JPH04341918A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve color resistance and durability by providing a substrate film and top coat film consisting of plasma-polymerized films contg. C and H and having a prescribed refractive index. CONSTITUTION:The substrate film, a ferromagnetic metallic thin film (magnetic layer) and the top coat film are successively provided on a nonmagnetic resin base body. The substrate film and the top coat film are formed of the plasma- polymerized films contg. the C and H and having >=1.8 refractive index. The content of the C and H in the film is specified preferably to >=85at.% and more preferably to >=95at.%. The atomic ratio of the H to the C is specified preferably to <=1.6H/C, more preferably to <=0.7. The content of the C in the film is set preferably to >=30at.%, more preferably to >=6Oat.% and the content of the H preferably to <=55at.%, more preferably to <=35at.%. 0, N, etc., in addition to the C and H may be incorporated at <=15at.% therein in some cases. The film thickness of the substrate film is specified to 100 to 500Angstrom and the film thickness of the top coat layer to 10 to 50Angstrom .

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a ferromagnetic metal thin film.

0002

[Prior Art] In recent years, magnetic tapes have become increasingly dense, and magnetic tapes using ferromagnetic metal thin films mainly composed of Co and added with Ni, etc. have a high saturation magnetic flux density and high coercive force. It is being actively researched.

This type of magnetic tape is manufactured by various methods, but particularly excellent methods include forming a single layer of a ferromagnetic metal thin film on a non-magnetic substrate by oblique evaporation, or forming a thin ferromagnetic metal film as a single layer on a non-magnetic substrate, or forming a thin film of two or more layers on a non-magnetic substrate. It has been proposed to stack them to form a multilayer structure.

[0004] The non-magnetic substrate of magnetic tape is usually
A resin film such as polyethylene terephthalate is used.

[0005] When a magnetic layer is formed on such a resin film by vapor deposition, moisture and air enter through the resin film, corrode the magnetic layer, and deteriorate electromagnetic conversion characteristics during recording and reproduction. It is also insufficient in terms of durability.

Hitherto, proposals have been made to apply various plasma polymerized films as a base film formed between a resin film and a magnetic layer or a top coat film formed on a magnetic layer. However, such conventional base films and top coat films are insufficient in blocking moisture, air, etc., and are insufficient in terms of corrosion resistance and durability. In particular, a decrease in corrosion resistance has a large effect on the aging deterioration of running friction, which poses a problem in terms of reliability.

[0007]

SUMMARY OF THE INVENTION The main object of the present invention is to significantly improve the corrosion resistance and durability of a magnetic recording medium whose magnetic layer is a ferromagnetic metal thin film.

[0008]

[Means for Solving the Problems] Such objects are achieved by the following configurations (1) to (4).

(1) In a magnetic recording medium having a base film, a ferromagnetic metal thin film, and a top coat film on a nonmagnetic resin substrate, the base film and the top coat film each contain C and H. , and a plasma polymerized film having a refractive index of 1.8 or more.

(2) The thickness of the base film is 100 to 5.
00A, the magnetic recording medium according to (1) above.

(3) The thickness of the top coat film is 1
The magnetic recording medium according to (1) or (2) above, wherein the magnetic recording medium is 0 to 50A.

(4) The magnetic recording medium according to any one of (1) to (3) above, wherein the ferromagnetic metal thin film contains Co as a main component and is formed by an oblique evaporation method.

[0013]

[Operation] The magnetic recording medium of the present invention is a magnetic tape,
A base film is provided between the resin base and the ferromagnetic metal thin film that is the magnetic layer, and a top coat film is provided on the magnetic layer.

[0014] Since both the base film and the top coat film are plasma polymerized films containing C and H, they have excellent water resistance and durability. Also, its refractive index is 1.8
Because of the above, it becomes precise.

[0015] By providing such an undercoat film and a top coat film in such a manner that they sandwich the ferromagnetic metal thin film from above and below, the occurrence of rust that progresses from both the base side and the magnetic layer surface side in the ferromagnetic metal thin film can be prevented. It can be effectively prevented.

[0016] Such an effect can only be obtained by providing the above-mentioned films on both sides of the magnetic layer, and cannot be obtained only with the base film or the top coat film.

As a result of preventing the occurrence of rust in this manner, cupping is prevented and running friction is prevented from changing over time, resulting in excellent electromagnetic conversion characteristics as a medium.

[0018]

[Specific Configuration] The specific configuration of the present invention will be explained in detail below.

The magnetic recording medium of the present invention is specifically a magnetic tape.

<Nonmagnetic Substrate> The material of the nonmagnetic substrate used in the present invention is not particularly limited, and various films that can withstand the heat during deposition of a ferromagnetic metal thin film, such as polyethylene terephthalate, can be used. Also, JP-A-63-1031
Each material described in Publication No. 5 can be used.

<Base film and top coat film> The base film and top coat film in the present invention are plasma polymerized films containing C and H, respectively, and have a refractive index of 1.8.
That's all. By using such a film, the effects of the present invention can be obtained.

In this case, the total content of C and H in the film is preferably 85 at % or more, preferably 95 at % or more, and it is preferable that the film contains substantially only C and H.

Further, the atomic ratio of H to C is preferably such that H/C is 1.6 or less, preferably 0.7 or less, and the C content in the film is 30 at% or more, preferably 60 at%.
t% or more, while the H content is preferably 55 at% or less, preferably 35 at% or less. Further, in some cases, in addition to C and H, O, N, etc. may be contained at 15 at% or less.

By regulating C, H, etc. in the film in this manner, the effects of the present invention are improved.

The content of C, H, and other elements in the plasma polymerized film may be analyzed using SIMS (secondary ion mass spectrometry), CHN coder, or the like.

When SIMS is used, calculation can be made by counting C, H, etc. on the surface of the plasma polymerized film. Alternatively, while performing ion etching with Ar etc., C, H
It may also be calculated by measuring a profile such as SIMS
Regarding the measurement of
84) Basics and Applications of Surface Analysis (P70) Follow the description in "SIMS and LAMMA".

In the present invention, as mentioned above, the refractive index of the plasma polymerized film is set to 1.8 or more, preferably 1.8 or more.
．． It is preferable to set it to 9-2.3.

An ellipsometer may be used to measure the refractive index.

By setting the refractive index within the above range, the density of the polymer film increases, imparting high rigidity to the magnetic recording medium and improving durability. And when the refractive index becomes less than 1.8,
This effect is critically reduced.

Various materials containing carbon and hydrogen can be used as the raw material source for forming such a plasma polymerized film, but generally, from the viewpoint of ease of operation,
One or more of methane, ethane, propane, butane, pentane, ethylene, propylene, butene, butadiene, acetylene, methylacetylene, and other saturated or unsaturated hydrocarbons, which are gases at room temperature, are used as the C and H source. Further, if necessary, a hydrocarbon that is liquid at room temperature may be used as a raw material.

[0031] When other elements are contained, O2, O3, H2O, N2
, NOx, such as NO, N2 O, NO2, H2,
A material gas to which one or more of NH3, CO, CO2, etc. is added as an N and O source may be used as the raw material gas.

The thickness of the plasma polymerized film formed using such raw materials is 100 to 50% when used as a base film.
0A, more preferably 400 to 500A. The effectiveness of the present invention is extremely high in film thicknesses within this range. If the film thickness is less than 100A, the present invention is not effective;
If it exceeds 0A, it is disadvantageous for mass production. When the film thickness is increased, no improvement in effectiveness is observed, and on the contrary, cracks tend to occur in the base film, resulting in a decrease in water, oxygen, and other barrier properties.

On the other hand, when used as a top coat film, 10
~50A, particularly preferably 20-30A. The effectiveness of the present invention is extremely high in this range of film thickness, and 50A
If this value is exceeded, stress will be generated strongly, and this effect will be critically reduced, further increasing the problem of spacing loss. Furthermore, in order to increase the film thickness, the magnetic layer must be exposed to plasma at high power or for a long time, which damages the magnetic layer. Also, the film thickness is 10A
If it is less than that, the effectiveness of the present invention will be reduced.

Note that an ellipsometer or the like may be used to measure the film thickness. Such film thickness can be controlled by limiting the reaction time, raw material gas flow rate, etc. during plasma polymerized film formation.

The plasma polymerized film is formed by bringing discharge plasma of the above-mentioned raw material gas into contact with the substrate or magnetic layer according to a known method. Electrode arrangement, applied current, processing time, operating pressure, etc. may be set to normal conditions.

Furthermore, the processing conditions are W/(F・M) [where,
W is the plasma input power (Joule/sec),
F is the organic raw material gas flow rate, M is the molecular weight of the raw material gas, and the unit of F・M is kg/sec.
It is preferable that the process be carried out in This value is 108 Joul
If it is less than e/kg, the refractive index decreases and the density of the plasma polymerized film becomes insufficient.

The actual conditions may be set so as to satisfy the above range. Therefore, if the raw material gas flow rate becomes larger than a value suitable under certain conditions, or if the plasma output becomes smaller, the effects of the present invention will deteriorate.

[0038] As the carrier gas, Ar, N2
, He, H2, etc. may also be used. As the plasma generation source, in addition to high frequency discharge, microwave discharge, direct current discharge, alternating current discharge, etc. can be used.

Such a plasma polymerized film has a so-called sandwich structure in which the magnetic layers described below are sandwiched above and below, and is used as a base film between the substrate and the magnetic layer and as a top coat film on the magnetic layer. It is something that can be done. By using it in this form, the antirust effect of the magnetic layer is significantly improved, and the effects of the present invention can be obtained.

In the present invention, when used as a base film or a top coat film, the plasma polymerized film is preferably formed on a substrate or magnetic layer, particularly on a plasma-treated substrate or magnetic layer. Plasma treatment of the surface of the substrate or magnetic layer improves the adhesion between the substrate and the magnetic layer, which in turn improves the adhesion between the substrate or magnetic layer and the plasma polymerized film. The principle, method, formation conditions, etc. of the plasma treatment method for the surface of the substrate and magnetic layer are basically almost the same as those of the plasma polymerization method described above.

However, in principle, plasma treatment uses an inorganic gas as a processing gas, whereas in the formation of a polymer film by the above-mentioned plasma polymerization method, as a general rule, an organic gas (an inorganic gas may be mixed in) is used. ) is used as the raw material gas. Further, the frequency of the plasma processing power source is not particularly limited, and may be any of direct current, alternating current, microwave, etc.

In the present invention, the base film and top coat film using the plasma polymerized film are used in a sandwich structure as described above, so there is no need to use other base films or protective films. Can be used in combination with others.

<Magnetic layer> The magnetic layer in the present invention is made of Co
It is preferable that the ferromagnetic metal thin film is composed of one or more layers of ferromagnetic metal thin film formed by an oblique vapor deposition method. In such a magnetic layer, the effects of the present invention are enhanced.

In the oblique vapor deposition method, for example, a long film-like nonmagnetic substrate unwound from a supply roll is fed along the surface of a rotating cooling drum, while oblique vapor deposition is performed from one or more stationary metal sources. It is wound onto a take-up roll.

At this time, when the angle between the incident angle of the ferromagnetic metal component during film formation and the normal to the substrate is θ, θ changes, and the deposition is performed in the range from the initial θmax to the final θmin. . And θmax during ferromagnetic thin film deposition is 8
It is preferably 0 to 90 degrees, and θmin is 10 to 6
Preferably it is 0 degrees.

Each ferromagnetic metal thin film constituting the magnetic layer is made of N
A Co--Ni alloy containing i is preferable, and an alloy containing about 80% or more of Co and about 20% or less of Ni in molar ratio is particularly preferable.

[0047] Furthermore, if necessary, it may contain 10% or less of Cr, and may also contain various metals described in JP-A-63-10315 and other metal components.

Furthermore, if necessary, corrosion resistance etc. can be improved by incorporating a small amount of oxygen into the surface layer of each layer or by interposing a nonmagnetic layer.

[0049] The total thickness of the magnetic layer is 1200 to 3000 mm.
It is preferable that it is about A. At this time, the output can be made sufficiently large.

The incident angle of the vapor-deposited metal particles is θma at the initial stage of vapor deposition.
It changes continuously from x to the final θmin, and columnar crystal grains of ferromagnetic metal whose main component is Co are grown on the surface of a nonmagnetic substrate in one arcuate direction and aligned. If the magnetic layer has a multilayer structure, this step is repeated.

[0051] In the present invention, various structures such as a back coat layer can also be added.

[0052]

[Examples] The present invention will be specifically explained below with reference to Examples. Example 1 A polyethylene terephthalate film with a thickness of 7 μm was fed out from a supply roll, moved along the circumference of a rotating cylindrical cooling drum, and after being evacuated to 10 −4 Pa, plasma polymerization was performed using CH4 as a raw material gas. Then, a base film was formed. The plasma polymerization conditions at this time are:
Same as above, W/(F・M)1.68×109 Jou
le/kg, flow rate 50SCCM, operating pressure 0.05To
rr, plasma output 1kW, plasma frequency 100kHz
z.

The thickness of the obtained base film was 400A. Note that the plasma polymerized film was measured using an ellipsometer. Also, the refractive index is 1.9 when measured with an ellipsometer.
It was 5.

[0054] The polyethylene terephthalate film on which the base film was formed was fed out from the supply roll in an Ar atmosphere of 10-4 Pa, and moved around a rotating cylindrical cooling drum to coat the 20 at% Ni-Co alloy. A ferromagnetic metal thin film was formed by oblique vapor deposition and wound up using a winding roll.

Next, using this winding roll as a supply roll, a ferromagnetic metal is obliquely vapor-deposited in an incident direction that intersects the incident direction during the above-mentioned oblique vapor deposition, with the normal direction of the PET film surface in between, to form a two-layer structure. A magnetic layer was provided.

Furthermore, a top coat film was formed on the magnetic layer by plasma polymerization using CH4 as a raw material gas. The plasma polymerization conditions at this time were the same as for the base film.
W/(F・M)1.68×109 Joule/kg,
The flow rate was 50 SCCM, the operating pressure was 0.05 Torr, the plasma output was 1 kW, and the plasma frequency was 100 kHz. The resulting top coat film had a thickness of 30A and a refractive index of 1.95.

[0057] This was used as magnetic recording medium sample No. Set to 1.

[0058] Also, sample No. 1, except that no top coat film is formed,
Sample No. I got 2.

Furthermore, sample No. Sample No. 1 was prepared in the same manner as in Sample No. 1 except that the base film was not formed. I got 3.

[0060] In addition, samples without the base film and top coat film were also prepared, and Sample No. I got 4.

Furthermore, sample No. Sample No. 1 was prepared by replacing the base film and top coat film with those obtained by plasma polymerization under the following conditions. Got 5.

For the base film, the plasma polymerization conditions were changed to W/(F
・M) 2.1×107 Joule/kg, flow rate 200
SCCM, operating pressure 0.05 Torr, plasma output 5
The layer was set at 0 W and a plasma frequency of 13.56 MHz. The film thickness was 400A, and the refractive index was 1.7.

[0063] The top coat film was prepared by changing the plasma polymerization conditions to
As above, W/(F・M)2.1×107 Jou
le/kg, flow rate 200SCCM, operating pressure 0.05T
orr, plasma output 50W, plasma frequency 13.5
It was installed as a 6MHz layer. The film thickness was 30A, and the refractive index was 1.7.

[0064] Also, sample No. Sample No. 1 was prepared in the same manner as in Sample No. 1, except that the top coat film was applied under the same plasma polymerization conditions and the film thickness was changed to 5A.
6 was produced.

[0065] Also, sample No. In 1, the base film was deposited under the same plasma polymerization conditions, and the film thickness was 50%.
Sample No. A was prepared in the same manner except that sample No. 7 was produced.

Furthermore, sample No. In 1, the raw material gas was changed to C2H2 and W/(F・M)1.68×
Under plasma polymerization conditions of 109 Joule/kg, flow rate 30 SCCM, operating pressure 0.05 Torr, plasma output 1 kW, and plasma frequency 100 kHz, the film thickness was 30
Except for depositing the top coat film A and depositing the base film with a thickness of 400A under the same plasma polymerization conditions.
Similarly, sample No. 8 was produced. At this time, the refractive index of both the top coat film and the base film was 1.95.

[0067] Also, sample No. In 1, the raw material gas was changed to C3 F6 and W/(F・M)1.68×
The film thickness was 30A under plasma polymerization conditions of 109 Joule/kg, flow rate 5SCCM, operating pressure 0.05 Torr, plasma output 1kW, and plasma frequency 100kHz.
Sample No. 1 was prepared in the same manner, except that a top coat film of No. 1 was applied and a base film of 400 Å thick was applied under the same plasma polymerization conditions. 9 was produced. The refractive index of both the top coat film and the base film was 1.85.

These magnetic recording medium sample No. 1
~No. 9, an 8mm video deck (Sony S9)
00), and the following evaluation was performed.

(1) Δφm Maximum magnetic flux density φ after storage for one week at 80°C and 90% RH
m was measured, and the increase with respect to the initial φm was determined.

(2) Change in running friction over time The dynamic friction coefficient μ was measured after storage for one week at 80° C. and 90% RH, and the rate of increase with respect to the initial μ was determined.

(3) Cycle test Each magnetic recording medium sample was cut into a size of 9.5 cm x 8 mm and stored under the following conditions. ■Room temperature 24 hours ■70℃, 80%RH 24 hours ■0℃
Storage for 24 hours ■ to ■ was repeated for 3 weeks. The rate of change Δφm (%) between the initial φm and the φm after storage was determined and evaluated. Δφm (%) = [φm (initial) - φm (after storage)] / φm (initial) x 100

The results are shown in Table 1. In the table, film thickness, refractive index, etc. are also listed.

[0073]

[Table 1]

From Table 1, the effects of the present invention are clear.

Note that sample No. Sample No. 1 was prepared in the same manner as in Sample No. 1, except that the thickness of the base film was made to exceed 500 A. 10 were produced. In this one,
No improvement in the effects of the present invention was observed; rather, it was found that increasing the film thickness not only resulted in poor mass productivity, but also made the base film more prone to cracking, resulting in poor barrier properties against water, oxygen, etc. Ta.

[0076] Also, sample No. Sample No. 1 was prepared in the same manner as in Sample No. 1, except that the thickness of the top coat film was made to exceed 50A. 11 was produced. It was found that this method not only increases the problem of spacing loss, but also damages the magnetic layer because it is exposed to plasma for a long time in order to increase the film thickness.

[0077]

[Effects of the Invention] According to the present invention, corrosion resistance and durability are significantly improved.

Claims (4)

[Claims] 1. A magnetic recording medium having a base film, a ferromagnetic metal thin film, and a top coat film on a non-magnetic resin substrate, wherein the base film and the top coat film each contain C and H, A magnetic recording medium comprising a plasma polymerized film having a refractive index of 1.8 or more. 2. The thickness of the base film is 100 to 500A.
The magnetic recording medium according to claim 1. 3. The top coat film has a thickness of 10 to 5.
The magnetic recording medium according to claim 1 or 2, wherein the magnetic recording medium is 0A. 4. The ferromagnetic metal thin film contains Co as a main component and is formed by an oblique evaporation method.
4. The magnetic recording medium according to any one of 3 to 3.