JPWO2015046603A1 - Silica abrasive, method for producing silica abrasive, and method for producing glass substrate for magnetic disk - Google Patents

Abstract

Disclosed is a silica abrasive that does not cause damage to an object to be polished and does not reduce the polishing rate. It is a silica abrasive grain in which the ratio (Si—OH) / Si of silanol groups (Si—OH) inside the abrasive grains to silicon element (Si) in the whole abrasive grains is 0.4 or more.

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.

  2. Description of the Related Art Today, a personal computer, a DVD (Digital Versatile Disc) recording device, or the like 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 the substrate of this magnetic disk, a glass substrate having a property that is less likely to be plastically deformed than a metal substrate (aluminum substrate) or the like is preferably used.

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

In order to reduce the surface unevenness of the glass substrate for magnetic disk, the glass substrate is subjected to polishing treatment. 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.

  There is also a method in which silicic acid is generated by hydrolysis of orthosilicates and silica abrasives having a predetermined particle size are obtained by condensation polymerization of the silicic acid (sol-gel method). A base catalyst such as ammonia is used for hydrolysis of orthosilicates. Since orthosilicates can be purified by distillation, high-purity silica can be obtained relatively easily.

JP 2003-36528 A JP 2000-247625 A

  In the conventional production method, the polymerization of silica could not be controlled, and the proportion of unreacted silanol groups remaining in the silica abrasive grains was low. Specifically, the ratio (Si—OH) / Si of the unreacted silanol group (Si—OH) remaining inside the silica abrasive grains to the silicon element (Si) of the entire abrasive grains was 0.3 or less. . For this reason, dense and hard abrasive grains were obtained.

  When performing a polishing process using dense abrasive grains, if the abrasive grain size is large, the abrasive grains may damage the object to be polished when an excessive pressure is applied during the polishing process. On the other hand, if the grain size of the abrasive grains is reduced in order to prevent damage to the polishing object, the contact area between the abrasive grains and the polishing object is reduced, and there is a problem that the polishing rate is reduced. In addition, since the silica abrasive grains having a small particle diameter have a small radius of curvature and can be said to be sharp, there is a problem in that minute scratches are generated when the polishing load is increased to increase the polishing rate.

  Accordingly, the present invention provides silica abrasive grains that do not cause damage to the object to be polished and do not reduce the polishing rate, a method for producing silica abrasive grains, and glass for magnetic disks using silica abrasive grains. An object is to provide a method for manufacturing a substrate.

The first aspect of the present invention has a polishing process of supplying a polishing liquid containing silica abrasive grains as free abrasive grains between the main surface of the glass substrate and the polishing pad, and polishing the main surface of the glass substrate. A method for producing a glass substrate for a magnetic disk.
The silica abrasive grains have a ratio (Si—OH) / Si of silanol groups (Si—OH) inside the abrasive grains to silicon element (Si) of the entire abrasive grains is 0.4 or more.

The second aspect of the present invention has a polishing process in which a polishing liquid containing 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. A method for producing a glass substrate for a magnetic disk.
The silica abrasive is
After trimethylsilylating silanol groups (Si-OH) on the surface of the abrasive grains with hexamethyldisilazane, only the spectral intensity of Si directly bonded to OH and O measured by nuclear magnetic resonance spectroscopy ( ²⁹ Si-NMR) The ratio (Si—OH) / Si with the spectral intensity of Si directly bonded is 0.4 or more.

  The polishing liquid containing the silica abrasive grains as free abrasive grains is preferably alkaline.

The polishing process is performed in a plurality of stages,
It is preferable to perform the final stage treatment using an alkaline polishing liquid containing the silica abrasive grains as free abrasive grains.

A third aspect of the present invention is a silica abrasive grain. The silica abrasive is
The ratio (Si—OH) / Si of silanol groups (Si—OH) inside the abrasive grains to the silicon element (Si) of the entire abrasive grains is 0.4 or more.
The ratio (Si—OH) / Si is preferably 0.4 or more and 0.5 or less.

A fourth aspect of the present invention is silica abrasive grains. The silica abrasive is
After trimethylsilylating silanol groups (Si-OH) on the surface of the abrasive grains with hexamethyldisilazane, only the spectral intensity of Si directly bonded to OH and O measured by nuclear magnetic resonance spectroscopy ( ²⁹ Si-NMR) The ratio (Si—OH) / Si with the spectral intensity of Si directly bonded is 0.4 or more.
The ratio (Si—OH) / Si is preferably 0.4 or more and 0.5 or less.

A fifth aspect of the present invention is a method for producing the above silica abrasive grains. The manufacturing method is
A process of condensation-polymerizing silicic acid to produce primary particles of silica;
A process for producing fused silica particles by agglomerating the primary particles;
including.

  It is preferable to produce the fused particles by condensation polymerization of silanol groups on the surface of the primary particles.

In the treatment for generating the primary particles, the aqueous solution containing the primary particles is generated by promoting the polycondensation of silicic acid by lowering the pH of the aqueous solution of silicic acid and heating.
In the process of generating the fused particles, the pH of the aqueous solution containing the primary particles is lowered than the process of generating the primary particles, and the temperature of the aqueous solution containing the primary particles is increased than the process of generating the primary particles. It is preferable to promote the formation of the fused particles.
It is preferable to lower the pH by adding a cation exchange resin to the aqueous silicic acid solution. The cation exchange resin is preferably a proton type ion exchange resin.

In the treatment for generating the primary particles, the pH of the aqueous silicic acid solution is lowered to 9 or lower and heated to 90 ° C. or higher.
In the treatment for generating the fused particles, it is preferable to lower the pH of the aqueous silicic acid solution to 8.6 or lower and to heat to 120 ° C. or higher.

  It is preferable to lower the pH by adding a cation exchange resin to the aqueous silicic acid solution. The cation exchange resin is preferably a proton type ion exchange resin.

  According to the present invention, since the ratio (Si—OH) / Si of silanol groups (Si—OH) in the silica abrasive grains to the silicon element (Si) of the entire abrasive grains is 0.4 or more, it is softer than before. Silica abrasive grains are obtained. By using this abrasive grain, there is no risk of scratching the object to be polished, and the polishing process can be performed without reducing the polishing rate.

Hereinafter, the silica abrasive grains according to the embodiment of the present invention will be described in detail.
Usually, silica abrasive grains are manufactured by growing silica particles to a desired particle diameter by condensation polymerization of silanol groups of silicic acid. The entire abrasive grains of silanol groups (Si—OH) inside the abrasive grains are produced. The ratio (Si—OH) / Si with respect to silicon element (Si) is 0.3 or less.
In contrast, in the silica abrasive grains according to the embodiment of the present invention, the ratio (Si—OH) / Si of silanol groups (Si—OH) in the abrasive grains to the silicon element (Si) of the entire abrasive grains is 0.4. That's it. Since such silica abrasive grains are softer than conventional silica abrasive grains and have an appropriate hardness, even if the particle size is increased in order to maintain the polishing rate, the object to be polished is scratched. Hateful.

In addition, ratio (Si-OH) / Si with respect to the silicon element (Si) of the whole abrasive grain of the silanol group (Si-OH) inside a silica abrasive grain can be measured as follows, for example.
The silanol groups on the surface of the silica abrasive grains are trimethylsilylated with hexamethyldisilazane, the solvent is evaporated and the abrasive grains are dried. Then, by means of nuclear magnetic resonance spectroscopy ( ²⁹ Si-NMR), Si bonded directly to OH The ratio of (Si—OH) / Si can be obtained by measuring the ratio between the spectral intensity and the spectral intensity of Si that is directly bonded only to O.
Hereinafter, the manufacturing method of the silica abrasive grain which concerns on embodiment of this invention is demonstrated.

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

(4) Generation of primary particles by condensation polymerization of silica particles Next, the above-described aqueous silicic acid solution is diluted as necessary, and then the pH of the aqueous silicic acid 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 silicic acid aqueous solution, for example, a proton type cation exchange resin can be used. In this case, when the pH of the aqueous silicic acid 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 aqueous silicic acid solution whose pH has been lowered. For example, the silicic acid aqueous solution is stirred for 8 to 16 hours while being heated to 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 stage heat treatment, condensation polymerization of silanol groups of silica is promoted in an aqueous silicic acid solution, and primary particles of silica are generated.
In addition, after the first stage heat treatment, the aqueous silicic acid solution is gently stirred at room temperature for 18 to 48 hours, and then the aqueous silicic acid solution is passed through a membrane filter to obtain a predetermined particle size that causes coarse particles. The above substances 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) Generation of fused particles by fused growth of primary particles Next, a second-stage heat treatment is performed on the solution containing the primary particles of silica. Here, the second-stage heat treatment is performed under such conditions that the reaction rate is higher than that of the first-stage heat treatment.
For example, the pH of the solution containing the primary particles of silica is lowered to a lower setting value, for example, pH 8.6 than in the process of generating the primary particles. Here, in order to lower the pH of the solution containing the primary particles of silica, for example, a proton type cation exchange resin can be used. In this case, when the pH of the solution containing the primary particles of silica reaches a set value, the proton-type cation exchange resin is removed by filtration.
Further, the heating is performed at a temperature higher than that of the first stage heat treatment, preferably 120 ° C. or higher. For example, an autoclave can be used as a heating device used for the second stage heat treatment.
Alternatively, the second stage heat treatment may be performed at a higher pressure than the first stage heat treatment. For example, the first-stage heat treatment may be performed in an atmosphere of atmospheric pressure (about 0.1 MPa), and the second-stage heat treatment may be performed in an environment pressurized with an autoclave (for example, about 0.25 MPa). .
Alternatively, the second stage heat treatment may be performed for a longer time than the first stage heat treatment. For example, the second stage heat treatment is performed with stirring for 12 to 48 hours.
Thus, by performing the second-stage heat treatment under conditions that increase the reaction rate than the first-stage heat treatment, the silanol groups on the surfaces of the primary particles are more than the hydrolysis of silica from the primary particles. The condensation polymerization between them is promoted. Thereby, the primary particles are fused to produce fused particles.
Thereafter, if necessary, the solution containing the fused particles is concentrated by evaporating water using, for example, an evaporator.
As described above, colloidal silica containing fused particles having a predetermined particle diameter is obtained. In the thus obtained fused particles, the primary particles are bonded to each other by only a part of the silanol groups on the surface of the primary particles, so that silanol groups that are not used for bonding silicon remain inside the fused particles. For this reason, ratio (Si-OH) / Si with respect to the silicon element (Si) of the whole abrasive grain of the silanol group (Si-OH) inside a fusion particle can be 0.4 or more.

Such fused silica particles are softer than silica abrasives produced by conventional methods. For this reason, by using the fused particles as abrasive grains, there is no risk of scratching the object to be polished, and the polishing process can be performed without reducing the polishing rate.
Moreover, the silica particle of arbitrary particle diameters can be produced | generated by aggregating a primary particle and producing | generating a fused particle. In the above embodiment, the case where fused particles are produced by condensation polymerization of silanol groups on the surface of primary particles has been described, but the present invention is not limited to this, and primary particles are aggregated by an arbitrary method. Fusion particles may also be generated.
In addition, by adding a cation exchange resin, the pH of the aqueous solution of silicic acid can be reduced, so that no mineral acid can be used for neutralization, and there is no need to remove the anion of the mineral acid. Can be reduced.

  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, amorphous 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. Next, a hole is made in the central portion of the produced glass blank to produce a ring-shaped (annular) glass substrate. Next, shape processing is performed on the glass substrate with holes. Thereby, a glass substrate is produced | generated. Next, end face polishing is performed on the glass substrate that has been processed into a shape. Grinding with a fixed abrasive is performed on the glass substrate on which the end surface has been polished. Next, the first polishing is performed on the main surface of the glass substrate. Next, chemical strengthening is performed on the glass substrate. Next, the second polishing is performed on the chemically strengthened glass substrate. 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 lump of the molten glass which cut | disconnected the front-end | tip part of the molten glass flow is pinched | interposed between the press molding surfaces of a pair of metal molds, and is pressed to form a glass blank. After pressing for a predetermined time, the mold is opened and the glass blank is taken out.

(B) Circular hole formation treatment A glass substrate having a circular central hole can be obtained by forming a circular hole on a glass blank using a core drill or the like.

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

(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 using the fixed abrasive grains, the main surface of the glass substrate is ground using a double-side 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.

  In the first polishing process, a glass substrate is polished using a double-side polishing apparatus having a configuration similar to that of a double-side polishing apparatus while applying a polishing slurry containing loose abrasive grains to the double-side polishing apparatus. As the free abrasive grains, for example, cerium oxide abrasive grains or zirconia abrasive grains (particle size: diameter of about 1 to 2 μm) is used. 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. While supplying the polishing liquid between the main surface of the glass substrate and the polishing pad, the glass substrate and the polishing pad move relatively by moving either the upper surface plate, the lower surface plate, or both. Then, both main surfaces of the glass substrate are polished.

(G) Chemical strengthening treatment In the chemical strengthening treatment, the glass substrate is chemically strengthened by immersing the glass substrate in a chemical strengthening solution. As the chemical strengthening liquid, for example, a mixed melt of potassium nitrate and sodium nitrate can be used. The chemical strengthening process may not be performed.

(H) Second polishing (final polishing) treatment The second polishing treatment aims at mirror polishing of the main surface. Also in the second polishing, a double-side polishing apparatus having the same configuration as the double-side polishing apparatus used for the first polishing is used. In the second polishing treatment, in order to make the main surface extremely low roughness, it is preferable to perform the polishing treatment using a polishing liquid containing colloidal silica having an average particle diameter of 5 to 50 nm as free abrasive grains. Here, the average particle diameter (d50) indicates a median diameter measured based on a volume distribution using a laser diffraction / scattering method. The pH of the polishing liquid can be varied from acidic to alkaline, but if it is polished with an acid, a relatively high polishing rate is likely to be obtained. The machining allowance by 2nd grinding | polishing is about 0.1-5 micrometers, for example. The polishing load is preferably in the range of 50 to 200 g / cm ² from the viewpoint of achieving both a polishing rate and scratch prevention. The second polishing process is different from the first polishing process in that the type and particle size of the free abrasive grains are different and the hardness of the resin polisher is different.
Further, the second polishing process may be further performed in two or more stages. In this case, it is preferable to carry out by changing the pH of the polishing liquid at each stage. Specifically, for example, it is preferable that the first stage performs silica polishing under acidic conditions, and the second stage (final stage) performs silica polishing under alkaline conditions.
When polished under acidic conditions, a leaching action occurs in which alkali ions contained in the glass substrate are eluted during polishing. While this improves the polishing rate, a brittle leaching layer is generated deeply, and the surface roughness tends to deteriorate due to the alkali etching action in the alkali cleaning treatment after the polishing treatment.
Therefore, by performing multistage silica polishing under acidic conditions and finally under alkaline conditions, it is possible to suppress the formation of a brittle leaching layer before the alkali cleaning treatment, so that the surface cleanliness is kept extremely high. The surface roughness can be further reduced.
The pH when performing the second stage (final stage) silica polishing in an alkaline manner is preferably 10 or more in order to suppress the formation of the leaching layer. Further, it is preferably set to 13 or less in order to suppress an increase in roughness during polishing by etching.

In the present embodiment, a polishing liquid containing colloidal silica (particle size of about 5 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 made 0.25 nm or less and the micro waveness of the main surface can be made 0.1 nm or less. The roughness (Ra) of the main surface is more preferably 0.2 nm or less, further preferably 0.15 nm or less, and even more preferably 0.10 nm or less.
Thereafter, the glass substrate subjected to the second polishing is cleaned using an alkaline cleaning solution or the like 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.
[Example 1]
[Creation of aqueous silicic acid solution]
100 g of fumed silica, 302 g of tetramethylammonium hydroxide (TMAH) pentahydrate, and 598 g of reverse osmosis membrane filtered water (RO water) are mixed, and this mixture is stirred for 48 hours while heating to 120 ° C. in an autoclave. Thus, a colorless and transparent aqueous silicic acid solution was prepared.
Dilute the above silicic acid aqueous solution 10 times with RO water, add proton cation exchange resin while monitoring pH, and remove proton cation exchange resin by filtration when pH reaches 8.8. did. Thereafter, the obtained silicic acid aqueous solution was gently stirred at room temperature for 24 hours, and then the silicic acid aqueous solution was passed through a membrane filter to remove substances having a predetermined particle diameter or more that caused coarse particles.

[Creation of colloidal silica]
(Generation of primary particles)
Next, the aqueous silicic acid solution from which the proton-type cation exchange resin was removed was placed in an eggplant flask and stirred for 16 hours while heating to 93 ° C. in an oil bath to obtain colloidal silica containing primary particles of silica. When the particle size of the primary particles was measured by a dynamic light scattering method, the average particle size was 8.4 nm and the standard deviation was 2.7 nm.
(Generation of fused particles)
Next, proton type cation exchange resin was added to colloidal silica containing primary particles of silica, the pH was lowered to 8.6, and the proton type cation exchange resin was removed by filtration. Thereafter, the colloidal silica containing the primary particles was stirred for 12 hours while heating to 120 ° C. in an autoclave to obtain colloidal silica containing fused silica particles.
When the particle size of the fused particles was measured by a dynamic light scattering method, the average particle size was 10.4 nm and the standard deviation was 3.4 nm.

The colloidal silica was treated with hexamethyldisilane to trimethylsilylate silanol groups on the surface of the fused particles, and then the solvent was evaporated to dry the abrasive grains. Thereafter, when the intensity ratio of the ²⁹ Si spectrum was measured by nuclear magnetic resonance spectroscopy, the molar ratio of (Si—OH) / Si was 0.406.

[Example 2]
Colloidal silica was obtained in the same manner as in Example 1 except that the heating temperature of the autoclave in the production of the fused particles was 150 ° C.
When the particle size of the fused particles was measured by a dynamic light scattering method, the average particle size was 14.8 nm, and the standard deviation was 4.2 nm.

The colloidal silica was treated with hexamethyldisilane to trimethylsilylate silanol groups on the surface of the fused particles, and then the solvent was evaporated to dry the abrasive grains. Thereafter, when the intensity ratio of the ²⁹ Si spectrum was measured by nuclear magnetic resonance spectroscopy, the molar ratio of (Si—OH) / Si was 0.463.

Example 3
Colloidal silica was obtained in the same manner as in Example 1 except that SiO ₂ was concentrated to 2.5% by weight before the formation of the fused particles.
When the particle size of the fused particles was measured by a dynamic light scattering method, the average particle size was 21.2 nm and the standard deviation was 5.6 nm.

The colloidal silica was treated with hexamethyldisilane to trimethylsilylate silanol groups on the surface of the fused particles, and then the solvent was evaporated to dry the abrasive grains. Thereafter, when the intensity ratio of the ²⁹ Si spectrum was measured by nuclear magnetic resonance spectroscopy, the molar ratio of (Si—OH) / Si was 0.502.

Example 4
100 g of ethyl orthosilicate and 90 g of triethoxysilane were mixed and dissolved in 200 g of ethanol. This mixed solution was quickly put into a mixed solution of 25 g of a 25 wt% aqueous ammonia solution, 500 g of RO water and 100 g of ethanol at room temperature, and stirred at room temperature for 20 hours to obtain a solution containing silica primary particles.
Next, the solution containing the primary particles of silica is concentrated with an evaporator until the total amount becomes 200 g, and 600 g of pure water is added to the obtained concentrated solution, followed by stirring for 12 hours while heating to 120 ° C. in an autoclave. Colloidal silica containing fused particles was obtained.
When the particle size of the fused particles was measured by a dynamic light scattering method, the average particle size was 18.0 nm and the standard deviation was 3.1 nm.

The colloidal silica was treated with hexamethyldisilane to trimethylsilylate silanol groups on the surface of the fused particles, and then the solvent was evaporated to dry the abrasive grains. Then, when the intensity ratio of the spectrum of ²⁹ Si was measured by nuclear magnetic resonance spectroscopy, the molar ratio of (Si—OH) / Si was 0.461.

<Comparative Example 1>
Colloidal silica was obtained by adding a cation exchange resin to the silicic acid aqueous solution prepared in the same manner as in the Examples, lowering the pH to 8.4, and stirring for 12 hours while heating to 120 ° C. When the particle size of the silica particles was measured by a dynamic light scattering method, the average particle size was 17.8 nm and the standard deviation was 2.7 nm.

The colloidal silica was treated with hexamethyldisilane to trimethylsilylate silanol groups on the surface of the silica particles, and then the solvent was evaporated to dry the abrasive grains. Thereafter, when the intensity ratio of the ²⁹ Si spectrum was measured by nuclear magnetic resonance spectroscopy, the molar ratio of (Si—OH) / Si was 0.203.

<Comparative example 2>
Commercially available colloidal silica (average particle size: 20 nm) produced by ion exchange using water glass as a raw material was obtained. The colloidal silica was treated with hexamethyldisilane to trimethylsilylate silanol groups on the surface of the silica particles, and then the solvent was evaporated to dry the abrasive grains. Thereafter, when the intensity ratio of the ²⁹ Si spectrum was measured by nuclear magnetic resonance spectroscopy, the molar ratio of (Si—OH) / Si was 0.285.

The glass substrate for performing 2nd grinding | polishing was prepared using said manufacturing method of the glass substrate for magnetic discs. The 1st grinding | polishing process was performed using the polishing liquid which contains a cerium oxide abrasive grain as a loose abrasive grain, and prepared the glass substrate which performed the chemical strengthening process after that. Here, when the surface roughness Ra of the main surface was measured using AFM, it was 0.5 nm.
Next, the 2nd grinding | polishing process of the glass substrate was performed on the acidic conditions of pH3 using the polishing liquid containing the colloidal silica of the said Examples 1-4 and Comparative Examples 1-2. 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. The polishing allowance was 3 μm in terms of plate thickness. The polishing liquid was used while being circulated. The polishing pad was a polyurethane foam suede type with an Asker C hardness of 70. The polishing load was 100 g / cm ² .
Finally, it was cleaned using an alkaline cleaning solution and dried to obtain a glass substrate for magnetic disk.

<Processing rate>
The processing rate was evaluated by the weight change of the glass substrate before and after the polishing treatment.
<Surface roughness>
The main surface of the glass substrate after the polishing treatment was scanned with an atomic force microscope (AFM), and an arithmetic average roughness Ra (JIS B 0601: 2001) was obtained. The AFM measurement range was 1 μm square, and measurement was performed with a resolution of 256 × 256.
<Scratch>
The number of scratches formed on the main surface of the glass substrate after the cleaning treatment and having a maximum valley depth Rv (JIS B 0601: 2001) of 50 nm or more is detected using a laser-type surface defect inspection apparatus, SEM, and AFM, Measured. Here, the scratch is a defect that has a dent and looks like a scratch or a hole when analyzed by SEM or AFM.
Evaluation was performed at levels 1 to 3 in order from a glass substrate having a small number of scratches per surface. If it is level 2 or less, it can withstand practical use. The criteria for level classification are as follows.
Level 1: Number of scratches is 1 or less Level 2: Number of scratches is 2 or more and 3 or less Level 3: Number of scratches is 4 or more The results are shown in Table 1.

  In Examples 1 to 4 in which (Si—OH) / Si is 0.4 or more, a processing rate equal to or higher than that in Comparative Examples 1 to 2 in which (Si—OH) / Si is less than 0.4 is maintained. However, the surface roughness could be reduced as compared with the comparative example, and the scratch could be reduced as compared with the comparative examples 1 and 2. From the viewpoint of scratching, better results were obtained by setting (Si—OH) / Si to 0.5 or less.

Next, in Examples 5 to 8 and Comparative Examples 3 to 4, the second polishing treatment was performed in two stages.
In the first stage polishing treatment, the main surface of the glass substrate was polished under an acidic condition of pH3. The types of abrasive grains used in Examples 5 and 6 and Comparative Example 3 were the same as those in Comparative Example 1, and those in Examples 7 and 8 and Comparative Example 4 were the same as those in Example 1.
The polishing allowance was 3 μm in terms of plate thickness. The polishing liquid was used while being circulated. The polishing pad was a polyurethane foam suede type with an Asker C hardness of 70. The polishing load was 100 g / cm ² .

In the second stage polishing treatment, the main surface of the glass substrate was polished under an alkaline condition of pH 11.5. The types of abrasive grains used in Examples 5 and 7 are the same as those in Example 1, Examples 6 and 8 are the same as those in Example 4, and Comparative Examples 3 and 4 are the same as those in Comparative Example 1. It was used.
The polishing allowance was 1 μm in terms of plate thickness. The polishing liquid was used while being circulated. The polishing pad was a polyurethane foam suede type with an Asker C hardness of 70. The polishing load was 100 g / cm ² .
Finally, it was cleaned using an alkaline cleaning solution and dried to obtain a glass substrate for magnetic disk.
The obtained glass substrate was evaluated for surface roughness and scratch in the same manner as described above. The results are shown in Table 2.

実施例のシリカ砥粒を含むアルカリ性の研磨液を用いて第二研磨の第二段階処理を行なうと、スクラッチを増加させることなく、さらに低粗さにすることができる。
実施例のシリカ砥粒を含む研磨液を第１段階の酸性研磨処理及び第２段階のアルカリ性研磨処理の両方に用いると、スクラッチを増加させることなく、なお一層低粗さにすることができる。
比較例のシリカ砥粒を第二段階処理に用いると、前段の処理に用いる研磨砥粒の種類にかかわらず、スクラッチ特性を改善できない。また、表面粗さもあまり低減できない。

When the second stage treatment of the second polishing is performed using the alkaline polishing liquid containing the silica abrasive grains of the embodiment, the roughness can be further reduced without increasing the scratches.
When the polishing liquid containing the silica abrasive grains of the example is used for both the first-stage acidic polishing treatment and the second-stage alkaline polishing treatment, the surface roughness can be further reduced without increasing scratches.
If the silica abrasive grains of the comparative example are used in the second stage treatment, the scratch characteristics cannot be improved regardless of the type of abrasive grains used in the previous stage treatment. Also, the surface roughness cannot be reduced much.

Claims (13)

A method for producing a glass substrate for a magnetic disk, comprising a polishing treatment for supplying a polishing liquid containing silica abrasive grains as free abrasive grains between a main surface of a glass substrate and a polishing pad, and polishing the main surface of the glass substrate. Because
The silica abrasive is a glass substrate for a magnetic disk, wherein the ratio of silanol groups (Si—OH) inside the abrasive to the silicon element (Si) of the entire abrasive (Si—OH) / Si is 0.4 or more. Production method. A method for producing a glass substrate for a magnetic disk, comprising a polishing treatment for supplying a polishing liquid containing silica abrasive grains as free abrasive grains between a main surface of a glass substrate and a polishing pad, and polishing the main surface of the glass substrate. Because
The silica abrasive is
After trimethylsilylating silanol groups (Si-OH) on the surface of the abrasive grains with hexamethyldisilazane, only the spectral intensity of Si directly bonded to OH and O measured by nuclear magnetic resonance spectroscopy ( ²⁹ Si-NMR) A method for producing a glass substrate for a magnetic disk, wherein a ratio (Si—OH) / Si with a spectral intensity of Si directly bonded is 0.4 or more.   The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the polishing liquid containing the silica abrasive grains as free abrasive grains is alkaline. The polishing process is performed in a plurality of stages,
The manufacturing method of the glass substrate for magnetic discs as described in any one of Claims 1-3 which performs the process of the last step using the alkaline polishing liquid which contains the said silica abrasive grain as a loose abrasive grain. Silica abrasive grains,
Silica abrasive grains having a ratio (Si—OH) / Si of silanol groups (Si—OH) inside the abrasive grains to silicon element (Si) of the entire abrasive grains is 0.4 or more. Silica abrasive grains,
After trimethylsilylating silanol groups (Si-OH) on the surface of the abrasive grains with hexamethyldisilazane, only the spectral intensity of Si directly bonded to OH and O measured by nuclear magnetic resonance spectroscopy ( ²⁹ Si-NMR) Silica abrasive grains having a ratio (Si—OH) / Si of 0.4 or more to the spectral intensity of directly bonded Si.   The silica abrasive according to claim 5 or 6, wherein the ratio (Si-OH) / Si is 0.4 or more and 0.5 or less. It is a manufacturing method of the silica abrasive grain according to any one of claims 5 to 7,
A process of condensation-polymerizing silicic acid to produce primary particles of silica;
A process of generating fused particles of silica by fusing and growing the primary particles;
A method for producing silica abrasive grains.   The method for producing silica abrasive grains according to claim 8, wherein the fused particles are produced by condensation polymerization of silanol groups on the surface of the primary particles. In the treatment for generating the primary particles, the aqueous solution containing the primary particles is generated by promoting the polycondensation of silicic acid by lowering the pH of the aqueous solution of silicic acid and heating.
In the process of generating the fused particles, the pH of the aqueous solution containing the primary particles is lowered than the process of generating the primary particles, and the temperature of the aqueous solution containing the primary particles is increased than the process of generating the primary particles. The manufacturing method of the silica abrasive grain of Claim 8 or 9 which accelerates | stimulates the production | generation of the said fusion particle. In the treatment for generating the primary particles, the pH of the aqueous silicic acid solution is lowered to 9 or lower and heated to 90 ° C. or higher.
11. The method for producing silica abrasive grains according to claim 10, wherein in the treatment for generating the fused particles, the pH of the aqueous silicic acid solution is lowered to 8.6 or lower and heated to 120 ° C. or higher.   The method for producing silica abrasive grains according to claim 10 or 11, wherein the pH is lowered by adding a cation exchange resin to the aqueous solution of silicic acid.   The method for producing silica abrasive grains according to claim 12, wherein the cation exchange resin is a proton type cation exchange resin.