Abstract: Provided are microcapsules enclosing therein a magnetic fluid, which are useful for imparting sound-absorbing and insulating ability to building materials, etc. by incorporation thereinto or adhesion thereto by means of an adhesive, and processes for producing the microcapsules. The heat-expandable microcapsule of the present invention comprises (i) a shell composed of a thermoplastic resin and (ii) a magnetic fluid which is a dispersion of magnetic substance fine particles having an average particle diameter of 5-200 nm in a hydrophobic organic solvent and a hydrophobic liquid foaming agent, both enclosed in the shell. The hollow microcapsule of the present invention comprises (i) a shell composed of a thermoplastic resin, and (ii) a magnetic fluid which is a dispersion of magnetic substance fine particles having an average particle diameter of 5-200 nm in a hydrophobic organic solvent and a vacant cell both included in the shell.

Abstract: A light-weight sound absorbing and insulating plastic sheet material which exhibits an excellent sound absorbing and insulating effect even in the low- and medium-pitched sound range for use in building materials and sound-proof walls and a sound absorbing and insulating plastic panel using the plastic sheet material are provided. The sound absorbing and insulating plastic sheet material of the present invention comprises a plastic sheet-formed substance and magnetic fluid-enclosing capsules contained in the sheet-formed substance. The sound absorbing and insulating plastic panel of the present invention comprises the above-mentioned sound absorbing and insulating plastic sheet material and a fiber-reinforced plastic sheet bound to at least one side of the sheet material. The sound absorbing and insulating plastic sheet material and the sound absorbing and insulating plastic panel of the present invention are excellent also in electromagnetic wave shielding effect.