Magnetic recording medium and its manufacturing method

A magnetic recording medium comprising a non-magnetic substrate, a ferromagnetic thin film on the non-magnetic substrate, a hard carbon film on the ferromagnetic thin film, a modified layer of which atomic ratio of nitrogen/carbon is 0.8% or more, and of which thickness is less than 3 nm on the hard carbon film, and a lubricant layer on the modified layer, has excellent electromagnetic conversion characteristic, running stability, durability, and weatherability.

FIELD OF THE INVENTION 
The present invention relates to a magnetic recording medium possessing a 
ferromagnetic thin film to be used in VTR, magnetic disk apparatus, or the 
like, and more particularly to a magnetic recording medium of 
ferromagnetic thin film type excellent in electromagnetic conversion 
characteristic, running stability, running durability, and weatherability. 
BACKGROUND OF THE INVENTION 
Recently, the VTR is becoming higher in picture quality and higher in sound 
quality, and the magnetic disk apparatus has come to be higher in capacity 
and faster in speed. Accordingly, the magnetic recording medium is 
demanded to be higher in recording density. As the magnetic recording 
medium to meet this demand, a magnetic recording medium of ferromagnetic 
thin film type is known, and it is intensively developed and realized. The 
prior arts of the magnetic recording medium of this type include the 
Japanese Patent Laid-Open No. 62-58416 (prior art 1), No. 1-184722 (prior 
art 2), No. 2-125417 (prior art 3), No. 2-126418 (prior art 4), and No. 
4-134623 (prior art 5). 
Prior art 1 relates to a magnetic recording medium having a protective 
layer of organic high molecular compound with the ratio of nitrogen 
(N)/carbon (C) of 40 atomic % or more, provided on a ferromagnetic thin 
film. Prior art 2 relates to a magnetic recording medium having a hard 
carbon thin film containing boron (B), titanium (Ti) or silicon (Si), 
provided on a ferromagnetic thin film. Prior art 3 relates to a magnetic 
recording medium having a hard carbon film provided on a ferromagnetic 
thin film, having a plasma polymerization film involving nitrogen provided 
on the hard carbon film, and having a lubricant layer containing 
fluorinated carboxylic acid provided on the polymerization film containing 
nitrogen. Prior art 4 relates to a magnetic recording medium having a hard 
carbon film provided on a ferromagnetic thin film, treating the hard 
carbon film surface by glow discharge in the presence of ammonia gas, and 
having a lubricant layer containing fluorinated carboxylic acid provided 
on the hard carbon film. The carbon protective film provided on the 
ferromagnetic thin film of prior art 5 has the relative intensity of Raman 
bands (1400 cm.sup.-1 band/1550 cm.sup.-1 band) of 2.6 to 3.8. 
However, even in these prior arts, a further improvement was necessary in 
order to obtain a magnetic recording medium excellent in electromagnetic 
conversion characteristic, running stability, running durability, and 
weatherability. 
For example, in the constitution of prior art 1 in which the protective 
layer of organic high molecular compound with the ratio of N/C of 40 
atomic % or more is provided on the ferromagnetic thin film, the hardness 
of the protective layer of organic high molecular compound itself (film 
thickness:15 nm) is lowered and is easily worn, and hence running 
stability and running durability cannot be satisfied sufficiently. In the 
constitution of prior art 2 in which the lubricant layer is provided on 
the hard carbon thin film containing B, Ti and Si, although the adhesion 
strength between hard carbon thin film and lubricant layer is improved, 
the hardness of the hard carbon thin film itself (film thickness:8 nm) is 
lowered, and hence the durability of still characteristics or the like is 
worsened. In the constitution of prior art 3 in which the plasma 
polymerization film containing nitrogen (film thickness:3 nm) is provided 
between hard carbon film and lubricant layer, but the plasma 
polymerization film containing nitrogen is too thick, low in hardness and 
easily worn, and hence the running stability and running durability cannot 
be satisfied sufficiently. In the constitution of prior art 4 in which the 
lubricant layer is provided after treating the hard carbon film surface by 
glow discharge in the presence of ammonia gas, since the surface of the 
hard carbon film is heavily damaged by the impact of charged particles 
generated from ammonia, durability, and weatherability are lowered. In 
prior art 5, in order to obtain the optimum hardness, toughness and 
coefficient of kinematic friction of the carbon protective film (film 
thickness:15 nm), the relative intensity of Raman bands (1400 cm.sup.-1 
band/1550 cm.sup.-1 band) is defined in a range of 2.6 to 3.8, but 
weatherability is not sufficient. 
SUMMARY OF THE INVENTION 
A magnetic recording medium excellent in electromagnetic conversion 
characteristic, running stability, running durability, and weatherability 
is obtained by forming a ferromagnetic thin film on a non-magnetic 
substrate, forming a hard carbon film on the ferromagnetic thin film, 
exposing the surface of the hard carbon film to glow discharge plasma by a 
gaseous mixture of nitrogen involving an organic gas and an inorganic gas, 
or a gaseous mixture of nitrogen involving an organic gas, a hydrocarbon 
gas and an inorganic gas to form a modified layer which has atomic ratio 
of nitrogen/carbon of 0.8% or more and which has thickness of less than 3 
nm, and forming a lubricant layer on the modified layer.

DETAILED DESCRIPTION OF THE INVENTION 
EXAMPLE 1 
The thin film magnetic tape (hereinafter called magnetic tape) of the first 
embodiment of the invention and its manufacturing method are explained 
below while referring to FIG. 1 and FIG. 2. 
EXAMPLE 1-1 
FIG. 1 is a sectional view of the magnetic tape of the embodiment. 
In the diagram, numeral 1 is a non-magnetic substrate of polyethylene 
terephthalate (PET) of 10 .mu.m in film thickness, of which one surface is 
uneven and provided with bumps 2 (also called protrusions 2) of 30 .mu.m 
in height and 200 nm in diameter as analyzed by scanning tunnel microscope 
(STM), by 10.sup.5 to 10.sup.9 pieces per 1 mm.sup.2. These protrusions 2 
are intended to decrease the friction against the magnetic head by 
controlling the surface roughness of the magnetic tape surface. Numeral 3 
is a ferromagnetic thin film of Co(80)-Ni(20) of 180 nm in film thickness, 
disposed while feeding oxygen by oblique vacuum deposition process. 
Numeral 4 is a back coat layer of 500 nm in film thickness, which is 
obtained by applying and drying a methylethylketone/toluene/cyclohexane 
solution with solid content of 30% composed of polyurethane, 
nitrocellulose, and carbon black, by wet process coating method (reverse 
roll coater). Numeral 5 is a hard carbon film with a film thickness of 
13.0 nm and Vickers hardness of 2500 kg/mm.sup.2 provided by plasma CVD 
method on the ferromagnetic thin film 3. Numeral 6 is a modified layer 
comprised of carbon, nitrogen and oxygen. The modified layer of the 
present invention involves modified surface having a thickness less than 
monolayer thickness. Numeral 7 is a lubricant layer of fluorinated 
carboxylic acid, C.sub.5 F.sub.11 (CH.sub.2).sub.10 COOH, with film 
thickness of 4 nm provided on the modified layer 6. 
Referring now to FIG. 2, the manufacturing method of hard carbon film 5 and 
modified layer 6 of the magnetic tape of the embodiment is described 
below. 
In FIG. 2, numeral 8 is a vacuum chamber, which is evacuated by a vacuum 
pump 9 until the internal degree of vacuum becomes 10.sup.-4 to 10.sup.-5 
torr. Numeral 10 is a 500 mm wide tape, having the ferromagnetic thin film 
3 and back coat layer 4 provided on the PET 1, and it is sent out from a 
unwinder roll 11, and is taken up on a winder roll 15 by way of two pass 
rolls 12, 13 and a cylindrical cooling can 14. The cooling can 14 is 
responsible for controlling the rotation so that the tape 10 may be 
conveyed at a specific speed. Numeral 16 is a discharge tube (CVD plasma 
generation space) for forming the hard carbon film 5 on the ferromagnetic 
thin film 3 of the tape 10, and a pipe-shaped discharge electrode 17 is 
installed in its inside. The pipe-shaped discharge electrode 17 is 
connected to a plasma generation power source 18. Numeral 19 is a material 
gas feed port for feeding material gas into the discharge tube 16. 
In such apparatus, the hard carbon film 5 of the embodiment was formed in a 
film thickness of 13 nm, by setting the conveying speed of the tape 10 at 
3 to 5 m/min, keeping the total gas pressure at 0.3 torr, feeding the 
material gas at pressure ratio of 4:1 of hexane (C.sub.5 H.sub.14 : 
hydrocarbon gas) and argon (Ar: inorganic gas) into the discharge tube 16 
and applying 1000 V DC to the pipe-shaped discharge electrode 17. 
Subsequently, from the material gas feed port 23 into the discharge tube 
20, pyridine (C.sub.5 H.sub.5 N:nitrogen involving organic gas) and 
hydrogen (H.sub.2 : inorganic gas) were fed at pressure ratio of 3:2, 
keeping the total gas pressure of 0.1 torr, and 1500 V DC was applied to 
the punching metal discharge electrode 21 installed in the discharge tube 
20 to generate a non-equilibrium plasma, and the modified layer 6 of 1.0 
nm in thickness was formed on the hard carbon film 5. On the modified 
layer 5, subsequently, the lubricant layer 7 of fluorinated carboxylic 
acid, C.sub.5 F.sub.11 (CH.sub.2).sub.10 COOH, in a film thickness of 4 nm 
was formed by wet process coating method (reverse rollcoater). Then, the 
500 mm wide tape was cut in a width of 8 mm by a slitter, and a magnetic 
tape for measurement of characteristic was obtained. 
EXAMPLE 1-2 
What is different from Example 1-1 is that pyridine was replaced by 
allylamine (C.sub.3 H.sub.7 N:nitrogen involving organic gas). 
To clarify the effect of the embodiments, three comparative examples were 
fabricated. 
COMATIVE EXAMPLE 1-1 
The same composition as Example 1-1 except that pyridine was replaced by 
benzene (C.sub.6 H.sub.6 :hydrocarbon gas). 
COMATIVE EXAMPLE 1-2 
The same composition as Example 1-1 except that the mixture gas of pyridine 
and hydrogen was replaced by a mixture gas of pyridine, benzene and oxygen 
(O.sub.2 :inorganic gas), at a pressure ratio of 1:5:1. 
COMATIVE EXAMPLE 1-3 
The same composition as Example 1-1 except that the thickness of the 
modified layer was 6 nm. 
COMATIVE EXAMPLE 1-4 
The same composition as Example 1-1 except that the Vickers hardness of the 
hard carbon film 5 was 1300 kg/mm.sup.2. 
The chemical composition of the modified layer 6 was analyzed by the X-ray 
photoelectron spectroscopy within 4 nm from the surface of the modified 
layer 6 by using a magnetic tape before forming a lubricant layer 7. 
Besides, the Vickers hardness of the hard carbon film 5 was obtained in 
the following method. 
First, several specimens formed hard carbon film in the thickness of about 
1 to 3 .mu.m on a silicon wafer instead of the tape 10, was fabricated, 
subseqently, the Vickers hardness of the specimens were measured by using 
a micro hardness meter. And from the relation between the film thickness 
and the Vickers hardness, the Vickers hardness of the hard carbon film 5 
corresponding to the film thickness of 13 nm was calculated by 
extrapolation. The film thickness of the hard carbon film was measured by 
an ellipsometer. The magnetic tapes obtained in the embodiments and 
comparative examples were measured in the following items. 
The results are compiled in Tables 1 and 2. 
In Table 2, running durability and weatherability were evaluated in the 
following method. 
(1) Magnetic head clogging, tape damage 
Using an 8 mm VTR modified for RF output level measurement, running 
durability test was conducted by driving the magnetic tape for 300 hours 
in 300 passes in the environment of 40.degree. C.--80% RH. Before test, 
video signals are recorded, the RF level output reproduced while running 
was rectified, and the result was recorded in a pen recorder (model 
VP-6524A of Matsushita Communication Industrial Co., Ltd.). It was 
regarded as magnetic head clogging when the RF output level was lowered by 
6 dB or more, and the total time was measured. To evaluate the tape 
damage, the state was visually observed after running durability test, and 
was judged in five ranks. The ranking was 5 when there was no problem at 
all practically, and 1 when a practical problem was found. 
(2) Change of friction coefficient (.mu.k change) 
Before and after the running durability test, the friction coefficient of 
the magnetic tape was measured. The measuring conditions were as follows. 
On a stainless steel (material:15 MH) column of 4 mm in diameter and 0.2 S 
in surface roughness, the tape was wound with the magnetic surface inside 
at an embrace angle of 180 degrees, and driven at the input tension of 10 
g, 14 mm/sec, and the output tension was measured and the friction 
coefficient was determined in the following formula. 
EQU .mu.=1/.pi..1n(output tension: xg/input tension: 10 g) 
The measuring environment was 25.degree. C.--30% RH, and the measurement at 
the 30th path of running was taken as the friction coefficient. 
(3) Rust, peeling 
In weatherability test, the magnetic tape was left in the environment of 
40.degree. C.--90% RH for 30 days. After weatherability test, the state of 
the tape specimens was observed by differential interference microscope, 
and was evaluated in five ranks. The ranking was 5 when no problem was 
found practically, and 1 when a practical problem was found. 
(4) Change of dropout (DO change) 
Prior to weatherability test in (3), using an 8 mm VTR modified for dropout 
measurement, video signals were recorded in magnetic tape, and dropout was 
measured. After the test, dropout was also measured, and the rate of 
dropout change before and after the test was expressed in magnification. 
The dropout was measured by using dropout counter (model VH01CZ of 
SHIBASOKU) in the conditions of 15 .mu.s-16 dB. 
(5) Environmental gas resistance test (H.sub.2 S gas, HCl gas) 
The magnetic tape was left in the air containing 1000 ppm of H.sub.2 S for 
72 hours, and the rusting state was observed by differential interference 
microscope and evaluated in five ranks. The ranking was 5 when no problem 
was found practically, and 1 when practical problem was found. 
In the magnetic tape of the embodiment, as known from Table 1 and Table 2, 
since the modified layer 6 with thickness of less than 3 nm containing a 
specific content of nitrogen atoms having a strong chemical affinity for 
the polar functional group (carboxyl group) introduced in the lubricant 
molecules is provided on the hard carbon film 5, the lubricant molecules 
can be firmly held on the tape surface without lowering the hardness of 
the protective film composed of hard carbon film and modified layer and 
without increasing the spacing loss between ferromagnetic thin film and 
magnetic head, so that running durability and weatherability have been 
remarkably improved. As the chemical composition of the modified layer 6, 
the atomic ratio of nitrogen/carbon is required to be 0.8% or more. More 
preferably, it is effective when the atomic ratio of nitrogen/oxygen is 
9.5% or more, and the atomic ratio of the total amount of carbon atoms, 
nitrogen atoms and oxygen atoms contributed to C--N bond and C--O bond to 
the total carbon atoms is preferred to be 3.0 atomic % or more, and the 
atomic ratio of the total amount of nitrogen atoms and oxygen atoms 
contributed to N--O bond to the total carbon atoms bond is 1.0 atomic % or 
less. Besides, the Vickers hardness of the hard carbon film 5 is preferred 
to be 2000 kg/mm.sup.2 or more. 
EXAMPLE 2 
The second embodiment of the invention is described below. 
What is different from Example 1 is that the nitrogen concentration of the 
modified layer 6 is decreased in the direction of the hard carbon film 5 
from the surface of the modified layer. 
EXAMPLE 2-1 
Referring to FIG. 3, the manufacturing method of the hard carbon film 5 and 
modified layer 6 of the embodiment is described below. 
In FIG. 3, setting the conveying speed of the tape 10 at 3 to 5 m/m keeping 
the total gas pressure at 0.3 torr, feeding the material gas at pressure 
ratio of 4:1 of hexane (C.sub.6 H.sub.14 :hydrocarbon gas) and argon 
(Ar:inorganic gas) into the discharge tube 16, and applying 1000 V DC to 
the pipe-shaped discharge electrode 17, the hard carbon film 5 of 13 nm in 
thickness was formed by plasma CVD method. The Vickers hardness of the 
hard carbon film 5 was 2500 kg/mm.sup.2. Subsequently, from a material gas 
feed port 24, a mixture gas of n-propylamine (C.sub.3 H.sub.7 NH.sub.2 : 
nitrogen-involving organic gas):methane (CH.sub.4 :hydrocarbon 
gas):hydrogen (H.sub.2 :inorganic gas) is introduced at 2:7:1, at total 
gas pressure of 0.1 torr, from a material gas feed port 25, a mixture gas 
of n-propylamine: methane:hydrogen is introduced at 4.5:4.5:1, at total 
gas pressure of 0.1 torr, and from a material gas feed port 26, a mixture 
gas of n-propylamine:methane:hydrogen is introduced at 7:2:1, at total gas 
pressure of 0.1 torr, respectively. By applying 2000 V DC to punching 
metal discharge electrodes 27, 28, 29, a non-equilibrium plasma was 
generated, a modified layer 6 was formed in three steps by 0.6 nm each 
step, and the modified layer 6 of 1.8 nm in thickness decreasing the 
concentration of nitrogen in the direction from the surface of the 
modified layer toward the hard carbon film was formed. At this time, the 
partial pressure of the nitrogen involving organic gas was 20, 45 and 70% 
of the total gas pressure. Furthermore, on the modified layer 6, a 
lubricant layer 7 of fluorinated carboxylic acid, C.sub.5 H.sub.11 
(CH.sub.2).sub.10 COOH, in a film thickness of 4 nm was formed by wet 
process coating method (reverse roll coater). Then, the 500 mm wide tape 
was cut to a width of 8 mm by slitter, and the magnetic tape for 
characteristic measurement was obtained. 
To clarify the effects of the embodiment, two examples and three 
comparative examples were fabricated. 
EXAMPLE 2-2 
What is different from Example 2-1 is that n-propylamine was replaced by 
dimethylformamide (C.sub.3 H.sub.7 NO). 
EXAMPLE 2-3 
What is different from Example 2-1 is that the modified layer was formed in 
three steps by 0.9 nm each step. 
COMATIVE EXAMPLE 2-1 
The same composition as Example 2-1 except that the lubricant layer 7 was 
disposed directly on the hard carbon film 5, without forming the modified 
layer 6 having a concentration gradient of nitrogen. 
COMATIVE EXAMPLE 2- 
The same composition as Example 2-1 except that the mixture gas of 
n-propylamine, methane and hydrogen was replaced by a mixture gas of 
n-propylamine, methane and oxygen (O.sub.2 :inorganic gas), at pressure 
ratio of 2:7:1, 4.5:4.5:1, 1:7:2. 
COMATIVE EXAMPLE 2-3 
The same composition as Example 2-1 except that the thickness of the 
modified layer 6 was formed in three steps by 2 nm each step. 
COMATIVE EXAMPLE 2-4 
The same composition as Example 2-1 except that the Vickers hardness of the 
hard carbon film 5 was 1300 kg/mm.sup.2. 
The chemical composition of the modified layer 6 of the magnetic tape, and 
the Vickers hardness and magnetic tape characteristic of the hard carbon 
film 5 are shown in Tables 3 and 4. The methods of measurement were same 
as in Example 1. 
In the magnetic tape of the embodiment, as known from Table 3 and Table 4, 
(a) since the modified layer 6 with thickness of less than 3 nm containing 
a specific content of nitrogen atoms having a strong chemical affinity for 
the polar functional group (carboxyl group) introduced in the lubricant 
molecules is provided on the hard carbon film 5, the lubricant molecules 
can be firmly held on the tape surface without lowering the hardness of 
the protective film composed of hard carbon film and modified layer and 
without increasing the spacing loss between ferromagnetic thin film and 
magnetic head, (b) since the concentration of nitrogen of the modified 
layer 6 is decreased in the direction from the surface of the modified 
layer to the hard carbon film, the internal stress of the hard carbon film 
itself is properly relaxed and the adhesion strength between modified 
layer and hard carbon film is increased, so that running durability and 
weatherability have been remarkably improved. As the chemical composition 
of the modified layer 6, the atomic ratio of nitrogen/carbon is required 
to be 0.8% or more. More preferably, it is effective when the atomic ratio 
of nitrogen/oxygen is 9.5% or more, and the atomic ratio of the total 
amount of carbon atoms, nitrogen atoms and oxygen atoms contributed to 
C--N bond and C--O bond to the total carbon atoms in the modified layer 
preferred to be 3.0 atomic % or more, and the atomic ratio of the total 
amount of nitrogen atoms and oxygen atoms contributed to N--O bond to the 
total carbon atoms bond to 1.0 atomic % or less. Besides, the Vickers 
hardness of the hard carbon film is preferred to be 2000 kg/mm.sup.2 or 
more. 
EXAMPLE 3 
The third embodiment of the invention is described below. 
What is different from Example 1 is that the modified layer 6 is island as 
shown in FIG. 4. 
EXAMPLE 3-1 
First, using the apparatus shown in FIG. 2, setting the conveying speed of 
tape 10 at 15 m/rain, keeping the total gas pressure at 0.2 torr, feeding 
the material gas at the pressure ratio of 4:1 of toluene (C.sub.7 H.sub.8 
:hydrocarbon gas) and argon (Ar:inorganic gas) into the discharge tube 16, 
and applying 1000 V DC to the pipe-shaped discharge electrode 17, the hard 
carbon film 5 of 10 nm in film thickness was formed. Subsequently, from 
the material gas feed port 23 into the discharge tube 20, pyridine and 
hydrogen were fed at pressure ratio of 3:2 keeping the total gas pressure 
of 0.1 torr, and 1200 V DC was applied to the punching metal electrode 21 
installed in the discharge tube 20, and a non-equilibrium plasma was 
generated to form an island 6 of 2 nm in thickness on the hard carbon film 
5. Consequently, on the island layer 6, a lubricant layer 7 of fluorinated 
carboxylic acid C.sub.5 F.sub.11 (CH.sub.2).sub.10 COOH was formed in a 
film thickness of 4 nm by the wet process coating method (reverse roll 
coater). Then, a 500 mm wide tape was cut in a width of 8 mm by a slitter, 
and a magnetic tape for characteristic measurement was obtained. The 
Vickers hardness of the hard carbon of this example was 2200 kg/mm.sup.2. 
EXAMPLE 3-2 
The same composition as Example 3-1 except that pyridine and hydrogen were 
replaced by butylamine and NH.sub.3. 
COMATIVE EXAMPLE 3-1 
The same composition as Example 3-1 except that the lubricant layer 7 was 
formed directly on the hard carbon film 5 without forming island 6 on the 
hard carbon film 5. 
COMATIVE EXAMPLE 3-2 
The same composition as Example 3-1 except that the island 6 was formed in 
a thickness of 10 nm on the ferromagnetic thin film 3 without forming hard 
carbon film 5. 
COMATIVE EXAMPLE 3-3 
The same composition as Example 3-1 except that pyridine was replaced by 
styrene (C.sub.8 H.sub.8 :hydrocarbon gas). 
COMATIVE EXAMPLE 3-4 
The same composition as Example 3-1 except that the thickness of the island 
6 was 8 nm. 
COMATIVE EXAMPLE 3-5 
The same composition as Example 3-1 except that the pressure ratio of 
pyridine and hydrogen was 19:1 and that the total gas pressure was 0.3 
tort. 
COMATIVE EXAMPLE 3-6 
The same composition as Example 3-1 except that the surface of the hard 
carbon film 5 was exposed to glow discharge plasma by pyridine gas only. 
COMATIVE EXAMPLE 3-7 
The same composition as Example 3-1 except that the surface of the hard 
carbon film 5 was exposed to glow discharge plasma by hydrogen only 
COMATIVE EXAMPLE 3-8 
The same composition as Example 3-1 except that the hard carbon film with 
Vickers hardness of 1200 kg/mm.sup.2 was formed on the ferromagnetic thin 
film 3 instead of the hard carbon film 5 with Vickers hardness of 2200 
kg/mm.sup.2. 
Incidentally, from the changes of maximum height roughness (R.sub.max) of 
the tape 10 before and after forming the island 6 observed by scanning 
tunnel microscope and the results of two dimensional analysis (surface 
analysis) by scanning auger microprobe (SAM), it was confirmed that the 
quantity of islands 6 formed on the hard carbon film 5 in the vicinity of 
convex part of the embodiment was more than that than in the vicinity of 
concave part of the surface of the hard carbon film. The Vickers hardness 
of the hard carbon film 5 in the embodiments and comparative examples, or 
the Vickers hardness of the plasma polymerization film in Comparative 
Example 3-8 was obtained in the following method. 
First, several specimens formed hard carbon film or plasma polymerization 
film of about 1 to 3 .mu.m on a silicon wafer instead of tape 10 were 
fabricated, subseqently, the Vickers hardness of the specimens was 
measured by using a micro hardness meter. And from the relation between 
the film thickness and the Vickers hardness, the Vickers hardness of the 
hard carbon film 5 or plasma polymerization film corresponding to the film 
thickness of 10 run was calculated by extrapolation. The film thickness of 
the hard carbon film or plasma polymerization film was measured by an 
ellipsometer. 
In the magnetic tapes obtained by the embodiments and comparative examples, 
the chemical composition and the characteristic of magnetic tape having 
the island 6 are shown in Tables 5 and 6. The characteristic of magnetic 
tapes in Table 6 was measured in the following methods. 
(1) Still frame life 
Using an 8 mm VTR modified for still frame life measurement, in the 
environment of 23.degree. C.--10% RH and the condition of 30 g bad, the 
still picture preliminarily recorded in the magnetic tape was reproduced 
in the still mode, and the time until the video signal dropped to 6 dB was 
measured. The measurement was suspended at the maximum duration of 180 
minutes. 
(2) Magnetic head clogging 
Using an 8 mm VTR modified for RF output measurement, in the environment of 
40%-80% RH, video signals were recorded in a magnetic tape of about 60 
minutes long, and reproduced in 300 passes. In durability test by repeated 
running, the time lowering the reproduction output by more than 6 dB 
continuously was accumulated, and the cumulative time was defined as the 
magnetic head clogging time. 
(3) Weatherability test 
In the weatherability test, in the environment of 40.degree. C.--90% RH, 
the magnetic tape was left for about 30 days, and uneven coating, rust, 
crystal, peeling and other changes were observed by an optical microscope, 
and were evaluated in five ranks. The ranking was 5 when there was no 
practical problem, and 1 when practical problem was found. 
(4) Friction coefficient .mu.k 
On a stainless steel column (SUS420J2) of 4 mm in diameter and 0.2 S in 
surface roughness, a magnetic tape was wound to contact over 90.degree., 
and by setting the input tension at 30 g to the stainless steel column and 
tape running speed of 0.5 mm/sec, the output tension Xg was measured, and 
the friction coefficient was determined in the following formula. 
.mu.k=2/.pi. 1 nX/30 
The measuring environment was 25.degree. C.--30% RH, and the friction 
coefficient at the 30th pass of running was taken. 
As clear from Table 5 and Table 6, in Examples 3-1 and 3-2, since the 
island 6 of less than 3 nm in thickness with a proper content of nitrogen 
atoms having a strong chemical affinity for the polar functional group 
(carboxyl group) introduced in the lubricant molecules is provided on the 
hard carbon film 5, (a) the hardness of the protective film composed of 
hard carbon film and island is not lowered, (b) the spacing loss between 
ferromagnetic thin film and magnetic head is not increased, and (c) the 
lubricant molecules can be firmly held on the vicinity of the concave part 
of the tape protrusion substantially contacting with the magnetic head of 
the VTR rotating at high speed, metal cylinder and fixed post, so that the 
notable enhancement of still frame life, marked improvement of magnetic 
head clogging, outstanding enhancement of weatherability, and keeping of 
running stability can be achieved at the same time. 
In Comparative Example 3-1, since the island-shaped modified layer 6 is not 
provided on the hard carbon film 5, or in Comparative Example 3-3, since 
nitrogen is not contained in molecules, the adhesion of hard carbon film 
and fluorinated lubricant layer is not improved, which gave rise to 
occurrence of magnetic head clogging in the course of a long time. In 
Comparative Example 3-2, the Vickers hardness of the island shaped is 
lower than the Vickers hardness of the hard carbon film, and in 
Comparative Examples 3-4 to 3-6, the sum of nitrogen atoms and oxygen 
atoms contributed to N--O bond in the island shaped 6 exceeds the 
appropriate range of the invention, and therefore the island layer is 
likely to be worn, thereby worsening the tape running stability and 
shortening the still frame life. In particular, in Comparative Example 
3-4, by the chemical affinity of the elements (N, O) contained in the 
island layer and the polar functional group (carboxyl group) introduced in 
the lubricant molecules, although the hard carbon film and lubricant layer 
are firmly adhered with the island layer as intermediate layer, since the 
island layer is too thick, synergistic effects of the wear resistance of 
the hard carbon film and low shearing force of the lubricant layer are not 
exhibited sufficiently, and therefore the running stability of magnetic 
tape is worse and the still frame life is shortened. Moreover, in 
Comparative Example 3-6, since only nitrogen involving organic gas is used 
as the material gas of the island shaped, the hard carbon film surface is 
not purified, and chemical seeds (reaction active seeds) are deposited, 
and firm adhesion of the hard carbon film and island layer cannot be 
maintained, which leads to decrease of still frame life and occurrence of 
magnetic head clogging in long time. In Comparative Example 3-7, since the 
hard carbon film surface is heavily damaged by the impact of charged 
particles generated from H.sub.2 which is inorganic gas, extreme decrease 
of still frame life and worsening of weatherability are caused. In 
Comparative Example 3-8, since the Vickers hardness of hard carbon film is 
low, the still frame life is shorter. Hence, the thickness of the 
island-shaped modified layer 6 should be less than 3 nm, and the chemical 
composition should have an atomic ratio of 0.8% or more of 
nitrogen/carbon. More specifically, it is effective when the atomic ratio 
of nitrogen/oxygen is 9.5% or more, and the sum of carbon, nitrogen and 
oxygen contributed to carbon-nitrogen bond and carbon-oxygen bond should 
be 3.0 atomic % or more, and the sum of nitrogen and oxygen contributed to 
nitrogen-oxygen bond is desired to be 1.0 atomic % or less. The diameter 
of the island-shaped modified layer 6 is preferably in a range of 1 to 100 
nm, or more preferably 10 to 50 nm. In this embodiment, the nitrogen 
concentration in the island-shaped modified layer 6 is constant, but same 
effects are obtained if it is decreased in the direction from the surface 
of the modified layer toward the hard carbon film as in Example 2. 
EXAMPLE 4 
The fourth embodiment of the invention is described below. 
What is different from the magnetic tape in Example 1 is that a modified 
layer 6 is provided on a hard carbon film 5 possessing a specific 
property. 
EXAMPLE 4-1 
The hard carbon film 5 of the embodiment was formed by setting the pressure 
ratio of methane and argon in a discharge tube 16 at 4:1, total gas 
pressure at 0.25 torr, and the temperature of a cylindrical cooling can 14 
at 15.degree. C., conveying the tape 10 at running speed of 3 to 5 m/min, 
applying 800 V DC to a pipe-shaped discharge electrode 17, and generating 
a non-equilibrium plasma. The film thickness was 10 nm. The Vickers 
hardness of the hard carbon film 5 of the embodiment was 2800 kg/mm.sup.2, 
the density is 2.3 g/cm.sup.3, and the relative intensity of Raman bands 
is 0.94. The density was measured by Rutherford backscattering 
spectrometry (RBS) method. The relative intensity ratio A/B of Raman bands 
(herein after called A/B) corresponds, in the Raman spectrum shown in FIG. 
5, to the intensity area ratio A/B, where A is the intensity area of 
Gaussian curve at peak A near 1380 cm.sup.-1 and B is the intensity area 
of Gaussian curve at peak B near 1550 cm.sup.-1. The modified layer 6 was 
formed in a thickness of 1 nm on the hard carbon film 5, by introducing 
pyridine and hydrogen from the material gas feed port 23 into the 
discharge tube 20 at pressure ratio of 3:2 and total gas pressure of 0.1 
torr, applying 1500 V I)C to the punching metal discharge electrode 21 
installed in the discharge tube 20, and generating a non-equilibrium 
plasma. The other constitution is same as the magnetic tape in Example 
1-1. 
EXAMPLE 4-2 
Same as Example 4-1 except that the pressure ratio of methane and argon is 
3:1, total gas pressure is 0.20 torr and applied voltage is 1300 V DC. 
COMATIVE EXAMPLES 4-1 TO 4-3 
To clarify the effect of the embodiments, three comparative magnetic tapes 
were prepared by forming hard carbon film 5 differing in A/B, density, and 
Vickers hardness in the same method as in Example 4-1, except that the 
pressure ratio of methane and argon, total gas pressure, temperature of 
cylindrical cooling can, and applied voltage were changed. In Comparative 
Example 4-3, benzene (C.sub.6 H.sub.6 :hydrocarbon gas) was used instead 
of pyridine (nitrogen involving organic gas), and the modified layer was 
formed in the same method as in Example 4-1. 
COMATIVE EXAMPLE 4-4 
The same composition as Example 4-1 except that pyridine was replaced by 
tetramethyl tin (organic metal compound). 
In these magnetic tapes obtained in examples and comparative examples, the 
chemical composition of modified layer 6, properties of hard carbon film 
5, and magnetic tape characteristics are shown in Tables 7 and 8. In Table 
8, the still frame life, weatherability, and friction coefficient .mu.k 
were measured in the same manner as in Example 3. The decrease of output 
signal in Table 8 was tested by recording video signals in 60-minute long 
magnetic tape and reproducing by 100 passes in the environment of 
23.degree. C.--10% RH. The decrease of output signal was defined by the 
greatest decrease of output signal in 100-pass reproduction (lowest output 
value), in comparison with the first pass output (0 dB), expressed in the 
decibel unit. 
As clear from Tables 7 and 8, in Examples 4-1 and 4-2, since the modified 
layer 6 of less than 3 nm in thickness containing only a specific amount 
of nitrogen atoms having a strong chemical affinity for the lubricant 
possessing a polar functional group (carboxyl group) is provided on the 
hard carbon film 5 having specific properties of A/B, density and Vickers 
hardness, (a) the spacing loss between the ferromagnetic thin film and 
magnetic head is not increased, and (b) synergistic effects of wear 
resistance of hard carbon film and low shearing force of lubricant layer 
can be exhibited sufficiently, so that outstanding improvement of 
weatherability and running stability can be achieved at the same time. By 
contraries, in Comparative Examples 4-1 and 4-3, A/B of the hard carbon 
film 5 is large (the existence rate of SP.sup.3 bond is small) and the 
Vickers hardness is low, and hence the still frame life is worse. 
Furthermore, since the density of the hard carbon film 5 is small, 
moisture invades in the interface of the hard carbon film 5 and 
ferromagnetic thin film 3, and in the interface of the ferromagnetic thin 
film 3 and non-magnetic substrate 1, thereby causing peeling. In 
Comparative Example 4-2, since A/B of the hard carbon film 5 is small (the 
existence rate of SP.sup.3 bond is large), a step (uneven wear) is formed 
between the amorphous (sendust) part and ferrite part of the sliding 
surface of magnetic head; thereby increasing the decrease of output 
signal. In Comparative Example 4-4, by the metal contained in the modified 
layer 6, metal adhesion occurred on the sliding surface of magnetic head 
in low humidity environments, and hence the still frame life was extremely 
decreased and the decrease of output signal was largely worsened. 
Furthermore, rusting on the surface of magnetic tape and other 
deterioration of weatherability also occurred. In this embodiment, the 
nitrogen concentration in the modified layer 6 is constant, but same 
effects are obtained if it is decreased in the direction from the surface 
of the modified layer toward the hard carbon film as in Example 2. 
EXAMPLE 5 
The fifth embodiment of the invention is described below. 
What is different from Example 4 is that the modified layer 6 is not formed 
as shown in FIG. 6. 
EXAMPLE 5-1 
The hard carbon film 5 in the embodiment was fabricated in the same method 
as in Example 4-1, and the Vickers hardness was 2800 kg/mm.sup.2, the 
density was 2.3 g/cm.sup.3, and A/B was 0.94. Furthermore, a lubricant 
layer 7 of fluorinated carboxylic acid C.sub.5 F.sub.11 (CH.sub.2).sub.10 
COOH in a film thickness of 4 nm was directly disposed on the hard carbon 
film 5 without forming modified layer 6. 
To clarify the effect of the embodiment, magnetic tapes were fabricated by 
forming hard carbon film 5 differing in A/B, density and Vickers hardness, 
in the same method as in Example 5-1, except that the pressure ratio of 
methane and argon, total gas pressure, temperature of cylindrical cooling 
can and applied voltage were changed. 
In these magnetic tapes obtained in examples and comparative examples, 
properties of hard carbon film 5 and magnetic tape characteristics are 
shown in Table 9. The still frame life, the decrease of output signal and 
friction coefficient .mu.k were measured. 
As clear from Table 9, in Examples 5-1 through 5-4, since density and 
Vickers hardness of the hard carbon film 5 settled within proper range of 
the invention, the enhancement of still frame life and improvement of 
output drop were achieved at the same time. By contraries, in Comparative 
Examples 5-1 and 5-3, A/B of the hard carbon film 5 is large (the 
existence rate of SP.sup.a bond is small) and the Vickers hardness is low, 
and hence the still frame life is worse. Furthermore, since the density of 
the hard carbon film is small in Comparative Example 5-2, the wear 
resistance is small, and the still frame life is decreased. In Comparative 
Example 5-4, since A/B of hard carbon film 5 is small (the existence rate 
of SP.sup.3 bond is large), a step (uneven wear)is formed between 
amorphous (sendust) part and ferrite part of the sliding surface of 
magnetic head, thereby increasing the decrease of output signal. Hence, as 
the hard carbon film of magnetic tape, A/B is desired to be 0.8 to 3.0, 
the density to be 1.5 g/cm.sup.3, and the Vickers hardness to be 2000 
kg/mm.sup.2 or more. 
In the embodiments, only the magnetic tape for 8 mm VTR is explained, but 
it is not limitative, and the invention may be similarly applied to 
magnetic tapes for other uses, magnetic disks, and other magnetic 
recording media. Incidentally, examples of nitrogen involving organic gas 
used when forming the modified layer include, among others, n-propylamine, 
dimethylformamide, pyridine, dimethylamine, trimethylamine, triethylamine, 
isopropylamine, n-butylamine, aniline, and formamide. As inorganic gas, 
Hi, He, Ar, N.sub.2, and NH.sub.3 are useful. The partial pressure of the 
nitrogen involving organic gas when forming the modified layer is desired 
to be 20 to 90% of the total gas pressure. In the foregoing embodiments, 
as the polar functional group, only the fluorinated lubricant introducing 
carboxylic group into molecule is presented, but any fluorinated lubricant 
containing at least one polar functional group selected from the group 
consisting of --OH, --SH, --NH.sub.2, .dbd.NH, --NCO, --CONH.sub.2, 
--CONHR, --CONR.sub.2, --COOR, --PR, .dbd.PRO, .dbd.PRS, --OPO (OH).sub.2, 
--OPO(OR).sub.2, --SO.sub.3 M (where R is a hydrocarbon group with 1 to 22 
carbon atoms, M is hydrogen, alkaline metals or alkaline earth metals) may 
be similarly applied. 
In the embodiments, as the non-magnetic substrate, PET was used, but the 
PET may be replaced by high molecular film such as polyethylene 
naphthalate, polyamide and polyimide. In the embodiments, the hard carbon 
film and the modified layer were formed by plasma CVD method, but this 
forming method is not limitative, and ion beam deposition method, ion beam 
sputtering method, and laser deposition method may be similarly used. The 
fluorinated lubricant layer was formed by wet process mating method in the 
embodiments, but it may be also formed by organic deposition method. 
TABLE 1 
__________________________________________________________________________ 
Atomic ratio of C, N, O 
N/C N/O contributed to 
Atomic ratio of N, O 
Thickness 
Vickers hardness 
atomic 
atomic 
C--N bond, contributed to 
of modified 
of hard carbon 
ratio ratio 
C--O bond N--O bond surface film 
Magnetic tape 
(%) (%) (atomic %) (atomic %) (nm) (kg/mm.sup.2) 
__________________________________________________________________________ 
Example 1-1 
3.4 33 6.2 .ltoreq.1.0 1 2500 
Example 1-2 
2.9 27 4.5 .ltoreq.1.0 1 2500 
Comparative 
-- -- 2.5 -- 1 2500 
Example 1-1 
Comparative 
0.6 8.5 2.7 .ltoreq.1.0 1 2500 
Example 1-2 
Comparative 
3.1 40 6.8 1.3 6 2500 
Example 1-3 
Comparative 
3.4 33 6.2 .ltoreq.1.0 1 1300 
Example 1-4 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Running durability 
Magnetic Weatherability 
head Corrosion resistance 
clogging 
Tape .mu.k D.O. 
Environmental gas resistance 
(sec) 
damage 
change 
Rust, peel 
(times) 
H.sub.2 S 
HCl 
__________________________________________________________________________ 
Example 1-1 0 5 0.19/0.19 
5 1.1 5 5 
Example 1-2 0 5 0.19/0.20 
5 1.1 5 5 
Comparative Example 1-1 
13.0 2 0.27/0.29 
2 3.5 3 3 
Comparative Example 1-2 
40.0 1 0.25/0.33 
1 5.8 1 1 
Comparative Example 1-3 
21.0 2 0.23/0.31 
4 4.0 4 4 
Comparative Example 1-4 
6.0 3 0.20/0.28 
2 4.1 3 2 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
Atomic ratio of C, N, O 
N/C N/O contributed to 
Atomic ratio of N, O 
Thickness 
Vickers hardness 
atomic 
atomic 
C--N bond, contributed to 
of modified 
of hard carbon 
ratio ratio 
C--O bond N--O bond surface film 
Magnetic tape 
(%) (%) (atomic %) (atomic %) (nm) (kg/mm.sup.2) 
__________________________________________________________________________ 
Example 2-1 
2.3 31.0 5.0 .ltoreq.1.0 1.8 2,500 
Example 2-2 
1.4 15.0 3.8 .ltoreq.1.0 0.45 2,500 
Example 2-3 
3.0 40.0 6.0 .ltoreq.1.0 2.7 2,500 
Comparative 
-- -- -- -- 0 2,500 
Example 2-1 
Comparative 
0.5 7.5 2.4 .ltoreq.1.0 1.8 2,500 
Example 2-2 
Comparative 
2.2 40.0 7.5 1.2 6.0 2,500 
Example 2-3 
Comparative 
2.3 31.0 5.0 .ltoreq.1.0 1.8 1,300 
Example 2-4 
__________________________________________________________________________ 
TABLE 4 
__________________________________________________________________________ 
Running durability 
Magnetic Weatherability 
head Corrosion resistance 
clogging 
Tape .mu.k D.O. 
Environmental gas resistance 
(sec) 
damage 
change 
Rust, peel 
(times) 
H.sub.2 S 
HCl 
__________________________________________________________________________ 
Example 2-1 0 5 0.20/0.20 
5 0.9 5 5 
Example 2-2 0 5 0.20/0.20 
5 1.0 5 5 
Example 2-3 0 5 0.21/0.21 
5 1.0 5 5 
Comparative Example 2-1 
12.0 3 0.26/0.29 
2 3.3 1 1 
Comparative Example 2-2 
30.0 1 0.26/0.32 
1 4.9 1 1 
Comparative Example 2-3 
25.5 1 0.21/0.37 
4 6.2 4 4 
Comparative Example 2-4 
5.5 2 0.20/0.28 
3 4.1 3 2 
__________________________________________________________________________ 
TABLE 5 
__________________________________________________________________________ 
Atomic ratio of C, N, O 
N/C N/O contributed to 
Atomic ratio of N, O 
Thickness 
Vickers hardness 
atomic 
atomic 
C--N bond, contributed to 
of modified 
of hard carbon 
ratio ratio 
C--O bond N--O bond surface film 
Magnetic tape 
(%) (%) (atomic %) (atomic %) (nm) (kg/mm.sup.2) 
__________________________________________________________________________ 
Example 3-1 
1.8 18 4.3 .ltoreq.1.0 2 2200 
Example 3-2 
2.6 24 5.3 .ltoreq.1.0 2 2200 
Comparative 
-- -- -- -- -- 2200 
Example 3-1 
Comparative 
2.2 21 4.7 .ltoreq.1.0 10 -- 
Example 3-2 
Comparative 
-- -- 2.3 -- 2 2200 
Example 3-3 
Comparative 
2.9 31 6.2 1.4 8 2200 
Example 3-4 
Comparative 
2.4 22 5.9 1.7 2 2200 
Example 3-5 
Comparative 
3.2 38 6.1 22.1 2 2200 
Example 3-6 
Comparative 
-- -- 1.9 -- -- 2200 
Example 3-7 
Comparative 
1.8 19 4.3 .ltoreq.1.0 2 1200 
Example 3-8 
__________________________________________________________________________ 
TABLE 6 
__________________________________________________________________________ 
Evaluation result of magnetic type 
Magnetic head 
Weatherability 
Friction 
Still 
clogging 
test coefficient 
Magnetic tape 
frame life 
(sec/300 hr) 
(rated in 5 ranks) 
.mu.k 
__________________________________________________________________________ 
Example 3-1 &gt;180 1 5 Not occurring 
0.18 
Example 3-1 &gt;180 1 5 Not occurring 
0.19 
Comparative Example 3-1 
120 10 2 Crystal 
0.22 
Comparative Example 3-2 
15 9 5 Not occurring 
0.27 
Comparative Example 3-3 
30 18 2 Crystal 
0.25 
Comparative Example 3-4 
90 5 5 Not occurring 
0.23 
Comparative Example 3-5 
25 12 4 Uneven coating 
0.26 
Comparative Example 3-6 
50 47 3 Uneven coating 
0.23 
Comparative Example 3-7 
5 15 1 Rust, crystal 
0.25 
Comparative Example 3-8 
40 5 5 Not occurring 
0.24 
__________________________________________________________________________ 
TABLE 7 
__________________________________________________________________________ 
Atomic ratio of C, N, O 
Thickness 
N/C N/O contributed to 
Atomic ratio of N, O 
of Characteristics of hard 
carbon film 
atomic 
atomic 
C--N bond, contributed to 
modified Vickers 
Magnetic 
ratio 
ratio 
C--O bond N--O bond layer A/B of Raman 
Density 
hardness 
tape (%) (%) (atomic %) (atomic %) (nm) spectrum 
(g/cm.sup.3) 
(kg/mm.sup.2) 
__________________________________________________________________________ 
Example 4-1 
3.3 31 6.1 .ltoreq.1.0 
1 0.94 2.3 2800 
Example 4-2 
3.1 28 5.0 .ltoreq.1.0 
1 0.83 2.7 3200 
Comparative 
3.9 41 6.7 .ltoreq.1.0 
1 4.67 1.0 1000 
Example 4-1 
Comparative 
2.6 24 4.1 .ltoreq.1.0 
1 0.70 2.9 4000 
Example 4-2 
Comparative 
-- -- 2.4 -- 1 4.61 1.2 800 
Example 4-3 
Comparative 
-- -- 2.8 -- 1 0.94 2.3 2800 
Example 4-4 
__________________________________________________________________________ 
TABLE 8 
__________________________________________________________________________ 
Magnetic tape characteristic 
Decrease of Friction 
Still 
output coefficient 
Magnetic tape 
frame life 
signal (dB) 
Weatherability 
.mu.k 
__________________________________________________________________________ 
Example 4-1 &gt;180 0 Not occurring 
0.16 
Example 4-2 &gt;180 +0.5 Not occurring 
0.14 
Comparative Example 4-1 
30 -3.0 Peeling 0.27 
Comparative Example 4-2 
60 -5.5 Not occurring 
0.18 
Comparative Example 4-3 
15 -3.5 Peeling 0.28 
Comparative Example 4-4 
10 -8.0 Rusting 0.20 
__________________________________________________________________________ 
TABLE 9 
__________________________________________________________________________ 
Characteristic of hard carbon film 
Magnetic tape characteristic 
Vickers 
Still frame 
Decrease of 
A/B of Raman 
Density 
hardness 
life output signal 
Magnetic tape 
spectrum 
(g/cm.sup.3) 
(kg/mm.sup.2) 
(min) (dB) 
__________________________________________________________________________ 
Example 5-1 0.94 2.3 2800 120 -0.5 
Example 5-2 0.83 2.7 3200 120 -1.0 
Example 5-3 1.24 2.1 2500 120 0 
Example 5-4 2.93 1.6 2000 120 -0.5 
Comparative Example 5-1 
3.51 1.7 1000 40 -2.0 
Comparative Example 5-2 
2.88 1.0 2100 50 -1.5 
Comparative Example 5-3 
4.61 1.2 800 20 -3.0 
Comparative Example 5-4 
0.71 2.9 4000 120 -6.0 
__________________________________________________________________________