JPH03210536A - Combined film of high-polymer liquid crystal and production thereof - Google Patents

Abstract

PURPOSE:To improve responsiveness by slowly cooling 1st and 2nd transparent conductive films in a state in which an electric field is applied to the films and turning off the electric field after the temps. thereof passes the lower limit value of the property temp. range of a high-polymer liquid crystal. CONSTITUTION:The high-polymer liquid crystal is mixed with acetone and after the mixture is dissolved, a low-polymer liquid crystal is mixed with this soln. and the mixture is dissolved. This soln. 4 is thinly spread on the electrode of the 1st transparent conductive film 7 and the solvent is evaporated to form a film 9 consisting of the high-polymer liquid crystal and the low-polymer liquid crystal. The electrode of the 2nd transparent conductive film 10 is brought into tight contact with the surface of this film. The 1st and 2nd transparent conductive films 7, 10 which are brought into tight contact with each other are heated to transfer the low-polymer liquid crystal 12 and the high-polymer liquid crystal 11 to an isotropic liquid. The electric field is applied thereto while the films are kept heating. After the temp. rises at the lower limit value of the property temp. range of the high-polymer liquid crystal 11, this magnetic field is turned off and further, the films are slowly cooled down to ordinary temp. The combined film of the high-polymer liquid crystals which allows the low- voltage driving and have the good responsiveness is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a polymer/liquid crystal composite film in which liquid crystal particles are dispersed in a polymer material film, and a method for manufacturing the same.

``Prior Art'' Polymer/liquid crystal composite films are used in light control films for liquid crystal display devices and the like. The manufacturing method is to dissolve liquid crystals and polymers in a common solvent, spread the solution on the electrode side of a transparent conductive film so that the film thickness is constant, and then evaporate the solvent to increase the A molecular/liquid crystal composite film was obtained. A flexible liquid crystal film is obtained by attaching another transparent conductive film to the composite film from the electrode side.

Another manufacturing method is to mix and dissolve a polymer and liquid crystal in a mixed solvent of a good solvent and a poor solvent, spread this solution on the water surface, dissolve the good solvent in water, evaporate the poor solvent, and then dissolve the polymer and liquid crystal on the water surface. A polymer/liquid crystal composite film has been obtained by taking up this method. This polymer/liquid crystal composite film is sandwiched between two transparent conductive films with the electrode surfaces inside to form a flexible liquid crystal film.

“Problem to be solved by the invention J In a polymer/liquid crystal composite film, the conductivity of the polymer is σ7,
If the electrical conductivity of the liquid crystal is σLC%, the voltage applied to the polymer is El, and the voltage applied to the liquid crystal is ELC, then the following formula holds true at low frequencies below 200 Hz (University of Japan, Polymer Proceedings, ν
o1.38, Nα3.1989).

ELCσP EF σLC Therefore, the electric field applied to the liquid crystal is determined by the ratio of the conductivity of the polymer and the liquid crystal, and the conductivity of the liquid crystal is σ5. When σ is constant, the larger the conductivity σ of the polymer is, the higher it becomes, and low voltage driving at low frequency becomes possible.

In addition, at frequencies above 200Hz, the dielectric constant IP of the polymer
-, dielectric constant of liquid crystal ε4. Then, ELCεP ζ EP ttc holds true (Ibid. Proceedings).

Therefore, the electric field applied to the liquid crystal is determined by the ratio of the dielectric constants of the polymer and the liquid crystal.If the dielectric constant of the liquid crystal is constant, the higher the dielectric constant of the polymer, the larger the electric field, allowing low voltage driving at frequencies of 200Hz or higher. 9 However, the polymer materials used in conventional polymer/liquid crystal composite films are insulating materials with low electrical conductivity, for example, resistivity (reciprocal of electrical conductivity) is 1.
Therefore, at low frequencies below 200 Hz, the voltage applied to the liquid crystal is small, making low-voltage driving impossible, and the change in transmittance is small when the electric field is turned on and off, making it possible to obtain a large contrast ratio. There was a drawback that it could not be used because it could not be used. Further, the same situation was observed at frequencies of 200 Hz or higher.

Further, the conventional polymer/liquid crystal composite film has a relatively thick film thickness of about 5 to 10 μm, so a large driving voltage is required, and the film thickness is uneven, resulting in uneven transmittance. Furthermore, because the arrangement of the polymers was irregular, the liquid crystal molecules did not move easily when the electric field was turned on and off, resulting in poor responsiveness.

An object of the present invention is to provide a polymer/liquid crystal composite film that can be driven at low voltage and has good responsiveness, and a method for manufacturing the same.

"Means for Solving the Problems" The method for producing a polymer/liquid crystal composite film of the present invention includes a step of dissolving a polymer liquid crystal and a low molecular liquid crystal in a common solvent, and dissolving the solution in a first transparent conductive film. a step of forming a film consisting of a polymer liquid crystal and a low molecular liquid crystal by spreading the transparent film on the electrode, and evaporating the solvent, and a step of closely adhering the electrode of the second transparent conductive film onto the film. , heating the closely attached first and second transparent conductive films to transfer the low molecular liquid crystal and polymer liquid crystal to an isotropic liquid; A step of heating the first and second transparent conductive films transferred to the liquid and applying an electric or magnetic field to the liquid, and slowing down the first and second transparent conductive films while applying the electric field or magnetic field. After the temperature has passed the lower limit of the temperature range of the physical properties of the polymer liquid crystal, the electric field or magnetic field is turned off, and further cooling is performed gradually to room temperature.

The polymer/liquid crystal composite film of the present invention is manufactured by the above manufacturing method.

EXAMPLES The polymeric liquid crystal used in this invention is usually poly(4-methoxybiphenyl), which is a liquid crystal bonded to a polymer such as acrylic acid or methacrylic acid.

4'-hexamethylene ether) acrylic ester (
These polymeric liquid crystals are: The temperature range of physical properties (temperature range in which the physical properties of a nematic liquid crystal can be maintained) is higher than that of ordinary liquid crystals (commonly called low-molecular liquid crystals for polymer liquid crystals); 13
6°C, and 101 to 121°C for the polymer liquid crystal shown in FIG. 2B.

On the other hand, it is desirable that the low-molecular liquid crystal used in this invention has a physical property temperature range lower than that of the polymer liquid crystal used, and the liquid crystal must not decompose at this temperature, which is heated when aligning the polymer liquid crystal. As such a liquid crystal, a cyanobiphenyl liquid crystal, for example, E-44 manufactured by Merck & Co., USA, is used. Its physical properties temperature range is 0 to 10
It is 0°C.

Both polymer liquid crystals and low molecular liquid crystals become isotropic liquids above the physical temperature range, and become solids below the physical temperature range.

FIG. 3 shows the state changes with respect to temperature of the low-molecular liquid crystal (E-44) and the polymer liquid crystal (FIG. 2B).

Now, the method for manufacturing the polymer/liquid crystal composite film of this invention will be explained step by step.

(1) Adjust the weight ratio of polymer liquid crystal and low molecular liquid crystal to 4:6, and add a solvent common to both liquid crystals, such as acetone, to the weight ratio of acetone to (polymer liquid crystal and low molecular liquid crystal). Prepare each so that the ratio is 6:4.

First, polymer liquid crystal is mixed with acetone and dissolved, and then
A low-molecular liquid crystal is mixed into the solution and dissolved. For mixing and dissolving these, a stirring device as shown in FIG. 1A is used. B, a glass container 3 with stirring blades 2 is set on the magnetic stirrer 1, and the magnetic stirrer 1 is placed on top of the magnetic stirrer 1.
The stirring blades 2 are rotationally driven by the rotation of the magnet within the stirrer.

In this way, the polymer liquid crystal and the low molecular liquid crystal are dissolved in a common solvent, and a mixed solution 4 is completed in the glass container 3.

(2) As shown in FIG. 1B, a tool is used in which a tape 6 of a predetermined thickness is attached to the opposing edges of a rectangular glass plate 5. A first transparent conductive film 7 is placed on the glass plate 5,
Place it with the electrode side facing up, and tape the end with cellophane 6a.
A zero-order glass dropper 6b fixed to the glass plate 5 with etc.
etc., take in a predetermined amount of the mixed solution 4 made in step (1), and
onto the electrode surface of the transparent conductive film 7, quickly move the glass round rod 8 onto the tape, spread the mixed solution 4 widely and uniformly, and leave it in this state to evaporate the solvent (first step). Figure 1C).

(3) The electrode surface of the second transparent conductive film 10 is brought into close contact with the liquid crystal film 10 in (2) (Fig. 1D). Since the liquid crystal film 9 is slightly wet, the glass round rod 8 is 2. It can be easily brought into close contact with the transparent conductive film 10 by simply moving it onto the film.

(4) The liquid crystal element obtained by sandwiching the liquid crystal film 9 from (3) with the first and second transparent conductive films 7.10 is placed in a constant temperature bath and heated to a temperature above the physical property temperature range of the polymer liquid crystal. Convert molecular liquid crystals and low molecular liquid crystals to isotropic liquids. At this time, the particle size of the low-molecular liquid crystal is determined by the difference in viscosity and surface tension between the high-molecular liquid crystal and the low-molecular liquid crystal.
The grain shape is spherical with the same size.

(5) In the state of (4), a frequency of 0.5 to 2 kHz is applied between each electrode of the first and second transparent conductive films 7 and lO.
When an electric field with a minimum peak value of several kV/cm or more and a maximum peak value of 100 kV/cm or less is applied and the temperature is gradually lowered, the polymer liquid crystal 11 enters its physical temperature range, and its molecules arranged parallel to the direction of the electric field. Furthermore, the molecular orientation direction of the low-molecular liquid crystal 12 also coincides with the direction of the electric field (FIG. 1E).

The arrows in the figure indicate the orientation direction of molecules and are called directors. The temperature is further lowered, and when it falls below the physical property temperature range of polymer liquid crystal, the electric field is turned off and the temperature is returned to room temperature.
As a result, the polymer liquid crystal molecules are frozen in a state in which they are aligned parallel to the electric field (FIG. 1F), and the polymer/liquid crystal composite film 20 of the present invention is obtained. ((5) Line) As shown in FIG. 4, when light is incident on one surface of the composite film 2o and an electric field is applied, the molecular orientation directions of the polymer liquid crystal 11 and the low molecular liquid crystal 12 are both in the direction of the electric field. The light passes through the liquid crystal and exits from the other side. When the electric field is turned off, the molecular orientation direction of the polymer liquid crystal 11 does not change;
The molecular orientation direction of the low-molecular liquid crystal 12 is random along the spherical surface of the particle, and light is scattered in the liquid crystal, and weaker scattered light is emitted from both surfaces of the composite film 20.

Note that when the composite film 20 is used as a light control film, the magnitude of the applied electric field is appropriately set to change the degree of light control, or the electric field is turned off to block light.

In addition, in the above item (5), it is assumed that an electric field is applied, but even if a magnetic field of about 20 kG is applied instead,
The same effect can be obtained.

"Effects of the Invention" According to the present invention, the molecules of the polymer liquid crystal are always oriented in the thickness direction of the synthetic film, so that when an electric field is applied, the particles of the polymer liquid crystal are oriented in the direction of the polymer liquid crystal. It is in a state where it is easy to move in the direction, and the response speed is improved.

In addition, before the alignment process, the polymeric liquid crystal and the low-molecular liquid crystal are heated until they become isotropic liquids, and due to the difference in viscosity and surface tension of both liquid crystals, the particle shapes of the low-molecular liquid crystals are the same. It is spherical in size and has a shape that allows for easy movement. This also leads to improvement in response speed.

As mentioned above, polymer liquid crystal molecules are always oriented, so the conductivity becomes high at frequencies below 200 Hz, and the dielectric constant becomes high at frequencies above that, so as already mentioned,
Low voltage drive is possible over all frequencies.

In the conventional example, the response speed (the time it takes for the light transmittance to change from 10% to 90%) and the driving voltage required several milliseconds and several tens of V, respectively, but with this invention, the response speed is faster than the conventional example. The voltage is V 1/10, and the driving voltage is approximately IOV, which provides extremely excellent characteristics.

[Brief explanation of drawings]

Fig. 1 is a principle diagram showing an example of the manufacturing method of this invention in the order of manufacturing steps, Fig. 2 is a diagram showing a chemical formula of an example of a polymer liquid crystal used in this invention, and Fig. 3 is a low-molecular liquid crystal E-44. and second
Figure B shows the state change caused by temperature changes with the polymer liquid crystal, and Figure 4 shows the alignment state of liquid crystal molecules when the electric field applied to the polymer/liquid crystal composite film of the present invention is turned on and off. It is a diagram.

Claims (2)

[Claims] (1) A step of dissolving the polymer liquid crystal and the low molecular liquid crystal in a common solvent, spreading the solution thinly on the electrode of the first transparent conductive film, evaporating the solvent, and dissolving the polymer liquid crystal and the low molecular liquid crystal in a common solvent. A step of forming a film made of molecular liquid crystal, a step of closely contacting an electrode of a second transparent conductive film on the film, and a step of heating the first and second transparent conductive films that have been brought into close contact with each other. a step of transferring the low-molecular liquid crystal and the polymer liquid crystal to an isotropic liquid; and keeping the first and second transparent conductive films, to which the low-molecular liquid crystal and the polymer liquid crystal have been transferred to the isotropic liquid, heated. a step of applying an electric field or a magnetic field, and slowly cooling the first and second transparent conductive films while the electric field or magnetic field is applied, until the temperature thereof passes the lower limit of the physical property temperature range of the polymer liquid crystal; A method for producing a polymer/liquid crystal composite film, which comprises the following steps: after that, the electric field or magnetic field is turned off, and the film is slowly cooled to room temperature. (2) A polymer/liquid crystal composite film produced according to claim (1).