JP2007207393A - Method for manufacturing glass substrate for magnetic disk, glass substrate for magnetic disk, and method for manufacturing magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately remove a foreign matter from a polishing solution, which is to be a problem in a glass substrate for a magnetic disk. <P>SOLUTION: A method for manufacturing the glass substrate for the magnetic disk includes: a substrate preparing process for preparing the glass substrate; and a substrate polishing process for mirror polishing the glass substrate. The glass substrate is polished, while circulating the polishing solution through a magnet filter 106 in the substrate polishing process. The magnet filter impresses a magnetic field in the polishing solution, which is at least 5,000 gauss or more in magnetic flux density. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk, a glass substrate for a magnetic disk, and a method for manufacturing a magnetic disk.

  In recent years, glass substrates have been used as substrates for magnetic disks. Also, the magnetic head has been changed from a thin film head to a magnetoresistive head (MR head) and a large magnetoresistive head (GMR head) as the recording density is increased. Therefore, it is considered that reproducing a magnetic recording medium using a glass substrate with a magnetoresistive head will be a major trend in the future.

When a glass substrate is used as a magnetic disk substrate, if particles are present on the glass substrate, a convex portion is formed on the surface of the magnetic disk, which may cause thermal asperity. Therefore, conventionally, for the purpose of preventing thermal asperity, a method of polishing an inner peripheral end surface and / or an outer peripheral end surface of a glass substrate is known (for example, see Patent Documents 1 and 2).
JP-A-11-221742 JP 2000-185927 A

  The polishing of the glass substrate is performed while supplying the polishing liquid to the portion to be polished using, for example, a polishing brush or a polishing pad. In order to reduce the manufacturing cost of the glass substrate and the amount of waste liquid, it is preferable to circulate the polishing liquid using a circulation pump or the like.

  Here, the atmosphere in which the glass substrate is polished contains foreign matter such as dust generated from a polishing machine or the like. For this reason, when the polishing liquid is circulated and used, there is a possibility that foreign substances contained in the polishing liquid gradually increase. Therefore, when circulating the polishing liquid, it is necessary to remove foreign matters mixed in the polishing liquid from the atmosphere. Further, in order to suppress the generation of particles that cause thermal asperity, it is necessary to remove foreign matters having a size equal to or smaller than that of the abrasive grains contained in the polishing liquid. As a method for removing foreign substances in the polishing liquid, for example, a method using a filtration filter or the like can be considered.

  However, when removing foreign substances having such a size using a filtration filter, the abrasive grains are also collected by the filtration filter. When the abrasive grains are collected, the particle size distribution of the abrasive grains is disturbed, and the polishing conditions and the like are changed. Further, the filter is clogged, and the circulation of the polishing liquid is stopped. Therefore, conventionally, it has been difficult to properly remove foreign substances in the polishing liquid.

  An object of this invention is to provide the manufacturing method of the glass substrate for magnetic discs which can solve said subject, the glass substrate for magnetic discs, and the manufacturing method of a magnetic disc.

  The inventor of the present application has conducted extensive research on a method for removing foreign matter in a circulating polishing liquid, paying attention to the property that iron-based foreign matter (contamination) is particularly problematic in a magnetic disk glass substrate. And, it was found that if a foreign matter that can be magnetized such as an iron-based foreign matter can be appropriately removed, a glass substrate with sufficient quality can be manufactured without necessarily removing all foreign matters having the same size as the abrasive grains. . This invention is made | formed as a result of the said earnest research, and has the following structures.

  (Configuration 1) A method for manufacturing a glass substrate for a magnetic disk, comprising: a substrate preparation step for preparing a glass substrate; and a substrate polishing step for mirror polishing the glass substrate, wherein the substrate polishing step passes a polishing liquid through a magnet filter. The glass substrate is polished while circulating. In the substrate polishing step, for example, at least one of the main surface, the inner peripheral end surface, and the outer peripheral end surface of the glass substrate is mirror-polished. The magnet filter removes foreign matter that can be magnetized, for example, having a particle diameter of 1 μm or more, more preferably 0.5 μm or more, and even more preferably 0.2 μm or more.

  In this way, it is possible to selectively and efficiently remove, for example, a foreign matter that can be magnetized, which is a particular problem in a glass substrate for magnetic disks, such as an iron-based foreign matter. Further, since non-magnetic abrasive grains are not collected, the particle size distribution of the abrasive grains in the polishing liquid is not disturbed. Furthermore, since it is not necessary to remove foreign matters having the same size as the abrasive grains by filtration, problems such as clogging of the filtration filter do not occur. Therefore, foreign matters in the polishing liquid can be removed appropriately. This also makes it possible to appropriately suppress the generation of particles that cause thermal asperity. Furthermore, since the polishing liquid can be circulated appropriately, the manufacturing cost of the magnetic disk glass substrate can be reduced. Moreover, the burden of waste liquid treatment can be reduced by circulatingly using the polishing liquid.

  The magnetic disk glass substrate is, for example, a magnetic disk glass substrate having a diameter of less than 2.5 inches, such as 2.5 inches, 1.8 inches, or 1 inch. In such a small-diameter glass substrate for a magnetic disk, smaller foreign matter becomes a problem. However, with the configuration 1, foreign matters in the polishing liquid can be appropriately removed. For this reason, generation of particles that cause thermal asperity can be appropriately suppressed.

  Further, the magnetic disk glass substrate may be a magnetic disk glass substrate that is used in applications that are susceptible to impact when a portable terminal or the like (for example, a portable music player or a notebook computer) is used. The glass substrate for a magnetic disk may be a glass substrate for a magnetic disk for a magnetoresistive head (MR head) or a large magnetic recording head (GMR head), for example. Further, it may be a glass substrate for a magnetic disk for a perpendicular magnetic recording disk. The glass substrate for magnetic disk may be, for example, a glass substrate for magnetic disk having a rotational speed of 5400 rpm or more.

  (Configuration 2) The magnet filter applies a magnetic field having a magnetic flux density of at least 5000 gauss or more to the polishing liquid. In this way, foreign substances that can be magnetized can be removed appropriately. The magnetic field applied by the magnet filter to the polishing liquid is preferably 7000 gauss or more, more preferably 9000 gauss or more.

The magnet used for the magnet filter may be a permanent magnet or an electromagnet. Use of a permanent magnet is convenient because an external power source is not required. A permanent magnet is preferable because a high magnetic field can be created. As the permanent magnet, a permanent magnet containing a rare earth element is particularly preferable. This is because rare earth magnets can create a high magnetic field. As a permanent magnet containing a rare earth element, a samarium magnetic right (SmCo compound magnet, eg, SmCo ₅ compound magnet) or a neodymium magnet (NdFeB compound magnet, eg, Nd ₂ Fe ₁₄ B compound magnet) is suitable. It is particularly preferable to select a neodymium magnet that can create a particularly high magnetic field.

  (Configuration 3) The polishing liquid contains polishing abrasive grains having an average particle diameter of 0.01 to 1.5 μm, and the substrate polishing step further passes through a filtration filter that collects particles larger than the polishing abrasive grains. Circulate.

  In this way, non-magnetic foreign matter can be appropriately removed. In addition, since a magnetized filter removes a magnetizable foreign substance that is a particular problem in the glass substrate for magnetic disks, a filtration filter having a sufficiently large opening compared with the average particle diameter of the abrasive grains can be used. Therefore, if it does in this way, clogging of a filtration filter can be prevented. Further, the particle size distribution of the abrasive grains is not disturbed.

  (Configuration 4) The method further includes a chemical strengthening step of chemically strengthening the glass substrate that has been mirror-polished in the substrate polishing step. If a chemical strengthening step is performed when iron-based foreign matter or the like is present, adhesion of the foreign matter to the glass substrate is promoted. Therefore, when performing a chemical strengthening process, presence of an iron-type foreign material becomes a problem especially. However, if it is made like the structure 4, an iron-type foreign material etc. can be removed appropriately before a chemical strengthening process. Thereby, a chemical strengthening process can be performed appropriately.

  (Structure 5) A magnetic disk glass substrate manufactured by the method for manufacturing a magnetic disk glass substrate according to any one of Structures 1 to 4. In this way, the same effects as those of configurations 1 to 4 can be obtained.

  (Structure 6) A method of manufacturing a magnetic disk, wherein at least a magnetic recording layer is formed on the magnetic disk glass substrate according to Structure 5. In this way, the same effect as in configuration 5 can be obtained.

  According to the present invention, foreign matters that are problematic in the magnetic disk glass substrate can be appropriately removed from the polishing liquid.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.
FIG. 1 shows an example of a configuration of a polishing system 100 used in a method for manufacturing a glass substrate for a magnetic disk according to an embodiment of the present invention. The polishing system 100 is a polishing system that performs mirror polishing of a glass substrate while circulating a polishing liquid, and includes a tank 102, a pump 104, a magnet filter 106, and a polishing machine 108.

  The tank 102 is provided downstream of the polishing machine 108 and receives and stores the polishing liquid used for polishing from the polishing machine 108. The pump 104 is provided between the tank 102 and the magnet filter 106, and pumps the polishing liquid from the tank 102 and supplies it to the magnet filter 106.

  The magnet filter 106 is provided between the pump 104 and the polishing machine 108, removes foreign matter from the polishing liquid received from the tank 102 via the pump 104, and supplies it to the polishing machine 108. The magnet filter 106 may further have a function of a filtration filter. In this case, it is preferable that the opening of the filtration filter is larger than the average particle diameter of the abrasive grains contained in the polishing liquid. For example, when the average particle diameter of the abrasive grains is 0.01 to 1.5 μm, the opening of the filtration filter is, for example, 2 to 50 μm. If comprised in this way, a nonmagnetic foreign material can be removed appropriately, without disturbing the particle size distribution of an abrasive grain. In addition, the polishing system 100 may further include a filtration filter in addition to the magnet filter 106. In this case, the filtration filter is provided between the magnet filter 106 and the polishing machine 108, for example.

  The polishing machine 108 polishes the glass substrate using the polishing liquid received from the magnet filter 106. For example, the polishing machine 108 performs mirror polishing of the main surface, outer peripheral end surface, or inner peripheral end surface of the glass substrate. As a result, the polishing system 100 polishes the glass substrate while circulating the polishing liquid through the magnet filter 106.

  Here, in this example, the glass substrate for magnetic disks is manufactured through a substrate preparation step, an inner peripheral end surface polishing step, an outer peripheral end surface polishing step, a main surface polishing step, and a chemical strengthening step. The inner peripheral end surface polishing step, the outer peripheral end surface polishing step, and the main surface polishing step are examples of the substrate polishing step. In addition, each of the inner peripheral end surface polishing step, the outer peripheral end surface polishing step, and the main surface polishing step performs, for example, mirror polishing of a glass substrate using a polishing system 100 including a polishing machine 108 configured according to a portion to be polished. Do. Hereinafter, the above steps will be described in more detail.

  The substrate preparation step is a step of preparing a disk-shaped glass substrate having a circular hole in the center. In the substrate preparation step, for example, a glass substrate that has been ground and lapped to a predetermined roughness is prepared.

  The inner peripheral end surface polishing step is a step of mirror polishing the inner peripheral end surface of the glass substrate, and the inner peripheral end surface is polished to, for example, a mirror surface having an arithmetic average surface roughness Ra of 0.5 μm or less. In the inner peripheral end surface polishing step, the inner peripheral end surface is polished to a mirror surface having a maximum height Rmax of 5 μm or less, for example.

  The outer peripheral end surface polishing step is a step of mirror polishing the outer peripheral end surface of the glass substrate, and the outer peripheral end surface is polished to, for example, a mirror surface having an arithmetic average surface roughness Ra of 0.5 μm or less. In the outer peripheral end surface polishing step, the outer peripheral end surface is polished to a mirror surface having a maximum height Rmax of 5 μm or less, for example.

  The main surface polishing step is a step of mirror polishing the main surface of the glass substrate, and the main surface is, for example, 0.5 nm or less (for example, 0.1 to 0.5 nm) in terms of arithmetic average surface roughness Ra, more preferably Polishing to a mirror surface of 0.4 nm or less, more preferably 0.3 nm or less. In the main surface polishing step, for example, the main surface is polished to a mirror surface having a maximum height Rmax of 5 nm or less (for example, 1 to 5 nm), more preferably 4 nm or less, and further preferably 3 nm or less.

  The chemical strengthening step is a step of chemically strengthening the glass substrate. In the chemical strengthening step, for example, by bringing the glass substrate into contact with the chemical strengthening treatment liquid, by replacing some ions contained in the glass substrate with ions in the treatment liquid having an ion diameter larger than that ion. Strengthen the glass substrate.

  The glass substrate is completed through the above steps. The completed glass substrate is used for manufacturing a magnetic disk. In the magnetic disk manufacturing process, at least a magnetic recording layer is formed on a glass substrate.

  FIG. 2 shows an example of the configuration of the magnet filter 106. The magnetic filter 106 includes a clamp 206, a housing 202, and an insert portion 204. The clamp 206 is a member for fixing the insert portion 204 to the housing 202.

  The housing 202 is a cylindrical body that allows the polishing liquid to pass through, and has an inlet 302 that receives the polishing liquid from the pump 104 and an outlet 304 that supplies the polishing liquid to the polishing machine 108. The lower end of the housing 202 is closed by the lower surface so that the polishing liquid is accumulated inside. Further, the upper end of the housing 202 is opened to insert the insert portion 204. In this example, the outlet 304 is provided above the inlet 302.

The insert part 204 has a lid part 308 and a magnet part 306. The lid 308 is a part that closes the opening at the upper end of the housing 202. The magnet portion 306 is a portion inserted into the housing 202 and extends in a bar shape from the lower surface of the lid portion 308 toward the lower end of the housing 202. In this example, the magnet unit 306 generates a magnetic field using a neodymium (Nd ₂ Fe ₁₄ B) magnet. The magnet part 306 is comprised by the rod-shaped neodymium magnet and the metal cylinder which accommodates this neodymium magnet inside, for example.

  Here, the size of each part of the magnetic filter 106 and the strength of the magnetic field will be described in more detail. In this example, the height h1 of the magnet filter 106 is, for example, 250 to 400 mm, the height h2 of the housing 202 is, for example, 200 to 350 mm, and the insertion height h3 of the insert portion 204 is, for example, 150 to 250 mm. Note that the insertion height h3 of the insert portion 204 is, for example, the distance from the lower end of the insert portion 204 to the central axis of the outlet 304.

  Further, the housing 202 has an outer diameter of, for example, 30 to 70 mm, the magnet portion 306 has an outer diameter of, for example, 15 to 40 mm, and the inlet 302 and the outlet 304 have an inner diameter of, for example, 10 to 30 mm.

  Further, the magnet filter 106 applies a magnetic field of 5000 gauss or more in magnetic flux density to the polishing liquid. The magnetic field applied by the magnet filter 106 is more preferably 7000 gauss or more, and still more preferably 9000 gauss or more. The magnetic field applied by the magnet filter 106 is, for example, the magnetic field received by the polishing liquid that passes through the region where the magnetic field is weakest in the magnet filter 106 among the magnetic fields generated by the magnet unit 306. It is the residual magnetic flux density. If comprised as mentioned above, the foreign material which can be magnetized, such as an iron-type foreign material with a particle diameter of 0.2 micrometer or more, can be removed appropriately from the polishing liquid circulated in the polishing system 100 (see FIG. 1).

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.
Example 1
The glass substrate which concerns on Example 1 was manufactured through the following processes.
(1) Substrate preparation step A glass substrate having a circular hole was prepared by the following steps. First, a glass substrate made of aluminosilicate glass cut into a disk shape having a diameter of 66 mmφ and a thickness of 1.1 mm from a sheet glass formed by the downdraw method is ground with a relatively rough diamond grindstone. , 65 mm (2.5 inch) diameter, and 0.6 mm thick. In this case, instead of the downdraw method, the molten glass may be directly pressed using an upper mold, a lower mold, and a body mold to obtain a disk-shaped glass substrate. As the aluminosilicate glass, SiO ₂ is 57 to 74%, ZrO ₂ is 0 to 2.8%, Al ₂ O ₃ is ₃ to 15%, LiO ₂ is 7 to 16%, Na ₂ O in mol%. The glass for chemical strengthening which contains 4-14% as a main component was used.

  Subsequently, the glass substrate was sanded. This sanding step is intended to improve dimensional accuracy and shape accuracy. The sanding process was performed using a lapping apparatus, and the grain size of the abrasive grains was # 400. Specifically, by using alumina abrasive grains having a particle size of # 400, the load L is set to about 100 kg, and the inner rotation gear and the outer rotation gear are rotated, so that both surfaces of the glass substrate housed in the carrier have surface accuracy of 0 to 0. Wrapping to about 1 μm and surface roughness (Rmax) (measured by JIS B 0601) of about 6 μm.

  Next, a circular hole (diameter 20 mmφ) was opened in the center of the glass substrate using a cylindrical grindstone, and predetermined chamfering was performed on the outer peripheral end face and the inner peripheral end face. The surface roughness of the inner and outer peripheral end faces of the glass substrate at this time was about 14 μm in Rmax.

(2) Inner peripheral end face polishing step The inner peripheral end face of the glass substrate was mirror-polished by the same polishing system as described with reference to FIG. In the polishing machine used in the inner peripheral end face polishing step, the rotating brush was inserted into the circular hole of the glass substrate, and the rotating brush was rotated while supplying the polishing liquid into the circular hole. As the polishing liquid, a polishing liquid containing cerium oxide abrasive grains was used.

(3) Outer peripheral end surface polishing step The outer peripheral end surface of the glass substrate was mirror-polished by the same polishing system as described with reference to FIG. In the polishing machine used in the outer peripheral end surface polishing step, the rotary brush was brought into contact with the outer peripheral end surface of the glass substrate, and the rotating brush was rotated while supplying the polishing liquid to the outer peripheral end surface. As the polishing liquid, a polishing liquid containing cerium oxide abrasive grains was used.

(4) Main surface polishing step The following first polishing step and second polishing step were performed. This first polishing process is intended to remove scratches and distortions remaining in the sanding process, and as a polishing machine, a polishing machine that holds a glass substrate between an upper surface plate and a lower surface plate Was used. Specifically, a hard polisher was used as the polisher (polishing pad, polishing cloth), and the first polishing step was performed under the following polishing conditions.
Polishing liquid: cerium oxide + water load: 300 g / cm ² (L = 238 kg)
Polishing time: 15 minutes Removal amount: 30 μm
Lower platen rotation speed: 40rpm
Upper platen rotation speed: 35rpm
Inner gear speed: 14rpm
Outer gear speed: 29rpm

  Moreover, the glass substrate which finished the said 1st grinding | polishing process was immersed in each washing | cleaning tank of neutral detergent, a pure water, a pure water, IPA (isopropyl alcohol), and IPA (steam drying) sequentially, and was wash | cleaned.

Next, using the polishing machine used in the first polishing process, the polisher was changed from a hard polisher to a soft polisher, and a second polishing process was performed. The polishing conditions were the same as those in the first polishing step, except that a polishing liquid containing cerium oxide polishing grains and water was used, the load was 100 g / cm ² , the polishing time was 5 minutes, and the removal amount was 5 μm. Moreover, the glass substrate which finished the said 2nd grinding | polishing process is immersed in each washing tank of a neutral detergent, a neutral detergent, a pure water, a pure water, IPA (isopropyl alcohol), and IPA (steam drying) sequentially, and is wash | cleaned. did. An ultrasonic wave was applied to each cleaning tank.

(5) Chemical strengthening process Next, the glass substrate was chemically strengthened. For chemical strengthening, a chemical strengthening solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and the chemically strengthened solution is heated to 400 ° C., and the cleaned glass substrate preheated to 300 ° C. is reduced to about It was immersed for 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, the plurality of glass substrates were stored in a holder so as to be held by the end surfaces.

  Thus, by immersing in the chemical strengthening solution, the lithium ions and sodium ions on the surface of the glass substrate are replaced with sodium ions and potassium ions in the chemical strengthening solution, respectively, and the glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 to 200 μm.

  Moreover, the glass substrate which finished the said chemical strengthening was immersed in a 20 degreeC water tank, rapidly cooled, and maintained for about 10 minutes. The glass substrate after the rapid cooling was washed by immersing it in concentrated sulfuric acid heated to about 40 ° C. Further, the glass substrate that had been subjected to the sulfuric acid cleaning was immersed in each cleaning bath of pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying) in order and cleaned. An ultrasonic wave was applied to each cleaning tank.

  Here, in the inner peripheral end surface polishing step, the outer peripheral end surface polishing step, and the main surface polishing step, a polishing liquid containing polishing abrasive grains having an average particle size of 0.5 to 1.5 μm was used. In this embodiment, in the inner surface end surface polishing step, the outer surface end surface polishing step, and the main surface polishing step, which are mirror polishing steps, contained in the polishing liquid by applying a magnetic field to the polishing liquid containing the abrasive grains. The removal process of the foreign material which can be magnetized was performed. In this embodiment, the foreign matter removing process according to the present invention is performed in all polishing steps. However, the effect can be obtained even if the foreign matter removing process according to the present invention is performed in at least one polishing step. It is preferable to carry out the foreign matter removal treatment according to the present invention at least in the final polishing step of the glass substrate.

  A neodymium magnet was used for the magnet part. The residual magnetic flux density on the surface of the casing by this magnet was 9000 gauss. The casing was made of stainless steel.

(Comparative Example 1)
A glass substrate according to Comparative Example 1 was manufactured in the same manner as in Example 1 except that the magnet filter was not used in the inner peripheral end surface polishing step, the outer peripheral end surface polishing step, and the main surface polishing step.

(Evaluation)
As a means for investigating the transition of magnetizable foreign matter contained in the polishing liquid, the transition of iron (Fe) element contained in the polishing liquid was monitored. This is because iron and its compounds are typical magnetic substances, and the transition of the amount of the substance that can be magnetized contained in the polishing liquid can be monitored by monitoring using the Fe element as an index. Specifically, a certain amount of polishing liquid supplied to the glass substrate is extracted and dried, and then elemental analysis is performed to analyze the mass of Fe element. Incidentally, cerium oxide which is a polishing abrasive contained as a main component in the polishing liquid is a non-magnetic substance.

Table 1 compares the mass of Fe element contained in 1 kg of polishing liquid before and after exposure to a magnetic field. By subjecting the polishing liquid to a magnetic field exposure treatment, the Fe and Fe compounds contained in the polishing liquid could be reduced from 1060 mg to 737 mg in terms of the amount of Fe element. The percentage could be reduced by 30% by mass. It was found that by subjecting the polishing liquid to a magnetic field exposure treatment, the foreign matter removal processing action worked and the polishing liquid could be cleaned.

  Next, in the above-described Example 1, the mass of Fe element contained in the polishing liquid supplied to the glass substrate was investigated. As a result, in any polishing process, the amount of Fe element contained per 1 kg of the polishing liquid was 900 mg or less. In particular, in the second polishing step, which is the final polishing step, the magnet filter was controlled to be 800 mg or less.

  In Comparative Example 1, the mass of Fe element contained in the polishing liquid supplied to the glass substrate was investigated. As a result, in any polishing step, the amount of Fe element contained per 1 kg of the polishing liquid was 1000 mg or more. In the second polishing step, which is the final polishing step, 1100 mg of Fe element was detected.

  Next, the glass substrate obtained in Example 1 and Comparative Example 1 was inspected. When the glass substrate of Example 1 was inspected, the surface state was a mirror surface, and it was finished to a uniform surface. The surface roughness of the main surface was 0.4 nm in Ra. Rmax was 4 nm.

  When the glass substrate of Comparative Example 1 was inspected, minute foreign matters were found. When this foreign material was analyzed, there were some containing Fe as a main component and some amount of Cr. From the analysis results, it was judged to be a stainless steel alloy having magnetism. Since these foreign substances were adhered, the surface roughness of the glass substrate was larger than that of Example 1.

  Next, an underlayer, a magnetic layer, a protective layer, and a lubricating layer were sequentially formed on the surface of the glass substrate obtained in Example 1 and Comparative Example 1 to manufacture a magnetic disk. Specifically, the CrTi layer as the first underlayer, the AlRu layer as the second underlayer, the CrMo layer as the third underlayer, the CoCrPtB magnetic layer as the magnetic layer, the hydrogenated carbon layer as the protective layer, and the perfluoropoly layer as the lubricating layer An ether compound layer was formed. The obtained magnetic disk was mounted on a hard disk drive, and a recording / reproduction test was conducted. A magnetic head having a flying height of 7 nm was used. The reproducing element is a reproducing element using a magnetoresistive effect. Specifically, a magnetic head equipped with a TMR element (tunnel magnetoresistive effect element) was used. The reproducing element using the magnetoresistive effect is not limited to the TMR, and a GMR element or an AMR element may be used.

  As a result, no error signal was detected from the magnetic disk using the glass substrate of Example 1, and it was confirmed that a normal recording / reproducing operation was performed. On the other hand, a thermal asperity signal was detected as an error signal from the magnetic disk using the glass substrate of Comparative Example 1. When the error signal detection location was analyzed, Fe-based foreign matter was detected. In this example, a magnetic head equipped with a TMR element was used as a reproducing element. This is because the TMR element has excellent reproduction sensitivity. However, thermal asperity signals tend to be generated. Therefore, the glass substrate according to the present invention is particularly suitable as a method for producing a glass substrate for a magnetic disk that is reproduced by a TMR reproducing element.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

The present invention includes the following configurations.
(Configuration A-1)
A method for producing a glass substrate for a magnetic disk, comprising a step of supplying a polishing liquid to the surface of a glass substrate and polishing the surface of the glass substrate,
A method of manufacturing a glass substrate for a magnetic disk, wherein the polishing liquid is subjected to a magnetic field exposure process in advance during the polishing process.
(Configuration A-2)
The method for producing a glass substrate for a magnetic disk according to Configuration A-1, wherein the polishing liquid contains non-magnetic abrasive grains.
(Configuration A-3)
The magnetic disk glass substrate according to Configuration A-1 or Configuration A-2, wherein the magnetic field exposure treatment selectively removes magnetizable foreign matter contained in the polishing liquid. Method.
(Configuration A-4)
The polishing process is a process of supplying a polishing liquid to the surface of a glass substrate, bringing the glass substrate and a polishing tool into contact with each other, and moving the polishing tool and the glass substrate relatively. A method for producing a glass substrate for a magnetic disk according to any one of A-1 to A-3.
(Configuration A-5)
The magnetic disk according to any one of configurations A-1 to A-4, wherein the polishing tool is at least one means selected from a polishing pad, a polishing brush, and a polishing tape. A method for producing a glass substrate.
(Configuration A-6)
The method for producing a glass substrate for a magnetic disk according to any one of configurations A-1 to A-5, wherein the surface of the glass substrate is polished to a mirror surface by the polishing treatment.
(Configuration A-7)
Any one of configurations A-1 to A-6, wherein the polishing process creates a desired uniform surface having a surface roughness Ra of 0.5 nm or less on the surface of the glass substrate. The manufacturing method of the glass substrate for magnetic discs as described in any one of.
(Configuration A-8)
A method for manufacturing a glass substrate for a magnetic disk according to any one of Configuration A-1 to Configuration A-7, wherein the magnetic disk glass is adapted to be recorded and reproduced by a magnetic head having a flying height of 7 nm or less. A method for manufacturing a substrate.

(Configuration B-1)
A method for producing a glass substrate for a magnetic disk in which a desired surface is created by a plurality of polishing processes,
At least one of the plurality of polishing processes is:
A polishing process for a glass substrate for a magnetic disk including a process of supplying a polishing liquid to the surface of the glass substrate and polishing the surface of the glass substrate, and in this polishing process, the polishing liquid is subjected to a magnetic field exposure process in advance. A method for producing a glass substrate for a magnetic disk.
(Configuration B-2)
The method for producing a glass substrate for a magnetic disk according to Configuration B-1, wherein the polishing liquid contains non-magnetic abrasive grains.
(Configuration B-3)
Manufacture of a magnetic disk glass substrate according to Configuration B-1 or Configuration B-2, wherein magnetized foreign matter contained in the polishing liquid is selectively removed by the magnetic field exposure treatment. Method.
(Configuration B-4)
The polishing process is a process of supplying a polishing liquid to the surface of a glass substrate, bringing the glass substrate and a polishing tool into contact with each other, and moving the polishing tool and the glass substrate relatively. The manufacturing method of the glass substrate for magnetic discs in any one of B-1 thru | or composition B-3.
(Configuration B-5)
The magnetic disk according to any one of configurations B-1 to B-4, wherein the polishing tool is at least one means selected from a polishing pad, a polishing brush, and a polishing tape. A method for producing a glass substrate.
(Configuration B-6)
The method of manufacturing a glass substrate for a magnetic disk according to any one of configurations B-1 to B-5, wherein the surface of the glass substrate is polished to a mirror surface by the polishing treatment.
(Configuration B-7)
Any one of configurations B-1 to B-6, wherein the polishing process creates a desired uniform surface having a surface roughness Ra of 0.5 nm or less on the surface of the glass substrate. The manufacturing method of the glass substrate for magnetic discs as described in any one of.
(Configuration B-8)
A method of manufacturing a glass substrate for a magnetic disk according to any one of Configuration B-1 to Configuration B-7, wherein the magnetic disk glass is compatible with a magnetic disk recorded and reproduced by a magnetic head having a flying height of 7 nm or less. A method for manufacturing a substrate.

(Configuration C-1)
A method for producing a glass substrate for a magnetic disk, comprising a step of supplying a polishing liquid to the surface of a glass substrate and polishing the surface of the glass substrate,
The mass of Fe element contained in the polishing liquid supplied to the glass substrate is 900 mg or less per 1 kg of the polishing liquid.
(Configuration C-2)
A method for producing a glass substrate for a magnetic disk, comprising a step of supplying a polishing liquid to the surface of a glass substrate and polishing the surface of the glass substrate,
In the polishing process, the polishing liquid is cleaned in advance so that the mass of Fe element contained in the polishing liquid supplied to the glass substrate is 900 mg or less per 1 kg of the polishing liquid. A method for producing a glass substrate for a disk.
(Configuration C-3)
The method for producing a glass substrate for a magnetic disk according to Configuration C-1 or C-2, wherein the polishing liquid contains non-magnetic abrasive grains.
(Configuration C-4)
The polishing process is a process of supplying a polishing liquid to the surface of a glass substrate, bringing the glass substrate and a polishing tool into contact with each other, and moving the polishing tool and the glass substrate relatively. The method for producing a glass substrate for a magnetic disk according to any one of C-1 to C-3.
(Configuration C-5)
The magnetic disk according to any one of Configurations C-1 to C-4, wherein the polishing tool is at least one means selected from a polishing pad, a polishing brush, and a polishing tape Glass substrate manufacturing method,
(Configuration C-6)
The method of manufacturing a glass substrate for a magnetic disk according to any one of configurations C-1 to C-5, wherein the surface of the glass substrate is polished to a mirror surface by the polishing treatment.
(Configuration C-7)
Any one of configurations C-1 to C-6, wherein a desired uniform surface having a surface roughness Ra of 0.5 nm or less is created on the surface of the glass substrate by the polishing treatment. The manufacturing method of the glass substrate for magnetic discs as described in any one of.
(Configuration C-8)
A method of manufacturing a glass substrate for a magnetic disk according to any one of Configuration C-1 to Configuration C-7, wherein the magnetic disk glass is adapted to be recorded and reproduced by a magnetic head having a flying height of 7 nm or less. A method for manufacturing a substrate.

  The present invention can be suitably used for, for example, a method for manufacturing a magnetic disk glass substrate, a magnetic disk glass substrate, and a magnetic disk manufacturing method.

It is a figure which shows an example of a structure of the grinding | polishing system 100 used with the manufacturing method of the glass substrate for magnetic discs concerning one Embodiment of this invention. 3 is a diagram illustrating an example of a configuration of a magnet filter 106. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Polishing system, 102 ... Tank, 104 ... Pump, 106 ... Magnet filter, 108 ... Polishing machine, 202 ... Housing, 204 ... Insert part, 206 ...・ Clamp 302 ... Inlet 304 ... Exit 306 ... Magnet part 308 ... Lid part

Claims (6)

A method of manufacturing a glass substrate for a magnetic disk,
A substrate preparation step of preparing a glass substrate;
A substrate polishing step for mirror polishing the glass substrate,
The method of manufacturing a glass substrate for a magnetic disk, wherein the substrate polishing step comprises polishing the glass substrate while circulating a polishing liquid through a magnet filter.   2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the magnet filter applies a magnetic field having a magnetic flux density of at least 5000 gauss or more to the polishing liquid. The polishing liquid contains abrasive grains having an average particle size of 0.01 to 1.5 μm,
3. The manufacturing method of a glass substrate for a magnetic disk according to claim 1, wherein in the substrate polishing step, the polishing liquid is circulated through a filtration filter that collects particles larger than the abrasive grains. Method.   4. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, further comprising a chemical strengthening step of chemically strengthening the glass substrate that has been mirror-polished in the substrate polishing step.   A glass substrate for a magnetic disk produced by the method for producing a glass substrate for a magnetic disk according to claim 1. A method for producing a magnetic disk, comprising forming at least a magnetic recording layer on the glass substrate for a magnetic disk according to claim 5.