JPH0634954A - Optical modulating element and its production - Google Patents

Abstract

PURPOSE:To provide the optical modulating element having excellent characteristics by enabling easy pattern coating and easily executing coating only in the plural block chambers segmented by partition walls consisting of an electrical insulating material and the process for production of such element. CONSTITUTION:This optical modulating element is constituted by using a liquid crystal/high-polymer composite film formed by dispersing liquid crystal particles into a high-polymer matrix. The liquid crystal/high-polymer composite film which consists of liquid crystal particles, polyvinyl alcohol (PVA) having 300 to 1,200 degrees of polymn. and 50 to 85% degree of saponification and superfine particles of silica and has 5/95 to 50/50 mixing ratios (by weight) of the PVA/ liquid crystal is used for the above-mentioned composite film. This process for production produces the optical modulating element by using such composite film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light modulation element using a liquid crystal / polymer composite film having a response to an electric field and heat and capable of displaying and recording various information, and a method for manufacturing the same. The optical modulator of the present invention can be widely applied to light control panels, displays, recording media and the like.

[0002]

2. Description of the Related Art Conventionally, liquid crystal displays have been widely used as wristwatches, calculators, personal computers, televisions, etc., as a display medium for characters and images because they have characteristics such as low power consumption, light weight and thin shape. . A general TN or STN-liquid crystal display is one in which liquid crystal is enclosed in a liquid crystal cell in which a glass plate having transparent electrodes is provided with a predetermined seal or the like, and is sandwiched by polarizing plates from both sides. However, (1) since two polarizing plates are required, the viewing angle is narrow, and because of insufficient brightness, a backlight with high power consumption is required. (2) Cell thickness dependence Large and difficult to make large area, (3) complicated structure, and difficult to enclose liquid crystal in the cell, so there are problems such as high manufacturing cost, liquid crystal display weight reduction, thinning, large area There is a limit to reduction in cost, power consumption, and cost.

As a liquid crystal display medium for solving such a problem, an application of a light modulation element based on a light scattering mechanism using a liquid crystal / polymer composite film in which liquid crystal is dispersed in a polymer matrix is expected, and its research is expected. Development has become active. already,
A large number of light modulation devices using a liquid crystal / polymer composite film and a method for manufacturing the same have been disclosed. One of them is a method for manufacturing a liquid crystal from an emulsion in which a polyvinyl alcohol (PVA) aqueous solution is dispersed. No. 52843). The light modulation element manufactured by this method is characterized in that the contrast ratio can be improved by adding a dichroic dye, and the transmittance is low when the voltage is OFF.

[0004]

Problems to be Solved by the Invention P of the above liquid crystal
The light modulation element prepared from the VA dispersed aqueous solution has the characteristics as described above, but the liquid crystal PVA dispersed aqueous solution is
The wettability with respect to the electrode substrate is poor, and it is difficult to form a uniform liquid crystal / polymer composite film that can be used in a light modulation element. As PVA, a suitable degree of polymerization (300-
1,200) and a saponification degree (85% to 50%), it is possible to form a film with no problem with the blade coating by blade coating. In addition, there are problems such as uneven coating at the end of coating and use of an expensive extra dispersion liquid.

Further, since the aqueous solution of PVA has a low viscosity,
A conventional processing method (blade coating, etc.) can be applied in order to perform pattern coating for forming a composite film only on a necessary portion of an electrode substrate with an emulsion obtained by emulsifying liquid crystal in the aqueous solution. There is a problem that it can not be done, and the emulsion is filled only in a plurality of compartments partitioned by partition walls made of electrically insulating material formed on the electrode substrate and screen printing without mesh, and after drying, the height of the partition walls Even if the method of connecting the conductive substance and the electrode by filling the space between the liquid crystal / polymer composite film formed in the compartment and the counter electrode substrate with the conductive substance is used, Since it is low, there are problems such as the backside of the dispersion liquid on the back surface of the plate and a film dent in the center of the compartment.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, to easily perform pattern coating, and to divide a plurality of compartments by partition walls made of an electrically insulating material. It is an object of the present invention to provide a light modulation element having excellent characteristics, which can be easily coated, and a manufacturing method thereof.

[0007]

The above object can be achieved by the present invention described below. That is, the present invention provides a light modulation element using a liquid crystal / polymer composite film in which liquid crystal particles are dispersed in a polymer matrix, wherein the composite film comprises liquid crystal particles.
Polymerization degree is 300-1,200 and saponification degree is 50% -85
% Polyvinyl alcohol (PVA) and silica ultrafine particles, and the mixing ratio (weight ratio) of PVA / liquid crystal is 5 /
A light modulation element characterized by using a liquid crystal / polymer composite film of 95 to 50/50, and a manufacturing method thereof.

[0008]

The dispersibility of the PVA dispersion liquid crystal has a great influence on the electro-optical characteristics as well as the processability, particularly the wettability to the electrode substrate. Therefore, the dispersibility of the liquid crystal is adjusted to P with a polymerization degree of 300 to 1,200 and a saponification degree of 50% to 85%.
A liquid crystal having excellent processability and electro-optical properties, which is improved by using an aqueous solution of VA and the fluidity of the liquid crystal dispersion is improved by adding appropriate silica ultrafine particles, particularly preferably hydrophobic silica ultrafine particles. / It has become possible to fabricate polymer composite membranes.

That is, first, the liquid crystal is made to have a polymerization degree of 300 to 1,2.
00 and a degree of saponification of 50% to 85%, and then dispersed in an aqueous solution of PVA.
A PVA dispersion of liquid crystal prepared by adding 1 to 10% by weight of hydrophobic silica ultrafine particles is used, and is partitioned by, for example, metal screen printing without mesh and partition made of an electrically insulating material formed on an electrode substrate. In addition, the emulsion is filled only in the plurality of compartments, and after drying, the space between the liquid crystal / polymer composite film formed in the compartments and the counter electrode substrate, which is lower than the height of the partition walls, is filled with a conductive substance. By connecting the conductive material and the electrode, it becomes possible to carry out the pattern coating for forming the liquid crystal / polymer composite film only in a necessary place.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in more detail with reference to preferred embodiments. As shown in Table 1 below and FIG. 1, the surface tension of the aqueous solution varies depending on the degree of polymerization and the degree of saponification of PVA. That is, the degree of polymerization and saponification of PVA causes a difference in the ability of PVA to disperse liquid crystals. Thus, the lower the degree of polymerization and the lower the degree of saponification, the more P
The ability of the VA to disperse the liquid crystal is increased.

[0011]

[Table 1] Degree of saponification and degree of polymerization of various PVA

As a result, when the liquid crystal (E-44) was dispersed using the various PVA aqueous solutions shown in Table 2 below, each PV
The dispersibility of the liquid crystal particles differs depending on A, and the particle size distribution of the liquid crystal particles changes as shown in FIGS. 2 and 3.

[Table 2] Structure and processability of PVA in liquid crystal (E-44) dispersion system of various PVA

On the other hand, when the degree of saponification of PVA is high, the dispersibility of liquid crystal particles is deteriorated, the proportion of liquid crystals present in the aqueous phase is increased, and the particle size distribution is wide and the particle size is large. As a result, when the dispersibility is poor, the wettability to the electrode substrate is poor, the processability is degraded (Table 2), and the particle size distribution of the liquid crystal / polymer composite film is wide and the particle size is large (FIG. 4). ), The electro-optical characteristics are also degraded (FIG. 5). or,
Even when the degree of polymerization of PVA is large, the dispersibility of the liquid crystal particles is poor, the particle size distribution is wide, the particle size is large, and the electro-optical characteristics are deteriorated (FIG. 5), but the viscosity is high, and therefore the processability is high. Get better. In such a situation, an appropriate degree of polymerization (300-
1,200) and the degree of saponification (85% to 50%) of PVA reach a level at which there is no problem with regard to the wettability of the electrode substrate, but in order to perform pattern coating only where it is necessary, Since PVA has a low viscosity and does not have thixotropic properties, conventional processing methods cannot be applied.

By adding 1 to 10% by weight of silica fine particles to a liquid crystal PVA dispersion having excellent electro-optical properties as described above, thixotropic properties are imparted, and processability and electro-optical properties are improved. Both can be satisfied. Using the dispersion liquid with this processability, for example, a liquid crystal emulsion is filled only in a plurality of compartments partitioned by partition walls made of an electrically insulating material formed on a metal screen printing and electrode substrate without a mesh and dried. After that, by filling the space between the liquid crystal / polymer composite film formed in the compartment, which is lower than the height of the partition wall, and the counter electrode substrate with a conductive substance and connecting the conductive substance and the electrode, it is necessary. The pattern coating that forms the liquid crystal / polymer composite film can be performed only at certain places.

More specifically, first, as a PVA in which liquid crystal is dispersed so as to satisfy the electro-optical characteristics,
A polymer having a degree of polymerization of 300 to 1,200 and a degree of saponification of 50% to 85% is used. When the degree of polymerization is less than 300, the mechanical strength of PVA as a liquid crystal / polymer composite film is insufficient. When the degree of polymerization exceeds 1,200, the dispersibility of liquid crystal becomes poor. As a dispersion condition, a liquid crystal is added to an aqueous solution of 1 to 15% by weight of PVA so that PVA / liquid crystal = 5/95 to 50/50 and dispersed by a film emulsification method, mechanical stirring, ultrasonic waves, or the like. Is preferred. In particular, by dispersing by a film emulsification method, the particle size of liquid crystal droplets becomes uniform, and a film having excellent electro-optical characteristics can be obtained. If the amount of PVA used is less than 5/95, the strength of the film cannot be maintained, and the light scattering ability of the resulting device will decrease. If the amount of PVA used exceeds PVA / liquid crystal = 50/50, the driving voltage of the device becomes high and the response becomes poor.

Next, as the silica fine particles for improving the processability, hydrophobic silica fine particles whose surface is subjected to a hydrophobic treatment are preferable. As such hydrophobic silica fine particles,
It is marketed as Aerosil (trade name of Nippon Aerosil Co., Ltd.). , For example, AEROS having a particle size of 7 to 50 μm
It can be obtained in trade names such as IL 130, 200, 300, OX50 and used in the present invention. The addition amount is preferably in the range of 1% by weight to 10% by weight, and outside this range,
It is not possible to impart sufficient thixotropic properties.

The liquid crystal referred to in the present invention is an organic mixture showing a liquid crystal state at around room temperature, and includes nematic liquid crystal, cholesteric liquid crystal and smectic liquid crystal. Among these, nematic liquid crystal or nematic liquid crystal to which cholesteric liquid crystal is added is preferable in terms of characteristics. The liquid crystal may contain a dye in order to improve the contrast or the color tone. When a dichroic dye is added, it can be used not only as a scattering-transmissive composite film, but also as a composite film that switches in a light absorption (coloring) -transparent state by the guest-host effect of the dye. . As a method of dispersing the liquid crystal in the PVA aqueous solution, an emulsification method using various stirring devices such as an ultrasonic disperser, or a film emulsification method (Tadao Nakajima, Masataka Shimizu, PHARMTECH JAPAN)
Emulsification methods such as Volume 4, No. 10 (1988)) are effective. The size of the liquid crystal emulsion particles depends on the dispersion method used, but generally it is preferably in the range of 0.5 to 7 μm, and more preferably in the range of 1 to 4 μm.

The method of the present invention for forming a liquid crystal / polymer composite film from the liquid crystal particle dispersion thus obtained is a method of coating and drying the emulsion on a suitable electrode substrate by a conventional coating method. . As a coating method, when a liquid crystal polymer composite film is formed on the entire surface of the electrode substrate, a usual coating method may be used. However, when a uniform composite film is formed in a pattern only on a predetermined position or a predetermined part of the substrate, it is coated with a metal screen without a mesh, or an electrically insulating material formed on the electrode substrate is used. When a liquid crystal emulsion is filled in a compartment partitioned by the partition wall, it is desirable to use a method using a metal screen plate without a mesh and a squeegee.
The thickness of the composite film thus obtained is preferably about 5 to 15 μm.

In another preferred embodiment of the present invention, the liquid crystal emulsion is treated to prepare microcapsules containing liquid crystal, and the microcapsule dispersion is prepared as it is or after separation to prepare a coating liquid again. A liquid crystal / polymer composite film can be prepared by the method described above. As a method for producing microcapsules from an emulsion in which liquid crystal is dispersed, both a chemical production method and a physicochemical production method can be used. As the chemical preparation method, there are an interfacial polymerization method using a synthetic reaction, an in situ polymerization method, and an in-liquid hardening coating method that causes a change in physical properties of a polymer. The interfacial polymerization method is a method in which a water-soluble monomer and an oil-soluble monomer are selected as two kinds of monomers that undergo polycondensation or polyaddition reaction, and either of them is dispersed and reacted at the interface. i
The n situ polymerization method is a method in which a reactant (a monomer and an initiator) is supplied from one of the inside and the outside of the core material to cause the reaction on the surface of the capsule wall film.

As a physicochemical preparation method, a coacervation method utilizing phase separation, an interfacial precipitation method, a liquid concentration method,
In-liquid drying method and secondary emulsion method are available. A simple coacervation method in which phase separation is caused by a decrease in solubility and a complex coacervation method in which phase separation is caused by an electrical interaction can also be used. The interfacial precipitation method is a method capable of encapsulation under mild conditions without violent reaction or rapid pH change. For example, an emulsion in which a liquid crystal core material is dispersed is dispersed in a solvent solution of a hydrophobic polymer. And then redispersed in a protective colloid aqueous solution.

[0021]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative Examples. Example 1 KP-06 (manufactured by Nippon Synthetic Chemical Industry, degree of polymerization: about 600,
Saponification degree: 71.0 to 75.0)
-44 (manufactured by Merck) has a PVA / liquid crystal mixing ratio of 20 /
80 (w / w) was added and dispersed by ultrasonic waves.
5% by weight of AEROSIL 380 was added to this dispersion to prepare a target liquid crystal dispersion having thixotropic properties. Using the above liquid crystal dispersion liquid, a film was formed on the element substrate by mesh-free metal screen printing, and as a result, a good pattern coat was formed.

COMPARATIVE EXAMPLE 1 E-44 was added to KP-06 in a 10 wt% aqueous solution of KP-06.
/ E-44 = 20/80 (w / w)
Using the dispersion obtained by ultrasonic dispersion, a pattern coating without mesh was performed on the element substrate.Because the viscosity is extremely low, the backside of the dispersion and the squeegee of the dispersion on the back of the plate There was a problem with the uniformity of the film thickness when printed.

[0023]

According to the present invention, a liquid crystal / polymer composite film can be formed only on a necessary portion of a substrate element,
Not only can a patterned light modulation element which has not been used in the past can be manufactured, but also cost reduction of the element can be achieved. Further, it is also possible to improve the visibility due to uneven application of the liquid crystal dispersion, the defective bonding of the counter electrode substrate, and the like. On the other hand, liquid crystal /
The mechanical strength of the polymer composite film is improved, and it is effective in stabilizing the electro-optical characteristics.

[0024]

[Brief description of drawings]

FIG. 1 Relation between saponification degree and molecular weight of PVA and surface tension of PVA aqueous solution (4% PVA aqueous solution, measurement temperature 20 ° C.)
FIG.

FIG. 2 is a diagram illustrating a particle size distribution of liquid crystal particles in various PVA.

FIG. 3 is a diagram illustrating a particle size distribution of liquid crystal particles in various PVA.

FIG. 4 is a diagram illustrating a structure of a liquid crystal / various PVA composite film.

FIG. 5 is a diagram illustrating electric field response of liquid crystal / various PVA composite films.

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[Procedure amendment]

[Submission date] February 18, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 Relation between saponification degree and molecular weight of PVA and surface tension of PVA aqueous solution (4% PVA aqueous solution, measurement temperature 20 ° C.)
FIG.

FIG. 2 is a diagram illustrating a particle size distribution of liquid crystal particles in various PVA.

FIG. 3 is a diagram illustrating a particle size distribution of liquid crystal particles in various PVA.

FIG. 4 is a photograph explaining the structure of a liquid crystal / various PVA thin film.

FIG. 5 is a diagram illustrating electric field response of liquid crystal / various PVA composite films.

Claims (6)

[Claims] 1. A light modulation element using a liquid crystal / polymer composite film in which liquid crystal particles are dispersed in a polymer matrix, wherein the composite film has liquid crystal particles and a degree of polymerization of 300 to 1,2.
00 and a saponification degree of 50% to 85% consisting of polyvinyl alcohol (PVA) and silica ultrafine particles.
A light modulation element comprising a liquid crystal / polymer composite film having a liquid crystal mixture ratio (weight ratio) of 5/95 to 50/50. 2. The light modulation element according to claim 1, wherein the ultrafine silica particles are hydrophobic ultrafine silica particles. 3. A method of manufacturing a light modulation device using a liquid crystal / polymer composite film, comprising liquid crystal particles dispersed in a polymer matrix, wherein the composite film comprises a liquid crystal and a polymerization degree of 300 to 300.
1,200 and a saponification degree of 50% to 85% in a PVA aqueous solution, the PVA / liquid crystal mixing ratio (weight ratio) is 5/95 to 5
A method for producing a light modulation element, comprising a step of forming a liquid crystal emulsion obtained by adding ultrafine silica particles after adding and dispersing so as to be 0/50. 4. The method for producing a light modulation element according to claim 1, wherein the ultrafine silica particles are hydrophobic ultrafine silica particles. 5. A liquid crystal emulsion film is formed by pattern-coating a metal screen plate having no mesh on an electrode substrate with a squeegee, and then drying and bonding a counter electrode substrate having a seal material formed thereon. The method for manufacturing the light modulation element according to claim 3, which is performed as follows. 6. A liquid crystal emulsion is filled only in a plurality of compartments partitioned by partition walls made of an electrically insulating material formed on an electrode substrate, and after drying, the liquid crystal emulsion is formed in the compartments lower than the height of the partition walls. 4. The method for manufacturing a light modulation element according to claim 3, wherein the space between the liquid crystal / polymer composite film and the counter electrode substrate is filled with a conductive substance to connect the conductive substance and the electrode.