JPS61205923A - 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 alkoxy or 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 from 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 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. 6 Concerning Liquid Crystal Elements with Improved Display and Driving Characteristics [Prior Art] Conventional liquid crystal elements include, for example, M-Shut CM,
5chadt) and Double Fist Helfritz (W, H
``Applied Physics Leaders'' (author)
sLetters”) No. 18@, No. 4 (February 1971
``Voltage Dependant to Optical Activity - of a Twisted Nematic Liquid Crystal''
ntOptical Activity of
aTwisted Nematic Liquor
Twisted knematic shown in idCrystal”
tic) A device using liquid crystal is known. This T
N liquid crystals have a problem in that crosstalk occurs during time division driving using a matrix electrode structure with high pixel density, so the number of pixels has been 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.

To improve the drawbacks of conventional liquid crystal devices, the use of bistable liquid crystal devices is proposed by Clark (C1
ark) and Lagauer (Lage rwa l l
) (Japanese Unexamined Patent Publication No. 56-107216, U.S. Pat. No. 4,367,924, etc.), liquid crystals having bistability are generally composed of chiral smectate C phase (SmC") or H A ferroelectric liquid crystal having a phase (S mH") is used.

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 placed between a pair of parallel substrates, regardless of the state of applied electric field.

It is necessary that the molecules be in such a state that conversion between the above two stable states occurs effectively.

For example, for a ferroelectric liquid crystal having an SmC" or SmH" phase, a region in which 3m0 or a layer of liquid crystal molecules having an SmH" phase is perpendicular to the substrate surface, and therefore the liquid crystal molecular axes are aligned approximately parallel to the substrate surface. However, in conventional ferroelectric liquid crystal devices with bistability, the alignment state of the liquid crystal having such a domain structure was not necessarily formed satisfactorily. The reality is that sufficient characteristics could not be obtained.

For example, according to C1ark et al., methods of applying a magnetic field, methods of applying a shear force, and small spacing between substrates are used to provide such an orientation state.

A method of arranging parallel ridges has been proposed. However, none of these methods necessarily gave satisfactory results. For example, the method of applying a magnetic field requires large-scale equipment and is incompatible with thin-layer cells with good operating characteristics. This method has the disadvantage that it is incompatible with the method of injecting liquid crystal. 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. Cholesteric phase (chiral nematic phase).

When a phase transition is caused by slow cooling from a nematic phase or a tomoyoshi phase, for example, during the formation of SmA, a monodomain in which liquid crystal molecules are aligned in one direction can be formed, resulting in the bistability of the ferroelectric liquid crystal. It has been found that a liquid crystal element can be obtained with a structure that allows both the operation of the element based on the above 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 phase transition from the phase on the higher temperature side, and has the effect of arranging in one direction with priority given to the direction of the molecular axis where the surface of at least one of the pair of substrates is in contact with the interface. It has characteristics.

General formula (1) In the formula, R is an alkoxy group or an alkyl group, and a straight chain,
It may be a branched or cyclocyclic alkoxy group, particularly a straight chain alkoxy group (Cnl(2n+10-) is preferable, and the number of carbon atoms n is 1
-18 is suitable. Further, R* in the formula is an optically active group having an asymmetric carbon atom, and particularly preferred is a residue of the following formula (2) or (3).

Formula (2) %Formula% Formula (3) CH3 ■ -CH-C6H13 Tree The compound represented by the above-mentioned general formula (1) is 1, for example, JP-A-4
It can be obtained by the synthesis method disclosed in s9-9aosx publication.

〔Example〕

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

The liquid crystal used in the present invention has ferroelectricity, and specifically has a chiral smect C phase (Smc type).
, H phase (SmH industry), 1 phase (SmI”), J phase (SmJ
A liquid crystal having a phase (SmK''), a G phase (S m G ''), or an F phase (SmF phase) can be used.

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

(n = 4. 5. 6. 7. 8. 9. 10.
11゜12, 14. 16. 18) (n=4.8) These liquid crystal compositions are similar to other ferroelectric liquid crystals, such as DOB.
AMBC, decyloxybenzylidene-P'-amino-2
It can be used in combination with -methylbutylcinnamate, HOBACPC, hexyloxybenzylidene-P'-7 minnow-2-chloropropylcinnamate, and the like.

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

"degree~ 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 n203.5n02 or ITO (Indi
A substrate (glass plate) coated with a transparent electrode made of a thin film such as um-Tin oxide), between which a liquid crystal molecular layer 22 is oriented perpendicular to the glass surface.
) K phase or SmH* phase liquid crystal is sealed.

A thick line 23 represents liquid crystal molecules.

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 21a and 21b, the helical structure of the liquid crystal molecules 23 is unraveled, and the liquid crystal molecules 23 are aligned so that the dipole moment (P) 24 is all oriented in the direction of the electric field. You can change direction.

The liquid crystal molecules 23 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass surface, the optical polarity changes depending on the voltage applied polarity. It is easily understood that the liquid crystal optical modulation element has variable characteristics.

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, and the dipole moment Pa or Pb is either 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 the voltage applying means 31a and 31b as shown in FIG. 2, the dipole moment corresponds to the electric field vector of the electric field Ea or Eb. The liquid crystal molecules change direction upward 34a or downward 34b, and accordingly the liquid crystal molecules enter the first stable state 3.
3a or the second stable state 33b.

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. Further, as long as the applied electric field Ea does not exceed a certain threshold value, each orientation state is maintained. In order to effectively realize such fast response speed and 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 Sm
A layer having a C* phase or SmH)k phase is aligned perpendicularly to the substrate surface, and liquid crystal molecules are aligned approximately parallel to the substrate surface.
It is difficult to form cells with high monodomain properties, and the main purpose of the present invention is to provide a solution to this problem.

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

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

In the cell structure loo shown in FIG. 3, a pair of substrates 101a and 101b made of glass plates or plastic plates are held at a predetermined distance by a spacer 104, and are bonded 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 by Board 1
An electrode group (for example, a signal voltage application electrode group in a 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 is made of silicon oxide or silicon dioxide, for example.

aluminum oxide, zirconia, magnesium fluoride,
Inorganic insulating materials such as cerium oxide, cerium fluoride, silicon nitride, silicon carbide, boron nitride, and polyvinyl alcohol.

Polyimide, polyamideimide, polyesterimide,
The alignment control film 105 may be formed using an organic insulating material such as polyparaxylerin, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide, polystyrene, cellulose resin, melamine resin, urea resin, or acrylic resin. can.

The orientation control film 105 is obtained by forming a film of an inorganic insulating material or an organic insulating material as described above, and then rubbing the surface of the film 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 coating L of the substrate 101b with an inorganic insulating material such as SiO or 5i02 by an oblique vapor deposition method.

In the apparatus shown in FIG. 5, a Pel jar 501 is placed on an insulating substrate 503 having a suction port 505, and a vacuum pump (not shown) extending from the suction port 505 evacuates the Pel jar 501. . Crucible 507 made of tungsten or molybdenum is Pelger 50
placed inside and at the bottom of 1.

Crucible 507 has several grams; ym sio, 5i02゜M
A crystal 508 such as g F 2 is placed. Crucible 507
has two lower arms 507a, 507b,
The arms 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. Board 5
02 is placed inside the Pel jar 501 directly above the crucible 507 at an angle of θ with respect to the vertical axis of the Pel jar 501.

When the switch 504 is opened, the Pel jar 501 is first evacuated to approximately 10-5 mmHg pressure, and then the switch 504 is closed and the power supply 506 is turned on until the crucible 507 becomes 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 above-mentioned "incident angle °", and the direction of the fluid S is the above-mentioned "oblique deposition direction". The thickness is determined by calibration. When a coating of appropriate thickness is formed, the power from the power source 506 is reduced, and the switch 504 is opened to cool the Pel jar 501 and its inside. The pressure is reduced to atmospheric pressure. Remove the board 502 from the Pelger 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 totb, 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 alignment control film 105 also functions as an insulating film at the same time.
The film thickness of No. 5 can be generally set in the range of 100 to 1, preferably 500 to 5,000. 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.
Therefore, even if the operation is repeated, the liquid crystal compound will not deteriorate.

Further, in the liquid crystal element of the present invention, a film similar to the above-described alignment control film 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)k.

SmJ*, SmK*, SmG*, SmF)k. The liquid crystal phase 103 of the chiral smectic phase is formed by a temperature decreasing process by gradual cooling (1°C to 10°C/hour) from a phase higher than the smectic phase, such as a cholesteric phase (chiral nematic phase), a nematic phase, or an etiostatic phase. It is formed by undergoing a phase transition to SmA (smectic A phase), and then to a chiral smectic phase during the temperature decreasing process by slow cooling.

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

In the liquid crystal composition used in the present invention, in the cooling process, a tooyoshitic phase-cholesteric phase 2 SmA-chiral smectic phase, a tokitoshitic phase-cholesteric phase-irradial smectic phase, or a tokitoshitic phase-SmA-chiral smectic phase are used. The composition may undergo a phase transition with the critical 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, for example, the orientation control W film 10.
St, , 5t0 on the substrate 101a on which 5 is provided.
2, A intersection 203. Inorganic compounds such as TiO2, or polyvinyl alcohol, polyimide, polyamideimide, polyesterimide, polyparaxylylene, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene.

Cellulose resin, melamine resin, yurya 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.

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

Example 1 A square glass substrate was prepared on which a striped ITO film with a pitch of 100 #Lm and a width of 62.5 m was provided as an electrode, and the side on which the ITO film serving as the electrode was provided faced downward. It was set in the oblique evaporation apparatus shown in FIG. 5, and then a crystal of 5i02 was set 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 (rPrQJ manufactured by Hitachi Chemical Co., Ltd.; non-volatile content concentration 14.5 wt%) was placed on a glass substrate on which a similar striped ITO film was formed.
was applied using a spinner coater to form a film of 800 people (electrode plate B).

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 using a screen printing method, 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 2 m using a polyimide spacer.

A liquid crystal composition A shown below having a tokiyoshi phase was injected into the thus prepared cell through an injection port, and the injection port was sealed. When this cell was cooled slowly and then observed under a microscope with a pair of polarizers placed in a crossed nicol state while maintaining the temperature at room temperature, it was found that it had a non-helical structure and a monodomain SmC* was formed. It turned out that there was.

Example 2 Two square glass substrates were prepared with striped ITO electrodes with a pitch of 100 ILm and a width of 62.5 lm. , a polyimide forming solution (same as in Example 1) was applied onto each substrate using a spinner coater, and aO
O polyimide films were formed.

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

Next, the two substrates were stacked so that the rubbing directions were parallel to each other, and a thermosetting epoxy adhesive was applied to the periphery of one substrate by screen printing except for the area that would become the injection port. The two substrates were stacked on top of each other, and the distance between the two substrates was maintained at 21 Lm using a polyimide spacer.

The above-mentioned liquid crystal composition A, which was in the isokyoshi phase, was injected into the cell thus prepared through the injection port, and the injection port was sealed. The temperature of this cell was lowered by slow cooling, and while the temperature was maintained at room temperature, a pair of polarizers was placed in a crossed Nicol state, and microscopic observation revealed that it had a non-helical structure.

It was found that monodomain SmC* was formed.

Example 3 A ferroelectric liquid crystal was produced in exactly the same manner as in Example 2, except that liquid crystal composition B was used in place of liquid crystal composition A used to create the liquid crystal element in Example 2. The element was created.

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

Lri@B Wood 50% by weight 5% by weight [Effects of the Invention] As described above, according to the present invention, by using the above-mentioned specific liquid crystal, it is possible to form a smectic phase free from alignment defects. 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, and FIG. 3(B)
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 a liquid crystal element according to the present invention. Patent applicant: Canon Co., Ltd. Figure 5, 94

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 is an alkoxy group or an alkyl group, and R^
* is an optically active group having an asymmetric carbon atom. )