JPH07101265B2 - Optical element and manufacturing method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel optical element utilizing the change in alignment of liquid crystal due to light. More specifically, the present invention causes a change in orientation of the liquid crystal layer by the action of a poly (vinyl acetate) saponified layer in which a residue that reversibly changes its structure by light is bonded to the interface with the liquid crystal layer, The present invention relates to an optical element that reversibly changes the transmittance of light by utilizing it.

2. Description of the Related Art As an optical element using a liquid crystal, one that widely controls the orientation of the liquid crystal by utilizing an electric action is widely known, and is mainly used for display, and further applied to optical recording. There are also examples.

By the way, a liquid crystal optical element that changes its optical properties by using an electrical effect loses its function when the power supply is stopped. It is necessary to use a patterned electrode, and it is unsuitable as an optical element with low resolution and high capacity.

On the other hand, as a liquid crystal optical element that utilizes the action of light,
There is a type that uses heat such as a laser beam,
The range of use is unavoidable. In addition, in a type in which a compound whose structure is changed photochemically is mixed and a phase is changed by the action of light, optical properties such as resolution tend to be remarkably deteriorated with the passage of time because liquid crystal flows. . For example, a photochromic cholesteric liquid crystal obtained by dissolving chiral azobenzene in nematic liquid crystal changes to an isotropic phase by the action of ultraviolet rays, and it can be used for optical recording by changing the transmittance of polarized light. The liquid crystal flows over time, and the recorded image becomes unclear. (See 1986 Proceedings of 52nd Annual Meeting of the Chemical Society of Japan).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention is an optical element for recording information by utilizing alignment change of liquid crystal due to light, and which does not cause deterioration of resolution due to its fluidity with time. It is made for the purpose of providing.

Means for Solving the Problems The inventors of the present invention have conducted diligent research in order to develop an optical element utilizing the change in alignment of liquid crystal due to light. As a result, a poly (vinyl acetate) saponified layer is formed on a transparent substrate. In the laminated body in which the liquid crystal layer is further provided thereon, the photochromic compound is bound to the interface of the poly (vinyl acetate) saponified layer in contact with the liquid crystal layer, and the photochromic compound is reversibly changed by light. Liquid crystals corresponding to two kinds of structures of units are reversibly arranged in parallel or vertically, and the arrangement of the liquid crystal layer is rapidly transmitted even if the molecules overlap by 10,000 times or more of the above compound. Therefore, the inventors have found that the liquid crystal layer does not change and the optical properties are retained for a long period unless the light state changes, and the present invention has been completed based on this finding.

That is, the present invention provides a poly (vinyl acetate) on a transparent substrate.
In a laminate having a saponified layer and a liquid crystal layer formed thereon, a photochromic compound is chemically bonded to the interface of the poly (vinyl acetate) saponified layer in contact with the liquid crystal layer, and if desired, the liquid crystal is further added. An optical element having a layer containing a dichroic dye is provided.

The optical element of the present invention is preferably one in which a formyl group or a carboxyl group or a reactive derivative group thereof is introduced into a photochromic compound, and then poly (acetic acid) is added to a solution containing the photochromic compound derivative thus obtained. A transparent substrate having a (vinyl) saponified material layer is dipped to acetalize or esterify the hydroxyl groups of the poly (vinyl acetate) saponified material, and the above photochromic compound is chemically bonded. It can be produced by providing a liquid crystal layer optionally containing a dichroic dye on the poly (vinyl acetate) saponified layer.

As the transparent substrate in the present invention, ordinary silica glass, hard glass, quartz, sheets of various plastics or the surface thereof, silicon oxide, tin oxide, indium oxide, aluminum oxide, titanium oxide, chromium oxide,
A metal oxide such as zinc oxide or a material having a coating such as silicon nitride silicon carbide is used. Further, these may be surface-treated in advance by a known method with a silylating agent or the like.

Usually, the liquid crystal is used as a sandwich structure filled between two substrates, but in the present invention, at least one of the two substrates may be a transparent substrate, and the other may be copper or iron. It is also possible to use a sheet of metal such as aluminum, platinum, or the like, or a sheet coated with these metals. These substrates are usually used as a sheet having a smooth surface with a thickness of 0.01 to 1 mm.

In the present invention, a poly (vinyl acetate) saponified layer in which a photochromic compound is chemically bonded to the interface in contact with the liquid crystal layer (hereinafter referred to as photochromic bonded polymer layer)
Need to be provided on the substrate.

This 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, berynaftindigo, hemiindigo, hemithioindigo, azomethine, etc. are examples of photochromic compounds based on the heterolytic photo-opening / closing reaction. Oxazine, benzothiazolinospyrobenzopyran, indolinospyrobenzothiopyran, spiroindolizine, and the like, examples of photochromic compounds based on the photocyclization reaction include stilbene and fulgide.
Examples of the photochromic compound based on the photochromic isomerization reaction include compounds having salicylidene anil, o-hydroxyazobenzene, o-nitrobenzyl and the like as basic skeletons.

In order to bond such a photochromic compound used in the present invention to a saponified poly (vinyl acetate), a formyl group having reactivity with a hydroxyl group of this polymer,
A carboxyl group or a derivative substituent thereof may be introduced into these photochromic compounds.

The poly (vinyl acetate) saponified product to which the photochromic compound used in the present invention has a degree of polymerization of 30.
Anything in the range of 0 to 3000 may be used. If the degree of polymerization is less than this, the physical strength will be poor and the durability as an optical recording element will be reduced, and if the molecular weight is above this range, it will be difficult to provide a uniform coating film. The saponification degree is preferably 50% or more. If it is less than this, the photochromic compound cannot be sufficiently bonded to the surface of the polymer film, and the alignment change of the liquid crystal cannot be caused.

The method for producing the photochromic bonding polymer layer according to the present invention will be described below. A solution of saponified poly (vinyl acetate) is applied onto a transparent substrate by a usual method such as casting and spin coating. Since the photochromic compound may be monomolecularly bonded to the surface of the saponified poly (vinyl acetate) layer, the thickness of the film may be in the range of several hundred angstroms to several tens of millimeters.

In order to introduce the photochromic compound to the surface of the saponified poly (vinyl acetate) layer provided on the substrate by an acetal bond, the photochromic compound having a formyl group is dissolved in a solvent, and then an acid is used as a catalyst for accelerating the reaction. Is added. Any solvent may be used as long as it does not dissolve the saponified poly (vinyl acetate).
Chloroform, benzene, toluene and the like are preferable. A substrate provided with a saponified poly (vinyl acetate) may be dipped in this solution. The time required for the reaction depends on the reaction temperature, the concentration of the photochromic compound, the amount of the acid catalyst, the saponification rate of the saponified poly (vinyl acetate), and the like.
The range of hours to 20 hours is preferred. If the reaction temperature is from room temperature to about 50 ° C., the lower the temperature, the easier the control of the reaction, and thus the room temperature is suitable. If the reaction time is too short, the introduction rate of the photochromic compound will be too low, and if it is too long, the reaction will proceed too much and the smoothness of the surface of the saponified poly (vinyl acetate) layer will be lost.

In order to introduce the photochromic compound by the ester bond, the carboxyl group is converted into acid chloride or the like for activation, and the substrate provided with the poly (vinyl acetate) saponified layer is immersed in the solution. Then, a catalyst such as triethylamine or pyridine is added to accelerate the reaction. The reaction time depends on the concentration of the photochromic compound, the reaction temperature and the saponification ratio of the saponified poly (vinyl acetate), as in the case of the acetalization reaction, but is preferably 5 minutes to 5 hours. Similarly, if the reaction time is too short, the introduction rate of the photochromic compound is too low, and if it is too long, the smoothness of the surface of the saponified poly (vinyl acetate) layer is lost.

Under the above conditions, the acetalization or esterification reaction selectively occurs on the surface of the saponified poly (vinyl acetate).
Therefore, the photochromic compound can be introduced without changing the surface smoothness and physical strength of the saponified poly (vinyl acetate). Since it is introduced only into the surface layer, for example, in the case of an azobenzene unit having an extinction coefficient of about 30,000, the absorbance of this bound chromophore stays in the range of 0.005 to 0.1. Incidentally, an absorbance of 0.01 corresponds to that of a monolayer of azobenzene.

In order to obtain a clear change in the optical properties due to the reversible change in orientation of the liquid crystal, it is desirable to take a homogeneous orientation in which the long axes of the liquid crystal molecules are oriented in one direction. For this purpose, the surface of the saponified poly (vinyl acetate) layer in which the photochromic compound is introduced may be rubbed.

Next, as the liquid crystal of the liquid crystal layer provided on the photochromic coupling polymer layer, any one can be selected from conventionally known nematic, smectic, and cholesteric liquid crystal substances. In the case of a liquid crystal substance, it is necessary to select a substance that takes a nematic liquid crystal phase at a certain temperature. 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) et al., “Molecular crystals and liqui”
d Crystals) ", Vol. 115, page 1. Polymeric liquid crystal materials are commercially available, for example, in Advances in Polymer Science.
nce), Volume 60/61 (1984). These liquid crystal substances may be used alone or in combination of two or more.

In the present invention, a dichroic dye can be contained in the liquid crystal layer as desired, and by dissolving the dichroic dye in such a liquid crystal layer, only one polarizing plate is used. It is possible to change the optical properties depending on the lightness and darkness of. As the dichroic dye, for example, those described in Takatake Matsumura, "Dyeing Industry", Volume 32, page 215 are used.

In this case, a temperature-dependent liquid crystal substance, for example, a liquid crystal substance that does not change its structure when irradiated with light at room temperature, but changes its structure by light irradiation when heated above a certain temperature, You can get a permanent record based on shading.

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 the present invention, in which a photochromic bonding polymer layer 2 is fixed on a transparent substrate 1 and further covered with a substrate in order to prevent scattering and damage. There is. This substrate may be transparent or opaque, the surface of which is coated with a photochromic bonding polymer layer may be used, and a homogeneous alignment having a function of aligning liquid crystals in parallel with the surface may be used. It is also possible to use those coated with layers.

FIG. 2 is a cross-sectional view showing an example of a preferred embodiment of the present invention, which is a sandwich in which a liquid crystal layer is sandwiched between two substrates 1 having a photochromic bonding polymer layer 2 as a surface layer. It has a structure.

And, in this figure, I shows the state before light irradiation, and II shows the state after light irradiation. Before the light irradiation, the liquid crystal layer has a liquid crystal layer in a direction (homeomorphic) perpendicular to the substrate surface by the action of the photochromic bonding polymer layer. (Tropically) arranged regularly (I). Next, when a part (A) of this optical recording element is irradiated with light, the photochromic residue undergoes a structural change, so that the above vertical alignment in that part is destroyed and the liquid crystal is parallel to the surface (parallel or homogeneous). ) Array.

Therefore, when placed between two polarizers that are orthogonal to each other, the part (B) which is not irradiated with light is dark and the part (A) which is irradiated with light changes to be bright, so that the light transmittance is changed. .

Next, FIG. 3 is an example of an embodiment different from the case of FIG. 2, and is an example in which the homogeneous alignment layer 4 is provided on one of the two substrates. This homogeneous alignment layer is
Rubbing the surface of the substrate with polyvinyl alcohol, polyimide resin, polyoxyethylene, etc., or
It can be provided by vapor-depositing an oxide such as SiO ₂ from an oblique direction. In this example, on the photochromic binding polymer layer side, the liquid crystals are arranged in a direction perpendicular to the substrate surface as shown in FIG. 3I, but on the homogeneous alignment layer side, they are arranged in a direction parallel to the substrate. It has a structure that When this is irradiated with light, the liquid crystal is aligned in parallel with the surface of the photochromic polymer layer in the irradiated portion (A), so that the whole is in a homogeneous alignment state, and the transmittance of polarized light changes in the same manner as described above. To do.

FIG. 4 is a sectional view showing an example of a preferred embodiment of the present invention. It has a photochromic bonding polymer layer 2
It has a sandwich structure in which a liquid crystal layer is sandwiched between a plurality of substrates 1. Then, the two substrates are configured such that the directions in which the substrate surfaces are finely deformed are parallel to each other.
In this figure, I shows the state before light irradiation, and II shows the state after light irradiation. Before the light irradiation, the liquid crystal is deposited on the substrate surface by the action of the photochromic compound chemically bonded to the poly (vinyl acetate) saponified layer. They are regularly arranged in the vertical direction (homeotropic) (I). Then, when a part (A) of this optical element is irradiated with light, the photochromic compound undergoes a structural change, so that the liquid crystal in which the above-mentioned vertical alignment is destroyed is arranged in parallel (homogeneous) alignment with the surface. To take.
In the photochromic coupling polymer layer after the structure is changed by light in this way, if the surface is finely deformed by rubbing treatment beforehand, the long axis of the liquid crystal is aligned in the same direction parallel to the surface. The fact that it does is first discovered by the present inventors.
Therefore, if this optical recording element is sandwiched between two polarizers whose polarization axes are orthogonal to each other, the portion not irradiated with light (B)
Is dark, but the part (A) irradiated with light becomes bright.

FIG. 5 is different from the case of FIG. 2 in that two substrates are configured such that the directions in which the surface is finely deformed in advance by rubbing treatment are orthogonal to each other. In this case, the light irradiation portion has a twisted nematic phase, so that an optically clear image can be obtained by a known method.

In the optical element of the present invention, by irradiating two kinds of light having different wavelengths, a reversible liquid crystal orientation change corresponding to a reversible change of the photochromic unit occurs, and the optical properties can be repeatedly changed.

EFFECTS OF THE INVENTION The optical element of the present invention has the advantage that it does not exhibit the drawbacks of the optical element using the conventional photochromic material, for example, the fact that the information once recorded is gradually erased by repeated reading, and also the liquid crystal. Since the arrangement of is controlled by the photochromic compound bonded to the interface of the poly (vinyl acetate) saponified layer in contact with the liquid crystal layer, the resolution with the liquid crystal having fluidity is that obtained by adding a conventional photochromic compound to the liquid crystal. Is much better than using. Further, the optical element of the present invention can be suitably used not only for reversible optical information storage but also for optical address type display.

Next, the present invention will be described in more detail with reference to Examples.

Example 1 4-hexyl-4'-hydroxyazobenzene (1) 1.
50 g (1.00 g (6.39 mmol) of 4-chlorobutanal diethyl acetal in 5.32 mmol) and 1.46 g of anhydrous potassium carbonate were added to 20 ml of dimethylacetamide, and the mixture was heated at 80 ° C. for 2 hours.
After the reaction was completed, water was added, the mixture was extracted with benzene, dried over magnesium sulfate, and the solvent was distilled off under reduced pressure. This is silica gel chromatography (distillate: hexane: ethyl acetate = 1
Purification at 0: 1) gave 2.05 g of 4- {4- (4-hexylphenylazo) -phenoxy} butanol diethyl acetal (2).

50 mg of (2) and 30 mg of p-toluenesulfonic acid were dissolved in 10 ml of chloroform. A glass substrate coated with poly (vinyl acetate) (polyvinyl alcohol) having a degree of polymerization of 1700 and a saponification rate of 81.5% was immersed in this for 1 hour at room temperature.
Then, it was washed with chloroform and dried at 100 ° C. for 10 minutes. One side of this substrate was modified with an azobenzene derivative, and its absorption at 350 nm was 0.116. Using the substrate thus treated, a glass rod spacer of 8 um was included, and cyclohexanecarboxylic acid phenyl ester-based mixed liquid crystal (K-17-N-73-1) was sandwiched,
A sandwich cell was prepared by sealing with an epoxy resin. This liquid crystal cell was placed between crossed Nicols, and the amount of transmitted light was monitored with a He-Ne laser. The cell before UV irradiation had zero transmittance under cross-polarized Nicols, and when it was irradiated with 365 nm UV, the amount of transmitted light increased as azobenzene photoisomerized from trans to cis. Next, when visible light of 440 nm or longer was irradiated, the amount of transmitted light decreased again as isomerization to trans occurred. The amount of transmitted light reversibly changed in response to alternate irradiation with ultraviolet light and visible light. Also, when the same cell was irradiated with ultraviolet rays through a negative, a clear image was observed with crossed Nicols. This image was not disturbed when pressure was applied to the cell to cause the liquid crystal to flow.

Example 2 A cell was similarly constructed by using a liquid crystal in which 1% by weight of anthraquinone dichroic dye was dissolved instead of the liquid crystal of Example 1. When this was irradiated with ultraviolet rays, the blue color of the dye increased. When it was irradiated with visible light of about 440 nm, it returned to the original light blue color. This change in color tone reversibly changed in response to alternate irradiation of ultraviolet rays and visible light. When the same cell was irradiated with ultraviolet rays through a negative image, a clear image was recognized. This image was not disturbed when pressure was applied to the cell to cause the liquid crystal to flow.

Example 3 Compound (2) was hydrolyzed in tetrahydrofuran containing 2N hydrochloric acid to give 4- {4- (4-hexylphenylazo) phenoxy} butanal (3). Using this, a polyvinyl alcohol film was treated in the same manner as in Example 1 to prepare a liquid crystal cell, and the liquid crystal cell was irradiated with ultraviolet light and visible light. As a result, a reversible change in the amount of transmitted light was observed under crossed Nicols.

Example 4 In Example 1, 4-butyl-4-hydroxyazobenzene (4) was used in place of 4′-hexyl-4-hydroxyazobenzene (1), and 4- {4- (4-butylphenylazo) was used. Phenoxy} butanal was synthesized.
Using this, a film in which an azobenzene derivative was bonded to the surface of polyvinyl alcohol was prepared in the same manner as in Example 1. Now, a liquid crystal cell is prepared in the same manner as in Example 1,
Irradiation with ultraviolet light and visible light showed reversible change in transmitted light quantity under crossed Nicols.

Example 5 A liquid crystal cell was prepared by rubbing the surface of the polymer in which the azobenzene unit was introduced in Example 1 in a certain direction, and aligning the two substrates with each other in the rubbing direction. When the liquid crystal cell was installed under the crossed Nicols, the transmitted light intensity of the He-Ne laser was zero. When irradiated with ultraviolet light,
The transmitted light intensity was zero when the angle between the rubbing direction and the polarization plane of the He-Ne laser was 0 and 90 degrees, and the maximum was 45 degrees.

Example 6 In the same manner as in Example 5, the polymer surface having azobenzene units bonded to the surface was rubbed in a certain direction. Create a liquid crystal cell so that the rubbing directions are orthogonal to each other,
Irradiation with 365 nm ultraviolet light increased the transmitted light intensity of He-Ne laser under crossed Nicols. Next, when the visible light above 440 nm was irradiated, the transmitted light intensity of the He-Ne laser decreased. The intensity of transmitted light of He-Ne laser increased and decreased reversibly when UV and visible light were irradiated alternately. Moreover, when the optical rotation of the liquid crystal cell was measured, it was 0 degree before irradiation with ultraviolet light,
When it was irradiated with ultraviolet light, it changed to 81 degrees. Then, when it was irradiated with visible light, the optical rotation returned to 0 degree. This change was reversibly produced by alternately irradiating ultraviolet light and visible light.

Example 7 A liquid crystal cell was prepared by sandwiching a liquid crystal obtained by doping the cyclohexylcarboxylic acid phenyl ester nematic liquid crystal of Example 5 with 1% by weight of a dichroic dye. When the absorbance at 633 nm was measured, it was 0.19 before irradiation with ultraviolet light, and changed to 0.92 when irradiated with visible light. Next, when it was irradiated with visible light, it returned to 0.19 again. As described above, the light and shade of color reversibly occurred due to the photoisomerization of azobenzene.

Example 8 An ester obtained from 4-hexyl-4'-hydroxyazobenzene (1) and ethyl bromoacetate was hydrolyzed to obtain 4-hexyl-4'-carboxymethoxyazobenzene (5). 50 mg of this carboxylic acid (5), 92 mg of triphenylphosphine, and 0.5 ml of carbon tetrachloride were dissolved in 0.5 ml of dimethylformamide and left at room temperature for 1 hour to give acid chloride. After diluting 0.5 ml of this solution with 3 ml of benzene, a glass plate provided with a 100% saponified poly (vinyl acetate) (polyvinyl alcohol) film was immersed, 5 drops of pyridine was added, and the mixture was allowed to stand at room temperature. After 1 hour, the glass plate was taken out, thoroughly washed with acetone and dried. The absorbance of azobenzene was 0.35. Example 1 using two glass plates
When a liquid crystal cell was constructed in the same manner as above and the ultraviolet ray and the visible light were alternately irradiated, the transmittance of polarized light reversibly changed.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of the structure of an optical element of the present invention,
FIG. 2 is a cross-sectional view showing another example and the alignment state of the liquid crystals before and after the light irradiation, and FIG. 3 is a cross-sectional view showing another example and the alignment state of the liquid crystals before and after the light irradiation. In the figure, reference numeral 1 is a substrate, 2 is a photochromic bonding polymer layer, 3 is a liquid crystal layer,
4 is a homogeneous alignment layer. FIG. 4 and FIG. 5 show still another example, in which case 2 has been subjected to an alignment treatment by a rubbing treatment in advance. In Figure 4,
The rubbing directions on the two substrates are the same,
In the figure, the rubbing directions of the two substrates are orthogonal to each other.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G02F 1/1337

Claims (3)

[Claims] 1. A laminate in which a poly (vinyl acetate) saponified layer is provided on a transparent substrate and a liquid crystal layer is further provided thereon, and a photo is formed at the interface of the poly (vinyl acetate) saponified layer in contact with the liquid crystal layer. An optical element characterized by chemically binding a chromic compound. 2. A laminate having a poly (vinyl acetate) saponified layer provided on a transparent substrate and a liquid crystal layer further provided thereon, wherein a photo layer is provided at the interface of the poly (vinyl acetate) saponified layer in contact with the liquid crystal layer. An optical element characterized in that a chromic compound is chemically bound and a dichroic dye is contained in the liquid crystal layer. 3. A poly (vinyl acetate) saponified layer in which a formyl group, a carboxyl group or a reactive derivative group thereof is introduced into a photochromic compound and then the solution containing the photochromic compound derivative thus obtained is introduced. After dipping a transparent substrate having a to acetalize or esterify the hydroxyl groups of the poly (vinyl acetate) saponified product, and after chemically treating the photochromic compound,
A method for producing an optical element, comprising providing a liquid crystal layer on the poly (vinyl acetate) saponified layer thus treated.