JPH0743685A - Liquid crystal display element and liquid crystal display device formed by using the same - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display element which is less restricted by kinds of dyestuff to be utilized and the amts. of the dyestuff to be mixed and is suitable for a color display of a projection type by providing the liquid crystal display device with a liquid crystal material layer consisting of a mixture composed of a low-molecular liquid crystal material and a high-molecular material having at least one kind of dyestuff at the side chains. CONSTITUTION:This liquid crystal display device is provided with the mixture composed of the low-molecular liquid crystal material 4 and the high-molecular material 3 having at least one kind of the dyestuff at the side chains. The liquid crystal material 4 and the high-molecular material 3 are preferably used by mixing these materials in such a manner that the weight ratio thereof attains a 4:6 to 8:2 range in order to obtain good scattering characteristics when the liquid crystal material is mixed with the high-molecular material 3. A difference between the refractive index of the high-molecular material 3 and the refractive index to ordinary light of the material 4 is preferably small and this difference is preferably <=0.02 in order to obtain high transparency at the time of impressing an electric field. The high molecular material having the dyestuff at the side chains is preferably transparent materials, such as (meth)acrylic resin and styrene resins, and has preferably at least one kind of the dyestuff at the side chains.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light scattering type liquid crystal display element which scatters incident light when no electric field is applied and transmits light when an electric field is applied, and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art In recent years, a light-scattering type liquid crystal material having a liquid crystal material layer made of a mixture of a low molecular weight liquid crystal material and a polymer material, which scatters incident light when no electric field is applied and transmits light when an electric field is applied. Liquid crystal display devices have been developed. This liquid crystal display device utilizes the birefringence of a low molecular weight liquid crystal material and is characterized in that a mixture of a low molecular weight liquid crystal material and a high molecular weight material is in a phase separated state. That is, since the phases are separated, the incident light is scattered because the refractive index of the low molecular weight liquid crystal material and the refractive index of the high molecular weight material are different when the electric field is not applied, while the incident light is scattered when the electric field is applied. Incident light is transmitted because the material is homeotropically oriented and matches the refractive index of the polymeric material. Since this liquid crystal display element does not require a polarizing film, it is expected to enable bright display. As the liquid crystal material, a nematic liquid crystal is used, as the polymer material, a polymer material soluble in an organic solvent such as acrylic, styrene or rubber, or a water soluble resin such as polyvinyl alcohol, gelatin or cellulose is used. It is often done. Further, a thermosetting epoxy resin or a curable acrylic or urethane acrylate monomer or oligomer is mixed with the liquid crystal material and then polymerized to combine the high molecular liquid crystal material with the low molecular liquid crystal material during photopolymerization or thermal polymerization. Techniques for separation have been developed.

On the other hand, a technique has been developed in which a dichroic dye is mixed with a polymer material together with a liquid crystal material in order to perform color display using the above-mentioned light scattering type liquid crystal display element. The dichroic dye mixed in the liquid crystal material responds to the electric field together with the liquid crystal. Therefore, when the electric field is not applied, the dichroic dye is randomly oriented and thus is in a colored state and scatters light. When an electric field is applied, the dichroic dye is homeotropically aligned with the liquid crystal, becomes a colorless state, and transmits light. Also,
Techniques for mixing dyes having a dichroic ratio of 1 or less have been developed. Since a dye having a dichroic ratio of 1 or less does not easily react with the liquid crystal due to the electric field, the dye is not homeotropically aligned when an electric field is applied, and the incident light passing through the liquid crystal display element is colored. At this time, the dye is dissolved only in the liquid crystal material or in both the liquid crystal material and the polymer material.

[0004]

The technique of mixing the above-mentioned dichroic dye with a polymer material together with a liquid crystal material becomes transparent when an electric field is applied, and is therefore suitable for direct-view type color display, but the Schlieren optical system. It is not suitable for projection type display using. Further, the types of dyes that can be used in the technique of mixing dyes having a dichroic ratio of 1 or less are limited, and generally, the dyes have poor compatibility with polymer materials and liquid crystal materials,
In order to obtain a sufficient contrast with a small amount of dye mixed, it was necessary to thicken a film made of a mixture of a liquid crystal material and a polymer material. Further, since the solubility of the dye is limited, a special technique is required for manufacturing the liquid crystal display device so that the dye is not phase-separated.

The present invention has been made in view of the above problems, and there are few restrictions on the type of dye used and the amount of dye mixed, and a liquid crystal display device suitable for projection type color display and a liquid crystal using the same. An object is to provide a display device.

[0006]

A liquid crystal display device of the present invention for solving the above problems comprises a liquid crystal material layer made of a mixture of a low molecular weight liquid crystal material and a polymer material having at least one dye in a side chain. It is characterized by In the liquid crystal display element of the present invention, a dye that realizes colorization is present in the side chain of the polymer material in the mixture of the liquid crystal material and the polymer material,
The dye does not exist alone or in the low molecular weight liquid crystal material. Therefore, the dye can be introduced only into the polymer material part in the liquid crystal material layer by copolymerizing a monomer having the dye in the side chain, and the amount and type of the dye can be arbitrarily changed. Sex does not matter.

The liquid crystal material used in the present invention is, for example, E-7, E-8, E-44, E-6 manufactured by Merck & Co., Inc.
Commercially available mixed liquid crystals that are nematic in the room temperature region, such as 3, ZLI-2061 and ZLI-1132, and mixtures of a plurality of commercially available liquid crystal materials are preferably used. In order to obtain good scattering characteristics when mixed with the polymer material, it is preferable to mix and use the liquid crystal material and the polymer material in a weight ratio of 4: 6 to 8: 2. Further, in order to obtain high transparency when an electric field is applied, the difference between the refractive index of the polymer material and the refractive index of the material with respect to ordinary light is preferably small, and the difference is preferably 0.02 or less.

The polymeric material having a dye in the side chain used in the present invention is a transparent material such as (meth) acrylic resin or styrene resin, and has at least one kind of dye in the side chain. Anything is fine. Such a polymer material can be obtained, for example, by copolymerizing a polymerizable monomer having a dye in its side chain with a polymerizable monomer forming a transparent resin. In addition, the above polymeric material,
Mixing a monomer or oligomer that is polymerized by light or heat, and a polymerizable monomer having a dye in the side chain,
It can also be obtained by mixing a low molecular weight liquid crystal material with this and then polymerizing it. Examples of the polymerizable monomer include (meth) acrylic acid esters having a dye represented by the general formula (I) in the side chain (wherein R ₁ is a hydrogen atom or a methyl group, and R ₂ is a dye). It is.)

[Chemical 1] On the other hand, the dye introduced into the side chain is represented by the following formula (I
I), (III)

[Chemical 2] (Wherein, n is an integer of 1 to 15, m is an integer of 1 to 5, R ₃ is an alkyl group, R ₄ is an alkyl group, an alkoxyl group such as a methoxy group, and a cyano group) A group, a nitro group or a hydrogen atom), and the following formulas (IV) and (V)

[Chemical 3] Anthraquinone dye represented by
Is an integer of 1 to 15, and R ₅ to R ₁₁ represent an amino group, an alkylamino group, a hydroxyl group or a hydrogen atom. )
And so on. In the present invention, there is no limitation on the dichroic ratio of the dyes, and a dichroic dye or a dye having no dichroism may be used. When the dye has dichroism, the glass transition point of the polymer material having the dye in the side chain is
It is preferably higher than the operating temperature range of the low molecular weight liquid crystal material. Further, when the polymer material is liquid crystalline, the polymer material does not change within the temperature range in which the low molecular weight liquid crystal material responds to the electric field, and therefore the glass transition point of the polymer material is from the liquid crystal state of the liquid crystal material. It is preferable that the temperature is higher than the temperature of transition to the amorphous state.

An example of the structure of the liquid crystal display device of the present invention is shown in FIG.
Shown in. In the figure, 1 is a substrate, 2 is a transparent electrode, 3 is a polymer material having a dye in a side chain, 4 is a low-molecular liquid crystal material, and a polymer material 3 having a dye in a side chain is a low-molecular liquid crystal material. The substrate 1 has transparent electrodes 2 on both sides of the liquid crystal material layer in which 4 is dispersed.
Are stacked so as to interpose. The substrate may be a hard material such as glass or plastic glass or a flexible material such as a plastic film. At least one of the two substrates is transparent. According to the present invention, when a mixture of a polymer material having a dye in a side chain and a low molecular weight liquid crystal material is used for a light scattering projection type liquid crystal display element, the low molecular weight liquid crystal material is high in a portion to which an electric field is not applied. Since the liquid crystal is in a phase-separated state from the molecular material and the liquid crystal is dispersed in random directions, light is scattered and the liquid crystal becomes black. On the other hand, in the part to which an electric field is applied, only the liquid crystal is homeotropically aligned, and the refractive index is close to that of the polymer material, making it transparent, but the dye does not participate in the alignment and absorbs incident light, so it colors the light. It transmits in the state and exhibits a clear hue. Therefore, by projecting white light on the liquid crystal display element, the hue can be projected.

FIG. 2 is a schematic diagram showing an example of a liquid crystal display device using the liquid crystal display element of the present invention in a Schlieren optical system. In the liquid crystal display device, the light from the white light source 5 arranged on the rear surface of the liquid crystal display element 6 of the present invention is scattered by the liquid crystal display element 6 when no electric field is applied, passes through the lens 7, and then is stopped by the diaphragm 8. It is shut off (10 in the figure). On the other hand, when an electric field is applied, it passes through the diaphragm 8 and is projected on the projection surface 9 (11 in the figure). The liquid crystal display device according to the present invention is
In addition to such a projection type display device suitable for color display, the display device is used for a window of a building, an electronic display switchable display device used for advertisement and the like.

[0011]

EXAMPLES The present invention will be described in detail below based on examples. Example 1 As a polymer material having a dye in a side chain, a 9: 1 copolymer of methyl methacrylate and 4 ′ [(2-methacryloyloxyethyl) ethylamino] -4′nitroazobenzene (the following formula ( VI)) was synthesized. The maximum absorption wavelength of the film made of this copolymer was 478 nm, and the glass transition point thereof was 131 ° C.

[Chemical 4] 4 parts by weight of this copolymer and nematic liquid crystal E-7 (transition temperature from liquid crystal state to amorphous state: 58 ° C.) manufactured by Merck Ltd. 6
Parts by weight and chloroform are dissolved, the solution is spin-coated on a glass substrate coated with ITO, and then the liquid crystal material layer is produced by sandwiching the liquid crystal material layer so that air bubbles do not enter into another ITO substrate. did. Here, the liquid crystal material and the polymer material are well phase-separated, and when the electric field is not applied, the incident light is well scattered and the wavelength 6
The light transmittance at 33 nm was 3.1%. On the other hand, when an electric field of a rectangular wave of 60 V and 1 kHz was applied to this liquid crystal display element, the liquid crystal material layer turned red, and when white light was incident on the liquid crystal display element, red light was projected.
FIG. 3 shows changes in the transmittance of this liquid crystal display device.
Here, (a) is when the electric field is applied, and (b) is when the electric field is not applied.

Example 2 As a polymer material having a dye in its side chain, a copolymer represented by the following formula (VII) having an anthraquinone dye was synthesized. The maximum absorption wavelength of the film made of this copolymer was 678 nm.

[Chemical 5] 3 parts by weight of this copolymer and 7 parts by weight of a nematic liquid crystal E-7 manufactured by Merck & Co., Inc. were dissolved in chloroform, and the glass substrate coated with ITO was spin-coated with the solution, and then another ITO substrate was prepared. A liquid crystal display element was manufactured by sandwiching the liquid crystal material layer so that air bubbles would not enter. Also in this liquid crystal display element, the liquid crystal material and the polymer material are well phase-separated, and when the electric field is not applied, the incident light is well scattered and the Schlieren optical system (wavelength: 6
The light transmittance at 33 nm) was 1%. When an electric field having a rectangular wave of 60 V and 1 kHz was applied to this liquid crystal display element, the liquid crystal material layer turned blue, and when white light was incident on the liquid crystal display element, blue light was projected.

In the above examples, the copolymers each having one kind of dye in the side chain were used, but various hues can be obtained by using the polymer material having several kinds of dyes in the side chains. The projection light it has is obtained.

[0014]

According to the liquid crystal display device of the present invention, there are few restrictions on the types of dyes used and the dyes, and it is possible to electrically switch between opaque and color, so that it is suitable for a projection type liquid crystal display device. Can be used.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of the structure of a liquid crystal display element of the present invention.

FIG. 2 is a cross-sectional view showing an example of a liquid crystal display device using the liquid crystal display element of the present invention.

FIG. 3 is a diagram showing a transmission spectrum when an electric field is applied and when no electric field is applied in the liquid crystal display element of the example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 substrate 2 transparent electrode 3 polymer material having a dye in a side chain 4 liquid crystal material 5 white light source 6 liquid crystal display element according to the present invention 7 lens 8 diaphragm 9 projection surface 10 optical path when no electric field is applied 11 electric field is applied Optical path

Claims (2)

[Claims] 1. A liquid crystal display device comprising a liquid crystal material layer made of a mixture of a low molecular weight liquid crystal material and a polymer material having at least one dye in a side chain. 2. A liquid crystal display device using the liquid crystal display element according to claim 1 in a Schlieren optical system.