JPH04110925A - Dimming element - Google Patents

Abstract

PURPOSE:To prevent a color from being left at the time of decoloring by forming electrodes on both surfaces of a specific smectic liquid crystal film, and making at least one of the opposite electrodes transparent. CONSTITUTION:The electrodes 11 are formed on both surfaces of the smectic liquid crystal film consisting of dichroic pigment made of side chain type high molecular liquid crystal wherein a mesogen group is coupled with the side chain of the skeleton chain of a polymer and a low-molecular nematic liquid crystal and at least one of the opposite electrodes 1 is made transparent. This composite liquid film 2 is smectic liquid crystal in a constant temperature range. When an electric field of low frequency is applied, the light transmissivity becomes considerably lower than that before the electric field is applied and the opaqueness increases, but when an electric field of high frequency is applied, the film increases in light transmissivity to come to transparent, and the transparency varies continuously with the frequency of the applied electric field, so that the previous transparency is maintained when the application of electric field is turned off. Consequently, no color is left at the time of decoloring.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is characterized in that by applying a low frequency voltage, the state becomes a colored opaque state, and by applying a high frequency voltage, the state becomes a colorless and transparent state, and each state is The present invention relates to a light control element that is memorized even when the voltage is turned off.

[Prior art 1] A composite liquid crystal film in which a low-molecular nematic liquid crystal is dispersed in a polymeric medium as an independent droplet phase, as a continuous phase, or as a mixture of an independent phase and a continuous phase, is transparent on both sides. The dimmer element with electrodes has a voltage of ON10 F F
According to patent publications (Japanese Patent Publication No. 58-501631, Japanese Unexamined Patent Publication No. 2526-1982), transparent/opaque light control is possible.
87, Japanese Patent Application Laid-Open No. 61-501345, Japanese Patent Application Publication No. 61-502128, Japanese Patent Application Laid-Open No. 6248789, Japanese Patent Application Publication No. 63-501512).

The above dimming is possible because when the voltage is off, the refractive index of the low-molecular nematic liquid crystal and the refractive index of the polymer medium are different, so the incident light is scattered, and the light is scattered within the low-molecular nematic liquid crystal. Because the direction is bent, the composite liquid crystal film becomes opaque, and when the voltage is ○N, the liquid crystal is oriented in the direction of the electric field, and the refractive index of the oriented liquid crystal and the refractive index of the polymer medium almost match, so that the incident light is This is because the composite liquid crystal film becomes transparent because the light is not scattered.

In 1968, G.H., Heilmeier, L.A.
The guest-host effect was announced by Zanoni et al.
G, H, Hei 1meier and L, A, Za
noni; Appl, Phys, Lett, 13
．． p91 (68)), it has already been mentioned in the above-mentioned patent that this guest-host effect can be applied to a light control element using the above-mentioned composite liquid crystal film to obtain a colored light control element. That is, by using a composite liquid crystal film obtained by (1) dispersing a liquid crystal containing a dichroic dye in a polymeric medium, or (2) microcapsulating a liquid crystal containing a dichroic dye and dispersing it in a polymeric medium. This is to create a light control element.

However, in method (2), the dichroic dye contained in the liquid crystal is partially dissolved in the polymer medium, and the orientation of the dichroic dye dissolved in the polymer medium does not change due to the electric field. When the voltage is turned on, the colorlessness of the composite liquid crystal film is prevented,
There was a problem that the coloring caused by the dichroic dye remained.

On the other hand, the method (2) does not have the same problems as the method (2), but it does have the difficulty of requiring microcapsules using a special material. There was a need for liquid crystal films for optical devices.

[Problems to be Solved by the Invention] The present invention has been made to solve the above-mentioned drawbacks.
It is an object of the present invention to provide a colored light control element that does not leave any coloring when it is made colorless without requiring complicated steps.

[Means for Solving the Problems] The present invention provides a smectic material comprising a side chain type polymer liquid crystal in which a mesogenic group is bonded to the side chain of a polymer backbone chain, a low molecular weight nematic liquid crystal, and a dichroic dye. This is a light control element characterized in that electrodes are formed on both sides of a liquid crystal film, and at least one of the opposing electrodes is transparent.

A composite liquid crystal obtained by using a side-chain type polymer liquid crystal in which mesogenic groups are bonded to the side chains of the polymer backbone chain as a polymer medium and mixing a low-molecular nematic liquid crystal with this polymer medium can be obtained within a certain mixing ratio range. One of the inventors of the present invention has revealed that the liquid crystal becomes a smectic liquid crystal. + (T
, Kajiyama, et al, , Chemistry
y Letters, 817-820 (1989))
The composite liquid crystal that becomes this smectic liquid crystal has a structure without phase separation, and in the present invention, by uniformly dispersing the dichroic dye in this composite liquid crystal and making the entire system a structure without phase separation, all The orientation of the dichroic dye is controlled by an electric field, and as a result, it is possible to solve the conventional problem of coloring remaining when colorless.

The present invention will be explained in detail below.

The structure of the light control element of the present invention is as shown in FIG.
and a composite liquid crystal film 2 sandwiched therebetween.The electrodes 1 of the present invention are arranged on both sides of the liquid crystal film 20, and at least one of the opposing layers is a transparent electrode. To give an example of a transparent IIT film, a transparent conductive film (made of tin and indium oxide) is placed on a glass plate.
There are electrodes formed with an ITO film (hereinafter abbreviated as ITO film). Examples of non-transparent electrodes include metals such as copper and aluminum.

The composite liquid crystal film of the present invention is a smectic liquid crystal within a certain temperature range, and when an electric field with a low frequency of several Hz or less is applied, the light transmittance decreases significantly compared to before the electric field is applied, the opacity increases, and the film becomes smectic. When an electric field with a high frequency of Hz or more is applied, the light transmittance increases and becomes transparent.The transparency changes continuously depending on the frequency of the applied electric field, and when the electric field is
When turned OFF, it has the property of retaining the transparency before turning OFF. In this way, a liquid crystal film made by mixing a conventional nematic low-molecular liquid crystal and a polymer medium has a voltage of ON10.
FF achieves a transparent/opaque light control function, whereas the composite liquid crystal film of the present invention performs a light control function by varying the frequency of the electric field.

The property that the transparency changes depending on the frequency of the applied electric field will be explained using a conceptual diagram of the molecular orientation state.

Figure 2 shows the molecules of a composite liquid crystal film formed by mixing a side-chain type polymer liquid crystal in which mesogenic groups 4 are bonded to the side chains of the polymer backbone chain, a low-molecular nematic liquid crystal 5, and a dichroic dye 6. The orientation state of the low-molecular nematic liquid crystal 5 and the dichroic dye 6 is random, so it becomes colored and opaque. When a low-frequency electric field is applied to the composite liquid crystal film, the liquid crystal changes. The arrangement is disordered, and as shown in FIG. 3, the molecular orientation state is more disordered than before the low frequency electric field is applied, and the opacity increases. Furthermore, when a high-frequency electric field is applied to the composite liquid crystal film, the side chains of the side-chain polymer liquid crystal and the low-molecular 7-machine liquid crystal become homeotropically aligned perpendicular to the electrodes due to the dielectric anisotropy. Accordingly, the dichroic dye also becomes homeotropically oriented, and the composite liquid crystal film becomes colorless and transparent. FIG. 4 shows the molecular orientation state of the composite liquid crystal film when homeotropically aligned by applying this high frequency electric field.

In the present invention, the side chain type polymer liquid crystal in which mesogen groups are bonded to the side chains of polymer skeletons is schematically represented as follows.

is a flexible molecular chain between the main chain and the mesogenic group of the side chain, and an example is an alkylene chain with an appropriate length. The above-mentioned mesogenic group may be a group that interacts with itself or the low-molecular nematic liquid crystal to be mixed and can be orientated under an electric field, and is preferably a group that is rigid and has appropriate polarity.

Examples of such side-chain polymer liquid crystals include polymer compounds represented by the following general formula.

Examples of the main chain include a siloxane chain, an acrylic chain, and a methacrylic chain. The above spacer C=O m-0 or 11 In the present invention, the low-molecular nematic liquid crystal may be one having positive dielectric anisotropy. Examples include those having the following chemical structure.

C1H 10 Pen (Toc N C1 H,, Oi-Ne-G-CN) These low-molecular nematic liquid crystals can be used alone or in combination.The mixing ratio of low-molecular nematic liquid crystal to high-molecular liquid crystal is mixed. It is set within a range in which the composite liquid crystal takes a smectic state.In other words, if the proportion of low-molecular-weight nematic liquid crystal in -g becomes too large, the smectic property will be lost, while if it is too small, the responsiveness to an electric field will deteriorate, so the purpose of the limitation is that Although it is not a composite LCD overall 10
A range of 80% by weight is preferred.

As the dichroic dye used in the present invention, a P-type dichroic dye having a transition moment in the long axis direction of the dye molecule, which is known as a dichroic dye for liquid crystal display, is used. The reason why P-type dye molecules are used is that when the smectic state formed from a low-molecular-weight liquid crystal with positive dielectric anisotropy undergoes homeotropic alignment under a high-frequency electric field, P-type dye molecules undergo homeotropic alignment. This is because the optical element can be made transparent and colorless. These dichroic dyes include merocyanine, styryl, azomethine, azo, anthraquinone, and tetrazine dyes based on their molecular structures. These dichroic dyes preferably have a large dichroic ratio, high solubility in low-molecular liquid crystals, and good chemical and photochemical stability. The amount of these dichroic dyes added to the composite liquid crystal varies depending on the desired color tone, but it is practical in the range of 0.2 to 10% of the total composite liquid crystal.

A light control device using a composite liquid crystal film in which a dichroic dye is dispersed is produced by dissolving its constituent components, such as a side-chain polymer liquid crystal, a low molecular liquid crystal, and a dichroic dye, in a common solvent (e.g. acetone). It can be created by casting on a bridge, removing the solvent, and then adhering an electrode to the other liquid crystal sheet surface. Alternatively, the composite liquid crystal material from which the solvent has been removed may be thermoformed to form a film, and electrodes may be formed on both sides of the film.

The composite liquid crystal film of the light control element created in this way can be colored and opaque in the low frequency range and colorless and transparent in the high frequency range by driving the electric field at two frequencies, and can be made transparent and colorless in the high frequency range. It also has a memory effect that allows it to retain its state.

[Function] A composite liquid crystal film formed by mixing a side chain type polymer liquid crystal in which a mesogenic group is bonded to the side chain of the polymer skeleton of the present invention, a low-molecular dimatic liquid crystal, and a dichroic dye is as follows: The entire system has a structure without phase separation, and the orientation of all dichroic dyes in the system is controlled by an electric field.

[Example] Example 1 Poly(4
methoxyphenyl-4probyloxybenzoate-methylsiloxane) was used. (Hereinafter abbreviated as PMPPS) 4-cyano-4-pentyloxybiphenyl represented by the following structural formula was used as a low molecular weight nematic liquid crystal. (Hereafter 50C
(abbreviated as B) 50% by weight of the above PMPPS and 48% by weight of 50CB
and 2% by weight of purple dichroic dye 5l-152 manufactured by Mitsui Toatsu Dye Co., Ltd., and this mixture was dissolved in acetone to obtain an acetone solution. This acetone solution was cast on a glass plate with an ITO film to form a composite liquid crystal film with a film thickness of 16 μm.Furthermore, a glass plate with an ITO film was adhered to the surface of this composite liquid crystal film to create a light control element. did.

It was confirmed by X-ray diffraction, DSC, and observation using a polarizing microscope that this composite liquid crystal film was in a smectic state in a temperature range of 7 to 77°C.

This light control element has 200V, , 0. When an alternating current voltage of OIHz was applied, the parallel light transmittance (transparency) was 8% and a purple color was exhibited. Also, 200V.

, when an alternating current voltage of 1 KHz was applied, the parallel light transmittance (transparency) was 98% and the color tone was colorless.

Note that each state was maintained even when the voltage was turned off, confirming that the light control element had memory properties.

Example 2 4hexyloxyphenyl-4'pentyl benzoate (hereinafter abbreviated as HPPB) represented by the following structural formula was used together with 50CB as a low molecular weight nematic liquid crystal.

HPPB: 30% by weight of PMPPS as side chain polymer liquid crystal, 47% by weight of 50CB as low molecular weight nematic liquid crystal, HPP
20% by weight of B, dichroic dye manufactured by Mitsui Toatsu Dye Co., Ltd.
The red dichroic dye M-86 was mixed in a proportion of 3% by weight to obtain a mixture.

A composite liquid crystal film and a light control element were produced in the same manner as in Example 1 except that this mixture was used.

It was confirmed by X-ray diffraction, DSC, and observation using a polarizing microscope that this composite liquid crystal film entered a smectinic state in a temperature range of 7 to 67°C.

This light control element has 200V-p, 0. When an AC voltage of OIHz was applied, the parallel light transmittance (transparency) was 2% and a red color was exhibited. Also, 200V.

, when an alternating current voltage of IKHz was applied, the parallel light transmittance (transparency) was 98% and the color tone was colorless.

Note that each state was maintained even when the voltage was turned off, confirming that the light control element had memory properties.

[Effects of the Invention] The light control element of the present invention is a colored light control element that can be produced without the need for complicated processes such as encapsulation, and does not remain colored when it is made colorless. The device is useful for use in lighting equipment to control its dimming state, for applications in partitions and windows in homes and offices, and as a color display material.

[Brief explanation of the drawing]

FIG. 1 is a schematic side sectional view of a light control element of the present invention. FIG. 2 is a conceptual diagram of the molecular orientation state of the composite liquid crystal film of the present invention immediately after its creation. FIG. 3 is a conceptual diagram of the molecular orientation state when a low frequency electric field is applied to the composite liquid crystal film of the present invention. FIG. 4 is a conceptual diagram of the molecular orientation state when a high frequency electric field is applied to the composite liquid crystal film of the present invention. DESCRIPTION OF SYMBOLS 1... Electrode, 2... Composite liquid crystal film, 4... Mesogenic group, 5... Low molecular weight nematic liquid crystal, 6... Dichroic dye, E... High frequency electric field

Claims (1)

[Claims] (1) Electrodes are formed on both sides of a smectic liquid crystal film consisting of a side chain type polymer liquid crystal in which a mesogenic group is bonded to the side chain of a polymer backbone chain, a low molecular weight nematic liquid crystal, and a dichroic dye. A light control element characterized in that at least one of the electrodes is transparent.