JPH11209504A - Production of expandable microsphere - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an expandable microsphere capable of preventing the aggregation of produced polymer particles and sticking of scales to a polymerizer wall at the time of polymerization, having a truly spherical uniform particle shape and capable of providing a sharply expanded and uniform foam. SOLUTION: The suspension polymerization of a polymerizable mixture is carried out in the presence of at least one kind of compound selected from the group consisting of an alkali metal nitrite, stannous chloride, stannic chloride, water-soluble ascorbic acids and boric acid in a method for producing an expandable microsphere containing the foaming agent enclosed in the outer shell of the produced polymer comprising carrying out the suspension polymerization of the polymerizable mixture containing at least the foaming agent and a polymerizable monomer in an aqueous dispersion medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing expandable microspheres, and more particularly, to prevent agglomeration of produced polymer particles and adhesion of scale to the wall of a polymerization vessel during polymerization, and reduce the particle shape. The present invention relates to a method for producing expandable microspheres capable of giving a uniform foam having a uniform spherical shape and a sharp foam. The expandable microspheres obtained by the production method of the present invention can be used in a wide range of technical fields including the field of paints and inks.

[0002]

2. Description of the Related Art In recent years, foamable microspheres have been used in various fields, such as foaming inks, paints and plastic fillers for weight reduction, and the like. Foamable microspheres are usually microcapsules of a volatile liquid foaming agent (also referred to as a physical foaming agent or a volatile expanding agent) with a thermoplastic resin. Conventionally, such foamable microspheres have been produced by a method in which a polymerizable mixture containing at least a foaming agent and a polymerizable monomer is suspension-polymerized in an aqueous dispersion medium. As the polymerization reaction proceeds, an outer shell is formed by the resulting polymer, and an expandable microsphere containing the expandable agent is obtained.

[0003] For example, Japanese Patent Publication No. 42-52424 discloses a single-cell-like thermoplastic resin-like polymer having a volatile liquid foaming agent which becomes gaseous at a temperature lower than the softening point of the polymer. (Ie, expandable microspheres) are described. The publication discloses that a blowing agent such as a low-boiling aliphatic hydrocarbon is added to a monomer, an oil-soluble catalyst is mixed with the monomer mixture, and then a monodispersion is carried out in an aqueous dispersion medium containing a dispersant. A method for producing spherical particles in which a foaming agent is wrapped in a shell made of a thermoplastic resin by adding a monomer mixture with stirring and performing suspension polymerization is disclosed. Japanese Patent Application Laid-Open No. 62-286534 discloses that a volatile swelling agent is microencapsulated by using a polymer obtained from a component containing a nitrile monomer of 80% by weight or more, a non-nitrile monomer of 20% by weight or less, and a crosslinking agent. A method for producing thermally expandable microcapsules (ie, expandable microspheres) is described. In these conventional production methods, in an aqueous dispersion medium containing colloidal silica as a dispersion stabilizer (suspension agent), a diethanolamine-adipate condensation product as an auxiliary stabilizer, and potassium dichromate as a polymerization aid, Foamable microspheres are produced by subjecting a polymerizable mixture containing a foaming agent, a polymerizable monomer, and a polymerization initiator to suspension polymerization.

[0004] However, in these conventional methods, there is a problem that potassium dichromate used as a polymerization aid has toxicity. Moreover, when potassium dichromate is used, the foamable microspheres are colored yellow due to the remaining chromium ions, and the color tone of various products containing the foamable microspheres in an unfoamed or foamed state is impaired. . In particular, when such a colored product contains such yellow expandable microspheres, the color tone tends to be dull.

[0005] On the other hand, if potassium dichromate is not used during suspension polymerization, a problem that the produced polymer particles tend to agglomerate or that the produced polymer adheres to the wall of the polymerization vessel as a scale tends to occur. . When the polymer particles aggregate, the viscosity of the suspension polymerization reaction system increases, which adversely affects the progress of the polymerization reaction and the particle shape of the expandable microspheres. When the polymer scale covers the polymerization vessel wall, the heat removal capability of the polymerization vessel is reduced, and the yield of expandable microspheres is reduced. When agglomerates of polymer particles and adhered polymer-scale exfoliated materials are mixed in the expandable microspheres, the expandable microspheres are used, for example, as a lightening agent or a function-imparting agent such as a high-performance paint. When used, these agglomerates and scale exfoliated matter are coarse particles, which causes a problem that the finished surface becomes rough. These coarse particles and non-spherical particles cause problems such as easy foaming at low temperature and easy removal of the foaming agent, and a low expansion ratio, as compared with true spherical particles. Such a problem is a fatal drawback particularly for ultra-thin coating applications that can take advantage of the characteristics of the expandable microspheres. In the case of air spray applications, clogging of the gun and uneven application are likely to occur.

[0006] Japanese Patent Application Laid-Open No. 4-292463 (Patent No. 2)
JP-A-584376) has a sedimentation inhibitor (dispersion stabilizer).
Discloses a method for producing an expandable thermoplastic microsphere using a powder stabilizer such as magnesium hydroxide which is insoluble in an aqueous medium at the pH of the aqueous medium during polymerization. The publication states that according to this method, the powder stabilizer can be dissolved and removed by lowering the pH of the aqueous medium after the polymerization, so that foamable microspheres having a clean polymer surface can be obtained. ing. However, even with this method, the problem of aggregation of polymer particles cannot be solved.

[0007] Foamable microspheres are:
In addition to being blended with inks, paints, plastics, and the like in an unfoamed state, it may be used in a foamed state depending on the application. That is, since the foamed body (hollow plastic balloon) of the foamable microsphere is extremely lightweight, it is used as a filler for paint in order to reduce the weight of an object to be coated such as an automobile. ing. This foam usually has a bulk density of 0.02 to 0.02.
About 0.03 g / cm ³ and an average particle diameter of 20 to 200
Since it is a very light fine powder of about μm, when it is taken out of the container and mixed with a base material such as paint, it is easily scattered in the air. Further, when the foam is stirred and mixed with the base material, the foam collects on the upper portion of the base material, and it is very difficult to perform uniform mixing.

Therefore, Japanese Patent Application Laid-Open No. 7-196813 discloses that an unfoamed expandable microsphere and a plasticizer are mixed at a temperature lower than the foaming start temperature of the expandable microsphere.
Next, a plasticizer heated to a temperature equal to or higher than the foaming start temperature of the foamable microspheres is brought into contact with the mixture, and after foaming the foamable microspheres, the foamable microspheres are cooled to prevent over-foaming from occurring. (Non-scattering hollow plastic balloons) have been proposed. According to this method, the unexpanded expandable microspheres can be dispersed in a plasticizer to obtain a fluid state that can be supplied by a pump at a constant rate. There is an advantage that a non-scattering foamed microsphere can be obtained, and the amount of the plasticizer used can be extremely reduced as compared with a method of simply wetting with a plasticizer. To adopt such a method, foamable microspheres
The following properties are required: (1) Since a plasticizer is used as a wetting agent, the solvent resistance is good. (2) The viscosity when the foamable microspheres are dispersed in the plasticizer should be as low as possible so that a small amount of the plasticizer can be supplied by a pump at a constant rate. (3) Foaming should occur sharply in terms of process and product quality. (4) Aggregates cannot be formed during the foaming process. Therefore, a foamable microsphere having these characteristics (1) to (4) is desired.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to prevent agglomeration of produced polymer particles during polymerization and adhesion of scale to a polymerization vessel wall, to make the particle shapes exactly spherical, and to produce sharp and uniform foaming. An object of the present invention is to provide a method for producing expandable microspheres that can provide a stable foam. The present inventors have made intensive studies to overcome the problems of the prior art, and as a result, suspension polymerization of a polymerizable mixture containing at least a blowing agent and a polymerizable monomer in an aqueous dispersion medium, In a method for producing a foamable microsphere containing a foaming agent wrapped in an outer shell of a produced polymer, the method comprises the steps of: using an alkali metal nitrite, stannous chloride, stannic chloride, water-soluble ascorbic acids, and boric acid. In the presence of at least one compound selected from the group consisting of, by performing suspension polymerization of the polymerizable mixture, during polymerization, aggregation of the polymer particles do not occur, the polymer does not adhere to the polymerization can wall It has been found that foamable microspheres can be stably produced while efficiently removing heat generated by polymerization. Further, the expandable microsphere obtained by the production method of the present invention has a small amount of non-spherical particles and agglomerated particles, so that the foam is sharp and a uniform foam is obtained. The present invention has been completed based on these findings.

[0010]

According to the present invention, a polymerizable mixture containing at least a foaming agent and a polymerizable monomer is subjected to suspension polymerization in an aqueous dispersion medium to form a polymer in an outer shell. A method for producing a foamable microsphere containing a foaming agent wrapped therein, comprising at least one selected from the group consisting of alkali metal nitrite, stannous chloride, stannic chloride, water-soluble ascorbic acids, and boric acid Wherein the suspension polymerization of the polymerizable mixture is carried out in the presence of the compound of the formula (1).

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The production method of the present invention is characterized in that a polymerizable mixture containing at least a foaming agent and a polymerizable monomer is subjected to suspension polymerization in an aqueous dispersion medium to form an outer shell of a produced polymer. In a method for producing a foamable microsphere containing a foaming agent contained therein, suspension polymerization of a polymerizable mixture is performed in the presence of a specific compound. In particular,
In an aqueous dispersion medium, alkali metal nitrite, stannous chloride, stannic chloride, water-soluble ascorbic acids, and at least one compound selected from the group consisting of boric acid is present, the suspension of the polymerizable mixture Perform polymerization.

Although the mechanism of action of these compounds is not always clear at this stage, the presence of these compounds in a suspension polymerization reaction system can suppress aggregation of polymer particles produced during polymerization. The effect of suppressing the adhesion of polymer scale to the polymerization can wall, suppressing the generation rate of deformed particles, and obtaining foamable microspheres having a perfectly spherical particle shape. Can play. By suppressing the aggregation of the polymer particles, it is possible to prevent the increase in the viscosity of the slurry during the polymerization, and by suppressing the adhesion of the polymer scale, it is possible to efficiently remove the heat generated by the polymerization. Can be performed stably, and as a result, a foamable microsphere having a true spherical shape and sharp foaming can be obtained.

The foamable microspheres obtained by the production method of the present invention are uniformly foamed. For example, by observing the foaming state of the expandable microspheres while raising the temperature with a microscope equipped with a hot stage, the expandable microspheres obtained by the production method of the present invention can be used in a narrow foaming temperature range, like popcorn. It foams at once and becomes a uniform foam. On the other hand, the foamable microspheres obtained by suspension polymerization in the absence of the specific compound are partially compared with the foamable microspheres obtained by the production method of the present invention. However, some foaming starts at a temperature as low as 10 ° C. or more, and sometimes as low as 30 ° C. or more.
When the foamable microspheres obtained by suspension polymerization in the absence of the specific compound are measured for weight loss when the temperature is increased by a thermobalance (TGA), the foaming microspheres can be used at a temperature below the foaming start temperature. In some cases, significant weight loss due to volatilization is observed. Such a weight loss is due to the foaming agent dissipating from the foamable microspheres before foaming occurs, whereby a predetermined foaming ratio cannot be obtained, or if foaming occurs severely, foaming does not occur at all. Sometimes. When the method described in JP-A-7-196813 is applied to such an expandable microsphere having uneven foaming, when a mixture of the expandable microsphere and a plasticizer is preheated, Some foaming occurs. Foamable microspheres, when foamed, have a volume ratio of 60 to 1
Since it expands by about 00 times, even if a very small amount of foaming occurs, the mixture with the plasticizer loses fluidity and cannot be pumped.

According to the production method of the present invention, at least one compound selected from the group consisting of alkali metal nitrite, stannous chloride, stannic chloride, water-soluble ascorbic acids, and boric acid is added to an aqueous dispersion medium. By carrying out the suspension polymerization of the polymerizable mixture in the presence of the compound, the above-mentioned disadvantages can be solved and foamable microspheres having excellent various properties can be stably obtained. Among the alkali metal nitrites, sodium nitrite and potassium nitrite are preferred in terms of availability and price. Examples of ascorbic acids include ascorbic acid, metal salts of ascorbic acid, and esters of ascorbic acid. In the present invention, water-soluble ascorbic acids are preferably used.
Here, the 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 an alkali metal salt thereof are preferable. Among these, L-ascorbic acid (vitamin C), sodium ascorbate and potassium ascorbate are particularly preferably used in terms of availability, price, and effect. These compounds are polymerizable monomer 1
It is used in an amount of usually 0.001 to 1 part by weight, preferably 0.01 to 0.1 part by weight, based on 00 parts by weight.

In the production method of the present invention, the foaming agent, polymerizable monomer, and other auxiliaries are not particularly limited, and conventionally known ones can be used. That is, the production method of the present invention can be applied to production of all types of expandable microspheres. The blowing agent used in the present invention is a substance which usually becomes gaseous at a temperature lower than the softening point of the polymer forming the outer shell. As such a foaming agent, a low-boiling organic solvent is suitable, for example, ethane,
Low molecular weight hydrocarbons such as ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, petroleum ether; CCl ₃ F, CCl
₂ F _2, CClF _3, chlorofluorocarbons such as CClF ₂ -CCl ₂ F _2; tetramethylsilane, trimethylethyl silane, trimethyl isopropyl silane, tetraalkyl silane such as trimethyl -n- propyl silane; and the like. These can be used alone or in combination of two or more. Among these, isobutane, n-butane, n-pentane, isopentane, n-hexane, petroleum ether, and a mixture of two or more thereof are preferred. If desired, a compound which is thermally decomposed by heating and becomes gaseous may be used.

Examples of the polymerizable monomer include acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate and dicyclopentenyl acrylate; methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobornyl methacrylate and the like. Methacrylic acid esters; acrylonitrile, methacrylonitrile, vinylidene chloride, vinyl chloride, styrene, vinyl acetate, α-methylstyrene, chloroprene, neoprene, butadiene and the like. These polymerizable monomers can be used alone or in combination of two or more. The foamable microsphere is preferably one in which the polymer forming the outer shell is thermoplastic and has gas barrier properties. From this viewpoint, a copolymer containing vinylidene chloride and a copolymer containing (meth) acrylonitrile are preferable as the polymer forming the outer shell.

Examples of the copolymer containing vinylidene chloride include:
As a polymerizable monomer, vinylidene chloride 30 to 95% by weight
And a copolymer obtained by using 5 to 70% by weight of a monomer copolymerizable therewith. Examples of monomers copolymerizable with vinylidene chloride include acrylonitrile, methacrylonitrile, methacrylate, acrylate, styrene, and vinyl acetate. That is, as the polymerizable monomer, (a) 30 to 95% by weight of vinylidene chloride and (b) at least one selected from the group consisting of acrylonitrile, methacrylonitrile, acrylate, methacrylate, styrene, and vinyl acetate It is preferable to produce foamable microspheres using a monomer mixture containing 5 to 70% by weight of one kind of monomer. If the copolymerization ratio of vinylidene chloride is less than 30% by weight, the gas barrier properties decrease, and if it exceeds 95% by weight, the foaming temperature range becomes too low, which is not preferable.

Examples of the copolymer containing vinylidene chloride include:
As the polymerizable monomer, (a) vinylidene chloride 40 to 80
% By weight, (b1) at least one monomer 1 selected from the group consisting of acrylonitrile and methacrylonitrile
A copolymer obtained using a monomer mixture containing 9 to 50% by weight and (b2) 1 to 20% by weight of at least one monomer selected from the group consisting of acrylates and methacrylates is It is more preferable because it is easy to design a practical foaming temperature and it is easy to achieve a high foaming ratio.

If solvent resistance or foaming at high temperatures is desired, the outer shell is preferably formed from a copolymer containing (meth) acrylonitrile as a main component. Specifically, as polymerizable monomers, (c) 51 to 95% by weight of at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, and (d) vinylidene chloride;
It is possible to produce foamable microspheres using a monomer mixture containing 5 to 49% by weight of at least one monomer selected from the group consisting of acrylic acid esters, methacrylic acid esters, styrene, and vinyl acetate. preferable. More preferably, the monomer mixture is (c) 51 to 95% by weight of at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile,
(D1) 1 to 40% by weight of vinylidene chloride, and (d2)
1 to 48% by weight of at least one monomer selected from the group consisting of acrylic esters and methacrylic esters
It contains. If the copolymerization ratio of (meth) acrylonitrile is less than 51% by weight, solvent resistance and heat resistance decrease, and if it exceeds 95% by weight, the thermal expansion property is lowered, which is not preferable.

The copolymer containing no vinylidene chloride includes, as a polymerizable monomer, (e) 70 to 95% by weight of at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile; and (f) A copolymer obtained using a monomer mixture containing 5 to 30% by weight of at least one kind of monomer selected from the group consisting of acrylic acid esters and methacrylic acid esters is preferred. More preferably, the monomer mixture is selected from the group consisting of (e1) 55 to 75% by weight of acrylonitrile, (e2) 20 to 40% by weight of methacrylonitrile, and (f) acrylate and methacrylate. It contains at least 1 to 10% by weight of a monomer.
Even with such a copolymer, foamable microspheres having excellent gas barrier properties, solvent resistance, heat resistance, foamability, and the like can be obtained.

A crosslinkable monomer can be used together with the polymerizable monomer as described above to improve foaming characteristics and heat resistance. As the crosslinkable monomer, a compound having two or more carbon-carbon double bonds is usually used. More specifically, as a crosslinkable monomer, for example, divinylbenzene, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, allyl methacrylate, triallyl isocyanate, triacrylformal, triacrylformal (Meth) acrylic acid trimethylolpropane, dimethacrylic acid 1,3-butyl glycol, pentaerythritol tri (meth) acrylate, and the like. The usage ratio of the crosslinkable monomer is usually 0.1 to 1% by weight, preferably 0.2 to 0.8% by weight of the polymerizable monomer.

The polymerization initiator is not particularly limited, and those generally used in this field can be used, but an oil-soluble polymerization initiator soluble in the polymerizable monomer used is preferable. Examples of the polymerization initiator include dialkyl peroxide, diacyl peroxide, peroxycyester, peroxydicarbonate, and azo compound. More specifically, methyl ethyl peroxide, di-
dialkyl peroxides such as t-butyl peroxide and dicumyl peroxide; diacyl peroxides such as isobutyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide and 3,5,5-trimethylhexanoyl peroxide; t-butyl peroxy pivalate, t-hexyl peroxy pivalate, t-butyl peroxy neodecanoate, t-hexyl peroxy neodecanoate, 1-cyclohexyl-1-methylethyl peroxy neodecanoate , 1,
1,3,3-tetramethylbutyl peroxy neodecanoate, cumyl peroxy neodecanoate, (α, α
Peroxyesters such as -bis-neodecanoylperoxy) diisopropylbenzene; bis (4-t-butylcyclohexyl) peroxydicarbonate, di-n
-Propyl-oxydicarbonate, di-isopropylperoxydicarbonate, di (2-ethylethylperoxy) dicarbonate, di-methoxybutylperoxydicarbonate, di (3-methyl-3-methoxybutylperoxy) di Peroxydicarbonates such as carbonate; 2,2'-azobisisobutyronitrile;
Such as 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile) and 1,1'-azobis (1-cyclohexanecarbonitrile) Azo compounds, etc. The polymerization initiator is usually based on an aqueous dispersion medium,
It is used in a ratio of 0.0001 to 3% by weight.

In the suspension polymerization, a dispersion stabilizer (suspension agent) is usually used.
In an aqueous dispersion medium containing Examples of the dispersion stabilizer include silica, calcium phosphate, magnesium hydroxide, aluminum hydroxide, ferric hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, barium carbonate, and magnesium carbonate. Can be. Other co-stabilizers, for example, condensation products of diethanolamine and aliphatic dicarboxylic acids, condensation products of urea and formaldehyde, polyvinylpyrrolidone, polyethylene oxide, polyethyleneimine, tetramethylammonium hydroxide,
Gelatin, methylcellulose, polyvinyl alcohol,
Dioctyl sulfosuccinate, sorbitan ester,
Various emulsifiers and the like can be used. The dispersion stabilizer is
Usually, 0.1 to 2 parts by weight per 100 parts by weight of the polymerizable monomer.
Used in a proportion of 0 parts by weight.

The aqueous dispersion medium containing a dispersion stabilizer is usually prepared by mixing a dispersion stabilizer and 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 the dispersion stabilizer and the auxiliary stabilizer to be used. For example, when silica such as colloidal silica is used as a dispersion stabilizer, polymerization is performed in an acidic environment. To make the aqueous dispersion medium acidic, the pH of the system is adjusted to about 3 to 4 by adding an acid as needed. If magnesium hydroxide or calcium phosphate is used, polymerize in an alkaline environment.

One of the preferred combinations is a combination of colloidal silica and a condensation product. The condensation product is preferably a condensation product of diethanolamine and an aliphatic dicarboxylic acid, particularly preferably a condensation product of diethanolamine and adipic acid or a condensation product of diethanolamine and itaconic acid. Condensates are defined by their acid number. Preferably, the acid value is 60 or more and less than 95. Particularly preferred is a condensate having an acid value of 65 or more and 90 or less. Further, when an inorganic salt such as sodium chloride or sodium sulfate is added, foamable microspheres having a more uniform particle shape can be easily obtained. As the inorganic salt, salt is preferably used. The amount of colloidal silica used varies depending on the particle size, but is usually used in a proportion of 1 to 20 parts by weight, preferably 2 to 10 parts by weight, per 100 parts by weight of the polymerizable monomer. The condensation product is usually added in an amount of 0.05 to 100 parts by weight of the polymerizable monomer.
Used in a proportion of ~ 2 parts by weight. The inorganic salt is used at a ratio of about 0 to 100 parts by weight based on 100 parts by weight of the polymerizable monomer.

Another preferred combination is a combination of colloidal silica and a water-soluble nitrogen-containing compound. Examples of water-soluble nitrogen-containing compounds include polyvinylpyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, polydialkylaminoalkyl (meth) acrylate represented by polydimethylaminoethyl methacrylate and polydimethylaminoethyl acrylate, and polydimethylaminopropyl. Examples thereof include polydialkylaminoalkyl (meth) acrylamide represented by acrylamide and polydimethylaminopropyl methacrylamide, polyacrylamide, polycationic acrylamide, polyamine sulfone, and polyallylamine. Among these, a combination of colloidal silica and polyvinylpyrrolidone is preferably used. Another preferred combination is a combination of magnesium hydroxide and / or calcium phosphate with an emulsifier.

As the dispersion stabilizer, a poorly water-soluble metal water obtained by a reaction of a water-soluble polyvalent metal compound (eg, magnesium chloride) with an alkali metal hydroxide (eg, sodium hydroxide) in an aqueous phase. Colloids of oxides (eg, magnesium hydroxide) can be used. Also,
As the calcium phosphate, it is possible to use a reaction product of sodium phosphate and calcium chloride in an aqueous phase. As the emulsifier, an anionic surfactant such as a dialkyl sulfosuccinate or a phosphoric acid ester of polyoxyethylene alkyl (allyl) ether may be used.

The order of adding each component to the aqueous dispersion medium is as follows:
Although optional, usually, water, a dispersion stabilizer and, if necessary, a stabilizing aid are added to a polymerization can to prepare an aqueous dispersion medium containing the dispersion stabilizer. In the present invention, at least one compound selected from the group consisting of alkali metal nitrite, stannous chloride, stannic chloride, water-soluble ascorbic acids, and boric acid is added to the aqueous dispersion medium. The polymerizable monomer and the foaming agent may be separately added to the aqueous dispersion medium and then integrated in the aqueous dispersion medium to form a polymerizable mixture (oil-based mixture). And then
Add to the aqueous dispersion medium. The polymerization initiator can be used by adding it to the polymerizable monomer in advance, but if it is necessary to avoid premature polymerization, for example, an aqueous dispersion of a mixture of the polymerizable monomer and the blowing agent is used. The polymerization initiator may be added to the medium while stirring, and may be integrated in an aqueous dispersion medium. The polymerizable mixture (oil-based mixture) and the aqueous dispersion medium may be mixed in a separate container, stirred and mixed, and then charged into a polymerization can.

A polymerizable mixture containing a foaming agent, a polymerizable monomer, a polymerization initiator, and the like forms an oil phase in an aqueous dispersion medium. It can be granulated into droplets. Upon stirring and mixing, conditions such as the type of the stirrer and the number of rotations are set according to the desired particle size of the expandable microspheres. At this time, conditions are selected in consideration of the size and shape of the polymerization can, the presence or absence of a baffle, and the like. As the stirrer, a homogenizer having a high shearing force is preferable. The polymerization is usually carried out at a temperature of 40 to 80 ° C. by degassing or replacing with an inert gas. After polymerization, the aqueous phase is removed, for example, by filtration, centrifugation, sedimentation. If desired, the expandable microspheres are dried at a relatively low temperature such that the blowing agent does not gasify.

The particle size of the unexpanded expandable microspheres and the particle size after expansion can be varied in a wide range and are designed based on the properties required for the final product.
The average particle size of the expandable microspheres obtained by the present invention is, in an unfoamed state, usually about 3 to 100 μm, preferably 5 to 50 μm. The content of the foaming agent is usually about 5 to 30% by weight, preferably about 10 to 25% by weight.
It is. By controlling the combination and ratio of the polymerizable monomers to be used and the selection of the foaming agent, it is possible to produce foamable microspheres exhibiting various foaming behaviors.

The expandable microspheres obtained according to the present invention are used in various fields as they are expanded (expanded) or unexpanded. Foamable microspheres are used as fillers for paints for automobiles and the like, foaming agents for foaming inks (for giving relief patterns such as wallpapers and T-shirts), shrinkage inhibitors and the like by utilizing their expandability. You. In addition, foamable microspheres use a volume increase due to foaming to make plastics, paints, various materials, etc. lighter and more porous, and impart various functions (for example, slip properties,
It is used for the purpose of heat insulation, cushioning, sound insulation, etc.). In particular, the expandable microspheres according to the present invention are:
It can be suitably used in the field of paints and inks requiring surface properties and smoothness.

[0032]

The present invention will now be described more specifically with reference to examples and comparative examples. [Measurement method and definition] (1) Expansion ratio: expandable microsphere 0.7 g
Is placed in a gear oven and heated at a predetermined temperature (foaming temperature) for 2 minutes to foam. The obtained foam is put into a measuring cylinder, the volume is measured, and the volume is divided by the volume when not foamed to obtain a foaming ratio. (2) ΔT: represents a temperature difference between the temperature of the polymerization slurry in the polymerization canister and the temperature of a hot water bath (60 L of hot water) in which the polymerization canister is immersed during the polymerization of the 1.5 L polymerization canister.

[Comparative Example 1] A polymerization can with a stirrer (1.5
L) to 16.5 g of colloidal silica (solid content 40% by weight)
41.3 g of silica dispersion), diethanolamine-adipic acid condensation product (acid value 78 mgKOH / g) 1.6
An aqueous dispersion medium was prepared by charging 5 g (3.3 g of a 50% solution), 169.8 g of common salt and 557 g of water in total. Hydrochloric acid was added to adjust the pH of the aqueous dispersion medium to 3.2. On the other hand, an oily mixture composed of 147.4 g of acrylonitrile, 68.2 g of methacrylonitrile, 4.4 g of methyl methacrylate, 0.66 g of trimethylolpropane trimethacrylate, 26.2 g of n-pentane, and 15 g of petroleum ether was prepared (weight). Part ratio: acrylonitrile / methacrylonitrile / methyl methacrylate = 67/31/2). This oily mixture and the aqueous dispersion medium prepared above were stirred and mixed with a homogenizer to form fine droplets of the oily mixture.

An aqueous dispersion medium containing fine droplets of the oily mixture was charged into a polymerization vessel (1.5 L) equipped with a stirrer, and reacted at 60 ° C. for 20 hours using a hot water bath. It was difficult to remove the heat, and ΔT reached 2.7 ° C.
In addition, the viscosity of the polymerization slurry rapidly increased during the polymerization reaction, and the fluidity was extremely deteriorated. The sieving property of the slurry obtained after the polymerization was also poor. Many aggregates are observed in the slurry,
The polymer adhered to the can wall as scale. The obtained reaction product was repeatedly filtered and washed with water, and dried to obtain an expandable microsphere having an average particle size of 30 μm and a bulk density of 0.36 g / cm ³ . The expansion ratio of this expandable microsphere at an expansion temperature of 170 ° C. was 45 times. When the foaming behavior was observed while heating at a rate of 10 ° C./min using a microscope equipped with a hot stage,
Many foams were formed at a temperature of 30 ° C. or lower. 33. Diisonolyl phthalate of unfoamed expandable microspheres (hereinafter sometimes abbreviated as "DINP")
The viscosity of the 3% by weight solution was as high as 1600 centipoise. In addition, when the scale was increased to a 10-L polymerization can according to the above-mentioned formulation, the reaction temperature could not be controlled.

[Example 1] Except that 0.11 g of sodium nitrite was further added during preparation of the aqueous dispersion medium.
In the same manner as in Comparative Example 1, foamable microspheres were prepared. ΔT was as very small as 0.2 ° C., and even when scaled up to a 10 L polymerization vessel, the heat of polymerization was sufficiently removed. The viscosity of the slurry at the time of polymerization in the 1.5 L polymerization vessel was low, the fluidity was very good, and the sieving property of the obtained slurry was also good. Agglomerates and adhesion of polymer scale to the can wall were hardly observed. The obtained reaction product is repeatedly filtered and washed with water, dried and dried to have an average particle size of 28.
Foamable microspheres having a μm and a bulk density of 0.43 g / cm ³ were obtained. The expansion ratio of this expandable microsphere at an expansion temperature of 170 ° C. was 55 times. When the foaming behavior was observed while raising the temperature at a rate of 10 ° C./min with a microscope equipped with a hot stage,
Almost no foaming was observed at the following temperatures. Therefore, it is determined that foaming has occurred sharply.
DINP 33.3 of unexpanded effervescent microspheres
The viscosity of the weight% solution was as low as 720 centipoise, and the fluidity was good.

[Comparative Example 2] A polymerization can with a stirrer (1.5
792 g of deionized water was added to L), and 39.6 g of magnesium chloride hexahydrate was added and dissolved with stirring. To this, 0.044 g of Perex OT-P (manufactured by Kao Corporation, sodium dialkylsulfosuccinate) and 23.8 g of sodium hydroxide having a solid content of 25% by weight were added to prepare a magnesium hydroxide colloid dispersion. The pH of this aqueous dispersion (aqueous dispersion medium) was 9.8. On the other hand, 182.6 g of acrylonitrile, 26.4 g of methyl methacrylate, 11 g of methyl acrylate, 0.44 g of trimethylolpropane trimethacrylate, 1.1 g of 2,2'-azobis-2,4-dimethylvaleronitrile, and 39 g of pentane. An oily mixture consisting of 6 g was prepared (weight ratio: acrylonitrile / methyl methacrylate / methyl acrylate = 83).
/ 12/5). Next, the oily mixture and the aqueous dispersion prepared above were stirred and mixed with a homogenizer to granulate fine droplets of the oily mixture, and then charged into the polymerization can,
The reaction was performed at 57 ° C. for 20 hours.

When ΔT was as large as 6 ° C. and scaled up to a 10 L polymerization vessel, the heat removal of the polymerization heat was insufficient and the polymerization temperature could not be controlled. Also, the viscosity of the slurry at the time of polymerization in a 1.5 L polymerization vessel sharply increased, the fluidity was very poor,
The sieving property of the obtained slurry was also poor. Many aggregates were observed, and polymer scale was attached to the can wall and the stirring blade. The obtained reaction product is repeatedly filtered and washed with water, dried and dried to have an average particle size of 30 μm and a bulk density of 0.35 g / cm.
³ was obtained. The expansion ratio of this expandable microsphere at an expansion temperature of 170 ° C. was 39 times. The viscosity of a 33.3% by weight DINP solution of unexpanded expandable microspheres was as high as 2500 centipoise. When the foaming behavior was observed while raising the temperature at a rate of 10 ° C./min with a microscope equipped with a hot stage, many foams were observed at a temperature of 130 ° C. or lower.

Example 2 The procedure of preparing an aqueous dispersion (aqueous dispersion medium) was the same except that 0.11 g of boric acid was further added.
In the same manner as in Comparative Example 2, foamable microspheres were prepared. ΔT was as small as 2 ° C., and even if the scale was increased to a 10 L polymerization vessel, heat removal of the polymerization heat was sufficiently possible. The viscosity of the slurry at the time of polymerization in the 1.5 L polymerization vessel was low, the fluidity was good, and the sieving property of the obtained slurry was also good. Agglomerates and adhesion of polymer scale to the can wall were hardly observed. The obtained reaction product was repeatedly filtered and washed with water, and dried to obtain an expandable microsphere having an average particle size of 28 μm and a bulk density of 0.38 g / cm ³ . The foaming temperature of this foamable microsphere 1
The expansion ratio at 70 ° C. was 49 times. In addition, while heating at a rate of 10 ° C./min with a microscope equipped with a hot stage,
When the foaming behavior was observed, almost no foaming occurred at a temperature of 140 ° C. or lower. Therefore, it is determined that foaming has occurred sharply. The viscosity of a 33.3% by weight DINP solution of unexpanded expandable microspheres was as low as 1300 centipoise, indicating a marked improvement in flowability.

[Comparative Example 3] A polymerization can with a stirrer (1.5
To L), 770 g of deionized water and 11 g of colloidal silica having a solid content of 40% by weight were added and dissolved. Further, hydrochloric acid was added to prepare an aqueous dispersion medium having a pH of 3.5. On the other hand, 123.2 g of vinylidene chloride and 85.8 of acrylonitrile.
g, 11 g of methyl methacrylate, 0.33 g of trimethylolpropane trimethacrylate, 2,2'-azobis-
1.1 g of 2,4-dimethylvaleronitrile, butane 3
An oily mixture consisting of 5.2 g was prepared (weight ratio: vinylidene chloride / acrylonitrile / methyl methacrylate = 56/39/5). Next, the oily mixture and the aqueous dispersion medium prepared as described above were stirred and mixed with a homogenizer to granulate fine droplets of the oily mixture, charged in the polymerization can, and reacted at 50 ° C. for 22 hours. ΔT is 7 ° C
When scaled up to a large 10L polymerization can,
The removal of the heat of polymerization was insufficient and the polymerization temperature could not be controlled.
Further, the viscosity of the polymerization slurry in the 1.5-L polymerization vessel also sharply increased, and the fluidity was very poor. The sieving property of the obtained slurry was also poor. Many agglomerates were observed, and a large amount of polymer scale adhered to the can wall and the stirring blade. The obtained reaction product is repeatedly filtered and washed with water, and dried to have an average particle size of 1
An expandable microsphere having a size of 4 μm was obtained. The expandable microspheres are sifted to 200 mesh (mesh size 75
μm), the amount remaining on the mesh was 5% by weight. The expansion ratio of this expandable microsphere at an expansion temperature of 120 ° C. was 40 times.

Example 3 Foamable microspheres were prepared in the same manner as in Comparative Example 3 except that 0.088 g of stannic chloride was further added during the preparation of the aqueous dispersion medium. ΔT was as small as 1.5 ° C., and even when the scale was increased to a 10 L polymerization vessel, the heat of polymerization was sufficiently removed. The viscosity of the slurry at the time of polymerization in the 1.5 L polymerization vessel was low, the fluidity was good, and the sieving property of the obtained slurry was also good. Agglomerates and adhesion of polymer scale to the can wall were hardly observed. The obtained reaction product was repeatedly filtered and washed with water, and dried to obtain an expandable microsphere having an average particle size of 15 μm. When this expandable microsphere was sieved with a 200-mesh (mesh size: 75 μm) sieve, the amount remaining on the mesh was 0.1% by weight.
The following were very few. The expansion ratio of this expandable microsphere at an expansion temperature of 120 ° C. was 50 times.

Comparative Example 4 Foaming was carried out in the same manner as in Comparative Example 1, except that 1.1 g of polyvinylpyrrolidone having a molecular weight of 10,000 was added instead of the diethanolamine-adipic acid condensation product during the preparation of the aqueous dispersion medium. A microsphere was prepared. ΔT was as large as 3 ° C., and when a 10-liter polymerization vessel was scaled up, the heat removal of the polymerization heat was insufficient and the polymerization temperature could not be controlled. In addition, the viscosity of the slurry at the time of polymerization in the 1.5 L polymerization vessel rapidly increased, the fluidity was extremely poor, and the obtained slurry had poor sieving properties. Many aggregates were observed, and polymer scale was attached to the can wall and the stirring blade. The obtained reaction product is repeatedly filtered and washed with water, and dried to have an average particle size of 32 μm and a bulk density of 0.36 g.
/ Cm ³ was obtained. The expansion ratio of this expandable microsphere at an expansion temperature of 170 ° C. was 42 times. The viscosity of 33.3% by weight of DINP of the unfoamed expandable microsphere was as high as 2700 centipoise. When the foaming behavior was observed while raising the temperature at a rate of 10 ° C./min with a microscope equipped with a hot stage, many foams were observed at a temperature of 130 ° C. or lower.

Example 4 Except that 0.13 g of sodium nitrite was added during preparation of the aqueous dispersion medium,
In the same manner as in Comparative Example 4, foamable microspheres were prepared. ΔT is as small as 0.3 ° C. and becomes 10 L
Even when the scale was increased to a polymerization can, heat removal of the polymerization heat was sufficiently possible. The viscosity of the slurry at the time of polymerization in the 1.5 L polymerization vessel was low, the fluidity was good, and the sieving property of the obtained slurry was also good. Agglomerates and adhesion of polymer scale to the can wall were hardly observed. The obtained reaction product was repeatedly subjected to filtration and washing with water, dried, and had an average particle size of 31.
An expandable microsphere having a μm and a bulk density of 0.42 g / cm ³ was obtained. The expansion ratio of this expandable microsphere at an expansion temperature of 170 ° C. was 57 times. The viscosity of 33.3% by weight of DINP of the unexpanded expandable microsphere was as low as 800 centipoise, and the flowability was good. In addition, 10 ° C /
When the foaming behavior was observed while the temperature was raised at a rate of minutes, few foams were observed at a temperature of 140 ° C. or lower. Therefore, it is determined that foaming has occurred sharply.

Example 5 An effervescent microparticle was prepared in the same manner as in Example 4 except that 0.3 g of L-ascorbic acid (vitamin C) was added instead of sodium nitrite during preparation of the aqueous dispersion medium. A sphere was prepared. ΔT is
The temperature was very low at 0.3 ° C., and even when the scale was increased to a 10-L polymerization vessel, it was possible to sufficiently remove the heat of polymerization.
The viscosity of the slurry at the time of polymerization in the 1.5 L polymerization vessel was low, the fluidity was good, and the sieving property of the obtained slurry was also good. Agglomerates and adhesion of polymer scale to the can wall were hardly observed. The obtained reaction product was repeatedly filtered and washed with water, and dried to obtain an expandable microsphere having an average particle size of 32 μm and a bulk density of 0.43 g / cm ³ . The foaming temperature of this foamable microsphere is 170
The expansion ratio at ° C was 62 times. The viscosity of DIPP 33.3% by weight of the unfoamed expandable microspheres is 7
It was as low as 50 centipoise, and the fluidity was good. When the foaming behavior was observed while raising the temperature at a rate of 10 ° C./min with a microscope equipped with a hot stage,
What foamed at the following temperature was not so much recognized.
Therefore, it is determined that foaming has occurred sharply.

[0044]

According to the production method of the present invention, at the time of polymerization,
Since the aggregation of polymer particles is prevented and the polymer does not adhere to the polymerization vessel wall, heat generation due to polymerization can be efficiently removed, and high-quality foamable microspheres can be stably produced. Can be manufactured. Foamable microspheres obtained by the production method of the present invention,
Since the shape of the spherical particles is uniform and the number of non-spherical particles and agglomerated particles is small, the foaming is sharp and a uniform foam can be formed.

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Claims (9)

[Claims] 1. A foamable composition comprising a polymerizable mixture containing at least a foaming agent and a polymerizable monomer in an aqueous dispersion medium, which is subjected to suspension polymerization, and wherein the foaming agent is encapsulated in an outer shell of a produced polymer. In the method for producing microspheres, in the presence of at least one compound selected from the group consisting of alkali metal nitrite, stannous chloride, stannic chloride, water-soluble ascorbic acids, and boric acid, a polymerizable mixture A method for producing expandable microspheres, comprising performing suspension polymerization of 2. The method for producing expandable microspheres according to claim 1, wherein the alkali metal nitrite is sodium nitrite or potassium nitrite. 3. The method for producing expandable microspheres according to claim 1, wherein the water-soluble ascorbic acids are ascorbic acid, sodium ascorbate, or potassium ascorbate. 4. The polymerizable monomer comprises: (a) 30 to 95% by weight of vinylidene chloride; and (b) acrylonitrile;
4. A monomer mixture containing 5 to 70% by weight of at least one monomer selected from the group consisting of methacrylonitrile, acrylate, methacrylate, styrene, and vinyl acetate. Or 1
The method for producing an expandable microsphere according to the above item. 5. The monomer mixture comprises: (a) 40 to 80% by weight of vinylidene chloride; (b1) 19 to 50% by weight of at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile; (B2) The method for producing expandable microspheres according to claim 4, comprising 1 to 20% by weight of at least one monomer selected from the group consisting of acrylates and methacrylates. 6. The polymerizable monomer is (c) 51 to 95% by weight of at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile; and (d)
4. A monomer mixture containing from 5 to 49% by weight of at least one monomer selected from the group consisting of vinylidene chloride, acrylates, methacrylates, styrene, and vinyl acetate. A method for producing the expandable microsphere according to claim 1. 7. The monomer mixture comprises (c) 51 to 95% by weight of at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, (d1) 1 to 40% by weight of vinylidene chloride, and (D2) The method for producing expandable microspheres according to claim 6, which comprises 1 to 48% by weight of at least one monomer selected from the group consisting of acrylates and methacrylates. 8. The polymerizable monomer is selected from the group consisting of (e) 70 to 95 weight parts of at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, and (f) acrylic acid ester and methacrylic acid ester. The method for producing expandable microspheres according to any one of claims 1 to 3, wherein the mixture is a monomer mixture containing 5 to 30% by weight of at least one monomer selected from the group consisting of: 9. The monomer mixture is selected from the group consisting of (e1) 55 to 75% by weight of acrylonitrile, (e2) 20 to 40% by weight of methacrylonitrile, and (f) acrylate and methacrylate. 9. The method for producing expandable microspheres according to claim 8, comprising 1 to 10% by weight of at least one type of monomer.