JPH0468605B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to liquid crystal elements used in liquid crystal display elements, liquid crystal light shutters, etc., particularly liquid crystal elements using ferroelectric liquid crystal, and more specifically to improving the initial alignment state of liquid crystal molecules. This invention relates to a liquid crystal element with improved display characteristics. [Prior Art] Clark and Lagerwall have proposed a type of display element that uses the refractive index anisotropy of ferroelectric liquid crystal molecules to control transmitted light in combination with a polarizing element. (Japanese Patent Application Laid-Open No. 107216/1983, US Pat. No. 4,367,924, etc.). This ferroelectric liquid crystal generally has a chiral smectic C phase (SmC) in a specific temperature range.
*) or H phase (SmH ^* ), and in this state, takes either a first optically stable state or a second optically stable state in response to an applied electric field,
In addition, it has the property of maintaining its state when no electric field is applied, that is, it has bistability, and it also responds quickly to changes in the electric field, so it is expected to be widely used as a high-speed and memory-type display element. . In order for an optical modulation element using this bistable liquid crystal to exhibit predetermined driving characteristics, the liquid crystal placed between a pair of parallel substrates must maintain the above two stable characteristics, regardless of the applied state of the electric field. It is necessary that the molecules be in such a state that conversion between states can occur effectively. For example, for ferroelectric liquid crystals with SmC ^* or SmH ^* phase, SmC ^* or
It is necessary to form a region (monodomain) in which the liquid crystal molecular phase having the SmH ^* phase is perpendicular to the substrate surface, and the liquid crystal molecular axes are arranged approximately parallel to the substrate surface. By the way, as a method for aligning ferroelectric liquid crystal,
Generally, a method using an alignment control film subjected to uniaxial alignment treatment such as rubbing treatment or oblique evaporation treatment is known. Most of these conventional alignment methods have been applied to ferroelectric liquid crystals having a helical structure that does not exhibit bistability. For example, JP-A-60-
The alignment method disclosed in Japanese Patent Publication No. 230635 involves controlling the alignment of a ferroelectric liquid crystal using a polyimide film subjected to rubbing treatment under a state of a helical structure that does not exhibit bistability. However, when the conventional alignment control film as described above is applied to control the alignment of a ferroelectric liquid crystal with a non-helical structure exhibiting bistability as announced by Clark and Lagauer, the following problems arise. It had [Problems to be Solved by the Invention] According to experiments conducted by the present inventors, the tilt angle (described below) of a ferroelectric liquid crystal with a non-helical structure obtained by alignment using a conventional alignment control film (the angle shown in Figure 3) is smaller than the tilt angle (corresponding to 1/2 of the apex angle of the triangular pyramid shown in Figure 2 below) in a ferroelectric liquid crystal with a helical structure. There was found. In particular, the tilt angle θ of a ferroelectric liquid crystal with a non-helical structure obtained by alignment using a conventional alignment control film is generally about 10°, and the transmittance at that time is about 3 to 5% at most. . Thus, according to Clark and Lagauer, the tilt angle of a ferroelectric liquid crystal with a non-helical structure that achieves bistability should be the same as the tilt angle of a ferroelectric liquid crystal with a helical structure. However, in reality, the tilt angle θ in the non-helical structure is smaller than that in the helical structure. Furthermore, it has been found that the reason why the tilt angle θ in the non-helical structure is smaller than that in the helical structure is due to the twisted arrangement of the liquid crystal molecules in the non-helical structure. In other words, in a ferroelectric liquid crystal with a non-helical structure, the axis of the liquid crystal molecules adjacent to the upper substrate is 4 with respect to the normal to the substrate, as shown in Figure 4.
2, the liquid crystal molecules adjacent to the lower substrate are continuously twisted and arranged at a twist angle δ toward the axis 43 (twist alignment direction 44), and this means that the tilt angle θ in the non-helical structure is similar to that in the helical structure. This causes the tilt angle to be smaller than the tilt angle. Note that 41 in the figure represents a uniaxial alignment axis obtained by a rubbing process or an oblique vapor deposition process formed on the upper and lower substrates. By the way, in the case of a liquid crystal element that utilizes the birefringence of liquid crystal, the transmittance under crossed Nicols is I/Io=sin ² 4θsin ² △nd/λπ In the formula: Io is the incident light intensity, I is the transmitted light intensity, θ is the tilt angle, Δn is the refractive index anisotropy, d is the thickness of the liquid crystal layer, and λ is the wavelength of the incident light. It is expressed as The tilt angle θ in the non-helical structure described above appears as an angle between the average molecular axes of the twisted liquid crystal molecules in the first and second alignment states. According to the above formula, the tilt angle θ is
The maximum transmittance occurs when the angle is 22.5°, but the tilt angle θ in a non-helical structure that achieves bistability is at most about 10°, so when considering application as a display device, Its transmittance is 3-5%
There are problems in which degree is not enough. It is therefore an object of the present invention to solve the aforementioned problems, namely that at least two stable states;
In particular, the object of the present invention is to provide a liquid crystal element in which the tilt angle of a non-helical ferroelectric liquid crystal realizing bistability is increased, thereby improving the transmittance when the pixel shutter is opened. Another object of the present invention is to provide a liquid crystal element using an alignment control film suitable for forming monodomains of ferroelectric liquid crystal. [Means for Solving the Problems] and [Operation] That is, the present invention provides a pair of parallel substrates and a plurality of layers of molecules that are perpendicular or substantially perpendicular to the planes of the pair of parallel substrates. In a liquid crystal element having an aligned ferroelectric liquid crystal, at least one of the pair of parallel substrates has a coating of a polymeric substance that preferentially orients the plurality of layers in one direction, and in particular, A coating of a polymeric substance is formed by a monomolecular film or a monomolecular cumulative film of a polymeric compound having both a hydrophilic part and a hydrophobic part in the same molecule, and the monomolecular film or monomolecular cumulative film is further formed on the surface of the substrate. This liquid crystal element is characterized by being subjected to an alignment treatment for preferentially aligning a film in one direction. In particular, in the liquid crystal element of the present invention, the substrate surface is subjected to an alignment treatment, and specifically, fine irregularities are formed on the substrate surface in order to preferentially orient a monomolecular film or a monomolecular cumulative film in one direction. or a liquid crystal element in which the surface of the substrate is rubbed in a certain direction. The present invention will be explained in detail below. FIG. 1 is a sectional view showing one embodiment of the liquid crystal element of the present invention. The liquid crystal element shown in FIG. 1 includes a pair of upper and lower substrates 11a and 11b which are arranged in parallel and have fine irregularities on their surfaces, and transparent electrodes 12a and 12b wired to each substrate. A ferroelectric liquid crystal, preferably a non-helical ferroelectric liquid crystal 13 exhibiting at least two stable states, is arranged between the upper substrate 11a and the lower substrate 11b. The transparent electrodes 12a and 12b described above are used to multiplex drive the ferroelectric liquid crystal 13.
It is preferable that the wires are arranged in a stripe shape, and the stripe shapes are arranged to intersect with each other. In the liquid crystal element of the present invention, alignment control films 14a and 14b formed of a monomolecular film or a monomolecular cumulative film of a polymer compound are disposed on substrates 11a and 11b, respectively. The polymer compound constituting the monomolecular film or monomolecular cumulative film in the present invention is a polymer that has both a hydrophobic part and a hydrophilic part in its molecule, and these parts are arranged in a well-balanced higher order structure. Any compound can be used. In general, typical constituent elements of the hydrophobic moiety are alkyl groups and unsaturated hydrocarbon groups, and both linear and branched groups can be used. Further examples include hydrophobic groups such as fused polycyclic phenyl groups such as phenyl, naphthyl, anthranyl, etc., and chain polycyclic phenyl groups such as biphenyl and terphenyl. Each of these may be used alone or in combination to form the hydrophobic portion of the molecule. On the other hand, the most typical constituent elements of the hydrophilic moiety are, for example, carboxyl groups and their metal salts and amine salts, sulfonic acid groups and their metal salts and amine salts, sulfonamide groups, amide groups, amino groups, and imino groups. , a hydroxyl group, a quaternary amino group, an oxyamino group, an oximino group, a diazonium group, a guanidine group, a hydrazine group, a phosphoric acid group, a silicate group, an aluminate group, and other hydrophilic groups. These also constitute the hydrophilic portion of the above molecule either singly or in combination. Here, having a hydrophilic part and a hydrophobic part in a molecule means, for example, that a molecule has both one hydrophilic group and one hydrophobic group as described above, or one or more hydrophobic groups in a molecule. When it has a hydrophilic group and a hydrophobic group, one part of the entire molecule is hydrophilic in relation to other parts, while the latter part is hydrophobic in relation to the former part. means. In polymer compounds, hydrophobic groups and hydrophilic groups have not only one-dimensional arrays but also secondary structures such as α-helices and β-sheet structures, and even higher-order structures such as three-dimensional structures. It is necessary that hydrophobic groups and hydrophilic groups are distributed in a well-balanced higher-order structure. By arranging and orienting molecules having these higher-order structures in a highly ordered manner, it is expected that an orientation control function not found in conventional orientation control films will be exhibited. Specific examples of the above-mentioned polymer compounds constituting the monomolecular film or monomolecular cumulative film in the present invention include the following polymers. Polypeptide derivatives For example, synthetic polypeptides include poly-γ-methyl-L-glutamate (PMLG) poly-γ-benzyl-L-glutamate (PBLG) poly-ε-benzyloxycarbonyl-L-
Polypeptides with a molecular weight of 10,000 to 1 million, preferably 100,000 to 700,000, obtained by dehydration polymerization of amino acids and their derivatives such as lysine (PBCL), and natural proteins such as bacteriorhodopsin, cytochrome C, and chymotrypsin. Examples include particulate proteins such as bovine serum albumin and trypsin. Aleic anhydride polymer derivatives include, for example, poly-n-octadecyl vinyl ether-maleic anhydride, poly-octadecene-1-maleic anhydride, and poly-styrene-maleic anhydride. A molecular weight of 1,000 to 100,000 is preferable. Polyamic acid derivatives Acid anhydrides such as 3,3',4,4'-diphenyltetracarboxylic acid or pyromethic acid and p-phenylenediamine, 4,4'-diaminodiphenyl and 4,4'-diaminoterphenyl , and further, long-chain alkylamine salts of polyamic acids obtained by 1:1 dehydration condensation with diamino compounds such as 4,4'-diaminodiphenyl ether (e.g., N(CH ₃ ) ₂ (-CH ₂ ) _-o CH ₃ , 10≦n≦25). These polyamic acid monomolecular films are turned into polyimide monomolecular films by acid and heat treatment, and this polyimide film is used as an alignment control film. An overview of the method for producing a monomolecular film or a monomolecular cumulative film in the present invention will be explained using an example of a film forming apparatus using the Langmiur-Blodget method devised by the generally well-known research group of Kuhm. do. In this example, the liquid for developing the monomolecular film is water. First, the above-mentioned molecules are used as film-forming molecules and are dissolved in a volatile solvent such as benzene or chloroform. This solution is dropped into a tank (trough) using a dropper or the like, and a monomolecular film of the film-forming molecules is developed on the aqueous phase. Next, the float (or partition plate) provided to prevent the monomolecular film from spreading freely on the aqueous phase and spreading too much is moved to reduce the spread area of the monomolecular film and to prevent the monomolecular film from spreading too much. Apply surface pressure to the monolayer until it becomes a two-dimensional solid film. While maintaining this surface pressure, the monomolecular film is transferred onto the substrate by gently moving the substrate up and down perpendicular to and across the water surface. A monomolecular film is produced in the above manner, and a monomolecular cumulative film having a desired degree of accumulation is formed by repeating the above-mentioned up and down operations. The case where a monomolecular film or a monomolecular cumulative film is created using Kuhm's film forming apparatus has been described above. The method is not limited to the above, and it is possible to use a wide range of other film forming apparatuses based on the principles of the Langmire-Blodget method, such as the horizontal deposition method and the cylindrical rotation method. It is known that in a monomolecular film or a monomolecular cumulative film of a polymer compound formed on a substrate in this manner, the molecules constituting the film exhibit a constant orientation characteristic with respect to the direction in which the substrate is pulled up. That is, the monomolecular film or monomolecular cumulative film of the polymer compound is considered to have a uniaxial orientation control effect in the dipping direction. These alignment films can also function as an insulating film, and are usually formed with a thickness in the range of about 50 Å to 1 μm, preferably 100 Å to 1000 Å. By applying an external factor when transferring the monomolecular film developed on the liquid surface to the substrate, the arrangement or orientation of the film constituent molecules after accumulation can be further enhanced. It becomes possible to improve the uniaxial orientation control function. The external factor specifically refers to the substrate surface shape (unevenness), and in the present invention, a substrate having grooves, specifically about 0.1 μm to 10 μm, preferably
This can be obtained by using a substrate having grooves (hereinafter referred to as groups) with a pitch of about 0.1 μm to 1 μm or a substrate rubbed in a certain direction. The arrangement and orientation of the constituent molecules of the monomolecular film or monomolecular cumulative film can be significantly improved, and the alignment control films 14a and 14b can be obtained which have been subjected to uniaxial alignment treatment. In the present invention, the grooves can be formed by dry etching the surface of the glass substrate using a known lithography technique. and,
An ITO electrode is sputtered onto the groove to form a transparent electrode substrate. However, on the glass substrate, first
After forming an ITO electrode, organic resist or SiO ₂ grooves are formed on the surface of the electrode substrate, which may be used as a transparent electrode substrate. The shape of the group is preferably one with sharp edges and a groove depth of about 20 Å to 1000 Å, preferably 100 Å to 500 Å. Next, a ferroelectric liquid crystal having molecular alignment forming a plurality of layers perpendicular to the planes of a pair of parallel substrates used in the liquid crystal element of the present invention will be described. FIG. 2 schematically depicts an example of a ferroelectric liquid crystal cell using a helical structure. 21a and 2
1b is In ₂ O ₃ , SnO ₂ or ITO (Indium Tin
A substrate (glass plate) coated with a transparent electrode such as SmC ^* (chiral smectic C), in which multiple liquid crystal molecular layers 22 are oriented perpendicularly to the glass substrate surface. ) liquid crystal is enclosed. A thick line 23 represents a liquid crystal molecule, and this liquid crystal molecule 23 has a dipole moment (P ⊥) 24 in the direction perpendicular to the molecule.
have. At this time, the angle forming the apex angle of the triangular pyramid represents the tilt angle in the chiral smectic phase of the helical structure. Substrates 21a and 21
When a voltage higher than a certain threshold is applied between the electrodes on b, the helical structure of the liquid crystal molecules 23 is unraveled, and the alignment direction of the liquid crystal molecules 23 is changed so that the dipole moment (P ⊥) 24 is all oriented in the direction of the electric field. I can do it. However, the ferroelectric liquid crystal using this helical structure returns to the original helical structure when no electric field is applied, and does not exhibit the bistability described below. In a preferred embodiment of the invention, a ferroelectric liquid crystal element as shown in FIG. 3 can be used which has at least two stable states, especially a bistable state. In other words, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1μ), the helical structure of the liquid crystal molecules unravels even in the absence of an applied electric field and becomes a non-helical structure, as shown in Figure 3. child moment
Pa or Pb takes either an upward direction 34a or a downward direction 34b, and a bistable state is formed.
When an electric field Ea or Eb of different polarity above a certain threshold value is applied to such a cell as shown in Fig. 3,
The dipole moment electric field Ea or Eb changes direction to an upward direction 34a or a downward direction 34b in accordance with the electric field vector, and accordingly, the liquid crystal molecules are placed in either the first stable state 33a or the second stable state 33b. Orient. At this time, 1/2 of the angle formed by the first and second stable states corresponds to the tilt angle θ. There are two advantages to using such a ferroelectric liquid crystal as an optical modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has bistability. To explain the second point using, for example, FIG. 3, when the electric field Ea is applied, the liquid crystal molecules are oriented in the first stable state 33a, but
This state remains stable even when the electric field is turned off. Furthermore, when an electric field Eb in the opposite direction is applied, the liquid crystal molecules are oriented to a second stable state 33b and the orientation of the molecules is changed, but they remain in this state even after the electric field is turned off. In order to effectively realize such fast response speed and memory effect due to bistability, it is preferable for the cell to be as thin as possible, and generally 0.5μ to 20μ, especially 1μ to 5μ is suitable. ing. A liquid crystal electro-optical device having a matrix electrode structure using this type of ferroelectric liquid crystal has been proposed, for example, by Clark and Ragaval in US Pat. No. 4,367,924. Examples of the ferroelectric liquid crystal that can be used in the liquid crystal element of the present invention include p-decyloxybenzylidene-p'-amino-2-methylbutylcinnamate (DOBAMBC), p-hexyloxybenzylidene-p'-amino- 2-Chlorpropylcinnamate (HOBACPC), p-decyloxybenzylidene-p'-amino-2-methylbutyl, α-cyanocinnamate (DOBAMBCC), p-tetradecyloxybenzylidene-p'-amino-2-methylbutyl- α-cyanocinnamate (TDOBAMBCC), p-octyloxybenzylidene-p′-amino-2-methylbutyl-α-chlorocinnamate (OOBAMBCC), p-octyloxybenzylidene-p′-amino-2-methylbutyl-α- Methyl cinnamate, 4,4'-azoxycinnamic acid bis(2-methylbutyl) ester, 4-o-(2-methyl)butylresocylidene-4'-octylaniline, 4-
(2′-Methylbutyl)phenyl-4′-octyloxybiphenyl-4-carboxylate, 4-hexyloxyphenyl-4-(2″-methylbutyl)
Biphenyl-4'-carboxylate, 4-octyloxyphenyl-4-(2''-methylbutyl)biphenyl-4'-carboxylate, 4-heptylphenyl-4-(4''-methylhexyl)biphenyl-4'-carboxy 4-(2″-methylbutyl)phenyl-4-(4″-methylhexyl)biphenyl-4′-carboxylate, which can be used alone or in combination of two or more, and Other cholesteric liquid crystals or smectic liquid crystals can be included as long as they exhibit ferroelectricity. Further, in the present invention, a chiral smectic phase can be used as the ferroelectric liquid crystal, and specifically,
Chiral smectonic C phase (SmC ^* ), H phase (SmH ^* ), I phase (SmI ^* ), K phase (SmK ^* ) and G phase (SmG ^* ) can be used. Next, in the present invention, the uniaxial alignment axes of the upper and lower alignment control films controlled by the group axis or rubbing axis as described above can be parallel to or intersect with each other, but in the present invention, as shown in FIG. It is preferred that the uniaxial orientation axes intersect. That is, as shown in FIG. 5, on the uniaxially oriented surfaces formed on the upper and lower substrates, in the absence of an electric field, the uniaxially oriented axes 51 and 52 are twisted in the direction 44 shown in FIG. 4. They intersect at angles in opposite directions 55. When the chiral smectic phase is oriented in the presence of such a uniaxially oriented surface by lowering the temperature of the phase on the higher temperature side, the axes 53 of the liquid crystal molecules adjacent to the upper and lower substrates become parallel to each other. In this chiral smectic phase, the uniaxial orientation axis 5
The liquid crystal molecules are oriented at a tilt angle θ (or -θ) from the axis 54 of the liquid crystal molecules in the smectic A phase (SmA) oriented at an intermediate angle between 1 and 52,
First and second stable states (a first stable state when the tilt angle is θ and a second stable state when the tilt angle is −θ) can be formed. In this liquid crystal element, when one polarization axis 56 of crossed Nicols is set parallel to the axis 53 of the liquid crystal molecules corresponding to the molecular axis direction in the first stable state, and the other polarization axis 57 is made orthogonal to the polarization axis 56, the maximum You can get contrast. In a preferred embodiment of the present invention, the above-mentioned tilt θ can be increased to an angle that is equal to or comparable to the tilt in the helical structure by the AC application pre-treatment. Let the tilt angle at this time be θ'. The AC used at this time is a voltage of 20 to 500.
Frequency 10~ at volts, preferably 30~150 volts
500 Hz, preferably 10 to 200 Hz can be used, and the AC application pretreatment can be performed with an application time of about several seconds to 10 minutes. Further, such AC application pre-processing is performed at a stage before writing is performed on the liquid crystal element according to, for example, a video signal or an information signal, and is preferably performed to reduce the wait time when such a liquid crystal element is incorporated into a device and the device is operated. The above-mentioned alternating current application pretreatment can be performed, or alternatively, the alternating current application pretreatment can be performed even during the manufacture of such a liquid crystal element. Such AC application pretreatment is based on an experiment conducted by the present inventors, namely, when an AC electric field is applied to a ferroelectric liquid crystal element having a bistable state shown in FIG. 4 or FIG. 5, the tilt angle θ before application is The tilt angle θ' can be increased to the same extent as the tilt in the helical structure, and in the case of the state shown in FIG. The angle θ' can be maintained. In addition, such AC application pretreatment is performed on ferroelectric liquid crystals with large spontaneous polarization (for example, 5 nc/cm ² or more at 25°C, preferably 10 nc/cm ² to 300 nc/cm ² ; nc is a unit indicating nanocoulombs). It is valid for This spontaneous polarization can be measured using a triangular wave application method ^* in a 100μ cell. ^* Japanese Journal of Applied Physics
K. Miyasato (K. Applied Physics) No. 22 (10), pp. 661-663 (1983).
Miyasato et al.
Triangular Waves for Measuring Spontaneous
Polarization in Ferroelectric Liquid
According to the present invention, the above-mentioned alignment control films 14a and 14
The use of one of the alignment control films in b can be omitted. Further, in another specific example of the present invention, one of the alignment control films 14a and 14b described above may be replaced by another alignment control film. Other coatings forming the orientation control film include, for example, polyvinyl alcohol, polyamide,
polyester, polyimide, polyamideimide,
Examples include coatings such as polyesterimide. Further, as another orientation control film, a film formed by oblique vapor deposition of an inorganic substance such as SiO or SiO ₂ can also be used. [Example] Hereinafter, the present invention will be explained by showing Examples and Comparative Examples, and further by giving specific examples. Example 1 Two glass plates with a thickness of 0.7 mm were prepared, each was scrubbed with a neutral detergent, heat treated at 120°C for 30 minutes, and then spin-coated with the surface treatment agent HMDS [Tokyo Chitsuso Co., Ltd.]. 2500rpm.30sec) and then 150
Heat treatment was performed at ℃ for 10 minutes. A negative resist agent RD-2000N-10 [Hitachi Chemical Co., Ltd.] was applied to the glass substrate surface-treated in this way under the following conditions. 1st (1ST) 4000rpm 1sec 2nd (2ND) 3000rpm 40sec Heat treatment at 80℃ for 20 minutes reduces the film thickness to 0.7μ
A resist film of m was formed. This negative resist is exposed to deep UV exposure equipment.
After a latent image of a mask pattern was formed by exposure with PLA-500S for 2.5 counts, this latent image was developed at 23° C. for 80 seconds using a dedicated developing solution. Finally, by washing with pure water, drying, and post-lithifying for 60 seconds, 1μm pitch (L0.5μm/
A grating pattern having a diameter of 0.5 μm) was formed on the surface of the glass substrate. Using the resist pattern formed as described above as a mask, grooves (grating pattern) having a groove depth of 500 Å were etched on the surface of the glass substrate using a parallel plate dry etching apparatus under the following conditions. Etching gas CF ₄ Flow rate 10 SCCM Pressure 7 Pa Input power 100 W Etching rate 250 Å/min In this example, a dry etching method was used to form a pattern on the glass substrate surface, but conventional lift-off methods such as EB evaporation of SiO ₂ may also be used. is also possible. An ITO electrode having a film thickness of 1000 Å was formed on the grooved glass surface thus created by a lift-off method. Next, the synthetic polypeptide poly-γ-benzyl-L-glutamate (PBLG, molecular weight 640,000) was dissolved in methylene chloride (concentration 1 mg/ml), and then pure water at a temperature of 17°C (conductivity 0.03 μs/cm) was dissolved in methylene chloride (concentration 1 mg/ml). ). After the solvent methylene chloride was removed by evaporation, the surface pressure was increased to 5 dyn/cm to form a monolayer film on the water surface. After keeping the surface pressure at 5 dyn/cm and leaving it for 1.5 hours, the groove axis of the ITO electrode substrate crosses the water surface vertically or almost vertically at a vertical speed.
20 layers were accumulated by gently moving up and down at 2.5 mm/min. Under this accumulation condition, PBLG is accumulated only during pulling, resulting in a Z-type monomolecular accumulated film (film thickness approximately 220 Å).
I got it. Two glass substrates were assembled into cells so that the groove axes of the upper and lower electrode substrates were parallel to each other. The cell membrane (distance between the upper and lower substrates) was held by photoresist spacers previously formed on the lower substrate. The liquid crystal mixture described below is injected under vacuum into this liquid crystal cell (this is called a 1.8 μm cell) in an isotropic phase, and then the liquid crystal is oriented by slowly cooling it from the isotropic phase to 30°C at a rate of 0.5°C/h. did it. Subsequent experiments were conducted at 30°C. Mixed liquid crystal (weight ratio) 2 1 0.3 (Temperature range of SmC ^* : 3 to 35°C) When this cell was observed under crossed nicol conditions, monodomains were obtained that formed a chiral smectic C phase with a uniform, defect-free, non-helical structure. Pulse electric field (20V, 500μsec) is applied to this liquid crystal cell.
By applying a By applying a pulsed electric field of opposite polarity (-20V, 500μsec), the state is transferred to the other stable molecular alignment state and made into a bright state, and then the liquid crystal cell is rotated again to adjust the angle at which the darkest state occurs. i got you. The positions of the two darkest states described above correspond to the detection of a stable average molecular axis of the liquid crystal, and the angle between these two states corresponds to the tilt angle 2θ. When the tilt angle of the above-mentioned liquid crystal cell was thus measured, it was 14°. That is, the liquid crystal cell of this example exhibited a large tilt angle that was not found in the conventional cell under the memory state achieved by the bistable chiral smectic phase. Furthermore, when the amount of transmitted light in this liquid crystal cell in its brightest state was measured, it was 12%. The amount of transmitted light at this time was measured using a photometer. Next, the present inventors measured the twist alignment angle and direction of the liquid crystal molecules with respect to the normal direction of the substrate in the liquid crystal cell described above. For this measurement, a liquid crystal cell (referred to as a 3.0 μm cell) was prepared in exactly the same manner, except that 3.0 μm alumina beads were used as spacers instead of the 1.8 μm photoresist spacers used in the liquid crystal cell described above. Created. To measure the twist alignment angle of liquid crystal molecules, rotate one of the analyzers from the intersection angle at the darkest state under crossed Nicols, change the intersection angle, find the position where the state becomes even darker, and then The angle at which one analyzer was rotated was measured. This angle is
This corresponds to the twist angle δ mentioned above. Therefore, regarding the 3.0 μm cell mentioned above, if clockwise rotation is considered positive (+) and counterclockwise rotation is negative (-) from the perspective of the observer, then the analyzer must be rotated 5 to 6 degrees in the negative direction from the orthogonal Nicols. Then, the liquid crystal cell could be rotated to search for the dark state. Further, even when the polarizer was rotated 5 to 6 degrees in the positive direction from crossed Nicols, a dark state was similarly obtained. Therefore, the liquid crystal molecules in this device form a twisted arrangement in the positive direction, and the long axes of the liquid crystal molecules on the adjacent surfaces of the upper and lower substrates are twisted with a twist angle δ of 5 to 6 degrees. I found out. Example 2 Completely the same as Example 1, except that instead of the parallel rubbing axes used in the 1.8 μm cell of Example 1, rubbing axes crossed at angles of 45° and 20° in the negative direction (−) were used. A liquid crystal cell was created in a similar manner. When the tilt angles of this liquid crystal cell were measured, they were all 14°. In both of these two liquid crystal cells, SmA exists on the high temperature side of SmC ^* , but
It was found that the optical axis of SmA lies on the bisector of the angle formed by the crossed rubbing axes. Next, a high electric field alternating current with a voltage of 70 volts and a frequency of 70 Hz was applied to each of the two types of liquid crystal cells described above for about 5 minutes (alternating current application pretreatment). The tilt angle θ' at this time was measured. The results are shown in Table 1 below.

[Table] For these two types of liquid crystal cells, the twist angle δ shown in Figure 4 was measured using the same method used to measure the twist angle δ in the liquid crystal element of the 3 μm cell described above. In the liquid crystal device using crossed rubbing axes of 45° and -20°, no twist angle δ of the liquid crystal molecules with respect to the normal to the upper and lower substrates was observed, and it was found that the liquid crystal molecular axes adjacent to the upper and lower substrates were parallel to each other. Ivy. Moreover, in a liquid crystal device using crossed rubbing axes with crossing angles of -45° and -20°, the tilt angle θ' shown in Table 1 is maintained even if +20 volts and -20 volts driving rectangular pulses are applied alternately at 1 msec. We were able to.
This is true when a time-division driving method such as that described in JP-A-59-193426 and JP-A-59-19347 is actually applied to this liquid crystal element according to video signals and information signals. This corresponds to the point that the maximum tilt angle θ' can be maintained even if Also, when the transmittance at this time was measured, it was about 17% in both cases. The direction of the twisted state with twist angle δ is determined by the interaction between the substrate and the liquid crystal near its interface. In other words, whether the polarization direction of liquid crystal molecules near the interface is inward or outward with respect to the substrate is determined by the properties of the substrate, and if the same alignment control film is used for both the upper and lower substrates, the liquid crystal between the substrates is forced to oriented in a twisted arrangement. When the direction of the twisted alignment along the normal line of the substrate and the direction of shift of the uniaxial alignment axis are the same, the molecules near the interface of the substrates are aligned in the direction of the alignment axis of each substrate, making the twisted alignment state more stable. After the above-mentioned alternating current application pretreatment, a state of tilt angle θ' results in a metastable orientation state. In the state of tilt angle θ' after the above-mentioned alternating current application pretreatment, the polarization of molecules near the interface must be arranged inward on one substrate and outward on the other substrate. When the uniaxial alignment axis is shifted in the opposite direction to the twisted alignment direction of the liquid crystal, that is, when the uniaxial alignment axis is crossed at an angle opposite to the twisted alignment direction,
The stabilization energy due to forced anchoring by the uniaxial orientation axis is greater than the stabilization energy due to the interaction between molecular polarization and the interface, and therefore a state with a stable tilt angle θ' can be realized. Therefore, in order to realize a ferroelectric liquid crystal element with high transmittance, it is necessary to eliminate the twisted alignment state and to stabilize the ideal alignment state added by the AC application pretreatment. It is necessary that the orientation axes be offset from each other. The direction is opposite to the direction in which the liquid crystal is twisted, with a twist angle δ determined by the interface between the liquid crystal and the substrate. Comparative Example 1 As the alignment control film used when creating the 1.8 μm cell in Example 1, 3,3',4,4'-diphenyltetracarboxylic acid anhydride and p-phenylenediamine were mixed in a 1:1 ratio. The coating film of polyamic acid obtained by dehydration condensation reaction at a molar ratio of 3.5% by weight N-methyl-2-pyrrolidone solution was replaced with a polyimide coating film formed by dehydration and ring closure, and the groove was further improved. A liquid crystal cell was created in exactly the same manner, except that a non-containing substrate was used. When the tilt angle θ and transmittance of this liquid crystal cell were measured in the same manner as in Example 1, the tilt angle θ was 6° to 8°, and the transmittance at that time was about 3% to 5%. That is, this comparison cell has a small tilt angle under a memory state realized by a bistable chiral smectic phase, and its transmittance is completely insufficient for application to a display device. Comparative Example 2 As the alignment control film used when creating the 1.8 μm cell in Example 1, 3,3',4,4'-diphenyltetracarboxylic acid anhydride and 4,4'-diaminodiphenyl were combined :3.5% by weight N-methyl- of polyamic acid obtained by dehydration condensation reaction at a molar ratio of 1
A liquid crystal cell was prepared in exactly the same manner, except that the coating film of 2-pyrrolidone liquid was replaced with a polyimide coating film formed by dehydration and ring closure, and rubbed, and a substrate without grooves was used. When the tilt angle θ and transmittance of this liquid crystal cell were measured in the same manner as in Example 1, the tilt angle θ was 6° to 7°, and the transmittance at that time was about 3% to 4%. Comparative Example 3 As the alignment control film used when creating the 1.8 μm cell in Example 1, 3,3',4,4'-diphenyltetracarboxylic acid anhydride and 4,4'-diaminoterphenyl were combined into 1 : Substituting a polyimide coating film formed by dehydrating and ring-closing a coating film made of a 3.5% by weight N-methyl-2-pyrrolidone solution of polyamic acid obtained by dehydration condensation reaction at a molar ratio of 1:1 and rubbing treatment; Furthermore, a liquid crystal cell was created in exactly the same way, except that a substrate without grooves was used. When the tilt angle θ and transmittance of this liquid crystal cell were measured in the same manner as in Example 1, the tilt angle θ was 5° to 7°, and the transmittance at that time was about 3% to 4%. Example 3 A liquid crystal cell was manufactured in exactly the same manner as in Example 1, except that a transparent electrode substrate subjected to ITO electrode rubbing treatment was used in place of the grooved transparent electrode substrate used in the 1.8 μm cell in Example 1. Created. When the tilt angle θ and transmittance of this liquid crystal cell were measured in the same manner as in Example 1, the tilt angle θ was 12° and the transmittance at that time was 9%. Example 4 Instead of the grooved transparent electrode substrate used in the 1.8 μm cell of Example 1, 3,3',4,4'-diphenyltetracarboxylic anhydride and p-phenylenediamine were used in a 1:1 ratio. 3.5% by weight of N-methyl-2 of polyamic acid obtained by dehydration condensation reaction at a molar ratio of
- In the same manner as in Example 1, using a transparent electrode substrate in which a polyimide coating film formed by forming a coating film of a pyrrolidone solution on an ITO electrode and then subjecting the coating film to a rubbing treatment by dehydrating and ring-closing the coating film, Two layers of PBLG were accumulated. A liquid crystal cell was then produced in exactly the same manner as in Example 1. When the tilt angle θ and transmittance of this liquid crystal cell were measured in the same manner as in Example 1, the tilt angle θ was 13° and the transmittance at that time was 10%. Examples 5 to 9 Completely the same method as in Example 1, except that the alignment control film used in the 1.8 μm cell in Example 1 was used in place of the monomolecular cumulative film of the polymer compound listed in Table 2 below. After creating a liquid crystal cell, the tilt angle θ and the transmittance at that time in the liquid crystal cell were measured using the same method. The results are shown in Table 2.

[Table] [Effects of the Invention] By controlling the alignment using the liquid crystal element of the present invention, a ferroelectric liquid crystal, particularly a monodomain of a ferroelectric liquid crystal having at least two stable states obtained by a non-helical structure, can be obtained. The first effect is that the non-helical structure of the ferroelectric liquid crystal causes tilting under at least two stable states, especially under bistable states (i.e., under memory states). The second point is that the angle θ can be increased.
It has excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of the liquid crystal device of the present invention, FIG. 2 is a perspective view schematically showing a liquid crystal device using a ferroelectric liquid crystal with a helical structure, and FIG. 3 is a non-helical structure. FIG. 4 is an explanatory diagram showing the relationship between the uniaxial orientation axis of the substrate and the axis of the ferroelectric liquid crystal molecules having a non-helical structure, and FIG. The figure is an explanatory diagram showing the relationship between the uniaxial alignment axis and the axis of liquid crystal molecules used in the liquid crystal element of the present invention. 11a...upper substrate, 11b...lower substrate, 12
a, 12b...transparent electrode, 13...ferroelectric liquid crystal, 14a, 14b...alignment control film, 21...substrate, 22...liquid crystal molecule layer, 23...liquid crystal molecule, 2
4...Dipole moment, 33a...First stable state, 33b...Second stable state, 34a...Upward dipole moment, 34b...Downward dipole moment,...Tilt angle in helical structure, θ
... Tilt angle in non-helical structure, Ea, Eb ... Electric field, 41 ... Uniaxial alignment axis formed on the upper and lower substrates,
42...Axes of liquid crystal molecules adjacent to the upper substrate, 43...
...Axes of liquid crystal molecules adjacent to the lower substrate, 44... Direction of twisted arrangement, δ... Torsion angle, 51... Uniaxial alignment axis formed on the upper substrate, 52... Uniaxial alignment axis formed on the lower substrate , 53...Axes of liquid crystal molecules adjacent to the upper and lower substrates, 54...Axes of liquid crystal molecules in SmA,
55...Direction opposite to the direction of the twisted arrangement, 56...
One polarization axis of crossed Nicols, 57...the other polarization axis of crossed Nicols.

Claims (1)

[Claims] 1. A liquid crystal element having a pair of parallel substrates and a ferroelectric liquid crystal having molecules arranged to form a plurality of layers perpendicular or substantially perpendicular to the planes of the pair of parallel substrates. At least one of the pair of parallel substrates has a coating of a polymeric substance that preferentially orients the plurality of layers in one direction, and in particular, the coating of the polymeric substance has hydrophilic properties within the same molecule. formed from a monomolecular film or a monomolecular cumulative film of a polymer compound having both a hydrophobic part and a hydrophobic part, and further for orienting the monomolecular film or monomolecular cumulative film preferentially in one direction on the surface of the substrate. A liquid crystal element characterized by being subjected to alignment treatment. 2. The liquid crystal element according to claim 1, wherein the alignment treatment applied to the substrate surface is minute irregularities formed on the substrate surface. 3. The liquid crystal element according to claim 1, wherein the alignment treatment applied to the substrate surface is a rubbing treatment. 4. The liquid crystal element according to claim 1, wherein the ferroelectric liquid crystal is a liquid crystal having at least two stable states. 5. The liquid crystal element according to claim 1, wherein the ferroelectric liquid crystal is a bistable liquid crystal. 6. The liquid crystal element according to claim 1, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal. 7. The liquid crystal device according to claim 1, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal with a non-helical structure.