaction of p-dimethylcyclophane represented by (1)
The liquid crystal alignment film according to the item.

(3) A liquid crystal display device provided with the liquid crystal alignment film as described in (1) or (2).

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION As a method for providing a liquid crystal alignment film of the present invention on a substrate, p-dimethylcyclophane was vapor-phase thermally decomposed and then vapor-deposited and polymerized at room temperature to produce a film. Specifically, a polymer film is formed on the surface of the substrate without pretreatment or after treatment with a silane coupling agent. After that, the coated surface is rubbed in one direction with a cloth or the like, or an alignment treatment for imparting a fine shape is performed by another method 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. The enclosed liquid crystal is not particularly limited, and various liquid crystals such as nematic liquid crystal, liquid crystal added with a dichroic dye, and ferroelectric liquid crystal can be used.

The liquid crystal display device of the present invention is provided with a colorless and transparent alignment control film that can be formed on a substrate under mild conditions, that is, at room temperature, and also has good liquid crystal orientation and good voltage holding characteristics. It is characterized by doing.

[0019]

EXAMPLES In the following examples and comparative examples, the voltage holding ratio was measured with a circuit as shown in FIG. The measuring method is to monitor the drain voltage (V _D ) which changes by applying a rectangular wave (V _S ) having a gate pulse width of 69 μs, a frequency of 30 Hz and a wave height of ± 4.5 V to the source.
For example, when a positive rectangular wave is applied to the source, the drain (V _D ) shows a positive value until the next negative rectangular wave is applied. If the retention rate is 100%, V shown in FIG.
_D takes a rectangular orbit represented by a dotted line, but normally V
_D is a solid trajectory that gradually approaches zero. Therefore, the area of the measured track (the area surrounded by the track V = 0 and the track), that is, the shaded area is calculated, and such measurement is performed four times to obtain the average value of the areas. When the voltage was not reduced at all, the area was defined as 100%, and the relative value of the measured area was calculated, and this was defined as the voltage holding ratio (%).

Further, the liquid crystal alignment property means that a compound for an alignment film is formed on a transparent glass substrate having an ITO electrode on one side and subjected to a rubbing treatment so that the rubbing directions are parallel and face each other. A liquid crystal cell with a cell thickness of 6 microns was assembled, FB01, a fluorine-based liquid crystal manufactured by Chisso Corporation, was enclosed, and after isotropic treatment at 120 ° C for 30 minutes, the cell was gradually cooled to room temperature under a crossed Nicol. It was evaluated whether or not the domain orientation was shown and the display uniformity.

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 20 g of p-dimethylcyclophane (manufactured by Daisan Kasei Co., Ltd., trade name diX-2M) was placed at the end of a quartz tube.
After reducing the pressure to 3 × 10 ^{-2 to} 1.3 × 10 ^-3 kPa, 100
Steamed p-dimethylcyclophane at ~ 150 ° C.
After passing the evaporate through a decomposition furnace at 600 to 700 ° C., it was introduced into a vapor deposition chamber at room temperature, and a polymonomethylparaxylylene film was formed on a transparent glass substrate having an ITO electrode on one surface at room temperature. The coated surfaces of the two substrates on which the polymonomethylparaxylylene film was formed were rubbed to form liquid crystal alignment films, and liquid crystal cells with a cell thickness of 6 microns were assembled so that the rubbing directions were parallel and opposed to each other. ,
FB01, which is a fluorine-based liquid crystal manufactured by Chisso Corporation, 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 orientation of this liquid crystal element was good, and the voltage holding ratio of this cell was 25 ° C.
Was 99.3%.

COMPARATIVE EXAMPLE 1 20 g of p-cyclophane was placed at the end of a quartz tube for 1.3.
After depressurizing to × 10 ^{-2 to} 1.3 × 10 ^-3 kPa, 100 to
P-cyclophane was vaporized at 150 ° C. Evaporate 6
After passing through a decomposition furnace at a temperature of 00 to 700 ° C., the film was introduced into a vapor deposition chamber at room temperature, and a polyparaxylylene film was formed on a transparent glass substrate having an ITO electrode on one surface at room temperature. The coating surfaces of the two substrates on which the polyparaxylylene film is formed are rubbed to form liquid crystal alignment films, and liquid crystal cells having a cell thickness of 6 microns are assembled so that the rubbing directions are parallel and face each other. FB01, which is a fluorine-based liquid crystal manufactured by Chisso Corporation, 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 orientation of this liquid crystal element was good, and the voltage holding ratio of this cell was 92.2% at 25 ° C.

Comparative Example 2 20 g of p-dichlorocyclophane was placed at the end of a quartz tube and the pressure was reduced to 1.3 × 10 ^{-2 to} 1.3 × 10 ^-3 kPa.
P-dichlorocyclophane was vaporized at 100-150 ° C. After passing the evaporate through a decomposition furnace at 600 to 700 ° C., it was introduced into a vapor deposition chamber at room temperature, and a polymonochloroparaxylylene film was formed on a transparent glass substrate having an ITO electrode on one surface at room temperature. The coated surfaces of the two substrates having the polymonochloroparaxylylene film formed thereon are rubbed to form liquid crystal alignment films, and liquid crystal cells having a cell thickness of 6 microns are assembled so that the rubbing directions are parallel and face each other. FB01, which is a fluorine-based liquid crystal manufactured by Chisso Corporation, 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 orientation of this liquid crystal element was good, and the voltage holding ratio of this cell was 89.0% at 25 ° C.

Comparative Example 3 20 g of p-diethylcyclophane was placed at the end of a quartz tube and the pressure was reduced to 1.3 × 10 ^{−2 to} 1.3 × 10 ⁻³ kPa.
P-diethylcyclophane was vaporized at 100-150 ° C. After passing the evaporate through a decomposition furnace at 600 to 700 ° C., it was introduced into an evaporation chamber at room temperature, and a polymonoethylparaxylylene film was formed on a transparent glass substrate having an ITO electrode on one surface at room temperature. The coating surfaces of the two substrates on which the polymonoethylparaxylylene film is formed are rubbed to form liquid crystal alignment films, and liquid crystal cells having a cell thickness of 6 microns are arranged so that the rubbing directions are parallel and face each other. After assembly, FB01, which is a fluorine-based liquid crystal manufactured by Chisso Corporation, 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 orientation of this liquid crystal element is poor, and the voltage holding ratio of this cell is 25 ° C.
Was 93.0%.

Comparative Example 4 8.06 g of 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 4.36 g of pyromellitic dianhydride and 0.11 g of paraaminophenyltrimethoxysilane in NMP. Polymerization was carried out to obtain a polyamic acid solution. 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 applied by spin coating (spinner method) on a transparent glass substrate having an ITO electrode on one side. . After the coating film was dried at 100 ° C. for 10 minutes, the temperature was raised to 180 ° C. in an oven for 1 hour and heat treatment was performed at 180 ° C. for 90 minutes to obtain a polyimide film. 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 having a cell thickness of 6 microns is assembled so that the rubbing directions are parallel and face each other. Company T
The liquid crystal FB01 for FT was enclosed. 30 after encapsulation at 120 ° C
The liquid crystal element was obtained by performing isotropic treatment for minutes and gradually cooling to room temperature. The orientation of this liquid crystal element was good, but the voltage holding ratio of this cell was only 75.0% at 25 ° C. For comparison, the results of Examples and Comparative Examples are summarized in Table 1.

[0026]

[Table 1]

[0027]

The liquid crystal alignment film of the present invention can be formed as a colorless and transparent film on a substrate under mild conditions, that is, at room temperature, and is uniformly rubbed over the entire substrate having a wide display area by rubbing or the like. The liquid crystal can be aligned.
Further, a liquid crystal display device using the liquid crystal alignment film has a good voltage holding ratio, no flicker on the display screen, and is bright and of high quality.

[Brief description of drawings]

FIG. 1 is a circuit diagram used for measuring a voltage holding ratio.

[Figure 2] V _S, the gate pulse width 69μs, frequency 30
It is a rectangular wave of Hz and a wave height of ± 4.5V. V _D is a waveform read by an oscilloscope by applying V _S to the source of the circuit shown in FIG.

Claims (3)

[Claims] 1. A compound of the general formula A liquid crystal alignment film comprising polymonomethylparaxylylene having a repeating unit represented by: 2. Polymonomethylparaxylylene is represented by the general formula: The liquid crystal alignment film according to claim 1, which is a compound represented by the formula (1) obtained by a gas phase thermal decomposition polymerization reaction of p-dimethylcyclophane. 3. A liquid crystal display device comprising the liquid crystal alignment film according to claim 1.