JPH0589459A - Production of glass substrate for magnetic disk and magnetic disk as well as glass substrate for magnetic disk and magnetic disk - Google Patents

Abstract

PURPOSE:To expand the smoothness at which high-density recording is possible and a recording area up to a peripheral edge by selecting polishing and working pressures and working time at the time of executing 2nd polishing by using a soft polisher. CONSTITUTION:The 2nd polishing is executed by using surface plates 3, 4 adhered with soft polishers 5 on the inside surfaces and water polishers 9a consisting of cerium oxide. The value of the product Pt of the working pressure P and the working time (t) is set in a 1000<Pt<1500 range. The scratches (flaws entailing cracks) remaining in the 1st polishing can be decreased to the extent that the disk can withstand high-density recording and simultaneously, the ski jump value and roll off value of the glass substrate 1 can be decreased to the extent that the magnetic head can fly near this part without hindrance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass substrate for a magnetic disk used for a magnetic disk capable of high density recording, a method for manufacturing a magnetic disk using the glass substrate, and a glass for a magnetic disk manufactured by the above manufacturing method. The present invention relates to a substrate and a magnetic disk using the glass substrate.

[0002]

2. Description of the Related Art Even in a magnetic disk using a glass substrate, there is a strong demand for improvement in recording capacity, and there is an urgent need for high density recording and expansion of a recording area.

In order to enable high-density recording, it is necessary to make the surface of the glass substrate, which will be the recording portion (hereinafter referred to as the main surface), as smooth as possible, while in order to enlarge the recording area, this smoothing is required. It is necessary to secure as wide an area as possible.

By the way, with respect to a substrate obtained by metal-plating an aluminum alloy and a crystallized glass substrate, attempts have been made to smooth the surface of the substrate with high precision in order to enable high-density recording (for example, Japanese Patent Laid-Open No. Sho-sho). However, the actual situation is that the surface smoothing has not yet been performed on the glass substrate from such a point of view (see 60-229234 and Japanese Patent Publication No. 62-40140).

[0005]

Therefore, the inventor of the present invention
An attempt was made to smooth the disk-shaped glass substrate with high accuracy to enable high-density recording over the entire substrate. As is well known, the glass surface finishing process is roughly divided into (1) roughing (rough grinding), (2) sanding (fine grinding), and (3) polishing. Become. Of these, the sanding step (2) is called so-called lapping and is intended to improve the dimensional accuracy and shape accuracy of the workpiece. The polishing step (3) is called polishing, and its purpose is to improve surface smoothness (reduce surface roughness) and reduce processing strain. The polishing step (3) is usually further divided into two steps, and includes a first polishing step using a hard polisher and a second polishing (final polishing) step using a soft polisher. Here, polishing was performed close to the highest degree considered in the second polishing step.

However, when such a polishing finish is applied, sufficient smoothness can be obtained, but a ridge that is harmful to the flying of the magnetic head is formed at the outer peripheral edge of the substrate (peripheral edge of the substrate). I understood it.

That is, the surface shape measuring instrument (RANK TAYLOR
As shown in FIG. 9, using the Talysurf of HOBSON, move the stylus from the position A toward the center of the glass substrate 2 about 10 mm from the outer peripheral edge to the outer peripheral edge B to move the glass substrate 1 When the straightness accuracy in the diametrical direction was measured, the results shown in FIG. 10 were obtained. According to this, the raised portion (frame) 1c is formed in the vicinity of the outer peripheral edge of the glass substrate.
It is confirmed that a rim is formed at the portion where the ridge 1c transitions to the outer peripheral end face, and the height of the ridge 1c is high, which may hinder the flying of the magnetic head. It was confirmed. Here, the surface of the raised portion 1c is hereinafter referred to as ski jump, and the surface of the rim is referred to as roll-off. In this case, the maximum height S of the ski jump (distance between the flat surface and the apex of the ski jump) S with reference to the flat surface is called the value of the ski jump, and the apex of the ski jump and the chamfer The distance R to the boundary with the surface is called the roll-off value. Then, the ski jump value S was 0.45 μm. If the value of the ski jump is such a large value, the magnetic head cannot fly this portion, so that this portion cannot be an effective recording portion. Therefore, there is a problem that the recording area is narrowed by that amount.

Then, the present inventor has investigated the cause of this, and at the stage of finishing the first polishing step, which is a step before the second polishing (final polishing) step, as shown in FIG.
It was found that the ski jump value S had a sufficiently small value, as shown in FIG. Therefore, it was found that the increase in the value S of the ski jump is caused by the second polishing process.

The present invention has been made under the background described above, has a smoothness sufficient for high-density recording, and can expand the recording area to the peripheral edge. It is an object of the present invention to provide a glass substrate for a magnetic disk, a method for manufacturing a magnetic disk using the glass substrate, a glass substrate for a magnetic disk manufactured by the above manufacturing method, and a magnetic disk using the glass substrate. ..

[0010]

In order to solve the above problems, the present invention provides (1) a main surface of a disk-shaped glass substrate,
In a method of manufacturing a glass substrate for a magnetic disk, in which grinding, first polishing using a hard polisher, and second polishing using a soft polisher are sequentially performed to make the main surface a mirror surface, a polishing process at the time of performing the second polishing The value of the pressure P (g / cm ² ) is P <300, the value of the polishing processing time t (min) is 15 <t <75, and the value Pt of P and t is 3000 <Pt. The polishing processing pressure P and the polishing processing time t were selected so as to be in the range of <10,000.

As a mode of the configuration 1,
(2) In the method of manufacturing a glass substrate for a magnetic disk having the structure 1, the polishing processing pressure P (g
/ Cm ² ) and the polishing processing time t (min), the polishing processing pressure P and the polishing processing time t are selected such that the value of Pt is in the range of 3000 <Pt <9000. It was composed.

Further, as a magnetic disk glass substrate manufactured by the method for manufacturing a glass substrate for a magnetic disk having the structure 1 or 2, (3) For a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk having the structure 1 or 2. In the glass substrate, the maximum height of the raised portion formed on the peripheral portion of the main surface is less than 0.35 μm based on the other flat portion of the main surface.

Further, as a method for producing a magnetic disk using the glass substrate for a magnetic disk produced by the method for producing a glass substrate for a magnetic disk having the constitution 1 or 2,
(4) A magnetic disk is manufactured by performing a step including a step of forming a magnetic film on the main surface of the glass substrate for a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk according to Structure 1 or 2. Was adopted.

A magnetic disk manufactured by the method of Structure 3 is characterized in that (5) a film containing a magnetic film is formed on the main surface of the glass substrate for a magnetic disk according to Structure 3. It is what

[0015]

According to the method of the above constitution 1, a glass for a magnetic disk having a smoothness sufficient for high density recording and capable of expanding an effective recording area to the peripheral edge. It was confirmed that a substrate was obtained. This result was obtained for the first time as a result of various experiments conducted by the present inventor on the basis of the above-mentioned elucidation results, by widely changing polishing conditions without sticking to the common knowledge of the conventional glass polishing process.

Further, it has been confirmed that according to the constitution 2, a glass substrate for a magnetic disk having a smoothness capable of high density recording while ensuring an effective recording area in the constitution 1 can be obtained.

Further, the glass substrate having the structure 3 can be used as a glass substrate for a magnetic disk capable of high density recording up to the peripheral edge of the substrate.

According to the constitutions 4 and 5, it is possible to obtain a magnetic disk capable of high density recording up to the peripheral edge of the substrate.

[0019]

【Example】

(One Example of Method for Manufacturing Glass Substrate for Magnetic Disk) FIG. 1 is an explanatory view of first and second polishing steps, FIG. 2 is an explanatory view of a sanding step, and FIG. 3 is a diagram showing measured values and evaluation after polishing. 4 and 5 are views showing an example of measuring the profile of the main surface after polishing, FIG. 6 is a view showing the relationship between ski jump and processing pressure and processing time, and FIG. 7 is roll-off, processing pressure and processing. FIG. 8 is a diagram showing the relationship with time, and FIG. 8 is an explanatory diagram for measuring the contact state with the magnetic head. Hereinafter, a method of manufacturing a glass substrate for a magnetic disk according to an embodiment will be described with reference to these drawings.

The steps of the method of this embodiment are roughly classified into (1) roughing (rough grinding), (2) sanding (fine grinding),
(3) First polishing, (4) Second polishing (final polishing), and among these steps, (4) Second polishing (final polishing) is a feature of the present invention. .. Hereinafter, these steps will be described in detail.

(1) Roughing Step First, a glass substrate made of aluminosilicate glass pressed into a disk shape having a diameter of 96 mmφ and a thickness of 3 mm is ground by a relatively coarse diamond grindstone to obtain a diameter of 96 mmφ and a thickness. The thickness is 1.5 mm.

Next, both sides of the glass substrate are ground one by one with a diamond grindstone having a finer grain size than that of the grindstone. The load at this time is about 100 kg. As a result, the surface roughness of both surfaces is finished to Rmax of about 10 μ.

Then, a hole is made in the central portion of the glass substrate using a cylindrical grindstone, the outer peripheral end face is also ground to have a diameter of 95 mm, and then the outer peripheral end face and the inner peripheral face are subjected to a predetermined chamfering process.

(2) Sanding process Next, sanding is performed. This sanding process is performed using a polishing apparatus as shown in the schematic cross section of FIG. 2 and is performed twice with the grain size of the abrasive grains changed to # 400 and # 1000.

In FIG. 2, reference numeral 1 is a glass substrate, reference numeral 2 is a carrier slightly thinner than the glass substrate 1, reference numerals 10 and 11 are lapping machines made of cast iron, reference numeral 6 is an inner gear, and reference numeral 7 is. The outer gear, numeral 9 is alumina abrasive grains.

First, by using alumina abrasive grains having a grain size of # 400 and setting the load L to about 100 Kg and rotating the inner gear 6 and the outer gear 7, both surfaces of the glass substrate 1 housed in the carrier 2 are coated. Lapping is performed with an accuracy of 0 to 1 μ and a surface roughness Rmax of about 6 μ.

Next, the alumina abrasive grains are changed to # 1000, and lapping is performed to have a surface accuracy of 0 to 1 μ and a surface roughness Rmax of about 2 μ.

(3) First Polishing Step Next, a first polishing process is performed. This first polishing process is shown in FIG.
Using a polishing device as shown in its schematic cross section,
The scratches and distortions remaining in the sanding step are removed. Here, in the polishing apparatus shown in FIG. 1, instead of the lapping machine in the polishing apparatus shown in FIG. 2, surface plates 3 and 4 having a polisher 5 adhered to the inner surface are used, and instead of using alumina abrasive grains 9. 2 is the same as that shown in FIG. 2 except that a polishing liquid 9a in which cerium oxide having a particle diameter of 1 μm is dissolved in water is used.

In the first polishing step, a hard polisher (trade name "Cerium Pad MHC15" manufactured by Speed Fam Co., Ltd.) was used as the polisher 5 under the following polishing conditions: Polishing liquid ... cerium oxide + water load ... 300 g / Cm ² (L = 238 Kg) Polishing time… 15 minutes Removal amount… 30 μ Lower surface plate rotation speed… 40 RPM Upper surface plate rotation speed… 35 RPM Inner gear rotation speed… 14 RPM Outer gear rotation speed… 29 RPM Glass by this first polishing process The surface roughness of the substrate 1 was Rmax 100 angstrom and the number of scratches (scratches with cracks) was about 50. The straightness accuracy of the glass substrate 1 in the diametrical direction at this time was measured by the above-mentioned surface shape measuring device (RANK). TAYLOR HOBSON's Talysurf)
When measured in the same manner, the same result as that shown in FIG. 11 was obtained.

(4) Second Polishing Step Next, using the polishing apparatus (FIG. 1) used in the first polishing step,
The second polishing process was performed by changing the polisher 5 from a hard polisher to a soft polisher (trade name "Porelax" manufactured by Speed Fam Co., Ltd.). In this second polishing step, the processing pressure P
P which is the product of (g / cm ² ) and the processing time t (min)
The value of t was set to be in the range of 1000 <Pt <15000. This is a feature of the present invention. By setting the Pt value in this range, the scratches remaining in the first polishing are reduced to the extent that they can withstand high-density recording, and at the same time, the ski jump value (s) of the glass substrate 1 is reduced.
And the roll-off value (r) could be made small enough to allow the magnetic head to fly in the vicinity thereof without any trouble. The other polishing conditions at this time are the same as those in the first polishing step.

FIG. 3 shows the processing pressure P in the second polishing process.
(G / cm ² ) and the processing time t (min) were variously changed, and the ski jump value (s) and the roll-off value (r) of each glass substrate were actually measured. , Checking whether flying with a magnetic head,
Furthermore, the number of scratches remaining on the surface of each glass substrate was inspected, and the evaluation based on these results was shown. Further, FIGS. 4 and 5 show a side surface example of the main surface profile obtained during the actual measurement of the ski jump value (s) and the roll-off value (r), and FIGS. 6 and 7 show Based on the measured results, the relationship between the processing time and the ski jump and the relationship between the processing time and the roll-off are shown in a graph with the processing pressure as a parameter. In this case, the ski jump value (s) and the roll-off value (r) are actually measured by the method shown in FIG. 9 using the above-mentioned surface profile measuring device (Talysurf of RANK TAYLOR HOBSON). The same measurement method was used when the results shown in FIG. 10 and FIG. 11 were obtained.

As to whether or not the magnetic head can fly, as shown in FIG. 8, the reading surface of the magnetic head 20 is separated by 0.1 μm from the main surface of the glass substrate 1 while the glass substrate 1 is rotated. The magnetic head 20 was repeatedly moved 10 times from the inner peripheral side to the outer peripheral side of the substrate 1 to check for contact. The presence or absence of contact was detected by a piezo element attached to the reading surface of the magnetic dehead. Further, the magnetic head 20 was stopped at a position where the outer end portion of the magnetic head 20 was located 1 mm inside from the outer peripheral end surface of the glass substrate 1.

Further, for the inspection of scratches (including both scratches with cracks and scratches without cracks), the transmitted light is applied to the glass substrate 1 and the number of scratches remaining in the entire area of the glass substrate 1 with a microscope. Done by counting.

The evaluation criteria for these results were first unsuitable when the flying by the magnetic head could not be performed four times or more. The number of scratches is 1
The case where one or more was observed was also unsuitable. In FIG. 3, the evaluation results are shown by the following symbols.

“Appropriate” evaluation ◎ …… 10 times all flying possible No scratch ○ …… 10 times all flying possible Scratch 1 to 5 pieces △ ₂ …… 10 times all flying possible 5 to 10 scratches △ ₁ … … No flying 1 to 3 times out of 10 scratches No scratch rating “Inappropriate” × ₁ …… No flying more than 4 times out of 10 No scratches × ₂ …… All flying 10 times possible 11 or more scratches Clear from Fig. 3 Therefore, the value of Pt is 1000 <Pt
When it is <15,000, some anxiety remains in the flying, and some scratches remain on the main surface of the glass substrate, but there is no practical problem, and the Pt value is 3000 <Pt <10000 (◎ In the case of), the ski jump value is 0.3 μm or less, and the roll-off value is 0.5 μm. The ski-jump value is sufficiently low and the roll-off value is small. Since the position of the apex is also located closer to the outer peripheral end, the possibility of impeding the flying is completely eliminated. Further, in this case, since scratches are almost completely removed, high density recording can be performed with high quality.

(One Embodiment of Method for Manufacturing Magnetic Disk) Next, one embodiment of a method for manufacturing a magnetic disk using the glass substrate obtained by the method for manufacturing a glass substrate for a magnetic disk according to the above-mentioned embodiment. An example will be described. First,
The surface of the glass substrate obtained by the method for manufacturing a glass substrate for a magnetic disk according to the above-mentioned embodiment is chemically strengthened by replacing Na ions on the surface portion with K ions by ion exchange.

Next, on the one main surface of the glass substrate, Cr
Film (thickness: 1800 Å), Cr-Co-Ni alloy film (1000 Å), SiO ₂
A magnetic disk is obtained by sequentially depositing films (1000 angstroms) by sputtering.

In the magnetic disk thus obtained,
The Cr-Co-Ni alloy film is a magnetic film, the underlayer Cr film is an underlayer that improves the magnetic characteristics of the magnetic film, and the SiO ₂ film is a protective film.

When this magnetic disk was subjected to the same flying test of the magnetic head as in the above-mentioned embodiment, no contact between the magnetic head and the protective film was observed.

A magnetic disk according to this embodiment,
The flying distance of the magnetic head differs from that of the magnetic disk using the glass substrate for the magnetic disk manufactured by the conventional method as shown in FIG. 10 by about 1 mm. The difference in storage capacity due to this corresponds to about 4%. Further, since there are few scratches on the main surface of the glass substrate which is the base of the magnetic film, it is possible to prevent the possibility of causing an error in recording or reading information.

In each of the above-mentioned embodiments, an example in which aluminosilicate glass is used as the glass material forming the glass substrate is used. However, other glass materials such as saw lime glass and quartz glass are used. May be.

Further, the chemical strengthening at the time of manufacturing the magnetic disk is not necessarily required.

Further, the hardness of the hard polisher used in the first polishing step is 80 to 95 (JIS K6301 A type), and the hardness of the soft polisher used in the second polishing is 60 to.
About 80 (JIS K6301 A type) is a standard,
The soft polisher is made of suede and velour, and the hard polisher is hard velor.
Urethane foam, pitch impregnated suede, etc. can be used.

As the polishing agent that can be used in the first and second polishing steps, zircon oxide, colloidal silica or the like can be used.

The polishing method may be one-side polishing instead of double-side polishing, and a method such as pitch polishing or float polishing may be used.

[0046]

As described above in detail, the glass substrate for a magnetic disk, the method for manufacturing the magnetic disk, the glass substrate for a magnetic disk and the magnetic disk according to the present invention are subjected to the second polishing which is the final polishing in the polishing process. Polishing processing pressure P (g / cm ² ) and polishing processing time t
The value of the product Pt with (min) is 1000 <Pt <150
The polishing processing pressure P and the polishing processing time t are selected so as to be in the range of 00, which has sufficient smoothness to enable high density recording,
In addition, it is possible to obtain a glass substrate for a magnetic disk and a magnetic disk capable of expanding the recording area to the peripheral edge.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of first and second polishing steps.

FIG. 2 is a diagram illustrating a sanding process.

FIG. 3 is a diagram showing measured values and evaluation after polishing.

FIG. 4 is a view showing an example of a profile of a profile of a main surface after polishing.

FIG. 5 is a view showing an example of a profile of a main surface profile after polishing.

FIG. 6 is a diagram showing a relationship between a ski jump, a processing pressure, and a processing time.

FIG. 7 is a diagram showing the relationship between roll-off, processing pressure, and processing time.

FIG. 8 is an explanatory diagram of contact state measurement with a magnetic head.

FIG. 9 is an explanatory diagram of straightness accuracy measurement in a diameter direction of a glass substrate.

FIG. 10 is a diagram showing a measurement result of a peripheral portion of a glass substrate after a conventional second polishing step.

FIG. 11 is a diagram showing a measurement result of a peripheral portion of the glass substrate after the conventional first polishing step.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Carrier, 3 ... Lower surface plate, 4 ... Upper surface plate, 5 ... Polisher, 6 ... Inner gear, 7 ... Outer gear,
9 ... Alumina abrasive grains, 9a ... Polishing liquid, 10, 11 ... Lapping machine.

Claims (5)

[Claims] 1. A glass substrate for a magnetic disk in which a main surface of a disk-shaped glass substrate is sequentially subjected to grinding, first polishing using a hard polisher and second polishing using a soft polisher to make the main surface a mirror surface. Manufacturing method, the polishing processing pressure P (g / cm ² ) at the time of performing the second polishing
The value of the product Pt of the polishing time t (min) is 100
A method of manufacturing a glass substrate for a magnetic disk, wherein the polishing processing pressure P and the polishing processing time t are selected so that 0 <Pt <15000. 2. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein a polishing processing pressure P (g / cm ² ) when performing the second polishing.
Value of P <300, and polishing processing time t (min)
Is 15 <t <75, and the product P of P and t
A method of manufacturing a glass substrate for a magnetic disk, wherein the polishing processing pressure P and the polishing processing time t are selected so that the value of t falls within the range of 3000 <Pt <10000. 3. A glass substrate for a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk according to claim 1 or 2, wherein a maximum height of a raised portion formed on a peripheral portion of a main surface is: A glass substrate for a magnetic disk, which is less than 0.35 μm based on the other flat portion of the main surface. 4. A magnetic disk is obtained by performing a step including a step of forming a magnetic film on the main surface of the glass substrate for a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk according to claim 1 or 2. A method of manufacturing a magnetic disk, which is characterized by manufacturing. 5. A magnetic disk comprising the glass substrate for a magnetic disk according to claim 3 and a film including a magnetic film formed on the main surface thereof.