Patent ID: 7947294

Claim:
Microparticles comprising a matrix polymer containing an effective coloring amount of at least 1 colorant and secondary particles distributed throughout the matrix polymer, wherein said colorant is entrapped in the matrix polymer, which matrix polymer is impermeable to the colorant and has been formed from a blend of monomers comprising a first monomer which is an ethylenically unsaturated ionic monomer and a second monomer which is an ethylenically unsaturated hydrophobic monomer selected from styrene, methyl methacrylate, tertiary butyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate and isobornyl methacrylate which is capable of forming a homopolymer of glass transition temperature in excess of 50° C., and wherein the secondary particles comprise a core of a hydrophobic polymer that has been formed from an ethylenically unsaturated hydrophobic monomer selected from styrene, methyl methacrylate, tertiary butyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate and isobornyl methacrylate which is capable of forming a homopolymer having a glass transition temperature in excess of 50° C. and optionally other monomers, which hydrophobic polymer is different from that of the matrix polymer, and which core is surrounded by a shell comprising the matrix polymer of the microparticle.