KR20100065552A - Method of forming microcapsule containing dispersion medium of liquid crystal, the microcapsule formed thereby, and an electronic paper comprising the same - Google Patents

Abstract

The present invention relates to a method for producing a microcapsule comprising a liquid crystal dispersion medium, a microcapsule prepared thereby, and an electronic paper comprising the same. According to this method, a dispersed liquid is prepared by dispersing charged pigment fine particles in a dispersion medium containing liquid crystal, and a microcapsules containing this dispersion as a core material are prepared. Since the liquid crystal has a higher dielectric constant? And anisotropy than oil, the response time of the electronic paper can be increased.

Description

Method of forming microcapsule containing dispersion medium of liquid crystal, the microcapsule formed thereby, and an electronic paper comprising the same}

The present invention relates to a method for producing a microcapsule comprising a liquid crystal dispersion medium, a microcapsule prepared thereby, and an electronic paper comprising the same.

The present invention is derived from the research conducted as part of the IT source technology development project of the Ministry of Knowledge Economy and the Ministry of Information and Communication Research and Development. [Task management number: 2008-F-024-01, Task name: Mobile flexible input / output platform]

Electronic paper is a display that contains the advantages of paper to the fullest, and is attracting much attention as a next-generation reflective display that satisfies the low power consumption for long-term use with visibility and flexibility comparable to printing on paper. Electronic paper can minimize power consumption by using bistability, which basically preserves the original image for a long time even when the voltage is removed. Among the electronic paper technologies exhibiting these characteristics, electrophoretic displays have been studied for the longest time since 1970. The development of new displays has been in progress since the 1970s, but until 1997, the stability of particles was solved by introducing microcapsules, which led to the advancement of electrophoretic display-type electronic paper.

An electrophoretic display is a display in which a charged particle moves up and down by electrophoresis and outputs an image when an electric field is applied to a solution and particles of contrasting colors. For example, if you want to print an image with white and black colors, you can disperse differently charged white and black particles in oil and apply an electric field in a specific direction. The weak point of the initial electrophoretic display was that as the particles dispersed in the oil repeatedly applied the electric field, the particles aggregated to reduce the resolution of the image, and ultimately, the aggregation size of the particles increased to eliminate the image change. In order to solve this drawback, a technique has been proposed to provide spatial stability by microencapsulating an electron ink in which electrophoretic particles are dispersed in oil to a size smaller than a critical size at which aggregation occurs. The encapsulated electron ink has a narrow gap between the electrodes, greatly improves stability, shows high bi-stability, excellent contrast ratio, reflectance and low driving voltage. However, the conventional electronic ink microcapsule electronic paper having the above advantages, since the oil is used as a medium, the response speed is slow compared to the electronic paper of other methods, there is a disadvantage that can not implement a video.

Accordingly, an object of the present invention is to provide a method of manufacturing microcapsules required to implement an electronic paper having a fast response speed.

Another object of the present invention is to provide a microcapsule necessary for implementing an electronic paper having a fast response speed.

Another object of the present invention is to provide an electronic paper having a fast response speed.

Method for producing a microcapsules according to the present invention for achieving the above object is, by dispersing the charged pigment fine particles in a dispersion medium containing a liquid crystal to prepare a dispersion; Emulsifying the dispersion in an aqueous solution to form an emulsion; And preparing a microcapsule by putting a wall forming material in the emulsion.

The dispersion medium may further include a dielectric oil.

Dispersing the charged pigment fine particles in the dispersion medium containing the liquid crystal to prepare a dispersion may include adding a dispersion stabilizer, the dispersion stabilizer may be a nonionic surfactant or a polymeric material.

The preparation of the microcapsules by adding the wall forming material to the emulsion may include an in-situ method or a coaservation method.

The liquid crystal is preferably a nematic liquid crystal or a smectic liquid crystal.

The microcapsules according to the present invention for achieving the above another object includes a dispersion in which the charged pigment fine particles are dispersed in a dispersion medium containing a liquid crystal as a core material.

Electronic paper according to the present invention for achieving the another object is the upper substrate; Lower substrate; A common transparent electrode on a lower surface of the upper substrate; A plurality of pixel electrodes arranged on the lower substrate and separated from each other; And a dispersion liquid interposed between the common transparent electrode and the pixel electrode and having a charged pigment fine particle dispersed in a dispersion medium including a liquid crystal as a core material.

According to the method for producing a microcapsule according to an embodiment of the present invention, a dispersed liquid is prepared by dispersing charged pigment fine particles in a dispersion medium containing liquid crystal, and a microcapsules containing the dispersion as a core material are prepared. Since the liquid crystal has a higher permittivity (ε) than the oil, the response time can be faster. This can be explained by the following correlations 1 and 2.

Specifically, by using the fact that when the electrophoretic particles flowing in the dielectric fluid are in a steady state, the resistance of the fluid (Viscous drag force) and the electrophoretic force applied to the electrophoretic particles are equal, The correlation 1 can be obtained.

Correlation 1

는 유전성 유체에서 유동하는 전기영동입자의 전기영동 이동도(electrophoretic mobility, [m²/Vs]),

는 전기영동 입자의 속도 ,

는 인가된 전기장의 세기 [V/m] ,

은 유전성 유체의 유전율,

는 전기영동입자의 제타 전위 (Zeta potential, [V]),

는 분산계의 점성계수 [kg/m·s]이다. In correlation 1,

Is the electrophoretic mobility (m ² / Vs) of the electrophoretic particles flowing in the dielectric fluid,

Is the speed of electrophoretic particles,

Is the strength of the applied electric field [V / m],

Is the permittivity of the dielectric fluid,

Is the zeta potential (V) of the electrophoretic particles,

Is the viscosity coefficient [kg / m · s] of the dispersion system.

)로 나눈 것이며 여기에 상관식 1을 대입하면 다음의 상관식 2를 얻을 수 있다. On the other hand, the response time (operating time, t _switch ) of the electrophoretic particles is the distance (h) the flow of the electrophoretic particles to the speed of the electrophoretic particles (

), And by substituting Correlation 1, we get the following Correlation 2.

Correlation 2

)이 커질수록, 응답시간(operating time, t_switch)은 작아진다. Therefore, according to correlation 2, the dielectric constant of the dielectric fluid (

), The smaller the operating time (t _switch ).

In addition, according to the method for manufacturing a microcapsule according to an embodiment of the present invention, a nematic liquid crystal or a smectic liquid crystal is used. Nematic liquid crystals and smectic liquid crystals have anisotropic properties that line up in one direction when a voltage is applied. As a result, when a voltage is applied between the upper and lower plates, the liquid crystals are lined up to form a passage up and down between the liquid crystals, and the charged pigment fine particles move through the passages, thereby allowing the pigment fine particles to move more quickly. There is a quick response.

Applying the microcapsules prepared in this way to the electronic paper, it is possible to increase the response speed of the electronic paper, and also to implement a video. In addition, passive operation of electronic paper is possible due to the threshold voltage characteristic of the liquid crystal, thereby lowering the production cost of electronic paper, thereby increasing the price competitiveness of the electronic paper.

In addition, by microencapsulating a dispersion in which pigment particles are dispersed in a liquid crystal, it is possible to prevent aggregation of pigment particles and to prevent the movement of pigment particles in an undesired direction, thereby realizing better image quality, and forming a barrier between adjacent pixels. The parasitic field may be further blocked. In addition, microencapsulation can increase processability and process convenience.

Hereinafter, the present invention will be described in more detail. However, the following embodiments are provided to those skilled in the art to fully understand the present invention, and may be modified in various forms, and the scope of the present invention is limited to the embodiments described below. It doesn't happen.

According to the manufacturing method of the microcapsules according to the present embodiment, (1) dispersing charged pigment fine particles in a dispersion medium containing liquid crystal to prepare a dispersion, (2) forming an emulsion by emulsifying the dispersion in an aqueous solution, and (3) And preparing a microcapsule by putting a wall forming material in the emulsion. This will be described in detail.

1) dispersing the charged pigment fine particles in a dispersion medium containing a liquid crystal to prepare a dispersion liquid.

In this step, the nematic liquid crystal or smectic liquid crystal is used as the dispersion medium, and the charged pigment fine particles are dispersed to prepare a dispersion liquid. A dielectric oil having affinity with the liquid crystal may be further added to the dispersion medium for viscosity control. In addition, a dispersion stabilizer may be further added to improve dispersion stability, and a nonionic surfactant or polymer materials may be used as the dispersion stabilizer. It is preferable that the value of the difference ( _Δε ) of the dielectric constant of the dispersion medium including the liquid crystal, specifically, the dielectric constant ( _ε│ ) in the direction parallel to the electric field direction and the dielectric constant (ε _┴ ) in the direction perpendicular to the electric field direction is 5 or more. . For example, the difference value Δε may be 5 to 22. Dispersion can be carried out using, for example, an ultrasonic disperser. As the pigment fine particles, inorganic particles such as titanium dioxide (TiO ₂ , white), carbon black, or crosslinked polymer particles, or composite particles of inorganic particles and polymer particles may be used. The surface of the pigment fine particles may be modified to have a high zeta potential. The pigment fine particles may be added in various ranges up to 1 to 30% of the volume of the dispersion medium depending on the color. One or more pigment fine particles may be added. In this step, the color of the dispersion medium may be adjusted by dissolving a dye in the dispersion medium itself including the liquid crystal.

② emulsifying the dispersion in an aqueous solution to form an emulsion.

In this step, an aqueous solution is first prepared. In the preparation of microcapsules by coacervation, the aqueous solution is for example gelatin, acacia gum, carrageenan, carboxymethylcellulose, hydrolyzed styrene anhydride copolymers, casein, albumin, methyl vinyl ether co-male At least one selected from the group consisting of acid anhydrides, and cellulose phthalates. In the case of preparing the microcapsules in an in-situ method, the aqueous solution may include, for example, melamine or urea. After dissolving the selected ones of the above in water to prepare an aqueous solution, the dispersion prepared in step ① is slowly poured into the aqueous solution and stirred to form an emulsion.

③ preparing microcapsules by putting the wall-forming material in the emulsion.

After the emulsion is prepared, the temperature, pH and the like of the emulsion are adjusted, and aldehydes such as formaldehyde and glutaric aldehyde are added as a crosslinking agent or a curing agent. As a result, the wall material of the microcapsules may be formed to manufacture the microcapsules.

Microcapsules prepared according to one embodiment of the invention may be depicted as in FIG. 1. Referring to FIG. 1, the microcapsules 10 include a core material including a dispersion 5 in which pigment particles 1a and 1b are dispersed in a wall material 7 and a dispersion medium 3 containing a liquid crystal therein. . The wall material 7 may be a natural polymer such as gelatin, gum arabic, sodium alginate, semisynthetic polymer such as carboxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, nylon, polyurethane, polyester, epoxy, melamine-formalin, or the like. It can be made of synthetic polymers and the like. The dispersion medium 3 may further include at least one of a dielectric oil and a dispersion stabilizer. The liquid crystal may be a nematic or smectic liquid crystal. As the pigment fine particles 1a and 1b, inorganic particles or crosslinked polymer particles or composite particles of inorganic particles and polymer particles may be used.

2 is a view showing the movement of the pigment fine particles in the microcapsules according to an embodiment of the present invention. When an electric field is formed by applying a voltage to predetermined regions of the upper and lower portions of the microcapsules 10 of FIG. 1, the nematic or smectic liquid crystals 3 are arranged side by side, and a passage is formed between the liquid crystal arrays. Through this passage, the pigment fine particles 1 are moved up and down, thereby increasing the response speed. In addition, as described above through Correlation 1 and Correlation 2, since the dielectric constant ε of the liquid crystal is larger than that of the oil, the response time t _switch can be shortened by using the liquid crystal.

Such microcapsules can be applied to electronic paper as in FIG. 3. 3 is a cross-sectional view of an electronic paper according to an embodiment of the present invention.

Referring to FIG. 3, in the electronic paper 100 according to the present embodiment, a plurality of microcapsules 10 is disposed between the upper substrate 20 and the lower substrate 22. A common transparent electrode 30 such as ITO may be disposed on a lower surface of the upper substrate 20, and pixel electrodes 32 may be disposed on an upper surface of the lower substrate 22. At least the upper substrate 20 is transparent, and the upper substrate 20 and the lower substrate 22 may be a glass substrate or a flexible plastic substrate. Since the electronic paper 100 according to the present embodiment includes the microcapsules 10 including the dispersion 5 in which the pigment fine particles 1a and 1b are dispersed in the liquid crystal 3 as a core material, the response It's fast, so you can make a video. In addition, a passive driving system may be applied using a threshold voltage at which liquid crystal molecules start alignment, thereby lowering the production cost of electronic paper. Although not shown in FIG. 3, the electronic paper 100 may further include an alignment layer.

Experimental Example 1

1) Dispersion Preparation

A blue liquid-doped liquid crystal was prepared by dissolving an oil blue N dye in 10 ml E7 (Merck Co.), a nematic liquid crystal, in a 20 ml vial to give 2% of the volume of the liquid crystal (E7). 1.2 g of titanium dioxide (TiO ₂ , R-706) was added to the liquid crystal thus prepared. This mixture was then sonicated in an ultrasonic disperser for 1 hour to form a dispersion.

2) Aqueous Solution Preparation and Emulsion Formation

10 g of Acacia gum was dissolved in 100.0 g of water with stirring for 30 minutes in a 60 ° C. hot water bath. The resulting mixed aqueous solution was centrifuged to remove the precipitate. A 200 ml double jacket reactor was then prepared and 16.2 g of purified acacia aqueous solution was poured into the reactor, and then the temperature of the reactor was heated to 40 ° C. When the temperature reaches 40 ° C., 90 ml of water is poured into the reactor, and then 1.62 g of gelatin (300 Bloom, Type A, Aldrich) is slowly added to form no lumps while stirring the 6 blade paddle stirrer at 100 rpm. The solution was prepared by stirring for 30 minutes to dissolve the gelatin.

The stirring speed of the reactor was set at 200 rpm, the aqueous solution was placed in the reactor, and the dispersion was slowly poured into the aqueous solution through the burette over about 1 minute. The resulting liquid crystal / water O / W emulsion was emulsified for 10 minutes.

3) Microcapsule Preparation

To the emulsion was slowly added 100 g of water previously heated to 40 ° C. 10% citric acid solution was then added to reduce the pH of the emulsion to 4.4 and cooled to 8 ° C. When the temperature of the solution reached 8 ° C., 2.12 ml of glutaric aldehyde solution (Aldrich) was added to crosslink the microcapsule wall and the solution was stirred for 60 more minutes. After one hour, the set temperature of the reactor was released, and the microcapsule slurry was stirred at room temperature for 24 hours. The resulting microcapsules were then aged in a beaker and then aged for another 24 hours to obtain microcapsules. 4 is an optical microscope (600 times) photograph of the electrophoretic liquid crystal dispersion microcapsules in which titanium dioxide is thus dispersed. Referring to Figure 4, it can be seen that the microcapsules having an effective diameter of approximately 70 ~ 75μm size is formed.

4) electric paper manufacturing

An upper substrate having an ITO formed thereon and a lower substrate having pixel electrodes formed thereon were prepared. The microcapsules and the binder were mixed and the microcapsules were applied to the lower substrate by a roll-to-roll process. Then, the upper substrate was adhered to the microcapsules and compressed to prepare electronic paper. Surface photographs of the electronic paper when + 10V and -10V are respectively applied to the pixel electrode are shown in FIGS. 5A and 5B, respectively. Referring to FIGS. 5A and 5B, when a positive voltage is applied, white titanium dioxide all rises to the surface of the microcapsule, and the surface of the electronic paper has a light blue color close to white. On the contrary, when a negative voltage is applied, Titanium sank to the underside of the microcapsules so that the surface of the electronic paper became blue due to the blue doped liquid crystal. In this case, the response speed was about 30ms.

Experimental Example 2

10 ml of the liquid crystal-oil mixture was prepared by mixing 5 ml of a hydrocarbon dielectric oil (Isopar-G) with 5 ml of the E7 liquid crystal. Thereafter, an internal phase dispersion was prepared in the same manner as in Experimental Example 1, and the microencapsulation process was performed in the same procedure.

1 is a cross-sectional view of a microcapsule according to an embodiment of the present invention.

2 is a view showing the movement of the pigment fine particles in the microcapsules according to an embodiment of the present invention.

3 is a cross-sectional view of an electronic paper according to an embodiment of the present invention.

4 is a photograph of a microcapsule prepared according to an experimental example of the present invention.

Figure 5a is a photograph showing the result of applying + 10V to the electronic paper prepared according to an experimental example of the present invention.

Figure 5b is a photograph showing the result of applying -10V to the electronic paper prepared according to an experimental example of the present invention.

Claims (10)

Preparing a dispersion solution by dispersing charged pigment fine particles in a dispersion medium including a liquid crystal; Emulsifying the dispersion in an aqueous solution to form an emulsion; And Method of producing a microcapsule comprising the step of preparing a microcapsule by putting the wall-forming material in the emulsion. The method of claim 1, The dispersion medium is a method for producing a microcapsule, characterized in that it further comprises a dielectric oil (dielectric oil). The method of claim 1, Dispersing the charged pigment fine particles in the dispersion medium containing the liquid crystal to prepare a dispersion includes adding a dispersion stabilizer, the dispersion stabilizer is a non-ionic surfactant or a polymer material Manufacturing method. The method of claim 1, Wherein the liquid crystal is a nematic liquid crystal or a smectic liquid crystal. A microcapsule comprising a dispersion in which pigment fine particles charged in a dispersion medium containing liquid crystal is dispersed. The method of claim 5, Wherein the liquid crystal is a nematic liquid crystal or a smectic liquid crystal. The method of claim 5, The dispersion medium is a microcapsule, characterized in that it further comprises a dielectric oil (dielectric oil). An upper substrate; A lower substrate facing the upper substrate; A common transparent electrode on a lower surface of the upper substrate; A plurality of pixel electrodes arranged on the lower substrate and separated from each other; And An electronic paper comprising a plurality of microcapsules interposed between the common transparent electrode and the pixel electrode, wherein the charged pigment fine particles include a dispersion liquid dispersed in a dispersion medium including a liquid crystal as a core material. The method of claim 8, And said liquid crystal is a nematic liquid crystal or a smectic liquid crystal. The method of claim 8, The dispersion paper further comprises a dielectric oil (dielectric oil).

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