WO2010070987A1

WO2010070987A1 - Process for producing hollow microspheres and process for producing porous molded ceramic

Info

Publication number: WO2010070987A1
Application number: PCT/JP2009/068869
Authority: WO
Inventors: 江尻哲男; 佐竹義克
Original assignee: 株式会社クレハ
Priority date: 2008-12-18
Filing date: 2009-11-05
Publication date: 2010-06-24
Also published as: CN102256695B; KR101278410B1; JP5588880B2; KR20110106359A; JPWO2010070987A1; CN102256695A

Abstract

A process for producing hollow microspheres which comprises: a step (1) in which heat-expandable microspheres having a microcapsular structure comprising a shell formed from a thermoplastic resin and, encapsulated therein, a blowing agent capable of gasifying or generating a gas and a solid material having an average particle diameter or average major-axis length smaller than the average particle diameter of the heat-expandable microspheres are dispersed in a liquid dispersion medium to prepare a slurry; and a step (2) in which the heat-expandable microspheres are heated in the slurry to soften and thermally expand the shells thereof, thereby forming hollow microspheres having the solid material adherent to the surface of the softened shells.

Description

Method for producing hollow microsphere and method for producing porous ceramic molded body

The present invention relates to a method for producing hollow microspheres in which solid materials such as fine particles and fine fibers are firmly attached to the outer shell surface. Moreover, this invention relates to the manufacturing method of the porous ceramics molded object used as a porous formation agent of this hollow microsphere.

The thermally expandable microsphere has a microcapsule structure in which a foaming agent capable of gasification or gas generation is enclosed in an outer shell formed of a thermoplastic resin. Thermally expandable microspheres are also referred to as thermally foamable microspheres or thermally expandable microcapsules. When the heat-expandable microsphere is heated to a temperature equal to or higher than the softening point of the thermoplastic resin forming the outer shell, the heat-expandable microsphere is thermally expanded by gasification of the foaming agent itself or pyrolysis gas of the foaming agent. Hollow microspheres, which are hollow body particles, are formed by thermal expansion of the thermally expandable microspheres.

熱 Thermal expansion due to heating of thermally expandable microspheres is generally called heating foaming or foaming. Thermally expandable microspheres form hollow microspheres as independent foam particles after foaming. On the other hand, expandable polystyrene particles impregnated with a liquid foaming agent are filled into a mold and heated and foamed to form a foam molded body having a predetermined shape in which the foam particles are fused and integrated. It is formed and is not a thermally expandable microsphere.

Hollow microspheres are also called plastic balloons or plastic hollow beads. Thermally expandable microspheres can form hollow microspheres with a low specific gravity by thermal expansion. Therefore, the heat-expandable microsphere is added to various base materials such as ink, paint, and plastic for the purpose of weight reduction and designability.

As the application field of thermally expandable microspheres expands and higher performance is required in each application field, the required level for thermally expandable microspheres is also increasing. One of the required properties for the thermally expandable microspheres is that there is little aggregation due to fusion between the foam particles during and after heat foaming, and furthermore, there is almost no aggregation.

Thermally expandable microspheres are not only foamed but are often blended in a foamed state as well as blended with substrates such as inks, paints and plastics. Foam particles (hollow microspheres) in which thermally expandable microspheres are foamed are extremely lightweight. For example, when they are contained in a paint, the object to be coated can be reduced in weight. However, if the foam particles are aggregated, mixing with a substrate such as a paint becomes difficult, and further, the foam particles may be destroyed during the mixing.

As a method for preventing aggregation between the foam particles, a method of covering the outer shell surface of the unexpanded thermally expandable microsphere with solid fine particles such as inorganic fine particles and organic fine particles is conceivable. However, it is extremely difficult to uniformly attach the solid fine particles to the outer shell surface of the thermally expandable microsphere and to strictly control the amount of the solid fine particles. If the solid fine particles cannot be uniformly attached to the outer shell surface of the thermally expandable microsphere, uniform foaming becomes difficult. If the adhesion amount of the solid fine particles is too small, it is not possible to sufficiently prevent the fusion during heating and foaming. If the amount of solid fine particles attached is too large, foaming becomes difficult, and in the worst case, foaming may be impossible.

Since the foam particles (hollow microspheres) of the thermally expandable microsphere are extremely lightweight, it may be difficult to apply to new applications. For example, as disclosed in Japanese Patent Application Laid-Open No. 2007-39333 (Patent Document 1), a porous ceramic molded body is formed by molding a mixture containing a ceramic raw material and a porous forming agent into a molded body having a predetermined shape, Next, the molded body is manufactured by a method of firing. By using thermally expandable microsphere foam particles (hollow microspheres) as a porous forming agent, it is possible to obtain a porous ceramic molded body having a desired porous structure corresponding to the size of the foam particles. it can.

However, the low specific gravity hollow microspheres that are the foam particles and the high specific gravity ceramic raw material that is the inorganic material are too difficult to uniformly disperse because the specific gravity difference is too large. Therefore, when hollow microspheres are used as the porous forming agent, it is difficult to obtain a porous ceramic molded body having a uniform porous structure. The porous ceramic molded body is used for, for example, a diesel particulate filter (DPF) for reducing particulate matter contained in exhaust gas of a diesel engine, but the porous structure is not uniform. And sufficient performance as a filter cannot be demonstrated.

When producing a thermally expandable microsphere by suspension polymerization in an aqueous dispersion medium, if an aqueous dispersion medium containing inorganic fine particles such as colloidal silica as a dispersion stabilizer is used, Inorganic fine particles adhere to the shell surface. However, since the adhesive force between the inorganic fine particles and the thermally expandable microspheres is small, an amount of inorganic fine particles sufficient to prevent the fusion between the foam particles is strongly adhered to the outer shell surface of the thermally expandable microspheres. Is difficult.

When the reaction mixture containing the generated thermally expandable microspheres is filtered and washed in the recovery step after the polymerization is completed, most of the inorganic fine particles used as the dispersion stabilizer fall off. A small amount of inorganic fine particles adhering to the outer shell surface of the recovered heat-expandable microsphere is also easily detached in the subsequent processing step.

When the amount of the dispersion stabilizer such as colloidal silica is increased, the amount of inorganic fine particles attached to the outer shell surface of the thermally expandable microsphere can be increased, and the specific gravity can be increased to some extent. However, this method does not solve the problem of desorption of inorganic fine particles in the cleaning process and the subsequent processing process. In addition, when the amount of inorganic fine particles attached to the outer shell surface of the thermally expandable microsphere is increased by such a method, the average particle size of the obtained thermally expandable microsphere is decreased and the particle size distribution is increased. Occurs.

In order to impart various functions to the hollow microsphere, it is effective to attach solid particles having various functions to the outer shell surface. However, it is a very difficult problem to firmly attach solid fine particles having various functions to the outer shell surface of the hollow microsphere and to control the amount of adhesion within a desired range.

Conventionally, several proposals have been made as a method of attaching solid fine particles to the outer shell surface of a thermally expandable microsphere. Japanese Patent Laid-Open No. 2002-363537 (Patent Document 2) discloses the presence of an organosilicon compound having a reactive group capable of polymerizing a polymerizable mixture containing a polymerizable monomer and a foaming agent in an aqueous dispersion medium. A method for producing thermally expandable microspheres by suspension polymerization below has been proposed. According to the method of Patent Document 2, various solid fine particles such as colloidal silica can be attached to the outer shell surface of the thermally expandable microsphere by the action of the organosilicon compound. This method requires the use of an expensive organosilicon compound, and it is difficult to strongly adhere a large amount of solid fine particles with high specific gravity to the outer shell surface of the foam particles after foaming.

Japanese Patent Application Laid-Open No. 2003-112039 (Patent Document 3), International Publication No. 2005/049698 Pamphlet (Patent Document 4), and Japanese Patent Application Laid-Open No. 2006-213930 (Patent Document 5) disclose thermally expandable microspheres and solid fine particles. And a method for producing thermally expandable microspheres in which solid fine particles are adhered to the surface of the outer shell. However, with a simple mixing method, solid fine particles cannot be firmly attached to the outer shell surface of the thermally expandable microsphere, and the solid fine particles easily fall off in the subsequent processing steps.

Several proposals have also been made for a method of attaching solid fine particles to the outer shell surface of foam particles (hollow microspheres) of thermally expandable microspheres. In JP-A-3-273037 (Patent Document 6), a wet cake of thermally expandable microspheres is mixed with a granular or fibrous solid, dried until the water content is less than 1% by weight, and then heated and foamed. Is disclosed. However, the method disclosed in Patent Document 6 is difficult to suppress aggregation and premature foaming of thermally expandable microspheres in the drying process.

Japanese Patent Laid-Open No. 2001-98079 (Patent Document 7) proposes a method of attaching colloidal calcium carbonate together with a surface treatment agent or a dispersant to the surface of foam particles of thermally expandable microspheres. According to the method disclosed in Patent Document 7, although it is possible to suppress the foam particles from being scattered in the air, it is difficult to firmly attach the solid fine particles to the outer shell surface of the foam particles. is there.

Japanese Patent Application Laid-Open No. 2006-35092 (Patent Document 8) describes a mixture of a thermally expandable microsphere aqueous dispersion and inorganic fine particles, followed by solid-liquid separation to form a cake, or solid-liquid separation followed by drying to obtain a powder. A method has been proposed in which a thermally expandable microsphere is heated and expanded. According to the method disclosed in Patent Document 8, although scattering of the foam particles can be prevented, it is difficult to suppress aggregation and early foaming of the thermally expandable microspheres.

JP-A-2006-137926 (Patent Document 9) discloses drying a hydrous cake of thermally expandable microspheres having an acrylic polymer outer shell obtained by using dispersion stabilizer particles such as colloidal silica. There has been proposed a method for producing hollow microspheres that is heated and expanded. Since the method disclosed in Patent Document 9 does not require a drying step, it is possible to suppress fusion and early foaming between the hollow microspheres and to mix the hollow microspheres with solid fine particles. And solid fine particles can be obtained. However, in order to heat and foam the water-containing cake, it is necessary to heat it under mechanical shearing using a powder mixer, so that the thermally expandable microspheres and hollow microspheres are likely to be fused or damaged. Further, in the method of Patent Document 9, since the dispersion stabilizer particles are attached to the outer shell surface of the thermally expandable microsphere at the time of polymerization, it is difficult to firmly attach other solid fine particles, and the attached dispersion stability. Agent particles are likely to fall off.

JP 2007-39333 A JP 2002-363537 A Japanese Patent Laid-Open No. 2003-112039 International Publication No. 2005/049698 Pamphlet JP 2006-213930 A JP-A-3-273037 JP 2001-98079 A JP 2006-35092 A JP 2006-137926 A

An object of the present invention is that organic or inorganic fine particles, fine fibers, etc. are not required without requiring complicated operations and the use of expensive compounds, and without causing fusion or premature foaming between thermally expandable microspheres. Another object of the present invention is to provide a method for producing hollow microspheres in which the solid material is firmly attached to the outer shell surface.

Another object of the present invention is to provide use of a hollow microsphere as a porous forming agent. More specifically, another object of the present invention is to provide a method for producing a porous ceramic molded body using the hollow microspheres obtained by the above method as a porous forming agent.

As a result of intensive studies to achieve the above-mentioned problems, the present inventors have made a method in which thermally expandable microspheres and a solid material are dispersed in a liquid dispersion medium to form a slurry, and heated steam is blown into the slurry. It was found that when the thermally expandable microspheres were heated and foamed (thermally expanded), the solid material adhered firmly to the outer shell surface softened during the heating and foaming.

中空 Hollow microspheres with various functions can be obtained by selecting the amount and type of solid material. For example, hollow microspheres in which a solid material having a high specific gravity is attached to the outer shell surface can be suitably used as a porous forming agent of a raw material for producing a porous ceramic molded body because the entire particle has a high specific gravity. .

Slurries in which thermally expandable microspheres and solid materials are dispersed were thought to be unsuitable for foaming by heating under high temperature conditions. However, by adopting a method of blowing heated steam, etc. It has been found that the sphere can be heated and foamed, and at that time, a fine solid material can be firmly attached to the softened outer shell surface. The present invention has been completed based on these findings.

According to the present invention, the following steps 1 and 2:
(1) Thermal expansion that has a microcapsule structure in which a foaming agent capable of gasification or gas generation is enclosed in an outer shell formed of a thermoplastic resin, and that thermally expands by heating to form hollow microspheres. And (2) preparing a slurry by dispersing a solid material having an average particle size or an average major axis smaller than the average particle size of the expandable microsphere and the average particle size of the thermally expandable microsphere in a liquid dispersion medium; The thermally expandable microspheres are heated in the slurry to soften the outer shell, and thermally expanded by gasification of the foaming agent or gas generated from the foaming agent, thereby softening the outer shell surface. Forming a hollow microsphere having the solid material attached thereto in step 2;
A method for producing hollow microspheres having a solid material attached to the outer shell surface is provided.

In addition, according to the present invention, the ceramic raw material and the porous forming agent are mixed to prepare a mixture; the step a; the mixture is formed into a predetermined shaped body b; and the shaped body is cured or fired. In the method for producing a porous ceramic formed body comprising the step c), hollow microspheres obtained by the above production method and having a solid material attached to the surface of the outer shell are used as the porous forming agent. A method for producing a porous ceramic molded body is provided.

According to the production method of the present invention, such as fine particles and fine fibers, without requiring complicated operations and the use of expensive compounds, and without causing fusion or early foaming between the thermally expandable microspheres. It is possible to provide hollow microspheres in which a solid material is firmly attached to the outer shell surface.

According to the method of the present invention, since the thermally expandable microspheres that are freely dispersed in the slurry are foamed, fusion between the thermally expandable microspheres during foaming hardly occurs, and hollow microspheres obtained after foaming It is difficult to cause mutual fusion. According to the method of the present invention, since the solid material is adhered to the outer shell surface that softens during heating and foaming, the foam of the thermally expandable microsphere is not inhibited, and the solid material is firmly attached to the softened outer shell surface. Can be attached to. By changing the amount and type of the solid material dispersed in the slurry, the amount and type of the solid material adhered to the outer shell surface can be arbitrarily controlled.

Using high-specific gravity inorganic fine particles as a solid material, and thermally expanding the thermally expandable microspheres while uniformly dispersing each component by stirring the slurry, the high-specific gravity inorganic fine particles firmly adhere to the outer shell surface. Thus, hollow microspheres having a high specific gravity of the entire particle can be obtained. Hollow microspheres with increased specific gravity can be mechanically and uniformly mixed with high specific gravity particles such as ceramic raw materials. Therefore, when a hollow microsphere having a solid material with a high specific gravity attached to the outer shell surface is used as a porous forming agent, a porous ceramic molded body having a uniform porous structure can be produced.

FIG. 1 is an explanatory diagram showing the thermal expansion of the thermally expandable microsphere. FIG. 2 is an explanatory view showing a method for producing hollow microspheres in which a solid material adheres to the outer shell surface of the present invention.

DESCRIPTION OF SYMBOLS 1 Thermally expandable microsphere 2 Outer shell 3 Foaming agent 101 Hollow microsphere 102 Outer shell 103 Hollow 21 Container 22 Liquid dispersion medium 23 Solid material

The thermally expandable microsphere used in the present invention has a microcapsule structure in which a foaming agent capable of gasification or gas generation is enclosed in an outer shell formed of a thermoplastic resin, and is thermally expanded by heating. As long as it is a thermally expandable microsphere that forms a hollow microsphere, it may be obtained by any manufacturing method.

As shown in FIG. 1A, the thermally expandable microsphere 1 has a structure in which a foaming agent 3 is enclosed by an outer shell 2 made of a thermoplastic resin. When the thermally expandable microsphere 1 is heated to a temperature equal to or higher than the softening point of the thermoplastic resin constituting the outer shell 2, as shown in FIG. 1B, the foaming agent 3 is gasified or generated from the foaming agent. A hollow microsphere 101 having a hollow 103 inside the expanded outer shell 102 is obtained by thermal expansion with gas.

Generally, thermally expandable microspheres can be produced by a method in which a polymerizable monomer mixture containing at least a foaming agent and a polymerizable monomer is subjected to suspension polymerization in an aqueous dispersion medium. By suspension polymerization, a polymer (thermoplastic resin) formed by polymerization of a polymerizable monomer forms an outer shell, and a thermally expandable microsphere having a structure in which a foaming agent is enclosed in the outer shell is generated. To do.

As the polymerizable monomer, a radically polymerizable monomer is usually used. Specific examples of the polymerizable monomer include nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile; acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid Carboxyl group-containing monomers such as citraconic acid; acrylic acid such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, isobornyl acrylate, cyclohexyl acrylate, benzyl acrylate, β-carboxy acrylate Ester monomers: methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, isobornyl methacrylate, Methacrylic acid ester monomers such as hexyl methacrylate, benzyl methacrylate, β-carboxy methacrylate; vinylidene chloride; vinyl acetate; styrene monomers such as styrene, α-methylstyrene, chlorostyrene; acrylamide, methacrylamide, etc. Acrylamide monomers; maleimide monomers such as N-phenylmaleimide, N- (2-chlorophenyl) maleimide, N-cyclohexylmaleimide, and N-laurylmaleimide;

The thermally expandable microspheres are preferably those in which the polymer forming the outer shell is a thermoplastic resin and has gas barrier properties. From these viewpoints, vinylidene chloride (co) polymers and (meth) acrylonitrile (co) polymers are preferable, but not limited thereto. The “(co) polymer” means a homopolymer and / or a copolymer. The “(meth) acrylonitrile” means acrylonitrile and / or methacrylonitrile.

As the vinylidene chloride (co) polymer, a (co) polymer obtained by using, as a polymerizable monomer, vinylidene chloride alone or a mixture of vinylidene chloride and a vinyl monomer copolymerizable therewith is used. Can be mentioned. Examples of the monomer copolymerizable with vinylidene chloride include acrylonitrile, methacrylonitrile, methacrylic acid ester, acrylic acid ester, styrene, and vinyl acetate.

The vinylidene chloride (co) polymer is selected from the group consisting of 30 to 100% by weight of vinylidene chloride as a polymerizable monomer, and acrylonitrile, methacrylonitrile, acrylate ester, methacrylate ester, styrene, and vinyl acetate. A (co) polymer obtained using 0 to 70% by mass of the at least one monomer is preferred. If the copolymerization ratio of vinylidene chloride is less than 30% by mass, the gas barrier property becomes too low, which is not preferable.

Examples of the vinylidene chloride (co) polymer include 40 to 80% by mass of vinylidene chloride, 0 to 60% by mass of at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, and acrylates and methacrylates. A copolymer of 0 to 60% by mass of at least one monomer selected from the group consisting of By setting it as the copolymer of such a composition, design of foaming temperature is easy and it is easy to achieve a high foaming ratio.

When solvent resistance and high-temperature foamability are desired, the outer shell is preferably formed from a (meth) acrylonitrile (co) polymer. The (meth) acrylonitrile (co) polymer is obtained by using (meth) acrylonitrile alone or (meth) acrylonitrile and a vinyl monomer copolymerizable therewith as the polymerizable monomer (co). A polymer can be mentioned. Examples of the vinyl monomer copolymerizable with (meth) acrylonitrile include vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, and vinyl acetate.

The (meth) acrylonitrile (co) polymer includes, as a polymerizable monomer, at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, 30 to 100% by mass, vinylidene chloride, and acrylate A (co) polymer obtained by using 0 to 70% by mass of at least one monomer selected from the group consisting of methacrylic acid ester, styrene, and vinyl acetate is preferred. When the copolymerization ratio of (meth) acrylonitrile is less than 30% by mass, the solvent resistance and heat resistance are insufficient.

(Meth) acrylonitrile (co) polymer has a high proportion of (meth) acrylonitrile and a high foaming temperature (co) polymer, a small proportion of (meth) acrylonitrile and a low foaming temperature (co) heavy Can be divided into coalescence. As the (co) polymer having a large proportion of (meth) acrylonitrile used, as a polymerizable monomer, at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, 80 to 100% by mass, and chloride (Co) polymers obtained by using 0 to 20% by mass of at least one monomer selected from the group consisting of vinylidene, acrylic acid ester, methacrylic acid ester, styrene, and vinyl acetate.

The (co) polymer having a small proportion of (meth) acrylonitrile used is at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile as a polymerizable monomer, but not less than 30% by mass and less than 80% by mass. , And at least one monomer selected from the group consisting of vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, and vinyl acetate in excess of 20% by mass and 70% by mass or less. Coalescence is mentioned.

Examples of the (meth) acrylonitrile (co) polymer include at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, 51 to 100% by mass, vinylidene chloride, 0 to 40% by mass, and acrylates and methacrylic esters. Preference is given to (co) polymers obtained using 0 to 48% by weight of at least one monomer selected from the group consisting of acid esters.

When a (co) polymer containing no vinylidene chloride is desired as the outer polymer, at least one monomer 30 selected from the group consisting of acrylonitrile and methacrylonitrile is used as the polymerizable monomer. A (meth) acrylonitrile (co) polymer obtained using ˜100% by mass and at least one monomer selected from the group consisting of acrylic acid ester and methacrylic acid ester is preferred.

Other (co) polymers not containing vinylidene chloride include, as a polymerizable monomer, acrylonitrile 1 to 99% by mass, methacrylonitrile 1 to 99% by mass, and a group consisting of acrylic acid ester and methacrylic acid ester. A copolymer obtained by using 0 to 70% by mass of at least one selected monomer is preferred.

In order to obtain thermally expandable microspheres with particularly excellent processability, foamability, gas barrier properties, and solvent resistance, (meth) acrylonitrile (co) polymer in the outer shell is used as the polymerizable monomer. Copolymer obtained using 20 to 80% by mass of methacrylonitrile, 20 to 80% by mass of methacrylonitrile, and 0 to 20% by mass of at least one monomer selected from the group consisting of acrylic acid ester and methacrylic acid ester It is preferable that

A crosslinkable monomer can be used in combination with the polymerizable monomer in order to improve foaming characteristics, processing characteristics, solvent resistance, and heat resistance. As the crosslinkable monomer, a compound having two or more carbon-carbon double bonds is usually used. Examples of the crosslinkable monomer include divinylbenzene, divinylnaphthalene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di ( (Meth) acrylate, 1,9-nonanediol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, glycerin di (meth) acrylate, dimethylol-tricyclodecane di (meth) acrylate, PEG # 200 di Bifunctional crosslinkable monomers such as (meth) acrylate, PEG # 400 di (meth) acrylate, PEG # 600 di (meth) acrylate; trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, tria Trifunctional crosslinkable monomers such as diisocyanate and triacryl formal; trifunctional or more polyfunctional crosslinks such as pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate and dipentaerythritol hexa (meth) acrylate Monomer, etc. The proportion of the crosslinkable monomer used is preferably 0.05 to 5% by mass, more preferably 0.1 to 3% by mass, based on the total amount of the polymerizable monomer.

As the foaming agent, a substance capable of gasification or gas generation by heating is used. As the foaming agent, a compound that gasifies at a temperature below the softening point of the polymer (thermoplastic resin) forming the outer shell is preferable. As such a foaming agent, a low-boiling organic solvent is suitable. For example, ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, 2,2,4 Hydrocarbons such as trimethylpentane, n-hexane, isohexane, n-heptane, 2,2,4,6,6-pentamethylheptane (ie isododecane), petroleum ether; CCl ₃ F, CCl ₂ F ₂ , CClF ₃ , chlorofluorocarbons such as CClF ₂ -CClF ₂ ; tetraalkylsilanes such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, trimethyl-n-propylsilane; and the like. These can be used alone or in combination of two or more.

Of these, isobutane, n-butane, n-pentane, isopentane, n-hexane, isohexane, heptane, 2,2,4-trimethylpentane, isododecane, petroleum ether, and mixtures of two or more thereof are preferred. A foaming agent capable of generating a gas by heating is a compound that generates a gas by being thermally decomposed by heating, such as azodicarbonamide.

The content of the foaming agent enclosed in the heat-expandable microsphere is preferably 5 to 50% by mass, more preferably 7 to 40% by mass. It is preferable to adjust the usage ratio of the polymerizable monomer and the foaming agent so that the outer shell polymer and the foaming agent have the above ratio after the polymerization.

The polymerization initiator is preferably an oil-soluble polymerization initiator that is soluble in the polymerizable monomer. Examples of the polymerization initiator include dialkyl peroxide, diacyl peroxide, peroxyester, peroxydicarbonate, and azo compound. The polymerization initiator is usually contained in the monomer mixture. However, when it is necessary to suppress early polymerization, a part or all of the polymerization initiator is added to the aqueous dispersion medium during or after the granulation step. It may be added and transferred into droplets of the polymerizable mixture. The polymerization initiator is usually used in a proportion of 0.0001 to 3% by mass based on the aqueous dispersion medium.

Suspension polymerization is usually performed in an aqueous dispersion medium containing a dispersion stabilizer. Examples of the dispersion stabilizer include inorganic fine particles such as silica and magnesium hydroxide. In addition, auxiliary stabilizers such as a condensation product of diethanolamine and an aliphatic dicarboxylic acid, polyvinyl pyrrolidone, polyethylene oxide, various emulsifiers and the like can be used. The dispersion stabilizer is usually used at a ratio of 0.1 to 20 parts by mass with respect to 100 parts by mass of the polymerizable monomer.

An aqueous dispersion medium containing a dispersion stabilizer is usually prepared by blending a dispersion stabilizer or an auxiliary stabilizer with deionized water. The pH of the aqueous phase at the time of polymerization is appropriately determined depending on the type of dispersion stabilizer and auxiliary stabilizer used. For example, when silica such as colloidal silica is used as a dispersion stabilizer, polymerization is performed in an acidic environment. In order to make the aqueous dispersion medium acidic, an acid is added as necessary to adjust the pH of the system to 7 or less, preferably pH 6 or less, particularly preferably about pH 3 to 4. In the case of a dispersion stabilizer that dissolves in an aqueous dispersion medium under an acidic environment such as magnesium hydroxide or calcium phosphate, the polymerization is carried out in an alkaline environment.

One preferred combination of dispersion stabilizers is a combination of colloidal silica and a condensation product. As the condensation product, a condensation product of diethanolamine and an aliphatic dicarboxylic acid is preferable, and a condensation product of diethanolamine and adipic acid or a condensation product of diethanolamine and itaconic acid is particularly preferable. The acid value of the condensation product is preferably 60 or more and less than 95, and more preferably 65 to 90. Furthermore, when an inorganic salt such as sodium chloride or sodium sulfate is added, it becomes easier to obtain thermally expandable microspheres having a more uniform particle shape. As the inorganic salt, sodium chloride is usually preferably used.

The amount of colloidal silica used varies depending on the particle size, but is usually in the range of 0.5 to 20 parts by mass, preferably 1 to 15 parts by mass, with respect to 100 parts by mass of the polymerizable monomer. The condensation product is usually used at a ratio of 0.05 to 2 parts by mass with respect to 100 parts by mass of the polymerizable monomer. The inorganic salt is used in a ratio of 0 to 100 parts by mass with respect to 100 parts by mass of the polymerizable monomer.

As a polymerization assistant, at least one compound selected from the group consisting of alkali metal nitrite, stannous chloride, stannic chloride, water-soluble ascorbic acid, and boric acid can be present in the aqueous dispersion medium. . When suspension polymerization is performed in the presence of these compounds, polymerization particles do not agglomerate at the time of polymerization, the polymer does not adhere to the polymerization can wall, and is stable while efficiently removing heat generated by polymerization. Thus, a thermally foamable microsphere can be produced.

Among the alkali metal nitrites, sodium nitrite and potassium nitrite are preferable in terms of availability and price. Examples of ascorbic acids include ascorbic acid, metal salts of ascorbic acid, esters of ascorbic acid, and the like. Among these, water-soluble ones are preferably used. Water-soluble ascorbic acids mean those having a solubility in water at 23 ° C. of 1 g / 100 cm ³ or more, and ascorbic acid and alkali metal salts thereof are preferred. Among these, L-ascorbic acid (vitamin C), sodium ascorbate, and potassium ascorbate are preferable. The polymerization aid is usually used in a proportion of 0.001 to 2 parts by mass, preferably 0.01 to 1 part by mass, with respect to 100 parts by mass of the polymerizable monomer.

The order of adding each component to the aqueous dispersion medium is arbitrary, but usually an aqueous dispersion containing a dispersion stabilizer by adding water and a dispersion stabilizer, and if necessary, a stabilizer or a polymerization assistant. Prepare the medium. On the other hand, the polymerizable monomer and the foaming agent may be separately added to the aqueous dispersion medium and integrated in the aqueous dispersion medium to form a polymerizable monomer mixture (oil-based mixture). Both are mixed in advance and then added to the aqueous dispersion medium. The polymerization initiator can be used by adding it to the polymerizable monomer in advance, but when it is necessary to avoid early polymerization, for example, a mixture of the polymerizable monomer and the foaming agent is dispersed in water. The polymerization initiator may be added to the medium while stirring, and may be integrated in the aqueous dispersion medium. The polymerization mixture and the aqueous dispersion medium may be mixed in a separate container, stirred and mixed with a stirrer or disperser having high shearing force, and then charged into a polymerization can.

A polymerizable monomer mixture droplet is formed in the aqueous dispersion medium by stirring and mixing the polymerizable monomer mixture and the aqueous dispersion medium. It is preferable that the average particle size of the liquid droplets is approximately the same as the average particle size of the target thermally expandable microsphere. The suspension polymerization is usually carried out by degassing the inside of the reaction vessel or replacing it with an inert gas and raising the temperature to 30 to 100 ° C.

After suspension polymerization, the aqueous phase is removed by, for example, filtration, centrifugation, and sedimentation. The thermally expandable microspheres are dried after being filtered and washed. The thermally expandable microsphere is dried at a relatively low temperature such that the foaming agent is not gasified.

The average particle size of the thermally expandable microspheres of the present invention is usually in the range of 0.5 to 150 μm, preferably 1 to 130 μm, more preferably 3 to 100 μm, and particularly preferably 5 to 50 μm. The content of the blowing agent in the thermally expandable microsphere of the present invention is usually 5 to 50% by mass, preferably 7 to 40% by mass. The foaming temperature of the thermally expandable microsphere varies depending on the type and thickness of the thermoplastic resin (polymer) constituting the outer shell.

The production method of the present invention is a method for producing hollow microspheres including the following steps 1 and 2, in which a solid material adheres to the outer shell surface.

(1) Thermal expansion that has a microcapsule structure in which a foaming agent capable of gasification or gas generation is enclosed in an outer shell formed of a thermoplastic resin, and that thermally expands by heating to form hollow microspheres. And (2) preparing a slurry by dispersing a solid material having an average particle size or an average major axis smaller than the average particle size of the expandable microsphere and the average particle size of the thermally expandable microsphere in a liquid dispersion medium; The thermally expandable microspheres are heated in the slurry to soften the outer shell, and thermally expanded by gasification of the foaming agent or gas generated from the foaming agent, thereby softening the outer shell surface. Step 2 of forming a hollow microsphere having the solid material attached thereto.

The outline of the production method of the present invention will be described with reference to FIG. As shown in FIG. 2A, a slurry in which the thermally expandable microspheres 1 and the solid material 23 are dispersed in a liquid dispersion medium 22 is charged in a container 21. In order to disperse | distribute the thermally expansible microsphere 1 and the solid material 23 uniformly, it is preferable to stir. When the thermally expandable microspheres are heated and foamed by heating means such as blowing heated steam into the slurry, as shown in FIG. 2 (b), a foam (hollow microsphere) 101 is generated, A large number of solid materials 23 adhere to the surface.

The solid material used in Step 1 is a fine solid material that is solid at normal temperature (25 ± 15 ° C.) and has an average particle diameter or an average major axis smaller than the average particle diameter of the thermally expandable microsphere. The shape of the solid material is not particularly limited, and may be granular, spherical, cubic, spindle, rod, plate, needle, fiber, or the like. The material of the solid material may be inorganic or organic.

Examples of inorganic solid materials include natural products such as silica, limestone, quartz, apatite, magnetite, zeolite, clay (montmorillonite, hectorite, saponite, vermiculite, talc, mica, mica, etc.); metal carbonates such as calcium carbonate Metal sulfates such as barium sulfate, aluminum sulfate, cobalt sulfate, copper sulfate, nickel sulfate; metals such as titanium oxide, zinc oxide, aluminum oxide, tin oxide, vanadium oxide, indium oxide, chromium oxide, tungsten oxide, iron oxide Oxides; Metal hydroxides such as aluminum hydroxide and magnesium hydroxide; Metal sulfides such as copper sulfide and lead sulfide; Metal borates such as aluminum borate and zinc borate; Aluminum nitride, chromium nitride and cobalt nitride Metal nitride such as glass frame Glass such as glass beads; Ceramics such as ceramic beads; Fine particles of metal or alloy; Carbides such as carbon black, carbon nanotubes, graphite, activated carbon, fullerene; Crystal beads, mica, nepheline sinite, hydrotalcite, synthetic silica Examples thereof include fine powders such as acid, quartz powder, quartzite powder, diatomaceous earth, pumice powder, and other inorganic pigments.

Examples of colloidal inorganic solid materials include colloidal silica, colloidal calcium carbonate, magnesium hydroxide colloid, and calcium phosphate colloid. Examples of the needle-like or fibrous inorganic solid material include glass fiber, carbon fiber, alumina fiber, potassium titanate whisker, aluminum borate whisker, and wollastonite.

Examples of the organic solid material include fine particles of organic resin such as polystyrene beads, polymethyl methacrylate beads, and polytetrafluoroethylene beads, cotton fibers, and polyamide fibers. The organic resin fine particles include organic resin fine particles introduced with a crosslinked structure, organic resin fine particles introduced with a functional group or a polar group, and the like.

These solid materials can be used alone or in combination of two or more. The solid material may be subjected to a surface treatment such as a hydrophobic treatment. By selecting the type of solid material to be attached to the outer shell surface of the hollow microsphere, the specific gravity can be controlled, heat insulation, slip, sound insulation, conductivity, magnetism, piezoelectricity, bactericidal, ultraviolet absorption, etc. Can be added.

The average particle diameter or average long diameter of the inorganic and / or organic solid material is preferably sufficiently smaller than the average particle diameter of the thermally expandable microsphere, and is usually 10 μm or less, preferably 3 μm or less, more preferably 1 μm or less. Particularly preferably, it is 0.1 μm or less. The lower limit of the average particle diameter or the average major axis is about 0.001 μm from the viewpoints of effects and handleability. The average particle diameter of the solid material is an average diameter or an average major axis of primary particles measured by an observation counting method using an electron microscope or an optical microscope.

The solid material has an average particle size of 3 μm or less, preferably 1 μm or less, more preferably 0.1 μm or less, and a specific gravity (true specific gravity) of 1.5 to 6.0 g / cm ³ , preferably 2.0 to 6. By using at least one inorganic substance in the range of 0 g / cm ³ , more preferably 2.5 to 5.8 g / cm ³ , the specific gravity of the hollow microsphere can be increased. Examples of such inorganic substances include calcium carbonate (for example, heavy calcium carbonate having a specific gravity of about 2.70 g / cm ³ , light and colloidal calcium carbonate having a specific gravity of about 2.60 g / cm ³ ), crystalline silica, and the like. (Specific gravity = 2.6 g / cm ³ ), aluminum oxide (specific gravity = 3.98 g / cm ³ ), kaolin (clay) (specific gravity = 2.5 to 2.6 g / cm ³ ), titanium oxide (for example, specific gravity = anatase or rutile type specific gravity = 4.2 g / cm ³ of 3.9g / cm ^3), barium sulfate (specific gravity = 4.50g / ^cm 3), typically oxide of zinc oxide (specific gravity = 5.70 g / cm ³ Zinc or tetrapot-type zinc oxide having a specific gravity of 5.78 g / cm ³ ).

The content (adhesion amount) of the solid material can be appropriately determined according to the desired function and the type of the solid material, but usually 1 to 99.9 masses based on the total amount of the hollow microspheres to which the solid material is adhered. %, Preferably 10 to 99.5% by mass, more preferably 15 to 99.3% by mass, particularly preferably 20 to 99.0% by mass. However, the amount of dispersion stabilizer (for example, inorganic fine particles such as silica and magnesium hydroxide) used for controlling the particle size of the thermally expandable microsphere is excluded from these.

The amount of the solid material attached to the outer shell surface of the hollow microsphere can be generally calculated based on the mass difference between the hollow microspheres obtained in the presence and absence of the solid material. When the solid material is inorganic, the amount of solid material deposited can be calculated by burning the hollow microsphere with the solid material adhered to the outer shell surface and measuring the amount of ash after combustion. .

When the content of the solid material is too small, it becomes difficult to sufficiently exhibit various functions while preventing aggregation of the thermally expandable microspheres. When the content of the solid material is excessively large, it is difficult to foam the thermally expandable microsphere.

In step 1, the thermally expandable microsphere and a solid material having an average particle diameter or an average major axis smaller than the average particle diameter of the thermally expandable microsphere are dispersed in a liquid dispersion medium to prepare a slurry. .

As the liquid dispersion medium, a medium that does not dissolve the thermoplastic resin that forms the outer shell of the thermally expandable microsphere or has a low solubility is preferable. The liquid dispersion medium is preferably a medium that does not decompose or has a low degree of decomposition of the thermoplastic resin that forms the outer shell of the thermally expandable microsphere.

Specific examples of the liquid dispersion medium include water; organic solvents such as isopropyl alcohol, ethylene glycol, glycerin, phthalate ester, silicone oil, and paraffin oil; mixed solvents such as water / ethylene glycol mixed solution and water / glycerin mixed solution; Etc. Among these, water and an aqueous dispersion medium such as a mixed solvent containing water are preferable, and water is particularly preferable. If desired, a surfactant or a dispersion stabilizer may be added to the liquid dispersion medium.

The concentration of the heat-expandable microspheres in the liquid dispersion medium is usually 0.1 to 10% by mass, preferably 0.1 to 8% by mass, more preferably 0.2 to 7% by mass, and particularly preferably 0.8. It is within the range of 3 to 5% by mass. If this concentration is too high, the thermal expansion of the thermally expandable microspheres tends to cause thermal fusion between the foams, or the amount of solid material added must be reduced. If this concentration is too low, the production efficiency decreases.

When the heat-expandable microspheres are formed by suspension polymerization of a polymerizable monomer mixture containing a polymerizable monomer and a foaming agent in an aqueous dispersion medium, By adding the solid material in the aqueous dispersion medium during or after the suspension polymerization, a slurry in which the thermally expandable microspheres and the solid material are dispersed in the aqueous dispersion medium can be prepared. In this case, the solid material may be added in several batches before and after suspension polymerization, before suspension polymerization and during suspension polymerization. When the solid material is a dispersion stabilizer such as colloidal silica, it is usually added during suspension polymerization or after suspension polymerization. In order to adjust the concentration of the thermally expandable microspheres in the slurry, a liquid dispersion medium such as water may be added, or a part of the aqueous dispersion medium may be removed by filtration or tilting.

When the heat-expandable microsphere is formed by suspension polymerization of a polymerizable monomer mixture containing a polymerizable monomer and a foaming agent in an aqueous dispersion medium, the heat recovered from the aqueous dispersion medium The expandable microspheres can be dispersed with a solid material in a liquid dispersion medium to prepare a slurry.

In the step 2, the thermally expandable microspheres are heated in the slurry to soften the outer shell, and thermally expanded by the gasification of the foaming agent or the gas generated from the foaming agent, thereby softening the outer shell. Hollow microspheres with solid material attached to the surface are formed.

Since there is usually a specific gravity difference between the thermally expandable microsphere and the solid material, the slurry is charged into a container (tank, polymerization can, etc.) equipped with a stirring device, stirred, and thermally expanded microsphere. It is preferable that the solid material is uniformly dispersed in the slurry. The thermal expansion of the thermally expandable microsphere is also preferably performed while stirring the slurry.

As the heating and foaming means, there are a method of heating the slurry, a method of blowing heated steam into the slurry, a dielectric heating method and the like. When a liquid that evaporates at a relatively low temperature, such as an aqueous dispersion medium, is used as the liquid dispersion medium, it may be heated and pressurized. Among these, the method of blowing heated steam into the slurry is particularly preferable because the thermally expandable microsphere can be heated and foamed in a very short time. The temperature of the heated steam is usually 100 to 200 ° C., preferably 110 to 190 ° C., more preferably 120 to 180 ° C., although it depends on the foaming temperature of the thermally expandable microsphere. The pressure at which heated steam is blown is usually in the range of 0.1 to 1.56 MPa, preferably 0.14 to 1.26 MPa, more preferably 0.2 to 1.0 MPa.

After heating and foaming in the slurry, hollow microspheres in which the solid material is firmly attached to the outer shell surface are collected by a method of filtering the slurry and washing the foam particles. In the hollow microsphere of the present invention, the outer shell made of a thermoplastic resin is softened at the time of heating and foaming, and the solid material adheres to the surface of the softened outer shell. There is nothing to do.

The average particle size of the hollow microspheres of the present invention is preferably in the range of 2 to 200 μm, more preferably 5 to 100 μm, particularly preferably 10 to 60 μm. If the average particle size of the hollow microspheres is too small, when the hollow microspheres are used as a porous forming agent, formation of a porous structure tends to be insufficient. On the other hand, if the average particle size of the hollow microspheres is too large, the hollow microspheres may be hollow when kneaded with a raw material constituting a porous molded body such as a porous ceramic molded body and / or when a mixture obtained by kneading is molded. Microspheres are liable to collapse, and as a result, the formation of a porous structure may be insufficient.

Since the hollow microsphere of the present invention has a solid material attached to the outer shell surface thereof, mutual fusion is prevented, and scattering from the air during the handling is suppressed. Various functions can be imparted to the hollow microsphere by adjusting the type and amount of the solid material to be attached to the outer shell surface.

The hollow microsphere of the present invention can increase the specific gravity (apparent specific gravity) of the entire particle by attaching a solid material having a high specific gravity to the outer shell surface. Uniform mixing is facilitated. The hollow microsphere having a high specific gravity is suitable as a porous forming agent used in the production process of a porous ceramic molded body, for example. A porous ceramic molded body using a porous forming agent can be produced, for example, by a production method disclosed in Japanese Patent Application Laid-Open No. 2007-39333 (Patent Document 1).

Specifically, a process a for mixing a ceramic raw material and a porous forming agent to prepare a mixture; a process b for forming the mixture into a molded body having a predetermined shape; and a process c for firing the molded body. In the method for producing a porous ceramic formed body, hollow microspheres obtained by the above production method and having a solid material attached to the outer shell surface are used as the porous forming agent.

Examples of ceramic raw materials include ceramic mixtures such as talc, kaolin, aluminum oxide, aluminum hydroxide, and silica, silicon carbide, and metal silicon. The use ratio of the hollow microsphere having a solid material attached to the outer shell surface can be appropriately determined according to the desired porous structure. The firing temperature is about 1400 to 2000 ° C.

In general, the group of substances called ceramics is extremely wide and has various characteristics. Types of ceramics include ceramics, glass, cement, gypsum, enamel, fine ceramics (new ceramics) and the like.

The hollow microsphere of the present invention is also used as a porous forming agent for lightweight cellular concrete (ALC), for example. The ALC containing the porous forming agent includes closed cells inside, and exhibits excellent properties such as relatively high strength while being very lightweight. ALC is widely used as a building material for walls and floors of buildings because it is lightweight, relatively strong, and excellent in fire resistance, heat insulation, and workability.

In the production of ALC, siliceous raw materials such as silica and calcareous raw materials such as cement and lime are generally used as main raw materials, and gypsum and process repetition raw materials are used as auxiliary raw materials. Water and a porous molding agent are added to these raw material fine powders to form a slurry, which is then placed in a mold and semi-cured. Next, ALC can be obtained by subjecting the semi-cured product to high-temperature and high-pressure steam curing with an autoclave.

Thus, the step of producing ALC as a porous ceramic molded body includes a step of preparing a mixture by mixing a ceramic raw material and a porous forming agent; a step b of molding the mixture into a molded body having a predetermined shape. And a step c of curing the shaped body. In the process of producing a porous ceramic molded body using cement or gypsum as a ceramic raw material, curing may be performed instead of firing. In the present invention, the hollow microsphere of the present invention is used as a porous forming agent such as ALC.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. In the present invention, methods for measuring physical properties and characteristics are as follows.

(1) Foaming magnification 0.7 g of thermally expandable microspheres was placed in a gear-type oven and heated at a predetermined foaming temperature for 2 minutes for foaming (thermal expansion). The resulting hollow microspheres were placed in a graduated cylinder and the volume was measured. The volume of the hollow microsphere was divided by the volume of the unexpanded thermally expandable microsphere to calculate the expansion ratio. At this time, the foaming temperature was increased from 70 ° C. in increments of 5 ° C. and foamed at each temperature. The expansion ratio at a temperature at which the maximum expansion ratio was obtained under these conditions was defined as the maximum expansion ratio.

(2) Average particle diameter Using Microtrac MT3300EX (registered trademark) manufactured by Nikkiso Co., Ltd., the average particle diameter (median diameter) of thermally expandable microspheres and foam particles was measured.

(3) Specific gravity The specific gravity of the thermally expandable microsphere and the hollow microsphere means the specific gravity of the whole particle, and was measured by a measuring method using a specific gravity bottle defined in JIS Z 8807.

(4) Content rate of solid material The content rate of the solid material adhering to the outer shell surface of the thermally expandable microsphere and the hollow microsphere was calculated by measuring the mass of ash after combustion. The specific procedure is as follows.

<Quantity of foaming agent>
The amount and ratio of the remaining foaming agent contained in the hollow microsphere (dried sample) that has been stored in a desiccator for one day after air drying and dried are measured by the following procedure.

a) About 0.2 g of the dried sample is put into an aluminum cup (diameter 6 cm, height 3 cm). At this time, the exact mass of the dried sample is measured by weighing the mass of only the cup before putting the sample, weighing it with the cup after putting the sample, and calculating the difference.

b) After that, the cup was covered with an upper lid made of aluminum, subjected to heat treatment at 200 ° C. for 10 minutes to vaporize the foaming agent, and then subjected to the heat treatment (hereinafter referred to as “foaming agent”). The “removed sample”) was weighed.

c) Here, when the mass difference before and after the heat treatment is determined, it corresponds to the amount of the foaming agent volatilized from the particles of the dried sample. Using this numerical value, the ratio (f: mass%) of the remaining blowing agent relative to the entire dried sample was calculated. The quantitative experiment was performed twice.

<Quantification of ash content>
d) Weigh 1.5 to 1.7 g of the blowing agent-removed sample prepared in the same procedure as the above “quantitative determination of blowing agent” on the medicine-wrapped paper, and let the weighed value be Wdf (g).

e) The empty mass of the magnetic crucible is accurately weighed, and the weighed value is defined as Wa (g).

f) Place the weighed foaming agent-removed sample in small amounts in a magnetic crucible and repeat pre-carbonization with an electric heater. Made it.

g) After cooling, weigh the mass of the magnetic crucible including the ash, and let the weighed value be Wb (g).

h) The amount of ash Ws (g) was obtained from the following equation.
Ws (g) = Wb (g) -Wa (g)

i) These numerical values were substituted into the following calculation to calculate the amount of ash (% by mass) based on the entire dry sample. The quantitative experiment was performed twice, and the average value was calculated.

[Preparation Example 1]
(1) Preparation of aqueous dispersion medium 22 g of colloidal silica having a solid content of 40% by mass was added to 770 g of deionized water and dispersed therein. Next, 0.8 g of diethanolamine-adipic acid condensate and 0.13 g of sodium nitrite were added to the dispersion and dissolved. Furthermore, hydrochloric acid was added to the dispersion to prepare an aqueous dispersion medium having a pH of 3.5.

(2) Preparation of polymerizable monomer mixture 123 g of vinylidene chloride, 86 g of acrylonitrile, 11 g of methyl methacrylate, 0.33 g of diethylene glycol dimethacrylate, 1.1 g of 2,2′-azobis-dimethylvaleronitrile and 35 g of n-butane By mixing, a polymerizable monomer mixture was prepared. The mass% of each polymerizable monomer in the polymerizable monomer mixture is vinylidene chloride / acrylonitrile / methyl methacrylate = 56/39/5.

(3) Formation of droplets The aqueous dispersion medium prepared in the above (1) and the polymerizable monomer mixture prepared in the above (2) are stirred and mixed with a homogenizer, and the polymerizable monomer is mixed in the aqueous dispersion medium. Small droplets of body mixture were formed.

(4) Suspension polymerization An aqueous dispersion medium in which droplets of a polymerizable monomer mixture were dispersed was charged into a 1.5-liter polymerization can equipped with a stirrer. This polymerization can was placed in a warm water bath and held at 50 ° C. for 22 hours to polymerize the polymerizable monomer mixture. By this polymerization reaction, thermally expandable microspheres having a microcapsule structure in which n-butane as a foaming agent was enclosed in an outer shell formed from a vinylidene chloride-acrylonitrile-methyl methacrylate copolymer were formed. After the polymerization reaction, the reaction mixture in the polymerization can was filtered and washed with water. Further, washing with water and filtration were repeated twice, followed by drying to collect thermally expandable microspheres.

(5) Thermally expandable microspheres The thermally expandable microspheres thus obtained have an average particle size of 14 μm, a maximum expansion ratio of 50 times at a foaming temperature of 130 ° C., and a specific gravity of 0. 0.02 g / cm ³ . This thermally expandable microsphere contained 3.3% by mass of colloidal silica used as a dispersion stabilizer.

[Comparative Example 1]
Deionized water was added to the thermally expandable microsphere obtained in Preparation Example 1 to prepare 500 g of an aqueous slurry having a concentration of 1% by mass of the thermally expandable microsphere. This aqueous slurry was charged into a 1.5-liter polymerization can equipped with a stirrer. While stirring the aqueous slurry, steam at a temperature of 150 ° C. was blown in at a pressure of 0.48 MPa to heat and expand the thermally expandable microspheres. The foam particles (hollow microspheres) formed by foaming the thermally expandable microspheres all floated to the upper part, and some of them were thermally fused.

[Comparative Example 2]
Deionized water was added to the thermally expandable microsphere obtained in Preparation Example 1 to prepare 500 g of an aqueous slurry having a concentration of 1% by mass of the thermally expandable microsphere. This aqueous slurry was charged into a 1.5-liter polymerization can equipped with a stirrer. While stirring the aqueous slurry at room temperature (23 ° C.) for 1 hour, the aqueous slurry became cloudy due to the released colloidal silica.

When this aqueous slurry was filtered to collect thermally expandable microspheres, it was confirmed that the content of colloidal silica was reduced from 3.3% by mass to 2.4% by mass. When this thermally expandable microsphere was heated to 130 ° C. and foamed, strong fusion was observed between the foam particles. The maximum expansion ratio of this thermally expandable microsphere at a foaming temperature of 130 ° C. was 50 times.

[Example 1]
Deionized water was added to the thermally expandable microsphere obtained in Preparation Example 1 to prepare 500 g of an aqueous slurry having a concentration of 1% by mass of the thermally expandable microsphere. After adding 40 g of colloidal calcium carbonate (average particle diameter 50 nm) to this aqueous slurry, it was charged into a polymerization can equipped with a stirrer having a capacity of 1.5 liters. While stirring the aqueous slurry, steam heated to a temperature of 150 ° C. was blown in at a pressure of 0.48 MPa to heat and expand the thermally expandable microspheres. Foam particles (hollow microspheres) were dispersed in the aqueous slurry after foaming without forming aggregates.

The foam particles in the aqueous slurry were filtered and washed with water. Further, washing with water and filtration were repeated twice, followed by drying to collect foam particles (hollow microspheres). The foam particles had an average particle size of 50 μm and a specific gravity of 0.095 g / cm ³ . The total content of inorganic substances contained in the foam particles was 80% by mass. The hollow microspheres obtained in this way were those whose scattering properties in air were remarkably suppressed and excellent in mixing properties with inorganic substances having a high specific gravity.

[Example 2]
Foam particles (hollow microspheres) were produced in the same manner as in Example 1 except that 100 g of colloidal silica (solid content 40% by mass, average particle size 12 nm) was used instead of 40 g of colloidal calcium carbonate. The foam particles had an average particle size of 53 μm and a specific gravity of 0.10 g / cm ³ . The total content of inorganic substances contained in the foam particles was 85% by mass. The hollow microspheres obtained in this way were those whose scattering properties in air were remarkably suppressed and excellent in mixing properties with inorganic substances having a high specific gravity.

The hollow microsphere having a solid material adhered to the outer shell surface of the present invention can be used in a wide range of technical fields for the purpose of reducing the weight, making it porous, and imparting various functions to plastics, paints, and various materials. The hollow microsphere having a high specific gravity can also be used as a porous forming agent for a porous ceramic molded body.

Claims

Steps 1 and 2 below:
(1) Thermal expansion that has a microcapsule structure in which a foaming agent capable of gasification or gas generation is enclosed in an outer shell formed of a thermoplastic resin, and that thermally expands by heating to form hollow microspheres. And (2) preparing a slurry by dispersing a solid material having an average particle size or an average major axis smaller than the average particle size of the expandable microsphere and the average particle size of the thermally expandable microsphere in a liquid dispersion medium; The thermally expandable microspheres are heated in the slurry to soften the outer shell, and thermally expanded by gasification of the foaming agent or gas generated from the foaming agent, thereby softening the outer shell surface. Forming a hollow microsphere having the solid material attached thereto in step 2;
A method for producing hollow microspheres comprising a solid material attached to the outer shell surface.
The manufacturing method according to claim 1, wherein in the step 1, a slurry in which the concentration of the thermally expandable microsphere is in a range of 0.1 to 10% by mass is prepared.
2. The solid material according to claim 1, wherein the solid material is at least one solid material selected from the group consisting of inorganic materials and organic materials having a granular, spherical, cubic, spindle, rod, plate, needle or fiber shape. Production method.
The production method according to claim 1, wherein the solid material is at least one inorganic substance having an average particle diameter of 3 µm or less and a specific gravity in the range of 1.5 to 6.0 g / cm 3 .
The method according to claim 1, wherein the solid material is at least one inorganic substance selected from the group consisting of calcium carbonate, crystalline silica, aluminum oxide, kaolin, titanium oxide, barium sulfate, and zinc oxide.
The production method according to claim 1, wherein the thermally expandable microspheres have an average particle size in the range of 0.5 to 150 µm.
The production method according to claim 1, wherein the liquid dispersion medium is an aqueous dispersion medium.
The thermally expandable microsphere is formed by suspension polymerization of a polymerizable monomer mixture containing a polymerizable monomer and a foaming agent in an aqueous dispersion medium, and the step 1 is A slurry in which the thermally expandable microspheres and the solid material are dispersed in the aqueous dispersion medium is prepared by adding the solid material into the aqueous dispersion medium before, during or after the suspension polymerization. The manufacturing method according to claim 1, which is a process.
The thermally expandable microspheres are formed by suspension polymerization of a polymerizable monomer mixture containing a polymerizable monomer and a blowing agent in an aqueous dispersion medium, and then recovered from the aqueous dispersion medium The manufacturing method according to claim 1, wherein in the step 1 obtained, the thermally expandable microspheres are dispersed together with a solid material in a liquid dispersion medium to prepare a slurry.
The manufacturing method according to claim 1, wherein in the step 2, heated steam is blown into the slurry to heat and expand the thermally expandable microsphere.
The method according to claim 1, wherein, in the step 2, hollow microspheres are formed in which a solid material in the range of 1 to 99.9% by mass based on the total amount of the hollow microspheres adheres to the outer shell surface.
The production method according to claim 1, wherein the hollow microspheres have an average particle diameter in the range of 2 to 200 µm.
A porous material comprising: a step of mixing a ceramic raw material and a porous forming agent to prepare a mixture; a step b of forming the mixture into a formed body having a predetermined shape; and a step c of curing or firing the formed body. In a method for producing a ceramic molded body, a porous microsphere obtained by the production method according to claim 1 and having a solid material attached to the outer shell surface is used as the porous forming agent. A method for producing a ceramic molded body.
The production method according to claim 13, wherein the solid material is at least one inorganic substance having an average particle diameter of 3 µm or less and a specific gravity in the range of 1.5 to 6.0 g / cm 3 .
The method according to claim 13, wherein the solid material is at least one inorganic substance selected from the group consisting of calcium carbonate, crystalline silica, aluminum oxide, kaolin, titanium oxide, barium sulfate, and zinc oxide.