Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-06-20
2003-11-25
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S900000, C428S332000
Reexamination Certificate
active
06652998
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a producing method of a thin film magnetic tape and the thin film magnetic tape produced by applying an oblique evaporation process.
2. Description of the Related Art
Currently magnetic tapes applied to digital video recorders and audio tape recorders, especially, thin film magnetic tapes produced by applying an oblique evaporation process, are gaining attention in order to accomplish high density and reduced thickness of the tapes.
FIG. 5
is a plan view of a thin film magnetic tape producing apparatus of the prior art, which applies the oblique evaporation process.
FIG. 6
is a perspective view of the thin film magnetic tape producing apparatus of
FIG. 5
, with parts broken away and in section, showing proximity of a cooling can roll.
A magnetic layer of the above mentioned thin film magnetic tape is generally formed in a thin film by the oblique evaporation process. As shown in
FIG. 5
, the thin film magnetic tape producing apparatus
1
A of the prior art, which applies the oblique evaporation process maintains a vacuum condition inside a vacuum chamber
2
by a vacuum pump (not shown). Inside the vacuum chamber
2
, there provided a set of film winding rolls
3
A and
3
B, a set of tape guide rolls
4
A and
4
B, and a cooling can roll
5
being rotatable freely. During ordinarily forming a film on a base film F, the base film F wound on the film winding roll (hereinafter referred to a supply roll)
3
A runs through the tape guide roll
4
A, the cooling can roll
5
, and the tape guide roll
4
B in a forward direction shown by an arrow S
1
to the film winding roll (hereinafter referred to a take-up roll)
3
B.
The base film F is made by a PET (polyethylene terephthalate) film having a thickness of approximately 6.4 &mgr;m as a substrate for the thin film magnetic tape. A cooling apparatus (not shown) is installed inside the cooling can roll
5
so as to control deformation of the base film F due to increased temperature during a evaporation process.
A crucible
6
, which is made from MgO (Magnesia) and formed in a box shape, is installed at a lower right hand corner from the cooling can roll
5
inside the vacuum chamber
2
. A magnetic metal
7
such as Co is contained inside the crucible
6
.
A piercing electron gun
8
, which is an evaporation heat source to melt and evaporate the magnetic metal
7
, is mounted on a right wall
2
a
of the vacuum chamber
2
with pointing at the crucible
6
located diagonally downward. The piercing electron gun
8
emits an electron beam
8
a
towards the magnetic metal
7
inside the crucible
6
. The electron beam
8
a
melts the magnetic metal
7
and evaporates so as to coat a surface of the base film F, which is moving along the cooling can roll
5
.
It is necessary to cover both edges of the base film F so as to prevent a magnetic metal vapor
7
a
, which evaporated from the crucible
6
, from evaporating on the cooling can roll
5
while the base film F is running. Further, it is also necessary to control an incidence angle of evaporation of the magnetic metal vapor
7
a
such as evaporated Co (generally called oblique evaporation) with respect to a surface of the base film F due to the requirements for electromagnetic transducing characteristics when producing a thin film magnetic tape. In order to prevent deposits in inappropriate areas, an incidence angle controlling mask
9
is installed between the cooling can roll
5
and the crucible
6
as shown in FIG.
6
.
A width of the base film F is narrower than a width of the cooling can roll
5
in this situation shown in FIG.
6
. In order to prevent the magnetic metal vapor
7
a
from evaporating on or invading into the cooling can-roll
5
at proximity of both edges of the base film F, the incidence angle controlling mask
9
covers an area between an edge of the cooling can roll
5
and a few centimeter inwards an edge of the base film F. An opening
9
a
of the incidence angle controlling mask
9
is extremely small in order to control an incidence angle of the magnetic metal vapor
7
a
such as evaporated Co to the surface of the base film F and a growth angle of particles growing on the base film F.
Referring back to
FIG. 5
, an evaporation incidence angle of the above mentioned opening
9
a
of the incidence angle controlling mask
9
is an incidence angle of evaporating the magnetic metal vapor
7
a
such as evaporated Co on the base film F with respect to a line normal to the surface of the base film F being wraparound the cooling can roll
5
. The evaporation incidence angle is set within a range of angle from a maximum incidence angle &thgr; max to a minimum incidence angle &thgr; min.
An oxygen gas injection pipe
10
is attached on an inner surface of the incidence angle controlling mask
9
with facing toward the cooling can roll
5
in a direction to the minimum incidence angle &thgr; min side. Oxygen gas O
2
blows off through several holes provided on the oxygen gas injection pipe
10
towards the magnetic metal vapor
7
a
evaporated from the crucible
6
.
The electron beam
8
a
emitted from the piercing electron gun
8
is controlled by a deflection magnet
11
, which impresses a deflection magnetic field onto a trajectory of the electron beam
8
a
, and another deflection magnet
12
, which is installed near the crucible
6
. By scanning the electron beam
8
a
in the longitudinal direction of the crucible
6
, the magnetic metal vapor
7
a
such as evaporated Co is thinly laminated on the surface of the base film F as a Co—CoO magnetic film in a lateral direction of the base film F. By laminating the Co—CoO Magnetic film on the base film F continuously in the longitudinal direction of the base film F, a long enough thin film magnetic tape is wound on the take-up roll
3
B.
In a case of producing a thin film magnetic tape as mentioned above, a size of the opening
9
a
of the incidence angle controlling mask
9
is strictly limited. An efficiency of actual usage of the magnetic metal vapor
7
a
such as Co evaporated from the crucible
6
is only about 10 to 15% while almost all of the magnetic metal vapor
7
a
became unnecessary evaporation. In order to improve a usage efficiency of the magnetic metal vapor
7
a
by increasing a size of the opening
9
a
of the incidence angle controlling mask
9
even slightly, it is necessary to further improve magnetostatic characteristics.
With emergence of magnetoresistive heads such as a GMR (giant magnetoresistive) head and an MR (magnetoresistive) head, there exists a certain tendency to install such a magnetoresistive head into a digital video tape recorder. Therefore, an urgency to drastically decrease layer thickness of a magnetic layer of a thin film magnetic tape exists in order to improve a SN ratio of the thin film magnetic tape. However, there is existed a problem such that magnetostatic characteristics of a thin film magnetic tape is deteriorated if layer thickness of a magnetic layer of the thin film magnetic tape is decreased in accordance with a current method.
An idea of placing a CoO nonmagnetic underlayer underneath a magnetic layer of a thin film magnetic tape is suggested. This method will be explained in a [Comparative Example 2] section. With a deposit of Co—CoO magnetic layer on a top of growth particles (columns) of an isolated CoO nonmagnetic underlayer and isolation of growth particles (columns) of a Co—CoO magnetic layer in accordance with the growth particles (columns) of CoO nonmagnetic underlayer, dimishing magnetic interaction among Co—CoO magnetic layer particles prevents degradation of magnetostatic characteristics associated with an extremely thin Co—CoO magnetic layer.
When placing a nonmagnetic underlayer underneath a magnetic layer of a thin film magnetic tape, further isolation of a magnetic layer effectively reduces magnetic interaction among magnetic layer particles. Such a method to favorably deposit a nonmagnetic underlayer for this purpose, however, had not yet been discover
Segawa Masaru
Sugiyama Masahiko
Anderson Kill & Olick P.C.
JVC - Victor Company of Japan, Ltd.
Lieberstein Eugene
Meller Michael N.
Rickman Holly
LandOfFree
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