MICROWAVE HEATABLE MATERIALS

43031 CAN 9A This invention relates to articles capable of being heated by microwave energy. The use of microwave radiation to generate heat in materials is becoming increasingly more prevalent in both consumer applications and in industrial applications because of the increased speed and lower power consumption of microwave processes, when contrasted with conventional heating processes. Microwave susceptors are materials that absorb microwave energy, convert the absorbed energy to heat energy, and thereby heat surrounding media. Two general categories of susceptors are: (1) thin-film susceptors; and (2) particulate susceptors. Particulate susceptors can be conveniently classified into two groups, namely electrically continuous particulate susceptors and electrically discontinuous particulate susceptors. The disadvantages of electrically continuous susceptors include non-uniform heating, the possibility of catastrophic arcing, and difficulty in regulating the heating rate. The disadvantages of electrically discontinuous susceptors can include high density, high expense, and non-uniform dispersion. This invention provides a composition comprising (a) susceptors having the capability of absorbing microwave energy, said susceptors comprising a particulate substrate substantially non-reflective of microwave energy and a coating capable of absorbing microwave energy, and (b) a matrix substantially non-reflective of microwave energy. Susceptors are typically particles having a thin-film coating thereon. The matrix typically comprises polymeric or ceramic materials that are stable at temperatures conventionally used in microwave cooking. The composition allows reuse of the susceptors, eliminates decline in heating rate, eliminates arcing, allows the heating rate to be controlled, allows overheating to be controlled, and allows formation of microwave heatable composite materials having very low metal content.