WO2015072569A1

WO2015072569A1 - Method for manufacturing glass substrate for magnetic disk and method for manufacturing magnetic disk

Info

Publication number: WO2015072569A1
Application number: PCT/JP2014/080373
Authority: WO
Inventors: 秀雄酒井
Original assignee: Hoya株式会社
Priority date: 2013-11-15
Filing date: 2014-11-17
Publication date: 2015-05-21
Also published as: CN105745708B; CN105745708A; JPWO2015072569A1; MY183852A; JP6280561B2

Abstract

A method for manufacturing a glass substrate for a magnetic disk comprises polishing treatment for pressing main surfaces on both sides of a glass substrate by polishing pads, and relatively moving the main surfaces and the polishing pads while supplying polishing slurry containing colloidal silica as polishing abrasive grains between the glass substrate and the polishing pads to thereby polish the main surfaces. The polishing slurry is produced by adjusting original polishing slurry that is a starting material of the polishing slurry used in the polishing treatment to an acid state, and further filtering and removing silica precipitates in the original polishing slurry, which have been produced by the adjustment to the acid state.

Description

Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk

The present invention relates to a method for manufacturing a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk.

One of information recording media mounted on a magnetic recording apparatus such as a hard disk drive apparatus is a magnetic disk. A magnetic disk is configured by forming a thin film such as a magnetic layer on a substrate, and a glass substrate is used as the substrate. The surface of the glass substrate is polished with high accuracy so that the flying height of the magnetic head of the magnetic recording apparatus can be reduced as much as possible to achieve high recording density. In recent years, in response to demands for further increase in recording capacity and price of hard disk drive devices, there has been a demand for further improvement in quality and cost of glass substrates for magnetic disks.
As a recent improvement in the quality of glass substrates for magnetic disks, for example, it is required to reduce the surface roughness of the glass substrate and to eliminate defects such as surface line scratches and minute deposits. ing.

In order for a magnetic disk manufactured using such a glass substrate to realize a large recording capacity, it is necessary to reduce the flying height of the magnetic head of the magnetic recording apparatus from the surface of the glass substrate. In order to reduce the flying height, it is desirable to suppress as much as possible the occurrence of scratches on the surface of the glass substrate and defects in deposits. In particular, it is not preferable that deposits adhere to the surface of the glass substrate. In the production of the glass substrate, the surface of the glass substrate is polished using a polishing slurry containing colloidal silica having a very small particle size as the final polishing.

It is known that a conventional glass substrate polishing method generates a scratch extending linearly due to polishing slurry, that is, a linear mark (scratch), on the substrate surface. As a measure for reducing this scratch, in the polishing step, a polishing liquid composition containing at least an abrasive and water and having a pH of 0.1 to 7 and abrasive particles of 0.56 μm or more and less than 1 μm are contained in the polishing liquid composition. There is a method of polishing a substrate by supplying a polishing composition having 500,000 or less per 1 cm ³ to a polishing machine equipped with a surface plate at a flow rate of 0.06 cm ³ / min or more per 1 cm ^{2 of} the substrate to be polished. Known (Patent Document 1).
As a measure for reducing this scratch, there is also known a method of polishing using a polishing liquid in which the ratio of dissolved silica to total silica is 1000 ppm or less in the polishing step (Patent Document 2).

JP 2006-102829 A JP 2010-95568 A

In recent years, for example, a glass substrate for a magnetic disk such as 750 gigabytes has been demanded, and surface roughness of the surface of the glass substrate, and defects due to concave line-shaped scratches and minute deposits on the surface are compared with the conventional one. More stringent requirements are demanded of glass substrates. For this reason, the magnetic head may come into contact with the magnetic disk and crash even with a convex defect caused by deposits on the substrate, which has not been a problem in the past. This means that there is a problem even if the thickness of the deposit on the glass substrate is several nm. The polishing methods disclosed in Patent Documents 1 and 2 described above can reduce scratches on the glass substrate after polishing, but do not mention any deposits on the substrate surface.

Therefore, an object of the present invention is to provide a method for manufacturing a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk, which can reduce deposits that become defects on the glass substrate.

The present invention includes the following forms.

(Form 1)
A method of manufacturing a glass substrate for a magnetic disk,
The main surface on both sides of the glass substrate is pressed with a polishing pad, and the main surface and the polishing pad are relative to each other while supplying a polishing slurry containing colloidal silica as abrasive grains between the glass substrate and the polishing pad. Polishing the main surface by moving it mechanically;
Before polishing the main surface, the silica in the original polishing slurry generated by adjusting the original polishing slurry, which is the source of the polishing slurry used in the polishing process, to an acidic state and further adjusting to the acidic state And a step of producing the polishing slurry by removing the precipitates by filtering. The method for producing a glass substrate for a magnetic disk, comprising:

(Form 2)
The method for manufacturing a glass substrate for a magnetic disk according to mode 1, wherein the original polishing slurry is an alkaline slurry.

(Form 3)
3. The method for producing a glass substrate for a magnetic disk according to aspect 1 or 2, wherein the pH of the original polishing slurry after being adjusted to the acidic state is 1 to 5.

(Form 4)
The method for producing a glass substrate for a magnetic disk according to any one of aspects 1 to 3, wherein the concentration of dissolved silica in the polishing slurry is 0.02% by mass or less.

(Form 5)
The colloidal silica is a glass substrate for a magnetic disk according to any one of modes 1 to 4, which is obtained by heating active silicic acid obtained by ion exchange of an aqueous sodium silicate solution with a cation exchange resin. Production method.

(Form 6)
The magnetic material according to any one of embodiments 1 to 5, wherein the polishing slurry is used for polishing the main surface of the glass substrate, and then recovered and used for polishing the main surface of another glass substrate. A method for producing a glass substrate for a disk.

(Form 7)
The method for producing a glass substrate for a magnetic disk according to any one of Embodiments 1 to 6, wherein the colloidal silica has an average particle diameter of 10 to 100 nm.

(Form 8)
The magnetic disk according to any one of modes 1 to 7, wherein the filtering includes filtering with a depth filter, and filtering with a cationized filter after filtering with the depth filter. Method for manufacturing glass substrate.

(Form 9)
A method for manufacturing a magnetic disk, comprising: forming at least a magnetic layer on the main surface of a glass substrate for a magnetic disk manufactured by the manufacturing method according to any one of modes 1 to 8.

According to the above-described method for manufacturing a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk, it is possible to reduce deposits that become defects on the glass substrate.

It is a figure explaining the structure of the grinding | polishing apparatus which performs the grinding | polishing process performed with the manufacturing method of the glass substrate for magnetic discs of this embodiment. It is a figure explaining the principal part of the polish device of this embodiment.

Hereinafter, the manufacturing method of the glass substrate for magnetic disks of this invention and the manufacturing method of a magnetic disk are demonstrated in detail.
As a result of intensive studies on the deposits that become defects on the main surface of the glass substrate, the present inventors found that the deposits on the main surface of the glass substrate when using a polishing slurry containing colloidal silica are silica aggregates. Or it discovered that it was a gel-like substance of silica and adhered firmly to the main surface of the glass substrate. It is presumed that this deposit is likely to occur because both glass and silica contain a large amount of SiO ₂ and have similar properties. Therefore, during polishing, we found that suppressing the generation of silica agglomerates and silica gels from the polishing slurry containing colloidal silica is the most important for suppressing deposits on the main surface of the glass substrate, The present inventor has conceived a technique including the following embodiment.
Arithmetic average roughness Ra and Rmax, which are indices of surface roughness described in the specification below, are surface roughness specified in JIS B0601. This surface roughness is obtained based on data obtained by measuring a range of 1 μm × 1 μm with a resolution of 512 × 256 pixels using an atomic force microscope (AFM).
FIG. 1 is a diagram illustrating a configuration of a polishing apparatus that performs a polishing process performed by the method for manufacturing a glass substrate for a magnetic disk of the present embodiment. FIG. 2 is a diagram for explaining a main part of the polishing apparatus 1.

As shown in FIG. 1, the polishing apparatus 1 mainly includes a polishing main body 18, and an upper support 12 and a lower support 14 that support the polishing main body 18.
The upper support 12 and the lower support 14 are provided with drive mechanisms (not shown) for driving the upper rotary shaft 65 and the lower rotary shaft 66 of the polishing body 18, and the upper rotary shaft 65 is driven by this drive mechanism. And the lower rotating shaft 66 rotates freely.

The polishing body 18 includes an upper surface plate 40, a lower surface plate 60, a sun gear 61, an internal gear 62, a supply pipe 63, an upper plate member 64, an upper rotating shaft 65, and a lower rotating shaft 66. Including mainly.
In the polishing apparatus 1, as shown in FIG. 2, the polishing pad 10 is attached to the upper surface of the lower surface plate 60 and the bottom surface of the upper surface plate 40. In FIG. 2, the polishing pad 10 is shown in a sheet form. As the polishing pad 10, for example, a urethane pad made of a urethane foam resin can be used.

When the main surface of the glass substrate G to be polished is polished between the upper surface of the lower surface plate 60 and the lower surface of the upper surface plate 40 by sandwiching the disk-shaped glass substrate G between two surface plates, the glass substrate G is A carrier 30 having a holding hole for holding is arranged. In FIG. 2, only one carrier 30 is shown, but a plurality of carriers 30 are used. Specifically, the carrier 30 includes a tooth portion 31 provided on the outer peripheral portion and meshing with the sun gear 61 and the internal gear 62, and one or a plurality of holding holes 32 for receiving and holding the glass substrate G. . The sun gear 61, the internal gear 62 provided on the outer edge, and the disk-shaped carrier 30 constitute a planetary gear mechanism centering on the rotation center axis O of the upper rotary shaft 65 and the lower rotary shaft 66 as a whole. The disc-shaped carrier 30 meshes with the sun gear 61 on the inner peripheral side and meshes with the internal gear 62 on the outer peripheral side, and accommodates and holds one or more glass substrates G (workpieces). On the lower surface plate 60, the carrier 30 revolves while rotating as a planetary gear, and the glass substrate G and the lower surface plate 60 are relatively moved. For example, if the sun gear 61 rotates in the CCW (counterclockwise) direction, the carrier 30 rotates in the CW (clockwise) direction, and the internal gear 62 rotates in the CCW direction. As a result, a relative motion occurs between the lower surface plate 60 and the glass substrate G. Similarly, the glass substrate G and the upper surface plate 40 may be moved relatively.

During the operation of the relative movement, the upper surface plate 40 is pressed against the glass substrate G held by the carrier 30 (that is, in the vertical direction) with a predetermined pressure, and thereby the polishing pad is pressed against the glass substrate G. 10 presses. During polishing, a polishing slurry is supplied between a glass substrate G and the polishing pad 10 from a supply tank (not shown) or via a plurality of supply pipes 63 by a pump (not shown). The supply pipe 63 extends to the upper surface plate 40 through the upper plate member 64. The polishing slurry is a liquid in which abrasive grains of colloidal silica are dispersed in an aqueous solution.

A lower rotating shaft 66 connected to a drive motor (not shown) is fixed to the lower surface plate 60. An upper rotary shaft 65 connected to a drive motor (not shown) is fixed to the upper surface plate 40. Therefore, the upper surface plate 40 and the lower surface plate 60 can rotate freely.

As the glass substrate G to be polished, for example, aluminosilicate glass is used. The aluminosilicate glass contains SiO ₂ and Al ₂ O ₃ as components.
The polishing slurry used for such a polishing apparatus 1 contains colloidal silica as abrasive grains and is produced as follows. Specifically, the original polishing slurry containing colloidal silica that is the basis of the polishing slurry is adjusted to an acidic state. Thereafter, large silica precipitates and gel-like substances produced in the original polishing slurry are removed by filtering. By doing so, the amount of dissolved silica in the original polishing slurry is reduced. That is, the polishing slurry used in the polishing apparatus of the present embodiment is obtained by subjecting an alkaline original polishing slurry having a relatively high dissolved silica concentration to a dissolved silica reduction process before the glass substrate polishing process. The concentration of dissolved silica in the original polishing slurry is, for example, 0.03% by mass or more. It has been found that the amount of silica dissolved in the original polishing slurry containing colloidal silica is large in the alkaline state, while the amount of silica dissolved in the original polishing slurry is relatively small in the acidic state. Therefore, the polishing slurry is prepared by reducing the amount of dissolved silica contained in the original polishing slurry in advance and removing the dissolved silica precipitates and silica gel substances by filtering before using the polishing slurry. Further, it is possible to suppress the precipitation of silica from the dissolved silica on the main surface of the polishing pad 10 or the glass substrate G during polishing. Since the original polishing slurry containing colloidal silica is usually stored under alkaline conditions of pH 8 to 12 from the viewpoint of dispersibility, the pH is adjusted from alkaline to acidic conditions when used for polishing.

In particular, in the range of pH 1 to 5, the concentration of dissolved silica is preferably maintained stably at a low level in the range of 0.02% by mass or less. At this time, the concentration of dissolved silica is 0.005% by mass or more. For this reason, it is preferable that the original polishing slurry adjusted to an acidic state has a pH of 1 to 5 in terms of stably suppressing the precipitation of silica during polishing. In particular, pH 2 or higher is preferable from the viewpoint of not roughening the main surface of the glass substrate G, and pH 4 or lower is preferable from the viewpoint of cleanliness. For example, in an alkaline state having a pH of 10 or more, the concentration of dissolved silica is 0.03% by mass or more. When the pH is 10 or more, the concentration of dissolved silica increases rapidly. Accordingly, it is preferable to adjust the alkaline original polishing slurry having a pH of 10 or more to acidic, because the concentration of dissolved silica can be greatly reduced and more silica precipitates and gel-like substances can be removed. Further, the difference in pH before and after pH adjustment from alkaline to acidic is preferably 5 or more, and more preferably 6 or more. As the difference in pH is larger, the amount of silica deposits and gel-like substances during polishing can be reduced, and the amount of deposits on the substrate surface after polishing can be reduced.
The above-described dissolved silica means a silica component other than the silica component present in the polishing slurry as solid particles. Specifically, dissolved silica passes through the separation membrane when the polishing slurry is centrifuged for 90 minutes at a centrifugal force of 4500 G using a separation tube with a separation membrane having a separation membrane with a molecular weight cut off of 10,000. This indicates a silica component present in the dispersion medium that has moved to the lower part of the centrifuge tube. For example, it is assumed that a silica oligomer corresponds to this.
The concentration of dissolved silica can be measured, for example, by the following method. The polishing slurry is centrifuged using a centrifuge equipped with a centrifuge tube with a separation membrane (separation membrane fraction molecular weight 10,000), and separated into a solution component containing dissolved silica and a solid component containing silica particles. Then, about the collect | recovered solution component, the amount of dissolved silica is quantified by molybdenum reaction, The molecular weight is measured by GPC (gel permeation chromatography analysis).

In order to make the colloidal silica solution acidic, for example, inorganic acids such as sulfuric acid and nitric acid, and organic acids such as citric acid and tartaric acid can be used.
The colloidal silica of this embodiment used for the polishing treatment is obtained by heating active silicic acid obtained by ion exchange of a sodium silicate aqueous solution with a cation exchange resin, and the effect of the dissolved silica reduction treatment is obtained. It is preferable in that it can be exerted greatly. Although the colloidal silica solution obtained by this method is low in cost, the amount of dissolved silica is large because it is an alkaline solution. For this reason, the solution of colloidal silica is made acidic before polishing treatment, the amount of dissolved silica is reduced, and the dissolved silica is reduced from the dissolved silica during polishing by removing the precipitated silica by filtering. Has a great effect of suppressing the precipitation on the main surface of the polishing pad 10 and the glass substrate G.

The average particle diameter (d50) of the colloidal silica is 10 to 100 nm in that the arithmetic average roughness Ra of the surface roughness of the main surface of the glass substrate G is reduced to 0.2 nm or less by polishing the glass substrate G. preferable. More preferably, the average particle diameter (d50) is 10 to 40 nm.
In the filtering process, it is preferable that the original polishing slurry is filtered with a depth filter and further filtered with a pleated filter. In particular, after filtering the original polishing slurry with a depth filter, further including filtering the original polishing slurry with a cationized filter removes the deposited large silica and gel-like substances and becomes ions. This is preferable in that the amount of dissolved silica dissolved is reduced. A pleated filter can be used as the cationized filter.
The depth type filter is a type of filter in which the hole diameter decreases as it goes from the outside to the inside (from the upstream side to the downstream side of the polishing slurry flowing through the filter). In other words, in the depth filter, the pore structure of the filter medium is rough on the inlet side (upstream side), finer on the outlet side (downstream side), and finer continuously or stepwise from the inlet side to the outlet side. Has characteristics. In the depth type filter, large particles among the coarse particles are collected near the inlet side, and small particles are collected near the outlet side, so that effective filtration is possible. The shape of the depth filter may be a bag-like bag type or a hollow cylindrical cartridge type.
As the pleated filter used in the present embodiment, a filter type that is generally formed into a pleated shape by filtering a filtering material into a hollow cylindrical cartridge type can be used. Unlike depth filters that collect in each part in the thickness direction, pleated filters are said to have a thin filter material and are mainly collected on the filter surface, and generally have high filtration accuracy. It is a feature.
The pore size of the depth type filter and the pleated type filter is generally expressed as a filtration accuracy capable of removing 99%. For example, a pore size of 1.0 μm indicates a filter capable of removing 99% of particles having a diameter of 1.0 μm. The pore size of the depth filter is preferably 1.5 μm or less, more preferably 1.0 μm or less, from the viewpoint of reducing the coarse particle removal load. The pore size of the pleated filter is preferably 1.0 μm or less, more preferably 0.8 μm or less, and still more preferably 0.5 μm or less from the viewpoint of reducing coarse particles.
While supplying such a polishing slurry between the glass substrate G pressed by the polishing pad 10 and the polishing pad 10, the glass substrate 10 and the polishing pad 10 are moved relatively to each other on both sides of the glass substrate G. The main surface is polished.

(Glass substrate manufacturing method)
A glass substrate that is polished using such colloidal silica is produced by the following method for producing a glass substrate. In the method for manufacturing a glass substrate for a magnetic disk according to the present embodiment, first, a glass blank as a raw material for a plate-like magnetic disk glass substrate having a pair of main surfaces is formed. Next, the rough grinding process of this glass blank is performed. Thereafter, the glass blank is subjected to a shape processing treatment and an end surface polishing treatment. Then, the precise grinding process which uses a fixed abrasive for the glass substrate obtained from the glass blank is performed. Thereafter, a first polishing process, a chemical strengthening process, and a second polishing process are performed on the glass substrate. In the present embodiment, the above-described process is performed, but it is not necessary to have all the above processes, and these processes may not be performed as appropriate. Hereinafter, each process will be described. In addition, the object of the grinding | polishing process of the glass substrate G using the grinding | polishing slurry containing the colloidal silica which performed the dissolved silica reduction process mentioned above is a 2nd grinding | polishing process.

(A) Glass blank molding process In the molding of a glass blank, for example, a press molding method can be used. A circular glass blank can be obtained by the press molding method. Furthermore, it can manufacture using well-known manufacturing methods, such as a downdraw method, a redraw method, a fusion method, and a float method. A disk-shaped glass substrate serving as a base of the magnetic disk glass substrate can be obtained by appropriately performing shape processing on the plate-shaped glass blanks produced by these known production methods.

(B) Coarse grinding process In the coarse grinding process, specifically, the glass blank is mainly held on both sides of the glass blank while being held in a holding hole provided in a holding member (carrier) mounted on a well-known double-side grinding apparatus. Surface grinding is performed. At this time, the carrier 30 described above may be used. For example, loose abrasive grains are used as the abrasive. In the rough grinding process, the glass blank is ground so as to approximate the target plate thickness dimension and the flatness of the main surface. The rough grinding process is performed according to the dimensional accuracy or surface roughness of the molded glass blank, and may not be performed depending on the case.

(C) Shape processing processing Next, shape processing processing is performed. In the shape processing, after forming the glass blank, a circular hole is formed using a known processing method to obtain a disk-shaped glass substrate having a circular hole. Thereafter, the end surface of the glass substrate is chamfered. Thereby, a side wall surface orthogonal to the main surface and an inclined surface (intervening surface) connecting the side wall surface and the main surface are formed on the end surface of the glass substrate.

(D) End surface polishing treatment Next, an end surface polishing treatment of the glass substrate is performed. The end surface polishing process is a process for performing polishing by supplying a polishing liquid containing loose abrasive grains between the polishing brush and the end surface of the glass substrate and relatively moving the polishing brush and the glass substrate. In the end surface polishing, the inner peripheral side end surface and the outer peripheral side end surface of the glass substrate are to be polished, and the inner peripheral side end surface and the outer peripheral side end surface are in a mirror state.

(E) Fine grinding process Next, a fine grinding process is performed on the main surface of the glass substrate. Specifically, the main surface of the glass substrate is ground using a well-known double-side grinding apparatus. In this case, the fixed abrasive is provided on the surface plate for grinding. Specifically, the main surfaces on both sides of the glass substrate are ground while holding the glass substrate in a holding hole provided in a carrier which is a holding member of a double-side grinding apparatus.
In the grinding process of the present embodiment, the grinding surface containing the fixed abrasive and the main surface of the glass substrate are brought into contact with each other to grind the main surface of the glass substrate. However, grinding using loose abrasive grains may be performed.

(F) First polishing treatment Next, a first polishing treatment is performed on the main surface of the glass substrate. Specifically, polishing the main surface on both sides of the glass substrate while holding the outer peripheral side end face of the glass substrate in a holding hole provided in the carrier of the polishing apparatus having the same configuration as the polishing apparatus shown in FIGS. Is done. The first polishing process uses a polishing pad attached to a surface plate using loose abrasive grains. The first polishing removes cracks and distortions remaining on the main surface when, for example, grinding with fixed abrasive grains is performed while adjusting the thickness of the glass substrate. In the first polishing, it is possible to reduce the surface roughness of the main surface, for example, the arithmetic average roughness Ra, while preventing the shape of the end portion of the main surface from excessively dropping or protruding. In the first polishing treatment, colloidal silica is not used as the polishing slurry, and for example, cerium oxide abrasive grains or zirconia abrasive grains are used. For this reason, in the first polishing process, the polishing slurry subjected to the dissolved silica reduction process is not used. In addition, although the kind in particular of a polishing pad is not restrict | limited, For example, a hard foaming urethane resin polisher is used.

(G) Chemical strengthening treatment The glass substrate can be appropriately chemically strengthened. As the chemical strengthening liquid, for example, a molten liquid obtained by heating potassium nitrate, sodium nitrate, or a mixture thereof can be used. Then, by immersing the glass substrate in the chemical strengthening solution, lithium ions and sodium ions in the glass composition on the surface of the glass substrate are converted into sodium ions and potassium ions having relatively large ion radii in the chemical strengthening solution, respectively. By replacing each, a compressive stress layer is formed in the surface layer portion, and the glass substrate is strengthened.
The timing of performing the chemical strengthening treatment can be determined as appropriate. However, if the polishing treatment is performed after the chemical strengthening treatment, the foreign matter fixed to the surface of the glass substrate by the chemical strengthening treatment can be removed together with the smoothing of the surface. This is particularly preferable because it can be performed. Further, the chemical strengthening treatment may be performed as necessary, and may not be performed.

(H) Second polishing (mirror polishing) treatment Next, the glass substrate after the chemical strengthening treatment is subjected to second polishing. The second polishing is intended for mirror polishing of the main surface. Also in the second polishing, the double-side polishing apparatus shown in FIGS. By doing so, it is possible to reduce the roughness of the main surface while finely adjusting the thickness of the glass substrate G and preventing the shape of the end portion of the main surface from excessively dropping or protruding. Thereby, arithmetic mean roughness Ra of the main surface of the glass substrate G can be 0.2 nm or less, Preferably it can be 0.15 nm or less. At this time, the maximum roughness Rmax is preferably 2.0 nm or less. In the second polishing process, the hardness of the resin polisher of the polishing pad is softer than in the first polishing process. The hardness of the polishing pad used for the second polishing treatment is preferably 60 to 80 in terms of Asker C hardness.

As the free abrasive grains used in the second polishing treatment, the above-described colloidal silica subjected to the dissolved silica reduction treatment is used as the abrasive grains. That is, in the second polishing process, a polishing slurry containing colloidal silica as abrasive grains is used. In this polishing slurry, since the dissolved silica reduction treatment is performed and the amount of dissolved silica is small, it is possible to suppress the precipitation of part of the dissolved silica during polishing. Therefore, it is possible to reduce deposits that become defects on the main surface of the glass substrate, which has been a problem in the past.

Such a polishing slurry may be used for polishing the main surface of the glass substrate, and then recovered and used for polishing the main surface of another glass substrate. At this time, after the polishing slurry is repeatedly used for the polishing treatment, it is preferable that the above-described dissolved silica reduction treatment is performed on the polishing slurry containing colloidal silica as the abrasive grains, and further used for polishing another glass substrate. .
When the polishing slurry is used by circulating the polishing slurry, it is preferable to use the above-described dissolved silica reduction treatment. When the polishing process is repeated, a part of the abrasive grains may be dissolved and the concentration of dissolved silica may increase due to frictional heat caused by sliding between the polishing pad and the glass substrate. In such a case, silica agglomerates or gel-like substances may be newly generated from the dissolved silica in the polishing slurry. For this reason, when the polishing slurry is repeatedly used, it is preferable that the dissolved silica reduction treatment as in this embodiment is performed before the polishing is started.

For example, an adhesion layer, a soft magnetic layer, an underlayer, a perpendicular magnetic recording layer, a carbon protective layer, and a lubricating layer are sequentially formed on the main surface of the magnetic disk glass substrate thus manufactured. Thereby, a magnetic disk is produced. The carbon protective layer is for preventing the magnetic recording layer from deteriorating due to contact with the magnetic head, and is made of hydrogenated carbon, for example, and provides wear resistance. Further, for example, an alcohol-modified perfluoropolyether liquid lubricant is used for the lubricating layer.

[Experimental example]
In order to confirm the effect of the present embodiment, the presence or absence of the dissolved silica reduction treatment in the original polishing slurry before producing the polishing slurry used for the second polishing treatment, and the contents of the filter treatment in the dissolved silica reduction treatment are variously changed. A polishing slurry was prepared, and a glass substrate was prepared by performing a second polishing process using the polishing slurry. Further, a magnetic disk was produced using this glass substrate.
First, after the glass substrate G of aluminosilicate glass is subjected to the chemical strengthening process of (g) described above, the second polishing process is performed using a polishing slurry in which the presence or absence of the dissolved silica reduction process and the content of the filter process are variously changed. went.
The polishing pad used in each of the following examples is a polishing pad made of a soft polisher (suede) (a foamed polyurethane resin having an Asker C hardness of 72). The second polishing process maintains a smooth main surface of the main surface of the glass substrate G obtained by the first polishing process described above, and the surface roughness of the main surface of the glass substrate G is about 2 nm or less in terms of Rmax. This is a mirror-polishing process for finishing. The load in the second polishing process was 100 g / cm ² and the polishing time was 10 minutes. The glass substrate G that had been subjected to the second polishing treatment was immersed in a cleaning bath of neutral detergent, pure water, pure water, and IPA in order to perform ultrasonic cleaning, followed by vapor drying with IPA.

Example 1
As the polishing slurry, water (pH 10) in which 15% by weight of an abrasive of colloidal silica (average particle size (d50) 15 nm) is dispersed is used as an original polishing slurry, and sulfuric acid for adjusting pH is added to the original polishing slurry to make it acidic. After adjusting to (pH 4) and using a depth type filter and a pleat type filter in this order, a polishing slurry was obtained. As the depth filter, a filter having a pore diameter of 1 μm was used. As the pleated filter, a filter having a pore diameter of 0.5 μm was used.

(Example 2)
In Example 2, sulfuric acid for pH adjustment was added to the same original polishing slurry as in Example 1 to make it acidic (pH 4), and after a depth type filter having a pore diameter of 1 μm, a cationized pleated type Filter processing was performed using the filter and then the pleated filter, and second polishing was performed as a polishing slurry. The cationized pleated filter is obtained by cationizing a pleated filter having a pore size of 1 μm.

Example 3
In Example 3, the same treatment as in Example 1 was performed except that sulfuric acid for pH adjustment was added to adjust to pH 5 acidity.

Example 4
In Example 4, the same treatment as in Example 1 was performed, except that pH-adjusting sulfuric acid was added to adjust to acidic pH2.

(Example 5)
In Example 5, the same treatment as in Example 1 was performed except that sulfuric acid for pH adjustment was added to adjust to pH 1 acidity.

(Example 6)
In Example 6, the same treatment as in Example 2 was performed, except that pH-adjusting sulfuric acid was added to adjust the acidity to pH 5.

(Example 7)
In Example 7, the same treatment as in Example 2 was performed, except that pH-adjusting sulfuric acid was added to adjust to acidic pH2.

(Example 8)
In Example 8, the pleated type filter and the depth type filter, which were filtered in this order, were used as the polishing slurry, the pleated type filter was a filter having a pore size of 1 μm, and the depth type filter had a pore size of 0. The same processing as in Example 1 was performed except that a filter having a condition of 5 μm was used.

(Comparative Example 1)
In Comparative Example 1, the same original polishing slurry as in Example 1 was not subjected to filter treatment before polishing, and adjusted to acidity (pH 4) as in Example 1 before being used for polishing.

(Comparative Example 2)
In Comparative Example 2, the same original polishing slurry as in Example 1 was filtered using the depth filter and the pleated filter in this order, and then adjusted to acidic (pH 4) as in Example 1. In addition, this polishing slurry was used for polishing.

(Comparative Example 3)
In Comparative Example 3, the same original polishing slurry as that of Example 1 was subjected to a depth filter (with a pore diameter of 1 μm), and then the cationized pleated filter (with a pore diameter of 1 μm), and then a pleated filter. Filtering (filtering) was performed using (conditions with a pore diameter of 0.5 μm). The polishing slurry subjected to this filter treatment was dispersed in water by 15% by weight and adjusted to acidity (pH 4) in the same manner as in Example 1 before being used for polishing.

The glass substrate obtained in each of the above examples was observed with OSA (Optical Surface na Analyzer), and each defect point was subjected to SEM (scanning electron microscope) / EDX (energy dispersive X-ray spectroscopy). Detailed analysis of defects was performed.

In Example 1, among the defects detected on the main surface of the glass substrate, the number of defects of the silica aggregate and the gel-like substance was 36 points. Similarly, in the order of Examples 2 to 8, Comparative Example 1, Comparative Example 2, and Comparative Example 3, the silica aggregate and the gel substance were 20, 44, 29, 24, 24, 10, 38, 98, 71. 62 points were detected as defects. Table 1 below shows the results. In the following table, the depth type filter is called a depth filter, the pleated type filter is called a pleated filter, and the cationized pleated type filter is called a cationized pleated filter.

From the comparison result of the evaluation of Example 1 and Comparative Example 2 and the comparison result of the evaluation of Example 2 and Comparative Example 3, it is obtained by performing the filter treatment after the original polishing slurry is changed from the alkaline state to the acidic state. It can be seen that the polishing slurry thus produced is effective in that silica agglomerates and gel-like substances do not adhere to the main surface of the glass substrate.
Further, from the comparison results of the evaluations of Example 1 and Comparative Example 1, the silica aggregate and the gel-like substance were removed from the main surface of the glass substrate if no filtering was performed even when the polishing slurry was made acidic and the dissolved silica was reduced. It can also be seen that it cannot be suppressed from adhering to the surface.
From the comparison results of the evaluations of Example 1 and Example 2, it is understood that it is more preferable to further include filtering the polishing slurry using a cationized filter after filtering the polishing slurry with a depth filter. .
Further, from the comparison results of the evaluations of Examples 3 to 5 and the comparison results of the evaluations of Examples 6 and 7, in pH adjustment, the silica aggregates and the gel-like substance are placed on the main surface of the glass substrate as the pH is lowered. It is preferable at the point which suppresses adhering, It is preferable to set it as pH 5 or less, and it is more preferable to set it as pH 2 or less.
Moreover, it can be seen from the comparison results of the evaluations of Example 1 and Example 8 that it is preferable to use the depth type filter and the pleat type filter in this order in the filter processing. In Example 8, it was observed that the used filter was more easily clogged than Example 1.
From this, the effect of this embodiment is clear.

As mentioned above, although the manufacturing method of the glass substrate for magnetic disks of this invention and the manufacturing method of a magnetic disk were demonstrated in detail, this invention is not limited to the said embodiment and Example, In the range which does not deviate from the main point of this invention, Of course, various improvements and changes may be made.

DESCRIPTION OF SYMBOLS 1 Polishing apparatus 10 Polishing pad 12 Upper support stand 14 Lower support stand 18 Polishing main-body part 30 Carrier 31 Tooth part 32 Holding hole 40 Upper surface plate 60 Lower surface plate 61 Sun gear 62 Internal gear 63 Supply pipe 64 Upper plate material 65 Upper rotation shaft 66 Lower rotating shaft

Claims

A method of manufacturing a glass substrate for a magnetic disk,
The main surface on both sides of the glass substrate is pressed with a polishing pad, and the main surface and the polishing pad are relative to each other while supplying a polishing slurry containing colloidal silica as abrasive grains between the glass substrate and the polishing pad. Polishing the main surface by moving it mechanically;
Before polishing the main surface, the silica in the original polishing slurry generated by adjusting the original polishing slurry, which is the source of the polishing slurry used in the polishing process, to an acidic state and further adjusting to the acidic state And a step of producing the polishing slurry by removing the precipitates by filtering. The method for producing a glass substrate for a magnetic disk, comprising:
2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the original polishing slurry is an alkaline slurry.
The method for producing a glass substrate for a magnetic disk according to claim 1 or 2, wherein the pH of the original polishing slurry after being adjusted to the acidic state is 1 to 5.
The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 3, wherein the concentration of dissolved silica in the polishing slurry is 0.02 mass% or less.
The glass substrate for a magnetic disk according to any one of claims 1 to 4, wherein the colloidal silica is obtained by heating active silicic acid obtained by ion exchange of a sodium silicate aqueous solution with a cation exchange resin. Manufacturing method.
6. The polishing slurry according to claim 1, wherein the polishing slurry is used for polishing the main surface of the glass substrate, and then recovered and used for polishing the main surface of another glass substrate. Manufacturing method of glass substrate for magnetic disk.
The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 6, wherein the colloidal silica has an average particle diameter of 10 to 100 nm.
The magnetic filter according to any one of claims 1 to 7, wherein the filtering includes filtering with a depth filter, and filtering with a cationized filter after filtering with the depth filter. A method for producing a glass substrate for a disk.
A method for manufacturing a magnetic disk, wherein at least a magnetic layer is formed on the main surface of the glass substrate for a magnetic disk manufactured by the manufacturing method according to any one of claims 1 to 8.