Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-08-24
2002-01-15
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C335S296000, C335S297000, C336S233000, C075S348000, C148S306000, C252S062530
Reexamination Certificate
active
06338900
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a soft magnetic composite material obtained by dispersing a powdered magnetic material composed of soft ferrite in a polymer, and more particularly to a soft magnetic composite material which has moderate permeability and moreover exhibits high electrical insulating property and has excellent dielectric strength.
BACKGROUND ART
Compounds (MO·Fe
2
O
3
) composed of ferric oxide and an oxide of a divalent metal are generally soft magnetic materials having high permeability &mgr; and are called soft ferrite. The soft ferrite is produced by a method of powder metallurgy and is hard and lightweight. Among various kinds of soft ferrite, Ni—Zn ferrite, Mg—Zn ferrite and Cu ferrite have feature that the resistivity is high, and the permeability is high in a high-frequency band. The soft ferrite is a ferrimagnetic oxide and mainly has a spinel type crystal structure. However, those having a ferroxplana type or garnet type crystal structure are also included. The soft ferrite has heretofore been used as a deflecting yoke material, high-frequency transformer, magnetic head material, etc.
The soft ferrite has a defect that it is fragile. However, it has been attempted to develop soft magnetic composite materials obtained by dispersing its powder in a polymer into new use applications as choke coils, rotary transformers, line filters, electromagnetic interference shielding materials (EMI shielding materials), etc., making the best use of its feature that the electric resistance is high. Since the soft magnetic composite materials use a polymer as a binder, they can be formed into molded or formed products of desired shapes by various kinds of molding or forming methods such as injection molding, extrusion and compression molding. However, a soft magnetic composite material obtained by dispersing soft ferrite powder having a high electric resistance in a polymer having high electrical insulating property has involved problems that it does not exhibit such a high electric resistance as expected from the electrical properties of both components, and is poor in dielectric strength.
The soft ferrite is generally produced as a sintered magnetic material through the steps of (i) mixing, (ii) calcination, (iii) grinding, (iv) granulation, (v) molding and (vi) sintering of raw materials such as Fe
2
O
3
, CuO, NiO, MgO and ZnO (dry process). A method in which finely particulate oxide powder is prepared by a co-precipitation process or atomization and thermal decomposition process also exists. In any method, oxide powder is formed into a sintered magnetic material through the steps of granulation, molding and sintering. The soft ferrite exhibits a high electric resistance (electrical insulating property) in the state of sintered magnetic material. However, it shows a tendency to markedly lower its electrical insulating property when the sintered magnetic material is ground and the resultant powdered magnetic material is blended with a polymer to prepare a composite material (resin composition).
Therefore, a molded or formed product obtained by molding or forming the composite material with the powdered magnetic material composed of the soft ferrite dispersed in the polymer cannot be used in an application field of which high electrical insulating property is required. In particular, such a molded or formed product has involved a problem that when it is used as a part of a power supply apparatus, such as a line filter of which dielectric strength of 1,500 V or higher is required, it generates heat during use or test to become unusable. Among various kinds of soft ferrite, Mg—Zn ferrite, Ni—Zn ferrite and Cu ferrite exhibit a high electric resistance in the state of sintered magnetic material. However, each of them shows a tendency to markedly lower the electric resistance when the sintered magnetic material is ground and the resultant powdered magnetic material is dispersed in a polymer.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a soft magnetic composite material which has moderate permeability and moreover exhibits high electrical insulating property and has excellent dielectric strength.
The present inventors have carried out an extensive investigation with a view toward overcoming the above-described problems involved in the prior art. As a result, it has been found that when soft ferrite in a sintered state is ground into a powdered magnetic material in such a manner that the average particle size of the powdered magnetic material amounts to at least twice the average crystal grain size of the sintered magnetic material, a soft magnetic composite material exhibiting a high electric resistance and having far excellent dielectric strength can be obtained by dispersing such a powdered magnetic material in a polymer to prepare the composite material.
Even when the average particle size of the powdered magnetic material is made comparatively small, high dielectric strength can be achieved so far as conditions of granulation, sintering, etc. are controlled in such a manner that the average crystal grain size of the resulting sintered magnetic material becomes small. Accordingly, the powdered magnetic material even in particle size distribution and comparatively small in particle size can be uniformly dispersed in the polymer, thereby providing a high-quality soft magnetic composite material. In the present invention, a soft magnetic composite material having particularly excellent dielectric strength and moderate permeability can be provided when Mg—Zn ferrite is used as the soft ferrite.
The present invention has been led to completion on the basis of these findings.
According to the present invention, there is thus provided a soft magnetic composite material obtained by dispersing a powdered magnetic material (A) composed of soft ferrite in a polymer (B), wherein the powdered magnetic material (A) is a powdered magnetic material of a random form obtained by grinding a sintered magnetic material, and the average particle size (d
2
) of the powdered magnetic material (A) is greater than the average crystal grain size (d
1
) of the sintered magnetic material by at least twice.
The powdered magnetic material (A) composed of soft ferrite may be preferably a powdered magnetic material composed of Mg—Zn ferrite.
BEST MODE FOR CARRYING OUT THE INVENTION
The soft ferrite useful in the practice of the present invention is a compound (MO·Fe
2
O
3
) composed of ferric oxide (Fe
2
O
3
) and an oxide (MO) of a divalent metal and is generally produced as a sintered material through the steps of mixing, calcination, grinding, granulation, molding and sintering of the raw materials by a dry process. When high-quality ferrite is produced, a co-precipitation process and an atomization and thermal decomposition process are used. Typical raw materials include Fe
2
O
3
, MnO
2
, MnCO
3
, CuO, NiO, MgO, ZnO, etc.
In the dry process, the respective raw materials are mixed on the basis of calculation so as to give the prescribed blending ratio. In the calcination step, the mixture is generally heated to a temperature of 850 to 1,100° C. in a furnace. The calcined ferrite is ground into powder having a particle size of about 1 to 1.5 &mgr;m. Before molding the ferrite powder in a mold, it is granulated into granules to attain a high bulk density and good flowability. The granulated ferrite powder is filled into the mold and compression-molded into the prescribed form by a molding machine. The molded ferrite is sintered in a large-sized tunnel type electric furnace or the like.
In the co-precipitation process, a strong alkali is added to an aqueous solution of metal salts to precipitate hydroxides. The hydroxides are oxidized to obtain finely particulate ferrite powder. The ferrite powder is formed into a sintered magnetic material through the steps of granulation, molding and sintering. In the atomization and thermal decomposition process, an aqueous solution of metal salts is subjected to thermal decomposition to obtain finely particulate
Suzuki Keiichiro
Tada Masahito
Bernatz Kevin M.
Dinsmore & Shohl LLP
Kureha Kagaku Kogyo K.K.
Resan Stevan A.
LandOfFree
Soft magnetic composite material does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Soft magnetic composite material, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Soft magnetic composite material will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2858423