U.S. patent application number 11/903609 was filed with the patent office on 2008-01-31 for magnetic recording medium and method of fabricating the same.
This patent application is currently assigned to SONY CORPORATION. Invention is credited to Hitoshi Wako.
Application Number | 20080026259 11/903609 |
Document ID | / |
Family ID | 34213820 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080026259 |
Kind Code |
A1 |
Wako; Hitoshi |
January 31, 2008 |
Magnetic recording medium and method of fabricating the same
Abstract
The present invention is to provide a method of fabricating a
magnetic recording medium capable of forming a protective layer
with a stable performance even in a case where a thickness thereof
is as thin as 100 nm or less, and a magnetic recording medium
fabricated by the method. A magnetic recording medium is fabricated
in the following manner, that is, a magnetic layer having a
ferromagnetic metal thin film having a thickness as thin as 100 nm
or less is formed on one main surface of a long non-magnetic
support, and on the magnetic layer, a protective layer containing
carbon is formed by the chemical vapor deposition process using an
ion source equipped with a hollow cathode.
Inventors: |
Wako; Hitoshi; (Miyagi,
JP) |
Correspondence
Address: |
ROBERT J. DEPKE;LEWIS T. STEADMAN
ROCKEY, DEPKE & LYONS, LLC
SUITE 5450 SEARS TOWER
CHICAGO
IL
60606-6306
US
|
Assignee: |
SONY CORPORATION
|
Family ID: |
34213820 |
Appl. No.: |
11/903609 |
Filed: |
September 24, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10920685 |
Aug 18, 2004 |
|
|
|
11903609 |
Sep 24, 2007 |
|
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Current U.S.
Class: |
428/836.1 ;
G9B/5.3 |
Current CPC
Class: |
G11B 5/72 20130101; Y10T
428/265 20150115; G11B 5/70 20130101; G11B 5/8408 20130101 |
Class at
Publication: |
428/836.1 |
International
Class: |
G11B 5/65 20060101
G11B005/65 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 25, 2003 |
JP |
P2003-300303 |
Claims
1-4. (canceled)
5. A magnetic recording medium comprising: a long non-magnetic
support; a magnetic layer having a ferromagnetic metal thin film
having a thickness of 100 nm or less, and formed on one surface of
the non-magnetic support; and a carbon-containing protective layer
formed on the magnetic layer by the chemical vapor deposition
process using an ion source equipped with a hollow cathode.
6. The magnetic recording medium according to claim 5, wherein said
protective layer has a thickness of 2 nm to 16 nm.
7. The magnetic recording medium according to claim 5, wherein said
protective layer has a ratio (D/G) of an 15 intensity (G) having a
peak of 1,550 cm.sup.-1 or more and 1,650 cm.sup.-1 or less and an
intensity (D) having a peak of 1,350 cm.sup.-1 or more and 1,450
cm.sup.-1 or less in Raman scattering spectrum being 1.0 or
less.
8. The magnetic recording medium according to claim 6, wherein said
protective layer has a ratio (D/G) of an 15 intensity (G) having a
peak of 1,550 cm.sup.-1 or more and 1,650 cm.sup.-1 or less and an
intensity (D) having a peak of 1,350 cm.sup.-1 or more and 1,450
cm.sup.-1 or less in Raman scattering spectrum being 1.0 or less.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The subject matter of application Ser. No. 10/920,685 is
incorporated herein by reference. The present application is a
divisional of U.S. application Ser. No. 10/920,685, filed Aug. 18,
2004, which is based on Japanese priority Document JP 2003-300303,
filed in the Japanese patent office on Aug. 25, 2003, the entire
contents of which being incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a magnetic tape and a
method of fabricating the same.
[0004] 2. Description of Related Art
[0005] Conventionally, as magnetic recording tapes such as an audio
tape, a video tape and so forth, a coating-type magnetic recording
medium have widely been used, wherein a magnetic layer of which
being formed by coating and drying a magnetic coating material,
having a powdery magnetic material such as oxide magnetic powder,
alloyed magnetic powder and so forth dispersed in an organic binder
such as vinyl chloride/vinyl acetate-base copolymer, polyester
resin, urethane resin, polyurethane resin and so forth, on a
non-magnetic support.
[0006] On the other hand, for the purpose of application in data
storage with an increasing demand on high-density magnetic
recording, a magnetic recording medium of so-called, ferromagnetic
metal film type has been proposed and has attracts public
attention, wherein a magnetic layer of which being formed by
directly depositing a ferromagnetic metal material such as
Co--Ni-base alloy, Co--Cr-base alloy, Co--O or the like on a
non-magnetic support such as polyester film, polyamide film,
polyimide film or the like by a vacuum thin film forming process
such as vacuum evaporation process, sputtering process, ion plating
or the like, or by plating.
[0007] The above-described magnetic recording medium having a
ferromagnetic metal thin film as the magnetic layer is excellent in
coercive force, square ratio, and electro-magnetic conversion
characteristics in the short-wavelength region, and is advantageous
in many aspects, such as having an extremely small recording
demagnetization and thickness loss during reproduction because the
magnetic layer can be made extremely thin, and such as being
successful in raising packing density of the magnetic material
because there is no need of mixing a non-magnetic binder in the
magnetic layer.
[0008] For the purpose of improving the electromagnetic conversion
characteristics and of obtaining a larger output of this sort of
magnetic recording medium, there is also proposed an oblique
evaporation by which the magnetic layer is obliquely deposited in
the formation of the magnetic layer of the magnetic recording
medium, and this has already been put into practical use as a
magnetic tape for commercial video (8-mm, Hi-8 system, DV system)
or professional-use video (DVCAM).
[0009] A magnetic tape, which is the above-described magnetic
recording medium, is configured so that a magnetic layer typically
composed of a ferromagnetic metal thin film formed by the oblique
evaporation, and a protective layer for raising travel durability,
composed of a carbon film called a diamond-like carbon (DLC) or a
hydrogen-containing carbon film, and so forth are sequentially
formed on a long non-magnetic support, and so that a lubricant
layer, if necessary, is formed on the protective layer using a
predetermined lubricant, and a back-coat layer is formed on the
surface of the non-magnetic support opposite to that having the
magnetic layer formed thereon.
[0010] Sputtering process and plasma CVD (chemical vapor
deposition) process are techniques widely used for forming the
protective layer, wherein the plasma CVD process has a larger
opportunity of use in view of running durability and
productivity.
[0011] In the formation of the protective layer applied with the
plasma CVD process, a source gas is introduced into a vacuum
chamber, an electrode is disposed so as to oppose with the magnetic
layer deposited on the non-magnetic support, a plasma is excited by
applying a high voltage between the electrode and magnetic layer to
thereby decompose the source gas by the plasma, and to allow it to
deposit as a DLC film on the magnetic layer.
[0012] Patent Document 1 describes a method of controlling film
quality of thus-formed protective layer on the basis of a peak
intensity (G) appeared at around 1,500 cm.sup.-1 and a peak
intensity (D) appeared at around 1,300 cm.sup.-1 observed in Raman
spectrometry, and a desirable range of D/G ratio.
[0013] In the above-described formation of the protective layer by
the plasma CVD process, the magnetic layer deposited on the
non-magnetic support is used as an electrode, wherein any changes
in the film composition and thickness of the magnetic layer result
in fluctuation in the voltage for exciting the plasma. Because
properties of the carbon protective layer largely vary depending on
the excitation voltage, it is difficult to obtain the same
characteristics of the protective layer over the magnetic layers
having different configurations. From another viewpoint of
production, any compositional variation of the magnetic layer
results in variation of the protective layer, and seriously
degrades the productivity.
[0014] There is also a tendency towards a thinner thickness of the
magnetic layer in association with increase in the recording
density, and this tends to raise sheet resistance of the magnetic
layer. The increase in the resistance of the magnetic layer makes
it more difficult to apply a high voltage between the metal
evaporated tape and the electrode.
[0015] The above-described event becomes distinct in particular for
a thickness of the magnetic layer of 100 nm or less, and this
substantially makes the film formation unavailable. FIG. 7 shows a
graph plotting a thickness t.sub.mag of the magnetic layer on the
abscissa, and plotting a ratio (D/G) of the peak intensity (G)
appeared at around 1,500 cm.sup.-1 and the peak intensity (D)
appeared at around 1,300 cm.sup.-1 observed in Raman spectrometry
on the ordinate. The value D/G indicating the thickness of the
protective layer varies with the thickness t.sub.mag of the
magnetic layer, and a variable range for D/G can be altered by
varying voltage applied to the magnetic layer and the electrode
(V.sub.1, V.sub.2, for example), wherein the thickness t.sub.mag of
the magnetic layer in a small region falls in a film unformable
region R.sub.imp where voltage application is impossible, which
typically corresponds to a region of the thickness of the magnetic
layer of 100 nm or less.
[0016] Besides this, a method of forming a DLC film is also
described typically in Patent Document 2. [0017] [Patent Document
1] [0018] Japanese Patent Application Publication No. 2000-207735.
[0019] [Patent Document 2] [0020] Published Japanese Translations
of PCT International Publication for Patent Applications No.
2002-541604.
SUMMARY OF THE INVENTION
[0021] A problem to be solved is that, in the formation of the
protective layer on the magnetic layer, it becomes more difficult
to form the protective layer having stable characteristics as the
thickness of the magnetic layer becomes thinner.
[0022] A method of fabricating a magnetic recording medium of the
present invention comprises the steps of forming, on one main
surface of a long non-magnetic support, a magnetic layer having a
ferromagnetic metal thin film; and forming, on the magnetic layer,
a carbon-containing protective layer by the chemical vapor
deposition process using an ion source equipped with a hollow
cathode.
[0023] In the above-described method of fabricating a magnetic
recording medium of the present invention, a magnetic layer having
a ferromagnetic metal thin film is formed on one main surface of a
long non-magnetic support, and on this layer, a carbon-containing
protective layer is formed by the chemical vapor deposition process
using an ion source equipped with a hollow cathode.
[0024] A magnetic recording medium of the present invention
comprises a long non-magnetic support; a magnetic layer having a
ferromagnetic metal thin film having a thickness of 100 nm or less,
and formed on one surface of the non-magnetic support; and a
carbon-containing protective layer formed on the magnetic layer by
the chemical vapor deposition process using an ion source equipped
with a hollow cathode.
[0025] The magnetic recording medium of the present invention has,
as being formed on one main surface of the non-magnetic support, a
magnetic layer having a ferromagnetic metal thin film having a
thickness of 100 nm or less, and has, as being formed on this
layer, a carbon-containing protective layer formed by the chemical
vapor deposition process using an ion source equipped with a hollow
cathode.
[0026] According to the method of fabricating a magnetic recording
medium of the present invention, a protective layer is formed on
the magnetic layer by the chemical vapor deposition process using
an ion source equipped with a hollow cathode, and this makes it
possible to form the protective layer stabilized in its property,
even if the thickness of the magnetic layer is reduced to as thin
as 100 nm or less.
[0027] The magnetic recording medium of the present invention is
such as having the protective layer stabilized in its property even
on the magnetic layer having a thickness reduced to as thin as 100
nm or less.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description of the presently preferred exemplary embodiments of the
invention taken in conjunction with the accompanying drawings, in
which:
[0029] FIG. 1 is a cross-sectional view of a magnetic recording
medium according to an embodiment of the present invention;
[0030] FIG. 2 is a view showing a schematic configuration of an ion
source equipped with a hollow cathode, used in a hollow cathode CVD
apparatus;
[0031] FIG. 3 is a view showing a schematic configuration of the
hollow cathode CVD apparatus using the ion source equipped with the
hollow cathode;
[0032] FIG. 4 is a view showing a schematic configuration drawing
of a vacuum evaporation apparatus;
[0033] FIG. 5 is a graph obtained by plotting a D/G ratio with
respect to a discharge voltage;
[0034] FIG. 6 is a graph obtained by plotting an amount of head
wear in Examples with respect to a thickness of a protective layer
(DLC); and
[0035] FIG. 7 is a graph obtained by plotting the D/G ratio in
Raman spectrum of the protective layer with respect to a thickness
of a magnetic layer, in the formation of the protective layer by a
conventional plasma CVD process.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0036] The following paragraphs will describe modes of embodiment
of the magnetic recording medium and the method of fabricating the
same, referring to the attached drawings.
[0037] FIG. 1 is a schematic sectional view of the magnetic
recording medium according to this embodiment. The magnetic
recording medium is configured so that a magnetic layer 2 and a
protective layer 3 are sequentially formed on a long non-magnetic
support 1. The magnetic layer 2 comprises a ferromagnetic metal
thin film. A lubricant layer 4 is formed on the magnetic layer 3
using a predetermined lubricant if necessary. On the surface of the
non-magnetic support 1 opposite to that having the magnetic layer 2
formed thereon, a back-coat layer 5 is formed.
[0038] Materials for composing the non-magnetic support 1 include
polyesters such as polyethylene terephthalate (PET) and
polyethylene naphthalate (PEN); polyolefins such as polyethylene
and polypropylene; cellulose derivatives such as cellulose
triacetate; and plastics such as polycarbonate, polyimide,
polyamide and polyamideimide.
[0039] The magnetic layer 2 is a ferromagnetic metal thin film
having an orthorhombic columnar structure, typically formed by the
vacuum thin film forming technique, and ferromagnetic metal
materials for composing of the layer include Co--Ni-base alloy,
Co--Cr-base alloy and Co--O for example, which are typically formed
by an oblique evaporation using a vacuum evaporation apparatus.
[0040] The protective layer 3 is a layer provided for protecting
the magnetic layer 2 from friction with a magnetic head, and is
composed, for example, of a carbon film called diamond-like carbon
(DLC) and a hydrogen-containing carbon film. The magnetic recording
medium has been improved in the surface smoothness so as to
suppress the spacing loss in response to an increasing trend in
recording density, but the surface smoothness of the magnetic layer
2 increases friction force with the magnetic head due to increased
contact area therewith, and consequently increases shearing force
applied to the magnetic layer 2. The protective layer 3 is
important to protect the magnetic layer 2 from this severe
frictional condition.
[0041] In this embodiment, the protective layer 3 is a film formed
by the chemical vapor deposition process using an ion source
equipped with a hollow cathode. The chemical vapor deposition
process using an ion source equipped with a hollow cathode
(referred to as hollow cathode CVD process, hereinafter) will be
described later.
[0042] The lubricant layer 4 plays an important role governing the
durability and running property, and is typically formed by coating
an arbitrary lubricant of perfluoropolyether base.
[0043] The back-coat layer 5 is provided for the purpose of raising
the durability of the non-magnetic support 1, preventing scratching
during the use, and reducing friction between the tapes, and is
indispensable in view of raising the travel performance and
durability. The back-coat layer 5 is typically formed by coating a
back-coat layer coating material obtained by dispersing solid
particles such as inorganic pigment into a binder and kneaded
together with an organic solvent adapted to the binder. In another
case, a DLC film formed by the sputtering process using carbon as a
target is used as the back-coat layer.
[0044] It is still also allowable to dispose a magnetic layer
underlying layer formed under the magnetic layer 2, and a back-coat
underlying layer formed under the back-coat layer 5, if
necessary.
[0045] According to the magnetic recording medium of this
embodiment, the protective layer is a carbon-containing layer
formed by the chemical vapor deposition process using an ion source
equipped with a hollow cathode, and the magnetic recording medium
is configured so as to have the protective layer with stable
properties even if the thickness of the magnetic layer is reduced
to as thin as 100 nm or below.
[0046] The magnetic recording medium according to this mode of
embodiment is fabricated as described below. First, the magnetic
layer 2 having a ferromagnetic metal thin film is formed on one
main surface of the long non-magnetic support 1 typically by the
oblique evaporation. Next, on the magnetic layer 2, the
carbon-containing protective layer 3 comprising a carbon film
called diamond-like carbon (DLC) or a hydrogen-containing carbon
film is formed by the hollow cathode CVD process. The lubricant
layer 4 is formed further on the protective layer 3, and the
back-coat layer 5 is formed on the opposite main surface of the
non-magnetic support 1, and thereby the magnetic recording medium
shown in FIG. 1 is fabricated.
[0047] The above-described hollow cathode CVD process will be
explained. FIG. 2 is a schematic configuration drawing showing an
ion source equipped with a hollow cathode used for the
above-described hollow cathode CVD apparatus. The ion source 10 has
a hollow cathode unit 11, an electrode 12, a gas introducing pipe
13, an anode unit 14, an anode electrode 15, a gas introducing pipe
16, an electromagnet 17 and a source gas supply pipe 18.
[0048] The hollow cathode ion source 10 has a cylindrical shape,
and has the hollow cathode unit 11 placed in the center portion
thereof. The electrode 12 and the gas introducing pipe 13 for
introducing Ar or other gases are disposed inside the hollow
cathode unit 11. The anode unit 14 having an annular form is
disposed in an area surrounding the hollow cathode unit 11. The
anode electrode 15 and the gas introducing pipe 16 for introducing
Ar or other gases are disposed at the bottom portion of the anode
unit 14. The electromagnet 17 is disposed between the hollow
cathode unit 11 and the anode unit 14.
[0049] In the hollow cathode unit 11 at the center, high voltage is
applied to the electrode 12 while introducing Ar gas through the
gas introducing pipe 13 to thereby activate electric discharge, and
the anode electrode 15 is set to a potential higher than that of
the hollow cathode unit 11 while introducing Ar gas through the gas
introducing pipe 16 so as to activate electric discharge between
the hollow cathode unit 11 and the anode electrode 15, and thereby
a plasma P is formed in the vicinity of the surface of the ion
source 10. Magnetization of the electromagnet 17 herein is
successful in raising density of the plasma P.
[0050] When the source gas is supplied through the source gas
supply tube 18 disposed on the outer side of the anode unit 14, the
source gas is decomposed in the plasma P. A portion of electrons
supplied from the hollow cathode unit 11 go towards the magnetic
layer 2 of a support 22 having the magnetic layer 2 formed thereon,
and the source gas ionized in the plasma P is accelerated towards
the direction of the magnetic layer 2, and deposits thereon.
[0051] FIG. 3 is a schematic configuration drawing of a hollow
cathode CVD apparatus using the ion source equipped with the hollow
cathode shown in FIG. 2. The CVD apparatus has an evacuation system
20, a vacuum chamber 21, a feed roll 23, a winding roll 24, a
cooling can 25, guide rolls (26, 27), and the hollow cathode ion
source 10.
[0052] The feed roll 23 which rotates in the clockwise direction in
the drawing and the winding roll 24 which rotates again in the
clockwise direction in the drawing are disposed in the vacuum
chamber 21 kept at a high degree of vacuum with the aid of the
evacuation system 20 disposed at the top portion thereof, and the
support 22 having the magnetic layer is arranged to successively
travel from the feed roll 23 to the winding roll 24.
[0053] In the middle way along which the support 22 having the
magnetic layer travels from the feed roll 23 to the winding roll
24, the cooling can 25 having a diameter larger than those of the
feed roll 23 and the winding roll 24 is disposed. The cooling can
25 is disposed so as to draw the support 22 having the magnetic
layer downward in the illustration, and configured so as to rotate
clockwisely in the illustration at a constant speed. It is to be
noted that each of the feed roll 23, the winding roll 24 and the
cooling can 25 have a cylindrical form having a length almost
equivalent to the width of the support 22 having the magnetic
layer.
[0054] The support 22 having the magnetic layer is, therefore,
arranged so as to be successively reeled out from the feed roll 23,
pass over the circumferential surface of the cooling can 25, and be
taken up by the winding roll 24. It is to be noted that the guide
rolls 26, 27 are disposed respectively between the feed roll 23 and
the cooling can 25, and between the cooling can 25 and the winding
roll 24, so as to apply a predetermined tension to the support 22
having the magnetic layer which travels from the feed roll 23 via
the cooling can 25 to the winding roll 24, so that the support 22
having the magnetic layer can smoothly run.
[0055] In the vacuum chamber 21, the hollow cathode ion source 10
is disposed below the cooling can 25. The hollow cathode ion source
10 generates plasma as described in the above, decomposes and
ionizes the source gas, and this allows successive film formation
of the DLC film or the like on the running support 22 having the
magnetic layer.
[0056] Unlike the plasma CVD process adopted in the prior art, the
above-described hollow cathode CVD process does not use the
magnetic layer, evaporated on the non-magnetic support, as an
electrode. Voltage for exciting the plasma, therefore, does not
fluctuate even if the film composition and thickness of the
magnetic layer should vary, and this makes it possible to form the
protective layer having stable characteristics.
[0057] The next paragraphs will explain the oblique evaporation for
forming the magnetic layer FIG. 4 is a schematic sectional view
showing a vacuum evaporation apparatus for carrying out the oblique
evaporation. The vacuum evaporation apparatus has evacuation
systems 30, a vacuum chamber 31, a feed roll 33, a winding roll 34,
a cooling can 35, guide rolls 36, 37, a crucible 38, a metal
magnetic material 39, an electron gun 40, a shutter 41 and an
oxygen gas introducing pipe 42.
[0058] The feed roll 33 which rotates in the clockwise direction in
the illustration and the winding roll 34 which rotates again in the
clockwise direction in the illustration are disposed in the vacuum
chamber 31 kept at a high degree of vacuum with the aid of the
evacuation systems 30 disposed respectively at the top and bottom
portions thereof, and the tape-formed non-magnetic support 1 is
arranged to successively run from the feed roll 33 to the winding
roll 34.
[0059] In the middle way along which the non-magnetic support 1
runs from the feed roll 33 to the winding roll 34, the cooling can
35 having a diameter larger than those of the feed roll 33 and the
winding roll 34 is disposed. The cooling can 35 is disposed so as
to draw the non-magnetic support 1 downward in the illustration,
and configured so as to rotate clockwisely in the illustration at a
constant speed. It is to be noted that each of the feed roll 33,
the winding roll 34 and the cooling can 35 have a cylindrical form
having a length almost equivalent to the width of the non-magnetic
support 1, and the cooling can 35 has a not-shown cooling device
incorporated therein, so as to make it possible to suppress any
deformation of the non-magnetic support 1 due to temperature
rise.
[0060] The non-magnetic support 1 is arranged so as to be
successively reeled out from the feed roll 33, pass over the
circumferential surface of the cooling can 35, and be taken up by
the winding roll 34. It is to be noted that the guide rolls 36, 37
are disposed respectively between the feed roll 33 and the cooling
can 35, and between the cooling can 35 and the winding roll 34, so
as to apply a predetermined tension to the non-magnetic support 1
which runs from the unwinding roll 33 via the cooling can 35 to the
winding roll 34, so that the non-magnetic support 1 can smoothly
travel.
[0061] In the vacuum chamber 31, the crucible 38 is disposed below
the cooling can 35, and the metal magnetic material 39 is placed in
the crucible 38. The crucible has a width almost equivalent to that
of the cooling can 35.
[0062] On the side wall portion of the vacuum chamber 31, the
electron gun 40 for heating and evaporating the metal magnetic
material 39 placed in the crucible 38 is attached. The electron gun
40 is positioned so that an electron beam X emitted therefrom can
irradiate the metal magnetic material 39 in the crucible 38. The
metal magnetic material 39 evaporated by the electron gun 40 is
arranged to deposit and form a film as the magnetic layer on the
non-magnetic support 1 traveling at a constant speed on the
circumferential surface of the cooling can 35.
[0063] The shutter 41 is disposed between the cooling can 35 and
the crucible 38, in the vicinity of the cooling can 35. The shutter
41 is formed so as to cover a predetermined area of the
non-magnetic support 1 traveling at a constant speed on the
circumferential surface of the cooling can 35, and by this shutter
41, the metal magnetic material 39 is allowed to deposit obliquely
on the non-magnetic support 1 within a predetermined angular range
(e.g., angle of incidence of 45.degree. to 90.degree.). During the
vacuum evaporation, oxygen gas is supplied to the surface of the
non-magnetic support 1 through the oxygen gas introducing pipe 42
disposed so as to penetrate the side wall portion of the vacuum
chamber 31, aiming at improving magnetic characteristics and
durability of the magnetic layer to be deposited.
[0064] According to the method of fabricating a magnetic recording
medium of this mode of embodiment, in the process step of forming
the protective layer, the carbon-containing protective layer is
formed by the chemical vapor deposition process using the ion
source equipped with the hollow cathode. The chemical vapor
deposition process using the ion source equipped with the hollow
cathode does not use the magnetic layer as an electrode, unlike the
conventional plasma CVD process, and makes it possible to form the
protective layer having stable characteristic even if the thickness
of the magnetic layer is reduced to as thin as 100 nm or less.
EXAMPLE 1
[0065] Next, a magnetic recording medium (magnetic tape) of Example
1 was fabricated according to this embodiment, and subjected to the
test below. First, on a base film (polyethylene terephthalate,
thickness: 8 .mu.m, width: 150 mm) as the non-magnetic support, the
magnetic layer was formed by the oblique evaporation process using
the vacuum evaporation apparatus under the vacuum evaporation
conditions described below:
[0066] Vacuum Evaporation Conditions for Magnetic Layer: [0067]
Ingot (metal magnetic material): Co, 100 wt % [0068] Angle of
incidence: 45.degree. to 90.degree. [0069] Introduced gas: oxygen
gas [0070] Amount of introduced oxygen: 4.4.times.10.sup.-6
m.sup.3/sec [0071] Degree of vacuum during vacuum evaporation:
2.times.10.sup.-2 Pa [0072] Thickness of magnetic layer: 45 nm
[0073] Next, the support having the magnetic layer formed thereon
was taken out from the vacuum evaporation apparatus, loaded on the
feed roll side of the hollow cathode CVD apparatus, and'subjected
to formation of the DLC film as the protective layer under the
conditions for CVD using the ion source equipped with the hollow
cathode, as described below: [0074] Formation Conditions for
Protective Layer: [0075] Ar flow rate around hollow cathode: 20
sccm [0076] Ar flow rate around anode: 40 sccm [0077] Source gas:
C.sub.2H.sub.4 [0078] Flow rate of source gas: 30 sccm [0079]
Process pressure: 1 mTorr [0080] Discharge voltage: 50 V [0081]
Thickness of protective layer: 2 nm
[0082] Next, a back-coat composition having a chemical composition
shown below was put in a ball mill, allowed to disperse-and mix for
24 hours, added with a crosslinking agent to thereby prepare a
back-coat coating material, and this was coated on the surface of
the non-magnetic support opposite to the magnetic layer to thereby
form the back-coat layer of 0.6 .mu.m thick. [0083] Back-Coat
Composition: [0084] Carbon black: 50 wt % [0085] Polyurethane
resin: 50 wt %
[0086] The master tape sheet having the magnetic layer, the
protective layer and the back-coat layer thus formed thereon was
slit into 3.8-mm width to thereby fabricate sample tapes (Example
1) of the magnetic recording medium.
EXAMPLES 2, 3, AND COMPARATIVE EXAMPLES 1 TO 4
[0087] Magnetic tapes of Examples 2 and 3, and Comparative Examples
1 to 4 were fabricated under the discharge voltage and thickness of
the protective layer altered into various values as listed below in
the process step of forming the protective layer by the hollow
cathode CVD process. It is to be noted that the thickness of the
protective layer can be altered by the feed speed of the
support.
EXAMPLE 1
[0088] Discharge voltage 50 V, [0089] Thickness of protective layer
2 nm
EXAMPLE 2
[0089] [0090] Discharge voltage 120 V, [0091] Thickness of
protective layer 8 nm
EXAMPLE 3
[0091] [0092] Discharge voltage 80 V, [0093] Thickness of
protective layer 16 nm
COMPARATIVE EXAMPLE 1
[0093] [0094] Discharge voltage 80 V, [0095] Thickness of
protective layer 1 nm
COMPARATIVE EXAMPLE 2
[0095] [0096] Discharge voltage 80 V, [0097] Thickness of
protective layer 18 nm
COMPARATIVE EXAMPLE 3
[0097] [0098] Discharge voltage 150 V, [0099] Thickness of
protective layer 8 nm
COMPARATIVE EXAMPLE 4
[0099] [0100] Discharge voltage 180 V, [0101] Thickness of
protective layer 4 nm
[0102] In the fabrication of above-described Examples 1 to 3 and
Comparative Examples 1 to 4, any alteration of the discharge
voltage and thickness into various values never resulted in any
unstable discharge situation such as arc discharge during the film
formation, and instead resulted in stable film formation. On the
contrary, the film formation under similar conditions by the
conventional plasma CVD process failed in maintaining the discharge
because of a thickness of the magnetic layer as thin as 45 nm.
(Raman Spectrometry)
[0103] Raman scattering measuring apparatus generally comprises
four sections, which are an excitation light source, a sample unit,
a dispersion system and a detector. Ion gas (Ar, He--Ne, Kr) laser
is used for the excitation light. The sample unit comprises optical
systems for sample irradiation and concentration of scattered
light. Raman scattered light is dispersed by a double monochrometer
in which single spectrophotometers are connected in series, and
then detected by the detector. Photomultiplier tube has been used
for the detector, but multi-channel photodetector has increasingly
been used in recent years. The multi-channel photodetector can
measure spectrum at the same time, and this advantageously needs
only several seconds for the measurement.
[0104] The individual samples (Examples 1 to 3, and Comparative
Examples 1 to 4) were tested by Raman spectrometry. The ratio (D/G)
of the spectral intensity (G) having a peak from 1,550 cm.sup.-1 to
1,650 cm.sup.-1 and the spectral intensity (D) having a peak from
1,350 cm.sup.-1 to 1,450 cm.sup.-1 in Raman spectrum was
investigated.
(Practical Performance Test)
[0105] The individual samples (Examples 1 to 3, and Comparative
Examples 1 to 4) were subjected to a head wear test and an
electromagnetic conversion characteristic test, as evaluations for
practical performance. In the head wear test, the amount of wear of
an MR head was measured by carrying out 60-min shuttle run for 300
times on Micro MV camcorder (product of SONY Corporation) under a
-5.degree. C. environment. The amount of head wear was found to
seriously affect the electromagnetic conversion characteristic when
it exceeded 1 .mu.m, so that it was found necessary to suppress the
wear to 1 .mu.m or less.
[0106] The electromagnetic conversion characteristic test was also
carried out using a drum tester. Recording was carried out at
recording wavelengths of 2.0 .mu.m and 0.3 .mu.m, using an MIG head
having a gap length of 0.22 .mu.m and a track width of 20 .mu.m,
and carrier output obtained when reproduction was made using an
NiFe MR head having a track width of 5 .mu.m was measured. The
measurement was respectively made while allowing the magnetic tape
and magnetic head relatively move in the normal direction and
inverse direction, and an average value was found. Relative speed
of the magnetic tape and the MR head was set to 7 m/sec. The
carrier output was expressed in dB assuming Example 2 as a
reference. It is to be understood that a carrier output of -3 dB or
less is not a signal appropriate for the recording/reproduction
system.
[0107] The D/G ratio respectively measured by Raman spectrometry,
and results of the head wear test and the electromagnetic
conversion characteristic test were shown in Table 1.
TABLE-US-00001 TABLE 1 Thickness Amount of of Electromagnetic
Discharge Protective Head Conversion Voltage Layer D/G Wear
Characteristic Example 1 50 V 2 nm 0.2 0.1 .mu.m +2.2 dB Example 2
120 V 8 nm 1.0 0.7 .mu.m 0.0 dB Example 3 80 V 16 nm 0.6 0.8 .mu.m
-2.7 dB Comparative 80 V 1 nm 0.6 0.1 .mu.m Not Measurable Example
1 (scratch) Comparative 80 V 18 nm 0.6 1.2 .mu.m -3.7 dB Example 2
Comparative 150 V 8 nm 1.2 1.3 .mu.m +0.2 dB Example 3 Comparative
180 V 4 nm 1.5 1.2 .mu.m +1.2 dB Example 4
[0108] As is obvious from Table 1, the magnetic recording medium is
successfully given with a small head wear property and sufficient
output signal by forming the carbon protective layer to a thickness
of 2 to 16 nm using the hollow cathode CVD process, and by
adjusting the ratio of intensity of a spectrum having a peak from
1,550 cm.sup.-1 to 1,650 cm.sup.-1 and intensity of a spectrum
having a peak from 1,350 cm.sup.-1 to 1,450 cm.sup.-1 to 1.0 or
below.
[0109] FIG. 5 is a graph obtained by plotting D/G ratio with
respect to discharge voltage V.sub.elec based on Table 1. The D/G
ratio strongly correlates to the discharge voltage, wherein a
higher discharge voltage results in a smaller D/G ratio. The D/G
ratio is preferably 1.0 or less as described in the above, and to
realize this, it is preferable to set the discharge voltage, under
the above-described conditions in the hollow cathode CVD process,
to 120 V or less.
[0110] FIG. 6 is a graph obtained by plotting the amount of head
wear HW with respect to a thickness t.sub.DLC of the protective
layer (DLC layer film). Numerals given in the graph indicate the
discharge voltage. It is found from the graph that the amount of
head wear increases as the thickness of the protective layer (DLC
film) increases, and as the discharge voltage increases. Because
the amount of head wear is preferably suppressed to 1.0 .mu.m or
less as described in the above, ranges of the thickness of the
protective layer and the discharge voltage can be determined
depending on FIG. 6.
[0111] It was made possible to carry out a stable film formation by
using the hollow cathode CVD process even on a magnetic tape having
a thin magnetic layer, which has been difficult in the prior art.
Use of the hollow cathode CVD process made it possible to improve
stability in the film formation, to form the film for a long
duration of time, and to improve the yield ratio. Use of the hollow
cathode CVD process can realize arbitrary film quality of the
protective layer.
[0112] The magnetic recording medium and the method of fabricating
the same according to the present invention are by no means limited
to the description in the above. For example, although the medium
of the above-described mode of embodiment has the DLC film as the
protective layer, the protective layer may have any other
characteristics such as composition, thickness and film quality.
Also the layer configuration and so forth of the magnetic recording
medium is by no means limited to those exemplified in the mode, and
various layers such as a magnetic layer underlying layer and a
back-coat underlying layer may be provided. Any other modifications
may be allowable without departing from the spirit of the present
invention.
[0113] The magnetic recording medium and the method of fabricating
the same are applicable to magnetic tape for data storage, and a
method for fabricating the same.
[0114] Although the invention has been described in its preferred
form with a certain degree of particularity, obviously many changes
and variations are possible therein. It is therefore to be
understood that the present invention may be practiced otherwise
than as specifically described herein without departing from the
scope and the sprit thereof.
* * * * *