JPH04291234A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal display element having oriented films which can impart a large pretilt angle to a liquid crystal by forming the oriented films consisting of specific polyimide on at least either of transparent electrodes. CONSTITUTION:Two sheets of the transparent electrode substrates formed by laminating the striped or grid-shaped transparent electrodes 2a, 2b on substrates 1a, 1b are disposed in such a manner that the respective transparent electrodes 2a, 2b are positioned on the inner side. The liquid crystal 4 is sealed therebetween. The oriented films 3a, 3b consisting of the polyimide obtd. from the diamine compd. expressed by formula I and tetracarboxylic acid or its deriv. are formed on at least either of the transparent electrodes 2a, 2b at this time. In the formula I, R<1> and R<2> respectively independently denote a bivalent org. group; X denotes 1 to 24C alkyl group, hydrogen atom or halogen; (n) denotes integer 1 to 4. More preferably, R<1> and R<2> respectively independently denote any one among 1 to 24C alkylene group, cycloalkylene group and arylene group; X denotes 1 to 24C alkyl group; (n) is 1 or 2.

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 having a polyimide alignment film.

0002

[Prior Art] The basic structure of liquid crystal display elements conventionally used in displays for watches, computers, word processors, etc. is two transparent electrode substrates each having an alignment film on a transparent electrode. Usually, the structure is such that the liquid crystal is placed inside and the liquid crystal is sealed between them. The transparent electrodes of such liquid crystal display elements are generally formed in the form of display patterns such as stripes or grids on a substrate, and the alignment film is formed on the transparent electrodes and the exposed substrate (other than the display pattern). It is provided on the entire surface by coating or vapor deposition. A liquid crystal display element is manufactured by disposing these two transparent electrode substrates with their alignment films on the inside, and sealing liquid crystal between them. Generally, the alignment film is provided because it is necessary to align, or align, liquid crystals in a certain direction, thereby aligning liquid crystal molecules.

The mainstream of such liquid crystal display elements is a twisted nematic (TN) mode display in which a nematic liquid crystal has a twisted structure. However, since this TN type liquid crystal display element does not have a steep threshold value, it is not suitable for large-capacity display using high multiplex driving (time division driving generally used for dot matrix). In addition, TN type liquid crystal display elements have a slow response speed, currently limited to 20 milliseconds, which is a major problem when used in television panels, etc., which require high-speed response. There is.

[0004]Recently, it has been developed to have the above-mentioned high-speed responsiveness that quickly responds to changes in the electric field, and also to change either the first optically stable state or the second optically stable state in response to the applied electric field. Ferroelectric liquid crystals are attracting attention because they have the property of retaining the same state when no voltage is applied, that is, have memory properties (also referred to as bistability). and,
A liquid crystal display element using this is being considered because it has a simple structure and can achieve high-speed response.

The operating principle of the TN mode uses the optical rotation of a liquid crystal cell with a twist angle of around 90 degrees, but if the SBE (super twist birefringence) mode using nematec liquid crystal is used, a steep threshold can be achieved. Since the value can be obtained, large-capacity display by high multiplex drive becomes possible. The SBE (super twisted birefringence) mode in which such a steep threshold value can be obtained utilizes the birefringence of a liquid crystal cell with a twist angle of 180 degrees or more using the above-mentioned liquid crystal. That is, it is necessary to twist the liquid crystal by 180 degrees or more between the upper and lower substrates in the alignment direction. For this purpose, the liquid crystal molecules are required to have a pretilt angle of 3 to 30 degrees at the substrate-electrode interface. Generally, such a pretilt angle is provided by an alignment film. On the other hand, if an alignment film giving such a pretilt angle is used, alignment defects in smectic liquid crystals such as the above-mentioned ferroelectric liquid crystals can be generally extremely reduced, and bistability can also be improved.

However, when an alignment film made of an organic material such as a polymer is formed on an electrode substrate and rubbed, which is used in the conventional TN mode, the pretilt angle of the aligned liquid crystal molecules is at most 2 degrees. It is not possible to obtain a large value. Furthermore, if an obliquely deposited film such as SiO is used as the alignment film, a large pretilt angle can be obtained, but forming the alignment film by vapor deposition has low mass productivity.
This cannot be said to be advantageous in terms of manufacturing.

As a coating-type alignment film material capable of obtaining a large pretilt angle, a polyamic acid composition comprising a component having a fluorine atom in at least one of a carboxylic acid anhydride and a diamine (Japanese Unexamined Patent Publication No. 127827/1982); and polyimide resin alignment treatment materials obtained from diamines, tetracarboxylic dianhydrides, and specific monoamines (
JP-A No. 62-297819) is disclosed.

However, when liquid crystals are aligned using the above-mentioned alignment film, there is a problem that a large pretilt angle cannot always be obtained, and that the pretilt angle tends to change depending on the conditions of post-treatment such as rubbing treatment.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display element having a polyimide alignment film capable of imparting a large pretilt angle to liquid crystal.

Another object of the present invention is to provide a liquid crystal display element having a polyimide alignment film suitable for multiplex driving.

[0011]

[Means for solving the problem] The above purpose is to
In a liquid crystal display element in which two transparent electrode substrates each having a laminated striped or lattice-like transparent electrode are arranged with each transparent electrode facing inside, and a liquid crystal is sealed between them, at least On one side, the following general formula (I
):

[Formula 2] [However, R1 and R2 each independently represent a divalent organic group, X represents an alkyl group having 1 to 24 carbon atoms, a hydrogen atom or a halogen, and n represents 1
This can be achieved by a liquid crystal display element characterized in that an alignment film is formed of a polyimide obtained from a diamine compound represented by [representing an integer of ~4] and a tetracarboxylic acid or a derivative thereof.

Preferred embodiments of the liquid crystal display element of the present invention are as follows.

1) The liquid crystal display element described above, wherein R1 and R2 each independently represent any one of an alkylene group, a cycloalkylene group, and an arylene group having 1 to 24 carbon atoms.

2) R1 and R2 are each independently an unsubstituted linear alkylene group having 1 to 24 carbon atoms;
The above-mentioned liquid crystal display element represents any one of a cyclohexylene group, a phenylene group, and a biphenylene group.

3) The liquid crystal display element described above, wherein X is an alkyl group having 1 to 24 carbon atoms, and n is 1 or 2.

4) X represents an unsubstituted alkyl group having 1 to 24 carbon atoms or an alkyl group substituted with a halogen or alkoxy group having 1 to 24 carbon atoms, and n represents 1; The above liquid crystal display element is characterized by:

5) X represents an unsubstituted alkyl group having 3 to 22 carbon atoms or an alkyl group substituted with a halogen or alkoxy group having 1 to 22 carbon atoms, and n represents 1; The above liquid crystal display element is characterized by:

6) The liquid crystal display element described above, wherein the tetracarboxylic acid derivative or its derivative is a tetracarboxylic dianhydride.

7) The liquid crystal display element described above, characterized in that the transparent electrodes are formed in a stripe shape.

[0020]

Effects of the Invention The liquid crystal display element of the present invention includes a polyimide obtained by using the diamine compound of the present invention represented by the above general formula (I) as an amine component in an alignment film for aligning an encapsulated liquid crystal. I am using it. By using such an alignment film, it is possible to align the liquid crystal at a large pretilt angle that can only be obtained with an alignment film formed by oblique evaporation of SiO. Furthermore, by rubbing the alignment film, a liquid crystal with a large pretilt angle can be stably obtained. Furthermore, since the alignment film of the present invention can be formed by coating, it is advantageous in manufacturing. Further, an element in which a ferroelectric liquid crystal is sealed in a cell having an alignment film of the present invention has almost no alignment defects and has improved bistability.

[Structure of the Invention] The structure of a liquid crystal display element obtained by the manufacturing method of the present invention will be explained with reference to the accompanying drawings.

FIG. 1 is a sectional view of an example of the liquid crystal display element of the present invention.

[0023] Transparent electrodes 2a,
2b and the alignment films 3a and 3b are laminated in this order to constitute two transparent electrode substrates. The two transparent electrode substrates are arranged so that the alignment films 3a and 3b face each other, and a ferroelectric liquid crystal 4 is sealed between them. If desired, an insulating layer may be provided between the transparent electrode and the alignment film. The transparent electrodes 2a and 2b are formed in a striped display pattern on the transparent substrates 1a and 1b, respectively.

As described above, the transparent electrodes 2a and 2b are formed in the form of stripes, with the stripes being orthogonal to each other. This enables matrix display. Furthermore, only one of the transparent electrodes may be formed in a stripe shape. Further, it is not necessary to have both alignment films, and only one of them may be used.

[0025] The liquid crystal display element of the present invention has the above-mentioned alignment film 3a.
and 3b are formed from polyimide using the diamine compound of the above general formula (I) as a diamine component. By using this alignment film, the liquid crystal can be aligned at a large pretilt angle that can only be obtained with an alignment film formed by oblique evaporation of SiO.

The liquid crystal display element of the present invention is not limited to the one shown in FIG. 1, but can be made in any manner that is used for ordinary liquid crystal display elements, such as using spacers. In particular, the gap between both alignment films (i.e. the thickness of the liquid crystal layer)
Preferably, a spacer is used to ensure that. As a spacer, glass fiber, glass
Beads, plastic beads, metal oxide particles such as alumina and silica are used. The particle size of the spacer is
It varies depending on the liquid crystal used, alignment film material, cell gap setting, particles used as spacers, etc., but it is 1.2
Generally, the thickness is from μm to 6 μm.

The liquid crystal display element of the present invention can be manufactured, for example, as follows.

Examples of the transparent substrate of the present invention include glass such as float glass with good smoothness, polyesters such as polyethylene terephthalate and polybutylene terephthalate, epoxy resins, phenol resins, polyimides, polycarbonates, polysulfones, polyethersulfones, Heat-resistant resins such as polyetherimide, acetyl cellulose, polyamino acid esters, and aromatic polyamides; vinyl polymers such as polystyrene, polyacrylic esters, polymethacrylic esters, polyacrylamide, polyethylene, and polypropylene; and fluorine-containing polymers such as polyvinylidene fluoride. Examples include plastic films formed from resins and modified products thereof.

A transparent electrode in a display pattern such as a stripe or a grid is formed on the substrate by a conventional method. As the transparent electrode, for example, indium oxide (I
n2O3), tin oxide (SnO2), and ITO (indium tin oxide).

Note that a color filter and a protective layer may be formed in this order on the surface of the substrate. The alignment film of the present invention is formed on the transparent electrode (and substrate), for example, in the following manner.

The alignment film of the present invention is obtained by further dehydrating and condensing part or all of a polyamic acid obtained from a diamine compound represented by the following general formula (I) and a tetracarboxylic acid or a derivative thereof. Made of polyimide.

[0032]

[Formula 3] [However, R1 and R2 each independently represent a divalent organic group, X represents an alkyl group having 1 to 24 carbon atoms, a hydrogen atom or a halogen, and n is 1
~ represents an integer of 4]

In general formula (I), R1 and R2
are generally an alkylene group, cycloalkylene group, or arylene group each independently having 1 to 24 carbon atoms, and each independently having 1 to 12 carbon atoms.
, unsubstituted linear alkylene group, cyclohexylene group,
Preferably, it is a phenylene group or a biphenylene group.

Specific examples of R1 and R2 include:

[0035]

[C4] Straight chain alkylene groups such as;

[0036]

[C5] Cycloalkylene groups such as;

[0037]

[C6] Arylene groups such as;

The following can be mentioned.

In the general formula (I), X generally represents an alkyl group having 1 to 24 carbon atoms, a hydrogen atom or a halogen (preferably F, Cl or Br), and or an alkyl group substituted with a halogen or alkoxy group having 1 to 24 carbon atoms, particularly preferably 3 to 22 carbon atoms. The alkyl group may be branched or linear. Moreover, it is preferable that n is 1 or 2, and it is particularly preferable that n is 1.

The tetracarboxylic acid derivative is preferably a tetracarboxylic dianhydride, for example,

[
0041

[C7]

[0042]

[Chemical formula 8]

[0043]

[Chemical formula 9]

[0044]

[Chemical formula 10]

[0045]

[Chemical formula 11]

[0046]

[Chemical formula 12]

[0047]

[Chemical formula 13]

[0048]

[Image Omitted] The diamine compound represented by the above general formula (I) and the tetracarboxylic acid or its derivative may be used alone or in combination of two or more.

The alignment film of the present invention is prepared by dissolving polyamic acid (PAA) synthesized from the diamine compound represented by the above general formula (I) and the above tetracarboxylic acid derivative in a solvent to form a coating solution for forming an alignment film. It is formed by preparing a polyimide film, coating it on a substrate, drying it, and subjecting it to a heat treatment to further polymerize it to form a polyimide film.

A synthesis example of the above polyamic acid (PAA) is shown below.

[Synthesis Example 1]

[0052]

[Chemical formula 15]

As shown in the above reaction formula, compound [1]3
．． 88 g (0.02 mol), p-bromonitrobenzene [2] 10.1 g (0.05 mol) and K2 CO3
17 g (0.05 mol) of dimethylacetamide (D
MAc) in 80 ml and heated and stirred at 120-135°C for 8 hours. Next, the reaction solution was poured into water, extracted with CHCl3, and the extracted organic components were purified on silica gel using chloroform as a solvent to obtain 5.7 g of dinitro compound [3].

[0054] 5.7 g of dinitro compound [3] (0.0 .013 mol) was added and the mixture was reduced at 90°C for 7 hours. Next, the reaction solution was poured into water, extracted with ethyl acetate, and the extracted organic components were purified on silica gel using chloroform as a solvent to obtain 1.96 g of diamine compound [4].

[0055]

[Chemical formula 16]

As shown in the above reaction formula, compound [4] 1
．． 13g (0.003mol) of NMP (N-methyl-2
-Pyrrolidone) dissolved in 11 ml of NMP1
Add benzophenonetetracarboxylic dianhydride [5
] A solution containing 1.0 g (0.0031 mol) was added and polymerized at room temperature for 6 hours to obtain polyamic acid (PAA).

[Synthesis Example 2]

[0058]

[Chemical formula 17]

As shown in the above reaction formula, 3.76 g (0.01 mol) of compound [4] obtained in Synthesis Example 1 was added to NMP.
(N-methyl-2-pyrrolidone) was dissolved in 37 ml, and a solution of 1.96 g (0.01 mol) of cyclobutene tetracarboxylic dianhydride [6] dissolved in 20 ml of NVP was added thereto and polymerized at room temperature for 6 hours. Polyamic acid (P
AA) was obtained.

[0060] The coating liquid for forming an alignment film is prepared by mixing the polyamic acid obtained above with pyridine, N-methyl-2-
A solution is prepared in a suitable solvent such as pyrrolidone, dioxane, THF, or a glycol derivative. In addition to the above-mentioned components, this coating solution may contain other subcomponents such as high molecular weight polymers and organic metals for the purpose of increasing adhesion to the substrate or adjusting the viscosity of the coating solution. good.

[0061] The above coating solution for forming an alignment film is applied onto the transparent electrode and the exposed substrate using a spin coater or the like, and then heated at room temperature to 150°C for 1 to 120 minutes (preferably at 80 to 120°C). 10 to 60 minutes). Next, the coating film is heat-treated at 150-300°C for 0.5-3 hours. 0.5 at 150-300°C
Only heating for ~3 hours is sufficient. This forms a polyimide alignment film.

The thickness of the alignment film obtained varies depending on the liquid crystal used and the type of alignment film, but is generally 10 to 800 nm.
m, preferably 20 to 100 nm.

The alignment film provided on the transparent electrode substrate (and protective layer) is rubbed with synthetic fibers such as nylon, polyester, and polyacrylonitrile, and natural fibers such as cotton and wool.

The polyimide alignment film of the present invention thus formed allows liquid crystal to be aligned at a large pretilt angle. This polyimide alignment film uses a diamine compound represented by the above general formula (I) as a diamine component of polyimide. This compound has a structure in which an organic group having two amino groups is bonded to a central benzene ring via oxygen. In particular, it is characterized by a structure in which substituents such as alkyl groups protrude from the central bulky benzene ring, and it is speculated that this contributes to the alignment of the liquid crystal.

[0065] A transparent substrate manufactured as described above,
Two transparent electrode substrates consisting of a transparent electrode and an alignment film are placed facing each other with a gap between them, with each alignment film facing inside, to form a cell. The size of this gap, ie, the cell gap, is generally about 0.5 μm to 6 μm.

Next, inject the following liquid crystal into this cell,
After sealing, it is slowly cooled to create a liquid crystal display element.

As the liquid crystal used in the present invention, conventionally known liquid crystals can be used.

[0068] Preferred liquid crystals used in the present invention include those that can be used in SBE mode and ferroelectric liquid crystals.

Liquid crystals having ferroelectricity are specifically chiral smectic C phase (SmC*), H phase (SmH*
), I phase (SmI*), J phase (SmJ*), K phase (SmK*), G phase (SmG*) or F phase (Sm
F*). For example, "High-speed liquid crystal technology" (published by CMC) p. All known ferroelectric liquid crystals, such as those described in 127-161, can be used in the present invention.

[0070] Specific liquid crystal compositions include CS-1018, CS-1023, and CS- manufactured by Chisso Corporation.
1025, CS-1026, DO manufactured by Roddick Co., Ltd.
F0004, DOF0006, DOF0008, ZLI-4237-000, ZLI-4237- manufactured by Merck & Co.
100, ZLI-4654-100ZLI-2293, and the like. There is no problem in adding dichroic dyes, viscosity reducers, etc. which are soluble in the liquid crystal to these liquid crystals.

The liquid crystal display element thus obtained is as follows:
It has a specific alignment film of the present invention. Therefore, the encapsulated liquid crystal can be oriented at a large pretilt angle. The pretilt angle of liquid crystal is generally 3 degrees to 90 degrees. 5 degrees to 40 degrees is preferable.

[0072] The liquid crystal display element manufactured as described above may be provided with polarizing plates on both substrates of the cell depending on the purpose of use. An insulating layer, a color filter, a protective layer, etc. may be provided between the transparent electrode and the alignment film. Furthermore, the liquid crystal display element of the present invention can be provided with structures provided in conventional liquid crystal display elements, such as a reflection plate and a retardation plate, depending on the purpose of use.

[0073]

[Examples] Next, examples of the present invention and comparative examples will be described. However, the present invention is not limited to this example.

[Example 1] Transparent electrodes made of indium-tin oxide (ITO) were formed in stripes (electrode width: 100 μm, gap between electrodes: 15 μm) on two 1.1 mm thick glass substrates. Formed.

[0075] On these two glass substrates with transparent electrodes,
An insulating layer with a thickness of 100 nm was formed by vapor depositing SiO.

[0076] On the above insulating layer, the following diamine compound,

[Chemical formula 18] The following tetracarboxylic dianhydride,

[0077]

[Chemical formula 19] The following structure obtained by reaction with

[0078]

A coating solution containing 3 parts by weight of polyamic acid [Image Omitted] dissolved in 97 parts by weight of N,N-dimethylacetamide was applied using a spinner.

The conditions for the spinner are a rotation speed of 2500 r. p
．． m. , the time was 30 seconds. After application, 280°C, 1
A polyimide alignment film was formed by drying for hours.

[0080] Both surfaces of this coating film were rubbed with a nylon napkin, and two glass plates were placed with each rubbed surface facing inward so that the rubbing directions were antiparallel and the electrode patterns were orthogonal. They were overlapped with a 3 μm spacer interposed therebetween to create a cell with a cell gap of 3 μm. In this cell, 10 pieces of Merck's liquid crystal ZLI-2293 were installed.
The mixture was injected at 0°C and slowly cooled to room temperature at a rate of about 2°C/min.

The pretilt angle of the obtained liquid crystal display element was measured by the crystal rotation method using a polarizing microscope manufactured by Nikon Corporation, and it was found to be 12°.

[Example 2] In Example 1, the following diamine compounds were used as the polyamic acid.

[0083]

[C21] and the following tetracarboxylic dianhydride,

[0084]

[C22] The following structure obtained by reaction with

[0085]

A polyamic acid of [Chemical 23] was used, and the drying temperature was 280°C.
A liquid crystal display element was manufactured in the same manner as in Example 1 except that the temperature was changed from 200°C to 200°C.

The pretilt angle of the obtained liquid crystal display element was measured in the same manner as in Example 1, and was found to be 14°.

[Example 3] In Example 1, the following diamine compounds were used as the polyamic acid.

[0088]

[C24] and the following tetracarboxylic dianhydride,

[0089]

[C25] The following structure obtained by reaction with

[0090]

A liquid crystal display element was produced in the same manner as in Example 1, except that the polyamic acid represented by the following formula was used.

The pretilt angle of the obtained liquid crystal display element was measured in the same manner as in Example 1, and was found to be 10°.

[Example 4] In Example 1, the following diamine compounds were used as the polyamic acid.

[0093]

[C27] and the following tetracarboxylic dianhydride,

[0094]

[C28] The following structure obtained by reaction with

[0095]

A polyamic acid of [Chemical 29] was used, and the drying temperature was 280°C.
A liquid crystal display element was manufactured in the same manner as in Example 1 except that the temperature was changed from 270°C to 270°C.

The pretilt angle of the obtained liquid crystal display element was measured in the same manner as in Example 1, and was found to be 14°.

[Example 5] In Example 2, during the rubbing treatment with the nylon raised cloth, the rubbing direction was changed from antiparallel to the same direction with each rubbed surface facing inside, and the spacer was changed from 3 μm to 2 μm. and changed the liquid crystal from Merck's ZLI-2293 to Chisso (
A liquid crystal display element was manufactured in the same manner as in Example 2 except that the ferroelectric liquid crystal CS-1023 manufactured by Co., Ltd. was used.

When the alignment state of the above liquid crystal display element was observed, a good alignment state with no zigzag defects was obtained. Furthermore, when the liquid crystal display element was subjected to multiplex driving (time division driving), good contrast was obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing a configuration example of a liquid crystal display element of the present invention.

[Explanation of symbols]

1a, 1b Transparent substrate 2a, 2b Transparent electrode 3a, 3b Alignment film 4.LCD

Claims (1)

[Claims] 1. A liquid crystal display element, in which two transparent electrode substrates each having striped or lattice-shaped transparent electrodes laminated on the substrate are arranged with each transparent electrode facing inside, and a liquid crystal is sealed between them. , on at least one of the transparent electrodes, the following general formula (I): [Formula 1] [wherein R1 and R2 each independently represent a divalent organic group, and X has 1 to 1 carbon atoms] 24 alkyl group, hydrogen atom or halogen, and n is
Represents an integer from 1 to 4. ] A liquid crystal display element comprising an alignment film made of polyimide obtained from a diamine compound represented by the following formula and a tetracarboxylic acid or a derivative thereof.