JPS60125822A - Orientation control method of liquid crystal - Google Patents

Abstract

PURPOSE:To form a monodomain of liquid crystal in uniaxial phase and realize bistability effectively by arranging an orientation control member which orients the molecular axis of the liquid crystal vertically between a couple of substrates, and lowering the termperature of the uniaxial anisotropic liquid crystal from a high temperature phase. CONSTITUTION:A liquid crystal cell 100 is formed by holding the couple of substrates 101 and 101' at a specific interval with spacers and adhering them with an adhesive 106, and plural transparent electrodes 102 and 102' which cross each other at right angles are arranged on the substrates 101 and 101'. The cell 100 includes a SmC* or SmH* liquid-crystal layer 103 and is equipped with a heating body 105 and the orientation contol member 104 having a side wall surface 104' for orienting liquid crystal molecules vertically. The luquid-crystal layer 103 is heated by the heating body 105 to cause transition to an isotropic phase, and then the temperature is lowered according to a temperature gradient to form a monodomain in SmA phase. Thus, the bistability of the liquid-crystal layer 103 is realized effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the alignment of liquid crystal used in liquid crystal display elements, liquid crystal-optical shutters, etc., and more specifically, to improve display and drive characteristics by improving the initial alignment state of liquid crystal molecules. This invention relates to a method for controlling the alignment of liquid crystals.

Conventionally, liquid crystal display elements that display images or information by configuring a scanning electrode group and a signal electrode group in a matrix shape and filling a liquid crystal compound between the electrodes to form a large number of pixels have often been used. Are known.

The driving method for this display element is time-division driving, in which an address signal is selectively and periodically applied to a group of scanning electrodes, and a predetermined information signal is selectively applied in parallel to a group of signal electrodes in synchronization with the address signal. However, this display element and its driving method have major and fatal drawbacks as described below.

That is, it is difficult to increase the pixel density or enlarge the screen. Among conventional liquid crystals, most of them are practically used as display elements because they have a relatively high response speed and low power consumption.
T and W, written by He 1frich” Applied
Physics Letters”VO,’18, No.
, 4 (1971, 2, 15), P, 127-128 '''%/'oltage-Dependent 0p
tical Activity of a Twist
edNematic Liquid Crystal”
TN (twisted nematic
) type of liquid crystal is also used; this type of liquid crystal forms a structure (helical structure) in which nematic liquid crystal molecules with positive dielectric anisotropy are twisted in the thickness direction of the liquid crystal layer in the absence of an electric field.
A structure is formed in which the molecules of this liquid crystal are arranged in parallel with both 1 being polar planes. On the other hand, when an electric field is applied, nematic liquid crystals with positive dielectric anisotropy are aligned in the direction of the electric field, resulting in optical modulation. When a display element is constructed with a matrix electrode structure using this type of liquid crystal, the area (selection point) K where both the scanning electrode and the signal magnetic pole are selected is
A voltage higher than the threshold required to align the liquid crystal molecules perpendicularly to the electrode surface is applied, and in the area where neither the scanning electrode nor the signal electrode is selected (non-selected point), 1 voltage is not applied, and therefore the liquid crystal molecules do not align with the electrodes. By arranging linear polarizers in a cross Nicol relationship above and below such a liquid crystal cell, which maintains a stable alignment parallel to the plane, no light is transmitted at selected points, and light is not transmitted at non-selected points. is transmitted through it, so it can be used as an image element.

However, when a matrix electrode structure is configured, there are areas where scan electrodes are selected and signal electrodes are not selected, or areas where scan electrodes are not selected and signal-poles are selected (
A finite electric field is also present at the so-called ``half-selected point.''

If the difference between the voltage applied to the selected point and the voltage applied to the half-selected point is large enough to align the liquid crystal molecules perpendicular to the field, the display element will operate normally, but the scanning line If the number (N) is increased, the time during which an effective electric field is applied to one selected point (duty ratio) while scanning the entire screen (one frame) will decrease at the rate of l/N. . For this reason, when repeated scanning is performed, the effective voltage difference between selected points and non-selected points becomes smaller as the number of scanning lines increases, resulting in a decrease in image contrast and crosstalk. This is a drawback that is difficult to avoid. This phenomenon is caused by liquid crystals that do not have bistability (in a stable state, the liquid crystal molecules are oriented horizontally with respect to the electrode surface, and only when an electric field is effectively applied, they are oriented vertically). This is an essentially unavoidable problem that arises when driving (that is, repeatedly scanning) an object (orienting the object) using the temporal accumulation effect. In order to improve this point, voltage averaging method, dual frequency driving method, multiplex IJ method, etc. have already been proposed, but all of these methods are insufficient and cause the display element to deteriorate. The current situation is that it has reached a plateau.

On the other hand, looking at the field of printers, laser beam printers provide electrical image signals in the form of light to electrophotographic photoreceptors in terms of both pixel density and speed, as a means of obtaining hard copies using electrical signals as input. (LBP) is also excellent in current quantity. However, LBP has drawbacks such as: 1. The device used as a printer is large; 2. It has a high-speed driving part such as a polygon scanner, which generates noise, and requires strict mechanical precision. In order to overcome these drawbacks, a liquid crystal shutter array has been proposed as an element that converts electrical signals into optical signals. However, when providing pixel signals using a liquid crystal shutter array, for example, in order to write pixel signals at a rate of 16 dots (7) within a length of 210=, it is necessary to have more than 3000 signal generating units. Therefore, in order to give independent signals to each of the five elements, it was necessary to wire IJ-do lines for sending signals to all of the signal generating parts of each of the five elements, which was difficult to manufacture.

Therefore, an attempt has been made to provide pixel signals for ILINE (line) in a time-division manner using a signal generating section divided into several lines. In this way, the electrode that gives the signal can be
This is because it can be made common to a plurality of signal generating sections, and the actual wiring can be significantly reduced. However, if the number of lines (N) is increased using a liquid crystal that does not have bistability, as is usually done in this case, the signal ON time becomes essentially 1/N, which reduces the amount of light that can be obtained on the photoreceptor. However, there is a problem in that the amount of light emitted is reduced, resulting in the problem of crosstalk.

To improve the drawbacks of conventional liquid crystal devices, C1ark and Lagerwal proposed the use of a bistable liquid crystal device (Japanese Unexamined Patent Publication No. 56-107216, U.S. Patent No. 436792).
4 specification, etc.). Bistable liquid crystals generally include chiral smectate C phase (SmC') or H
It has a bistable state consisting of a ferroelectric phase (SmH"), and is therefore different from the optical modulation element used in the above-mentioned TN type liquid crystal.

For example, a liquid crystal is aligned in a first optically stable state for one electric field vector, and a second optically stable state for the other electric field vector.
The liquid crystal is aligned in an optically stable state. Furthermore, this type of liquid crystal has the property of very quickly taking one of the above two stable states in response to an applied magnetic field, and maintaining that state when no electric field is applied. By utilizing such properties, many of the problems of the conventional TNq elements mentioned above can be significantly improved. This point will be explained in more detail below in connection with the present invention. However, in order for an optical modulation element using this bistable liquid crystal to exhibit predetermined drive characteristics, the liquid crystal placed between a pair of parallel substrates must be effectively converted between states. It is necessary for the molecules to be arranged in such a state. For example, in a ferromagnetic liquid crystal having an 8mC or SmH phase, the liquid crystal molecular layer supporting the 8mC or SmH phase is perpendicular to the substrate surface, and therefore the region ( monodomain) needs to be formed. However, in conventional optical modulation elements using liquid crystals with bistability, the alignment state of the liquid crystals having such a monodomain structure was not always formed satisfactorily, and therefore sufficient characteristics could not be obtained. is the reality.

For example, methods of applying a magnetic field, methods of applying shear force, etc. have been proposed in order to provide such an orientation state. However, none of these methods necessarily gave satisfactory results. for example,
The method of applying a magnetic field requires a large-scale device and is incompatible with thin-layer cells with good operating characteristics.The method of applying a shear force requires a large-scale device and is difficult to use in thin-layer cells with good operating characteristics. The problem is that it is incompatible with the injection method.

By the way, in the device using the TN type liquid crystal as mentioned above,
One way to form monodomains of liquid crystal molecules parallel to the substrate surface is to rub the substrate surface with something like a knife (
A rubbing method, a method of diagonally depositing SiO, etc. are used.

For example, the liquid crystal in contact with the rubbed substrate surface is given a directionality, and the liquid crystal molecules preferentially align in that direction, which has the lowest energy (that is, is stable).
state. Such a rubbed surface has the effect of preferentially arranging liquid crystal molecules in one direction. A structure with a plane to which this orientation effect is applied is, for example,
It is shown in Canadian Patent No. 1010136 by W. Helfrich and M. 8chadt. In addition to the method of forming an alignment effect by this rubbing method, a structure with a plane formed by diagonally vapor depositing SiO or Sin on a substrate is used, and SiO or 8i0. The plane having -axial anisotropy has the effect of preferentially aligning liquid crystal molecules in one direction.

As described above, orientation control methods such as rubbing and oblique evaporation are one of the preferred methods for producing liquid crystal elements, but these methods do not allow diorientation for liquid crystals that have bistability. When controlled, a plane having a wall effect that preferentially orients the liquid crystal in only one direction is formed, which has the drawback of inhibiting bistability to electric fields, high-speed response, and monodomain formation.

In view of the above-mentioned circumstances, the main object of the present invention is to provide a bistable device that has potential suitability as a display element with high-speed response, high-density pixels, and a large area, or an optical shutter with a high shutter speed. An object of the present invention is to provide a method for controlling the alignment of a liquid crystal that can fully exhibit its characteristics by improving monodomain formation or initial alignment, which has been a problem in the past, in an optical modulation element using a liquid crystal having the following properties.

As a result of further research for the above-mentioned purpose, the present inventors discovered a method of rubbing the flat surface of the substrate, and a method of rubbing 8i0 and S10 on the flat surface of the substrate.
．． This is not done by an orientation control method such as oblique evaporation, but by the process of cooling from a high-temperature phase (e.g., isobathic phase, nematic phase, cholesteric phase) to an axial hethoptic phase (e.g., smectic phase, nematic phase). It has been found that monodomains can be formed by controlling the alignment direction of liquid crystals with sidewall surfaces that have the effect of aligning the liquid crystals perpendicularly or substantially perpendicularly to the molecular axis of the liquid crystals when a phase transition occurs.

The liquid crystal element of the present invention was made based on this knowledge, and more specifically, the liquid crystal element has a side wall surface between a pair of substrates that has the effect of preferentially arranging the molecular axis direction of the liquid crystal in a vertical or substantially vertical direction. A control member is disposed between the pair of substrates near the interface with the side wall surface of the member, and a liquid crystal in which the molecular axis direction of the liquid crystal is aligned perpendicularly or substantially perpendicularly to the side wall surface is arranged. A uniaxial auspicious phase of liquid crystals arranged in a direction parallel to the liquid crystal alignment direction of the -axis auspicious phase at the phase boundary between a phase (e.g. phase, nematic phase) and another phase on a higher temperature side than the other phase (equivalent phase, nematic phase, cholesteric phase). The present invention is characterized by a liquid crystal alignment control method in which a liquid crystal monodomain aligned in one direction is formed by causing a phase transition to occur continuously from the phase interface in a direction perpendicular to the phase interface. There is.

Hereinafter, the present invention will be described in further detail with reference to the drawings as necessary.

Particularly suitable liquid crystal materials for use in the present invention are liquid crystals with bistability and ferroelectricity, specifically chiral smectate C phase (SmC).
) or H phase (SrnH") can be used.

For more information on ferroelectric liquid crystals, see for example “LE J
O(JRNAL DE Pi-IYSIQUE LET
TER8" 36 (L69) 1975, l'-Fer
roelectric Liquid Crystal
s J:''App ed Physics Let
ters″36 (L-69) 1975° [Ferro
electric liquid crystals
J;”Applied Physics Letter
rs″36 (11) 1980.

r, Q++kryi, r^Qmxm+At); -a-c
+-r--mu---2Switching in
Liquid Crystals J; "Solid State Physics" 16 (141) 1981 r Liquid Crystals, etc., and the ferroelectric liquid crystals disclosed therein can be used in the present invention.

Specific examples of ferroelectric liquid crystal compounds include decyloxybenzylidene-p-amino-2-methylbutylcinname) (DOBAMBC), hexyloxybenzylidene-p-amino-2-lytetrapropylcinname) (H
OBACPC), 4-0-(2-methyl)-phthyl resol cylidene-4'-octylaniline (MBR, No. 8)
can be mentioned.

When constructing an element using these materials, the element is supported by a force such as a copper block in which a heater is embedded, as necessary, in order to maintain the temperature state such that the liquid crystal compound becomes the SmC phase or SmH phase. be able to.

FIG. 1 schematically depicts an example of a cell for explaining the operation of a ferroelectric liquid crystal. 11 and 11' are In,
02. SnO or ITO (Indium-Ti
A substrate (glass plate) coated with a transparent electrode made of a thin film such as 8mC phase or SmH with a liquid crystal molecular layer 12 oriented perpendicular to the glass surface.
Phase liquid crystal is enclosed. A thick line 13 represents a liquid crystal molecule, and this liquid crystal molecule 13 has a dipole moment (PL) 14 in a direction perpendicular to the molecule. When a voltage higher than a certain threshold is applied between the substrate 11 and the electrodes on it', the helical structure of the liquid crystal molecules 13 is unraveled, and the liquid crystal molecules 13 are turned so that all the dipole moments (PL) 14 are oriented in the direction of the electric field. The orientation direction can be changed. The liquid crystal molecules 13 have an elongated shape and exhibit refractive index anisotropy in the major axis direction and minor axis direction. Therefore, for example, if cross-niffle polarizers are placed above and below the glass surface, one pressure applied polarity It is easily understood that the liquid crystal optical modulation element has optical characteristics that change depending on the amount of the liquid crystal.

The liquid crystal cell preferably used in the liquid crystal element of the present invention can have a sufficiently thin thickness (for example, 10 μm or less). As the liquid crystal layer becomes thinner in this way, the helical structure of the liquid crystal molecules unwinds and becomes a non-helical structure even when no electric field is applied, as shown in FIG. 2, and its dipole moment P'! The straddle P' is either upward (24) or downward (24'). When an electric field E or E' of different polarity above a certain threshold value is applied to such a cell by the voltage applying means 21 and 21' as shown in FIG. 2, the dipole moment is The liquid crystal molecules are oriented either upward 24 or downward 24' in response to the electric field vector, and accordingly the liquid crystal molecules are oriented either in the first stable state 23 or in some cases in the second stable state 23'. .

As mentioned above, there are two advantages to using such ferroelectricity as a liquid crystal element. The first is that the response speed is extremely fast, and the second is that the alignment of liquid crystal molecules has bistability. To further explain the second point, for example, with reference to FIG. 2: - When a field E is applied, the liquid crystal molecules are oriented in a first stable state 23, and this state remains stable even when the electric field is turned off. Also, when applying an electric field E' in the opposite direction,
The liquid crystal molecules are aligned in the second stable state 1M23' and change their orientation, but they remain in this state even after the electric field is turned off. Further, as long as the applied electric field E does not exceed a certain threshold value, each orientation state is maintained. In order to effectively achieve such fast response speed and bistability, it is preferable for the cell to be as thin as possible, which is the biggest problem when forming an element using a liquid crystal with ferroelectric properties. This is because, as mentioned earlier, the cell has a highly monodomain property in which the SmC" phase or SmH layer is aligned perpendicularly to the substrate surface, and the liquid crystal molecules are aligned approximately parallel to the substrate surface. It is difficult to form a liquid crystal element, and it is the main purpose of the present invention to provide a solution to this point. This is a partial plan view of the example, and FIG. 3(B) is a cross-sectional view taken along the line A-A.In order to make the cell structure easier to understand, neither figure is drawn to an accurate scale.In this example, A liquid crystal cell 100 shown in FIG. 3, which shows an example of the configuration of a shutter array for a printer, includes a pair of substrates 101 and 10 made of glass plates, plastic plates, or the like.
1' are held at predetermined intervals with spacers (not shown),
It has a cell structure in which the pair of substrates are bonded together with an adhesive 106, and furthermore, a plurality of transparent electrodes 1 are disposed on the substrate 101.
A group of electrodes (for example, a group of electrodes for applying a scanning voltage in an IJ electrode structure) consisting of 02 is formed in a predetermined pattern such as a strip pattern. On the substrate 101', there is an electrode group (for example, a signal voltage application electrode group in a matrix electrode structure) consisting of a plurality of transparent electrodes 102' intersecting with the transparent electrode 102 described above, as shown in the figure (107). The transparent electrode 102 is connected to the lead 107, and the transparent electrode 102' is connected to the lead 107, so that signals from the external circuit are connected to the leads 107 and 1, respectively.
Manually connected to the terminal of 07".This kind of board lol and 10
1' includes, for example, silicon oxide, silicon dioxide, aluminum oxide, zirconia, magnesium fluoride, cerium oxide, cerium fluoride, silicon nitride, silicon carbide, boron nitride, polyvinyl alcohol, polyimide,
Insulating film formed using polyamideimide, polyesterimide, polyparaxylerin, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide, polystyrene, cellulose resin, melamine resin, urea resin, acrylic resin, etc. (not shown) )
can be provided. This insulating film also has the advantage of being able to prevent the generation of current caused by trace amounts of impurities contained in the liquid crystal layer 103, and therefore does not deteriorate the liquid crystal compound even if the operation is repeated.

The cell structure in this specific example includes a liquid crystal layer 103 that exhibits strong S properties at a predetermined temperature as described above, and a side wall surface 104 that has the effect of aligning the molecular axes of the liquid crystal vertically or approximately vertically.
' (hereinafter referred to as a vertical alignment control member) 104 and a heating element 105 such as a heater.

An important point in the present invention is that when the phase transition is first carried out from a high-temperature phase to SmA (smectic acid), the molecular axis alignment of the liquid crystal exhibiting SmA changes the molecular axis of the liquid crystal that contacts at the interface to the side wall surface 104'.
The S of the monodomain is controlled by the side wall surface 104' which has the effect of orienting the S
It is at the point where mA is formed.

The side wall surface 104', which has the effect of arranging the molecular axes of the liquid crystals in contact with each other at the interface in a vertical or substantially vertical direction, can be obtained by, for example, forming a film of a fluororesin in a band-like shape. The fluorine-based resin preferably used in this case is one that is soluble in organic solvents.Specific fluorine-based resins include, for example, fluoroolefin, cyclohexyl vinyl ether, alkyl vinyl ether, and hydroxyl resin. Copolymers using alkyl vinyl ethers (fluoroolefins such as chlorotrifluoroethylene, tetrafluoroethylene, etc.)
4% Q-Q trs (using one having a linear or branched alkyl group, hydroxyalkyl vinyl ether such as hydroxybutyl vinyl ether is suitable), fluoroolefins and carboxylic acid esters as monomers Copolymers using fluoroolefins having groups (fluoroolefins using chlorotrifluoroethylene, tetrafluoroethylene, fluoroolefins having carboxylic acid ester groups such as CF, =CFO(CF2), C
00CH,,CF,=CFO(CJ',) C00C
H,,CF,=Cl1'OCF,CF'0(CF',)
.

CF, 1-CO0CH, etc.) can be used. Among them, fluoroolefins, cyclohexyl vinyl ethers, which can form a cured film in the presence of a crosslinking agent (for example, compounds having two or more active groups such as butylated melamine, methylated melamine, incyanate, and glyoxal are suitable) A copolymer containing an alkyl vinyl ether and a hydroxyalkyl vinyl ether as monomer components is one of the preferred fluororesins.

Further, other monomers such as glycidyl vinyl ether, ethylene, propylene, imbutylene, vinyl chloride, vinylidene chloride, ethyl vinyl ether, isobutyl vinyl ether, n-butyl vinyl ether, etc. can be added to the above-mentioned fluororesin.

The fluororesin used in the present invention can generally contain fluoroolefin in a proportion of 40 to 60 mol%, and can contain other monomer components in a proportion of 40 to 60 mol%.

The fluorine-based copolymer resin capable of forming a film includes disuccinic acid peroxide, diglutaric acid peroxide, monosuccinic acid peroxide, azobisisobutyramidine dibasic es t-butylperoxyisobutyrate, t-butylperoxyacetate, etc. It can be obtained by copolymerizing the monomer components described above in the presence of a polymerization initiator. Examples of the reaction solvent used in this polymerization include t-butanol, esters, and fluorine-based hydrocarbons. In addition, this fluororesin includes aromatic hydrocarbons such as xylene and toluene, alcohols such as n-butanol, esters such as butyl acetate, ketones such as methyl isobutyl ketone, glycol ethers such as ethyl cellosolve, etc. can be dissolved in organic solvents.

1 Lumiflon" (manufactured by Asahi Glass Co., Ltd.) can be used as a commercially available fluororesin capable of forming a film on the mallet.

Therefore, in forming the side wall surface 104', first, a coating solution obtained by dissolving the fluororesin in an organic solvent as described above is applied onto the substrate by a spinner coating method, and after preheating, A photoresist material is applied on top of this coating film, exposed to a predetermined amount of light, and then developed to form an etching mask.Then, the fluororesin coating is etched with an organic solvent, and then the etching mask is removed. After that, the vertical alignment control member 104 can be formed by heating the coating film formed in a band shape. In addition, it is also possible to coat the side wall surface 10 by applying a fluororesin solution to a predetermined position using a screen printing method.
A vertical alignment control member 104 having a diameter of 4' can be obtained. Furthermore, as the heating element 105, for example, indium oxide, tin oxide, or ITO (Indium Tin Oxide) can be used.
It is suitable to stiffen thin film resistors such as

In such a liquid crystal cell lOO, polarizers 108 and 108' in a crossed nicol state or a parallel nicol state are arranged on both sides of substrates 101 and 101', respectively, and electrodes 1
Optical modulation will occur when a voltage is applied between 02 and 102'.

To give a more specific example of the liquid crystal cell lOO shown in FIG. 3, for example, the transparent electrode 102 is a strip-shaped scanning electrode group with a width of 62.5 μm, while the transparent electrode 102' forms one pixel, The signal electrode group can be 62.5 μm×62.5 μm. In addition, the liquid crystal layer 1 is made of a thin film.
03 is preferably maintained at a thickness of 2 μm.

Such a liquid crystal cell 100 is housed in a heating case (not shown), and polarizers 108 and 108' are vertically orthogonal to each other.
can be arranged and operated as a liquid crystal shutter array for an electrophotographic printer. In this case, the third
Arrow B in Figure (A) is the rotation direction of the electrophotographic photosensitive drum.

Below, DOBAM is a liquid crystal material that exhibits ferroelectric properties at a certain temperature.
Taking the case of BC as an example, a method for controlling the alignment of the liquid crystal layer 103 will be specifically explained using FIG. 3. First, D.O.B.
The liquid crystal cell 100- in which AMBC is sealed is set in a heating case (not shown) in which the entire cell is heated uniformly. Next, the temperature of the heating case is controlled so that the average temperature of the cell is, for example, 90°C. At this time, DOBAMBC has SmC” as a liquid crystal phase.
phase or 8mA phase state. Here, a current is passed through the heating element (heater) 105, and only the vicinity of the primary dot is Sm.
The A→isotropic phase transition temperature of about 118° C. is exceeded, and a phase transition occurs to an isotropic phase, that is, a liquid phase state. As the current is further increased, the equi-lucky phase region expands while remaining substantially parallel to the heating element 105, and eventually the entire liquid crystal layer 103 becomes an equi-lucky phase.

In this state, the longitudinal direction of the liquid crystal cell 100 (FIG. 3(A)
) is uniform in the direction C), and there is a temperature gradient such that the temperature gradually increases from the vertical alignment control member 104 to the heating element 105 in the transverse direction (direction B in FIG. 3(A)). It is formed. For example, the vicinity of the side wall surface 104' of the vertical alignment control member 104 is set to about 120 degrees Celsius, and about 1
．． A temperature gradient is formed by setting the temperature in the vicinity of the heating element 105, which is 5 degrees away, to, for example, 140°C.

Next, when the temperature of the case in which the cell lOO is set is gradually lowered from 90°C with the above-mentioned temperature gradient applied to the cell 100, for example, at a rate of 10C/h, the temperature is lowered gradually. In Figure (B), first, the vertical alignment control member 104 is placed on the outermost side.
The temperature near the side wall surface 104' of
It becomes lower than the phase transition temperature (approximately 116° C.), and in this region, the nucleus of the 8rnA phase is formed.

At this time, since it has the effect of aligning the liquid crystal molecules in the vertical direction on the side wall surface 104' of the vertical alignment control member 104,
When the SmA phase is formed near the side wall surface 104', the liquid crystal molecular axes are aligned within the plane (109) of the substrate 101 and perpendicular to the longitudinal direction of the side wall surface 104' of the vertical alignment control member 104. The S formed under the force of
The nucleus of the mA phase is a monodomain oriented vertically to the side wall surface 104 and horizontally to the surface 109 of the substrate 101. Furthermore, when the temperature of the case is lowered, a phase transition occurs in SmA such that the isokyoshi phase near the phase interface between the already formed SmA and the togoyoshi phase becomes parallel to the alignment direction of SmA near the phase interface. As a result, as the temperature continues to fall under a temperature gradient, the monodomain region of the 8 mA phase expands continuously. At this time, the growth rate of the phase interface between the monodomain region of the SmA phase and the isokyoshi phase region is the growth rate in the longitudinal direction of the liquid crystal cell 100 (in the direction of arrow C in FIG. 3 rA).
It is desirable that the speed be the same throughout.

For example, when the temperature of the case reaches about 70°C, the heating element 10
Except for the vicinity of 5, almost the entire liquid crystal undergoes a phase transition to the SmA phase.

Next, when the current flowing through the heating element 105 is gradually lowered to eliminate the temperature gradient, the temperature of the liquid crystal cell 100 becomes
The entire temperature uniformly reaches 70° C., and the phase transitions from liquid crystal to SmC phase. At this time, the molecular arrangement of the liquid crystal near the heating element 105 may be in a random state;
The region where 2 and 102 are formed is a uniform monodomain.

In the liquid crystal alignment method described above, the important point is that it is desirable to provide as large a temperature gradient as possible in the B direction in Figure 3 (A), but that the temperature is uniform in the C direction. 0 Figure 4 (A/) shows that this element is SmA
In Figure 0, which schematically shows the growth process of the SmA phase region during the temperature decreasing process by slow cooling when forming the phase, 201 is SmA.
It represents the phase interface between the A phase region 202 and the tokiyoshi phase region 203.

FIG. 4(B) shows the improved shape of the heating element 105. As shown in the figure, by narrowing the width of the heater pattern at the end of the heating element 105, the resistance value of the heating element at that end is increased, and the amount of heat generated at that end is increased. The temperature in the longitudinal direction of the liquid crystal cell 100 can be made uniform. Therefore, 8mA
The phase interface 201 between the phase 202 and the Tokichi phase 203 is located on the side wall surface 1
04', and a uniform monodomain is obtained as a whole.

Now, the alignment is completed through the steps described above, but even though it appears that the monodomains are uniformly completed, in reality, a voltage is applied between the electrodes 102-102' to achieve optical modulation of the liquid crystal. When examining the switching characteristics of an element, non-uniformity in optical contrast and response speed may occur depending on the region. This phenomenon is thought to be due to structural distortion caused by the temperature gradient set during installation. To deal with this, after the alignment process is completed, the temperature of the carrier case is increased, the liquid crystal undergoes a single carrier phase transition from the 8mC phase to the SmA phase, and then the temperature of the case is gradually lowered to the SmC state again. This has the effect of eliminating the above-mentioned distortion due to structural relaxation.

FIG. 5 shows another example of a heating element for preventing the temperature at the ends of the liquid crystal cell 100 from becoming lower than that at the center during the formation of a temperature gradient during the alignment process. heating element 10
5 is a heating element 301 that heats the end of the liquid crystal cell ioo
, 302, it is possible to compensate for the temperature drop at the end as described above. Like this, liquid crystal cell 1
By providing heating elements 105, 301, and 302 around 00, a uniform monodomain of SmA phase is formed.

FIG. 6 shows another embodiment based on the present invention, in which a heating element 105 is separately provided on the back side of a substrate 1010. The heating element 105 heats the entire liquid crystal cell 100, and is used in common with the heating element 105, for example, when the alignment of the liquid crystal is disturbed due to some trouble when actually used as a liquid crystal optical modulation element. By doing so, it is possible to carry out reorientation through predetermined steps.

That is, the 8mC phase formed by the method described above is heated with the heating element 105', and the entire liquid crystal cell 100 is heated with SmA.
phase, and then slowly cooled to the SmC phase to form a uniform monodomain again. This heating element 1
05' can of course be provided on the back side of the substrate 101'.

A liquid crystal cell 100 shown in FIG. 7 represents a specific example in which a heating element 110 made of ITO or a Ni--Cr alloy thin film is provided on the outside of a substrate 101' instead of the heating element 105 described above. The shape of this heating element 110 is as follows.
It is preferable to use the shape shown in FIG. 5(D) or FIG.

Furthermore, the liquid crystal cell 100 shown in FIG.
Horizontal ITO+Ni with gradient thickness instead of 5
A specific example in which a heating element 111 formed of a -Cr thin film is provided is shown in FIG.

When a constant voltage is applied in the longitudinal direction (perpendicular to the plane of the paper) of this liquid crystal cell 100, the side wall surface 104 of the nucleation member 104
A temperature gradient is formed in which the temperature increases from the vicinity of ' in the vertical direction.

At this time, an organic insulating film such as polyimide or an inorganic insulating film 112 such as SiO□ is provided between the heating element 111 and the electrode 102.
It is desirable to have a

In a preferred embodiment of the present invention, it can be used with an alignment control member (hereinafter referred to as a parallel alignment control member) having a side wall surface that has the effect of arranging the molecular axis direction of liquid crystal in a direction parallel or substantially parallel to the side wall surface. can. Naochi, 9th
The side wall surface 901 shown in the figure is a cut surface of the parallel alignment control member 901 that has been given a rubbing effect when a film such as a polyester film or a polyimide film is cut into strips with a metal blade or a diamond blade, glass fiber, or ivory. The side wall surface 901 when used as the parallel alignment control member 901 can be used.

In addition, polyimide, polyester, and S
Parallel orientation control member 901 such as iO or siO
By rubbing, a side wall surface 901' is formed which has the effect of aligning the molecular axes of the liquid crystals in contact at the interface in parallel or substantially parallel directions. Such a rubbed side wall surface 901 can be obtained, for example, by the following method. That is, ITO (Indium-Tin-Oxide)
A harder coating, for example, a SiC:H film, is formed on a glass substrate on which patterned electrodes are formed in a strip shape, and then, after coating, for example, a polyimide precursor solution on this SiC:H film, exposure and An etching mask is formed through a development process, and then the polyimide precursor coating is etched, and a strip-shaped polyimide coating that will become the parallel alignment control member 104 is formed at a predetermined position by heating, and then the etching mask is removed. After that, the substrate is rubbed in the same direction as the strip direction. The substrate surface has higher hardness and does not have the orientation control effect of rubbing.
Only the side wall surface 901 of the strip-shaped polyimide film has a parallel orientation control effect by rubbing.

Alternatively, a polymer liquid crystal forming highly oriented fibers can be used as the parallel alignment control member 901, and the molecular axes of the liquid crystal whose side wall surfaces 901' are in contact with each other at the interface can be aligned in parallel or substantially parallel directions.

Examples of polymeric liquid crystals used to form such highly oriented fibers include liquid crystals spun from a sulfuric acid solution of boIJ (p-phenylene terephthalamide) or a dimethylacetamide solution of poly(p-benzamide). Fiber is a typical fiber. In addition, liquid crystal solutions of poly(amide-hydrazide) and polyhydrazide in sulfuric acid, fluorosulfuric acid, or mixed solvents of these, polyphosphoric acid and poly(p-phenylenebenzobisoxazole) and poly(p-phenylenebenzobisthiazole), etc. Liquid crystalline solution of methylsulfonic acid etc., liquid crystalline melt of polyester formed from para-hydroxybenzoic acid, 1,2-bis(para-carboxyphenooxy)ethane, terephthalic acid and substituted or unsubstituted hydroquinone, rose-hydroxybenzoic acid Benzoic acid, 1.2-
Bis(para-carboxyphenoxy)ethane, terephthalic acid and bisphenol The liquid crystalline melt of polyester produced from bisphenol A diacetate and the liquid crystalline melt of polyester represented by the following general formula (1) or (2) Examples include fibers obtained by spinning from liquid.

General Formula (1) General Formula (2) (In the formula, n = an integer of 2 to 11) By using such fibers in the parallel orientation control member 901, it is possible to contact the highly oriented side wall surface 901 of the fibers. The liquid crystal can be aligned in a direction parallel or substantially parallel to the wall surface 901'.

Further, as shown in FIGS. 10(A) and 10(B), an orientation controlling member 801 (104) similar to the aforementioned orientation controlling members 104 and 901 is used as a sealing member.
(same material as 104) and 802 (same material as 901) can be used, and orientation control members 803 (same material as 104) and 804 which function as spacer members
(same material as 901) can be used. That is, the orientation control members 801 and 803 in FIG. 10(A)
The side wall surfaces of the orientation control members 802 and 804 in FIG. 1O(B) have the same orientation control effect as the side wall surface 104' shown in FIG. It has the same orientation control effect as the side wall surface 901'.Next, regarding the method for manufacturing the liquid crystal element of the present invention, a method for controlling the orientation of the liquid crystal layer 103 will be described, taking as an example the liquid crystal material DOBAMBC which exhibits ferroelectricity at a predetermined temperature. This will be specifically explained using FIG. 11.

FIG. 11(A) is a perspective view schematically showing the method for producing the liquid crystal element of the present invention.

FIG. 10(B) is a c-c' cross-sectional view of the same, and FIG.
C) is a sectional view taken along line D-D'. Note that among the symbols in the drawings, the same ones as in the previous figure represent the same members.

First, cell structure 1 in which DOBAMBC is enclosed
00 is set in a heating case (not shown) in which the entire cell 100 is heated uniformly. Next, the temperature of the heating case is controlled so that the average temperature of the cell lOO is, for example, 70°C to 90°C.

A liquid crystal layer 103 of SmA phase or SmC phase is formed.

The liquid crystal layer 103 at this time is in a state before the lower alignment control method is applied, and no SmA or SmC monodomains are formed.

Here, the heating element 902 as a heating means is moved in the direction of the arrow 903. At this time, the heating element 902 causes 8
The liquid crystal layer 103 in the region where the temperature is raised above the phase transition temperature to the m&-+ isotropic phase (approximately 118° C.) enters the isotropic phase state.
As the heating element 902 continues to move in the direction of the arrow 903, this region immediately undergoes a cooling process from the isotropic phase state, and thus again reaches the phase transition temperature from the isokyoshi phase to SmA (approximately 116
℃), the unidirectionally oriented Sm
A monodomain is formed.

At this time, since the vertical alignment control member 104 is provided in the present invention, heating by the heating element 902 causes
First, after the temperature in the vicinity of the side wall surface 104' of the vertical alignment control member 104 reaches a temperature higher than the phase transition temperature from SmA to isotropic phase, the heating element 902 moves in the direction of the arrow, causing a temperature decreasing process. , and the liquid crystal molecules aligned in one direction are controlled by the side/wall surface 901' of alignment perpendicularly or approximately perpendicularly to the side wall surface 104 below the phase transition temperature from the Tokichi phase to SmA. SmA is formed. moreover,
The positive phase that occurs continuously due to the movement of the heating element 902→S
The forcing force and the forcing force by the side wall surface 901' (parallel alignment control 901) resulting in an overall alignment parallel to the side wall surface 10.
A monodomain vertical to the longitudinal direction of 4' is formed.

After that, in the process of cooling down from this SmA, SmH or S
For example, if the cell thickness is 2 species, monodomain SmC with a non-helical structure
Or SmH can be obtained.

The heating element 902 used as a heating means is SmA or Sm
C"' or SmH becomes SmA or SmC" in the temperature rising process
The cell structure 100 is heated to a temperature sufficient to cause a phase transition to a higher-temperature equi-yoshitic phase, nematic phase, or cholesteric phase, and the heating element 902 is moved in the direction of arrow 903 to reduce the temperature during the cooling process. It is moved at a speed that is sufficient to cause a phase transition to SmA or SmC.

The heating element 902 used in such a method is, for example, a wire-shaped, roll-shaped, rod-shaped, or plate-shaped (band-shaped) nickel-chromium alloy or ITO.

A resistive heating element such as tin oxide or indium oxide can be used. When these heating elements are wire-shaped, roll-shaped, or rod-shaped, their diameter is 0.1
Approximately 0.5 mm to 5 mm, preferably 0.5 rtan to 2 mm, and in the case of a plate or strip shape, the width is approximately 0.1 mm to 5 m+m, preferably 0.5 rtan to 2 mm. 2 pottery is suitable. Also, its moving speed is t
mm/h to 5 mm/h is suitable.

Figure 12 shows a matrix with a ferroelectric liquid crystal compound sandwiched in the middle.
FIG. 4 is a schematic diagram of a cell 41 having an IJ square electrode structure.

42 is a scanning electrode group, and 43 is a signal electrode group. FIGS. 13(a) and (b) show the selected scan '1, respectively.
The electrical signals given to the pole 42(S)K and the electrical signals given to the other scanning electrodes (unselected scanning electrodes) 42(n) are shown, and FIGS. 12(C) and 12(d) show the selected signals, respectively. An electric signal applied to the electrode 43(S) and an electric signal applied to the unselected signal electrode 43(n) are shown. In FIGS. 13(a) to 13(d), the horizontal axis represents time.

The vertical axis represents voltage. For example, when displaying a moving image, the scanning electrode groups 42 are sequentially and periodically selected.

Now, let us assume that the threshold voltage for providing the first stable state of the liquid crystal cell having bistability is th, and the threshold voltage for providing the second stable state is -yth. As shown in FIG. 13(a), the electrical signal applied to (St) is an alternating voltage such that it is V at phase (time) tI and -■ at phase (time) t. The other scanning electrodes 42(n) are shown in FIG.
As shown in b), it is in a grounded state and the electrical signal is O. On the other hand, the electric signal given to the selected signal electrode 43(s) is v as shown in FIG. 13(C),
Further, the electrical signal applied to the unselected signal electrode 43(n) is <-V as shown in FIG. 13(d).

In the above, the voltage V is set to a desired value that satisfies V(Vth, (2V and -V) - Vth, ) -2V. FIG. 14 shows the voltage waveform applied to each pixel when such an electric signal is applied. 14(a) to (d) correspond to pixels A, B%C, and D in FIG. 12, respectively. That is, as is clear from FIG. 14, in the pixel on the selected scanning line, the voltage 2 exceeding the threshold value vth at the phase t2
V is applied. Further, to the pixel B existing on the same scanning line, a voltage -2■ exceeding the threshold value -vth2 is applied at phase t. Therefore, depending on whether a signal electrode is selected on the selected scanning electrode line, if the signal electrode is selected, the liquid crystal molecules are aligned in the first stable state, and if not selected, the liquid crystal molecules are aligned in the second stable state. Align the orientation to a stable state. In any case, it has nothing to do with the previous history of each pixel.

On the other hand, on unselected scanning lines, such as those applied to pixels C and D, the voltages applied to all pixels C and D are +■ or -■, neither of which exceeds the threshold voltage. Therefore, the liquid crystal molecules in each pixel C and D maintain the orientation corresponding to the signal state when scanned last time without changing the orientation state. That is, when a scanning electrode is selected, a signal for that one line is written, and -
The signal state can be maintained until the next selection after the end of the frame. Therefore, even if the number of scanning electrodes increases, the actual duty ratio does not change, and contrast reduction and crosstalk do not occur at all. On this occasion,
'The value of voltage value ■ and the value of phase (t, +t,)=, T value depends on the liquid crystal material used and the thickness of the cell, but it is usually 3 volts to 70 volts and 0.1μ crown to 2m5ec.
range is used. Therefore, in this case, the electrical signal applied to the selected scanning electrode changes from the first stable state (assumed to be in the "bright" state when converted into an optical signal) to the second stable state.
It is also possible to cause a change in the deviation to a stable state (assumed to be a "dark" state when converted to an optical signal) or vice versa.

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

[Example 1] A liquid crystal element was prepared by the method shown in Fig. 11. below,
This point will be explained in detail.

A square glass substrate was prepared, on which a striped ITO film with a width of 62.5 μm and a pinch of 100 μm was provided as an electrode.

Next, on this substrate, 100 parts by weight of a fluororesin "Lumiflon" (Asahi Glass ff), 80M parts of xylene, 80 parts by weight of n-butanol, 2ON parts of methylated melamine and 0.5 parts by weight were added. Weight part "Catalys" 60
A coating solution consisting of 0 J (manufactured by Asahi Glass ■) was applied using a spinner coater and dried to form a 2 μm thick fluororesin film.

Next, a positive resist solution (5hi
AZ1350'' (manufactured by Pley) was applied with a spinner and prebaked. An exposure mask was placed on this resist layer. However, this exposure mask was one that masked both ends of the glass substrate in a band shape. .

Subsequently, after exposure, development was performed with a developer "MP312" containing tetramethylammonium hydroxide to remove the resist film in the exposed portions and form an etching mask. Thereafter, the fluororesin film was etched with a mixed solvent of xylene and phthanol (50:50).

Next, the resin film is cured by heating under predetermined curing conditions, and then the etching mask is removed.

Vertical alignment control members were formed at both ends of the glass substrate.

Next, a band-shaped Mylar film (registered product 1 polyethylene terephthalate film, manufactured by Dubo/Inc., USA) cut with a metal blade was placed on the other ends of the glass substrate as a parallel alignment control member, thereby producing an electrode plate (A).

Then, 111i with a pinch lOOμm was placed on the glass substrate.
An electrode plate (B) was prepared by providing striped electrodes of 62.5 μm. CB)! After applying epoxy adhesive to the periphery of the electrode plate using a screen printing method except for the area that will become the injection port, the striped pattern electrodes of (A) the TIE electrode plate and (B) the electrode plate are overlapped so that they are perpendicular to each other. The cells were created by curing the adhesive under predetermined curing conditions.

After that, the Tokichi-phase DOBAMBC was created using the vacuum injection method.
was injected into the cell through the injection port, and the injection port was sealed.

After installing a pair of polarizers in a crossed nicol state on both sides of the cell into which DOBAMBC was injected, the cell was placed in a heating case controlled at a temperature of 90°C and observed under a microscope. As a result, SmC was formed. However, it was confirmed that it was not a monodomain.

While this liquid crystal cell was maintained at 90°C, a wire with a diameter of 0.2 degrees centigrade was placed near one of the vertical alignment control members, and parallel to it, a heater was placed in the cell as shown in Figure 11. After arranging the wire heaters, a current was applied to the wire heaters to generate heat. At this time, the temperature of the liquid crystal cell heated by the wire heater is 120'C to 140'C.
After confirming that the temperature is 0°C, move this wire heater at a speed of 2 mm/h in the direction of arrow 90 shown in Figure 11.
Moved in direction 3.

A pair of polarizers was placed on both sides of the liquid crystal thus created in a crossed nicol state, and when it was observed under a microscope while maintained at a temperature of 90°C, it was confirmed that monodomain SmC was formed. Ta.

If a voltage is applied between them and the switching characteristics of the liquid crystal optically variable element are investigated, non-uniformity in optical contrast or response speed may occur depending on the region. This phenomenon is thought to be caused by structural strain caused by movement of the heater set during orientation. To deal with this, after the orientation process is completed, the temperature of the -carrying case is increased to cause a single-carrying phase transition of the liquid crystal from the SmC phase to the SmA phase, and then the temperature of the case is gradually lowered to the SmC state again. In particular, structural relaxation has the effect of eliminating the above-mentioned distortions.

[Brief explanation of the drawing]

1 and 2 are perspective views showing a liquid crystal cell used in the present invention. FIG. 3(A) is a plan view of a liquid crystal element used in the present invention, and FIG. 3(B) is a sectional view thereof taken along line AA. FIG. 4(A) is a plan view schematically showing the growth process of liquid crystal. FIG. 4(B) is a plan view showing another embodiment of the liquid crystal cell used in the present invention. FIG. 5 is a plan view showing another embodiment of the liquid crystal cell used in the present invention. 6th
7 and 8 are cross-sectional views showing preferred embodiments of the liquid crystal cell of the present invention. FIG. 9(A) is a plan view showing another liquid crystal element used in the method of the present invention, FIG. 9(B) is a sectional view taken along the line AA, and FIG. 9(C) is a sectional view taken along the line BB'. FIG. Figure 10 (A
) and FIG. 10(B) u are cross-sectional views showing another specific example of the liquid crystal element used in the method of the present invention. Figure 11 (
A) is a perspective view schematically showing the method of the present invention;
FIG. 11(B) is a sectional view taken along line c-c', and FIG. 11(C) is a sectional view taken along line DD'. FIG. 12 is a plan view schematically showing the 'bopolar structure of the liquid crystal element used in the present invention. FIGS. 13(a) to 13(d) are explanatory diagrams showing signals for driving the liquid crystal element used in the present invention. FIG. 14 is an explanatory diagram. 100...liquid crystal cell, 101. 101...Substrate,
102. 102...' polarization, 103... liquid crystal layer, 104...
- Vertical alignment control member, 104... Side wall surface of vertical alignment control member, 901... Parallel alignment control member, 901...
Side wall surface of parallel alignment control member, 105.105.301
, 302.110.111°902... heating element, 10
6...Adhesive, 107, 107', 107''...
・Lead wire, 108. 108...Polarizer, 109
. . . Surface of substrate 101, 112 . . . Insulating film, 201.
...Phase interface, 202...SmA phase, 202'...Long axis direction of liquid crystal molecules, 203...Iso-yellow phase, 801...Sealing member using vertical alignment member, 802...Parallel alignment member 8o3...A spacer member using a vertical alignment control member, 804...A spacer member using a parallel alignment control member. lθ2 102 1θ4 104'#2/M' /174th H1 (C
) (b) (cl) (b) (d no Otsu V

Claims (1)

[Scope of Claims] (1) An alignment control member having a side wall surface having the effect of preferentially aligning the molecular axis direction of liquid crystal in a vertical or substantially vertical direction is disposed between a pair of substrates, Near the interface with the side wall surface of the member, there is a phase interface between a uniaxial auspicious phase of liquid crystal in which the molecular axis direction of the liquid crystal is aligned perpendicularly or substantially perpendicularly to the side wall surface and another phase on the higher temperature side than the phase. forming another phase near the phase interface to a uniaxial auspicious phase of liquid crystals aligned in a direction parallel to the liquid crystal alignment direction of the -axis auspicious phase under decreasing temperature;
A method for controlling the alignment of liquid crystals, characterized in that a monodomain of liquid crystals aligned in one direction is formed by continuously causing the phase transition from the phase interface in a direction perpendicular to the phase interface. (2) Patent claim (3) in which the phase interface has linearity
2.) A method for controlling the orientation of a liquid crystal according to claim 1, wherein the liquid crystal has a smectic physiognomy. (4) Claim 3 in which the temperature of the smectic human phase is lowered to cause a phase transition to the smectic C phase or H phase.
Liquid crystal orientation control method described in Section 1. (5) The liquid crystal orientation control method according to claim 4, wherein the smectic C phase or H phase is a chiral smectic C phase or H phase. (6) The liquid crystal orientation control method according to claim 5, wherein the chiral smect C phase or H phase is arranged in a non-helical structure. (Force) The liquid crystal orientation control method according to claim 1, wherein the other phase on the higher temperature side than the -axis auspicious phase is a nematic phase, a cholesteric phase, or an iso-yoshitic phase. (8) The side wall surface is made of a fluorine-based resin. A method for controlling the alignment of a liquid crystal according to claim 1, wherein the liquid crystal is formed by forming two or more side walls between the pair of substrates with a flat stone
+ Scope of the claim affected by the parallel relationship 1. Liquid crystal alignment control method according to claim 1〇〇0) Claim 1 wherein the side wall surface is a side wall surface of a sealing member A method for controlling the alignment of liquid crystals. (I)) Liquid crystal alignment control method 0 according to claim 1, wherein the side wall surface is a side wall surface of a spacer member.