JP2006326501A - Hollow microcapsule and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a hollow microcapsule capable of producing a hollow microcapsule having a small particle diameter in good controllability, and the hollow microcapsule produced according to the method. <P>SOLUTION: The method for producing a hollow microcapsule comprises the steps of: mixing a dispersed phase including a volatile solvent as a core material, and a monomer mixture having a vinyl group containing 1,1-dichloroethylene, an acrylic acid monomer and acrylonitrile or methacrylonitrile as a material for forming a protection film with a continuous phase to form a dispersion liquid, and then forming a microcapsule containing the volatile solvent in the protection film by a polymerization reaction in the dispersion liquid; and vaporizing the volatile solvent to form a hollow microcapsule containing a gas in the protection film during or after forming the microcapsule, wherein the monomer mixture contains 30 to 50% by mass of 1,1-dichloroethylene, and an amount of the acrylic acid monomer to be added is larger than an amount of acrylonitrile or methacrylonitrile to be added. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hollow microcapsule and a method for producing the same.

  The microcapsule is a functional polymer fine particle containing a core substance having various functions. In recent years, the needs for microcapsules in the medical, food, and industrial fields have increased, and various attempts have been made to further enhance the functions of microcapsules. Active development of various functional polymer fine particles has been actively conducted. It has been broken.

  Conventionally, for example, a thermally expandable microcapsule described in Patent Document 1 is known as a hollow microcapsule produced by suspension polymerization. A thermally expandable microcapsule is a microcapsule containing a low boiling point organic solvent as a core material and a low boiling point organic solvent in a protective film made of a thermoplastic resin obtained by polymerizing a vinyl group-containing monomer as a protective film forming material. It is a capsule.

  When this thermally expandable microcapsule is heated, when the resin film of the microcapsule is softened, the low-boiling organic solvent that is the core material is vaporized and expanded, and the resin film is thinly stretched to form a hollow microcapsule having a large particle size. A capsule is formed.

Since such hollow microcapsules are heated to expand the gas and the film extends, the film thickness is reduced compared to the capsule after film formation by polymerization, the gas barrier property is lowered, and the core material gas is not expanded. May leak out of the capsule. If it does so, a microcapsule will be crushed and a hollow microcapsule cannot be obtained. Therefore, as a monomer used for the protective film forming substance of the thermally expandable microcapsule, a substance capable of forming a protective film having gas barrier properties has been required so far.
However, the thermally expandable microcapsule usually expands several tens of times, and the particle size before thermal expansion needs to be about 10 to 15 μm. I do not get.

  As a method for producing a thermally expandable microcapsule having a small particle size, a method using a compound having a hydrophilic group and a long-chain hydrocarbon group (see, for example, Patent Document 2), a low-boiling volatile swelling agent and a surfactant A method for polymerizing a monomer in the presence of (see, for example, Patent Document 3) is known.

  However, these methods expand small particles having a particle size of about 10 μm or less before polymerization several tens of times. The particle size changes greatly before and after expansion, and the control of the particle size is extremely high. There is a problem that it is difficult.

In addition, in order to expand, when a substance that easily becomes liquid with a small amount of pressure, such as butane and isobutane, is present in a gas at normal temperature and pressure, a sealed container is used during the reaction. Since it must be used, there has been a problem that the cost of the apparatus becomes high.
Japanese Patent Publication No.42-286534 Japanese Patent Laid-Open No. 5-309262 JP 2003-220329 A

  The present invention is made under the circumstances as described above, and provides a method for producing a hollow microcapsule capable of producing a hollow microcapsule having a small particle size with good controllability and a hollow microcapsule produced thereby. For the purpose.

  As a result of repeated studies on the substance for forming a protective film for hollow microcapsules, the present inventors have obtained a protective film having an appropriate gas permeability when a monomer mixture having a vinyl group having a predetermined composition is used. Further, it has been found that even when the volatile solvent as the core material is vaporized, the particle size of the microcapsules does not change greatly, and the hollow microcapsules can be obtained without being crushed. The present invention has been made based on such findings.

  That is, the first aspect of the present invention is a monomer mixture having a vinyl group containing a volatile solvent as a core substance and 1,1-dichloroethylene, an acrylic acid-based monomer, and acrylonitrile or methacrylonitrile as a protective film forming substance. Forming a dispersion by mixing a dispersed phase containing a continuous phase with a continuous phase, and forming a microcapsule containing a volatile solvent in the protective film by a polymerization reaction in the dispersion, and during or forming the microcapsule The method further comprises the step of vaporizing the volatile solvent to form hollow microcapsules containing gas in the protective film, wherein the monomer mixture contains 30 to 50% by mass of 1,1-dichloroethylene, Hollow microcapsule characterized in that the amount of acid monomer is greater than the amount of acrylonitrile or methacrylonitrile. To provide a method of manufacturing.

In the method for producing the hollow microcapsules, the polymerization reaction can be suspension assembly or emulsion polymerization.
The acrylic acid-based monomer is desirably present in an amount of 20 to 40% by mass in the monomer mixture having a vinyl group. As the acrylic monomer, one selected from the group consisting of acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, and styrene can be used.

  As the volatile solvent, pentane, hexane, or cyclohexane can be used. The volatile solvent is desirably 5 to 50 parts by mass with respect to 100 parts by mass of the protective film forming substance.

The dispersion used for the polymerization reaction can contain an emulsion stabilizer selected from the group consisting of hydroxymethylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, and colloidal silica.
The second aspect of the present invention provides a hollow microcapsule produced by the method as described above.

  According to the present invention, since the protective film formed using the monomer mixture having a vinyl group having a predetermined composition has gas permeability, the volatile solvent contained in the protective film is vaporized to form a gas. In addition, excessive expansion of the microcapsules is suppressed, so that the particle size of the microcapsules can be easily controlled, and microcapsules having a desired particle size can be obtained.

The best mode for carrying out the invention will be described below.
A method for producing hollow microcapsules according to an embodiment of the present invention includes a continuous phase comprising a volatile solvent as a core substance and a dispersed phase containing a monomer mixture having a vinyl group having a predetermined composition as a protective film-forming substance. Mixing to form a dispersion liquid, forming a microcapsule containing a volatile solvent in the protective film by a polymerization reaction in the dispersion liquid, vaporizing the volatile solvent, and forming a hollow microcapsule containing a gas in the protective film To form.

  In such a method for producing hollow microcapsules, a monomer mixture having a vinyl group containing 1,1-dichloroethylene, an acrylic acid-based monomer, and acrylonitrile or methacrylonitrile is used as the protective film-forming substance. In this monomer mixture, the blending amount of 1,1-dichloroethylene is 30 to 50% by mass, and the blending amount of the acrylic acid monomer needs to be larger than the blending amount of acrylonitrile or methacrylonitrile.

  By using a monomer mixture having a vinyl group having such a composition as a protective film-forming substance, a protective film having an appropriate gas permeability can be obtained by a polymerization reaction at room temperature and normal pressure, and a good hollow microcapsule can be obtained. Can be formed.

  In this case, when the blending amount of 1,1-dichloroethylene in the monomer mixture is less than 30% by mass, the gas inside the capsule expands due to heating, and the protective film forming substance easily expands, and exceeds 50% by mass. Then, the protective film-forming substance becomes soft, and the hollow microcapsules are easily crushed. Further, when the blending amount of the acrylic monomer in the monomer mixture is less than the blending amount of acrylonitrile or methacrylonitrile, the gas inside the capsule expands due to heating, and the protective film forming substance is easily expanded.

  As acrylic monomers, acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, acrylic Examples include 2-methoxyethyl acid and 2-methoxybutyl acrylate.

The core material is preferably a water-insoluble organic solvent that does not dissolve the polymer when the protective film-forming material is polymerized to form a polymer (solid). In particular, it is desirable to use an aliphatic organic solvent that does not dissolve the polymer and has good miscibility with the monomer. Moreover, in order to evaporate and expand | swell and form a hollow microcapsule, it is desirable to have a low boiling point.
Considering the above, it is preferable to use, for example, pentane, hexane, cyclohexane, cyclopentane, etc. as the core substance.

  When the liquid component of the core substance is 5 to 50 parts by mass when the protective film-forming substance is 100 parts by mass, good hollow microcapsules can be obtained. If the amount is less than 5 parts by mass, the liquid component volatilizes during the polymerization reaction of the protective film-forming substance, and it is difficult to form a capsule. On the other hand, if the amount exceeds 50 parts by mass, it is difficult to hold the liquid component.

  A dispersion liquid is obtained by gradually adding a dispersed phase containing a volatile solvent as a core substance and a monomer mixture as a protective film-forming substance to the continuous phase and dispersing at high speed. Water can be used as the continuous phase.

  By subjecting such a dispersion to a polymerization reaction by suspension polymerization or polymerization reaction, a microcapsule slurry containing a volatile solvent in the protective film is obtained. As the polymerization reaction, it is desirable to use suspension polymerization in which the particle size of the microcapsules can be easily controlled to 0.1 to 50 μm.

  The suspension polymerization can be carried out by reacting in the presence of a dispersant at a predetermined temperature, for example, 40 to 80 ° C., with stirring for a predetermined time, for example, 6 to 24 hours. What is necessary is just to use what can be used for normal radical polymerization as a polymerization initiator.

  In order to maintain a stable dispersion, i.e. suspension or emulsion, during the reaction, it is desirable to use an emulsion stabilizer that can be used for both suspension polymerization and emulsion polymerization. As the emulsion stabilizer, for example, a cellulose-based water-soluble polymer such as hydroxymethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, colloidal silica or the like as an inorganic substance can be used.

  During the reaction, the volatile solvent in the protective film is vaporized and the vaporized volatile solvent is replaced with air, so that a hollow microcapsule containing air in the protective film is obtained. Alternatively, the microcapsule slurry may be once washed to separate the microcapsule and water, and then dried to vaporize the volatile solvent in the protective film. The drying conditions for vaporizing the volatile solvent are not particularly limited, but it is desirable to heat and dry at an appropriate temperature and time in consideration of the temperature characteristics of the protective film and the volatility of the volatile solvent. Such temperature and time are, for example, 60 to 120 ° C. and 1 to 24 hours.

  When the volatile solvent in the protective film evaporates, the protective film expands, but the formed protective film has gas permeability, so the vaporized gas permeates the protective film and exceeds a predetermined size. There is no expansion. Therefore, the particle size of the microcapsule does not change greatly before and after expansion, and the particle size of the microcapsule can be easily controlled.

  Examples of the present invention will be described below.

Examples The components of the composition shown in Table 1 below were mixed to form a dispersed phase and a continuous phase. Next, the dispersed phase and the continuous phase were mixed, and four types of emulsions (Examples 1 to 4) were formed using a high-speed stirring emulsifier such as a homogenizer.

  Next, the emulsion was added to a four-necked flask equipped with a stirrer, a thermometer, and a reflux condenser, and the inside of the apparatus was purged with nitrogen. While stirring, the reaction temperature was heated to 60 ° C. and the reaction was allowed to proceed for 16 hours.

  After the reaction, washing and lyophilization were carried out to obtain powder, and four kinds of fine particles were obtained.

  When the particle size of the obtained fine particles was measured with LA-920 (Laser diffraction / scattering type particle size distribution meter, manufactured by Horiba, Ltd.), the median diameter was 6.1 μm (Example 1), 5.4 μm ( Example 2), 5.2 μm (Example 3), and 6.0 μm (Example 4).

When the appearance and cross section were observed with a microscope and SEM, it was confirmed that all the fine particles were hollow microcapsules.

* 1: Parroyl IPP (Nippon Yushi Co., Ltd.)
* 2: PVP K-30 (polyvinylpyrrolidone, manufactured by Wako Pure Chemical Industries, Ltd.)
Comparative Example Each component of the composition shown in Table 2 below was mixed to form a dispersed phase and a continuous phase, and three types of fine particles were obtained in the same procedure as in the example.

  When the particle size of the obtained fine particles was measured with LA-920 (Laser diffraction / scattering type particle size distribution meter, manufactured by Horiba, Ltd.), the median diameter was 4.6 μm (Comparative Example 1), 5.3 μm ( Comparative Example 2) was 5.4 μm (Comparative Example 3).

When the appearance and the cross section were observed with a microscope and an SEM, the fine particles of Comparative Examples 1 and 2 did not maintain a spherical shape because the particles were crushed. In the fine particles of Comparative Example 3, it was observed that the liquid contained inside the dried particles, and the microcapsules contained the liquid in the protective film.

* 1: Parroyl IPP (Nippon Yushi Co., Ltd. product)
* 2: PVP K-30 (polyvinylpyrrolidone manufactured by Wako Pure Chemical Industries, Ltd.)
From the results shown in Table 1 and Table 2, in Examples 1 to 4, 1,1-dichloroethylene is 30 to 50% by mass with respect to the total monomer amount, and the blending amount of the acrylic monomer is larger than that of acrylonitrile. Therefore, good hollow microcapsules are obtained by the polymerization reaction under normal temperature and normal pressure.

  On the other hand, in Comparative Example 1, the blending amount of acrylonitrile is larger than the blending amount of the acrylic acid monomer, and in Comparative Example 2, the blending amount of acrylonitrile is larger than the blending amount of the acrylic acid monomer. Since 1-dichloroethylene exceeds 50% by mass with respect to the total monomer amount, no spherical hollow microcapsules are obtained. In Comparative Example 3, only the microcapsules containing the liquid in the protective film are obtained because the amount of acrylonitrile is larger than the amount of acrylic acid monomer and 1,1-dichloroethylene is not present.

  In Examples 1 to 4, acrylonitrile is used, but methacrylonitrile may be used instead of acrylonitrile, and methyl acrylate is used as the acrylic monomer. Instead, a monomer having one vinyl group such as styrene may be used.

Claims (8)

A disperse phase containing a volatile solvent as a core substance and 1,1-dichloroethylene as a protective film forming substance, an acrylic acid monomer, and a monomer mixture having a vinyl group containing acrylonitrile or methacrylonitrile is mixed with a continuous phase. Forming a dispersion liquid, forming a microcapsule containing a volatile solvent in the protective film by a polymerization reaction in the dispersion liquid, and evaporating the volatile solvent during or after the formation of the microcapsule, Forming a hollow microcapsule containing a gas in the protective film, wherein the monomer mixture contains 30 to 50% by mass of 1,1-dichloroethylene, and the blending amount of the acrylic monomer is acrylonitrile or methacrylo The manufacturing method of the hollow microcapsule characterized by having more than the compounding quantity of a nitrile.   The method for producing hollow microcapsules according to claim 1, wherein the polymerization reaction is suspension aggregation or emulsion polymerization.   The method for producing hollow microcapsules according to claim 1 or 2, wherein the acrylic monomer is present in an amount of 20 to 40% by mass in a monomer mixture having a vinyl group.   The said acrylic acid type monomer is a manufacturing method of the hollow microcapsule in any one of Claims 1-3 chosen from the group which consists of acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, and styrene.   The method for producing a hollow microcapsule according to claim 1, wherein the volatile solvent is selected from the group consisting of pentane, hexane, and cyclohexane.   The method for producing hollow microcapsules according to any one of claims 1 to 5, wherein the volatile solvent is 5 to 50 parts by mass with respect to 100 parts by mass of the protective film forming substance.   The method for producing hollow microcapsules according to any one of claims 1 to 6, wherein the dispersion contains an emulsion stabilizer selected from the group consisting of hydroxymethylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, and colloidal silica. .   A hollow microcapsule produced by the method according to claim 1.