JPH07120736A - Polymer dispersion type liquid crystal display device and its production - Google Patents

Abstract

PURPOSE:To provide a polymer dispersion type liquid crystal display device having a polymer dispersion liquid crystal layer in which liquid crystal puddles of uniform shape and uniform size are uniformly dispersed. CONSTITUTION:A pair of transparent substrates 11, 12 having transparent electrodes 13, 14 are joined with a sealing material 15 to form a cell 10. Fluorinated films or fluorocarbon resin films 22, 23 having low surface energy are disposed in the cell 10. A mixture soln. of a liquid crystal 19 and a polymerizable material is injected into the cell 10. The polymerizable material is polymerized to cause phase separation of the liquid crystal 19 and the polymer resin 17. Thus, a polymer dispersion liquid crystal layer 16 in which liquid crystal reservoirs 18 of almost uniform shape and size are uniformly dispersed is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer dispersed liquid crystal display device, and more particularly to a polymer dispersed liquid crystal display device having a polymer dispersed liquid crystal layer in which liquid crystal domains are uniformly arranged.

[0002]

2. Description of the Related Art A polymer-dispersed liquid crystal display device has a structure in which a pair of transparent substrates made of glass or the like having transparent electrodes made of ITO or the like are bonded together through a frame-shaped sealing material to form a cell. A polymer dispersed liquid crystal layer in which liquid crystal is dispersed in a molecular resin is provided. As the liquid crystal, for example, nematic liquid crystal having a positive dielectric anisotropy is used.

This polymer-dispersed liquid crystal display device is driven for display by applying a voltage between the transparent electrodes of both substrates. The liquid crystal molecules in the polymer dispersed liquid crystal layer are oriented in various directions when no voltage (electric field) is applied, and the incident light is scattered by the light scattering action of the polymer dispersed liquid crystal layer. Therefore, the screen becomes cloudy (dark). When a voltage equal to or higher than the threshold voltage is applied between the transparent electrodes, the liquid crystal molecules are evenly arranged perpendicularly to the substrate surface, and the refractive index for light traveling in the direction of the director of the liquid crystal, that is, the ordinary light refractive index The refractive index of the polymer resin becomes almost equal, and the incident light is transmitted through the polymer dispersed liquid crystal layer with almost no light scattering effect. Therefore, the screen becomes transparent (bright).

That is, the polymer-dispersed liquid crystal display device realizes a display by controlling the amount of transmitted light and the amount of scattered light, does not require a polarizing plate, and is commonly used in TN type liquid crystal display devices and the like. Compared with this, it has the advantage that the screen is bright.

[0005]

A polymer-dispersed liquid crystal display device is conventionally assembled by joining a pair of substrates to assemble a cell and injecting a mixed solution of a liquid crystal and a polymer material into the cell by a vacuum injection method. It is manufactured by a method of polymerizing a polymer material to form a polymer dispersed liquid crystal layer.

However, as shown in FIG.
A glass substrate is used as 2, and electrodes 13 and 14 are I
When TO electrodes are used, their surface energy is high, and the interaction between the substrates 11, 12 and the electrodes 13, 14 and the liquid crystal 19 is large. Therefore, the shape and size of the liquid crystal domain 18 included in the polymer dispersed liquid crystal layer (composite layer of liquid crystal and polymer resin) 16 formed by phase separation (polymerization) is the same as that of the central portion of the polymer dispersed liquid crystal layer 16. Substrates 11, 12
Also, the surface portions of the electrodes 13 and 14 are greatly different.

If the shape, size, etc. of the liquid crystal reservoir 18 are different from place to place, the voltage (electric field) applied to the liquid crystal 19 will be different from place to place. For this reason, the alignment state varies for each liquid crystal domain 18 and for each liquid crystal molecule in the liquid crystal domain 18, and the change in the transmittance with respect to the applied voltage between the electrodes 13 and 14 becomes gradual. Further, if the shape, size, distribution, etc. of the liquid crystal domains 18 are not uniform, uneven light scattering occurs when the liquid crystal domains 18 are turned off, which deteriorates the quality of the displayed image.

The present invention has been made in view of the above circumstances, and a method of manufacturing a polymer dispersed liquid crystal layer and a polymer dispersed liquid crystal display device capable of almost uniformly dispersing liquid crystal domains in the polymer dispersed liquid crystal layer. The purpose is to provide. Another object of the present invention is to provide a polymer-dispersed liquid crystal display device capable of obtaining steep voltage-transmittance characteristics and a method for manufacturing the same. Another object of the present invention is to provide a polymer dispersed liquid crystal display device capable of displaying high quality images and a method for manufacturing the same.

[0009]

In order to achieve the above object, a polymer dispersion type liquid crystal display device according to the present invention is a high-performance liquid crystal display device comprising a composite film of resin and liquid crystal between a pair of substrates provided with electrodes respectively. A molecular dispersed liquid crystal layer is provided, and a film having a surface energy smaller than that of the substrate, for example, a fluorine film, a fluororesin film, or a surfactant film is formed between the inner surface of the substrate and the polymer dispersed liquid crystal layer. .

Further, in the method for manufacturing a polymer dispersed liquid crystal display device according to the present invention, a film made of a substance having a surface energy smaller than that of the substrates is formed on the inner surfaces of the pair of substrates, or a nonionic surface active material is formed on the inner surfaces. A step of applying the agent,
A mixed solution layer of liquid crystal and a polymer material is arranged between the substrates, the polymer resin obtained by polymerizing the polymer material in the mixture solution layer and the liquid crystal are phase separated, and a liquid crystal pool dispersed in the polymer resin is formed. And a step of forming a polymer dispersed liquid crystal layer having the same.

[0011]

FUNCTION The surface energy of the fluorine film and the fluorine resin film is small, and the compulsory force (interaction force) against the liquid crystal is smaller than that of the substrate (glass). On the other hand, when the surface active agent is applied to the substrate to form the surface active agent film, the surface energy of the surface of the substrate is reduced by the surface active agent. Therefore, also in this case, the force of the substrate on the liquid crystal becomes small. Therefore, the surface energy of the portion of the liquid crystal cell in contact with the liquid crystal becomes small, and when forming the polymer dispersed liquid crystal layer, a relatively uniform liquid crystal pool (liquid layer domain) can be formed even in the portion near the substrate. As a result, liquid crystal pools having a relatively uniform shape and size can be dispersed at a substantially uniform density throughout the polymer dispersed liquid crystal layer.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a sectional view of a polymer dispersion type liquid crystal display device according to a first embodiment of the present invention. As shown in the figure, the polymer-dispersed liquid crystal display device of this embodiment has a pair of transparent substrates (for example, glass substrates) 11 and 12 provided with transparent electrodes 13 and 14.
A cell 1 formed by joining the two through a frame-shaped sealing material 15
Polymer dispersed liquid crystal layer in 0 (Composite film of polymer resin and liquid crystal)
16 is provided. Fluorine films 22 and 23 are formed on the transparent electrodes 13 and 14 and the transparent substrates 11 and 12, respectively. The film thickness of the fluorine films 22 and 23 is 0.2 μm.
m to 1 μm, preferably 0.3 to 0.7 μm.

FIG. 2 is an enlarged sectional view of the polymer dispersion type liquid crystal display device shown in FIG. As shown in the figure, the polymer dispersed liquid crystal layer 16 has a structure in which a pool (liquid crystal pool, domain) 18 of liquid crystals 19 is dispersed in a transparent polymer resin 17. The liquid crystal 19 fills the space formed in the polymer resin 17 in a mesh shape, and is a so-called phase separation type PN.
LC (Polymer Network Liquid Crystal).

The surface energy of the fluorine films 22 and 23 is much smaller than the surface energy of the glass substrates 11 and 12 and the transparent electrodes 13 and 14. Therefore, the shape of the liquid crystal pool 18 is not significantly distorted, and the plurality of liquid crystal pools 18 are not formed large on the substrate surface. Therefore, the liquid crystal pool 18 is formed in the central portion of the polymer dispersed liquid crystal layer 16 and in the vicinity of the substrate.
The shape, size, etc. do not differ greatly. That is, in this embodiment, the liquid crystal pool 18 having a relatively uniform shape and size is relatively uniformly dispersed in the polymer dispersed liquid crystal layer 16.

Therefore, the voltage applied to each liquid crystal pool 18 becomes substantially constant, and each liquid crystal pool 1 corresponds to the applied voltage.
The liquid crystal molecules in 8 operate similarly. That is, the response of the liquid crystal molecules to the applied voltage is made uniform, and a steep voltage-transmittance characteristic is obtained. In addition, when it is off (transparent electrodes 13, 14
Light scattering (when no voltage is applied between them) occurs relatively uniformly in the polymer-dispersed liquid crystal layer 16, and a high-quality image without unevenness can be displayed.

Next, a method of manufacturing the polymer dispersion type liquid crystal display device having the above structure will be described. First, ITO is sputtered on the transparent substrates 11 and 12 made of glass or the like.
(Indium Tin Oxide) film is formed. Next, this ITO
Etching the film using a photo etching process,
The transparent electrodes 13 and 14 are formed.

Next, 0.3 μm to 0.8 of fluorine or the like is applied to the inner surface of the transparent substrates 11 and 12 on which the transparent electrodes 13 and 14 are formed by using a vacuum deposition method or a spin coating method.
Coat to a thickness of μm. Further, the cells 10 are assembled by joining the substrates 11 and 12 with each other through the spacer and the sealing material 15. Next, for example, a nematic liquid crystal (polymer dispersed liquid crystal layer 16) is injected into the cell 10 by a vacuum injection method or the like.
(60 to 80% by weight) with a polymerizable material. For injection of the mixed solution, for example, the cell 10 is set in a vacuum tank, the pressure in the tank is reduced to a vacuum state, and then the cell 1
The liquid crystal injection port of No. 0 is immersed in the mixed solution, and then the pressure inside the vacuum chamber is raised to atmospheric pressure or slightly higher than atmospheric pressure.

When the injection of the mixed solution is completed, the cell 10 is irradiated with ultraviolet rays to photopolymerize the polymer material of the mixed solution in the cell 10 to form the polymer dispersed liquid crystal layer 16 shown in FIG. Here, since the surface energy of the fluorine films 22 and 23 is small, the influence of the fluorine films 22 and 23 on the liquid crystal 19 injected into the cell 10 is small. Therefore, the liquid crystal 1
9 and the polymer resin 17 are phase-separated, the polymer-dispersed liquid crystal layer 16 has a relatively uniform shape and / or size regardless of whether it is the end portion (the portion in contact with the substrate) or the central portion. The liquid crystal pool 18 is formed substantially uniformly. After the polymer dispersed liquid crystal layer 16 is formed, the injection port of the cell 10 is sealed with a photo-curable resin or the like to complete the polymer dispersed liquid crystal display device shown in FIG.

A manufacturing method other than the above may be adopted. For example, first, one transparent substrate 12 on which the transparent electrode 14 and the fluorine film 23 are formed is spin-coated with a mixed solution of liquid crystal and a polymer material such as a monomer or an oligomer. Next, the transparent substrate 12 and the transparent substrate 11 on which the transparent electrode 13 and the fluorine film 22 are formed are bonded via the sealing material 15. After that, the polymer material may be polymerized to form the polymer dispersed liquid crystal layer 16. Also in this case, by the action of the fluorine films 22 and 23, the polymer dispersed liquid crystal layer 16 in which the liquid crystal reservoirs 18 having a relatively uniform shape and size are dispersed relatively uniformly can be formed. Further, the polymer resin is not limited to the photopolymerizable one, and may be a thermopolymerizable one.

The present invention is not limited to the above embodiment, and various modifications and applications are possible. For example, in the above embodiment, the fluorine films 22 and 23 were formed on the inner surface of the cell 10, but other films having a surface energy smaller than that of the transparent substrates 11 and 12 and the transparent electrodes 13 and 14, for example, a fluororesin film (polytetrafluoroethylene film). Fluoroethylene, polychlorotrifluoroethylene, etc.) may also be used.

Further, for example, a surfactant is applied to the inner surface of the cell 10 (on the transparent substrates 11 and 12 and the transparent electrodes 13 and 14) to reduce the surface energy of the inner surface of the cell 10, and then the inside of the cell 10 is reduced. You may make it phase-separate by injecting the mixed solution of a liquid crystal and a polymeric material, and polymerizing a polymeric material. In this case, due to the action of the surfactant, the transparent substrate 1
The wettability of 1 and 12 and the transparent electrodes 13 and 14 becomes poor, and a relatively homogeneous liquid crystal pool 18 can be formed even in the vicinity of the transparent substrates 11 and 12. As the surfactant, there are ionic (cationic or anionic) surfactants and amphoteric surfactants. The ionic surfactants are the electrodes 13 and 14
The amphoteric surfactant is used for different purposes because it causes leakage current between the two. Therefore, as described above, it is desirable to use a nonionic surfactant.

A conventional polymer dispersed liquid crystal display device formed by injecting a mixed liquid of a liquid crystal and a polymer material into a cell formed of a glass substrate having an ITO electrode and photopolymerizing the polymer material, and having an ITO electrode Polymer dispersed liquid crystal display formed by forming a 0.5 μm thick fluorine film on a glass substrate, forming a cell, injecting a mixed liquid of liquid crystal and a polymerization material into the cell, and photopolymerizing the mixture. With respect to the device, the change in the transmittance T (%) with respect to the applied voltage was measured. Figure 3 shows the measurement results.
Shown in. As is clear from FIG. 3, the polymer dispersion type liquid crystal display device in which the fluorine film is formed in the cell has steeper characteristics and better electric characteristics. It is presumed that this is because, as described above, the liquid crystal pool having a uniform shape and size is formed with a uniform density by the action of the fluorine film having a small surface energy.

The present invention is a simple matrix type polymer dispersion type liquid crystal display device and a TFT (thin film transistor).
The present invention can be applied to any active matrix type polymer dispersed liquid crystal display device such as a polymer dispersed liquid crystal display device. The present invention is not limited to the above embodiment, and various changes can be made. For example, in the above embodiment, a fluorine film, a fluororesin film, a film of a surfactant, etc. were formed in order to reduce the surface energy of the substrate, but if the surface energy is smaller than that of the substrate, electrodes, etc., another film may be formed. May be used. Further, the liquid crystal 19 is not limited to nematic liquid crystal, and cholesteric liquid crystal, smectic liquid crystal, liquid crystal having ferroelectricity, guest-host type liquid crystal containing a dye, or the like may be used.

[0024]

As described above, according to the present invention,
In order to reduce the surface energy of the inner surface of the cell, a fluorine film, a fluororesin film, a surfactant film, etc. were arranged. Therefore, in the process of forming the liquid crystal puddle, the interaction of the interfaces is small, and even in the vicinity of the substrate, a polymer dispersed liquid crystal layer in which the liquid crystal puddle having a relatively uniform shape and a uniform size is uniformly dispersed can be formed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a polymer dispersed liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a configuration of a polymer dispersed liquid crystal display device.

FIG. 3 is a graph showing a relationship between an applied voltage and a light transmittance T (%) of a polymer dispersed liquid crystal display device according to an embodiment of the present invention and a conventional polymer dispersed liquid crystal display device.

FIG. 4 is a cross-sectional view showing the structure of a conventional polymer-dispersed liquid crystal display device.

[Explanation of symbols]

11, 12 ... Transparent substrate, 13, 14 ... Transparent electrode, 15
... Sealing material, 16 ... Polymer dispersed liquid crystal layer, 17 ... Polymer resin, 18 ... Liquid crystal pool (domain), 19 ... Liquid crystal, 22, 23 ... Fluorine film

Claims (6)

[Claims] 1. A polymer-dispersed liquid crystal display device comprising a polymer-dispersed liquid crystal layer formed of a composite film of resin and liquid crystal between a pair of substrates each having electrodes on the inner surface, wherein the inner surface of the substrate and the polymer A polymer dispersed liquid crystal display device, wherein a film having a surface energy smaller than that of the substrate is formed between the dispersed liquid crystal layer and the substrate. 2. The polymer dispersed liquid crystal display device according to claim 1, wherein the film having a surface energy smaller than that of the substrate is formed of fluorine, a fluororesin or a surfactant. 3. The fluorine film or fluorine resin film is 0.2.
3. The polymer dispersed liquid crystal display device according to claim 2, which has a thickness of .mu.m to 1.0 .mu.m. 4. A step of forming a film made of a substance having a surface energy smaller than that of the inner surfaces of a pair of substrates each having an electrode provided on the inner surface, and a mixed solution of a liquid crystal and a polymer material between the substrates via the film. And a step of forming a polymer dispersed liquid crystal layer having a liquid crystal pool dispersed in a polymer resin obtained by polymerizing the polymer material in the mixed solution. A method for manufacturing a molecular dispersion type liquid crystal display device. 5. The polymer according to claim 4, wherein the substrate is made of glass, the film is made of fluorine or fluororesin, and the thickness thereof is 0.2 μm to 1.0 μm. Manufacturing method of dispersed liquid crystal display device. 6. A step of applying a nonionic surfactant on the inner surfaces of a pair of substrates each having an electrode on the inner surface, for reducing the surface energy of the inner surfaces, and the substrate coated with the surfactant. A step of arranging a mixed solution layer of liquid crystal and a polymer material in between, and forming a polymer dispersed liquid crystal layer having a liquid crystal pool dispersed in a polymer resin obtained by polymerizing the polymer material in the mixed solution layer. A method of manufacturing a polymer-dispersed liquid crystal display device, comprising: