Abstract: Polymer fine particles are obtained by emulsion-polymerizing one or more monomers having a carboxylate group represented by the following formula and an unsaturated group that is radical polymerizable:--COO.sup.- X.sup.+ (I)wherein in the formula (I), X.sup.+ is one species selected from the group consisting of monovalent metal ion, ##STR1## wherein R.sub.1 to R.sub.5 may be the same or different, representing hydrocarbon groups having a number of carbon atom or atoms of 1 to 4 respectively. Alternatively, polymer fine particles may be obtained by performing emulsion polymerization in the presence of a compound containing the foregoing carboxylate group. In the obtained polymer fine particles, the carboxylate group is incorporated into surfaces of the fine particles by the aid of covalent bond or physical adsorption. Metallic parts such as those contained in a printer are not corroded owing to the presence of the carboxylate group on the surfaces of the fine particles.

Abstract: Polymer fine particles are obtained by emulsion-polymerizing one or more monomers having a carboxylate group represented by the following formula and an unsaturated group that is radical polymerizable:--COO.sup.- X.sup.+ (I)wherein in the formula (I), X.sup.+ is one species selected from the group consisting of monovalent metal ion, ##STR1## wherein R.sub.1 to R.sub.5 may be the same or different, representing hydrocarbon groups having a number of carbon atom or atoms of 1 to 4 respectively. Alternatively, polymer fine particles may be obtained by performing emulsion polymerization in the presence of a compound containing the foregoing carboxylate group. In the obtained polymer fine particles, the carboxylate group is incorporated into surfaces of the fine particles by the aid of covalent bond or physical adsorption. Metallic parts such as those contained in a printer are not corroded owing to the presence of the carboxylate group on the surfaces of the fine particles.