JPH0816980B2 - Magnetic disk substrate and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a magnetic disk substrate made of a thermoplastic resin used for a hard magnetic disk for high-density recording and reproduction, and a method for manufacturing the same.

<Prior Art> In recent years, a flat and smooth disk-shaped substrate was manufactured by injection molding using a thermoplastic resin as a magnetic disk for high-density recording, and a magnetic thin film was provided on the surface by a plating method or a sputtering method. Things began to be considered.

The magnetic head (hereinafter simply referred to as head) of the magnetic disk device is generally a contact start stop type levitation type. While the magnetic disk is rotating, the head is floating, but when the rotation is stopped, The head is in contact with the magnetic disk. Due to the recent demand for higher recording density, efforts have been made to reduce the flying height of the head as much as possible, and the surface of the magnetic disk is particularly flat and highly mirror finished.

However, as the surface finish of the magnetic disk becomes more sophisticated, a phenomenon occurs in which the head is attracted to the magnetic disk.
That is, if the head remains in contact with the magnetic disk, the head is attracted to the magnetic disk, and the static friction coefficient increases when the magnetic disk starts to rotate again. In particular, the adsorption phenomenon is more likely to occur as the stop time of the magnetic disk becomes longer, resulting in a decrease in reliability of the magnetic disk device.

Conventionally, a magnetic disk substrate that has been polished to prevent the occurrence of such a head adsorption phenomenon is rotated, and an abrasive such as sandpaper is pressed against the magnetic disc substrate to form fine circular concentric grooves on the surface of the substrate. A method of producing and roughening is known (Japanese Patent Laid-Open No. 53-123906). There is also known a method of roughening the surface of a magnetic disk substrate by roughing it with a rough polishing cloth or by irradiating a laser beam to burn the surface layer of the substrate (JP-A-54). -23508
Issue).

There is also known a method in which the surface of a magnetic disk is mechanically chemically polished with an abrasive to obtain an appropriate surface roughness (JP-A-61-267931).

Further, by disposing abrasive grains or the like on the surface of the non-magnetic substrate and rotating the non-magnetic substrate, a scratch on the non-magnetic substrate is formed in a substantially concentric or spiral shape, and the surface is scratched. When a magnetic film is formed by plating, the magnetic film is affected by the underlying surface, and the magnetic film is magnetically oriented in the circumferential direction.
It is known that magnetic characteristics are improved (Japanese Patent Laid-Open No. 61-168).
118, JP-A 61-202324, and JP 61-242
No. 334).

Further, since the groove is formed in a circular shape, the magnetic alloy thin film formed thereon has a high squareness ratio in the circumferential direction, that is, the effect of obtaining a disk magnetically oriented in the circumferential direction is obtained. is there. It is also known that the greater the number of grooves and the more regular the shape of the grooves, the higher the orientation (E.Teng, N. Ballard: IEEE Trans.Mag., Vol.MAG-22, No.
5, September 1986).

<Problems to be Solved by the Invention> However, with such a polishing method or a laser beam irradiation method, the grooves on the disk become non-uniform. That is, the width and depth of the groove and the groove pitch (distance between the grooves) vary. In addition, a swelling occurs on the edge of the groove formed by cutting with the abrasive. If the grooves are uneven or risen in this manner, the flying of the head becomes unstable and causes head clash.

Further, in order to form a groove in the circumferential direction by the above-mentioned method, it is necessary to finish the surface of the groove to form a mirror-finished surface, so that there is a drawback that the manufacturing process of the substrate becomes long.

It is an object of the present invention to solve these problems and provide a magnetic disk substrate having desired characteristics.

<Means for Solving the Problem> When manufacturing a magnetic disk substrate having a smooth surface by injection molding from a thermoplastic resin, the inventors faithfully transfer minute scratches on the surface of the mold to the surface of the magnetic disk substrate. As a result of various studies focusing on the fact that the injection molding is performed on the substrate obtained by injection molding regularly, by performing processing of the reverse shape for transferring the concentric circular groove to the mold to be injection molded here. It has been found that a concentric groove can be easily formed.

That is, the present invention is, firstly, on a thermoplastic resin disk whose surface is a mirror surface, with a groove width of 500 to 20000Å, a groove depth of 200 to 2000Å,
A magnetic disk substrate having a large number of concentric circular or spiral grooves of groove pitch 1000 to 20000Å formed by an injection molding method.

In the second aspect of the present invention, when a thermoplastic resin is molded to manufacture a magnetic disk substrate having a mirror surface, a large number of concentric convex ridges are formed on the surface of a mold that abuts the surface of the substrate. Another method is to manufacture a magnetic disk substrate having a large number of concentric grooves formed by using a metal mold.

Hereinafter, the present invention will be described in detail. In the present invention, the thermoplastic resin is a polyetherimide resin, a polyether sulfone resin, a polycarbonate resin, a polysulfone resin, an acrylic resin, a modified maleimide resin, a polyamide resin, a polyphenylene oxide resin, a polyphenylene sulfide resin, PBT resin , Polyacetal resin, etc., preferably their heat distortion temperature (ASTM D-64
Measured with a load of 18 and 6 kg / cm ² according to 8) above 100 ° C. If the surface is a mirror surface, its irregularities do not hinder the flying of the head.
Is less than 3000Å, preferably less than 200Å. Rmax is 300
If it exceeds 0Å, the flying height of the head must be made higher, and high-density recording cannot be performed.

The large number of concentric grooves is a large number of concentric grooves or a spiral groove having a large number of turns. The groove width should be in the range of 500 to 20000Å, preferably 1000 to 10000Å. The groove pitch should be in the range of 1000 to 20000Å, preferably 2000 to 20000Å. If the groove width or groove pitch is outside the above range, there is no effect of preventing the head adsorption phenomenon. The depth of the groove must be in the range of 200-2000Å,
It is preferably 500 to 1000Å. If the depth of the groove is less than 200Å, there is no effect of preventing the head adsorption phenomenon. On the other hand, if it exceeds 2000Å, the distance between the head and the magnetic medium on the magnetic disk surface becomes large and the reproduction output decreases. The cross-sectional shape of the groove is not particularly limited and may be V-shaped or U-shaped.

The mold used for forming the groove on the surface of the magnetic disk substrate is a mold in which a large number of concentric convex ridges are formed on the surface of the mold that contacts the surface of the substrate. A convex bank is a slender rise from a plane. Since the convex bank on the surface of the mold is transferred and the groove is formed on the magnetic disk substrate, the convex bank has unevenness opposite to the groove, but its width is
The characteristics of the pitch and the like are the same as those of the groove described above.

In order to manufacture a mold provided with such a convex bank, a master substrate must first be manufactured. The first method of manufacturing the master substrate is to first manufacture a disk having the same shape and size as the magnetic disk substrate, and form a groove on the disk by diamond cutting to obtain the master substrate.

This is a method of using a second laser cutting technique and a photoresist as a method of manufacturing a master substrate. That is, first, a photoresist is thinly applied to the surface of a glass disk having the same shape and size as the magnetic disk substrate, and spots of a laser beam are irradiated concentrically or spirally on the surface of the disk to cure the photoresist. This is a method of forming a concentric circular or spiral convex bank of objects and using it as a master substrate.

To manufacture a die from the master substrate, electroforming is performed on the master substrate to transfer the irregularities on the surface of the master substrate onto the metal foil, and the metal foil is backed and reinforced to complete the die. The mold may be a mold insert for injection molding, or may be an injection molding mold having a stamper molding specification used for molding an optical disc, a compact disc, or the like.

<Examples> Hereinafter, the present invention will be described in detail with reference to Examples. Example 1 First, an aluminum plate was cut to manufacture a disk having the same dimensions as a magnetic disk substrate. After the disk was nicked, the surface was polished to a super-mirror surface with a roughness Rmax of 0.02 μm or less.

Next, by diamond cutting, the groove width of 1000 ~
A master substrate was prepared by forming a groove having a V-shaped cross section with 2000Å, a groove depth of 500 to 1000Å, and a groove pitch of 2000 to 4000Å.

As shown in FIG. 1, nickel electroforming 2 is performed on the master substrate 1 and then the nickel foil 3 is peeled off to obtain a nickel foil 3 shown in FIG. 2. The nickel foil 3 is lined with nickel as shown in FIG. Was reinforced to form a mold insert with a wall thickness of 25 mm.

As shown in Fig. 4, put the mold inserts 6, 7 in the mold,
The mold was clamped. Polyetherimide melt (temperature 390
(° C.) was injected from the injection port 5 into a mold heated to a temperature of 150 ° C. The mold was cooled and the solidified molded product 8 was removed.

Next, a chrome film (thickness: 1000 to 1200Å), magnetic film (composition: Co-Ni-Cr, thickness:
700 Å) and a carbon protective film (thickness 200 to 300 Å) were applied in this order to form a magnetic disk.

After repeating the start and stop of the completed magnetic disk by the contact start and stop device (CSS device), the rotation of the magnetic disk is stopped for a certain period of time.
Then, it was confirmed by a strain gauge whether the head did not adsorb to the magnetic disk when it was rotated at a low speed. As a result, the static friction coefficient was 0.3 or less and no adsorption phenomenon was observed. In addition, as a result of measuring the magnetic characteristics of this magnetic disk with a vibrating sample magnetometer (VSM device), the ratio (θ / γ) between the squareness ratio θ in the circumferential direction and the squareness ratio γ in the direction perpendicular to the circumference is It was 1.3, and the magnetic substance was oriented in the circumferential direction.

Example 2 First, a glass plate was processed to manufacture a disk having the same dimensions as the magnetic disk substrate, and the surface thereof was finished into a super-mirror surface.

Next, a stamper for a magnetic disk substrate was manufactured by using a process of manufacturing a stamper for transferring an information surface when molding a compact disk or an optical disk substrate.
That is, first, a photocurable photoresist was uniformly applied to the surface of the glass disk. Next, while rotating the disk, the spot of the laser beam (diameter about 500Å) was moved in the radial direction of the disk to cure the photoresist on the surface of the disk in a spiral shape. The uncured photoresist was removed by washing with a solvent. In the above direction, the convex bank has a width of 5000 to 10000Å, a height of 500 to 1000Å, and a pitch of 1000 on the surface of the disk.
The reverse master substrate 13 was formed by forming a convex bank with an inverted U-shaped cross section of 0 to 20000Å. Nickel electroforming 14 was performed on the reverse master substrate, and the nickel foil was peeled off to obtain a nickel foil, which was then reinforced with a backing 15 to obtain a master substrate.

This master substrate was transferred by Nickel electroforming 16 to form a stamper 17 having a convex bank formed thereon, and this stamper 17 was attached to an injection molding die for stamper molding and molded in the same manner as in Example 1 to obtain a magnetic disk substrate. .

A chrome film, a magnetic film and a carbon protective film were applied in the same manner as in Example 1 to complete a magnetic disk. Example 1
As a result of investigating the presence or absence of the adsorption phenomenon of the head by the same method as the above, the static friction coefficient was 0.3 or less, and the phenomenon that the head was adsorbed to the magnetic disk was not recognized at all.

<Effect of the Invention> Since the magnetic disk manufactured from the magnetic disk substrate of the present invention has no phenomenon of adsorption to the magnetic disk surface of the head,
There is no risk of the head being damaged even if the contact start stop of the magnetic disk is repeated.

Further, according to the method of the present invention, the above-mentioned magnetic disk substrate can be manufactured without any special process, and in particular, in the method of the present invention, an extra swelling does not occur at the edge of the groove in principle. In this respect as well, there is no risk of head damage.

Further, since the magnetic disk manufactured from the magnetic disk substrate of the present invention has a particularly high squareness ratio in the circumferential direction, it is advantageous in performing magnetic recording at high density. As described above, according to the present invention, it is not necessary to form the groove over the entire surface of the substrate because the contact start stop region and the data recording region can obtain independent effects.

[Brief description of drawings]

1 to 3 are cross-sectional views of a mold insert used in the manufacture of the magnetic disk substrate of the present invention during manufacture. FIG. 4 is a sectional view of a mold used for manufacturing the magnetic disk substrate of the present invention. 5 to 9 are sectional views of the stamper used for manufacturing the magnetic disk substrate of the present invention during manufacture. Reference numeral 1 ... Master substrate, 2, 14, 16 ... Nickel electroforming, 3 ...
… Nickel foil, 4,15 …… lining, 5 …… injector, 6,7…
… Mold insert, 8 …… Molded product, 9… Sprue bush,
10: Edger rod, 11: Solid side template, 12 ...
Movable side template, 13 …… Reverse master board, 17 …… Stamper

Claims (2)

[Claims] 1. A groove width is formed on a thermoplastic resin disk whose surface is a mirror surface.
500 to 20000Å, groove depth 200 to 2000Å, groove pitch 1000 to 200
A magnetic disk substrate with a large number of concentric 00Å grooves formed by injection molding. 2. A mold in which a large number of concentric convex ridges are formed on the surface of a mold which is in contact with the surface of a substrate when the thermoplastic resin is molded to produce a magnetic disk substrate having a mirror surface. A method of manufacturing a magnetic disk substrate having a large number of concentric grooves formed therein.