JPH063652A - Liquid crystal display device and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Object] It is an object of the present invention to provide a polymer scattering type liquid crystal display device having a PDLC structure which reduces the hysteresis of the TV characteristic and provides a high contrast, and a method for manufacturing the same. [Structure] A liquid crystal layer made by dispersing a liquid crystal material in a polymer material is sandwiched between two substrates with electrodes, and a voltage is applied between the electrodes to control the light transmittance of the liquid crystal layer. In the polymer scattering type liquid crystal display device, a layer composed of a material different from the polymer material and controlling the anchoring strength of the liquid crystal, between the polymer material forming the liquid crystal layer and the liquid crystal layer. A polymer scattering type liquid crystal display device characterized by comprising: and a manufacturing method thereof.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art Liquid crystal display devices have been put into practical use as twisted nematic (TN) type and super twisted nematic (STN) type which use nematic liquid crystal as an information display device which replaces CRT because of their light weight, thinness and low power consumption. Has been done. In recent years, unlike the TN type and the STN type, a polymer dispersed liquid crystal display device in which a liquid crystal is dispersed in a polymer material has been vigorously developed as a liquid crystal display device that does not require a polarizing plate. As a method for dispersing the liquid crystal in the polymer material, the liquid crystal is dispersed in a solution in which the polymer resin is dissolved in the form of droplets, and then the resin is cured by heat or ultraviolet rays (Japanese Patent Laid-Open No. 61-502128). , 62-22
31) and a method of forming a liquid crystal layer by phase separation by evaporating a solvent from a solution in which a resin and a liquid crystal are uniformly dissolved (JP-A-63-501512). The polymer scattering type liquid crystal display is bright, has a wide field of view, high response speed, etc.
Although it is superior to the N-type, it has a problem that the driving voltage is high, and the lowering of voltage is being promoted by improving the shape, material, liquid crystal material and the like of the polymer resin portion. (JP-A-1
However, there are problems that the voltage-transmittance characteristic (T-V characteristic) has hysteresis, and it is difficult to obtain contrast. Therefore, commercialization of light control glass, character display device, etc. is advancing. However, dot matrix type display devices such as televisions and displays have not yet been put to practical use. Although the electro-optical characteristics (mainly TV characteristics) of PDLC vary depending on the shape of the polymer resin as well as the polymer material and the liquid crystal material,
The relationship between its structure and electro-optical properties has not yet been clarified. Although the shape of the polymer resin changes depending on the manufacturing method of the PDLC, the compatibility of the liquid crystal, the polymer, the solvent, the dye to be added, and the curing conditions of the resin largely limits the materials that can be used depending on the manufacturing method.

[0003]

[Objective] The present invention reduces the hysteresis of the TV characteristic,
The present invention relates to a structure of a PDLC which gives a high contrast and a manufacturing method thereof.

[0004]

[Structure] Polymer scattering type liquid crystal (PDLC) has a liquid crystal layer dispersed in a droplet form as shown in FIG. 1 and a continuous phase as shown in FIG. It may have become. When no voltage is applied, the director of the liquid crystal is in a random state and scatters light as shown in FIG. 1 and FIG.
As shown in (b), the liquid crystal is aligned in the direction of the electric field and transmits light. When the voltage is switched from the applied state to the non-applied state, the director of the liquid crystal returns to the random state again due to the anchoring of the polymer resin surface. The anchoring of the liquid crystal by the polymer resin is very weak unlike the alignment of the liquid crystal in the TN or STN type, and it affects not only the microscopic surface property of the polymer resin but also the macroscopic structure. It is believed that. The anchoring is a general term for a force (excluding electrical one) that the liquid crystal receives from the outside.
In the conventional PDLC, since the anchoring strength of the liquid crystal by the polymer resin is not controlled, the aligned liquid crystal does not return to the original state due to the electric field, and hysteresis occurs in the TV characteristic. An example of the TV characteristic in the conventional PDLC is shown in FIG. In the present invention, a layer made of a material different from the polymer resin is provided between the polymer resin and the liquid crystal,
We propose to control the anchoring strength of the liquid crystal.

As a method for dispersing the liquid crystal in the polymer material, as described above, (1) the liquid crystal is dispersed in a solution in which the polymer resin is dissolved in the form of droplets, and then the resin is heated or irradiated with ultraviolet rays. There are a method of curing and (2) a method of forming a liquid crystal layer by phase separation by evaporating a solvent from a solution in which a resin and liquid crystal are uniformly dissolved, but a polymer resin for controlling the anchoring strength of the liquid crystal. The surface treatment is carried out by the method of (1) above, in which a surface treatment agent that precipitates on the resin surface after the resin is cured is added to the mixed solution of the polymer resin, particularly the photocurable resin and the liquid crystal, or , PDL once prepared by the method of (1) or (2) above
A method of extracting the liquid crystal from C and subjecting the surface of the polymer resin to the surface treatment and then impregnating the liquid crystal again can be considered, but the latter method has a higher degree of freedom in terms of resin, structure and material selectivity. Further, in the method of extracting the liquid crystal from the PDLC composed of the dispersion layer of the resin and the liquid crystal, surface-treating the surface of the polymer resin, and impregnating the liquid crystal again, the liquid crystal is removed after the formation of the dispersion layer. It is not necessary to use liquid crystal for the production of PDLC in the methods (1) and (2), and a solvent that does not dissolve the polymer resin can be used instead of the liquid crystal. Examples of such a solvent include water. In order to extract the liquid dispersed in the resin after forming the polymer resin layer, to treat the surface of the resin, or to impregnate the liquid crystal, the dispersed liquid must be a continuous phase, but the liquid is Whether the continuous phase shown in 2 or the independent phase shown in FIG. 1 is determined by the polymer material, the liquid crystal material, the polymer / liquid crystal mixing ratio, and the manufacturing method. In order to perform the surface treatment on the resin surface when the independent phase as shown in FIG. 1 is formed, it is necessary to connect the individual droplets three-dimensionally and change it into the continuous phase. Water does not dissolve in most solvents that dissolve polymeric resins. Therefore,
Water is emulsified and dispersed in a solution in which a polymer resin is dissolved, and a polymer resin / water composite film in which small water droplets are dispersed in the polymer film instead of liquid crystal is produced. Water has the highest density at 4 ° C, and becomes about 0.9 when solidified. Therefore, the volume of water is increased by solidifying the water droplets enclosed in the polymer resin, and as a result, the polymer resin is cracked. When the water droplets dispersed in the polymer resin are close to each other, the water droplets are connected by a crack to form a continuous phase. In order to generate such cracks, the mixing ratio (volume ratio) of the polymer resin and water is polymer / water = 1/1 to 1
It is good to be / 3. When the proportion of water is small, the distance between water droplets becomes long, and thus dispersed water droplets cannot be connected three-dimensionally. Further, when the proportion of water is too large, the polymer resin and water are phase-separated. After removing the water in the composite film produced in this manner, the polymer resin is impregnated with liquid crystal to produce a PDLC.

The polymer resin used in the present invention is not particularly limited as long as it has optical transparency.
Examples include polymethylmethacrylate, polystyrene, polyvinyl homer, polyester, and epoxy resin. The surface treatment agent for the resin surface includes polyvinyl alcohol, polyimide, lecithin, stearic acid, organic silane, polyoxyethylene, and basic chromium complex.
In addition, a dichroic dye may be added to the liquid crystal layer in order to obtain a high-contrast PDLC, but in the conventional manufacturing method, the polymer resin takes in the dye, or the dye, especially the azo dye, is photocured. Although the curing of the resin was sometimes inhibited, the above-mentioned production method was used to prepare a polymer resin / water composite film obtained by curing a photocurable resin, and after removing water from the composite film, an azo-based two-color Of a photo-curing resin containing an azo dichroic dye by impregnating a liquid crystal composition containing a dye
Is obtained.

Example 1 Polymethylmethacrylate (PMMA) and nematic liquid crystal (E-7 made by BDH) were mixed in a volume of 40/60, and dissolved in chloroform so that the concentration of nonvolatile components was 20%. . This solution was applied on a glass substrate having a transparent electrode and dried at room temperature to obtain a polymer resin / liquid crystal composite film having a film thickness of about 10 μm. In the liquid crystal layer in the PDLC thus manufactured, the polymer resin forms a network matrix, and the liquid crystal layer exists as a continuous phase. Liquid crystals were extracted with hot ethanol and exposed to organosilane (HMDS) vapor. After applying a heat treatment at 80 ° C. for 10 minutes, the nematic liquid crystal heated to an isotropic state (the same E-
7), and the polymer resin was impregnated with liquid crystal. After washing away excess liquid crystal, a room temperature curing type two-component epoxy resin was applied to the peripheral portion of the PDLC and bonded to a glass substrate with a transparent electrode to prepare a polymer dispersion type liquid crystal display device. This liquid crystal panel was milky white when no voltage was applied, and became transparent when a voltage was applied. At this time, the hysteresis width in the TV characteristic was reduced to 1/4 of that without the organosilane treatment.

Example 2 In a toluene solution in which polystyrene (PS) was dissolved, water was added in a volume ratio of polystyrene to polystyrene / water = 40/6.
After mixing and stirring so as to be 0, it was applied on a glass substrate having a transparent electrode and dried to obtain a polymer resin / water composite film. The water in the composite film produced in this way is in the form of droplets, and each droplet is adjacent to other droplets, but is in an independent phase. The composite film, together with the glass substrate, was immersed in liquid nitrogen to coagulate water and cause cracks in the polystyrene resin. After removing water drops in the resin by vacuum drying, the resin was immersed in a 1% monobasic chromium complex (chromium perfluorononanoate complex) aqueous solution. After moisture in the resin was removed again by vacuum drying, a nematic liquid crystal (BL001 made by Merk) was impregnated in the same manner as in Example 1 to prepare a liquid crystal panel. By utilizing the volume change of water due to solidification, the droplet-shaped cavities in the resin are connected three-dimensionally,
The surface treatment of the resin and the impregnation of the liquid crystal could be made possible.

Example 3 Acrylate-based UV curable resin (concentration of photopolymerization initiator 1
%) Was mixed with water in a volume ratio of polystyrene to ultraviolet curable resin / water = 40/60, stirred, and then coated on a glass substrate having a transparent electrode and dried. The resin was cured by irradiating it with ultraviolet light under a nitrogen atmosphere to obtain a polymer resin / water composite film. After cracking the resin in the same manner as in Example 2, removing water in the resin and treating the resin surface with a monobasic chromium complex, yellow (azo type), blue (anthraquinone type), violet ( A nematic liquid crystal (ZLI-1840 manufactured by Merk) containing an azo-based dye was impregnated to prepare a liquid crystal panel. In the conventional method, the UV curable resin could not be cured in the presence of an azo dye, but this manufacturing method greatly expanded the selection range of dyes and other materials.

[0010]

[Effect] By performing the surface treatment of the polymer resin in PDLC, the hysteresis width of the TV characteristic could be reduced. Further, by utilizing the volume change of water droplets dispersed in the polymer resin, the droplets in the polymer resin are changed from a single phase to a continuous phase, which enables surface treatment of the polymer resin and liquid crystal impregnation. As a result, the selection range of the PDLC material was greatly expanded, and a liquid crystal panel with favorable characteristics could be manufactured. Further, in the conventional method, the ultraviolet curable resin could not be cured in the presence of the azo dye, but the production method of the present invention increased the selection range of the dye.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a structure of a PDLC in which a liquid crystal layer is in the form of droplets, where (a) shows a state when no voltage is applied and (b) shows a state when a voltage is applied.

FIG. 2 is a schematic diagram showing a structure of a PDLC having a liquid crystal layer of a continuous phase. (A) shows a state when no voltage is applied, and (b) shows a state when voltage is applied.

FIG. 3 is a TV of a liquid crystal in a conventional PDLC.
It is a figure which shows a characteristic.

[Explanation of symbols]

 1 liquid crystal layer 2 polymer layer 3 liquid crystal molecule

Claims (5)

[Claims] 1. A light-transmitting property of a liquid crystal layer formed by sandwiching a liquid crystal layer made by dispersing a liquid crystal material in a polymer material between two substrates with electrodes, and applying a voltage between the electrodes. In a polymer scattering type liquid crystal display device for controlling the liquid crystal display device, between the polymer material forming the liquid crystal layer and the liquid crystal layer, a material different from the polymer material and controlling the anchoring strength of the liquid crystal is used. A polymer scattering type liquid crystal display device, which is characterized in that a layer is provided. 2. The liquid crystal layer in the polymer material is in the form of droplets,
The polymer scattering type liquid crystal display device according to claim 1, wherein the liquid crystal layer is three-dimensionally connected to an adjacent liquid crystal layer, and the liquid crystal layer is in a continuous phase. 3. A composite film made of a polymer material and a solvent or liquid crystal that does not dissolve the polymer material is formed on one electrode-attached substrate, and the polymer or the polymer is obtained after removing the solvent or liquid crystal from the composite film. The surface of the polymer material is treated with a surface treatment agent composed of a material different from the material and controlling the anchoring strength of the liquid crystal, and then a liquid crystal composition which may contain a dye is added to the surface treatment agent. The method for producing a polymer scattering type liquid crystal display device according to claim 1 or 2, which comprises producing a substrate with a liquid crystal layer by impregnating it with a molecular material, and laminating the substrate with the liquid crystal layer and the other substrate. 4. A composite film composed of a polymeric material / droplet-shaped water dispersed in the polymeric material is formed on one electrode-attached substrate, and then the water in the polymeric material is solidified, The volume expansion of water forms cracks in the polymer material, three-dimensionally connects the droplets, and then removes water. Then, the material is different from the polymer material and the anchoring strength of the liquid crystal is controlled. The surface of the polymer material is treated with a surface treatment agent composed of the material, and then a liquid crystal composition which may contain a dye is impregnated into the polymer material to prepare a substrate with liquid crystal. The method for producing a polymer scattering type liquid crystal display device according to claim 1 or 2, which comprises laminating a substrate with a liquid crystal layer and the other substrate. 5. The polymer material / water mixture ratio (volume ratio) of the polymer material / water of the composite film composed of the polymer material / droplet-shaped water dispersed in the polymer material is polymer material / water = 1/1. The method for producing a polymer-scattering liquid crystal display device according to claim 4, wherein the ratio is ⅓.