JPH0754563B2 - Magnetic recording method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Technical Field The present invention particularly relates to a magnetic recording method using a metal thin film type magnetic recording medium.

2. Description of the Related Art Prior Art and Problems There are active developments of magnetic recording media for video, audio, etc., which have a metal thin film type magnetic layer because of their compactness when formed into a tape and wound.

The magnetic layer of such a metal thin film type medium is characteristically made of Co-based, Co-Ni-based, or the like, which is formed by a so-called oblique vapor deposition method in which vapor deposition is performed at a predetermined inclination angle with respect to the substrate normal line. Evaporated films are preferred.

For such media, research has been made on media such as 10 μm or less for miniaturization and long-time recording. However, runnability, durability, strength of ferromagnetic metal thin film, etc. There is a problem with.

Therefore, in order to eliminate these disadvantages, it is proposed to provide a metal thin film reinforcing layer on the back surface of the film (JP-A-56-16939).
No. 58-97131, No. 57-78627, No. 57-37737) or a proposal that fine particles are provided on the film surface to improve the head touch and running surface (Japanese Patent Laid-Open No. 58-68227). , 58-1
00221) etc. have been made.

Various proposals have been made to divide the ferromagnetic metal thin film layer into two layers in order to improve durability and electromagnetic conversion characteristics (Japanese Patent Laid-Open No. 54-141608, Japanese Patent Publication No. 56-26892). JP-A-5
7-130228 etc.).

However, the technique described in the above publication does not completely solve the problem in the medium using a film of 10 μm or less.
Further, today, in order to realize recording for a longer time, there is a strong demand for a medium having a film thickness of 8 μm or less, which has both runnability, durability of a magnetic layer, and stability of magnetic characteristics. , The handling is insufficient. In particular, the reduction of high frequency output above 5MHz is a big problem.

II Aim of the invention The main object of the present invention is to use a film support having a film thickness of 8 μm or less, good running property and durability of the medium, less cracking and scratching of the magnetic layer due to running, and further head wear amount and drop. An object of the present invention is to provide a magnetic recording method capable of greatly improving high-frequency output by using a metal thin film type magnetic recording medium with little out.

III DISCLOSURE OF THE INVENTION Such an object is achieved by the present invention described below.

That is, the present invention has an upper layer and a lower layer of a ferromagnetic metal thin film layer having a structure in which columnar crystal grains containing Co, Ni, and O, both of which are inclined, are gathered on a plastic film having a thickness of 8 μm or less, Using a magnetic recording medium in which the ratio of the thickness of the upper layer and the thickness of the lower layer is 0.2 to 0.9, the upper layer mainly holds signals in the high frequency region of 5 MHz or more, and mainly the signals in the low frequency region of 0.75 MHz or its vicinity. In the magnetic recording method, magnetic recording is performed so that the lower layer retains the signal, and the output of signals in the high frequency region is improved.

IV Specific Configuration of the Invention Hereinafter, the specific configuration of the present invention will be described in detail.

The ferromagnetic metal thin film layer as the magnetic layer in the present invention is Co
Is a main component, contains Ni and O, and further contains Cr if necessary. The weight ratio of Co / Ni is
It is preferably 1.5 or more.

Further, Cr may be contained in the ferromagnetic metal thin film layer.

In such a case, the weight ratio of Cr / Co or Cr / (Co + Ni) is 0.1 or less, particularly 0.001 to 0.1, and more preferably 0.005 to
It is preferably 0.05.

Further, O is contained in the ferromagnetic metal thin film.

The average oxygen content in a ferromagnetic metal thin film is determined by the atomic ratio, especially O / (Co
Alternatively, the atomic ratio of Co + Ni is 0.5 or less, more preferably
It is preferably 0.05 to 0.5.

In this case, oxygen forms an oxide with the ferromagnetic metal (Co, Ni) on the surface of the ferromagnetic metal thin film layer.

That is, a peak showing an oxide is recognized by Auger spectroscopic analysis in the surface portion, particularly in the range of 50Å to 500Å, more preferably 50 to 200Å from the surface. The oxygen content of this oxide layer is 0 in atomic ratio.
It is about 5 to 1.0.

Incidentally, in such a ferromagnetic metal thin film, further other trace components, especially transition elements such as Fe, Mn, V, Zr, Nb, T
It may contain a, Ti, Zn, Mo, W, Cu and the like.

In a preferred embodiment, such a ferromagnetic metal thin film layer is composed of an aggregate of columnar crystal grains containing Co as the main component.

In this case, the total thickness of the ferromagnetic metal thin film layer is 0.05 to 0.
The thickness is 5 μm, preferably 0.07 to 0.3 μm.

The ferromagnetic metal thin film layer of the present invention has two layers, an upper layer and a lower layer.
It is composed of layers.

And the thickness of the upper layer is smaller than that of the lower layer.

In this case, the ratio of the thickness of the upper layer and the thickness of the lower layer is 0.2-0.9,
The range is more preferably 0.4 to 0.9.

The columnar crystal grains have a length extending over almost the entire area in the thickness direction of each layer, and the angle at which the longitudinal direction is inclined with respect to the normal to the main surface of the substrate is not particularly limited.

In this case, the crystal grains of the lower layer and the crystal grains of the upper layer may be tilted in the same direction in the length direction of the medium with respect to the normal line of the main surface of the substrate, but preferably in opposite directions. Is preferred.

FIG. 1 and FIG. 2 are typical examples of such crystal grain inclination directions.

In FIGS. 1 and 2, a magnetic recording medium 1 has a ferromagnetic metal thin film lower layer portion 3 and a ferromagnetic metal thin film upper layer portion 4 on a substrate 2. Then, the tilt direction of the lower layer crystal grains 5 in the ferromagnetic metal thin film lower layer portion 3, the ferromagnetic metal thin film upper layer portion 4
The upper layer crystal grains 6 in the inside are inclined in opposite directions in the longitudinal direction a of the medium in FIG. 1, and in the longitudinal direction a of the medium in FIG.

In the present invention, the crystal grain gradient shown in FIG. 1 or 2 may be used, but the crystal grain gradient shown in FIG. 1 is preferable.

It should be noted that oxygen is present in the form of a compound on the surface of the columnar crystal grains in the surface portion as described above.

Further, there is no particular limitation on the oxygen concentration gradient of the ferromagnetic metal thin film layer.

Further, the minor axis of the crystal grains preferably has a length of about 50 to 500Å.

In this way, the ferromagnetic metal thin film layer has a two-layered structure, so that the length of the columnar crystal grains is small, so that the film strength of the ferromagnetic metal thin film layer is improved. Also, because the ratio of the thickness of the upper layer to the thickness of the lower layer is 0.2 to 0.9, a signal of about 5 MHz with a relatively shallow magnetic field is held by the upper layer with a thin layer thickness, and about 0.75 MHz with a relatively deep magnetic field. The signal is that the layer thickness is large, and the columnar crystal grains are effectively held in the lower layer having a structure closer to the state of being more upright with respect to the main surface of the substrate.

The substrate for forming such a ferromagnetic metal thin film layer is not particularly limited as long as it is a non-magnetic one, but a particularly flexible substrate, particularly a polyester film, a polyamide film, a plastic film such as a polyimide film is used. Preferably there is.

The thickness is preferably 8 μm or less, and particularly preferably about 5 to 7 μm.

If the thickness exceeds 8 μm, the objectives of downsizing the medium, recording for a long time, etc. cannot be achieved. If this thickness is too thin, the effect of improving the film strength by making the magnetic layer into a two-layer structure as described above is offset, and the running property and the output decrease,
Problems such as head wear occur.

In the case of a conventional ferromagnetic metal thin film layer having a single-layer structure, if the base thickness is set to 8 μm or less, the output, particularly the output in the high frequency band of about 5 MHz or more, is greatly reduced, which is not practical.

On the other hand, when the base thickness is larger than 8 μm, if the ferromagnetic metal thin film layer has a two-layer structure, the output and durability are improved as conventionally proposed.

Even if the base thickness is 8 μm or less, if the two-layer structure is adopted, the output and durability are similarly improved.

However, the effect of improving the characteristics, particularly the electromagnetic conversion characteristics, by the two-layer structure of the ferromagnetic metal thin film layer having a predetermined film thickness ratio in the present invention is extremely remarkable when the thickness of the substrate is as thin as 8 μm or less. And appears critically.
This is something that could not have been predicted in the past.

More specifically, for example, when the thickness of the substrate is 10 μm, the ferromagnetic metal thin film layer is changed from the conventional single-layer structure to the same as in the present invention.
The improvement in electromagnetic conversion characteristics due to the layered structure is 0.75
A signal in the low frequency region of MHz is about +2 (dB), and a signal in the high frequency region of 5 MHz is about +2 (dB).

On the other hand, when the substrate thickness is 7 μm, the improvement width is 0.75
Substrate thickness 10μ at +2 (dB) for low-frequency signal of MHz
Although it is the same as the case of m, it significantly increases up to about +4 (dB) in the signal in the high frequency region of 5 MHz.

In this way, the improvement in the electron conversion characteristics of the 7 μm thick substrate is remarkable as compared with the 10 μm thick substrate.
When the thickness is changed from 7 μm to 7 μm, the head touch abruptly deteriorates due to the lack of rigidity of the substrate, and this effect is greater in a high frequency region such as 5 MHz, and in such a case, the effect of the present invention is exhibited.

Therefore, a medium having a base thickness of 8 μm or less, which cannot be practically used in the past in terms of output particularly in a high range, is used to realize a medium having an output and durability enough to be practically used.

It is preferable to form various known backing layers on the other surface of the plastic film on which the magnetic layer is not provided. The material of the backing layer is not particularly limited, but a material containing a pigment and a radiation curable resin is particularly preferable. The thickness of the backing layer is 0.05 to 1.5 μm, more preferably 0.07 to 1.0 μm.

If this film thickness exceeds 1.5 μm, cracking of the magnetic layer and magnetic surface deviation occur due to running. Further, the amount of head wear increases. And dropout increases. On the other hand, if the film thickness is less than 0.05 μm, the running stability is deteriorated, the head touch failure occurs, and the output decrease and the envelope failure occur.

Fine protrusions may be provided at a predetermined density on the surface of the magnetic recording medium of the present invention.

The fine protrusions have a height of 30 to 300Å, more preferably 50 to 250Å.

That is, the protrusions of the present invention can be observed with an optical microscope and can be observed with a scanning electron microscope, not with a stylus type surface roughness meter.

If the projection height exceeds 300Å and can be observed with an optical microscope, electromagnetic conversion characteristics will deteriorate and running stability will decrease.

Also, if it is less than 50Å, the improvement of physical properties is not effective.

The density is 10 ⁵ or more per mm ^{2 on} average, more preferably 10 ⁵ to 10 ⁹ , and particularly 10 ⁶ to 10 ⁸ .

When the protrusion density is less than 10 ⁵ pieces / mm ² , noise increases,
The physical properties are deteriorated, such as the deterioration of the still characteristics, and it cannot be put to practical use.

On the other hand, if it exceeds 10 ⁹ pieces / mm ² , the effect on the physical properties will be reduced.

The diameter of the protrusion is generally about 200 to 1000Å.

In order to provide such protrusions, it is usually sufficient to dispose fine particles on the substrate. The particle size should be 30 to 1000Å,
As a result, fine protrusions corresponding to the particle diameter are formed.

The fine particles used are those generally known as colloidal particles, for example, SiO ₂ (colloidal silica), Al ₂ O ₃ (alumina sol), MgO, TiO ₂ , ZnO, Fe.
₂ O ₃ , zirconia, CdO, NiO, CaWO ₄ , CaCO ₃ , BaCO ₃ , Co
CO ₃ , BaTiO ₃ , Ti (titanium black), Au, Ag, Cu, N
i, Fe, various hydrosols, resin particles and the like can be used. In this case, it is particularly preferable to use an inorganic substance.

Such fine particles may be used as a coating solution using various solvents, which may be coated on a substrate and dried, or a coating solution to which a resin component such as various aqueous emulsions is added may be coated and dried. Good.

In some cases, the coating liquid may be provided as a top coat layer on the magnetic thin film layer instead of being provided on the substrate.

Further, when a resin component is used, it is possible to provide a gentle protrusion by superposing on the fine protrusion based on these fine particles, but it is not usually necessary to do so.

If necessary, a nonmagnetic metal thin film layer may be interposed between the upper and lower layers of the ferromagnetic metal thin film layer.

In the present invention, the magnetic layer is preferably formed by a so-called oblique vapor deposition method.

In this case, the minimum value of the incident angle of the vapor deposition material with respect to the substrate normal is not particularly limited.

Further, the magnetic layer may be formed by continuously forming the lower layer and the upper layer in one step, but it is usually preferable that after the lower layer is formed, the upper layer is formed by flowing again to the vapor deposition step.

In this way, by dividing the layer of the magnetic layer into two steps of the lower layer and the upper layer, as described above, the direction of the inclination of the magnetic columnar crystal grains with respect to the normal to the substrate is different between the upper layer and the lower layer. The directions are opposite to each other in the length direction.

With such a magnetic layer structure, the electromagnetic conversion characteristics become extremely good.

The vapor deposition atmosphere is usually an atmosphere containing oxygen gas in an inert atmosphere such as argon, helium, or vacuum, and 10 ^-5
And to 10 ⁰ Pa pressure of about, also deposition distance, the substrate transport direction, the structure of the can and the mask, arrangement and the like may be the same as known conditions.

Then, a metal oxide film is formed on the surface by vapor deposition in an oxygen atmosphere. The oxygen gas partial pressure at which the metal oxide is formed can be easily obtained from experiments.

Various oxidation treatments can be performed to form a metal oxide film on the surface.

The following oxidation treatments can be applied.

1) Dry process a. Energetic particle treatment As described in Japanese Patent Application No. 58-76640, oxygen is energized to the magnetic layer as energetic particles by an ion gun or a neutral gun in the latter stage of vapor deposition.

b. Glow treatment O ₂ , H ₂ O, O ₂ + H ₂ O etc. and an inert gas such as Ar, N ₂ are used,
Glow discharge is performed to generate plasma, and the surface of the magnetic film is exposed to this plasma.

c. Oxidizing gas A gas that blows an oxidizing gas such as ozone or heated steam.

d. Heat treatment A substance that is oxidized by heating. The heating temperature is about 60-150 ℃.

2) Wet treatment a. Anodizing b. Alkali treatment c. Acid treatment Chromate treatment, permanganate treatment, phosphate treatment, etc. are used.

d. Oxidant treatment H ₂ O ₂ or the like is used.

The organic topcoat layer of the present invention contains a radiation-curable compound, that is, at least one of a radiation-curable polymer, a monomer and an oligomer, an antioxidant and, if necessary, a lubricant, and has a predetermined density. It is provided on a ferromagnetic metal thin film having protrusions of

Further, in the medium of the present invention, a surface layer may be provided on the magnetic layer to further improve the running property.

As the surface layer, various known ones can be applied, for example, various polymer material coatings, or those containing a lubricant, an antioxidant, a surfactant, inorganic fine particles or the like, or various lubricants. There is a coating film or a vapor deposition film.

The thickness of the surface layer is about 5 to 300 liters.

V. Specific Actions and Effects of the Invention According to the present invention, since a substrate having a thickness of 8 μm or less is used, it is possible to downsize the medium and record for a long time.

In addition, since the magnetic layer has a two-layer structure of an upper layer and a lower layer, the length of the magnetic columnar crystal grains is small, so that the film strength of the magnetic layer is improved. Therefore, running stability is extremely high, cracks in the magnetic layer and scratches on the magnetic surface due to running are extremely small, and the amount of head wear is also extremely small.

Furthermore, the ratio of the thickness of the upper layer of the magnetic layer to the thickness of the lower layer is 0.2.
~ 0.9, 5MHz with relatively shallow magnetic field
A signal of the order of magnitude is retained in the upper layer having a small layer thickness, and a signal of about 0.75 MHz having a relatively deep magnetic field is effectively retained in the lower layer of a large layer thickness.

VI Specific Examples of the Invention Hereinafter, specific examples of the present invention will be shown to explain the present invention in more detail.

Example 1 A polyester (PET) film having a thickness shown in Table 1 below was moved along the circumferential surface of a cylindrical cooling can to remove O ₂ + Ar.
(Volume ratio 1: 1) flows at a speed of 800cc per minute and the degree of vacuum is 1.0 x 1
Co80, Ni20 (weight ratio) in a chamber set to 0 ^-4 Torr
The alloy of Fig. 1 is melted and the incident angle is 60 ° to 90 ° for the lower layer and 10 ° to 90 ° for the upper layer, and the Co-Ni-O thin film as shown in Fig. 1 is formed by oblique vapor deposition. Formed. As a comparison, the film thickness of 0.15 μm is obtained by obliquely vapor-depositing only the part where the incident angle is 30 to 90 °.
Co-Ni-O single-layer thin film was formed.

A large amount of oxygen was unevenly distributed in the interface between the lower layer and the upper layer and the surface opposite to the base. Also, the surface opposite to the base was almost entirely covered with oxide.

Hc = 1000 Oe. The average oxygen content in the film is the atomic ratio to Co and Ni. Was 40%.

On the magnetic layer thin film, a surface layer of isopropyl myristate was formed with a film thickness of 25 Å, and on the back side of the substrate was 0.
A backing layer containing carbon, silica and a radiation curable resin was formed to a thickness of 5 μm.

The following measurements were carried out for each of the samples formed in this way and shown in Table 1 below.

1) Durability A continuous running test was conducted under the conditions of a temperature of 20 ° C and a humidity of 60% RH.

Deck used: SONY A-300 Head: Sputter sendust Note that the running direction of the medium and the direction of the inclination of the magnetic crystal grains with respect to the normal line to the substrate of the lower layer were the same direction.

2) Electromagnetic conversion characteristics The outputs at center frequencies 0.75MHz and 5MHz were measured, and the value when the output of sample No. 10 was set to 0dB was obtained.

Deck used: SONY A-300 Head: Sputter Sendust mode: SP mode In addition, sample Nos. 1 to 6 (base thickness: 7μ) for the output of sample No. 7 (base thickness: 7 μm, magnetic layer configuration: single layer)
m, magnetic layer constitution: 2 layers) is shown in the parentheses in Table 1 for the improvement of output.

From the results shown in Table 1, the effect of the present invention is clear.

That is, when the upper layer thickness / lower layer thickness is 0.2 to 0.9, especially when the base thickness is 8 μm or less, a particularly high improvement of 5 MHz output is seen, and even a thin base thickness that is not practical for 5 MHz output is sufficient. It can be seen that it shows a practical electromagnetic conversion characteristic.

[Brief description of drawings]

FIG. 1 is a schematic view of a cross section parallel to the medium direction of one embodiment of the magnetic recording medium of the present invention. FIG. 2 is a schematic view of a cross section parallel to the medium direction of another embodiment of the magnetic recording medium of the present invention. DESCRIPTION OF SYMBOLS 1 ... Magnetic recording medium, 2 ... Substrate, 3 ... Ferromagnetic metal thin film lower layer, 4 ... Ferromagnetic metal thin film upper layer, 5 ... Lower crystal grain, 6 ... Lower crystal grain, arrow a: Medium length direction

Claims (1)

[Claims] 1. An upper layer and a lower layer of a ferromagnetic metal thin film layer having a structure in which columnar crystal grains containing Co, Ni, and O and inclined together are formed on a plastic film having a thickness of 8 μm or less. The ratio of the thickness of the lower layer to the thickness of the lower layer is 0.2 to 0.9 is used, and the upper layer mainly holds signals in the high frequency region of 5 MHz or more, and mainly the signals in the low frequency region of 0.75 MHz or its vicinity. A magnetic recording method in which magnetic recording is performed so that the lower layer holds the signal, and the output of signals in the high frequency region is improved.