JP2000221510A - Liquid crystal device and production of liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a display having high contrast and high quality without defects by using a polyamic acid having a specified structure which forms imide rings in a specified proportion to align liquid crystal molecules in the perpendicular direction as a liquid crystal alignment film material. SOLUTION: A polyamic acid is imidized by using acetic acid anhydride and pyridine as an imidizing agent in N-methyl-2-pyrrolidone and then purified to obtain a polyimide. By controlling the add amt. of the imidizing agent, the imidization degree can be controlled. The imidization degree is preferably 25 to 99%, and more preferably 50 to 95%. After the imidization reaction, the imidizing agent used is removed. The proportion of the add amt. (the amt. of functional groups) of the crosslinking agent calculated as the chemical equiv. to the amt. of functional groups when all polymers are regarded as a polyamic acid is preferably 1 to 50% and properly 5 to 20%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal device used for a personal computer, a word processor, a portable information terminal, a power coder, a digital still camera, a video projector, and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal device, particularly a display liquid crystal device, a liquid crystal molecule is oriented horizontally with respect to a substrate mainly in a state where no electric field is applied, and is twisted by 90 ° in a cell thickness direction (hereinafter referred to as a twisted nematic method). TN) or similarly 240
A display method called a super-twisted nematic method, which is twisted by ２270 °, has been used. On the other hand, in order to improve the display contrast and increase the response speed, liquid crystal molecules are aligned perpendicular to the substrate, and a vertical alignment display method is being studied in combination with a liquid crystal material having a negative dielectric anisotropy. For the first time, usage examples are being reported mainly for projector applications. Although the vertical alignment method has the above advantages, it has not been widely used in the market because there is no vertical alignment film for vertically aligning the liquid crystal having excellent alignment stability. This is because, in such a vertical alignment film, it is necessary to align the liquid crystal molecules with a slight inclination with respect to the normal direction of the film surface even if it is vertical, and it is necessary to stably obtain this inclination. Is difficult. Therefore, a method using oblique evaporation of silicon oxide, which is very difficult to increase in area and lacks in mass productivity, a method in which a notch is provided in a pixel electrode or a counter electrode which has a defect of a decrease in luminance, and a very complicated manufacturing process However, there has been reported an example in which a liquid crystal display device is prototyped using a method of forming irregularities on the surfaces of two substrates.

[0003]

As described above, the prior art has problems such as mass productivity, display quality, and an increase in manufacturing cost due to the complexity of the manufacturing process. Had not been reached.

[0004]

Means for Solving the Problems The present inventors have made polyamic acid having a specific structure in which an imide ring is formed at a certain ratio and vertically aligning liquid crystal molecules as a material for a liquid crystal alignment film. As a result of intensive studies, it was found that the larger the ratio of the imide moiety in the liquid crystal alignment film, the larger the degree of inclination that can be given to the liquid crystal molecules. According to the present invention, a cross-linking reaction is caused in the unreacted amic acid portion in the alignment film, and the strength of the film is increased by binding the polymer main chains. When the tilt angle of the liquid crystal molecules is controlled by aligning the tilt angles given to the molecules and controlling the tilt direction of the liquid crystal molecules by an alignment process such as a rubbing process, a liquid crystal display device having an alignment film with a stable alignment state and a scratch-resistant film surface is provided. Can be provided. Further, by setting the timing of performing the alignment treatment to a specific step, a larger inclination can be given to the liquid crystal molecules.

According to the liquid crystal device of the present invention, when no electric field is applied, the liquid crystal molecules are stably vertically aligned at a slight tilt angle, and the tilt angles are uniform and the alignment film surface is not damaged. Due to the fact that it is difficult to attach, it is possible to obtain an image of high display quality without display unevenness.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described by taking an active matrix type liquid crystal display device having an inverted staggered thin film transistor array formed on a glass substrate as an example.

A gate electrode was formed using a conductive material on a glass substrate, and a gate insulating film was formed using an insulating material. A semiconductor layer of an amorphous silicon or polysilicon film was formed thereon in a predetermined shape. Then
Source and drain electrodes were formed using a conductive material, an interlayer insulating film was deposited, a contact hole was formed, and a pixel electrode was formed from a transparent conductive material to obtain an array-side substrate. On another substrate, a light-shielding film for preventing light leakage from unnecessary portions was formed in a predetermined shape, and a counter electrode was formed of a transparent conductive film. A liquid crystal alignment film material having a capability of vertically aligning liquid crystal is applied onto these two substrates. The coating method, spin coating method, printing method, spray method, slot coating method, bar coating method, it is possible to use various methods such as dipping method,
Here, a spin coating method was used.

As the precursor of the liquid crystal alignment film material used here, for example, those described in JP-A-9-241646 can be used. Among them, polyamic acid obtained by dehydrating and condensing 2,3,5-tricarboxycyclopentylacetic acid with a specific diamine compound having a cholestanol skeleton represented by the following formula (1) and 4,4'-diaminodiphenylmethane Can be used. As such a precursor, it is also possible to use pyromellitic dianhydride or p-phenylenediamine in addition to the materials listed here. However, when an aromatic tetracarboxylic acid such as pyromellitic acid is used, the solubility in a solvent after the imidization reaction is remarkably reduced, so that the production problem is large and is not very practical. From the viewpoint of electrical characteristics such as specific resistance value and stability of liquid crystal alignment state, the precursor is preferably an aliphatic one having a cyclic structure. Also,
It is not preferable to use a linear or cyclic aliphatic diamine for the diamine portion in view of the heat resistance of the film and a decrease in the alignment regulating force. Therefore, it is preferable to use a compound having an aliphatic cyclic structure for the tetracarboxylic acid portion and an aromatic material for the diamine portion.

[0009]

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Furthermore, for the purpose of vertically aligning the liquid crystal, a specific diamine having a cholestanol skeleton or a diamine compound having a side chain capable of imparting vertical alignment such as alkylphenyl fluoride or alkoxyphenyl fluoride is used. 5 to 5 in molar ratio of diamine compound
It must contain 70%. Depending on the liquid crystal material,
When this ratio is 5 to 25% or less, it may be impossible to vertically align the liquid crystal. Also, from the viewpoint of solubility in a solvent, it is difficult for this ratio to exceed 70%.
Here, the ratio of the diamine compound was 30%.
As a result of examination, the tilt angle that can be given to the liquid crystal hardly depends on this ratio. Further, in consideration of the practicality of the display liquid crystal device, the tilt angle of the liquid crystal molecule alignment with respect to the normal direction of the substrate is preferably 1 to 15 °, and when importance is placed on display contrast, 1 to 5 ° is more preferable. .

A polyimide can be obtained by imidizing and purifying the above-mentioned polyamic acid by using acetic anhydride and pyridine as an imidizing agent in N-methyl-2-pyrrolidone. The imidization ratio can be controlled by adjusting the amount of the imidizing agent added. This imidation ratio is preferably from 25 to 99%, more preferably from 50 to 95%. After the imidization reaction, the imidizing agent used here is removed.
The material thus prepared was dissolved in N-methyl-2-pyrrolidone to prepare a varnish. If the solubility is not sufficient, a solvent such as butyl cellosolve may be added thereto. Here, for example, a bifunctional or tetrafunctional epoxy-based crosslinking agent disclosed in JP-A-9-146100, as shown in the following formula (2) or (3), is added. The ratio of the chemical equivalent of the amount of the crosslinking agent (the amount of the functional group) to the amount of the functional group when the polymer is assumed to be a polyamic acid (hereinafter referred to as “crosslinking agent addition rate”) is 1 to 50%. Preferably, 5 to 20% is appropriate.

[0012]

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[0013]

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The material for liquid crystal alignment film prepared above is applied on a glass substrate by spin coating,
After calcination at 0 ° C. for 1 to 5 minutes to remove the solvent, 180
This was calcined at ~ 200 ° C for 1-2 hours to cause a crosslinking reaction and to remove the residual solvent. When the infrared spectrum of the alignment film thus manufactured was measured before and after the main baking, no significant increase in the imidization ratio was observed. If the firing temperature at this time exceeds 200 ° C., elimination of side chains occurs, which is not preferable. Here, as the alignment treatment, rubbing treatment using a rubbing cloth made of rayon was performed in an antiparallel direction on the upper and lower substrates under general conditions. Thereafter, spacers were sprayed, and the periphery was sealed with a sealant. Next, a liquid crystal material having negative dielectric anisotropy was injected, and the injection port was sealed to obtain a liquid crystal display device. As a liquid crystal material having negative dielectric anisotropy, trade name M
Commercial products such as LC6608 or MLC6609 (manufactured by Merck Japan KK) can be used. Also,
The orientation may be performed in such a direction as to twist each other. A liquid crystal display device was obtained by attaching a polarizing plate to the panel thus manufactured, mounting a liquid crystal driver, connecting to a drive circuit, and incorporating other necessary components.

Several kinds of liquid crystal display devices such as a transmission type, a reflection type and a direct-view type projection type are manufactured using an alignment film material having different imidation ratios and cross-linking agent addition ratios. The angle of inclination from the substrate normal direction and the degree of display unevenness were examined. Table 1 shows the measurement results for the reflective projection type. From these results, the imidization rate was 25 to 99.
% And the range of 1 to 50% as the crosslinking agent addition rate was found to be practically usable.

Further, an imidization ratio of 80% and a crosslinking agent addition ratio of 2
The same evaluation was performed on a rubbing treatment between preliminary firing and main firing using a 0% alignment film (Preparation Example 15), and a rubbing treatment was performed after main firing (Preparation Example 5). It was found that a larger tilt angle can be obtained as compared with. The results are also shown in Table 1.

[0017]

[Table 1]

[0018]

By using the liquid crystal device of the present invention,
Regardless of the transmission type reflection type and the direct-view type projection type, high contrast, high quality and defect-free display could be obtained.

Continued on front page F-term (reference) 2H090 HB08Y HB09Y HB10Y HC05 KA04 LA04 MA01 MA11 MB01 4J002 CD01X CD13X CM04W 4J043 PA02 PA19 PC145 PC205 QB15 QB26 QB31 RA06 RA35 SA06 SB01 TA14 TA22 TB01 UA012 UA131 UA121 UA121 UA121 UA121 UA121 UA121 UA121

Claims (8)

[Claims] 1. The method according to claim 1, wherein the liquid crystal molecules are moved from 0 to the normal direction of the substrate.
A liquid crystal material having such a property that a molecular major axis direction is arranged perpendicular to an electric field direction between two substrates on which a liquid crystal alignment film having a property of being arranged at an inclination angle of 15 ° and an electrode are formed. In the liquid crystal device, the alignment film is a soluble partially imidized polyamic acid having an imidization ratio of 25% or more and 99% or less, and the amount of the functional group is assumed to be all polyamic acid. The liquid crystal device is cross-linked by adding a cross-linking agent having a functional group amount having a chemical equivalent ratio of 1 to 50%. 2. The liquid crystal device according to claim 1, wherein the tetracarboxylic acid portion of the soluble partially imidized polyamic acid has an aliphatic cyclic skeleton. 3. The liquid crystal device according to claim 1, wherein the diamine portion of the soluble partially imidized polyamic acid has an aromatic cyclic skeleton. 4. The liquid crystal device according to claim 1, further comprising a structure having a cholestanol skeleton in a part of the diamine portion of the soluble partially imidized polyamic acid. Liquid crystal device. 5. The liquid crystal device according to claim 1, wherein said cross-linking agent is an epoxy compound having two or four functional groups. 6. A ratio of a chemical equivalent of 1 to a soluble partially imidized polyamic acid having an imidization ratio of 25% or more and 99% or less and a functional group amount assuming that all of the polymer is a polyamic acid. A material for a liquid crystal alignment film containing a cross-linking agent having a functional group content of 50% and a solvent is applied, and then the solvent is removed and the cross-linking reaction is performed without substantially changing the imidation ratio after the application of the material for a liquid crystal alignment film. A method for producing a liquid crystal device, wherein only one or more firing steps at a temperature of 200 ° C. or less are performed. 7. The method for manufacturing a liquid crystal device according to claim 6, wherein
A method for manufacturing a liquid crystal device, comprising a first baking step mainly for removing a solvent and a second baking step mainly for advancing a cross-linking reaction after application of a liquid crystal alignment film material. 8. The method for manufacturing a liquid crystal device according to claim 7, wherein an alignment treatment is performed between the first firing step and the second firing step.