Patents by Inventor Toshitada Shigemura

Toshitada Shigemura has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Cobalt-coated acicular magnetic iron oxide particles
    Patent number: 5968405
    Abstract: Cobalt-coated acicular magnetic iron oxide particles of the present invention have an average major axial diameter of 0.15 to 0.50 .mu.m, and comprise:as seed crystal particles, acicular magnetic iron oxide particles containing 0.05 to 1.0 wt % of phosphorus, calculated as P, based on the weight of the cobalt-coated acicular magnetic iron oxide particles;as inner layers, spinel ferrite layers containing cobalt formed on the surfaces of said seed crystal particles; andas outer layers, coating layers comprising a hydroxide of magnesium formed on said spinel ferrite layers.Such cobalt-coated acicular magnetic iron oxide particles show a smaller change of coercive force with temperature, have a small switching field distribution and, hence, are suitable as magnetic particles for magnetic recording media.
    Type: Grant
    Filed: June 23, 1997
    Date of Patent: October 19, 1999
    Assignee: Toda Kogyo Corporation
    Inventors: Minoru Yamasaki, Katsunori Fujimoto, Toshitada Shigemura, Katsumi Yamashita
  • Acicular magnetic iron oxide particles and process for producing the same
    Patent number: 5648014
    Abstract: Acicular magnetic iron oxide particles comprise:acicular magnetite particles having 10 to 24% by weight of ferrous as core particles;a magnetite coating which is formed on the surfaces of said acicular magnetite particles by epitaxial growth and which has maghemite at least in a part of the surface of said magnetite coating; anda cobalt-containing oxide layer which is formed on said magnetite coating and which contains cobalt of 1.5 to 2.5 wt % based on the total weight of said acicular magnetic iron oxide particles.
    Type: Grant
    Filed: December 8, 1995
    Date of Patent: July 15, 1997
    Assignee: Toda Kogyo Corporation
    Inventors: Mitsuaki Hatatani, Osamu Okimoto, Toshitada Shigemura, Yoshifumi Fukuhara, Hideaki Sadamura
  • Acicular magnetic iron oxide particles
    Patent number: 5294492
    Abstract: Disclosed herein is a process for producing acicular magnetic iron oxide particles comprising the steps of: mixing an aqueous dispersion of acicular magnetic iron oxide particles with an aqueous solution of a Co salt and an alkaline aqueous solution, or an aqueous solution of a Co salt, an aqueous solution of an Fe(II) salt and and an alkaline aqueous solution; and heat-treating the alkaline suspension solution obtained at 50.degree. to 100.degree. C.
    Type: Grant
    Filed: July 2, 1991
    Date of Patent: March 15, 1994
    Assignee: Toda Kogyo Corp.
    Inventors: Hiroshi Oka, Kazuaki Kouziro, Toshitada Shigemura, Tomohisa Moriya, Katsumi Yamashita, Kazushi Takama, Takanobu Uemoto, Kazuhiro Fujita