JPH07101264B2 - Liquid crystal material alignment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is directed to aligning molecules in a thin film by linearly polarized light irradiation,
The present invention relates to a novel liquid crystal alignment method characterized by aligning a liquid crystal layer to be laminated with this in a predetermined direction. More specifically, according to the present invention, a chemical substance layer having a property of orienting at a specific angle with respect to a vibration direction of light and a liquid crystal layer are laminated on a substrate, and linearly polarized light is irradiated for a predetermined time to thereby obtain a predetermined direction. Is a method for obtaining a homogeneously aligned liquid crystal material, in addition, by re-irradiating linearly polarized light having a different plane of polarization, the orientation axis of the homogeneously aligned can also be realigned to a predetermined angle, using linearly polarized light The present invention relates to a characteristic liquid crystal alignment method.

(Prior Art) A liquid crystal is a fluid having a flexible structure, but it is essential to provide orientation in materialization. Therefore, a sandwich structure in which a liquid crystal layer is filled between two substrates is used.
A means for inducing a homogeneous alignment of the liquid crystal is secondarily taken by the surface of the substrate. As a surface for inducing such orientation, a glass surface having fine grooves in a certain direction, a stretched polymer film, a polymer film accumulated by the Langmuir-Blodgett method, a vacuum vapor deposition method, a chemical vapor deposition method. And the like, and a polymer film polycondensed at the interface with the oriented liquid crystal. The homogeneous alignment axis of the liquid crystal induced by the surface is determined by the conditions at the time of producing the liquid crystal cell, and is permanently fixed. Electric field application / heat
The phase transition of the liquid crystal can be promoted or the constraint of the liquid crystal by the surface can be strengthened or weakened by the photoreaction of the chemical substance added to the liquid crystal layer, but the homogeneous alignment axis cannot be changed. Further, it is difficult to form a fine domain having an orientation axis in a predetermined direction in one material as long as the method has been used so far.

(Problems to be Solved by the Invention) The present invention has been made for the purpose of obtaining a liquid crystal material homogeneously aligned at a predetermined angle by irradiating the liquid crystal material with linearly polarized light for a certain period of time.

(Means for Solving the Problems) As a result of intensive research conducted by the present inventors to develop a method of giving a predetermined alignment to a liquid crystal material by light, the liquid crystal molecules are aligned at a specific angle with respect to the vibration direction of light. By irradiating a liquid crystal material in which a chemical substance layer having a property and a liquid crystal layer are laminated in this order on a substrate with linearly polarized light for a certain period of time, the liquid crystal layer laminated with this is aligned with the orientation of the chemical substance in the thin film. Even if the alignment axis of the homogeneously aligned liquid crystal layer can be rotated by rotating the plane of polarization of the linearly polarized light, even if the thickness of the liquid crystal layer is 10,000 times or more that of the molecules overlapping the substrate surface layer. It was found that the orientation is rapidly transmitted, and that the homogeneous orientation of the liquid crystal is maintained for a long period of time even if the light irradiation is stopped, and the present invention has been completed based on this finding.

That is, the present invention provides a liquid crystal material having a transparent substrate and a liquid crystal layer laminated thereon, a photochromic compound layer between the substrate and the liquid crystal layer, and through the transparent substrate, substantially all liquid crystal molecules. Is a method of obtaining a liquid crystal material that is homogeneously aligned in a predetermined direction by irradiating linearly polarized light for a sufficient time to align in a predetermined direction, and the alignment axis of the homogeneous alignment is obtained by re-irradiating linearly polarized light with different polarization planes. It is intended to provide a liquid crystal alignment method using linearly polarized light, which is characterized in that it can be re-aligned at a predetermined angle.

In the sandwich type liquid crystal cell which can be homogeneously aligned by this method, at least one of the two substrates needs to be a transparent substrate, and the other is coated with a sheet of metal such as copper, iron, aluminum or platinum, or coated with these metals. You can also make a sheet. These substrates are usually used as a sheet having a smooth surface with a thickness of 0.01 to 1 mm.

As the transparent substrate, ordinary silica glass, hard glass,
Sheets of quartz, various plastics, etc. or those with a surface coated with a metal oxide such as silicon oxide, tin oxide, indium oxide, aluminum oxide, titanium oxide, chromium oxide, zinc oxide, etc. or silicon nitride silicon carbide are used. To be

In the present invention, it is necessary that a chemical substance having the property of being oriented by linearly polarized light is bound to at least one of the substrates, and a photochromic compound is most commonly used as this chemical substance.

The photochromic compound is a compound that undergoes a structural change under the action of light and changes its behavior with respect to light, for example, the color tone, and has hitherto been carbon-carbon, carbon-nitrogen, nitrogen-
A wide variety of compounds are known that utilize photogeometric isomerization reactions of unsaturated double bonds between nitrogen atoms, valence photoisomerization reactions, heterolytic photocyclization ring reactions, photocyclization reactions, phototautomerization reactions, etc. ing. [See, for example, "Photochromism" (1971), published by Willy Interscience, edited by G, H, Brown]. Among such compounds, examples of photochromic compounds based on photogeometric isomerization include:
Azobenzene, indigo, acylindigo, thioindigo, selenoindigo, perinaphthoindigo, hemiindigo, hemithioindigo, azomethine, etc. , Benzothiazolinospyrobenzopyran, indolinospyrobenzothiopyran, spiroindolizine, and the like, and examples of photochromic compounds based on the photocyclization reaction include stilbene, fulgide, and the like.
Further, examples of the photochromic compound based on the phototautomerization reaction include compounds having salicylidene anil, o-hydroxyazobenzene, o-nitrobenzyl, etc. as basic skeletons.

To provide a thin film of a photochromic compound on a substrate, a method usually used for vertical alignment of liquid crystals, for example, a method of treating the substrate with a photochromic compound having a surface active group, substitution with at least one halogen atom or an alkoxy group is used. The photochromic compound having a silyl group may be treated, or the substrate surface may be treated with a silylating agent having an amino group and then a photochromic compound having a carboxyl group or a vinyl group may be bonded thereto. J. Cognard, "Molecular Crystals and Liquid Crystals
s) ”, Supplement 1 (1982), and Shoichi Matsumoto, Kazuyoshi Tsunoda,“ Latest Liquid Crystal Technology ”(1983)].

Examples of the surface active group of the photochromic compound having the surface active group include a carboxylic acid residue, a malonic acid residue, an alkylaluminum salt residue, an alkylpyridinium salt residue, an alkylquinolinium salt residue, and a carboxy group. Examples thereof include a latochromium complex residue, an ester residue, a nitrile residue, a urea residue, an amine residue, an alcohol residue, a phenol residue and a betaine residue. In order to form such a thin film of a photochromic compound having a surface active group on a substrate, it may be applied directly or dissolved in a liquid crystal substance and used. In the latter case, the amount of the photochromic compound having a surface active group added is in the range of 0.01 to 5.0% based on the weight of the liquid crystal.

Examples of the photochromic compound having a silyl group substituted with at least one halogen atom or an alkoxy group described above include triethoxysilylazobenzene, monochlorodiethoxysilylazobenzene, trichlorosilylazobenzene, triethoxysilylindigo, triethoxysilylindo. Rinospirobenzopyran and the like. Treatment with these compounds is carried out by coating the surface of the substrate as a solution having a concentration in the range of 0.1 to 10%, preferably 0.5 to 5%, or by immersing the substrate in this solution. As the solvent at this time, acetic acid, toluene, acetone, dimethylformamide and the like are suitable. The processing time is 1 second to 1 hour, usually 30 seconds to 10 minutes.

Next, the silylating agent used when the substrate surface is treated with a silylating agent having an amino group and then with a photochromic compound having a carboxyl group or a vinyl group is, for example, aminopropyltriethoxysilane or aminopropyldiethylsilane. Examples include ethoxysilane, aminobutylmethyldiethoxysilane, and aminobutyltriethoxysilane. The treatment with these silylating agents reduces this to 0.1-10
%, Preferably 0.5 to 5%, as a solution having a concentration in the range of 0.5% to 5%, or by immersing the substrate in the solution. As the solvent in this case, water, ethanol, acetic acid, toluene, acetone, dimethylformamide and the like are preferable. The processing time is usually within the range of several seconds to tens of minutes.

After the treatment with this silylating agent, the amino group of the silylating agent is reacted with a photochromic compound having a carboxyl group according to a conventional method to form an amide bond.

Alternatively, a photochromic compound having a vinyl group can be added to the amino group of the silylating agent by Michael. To add a photochromic compound having a vinyl group to Michael, apply it as a 0.1 to 10% solution on the substrate and heat it for several minutes to several hours, or immerse the substrate in this solution for several tens of minutes to several hours. It is done by heating.

The chemicals on the surface of the substrate can perform their function satisfactorily by forming a monolayer, but can be bilayer or more if desired.

Next, as the liquid crystal used in the material, any one can be selected from conventionally known nematic, smectic and cholesteric liquid crystal substances. Further, it goes without saying that the liquid crystal substance includes not only low molecular weight substances but also high molecular weight substances.

Such a liquid crystal material is, for example, A.
n) Others, “Molecular Crystals and Liquis
d Crystals) ", Vol. 115, page 1. The polymer liquid crystal material is, for example, in Advances in Polymer Science.
e), Volume 60/61 (1984). These liquid crystal substances may be used alone or in combination of two or more.

As one of the methods for obtaining linearly polarized light used in the present invention, there is a method of passing light from a non-polarized light source through a linear polarizer. As such a linear polarizer, for example, a polaroid plate,
Dichroic film polarizer such as polar coat film, Nicol prism,
Examples thereof include birefringent polarizers such as Glan-Thomson prism, Ahren's prism, Gran-Foucault prism, Lotion prism, Wollaston prism, and laminated plate polarizer. When laser light is used as the light source, the output and the spatial controllability are high, so that it is possible to create fine domains with different alignment axes at high speed in the liquid crystal material. In this case, if a laser that outputs a linearly polarized light is used in advance, the linear polarizer may not be used.

As a simple method, the irradiation condition of linearly polarized light can be obtained by making ordinary light incident at an angle equal to the Brewster's angle of the substrate constituting the liquid crystal material.

This linearly polarized light irradiation needs to be performed for a sufficient time so that substantially all liquid crystal molecules are aligned in a predetermined direction. By performing such a treatment, a homogeneous alignment of the liquid crystal layer can be obtained, and the homogeneous alignment can be maintained for a long time even when the light irradiation is stopped.

The present invention will now be described in more detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing the basic structure of a liquid crystal material used in the present invention. A molecular layer 2 made of a chemical substance oriented by linearly polarized light is fixed on a transparent substrate 1, and a liquid crystal layer 3 is further formed thereon. Is laminated and is further covered with a substrate 4 in order to prevent dissipation and damage. This substrate may be transparent or opaque, and has a function of homogeneously orienting the molecular layer composed of a chemical substance whose surface is aligned by linearly polarized light or the liquid crystal in a permanently fixed direction. It is possible to use an alignment film, or one coated with a molecular layer of a vertical alignment agent having a function of vertically aligning liquid crystals.

That is, the orientation of the liquid crystal layer in the material is not constant before the irradiation with linearly polarized light. When linearly polarized light is incident on a part of the material from the side of the substrate 1, the photochromic residue on the surface of the substrate undergoes a structural change, and at the same time, the photochromic residue is oriented at a specific angle with respect to the polarization plane. The liquid crystal layer is aligned.

For example, when a material using the substrate 4 treated with the vertical alignment agent is irradiated with linearly polarized light from the substrate 1 side and placed between two orthogonal polarizers and the material is rotated, the portion irradiated with linearly polarized light is (π
/ 2) Light and dark appear with a cycle of radians. Further, by re-irradiating linearly polarized light having a different plane of polarization, the light can be reoriented in a different direction, and a phase difference can be imparted to the period of intensity of transmitted light by the rotation angle of the plane of polarization.

Further, when the dichroic dye is dissolved in the liquid crystal layer in advance and aligned by irradiation with linearly polarized light, it is possible to see the light and shade of the dye through one polarizer. At this time, light and shade appear with a period of π radians.

As the dichroic dye, for example, those described in Takatake Matsumura, "Dyeing Industry", Volume 32, page 215 (1984) are used.

(Effects of the Invention) As a conventional liquid crystal material alignment method, a method of inducing a homogeneous alignment of liquid crystal by a surface of a substrate is secondary,
The orientation axis is permanent or fixed, which is determined in the manufacturing process of the liquid crystal cell. Therefore, the degree of orientation and orientation must be adjusted empirically each time, and it is impossible to change the orientation direction minutely in the material to obtain a complicated pattern. The size of the obtained pattern was limited to the size of the electrode, and the pattern disappeared when the electric field was removed.

The method of aligning a liquid crystal material using linearly polarized light according to the present invention expands the limited application range of the liquid crystal material by the existing alignment technology. That is, the orientation direction can be determined by the plane of polarization of the linearly polarized light to be irradiated, and the degree of orientation changes the linear polarization property of the irradiated light, that is, the component ratio of P wave and S wave.
Alternatively, it can be easily adjusted by changing the intensity of light. In addition, re-irradiation with linearly polarized light having different planes of polarization allows for reorientation. Since light is used, it is possible to create a domain in the material having a fineness almost equal to the size of the condensed light and having a uniform alignment direction, and thus a complicated pattern can be easily obtained. The alignment of the liquid crystal obtained by irradiation with linearly polarized light is maintained even if the light irradiation is stopped.

(Example) Next, an Example demonstrates this invention still in detail.

Example 1 A 20 mm × 20 mm × 1 mm glass plate surface-treated with aminopropyltriethoxysilane by a conventional method was used to prepare a structural formula I It was immersed in a 1.0% chloroform solution of 4-methoxy-4'-acryloyloxyazobenzene shown in 10 minutes for 10 minutes, then pulled out from the solution and air dried. This was heated in an oven at 100 ° C. for 1 hour to fix azobenzene by a Michael addition reaction. This glass plate was repeatedly ultrasonically cleaned with chloroform (substrate A). 20mm × 20mm × 1m treated with octadecyltrichlorosilane by conventional method
A sandwich type cell was constructed by sandwiching a cyclohexanecarboxylic acid phenyl ester mixed liquid crystal (K-17 ° C-N-73 ° C-I) through an 8 μm spacer between a glass plate of m and a substrate A and sealing it with an epoxy resin. ..

The cell before light irradiation has homeotropic orientation and does not transmit any light when placed between two crossed polarizers. When 365 nm light was linearly polarized through a polarizing prism and then was incident on the cell from the side of the substrate A, the liquid crystal changed to a homogeneous alignment due to photoisomerization of azobenzene on the surface of the substrate. At this time, the exchange of the polarization plane of the irradiation light and the cell is L _θ . When the polarized light irradiation is stopped and the cell is rotated between two orthogonal polarizers, the angle formed by L _θ with one polarizer is θ (radian unit), and θ = {(2n + 1) / 4} π is bright, and θ
It became dark at = (n / 2) π (n is an integer).

In the homogeneously aligned cell, the angle giving the maximum and minimum values of the transmitted light was the angle rotated by α radians with respect to the previous θ after irradiation with 365 nm linearly polarized light whose polarization plane was rotated by α radians for a certain period of time. . That is, the alignment axis of the homogeneous alignment of the liquid crystal rotated by α radians. Reorientation of the liquid crystal by rotation of the plane of polarization of the linearly polarized light could be repeated many times for arbitrary α.

[Example 2] A substrate A was obtained by the method described in Example 1. Structural formula II The cyclohexanecarboxylic acid phenyl ester mixed liquid crystal (K-17 ° C-N-73 ° C-I) containing 1.0% by weight of the anthraquinone type dichroic dye is sandwiched between two substrates A via an 8 μm spacer. A sandwich type cell was constructed by sealing with an epoxy resin.

The cell before light irradiation had homeotropic alignment. 365n
When the light of m was made into linearly polarized light through a polarizing prism and then incident on the cell, the liquid crystal became homogeneously aligned with the photoisomerization of azobenzene on the surface of the substrate. The line of intersection between the polarization plane of the irradiation light and the cell is L _θ . At the absorption wavelength of the dichroic dye, the light transmitted through the cell through one polarizer is L
_{If the} angle that θ makes with the polarizer is θ (in radians), then θ
= Nπ brightened, and θ = {n + (1/2)} π darkened (n is an integer).

After irradiating a homogeneously oriented cell with 365 nm linearly polarized light whose polarization plane was rotated by α radians for a certain period of time, the angle giving the maximum or minimum value of the transmitted light was the angle rotated by α radians with respect to θ. . That is, the alignment axis of the homogeneous alignment of the liquid crystal rotated by α radians. Reorientation of the liquid crystal by rotation of the plane of polarization of the linearly polarized light could be repeated many times for arbitrary α.

"Example 3" Structural formula III The azobenzene derivative having a carboxylic acid residue shown in (10
0mg), aminopropyltriethoxysilane (61mg) 5
It was dissolved in ml of dehydrated methylene chloride and cooled to 0 ° C. One, three
-Dicyclohexylcarbodiimide (57 mg) was added, and the mixture was stirred for 1 hr and then at room temperature for 5 hr. After filtering off the by-product carbourea, 20 ml of ethanol was added.
The solution was immersed in a washed glass plate for 30 minutes, air-dried, and then heated at 120 ° C. for 1 hour. After repeated ultrasonic cleaning with chloroform, it was dried and cyclohexanecarboxylic acid phenyl ester mixed liquid crystal (K
A sandwich type cell was constructed by sandwiching -17 ° C-N-73 ° C-I) and sealing with an epoxy resin.

The cell before light irradiation had a homeotropic orientation and did not transmit any light when placed between two crossed polarizers. 36
When 5 nm light was linearly polarized through a polarizing prism and incident on the cell, the liquid crystal was homogeneously aligned with the photoisomerization of azobenzene on the substrate surface. When the polarized light was blocked and the cell was rotated between two orthogonal polarizers, alternating light and dark appeared at every (π / 4) radian.

This cell is irradiated with 365 nm linearly polarized light by rotating the plane of polarization by α radians for a certain period of time, and after blocking the irradiation, the angle that gives the maximum and minimum values of the transmitted light is the angle rotated by α radians with respect to the previous θ. Became. That is, the homogeneous alignment axis of the liquid crystal rotated by α radians. Reorientation of the liquid crystal by rotation of the plane of polarization of the linearly polarized light could be repeated many times for arbitrary α.

[Brief description of drawings]

The figure is a cross-sectional view showing the basic structure of a liquid crystal material to which the alignment method of the present invention can be applied. In the figure, reference numeral 1 is a transparent substrate, 2
Is a molecular layer made of a chemical substance that is aligned by linearly polarized light, 3 is a liquid crystal layer, and 4 is a substrate for preventing dissipation and damage.

Claims (2)

[Claims] 1. A liquid crystal material having a transparent substrate and a liquid crystal layer laminated on the transparent substrate, a photochromic compound layer is provided between the substrate and the liquid crystal layer, and substantially all liquid crystal molecules pass through the transparent substrate. A method for orienting a liquid crystal material, which comprises irradiating linearly polarized light for a time sufficient to orient in a predetermined direction. 2. The alignment method according to claim 1, wherein the liquid crystal layer is a liquid crystal material containing a dichroic dye.