JPS61205922A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To prevent the generation of an orientation defect by using a specific liquid crystal element, forming the Sm phase of the liquid crystal by the phase transfer on the higher temp. side than the same and subjecting the surface of a substrate which contacts with the liquid crystal to an orientation treatment. CONSTITUTION:The liquid crystal compsn. contg. >=2 kinds of the liquid crystal compd. expressed by the formula (R is an alkyl, R* is an optically active group having an asymmetric C atom) is sealed between a pair of the substrates 101a and 101b. The Sm phase of the liquid crystal compsn. is formed by the phase transfer form the higher temp. side than the Sm phase. The surface of at least one substrate 101a of a pair of the substrates 101a, 101b is subjected to the uniaxial orientation treatment. The mono-domain in which the liquid crystal molecules are arranged in one direction is formed in the case of forming, for example, the SmA phase by slow cooling from the phase on the higher temp. side than the Sm phase in the above-mentioned manner. The liquid crystal element made into the construction in which the operation of the element based on the bistability of the ferroelectric liquid crystal and the mono-domain charac teristic of the liquid crystal layer 103 are compatible is obtd. The Sm phase having no orientation defect is thus formed.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a liquid crystal element applied to a liquid crystal display element, a liquid crystal-optical shutter array, etc., and more specifically, the present invention relates to a liquid crystal element applied to a liquid crystal display element, a liquid crystal-optical shutter array, etc. This invention relates to a liquid crystal element with improved driving characteristics.

[Conventional technology]

As a conventional liquid crystal element, for example, M-kai shut (M,
5chadL) and W Helfrich (W, H
``Applied Physics Leaders'' (author)
sLetters”) Volume 18, No. 4 (February 1971)
``Voltage Dependent - Optical 7 Activity Ichiban of a Twisted Conflict Nematic Meets Kid φ Crystal'' on pages 127-12B), pp. 127-12B
ptical Activity of aTw
isted Nematic LiquidC
Twisted nematic shown in
One that uses liquid crystal is known. This TN liquid crystal has a problem in that crosstalk occurs during time-division driving using a matrix electrode structure with a high pixel density, so the number of pixels per pixel is limited.

Furthermore, a display element is known in which a switching element using a thin film transistor is connected to each pixel, and each pixel is switched. However, the process of forming the thin film transistor on the substrate is extremely complicated, and it is difficult to use a display element with a large area. There are some problems that make it difficult to create.

In order to improve the drawbacks of conventional liquid crystal devices, the use of bistable liquid crystal devices is proposed by Clark (C).
1ark) and Lage rwa l
It was proposed by
6, U.S. Pat. No. 4,367,924, etc.), ferroelectric liquid crystals having chiral smectic C phase (SmC bundle) or H phase (SmH\) are generally used as the liquid crystal having bistability. It will be done.

This liquid crystal has a bistable state consisting of a first optically stable state and a second optically stable state with respect to an electric field. Therefore, unlike the optical modulation element used in the TN type liquid crystal described above, for example, one The liquid crystal is aligned in a first optically stable state with respect to the electric field vector, and the liquid crystal is aligned in a second optically stable state with respect to the other electric field vector. In addition, this type of liquid crystal responds to an applied electric field and very quickly responds to the above-mentioned
It has the property of taking one of two stable states and maintaining that state when no electric field is applied. By utilizing such properties, many of the problems of the conventional TN type device described above can be significantly improved. This point will be explained in more detail below in connection with the present invention. However, in order for this ferroelectric liquid crystal with bistability to exhibit predetermined driving characteristics, the liquid crystal placed between a pair of parallel substrates must be in the above two stable states regardless of the applied state of the electric field. It is necessary that the molecules be arranged in such a state that conversion between them can occur effectively.

For example, for a ferroelectric liquid crystal having an SmC" or SmH" phase, a region in which the liquid crystal molecular layer having an SmC" or SmH" phase is perpendicular to the substrate surface, and therefore the liquid crystal molecular axes are aligned approximately parallel to the substrate surface. (monodomain) needs to be formed. However, in conventional ferroelectric liquid crystal devices with bistability, the alignment state of the liquid crystal with such a domain structure was not always formed satisfactorily, so the actual situation was that sufficient characteristics could not be obtained. It is.

For example, according to C1ark et al., in order to provide such an orientation state, there are methods of applying a magnetic field, methods of applying a shear force, and methods of applying parallel ridges at small intervals between substrates.
) have been proposed. However, none of these methods necessarily gave satisfactory results. For example, the method of applying a magnetic field is
There are disadvantages in that it requires large-scale equipment and is incompatible with thin-layer cells with good operating characteristics.Also, the method of applying shear force is incompatible with the method of injecting liquid crystal after creating the cell. There are some difficulties. Further, the method of arranging parallel apertures within the cell cannot provide a stable alignment effect by itself.

[Problem that the invention seeks to solve]

In view of the above-mentioned circumstances, an object of the present invention is to provide a ferroelectric liquid crystal element that has potential suitability as a display element having high-speed response, high-density pixels, and a large area, or an optical shutter having a high shutter speed. The object of the present invention is to provide a ferroelectric liquid crystal element that can fully exhibit its characteristics by improving the monodomain formation property or initial orientation, which has been a problem in the past.

[Effect]

As a result of research in line with the above-mentioned purpose, the present inventors have discovered that a specific liquid crystal or a composition containing the liquid crystal is sandwiched between substrates to which a uniaxial alignment treatment effect has been imparted, and a phase on the higher temperature side than the smectic phase, e.g. When a phase transition is caused by slow cooling from a cholesteric phase (chiral nematic phase), nematic phase, or togoyoshi phase, for example, when forming SmA, a monodomain in which liquid crystal molecules are aligned in one direction can be formed, and as a result, It has been found that a liquid crystal element can be obtained that has a structure that allows both the operation of the element based on the bistability of ferroelectric liquid crystal and the monodomain property of the liquid crystal layer.

[Means for solving problems]

The liquid crystal element of the present invention is based on the above-mentioned findings,
More specifically, a cell structure is formed in which a liquid crystal composition containing two or more types of liquid crystal compounds represented by the following general formula (1) is sealed between a pair of substrates, and the smectate phase of the liquid crystal composition is It is formed by a phase transition from a phase on the higher temperature side, and has the effect of arranging the molecules in one direction with priority given to the direction of the molecular axis where the surfaces of at least one of the pair of substrates meet at the interface. It has characteristics.

General formula (1) %Formula% In the formula, R represents an alkyl group, and R* represents an optically active group having an asymmetric carbon atom, particularly an alkyl group having 1 to 18 carbon atoms, An alkyl group is preferred, and an optically active group represented by the following general formula (2) is particularly preferred.

General formula (2) %Formula% Here, R1 and R2 are either an alkyl group, an alkyloxy group, a cyano group, or a halogen atom, but R1, R,
2 are different, and cases where R1 and R2 are both halogen atoms are excluded. Also, in the above formula, n is O~8
is an integer. Among the compounds of formula (1), those with n=1 are particularly suitable for practical production, from the viewpoint of ease of obtaining optically active raw materials. Rx=CH3゜R2=C2H5, that is, the R tree is 2-methylbutyl group, and n=o
, R1=CH3.

It is a compound where R2=C6H13, that is, R water is a 2-octyl group.

The compound of general formula (1) is 4-furkyloxy-4
It is most preferably synthesized by reacting '-biphenylcarboxylic acid with a halogenating agent such as thionyl chloride or phosphorus pentachloride to form an acid halide, and then reacting this with an optically active alcohol in a basic solvent such as pyridine. be done.

Details are disclosed in Japanese Unexamined Patent Publication No. 118744/1983.

〔Example〕

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

The liquid crystal used in the present invention has ferroelectricity, and specifically has chiral smectate C phase (SmC").
, H phase (SmH"), I phase (SmI"), J phase (Sm
A phase (SmK"), G phase (SmC yi) or F phase (SmF") I, self+spring JL field → appear.

Specific examples of the compound represented by the general formula (1) are as follows.

(m=7.8, 9.10.12) These liquid crystal compositions can be used with other ferroelectric liquid crystals, such as DOB.
AMBC; decyloxybenzylidene-y-amino-2-
Good results can also be obtained by combining with methylbutyl cinnamate, HOB A CP C; hexyloxybenzylidene-Y-amino-2-chloropropyl cinnamate, etc.

When constructing an element using these materials, in order to maintain the temperature such that the liquid crystal composition is in the SmC)le phase or 5rnH* phase, the element may be placed in a copper block with a heater embedded, etc., as necessary. can be supported.

Figure 1 is for explaining the operation of ferroelectric liquid crystal.

This is a schematic drawing of an example of a cell. 21a and 21b
I n203, S n02 or ITO (Ind
It is a substrate (glass plate) coated with a transparent electrode made of a thin film such as Sm-Tin Oxide), between which a liquid crystal molecular layer 22 is oriented perpendicular to the glass surface.
C* phase or SmH* phase liquid crystal is sealed.

A thick line 23 represents a liquid crystal molecule, and this liquid crystal molecule 23 has a dipole moment (P) 24 in a direction perpendicular to the molecule.

When a voltage equal to or higher than a certain threshold is applied between the electrodes on the substrates 2ta and 21b, the helical structure of the liquid crystal molecules 23 is unraveled, and the liquid crystal molecules 23 are oriented so that all dipole moments (P) 24 are oriented in the direction of the electric field. You can change direction. The liquid crystal molecules 23 are.

It has an elongated shape and exhibits refractive index anisotropy in its long and short axis directions. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass surface, the optical properties change depending on the polarity of voltage application. It is easily understood that this serves as an optical modulation element.

The liquid crystal cell preferably used in the liquid crystal element of the present invention can be made sufficiently thin (for example, 10 g or less).As the liquid crystal layer becomes thinner, the electric field can be reduced as shown in FIG. Even when no voltage is applied, the helical structure of the liquid crystal molecules unwinds and assumes a non-helical structure, with its dipole moment Pa or Pb pointing upward (34a).

or downward (34b). When an electric field Ea or Eb of different polarity above a certain threshold value is applied to such a cell by voltage applying means 31a and 31b, as shown in FIG.

The dipole moment changes its direction upward 34a or downward 34b in response to the electric field vector of the electric field Ea or Eb, and accordingly, the liquid crystal molecules are in the first stable state 33a or in the second stable state 33b. orient to one side.

As mentioned earlier, there are two advantages to using such ferroelectricity as an optical modulation 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, the electric field Ea
When the voltage is applied, the liquid crystal molecules are aligned in a first stable state 33a, and this state remains stable even when the electric field is turned off. When an electric field Eb in the opposite direction is applied, the liquid crystal molecules are oriented to a second stable state 33b and change their orientation, but they remain in this state even after the electric field is turned off. Also, the electric field E
As long as a does not exceed a certain threshold, each orientation state is maintained. Such fast response speed and
In order to effectively realize bistability, it is preferable that the cell be as thin as possible.

The biggest problem in forming devices using liquid crystals with such ferroelectricity is, as mentioned earlier, that SmC
It is difficult to form a highly monodomain cell in which a layer having a *phase or an SmH* phase is aligned perpendicular to the substrate surface and liquid crystal molecules are aligned approximately parallel to the substrate surface, and this It is the main objective of the present invention to provide a solution to this point.

FIGS. 3(A) and 3(B) show an embodiment of the liquid crystal element of the present invention. Figure 3(A) is.

FIG. 3(B) is a top view of the liquid crystal element of the present invention.
It is an A' sectional view.

In the cell structure 100 shown in FIG. 3, a pair of substrates 101a and 101b made of glass or plastic plates are held at a predetermined distance by a spacer 104, and are bonded together with an adhesive 106 to seal the pair of substrates. Further, on the substrate 101, an electrode group (for example, a scanning voltage application electrode group of a matrix electrode structure) consisting of a plurality of transparent electrodes 102a is arranged in a predetermined pattern such as a strip pattern. It is formed. Substrate 10
An electrode group (for example, a signal voltage application electrode group of the matrix electrode structure) is formed on the transparent electrode 102a and the plurality of transparent electrodes 102b intersecting with the transparent electrode 102a.

The substrate 101b provided with such a transparent electrode 102b contains 1, for example, silicon oxide, silicon dioxide, aluminum oxide,
Inorganic insulating materials such as zirconia, magnesium fluoride, cerium oxide, cerium fluoride, silicon nitride, silicon carbide, boron nitride, and polyvinyl alcohol.

Polyimide, polyamideimide, polyesterimide,
Polyvaraxylerin, polyester, polycarbonate, polyvinyl acetal.

An alignment control film 105 formed using an organic insulating material such as polyvinyl chloride, polyamide, polystyrene, cellulose resin, or melamine resin 1 urea resin or acrylic resin
can be provided.

This alignment control film 105 is formed after forming an inorganic insulating material or an organic insulating material as described above.

It is obtained by rubbing the surface in one direction with velvet, cloth, or paper.

In another preferred embodiment of the present invention, the alignment control film 105 can be obtained by depositing an inorganic insulating material such as SiO or 5i02 on the north side of the substrate 101b by oblique vapor deposition.

In the apparatus shown in FIG. 5, a Pelger 501 is placed on an insulating substrate 503 having a suction port 505! ll! placed,
A vacuum pump (not shown) extending from the outlet 505 evacuates the pelger 501 . A crucible 507 made of tungsten or molybdenum is placed inside and at the bottom of the Pelger 501.

The crucible 507 contains several grams of Sin, S [02.

A crystal 508 such as MgF2 is placed. The crucible 507 has two lower arms 507a, 507b, which are connected to conductive wires 509 and 510, respectively. A power supply 506 and a switch 504 are connected in series between external conductors 509 and 510 of Pelger 501. Substrate 502
is located inside the Pelger 501 directly above the crucible 507 at an angle θ with respect to the vertical axis of the Pelger 501 .

When the switch 504 is opened, the Pel jar 501 is first evacuated to a pressure of about to-5 mmHg, and then the switch 504 is closed and the power supply 506 is turned on until the crucible 507 is incandescent at a suitable temperature and the crystal 508 is evaporated. Power is supplied in a regulated manner. The required current for a suitable temperature range (700-1000°C) is about 100100A. The crystal 508 is then evaporated to form an upward molecular stream indicated by S in the figure, and the fluid S is incident on the substrate 502 at an angle θ with respect to the substrate 502, so that the substrate 502 coated. The angle θ is the angle of incidence described above, and the direction of the fluid S is the oblique deposition direction described above. It is determined by calibrating the thickness with respect to time.When a film of appropriate thickness is formed, the power supply 50
6 and open the switch 504 to cool the Pel jar 501 and its interior.Then, the pressure is raised to atmospheric pressure and the substrate 502 is removed from the Pel jar 501.

In another specific example, after forming a film of the above-mentioned inorganic insulating material or organic insulating material on the surface of the substrate 101b made of glass or plastic or on the substrate 101b, the surface of the film is etched by an oblique etching method. Accordingly, an orientation control effect can be imparted to the surface.

It is preferable that the above-mentioned orientation control film 105 also functions as an insulating film, and for this purpose, the orientation control film 111
The film thickness of 105 is generally 100 to 100 lk, preferably 50 lk.
It can be set in a range of 0 to 5000 people. 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.

In addition, the liquid crystal element of the present invention has the above-mentioned alignment control.

Something similar to membrane 105 can be provided on the other substrate 101.

The liquid crystal layer 103 in the cell structure 100 shown in FIG.
SmC*, SmH*, SmI*.

SmJ*, SmK)k, SmG)k, SmF*
The liquid crystal phase 103 of the chiral smectate phase is a phase on the higher temperature side than the smectate phase, for example, a cholesteric phase (chiral nematic phase).
, nematic phase, slow cooling from Tokichi phase (l″C!-10℃
It is formed by undergoing a phase transition to SmA (smectic A phase) during the temperature cooling process (/hour), and further to a chiral smectic phase during the temperature cooling process due to slow cooling.

The important point of the present invention is that monodomain SmA can be formed when the above-mentioned liquid crystal is used in the temperature decreasing process by slow cooling, and a chiral smectate phase of monodomain can be formed according to the monodomain nature of this SmA. can be formed.

The liquid crystal composition used in the present invention may be a monophase-cholesteric phase-SmA-chiral smectic phase, a mono-cholesteric phase-chiral smectic phase, or a monophase-cholesteric phase-chiral smectic phase, or The composition may undergo a phase transition with the smectic phase.

FIG. 4 shows another specific example of the liquid crystal element of the present invention. The liquid crystal element shown in FIG. 4 consists of a pair of substrates 101a and 1
A plurality of spacer members 203 are arranged between 01b. This spacer member 203 is 1, for example, an alignment control film 10.
SiO, 5t0 is placed on the substrate 101a on which 5 is provided.
2, A-cross 203, inorganic compounds such as TiO2, or polyvinyl alcohol, polyimide, polyamideimide,
Polyesterimide, polyvaraxylylene, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene, cellulose resin, melamine resin, yulya resin.

It can be obtained by forming a film of resin such as acrylic resin or photoresist resin by an appropriate method, and then etching it so that the spacer member 203 is placed at a predetermined position.

Such a cell structure 100 includes substrates 101a and 101b.
Polarizers 107 and 108 in a crossed Nicol state or a parallel Nicol state are respectively arranged on both sides of the electrodes 102a and 102b, and optical modulation occurs when a voltage is applied between the electrodes 102a and 102b.

The present invention will be explained below according to examples.

[Example 1] A square glass substrate on which a striped ITO film with a pitch of 100 lm and a width of 62.5 ILm was provided as an electrode was prepared, and the side on which the ITO film serving as the electrode was provided faced downward. The sample was placed in the oblique evaporation apparatus shown in FIG. 5, and then a 5i02 crystal was placed in a molybdenum crucible.

Thereafter, the inside of the vapor deposition apparatus was made into a vacuum state of about 10-5 Torr, and 5i02 was obliquely vapor-deposited on the glass substrate by a predetermined method to form an obliquely vapor-deposited film of 800 people (electrode plate A).

On the other hand, a polyimide forming solution (rPIQJ manufactured by Hitachi Chemical Co., Ltd., non-volatile content concentration 14°5 wt%) was applied using a spinner coater onto a glass substrate on which a similar striped ITO film was formed. A film was formed (B electrode plate).

Next, a thermosetting epoxy adhesive is applied to the periphery of the A electrode plate except for the area that will become the injection port by screen printing, and then the striped pattern electrodes of the A electrode plate and the B electrode plate are overlapped so that they are perpendicular to each other. The distance between the two electrode plates was maintained at 2fiLm using a polyimide spacer.

Next, 5 parts by weight of cholesteryl nonanate was added to 100 parts by weight of 4-hexyloxyphenyl-4-(2''-methylbutyl)biphenyl-4'-lupoxylate to prepare a liquid crystal composition.

The following liquid crystal composition A having a uniform phase was injected into the cell thus prepared through the injection port, and the injection port was sealed. When the temperature of this cell was lowered by slow cooling and a pair of polarizers were placed in a crossed nicol state, microscopic observation revealed that it had a non-helical structure and a monodomain S m C* was formed.

Composition [Example 2] Two square glass substrates were prepared with striped ITO electrodes with a pitch of 100 gm and a width of 62.5 h, and a polyimide forming solution (Example 1) was prepared on each substrate. (similar to) using a spinner coater, and
0 polyimide films were formed.

The polyimide films formed on these two substrates were rubbed with velvet so that when they were stacked, the rubbing directions were parallel and the striped ITO electrodes were perpendicular to each other.

Next, the two substrates were placed on top of each other so that the rubbing directions were parallel to each other, and heat-curing epoxy adhesive was applied to the periphery of one substrate except for the area that would become the injection hole by screen printing. The two substrates were stacked on top of each other, and the distance between the two substrates was maintained at 2 gm using a boilimide spacer.

The liquid crystal composition A used in the above-mentioned Example 1, which was in an isokyoshi phase, was injected into the cell thus prepared through the injection port, and the injection port was sealed. The temperature of this cell is lowered by slow cooling,
A pair of polarizers was provided in a crossed nicol state while the temperature was maintained at room temperature, and microscopic observation revealed that a monodomain SmC* was formed with a non-helical structure.

[Example 3] In place of the liquid crystal compound used when creating the liquid crystal element of Example 2, liquid crystal composition B having the following composition was used.
A ferroelectric liquid crystal device was produced in exactly the same manner as in Example 2.

When observing this ferroelectric liquid crystal element with a polarizing microscope, we found that
A non-helical monodomain with no orientation defects was confirmed.

〔Effect of the invention〕

As described above, according to the present invention, by using the specific liquid crystal described above, it is possible to form a smectate phase free of alignment defects, and in particular, a ferroelectric liquid crystal phase with a non-helical structure free of alignment defects. can be formed.

[Brief explanation of drawings]

FIG. 1 is a perspective view schematically showing a liquid crystal element using chiral smectic liquid crystal. FIG. 2 is a perspective view schematically showing the bistability of the liquid crystal element. Figure 3 (A)
is a plan view showing the liquid crystal element of the present invention; FIG. 3 CB)
is a sectional view taken along line AA'. FIG. 4 is a sectional view showing another specific example of the liquid crystal element of the present invention. FIG. 5 is a cross-sectional view schematically showing an oblique evaporation apparatus used in producing the liquid crystal element of the present invention.

Claims (1)

[Claims] (1) A cell structure is formed in which a liquid crystal composition containing two or more types of liquid crystal compounds represented by the following general formula (1) is sealed between a pair of substrates, and the smectate phase of the liquid crystal composition is separated from the smectate phase. It is characterized by being formed by phase transition from a phase on the high temperature side, and having the effect of arranging in one direction preferentially the molecular axis direction where the surface of at least one of the pair of substrates contacts at the interface. A liquid crystal element. General formula (1) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, R represents an alkyl group, and R^* represents an optically active group having an asymmetric carbon atom.)