JPH025836B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention applies anodizing treatment to aluminum or aluminum alloy material, immerses the fine pores of the produced anodized film in an acid or alkaline bath to chemically dissolve a part of the film, and enlarges the pore diameter. The present invention relates to a method of manufacturing a material for high-density magnetic recording by filling the material with a magnetic metal and then physically grinding, polishing, etc. the surface of the material. Aluminum or aluminum alloy material (hereinafter referred to as aluminum material) is anodized, and the countless pores formed in the resulting anodic oxide film are filled with magnetic metal using various methods to form a magnetic film. It is already known to produce magnetic recording materials and use them as magnetic recording materials. A remarkable feature of the magnetic recording material made by this method is that the magnetic material is contained in pores perpendicular to the surface of the anodic oxide film, resulting in the so-called "perpendicular magnetization characteristic."
This means that the recording density can be dramatically increased compared to a conventional horizontal magnetization type magnetic recording material in which a general magnetic material is coated on the substrate surface. However, when a magnetic film obtained by filling the pores of such an anodized film with a magnetic material is used as a magnetic recording material, it is difficult to physically grind and polish the surface of the formed anodic oxide film. The surface must be sufficiently smooth, and the film thickness after polishing must be at least 2 μm in order to avoid damage caused by the head and to obtain sufficient magnetization characteristics, regardless of whether the magnetic head is used as a contact or floating type. It is desirable that the magnetization characteristics be able to take an appropriate value depending on the type of head, and that the characteristics be as uniform as possible over the entire surface of the material. However, in the anodic oxide film obtained under conventional anodizing treatment conditions, the pore diameter is small, so the coercive force (Hc) is too high, making recording and reproducing impossible. However, there were problems in that the magnetic properties as a magnetic recording material were not appropriate, such as the output being too small. It is known that the pore size in this anodic oxide film varies greatly depending on the type of electrolytic bath used during treatment. For example, when a sulfuric acid bath, which is the most common treatment bath, The pore diameter of the coating film is 100 to 200 Å, whereas in the case of a phosphoric acid bath, it is approximately 500 to 1000 Å. The film formed by this bath tends to be brittle, and a film with a thickness of about 2 μm at most can only be obtained. On the other hand, the anodic oxide film obtained by electrolytic treatment using sulfuric acid, oxalic acid, sulfosalicylic acid, or a bath mainly composed of these acids has a strong film quality and a film of sufficient thickness, but the pores are small. Since the pore size of the pore size was small, it was necessary to expand the pore size through secondary treatment. Therefore, as proposed by the present inventors in Japanese Patent Application No. 103978/1983, an aluminum material that has been anodized using a general treatment bath is placed in an acid or alkaline bath as a method for enlarging the pores of an anodized film. When a part of the film, that is, the pore wall, is chemically dissolved by dipping in The patent application was filed after discovering that when a pore enlargement method using chemical dissolution is employed, the pore diameter can be controlled relatively freely by appropriately controlling the dissolution conditions. However, when a magnetic metal is precipitated into the enlarged pores as described above to produce a magnetic recording medium, the amount of precipitated magnetic metal is often microscopically non-uniform, and therefore it is not used as a high-density magnetic recording medium. A microscopically uniform metal filling is required since the output may be non-uniform and cause errors. Therefore, the present inventors conducted more detailed studies and overcame the above problems. That is, in the present invention, when obtaining an aluminum material for high-density magnetic recording by filling the pores of an anodized film obtained by anodizing an aluminum material with a magnetic metal, the aluminum material is first coated with a thickness of 4 μm or more. After forming an anodic oxide film, this is immersed in an acid or alkali bath to chemically dissolve a portion of the anodic oxide film to form pores in the range of 300 Å to 1400 Å. After enlarging the pores to a diameter of The magnetic metal is exposed on the surface of the anodic oxide film. Next, the method of the present invention will be explained in more detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing the steps of the method of the present invention. The aluminum material 1 used in the present invention is not particularly limited in type, but may be made of a material that is often coated with an anodic oxide film, such as pure aluminum, 5
Series, 6 series, etc. are preferred. As the electrolytic bath for anodizing treatment, a bath mainly containing sulfuric acid, oxalic acid, chromic acid, or these acids, or a bath containing an organic acid such as sulfosalcylic acid to which an inorganic acid is added can be used. It is also possible to use an alkaline bath containing etc. as the main ingredients. The composition and bath temperature of these baths are selected appropriately, and 0.1~
Anodizing is performed at a current density of 2.0 A/dm ² and a voltage of 5 to 20 V, which facilitates the precipitation and filling of magnetic metal in the next process, and also allows for grinding and polishing in relation to the aluminum material, as described later. The anodic oxide film 4 consisting of the porous layer 2 and the barrier layer 3 is formed to have a thickness of 4 μm or more so that the film thickness can be maintained at least about 2 μm or more later. The state after chemical dissolution is shown in Figure 1A. Note that with a film thickness of about 4 μm or less, it is difficult for the magnetic metal to precipitate locally and uniformly. In other words, if the magnetic metal comes out on the surface of the film 4 in one part, the current will concentrate there and cause precipitation in other parts. This results in a problem that the magnetic metal is not filled sufficiently above the pores 5. Next, as shown in FIG. 1B, the walls of the pores 5 after the anodizing treatment are chemically dissolved to enlarge the pore diameter. Since the pore diameter affects the coercive force, by strictly performing this process, it becomes possible to quantitatively control the coercive force. The bath used for this chemical dissolution is an acid bath containing phosphoric acid, chromic acid, sulfuric acid, oxalic acid, or two or more of these, or a dilute solution of caustic soda, caustic potash, or trisodium phosphate solution. An alkaline bath such as the above is preferably used, and the temperature is usually room temperature to about 50°C.
If the temperature or acid or alkali concentration is high, the dissolution is too fast and the pore diameter tends to become non-uniform, which may cause the film 4 to deteriorate more than necessary. The dissolution time is 5 to 30 minutes, preferably 10 to 30 minutes, depending on the desired pore size for anodizing.
It is easier to control if you keep it within 20 minutes. By doing so, the pore diameter can be adjusted to 300 to 1400 Å, preferably 400 to 1400 Å.
Make it 1000Å. Note that when the pores 5 are enlarged with acid or alkali, the thickness of the barrier layer 3 at the bottom of the pores becomes uneven due to the chemical dissolution treatment, and if this continues, the magnetic metal will not be deposited uniformly. can't get it. Therefore, it is preferable to perform a treatment for adjusting the barrier layer. The energization treatment for this purpose can be performed in the bath used for the chemical dissolution treatment. At this time, if the voltage is too high, the barrier layer 3 will become too thick, making it difficult for the next magnetic metal to be deposited.If the voltage is too low, the barrier layer 3 will become too thin, and the film will not be formed during the magnetic metal deposition process. For direct current, 5 to 25V, preferably
Approximately 10 to 20V is good, and for AC, 6 to 20V,
Preferably it is about 10 to 17V. Note that it usually takes 3 to 10 minutes for the current to stabilize.
In this way, a barrier layer with a uniform thickness of 100 to 400 Å can be obtained. Next, the aluminum material whose pores have been enlarged or whose barrier layer has been adjusted as described above,
Water-soluble salts containing magnetic metal ions such as Fe, Co, Ni, etc., including sulfates, sulfamates, etc.
Furthermore, in order to facilitate electrolytic deposition, it is immersed in a bath containing a supporting electrolyte such as magnesium sulfate that is not electrolyzed, and a direct current (aluminum material is used as the cathode) is connected to an insoluble counter electrode such as graphite or stainless steel. ), a magnetic metal is deposited and filled into the pores through alternating current or a superimposed current. At that time, in the case of direct current, the current density is 0.05 to 1.5A/
In the case of _dm2 , alternating current, 10-20V is preferred. However, as schematically shown in FIG. 1C, the magnetic metal deposited in the pores has a different filling amount because the height l of the filled magnetic metal 6 differs even between adjacent pores 5. , which causes the magnetization properties of individual filled metal columns to be different. Therefore, in the present invention, in order to avoid the above-mentioned tendency, as shown in FIG.
physically remove the surface. The amount to be removed is the minimum height l min of the filled magnetic metal column l, or about 10% less than that, and the height of the metal column after this deletion is defined as l ₂ . Also, l ₂ is the thickness of porous layer 2, which is 50~
Since the amount of porous layer 2 is about 80%, it is desirable to remove 40 to 60% of the porous layer 2 from its surface, so that the entire upper surface of the filled magnetic metal is exposed to the surface of the anodic oxide film. As a result, the heights of the magnetic metal columns are almost constant, so the magnetization characteristics of the individual magnetic metals are almost uniform, and the time axis of the reproduction output of the AC signal recorded on the envelope-magnetic recording medium is shortened. The band-shaped reproduced output figure obtained by recording on a chart also becomes good, and high density is achieved. That is, the envelope is shown in Fig. 2, and the one in which the surface of the anodic oxide film is shaved after filling with magnetic metal as in the present invention is good as shown in Fig. 2 (b), whereas the envelope is as shown in Fig. 2 (a). If the surface of the film is not scraped, the magnetic properties of the medium may be uneven,
Also, the distance between the medium and the head is not uniform, and the envelope is poor. As described above, according to the present invention, a magnetic metal column is placed in each pore of an anodic oxide film of uniform thickness applied to the surface of an aluminum material at the same height as the depth of the pore, and the magnetic metal column is In either case, it is possible to obtain magnetic recording material filled with approximately the same height. At that time, depending on the filling magnetic metal, for example,
In the case of Fe, if the diameter of the magnetic metal column is D and the height is l ₂ (assuming it is a cylinder), if l ₂ /D>10, it exhibits perpendicular magnetization characteristics, and in the case of Co, l ₂ /D＞20
The same applies if so. However, if D is made smaller in order to improve the perpendicular magnetization characteristic, the coercive force becomes too large, resulting in problems such as the need for a powerful magnetic head. Note that the present invention does not necessarily aim at perpendicular magnetization characteristics, but can also utilize horizontal magnetization characteristics for metals that do not exhibit perpendicular magnetization characteristics when l ₂ /D > 10, and can be applied to metals that do not exhibit perpendicular magnetization characteristics using conventional methods such as coating methods. Sufficiently high density can be achieved compared to horizontal magnetization. The magnetic film obtained above can be finished by washing with water and drying, but as an anti-corrosion treatment, it can be sealed with hot water using a conventional method, or by dry surface treatment, such as sputtering with silicon oxide, to give the surface a very strong surface. A thin protective coating may also be applied. Examples of the present invention will be described below. Example 1 JIS A5086 aluminum donut plate (5
1/4 inch diameter, 2 mm thickness) was processed under the following conditions, the static magnetization characteristics were determined using a vibrating magnetization measuring device, and the envelope of the playback output was determined, and the results shown in Table 1 were obtained. . However, the barrier layer was prepared in a chemical dissolution treatment bath, and the magnetic metal was deposited and filled in a bath containing 120 g of ferrous sulfate, 70 g of magnesium sulfate, and 20 g of citric acid at a bath temperature of 30°C. Electricity was applied at 60 Hz, 15 V AC for 15 minutes using graphite as the counter electrode. After filling with magnetic metal, the anodized film is polished using a buffing polisher for 15 minutes using high-purity (99.99%) alumina abrasive grains (particle size 1 μm) to achieve an average surface roughness Rmax.
=0.04μm was obtained. For comparison, if physical deletion is not performed (No.
4) and without chemical dissolution treatment (No.
The measured values of 5) are also listed in Table 1. As can be seen from the table, unless physical polishing or grinding is performed, the dynamic magnetization characteristics will vary and the material cannot be used as a magnetic recording material.

【table】

[Table] Example 2 Example 1 (No.
After performing anodization treatment and chemical dissolution treatment under the same conditions as in 1), Co and Ni were precipitated and filled into the pores. At that time, the precipitation filling was 30g of cobalt sulfate/
, nickel sulfate 70g/, boric acid 20g/, glycerin 2g/ in a bath with a bath temperature of 30℃, and with graphite as the counter electrode, AC 60Hz, 15V, 3-15
The test was carried out by applying electricity for a minute. Next, it was varied depending on the amount of physical removal and the thickness of the anodic oxide film. Surface roughness Rmax=0.03 μm was obtained. The results of the magnetization characteristics are shown in Table 2.

【table】 [Brief explanation of drawings]

Figures 1A to 2D are schematic diagrams schematically showing the steps of the method of the present invention, and Figures 2A and 2B are diagrams showing the envelope of the playback output when physical deletion is not performed and when physical deletion is performed. be. 1... Aluminum material, 2... Porous, 3...
Barrier layer, 4... anodized film, 5... pores,
6...Magnetic metal.

Claims (1)

[Claims] 1. Filling the pores of an anodized film obtained by anodizing an aluminum material with a magnetic metal,
To obtain an aluminum material for magnetic recording, first an anodic oxide film with a thickness of 4 μm or more is formed on the aluminum material, and then a part of the anodic oxide film is chemically dissolved by immersing it in an acid or alkaline bath. In particular, the pores in the anodic oxide film can be reduced to 300 Å or more.
After enlarging the pores to a desired diameter within the range of 1400 Å and performing electrolytic treatment in a bath containing magnetic metal ions to precipitate the magnetic metal in the pores, the surface of the anodic oxide film is physically scraped. A method for producing an aluminum material for magnetic recording, characterized in that the filled magnetic metal is exposed on the surface of the film. 2 Filling the pores of the anodic oxide film obtained by anodizing the aluminum material with magnetic metal,
To obtain an aluminum material for magnetic recording, first an anodic oxide film with a thickness of 4 μm or more is formed on the aluminum material, and then a part of the anodic oxide film is chemically dissolved by immersing it in an acid or alkaline bath. In particular, the pores in the anodic oxide film can be reduced to 300 Å or more.
The barrier layer in the anodic oxide film is adjusted by enlarging the pores to a desired diameter in the range of 1400 Å and then briefly passing an electric current through an immersion bath, followed by electrolytic treatment in a bath containing magnetic metal ions. Then, a magnetic metal is precipitated into the pores, and then,
A method for producing an aluminum material for magnetic recording, which comprises physically scraping the surface of an anodized film to expose the filled magnetic metal on the surface of the film.