JPH0765044B2 - Liquid crystal optical element - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a liquid crystal optical element used for an information recording medium or a display, etc., which utilizes the memory effect of liquid crystal.

[Prior art]

In recent years, active research has been conducted on memory materials or display materials using ordinary nematic liquid crystals. Examples thereof include JP-A-58-125247 and JP-A-59-10930. However, these methods have a problem that it is difficult to obtain uniform orientation, and as a result, sufficient contrast cannot be obtained.

[Purpose of the present invention]

An object of the present invention is to improve the orientation of the side chain type polymer liquid crystal.

[Configuration of the present invention]

 First, the operating principle of the present invention will be described.

A liquid crystal composition mainly composed of a polymer liquid crystal having a liquid crystal group in a side chain and terphenyl or a derivative thereof is enclosed between glass or plastic substrates having a transparent electrode such as ITO, and a vertical alignment state is obtained by an electric field or the like. In this state, the cell is transparent. When the cell is locally heated by, for example, a laser beam to a temperature near the isotropic liquid Tcl and cooled, a light-scattering or birefringent recording point is formed.
When this portion is heated and then cooled while applying voltage, the original transparent vertical alignment state is restored again. This corresponds to a so-called erasing process. If the heating area is limited to a part, partial erasing can be performed, and if the heating area is entirely, erasing can be performed. Of course, the recording and erasing described above can be performed in reverse. In this case, a vertically aligned transparent recording point is formed by heating and cooling while applying a voltage, and heating and cooling may be simply performed at the time of erasing.

Hereinafter, a specific configuration of the present invention will be described in detail.

The side chain type polymer liquid crystal used in the present invention is a polymer compound having a liquid crystal group in the side chain via an alkyl chain.

That is, the side chain type polymer liquid crystal is formed of three parts of a main chain, a spacer and a liquid crystal group. Although various polymer main chains can be used as the main chain, polyacrylate, polysiloxane, polymethacrylate and the like are preferable. The spacer is preferably a methylene chain having 2 to 18 carbon atoms or an oxymethylene chain. When the carbon number is 1 or 0, the main chain hinders the orientation, and when the carbon number is 19 or more, the orientation does not occur due to crystallization. Examples of the liquid crystal group include those having the following structural formula.

Here _{R: OCH 3, OC 2 H} 5, OC 3 H 7, OC 4 H 9, OC 5 H 11, OC 6 H 13, CH 3, C
₂ H ₅ , C ₃ H ₇ , C ₄ H ₉ , C ₅ H ₁₁ , C ₆ H ₁₃ , C ₇ H ₁₅ , C ₈ H ₁₇ , H, Cl, B
r, C ₉ H ₁₉ , C ₁₀ H ₂₁ , C ₁₁ H ₂₃ , C ₁₂ H ₂₅ , C ₁₄ H ₂₉ , C ₁₆ H ₃₃ , Here, polyacrylate and polymethacrylate may be copolymerized with a spacer, an alkyl chain different from a side chain composed of a liquid crystal group, an aryl group and the like having a side chain. In addition, within the limit that does not impair the liquid crystal state, low-molecular liquid crystal,
Polymers and dyes may be mixed.

0.01 to 12 wt%, preferably 0.1 to 8 wt% of terphenyl or terphenyl derivative described below in the above-mentioned polymer liquid crystal
The addition improves the orientation due to the electric field and the like.

The terphenyl or terphenyl derivative used in the present invention is represented by the general formula [I].

General formula [I] In the general formula [I], X and Y are H, an alkyl group, an oxyalkyl group, a halogen, a nitro group and an alkyl ester group. As the alkyl group, those having 1 to 9 carbon atoms can be used. If it is 10 or more, the solubility in the polymer liquid crystal is low and the intended effect cannot be obtained. As the oxyalkyl group, those having 1 to 12 carbon atoms can be used. When the carbon number is 13 or more, the solubility in the polymer liquid crystal is too low to be used.

Examples of structural formulas suitable for the present invention are shown below.

The terphenyl or terphenyl derivative is added in an amount of 0.01 to 12 wt%, preferably 0.1 to 8%, based on the polymer liquid crystal.
wt%. If it is less than 0.01 wt%, the alignment property of the polymer liquid crystal is not improved, and if it is added more than 12 wt%, recording and erasing are repeated, resulting in partial crystallization, which causes an error during recording or reproduction. When displaying an image or the like, there is a drawback that the image quality is deteriorated.

Further, the above terphenyl or terphenyl derivative may be added as a mixture of two or more kinds, but it is desirable that the total amount of addition is within the above range of 0.01 to 12 wt%.

As the cell substrate used in the present invention, there are glass, plastic sheet, and the like, and as the specific substance of the latter, nitrocellulose, a cellulose derivative such as cellulose triacetate,
Examples thereof include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polycarbonate such as polycarbonate, polypropylene and polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, nylon, polystyrene and polyether sulfone. Further, in the case of applying the electric field as described above, it is necessary to provide a transparent electrode layer on these substrates, and as the transparent electrode layer, a usual oxide of indium or tin can be used. When a polymer liquid crystal composition having a positive dielectric anisotropy is used, the alignment state is vertical alignment. A vertical aligning agent may be used to make this vertical alignment uniform. As a vertical alignment agent, stearic acid,
Hexadecyltrimethylammonium, bromide, basic carboxylic acid chromium complex, organosilane such as DMOAP,
Hexamethyl, dicyclohexane, perfluorodimethylcyclohexane, tetrafluoroethylene, polytetrafluoroethylene, vermicide 100, octadecylmalonic acid and the like can be used.

In order to carry the polymer liquid crystal composition between the substrates, the polymer liquid crystal composition is solvent-coated on one substrate, or is applied in a state of being melted with a liquid crystalline siloxane oligomer-Tcl or more, and then the solvent is dried or After bringing the melt to room temperature,
It can be attached to the other substrate.

Hereinafter, means for applying heat to the liquid crystal layer to cause a phase transition in the present invention will be described. First, as a heating means for forming a recording point in a transparent alignment state, a laser beam,
Examples include a flash lamp such as xenon, a heating head, or a scanning electrode as a heating element. Among them, laser light is desirable as a method for forming high density recording points. In this case, a dye capable of efficiently converting light into heat may be added to the liquid crystalline siloxane oligomer layer, or a thin layer of the dye may be formed on the substrate and used as the light absorbing layer. As such a dye, any dye may be used as long as it has absorption at the wavelength of the laser light used, and preferably has absorption maximum. For example, when a 1.06 μm YAG laser is used,
NKX114G manufactured by Japan Photosensitive Dye Research Institute or the like can be used. In this wavelength, indium and tin oxides used as the transparent electrode may serve as a light absorber, and it may not be necessary to separately provide a light absorbing layer.

On the other hand, in the case of forming a transparent vertically aligned recording point in an unaligned state exhibiting opacity or birefringence, a liquid crystal is formed by the above-mentioned laser beam, flash lamp, heating head or scanning electrode serving as a heating element while applying an electric field. The layers can be heated. In the cooling process, vertically aligned recording points are formed.

The above is the method for forming the recording point. To erase the recording point, in the case of the recording point formed in the transparent alignment state, it is sufficient to heat and cool while applying a voltage, or to make the recording point opaque or complex. In the case of a recording point formed in a non-oriented state that exhibits refraction, it may be heated and cooled as it is. The heating means used is the same as that used for forming the recording points.

The voltage application condition is preferably a voltage of 10 ⁷ V / cm or less in order to prevent a short circuit. Further, either direct current or alternating current may be used, but alternating current is preferable from the viewpoint of deterioration with time, and the frequency is preferably between 10 Hz and 50 KHz. If it is less than 10 Hz, deterioration with time occurs, and if it is more than 50 KHz, the orientation tends to be insufficient.

As the reproducing means in the present invention, optical transmittance and reflectance can be used. Also, combining with a polarizing plate,
Alternatively, the cells may be detected under orthogonal Nicols.

Although the present invention has been described above as a recording medium, it can also be used as a projection display in which a charactor or graphic image is recorded in a cell in the same manner as described above and is projected on a screen by halogen light or the like.

The present invention will be described below with reference to specific examples, but the present invention is not limited to these examples.

Example 1 Cetyltrimethylammonium bromide as an aligning agent was applied to the transparent electrode side of a transparent conductive PET base to form an aligning agent layer, and then 2 wt% of terphenyl was added to the polymer liquid crystal 1 between the bases. A liquid crystal cell was prepared by enclosing the polymer liquid crystal composition in a thickness of 7 μm.

After heating the liquid crystal cell to 130 ° C., a voltage was applied between the cells under the condition of 100 Hz and 50 V to vertically align the cells. When the liquid crystal cell was placed under crossed Nicols and observed, no white turbidity was observed, and it was found that the liquid crystal cell was in a uniform vertical alignment state with very small birefringence. Comparative Example 1 A liquid crystal cell was prepared in the same manner as in Example 1, but no additive such as terphenyl was added at this time.

It was found that in this liquid crystal cell, white turbidity that was clearly recognized was visually observed, and the vertical alignment state was considerably nonuniform.

〔The invention's effect〕

As is clear from the above examples, the present invention remarkably promotes the orientation of the polymer liquid crystal by adding a terphenyl or terphenyl derivative to the polymer liquid crystal. It makes a great contribution to improving the reliability of the spray.

[Brief description of drawings]

1 to 4 are examples of optical elements to which the present invention is applied. FIG. 1 shows an example of a transmissive element in which an orienting agent layer is provided on a transparent conductive layer, and FIG. 2 shows a polarizing plate provided thereon. FIG. 3 is an example of a transmissive element provided with a light absorption layer in FIG. FIG. 4 shows an example of a reflection type element in which a reflection layer is provided on one side of a support. The configuration of the present invention is not limited to these. 1. Support, 2. Transparent conductive layer 3. Alignment agent layer, 4. Liquid crystal layer 5. Reflection layer, 6. Light absorption layer 7. Polarizing plate

Claims (1)

[Claims] 1. A side chain type polymer liquid crystal having a liquid crystal group in a side chain, to which terphenyl or a derivative thereof represented by the following general formula (I) is added by 0.01 to 12 wt% relative to the polymer liquid crystal. Liquid crystal optical element. General formula (I) X and Y are H, an alkyl group, an oxyalkyl group, a halogen, a nitro group, and an alkyl ester group.