JP2003220329A - Method for producing heat-expandable microcapsules and heat-expandable microcapsules - Google Patents

Abstract

(57) [Summary] An object of the present invention is to provide a heat-expandable microcapsule having a very high expansion ratio and capable of obtaining a high expansion ratio even with particles of 10 μm or less. In a method for producing a heat-expandable microcapsule, a volatile swelling agent is included in oil droplets of a polymerizable monomer, and a surfactant is present in a dispersion medium and / or oil droplets. Preferably, the surfactant is chemically bonded to the polymer forming the shell portion of the microcapsule, and a reactive surfactant having a double bond is particularly preferable.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a heat-expandable microcapsule, and more particularly to a method for producing a heat-expandable microcapsule having excellent heat-expandability.

[0002]

2. Description of the Related Art Thermoexpandable microcapsules can be obtained by microencapsulating a volatile expander which volatilizes at a temperature below the softening point of a thermoplastic polymer into the thermoplastic polymer.

A method for producing such a heat-expandable microcapsule has been known for a long time.
In JP-A 2-26524, an oil-soluble catalyst is mixed with an oil-based mixed liquid obtained by adding a volatile expanding agent such as an aliphatic hydrocarbon having a low boiling point to a polymerizable monomer, and then an aqueous dispersion containing an inorganic dispersant is added. A method for producing spherical microcapsules containing a volatile swelling agent by adding an oily mixture to a dispersion medium while stirring and performing suspension polymerization is disclosed.

However, according to the manufacturing method disclosed in Japanese Patent Publication No. 42-26524, it is not possible to obtain heat-expandable microcapsules having excellent heat-expandability.
The microcapsules having a small particle size of 0 μm or less have a drawback that the expansion ratio decreases.

Therefore, for example, Japanese Unexamined Patent Publication No. 5-309262
The publication discloses heat-expandable microcapsules of 10 μm or less obtained by polymerizing while suspending a mixed liquid containing a long-chain alkyl alcohol and the like in addition to a polymerizable monomer and a volatile expansion agent. There is. The heat-expandable microcapsules having a small particle size obtained by this method have an expansion ratio slightly improved as compared with the conventional one, but have an expansion ratio of 20.
More than double the number was limited to particles containing vinylidene chloride in the shell composition, and the applications of the heat-expandable microcapsules were limited.

Further, in Japanese Patent Laid-Open No. 5-329360, a thermal expansion microcapsule obtained by encapsulating two or more kinds of low boiling point hydrocarbons having different boiling points as a volatile expansion agent is prepared before foaming. It is described that the heat treatment is performed at a temperature below the foaming temperature. The heat-expandable microcapsules obtained by this method also have improved expansion ratios as compared with conventional ones, but they cannot be said to be heat-expandable microcapsules having sufficiently excellent heat-expandability, and are described in the examples. The maximum expansion coefficient of the heat-expandable microcapsule is less than 80 times.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-expandable microcapsule having an excellent heat-expanding property in view of the above problems, and a method for producing a heat-expandable microcapsule having an excellent heat-expanding property. Is to provide.

[0008]

The method for producing heat-expandable microcapsules according to claim 1 is a volatilization that volatilizes at a temperature lower than the softening point of the polymerizable monomer and the polymer forming the shell portion of the microcapsules. In a method for producing a thermally expandable microcapsule in which a volatile expansion agent is dispersed in a dispersion medium and a volatile expansion agent is included in oil droplets of a polymerizable monomer, polymerization is performed, and a surface active agent is used in the dispersion medium and / or oil droplets. It is characterized by the presence of an agent.

The method for producing heat-expandable microcapsules according to claim 2 is a dispersion medium comprising a polymerizable monomer and a volatile expander which volatilizes at a temperature lower than the softening point of the polymer forming the shell portion of the microcapsule. In the method for producing a thermally expandable microcapsule in which the volatile expanding agent is polymerized in the oil droplet of the polymerizable monomer, the polymerizable monomer and the volatile expanding agent are reacted in the oil droplet. A characteristic surfactant is contained.

The method for producing heat-expandable microcapsules according to claim 3 is the heat-expandable microcapsule according to claim 1 or 2, wherein the surfactant is a nonionic surfactant. And

The heat-expandable microcapsule according to claim 4 is characterized in that the surfactant is contained inside the particles and / or on the surface of the particles.

The heat-expandable microcapsule according to a fifth aspect is the heat-expandable microcapsule according to the fourth aspect, characterized in that the surfactant is a nonionic surfactant.

The heat-expandable microcapsule according to claim 6 is the heat-expandable microcapsule according to claims 4 and 5, wherein the surfactant chemically reacts with the polymer forming the shell portion of the microcapsule. It is characterized by being combined.

The thermally expandable microcapsule according to claim 7 is characterized in that it has an average particle size of 1 to 10 μm, a maximum volume expansion ratio of 20 times or more, and does not contain a substance containing chlorine.

The polymerizable monomer used in the method for producing the heat-expandable microcapsule of the present invention includes (meth) acrylic acid, itaconic acid, maleic acid, fumaric acid, vinylbenzoic acid and their esters and amides, Styrene, methyl styrene, ethyl styrene,
Examples thereof include styrenes such as chlorostyrene; vinyl compounds such as vinyl chloride and vinyl acetate; vinylidene compounds such as vinylidene chloride. These can be used alone or in combination of two or more kinds.

Among them, nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile and fumaronitrile, mixtures of these nitrile monomers, methyl acrylate, ethyl acrylate, butyl acrylate, dicyclo Acrylic esters such as pentenyl acrylate;
Non-nitrile monomers such as methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate and isobornyl methacrylate are preferred.

A mixture of a nitrile-based monomer and a non-nitrile-based monomer is preferable as the polymerizable monomer because of its excellent solvent resistance and foamability at high temperature. Acrylonitrile and methacrylonitrile are particularly preferable as the nitrile-based monomer, and methyl methacrylate, ethyl methacrylate, and methyl acrylate are particularly preferable as the non-nitrile-based monomer.

Further, since the solvent resistance and the foamability at high temperature are particularly excellent, the nitrile-based monomer is 80% by weight or more, more preferably 90 to 97% by weight in the polymerizable monomer, and the non-nitrile-based monomer is It is preferably 20% by weight or less, more preferably 10 to 3% by weight.

If desired, a polyfunctional monomer may be added to the polymerizable monomer. By using a polyfunctional monomer, a cross-linked network is formed in the polymer forming the shell part, the gas barrier property is improved and the expansion ratio is improved, and the stickiness of the particle surface is suppressed without impairing the expandability during heating, It is considered that the secondary aggregation of the above can be prevented.

The type of polyfunctional monomer is not particularly limited, but for example, as di (meth) acrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, trimethylolpropane di (meth) acrylate and the like can be mentioned. Examples of the tri (meth) acrylate include trimethylolpropane tri (meth) acrylate and ethylene oxide-modified trimethylolpropane tri (meth) acrylate. Examples thereof include acrylate and pentaerythritol tri (meth) acrylate. Other polyfunctional monomers include pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, diallyl phthalate,
Examples thereof include di- or triallyl compounds such as diallyl malate, diallyl fumarate, diallyl succinate and triallyl isocyanurate, and divinyl compounds such as divinylbenzene and butadiene. These can be used alone or in combination of two or more kinds. .

The volatile swelling agent contained in the microcapsules is a substance that volatilizes at a temperature below the softening point of the polymer polymerized from the above polymerizable monomer component, and a low boiling point organic solvent is preferable. Specifically, for example, low molecular weight hydrocarbons such as ethane, 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, CClF ₂ chlorofluorocarbons such as -CCl ₂ F _2; tetramethylsilane, trimethylethyl silane, trimethyl isopropyl silane, trimethyl -n-
Tetraalkylsilane such as propylsilane; 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 preferable. Further, if desired, a compound which is thermally decomposed into a gas by heating may be used.

Examples of the dispersion medium in the present invention include deionized water to which a dispersion stabilizer or a co-stabilizer is added. Here, the pH of the aqueous phase at the time of polymerization is appropriately determined depending on the type of dispersion stabilizer or auxiliary stabilizer used. For example, when silica such as colloidal silica is used as the dispersion stabilizer, the polymerization is performed in an acidic environment. To make the aqueous medium acidic, the pH of the system is adjusted to 3 to 4 by adding an acid such as hydrochloric acid as needed. If magnesium hydroxide or calcium phosphate is used, polymerize in an alkaline environment.

Examples of the dispersion stabilizer in the present invention include silica, calcium phosphate, magnesium hydroxide,
Examples thereof include aluminum hydroxide, ferric hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, calcium carbonate, barium carbonate and magnesium carbonate. As the auxiliary stabilizer, for example, a condensation product of diethanolamine and an aliphatic dicarboxylic acid, a condensation product of urea and formaldehyde, polyvinylpyrrolidone, polyethylene oxide,
Polyethyleneimine, tetramethylammonium hydroxide, gelatin, methylcellulose, polyvinyl alcohol, dioctylsulfosuccinate, sorbitan ester and the like can be used.

One of the preferable 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, and particularly preferably a condensation product of diethanolamine and adipic acid or a condensation product of diethanolamine and itaconic acid. Furthermore, when an inorganic salt such as sodium chloride or sodium sulfate is added, it becomes easy to obtain heat-expandable microcapsules having a more uniform particle shape. The amount of colloidal silica used is adjusted depending on the particle diameter, but is preferably 1 to 20 parts by weight, and more preferably 2 to 10 parts by weight, relative to 100 parts by weight of the polymerizable monomer. The condensation product is the polymerizable monomer 10
It is preferable that the proportion is 0.05 to 2 parts by weight with respect to 0 parts by weight. The amount of the inorganic salt is preferably 0 to 100 parts by weight with respect to 100 parts by weight of the polymerizable monomer.

Another preferable combination is a combination of colloidal silica and a water-soluble nitrogen-containing compound. Examples of the water-soluble nitrogen-containing compound 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 polydimethylaminopropylmethacrylamide, polyacrylamide, polycationic acrylamide, polyamine sulfone, and polyallylamine. Among these, colloidal silica and polyvinylpyrrolidone are preferably used. Other preferred combinations include combinations of magnesium hydroxide and / or calcium phosphate with emulsifiers.

In the combination of colloidal silica and polyvinylpyrrolidone, the particle size can be adjusted by changing the addition amounts of colloidal silica and polyvinylpyrrolidone.

The production method of the present invention is a method for producing heat-expandable microcapsules by polymerizing a monomer in the presence of a low-boiling volatile swelling agent, characterized in that a surfactant is present in the polymerization system. And In addition, the heat-expandable microcapsules obtained by the production method of the present invention are characterized by containing a surfactant inside the particles and / or on the surface of the particles, so that a high expansion ratio can be obtained during expansion.

Although the mechanism of action of the surfactant of the present invention is not clear, when the heat-expandable microcapsules are expanded by heating, they can be plasticized without impairing the strength of the polymer forming the shell portion, and the shell layer is formed. It is considered that the heat-expandable microcapsules exhibiting excellent heat-expanding property and excellent strength are formed because they are uniformly stretched. That is, although it is possible to plasticize the shell layer with a low molecular weight alcohol or organic acid, it is presumed that a surfactant having a large molecular weight was suitable for maintaining the mechanical strength of the polymer forming the shell layer. It

The surfactant is not particularly limited,
For example, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether phosphate, polyoxyethylene polyoxypropylene block polymer, polyoxyethylene oleate, polyoxyethylene distearate, sorbitan alkyl Ester, nonionic surfactants such as polyoxyethylene sorbitan acid alkyl ester, sodium alkylbenzene sulfonate, sodium dialkylsulfosuccinate, polyoxyethylene dialkyl allyl ether sulfate ammonium, polyoxyethylene dialkenyl allyl ether sulfate ammonium, polyoxyethylene Dialkyl phenyl ether sulfate ammonium and Sodium, anionic surfactants such as sodium higher alcohol sulfate esters, and other cationic surfactants, and the like reactive surfactant introduced a vinyl group on the surfactant.

In the above surfactants, it is preferable to use nonionic surfactants in order to prevent salting out with the inorganic dispersant. Further, a reactive surfactant having a double bond in the molecule is more preferable, and examples thereof include polyoxyethylene-propenylalkylphenyl ether and polyoxyethylene-propenylalkylphenyl ether sulfate. These reactive surfactants may be used alone or in combination of two or more. Specifically, among the reactive surfactants, polyoxyethylene alkyl propylene phenyl ether (Aqualon RN manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), which is a nonionic surfactant, is preferable.

When the amount of the above-mentioned surfactant added is too small, the effect of improving the expansion ratio cannot be obtained, and when it is too large, the polymerization reaction becomes unstable. Therefore, the monomer, the volatile expansion agent, and the polymerization initiator are combined. 0.1 to 100 parts by weight of oil component
It is preferable to use 10 parts by weight, more preferably 0.5 to 5 parts by weight, and further preferably 1 to 5 parts by weight. A surfactant may be used as a dispersion aid for a dispersion stabilizer such as magnesium hydroxide and / or calcium phosphate, but if the surfactant is excessively present in the dispersion medium, microencapsulation becomes difficult. Therefore, the surfactant which is present as a dispersion aid is only slightly present in the dispersion medium in the first place.
Therefore, in the method for producing heat-expandable microcapsules of the present invention, when the surfactant is present only in the dispersion medium, it is preferable that the surfactant is present in the dispersion medium slightly in excess of the amount of the surfactant required as a dispersion aid.

The above-mentioned surfactant may be added to either the oily mixed liquid or the dispersion medium, or may be added to the mixture of the oily mixed liquid and the dispersion medium, but it is present in the dispersion medium for the above-mentioned reason. Since it is not preferable to make the amount of the surfactant to be present excessively, it is preferable to add the surfactant to the oily mixed solution or both the oily mixed solution and the dispersion medium so that the surfactant can be contained in a large amount. It is preferable because the polymerization can be stably carried out easily.

The order of adding the respective components to the dispersion medium is arbitrary, but normally, the dispersion medium containing the dispersion stabilizer is prepared by adding water, a dispersion stabilizer and, if necessary, a co-stabilizer to the polymerization vessel. Adjust. If necessary, compounds such as alkali metal nitrite, stannous chloride, stannic chloride and potassium dichromate are added. The polymerizable monomer and the volatile swelling agent may be separately added to the dispersion medium to form an oily mixed solution in the dispersion medium, but usually both are mixed in advance and then added to the dispersion medium. The polymerization initiator can be used by adding it to the above oily mixed solution in advance, but may be added after stirring and mixing the dispersion medium and the oily mixed solution in the polymerization vessel. Alternatively, the oily mixed liquid and the dispersion medium may be mixed in another container, mixed and stirred, and then charged in a polymerization vessel.

The polymerization initiator that can be used in the polymerization in the present invention is not particularly limited, and those generally used can be used, but it is an oil-soluble polymerization initiator that is soluble in the polymerizable monomer. Preferably there is. For example,
Examples include dialkyl peroxides, diacyl peroxides, peroxyesters, peroxydicarbonates, and azo compounds. More specifically, diethyl peroxide such as methyl ethyl peroxide, di-t-butyl peroxide, dicumyl peroxide; isobutyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 3,5, Diacyl peroxide such as 5-trimethylhexanoyl peroxide; t-butylperoxypivalate, t-hexylperoxypivalate, t-butylperoxyneodecanoate, t-hexylperoxyneodecanoate, 1 -Cyclohexyl-1-methylethylperoxy neodecanoate,
1,1,3,3-tetramethylbutyl peroxy neodecanoate, cumyl peroxy neodecanoate, (α,
α-bis-neodecanoylperoxy) diisopropylbenzene and other peroxyesters; bis (4-t-butylcyclohexyl) peroxydicarbonate, di-
n-propyl-oxydicarbonate, di-isopropylperoxydicarbonate, di (2-ethylethylperoxy) dicarbonate, di-methoxybutylperoxydicarbonate, di (3-methyl-3-methoxybutylperoxy) Peroxydicarbonates such as dicarbonates; 2,2'-azobisisobutyronitrile,
2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 1,1′-azobis (1-cyclohexanecarbonitrile), etc. Azo compounds; and the like.

The heat-expandable microcapsule of the present invention can be obtained by the above-mentioned production method, and is characterized in that the surfactant is contained inside and / or on the surface of the particle. The surfactant contained in the heat-expandable microcapsules is preferably a nonionic surfactant for the above-mentioned manufacturing reasons. further,
Thermally expandable microcapsules preferably have a surfactant chemically bonded to the polymer forming the shell portion of the microcapsules. A reactive surfactant having a double bond can be chemically bonded when a polymerizable monomer is polymerized to form a polymer forming a shell portion.

The heat-expandable microcapsule of the present invention is preferably a heat-expandable microcapsule having an average particle size of 1 to 10 μm, a maximum volume expansion ratio of 20 times or more, and containing no substance containing chlorine. The maximum expansion ratio here is the thermal expansion microcapsule itself at the optimum foaming temperature at which the expansion ratio becomes maximum when the expansion ratio is measured by changing the heating temperature in the temperature range in which the thermally expandable microcapsule can expand. Is the expansion ratio of.

[0037]

[Examples] Examples 1 to 4 The oily mixed solution and the dispersion medium prepared according to the formulation of Table 1 were stirred and mixed by a homogenizer, and then charged into a nitrogen-substituted pressure polymerization vessel (20 L) and pressurized (0. 2MP
a) Reaction was carried out at 60 ° C. for 8 hours. The obtained reaction product was filtered, washed with water and dried to obtain heat-expandable microcapsules. The expansion ratio (volume ratio) of the obtained microcapsules was measured while changing the heating conditions. Also, the secondary aggregation state during heating was evaluated. The evaluation results are shown in Table 1.

Comparative Example 1 Thermally expandable microcapsules were obtained in the same manner as in Example 1 according to the formulation shown in Table 1. However, the only difference is that no surfactant was added. The obtained microcapsules were evaluated in the same manner as in Example 1 and the results are shown in Table 1.

Comparative Example 2 Thermally expandable microcapsules were obtained in the same manner as in Example 1 according to the formulation shown in Table 1. However, the only difference is that the amount of surfactant added is increased. As a result of the polymerization, a large amount of particle aggregates were generated, and it was not possible to evaluate the foaming of the particles.

Comparative Example 3 Thermally expandable microcapsules were obtained in the same manner as in Example 1 according to the formulation shown in Table 1. However, the only difference is that no surfactant was added. The obtained microcapsules were evaluated in the same manner as in Example 1 and the results are shown in Table 1.

[Measurement Method] (Average Particle Diameter) The volume average particle diameter of the thermally expandable microcapsules was measured using a laser diffraction particle size distribution analyzer manufactured by Horiba Ltd. (Expansion Ratio) 0.5 g of the heat-expandable microcapsules was placed in a gear-type oven and heated at 170 ° C. for 2 minutes to foam. The obtained foam was put into a graduated cylinder, the volume was measured, and the expansion ratio was obtained by dividing the volume by the volume before unfoaming.

[0042]

[Table 1]

[0043]

The heat-expandable microcapsules of the present invention have a very high expansion ratio, and a high expansion ratio can be obtained even with particles of 10 μm or less.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuhiro Kawaguchi             4560 Kaisei-cho, Shinnanyo-shi, Yamaguchi Prefecture Tokuyama Sekisui Industry Co., Ltd.             Within the corporation (72) Inventor Toshiharu Furukawa             4560 Kaisei-cho, Shinnanyo, Yamaguchi Prefecture Sekisui Chemical Co., Ltd.             Within the corporation F-term (reference) 4G005 AA01 AB05 AB14 AB17 AB30                       BA03 BB02 BB06 DA05X                       DA14X DC02X DC26Z DC34Y                       DC41Y DD02Z DD04Z DD08Z                       DD12Z DD32X DD58Z DD66Z                       DD77X                 4J011 KA29 KB29 KB30 PA23 PA24                       PA47 PB37

Claims (7)

[Claims] 1. A polymerizable monomer and a volatile swelling agent that volatilizes at a temperature lower than the softening point of the polymer forming the shell portion of the microcapsule are dispersed in a dispersion medium, and volatile expansion occurs in oil droplets of the polymerizable monomer. A method for producing heat-expandable microcapsules, which comprises polymerizing in the state of containing an agent, wherein a surfactant is present in a dispersion medium and / or oil droplets. 2. A polymerizable monomer and a volatile swelling agent that volatilizes at a temperature lower than the softening point of the polymer forming the shell portion of the microcapsule are dispersed in a dispersion medium, and volatile expansion occurs in oil droplets of the polymerizable monomer. In the method for producing a heat-expandable microcapsule in which an agent is polymerized in a state of being encapsulated, the oil-droplet is characterized by containing a reactive surfactant in addition to the polymerizable monomer and the volatile expander. Manufacturing method of microcapsules. 3. The method for producing thermally expandable microcapsules according to claim 1, wherein the surfactant is a nonionic surfactant. 4. A heat-expandable microcapsule containing a surfactant inside and / or on the surface of the particle. 5. The heat-expandable microcapsule according to claim 4, wherein the surfactant is a nonionic surfactant. 6. The heat-expandable microcapsule according to claim 4, wherein the surfactant is chemically bonded to the polymer forming the shell portion of the microcapsule. 7. A heat-expandable microcapsule having an average particle diameter of 1 to 10 μm, a maximum volume expansion ratio of 20 times or more and containing no substance containing chlorine.