JPH04284421A - Liquid crystal orientation method by diagonal light - Google Patents

Abstract

PURPOSE:To allow the inpartation of prescribed homogeneous orientation to a liquid crystal layer by diagonally irradiating this layer with reaction light and to allow the application of the fresh homogeneous orientation thereto by reirradiating the layer with the reaction light entering in different optical paths. CONSTITUTION:The liquid crystal material formed by successively laminating a photochromic compd. layer and a liquid crystal layer on a transparent substrate is irradiated diagonally with the reaction light from the transparent substrate side, by which the homogeneous orientation in a prescribed direction is obtd.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a novel liquid crystal alignment method that can homogeneously align a liquid crystal layer in contact with a molecular layer that performs a selective photochromic reaction depending on the incident optical path of light. be. More specifically, the present invention provides a transparent substrate provided with a photochromic compound layer that reversibly changes its structure in response to two lights of different wavelengths.
This is a method in which selective photochromism is performed by irradiating reaction light at an angle from the perpendicular to the substrate, thereby creating anisotropy on the surface of the photochromic compound layer and imparting a predetermined homogeneous orientation to the liquid crystal layer in contact with the photochromic compound layer. In addition, the present invention relates to a liquid crystal alignment method using oblique light irradiation onto a liquid crystal material, which can also provide a new homogeneous alignment axis by re-irradiating incident reaction light on a different optical path.

0002

[Prior Art] Liquid crystal is a fluid with a flexible structure.
It is necessary to give a predetermined orientation when making the material. For this reason, a sandwich structure is usually used in which a liquid crystal layer is filled between two substrates, and alignment is induced by the restraining force of the substrate surfaces. For example, as a surface to give homogeneous orientation, a glass surface with fine grooves cut in a certain direction, a stretched polymer film, a polymer film accumulated by the Langmuir-Blodgett method, a vacuum evaporation method, a chemical vapor deposition method, etc. Examples include a vapor-deposited film made by a liquid crystal, a polymer film polycondensed at the interface with an aligned liquid crystal, and the like. However, in such a method, the homogeneous orientation axis of the liquid crystal induced by it is determined at the time of manufacturing the liquid crystal cell, and is permanent and unique to the material, so the restraining force by the surface due to the application of an electric field, heat, etc. However, it is not possible to change the homogeneous orientation axis, and it is difficult to create fine domains with different orientation axes in one material.

0003

[Problems to be Solved by the Invention] Under these circumstances, the present invention aims to achieve high controllability by using light.
The purpose of this invention is to provide a method for imparting a predetermined orientation to any position or area in a liquid crystal material.

[Means for Solving the Problems] As a result of intensive research to develop a method for imparting a predetermined orientation to a liquid crystal material using light, the present inventors have found that the liquid crystal material can be oriented at a specific angle with respect to the incident direction of light. In a liquid crystal material in which a photochromic compound layer with properties and a liquid crystal layer are laminated in this order, anisotropic alignment in the photochromic compound layer is induced by irradiating reaction light at an angle from the perpendicular to the substrate. Along with this, the liquid crystal layer laminated on the photochromic compound layer is homogeneously aligned, the homogeneous alignment axis of the liquid crystal layer can also be rotated by rotating the optical path of the incident light with respect to the substrate, and the thickness of the liquid crystal layer is similar to that of the substrate. Based on this knowledge, we discovered that alignment is rapidly transmitted even when molecules overlap more than 10,000 times as much as the surface layer, and that the homogeneous alignment of liquid crystals is maintained for a long period of time even when light irradiation is stopped. The present invention has been accomplished. That is, the present invention obtains homogeneous alignment in a predetermined direction by obliquely irradiating reaction light from the transparent substrate side to a liquid crystal material formed by sequentially laminating a photochromic compound layer and a liquid crystal layer on a transparent substrate. The present invention provides a method for aligning liquid crystals using oblique light, which is characterized by the following. The liquid crystal material used in the present invention has a structure in which a photochromic compound layer and a liquid crystal layer are sequentially laminated on a transparent substrate, but it is usually used as a sandwich type material in which a substrate is further provided on the liquid crystal layer. . This substrate may be transparent or may be a non-transparent substrate such as a sheet of metal such as copper, iron, aluminum, platinum, or a sheet coated with these metals. These substrates are usually 0.
It is used as a sheet with a smooth surface and a thickness of 0.01 to 1 mm. On the other hand, as a transparent substrate, a sheet of ordinary silica glass, hard glass, quartz, various plastics, etc. or a metal such as silicon oxide, tin oxide, indium oxide, aluminum oxide, titanium oxide, chromium oxide, zinc oxide, etc. Those coated with oxide, silicon nitride, silicon carbide, etc. are used. In the present invention, it is necessary that a layer made of a photochromic compound having a property of being oriented anisotropically with respect to the optical path of reaction light is provided on a transparent substrate. The photochromic compound is a compound that undergoes a structural change under the action of light and changes its behavior with respect to light, such as color tone. A wide variety of compounds are known that utilize photogeometric isomerization reactions of heavy bonds, valence photoisomerization reactions, heterolytic photoopening and closing reactions, photoring closure reactions, phototautomerization reactions, etc. See "Photochromism" (1971), edited by G. H. Brown, published by Science Publishing.] Among such compounds, examples of photochromic compounds based on photogeometric isomerization include azobenzene, indigo, acylindigo, thioindigo, selenoindigo, perinaphthoindigo, hemiindigo, hemithioindigo, azomethine, etc. Examples of reaction-based photochromic compounds include indolinospirobenzopyran, indolinospironaphthoxazine, benzothiazolinospirobenzopyran, indolinospilobenzothiopyran, and spiroindolizine. Examples of chromic compounds include stilbene and fulgide, and examples of photochromic compounds based on phototautomerization reactions include salicylideneanyl, ο-hydroxyazobenzene, and ο-nitrobenzyl. Examples include compounds that Thin films of these photochromic compounds can be provided on substrates by methods commonly used for vertical alignment of liquid crystals, such as by treating the substrate with a photochromic compound having surface-active groups, at least one halogen atom or A method in which the substrate surface is treated with a photochromic compound having a silyl group substituted with an alkoxy group, a method in which the substrate surface is treated with a silylating agent having an amino group and then a photochromic compound having a carboxyl group or a vinyl group is bonded, or a method in which a photochromic compound having a carboxyl group or a vinyl group is bonded. This can be carried out by applying or adsorbing a polymer compound having a chromic residue [as described in "Molecular Crystals and Liquid Crystals" written by J. Cognard.
dLiquid Crystals), Supplement 1 (1982), and Shoichi Matsumoto and Kazuyoshi Tsunoda, Latest Technology in Liquid Crystals (1983)]. Examples of the surface-active groups of photochromic compounds having the above-mentioned surface-active groups include carboxylic acid residues, malonic acid residues, alkyl aluminum salt residues, alkylpyridinium salt residues, alkylquinolinium salt residues, carboxylic acid residues, Examples include latchromium complex residues, ester residues, nitrile residues, urea residues, amine residues, alcohol residues, phenol residues, and betaine residues. To provide a thin film of a photochromic compound having such surface-active groups on a substrate, it may be applied directly or dissolved in a liquid crystal material. In the latter case, the amount of the photochromic compound having a surface active group added is usually selected in the range of 0.01 to 5.0% by weight, based on the weight of the liquid crystal. As the photochromic compound having a silyl group substituted with at least one halogen atom or alkoxy group,
Examples include triethoxysilylazobenzene, monochlorodiethoxysilylazobenzene, trichlorosilylazobenzene, triethoxysilyl indigo, triethoxysilylindolinospirobenzopyran, and the like. Treatment with these compounds is usually 0.1 to 10% by weight.
, preferably by applying it to the substrate surface as a solution at a concentration in the range of 0.5 to 5% by weight, or by immersing the substrate in this solution. Suitable solvents at this time include acetic acid, toluene, acetone, and dimethylformamide. Further, the processing time is 1 second to 1 hour, usually 30 seconds to 10 minutes. Next, when the substrate surface is treated with a silylating agent having an amino group and then treated with a photochromic compound having a carboxyl group or a vinyl group, the silylating agent used is as follows:
Examples include aminopropyltriethoxysilane, aminopropyldiethoxysilane, aminobutylmethyldiethoxysilane, and aminobutyltriethoxysilane. Treatment with these silylating agents usually reduces this to 0.
．． It is carried out by applying it to the substrate surface as a solution with a concentration in the range of 1 to 10% by weight, preferably 0.5 to 5% by weight, or by immersing the substrate in this solution. Suitable solvents in this case include water, ethanol, acetic acid, toluene, acetone, and dimethylformamide. Further, the processing time is usually within a range of several seconds to several tens of minutes. After 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. Furthermore, a photochromic compound having a vinyl group can be added to the amino group of the silylating agent by Michael addition. To perform Michael addition with a photochromic compound having a vinyl group, apply it to a substrate as a solution of about 0.1 to 10% by weight and heat it for several minutes to several hours, or immerse the substrate in this solution. This is done by heating for several tens of minutes to several hours. The chemical substance on the substrate surface can function well by forming a monomolecular layer, but bimolecular layers or more can be formed if desired. Therefore, polymer compounds having photochromic residues can also be used. Such polymeric compounds may be produced by pre-producing monomers having photochromic units and then subjecting them to a polymerization reaction, or by bonding the photochromic compound to the polymeric compound by a known reaction. Good (see Masahiro Irie, "Synthesis and Application of Photofunctional Polymers" (1984), published by CMC). In this case, the photochromic residue may be incorporated into the main chain of the polymer or may be bonded to the side chain, but from the viewpoint of efficient reversible structural change by light, photochromic residues are More preferably, the chromic residue is attached to a side chain. Examples of the basic polymer compound that provides a polymer compound having a photochromic residue include polyvinyl alcohol, polyimide resin, poly(meth)acrylic acid ester, poly(meth)acrylic acid amide, poly(L-glutamic acid ester), poly( L-lysine), polystyrene,
Examples include, but are not limited to, polyester, polyamide, polysiloxane, polysulfone, and the like. The rate of introduction of photochromic units into these basic polymer compounds can be set so that the molecular weight per photochromic unit is in the range of 0 to 500 as calculated by dividing the photochromic unit. desirable. If the value is higher than this, or in other words, if the introduction rate is lower than this, it will no longer be possible to impart a predetermined orientation by light. Next, as the liquid crystal used in the liquid crystal material, any one can be selected from among conventionally known nematic, smectic, and cholesteric liquid crystal materials. It goes without saying that liquid crystal substances include not only low molecular weight substances but also high molecular weight substances. Such liquid crystal materials are described, for example, in "Molecular Crystals and Liquids" by A. Bequin et al.
Molecular Crystal
s and Liquid Crystals)”, No. 1
It is described in Volume 15, page 1. Polymer liquid crystal materials are described, for example, in Advances in Polymer Science.
ence), Volume 60/61 (1984). These liquid crystal substances may be used alone or in combination of two or more.

Next, the present invention will be explained in more detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing the basic structure of the liquid crystal material used in the present invention, in which a photochromic compound layer 2 is fixed on a transparent substrate 1, and a liquid crystal layer 3 is further laminated on top of this. In order to prevent this, this is further covered with a substrate 4. This substrate may be transparent or opaque, and its surface is coated with a photochromic compound layer, or a molecular layer or alignment film that has the function of homogeneously or vertically aligning the liquid crystal in a predetermined direction. can be used. When reaction light is obliquely incident on this liquid crystal material from the transparent substrate side, the photochromic molecules on the substrate undergo a structural change at a reaction rate depending on the molecular orientation, resulting in anisotropy on the surface. The alignment of the liquid crystal layer in contact with the anisotropic surface is homogeneous, and the alignment axis correlates with the direction in which the reaction light path is projected onto the substrate. FIG. 2 shows a layout diagram in a liquid crystal alignment method using oblique light. In the figure, L is the temporary axis of the liquid crystal material, and the reaction light obliquely enters a point P above L from K. MP projects the reaction light onto the substrate.
The angle that MP makes with L is an incident azimuth angle θ, and the angle that KP makes with L is an incident angle α. This angle of incidence α may have a value of 1° to 89°, but is preferably approximately 55° to 80°. If the angle is larger than this, the effect of oblique irradiation will not be exhibited easily, and if the angle is small, the incident light efficiency will decrease. In particular, if the angle is below Brewster's angle, the incident light will become linearly polarized, which is undesirable. A homogeneously aligned liquid crystal layer provides light and dark with a period of 90° when rotated between orthogonal polarizers. If a dichroic dye is dissolved in advance in the liquid crystal layer, the shade of the dye can be seen through a single polarizer. At this time, shading appears with a period of 180°. As the dichroic dye, for example, those described in Naotake Matsumura, "Sensing Industry", Vol. 32, p. 215 (1984) are used.

[0005]

Effects of the Invention: The conventional method for aligning liquid crystal materials is to homogeneously align the liquid crystal using the restraining force of substrates that sandwich the liquid crystal, and the alignment axis is a permanent and fixed alignment axis that is determined during the manufacturing process of the liquid crystal cell. It is something like that. therefore,
The degree of orientation and orientation direction must be adjusted empirically each time, and it is even more impossible to obtain a complex pattern by minutely changing the orientation direction in the material. For example, patterns obtained electrically using electrodes are limited in size to approximately the size of the electrode, and furthermore, the pattern disappears when the electric field is removed, so the scope of use is limited. The method of aligning a liquid crystal material using oblique irradiation of reaction light according to the present invention expands the limited range of use of liquid crystal materials by existing alignment techniques. That is, the alignment axis can be arbitrarily determined by the incident direction of the reaction light, and the degree of alignment can be easily adjusted by changing the degree of spread or intensity of the incident light. Furthermore, reorientation is possible by re-irradiating light with a different incident direction. Because it uses light, it has extremely high spatial controllability, and can create domains in the material with fineness almost equal to the focused size of the light and with uniform orientation.
It is also possible to obtain complex patterns.

[0006]

EXAMPLES Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples in any way. Example 1 Completely saponified polyvinyl alcohol with a degree of polymerization of 500 and 4-(4-hexylphenylazo) produced by a conventional method
Phenoxyacetyl chloride with dimethylformamide
The formula was heated in a benzene mixed solvent for several hours to introduce about 30% by weight of azobenzene units.

A polyvinyl alcohol represented by the following formula was produced. Next, this polyvinyl alcohol was spin-coated onto a washed glass plate using a 1% by weight chloroform solution, and
After producing the A1 substrate, a glass plate (ODS substrate) treated with octadecyltrichlorosilane by a conventional method and the A1
A cyclohexanecarboxylic acid phenyl ester mixed liquid crystal (DON-10
3/Roddick) and sealed with epoxy resin to construct a sandwich type cell. The cell before light irradiation was in a homeotropic orientation and did not transmit any light when placed between two orthogonal polarizers. When 365 nm parallel light from a 500 W ultra-high pressure mercury lamp enters the liquid crystal cell from the substrate A1 side at an incident angle of 80 degrees and θ = 45 degrees, the liquid crystal becomes homogeneously aligned due to photoisomerization of azobenzene on the substrate surface. It has changed. When the irradiation was stopped and the cell was rotated between two orthogonal polarizers, the brightness changed with a period of 90°. Subsequently, when irradiation was performed again with θ=90°, a homogeneously oriented plane with a phase difference of 45° was obtained (FIG. 3). Example 2 Radical polymerization of 4-acryloyloxy-4'-methoxyazobenzene was carried out in benzene using azoisobutyronitrile as an initiator, and the formula

A polymer compound represented by the following formula was obtained. Next, this polymer compound was spin-coated using a 1% by weight chloroform solution on the cleaned glass plate to prepare an A2 substrate, and then the A2 substrate and the ODS substrate (see Example 1) were coated with the following: 1
A nematic liquid crystal (see Example 1) containing % by weight of a dichroic dye (LCD118/Nippon Kayaku Co., Ltd.) was sandwiched through an 8 μm spacer to form a scissor cell. The cells before light irradiation were in a homeotropic orientation. When parallel light of 365 nm from a mercury lamp was incident on the cell at an incident angle of 80° and θ=0°, the liquid crystal became homogeneously aligned. When plane-polarized monitor light was incident on the cell and the dependence of the transmittance on the rotation angle of the cell was examined, light and darkness appeared with a period of 180°. (Figure 4)
For homogeneously oriented cells, θ=45° or θ=90
When the light is irradiated obliquely at
Periodicity with deviations of 5° and 90° appeared. That is, the homogeneous orientation axis rotated with θ.

[0007]

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the basic structure of a liquid crystal material used in the present invention.

FIG. 2 is a layout diagram in one example of a liquid crystal alignment method using oblique light.

[Figure 3] In Example 1, θ=45° or 90°
A diagram showing the dependence of the transmittance between orthogonal polarizers on the cell rotation angle of a liquid crystal cell homogeneously aligned with oblique light of .degree.

[Figure 4] In Example 2, θ=0°, 45°, 9
FIG. 3 is a diagram showing the cell rotation angle dependence of the transmittance for plane polarized light of a liquid crystal cell containing a dichroic dye that is homogeneously aligned with 0° oblique light.

[Explanation of symbols]

1=transparent substrate, 2=photochromic compound layer, 3=liquid crystal layer, 4=substrate, S=liquid crystal material, L=temporary axis of material S, P=
Point of incidence of reaction light, KP = direction of incidence of reaction light, MP = projection of reaction light onto substrate, θ = angle of incidence azimuth, α = angle of incidence.

Claims (1)

[Claims] [Claim 1] Obtaining homogeneous alignment in a predetermined direction by obliquely irradiating reaction light from the transparent substrate side to a liquid crystal material formed by sequentially laminating a photochromic compound layer and a liquid crystal layer on a transparent substrate. A liquid crystal alignment method using oblique light.