Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
2002-12-12
2004-11-30
Resan, Stevan A. (Department: 1773)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S599000, C427S130000, C264S427000, C360S016000
Reexamination Certificate
active
06824835
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high-density magnetic recording media, and particularly to a flexible magnetic recording medium that is preformatted by magnetic transfer, suitable for high-capacity magnetic disks.
2. Description of the Related Art
With an increase in the quantity of data, there is demand for a magnetic recording medium that is large in memory capacity, low in cost, and capable of high-speed access to a desired block of data. As an example of such a magnetic recording medium, there is known a high-density flexible disk. In realizing the large memory capacity, a so-called tracking servo technique, in which the width of a narrow data track is scanned accurately with a magnetic head to generate signals at a high signal-to-noise ratio (S/N ratio), plays an important role. In the tracking servo technique, a tracking servo signal, an address data signal, a reproduction clock signal, etc., are “preformatted”, that is, recorded in advance, on a disk at predetermined intervals along one rotation thereof.
The magnetic head is accurately positioned over a desired data track by reading out the above-described preformatted signals and then correcting its position. Existing pre-formats are recorded on disks one sheet at a time, one track at a time, with a dedicated servo recorder.
However, the dedicated servo recorder is expensive. In addition, pre-formatting is time-consuming and therefore occupies a large part of the manufacturing cost. For the purpose of reducing the cost, methods have also been proposed, in which pre-formatting is performed no tone track at a time, but by magnetic transfer.
As disclosed in Japanese Unexamined Patent Publication No. 63(1988)-183623 and U.S. Pat. No. 6,347,016, for example, a microscopic “land/groove” pattern corresponding to data signals is formed in the surface of a substrate. The surface of a master carrier, equipped with a ferromagnetic thin film formed on at least the lands of the land/groove pattern, is brought into contact with the surface of a magnetic recording sheet or a disk which has a ferromagnetic thin film or ferromagnetic powder coated layer. In this state, by applying an AC bias magnetic field or a DC magnetic field and exciting the ferromagnetic material of the land portions, a magnetization pattern corresponding to the land/groove pattern is magnetically transferred to the magnetic recording medium.
In the above-described method, the lands of a land/groove pattern formed in the master carrier are brought into intimate contact with a magnetic recording medium to be preformatted, and at the same time, the ferromagnetic material constituting the lands is excited. In this way, a predetermined format is formed in the magnetic recording medium. Because magnetic recording can be performed statically without changing the relative position between the master carrier and the magnetic recording medium, accurate pre-formatting can be performed and the time required for pre-formatting is extremely short.
As described above, the magnetic transfer is advantageous in that it can perform pre-formatting accurately and in a short time. However, if magnetic transfer is performed repeatedly on a magnetic recording medium, the master carrier surface will be flawed by an abrasive contained in the magnetic recording medium. As a result, the quality of recorded signals will be degraded and it will become difficult to perform recording on a plurality of magnetic recording disks or a long tape length. Since the abrasive in the magnetic recording medium is indispensable to maintain the high electromagnetic transfer characteristic and durability of the magnetic recording medium, the above-described problem cannot be overcome by simply reducing the quantity of the abrasive.
In addition, if magnetic transfer is performed repeatedly on magnetic recording mediums, there is another problem that the master carrier surface will be gradually corroded by vinyl chloride, etc. contained in the magnetic recording medium and therefore the quality of signals recorded will be degraded.
To enhance the quality of transfer in the above-described magnetic transfer, it is necessary to make the gap between the master carrier and the magnetic recording medium uniform. However, as it is difficult to keep the gap uniform over the entire surface, the master carrier and the slave medium are usually brought into intimate contact with each other. Even in this case, it is extremely important to keep the intimate contact uniform over the entire surface. If there is an imperfect contact portion, magnetic transfer will not be performed on that portion. If magnetic transfer is not performed, then signal dropouts will occur in the magnetic data transferred to the magnetic recording medium and therefore signal quantity will be degraded. In the case where the signals recorded are servo signals, the tracking function is not sufficiently obtained. As a result, there is a problem that reliability will be reduced.
The contact between the magnetic recording medium and the master carrier can be enhanced by pressing the entire back surface of the master carrier with uniform pressure by elastic means (see Japanese Unexamined Patent Publication No. 7(1995)-78337)
The master carrier is usually generated by a lithographic method, a stamper method, etc. Since the master carrier generated by these methods has a warp of about a few 10 micrometers to a few 100 micrometers, it is difficult to apply uniform pressure to the entire surface. Therefore, it is contemplated that it is difficult to apply uniform pressure to the entire surface by simply removing a warp in the master carrier.
In addition, if a magnetic disk is rotated at high speeds, and a magnetic head is repeatedly positioned over the required data track on the magnetic disk over a predetermined time (e.g., 200 to 300 hours in a high-temperature environment), then there are cases where flaws will occur in the disk surface, data cannot be recorded or reproduced, and errors will occur. One of the causes of flaws in the magnetic disk surface lies in a reduction in the performance of a lubricant for the magnetic disk due to volatilization. That is, a lubricant is indispensable for magnetic disks, because it has a great influence on the durability and flaw-resisting property of the magnetic disks.
However, when tracking servo signals, an address data signal, a reproduction clock signal, etc., are prerecorded on a magnetic disk by a master carrier (magnetic transfer), a lubricant for the magnetic disk is accumulated on the master carrier and makes it difficult to magnetically transfer the signals to the magnetic disk.
That is, while a lubricant is required to maintain the durability and flaw-resisting property of the magnetic disk, the lubricant is obstructive when predetermined signals are prerecorded on a great number of magnetic disks by a master carrier.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-described circumstances.
Accordingly, a first object of the present invention is to provide a flexible magnetic recording medium that is capable of increasing the number of magnetic transfer cycles, by preventing flaws from occurring in the surface of a master carrier while maintaining the high electromagnetic transfer characteristics and durability of the magnetic recording medium.
A second object of the invention is to provide a flexible magnetic recording medium that is capable of increasing the number of magnetic transfer cycles, by preventing the surface of a master carrier from being corroded.
A third object of the invention is to provide a flexible magnetic recording medium which is capable of reducing signal dropouts during magnetic transfer and enhancing signal quality, by making the intimate contact between the recording medium and a master carrier sufficient.
A fourth object of the invention is to provide a flexible magnetic recording medium and a fabrication method thereof which are capable of assuring the long-term stability of the quality of re
Niitsuma Kazuhiro
Noguchi Hitoshi
Fuji Photo Film Co. , Ltd.
Resan Stevan A.
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