JPH07107734B2 - Magnetic recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, particularly to 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.

As a magnetic layer of such a metal thin film type medium, characteristically, vapor deposition is performed by a so-called oblique vapor deposition method in which vapor deposition is performed at a predetermined inclination angle with respect to the normal to the substrate, and vapor deposition of Co-based, Co-Ni-based, etc. Membranes are preferred.

For such media, research has been conducted on media using thinner films for downsizing, long-time recording, etc., but problems such as runnability, durability, strength of ferromagnetic metal thin film, etc. Occurs.

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)
Alternatively, it is proposed that fine particles are provided on the film surface to improve the head touch and the running surface (Japanese Patent Laid-Open No. 58-68227).
No. 58-100221).

Further, in order to improve durability and electromagnetic conversion characteristics, various proposals have been made that a ferromagnetic metal thin film layer has a multi-layered structure of two or more layers (Japanese Patent Laid-Open No. 54-141608 and Japanese Patent Publication No. 56-56). 2689
2, JP-A-57-130228, etc.).

However, at present, a technology which has good running property, durability, ferromagnetic thin film strength, and causes no inconvenience in terms of electromagnetic conversion characteristics has not yet been realized.

II Object of the invention The object of the present invention is a metal thin film type magnetic medium having good running property of the medium, less cracks and scratches of the magnetic layer due to running, less head wear and dropout, and good electromagnetic conversion characteristics. To provide a recording medium.

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

That is, the present invention has a ferromagnetic metal thin film layer containing Co as a main component on a plastic film substrate, and the ferromagnetic metal thin film layer has a multi-layer structure composed of two or more layers. The value obtained by dividing the oxygen concentration C ₂ in the vicinity of the interface with the uppermost layer of the layer adjacent to the uppermost layer of the layer by the oxygen concentration C ₁ in the vicinity of the surface of the uppermost layer opposite to the substrate is 0.2 to 0.92, and C ₁ is 0.2 to 0.7, and the average oxygen concentration of the uppermost layer and all layers is 0.1 to 0.5, respectively.

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

The ferromagnetic metal thin film layer as the magnetic layer in the present invention has a multi-layer structure including at least two layers. The ferromagnetic metal thin film layer used in the present invention has a composition containing Co as a main component, containing O, and optionally containing Ni and / or Cr.

That is, in a preferred embodiment, it may consist of Co alone or Co and Ni. If Ni is included,
The Co / Ni weight ratio 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 of the present invention.

The average oxygen amount C ^* of the entire layer in the ferromagnetic metal thin film is an atomic ratio, particularly the atomic ratio of O / (Co or Co + Ni), and the average oxygen amount C ₁ ^* in the uppermost layer is 0.1 to 0.5, preferably 0.1 to 0.5. 0.4.

If the average oxygen amount C ₁ ^* is less than 0.1, the corrosion resistance, running property, cracks in the magnetic layer, scratches, etc. are insufficient, and if it exceeds 0.5, the surface oxide layer increases and the output due to the head spacing. Causes a problem such as a decrease in

The oxygen concentration C _{2 in the} vicinity of the interface between the uppermost layer and the adjacent layer, especially the O / (Co or Co + Ni) atomic ratio, is the oxygen concentration in the vicinity of the surface opposite to the uppermost plastic film.
C ₁ , especially the value divided by the O / (Co or Co + Ni) atomic ratio C ₂ / C ₁
Is 0.2 to 0.92.

In this case, these oxygen concentrations are subjected to Auger spectroscopic analysis, SIMS (secondary ion mass spectrometry), etc. while Ar or the like ion-millinda or ion-etching the ferromagnetic metal thin film,
Can be measured.

That is, while performing ion etching, O, Co, Ni
Etc. are counted and the profiles in the film thickness direction are compared.

The O / (Co or Co + Ni) on the surface of the ferromagnetic metal thin film opposite to the plastic film is C ₁ .

Regarding C ₂ of the layer adjacent to the uppermost layer, O / (Co or Co
Calculate Co + Ni) and call this C ₂ . However, in each layer, the oxygen concentration becomes maximum on the surface opposite to the film substrate under normal film forming conditions. Therefore, normally, when O is counted while performing ion etching, the maximum value in the film may be C ₂ .

Ion etching and Auger spectroscopic analysis or SIMS measurement methods are well known in the art.

In this way, by relatively increasing the oxygen concentration C ₁ on the surface of the uppermost layer, the coercive force Hc increases, and the oxygen concentration of the portion below the surface of the uppermost layer and in the vicinity of the layer adjacent to the uppermost layer is also increased. Is relatively lower than C ₁ described above, the maximum residual magnetic flux φ _r and the squareness ratio S _Q are increased, and the magnetic layer has extremely good electromagnetic conversion characteristics. Therefore, the center frequency
A signal with a relatively shallow magnetic field of about 5 MHz is effectively retained in the uppermost layer.

Further, if the oxygen concentration C ₂ in the vicinity of the interface with the uppermost layer adjacent to the uppermost layer is regulated, the coercive force Hc at this portion increases, and the interface with the uppermost layer of the layer adjacent to the uppermost layer increases. By making the oxygen concentration in the lower portion from the vicinity relatively lower than the above C ₂ , the maximum residual magnetic flux φr and each diameter ratio S _Q become high, and a magnetic layer having extremely good electromagnetic conversion characteristics is obtained. Therefore, a signal with a comparatively deep magnetic field having a center frequency of about 0.7 MHz is effectively retained in the layers adjacent to the uppermost layer.

And, as described above, the relationship between C ₁ and C ₂ is such that C ₂ / C ₁ is 0.2.
When it is up to 0.92, it becomes an excellent magnetic layer with the best balance of the electromagnetic conversion characteristics and corrosion resistance of the magnetic layer.

The O / (Co or Co + Ni) C ₁ near the surface is generally 0.
It is 2 to 0.7, preferably 0.3 to 0.6.

Therefore, O / (Co or Co + Ni) C _{2 in the} vicinity of the uppermost layer adjacent to the uppermost layer is 0.07 to 0.6, preferably 0.1 to 0.5.

In addition, O / (Co or Co + Ni) C ₁ ^{* in the} entire top layer
Is 0.1 to 0.5, and more preferably 0.1 to 0.4. In addition, O / (Co or Co + in the entire layer adjacent to the uppermost layer
Ni) C ₂ ^* is preferably 0.5 or less, more preferably 0.3 or less.

At this time, electromagnetic conversion characteristics, corrosion resistance, running durability, magnetic film strength, etc. are extremely good.

In this case, in the case of a multi-layered structure having three or more layers, the O / (Co or Co + Ni) of each layer is generally 0.5 or less, preferably 0.3 or less.

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

That is, a peak showing an oxide is recognized by Auger spectroscopic analysis in the thickness range of 100Å to 2000Å, more preferably 500 to 1000Å from the surface of each layer.

In the present invention, the ferromagnetic metal thin film layer surface, and for controlling the oxygen concentration of the vicinity of the uppermost layer of the layer adjacent to the uppermost layer,
At that time, the predetermined effects of the present invention are realized.

Therefore, as described above, the oxygen concentration profile in the film thickness direction of the ferromagnetic metal thin film usually has a peak of oxygen distribution at least at the interface between the uppermost layer and the layer adjacent to the uppermost layer.

It should be noted that the ferromagnetic metal thin film usually has two layers, but it may have three or more layers, particularly 3 to 5 layers, if necessary.

In such a ferromagnetic metal thin film, other trace components, especially transition elements such as Fe, Mn, V, Zr, Nb, Ta, Ti, Z
It may contain n, Mo, W, Cu or 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 thickness ratio of each layer of such a ferromagnetic metal thin film layer is not particularly limited, but in the case of a two-layer structure, for example, the thickness ratio of the upper layer and the lower layer is preferably about 0.1 to 10.

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 inclines with respect to the normal line of the main surface of the substrate is not particularly limited.

In each of the intermediate layers in the structure of three or more layers, the tilt angle of the columnar crystal grains with respect to the normal to the main surface of the substrate is usually within the tilt angle range between the uppermost layer and the lowermost layer, and there is no particular limitation.

In this case, the directions of inclination of the crystal grains of the adjacent magnetic layers with respect to the normal line to the main surface of the substrate may be the same in the longitudinal direction of the medium, but are preferably opposite to each other. preferable.

FIG. 1 and FIG. 2 schematically show such a tilt direction of the crystal grains by taking a two-layer structure as an example.

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.

As described above, since the ferromagnetic metal thin film layer has a multi-layered structure including at least two layers, the length of the columnar crystal grains is small, and thus the film strength of the ferromagnetic metal thin film layer is improved.

Furthermore, by increasing the oxygen concentration in the uppermost layer, oxides such as Co and Ni, which have excellent wear resistance, are formed in the uppermost layer. Will have a higher film strength.

The material of the substrate used in the magnetic recording medium of the present invention is not particularly limited as long as it is a non-magnetic plastic, but usually polyethylene terephthalate, polyethylene 2,6
-Polyester such as naphthalate, polyamide, polyimide, polyphenylene sulfide, polysulfone,
Wholly aromatic polyester, polyetheretherketone,
Polyether sulfone, polyether imide, etc. are used. Further, the shape, size, and thickness are not limited, and may be selected depending on the application.

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 lining layer is 0.05 to 1.5 μm, more preferably 0.07 to 1.0 μm
m.

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.

And, the density is 10 ⁵ or more per 1 mm ^{2 on} average, more preferably 10 ⁵ to 10 ⁹ , and especially 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 diameter of the fine particles may be 30 to 1000Å, whereby fine protrusions corresponding to the diameter of the fine particles are formed.

The fine particles to be used are 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 , CoCo ₃ , BaTio ₃ , Ti (titanium black), Au, A
g, Cu, Ni, 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, these coating liquids may be provided as a top coat layer on the magnetic thin film layer instead of being provided on the substrate.

In addition, when a resin component is used, it is possible to form 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 non-magnetic metal thin film layer may be interposed between the uppermost layer and the lowermost layer 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 incident angle of the vapor deposition substance with respect to the normal to the substrate is not particularly limited.

Further, the magnetic layer may be formed by continuously forming two or more layers in one step, but it is usually preferable to form each layer by flowing it into the vapor deposition step.

In this way, by dividing the layers of the magnetic layer into layers, the directions of the inclinations of the magnetic columnar crystal grains with respect to the normal to the substrate are opposed to each other in the lengthwise direction of the medium as described above. It will be facing.

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 treatment a. Energetic particle treatment As described in Japanese Patent Application No. 58-76640, in the latter stage of vapor deposition,
An ion gun or neutral gun that causes oxygen to enter the magnetic layer as energetic particles.

b. Glow treatment O ₂ , H ₂ O, O ₂ + H ₂ O, etc. and an inert gas such as Ar, N ₂ etc. are used, and this is glow-discharged to generate plasma. What to expose.

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. Heating temperature is 60-150 ℃
degree.

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, the magnetic layer has a layered structure of two or more layers, so that 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, since the ratio C ₂ / C ₁ of the oxygen concentration C _{2 on} the surface of the layer adjacent to the uppermost layer and the oxygen concentration C _{1 on the} surface of the uppermost layer is 0.1 to 3.0, the coercive force Hc is relatively high in the uppermost layer. The signal having a relatively shallow magnetic field and a center frequency of about 5 MHz is effectively held, and the resolution is good. In the layers adjacent to the uppermost layer and below, the maximum residual magnetic flux φr and the squareness ratio are high, and the center frequency is 0.75 with a relatively deep magnetic field.
It effectively holds a signal of about MHz.

VI Specific Examples of the Invention Hereinafter, the present invention will be described in more detail by showing specific examples of the invention.

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) is flown 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
Was melted and the incident angle was set to the incident angle shown in Table 1 to form a Co-Ni-O two-layer thin film shown in FIG. 1 by oblique vapor deposition.

For comparison, only a portion having an incident angle of 30 to 90 ° was obliquely vapor-deposited to form a 0.15 μm thick Co—Ni—O single-layer thin film.

A large amount of oxygen was unevenly distributed on the interface between the lower layer and the upper layer and on 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%.

In Table 1, among the O / (Co or Co + Ni) atomic ratios obtained by performing Auger spectroscopic analysis while performing ion etching with Ar, C ₁ (surface), C ₁ ^* (upper layer average), and C ₂ ( The vicinity of the interface between the lower layer and the upper layer), C ₂ ^* (lower layer average), and C ^* (all layer average) are also described.

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. The medium running direction and the direction of the inclination with respect to the base layer normal to the lower layer were the same direction.

1) Durability Temperature 20 ℃, Humidity 60% RH, Temperature 40 ℃, Humidity
A continuous running test was carried out under the condition of 80% RH, and the number of passes until the output decreased by 2 dB was obtained.

Deck used: SONY A-300 Head: Sputter Sendust 2) Electromagnetic conversion characteristics The outputs at center frequencies of 0.75MHz and 5MHz were measured, and the value when the output of sample No. 11 was set to 0dB was obtained.

Deck used: SONY A-300 Head: Spatter Sendust mode: SP mode Furthermore, the height of these initial outputs affects the output after storage. Therefore, the output after storage at 60 ° C. and 90% for 5 days was also measured.

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

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a cross section parallel to the medium direction of one embodiment of a 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 ... Upper crystal grain, arrow a: Medium length direction

Claims (1)

[Claims] 1. A ferromagnetic metal thin film layer containing Co as a main component on a plastic film substrate, and the ferromagnetic metal thin film layer has a multi-layer structure composed of two or more layers. The value obtained by dividing the oxygen concentration C ₂ in the vicinity of the interface with the uppermost layer of the layer adjacent to the uppermost layer of the layer by the oxygen concentration C ₁ in the vicinity of the surface of the uppermost layer opposite to the substrate is 0.2 to 0.92, and C ₁ is 0.2 to 0.7, and the average oxygen concentration of the uppermost layer and all layers is 0.1 to 0.5, respectively.