Patent ID: 8329298

Claim:
A method of producing heat-expandable microspheres, each heat-expandable microspheres comprising a shell of thermoplastic resin, and a non-fluorine blowing agent encapsulated therein having a boiling point not higher than the softening point of the thermoplastic resin, the production method comprising the step of: dispersing an oily mixture that includes: a polymerizable component essentially comprising a carboxyl-group-containing monomer and a nitrile monomer that define a monomer component, and being free of a monomer reactive with the carboxyl group in the carboxyl-group-containing monomer; the blowing agent; and a polymerization initiator in an aqueous dispersing medium; and polymerizing the polymerizable component; wherein the carboxyl-group-containing monomer is in an amount of 20 to 75 weight percent of the monomer component; wherein the nitrile monomer is in an amount of 25 to 60 weight percent of the monomer component; wherein the monomer reactive with the carboxyl group in the carboxyl-group-containing monomer is selected from the group consisting of N-methylol (meth)acrylamide, N,N-dimethyl aminoethyl (meth)acrylate, N,N-dimethyl aminopropyl (meth)acrylate, magnesium mono(meth)acrylate, zinc mono(meth)acrylate, vinyl glycidyl ether, propenyl glycidyl ether, glycidyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate; wherein the polymerization initiator contains at least one peroxydicarbonate selected from the group consisting of diethyl peroxydicarbonate, di-n-propyl peroxydicarbonate, bis(4-t-butylcyclohexyl) peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, di-3-methoxybutyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-2-octyl peroxydicarbonate, dicycrohexyl peroxydicarbonate, and dibenzyl peroxydicarbonate; and wherein the peroxydicarbonate constitutes 60 weight percent or more of the polymerization initiator.