JPH04232612A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the running property and durability of a magnetic recording medium by forming alumite by anodically oxidizing the and controlling the pore expanding process of the alumite. CONSTITUTION:An alumite layer composed of a porous layer 3 and a barrier layer 7 is formed by anodically oxidizing an aluminum substrate 5. The pore expansion of the alumite layer is stopped at a limit point at which the layer 3 can remain and the expanded pores are filled with a Co-based metal by plating. As a result, magnetic particle pillars 11 grow beyond the layer 3 from the vicinity of the center of a cell 9 and adjacent pillars come into contact and are coupled with each other in the upper section. The heights d1 and d2 of the layer 3 and pillars 11 are set so that the heights can satisfy a relation d2>=d1. In addition, gaps 13 are formed between pillars 11 and filled with a filler. As a result, the drying up of a lubricant in a short time due to the smoothness of the surface of a medium can be prevented and the surface can be coated with sufficient adhesion when the lubricant is applied to the entire surface of the medium. Therefore, the durability and running property of the magnetic recording medium can be improved for a long period.

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 specifically, the present invention relates to a magnetic recording medium with improved running performance and durability.

0002

2. Description of the Related Art Co alloy continuous thin films are used as high-density recording media. However, in such continuous thin film media, the surface smoothness of the magnetic layer is too high, so the lubricant applied to the surface of the magnetic layer is easily depleted within a short time due to the sliding of the magnetic head, making it difficult to run. It is known to have poor performance and durability.

[0003] 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. , is a new material that has been attracting particular attention recently.

[0004] Furthermore, in a magnetic film obtained by plating and filling the micropores of a porous layer with ferromagnetic metal, the ferromagnetic particles filled in the micropores 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.

[0005]

[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.

Therefore, conventionally, a relatively thick porous layer and a magnetic layer are formed, and then a polishing process is performed to polish the porous layer and the magnetic layer to a desired thickness.
It has been practiced to make the height of the magnetic layer constant.

However, it is technically very difficult to accurately polish the porous 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 porous 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 expose the magnetic particles in the alumite magnetic film to the surface of the medium without using a polishing or etching process, thereby achieving low spacing loss and excellent durability and runnability. An object of the present invention is to provide an alumite magnetic recording medium.

[0011]

[Means for Solving the Problems] In order to achieve the above object, in the present invention, the pores of porous alumite obtained by anodizing aluminum or aluminum alloy are expanded and filled with a ferromagnetic material by plating. In the magnetic recording medium, the thickness of the porous layer (d1) and the length of the long axis of the filled magnetic particles (d2) satisfy the relationship d2 ≧ d1, and the upper part of the magnetic particle in each hole is Provided is a magnetic recording medium characterized in that the upper portions of magnetic particles in each hole are in contact with each other.

0012

[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 (alumite), and then the fine pores of the alumite were enlarged. By controlling the process, the magnetic particles filled with plating later protrude from the alumite porous layer, and the protruding magnetic particles come into contact with each other so that the magnetic particles protruding from adjacent holes connect with each other, improving runnability and durability. It was discovered that a magnetic recording medium with excellent properties can be obtained.

The porous aluminum oxide (alumite) layer can be formed directly on the aluminum substrate by anodizing the aluminum substrate, but aluminum or an aluminum alloy is deposited on the non-magnetic substrate by physical vapor deposition. It can also be formed by anodizing the layer. Physical vapor deposition methods include vacuum evaporation, ion plating, sputtering, ion beam deposition, and chemical vapor deposition (CVD).
and so on.

[0014] Aluminum anodic oxidation methods are 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 pores.

The size (cell diameter, Dc) of the cell formed by anodizing treatment itself 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.

The pore enlargement treatment (that is, the dissolution treatment of the porous layer) can be carried out, for example, by immersing the substrate in an aqueous solution of an inorganic acid (for example, phosphoric acid) with a concentration within the range of about 1 wt% to 10 wt%. Can be implemented. 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 porous layer, but is generally within a range of several minutes to several tens of minutes.

When carrying out pore enlargement treatment (that is, dissolution treatment of the porous layer), the substrate is heated in an acid aqueous solution at about 30 rpm to 5.0 rpm.
It was discovered that rotating at a speed of 0.00 rpm uniformly dissolves the porous layer.

As shown in FIG. 1, as the dissolution process of the porous layer progresses, the pores (micropores) 1 change from the initial state (1) to the position (2) and then to (3). Expanding. At this time, a portion of the coating of the porous layer remains as a triangular prism 3. When the cell diameter is Dc, the interval Ds between the triangular prisms generally has a relationship of 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 before the triangular prisms are formed to the stage where only the barrier layer remains.

The magnetic material to be plated and filled after dissolving the porous layer is preferably a Co-based metal. For example, Co alone or C
o-Ni, Co-Fe-Ni, Co-Fe, Co-Fe
-Co alloys containing more than 50 at% of Co, such as -W.

[0020] 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 Co. 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 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

[0023] For these Co simple substances and Co alloys, tungsten (W) element is added in an amount of 0.05 at% to 50 at%.
It can also be contained in an amount of t%. W element content is 50a
If it exceeds t%, the saturation magnetization will be significantly reduced, leading to a decrease in reproduction output, which is not preferable. The lower limit of the content is not particularly limited because even a small amount of W element is effective in forming an in-plane magnetized film, but a general index is 0.0
It is 5 at% or more.

A tungsten compound soluble in the Co plating bath is used as a source of W element added to Co or Co alloy. As a tungsten compound, K
2WO4, Na2WO4, etc. can be suitably used.

An example of the basic structure of the magnetic recording medium of the present invention is shown in FIG. When the aluminum substrate 5 is anodized, an alumite layer is generated, and the alumite layer includes a porous layer (triangular prisms 3) and a barrier layer 7. This barrier layer is not dissolved even by the solution for dissolving the alumite layer. The pore expansion of the porous layer, that is, the dissolution treatment of the porous layer is performed, and the process is stopped at the limit point where the triangular prism 3 remains. Thereafter, Co-based metal is plated and filled into each enlarged hole. The cells 9 on the upper surface of the barrier layer have a slightly concave mortar shape, and the magnetic particle columns 11
grows from near the center of cell 9. The magnetic particle columns 11 grow beyond the triangular columns 3 of the porous layer, and adjacent particle columns come into contact with each other at their upper portions, forming a connected state.

As shown in FIG. 2, the remaining porous layer (
When the height of the triangular prism 3) is d1 and the height of each magnetic particle column filled with plating is d2, the relationship d2≧d1 is satisfied. Although not particularly limited, the height d2 of the magnetic particle column filled with plating is generally 500 to 10
Preferably, it is within the range of 0,000 angstroms. If the height d2 of the magnetic grain columns is less than 500 angstroms, the absolute value of the magnetization amount of the magnetic layer is too small to be used as a magnetic recording medium. On the other hand, if d2 exceeds 10,000 angstroms, sufficient overwrite characteristics cannot be obtained. In addition, the height of the porous layer can be controlled by pore enlarging treatment, but in general, the height of the porous layer is 0.
It is preferably within the range of ~10,000 angstroms.

As an alternative method, as shown in FIG. 3, the porous layer is dissolved and removed until the triangular prisms are completely eliminated, and magnetic particle columns 11 are grown from near the center of the cells 9 of the barrier layer 7. Magnetic recording media in contact with each other are also possible.

As shown in FIGS. 2 and 3, gaps 13 are generated between each magnetic particle column. Therefore, when the lubricant is filled, the filler is stored in this gap. As a result, as shown in FIG. 4, when the lubricant 15 is applied to the entire surface of the medium, short-term depletion of the lubricant due to the smoothness of the surface is prevented compared to conventional electroless plating or sputtering magnetic films. It can be coated with sufficient adhesion. In this way, a magnetic recording medium having excellent durability and running properties over a long period of time can be obtained.

When the magnetic particle columns are connected to each other, zigzag domain walls are generated, which increases the noise level. For this reason,
After completing the plating filling, the medium is heated in an oxidizing atmosphere for approximately 100%
It is preferable to perform a short heat treatment at a temperature of .degree. C. to 350.degree. C. to form an oxide layer on the outer surface of the magnetic particle columns. A schematic cross-sectional structure of such a medium is shown in FIG. As shown in the figure, the outer surface of each magnetic particle column 11 is coated with an oxide coating 17.
As a result, each magnetic particle is magnetically separated, making it difficult for complex zigzag domains to occur in the magnetization transition region, and reducing noise during reproduction.

In addition to the aluminum substrate, the nonmagnetic substrate used in the magnetic recording medium of the present invention includes 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.

Further, 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.

[0032]

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

Example 1 A 3.5-inch size aluminum disk substrate (outer diameter 95 mm; inner diameter 25 mm; plate thickness 1.27 mm) with a purity of 99.99% was degreased by ultrasonic cleaning in trichlorethylene to remove the surface oxidation layer. was removed in 5 wt% NaOH at 50°C, then neutralized in 6 vol% HNO3 at 20°C, and washed with water. After this pretreatment was completed, the temperature was 18°C.
A porous layer having a thickness of 0.45 μm was formed by constant voltage electrolysis at 17.5 V in a 1 mol/liter H 2 SO 4 bath. Thereafter, this substrate was immersed in a 1 wt % phosphoric acid bath at 30° C. for 18 minutes to enlarge the pores. This sample was
SO4: 0.2 mol/liter, H3 BO4: 0
．． Transferred to a plating bath containing 2 mol/liter, glycerin: 2 ml/liter, and NaPH2O2: 0.03 mol/liter, and heated at AC 500 Hz, 16 Vp-
Using a p power supply, -9V on the alumite side and +7 on the opposite electrode.
A DC bias was applied so that the voltage was V, and Co--P plating was performed at 20° C. for 10 minutes. The disc after plating is
The thickness of the porous layer on the barrier layer is 1200 angstroms, the thickness of the magnetic layer is 2200 angstroms, the diameter at the bottom of the magnetic particles is 380 angstroms, the maximum diameter at the top of the magnetic particles is 450 angstroms, and each magnetic particle is They touched each other at the top.

Example 2 A porous layer having a thickness of 0.45 μm was formed in the same manner as in Example 1, and then pore enlargement treatment was performed for 21 minutes at 30° C. in 1 wt % H3 PO4. After this, CoNiFe-W
Plating was performed in the following manner. The plating bath is CoSO4
・7H2O: 0.085 mol/liter, NiSO
4 ・6H2 O: 0.036 mol/liter, FeS
O4 (NH4)2 SO4 ・6H2 O:0.0
07 mol/liter, H3 BO4: 0.2 mol/liter, glycerin: 2 ml/liter, K2
WO4: It had a composition of 0.004 mol/liter. The power supply used for plating was AC500Hz, 2
5Vp-p, -15V on the alumite side, +1 on the opposite electrode
Apply DC bias so that it becomes 0V, and 10V at 20℃.
Plating was performed for minutes. After plating, the disk has a porous layer on the barrier layer with a thickness of 1200 angstroms, a magnetic layer with a thickness of 1900 angstroms, a diameter at the bottom of the magnetic grains of 370 angstroms, and a maximum diameter at the top of the magnetic grains of 455 angstroms. , and each magnetic particle was in contact with each other at the top.

Comparative Example 1 A 3.5-inch size aluminum disk substrate (outer diameter 95 mm; inner diameter 25 mm; plate thickness 1.27 mm) with a purity of 99.99% was degreased by ultrasonic cleaning in trichlorethylene to remove the surface oxidation layer. was removed in 5 wt% NaOH at 50°C, then neutralized in 6 vol% HNO3 at 20°C, and washed with water. After this pretreatment is completed, a zincate treatment is performed using a ZnO-containing bath, and the magnetic layer is coated with 2000 plating using a commonly known Co-P electroless plating bath.
Angstrom was set.

Each disk obtained in Examples 1 and 2 and Comparative Example 1 was coated with a fluorine-based lubricant, and the durability of each medium was evaluated by a steel ball reciprocating sliding test. The load of the slider steel ball was changed to 5g, 7g, and 9g,
The sliding movement was performed at an average sliding speed of 2 m/min, and the number of reciprocating sliding movements until scratches appeared on the medium surface was determined. The results are shown in Table 1 below.

[0037]

[Table 1] Table 1

As is clear from the results shown in Table 1, the magnetic recording medium of the present invention has the following advantages compared to the magnetic recording medium of the comparative example.
Durability has been dramatically improved.

Example 3 A 3.5-inch size aluminum disk substrate (outer diameter 95 mm; inner diameter 25 mm; plate thickness 1.27 mm) with a purity of 99.99% was degreased by ultrasonic cleaning in trichlorethylene to remove the surface oxidation layer. was removed in 5 wt% NaOH at 50°C, then neutralized in 6 vol% HNO3 at 20°C, and washed with water. After this pretreatment was completed, the temperature was 18°C.
A porous layer having a thickness of 0.45 μm was formed by constant voltage electrolysis at 17.5 V in a 1 mol/liter H 2 SO 4 bath. Thereafter, this substrate was immersed in a 1 wt % phosphoric acid bath at 30° C. for 18 minutes to enlarge the pores. This sample was
SO4: 0.2 mol/liter, H3 BO4: 0
．． Transferred to a plating bath containing 2 mol/liter, glycerin: 2 ml/liter, and NaPH2O2: 0.03 mol/liter, and heated at AC 500 Hz, 16 Vp-
Using a p power supply, -9V on the alumite side and +7 on the opposite electrode.
A DC bias was applied so that the voltage was V, and Co--P plating was performed at 20° C. for 10 minutes. The disc after plating is
The thickness of the porous layer on the barrier layer is 1200 angstroms, the thickness of the magnetic layer is 2200 angstroms, the diameter at the bottom of the magnetic particles is 380 angstroms, the maximum diameter at the top of the magnetic particles is 450 angstroms, and each magnetic particle is They touched each other at the top. Next, this medium was oxidized at a high temperature of 250° C. for 20 seconds in the air to form an oxide film on the surface of the magnetic particles.

Comparative Example 2 An alumite magnetic film was produced under the same conditions as Example 3,
No high temperature oxidation treatment was performed.

Example 4 A porous layer having a thickness of 0.45 μm was formed in the same manner as in Example 3, and then pore enlargement treatment was performed for 21 minutes at 30° C. in 1 wt % H3 PO4. After this, CoNiFe-W
Plating was performed in the following manner. The plating bath is CoSO4
・7H2O: 0.085 mol/liter, NiSO
4 ・6H2 O: 0.036 mol/liter, FeS
O4 (NH4)2 SO4 ・6H2 O:0.0
07 mol/liter, H3 BO4: 0.2 mol/liter, glycerin: 2 ml/liter, K2
WO4: It had a composition of 0.004 mol/liter. The power supply used for plating was AC500Hz, 2
5Vp-p, -15V on the alumite side, +1 on the opposite electrode
Apply DC bias so that it becomes 0V, and 10V at 20℃.
Plating was performed for minutes. After plating, the disk has a porous layer on the barrier layer with a thickness of 1200 angstroms, a magnetic layer with a thickness of 1900 angstroms, a diameter at the bottom of the magnetic grains of 370 angstroms, and a maximum diameter at the top of the magnetic grains of 455 angstroms. , and each magnetic particle was in contact with each other at the top. Next, this medium is placed in the atmosphere for 2
High temperature oxidation was performed at 50° C. for 20 seconds to form an oxide film on the surface of the magnetic particles.

Comparative Example 3 An alumite magnetic film was produced under the same conditions as in Example 4,
No high temperature oxidation treatment was performed.

Examples 3 and 4 and Comparative Examples 2 and 3
The S/N ratio of each medium obtained at a recording density of 42 kfci
Measurements were made by setting the current to the point where the output was maximum. The results are shown in Table 2 below.

[0044]

[Table 2] Table 2

As is clear from the results shown in Table 2,
The magnetic recording medium of the present invention in which the outer surface of magnetic particles is covered with an oxide film has a higher S/N ratio than a medium without an oxide film, and is superior as a magnetic recording medium.

[0046]

[Effects of the Invention] As explained above, according to the present invention,
Aluminum or aluminum alloy is anodized to form porous aluminum oxide (alumite), and then by controlling the micropore expansion process of the porous layer, the magnetic particles filled with plating later form porous alumite. By protruding from the layer and bringing the protruding magnetic particles into contact with each other so as to connect the protruding magnetic particles protruding from adjacent holes, a magnetic recording medium with excellent running properties and durability can be obtained.

Furthermore, by coating the outer surface of the magnetic particles of the medium with an oxide film, an excellent magnetic recording medium with a high S/N ratio can be obtained.

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, it is possible to obtain a magnetic recording medium with excellent durability and runnability without deterioration in lubricating performance even after long-term use.

[0049]

[Brief explanation of the drawing]

FIG. 1 is a plan view illustrating the progress of dissolution treatment of a porous 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 an example of the magnetic recording medium of the present invention filled and coated with a lubricant.

FIG. 5 is a schematic cross-sectional view of an example of the magnetic recording medium of the present invention in which the surface layer of magnetic particles is covered with a nonmagnetic oxide film.

[Explanation of symbols]

1...Pore 3...Triangular prism 5...Nonmagnetic substrate 7...Barrier layer 9...Cell 11...Magnetic particles 13...Void 15...Lubricant 17...Nonmagnetic oxide film

Claims (3)

[Claims] Claim 1: In a magnetic recording medium in which the pores of porous alumite obtained by anodizing aluminum or aluminum alloy are expanded and filled with a ferromagnetic material by plating, the thickness (d1) of the porous layer and The length (d2) of the long axis of the filled magnetic particles satisfies the relationship d2 ≧d1, and the upper part of the magnetic particle in each hole is in contact with the upper part of the magnetic particle in each adjacent hole. magnetic recording media. 2. In a magnetic recording medium in which the pores of porous alumite obtained by anodizing aluminum or aluminum alloy are expanded and filled with a ferromagnetic material by plating, the thickness (d1) of the porous layer and The length (d2) of the long axis of the filled magnetic particles satisfies the relationship d2≧d1, the top of the magnetic particle in each hole is in contact with the top of the magnetic particle in each adjacent hole, and further, A magnetic recording medium characterized in that the surface layer of each magnetic particle column is covered with a nonmagnetic oxide film. 3. The magnetic recording medium according to claim 1, wherein the length (d2) of the long axis of the magnetic particle columns is within the range of 500 to 10,000 angstroms.