JPH05281550A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To enable hardening at relatively low temperature and obtain a high pretilt angle so as to enable high-contrast display by forming an orientation film of a hardened film formed of mixture containing specific polyimide with florine atoms in the molecular structure or its precursor. CONSTITUTION:Two transparent electrode bases with transparent electrodes and orientation films laminated in this order are disposed with the respective orientation films placed inside, and a liquid crystal is filled between the transparent electrode bases to form a liquid crystal display element. In this liquid crystal display element, at least one orientation film is a hardened film formed of mixture containing a precursor of polyimide having fluorine atoms in the molecular structure and polyimide having the structure expressed by formulas I-III in the principal chain skeleton or its precursor. In the formulas I-III, (n) is an integer of 4-24, R<1> is a bivalent organic group of C2-24, Y is-O-, -COO-, -OCOO- or -CONH-, R<3>, R<3> are organic groups of C1-6, R<4> is a bivalent organic group, (m) is an integer of 1-20, and (p) is an integer of 2-24. Uniform orientation is thereby stabilized in the memory state.

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 an alignment film made of polyimide, and more particularly to a liquid crystal display device using a ferroelectric liquid crystal.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display element used for a display of a clock, a computer, a word processor or the like has a basic structure in which two transparent electrode substrates each having an alignment film on a transparent electrode have an alignment film. Usually, the structure is such that the liquid crystal is placed inside and the liquid crystal is enclosed between them. The transparent electrode of such a liquid crystal display device is generally formed on the substrate in the form of a display pattern such as a stripe pattern or a grid pattern, and the alignment film is formed on the transparent electrode and the exposed substrate (other than the display pattern). Is provided by coating or vapor deposition. A liquid crystal display element is manufactured by arranging the two transparent electrode substrates with the alignment films inside and enclosing a liquid crystal therebetween. In general, the alignment film is provided because it is necessary to align the liquid crystals in a certain direction, that is, to align the liquid crystals, and thereby the liquid crystal molecules are aligned.

The mainstream of such a liquid crystal display device is a display in a twisted nematic (TN) mode in which a nematic liquid crystal has a twisted structure. However, this TN type liquid crystal display element has a slow response speed and is currently limited to 20 milliseconds, which is a big problem when it is used for a television panel or the like which requires high speed response.

Recently, it has the above-mentioned high-speed responsiveness that responds quickly to changes in the electric field, and responds to the applied electric field to bring about either the first optically stable state or the second optically stable state. Attention has been paid to a ferroelectric liquid crystal which has a property of maintaining its state when no voltage is applied, that is, a memory property (also referred to as bistability). A liquid crystal display device using this has been actively studied because it has a simple structure and can realize high-speed response.

The above ferroelectric liquid crystals are required to have excellent contrast, which is a basic characteristic of a display element, but those having sufficient characteristics have not yet been obtained. A high contrast is generally obtained when the directions of spontaneous polarization are aligned upward or downward between the upper and lower substrates in two stable states when no electric field is applied, and the liquid crystal molecules have an untwisted orientation (uniform orientation).

However, in the conventional method of aligning the liquid crystal by rubbing a polyimide film or the like, the spontaneous polarization is directed in the opposite direction at the interface between the upper and lower substrates when no electric field is applied, and liquid crystal molecules are interposed between them. Has a strong tendency to take a continuously twisted orientation (twisted orientation), so uniform orientation is difficult to obtain, and high contrast has not been obtained yet.

In order to improve contrast, in a ferroelectric liquid crystal device, a chiral smectic phase (SmC ^* ) phase, which is a characteristic phase structure of a ferroelectric liquid crystal, is applied to a chevron structure by applying a large electric field to the device. Has proposed to change to a pseudo bookshelf structure, which is said to provide excellent contrast. However, in such an element, the pseudo bookshelf structure is easily collapsed due to a temperature change, so that there is a problem that the contrast is likely to be lowered.

Further, Japanese Patent Laid-Open No. 3-6529 discloses the use of a polyimide film having a specific molecular structure as an alignment film. In a ferroelectric liquid crystal device using this alignment film, a relatively stable uniform alignment can be obtained and a certain degree of effect on the contrast is recognized, but a liquid crystal with large spontaneous polarization (eg, 5 nc or more) or a large tilt angle. When a liquid crystal (for example, 15 degrees or more) is used, there is a problem that when the multiplex driving is performed by the simple matrix method, the twist alignment is stabilized and sufficient contrast cannot be obtained. Further, in order to form the above-mentioned polyimide film, it is necessary to dry and cure at a high temperature of 250 ° C. or higher, which is disadvantageous in manufacturing. In recent years, an attempt has been made to make a ferroelectric liquid crystal display device with high contrast by using an alignment film with high pretilt. For example, Japanese Journal of Applied Physics Vol. 28 (1989) March issue,
On pages 524 to 529, it is reported that a ferroelectric liquid crystal element using a high-pretilt alignment film exhibits good contrast, and further, the Institute of Electronics, Information and Communication Engineers Technical Report EID
91-47 also states that high contrast can be obtained in a ferroelectric liquid crystal cell by using a high pretilt alignment film. However, when the alignment film used here is used, in combination with a practical ferroelectric liquid crystal, a sufficiently high pretilt angle (for example, 10 degrees or more) capable of realizing high contrast can be uniformly obtained with good reproducibility. However, there are disadvantages in manufacturing such as the absence of the above and the need to dry and cure at a high temperature of 250 ° C. or higher. In particular, when a substrate with a color filter is used to realize color display, there is a problem that the performance of the color filter or the like is significantly deteriorated when the alignment film is dried and cured at a temperature of 250 ° C. or higher. Further, various high pretilt alignment films for STN liquid crystal display have been studied, and those which can be cured at a relatively low temperature of 250 ° C. or lower have been developed. Some of these alignment films can give a relatively high pretilt angle to the STN liquid crystal, but cannot give a high pretilt angle to the ferroelectric liquid crystal.
Alternatively, even if a high pretilt angle can be given to some extent, reproducibility is extremely poor and it is not suitable for practical use.

[0009]

In order to obtain a liquid crystal display device having a good display quality, particularly a ferroelectric liquid crystal display device having a high contrast, it is necessary to obtain a high pretilt angle with good reproducibility and use a color filter. For the color liquid crystal device, an alignment film that can be cured at a relatively low temperature and that can impart the above-described high pretilt angle so that heating for curing the alignment film does not damage the color filter substrate. is necessary.

An object of the present invention is to provide a liquid crystal display device which is easy to manufacture, can be cured at a relatively low temperature, and has an alignment film showing a high pretilt angle and which can perform high contrast display. It is another object of the present invention to provide a ferroelectric liquid crystal display device using a color filter substrate and capable of multicolor display.

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

[0012]

[Means for Solving the Problems] The above object is to provide a transparent electrode,
In the liquid crystal display element in which two transparent electrode substrates in which the alignment film and the alignment film are laminated in this order, each alignment film is placed inside, and liquid crystal is sealed between them, at least one alignment film is a molecule. A precursor of polyimide [1] having a fluorine atom in its structure and the following general formulas (A) to (C):

[0013]

[Chemical 3] [However, n represents an integer in the range of 4 to 24, and R ¹
Represents a divalent organic group having 2 to 24 carbon atoms, and Y
Is -O-, -COO-, -OCOO- or -CONH
Represents-, R ² represents an organic group having 1 to 6 carbon atoms, R ³ represents an organic group having 1 to 6 carbon atoms, R ⁴
Represents a divalent organic group, m represents an integer in the range of 1 to 20, and p represents an integer in the range of 2 to 24. ] It can be achieved by a liquid crystal display element characterized by being a cured film of a mixture containing a polyimide [2] having at least one of the structures represented by the above in the main chain skeleton or a precursor thereof.

Preferred embodiments of the liquid crystal display device of the present invention are as follows. 1) The polyimide [1] has the following general formula (D):

[0015]

[Chemical 4] [Wherein R ⁵ represents a tetravalent organic group, and X 5
Represents O, CH ₂ or S. ] The said liquid crystal display element which consists of a repeating unit represented by these.

2) The liquid crystal display device as described above, wherein the polyimide [1] has a property of giving a pretilt angle of 10 degrees or more to the liquid crystal when the polyimide is used for an alignment film.

3) The polyimide [1] uses a polymer obtained by curing the precursor of the polyimide [1] at a temperature of 280 ° C. or higher as an alignment film, and the rubbing directions of the alignment film are parallel. In a cell in which upper and lower substrates are combined so that the directions are opposite to each other, the pretilt angle (the angle formed between the substrate and the long axis of the liquid crystal molecule) of the liquid crystal molecules in the nematic phase or smectic phase of the liquid crystal used in the liquid crystal element is The above liquid crystal display device having a property of being 10 degrees or more.

4) The mixing ratio of the polyimide [1] and the polyimide [2] is 10 to 99:90 to 1 by weight.
(Polyimide [1]: Polyimide [2]) The above liquid crystal display device.

5) The polyimide [2] is the above (A).
The liquid crystal display device as described above, wherein the main chain skeleton contains any one of structures (1) to (C) in an amount of 10% by weight or more.

6) The liquid crystal display device, wherein the polyimide [2] is compatible with the polyimide [1] and its precursor.

7) The polyimide [1] does not have a glass transition point below 200 ° C., and the polymer [2] has a glass transition point of 20.
The above liquid crystal display device having a glass transition point at 0 ° C. or lower.

8) The liquid crystal display device, wherein the liquid crystal is a ferroelectric liquid crystal.

The pretilt angle is measured by rubbing an alignment film formed by imidizing the polyimide precursor (polyamic acid) at 280 ° C., and the rubbing directions of the alignment film are parallel to each other. Liquid crystal used in the liquid crystal element is injected into a cell in which upper and lower substrates are combined so that the liquid crystal molecules in the nematic phase or the smectic phase form an angle between the long axis of the liquid crystal molecule and the substrate surface. It was determined by measuring by the crystal rotation method. However, when the liquid crystal used is nematic liquid crystal, it is heated to room temperature, when it is a ferroelectric liquid crystal, it is heated to a temperature at which it transitions to a smectic A phase, and when there is no smectic A phase, it is at a temperature at which it transitions to a nematic phase (cholesteric phase). The temperature was raised to and measured. Further, as the liquid crystal used for evaluating the pretilt angle, it is preferable to use the liquid crystal that is actually injected into the liquid crystal element. In liquid crystals having different molecular structures, the pretilt angle is different, so that the accurate pretilt angle of the device cannot be measured.

[Constitution of the Invention] The liquid crystal display device of the present invention comprises:
It has a basic structure in which a liquid crystal is sealed between two transparent electrode substrates having a transparent electrode and an alignment film laminated thereon. The alignment film of the present invention is a film composed of two kinds of polyimides having different molecular structures, and comprises a precursor of polyimide [1] having a fluorine atom in the molecular structure and the above structures (A) to (C). A film obtained by curing a mixture containing polyimide [2] having at least one of the above in the main chain skeleton or a precursor thereof.

The structure of the liquid crystal display device of the present invention will be described in detail 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.

On the transparent substrates 1a and 1b, the transparent electrodes 2a,
2b, insulating films 3a and 3b, and alignment films 4a and 4b are respectively laminated in this order to form two transparent electrode substrates. The two transparent electrode substrates are oriented films 4a and 4 respectively.
The ferroelectric liquid crystal 5 is enclosed between them so as to face each other. The transparent electrodes 2a and 2b are formed in the form of display patterns on the transparent substrates 1a and 1b, respectively.

The transparent electrodes 2a and 2b are generally formed in a stripe shape, and the stripes are formed so that the stripe shapes are orthogonal to each other. This allows matrix display. Further, the transparent electrode may be formed in a stripe shape only on one side. The surface of the alignment film is subjected to rubbing treatment, and when two transparent electrode substrates are bonded together, it is preferable that the rubbing directions are substantially parallel and the same direction. However, the substrates may be attached so that the rubbing directions are parallel and opposite to each other depending on the application.

In the liquid crystal display device of the present invention, the alignment film 4 is used.
At least one of a and 4b is a precursor of polyimide [1] having a fluorine atom in its molecular structure and the above (A) to
It comprises a cured film of a mixture containing at least one of the structures of (C) in the molecular structure of polyimide [2] or its precursor. These polyimides have different molecular structures, and polyimide [1] has a temperature of 200 ° C.
The polymer [2] does not have a glass transition point below and is 2
It is preferable to have a glass transition point below 00 ° C. The polyimide [1] having a fluorine atom in the molecular structure preferably has a property of imparting a pretilt angle of 10 degrees or more to the liquid crystal used when it is used as an alignment film.

A polyimide precursor for forming a polyimide [1] having a fluorine atom in the molecular structure, and a polyimide [2] having at least one of the structures (A) to (C) in the molecular skeleton. Alternatively, the mixture with the precursor thereof is cured (imidized) at a high temperature to obtain the alignment film of the present invention.

In the case of a polyimide [1] having a fluorine atom in its molecular structure, particularly a polyimide having a rigid main chain structure, a relatively high pretilt angle (preferably 10 degrees or more) is obtained when used as an alignment film. Be done. However, such polyimides often have a glass point transfer far higher than 200 ° C. or are unclear, and usually require a high heating temperature (250 ° C. or higher) for imidization. That is, when imidization is insufficient, a high pretilt angle is often not obtained, and the pretilt angle tends to increase as the imidization ratio increases. On the other hand, (A) to
Since the polyimide [2] having at least one of the structures of (C) in the molecular structure has a relatively flexible molecular structure, the glass point transfer is often 200 ° C. or lower, and the imidization temperature is also high. Relatively low.

Based on these findings, the present inventor conducted further studies and found that the former precursor of polyimide [1] having a fluorine atom and at least one of the latter structures (A) to (C). By curing a polyimide [2] having one of the two in its main chain skeleton or a mixture thereof with a precursor thereof, the imidization reaction of the polyamic acid, which is the precursor of the former polyimide, can be promoted, and imidization alone can be performed. It was found that the former polyimide precursor can be imidized at a temperature lower than that. That is, a polyimide [1] precursor having a fluorine atom (which can impart a large pretilt angle) and a polyimide [2] having at least one of the structures (A) to (C) in the main chain skeleton, or By using both the precursor and the precursor, it was possible to lower the imidization temperature of the polyimide [1] precursor, which was difficult in the past, and the present invention reached the alignment film. The alignment film of the present invention has a relatively low curing temperature (imidization temperature) of 10 to 4
A large pretilt angle of 0 degree can be stably obtained (uniform alignment can be obtained in the case of a ferroelectric liquid crystal), and thus a liquid crystal display device exhibiting high contrast can be obtained. Furthermore, when the alignment film of the present invention is cured at a heating temperature of the polyimide capable of imparting the former large pretilt angle, it can impart an even larger pretilt angle to the liquid crystal and is cured at a temperature lower than the heating temperature. However, it is possible to obtain a pretilt angle similar to that obtained with the former polyimide film.

The liquid crystal display element of the present invention is not limited to the one shown in FIG. 1, but all the modes which are carried out for a normal liquid crystal display element such as using a spacer are possible. In particular, the gap between both alignment films (that is, the layer thickness of the liquid crystal layer)
It is preferred that a spacer be used to ensure As the spacer, glass fiber, glass
Beads, plastic beads, metal oxide particles such as alumina and silica are used. The particle size of the spacer is
Depending on the liquid crystal used, alignment film material, cell gap setting, particles used as spacers, etc., 1.2
Generally, it is from 6 μm to 6 μm.

The liquid crystal display device of the present invention can be manufactured, for example, as follows. As the transparent substrate of the present invention, for example, glass such as float glass having good smoothness, polyester such as polyethylene terephthalate and polybutylene terephthalate, epoxy resin, phenol resin, polyimide, polycarbonate, polysulfone, polyether sulfone, polyetherimide , Heat-resistant resins such as acetyl cellulose, polyamino acid ester, aromatic polyamide, vinyl polymers such as polystyrene, polyacrylic acid ester, polymethacrylic acid ester, polyacrylamide, polyethylene, polypropylene, and fluorine-containing resins such as polyvinylidene fluoride A plastic film formed from a modified product of the above can be mentioned.

On the substrate, a transparent electrode having a display pattern such as a stripe pattern or a grid pattern is formed by a conventional method. As the transparent electrode, for example, indium oxide (I
Examples include n ₂ O ₃ ), tin oxide (SnO ₂ ), and ITO (indium tin oxide). A color filter and a protective layer may be formed in this order on the surface of the substrate. Further, it is preferable that an insulating film is formed on the transparent electrode by spattering or the like. Examples of materials for the insulating film include SiO ₂ and TiO ₂ .
₂ , ZrO ₂ and Ta ₂ O ₅ can be mentioned.

On the transparent electrode (and the substrate), the alignment film of the present invention is formed, for example, as follows.

The alignment film of the present invention is obtained by applying a mixture of two kinds of polyimide precursors (one of which may be polyimide) and then curing the mixture. One of the two kinds of polyimide precursors is a precursor of polyimide [1] having a fluorine atom in its molecular structure (a polyimide precursor for forming a polyimide capable of imparting a pretilt angle of 10 degrees or more to a liquid crystal (that is, polyamide). Acid)) and the other is represented by the following general formulas (A) to (C):

[0037]

[Chemical 5] [However, n represents an integer in the range of 4 to 24, and R ¹
Represents a divalent organic group having 2 to 24 carbon atoms, and Y
Is -O-, -COO-, -OCOO- or -CONH
Represents-, R ² represents an organic group having 1 to 6 carbon atoms, R ³ represents an organic group having 1 to 6 carbon atoms, R ⁴
Represents a divalent organic group, m represents an integer in the range of 1 to 20, and p represents an integer in the range of 2 to 24. ] It is polyimide [2] or its precursor which has at least one of the structures represented by this in a main chain skeleton. R
¹ is preferably a divalent linear or branched hydrocarbon group having ^{2 to} 24 carbon atoms, and R ² is preferably a divalent linear or branched hydrocarbon group having ^{2 to} 24 carbon atoms, and particularly preferably Ethylene and propylene are preferred. Also, R ³ and R ⁴
Also, a divalent linear or branched hydrocarbon group is preferable. The polyimide [1] having a fluorine atom does not have a glass transition point at 200 ° C. or lower, and the polymer [2] having any of the structures (A) to (C) in the main chain skeleton is 2
It is preferable to have a glass transition point below 00 ° C. Further, the ratio of the polyimide [1] to the polyimide [2] or its precursor may be set within a range in which a desired pretilt angle is obtained, and generally, the mixing ratio of the polyimide [1] and the polyimide [2] is 10 to 99:90 to 1 by weight
The range of (polyimide [1]: polyimide [2]) is general, the range of 20 to 99:80 to 1 is preferable, and the range of 40 to 97:60 to 3 is more preferable. further,
The cured film (alignment film) of the mixture of these two kinds preferably exhibits a compatible state. The compatible state refers to a state in which two or more kinds of mixed polymers are uniformly mixed in a molecular unit without phase separation, and the confirmation can be confirmed by, for example, measuring the glass transition point of the mixed polymers as follows. It is performed like. When the mixed polymer is phase-separated, the individual glass transition points of the used polymer are measured, but when they are compatible, in addition to the individual glass transition points of the polymer, the glass transition of the new compatible system Points appear and are measured. The glass transition point of the compatible system is determined by the glass transition points of the individual mixed polymers and their mixing ratio. It is considered that the glass transition point of the alignment film of the present invention generally takes an intermediate value between the glass transition points of the above two kinds of polymers.

The polyimide [1] having a fluorine atom in the above molecular structure is represented by the following general formula (D):

[0039]

[Chemical 6] [Wherein R ⁵ represents a tetravalent organic group, and X 5
Represents O, CH ₂ or S. ] It is preferable that it consists of the repeating unit represented by these. When R ⁴ is a tetravalent aromatic group, a methyl group, a trifluoromethyl group or a halogen atom may be substituted on the aromatic ring.
The polyimide [1] is not limited in molecular weight and may be an oligomer or an oligomer containing a monomer.

The tetracarboxylic acid or its derivative used in the synthesis of the polyimide [1] having a fluorine atom in the above molecular structure is preferably tetracarboxylic dianhydride.
For example, the following can be mentioned. The present invention is not limited to these. 1,2,4,5-benzenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 1,4-bis (2,3-
Dicarboxyphenoxy) benzene dianhydride, 1,3-
Bis (2,3-dicarboxyphenoxy) benzene dianhydride, 1,2,4,5-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4 , 5,8-Naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4
5,8-Tetracarboxylic acid dianhydride, 2,7-Cyclolonaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 3,3 ', 4,4'-Diphenyltetracarboxylic acid dianhydride Substance, 2,2 ′, 3,3′-diphenyltetracarboxylic dianhydride, 4,4′-bis (3,4-dicarboxyphenoxy) diphenyl dianhydride, bis (2,3-dicarboxyphenyl) Ether dianhydride, 4,4′-bis (2,3-dicarboxyphenoxy) diphenyl ether dianhydride, 4,4′-bis (3,4-dicarboxyphenoxy) diphenyl ether dianhydride; bis (3
4-dicarfoxyphenyl) sulfide dianhydride,
4,4′-bis (2,3-dicaroxyphenoxy) diphenylsulfide dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, 4,4′-bis (2,3-di) Carboxyphenoxy) diphenylsulfone dianhydride, 4,4′-bis (3,4-dicarboxyphenoxy) diphenylsulfone dianhydride, 3,3 ′,
4,4'-benzophenone tetracarboxylic dianhydride,
2,2'3,3'-benzophenone tetracarboxylic dianhydride, 2,3 ', 3,4'-benzophenone tetracarboxylic dianhydride, 4,4-bis (3,4-dicarboxyphenoxy) benzophenone Dianhydride, bis (2,3
-Dicarboxyphenyl) methane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride,
1,2-bis (3,4-dicarboxoxyphenyl) ethane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) ethane dianhydride, 2,2bis (3,4-dicarboxy) Phenyl) ethane dianhydride, 2,2-bis [4-
(2,3-Dicarboxyphenoxy) phenyl] propane dianhydride, 4- (2,3-dicarboxyphenoxy-
4 '-(3,4-dicarboxyphenoxy) diphenyl-2,2-propane dianhydride, 2,2-bis [4-
(3,4-Dicarboxyphenoxy) -3,5-dimethylphenyl]] propane dianhydride, 2,3,4,5-thiophenetetracarboxylic acid dianhydride, 2,3,4,5-
Pyrrolidine tetracarboxylic dianhydride, 2,3,5,6
-Pyrazine tetracarboxylic dianhydride, 1,8,9,1
0-phenanthrenetetracarboxylic dianhydride, 3,
4,9,10-perylenetetracarboxylic dianhydride,
2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 1,3-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 1,1, -bis (3 , 4-dicarboxyphenyl)
-1-phenyl-2,2,2-trifluoroethane dianhydride, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] hexafluoropropane dianhydride,
1,1-bis [4- (3,4-dicarboxyphenoxy) phenyl] -1-phenyl-2,2,2-trifluoroethane dianhydride, 4,4′-bis [2- (3,4 −
Dicarboxyphenyl) hexafluoroisopropyl]
Diphenyl ether dianhydride, 2,3,5-tricarboxycyclopentyl acetic acid dianhydride, cyclopentane tetracarboxylic dianhydride, cyclobutane tetracarboxylic dianhydride, 5- (2,5-dioxotetrahydrofuryl) -3 -Methyl-3-cyclohexene dicarboxylic acid dianhydride, bicyclo [2,2,2] -oct-7-ene-
2,3,5,6-tetracarboxylic dianhydride, 3,5
6-tricarboxynorbornane-2-acetic acid dianhydride,
Tetrahydrofuran tetracarboxylic dianhydride. These may be used alone or in combination of two or more.

Among the above, as tetracarboxylic acid or its derivative, 1,2,4,5-benzenetetracarboxylic dianhydride (pyromellitic dianhydride), 3,3 '
4,4'-diphenyltetracarboxylic dianhydride, 3,
3'4,4'-benzophenone tetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl]
Hexafluoropropane, 1,4,5,8-naphthalenetetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, and cyclopentanetetracarboxylic dianhydride are preferred.

As the diamine compound, those having a fluorine atom in the molecule are preferable. Examples of the diamine having a fluorine atom include 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane,
2,2-bis [4- (3-aminophenoxy) phenyl] hexafluoropropane, 2,2-bis [4- (2
-Aminophenoxy) phenyl] hexafluoropropane, 2,2-bis [4- (2-aminophenoxy) 3,
5-dimethylphenyl] hexafluoropropane, p-
Bis (4-amino-2-trifluoromethylphenoxy) benzene, 4,4′-bis (4-amino-2-trifluoromethylphenoxy) biphenyl, 4,4′-bis (4-amino-3-trifluoro) Methylphenoxy)
Biphenyl, 4,4'-bis (4-amino-2-trifluoromethylphenoxy) diphenyl sulfone, 4,
4'-bis (3-amino-5-trifluoromethylphenoxy) diphenyl sulfone, 2,2-bis [4- (4
-Amino-2-trifluoromethylphenoxy) phenyl] hexafluoropropane and 4,4'-bis [(4
-Aminophenoxy) phenyl] hexafluoropropane and the like.

In particular, it is preferable to use the following. B-1 2,2-bis [4- (4-aminophenoxy) phenyl) hexafluoropropane B-2 2,2-bis [4- (4-aminophenylthio) phenyl) hexafluoropropane B-3 2, 2-bis [4- (4-aminobenzyl)
Phenyl) hexafluoropropane

An example of the synthesis of the above diamine is shown below.

Synthesis of B-3 2,2-bis [4- (4-phthalimidobenzoyl) phenyl] hexafluoropropane 4.0 g (0.005)
215 to 225 in the presence of 2.53 g (0.05 mol) of hydrazine monohydrate and 2.81 g (0.05 mol) of calcium hydroxide in 30 ml of diethylene glycol.
After stirring for 4 hours at 0 ° C., the mixture was poured into water, and the extract with chloroform was purified by column chromatography (acetic acid ethyl ester to silica gel) to obtain the diamine compound B
-3 was obtained 1.50 g (0.00292 mol).

Examples of the polyimide precursor having the repeating unit represented by the general formula (D) include, for example, N, N'-dimethylformamide, N, N'-dimethylacetamide or the diamine compound and tetracarboxylic dianhydride. N
It can be easily obtained by mixing in a solvent such as methylpyrrolidone.

An example of synthesizing a polyimide precursor having a bonding unit represented by the above general formula (D) is shown below. B-3
Diamine compound of 7.02 g (0.0137 mol) of N
-Methyl-2-pyrrolidone 90 g solution, 1, 2, 4,
5-benzenetetracarboxylic dianhydride 2.98 g
(0.137 mol) was added and stirred at room temperature for 6 hours, then 10
A t% polyimide precursor solution was obtained.

On the other hand, the polyimide [2] having at least one of the structures (A) to (C) in the main chain skeleton is
It is preferable that these structures are contained in the molecular structure in an amount of 10% by weight or more.

Further, the polyimide [2] is preferably a polyimide made of the following materials.

Such a polyimide can be obtained by dehydration condensation of a polyamic acid (precursor) obtained from a tetracarboxylic acid or its derivative and a diamine compound. The dicarboxylic acid and the tetracarboxylic acid dianhydride which is the tetracarboxylic acid or its derivative used for this synthesis contain the structure of said (A)-(C) in either tetracarboxylic acid or its derivative or a diamine compound. It is sufficient that it is contained (both contained in both), and the other is preferably a tetracarboxylic acid compound and its derivative used in the synthesis of the polyimide [1], and a diamine compound. It is preferably contained in the molecule.

As the diamine compound,

[0052]

[Chemical 7] [However, n represents an integer in the range of 8 to 20. ]

[0053]

[Chemical 8] [Wherein R represents a hydrogen atom, CH ₃ or CF ₃ , and n represents an integer in the range of ₃ to 18]. ]

[0054]

[Chemical 9] [Wherein R represents a hydrogen atom or CH ₃ and n represents an integer in the range of 1 to 4. ]

[0055]

[Chemical 10] [Wherein R represents a hydrogen atom or CH ₃ and n represents an integer in the range of 2 to 18]. ]

[0056]

[Chemical 11] [Wherein R represents a divalent organic group having 2 to 12 carbon atoms, n represents an integer in the range of 1 to 12, and m represents an integer in the range of 0 to 18]. ]

[0057]

[Chemical 12] [Wherein R represents a divalent aliphatic group having 2 to 20 carbon atoms, and n represents an integer in the range of 1 to 20]. It is preferable to use at least one of the above.

As the tetracarboxylic dianhydride,

[0059]

[Chemical 13] [Wherein R ⁶ represents a divalent organic group having 2 to 20 carbon atoms, and n represents an integer in the range of 1 to 20]. It is preferable to use at least one of the above.

The alignment film of the present invention comprises, for example, a polyimide precursor solution and the above-mentioned two types of polyamic acid (or polyamic acid and polymer) in N, N-dimethylformamide,
A solution prepared by dissolving N-methyl-2-pyrrolidone, a glycol derivative such as diethylene glycol monoalkyl ether, or the like in a suitable solvent is prepared. In addition to the above-mentioned components, this solution may contain other high molecular weight polymers or organometals as sub-components for the purpose of increasing the adhesion to the substrate, adjusting the viscosity of the coating liquid, or improving the compatibility. May be added. The above polyimide precursor solution is applied onto the transparent electrode and the exposed substrate by a spin coater or the like, and at room temperature to 150 ° C for 1 to 120 minutes (preferably 80 to 120 ° C for 10 to 60 minutes). dry. Next, the coating film is heated at 150 to 250 ° C. under normal pressure or reduced pressure for 10 minutes to 2 hours, preferably at 150 to 230 ° C.
Heat treatment is performed for 0 minutes to 1 hour. Heating after 150
~ 250 ° C, 10 minutes to 2 hours only. The thickness of the alignment film is generally 3 to 300 nm, preferably 5 to 100 nm.

The polyimide laminated film provided on the transparent electrode substrate (and the protective layer) is made of nylon, polyester,
An alignment film is formed by rubbing a synthetic fiber such as polyacrylonitrile, cotton, or a natural fiber such as wool. For the rubbing treatment, the method adopted in STN (Super Twisted Nematic) element can be used. For example, rubbing of the upper and lower substrates is preferably performed in parallel with each other. The rubbing direction at that time may be the same direction (parallel) or the opposite direction (anti-parallel).

With the polyimide alignment film of the present invention thus formed, liquid crystal can be aligned with a large pretilt angle. In particular, the ferroelectric liquid crystal can be stably aligned with good reproducibility at a pretilt angle that cannot be obtained by the conventional alignment film. When a ferroelectric liquid crystal is injected into a cell having the alignment film (parallel rubbing treated) of the present invention, the layer structure in the smectic C ^* phase of the liquid crystal has a chevron shape that is folded in a V shape at the center of the layer. It becomes a structure. Then, on the surfaces of the upper and lower substrates, the liquid crystal is tilted at an angle of about 10 to 35 degrees and aligned in a uniform shape. However, with the conventional alignment film, it is impossible to stably align the ferroelectric liquid crystal with a high pretilt angle of 10 degrees or more with good reproducibility. In particular, even when a high pretilt alignment film developed for STN is used, a pretilt angle of about 5 degrees can only be obtained. It is considered that this is because the molecular structure of the ferroelectric liquid crystal and the molecular structure of the nematic liquid crystal are significantly different. The following table shows the result of comparison between the pretilt angle of the nematic liquid crystal and the pretilt angle of the ferroelectric liquid crystal when the conventional high pretilt alignment film is used. When a nematic liquid crystal (ZLI-2293, manufactured by Merck) is used, a relatively high pretilt angle is obtained, whereas when a ferroelectric liquid crystal (CS-1023, manufactured by Chisso Corporation) is used. It shows a low pretilt angle. ──────────────────────────────────── Polyimide alignment film Pretilt angle Product name (Manufacturer) ZLI-2293 CS -1023 ──────────────────────────────────── PSI-A-2401 13.5 3.5 ( Chisso Petrochemical Co., Ltd. RN-715 12.5 2.0 (Nissan Chemical Co., Ltd.) RN-722 30.5 0.5 (Nissan Chemical Co., Ltd.) ──────────── ───────────────────────── As is clear from the table above, when a conventional alignment film is used for a ferroelectric liquid crystal display element, The tilt of liquid crystal molecules on the surfaces of the upper and lower substrates is 5 degrees or less, and twist alignment is likely to occur, so that sufficient contrast cannot be obtained.

The point that the liquid crystal display device of the present invention can easily obtain higher contrast than the conventional device will be described with reference to the accompanying drawings (FIGS. 2 to 5). FIG. 2 is a schematic diagram schematically showing the alignment state of liquid crystal molecules in the cell of the liquid crystal display device of the present invention (having the alignment film of the present invention subjected to parallel rubbing treatment). 2A shows one of the two stable states of the liquid crystal molecules of the liquid crystal layer sandwiched between the upper substrate 21 and the lower substrate 22, which is a stable alignment state. The liquid crystal layer has a structure in which a large number of liquid crystal molecular layers 23 are laterally stacked, and each liquid crystal molecular layer 23 has a chevron structure bent in a V shape as shown in the figure. In the device of the present invention, the liquid crystal molecules 24 in the memory state are less than 1
It is tilted from 0 to 35 degrees and is a continuous director (orientation vector) from the upper substrate to the lower substrate.
It is considered to have a distribution (Uup). 25 shows spontaneous polarization. FIG. 2B shows the distribution of the C-director 36 obtained by projecting the director onto the bottom surface of the cone formed by the long axes of the liquid crystal molecules. 2C and 2D show the other orientation state (director distribution (Udown)) and its C-director distribution.

FIG. 3 is a view of FIG. 2 seen from above and shows the tilt angle in the alignment state. 31 and 32 correspond to the average molecular axes when viewed from the substrate normal direction in the case of Uup and Udown, respectively. Therefore, these two average molecular axes 31, 3
1/2 of the angle formed by 2 is the tilt angle θ _U in the memory state. 33 and 34 are the average molecular axes at the time of electrolysis application, and 35 is the layer normal direction.

FIG. 4 is a schematic diagram schematically showing an alignment state of liquid crystal molecules in a cell of a conventional liquid crystal display element (having an organic alignment film subjected to parallel rubbing treatment). FIG. 4A shows one of the two stable states of the liquid crystal molecules of the liquid crystal layer sandwiched between the upper substrate 41 and the lower substrate 42, which is a stable alignment state. The liquid crystal layer has a structure in which a large number of liquid crystal molecular layers 43 are laterally stacked, and each liquid crystal molecular layer 43 has a chevron structure that is bent in a V shape as shown in the figure. In the device of the present invention, the liquid crystal molecules 44 in the memory state are tilted by about 0 to 5 degrees with respect to the substrates near the surfaces of the upper and lower substrates, and the director distribution is continuously twisted from the upper substrate to the lower substrate. (T1). 45 indicates spontaneous polarization. FIG. 4B shows the distribution of the C-directors 46 obtained by projecting the above directors onto the bottom surface of the cone. 4C and 4D show the other orientation state (director distribution (T2)) and its C-
The director distribution is shown.

FIG. 5 is a view of FIG. 4 seen from above and shows the tilt angle in the alignment state. 51 and 52 correspond to the average molecular axes when viewed from the substrate normal direction in Uup and Udown, respectively. Therefore, these two average molecular axes 51, 5
1/2 of the angle formed by 2 is the tilt angle θ _T in the memory state. 53 and 54 are the average molecular axes at the time of electrolysis application, and 55 is the layer normal direction.

From the above, since the tilt angle θ _U is much larger than the tilt angle θ _T , the liquid crystal display device of the present invention has improved contrast in the memory state as compared with the conventional device.

A transparent substrate manufactured as described above,
Two transparent electrode substrates composed of a transparent electrode and an alignment film are made to face each other with their alignment films inside so as to form a cell. The size of this gap, that is, the cell gap is generally about 0.5 μm to 6 μm in the case of a ferroelectric liquid crystal.

Next, the following liquid crystal was injected into this cell,
After sealing, the liquid crystal display element is prepared by gradually cooling.

As the above-mentioned liquid crystal used in the present invention, those conventionally known can be used. Further, preferable liquid crystals used in the present invention are ferroelectric liquid crystals and those usable in the SBE mode.

The liquid crystal having ferroelectricity is specifically a chiral smectic C phase (SmC ^* ) or H phase (SmH).
^* ), I phase (SmI ^* ), J phase (SmJ ^* ), K phase (S
mK ^* ), a G phase (SmG ^* ) or an F phase (SmF ^* ). For example, all known ferroelectric liquid crystals as described in "High-speed liquid crystal technology" (published by CMC) p. 127-161 can be used in the present invention.

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., Inc.
100, ZLI-4654-100ZLI-2293 and the like. There is no problem even if a dichroic dye, a viscosity reducing agent, or the like which dissolves in the liquid crystal is added to these liquid crystals.

The liquid crystal display device thus obtained is
It has a specific alignment film of the present invention. Therefore, the enclosed liquid crystal can be aligned with a large pretilt angle. The pretilt angle of the liquid crystal is preferably 5 degrees to 40 degrees, but the present invention can be almost achieved.

In the liquid crystal display element manufactured as described above, polarizing plates may be provided on both substrates of the cell depending on the purpose of use. A color filter, a protective layer, or the like may be provided between the transparent electrode and the alignment film. further,
The liquid crystal display element of the present invention can be provided with a structure such as a reflection plate and a retardation plate, which are provided in a conventional liquid crystal display element, depending on the intended use.

[0075]

EXAMPLES Examples of the present invention and comparative examples will be described below. However, the present invention is not limited to this embodiment.

[Example 1] (Preparation of liquid crystal display element A) Transparent electrodes of indium-tin oxide (ITO) were stripe-shaped (electrode width: 100 μm, on two 1.1 mm thick glass substrates). The gap between the electrodes was 15 μm).

On the above two glass substrates with transparent electrodes,
An insulating film of TiO _{2 having} a film thickness of 100 nm was formed by sputtering.

2.68 g of 1,4,5,8-naphthalenetetracarboxylic acid anhydride and 2,2-bis (p- (4-aminophenoxy) were placed on the insulating films of the two glass substrates with transparent electrodes. ) Phenyl) -1,1,1,3,3,3-hexafluoropropane N, N-dimethylacetamide of polyamic acid (a) (precursor of polyimide [1] having fluorine atom) obtained from 5.18 g 8.0 g of a 2 wt% solution of / 4-butoxypropanol / diethylene glycol monoethyl ether (1/2/2, weight ratio), 2.18 g of pyromellitic dianhydride and 2,2-bis (p-
(12- (4-aminophenoxy) dodecanoxy) phenyl) -1,1,1,3,3,3-hexafluoropropane Polyamic acid (b) obtained from 8.86 g (of the above (A) to (C)) N, N-dimethylacetamide / 4 of a precursor of polyimide [2]) having any of the structures
-A mixed solution obtained by thoroughly mixing 2.0 g of a 2 wt% solution of butoxypropanol / diethylene glycol monoethyl ether (1/2/2, weight ratio) was applied with a spinner.

The conditions for the spinner are 2500 rpm.
m., time 30 seconds. After coating, the polyimide film was formed by drying at 200 ° C. for 1 hour.

The surfaces of the coating films of the two substrates are rubbed in one direction with a nylon raised cloth, and the rubbing surfaces are inward so that the rubbing directions are parallel and the directions are the same. Further, two glass plates were superposed with a 1.8 μm spacer interposed therebetween so that the electrode patterns were orthogonal to each other to prepare a cell having a cell gap of 1.8 μm. Ferroelectric liquid crystal CS-1023 (manufactured by Chisso Corporation) was injected into this cell at 120 ° C., held at 120 ° C. for 1 hour, and then slowly cooled to room temperature at a rate of about 2 ° C./minute to give a liquid crystal. A display element A was obtained. This was used to measure the contrast.

(Preparation of liquid crystal display elements B and C) For measuring the pretilt angle, apart from the above element A, in the above element A, two substrates with a thickness of 1.1 mm were mounted on a glass substrate of 2 cm square. , Element A except that the transparent electrode of indium-tin oxide (ITO) was changed to one in which a pixel pattern of 1 cm square was formed, and the rubbing directions were parallel to each other on the upper and lower substrates and opposite to each other. Two liquid crystal cells were prepared in the same manner as in. Ferroelectric liquid crystal CS-1023 (manufactured by Chisso Corporation) was injected into one cell at 120 ° C., held at 120 ° C. for 1 hour, and then gradually cooled to room temperature at a rate of about 2 ° C./minute. Thus, a liquid crystal display element B was prepared. The other cell has a nematic liquid crystal ZLI-2293.
(Manufactured by Merck & Co.) was injected at 120 ° C, kept at 120 ° C for 1 hour, and then gradually cooled to room temperature at a rate of about 2 ° C / min.
A liquid crystal display element C was created.

Example 2 (Preparation of Liquid Crystal Display Element D) In Example 1, 2,2-bis (p) which is a material of the precursor (polyamic acid (a)) of the polyimide [1] having a fluorine atom is used. -(4-aminophenoxy) phenyl) -1,1,1,3,3,3-hexafluoropropane in place of 5.18 g 2,2-bis (p- (p-aminobenzyl) phenyl) 1,1 , 1,
A liquid crystal display was performed in the same manner as in Example 1 except that the precursor of the polyimide [1] having a fluorine atom (polyamic acid (c)) obtained by using 5.14 g of 3,3,3-hexafluoropropane was used. Element D was prepared. This was used to measure the contrast.

(Preparation of liquid crystal display elements E and F) In addition to the element D, the element D is used for pretilt angle measurement.
In two, the substrate was changed to a 1.1 cm square pixel pattern with a transparent electrode of indium-tin oxide (ITO) formed on a 2 cm square glass substrate having a thickness of 1.1 mm, and the rubbing direction was changed. Two liquid crystal cells were prepared in the same manner as in the device D except that the directions were parallel and opposite in the upper and lower substrates. Ferroelectric liquid crystal CS-1023 (manufactured by Chisso Corporation) was injected into one cell at 120 ° C., held at 120 ° C. for 1 hour, and then gradually cooled to room temperature at a rate of about 2 ° C./minute. Thus, a liquid crystal display element E was prepared. The other cell has a nematic liquid crystal ZLI-2293.
(Manufactured by Merck & Co.) was injected at 120 ° C, kept at 120 ° C for 1 hour, and then gradually cooled to room temperature at a rate of about 2 ° C / min.
A liquid crystal display element F was created.

Example 3 (Preparation of Liquid Crystal Display Element G) In Example 1, 2,2-bis (p- (12-) which is a material of the precursor (polyamic acid (b)) of polyimide [2] is used. (4-aminophenoxy)
Dodecanoxy) phenyl) -1,1,1,3,3,3-
Example except that a precursor (polyamic acid (d)) of polyimide [2] obtained by using 2.04 g of 1,4-bis (3-aminopropoxy) butane instead of 8.86 g of hexafluoropropane was used. A liquid crystal display element G was prepared in the same manner as in 1. This was used to measure the contrast.

(Preparation of liquid crystal display elements H and I) In addition to the element G, the element G is used for pretilt angle measurement.
In two, the substrate was changed to a 1.1 cm square pixel pattern with a transparent electrode of indium-tin oxide (ITO) formed on a 2 cm square glass substrate having a thickness of 1.1 mm, and the rubbing direction was changed. Two liquid crystal cells were prepared in the same manner as the element G except that the directions were parallel and opposite directions on the upper and lower substrates. Ferroelectric liquid crystal CS-1023 (manufactured by Chisso Corporation) was injected into one cell at 120 ° C., held at 120 ° C. for 1 hour, and then gradually cooled to room temperature at a rate of about 2 ° C./minute. Thus, a liquid crystal display element H was prepared. The other cell has a nematic liquid crystal ZLI-2293.
(Manufactured by Merck & Co.) was injected at 120 ° C, kept at 120 ° C for 1 hour, and then gradually cooled to room temperature at a rate of about 2 ° C / min.
A liquid crystal display element I was created.

Example 4 (Preparation of Liquid Crystal Display Element J) In Example 2, 2,2-bis (p- (12-) which is a material of the precursor (polyamic acid (b)) of polyimide [2] is used. (4-aminophenoxy)
Dodecanoxy) phenyl) -1,1,1,3,3,3-
Diethylene glycol di (3-aminopropyl) ether 2.03 in place of 8.86 g of hexafluoropropane
A liquid crystal display device J was prepared in the same manner as in Example 2 except that the polyimide [2] precursor (polyamic acid (e)) obtained by using g was used. This was used to measure the contrast.

(Production of Liquid Crystal Display Elements K and L) Apart from the above-mentioned element J, the above-mentioned element J is used for pretilt angle measurement.
In the above, the substrate was changed to two 1.1 mm thick glass substrates with a transparent electrode of indium-tin oxide (ITO) formed on a 1 cm square pixel pattern on a 2 cm square glass substrate, and the rubbing direction was changed. Two liquid crystal cells were prepared in the same manner as the element J except that the directions were parallel and opposite directions on the upper and lower substrates. Ferroelectric liquid crystal CS-1023 (manufactured by Chisso Corp.) was injected into one cell at 120 ° C., held at 120 ° C. for 1 hour, and then gradually cooled to room temperature at a rate of about 2 ° C./min. Thus, a liquid crystal display element K was prepared. The other cell has a nematic liquid crystal ZLI-2293.
(Manufactured by Merck & Co.) was injected at 120 ° C, kept at 120 ° C for 1 hour, and then gradually cooled to room temperature at a rate of about 2 ° C / min.
A liquid crystal display element L was created.

Example 5 (Preparation of Liquid Crystal Display Element M) In Example 3, 1,4,5,8-naphthalenetetracarboxylic acid, which is a material of the precursor of the polyimide [1] (polyamic acid (a)), is used. A precursor (polyamic acid (f)) of polyimide [1] obtained by using 1.09 g of pyromellitic acid anhydride and 1.47 g of biphenyltetracarboxylic acid anhydride instead of 2.68 g of acid anhydride was used. A liquid crystal display element M was prepared in the same manner as in Example 3. This was used to measure the contrast.

(Preparation of liquid crystal display elements N and O) In addition to the element M, the element M is used for pretilt angle measurement.
In two, the substrate was changed to a 1.1 cm square pixel pattern with a transparent electrode of indium-tin oxide (ITO) formed on a 2 cm square glass substrate having a thickness of 1.1 mm, and the rubbing direction was changed. Two liquid crystal cells were prepared in the same manner as the device M except that the directions were parallel and opposite directions on the upper and lower substrates. Ferroelectric liquid crystal CS-1023 (manufactured by Chisso Corp.) was injected into one cell at 120 ° C., held at 120 ° C. for 1 hour, and then gradually cooled to room temperature at a rate of about 2 ° C./min. Thus, a liquid crystal display element N was prepared. The other cell has a nematic liquid crystal ZLI-2293.
(Manufactured by Merck & Co.) was injected at 120 ° C, kept at 120 ° C for 1 hour, and then gradually cooled to room temperature at a rate of about 2 ° C / min.
A liquid crystal display device O was prepared.

Comparative Example 1 (Preparation of Liquid Crystal Display Devices P, Q, and R) In Example 1, two polyamic acids (a) and (b) of Example 1 were prepared.
A liquid crystal display element P was prepared in the same manner as in Example 1 except that only the 2% by weight solution of the polyamic acid (A) was used. This was used to measure the contrast.
Further, in the same manner as in Example 1, two types (Q and R) of liquid crystal display elements for pretilt angle measurement were manufactured.

Reference Example 1 (Preparation of Liquid Crystal Display Devices S, T, and O) In Example 1, two polyamic acids (a) and (b) of Example 1 were used.
Of 2% by weight of benzophenone tetracarboxylic acid dianhydride in place of the polyamic acid (II),
N, N-dimethylacetamide / 3 of polyamic acid obtained from 2,2-bis (p- (4-aminophenoxy) phenyl) -1,1,1,3,3,3-hexafluoropropane (5.18 g) -Butoxy-2-propanol / diethylene glycol monoethyl ether (1/2 /
A liquid crystal display element S was prepared in the same manner as in Example 1 except that a 2% by weight solution of a precursor (polyamic acid (g)) of polyimide [1] obtained by using (2, weight ratio) was used. This was used to measure the contrast. In the same manner as in Example 1, two types (T and O) of liquid crystal display elements for pretilt angle measurement were manufactured.

[Evaluation of Alignment Film] 1) Glass transition point (Tg) when the polyamic acid used was completely polyimidized: (a), (b), (c),
The Tg of each polyimide in (g) is obtained by heating the polyamic acid film at 280 ° C. for 1 hour to cure the film, and forming a film having a width of 5 mm, a length of 30 mm, and a thickness of 0.1 to 0.5 mm. The obtained film was measured using a viscoelasticity measuring device (Rheovibron DDV-II-EA, manufactured by Orientec Co., Ltd.). Films that could not be formed (polyimides obtained from polyamic acids (a), (c), and (g)) were measured by the TMA (thermal mechanical analyzer) method. 2) Pretilt angle (for polyimide obtained from each polyamic acid) By the same method as in Example 1, a liquid crystal cell using polyamic acids (a) to (g) as an alignment film was prepared. However, curing of each polyimide acid was performed under two conditions of 200 ° C. for 1 hour and 280 ° C. for 1 hour. Ferroelectric liquid crystal (CS-1023) was injected into the obtained liquid crystal cell to raise the temperature to 69 ° C. which is the temperature of the smectic A phase,
The pretilt angle was measured by the crystal rotation method using a polarization microscope manufactured by Nikon Corporation. The measurement results are shown in Table 1.

[0093]

[Table 1] Table 1 ──────────────────────────────── Polyimide glass transition point Pretilt angle Pretilt angle (polyamic acid) (℃) (Cure 200 ℃) (Cure 280 ℃) ──────────────────────────────── (A) 331 7 ° 20 ° (b) 107 2 ° 2 ° (c) 3179 9 ° 35 ° (d) −2 ° 1 ° (e) −1 ° 0 ° (f) −8 ° 16 ° (g) 260 1 ° 1 ° ────────────────────────────────

[Evaluation of Liquid Crystal Display Element] 1) Contrast Each of the liquid crystal display elements A, D, G, J, M, P and S is switched by applying a pulse of ± 30 V and 100 milliseconds between orthogonal Nicols. I went. At this time, the transmission intensity in light and dark was obtained, and the ratio was used as the contrast.

2) Pretilt angle The above liquid crystal display elements B, C, E, F, H, I, K, L,
Among N, O, Q, R, T and U, the B, E, H, K, N, Q and T elements injected with the ferroelectric liquid crystal are heated to a smectic phase temperature of 69 ° C., Further, the C, F, I, L, O, R and U elements in which nematic liquid crystal was injected were measured for pretilt angles at room temperature by a crystal rotation method using a polarization microscope manufactured by Nikon Corporation. The measurement results are shown in Table 2.

[0096]

[Table 2] Table 2 ──────────────────────────────── Pretilt angle (degrees) Contrast Ferroelectric liquid crystal Nematic liquid crystal ──────────────────────────────── Example 1 A −−−− 45: 1 B 20 −−−−− C −− 12 −− ──────────────────────────────── Example 2 D −−−− 38: 1 E 18 −−−− F −− 8 −− ───────────────────────────────── Example 3 G −−−− 50: 1 H 21 −−−− I −− 9 −− ───────────────────────────────── Example 4 J ---- 61: 1 K24 --- L--11 --- ──────────── ───────────────────────────────────────────────────────────────────── ──────────────────────── Comparative Example 1 P −−−− 3.5: 1 Q 7 −−−− R −− 4 −−− ─────────────────────────────── Comparative Example 2 S −−−− 2.3: 1 T 6 −−−−− U −− 5 −− ─────────────────────────────────

[0097]

The liquid crystal display device of the present invention has a precursor of polyimide [1] having a fluorine atom in its molecular structure and the above-mentioned specific structures ((A) to (C)) in its main chain skeleton. An alignment film formed by curing a mixture of polyimide [2] or its precursor is provided. As a result, a larger pretilt angle can be given to the liquid crystal sealed in the device than in the case where the conventional alignment film is used. In particular, since a high pretilt angle can be stably given to the ferroelectric liquid crystal, the uniform alignment is stable in the memory state in the ferroelectric liquid crystal device, and thus a large apparent tilt angle can be obtained. The contrast can be obtained. Further, according to the present invention, by mixing a polyimide precursor having conventionally required curing at a high temperature with a polyimide having a flexible molecular structure, a high pretilt angle can be obtained at a curing temperature lower than the conventional one. Therefore, it is advantageous in manufacturing a liquid crystal display device using a color filter substrate. Furthermore, the liquid crystal display device of the present invention enables good multiplex driving with high contrast even when using a ferroelectric liquid crystal having a large tilt angle or a large spontaneous polarization. Further, the liquid crystal display device of the present invention can obtain a high pretilt angle even for TN and STN liquid crystals, and can realize a sharp threshold characteristic especially when STN liquid crystals are used.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram schematically showing an alignment state of liquid crystal molecules in a cell of a liquid crystal display device of the present invention (having an alignment film of the present invention subjected to parallel rubbing treatment).

FIG. 3 is a view of FIG. 2 seen from above, showing a tilt angle in an alignment state.

FIG. 4 is a schematic diagram schematically showing an alignment state of liquid crystal molecules in a cell of a conventional liquid crystal display device (having an organic alignment film subjected to parallel rubbing treatment).

FIG. 5 is a view of FIG. 4 seen from above, showing a tilt angle in an alignment state.

[Explanation of symbols]

1a, 1b Transparent substrate 2a, 2b Transparent electrode 3a, 3b Insulating film 4a, 4b Alignment film 5 Liquid crystal 21, 41 Substrate 22, 42 Lower substrate 23, 43 Liquid crystal molecular layer 24, 44 Liquid crystal molecule 25, 45 Spontaneous polarization 31, 32, 51, 52 Average molecular axis when viewed from the substrate normal direction 33, 34, 53, 54 Average molecular axis when electrolysis is applied 35, 55 Layer normal direction θ _U , θ _T Tilt angle in memory state

Claims (3)

[Claims] 1. A liquid crystal display device comprising a transparent electrode and an alignment film, two transparent electrode substrates laminated in this order, each alignment film being placed inside, and a liquid crystal sealed between them. At least one of the alignment films has a precursor of polyimide [1] having a fluorine atom in the molecular structure, and the following general formula (A):
~ (C): [However, n represents an integer in the range of 4 to 24, and R ¹
Represents a divalent organic group having 2 to 24 carbon atoms, and Y
Is -O-, -COO-, -OCOO- or -CONH
Represents-, R ² represents an organic group having 1 to 6 carbon atoms, R ³ represents an organic group having 1 to 6 carbon atoms, R ⁴
Represents a divalent organic group, m represents an integer in the range of 1 to 20, and p represents an integer in the range of 2 to 24. ] A liquid crystal display device, which is a cured film of a mixture containing at least one of the structures represented by the formula [2] or a precursor thereof having a main chain skeleton. 2. A polyimide [1] having a fluorine atom in its molecular structure is represented by the following general formula (D): [Wherein R ⁵ represents a tetravalent organic group, and X 5
Represents O, CH ₂ or S. ] The liquid crystal display element of Claim 1 which consists of a repeating unit represented by these. 3. The polyimide [1] having a fluorine atom in the molecular structure has a property of imparting a pretilt angle of 10 degrees or more to a liquid crystal when the polyimide is used for an alignment film. 1. The liquid crystal display element according to 1.