JP2008204521A - Manufacturing method of glass substrate for magnetic disk and chemical strengthening device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the chemical strengthening device of a glass substrate for a magnetic disk capable of performing chemical strengthening at a low cost by melting a chemical strengthening salt in a short period of time and reducing foreign matter adhesion onto the glass substrate when chemical strengthening is performed by suppressing corrosion of a vessel. <P>SOLUTION: The chemical strengthening device 100 includes a salt casting vessel 120 in which a solid chemical strengthening salt 110 is casted, an electromagnetic wave generator 130 heating and melting the chemical strengthening salt 110 in the salt casting vessel 120 by using an electromagnetic wave 170 and a chemical strengthening vessel 150 to which a melted chemical strengthening salt 140 is supplied and in which the glass substrate for the magnetic disk is brought into contact with the chemical strengthening salt 140 to perform chemical strengthening. The solid chemical strengthening salt 110 is melted in an electromagnetic wave heating chamber 160 by using the electromagnetic wave generator 130 and the resultant chemical strengthening salt is supplied from the salt casting vessel 120 to the chemical strengthening vessel 150 through a supplying pipe 180. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk and a chemical strengthening apparatus.

  In recent years, with the advancement of information technology, information recording technology, particularly magnetic recording technology, has made remarkable progress. As a substrate for a magnetic recording medium such as an HDD (Hard Disk Drive) which is one of such magnetic recording media, an aluminum substrate has been widely used. However, with the miniaturization, thinning, and high-density recording of magnetic disks, there is an increasing demand for glass substrates that have superior substrate surface flatness and substrate strength compared to aluminum substrates.

  Such a glass substrate for a magnetic disk is formed through a plurality of processes. First, one wafer is cut into a disk shape, and an inner hole is further formed to form a glass substrate. Thereafter, the outer peripheral end surface and the inner peripheral end surface of the cut glass substrate are chamfered, and both end surfaces are polished. Subsequently, the main surface of the glass substrate is also polished, and finally the glass substrate that has been polished is subjected to a chemical strengthening treatment. Such chemical strengthening treatment can improve the impact resistance and vibration resistance of the glass substrate, and can prevent the glass substrate from being damaged by the impact and vibration.

  The chemical strengthening salt (alkali salt) is supplied as a solid (powder) because of its ease of handling. In a chemical strengthening process for performing chemical strengthening treatment, generally, a solid chemical strengthening salt is heated and melted, and the glass substrate to be treated is stored in a glass substrate holder and immersed in a molten salt (chemical strengthening treatment solution). The ion exchange is performed between the glass substrate and the molten salt.

Conventionally, the chemical strengthening salt is heated and melted by heating a container in which a solid chemical strengthening salt is charged with an electric heater or a gas heater. In such heating and melting, the chemically strengthened salt in the part in contact with the heated container reaches the melting point and is melted, and the heat of the molten chemically strengthened salt is gradually transferred to the chemically strengthened salt in the center of the container. Eventually, the chemical strengthening salt of the entire container has been melted (for example, Patent Document 1).
JP 2002-220260 A

  In recent years, with the spread of portable music players using notebook computers and hard disks (hereinafter abbreviated as HDDs), it has become necessary to manufacture glass substrates for HDDs in large quantities at low cost. In particular, batch processing for processing a large amount of substrates becomes mainstream, and accordingly, a large amount of chemically strengthened salt is required.

  As described in Patent Document 1, heating by a gas heater or an electric heater indirectly heats and melts the chemically strengthened salt inside the container by heating the container from the outside of the container. Therefore, the chemically strengthened salt in the portion that contacts the container wall is first melted, and heat gradually propagates to the chemically strengthened salt put in the central part away from the container wall, and eventually the entire chemically strengthened salt is melted. .

  However, the chemical strengthening salt that comes into contact with the wall surface of the container is a part of the whole and is in the form of powder, so the thermal conductivity is very poor. Therefore, it takes a long time to melt the conventional chemically strengthened salt, which causes an increase in manufacturing cost.

  Further, when heating from the outside of the container, the temperature of the container becomes higher than the target temperature of the chemically strengthened salt, which is one of the factors that shorten the life of the container due to corrosion of the container. The chemical strengthening tank is generally formed of stainless steel, but the temperature of chemical strengthening is 300 ° C. or more, and the chemical strengthening salt is a strong acid. Therefore, the higher the temperature, the greater the influence of corrosion. And if a chemical strengthening tank corrodes, a foreign material (particle) will generate | occur | produce and this will adhere to a glass substrate and will increase a defect rate, Therefore The chemical strengthening tank which began to corrode must be replaced | exchanged. Then, it becomes a factor which impairs cost reduction remarkably, such as the cost of the chemical strengthening tank itself, the cost of the chemical strengthening salt to replace | exchange, and the loss by temporary decline in production capacity. Although it is conceivable to install a heater inside the container, head crashes may occur due to impurities generated from the heater.

  As a result of diligent investigations and experiments on these problems, the inventors of the present invention have found that, if electromagnetic waves are used, the chemically strengthened salt can be heated directly rather than indirectly through a container, and the present invention has been completed. It came to do. Heating by electromagnetic waves is common as a household high-frequency heater (so-called microwave oven) for polar substances such as water, but a method for heating a chemically strengthened salt by electromagnetic waves is not generally known.

  The present invention can perform chemical strengthening by melting the chemically strengthened salt in a shorter time, and can reduce the adhesion of foreign matter on the glass substrate at the time of chemical strengthening by an inexpensive method that suppresses corrosion of the container. An object is to provide an apparatus.

  In order to solve the above-described problems, a method for manufacturing a glass substrate for a magnetic disk according to the present invention includes a chemical strengthening salt charging step of charging a solid chemical strengthening salt into a salt charging container, and a chemical strengthening salt in the salt charging container. A melting process that melts by heating with electromagnetic waves, a chemical strengthening salt supply process that supplies the molten chemically strengthened salt to the chemical strengthening tank, and a chemical that chemically contacts the glass substrate for magnetic disk with the melted chemically strengthened salt. And a strengthening step.

  According to another aspect of the present invention, a method of manufacturing a glass substrate for a magnetic disk according to the present invention includes a step of supplying a solid or liquid chemical strengthening salt to a chemical strengthening tank, and a chemical strengthening salt in the chemical strengthening tank. And heating the substrate with electromagnetic waves.

  In the heating step described above, the chemical strengthening salt in the chemical strengthening tank made of a material that transmits electromagnetic waves may be heated with electromagnetic waves from a plurality of different directions.

  In order to solve the above-mentioned problems, a chemical strengthening apparatus for a glass substrate for a magnetic disk according to the present invention heats the salt strengthening container into which a solid chemically strengthened salt is charged and the chemically strengthened salt in the salt throwing container with electromagnetic waves. And a chemical strengthening tank that is supplied with a molten chemically strengthened salt and chemically strengthens by bringing the glass substrate for magnetic disk into contact with the chemically strengthened salt.

  According to the above configuration, since the chemically strengthened salt can be directly and uniformly heated by electromagnetic waves, the chemically strengthened salt can be melted in a short time.

  According to another aspect of the present invention, a chemical strengthening apparatus for a glass substrate for a magnetic disk according to the present invention includes a chemical strengthening tank to which a solid or liquid chemical strengthening salt is supplied, and a chemical strengthening salt in the chemical strengthening tank as an electromagnetic wave. And a second electromagnetic wave generating means for heating at a temperature.

  In this way, by providing the second electromagnetic wave generating means, the salt is directly heated and the corrosion caused by excessive heating of the chemical strengthening tank can be suppressed, and the generation of particles from the chemical strengthening tank can be suppressed. It is possible to suppress.

  Further, if the chemical strengthening tank is made of a material that transmits electromagnetic waves, there may be a plurality of second electromagnetic wave generating means, and the chemical strengthening salt in the chemical strengthening tank is heated with electromagnetic waves from a plurality of different directions. It's okay. If the chemical strengthening tank is made of a material that transmits electromagnetic waves, the chemically strengthened salt can be heated by electromagnetic waves from various directions. In addition, with this configuration, the chemically strengthened salt can be uniformly heated and uniform chemical strengthening can be performed on the glass substrate.

  According to the present invention, the chemically strengthened salt can be directly and uniformly heated by electromagnetic waves, and the chemically strengthened salt can be melted in a short time. It is possible to supply a large amount of a magnetic glass glass substrate.

  In addition, when using a chemical strengthening tank made of stainless steel or the like, the salt in the chemical strengthening tank can be directly heated by irradiating electromagnetic waves from the direction not separated by the bottom or side walls of the chemical strengthening tank. The rise in the temperature is suppressed and corrosion of the chemical strengthening tank can be prevented. Thereby, generation | occurrence | production of the particle resulting from corrosion can be suppressed. As a result, adhesion of particles to the surface of the glass substrate for magnetic disk that has been chemically strengthened is suppressed, and a magnetic disk manufactured using such a glass substrate is less likely to cause thermal asperity failure or head crash.

  Next, embodiments of a method for manufacturing a glass substrate for a magnetic disk and a chemical strengthening apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the figure, elements not directly related to the present invention are not shown. Similar elements are denoted by the same reference numerals.

(First embodiment of chemical strengthening apparatus)
FIG. 1 is a diagram showing a first embodiment of a chemical strengthening apparatus according to the present invention. The chemical strengthening apparatus 100 for a magnetic disk glass substrate includes a salt charging container 120 into which a solid chemical strengthening salt 110 is charged, and a chemical strengthening salt 110 in the salt charging container 120 that is heated by an electromagnetic wave 170 to melt. It includes an electromagnetic wave generator 130 and a chemical strengthening tank 150 which is supplied with a molten chemically strengthened salt 140 and chemically strengthens the chemically strengthened salt 140 by bringing a glass substrate for magnetic disk (not shown) into contact therewith.

  In addition, the chemical strengthening apparatus 100 includes an electromagnetic wave heating chamber 160 sealed with a conductive metal in order to prevent leakage of electromagnetic waves. In the electromagnetic wave heating chamber 160, the aforementioned salt charging container 120 and the electromagnetic wave generator 130 are installed.

The chemical strengthening salt 110 may be, for example, potassium nitrate (KNO ₃ ), sodium nitrate (NaNO ₃ ), or a mixture thereof. FIG. 2 is a diagram showing the structural formulas of sodium nitrate (FIG. 2 (a)) and potassium nitrate (FIG. 2 (b)) used as the chemically strengthened salt 110 of FIG. According to these structural formulas, the structure of the chemically strengthened salt contains the most double bonds of nitrogen N and oxygen O.

  The salt charging container 120 in FIG. 1 is a ceramic (ceramic) that transmits electromagnetic waves. On the other hand, the material of the chemical strengthening tank 150 may typically be austenitic stainless steel or martensitic stainless steel. In such metal containers, an induced current is generated by electromagnetic waves, and the temperature of the container rises, but since austenitic stainless steel and martensitic stainless steel generally used as containers have low electrical resistance, it is difficult to generate heat, The temperature rise will be less than the temperature rise of the strengthening salt.

  In addition, when the salt in the chemical strengthening tank 150 is also heated by electromagnetic waves, the chemical strengthening tank 150 is also a ceramic (ceramic) that transmits electromagnetic waves, like the salt charging container 120.

The chemical strengthening tank 150 can hold 5 to 6 tons of molten chemically strengthened salt 140. Since the specific gravity of the molten chemically strengthened salt is twice that of water, when it is 6 tons, the chemical strengthened salt 140 is 3 m ^{3 in} volume. In general, the salt-strengthened salt container 110 is charged with the solid chemically strengthened salt 110 in about two to three times, and the chemically strengthened salt 140 melted at each time is supplied to the chemical strengthening tank 150.

  The electromagnetic wave 170 generated by the electromagnetic wave generator 130 may be at least a frequency capable of heating nitrate as a chemically strengthened salt. Specifically, for example, it is preferably a microwave of 1 GHz or more. This is because according to such a frequency, the chemical strengthening salt can be heated by exciting the double bond of nitrogen N and oxygen O which are most contained in the chemical strengthening salt.

  Alternatively, the electromagnetic wave generated by the electromagnetic wave generator 130 may be a microwave having a frequency of 2.45 GHz (wavelength is about 12 cm) employed in a microwave oven. Since this frequency matches the natural frequency of the water molecule, the water molecule contained in the chemically strengthened salt is vibrated, thereby generating frictional heat and heating the chemically strengthened salt.

  In the present embodiment, when the chemically strengthened salt 110 is melted, as shown in FIG. 1, first, the solid chemically strengthened salt 110 is charged into the salt charging container 120, and the chemically strengthened salt 110 in the salt charging container 120 is then added. Is melted by heating with electromagnetic wave 170. At this time, the heating by the electromagnetic wave 170 is directly performed on the chemically strengthened salt 110 by exciting the bonds between elements contained in the chemically strengthened salt 110 or vibrating water molecules.

  On the other hand, the conventional heating method using a heater or burner (not shown) first heats the chemical strengthening tank 150 supplied with the solid chemical strengthening salt 110 and indirectly contacts the chemical strengthening tank 150. In this method, the chemically strengthened salt 110 is heated. Since the solid chemical strengthening salt is in the form of powder, the thermal conductivity is very poor. Therefore, as compared with the embodiment of the present invention, a long heating time is required, for example, it takes twice as long to reach the state of the molten chemically strengthened salt 140.

  In the case of heating with a heater using a hot wire such as a nichrome wire, the temperature is high in the vicinity of the hot wire, and the temperature is low in other areas. Therefore, the metal container into which the chemically strengthened salt is charged shrinks for a long time, particularly in the vicinity of the heat ray, and in extreme cases, it may be distorted to the extent that it can be visually observed.

  Compared to this, in the embodiment of the present invention, the chemically strengthened salt 110 can be directly and uniformly heated by the electromagnetic wave 170, so that the chemically strengthened salt 110 can be melted in a short time.

  Then, the molten chemically strengthened salt 140 is supplied from the salt charging container 110 to the chemical strengthening tank 150 through the supply pipe 180. Since the supply pipe 180 has a portion extending horizontally from the salt charging container 120 as schematically shown in FIG. 1, the solid (powdered) chemical strengthening salt 110 is not supplied to the chemical strengthening tank 150, Only the molten chemical strengthening salt 140 is supplied to the chemical strengthening tank 150. This is to prevent undissolved residual chemical strengthening salt.

  Then, chemical strengthening is performed by bringing a glass substrate for magnetic disk (not shown) into contact with the molten chemically strengthened salt 140.

(Second Embodiment of Chemical Strengthening Device)
FIG. 3 is a view showing a second embodiment of the chemical strengthening apparatus according to the present invention. In FIG. 3, the electromagnetic wave heating chamber 160 similar to that of FIG. As shown in FIG. 3, the chemical strengthening apparatus 200 for a glass substrate for a magnetic disk in the present embodiment is a second electromagnetic wave that heats a chemically strengthened salt 140 in a chemical strengthening tank 150 with an electromagnetic wave 210 in an electromagnetic wave heating chamber 260. A generator 220 is included.

  Thus, by providing the second electromagnetic wave generator 200, even if the chemical strengthening tank 150 is made of stainless steel or the like and corrodes when heated excessively, the corrosion can be suppressed. The generation of particles from the chemical strengthening tank 150 can be suppressed. In the case of the present embodiment, even if the chemical strengthening tank 150 is made of a material that does not transmit electromagnetic waves, such as stainless steel, the electromagnetic wave is irradiated from the direction not separated by the bottom surface or the side wall of the chemical strengthening tank 150 as shown in FIG. Then, the salt in the chemical strengthening tank 150 can be directly heated.

  In the present embodiment, the second electromagnetic wave generator 200 is installed above the chemical strengthening tank 150. However, if the chemical strengthening tank 150 is made of a material such as ceramic (ceramic) that transmits electromagnetic waves, You may install in any position with respect to the chemical strengthening tank 150. FIG.

(Third embodiment of chemical strengthening apparatus)
FIG. 4 is a view showing a third embodiment of the chemical strengthening apparatus according to the present invention. Also in FIG. 4, the electromagnetic wave heating chamber 160 similar to that in FIG. As shown in FIG. 4, the chemical strengthening apparatus 300 for a glass substrate for a magnetic disk in the present embodiment radiates a chemically strengthened salt 140 in a chemical strengthening tank 150 from a plurality of different directions in an electromagnetic wave heating chamber 360. A plurality of second electromagnetic wave generators 220A to 220C that are heated by the electromagnetic waves 210A to 210C are included.

  In the case of this embodiment, the chemical strengthening tank 150 is a ceramic (ceramic) that transmits electromagnetic waves. Thereby, the chemically strengthened salt 140 can be directly heated by the electromagnetic waves 210A to 210C radiated from a plurality of different directions. Thus, the chemical strengthening salt 140 in the chemical strengthening tank 150 can be efficiently heated by providing the plurality of second electromagnetic wave generators 200A to 220C.

[Example]
Embodiments of a method for manufacturing a magnetic disk glass substrate and a method for manufacturing a magnetic disk to which the present invention is applied will be described below. This glass substrate for magnetic disk and magnetic disk are 0.8 inch type disk (inner diameter 6 mm, outer diameter 21.6 mm, plate thickness 0.381 mm), 1.0 inch type disk (inner diameter 7 mm, outer diameter 27.4 mm, It is manufactured as a magnetic disk having a predetermined shape such as a plate thickness of 0.381 mm) and a 1.8 inch type magnetic disk (inner diameter of 12 mm, outer diameter of 48 mm, plate thickness of 0.508 mm). Further, it may be manufactured as a 2.5 inch type disc or a 3.5 inch type disc.

(1) Shape processing step and first lapping step In the method of manufacturing a magnetic disk glass substrate according to this example, first, the surface of the plate glass is lapped (ground) to obtain a glass base material. Cut the material and cut out the glass disc. Various plate glasses can be used as the plate glass. This plate-like glass can be manufactured by using a known manufacturing method such as a press method, a float method, a downdraw method, a redraw method, or a fusion method using a molten glass as a material. Of these, plate glass can be produced at low cost by using the pressing method. As the material of the plate glass, amorphous glass or glass ceramics (crystallized glass) can be used. As the material for the plate glass, aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used. In particular, as an amorphous glass, an aluminosilicate glass can be preferably used in that it can be chemically strengthened and a magnetic disk substrate excellent in flatness of the main surface and substrate strength can be supplied.

In this example, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper mold, a lower mold, and a barrel mold to obtain an amorphous plate glass. As the aluminosilicate _glass, SiO 2: 58 to 75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: 3 to 10 _wt%, Na 2 O: 4 to 13 principal component weight% Chemically strengthened glass contained as

  Next, both main surfaces of the plate glass were lapped to form a disk-shaped glass base material. This lapping process was performed using alumina free abrasive grains with a double-sided lapping apparatus using a planetary gear mechanism. Specifically, the lapping platen is pressed on both sides of the plate glass from above and below, the grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relative to each other for lapping. went. By this lapping process, a glass base material having a flat main surface was obtained.

(2) Cutting process (coring, forming, chamfering)
Next, the glass base material was cut using a diamond cutter, and a disk-shaped glass substrate was cut out from the glass base material. Next, using a cylindrical diamond drill, an inner hole was formed in the center of the glass substrate to obtain an annular glass substrate (coring). Then, the inner peripheral end face and the outer peripheral end face were ground with a diamond grindstone and subjected to predetermined chamfering (forming, chamfering).

(3) Second Lapping Step Next, a second lapping process was performed on both main surfaces of the obtained glass substrate in the same manner as in the first lapping step. By performing this second lapping step, it is possible to remove in advance the fine unevenness formed on the main surface in the cutting step and end surface polishing step, which are the previous steps, and shorten the subsequent polishing step on the main surface. Will be able to be completed in time.

(4) End surface grinding | polishing process Next, mirror polishing was performed with the brush grinding | polishing method about the outer peripheral end surface of the glass substrate. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used.

  And the glass substrate which finished the end surface grinding | polishing process was washed with water. By this end face polishing step, the end face of the glass substrate was processed into a mirror state that can prevent the precipitation of sodium and potassium. In particular, the inner peripheral end face was in a good state without a decrease in tolerance and roundness of the inner hole even when a large number of about 200 to 300 sheets were laminated and polished.

(5) Main surface polishing step As the main surface polishing step, first, a first polishing step was performed. This first polishing step is mainly intended to remove scratches and distortions remaining on the main surface in the lapping step described above. In the first polishing step, the main surface was polished using a hard resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains were used.

  The glass substrate which finished this 1st grinding | polishing process was immersed in each washing tank of neutral detergent, a pure water, and IPA (isopropyl alcohol) one by one, and was wash | cleaned.

  Next, a second polishing step was performed as the main surface polishing step. The purpose of this second polishing step is to finish the main surface into a mirror surface. In the second polishing step, mirror polishing of the main surface was performed using a soft foamed resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains finer than the cerium oxide abrasive grains used in the first polishing step were used.

  The glass substrate which finished this 2nd grinding | polishing process was immersed in each washing tank of neutral detergent, a pure water, and IPA (isopropyl alcohol) sequentially, and was wash | cleaned. Note that ultrasonic waves were applied to each cleaning tank.

(6) Chemical Strengthening Process FIG. 5 shows temperature rise characteristics when 100 g of potassium nitrate (KNO ₃ ) is put into a porcelain container and heated by electromagnetic wave melting (point group 400) and when heated by an electric heater (point group 410). It is the graph which compared. As shown in FIG. 5, the time required for heating to 400 ° C. necessary for chemical strengthening using the melted chemical strengthening solution is approximately 30 minutes when heated by electromagnetic waves, and approximately 60 minutes when heated by an electric heater. Minutes. Thus, it can be seen that, as in the embodiment of the present invention, when the electromagnetic wave is heated, the heating time is about half as short as when a conventional heater is used. Therefore, the present invention is suitable for manufacturing a large number of glass substrates for magnetic disks at low cost.

  FIG. 6 is a graph showing the temperature rise characteristics of a beaker when only a SUS (Special Use Stainless steel) 403 beaker made of martensite stainless steel without chemical strengthening salt is heated by electromagnetic waves. In the case of FIG. 5 in which chemically strengthened salt is present as the contents of the beaker, the temperature rises to at least 400 ° C. as shown in the point group 400, while the temperature is 200 ° C. in FIG. 6 as shown in the point group 500. The temperature has risen only up to.

  From the above experimental results, the following can be understood. If the chemically strengthened salt of FIG. 5 is present and the container is heated and the chemically strengthened salt is heated by the influence thereof, the temperature of the container in which the chemically strengthened salt is raised to 400 ° C. is at least 400. Should have been heated above ℃. However, as shown in FIG. 6, when the container is heated alone, the temperature rises only up to 200 ° C. Thus, FIG. 6 is a proof that the electromagnetic wave acts directly on the chemically strengthened salt, not the container, and melts by heating.

  Based on the above experimental results, chemical strengthening was performed on the glass substrate after the lapping step and the polishing step. For chemical strengthening, first, a powdery chemical strengthening salt prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared as a solid chemical strengthening salt 110, and as shown in FIG. The electromagnetic wave generator 130 was used to melt by heating.

  As a result, the heating and melting with the conventional heater took about 8 hours, but the heating and melting was completed in half 4 hours, and a sufficient amount of the chemically strengthened salt 140 was put in the chemical strengthening tank 150. I was able to meet.

  Subsequently, as shown in FIG. 3 or FIG. 4, the chemical strengthening tank 150 is heated to 400 ° C. using the electromagnetic wave generator 220 or 220 </ b> A to 220 </ b> C, and the cleaned glass substrate is set to 300. This was performed by preheating to 0 ° C. and immersing in a chemical strengthening solution for about 3 hours.

  Thus, lithium ions and sodium ions in the glass substrate were replaced with sodium ions and potassium ions in the chemical strengthening solution, respectively, and the glass substrate was strengthened.

  Moreover, the detection rate of the particle by corrosion was compared with the following method half a year after starting operation as the chemical strengthening tank 150. That is, 1 kg of chemically strengthened salt before exchange after use for half a year was dissolved in water, filtered, and the amount of particles remaining on the filter was compared. Then, in the case of the heating and melting method using the conventional heater, 0.1% (1 g) of Fe, Cr, Ni (SUS-based contamination) was detected, but when using the present invention, it was only 20 ppm. It was.

  The glass substrate that had been subjected to the chemical strengthening treatment was immersed in a 20 ° C. water bath and rapidly cooled, and maintained for about 10 minutes. And the glass substrate which finished quenching was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned. Further, the glass substrate after the sulfuric acid cleaning was cleaned by immersing in a cleaning bath of pure water and IPA (isopropyl alcohol) sequentially.

  As described above, a flat and smooth, high-rigidity magnetic disk is obtained by performing the first lapping step, the cutting step, the second lapping step, the end surface polishing step, the first and second polishing steps, and the chemical strengthening step. A glass substrate was obtained.

(7) Magnetic disk manufacturing process On both surfaces of the glass substrate obtained through the above-described processes, an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoTaZr-based alloy, an underlayer made of Ru, and a CoCrPt group on the surface of the glass substrate A perpendicular magnetic recording disk was manufactured by sequentially forming a perpendicular magnetic recording layer made of an alloy, a protective layer made of hydrogenated carbon, and a lubricating layer made of perfluoropolyether. Although this configuration is an example of a configuration of a perpendicular magnetic disk, a magnetic layer or the like may be configured as an in-plane magnetic disk.

  A conventional method of heating the salt indirectly by heating the salt charging container and a method of directly heating the salt with the electromagnetic wave according to the present invention were carried out for half a year. And about the magnetic disk manufactured from each glass substrate, the thermal asperity test (TA test) was done on the conditions of glide height 6nm. As a result, in the examples according to the present invention, TA was not generated, but TA was generated in the conventional method.

  This is presumably because, in the conventional method, since the salt charging container is directly heated, particles due to corrosion are generated and TA is generated as a result.

  Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  The present invention can be applied to a method for manufacturing a glass substrate for a magnetic disk and a chemical strengthening apparatus.

It is a figure which shows 1st Embodiment of the chemical strengthening apparatus by this invention. It is a figure which shows the structural formula of sodium nitrate and potassium nitrate used as a chemical strengthening salt of FIG. It is a figure which shows 2nd Embodiment of the chemical strengthening apparatus by this invention. It is a figure which shows 3rd Embodiment of the chemical strengthening apparatus by this invention. It is the graph which compared the temperature rising characteristic with the case where electromagnetic wave heating melts potassium nitrate, and the case where it heats with an electric heater. It is a graph which shows the temperature rise characteristic of a beaker, when only an empty martensitic stainless steel beaker is heated by electromagnetic waves.

Explanation of symbols

100, 200, 300 Chemical strengthening device 110 Solid chemical strengthened salt 120 Salt charging vessel 130 First electromagnetic wave generator 140 Molten chemical strengthened salt 150 Chemical strengthening tank 160, 260, 360 Electromagnetic heating chamber 220, 220A, 220B, 220C Second electromagnetic wave generator

Claims (6)

A chemical strengthening salt charging step of charging solid chemical strengthening salt into a salt charging container;
A melting step of melting the chemically strengthened salt in the salt charging container by heating with electromagnetic waves;
A chemical strengthening salt supply step of supplying the molten chemically strengthened salt to a chemical strengthening tank;
A method of manufacturing a glass substrate for a magnetic disk, comprising: a chemical strengthening step in which the glass substrate for a magnetic disk is brought into contact with the molten chemically strengthened salt to chemically strengthen. Supplying a solid or liquid chemical strengthening salt to the chemical strengthening tank;
And a step of heating the chemically strengthened salt in the chemical strengthening tank with electromagnetic waves.   3. The glass substrate for a magnetic disk according to claim 2, wherein in the heating step, the chemical strengthening salt in the chemical strengthening tank made of a material that transmits electromagnetic waves is heated with electromagnetic waves from a plurality of different directions. Manufacturing method. A salt charging container into which a solid chemically strengthened salt is charged;
First electromagnetic wave generating means for heating and melting the chemically strengthened salt in the salt charging container with electromagnetic waves;
A chemical strengthening apparatus for a glass substrate for a magnetic disk, comprising: a chemical strengthening tank that is supplied with the molten chemically strengthened salt and chemically strengthens the chemically strengthened salt by bringing the glass substrate for a magnetic disk into contact therewith. A chemical strengthening tank to which a solid or liquid chemical strengthening salt is supplied;
A chemical strengthening apparatus for a glass substrate for a magnetic disk, comprising: a second electromagnetic wave generating means for heating the chemically strengthened salt in the chemical strengthening tank with an electromagnetic wave.   The chemical strengthening tank is made of a material that allows electromagnetic waves to pass therethrough, and there are a plurality of second electromagnetic wave generating means, and the chemical strengthening tank in the chemical strengthening tank is heated with electromagnetic waves from a plurality of different directions. The apparatus for chemically strengthening a glass substrate for a magnetic disk according to claim 5.

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