Patent ID: 6803164
Filing Date: 2004-10-12
Classification: G03G

Abstract:
A magnetic black toner comprising magnetic black toner particles containing at least a binder resin and a magnetic material;said toner having a weight-average particle diameter X (&mgr;m) of from 5 &mgr;m to 12 &mgr;m, and said toner having, in its particles of 3 &mgr;m or more in diameter, at least 90% by number of particles with a circularity (a) of 0.900 or more in number-based circularity distribution of circularity (a) as determined from the following equation (1), and having an average circularity of from 0.940 to 0.970; Circularity (a)=L0/Lâ€ƒâ€ƒ(1) where L0 represents the circumferential length of a circle having the same projected area as a particle image, and L represents the circumferential length of the particle image;said magnetic material comprising iron oxide particles which: 1) have an average particle diameter of from 0.10 &mgr;m to 0.30 &mgr;m; 2) contain titanium or a titanium compound in an amount of from 0.3% by weight to 1.5% by weight in terms of titanium, based on the total weight of the iron oxide particles; and 3) have the ratio of the proportion of FeO to the total Fe content in 10% by weight from the particle surface, A %, to the proportion of FeO to the total Fe content in the remainder 90% by weight, B %, which satisfies the following expression (2): 0.7&lE;A/B&lE;1.0â€ƒâ€ƒ(2); andan inorganic fine powder being externally added to the surfaces of said magnetic black toner particles.