WO2017115468A1 - Glass substrate for magnetic recording medium and magnetic recording medium - Google Patents

Abstract

The present invention provides a glass substrate for a magnetic recording medium such that thermal cracking that is caused by dramatic temperature changes can be minimized. The glass substrate for a magnetic recording medium according to the present invention is donut shaped and includes a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface. The outer peripheral end surface has an outer peripheral lateral surface and a pair of outer peripheral chamfers. The outer peripheral lateral surface has an arithmetic average roughness Ra of 0.1 μm or less. The outer peripheral lateral surface has an arithmetic average roughness Ra of 0.5 μm or less after being etched to 5 μm from the surface.

Description

Glass substrate for magnetic recording medium, magnetic recording medium

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, are being 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.

In the 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. And, in order to increase the degree of ordering (regularity) and realize high Ku, the base material including the glass substrate for magnetic recording medium is at least 600 ° C. at the time of film formation, before film formation, or after film formation. Heat treatment may be performed at a high temperature.

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

In the process of manufacturing a magnetic recording medium in this manner, 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, Patent Document 1 discloses a glass substrate for an information recording medium capable of forming a magnetic recording layer at a high temperature. Specifically, in terms of mole percentage, SiO ₂ is 62 to 74%, Al ₂ O ₃ is 7 to 18%, B ₂ O ₃ is 2 to 15%, and any one component of MgO, CaO, SrO and BaO 8 to 16% in total, the total content of the seven components is 95% or more, and any one or more of Li ₂ O, Na ₂ O and K ₂ O is contained in less than 1% in total Or a glass substrate for an information recording medium that does not contain any of these three components (except for a crystallized glass substrate and a tempered glass substrate).

Japanese Patent No. 50569883

However, when heat treatment is performed at a high temperature as described above, since a rapid temperature change is applied to the glass substrate for magnetic recording medium before and after the heat treatment, the glass substrate for magnetic recording medium exhibits rapid thermal expansion or contraction. And a large stress is applied to the glass substrate for a magnetic recording medium. Due to such stress, a thermal crack may occur in the glass substrate for a magnetic recording medium, and may be crushed depending on the degree of the thermal crack. As described above, when a thermal crack is generated or broken in the magnetic recording medium glass substrate during the production of the magnetic recording medium, it is necessary not only to reduce the yield but also to recover the broken substrate, clean the heat treatment apparatus, and the like. As a result, there is a problem in that productivity is greatly reduced.

Therefore, in view of the above-described problems of the related art, an object of the present invention is to provide a glass substrate for a magnetic recording medium that suppresses thermal cracking when a sudden temperature change is applied.

In order to solve the above problems, in one aspect of the present invention, a glass substrate for a magnetic recording medium having a donut shape and having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface, the outer peripheral end surface is It has an outer peripheral side part and a pair of outer peripheral chamfered parts,
The arithmetic average roughness Ra of the outer peripheral side surface portion is 0.1 μm or less,
Provided is a glass substrate for a magnetic recording medium in which an arithmetic average roughness Ra of an outer peripheral side surface after etching after etching 5 μm from the surface of the outer peripheral side surface portion is 0.5 μm or less.

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 suppresses thermal cracking when a sudden temperature change is applied.

FIG. 1 is an explanatory diagram of a glass substrate for a magnetic recording medium according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of minute cracks generated in the glass substrate for a magnetic recording medium. 3 (A) and 3 (B) are laser microscope images of the outer peripheral side surface before and after etching in Experimental Example 1 of the present invention. FIG. 3A shows an image before etching, and FIG. 3B shows an image after etching. 4 (A) and 4 (B) are laser microscope images of the outer peripheral side surface before and after etching in Experimental Example 10 of the present invention. FIG. 4A shows an image before etching, and FIG. 4B shows an image after etching.

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 a magnetic recording medium of the present embodiment is a glass substrate for a magnetic recording medium having a donut shape and having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface, and the outer peripheral end surface is an outer peripheral side surface. And a pair of outer peripheral chamfers.

Then, the arithmetic average roughness Ra of the outer peripheral side surface portion may be 0.1 μm or less, and the outer peripheral side surface portion may have an arithmetic average roughness Ra of 0.5 μm or less after etching after etching 5 μm from the surface. it can.

First, the structure of the glass substrate for a magnetic recording medium of the present embodiment (hereinafter also simply referred to as “glass substrate”) will be described with reference to FIG.

FIG. 1 schematically shows a perspective sectional view of the glass substrate of the present embodiment. 1 is a perspective cross-sectional view including a cross section in a plane passing through the center of the glass substrate 10 and perpendicular to the main surfaces 121 and 122. That is, in FIG. 1, the half of the glass substrate of this embodiment and sectional drawing are shown collectively.

As can be seen from FIG. 1, the glass substrate 10 has a circular shape on the outer periphery, and a circular shape in which a circular opening (center opening) 11 is provided in the center so as to be concentric with the outer periphery, that is, a donut. It has a shape.

The upper and lower surfaces are main surfaces 121 and 122. Moreover, the glass substrate 10 has the outer peripheral end surface 13 located in an outer periphery, and the inner peripheral end surface 14 located in an inner periphery.

The outer peripheral end surface 13 and the inner peripheral end surface 14 can have chamfered portions on the main surfaces 121 and 122 side, respectively. That is, the outer peripheral end surface 13 and the inner peripheral end surface 14 can each have a pair of chamfered portions. Specifically, the outer peripheral end surface 13 can have outer peripheral chamfered portions 131 and 133, and the inner peripheral end surface 14 can have inner peripheral chamfered portions 141 and 143, respectively.

Further, a side surface portion can be formed between the chamfered portions, the outer peripheral end surface 13 can have the outer peripheral side surface portion 132, and the inner peripheral end surface 14 can have the inner peripheral side surface portion 142. The outer peripheral side surface portion 132 and the inner peripheral side surface portion 142 can be formed so as to be substantially perpendicular to the main surfaces 121 and 122, respectively.

As described above, the outer peripheral end surface 13 can include the outer peripheral side surface portion 132 and the outer peripheral chamfered portions 131 and 133, and the inner peripheral end surface 14 can include the inner peripheral side surface portion 142 and the inner peripheral chamfered portions 141 and 143. .

In addition, the size of the glass substrate 10 of this embodiment is not specifically limited, It can select arbitrarily according to the specification of a glass substrate. The diameter D of the glass substrate of this embodiment can be made into the size according to the specification requested | required of glass substrates, such as 48 mm, 65 mm, or 95 mm, for example. In particular, the diameter of the glass substrate of the present embodiment is preferably 65 mm or more, for which demand has been increasing in recent years.

By the way, as described above, when the heat treatment is performed at a high temperature of 600 ° C. or higher, for example, 600 ° C. or higher and 700 ° C. or lower, in the manufacturing process of the energy assisted magnetic recording medium, a sudden temperature change is applied to the glass substrate and the generated stress. As a result, thermal cracks may occur in the glass substrate.

Therefore, the inventors of the present invention have conducted intensive studies on a glass substrate that can suppress the occurrence of thermal cracking when a sudden temperature change is applied.

The inventors of the present invention first examined the cause of thermal cracking when a sudden temperature change was applied.

When a sudden temperature change is applied to a glass substrate, stress is easily applied to a place where expansion or contraction is likely to occur. It was found that expansion and contraction easily occur in the outer peripheral portion of the glass substrate.

In addition, heat treatment is usually performed in a state where a plurality of locations on the outer peripheral side surface of the glass substrate are held by a metal holder, but the heat transfer between the holder and the glass substrate causes It has been found that the temperature distribution of the film tends to change particularly sharply.

For this reason, when performing heat treatment, the outer peripheral portion of the glass substrate is likely to be exposed to a rapid temperature change, and when exposed to a rapid temperature change, expansion and contraction are likely to occur. I found that it is easy to add.

Then, next, when the relationship between the properties of the outer peripheral side surface and the occurrence of thermal cracking was examined, if a micro crack with a depth of several μm to submicron exists on the outer peripheral side surface, stress concentrates on the crack tip. It was found that the cracks tend to extend and lead to large cracks.

Here, the microcracks are schematically shown in FIG. FIG. 2 schematically shows a cross section of the microcrack in a plane parallel to the depth direction of the microcrack 22 and passing through the microcrack.

The microcracks 22 generated on the outer peripheral side surface portion of the glass substrate are generated from the surface 21 of the outer peripheral side surface portion of the glass substrate toward the inside as shown in FIG. When a microcrack occurs, the stress concentration at the tip of the microcrack 22 has a correlation with the width R of the crack tip, and when the width R is small, the stress tends to concentrate particularly on the microcrack 22. Therefore, it can be seen that by reducing microcracks in the outer peripheral side surface portion, it is possible to provide a glass substrate that suppresses the occurrence of thermal cracking when a sudden temperature change is applied.

However, the micro crack 22 having a very small tip width R that is likely to cause thermal cracking has a small width of the opening 221 on the surface 21 side, and the opening 221 is covered with hydrate or the like. Therefore, it is difficult to detect from the surface 21 of the outer peripheral side surface portion of the glass substrate. For this reason, it was difficult to measure the presence frequency and depth at the outer peripheral side surface portion of the glass substrate with a surface roughness meter or the like.

Therefore, when a method for detecting such a microcrack was examined, it was found that by etching (etching) the outer peripheral side surface of the glass substrate, microcracks that are not detected before etching can be manifested on the outer peripheral side surface. I found it. This is considered to be because the hydrate etc. that covered the microcracks by etching can be removed, and furthermore, the size of the opening (pit) on the surface side of the microcracks can be increased by etching. .

From the above examination results, by etching the outer peripheral side surface, micro cracks on the outer peripheral side surface can be revealed, so that it can be detected by a surface roughness meter or the like. It was found that it is possible to grasp the amount quantitatively. Furthermore, it was found that there is a correlation between the arithmetic average roughness Ra of the peripheral side surface portion of the substrate after etching and the occurrence rate of thermal cracking.

Therefore, in the glass substrate of the present embodiment, it is preferable that the outer peripheral side surface portion has an arithmetic average roughness Ra of 0.5 μm or less after etching the outer peripheral side surface portion after etching 5 μm from the surface, that is, the outer peripheral side surface portion after etching. More preferably, it is 0.3 μm or less, and further preferably 0.2 μm or less.

As described above, fine cracks are evident on the outer peripheral side surface after etching, and by evaluating the arithmetic average roughness Ra of the outer peripheral side surface after etching, the minute cracks included in the outer peripheral side portion are evaluated. Existence frequency can be evaluated. That is, the smaller the arithmetic average roughness Ra of the outer peripheral side surface after etching, the smaller the frequency of presence of microcracks included in the outer peripheral side surface portion.

According to the study of the inventors of the present invention, when the arithmetic average roughness Ra of the outer peripheral side surface after etching is 0.5 μm or less, the presence frequency of microcracks can be sufficiently reduced, and the occurrence of thermal cracks is suppressed. it can. For this reason, when a rapid temperature change is added, it can suppress that a thermal crack arises in a glass substrate, and it is preferable.

In the glass substrate of the present embodiment, the etching amount when measuring the arithmetic average roughness Ra of the outer peripheral side surface after etching is set to 5 μm, but the same tendency is obtained if the etching amount is 1 μm or more and 20 μm or less. It is thought that. For this reason, the etching amount is not limited to 5 μm, and can be selected in the range of 1 μm to 20 μm.

In addition, when the etching amount is smaller than 1 μm, the size of the opening of the microcrack on the outer peripheral side surface after etching is not sufficiently large, and the existence frequency of the microcrack and the detailed shape are May be difficult to evaluate. On the other hand, if the etching amount is larger than 20 μm, the size of the opening portion of the microcrack on the outer peripheral side surface after etching is too large, and the existing frequency of the crack and the size do not reflect, There is a risk that proper evaluation cannot be performed.

For this reason, the etching amount is preferably 1 μm or more and 20 μm or less, particularly 5 μm, when the arithmetic average roughness Ra or the maximum height roughness Rz described later is evaluated for the outer peripheral side surface after etching. Is preferred.

In the glass substrate of this embodiment, the arithmetic mean roughness Ra of the outer peripheral side surface before etching is preferably 0.1 μm or less, and more preferably 0.05 μm or less.

This is because, as will be described later, when the arithmetic mean roughness Ra of the outer peripheral side surface is higher than 0.1 μm, abrasive grains and the like are likely to adhere, and dust is generated during cleaning and film formation, and contamination to the main surface. It is because there is a concern that it will lead to.

Furthermore, the outer peripheral side surface portion after etching preferably has a maximum height roughness Rz of 10 μm or less, more preferably 4 μm or less, and further preferably 3 μm or less.

The maximum height roughness Rz is considered to correspond to the maximum depth of microcracks existing in the measurement region. The microcracks are more likely to develop into thermal cracks as the depth increases. When the maximum height roughness Rz is 10 μm or less, the maximum depth of the microcracks is sufficiently shallow, and a rapid temperature change is applied. In this case, it is possible to suppress occurrence of thermal cracking in the glass substrate, which is preferable.

The method for etching the outer peripheral side surface portion of the glass substrate is not particularly limited, but etching can be performed by immersing the glass substrate in an etching solution for a predetermined time. When the glass substrate is immersed in the etching solution, the entire surface of the glass substrate is uniformly etched. For example, when 5 μm is etched from the surface of the outer peripheral side surface portion, the glass substrate is reduced in diameter by 10 μm.

The etchant is not particularly limited as long as it is a material that can etch the glass substrate, and for example, a mixed aqueous solution of hydrofluoric acid and hydrochloric acid can be used. Since the etching time varies depending on the etching solution and the glass material of the glass substrate, it is preferable to conduct a preliminary test or the like in advance to check the time required to etch the surface of the glass substrate by 5 μm.

The arithmetic average roughness Ra and the maximum height roughness Rz are defined in JIS B 0601 (2013), and are evaluated using, for example, a laser microscope, a contact-type surface roughness meter, a white interference method, or the like. It can be performed.

In addition, the glass substrate before etching 5 micrometers from the surface can be used as the glass substrate for magnetic recording media about the outer peripheral side surface part of the glass substrate of this embodiment.

This is because in the glass substrate etched on the surface of the outer peripheral side surface portion, the thermal crack can be suppressed because the width R of the tip of the microcrack becomes large, but it is clear from the fact that the microcrack has become obvious, The arithmetic average roughness Ra of the outer peripheral side surface portion becomes larger than that before etching. For this reason, the abrasive grains and the like are likely to adhere to the outer peripheral side surface, which may cause problems such as bringing in abrasive grains adhering in various polishing processes during cleaning and the like.

The micro cracks are mainly generated according to the manufacturing conditions of the glass substrate. For this reason, for the outer peripheral side surface portion of the glass substrate manufactured under the same conditions as in the actual manufacturing, the arithmetic average roughness Ra before and after the etching and, in some cases, the maximum height roughness Rz are further evaluated. Manufacturing conditions can be selected to satisfy the specifications of the glass substrate in the form.

Or, when manufacturing a glass substrate, usually a plurality of glass substrates are manufactured per lot. And since the glass substrate is manufactured on the same conditions in the same lot, the presence frequency and the maximum depth of the micro crack which arise in the outer peripheral side part become comparable. For this reason, one or more glass substrates for evaluation are selected from the same lot, and the arithmetic average roughness Ra before and after the etching or, in some cases, the maximum height roughness Rz is evaluated for the glass substrate for evaluation. be able to. And it can confirm that the prescription | regulation of the glass substrate of this embodiment is satisfied about the glass substrate of this lot.

As described above, when a rapid temperature change is applied to the glass substrate, a microcrack mainly included in the outer peripheral side surface is the starting point of thermal cracking. For this reason, when the arithmetic average roughness Ra before etching of the outer peripheral side surface portion and the arithmetic average roughness Ra after etching 5 μm from the surface of the outer peripheral side surface portion satisfy the above definition, a rapid temperature change was added. Even in the case, the occurrence of thermal cracking can be suppressed.

However, due to changes in the shape of the substrate holder of the glass substrate when heat treatment is performed at a high temperature, the holding location, temperature distribution during temperature rise, and temperature drop, the properties of the outer chamfered part and inner peripheral end surface also generate thermal cracks. May be affected.

Therefore, in addition to the outer peripheral side surface portion, the outer peripheral chamfered portions 131 and 133, the inner peripheral chamfered portions 141 and 143, and the inner peripheral side surface portion 142 described with reference to FIG. For each of the above parts, it is preferable that the arithmetic average roughness Ra after etching 5 μm from the surface, and in some cases, the maximum height roughness Rz after etching satisfy the same definition as the outer peripheral side part.

Further, the corner between the main surface and the chamfered portion and the corner between the side surface and the chamfered portion are also arithmetic average roughness Ra before etching, and arithmetic after etching 5 μm from the surface for each portion. It is preferable that the average roughness Ra, and in some cases, the maximum height roughness Rz after etching satisfy the same definition as that of the outer peripheral side surface portion.

In addition, the corner | angular part between a main surface and a chamfering part means each corner | angular part between main surface 121,122 in FIG. 1, outer peripheral chamfering part 131,133, and inner peripheral chamfering part 141,143. . The corner between the side surface portion and the chamfered portion is a corner portion between the outer peripheral chamfered portions 131 and 133 and the outer peripheral side surface portion 132, and between the inner peripheral chamfered portions 141 and 143 and the inner peripheral side surface portion 142. Means each corner.

The glass substrate of the present embodiment can be chemically strengthened. This is because by performing chemical strengthening treatment, it is possible to particularly suppress the occurrence of thermal cracking when a sudden temperature change is applied.

When performing chemical strengthening on the glass substrate, it is preferable to chemically strengthen at least a portion including the outer peripheral side portion in order to particularly suppress the influence of microcracks included in the outer peripheral side portion. When chemical strengthening is performed, it is particularly preferable to perform chemical strengthening on the entire surface of the glass substrate.

When chemical strengthening is performed, the degree is not particularly limited, but at least at the outer peripheral side surface portion of the glass substrate, the depth DOL of the compressive stress by the chemical strengthening treatment is 1 μm ≦ DOL ≦ 15 μm. preferable. In particular, the depth DOL of the compressive stress due to the chemical strengthening treatment is more preferably 1 μm ≦ DOL ≦ 15 μm for the entire surface of the glass substrate.

This is because, when the depth DOL of the compressive stress is 1 μm or more, it can be said that chemical strengthening is sufficiently performed, and thermal cracking can be particularly suppressed. However, if the DOL exceeds 15 μm, the flatness of the glass substrate may deteriorate due to the diffusion of ions into the glass substrate when performing a high-temperature heat treatment at 600 ° C. or higher, so the DOL may be 15 μm or less. preferable. Also from this point, the glass substrate used in a process that requires high-temperature heat treatment at 600 ° C. or higher is greatly affected by microcracks, and removal thereof is important.

The glass material constituting the glass substrate of the present embodiment is not particularly limited, and various glass materials can be used.

As explained so far, the glass substrate of the present embodiment has the arithmetic average roughness Ra of the outer peripheral side surface portion, and the arithmetic average roughness of the outer peripheral side surface portion after etching after etching 5 μm from the surface of the outer peripheral side surface portion. Thermal cracking can be suppressed by setting Ra to a predetermined range.

However, the glass material used for the glass substrate is preferably a glass substrate that hardly causes thermal cracking even when a sudden temperature change is applied.

For this reason, the glass substrate of the present embodiment is preferably made of a glass material having a thermal expansion coefficient of 70 × 10 ⁻⁷ / ° C. or lower in a temperature range of 50 ° C. or higher and 350 ° C. or lower. More preferably, it is made of a glass material having a thermal expansion coefficient in the temperature range of 55 × 10 ⁻⁷ / ° C. or less.

This is because when the thermal expansion coefficient in the temperature range of 50 ° C. or more and 350 ° C. or less is 70 × 10 ⁻⁷ / ° C. or less, the glass substrate can be prevented from expanding and contracting due to temperature change, so a rapid temperature change was applied. Even in this case, the thermal cracking can be suppressed in combination with the properties of the outer peripheral side surface.

The lower limit value of the thermal expansion coefficient in the temperature range of 50 ° C. or higher and 350 ° C. or lower is not particularly limited, and the glass substrate of the present embodiment has a thermal expansion coefficient in the temperature range of 50 ° C. or higher and 350 ° C. or lower. A glass material having a value greater than 0 can be used.

The glass substrate of this embodiment can suppress the occurrence of thermal cracking even when a sudden temperature change is applied as described above. For this reason, it can be particularly suitably used as a glass substrate for an energy-assisted magnetic recording medium that may be subjected to a rapid temperature change in the manufacturing process. When manufacturing an energy-assisted magnetic recording medium, in order to promote ordering of an FePt-based magnetic layer alloy (magnetic material) contained in the magnetic layer, 600 ° C. or higher and 700 ° C. during film formation of the magnetic layer or the like. Generally, heat treatment is performed at a high temperature of about the following. For this reason, when performing the heat processing at such a high temperature, the glass substrate of the present embodiment is made of a glass material having a glass transition point Tg of 650 ° C. or higher in order to suppress distortion and deformation of the glass substrate. The glass transition point Tg is more preferably 700 ° C. or higher.

As described above, when a heat treatment is performed at a high temperature of 600 ° C. or higher, particularly when producing an energy-assisted magnetic recording medium, a rapid temperature change may be applied to the glass substrate. In some cases, thermal cracking occurred. On the other hand, according to the glass substrate of the present embodiment, the arithmetic average roughness Ra of the outer peripheral side surface portion and the arithmetic average roughness Ra of the outer peripheral side surface portion after etching after etching 5 μm from the surface of the outer peripheral side surface portion. Is a predetermined range. For this reason, since the presence frequency of the microcracks contained in the outer peripheral side surface portion as a starting point of thermal cracking is sufficiently low, it is possible to suppress the occurrence of thermal cracking when a sudden temperature change is applied.

For this reason, the glass substrate of the present embodiment can be particularly suitably used as a glass substrate for a magnetic recording medium for an energy-assisted magnetic recording medium.

However, the use of the glass substrate of the present embodiment is not limited to a glass substrate for energy-assisted magnetic recording media, and can be suitably used as a glass substrate for various magnetic recording media.

Next, a configuration example of the glass substrate for a magnetic recording medium according to the present embodiment described so far (hereinafter 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 glass substrate manufacturing method of the present embodiment can include, for example, the following steps 1 to 5.
(Step 1) A shape imparting step in which a glass substrate is processed into a disk-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.

Here, the shape imparting step of (Step 1) includes a glass-shaped substrate formed by a float method, a fusion method, a press forming method, a down draw method or a redraw method, and a disk-shaped glass having a circular hole in the center. The substrate is processed. The glass substrate used may be amorphous glass, crystallized glass, or tempered glass having a tempered layer on the surface of the glass substrate.

In the chamfering step (step 2), the inner peripheral end surface and the outer peripheral end surface can be chamfered. By performing the chamfering step, as described with reference to FIG. 1, the inner peripheral chamfered portions 141 and 143 can be formed on the inner peripheral end surface 14, and the outer peripheral chamfered portions 131 and 133 can be formed on the outer peripheral end surface 13.

In the end surface polishing step (step 3), the end surface (side surface portion and chamfered portion) of the glass substrate can be subjected to end surface polishing.

In the main surface polishing step (step 4), for example, a double-side polishing apparatus supplies polishing liquid to the main surface of the glass substrate having a donut shape, 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 (primary polishing), primary polishing and secondary polishing may be performed, or tertiary polishing may be performed after secondary polishing.

In the main surface polishing step of (Step 4), wrapping of the main surface (for example, free abrasive wrap, fixed abrasive wrap, etc.) may be performed before performing the primary polishing of the main surface. In this case, only a primary lap may be used, and a plurality of lap processes such as a secondary lap may be performed.

Further, 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.

Furthermore, glass substrate cleaning (inter-process cleaning) or glass substrate surface etching (inter-process etching) may be performed between the above processes. 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 steps 1 to 5 described so far need not be performed in the order described, and for example, a main surface polishing step may be performed before the shape imparting step. 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, as for the glass substrate of this embodiment, it is preferable that the presence frequency of the micro crack of an outer peripheral side part is low as mentioned above. And the following two cases can be mainly considered as the cause of the occurrence of the micro cracks included in the outer peripheral side surface.
(Cause 1) In the chamfering step in step 2, not only the outer peripheral chamfered portion but also the outer peripheral side portion is ground. At this time, micro cracks are generated in the outer peripheral side portion, and the end surface polishing step in step 3 is sufficient. If it could not be removed.
(Cause 2) In the main surface polishing step of step 4, the glass substrate to be used for the main surface polishing step is inserted and held in a circular hole formed in the carrier, and the main surface of the glass substrate is polished by a double-side polishing apparatus. However, the glass substrate held in the hole of the carrier is also rotated during polishing. In this case, wrinkles occur due to rubbing between the carrier and the glass substrate.

Therefore, in order to cope with cause 1, it is preferable to perform a preliminary test or the like, adjust the polishing amount in the end surface polishing step, and be configured to remove the microcracks more reliably.

In order to cope with cause 2, the carrier used in the main surface polishing step is a method using a material that does not easily generate microcracks in the glass substrate, or the end surface of step 3 after the main surface polishing step. Examples include a method for performing a polishing step.

Usually, stainless steel, steel, glass fiber-containing epoxy resin, or the like is used as a carrier material for holding the glass substrate in the main surface polishing step, and these materials have high hardness or contain a substance having high hardness. For this reason, during the main surface polishing, the carrier and the outer peripheral side surface portion of the glass rub against each other, which may cause micro cracks in the outer peripheral side surface portion.

On the other hand, the material used in the main surface polishing process is selected from aramid fiber-containing epoxy resin, carbon, polyvinyl chloride resin, polycarbonate, bakelite, epoxy resin, and polyester resin as a material for at least the portion that contacts the glass substrate. When one or more types are used, the generation of microcracks can be suppressed. For this reason, generation | occurrence | production of the microcrack by the cause 2 can be suppressed by using such a carrier. When the main surface polishing step is performed a plurality of times, at least the main surface polishing step to be performed at least lastly uses a carrier using a predetermined material for at least the portion in contact with the glass substrate, thereby causing a microcrack due to cause 2. Can be suppressed.

The material used in the main surface polishing step of at least a portion in contact with the glass substrate is one or more kinds selected from polyvinyl chloride resin, polycarbonate, bakelite, epoxy resin, and polyester resin, which are softer resins. It is further desirable to use materials.

It should be noted that the entire carrier can be composed of one or more types selected from the above-mentioned material group. Moreover, in order not to generate micro cracks on the outer peripheral side surface portion of the glass substrate while maintaining the strength of the carrier, the main body uses a high-strength material such as stainless steel, and the above-mentioned material group in the portion of the glass substrate holding hole that comes into contact with the glass substrate A carrier using one or more materials selected from the above can also be used.

A carrier manufacturing method in which a main body formed of a high-strength material such as stainless steel and a hole portion that holds a glass substrate formed of a material selected from the above material group is not particularly limited. . For example, a method of coating the surface of a hole for holding a glass substrate provided on a carrier with a resin, a method of forming a hole portion for holding a glass substrate with a resin, and bonding it to a carrier body, and the like.

In order to cope with cause 2, when the end surface polishing step of step 3 is performed after the main surface polishing step, the maximum depth of micro cracks generated in the main surface polishing step is measured in advance, It is preferable to select conditions for the end face polishing step so that cracks can be removed.

The glass substrate described above can be manufactured by the method for manufacturing 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 the present embodiment can include the above-described glass substrate for a magnetic recording medium.

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. 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.

The configuration example of each layer will be described below.

The adhesion layer can be provided in order 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, for example, between the glass substrate and the magnetic recording layer.

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 film thickness of the soft magnetic underlayer 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.

Also, 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 film forming method of 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, the size of the magnetic crystal grains, and the like.

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

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.

The film formation method of the underlayer is not particularly limited, and for example, a film formation 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 method for forming the seed layer is not particularly limited, and a film forming method such as a sputtering method or a vacuum evaporation method can be used. The sputtering method includes, for example, an RF magnetron 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 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, a granular structure consisting 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 a Curie temperature Tc different from that of the first magnetic layer, for example, 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 are arranged so that the magnetic crystal grains are in the same position in the horizontal direction, that is, in the direction parallel to the glass substrate surface. It is preferable to do. This is because such an arrangement can improve performance such as signal-to-noise ratio (SNR).

The material constituting the second magnetic layer is not particularly limited, but for example, the magnetic crystal grains are preferably a material containing at least 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 that of 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 an arbitrary method such as a sputtering method (including a DC magnetron sputtering method) or a vacuum deposition method.

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 the present embodiment described above includes the above-described glass substrate for magnetic recording medium. That is, it includes a glass substrate for a magnetic recording medium that suppresses the occurrence of thermal cracking when a sudden temperature change is applied. For this reason, when the magnetic layer is formed, the occurrence of thermal cracking in the glass substrate can be suppressed, and the magnetic recording medium of this embodiment can be manufactured with high productivity.

Hereinafter, specific examples will be described. However, the present invention is not limited to these examples.

First, a method for evaluating a glass substrate for a magnetic recording medium in the following experimental example will be described.

(1) Arithmetic average roughness Ra of outer peripheral side surface, outer peripheral side surface after etching, and maximum height roughness Rz of outer peripheral side surface after etching
The arithmetic average roughness Ra of the outer peripheral side surface and the outer peripheral side surface after etching, and the maximum height roughness Rz of the outer peripheral side surface after etching are measured by Keyence's laser microscope (Violet Laser color 3D, VK-9710, manufactured by Keyence Corporation). The outer peripheral side surface portion was observed using Laser Scanning Microscope) and calculated using the observation result.

The observation of the outer peripheral side surface and the outer peripheral side surface after etching uses a 50 × objective lens, the measurement area is 200 μm × 200 μm, and the center of the measurement area is arranged in the center of the glass substrate in the thickness direction. Went.

The analysis and calculation of the arithmetic average roughness Ra and the maximum height roughness Rz were performed using the software VK analyzer (Ver.1.1.0.0) of the same laser microscope.

In the analysis, since the outer peripheral side surface portion of the glass substrate and the outer peripheral side surface portion after etching are curved surfaces, first, curved surface inclination correction was performed using automatic quadric surface correction in the X and Y directions. Thereafter, the arithmetic average roughness Ra and the maximum height roughness Rz were calculated with a cutoff λs of 0.25 μm and λc of 80 μm.

Etching of the outer peripheral side surface portion was performed by using a mixed aqueous solution of hydrofluoric acid and hydrochloric acid as an etchant and immersing a glass substrate to be evaluated in the etchant.

The concentration of hydrofluoric acid used in the etching solution was 1.0 wt%, and the concentration of hydrochloric acid was 18 wt%.

As described above, since the entire glass substrate is immersed in the etching solution, when the outer peripheral side surface portion is removed by 5 μm by etching, the outer diameter of the disk after etching is reduced by 10 μm compared to before etching.

Since the etching rate varies depending on the glass material of the glass substrate used in each experimental example, a preliminary test was performed to adjust the etching time so that the etching amount was 5 μm. When etching is performed as described above, since the glass substrate is immersed in an etching solution, the amount of removal by etching when adjusting the etching time by a preliminary test is the outer diameter of the glass substrate before and after the etching. Calculated from changes.

As described above, the etching time was different depending on the glass material of the glass substrate, but the etching time was in the range of 1 to 20 minutes.

Here, changes in the state of the outer peripheral side surface before and after etching will be described with reference to FIGS. 3 (A) and 3 (B) show the surface of Example 1 to be described later, and FIGS. 4 (A) and 4 (B) show the surface of the glass substrate of Example 10 to be described later before and after etching. The photograph at the time of enlarging and observing this state with the above-mentioned laser microscope is shown. In both cases, (A) is before etching and (B) is after etching. As is clear from comparison between FIGS. 3A, 4A, 3B, and 4B, an opening (pit) of a microcrack that could not be confirmed before etching. It can be confirmed that 31 and 32 become larger and clearer by etching.
(2) Thermal crack test About the glass substrate produced in each experiment example, the rapid temperature change was added and the occurrence rate of the thermal crack was evaluated.

The glass substrate produced in each experimental example was heated to 230 ° C. in an electric furnace and then taken out from the electric furnace without cooling. Then, the glass substrate is moved in a direction parallel to the main surface of the glass substrate to the water in the water tank in which the water temperature is 20 ° C. and the depth is 10 mm in advance, that is, the water surface and the main surface of the glass substrate It was thrown in while keeping it vertical.

When it was poured into water, it was determined that a thermal crack had occurred when a crack with a length of 5 mm or more from the outer peripheral portion or a crack occurred in the glass substrate.

For each experimental example, 100 glass substrates were tested in the same manner, and the ratio of the glass substrates determined to have undergone thermal cracking in the 100 glass substrates subjected to the test was defined as the thermal cracking rate.

In the thermal cracking test, the glass substrate was heated to 230 ° C. as described above, and then poured into water having a water temperature of 20 ° C. within 3 seconds. For this reason, a rapid temperature change of about 70 ° C./second is applied to the glass substrate. Even in the process of manufacturing the energy-assisted magnetic recording medium, the temperature change is, for example, about 65 ° C./second or less. Therefore, if the glass substrate has a sufficiently low thermal cracking rate when a temperature change of 70 ° C./second is applied as described above, a rapid temperature change can be applied like a glass substrate for energy-assisted magnetic recording media. It shows that it can be suitably used in applications.

The glass substrate used for the thermal cracking test and the glass substrate used for the evaluation of the arithmetic average roughness Ra and the maximum height roughness Rz of the outer peripheral side surface after etching were produced under the same conditions in each experimental example. Although they are used, they are not the same. This is because when the etching is performed for the measurement of the arithmetic average roughness Ra and the maximum height roughness Rz of the outer peripheral side surface after etching, the width R of the tip of the microcrack on the outer peripheral side surface portion increases, and cracks due to thermal stress occur. This is because no progress occurs and cracks do not occur. That is, in the thermal cracking test, a glass substrate that has not been etched is used.

Next, the manufacturing method of the glass substrate for magnetic recording media in each experimental example will be described. Experimental Examples 1 to 6, Experimental Examples 9 to 16, Experimental Example 19, and Experimental Example 21 are examples, and Experimental Example 7, Experimental Example 8, Experimental Example 17, Experimental Example 18, Experimental Example 20, Experimental example 22 is a comparative example.
[Experimental Example 1]
Each step was performed in the following order to produce a glass substrate for a magnetic recording medium.
(Shaping process)
In order to obtain a glass substrate for a magnetic recording medium having an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.8 mm, a glass substrate having a donut shape having a circular hole in the center portion of the glass substrate of glass A in Table 1 It was processed into.

The inner diameter means the diameter of the central opening.
(Chamfering process)
An inner peripheral chamfered portion and an outer peripheral chamfered portion were formed on the inner peripheral end surface and the outer peripheral end surface of the glass substrate obtained in the shape imparting step, respectively. At this time, each chamfered portion was chamfered so that a glass substrate having a chamfering width of 0.15 mm and a chamfering angle of 45 ° was obtained.

In the chamfering process, a grinding machine equipped with a diamond wheel is used to grind the inner peripheral end face and the outer peripheral end face at the same time while supplying a grinding liquid containing a surfactant to the grinding point. Formed.

In Experimental Examples 1 and 2, after grinding with electrodeposition type diamond # 500, the surface of 50 μm was subjected to finish grinding using resin bond type diamond # 600.

In Experimental Examples 3 to 22, which will be described later, grinding was performed using only electrodeposition type diamond # 500.
(Main surface polishing process: primary lapping process)
Using a fixed abrasive tool containing diamond particles having an average particle size of 9 μm as a polishing tool and a grinding liquid containing a surfactant, a double-side polishing apparatus (product name: 16BF, manufactured by Hamai Sangyo Co., Ltd.) The upper and lower main surfaces were ground. As a carrier for holding the glass substrate in the double-side polishing apparatus, a carrier made of glass fiber-containing epoxy resin was used.

After completion of the main surface polishing step (primary lapping step), the glass substrate was washed to remove grinding fluid and other dirt.

The average particle diameter means a particle diameter at a volume standard integrated value of 50% in a particle size distribution obtained by a laser diffraction / scattering method. In other parts of the present specification, the average particle size has the same meaning.
(End face polishing process)
The glass substrate which implemented on the same conditions to the main surface grinding | polishing process (primary lapping process) was laminated | stacked. Then, using a nylon brush as the polishing tool, while supplying a cerium oxide abrasive with an average particle diameter of 1 μm, the rotating brush is pressed against the inner and outer peripheral end surfaces of the laminated glass substrates. The peripheral end surface and the outer peripheral end surface were polished.

At this time, the polishing amount of the outer periphery polishing was 50 μm, and the polishing amount of the inner periphery polishing was 25 μm. The polishing amount in the inner and outer peripheral polishing indicates the amount of change in the outer diameter or inner diameter of the substrate. That is, the machining allowance on one side is half of this. For example, when the polishing amount is 10 μm, one side is polished by 5 μm.
(Main surface polishing process: secondary lapping process)
Using a fixed abrasive tool containing diamond particles having an average particle diameter of 4 μm as a polishing tool and a grinding liquid containing a surfactant, a double-side polishing machine (product name: 16BF, manufactured by Hamai Sangyo Co., Ltd.) The upper and lower main surfaces were ground.

As the carrier for holding the glass substrate in the double-side polishing apparatus, a carrier made of an epoxy resin containing glass fiber was used.

After completion of the main surface polishing step (secondary lapping step), the glass substrate was washed to remove grinding fluid and other dirt.
(Main surface polishing process: primary polishing process)
As a polishing tool, using a suede type polyurethane polishing pad and a grinding liquid containing cerium oxide having an average particle diameter of 1 μm, a double-side polishing apparatus (manufactured by Hamai Sangyo Co., Ltd., product name: 16BF) The main surface was polished.

In the main surface polishing step (primary polishing step), the removal amount by polishing was 25 μm. The polishing time is, for example, 50 minutes. The polishing amount in main surface polishing indicates the amount of change in substrate thickness. That is, the machining allowance on one side is half of this. For example, when the polishing amount is 10 μm, one side is polished by 5 μm.

As the carrier for holding the glass substrate in the double-side polishing apparatus, a carrier made of an epoxy resin containing glass fiber was used.

After completion of the main surface polishing step (primary polishing step), the glass substrate was washed to remove grinding fluid and other contaminants.
(Main surface polishing process: secondary polishing process)
As a polishing tool, using a suede type polyurethane polishing pad and a grinding liquid containing colloidal silica having an average particle size of 20 nm or less, a double-side polishing apparatus (product name: 16BF, manufactured by Hamai Sangyo Co., Ltd.) The upper and lower main surfaces were polished.

In the main surface polishing step (secondary polishing step), the removal amount by polishing was 1 μm. The polishing time is, for example, 30 minutes.

As the carrier for holding the glass substrate in the double-side polishing apparatus, a carrier made of an aramid fiber-containing epoxy resin was used.

After completion of the main surface polishing step (secondary polishing step), the glass substrate was washed to remove grinding fluid and other contaminants.
(Washing / drying process)
The glass substrate that has been subjected to the main surface polishing process (secondary polishing process) is sequentially subjected to scrub cleaning, ultrasonic cleaning in a state of being immersed in a detergent solution, and ultrasonic cleaning in a state of being immersed in pure water (precision cleaning). And drying with isopropyl alcohol vapor.

About the glass substrate for magnetic recording media obtained by the above procedure, the arithmetic average roughness Ra of the outer peripheral side surface portion, the arithmetic average roughness Ra of the outer peripheral side surface portion after etching, and the maximum height roughness of the outer peripheral side surface portion after etching Evaluation of thickness Rz and a thermal cracking test were carried out. The evaluation results are shown in Table 2.
[Experiment 2]
A glass substrate was manufactured and evaluated in the same manner as in Experimental Example 1 except that the polishing amount of the outer peripheral polishing in the end surface polishing step was 11 μm. The evaluation results are shown in Table 2.
[Experimental Example 3 to Experimental Example 6]
The glass substrate was produced and evaluated in the same manner as in Experimental Example 1 except for the following points.
(Change 1)
The order of steps from the main surface polishing step (primary lapping step) to the main surface polishing step (secondary polishing step) was changed in the following order.

In Experimental Examples 3 to 6, after the main surface polishing step (primary lapping step), the main surface polishing step (secondary lapping step), main surface polishing step (primary polishing step), end surface polishing step, main surface polishing step ( (Secondary polishing step).
(Change 2)
The carrier material used in the main surface polishing step (primary lapping step), main surface polishing step (secondary lapping step), main surface polishing step (primary polishing step), and main surface polishing step (secondary polishing step) is changed. did.

Specifically, in Experimental Example 3, a stainless steel carrier was used. In Experimental Example 4, a glass fiber-containing epoxy resin carrier was used, in Experimental Example 5, an aramid fiber-containing epoxy resin carrier was used, and in Experimental Example 6, a polyvinyl chloride resin carrier was used.

The conditions in each step are the same as in Experimental Example 1 except that the carrier material used in each main surface polishing step is different.

The evaluation results are shown in Table 2.
[Experimental Example 7 to Experimental Example 15]
The glass substrate was produced and evaluated in the same manner as in Experimental Example 1 except for the following points.
(Change 1)
The order of steps from the main surface polishing step (primary lapping step) to the main surface polishing step (secondary polishing step) was changed in the following order.

After the main surface polishing step (primary lapping step), the main surface polishing step (secondary lapping step), the main surface polishing step (primary polishing step), the main surface polishing step (secondary polishing step), and the end surface polishing step are performed in this order. did. In Experimental Example 7, the end face polishing step is not performed.
(Change 2)
The conditions of the end face polishing process were changed as follows.

For Experimental Example 7, the end surface polishing step was not performed. The polishing amount of the peripheral polishing in the end face polishing step in Experimental Example 8 to Experimental Example 15 is 5 μm (Experimental Example 8), 8 μm (Experimental Example 9), 11 μm (Experimental Example 10), 16 μm (Experimental Example 11), and 21 μm, respectively. (Experimental Example 12), 27 μm (Experimental Example 13), 32 μm (Experimental Example 14), and 38 μm (Experimental Example 15).
(Change 3)
The carrier material used in the main surface polishing step (primary lapping step), main surface polishing step (secondary lapping step), main surface polishing step (primary polishing step), and main surface polishing step (secondary polishing step) is changed. did.

In Experiment Example 7, a glass fiber-containing epoxy resin carrier was used, and in Experiment Examples 8 to 15, an aramid fiber-containing epoxy resin carrier was used.

Except for the above points, the conditions in each step are the same as in Experimental Example 1.

The evaluation results are shown in Table 2.
[Experimental Example 16]
In this experimental example, the experiment was performed except that the main surface polishing step (primary polishing step) was followed by the main surface polishing step (chemical strengthening step for performing chemical strengthening treatment of the glass substrate before performing the secondary polishing step). A glass substrate was produced and evaluated in the same manner as in Example 1. Table 2 shows the evaluation results.

The chemical strengthening was performed by immersing the glass substrate after the main surface polishing step (primary polishing step) in a dissolved salt at 400 ° C. containing 60% by weight of potassium nitrate and 40% by weight of sodium nitrate.

In addition, a process of preheating the glass substrate to 350 ° C. for 30 minutes was provided before the glass substrate was immersed in the dissolved salt. In addition, after immersing the glass substrate in the dissolved salt, the glass substrate was allowed to stand at 350 ° C. for 10 minutes and the dissolved salt was poured off, followed by slow cooling.

The chemical strengthening step was performed such that the depth DOL of the compressive stress at the outer peripheral side surface portion was 10 μm.
[Experimental Example 17, Experimental Example 18]
In this experimental example, the amount of outer peripheral polishing in the end surface polishing step was 5 μm, and in the chemical strengthening step, the depth DOL of the compressive stress in the outer peripheral side surface portion was 10 μm in experimental example 17 and 17 μm in experimental example 18. Thus, the glass substrate was produced and evaluated in the same manner as in Experimental Example 16 except that chemical strengthening was performed.

The evaluation results are shown in Table 2.
[Experimental Example 19, Experimental Example 21]
Production of a glass substrate in the same manner as in Experimental Example 1 except that a glass base substrate made of Glass B (Experimental Example 19) and Glass C (Experimental Example 21) in Table 1 was used as the glass substrate used in the shape imparting step. And evaluation. The evaluation results are shown in Table 2.
[Experimental Example 20, Experimental Example 22]
The glass substrate was subjected to the same procedure as in Experimental Example 8 except that a glass substrate made of glass B (Experimental Example 20) or Glass C (Experimental Example 22) in Table 1 was used as the glass substrate used in the shape imparting step. Manufacture and evaluation were performed. The evaluation results are shown in Table 2.

Table 3 shows the order of steps when manufacturing the glass substrate in each experimental example. In the same manner as described so far, each experimental example is performed in the order from step 1 to step 9 in Table 3.

According to the results shown in Table 2, the arithmetic average roughness Ra of the outer peripheral side surface portion is 0.1 μm or less, and the arithmetic average roughness Ra of the outer peripheral side surface portion after etching after etching 5 μm from the surface of the outer peripheral side surface portion. It is confirmed that the thermal cracking rate is 20% or less for the glass substrates of Experimental Example 1 to Experimental Example 6, Experimental Example 9 to Experimental Example 16, Experimental Example 19 and Experimental Example 21 in which the thickness is 0.5 μm or less. did it. This is because, for glass substrates having an arithmetic mean roughness Ra of the outer peripheral side surface after etching of 0.5 μm or less, the presence frequency of microcracks on the outer peripheral side surface is sufficiently low, so even when a sudden temperature change is applied. This is probably because the thermal cracking was suppressed.

On the other hand, the arithmetic average roughness Ra of the outer peripheral side surface portion is larger than 0.1 μm, and the arithmetic average roughness Ra of the outer peripheral side surface portion after etching after etching 5 μm from the surface of the outer peripheral side surface portion from 0.5 μm. For the large glass substrates of Experimental Examples 7, 8, and 20, it was confirmed that the thermal cracking rate exceeded 20%.

This is because, in the glass substrates of Experimental Examples 7, 8, and 20, the existence frequency of minute cracks in the outer peripheral side surface portion is high, and stress is concentrated on the minute cracks when a sudden temperature change is applied. This is thought to have occurred.

When the chemical strengthening depth DOL is 15 μm or more as in Example 18, the thermal cracking rate is low even if the arithmetic average roughness Ra of the outer peripheral side surface after etching is larger than 0.5 μm. However, as described above, the DOL of the glass substrate for energy-assisted magnetic recording medium is preferably 15 μm or less. Example 17 with a DOL of 10 μm reduces the thermal cracking rate compared to Example 8 with an equivalent arithmetic mean roughness Ra, but is more effective in Example 16 with an arithmetic mean roughness Ra lower than 0.5 μm. In addition, the thermal cracking rate can be reduced. That is, even in a glass substrate subjected to chemical strengthening, setting the arithmetic average roughness Ra to 0.5 μm or less is effective in reducing the thermal cracking rate.

Example 22 uses a glass material with a low coefficient of thermal expansion, so the rate of occurrence of thermal cracking is lower than Example 8 which has the same arithmetic mean roughness Ra, but the arithmetic mean roughness Ra is low with the same glass material. In Example 21, the thermal cracking rate is even lower. That is, even when a glass material having a low coefficient of thermal expansion is used, it is effective for reducing the thermal cracking rate to set the arithmetic average roughness Ra to 0.5 μm or less.

Further, comparing Experimental Examples 1 to 4, there is almost no difference in the arithmetic average roughness Ra of the outer peripheral side surface before etching, but there is a clear difference in the arithmetic average roughness Ra of the outer peripheral side portion after etching. Yes, it can be confirmed that the thermal cracking rate is changed accordingly. From this, it can be seen that the effect on thermal cracking can be evaluated only by performing etching.

Furthermore, when Example 2 and Experimental Example 9 are compared, the arithmetic average roughness Ra of the outer peripheral side surface after etching is the same, but the maximum height roughness Rz of the outer peripheral side surface after etching is different. And it can confirm that the incidence rate of a thermal crack is also changing according to it.

From the above results, it is important for the thermal cracking rate that the arithmetic average roughness Ra of the outer peripheral side surface after etching is 0.5 μm or less, but the maximum height roughness Rz of the outer peripheral side surface after etching is It was confirmed that it was important to set the thickness to 10 μm or less.

For reference, Table 4 shows the percentage of roughness at a load factor of 50%, which is used as a method for expressing the surface state of a part of the experimental example. Table 4 also shows the thermal cracking rates shown in Table 3.

簡 単 The roughness percentage when the load factor is 50% will be briefly explained.

Suppose that, in the measurement result of the surface shape of the near-surface area of the object to be measured, the near-surface area of the object to be measured is cut by a plane parallel to the surface that forms the macroscopic shape of the surface of the object to be measured.

In this case, the level of the height to be cut at the surface in contact with the maximum protruding portion that protrudes to the maximum in the surface vicinity region is set to 0% as the maximum height, and the surface in contact with the deepest valley portion that is deepest in the surface vicinity region The level of the height to be cut is set to a minimum height of 100%. The percentage of roughness represents the level of cutting height between the highest and lowest heights in percent.

The load factor is the cut surface of the sample to be measured when the area of the region existing on the cut surface of the sample to be measured is cut at 100% roughness when the sample is cut at a specific roughness percentage level. Divided by the area of the existing region.

Therefore, it can be said that the percentage of roughness when the load factor is 50% indicates the level of cutting height at which the load factor is 50%. That is, the results shown in Table 4 are the same as when measuring the arithmetic mean roughness Ra, and the end face of the glass substrate subjected to etching of 5 μm was measured in a measurement area of 200 μm × 200 μm, and the presence of the measurement object for the entire measurement area The percentage of roughness when the area ratio of the area to be processed is 50% is shown.

As is clear from the results in Table 4, there is no correlation between the thermal cracking rate and the roughness percentage when the load factor is 50%, which is an appropriate index for reducing the cracking rate. It can be confirmed that it is not.

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application filed on December 28, 2015 (Japanese Patent Application No. 2015-257144), which is incorporated by reference in its entirety.

10 Glass substrate for magnetic recording media (glass substrate)
121, 122 Main surface 13 Outer peripheral end surfaces 131, 133 Outer peripheral chamfered portion 132 Outer peripheral side surface 14 Inner peripheral end surface 141, 143 Inner peripheral chamfered portion 142 Inner peripheral side surface portion

Claims (7)

1. A glass substrate for a magnetic recording medium having a donut shape and having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface, the outer peripheral end surface having an outer peripheral side surface portion and a pair of outer peripheral chamfered portions ,
   The arithmetic average roughness Ra of the outer peripheral side surface portion is 0.1 μm or less,
   About the said outer peripheral side part, the glass substrate for magnetic recording media whose arithmetic mean roughness Ra of the outer peripheral side part after an etching after etching 5 micrometers from the surface is 0.5 micrometer or less.
2. The glass substrate for a magnetic recording medium according to claim 1, wherein the maximum height roughness Rz of the outer peripheral side surface after the etching is 10 μm or less.
3. The thermal expansion coefficient in the temperature range of 50 ° C. or higher and 350 ° C. or lower is 70 × 10 ⁻⁷ / ° C. or lower,
   The glass substrate for magnetic recording media according to claim 1 or 2, comprising a glass material having a glass transition point Tg of 650 ° C or higher.
4. 4. The glass substrate for a magnetic recording medium according to claim 1, comprising a glass material having a thermal expansion coefficient of 55 × 10 ⁻⁷ / ° C. or less in a temperature range of 50 ° C. or more and 350 ° C. or less.
5. The glass substrate for a magnetic recording medium according to any one of claims 1 to 4, wherein the depth DOL of the compressive stress by the chemical strengthening treatment is 1 μm ≦ DOL ≦ 15 μm at least on the outer peripheral side surface of the glass substrate.
6. The glass substrate for magnetic recording media according to any one of claims 1 to 5, which is a glass substrate for magnetic recording media for energy-assisted magnetic recording media.
7. A magnetic recording medium comprising the glass substrate for a magnetic recording medium according to any one of claims 1 to 6.

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