Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
1996-01-25
2001-07-17
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C118S620000, C427S128000, C427S130000, C427S550000, C427S599000
Reexamination Certificate
active
06261647
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a magnetic recording medium and an apparatus therefor, and, in particular, to a method for manufacturing such a medium by orienting magnetic powder particles contained in a magnetic layer thereof in an oblique direction with respect to the surface of the magnetic layer and an apparatus therefor.
DESCRIPTION OF THE PRIOR ART
Conventionally, a web-like magnetic recording medium has been manufactured by orienting magnetic powder particles contained in a magnetic layer thereof in a direction parallel to the surface of the magnetic layer and in the longitudinal direction of the magnetic recording medium.
However, in the case where magnetic powder particles are oriented in the longitudinal direction of a magnetic recording medium, the demagnetization field in the medium becomes greater. As a result, the improvement in recording density is limited. Namely, the output can be improved in the long wavelength region, but the output is poor in the short wavelength region.
Therefore, a vertical orientation method has been proposed in which the magnetic powder particles are oriented by applying a magnetic field in the thickness direction of the magnetic layer of the magnetic recording medium.
According to this method, the demagnetization field falls with increasing recording density. The method is therefore advantageous for high density recording and recording in the short wavelength region. However, the output in the long wavelength region decreases because the squareness ratio in the vertical direction cannot be increased to the desired value.
Because of this, it has been attempted to solve problems in orientation using an oblique orientation method which achieves an improvement in electromagnetic conversion characteristics and high output from the short wavelength region to the long wavelength region by orienting magnetic powder particles in an oblique direction making an angle of 10 degrees to 70 degrees with the longitudinal direction of the magnetic recording medium in a plane perpendicular to the surface of the magnetic layer and parallel to the longitudinal direction of the magnetic recording medium.
In the conventional oblique orientation method, a magnetic field oblique to the surface of the magnetic layer is generated by disposing a pair of magnets at a predetermined angle to the surface of the magnetic layer, thereby orienting the magnetic powder particles in the magnetic layer obliquely to the surface of the magnetic layer.
However, it is difficult in this method to generate a magnetic field having a small angle to the surface of the magnetic layer and, therefore, the magnetic powder particles cannot be oriented in the desired oblique direction. Further, since this method requires the positions of the pair of magnets to be changed so as to interpose the magnetic recording medium therebetween in accordance with the angle at which magnetic powder particles are to be oriented, the apparatus inevitably becomes large. Moreover, since the magnets are disposed at a predetermined angle to the surface of the magnetic layer, the area where the magnetic powder particles are oriented is small and, therefore, it is impossible to efficiently produce a magnetic recording medium having a high squareness ratio in a desired oblique direction.
Japanese Patent Application Laid Open No. 3-35420 therefore proposes an oblique orientation method which orients the magnetic powder particles in an oblique direction to the surface of the magnetic layer by simultaneously applying a magnetic field substantially perpendicular to the surface of the magnetic layer and a magnetic field substantially parallel to the surface of the magnetic layer and generating a magnetic field oblique to the surface of the magnetic layer as the vector sum of the two magnetic fields.
According to this method, the magnetic powder particles can be oriented at an arbitrary angle by appropriately selecting the strength of the magnet for generating the magnetic field substantially perpendicular to the surface of the magnetic layer and the magnet for generating the magnetic field substantially parallel to the surface of the magnetic layer. Since it is therefore unnecessary to change the positions of the magnets when the angle at which the magnetic powder particles are to be oriented is changed, the size of the apparatus can be reduced.
In this method, however, the oblique magnetic field must be applied to the magnetic powder particles for a long time in order to achieve uniformly orientation. Therefore, if the time period for orientation is made short, the magnetic powder particles cannot be sufficiently oriented and the squareness ratio of the magnetic recording medium is low. On the other hand, if the orientation is effected for a sufficient time period, the apparatus inevitably becomes large.
Japanese Patent Application Laid Open No. 6-309661 proposes an oblique orientation method which orients magnetic powder particles in an oblique direction to the surface of the magnetic layer by applying a magnetic field parallel to the surface of the magnetic layer in the longitudinal direction of the magnetic recording medium and then applying a magnetic field oblique to the surface of the magnetic layer.
This method once orients the magnetic powder particles in the longitudinal direction parallel to the surface of the magnetic layer by applying a magnetic field parallel to the surface of the magnetic layer in the longitudinal direction and then orients them at an angle to the surface of the magnetic layer by applying a magnetic field having an oblique angle thereto. However, even in this method, it is necessary to apply an oblique magnetic field to the magnetic powder particles for a long time in order to uniformly orient them. Therefore, if the time period for orientation is made short, the magnetic powder particles cannot be sufficiently oriented and the squareness ratio of the magnetic recording medium is low. On the other hand, if the orientation is to be effected for a sufficient time period, the apparatus inevitably becomes large.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and an apparatus for manufacturing a magnetic recording medium which can orient magnetic powder particles to a desired direction with respect to the surface of a magnetic layer and manufacture a magnetic recording medium having a high squareness ratio without increasing the size of the apparatus.
The above and other objects of the present invention can be accomplished by a method for manufacturing a magnetic recording medium comprising steps of forming at least one magnetic layer containing magnetic powder particles on a web-like non-magnetic support being continuously transported in one direction and applying a magnetic field to the magnetic layer by a plurality of magnets in such a manner that an angle of the magnetic field applied to the magnetic layer to the transporting direction of the non-magnetic support in a plane perpendicular to a surface of the magnetic layer and parallel to the transporting direction of the non-magnetic support gradually increases in the transporting direction of the non-magnetic support, thereby orienting the magnetic powder particles in an oblique direction with respect to the surface of the magnetic layer.
The above and other objects of the present invention can be also accomplished by an apparatus for manufacturing a magnetic recording medium comprising first magnet means for generating a magnetic field perpendicular to a surface of at least one magnetic layer formed on a non-magnetic support and containing magnetic powder particles and second magnet means for generating a horizontal magnetic field parallel to the surface of the magnetic layer and having a predetermined direction in the magnetic field generated by the first magnet means, the second magnet means generating the horizontal magnetic field so as to decrease gradually in strength from one end of the magnetic field generated by the fir
Komatsu Kazunori
Shibata Norio
Brinks Hofer Gilson & Lione
Fuji Photo Film Co. , Ltd.
Nichols G. Peter
Pianalto Bernard
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