JPH07134287A - Liquid crystal/polymer composite optical element - Google Patents

Abstract

PURPOSE:To obtain a liq. crystal/polymer composite optical element capable of being driven by a low voltage and having excellent electrooptical characteristic and reliability by using a highly dielectric or ferroelectric polymer as the polymer matrix when the liq. crystal/polymer composite film wherein liq. crystals are dispersed in the matrix is used. CONSTITUTION:When the liq. crystal/polymer composite film wherein liq. crystals are dispersed in the polymer matrix is used, the matrix consists of a highly dielectric or ferroelectric polymer. A couple of substrates with at least the one formed with ITO, SnO2, ZnO, etc., are used to form the optical element. A coating soln. is applied as it is on the surface of one substrate, the soln. is vaporized to form the composite film, and simultaleously, the liq. crystal is deposited in the formed in the form of fine particles to obtain a liq. crystal/polymer composite film. Doctor coating or blade coating is used in coating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal / polymer composite type optical element having a response to an electric field and capable of displaying and recording information, and more specifically, a light control panel,
The present invention relates to a liquid crystal / polymer composite type optical element useful as a constituent material of a display, a recording medium 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 cell in which a predetermined seal or the like is provided between a pair of glass plates having transparent electrodes, and is sandwiched by polarizing plates from both sides.

However, in the conventional liquid crystal display element,
(1) Since two polarizing plates are required, the viewing angle is narrow, and the brightness is insufficient. Therefore, a backlight with high power consumption is required. (2) Cell thickness dependency is large and large. It is difficult to reduce the area, and (3) the structure is complicated, and it is difficult to enclose the liquid crystal in the cell, so that there are problems such as high manufacturing cost, and the liquid crystal display is lightweight, thin, and has a large area. There are limits to low power consumption and low cost.

As a liquid crystal display device for solving such a problem, a liquid crystal in which a liquid crystal is dispersed in a polymer matrix /
Applications of polymer composite membranes are expected, and their research and development have been activated. The following techniques have already been disclosed.
The main manufacturing method of the liquid crystal / polymer composite film can be classified into an emulsion method and a phase separation method. The emulsion method includes a method of preparing an aqueous solution in which a liquid crystal is emulsified by using polyvinyl alcohol (PVA) as a protective colloid (JP-A-58-501631) and a method of preparing a liquid crystal emulsion from an aqueous solution by mixing it with a latex (Special Table). JP-A-60-252687) and the like. On the other hand, the phase separation method can be further classified into a method of fixing the phase separation state of the liquid crystal and the polymer matrix and a method of phase separation of the liquid crystal from the polymer matrix during film formation.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the prior art relating to liquid crystal / polymer composite films, there are problems such as liquid crystal bleeding, high driving voltage, large hysteresis, and low contrast. As a method for solving these problems, JP-A-1-203494 and various other documents propose microcapsulation of liquid crystals.
Even using the conventionally proposed liquid crystal-containing microcapsules,
The driving voltage was not sufficiently lowered, and a liquid crystal / polymer composite type optical element having excellent electro-optical characteristics and reliability could not be obtained. Therefore, an object of the present invention is to provide a liquid crystal / polymer composite type optical element having excellent electro-optical characteristics and reliability at a low driving voltage.

[0006]

The above object can be achieved by the present invention described below. That is, the present invention provides an optical element using a liquid crystal / polymer composite film in which liquid crystal is dispersed in a polymer matrix, wherein the polymer matrix is
It is a liquid crystal / polymer composite type optical element characterized by being a high dielectric or ferroelectric polymer.

[0007]

When the liquid crystal / polymer composite film is considered as a two-layer model in which the liquid crystal layer and the polymer layer are in series, the voltage actually applied only to the liquid crystal in the aligned state is V Then, the voltage (V _eff ) that needs to be applied to the entire liquid crystal / polymer composite film is expressed by the following equation. ρ _p : Volume resistivity of polymer [Ω · cm] ρ ₁ : Volume resistivity of liquid crystal [Ω · cm] x _p : Volume fraction of polymer [%] x ₁ : Volume fraction of liquid crystal [%] V: Voltage applied only to the oriented liquid crystal [V] Here, since the volume resistivity ρ and the relative permittivity ε are in inverse proportion to each other, the larger ε is, the liquid crystal necessary for the liquid crystal to be oriented. / The voltage applied to the entire polymer composite film can be small.
Therefore, in another preferred embodiment of the present invention, the driving voltage can be further reduced by using a polymer matrix having a high or high relative dielectric constant.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the preferred embodiments. 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. Of these, nematic liquid crystal or nematic liquid crystal to which cholesteric liquid crystal is added is preferable in terms of characteristics when used as a display element. When a memory function is required, it is desirable to use smectic liquid crystal. Incidentally, the liquid crystal may contain a dye in order to improve the contrast or the color tone. When a dichroic dye is added, not only as a scattering-transmissive composite film, but also due to the guest-host effect of the dye, light absorption (coloring)
-It can also be used as a composite film that switches in the transparent state.

The polymeric matrix used in the present invention is
High-dielectric or ferroelectric polymers, preferred as these polymers are, for example, polyvinylidene fluoride,
Fluorine-based polymers such as vinylidene fluoride-tetrafluoroethylene copolymer or vinylidene fluoride-trifluoroethylene copolymer, or, for example, vinylidene cyanide-vinyl acetate copolymer, cyanoethyl cellulose, cyanoethyl hydroxyethyl cellulose, cyanoethyl Polymers having a cyano group or a cyanoethyl group such as starch, cyanoethyl hydroxypropyl starch, cyanoethyl pullulan, cyanoethyl glycidol pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl sucrose and cyanoethyl sorbitol can be mentioned. Is a liquid crystal polymer having a side chain of mesogen having an optically active group, such as polysiloxane or polyarylate.

The above polymer matrix is based on solid content.
About 100 parts by weight of the liquid crystal 2 to 70 parts by weight
It is preferable to use the
Untrust is high, but drive voltage is also high
On the other hand, if it is too high, the drive voltage will decrease, but
It is not preferable because there is a problem such as low trust.
Yes.

Liquid from the liquid crystal and the polymer matrix
To form a crystalline / polymer composite film
When is a water-soluble polymer,
about 0.4 to 24% by weight, viscosity (VISCONIC EHD E type viscosity
Using a meter (manufactured by Tokyo Keiki Co., Ltd.), a temperature of 25.1 ° C and
Approximately 1,000 (when measured under the condition of rotation speed 10 ppm)
Dissolve it in water until it becomes ~ 5,000 cps.
A coating liquid obtained by emulsifying the liquid crystal is used. On the other hand, polymer
If the matrix is a water-insoluble polymer, the
Methyl ethyl ketone, toluene,
Solid in a suitable solvent such as xylene or dimethylformamide.
Min. 0.4 to 24% by weight, viscosity about 1,000 to 5,000
Use a coating solution that is dissolved so that it becomes 0 cps. Higher
When the molecular matrix is a polymer with a low softening point
Is heated by adding the liquid crystal to it without using a solvent.
It may be disintegrated and used as a coating liquid.

Next, the liquid crystal / polymer composite optical element of the present invention using the above coating liquid will be described in more detail. At least one of the substrates for forming the liquid crystal / polymer composite optical element of the present invention is, for example, ITO,
It is a pair of substrates such as glass and polymer film to which transparent conductivity such as SnO ₂ system and ZnO system is added. The coating solution obtained as described above is applied as it is to one surface of the element substrate to evaporate the solvent to form a film, and at the same time, the liquid crystal is precipitated into fine particles in the formed film. Thus, a liquid crystal / polymer composite film can be obtained. Further, the solution that has been dissolved by heating can be made into a liquid crystal / polymer composite film by precipitating liquid crystal into fine particles when it is solidified by cooling.

As a method of coating the coating liquid on the element substrate, there are a doctor coating method and a brazing method.
Any conventionally known coating method such as a coating method can be used. The thickness of the liquid crystal / polymer composite film thus formed is usually about 5 to 15 μm. The optical element of the present invention can be obtained by laminating the counter electrode on the liquid crystal / polymer film surface thus formed on the element substrate according to a conventional method.

[0014]

EXAMPLES Next, the present invention will be described more specifically with reference to examples. Example 1 Nematic liquid crystal BL-010 (manufactured by Merck) and 1 KHz
With a cyanoresin CR-V (manufactured by Shin-Etsu Chemical Co., Ltd.) having a relative dielectric constant of 15 at 60/40,
A 30% by weight solution of methyl ethyl ketone was prepared, cast on a glass substrate with ITO and dried to obtain a liquid crystal / polymer composite film. A glass substrate with ITO was laminated on this to prepare a liquid crystal / polymer composite type optical element of the present invention.

Example 2 A nematic liquid crystal BL-010 (manufactured by Merck & Co.) and a vinylidene cyanide-vinyl acetate copolymer (relative dielectric constant at 1 KHz = 5.5) were mixed at a weight ratio of 60/40. A 30% by weight solution of dimethylacetamide was prepared, and was cast on a glass substrate with ITO and dried to prepare a liquid crystal /
A polymer composite film was obtained. A glass substrate with ITO was laminated on this to prepare a liquid crystal / polymer composite type optical element of the present invention.

Example 3 Nematic liquid crystal BL-010 (manufactured by Merck) and liquid crystal polymer LCP-1 (manufactured by Merck) having an optically active group in a side chain.
A liquid crystal / polymer composite film was obtained by preparing a 30% by weight solution of methyl ethyl ketone so that the weight ratio of and became 60/40, casting and drying on a glass substrate with ITO. A glass substrate with ITO was laminated on this to prepare a liquid crystal / polymer composite type optical element of the present invention.

Example 4 NEOFLON VT-100 (manufactured by Daikin Industries, Ltd.) (1
30 parts by weight of relative permittivity at KHz = 9) and 70 parts by weight of nematic liquid crystal BL-010 (manufactured by Merck & Co., Inc.) were mixed at 200 ° C., and a liquid crystal cell (film thickness) kept at 200 ° C. while maintaining the temperature. : 10 μm). Then, by cooling to room temperature, a liquid crystal / polymer composite type optical element of the present invention in which a composite film in which liquid crystal was dispersed in a polymer matrix was sandwiched by ITO electrodes could be obtained.
The change of the parallel light transmittance with respect to the voltage of the liquid crystal / polymer composite type optical elements obtained in the above Examples 1 to 4 was measured by Fortal-5
000 (manufactured by Otsuka Electronics Co., Ltd.), a rectangular wave of 1 KHz was applied, and an examination was conducted at F-number 4.0. As a result, all the devices were able to display clearly with a low driving voltage.

[0018]

According to the present invention as described above, it is possible to provide a liquid crystal / polymer composite type optical element having excellent electro-optical characteristics and reliability at a low driving voltage.

Claims (6)

[Claims] 1. An optical element using a liquid crystal / polymer composite film in which liquid crystal is dispersed in a polymer matrix, wherein the polymer matrix is a high-dielectric or ferroelectric polymer. Liquid crystal / polymer composite type optical element. 2. The liquid crystal / polymer composite type optical element according to claim 1, wherein the polymer matrix is a fluorine-based polymer. 3. The fluorine-based polymer is polyvinylidene fluoride,
The liquid crystal / polymer composite optical element according to claim 2, which is a vinylidene fluoride-tetrafluoroethylene copolymer or a vinylidene fluoride-trifluoroethylene copolymer. 4. The liquid crystal / polymer composite optical element according to claim 1, wherein the polymer matrix is a polymer having a cyano group or a cyanoethyl group. 5. The liquid crystal / polymer composite optical element according to claim 1, wherein the polymer matrix is a vinylidene cyanide-vinyl acetate copolymer. 6. The liquid crystal / polymer composite type optical element according to claim 1, wherein the polymer matrix is a liquid crystal polymer having a side chain of mesogen having an optically active group.