JP2017120679A - Glass substrate for magnetic recording medium, magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass substrate for magnetic recording medium which suppresses cracks generated when the temperature abruptly changes.SOLUTION: There is provided a doughnut-shaped glass substrate for magnetic recording medium including a pair of principal surfaces, an outer peripheral end surface, and an inner peripheral end surface. In a cross section perpendicular to a pair of principal surfaces and passing through a centre axis of the glass substrate for magnetic recording medium, when an axis parallel to the principal surface is defined as an X-axis, an X-coordinate of the outer peripheral end surface in the most outer peripheral position is defined as 0, and an X-coordinate of the outer peripheral end surface closer to the centre axis of the glass substrate for magnetic recording medium than the most outer peripheral position is defined as positive, in the outer peripheral end surface, an angle formed between a straight line connecting a point of 5 μm in the X-coordinate and a point of 10 μm in the X-coordinate, and the X-axis is 81° or more and 85° or less; an angle formed between a straight line connecting a point of 10 μm in the X-coordinate and a point of 20 μm in the X-coordinate, and the X-axis is 69° or more and 83° or less; and an angle formed between a straight line connecting a point of 20 μm in the X-coordinate and a point of 30 μm in the X-coordinate, and the X-axis is 52° or more and 72° or less.SELECTED DRAWING: Figure 2

Description

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

  The magnetic recording apparatus includes a magnetic recording medium in which 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.

  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 raise the degree of ordering (order degree) and to realize high Ku, at the time of film formation of a magnetic layer, before film formation, or after film formation, a base material including a glass substrate for a magnetic recording medium is set to 600 ° C. Heat treatment may be performed at a high temperature of about 700 ° C.

  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.

  The glass substrate for a magnetic recording medium usually has a donut shape having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface, and the outer peripheral end surface includes an outer peripheral side surface portion and an outer peripheral side surface portion that are substantially perpendicular to the main surface. An outer peripheral chamfered portion is disposed between the main surface.

  Various studies have been made on the shape of the end face of a glass substrate for a magnetic recording medium. For example, Patent Document 1 discloses a glass substrate for a magnetic recording medium that is effective for countermeasures against magnetic disk corrosion.

  Specifically, it is a glass substrate for a magnetic disk manufactured by a manufacturing method including a grinding process step of a substrate end surface, and the end surface of the glass substrate includes a side wall surface, both main surfaces and side wall surfaces of the glass substrate. Between the two chamfered surfaces, the variation of the in-plane surface roughness Ra is within ± 0.01 μm, and the end surface of the glass substrate is a mirror surface. The surface roughness Rmax is 1 μm or less and Ra is 0.1 μm or less, and the angle variation between the chamfered surface and the side wall surface of the inner and outer periphery of the glass substrate is 0.8 with respect to the target angle. A glass substrate for a magnetic disk, which is characterized by being within the range, is disclosed.

Japanese Patent No. 5639215

  By the way, when a glass substrate for a magnetic recording medium is subjected to a rapid temperature change during heat treatment at a high temperature as described above or during cooling after the heat treatment, cracks or the like are generated starting from the outer peripheral end surface. was there. For this reason, there has been a demand for a glass substrate for a magnetic recording medium that can suppress the occurrence of cracks even when a sudden temperature change is applied during heat treatment.

  In view of the above-described problems of the prior art, an object of one aspect of the present invention is to provide a glass substrate for a magnetic recording medium in which cracking is suppressed when a sudden temperature change is applied.

In one aspect of the present invention, a glass substrate for a magnetic recording medium in a donut shape having 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 side surface portion, and an outer peripheral chamfered portion disposed between the outer peripheral side surface portion and the main surface,
In a cross section perpendicular to the pair of main surfaces and passing through the central axis of the glass substrate for magnetic recording medium,
The axis parallel to the main surface is the X axis, the X coordinate of the outermost peripheral surface of the outer peripheral end surface is 0, and the X coordinate on the central axis side of the glass substrate for a magnetic recording medium from the outermost peripheral position of the outer peripheral end surface is If positive,
Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 5 μm and a point having an X coordinate of 10 μm and the X axis is 81 ° to 85 °,
Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 10 μm and a point having an X coordinate of 20 μm and the X axis is 69 ° or more and 83 ° or less,
Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 20 μm and a point having an X coordinate of 30 μm and the X axis is 52 ° or more and 72 ° or less,
A glass substrate for a magnetic recording medium is provided.

  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 the occurrence of cracking when a sudden temperature change is applied.

Explanatory drawing of the glass substrate for magnetic recording media which concerns on embodiment of this invention. FIG. 2 is a partially enlarged view of a cross-sectional view of the magnetic recording medium glass substrate of FIG. 1. Explanatory drawing of the grindstone used at a chamfering process. Explanatory drawing of the structural example of the end surface grinding | polishing apparatus used at an end surface grinding | polishing process.

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 this embodiment is a glass substrate for a magnetic recording medium 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 portion and an outer peripheral side surface portion. And an outer peripheral chamfer disposed between the main surface and the main surface.
Here, in a cross section perpendicular to the pair of main surfaces and passing through the central axis of the glass substrate for magnetic recording medium, the axis parallel to the main surface is the X axis, the X coordinate of the outermost peripheral position of the outer peripheral end surface is 0, the outer periphery The X coordinate on the central axis side of the glass substrate for magnetic recording media is more positive than the outermost peripheral position of the end face.

In this case, an angle formed by a straight line connecting a point having an X coordinate of 5 μm and a point having an X coordinate of 10 μm on the outer peripheral end face and the X axis can be 81 ° or more and 85 ° or less. .
In addition, an angle formed by a straight line connecting a point having an X coordinate of 10 μm and a point having an X coordinate of 20 μm on the outer peripheral end surface and the X axis can be 69 ° or more and 83 ° or less.
In addition, an angle formed by a straight line connecting a point having an X coordinate of 20 μm and a point having an X coordinate of 30 μm on the outer peripheral end surface and the X axis may be 52 ° or more and 72 ° or less.

  First, the structure of a glass substrate for a magnetic recording medium according to 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. FIG. 1 is a perspective cross-sectional view including a cross section in a plane passing through the central axis O 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 an outer peripheral side surface portion 132, and the inner peripheral end surface 14 can have an 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.

  The inventors of the present invention have earnestly studied a glass substrate that can suppress the occurrence of cracking even when a sudden temperature change is applied during heat treatment or the like. The cracks that are generated when a sudden temperature change is applied during heat treatment or the like are caused mainly by the thermal expansion or contraction of the outer peripheral end surface, starting from minute cracks contained in the outer peripheral end surface. I found out.

  Therefore, the inventors of the present invention further studied, and the shape of the outer peripheral end surface, specifically, the shape of the outer peripheral end surface in a cross section perpendicular to the main surface and passing through the central axis of the glass substrate, that is, the contour shape of the outer peripheral end surface It has been found that cracking can be suppressed in the case of a predetermined shape.

  Here, the shape of the outer peripheral end face of the glass substrate of the present embodiment will be described with reference to FIG. FIG. 2 is an enlarged view of a region 15 indicated by a dotted line in FIG.

  FIG. 2 is an enlarged view of the periphery of the outer peripheral end face in a cross section perpendicular to the pair of main surfaces 121 and 122 and passing through the central axis O of the glass substrate 10 as shown in FIG.

  Here, as shown in FIG. 2, the axis parallel to the main surface 121 is taken as the X axis, the X coordinate of the outermost peripheral position of the outer peripheral end surface 13 is 0, and the outermost peripheral position of the outer peripheral end surface 13 is more than that for the magnetic recording medium. The X coordinate on the central axis side of the glass substrate is positive.

  As described with reference to FIG. 1, the outer peripheral end surface 13 includes an outer peripheral side surface portion 132 and outer peripheral chamfered portions 131 and 133, and the outer peripheral side surface portion 132 is substantially perpendicular to the pair of main surfaces 121 and 122. It has become. For this reason, when the outer peripheral side surface portion 132 includes a straight line portion perpendicular to the main surfaces 121 and 122, the straight line portion can be set to the outermost peripheral position where the X coordinate is zero. When the outer peripheral side surface 132 does not include a straight line portion perpendicular to the main surfaces 121 and 122, the X coordinate is 0 at the intersection of the tangent line of the outer peripheral side surface 132 perpendicular to the main surfaces 121 and 122 and the X axis. It can be set as the outermost peripheral position.

In this case, the glass substrate 10 of this embodiment, of the outer peripheral end surface 13, a point _{P 5} in the X-coordinate _{X 5} is 5 [mu] m, the straight line X-coordinate _{X 10} is connecting the point _{P 10} of 10 [mu] m, X axis The angle θ _5-10 formed by and can be 81 ° or more and 85 ° or less.

Note that parallel to the X-axis in the figure _2, it shows a straight line _{X A} through _{P 10,} and the straight line _{X A,} is the angle which the straight line _P 5 _{P 10} makes the above theta _5-10.

Further, of the outer peripheral end surface 13, a point _{P 10} of the X-coordinate _{X 10} is 10 [mu] m, the straight line X-coordinate _{X 20} is connecting the point _{P 20} of 20 [mu] m, the angle theta _10-20 where the X-axis to form 69 The angle can be not less than 83 ° and not more than 83 °. Note that parallel to the X-axis in the figure _2, it shows a straight line _{X B} through _{P 20,} and the straight line _{X B,} the angle formed by the meeting of a straight line _P 10 _{P 20} becomes the theta _10-20.

Further, of the outer peripheral end surface 13, a point _{P 20} of the X-coordinate _{X 20} is 20 [mu] m, the straight line X-coordinate _{X 30} is connecting the point _{P 30} of 30 [mu] m, the angle theta _20-30 where the X-axis to form 52 It can be set in the range from ° to 72 °. Note that parallel to the X-axis in the figure _2, shows a straight line _{X C} through the _{P 30,} and the straight line _{X C,} the angle the straight line _P 20 _{P 30} makes the above theta _20-30.

  The glass substrate of the present embodiment has the above shape from the outer peripheral chamfered portion to the outer peripheral chamfered portion, so that the inclination gradually changes from the outer peripheral side surface portion toward the outer peripheral chamfered portion, and has such a shape. Thus, it is possible to suppress the occurrence of cracks when a sudden temperature change is applied.

  By the way, when heat treatment is performed to form a magnetic layer or the like on a glass substrate, the heat treatment is performed in a state where the glass substrate is supported by a support member, and the magnetic layer or the like is formed depending on the process.

  During the heat treatment step and the step of forming a magnetic layer or the like on the glass substrate, the support member is pressed to each of a plurality of locations on the outer peripheral end surface so that the main surface is not covered with the support member, It is supported by sandwiching the glass substrate with a support member. At this time, the surface facing the outer peripheral end surface of the support member usually has a shape corresponding mainly to the outer peripheral side surface portion of the outer peripheral end surface.

  And since the outer peripheral end surface of the glass substrate of this embodiment has a gentle change in the inclination of the surface between the outer peripheral side surface portion and the outer peripheral chamfered portion as described above, the support member and the outer peripheral end surface A contact area becomes large and the force applied to a glass substrate from a supporting member can be disperse | distributed.

  For this reason, according to the glass substrate of this embodiment, it can suppress that force is locally applied to a glass substrate by a supporting member, and also from such a viewpoint, occurrence of cracking when a sudden temperature change is applied. Can be suppressed.

Furthermore, as described above, according to the glass substrate of the present embodiment, since θ _{5-10 and} θ _10-20 are large, the contact area between the glass substrate and the support member can be increased, and the glass substrate is added. Since the force can be dispersed, chipping, that is, chipping, can be suppressed between the outer peripheral side surface and the outer peripheral chamfered portion of the outer peripheral end surface of the glass substrate when the magnetic layer or the like is formed.

On the other hand, if θ _20-30 is too large, it becomes difficult as a result to increase the angle between the main surface and the outer peripheral chamfered portion. Chipping is likely to occur between the peripheral chamfered portion. On the other hand, according to the glass substrate of this embodiment, generation | occurrence | production of the chipping of the said part can also be suppressed.

Incidentally, by making the cross-sectional shape between the outer peripheral side surface portion and the outer peripheral chamfered portion a single radius of curvature within a certain range (for example, R = 0.6 to 0.8 mm), θ _5-10, θ _{10− Although} it is possible to increase the value of ₂₀ (for example, 81 ° to 85 °, 69 ° to 83 °, respectively), θ _20-30 becomes too large and a suitable range (for example, 52 ° to 72 °). I can't. Alternatively, it is possible to set the value of θ _20-30 to a suitable range by setting a single radius of curvature in another range (for example, R = 0.15 to 0.5 mm). _5-10 or θ _10-20 cannot be set to a sufficiently large range.

  Further, when a magnetic layer or the like is formed, a voltage may be applied to the base material including the glass substrate by the support member. However, when the magnetic layer is formed on the conventional glass substrate, the support member There was a case where the contact area between the glass substrate and the glass substrate was not sufficient, and the glass substrate was not stable and an arc was generated. When the arc is generated, dust is generated, and in some cases, the missing count increases in the inspection of the manufactured magnetic recording medium.

  On the other hand, in the glass substrate of this embodiment, since the outer peripheral end surface has the structure described above, the contact area between the support member and the outer peripheral end surface is increased, and the glass substrate can be stably supported. For this reason, since generation | occurrence | production of an arc can be suppressed and by extension dusting can be suppressed, it becomes possible to suppress a missing count in the magnetic recording medium obtained.

  In addition, the glass substrate of the present embodiment is perpendicular to the pair of main surfaces and passes through the central axis of the glass substrate, with the axis parallel to the main surface 121 as the X axis and the outermost peripheral position X of the outer peripheral end surface 13. More preferably, the following configuration is satisfied when the coordinate is 0 and the X coordinate on the central axis side of the glass substrate is positive rather than the outermost peripheral position of the outer peripheral end face 13.

Of the outer peripheral end surface 13, a point _{P 5} in the X-coordinate _{X 5} is 5 [mu] m, the straight line X-coordinate _{X 10} is connecting the point _{P 10} of 10 [mu] m, the angle theta _5-10 in which the X axis is formed 81 ° or more More preferably, it is 84 ° or less.

Further, of the outer peripheral end surface 13, a point _{P 10} of the X-coordinate _{X 10} is 10 [mu] m, the straight line X-coordinate _{X 20} is connecting the point _{P 20} of 20 [mu] m, the angle theta _10-20 where the X-axis to form the 75 It is more preferable that the angle is not less than ° and not more than 82 °.

Of the outer peripheral end surface 13, a point _{P 20} of the X-coordinate _{X 20} is 20 [mu] m, the straight line X-coordinate _{X 30} is connecting the point _{P 30} of 30 [mu] m, the angle theta _20-30 in which the X axis is formed 55 ° or more More preferably, it is 72 ° or less.

Of the outer peripheral end surface 13, a point _{P 30} of the X-coordinate _{X 30} is 30 [mu] m, the straight line X-coordinate _{X 40} is connecting the point _{P 40} of 40 [mu] m, the angle theta _30-40 in which the X axis is formed 51 ° or more More preferably, it is 68 ° or less. Note that parallel to the X-axis in the figure _2, it shows a straight line _{X D} through _{P 40,} and the straight line _{X D,} the angle formed by the meeting of a straight line _P 30 _{P 40} becomes the theta _30-40.

  2 shows an enlarged view of the periphery of the outer peripheral chamfered portion 131 and the outer peripheral side surface portion 132 in the outer peripheral end surface 13 shown in FIG. However, as shown in FIG. 1, the outer peripheral end surface 13 of the glass substrate of this embodiment has a pair of outer peripheral chamfered portions 131 and 133 and an outer peripheral side surface portion 132. For this reason, not only the part of one outer peripheral chamfer 131 and the outer peripheral side part 132 but also the other outer peripheral chamfer 133 and the outer peripheral side part 132 have the same configuration as described above. Can do.

  About the glass substrate of this embodiment, it does not specifically limit about glass material, Various glass materials can be used. However, as for the glass material used for the glass substrate, it is more preferable to use a glass substrate that does not easily crack even when a sudden temperature change is applied.

For this reason, it is more preferable that the glass substrate of this embodiment consists of a glass material whose average thermal expansion coefficient in a temperature range of 50 degreeC or more and 350 degrees C or less is less than ^50x10 < ^-7 > / ^degreeC .

This is because when the average coefficient of thermal expansion in the temperature range of 50 ° C. or more and 350 ° C. or less is less than 50 × 10 ⁻⁷ / ° C., the glass substrate can be prevented from expanding and contracting due to temperature change, and thus a rapid temperature change occurs. This is because even when added, cracking can be suppressed in combination with the shape of the outer peripheral end face.

  The lower limit value of the average 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, for example, thermal expansion in the temperature range of 50 ° C. or higher and 350 ° C. or lower. A glass material having a coefficient larger than 0 can be used.

As a glass material of the glass substrate of the present embodiment, SiO ₂ is 62% to 74%, Al ₂ O ₃ is 7% to 18%, and B ₂ O ₃ is 2% to 15% in terms of mole percentage. MgO is contained in an amount of 0 to 10%, CaO, SrO and BaO are contained in a total of 1% to 21%, and the total content of MgO, CaO, SrO and BaO is 8% to 21%. % Or less, and those having a total content of the above seven components of 95% or more can be suitably used.

Moreover, as a glass material of the glass substrate of the present embodiment, SiO ₂ is 62% or more and 74% or less, Al ₂ O ₃ is 7% or more and 18% or less, and B ₂ O ₃ is 0 or more and less than 2% in terms of mole percentage. , MgO, CaO, SrO and BaO with a total content of 5% or more and 18% or less and a total content of the seven components of 95% or more can be suitably used.

As the glass material of the glass substrate of this embodiment, the molar in percentage display, a SiO ₂ 60% to 75% or less, _Al 2 _{O 3} 17% 7% more or _less, B 2 _{O 3} 0 2% or more The total content of MgO, CaO, SrO and BaO is more than 18% and 26% or less, and the total content of the seven components is 95% or more.

  The glass substrate of this embodiment can suppress the occurrence of cracks 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 the ordering of an FePt-based magnetic layer alloy (magnetic material) contained in the magnetic layer, a temperature of 600 ° C. to 700 ° C. is used during the formation of the magnetic layer. Generally, heat treatment is performed at a high temperature.

  As described above, particularly when an energy-assisted magnetic recording medium is manufactured, when a heat treatment is performed at a high temperature of about 600 ° C. to 700 ° C., a rapid temperature change may be applied to the glass substrate. In some cases, cracks may occur. On the other hand, according to the glass substrate of this embodiment, since the shape of the outer peripheral end surface is a predetermined shape, it is possible to suppress the occurrence of cracking even when a sudden temperature change is applied.

  For this reason, the glass substrate of this embodiment can be used especially suitably as a glass substrate for magnetic recording media for energy-assisted magnetic recording media.

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

  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.

  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.

  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 addition, when it is set as the glass substrate which has the shape of the outer periphery end surface 13 as stated above, when forming the outer peripheral chamfered portions 131 and 133, the corners between the outer peripheral side surface portion 132 and the outer peripheral chamfered portions 131 and 133 are radiused. Is preferably a circular arc curve of a circle of 0.3 mm to 0.4 mm. Then, by appropriately selecting the conditions for the outer peripheral end face including the corner of the curved line in the end face polishing process described later, polishing the necessary and sufficient amount of polishing, and correcting the arc curve of the single curvature radius, It can be set as the shape of the outer peripheral end surface of a glass substrate.

  The chamfering of the outer peripheral end surface of the glass substrate is usually performed using a grindstone 31 having a substantially cylindrical shape as shown in FIG. 3A and having a plurality of grooves 32 formed on the peripheral surface.

  Then, as shown in FIG. 3A, the glass substrate 10 and the grindstone 31, the central axis O of the glass substrate 10, and the grindstone 31 in a state where the outer peripheral end of the glass substrate 10 is accommodated in the groove 32. The chamfering can be performed by rotating the central axis 33 as a rotation axis.

  For this reason, the groove | channel 32 has a cross-sectional shape corresponding to the shape of the outer peripheral end surface of the glass substrate to form. As described above, when the corner portion between the outer peripheral side surface portion 132 and the outer peripheral chamfered portions 131 and 133 is a circular arc curve having a radius of 0.3 mm or more and 0.4 mm or less, a groove having a cross-sectional shape corresponding thereto. 32 is required.

  FIG. 3B shows a cross-sectional view of the groove 32 on the surface 34 passing through the central axis 33 and the groove 32 of the grindstone 31. As described above, when the corner portion between the outer peripheral side surface portion 132 and the outer peripheral chamfered portions 131 and 133 is formed into a circular arc shape with a predetermined radius, the groove 32 includes the outer peripheral side surface portion 132, the outer peripheral chamfered portion 131, The portions 35 </ b> A and 35 </ b> B that grind the corners between the first and second portions 133 have a corresponding curved surface shape.

  Moreover, the groove | channel 32 can form the outer peripheral chamfering part of a predetermined chamfering angle by making side wall part angle 36A, 36B into an angle corresponding to the chamfering angle of an outer peripheral chamfering part.

  In addition, although it demonstrated centering on the chamfering process of an outer peripheral end surface here, chamfering can be similarly performed also about an inner peripheral end surface using the grindstone of the substantially cylindrical shape which has the groove | channel according to the shape of the inner peripheral end surface to form. it can.

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

  FIG. 4 illustrates a configuration example of an end surface polishing apparatus used in the end surface polishing step.

  In the end face polishing step, glass substrate laminates 41 and 42 obtained by laminating glass substrates that are objects to be polished can be prepared. The glass substrate laminates 41 and 42 can be laminated by arranging a spacer between the opposing main surfaces of the glass substrate.

  In addition, although the example which performs end surface grinding | polishing simultaneously about two glass substrate laminated bodies 41 and 42 was shown in FIG. 4, it is not limited to such a form, Even if end surface grinding | polishing is performed about one glass substrate laminated body Good. As a matter of course, the two glass substrate laminates 41 and 42 are arranged so as not to contact each other.

  And it can arrange | position so that the cylindrical brushes 43 and 44 may contact with the outer peripheral end surface of the glass substrate laminated body 41 and 42. FIG. At this time, the brushes 43 and 44 are preferably arranged so as to be sufficiently pressed against the glass substrate laminates 41 and 42.

  The brushes 43 and 44 can move along the height directions A and B in the drawing, respectively, and can polish the end faces of all the glass substrates included in the glass substrate laminate.

  Although it does not specifically limit about the brushes 43 and 44, It is preferable that the wire diameter of the brush hair of the brush 43 and the wire diameter of the brush hair of the brush 44 differ. This is because by using a combination of brushes having different bristle diameters, the outer peripheral chamfered portion surface on the main surface side can be polished while rounding the corner portion between the outer peripheral chamfered portion and the outer peripheral side surface portion. For example, it is preferable to use a brush having a bristle wire diameter of 0.3 mm in combination with a brush having a bristle wire diameter of 0.2 mm.

  With the glass substrate laminates 41 and 42 and the brushes 43 and 44 in a state where the glass substrate laminates 41 and 42 and the brushes 43 and 44 are in contact with each other, the rotation directions C, D, E, and By rotating in the direction F, the outer peripheral end face of the glass substrate in the glass substrate laminates 41 and 42 can be polished.

  In the end surface polishing step, it is preferable to polish the outer peripheral end surface of the glass substrate with a polishing amount of 40 μm or more and 70 μm or less. In the above-described chamfering step, the bristle is used in combination with, for example, the above-described wire diameter for the outer peripheral end surface of the glass substrate in which the corner portion between the outer peripheral side surface portion and the outer peripheral chamfered portion has a predetermined arc curve. By polishing the polishing amount, the shape of the outer peripheral end face of the glass substrate described above can be obtained.

  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 (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 or the like 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.

  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 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.

  According to the glass substrate for a magnetic recording medium of the present embodiment described above, since the shape of the outer peripheral end face is a predetermined shape, it is possible to suppress the occurrence of cracking when a sudden temperature change is applied. .

  Further, according to the glass substrate of the present embodiment, the contact area between the glass substrate and the support member when performing heat treatment or the like of the glass substrate can be widened, and the force applied to the glass substrate can be dispersed.

  For this reason, it can control that a crack arises also when a sudden temperature change is given to a glass substrate also from the viewpoint concerned.

  Furthermore, since the magnetic layer and the like are formed, it is possible to suppress chipping, that is, chipping, on the outer peripheral end surface of the glass substrate when the glass substrate is supported by the support member.

Moreover, in the glass substrate of this embodiment, since an outer peripheral end surface has the above-mentioned structure, the contact area of a supporting member and an outer peripheral end surface becomes large, and it can support a glass substrate stably. For this reason, when forming a magnetic layer etc., even when a voltage is applied with respect to the base material containing a glass substrate by a support member, generation | occurrence | production of an arc can be suppressed and dust generation can be suppressed. Therefore, the missing count can be suppressed in the obtained magnetic recording medium.
[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.

  An example of the configuration of the magnetic recording medium of the present embodiment will be described below. However, since the glass substrate for magnetic recording medium described above can be applied to magnetic recording media of various recording methods, the magnetic recording of the present embodiment The configuration of the medium is not particularly limited.

  The magnetic recording medium of the present embodiment can be manufactured by forming a perpendicular magnetic layer or the like serving as a perpendicular magnetization film on the main surface of the glass substrate described above. Examples of the magnetic material forming the perpendicular magnetic layer include a CoCrPt alloy and an FePt alloy.

  Specifically, the magnetic recording medium of the present embodiment can have a configuration in which, for example, a perpendicular magnetic layer, a protective layer, and a lubricating film are formed on the main surface of the glass substrate described above. A material corresponding to the perpendicular magnetic recording system can be used for the perpendicular magnetic layer. In order to further improve the recording density, an energy assisted magnetic recording method (for example, a heat assisted magnetic recording method, a microwave assisted magnetic recording method, etc.) is preferable. In this case, the perpendicular magnetic layer has an energy assisted magnetic recording method. A material corresponding to the recording method can be used.

  In the case of the perpendicular recording system, it is common to form a soft magnetic underlayer made of a soft magnetic material that plays a role of circulating a recording magnetic field from a magnetic head. For the soft magnetic underlayer, a soft magnetic material containing Co, Fe, Ni or the like is used. Specifically, FeCo alloy, FeNi alloy, FeAl alloy, FeCr alloy, FeTa alloy, FeMg alloy, FeZr alloy, FeC alloy, FeN alloy, FeSi alloy, FeP alloy, FeNb Alloys, FeHf alloys, FeB alloys and the like are used.

  Further, in order to suppress the corrosion of the soft magnetic underlayer due to the influence of the adsorbed gas and adsorbed moisture on the main surface of the glass substrate or the diffusion of the components contained in the glass substrate, between the glass substrate 10 and the soft magnetic underlayer. In addition, an adhesion layer may be provided. Examples of the material for forming the adhesion layer include Cr, Cr alloy, Ti, Ti alloy and the like, and a thickness of about 2 nm to 40 nm is preferable. The adhesion layer can be formed by film formation by sputtering, for example.

  By providing the orientation control layer between the soft magnetic underlayer and the perpendicular magnetic layer, the crystal grains of the perpendicular magnetic layer can be miniaturized and the recording / reproducing characteristics can be improved. The orientation control layer can be made of a material containing Ru, Ru alloy, Pt, Au and Ag, and a material such as CoCr alloy, Ti or Ti alloy, and the film thickness is preferably about 2 nm to 20 nm. This orientation control layer has a function of facilitating the epitaxial growth of the perpendicular magnetic layer and a function of breaking the magnetic exchange coupling between the soft magnetic underlayer and the perpendicular magnetic layer.

  Further, a seed layer for controlling the crystal grain size of the orientation control layer may be provided between the soft magnetic underlayer and the orientation control layer. For the seed layer, for example, a NiW alloy can be used. The perpendicular magnetic layer is a magnetic film having an easy axis of magnetization that is perpendicular to the main surface of the glass substrate, and is formed of a material containing Co, Cr, Pt, or the like.

The perpendicular magnetic layer preferably has a well-isolated fine particle structure, that is, a granular structure, in order to reduce intergranular exchange coupling that causes high intrinsic medium noise. Specifically, an oxide (SiO ₂ , SiO, Cr ₂ O ₃ , CoO, Ta ₂ O ₅ , TiO _2, etc.), Cr, B, Ta, Zr, or the like may be added to a CoCrPt alloy or the like. preferable.

  The perpendicular magnetic layer may have a structure in which magnetic layers and nonmagnetic layers are alternately stacked. In this case, for example, the nonmagnetic layer is made of Ru or a Ru alloy and has a thickness of 0.6 nm to 1.2 nm, whereby the magnetic layer can be AFC-coupled (antiferromagnetic exchange coupled). .

In order to prevent corrosion of the perpendicular magnetic layer and to prevent damage to the surface of the magnetic disk when the magnetic head comes into contact with the medium, a protective layer is formed on the perpendicular magnetic layer. The protective layer is formed of a material containing C, ZrO ₂ , SiO ₂ or the like, and can be formed by film formation by sputtering, CVD (chemical vapor deposition), or the like.

  A lubricating film can be disposed on the surface of the protective layer in order to reduce friction between the magnetic head and the magnetic recording medium. As the lubricating film, for example, perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acid, or the like can be used. These lubricating films can be formed by dipping, spraying, or the like.

  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 suppresses the occurrence of cracking when a sudden temperature change is applied. For this reason, when forming a magnetic layer, etc., it can suppress that a glass substrate cracks, and can manufacture the magnetic recording medium of this embodiment with high productivity.

  Specific examples will be described below, but 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) Shape of outer peripheral end surface The shape of the outer peripheral end surface of the glass substrate produced in each of the following experimental examples was measured by a contour shape measuring instrument (model: CONTOURRECORD 1600DH manufactured by Tokyo Seimitsu Co., Ltd.). The stylus tip R at the time of measurement was 30 μm, and the scanning speed was 0.3 mm / sec.

  In the measurement, as described with reference to FIG. 2, in the cross section perpendicular to the pair of main surfaces and passing through the central axis of the glass substrate for magnetic recording medium, the axis parallel to the main surface was taken as the X axis. And the X coordinate of the outermost peripheral position in the outline shape of the outer peripheral end surface of each glass substrate was set to 0, and the X coordinate on the central axis side of the glass substrate from the outermost peripheral position of the outer peripheral end surface was made positive.

  In each of the following experimental examples, the following angles described with reference to FIG. 2 were measured and calculated for the produced glass substrate.

Of the outer peripheral edge surface 13, the angle theta _5-10 to X coordinate _{X 5} is the point _{P 5} of 5 [mu] m, the straight line X-coordinate _{X 10} is connecting the point _{P 10} of 10 [mu] m, and the X-axis to form.

Of the outer peripheral edge surface 13, the angle theta _10-20 of X-coordinate _{X 10} is a point _{P 10} of 10 [mu] m, the straight line X-coordinate _{X 20} is connecting the point _{P 20} of 20 [mu] m, and the X-axis to form.

Of the outer peripheral edge surface 13, the angle theta _20-30 of X-coordinate _{X 20} is a point _{P 20} of 20 [mu] m, the straight line X-coordinate _{X 30} is connecting the point _{P 30} of 30 [mu] m, and the X-axis to form.

Of the outer peripheral edge surface 13, the angle theta _30-40 of X-coordinate _{X 30} is a point _{P 30} of 30 [mu] m, the straight line X-coordinate _{X 40} is connecting the point _{P 40} of 40 [mu] m, and the X-axis to form.
(2) Evaluation of crack occurrence rate due to abrupt temperature change The crack occurrence rate when a sudden temperature change is applied to the glass substrate produced in each experimental example is evaluated by the following procedure.

  About the glass substrate produced in each experimental example, it heats to 230 degreeC with an electric furnace, Then, it takes out from an 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 Insert while keeping the vertical position.

  It is determined that a crack has occurred when a crack having a length of 5 mm or more from the outer peripheral portion or a crack occurs in the glass substrate when thrown into water.

  For each experimental example, 100 glass substrates were tested in the same manner, and the ratio of the glass substrates determined to have cracked in the 100 glass substrates subjected to the test, that is, a length of 5 mm or more from the outer peripheral portion. The ratio of the glass substrate in which the crack or the crack has occurred is defined as the crack occurrence rate.

  In the crack occurrence rate evaluation test, as described above, the glass substrate was heated to 230 ° C. 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. In the process of manufacturing the energy-assisted magnetic recording medium, the most rapid temperature change is maintained, for example, from about 600 ° C. required for ordering the Fe—Pt alloy film to about 200 ° C. for forming the protective layer. This occurs when transferred to a CVD chamber. However, the temperature change is performed over a period of several tens of seconds to several tens of seconds. For this reason, even if the time required for the temperature change is estimated as 15 seconds, the temperature change is about 27 ° C./second.

Therefore, in order to more surely suppress the occurrence of cracking in the actual magnetic recording medium manufacturing process when a sudden temperature change is applied, here, the temperature is larger than the temperature gradient when manufacturing the magnetic recording medium. The evaluation is performed with a gradient.
(3) Peripheral chipping occurrence rate after film formation of magnetic layer As described later, a magnetic layer or the like is formed on the main surface of the glass substrate prepared in each experimental example to manufacture a magnetic recording medium.

  Therefore, evaluation of the occurrence rate of chipping is performed on the outer peripheral edge of the glass substrate after the magnetic layer is formed. Visual confirmation is made and it is determined that chipping has occurred for the glass substrate including chipping. For each experimental example, 10,000 glass substrates were tested, and the ratio of the glass substrates in which chipping occurred in the 10,000 glass substrates was defined as the chipping occurrence rate.

In the evaluation, the evaluation was performed separately between the outer peripheral chamfered portion and the outer peripheral chamfered portion and between the main surface and the outer peripheral chamfered portion. In Table 3, the occurrence rate of chipping between the outer peripheral chamfered part and the outer peripheral side part is described as between the outer peripheral chamfered part and the outer peripheral side part. Further, in Table 3, the occurrence rate of chipping between the main surface and the outer peripheral chamfered portion is described as between the main surface and the outer peripheral chamfered portion.
(4) Evaluation of magnetic recording medium Magnetic disk evaluation by missing bits is performed on the produced magnetic recording medium.

The missing bit is recorded under the conditions of a linear recording density of 1600 kBPI and a track density of 500 kTPI (surface recording density of 800 Gbit / inch ² ), and is evaluated by measuring the signal intensity when reproduced.

  When the output obtained during playback is less than the pass threshold (first threshold), the missing bit is used as the missing bit. Are the collectable missing bits (correctable missing bits), and those that cannot be modified (less than 80% of the first threshold) are uncorrectable missing bits (uncorrectable missing bits).

  Then, 500 magnetic recording media manufactured in each experimental example are measured and calculated as the number per one surface.

  The evaluation of the magnetic disk is indicated by ranks of A, B, C, and D based on the collectable missing bit and the uncorrectable missing bit measured as described above. Specifically, as shown in Table 1, when the collectable missing bit is 0.3 or less (pieces / face), the uncorrectable missing bit is 0.1 or less (pieces / face) , Rank A.

  Further, when the collectable missing bit is greater than 0.3 and less than or equal to 0.4 (pieces / face), the uncorrectable missing bit is greater than 0.1 and less than or equal to 0.2 (pieces / face). Rank B.

  Further, when the collectable missing bit is greater than 0.4 and less than or equal to 0.7 (pieces / face), the uncorrectable missing bit is greater than 0.2 and less than or equal to 0.3 (pieces / face). Rank C.

  Further, when the collectable missing bit exceeds 0.7 (pieces / face), the uncorrectable missing bit exceeds 0.3 (pieces / face), the rank is D.

Next, a glass substrate for a magnetic recording medium and a method for manufacturing the magnetic recording medium in each experimental example will be described. Experimental Examples 1 to 5 are examples, and Experimental Examples 6 to 9 are comparative examples.
[Experimental Example 1]
Each step is performed in the following order to manufacture a glass substrate for a magnetic recording medium and a magnetic recording medium.
(1) Glass substrate for magnetic recording medium (shape imparting step)
An aluminosilicate glass base plate having a glass composition A shown in Table 2 mainly composed of SiO ₂ and formed by a float process is prepared. Then, the glass base plate is processed into a glass substrate having a donut shape having a circular hole in the center so that 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 can be obtained.

The inner diameter means the diameter of the central opening.
(Chamfering process)
An inner peripheral chamfered portion and an outer peripheral chamfered portion are formed on the inner peripheral end surface and the outer peripheral end surface of the glass substrate obtained in the shape imparting step, respectively.

  In the chamfering step, an inner peripheral end face grinding grindstone for grinding the inner peripheral end face and an outer peripheral end face grindstone for grinding the outer peripheral end face are used. As shown in FIG. 3 (A), the inner peripheral end face grinding wheel and the outer peripheral end face grinding grindstone each have a substantially cylindrical shape, and use a grindstone having grooves 32 along the peripheral face. .

  As shown in FIG. 3B, the outer peripheral end surface polishing grindstone has a cross-sectional shape of the groove 32 on the surface 34 passing through the central axis 33 and the groove 32 of the grindstone 31, and the outer peripheral side surface portion 132, The portions 35A and 35B for grinding the corners between the outer peripheral chamfered portions 131 and 133 have an arc shape with a radius of 0.40 mm. That is, R is a curve of 0.40 mm. In Table 3, the grinding wheel bottom R is shown. Further, the side wall angle 36A, 36B is set to 43 °.

  The inner peripheral end surface polishing grindstone is a circular arc having a radius of 0.15 mm with respect to the portions 35A and 35B where the cross-sectional shape of the groove 32 grinds the corners between the inner peripheral side surface portion 142 and the inner peripheral chamfered portions 141 and 143. It has a shape. That is, a curve with R of 0.15 mm was used. Further, the side wall angle 36A, 36B is set to 43 °.

The chamfering process is performed in two steps for both the inner peripheral side surface portion and the outer peripheral side surface portion, and the first stage grindstone is a grain size # 325, and the second stage grindstone is a diamond electrodeposition grindstone of grain size # 800. Yes.
(Main surface polishing process: primary lapping process)
The upper and lower main surfaces of the glass substrate are ground by a 16B double-side polishing apparatus using a cast iron surface plate as a polishing tool and a grinding liquid containing alumina abrasive grains. After completion of the primary lapping process, the glass substrate is washed to remove grinding fluid and other dirt.
(End face polishing process: outer peripheral end face polishing process)
The outer peripheral side surface portion and the outer peripheral chamfered portion are polished using a polishing brush and an abrasive containing a cerium oxide abrasive having an average particle diameter (hereinafter, abbreviated as an average particle size) of about 1.5 μm. The wrinkles at the outer peripheral chamfered portion are removed, and the outer peripheral end surface is polished so as to be a mirror surface.

  More specifically, the outer peripheral end face is polished using the end face polishing apparatus shown in FIG.

  The glass substrate laminates 41 and 42 are formed by laminating 100 glass substrates that have been subjected to the main surface polishing step (primary lapping step) through a resin spacer having a thickness of 0.4 mm.

  Further, as the brush 43, a roll abrasive brush made of nylon having a bristle diameter of 0.3 mm is used, and as the brush 44, a roll abrasive brush having a bristle diameter of 0.2 mm is used.

  Then, the brushes 43 and 44 are pressed against the outer periphery of the glass substrate laminates 41 and 42 so that the brush pressing amount of each brush is 4 mm, and the glass substrate laminates 41 and 42 and the brushes 43 and 44 are rotated. Polishing is performed so that the polishing amount of the outer peripheral end face becomes 60 μm.

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.
(End polishing process: Inner peripheral edge polishing process)
About the inner peripheral end surface, the inner peripheral side surface portion and the inner peripheral chamfered portion of the glass substrate are polished using a polishing brush and a polishing agent containing cerium oxide abrasive grains having an average particle diameter of about 1.5 μm. . Thereby, the wrinkles of the inner peripheral side surface and the inner peripheral chamfered portion are removed, and the inner peripheral end surface is polished so as to be a mirror surface.

After polishing the outer peripheral end face and the inner peripheral end face, the glass substrate is washed to remove the abrasive and other dirt.
(Main surface polishing process: secondary lapping process)
The upper and lower main surfaces of the glass substrate are ground by a 16B double-side polishing apparatus 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.

After completion of the main surface polishing step (secondary lapping step), the glass substrate is washed to remove grinding fluid and other contaminants.
(Main surface polishing process: primary polishing process)
In the main surface polishing step (primary polishing step), as a polishing tool, a soft urethane polishing pad (suede type polishing pad) and a grinding liquid containing cerium oxide having an average particle size of about 1.0 μm as a main component are used. The upper and lower main surfaces of the glass substrate are polished by a 16B double-side polishing apparatus.

  The main polishing pressure is 12 kPa, the lower surface plate rotation speed is 30 rpm, the upper surface plate rotation speed is 10 rpm in the opposite direction to the lower surface plate, the polishing carrier revolution number is 10 rpm, the rotation speed is 3 rpm, and the upper and lower main planes are total in the plate thickness direction. Polish 30 μm.

After completion of the main surface polishing step (primary polishing step), the glass substrate is washed to remove grinding fluid and other contaminants.
(Main surface polishing process: secondary polishing process)
In the main surface polishing step (secondary polishing step), a polishing pad containing a soft urethane polishing pad and a colloidal silica abrasive having an average particle size of 20 nm is used as a polishing tool, and a 16B double-side polishing apparatus is used to make glass Polish the upper and lower main surfaces of the substrate.

  The main polishing pressure is 10 kPa, the lower surface plate rotation speed is 10 rpm, the upper surface plate rotation speed is 5 rpm in the opposite direction of the lower surface plate, the polishing carrier revolution number is 4.9 rpm, and the rotation speed is 1.7 rpm. A total of 1 μm is polished in the thickness direction.

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

The glass substrate for a magnetic recording medium obtained by the above procedure is evaluated for the shape of the outer peripheral end face and the crack occurrence rate due to a rapid temperature change. The results are shown in Table 3.
(2) Magnetic recording medium The obtained glass substrate is precisely cleaned to remove particles on the surface, and then an in-line type sputtering apparatus is used to form an adhesion layer on the main surface of the glass substrate and a film thickness of 10 nm using Cr as a target. The film is formed.

  In the in-line type sputtering apparatus, a supporting member is pressed against a plurality of locations on the outer peripheral end surface of the glass substrate, and the glass substrate is sandwiched between the supporting members to support the glass substrate.

  On the adhesion layer, a soft magnetic underlayer is formed with a thickness of 30 nm using a Co—Fe—Zr—Ta alloy as a target.

  Next, a seed layer is formed with a thickness of 10 nm using a NiW alloy as a target.

  On the seed layer, an orientation control layer is formed with a thickness of 10 nm using Ru as a target.

On the orientation control layer, a granular structure layer of CoCrPt—SiO ₂ is formed as a perpendicular magnetic layer with a thickness of 10 nm, a Ru film is formed as a nonmagnetic intermediate layer with a thickness of 0.6 nm, and a magnetic layer A granular structure layer of CoCrPt—SiO ₂ is formed with a thickness of 6 nm.

  The glass substrate on which each of the above layers is stacked is transferred from an in-line type sputtering apparatus, and a carbon film is formed with a thickness of 3 nm as a protective layer by a CVD method. Thereafter, a perfluoropolyether lubricating film having a thickness of 2 nm is formed on the protective layer by dipping.

The obtained magnetic recording medium is evaluated as described above. The results are shown in Table 3.
[Experimental Example 2, Experimental Example 3]
(1) Glass substrate for magnetic recording medium Glass in the same manner as in Experimental Example 1 except that in the chamfering process, the shape of the groove of the grinding wheel for outer peripheral end face grinding is different and the polishing amount of the outer peripheral end face in the end face grinding process is different. A substrate is prepared and evaluated.

  3A and 3B, the cross-sectional shape of the groove 32 on the surface 34 passing through the central axis 33 and the groove 32 of the grindstone 31 for outer peripheral end surface grinding is as follows. The portions 35A and 35B where the corners between the chamfered portions 131 and 133 are ground have an arc shape with a radius of 0.30 mm. That is, R is a curve of 0.30 mm.

  Further, as shown in Table 3, the polishing is performed so that the polishing amount of the outer peripheral end face in the end face polishing step is 50 μm (Experimental Example 2) or 40 μm (Experimental Example 3).

The evaluation results are shown in Table 2.
(2) Magnetic recording medium A magnetic recording medium is produced in the same manner as in Experimental Example 1 except that the glass substrate for magnetic recording medium produced in each experimental example is used.

The evaluation results are shown in Table 3.
[Experimental Examples 4 and 5]
(1) Glass substrate for magnetic recording medium A glass substrate is prepared and evaluated in the same manner as in Experimental Example 2 except for the glass base plate.

In addition, Example 4 is an aluminosilicate glass base plate having a glass composition B shown in Table 2 and composed mainly of SiO ₂ formed by a float process, and Example 5 is a glass similarly shown in Table 2. An aluminosilicate glass base plate having composition C is used.

The evaluation results are shown in Table 2.
(2) Magnetic recording medium A magnetic recording medium is produced in the same manner as in Experimental Example 1 except that the glass substrate for magnetic recording medium produced in each experimental example is used.

The evaluation results are shown in Table 3.
[Experimental Examples 6 to 9]
(1) Glass substrate for magnetic recording medium Glass in the same manner as in Experimental Example 1 except that in the chamfering process, the shape of the groove of the grinding wheel for outer peripheral end face grinding is different and the polishing amount of the outer peripheral end face in the end face grinding process is different. A substrate is prepared and evaluated.

  3A and 3B, the cross-sectional shape of the groove 32 on the surface 34 passing through the central axis 33 and the groove 32 of the grindstone 31 for outer peripheral end surface grinding is as follows. For the portions 35A and 35B for grinding the corners between the chamfered portions 131 and 133, a radius of 0.20 mm (Experimental example 6), a radius of 0.15 mm (Experimental example 7), a radius of 0.10 mm (Experimental example 8), The arc shape has a radius of 0.60 mm (Experimental Example 9). That is, the curves R are 0.20 mm, 0.15 mm, 0.10 mm, and 0.60 mm.

  Further, as shown in Table 3, the polishing is performed so that the polishing amount of the outer peripheral end face in the end face polishing step becomes 20 μm, 15 μm, 15 μm, and 30 μm in Examples 6, 7, 8, and 9, respectively. Specifically, in the end surface polishing apparatus shown in FIG. 4, the brushes 43 and 44 are placed on the outer periphery of the glass substrate laminates 41 and 42, and the brush pressing amount of each brush is 1.5 mm in Examples 6 and 7. The glass substrate laminates 41 and 42 and the brushes 43 and 44 are rotated so as to have the above polishing amount by being pressed so as to be 2 mm in 8 and 3 mm in Example 9. As for the brushes 43 and 44, both the hair diameters made of nylon in Examples 6 and 7 were 0.15 mm, the hair diameter in Example 8 was both 0.2 mm, and the hair diameter in Example 9 was 0. Each roll abrasive brush of 3 mm is used.

The evaluation results are shown in Table 2.
(2) Magnetic recording medium A magnetic recording medium is produced in the same manner as in Experimental Example 1 except that the glass substrate for magnetic recording medium produced in each experimental example is used.

  The evaluation results are shown in Table 3.

表３に示した結果によると、ガラス基板の外周端面の形状について、θ_５−１０、θ_{１０−２０}、θ_{２０−３０}がそれぞれ８１°以上８５°以下、６９°以上８３°以下、５２°以上７２°以下となっている実験例１〜実験例５のガラス基板はいずれも急激な温度変化による割れ発生率が５％以下と低くなっていることを確認できる。

According to the results shown in Table 3, with respect to the shape of the outer peripheral end face of the glass substrate, θ _5-10 , θ _10-20 , θ _20-30 are 81 ° to 85 °, 69 ° to 83 °, 52 °, respectively. It can be confirmed that all of the glass substrates of Experimental Examples 1 to 5 that are 72 ° or less have a low crack generation rate of 5% or less due to a rapid temperature change.

  Further, in Experimental Examples 4 and 5 in which the average thermal expansion coefficient of the glass is smaller than Experimental Examples 1 to 3, the outer peripheral end face shape is the same as that of Experimental Example 2, but the crack occurrence rate due to a rapid temperature change is lower than that of Experimental Example 2; %.

In contrast, in Experimental Examples 6 to 8 in which the shapes of the outer peripheral end faces θ _5-10 and θ _10-20 do not satisfy the above range, the crack occurrence rate due to a rapid temperature change exceeds 15%, which is very high. You can see that it is higher. In Experimental Example 9 in which the outer peripheral end face shapes θ _5-10 and θ _10-20 satisfy the above range, the crack occurrence rate due to a rapid temperature change is a relatively low level of 3%.

  From the above results, it can be confirmed that the crack occurrence rate due to a rapid temperature change is affected by the shape of the outer peripheral end face of the glass substrate, and that the crack occurrence rate can be suppressed by setting it to a predetermined shape.

  Moreover, about the glass substrate of Experimental example 1-Experimental example 5 whose shape of an outer peripheral end surface is the said shape, compared with the glass substrate of Experimental examples 6-9, the outer periphery chipping generation rate after magnetic layer film-forming is suppressed low. I can confirm that I can do it.

In Experimental Examples 6 to 8 in which the outer peripheral end face shape θ _5-10 and θ _10-20 are outside the above shape range, the occurrence rate of chipping between the outer peripheral side surface and the outer peripheral chamfered surface is high, and the outer peripheral end surface shape θ _In Experimental Examples 8 and 9 where _20-30 is out of the above range, the chipping rate between the main surface and the peripheral chamfered surface is high.

  Further, for the glass substrates of Experimental Examples 1 to 5, it was confirmed that the ranks of Collectable Missing Bit and Uncorrectable Missing Bit when used as magnetic recording media were also higher than those of the glass substrates of Experimental Examples 6 to 8. it can.

DESCRIPTION OF SYMBOLS 10 Glass substrate 121,122 for magnetic recording media Main surface 13 Outer peripheral surface 131, 133 Outer peripheral chamfer 132 Outer peripheral side 14 Inner peripheral end

In one aspect of the present invention, a glass substrate for a magnetic recording medium in a donut shape having 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 side surface portion, and an outer peripheral chamfered portion disposed between the outer peripheral side surface portion and the main surface,
In a cross section perpendicular to the pair of main surfaces and passing through the central axis of the glass substrate for magnetic recording medium,
The axis parallel to the main surface is the X axis, the X coordinate of the outermost peripheral surface of the outer peripheral end surface is 0, and the X coordinate on the central axis side of the glass substrate for a magnetic recording medium from the outermost peripheral position of the outer peripheral end surface is If positive,
Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 5 μm and a point having an X coordinate of 10 μm and the X axis is 81 ° to 85 °,
Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 10 μm and a point having an X coordinate of 20 μm and the X axis is 69 ° or more and 83 ° or less,
Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 20 μm and a point having an X coordinate of 30 μm and the X axis is 52 ° or more and 72 ° or less,
Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 30 μm and a point having an X coordinate of 40 μm and the X axis is 51 ° or more and 68 ° or less,
A glass substrate for a magnetic recording medium is provided.

Claims (8)

A glass substrate for a magnetic recording medium having a donut shape having 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 side surface portion, and an outer peripheral chamfered portion disposed between the outer peripheral side surface portion and the main surface,
In a cross section perpendicular to the pair of main surfaces and passing through the central axis of the glass substrate for magnetic recording medium,
The axis parallel to the main surface is the X axis, the X coordinate of the outermost peripheral surface of the outer peripheral end surface is 0, and the X coordinate on the central axis side of the glass substrate for a magnetic recording medium from the outermost peripheral position of the outer peripheral end surface is If positive,
Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 5 μm and a point having an X coordinate of 10 μm and the X axis is 81 ° to 85 °,
Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 10 μm and a point having an X coordinate of 20 μm and the X axis is 69 ° or more and 83 ° or less,
Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 20 μm and a point having an X coordinate of 30 μm and the X axis is 52 ° or more and 72 ° or less,
A glass substrate for a magnetic recording medium. Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 5 μm and a point having an X coordinate of 10 μm and the X axis is 81 ° or more and 84 ° or less,
Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 10 μm and a point having an X coordinate of 20 μm and the X axis is 75 ° to 82 °,
Of the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 20 μm and a point having an X coordinate of 30 μm and the X axis is 55 ° or more and 72 ° or less,
Among the outer peripheral end faces, an angle formed by a straight line connecting a point having an X coordinate of 30 μm and a point having an X coordinate of 40 μm and the X axis is 51 ° or more and 68 ° or less,
The glass substrate for magnetic recording media according to claim 1. 3. The glass substrate for a magnetic recording medium according to claim 1, wherein the glass substrate is made of a glass material having an average coefficient of thermal expansion of less than 50 × 10 ⁻⁷ / ° C. in a temperature range of 50 ° C. or more and 350 ° C. or less.   The glass substrate for magnetic recording media according to any one of claims 1 to 3, which is a glass substrate for magnetic recording media for energy-assisted magnetic recording media. 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%, MgO is 0% to 10%, CaO 1% or more and 21% or less in total of any one component of SrO and BaO, the total content of MgO, CaO, SrO and BaO is 8% or more and 21% or less, and the total content of the seven components is 95% The glass substrate for a magnetic recording medium according to any one of claims 1 to 4, wherein the glass substrate is made of at least% glass material. In terms of mole percentage, SiO ₂ is 62% or more and 74% or less, Al ₂ O ₃ is 7% or more and 18% or less, B ₂ O ₃ is 0 or more and less than 2%, and the total content of MgO, CaO, SrO and BaO is 5 The glass substrate for a magnetic recording medium according to any one of claims 1 to 4, wherein the glass substrate is made of a glass material having a total content of 7% to 18% and a total content of the seven components of 95% or more. In terms of mole percentage, the total content of SiO ₂ is 60% to 75%, Al ₂ O ₃ is 7% to 17%, B ₂ O ₃ is 0% to less than 2%, and MgO, CaO, SrO and BaO 5. The glass substrate for a magnetic recording medium according to claim 1, comprising a glass material having a content of more than 18% and 26% or less and a total content of the seven components of 95% or more.   A magnetic recording medium comprising the glass substrate for a magnetic recording medium according to claim 1.

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