Plastic and nonmetallic article shaping or treating: processes – Recycling of reclaimed or purified process material – Of process trim or excess blanked material
Reexamination Certificate
2000-04-03
2001-10-02
Derrington, James (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Recycling of reclaimed or purified process material
Of process trim or excess blanked material
C264S611000, C264S612000, C264S613000, C264S037100, C252S062560, C252S062590, C252S062620
Reexamination Certificate
active
06296791
ABSTRACT:
BACKGROUND OF THE INVENTIONS
1. Field of the Invention
The present invention relates to a process for producing an oxide magnetic material having soft magnetism, particularly Mn—Zn ferrite. More particularly, the invention relates to a process for producing Mn—Zn ferrite which enables scraps of a sintered product to be regenerated and reused.
2. Description of the Related Art
There is Mn—Zn ferrite as a representative oxide magnetic material having soft magnetism. This Mn—Zn ferrite has conventionally widely been used as low loss materials used in switching power supply transformer, flyback transformer or deflection yoke, various inductance elements, impedance elements for EMI countermeasure, electromagnetic wave absorbers and the like. This Mn—Zn ferrite generally has a composition comprising basic components of more than 50 mol % of Fe
2
O
3
, 52 to 55 mol % of Fe
2
O
3
on the average, 10 to 24 mol % of ZnO and the remainder being MnO. The Mn—Zn ferrite has conventionally been produced by mixing each raw material powder of Fe
2
O
3
, ZnO and MnO in predetermined proportion, forming the resulting mixture into a predetermined shape through each step of calcination, milling, component adjustment, granulation, pressing and the like, and then subjecting a green compact to sintering treatment such that the green compact is maintained at 1,200 to 1,400° C. for 3 to 4 hours in a reducing atmosphere having oxygen concentration greatly decreased by letting nitrogen gas flow.
The reason for sintering in a reducing atmosphere is that since the green compact contains Fe
2
O
3
in a large amount of 50 mol % or more, if it is sintered in the air, densification does not proceed sufficiently, and as a result, good soft magnetism is not obtained. Further, Fe
2+
to be formed by reduction of Fe
3+
has a positive crystal magnetic anisotropy, and therefore has the effect that it offsets a negative crystal magnetic anisotropy of Fe
3+
, thereby increasing soft magnetism. However, if sintered in the air, formation of Fe
2+
by such a reduction reaction cannot be expected. In the above described milling step, milling is conducted such that powder has an average particle size of about 1.0 to 1.4 &mgr;m. The reason for this is that if the average particle size is larger than 1.4 &mgr;m, the desired density is not obtained in sintering, and if the average particle size is smaller than 1.0 &mgr;m, it is difficult to handle the powder.
In the production of Mn—Zn ferrite as described above, many scraps are produced in each step for the reasons of a surplus of ferrite, defective ferrite or the like. Wastes produced in the steps before pressing have no specific problem on its regeneration utilization. However, regarding scraps of a sintered product due to defects such as dimensional defect, crack, breakage or the like in the sintering step, it is the trend that it is difficult to regenerate and reuse those for the reasons described hereinafter and those are disposed.
The reason why regeneration utilization of scraps of a sintered product is difficult is explained below.
The sintering step of Mn—Zn ferrite is rate-determined to a vacancy concentration of oxygen ion that has the slowest diffusion rate in the constituent ions. Factors which govern this are a content of Fe
2
O
3
and an oxygen concentration in an atmosphere. Vacancy of oxygen ion tends to be easily formed as the Fe
2
O
3
content is small and the oxygen concentration in an atmosphere is low. However, since the conventional Mn—Zn ferrite contains Fe
2
O
3
in an amount of more than 50 mol %, vacancy of iron ion, manganese ion and zinc ion is largely formed corresponding to decrease in vacancy of oxygen ion. In other words, if it is intended to mill and press a sintered product of the conventional Mn—Zn ferrite for reuse, sintering must be conducted under the condition that oxygen concentration in an atmosphere is considerably lowered. However, the oxygen concentration which can be lowered in the actual mass-production step is at most about 0.1%, and the oxygen concentration in this degree can not secure the necessary vacancy concentration of oxygen ion. As a result, sintering does not proceed smoothly, making it difficult to obtain the desirable density of the ferrite.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-described problems in the prior art. An object of the present invention is to provide a process for producing Mn—Zn ferrite which enables regeneration and reuse of scraps of a sintered product without involving specific difficulty in sintering.
The above-described object can be achieved by the following embodiments of the present invention.
According to a first aspect of the present invention, there is provided a process for producing Mn—Zn ferrite, which comprises reusing a powder obtained by milling a sintered product of Mn—Zn ferrite, subjecting the powder to a component adjustment so as to have a composition of 44.0 to 50.0 mol % of Fe
2
O
3
, 4.0 to 26.5 mol % of ZnO, 0.1 to 8.0 mol % of at least one member selected from the group consisting of TiO
2
and SnO
2
, and the remainder being MnO, pressing the resulting mixed powder after the component adjustment, and then sintering the green compact.
According to a second aspect of the present invention, there is provided a process for producing Mn—Zn ferrite, which comprises reusing a powder obtained by milling a sintered product of Mn—Zn ferrite, subjecting the powder to a component adjustment so as to have a composition of 44.0 to 50.0 mol % of Fe
2
O
3
, 4.0 to 26.5 mol % of ZnO, 0.1 to 8.0 mol % of at least one member selected from the group consisting of TiO
2
and SnO
2
, 0.1 to 16.0 mol % of CuO, and the remainder being MnO, pressing the resulting mixed powder after the component adjustment, and then sintering the green compact.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In first and second aspects of the present invention, the amount of the powder for reuse, i.e., regenerated power to be used is optional, and if the powder has the objective composition of components as it is, the entire amount of the mixed powder for pressing may be used as the regenerated powder. In the case that the regenerated powder alone does not have the objective composition of components, the component adjustment is of course conducted by adding an appropriate amount of each raw material powder of Fe
2
O
3
, ZnO, TiO
2
, SnO
2
, CuO, MnO and the like. Further, an average particle size of the regenerated powder is desirably restricted to about 1.0 &mgr;m in its lower limit as the same as in the conventional one, but the upper limit thereof may be a value exceeding 1.4 &mgr;m, for example about 2.0 &mgr;m.
The first and second aspects of the present invention restrict the Fe
2
O
3
content to 50 mol % less as described above. Therefore, even if a regenerated powder is used, vacancy of oxygen ion tends to be easily formed in the course of sintering, and even if the powder is sintered (heated-maintained-cooled) in the air or an atmosphere containing a certain amount of oxygen, a density thereof sufficiently increases. However, since too small Fe
2
O
3
content causes to invite a decrease in an initial permeability, Fe
2
O
3
should be contained in an amount of at least 44.0 mol %.
It is known that Ti and Sn receive an electron from Fe
2+
, thereby Fe
3+
is formed. Therefore, by containing Ti and Sn, Fe
2+
can be formed even by sintering the powder in the air or an atmosphere containing a certain amount of oxygen. In the first and second aspects of the present invention, it is made possible to obtain good soft magnetism by that the content of TiO
2
and/or SnO
2
in the composition of the basic components is adjusted to 0.1 to 8.0 mol % to control the amount of Fe
2+
to be formed, thereby optimizing an existence ratio of Fe
3+
and Fe
2+
in order to cancel out positive and negative crystal magnetic anisotropy. However, if the content of TiO
2
and/or SnO
2
is less than 0.1 mol %, its effect is small. On the oth
Honda Koji
Kawasaki Shunji
Kobayashi Osamu
Yamada Osamu
Derrington James
Minebea Co. Ltd.
Oliff & Berridg,e PLC
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