JPH0792567B2 - Liquid crystal alignment method by oblique light - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel liquid crystal aligning method capable of homogeneously aligning a liquid crystal layer in contact with a molecular layer which carries out a selective photochromic reaction according to an incident light path of light. is there. 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 having different wavelengths.
It is a method of irradiating reaction light at an angle with respect to the vertical line of the substrate to bring about anisotropy on the surface of the photochromic compound layer by performing selective photochromism, and to give a predetermined homogeneous alignment to the liquid crystal layer in contact with this. In addition, the present invention relates to a liquid crystal alignment method by oblique light irradiation to a liquid crystal material, which can give a new homogeneous alignment axis by re-irradiating reaction light incident on a different optical path.

[0002]

Liquid crystal is a fluid having a flexible structure,
It is necessary to give a predetermined orientation to the materialization. For this reason, a sandwich structure in which a liquid crystal layer is filled between two substrates is usually used, and a means for inducing the orientation by the binding force of the substrate surfaces is taken. For example, as a surface for giving homogeneous orientation, a glass surface with fine grooves in a certain direction, a stretched polymer film, a polymer film accumulated by the Langmuir-Blodgett method, a vacuum deposition method, a chemical vapor deposition method, etc. And the polymer film polycondensed at the interface with the oriented liquid crystal. However,
In such a method, the homogeneous alignment axis of the liquid crystal induced thereby is determined at the time of manufacturing the liquid crystal cell and is permanent and peculiar to the material.
Although the binding force by the surface can be increased or decreased by heat or the like, the homogeneous alignment axis cannot be changed, and it is difficult to create fine domains having different alignment axes in one material.

[0003]

SUMMARY OF THE INVENTION Under the circumstances, the present invention provides high controllability by using light.
The object of the present invention is to provide a method for giving a predetermined alignment to an arbitrary position or an arbitrary area in a liquid crystal material.

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to develop a method of giving a predetermined alignment to a liquid crystal material by light, and as a result, they are aligned at a specific angle with respect to the incident direction of light. In a liquid crystal material in which a photochromic compound layer having a property and a liquid crystal layer are stacked in this order, an anisotropic orientation in the photochromic compound layer is induced by irradiating reaction light at an angle from the perpendicular of the substrate. That is, the liquid crystal layer laminated on the photochromic compound layer is homogeneously aligned with this, and the homogeneous alignment axis of the liquid crystal layer can be rotated by rotating the incident light optical path with respect to the substrate. It is seen that the alignment is rapidly transmitted even if the molecules overlap 10,000 times or more of the surface layer, and that the homogeneous alignment of the liquid crystal is maintained for a long time even when the light irradiation is stopped. However, the present invention has been accomplished based on this finding. That is, the present invention obtains a homogeneous alignment in a predetermined direction by irradiating a liquid crystal material formed by sequentially stacking a photochromic compound layer and a liquid crystal layer on a transparent substrate with reaction light obliquely from the transparent substrate side. The present invention provides a liquid crystal alignment method using oblique light.
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, and is usually used as a sandwich type 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 a metal such as copper, iron, aluminum or platinum or a sheet coated with these metals. These substrates are typically 0.
It is used as a sheet having a smooth surface with a thickness of 01 to 1 mm. On the other hand, as a transparent substrate, a sheet of ordinary silica glass, hard glass, quartz, various plastics or the like, or a metal such as silicon oxide, tin oxide, indium oxide, aluminum oxide, titanium oxide, chromium oxide or zinc oxide is provided on the surface thereof. Those having a coating of oxide, silicon nitride, silicon carbide, etc. are used. In the present invention, it is necessary to provide a layer made of a photochromic compound having a property of anisotropically orienting with respect to the optical path of the reaction light on the 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, for example, the color tone.
Utilizing photogeometric isomerization reaction of carbon-nitrogen and nitrogen-nitrogen unsaturated double bonds, valence photoisomerization reaction, heterolytic photo-opening / closing ring reaction, photo-ring closing reaction, photo-tautomerization reaction, etc. A wide variety of compounds are known [see, for example, "Photochromism" (1971), published by Willy Interscience, edited by G, H, Brown). Among such compounds, examples of the photochromic compound based on photogeometric isomerization include azobenzene, indigo, acylindigo, thioindigo, selenoindigo, perinaphthoindigo, hemiindigo, hemithioindigo, azomethine, and the like, which are heterolithic photoopening / closing rings. Examples of photochromic compounds based on the reaction include indolinospirobenzopyran, indolinospironaphthoxazine, benzothiazolinospirobenzopyran, indolinospirobenzothiopyran, and spiroindolizine. Examples of chromic compounds include stilbene, fulgide, etc., and examples of photochromic compounds based on a phototautomerization reaction include salicylideneanyl, ο-hydroxyazobenzene, ο-nitrobenzyl and the like. Mention may be made of a compound that with the respective basic skeleton. To provide a thin film of these photochromic compounds on a substrate, a method usually used for vertical alignment of liquid crystals, for example, a method of treating a substrate with a photochromic compound having a surface active group, at least one halogen atom or A method of treating with a photochromic compound having an silyl group substituted with an alkoxy group, a method of treating a substrate surface with a silylating agent having an amino group and then binding a photochromic compound having a carboxyl group or a vinyl group, or It can be carried out by a method of coating or adsorbing a high molecular compound having a chromic residue [J. Cognard, "Molecular Crystals and Liquid Crystals (Mo
lecular Crystals and Liquid Crystals) ", Supplement 1 (1982), and Shoichi Matsumoto, Kazuyoshi Tsunoda," Latest Technology of Liquid Crystals "(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 addition amount of the photochromic compound having a surface active group is usually 0.0 based on the weight of the liquid crystal.
It is selected in the range of 1 to 5.0% by weight. 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,
Examples thereof include triethoxysilylindigo and triethoxysilylindolinospirobenzopyran. The treatment with these compounds is usually carried out by coating the surface of the substrate with a solution having a concentration in the range of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, or by immersing the substrate in this solution. Done. 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 thereof include ethoxysilane, aminobutylmethyldiethoxysilane and aminobutyltriethoxysilane. The treatment with these silylating agents usually gives this
It is carried out by applying to the surface of the substrate as a solution having 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. As the solvent at this time, 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 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. Further, a photochromic compound having a vinyl group can be added to the amino group of the silylating agent by Michael. The Michael addition of a photochromic compound having a vinyl group is carried out by applying a solution of about 0.1 to 10% by weight onto a substrate and heating it for a few minutes to a few hours, or immersing the substrate in this solution. It is carried out by heating for several dozen minutes to several hours. The chemicals on the surface of the substrate can function satisfactorily by forming a monolayer, but can be bilayer or more if desired. Therefore, a polymer compound having a photochromic residue can also be used. Such a polymer compound may be produced by previously preparing a monomer having a photochromic unit and then subjecting it to a polymerization reaction, or by coupling the photochromic compound to the polymer compound by a known reaction. Good (see CMC, Masahiro Irie, "Synthesis and Application of Photofunctional Polymers" (1984)).
In this case, the photochromic residue may be incorporated in the main chain of the polymer or may be bonded to the side chain, but in terms of efficient reversible structural change by light, More preferably, the chromic residue is attached to the side chain. The basic polymer compound that gives a polymer compound having a photochromic residue, polyvinyl alcohol, polyimide resin, poly (meth) acrylic acid ester,
Examples thereof include, but are not limited to, poly (meth) acrylic acid amide, poly (L-glutamic acid ester), poly (L-lysine), polystyrene, polyester, polyamide, polysiloxane, and polysulfone. The introduction rate of photochromic units into these basic polymer compounds can be set so that the molecular weight per photochromic unit is converted to a value obtained by dividing the photochromic unit to be in the range of 0 to 500. desirable. At a value higher than this, in other words, at a low introduction rate lower than this, it is not possible to give the predetermined alignment by light. Next, as the liquid crystal used for the liquid crystal material, any one of conventionally known nematic, smectic and cholesteric liquid crystal substances can be selected.
Further, it goes without saying that the liquid crystal substance includes not only low molecular weight substances but also high molecular weight substances. Such liquid crystal substances are described in, for example, A. Bequin et al., “Molecular Crystals and Liquid Crystals”.
(Molecular Crystals and Liquid Crystals) ", No. 11
Volume 5, page 1. Polymeric liquid crystal substances are described in, for example, Advances in Polymer Science, Volume 60/61 (1
984). These liquid crystal substances may be used alone or in combination of two or more.

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, in which a photochromic compound layer 2 is fixed on a transparent substrate 1 and a liquid crystal layer 3 is further laminated on the photochromic compound layer 2 to prevent scattering or damage. To prevent this, a substrate 4 is further coated on this. This substrate may be transparent or opaque, and its surface is coated with a photochromic compound layer, or a molecular layer or alignment film having a function of homogeneously or vertically aligning liquid crystals in a predetermined direction. Can be used. When reaction light is obliquely incident on the liquid crystal material from the transparent substrate side, the photochromic molecules on the substrate undergo a structural change at a reaction rate according to the molecular orientation, resulting in anisotropy on the surface. The orientation of the liquid crystal layer in contact with the anisotropic surface is homogeneous, and its orientation axis correlates with the projection direction of the reaction light optical path onto the substrate. FIG. 2 shows a layout of the liquid crystal alignment method using oblique light.
In the figure, L is a temporary axis of the liquid crystal material, and reaction light is obliquely incident on a point P above L above K. MP projection of reaction light onto the substrate,
The angle formed by MP with L is the incident azimuth angle θ, and the angle formed by KP with L is the incident angle α. The incident angle α may be a value of 1 ° to 89 °, but is preferably about 55 ° to 80 °. If the angle is larger than this, the effect of oblique irradiation is hard to be exhibited, and if the angle is small, the incident light efficiency is lowered. In particular, if the Brewster angle is less than the angle, the incident light may be linearly polarized, which is not preferable. The homogeneously aligned liquid crystal layer provides light and dark with a 90 ° period when rotated between orthogonal polarizers. When the dichroic dye is dissolved in the liquid crystal layer in advance, the tint of the dye can be seen through one polarizer. At this time, light and shade appear with a cycle of 180 °. As the dichroic dye, for example, those described in Takatake Matsumura, "Dyeing Industry", Volume 32, p. 215 (1984) are used.

[0005]

As a conventional method for aligning liquid crystal materials, a method of homogeneously aligning the liquid crystal by the restraining force of the substrate sandwiching the liquid crystal is used, and the alignment axis is permanent and fixed in the process of manufacturing the liquid crystal cell. It is a target. Therefore,
The degree of alignment and the alignment direction must be adjusted empirically each time, and it is even impossible to minutely change the alignment direction in the material to obtain a complicated pattern. For example, the size of a pattern electrically obtained by using an electrode is limited to about the size of the electrode, and the pattern disappears when the electric field is removed. The alignment method of a liquid crystal material using oblique irradiation of reaction light according to the present invention expands a limited range of use of the liquid crystal material by the existing alignment technology. That is, the orientation axis can be arbitrarily determined according to the incident direction of the reaction light, and the degree of orientation can be easily adjusted by means such as changing the extent or intensity of the incident light. Furthermore, re-irradiation can be performed by re-irradiating with light having different incident directions. 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 aligned in the orientation direction, and it is possible to obtain a complicated pattern.

[0006]

EXAMPLES The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. Example 1 Completely saponified polyvinyl alcohol having a degree of polymerization of 500, and 4- (4-hexylphenylazo) produced by a conventional method
Phenoxyacetyl chloride was added to dimethylformamide-
After heating for several hours in a mixed solvent of benzene, about 30% by weight of azobenzene unit was introduced, the formula

[Chemical 1] A polyvinyl alcohol represented by Next, this polyvinyl alcohol was spin-coated on the washed glass plate using the 1 wt% chloroform solution,
After producing an A1 substrate, octadecyltrichlorosilane-treated glass plate (ODS substrate) and the A1 substrate were prepared by a conventional method.
Depending on the substrate, cyclohexanecarboxylic acid phenyl ester mixed liquid crystal (DON-10
3 / Rodick) and sandwiched with epoxy resin to form a sandwich type cell. The cell before light irradiation had a homeotropic orientation and did not transmit any light when placed between two crossed polarizers. A parallel light of 365 nm from a 500 W ultra-high pressure mercury lamp is incident on a liquid crystal cell at an incident angle of 80.
When incident from the side of the substrate A1 at θ, θ = 45 °, the liquid crystal changed to a homogeneous alignment due to the photoisomerization of azobenzene on the substrate surface. When the irradiation was stopped and the cell was rotated between two orthogonal polarizers, the brightness changed in a 90 ° cycle. Subsequent re-irradiation with θ = 90 ° gave a homogeneously oriented surface with a phase difference of 45 ° (FIG. 3). Example 2 Radical polymerization of 4-acryloyloxy-4′-methoxyazobenzene in benzene with azoisobutyronitrile as an initiator

[Chemical 2] A polymer compound represented by Next, this polymer compound was spin-coated on the washed glass plate using the 1 wt% chloroform solution to prepare an A2 substrate, and then the A2 substrate and the ODS substrate (see Example 1) were prepared. 1
A nematic liquid crystal (see Example 1) containing wt% dichroic dye (LCD118 / Nippon Kayaku Co., Ltd.) was used as a scissor cell via an 8 μm spacer. The cell before light irradiation had homeotropic alignment. 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 was in a homogeneous alignment. 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, bright and dark appeared at a cycle of 180 °. (Figure 4)
In a homogeneously oriented cell, θ = 45 ° or θ = 90
When oblique light is radiated as ゜, the light and dark phases are 4
A periodicity of 5 ° and 90 ° was observed. That is, the homogeneous orientation axis rotated with θ.

[0007]

[Brief description of drawings]

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

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

FIG. 3 is a diagram showing cell rotation angle dependence of transmittance between orthogonal polarizers of a liquid crystal cell homogeneously aligned with oblique light of θ = 45 ° or 90 ° in Example 1.

[FIG. 4] In Example 2, θ = 0 °, 45 °, 90
The figure which shows the cell rotation angle dependence of the transmittance | permeability with respect to plane polarized light of the liquid crystal cell containing the dichroic dye homogeneously aligned by the oblique light of (degree).

[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 =
Incident point of reaction light, KP = incident direction of reaction light, MP = projection of reaction light on substrate, θ = incident azimuth angle, α = incident angle.

Claims (1)

[Claims] 1. A homogeneous alignment in a predetermined direction is obtained by irradiating a liquid crystal material, which is formed by sequentially stacking a photochromic compound layer and a liquid crystal layer on a transparent substrate, with reaction light obliquely from the transparent substrate side. A liquid crystal alignment method using oblique light.