JPH11114826A - Polishing device for glass substrate for magnetic recording medium - Google Patents

Abstract

An object of the present invention is to provide an apparatus for polishing a glass substrate for a magnetic recording medium, which can reduce scratches generated on the surface during polishing of the glass substrate for a magnetic recording medium. SOLUTION: A double-side polishing machine 1 for polishing a glass substrate for a magnetic recording medium using a polishing liquid mixed with an abrasive.
And a polishing liquid circulation device 2 for supplying the polishing liquid used for polishing to the double-side polishing machine 1 again. The polishing liquid circulation device 2 includes a first tank 21 into which a polishing liquid used for polishing flows, and a second tank 22 disposed between the first tank 21 and the double-side polishing machine 1. ,
After the sedimentation and separation of the glass material and the abrasive in the first tank 21, the polishing liquid containing only the precipitated abrasive is discharged to the second tank 22, and only the abrasive is discharged from the second tank 22. The mixed polishing liquid is supplied to the double-side polishing machine 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for polishing a glass substrate for a magnetic recording medium, which polishes the surface of the glass substrate for a magnetic recording medium.

[0002]

2. Description of the Related Art As a substrate for a magnetic recording medium, a substrate made of a metal such as an aluminum alloy has conventionally been used. However, glass and crystallized glass have a higher mechanical strength than an aluminum alloy and have higher machinability. Because of its superiority, it has recently been regarded as a promising substrate for magnetic recording media.

In recent years, with the demand for higher density of information recording capacity, it has been required to improve the smoothness of the surface of a magnetic recording medium substrate. That is, a magnetic disk device using a magnetic disk formed by a substrate for a magnetic recording medium has a remarkable increase in capacity, size, and price as a typical external recording device of a personal computer. Advances in such magnetic disk devices have been realized by increasing the performance of magnetic disks for recording and reproducing information, improving the performance of magnetic heads, increasing the speed of recording and reproducing channels, and increasing the speed and accuracy of servo circuits. Although it is due to the high performance of parts and individual technologies, it is largely due to the improvement of the characteristics of magnetic disks and magnetic heads, which are the core components directly related to recording and reproduction.

In order to increase the density of a magnetic disk, particularly to improve the linear recording density, the effect of reducing the flying height of a magnetic head together with the improvement of a magnetic film is great. With the latest magnetic disk drives, 50-
A flying height of about 60 nm is being realized. In order to achieve such low flying height, the surface of the magnetic disk is required to be flat and smooth, and a sophisticated technique is required for this polishing.

For this reason, in the process of manufacturing a substrate for a magnetic recording medium, a polishing process is provided as a process of finishing the substrate. Here, in the case of a metal accompanied by plastic deformation, such as an aluminum alloy, the work strain layer generally becomes deep in the polishing, and so-called burrs and abnormal projections tend to remain after the polishing. However, in the case of glass, since polishing is performed by brittle fracture without plastic deformation, the processing strain layer is shallow, and burrs and abnormal projections do not occur. Therefore, glass is a material that can easily obtain surface smoothness.

Many studies have been made on the principle of polishing glass, but no clear view has yet been established, and the following three concepts are generally in parallel. The first theory, micro-cutting theory, is based on the theory that the flattening of the surface progresses due to the crushing action of the abrasive grains and it is performed microscopically, so that unevenness on the surface will not be recognized by optical means. is there. The second theory, the flow theory, is that polishers and abrasive grains instantaneously create a high-pressure, high-temperature state on the glass surface, resulting in viscous flow or plastic flow, which smoothes the surface irregularities. is there. The third theory, a chemical action theory, is based on the assumption that a chemical reaction occurs between the abrasive grains, the polisher, and the polishing liquid and the glass in polishing, thereby making the surface uneven.

The glass properties most closely related to each of these theories are that the hardness corresponding to the first theory is the hardness of the glass, and the glass property corresponding to the second theory is that the glass easily flows with respect to the temperature of the glass. That is, the softening point, and the one corresponding to the third theory is considered to be chemical durability.

Therefore, in a polishing step of a glass substrate for a magnetic recording medium (hereinafter referred to as a “glass substrate”),
In order to finish the glass substrate to a mirror surface without pits or scratches, various polishing apparatuses manufactured based on the above-mentioned theories are used in consideration of the characteristics of the glass used.
Here, in the case of polishing a small glass substrate such as 2.5 or 3.5 inches, a so-called double-sided polishing machine of a double-sided lapping method which is used for polishing a silicon wafer and has high productivity is widely used. Have been.

In this double-side polishing machine, a polishing tool having a polyurethane polishing pad fixed thereto is brought into close contact with both surfaces of a glass substrate, and a polishing liquid is supplied between the pad and the polishing surface of the glass substrate to form a polishing pad between the pad and the glass substrate. Are rotated and slid relatively to simultaneously grind both surfaces of the glass substrate. Each of the glass substrates to be polished is held by a carrier, and the carrier itself performs planetary motion in a double-sided polishing machine, so that the surface of the glass substrate held there is polished.

Polishing of glass and crystallized glass is generally performed using a polishing tool having a polyurethane polishing pad fixed thereto.
This is performed using cerium oxide (CeO ₂ ) as an abrasive. The polishing removal amount varies depending on the type of glass (glass type such as glass hardness and softness), but the cerium oxide abrasive can obtain a good polished surface without damaging regardless of the type of glass.

[0011]

As described above, when a double-side polishing is performed using a polishing liquid containing cerium oxide, there are many cases where a scratch is generated on a glass substrate as a workpiece. I will. This is because small pieces of the glass substrate are mixed in the polishing liquid, and the small pieces damage the surface of the glass substrate to be processed.

In order to supply a polishing liquid to a double-side polishing machine,
The polishing liquid stored in one tank is guided to a double-side polishing machine, and the polishing liquid used for polishing is circulated such that the polishing liquid returns to the tank again. The results of the survey are shown below.

[0013] 50 cc of the polishing liquid used in the polishing step was collected, centrifuged, and about 2 cc of the precipitate was thinly spread on a petri dish and observed with a stereoscopic microscope. When the precipitate is dried, a gel-like white substance, which is considered to be silicon oxide on the glass substrate for a magnetic recording medium and formed by polishing, can be observed in the flesh-colored substance that is cerium oxide. From this, it can be seen that small pieces of a glass substrate as a workpiece are mixed in the polishing liquid used in the polishing step.

Next, as shown in FIG. 4, a 15 cc sample of the polishing liquid was placed in a test tube and allowed to stand to settle naturally.
A sample of the polishing liquid was composed of a colloid layer at the top, a CeO ₂ mixed layer that was not clearly separated but became darker as the skin color became lower, and a skin color precipitate (CeO ₂ ) layer at the bottom. Separated into layers. Here, the uppermost colloidal substance became a white hard substance when dried. When a sample of the polishing liquid is left in a test tube for 2 to 3 days, the glass modified material generated by polishing and the polishing agent are easily settled and separated.

The separated glass alteration is colloidal. When this is dried, it becomes a glassy hard mass. This indicates that the upper part (water surface) of the tank connected to the double-side polishing machine and supplying and circulating the polishing liquid contains a colloidal glass material that easily solidifies and forms a hard lump. Recognize.

Since the polishing liquid supplied to the double-side polishing machine is circulated through the one stored in one tank, even when the polishing liquid in the tank is stirred, the polishing liquid contains colloidal liquid. Contains glass material. Then, once the colloidal glass material is dried, it becomes a glassy hard mass. If the glass substrate is polished while the glass-like hard lump is mixed in the polishing liquid, scratches occur on the surface of the polished glass substrate.

As described above, if a scratch is present on the glass substrate for a magnetic recording medium, there arises a problem that information cannot be recorded on the scratched portion. In the presence of even larger flaws, a head crash problem may also occur. In addition, if there is a scratch on the glass substrate, the scratch may cause the substrate to break.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has an apparatus for polishing a glass substrate for a magnetic recording medium capable of reducing scratches generated on the surface during polishing of the glass substrate for a magnetic recording medium. It is intended to provide.

[0019]

In order to achieve the above object. The polishing apparatus for a glass substrate for a magnetic recording medium according to the present invention includes a polishing machine for polishing a glass substrate for a magnetic recording medium using a polishing liquid mixed with an abrasive, and a polishing liquid used for the polishing processing. And a polishing liquid circulation means for supplying the polishing liquid to the polishing machine again. The polishing liquid circulating means collects the polishing liquid used for the polishing process, removes the glass substance mixed in the polishing liquid, and supplies the polishing liquid to the polishing machine again.

The polishing liquid circulation means has a separation tank for removing glass substances mixed in the polishing liquid. The separation tank stores the polishing liquid used for polishing, and sediments and separates the polishing liquid containing only the abrasive from the polishing liquid containing the glass material. Thereafter, a polishing liquid containing only the precipitated abrasive is supplied to the polishing machine.

In the polishing apparatus for a glass substrate for a magnetic recording medium configured as described above, a glass material is mixed into a used polishing liquid with polishing, and this glass material has a specific gravity higher than that of an abrasive. light. For this reason, if the polishing liquid used for the polishing process is left as it is, the polishing agent in the polishing liquid precipitates and the glass material becomes a colloidal supernatant. Therefore, if a portion other than the supernatant is supplied to the polishing machine in the used polishing liquid collected in the separation tank, the glass for a magnetic recording medium in the polishing liquid containing only the polishing agent containing no glass substance is mixed. The substrate can be polished.

In the apparatus for polishing a glass substrate for a magnetic recording medium according to the present invention, the separation tank is provided with a first tank into which a polishing liquid used for polishing first flows, It is preferable that the second tank is provided between the polishing machine and the polishing machine. After the sedimentation and separation of the glass material and the abrasive in the first tank, the polishing liquid containing only the precipitated abrasive is discharged into the second tank, and only the abrasive is mixed from the second tank. The polishing liquid is supplied to the polishing machine.

With such a configuration, the polishing liquid containing only the abrasive can be supplied to the polishing machine only from the second tank, so that the sedimentation of the glass material and the abrasive in the first tank is achieved. The used polishing liquid can be left for a time required for separation. Therefore, it is possible to continuously supply the polishing liquid in which the glass substance is not mixed.

Further, in the apparatus for polishing a glass substrate for a magnetic recording medium according to the present invention, the first tank is provided with a first tank stirring means, and the second tank is provided with a second tank stirring means. Is preferred. The first tank agitating means is configured to agitate only the polishing liquid mixed with only the precipitated abrasive without stirring the colloidal supernatant glass material in the first tank. ing. Further, the second tank stirring means is configured to stir the entire polishing liquid stored in the second tank.

With such a structure, the polishing agent in the polishing liquid does not solidify, and the polishing liquid containing only the polishing agent can be smoothly supplied from the first tank to the second tank. Or from the second tank to the polishing machine. Each of the stirring means may be configured to rotate the stirring blades in the polishing liquid for stirring, or may be configured to send air by a pump to perform stirring.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the apparatus for polishing a glass substrate for a magnetic recording medium according to the present invention will be described below. The polishing apparatus has a polishing machine for polishing a glass substrate for a magnetic recording medium using a polishing liquid mixed with an abrasive, and further includes a polishing liquid for efficiently using the polishing liquid. It has a circulation device (polishing liquid circulation means). As the polishing machine, a commercially available double-side polishing machine capable of simultaneously processing both surfaces of a work (glass substrate for a magnetic recording medium) is used. Further, the polishing liquid circulating device is provided with a polishing liquid circulating device, in which the polishing liquid circulating by the polishing liquid circulating device eliminates the formation of a hard glassy lump in the polishing liquid, which causes scratches on the glass substrate for magnetic recording media. It is configured so that glass material is not contained.

That is, a tank connected to a double-side polishing machine used for polishing is constituted in a two-tank type by two tanks comprising a first tank and a second tank, and the polishing liquid used for polishing is initially Into the first tank.
Next, the polishing liquid is left in the first tank for a certain period of time, and the polishing liquid containing only the abrasive is settled and separated from the polishing liquid containing the glass material.

The first tank is provided with stirring blades (first tank stirring means) near the bottom of the tank.
Only the polishing liquid containing only the abrasive which has settled and settled is stirred to prevent the abrasive from hardening at the bottom of the tank.

Then, without collecting the portion containing the colloidal glass material, which is the supernatant of the polishing liquid in the first tank, the polishing agent, which is the portion other than the supernatant of the polishing liquid in the first tank, is collected. Only the portion containing only the mixture is introduced into the other second tank using a pump. The second tank is also provided with stirring blades (second tank stirring means). However, unlike the stirring blades provided in the first tank, the stirring blades remove the entire polishing liquid in the second tank. It is configured to be capable of stirring.

For this reason, even if a large amount of polishing liquid is stored in the second tank and the polishing liquid is supplied to the double-side polishing machine little by little, the polishing agent in the polishing liquid in the second tank is reduced. There is no hardening. As described above, if a large amount of polishing liquid can be stored in the second tank, it is possible to secure time for sedimentation and separation of the polishing liquid in the first tank even if polishing is performed continuously. Then, the polishing liquid is re-supplied from the second tank to the double-side polishing machine and used for polishing, and then the polishing liquid after polishing is returned to the first tank again.

In this polishing liquid circulation device, the supernatant of the polishing liquid stored in the first tank is discarded, and only the polishing liquid stored in the second tank is supplied to the processing portion of the polishing machine by the pump. It is configured to supply. For this reason, a hard glass-like lump that causes scratches can be eliminated from the polishing liquid without mixing the colloidal glass substance into the second tank.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of the apparatus for polishing a glass substrate for a magnetic recording medium according to the present invention will be described with reference to FIGS. This polishing apparatus comprises a commercially available double-side polishing machine (polishing machine) 1 and a polishing liquid circulating apparatus (polishing liquid circulating means) 2 for supplying the polishing liquid 19 to the double-side polishing machine 1 and recovering the glass material. Have been.

The double-side polishing machine 1 is constituted by attaching polyurethane polishing pads 18 and 18 to an upper platen 13 and a lower platen 14 made of cast iron, respectively. Then, the upper and lower surface plates (polishing tools) 1 to which the polishing pads 18 are fixed.
A glass substrate 12 for a magnetic recording medium (hereinafter, referred to as a “glass substrate 12”) is brought into close contact between the polishing pads 3 and 14, and is polished between polishing pads 18, 18 made of polyurethane and a polishing surface of the glass substrate 12. Cerium oxide (C
The polishing liquids 19 and 19 containing eO ₂ ) are supplied and rotated and slid to simultaneously polish both surfaces of the glass substrate 12.

Specifically, a glass substrate 12 which is a work of the double-side polishing machine 1 is held by a carrier 15, and this carrier 15 is meshed with a sun gear 16 and an internal gear 17, and the glass substrate 12 is placed on an upper platen. By rotating the carrier 15 in a state where the carrier 15 is held and pressed between the polishing pad 18 and the lower surface plate 14, the polishing pad 18 and the glass substrate 1 are pressed.
2 is relatively rotated to polish. In addition, as abrasive grains as an abrasive, the average particle size is 1.2 μm, and the maximum particle size is 8.8.
A relatively small particle size of 4 μm is used.

Next, the polishing liquid circulation device 2 for supplying the polishing liquid 19 to the double-side polishing machine 1 will be described. The polishing liquid circulation apparatus 2 has a configuration having a two-tank type tank (separation tank) composed of a first tank 21 and a second tank 22, and the polishing liquid 19 used for the polishing process reaches first. A portion other than the supernatant of the polishing liquid 19 stored in the first tank 21 is collected without collecting the supernatant of the polishing liquid 19 stored in the first tank 21.
2. Then, the polishing liquid 19 is supplied from the second tank 22 to the double-side polishing machine 1 again,
The polishing liquid circulating mechanism is configured such that the polishing liquid 19 is circulated in the above-mentioned flow.

In the polishing liquid circulation device 2, the polishing liquid inflow hole of the first tank 21 and the polishing liquid outflow hole of the double-side polishing machine 1 are connected by a first pipe 25.
The polishing liquid outflow hole of the second tank 22 is connected to the polishing liquid outflow hole of the second tank 22. The polishing liquid outflow hole of the second tank 22 and the polishing liquid inflow hole of the double-side polishing machine 1 are connected by a third pipe 27. The first tank 21 and the second tank 22 are provided with stirring blades 23 and 24, respectively.

In the polishing liquid circulating apparatus 2 configured as described above, the polishing liquid 19 used for polishing in the double-side polishing machine 1 first flows into the first tank 21 through the first pipe 25. The flowing polishing liquid 19 is supplied to the first tank 21.
At a predetermined time, and the supernatant containing the colloidal glass material (polishing liquid mixed with the glass material)
And a portion other than the supernatant portion (a polishing liquid containing only the polishing agent).

The polishing liquid 19 in the first tank 21 is stirred by the rotation of the stirring blades 23 mounted on the first tank 21. In the first tank 21 and the stirring blades 23, By optimizing the shape of the blade 21 and the shape and rotation conditions of the blade, the first tank 21
The upper part of the polishing liquid 19 stored in the polishing liquid 19 can be agitated without stirring. Therefore, in the portion other than the supernatant portion of the polishing liquid 19 to be stirred, only the abrasive is prevented from settling and hardening.

In the first tank 21 configured as described above, the supernatant portion containing the unstirred colloidal glass material is discarded at the time of cleaning and maintenance of the polishing apparatus for the magnetic recording medium glass substrate. The portion other than the supernatant of the polishing liquid 19 stirred in the first tank 21 flows into the second tank 22 through the second pipe 26. Therefore, at this time, the polishing liquid 19 stored in the second tank 22 does not contain a colloidal glass substance.

In the second tank 22, the stored polishing liquid 19 is uniformly stirred using the stirring blades 24. Then, the agitated polishing liquid 19 is returned to the double-side polishing machine 1 through the third pipe 27 and used for polishing the glass substrate 12. The outflow of the polishing liquid 19 from the first tank 21 to the second tank 22 and the supply of the polishing liquid 19 from the second tank 22 to the double-side polishing machine 1 are performed using a pump (not shown).

The polishing conditions in the polishing apparatus for a glass substrate for a magnetic recording medium configured as described above are as follows. The polishing liquid 19 is a suspension using cerium oxide as an abrasive as described above. Polishing pressure is 30-120
g / cm ² , and the number of rotations of the upper and lower platens 13 and 14 is 5 to 40.
The RPM and polishing removal amount are 0.1 to 1 μm / min.
The surface roughness Ra of the glass substrate 12 produced by this polishing was 10 × 10 ⁻¹⁰ m or less. The surface roughness of the glass substrate 12 was measured using a surface roughness / fine shape measuring device (Tencor P-12 manufactured by Tencor) dedicated to a contact type disk.

The defect rate due to scratches on the polished surface of a glass substrate polished using a polishing apparatus which circulated and supplied the polishing liquid from one conventional tank was 1.2%. On the other hand, the defect rate due to scratches on the polished surface of the glass substrate polished using the glass substrate polishing apparatus for a magnetic recording medium according to the present invention was improved to 0.3%.

In the above embodiment, after the polishing liquid circulating apparatus 2 separates the supernatant containing the colloidal glass material from the supernatant, and then separates the supernatant of the polishing liquid 19 from the supernatant. In order to return the other parts to the double-side polishing machine 1, a case where a two-tank type polishing liquid circulating means having a first tank 21 and a second tank 22 is used as the polishing liquid circulating means has been described. Is not limited to such a configuration. For example, one or three or more tanks may be provided, and the stirring blades 23 and 24 are not necessarily required.

[0044]

As described above, the polishing apparatus for a glass substrate for a magnetic recording medium according to the present invention stores the polishing liquid used for polishing and mixes only the polishing agent with the polishing liquid containing the glass material. The polishing liquid is settled and separated, and the polishing liquid containing only the abrasive is supplied to the polishing machine again. For this reason, since the glass substance is removed from the polishing liquid supplied to the polishing machine, a hard glass lump is not generated in the polishing liquid.

Therefore, the scratches generated on the polished surface of the glass substrate for a magnetic recording medium can be reduced, so that it is not possible to record information on the scratched portion due to the scratches existing on the magnetic recording medium substrate. Further, it is possible to prevent the occurrence of a large scratch which may cause a head crash. Further, since the problem that the substrate is broken due to a scratch generated on the glass substrate can be solved, the mechanical strength of the glass magnetic recording medium substrate can be improved.

In the above-described apparatus for polishing a glass substrate for a magnetic recording medium, the separation tank was composed of a first tank and a second tank, and the glass material and the abrasive were settled and separated in the first tank. After that, it is preferable that the polishing liquid containing only the precipitated abrasive is discharged to the second tank, and the polishing liquid containing only the abrasive is supplied from the second tank to the polishing machine. .

With such a configuration, the glass substance can be reliably separated in the first tank, so that no lump of glass is generated even if the polishing liquid is left in the second tank. . In addition, since the polishing liquid is supplied only from the second tank to the polishing machine, the polishing liquid that is not sufficiently separated even if the polishing is performed continuously for a long time is not supplied to the polishing machine, so that the polishing liquid is supplied to the polishing machine. The polishing liquid containing the substance is not supplied to the polishing machine.

Further, in the above-mentioned apparatus for polishing a glass substrate for a magnetic recording medium, the first tank is provided with a first tank stirring means for stirring only the polishing liquid mixed with only the abrasive, and the second tank is provided with the first tank stirring means. It is preferable to provide a second tank stirring means for stirring the entire polishing liquid. With such a configuration, the polishing agent in the polishing liquid does not solidify, and the polishing liquid containing only the polishing agent can be smoothly supplied from the first tank to the second tank, It can be supplied from a tank to a polishing machine.

[Brief description of the drawings]

FIG. 1 is a front view showing an apparatus for polishing a glass substrate for a magnetic recording medium according to the present invention.

FIG. 2 is a front view showing the concept of a double-side polishing machine used in the above-mentioned apparatus for polishing a glass substrate for a magnetic recording medium.

FIG. 3 is a plan view showing the concept of the double-side polishing machine.

FIG. 4 is a conceptual diagram showing the state of spontaneous sedimentation and separation of a polishing liquid obtained by polishing a glass substrate for a magnetic recording medium.

[Explanation of symbols]

 Reference Signs List 1 double-side polishing machine (polishing machine) 2 polishing liquid circulation device (polishing liquid circulation means) 12 substrate for magnetic recording medium 13 upper surface plate 14 lower surface plate 15 carrier 16 sun gear 17 internal gear 19 polishing solution 21 first tank 22 first Two tanks 23, 24 stirring blades (stirring means)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoru Kameyama 3330-1 Tana, Sagamihara-shi, Kanagawa Pref. Sagami Opto Co., Ltd. (72) Inventor Tatsuichi Kusano 3330-1 Tana, Sagamihara-shi, Kanagawa Pref. Within the Opto (72) Inventor Masaharu Ozawa 1-3-25 Futaba, Shinagawa-ku, Tokyo Inside Nikon Technical Studio

Claims (3)

[Claims] 1. A polishing machine for polishing a glass substrate for a magnetic recording medium using a polishing liquid mixed with an abrasive, and a polishing liquid used for the polishing processing is collected.
A polishing liquid circulation means for removing a glass substance mixed in the polishing liquid used for the polishing process and supplying the polishing liquid to the polishing machine again, wherein the polishing liquid circulation is performed. Means for storing the polishing liquid used for the polishing process, sedimenting and separating the polishing liquid containing only the abrasive from the polishing liquid containing the glass material, and causing the precipitated polishing liquid An apparatus for polishing a glass substrate for a magnetic recording medium, comprising: a separation tank capable of supplying a polishing liquid mixed only with the polishing liquid to the polishing machine. 2. The separation tank comprises a first tank into which a polishing liquid used for the polishing process flows, and a second tank disposed between the first tank and the polishing machine, After performing the sedimentation separation in the first tank, the polishing liquid containing only the precipitated abrasive is discharged into the second tank, and only the abrasive is mixed from the second tank. The apparatus for polishing a glass substrate for a magnetic recording medium according to claim 1, wherein a polishing liquid is supplied to the polishing machine. 3. A first tank stirring means for stirring a polishing liquid in which only the abrasive precipitated in the first tank is mixed, and only the abrasive stored in the second tank is mixed. 3. The polishing apparatus for a glass substrate for a magnetic recording medium according to claim 2, further comprising a second tank stirring means for stirring the polishing liquid.