JP2015040994A - Manufacturing method of liquid crystal dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of liquid crystal dispersion in which liquid crystal compound particles composed of a liquid crystal compound are dispersed, and with which the particle diameter of the liquid crystal compound particles can be made uniform and the particles can be stably provided with a simple method.SOLUTION: A manufacturing method of liquid crystal dispersion includes a step of arranging a compound liquid including a liquid crystal compound partitioned by an aqueous solution and a porous membrane, and a repeatedly passing step of passing the compound liquid on both surface sides of the porous membrane a plurality of times in a reciprocating manner.

Description

  The present invention relates to a method for producing a liquid crystal dispersion in which liquid crystal compound particles are dispersed in an aqueous solution, and more particularly to a method for producing a liquid crystal dispersion in which liquid crystal compound particles having a predetermined particle diameter are dispersed in an aqueous solution.

  For example, as described in Patent Document 1, in a liquid crystal display element using a composite in which liquid crystal compound particles are dispersed in a polymer, color display is possible without using a polarizing plate or a color filter. Become. That is, since light transmitting elements that can greatly reduce the light intensity of transmitted light can be reduced, brighter display is possible even with the same light source as before. In addition, since it has display memory characteristics and can continue display without a power source, it is expected to be practically used for electronic paper with low power consumption.

  By the way, a composite in which liquid crystal compound particles are dispersed in a polymer is obtained by drying a liquid crystal dispersion in which liquid crystal compound particles are dispersed in an aqueous solution. Such a liquid crystal dispersion is prepared by dispersing liquid crystal compound particles in an aqueous solution to which an emulsifier such as a surfactant or a water-soluble polymer is added, using a high-speed stirrer or an ultrasonic homogenizer. In addition, a method is also known in which a liquid crystal compound is passed through a porous film to form particles and dispersed in an aqueous solution as described above.

  For example, in Patent Document 2, a dispersion medium mainly composed of water containing a protective colloid such as polyvinyl alcohol or a surfactant is allowed to flow along one surface of a membrane having many through holes such as porous glass. Discloses that an oil-in-water emulsion in which liquid crystal compound particles are dispersed can be produced by applying a predetermined pressure with a pump from the other surface of the membrane and press-fitting the liquid crystal compound into the dispersion medium. ing. When the liquid crystal dispersion obtained in this step is applied onto a substrate and dried, a composite in which liquid crystal compound particles are dispersed in a polymer matrix can be formed. It is stated that liquid crystal compound particles having a uniform particle size can be dispersed, and as a result, a liquid crystal display element excellent in display characteristics such as high contrast, low voltage driving and steepness is provided.

  Further, Patent Document 3 discloses a method in which a liquid crystal compound is pressurized to permeate a porous glass film and the liquid crystal compound particles are dispersed in an aqueous polyvinyl alcohol solution. Here too, it is stated that the liquid crystal compound particles can be made more uniform by passing the liquid crystal compound through the porous film and making it into particles than the liquid crystal dispersion liquid dispersed and emulsified by stirring. As an example, a liquid crystal compound that has been transmitted through a porous glass film having an average pore size of 0.32 μm by pressurization has a particle size of about 2.5 μm.

  Furthermore, Patent Document 4 also discloses a method for producing a liquid crystal dispersion using a porous film. Here, a pre-emulsion having a relatively large particle size is first prepared and then passed through a porous film having through holes having an average pore size within a predetermined range to prepare a liquid crystal dispersion. By adopting such a two-stage emulsification process, it is said that poor emulsification can be suppressed and emulsification can be performed at high speed, and the generation of coarse particles can be suppressed.

JP-A-5-80303 JP-A-6-27447 JP-A-6-242420 JP 2010-190946 A

  A liquid crystal display element using a composite in which liquid crystal compound particles are dispersed in a polymer is required to be driven at a low voltage and to have a high electric field response for high-speed display. On the other hand, surfactants and emulsifiers used for dispersion stability of liquid crystal compound particles and predetermined particle size adjustment exert a regulating force on the liquid crystal particles to lower the electric field orientation, and drive voltage in the liquid crystal display element. This is a cause of lowering the electric field response. In addition, power consumption is increased.

  Furthermore, in order to make the particle size of the liquid crystal compound particles more uniform, a high-speed stirrer, an ultrasonic homogenizer, or a porous membrane is appropriately combined, and pre-emulsification is required. It is also pointed out that it is difficult to obtain manufacturing conditions and that stable manufacturing is difficult.

  The present invention has been made in view of the above situation, and an object of the present invention is a method for producing a liquid crystal dispersion in which liquid crystal compound particles are dispersed in an aqueous solution. An object of the present invention is to provide a production method capable of making the particle size uniform and stably providing the particle size by a simple method.

  The production method according to the present invention is a production method of a liquid crystal dispersion in which liquid crystal compound particles are dispersed in an aqueous solution, the compound liquid containing the liquid crystal compound being arranged with the aqueous solution and a porous film being separated, and the compound liquid And a repetitive passing step of reciprocating a plurality of times on both sides of the porous membrane.

  According to this invention, a simple apparatus can be used without using a pipe for connecting a pump or the like, and the liquid crystal compound has a uniform particle size without excessive use of a surfactant or an emulsifier. A liquid crystal dispersion in which particles are dispersed can be obtained stably. That is, a liquid crystal display element using a composite obtained from such a liquid crystal dispersion can be driven at a low voltage and has a high electric field response for high-speed display.

  In the above-described invention, the repetitive passing step applies a flow pressure from one surface side of the porous membrane to the other surface side, and then continues from the other surface side of the porous membrane to the one surface side. It is good also as repeating to give flow pressure towards. According to this invention, it is possible to stably obtain a liquid crystal dispersion in which liquid crystal compound particles having a uniform particle size are dispersed without excessive use of a surfactant or an emulsifier, while being a simple apparatus. .

  In the above-described invention, the repeated passage step may be performed while heating the compound liquid and the aqueous solution. The compound liquid may include a liquid crystal compound that is in a crystalline phase at room temperature. According to this invention, it is possible to simplify a liquid pressure dispersion in which liquid crystal compound particles having a uniform particle diameter are dispersed without excessive use of a surfactant or an emulsifier with a simple apparatus that can simplify a mechanism for applying a flow pressure. Can be obtained.

  In the above-described invention, the porous film may have a target particle diameter of the liquid crystal compound particles as an average pore diameter. According to this invention, it is possible to stably obtain a liquid crystal dispersion in which liquid crystal compound particles having a uniform particle size are dispersed without excessive use of a surfactant or an emulsifier, while being a simple apparatus. .

  In the above-described invention, the aqueous solution may be water. According to this invention, a liquid crystal dispersion in which liquid crystal compound particles having a uniform particle diameter are dispersed can be stably obtained without using a surfactant or an emulsifier. That is, a liquid crystal display element using a composite obtained from such a liquid crystal dispersion can be driven at a low voltage and has a high electric field response for high-speed display.

FIG. 2 shows a device according to the invention. FIG. 3 shows the operation of the device according to the invention. FIG. 3 shows the operation of the device according to the invention. It is a figure which shows dispersion | distribution of a liquid crystal compound. It is a figure which shows the polarization of a liquid crystal compound. It is a structural formula of the liquid crystal compound used for the test. It is a microscope picture of a liquid crystal dispersion. It is a microscope picture of a liquid crystal dispersion. It is a microscope picture of a liquid crystal dispersion. It is a microscope picture of a liquid crystal dispersion. It is a microscope picture of a liquid crystal dispersion. It is a graph of the zeta potential measurement of a liquid crystal dispersion. It is a microscope picture of a liquid crystal dispersion. It is a microscope picture of a liquid crystal dispersion.

  A method for producing a liquid crystal dispersion as one embodiment according to the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the apparatus 30 used for the manufacturing method of a liquid crystal dispersion has the structure which connected the 1st syringe 31 and the 2nd syringe 32 via the mixing chamber 33 which is an airtight container. The inside of the mixing chamber 33 is divided into a first chamber 33 a and a second chamber 33 b with a porous film 34 interposed therebetween.

  The first syringe 31 includes a syringe body 31a and a piston body 31b that can be fitted to the syringe body 31b, and the tip of the syringe body 31a communicates with the first chamber 33a. It can be introduced into the chamber 33a. Similarly, the second syringe 32 includes a syringe body 32a and a piston body 32b that can be fitted and moved to the syringe body 32a. The tip of the syringe body 32a communicates with the second chamber 33b through the cock 35. That is, the liquid inside the syringe body 32b can be introduced into the second chamber 33b only when the cock 35 is opened.

  The porous film 34 has a through-hole diameter corresponding to a target particle diameter of liquid crystal dispersed particles described later. The porous film 34 is sandwiched between support bodies (not shown) and installed in the mixing chamber 33.

  As shown in FIG. 2A, a liquid crystal compound or a compound liquid composed of this mixture is placed in the second syringe 32 and the cock 35 is closed. Further, a dispersion medium solution such as water or an aqueous solution is put into the first syringe 31. At this time, the dispersion medium solution in the first syringe 31 and the compound liquid in the second syringe 32 are given at a predetermined ratio.

  Next, as shown in FIG. 2B, the cock 35 is opened, the piston body 32 b is pushed into the syringe body 32 a, and the liquid in the second syringe 32 is pushed into the mixing chamber 33. At the same time, the piston body 31 b is pulled out from the syringe body 31 a and the liquid is drawn into the first syringe 31 from the mixing chamber 33. At this time, the liquid moves from the second chamber 33b to the first chamber 33a through the porous film 34. That is, a part of the compound liquid passes through the porous film 34 and moves to the first chamber 33a, and the compound liquid and the dispersion medium solution are mixed.

  Subsequently, as shown in FIG. 2C, this time, the piston body 32 b is pulled out from the syringe body 32 a and the compound liquid and / or the dispersion medium solution in the mixing chamber 33 is drawn into the second syringe 32. At the same time, the piston body 31 b is pushed into the syringe body 31 a to push the liquid in the first syringe 31 into the mixing chamber 33. At this time, the liquid moves from the first chamber 33a to the second chamber 33b via the porous film 34. That is, a part of the compound liquid again passes through the porous film 34 and moves to the second chamber 33b, and the compound liquid and the dispersion medium solution are further mixed.

  2B and 2C is repeated, the liquid in the mixing chamber 33, particularly the compound liquid, moves between the first chamber 33a and the second chamber 33b through the porous film 34. Is repeated.

  Specifically, as shown in FIG. 3, a compound liquid is continuously passed on both sides of the porous film 34 to form a liquid crystal compound (or a mixture, hereinafter referred to as “liquid crystal compound”). A monomolecular dispersion in which the particles 36 are dispersed can be obtained. As shown in FIG. 3A, most of the particles 36 are immediately after the start of the repetitive operation of the first syringe 31 and the second syringe 32 (hereinafter simply referred to as “reciprocating operation”) as described above. Are coarse particles.

  As shown in FIG. 3 (b), when the reciprocating operation is repeated about 10 times, the coarse particles 36 are split, the particle size is reduced, and the number of particles is increased.

  As shown in FIG. 3C, when the reciprocating operation is further repeated 20 times or more, a liquid crystal dispersion of monodispersed particles composed of particles 36 having a particle diameter substantially the same as the through-hole diameter of the porous film 34 is obtained.

  In the reciprocating operation, the mixing chamber 33 and the like may be appropriately heated by a heating device. When the compound liquid is composed of a thermotropic liquid crystal that is a crystal phase at room temperature, the liquid crystal phase or the isotropic phase is adjusted by such heating.

  By the way, a liquid crystal compound in water when a compound liquid composed of a liquid crystal compound is reciprocated a plurality of times on both sides of the porous film 34 together with water will be described.

  FIG. 4 schematically shows the intermolecular interaction (formation of hydrogen bonds) at the interface between the liquid crystal particles 36 and the water 37. In particular, at such an interface, the polar group 36 c of the liquid crystal molecule 36 a faces the interface between the liquid crystal particle 36 and the water 37 and forms a hydrogen bond 38 with the water molecule 37 a. As a result, the interface between the liquid crystal particles 36 and the water 37 is stabilized, and the liquid crystal particles 36 are dispersed and stabilized. Here, as shown in FIG. 5, the polar group 39 has a polarization 40 of a cyano group 39a, a fluoro group 39b, and the like, so that the above-described hydrogen bond can be formed.

  As described above, in this example, a crystalline phase is heated at room temperature to form a liquid crystal phase or an isotropic phase by heating, or a mixture composed of a liquid crystal compound in which at least one component is a crystalline phase, In this method, a thermotropic liquid crystal compound that forms a liquid crystal phase at room temperature and a mixture containing them as a main component are dispersed in water or an aqueous solution. The liquid crystal compound includes a liquid crystal compound or a mixture of particles having a uniform particle diameter in a simple one-step process such that the liquid crystal compound is continuously reciprocated through a porous film having a through-hole diameter corresponding to a target particle diameter. A liquid crystal dispersion can be produced. Regardless of whether an emulsifier is added or not, a liquid crystal dispersion in which a liquid crystal compound or mixture and water or an aqueous solution are adjusted at an arbitrary ratio can be obtained.

  Next, some test results of the liquid crystal dispersion will be described with reference to FIG.

<Test 1>
A preparation test of a liquid crystal dispersion in which particles of a liquid crystal compound that is a liquid crystal phase at room temperature are dispersed will be described.

  Compound 1 (5CB) shown in FIG. 6A was put in 0.05 ml of the second syringe 32 of the apparatus 30, and 0.95 ml of water was put in the first syringe 31, and these were heated to 33 ° C. In addition, the product name: Nuclepore Track-Etch Membrane made by Whatman having a through-hole diameter of 10 μm was used for the porous membrane 34. After performing the above-described reciprocating operation 20 times, heating was stopped and the temperature was returned to room temperature. FIG. 7 shows a micrograph of the liquid crystal particles of the liquid crystal dispersion. According to this, a liquid crystal dispersion was obtained in which liquid crystal particles 36 having a particle diameter of about 7 to 10 μm, that is, a liquid crystal particle 36 having almost the same size as the through-hole diameter of the porous film 34 were dispersed without agglomeration.

<Test 2>
A preparation test of a liquid crystal dispersion in which particles of a liquid crystal compound that is a crystalline phase at room temperature are dispersed will be described.

  While adding 0.05 g of compound 4 (F1) shown in FIG. 6 (d) to the second syringe 32, 0.95 g of water was added to the first syringe 31, and these were heated to 63 ° C. Note that the same membrane as that in Test 1 was used as the porous membrane 34. After performing the above-described reciprocating operation 50 times, heating was stopped and the temperature was returned to room temperature. FIG. 8 shows a photomicrograph of the liquid crystal particles of the liquid crystal dispersion. According to this, a liquid crystal dispersion liquid was obtained in which liquid crystal particles 36 having a particle diameter of about 7 μm, that is, substantially the same size as the through-hole diameter of the porous film 34 were dispersed without aggregation.

<Test 3>
The preparation of a liquid crystal dispersion in which particles of a liquid crystal compound that is a crystalline phase at room temperature and in which a mixture that becomes a liquid crystal phase at room temperature is dispersed will be described.

The liquid crystal compound 2 (7CB) and the liquid crystal compound 3 (5CHB) in the crystalline phase at room temperature shown in FIGS. 6B and 6C were taken at a molar ratio of 1: 2, and 0.05 ml was put in the second syringe 32. . Such compounds are in the liquid crystal phase at room temperature. In addition, 0.95 ml of water was placed in the first syringe 31. As the porous film 34, the same film as in Test Example 1 was used, and the above-described reciprocating operation was performed 20 times. FIG. 9 shows a micrograph of the liquid crystal particles 36 of the liquid crystal dispersion after 6 months. According to this, monodispersity in liquid crystal particles having a particle diameter of about 3 μm was maintained even after 6 months from the production.

<Test 4>
The preparation of a liquid crystal dispersion liquid in which particles of a mixture of liquid crystal compounds having different polar groups and in a liquid crystal phase at room temperature are dispersed will be described.

  The compound 2 (7CB) having a cyano group that is a crystalline phase at room temperature and the compound 4 (F1) having a fluoro group shown in FIGS. 6B and 6C at a molar ratio of 1: 1 are taken, and the second syringe 32 is used. 0.05 ml was placed in the container. In addition, 0.95 ml of water was placed in the first syringe 31. These were warmed to 30 ° C. As the porous membrane 34, the same membrane as in Test Example 1 was used, and after performing the above-described reciprocating operation 20 times, the heating was stopped and the temperature was returned to room temperature. FIG. 10 shows a micrograph of the liquid crystal particles of the liquid crystal dispersion. According to this, a liquid crystal dispersion was obtained in which liquid crystal particles 36 having a particle diameter of about 2 to 7 μm were dispersed without agglomeration.

<Test 5>
The results of tests in which the number of passages through the porous membrane (number of reciprocation operations) in the preparation of the liquid crystal dispersion are described.

  While putting 0.01 ml of compound 1 (5CB) shown in FIG. 6 (a) into the second syringe 32, 0.99ml of water was put into the first syringe 31, and these were heated to 33 ° C. In addition, the same membrane as the test 1 was used for the porous membrane 34, and the above-described reciprocation operation was performed 1, 3, and 5 times, respectively, and heating was stopped and returned to room temperature. FIG. 11 shows a photomicrograph of the liquid crystal particles of the liquid crystal dispersion. According to this, when the number of reciprocating operations was 5 or more, coarse particles disappeared, and a monodispersed particle dispersion having a uniform particle size was obtained.

<Test 6>
The dispersion stability of the liquid crystal particles obtained by the production method according to the present invention is very high, and as described above, the liquid crystal particles obtained in Example 3 maintain the monodispersity even after 6 months from the production. . Then, next, the result of the zeta potential measurement of liquid crystal particles will be described.

In Test 3 described above, the zeta potential was measured while changing the concentration of the dispersion medium salt (NaCl). The result is shown in FIG. Here, the zeta potential corresponds to the surface potential of the liquid crystal particles dispersed in water, and the larger the absolute value, the higher the dispersion stability. According to FIG. 12, the zeta potential was −55 ± 5 mV (pH 5.8, 10 ⁻⁵ M NaCl). This is, for example, more than -50 mV (NANOLETTERS, Vol. 6, No. 10, 2006, pp. 22243-2248) at zeta potential, pH 5.8 of liquid crystal particles prepared using polystyrene sulfonic acid as an emulsifier. large. That is, the dispersion stability of such liquid crystal particles is high.

<Test 7>
The electric field response test results of the liquid crystal particles obtained by the production method according to the present invention will be described.

  Using the dispersion obtained in Test 1, an alternating electric field having a frequency of 1 kHz was applied thereto, and the appearance of the formation of a continuous array of liquid crystal particles 36 was observed. The resulting micrographs are shown in FIGS.

  The tandem array is formed by inducing a dipole by causing polarization at the liquid crystal compound / water interface by application of an electric field. In this case, at 28.6 Vrms / cm, the liquid crystal particles begin to respond sensitively to the electric field, and at 42.4 Vrms / cm, a string array 36 'is formed as shown in FIG.

  In Test 1, a liquid crystal dispersion produced using sodium dodecyl sulfate (SDS, 3.28 mM) as an emulsifier was also subjected to observation of liquid crystal particles 36 by applying an alternating electric field having a frequency of 1 kHz. The resulting micrograph is shown in FIG. In this case, a continuous arrangement of liquid crystal particles was not formed at 42.4 Vrms / cm. That is, compared with FIG. 13, in the present invention that can produce a liquid crystal dispersion without using an emulsifier, by using no emulsifier, it is possible to respond with a lower electric field. Reduction of power consumption can be expected.

  As mentioned above, although the Example by this invention and the modification based on this were demonstrated, this invention is not necessarily limited to this, A person skilled in the art will deviate from the main point of this invention, or the attached claim. Various alternative embodiments and modifications could be found without doing so.

31 First Syringe 32 Second Syringe 33 Mixing Chamber 34 Porous Film 35 Cock 36 Liquid Crystal Particles

Claims (6)

A method for producing a liquid crystal dispersion in which liquid crystal compound particles are dispersed in an aqueous solution,
A liquid crystal dispersion comprising: disposing a compound liquid containing a liquid crystal compound across the aqueous solution and a porous film; and repeatedly passing the compound liquid a plurality of times on both sides of the porous film. Liquid manufacturing method.   In the repeated passage step, a flow pressure is applied from one surface side of the porous membrane to the other surface side, and then the flow pressure is applied from the other surface side of the porous membrane to the one surface side. The method for producing a liquid crystal dispersion liquid according to claim 1, wherein the step of applying a liquid crystal is repeated.   The method for producing a liquid crystal dispersion according to claim 1, wherein the repeated passage step is performed while heating the compound liquid and the aqueous solution.   The method for producing a liquid crystal dispersion according to claim 3, wherein the compound liquid contains a liquid crystal compound that is in a crystalline phase at room temperature.   The method for producing a liquid crystal dispersion according to claim 1, wherein the porous film has a target particle diameter of the liquid crystal compound particles as an average pore diameter.   The method for producing a liquid crystal dispersion liquid according to claim 1, wherein the aqueous solution is water.

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