WO2013146090A1 - Method for manufacturing glass substrate for magnetic disk - Google Patents

Abstract

This invention provides a method for manufacturing a glass substrate for a magnetic disk in which malfunctions such as head crashes and/or thermal asperities are less likely to occur when manufacturing a glass substrate for a magnetic disk by polishing the substrate using a zirconia abrasive as the polishing abrasive in a loose abrasive. A method for manufacturing a glass substrate for a magnetic disk having a polishing step in which, in a state where a donut-shaped glass substrate having at least a pair of main surfaces and two sidewall surfaces forming an inner hole and the contour of the glass substrate is held in a carrier, the pair of main surfaces are sandwiched by polishing pads attached to a turntable, and the glass substrate is polished due to the planetary gear motion of the carrier while a polishing solution is supplied to the pair of main surfaces, the manufacturing method being characterized in that the polishing solution contains, as the polishing abrasive, zirconia particles manufactured using a wet process.

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 or a DVD (Digital Versatile Disc) recording device has a built-in hard disk device (HDD: Hard Disk Drive) for data recording. In particular, in a hard disk device used in a portable computer such as a notebook personal computer, a magnetic disk in which a magnetic layer is provided on a glass substrate is used, and the magnetic head slightly floats above the surface of the magnetic disk. Thus, magnetic recording information is recorded on or read from the magnetic layer. As a substrate for this magnetic disk, a glass substrate is preferably used because it has a property that it is less likely to be plastically deformed than a metal substrate (aluminum substrate) or the like.

In addition, in response to a request for an increase in storage capacity in a hard disk device, the density of magnetic recording has been increased. For example, the magnetic recording information area (recording bit) 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. Furthermore, in order to further increase the storage capacity, the distance from the magnetic recording layer is extremely shortened by further protruding the recording / reproducing element portion of the magnetic head, thereby further improving the accuracy of information recording / reproducing (S / N). To improve the ratio). Such control of the recording / reproducing element portion of the magnetic head is called a DFH (Dynamic Flying Height) control mechanism, and a magnetic head equipped with this control mechanism is called a DFH head. In a substrate for a magnetic disk used in an HDD in combination with such a DFH head, the surface irregularity of the substrate is extremely small in order to avoid collision and contact with the magnetic head and the recording / reproducing element portion protruding further therefrom. It is made to be smaller.

In the process of producing the glass substrate for magnetic disk, the main surface of the plate-like glass material that has become flat after press molding is ground on the main surface, and the grinding process remains on the main surface. A main surface polishing step is included for the purpose of removing scratches and distortions.
Conventionally, in the polishing process of the main surface of the glass substrate for magnetic disks, methods using various abrasive grains such as cerium oxide (cerium dioxide), silicon dioxide, zirconium dioxide (zirconia) as an abrasive are known. For example, Patent Document 1 discloses a method of polishing a glass substrate for a magnetic disk using a polishing liquid in which calcium aluminate, magnesium sulfate, magnesium chloride or the like is added to zirconia abrasive grains.

Japanese Patent No. 2783329

However, when a magnetic layer was formed on a glass substrate made of zirconia as a polishing material for loose abrasive grains on a glass base plate, a magnetic disk was prepared, and a glide test was performed using a glide head. Compared to a glass substrate produced using an abrasive, a decrease in yield (that is, an increase in defect occurrence rate) was observed. The glide inspection is to determine whether or not the magnetic head can stably operate with a predetermined flying height with respect to the magnetic disk. In the glide inspection, a glide head equipped with a piezoelectric element or the like is caused to fly with a predetermined flying height with respect to the main surface of the magnetic disk, and whether or not there is a collision between the glide head and a projection such as a foreign object on the main surface of the magnetic disk. The detection is performed by a piezoelectric element or the like.

Therefore, the present invention manufactures a magnetic disk glass substrate in which foreign substances are unlikely to remain on the glass substrate when the magnetic disk glass substrate is manufactured by polishing using zirconia abrasive as an abrasive for free abrasive grains. An object of the present invention is to provide a method for manufacturing a glass substrate for a magnetic disk.

The inventors of the present application have conducted intensive studies in order to investigate the cause of the decrease in yield due to the above glide inspection. As a result, the main surface of the glass substrate has zirconia particles adhering to the main surface during the formation of the magnetic layer, even after the main surface is sufficiently cleaned and the particles are removed after polishing with a mirror finish. I found out that there was a case. In this case, since a magnetic layer or the like is laminated above the zirconia particles, minute convex portions are formed on the surface of the magnetic disk. And this minute convex part causes troubles, such as a head crash trouble and a thermal asperity trouble. Furthermore, the zirconia particles adhering to the main surface of the glass substrate are also derived from zirconia abrasive grains used for polishing or a part thereof, which are attached to the outer peripheral surface and inner peripheral surface of the glass substrate. It was. In addition, the washing | cleaning method which removes effectively the zirconia particle adhering to the glass substrate is not established.

The inventors of the present application consider the reason why zirconia particles may adhere to the main surface when the magnetic layer is formed even if the main surface is sufficiently washed and particles are removed. Yes. In other words, even if zirconia particles remain on the glass base plate by main surface polishing with zirconia abrasive grains, the zirconia particles remaining on the main surface are removed by final polishing on the main surface, but on the side wall surface of the glass base plate. Residual or adhered zirconia particles are not removed by subsequent cleaning of the glass base plate. In particular, in the main surface polishing with zirconia abrasive grains, when the glass base plate is held on a carrier, the zirconia particles adhere to the side wall surface of the glass base plate by the glass base plate contacting the carrier during polishing. Conceivable. And in the process after the main surface grinding | polishing by a zirconia abrasive grain, it is guessed that the zirconia particle adhering to the side wall surface will detach | leave and adhere to the main surface of a glass base plate or the glass substrate for magnetic discs. For example, after polishing the main surface of the glass base plate, the side wall surface of the glass base plate or the magnetic disk glass substrate is gripped in the process so as not to deteriorate the surface properties of the main surface. It is considered that the particles are detached. In addition, zirconia particles are detached from the side wall surface when the outer side wall surface is gripped in the film forming process on the magnetic disk glass substrate, or from the outer side wall surface in the magnetic disk glass substrate cleaning process. It is also possible that the particles are detached.

In view of the above-mentioned points, the inventors of the present application make the zirconia particles used as polishing abrasive grains in the polishing step into a shape that is difficult to adhere to the side wall surface of the glass base plate, thereby forming the side wall surface of the glass base plate. It has been found that the amount of zirconia particles remaining after being fixed is reduced, whereby zirconia is less likely to adhere to the main surface in a later step. Specifically, it has been found that by making the primary particles of zirconia particles rounded, the zirconia particles are difficult to adhere to the side wall surface of the glass substrate. Then, one of the measures for making the primary particles of the zirconia particles rounded is to manufacture the zirconia particles by a wet method, and the invention of the embodiment described below is conceived. It came.

That is, according to one embodiment of the present invention, a doughnut-shaped glass substrate having at least a pair of main surfaces and two side wall surfaces constituting an inner hole and an outer shape is attached to a polishing platen while being held by a carrier. Manufacturing a glass substrate for a magnetic disk having a polishing step of polishing the glass substrate by planetary gear motion of the carrier while sandwiching the pair of main surfaces with the polishing pad provided and supplying a polishing liquid to the pair of main surfaces The method is characterized in that the polishing liquid contains zirconia particles produced by a wet method as abrasive grains.

In the above method for producing a glass substrate for a magnetic disk, the zirconia particles are preferably formed by agglomeration of primary particles having a particle size in the range of 70 to 200 nm.

In the method for manufacturing a glass substrate for a magnetic disk, the BET specific surface area of the zirconia particles is preferably in the range of 4 to 15 m ² / g.

In the method for producing a glass substrate for a magnetic disk, it is preferable that the average particle diameter (D50) of the zirconia particles is in the range of 0.2 to 0.6 μm.

In the above method for producing a glass substrate for magnetic disk, when the length of the major axis of the primary particles of the zirconia particles is X1, and the length of the minor axis perpendicular to the major axis is X2, X1 / X2 is 1. It is preferably 0 to 1.3.

In the method for manufacturing a glass substrate for a magnetic disk, the surface roughness of the end face of the carrier that contacts the side wall surface of the glass substrate is preferably 5 μm or less.

In the method for producing a glass substrate for magnetic disk, the surface roughness of the side wall surface of the glass substrate before being polished with the polishing liquid having zirconia particles is 0.1 μm or less in terms of arithmetic average roughness Ra. Is preferred.

In the method for manufacturing a glass substrate for magnetic disk, the glass substrate for magnetic disk preferably has a diameter larger than 2.5 inches and a plate thickness of 0.6 mm or less.

In the method for manufacturing a glass substrate for a magnetic disk, after the polishing step, the fracture toughness value K _1c of the glass substrate is 0.7 [MPa / m ^1/2 ] or more as measured by a Vickers hardness meter. It is preferable to have a chemical strengthening step for chemically strengthening the glass substrate.

The disassembled perspective view of the grinding | polishing apparatus (double-side polish apparatus) used at a 1st grinding | polishing process. Sectional drawing of the polisher (double-side polish apparatus) used at a 1st grinding | polishing process. The figure which shows typically the zirconia particle (secondary particle) of embodiment. The figure for demonstrating the effect | action of the zirconia particle of embodiment. It is a figure which shows the state by which the zirconia particle was pressed on the side wall surface of a glass base plate, and shows the case of the zirconia particle manufactured by the wet method, and the case of the zirconia particle manufactured by the dry method. In the case of zirconia particles produced by a wet method, schematically showing the state when the zirconia particles are acting in the polishing process between the main surface of the glass base plate and the polishing pad (this polishing step) And the case of zirconia particles produced by a dry method, unlike the polishing step. The figure which shows the measuring method of the particle size of the primary particle of a zirconia particle.

Hereinafter, the manufacturing method of the glass substrate for magnetic disks of this embodiment will be described in detail.

[Magnetic disk glass substrate]
Aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used as the material for the magnetic disk glass substrate in the present embodiment. 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. More preferably, it is an amorphous aluminosilicate glass.

Although the composition of the glass substrate for a magnetic disk of this embodiment is not limited, the glass substrate of this embodiment is preferably converted to an oxide standard and expressed in mol%, SiO ₂ is 50 to 75%, Al _{2 to} O ₃ to 1 to 15%, at least one component selected from Li ₂ O, Na ₂ O and K ₂ O in total 5 to 35%, selected from MgO, CaO, SrO, BaO and ZnO 0-20% in total of at least one component, and at least one selected from ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂ An amorphous aluminosilicate glass having a composition having a total of 0 to 10% of components.

The glass substrate for magnetic disk in this embodiment is an annular thin glass substrate. Although the size of the glass substrate for magnetic disks is not ask | required, for example, it is suitable as a glass substrate for magnetic disks with a nominal diameter of 2.5 inches.

[Method of manufacturing glass substrate for magnetic disk]
Hereinafter, the manufacturing method of the glass substrate for magnetic disks of this embodiment is demonstrated for every process. However, the order of each step may be changed as appropriate.

(1) Molding and lapping process of glass base plate In the process of forming a glass base plate by, for example, the float process, first, for example, molten glass having the above-described composition is continuously poured into a bath filled with a molten metal such as tin. To obtain plate glass. The molten glass flows along the traveling direction in a bathtub that has been subjected to a strict temperature operation, and finally a plate-like glass adjusted to a desired thickness and width is formed. From this plate glass, a glass base plate having a predetermined shape as a base of the glass substrate for a magnetic disk is cut out. Since the surface of the molten tin in the bath is horizontal, the flatness of the surface of the glass base plate obtained by the float process is sufficiently high.
For example, in a glass base plate molding process by a press molding method, a glass gob made of molten glass is supplied onto a lower mold that is a receiving gob forming mold, and an upper mold that is a lower mold and an opposing gob forming mold is used. Glass gob is press molded. More specifically, after a glass gob made of molten glass is supplied onto the lower mold, the lower surface of the upper mold cylinder and the upper surface of the lower mold cylinder are brought into contact with each other, and the upper mold and the upper mold mold are slid. Form a thin glass blank forming space outside the moving surface and the sliding surface of the lower mold and the lower mold body, and lower the upper mold to perform press molding. To rise. Thereby, the glass base plate used as the origin of the glass substrate for magnetic discs is shape | molded.
In addition, a glass base plate can be manufactured using not only the method mentioned above but well-known manufacturing methods, such as a downdraw method, a redraw method, and a fusion method.

Next, lapping processing using alumina-based loose abrasive grains is performed on both main surfaces of the glass base plate cut into a predetermined shape, if necessary. Specifically, the lapping platen is pressed on both sides of the glass base plate from above and below, a grinding liquid (slurry) containing free abrasive grains is supplied onto the main surface of the glass base plate, and these are moved relatively. Perform lapping. In addition, when a glass base plate is shape | molded with the float glass process, since the precision of the roughness of the main surface after shaping | molding is high, you may abbreviate | omit this lapping process.

(2) Coring process Using a cylindrical diamond drill, an inner hole is formed in the center of the glass base plate to obtain an annular glass base plate.

(3) Chamfering step After the coring step, a chamfering step of forming a chamfered portion at the ends (outer peripheral end and inner peripheral end) is performed. In the chamfering step, the outer peripheral end and the inner peripheral end of the annular glass base plate are chamfered with, for example, a metal bond grindstone using diamond abrasive grains to form a chamfered portion.

(4) End face polishing step Next, end face polishing (edge polishing) of an annular glass base plate is performed.
In the end surface polishing, the inner peripheral side wall surface (end surface) and the outer peripheral side wall surface (end surface) of the glass base plate are mirror-finished by brush polishing. At this time, a slurry containing fine particles such as cerium oxide as free abrasive grains is used. By performing end surface polishing, removal of contamination such as dust on the side wall surface of the glass base plate, damage or scratches, etc., preventing the occurrence of thermal asperity, corrosion of sodium and potassium, etc. It is possible to prevent the occurrence of ion precipitation that is a cause.
In order to make the end face of the glass base plate smooth, thereby making it difficult for the zirconia abrasive grains to adhere to the side wall surface of the glass base plate in the first polishing step of the subsequent step, the end face polishing step is performed before the first polishing step. It is preferable to carry out. For example, it is preferable to perform the end surface polishing so that the arithmetic average roughness Ra of the end surface of the glass base plate after the end surface polishing step is 0.1 μm or less.

(5) Grinding process using fixed abrasive grains In the grinding process using fixed abrasive grains, grinding is performed on the main surface of the annular glass base plate using a double-side grinding apparatus equipped with a planetary gear mechanism. The double-sided grinding apparatus has a pair of upper and lower surface plates (upper surface plate and lower surface plate), and an annular glass base plate is sandwiched between the upper surface plate and the lower surface plate. Then, by moving both the upper surface plate and the lower surface plate, or both of them, the main surface of the glass base plate is ground by relatively moving the glass base plate and each surface plate. be able to.

(6) 1st grinding | polishing (main surface grinding | polishing) process Next, 1st grinding | polishing is given to the main surface of the ground glass base plate. The machining allowance by the first polishing is, for example, about several μm to 50 μm.

(6-1) Polishing Device A polishing device used in the first polishing step will be described with reference to FIGS. FIG. 1 is an exploded perspective view of a polishing apparatus (double-side polishing apparatus) used in the first polishing step. FIG. 2 is a cross-sectional view of a polishing apparatus (double-side polishing apparatus) used in the first polishing process. Note that the same configuration as this polishing apparatus can be applied to a grinding apparatus used in the above-described grinding process.

As shown in FIG. 1, the polishing apparatus has a pair of upper and lower surface plates, that is, an upper surface plate 40 and a lower surface plate 50. An annular glass base plate G is sandwiched between the upper surface plate 40 and the lower surface plate 50, and either one or both of the upper surface plate 40 and the lower surface plate 50 are moved to operate the glass base plate G. By moving the surface plates relative to each other, both main surfaces of the glass base plate G can be polished.

The configuration of the polishing apparatus will be described more specifically with reference to FIGS.
In the polishing apparatus, an annular flat polishing pad 10 is attached to the upper surface of the lower platen 50 and the bottom surface of the upper platen 40 as a whole. The carrier 30 includes a tooth portion 31 that is provided on the outer peripheral portion and meshes with the sun gear 61 and the internal gear 62, and one or a plurality of holes 32 that accommodate and hold the glass base plate 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 centered on the central axis CTR 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 base plates G (workpieces). On the lower surface plate 50, the carrier 30 revolves while rotating as a planetary gear, and the glass base plate G and the lower surface plate 50 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, relative movement occurs between the polishing pad 10 and the glass base plate G. Similarly, the glass base plate G and the upper surface plate 40 may be relatively moved.

During the relative movement, the upper surface plate 40 is pressed against the glass base plate G (that is, in the vertical direction) with a predetermined load, and the polishing pad 10 is pressed against the glass base plate G. A polishing liquid (slurry) is supplied between the glass base plate G and the polishing pad 10 from the polishing liquid supply tank 71 via one or a plurality of pipes 72 by a pump (not shown). The main surface of the glass base plate G is polished by the abrasive contained in the polishing liquid. Here, it is preferable that the polishing liquid used for polishing the glass base plate G is discharged from the upper and lower surface plates, returned to the polishing liquid supply tank 71 by a filter and a return pipe (not shown), and reused.

In this polishing apparatus, it is preferable that the load of the upper surface plate 40 applied to the glass base plate G is adjusted for the purpose of setting a desired polishing load on the glass base plate G. Load, 50 g / cm ² or more is preferred from the viewpoint of high polishing rate achieved, more preferably 70 g / cm ² or more, 90 g / cm ² or more is more preferable. Further, from the viewpoint of reducing scratches and stabilizing the quality, the polishing load is preferably 180 g / cm ² or less, more preferably 160 g / cm ² or less, and even more preferably 140 g / cm ² or less. That is, the load is preferably 50 g / cm ² to 180 g / cm ^2, more preferably 70 g / cm ² to 160 g / cm ^{2, and} still more preferably 90 g / cm ² to 140 g / cm ² .

The supply rate of the polishing liquid during polishing processing varies depending on the polishing pad 10, the composition and concentration of the polishing liquid, and the size of the glass base plate G, but is preferably 500 to 5000 ml / min, more preferably from the viewpoint of improving the polishing rate. Is 1000 to 4500 ml / min, more preferably 1500 to 4000 ml / min. The rotation speed of the polishing pad 10 is preferably 10 to 50 rpm, more preferably 20 to 40 rpm, and further preferably 25 to 35 rpm.

(6-2) Polishing abrasive (Zirconia (ZrO ₂ ))
(A) Polishing Abrasive Grain Purification Method The polishing liquid used in the polishing apparatus of FIG. 1 contains zirconia (ZrO ₂ ) particles produced by a wet method rather than a dry method as abrasive grains.
Here, the dry method is a method of producing by pulverized product of zirconia or desiliconized zirconia obtained by electrofusion method, pulverized product of baderite or the like. The electrofusion method is a process in which zircon sand, badelite or the like is heated to about 2,700 ° C. to evaporate silicon to lower the silicon concentration and improve the zirconium concentration. Desiliconized zirconia is a powder in which the silicon concentration is reduced by electrofusion. Badelite is a natural mineral, and is a relatively high purity zirconia having a low silicon concentration at the time of the natural mineral.
On the other hand, unlike the dry method, the wet method produces a solution in which a compound containing zirconium is dissolved in a chemical, and crystal growth is performed in the solution to produce a sol containing zirconium, which is then fired to produce zirconium. It is a manufacturing method to do. For example, in a known wet method, a zirconia powder is generally produced through the following steps (I) to (V).

(I) Flotation process: Zircon concentrate by selecting ilmenite, rutile, and monazite using specific gravity ore, using the difference in specific gravity, removing silica sand, and using the difference in specific gravity, magnetism, and conductivity. (Zircon sand).
(II) Caustic soda melting step: Silica is separated by melting zircon sand with caustic soda.
(III) Hydrochloric acid decomposition step: Decompose and concentrate with hydrochloric acid to produce zirconium oxychloride (ZrOCl ₂ · 8H ₂ O).
(IV) Washing and filtration step: Zirconium oxychloride is washed with water and filtered to obtain zirconium hydroxide (Zr (OH) ₄ ).
(V) Firing and pulverizing step: Zirconium hydroxide is baked and pulverized to produce zirconia powder.

Regardless of whether the dry method or the wet method is used, a pulverizing step of pulverizing zirconia with any of a ball mill, a jet mill, and a bead mill, or a combination thereof, is performed in order to produce powdered zirconia. The mill used in the pulverization process and its setting vary depending on the target particle size of zirconia and the like. Here, the zirconia produced by the dry method causes intragranular cracking of zirconia in the pulverization step, and becomes particles having a sharp tip. On the other hand, zirconia produced by a wet method is cut at the interface between primary particles with little intragranular cracking in the pulverization process (that is, it becomes a grain boundary crack), and the tip is as in the dry method. Are sharp and few sharp particles are formed. As a result, the primary particles of the zirconia particles produced by the wet method have a rounded shape unlike the dry method.
The zirconia particles used as abrasive grains take the form of secondary particles (aggregates of primary particles), and the secondary particles (made by a wet method) are schematically shown in FIG. Show. As shown in FIG. 3, zirconia particles as abrasive grains take the form of an aggregate of a plurality of primary particles. As shown in FIG. 3, the shape of primary particles of zirconia particles produced by a wet method is rounded as a whole.

With reference to FIGS. 4 and 5, description will be given of the action of adding zirconia particles produced by a wet method in the polishing liquid as polishing abrasive grains in this polishing step.
FIG. 4 is a diagram illustrating a state in which the glass base plate G is accommodated in the hole 32 of the carrier 30. As shown in FIG. 4, in a state where the glass base plate G is accommodated in the carrier 30 of the polishing apparatus, in order to enable the glass base plate G to be detached from the carrier 30, between the carrier 30 and the glass base plate G. Is provided with a slight gap CL in the horizontal direction (that is, the direction parallel to the main surface of the glass base plate G). That is, D2> D1 is established when the outer diameter of the glass base plate G to be polished is D1 and the diameter of the hole 32 of the carrier 30 (the diameter of the contact surface with which the glass base plate abuts) is D2. Thus, during polishing, the gap CL between the side wall surface Gt of the glass base plate G and the side wall surface 30t that forms the hole 32 of the carrier 30 has an abrasive of zirconia (ZrO ₂ ) in the polishing liquid. Grain comes in.

During the polishing process, the glass base plate G moves in an unconstrained state in the hole 32 of the carrier 30 in a direction parallel to the main surface while being subjected to a load by the surface plate in the thickness direction. At this time, the side wall surface Gt of the glass base plate G is brought into contact with the side wall surface 30t forming the hole 32, and the zirconia abrasive grains that have entered the gap CL are pressed against the side wall surface Gt of the glass base plate G. FIG. 5 schematically shows a state when the zirconia particles (secondary particles) are pressed against the side wall surface Gt of the glass base plate G. In the case of zirconia particles manufactured by a wet method (main polishing) In the case of a process), the case of the zirconia particle manufactured by the dry method different from this polishing process is shown. The figure in the case of zirconia particles produced by a dry process is shown for comparison.

As shown in the upper part of FIG. 5, since the zirconia abrasive grains used in this polishing step are manufactured by a wet method, the primary particles are rounded, and are the main forms during polishing. The surface of some secondary particles is also rounded. Therefore, even if the zirconia abrasive grains are pressed against the side wall surface Gt of the glass base plate G, the side wall surface Gt is hardly pierced and the possibility that zirconia particles remain on the side wall surface Gt after polishing is low. Since the side wall surface Gt is hardly scratched, scratches due to polishing are less likely to occur. On the other hand, in the case of the zirconia particles manufactured by the dry method (lower part of FIG. 5), since the particles having a sharp pointed tip are formed, the side wall surface Gt is easily pierced and then polished on the side wall surface Gt. There is a high possibility that zirconia particles remain, and the side wall surface Gt may be scratched during polishing, and scratches due to polishing are likely to occur.

FIG. 6 schematically shows a state in which zirconia particles (secondary particles) are acting in the polishing process between the main surface Gp of the glass base plate G and the polishing pad 10. In the case of the zirconia particles manufactured in (in the case of the main polishing step), the case of the zirconia particles manufactured by the dry method is different from the main polishing step. The figure in the case of zirconia particles produced by a dry process is shown for comparison.
It is the individual primary particles constituting the zirconia particles that are in the form of secondary particles that contribute to the polishing by contacting with the main surface Gp of the glass base plate G during the polishing process. Since the zirconia abrasive grains used in this polishing step are manufactured by a wet method, the primary particles are rounded, and therefore scratches are less likely to occur due to contact with the main surface Gp. On the other hand, in the case of zirconia particles produced by the dry method (lower part of FIG. 6), the shape of the primary particles that contact the main surface Gp has many sharp points such as rocks. The main surface Gp is easily scratched, and scratches due to polishing are likely to occur.

In short, in this polishing step, since zirconia particles produced by a wet method are contained in the polishing liquid as polishing abrasive grains, the zirconia particles hardly remain on the side wall surface Gt of the glass base plate G after polishing, and the side wall surface There is an advantage that scratches hardly occur on Gt and the main surface Gp.

(B) Primary particle size of abrasive grains (hereinafter referred to as “primary particle size”)
Since the contact point with the main surface of the glass base plate G increases during the polishing process as the primary particle diameter of the zirconia abrasive grains is smaller (that is, contact is made by many primary particles) The force that the primary particles receive from the surface plate is reduced, and as a result, scratches generated on the glass base plate G are reduced. On the other hand, if the primary particles of the zirconia abrasive grains are too small, the contact area with the glass base plate G is reduced, so that the zirconia abrasive grains are easily slipped on the glass base plate G during the polishing process. Will not function effectively and the polishing rate will decrease. Therefore, there is a lower limit for the preferred particle size of the primary particles of zirconia abrasive grains.
Moreover, when the primary particle diameter of a zirconia abrasive grain becomes large, the force which each primary particle receives from a surface plate will increase relatively, and the scratch which arises in the glass base plate G will increase as a result. Therefore, there is an upper limit for the preferred particle size of the primary particles of zirconia abrasive grains.
According to the results of trial and error by the present inventors, the zirconia particles as the abrasive grains are preferably formed by agglomeration of primary particles having a particle size in the range of 70 to 200 nm.

A method for measuring primary particles is shown in FIG. As shown in FIG. 7, the zirconia abrasive grains were observed with an SEM (scanning electron microscope) at a magnification of, for example, 30,000 to 100,000 times, and the major axis length (X1) of the primary particles and the minor axis length were observed. The average value of (X2) ((X1 + X2) / 2) is defined as the primary particle diameter. The major axis and the minor axis are assumed to be orthogonal.
The aspect ratio (X1 ÷ X2 in FIG. 6) of the primary particles of the present embodiment is 1.0 to 1.3, and has a rounded shape as a whole.

Further, the BET specific surface area is known as an index having a certain correlation with the primary particle diameter of the abrasive grains. Similarly, from the viewpoint of the BET specific surface area, according to the results of trial and error by the inventors, the BET specific surface area of the primary particles of the abrasive grains may be in the range of 4 to 15 m ² / g. preferable. The BET specific surface area can be measured by a BET single point method by a gas adsorption method using a flow type specific surface area measuring device.
Depending on the manufacturing conditions, zirconia fine particles that are sufficiently small not to contribute to the polishing ability may be contained, but the BET specific surface area can also be increased by increasing the amount of the fine particles. In this case, the BET specific surface area can be changed without changing the primary particle diameter of the zirconia particles contributing to the polishing ability.

(C) Secondary particle size of the abrasive grains (hereinafter referred to as “secondary particle size”)
Regarding the secondary particle diameter of zirconia abrasive grains, which is the main form at the time of polishing, the lower limit value and the upper limit value are determined by the same idea as the primary particle diameter described above. In addition, when the secondary particle diameter is too large, there is a possibility that the polishing rate may be lowered by reducing the number of secondary particles acting on the polishing under a certain slurry concentration. Therefore, the lower limit value and the upper limit value of the secondary particles are determined from the viewpoint that the polishing action functions effectively (that is, the polishing rate is ensured) and scratches can be reduced.
According to the results of trial and error by the present inventors, the secondary particle diameter (average particle diameter D50) of the abrasive grains is preferably in the range of 0.2 to 0.6 μm. In addition, when the zirconia abrasive grains are granulated, or when the zirconia abrasive grains are aggregated to such an extent that they are broken by the polishing process, the preferable particle diameter range is a value in a state where the zirconia abrasive grains are scattered by the polishing process. Become a range. That is, zirconia is generally used for ceramics, electronic materials, and refractory applications. In ceramics, in order to increase the density of zirconia during ceramic production, wet pulverization was performed to an average particle size of 1 um or less during zirconia production. Thereafter, the secondary particle diameter can be intentionally increased to about several tens of μm by using spray drying or the like in the drying step. Thus, intentionally increasing the secondary particle diameter is called granulation, but the granulated zirconia is easily broken by polishing. Similarly, when zirconia is aggregated with a weak cohesive force due to moisture aggregation or the like, the aggregated zirconia is easily broken by polishing. Therefore, it is preferable to evaluate the secondary particle diameter of the abrasive grains by a value in a state where the abrasive grains are scattered by the polishing process.
The average particle size (D50) means a particle size at which the cumulative volume frequency calculated by the volume fraction is 50% calculated from the smaller particle size.

The surface roughness (Ra) of the side wall surface of the glass base plate before the first polishing is preferably 0.1 μm or less, and more preferably 0.05 μm or less. The surface roughness (Ra) here can be measured with a stylus roughness meter. Since the surface roughness of the side wall surface of the glass base plate G is so small, the contact area with the carrier 30 can be increased, and the number of abrasive grains entering between the glass base plate G and the carrier 30 increases. And since force will be disperse | distributed to more abrasive grains, it will become difficult to pierce the zirconia particle to the side wall surface of the glass base plate G. FIG. Further, if the surface roughness of the side wall surface of the glass base plate G before the first polishing is small, scratches caused by the carrier 30 when entering the carrier 30 are difficult to enter, so zirconia abrasive grains captured by the scratch By reducing the number, the probability of piercing the side wall surface of the glass base plate G can be reduced indirectly. For this reason, it is difficult for zirconia abrasive grains to stick to the side wall surface of the glass base plate G during the first polishing.

In addition, the surface roughness of the end surface (wall surface facing the side wall surface of the glass base plate G) in the hole 32 of the carrier 30 that is in contact with the side wall surface of the glass base plate G is 5 μm or less, preferably 3 μm or less. The surface roughness (Ra) wrinkle here can be measured by moving the needle in the circumferential direction with respect to the end face of the hole 32 using a stylus type roughness meter. Since the surface roughness of the end face of the hole portion 32 of the carrier is so small, the contact area with the glass base plate G can be increased, so that the number of abrasive grains entering between them increases, and more Since the force is dispersed in the abrasive grains, the zirconia particles are less likely to pierce the side wall surface of the glass base plate G. Further, if the roughness of the end surface of the hole 32 of the carrier 30 is small, scratches are less likely to enter the glass base plate G when the end surface comes into contact with the glass base plate G. Therefore, the zirconia abrasive grains captured by the scratches By reducing the number, the probability of piercing the side wall surface of the glass base plate G can be reduced indirectly. While the first polishing is performed, the side wall surface of the glass base plate G is prevented from being excessively roughened, and the zirconia abrasive grains are difficult to adhere to the side wall surface of the glass base plate G.

The manufacturing method of this embodiment is suitable for manufacturing a glass substrate for a magnetic disk having a diameter larger than 2.5 inch size and a plate thickness of 0.6 mm or less. Such a glass substrate for a magnetic disk has a higher aspect ratio (diameter / plate thickness) than the conventional one. For this reason, since the plate | board thickness of a glass base plate is thin and a contact area with the end surface of a carrier is small, a glass base plate tends to contact the end surface of a carrier with a stronger force. Moreover, since the area of the main surface of a glass base plate is large and it is easy to receive a frictional force from a polishing pad, this also makes a glass base plate contact the end surface of a carrier with a stronger force. For these reasons, zirconia particles are likely to adhere to the side wall surface of the glass base plate, and the proportion of zirconia particles attached to the side wall surface of the glass base plate tends to be relatively high. However, according to the manufacturing method of the present embodiment, as described above, since the secondary particles, which are the main forms of zirconia abrasive grains, are rounded, the surfaces thereof are rounded. Even if the abrasive grains are pressed against the side wall surface Gt of the glass base plate G, the occurrence of such a problem can be suppressed because the side wall surface Gt is rarely pierced.

(6-3) Surface irregularities on the main surface of the glass base plate In the first polishing step, the roughness (Ra) of the main surface of the glass base plate is set to 0.5 nm or less and the micro waveness (MW- Polishing is performed so that Rq) is 0.5 nm or less. Here, the micro waveness can be expressed by an RMS (Rq) value calculated as a roughness of a wavelength band of 100 to 500 μm in an area having a radius of 14.0 to 31.5 mm on the entire main surface. It can be measured using a surface profile measuring machine.
The roughness of the main surface is expressed by an arithmetic average roughness Ra defined by JIS B0601: 2001. When the roughness is 0.006 μm or more and 200 μm or less, for example, the roughness is measured with a stylus type roughness measuring machine, and JIS B0633: It can be calculated by the method defined in 2001. As a result, when the roughness is 0.03 μm or less, for example, the roughness can be measured by a scanning probe microscope (atomic force microscope; AFM) and calculated by a method defined in JIS R1683: 2007. In the present application, it is possible to use the arithmetic average roughness Ra when measured at a resolution of 256 × 256 pixels in a measurement area of 1 μm × 1 μm square.

(7) Chemical strengthening process Next, the glass base plate after the first polishing is chemically strengthened.
As the chemical strengthening solution, for example, a mixed solution of potassium nitrate (60% by weight) and sodium sulfate (40% by weight) can be used. In chemical strengthening, the chemical strengthening liquid is heated to, for example, 300 ° C. to 400 ° C., and after the cleaned glass base plate is preheated to, for example, 200 ° C. to 300 ° C., the glass base plate is placed in the chemical strengthening liquid, for example, 1 Soak for 5 to 5 hours. The immersion is preferably performed in a state of being housed in a holder so that the plurality of glass base plates are held by the side wall surfaces so that the entire main surfaces of both glass base plates are chemically strengthened.
In this way, by immersing the glass base plate in the chemical strengthening solution, lithium ions and sodium ions on the surface layer of the glass base plate are replaced with sodium ions and potassium ions having a relatively large ion radius in the chemical strengthening solution, respectively. The glass base plate is strengthened. The chemically strengthened glass base plate is washed. For example, after washing with sulfuric acid, it is washed with pure water or the like.

(8) Second Polishing Step Next, the glass substrate that has been chemically strengthened and sufficiently cleaned is subjected to final polishing. The machining allowance by the final polishing is 5 μm or less. In the final polishing, for example, the polishing apparatus used in the first polishing is used. At this time, the difference from the first polishing is that the type and particle size of the free abrasive grains are different and the hardness of the resin polisher is different. As the free abrasive grains used in the final polishing, for example, fine particles (particle size: diameter of about 10 to 50 nm) such as colloidal silica made turbid in the slurry are used.
A glass substrate for a magnetic disk can be obtained by washing the polished glass base plate with a neutral detergent, pure water, IPA or the like.

As mentioned above, although the manufacturing method of the glass substrate for magnetic discs of this embodiment was demonstrated for every process, the order of a process is not restricted to the order mentioned above.
In the second polishing step, particles such as colloidal silica are supplied between the glass base plate and the hole of the carrier, whereby the side wall surface of the glass base plate is polished and adhered to the side wall surface. The zirconia particles that may be removed may be removed.

In the manufacturing method of the glass substrate for magnetic disks mentioned above, you may perform in order of a chemical strengthening process, a 1st grinding | polishing process, and a 2nd grinding | polishing process. In the case of performing in this order of steps, in the chemical strengthening step, the fracture toughness value K _1c of the glass base plate after chemical strengthening is 0.7 [MPa / m ^1/2 ] or more as measured by a Vickers hardness meter. Thus, it is preferable to adjust the treatment conditions for chemical strengthening. By performing chemical strengthening under such processing conditions, the compressed layer formed on the side wall surface of the glass base plate by chemical strengthening is used to make the zirconia abrasive grains, which are abrasive grains in the first polishing step, which is a subsequent step, of the glass base plate. It can function as a sticking prevention layer for preventing sticking to the side wall surface.

In this case, the chemical strengthening treatment conditions such that the fracture toughness value K _1c of the glass base plate after chemical strengthening is 0.7 [MPa / m ^1/2 ] or more as measured by a Vickers hardness meter are, for example, in advance It may be determined by changing various chemical treatment conditions. The fracture toughness value K _1c is more preferably 1.0 [MPa / m ^1/2 ] or more. Moreover, it is still more preferable in it being 1.3 [MPa / m ^1/2 ] or more. Fracture toughness value _{K 1c} is preferably higher, the upper limit of the fracture toughness value _{K 1c} is not particularly provided. Here, the fracture toughness value K _1c is a sharp diamond indenter of known Vickers hardness meter can be measured by the method of pushing the glass workpiece. That is, the fracture toughness value _K1c is obtained by the following equation from the size of the indentation of the indenter remaining on the glass base plate when the Vickers indenter is pushed in and the length of the crack generated from the corner of the indentation. P is the indentation load [N] of the Vickers indenter, and a is the length [m] half of the diagonal length of the Vickers indentation. E is the Young's modulus [Pa] of the glass base plate, and C is the length [m] that is half the length of the string.

The chemical strengthening treatment conditions include the type of chemical strengthening solution (for example, the mixing ratio of potassium nitrate and sodium sulfate), the temperature of the chemical strengthening solution, the chemical strengthening treatment time, and the like. It is also possible to select a glass composition of the glass base plate such that the fracture toughness value K _1c of the glass base plate after chemical strengthening is 0.7 [MPa / m ^1/2 ] or more as described above.
In the present embodiment, the main surface of the glass base plate is a measurement target of the fracture toughness value _K1c , but the chemical strengthening is performed because the side wall surface of the end face of the glass base plate is chemically strengthened in the same manner as the main surface. fracture toughness K _1c of the side wall surface of the glass workpiece is the same as the measurement results of fracture toughness K _1c of the main surface can be replaced by fracture toughness K _1c of the main surface.

[Magnetic disk]
A magnetic disk is obtained as follows using a magnetic disk glass substrate.
The magnetic disk is, for example, on the main surface of a glass substrate for magnetic disk (hereinafter simply referred to as “substrate”), in order from the closest to the main surface, at least an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), and a protective layer. A layer and a lubricating layer are laminated.
For example, the substrate is introduced into a film forming apparatus that has been evacuated, and a film is sequentially formed from an adhesion layer to a magnetic layer on the main surface of the substrate in an Ar atmosphere by a DC magnetron sputtering method. For example, CrTi can be used as the adhesion layer, and CrRu can be used as the underlayer. As the magnetic layer, for example, a CoPt alloy can be used. It is also possible to form a CoPt-based alloy and FePt based alloy L ₁₀ regular structure and magnetic layer for heat-assisted magnetic recording. After the above film formation, a magnetic recording medium can be formed by forming a protective layer using, for example, C ₂ H ₄ by a CVD method and subsequently performing nitriding treatment for introducing nitrogen into the surface. Thereafter, for example, PFPE (perfluoropolyether) is applied on the protective layer by a dip coating method, whereby a lubricating layer can be formed.
The produced magnetic disk is preferably incorporated in an HDD (Hard Disk Drive) as a magnetic recording / reproducing apparatus together with a magnetic head equipped with a DFH (Dynamic Flying Height) control mechanism.

[Examples and Comparative Examples]
In order to confirm the effect of the manufacturing method of the glass substrate for magnetic disk of this embodiment, a 2.5-inch magnetic disk was produced from the manufactured glass substrate for magnetic disk. The produced glass substrate for a magnetic disk is an amorphous aluminosilicate glass having the following composition.
[Glass composition]
Converted to oxide basis, expressed in mol%, SiO ₂ is 50 to 75%, Al ₂ O ₃ is 1 to 15%, at least one component selected from Li ₂ O, Na ₂ O and K ₂ O 5 to 35% in total, 0 to 20% in total of at least one component selected from MgO, CaO, SrO, BaO and ZnO, and ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Amorphous aluminosilicate glass having a composition having a total of 0 to 10% of at least one component selected from Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂

Each process of the manufacturing method of the glass substrate for magnetic disks of this embodiment was performed in order.
here,
For forming the glass base plate (1), a press molding method used in the method for producing a glass substrate for a magnetic disk described in JP 2011-138589 A was used. In lapping, alumina-based free abrasive grains having an average particle diameter of 20 μm were used.
In the end face polishing of (4), a plurality of glass base plates laminated with a spacer interposed between the glass base plates is polished using cerium oxide having an average particle size (D50) of 1.0 μm as free abrasive grains. Polished with a brush.
In the grinding with the fixed abrasive of (5), the diamond sheet was ground using a grinding device that was bonded to the upper surface plate and the lower surface plate.
In the first polishing of (6), polishing was performed for 60 minutes using the polishing apparatus of FIGS. Detailed polishing conditions are as shown below.
In the chemical strengthening of (7), a liquid mixture of potassium nitrate (60% by weight) and sodium nitrate (40% by weight) is used as the chemical strengthening liquid, the temperature of the chemical strengthening liquid is set to 350 ° C., and preheated to 200 ° C. in advance. The glass base plate was immersed in the chemical strengthening solution for 4 hours.
In the second polishing of (8), polishing was performed for a predetermined time using colloidal silica having a particle diameter of 10 to 50 μm using another polishing apparatus similar to that shown in FIGS. Thereby, arithmetic mean roughness Ra (JIS B0601: 2001) of the main surface was made into 0.15 nm or less. The glass substrate after the final polishing was cleaned using a neutral cleaning solution and an alkaline cleaning solution. This obtained the glass substrate for magnetic discs.

<Polishing conditions for first polishing>
・ Polishing pad: Hard urethane pad (JIS-A hardness: 80-100)
Polishing load: 120 g / cm ²
・ Surface plate speed: 30 rpm
Polishing fluid supply flow rate: 3000 L / min
Polishing liquid: containing 10% by weight of zirconia (ZrO ₂ ) abrasive grains. All the zirconia abrasive grains of the examples were prepared by a wet method. The zirconia abrasive grains of the comparative example were produced by a dry method.

In the process of producing the glass substrate for magnetic disk, the setting of the zirconia abrasive grains in the first polishing of (6) was changed to evaluate the polishing rate in the polishing process and the presence or absence of scratches on the glass base plate after the polishing process. The results shown in Table 1 and Table 2 were obtained. In addition, the said evaluation was performed about what wash | cleaned and dried after the 1st grinding | polishing process.
Here, the secondary particle diameter (average particle diameter D50) of the zirconia abrasive grains was measured by a light scattering method using a particle diameter / particle size distribution measuring apparatus. The average particle size D50 is the particle size at which the cumulative volume frequency is 50% when the total volume frequency is determined with the total volume of the powder population in the particle size distribution measured by the light scattering method as 100%. is there. The primary particle diameter was measured by a method as shown in FIG. 7 with zirconia abrasive grains magnified 30,000 to 100,000 times with a scanning electron microscope. Further, the BET specific surface area was measured by a BET single point method by a gas adsorption method using a fluid specific surface area measuring device.

In Tables 1 and 2, the evaluation criteria for polishing rate and scratch evaluation were as follows.
Polishing rate evaluation criteria The polishing rate was evaluated based on the following criteria by measuring the polishing rate of the first batch. ◎, ○ or △ is acceptable.
◎: Greater than 1.8 μm / min ○: Greater than 1.6 μm / min, 1.8 μm / min or less Δ: Greater than 1.4 μm / min, 1.6 μm / min or less X: 1.4 μm / min or less

・ Evaluation criteria for scratch evaluation Scratch evaluation was performed by visually inspecting the main surface after polishing of N = 200 glass base plates in each Example by irradiating a condensing lamp in a dark curtain in CR. Evaluation was based on the ratio of inspection OK products. In the visual inspection OK product, scratches were not confirmed by visual inspection on the main surface of the glass base plate, and in the visual inspection NG product, scratches were confirmed by visual inspection on the main surface of the glass base plate. . ◎, ○ or △ is acceptable.
A: Visual inspection OK product is 95% or more of the whole ○: Visual inspection OK product is 90% or more and less than 95% Δ: Visual inspection OK product is 70% or more and less than 90% of the whole ×: Visual inspection OK product is whole Less than 70%

From the results shown in Table 1, it was confirmed that the scratch evaluation was rejected in the case of zirconia particles produced by a dry method. It was found that when the primary particle diameter of the zirconia particles produced by the wet method is in the range of 70 to 200 nm, good results are obtained in both the polishing rate and scratch evaluation. Further, from the results of Table 2, when the BET specific surface area of the zirconia particles used as the abrasive grains is in the range of 4 to 15 m ² / g, good results are obtained in both the polishing rate and the scratch evaluation. I understood.
In addition, it was found that when the average particle diameter (D50) of the zirconia particles is in the range of 0.2 to 0.6 μm, better results are obtained in both polishing rate and scratch evaluation.

Next, a magnetic disk was manufactured by laminating an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer on the glass substrates for magnetic disks of Examples 1 to 13 and Comparative Example, and a glide head. The glide test was performed with the flying height of 7 nm set to 7 nm. As a result, the yield (inspection pass rate) when 100 sheets were inspected for each example was 90% or more, and all passed.
On the other hand, in the comparative example using the zirconia abrasives produced by the dry method, the yield was lower than 90%, which was unacceptable. Furthermore, when the defect position detected by the glide inspection was observed by SEM / EDX, a foreign matter was found. Composition analysis of the found foreign matter revealed that it was a foreign matter derived from a zirconia abrasive. That is, it is considered that the zirconia particles used in the polishing step were found as foreign substances by attaching to the glass base plate during the polishing process.

It should be noted that the order of the steps is (7) chemical strengthening, (6) first polishing, (8) second polishing, not (6) first polishing, (7) chemical strengthening, and (8) second polishing. The glass substrate for magnetic disks was produced by changing the above. At this time, the manufacturing method of zirconia abrasive grains in the first polishing and the primary particle diameter and secondary particle diameter D50 of the zirconia abrasive grains were the same as those in Example 3 in Table 1. Further, the glass substrate for a magnetic disk with various changes in the fracture toughness value K _1c was prepared as shown in Table 3 below by appropriately changing the strengthening temperature and the immersion time in the chemical strengthening step (Example 14 in Table 3). 15). Table 3 shows the evaluation results of the glass base plate after the first polishing at this time.

As shown in Table 3, by performing the chemical strengthening under the chemical strengthening treatment conditions such that the fracture toughness value K _1c is 0.7 [MPa / m ^1/2 ] or more before the first polishing, the better It was found that a scratch evaluation can be obtained. This is considered to be because the compression layer formed on the side wall surface of the glass substrate by chemical strengthening functioned as an anti-adhesion layer for zirconia abrasive grains used in the first polishing performed thereafter.

Next, the production method of the zirconia abrasive grains, the primary particle diameter of the zirconia abrasive grains, and the secondary particle diameter D50 are the same as those in Example 8 of Table 1, and carriers having different surface roughness of the end faces are used in the polishing apparatus for the first polishing. Using this, first polishing was performed to produce glass substrates for magnetic disks (Examples 16 to 18 in Table 4). At this time, in the same manner as in Example 8, the order of the steps was (6) first polishing, (7) chemical strengthening, and (8) second polishing in this order to produce a magnetic disk glass substrate. Table 4 shows the evaluation results of the glass base plate after the first polishing at this time.

As shown in Table 4, the scratch evaluation was good when the surface roughness Ra of the end face of the carrier was 5 μm or less, and even better when it was 3 μm or less. This is because, as the surface roughness of the end face of the carrier is smaller, the number of zirconia abrasive grains entering between the glass base plate and the carrier increases, and the force is dispersed to more abrasive grains. This is considered to be because it is difficult to pierce the side wall surface of the glass base plate.

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, In the range which does not deviate from the main point of this invention, even if various improvement and a change are carried out. Of course it is good.

Claims (9)

1. A pair of main surfaces and a pair of main surfaces with a polishing pad attached to a polishing surface plate in a state where a donut-shaped glass substrate having at least two side walls constituting an inner hole and an outer shape is held by a carrier. A method for producing a glass substrate for a magnetic disk comprising a polishing step of polishing the glass substrate by planetary gear movement of the carrier while sandwiching surfaces and supplying a polishing liquid to the pair of main surfaces,
   The method for producing a glass substrate for a magnetic disk, wherein the polishing liquid contains zirconia particles produced by a wet method as abrasive grains.
2. The zirconia particles are characterized in that primary particles having a particle size in the range of 70 to 200 nm are aggregated.
   The manufacturing method of the glass substrate for magnetic discs described in Claim 1.
3. The BET specific surface area of the zirconia particles is in the range of 4 to 15 m ² / g,
   The manufacturing method of the glass substrate for magnetic discs described in Claim 1.
4. The average particle diameter (D50) of the zirconia particles is in the range of 0.2 to 0.6 μm,
   The manufacturing method of the glass substrate for magnetic discs described in Claim 2 or 3.
5. X1 / X2 is 1.0 to 1.3, where X1 is a major axis length of primary particles of the zirconia particles and X2 is a minor axis perpendicular to the major axis. The method for producing a glass substrate for a magnetic disk according to any one of claims 2 to 4.
6. The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 4, wherein the surface roughness of the end face of the carrier that contacts the side wall surface of the glass substrate is 5 μm or less.
7. The surface roughness of the side wall surface of the glass substrate before being polished with the polishing liquid having zirconia particles is an arithmetic average roughness Ra of 0.1 μm or less, characterized in that The manufacturing method of the glass substrate for magnetic discs described in one.
8. After the polishing step, the glass substrate is chemically strengthened under processing conditions such that the fracture toughness value K _1c of the glass substrate is 0.7 [MPa / m ^1/2 ] or more as measured by a Vickers hardness meter. The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 7, further comprising a chemical strengthening step.
9. 9. The magnetic disk according to claim 1, wherein the glass substrate for a magnetic disk has a diameter larger than 2.5 inch size and a plate thickness of 0.6 mm or less. Method for manufacturing glass substrate.
   

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