Patent Number: 
Section: claims

1. An electromagnetic wave-absorbing composition comprising a curable organopolysiloxane as a base polymer and a magnetic powder coated with electrically insulating inorganic submicron fines in an RF thermal plasma method, dispersed therein,said composition having an Asker C hardness of up to 80 when cured. 2. The composition of claim 1 wherein the magnetic powder is of a magnetic metal material containing at least 15% by weight of iron. 3. The composition of claim 1 which exhibits a breakdown voltage of at least 50 V when molded into a sheet of 1 mm thick. 4. An electromagnetic wave-absorbing composition comprising a curable organopolysiloxane as a base polymer, and a magnetic powder coated with electrically insulating inorganic submicron fines in an RF thermal plasma method and a heat conductive powder, both dispersed therein, said composition having an Asker C hardness of up to 80 when cured. 5. The composition of claim 4 wherein the magnetic powder is of a magnetic metal material containing at least 15% by weight of iron. 6. The composition of claim 4 which exhibits a breakdown voltage of at least 50 V when molded into a sheet of 1 mm thick. 7. The composition of claim 4 wherein the base polymer is a curable organopolysiloxane. 8. The composition of claim 4 which has an Asker C hardness of up to 80 when cured. 9. A sheet obtained by molding and heat curing an electromagnetic wave-absorbing composition comprising a curable organopolysiloxane as a base polymer and a magnetic powder coated with electrically insulating inorganic submicron fines in an RF thermal plasma method, dispersed therein, said composition having an Asker C hardness of up to 80 when cured. 10. A sheet obtained by molding and heat curing an electromagnetic wave-absorbing composition comprising a curable organopolysiloxane as a base polymer, and a magnetic powder coated with electrically insulating inorganic submicron fines in an RF thermal plasma method and a heat conductive powder, both dispersed therein, said composition havening an Asker C hardness of up to 80 when cured. 11. The composition of claim 1 or 4 wherein the composition when cured has a thermal conductivity of at least 1.0 W/mk. 12. A sheet of claim 9 or 10 wherein the composition when cured has a thermal conductivity of at least 1.0 W/mk. 13. The composition of claim 1 or 4 wherein the curable organopolysiloxane has at least two alkenyl radicals per molecule and has the average compositional formula (1)R1aSiO(4−a)/2  (1)wherein, R1, which may be the same or different, stands for substituted or unsubstituted monovalent hydrocarbon radicals having 1 to 10 carbon atoms, and the subscript “a” is a positive number from 1.98 to 2.02, and the composition further comprises a combination of an organohydrogenpolysiloxane and an addition reaction catalyst or an organic peroxide so that a silicone rubber or silicone gel having an Asker C hardness of up to 80 is obtained when cured. 14. The sheet of claim 9 or 10 wherein the curable organopolysiloxane has at least two alkenyl radicals per molecule and has the average compositional formula (1)R1aSiO(4−a)/2  (1)wherein, R1, which may be the same or different, stands for substituted or unsubstituted monovalent hydrocarbon radicals having 1 to 10 carbon atoms, and the subscript “a” is a positive number from 1.98 to 2.02, and the composition further comprises a combination of an organohydrogenpolysiloxane and an addition reaction catalyst or an organic peroxide so that a silicone rubber or silicone gel having an Asker C hardness of up to 80 is obtained when cured.