JPH07262554A - Production of magnetic disk substrate - Google Patents

Abstract

PURPOSE:To obtain a production method of a magnetic disk substrate by which even when a magnetic disk is made thin, the generation of undesirable warpage due to residual stress in the succeeding process can be prevented. CONSTITUTION:For example, aluminum or an aluminum alloy raw material is punched into a disk to produce a blank. After the inner and outer diameters of the blank are subjected to a cutting work, the surface of the blank is subjected to grinding of rough grinding and finish grinding at least once. Then the surface of a ground substrate is plated and then polished. After the end of the final grinding, the surface layer is chemically dissolved and removed by using, for example, caustic soda.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk substrate manufacturing method suitable for manufacturing a thin magnetic disk.

[0002]

2. Description of the Related Art Conventionally, an aluminum alloy magnetic disk substrate is manufactured by the following steps. That is, first, a rolled material of aluminum alloy is punched into a disk shape having a predetermined size to obtain a blank, and then, while the blank is held by vacuum suction, its inner and outer diameters are cut and processed by an NC lathe or the like to measure the size. I do. Next, both surfaces of the blank are ground by a coarse grinder using a grindstone with a roughness of about 800, and then the blank is annealed to remove strain. Next, as shown in FIGS. 4 and 5, the carrier 1 holds the blanks 2 ... And the inner teeth 3 are rotated to rotate the inner teeth 3 and the outer teeth 4.
And a planetary gear movement between them, and both sides of these blanks 2 are sandwiched by a pair of grindstones 5 and 5 having a roughness of about 3000 to 4000, and these are rotated in reverse to finish grinding. At the same time, the surface roughness is adjusted to a predetermined value. Then, after the both sides of the obtained grinding base are plated, they are manufactured by polishing (polishing) and finishing to a mirror surface. The magnetic disk substrate thus obtained is formed into a magnetic disk by forming a magnetic film by the subsequent steps of texture and sputtering.

By the way, in the magnetic disk manufactured as described above, in actual use, the magnetic head moves over the magnetic disk rotating at a high speed through a very small interval of several micro inches. Thus, reading and writing of magnetic signals is performed. The gap between the magnetic disk and the magnetic head tends to become smaller due to the recent demand for miniaturization and high density of the magnetic disk. For this reason, the requirement for the flatness of the magnetic disk substrate is becoming more severe, and the allowable warp shape is such that the laser interference fringes have the diametrical end portions 10 and 10 as shown in FIG. A warp that bends toward both ends 1 in the diametrical direction as shown in FIG.
The warp in which 1 and 11 are bent upward and the diametrical end portions 12 and 12 orthogonal to this are bent downward is inconvenient because the magnetic head cannot follow. Therefore, a concentric shape as shown in FIG. Is required.

[0004]

However, in the above-described conventional method for manufacturing a magnetic disk substrate, the blank is first held by vacuum suction during cutting of the inner and outer diameters thereof, so that residual stress is generated on the surface of the blank.
In addition, at the time of rough grinding and finish grinding, a temperature difference occurs between the surface and the inside of the blank due to processing heat and residual stress is generated, and residual stress is also generated by cutting with a grindstone. In particular, at the time of grinding, as shown in FIG. 6, the blank receives a grinding load in a lateral direction parallel to one diametrical direction. The tensile stress remains in the grinding direction, and the compressive stress remains in the direction orthogonal to this. Among the residual stresses generated on the surface of the grinding base, those generated during vacuum adsorption and rough grinding are almost removed by the subsequent annealing. However, after the above finish grinding, these stresses remain in the surface layer of the grinding base as they are until the subsequent process.

In this way, several μm from the surface of the blank
The residual stress in the layer in the range of (3) does not appear as an adverse effect such as a warp in a post process because the overall rigidity is high in a blank having a large thickness dimension.
However, due to the thinning of magnetic disks in recent years,
For example, in the case of the 3.5-inch type that is currently the mainstream and the thickness dimension is 0.8 mm, or the thickness dimension is less than 300 mm, it is 300
When it is heated to near 0 ° C., the residual stress is released, and there is a problem in that a warp unsuitable for this type of magnetic disk as shown in FIGS. 2 and 3 occurs.

The present invention has been made to effectively solve the above-mentioned problems in the conventional method for manufacturing a magnetic disk substrate. Even when the magnetic disk is thinned, an inconvenient warp caused by residual stress in a subsequent step is caused. It is an object of the present invention to provide a method for manufacturing a magnetic disk substrate that does not cause the above-mentioned problems.

[0007]

According to a method of manufacturing a magnetic disk substrate of the present invention, a blank made of, for example, aluminum or an aluminum alloy is punched into a disk shape, and the inner and outer diameters of the blank are cut. After that, the surface of the blank is subjected to at least one grinding process such as rough grinding and finish grinding, and then the surface of the obtained grinding base is subjected to a plating process, and then a polishing process is performed on the surface. After that, the surface layer is chemically dissolved and removed by using, for example, caustic soda or the like.

[0008]

According to the method of manufacturing a magnetic disk substrate of the present invention having the above structure, after the final grinding process, the surface layer of the grinding base is chemically dissolved and removed,
The stress layer remaining on the surface of the grinding base is removed by the cutting and grinding processes up to that point. Therefore, even if the grinding base is heated in a subsequent step, distortion such as warpage due to the release of residual stress does not occur.

[0009]

EXAMPLE An example of a method of manufacturing a magnetic disk substrate according to the present invention will be described below. First, a rolled material of an aluminum alloy was punched into a 3.5-inch disk shape to obtain a plurality of blanks, which were subjected to pressure annealing. Then
While holding both surfaces of these blanks by vacuum suction, the inner and outer diameters thereof were cut by an NC lathe or the like for dimensioning. Next, both surfaces of the blank are ground by a rough grinder using a grindstone having a roughness of about 800 on one side by about 40 μm, and the surface roughness is Rmax =
After reducing the thickness to 2 μm or less, the blank is applied to the blank at about 270 ° C. for about 2
Annealing was performed for a period of time to remove residual stress and remove strain. Next, as shown in FIGS. 4 and 5, the carrier 1
, And the inner teeth 3 are rotated to cause a planetary gear movement between the inner teeth 3 and the outer teeth 4, and both surfaces of these blanks 2 ... Have a roughness of about 3000. By sandwiching them with the grindstones 5 and 5 and rotating them in opposite directions, finish grinding for removing about 15 μm on both surfaces is performed, whereby the surface roughness Rmax = 0.
At 5 μm or less, Ra was adjusted to a value of 0.05 μm or less.

Next, the surface layer of the blank was chemically dissolved and removed with caustic soda. At this time, the dissolution time was 150 seconds, and the surface layer having a thickness of 0.28 μm was removed. Then, after plating both surfaces of the obtained grinding base, the surface roughness is Ra = 30Å (0.003 μm) by polishing (polishing) with an acidic polishing liquid such as nickel sulfate and abrasive grains such as alumina. Finished to a mirror surface. By the way, the polishing amount at this time is about 1.5 μm on one side, and the final thickness dimension is 0.8 μm.
It was mm.

After the magnetic disk substrate obtained by the above steps was formed into a magnetic disk by forming a magnetic film by the subsequent steps of texture and sputtering, the surface shape of these was inspected by laser interference fringes, and finish grinding was performed. In the conventional one in which the surface layer of the grinding base is not chemically removed afterward, the warpage as shown in FIG. 2 or FIG. 3 occurred, whereas in the one according to the above embodiment, About 90% of them were concentric circles as shown in FIG. 1, and thus were acceptable as products. As described above, according to the method for manufacturing a magnetic disk substrate, after the final grinding process is performed, the surface layer of the grinding base is chemically dissolved and removed with caustic soda, thereby cutting and grinding processes up to that point. Since the stress layer remaining on the surface of the grinding base can be removed by
Even if the grinding base is heated in the subsequent step, distortion such as warpage due to the release of residual stress does not occur. Therefore, even if the magnetic disk becomes thin,
It is possible to easily and reliably manufacture a magnetic disk substrate having excellent flatness and an appropriate warp shape.

[0012]

As described above, according to the method for manufacturing a magnetic disk substrate of the present invention, a blank is manufactured by punching a blank made of, for example, aluminum or aluminum alloy into a disk shape, and cutting the inner and outer diameters of the blank. After processing,
At least one grinding process such as rough grinding and finish grinding is performed on the surface of the blank, and then the final grinding process is performed when polishing the surface of the obtained grinding base and then polishing the surface. After that, since the surface layer of the grinding base is chemically dissolved and removed using, for example, caustic soda, it is possible to remove the stress layer remaining on the surface of the grinding base by cutting or grinding. Even if the grinding base is heated in a subsequent process, the final product magnetic disk will not be warped or otherwise distorted due to the release of the residual stress during manufacturing. Also in this, it is possible to easily and reliably manufacture a magnetic disk substrate having excellent flatness and an appropriate warp shape.

[Brief description of drawings]

FIG. 1 is a diagram showing laser interference fringes in a magnetic disk manufactured by an embodiment of a method for manufacturing a magnetic disk substrate of the present invention.

FIG. 2 is a diagram showing laser interference fringes in a magnetic disk manufactured by a conventional method for manufacturing a magnetic disk substrate.

FIG. 3 is a diagram showing laser interference fringes in another magnetic disk of FIG.

FIG. 4 is a side view showing an example of a grinding device used for finish grinding in the method for manufacturing a magnetic disk substrate.

FIG. 5 is a plan view of FIG.

6 is a plan view showing a magnetic disk substrate ground by the grinding device of FIGS. 4 and 5. FIG.

[Explanation of symbols]

 2 Blank (grinding base)

Claims (3)

[Claims] 1. A blank is produced by punching a blank into a disk shape, the inner and outer diameters of the blank are cut, and then the surface of the blank is subjected to at least one grinding step, and then the obtained grinding base is obtained. In the method for manufacturing a magnetic disk substrate, in which the surface is subjected to a plating treatment and then the surface is polished to obtain a magnetic disk substrate, the surface layer of the grinding base is chemically dissolved after the final grinding process is performed. A method of manufacturing a magnetic disk substrate, which comprises removing the magnetic disk substrate. 2. A blank is manufactured by punching a blank into a blank, the inner and outer diameters of the blank are cut, and the surface of the blank is subjected to rough grinding at least once, and then the obtained grinding is performed. After the substrate is annealed, the surface of the grinding substrate is further finish-ground, and then the surface of the grinding substrate is subjected to a plating treatment, and then the surface is polished to obtain a magnetic disk substrate. A method of manufacturing a magnetic disk substrate, comprising chemically dissolving and removing a surface layer of the grinding base after performing the finish grinding. 3. The magnetic disk substrate manufacturing method according to claim 1, wherein the material is aluminum or an aluminum alloy, and the surface layer of the grinding base is chemically dissolved and removed with caustic soda. Method.