JP2008204499A - Glass substrate for information recording medium and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for an information recording medium provided as a base body of a magnetic recording medium wherein operation of a magnetic head at an outer peripheral end part is stabilized especially in a LUL (Load Unload) system. <P>SOLUTION: In the glass substrate for the information recording medium, a position R1 and a position R2 apart from the position R1 by a fixed interval in a direction to an outer peripheral end surface are determined on a contour on the same principal surface side of a cross section vertical to the principal surface in a radial direction of the glass substrate, the contour descends on the substrate side from the position R1 to the position R2, the descending contour has one inflection point between positions R1 and R2, the maximum angle θ1 formed by a first tangent tangential to the contour from the position R1 to the inflection point and a reference plane of a flat part of the principal surface as a reference and the maximum angle θ2 formed by a second tangent tangential to the contour from the inflection point to the position R2 and the first tangent satisfy a certain conditional expression and the contour from the position R2 in the direction to the outer peripheral end surface exists on the substrate side of the reference plane and extends from the reference plane to the outer peripheral end surface. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  Conventionally, an aluminum substrate has been generally used as a magnetic disk substrate used in a computer or the like. However, as the magnetic disk is reduced in size and thickness, the recording density is increased, and the magnetic head mechanism is shifting from the CSS (Contact Start Stop) method to the LUL (Load Unload) method as the magnetic head is lowered. In the LUL method, since the magnetic head can be moved at a low flying height compared to the CSS method, higher density recording is possible and it is possible to cope with an increase in recording capacity. With the shift from the CSS system to the LUL system, the adoption of glass substrates that are superior in hardness, strength and flatness compared to aluminum substrates is increasing.

  In this LUL method, when the magnetic disk is stopped, the magnetic head waits outside the magnetic disk, and after the magnetic disk rotates, the magnetic head is moved from the outside of the disk to the disk surface by using a guide mechanism. Move to record / playback. In general, the LUL type magnetic head has a low flying height as compared with the CSS type. For this reason, in order to ensure the flying stability of the magnetic head at the outer peripheral edge of the magnetic disk, it is necessary to strictly define the outer peripheral edge shape of the magnetic disk as compared with the CSS system.

Recording at a certain distance from the outer peripheral end position of the glide area (the area in which the magnetic head flies but does not perform recording / reproduction) of a glass substrate for magnetic disk (hereinafter also referred to as a substrate) that is compatible with the LUL system. In the area up to the outermost peripheral end position of the area, there are those that define (1) and (2) below.
(1) Using the flat portion of the main surface of the substrate as a reference plane, the highest point (ski jump point) value (ski jump value) is within ± 0.35 μm.
(2) The value (roll-off value) of the outer peripheral end position (roll-off point) of the glide region is within ± 0.35 μm. (See Patent Document 1).
JP 2001-167427 A

  However, the shape of the outer peripheral end of the glass substrate for magnetic disk described in Patent Document 1 shows only the ski jump value, the roll-off value, and the region having these values. In the example of a 2.5 inch substrate (φ65 mm), the outer peripheral end position of the glide region is set to a position of 31.5 mm from the center of the substrate, and the position of a point in the recording area that is separated by a fixed interval is set to a position of 27.1 mm. In the range from 27.1 mm to 31.5 mm from the center, the shape of the outer peripheral end portion having the ski jump value and the roll-off value is not defined. For this reason, even if the ski jump value and the roll-off value are the same, the glass substrate surface around the position having these values has a steep slope to the extent that the magnetic head cannot travel stably especially during LUL. There is a case. In such a magnetic disk provided with a magnetic film on a magnetic disk glass substrate, the flying stability of the magnetic head is deteriorated, and the magnetic disk surface collides with the magnetic disk surface, or the magnetic head itself is damaged. Thus, it is conceivable that the magnetic disk drive device provided with the glass substrate or the magnetic head becomes unusable.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a magnetic recording medium and a magnetic recording medium that make the operation of the magnetic head at the outer peripheral end more stable, particularly during LUL. It is providing the glass substrate for information recording media provided as a base | substrate of this.

  Said subject is solved by the following structures.

1. In a glass substrate for an information recording medium having a donut shape having an outer peripheral end surface and an inner peripheral end surface concentric with a main surface having a flat portion,
On the same main surface side contour line in the radial direction of the glass substrate for information recording medium and perpendicular to the main surface, the position R1 is spaced apart from the position R1 in the direction from the position R1 to the outer peripheral end surface. R2 is determined,
The contour line is lowered from the position R1 to the position R2 toward the information recording medium glass substrate side,
There is one inflection point until the descending contour line reaches the position R2.
The maximum angle θ1 formed by a first tangent line that contacts the contour line from the position R1 to the inflection point and a reference plane that uses the flat portion of the main surface as a reference, and the contour from the inflection point to the position R2 The maximum angle θ2 formed by the second tangent tangent to the line and the first tangent satisfies the following conditional expression:
0 ° <θ1 ≤ 5 °
θ1 × 0.5 ≦ θ2 ≦ θ1 × 2
The contour line in the direction from the position R2 to the outer peripheral end surface is closer to the substrate than the reference plane, extends in a direction away from the reference plane, and reaches the outer peripheral end surface. Glass substrate.
However,
Position R1: Position R2 where the distance from the central axis of the glass substrate for information recording medium is R × 0.90: Position R where the distance from the central axis of the glass substrate for information recording medium is R × 0.975: Maximum distance θ1 from the central axis of the glass substrate for information recording medium to the outer peripheral end surface: an angle (plus) from the reference plane toward the first tangent.
Maximum angle θ2: An angle (plus) from the first tangent to the second tangent.

  2. 2. A magnetic recording medium comprising a magnetic film on the surface of the glass substrate for information recording medium according to 1.

  3. 3. The magnetic recording medium according to 2, which is an LUL type magnetic recording medium.

  According to the present invention, the shape from the position R1 to the position R2 of the glass substrate for information recording medium can be defined. The shape in the range from the position R1 to the position R2 is constituted by a slope whose inclination with respect to the reference plane is within ± 5 °, and does not include a steep slope. The shape in the range from the position R2 to the outer peripheral end surface reaches the outer peripheral end surface without exceeding the reference plane. Therefore, the magnetic head can fly and travel stably at the outer peripheral end portion. Stability of the magnetic head at the outer peripheral edge is particularly advantageous during LUL.

  Therefore, it is possible to provide a magnetic recording medium that makes the operation of the recording head more stable during the magnetic head, particularly LUL, and a glass substrate for a recording medium that serves as a base of the magnetic recording medium.

  Although the present invention will be described based on the illustrated embodiment, the present invention is not limited to the embodiment.

  FIG. 2 shows the overall configuration of a glass substrate for information recording medium (hereinafter also referred to as a glass substrate) 1 according to the present invention. As shown in FIG. 2, the glass substrate 1 has a donut-like disk shape with a hole 13 formed in the center. Reference numeral 14 denotes an outer peripheral end face, 15 denotes an inner peripheral end face, 10a denotes a front main surface, and 10b denotes a back main surface. FIG. 3 is a diagram showing an example of the magnetic recording medium D provided with the magnetic film 2 on the front main surface 10a of the glass substrate 1 shown in FIG. The magnetic film 2 can also be provided on the back main surface 10b.

  Consider a cross section cut through a plane that passes through the center of the glass substrate 1 shown in FIG. 2 and is perpendicular to the front main surface 10a. In this cross section, the peripheral portion of the outer peripheral end on the front main surface 10a side in the glass substrate 1 is schematically enlarged and shown in FIG. The shape shown in FIG. 1 is the same as that of the front main surface 10a even on the back main surface 10b. To do.

  In FIG. 1, BL is a contour line of the glass substrate 1 on the front main surface 10 a side, SH is a reference plane based on a flat portion of the main surface 10 a, and Rt is an outer periphery whose distance from the central axis of the glass substrate 1 is R. The position of the end face 14, R 1 indicates a position with a distance of 0.9 × R from the central axis, and R 2 indicates a position with a distance of 0.975 × R from the central axis. The contour line BL is lowered from between the position R1 and the position R2.

  Taking a 2.5 inch glass substrate as an example, position R1, position R2, and position Rt are as follows. Assuming that the center of the glass substrate 1 is 0, the position Rt is 32.5 mm (= R), the position R1 is 29.25 mm, and the position R2 is 31.69 mm. Since the position in the radial direction defining the roll-off shown in Patent Document 1 is 31.5 mm as described above, the position R2 is slightly on the outer peripheral end side.

  Hp is an inflection point of the contour line BL between the positions R1 and R2, TL1 is an example of a first tangent line that touches the contour line BL from the position R1 to the inflection point Hp, and TL2 is an inflection point. An example of a second tangent line in contact with the contour line BL from the point Hp to the position R2 is shown.

  In FIG. 1, the maximum angle θ1 formed by the first tangent line TL1 and the reference plane SH (the angle in the direction from the reference plane SH toward the tangent line TL1 (clockwise direction indicated by the arrow in the drawing)) is as follows. Formula (1) is satisfied.

0 ° <θ1 ≦ 5 ° (1)
The contour line BL defined by the conditional expression (1) is in the thickness direction of the glass substrate from the reference plane SH in a range where the maximum angle formed with the reference plane SH between the position R1 and the position R2 exceeds 0 ° and is 5 ° or less. It extends in the direction away from Therefore, the main surface indicated by the contour line BL is a surface away from the reference surface in the thickness direction of the glass substrate with respect to the reference plane, and the inclination of the surface is in the range of more than 0 ° to 5 ° or less, and is steep. It does not include a serious aspect. The main plane does not have a convex shape that exceeds the reference plane on the opposite side of the glass substrate. Therefore, the magnetic head can stably fly and travel at the outer peripheral end portion of the glass substrate. Good stability of the magnetic head at the outer peripheral edge is particularly advantageous during LUL.

  Further, the contour line BL extending within the above-mentioned angle range has an inflection point Hp before reaching the position R2. After the inflection point Hp is exceeded, the descending angle (the angle toward the thickness direction of the glass substrate) becomes gradual, and in some cases, it begins to rise. The maximum angle θ2 formed by the second tangent line TL2 and the first tangent line TL1 in the contour line BL exceeding the inflection point Hp (the direction indicated by the arrow in the drawing from the first tangent line TL1 toward the second tangent line TL2) (Counterclockwise direction)) satisfies the following conditional expression.

θ1 × 0.5 ≦ θ2 ≦ θ1 × 2 (2)
The contour line BL defined by the conditional expression (2) is that the contour line BL after the inflection point Hp has a maximum angle of 2.5 ° to 10 ° with the first tangent TL1 at the maximum angle θ1. And the maximum angle formed with the reference plane SH is in the range of −2.5 ° (downward direction) to + 5 ° (upward direction). Therefore, the main surface indicated by the contour line BL is composed of slopes having an inclination with respect to the reference plane in the range of −2.5 ° to 5 °, and does not include a steep slope. Therefore, the magnetic head can fly and travel stably at the outer peripheral end portion. Good stability of the magnetic head at the outer peripheral edge is particularly advantageous during LUL.

  Accordingly, the contour line BL defined by the conditional expressions (1) and (2) has a maximum angle of ± 5 ° or less within the range from the position R1 to the position R2 between the contour line BL and the reference plane SH including the front main surface 10a. It becomes. In the information recording medium in which the magnetic film is provided using the glass substrate having the above shape as a base, there is no steep slope from the position R1 to the position R2. Therefore, the magnetic head can stably fly and move at the outer peripheral edge, and the magnetic head does not collide with the surface of the magnetic disk to damage the surface of the magnetic disk or damage the magnetic head itself. Good stability of the magnetic head at the outer peripheral edge is particularly advantageous during LUL.

  Further, the outer peripheral end face 14 is raised at a maximum angle + 5 ° upward from the position R2 toward the outer peripheral end face because the inner and outer diameter machining steps, the inner circumference and the outer peripheral end face are processed in the manufacturing process described later. Even the contour line BL does not exceed the reference plane SH, and eventually converges to the end surface processed surface and reaches the outer peripheral end surface 14. Accordingly, there is no convex portion that becomes an obstacle when the magnetic head performs LUL from the position R2 to the outer peripheral end face. Therefore, the magnetic head can move stably during the LUL.

  Further, since there is no steep slope at the outer peripheral end, when a magnetic recording medium having a glass substrate as a base is rotated at a high speed of, for example, about 7200 rpm, the occurrence of abnormal air flow at the outer peripheral end can be suppressed. Therefore, the rotational speed can be stabilized and the movement of the magnetic head can be stabilized.

  The magnetic recording medium based on the glass substrate having the shape of the outer peripheral end described above can obtain the most effect by using the LUL magnetic recording medium.

  The glass substrate for an information recording medium of the present invention is not limited to a magnetic recording medium, and can be used for a magneto-optical disk or an optical disk.

(Manufacturing process of glass substrate for information recording medium)
The manufacturing process of the glass substrate for information recording media will be described. As an example of the manufacturing method of a glass substrate, it demonstrates below using the manufacturing flow shown in FIG.

  There is no limitation on the size of the glass substrate. For example, there are glass substrates of various sizes such as an outer diameter of 2.5 inches, 1.8 inches, 1 inch, and 0.8 inches. Further, the thickness of the glass substrate is not limited, and there are glass substrates having various thicknesses such as 2 mm, 1 mm, and 0.63 mm.

  First, a glass material is melted (glass melting step), molten glass is poured into a lower mold, and press molding is performed with an upper mold to obtain a disk-shaped glass substrate precursor (press molding process). The disc-shaped glass substrate precursor may be produced by cutting a sheet glass formed by, for example, a downdraw method or a float method with a grinding stone, without using press molding.

The material of the glass substrate is not particularly limited as long as it can be chemically strengthened by ion exchange. For example, soda lime glass mainly composed of SiO ₂ , Na ₂ O, CaO; aluminosilicate glass mainly composed of SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li); borosilicate Glass; Li ₂ O—SiO ₂ glass; Li ₂ O—Al ₂ O ₃ —SiO ₂ glass; R′O—Al ₂ O ₃ —SiO ₂ glass (R ′ = Mg, Ca, Sr, Ba) Etc. can be used. Among these, aluminosilicate glass and borosilicate glass are particularly preferable because they are excellent in impact resistance and vibration resistance.

  The press-molded glass substrate precursor is drilled in the center with a core drill or the like having a diamond grindstone or the like in the cutter (coring process).

  Next, both surfaces of the glass substrate are polished to preliminarily adjust the overall shape of the glass substrate, that is, the parallelism, flatness, and thickness of the glass substrate (first lapping step).

  Next, the inner and outer diameters are processed by grinding the outer peripheral end surface and the inner peripheral end surface of the glass substrate with, for example, a grinding wheel such as a drum-shaped diamond (inner / outer diameter processing step). By this inner / outer diameter processing, the outer diameter and roundness of the glass substrate, the inner diameter of the hole, and the concentricity between the glass substrate and the hole are finely adjusted. For example, a 45 ° chamfer of about 0.1 mm to 0.2 mm is performed. Thereafter, the inner peripheral end face of the glass substrate is made to have a curved corner at the chamfered portion by brush polishing using a polishing liquid, and fine scratches and the like are removed (inner peripheral end face processing step).

  Next, both surfaces of the glass substrate are polished again to finely adjust the parallelism, flatness and thickness of the glass substrate (second lapping step). Then, the outer peripheral end surface of the glass substrate is subjected to brush polishing using a polishing liquid so that the corner portion of the chamfered portion is curved, and fine scratches and the like are removed (outer peripheral end surface processing step).

  The order from the first lapping step after the coring processing to the outer peripheral end surface processing step is not limited to that shown in FIG. 5 and can be changed as appropriate according to the situation. For example, the lapping process may be performed first, and then the inner / outer diameter machining process, the inner circumference, and the outer circumference end face machining process may be performed. Further, after the first lapping step and the inner / outer diameter machining step, a second lapping step, an inner circumference and an outer circumference end face machining step may be performed.

  In the manufacturing process up to the outer peripheral end face machining step, the final shape of the outer peripheral end face 14 is almost determined from the position R2. Further, the shape in the range from the position R1 to the position R2 of the outer peripheral end portion of the main surface 10a can be made into a desired shape according to the present invention particularly in the first polishing step described below. Therefore, the shape in the range from the position R1 to the position R2 formed in the steps so far does not need to be particularly limited, but it is a shape that does not impose a large burden in order to obtain a desired shape in the subsequent manufacturing process. Is preferred. Further, the shape of the outer peripheral end portion from the position R2 to the outer peripheral end face 14 is smoothly and continuously formed from the shape formed from the position R1 to the position 2 by the first and second polishing to the shape formed by the outer peripheral end face processing. Then, it can be in a state that continues.

  A polishing machine that polishes the glass substrate in the first and second lapping steps will be described. As the polishing machine, a known polishing machine called a double-side polishing machine can be used. The double-side polishing machine includes a disk-shaped upper surface plate and a lower surface plate that are arranged vertically so as to be parallel to each other, and rotate in opposite directions. A plurality of diamond pellets for polishing the main surface of the glass substrate are attached to the opposing surfaces of the upper and lower surface plates. Between the upper and lower surface plates, there are a plurality of carriers that rotate in combination with an internal gear provided in an annular shape on the outer periphery of the lower surface plate and a sun gear provided around the rotation axis of the lower surface plate. The carrier is provided with a plurality of holes, and a glass substrate is fitted into the holes. The upper and lower surface plates, the internal gear, and the sun gear can be operated by separate driving.

  The polishing operation of the polishing machine is such that the upper and lower surface plates rotate in opposite directions, and the carrier sandwiched between the surface plates via the diamond pellets rotates with the surface plate holding a plurality of glass substrates. Revolves in the same direction as the lower surface plate with respect to the center of rotation. In such an operating polishing machine, the glass substrate can be polished by supplying a grinding liquid between the upper surface plate and the glass substrate, and the lower surface plate and the glass substrate.

When using this double-side polishing machine, the weight of the surface plate applied to the glass substrate and the number of rotations of the surface plate are adjusted as appropriate according to the desired polishing state. The weight in the first and second lapping steps is preferably 60 g / cm ² to 120 g / cm ² . Further, the rotation speed of the surface plate is preferably about 10 to 30 rpm, and the rotation speed of the upper surface plate is preferably about 30 to 40% slower than the lower surface rotation speed. Increasing the load on the surface plate and increasing the rotation speed of the surface plate increases the amount of polishing, but if the load is increased too much, the surface roughness will not be good, and if the rotation speed is too high, the flatness will be good. Not. Further, when the load is small and the rotation speed of the surface plate is slow, the polishing amount is small and the production efficiency is lowered.

  When the second lapping process is completed, defects such as large waviness, chipping and cracks are removed, and the surface roughness of the main surface of the glass substrate is about 2 μm to 4 μm for Rmax and about 0.2 μm to 0.4 μm for Ra. Is preferable. By setting it as such a surface state, it can polish efficiently by a 1st polishing process through the following chemical strengthening process.

  In the first lapping step, roughly large undulations, chips and cracks are efficiently removed so that the second lapping step can be performed efficiently. For this reason, it is preferable to use diamond pellets of # 800 mesh to # 1200 mesh which are coarser than # 1300 mesh to # 1700 mesh used in the second wrapping. The surface roughness at the time when the first lapping step is completed is preferably such that Rmax is 4 μm to 8 μm and Ra is about 0.4 μm to 0.8 μm.

  The inner peripheral and outer peripheral end faces of the glass substrate are polished by brush polishing in the inner peripheral and outer peripheral end face processing steps. The brush is preferably made of nylon, polypropylene or the like having a diameter of about 0.2 to 0.3 mm. The polishing liquid is preferably cerium oxide having a particle size of about several μm. As a result of brush polishing, it is preferable that the surface roughness of the inner and outer end faces is such that Rmax is 0.2 μm to 0.4 μm and Ra is about 0.02 μm to 0.04 μm. The shape of the end surface of the glass substrate that has undergone the inner and outer diameter processing steps and the inner and outer peripheral end surface processing steps is such that the corner formed by the main surface and the end surface is removed, and the position is about 0.2 mm to 0.5 mm from the outer peripheral end surface. From the main surface.

  Here, Ra (center line average roughness) and Rmax (maximum height) are defined in JIS B0601: 2001. These can be measured by an atomic force microscope (AFM) or the like. These rules and measurement methods also apply to Ra and Rmax described below.

  In the above example, the diamond pellet and the grinding liquid are used when polishing the glass substrate. However, it is also possible to apply a polishing method by attaching a pad to the polishing surface of the upper and lower surface plates and supplying the polishing liquid. . Examples of the abrasive include cerium oxide, zirconium oxide, aluminum oxide, manganese oxide, colloidal silica, and diamond. These are dispersed in water and used as a slurry. The pad is divided into a hard pad and a soft pad, but can be appropriately selected and used as necessary. Examples of the hard pad include pads made of hard velor, urethane foam, pitch-containing suede, etc., and examples of the soft pad include pads made of suede, velor, etc.

  A polishing method using a pad and a polishing agent can cope with rough polishing to precision polishing by changing the particle size of the polishing agent and the type of the pad. Therefore, in the first lapping step and the second lapping step, the abrasive material, abrasive particle size, and pad are appropriately combined so that the above-mentioned surface roughness can be obtained by efficiently removing large undulations, chips, cracks, etc. Can respond.

  Moreover, it is preferable to perform the washing | cleaning process for removing the abrasive | polishing agent and glass powder which remained on the surface of the glass substrate after the 1st and 2nd lapping process.

  It should be noted that the polishing machines used in the first lapping process and the second lapping process have the same configuration, but it is preferable to perform polishing using different polishing machines prepared exclusively for the respective processes. This is because the dedicated diamond pellets are pasted, so that the replacement is a large-scale operation, and complicated operations such as resetting the polishing conditions are required, resulting in a reduction in manufacturing efficiency.

  Following the second lapping step, the glass substrate is immersed in a chemical strengthening solution to form a chemically strengthened layer on the glass substrate (chemical strengthening step). By forming the chemical strengthening layer, impact resistance, vibration resistance, heat resistance and the like can be improved.

  In the chemical strengthening step, by immersing the glass substrate in a heated chemical strengthening solution, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are converted into alkali ions such as potassium ions having a larger ion radius. This is performed by the ion exchange method for substitution. Compressive stress is generated in the ion-exchanged region due to the distortion caused by the difference in ion radius, and the surface of the glass substrate is strengthened.

  There is no restriction | limiting in particular in a chemical strengthening process liquid, A well-known chemical strengthening process liquid can be used. In general, a molten salt containing potassium ions or a molten salt containing potassium ions and sodium ions is generally used. Examples of the molten salt containing potassium ions and sodium ions include potassium and sodium nitrates, carbonates, sulfates, and mixed molten salts thereof. Among these, from the viewpoint that the melting point is low and deformation of the glass substrate can be prevented, it is preferable to use nitrate.

  The chemical strengthening treatment liquid is heated to a temperature higher than the temperature at which the above components melt. On the other hand, when the heating temperature of the chemical strengthening treatment liquid is too high, the temperature of the glass substrate is excessively increased, and the glass substrate may be deformed. For this reason, the heating temperature of the chemical strengthening treatment liquid is preferably lower than the glass transition point (Tg) of the glass substrate, more preferably lower than the glass transition point −50 ° C.

  In addition, in order to prevent the occurrence of cracks and fine cracks in the glass substrate due to thermal shock when immersed in the heated chemical strengthening treatment liquid, the glass substrate is placed in a preheating tank prior to immersion in the chemical strengthening treatment liquid. You may have the preheating process heated to predetermined temperature.

  The thickness of the chemically strengthened layer is preferably in the range of about 5 μm to 15 μm in view of improving the strength of the glass substrate and shortening the time of the polishing process. When the thickness of the reinforcing layer is within this range, a glass substrate having good impact resistance, which is flatness and mechanical strength, can be obtained.

  The shape of the outer peripheral end portion of the main surface 10a after the chemical strengthening step is almost the same as that before the chemical strengthening step, and the above-mentioned chemical strengthening layer of about 5 μm to 15 μm is almost uniformly placed on the entire surface of the glass substrate. Become.

  Next, the polishing process will be described. In the polishing process, the surface of the glass substrate is precisely finished, and the shape of the outer peripheral end of the main surface is polished so as to obtain the shape of the present invention.

  First, in the first polishing step, the surface roughness is improved and the shape of the present invention is finally efficiently improved so that the surface roughness finally required in the second polishing step can be efficiently obtained. Polishing can be obtained.

  The polishing method uses a polishing machine having the same configuration as the polishing machine used in the first and second lapping processes except that a pad and a polishing liquid are used instead of the diamond pellets and the grinding liquid used in the lapping process.

  The pad is preferably a hard pad having a hardness A of about 80 to 90, for example, urethane foam. When the pad hardness becomes soft due to heat generated by polishing, the shape change of the polished surface increases, so it is preferable to use a hard pad. The abrasive is preferably used in the form of a slurry by dispersing cerium oxide or the like having a particle size of 0.6 to 2.5 μm in water. The mixing ratio of water and abrasive is preferably about 1: 9 to 3: 7.

The weight applied to the glass substrate by the surface plate is preferably 90 g / cm ² to 110 g / cm ² . The load applied to the glass substrate by the surface plate greatly affects the shape of the outer peripheral edge. As the weight is increased, the inner side of the outer peripheral end portion tends to decrease and increase toward the outer side. Further, when the weight is reduced, the outer peripheral end portion tends to be close to a plane and the surface sagging increases. The weight can be determined while observing these trends.

  Moreover, the rotation speed of the surface plate is changed from 25 rpm to 50 rpm so that the flatness obtained until the chemical strengthening process is maintained and the surface roughness is further improved, and the rotation speed of the upper surface plate is lower than the rotation speed of the lower surface plate. It is preferable to slow by 30% to 40%.

  The polishing amount is preferably 30 μm to 40 μm depending on the above polishing conditions. If it is less than 30 μm, scratches and defects cannot be removed sufficiently. On the other hand, when it exceeds 40 μm, the surface roughness can be in the range of Rmax from 2 nm to 60 nm and Ra from 2 nm to 4 nm.

  The second polishing step is a step of further precisely polishing the surface of the glass substrate after the first polishing step. The pad used in the second polishing step is a soft pad having a hardness of about 65 to 80 (Asker-C) softer than the pad used in the first polishing step. For example, urethane foam or suede is preferably used. As the abrasive, cerium oxide or the like similar to that in the first polishing step can be used, but it is preferable to use an abrasive having a finer particle size and less variation in order to make the surface of the glass substrate smoother. An abrasive having an average particle diameter of 40 nm to 70 nm is dispersed in water to form a slurry and used as a polishing liquid. The mixing ratio of water and abrasive is preferably about 1: 9 to 3: 7.

The weight applied to the glass substrate by the surface plate is preferably 90 g / cm ² to 110 g / cm ² . The weight applied to the glass substrate by the surface plate greatly affects the shape of the outer peripheral edge as in the first polishing step, but the shape cannot be changed as efficiently as the first polishing step because the polishing rate is slow. The change in the shape of the outer peripheral end due to the increase / decrease of the weight is the same as in the first polishing step, and when the weight is increased, the inner side of the outer peripheral end tends to fall and rise outward. Further, when the weight is reduced, the outer peripheral end portion tends to be close to a plane and the surface sagging increases. In order to obtain the shape of the outer peripheral edge, the weight can be determined while observing such a tendency. The rotation speed of the surface plate is preferably 15 rpm to 35 rpm, and the rotation speed of the upper surface plate is preferably 30% to 40% slower than the rotation speed of the lower surface plate.

  As described above, the polishing conditions in the second polishing step are adjusted to obtain the shape of the outer peripheral edge of the present invention, and the surface roughness is Rmax from 2 nm to 6 nm and Ra is from 0.2 nm to 0.4 nm. It can be a range.

  The polishing amount is preferably 2 to 5 μm. When the polishing amount is within this range, minute defects such as minute roughness and undulation generated on the surface and minute scratches generated in the process so far can be efficiently removed.

  The first and second polishing steps reduce chemically strengthened areas on the surface of the glass substrate. There is no limitation on whether or not the chemically strengthened region remains on the surface of the glass substrate after the first and second polishing steps, or on the thickness of the remaining strengthened region.

  After completion of the second polishing process, the glass substrate is cleaned and inspected to complete the information recording medium glass substrate.

  In addition, in the manufacturing method of the glass substrate for information recording media, you may have various processes other than the above. For example, an annealing process for relaxing internal distortion of the glass substrate, a heat shock process for confirming the reliability of the strength of the glass substrate, and removing foreign substances such as abrasives and chemical strengthening treatment liquid remaining on the surface of the glass substrate. You may have a washing process, various inspection and evaluation processes, etc.

  Further, in the second polishing step, it is preferable not to use the polishing machine used in the first polishing process as it is, but to perform polishing using another polishing machine having the same configuration but prepared for each process. . This is because, if the polishing machine used in the first polishing process is used as it is, the polishing accuracy in the second polishing process decreases due to the abrasive remaining in the first polishing process, and the polishing conditions are reset. This is because work is required and manufacturing efficiency is lowered.

  Next, the magnetic recording medium provided on the glass substrate for information recording medium will be described. Hereinafter, a magnetic recording medium will be described with reference to the drawings.

  FIG. 3 is a perspective view of a magnetic disk as an example of a magnetic recording medium. In the magnetic disk D, a magnetic film 2 is directly formed on the surface of a circular glass substrate 1 for an information recording medium. As a method for forming the magnetic film 2, a conventionally known method can be used. For example, a method in which a thermosetting resin in which magnetic particles are dispersed is spin-coated on a substrate, or a method by sputtering or electroless plating is used. A method is mentioned. The film thickness by spin coating is about 0.3 μm to 1.2 μm, the film thickness by sputtering is about 0.04 μm to 0.08 μm, and the film thickness by electroless plating is 0.05 μm to 0.1 μm. From the viewpoint of thinning and densification, film formation by sputtering and electroless plating is preferable.

The magnetic material used for the magnetic film is not particularly limited and conventionally known materials can be used. However, in order to obtain a high coercive force, Ni having high crystal anisotropy is basically used, and Ni or A Co-based alloy to which Cr is added is suitable. Specific examples include CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, and CoNiPt containing Co as a main component, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, and CoCrPtSiO. The magnetic film may have a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa) that is divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) to reduce noise. In addition to the above magnetic materials, granular materials such as ferrite, iron-rare earth, non-magnetic films made of SiO ₂ , BN, etc. in which magnetic particles such as Fe, Co, FeCo, CoNiPt are dispersed, etc. Also good. Further, the magnetic film may be either an inner surface type or a vertical type recording format.

  In addition, a lubricant may be thinly coated on the surface of the magnetic film in order to improve the sliding of the magnetic head. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

  Furthermore, you may provide a base layer and a protective layer as needed. The underlayer in the magnetic disk is selected according to the magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. In the case of a magnetic film containing Co as a main component, Cr alone or a Cr alloy is preferable from the viewpoint of improving magnetic characteristics. Further, the underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

Examples of the protective layer that prevents wear and corrosion of the magnetic film include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be formed continuously with an in-line type sputtering apparatus, such as an underlayer and a magnetic film. In addition, these protective layers may be a single layer, or may have a multilayer structure including the same or different layers. Note that another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, tetraalkoxysilane is diluted with an alcohol-based solvent on a Cr layer, and then colloidal silica fine particles are dispersed and applied, followed by baking to form a silicon dioxide (SiO ₂ ) layer. It may be formed.

  By using the magnetic recording medium based on the glass substrate for information recording medium of the present invention obtained as described above, the operation of the magnetic head during LUL and high-speed rotation can be stabilized.

It is an enlarged view schematically showing the shape of the part from the front main surface to the outer peripheral end surface in the glass substrate for information recording medium. It is a figure which shows the whole structure of the glass substrate for information recording media. It is a figure which shows the example of the magnetic recording medium provided with the magnetic film on the front main surface of the glass substrate for information recording media. It is a flowchart explaining the process in manufacture of the glass substrate for information recording media.

Explanation of symbols

1 Glass substrate for information recording media (glass substrate)
2 magnetic film 10a front main surface 10b back main surface 13 hole 14 outer peripheral end surface 15 inner peripheral end surface D magnetic disk R1, R2, Rt position BL contour SH reference plane TL1 first tangent TL2 second tangent Hp inflection point θ1 , Θ2 Maximum angle

Claims (3)

In a glass substrate for an information recording medium having a donut shape having an outer peripheral end surface and an inner peripheral end surface concentric with a main surface having a flat portion,
On the same main surface side contour line in the radial direction of the glass substrate for information recording medium and perpendicular to the main surface, the position R1 is spaced apart from the position R1 in the direction from the position R1 to the outer peripheral end surface. R2 is determined,
The contour line is lowered from the position R1 to the position R2 toward the information recording medium glass substrate side,
There is one inflection point until the descending contour line reaches the position R2.
The maximum angle θ1 formed by a first tangent line that contacts the contour line from the position R1 to the inflection point and a reference plane that uses the flat portion of the main surface as a reference, and the contour from the inflection point to the position R2 The maximum angle θ2 formed by the second tangent tangent to the line and the first tangent satisfies the following conditional expression:
0 ° <θ1 ≤ 5 °
θ1 × 0.5 ≦ θ2 ≦ θ1 × 2
The contour line in the direction from the position R2 to the outer peripheral end surface is closer to the substrate than the reference plane, extends in a direction away from the reference plane, and reaches the outer peripheral end surface. Glass substrate.
However,
Position R1: Position R2 where the distance from the central axis of the glass substrate for information recording medium is R × 0.90: Position R where the distance from the central axis of the glass substrate for information recording medium is R × 0.975: Maximum distance θ1 from the central axis of the glass substrate for information recording medium to the outer peripheral end surface: an angle (plus) from the reference plane toward the first tangent.
Maximum angle θ2: An angle (plus) from the first tangent to the second tangent. A magnetic recording medium comprising a magnetic film on a surface of the glass substrate for information recording medium according to claim 1. The magnetic recording medium according to claim 2, wherein the magnetic recording medium is an LUL type magnetic recording medium.

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