WO2016002825A1

WO2016002825A1 - Method for producing glass substrate for magnetic disc

Info

Publication number: WO2016002825A1
Application number: PCT/JP2015/068926
Authority: WO
Inventors: 田村　健; 順平深田
Original assignee: Hoya株式会社
Priority date: 2014-06-30
Filing date: 2015-06-30
Publication date: 2016-01-07
Also published as: JP6063611B2; CN106463146A; MY178448A; SG11201609794RA; CN106463146B; JPWO2016002825A1

Abstract

In the present invention, in a glass substrate polishing process, the occurrence of protrusions at the outer peripheral ends of the primary surface of the glass substrate is suppressed. In the polishing process for polishing the primary surface of a glass substrate, when the particle size (μm) for free grit contained in a polishing liquid supplied between a polishing pad and the primary surface of the glass substrate is x (x>0), the relative abundance (%) of grit for each particle size (x) is y, and y is a function f(x) of x, there is a maximum value (y₁) of y in the domain 0.5 μm ≤ x ≤ 1.0 μm, y₁ is the maximum value of y, and when the particle size corresponding to y₁ is x₁, the curve y = f(x) in the xy coordinate plane has three inflection points P2 (x₂, y₂), P3 (x₃, y₃) and P4 (x₄, y₄) (where x₁ < x₂ < x₃ < x₄, y₂ = f(x₂), y₃ = f(x₃), and y₄ = f(x₄)) in the region x > x₁, and the ratio (y_lm/y₁) of the maximum value (y_lm) of y in the domain x₃ ≤ x ≤ x₄ and y₁ is such that 0.5 ≤ y_lm/y₁ < 1.

Description

Manufacturing method of glass substrate for magnetic disk

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

Today, a personal computer, a DVD (Digital Versatile Disc) recording device, and the like have a built-in hard disk device (HDD: Hard Disk Drive) for data recording.
In a hard disk device, a magnetic disk having a magnetic layer provided on a substrate is used, and magnetic recording information is recorded on or read from the magnetic layer by a magnetic head slightly floated on the surface of the magnetic disk. As the substrate of this magnetic disk, a glass substrate having a property that is less likely to be plastically deformed than a metal substrate (aluminum substrate) or the like is preferably used.

In order to increase the storage capacity in the hard disk device, the magnetic recording has been increased in density. For example, the magnetic recording information area is miniaturized by using a perpendicular magnetic recording method in which the magnetization direction in the magnetic layer is perpendicular to the surface of the substrate. Thereby, the storage capacity of one disk substrate can be increased. In such a disk substrate, it is preferable to make the surface of the substrate as flat as possible and align the growth direction of the magnetic grains in the vertical direction so that the magnetization direction of the magnetic layer is substantially perpendicular to the substrate surface.
Furthermore, in order to further increase the storage capacity, a magnetic head equipped with a DFH (Dynamic Flying Height) mechanism is used to significantly shorten the flying distance from the magnetic recording surface, so that the recording / reproducing element of the magnetic head and the magnetic It is also practiced to increase the accuracy of recording / reproducing information (to improve the S / N ratio) by reducing the magnetic spacing between the magnetic recording layers of the disk. Even in this case, the surface irregularities of the substrate of the magnetic disk are required to be as small as possible in order to read and write magnetic recording information by the magnetic head stably over a long period of time.

In order to reduce the surface unevenness of the magnetic disk glass substrate, the glass substrate is polished. There is a method of using an abrasive containing fine abrasive grains such as cerium oxide and colloidal silica for precise polishing for making a glass substrate into a final product (see, for example, Patent Document 1).

JP 2010-59310 A

By the way, when a disc-shaped glass substrate is polished using cerium oxide as an abrasive, the outer peripheral end portion of the main surface of the glass substrate may be raised from the center portion. When a magnetic head equipped with a DFH mechanism is used, this bulge cannot be allowed because the flying distance from the magnetic recording surface is short. Further, in order to increase the storage capacity of one disk substrate, it is preferable that the outer peripheral end portion of the main surface of the glass substrate is flat.

Therefore, an object of the present invention is to provide a method for manufacturing a glass substrate for a magnetic disk that can suppress the occurrence of bulges at the outer peripheral edge of the main surface of the glass substrate in the polishing treatment of the glass substrate.

When the present inventor performed the polishing process while changing the grain size of the abrasive grains, the polishing rate increased when the polishing process was performed using the abrasive grains having a large average particle diameter, while the outer peripheral edge of the main surface of the glass substrate It was found that the bumps occurring in On the other hand, it was found that when polishing is performed using abrasive grains having a small average particle diameter, the occurrence of bulges at the outer peripheral edge of the main surface of the glass substrate is suppressed, but the polishing rate is lowered.
Therefore, the present inventor has studied that by using a mixture of abrasive particles having a large particle diameter and abrasive particles having a small particle diameter, the polishing rate is increased with the abrasive particles having a large particle diameter, and the polishing having a small particle diameter is performed. It turned out that generation | occurrence | production of the protrusion in the outer peripheral edge part of the main surface of a glass substrate can be suppressed by using particle | grains. In other words, it was found that by appropriately controlling the particle size distribution of the abrasive grains, it is possible to suppress the occurrence of bulges at the outer peripheral end of the main surface of the glass substrate.

A first aspect of the present invention is for a magnetic disk having a polishing process for supplying a polishing liquid containing free abrasive grains between a main surface of a glass substrate and a polishing pad and polishing the main surface of the glass substrate. It is a manufacturing method of a glass substrate.
The particle size (μm) of the free abrasive grains contained in the polishing liquid is x (x> 0), the relative frequency (%) of the abrasive grains with the particle size x is y, and y is a function f (x) of x. When considering
There is a maximum value y _{1 of} y in the range of 0.5 μm ≦ x ≦ 1.0 μm, and y ₁ is the maximum value of y,
When the particle size corresponding to y ₁ is x ₁ , the curve y = f (x) in the xy coordinate plane has at least three inflection points P2 (x ₂ , y ₂ ), P3 (in the region of x> x ₁ x ₃ , y ₃ ), P 4 (x ₄ , y ₄ ) (x ₁ <x ₂ <x ₃ <x ₄ , y ₂ = f (x ₂ ), y ₃ = f (x ₃ ), y ₄ = f (X ₄ ))
The ratio y _lm / y ₁ between the maximum value y _lm and y ₁ of y in the range of x ₃ ≦ x ≦ x ₄ is 0.5 ≦ y _lm / y ₁ <1.
For example, f (x) may be an interpolation polynomial for all data points indicating the frequency y for each particle size x of the loose abrasive grains actually measured, or a spline function using individual polynomials between the data points. It may be f (x).
The curve y = f (x) has a raised shape that is convex in the positive direction of the y-axis with respect to the line segment connecting P3 and P4 on the xy coordinate plane between the inflection points P3 and P4. The curve y = f (x) may have a maximum value between P3 and P4, and the shape between the inflection points P3 and P4 may be a so-called “shoulder”. . “Shoulder” refers to a line segment connecting P3 and P4, although y = f (x) does not have a maximum value between the inflection points P3 and P4 (the sign of the differential value does not change). That is, the curve y = f (x) appears to protrude in the positive direction of the y-axis. Between the inflection points P3 and P4, as the value of x increases, the slope of the curve y = f (x) changes from a value larger than the slope of the line segment connecting P3 and P4 to a smaller value. It becomes “shoulder” when does not change.

When the relative frequency of free abrasive grains of twice the particle size _{x n} of the _{x 1} and _{y n,} is preferably _{_{0.5 ≦ y n / y 1 <}} 1.

A second aspect of the present invention is for a magnetic disk having a polishing process for supplying a polishing liquid containing free abrasive grains between a main surface of a glass substrate and a polishing pad and polishing the main surface of the glass substrate. A method of manufacturing a glass substrate,
The particle size distribution of the volume distribution has a particle size distribution with a particle diameter ds-50 value of 0.9 μm to 1.4 μm at a point where the cumulative relative frequency obtained by accumulating the relative frequency of the free abrasive grains from the smaller particle diameter side becomes 50%. Let the free abrasive grain group be the first free abrasive grain group,
When the free abrasive grain group having a particle size distribution with the ds-50 value of 0.5 μm to 0.8 μm is defined as the second free abrasive grain group,
The loose abrasive contained in the polishing liquid is obtained by mixing the first loose abrasive grain group and the second loose abrasive grain group,
The outer peripheral edge of the main surface after polishing the main surface using a polishing liquid containing the obtained free abrasive grains and the mass ratio of the first free abrasive grain group and the second free abrasive grain group Check the correlation with the edge shape evaluation value to evaluate the shape of the part,
The mixture ratio is determined based on the correlation so that the end shape evaluation value falls within a desired range.
Here, the “end shape evaluation value” is, for example, a virtual straight line drawn from the center point of the glass substrate toward an arbitrary point on the outer edge, and a position on the main surface (Z1 and 30 mm away from the center point). When the profile of the main surface protrudes from a virtual straight line L that connects the position (Z2) on the main surface separated by 31.5 mm, the maximum protrusion amount (from the virtual straight line) The maximum distance) represented by a plus value (hereinafter referred to as “index value A”) can be used. For example, an optical surface shape measuring device can be used to measure the index value A.
“The end shape evaluation value falls within a desired range” means, for example, that the index value A is 0 to −20 nm.
The loose abrasive contained in the polishing liquid is a ratio of the mass of the first loose abrasive grain group to the mass of the second loose abrasive grain group (mass of the first loose abrasive grain group / second loose grain). It is preferably obtained by mixing so that the mass of the abrasive grains group is in the range of 1.0 to 2.0.

The main component of the free abrasive grains is preferably one kind of abrasive grains selected from cerium oxide or zirconium oxide.
Here, the “main component” is a component that occupies 50% or more, more preferably 70% or more of the components in the free abrasive grains. Most preferably, the loose abrasive is substantially one type of component.
Examples of the free abrasive grains include cerium oxide abrasive grains, cerium hydroxide abrasive grains, zirconium oxide, and zirconium silicate. In particular, in order to improve the polishing rate, it is preferable to select from cerium oxide or cerium hydroxide, and it is most preferable to use cerium oxide as the free abrasive grains.

As a dispersant for dispersing free abrasive grains in a solvent, a phosphoric acid compound or a polymer compound having various functional groups can be used. As the phosphoric acid compound, for example, sodium hexametaphosphate, sodium pyrophosphate, potassium pyrophosphate and the like can be used. In addition, for example, a polymer compound having a carboxylic acid or a carboxylate salt, a sulfonic acid or a sulfonate salt as a functional group can be used as a dispersant as necessary. The counter cation that forms the salt may be selected from alkali metal ions, ammonium ions, and the like.

The polishing process includes a first polishing process for polishing the main surface of the glass substrate with the free abrasive grains, and a free abrasive grain different from the free abrasive grains, and the glass substrate after the first polishing process. Including a second polishing process for polishing the main surface;
The loose abrasive used for the second polishing treatment is preferably colloidal silica.

A third aspect of the present invention is a polishing that includes loose abrasive grains and is supplied between the main surface of the glass substrate and the polishing pad when performing a polishing process for polishing the main surface of the glass substrate for a magnetic disk. Liquid,
The particle size (μm) of the free abrasive grains contained in the polishing liquid is x (x> 0), the relative frequency (%) of the abrasive grains with the particle size x is y, and y is a function f (x) of x. When considering
There is a maximum value y _{1 of} y in the range of 0.5 μm ≦ x ≦ 1.0 μm, and y ₁ is the maximum value of y,
When the particle size corresponding to y ₁ is x ₁ , the curve y = f (x) in the xy coordinate plane has at least three inflection points P2 (x ₂ , y ₂ ), P3 (in the region of x> x ₁ _{_{_{_{x 3, y 3), (}}}} x 4, y 4) (x 1 <x 2 <x 3 <x 4, y 2 = f (x 2), y 3 = f (x 3), y 4 = f ( x ₄ ))
The ratio y _lm / y ₁ between the maximum value y _lm and y ₁ of y in the range of x ₃ ≦ x ≦ x ₄ is 0.5 ≦ y _lm / y ₁ <1.

According to the present invention, in the polishing treatment of the glass substrate, it is possible to suppress the occurrence of bulging at the outer peripheral end portion of the main surface of the glass substrate.

It is a schematic diagram which shows an example of the particle size distribution of a loose abrasive grain. It is a schematic diagram which shows another example of the particle size distribution of a loose abrasive grain.

Hereinafter, a method for manufacturing a glass substrate for magnetic disks according to an embodiment of the present invention will be described in detail. The present invention is suitable for manufacturing a glass substrate for a magnetic disk having a nominal size of 2.5 to 3.5 inches (diameter 65 to 95 mm) and a plate thickness of 0.4 to 2.0 mm.

(Magnetic disk glass substrate)
First, the glass substrate for magnetic disks will be described. The glass substrate for a magnetic disk has a disc shape and a ring shape in which a circular center hole concentric with the outer periphery is cut out. A magnetic disk is formed by forming magnetic layers (recording areas) in the annular areas on both sides of the glass substrate for a magnetic disk.

A glass blank for magnetic disk (hereinafter simply referred to as a glass blank) is a circular glass plate produced by press molding, and is in a form before the center hole is cut out. As a material for the glass blank, aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used. In particular, aluminosilicate glass can be suitably used in that it can be chemically strengthened and a glass substrate for a magnetic disk excellent in the flatness of the main surface and the strength of the substrate can be produced.

(Method for producing glass substrate for magnetic disk)
Next, a method for manufacturing a magnetic disk glass substrate will be described. First, a glass blank as a material for a plate-shaped magnetic disk glass substrate having a pair of main surfaces is produced by press molding (press molding process). Next, a circular hole is formed in the center part of the produced glass blank, and it is set as a ring-shaped (annular) glass substrate (circular hole formation process). Next, shape processing is performed on the glass substrate in which the circular holes are formed (shape processing processing). Thereby, a glass substrate is produced | generated. Next, end-face polishing is performed on the shape-processed glass substrate (end-face polishing process). Grinding with a fixed abrasive is performed on the glass substrate that has been subjected to end surface polishing (grinding treatment). Next, 1st grinding | polishing is performed to the main surface of a glass substrate (1st grinding | polishing process). Next, chemical strengthening is performed on the glass substrate (chemical strengthening treatment). The chemical strengthening process may not be performed. Next, second polishing is performed on the chemically strengthened glass substrate (second polishing treatment). The glass substrate for magnetic disks is obtained through the above processing. Hereinafter, each process will be described in detail.

(A) Press molding process The front-end | tip part of a molten glass flow is cut | disconnected with a cutter, the cut molten glass lump is pinched | interposed between the press molding surfaces of a pair of metal molds, and a glass blank is formed by pressing. After pressing for a predetermined time, the mold is opened and the glass blank is taken out.

(B) Circular hole formation treatment A disk-shaped glass substrate having a circular hole can be obtained by forming a circular hole in a glass blank using a drill or the like.

(C) Shape processing In the shape processing, chamfering is performed on the end of the glass substrate after the circular hole formation processing.

(D) End surface polishing process In the end surface polishing process, mirror finishing is performed on the inner end face and the outer peripheral end face of the glass substrate by brush polishing. At this time, an abrasive slurry containing fine particles such as cerium oxide as free abrasive grains is used.

(E) Grinding process In the grinding process, grinding is performed on the main surface of the glass substrate using a double-sided grinding apparatus having a planetary gear mechanism. Specifically, the main surface on both sides of the glass substrate is ground while holding the outer peripheral side end face of the glass substrate generated from the glass blank in the holding hole provided in the holding member of the double-side grinding apparatus. The double-sided grinding apparatus has a pair of upper and lower surface plates (upper surface plate and lower surface plate), and a glass substrate is sandwiched between the upper surface plate and the lower surface plate. Then, by moving one or both of the upper surface plate and the lower surface plate and relatively moving the glass substrate and each surface plate, both main surfaces of the glass substrate can be ground.

(F) First polishing treatment In the first polishing, for example, when grinding with fixed abrasive grains is performed, scratches and distortions remaining on the main surface are removed, or fine surface irregularities (microwaveness, roughness) are adjusted. Objective. Specifically, the main surface on both sides of the glass substrate is polished while holding the outer peripheral side end face of the glass substrate in a holding hole provided in the polishing carrier of the double-side polishing apparatus.

In the first polishing process, the glass substrate is polished while applying a polishing slurry by using a double-side polishing apparatus having the same configuration as the double-side grinding apparatus used for the grinding process using fixed abrasive grains. In the first polishing process, a polishing slurry containing free abrasive grains is used instead of fixed abrasive grains, unlike grinding with fixed abrasive grains. As the free abrasive grains used for the first polishing, for example, cerium oxide abrasive grains, cerium hydroxide abrasive grains, zirconium oxide, zirconium silicate and the like are used. In particular, in order to improve the polishing rate, it is preferable to use cerium oxide abrasive grains or zirconium oxide, and it is most preferable to use cerium oxide as free abrasive grains. The particle size distribution of the free abrasive grains used for the first polishing will be described later.

Similar to the double-side grinding apparatus, the double-side polishing apparatus has a pair of upper and lower surface plates (upper surface plate and lower surface plate), and a glass substrate is sandwiched between the upper surface plate and the lower surface plate. An annular flat polishing pad (for example, a resin polisher) is attached to the upper surface of the lower surface plate and the bottom surface of the upper surface plate as a whole. Both main surfaces of the glass substrate are polished by moving either the upper surface plate or the lower surface plate or both of them to move the glass substrate and each surface plate relatively. The polishing load is preferably 50 to 200 g / cm ² . The polishing rate is preferably 0.6 (μm / min). The polishing allowance is preferably 5 to 50 μm.
There is no restriction | limiting in the polishing pad used by the 1st grinding | polishing process of this invention, According to the objective, it can select. For example, an abrasive cloth generally referred to as a “suede pad” having an Asker C hardness of 90 or less, an opening formed in the polishing surface, and a hole extending vertically from the opening in the thickness direction is formed. Can be used. The opening ratio of the polished surface of the suede pad is, for example, 10 to 80% for the case where the diamond dress is used, and 50 to 80% for the case where the buffing is performed. The cross-sectional shape is a foam having pores having an average pore diameter in the horizontal direction of 10 μm or more and 500 μm or less and an average pore diameter in the vertical direction of 50 μm or more. The Asker C hardness is preferably 50 or more, and if it is less than 50, the polishing rate may decrease. The material is generally polyurethane. Since the outermost surface of the suede pad is relatively soft, it can be polished so as to reduce roughness and microwaviness without generating fine scratches. For example, the roughness and fine waviness can be set to 1.0 nm or less in terms of Ra.
The micro waviness is an average roughness (Ra) at a wavelength of 50 to 200 μm, and can be evaluated by measuring a main surface having a radius of 15 mm to 30 mm from the center of the substrate using an optical surface profile measuring machine.
The roughness is an average roughness (Ra) obtained by measuring an area of 1 μm square on the main surface with a resolution of 256 × 256 using AFM.

(G) Chemical strengthening process In a chemical strengthening process, a glass substrate is chemically strengthened by immersing a glass substrate in a chemical strengthening liquid. As the chemical strengthening liquid, for example, a mixed melt of potassium nitrate and sodium sulfate can be used.

(H) Second polishing (final polishing) treatment The second polishing treatment aims at mirror polishing of the main surface. Also in the second polishing, a double-side polishing apparatus having the same configuration as the double-side polishing apparatus used for the first polishing is used. Specifically, the main surface on both sides of the glass substrate is polished while holding the outer peripheral side end face of the glass substrate in a holding hole provided in the polishing carrier of the double-side polishing apparatus. The machining allowance by the second polishing is, for example, about 1 to 10 μm. The second polishing process is different from the first polishing process in that the type and particle size of the free abrasive grains are different and the hardness of the resin polisher is different. Specifically, a polishing liquid containing colloidal silica having a particle size of about 5 to 100 nm as free abrasive grains is supplied between the polishing pad of the double-side polishing apparatus and the main surface of the glass substrate, and the main surface of the glass substrate is polished. The The polished glass substrate is washed with a neutral detergent, pure water, isopropyl alcohol or the like to obtain a magnetic disk glass substrate.
By performing the second polishing treatment, the roughness (Ra) of the main surface can be made 0.3 nm or less, preferably 0.1 nm or less. In addition, the micro surface of the main surface can be 0.1 nm or less. In this manner, the glass substrate subjected to the second polishing is appropriately washed and dried to become a glass substrate for a magnetic disk.

Next, the particle size distribution of the free abrasive grains contained in the polishing slurry used for the first polishing will be described. The particle size distribution of the free abrasive grains can be obtained by a particle size distribution measuring apparatus using a laser diffraction / scattering method. In order to obtain a smooth approximate curve as described later, for example, the particle size distribution is preferably measured with a resolution at which the difference between adjacent measurement target particle sizes is 20% or less of any adjacent particle size. For example, by setting the difference between adjacent measurement target particle sizes to 10% or less of the measurement target particle size, sufficient measurement points can be secured even when the horizontal axis is displayed in logarithm (Log). In addition, although the minimum value of the pitch of a measurement particle diameter can be 1 nm, for example, it is not necessary to measure with the same pitch over the whole area | region.
In this embodiment, the polishing slurry used for the first polishing includes a predetermined dispersion medium (for example, water) and free abrasive grains dispersed in the dispersion medium, and a dispersing agent that disperses the free abrasive grains in the dispersion medium. Further included if necessary.
The particle size distribution (relative frequency) of the free abrasive grains in this embodiment has a peak (maximum value) in the range of 0.5 μm to 1.0 μm. This local maximum is the maximum relative frequency. When this frequency maxima and y _1, the particle size corresponding to y ₁ and _{x 1,} the frequency of free abrasive grains of 2 times the particle size _{x n} of the particle size _{x 1} and _{y n,} 0.5 It is preferable that ≦ y _n / y ₁ <1.

Here, as shown in FIG. 1, the particle size distribution function of the relative frequency y with respect to the particle size x of the free abrasive grains is defined as f (x). As the function f (x), for example, an interpolation polynomial that minimizes the residual sum of squares for all data points indicating the frequency y for each actually measured particle diameter x may be used as an approximate expression. In this case, it is preferable that the error from the data point is 1/100 or less. Also, a spline function using an individual polynomial (a third or higher order polynomial that can be differentiated twice) between each data point may be used as f (x).
At this time, the curve y = f (x) on the xy coordinate plane has a point P1 (x ₁ , y ₁ ) having a maximum value y _{1 of} y in the range of 0.5 μm ≦ x ≦ 1.0 μm, and y ₁ Is the maximum value of y. curve y = f (x) is three inflection points in the region of x> _{x 1} in the xy coordinate plane _{_{_{_{(x 2, y 2),}}}} (x 3, y 3), (x 4, y 4) (x 1 _{_{_{_{<x 2 <x 3 <x}}}} 4, y 2 = f (x 2), y 3 = f (x 3), having a _{y 4 = f (x 4)} ). Here, as shown in FIG. _1, _<is preferably _{_{x n <x 3, y 2}} > y n and _y 3> x ₂ is preferably _{y n.}
The inflection point is a point where the tangent to the curve y = f (x) at that point intersects the curve y = f (x), and the sign of curvature (2 on the curve y = f (x)). The sign of the second derivative f ″ (x)) changes.
_x ₃ ≦ x ≦ x y is the maximum value in the range of ₄ (maximum _value) that takes the _{_{_{_{y lm P lm (x lm,}}}} y lm) when the _ratio _y lm / _{y 1} and _{y lm} and _{y 1} Is 0.5 ≦ y _lm / y ₁ <1.

The polishing slurry having the above particle size distribution requires a first free abrasive grain group having a small average particle diameter and a second free abrasive grain group having an average particle diameter larger than that of the first free abrasive grain group. Accordingly, it can be obtained by mixing with a dispersant at a predetermined ratio.
For example, the particle diameter ds-3 at the point where the cumulative relative frequency of 3% of the cumulative relative frequency of the free abrasive grains from the smaller particle diameter becomes 0.3% is 0.3 μm or more, and the particle diameter at the cumulative relative frequency of 50%. A free abrasive group having a particle size distribution with a ds-50 value of 0.9 μm to 1.45 μm and a cumulative relative frequency of 95% and a particle size ds-95 value of 2.8 μm or less is defined as the first free abrasive group. . A free abrasive grain group having a particle size distribution with a ds-3 value of 0.32 μm or more, a ds-50 value of 0.5 μm to 0.8 μm, and a ds-95 value of 1.0 μm or less is defined as a second free abrasive grain group. At this time, the loose abrasive contained in the polishing liquid is a ratio of the mass of the first loose abrasive grain group to the mass of the second loose abrasive grain group (mass of the first loose abrasive grain group / second loose grain). It is preferable to obtain the above polishing slurry by mixing so that the mass of the abrasive grains group is in the range of 1.0 to 2.0.
In addition, it is preferable that the composition of the free abrasive grains contained in the first free abrasive grain group and the composition of the free abrasive grains contained in the second free abrasive grain group are substantially the same.

As the dispersant, a phosphoric acid compound or a polymer compound having various functional groups can be used. As the phosphoric acid compound, for example, sodium hexametaphosphate, sodium pyrophosphate, potassium pyrophosphate and the like can be used. In addition, for example, a polymer compound having a carboxylic acid or a carboxylate salt, a sulfonic acid or a sulfonate salt as a functional group can be used as a dispersant as necessary. The counter cation that forms the salt may be selected from alkali metal ions, ammonium ions, and the like.

The first loose abrasive grain group and the second loose abrasive grain group may be mixed in advance using a stirrer and then supplied to the double-side polishing apparatus. In addition, the first loose abrasive grain group and the second loose abrasive grain group are separately supplied to the double-side polishing apparatus, and the second loose abrasive grain group with respect to the mass of the second free abrasive grain group in the middle of the supply flow path to the double-side polishing apparatus, So that the ratio of the mass of one free abrasive grain group (the mass of the first free abrasive grain group / the mass of the second free abrasive grain group) is in the range of 1.0 to 2.0. The supply amount may be adjusted respectively.

By polishing the main surface of the glass substrate using a polishing slurry containing free abrasive grains having a particle size distribution as described above, the polishing rate is increased with large abrasive particles, and abrasive particles with small particle sizes are used. Thus, the occurrence of bulges at the outer peripheral end of the main surface of the glass substrate can be suppressed.
Here, the outer peripheral edge of the main surface after polishing the main surface using the polishing liquid containing the obtained free abrasive grains and the mass ratio between the first free abrasive grains group and the second free abrasive grains group The correlation with the edge shape evaluation value for evaluating the shape (bump) of the part is examined, and the mixing ratio is determined based on the investigated correlation so that the edge shape evaluation value falls within the desired range. May be.

In the schematic diagram of the particle size distribution shown in FIG. 1, the point P _lm (x _lm , y _lm ) having the maximum value y _lm also has a peak in the range of x ₃ ≦ x ≦ x ₄ , but the present invention is not limited to this. Absent. For example, it is not necessary to have a frequency peak (maximum value) in the range of x ₃ ≦ x ≦ x ₄ . The maximum value y _lm of y in the range of x ₃ ≦ x ≦ x ₄ may be equal to y ₃ . Further, when x = x ₃ , the first derivative f ′ (x) may be 0 (f ′ (x ₃ ) = 0) or f ′ (x ₃ ) <0.

FIG. 2 is a schematic diagram showing another example of the particle size distribution of loose abrasive grains. The particle size distribution shown in FIG. _{_{2, x 3 ≦ x ≦ x}} 4 ranging the frequency of the peak (maximum value) not not have a maximum value _{y lm} range in the y of _{_x 3} ≦ _x ≦ _x ₄ is y Equal to ₃ .
In the particle size distribution shown in FIG. 2, the curve y = f (x) does not have a maximum value between P3 and P4. That is, the sign of the differential value y = f (x) remains negative between the inflection points P3 and P4. Between the inflection points P3 and P4, the shape of the curve y = f (x) is a so-called “shoulder” shape. That is, the slope of the curve y = f (x) at P3 is larger than the slope of the line segment connecting P3 and P4, and the slope of the curve y = f (x) at P4 is the slope of the line segment connecting P3 and P4. The slope of the curve y = f (x) between the inflection points P3 and P4 is smaller than a value larger than the slope of the line segment connecting P3 and P4 as x increases. The value has changed. Therefore, the curve y = f (x) appears to protrude in the positive direction of the y axis with respect to the line segment connecting P3 and P4.
The main surface of the glass substrate may be polished using a polishing slurry containing free abrasive grains having a particle size distribution shown in FIG.

The present invention is particularly effective when the second polishing process with a small machining allowance is subsequently performed because the bulge of the end shape can be reduced immediately after polishing. This is because when the silica abrasive grains are used in the second polishing treatment, the outer peripheral end on the main surface tends to have a sagging shape to be described later. When silica polishing is performed after the polishing treatment of the present invention, the polishing allowance is preferably 0.1 to 1.5 μm or less in terms of plate thickness. By doing so, the production cost can be further reduced.

As mentioned above, although the manufacturing method of the glass substrate for magnetic discs of this invention was 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, various improvement and a change are carried out. Of course.

Examples of the present invention and comparative examples will be described below.
[Example 1]
The free abrasive grains of cerium oxide having a particle size distribution with a ds-3 value of 0.35 μm or more, a ds-50 value of 1.438 μm, and a ds-95 value of 2.8 μm or less are the first free abrasive grains (first abrasive grains) It was.
Free abrasive grains of cerium oxide having a particle size distribution with a ds-3 value of 0.32 μm or more, a ds-50 value of 0.52 μm, and a ds-95 value of 1.0 μm or less are the second free abrasive grains (second abrasive grains) It was.
The ratio of the mass of the first loose abrasive grain group to the mass of the second loose abrasive grain group (the mass of the first loose abrasive grain group / the mass of the second loose abrasive grain group) is 1.0. In addition, by mixing the first loose abrasive grain group and the second loose abrasive grain group at a mass ratio of 1: 1, a polishing liquid containing free abrasive grains having a particle size distribution shown in Table 1 was obtained. .

[Example 2]
The ratio of the mass of the first free abrasive grain group to the mass of the second free abrasive grain group (the mass of the first free abrasive grain group / the mass of the second free abrasive grain group) is 1.5. In addition, the first loose abrasive grain group and the second loose abrasive grain group were mixed at a mass ratio of 3: 2 to obtain a polishing liquid.

Example 3
The ratio of the mass of the first loose abrasive grain group to the mass of the second loose abrasive grain group (the mass of the first loose abrasive grain group / the mass of the second loose abrasive grain group) is 2.0. In addition, a polishing liquid was obtained by mixing the first loose abrasive grain group and the second loose abrasive grain group at a mass ratio of 2: 1.

[Comparative Example 1]
A polishing liquid was obtained using only the second loose abrasive grain group.

[Comparative Example 2]
The ratio of the mass of the first loose abrasive grain group to the mass of the second loose abrasive grain group (the mass of the first loose abrasive grain group / the mass of the second loose abrasive grain group) is 0.7. In addition, the first loose abrasive grain group and the second loose abrasive grain group were mixed at a mass ratio of 0.7: 1 to obtain a polishing liquid.

[Comparative Example 3]
The ratio of the mass of the first loose abrasive grain group to the mass of the second loose abrasive grain group (the mass of the first loose abrasive grain group / the mass of the second loose abrasive grain group) is 2.3. In addition, by mixing the first loose abrasive grain group and the second loose abrasive grain group at a mass ratio of 2.3: 1, a polishing liquid containing the loose abrasive grains having the particle size distribution shown in Table 1 is obtained. Obtained.

[Comparative Example 4]
A polishing liquid was obtained using only the first loose abrasive grain group.

[Evaluation]
The particle size distribution of the free abrasive grains contained in the polishing liquids of Examples 1 to 3 and Comparative Examples 1 to 4 was determined by a particle size distribution measuring apparatus using a laser diffraction / scattering method. The relative frequency in the range of particle size 0.5 ~ 1.0 .mu.m was determined a particle size _{x 1} as the maximum value _{y 1.} Also, determine the relative frequency y _n at twice the particle diameter x _n of x _1, it was calculated the ratio of the two y _n / y _1.
Based on the information on the obtained particle size distribution, the relative frequency y with respect to the particle size x of the loose abrasive grains was approximated by a polynomial of x. As a result, in any of the approximate curves of Examples 1 to 3 and Comparative Example 1, x> x _One region had three inflection points.
The x coordinate of the inflection point is x ₂ , x ₃ , x ₄ (x ₁ <x ₂ <x ₃ <x ₄ ), and the maximum value y _lm of y in the range of x ₃ ≦ x ≦ x ₄ and at this time determined particle size x _lm of, determine the ratio y _lm / y ₁ and y _1.
Table 1 shows x ₁ , x _lm , y _n / y ₁ , and y _lm / y ₁ .

Using the polishing liquids of Examples 1 to 3 and Comparative Examples 1 to 4, a first glass substrate (diameter 65 mm, plate thickness 0.635 mm) was subjected to a first polishing treatment. While supplying the above polishing liquid between the main surface of the glass substrate and the suede type polyurethane foam polishing pad, the main surface of the glass substrate is moved relative to the main surface of the glass substrate. Polished. The polishing load was 100 g / cm ² . The polishing allowance was 30 μm.

[Indicator value A]
After cleaning the glass substrate after the first polishing treatment, the end shape at the outer edge was evaluated. Here, evaluation was performed using the index value A as an index of the end shape. In order to calculate the index value A, first, a virtual straight line is drawn from the center point of the glass substrate toward an arbitrary point on the outer edge, and a position on the main surface 30 mm away from the center point (referred to as Z1). And a position (referred to as Z2) on the main surface separated by 31.5 mm. And when the profile of the main surface protrudes with respect to the virtual straight line L which connects Z1 and Z2, the edge part of a glass substrate is defined as a sagging shape, The maximum protrusion amount (maximum distance from a virtual straight line) is set. Expressed as a positive value. Conversely, when the profile of the main surface is recessed with respect to the imaginary straight line L, the end of the glass substrate is defined as a raised shape, and the maximum dent amount (maximum distance from the imaginary straight line) is represented by a negative value. . For example, an optical surface shape measuring device can be used to measure the index value A.
In addition, with respect to one annular glass substrate, the index value A was calculated and averaged at four locations on one side at intervals of 90 degrees and a total of eight locations on both sides, and the average value of the annular glass substrate was calculated. The index value was A. The index value A is practically acceptable if it is in the range of −20 nm to 0 nm, and more preferably in the range of −10 nm to 0 nm. In addition, it is not preferable that the index value A exceeds 0 and becomes the plus side (sagging shape side) because the sagging shape may be further deteriorated after the second polishing.
The results are shown in Table 1.

[Polishing speed]
The polishing rate was measured by measuring the amount of displacement of the main surface after the first polishing treatment relative to the main surface before the first polishing treatment. The relative values when the polishing rate of Example 1 is 1 are shown in Table 1.

In Examples 1 to 3, the occurrence of bulges at the outer peripheral edge of the main surface of the glass substrate after the polishing treatment could be suppressed. In Examples 1 to 3, the polishing rate could be maintained at a high level.
On the other hand, in Comparative Examples 1 and 2, it can be seen that the outer peripheral end portion of the main surface of the glass substrate after the polishing treatment has a sagging shape. It can also be seen that the polishing rate decreases because the ratio of the second loose abrasive grains having a small particle size is high.
In Comparative Examples 3 and 4, bumps occurred at the outer peripheral edge of the main surface after the glass substrate was polished. It turns out that generation | occurrence | production of the protrusion in the outer peripheral edge part of the main surface of the glass substrate after grinding | polishing processing can be suppressed by performing grinding | polishing processing using the loose abrasive grain which has a particle size distribution of a present Example.

[Examples 4 and 5]
By appropriately mixing two types of loose abrasive grains different from those in Examples 1 to 3 and Comparative Examples 1 to 4, x ₁ , x _lm , y _n / y ₁ , y _lm / y shown in Table 2 are used. A polishing liquid containing free abrasive grains having a particle size distribution showing a value of ₁ was obtained.

Using the polishing liquid of Example 1 and the polishing liquids of Examples 4 and 5, a disk-shaped glass substrate (diameter 65 mm, plate thickness 0.635 mm) was subjected to a first polishing process. While supplying the above polishing liquid between the main surface of the glass substrate and the suede type polyurethane foam polishing pad, the main surface of the glass substrate is moved relative to the main surface of the glass substrate. Polished. The surface of 100 glass substrates after the first polishing process and the cleaning process was visually inspected under a condensing lamp in a dark room to obtain scratches, and the occurrence rate of scratches was calculated.
The results are shown in Table 2.

In Example 4, scratches occurred on one of the 100 glass substrates, whereas in Examples 5 and 1, no scratches occurred. When Example 4 and Example 5 are compared, it can be seen that when y _n / y ₁ is less than 0.5, scratches are likely to occur. If y _n / y ₁ is less than 0.5, the continuity of the particle size becomes low, so that it is easy to apply a polishing load only to the large-diameter abrasive grains, and as a result, scratches are likely to occur. .
Note that the evaluation of the index value A for the glass substrates of Examples 4 and 5 was the same as that of Example 1.

Example 6
Zirconium oxide (ZrO ₂ ) is used as the abrasive grains, and free abrasive grains having a particle size distribution showing the values of x ₁ , x _lm , y _n / y ₁ , y _lm / y ₁ as in Example 1 are included. A polishing liquid was obtained.

Example 7
Free abrasive grains having a particle size distribution showing values of x ₁ , x _lm , y _n / y ₁ , y _lm / y ₁ as in Example 1 using zirconium silicate (ZrSiO ₄ ) as abrasive grains A polishing liquid containing was obtained.

The first polishing process is performed using the polishing liquids of Example 6 and Example 7, and the amount of displacement of the main surface after the first polishing process relative to the main surface before the first polishing process is measured, whereby the polishing rate is increased. Measured. Table 3 shows the relative values when the polishing rate of Example 1 is 1.

In the polishing liquid of Example 6 using zirconium oxide as the polishing abrasive grains, the polishing rate was almost the same as that of Example 1. On the other hand, in the polishing liquid of Example 7 using zirconium silicate as the abrasive grains, the polishing rate was 6% lower than that of Example 1.
When the index value A was evaluated for the glass substrates of Examples 6 and 7, it was the same as Example 1.
From the viewpoint of the polishing rate, it is understood that cerium oxide or zirconium oxide is preferably used as the abrasive grains.

Claims

A method for producing a glass substrate for a magnetic disk, comprising a polishing process for supplying a polishing liquid containing free abrasive grains between a main surface of a glass substrate and a polishing pad and polishing the main surface of the glass substrate,
The particle size (μm) of the free abrasive grains contained in the polishing liquid is x (x> 0), the relative frequency (%) of the abrasive grains with the particle size x is y, and y is a function f (x) of x. When considering
There is a maximum value y 1 of y in the range of 0.5 μm ≦ x ≦ 1.0 μm, and y 1 is the maximum value of y,
When the particle size corresponding to y 1 is x 1 , the curve y = f (x) in the xy coordinate plane has at least three inflection points P2 (x 2 , y 2 ), P3 (in the region of x> x 1 x 3 , y 3 ), P 4 (x 4 , y 4 ) (x 1 <x 2 <x 3 <x 4 , y 2 = f (x 2 ), y 3 = f (x 3 ), y 4 = f (X 4 ))
The ratio y lm / y 1 between the maximum value y lm and y 1 in the range of x 3 ≦ x ≦ x 4 is 0.5 ≦ y lm / y 1 <1. A method for producing a glass substrate.
Characterized in that when said relative frequencies of free abrasive grains of 2 times the particle size x n of x 1 and y n, it is 0.5 ≦ y n / y 1 < 1, according to claim 1 Manufacturing method of glass substrate for magnetic disk.
A method for producing a glass substrate for a magnetic disk, comprising a polishing process for supplying a polishing liquid containing free abrasive grains between a main surface of a glass substrate and a polishing pad and polishing the main surface of the glass substrate,
The particle size distribution of the volume distribution has a particle size distribution with a particle diameter ds-50 value of 0.9 μm to 1.4 μm at a point where the cumulative relative frequency obtained by accumulating the relative frequency of the free abrasive grains from the smaller particle diameter side becomes 50%. Let the free abrasive grain group be the first free abrasive grain group,
When the free abrasive grain group having a particle size distribution with the ds-50 value of 0.5 μm to 0.8 μm is defined as the second free abrasive grain group,
The loose abrasive contained in the polishing liquid is obtained by mixing the first loose abrasive grain group and the second loose abrasive grain group,
The outer peripheral edge of the main surface after polishing the main surface using a polishing liquid containing the obtained free abrasive grains and the mass ratio of the first free abrasive grain group and the second free abrasive grain group Check the correlation with the edge shape evaluation value to evaluate the shape of the part,
The method of manufacturing a glass substrate for a magnetic disk, wherein the mixing ratio is determined based on the correlation so that the end shape evaluation value falls within a desired range.
The loose abrasive contained in the polishing liquid is a ratio of the mass of the first loose abrasive grain group to the mass of the second loose abrasive grain group (mass of the first loose abrasive grain group / second loose grain). The method for producing a glass substrate for a magnetic disk according to claim 3, obtained by mixing so that the mass of the abrasive grain group) is in the range of 1.0 to 2.0.
The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 4, wherein the main component of the free abrasive grains is one kind of abrasive grains selected from cerium oxide or zirconium oxide.
The polishing process includes a first polishing process for polishing the main surface of the glass substrate with the free abrasive grains, and a free abrasive grain different from the free abrasive grains, and the glass substrate after the first polishing process. Including a second polishing process for polishing the main surface;
The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 5, wherein the loose abrasive grains used in the second polishing treatment are colloidal silica.
A polishing liquid that is provided between the main surface of the glass substrate and the polishing pad when performing a polishing process that includes free abrasive grains and polishes the main surface of the glass substrate for magnetic disk,
The particle size (μm) of the free abrasive grains contained in the polishing liquid is x (x> 0), the relative frequency (%) of the abrasive grains with the particle size x is y, and y is a function f (x) of x. When considering
There is a maximum value y 1 of y in the range of 0.5 μm ≦ x ≦ 1.0 μm, and y 1 is the maximum value of y,
When the particle size corresponding to y 1 is x 1 , the curve y = f (x) in the xy coordinate plane has at least three inflection points P2 (x 2 , y 2 ), P3 (in the region of x> x 1 x 3, y 3), ( x 4, y 4) (x 1 <x 2 <x 3 <x 4, y 2 = f (x 2), y 3 = f (x 3), y 4 = f ( x 4 ))
A polishing liquid, wherein a ratio y lm / y 1 between a maximum value y lm and y 1 of y in a range of x 3 ≦ x ≦ x 4 is 0.5 ≦ y lm / y 1 <1.