Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-09-03
2002-01-29
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S431000, C252S062200, C252S062200
Reexamination Certificate
active
06342557
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a resin composition comprising a synthetic resin and a powdered magnetic material, and particularly to a resin composition which comprises, as a powdered magnetic material, soft ferrite powder having a low rate of permeability change by temperature and can be suitably used in a field of filters such as duplexers and multiplexers, and a molded or formed product from such a resin composition.
BACKGROUND OF THE INVENTION
Compounds (MO·Fe
2
O
3
) composed of ferric oxide and an oxide of a divalent metal are soft magnetic materials exhibiting a high permeability and generally called soft ferrite. Sinter molded or formed products from soft ferrite such as Ni—Zn ferrite, Mg—Zn ferrite or Mn—Zn ferrite are widely used as, for example, magnetic cores for radios, televisions, communication equipment, OA apparatus, inductors for switching power sources and the like, transformers, filters, etc.; head cores for video or image apparatus and magnetic disk apparatus; and the like.
In recent years, composite materials (resin compositions) obtained by dispersing a powdered magnetic material in a polymer have attracted attention as new magnetic materials, since they can be formed into molded or formed products of desired shapes and sizes by melt processing processes such as injection molding, extrusion and compression molding. Resin compositions making use of soft ferrite powder as a powdered magnetic material have also been proposed. However, the soft ferrite powder tends to undergo changes in its magnetic properties, for example, reduction in effective permeability by the formation of its composite with a synthetic resin. Therefore, the application fields of the resin compositions comprising the synthetic resin and soft ferrite powder are limited under the circumstances to choke coils, rotary transformers, electromagnetic wave shielding materials, etc.
Investigations have heretofore been made to apply resin compositions comprising a synthetic resin and soft ferrite powder to an application field of noise filters. A filter has a function that an electric current within a certain frequency band is caused to pass through, and great attenuation is given to electric currents within other frequency bands than that frequency band. Such a resin composition may be used as a various kinds of noise filters that suppress noises in a wide frequency band. Since the resin composition has a too high rate of permeability change by temperature, however, it has involved a problem that in a field of filters such as duplexers and multiplexers that perform a separation of a specific frequency band, or the like, the frequency band to be separated varies due to changes in environmental temperature, resulting in a failure to use it.
More specifically, in the conventional resin compositions making use of soft ferrite powder, the rate of permeability change by temperature amounts to higher than 0.025%/° C. or lower than −0.025%/° C. in a temperature range of from 20° C. to 80° C. Therefore, the inductance of an electronic part making use of a molded or formed product (hereinafter may be referred to as “molded product” merely) from such a resin composition greatly varies according to changes in environmental temperature. When the inductance greatly varies, a frequency band to be separated changes, and so the electronic part has been unable to be used as an electronic part for separating a specific frequency, such as a duplexer or multiplexer.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a resin composition which comprises a synthetic resin and a powdered magnetic material, has an extremely low rate of permeability change by temperature and can be applied to an application field of filters which separate a specific frequency, such as duplexers and multiplexers.
Another object of the present invention is to provide a molded product from such a resin composition.
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 soft ferrite powder having a rate of permeability change by temperature ranging from −0.040 to 0.010%/° C. in a temperature range of from 20° C. to 80° C. is used as a powdered magnetic material in combination with a synthetic resin, whereby the rate of permeability change by temperature of a molded product from a resin composition comprising the synthetic resin and the powdered magnetic material can be lowered within a range of ±0.025%/° C., preferably ±0020%/° C. It has also been found that when the average particle diameter and blending proportion of the soft ferrite powder are selected within respective specific ranges, a resin composition well balanced between magnetic properties such as permeability, and the molding and processing ability can be provided. The present invention has been led to completion on the basis of these findings.
According to the present invention, there is thus provided a resin composition comprising a synthetic resin and a powdered magnetic material, wherein:
(1) the powdered magnetic material is soft ferrite powder having a rate of permeability change by temperature ranging from −0.040 to 0.010%/° C. in a temperature range of from 20° C. to 80° C. and an average particle diameter ranging from 2 to 1,000 &mgr;m, and
(2) the powdered magnetic material is contained in a proportion of 50 to 1,400 parts by weight per 100 parts by weight of the synthetic resin.
According to the present invention, there is also provided a molded or formed product obtained by molding or forming the resin composition.
DETAILED DESCRIPTION OF THE INVENTION
Soft Ferrite Powder:
No particular limitation is imposed on the composition and production process of the soft ferrite powder useful in the practice of the present invention so far as it is soft ferrite powder having a rate of permeability change by temperature ranging from −0.040 to 0.010%/° C. in a temperature range of from 20° C. to 80° C. and an average particle diameter ranging from 2 to 1,000 &mgr;m.
The soft ferrite is generally a compound (MO·Fe
2
O
3
) composed of ferric oxide (Fe
2
O
3
) and an oxide (MO) of a divalent metal. Examples of M include Ni, Mn, Co, Cu, Zn, Mg and Cd. Among various kinds of soft ferrite, soft ferrite having a composition represented by the general formula, (XO)
x
(ZnO)yFe
2
O
3
is preferred. In the general formula, X means one or more of divalent metals such as Ni, Cu, Mg, Co and Mn. x and y denote a compositional ratio (molar ratio) of XO to ZnO. A molar ratio of (XO)
x
(ZnO)
y
(=x+y) to Fe
2
O
3
is generally about 0.3:0.7 to 0.7:0.3, preferably about 0.4:0.6 to 0.6:0.4. Examples of such soft ferrite include Ni—Zn ferrite, Mg—Zn ferrite and Mn—Zn ferrite.
In order to improve the permeability and the like of the soft ferrite used in the present invention, a small amount of additives, for example, SiO
2
, PbO, PbO
2
, As
2
O
3
, V
2
O
5
and the like, may be added to the soft ferrite in the course of the preparation thereof. In the soft ferrite, it is also preferred to control the content of an iron oxide in order to suppress the deposition of hematite.
The soft ferrite powder used in the present invention can be obtained in accordance with the publicly known process such as the dry process, co-precipitation process or atomization and thermal decomposition process. Main raw materials of the soft ferrite are, for example, metal oxides such as Fe
2
O
3
, NiO, MnO
2
, ZnO, MgO, CuO, etc. and/or metal carbonates. In the dry process, the raw materials such as the metal oxides and/or the metal carbonates are mixed with each other with their blending proportions calculated so as to give a prescribed blending ratio, fired and then ground. In this dry process, it is preferred that the raw mixture be calcined at a temperature of 850 to 1,100° C. and ground into fine particles and then granulated into granules, and the granules be further really fire
Suzuki Keiichiro
Tada Masahito
Cain Edward J.
Dinsmore & Shohl LLP
Kureha Kagaku Kogyo K.K.
Wyrozebski Katarzyna Lee
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