JP6004129B1 - Glass substrate for magnetic recording medium, magnetic recording medium - Google Patents

Abstract

An object of the present invention is to provide a glass substrate for a magnetic recording medium capable of suppressing deterioration of flatness when heat treatment is performed. A glass substrate for a magnetic recording medium comprising a glass material having an internal friction of 0.01 or less at 350 ° C. or less is provided. (However, the internal friction means that a test body made of the glass material processed into a plate shape having a length of 60 mm, a width of 5 mm, and a plate thickness of 0.5 mm is disposed along the length direction, and the support interval is 50 mm. Supporting from the lower surface side by two supporting members, pressing and releasing the pressure so that the center part of the test body is further 120 μm in amplitude and 1 Hz in frequency with a static load of 1 N applied downward. It is calculated based on the change of the stress measured by repeating the above.) [Selection] Fig. 3

Description

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

  In a magnetic recording apparatus, a magnetic layer or the like is formed on a magnetic recording medium substrate, and information can be recorded using the magnetic layer.

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

  In recent years, magnetic recording media using an energy-assisted magnetic recording system, that is, energy-assisted magnetic recording media, have been studied in order to meet the increasing demand for higher recording density. The energy-assisted magnetic recording medium can also have a configuration in which a glass substrate for a magnetic recording medium is used as a substrate and a magnetic layer or the like is disposed on the main surface of the glass substrate for a magnetic recording medium.

  However, in an energy-assisted magnetic recording medium, an ordered alloy having a large magnetic anisotropy coefficient Ku (hereinafter also referred to as “high Ku”) is used as the magnetic material of the magnetic layer. For this reason, in order to achieve a high Ku by increasing the degree of ordering (regularity), the base material including the glass substrate for magnetic recording medium is formed at 600 ° C. at the time of film formation, before film formation, or after film formation. Heat treatment is often performed at the above high temperature. In particular, in order to increase the degree of order, a high temperature exceeding 650 ° C. and close to 700 ° C. may be required.

  When the magnetic layer is formed, heat treatment at a high temperature is performed before or after the film formation. For example, in a FePt alloy suitable as a magnetic material of the magnetic layer of the energy-assisted magnetic recording medium, the heat treatment temperature is increased. This is also because the coercive force can be increased.

  Thus, in the process of manufacturing a magnetic recording medium, the glass substrate for magnetic recording medium may be heat-treated at a high temperature, so that the glass substrate for magnetic recording medium is also required to have heat resistance.

For example, according to Patent Document 1, in order to form a magnetic recording layer made of a high Ku magnetic material, the glass substrate is required to have high heat resistance that can withstand high temperature processing, that is, high glass transition temperature. ing. In Patent Document 1, the glass transition temperature is 600 ° C. or higher, the average linear expansion coefficient at 100 to 300 ° C. is 70 × 10 ⁻⁷ / ° C. or higher, the Young's modulus is 81 GPa or higher, the specific modulus is 30 MNm / kg or higher, And the glass substrate for magnetic recording media which consists of glass whose fracture toughness value is 0.9 Mpa * m < ^1/2 > or more is disclosed.

International Publication No. 2012/088664 JP 2001-266329 A JP 2012-126625 A

However, even when a glass substrate for a magnetic recording medium made of a glass material having a glass transition temperature higher than the heat treatment temperature is used, the glass substrate for the magnetic recording medium is warped during the heat treatment, and the glass substrate for the magnetic recording medium In some cases, the flatness increased and the flatness deteriorated.
When the flatness of the glass substrate for a magnetic recording medium increases in the manufacturing process of the magnetic recording medium, the flatness of the obtained magnetic recording medium also increases, and depending on the flatness of the magnetic recording medium, when incorporated in a magnetic recording device, There is a risk of contact between the magnetic head and the magnetic recording medium. For this reason, the glass substrate for magnetic recording media is required to suppress deterioration of flatness due to heat treatment such as when a magnetic layer is formed.

  In view of the above-described problems of the related art, an object of one aspect of the present invention is to provide a glass substrate for a magnetic recording medium that can suppress deterioration of flatness when heat treatment is performed.

In order to solve the above problems, according to one aspect of the present invention, there is provided a glass substrate for a magnetic recording medium made of a glass material having an internal friction of not more than 0.01 at 350 ° C.
(However, the internal friction is
A test body made of the glass material processed into a plate shape having a length of 60 mm, a width of 5 mm, and a plate thickness of 0.5 mm,
It is arranged along the length direction and is supported from the lower surface side by two support members having a support interval of 50 mm,
In a state where a static load of 1 N is applied downward to the central portion of the test body, the stress measured by repeatedly pressing and releasing the pressure so that the amplitude is 120 μm and the frequency is 1 Hz. Calculated based on change. )

  According to one aspect of the glass substrate for a magnetic recording medium of the present invention, it is possible to provide a glass substrate for a magnetic recording medium that can suppress deterioration in flatness when heat treatment is performed.

Explanatory drawing of a three-point bending measuring jig. Explanatory drawing of the glass substrate for magnetic recording media which concerns on embodiment of this invention. Explanatory drawing of the change of the internal friction tan-delta with respect to the temperature of the glass A-glass E used in the experiment example of this invention.

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.
(Glass substrate for magnetic recording media)
One structural example of the glass substrate for magnetic recording media of this embodiment is demonstrated.

  The glass substrate for magnetic recording media of this embodiment can be a glass substrate for magnetic recording media made of a glass material having an internal friction of 0.01 or less at 350 ° C. or less.

  The internal friction can be calculated as follows.

  A test body made of the above glass material processed into a plate shape having a length of 60 mm, a width of 5 mm, and a plate thickness of 0.5 mm is arranged along the length direction of the test body, and is supported by two support members having a support interval of 50 mm. Support from the bottom side. The stress measured by repeatedly performing pressing and releasing the pressure so that the amplitude is 120 μm and the frequency is 1 Hz in a state where a static load of 1 N is applied downward to the central portion of the specimen. It can be calculated based on the change of.

  A glass substrate for a magnetic recording medium (hereinafter, also simply referred to as “glass substrate”) generally has a disc shape having an opening at the center, and a magnetic layer or the like is formed on the main surface thereof. Thus, a magnetic recording medium can be obtained.

  Then, when manufacturing an energy-assisted magnetic recording medium that is currently being studied for practical use, as described above, the film is formed at 600 ° C. with respect to the substrate including the glass substrate at the time of forming the magnetic layer. As described above, the heat treatment is performed at a high temperature of, for example, 600 ° C. or higher, or 650 ° C. or higher and 700 ° C. or lower. For this reason, the glass substrate is also required to have heat resistance to a high temperature of 600 ° C. or higher. Until now, focusing on the glass transition point of the glass material of the glass substrate, the glass transition temperature is higher than the heat treatment temperature to be performed. A glass substrate made of a glass material is employed. This is because when heated at a temperature lower than the glass transition point, the glass of the glass substrate does not exhibit fluidity, and it is considered that the glass substrate does not undergo deformation such as warping.

  However, although a glass material having a glass transition temperature higher than the heat treatment temperature to be used is used, the glass substrate may be warped during the heat treatment, and the flatness of the glass substrate after the heat treatment may deteriorate. It was.

  Accordingly, the inventors of the present invention have studied a glass substrate that can suppress deterioration in flatness when heat treatment is performed at a high temperature of 600 ° C. or higher when manufacturing an energy-assisted magnetic recording medium. And it has been found that the deterioration of flatness when heat treatment is performed at a high temperature of 600 ° C. or higher can be suppressed by using a glass material having an internal friction tan δ at 350 ° C. or lower of 0.01 or lower for the glass substrate. Was completed.

  The internal friction tan δ indicates the tangent of the phase shift of the stress response when strain is applied to the specimen of the glass material that is the measurement sample. The change of the internal friction tan δ with respect to the temperature is, for example, dynamic viscoelasticity measurement It can be measured by a device (DMA: Dynamic Mechanical Analysis).

  Here, a method for measuring a change in internal friction tan δ with respect to temperature using a dynamic viscoelasticity measuring apparatus will be described with reference to FIG. The change of the internal friction tan δ with respect to temperature can be carried out by setting a plate-like test body 11 made of, for example, a glass material on a three-point bending measuring jig provided with support members 12A and 12B and a pressing member 13.

  The plate-like test body 11 can have a length l of 60 mm, a width (perpendicular to the plane of FIG. 1) of 5 mm, and a plate thickness d of 0.5 mm, for example. When the plate-shaped test body 11 is set on the three-point bending measurement jig, the support members 12A and 12B have a mutual distance, that is, a support interval L of 50 mm along the length direction of the test body. Can be placed.

  As shown in FIG. 1, a plate-shaped glass material test body 11 set in a three-point bending measuring jig can support both ends from the lower surface side by support members 12 </ b> A and 12 </ b> B. And the center part of the upper surface of the test body 11 can be made into the state applied with the static load of 1N downward by the press member 13. FIG. At this time, it is preferable that the pressing member 13 is configured to simultaneously press the central portion between the support member 12A and the support member 12B.

  Then, with the static load applied to the test body 11, while the temperature of the test body 11 is increased, the center portion of the upper surface of the test body 11 is periodically pressed so that the amplitude is 120 μm and the frequency is 1 Hz. 13, the downward pressing and the releasing of the pressing can be repeatedly performed. Thus, by pressing the test body 11 with the pressing member 13, the test body 11 can be strained, the stress when the strain is applied can be measured, and the internal friction tan δ can be calculated from the measurement result.

  As a general internal friction measurement method, a resonance method or a forced vibration method is known. In the resonance method, an attenuation method, a half-width method, or the like is used, and measurement can be performed with a simple mechanism, which is widely used. For example, in Patent Literature 2 and Patent Literature 3, internal friction measurement is performed by a resonance method. However, if the internal friction measurement using the resonance method is performed at a high temperature, false vibration is likely to occur, and correct measurement cannot be performed. In the resonance method, the frequency is fixed at the resonance point, and the resonance frequency depends on the sample shape, and it is difficult to evaluate the same condition between different samples.

  On the other hand, a phase difference method is used for the forced vibration method, and a slight displacement can be detected by measuring at a frequency of approximately 10 Hz or less. However, it is difficult to perform measurement with sufficient accuracy on a material having high rigidity, and care is required for measurement conditions. Moreover, since internal friction has measurement frequency dependence, it evaluated by fixing a frequency to 1 Hz in the forced vibration method here.

  In addition, the frequency at the time of pressing the test body 11 with the press member 13 has selected 1 Hz as a suitable frequency in order to evaluate the slow deformation | transformation of the test body 11 at the time of heating. In the forced vibration method in the present embodiment, a frequency of 1 Hz is most preferable, but an arbitrary frequency can be selected from a range of 0.1 Hz to 100 Hz.

  The glass material has a network former (network forming component) and a network modifier (network modifying component) that is not incorporated in the network former. When the glass material is heated, even if the glass material at a temperature lower than the glass transition point is not flowing, for example, a part of the network modifier in the glass material can move in the material. There are cases where a microstructural change occurs in the glass material at a temperature of. When a microscopic structural change occurs in the glass material when the glass material is heated, the internal friction tan δ exhibits a peak at the temperature at which the change has occurred. Therefore, the change in the internal friction tan δ with respect to the temperature of the glass material should be measured. Thus, it is possible to detect a micro structural change in the glass material.

  The inventors of the present invention pay attention to the change in the micro structure in the glass material during the temperature rising process for causing the warpage and the like to deteriorate when the heat treatment is performed on the glass substrate. did. And about the glass substrate of various glass materials, the change of internal friction tan-delta with respect to temperature was measured, and the relationship with the generation | occurrence | production of the curvature at the time of heat-processing at 600 degreeC or more high temperature, for example, 600 degreeC or more and 700 degrees C or less was examined. .

  As a result, a peak of internal friction tan δ is generated in a temperature region of 350 ° C. or lower, and the larger the peak, the easier the warpage occurs when heat treatment is performed at a high temperature of 600 ° C. or higher, for example, 600 ° C. or higher and 700 ° C. or lower. Was confirmed.

  The direct causal relationship between the peak and magnitude of the internal friction tan δ generated in the temperature region of 350 ° C. or lower and the warpage of the glass substrate when heat treatment is performed at a high temperature of 600 ° C. or higher is not clear.

  However, when it has a peak of internal friction tan δ at 350 ° C. or less, it is considered that a change in the micro structure in the glass material, for example, a change in which a specific network modifier becomes easy to move in the glass material. And it is presumed that the greater the degree of change in the micro structure, the easier the glass substrate is deformed in a temperature region of 600 ° C. or higher.

  On the other hand, in the case of a glass substrate made of a glass material having an internal friction tan δ of 0.01 or less at 350 ° C. or less, it is considered that there is almost no change in the micro structure in a temperature region of 350 ° C. or less. For this reason, it is considered that deformation such as warpage of the glass substrate can be suppressed during heat treatment at 600 ° C. or higher.

  According to the study of the inventors of the present invention, the smaller the internal friction tan δ of the glass material at 350 ° C. or lower, the flatter the glass substrate using the glass material when the heat treatment is performed at 600 ° C. and 700 ° C. The amount of change in the degree can be suppressed. For this reason, in order to use for the heat processing which exceeds 650 degreeC and close to 700 degreeC in order to obtain a magnetic recording medium with a higher degree of order and high coercive force, the glass substrate for magnetic recording media of this embodiment is at 350 degrees C or less. More preferably, the internal friction tan δ is made of a glass material having 0.004 or less.

  As described above, the glass substrate of the present embodiment has an internal friction tan δ over the entire range of 350 ° C. or lower, that is, over a range of, for example, absolute zero (−273 ° C.) or higher and 350 ° C. or lower. It is preferable that However, since the internal friction tan δ tends to decrease or not change at a temperature lower than −50 ° C., for example, if the internal friction tan δ satisfies the range described so far over a range of −50 ° C. to 350 ° C. Good.

Moreover, since the one where the internal friction tan-delta in 350 degrees C or less of the glass material used for the glass substrate of this embodiment is smaller is preferable, a lower limit is not specifically limited. For this reason, the lower limit value of the internal friction tan δ at 350 ° C. or less of the glass material used for the glass substrate of the present embodiment can be set to 10 ⁻⁴ or more, for example.

  As described above, the glass substrate of the present embodiment can be made of a glass material having an internal friction tan δ of 0.01 or less at 350 ° C. or less. According to such a glass material, at least 350 ° C. or less, Changes in the structure can be suppressed. That is, for example, when the glass substrate is heated, the movement and diffusion of the network modifier included in the glass material can be suppressed. For this reason, when a magnetic layer or the like is formed on a glass substrate in order to obtain a magnetic recording medium, the ionic species of the network modifier in the glass material diffuses into the magnetic layer or the like and adversely affects the magnetic film or the like. Can also be suppressed.

  Next, the shape of the glass substrate of this embodiment is demonstrated using FIG.

  FIG. 2 schematically shows a perspective sectional view of the glass substrate of the present embodiment. FIG. 2 is a perspective cross-sectional view including a cross section in a plane passing through the center of the glass substrate 20 and perpendicular to the main surfaces 221 and 222. That is, FIG. 2 shows a half of the glass substrate of this embodiment and a cross-sectional view.

  As can be seen from FIG. 2, the glass substrate 20 has a circular outer periphery and can have a disk shape with an opening at the center. The opening 21 is preferably formed so as to be concentric with the outer circumference of the glass substrate 20. That is, the glass substrate 20 can have a donut shape.

  The upper and lower surfaces are main surfaces 221 and 222. Moreover, the glass substrate 20 has the outer peripheral end surface 23 located in an outer periphery, and the inner peripheral end surface 24 located in an inner periphery.

  The outer peripheral end surface 23 and the inner peripheral end surface 24 can have chamfered portions on the main surfaces 221 and 222 side, respectively. That is, the outer peripheral end surface 23 and the inner peripheral end surface 24 can each have a pair of chamfered portions. Specifically, the outer peripheral end surface 23 can have outer peripheral chamfered portions 231 and 233, and the inner peripheral end surface 24 can have inner peripheral chamfered portions 241 and 243, respectively.

  Further, a side surface portion can be formed between the chamfered portions, the outer peripheral end surface 23 can have the outer peripheral side surface portion 232, and the inner peripheral end surface 24 can have the inner peripheral side surface portion 242. The outer peripheral side surface portion 232 and the inner peripheral side surface portion 242 can be formed so as to be substantially perpendicular to the main surfaces 221 and 222, respectively.

  The size of the glass substrate is not particularly limited, and can be arbitrarily selected according to the specifications required for the glass substrate. The diameter D of the glass substrate 20 can be a size according to specifications required for the glass substrate, such as 48 mm, 65 mm, or 95 mm or more.

  However, according to the glass substrate of the present embodiment, deterioration of flatness can be suppressed even when heat treatment is performed at a high temperature of 600 ° C. or higher. And, as the diameter D of the glass substrate increases, the flatness is likely to deteriorate when heat treatment is performed, so that a particularly high effect can be exhibited in a glass substrate having a long diameter D. For this reason, it is preferable that the diameter D of the glass substrate of this embodiment is 95 mm or more.

  In addition, although the upper limit of the diameter D of the glass substrate 20 is not specifically limited, For example, it can be 130 mm or less.

  Further, although the thickness of the glass substrate 20, that is, the plate thickness T is not particularly limited, the flatness is likely to deteriorate when heat treatment is performed as the plate thickness T of the glass substrate is reduced. A particularly high effect can be exhibited in a glass substrate having a thin plate thickness T. For this reason, it is preferable that the plate | board thickness T of the glass substrate of this embodiment is 0.635 mm or less.

  In addition, the lower limit value of the thickness T of the glass substrate 20 is not particularly limited, but can be set to, for example, 0.38 mm or more in consideration of productivity and the like.

  Moreover, about the glass substrate of this embodiment, it is preferable that flatness is 5 micrometers or less before heat processing of 600 degreeC or more, and it is preferable that it is 3 micrometers or less. This is because the flatness of the obtained magnetic recording medium can be reduced as the flatness of the glass substrate before the heat treatment decreases, even if the flatness deteriorates due to the heat treatment.

  The flatness can be evaluated using, for example, an interference flat tester manufactured by NIDEK.

  As described above, when manufacturing the energy-assisted magnetic recording medium, the base material including the glass substrate is heat-treated at a high temperature of 600 ° C. or more when forming the magnetic layer. By using the glass material described above, the amount of change in flatness before and after heat treatment can be reduced.

  Specifically, according to the glass substrate of the present embodiment, for example, the amount of change in flatness when heat-treated at 600 ° C. for 10 minutes can be set to 2.0 μm or less, more preferably 1.5 μm or less. can do.

  Further, according to the glass substrate of the present embodiment, for example, the amount of change in flatness when heat-treated at 700 ° C. for 10 minutes can be set to 26.0 μm or less, more preferably 6.0 μm or less. be able to.

  In any of the above cases, the heat treatment is performed in a nitrogen atmosphere, and the flatness indicates a value measured after cooling to room temperature after the heat treatment.

  The glass substrate of this embodiment can suppress deterioration of flatness even when heat-treated at a high temperature of 600 ° C. or higher as described above. For this reason, it is preferable to use as a glass substrate for energy-assisted magnetic recording media in which a base material including a glass substrate is heat-treated at a high temperature in the production process. However, the application is not limited to the energy-assisted magnetic recording medium, and can naturally be used as a glass substrate for various magnetic recording media.

  Since the glass substrate for a magnetic recording medium of the present embodiment described above is made of a glass material having an internal friction tan δ at 350 ° C. or lower of 0.01 or less, the change in flatness is reduced even when heat-treated at a high temperature, Deterioration of flatness can be suppressed. Therefore, the flatness of the magnetic recording medium including the glass substrate for magnetic recording medium of the present embodiment can be reduced. When the magnetic recording medium is applied to a magnetic recording apparatus, the flying stability of the recording / reproducing head can be ensured.

  Next, a structural example of the method for manufacturing the glass substrate for a magnetic recording medium of the present embodiment described so far (hereinafter also simply referred to as “glass substrate manufacturing method”) will be briefly described.

  In addition, according to the manufacturing method of the glass substrate of this embodiment, the glass substrate for magnetic recording media as stated above can be manufactured. For this reason, some description is abbreviate | omitted about the part which overlaps with the content demonstrated in the glass substrate for magnetic recording media.

The manufacturing method of the glass substrate of this embodiment can include the following steps 1 to 5, for example.
(Step 1) A shape imparting step of processing from a glass base plate into a disc-shaped glass substrate having a circular hole in the center.
(Step 2) A chamfering step for chamfering the inner surface and the outer edge of the glass substrate.
(Step 3) 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 4) A main surface polishing step for polishing the main surface of the glass substrate.
(Step 5) A cleaning / drying step of cleaning and drying the glass substrate.

  It is not necessary to perform the said process in the order described, for example, you may perform a main surface polishing process before a shape provision process. Further, each step is not limited to one time, and can be performed any number of times according to the required glass substrate specifications. For example, the main surface polishing step may be performed after the shape imparting step, and then the chamfering step and the end surface polishing step may be performed, and then the main surface polishing step may be performed again.

  However, the glass substrate of this embodiment can be comprised from the glass material whose internal friction tan-delta in 350 degrees C or less is 0.01 or less. For this reason, for a candidate glass material, the change in internal friction tan δ with respect to temperature is measured by a dynamic viscoelasticity measuring device, and a glass material having an internal friction tan δ at 350 ° C. or lower of 0.01 or lower is selected. Is preferred. And it is preferable to use for the shape provision process the glass base plate which consists of this glass material. For this reason, the manufacturing method of the glass substrate of this embodiment uses the glass material selected in the glass material selection process which selects the glass material whose internal friction tan-delta in 350 degrees C or less is 0.01 or less, and a glass material selection process. It is preferable to further include a glass base plate manufacturing process for manufacturing the glass base plate. When the manufacturing method of the glass substrate of this embodiment has a glass material selection process and a glass base plate manufacturing process, these processes will be implemented before performing process 1-process 5.

  Here, the shape imparting step of (Step 1) is a glass-shaped glass plate formed by a float method, a fusion method, a press molding method, a down draw method or a redraw method. The substrate is processed. The glass base plate used may be amorphous glass, crystallized glass, or tempered glass having a tempered layer on the surface layer of the glass substrate.

  However, as described above, a glass base plate made of a glass material having an internal friction tan δ at 350 ° C. or lower of 0.01 or lower can be used.

  In the chamfering step (step 2), the inner peripheral end surface and the outer peripheral end surface can be chamfered. By performing the chamfering process, the inner peripheral chamfered portions 241 and 243 can be formed on the inner peripheral end surface 24 and the outer peripheral chamfered portions 231 and 233 can be formed on the outer peripheral end surface 23 as described with reference to FIG.

  The end surface polishing step of (Process 3) can perform end surface polishing of the inner peripheral end surface and the outer peripheral end surface (side surface portion and chamfered portion) of the glass substrate.

  In the main surface polishing step of (Step 4), the polishing liquid is supplied to the main surface of the glass substrate having a donut shape by, for example, a double-side polishing apparatus, and the upper and lower main surfaces of the glass substrate having a donut shape can be simultaneously polished. The main surface polishing step may be only primary polishing, may be primary polishing and secondary polishing, or may be tertiary polishing after secondary polishing.

  In addition, before the main surface polishing step of (Step 4), a main surface wrap (for example, loose abrasive wrap, fixed abrasive wrap, etc.), that is, a main surface grinding step may be performed. Even when the main surface grinding step is performed, only the primary grinding may be performed, or a plurality of grinding steps such as primary grinding and secondary grinding 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. Here, the main surface lapping is a broad surface main surface polishing.

  The cleaning / drying step of (Step 5) is a step of cleaning and drying the polished glass substrate. A specific cleaning method is not particularly limited. For example, cleaning can be performed by scrub cleaning using a detergent, ultrasonic cleaning in a state immersed in a detergent solution, ultrasonic cleaning in a state immersed in pure water, or the like. Moreover, it does not specifically limit about the drying method, For example, it can dry with isopropyl alcohol vapor | steam.

  Further, glass substrate cleaning (inter-process cleaning) and glass substrate surface etching (inter-process etching) may be performed between the above steps. Further, when high mechanical strength is required for the glass substrate, the reinforcing step (for example, chemical strengthening step) for forming a reinforcing layer on the surface layer of the glass substrate is performed before or after the polishing step mentioned in steps 3 and 4, Or you may implement between grinding | polishing processes.

  The glass substrate described above can be produced by the method for producing a glass substrate including the steps described above.

And the glass substrate obtained by the manufacturing method containing each said process can be used as a magnetic recording medium by further performing the process of forming thin films, such as a magnetic layer, on the main surface.
[Magnetic recording medium]
Next, a configuration example of the magnetic recording medium of this embodiment will be described.

  The magnetic recording medium of this embodiment can include the glass substrate for magnetic recording medium described above.

  As long as the magnetic recording medium of the present embodiment includes the above-described glass substrate for a magnetic recording medium, the recording method and the like are not particularly limited. For example, various types such as the energy-assisted magnetic recording medium described above can be used. It can be a magnetic recording medium. Here, an energy-assisted magnetic recording medium will be described as an example.

  The magnetic recording medium of the present embodiment is not limited in its configuration, but can have, for example, an adhesion layer, an underlayer, a seed layer, a magnetic recording layer, a protective layer on the surface of the glass substrate for magnetic recording medium, These layers can be laminated | stacked on the glass substrate in the above-mentioned order, for example. Moreover, it can replace with the above-mentioned layer, or can also provide arbitrary layers in addition to the above-mentioned layer.

  A configuration example of each layer will be described below.

  The adhesion layer can be provided to enhance the adhesion layer between the layer formed on the adhesion layer and the layer formed below the adhesion layer. As a material for forming the adhesion layer, for example, one or more kinds of metals selected from Ni, W, Ta, Cr, and Ru can be included, and an alloy including a metal selected from such a metal group can also be included. .

  The adhesion layer can be composed of one layer, but it can also be a laminated structure of two or more layers.

  Also, a soft magnetic backing layer can be arbitrarily provided between the glass substrate and the magnetic recording layer, for example.

  The soft magnetic underlayer can improve the recording / reproducing characteristics of the magnetic recording medium by controlling the magnetic flux from the magnetic head. The material for forming the soft magnetic backing layer is not particularly limited, but for example, crystalline materials such as NiFe alloy, Sendust (FeSiAl) alloy, CoFe alloy, microcrystalline materials such as FeTaC, CoFeNi, CoNiP, CoZrNb, CoTaZr, etc. An amorphous material containing a Co alloy can be preferably used.

  The thickness of the soft magnetic backing layer is not particularly limited, but can be selected according to, for example, the structure and characteristics of a magnetic head used for magnetic recording. When a soft magnetic backing layer is formed by continuous film formation with other layers, the soft magnetic backing layer preferably has a thickness of 10 nm to 500 nm.

  In addition, a heat sink layer can be optionally provided. The heat sink layer can effectively absorb excess heat of the magnetic recording layer generated during energy assist / magnetic recording. The heat sink layer is preferably formed using a material having high thermal conductivity and specific heat capacity. Specifically, for example, Cu alone, Ag alone, Au alone, or an alloy material containing one or more kinds of metals selected from the metal group as a main component can be used.

  Here, including as a main component indicates that the content ratio of the metal in the material is 50 wt% or more.

  The heat sink layer can also be formed using an Al—Si alloy, a Cu—B alloy, or the like from the viewpoint of strength and the like.

  In addition, a heat sink layer is formed using Sendust (FeSiAl) alloy, soft magnetic CoFe alloy, etc., and the vertical magnetic field generated by the head, which is the function of the soft magnetic backing layer, is concentrated on the magnetic recording layer. It can also be granted.

  The film thickness of the heat sink layer is not particularly limited, and can be selected according to, for example, the amount of heat and heat distribution during energy assisted magnetic recording, the layer configuration of the magnetic recording medium, the thickness of each component layer, and the like. . The film thickness of the heat sink layer is preferably 10 nm or more and 100 nm or less, for example.

  The method of forming the heat sink layer is not particularly limited, but can be formed by using, for example, a sputtering method. The heat sink layer can be provided, for example, between the glass substrate and the magnetic recording layer, and in consideration of characteristics required for the magnetic recording medium, between the glass substrate and the adhesion layer, or between the adhesion layer and the underlayer. Etc. can be provided.

  Next, the underlayer will be described.

  The underlayer is a layer provided to block the influence of the crystal structure of the layer formed thereunder on the crystal orientation of the magnetic recording layer and the size of the magnetic crystal grains.

  When the soft magnetic underlayer is provided as described above, the underlayer is required to be nonmagnetic in order to suppress the magnetic influence on the soft magnetic underlayer.

Examples of the material for forming the underlayer include oxides such as MgO and SrTiO ₃ , nitrides such as TiN, metals such as Cr and Ta, NiW alloys, and Cr-based alloys such as CrTi, CrZr, CrTa, and CrW Etc.

  A method for forming the underlayer is not particularly limited, and a film forming method such as a sputtering method can be used.

  Next, the seed layer will be described.

The seed layer is a layer for controlling the grain size and crystal orientation of the magnetic crystal grains of the magnetic layer in the magnetic recording layer in contact with the seed layer, while ensuring adhesion between the underlayer and the magnetic recording layer. It is. Specifically, the seed layer on the magnetic layer formed thereon, to promote the magnetic crystal grains comprising L1 ₀ type ordered alloys, the separation of a non-magnetic grain boundary containing Ti, the magnetic The coercive force Hc of the magnetic recording layer including the layer can be increased.

  The seed layer can contain, for example, Pt, and is particularly preferably composed of Pt.

  The seed layer formation method is not particularly limited, and a film formation method such as a sputtering method or a vacuum evaporation method can be used. The sputtering method includes, for example, an RF magnet sputter sputtering method.

  The conditions for forming the seed layer are not particularly limited. For example, the film formation may be performed in a state where a base material for forming the seed layer including a glass substrate is heated to a temperature of 250 ° C. or higher and 700 ° C. or lower. preferable.

  The thickness of the seed layer is not particularly limited, but is preferably, for example, 0.1 nm or more, more preferably 0.5 nm or more and 50 nm or less, and further preferably 1 nm or more and 20 nm or less.

  The magnetic recording layer can include a single magnetic layer or a plurality of magnetic layers. Hereinafter, the magnetic layer in contact with the seed layer is referred to as a first magnetic layer.

The magnetic layer can contain, for example, Fe, Pt and Ti. The first magnetic layer is specifically, for example, may have a magnetic crystal grains having an L1 ₀ type ordered alloy containing Fe and Pt, the graphene two Yura structure composed of a non-magnetic grain boundary containing Ti.

L1 ₀ type ordered alloy constituting the magnetic crystal grains can for the purpose of characteristic modulation of the magnetic crystal grains, Ni, Mn, Ag, may further comprise at least one element selected from the group consisting of Au and Cr . Desirable characteristic modulation comprises a reduction in the temperature required for ordering of the L1 ₀ type ordered alloy.

In the magnetic crystal grains, not all atoms may have a regular structure. The regularity S representing the degree of the regular structure may be greater than or equal to a predetermined value. The degree of order S can be calculated by measuring the magnetic recording medium by XRD and calculating the ratio between the measured value and the theoretical value when it is completely ordered. For L1 ₀ type ordered alloy is calculated using from ordered alloy (001) and the integrated intensity of the (002) peak. The ratio of the (002) peak integrated intensity to the (001) peak integrated intensity calculated theoretically when the value of the ratio of the (002) peak integrated intensity to the measured (001) peak integrated intensity is perfectly ordered The regularity S can be obtained by dividing by. If the degree of order S obtained in this way is 0.5 or more, the magnetic recording medium has a practical magnetic anisotropy coefficient Ku.

  The nonmagnetic grain boundary can contain Ti, and is more preferably composed of Ti. The first magnetic layer preferably contains 4 at% or more and 12 at% or less of Ti, more preferably 5 at% or more and 10 at% or less of Ti based on the total number of atoms of the first magnetic layer.

  When the nonmagnetic crystal grain boundary contains Ti within the above range, the separation between the magnetic crystal grain and the nonmagnetic crystal grain boundary can be promoted, and the coercive force Hc of the magnetic layer can be rapidly increased.

  The magnetic recording layer can further include a second magnetic layer in addition to the first magnetic layer. By having the second magnetic layer, the performance of the magnetic recording medium can be further improved.

  The configuration of the second magnetic layer is not particularly limited, but the second magnetic layer has, for example, a Curie temperature Tc different from that of the first magnetic layer, and can be provided for the purpose of Tc control. By setting the recording temperature for both the first magnetic layer and the second magnetic layer, the reversal magnetic field of the entire magnetic recording medium required at the time of recording can be reduced.

  For example, a magnetic layer having a Curie temperature Tc lower than the Curie temperature Tc of the first magnetic layer is formed as the second magnetic layer. If the recording temperature is set to be intermediate between the Curie temperatures of both magnetic layers, the magnetization of the second magnetic layer disappears during recording, and the magnetic field required to reverse the recording can be reduced. In this way, the magnetic field generated during recording required for the magnetic recording head can be reduced, and good magnetic recording performance can be exhibited.

  The second magnetic layer also preferably has a granular structure, and the first magnetic layer and the second magnetic layer have the same position in the horizontal direction, that is, in the direction parallel to the glass substrate surface. It is preferable to arrange. This is because such an arrangement can improve performance such as signal-to-noise ratio (SNR).

  Although the material which comprises a 2nd magnetic layer is not specifically limited, For example, it is preferable that a magnetic crystal grain is a material containing at least any one of Co and Fe. In particular, the magnetic crystal grains preferably further contain one or more kinds selected from Pt, Pd, Ni, Mn, Cr, Cu, Ag, and Au.

As a material for the magnetic crystal grains of the second magnetic layer, for example, a CoCr alloy, a CoCrPt alloy, a FePt alloy, a FePd alloy, or the like can be used. Magnetic crystal grains, L1 ₀ type, L1 ₁ type, and ordered structure, such as a L1 ₂ type, hcp structure (hexagonal close-packed structure), it may be a fcc structure (face-centered cubic structure).

As the material of the nonmagnetic crystal grains constituting the second magnetic layer, for example, oxides such as ZnO, SiO ₂ and TiO ₂ , nitrides such as SiN and TiN, C, B and the like can be used.

  Note that a layer having a different composition using the same material as the first magnetic layer may be used as the second magnetic layer. The second magnetic layer may be, for example, a layer in which the Ti ratio in the first magnetic layer is changed, a layer in which an element such as Ni added to the ordered alloy is changed, or the like.

  In addition, the magnetic recording layer is, for example, an exchange coupling control layer between the first magnetic layer and the second magnetic layer in order to adjust the magnetic exchange coupling between the first magnetic layer and the second magnetic layer. Can also be arranged.

  A protective layer can be provided on the top surface of the magnetic recording layer, and the protective layer can be formed using a material conventionally used in the field of magnetic recording media. Specifically, the protective layer can be formed using a nonmagnetic metal such as Pt, a carbon-based material such as diamond-like carbon, or a silicon-based material such as silicon nitride. The protective layer may be a single layer or may have a laminated structure. The protective layer having a laminated structure may be, for example, a laminated structure of two types of carbon materials having different characteristics, a laminated structure of metals and carbon materials, or a laminated structure of metal oxide films and carbon materials. .

  The protective layer can be formed using any method such as sputtering (including DC magnet sputtering) and vacuum deposition.

  Further, a liquid lubricant layer or the like can be further provided on the protective layer. The liquid lubricant layer can be formed using, for example, a perfluoropolyether lubricant. The liquid lubricant layer can be formed using, for example, a coating method such as a dip coating method or a spin coating method.

  In the present embodiment, the energy-assisted magnetic recording medium has been described as an example of the configuration of the magnetic recording medium. However, the energy-assisted magnetic recording medium is not limited to the above embodiment. For example, various layers can be further provided as necessary.

  The magnetic recording medium of this embodiment described above includes the glass substrate for magnetic recording medium described above. That is, it includes a glass substrate for a magnetic recording medium that can reduce changes in flatness and suppress deterioration of flatness even when heat treatment is performed at a high temperature when forming a magnetic layer.

  For this reason, the flatness of the magnetic recording medium of this embodiment including the glass substrate for magnetic recording medium can be reduced. For this reason, when the magnetic recording medium of this embodiment is applied to a magnetic recording apparatus, the flying stability of the recording head can be ensured.

Specific examples will be described below, but the present invention is not limited to these examples.
[Experiment 1 to Experiment 5]
The glass substrates of Experimental Examples 1 to 5 were prepared and evaluated by the following procedure.
(Glass material selection process)
In preparing the glass substrates of Experimental Examples 1 to 5, Glass A to Glass E having different compositions were prepared as shown in Table 1, and changes in internal friction tan δ with respect to temperature were measured by the following procedure. And from the measured result, it decided to implement the glass material selection process which selects the glass material whose internal friction tan-delta in 350 degrees C or less is 0.01 or less, and produces the glass substrate of each experiment example.

  First, a method for measuring the internal friction tan δ with respect to temperature will be described.

  The change of the internal friction tan δ with respect to temperature was performed by the following procedure using a dynamic viscoelasticity measuring apparatus (model number: Q800 DMA, manufactured by TA Instruments).

  As shown in FIG. 1, the internal friction tan δ was measured using a test piece 11 processed into a plate shape for each glass material in a three-point bending measurement jig. As the test body 11, one in which each glass material was molded so that the length 1 was 60 mm × width (in the direction perpendicular to the paper surface in FIG. 1) was 5 mm × plate thickness d was 0.5 mm was used.

  And first, the test body 11 was arrange | positioned on support member 12A, 12B. The support interval (span) L between the support member 12A and the support member 12B is 50 mm.

  Next, in the state where a static load of 1 N is applied downward in the figure by the pressing member 13 to the central portion of the upper surface of the test body 11 and the central portion of the supporting member 12A and the supporting member 12B, the amplitude is further 120 μm. The pressing member 13 periodically repeated downward pressing and releasing the pressing so that the period was 1 Hz. In this way, vibration strain was applied to the test body 11 by pressing the test body 11. Then, the internal friction tan δ was calculated from the change in stress measured at this time.

  In the measurement of tan δ, the temperature was increased from −80 ° C. at a temperature increase rate of 5 ° C./min, and the change in internal friction tan δ with respect to the temperature in the range of −80 ° C. to 350 ° C. A curve was obtained.

  FIG. 3 shows the change in the internal friction tan δ with respect to the temperature of the specimen of each glass material when the above measurement is performed. Table 1 shows the names of the glass materials used in each experimental example and the internal friction tan δ at 0 ° C., 100 ° C., 200 ° C., and 350 ° C.

  According to the result shown in FIG. 3, it is confirmed that the internal friction tan δ at 350 ° C. or less is 0.01 or less for glass A to glass C. On the other hand, about the glass D and the glass E, it has confirmed that the internal friction tan-delta in 350 degrees C or less exceeded 0.01. In particular, it was confirmed that the specimens using glass D and glass E had a clear peak in the temperature range of 350 ° C. or less in the curve of the change in internal friction tan δ with respect to temperature.

  From the above results, Examples 1 to 3 were used as examples, and Glass A to Glass C were used as shown in Table 1, respectively. Moreover, as shown in Table 1, glass 4 and glass E were respectively used as experimental examples 4 and 5 as comparative examples.

And the glass substrate of each experiment example was produced by implementing the following processes. Since the glass substrate was produced in the same manner as in Experimental Example 1 to Experimental Example 5 except that the glass material of the glass base plate manufactured in the glass base plate manufacturing process was different from the plate thickness, the glass substrate is described collectively below.
(Glass base plate manufacturing process)
From the result of the glass material selection step, in Experimental Examples 1 to 5, as described above, glass substrates were prepared using Glass A to Glass E, respectively.

  For this reason, a glass base plate is produced by a float method using glass A, B, D, and glass E, and a glass base plate is produced by a press method using glass C, and used for the shape imparting step in each experimental example. did.

In addition, about Experimental example 1 and Experimental example 3-Experimental example 5, the plate | board thickness of the glass base plate was adjusted and produced so that the plate | board thickness of the obtained glass substrate might be set to 0.635 mm. Moreover, the glass base plate used for Experimental Example 2 was prepared by adjusting the thickness of the glass base plate so that the thickness of the obtained glass substrate was 0.5 mm.
(Shaping process)
In order to obtain a glass substrate having an outer diameter of 95 mm and an inner diameter of 25 mm, as described with reference to FIG. It processed into the glass substrate which has a donut shape which has.

Here, the inner diameter means the diameter of the circular hole at the center.
(Chamfering process)
Chamfering was performed so that a glass substrate for a magnetic recording medium having a chamfering width of 0.15 mm and a chamfering angle of 45 ° was obtained between the inner peripheral end surface and the outer peripheral end surface of the glass substrate having a donut shape obtained in the shape imparting step. .
(Primary main surface grinding process)
Using the alumina abrasive grains, the upper and lower main surfaces of the obtained glass substrate were lapped.

  The primary main surface grinding step was performed with a 16B double-side polishing apparatus using a mold surface plate as a polishing tool and a grinding liquid containing alumina abrasive grains.

Moreover, about the glass substrate after a primary main surface grinding process, the abrasive grain was wash | cleaned and removed.
(Outer peripheral edge polishing process)
Next, the outer peripheral side surface portion and the outer peripheral chamfered portion of the glass substrate are polished with a polishing brush and a polishing liquid containing cerium oxide abrasive grains, and a work-affected layer (such as a scratch) on the outer peripheral side surface portion and the outer peripheral chamfered portion. The outer peripheral end face was polished so as to have a mirror surface.

Even after the outer peripheral end surface polishing step, the glass substrate was subjected to cleaning and removal of abrasive grains.
(Inner end face polishing process)
After the outer peripheral end surface polishing, the inner peripheral side surface portion and the inner peripheral chamfered portion of the glass substrate for magnetic recording medium are polished with a polishing liquid containing a polishing brush and cerium oxide abrasive grains, and the inner peripheral side surface portion and the inner peripheral surface are polished. The work-affected layer (scratches, etc.) in the chamfered portion was removed, and the inner peripheral end surface was polished so as to be a mirror surface.

The abrasive grains were cleaned and removed from the glass substrate even after the inner peripheral end face was polished.
(Secondary main surface grinding process)
Next, lapping of the upper and lower main surfaces of the glass substrate was performed.

  The secondary main surface grinding step was carried out by a 16B double-side polishing apparatus using a fixed-grain tool containing diamond abrasive grains having an average particle diameter of 4 μm as a polishing tool and a grinding liquid containing a surfactant.

  In addition, the abrasive grains were cleaned and removed from the glass substrate even after the secondary grinding process was completed.

The average particle size means the particle size at an integrated value of 50% in the particle size distribution obtained by the laser diffraction / scattering method. In other parts of the present specification, the average particle size has the same meaning.
(Primary main surface polishing process)
Next, using a polishing pad containing soft urethane as a polishing tool (suede-based polishing pad) and a polishing liquid containing cerium oxide abrasive grains, the upper and lower main surfaces were polished by a 16B double-side polishing apparatus. As the polishing liquid containing cerium oxide abrasive grains, a polishing liquid composition containing cerium oxide having an average particle diameter of about 1.0 μm was used.

  Further, in the primary main surface polishing step, the upper and lower main surfaces are polished for a total thickness of 30 μm in the plate thickness direction.

Even after the completion of the primary main surface polishing step, the glass substrate was cleaned and removed of cerium oxide.
(Secondary main surface polishing process)
After the completion of the primary main surface polishing step, a secondary main surface polishing step was performed on both main surfaces of the cleaned glass substrate.

  The secondary main surface polishing step was performed with a 16B double-side polishing apparatus using a polishing pad made of soft urethane as a polishing tool and a polishing liquid containing colloidal silica abrasive grains having an average particle diameter of 20 nm.

Even after the completion of the secondary main surface polishing step, the colloidal silica was washed and removed from the glass substrate.
(Washing / drying process)
The glass substrate that has been subjected to the secondary main surface polishing step is sequentially subjected to scrub cleaning, ultrasonic cleaning in a state of immersion in a detergent solution, and ultrasonic cleaning in a state of immersion in pure water (precision cleaning). And dried with isopropyl alcohol vapor.

  The glass substrate of each experimental example was produced by the above procedure, and the flatness before and after the heat treatment was evaluated for the obtained glass substrate.

  In each experimental example, 100 glass substrates are produced by the above-described procedure. For this reason, in each experimental example among the produced glass substrates, two glass substrates having substantially the same flatness were selected, and the flatness (X1) of the glass substrate before the heat treatment was selected.

  The flatness is measured by the interference flatness tester FT-17 manufactured by NIDEK before and after the above heat treatment and after the heat treatment described below.

  And about one glass substrate, it heat-processed for 10 minutes at 600 degreeC in nitrogen atmosphere, and measured the flatness, after cooling to room temperature. Table 1 shows the evaluation result of the flatness (Y1) after the heat treatment and the calculation result of the change amount (Y1-X1) of the flatness before and after the heat treatment.

  Further, another glass substrate was heat-treated at 700 ° C. for 10 minutes in a nitrogen atmosphere, cooled to room temperature, and then measured for flatness. Table 1 shows the evaluation result of the flatness (Y2) after the heat treatment and the calculation result of the amount of change (Y2-X1) in the flatness before and after the heat treatment.

３５０℃以下における内部摩擦ｔａｎδが、０．０１以下であるガラスＡ〜ガラスＣを用いて作製した実験例１〜実験例３のガラス基板は、６００℃で熱処理を行った場合、熱処理前後での平坦度の変化量が１．５μｍ以下になることを確認できた。また、実験例１〜実験例３のガラス基板は、７００℃で熱処理を行った場合でも、熱処理前後での平坦度の変化量が２６．０μｍ以下に、更に３５０℃以下における周波数１Ｈｚでの内部摩擦ｔａｎδが、０．００４以下であるガラスＡを用いて作成した実験例１のガラス基板は６．０μｍ以下になっていることを確認できた。

When the glass substrates of Experimental Example 1 to Experimental Example 3 manufactured using Glass A to Glass C whose internal friction tan δ at 350 ° C. or less is 0.01 or less are subjected to heat treatment at 600 ° C., the glass substrates before and after the heat treatment are obtained. It was confirmed that the amount of change in flatness was 1.5 μm or less. Further, even when the glass substrates of Experimental Examples 1 to 3 were heat-treated at 700 ° C., the amount of change in flatness before and after the heat treatment was 26.0 μm or less, and further, the internal at a frequency of 1 Hz at 350 ° C. or less. It was confirmed that the glass substrate of Experimental Example 1 prepared using the glass A having a friction tan δ of 0.004 or less was 6.0 μm or less.

  On the other hand, when the glass substrate of Experimental Example 4 and Experimental Example 5 produced using Glass D and Glass E having an internal friction tan δ at 350 ° C. or lower of more than 0.01 is subjected to heat treatment at 600 ° C., It was confirmed that the amount of change in flatness before and after the heat treatment exceeded 30 μm. In addition, since the glass substrate of Experimental example 4 and Experimental example 5 may be damaged when it heat-processes at 700 degreeC, and heating was not implemented, flatness cannot be evaluated.

  From the above results, it was confirmed that, according to the glass substrate for a magnetic recording medium made of a glass material having an internal friction tan δ at 350 ° C. or less of 0.01 or less, deterioration of flatness can be suppressed even when heat treatment is performed at high temperature. .

20 Glass substrate for magnetic recording medium

Claims (4)

A glass substrate for a magnetic recording medium comprising a glass material having an internal friction of 0.01 or less at 350 ° C. or less.
(However, the internal friction is
A test body made of the glass material processed into a plate shape having a length of 60 mm, a width of 5 mm, and a plate thickness of 0.5 mm,
It is arranged along the length direction and is supported from the lower surface side by two support members having a support interval of 50 mm,
In the state where a static load of 1 N is applied to the center of the test body in the downward direction, the stress measured by repeatedly pressing and releasing the pressure so that the amplitude is 120 μm and the frequency is 1 Hz. Calculated based on change. )   The glass substrate for a magnetic recording medium according to claim 1, wherein the glass substrate is made of a glass material having an internal friction of 0.004 or less at 350 ° C. or less. It has a disc shape with an opening in the center,
The glass substrate for a magnetic recording medium according to claim 1 or 2, wherein the diameter is 95 mm or more and the plate thickness is 0.635 mm or less.   The magnetic recording medium containing the glass substrate for magnetic recording media as described in any one of Claims 1 thru | or 3.

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