Patent ID: 8058320

Claim:
A thermally foamable microsphere having a structure that a foaming agent is encapsulated in an outer shell formed from a polymer, wherein the thermally foamable microsphere has a foaming start temperature which is higher than 180Â° C., and has a foaming start temperature after a heat treatment at 170Â° C. for 2 minutes which is at most 180Â° C., wherein the thermally foamable microsphere exhibits 60 to 85% with respect to a percent reduction in expansion ratio, which is represented by the equation [(R2/R1)Ã—100], where R1 is an expansion ratio when heated and foamed for 1 minute at 200Â° C. after the heat treatment is conducted at 170Â° C. for 2 minutes, and R2 is an expansion ratio when heated and foamed for 4 minutes at 200Â° C. after the heat treatment is conducted at 170Â° C. for 2 minutes, wherein the outer shell formed of at least one of the following: (a) a vinylidene (co)polymer consisting of: (A) 30 to 100% by weight of vinylidene chloride, (B) 0 to 70Â° A by weight of at least one vinyl monomer selected from the group consisting of acrylonitrile, methacrylonitrile, acrylic esters, methacrylic esters, styrene and vinyl acetate, and (C) a crosslinkable monomer in a proportion of at most 5 parts by weight per 100 parts by weight in total of (A) and (B), or (b) a (meth)acrylonitrile (co)polymer consisting of: (D) 30 to 100% by weight of at least one nitrile monomer selected from the group consisting of acrylonitrile and methacrylonitrile, (E) 0 to 70% by weight of at least one other vinyl monomer selected from the group consisting of vinylidene chloride, acrylic esters, methacrylic esters, styrene and vinyl acetate, and (F) a crosslinkable monomer in a proportion of at most 5 parts by weight per 100 parts by weight in total of (D) and (E), and wherein the foaming agent is a mixture containing (G) 50 to 90% by weight of isododecane and (H) 10 to 50% by weight of foaming agent(s) having a boiling point lower than the boiling point of isododecane, wherein the percentages for (G) and (H) are based on a total weight of the mixture.