Magnetic iron oxide pigment prodn. for tape - comprises coating iron oxide core with cobalt ferrite and/or bertholloid cpd. contg. cobalt in three stages

摘要

In the prodn. of magnetic Fe oxide pigments (I), a magnetic Fe oxide core material (II) with the compsn. FeOx (x is over 1.33-1.5) is coated (1) with CoxFe(II)(1-x)(OH)2 (III) (x is over 0-1) by pptn. with aq. alkaline soln. then (2) with a Co cpd. and finally (3) opt. under oxidising conditios, with more Co cpd. Stage (1) pref. uses a Fe (II, III) salt with Fe (III) content of 0-67% and a Co salt and is carried out under oxidising conditions (air) or inert conditions, in alkaline medium. The soln. is stirred until Fe (III) is no longer present in the soln. before stage (3). The Co cpd. is Co (II) salt, pref. CoSO4.7H20. The Co content is 0.5-10% w.r.t. (II). Stage (3) can be carried out directly after stage (2) or after an intermediate coating, pref. over a time span extending to the end of the process. The temp. is between 20 deg. and the b.pt. pref. under 50 deg.C after stage (2) and then over 50 deg.C. USE/ADVANTAGE - (I) have good switching field distribution (sfd) and high coercivity and can be produced quickly at temps. below 100 deg.C. They are useful in magnetic tape