JP2971558B2 - Magnetic recording tape excellent in abrasion resistance and corrosion resistance and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording tape excellent in abrasion resistance and corrosion resistance and a method for manufacturing the same.

(Prior Art) In the present age, advanced informationization is particularly important, as is called the advanced information age.

Magnetic recording media such as floppy disks and video tapes are one of the wings that support such advanced information technology. In particular, flexible tapes using CoCr perpendicular magnetic recording media are used in HDTV (Hi
gh Definition TV) is expected as a medium for VTR.

By the way, such a magnetic recording medium is required to have corrosion resistance in terms of long-term storage of recording, and wear resistance in terms of high-speed contact between the medium surface and the sensor during use. Therefore, in a magnetic recording tape in which a magnetic recording medium is formed on a plastic substrate, a top coat is applied to the surface for the purpose of protecting the surface of the magnetic recording medium, and static electricity is prevented, a friction coefficient of the tape surface is reduced, and slip between the tapes is improved. From the viewpoint, it is necessary to apply a back coat to the back surface.

Conventionally, various thin films such as carbon, carbide, and nitride have been studied for such purpose, and recently, diamond-like thin films have been studied. However, it has been pointed out that such a satisfactory performance has not been obtained, and that a defect such as a head which comes into contact with a medium is particularly damaged.

As the substrate of the magnetic recording tape, besides polyimide tape, a thermoplastic tape such as polyethylene naphthalate tape or polyethylene terephthalate tape is preferable. However, there still remains a problem in that the film is susceptible to thermal damage during film formation.

(Problems to be Solved by the Invention) The present invention advantageously solves the above-mentioned problems, and has a magnetic recording layer having a protective film which is excellent in abrasion resistance and corrosion resistance and which does not cause damage to a partner when contacted. The aim is to propose a tape together with its advantageous production method.

(Means for Solving the Problems) The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned problems, and as a result, have come to think of using an iron-based boride-based alloy as a material for a protective coating.

Such an alloy has excellent properties as a high-hardness substance, but has poor wettability with various metals and makes it difficult to obtain a dense sintered body.

However, among them, in particular, an iron-based double-boride-based hard alloy comprising a Mo ₂ FeB ₂ type double-boride-based hardened phase and an iron-based bonded phase containing Cr, Mo, Ni, etc. (1) has excellent wear resistance (2) Minimal wear of the mating material, (3) High corrosion resistance and high-temperature oxidation resistance, (4) Magnetic properties can be changed by changing the composition of the binder phase. Therefore, if such an alloy can be thinned by some method and applied to the surface of the tape substrate without thermally damaging the tape substrate, it can be expected that its wear resistance and corrosion resistance will be improved. It is.

In addition, such iron-based double boride based hard alloys have been used only in so-called bulk, such as hot extrusion dies for copper, parts for injection molding machines, seaming rolls for can-making, and as thin films of 1 μm or less. There has been no attempt to use.

Therefore, the present inventors have repeated studies on a method of forming a thin film of such an iron-based double boride-based hard alloy, and as a result, if the opposed target sputtering method is used, the tape substrate is not damaged by plasma during the film formation without being damaged. In addition, it has been found that the above alloy can be advantageously formed into a film.

 The present invention is based on the above findings.

That is, the present invention relates to the surface of a magnetic recording tape and / or
Or an iron-based double-boride hard alloy comprising a Mo ₂ FeB ₂ type double-boride hard phase and an iron-based binder phase containing Cr, Mo and Ni as a protective film on the back surface, Fe: 25 wt% B + Mo: 60 wt% or less, Cr + Ni: The remaining composition, and a non-magnetic thin film having a film thickness of 10 to 10,000 mm, which is excellent in abrasion resistance and corrosion resistance (first invention). is there.

In addition, the present invention provides an iron-based bond containing Cr, Mo and Ni and a Mo ₂ FeB ₂ type double-boride hard phase on the front and / or back surface of a tape substrate having a magnetic recording medium by a facing target sputtering method. An iron-based double boride based hard alloy composed of a phase and Fe: 25 wt% or less, B + Mo: 60 wt% or less, Cr + Ni: An alloy having the remaining composition is formed in a film thickness of 10 to 10,000 mm. This is a method for producing a magnetic recording tape excellent in wear resistance and corrosion resistance (second invention).

According to the present invention, in the iron-based double boride hard alloy,
It is advantageous to set the atomic ratio B / Mo between Mo and Mo in the range of 0.5 to 1.5. This is because in this range, a hard phase of Mo ₂ FeB ₂ is easily obtained.

In particular, when applying the top coat and / or the back coat to the magnetic recording tape according to the second invention, it is preferable to apply the RF (eg, 13.56 MHz) bias to the tape substrate. This is because the surface morphology (such as unevenness) of the protective film can be controlled by such a bias application method.

Further, in the present invention, as the magnetic recording tape to be coated with a protective film, any conventionally known magnetic recording tape is suitable,
A CoCr perpendicular magnetic recording tape, which may be an in-plane magnetic recording medium or a perpendicular magnetic recording medium, is particularly suitable.

(Operation) As described above, the iron-based double boride-based hard alloy can change the magnetic properties by changing the composition of the binder phase. Investigation into the range of non-magnetic composition revealed that non-magnetic coatings of the same composition could be obtained by using targets with Fe: 25 wt% or less, B + Mo: 60 wt% or less, and Cr + Ni: remaining composition. . Therefore, if a non-magnetic film having such a composition can be used as a top coat and a back coat of a magnetic recording medium, a significant improvement in the wear resistance and corrosion resistance of a magnetic recording tape can be expected.

B: 5.85 wt%, Mo: 43.9 wt%, Cr: 20.6 wt% and Ni: 8.2
A top coat is formed on the CoCrTa magnetic recording layer using a target containing an alloy containing wt% and the balance being substantially Fe, and the presence or absence of a change in the MH loop of the magnetic recording medium is examined at this time. Was.

First, the result of measuring the saturation magnetization of the target with VSM is:
The value was 0.2 emu / cc or less, and it was confirmed that the film was substantially nonmagnetic.

Next, a 11 μm-thick polyethylene naphthalate (PE
N) On the tape, by facing target type sputtering method,
(1500Å-Co ₈₀ Cr ₁₇ Ta ₃ / PEN) and (1500Å-protective film / 1500
Å-Co ₈₀ Cr ₁₇ Ta ₃ / PEN)
The -H loop was compared.

 The results are shown in FIGS. 1a and 1b, respectively.

As is clear from the figure, there was no change in the MH loop due to the formation of the protective film, and thus it was confirmed that the protective film had no adverse effect on the magnetic characteristics.

By the way, as the substrate tape of the magnetic recording tape, besides polyimide tape, thermoplastic tape such as polyethylene naphthalate tape or polyethylene terephthalate tape is preferable. The condition required for the method of forming a film on the tape is that the tape is not thermally damaged.

 Then, the film forming method was examined next.

Iron-based double boride-based hard alloys have electrical conductivity, so they are neutral,
By converting the gas into an ion, excited state, atomic, molecular, or cluster gas, and then rapidly aggregating it on the surface of the object in a vacuum, a thin film having a thickness of 10 to 10,000 ° can be obtained. According to this method, coating can be performed regardless of the shape of the object as long as the object to be coated can be drawn to an appropriate degree of vacuum in a vacuum chamber.
Therefore, various attempts were made to form a film. If the target sputtering method was used, the target object could be formed in a plasma-free state without being exposed to plasma, and was relatively thermally damaged like a plastic thin film. It has been determined that coatings can be applied on sensitive objects without damage.

Here, the facing target sputtering method refers to two targets 1-1 and 1-2 of about 10 × 10 cm ² as shown in FIG.
Are placed face-to-face and about 10 cm apart, and magnetic poles 2-1 and 2-2, which are made of permanent magnets, are installed on the back side of each target 1-1 and 1-2. In this method, a magnetic field is caused to run perpendicularly to each target surface to perform sputtering while confining plasma between two targets. At this time, the coated substrate is set at a distance of 3 to 10 cm from the ends of the two targets 1-1 and 1-2, perpendicular to the target surface and at the center between the targets. Therefore, the substrate can be formed in a plasma-free state without being exposed to the plasma. In such a sputtering, the sputtering Ar gas pressure P _Ar is preferably set to about 5 mTorr or less. In the figure, 3 is a mask, 4 is a slit provided in the mask 3, 5 is a flexible tape as a substrate, 6 is a can roll, and 7 is a matching circuit for applying an FR bias.

In general, in the sputtering of an alloy target, the composition of the target may be different from the composition of the film, but in the plasma-free facing target sputtering method, the difference can be minimized. Also, in general, the magnetic properties of the target and the sputtered film may be different, but in this regard, there is no difference in the facing target sputtering method, and a nonmagnetic coating film can be obtained by using a target having a nonmagnetic composition. Was confirmed.

Further, when applying a top coat and / or a back coat, a film is formed while applying a bias voltage of RF (for example, 13.56 MHz) to the tape substrate. In particular, when the sputtering Ar gas pressure is 0.5 mTorr or less, the surface unevenness is reduced. As a result, it becomes possible to control the surface unevenness of the coating layer, which proved to be particularly advantageous in obtaining a desired coefficient of friction.

For back coating on 11μm thick polyethylene terephthalate (PEN) tape,
When forming a film while applying a 13.56 MHz RF bias,
The surface irregularities were investigated.

At this time, the potential of the tape substrate was set to about -100 V lower than the ground, and the Ar gas pressure was set in the range of 0.25 mTorr to 4 mTorr.

As a result, it was found that the surface unevenness was observed when no bias was applied, whereas the surface unevenness was reduced when the bias was applied. It was also found that the effect of reducing surface irregularities was further exhibited when the gas pressure was low.

(Example) Preliminary experiment B: 5.85 wt%, Mo: 43.9 wt%, Cr: 20.6 wt%, and Ni: 8.2
wt., the balance being substantially 10 × 10 cm ²
Using a square alloy as a target, a film having a thickness of about 1500 ° was formed on a 10 μm-thick polyethylene naphthalate tape and a glass substrate at room temperature by a facing target type sputtering method. At this time, the sputter-argon gas pressure was 0.25 to 4.0 mTo
I went with rr. Glass substrates are further vacuumed, 400
Annealed at 1 ° C. for 1 hour. The crystal structure of these thin films was examined by x-ray diffraction, and the magnetic properties were examined by VSM.

Before annealing, the films on both substrates did not show any x-ray diffraction peaks, indicating that they were amorphous films. It was also found that the above-described annealing did not show a crystal structure and the amorphous structure was stable. Furthermore, it was found that the film was a non-magnetic film than VSM.

Example 1 The amorphous film in the preliminary experiment was flexible, and the structure was dense because it was made plasma-free by the opposed target sputtering method, and it was a non-magnetic film, so this was prototyped as a back coat for magnetic recording tape. did. The magnetic recording tape used was a polyimide tape having a width of 1/2 inch and a thickness of 11 μm, on which a Ni ₈₀ Fe ₂₀ backing layer of 750 ° and a Co ₇₉ Cr ₂₁ layer of 1500 ° were further formed. Here, a can roll having a diameter of 15 cm was installed at the position of the coated substrate, and a film having the same composition as that of the preliminary experiment was continuously formed on the back surface of the tape while conveying the magnetic recording tape in synchronization with the rotation of the roll. To a film thickness of

In this example, it was examined whether the back coat layer magnetically adversely affected the magnetic recording layer and whether the back coat layer forming process caused thermal damage to the magnetic recording layer and the polyimide tape.

As a result, it was confirmed that the magnetic properties of the Co ₇₉ Cr ₂₁ layer did not change even after the back coating, and that there was no damage such as thermal deformation of the tape.

Example 2 The coefficient of friction of the back coat surface of the tape produced in Example 1 was evaluated. The tension T2 was measured by the apparatus shown in FIG. 3, and the coefficient of friction was determined from Euler's equation. Euler's equation is represented by μk = 2 / In (T2 / T1).

As a result, the coefficient of friction on the surface of the polyimide tape without the backcoat was as large as 0.46, whereas the coefficient of friction on the surface of the backcoated surface was significantly reduced to 0.29. This value was almost equal to the value of 0.28 which is the value of the tape surface of the commercially available coated tape, indicating that the coefficient of friction could be improved to a level equivalent to that of the commercially available tape. Therefore, rubbing between the tapes can be reduced by such a back coat, and the durability of the magnetic tape can be expected to increase.

(Effects of the Invention) According to the first aspect of the invention, it is possible to obtain a magnetic recording tape which is excellent in abrasion resistance and corrosion resistance, and in which the wear of a mating material is slight.

According to the second aspect of the present invention, since a film can be formed in a plasma-free condition in which the object to be processed is not exposed to plasma, it is possible to damage even a tape substrate such as a plastic tape which is relatively easily damaged by heat. Without a protective coating can be applied.

[Brief description of the drawings]

FIGS. 1a and 1b are diagrams showing MH loops when a protective film is formed according to the present invention and when they are not formed, respectively. FIG. 2 is a perspective view of a facing target type sputtering apparatus. The figure is a schematic diagram of a device for measuring the coefficient of friction. 1-1, 1-2 ... target, 2-1, 2-2 ... magnetic pole 3 ... mask, 4 ... slit 5 ... board tape, 6 ... can roll 7 ... matching circuit

Claims (6)

(57) [Claims] An iron-based composite comprising a Mo ₂ FeB ₂ type double boride hard phase and an iron-based binder phase containing Cr, Mo and Ni as a protective coating on the front and / or back surface of a magnetic recording tape. Abrasion resistance characterized by comprising a non-magnetic thin film having the following composition: Fe: 25 wt% or less, B + Mo: 60 wt% or less, Cr + Ni: Remaining composition, and a film thickness of 10 to 10,000 mm. Magnetic recording tape with excellent corrosion resistance. 2. The magnetic recording tape according to claim 1, wherein the iron / polyboride-based hard alloy has an atomic ratio B / Mo of B to Mo of 0.5 to 1.5, and is excellent in wear resistance and corrosion resistance. 3. The magnetic recording tape according to claim 1, wherein the magnetic recording tape to be coated with a protective film is a CoCr perpendicular magnetic recording tape, which has excellent wear resistance and corrosion resistance. 4. A Mo ₂ FeB ₂ type double boride hard phase and Cr, Mo and Ni are provided on the front and / or back surface of a tape substrate having a magnetic recording medium by a facing target sputtering method.
An iron-based double boride-based hard alloy composed of an iron-based bonded phase containing: Fe: 25 wt% or less, B + Mo: 60 wt% or less, Cr + Ni: An alloy having the remaining composition, with a film thickness of 10 to 10,000 mm. A method for producing a magnetic recording tape excellent in abrasion resistance and corrosion resistance characterized by being formed. 5. A method for producing a magnetic recording tape according to claim 4, wherein a top coat and / or a back coat thin film is produced while applying an RF bias to the tape substrate. 6. The magnetic recording tape according to claim 4, wherein the magnetic recording tape to be coated with a protective film is a CoCr perpendicular magnetic recording tape, which is excellent in wear resistance and corrosion resistance.