JP2016173873A - Glass substrate for magnetic recording medium, and magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass substrate for magnetic recording medium that is used for a magnetic recording medium with a small error generation rate.SOLUTION: A glass substrate for magnetic recording medium is provided. A pseudo-elastic deformation amount A is 2.0 μm or less, where the pseudo-elastic deformation amount A denotes an absolute value of a difference between a flatness obtained by supporting opposite ends of the glass substrate in a diameter direction from a lower surface side, applying load to a central upper surface of the glass substrate for 48 hours and then removing the load, and leaving the glass substrate for 5 hours, and a flatness before application of the load. The glass of the glass substrate contains AlOof 5 mol% or more. The content of BOis 0.1 mol% or more and 15 mol% or less, or one or less type of alkali metal oxide is contained. The content of the alkali metal oxide is 0 mol% or more and 25 mol% or less, or two or more types of the alkali metal oxide are contained. The content of the alkali metal oxide is more than 0 mol% and equal to or less than 20 mol%.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a glass substrate for a magnetic recording medium and a magnetic recording medium.

  Conventionally, an aluminum alloy substrate has been used as a substrate for a magnetic recording medium used in a magnetic recording apparatus or the like. However, with the demand for higher recording density, it is harder and more flat and smooth than an aluminum alloy substrate. Excellent glass substrates are becoming mainstream.

  In recent years, magnetic recording media have further increased in recording density and speeded up, so that the magnetic head has lost the servo information recording the radius / track position information of the magnetic recording medium, and read / write errors (hereinafter referred to as “read / write errors”). , Which is also referred to as an error) occurs more frequently than before.

  The occurrence of such errors has been considered to be caused by mechanical vibration due to the occurrence of disk fluttering accompanying the narrowing of track width and high-speed rotation accompanying high recording density.

  For this reason, in order to suppress such an error, for example, a material having high specific elasticity has been used as a material for a glass substrate for a magnetic recording medium, and fluttering has been suppressed. The specific elasticity is also referred to as specific Young's modulus, which is an amount obtained by dividing the Young's modulus by the density of the glass, and is an amount that serves as a guideline indicating characteristics such as light and strong, light and difficult to deform.

  Further, in Patent Document 1, by selecting a glass substrate for a magnetic recording medium whose symmetry in the thickness direction is within a predetermined range, errors in servo information recorded on the magnetic recording medium when a hard disk is formed can be reduced. A method for manufacturing a glass substrate for a magnetic disk is described.

JP 2010-277679 A

  As described above, methods for suppressing the occurrence of errors in the magnetic recording medium by selecting the glass substrate for the magnetic recording medium have been studied, but the occurrence of errors has not been sufficiently suppressed.

  SUMMARY OF THE INVENTION In view of the above-described problems of the prior art, an object of the present invention is to provide a glass substrate for a magnetic recording medium used for a magnetic recording medium having a low error rate.

In order to solve the above problems, the present invention is a glass substrate for a magnetic recording medium,
Supporting both ends in the diameter direction of the glass substrate from the lower surface side, removing the load after applying the load to the upper surface of the central portion of the glass substrate for 48 hours, flatness at the time of 5 hours after removing the load,
When the absolute value of the difference from the flatness before applying a load is the pseudoelastic deformation amount A,
The pseudoelastic deformation amount A is 2.0 μm or less,
The glass of the glass substrate contains 5 mol% or more of Al ₂ O ₃ ,
The content of B ₂ O ₃ is 0.1 mol% or more and 15 mol% or less, or the alkali metal oxide is contained in one or less, and the content of alkali metal oxide is 0 mol% or more and 25 mol% or less, or alkali metal oxidation Provided is a glass substrate for a magnetic recording medium containing two or more kinds of substances and having an alkali metal oxide content of more than 0 mol% and no more than 20 mol%.

  ADVANTAGE OF THE INVENTION According to this invention, the glass substrate for magnetic recording media used for the magnetic recording medium with a low incidence rate of an error can be provided.

Explanation of buckling deformation and bending deformation Explanatory drawing of a configuration example of the holding jig in the magnetic layer deposition process Explanatory diagram of measurement flow for pseudoelastic deformation Explanatory diagram of load application method for pseudoelastic deformation measurement The figure which shows the load application time dependence before the load removal of the flatness immediately after the load removal in the Example of this invention. The figure which shows the load application time dependence before the load removal of the flatness immediately after the load removal in the Example of this invention. The figure which shows the elapsed time dependence after the load release of the flatness after a load removal in the Example of this invention after 24h load application. The figure which shows the elapsed time dependence after the load release of the flatness after a load removal in the Example of this invention after 24h load application.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and the following embodiments are not departed from the scope of the present invention. Various modifications and substitutions can be made.
[First Embodiment]
A configuration example of a method for manufacturing a magnetic recording medium according to the present embodiment will be described.

  The method for manufacturing a magnetic recording medium according to this embodiment is a method for manufacturing a magnetic recording medium including a glass substrate, and includes generating at least one of buckling deformation and bending deformation on the glass substrate.

Then, the glass of the glass substrate, the _Al 2 _{O 3} may contain more than 5 mol%.

Further, the glass of the glass substrate has a B ₂ O ₃ content of 0.1 mol% or more and 15 mol% or less, or the glass of the glass substrate contains one or less alkali metal oxides, The oxide content can be 0 mol% or more and 25 mol% or less, or two or more kinds of alkali metal oxides can be contained, and the alkali metal oxide content can be more than 0 mol% and 20 mol% or less.

  The inventors of the present invention have examined the cause of the error in the magnetic recording medium even when a material having high specific elasticity is used as the material of the glass substrate (glass substrate for magnetic recording medium). . The specific elasticity is also referred to as specific Young's modulus, which is an amount obtained by dividing the Young's modulus of glass by the density of the glass, and is an amount that serves as a guideline indicating the characteristics of being light and strong, light and difficult to deform.

  As a result of investigation, when a force (load) is applied to the glass substrate in the magnetic recording medium manufacturing process to cause buckling deformation or bending deformation, the glass substrate returns to its original shape when the force (load) is removed after the deformation. However, it has been found that the behavior after removing the force (load) varies depending on the glass composition of the glass substrate. In other words, the glass composition returns to the original shape in a short time after removing the force (load) despite the same shape, and gradually takes a long time after removing the force (load). It was found that there was a glass substrate that returned to its original shape. Such deformation that takes a long time to remove the force (load) and return to the original shape may be referred to as delayed restoration deformation. In the following description, even when “deformation” is simply described, it may indicate “deformation accompanied by delay restoration deformation”.

  And in the case of a magnetic recording medium including a glass substrate that takes a long time from the removal of force (load) until the original deformation returns, the glass substrate (magnetic recording medium) may be restored depending on the writing timing of servo information. Servo information will be written in the middle. For this reason, since the position of the servo information is changed after the servo information is written, it has been found that this is one of the causes of errors, and the present invention has been completed.

  In the method of manufacturing a magnetic recording medium according to this embodiment, as described above, at least one of buckling deformation and bending deformation is generated in the glass substrate during the manufacturing process.

  Here, buckling deformation and bending deformation will be described with reference to FIG.

  First, buckling deformation will be described with reference to FIG. FIG. 1A shows the glass substrate 10 as viewed from the side. Buckling deformation is when two opposing forces parallel to the main planes 11 and 12 of the glass substrate 10 are applied to the side surface of the glass substrate 10 as indicated by the block arrows X1 and X2 in the figure. Further, as shown by the dotted line in the figure, the glass substrate is a deformation that occurs in a direction perpendicular to the main planes 11 and 12. Note that FIG. 1A illustrates an example in which the glass substrate is deformed in a downwardly convex shape, but the present invention is not limited to such a form, and the glass substrate may be deformed in an upwardly convex shape.

  The bending deformation will be described with reference to FIG. FIG. 1B shows the glass substrate 10 as viewed from the side. Bending deformation means that, for example, forces Y1 and Y2 that are substantially perpendicular to the main planes 11 and 12 and are opposite to each other are applied to one main plane 11 and the other main plane 12 of the glass substrate 10, respectively. As indicated by the dotted line, the glass substrate is deformed in a direction perpendicular to the main planes 11 and 12.

  That at least one of buckling deformation and bending deformation occurs in the glass substrate means that the above-mentioned force is applied to the glass substrate alone or the magnetic recording medium, and the glass substrate alone or the glass substrate and the surface of the glass substrate are formed. This means that the formed magnetic layer or the like is deformed. When a force (load) is applied to the magnetic recording medium, the magnetic layer and the like are deformed in accordance with the deformation of the glass substrate, so that the magnetic recording medium behaves similarly to the glass substrate included in the magnetic recording medium. Become. In addition, even when the deformation of the glass substrate is delayed recovery deformation, the magnetic layer and the like are similarly deformed in accordance with the deformation of the glass substrate. Will be shown.

  As a case where force (load) is applied to the glass substrate, there are cases where the glass substrate is held and transported by a holding jig, or when the glass substrate is placed in a cassette or the like, and the glass substrate is mainly in contact with the jig or the like. It is considered that deformation occurs when transported in the state of being carried out.

  As will be described later, the method of manufacturing a magnetic recording medium according to the present embodiment includes a magnetic layer film forming step for forming a magnetic layer on a glass substrate and a magnetic recording medium holding step for holding the magnetic recording medium in a cassette. It is preferable to have one or more steps selected.

  In the magnetic layer forming step, as described later, the glass substrate is held and transported by a holding jig and used for the film forming step. Therefore, force is applied by the holding jig, and the glass substrate is likely to be deformed. This is because the magnetic layer is formed before or after the magnetic layer is formed, for example, because the magnetic layer is formed on both surfaces of the glass substrate. In order to protect the magnetic layer, it is preferable to hold the glass substrate at the end surface (side surface) portion of the glass substrate. However, as shown in FIG. 6 to be described later, depending on the material of the glass substrate, delayed restoration deformation may occur even when a load (force) is applied continuously for about 30 seconds. For this reason, when the end surface portion of the glass substrate is held in the magnetic layer forming step, the delayed recovery deformation accompanying the above-described buckling deformation is likely to occur. In particular, in a heat-assisted magnetic recording type magnetic recording medium that has been attracting attention in recent years, it is said that it is necessary to perform heat treatment at a high temperature in the magnetic layer forming step. In the case of heat treatment at high temperature, it is necessary to hold the glass substrate for a long time in order to raise and lower the temperature (heating and cooling), so that deformation of the glass substrate in the magnetic layer deposition process will become a problem in the future. Conceivable.

  Next, the magnetic recording medium holding step is a step of holding the glass substrate in the cassette, and the glass substrate is stored in a decompressed packing container and shipped and transported. . For this reason, at least one of buckling deformation and bending deformation can occur in the glass substrate in one or more processes selected from, for example, a magnetic layer film forming process and a magnetic recording medium holding process.

  Although the magnetic layer film forming step and the magnetic recording medium holding step have been described, the application of force (load) to the glass substrate is not limited to such a step. In addition to the magnetic layer film forming step, for example, the glass substrate is mechanically transported between the steps of the method for manufacturing the magnetic recording medium. Therefore, when the glass substrate is held and transported by the holding jig, a force (load) is applied to the glass substrate. May join. For this reason, even when the glass substrate is transported between the steps of the method of manufacturing the magnetic recording medium, the glass substrate may be buckled or bent.

The method of manufacturing a magnetic recording medium of the present embodiment, the glass of a glass substrate included in the magnetic recording medium, the Al ₂ O ₃ may contain more than 5 mol%. Furthermore, the glass of the glass substrate contained in the magnetic recording medium has a B ₂ O ₃ content of 0.1 mol% or more and 15 mol% or less, or contains one or less alkali metal oxides. The content is preferably 0 mol% or more and 25 mol% or less, or two or more kinds of alkali metal oxides are contained, and the content of alkali metal oxides is preferably more than 0 mol% and 20 mol% or less. In addition, the alkali metal oxide here may be any alkali metal oxide, and includes any alkali metal oxide. Typically, examples of the alkali metal oxide include Li ₂ O, Na ₂ O, and K ₂ O.

This is because, according to the study by the inventors of the present invention, the Young's modulus of the glass substrate can be sufficiently increased by setting the content of Al ₂ O ₃ to 5 mol% or more.

Further, the content of B ₂ O _{3 in} the glass of the glass substrate is 0.1 mol% or more and 15 mol% or less, or the alkali metal oxide contained in the glass of the glass substrate is one or less, and the content of the alkali metal oxide When the amount is 0 mol% or more and 25 mol% or less, or when the glass of the glass substrate contains two or more kinds of alkali metal oxides and the content of alkali metal oxides is more than 0 mol% and 20 mol% or less, force (load) is applied to the glass substrate. This is because, even when the deformation is caused by the addition of (), the time from the removal of the force (load) to the return to the original shape is shortened. That is, after the force (load) applied to the glass substrate is removed, the time during which the glass substrate is deformed is shortened.

In the method for producing a magnetic recording medium of the present embodiment, the glass substrate glass contained in the magnetic recording medium preferably has a B ₂ O ₃ content of 0.1 mol% or more and 15 mol% or less. This is because even when a force (load) is applied to the glass substrate and the glass substrate is deformed, the time from the removal of the force (load) to returning to the original shape can be shortened.

In particular, if the glass of the glass substrate included in the magnetic recording medium contains _B 2 _{O 3,} the lower limit of the content of B 2 _{O 3} is more preferably not less than 0.2 mol%, further preferably at least 0.5 mol% . Further, the upper limit of the content of B ₂ O ₃ is preferably 12 mol% or less, more preferably 10 mol% or less, further preferably 5 mol% or less, and particularly preferably less than 2 mol%. When the content of B ₂ O ₃ is less than 2 mol%, a force (load) is applied to the glass substrate, and when it is deformed, the displacement time after removing the force (load) can be shortened. A high glass substrate can be obtained. For this reason, even when the magnetic recording medium is rotated at a high speed, the occurrence of fluttering can be further suppressed, and the occurrence of reading / writing errors of the magnetic recording medium can be particularly suppressed.

In addition, when the glass of the glass substrate included in the magnetic recording medium is a glass having one or less alkali metal oxides and an alkali metal oxide content of 0 mol% or more and 25 mol% or less, an alkali metal is used. The oxide content is more preferably 22 mol% or less. More preferably, the content of the alkali metal oxide is 10 mol% or less. In addition, the alkali metal oxide to be contained is one kind or less, for example, contains one kind of alkali metal oxide selected from alkali metal oxides such as Na ₂ O, K ₂ O, Li ₂ O, This means that no alkali metal oxide is contained.

  When the glass of the glass substrate included in the magnetic recording medium of the present embodiment contains two or more kinds of alkali metal oxides and the glass having an alkali metal oxide content of more than 0 mol% and no more than 20 mol%, an alkali is used. The content of the metal oxide is more preferably 17 mol% or less, and further preferably 10 mol% or less.

In addition, containing two or more types of alkali metal oxides includes, for example, two or more types of alkali metal oxides selected from alkali metal oxides such as Na ₂ O, K ₂ O, and Li ₂ O. Means. In this case, the content of each alkali metal oxide is not particularly limited, and can be any content. For example, the content (mol%) of each alkali metal oxide can be made uniform.

  As described above, by using glass containing a predetermined component as the glass of the glass substrate included in the magnetic recording medium of the present embodiment, force (load) is applied to the glass substrate, and servo information is written even when the glass substrate is deformed. By the time, the glass substrate has finished or almost finished displacement due to the restoring force after removing the force (load). For this reason, the glass substrate (magnetic recording medium) after the servo information has been written is not displaced, or the degree of displacement is small, preventing the position of the written servo information from shifting and suppressing the error rate. be able to.

Moreover, it is preferable that the glass of the glass substrate contained in the magnetic recording medium of this embodiment contains 5 mol% or more and 20 mol% or less of Al ₂ O ₃ . The lower limit of the Al ₂ O ₃ content is more preferably 8 mol% or more, further preferably 10 mol% or more, and particularly preferably 11.5 mol% or more. The upper limit of the content of Al ₂ O ₃ is more preferably 17.5 mol% or less, and further preferably 15 mol% or less.

Further, in the method of manufacturing a magnetic recording medium according to the present embodiment, the glass of the glass substrate included in the magnetic recording medium has a SiO ₂ content of 55 mol% to 75 mol% and an alkaline earth metal oxide content of 0 mol% to 30 mol%. It is preferable to contain. In particular, SiO ₂ is preferably contained in an amount of 66 mol% to 75 mol%, and more preferably 66 mol% to 70 mol%. The alkaline earth metal oxide is more preferably contained in an amount of 5 mol% to 30 mol%, and more preferably 16 mol% to 30 mol%.

When glass having a B ₂ O ₃ content of 0.1 mol% or more and 15 mol% or less is used as the glass of the glass substrate included in the magnetic recording medium, an alkali metal oxide may be contained in an amount of 0 mol% or more and 25 mol% or less. preferable. In particular, the alkali metal oxide is more preferably contained in an amount of 0 mol% or more and 15 mol% or less, and further preferably 0 mol% or more and 2.5 mol% or less.

  The glass substrate preferably has a high specific elasticity (specific Young's modulus), for example, preferably 32 MNm / kg or more, and more preferably 33 MNm / kg or more. Due to the high specific elasticity, even when the magnetic recording medium is rotated at high speed, the occurrence of fluttering can be further suppressed, and the occurrence of read / write errors of the magnetic recording medium can be particularly suppressed.

  Furthermore, it is preferable that the glass substrate to be used is a glass substrate whose flatness hardly changes even when a load is applied. For example, when a load is applied for 24 hours in the same manner as when measuring the amount of pseudoelastic deformation described later, that is, both ends in the diameter direction of the glass substrate are supported from the lower surface side, and the load 24 is applied to the upper surface of the central portion of the glass substrate. When time is added, it is preferable that the rate of change in flatness before and after the load is applied is 200% or less. In particular, the rate of change in flatness before and after applying a load is more preferably 100% or less.

The flatness change rate before and after the load was applied was F (24 h) after the load was applied to the glass substrate for 24 hours, and the flatness of the glass substrate before the load was applied. Where F (−24h) is expressed by the following formula.
(Change rate of flatness before and after applying load) = | F (24h) −F (−24h) | / F (−24h) × 100
Next, a configuration example of specific steps of the method for manufacturing a magnetic recording medium according to the present embodiment will be described.

  The method for manufacturing a magnetic recording medium according to the present embodiment is selected from a magnetic layer forming process for forming a magnetic layer on a glass substrate and a magnetic recording medium holding process for holding the magnetic recording medium in a cassette. It is preferable to have one or more steps. Moreover, it is not limited to the process concerned, A process can be provided arbitrarily further.

Specifically, for example, the following steps can be included.
(A) Glass substrate preparation step for preparing a glass substrate (b) Magnetic layer formation step for forming a magnetic layer on the glass substrate (c) Magnetic recording medium obtained in the magnetic layer formation step is held in a cassette Magnetic Recording Medium Holding Process Each process will be described below.
(A) Glass substrate preparation process A glass substrate preparation process is a process of preparing the glass substrate according to the specification requested | required of a magnetic recording medium, The details are not specifically limited.

The glass substrate preparation step can further include the following steps 1 to 4, for example.
(Step 1) A shape imparting step of chamfering the inner peripheral end surface and the outer peripheral end surface after processing from a glass base substrate into a disk-shaped glass substrate having a circular hole in the center.
(Step 2) An end surface polishing step for polishing the end surfaces (the inner peripheral end surface and the outer peripheral end surface) of the glass substrate.
(Step 3) A main surface polishing step for polishing the main surface of the glass substrate.
(Step 4) A cleaning step of cleaning and drying the glass substrate.

  Here, the shape imparting step of (Step 1) includes a glass substrate having a circular shape in the center, and a glass substrate formed by a float method, a fusion method, a press forming method, a down draw method or a redraw method. To be processed.

  Although the glass substrate used is not particularly limited, it is preferable to use a glass substrate having the same composition as the glass of the glass substrate contained in the magnetic recording medium described above.

Specifically, the glass of the glass base substrate to be used can contain 5 mol% or more of Al ₂ O ₃ . Furthermore, the glass of the glass base substrate has a B ₂ O ₃ content of 0.1 mol% or more and 15 mol% or less, or contains one or less alkali metal oxide, and the content of alkali metal oxide is 0 mol%. It is preferable that the content is 25 mol% or less, or two or more alkali metal oxides are contained, and the content of the alkali metal oxide is more than 0 mol% and 20 mol% or less.

If the glass of the glass-containing substrate contains _B 2 _{O 3,} the lower limit of the content of B 2 _{O 3} is more preferably not less than 0.2 mol%, more 0.5 mol% is more preferred. Further, the upper limit of the content of B ₂ O ₃ is preferably 12 mol% or less, more preferably 10 mol% or less, further preferably 5 mol% or less, and particularly preferably less than 2 mol%.

  In addition, when the glass of the glass base substrate contains not more than one kind of alkali metal oxide and the glass having an alkali metal oxide content of 0 mol% or more and 25 mol% or less, the content of alkali metal oxide is used. Is more preferably 22 mol% or less. More preferably, the content of the alkali metal oxide is 10 mol% or less. Note that the alkali metal oxide may not be included.

  When the glass of the glass base substrate contains two or more kinds of alkali metal oxides, and the glass having an alkali metal oxide content of more than 0 mol% and no more than 20 mol%, the alkali metal oxide content is 17 mol%. The following is more preferable, and 10 mol% or less is more preferable.

The glass of the glass-containing substrate is preferably containing _Al 2 _{O 3} less 5 mol% or more 20 mol%. The lower limit of the content of Al ₂ O ₃ is preferably 8 mol% or more, more preferably 10 mol% or more, and further preferably 11.5 mol% or more. The upper limit of the content of Al ₂ O ₃ is more preferably 17.5 mol% or less, and further preferably 15 mol% or less.

Furthermore, the glass of the glass base substrate preferably contains 55 mol% or more and 75 mol% or less of SiO ₂ and 0 mol% or more and 30 mol% or less of alkaline earth metal oxide. In particular, SiO ₂ is preferably contained in an amount of 66 mol% or more and 75 mol% or less, and more preferably 66 mol% or more and 70 mol% or less. The alkaline earth metal oxide is more preferably contained in an amount of 5 mol% to 30 mol%, and more preferably 16 mol% to 30 mol%.

When glass having a B ₂ O ₃ content of 0.1 mol% or more and 15 mol% or less is used as the glass of the glass base substrate, the alkali metal oxide is preferably contained in an amount of 0 mol% or more and 25 mol% or less. In particular, the alkali metal oxide is more preferably contained in an amount of 0 mol% or more and 15 mol% or less, and further preferably 0 mol% or more and 2.5 mol% or less.

  The glass substrate preferably has a high specific elasticity (specific Young's modulus), for example, preferably 32 MNm / kg or more, and more preferably 33 MNm / kg or more.

  And the end surface grinding | polishing process of (process 2) end-polishes the end surface (a side surface part and a chamfering part) of a glass substrate.

  About the main plane polishing process of (Process 3), the upper and lower main planes of a glass substrate are grind | polished simultaneously using a double-side polish apparatus, supplying polishing liquid to the main plane of a glass substrate. The glass substrate may be polished only by primary polishing, primary polishing and secondary polishing may be performed, or tertiary polishing may be performed after secondary polishing.

Prior to the main plane polishing step (step 3), a main plane wrap (eg, loose abrasive wrap, fixed abrasive wrap, etc.) may be performed. In addition, glass substrate cleaning (inter-process cleaning) and glass substrate surface etching (inter-process etching) may be performed between the processes. The main plane lapping is polishing of the main plane in a broad sense.
(B) Magnetic Layer Film Formation Step The magnetic layer film formation step is a step of forming a magnetic layer (magnetic film) on the glass substrate. The configuration of the magnetic layer formed at this time is not particularly limited, and can be arbitrarily selected depending on the performance required for the magnetic recording medium.

  In addition to the magnetic layer, the underlayer, protective layer, lubricating layer, and the like can be arbitrarily selected and formed between the glass substrate and the magnetic layer or on the surface of the magnetic layer.

  The magnetic recording medium includes, for example, a horizontal magnetic recording system, a perpendicular magnetic recording system, a heat-assisted magnetic recording system, and the like, and the magnetic recording medium manufacturing method of this embodiment is applicable to any type of magnetic recording medium. be able to. Here, the perpendicular magnetic recording method is taken as an example, and the formation procedure of each layer constituting a magnetic recording medium including a magnetic layer on the glass substrate surface will be described below.

  For example, the magnetic recording medium may have a structure including a magnetic layer, a protective layer, and a lubricating film on the surface thereof. In the case of the perpendicular magnetic recording system, a soft magnetic underlayer made of a soft magnetic material that plays a role of circulating a recording magnetic field from a magnetic head is generally provided. For this reason, in order from the glass substrate surface, for example, a soft magnetic underlayer, a nonmagnetic intermediate layer, a perpendicular recording magnetic layer, a protective layer, and a lubricating film can be laminated.

  Each layer constituting the perpendicular magnetic recording type magnetic recording medium will be described below.

  As the soft magnetic underlayer, for example, CoNiFe, FeCoB, CoCuFe, NiFe, FeAlSi, FeTaN, FeN, FeTaC, CoFeB, CoZrN, or the like can be used.

  The nonmagnetic intermediate layer can be made of Ru, Ru alloy or the like. This nonmagnetic intermediate layer has a function for facilitating the epitaxial growth of the perpendicular recording magnetic layer and a function for breaking the magnetic exchange coupling between the soft magnetic underlayer and the recording magnetic layer.

The perpendicular recording magnetic layer is a magnetic film having an easy axis of magnetization oriented in a direction perpendicular to the substrate surface, and includes at least Co and Pt. In order to reduce intergranular exchange coupling that causes high intrinsic medium noise, a well-isolated fine particle structure (granular structure) is preferable. Specifically, an oxide (SiO ₂ , SiO, Cr ₂ O ₃ , CoO, Ta ₂ O ₃ , TiO _2, etc.), Cr, B, Cu, Ta, Zr or the like added to a CoPt alloy or the like Should be used.

  The soft magnetic underlayer, nonmagnetic intermediate layer, and perpendicular recording magnetic layer described so far can be continuously manufactured by an in-line sputtering method, a DC magnetron sputtering method, or the like.

Next, the protective layer is provided to prevent corrosion of the perpendicular recording magnetic layer and to prevent damage to the surface of the medium even when the magnetic head comes into contact with the medium, and is provided on the perpendicular recording magnetic layer. . As the protective layer, a material containing C, ZrO ₂ , SiO ₂ or the like can be used.

  As the formation method, for example, an in-line sputtering method, a CVD method, a spin coating method, or the like can be used.

  A lubricating layer is formed on the surface of the protective layer in order to reduce friction between the magnetic head and the magnetic recording medium (magnetic disk). For the lubricating layer, for example, perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acid, or the like can be used. The lubricating layer can be formed by a dip method, a spray method, or the like.

Here, the perpendicular magnetic recording type magnetic recording medium has been described. However, the present invention is not limited to the above-described form, and other magnetic recording media such as a thermally assisted magnetic recording type may be used. For example, when a magnetic recording medium of a thermally assisted magnetic recording system is used, the magnetic layer preferably contains FePt, SmCo ₅ or the like. Also, the configuration other than the magnetic layer can be arbitrarily configured according to each recording method.

  The magnetic recording medium manufacturing method of this embodiment can include a magnetic layer film forming step. Then, in the magnetic layer forming step, for example, the magnetic layer can be formed on the surface of the glass substrate while holding the glass substrate with a holding jig such as a chuck and performing heating or the like. The holding jig used in the magnetic layer film forming step is not particularly limited. For example, as shown in FIG. 2, holding members 211 of a plurality of holding jigs at a plurality of points on the end surface portion (side surface portion) of the outer diameter of the glass substrate 20. 212 and 213 can be held. These holding members 211 to 213 can hold the glass substrate 20 by applying a force toward the center of the glass substrate as indicated by block arrows A, B, and C in FIG. The holding members 211 to 213 apply a force in a direction parallel to the main plane of the glass substrate 20, but depending on the magnitude of the force, the glass substrate 20 is buckled and deformed in a direction perpendicular to the main plane. There is. The glass substrate 20 in the vicinity of the holding members 211 to 213 is often accompanied by local deformation, and delay restoration deformation may occur. When the delay restoration deformation occurs, a servo information reading error is likely to occur.

  In FIG. 2, the holding jig that holds the glass substrate at three points has been described as an example. However, the holding jig is not limited to three points, and a holding jig that holds two or more points can also be used.

  Here, although the example which hold | maintained the glass substrate by applying force with the holding jig toward the center direction from the outer diameter side of the glass substrate was demonstrated, it is not limited to the form which concerns. For example, two or more holding members are disposed in the opening formed in the central portion of the glass substrate, and a force is applied in the outer diameter direction from the end surface (hereinafter also referred to as an inner diameter) side of the glass substrate opening. In addition, a glass substrate can be held.

  In addition, a plurality of holding members can be provided in both the opening formed in the central portion of the glass substrate and the end surface portion of the outer diameter of the glass substrate. In this case, the holding member provided in the opening formed in the central portion of the glass substrate applies a force from the inner diameter side toward the outer diameter direction, and the holding member disposed on the end surface portion of the outer diameter of the glass substrate is on the outer diameter side. The glass substrate can be held by applying a force from the center toward the center.

  The present invention is not limited to a holding jig that applies force to a plurality of points on the end surface portion of the glass substrate 20 as described above, and a magnetic layer is formed on the glass substrate while being held by another form of holding jig. You can also.

Although the case where the magnetic layer is formed has been described here, the underlayer, the protective layer, the lubricating layer, and the like are formed on the glass substrate (the underlayer forming step, the protective layer forming step, the lubricating layer forming step). Etc.) can also be formed using the same holding jig, and in this case, buckling deformation may occur in the same manner.
(C) Magnetic recording medium holding step The magnetic recording medium holding step is a step of holding the magnetic recording medium obtained in the magnetic layer forming step in the cassette.

  Generally, a magnetic recording medium obtained by forming a magnetic layer or the like on a glass substrate is shipped and transported to a hard disk drive manufacturing factory.

  For this reason, the magnetic recording medium is housed in the cassette and the manufacturing process is completed. The magnetic recording medium need only be stored in the cassette, but it is preferable that the magnetic recording medium is further stored in a decompressed packing container (packaging).

  A load is applied to the magnetic recording medium (glass substrate), which is held in a cassette and stored in a decompressed packing container in some cases, and buckles the magnetic recording medium, that is, the glass substrate included in the magnetic recording medium. Deformation or bending deformation may occur. For this reason, in the packaging of the cassette holding the magnetic recording medium in the magnetic recording medium holding step, a force is applied to the magnetic recording medium, and the force is removed by opening the packaging, and the magnetic recording medium (glass substrate) ) Will be displaced to the original shape.

  For example, when the hard disk drive manufacturing process is performed without changing the location after the magnetic recording medium film forming process, this process can be omitted.

  The magnetic recording medium obtained by the magnetic recording medium manufacturing method described above is further subjected to a hard disk assembly process for incorporating the magnetic recording medium into a hard disk drive (HDD) and a servo information writing process for writing servo information. Can manufacture hard disk drives.

Then, according to the manufacturing method of the magnetic recording medium of the present embodiment, as the glass of the glass substrate included in the magnetic recording medium, the Al ₂ O ₃ may contain more than 5 mol%. Further, as the glass of the glass substrate included in the magnetic recording medium of the present embodiment, a glass substrate containing a predetermined amount of B ₂ O ₃ or a glass substrate having an alkali metal oxide content within a predetermined range, Used. For this reason, even when the method of manufacturing a magnetic recording medium includes the generation of at least one of buckling deformation and bending deformation in the glass substrate, the force (load) is removed and then returned to the original shape. The time to return is particularly short. For this reason, a force (load) is applied to the glass substrate (magnetic recording medium), and even when the glass substrate (magnetic recording medium) is deformed, the glass substrate (magnetic recording medium) is displaced by the restoring force after the force (load) is removed before servo information is written. Finished or almost finished. Therefore, the glass substrate (magnetic recording medium) after the servo information is written is not displaced, or the degree of displacement is slight, preventing the position of the written servo information from shifting and suppressing the error rate. Can do.

  Next, the magnetic recording medium of this embodiment will be described.

The magnetic recording medium of this embodiment can be a magnetic recording medium in which a magnetic layer is formed on a glass substrate, and in particular, a magnetic recording medium for servo information writing in which a magnetic layer is formed on a glass substrate; can do. On the glass substrate of the magnetic recording medium, for example, a magnetic layer, an underlayer, a protective layer, a lubricating layer, and the like can be arbitrarily provided. And, in the magnetic recording medium of the present embodiment, the glass of the glass substrate, the _Al 2 _{O 3} may contain more than 5 mol%. In the magnetic recording medium of the present embodiment, the glass of the glass substrate has a B ₂ O ₃ content of 0.1 mol% or more and 15 mol% or less, or contains one or less alkali metal oxides. The metal oxide content is preferably 0 mol% or more and 25 mol% or less, or two or more alkali metal oxides are contained, and the alkali metal oxide content is preferably more than 0 mol% and 20 mol% or less. The alkali metal oxide here may be any alkali metal oxide, and includes any alkali metal oxide. Typically, examples of the alkali metal oxide include Li ₂ O, Na ₂ O, and K ₂ O.

This is because the Young's modulus of the glass substrate can be sufficiently increased by setting the Al ₂ O ₃ content of the glass of the glass substrate to 5 mol% or more.

Further, the content of B ₂ O _{3 in} the glass of the glass substrate is 0.1 mol% or more and 15 mol% or less, or the alkali metal oxide contained in the glass of the glass substrate is one or less, and the content of the alkali metal oxide When the amount is 0 mol% or more and 25 mol% or less, or when the glass of the glass substrate contains two or more kinds of alkali metal oxides and the content of alkali metal oxides is more than 0 mol% and 20 mol% or less, force (load) is applied to the glass substrate. This is because, even when the deformation is caused by the addition of (), the time from the removal of the force (load) to the return to the original shape is shortened. That is, after the force (load) applied to the glass substrate is removed, the time during which the glass substrate is deformed is shortened.

In the magnetic recording medium of the present embodiment, the glass of the glass substrate contained in the magnetic recording medium preferably has a B ₂ O ₃ content of 0.1 mol% or more and 15 mol% or less. This is because even when a force (load) is applied to the glass substrate and the glass substrate is deformed, the time from the removal of the force (load) to returning to the original shape can be shortened.

In particular, if the glass of the glass substrate included in the magnetic recording medium contains _B 2 _{O 3,} the lower limit of the content of B 2 _{O 3} is more preferably not less than 0.2 mol%, further preferably at least 0.5 mol% . Further, the upper limit of the content of B ₂ O ₃ is preferably 12 mol% or less, more preferably 10 mol% or less, further preferably 5 mol% or less, and particularly preferably less than 2 mol%. When the content of B ₂ O ₃ is less than 2 mol%, a force (load) is applied to the glass substrate, and when it is deformed, the displacement time after removing the force (load) can be shortened. A high glass substrate can be obtained. For this reason, even when the magnetic recording medium is rotated at a high speed, the occurrence of fluttering can be further suppressed, and the occurrence of reading / writing errors of the magnetic recording medium can be particularly suppressed.

In addition, when the glass of the glass substrate included in the magnetic recording medium is a glass having one or less alkali metal oxides and an alkali metal oxide content of 0 mol% or more and 25 mol% or less, an alkali metal is used. The oxide content is more preferably 22 mol% or less. More preferably, the content of the alkali metal oxide is 10 mol% or less. In addition, the alkali metal oxide to be contained is one kind or less, for example, contains one kind of alkali metal oxide selected from alkali metal oxides such as Na ₂ O, K ₂ O, Li ₂ O, This means that no alkali metal oxide is contained.

  When the glass of the glass substrate included in the magnetic recording medium of the present embodiment contains two or more kinds of alkali metal oxides and the glass having an alkali metal oxide content of more than 0 mol% and no more than 20 mol%, an alkali is used. The content of the metal oxide is more preferably 17 mol% or less, and further preferably 10 mol% or less.

In addition, containing two or more types of alkali metal oxides includes, for example, two or more types of alkali metal oxides selected from alkali metal oxides such as Na ₂ O, K ₂ O, and Li ₂ O. Means. In this case, the content of each alkali metal oxide is not particularly limited, and can be any content. For example, the content (mol%) of each alkali metal oxide can be made uniform.

  As described above, by using a glass substrate containing a predetermined component as the glass of the glass substrate included in the magnetic recording medium of the present embodiment, force (load) is applied to the glass substrate and servo information can be obtained even when the glass substrate is deformed. By the time the writing is completed, the glass substrate finishes or is almost completely displaced by the restoring force after removing the force (load). For this reason, the glass substrate (magnetic recording medium) after the servo information has been written is not displaced, or the degree of displacement is small, preventing the position of the written servo information from shifting and suppressing the error rate. be able to.

Moreover, it is preferable that the glass of the glass substrate contained in the magnetic recording medium of this embodiment contains 5 mol% or more and 20 mol% or less of Al ₂ O ₃ . The lower limit of the Al ₂ O ₃ content is more preferably 8 mol% or more, further preferably 10 mol% or more, and particularly preferably 11.5 mol% or more. The upper limit of the content of Al ₂ O ₃ is more preferably 17.5 mol% or less, and further preferably 15 mol% or less.

The glass of the glass substrate included in the magnetic recording medium of the present embodiment preferably contains 55 mol% or more and 75 mol% or less of SiO ₂ and 0 mol% or more and 30 mol% or less of alkaline earth metal oxide. . In particular, SiO ₂ is preferably contained in an amount of 66 mol% to 75 mol%, and more preferably 66 mol% to 70 mol%. The alkaline earth metal oxide is more preferably contained in an amount of 5 mol% to 30 mol%, and more preferably 16 mol% to 30 mol%.

In particular, when a glass having a B ₂ O ₃ content of 0.1 mol% or more and 15 mol% or less is used as the glass of the glass substrate included in the magnetic recording medium, the alkali metal oxide is contained in an amount of 0 mol% or more and 25 mol% or less. It is preferable. Furthermore, it is more preferable to contain 0 mol% or more and 15 mol% or less of an alkali metal oxide, and it is further more preferable to contain 0 mol% or more and 2.5 mol% or less.

  Further, the glass substrate included in the magnetic recording medium of the present embodiment preferably has a high specific elasticity (specific Young's modulus), for example, preferably 32 MNm / kg or more, and more preferably 33 MNm / kg or more. . Due to the high specific elasticity, even when the magnetic recording medium is rotated at high speed, the occurrence of fluttering can be further suppressed, and the occurrence of read / write errors of the magnetic recording medium can be particularly suppressed.

  The glass substrate included in the magnetic recording medium of the present embodiment preferably has a pseudoelastic deformation amount A of 2.0 μm or less. The lower limit value of the pseudoelastic deformation amount A is 0 μm. The same can be said for the pseudoelastic deformation amount B and the pseudoelastic deformation amount C described later.

  Here, the pseudo elastic deformation amount A means that both ends of the glass substrate in the diameter direction are supported from the lower surface side, the load is removed for 48 hours after being applied to the upper surface of the central portion of the glass substrate, and 5 hours after the load is removed. It means the absolute value of the difference between the flatness at the time of elapse and the flatness before the load is applied.

In particular, the pseudoelastic deformation amount A can be specifically calculated as follows, for example. First, it is surrounded by a string and an arc provided at two opposing positions on the glass substrate, and the maximum distance between the string and the arc is 2.3% to 7.7% of the diameter of the glass substrate. A certain diametrical both ends are supported from the lower surface side. Then, the width is 35 to 80% of the diameter of the glass substrate, and the center line in the width direction passes through the center of the glass substrate and is on the upper surface of the central region of the glass substrate that is parallel to the string (of the glass substrate). The area calculated by the area of the main plane) mm ² × 2.28 mN / mm ² is applied for 48 hours. Thereafter, the load is removed, and the absolute value of the difference between the flatness after 5 hours from the removal of the load and the flatness before the load is applied can be defined as the pseudoelastic deformation amount A.

  Therefore, the smaller the value of the pseudoelastic deformation amount A, the more the glass substrate or magnetic recording medium that can return to its original shape in a short time after removing the load (force) that deformed the glass substrate. .

  When measuring the pseudoelastic deformation amount A, the load is applied to the glass substrate for 48 hours, according to the study of the inventors of the present invention, the time for applying the load to the glass substrate regardless of the composition of the glass substrate. It was confirmed that the change in flatness was saturated in about 16 hours. For this reason, the change in flatness is saturated, and the time is set to 48 hours from the viewpoint that the change in flatness does not occur even when a load is applied for a longer time.

  The flatness after 5 hours after removing the load is the target of comparison. After the magnetic recording medium is manufactured, the magnetic recording medium holding process, etc. are performed, and the servo information is written. In the meantime, a hard disk assembling step for incorporating the magnetic recording medium into the hard disk is performed. For this reason, it usually takes at least 5 to 12 hours to write servo information after the magnetic recording medium is manufactured, that is, after the magnetic layer deposition process or after opening the package formed in the magnetic recording medium holding process. Because.

  When the pseudo-elastic deformation amount A of the glass substrate included in the magnetic recording medium of the present embodiment is in the above range, even when the glass substrate (magnetic recording medium) is deformed such as buckling deformation or bending deformation, the glass substrate, magnetic It shows that the recording medium can return to its original shape in a short time. Further, even when the displacement is caused by the passage of time, the displacement width is equal to or less than the value of the pseudoelastic deformation amount A, indicating that the displacement width of the flatness is small. For this reason, when the pseudo elastic deformation amount A has the above range, the displacement width after writing the servo information becomes small, and it becomes possible to further suppress the occurrence of an error.

  In the glass substrate of the magnetic recording medium, the pseudoelastic deformation amount A is more preferably 1.5 μm or less, further preferably 1.0 μm or less, and particularly preferably 0.4 μm or less.

  Further, in the glass substrate included in the magnetic recording medium of the present embodiment, both end portions in the glass substrate diameter direction are supported from the lower surface side, and a load is applied to the upper surface of the central portion (central region including the center) of the glass substrate for 48 hours. The absolute value of the difference between the flatness after 5 hours after removing the load and the flatness after 48 hours after removing the load is defined as a pseudoelastic deformation amount B. In this case, the glass substrate preferably has a pseudoelastic deformation amount B of 1.5 μm or less.

Specifically, the pseudoelastic deformation amount B can be calculated as follows, for example. First, it is surrounded by a string and an arc provided at two opposing positions on the glass substrate, and the maximum distance between the string and the arc is 2.3% to 7.7% of the diameter of the glass substrate. A certain diametrical both ends are supported from the lower surface side. The width is 35 to 80% of the diameter of the glass substrate, and the center line in the width direction passes through the center of the glass substrate and is on the upper surface of the central region of the glass substrate parallel to the chord (the main plane of the glass substrate The load calculated by mm ² × 2.28 mN / mm ² is applied for 48 hours. Thereafter, the load is removed, and the absolute value of the difference between the flatness after the lapse of 5 hours after the removal of the load and the flatness after the lapse of 48 hours after the removal of the load can be set as the pseudoelastic deformation amount B.

  The pseudo-elastic deformation amount B means the amount of change in flatness between the lapse of 5 hours and the lapse of 48 hours after the load is removed. For this reason, it means that the smaller the value is, the smaller the amount of change in flatness after 5 hours after removing the load.

  Accordingly, if the pseudo-elastic deformation amount B satisfies the above-mentioned definition, for example, when servo information is written 5 hours after the load is removed, the subsequent flatness change is small, that is, the glass substrate (magnetic recording medium) The amount of displacement will be small. For this reason, it is possible to prevent the position of the written servo information from shifting and to further suppress the error occurrence rate.

  The value of the pseudo-elastic deformation amount B is not particularly limited as long as it is a deformation amount allowed when data is read and written after servo information is written, but is 1.5 μm or less as described above. It is preferable. The pseudoelastic deformation amount B is more preferably 1.0 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.4 μm or less.

  Further, in the glass substrate included in the magnetic recording medium of the present embodiment, both ends in the diameter direction of the glass substrate are supported from the lower surface side, and a load is applied to the upper surface of the central portion (central region including the center) of the glass substrate for 48 hours. After removing the load, the flatness after the lapse of 5 hours is defined as a pseudoelastic deformation amount C after the load is removed. In this case, the glass substrate preferably has a pseudoelastic deformation amount C of 2.5 μm or less, preferably 2.0 μm or less, preferably 1.5 μm or less, and 1.0 μm or less. Is more preferable.

Specifically, the pseudoelastic deformation amount C can be calculated as follows, for example. First, it is surrounded by a string and an arc provided at two opposing positions on the glass substrate, and the maximum distance between the string and the arc is 2.3% to 7.7% of the diameter of the glass substrate. A certain diametrical both ends are supported from the lower surface side. The glass substrate has a width of 35 to 80% of the diameter of the glass substrate, and the center line in the width direction passes through the center of the glass substrate and is placed on the upper surface of the central region of the glass substrate parallel to the chord (main glass substrate). The area calculated by plane area) mm ² × 2.28 mN / mm ² is applied for 48 hours. Thereafter, the load is removed, and after removing the load, the flatness after the lapse of 5 hours can be set as the pseudoelastic deformation amount C.

  The pseudoelastic deformation amount C indicates that the smaller the value is, the smaller the flatness is after 5 hours have elapsed after the load is removed. A glass substrate that satisfies such parameters shows that although the load is applied for 48 hours, the deformation is small and / or the flatness is restored in 5 hours after the load is removed. . For this reason, even if servo information is written when five hours have elapsed after the load is removed, the subsequent deformation amount of the glass substrate is small, and the error rate can be further suppressed.

  A method for measuring the pseudoelastic deformation amounts A to C described so far will be described with reference to FIGS.

  In the following description and FIG. 3, the flatness at each time is expressed as F (xh). In the equation, x represents the elapsed time since the load was removed, with the time when the load was removed as the reference (0h). Also, the time before the load is removed is represented by a minus value. Therefore, for example, F (−48h) indicates the flatness of the glass substrate 48 hours before removing the load, that is, before applying the load.

  First, the pseudo-elastic deformation measurement flow will be described with reference to FIG.

  As shown in FIG. 3, first, before applying a load, the flatness F (−48 h) of the glass substrate is measured (point (1) in FIG. 3). Thereafter, a load is applied to the glass substrate by a method described later for 48 hours. This is because according to the study by the present inventors, it was confirmed that the change in flatness was saturated in about 16 hours after applying a load on any glass substrate. For this reason, the change in flatness is saturated, and the time is set to 48 hours from the viewpoint that the change in flatness does not occur even when a load is applied for a longer time.

  The load was removed after 48 hours (point (2) in FIG. 3), and the flatness was measured again when 5 hours passed after the load was removed (point (3) in FIG. 3). 5h). This is because, as described above, servo information is generally written after about 5 to 12 hours after opening the package formed in the magnetic layer forming step or the magnetic recording medium holding step. It is.

  Further, after removing the load, the flatness when 48 hours passed was measured (point (4) in FIG. 3), and this was defined as F (48h). This is because, in a general hard disk drive assembly process, a read / write test is performed when about 48 hours have elapsed after opening the package formed in the magnetic layer deposition process or the magnetic recording medium holding process.

  Then, as described above, the pseudoelastic deformation amount A is calculated by the absolute value of the difference between the flatness F (−48 h) before the load is applied and the flatness when 5 hours have elapsed after the load is removed, It is represented by the following formula.

(Pseudoelastic deformation amount A) = | F (5h) −F (−48h) |
It shows that the smaller the value of the pseudoelastic deformation amount A is, the more the shape (flatness) is restored from the deformation caused by applying the load.

  The pseudoelastic deformation amount B is calculated by the absolute value of the difference between the flatness when 5 hours have elapsed after removing the load as described above and the flatness when 48 hours have elapsed, and is expressed by the following equation. .

(Pseudoelastic deformation amount B) = | F (5h) −F (48h) |
The pseudoelastic deformation amount C represents the flatness when 5 hours have elapsed after the load is removed. For this reason, it is represented by the following formula.

(Pseudoelastic deformation amount C) = F (5 h)
The means for measuring the flatness of the glass substrate is not particularly limited, and for example, measurement can be performed by a phase measurement interferometry (phase shift method).

  Next, a method for applying a load to the glass substrate when measuring the amount of pseudoelastic deformation will be described below.

  When applying a load to the glass substrate, both ends in the diametrical direction facing the glass substrate are supported from the lower surface side, and the load is applied vertically downward from the upper surface of the glass substrate to the central portion including the center of the glass substrate. .

  A specific example will be described with reference to FIG.

  FIG. 4 shows a configuration example in which a load 45 is applied to the glass substrate 43 in order to measure the amount of pseudoelastic deformation. FIG. 4 (A) is a lateral side view, and FIG. 4 (B) is a top view. Is shown respectively.

  As shown in FIG. 4, a V-shaped block 41 is used to support both ends of the glass substrate 43, and a glass substrate 43 and a load (heavy stone) 45 are arranged thereon to apply a load to the glass substrate 43.

  The V-shaped block 41 has a V-shaped cutout 42 at the center thereof. And it arrange | positions so that the both ends 44 of the glass substrate 43 can be supported from the lower surface side by arrange | positioning the glass substrate 43 so that the V-shaped cut | notch part 42 may be covered. The member that supports the glass substrate 43 is not limited to the V-shaped block, and any member that can support both end portions 44 of the glass substrate 43 may be used. For example, two rectangular column shaped blocks may be arranged so as to support both end portions 44 of the glass substrate 43 with a predetermined interval.

  In this case, both end portions (support portions) 44 that are in contact with the V-shaped block and are provided at two diametrical ends that support the glass substrate 43 are surrounded by strings 441 and 442 and arcs, respectively. The strings 441 and 442 are the end portions of the cut portion of the V-shaped block and are parallel to each other. Then, the maximum value of the distance between the chord and the arc, that is, W1 in FIG. 4 is preferably set to a length of 2.3% to 7.7% of the diameter of the glass substrate 43, for example. More preferably, the content is set to 0.0% to 6.0%. This is because if the range of the portion to be supported is too narrow, the glass substrate 43 may slip off and be damaged when a load is applied. If it is too wide, the distance between the load portion will be shortened, This is because the flatness hardly changes and the resolution of measurement is lowered.

  The load is not particularly limited as long as the load can be applied to the central portion including the center of the glass substrate 43, and the arrangement and the magnitude of the load are not particularly limited.

  For example, as shown in FIG. 4, it can be performed by placing a rectangular parallelepiped load (weight) in the center of the glass substrate 43. In this case, it is preferable that the load be arranged so as to be parallel to the strings 441 and 442 constituting both end portions supporting the glass substrate 43. Further, as shown in FIG. 4B, the load is preferably arranged so as to cover the entire glass substrate 43 having a width (range) of a certain distance from the center line parallel to the strings 441 and 442. For example, a rectangular parallelepiped whose width, that is, the length of W2 in FIG. 4 is 35% to 80% of the diameter of the glass substrate 43 can be preferably used as the load (weight), and more than 35% to 50%. It can be preferably used.

  This is because, for example, when the range to which the load is applied is too narrow, the glass substrate 43 may be damaged due to the load being concentrated in a narrow range, the load becoming unstable and falling, and the range to which the load is applied is wide. This is because if the distance is too large, the distance between the two supporting end portions becomes narrow, the flatness hardly changes, and the measurement resolution becomes low.

  The length of the load (heavy stone) in the vertical direction is preferably the same length as the diameter of the glass substrate 43 as described above, or a length longer than that.

  The weight of the load is not particularly limited as long as it is within a range in which deformation due to pseudoelasticity occurs sufficiently and the glass substrate 43 is not damaged, and is selected according to the area and strength of the glass substrate 43 to be used. be able to.

For example, the load can be selected to be 0.233 gf (2.28 mN) per 1 mm ² of the main plane area of the glass substrate 43. That is, a load calculated by (area of main plane of glass substrate (for magnetic recording medium)) mm ² × 0.233 gf / mm ² (2.28 mN / mm ² ) can be applied. For example, in the case of a glass substrate (2.5 inch glass substrate) having an outer diameter of 65 mm and an inner diameter (diameter of the circular hole in the central portion) of 20 mm, a load of 700 gf (6.86 N) is applied to the upper surface of the central portion of the glass substrate 43. Will be added to.

  Even if the force (load) applied to the glass substrate is the same, if the plate thickness of the glass substrate is reduced, both the buckling deformation and the bending deformation increase as stress, so that local deformation is more likely to occur. In such a case, the magnetic recording medium disclosed in the present embodiment functions more effectively. For example, the deflection amount d of the central portion when both ends of a simple beam of a rectangular column having a rectangular cross section are held at the center and given a constant load is given by the following equation.

d = (PL ³ ) / (48EI)
P: center load L: length of beam E: Young's modulus of material I = second moment of section = (bh ³ ) / 12 b: width of prism h: thickness Therefore, the amount of delayed recovery deformation is also 3 of the thickness of the glass substrate There is a possibility that the amount of delayed restoration deformation increases remarkably as the thickness is reduced in inverse proportion to the power. However, according to the magnetic recording medium of the present embodiment, even when the glass substrate is thin, the displacement is finished or almost finished before the servo information is written.

The magnetic recording medium of the present embodiment has been described above. However, even when a force (load) is applied to the glass substrate included in the magnetic recording medium of the present embodiment and deformed, the glass substrate (magnetic recording The medium is in a state where the displacement due to the restoring force after removing the force (load) is finished or almost finished. Therefore, the glass substrate after the servo information is written is not displaced, or the degree of displacement is small, and the position of the written servo information is prevented from shifting, and the error rate can be suppressed.
[Second Embodiment]
A configuration example of the magnetic recording medium of the present embodiment will be described.

  The magnetic recording medium of this embodiment is a servo information writing magnetic recording medium in which a magnetic layer is formed on a glass substrate. The pseudo elastic deformation amount A of the glass substrate included in the magnetic recording medium is preferably 2.0 μm or less. The lower limit value of the pseudoelastic deformation amount A is 0 μm. The same can be said for the pseudoelastic deformation amount B and the pseudoelastic deformation amount C described later.

  Here, the pseudoelastic deformation amount A means that both ends in the diameter direction of the glass substrate included in the magnetic recording medium are supported from the lower surface side, and the load is removed after the load is applied to the upper surface of the central portion of the glass substrate for 48 hours. It means the absolute value of the difference between the flatness when 5 hours have elapsed after removing the load and the flatness before applying the load.

In particular, the pseudoelastic deformation amount A can be specifically calculated as follows, for example. First, it is surrounded by a string and an arc provided at two opposing positions on the glass substrate, and the maximum distance between the string and the arc is 2.3% to 7.7% of the diameter of the glass substrate. A certain diametrical both ends are supported from the lower surface side. Then, the width is 35 to 80% of the diameter of the glass substrate, and the center line in the width direction passes through the center of the glass substrate and is on the upper surface of the central region of the glass substrate that is parallel to the string (of the glass substrate). The area calculated by the area of the main plane) mm ² × 2.28 mN / mm ² is applied for 48 hours. Thereafter, the load is removed, and the absolute value of the difference between the flatness after 5 hours from the removal of the load and the flatness before the load is applied can be defined as the pseudoelastic deformation amount A.

  Therefore, the smaller the value of the pseudoelastic deformation amount A, the more the magnetic recording medium can return to its original shape in a short time after removing the load (force) that deformed the magnetic recording medium (glass substrate). Indicates.

  When measuring the pseudoelastic deformation amount A, the load is applied to the glass substrate for 48 hours, according to the study of the inventors of the present invention, the time for applying the load to the glass substrate regardless of the composition of the glass substrate. It was confirmed that the change in flatness was saturated in about 16 hours. For this reason, the change in flatness is saturated, and the time is set to 48 hours from the viewpoint that the change in flatness does not occur even when a load is applied for a longer time.

  The flatness after 5 hours after removing the load is the target of comparison. After the magnetic recording medium is manufactured, the magnetic recording medium holding process, etc. are performed, and the servo information is written. In the meantime, a hard disk assembling step for incorporating the magnetic recording medium into the hard disk is performed. For this reason, it usually takes at least 5 to 12 hours to write servo information after the magnetic recording medium is manufactured, that is, after the magnetic layer deposition process or after opening the package formed in the magnetic recording medium holding process. Because.

  When the pseudo-elastic deformation amount A of the glass substrate included in the magnetic recording medium of the present embodiment is in the above range, even when the glass substrate (magnetic recording medium) is deformed such as buckling deformation or bending deformation, the glass substrate, magnetic It shows that the recording medium can return to its original shape in a short time. Further, even when the displacement is caused by the passage of time, the displacement width is equal to or less than the value of the pseudoelastic deformation amount A, indicating that the displacement width of the flatness is small. For this reason, when the pseudo elastic deformation amount A has the above range, the displacement width after writing the servo information becomes small, and it becomes possible to further suppress the occurrence of an error.

  In the glass substrate of the magnetic recording medium, the pseudoelastic deformation amount A is more preferably 1.5 μm or less, further preferably 1.0 μm or less, and particularly preferably 0.4 μm or less.

  Further, in the glass substrate included in the magnetic recording medium of the present embodiment, both end portions in the glass substrate diameter direction are supported from the lower surface side, and a load is applied to the upper surface of the central portion (central region including the center) of the glass substrate for 48 hours. The absolute value of the difference between the flatness after 5 hours after removing the load and the flatness after 48 hours after removing the load is defined as a pseudoelastic deformation amount B. In this case, the glass substrate preferably has a pseudoelastic deformation amount B of 1.5 μm or less.

Specifically, the pseudoelastic deformation amount B can be calculated as follows, for example. First, it is surrounded by a string and an arc provided at two opposing positions on the glass substrate, and the maximum distance between the string and the arc is 2.3% to 7.7% of the diameter of the glass substrate. A certain diametrical both ends are supported from the lower surface side. The width is 35 to 80% of the diameter of the glass substrate, and the center line in the width direction passes through the center of the glass substrate and is on the upper surface of the central region of the glass substrate parallel to the chord (the main plane of the glass substrate The load calculated by mm ² × 2.28 mN / mm ² is applied for 48 hours. Thereafter, the load is removed, and the absolute value of the difference between the flatness after the lapse of 5 hours after the removal of the load and the flatness after the lapse of 48 hours after the removal of the load can be set as the pseudoelastic deformation amount B.

  The pseudo-elastic deformation amount B means the amount of change in flatness between the lapse of 5 hours and the lapse of 48 hours after the load is removed. For this reason, it means that the smaller the value is, the smaller the amount of change in flatness after 5 hours after removing the load.

  Therefore, when the pseudo-elastic deformation amount B satisfies the above-mentioned definition, for example, when servo information is written 5 hours after the load is removed, the change in flatness after that is small, that is, the magnetic recording medium (glass substrate) The amount of displacement will be small. For this reason, it is possible to prevent the position of the written servo information from shifting and to further suppress the error occurrence rate.

  The value of the pseudo-elastic deformation amount B is not particularly limited as long as it is a deformation amount allowed when data is read and written after servo information is written, but is 1.5 μm or less as described above. It is preferable. The pseudoelastic deformation amount B is more preferably 1.0 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.4 μm or less.

  Further, in the glass substrate included in the magnetic recording medium of the present embodiment, both ends in the diameter direction of the glass substrate are supported from the lower surface side, and a load is applied to the upper surface of the central portion (central region including the center) of the glass substrate for 48 hours. After removing the load, the flatness after the lapse of 5 hours is defined as a pseudoelastic deformation amount C after the load is removed. In this case, the glass substrate preferably has a pseudoelastic deformation amount C of 2.5 μm or less, preferably 2.0 μm or less, preferably 1.5 μm or less, and 1.0 μm or less. Is more preferable.

Specifically, the pseudoelastic deformation amount C can be calculated as follows, for example. First, it is surrounded by a string and an arc provided at two opposing positions on the glass substrate, and the maximum distance between the string and the arc is 2.3% to 7.7% of the diameter of the glass substrate. A certain diametrical both ends are supported from the lower surface side. The glass substrate has a width of 35 to 80% of the diameter of the glass substrate, and the center line in the width direction passes through the center of the glass substrate and is placed on the upper surface of the central region of the glass substrate parallel to the chord (main glass substrate). The area calculated by plane area) mm ² × 2.28 mN / mm ² is applied for 48 hours. Thereafter, the load is removed, and after removing the load, the flatness after the lapse of 5 hours can be set as the pseudoelastic deformation amount C.

  The pseudoelastic deformation amount C indicates that the smaller the value is, the smaller the flatness is after 5 hours have elapsed after the load is removed. A glass substrate that satisfies such parameters shows that although the load is applied for 48 hours, the deformation is small and / or the flatness is restored in 5 hours after the load is removed. . For this reason, even if the servo information is written when 5 hours have elapsed after the load is removed, the subsequent deformation amount of the magnetic recording medium (glass substrate) is small, and the error occurrence rate can be further suppressed.

  Since the measurement of the pseudo elastic deformation amounts A to C described so far can be performed in the same manner as the measurement method of the pseudo elastic deformation amounts A to C described in the first embodiment, the description is omitted here.

  The magnetic recording medium according to the present embodiment has been described above. However, the magnetic recording medium according to the present embodiment does not have the magnetic recording medium until the servo information is written even when a force (load) is applied to the magnetic recording medium and the magnetic recording medium is deformed. The displacement due to the restoring force after removing the force (load) is finished or almost finished. Therefore, the magnetic recording medium after the servo information is written does not displace or the degree of displacement becomes small, and the position of the written servo information can be prevented from shifting and the error rate can be suppressed.

  Specific examples will be described below, but the present invention is not limited to these examples.

[Experiment 1]
First, an evaluation method of a glass substrate used for a magnetic recording medium in the following examples and comparative examples, and an evaluation method of a magnetic recording medium in which a thin film such as a magnetic layer is formed on the glass substrate surface will be described.
(1) Evaluation of dependence of flatness immediately after load removal on load application time before load removal The load application time before load removal was changed, and the change in flatness immediately after the load (force) was removed was evaluated.

  A method for applying a load (force) to the glass substrate will be described.

First, as shown in FIG. 4, support portions 44 in which both end portions of a glass substrate 43 used for a magnetic recording medium are supported by V-shaped blocks 41 are arranged at both ends in the diametrical direction, and two end portions (support portions) are It is surrounded by the strings 441 and 442 and an arc (which is the shorter arc cut by the string), and the two ends are identical in shape. The maximum distance W1 between the chords 441 and 442 and the circular arc is 5.4% (3.5 mm) of the diameter of the glass substrate 43.

  Next, a load 45 was placed on the main plane of the glass substrate 43 so as to be parallel to the strings 441 and 442 constituting both end portions supported by the V-shaped block 41. In this embodiment, as the size of the load 45, the width, that is, W2 in FIG. 4 is 38.5% (25 mm) of the diameter of the glass substrate 43, and a load of 700 gf (6.86 N) is used. It was. In this case, the load 45 is arranged so that the center line in the width direction passes through the center of the glass substrate 43.

  Further, in the vertical direction, the one longer than the diameter of the glass substrate 43 was used so as to completely cover the glass substrate 43 over the entire width range of the load 45 as in the case shown in FIG.

  In the evaluation of the change in flatness due to the load time, the load application time shown in Table 2 shown below for each sample is performed in order to change the time during which the load (force) is applied and thereby evaluate the flatness of the glass substrate. In the meantime, the load was placed on the glass substrate as described above, and the flatness was measured immediately after the load was removed.

And the flatness immediately after removing this after adding a load about each glass substrate for the predetermined time was measured. The flatness was measured by phase measurement interferometry (phase shift method). Specifically, an interference type flatness measuring device (manufactured by Zygo, model: Zygo GI Flat (MESA)) was used, and measurement was performed at a measurement wavelength of 680 nm.
(2) Evaluation of dependency of flatness after load removal on elapsed time after release of load After a load was applied to the glass substrate for 24 hours, the load was removed, and the change in flatness after the load was removed was evaluated.

  The method of applying a load to the glass substrate was performed in the same manner as in the case of (1) the evaluation of the load application time dependency of the flatness immediately after the load removal before the load removal, and the load was applied for 24 hours.

Then, after removing the load, the flatness was measured every predetermined time indicated by the elapsed time after the load release in Table 3 to be described later. The flatness was measured by (1) phase measurement interferometry (phase shift method) in the same manner as in the case of evaluation of the load application time dependency of the flatness immediately after load removal and before load removal.
(3) Pseudoelastic deformation amounts A to C
In evaluating the pseudoelastic deformation amounts A to C, as described in the first embodiment, the flatness F (−48 h) before applying a load to the glass substrate, and after applying the load for 48 hours, The flatness F (5 h) and F (48 h) at the lapse of 5 hours and 48 hours after the removal were measured.

  The flatness at each time was measured by a phase measurement interferometry (phase shift method). Specifically, an interference type flatness measuring device (manufactured by Zygo, model: Zygo GI Flat (MESA)) was used, and measurement was performed at a measurement wavelength of 680 nm.

Thereafter, pseudoelastic deformation amounts A to C were calculated from the measured flatnesses by the following formula.
(Pseudoelastic deformation amount A) = | F (5h) −F (−48h) |
(Pseudoelastic deformation amount B) = | F (5h) −F (48h) |
(Pseudoelastic deformation amount C) = F (5 h)
Here, the method of applying a load to the glass substrate was performed in the same manner as in the case of (1) the evaluation of the load application time dependency of the flatness immediately after the load removal before the load removal, and the load was applied for 48 hours.
(4) Read / Write Test The obtained magnetic recording medium was subjected to a read / write test according to the procedure described below.

  Specifically, a magnetic recording medium having a magnetic layer formed on a glass substrate was incorporated into a hard disk drive (HDD), and servo information was written according to the following procedure. Thereafter, according to the procedure of the following embodiment, a magnetic signal is recorded under the condition of a track density of about 254 kTPI (Track per inch) and a linear recording density of about 1500 BPI (Bit per inch), and whether or not an error occurs when reading the signal confirmed.

  In this example, the magnetic recording media of Examples 1 to 10 were prepared and evaluated. As shown in Table 1, the magnetic recording media of Examples 1 to 10 differ in the glass composition of the glass substrate included in the magnetic recording medium. Examples 1 to 7 are examples, and examples 8 to 10 are comparative examples.

（ガラス基板の製造）
各ガラス基板は、表１の例１〜例１０のガラス組成を有するガラス素基板を用いて、以下の手順により、直径６５ｍｍ、板厚０．６３５ｍｍ、中央部に２０ｍｍの円孔を有するドーナツ形状に加工した。なお、表１中ＲＯはガラス素基板のガラス組成のうちのアルカリ土類金属酸化物の含有量について、Ｒ_２Ｏはガラス素基板のガラス組成のうちアルカリ金属酸化物の含有量についてそれぞれ示している。また、表中「−」は係る成分を含まない、すなわち係る成分の含有量が０であることを意味している。

(Manufacture of glass substrates)
Each glass substrate is a donut shape having a diameter of 65 mm, a plate thickness of 0.635 mm, and a central hole of 20 mm using the glass base substrate having the glass composition of Examples 1 to 10 in Table 1 according to the following procedure. It was processed into. In Table 1, RO represents the content of alkaline earth metal oxide in the glass composition of the glass substrate, and R ₂ O represents the content of alkali metal oxide in the glass composition of the glass substrate. Yes. In the table, “-” means that such a component is not included, that is, the content of the component is 0.

  First, the glass base substrate is processed into a disk-shaped glass substrate having a circular hole in the center.

  The inner peripheral end surface and the outer peripheral end surface of the disk-shaped glass substrate are chamfered so as to obtain a glass substrate with a chamfering angle of 45 ° (inner peripheral chamfering step, outer peripheral chamfering step).

  After chamfering, the upper and lower principal planes of the glass substrate are lapped using alumina abrasive grains, and the abrasive grains are washed and removed.

  Next, the outer peripheral side surface portion and the outer peripheral chamfered portion of the glass substrate are polished using a polishing liquid containing a polishing brush and cerium oxide abrasive grains, and the work-affected layer (such as scratches) on the outer peripheral side surface and outer peripheral chamfered portion is removed. The outer peripheral end face is polished so as to be a mirror surface (outer peripheral end face polishing step).

  After the outer peripheral end surface is polished, the inner peripheral side surface portion and inner peripheral chamfered portion of the glass substrate are polished with a polishing liquid containing a polishing brush and cerium oxide abrasive grains, and a work-affected layer (scratches) on the inner peripheral side surface portion and inner peripheral chamfered portion Etc.) and the inner peripheral end face is polished so as to be a mirror surface (inner peripheral end face polishing step). The glass substrate subjected to the inner peripheral end surface polishing removes the abrasive grains.

  After processing the end face of the glass substrate, the upper and lower main planes of the glass substrate are lapped using a fixed grain tool containing diamond abrasive grains and a grinding liquid, and cleaned.

  Next, using a polishing liquid containing a hard urethane polishing pad and cerium oxide abrasive grains as a polishing tool, a 22B-type double-side polishing apparatus (product name: DSM22B-6PV-4MH manufactured by Speedfam Co., Ltd.) Was ground to remove cerium oxide.

  The glass substrate after the primary polishing is a 22B double-sided polishing using a polishing pad containing a soft urethane polishing pad as a polishing tool and a cerium oxide abrasive having an average particle size smaller than that of the cerium oxide abrasive. The upper and lower main planes were secondarily polished by an apparatus, and cerium oxide was removed by washing.

  The glass substrate after the secondary polishing is subjected to tertiary polishing (finish polishing). Using a polishing liquid containing a soft urethane polishing pad and colloidal silica as a polishing tool for tertiary polishing, the upper and lower main planes were polished by a double-side polishing apparatus.

  The glass substrate after final polishing (tertiary polishing) is subjected to scrub cleaning, ultrasonic cleaning immersed in a detergent solution, ultrasonic cleaning immersed in pure water (precision cleaning), and isopropyl alcohol vapor. Dried.

  For each glass substrate obtained, (1) evaluation of load application time dependence before load removal of flatness immediately after load removal, (2) evaluation of elapsed time dependence after load release of flatness after load removal, (3) Pseudoelastic deformation amounts A to C were evaluated.

  First, with respect to the glass substrates used in the magnetic recording media of Examples 1, 8, and 9, (1) The load application time dependency of the flatness immediately after the load removal before the load removal was evaluated, and the results are shown in Table 2. . Moreover, what made the result of Table 2 into a graph is shown in FIG. 5, FIG. FIG. 6 shows the load application time shown on the horizontal axis as a logarithmic axis.

表２、図５、図６の結果から明らかなように、例８、例９の磁気記録媒体で用いるガラス基板については、荷重を加えることにより平坦度が大きくなり、１０時間を越えた辺りで平坦度の変化が飽和することが確認できた。この場合、荷重を加えはじめてから２４時間における平坦度の変化率は、例８のガラス基板は８７０％、例９のガラス基板は３３００％であった。

As is apparent from the results of Table 2, FIG. 5, and FIG. 6, the glass substrates used in the magnetic recording media of Examples 8 and 9 increased in flatness by applying a load, and exceeded about 10 hours. It was confirmed that the change in flatness was saturated. In this case, the rate of change in flatness after 24 hours from the start of applying the load was 870% for the glass substrate of Example 8 and 3300% for the glass substrate of Example 9.

  On the other hand, for the glass substrate used in the magnetic recording medium of Example 1 as an example, the flatness hardly changes even when a load is applied, and the change rate of the flatness in 24 hours after the load is applied is 20%. It was confirmed that.

From these results, it was confirmed that the change in flatness with respect to the load differs depending on the composition of the glass substrate. In particular, for the glass substrate of Example 1 containing 7.6 mol% of B ₂ O ₃ , it was confirmed that the change in flatness was small as described above.

  Next, since the dependence of the flatness after load removal on the elapsed time after the load release was evaluated for the glass substrates of Examples 1 to 10, the results are shown in Table 3. Moreover, what made the result of Table 3 into a graph is shown in FIG. 7, FIG. FIG. 8 is an enlarged view of a region having a small flatness in FIG.

  (2) The evaluation of the dependence of the flatness after removing the load on the elapsed time after release of the load is as follows. After the load was applied for 24 hours, the load was removed and the change in the flatness after removing the load was evaluated. is there.

表３の結果によると、例１〜例７の磁気記録媒体で用いるガラス基板についてはいずれも２４時間荷重を加えた直後の平坦度が小さく、荷重を除去した後、時間の経過に関わらず平坦度の変化は殆ど見られなかった。

According to the results in Table 3, the glass substrates used in the magnetic recording media of Examples 1 to 7 all have a small flatness immediately after applying a load for 24 hours, and are flat regardless of the passage of time after the load is removed. Little change in degree was seen.

  In contrast, the glass substrates used in the magnetic recording media of Examples 8 to 10 have higher flatness immediately after the load is applied for 24 hours, and the flatness gradually decreases with the passage of time after the load is removed. It was confirmed that

  From these results, it was confirmed that the change in flatness when a load was applied was different depending on the glass composition of the glass substrate. Moreover, it has confirmed that the displacement by the restoring force after removing a load also changes with glass compositions of a glass substrate.

  In particular, in the case of the glass substrate used in the magnetic recording media of Examples 8 to 10, it was confirmed that the change in flatness when a load was applied was large. For this reason, when these glass substrates are used as magnetic recording media, for example, if servo information is written 5 hours after the load is removed, the position of the servo information will change greatly thereafter, causing an error. .

  Table 4 shows the evaluation results of the pseudoelastic deformation amounts A to C and the calculation results of specific elasticity for the glass substrates of Examples 1 to 10.

表４によると、例１〜７の磁気記録媒体に用いるガラス基板は比弾性が２９ＭＮｍ／ｋｇ以上と高くなっていることが確認できる。中でもＢ_２Ｏ_３の含有量が２．０ｍｏｌ％未満である例５、例６のガラス基板については比弾性が３４ＭＮｍ／ｋｇと特に高くなっていることが確認できた。また、Ｂ_２Ｏ_３を含有していないが、アルカリ金属酸化物の含有量が０ｍｏｌ％である例７のガラス基板についても比弾性が３４ＭＮｍ／ｋｇと特に高くなっていることが確認できた。比弾性が高い値をとることにより、磁気記録媒体とした場合に、磁気記録媒体を高速回転させた場合でも、フラッタリングの発生を抑制し、磁気記録媒体の読み取り／書き込みエラーの発生を特に抑制することが可能になる。

According to Table 4, it can be confirmed that the glass substrate used for the magnetic recording media of Examples 1 to 7 has a high specific elasticity of 29 MNm / kg or more. In particular, it was confirmed that the specific elasticity of the glass substrates of Examples 5 and 6 in which the content of B ₂ O ₃ was less than 2.0 mol% was as high as 34 MNm / kg. Moreover, it was confirmed that the specific elasticity of the glass substrate of Example 7 which does not contain B ₂ O ₃ but has an alkali metal oxide content of 0 mol% is particularly high at 34 MNm / kg. By taking a high value of specific elasticity, even when a magnetic recording medium is used, even when the magnetic recording medium is rotated at a high speed, fluttering is suppressed and reading / writing errors of the magnetic recording medium are particularly suppressed. It becomes possible to do.

  The pseudoelastic deformation amount A, which shows the absolute value of the difference between the flatness before applying the load and the flatness after 5 hours have passed since the load was added and removed, is the magnetic recording medium of Examples 1-7. It was confirmed that the glass substrate used in 1 was 2.0 μm or less, which was a smaller value than the glass substrate used in the magnetic recording media of Examples 8 to 10. In particular, it was confirmed that the glass substrate used in the magnetic recording media of Examples 1 to 6 had a pseudo-elastic deformation amount A of 0.1 μm or less and a smaller value.

  Further, the pseudo-elastic deformation amount B indicating the absolute value of the difference between the flatness after 5 hours from the removal of the load and the flatness after 48 hours from the removal of the load is also used in the magnetic recording media of Examples 1 to 7. It was confirmed that all the glass substrates were 1.5 μm or less, which was a very small value compared to the glass substrates used in the magnetic recording media of Examples 8 to 10. Also in this case, the pseudoelastic deformation amount B of the glass substrate used in the magnetic recording media of Examples 1 to 6 was 0.1 μm or less, and it was confirmed that it was particularly small.

  Further, the pseudoelastic deformation amount C indicating the flatness after the lapse of 5 hours after removing the load is 2.5 μm or less for the glass substrate used in the magnetic recording media of Examples 1 to 7, and the magnetic recording media of Examples 8 to 10 It was confirmed that the value was smaller than that of the glass substrate used. Further, the glass substrate used in the magnetic recording media of Examples 1 to 6 had a particularly small value of 1.0 μm or less.

Although the time for applying the load is different, (2) the glass substrate used in the magnetic recording media of Examples 1 to 7 is immediately after the removal of the load, as described in the evaluation of the dependence of the flatness after the load removal on the elapsed time after the release of the load. The flatness is small, and the change in flatness after removing the load is also small. For this reason, it is considered that the amount of pseudoelastic deformation is also reduced as described above.
(Manufacture of magnetic recording media)
Next, an underlayer, a magnetic layer, a protective layer, and a lubricating layer were sequentially provided on each glass substrate used in the magnetic recording media of Examples 1 to 10, and 100 magnetic recording media of Examples 1 to 10 were manufactured. .

The specific procedure will be described. On the surface of the glass substrate for each magnetic recording medium of Examples 1 to 10, using an in-line type sputtering apparatus, a NiFe layer as a soft magnetic underlayer, a Ru layer as a nonmagnetic intermediate layer, a perpendicular layer A CoCrPtSiO ₂ granular structure layer was sequentially laminated as a magnetic recording layer. Next, a diamond-like carbon film was formed as a protective layer by a CVD method. Thereafter, a lubricating film having perfluoropolyether was formed by a dip method to obtain a magnetic recording medium.

  Each of the obtained magnetic recording media was stored in a shipping cassette (manufactured by Entegris), vacuum packaged in an Al laminate bag at a vacuum degree of 400 mmHg, and left for 48 hours.

  After 48 hours, the package was opened, the magnetic recording medium was taken out, assembled into an HDD device, and servo information was written under conditions corresponding to 254 kTPI. Servo information was written 5 hours after opening. An HDD read / write test was performed 43 hours after servo information writing (48 hours after opening).

  As a result of the read / write test, no error occurred in any of the 100 magnetic recording media subjected to the test in the magnetic recording media of Examples 1 to 7, but in the magnetic recording media of Examples 8 to 10. An error of about 1% was concentrated on the outer periphery.

  The cause of the increased error occurrence rate in the magnetic recording media of Examples 8 to 10 is considered as follows.

  The magnetic recording medium held in the shipping cassette is deformed by the pressure from the atmosphere by vacuum packaging, and after opening, gradually returns to the original shape according to the characteristics of the glass substrate contained in each magnetic recording medium. However, in Examples 8 to 10, as apparent from the evaluation of the glass substrate, the shape of the glass substrate gradually changes when the load is removed after the load is applied. For this reason, the shape of the glass substrate is still changing when the servo information is written, and the shape further changes after the servo information is written. Therefore, it is considered that the servo information is misaligned during the read / write test after writing the servo information.

  Since the change in shape is more noticeable at the outer periphery, it is presumed that errors are concentrated on the outer periphery depending on the glass substrate.

  The glass substrates used in the magnetic recording media of Examples 8 and 9 have higher specific elasticity than the glass substrates used in Examples 1 to 4 and can suppress fluttering. Therefore, according to the conventional magnetic recording media, In addition, the occurrence of errors should be suppressed in the mounting evaluation of the magnetic recording medium. However, the error rate was high as described above.

  This is because, in spite of buckling deformation or bending deformation of the glass substrate in the manufacturing processes of the magnetic recording media of Examples 8 and 9, the selection of the glass composition of the glass substrate was not appropriate, so that after the deformation, This is probably because the servo information was written in the process of returning to the shape.

From these results, in order to sufficiently suppress the occurrence of errors in the magnetic recording medium, it is not sufficient to use a glass substrate having a high specific elasticity as a glass substrate as conventionally considered, and B ₂ O ₃ It can be seen that it is necessary to select a glass substrate having a predetermined content within a predetermined range or a glass substrate having an alkali metal oxide content equal to or lower than a predetermined amount.
[Experiment 2]
In this example, magnetic recording media of Examples 11 to 24 were prepared and evaluated. As shown in Table 5, the magnetic recording media of Examples 11 to 24 differ in the glass composition of the glass substrate included in the magnetic recording medium. Examples 11 to 21 are examples, and examples 22 to 24 are comparative examples.
(Manufacture of glass substrates)
For each glass substrate, a glass substrate having the glass composition of Examples 11 to 24 in Table 5 is used to produce a donut-shaped glass substrate having a diameter of 65 mm, a plate thickness of 0.635 mm, and a 20 mm circular hole in the center. did. Since the glass substrate was manufactured in the same manner as in Experimental Example 1, the description thereof was omitted.

In Table 5, RO represents the content of alkaline earth metal oxide in the glass composition of the glass base substrate, and R ₂ O represents the content of alkali metal oxide in the glass composition of the glass base substrate. In the table, “-” means that such a component is not included, that is, the content of the component is 0.

  For each of the obtained glass substrates, the pseudoelastic deformation amount A was evaluated in the same manner as in Experimental Example 1.

  The results are shown in Table 5.

表５に示した結果によるとアルカリ金属酸化物を１種類含み、アルカリ金属酸化物の含有量が０ｍｏｌ％以上２５ｍｏｌ％以下の例１１、１３、１４、１８、１９、２１は擬弾性変形量Ａが０．６μｍ未満となっていることを確認できた。

According to the results shown in Table 5, Examples 11, 13, 14, 18, 19, and 21 containing one kind of alkali metal oxide and having an alkali metal oxide content of 0 mol% or more and 25 mol% or less are pseudoelastic deformation amounts A. Has been confirmed to be less than 0.6 μm.

Examples 12, 15-17, and 20 containing two or more kinds of alkali metal oxides and having a total content of alkali metal oxides of more than 0 mol% and 20 mol% or less have a pseudoelastic deformation amount A of 2.0 μm or less. I was able to confirm that On the other hand, it is a comparative example and contains two types of alkali metal oxides, and in Examples 22 to 24 in which the total content of alkali metal oxides exceeds 20 mol%, the pseudoelastic deformation amount A is Examples 11 to 21. It was confirmed that it was very large compared to.
(Manufacture of magnetic recording media)
Next, an underlayer, a magnetic layer, a protective layer, and a lubricating layer were sequentially provided on each glass substrate used in the magnetic recording media of Examples 11 to 24, and 100 magnetic recording media of Examples 11 to 24 were manufactured.

  Since the magnetic recording medium was manufactured by the same procedure as in Experimental Example 1, description thereof is omitted.

  The manufactured magnetic recording medium was housed in a shipping cassette (manufactured by Entegris) in the same manner as in Experimental Example 1, vacuum packed in an Al laminate bag at a vacuum degree of 400 mmHg, and left for 48 hours. After 48 hours, the package is opened, the magnetic recording medium is taken out and assembled into an HDD device, and servo information is written under conditions corresponding to 254 kTPI. Servo information writing is performed 5 hours after opening, and 43 hours after writing servo information. Later (48 hours after opening), an HDD read / write test was performed.

  When a read / write test was performed, no error occurred in any of the magnetic recording media of Examples 11 to 21, but an error of about 1% was observed in the outer peripheral portion of the magnetic recording media of Examples 22 to 24. Concentrated to occur.

  The cause of the increased error rate in the magnetic recording media of Examples 22 to 24 can be considered as follows.

  The magnetic recording medium held in the shipping cassette is deformed by at least one of buckling deformation and bending deformation due to pressure from the atmosphere by vacuum packaging, and after opening, the characteristics of the glass substrate contained in each magnetic recording medium Gradually return to the original shape. However, in Examples 22 to 24, as is apparent from the evaluation of the glass substrate, the pseudoelastic deformation amount A is larger than that of Examples 11 to 21. For this reason, the shape of the glass substrate is still changing when servo information is written, and the shape changes further after writing servo information, and the servo information is misaligned during the read / write test after writing servo information. Conceivable.

  And since the change of a shape is so remarkable that it is outer periphery, it is guessed that the error concentrated on the outer peripheral part depending on the glass substrate.

43 Glass substrate 44 Both ends 45 Load

Claims (7)

A glass substrate for a magnetic recording medium,
Supporting both ends in the diameter direction of the glass substrate from the lower surface side, removing the load after applying the load to the upper surface of the central portion of the glass substrate for 48 hours, flatness at the time of 5 hours after removing the load,
When the absolute value of the difference from the flatness before applying a load is the pseudoelastic deformation amount A,
The pseudoelastic deformation amount A is 2.0 μm or less,
The glass of the glass substrate contains 5 mol% or more of Al ₂ O ₃ ,
The content of B ₂ O ₃ is 0.1 mol% or more and 15 mol% or less, or the alkali metal oxide is contained in one or less, and the content of alkali metal oxide is 0 mol% or more and 25 mol% or less, or alkali metal oxidation A glass substrate for a magnetic recording medium, containing two or more kinds of substances and having an alkali metal oxide content of more than 0 mol% and no more than 20 mol%. Supporting both ends in the diameter direction of the glass substrate from the lower surface side, removing the load after applying the load to the upper surface of the central portion of the glass substrate for 48 hours, flatness at the time of 5 hours after removing the load,
When the absolute value of the difference from the flatness after 48 hours after removing the load is the pseudoelastic deformation amount B,
The glass substrate for a magnetic recording medium according to claim 1, wherein the pseudoelastic deformation amount B is 1.5 μm or less.   The both ends in the diameter direction of the glass substrate are supported from the lower surface side, the load is removed for 48 hours after the load is applied to the upper surface of the central portion of the glass substrate, and the flatness after 5 hours has elapsed after removing the load The glass substrate for a magnetic recording medium according to claim 1, wherein the pseudoelastic deformation amount C is 2.5 μm or less.   The glass substrate for a magnetic recording medium according to any one of claims 1 to 3, which is a glass substrate for a heat-assisted magnetic recording type magnetic recording medium. The glass substrate for magnetic recording media according to claim 1, wherein the glass of the glass substrate contains Al ₂ O _{3 in an amount} of 5 mol% to 20 mol%. The glass of the glass substrate is
SiO ₂ 55 mol% or more and 75 mol% or less,
Alkaline earth metal oxide 0 mol% or more and 30 mol% or less,
The glass substrate for magnetic recording media as described in any one of Claims 1-5 containing this.   A magnetic recording medium comprising a glass layer according to any one of claims 1 to 6 and a magnetic layer for a heat-assisted magnetic recording system.

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