Electromagnetic wave absorbing compositions
An electromagnetic wave-absorbing composition is obtained by dispersing in a base polymer a magnetic powder coated with electrically insulating inorganic fines and optionally, a heat conductive powder. The composition has a high breakdown voltage, and can be applied to any adequate site within electronic equipment without a need to pay substantial attention to short-circuits.
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)
R 1 a SiO (4−a)/2 (1)
wherein, R 1 , 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)
R 1 a SiO (4−a)/2 (1)
wherein, R 1 , 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.