JP2567128B2 - Liquid crystal element - Google Patents

Description

TECHNICAL FIELD The present invention relates to a liquid crystal element used in a liquid crystal display element, a liquid crystal-optical shutter or the like, particularly a ferroelectric liquid crystal element, and more specifically, to improve the alignment state of liquid crystal molecules. Thus, the present invention relates to a liquid crystal element having improved display characteristics.

[Prior art]

A display element of the type in which transmitted light rays are controlled by combining with a polarizing element by utilizing the refractive index anisotropy of ferroelectric liquid crystal molecules has been proposed by Clark and Lagerwall (JP-A-56). -107216, U.S. Pat. No. 4,367,924, etc.). In general, this ferroelectric liquid crystal has a non-helical chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) in a specific temperature range.
In this state, in response to an applied electric field, one of the first optically stable state and the second optically stable state is maintained, and the property of maintaining that state when no electric field is applied, that is, bistable state In addition, it is expected to be widely used as a high-speed and memory-type display element because of its quick response to changes in electric field, and its function is expected to be applied as a high-definition display with a large screen. ing.

In order for the optical modulation element using the liquid crystal having the bistability to exhibit a predetermined driving characteristic, the liquid crystal arranged between the pair of parallel substrates has the two stable states regardless of the electric field application state. It is necessary to be in a state of molecular alignment such that conversion between states can occur effectively.

Also, in the case of a liquid crystal element that utilizes the birefringence of liquid crystal, the transmittance under orthogonal Nicolo is [Wherein, I ₀ : incident light intensity, I: transmitted light intensity, θ: tilt angle, Δn: refractive index anisotropy, d: thickness of liquid crystal layer, λ: wavelength of incident light. The tilt θ in the non-helical structure described above appears as an angle in the average molecular axis direction of the twisted liquid crystal molecules in the first and second alignment states. According to the above equation, the maximum transmittance is obtained when the tilt θ is an angle of 22.5 °, and it is necessary that the tilt angle θ in the non-helical structure for realizing bistability is as close as possible to 22.5 °.

By the way, as a method of orienting a ferroelectric liquid crystal, a molecular layer composed of a plurality of molecules forming a smectic liquid crystal can be uniaxially oriented along its normal line over a large area, and a manufacturing process It is desirable that the process can be realized by a simple rubbing process.

As an alignment method for a ferroelectric liquid crystal, especially a chiral smectic liquid crystal having a non-helical structure, for example, US Pat. No. 4,561,726 is known.

However, when the alignment method used so far, especially the alignment method using a rubbed polyimide film, is applied to the non-helical ferroelectric liquid crystal exhibiting bistability published by Clark and Ragall. Had the following problems.

That is, according to the experiments conducted by the present inventors, the tilt angle (angle shown in FIG. 3 to be described later) in the ferroelectric liquid crystal having a non-helical structure obtained by aligning with the conventional rubbing-treated polyimide film is spiral. It was found that the tilt angle was smaller than that of the structured ferroelectric liquid crystal (1/2 angle of the apex angle of the triangular pyramid shown in FIG. 2 described later). (Especially, the tilt angle θ of a non-helical ferroelectric liquid crystal obtained by orientation using a conventional rubbed polyimide film.
Was generally about 3 ° to 8 °, and the transmittance at that time was about 3 to 5% at most. Thus, according to Clark and Ragall, the tilt angle of a non-helical ferroelectric liquid crystal that realizes bistability should be the same as the tilt angle of a ferroelectric liquid crystal having a helical structure. However, in practice, the tilt angle θ in the non-helical structure is smaller than the tilt angle in the helical structure. Moreover, it was found that the cause of the tilt angle θ in the non-helical structure being smaller than the tilt angle in the helical structure is attributed to the twist alignment of the liquid crystal molecules in the non-helical structure. In other words, in the ferroelectric liquid crystal having a non-helical structure, the liquid crystal molecules are aligned with respect to the normal of the substrate as shown in FIG. 43 (twisted direction 44) is continuously twisted and arranged at a twist angle δ, which causes the tilt angle θ in the non-helical structure to be smaller than the tilt angle in the helical structure.

Further, the alignment state of the chiral smectic liquid crystal generated by the conventional rubbing-treated polyimide alignment film is the first optically stable state due to the presence of the polyimide alignment film as an insulator layer between the electrode and the liquid crystal layer ( For example, when a one-polarity voltage for switching from a white display state to a second optically stable state (for example, a black display state) is applied, after the application of the one-polarity voltage is released, the ferroelectric liquid crystal layer On the other hand, a reverse electric field V _rev of the other polarity occurs, and this reverse electric field V _rev caused an afterimage at the time of display. The reverse electric field generation phenomenon described above has been clarified, for example, in "Switching Characteristics of SSFLC" by Akio Yoshida, "Liquid Crystal Conference Proceedings", October 1987, pp. 142-143.

[Outline of Invention]

Therefore, an object of the present invention is to provide a ferroelectric liquid crystal device that solves the above-mentioned problems, and particularly to generate a large tilt θ in the non-helical structure of a chiral smectic liquid crystal and display a high-contrast image. Another object of the present invention is to provide a ferroelectric liquid crystal element capable of achieving a display without causing an afterimage.

The liquid crystal device of the present invention is a liquid crystal device in which a chiral smectic liquid crystal having at least two stable states is sandwiched between a pair of substrates, and at least one substrate of the pair of substrates is sandwiched. Is provided with a polyimide coating film in which fluorine atoms are bonded in the molecule, and the pair of substrates are each subjected to an alignment treatment in one direction so as to intersect each other on the surface adjacent to the chiral smectic liquid crystal. The chiral smectic liquid crystal has a layer structure composed of a plurality of liquid crystal molecules, and the layer has a bent structure, and the layer having the bent structure is adjacent to the adjacent substrate. The rotation direction and the floating rotation direction of the liquid crystal molecules adjacent to the adjacent substrate are the same direction.

In particular, the present invention can use, as the above-mentioned polyimide, a polyimide having in its molecule at least one of the structural formulas represented by the following general formulas (I) to (VIII).

General formula (I) (In the formula, 1 and m are 0 or an integer of 1-3.
l + m ≧ 1. ) (In the formula, R ₂₁ and R ₂₂ are a hydrogen atom, a fluorine atom, or −
CF ₃ However, at least one of R ₂₁ and R ₂₂ is a fluorine atom or —CF ₃ . ) (Wherein, R _31, R _32, R ₃₃ and R _34, a hydrogen atom, a fluorine atom or -CF _3. However, at least one of hydrofluoric of R _31, R _32, R ₃₃ and R ₃₄ atom or -CF _3.) (In the formula, R ₄₁ , R ₄₂ , R _43, and R ₄₄ are a hydrogen atom, a fluorine atom, or —CF _3. However, at least one of R ₄₁ , R ₄₂ , R _43, and R ₄₄ is hydrogen. atom or -CF _3.) (In the formula, R ₅₁ , R ₅₂ , R ₅₃ , R ₅₄ , R ₅₅ , R ₅₆ , R ₅₇ , R ₅₈ , R ₅₉ , R ₁₀ , R
₁₁ , R ₁₂ , R ₁₃ and R ₁₄ are a hydrogen atom, a fluorine atom or --CF ₃
Is. However, at least one of R _{51 to} R ₁₄ described above is a fluorine atom or —CF ₃ . ) (In the formula, R ₆₁ is Alternatively, in CF _{2 n1} , n ₁ is 0 or an integer of 1 to 7. R ₆₂
And R ₆₇ is a hydrogen atom or -CF ₃ , and R ₆₃ , R ₆₄ , R ₆₅ and R _67
66 is a hydrogen atom, an alkyl group, a halogen atom or -CF ₃
Is. However, when n ₁ is 0, at least one of R ₆₂ , R ₆₃ , R ₆₄ , R ₆₅ , R _66, and R ₆₇ is —CF ₃ . ) (In the formula, R ₇₁ is Alternatively, in CF _{2 n2} , n ₂ is 0 or an integer of 1 to 7. R ₇₂
And R ₇₇ is a hydrogen atom or —CF ₃ . R ₇₃ , R ₇₄ , R ₇₅ and R
₇₆ is a hydrogen atom, an alkyl group, a halogen atom or -CF ₃
Is. However, when n ₂ is 0, R ₇₂ , R ₇₃ , R ₇₄ , R ₇₅ and R ₇₆
At least one of is -CF _3. ) (In the formula, l ₈ , m ₈ and n ₈ are 0 or an integer of 1 to 3, and l ₈
+ M ₈ + n ₈ ≧ 1. [Detailed Description of Embodiments of the Invention] FIG. 1 (A) schematically illustrates an example of a ferroelectric liquid crystal cell of the present invention.

11a and 11b are In ₂ O ₃ and ITO (Indium Tin Oxid), respectively.
e) a substrate (glass plate) covered with transparent electrodes 12a and 12b, etc., on which insulating films 13a and 13
b (SiO ₂ film, TiO ₂ film, Ta ₂ O ₅ film, etc.) and a polyimide film of the general formula 50 Å ~ 1000 Å thickness alignment control film 14a
And 14b are respectively laminated.

At this time, they are parallel and in the same direction (A in FIG. 1A).
The orientation control films 14a and 14b that have been rubbed (in the direction of the arrow) are arranged so that they are oriented in the same direction. A ferroelectric smectic liquid crystal 15 is arranged between the substrates 11a and 11b, and the substrate 11a
And the distance between 11b and the ferroelectric smectic liquid crystal 15
The ferroelectric smectic liquid crystal 15 is set to a bistable orientation state by setting a distance (for example, 0.1 μm to 3 μm) small enough to suppress the formation of the helical alignment structure. The sufficiently small distance described above is provided by the bead spacers 16 (silica beads, alumina beads) arranged between the substrates 11a and 11b.
Held by

According to the experiments of the present inventors, by using the alignment method using a specific polyimide alignment film subjected to rubbing treatment which will be clarified in the examples described below, a large optical contrast in a bright state and a dark state is exhibited, and particularly, , U.S. Pat.
No. 561, etc., achieves high contrast for non-selected pixels during multiplexing drive, and achieves an alignment state that does not cause optical response delay during switching (during multiplexing drive) that causes afterimages during display Was done.

The polyimide film used in the present invention is obtained by heat-cyclizing a polyamic acid synthesized by subjecting a carboxylic anhydride and a diamine to a condensation reaction.

Examples of the carboxylic acid anhydride used in the present invention for forming the polyimide having the structural formulas of the general formulas (I) to (VIII) in the molecule include, for example, the case of the general formula (I): I- (1) 5,5'-bis (trifluoromethyl) -3,
3 ', 4,4'-tetracarboxybenzophenone II- (2) 2,2 ', 5,5'-tetra (trifluoromethyl) -3,3', 4,4'-tetracarboxybenzophenone In the case of the general formula (II): II- (1) (trifluoromethyl) pyromellitic anhydride II- (2) Bis (trifluoromethyl) pyromellitic anhydride II- (3) Fluoropyromellitic anhydride In the case of the general formula (III): III- (1) 5,5′-bis (trifluoromethyl) -3,
3 ', 4,4'-tetracarboxybiphenyl anhydride III- (2) 2,2 ', 5,5'-tetrakis (trifluoromethyl) -3,3', 4,4'-tetracarboxybiphenyl anhydride III- (3) 5,5'-difluoro-3,3 ', 4,4'-tetracarboxybiphenyl anhydride In the case of the general formula (IV); IV- (1) 5,5′-bis (trifluoromethyl) -3,
3 ', 4,4'-tetracarboxydiphenyl ether anhydride IV- (2) 2,2 ', 5,5'-tetra (trifluoromethyl) -3,3', 4,4'-tetracarboxydiphenyl ether anhydride IV- (3) 5,5'-bis (trifluoromethyl) -3,
3 ', 4,4'-tetracarboxydiphenyl ether anhydride IV- (4) 5,5'-bis (trifluoromethyl) -2,
2 ', 3,3'-teroracarboxydiphenyl ether anhydride In the case of the general formula (V): V- (1) bis (dicarboxyphenoxy) bis (trifluoromethyl) biphenyl V- (2) Bis (dicarboxyphenoxy) tetrakis (trifluoromethyl) biphenyl V- (3) Bis [(trifluoromethyl) dicarboxyphenoxy] biphenyl V- (4) Bis [(fluoro) dicarboxyphenoxy] biphenyl In the case of the general formula (VI); VI- (1) 2,2-bis [4- (3,4-dicarboxybenzoyloxy) -3-bromophenyl] bexafluoropropane anhydride VI- (2) 2,2-bis [4- (3,4-dicarboxybenzoyloxy) -3,5-dibromophenyl] hexafluoropropane anhydride VI- (3) 2,2-bis [4- (3,4-dicarboxybenzoyloxy) -3,5-dimethylphenyl] hexafluoropropane anhydride VI- (4) 2,2-bis [4- (3,4-dicarboxybenzoyloxy) phenyl] octafluorobutane anhydride VI- (5) 2,2-bis [4- (2-trifluoromethyl 3,4-dicarboxybenzoyloxy) phenyl] hexafluoropropane anhydride VI- (6) 1,3-bis [4- (3,4-dicarboxybenzoyloxy) phenyl] hexafluoropropane anhydride VI- (7) 1,5-bis [4- (3,4-dicarboxybenzoyloxy) phenyl] decafluoropentane anhydride VI- (8) 1,6-bis [4- (3,4-dicarboxybenzoyloxy) phenyl] dodecafluorohexane anhydride VI- (9) 1,7-bis [4- (3,4-dicarboxybenzoyloxy) phenyl] tetradecafluoropentane anhydride VI- (10) 1,5-bis [4- (3,4-dicarboxybenzoyloxy) -3,5-dibromophenyl] decafluoropentane anhydride VI- (11) 1,5-bis [4- (3,4-dicarboxybenzoyloxy) -3,5-bistrifluoromethylphenyl] decafluoropentane anhydride VI- (12) 1,5-bis [4- (2-trifluoromethyl 3,5-dicarboxybenzoyloxy) phenyl] decafluoropentane anhydride In the case of the general formula (VII): VII- (1) 1,5-bis [4- (3,4-dicarboxyphenoxy) phenyl] decafluoropentane anhydride VII- (2) 1,6-bis [4- (3,4-dicarboxyphenoxy) phenyl] dodecafluorohexane anhydride VII- (3) 1,7-bis [4- (3,4-dicarboxyphenoxy) phenyl] tetradecafluoropentane anhydride VII- (4) 1,5-bis [4- (3,4-dicarboxyphenoxy) -3,5-dibromophenyl] decafluoropentane anhydride VII- (5) 1,5-bis [4- (3,4-dicarboxyphenoxy) -3,5-bistrifluoromethylphenyl]
Decafluoropentane anhydrous VII- (6) 1,5-bis [4- (3,4-dicarboxy-
2-Trifluoromethylphenoxy) phenyl] decafluoropentane anhydride VII- (7) 2,2-bis [4- (3,4-dicarboxyphenoxy) -3-bromophenyl] hexafluoropropane anhydride VII- (8) 2,2-bis [4- (3,4-dicarboxyphenoxy) -3,5-dibromophenyl] hexafluoropropane anhydride VII- (9) 2,2-bis [4- (3,4-dicarboxyphenoxy) -3,5-dimethylphenyl] hexafluoropropane anhydride VII- (10) 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] octafluorobutane anhydride VII- (11) 2,2-bis [4- (3,4-dicarboxy-
2-Trifluoromethylphenoxy) phenyl] hexafluoropropane anhydride VII- (12) 1,3-bis [4- (3,4-dicarboxyphenoxy) phenyl] hexafluoropropane anhydride VII- (13) 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] hexafluoropropane anhydride In the case of general formula (VIII): VIII- (1) bis (dicarboxyphenoxy)-(trifluoromethyl) benzene anhydride VIII- (2) Bis (dicarboxyphenoxy) -bis (trifluoromethyl) benzene anhydride VIII- (3) Bis (dicarboxyphenoxy) -tetraxy (trifluoromethyl) benzene anhydride VIII- (4) Bis [(trifluoromethyl) dicarboxyphenoxy] benzene anhydride VIII- (5) Bis [(trifluoromethyl) dicarboxyphenoxy] (trifluoromethyl) benzene And the like.

Examples of the diamine used in the present invention include m-phenylenediamine, p-phenylenediamine, m-xylenediamine, p-xylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane. , 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3 ', 5,5'-tetramethyl-4,4'-diaminodiphenylmethane, 2,2'-bis (4- Aminophenyl) propane, 4,4'-methylenedianiline, benzidine, 4,
4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 1,5-diaminonaphthalene, 3,3 '
-Dimethylbenzidine, 3,3'-dimethoxybenzidine and the like, and in addition to these diamines, for example, 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-trifluoromethylphenoxy) biphenyl, 4,4'-bis (4-amino-2-
Trifluoromethylphenoxy) diphenyl sulfone,
4,4'-bis (3-amino-5-trifluoromethylphenoxy) diphenyl sulfone, 2,2-bis [4- (4
Fluorine-based diamines such as -amino-2-trifluoromethylphenoxy) phenyl] hexafluoropropane and 4,4'-bis [(4-aminophenoxy) phenyl] hexafluoropropane can be used.

In the present invention, it is possible to use two or more kinds of the above-mentioned carboxylic acid anhydrides and / or two or more kinds of diamines.
Further, in the present invention, it is also possible to prepare a copolymer in which the following carboxylic acid anhydride is combined with the above-mentioned carboxylic acid anhydride.

Pyromellitic anhydride, 2,3,6,7-naphthalenetetracarboxylic anhydride, 3,3 ', 4,4'-diphenyltetracarboxylic anhydride, 1,2,5,6-naphthalenetetracarboxylic acid Anhydride, 2,2 ', 3,3'-diphenyltetracarboxylic acid anhydride, thiophene-2,3,4,5-tetracarboxylic acid anhydride, 2,2-bis (3,4-biscarboxylic anhydride (Enyl) propane anhydride, 3,4-dicarboxyphenyl sulfone anhydride, perylene-3,4,9,10-tetracarboxylic acid anhydride, bis (3,4-dicarboxyphenyl) ether anhydride, 3 ,
3 ', 4,4'-benzophenone tetracarboxylic acid anhydride.

When providing the polyimide film used in the present invention on the substrate, the polyamic acid precursor of the polyimide is dissolved in a solvent such as dimethylformamide, dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone 0.01 to 40. (% By weight) After applying the solution on a substrate by a spinner coating method, a spray coating method, a roll coating method, or the like, the solution is heated at a temperature of 100 to 350 ° C., preferably 200 to 300 ° C. to be dehydrated and closed. To form a polyimide film. This polyimide film is then rubbed with a cloth or the like. Further, the polyimide film used in the present invention is set to a film thickness that can also function as an insulating film, for example, about 30Å to 1 μm, preferably 200Å to 2000Å. At this time, the insulating film 13 shown in FIG.
The use of a and 13b can be omitted. Further, in the present invention, when a polyimide film is provided on the insulating films 13a and 13b, the thickness of the polyimide film is 200 Å or less, preferably 1
It can be set below 00Å.

The liquid crystal substance used in the present invention is preferably a liquid crystal that produces a chiral smectic C phase through an isotropic phase, a cholesteric phase, and a smectic A phase in the temperature lowering process. In particular,
The pitch in the cholesteric phase is preferably 0.8 μm or more (the pitch in the cholesteric phase is measured at the center point in the temperature range of the cholesteric phase). Specific liquid crystals include the liquid crystal substances “LC-1” and “80
A liquid crystal composition containing "B" and "80SI ^* " in the following ratio is preferably used.

Liquid crystal (1) (LC-1) ₉₀ / (80B) ₁₀ (2) (LC-1) ₈₀ / (80B) ₂₀ (3) (LC-1) ₇₀ / (80B) ₃₀ (4) (LC-1 ) ₆₀ / (80B) ₄₀ (5) 80SI ^* (The subscripts in the table represent the weight ratios respectively.) FIG. 1 (B) is a plan view showing another preferred embodiment of the present invention. . In the figure, 1 is a pair of overlapping substrates,
2A is a rubbing treatment axis in one direction (arrow direction) applied to the substrate near the observation position (upper side of the paper), and 2B is one rubbing treatment axis applied to the substrate in a position far from the observation position. . θ _X is an intersection angle between the rubbing processing axes 2A and 2B.
In the present invention, this intersection angle θ _X is set in the range of 2 ° to 15 °, preferably 3 ° to 12 °. In particular, in a preferred embodiment of the present invention, the rubbing treatment axis 2A may intersect the rubbing treatment axis 2B at a crossing angle θ _X (−θ _X ) in the counterclockwise direction with respect to the rubbing treatment axis 2B.

FIG. 2 is a schematic drawing of an example of a cell for explaining the operation of the ferroelectric liquid crystal. 21a and 21b are In ₂ O ₂ , S
A substrate (glass plate) covered with a transparent electrode made of a thin film of nO ₂ or ITO, between which an SmC ^* (chiral smectic C) phase or a liquid crystal molecule layer 22 is oriented so as to be perpendicular to the glass surface. Liquid crystal of SmH ^* (chiral smectic H) phase is enclosed. A thick line 23 represents a liquid crystal molecule, and the liquid crystal molecule 23 has a dipole moment (P⊥) 24 in a direction orthogonal to the molecule. substrate
When a voltage above a certain threshold is applied between the electrodes on 21a and 21b, the helical structure of the liquid crystal molecules 23 is unraveled, and all the dipole moments (P⊥) 24 are oriented in the electric field direction.
Can change the orientation direction. The liquid crystal molecule 23 has an elongated shape and exhibits refractive index anisotropy in the major axis direction and the minor axis direction thereof. Therefore, for example, if crossed Nicols polarizers are placed above and below the glass surface, the voltage application polarity is It can be easily understood that the liquid crystal optical modulation element changes its optical characteristics depending on the situation.

The surface stable ferroelectric liquid crystal cell in a bistable alignment state used in the liquid crystal element of the present invention can be made sufficiently thin (for example, 0.1 μm to 3 μm). As shown in FIG. 3, as the liquid crystal layer becomes thinner, the helical structure of the liquid crystal molecules is unwound and becomes a non-helical structure even when no electric field is applied, and the dipole moment P or P 'thereof is upward ( 34a) or downward (34b). When an electric field Ea or Eb having a polarity equal to or higher than a certain threshold is applied to such a cell by the voltage applying means 31a and 31b, the dipole moment corresponds to the electric field vector of the electric field Ea or Eb. And the liquid crystal molecules are oriented in either the stable state 33a or the second stable state 33b of FIG. 1 accordingly.

The effects obtained by this ferroelectric liquid crystal cell are, firstly, that the response speed is extremely fast, and that the alignment of the second liquid crystal molecules has bistability. The second point will be further explained with reference to FIG. 3, for example. When the electric field Ea is applied, the liquid crystal molecules are aligned in the first stable state 33a,
This state is stable even when the electric field is cut off. When a reverse electric field Eb is applied, the liquid crystal molecules are oriented in the second stable state 33b to change the orientation of the molecules, but they remain in this state even when the electric field is cut off. Further, unless the applied electric field Ea exceeds a certain threshold value, the respective alignment states are also maintained.

FIG. 4 (A) is a cross-sectional view schematically illustrating the alignment state of liquid crystal molecules generated in the alignment direction of the present invention, and FIG. 4 is a view showing its C-direct.

Reference numerals 61a and 61b shown in FIG. 4A represent an upper substrate and a lower substrate, respectively. A molecular layer 60 is composed of liquid crystal molecules 62, and the liquid crystal molecules 62 are arranged at different positions along the bottom surface 64 (circle) of the cone 63. 66a and 66b are rotation directions with respect to the adjacent substrates 61a and 61b of the bent structure of the molecular layer 60 which has the bent structure, respectively. 65
Symbols a and 65b are floating rotation directions of the liquid crystal molecules 62 adjacent to the adjacent substrates 61a and 61b, respectively.

FIG. 4 (B) is a diagram showing C-Direct. U _{1 in} FIG. 4 (B) is C-Direct 81 in one stable orientation state, and U ₂ is C-Direct 81 in the other stable orientation state.
Is. The C-director 81 is a projection of the molecular long axis onto a virtual plane perpendicular to the normal of the molecular layer 60 shown in FIG. 4 (A).

On the other hand, the orientation state produced by the conventional rubbed polyimide film is shown by the C-director diagram in FIG. 4 (C). In the orientation state shown in FIG. 4C, the tilt of the molecular axis is large from the upper substrate 61a to the lower substrate 61b, so that the tilt angle θ is small.

FIG. 5 (A) is a plan view for showing the tilt angle θ of the C-director 81 in the state of FIG. 4 (B) (referred to as the uniform alignment state), and is the C-director of FIG. 5 (B). 81
FIG. 4 is a plan view showing the tilt angle θ in the state of FIG. 4 (C) (referred to as splay alignment state). In the figure, 50 denotes the rubbing axis was subjected to a particular polyimide film of the present invention described above, the average molecular axis in 51a the orientation state U _1, 51b denotes an average molecular axis in the orientation state U _2, 52a are aligned state the average molecular axis in the S _1, 52 b denotes an average molecular axis in the orientation state S _2. The average molecular axes 51a and 51b can be converted by applying opposite polarity voltages exceeding the threshold voltage to each other. The same thing occurs between the average molecular axes 52a and 52b.

Next, the usefulness of the uniform alignment state for the optical response (afterimage) due to the reverse electric field V _rev will be described.

Capacitance C _i of the insulating layer of the liquid crystal cell (alignment layer), the capacitance of the liquid crystal layer to the C _LC and _the spontaneous polarization of the liquid crystal and Ps, V _rev causing after-image is expressed by the following equation.

FIG. 6 is a cross-sectional view schematically showing the distribution of charges in a liquid crystal cell, the direction of Ps, and the direction of a reverse electric field. FIG. 6 (A) shows the distribution state of the electric charge under the memory state before the application of the pulse electric field, and the direction of the spontaneous polarization Ps at this time is from the electric charge to the electric charge. Fig. 6 (B)
Is that the direction of the spontaneous polarization Ps immediately after the release of the pulse electric field is opposite to the direction in FIG. 6A (therefore, the liquid crystal molecules are inverted from one stable alignment state to the other stable alignment state). ), And the distribution state of the charge is the sixth
Since it is the same as in the case of FIG. (A), the reverse electric field V _rev ,
Occurs in the direction of the arrow. After a while, the reverse electric field V _rev disappears as shown in FIG. 6C, and the distribution state of the charge changes.

FIG. 7 shows a change in optical response in a splay alignment state caused by a conventional polyimide alignment film in place of a change in tilt angle θ. According to Figure 7, when the pulse electric field is applied, the average molecular axis S under splay alignment state (A) to an average molecular axis U ₂ under Yunifuomu alignment state in the vicinity of the maximum tilt angle along the direction of Shirushishirube X ₁ over-sheet Ute, immediately after pulsed electric field cancellation is working action of the reverse electric field V _rev as shown in FIG. 6 (B), Yashirube X ₂ average molecular axis under splay alignment state along the direction S (B ) tilt angle θ is reduced to, and by the action of attenuation of the reverse electric field V _rev as shown in FIG. 6 (C), to an average molecular axis S under splay alignment state along the direction of Yashirube X ₃ (C) A stable alignment state in which the tilt angle θ is slightly increased can be obtained. The optical response at this time is clarified in FIG.

According to the present invention, in the alignment state obtained by the alignment method using the above-mentioned fluorine atom-containing polyimide film,
Average molecular axis S (A), S under the spray condition shown in the figure
(B) and S (C) do not occur, and thus can be arranged on the average molecular axis that produces a tilt angle θ close to the maximum tilt angle. FIG. 9 shows the optical response of the present invention at this time. According to FIG. 9, it can be seen that the optical response is not deteriorated due to the afterimage and that the high contrast in the memory state is caused.

 Hereinafter, the present invention will be described according to examples.

Example 1 Two 1.1 mm-thick glass plates provided with a 1000Å-thick ITO film were prepared, and N-methylpyrrolidone / n-butylcellosolve of polyamic acid represented by the following formula was set on each glass plate = 5/1. Was applied for 30 minutes with a spinner at a rotation speed of 3000 rpm.

After film formation, heating and baking treatment was performed at 250 ° C. for about 1 hour. The film thickness at this time was 450Å. This coating film was subjected to a one-way rubbing treatment with a nylon touch cloth.

After that, alumina beads having an average particle size of about 1.5 μm were dispersed on one glass plate, and the rubbing shaft 2A was rotated counterclockwise with respect to the rubbing shaft 2B as shown in FIG. 1 (B). A cell was prepared by intersecting the rubbing shafts 2A and 2B such that the rubbing shafts 2A and 2B were crossed so as to be set at a position rotated by a degree of 2 and overlapping two glass plates.

The cell name "CS-1014", which is a ferroelectric smectic liquid crystal manufactured by Chitso Co., Ltd., was vacuum-injected into this cell in the isotropic phase and then gradually increased from the isotropic phase to 30 ° C at 0.5 ° C / h. It was possible to orient by cooling. The phase change in the cell of this example using "CS-1014" was as follows.

The subsequent experiments were carried out at a temperature of 25 ° C.

After sandwiching the above liquid crystal cell between a pair of 90 ° crossed Nicol polarizers, and applying a 30 μV pulse of 50 μsec,
Set the 90 ° crossed Nicols to the extinction position (darkest state), measure the transmittance at this time with a photomultiplier, and then apply a -30 V pulse of 50 μsec, and check the transmittance (bright state) at this time. When measured by the same method, the tilt angle θ was 15
And the transmittance in the brightest state was 44%, the transmittance in the darkest state was 1.0%, and the contrast ratio was 44: 1.

The optical response that caused the afterimage was less than 0.2 seconds.

When this liquid crystal cell was displayed by multiplexing drive using the drive waveform shown in Fig. 10, a high-contrast, high-quality display was obtained, and the entire screen was in a white state after the image was displayed by inputting a predetermined character. After erasing, the afterimage was illegible. In addition, S _N , S _{N + 1} , S in FIG.
_{N + 2} represents a voltage waveform applied to the scanning line, and I represents a voltage waveform applied to a typical information line.
(I-S _N ) is a composite waveform applied to the intersection of the information line I and the scanning line _SN . In this embodiment, V ₀ = 5 to 8 V and T = 20 to 70 μsec.

Examples 2 to 49 Cells were obtained in the same manner as in Example 1 except that the alignment control film and the liquid crystal material shown in Table 1 were used.

 The same test as in Example 1 was performed for each.

The results of contrast ratio and optical response time are shown in Table 2 (the polymerization degree of polyamic acid in the table is 70
0 to 2000).

Further, when a display was performed by the same multiplexing driving as in Example 1, the same results as in Example were obtained with respect to contrast and afterimage. Table 2 shows the results.

Comparative Examples 1 to 4 A cell was prepared in exactly the same manner as in Example 1 except that the alignment control film and the liquid crystal material shown in Table 3 were used (the degree of polymerization of the polyamic acid varnish in the table is 700 to 2000). Is). Table 4 shows the contrast ratio and the optical response of each cell.

Further, when the display was performed by the same multiplexing driving as in Example 1, the contrast was smaller than that in Example 1 and an afterimage was generated.

Table 4 Comparative example Contrast ratio Optical response blob (sec) 1 9: 1 1.5 2 7: 1 2.5 3 11: 1 1.2 4 7: 1 2.2 [Effect of the invention] As clarified in the above examples and comparative examples. In addition, according to the present invention, the contrast in the bright state and the dark state is high, the display contrast is very large especially in the case of multiplexing driving, and a high-quality display can be obtained, and there is an effect that a noticeable afterimage phenomenon does not occur.

[Brief description of drawings]

FIG. 1 (A) is a sectional view of a liquid crystal element of the present invention. FIG. 1 (B) is a plan view of the liquid crystal element used in the present invention. FIG. 2 is a perspective view showing an alignment state of a chiral smectic liquid crystal having a helical structure, and FIG. 3 is a perspective view showing an alignment state of a chiral smectic liquid crystal having a non-helical molecular arrangement. . FIG. 4 (A) is a sectional view showing an alignment state of the chiral smectic liquid crystal aligned by the alignment method of the present invention, and FIG. 4 (B) is a C-director diagram in the uniform alignment state, and FIG. (C) is a C-director diagram in a splay alignment state. FIG. 5 (A) is a plan view showing the tilt angle θ in the uniform alignment state, and FIG. 5 (B) is a plan view showing the tilt angle θ in the splay alignment state. FIG. 6 is a sectional view showing the charge distribution in the ferroelectric liquid crystal, the direction of the spontaneous polarization Ps, and the direction of the reverse electric field V _rev . FIG. 7 is a plan view showing changes in tilt angle θ when and after an electric field is applied. FIG. 8 shows an optical response characteristic in a conventional example, and FIG. 9 shows an optical response characteristic in an example of the present invention. FIG. 10 is a waveform diagram of the drive voltage used in this embodiment.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 62-18522 (JP, A) JP 62-127827 (JP, A) JP 62-175712 (JP, A) JP 64-1 49023 (JP, A) JP 63-151927 (JP, A) JP 1-158415 (JP, A)

Claims (15)

(57) [Claims] 1. A liquid crystal device sandwiching at least two stable chiral smectic liquid crystals in which formation of a helical alignment structure is suppressed between a pair of substrates, wherein at least one of the pair of substrates has at least one substrate. , A polyimide coating formed by bonding fluorine atoms in the molecule is provided, and each of the pair of substrates is subjected to an alignment treatment in one direction so as to intersect with each other on the surface adjacent to the chiral smectic liquid crystal. The chiral smectic liquid crystal has a layered structure composed of a plurality of liquid crystal molecules, and the layer has a bent structure, and the direction of rotation of the layer having the bent structure with respect to an adjacent substrate And a liquid crystal element adjacent to the adjacent substrate is in the same direction as the floating rotation direction of the liquid crystal molecules. 2. The liquid crystal element according to claim 1, wherein the unidirectional alignment treatment is a rubbing treatment. 3. The liquid crystal element according to claim 1, wherein both of the pair of substrates are provided with the oriented polyimide film. 4. The liquid crystal device according to claim 3, wherein the unidirectional alignment treatment is a rubbing treatment. 5. The liquid crystal device according to claim 1, wherein the polyimide has an imide residue in which a fluorine atom or a fluorine-containing residue is substituted. 6. The polyimide represented by the following general formulas (I) to (VI
The liquid crystal device according to claim 1, which has at least one of the structural units represented by II) in the molecule. General formula (I) (In the formula, 1 and m are 0 or an integer of 1-3.
l + m ≧ 1. ) General formula (II) (In the formula, R ₂₁ and R ₂₂ are a hydrogen atom, a fluorine atom, or
CF ₃ However, at least one of R ₂₁ and R ₂₂ is a fluorine atom or —CF ₃ . ) General formula (III) (In the formula, R ₃₁ , R ₃₂ , R ₃₃ and R ₃₄ are a hydrogen atom, a fluorine atom or -CF _3. However, at least one of R ₃₁ , R ₃₂ , R ₃₃ and R ₃₄ is a fluorine atom. or -CF _3.) general formula (IV) (In the formula, R ₄₁ , R ₄₂ , R _43, and R ₄₄ are a hydrogen atom, a fluorine atom, or —CF _3. However, at least one of R ₄₁ , R ₄₂ , R _43, and R ₄₄ is a fluorine atom. or -CF _3.) general formula (V) (Wherein, R ₅₁ , R ₅₂ , R ₅₃ , R ₅₄ , R ₅₅ , R ₅₆ , R ₅₇ , R ₅₈ , R
₅₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ and R ₁₄ are a hydrogen atom, a fluorine atom or —CF ₃ . However, R ₅₁ , R ₅₂ , R ₅₃ , R ₅₄ ,
R ₅₅ , R ₅₆ , R ₅₇ , R ₅₈ , R ₅₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ and R ₁₄
At least one of a fluorine atom or -CF _3. ) General formula (VI) (In the formula, R ₆₁ is Or CF _{2 n1} , and n ₁ is 0 or an integer of 1 to 7. R ₆₂ and R ₆₇ are a hydrogen atom or —CF ₃ , and R ₆₃ , R ₆₄ , R ₆₅ and R ₆₆ are a hydrogen atom, an alkyl group, a halogen atom or —CF ₃ . However, when n ₁ is 0, at least one of R ₆₂ , R ₆₃ , R ₆₄ , R ₆₅ , R ₆₆ and R ₆₇ is a fluorine atom or —CF ₃ . ) General formula (VII) (In the formula, R ₇₁ is Or CF _{2 n2} , and n ₂ is 0 or an integer of 1 to 7. R ₇₂ and R ₇₇ are hydrogen atoms or —CF ₃ , and R ₇₃ , R ₇₄ , R ₇₅ and R ₇₆ are hydrogen atoms, alkyl groups, halogen atoms or —CF ₃ . However, when n ₂ is 0, at least one of R ₇₂ , R ₇₃ , R ₇₄ , R ₇₅ , R ₇₆ and R ₇₇ is a fluorine atom or —CF ₃ . ) General formula (VIII) (Wherein, l _8, m ₈ and n ₈ is an integer of 0 or 1 to 3, l ₈
+ M ₈ + n ₈ ≧ 1. ) 7. The liquid crystal device according to claim 1, wherein the polyimide coating film that has been oriented in one direction is provided on an electrode formed on a substrate via an insulating film. 8. The liquid crystal device according to claim 1, wherein the film thickness of the polyimide film is 50 Å to 1000 Å, and the film thickness of the insulating film is 200 Å to 1000 Å. 9. The liquid crystal device according to claim 1, wherein the film thickness of the polyimide coating is 100 angstroms or less. 10. A polyimide coating film, which is oriented in one direction, is provided on electrodes formed on a pair of substrates via an insulating film, respectively, and the orientation treatment directions of both substrates are set to two directions.
The liquid crystal element according to claim 1, wherein the liquid crystal elements intersect at an angle of 15 degrees. 11. The crossing angle is 3 to 12 degrees.
10. The liquid crystal device according to item 10. 12. A unidirectional orientation treatment axis applied to the substrate side farther from the observation position is counterclockwise twice from a unidirectional orientation treatment axis applied to the substrate side closer to the observation position. The liquid crystal element according to claim 1, wherein the liquid crystal element is set at a position rotated by -15 degrees. 13. A unidirectional alignment treatment axis applied to the substrate side farther from the observation position is 3 degrees counterclockwise from a unidirectional alignment treatment axis applied to the substrate side closer to the observation position. The liquid crystal element according to claim 1, wherein the liquid crystal element is set at a position rotated by -12 degrees. 14. The liquid crystal device according to claim 1, wherein the chiral smectic liquid crystal produces at least two stable alignment states by cooling from a temperature higher than that of the smectic A phase. 15. Between the pair of substrates, at least molecules of a chiral smectic liquid crystal including molecules adjacent to the polyimide film are switched between the first and second states by applying an electric field having a polarity. The liquid crystal device according to claim 1.