MnMgCuZn ferrite material

Details MnMgCuZn ferrite material MnMgCuZn ferrite material

1999-03-18

2001-03-13

Koslow, C. Melissa (Department: 1755)

Compositions

Magnetic

Iron-oxygen compound containing

C252S062590, C252S062620, C252S062640

Reexamination Certificate

active

06200493

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an MnMgCuZn ferrite material, particularly to an MnMgCuZn ferrite material which has a low magnetic loss and a sufficient saturated magnetic flux density and which can be used in a deflection yoke core or a transformer for a high speed scanning cathode-ray tube, particularly a high-definition high-speed scanning cathode-ray tube.
For example, an MnMgZn ferrite material (Japanese Patent Application Laid-open No. 65499/1973) is heretofore used in a deflection yoke core for a high speed scanning cathode-ray tube (hereinafter referred to as CRT). Since the MnMgZn ferrite material is relatively high in resistivity and low in material cost, it has been broadly used as a ferrite material for the deflection yoke core not only domestically but also internationally.
In a method of manufacturing the deflection yoke core, in the same manner as a general ferrite core, materials are mixed, calcined, ground, kneaded together with an appropriate binder, granulated, and press-molded in a predetermined shape using a metallic mold, and the molded material is sintered. When the conventional MnMgZn ferrite material is used, sintering is performed at a temperature of 1250° C. or higher.
Furthermore, recently, CRT display has progressed in raising definition and increasing screen size, while household television has progressed in increasing speed and enlarging angle. Additionally, for the increased definition and speed, a horizontal frequency has become very high. As a result, a ferrite core for use in a deflection yoke is requested to reduce a magnetic loss. Moreover, for the enlarged screen and angle, the ferrite core for use in the deflection yoke needs to have a high saturated magnetic flux density.
On the other hand, in order to prevent thermal runaway at an operation temperature, it is desirable in the deflection yoke core that a temperature coefficient of magnetic loss in the vicinity of 100° C. be negative. In a technique for making negative the temperature coefficient of magnetic loss, a ferrite having a high Curie point is used, and the Curie point necessary for the deflection yoke is about 140° C. or higher.
To suppress ringing phenomenon, the deflection yoke core needs to have a high resistivity. In the ringing phenomenon, an electrostatic capacity is generated between coils or between coil and core, and vertical streaks appear on screen by modulated currents. In order to suppress the ringing phenomenon, the necessary resistivity of the ferrite core is set to 10
6
&OHgr;cm or more (Japanese Patent Publication No. 75714/1993).
In the aforementioned circumstances, it is disclosed in Japanese Patent Publication No. 66254/1991, 75714/1993 and Journal of the Magnetics Society of Japan 21,915-918(1997) that when copper oxide is applied in the range of 5 mol % or less (in terms of CuO) to the conventional MnMgZn ferrite material, the magnetic loss is reduced. In order to further increase the saturated magnetic flux density and Curie point, however, the content of copper oxide needs to be increased. In an MnMgCuZn ferrite material containing more than 5 mol % of copper oxide in terms of CuO, there is a problem that when calcining is performed at a temperature of 1250° C. or higher, abnormal grain growth and Cu segregation are caused in a crystal structure, and electromagnetic properties are remarkably deteriorated.
Moreover, it is proposed that the magnetic loss is reduced by remarkably increasing the content of manganese oxide (9 to 15 mol % in terms of MnO, 4.5 to 7.5 mol % in terms of Mn
2
O
3
) in the MnMgCuZn ferrite material (Japanese Patent Application Laid-open No. 25114/1998). When the content of manganese oxide is increased in the MnMgCuZn ferrite material, however, the saturated magnetic flux density at the operation temperature of the deflection yoke (around 100° C.) becomes remarkably low, which disadvantageously reduces the allowable amount of electric currents passed through a deflection yoke coil. Furthermore, since the Curie point is lowered, a problem occurs that the thermal runaway is caused in the operation of the deflection yoke at 100° C. or higher.
SUMMARY OF THE INVENTION
In consideration of the problems, an object of the present invention is to utilize advantages of an MnMgCuZn ferrite material that resistivity is relatively high and material cost is low and to provide a superior MnMgCuZn ferrite material which is much smaller in magnetic loss than conventional materials of the same series and which has a sufficient saturated magnetic flux density.
Specifically, the present invention provides an MnMgCuZn ferrite material which is in a composition range of 46.5 to 50.4 mol % of iron oxide, 10.5 to 22.0 mol % of magnesium oxide, 22.5 to 25.0 mol % of zinc oxide, 6.0 to 16.0 mol % of copper oxide, and 0.1 to 3.5 mol % of manganese oxide.
The MnMgCuZn ferrite material of the present invention is largely lower in magnetic loss, higher in saturated magnetic flux density, and higher in resistivity and Curie point as compared with the conventional MnMgCuZn ferrite material, and useful as a deflection yoke core or a transformer for a CRT, particularly a high-definition CRT. Moreover, sintering can be performed at a relatively low temperature of 1200° C. or less, e.g., about 1000 to 1150° C., and manufacture cost can be lower as compared with the conventional MnMgCuZn ferrite material.


REFERENCES:
patent: 4846987 (1989-07-01), Togane
patent: 48-65499 (1973-09-01), None
patent: 3-66254 (1991-10-01), None
patent: 5-75714 (1993-10-01), None
patent: 10-25114 (1998-01-01), None
patent: WO 99/16090 (1999-04-01), None
J. Sawai, et al., “Low Core Loss Characteristics of MnMgZn Ferrite with Substituted CuO,” Journal of Jpn. Appl. Mag., vol. 21, No. 5 (1997), pp. 915-918.
Patent Abstract of Japan, vol. 096, No. 005, May 31, 1996, JP 08 12335, Jan. 16, 1996.
Derwent Publications, AN 90-020182, JP 01 301524, Dec. 5, 1989.

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