US 7,572,505 B2
	Black magnetic iron oxide particles having high breakdown voltage
Naoki Uchida, Ohtake (Japan); Ryo Iwai, Ohtake (Japan); Mamoru Kamigaki, Ohtake (Japan); Shinji Uemoto, Ohtake (Japan); Koso Aoki, Ohtake (Japan); and Hiromitsu Misawa, Ohtake (Japan)
Assigned to Toda Kogyo Corporation, Hiroshima-shi, Hiroshima-ken (Japan)
Filed on Apr. 19, 2007, as Appl. No. 11/785,737.
Claims priority of application No. 2006-126173 (JP), filed on Apr. 28, 2006.
Prior Publication US 2007/0254157 A1, Nov. 01, 2007
Int. Cl. B32B 5/16 (2006.01)

U.S. Cl. 428—403  [428/329; 428/699; 428/701; 428/900]

5 Claims

1. Black magnetic iron oxide particles comprising core particles and a surface layer formed on a surface of the respective core particles, the surface layer consisting of a compound of at least one alkali earth metal element selected from the group consisting of Mg, Ca, Sr and Ba and an aluminum element, in which a content of the at least one alkali earth metal element present in the surface layer is from 100 ppm to 1000 ppm on the basis of a whole weight of the black magnetic iron oxide particles; a content of the aluminum element present in the surface layer is from 1000 ppm to 20000 ppm on the basis of a whole weight of the black magnetic iron oxide particles; a ratio [A/B] of the content [A (ppm)] of the aluminum element to the content [B (ppm)] of the at least one alkali earth metal element present in the surface layer is from 1 to 100; and said black magnetic iron oxide particles have a breakdown voltage of not less than 400 V/cm.