JPH06130367A - Liquid crystal/high polymer composite film - Google Patents

Abstract

PURPOSE:To provide the liquid crystal/high polymer composite film which has the sufficient steepness of the threshold characteristic in electrooptical response characteristics even if an impressed voltage is low and has a excellent contrast in a displayed image by using a liquid crystal material having specific properties. CONSTITUTION:The liquid crystal material which is lower in viscosity at 20 deg.C than 47cSt is used from a nematic liquid crystal which is an org. mixture indicating a liquid crystal state at about ordinary temp. or the nematic liquid crystal added with a cholesteric liquid crystal. More preferably, the liquid crystal material lower in threshold voltage in a TN cell of 7mum thickness than 1.64V and the liquid crystal material having >=0.1 refractive index anisotropy at 20 deg.C are used. Further, the liquid crystal having >=5 dielectric anisotropy at 20 deg.C is more preferable. A liquid crystal electrooptical element is obtd. by sticking a counter electrode to the surface of the resulted liquid crystal/high polymer composite film. The good threshold characteristic is obtd. in the electrooptical response of this element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display having a response to an electric field and heat and capable of displaying and recording information.
Regarding the polymer composite film, the liquid crystal / polymer composite film 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. . Common TN- and STN-
A liquid crystal display encloses a liquid crystal in a liquid crystal cell in which a predetermined seal or the like is applied between glass plates having transparent electrodes,
Further, it is sandwiched by polarizing plates from both sides.
However, in the conventional liquid crystal display, (1) since two polarizing plates are required, the viewing angle is narrow, and the brightness is insufficient, so a backlight with high power consumption is required.
(2) Large dependence on cell thickness makes it difficult to increase the area, (3)
Since the structure is complicated and it is difficult to enclose the liquid crystal in the cell, there are problems such as high manufacturing cost, and there is a limit to the weight reduction, thinning, large area, low power consumption, and cost reduction of the liquid crystal display. is there.

As a liquid crystal display medium for solving such problems, application of a liquid crystal / polymer composite film in which liquid crystal is dispersed in a polymer matrix is expected, and its research and development have been activated. The following techniques have already been disclosed. The liquid crystal / polymer composite film production method can be mainly 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 using polyvinyl alcohol (PVA) as a protective colloid (Japanese Patent Publication No. 58-501631), and a method of preparing a liquid crystal emulsion from an aqueous solution by mixing with a latex. Sho 6
No. 0-252687) 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 matrix resin and a method of phase separation of the liquid crystal from the matrix resin during film formation. As a method for fixing the phase-separated state, a method of dispersing a liquid crystal in an epoxy resin and then curing it (Japanese Patent Publication No. 61-502128) and a method of dispersing the liquid crystal in a UV curable resin and then curing it (special characteristic Table 62-2231) is disclosed. As a method of phase-separating liquid crystals at the time of forming a film, a method of phase-separating during curing, a method of phase-separating during solvent evaporation, and a method of phase-separating during cooling process of a thermoplastic resin are disclosed in JP-A-63-501512. Although disclosed in the publication, various improved techniques have been reported.

As a method of phase separation during curing, in a liquid crystal and UV curable resin mixture system, a method of phase separation of liquid crystal during UV curing (Japanese Patent Laid-Open Nos. 63-271233 and 1-252689). In a mixed system of liquid crystal and thermosetting epoxy resin, a method of phase-separating the liquid crystal during heat curing (Japanese Patent Laid-Open No. 63-287820, Japanese Patent Laid-Open No.
299022). As a method of phase separation during solvent evaporation, a method using an acrylic resin having an active hydrogen group as a matrix (Japanese Patent Laid-Open No. 1-230693) and a method using cellulose acetate as a matrix (Japanese Patent Laid-Open No. 63-124025). Using a resin that is incompatible with liquid crystals as a matrix (Japanese Patent Laid-Open No. 63-43).
993 gazette)).

[0006]

[Problems to be solved by the invention] However,
When the liquid crystal / polymer composite film is used as a member of the light modulation element in the above-mentioned conventional techniques, the steepness of the threshold characteristic in the electro-optical response characteristic is insufficient, the contrast of the display image is insufficient, and the applied voltage is high. Is required. Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a liquid crystal which has a sufficient steepness of the threshold characteristic in the electro-optical response characteristic even when the applied voltage is low, and which is excellent in the contrast of the displayed image. It is to provide a polymer composite membrane.

[0007]

The above object can be achieved by the present invention described below. That is, according to the present invention, in a liquid crystal / polymer composite film in which liquid crystal particles are dispersed and fixed in a polymer matrix, the liquid crystal material has a viscosity of 4 at 20 ° C.
It is a liquid crystal / polymer composite film characterized by being lower than 7 cSt.

[0008]

By using a liquid crystal material having specific physical properties for the constitution of the liquid crystal / polymer composite film, the steepness of the threshold characteristic in the electro-optical response characteristic is sufficient even when the applied voltage is low, and the display image is LCD with excellent contrast /
A polymer composite membrane can be provided.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in more detail with reference to 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. Among these, nematic liquid crystal or nematic liquid crystal to which cholesteric liquid crystal is added is preferable in terms of characteristics. In the present invention, a liquid crystal material having a viscosity of less than 47 cSt at 20 ° C., which is a known liquid crystal material as described above, preferably has a threshold voltage of 1.64 V in a 7 μm thick TN cell.
A lower liquid crystal material, more preferably a liquid crystal material having both of the above conditions, is used. Also, the threshold voltage of the liquid crystal material is 1.6
A liquid crystal material lower than V is more preferable, and the refractive index anisotropy of the liquid crystal material is 0.1 or more, preferably 0.18 or more. If the value is lower than this value, the scattering is insufficient when no voltage is applied. To do. Further, the liquid crystal material preferably has a dielectric constant refractive index of 5 or more, preferably 15 or more. If the liquid crystal material has a lower value than this, the electro-optical response will be poor unless the applied voltage is high. Table 1 below shows the viscosity, threshold voltage, refractive index anisotropy and dielectric anisotropy of commercially available liquid crystal materials.

[0010]

[Table 1] BL-005, 007 and 010 and E-44 are trade names of Merck.

The liquid crystal material has a viscosity of 47 cS at 20 ° C.
When the liquid crystal material is higher than t, the fall time in the electro-optical response cannot be made sufficiently short, and the steepness of the threshold characteristic in the electro-optical response cannot be sufficiently obtained, which is insufficient. Further, when a liquid crystal material having a threshold voltage of a TN cell with a thickness of 7 μm higher than 1.64 V is used, it is insufficient in that the threshold voltage in the electro-optical response cannot be obtained as a sufficiently low value. . The amount of these liquid crystals used is such that the mixing ratio (weight ratio) of the matrix resin / liquid crystal is 5/95 to 50/50, and if the amount of the liquid crystals used is too small, the transparency when voltage is turned on is insufficient. However, it is not sufficient in that it requires a large voltage to bring the film into a transparent state. On the other hand, if the amount of liquid crystal used is too large, scattering (turbidity) when the voltage is off is insufficient. In addition, it is not preferable because the strength of the film is lowered, and when the coating solution is applied to a suitable substrate, it causes repelling.
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,
Due to the guest-host effect of the dye, it can also be used as a composite film that switches in a light absorbing (coloring) -transparent state.

The polymer material used as the matrix in the present invention is PVA, gelatin, acrylic acid copolymer, alkyd resin, epoxy resin, acrylic resin, cellulose resin, UV curable resin, which is used in the prior art. Any electron beam curable resin can be used. Particularly preferred resins in the present invention are PVA and electron beam curable resins, and when PVA is used, there is an advantage that processing over a large area can be uniformly and easily performed, and electron beam curing is possible. In the case of using a hydrophilic resin, it is possible to crosslink the resin with a three-dimensional structure, so that the thermal property of the resin can be enhanced. This has an advantage that the deterioration of the optical response due to the deformation of the resin can be reduced. Hereinafter, the case of using PVA as the matrix resin and the case of using the electron beam curable resin will be mainly described. When PVA is used for producing the liquid crystal / polymer composite film, the emulsion method is suitable, and when PVA having a low saponification degree is used as PVA, PVA itself has a capability as a surfactant. In addition, the liquid crystal emulsion can be satisfactorily produced without using any other surfactant.

As shown in Table 2 below, 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 higher the ability of PVA to disperse liquid crystals.

[Table 2] Degree of saponification and degree of polymerization of various PVA

As a result, when the liquid crystal (E-44) was dispersed using an aqueous solution of various PVA shown in Table 3 below, each PV
Depending on A, the dispersibility and processability of the liquid crystal particles change.

[Table 3] 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 with respect to the electrode substrate is poor, the processability is degraded, and the particle size distribution of the liquid crystal in the liquid crystal / polymer composite film is wide and the particle size is large, so that the electro-optical characteristics are also improved. descend. Also, 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, the electro-optical characteristics are deteriorated, but the viscosity is high, so that the processability is improved.

Under such circumstances, a suitable degree of polymerization (300 to
1,200) and the degree of saponification (50% to 85%),
With regard to the wettability with respect to the electrode substrate, it reaches a level without problems. Further, in order to perform pattern coating only on a necessary portion of the electrode substrate, it is difficult to apply the conventional processing method because the PVA has a low viscosity. Therefore, a suitable thickener such as PVA may be used. A water-soluble polymer, a thixotropic agent, a PVA having a polymerization degree of 1,500 to 3,000 and a saponification degree of 50% to 100%, or ultrafine particles of hydrophobic silica are used. Further, when the problem of air bubbles occurs, a silicone-based emulsion type defoaming agent, for example,
KM71, KM75, KM85, KM73, etc. (all manufactured by Shin-Etsu Chemical Co., Ltd.), SM5512, SH5510, SM
5511 etc. (all made by Toray Silicone) and silicone-based modified oil type defoaming agents include KS68, KS5
It is preferable to use 02, KS506 and the like (Ijiro is manufactured by Shin-Etsu Chemical Co., Ltd.).

As a method for dispersing the liquid crystal in the PVA aqueous solution, a mixing method using various stirring devices such as an ultrasonic disperser or a film emulsification method (Tadao Nakajima, Masataka Shimizu, PHAR) is used.
A dispersion method such as MTECH JAPAN Vol. 4, No. 10 (1988)) is 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 1 to 5 μm.
The range of m is more preferable. The liquid crystal / polymer composite film can be formed from the liquid crystal particle dispersion thus obtained by electrodeposition coating method, screen coating, blade coating, knife coating, slide coating, screen coating, extrusion coating, fountain coating, etc. Therefore, a method of applying a predetermined application amount to the surface of the electrode substrate and drying it is preferable. The thickness of the composite film thus obtained is 5 to 15 μm.
The degree is suitable. In addition, it is also preferable that the PVA of the film formed by using a crosslinking agent or the like is subjected to a crosslinking treatment.

The electron beam curable resin preferably used in the present invention is a curable oligomer having a radically polymerizable double bond in its structure alone, a mixture of a curable oligomer and a curable monomer or a non-curable polymer. And a curable oligomer or a curable monomer, and a particularly preferable curable resin is mainly a thermoplastic resin such as a polyurethane resin and a (meth) acrylate monomer or oligomer. A preferred composition of the electron beam curable resin used in the present invention is substantially free of organic solvents other than monomers, is a non-fluid at room temperature, becomes fluid by heating, and has a sharp viscosity. The composition is lowered, for example, 100 to 5 at the temperature at which the liquid crystal and the resin melt.
Viscosity of about 0000 cps, and at the time of cooling, 10,000 cps or more, preferably 1
The composition has a viscosity of not less than 100,000 cps.

By using such a curable resin, the liquid crystal and these curable resins are mixed and heated to a temperature of room temperature or higher, for example, a temperature of 60 to 150 ° C. so that they are completely compatible with each other. And, since it has a low viscosity, it can be applied uniformly on the substrate, and after the substrate, preferably the electrode substrate is cooled, the liquid crystal is phase separated as fine particles,
Moreover, since the curable resin loses fluidity, the phase-separated liquid crystal particles are stably fixed in the matrix resin. An example of the electron beam curable resin whose viscosity remarkably depends on temperature is a thermoplastic resin, for example, an electron beam curable resin composed of a polyurethane resin and a (meth) acrylate monomer. The polyurethane resin used in the curable resin is obtained from polyisocyanate and polyol, and has a high cohesive force due to the presence of urethane bonds. When this is mixed with a (meth) acrylate monomer, the temperature dependence of viscosity is remarkable. It becomes a composition. As such a polyurethane resin, various grades are available from the market, and any of them can be used in the present invention. Particularly preferred in the present invention is a reaction of polyisocyanate, polyol and monofunctional alcohol. It is obtained by doing.

The polyisocyanate to be used includes, for example, toluidine diisocyanate, 4,4'-diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and the like.
1,4-butanediol, 1,3-butanediol, mono (or di, tri, tetra) ethylene glycol, mono (or di, tri, tetra) propylene glycol, 1,
6-hexamethylenediol and the like can be mentioned, and as the alcohol, methyl alcohol, ethyl alcohol, n-
Propyl alcohol, i-propyl alcohol, n-butyl alcohol, t-butyl alcohol, methyl cellosolve, ethyl cellosolve and the like can be mentioned. The polyurethane resin composed of the above components is reacted at an equivalent ratio of isocyanate / polyol + alcohol = 0.8 to 1.1, and an equivalent ratio of polyol / alcohol is 1/9 to
A ratio of about 1 is suitable. If the amount of alcohol used is too small, the molecular weight of the resulting polyurethane resin will not increase, and the temperature dependence of viscosity will decrease.On the other hand, if the amount of alcohol used is too large, the molecular weight of the polyurethane resin will become too low, resulting in adhesion. It is not preferable because it deteriorates the property. Therefore, the molecular weight of the polyurethane resin used in the present invention is 500 to
A range of about 1,500 is preferable.

Further, the (meth) acrylate monomer or oligomer used in the present invention may be a commercially available one, for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2 -Hydroxy-3-phenoxypropyl (meth) acrylate, N-methylol (meth) acrylate, N, N'-diethylaminoethyl (meth) acrylate, (meth) acryloyloxyethyl monosuccinate, (meth) acryloyloxyethyl monophthalate Etc. In addition, it is preferable to use a polyfunctional (meth) acrylate monomer or the like in combination in order to improve the strength and height of the matrix. A suitable amount of liquid crystal material is added to the curable resin, and the mixture is heated and melted to homogenize, and the coating solution is applied onto a substrate, preferably an electrode substrate, by blade coating, knife coating, slide coating, Examples include screen coating, extrusion coating, fountain coating and the like. The thickness of the composite membrane thus obtained is 5
Approximately 15 μm is suitable.

The coating layer may be crosslinked and hardened by an electron beam, or the coating layer may be directly irradiated with an electron beam.
Alternatively, the counter electrode substrate may be adhered to the surface of the coating layer, and then an electron beam may be irradiated through at least one substrate to crosslink and cure. Conventional technology can be used as it is as an irradiation device, for example, in the case of electron beam curing, Cockloft-Walton type, Van de Graaff type, resonance transformation type, insulating core transformer type, linear type, electro curtain type, dynamitron type, high frequency 50 emitted from various electron beam accelerators such as molds
An electron beam having an energy of ~ 1,000 KeV, preferably 100-300 KeV is used, and the irradiation dose is 1-
A dose of around 5 Mrad is preferred.

In another preferred embodiment of the present invention, a liquid crystal / polymer composite film can be prepared by the method as described above using microcapsules containing a liquid crystal. As a method for producing liquid crystal microcapsules, 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 a polycondensation or polyaddition reaction, and either of them is dispersed and reacted at the interface. The in 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 abrupt 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. In the present invention, the desired liquid crystal optical element is provided by bonding the counter electrode to the liquid crystal / polymer composite film preferably formed on the electrode substrate as described above.

[0025]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative Examples. Example 1 An aqueous PVA solution (trade name: Gohsenol KP-06, manufactured by Nippon Synthetic Chemical Industry) was added to a cyanobiphenyl liquid crystal E-4.
4, BL-005, BL-007 and BL-010 (manufactured by Merck) are emulsified and dispersed, and the counter electrode is attached to the surface of the liquid crystal / polymer composite film obtained by coating and drying on the electrode substrate surface. A liquid crystal optical element was obtained. The electro-optical response of the device is shown in FIG. Samples using a liquid crystal material exhibiting good threshold characteristics have a viscosity at 20 ° C. of less than 47 cSt and a threshold voltage of less than 1.64 V when used as a TN cell (7 μm).

Example 2 A system for obtaining a liquid crystal / polymer composite film structure by curing a bifunctional epoxy ester electron beam curable resin (trade name: Epoxy ester 40EM, manufactured by Kyoeisha Yushi-Seikagaku) by electron beam irradiation, and cyanobiphenyl Liquid crystal E-44, BL-0
No. 05, BL-007 and BL-010, and Example 1
The electro-optical response of each sample of the optical element obtained in the same manner as in is shown in FIG. Samples using a liquid crystal material exhibiting good threshold characteristics have a viscosity at 20 ° C. of less than 47 cSt and a threshold voltage of less than 1.64 V when used as a TN cell (7 μm).

Example 3 to (Please add if there are other examples)

As described above, according to the present invention, by using a liquid crystal material having specific physical properties for the constitution of the liquid crystal / polymer composite film, the threshold characteristic in the electro-optical response characteristic can be obtained even when the applied voltage is low. It is possible to provide a liquid crystal / polymer composite film having a sufficient steepness and excellent display image contrast.

[0028]

[Brief description of drawings]

FIG. 1 is a diagram illustrating a correlation between a threshold property of a liquid crystal / polymer composite film using PVA and a liquid crystal material.

FIG. 2 is a diagram illustrating a correlation between a threshold characteristic of a liquid crystal / polymer composite film formed by an electron beam-cured epoxy ester and a liquid crystal material.

Front page continuation (72) Inventor Masayuki Ando 1-1-1 Ichigaya-Kagacho, Shinjuku-ku, Tokyo Dai Nippon Printing Co., Ltd.

Claims (7)

[Claims] 1. A liquid crystal / polymer composite film in which liquid crystal particles are dispersed and fixed in a polymer matrix, wherein the liquid crystal material has a viscosity at 20 ° C. lower than 47 cSt. 2. The liquid crystal according to claim 1, wherein the threshold voltage in a TN cell having a thickness of 7 μm of the liquid crystal material is lower than 1.64V.
Polymer composite membrane. 3. The liquid crystal material has a viscosity at 20 ° C. of 47 c.
The liquid crystal / polymer composite film according to claim 1, wherein the liquid crystal / polymer composite film is lower than St and has a threshold voltage lower than 1.64 V in a TN cell having a thickness of 7 μm of the liquid crystal material. 4. The liquid crystal / polymer composite film according to claim 1, wherein the polymer is polyvinyl alcohol or a crosslinked product thereof. 5. The liquid crystal / polymer composite film according to claim 1, wherein the polymer is a cured product of an electron beam curable resin. 6. The liquid crystal / polymer composite film according to claim 1, wherein the liquid crystal material has a refractive index anisotropy at 20 ° C. of 0.1 or more. 7. The liquid crystal / polymer composite film according to claim 1, wherein the liquid crystal material has a dielectric anisotropy at 20 ° C. of 5 or more.