JPH04356720A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the magnetic recording medium which maintains the good noise characteristics expected for a magnetic recording medium formed by using anodized aluminum, allows the reduction in film thickness and has a sufficient overwriting characteristic. CONSTITUTION:The porous layer of porous aluminum oxide obtd. by anodizing aluminum or aluminum alloy is etched away by a wet process and thereafter, a magnetic material 11 is plated on a barrier layer 7 which remains on the aluminum or aluminum alloy base and maintains a cell 9 shape.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to magnetic recording media. More particularly, the present invention relates to reducing media noise, improving overwrite characteristics, and improving corrosion resistance.

0002

[Prior Art] A magnetic recording medium in which ferromagnetic metal is plated into the micropores of a porous aluminum oxide (alumite) layer formed by anodizing the surface of aluminum or an aluminum alloy has excellent corrosion resistance and durability. It is a new material that has been attracting particular attention recently.

Furthermore, in a magnetic film obtained by plating and filling ferromagnetic metal into the fine pores of an alumite layer, the ferromagnetic particles filled in the fine pores are completely magnetically insulated by the alumite surrounding them. Therefore, there is no exchange interaction between particles, and no domain wall is generated. Therefore, even when magnetic recording is performed, the generation of zigzag domain walls, which is the biggest cause of medium noise, is restricted, and it is possible to form a low-noise magnetic recording medium.

0004

[Problems to be Solved by the Invention] However, the ferromagnetic metal filled into the micropores does not fill evenly to the tips of the holes;
It is known that there are variations depending on each hole. For this reason, the magnetic properties were not constant and it could not be used as a magnetic recording medium in this state.

[0005] Furthermore, in order to perform sufficient magnetic recording on such a medium and obtain good overwrite characteristics, the thickness of the magnetic layer, that is, the thickness of the alumite layer, must be 0.2 μm or less, preferably 0.1 μm or less. There is a need to.

Therefore, conventionally, the height of the magnetic layer is kept constant by forming a relatively thick alumite layer and a magnetic layer, and then polishing the alumite layer and the magnetic layer to a desired thickness using a polishing process. Efforts have been made to align the

However, it is technically very difficult to accurately polish the alumite layer, ie, the magnetic layer, down to, for example, 0.05 μm using a polishing process. The thinner the magnetic layer is, the more difficult it becomes to maintain accuracy.

[0008] Furthermore, the highly polished surface of the magnetic film has too high a smoothness, making it difficult for lubricant to adhere to it. For this reason, the lubricant is lost in a short time due to the sliding of the magnetic head, making it easy to cause a head crash.

Furthermore, alumite and ferromagnetic metal have different hardness and mechanical strength. The alumite layer has high mechanical strength, but the ferromagnetic metal layer has low mechanical strength. Therefore, when polished, the surface of the ferromagnetic metal layer becomes recessed. Therefore, a gap is created between the magnetic head and the ferromagnetic metal layer, causing spacing loss.

Therefore, an object of the present invention is to provide a magnetic recording medium that maintains the good noise characteristics expected of a magnetic recording medium using alumite, allows thinning of the film, and has sufficient overwrite characteristics. It is to be.

[0011]

[Means for Solving the Problems] In order to achieve the above object, in the present invention, a porous layer of porous aluminum oxide obtained by anodizing aluminum or an aluminum alloy is removed by wet etching, and then the aluminum Alternatively, the present invention provides a magnetic recording medium characterized in that a magnetic material is plated on a barrier layer that maintains a cell shape and remains on an aluminum alloy base metal.

[0012] It is preferable that the respective magnetic columns plated on the barrier layer that maintains the cell shape do not contact each other.

[0013]

[Operation] As a result of extensive experiments and research carried out by the present inventors over many years, aluminum or aluminum alloy was anodized to form porous aluminum oxide, and then,
When the sample is immersed in a solution that has the effect of dissolving porous aluminum oxide for a certain period of time, the porous layer of alumite is removed, and a barrier layer that maintains the cell shape remains on the aluminum or aluminum alloy base metal. After this, when plating is performed using an AC power source, the magnetic material is precipitated from near the center of the barrier layer that maintains the cell shape, and by controlling the plating conditions, each magnetic material particle does not come into contact with each other, and the magnetic particles It has been discovered that the height can be made uniform to 0.1 μm or less.

[0014] It is difficult to make the magnetic particle length uniform with ordinary alumite, but in the present invention, the alumite is immersed in an etching solution until the porous layer is removed. It is thought that the length of the plated magnetic particles becomes uniform because the barrier layer existing at the bottom of the micropores is homogenized. Although it depends on the plating conditions, according to the present invention, the height of the magnetic particles can be made uniform with an accuracy of ±50 angstroms.

[0015] Furthermore, magnetic particles can be formed by AC electrolytic plating.
Since the magnetic particles grow from near the center of the barrier layer of each cell, for example, by controlling the plating time, even if the magnetic particles grow further, it is possible to prevent the magnetic particles from coming into contact with each other.

[0016] By this method, magnetic particles are separated using alumite, and it is possible to uniformly plate a magnetic layer of 0.1 μm or less, producing a magnetic recording medium with excellent noise characteristics and overwrite characteristics. can do.

The aluminum oxide (alumite) layer can be formed directly on the aluminum substrate by anodizing the aluminum substrate, but aluminum or aluminum alloy is deposited on the non-magnetic substrate by physical vapor deposition, and this vapor deposition layer is formed on the substrate. It can also be formed by anodic oxidation. Examples of the physical vapor deposition method include a vacuum evaporation method, an ion plating method, a sputtering method, an ion beam deposition method, and a chemical vapor deposition method (CVD method).

The method of anodizing aluminum is known. Generally, anodic oxidation of aluminum is performed using direct current (DC). In DC, increasing the current density increases the electric field strength and becomes more corrosive, resulting in the starting point (
pits). The pits generated at the initial stage of electrolysis are subsequently etched to form fine holes.

The size of the cell (cell diameter, Dc) itself formed by anodizing is not an essential requirement of the present invention. Similarly, the size of the pores within the cell (pore diameter, Dp) is not an essential requirement of the present invention. As a general guide, the cell diameter can be in the range of 200-2400 Angstroms. If the cell diameter is large, the magnetic layer can be formed thick. However, if the magnetic layer thickness is made too large, the resolution will decrease. Therefore, the preferred cell diameter range is approximately 200 angstroms to 2000 angstroms.

[0020] The dissolution treatment of the alumite layer can be carried out, for example, by treating the substrate with an inorganic acid (
For example, it can be carried out by immersion in an aqueous solution of phosphoric acid. Although this acid aqueous solution is preferably used at room temperature, it can be heated to about 50° C. if necessary. The treatment time varies depending on factors such as the concentration and temperature of the acid aqueous solution and the thickness of the alumite layer, but is generally within a range of several minutes to several tens of minutes.

It has been discovered that when performing the dissolution treatment, the alumite layer is uniformly dissolved when the substrate is rotated in an acid aqueous solution at a speed of about 30 rpm to 500 rpm.

As shown in FIG. 1, as the dissolution process of the alumite layer progresses, the pores (micropores) 1 change from the initial (1)
From the state, it passes through the position of (2) and expands to (3). At this time, a part of the coating of the alumite layer remains as a triangular prism 3. If the cell diameter is Dc, the interval D between the triangular prisms is
s generally has the relationship Ds=1/√3Dc. As the melting process progresses further, the tips of the triangular prisms begin to chip away, and in the end, only the barrier layer remains. The melting process in manufacturing the magnetic recording medium according to the present invention can be carried out over a wide range from the stage where the triangular prisms remain to the stage where only the barrier layer remains.

The magnetic material plated on the barrier layer after the alumite layer is melted is preferably a Co-based metal. For example, Co alone, Co-Ni, Co-Fe-Ni, Co-Fe
These include Co alloys containing more than 50 at% of Co, such as.

[0024] The element phosphorus (P) can also be contained in the amount of 0.05 to 33 at% in these Co simple substances and Co alloys. In particular, it is preferably within the range of 2 to 10 at%. Inclusion of phosphorus can improve in-plane magnetization characteristics. Even a small amount of phosphorus is effective in improving the in-plane magnetization characteristics, but the lower limit is 0.05 at%. If the phosphorus content exceeds 33 at %, the saturation magnetization of the magnetic particles will decrease significantly, resulting in a decrease in reproduction output, which is not preferable.

A phosphorus compound soluble in the Co plating bath is used as a source of the P element added to the Co or Co alloy. As the phosphorus compound, phosphites and hypophosphites in which the valence of phosphorus is 3 or less, such as sodium phosphite (Na2 HPO3) and sodium hypophosphite (NaPH2 O2), are preferably used. can. Phosphites and hypophosphites can be used alone or in combination of two or more. P whose valence is higher than trivalence is not mixed into Fe. Therefore, even if phosphoric acid (H3 PO4) is added to the Co plating bath, it is not incorporated into the Co in the alumite micropores. In this case, the valence of P is +5, and the electron arrangement of P is the same as that of Ne. Therefore, it is thought that this is related to the fact that +5-valent P is stabilized and does not exchange electrons during plating.

The content of P element in the Co or Co alloy magnetic material can be determined by changing the plating conditions such as the plating time, applied voltage, pH, and bath temperature, as well as the concentration of the phosphorus compound added to the plating bath. can be controlled by

The thickness (height) of the magnetic layer plated on the barrier layer is not particularly limited, but is generally from 0.02 to
It is within the range of 0.2 μm, preferably within the range of 0.02 to 0.1 μm. When the thickness of the magnetic layer is less than 0.02 μm, the absolute value of the amount of magnetization of the magnetic layer is too small to be used as a magnetic recording medium. On the other hand, if the thickness exceeds 0.2 μm,
Sufficient overwrite characteristics cannot be obtained.

FIG. 2 shows a schematic cross-sectional structure of an example of the magnetic recording medium of the present invention. A barrier layer 7 is present on the top surface of the non-magnetic substrate 5. The cell 9 on the upper surface of the barrier layer has a slightly concave mortar shape, and the root portion of the triangular prism 3 shown in FIG. 1 remains on the outer peripheral edge of this mortar. The magnetic particle column 11 grows from near the center of the cell 9. In this illustrated embodiment, each magnetic particle column 11 is isolated by the triangular column 3 remaining on the barrier layer, and contact between adjacent magnetic particle columns is prevented. What is particularly important here is that the height of the magnetic particle column 11 must be higher than the height of the remaining triangular column 3. If the magnetic particle column 11 is lower than the triangular column 3, the structure will be the same as that of a conventional alumite fine hole-filled magnetic recording medium, and a polishing step will be required.

Alternatively, a magnetic recording medium as shown in FIG. 3 can be implemented. In this case, the alumite layer is dissolved and removed until the triangular prism 3 is completely removed, leaving only the barrier layer 7, and the magnetic particles 11 are grown from near the center of the cell 9. In this illustrated embodiment, the grown magnetic particles are prevented from coming into contact with each other by controlling the plating conditions. In both embodiments shown in FIGS. 2 and 3 above, the height of the magnetic particles is indicated as the distance from the lowest part of the cell 9 to the highest part of the magnetic particles.

Furthermore, in the present invention, the magnetic particles are exposed and tend to be easily corroded by moisture, oxygen, etc. in the air. For this purpose, the ferromagnetic particles in the magnetic recording medium having the structures shown in FIGS. 2 and 3 are oxidized at high temperature to artificially form a magnetic oxide layer on the surface layer of each magnetic particle. A magnetic recording medium having a structure as shown in FIG. 5 can also be used. The oxide layer on the surface of each magnetic particle serves as a protective film, greatly improving the corrosion resistance of the medium. The thickness of the oxide layer on the surface of each magnetic particle is preferably within the range of 5 to 300 Å. If the thickness is less than 5 Å, the function as a protective film is insufficient, and satisfactory effects of improving corrosion resistance and durability cannot be obtained. On the other hand, if it exceeds 300 Å, spacing loss will increase and there is a risk that sufficient recording and reproducing characteristics will not be exhibited. High-temperature oxidation only requires that an oxide layer of a predetermined thickness be formed on the surface layer of the magnetic particles, and the specific content of the treatment method itself is not particularly limited, but it is generally oxidized at 100 to 400°C in air or oxygen atmosphere. It is preferable to do so.

[0031] In addition to aluminum substrates, polyimide,
Examples include polymer films such as polyethylene terephthalate, glass, ceramics, metal plates such as anodized aluminum and brass, Si single crystal plates, and Si single crystal plates whose surfaces have been thermally oxidized.

The magnetic recording medium of the present invention includes magnetic tapes and magnetic disks based on synthetic resin films such as polyester films and polyimide films, disks and drums made of synthetic resin films, aluminum plates, glass plates, etc. It includes various forms of structures that come into sliding contact with a magnetic head, such as a magnetic disk or a magnetic drum as a base.

[0033]

[Examples] The present invention will be explained in more detail with reference to Examples below.

Example 1 A 3.5-inch size aluminum substrate was cleaned and degreased in trichloroethane, and the surface oxidized layer was coated with 5 wt% N at 50°C.
removed in aOH, then 6 vol% HN at 20 °C.
Neutralized in O3. After this pretreatment is completed, 18℃
, in a 1 mol/liter H2SO4 bath, 17.5
Constant voltage electrolysis was carried out at V to form a porous alumite layer with a thickness of 0.5 μm. Thereafter, this substrate was immersed in a 1 wt % phosphoric acid bath at 30° C., and constant current electrolysis at 0.04 A/dm 2 was performed for 1 minute while rotating at a rotation speed of 60 rpm. Thereafter, the substrate was immersed in the bath for 18 minutes while rotating at a rotation speed of 60 rpm, and further, constant voltage electrolysis was performed at 8 V for 2 minutes while rotating at the same speed. As a result of observing this sample with a scanning electron microscope (SEM),
The porous alumite layer was removed, and only the barrier layer at the bottom of the micropores remained while maintaining the cell shape. This sample was mixed with CoSO4: 0.2 mol/liter, H3 BO
4: 0.2 mol/liter, glycerin: 2 ml/liter, NaPH2 O2: 0.03 mol/liter
Transfer to a plating bath containing liters, AC 500Hz, 1
Plating was performed for 5 minutes using a 6Vp-p power source. A part of this sample was cut out, bent, and the cross section was SEM
I observed it. As a result, the cross section has a structure as shown in Figure 1, in which the magnetic particles are not in contact with each other, and
Its height was uniform at 0.065 μm.

Example 2 The sample obtained in Example 1 was subjected to high-temperature oxidation treatment at 200° C. for 5 minutes in the air. The oxide layer formed on the surface layer of the ferromagnetic particles of this sample was examined by Auger analysis, and as a result, the film thickness was 100 Å.

The samples obtained in Examples 1 and 2 were cut into 1 cm x 1 cm pieces, and the deterioration rate of saturation magnetization was examined in an environment of 60° C. and 90% RH. The results are shown in FIG. As is clear from this figure, the sample with an artificial oxide layer formed on the surface layer of the magnetic particles through high-temperature oxidation treatment has a higher rate of deterioration of saturation magnetization over the test time than the sample without an oxide layer. It can be seen that the corrosion resistance is improved.

[0037]

As explained above, in the magnetic recording medium of the present invention, the magnetic material is plated on the barrier layer that maintains the cell shape and remains after the porous alumite layer is removed.
The height of the magnetic layer formed becomes approximately constant. This eliminates the need for a conventional polishing process. Furthermore, since the height of the magnetic layer is constant and the magnetic particles are not in contact with each other, the magnetic properties and electromagnetic conversion properties are significantly improved. In particular, according to the present invention, a magnetic recording medium with excellent noise characteristics and overwrite characteristics can be manufactured.

Furthermore, since the magnetic recording medium of the present invention has gaps between the magnetic particles, a large amount of liquid lubricant can be stored in the gaps. As a result, the lubrication performance does not deteriorate even after long-term use, and a magnetic recording medium with excellent durability can be obtained.

Furthermore, when an oxide layer is artificially formed on the surface layer of the magnetic particles by high-temperature oxidation, the surface oxide film acts as a protective layer, and corrosion resistance can be improved.

[Brief explanation of the drawing]

FIG. 1 is a plan view illustrating the progress of dissolving an alumite layer.

FIG. 2 is a schematic cross-sectional view of an example of the magnetic recording medium of the present invention.

FIG. 3 is a schematic cross-sectional view of another example of the magnetic recording medium of the present invention.

FIG. 4 is a schematic cross-sectional view of the magnetic recording medium of FIG. 2 in which an oxide layer is formed on the surface layer of the magnetic particles.

FIG. 5 is a schematic cross-sectional view of the magnetic recording medium of FIG. 3 in which an oxide layer is formed on the surface layer of the magnetic particles.

FIG. 6 is a characteristic diagram showing the corrosion resistance of samples obtained in Example 1 and Example 2.

[Explanation of symbols] 1 Pore 3 Triangular prism 5 Non-magnetic substrate 7 Barrier layer 9 Cell 11 Magnetic particles 12 Oxide layer

Claims (11)

[Claims] Claim 1: A barrier layer that retains the cell shape and remains on the aluminum or aluminum alloy base metal after a porous layer of porous aluminum oxide obtained by anodizing aluminum or an aluminum alloy is removed by wet etching. A magnetic recording medium characterized by having a magnetic material plated on top. 2. The magnetic recording medium according to claim 1, wherein the magnetic materials plated on the barrier layer that maintains the cell shape do not contact each other. [Claim 3] The magnetic material to be plated contains 50 at% Co.
The magnetic recording medium according to claim 1 or 2, characterized in that the magnetic recording medium contains a large amount. 4. The magnetic material contains 0.05 to 33 at% phosphorus.
4. The magnetic recording medium according to claim 3, further comprising a magnetic recording medium. 5. Claims 1 to 4, wherein the thickness of the magnetic layer plated on the barrier layer is within the range of 0.02 to 0.2 μm.
Any magnetic recording medium. 6. A barrier layer that retains the cell shape and remains on the aluminum or aluminum alloy base metal after a porous layer of porous aluminum oxide obtained by anodizing aluminum or an aluminum alloy is removed by wet etching. 1. A magnetic recording medium, characterized in that a magnetic material is plated thereon, and the surface layer of the magnetic material is covered with an oxide layer of the magnetic material. 7. The magnetic recording medium according to claim 6, wherein the thickness of the oxide layer is within the range of 5 to 300 Å. 8. The magnetic recording medium according to claim 6, wherein the magnetic materials plated on the barrier layer that maintains the cell shape do not contact each other. [Claim 9] The magnetic material to be plated contains 50 at% Co.
7. The magnetic recording medium according to claim 6, wherein the magnetic recording medium contains a large amount of 10. The magnetic material contains phosphorus at 0.05 to 33 at.
10. The magnetic recording medium according to claim 9, further comprising %. 11. The magnetic recording medium of claim 6, wherein the thickness of the magnetic layer plated on the barrier layer is within the range of 0.02 to 0.2 μm.