JPH0419616B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a novel optical recording element that utilizes the change in orientation of liquid crystal caused by light. More specifically, the present invention utilizes the action of a polymer compound having a residue that undergoes a reversible structural change when exposed to light.
The present invention relates to an element that causes a change in the orientation of a liquid crystal layer and uses this change to temporarily or permanently record information.

Prior Art There are two known types of recording elements using liquid crystals: those that store information using electrical action and those that store information using optical action.The former is mainly used for display purposes. has been done.

By the way, liquid crystal displays that use electrical effects to write information lose their information when the power supply stops, so special measures must be taken to preserve it permanently. Since patterned electrodes are used, the resolution is low and it is unsuitable for use as a high-capacity recording element.

On the other hand, methods that use heat such as laser beams to store information using the action of light can be applied to high-density optical recording, but their use is limited to pit recording. The range is inevitably limited. In addition, systems that mix compounds whose structure changes photochemically and whose phase changes under the action of light show excellent resolution during the initial period when information is input, but because liquid crystals flow, There is a tendency for resolution to drop significantly over time. For example, photochromic cholesteric liquid crystals obtained by dissolving chiral azobenzene in nematic liquid crystals change to an isotopic phase under the action of ultraviolet light, and this can be used to record information, but over time the liquid crystals deteriorate. It flows and the recorded image becomes unclear. (Refer to the proceedings of the 52nd Spring Annual Meeting of the Chemical Society of Japan, 1986).

Problems to be Solved by the Invention The present invention uses polychromatic light to record information using changes in the orientation of liquid crystals caused by light, and which does not cause a decrease in resolution over time due to the fluidity of the liquid crystal. It was made for the purpose of providing a recording element.

Means for Solving the Problems In order to develop an optical recording element that utilizes the change in the orientation of liquid crystals caused by light, the present inventors have conducted intensive research and found that the first step is to create a reversible structure on a substrate using light. If a polymer layer with residues that cause changes is provided and a liquid crystal layer is placed on top of that molecular layer, the liquid crystals can be reversibly aligned in parallel or parallel depending on the two types of structures of the residues that can be reversibly changed by light. The alignment of this liquid crystal layer is such that even if the molecules overlap more than 10,000 times that of the above compound, the liquid crystal layer can be transmitted quickly, so unless the light conditions change, the liquid crystal layer will not change and will remain long. It was discovered that information is retained over a period of time, and based on this knowledge, the present invention was accomplished.

That is, the present invention provides an optical recording element in which a liquid crystal layer is provided on a transparent substrate via a polymer layer having a residue that undergoes a structural change reversibly when exposed to light.

The transparent substrate in the present invention may be a sheet made of ordinary silica glass, hard glass, quartz, various plastics, or the like, or silicon oxide, silicon oxide, etc.
tin oxide, indium oxide, aluminum oxide,
Those coated with metal oxides such as titanium oxide, chromium oxide, zinc oxide, or silicon nitride or silicon carbide are used. Furthermore, these may be surface-treated in advance with a silylating agent or the like by a known method.

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

In the present invention, it is necessary to provide on the above-mentioned substrate a polymer layer having a residue that undergoes a structural change reversibly when exposed to light, and the compound constituting this residue is most commonly a photochromic compound. used for.

Photochromic compounds are compounds that undergo structural changes under the action of light and change their behavior toward light, such as color tone. A wide variety of compounds are known that utilize bond photogeometric isomerization reactions, valence photoisomerization reactions, heterolytic photoopening and closing reactions, photoring closure reactions, phototautomerization reactions, and the like. [See, for example, "Photochromism" (1971), edited by G., H., Brown, published by Wiley Interscience.] Among these compounds, examples of photochromic compounds based on photogeometric isomerization include azobenzene, indigo,
Examples of photochromic compounds based on heterolytic photo-opening and closing reactions include acylindigo, thioindigo, selenoindigo, perinaphthoindigo, hemiindigo, hemitioindigo, azomethine, etc., and indolinospirobenzopyran,
Indolinospironaphthoxazine, benzothiazolinospirobenzopyran, indolinospirobenzothiopyran, spiroindolizine, etc. Examples of photochromic compounds based on photocyclization reactions include stilbene, fulgide, etc. Examples of photochromic compounds based on chemical reaction include compounds each having a basic skeleton of salicylideneanyl, o-hydroxyazobenzene, o-nitrobenzyl, etc.

The polymer having such a photochromic residue used in the present invention may be produced by first producing a monomer having a photochromic unit and then subjecting it to a polymerization reaction, or by subjecting a photochromic compound to a known reaction. Therefore, it may be bonded to a polymer (see "Synthesis and Application of Photofunctional Polymers" by Masahiro Irie, published by CMC Co., Ltd. (1984)). 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 due to light, the photochromic residue is More preferably, it is bonded to a side chain.

The backbone polymer that provides the polymer having photochromic residues used in the present invention has a molecular weight of
It doesn't matter what type it is, as long as it's in the range of 1000 to 1000000. If the molecular weight is below this range, the physical strength will be poor and the durability as an optical recording element will be lowered, and if the molecular weight is above this range, it will be difficult to provide a uniform coating film. Specific examples of such backbone polymers include polyvinyl alcohol, polyimide resin, poly(meth)acrylic acid ester, poly(meth)acrylic acid amide, poly(L-glutamic acid ester), poly(L-lysine), polystyrene, polyester, polyamide,
Examples include, but are not limited to, the following.

The rate of introduction of photochromic units into these basic polymers is desirably set so that the molecular weight per photochromic unit is in the range of 0 to 500 as calculated by dividing the photochromic unit. If the value is higher than this, or in other words, if the introduction rate is lower than this, reversible alignment change of the liquid crystal will not be observed.

In order to provide the polymer having a photochromic residue according to the present invention on a transparent substrate, a conventional method such as casting a polymer solution or spin coating is used. In addition, the thickness of this polymer film is compatible with the purpose of the present invention even if it is a monomolecular layer, and the thickness is from several meters to several meters.
Any range of 10A is acceptable. In particular, in order to obtain an ultra-thin film, a solution of the polymer according to the present invention is spread on a water surface, and after the solvent evaporates, it is scooped onto a transparent substrate using a so-called Langmiur method.
The blogging method is suitable. Alternatively, in order to process a large-area substrate more easily, a polymer having photochromic units may be physically or chemically adsorbed onto the substrate. For this purpose, it is appropriate to provide a polymer with photochromic units on a transparent substrate that is untreated or treated with a silylation agent, heat it, and then wash it with a solvent to remove most of the polymer. be.

In order to obtain a clear recorded image by reversibly changing the orientation of the liquid crystal, it is desirable that the long axes of the liquid crystal molecules be homogeneously aligned in one direction. For this purpose, it is necessary to impart anisotropy to a transparent substrate coated with a polymer having photochromic residues. To do this, first prepare the transparent substrate itself.
Depositing oxides such as SiO ₂ from an oblique direction,
Alternatively, a method of finely deforming the surface by applying a rubbing treatment is effective. Alternatively, a rubbing treatment may be performed after coating a transparent substrate with a polymer having photochromic residues. Furthermore,
If the substrate is a polymer sheet, it can be coated with a polymer with photochromic residues and then stretched. As the liquid crystal, any one can be selected from conventionally known nematic, smectic, and cholesteric liquid crystal materials, but smectic liquid crystal materials are those that take a nematic liquid crystal phase at a certain temperature. You need to choose. 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 Liquid Crystals" by A. Bequin et al.
It is described in Volume 115, Page 1. Polymeric liquid crystal materials, for example, Advances in
Advances in Polymer Science
Science), 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 present invention. On a transparent substrate 1, a molecular layer 2 of a polymer compound having residues that undergoes a reversible structural change when exposed to light is fixed.
This is further covered with a substrate to prevent dissipation and damage. This substrate may be transparent or opaque, and its surface may be coated with a molecular layer of a polymer compound having a residue that undergoes a reversible structural change when exposed to light. It is also possible to use one coated with a homogeneous alignment layer that has the function of aligning liquid crystals parallel to the surface.

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

In this figure, the state before light irradiation and the state after light irradiation are shown. Before light irradiation, liquid crystals are regularly arranged in the direction perpendicular to the substrate surface (homeotropic) in the liquid crystal layer due to the action of the photochromic polymer layer. are doing. (). Next, when part (A) of this optical recording element is irradiated with light, the photochromic residues undergo a structural change, and the above-mentioned vertical arrangement in that part is destroyed, and the liquid crystal becomes parallel (parallel or homogeneous) to the surface. Take an array.

Therefore, when placed between two orthogonal polarizers, the area not irradiated with light (B) becomes dark and the area irradiated with light (A) changes brightly, so the optical information changes depending on the light transmittance. can be read. Since light at a wavelength that does not cause photochromism can be used to read information, the information will not be destroyed.

Next, FIG. 3 shows an example of an embodiment different from the case of FIG. 2, and is an example in which a homogeneous alignment layer 4 is provided on one of the two substrates. This homogeneous alignment layer can be provided by rubbing the substrate surface with polyvinyl alcohol, polyimide resin, polyoxyethylene, etc., or by obliquely vapor-depositing an oxide such as SiO ₂ . In this example, on the polymer layer side with photochromic residues, the liquid crystals are aligned in a direction perpendicular to the substrate surface, as shown in Figure 3I, but on the homogeneous alignment layer side, they are aligned in a direction parallel to the substrate. It has an arranged structure. When this is irradiated with light, the liquid crystals in the irradiated part (A) are aligned parallel to the surface of the photochromic polymer layer, so the whole becomes a homogeneous alignment state.
Optical information can be read out using polarized light in the same manner as described above.

In the optical recording element of the present invention, if it is desired to erase recorded information, it can be done by irradiating it with light having a wavelength different from that used during recording to restore the structure of the photochromic compound.

By dissolving a dichroic dye in advance in the liquid crystal layer, it is also possible to read out information based on the shade of the dye without using a polarizing plate.

As the dichroic dye, for example, those described in Naotake Matsumura, "Dyeing Industry", vol. 32, page 215 (198) are used.

In this case, if you use a temperature-dependent liquid crystal material, for example, a liquid crystal material that does not change its structure when irradiated with light at room temperature, but undergoes a structural change when heated above a certain temperature, it is possible to develop dichroism. A permanent record can be obtained based on the shade of the pigment.

Effects of the Invention The optical recording element of the present invention has the advantage that it does not exhibit the disadvantages of information recording using conventional photochromic materials, such as the disadvantage that once recorded information gradually disappears due to repeated reading, Since the alignment of the liquid crystals is controlled by the photochromic polymer layer, the resolution of fluid liquid crystals is much better than that of conventional liquid crystals in which photochromic compounds are added.
Further, the optical recording element of the present invention can be suitably used not only for reversible optical information storage but also for optically addressed display.

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

Example 1 4-hexyl-4'-hydroxyazobenzene (1)
5.03 g of ethyl bromoacetate, 3.57 g of ethyl bromoacetate, and 3.69 g of anhydrous potassium carbonate were added to 15 ml of acetone, which was heated under reflux and stirring for 2 hours. After completion of the reaction, the filtrate was filtered and the solvent was distilled off to obtain crystalline 4-hexyl-4'-ethoxycarbonylmethoxyazobenzene. Dissolve this in 40ml of dioxane and add
A methanol solution in which 1.44 g of potassium hydroxide was dissolved was added at once, and the mixture was stirred at room temperature for 1 hour. The precipitate was collected by filtration, suspended in water, acidified with hydrochloric acid, and stirred with heating for 1 hour. The crystals were collected by filtration and recrystallized from isopropyl alcohol to give 4-hexyl-4'-
4.80 g of carboxymethoxyazobenzene was obtained.
1.73 g of this carboxylic acid was added to 10 ml of benzene, 3.5 g of thionyl chloride and 5 drops of dimethylformamide were added, and the mixture was heated under reflux for 2 hours. Excess thionyl chloride was distilled off and the solvent was distilled off to obtain a crystalline acid chloride.

Suspend 200 ml of fully saponified polyvinyl alcohol (Nippon Gosei NL-05) with a degree of polymerization of 500 in 8 ml of dimethylformamide, and add 1 g of pyridine.
While heating and stirring at 110° C., 4 ml of a solution of this acid chloride in dimethylformamide was added, and the mixture was allowed to react for 1 hour. After adding 5 ml of benzene, 2 more
Allowed time to react. The reaction product was reprecipitated in 200 ml of methanol, and the yellow precipitate was collected by filtration and thoroughly washed with methanol. After drying, 1.40 g of a polymer having azobenzene in the side chain was obtained. From the absorption spectrum, the introduction rate of azobenzene units was 50 mol%.

A 1% toluene solution of this polymer was prepared and spin-coated onto two glass slides at 800 rpm. Cyclohexanecarboxylic acid phenyl ester mixed liquid crystal (K-17-N-73-I) containing 8 μm glass rod spacers on two glass plates.
Sandwich cells were created by sandwiching and sealing with epoxy resin. This colorless and transparent cell was placed between crossed nicols, and the amount of transmitted light was monitored using a He--Ne laser. The amount of transmitted light in the cell before UV irradiation was zero under crossed Nicol conditions, indicating that the cell had a homeotropic liquid crystal orientation. When this was irradiated with 365 nm ultraviolet light, the amount of transmitted light increased as azobenzene photoisomerized from trans to cis. Next, when visible light of 440 nm or more was irradiated, the amount of transmitted light decreased again as trans isomerization occurred. The amount of transmitted light changed reversibly in response to alternate irradiation with ultraviolet light and visible light. When the same cell was irradiated with ultraviolet light through a negative, a clear image with crossed Nicols was observed. This image remained undisturbed even when pressure was applied to the cell and the liquid crystal was made to flow.

Example 2 Azobenzene-bonded polyvinyl alcohol prepared in the same manner as in Example 1 was spin-coated onto two glass slides, and then heat-treated at 120° C. for 30 minutes. After allowing it to cool, it was immersed in toluene for 1 minute to remove most of the polymer. The absorbance at 340 nm was 0.002, confirming that the polymer was adsorbed on the glass plate. The mixed liquid crystal used in Example 1 was sandwiched between these glass plates to form a cell. When irradiated with ultraviolet rays and visible light alternately, a reversible change in the amount of transmitted light was observed under crossed Nicols conditions. After irradiating the entire surface with ultraviolet rays, a clear image was obtained by exposing it to 488 nm light from an Ar laser through a negative film.

Example 3 Azobenzene-bonded polyvinyl alcohol prepared in the same manner as in Example 1 was spin-coated onto two glass slides, and then heat-treated at 120° C. for 30 minutes. Rub these with cotton cloth,
An 8 μm mixed liquid crystal sandwich cell was constructed in the same manner as in Example 1, with the rubbing directions being matched. When irradiated with ultraviolet rays and visible light alternately, a reversible change in the amount of transmitted light was observed under crossed Nicols conditions.

Example 4 Azobenzene-bonded polyvinyl alcohol prepared in the same manner as in Example 1 was spin-coated onto a slide glass, and then heat-treated at 120° C. for 30 minutes. Polymerization degree 1400 on another glass plate
A 5% solution of partially saponified polyvinyl alcohol of
It was spin-coated at 1000 rpm, dried, and rubbed with a cotton cloth. A liquid crystal cell was constructed in the same manner as in Example 1 using these two glass plates. Place the cell between two polarizers crossed at right angles,
When irradiated with ultraviolet light and visible light alternately, a reversible change in the amount of transmitted light was observed. At this time, the rubbing direction of the polarizer and polyvinyl alcohol film is
At 45, the change in light intensity was particularly large.

Example 5 Azobenzenecarboxylic acid in Example 1 1.00
g was converted into an acid chloride using thionyl chloride, and then dissolved in dimethylacetamide (3 ml).
Add 2.00g of partially saponified polyvinyl alcohol with a degree of polymerization of 1400 (GM-14 manufactured by Nippon Gosei Kagaku) to a dimethylacetamide solution (25ml) heated and dissolved.
The mixture was stirred at 110°C for 12 hours. Reactant in acetone 300
ml and reprecipitated to obtain a yellow polymer. This was dissolved again in dimethylacetamide and precipitated again in acetone. This was dried in vacuum. Dissolve this polymer in dimethylacetamide and make 1%
This solution was spin-coated onto two glass slides and dried at 110°C. The liquid crystal used in Example 1 was sandwiched between these glass plates to form a cell. When this was irradiated with ultraviolet light through the negative image, a clear image was observed by placing it between two orthogonal polarizing plates.

Example 6 4-cyclohexyl azobenzene was used in place of 4-hexyl-4'-hydroxyazobenzene in Example 1 and reacted with polyvinyl alcohol in exactly the same manner as in Example 1 to obtain a yellow polymer. This was similarly spin-coated onto a glass plate, and then a liquid crystal cell was constructed. When this was irradiated with ultraviolet light through the negative image, a clear image was observed by placing it between two orthogonal polarizing plates.

Example 7 A liquid crystal cell was constructed in exactly the same manner as in Example 1 except that 4-octyl-4'-hydroxyazobenzene was used in place of 4-hexyl-4'-hydroxyazobenzene. When this was irradiated with ultraviolet light through the negative image, a clear image was observed by placing it between two orthogonal polarizing plates.

Example 8 Polymer 5.1 with azobenzene obtained in Example 1
mg was dissolved in 20 ml of chloroform and irradiated with ultraviolet rays to isomerize azobenzene from trans to cis form. Thereafter, 120μ of this solution was dropped onto the trough of a Lauda film balance to develop it as a monomolecular film. When this was scooped onto a clear quartz plate, it was observed that a monomolecular film was attached when the quartz plate was pulled up. It was confirmed by an ultraviolet-visible spectrophotometer that an azobenzene group was bonded. When a liquid crystal cell was constructed using the two plates prepared in this manner and alternately irradiated with visible light and ultraviolet light, the amount of transmitted light changed reversibly.

Example 9 Azobenzene-bonded polyvinyl alcohol prepared in the same manner as in Example 5 was spin-coated onto two glass slides, and then heat-treated at 120° C. for 30 minutes. After rubbing these with cotton cloth, a cell was constructed using the liquid crystal used in Example 1. At this time, the glass plates were arranged so that the respective rubbing directions were perpendicular to each other. Alternate irradiation with ultraviolet and visible light showed homeotropic and twisted orientation changes, and the amount of transmitted light was reversibly changed.

Example 10 Two glass plates spin-coated with the azobenzene-bonded polyvinyl alcohol prepared in Example 1 were used to prepare 4-, which is in a smectic liquid crystal phase at room temperature.
Octyl-4'-cyanobiphenyl (K-21-S-
33-N-40-I) sandwich cell (cell thickness
8 μm). Even when the cell was irradiated with ultraviolet rays at room temperature (approximately 20°C), no phase change was observed in the liquid crystal, but when the cell was heated to 35°C and then irradiated with ultraviolet rays, there was a change in the amount of transmitted light under crossed Nicols conditions. Admitted. The image obtained by passing a negative through this cell and irradiating it with ultraviolet light at 35°C remained stable for 6 months at room temperature. This image did not disappear even when the cell was irradiated with visible light. This indicates that the smectic liquid crystal has a memory effect.

Example 11 The azobenzene-containing polymer used in Example 1 was spin-coated onto a 50 μm thick polyester film, and this was cut into 5 cm x 5 cm. 2% by weight of anthracene dichroic dye (structural formula A) was dissolved in a cyclohexanecarboxylic acid phenyl ester mixed liquid crystal containing an 8 μm glass spacer, and this was sandwiched between two prepared films. When this was irradiated with ultraviolet light through a mask, a dark blue image with a pale blue background appeared in the exposed areas. When this was irradiated with visible light, the image disappeared and turned pale blue again.

Structural formula A

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one example of the structure of the optical recording element of the present invention, FIG. 2 is a cross-sectional view showing another example and the alignment state of the liquid crystal before and after light irradiation, and FIG. 3 is still another example. FIG. 3 is a cross-sectional view showing the arrangement state of liquid crystals before and after the light irradiation. In the figure, numeral 1 is a substrate, 2 is a polymer layer having residues that undergo a reversible structural change when exposed to light, 3 is a liquid crystal layer, and 4 is a homogeneous alignment layer.

Claims (1)

[Claims] 1. An optical recording material in which a liquid crystal layer is provided on a transparent substrate via a polymer layer containing residues that undergo structural changes reversibly when exposed to light.