Patent ID: 7351752

Claim:
Thermo-expansive microspheres comprising a shell of thermoplastic resin and a blowing agent encapsulated in the shell; said blowing agent being a fluorine-containing compound having ether linkage, being free of chlorine and bromine atoms, and gasifying at a temperature not higher than the softening point of said thermoplastic resin, wherein the fluorine-containing compound includes at least one member selected from the group consisting of C 3 F 7 OCH 3 , C 4 F 9 OCH 3 , C 4 F 9 OC 2 H 5 , and C 7 F 15 OC 2 H 5 ; the thermo-expansive microspheres have a CV, or coefficient of variation, of particle size distribution being 30% or less and said thermoplastic resin comprises a polymer of monomeric mixture containing 0.01 to 0.43 weight percent of a polymerizable monomer having at least two polymerizable double bonds.