JPH0679368B2 - Magnetic recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film magnetic recording medium, and more particularly to a thin film magnetic recording medium having improved wear resistance, corrosion resistance and electromagnetic conversion characteristics.

Prior art and its problems When the method of manufacturing a magnetic recording medium is divided from the method of forming a magnetic layer, it can be roughly classified into a coating method and a flying or plating method.

The one obtained by the coating method (hereinafter, the magnetic recording medium obtained by this method is referred to as the coating type magnetic recording medium) is γ-Fe ₂ O.
₃ , mixing ferromagnetic powder such as Fe with a suitable binder resin,
The magnetic coating material obtained by dispersion is applied onto a non-magnetic substrate and subjected to magnetic field orientation, drying, super calendering, etc. to obtain characteristics as a magnetic recording medium.

This coating type magnetic recording medium is aimed at increasing the coercive force, improving the recording density, and thinning the magnetic layer. However, in the method of coating the magnetic coating obtained by mixing the ferromagnetic powder with the binder on the non-magnetic substrate, there is essentially a limit to the substantial filling rate of the ferromagnetic powder, and it is aimed at achieving high density and thin film. Has difficult factors.

For this reason, in order to achieve high density and thin film,
Usually, a method of flying a magnetic material by a method such as vacuum deposition, sputtering, or ion plating to form a continuous thin film of a magnetic material on a non-magnetic substrate, and a method of forming by electrolysis or chemical plating (hereinafter, these The magnetic recording medium obtained by the above method is referred to as a thin film magnetic recording medium). With this thin film magnetic recording medium, it is possible to obtain a magnetic recording medium having high recording density characteristics in the short wavelength region which the coating type magnetic recording medium does not have such as high density and thin film.

However, thin-film magnetic recording media generally require improvements in physical and chemical characteristics such as corrosion resistance and abrasion resistance, and electromagnetic characteristics.

As one of the improvements of the thin film type magnetic recording medium produced by the above-mentioned vacuum deposition, sputtering, ion plating, etc., there are disclosed in JP-A Nos. 53-42010, 53-64008, and 54-19199.
The method of performing vapor deposition in an oxygen atmosphere disclosed in Japanese Patent No. 3,629,771 aims to miniaturize vapor-deposited magnetic thin film forming particles, improve coercive force, and obtain a magnetic recording medium suitable for high recording density. ing.

Further, the reduction of the film thickness of the thin film type magnetic recording medium results in a decrease in the mechanical strength of the thin film in addition to the defect of the chemical characteristics of the thin film material itself, and the improvement of the corrosion resistance and the wear resistance is particularly As a necessary improvement, various methods have been proposed for improving the corrosion resistance and the abrasion resistance by providing a protective layer on the upper portion of the thin film. For example, 1) wear-resistant metal overcoat layers are disclosed in JP-A-51-23704 and JP-A-51-4.
No. 7401, No. 53-7205, No. 53-39708, No. 53-73108
JP-A-52-4805, JP-A-52-4805, and JP-A-52-4805, which describe 2) metal oxide, nitride, and carbide overcoat layers.
No. 52-127204, No. 57-138054 and the like, 3) Overcoat layer of inorganic lubricant is disclosed in JP-A Nos. 50-146302 and 53-57.
No. 002, 002, 153707, No. 56-153534, No. 57-8927;
No. 58-130436, No. 58-150128, and the like. Further, 5) those coated or adsorbed with an organic lubricant such as esters of higher fatty acids and higher alcohols are disclosed in JP-A-55-93533 and JP-A-58-19736, and further, 6) the surface of the magnetic layer. An oxide film or a nitride film formed by the oxidation or nitridation of JP-A-50-33 is disclosed.
No. 806, No. 52-153407, No. 54-143111, No. 56-15011
No. 58-26321 and the like.

However, in these conventional techniques, in the method of forming a thin film by introducing oxygen, generally, the reaction amount of oxygen and a magnetic metal is increased in order to increase the mechanical strength of the film, but in this method, a film of 3000 Å or less is used. When the thickness is large, not only the thin film itself becomes brittle, but also the deterioration of the thin film is unavoidable in terms of magnetic characteristics due to a significant decrease in the saturation magnetization Ms.

Further, in each of the prior arts in which a protective layer is provided, 1),
In 2), 3) and 4), good effects on both corrosion resistance and wear resistance cannot be obtained unless the thickness of the coating is about 0.1 μm or more. At that thickness, spacing loss occurs and high density is achieved. Sufficient performance as a recording medium cannot be obtained. Further, since the film is additionally formed, the adhesive force between the magnetic layer and the film is insufficient, and delamination is likely to occur, which is particularly problematic in wear resistance. Further, in 5), the lubricant coating was easily peeled off and consumed, so that the characteristics such as still durability were not sufficient. In 6), a method of oxidizing or nitriding while applying heat or kinetic energy of particles is not suitable for a magnetic recording medium for video using a plastic substrate such as polyester because the temperature rises in the manufacturing process. In the method using the solution reaction of the wet system, when a film having practical characteristics is formed, the film thickness becomes large, resulting in spacing loss. When the film thickness is made thin, sufficient wear resistance cannot be obtained and corrosion is also caused. It caused secondary problems such as promoting

II Object of the Invention The present invention has been made to solve the above problems, and an object of the present invention is to provide a magnetic recording medium excellent in physical and chemical characteristics such as corrosion resistance and abrasion resistance, and electromagnetic conversion characteristics. Is to provide.

III Specific Configuration of the Invention The above object of the present invention is to provide a magnetic recording medium having a magnetic thin film on a non-magnetic substrate, in which an oxide crystal layer containing an oxide crystal phase of a magnetic metal is provided from the surface of the magnetic thin film to its vicinity. A layer containing the metal and the oxide of the metal mixed therein is formed continuously in the film thickness direction of the layer, and each layer is a film containing the metal and the metal oxide mixed. The surface of the magnetic thin film in which the ratio α of the oxide forming metal atoms to the total metal atoms forming the metal and the metal oxide at the layer depth decreases continuously in the film thickness direction from the surface of the magnetic thin film, and α is 0.5. The magnetic recording medium is characterized in that the depth position in the film thickness direction is 50Å to 95Å.

In the magnetic recording medium of the present invention, in the oxide crystal layer containing the oxide crystal phase of the magnetic metal from the surface of the magnetic thin film to the vicinity thereof, when the magnetic metal is, for example, Co—Ni alloy, CoO and Co ₃ are used as the oxide. Oxides satisfying the stoichiometry of O ₄ , NiO, Ni ₃ O _4, etc. (which may contain oxides of other trace atoms) are mixed to form an oxide crystal phase. Similarly, when the magnetic metal is another alloy or a metal composed of a simple substance, the molecules existing as a metal oxide satisfying the stoichiometry are present at a density that forms a crystal phase. This oxide crystal phase is, as will be described later, ESCA (Electron Spectroscopy For Chem
ical analysis), X-ray diffraction, electron diffraction, etc., and is determined as an oxide crystal phase from comparison with standard sample data.

This oxide crystal layer contains a physically and chemically stable oxide crystal phase, and since it exists from the surface to its vicinity, it functions as an effective protective layer with excellent wear resistance and corrosion resistance. Improves wear resistance and corrosion resistance of the recording medium.

The magnetic metal formed continuously in the thickness direction of the oxide crystal layer and the layer containing the oxide of the metal mixed therein have the same stoichiometry as the metal oxide contained in the oxide crystal layer. A metal oxide satisfying the condition is mixed with the magnetic metal, and the ratio α of the metal atoms forming the oxide to the total metal atoms forming the metal and the metal oxide at each film layer depth is continuous from the surface of the magnetic thin film in the film thickness direction. Will be reduced. In this mixed layer, the depth position in the film thickness direction of the magnetic thin film in which the value of α is 0.5 is practically preferably 50Å to 95Å,
65Å to 80Å is more preferable.

Further, the mixed layer in the present invention does not mean an interdiffusion region formed at the boundary between a normal magnetic thin film and a metal oxide layer formed thereon by another method such as heat treatment or coating. However, the mixed composition of the metal and the metal oxide that satisfies the stoichiometry is arbitrarily controlled. The film thickness of the mixed layer is large (100 Å or more), and the composition change is continuous and gradual (for example, 60 per 100 Å). %)).

Since this mixed layer is continuous with the metal oxide crystal layer that functions as a protective layer, the problem of peeling of the surface metal oxide crystal layer at the interface does not occur, and wear resistance is improved.
Further, the mixed composition of the mixed layer near the interface with the metal oxide crystal layer contains a large amount of metal oxides satisfying the stoichiometry and enhances the protective function, while the mixed layer is close to the substrate. The proportion of the metal oxide present decreases with the decrease, and the proportion occupied by the magnetic metal increases, which contributes to an increase in the output level of the magnetic recording medium. Furthermore, on the substrate side of the mixed layer, a trace amount of metal oxide is present in the magnetic metal, which suppresses the growth of the magnetic metal crystal particles and contributes to the fineness of the particles. A dramatic improvement in C / N of magnetic recording media is realized.

The magnetic thin film having the above characteristics has a spacing loss as small as 2 dB or less at a recording wavelength of about 0.6 μm, has no significant deterioration in electromagnetic conversion characteristics, has high mechanical strength, corrosion resistance, wear resistance and electromagnetic conversion characteristics. It has excellent properties.

Incidentally, the magnetic recording medium of the present invention defines the mixed composition of the magnetic metal and the metal oxide up to a depth of about 100 Å in the film thickness direction from the surface of the magnetic thin film of the mixed layer. It does not prescribe the structure of the magnetic layer in the film thickness direction, and does not exclude known structures such as magnetic layer stacks and non-magnetic layer stacks.

In the magnetic recording medium of the present invention, as a method for forming a magnetic thin film on a non-magnetic substrate, known vacuum deposition (including reactive deposition), sputtering, ion plating, CV
A method such as D (Chemical Vapor Deposition) may be used. Here, the electron beam reactive vapor deposition method is preferable.

Examples of magnetic metal materials that can be used in the magnetic recording medium of the present invention include magnetic metals such as Fe, Co and Ni, or Fe--Co and Fe.
-Ni, Co-Ni, Fe-Si, Fe-Rh, Fe-V, Fe-Cu, Fe-
Au, Co-P, Co-V, Co-Si, Co-Y, Co-La, Co-C
e, Co-Pr, Co-Sm, Co-Mn, Co-Pt, Ni-Cu, Co-Ni
-Fe, Co-Ni-Ag, Co-Ni-Zn, Co-Si-Al, Fe-Si-
Examples include alloy magnetic metals such as Al, Mn-Bi, Mn-Sb, and Mn-Al. Here, Co or Co-Ni alloy (Ni
The content rate is 30 wt% or less). In addition, you may contain other trace components as needed.

As the non-magnetic substrate, polyethylene terephthalate, polyethylene-2,6-naphthalate, polycarbonate,
Examples of the commonly used plastino substrate such as polypropylene, cellulose triacetate, polyimide and aramid are preferred, and polyethylene terephthalate is preferred.

Further, the magnetic recording medium of the present invention, for the purpose of improving slipperiness, preventing electrification, preventing transfer, improving storage stability, and improving abrasion resistance, for example, before and / or after formation of the above-mentioned magnetic thin film on the substrate, An overcoat layer or a backcoat layer may be provided by a known coating method, vapor deposition method, or the like. These coating methods and vapor deposition methods are described, for example, in JP-A No. 54-123922.
54-123923, 56-71284, 56-71286, 56-
71287, 56-11626, and 57-135442.

As materials for these overcoat layers and backcoat layers, various polymers (for example, urethane resins, epoxy resins, vinyl chloride-vinyl acetate copolymers) and organic oligomers and polymers such as silicon resins: carbon black, alumina, etc. Inorganic materials: Various materials such as antioxidants such as phenol derivatives and low molecular weight organic compounds such as singlet oxygen quenchers such as amine derivatives can be used, lubricants,
Various components called an abrasive, an antistatic agent, and a dispersant can be added and used.

FIG. 1 shows a cross-sectional view of an essential part of an embodiment of an apparatus used for manufacturing the magnetic recording medium of the present invention.

The inside of this apparatus is hermetically sealed from the outside by a casing indicated by reference numeral 1, and the inside of the casing 1 is divided by a partition wall 2 into a chamber for feeding / winding the non-magnetic substrate 3 and a vapor deposition chamber. An exhaust pipe 4 is provided at the bottom of the exhaust pipe 4, and the exhaust pipe 4 is connected to a vacuum exhaust device 5.

In the delivery / winding chamber, the delivery shafts 6 and 2 are provided as a substrate traveling system.
It has a free roller 7, a substrate support 8, and a winding shaft 9. In the vapor deposition chamber, an electron beam generator 10, as a vapor deposition system,
There is a crucible 11 and a magnetic material 12 to be attached which is put in the crucible 11. Further, a mask 13 is provided to project into a flight space formed between the substrate support 8 and the crucible 11, and the magnetic material is provided on the substrate 3. It is designed to control the angle of incidence of the 12 flying vapor streams. The mask 13 has a hollow structure, and the substrate 3 to be set on the substrate support 8 is provided in the vicinity of the incident angle regulating tip portion.
Is provided with a slit-shaped jet port 14 having a long side in the width direction of the gas G through a reactive gas introduction pipe 15 such as oxygen gas.
Is introduced and jetted at a predetermined angle from the slit-shaped jet port 14 toward the substrate 3. As shown in FIG. 2, the jet direction of the reactive gas is preferably such that the angle θ formed by the normal line standing on the substrate surface at the position where the jet gas collides with the substrate 3 and the jet direction of the gas is 90 ° or more, More preferably 14
It is 0 ° to 180 °.

Further, the distance between the ejection port 14 and the substrate surface is preferably 15 mm or less, more preferably 3 to 10 mm.

Velocity of the jet gas, the amount of the slit and the width of the slit of the jet outlet 14 is determined to be an appropriate value in correlation, but the width of the slit is preferably 5 mm or less, more preferably 0.5 to 2 mm, the velocity of the jet gas, the amount is , 2 × 10 ^-2 ~ 0.5Pacm ² / s per 10cm slit width
Is preferable, and more preferably 0.1 per slit width of 10 cm.
~ 0.3 Pacm ³ / s. At this time, a tank may be provided between the introduction pipe 15 and the introduction port in order to improve the uniformity of the velocity and amount of the ejected gas.

In addition, although the substrate support, the cooling mechanism in the mask, etc. are omitted, a technique known in the art can be optionally used.

Further, although the electron beam heating method is used in the embodiment, a resistance heating method, a laser beam heating method or the like may be used.

The reactive gas used in the present invention may be a gas containing at least one selected from oxygen, an allotrope of oxygen and an active species of oxygen, and another gas that can be used in combination with the gas is, for example, nitrogen (N ₂ ) Gas, helium gas (He),
Xenon gas (Xe), radon gas (Rn), argon (A
r), inert gas such as neon (Ne), carbon monoxide (C
O), carbon dioxide (CO ₂ ), hydrogen (H ₂ ), steam (H ₂ O) can be used alone or in combination of two or more.

In general, means such as Auger spectrum analysis, ESCA, and X-ray diffraction are used for composition analysis of magnetic thin films. In Auger spectrum analysis, the composition of atoms forming a thin film can be analyzed, and the combination of atoms The state and the like are unknown, and it is the current state of the art that it is not possible to distinguish, for example, whether oxygen atoms are present as metal oxide molecules or incorporated into the thin film in the form of free oxygen molecules. In the magnetic recording medium of the present invention, the composition of the magnetic metal and the oxide of the metal (which satisfies the stoichiometry) was determined by ESCA at the depth in the film thickness direction of each sample. Will be explained.

ESCA provides information on the state of oxidation and oxidation of metals. For example, by measuring a signal derived from a 2p photoelectron of Co, it is possible to find out whether Co is in a metallic state or an oxidized state. In order to analyze the film thickness direction of the sample, etching is performed with an argon ion gun or the like, and ESCA measurement is performed at each film thickness depth. The etching conditions are, for example, 5 kV, 25 mA, and 8 mm raster, and the etching rate is about 12 Å / min for a Co-Ni alloy of known thickness. Taking the case of using metallic cobalt as the magnetic metal as an example, the method for obtaining the composition ratio of the metal and the metal oxide in the magnetic thin film of the obtained magnetic recording medium sample is as follows.

First, the ESCA spectrum of the standard sample is obtained. Specifically, a cobalt pure metal standard sample is sufficiently etched to clean the surface, and then a standard spectrum of metal cobalt (shown in FIG. 3) is obtained by ESCA measurement. Next, cobalt oxide (Co
A standard spectrum (shown in FIG. 4) is similarly obtained for O). (Note that the spectra shown in FIGS. 3 and 4 are the Co ₂ p spectra after baseline correction.)
Comparison of 4 clearly shows the shift of the peak position (chemical shift) and the difference in the peak shape. Here, it is assumed that the sensitivity of each of metallic cobalt and cobalt oxide (the number of photoelectron signal counts per unit number of atoms) is almost equal,
Further, it is considered that the spectrum of the mixture of metallic cobalt and cobalt oxide is equal to the standard spectrum of the cobalt oxide of metallic cobalt multiplied by the respective mixing ratios and then added. At this time, the standard spectrum at each mixing ratio can be obtained by multiplying each standard spectrum of metallic cobalt and cobalt oxide by an appropriate constant corresponding to each mixing ratio, and then adding the result to obtain the standard spectrum at each mixing ratio. The mixing ratio of metallic cobalt and cobalt oxide can be estimated by comparing with the spectrum in FIG. Although only CoO is shown as the standard spectrum of cobalt oxide, in the following examples,
Co ₂ O _{3 which} is another component as cobalt oxide is X-ray diffraction, E
Considering that it can be almost ignored from the analysis result of the SCA spectrum, the cobalt oxide was considered as a CoO single compound here.

When a Co-Ni alloy is used as the magnetic metal, a standard spectrum is also created for the Ni metal in the same manner as for the Co metal simple substance described above, and a metal is obtained by comprehensively evaluating Co and Ni. The mixing ratio of metal oxides can be estimated. Other metals, alloys, and the like can be used in the same manner.

IV Specific Examples of the Invention Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1 A magnetic recording medium was manufactured under the following conditions by using a device shown in FIG. 1 to provide a slit-shaped oxygen gas ejection port in the vicinity of the tip of a mask for controlling the incidence angle of flying airflow.

Oxygen gas ejection rate 2.5kg / cm ² , 0.7 / min Gas ejection angle θ = 170 ° Distance between ejection port and substrate 7.0mm At pressure 7 × 10 ^-3 Pa, 12.5μm thick polyethylene terephthalate substrate is 50m / min The magnetic material of Co-Ni (80:20) was evaporated by electron beam heating and oxygen gas was ejected from the ejection port to form a magnetic thin film having a thickness of 1200 Å while running at the speed of. After forming the magnetic thin film, apply phosphate ester lubricant to the tape surface to a thickness of about 100Å,
An original tape of the magnetic recording medium was cut into a tape having a width of 12.65 mm to obtain Example Tape 1.

The ratio α of the metal atoms forming the oxide to the total metal atoms forming the metal and the metal oxide at each depth in the film thickness direction of Example Tape 1 was determined by the ESCA measurement method. The equipment used for ESCA measurement is Perkin-Elmer, PH1 Model 560 ESCA / SAM.
The conditions are 15 kV and 300 W using an Al anode. The energy resolution used was a pass energy of 25 eV.
The etching was performed with an argon ion gun, and the etching rate was about 12Å / min for the Co-Ni alloy. The result of ESCA measurement is shown in FIG. It can be seen that the oxide decreases as the distance from the surface (all oxides) increases. Further, FIG. 5 shows the X-ray diffraction spectrum pattern of the magnetic tape after the magnetic thin film was formed and before the lubricant was applied.

Furthermore, under the above conditions, the oxygen gas ejection rate is 2.5 kg / cm
Example tapes 2 to 5 were obtained in the same manner except that the rate was changed to ³ , 0.35 to 0.75 / min.

ESCA measurement was performed on Example tapes 2 to 5 in the same manner as in Example tape 1 to obtain the film thickness depth of α = 0.5. The still durability of each of the obtained tape samples was measured using a commercially available VTR deck. The still durability was set to a back tension of 12 g, and the time until the output decreased by 3 dB was obtained in minutes. The obtained results were measured using the depth position in the film thickness direction from the magnetic surface where α is 0.5 as an index, and the value obtained for each tape sample as the horizontal axis, and the corresponding still durability and C / N measurement at 5 MHz. The values are shown on the vertical axis in FIG. 7.
The C / N is measured with a commercially available VHS video tape as a reference (0 dB).

From FIG. 7, it is found that it is practically preferable that the depth position in the film thickness direction from the magnetic surface having α of 0.5 is 50Å to 95Å.

[Brief description of drawings]

The drawings show one embodiment of the present invention. FIG. 1 is a sectional view of an essential part of an apparatus used for manufacturing a magnetic recording medium of the present invention, and FIG. 2 is an enlarged view of an essential part of the apparatus. FIG. 3 is the ESCA spectrum of the standard metallic cobalt sample, FIG. 4 is the ESCA spectrum of the standard cobalt (II) oxide sample, FIG. 5 is the X-ray diffraction spectroscopic pattern of the magnetic thin film obtained in Example 1, and FIG. FIG. 7 is a compositional analysis diagram at each depth in the film thickness direction of the magnetic thin film obtained in Example 1, and FIG. 7 is a still durability of each tape sample having α = 0.5 and different depth positions in the film thickness direction obtained in Example 1. It is a figure which shows the sex and C / N characteristics.

Claims (2)

[Claims] 1. A magnetic recording medium having a magnetic thin film on a non-magnetic substrate, wherein an oxide crystal layer containing an oxide crystal phase of a magnetic metal is formed from the surface of the magnetic thin film to its vicinity, and the thickness of the layer. In a continuous direction, a layer containing the metal and the oxide of the metal mixed is formed, and in the layer containing the metal and the metal oxide mixed, the metal and the metal are formed at each film thickness depth. The ratio α of the metal atoms forming an oxide to all the metal atoms forming an oxide decreases continuously from the surface of the magnetic thin film in the film thickness direction, and the α is 0.5 from the surface of the magnetic thin film in the film thickness direction. A magnetic recording medium having a position of 50Å to 95Å. 2. The magnetic recording medium according to claim 1, wherein the magnetic metal is Co or a Co—Ni alloy (Ni content is 30 wt% or less).