JPH0329114A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To improve magnetic characteristics by forming fine pores in an anodized aluminum film in a manner that the bottom of a fine pore is made larger in diameter than a diameter of the pore in the upper layer in the alumite film, or that a pore has fine branches in its bottom, and then filling these fine pores with magnetic metal. CONSTITUTION:The anodized aluminum film consists of a primary film and secondary film. Fine pores are formed through the secondary film to the primary film so that the pore in the secondary film is made larger in diameter than the pore in the primary film, or the pore in the secondary film has branches. These pores are filled with magnetic metal such as iron, nickel or cobalt or a combination of these. It is particularly preferable that the pores in the lower film are filled with soft magnetic metal and the pores in the upper film are filled with magnetic metal such as iron. Thereby, a two-layer magnetic film having a loop shape can be formed, which largely improves the reproduction ourput power compared to a single-layer magnetic film comprising a perpendicular magnetic film only.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to aluminum or aluminum alloy (hereinafter referred to as A
This invention relates to a two-layer magnetic recording material using an anodic oxide film (hereinafter referred to as an alumite film) obtained by anodizing (hereinafter referred to as an alumite treatment) 1).

[Prior art] Currently, hard magnetic disks, floppy magnetic disks,
Magnetic recording materials such as magnetic encoders are on the market. Conventionally, the use of an alumite film has been known as an effective method for magnetic recording materials. That is, the material is lightweight and easy to handle, the micropores present in the alumite film grow perpendicular to the base material Affl, and the bore diameter can be arbitrarily controlled from about 100 to about 2000.
It is known that the film thickness that can be filled with magnetic metal into the micropores can be made to any desired thickness up to around 100 μm, and for this reason, it is possible to create a lightweight, high recording density perpendicular magnetic anisotropic film (hereinafter referred to as magnetic alumite film). It is possible to do so. In addition, magnetic alumite coating is a technology that is attracting attention because the magnetic material filled in the micropores does not deteriorate over time and has good wear resistance. Recently, there has been a demand for higher density and higher output. For this reason, a horizontal magnetic film is provided below the vertical magnetic film to form a magnetic loop and obtain high output.
Layered magnetic coatings are being considered. However, although it is effective to actually draw a continuous magnetic loop between a vertical magnetic film and a horizontal magnetic film, it is difficult to produce.
For this reason, various structures that exhibit pseudo loops have been studied, although they are somewhat less effective. Next, an example is shown: 1) A1 foil is attached to both sides of a plate-shaped soft magnetic material containing iron, such as permalloy, and then anodized with A1 foil.
! An alumite film is formed on the I-foil, and the fine pores of the obtained alumite film are filled with magnetic metal. With this structure, the lines of magnetic force that pass through the magnetic metal in the micropores enter the soft magnetic material provided in the lower layer, bend horizontally, and return vertically through the magnetic metal in the adjacent micropores. This results in a two-layer magnetic film.

2) Coat both sides of the soft magnetic material with a metal film of titanium, tantalum, etc. that can serve as a barrier film to a thickness of about 0.5 to 5 μm, and then coat AI on top of that. Thereafter, the Jll is subjected to an alumite treatment to form micropores even in the barrier film of titanium, tantalum, etc., and the micropores are filled with a magnetic metal. [Problems to be Solved by the Invention] However, in the method 1) above, although a two-layer film with preferable productivity can be obtained, the difference between the soft magnetic material as the substrate and the lowest part of the micropores of the alumite film is Distance becomes a big issue. In other words, the distance between the bottom of the micropore and the soft magnetic material (that is, the remaining A1 foil part)
The smaller it is, the more effective it is as a two-layer film.
However, if the distance is made small, the underlying soft magnetic material will be dissolved when the alumite film is formed. This is because the soft magnetic material melts through defects such as pinholes that exist in the A1 foil, and due to variations in the thickness of the Ajl foil, the lowest part of the micropores in the alumite film may partially reach the soft magnetic material. , melting of soft magnetic materials is unavoidable. In addition, measures are taken to improve adhesion between AJ foil and soft magnetic material by pressure bonding using mature diffusion, but in this case, the mutual interface tends to become rough. Therefore, if the /Ml foil is not left evenly on the order of several μm or more (10 μm or more considering the safety factor) after the alumite film is formed, the alumite film will reach the magnetic metal layer and dissolve the soft magnetic metal. Put it away. It is difficult to uniformly control the residual thickness of A1, and if AII of this order is left, the output characteristics will decrease in inverse proportion to the square of the distance, so it will hardly be effective as a magnetic loop. There is a problem. In addition, in 2), unlike 1>, there is little concern that the soft magnetic material that is the horizontal base material will be dissolved during the formation of the alumite film, and a seemingly stable effect can be expected. However, even with this method, pinholes in the thin barrier coating of metal such as titanium and tantalum cannot be completely eliminated, and there is an unavoidable risk that the underlying soft magnetic material will melt during alumite treatment. Even if melting of the soft magnetic material could be avoided, there is a distance of 1 μm or more between the horizontal film and the vertical film, and a significant drop in output characteristics is unavoidable. Furthermore, coatings of titanium, tantalum, etc. and AJ coatings require the use of vacuum plating, which poses important problems such as poor productivity and difficulty in precisely controlling the film thickness. [Means for Solving the Problems] As a result of intensive study on the above problem, the inventor of the present invention found that by bringing the bottoms of the micropores of the alumite film close to each other, a magnetic loop is formed between adjacent micropores. , has completed the present invention.

That is, the present invention uses a shape in which the diameter of the micropores at the bottom of the alumite film is arbitrarily larger than the diameter of the micropores in the upper layer, or a shape in which the micropores are branched at the bottom of the micropores, The present invention further relates to a magnetic recording material in which the micropores are filled with a magnetic metal, and a method for manufacturing the same.

Next, the magnetic recording material of the present invention will be specifically described.

The alumite film of the present invention is formed of a primary film and a secondary film located below it, and the primary film is a conventionally known film,
In other words, it is a film with elongated micropores, and the secondary film has 1
This is a film that has micropores with enlarged pore diameters or branched micropores that are continuous with the micropores of the secondary film. Basically, the shape of the micropores in the secondary coating is completely arbitrary as long as it is larger than the diameter of the micropores in the primary coating.By choosing this shape, the bottom of the micropores (secondary coating) In this case, adjacent micropores become close to each other,
This makes it possible to create a loop-shaped two-layer magnetic coating. The structure with branches at the bottom of the micropores is also similar. The magnetic metal to be filled into the micropores may be any metal as long as it has magnetism, but iron, nickel, cobalt, etc. may be used alone or in combination.
Particularly preferably, the secondary coating is filled with a soft magnetic metal,
It is best to fill the next coating with a magnetic metal such as iron. Next, to describe the manufacturing method of the present invention, there is a first step of alumite-treating AiI to produce a primary alumite film, and a second step of alumite-treating the primary alumite film to enlarge the bottoms of the micropores. to create a second alumite film, or after the first alumite film is formed,
A branched micropore is formed at the bottom of the micropore, and a second
The second step is to prepare an alumite film, and the third step is to expand each of the micropores as necessary, adjust the barrier layer, and electrodeposit a magnetic metal into the micropores. It is characterized by First, a conventional method can be used for alumite treatment including pretreatment as the first step. For pretreatment, neutralization treatment with nitric acid is performed after degreasing, and polishing treatment, satin treatment, etc. may be added depending on the purpose.Alumite treatment baths include inorganic acid baths such as sulfuric acid, and organic acid baths such as oxalic acid. Any of acid baths, mixed acid baths thereof, alkaline baths, treatment baths containing phosphate as a main ingredient, and baths in which various additives are added to these baths may be used.

Electrolytic conditions must be suitable for each bath set. For the primary film, it is necessary to select bath electrolysis conditions with a smaller bore diameter than for the secondary film, and a film obtained by direct current electrolysis in a bath containing sulfuric acid as the main component or a bath containing oxalic acid as the main component is preferable. ．． Next, in the second step, the bottoms of the micropores obtained in the previous step are expanded to create a second alumite film. Methods for enlarging include re-anodizing, or branching the micropores after the first alumite film is formed. In the method of re-anodizing, it is necessary to perform the treatment under conditions where the pore diameter is at least larger than the micropores of the primary alumite film. For example, when the first alumite treatment is performed by direct current electrolysis in a sulfuric acid bath, the alumite treatment is performed using direct current or alternating current in an oxalic acid bath or phosphoric acid bath, or the alumite treatment is performed using alternating current in a sulfuric acid bath. , to generate a secondary alumite film. Furthermore, when the first alumite treatment is performed by direct current electrolysis in an oxalic acid bath, the alumite treatment is performed in a phosphoric acid bath using direct current or alternating current, or the alumite treatment is performed in a sulfuric acid or oxalic acid bath using alternating current. Then, a secondary alumite film is generated.

The fine pores in the secondary alumite film obtained by the above method have a larger bore diameter than the primary alumite film.

In addition, an example of a process for making the secondary alumite film into a branched structure is that immediately after the first alumite film is applied, constant voltage electrolysis is performed in the same alumite process, and then the voltage is suddenly dropped. It utilizes the so-called current recovery phenomenon, in which current stops flowing for a certain period of time, but after a certain period of time, a current that matches the voltage starts flowing. It is known that branching occurs in the micropores until the current is restored. As another example, if chromic acid or low concentration phosphoric acid is used as an electrolytic bath after the primary alumite film is formed, the film will have a branched structure unique to the acid. After creating the secondary alumite film, perform bower widening and adjustment of the barrier layer as necessary. By performing bower widening, the amount of magnetic metal precipitated can be increased, and a magnetic film with high output can be obtained.

Adjustment of the barrier layer is performed to homogenize the thickness of the barrier layer for each micropore. This has the effect of making the precipitation of magnetic metal more uniform in each micropore. Next, as a third step, a magnetic metal is electrodeposited and filled into the micropores. The material is as described above.

The magnetic metal is electrodeposited using a so-called secondary electrolytic coloring technique. At this time, the bath composition, bath temperature,
Electrolytic conditions such as current waveform and current density must be appropriately set depending on the metal.

After the third step, preferably sealing treatment and surface lapping are performed as necessary. Sealing treatment improves the corrosion resistance of the filled magnetic metal, and surface lapping removes magnetic metal that overflows from the surface of the alumite film, or places magnetic metal in the upper layer (surface) of the micropores during manufacturing. may not be densely packed, in which case surface lapping will result in
It has the effect of improving magnetic properties. Next, an example will be described. [Example] ? Example 1 From 99.99% AII with solidified magnesium, φ
30X5. ■A disk-shaped drum with the outer circumferential surface of t as the effective surface was cut, and after degreasing by immersion using a conventional method, neutralization treatment was performed with nitric acid, and a primary alumite film of approximately 30 μm was formed under the following conditions. .

Bath composition Sulfuric acid 150g/J? Metal A
J minute: 0.5g/J Processing conditions: Bath temperature: 10±1℃ DC2. Constant current electrolysis with OA/da”《approx. tgv
> After thorough washing with water, branched micropores were generated at the bottom of the micropores under the following conditions.

Bath composition Sulfuric acid 150g/41 metal A
O as J minute. '5g/! I treatment conditions Bath temperature 3
0±1℃ constant voltage electrolysis with DC 15V, and when a steady current is detected, the voltage is lowered to IOV,
When a steady current commensurate with IOV flowed, the voltage was further lowered to 5 ■, and when a steady current commensurate with 5V flowed, electrolysis was stopped. After thorough washing with water, the barrier layer was prepared using a conventional method, and Fe-12 Nokel was electrodeposited at the bottom of the micropores under the following conditions. Bath composition Nickel sulfate 50g/. R ferrous sulfate 10 g/1 boron a 40 g/II citric acid
5g/I! PH4.5 Electrolysis conditions Bath temperature 20-23℃ Commercial AC 14V Break-in time 1 minute Slow start 30 seconds Electrolysis time 30 seconds After thorough washing with water, fully fill the iron-nickel in the micropores with iron under the following conditions and filled the micropores. Bath group precepts ferrous sulfate 50 g/II
Magnesium sulfate 80g/II Boric acid 40g/II Citric acid 5g/iIP84.5 Electrolysis conditions Bath temperature 20-23℃ Commercial AC 14V Break-in time 1 minute Slow start 30 seconds Electrolysis time 60 minutes Next, #4000 alumina abrasive grains Tape attached with (
The iron overflowing onto the surface of the alumite film was completely removed by wrapping with Nippon Micro Coating's wA #4000). Comparative Example 1 The pond in which the secondary alumite film was not formed and the Nickel iron was not electrodeposited into the fine pores of the alumite film was the same as in Example 1.
It was processed in the same way. Example 2 Using the same materials as in Example 1 and performing the same pretreatment, an alumite film of 20 μm was formed under the following conditions. Bathroom precepts oxalic acid 50 g/4
1 Metal AI 1 min 0.5g/iI Electrolysis conditions Bath temperature 20±1℃ Constant current electrolysis with DC 1.5A/da2 After thorough washing with water, a 1μm film was formed as a secondary alumite film under the following conditions. Ta. After electrolysis, widening was performed for 10 minutes in the same bath. Bath set or phosphoric acid 8
0g/j! Metal AI 1 minute: 0.2g/1 Electrolytic conditions Bath temperature: 25±1°C DC 1. Constant current electrolytic widening by OA/da”
After soaking for 10 minutes and thoroughly rinsing with water, nickel-iron was electrodeposited into the secondary alumite film under the same conditions as in Example 1, except that the barrier layer was adjusted by a conventional method and the electrolysis time was changed to 1 minute. After thorough washing with water, the nickel-iron in the micropores was sufficiently filled with iron-cobalt alloy to fill the micropores under the following conditions. Bath composition Ferrous sulfate 40g/j? Cobalt sulfate 20 g/ff boric acid
15g/iI Citric acid 5g/f P84.0 Electrolysis conditions Bath full 25±1"C Commercial AC 15V Break-in time 1 minute slow start 30 seconds Electrolysis time 60 minutes After thorough washing with water, boil pure water for 30 minutes After immersion and sealing, iron overflowed onto the surface of the alumite film.
Nickel was removed in the same manner as in Example 1. Comparative Example 2 Example 2 except that the secondary alumite film was not exposed and nickel-iron was not electrodeposited into the micropores of the alumite film.
It was processed in the same way. In both Examples 1 and 2, a reproduction output 1.5 times or more was obtained compared to the comparative example. E. Effects of the invention] The two-layer magnetic film according to the invention has the following effects and is very useful industrially. l. Compared to a single-layer magnetic film consisting of only vertically anisotropic magnetic films, the reproduction output voltage is approximately 1.5 times higher. 2. Changing the structure of the micropores in the alumite film can be done reliably and easily within the same production format, so
Compared to other two-layer membranes, it is easier to produce products with stable quality. 3. A homogeneous two-layer magnetic film can be easily produced on the surface of the base material without being restricted by the surface shape of the base material. 4. By masking and processing other than the effective surface, a two-layer magnetic film can be easily obtained only on the effective surface.

Claims (1)

[Claims] 1. The micropores in the anodic oxide film of aluminum or aluminum alloy have a shape in which the diameter at the bottom of the micropores is arbitrarily larger than the diameter of the micropores in the upper layer, or A magnetic recording material in which pores have a branched shape, and the micro pores are further filled with a magnetic metal. 2. A first step of anodizing aluminum or aluminum alloy to produce a primary anodic oxide film, and then anodizing the primary anodic oxide film again to form a primary anode at the bottom of the micropores. The second step is to form micropores with a larger pore diameter than the micropore diameter of the oxide film to produce a second anodic oxide film, and after enlarging each of the micropores as necessary, the barrier layer is adjusted. A method for producing a magnetic recording material, comprising: a third step of electrolytically filling a magnetic metal; 3. A first step of anodizing aluminum or aluminum alloy to produce a primary anodic oxide film, and after the formation of the primary anodic oxide film, forming micropores with a branched structure at the bottom of the micropores. The magnetic field consists of a second step of producing a secondary anodic oxide film, and a third step of enlarging the micropores of the anodic oxide film as necessary, adjusting the barrier layer, and electrodepositing magnetic metal. Method of manufacturing recording materials.