Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2001-01-19
2003-05-06
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C428S469000, C252S062570, C252S062590, C252S062620, C241S016000
Reexamination Certificate
active
06558807
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to oxide magnetic materials to be used in fields of high frequency and a method of producing the same, as well as coil components of bulk type using the oxide magnetic material, laminated coil components including internal conductors and a method of producing the same.
As oxide magnetic materials such as coil component to be used in fields of high frequency, Ni—Cu—Zn based ferrite is in general employed, and a producing method therefor is ordinarily a powder metallurgy method.
This method weighs oxides such as Fe
2
O
3
, NiO, CuO or ZnO to be predetermined percentages, wet- or dry-mixes and grinds, and pre-sinters the mixed and ground powders. Subsequently, the pre-sintered material is roughly ground and further finely ground. In a case of the wet-grind, the drying process is necessary.
The characteristics of ferrite much depend on the composition thereof, and from the viewpoint of production management, a composition of a final product should be deviated as little as possible from a target composition.
It is necessary that a material for a laminated coil be sintered at lower temperatures than a melting point of Ag, and in a final product, such a management of the composition is demanded at a level of 0.1 mol % of Fe
2
O
3
, NiO, CuO and ZnO. In particular, as to Fe
2
O
3
, coming nearer to a stoichiometric composition of ferrite, its reactivity goes up, but exceeding said level, the reactivity rapidly goes down, and accordingly, the most careful management of the composition is required among main components of ferrite.
Incidentally, for a conventional Ni—Cu—Zn ferrite, a stainless steel ball, alumina ball or zirconia ball were used as media beads in its manufacturing process, and materials having passed through mixture, grind, and pre-sintering were subjected to a rough and a fine grind. In the material for bulk typed coil, the pre-sintered material is ordinarily ground such that a specific surface area is 1.0 to 7.0 m
2
/g, and as the laminated typed material is necessarily sintered at lower temperature than a melting point of Ag, a long time is taken for grind, and the specific surface area is heightened to around 3.0 to 15.0 m
2
/g, thereby to improve the reactivity of the ground powders at low temperature.
In the stainless steel ball, Fe is a main component, and a part of Fe
2
O
3
being a main component in the composition of Ni—Cu—Zn ferrite is increased by a mechanochemical reaction when grind. This increase of Fe
2
O
3
changes the composition of Ni—Cu—Zn ferrite, and makes a management of stable composition difficult to an extent that the management is not available by weighed values. A difficulty was involved with the abrasion resistance also in other media beads and a problem was that abrasion powders of these beads might be mixed as impurities.
In the general media beads, an inside toughness, that is, the abrasion resistance is low in comparison with an outside toughness, and a deviation in the composition arises due to difference in a mixing amount during continuing productions, so that a stable composition might not be probably obtained, and the grind efficiency is low. In addition, a grind for a long time invites an increase of the mixing amount and deterioration of characteristics of sintered materials, accordingly. Abrasion powders mixed as impurities worsens the sintering property of Ni—Cu—Zn ferrite, and sintering temperature becomes high for obtaining a density and a permeability of sintered body in the vicinity of a theoretical density, resulting in a production cost-up and decrease of stability of products, and the sintering below the Ag melting point is difficult.
Japanese Patent No. 2708160 sets forth that, aiming at decreasing mixture of abrasion powders during grind, balls composed of fully stabilized zirconia (called as “FSZ” hereafter) of large abrasion resistance or partially stabilized zirconia (called as “PSZ” hereafter) are used as media beads for grinding Mn—Zn based ferrite.
The method disclosed in Japanese Patent No. 2708160 is to use the zirconia balls of 0.5 to 3.0 mm as the media beads in the fine grind process, thereby preventing inclusion of impurities to the most to be below 0.02 wt % vs. the main components. Further, by this method, if the sintering is carried out at lower temperature by around 100 to 200° C. with respect to the conventional pre-sintering temperature of 1200° C. or higher, a sintered body of the high density near the theoretical density is obtained, so that the sintering temperature decreases industrially and the production cost can be reduced.
Japanese Patent No. 2599887 shows an example that, for a purpose of offering a magnetic material of high mechanical strength, ZrO
2
of 0.01 to 3.0 wt % is mixed for main components of materials of Ni—Cu—Zn ferrite, and is sintered for 1.5 hours.
Postexamined Japanese patent publication JP-B-6-80613 discloses an example that, for a purpose of offering a Ni—Zn ferrite of a high density, Bi
2
O
3
is added in a range of 4<Bi
2
O3≦20 wt % with respect to main components of Ni—Zn based ferrite to obtain a magnetic material of a high density.
But the sintering temperature in the range of 1000° C. described in Japanese Patent No. 2708160 is high and it is not a temperature enabling to realize reduction of the sintering cost. Additionally, when Ag is used as a conductor, a simultaneous sintering with Ag of the melting point being around 960° C. is impossible. Being 1100° C. as in JP-A-7-133150, it is still more impossible to simultaneously sinter with Ag.
In the method described in the above mentioned Japanese Patent No. 2708160, the media beads of small diameter are used for controlling inclusion of impurities by abrasion of the media beads to be low, and a pre-sintered material is ground taking a long time, for example, 192 hours (8 days), creating a problem that a ball efficiency (material treating amount/ball weight), that is, the grind efficiency is poor.
In the producing method set forth in the above mentioned JP-B-6-80613, a sintering temperature is not clear. In the only example stating a temperature and containing 10 wt % Bi
2
O
3
, when the sintering temperature is 950° C., the density is around 4.86, and when ds (density) is 5 or higher, the sintering temperature is 960° C. or higher. Thus, the simultaneous sintering with Ag is difficult.
In view of the above mentioned problems involved with the prior arts, it is accordingly an object of the invention to provide oxide magnetic materials enabling to simultaneously sinter with Ag as an internal conductor, holding the sintering property and the permeability, and enabling to shorten the grind time, coil components using such oxide magnetic materials as well as a method of producing said oxide magnetic materials and a method of producing said coil components.
SUMMARY OF THE INVENTION
For accomplishing the object, the invention is to offer the oxide magnetic materials of the under mentioned (1) to (9), coil components using these oxide magnetic materials, as well as the method of producing the oxide magnetic materials and the method of producing the coil components.
(1) An oxide magnetic material where Fe
2
O
3
, ZnO, NiO and CuO are main components, is characterized in that Y
2
O
3
, ZrO
2
and Bi
2
O
3
are contained with respect to these main components, such that an amount of Y
2
O
3
is 0.007 to 0.028 wt % for the total amount, an amount of ZrO
2
is 0.12 to 0.55 wt % therefor and an amount of Bi
2
O
3
is 0.03 to 10.12 wt % for the same.
(2) A coil component of bulk type is characterized in that a sintered substance of the oxide magnetic material as set forth (1) is used.
(3) A laminated coil component is characterized in that a sintered substance of the oxide magnetic material as set forth in (1) is used, and the sintered substance is formed with an electric conductive layer.
(4) The laminated coil components as set forth in (3), characterized in that the electric conductive layer is Ag or Ag.Pd alloy being a main component.
(5) A method of producing oxide ma
Ito Ko
Takahashi Yukio
Blackwell-Rudasill G.
Jones Deborah
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
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