WO2013055028A1

WO2013055028A1 - Method of manufacturing microcapsule for display

Info

Publication number: WO2013055028A1
Application number: PCT/KR2012/006605
Authority: WO
Inventors: Hyun-Ha Hwang; Seung-Gon Kang
Original assignee: Imagelab Co., Ltd.
Priority date: 2011-10-10
Filing date: 2012-08-20
Publication date: 2013-04-18
Also published as: KR20130038455A

Abstract

The present invention provides a method of manufacturing a microcapsule having a uniform particle size, wherein microcapsules for displays, having a uniform particle size distribution, can be obtained by forming droplets using a porous membrane (membrane emulsification) and then encapsulating the droplets, differently from a conventional method that uses a homogenizer or an ultrasonic apparatus during an emulsification process for manufacturing a microcapsule for displays. The method includes the steps of: introducing a dispersed phase solution including a liquid crystal or electrophoretic material into a continuous phase solution including a surfactant by passing the dispersed phase solution through the pores of a membrane to prepare an oil-in-water emulsion in which droplets are formed; and encapsulating the droplets to form outer walls on the droplets.

Description

[DESCRIPTION]

[Invention Title]

METHOD OF MANUFACTURING MICROCAPSULE FOR DISPLAY

[Technical Field]

<i> The present invention relates to a method of manufacturing a microcapsule, and, more particularly, to a method of manufacturing a microcapsule having a uniform particle size distribution, in which the uniformity of the particle size distribution of the microcapsules used in displays can be improved.

[Background Art]

<2> A microcapsule is a particle having a diameter on the micrometer (/m) scale, and includes a wall material forming a capsule and a core material encapsulated with the^' wal 1_.material . Various kinds of materials may be used as the wall material and the core material. Examples of the core materials may include solvents, plast icizers , coloring materials, colorants, catalysts, adhesives, perfumes, recording materials, fuels, agricultural chemicals, biomaterials, expansion agents, medical supplies, foods, cosmetics, writing materials, building materials, acids, bases, and the like. Examples of the wall materials may include proteins, plant gum, cellulose, polymers, inorganic materials, organic materials, and the like.

<3> Particularly, with the development and spread of displays, microcapsule type displays employing microcapsules as a display element have lately been actively researched and developed. Typical examples of the microcapsule type displays include liquid crystal microcapsule displays using liquid crystal as the core material and electrophoretic microcapsule displays using an electrophoret ic material as the core material.

<4> Among these microcapsule type displays, the liquid crystal microcapsule displays are characterized in that the disturbance of images attributable to warpage or pressure is decreased because the fluidity of the liquid crystal is suppressed, they are suitable for realizing flexible displays, they do not use a polarizing plate, and they do not need a color filter. Therefore, the liquid crystal microcapsule displays have lately attracted considerable attention.

<5> Methods of preparing a microcapsule are largely classified into chemical methods, mechanical methods and physico-chemical methods. The physico-chemical methods include coacervation (phase separation), liquid-in drying, melt-dispersion cooling, spray drying, scattering (applying core material droplets onto the powder of a film), powder mixing (mixing core material particles with fine film particles and then melting the mixture using the heat of friction caused by electrification), interfacial precipitation, and the like.

<6> Among the physico-chemical methods, coacervation (phase separation) is a method of forming a precipitate by changing the solubility of a wall material according to the addition of a nonsolvent or the control of the pH. Particularly, in this method, a homogenizer or an ultrasonic apparatus is generally used during an emulsi f icat ion process for forming droplets.

<7> However, when conventional methods of preparing a microcapsule for displays are used, droplets having a large size difference are formed, and these droplets are directly encapsulated, and thus finally-obtained microcapsules have a nonuniform particle size distribution, too.

<8> When such conventional microcapsules having a large size difference are applied to displays, there is a problem in that a coating layer including microcapsules arranged in the form of a monolayer is not formed, and the coating layer includes microcapsules that are overlapped or laminated with each other at random, so that a large amount of light penetrating a microcapsule layer scatters and thus reduces light transmittance, thereby deteriorating the optical characteristics of displays and requiring a high drive voltage

<9> Meanwhile, Korean Unexamined Patent Application Publication No. 2009-

0061286 (2009.06.16) discloses a method of polymerizing a toner resin having a uniform particles size by passing a dispersed phase including a monomer mixture of a toner resin through a continuous phase including an aqueous dispersion in which a dispersant is dissolved in water to membrane-emulsify the dispersed phase. However, no technology exists yet for the manufacture of a microcapsule for displays in which droplets are formed using membrane emulsif ication and then the droplets are encapsulated.

[Disclosure]

[Technical Problem]

<io> Accordingly, the present invention has been devised to solve the above- mentioned problem, and an object of the present invention is to provide a method of manufacturing a microcapsule having a uniform particle size, wherein microcapsules for displays, having a uniform particle size distribution, can be obtained by forming droplets using a porous membrane (membrane emulsif ication) and then encapsulating the droplets, differently from a conventional method that uses a homogenizer or an ultrasonic apparatus during an emulsi f icat ion process for manufacturing a microcapsule for displays.

[Technical Solution]

<ii> In order to accomplish the above object, an aspect of the present invention provides a method of manufacturing a microcapsule for displays, including the steps of-^' introducing a dispersed phase solution containing a liquid crystal or electrophoret ic material into a continuous phase solution containing a surfactant by passing the dispersed phase solution through the pores of a membrane to prepare an oil-in-water emulsion in which droplets are formed; and encapsulating the droplets to form outer walls on the droplets.

[Advantageous Effects]

<12> According to the present invention, since droplets having a size deviation of 50% or less can be formed, microcapsules for displays, in which the uniformity of the particle size distribution of the microcapsules is remarkably improved compared to conventional microcapsules, can be obtained.

<i3> Further, when the microcapsule obtained by the method of the present invention is used to coat a display film, microcapsule particles adhere closely to each other to the highest degree possible, thus realizing a capsule layer including microcapsules arranged in the form of a monolayer. Therefore, the light transmittance of the capsule layer can be improved because light scattering is reduced, and the drive voltage can be reduced because the thickness of the capsule layer is decreased.

[Description of Drawings]

<i4> The above and other objects, features and other advantages of the present invention will be more clearly understood from the fol lowing detai led description taken in conjunction with the accompanying drawings, in which: <15> FIG. 1 is a flowchart showing a method of manufacturing a microcapsule having a uniform particle size according to the present invention;

<i6> FIG. 2 is a process view showing each process of the method shown in

FIG. 2;

<17> FIG. 3 is a schematic view showing a principle of forming liquid crystal droplets using a membrane according to the present invention',

<18> FIG. 4 is a photograph showing the liquid crystal droplets prepared according to Example 1 of the present invention;

<i9> FIG. 5 is a photograph showing the microcapsules finally manufactured according to Example 1 of the present invention;

<20> FIG. 6 is a photograph showing the conventional liquid crystal droplets prepared according to Comparative Example 1; and

<2i> FIG. 7 is a photograph showing the conventional microcapsules finally manufactured according to Comparative Example 1.

<22> < eference Numeral s>

<23> 10: membrane

<24> 15: membrane pore

<25> 20: dispersed phase solution

<26> 21: droplet

<27> 22: capsule outer wal 1

<28> 30: continuous phase solution

[Best Mode]

<29> The present invention is technically characterized in that a microcapsule for displays, having a uniform particle size distribution, can be manufactured using membrane emulsi f icat ion instead of a conventional method that uses a homogenizer or an ultrasonic apparatus when conducting an emulsi f icat ion process to manufacture microcapsules for displays.

<30> FIG. 1 is a flowchart showing a method of manufacturing a microcapsule having a uniform particle size according to the present invention, FIG. 2 is a process view showing each process of the method shown in FIG. 2, and FIG. 3 is a schematic view showing a principle of forming liquid crystal droplets using a membrane according to the present invention.

<3]> The method of manufacturing a microcapsule having a uniform particle size according to the present invention includes the steps of: providing a dispersed phase solution 20 to form a core material of a microcapsule; providing a continuous phase solution 30 to form an emulsion together with the dispersed phase solution 20; forming an oil-in-water emulsion by emulsi f icat ion; and forming a capsule outer wall 22 on a droplet.

<32> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<33> (1) Providing a dispersed phase solution (S10, FIG. 2(a))

<34> A microcapsule includes a core material and a wall material for forming an outer wall of the core material. In the step of providing a dispersed phase solution (S10), a dispersion solution 20 is provided to form the core material of the microcapsule.

<35> Generally, a microcapsule type display employs a liquid crystal microcapsule or an electrophoret ic microcapsule. The microcapsule manufactured by the method of the present invention is also a liquid crystal microcapsule or an electrophoret ic microcapsule. Therefore, in order to manufacture a liquid crystal microcapsule, the dispersed phase solution 20 corresponds to a solution including at least one selected from liquid crystal, a mixture of liquid crystal and dye and a mixture of liquid crystal and a chiral dopant, and, in order to manufacture an electrophoret ic microcapsule, the dispersed phase solution 20 corresponds to a solution including an electrophoret ic material in which negative charge and positive charge are mixed, that is, a charged molecular compound.

<36> In the embodiment of the present invention, the liquid crystal microcapsule is manufactured by doping liquid crystal with dichroic dye. In this case, S-428, M-483, M-412 or the like, manufactured by Mitsui Fine Chemical Co., Ltd., is used as the dichroic dye, and ZLI-1840, ZLI-1565, ZLI- 2806 or the like, manufactured by Merck Ltd., is used as the liquid crystal.

<37>

<38> (2) Providing a continuous phase solution (S20, FIG. 2(a))

<39> In the step of providing a continuous phase solution (S20), a continuous phase solution 30 is provided to form an emulsion together with the above-mentioned dispersed phase solution 20. Since the dispersed phase solution 20 and the continuous phase solution 30 do not mix with each other, it is difficult to form an emulsion. Therefore, in order to disperse the particles of the dispersed phase solution 20 in the continuous phase solution 30 and maintain this state, a solution including a surfactant for reducing interfacial tension and a dispersion stabilizer for stabilizing an emulsion is prepared.

<40> Specifically, the surfactant may be one or more selected from the group consisting of arabic gum, guar gum, karaya gum, carrageenan, albumin, alginate, casein, tragacanth gum, quince seed gum, xanthan gum, dextrin, fatty acid ester, gelatin, pectin, sodium carboxylmethylcel lulose, and carboxyvinyl polymer. They may be used independently or as a mixture.

<4i> The dispersion stabilizer may be one or more selected from the group consisting of ABS (acrylonitri le butadiene styrene), PP (polypropylene), PC (polycarbonate), PPC poly phenylene oxide), PVC (poly vinyl chloride), PET(poly ethylene terephthalate) , and PVA (poly vinyl alcohol). They may be used independently or as a mixture.

<42> Further, the amount of each of the surfactant and dispersion stabilizer included in the continuous phase solution 30 is not particularly limited. It is preferred that each of the surfactant and dispersion stabilizer be included in an amount of 0.5 ~ 15 wt% based on the total amount of the continuous phase solution 30.

<43>

<44> (3) Emulsification (S30, FIG. 2(b))

<45> In the step of emulsification (S30), an oil-in-water emulsion, in which particles of the dispersed phase solution 20 are dispersed in the continuous phase solution 30, is formed by emulsif ication. Here, liquid crystal droplets 21, corresponding to the core material of a microcapsule for displays, are formed by emulsif ication.

<46> Particularly, in the method of manufacturing a microcapsule having a uniform particle size according to the present invention, liquid crystal droplets 21, corresponding to a core material of a microcapsule for displays, are formed in aqueous solution including the above-mentioned synthetic polymer compound or natural polymer compound using a membrane 10, differently from a conventional method that uses a homogenizer or an ultrasonic apparatus during an emulsi f icat ion process. That is, the method of the present invention is technically characterized in that liquid crystal droplets 21 are formed by membrane emulsif ication which is performed using the difference in pressure between the inside and the outside of the membrane 10 having a porous property.

<47> Referring to FIG. 2(b) and FIG. 3, in the process of forming liquid crystal droplets according to the method of manufacturing a microcapsule of the present invention, when the dispersed phase solution 20 including the above-mentioned liquid crystal or electrophoret ic material is pressed by a predetermined amount of pressure, the dispersed phase solution 20 passes through the pores 15 of the membrane 10 to be introduced into the continuous phase solution 30, thereby forming an oil-in-water emulsion in which liquid crystal droplets 21 are dispersed in the continuous phase solution 30.

<48> The membrane 10 of the present invention may be made of at least one

- selected from porous alumina, porous zirconia and shirasu porous glass (SPG).

<49> Further, the pore size of the membrane 10 of the present invention is changed depending on the particle size of a microcapsule to be manufactured. In order to manufacture a liquid crystal microcapsule, it is preferred that a membrane having a pore size of 1 ~ 10 p be used.

<50> Further, the liquid crystal droplets 21 are formed by applying a predetermined amount of pressure to the dispersed phase solution 20 to pass the dispersed phase solution 20 through the pores 15 of the membrane 10. In this case, it preferred that the pressure be 5 ~ 50kPa. When the pressure is less than 5kPa, the dispersed phase solution 20 cannot pass through the pores 15 of the membrane, and when the pressure is more than 50kPa, the membrane 10 can be damaged. Like this, when the dispersed phase solution 20 is passed through the membrane 10 having uniform pores by applying a pressure of 5 ~ 50kPa to the dispersed phase solution 20, the liquid crystal droplets 21 having a uniform particle size are injected into the continuous phase solution 30 and are uniformly dispersed in the continuous phase solution 30.

<5 i> Further, in the emulsif ication, it is preferred that the continuous phase solution 30 be maintained at a temperature of 40 ~ 60^°C and that the emulsif ication be carried out for about 10 hours.

<52> Further, in the emulsi f icat ion, the liquid crystal droplets 21 injected into the continuous phase solution 30 can be uniformly dispersed in the continuous phase solution 30 by stirring the continuous phase solution 30 containing the liquid crystal droplets 21 using a stirrer provided in a tank filled with the continuous phase solution 30. In this case, it is preferred that the stirrer be operated at a rotation speed of 100 ~ 1,000 rpm.

<53>

<54> (4) Encapsulation (S40, FIG. 2(c))

<55> In the step of encapsulation (S40), outer walls 22 of the liquid crystal droplets 21 dispersed in the continuous phase solution 30 are formed. The method of preparing a microcapsule according to the present invention is characterized in that the outer walls 22 of the liquid crystal droplets 21 are formed by complex coascervat ion.

<56> In the process of encapsulating the liquid crystal droplets 21 using complex coacervation, coacervates made of water-soluble polymers (gelatin and arabic rubber) are formed by the adjustment of the pH of an aqueous solution, and then capsule outer walls 22 are formed by the bonding of gelatin and arabic rubber.

<57> According to the method of preparing a microcapsule according to the present invention, the pH of the aqueous solution is adjusted using citric acid or glacial acetic acid. Specifically, citric acid is added to a primary gelatin aqueous solution including 300g of a 10% gelatin aqueous solution and 700 g of pure water to adjust the pH of the primary gelatin aqueous solution to 4.5, and then 200g of a 10% gelatin aqueous solution and 500 g of pure water are slowly mixed with the primary gelatin aqueous solution to form a secondary gelatin aqueous solution, and then citric acid is added to the secondary gelatin aqueous solution to adjust the pH of the secondary gelatin aqueous solution to 4.4, thereby completing complex coacervat ion.

<58> Coacervat ion is a phase separation phenomenon in a colloidal system, and, specifically, is a phenomenon of a colloidal solution being separated into a colloid rich layer and a colloid poor layer by the precipitation or coagulation of colloidal particles. In the present invention, gelatin and arabic gum are electrically charged opposite to each other and coagulate with each other at a pH of about 4.4. This phenomenon is the coacervat ion phenomenon. Like this, when the coacervation phenomenon occurs, gelatin is charged with a positive (+) charge, and arabic gum is charged with a negative (-) charge, so that hydrophilic colloidal particles electrically charged opposite to each other coagulate with each other, thereby forming the outer walls 22 of microcapsules.

<59>

<60> (5) Gelation (S50, FIG. 2(d))

<6i> When the process of encapsulating liquid crystal droplets using coacervation is completed, a gelation process is performed. In the gelation process, the liquid crystal capsules provided with outer walls 22 are slowly cooled to a predetermined temperature, and then rapidly cooled at the predetermined temperature to gelate the outer walls 22 of the liquid crystal capsules .

<62> Further, in the gelation process, the rotation speed of a stirrer may be increased such that liquid crystal capsules are not agglomerated at low temperature by rapid cooling.

<63> According to a preferred embodiment of the present invention, the liquid crystal capsules may be slowly cooled at a cooling rate of about 0.1 °C/min from 60^°C to 20^°C , and then rapidly cooled at a cooling rate of about 0.6 ⁰C/min from 20^°C to.0^°C.

<64>

<65> (6) Curing (S60, FIG. 2(e))

<66> When the gelation process is completed, a process of curing the capsule outer walls 22 is performed. In the curing process, the capsule outer walls 22 are cured by the addition of a curing agent. Here, when glutaraldehyde or formaldehyde is used as the curing gent, the amino group of gelatin is crossl inked with glutaraldehyde or formaldehyde to cure the capsule outer walls 22, thereby manufacturing microcapsules. In a preferred embodiment of the present invention, the curing process was conducted by slowly adding lQg of glutaraldehyde.

<67>

<68> (7) Aging (S70, FIG. 5(f))

<69> When microcapsules 23 are manufactured by the process of curing capsule outer walls, in order to prevent the agglomeration of microcapsules 23 and to age microcapsules 23, a process of adding a binder is performed.

<70> According to a preferred embodiment of the present invention, PVA

(polyvinyl alcohol) is used as the binder, and the amount of the binder (PVA) that is added is the same as the amount of the emulsifying agent used in the continuous phase solution 30.

<7i> For example, when 500g of a 10% arabic gum aqueous solution is used as the continuous phase solution 30, 500g of the binder (PVA) is slowly added, thus preventing the agglomeration of the microcapsules. Subsequently, the mixed solution is stirred for abut 1 hour, left at room temperature to increase the temperature thereof to room temperature, and then aged for abut 24 hours to finally manufacture stable microcapsules for displays.

[Mode for Invention]

<72> Hereinafter, the method of manufacturing a microcapsule having a uniform particle size according to the present invention will be described in more detail with reference to the following Examples, and the microcapsules for displays, manufactured by the method of the present invention, will be explained and compared with the microcapsules for displays, manufactured by a conventional method.

<73>

<74> [Example 1]'

<75> In Example 1, liquid crystal microcapsules were manufactured under the condition that liquid crystal was doped with a dichroic dye. Here, one of S^~ 428, M-483 and M-412 (manufactured by Mitsui Fine Chemical Co. Ltd.) was used as the dichroic dye, and one of ZLI-1840, ZLI-1565 and ZLI-2806 (manufactured by Merck Ltd.) was used as the liquid crystal.

<76> lOOg of liquid crystal was used in the dispersed phase solution, and

500g of a 10% arabic gum aqueous solution was used as the continuous phase solution.

<77> Liquid crystal droplets were formed using shirasu porous glass (SPG) having a pore size of 5 ~ 10 p .

<78> In the emulsif ication process, the continuous phase solution was maintained at a temperature of 40 ~ 60^°C , the emulsi f icat ion was carried out for about 10 hours, and the stirrer was operated at a rotation speed of 100 ~ 1,000 rpm, thus allowing the liquid crystals to be uniformly mixed.

<79> In the curing process, lOg of glutar aldehyde was slowly added, thus curing the capsule outer walls 22.

<80>

<8i> [Comparative Example 1]

<82> In Comparative Example 1, liquid crystal droplets were formed using the same dispersed phase solution and continuous phase solution as in Example 1, except that homogenizer was used in the emulsi f icat ion process.

<83> Specifically, liquid crystal obtained by dissolving a dichroic dye in

500g of a 10% arabic gum aqueous solution was emulsified for 10 minutes or more using a homogenizer at a rotation speed of 6,500/7,500/8,500 while dropping the liquid crystal drop by drop.

<84> ^' · ^'

<85> FIG. 4 is a photograph showing the liquid crystal droplets prepared according to Example 1 of the present invention, FIG. 5 is a photograph showing the microcapsules finally manufactured according to Example 1 of the present invention, FIG. 6 is a photograph showing the conventional liquid crystal droplets prepared according to Comparative Example 1, and FIG. 7 is a photograph showing the conventional microcapsules finally manufactured according to Comparative Example 1.

<86> First, as shown in FIG. 6, it can be seen that liquid crystal droplets having a nonuniform size deviation of 50 ~ 100% are formed when a conventional method of manufacturing microcapsules for displays is used.

<87> However, as shown in FIG. 4, it can be seen that liquid crystal droplets having a uniform size deviation are formed when the method of manufacturing a microcapsule for displays according to the present invention is used. Specifically, the liquid crystal droplets formed by the membrane emulsif i cat ion of the present invention have a size deviation of 50% or less, and are formed into an oil-in-water emulsion.

<88> Further, as shown in FIG. 7, it can be seen that, according to the conventional method of manufacturing a microcapsule for displays, liquid crystal droplets having a very large size deviation are formed, and that the particle size distribution of the microcapsules finally obtained by directly encapsulating these liquid crystal droplets is not uniform, either.

<89> However, as shown in FIG. 4, it can be seen that, according to the method of manufacturing a microcapsule for displays of the present invention, microcapsules having a remarkably improved uniform particle size distribution can be manufactured by forming liquid crystal droplets having a size deviation of 50% or less as shown in FIG. 3 and then encapsulating these liquid crystal droplets using complex coacervat ion.

<90> Although the embodiments of the present invention have been disclosed for illustrative purposes, it will be appreciated that the present invention is not limited thereto, and those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention. Accordingly, any and all modifications, variations or equivalent arrangements should be considered to be within the scope of the invention, and the detailed scope of the invention will be disclosed by the accompanying claims.

Claims

[CLAIMS!

[Claim 1]

<92> A method of manufacturing a microcapsule for displays, comprising the steps of:

<93> introducing a dispersed phase solution including a liquid crystal or electrophoret ic material into a continuous phase solution including a surfactant by passing the dispersed phase solution through pores of a membrane to prepare an oil-in-water emulsion in which droplets are formed; and

<94> encapsulating the droplets to form outer walls on the droplets.

[Claim 2]

<95> The method of claim 1, wherein the membrane is made of at least one selected from porous alumina, porous zirconia and shirasu porous glass (SPG).

[Claim 3]

<96> The method of claim 1, wherein the membrane has a pore size of 1 ~ 10

[Claim 4]

<97> The method of claim 1, wherein the dispersed phase solution is passed through the pores of the membrane by applying a pressure of 5 ~ 50kPa to the dispersed phase solution.

[Claim 5]

<98> The method of claim 1, wherein a temperature of the continuous phase solution is 40 ~ 60 ^°C .

[Claim 6]

<99> The method of claim 1, wherein, in the step of encapsulating the droplets, the outer walls of the droplets are formed by complex coacervation.

[Claim 7]

<ioo> The method of claim 6, wherein the complex coacervation is performed by adjusting a pH within a range of 4.0 - 5.0.

[Claim 8]

<ioi> The method of claim 1, further comprising the step of, after the step of encapsulating the droplets^'- slowly cooling the droplets from 60 ^°C to 20 ^°C and then rapidly cooling the droplets from 20 ^°C to 0^°C to gelate the outer wal Is of the droplets .

[Claim 9]

<i02> The method of claim 1, wherein the surfactant is at least one selected from the group consisting of arabic gum, guar gum, karaya gum, carrageenan, albumin, alginate, casein, tragacanth gum, quince seed gum, xanthan gum, dextrin, fatty acid ester, gelatin, pectin, sodium carboxylmethylcel lulose, and carboxyvinyl polymer.

[Claim 10]

<103> The method of claim 1, wherein the continuous phase solution further includes a dispersion stabilizer, and the dispersion stabilizer is at least one selected from the group consisting of ABS (acrylonitri le butadiene styrene), PP (polypropylene), PC (polycarbonate), PP0 (poly phenyl ene oxide), PVC (poly vinyl chloride), PET (poly ethylene terephthalate), and PVA (poly vinyl alcohol).

[Claim 11]

<104> The method of claim 9, wherein the surfactant is included in an amount of 0.5 ~ 15 wt .

[Claim 12]

<i05> The method of claim 1, wherein the liquid crystal is liquid crystal doped with a dichroic dye or liquid crystal mixed with a chiral dopant.