JPH07787B2 - 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 polymer liquid crystals.

[Structure of Invention]

 First, the working 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 adamantane 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 to a temperature near the isotropic liquid Tcl by, for example, a laser beam and then cooled, a light-scattering or birefringent recording point is formed.
When this part is heated and cooled in the future while applying a voltage, the original transparent vertical alignment state is restored again. This is,
This is equivalent to a so-called erasing process. If the heating region is limited to a part, partial erasing can be performed, and if the heating region is performed on the entire surface, whole erasing can be performed. Of course, the above recording and erasing 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 simply heating and cooling at the time of erasing.

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

As the polymer liquid crystal used in the present invention, a polymer compound having a liquid crystal group as a side chain via an alkyl chain can be used.

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.

Where 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, Br, 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.

0.01-15 wt% of the adamantane or adamantane derivative described below is added to the above-mentioned polymer liquid crystal, preferably 0.1-10 wt%
%, The orientation due to the electric field and the like is improved. Adamantane is given by the structural formula [I].

Further, as the adamantane and its derivatives, the following can be preferably used.

Adamantane, 1,3-dimethyladamantane, 1-bromoadamantane, 1-chloroadamantane, 2-bromoadamantane, 2-chloroadamantane, 2-adamantane, 2-adamantanol, 1,3-dimethyladamantane-5,7-diol , 1-hydroxymethyladamantane, 1-cyanoadamantane, 1-adamantanecarboxylic acid ethyl ester, 1-acetylaminoadamantane, 1-aminomityladamantane.

The addition amount of the adamantane or the adamantane derivative is 0.01 to 15 wt% with respect to the polymer liquid crystal, preferably 0.1 to 1
It is 0 wt%. If it is less than 0.01 wt%, no improvement in the orientation of the polymer liquid crystal is observed, and if it is added in excess of 15 wt%, recording,
By repeating the erasing, there is a drawback that a part is crystallized and an error occurs during reproduction of recording, or the image quality is deteriorated when displaying an image or the like.

Further, two or more kinds of the adamantane or the adamantane derivative may be mixed and added, but it is desirable that the total amount of addition is within the above range of 0.01 to 15 wt%.

Examples of the cell substrate used in the present invention include glass and plastic sheets. Specific examples of the latter include nitrocellulose, cellulose derivatives such as cellulose triacetate, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polycarbonate, polypropylene, Examples include polyolefin such as polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, nylon, polystyrene, and polyether sulfone. Further, when applying an electric field as described above, it is necessary to provide a transparent electrode layer on these substrates,
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 the vertical alignment agent, stearic acid, hexadecyltrimethylammonium, bromide, basic carboxylic acid chromium complex, organic silane such as DMOAP, hexamethyl, dicyclohexane, perfluorodimethylcyclohexane, tetrafluoroethylene, polytetrafluoroethylene, vermicide 100. ,
Octadecyl malonic acid or 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 after the liquid crystal siloxane oligomer Tcl or more is applied in a melted state, the solvent is dried or melted. After the temperature is set to room temperature, the other substrate may be peeled off.

The means for applying heat to the liquid crystal layer to cause a phase transition in the present invention will be described below. First, as a heating means for forming a recording point in a transparent alignment state, there is a method using a laser beam, 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 addition, at this wavelength, the oxide of indium or tin used as the transparent electrode serves 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 recording point in a vertical alignment state in an unaligned state showing opacity or birefringence, while applying an electric field, the laser beam, the flash lamp, the heating head or the scanning electrode to be the heating element, The liquid crystal layer may 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 a recording point made in a transparent alignment state, it is sufficient to heat and cool while applying a voltage, or to be opaque or birefringent. In the case of the recording point formed in the non-oriented state, the heating and cooling may be performed 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 107 V / cm or less in order to prevent a short circuit. Either direct current or alternating current may be used, but alternating current is desirable from the viewpoint of deterioration over 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 50 KHz or more, the orientation tends to be insufficient.

As the reproducing means in the present invention, optical transmittance and reflectance can be used. It may also be combined with a polarizing plate or the cell may be detected under crossed Nicols.

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

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% adamantane was added to the polymer liquid crystal 1 between the bases. A polymer liquid crystal composition was sealed in a thickness of 5 μm to prepare a liquid crystal cell.

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 adamantane was added at this time.

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

〔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 adamantane or an adamantane derivative to the polymer liquid crystal. It makes a great contribution to improving the reliability of the spray.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 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 orientation agent layer is provided on a transparent conductive layer, and FIG. 2 shows a polarizing plate provided on it. FIG. 3 is an example of a transmissive element provided with a light absorption layer in FIG. FIG. 4 is an example of a reflective element in which a reflective 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 liquid crystal optical element comprising a polymer liquid crystal to which adamantane or a derivative thereof is added in an amount of 0.01 to 15 wt% with respect to the polymer liquid crystal.