JP2016011377A - Silica abrasive grain, method for producing silica abrasive grain and method for producing glass substrate for magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a polishing speed of a glass substrate.SOLUTION: A method for producing a silica abrasive grain comprises a first treatment of reducing a pH of an aqueous solution of silicic acid and heating to a first temperature to subject the silicic acid to condensation polymerization to thereby form a primary particle of silica and a second treatment of newly adding an aqueous solution of silicic acid to the liquid having been subjected to the first treatment, and then heating an aqueous solution including the primary particle and the silicic acid at a second temperature lower than the first temperature to subject the silicic acid to condensation polymerization on the surface of the primary particle to thereby form a silica abrasive grain.

Description

  The present invention relates to silica abrasive grains, a method for producing silica abrasive grains, and 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 glass 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 difficult to plastically deform compared to 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 subjected to a polishing process. There is a method of using an abrasive containing fine abrasive grains such as silica (SiO ₂ ) for precise polishing to make a glass substrate as a final product (for example, Patent Document 1). Silica can be produced by, for example, water glass (aqueous alkali silicate solution) as a raw material and polycondensing silicic acid dissolved by lowering the pH of the water glass (Patent Document 2). Then, silica abrasive grains having a predetermined particle diameter are obtained by polycondensing silicic acid on the surface of the silica particles in a silicic acid solution and growing it to a predetermined particle diameter.

JP 2003-36528 A JP 2000-247625 A

  When polishing a glass substrate using silica abrasive grains, the silanol groups on the surface of the silica abrasive grains undergo dehydration condensation with the silanol groups on the surface of the glass substrate, and then the silicon on the glass substrate side is desorbed to polish the glass substrate. Is believed to progress. For this reason, it is thought that a polishing rate becomes high, so that the density of the silanol group in the surface of a silica abrasive grain is high. However, in the conventional production method, the polymerization of silica cannot be controlled, and the density of silanol groups on the surface of the silica abrasive grains cannot be adjusted.

  Then, this invention aims at providing the manufacturing method of the silica abrasive grain which can improve the grinding | polishing speed | rate of a glass substrate, the silica abrasive grain, and the glass substrate for magnetic discs using a silica abrasive grain. And

  The first aspect of the present invention is a method for producing silica abrasive grains. In the manufacturing method, the first treatment for lowering the pH of the aqueous solution of silicic acid and heating it to the first temperature to cause polycondensation of silicic acid to produce primary particles of silica and the first treatment are completed. After a new aqueous solution of silicic acid is added later, the aqueous solution containing the primary particles and silicic acid is heated at a second temperature lower than the first temperature to cause polycondensation of silicic acid on the surface of the primary particles. The 2nd process which produces | generates a silica abrasive grain.

  It is preferable to make the second treatment time longer than the first treatment time. By reacting the primary particles and silicic acid for a longer time at a second temperature lower than the first temperature, the particle size of the silica abrasive grains increases due to the condensation of the existing primary particles, or a new primary While suppressing the generation of particles, the condensation polymerization of silicic acid onto the surface of the primary particles can be promoted. For this reason, a silanol group can be reliably increased on the surface of a silica abrasive grain.

The concentration of the silicic acid [Si (OH) ₄ ] (mol / L) and the concentration of the primary particles [SiO ₂ ] (mol / L) in the aqueous solution containing the primary particles and silicic acid heated at the second temperature [Si (OH) ₄ ] / [SiO ₂ ] is preferably 5 or more.

  The second aspect of the present invention is a method for producing a glass substrate for a magnetic disk. In the manufacturing method, a polishing liquid containing silica abrasive grains manufactured by the above method as free abrasive grains is supplied between a main surface of a glass substrate and a polishing pad to polish the main surface of the glass substrate. Have treatment.

A third aspect of the present invention is a silica abrasive grain. The silica abrasive grains have a density per unit surface area of silanol groups (Si—OH) on the abrasive grain surface of 4 mol / nm ² or more.

  A fourth aspect of the present invention is silica abrasive grains. The silica abrasive grains have a ratio (Si—OH) / Si of the silanol groups (Si—OH) on the abrasive grain surface to the silicon element (Si) of the entire abrasive grains is 0.05 or more.

  A fifth aspect of the present invention is a method for manufacturing a magnetic disk glass substrate. The manufacturing method includes a polishing process in which a polishing liquid containing the silica abrasive grains as free abrasive grains is supplied between the main surface of the glass substrate and the polishing pad to polish the main surface of the glass substrate.

  According to the present invention, since the density of silanol groups (Si—OH) on the surface of the silica abrasive grains is high, the polishing rate of the glass substrate can be improved as compared with the prior art.

Hereinafter, the silica abrasive grains according to the embodiment of the present invention will be described in detail.
Usually, a silica abrasive grain is manufactured by growing a silica particle to a desired particle size by condensation polymerization of silanol groups of silicic acid.
In this embodiment, the density per unit surface area of silanol groups (Si—OH) on the surface of the silica abrasive grains is 4 mol / nm ² or more. Further, the ratio (Si—OH) / Si of silanol groups (Si—OH) on the abrasive grain surface to the silicon element (Si) of the whole abrasive grains is 0.05 or more.
Since such silica abrasive grains have a higher density of silanol groups on the surface than silica abrasive grains obtained by conventional methods, the polishing rate can be improved.

The ratio (Si—OH) / Si of silanol groups (Si—OH) on the surface of the silica abrasive grains and silicon element (Si) in the entire abrasive grains can be measured, for example, as follows.
First, by ²⁹ Si-NMR, by measuring the intensity ratio of the spectrum of silicon directly bonded to OH and silicon not bonded directly to OH, the entire silanol groups (Si-OH) of the silica abrasive grains and the entire abrasive grains were measured. The ratio [(Si—OH) / Si] ₁ with silicon element (Si) is obtained.
Next, the silanol groups on the surface of the silica abrasive grains are trimethylsilylated with hexamethyldisilazane, and the solvent is evaporated to dry the abrasive grains. After that, by ²⁹ Si-NMR, it is not trimethylsilylated by measuring the intensity ratio of the spectrum of silicon directly bonded to OH and silicon not bonded directly to OH (excluding —O—Si (CH ₃ ) ₃ ). The ratio [(Si—OH) / Si] ₂ of silanol groups (Si—OH) inside the silica abrasive grains to the silicon element (Si) of the entire abrasive grains is determined.
Then, by calculating the difference between [(Si—OH) / Si] ₁ and [(Si—OH) / Si] ₂ , the silanol groups (Si—OH) on the surface of the silica abrasive grains and the silicon of the entire abrasive grains The ratio (Si—OH) / Si with the element (Si) can be obtained.
That is, the ratio of silanol groups (Si-OH) of the entire silica abrasive grains to silicon element (Si) of the entire abrasive grains [(Si-OH) / Si] ₁ and the silanol groups on the surface of the silica abrasive grains are trimethylsilylated The difference between the ratio of silanol groups (Si-OH) of the entire silica abrasive grains to the silicon element (Si) of the entire abrasive grains [(Si-OH) / Si] ₂ is 0.05 or more preferable.

Moreover, the density per unit surface area of the silanol group (Si-OH) on the surface of a silica abrasive grain can be calculated as follows, for example.
The average particle diameter of the silica abrasive grains is measured by a dynamic light scattering method. Next, the number of silicon elements per silica abrasive grain is calculated by multiplying the volume per silica abrasive grain calculated from the average particle diameter by the density of silicon elements per unit volume in silica (reference value). calculate. The number of surface silanol groups per silica abrasive grain is calculated by multiplying the calculated number of silicon elements by the calculated ratio of surface silanol groups (Si—OH) / Si. Next, by dividing the number of surface silanol groups per silica abrasive grain by the surface area per silica abrasive grain calculated from the average particle diameter, the silanol groups (Si-OH) on the surface of the silica abrasive grains The density per unit surface area can be calculated.

Hereinafter, the manufacturing method of the silica abrasive grain which concerns on this embodiment is demonstrated.
First, a silica raw material and a strong base used for the production of silica abrasive grains are prepared.
(1) Silica raw material Silica having a low content of metal impurities is used as the silica raw material. This is because when such impurities remain in the silica abrasive grains, metal ions are dissolved in the polishing liquid using the silica abrasive grains and defects may be formed on the object to be polished. Here, the metal impurities are, for example, Al, Ca, B, Ba, Co, Cr, Cu, Fe, Mg, Mn, Na, Ni, Pb, Sr, Ti, Zn, Zr, U, Th, and the like. . The low content of metal impurities means that the content of these metals is less than 5 ppm.
For example, fumed silica can be used as silica having a low content of metal impurities.
In addition, you may use the silicic acid aqueous solution from which the metal ion was removed by allowing water glass (sodium silicate aqueous solution) to pass through a cation exchange resin.

(2) Strong base A strong base maintains the pH of a solution alkaline in order to adjust the silicate aqueous solution. As such a strong base, for example, an organic strong base or an inorganic strong base can be used. As a specific example of the strong organic base, tetraalkylammonium hydroxide such as tetramethylammonium hydroxide can be used. For example, sodium hydroxide or potassium hydroxide can be used as the strong inorganic base.

Next, a method for producing silica abrasive grains using the above materials will be described.
(3) Preparation of silicate aqueous solution A silicate aqueous solution is obtained by dissolving the silica raw material and a strong base in water (for example, pure water, reverse osmosis membrane filtered water (RO water)). The pH of the silicate aqueous solution is adjusted to 11-14.
Specifically, a colorless and transparent silicate aqueous solution is obtained by stirring a mixed solution of the above silica raw material, strong base, and water for 48 hours while heating to 120 ° C. in an autoclave, for example. Can do.

(4) Generation of primary particles by condensation polymerization of silica particles (first treatment)
Next, after diluting the silicate aqueous solution as necessary, the pH of the silicate aqueous solution is lowered to a predetermined set value. This set value is, for example, 9 or less, preferably 8 to 9, and more preferably 8.5 to 8.8. Here, in order to lower the pH of the aqueous silicate solution, for example, a proton type cation exchange resin can be used. In this case, when the pH of the aqueous silicate solution reaches the set value, the proton-type cation exchange resin is removed by filtration.
By using a proton type cation exchange resin, it is not necessary to use a mineral acid for neutralization. For this reason, it is not necessary to remove the anion of the mineral acid, and the treatment cost of the acid waste water can be reduced.

Next, the first-stage heat treatment is performed on the silicate aqueous solution whose pH has been lowered. For example, the silicate aqueous solution is stirred for 8 to 16 hours while being heated to a first temperature (eg, 90 ° C. or higher, preferably 90 to 95 ° C.). For example, an oil bath or an autoclave can be used as the heating device. During the first heat treatment, condensation polymerization between silanol groups of silica is promoted in an aqueous silicate solution, and primary particles of silica are generated.
Before the first stage heat treatment, the silicate aqueous solution is gently stirred at room temperature for 18 to 48 hours, and then the silicate aqueous solution is passed through a membrane filter, thereby causing coarse particles. Substances larger than the particle size may be removed.
Further, primary particles of silica may be generated by a sol-gel method. For example, the silica raw material may be generated by hydrolyzing and polycondensating ethyl orthosilicate under acidic or basic conditions.

(5) Polycondensation of silicic acid on the surface of silica particles (second treatment)
Next, a heat treatment in the second stage is performed on the solution containing the primary particles of silica and silicic acid to cause polycondensation of silicic acid on the surface of the primary particles to produce silica abrasive grains. Here, the second-stage heat treatment is performed at a second temperature (for example, 50 ° C. to 75 ° C.) lower than the first temperature. For example, an oil bath or an autoclave can be used as the heating device. By performing the second stage heat treatment at a lower temperature than the first stage heat treatment, the silicic acid is polycondensed on the surfaces of the primary particles with the silanol groups of the silicic acid remaining. Thereby, the density of the silanol group in the surface of the silica abrasive grain produced | generated can be raised.
The time for the second treatment is preferably longer than the time for the first treatment. In the second treatment, the primary particles and silicic acid are reacted at a second temperature lower than the first temperature for a longer time, so that the particle size of the silica abrasive grains is increased by the condensation of the existing primary particles. In addition, the polycondensation of silicic acid on the surface of the primary particles can be promoted while suppressing the generation of new primary particles. For this reason, a silanol group can be reliably increased on the surface of a silica abrasive grain.

Here, when the concentration of primary particles of silica is [SiO ₂ ] (mol / L) and the concentration of silicic acid is [Si (OH) ₄ ] (mol / L) during the second stage heat treatment, [Si (OH) ₄ ] is sufficiently larger than [SiO ₂ ] ([Si (OH) ₄ ] >> [SiO ₂ ]) in order to promote the condensation polymerization of silicic acid primary particles to the surface. It is preferable that Specifically, the ratio [Si (OH) ₄ ] / [SiO ₂ ] between [Si (OH) ₄ ] and [SiO ₂ ] is preferably 5 or more. By setting [Si (OH) ₄ ] / [SiO ₂ ] to 5 or more, it is possible to promote condensation polymerization on the surfaces of primary particles rather than condensation polymerization between silicic acids.

After the second-stage heat treatment, the solution containing silica abrasive grains is concentrated by evaporating water with an evaporator, for example. The colloidal silica containing the silica abrasive grain of a predetermined particle diameter is obtained by the above.
In the silica abrasive grains thus obtained, silanol groups that are not used for bonding between silicon remain on the surface of the silica abrasive grains, so that the silicon element (Si ) Ratio (Si—OH) / Si can be 0.05 or more.

  The silica abrasive grains thus obtained have a higher density of silanol groups on the surface than silica abrasive grains produced by a conventional production method. For this reason, polishing rate can be improved by performing a polishing process using this silica abrasive grain.

  Next, the manufacturing method of the glass substrate for magnetic disks which concerns on embodiment of this invention is demonstrated in detail.

(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 magnetic disk glass blank (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). 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 that of the double-side grinding apparatus used for the grinding process using fixed abrasive grains. In the first polishing process, a polishing slurry containing loose abrasive grains is used instead of fixed abrasive grains, unlike grinding with fixed abrasive grains. For example, cerium oxide abrasive grains or zirconia abrasive grains are used as the free abrasive grains used in the first polishing. In the double-side polishing apparatus, similarly to the double-side grinding apparatus, the glass substrate is sandwiched between a pair of upper and lower surface plates. 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. Then, by moving either the upper surface plate or the lower surface plate, or both, the glass substrate and each surface plate are relatively moved, thereby polishing both main surfaces of the glass substrate.

(G) Chemical strengthening treatment Next, the glass substrate is chemically strengthened. As the chemical strengthening solution, for example, a mixed melt of potassium nitrate and sodium sulfate or the like is used, and the glass substrate is immersed in the chemical strengthening solution.

(H) Second polishing (final polishing) treatment Next, the glass substrate after the chemical strengthening treatment is subjected to second polishing. 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 2nd grinding | polishing is about 1-10 micrometers, for example. The second polishing process is different from the first polishing process in that the type or particle size of the free abrasive grains is different and the hardness of the resin polisher is different.

In the present embodiment, a polishing liquid containing colloidal silica (particle size of about 20 to 50 nm) manufactured by the above-described manufacturing method as free abrasive grains is supplied between the polishing pad of the double-side polishing apparatus and the main surface of the glass substrate. Then, the main surface of the glass substrate is polished. 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 set to 0.1 nm or less and the micro waveness of the main surface can be set to 0.1 nm or less. In this way, the glass substrate subjected to the second polishing is washed with water to become a glass substrate for a magnetic disk.

As mentioned above, although the manufacturing method of the silica abrasive grain of this invention and the manufacturing method of the glass substrate for magnetic discs were demonstrated in detail, this invention is not limited to the said embodiment and Example, In the range which does not deviate from the main point of this invention. Of course, various improvements and changes may be made.
For example, in the above embodiment, silica abrasive grains are used in the second polishing process, but the present invention is not limited to this, and silica abrasive grains may be used in the first polishing process.

Examples of the present invention and comparative examples will be described below.
1. Preparation of sodium silicate aqueous solution Silica sand and sodium carbonate were mixed, heated to (500 ° C.) and melted to produce sodium silicate. Next, water was added to the cooled sodium silicate and stirred for 48 hours while heating to 120 ° C. in an autoclave to obtain a colorless and transparent sodium silicate aqueous solution.

[Creation of silica abrasive grains]
(First stage heat treatment)
The obtained sodium silicate aqueous solution was put into an eggplant flask and stirred for 16 hours while heating to 93 ° C. in an oil bath to obtain an aqueous solution containing primary particles of silica.

(Second stage heat treatment)
Next, the aqueous solution containing the silica primary particles and silicic acid obtained by the first stage heat treatment is placed in an eggplant flask and stirred while heating in an oil bath, so that the silica is condensed on the surface of the silica primary particles. An aqueous solution containing polymerized silica abrasive grains was obtained. The heating temperature and heating time in the second stage heat treatment are as shown in Table 1. Further, the ratio [Si (OH) ₄ ] / [SiO ₂ ] between the concentration of silicic acid [Si (OH) ₄ ] and the concentration of primary particles of silica [SiO ₂ ] before the heat treatment is as shown in Table 1. is there.
The colloidal silica after the second heat treatment was classified to obtain silica abrasive grains having an average particle diameter of 20 nm.

[Comparative Example]
An aqueous solution containing silica abrasive grains was obtained in the same manner as in Example except that the second heat treatment was not performed.

[Calculation of ratio and density of surface silanol groups]
A part of the aqueous solution containing the silica abrasive grains is taken out, the solvent is evaporated to dry the silica abrasive grains, and the silanol groups (Si-OH) on the surface of the silica abrasive grains and the whole abrasive grains are dried by the method described above. Ratio with silicon element (Si) (Si-OH) / Si, The density per unit surface area of silanol groups (Si-OH) on the surface of silica abrasive grains was calculated. The obtained values are shown in Table 1.

[Glass substrate polishing]
Next, the glass substrate was polished using the polishing liquid containing colloidal silica of the above Examples and Comparative Examples. While supplying the polishing liquid containing the colloidal silica of Example or Comparative Example between the main surface of the glass substrate and the polishing pad made of polyurethane, the polishing pad is moved relative to the main surface of the glass substrate to supply glass. The main surface of the substrate was polished.

<Processing rate>
The processing rate was evaluated by the weight change of the glass substrate before and after the polishing treatment. The relative value which made the processing rate of the comparative example 1 1.00 was computed.
The results are shown in Table 1.

In Examples 1 and ² where (Si—OH) / Si is 0.05 or more and Si—OH density is 4 mol / nm ² or more, (Si—OH) / Si is less than 0.05 and Si—OH density is 4 mol. Compared with the comparative example of less than / nm ² , the processing rate could be increased.

Claims (6)

A first treatment that lowers the pH of the aqueous solution of silicic acid and heats it to a first temperature to cause polycondensation of silicic acid to produce primary particles of silica;
After newly adding an aqueous solution of silicic acid to the liquid that has undergone the first treatment, the aqueous solution containing the primary particles and silicic acid is heated at a second temperature lower than the first temperature. A second treatment for producing silica abrasive grains by polycondensing silicic acid on the surface;
A method for producing silica abrasive grains. The concentration of the silicic acid [Si (OH) ₄ ] (mol / L) and the concentration of the primary particles [SiO ₂ ] (mol / L) in the aqueous solution containing the primary particles and silicic acid heated at the second temperature The method for producing silica abrasive grains according to claim 1, wherein the ratio [Si (OH) ₄ ] / [SiO ₂ ] is 5 or more. A method of manufacturing a glass substrate for a magnetic disk,
A polishing liquid containing silica abrasive grains produced by the method according to claim 1 or 2 as free abrasive grains is supplied between the main surface of the glass substrate and the polishing pad to polish the main surface of the glass substrate. A method for producing a glass substrate for a magnetic disk, comprising a polishing treatment. Silica abrasive grains,
Silica abrasive grains having a density per unit surface area of silanol groups (Si—OH) on the abrasive grain surface of 4 mol / nm ² or more. Silica abrasive grains,
Silica abrasive grains having a ratio of silanol groups (Si—OH) on the abrasive grain surface to the silicon element (Si) of the entire abrasive grains (Si—OH) / Si of 0.05 or more. A method of manufacturing a glass substrate for a magnetic disk,
Between the main surface of the glass substrate and the polishing pad, supplying a polishing liquid containing the silica abrasive grains according to claim 4 or 5 as free abrasive grains, and having a polishing process for polishing the main surface of the glass substrate. Manufacturing method of glass substrate for magnetic disk.