JP2015067507A - Method for producing colloidal silica abrasive and method for producing glass substrate for magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing colloidal silica abrasives free from the risk of damaging a polishing object, and a method for producing a glass substrate for a magnetic disk using the obtained colloidal silica abrasives.SOLUTION: Provided is a method for producing colloidal silica abrasives, including: a treatment of subjecting silicic acid in the aqueous solution of silicic acid including metal of 5 ppm or higher to polycondensation to precipitate solid silica; a treatment of pulverizing the precipitated silica; and a treatment of cleaning the silica after the pulverization with an acid aqueous solution to remove the metal in such a manner that the concentration of the metal reaches below 5 ppm.

Description

  The present invention relates to a method for producing colloidal 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. The precise polishing to the glass substrate and the final product, there is a method of using a polishing agent containing silica (SiO ₂₎ fine abrasive grains and the like. Silica can be produced by, for example, polycondensation of dissolved silicic acid by lowering the pH of the water glass using water glass (alkali silicate aqueous solution) as a raw material (Patent Document 1). 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. In this manufacturing method, after producing silica particles from an aqueous solution of alkali silicate, impurities such as alkali metal ions are removed by acid cleaning.

JP 2000-247625 A

  However, in the conventional manufacturing method, metal ions remaining inside relatively large silica particles cannot be removed by acid cleaning, and 5 ppm or more of metal remains inside silica abrasive grains. When a glass substrate is polished using silica abrasive grains in which such impurities remain, defects may be formed on the polished glass substrate due to metal ions dissolved in the polishing liquid.

  Then, an object of this invention is to provide the manufacturing method of the colloidal silica abrasive grain which does not have a possibility of scratching a grinding | polishing target object, and the manufacturing method of the glass substrate for magnetic discs using colloidal silica abrasive grain.

The first aspect of the present invention is a method for producing colloidal silica abrasive grains. The manufacturing method is
A process of precipitating solid silica by polycondensing silicic acid in an aqueous solution of silicic acid containing 5 ppm or more of a metal;
A process of grinding the precipitated silica;
A process of removing the metal so that the concentration of the metal is less than 5 ppm by washing the silica after pulverization with an acidic aqueous solution,
including.

  The metal is, for example, at least one of Al, Ca, B, Ba, Co, Cr, Cu, Fe, Mg, Mn, Na, Ni, Pb, Sr, Ti, Zn, Zr, U, and Th.

The method for producing colloidal silica abrasive grains is as follows:
A process for producing silica primary particles by polycondensing silicic acid to the silica particles after removing the metal;
A process of generating fused particles of silica by fusing and growing 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.

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 second aspect of the present invention is a method for producing a glass substrate for a magnetic disk. The manufacturing method supplies a polishing liquid containing free colloidal colloidal silica abrasive particles manufactured by the above manufacturing method between the main surface of the glass substrate and the polishing pad, and polishes the main surface of the glass substrate. Having a polishing process.

  According to the present invention, the concentration of the metal remaining in the colloidal silica abrasive can be less than 5 ppm. For this reason, it can prevent that a metal ion melt | dissolves in the polishing liquid using a colloidal silica abrasive grain, and a defect is formed in a grinding | polishing target object. By polishing the glass substrate for magnetic disk using this colloidal silica abrasive grain, the glass substrate for magnetic disk with few defects can be manufactured.

It is a figure which shows an example of the flow of the manufacturing method of the glass substrate for magnetic discs of this embodiment.

  Hereinafter, the manufacturing method of the silica abrasive grain which concerns on embodiment of this invention is demonstrated in detail.

(1) Crude silica As a raw material of the silica abrasive according to this embodiment, solid crude silica having a metal impurity content of 5 ppm or more can be used. Here, the metal impurity is, for example, at least one of Al, Ca, B, Ba, Co, Cr, Cu, Fe, Mg, Mn, Na, Ni, Pb, Sr, Ti, Zn, Zr, U, and Th. Either.

Such crude silica can be obtained, for example, by neutralizing water glass (sodium silicate aqueous solution) with a mineral acid and filtering the precipitate. Specifically, a strong acid is added to water glass to lower the pH to 4 or less, preferably 2 or less. Then, condensation polymerization of silanol groups of silicic acid is promoted, and crude silica having a particle size of about 0.05 μm or more is formed. Here, as the strong acid, for example, a mineral acid such as hydrochloric acid, nitric acid, sulfuric acid or the like can be used. Thereafter, solid crude silica can be obtained by separating the precipitate by filtration, centrifugation or other solid-liquid separation methods.
Thereafter, a treatment for removing metal impurities from the crude silica is performed. However, since the particles of the crude silica are large, the metal impurities taken into the crude silica cannot be sufficiently removed. Therefore, after the following pulverization process is performed in advance, a metal impurity removal process is performed.

(2) Crude treatment of crude silica The crude silica is crushed. Dry pulverization may be performed on the crude silica, or wet pulverization may be performed. Crude silica can be pulverized by, for example, a ball mill, a bead mill, a jet mill, or ultrasonic waves.

(3) Metal impurity removal treatment Next, the crushed crude silica is washed with a strong acid aqueous solution to remove metal impurities. As the strong acid, mineral acids such as hydrochloric acid, nitric acid and sulfuric acid can be used. The pH of the strong acid is preferably 4 or less, and more preferably 2 or less.
Moreover, you may add the oxidizing agent which does not contain a metal to strong acid aqueous solution. Since oxidization of the metal impurities is promoted by the oxidizing agent, the metal impurities can be efficiently removed. For example, hydrogen peroxide or the like can be used as such an oxidizing agent.
Furthermore, a chelating agent in which a metal ion cationized with a strong acid or an oxidizing agent forms a chelate complex may be added to the strong acid aqueous solution. By the chelating agent, reattachment of metal ions to silica can be prevented and more reliably removed. Examples of such a chelating agent include N ′-(2-hydroxyethyl) ethylenediamine-N, N, N′-triacetic acid (HEDTA), 1-hydroxyethane-1,1-diphosphonic acid (HEDP), and nitrilotrimethyl. Acetic acid (NTA), N, N-di (2-hydroxyethyl) glycine (DHEG), ethylenediaminetetraacetic acid (EDTA), N- (2-hydroxyethyl) iminodiacetic acid (HIDA), diethylenetriaminepentaacetic acid (DTPA), Oxalic acid, malic acid, tartaric acid, fumaric acid, succinic acid, citric acid, gluconic acid, and the like can be used.
Then, purified silica having a metal impurity content of less than 5 ppm is obtained by removing the strong acid aqueous solution by filtration and washing with water.

In addition, when content of the metal impurity in the obtained refined silica is 5 ppm or more, the above treatments (2) and (3) may be repeated until the content of the metal impurity is less than 5 ppm. Good. Moreover, you may perform said (4) and the process of (5) simultaneously by wet-grinding the strong acid aqueous solution containing crude silica.
Thus, after pulverizing the crude silica having a metal impurity content of 5 ppm or more, the metal impurities taken into the crude silica can be removed by washing with a strongly acidic aqueous solution. Purified silica purified until the content of is less than 5 ppm can be obtained.

Silica abrasive grains can be produced by a known method using the purified silica thus obtained. For example, purified silica is dissolved in a strongly basic aqueous solution, neutralized, and stirred for a predetermined time while heating, whereby colloidal silica containing silica particles is obtained.
Hereinafter, an example of a method for producing silica abrasive grains using the purified silica of the present embodiment will be described. In addition, the manufacturing method of the silica abrasive grain of this invention is not restricted to the method demonstrated below.
First, a strong base for dissolving purified silica will be described.

(4) 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.

(5) Preparation of silicic acid aqueous solution The silicic acid aqueous solution is obtained by dissolving the purified silica 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 liquid of the above-described purified silica, strong base, and water for 48 hours while heating to 120 ° C. in an autoclave, for example. it can.

(6) Generation of primary particles by condensation polymerization of silica particles Next, after diluting the above silicic acid aqueous solution as necessary, the pH of the silicic acid 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 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 aqueous silicic acid 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.

(7) Formation of Fusion Particles by Fusion 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. As a result, the primary particles are fused and grown 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.
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.
Silanol groups on the surface of silica abrasive grains are trimethylsilylated with hexamethyldisilazane, the solvent is evaporated to dry the abrasive grains, and then the intensity ratio of the ²⁹ Si spectrum is measured by nuclear magnetic resonance spectroscopy (Si The ratio of —OH) / Si can be determined.

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, silica abrasive grains having an arbitrary particle diameter can be generated by fusing primary particles to produce fused particles. In the above embodiment, the case where the fused particles are generated by condensation polymerization of the silanol groups on the surface of the primary particles has been described. However, the present invention is not limited to this, and the primary particles are fused and grown by an arbitrary method. To produce fused particles.
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, 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, with reference to FIG. 1, the flow of the manufacturing method of the glass substrate for magnetic discs is demonstrated. FIG. 1 is a diagram showing an example of a flow of a method for producing a magnetic disk glass substrate of the present embodiment. As shown in FIG. 1, 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 (step S10). Next, the produced glass blank is scribed to produce a ring-shaped (annular) glass substrate having a hole in the center (step S20). Next, shape processing (chamfering) is performed on the scribed glass substrate (step S30). Thereby, a glass substrate is produced | generated. Next, end-face polishing is performed on the glass substrate that has been processed (step S40). Grinding with the fixed abrasive is performed on the glass substrate subjected to the end surface polishing (step S50). Next, 1st grinding | polishing is performed to the main surface of a glass substrate (step S60). Next, chemical strengthening is performed on the glass substrate (step S70). Next, the second polishing is performed on the chemically strengthened glass substrate (step S80). The glass substrate for magnetic disks is obtained through the above processing. Hereinafter, each process will be described in detail.

(A) Press molding process (step S10)
When a predetermined amount of the molten glass flow flows out from the lower outlet of the molten glass outflow pipe, the molten glass lump is dropped by cutting the tip of the molten glass flow with a cutter. Next, by bringing a pair of molds moving on both sides in a direction (for example, the horizontal direction) intersecting with the falling direction of the molten glass lump, the falling molten glass lump is placed on the press molding surface of the pair of molds. It is sandwiched between and pressed to form a glass blank (hereinafter referred to as a horizontal press method). After pressing for a predetermined time, the mold is opened and the glass blank is taken out.

(B) Scribe process (step S20)
In the scribing process, scribing is performed on the formed glass blank. Here, scribe refers to two concentric scratches formed by a scribe wheel made of super steel alloy or diamond particles on the surface of the glass blank in order to use the formed glass blank as a ring-shaped glass substrate of a predetermined size. This means providing a (cutting line). Specifically, the glass blank is moved by a robot hand to a scribe stage for performing a scribe process, positioned so as to be a scribe position determined as described later, and the glass blank is fixed by suction. Next, two concentric cutting lines are formed by rotating the scribe wheel along two concentric circles corresponding to the determined scribe positions. Here, the outer cutting line becomes the outer peripheral circle of the glass substrate, and the inner cutting line becomes the outline of the central hole.
The glass blank scribed in the shape of two concentric circles is partially heated, and due to the difference in thermal expansion of the glass blank, the outer portion of the outer concentric circle and the inner portion of the inner concentric circle are removed. As a result, a glass substrate having a circular central hole is obtained. In addition, the glass substrate with the circular center hole can also be obtained by forming a circular hole in the glass blank using a core drill or the like.

(C) Shape processing (step S30)
The shape processing includes chamfering (chamfering of the outer end surface and the inner end surface) for the end portion of the glass substrate after the scribe processing. A chamfering process is a shape process which chamfers with a diamond grindstone in the outer peripheral side end surface and inner side end surface of the glass substrate after a scribe process. A glass substrate having a predetermined shape is generated by this shape processing. The chamfering inclination angle is, for example, 40 to 50 degrees with respect to the main surface, and is preferably about 45 degrees.

(D) End face polishing process (step S40)
In the end surface polishing, mirror finishing is performed by brush polishing on the inner end surface and the outer peripheral side end surface of the glass substrate. At this time, an abrasive slurry containing fine particles such as cerium oxide as free abrasive grains is used. By polishing the end face, contamination such as dirt and scratches on the end face of the glass substrate is removed, and the occurrence of thermal asperity failure is prevented and ion precipitation that causes corrosion such as sodium and potassium is eliminated. Occurrence can be prevented.

(E) Grinding process with fixed abrasive (step S50)
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 machining allowance by grinding is, for example, about several μm to 100 μm. The particle size of the fixed abrasive is, for example, about 10 μm. 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 process (step S60)
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 a holding member of a double-side polishing apparatus. The machining allowance by the first polishing is, for example, about several μm to 50 μm. The purpose of the first polishing is, for example, to remove scratches or distortions remaining on the main surface when grinding with fixed abrasive grains, or to adjust minute surface irregularities (microwaveness, roughness). The machining allowance by the first polishing is, for example, about several μm to 50 μm.

  In the first polishing process, the glass substrate is polished while applying a polishing slurry by using a double-side polishing apparatus having the same configuration as the double-side grinding apparatus used for grinding with fixed abrasive grains (step S60). 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. As the free abrasive grains used in the first polishing, 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. 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 process (step S70)
In the chemical strengthening treatment, the chemical strengthening solution is heated to, for example, 300 ° C. to 400 ° C., and the cleaned glass substrate is preheated to, for example, 200 ° C. to 300 ° C. Then, the glass substrate is placed in the chemical strengthening solution, for example, 3 hours to 4 hours. Immerse. As the chemical strengthening solution, for example, a mixed solution of potassium nitrate (60% by weight) and sodium nitrate (40% by weight) can be used.
By immersing the glass substrate in the chemical strengthening solution, lithium ions and sodium ions in the glass composition on the surface layer of the glass substrate are respectively replaced with sodium ions and potassium ions having a relatively large ion radius in the chemical strengthening solution. Thus, a compressive stress layer is formed on the surface layer portion, and the glass substrate is reinforced.
Note that the chemically strengthened glass substrate is cleaned. For example, the glass substrate is washed with sulfuric acid and then with pure water or the like.

(H) Second polishing (final polishing) process (step S80)
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. The machining allowance by the second polishing is, for example, about 1 μm. The second polishing process is different from the first polishing process in that the type and particle size of the free abrasive grains are different and the hardness of the resin polisher is different.

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.

〔Example〕
The strong acid aqueous solution for washing crude silica was adjusted to pH 1 with sulfuric acid. As a chelating agent, 0.1 mol / L EDTA with respect to silicon was added to the strong acid aqueous solution, and as an oxidizing agent, hydrogen peroxide was added to the strong acid aqueous solution so as to be 2 wt% of the whole.
1000 g of Fuji Chemical No. 3 sodium silicate (JIS K1408) was diluted 3-fold with reverse osmosis membrane filtered water (RO water), 5000 mol of 1 mol / L sulfuric acid was added, and the mixture was stirred at room temperature for 12 hours. Thereafter, the resulting white precipitate was collected by suction filtration to obtain 520 g of crude silica.
The obtained crude silica was pulverized with a ball mill until the particle size became 0.1 μm or less. Then, the crushed crude silica was washed with a strong acid aqueous solution, and purified silica was obtained by removing the strong acid aqueous solution by filtration and washing with water.
Impurities in the purified silica thus obtained were detected by an inductively coupled plasma-atomic emission spectrometer (ICP-AES). As a result, aluminum (Al) was 3 ppm, iron (Fe) was 1 ppm, titanium ( Ti) was 1 ppm.

<Comparative example>
Purified silica was obtained in the same manner as in Example, except that crude silica was not pulverized by a ball mill.
When impurities in the obtained purified silica were detected by ICP-AES, Al was 10 ppm, Fe was 7 ppm, and Ti was 7 ppm.

[Creation of aqueous silicic acid solution]
Purified silica of Examples and Comparative Examples, tetramethylammonium hydroxide (TMAH) pentahydrate as a strong base (manufactured by Tokyo Chemical Industry), reverse osmosis membrane filtered water (RO water), SiO ₂ and TMAH molar ratio SiO ₂ / TMAH 0.5, and, SiO ₂ were mixed so as to be 10 wt%, create a silicate solution of colorless and transparent the mixture by stirring for 48 hours while heating at 120 ° C. in an autoclave did.
A proton type cation exchange resin (Amberlite (registered trademark) IR12BH) is added to the above silicic acid aqueous solution while monitoring the pH, and when the pH reaches 8.8, the proton type cation exchange resin is filtered. Was removed. Thereafter, the obtained silicic acid aqueous solution was gently stirred at room temperature for 48 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]
Next, the aqueous silicic acid solution from which the proton-type cation exchange resin was removed was stirred for 16 hours while being heated to 95 ° C. to obtain colloidal silica containing primary particles of silica. When the particle size of the primary particles was measured by the dynamic light scattering method, the average particle size was 8 nm and the standard deviation was 4 nm.
Next, proton type cation exchange resin (Amberlite (registered trademark) IR12BH) was added to colloidal silica containing primary particles of silica, pH was lowered to 8.6, and proton type cation exchange resin was removed by filtration. Then, it stirred for 12 hours, heating at 120 degreeC, and obtained the colloidal silica containing the fused particle of a silica.
When the particle size of the fused particles was measured by a dynamic light scattering method, the average particle size was 10 nm and the standard deviation was 4 nm.

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.
The number of convex defects having a maximum peak height Rp (JIS B 0601: 2001) of 50 nm or more and the maximum valley depth Rv (JIS B 0601: 2001) of 50 nm or more formed on the surface of the glass substrate after the polishing treatment. Was measured using AFM.
The results are summarized in Table 1.

The number of convex defects remaining on the glass substrate after polishing using the polishing liquid containing colloidal silica of the example was 6, and the number of concave defects was 13. On the other hand, the number of convex defects remaining on the glass substrate after polishing using the polishing liquid containing colloidal silica of Comparative Example was 18, and the number of concave defects was 37.

Claims (8)

A method for producing colloidal silica abrasive,
A process of precipitating solid silica by polycondensing silicic acid in an aqueous solution of silicic acid containing 5 ppm or more of a metal;
A process of grinding the precipitated silica;
A process of removing the metal so that the concentration of the metal is less than 5 ppm by washing the silica after pulverization with an acidic aqueous solution,
The manufacturing method of the colloidal silica abrasive grain containing this.   The metal is at least one of Al, Ca, B, Ba, Co, Cr, Cu, Fe, Mg, Mn, Na, Ni, Pb, Sr, Ti, Zn, Zr, U, and Th. 2. A method for producing a colloidal silica abrasive grain according to 1. A process for producing silica primary particles by polycondensing silicic acid to the silica particles after removing the metal;
A process of generating fused particles of silica by fusing and growing the primary particles;
The manufacturing method of the colloidal silica abrasive grain of Claim 1 or 2 containing this.   The manufacturing method of the colloidal silica abrasive grain of Claim 3 which produces | generates the said fusion | melting particle | grains by carrying out the condensation polymerization of the silanol groups of the surface of the said primary particle. 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 colloidal silica abrasive grain of Claim 3 or 4 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.
6. The method for producing colloidal silica abrasive grains according to claim 5, wherein, in the treatment for generating the fused particles, the pH of the aqueous silicic acid solution is lowered to 8.6 or less and heated to 120 ° C. or more.   The method for producing colloidal silica abrasive grains according to claim 5 or 6, wherein the pH is lowered by adding a cation exchange resin to the aqueous solution of silicic acid. A method of manufacturing a glass substrate for a magnetic disk,
A polishing liquid containing colloidal silica abrasive grains produced by the production method according to any one of claims 1 to 7 as free abrasive grains is supplied between the main surface of the glass substrate and the polishing pad, and the glass A method for producing a glass substrate for a magnetic disk, comprising a polishing process for polishing a main surface of a substrate.

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