JP2001242444A - Material for liquid crystal display, method for liquid crystal display and ilquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new material for a liquid crystal display, having superior contrast ratio, and to provide a method and device for display by using this material. SOLUTION: The material for a liquid crystal display is prepared by dispersing a liquid crystal in a polymer in a compatibilized state or phase separation state. The material for a liquid crystal display used has properties such that the liquid crystal made is compatible in the polymer at a high temperature and causes phase separation from the polymer at low temperature and that the contrast ratio B/A is >=2, where A is the reflectance of the display material, when it is cooled from the dissolved state at 10 deg.C/sec cooling rate and B is the reflectance of the display material, when it is cooled from the dissolved state at 4 deg.C/sec cooling rate. The display state can be kept by controlling the cooling rate of the material from the dissolved state, so as to keep the liquid crystal in a semitransparent state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display material, a liquid crystal display method, and a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display material in which a liquid crystal is dissolved or phase-separated in a polymer and a liquid crystal display method using thermal phase separation, wherein the liquid crystal is made translucent by controlling a cooling rate. The present invention relates to a liquid crystal display method and apparatus capable of maintaining a display state by maintaining the state.

[0002]

2. Description of the Related Art Liquid crystal display devices using polymer dispersed liquid crystal have been developed. The polymer-dispersed liquid crystal has superior characteristics in terms of brightness, contrast, viewing angle, and the like, as compared with a liquid crystal display device using polarized light. In addition, since the liquid crystal is dispersed in the polymer, the liquid crystal does not need to be sealed, and has a feature that the area can be easily increased.

[0003] Such a polymer-dispersed liquid crystal display is a display utilizing the fact that the optical properties of the liquid crystal change due to electric field response or thermal response. For example, Japanese Patent Application Laid-Open No. 3-52843 discloses a liquid crystal optical device using a polymer dispersed liquid crystal utilizing electric field response. This is because the ordinary light refractive index of the liquid crystal matches the refractive index of the polymer so that an electric field is applied to align the orientation of the liquid crystal molecules in the direction of voltage application to make it transparent, and when no electric field is applied, the liquid crystal molecules are at the polymer / liquid crystal interface. , Light is scattered at the interface based on the refractive index difference between the polymer and the liquid crystal, resulting in a cloudy state.

However, in this method, when the thickness of the polymer-dispersed liquid crystal layer is increased in order to increase the opacity when no electric field is applied, the driving voltage is also increased. Further, even when an electric field is applied, it is difficult to obtain a completely transparent state because minute liquid crystal droplets cannot respond to an electric field, or it is difficult to completely match the ordinary light refractive index of the liquid crystal with the refractive index of the polymer. . That is, there is an electro-optical limit in performing display with excellent contrast by low voltage driving.

[0005] Also, a display material investigation report II (edited by the Japan Electronics Industry Development Association, published in March 1991, paragraphs 85 to 97)
Item) describes a liquid crystal display device using a thermoresponsive polymer dispersed liquid crystal. In this liquid crystal display device,
A polymer-dispersed liquid crystal in which a nematic liquid crystal is dispersed in a polymer is used. FIG. 1A shows a non-heated state (nematic phase) of the polymer-dispersed liquid crystal.
(B) shows a mode change of a heating state (isotropic phase) of the polymer dispersed liquid crystal. FIG. 2 shows the relationship between the temperature and the refractive index of the polymer dispersed liquid crystal.

As shown in FIGS. 1 (a) and 2, the polymer-dispersed liquid crystal is opaque and opaque when not heated. This is because light is scattered at the polymer / liquid crystal interface, similarly to the liquid crystal display device using the electric field responsive polymer dispersed liquid crystal.

On the other hand, as shown in FIGS. 1B and 2, the polymer-dispersed liquid crystal is heated to a temperature above a certain temperature (nematic-isotropic phase transition point: TNI). Changes from cloudy to transparent. This is because the liquid crystal in the polymer-dispersed liquid crystal is heated above the nematic-isotropic phase transition point and loses liquid crystallinity, and the difference between the refractive index of the isotropic phase and the refractive index np of the polymer is reduced. It is. In this case, since heat is conducted uniformly without depending on the particle size of the liquid crystal droplet,
Although display response is good, it is still difficult to completely match the refractive index of the isotropic phase with the refractive index of the polymer, so that the contrast is not sufficient.

[0008] In addition, liquid crystal display technology (Industry Research Committee, published September 20, 1994, paragraphs 53 to 57), etc.
There is a report as a thermal writing device using both electric field and heat. For example, JP-A-6-18831 discloses a display device in which a layer in which a nematic liquid crystal is dispersed in a polymer is sandwiched on a substrate on which a transparent electrode and a heating wire are arranged.
In this method, the orientation of the liquid crystal in the direction of the electric field is fixed and the transparent state is maintained by using both the heating and the electric field.
Also in this case, there is an electro-optical limit for performing display with excellent contrast at low voltage driving, and further, there is a problem that the transparent state cannot maintain a high transmittance for a long period of time.

[0009]

Accordingly, an object of the present invention is to provide a novel liquid crystal display material having an excellent contrast ratio. Another object of the present invention is to provide a method and an apparatus for polymer-dispersed liquid crystal display capable of performing thermal writing / erasing while maintaining a translucent state.

[0010]

A first object of the present invention is to provide a liquid crystal display material in which liquid crystal is dispersed in a polymer in a state of being compatible or phase-separated. At a low temperature, the liquid crystal is phase-separated from the polymer and the reflectance of the display material cooled from the compatible state at a rate of 10 ° C./sec: A, and the display cooled from the compatible state at a rate of 4 ° C./sec. Material reflectance: B contrast ratio: B / A is 2
The problem is solved by a liquid crystal display material characterized by the above. Further, the second problem is that, in a polymer-dispersed liquid crystal display, liquid crystals are dispersed in a polymer when not heated,
Solved by maintaining the display state as it is by using a display medium with a material composition in which the liquid crystal is compatible with the polymer during heating, and controlling the cooling rate from the compatible state to control the particle size of the liquid crystal droplets. Is done.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present specification, each term has the following meaning. “Phase transition temperature T _NI ” means the phase transition temperature of the nematic phase-isotropic phase.
The liquid crystal is not limited to a nematic liquid crystal, but may be a smectic liquid crystal, a cholesteric liquid crystal, or the like. In that case, the phase transition temperature T _NI indicates the phase transition temperature between the liquid crystal phase and the isotropic phase. "Polymer-dispersed liquid crystal" is a composite film of a polymer and a low-molecular liquid crystal. It can be seen as one of the composite systems of polymer and low molecular liquid crystal.

FIG. 3 shows the principle of a polymer dispersion type liquid crystal display in a thermally driven display. FIG. 3A shows that nematic liquid crystal droplets 302 are dispersed in a polymer in a non-heated state,
Since scattering occurs at the polymer / liquid crystal interface based on the difference in the refractive index, an opaque cloudy state occurs. If the liquid crystal droplets are dispersed in a small particle size, the liquid crystal droplets have a high opacity, that is, a more opaque state. From the state of FIG.
By heating the polymer dispersion type liquid crystal layer in the above T _g or T _NI, compatible liquid crystal molecules 303 in the polymer, as shown in FIG. 3 (b), a fully transparent state. When the temperature is rapidly reduced while controlling the temperature from the compatible state in FIG. 3B, the liquid crystal droplets are dispersed in a very small state as shown in FIG. 3C. Therefore, the translucent state is maintained. This is because light scattering is drastically reduced when the particle size of the liquid crystal droplet is significantly smaller than the wavelength of light. Further, once the translucent state is formed, the translucent state is maintained at room temperature. As a result, power consumption in the thermally driven display can be saved, and a very economical liquid crystal display device with low running cost can be obtained.

When reheating is performed in the translucent state shown in FIG. 3 (c), the state returns to the compatible state shown in FIG. 3 (b). The state returns to the opaque state (cloudy state) in a). Therefore, in order to return from the translucent state to the opaque state, it is necessary to go through the compatible state shown in FIG.

To change from the transparent state shown in FIG. 3B to the translucent state shown in FIG. 3C, the temperature of the polymer-dispersed liquid crystal layer is set to 5 ° C.
/ Sec or more, for example, at a rate of 10 ° C./sec, to make the liquid crystal droplets smaller to a diameter of less than 1 μm. When the size of the liquid crystal droplet is more than 1 μm, light scattering is increased and transparency is reduced, and the contrast in display is also reduced. The average particle size of the liquid crystal droplets in the opaque (opaque) state is generally about 1 μm to 10 μm.
Therefore, in the present invention, the size of the liquid crystal droplet is reduced to about 1/10 of the size of the liquid crystal droplet when not heated.

The liquid crystal display device of the present invention will be described in more detail with reference to the drawings. FIG. 4 is a schematic perspective sectional view of an example of the liquid crystal display device 400 according to the present invention. As shown, the liquid crystal display device 400 of the present invention basically includes a base material 401, a polymer dispersed liquid crystal layer 402, a background layer 403, and a heating element 404. The liquid crystal display material of the present invention is used as a material for forming the polymer dispersed liquid crystal layer 402.

First, in the polymer-dispersed liquid crystal layer 402, in the present invention, a polymer whose glass transition temperature (T _g ) is close to the (nematic phase-isotropic phase) phase transition temperature (T _NI ) of the liquid crystal is used as a binder. Used as resin. Preferably −20 ° C. ≦ (T _g −T _NI )
It is preferable to satisfy the condition of ≦ 20 ° C. More preferably, it is in the range of 0 ° C. ≦ (T _g −T _NI ) ≦ 10 ° C.

Here, FIG. 5 shows the temperature relationship in which the liquid crystal is compatible with the polymer when the polymer-dispersed liquid crystal layer is heated, causing an optical change of cloudiness-transparency. The temperature at which the cloudiness-transparency changes is _{defined as Ttr} . If T _g > T _NI , then T
_tr is opaque and _{T NI} near the lower temperature - a change of the transparency, and if the _T g _{<T NI, T tr} is the lower of the temperature T
_In the vicinity of _g , it was found that the color changed from cloudy to transparent.
Here, when the temperature difference of ( _Tg - _TNI ) is large, a wide temperature range is required for the liquid crystal to be compatible with the polymer by heating, and as a result, the thermal response tends to be slow. Therefore, it is preferable to satisfy the condition of −20 ° C. ≦ (T _g −T _NI ) ≦ 20 ° C. _{Further, 0 ℃ ≦ (T g -T} N I) ≦ 1
More preferably, the temperature relationship of 0 ° C. is satisfied. This is-
When 20 ° C. <(T _g −T _NI ), thermal deformation of the polymer-dispersed liquid crystal layer occurs due to repeated thermal history, which may not be practically preferable.

Conventional polymer-dispersed liquid crystal displays are generally
As shown in FIGS. 1 and 2, the refractive indices of the polymer and the liquid crystal are shown in FIG.
Control of coincidence and non-coincidence and use of optical change as display
I do. Therefore, the ordinary refractive index of the liquid crystal and the refractive index of the polymer
Is the means to obtain a highly transparent state
In the selection of the refractive index of polymer and liquid crystal,
It will be limited. On the other hand, utilizing the thermal phase separation of the present invention
Display, the refractive index of the material must be
There is no limit of T_trIs determined by T _gAnd T
_NIBecause of the temperature relationship of_trCan be set
Can be. In addition, because of the use of thermal phase separation,
The transmittance does not depend on the film thickness.
Enables display with excellent turbidity and high transparency.
And found.

The polymer which can be used in the present invention is a highly transparent thermoplastic resin, preferably an acrylic resin. For example polyethyl methacrylate, polymethyl methacrylate tert-butyl, acrylic resin having a high T _g of the polyethylene glycol dimethacrylate, and alkyd modified acrylic resins, and styrene, methyl methacrylate, acrylonitrile, acrylic copolymer with a hard monomer such as acrylamide A polymer or the like can be used. However, polymers of these acrylic resins, the selection of the functional groups of various monomers, the molecular weight of the polymer, and by selection of the copolymerization ratio can be preferably set the T _g of the polymer.

Needless to say, -20 ° C. ≦ (T _g −T
_As long as the polymer satisfies the relationship of _NI ) ≦ 20 ° C., a polymer other than the acrylic resin can be used in the present invention. For example, various polymer resins such as polyvinyl butyral, polyester, polyurethane, vinyl chloride, vinyl acetate copolymer, silicone, polyvinyl alcohol, polyvinyl pyrrolidone, and various cyanoethylated compounds such as cyanoethylated pullulan can be used. The polymer used in the polymer-dispersed liquid crystal of the present invention may be used alone or in combination of two or more, provided that the relationship of −20 ° C. ≦ (T _g −T _NI ) ≦ 20 ° C. can be satisfied. May be used in combination.

The liquid crystal used in the polymer dispersed liquid crystal layer 402 of the present invention is a liquid crystal material having a large birefringence: Δn.
In addition, nematic liquid crystals containing cyanobiphenyl, cyanoterphenyl, and derivatives thereof as main components in consideration of heat durability and resistance to ultraviolet ray deterioration can be used. Birefringence: Δn is preferably 0.20 or more.
A liquid crystal material satisfying 35 or less is preferable. Δn is 0.2
If it is less than 0, the degree of white turbidity of the polymer-dispersed liquid crystal film is insufficient, and it is difficult to produce a practical liquid crystal material having Δn of more than 0.35. The TNI can be suitably adjusted by changing the composition of the mixture of these liquid crystal compositions. Therefore, the TNI of the liquid crystal can be adjusted according to the change temperature of the polymer dispersed liquid crystal display element.

The liquid crystal is not limited to the nematic liquid crystal, and is not particularly limited as long as it is a liquid crystal having a thermoresponsive property capable of reversibly discoloring by heat or reversibly changing from an opaque state to a transparent state. . For example, as a nematic liquid crystal other than cyanobiphenyl-based and cyanoterphenyl-based, cyanopyridine-based, Schiff base-based, azoxy-based, azo-based, benzoic acid phenyl ester-based, biphenyl-based having a polar group other than cyano group, other than cyano group Terphenyl-based, phenylcyclohexane-based, phenylpyridine-based, phenyldioxane-based, polycyclic ethane-based, phenylcyclohexene-based, cyclohexylpyridine-based, phenyl-based, and tolan-based compounds having a polar group of
Smectic liquid crystals, cholesteric liquid crystals and the like can also be suitably used.

The liquid crystal display material of the present invention, which is a material for forming the polymer dispersed liquid crystal layer 402, is basically a polymer in which liquid crystal is dispersed in a state of being dissolved or phase separated. In a high temperature state, the liquid crystal is compatible with the polymer, and in a low temperature state, the liquid crystal is separated from the polymer, and the liquid crystal is separated from the polymer by 10 ° C.
Assuming that the reflectivity of the liquid crystal display material when cooled at a rate of 4 / sec is A and the reflectivity of the liquid crystal display material cooled at a rate of 4 ° C./sec from the compatible state is B, The contrast ratio (B / A) of the liquid crystal display material is 2 or more and 16.6.
Is less than. However, this value is obtained when the background material 403 having a reflectance of 6% is used in the reflectance measurement of the display device 400. When the contrast ratio is less than 2, the contrast of the display state becomes worse, and it becomes difficult to identify the display information. It is not realistic that the contrast ratio becomes 16.6 or more. A preferable range of the contrast ratio (B / A) is as follows.
2 to 16.0. More preferable contrast ratio (B
The range of / A) is 2 to 13. The most preferable range of the contrast ratio (B / A) is 2 to 10.

According to the study of the present inventors, it has been found that, even among liquid crystals having the same birefringence, a liquid crystal having a higher viscosity has a higher contrast ratio. Therefore, when forming a liquid crystal display material having a desired contrast ratio, it is preferable to consider not only the birefringence of the liquid crystal but also the viscosity of the liquid crystal to be used.

As for the ratio of the polymer and the liquid crystal used in the polymer dispersed liquid crystal layer 402 of the present invention, if the compounding amount of the liquid crystal is higher than the compounding amount of the polymer, the oozing of the liquid crystal becomes a problem, and the polymer dispersed liquid crystal layer becomes a problem. The need to strictly seal 402 arises, making it unsuitable for a simple manufacturing process such as a coating process. On the other hand, when the compounding amount of the liquid crystal is smaller than the compounding amount of the polymer, the film-forming property is good, but the white turbidity of the polymer-dispersed liquid crystal layer when not heated is reduced. Therefore, the polymer in the polymer dispersed liquid crystal layer 402 of the present invention:
The weight ratio of the liquid crystal is preferably in the range of 30:70 to 70:30.

The thickness of the polymer-dispersed liquid crystal layer is not particularly limited, but is generally preferably in the range of 5 μm to 200 μm. If the film thickness is less than 5 μm, a sufficient display effect cannot be obtained. On the other hand, if the film thickness is more than 200 μm, the thermal response speed becomes slow, and it becomes difficult to display quickly and it is difficult to obtain a uniform film thickness.

The method of forming the polymer-dispersed liquid crystal layer 402 of the present invention is performed by coating using a solvent evaporation method. By forming the polymer dispersed liquid crystal layer 402 by coating, large-area coating can be performed at low cost. The method for forming the polymer-dispersed liquid crystal layer 402 is not limited thereto, and any method for forming a polymer-dispersed liquid crystal layer commonly or commonly used by those skilled in the art can be used in the present invention. For example, a method such as an encapsulation method, a polymerization phase separation method, or a thermal phase separation method can be appropriately selected and used.

In forming the polymer-dispersed liquid crystal layer 402 by coating, a mixed solution is prepared using a solvent that can dissolve both the polymer and the liquid crystal, and the mixed solution is placed on a substrate 401 by a blade coater, a die coater, and a roll. Coating can be performed by a conventional coating method such as a coater, a bar coater, screen printing, brush coating, doughing, and spraying. As a solvent, cellosolve, toluene, xylene, cyclohexanone, acetone, methyl ethyl ketone, ethyl acetate, carbon tetrachloride, acetonitrile, pyridine, N, N-dimethylformamide, N, N-dimethylacetamide, N
-Methyl-2-pyrrolidone and the like can be used. The solvent can be used alone or as a mixed solvent of two or more kinds.

The substrate 401 supports the polymer-dispersed liquid crystal layer 402 in a strong manner, and is not particularly limited in material and film thickness as long as it satisfies transparency, heat resistance and use strength. For example, a transparent plastic can be used, the cost is lower than that of glass, the surface can be curved due to its flexibility, and the suitability for production in the coating process is good. Examples of the plastic that can be used in the present invention include polyethylene terephthalate, polyethylene naphthalate, and polyether sulfone.

Since the liquid crystal display device 400 shown in FIG. 4 is a display in which the polymer dispersed liquid crystal layer 402 is changed to opaque-transparent by heat driving, it is necessary to improve the contrast between the non-heated state and the heated state. It is preferable to dispose a background layer 403 behind the liquid crystal layer 402. Background layers suitable for such purposes include, for example, silver, aluminum,
The reflection layer is made of tin, nickel, chromium, gold, platinum, or the like. Since these layers have high thermal conductivity, they are formed to have a suitable thickness so as not to hinder the heat conduction from the heating element 404. More preferably, in order to improve the contrast between the reflectance at the time of cloudiness and the reflectance at the time of transparency, the polymer dispersed liquid crystal layer 402
, A black background layer 403 having a low reflectance is disposed. The background layer 403 is not limited to black, and a color background layer can be used to display a background color.

The heating element 404 in FIG. 4 may be any as long as it can quickly supply a necessary and sufficient amount of heat. For example, a material that generates Joule heat by sandwiching carbon, nickel, etc. between electrodes and passing an electric current, or a nichrome wire,
Examples of such devices include a wire made of stainless steel or the like having a predetermined resistance value, which generates Joule heat, a semiconductor heat pump such as a Peltier device, or heat generated by laser irradiation.

A temperature control device 405 is connected to the heating element 404 in FIG. This temperature control device 405
In addition to the current supply device 406 for driving the heating element 404, a temperature sensor 4 for measuring the temperature of the heating element 404
07. According to the present invention, first, the current supply device 40
6 is operated to supply a current to the heating element 404, thereby heating the heating element 404 and raising it to a set temperature,
A transparent state as shown in FIG. 3B is formed. When the temperature sensor 407 detects that the temperature of the heating element 404 has reached the set temperature, the detection signal is sent to the controller 40.
8 and the MPU and CP inside the controller 408
The arithmetic processing is performed according to a temperature control program stored in U (not shown). The calculation result is transmitted to the current supply device 406 as a control signal, and the current supply device 40
6 controls the current value sent to the heating element 404. By repeating this processing operation, the temperature of the heating element 404 is reduced at a preset speed. Controller 408
When receiving a command signal for setting from the outside, the current supply device 406 is operated to supply a current to the heating element 404, and the temperature is controlled to a constant temperature to make the polymer / liquid crystal composite film transparent,
After a predetermined time, the temperature is reduced according to a predetermined function under the control of the controller 408, and the transparent state is maintained. The command signal also includes a signal for stopping the current supply device 406 after it is operated. Thereby, the liquid crystal display device can be returned from the translucent state to the cloudy state (opaque state) via the transparent state. In order to lower the temperature of the polymer / liquid crystal composite film in a compatible (transparent) state at a rate of 5 ° C./sec or more, if necessary, a publicly-known external cooling such as a heat sink, a cooling fan, a Peltier device, etc. A device (not shown) can be used together.

[0033]

The present invention will be described in more detail with reference to the following examples.

[0034] As Example 1 polymers, polymethyl methacrylate (manufactured by Asahi Kasei Corporation, Derupauda _60N, T g = 90 ℃) 2.5
g and 2 g of a cyanobiphenyl-based nematic liquid crystal (manufactured by Merck, E-8, T _NI = 72 ° C., Δn = 0.253, viscosity 35.0 cps (25 ° C.)) were dissolved in acetone to give 30 g. A solution of weight% was prepared, and the solution was applied and dried on a PET substrate 401 using an applicator. The polymer-dispersed liquid crystal layers of the two coated substrates were opposed to each other and bonded by thermocompression bonding to obtain a polymer-dispersed liquid crystal layer 402 having a thickness of 50 μm. By combining this with a black background material (reflectance 6%) 403 and a heating element 404 using a stainless steel heating element, a liquid crystal display cell A of the present invention was produced.

[0035] As Example 2 polymer, polymethyl methacrylate (manufactured by Asahi Kasei Corporation, Derupauda _60N, T g = 90 ℃) 2.5
g and a cyanobiphenyl-based nematic liquid crystal (manufactured by Dainippon Ink and Chemicals, Inc., T _NI = 80 ° C., Δn = 0.2)
31, 2 g of a viscosity of 38.1 cps (25 ° C.) was dissolved in acetone to prepare a 30% by weight solution. Using this solution, a liquid crystal display cell B was produced in the same manner as in Example 1.

Example 3 As a polymer, an acrylic resin obtained by partially introducing an amine into poly (methyl methacrylate) (Dainippon Ink and Chemicals, Inc.)
_{Ltd., BZ1161, T g = 85 ℃} ) and 2.5g, cyanobiphenyl nematic liquid crystal (Dainippon Ink Chemical Co., _{Ltd., T NI = 80 ℃, Δn} = 0.231, viscosity 3
2 g of 8.1 cps (25 ° C.) was dissolved in toluene to prepare a 30% by weight solution. Using this solution,
A liquid crystal display cell C was manufactured in the same manner as in Example 1.

Example 4 As a polymer, 2.5 _{g of} polyvinyl butyral (BL-S, manufactured by Sekisui Chemical Co., Ltd., Tg = 60 ° C.) and a cyanobiphenyl-based nematic liquid crystal (E-
8, T _NI = 72 ° C., Δn = 0.253, viscosity 35.0
2 g of cps (25 ° C.) was dissolved in methyl ethyl ketone to prepare a 30% by weight solution. Using this solution, a liquid crystal display cell D was produced in the same manner as in Example 1.

With respect to the cell B obtained in Example 2, the change in reflectance at each cooling rate was measured from the transparent state at the time of heating. The cooling was performed by lowering the temperature from a cloudiness-transparency change temperature (T _tr ) as a polymer-dispersed liquid crystal film to 40 ° C. at a predetermined rate. The reflectance was measured by disposing a black background material (reflectance: 6%) and a heating element behind each cell, and diffusing and irradiating from the front of the polymer dispersion type liquid crystal cell using an integrating sphere and a halogen light source. The brightness of the surface of the polymer-dispersed liquid crystal cell is measured using a brightness meter (BM
-7). At this time, set the value to the standard white plate (Mg
O), and the reflectance was determined. Therefore, when the reflectance of each cell is measured, the measured value does not fall below the reflectance of the background material. Further, the cross section of the polymer-dispersed liquid crystal film at each cooling rate was observed by SEM, and the average particle size of the liquid crystal droplets was also measured. Table 1 summarizes the results of these measurements.

[0039]

[Table 1] 85 ° C to 40 ° C Temperature drop rate Reflectivity Cooling time to average particle size (sec) (° C / sec) (%) (μm) 10 4.5 40 3 7 6.4 38 14 11 3 20 0.7 1 45.0 9 0.1

As is clear from the results shown in Table 1, the cell B of Example 2 of the present invention satisfying the condition of −20 ° C. ≦ (Tg−TNI) ≦ 20 ° C. is heated and is in a transparent state. When the liquid crystal was rapidly cooled at a temperature drop rate of 5 ° C./sec or more, the translucent state was maintained. The contrast ratio B / A of the reflectance A of the cell cooled at a rate of 10 ° C./sec and the reflectance B of the cell cooled at a rate of 4 ° C./sec was 2 or more. This translucent state was maintained after a lapse of 200 hours. The reflectance did not increase after quenching. In addition, the white turbid state and the translucent state could be freely displayed reversibly by heating again, cooling naturally, heating again, and controlling rapid cooling. Also,
It was confirmed that by performing the temperature control of the slow cooling, the particle size of the liquid crystal droplets could be controlled and the optical properties of the display element could be maintained. For cells A, C and D, cell B
The same test was performed, and similar results were obtained.
The results are summarized in Table 2 below.

[0041]

Table 2 Cooling rate Cooling rate 10 ° C / sec 4 ° C / sec Anti-contrast ratio in response to liquid crystal viscosity Cell number (cps) Emissivity B (%) Emissivity A (%) B / A A 35.0 38. 0 18.0 2.1 B 38.1 40.5 19.6 2.1 C 35.0 41.3 16.4 2.5 D 38.1 35.1 15.1 2.3

Example 5 As a polymer, 2.5 g of polymethyl methacrylate (Del Powder 60N, manufactured by Asahi Kasei Corp.) and a cyanobiphenyl-based nematic liquid crystal (manufactured by Dainippon Ink and Chemicals, Inc., Δn = 0.220) , Viscosity 30.6 cps (25
C)) is dissolved in methyl ethyl ketone to give 3 g.
A 0% by weight solution was prepared. Example 1 using this solution
A liquid crystal display cell E was produced in the same manner as in the above.

Example 6 As a liquid crystal, a cyanobiphenyl nematic liquid crystal (manufactured by Dainippon Ink and Chemicals, Inc., Δn = 0.220, viscosity 3)
0.6 cps (25 ° C.) and 1 g of 4-Pentyloxy-4-biphenylcarbonitrile (ALDRIC
1 g) was added to obtain 2 g of nematic liquid crystal.
At this time, Δn = 0.2134, viscosity 44.6 cps (25
° C). 2.5 g of the nematic liquid crystal of 2 g and polymethyl methacrylate (Del Powder 60N, manufactured by Asahi Kasei Corporation) were dissolved in methyl ethyl ketone to prepare a 30% by weight solution. Using this solution, a liquid crystal display cell F was produced in the same manner as in Example 1.

Example 7 As a polymer, 2.5 g of polymethyl methacrylate (Del Powder 60N, manufactured by Asahi Kasei Corp.) and a cyanopyridine-based nematic liquid crystal (Denippon Ink and Chemicals, Inc., Δn = 0.253) , Viscosity 51.0 cps (25
C)) is dissolved in methyl ethyl ketone to give 3 g.
A 0% by weight solution was prepared. Example 1 using this solution
A liquid crystal display cell G was manufactured in the same manner as in the above.

For each of the liquid crystal display cells obtained in Examples 5 to 7, the reflectance A 'when cooled at a rate of 45 ° C./sec from the compatible state and the rate of 2 ° C./sec from the compatible state. The reflectance B ′ when cooled in step is measured, and the contrast ratio B ′ is measured.
/ A '. The measurement of the reflectance was performed using the same method as described above. The results are summarized in Table 2 below.

[0046]

Table 3 Cooling rate Cooling rate 45 ° C./sec 2 ° C./sec Anti-contrast ratio in liquid crystal viscosity Cell number (cps) Emissivity B ′ (%) Emissivity A ′ (%) B ′ / A ′ E 30 6.6 41.2 12.5 3.3 F 44.6 39.2 8.7 4.5 G 51.0 34.7 6.4 5.4

As is clear from the results shown in Table 2, it is understood that the contrast ratio is improved by increasing the viscosity of the liquid crystal. Further, cell G (Example 7)
When a liquid crystal having a high viscosity and a high birefringence was used, a contrast ratio of 5.4 was obtained.

[0048]

As described above, according to the present invention,
A liquid crystal display material having high contrast can be obtained.
In a liquid crystal display device using a polymer and a liquid crystal, the glass transition point (Tg) of the polymer and the phase transition point (TNI) of the liquid crystal satisfy the requirement of −20 ° C. ≦ (Tg−TNI) ≦ 20 ° C. The translucent state can be formed by controlling the cooling rate from the liquid crystal droplet to reduce the size of the liquid crystal droplet, and the display state at the time of compatibility can be maintained as it is.

[Brief description of the drawings]

FIGS. 1A and 1B are schematic diagrams showing a state change of a polymer-dispersed liquid crystal layer when it is not heated and when it is heated, where FIG. 1A shows a non-heated state and FIG. 1B shows a heated state.

FIG. 2 is a characteristic diagram showing a change in a refractive index with respect to a temperature of a polymer-dispersed liquid crystal layer.

FIGS. 3A and 3B are schematic diagrams showing a liquid crystal display system using thermal phase separation according to the present invention, wherein FIG. 3A shows a non-heated state (opaque opaque state), and FIG. 3B shows a heated state (transparent). (C) shows a semi-transparent state when a sudden cooling is performed while controlling the temperature from a heating state to a non-heating state.

FIG. 4 is a schematic sectional view of an example of the liquid crystal display device of the present invention.

FIG. 5 is a diagram illustrating a glass transition point (T _g ) of a polymer and a phase transition point (T _NI ) of a liquid crystal in a liquid crystal display medium of the present invention.
3 shows the temperature relationship between the cloudiness and the transparent change temperature (T _tr ) of the polymer-dispersed liquid crystal layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Polymer resin 102 Liquid crystal droplet of a nematic phase 103 Liquid crystal droplet of an isotropic phase 301 Polymer resin 302 Ultrafine liquid crystal droplet of a nematic phase 303 Liquid crystal molecules compatible with a polymer by heating 400 Liquid crystal display device 401 Base material 402 Polymer dispersion Type liquid crystal layer 403 background layer 404 heating element 405 temperature control device 406 current supply device 407 temperature sensor 408 controller

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) G09G 3/18 G09G 3/18 3/20 641 3/20 641Z 3/36 3/36 (72) Inventor Keiko Kurata 1-88, Ushitora, Ichiro, Ibaraki-shi, Osaka (72) Inventor Yasuji Koji 1-88, Ushitora 1-chome, Ibaraki-shi, Osaka F-term (reference) 2H088 EA01 GA10 HA29 JA22 MA02 2H089 HA04 QA16 RA16 TA19 2H093 NA72 NA75 NC47 NC57 NC76 NC77 NC80 ND04 ND39 NE10 NF11 NF21 NG01 5C006 AB05 AF51 AF52 AF54 AF62 AF78 BA15 BD02 EA03 FA19 FA54 5C080 AA03 BB01 JJ01 DD05

Claims (12)

[Claims] 1. A liquid crystal display material in which liquid crystals are dispersed in a polymer in a state of being compatible or phase separated, wherein the liquid crystals are compatible with the polymer at a high temperature, and the liquid crystal undergoes phase separation with the polymer at a low temperature. The reflectance of the display material cooled from the compatible state at a rate of 10 ° C./sec: A, and 4 ° C. /
A liquid crystal display material characterized in that the display material cooled at a speed of seconds has a reflectance: B contrast ratio: B / A of 2 or more. 2. The liquid crystal display according to claim 1, wherein the liquid crystal dispersed in the polymer has an average particle diameter of less than 1 μm when cooled at a rate of 5 ° C./sec or more from the compatible state. material. 3. The liquid crystal has an anisotropic-isotropic phase transition temperature (T _NI ) and a glass transition point (T _g ) of a polymer of −20.
3. The liquid crystal display material according to claim 1, wherein the temperature satisfies a range of: C ≦ (T _g −T _NI ) ≦ 20 ° C. 4. 4. The liquid crystal has a birefringence of 0.20 to 0.1.
4. The liquid crystal display material according to claim 1, wherein a main component is a cyanobiphenyl-based or cyano-terphenyl-based nematic liquid crystal having 35 or less. 5. A liquid crystal display medium using a polymer / liquid crystal composite film in which the liquid crystal is compatible with the polymer at a temperature higher than the display change temperature and the polymer and the liquid crystal reversibly thermally phase-separate at a temperature lower than the display change temperature. 3. The liquid crystal display method according to claim 1, wherein the display information is retained by controlling a cooling rate from the compatible state to maintain the polymer / liquid crystal composite film in a translucent state. 6. The liquid crystal display method according to claim 5, wherein the temperature is lowered at a rate of 5 ° C./sec or more from the compatible state. 7. The liquid crystal dispersed in a polymer matrix when controlling the cooling rate from the compatible state to maintain the liquid crystal in a translucent state has an average particle size of less than 1 μm. The liquid crystal display method according to claim 5. 8. The liquid crystal display medium, wherein the liquid crystal anisotropic phase-isotropic phase transition temperature (T _NI ) and the glass transition point (T _g ) of the polymer are −20 ° C. ≦ (T _g −T _NI ). ≤20 ° C
The liquid crystal display method according to any one of claims 5 to 7, wherein a polymer and a liquid crystal satisfying the above range are used. 9. The liquid crystal display medium according to claim 1, wherein the birefringence of the liquid crystal is 0.20 or more and 0.35 or less. Item 10. The liquid crystal display method according to any one of Items 5 to 8. 10. A polymer-dispersed liquid crystal layer comprising a composition of a polymer and a liquid crystal is disposed on a heating element, and the heating element is provided with a temperature control for gradually lowering the temperature of the heating element. A liquid crystal display device to which a device is connected. 11. The temperature control device according to claim 5, wherein the liquid crystal is compatible with the polymer at a temperature equal to or higher than the display change temperature by 5 ° C.
11. The liquid crystal display device according to claim 10, wherein the temperature is reduced at a rate of not less than / sec. 12. The temperature control device, comprising: a temperature sensor for detecting a temperature of the heating element, a controller for generating a control signal based on a detection result of the temperature sensor, and a controller based on a control signal transmitted from the controller. The liquid crystal display device according to claim 10, further comprising a current supply device that supplies a current to the heating element.