Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1998-12-24
2001-06-26
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S336000, C428S690000, C428S690000, C428S900000, C427S128000, C427S129000, C427S130000, C427S131000
Reexamination Certificate
active
06251496
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium, a method and an apparatus for producing a magnetic recording medium, and in particular to a high recording density magnetic recording medium preferably used for information related equipment and audio-video equipment, a method and an apparatus for producing a high recording density magnetic recording medium.
2. Description of the Related Art
Recently, high-function thin film technologies have been remarkably developed and applied in a wide variety of fields. For example, the remarkable development in the magnetic recording medium is demonstrated by the improvement in the recording density. A conventional magnetic recording medium of a so-called coating type includes a ferromagnetic material such as &ggr;-Fe
2
O
3
powders, CrO
2
powders, or pure iron powders applied to a polymer film together with a binder such as a resin. Such a type of magnetic recording medium is used for audio and video tapes.
In order to improve the recording density, a metal thin film magnetic recording medium has been studied, which includes a ferromagnetic material such as Fe, Co, Ni or Cr vapor-deposited as a single metal material or an alloy or an insulating substrate such as a polymer film or a glass plate by ion plating, sputtering, cluster ion beam or the like. A vapor-deposition tape including such a metal material or an alloy applied to an insulating substrate by oblique vapor deposition has already been put into practice for use as a video-tape. Generally, a vapor-deposition tape is of an in-plane magnetic recording type, and includes a ferromagnetic metal film having an anisotropy (in a shape and/or in a magnetic property) in the tape plane. Such a ferromagnetic metal film is formed by obliquely growing ferromagnetic metal crystals using oblique vapor deposition.
FIG. 7
shows a conventional apparatus
70
for producing a metal thin film magnetic recording medium. The apparatus
70
utilizes a continuous winding vacuum vapor deposition to produce a metal thin film magnetic recording medium. The continuous winding vacuum vapor deposition is superior especially in the productivity and is a major candidate for a practical mass-production method.
The apparatus
70
operates in the following manner. A polymer film
72
wound around a feeding shaft
71
is continuously fed. The polymer film
72
is applied on a cooling drum
73
and wound around a winding shaft
74
. Arrows A and B show the running direction of the polymer film
72
. A ferromagnetic metal accommodated in a crucible
76
provided below the cooling drum
73
is irradiated with an electron beam
75
to melt and vaporize, thereby vapor-depositing the ferromagnetic metal to a surface of the polymer film
72
. At this point, an unnecessary portion of the ferromagnetic metal is blocked by blocking plates
77
a
and
77
b.
In this specification, the surface of the polymer film
72
to which the ferromagnetic metal is vapor-deposited will be referred to as a “vapor-deposition surface”. An area of the cooling drum
73
which is defined by the blocking plates
77
a
and
77
b
and to which the ferromagnetic metal is actually vapor-deposited on the vapor-deposition surface of the polymer film
72
will be referred to as a “vapor-deposition area”. In
FIG. 7
, the vapor-deposition area is represented by reference numeral
72
a.
After the polymer film
72
having the ferromagnetic metal to a prescribed thickness is wound around the winding shaft
74
, the polymer film
72
is cut or otherwise processed. Thus, a vapor-deposition tape is produced.
According to an alternative method using the apparatus
70
, oxygen gas is supplied from an oxygen gas supply opening
78
to the vapor-deposition surface in the direction of arrow C (i.e., substantially opposite to the running direction of the polymer film
72
), so that the depositing metal is oxidized (reactive deposition). A thin film recording medium produced by reactive deposition is formed of a ferromagnetic metal oxide or a ferromagnetic alloy oxide. In this specification, the term “thin film including a ferromagnetic metal material” refers to a thin film formed of a single ferromagnetic metal material, a thin film formed of a ferromagnetic alloy, and a thin film formed of a metal compound such as, for example, an oxide of a single ferromagnetic metal material or a ferromagnetic alloy. In the following description, the terms “ferromagnetic metal material” and “ferromagnetic metal thin film” will be used for simplicity. Unless otherwise specified, the term “ferromagnetic metal material” is replaceable with “ferromagnetic metal alloy” and “oxide of a ferromagnetic metal material”, and the term “ferromagnetic metal thin film” is replaceable with “thin film including a ferromagnetic metal material”
However, the continuous winding vacuum vapor deposition has the following problems.
In order to obtain a sufficient electro-magnetic conversion characteristic with the conventional apparatus
70
shown in
FIG. 7
, the incident angle &agr; of the metal depositing on the vapor-deposition surface is restricted by defining the vapor-deposition area
72
a.
The incident angle &agr; is defined as being with respect to the normal to the vapor-deposition surface. The maximum incident angle &agr; is represented as &agr;max, and the minimum incident angle &agr; is represented as &agr;min.
For example, when the cooling drum
73
has a diameter of about 1 m, a vapor-deposition tape having a sufficient electro-magnetic conversion characteristic is obtained where the minimum incident angle &agr;min. is about 40 degrees so that the component incident at a smaller angle than about 40 degrees is blocked. Since the maximum incident angle &agr;max. cannot exceed 90 degrees, the adhering efficiency of the ferromagnetic metal reduces as the minimum incident angle &agr; increases. The “adhering efficiency” is defined as the ratio of the weight of ferromagnetic metal deposited on the vapor-deposition surface with the total weight of the ferromagnetic metal vaporized, and is represented as a percentage.
In the case where the cooling drum
73
has a diameter of about 1 m, the minimum incident angle &agr;min. is about 40 degrees, and the maximum incident angle &agr;max. is about 90 degrees as shown in
FIG. 7
, the adhering efficiency is about 10 wt. %, which is seriously low.
As can be understood from
FIG. 7
, such a low adhering efficiency is due to a narrow expanding angle (vapor-deposition expanding angle) &ohgr; in the direction of incidence of the ferromagnetic metal. The “vapor-deposition expanding angle &ohgr;” is defined as an angle determined by lines connecting the center of a vaporizing surface of the ferromagnetic metal in the crucible
76
and both ends of the vapor-deposition area
72
a
(vapor-deposition starting end and vapor-deposition terminating end) in a plane including the running direction of the polymer film
72
. In the conventional method for producing a magnetic recording medium, the vapor-deposition expanding angle &ohgr; is restricted by the diameter of the cooling drum
73
to as small as 15 degrees.
In order to produce a ferromagnetic metal thin film having a prescribed thickness with the conventional method, the running speed of the polymer film
72
needs to be reduced due to such a low adhering efficiency. Accordingly, it is difficult to produce a vapor-deposition tape having a sufficient electro-magnetic conversion characteristic with a sufficient productivity. Under the circumstances, it has been strongly demanded to provide a method for producing a vapor-deposition tape for video equipment which has been more and more reduced in size due to a higher recording density and also a vapor-deposition tape for information equipment which has been demanded to realize higher density recording and lower cost.
In addition to the above-described problems, the present inventor has found that a ferromagnetic metal thin film produced by the conventional continuous winding vacuum vapor deposi
Kiliman Leszek
Matsushita Electric - Industrial Co., Ltd.
Renner Otto Boisselle & Sklar
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