Magnetic oxide and process for producing same

Details Magnetic oxide and process for producing same Magnetic oxide and process for producing same

1995-02-16

1996-07-23

Bonner, Melissa

Compositions

Magnetic

Iron-oxygen compound containing

252 6256, 252 6262, 252 6263, H01F 100, H01F 111, H01F 136

Patent

active

055386563

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a magnetic oxide suitable for use in a wide range of technical fields, e.g., those of toners and carriers for electrophotography, electric resistance elements and magnetic fluids, which magnetic oxide is produced by mixing a magnetization control material of Ca, Ti, Sn, Si or Mg with hematite, hematite+magnetite, or magnetite to obtain a mixed powder and sintering the mixed powder so that it exhibits a given saturation magnetization. Also, the present invention relates to a process for producing the above magnetic oxide.


BACKGROUND ART

A single phase magnetite powder as one of the magnetic oxides has been utilized in a wide range of technical fields, e.g., those of magnetic fluids, electric resistance elements and toners and carriers for electrophotography. It is highly desired in the art to mass-produce a single phase magnetite powder exhibiting any predetermined saturation magnetization at a lowered cost.
The following three general methods are known for producing such a magnetite, and it is know that they have respective drawbacks as described below. alkaline and coprecipitated. production, although fine particles each having a relatively high purity are readily obtained by coprecipitation. or steam to thereby be reduced. atmosphere, e.g., either high pressure steam or hydrogen and carbon monoxide, so that danger accompanies the mass production, and that large scale equipment is required. difficult to stably produce fine quality powder for a prolonged period of time.
The magnetite powders produced by the above conventional processes have a drawback in that their saturation magnetization values are so high as compared with those of the conventional spinel ferrite that it is unfeasible to attain control of the saturation magnetization by composition regulation with the result that the conventional magnetite powders cannot be employed in use in which the saturation magnetization values inherent in magnetite powder are unacceptable. Magnetite powder having a saturation magnetization value inherent therein (fixed value specified in the second experimental example described later, e.g., up to 92 emu/g) has only partly been employed in use in carriers for electrophotographic development and the like. Moreover, the above magnetite powder having the saturation magnetization value inherent therein as it is cannot replace ferrite or the like in uses in which it has been employed, and, when the replacement is to be made, it is required to alter the circuit or device to be employed disadvantageously.
Taking into account the advantages and disadvantages of the above processes, various proposals have been made with respect to the production of magnetite powder for use in magnetic toners for electrophotography, etc.
For example, Japanese Patent Publication Nos. 238,580/1987, 39,498/1990 and 51,505/1990 disclose processes for producing magnetite useful as a carrier component of an electrophotographic developer, especially a two-component developer composed of a toner and a carrier. Each of these processes comprises providing magnetite powder (or globular magnetite particles) as a starting material, granulating the same into globular grains through, for example, mixing with a binder, followed by heating (sintering), and applying a resin coating to the resultant globular magnetite particles according to the conventional technique.
The use of a material called soft ferrite as carrier particles is known (U.S. Pat. No. 3,929,657, etc.). In this connection, it is known that the carrier particles each composed of the above ferrite not only are excellent in magnetic properties but also do not require a resin coating layer, so that their durability is excellent. Nothing that ferrite particles have resistance variations depending on the control of sintering atmosphere, even with the same composition, attempts have been made to enlarge resistance variation ranges by changing the sintering atmosphere. As an example thereof, there can be mentioned an attempt described in Japanese

REFERENCES:
patent: 3929657 (1975-12-01), Jones

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