JP5425685B2 - Method for manufacturing glass substrate for magnetic recording medium - Google Patents

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic recording medium, and more particularly to a method for manufacturing a glass substrate for a magnetic disk that can reduce errors in reading servo information including track information recorded on a magnetic recording medium when a hard disk is used. Is.

  In recent years, with the advancement of information technology, information recording technology, particularly magnetic recording technology, has made remarkable progress.

  As described in Patent Document 1, an HDD (Hard Disk Drive) which is one of such magnetic recording technologies is a magnetic disk (magnetic) having a magnetic recording layer made of a magnetic thin film on the surface of a disk-shaped substrate. Recording medium), a spindle motor that rotates the magnetic disk at high speed, a magnetic head that is attached to the tip of the swing arm and reads / writes magnetic data on the magnetic recording layer of the magnetic disk, and moves the magnetic head in the radial direction on the magnetic disk The positioning device is a main component (Patent Document 1).

  Here, as a magnetic recording medium substrate, an aluminum substrate has been widely used in the past.

  However, along with the trend of downsizing, thinning, and high-density recording of magnetic disks due to computer mobilization, in recent years, the demand for glass substrates with excellent substrate surface flatness and substrate strength compared to aluminum substrates has increased. ing.

  For example, as shown in Patent Document 2, a glass substrate for a magnetic disk is formed by forming a glass into a disk shape, chamfering, polishing an end surface and a main surface, and thereafter improving impact resistance and vibration resistance. (Patent Document 2).

  Here, the glass substrate for a magnetic disk is manufactured to have a predetermined shape so as to satisfy characteristics required for the magnetic disk, specifically, mechanical strength, reading / writing accuracy, and the like.

  For example, the shape of the chamfered portion is formed so that the chamfering angle is 40 to 50 degrees in the glass substrate for magnetic disk described in Patent Document 3 (Patent Document 3).

  In addition, since the glass substrate for magnetic disks is normally mass-produced and a variation arises in a shape, it is manufactured so that the variation may fall within a predetermined numerical range (dimensional tolerance).

JP 2001-243735 A Japanese Unexamined Patent Publication No. 2000-076652 JP 2009-64514 A

  Here, with the recent increase in recording density and high-speed rotation in HDDs, the influence of TMR (Track Mis Resistration), that is, the magnetic head that floats on the magnetic disk due to the disk fluttering, is increased. There is a tendency for the phenomenon of losing sight of servo information including Track information in which track position information is recorded.

  This is mainly due to narrowing of the track width due to improvement in recording density and reading error due to mechanical vibration of the disk due to high speed rotation.

  For this reason, the magnetic disk glass substrate has a narrower track width than the magnetic disk and high-speed rotation of the HDD, so that the magnetic head can rotate stably so that the servo information including the track information is not lost. More severe conditions (for example, shape dimensions) are required.

  However, even when the shape and size management is performed by defining the parameters so far and a glass substrate for a magnetic disk is manufactured, the phenomenon of losing servo information is completely lost when an HDD is manufactured using this glass substrate as a magnetic disk. It has become impossible to prevent.

  In addition, in order to achieve a high recording density, the track width of the magnetic disk is narrowed, and the size per bit of the magnetic disk decreases as the recording capacity increases. On the other hand, the signal reading intensity is weakened, and it has become difficult to ensure a good S / N ratio. In order to obtain this good S / N ratio, it is required to form a uniform magnetic recording layer. However, as the recording density is improved, there is a problem of variations in signal intensity within the disk surface.

  On the other hand, improvement of the method for forming the magnetic layer and the film structure has been promoted, but there is also a problem that it is still insufficient.

  The present invention has been made to remedy such problems. The object of the present invention is to read out servo information including Track information recorded on a magnetic disk stably when the HDD is first used. An object of the present invention is to provide a method of manufacturing a glass substrate for a magnetic recording medium that can achieve this, and secondly, a method of manufacturing a glass substrate for a magnetic recording medium that can reduce in-plane variation of a magnetic recording signal when a magnetic disk is used.

  In order to solve the above problems, the present inventors have conducted intensive studies, and as a result, the cause of the marked increase in the servo information loss of the servo information including the track information by the magnetic head is determined at the time of high-speed rotation exceeding a certain number of rotations. It has also been found that this phenomenon is likely to occur when the recording density is 500 GB / P or more on a 2.5-inch magnetic disk. In particular, it has been found that this problem occurs frequently near the outermost periphery of the magnetic disk. In order to solve this problem, as a result of repeating various thoughts and errors, we thought about devising the magnetic disk film configuration, film formation process, and servo information formation process, but the results were insufficient. . As a result of further investigation, the symmetry in the thickness direction of the glass substrate (the symmetry of the glass substrate in the axis orthogonal to the rotation axis of the glass substrate) is important, not simply the shape of the end surface of the magnetic disk glass substrate. I found out.

  Conventionally, there are documents specifying the end shape, but most of them are related to particle countermeasures and head crash prevention, and the end surface shape on one main surface side is specified. In the prior art, which did not appear in the above, the symmetry in the thickness direction was not considered at all. However, the present inventors found that the above problems existed and completed the present invention.

  That is, the present invention has the following configuration.

(Configuration 1)
An end surface processing step for processing the inner peripheral end surface and / or the outer peripheral end surface of the donut-shaped glass substrate, an evaluation step for evaluating the symmetry in the thickness direction of the inner peripheral end surface and / or the outer peripheral end surface of the glass substrate, and the evaluation A method of manufacturing a glass substrate for a magnetic recording medium, wherein a glass substrate for a magnetic recording medium is determined as a non-defective product by the determination step.

(Configuration 2)
The evaluation step (a) obtains the outer profiles of both the main surface and the chamfered portion as viewed from the side surface of the glass substrate, (b) superimposes the outer profiles of the two main surfaces, and (c) the The manufacturing method of the glass substrate for magnetic recording media of the structure 1 which measures a symmetry from superimposition and evaluates the said symmetry.

(Configuration 3)
The step (b) obtains a least square line of an outer profile of the main surface of the glass substrate, obtains a center line with respect to the least square line, and superimposes the outer profile of the main surface along the center line. 3. A method for producing a glass substrate for a magnetic recording medium according to 2.

(Configuration 4)
(C) is a method for manufacturing a glass substrate for a magnetic recording medium according to Configuration 3, wherein symmetry is evaluated based on at least one of the following values. (I) The distance between the parallel lines of the non-overlapping portions of the chamfered portion when the parallel lines of the end face of the glass substrate are drawn. (Ii) The distance of the non-overlapping portion of the chamfered portion at the boundary between the main surface and the chamfered portion. (Iii) The area of the non-overlapping portion of the chamfered portion.

(Configuration 5)
(A) acquires the external profile by measuring the cross-sectional shape of the glass substrate, images the acquired external profile, and (b) superimposes the imaged main surfaces 4. A method for producing a glass substrate for a magnetic recording medium according to 4.

(Configuration 6)
(A) cutting the glass substrate so that the normal direction of the cross section is perpendicular to the central axis of the glass substrate, and acquiring the external profile by measuring the cross-sectional shape of the cut portion The manufacturing method of the glass substrate for magnetic recording media of the structure 5 which images the said external shape profile.

(Configuration 7)
The glass substrate for magnetic recording media manufactured by the manufacturing method of the glass substrate for magnetic recording media in any one of the structures 1-6.

(Configuration 8)
A magnetic recording medium comprising the glass substrate for a magnetic recording medium according to Configuration 7, and an underlayer, a magnetic layer, a protective layer, and a lubricating layer provided on a surface of the glass substrate for the magnetic recording medium.

(Configuration 9)
Magnetic recording including a doughnut-shaped glass substrate, comprising: an evaluation step for evaluating symmetry in the thickness direction of the inner peripheral end face and / or outer peripheral end face of the glass substrate on which the inner peripheral end face and / or outer peripheral end face is processed Evaluation method of glass substrate for medium.

(Configuration 10)
In the evaluation step, (a) obtaining the profile of both the main surface and the chamfered portion viewed from the side surface of the glass substrate, (b) superposing the shapes of the two main surfaces of the profile, 10) The method for evaluating a glass substrate for a magnetic recording medium according to Configuration 9, wherein the symmetry is measured from the superposition and the symmetry is evaluated from the measurement result.

(Configuration 11)
The magnetic recording according to Configuration 10, wherein (b) obtains a least square line of the main surface of the glass substrate, obtains a center line with respect to the least square line, and superimposes the shape of the main surface along the center line. Evaluation method of glass substrate for medium.

(Configuration 12)
The magnetic recording medium according to Configuration 11, wherein (c) measures at least one of the following values as a symmetry measurement, and determines that the glass substrate is a good product when the measured value is within a certain value: Evaluation method for glass substrate. (I) The distance between the parallel lines of the non-overlapping portions of the chamfered portion when the parallel lines of the end face of the glass substrate are drawn. (Ii) The distance of the non-overlapping portion of the chamfered portion at the boundary between the main surface and the chamfered portion. (Iii) The area of the non-overlapping portion of the chamfered portion.

(Configuration 13)
(A) acquires the external profile by measuring the cross-sectional shape of the glass substrate, and images the acquired external profile,
(B) is a method for evaluating a glass substrate for a magnetic recording medium according to Configuration 12, wherein the imaged main surface is superimposed.

(Configuration 14)
(A) cutting the glass substrate so that the normal direction of the cross section is perpendicular to the central axis of the glass substrate, and acquiring the external profile by measuring the cross-sectional shape of the cut portion The evaluation method of the glass substrate for magnetic recording media of the structure 13 which images the said external shape profile.

  In the present invention, when evaluating a glass substrate for a magnetic recording medium, symmetry is measured and evaluated rather than measuring and evaluating only the shape of each part constituting the glass substrate for a magnetic recording medium.

  For this reason, it is possible to make a more accurate non-defective product determination that can cope with a narrower track width by improving the recording density and a mechanical vibration of the disk due to high-speed rotation. By making such a determination, the track information is not lost. A method for producing a glass substrate for a recording medium can be provided.

1 is a plan view of a glass substrate 1. FIG. It is 1B-1B sectional drawing of FIG. 1A. 1 is a cross-sectional view showing a magnetic recording medium 100. FIG. 4 is a flowchart showing details of a method for manufacturing the glass substrate 1. It is a figure which shows the outline of step 109 of FIG. It is a flowchart which shows the detail of FIG. It is a figure for demonstrating step 201 of FIG. It is a figure for demonstrating step 201 of FIG. It is a figure for demonstrating step 202 of FIG. It is a figure for demonstrating step 203 of FIG. It is a figure for demonstrating step 204 of FIG. It is a figure for demonstrating step 205 of FIG. It is a figure for demonstrating parameter (i). It is a figure for demonstrating parameter (ii). It is a figure for demonstrating parameter (iii). It is an example of a symmetry profile. It is an example of a symmetry profile. It is an example of a symmetry profile. It is an example of a symmetry profile. It is an example of a symmetry profile. It is an example of a symmetry profile. It is the schematic which shows an example of the measurement system for acquiring an external shape profile.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  First, with reference to FIGS. 1A to 1C, the structure of a glass substrate 1 (glass substrate for magnetic recording medium) manufactured by the method for manufacturing a glass substrate 1 for magnetic recording medium according to the present embodiment will be briefly described.

  As shown in FIG. 1A, the glass substrate 1 has a donut shape, has a main body 3 having a disk shape, and an inner hole 5 is formed at the center of the main body 3.

  As shown in FIG. 1B, the main body 3 has substantially smooth main surfaces 7a and 7b.

  The main surfaces 7a and 7b are surfaces on which a layer for recording and reproducing information is formed. For example, as shown in FIG. 1C, one or both of the main surfaces 7a and 7b are provided with an underlayer 18a, a magnetic layer 18b, By providing the protective layer 18c and the lubricating layer 18d, the glass substrate 1 becomes the magnetic recording medium 100 (at least the magnetic layer 18b is necessary as a recording layer).

  As shown in FIG. 1B, the main body 3 has an inner peripheral end surface 11 and an outer peripheral end surface 9 that are orthogonal to the main surfaces 7a and 7b.

  The inner peripheral end face 11 and the outer peripheral end face 9 are chamfered, and inner peripheral chamfered portions 13a and 13b and outer peripheral chamfered portions 15a and 15b are provided on the main surfaces 7a and 7b, respectively.

Furthermore, the chemical strengthening layer 17 is formed on the surface of the main body 3.
The chemical strengthening layer 17 is, for example, a layer in which a part of glass ions that are the raw material of the glass substrate 1 is replaced with ions having a larger ion radius to form a compressive stress layer.

  Next, with reference to FIGS. 2-9C, the manufacturing method of the glass substrate 1 which concerns on this embodiment is demonstrated.

  First, as shown in FIG. 2, glass as a raw material is formed into a disk shape (step 101).

  Examples of the glass used as a raw material include soda lime glass, aluminosilicate glass, borosilicate glass, and crystallized glass produced by a float method, a downdraw method, a redraw method, or a press method.

  In the following embodiments, glass manufactured by a press method will be described as an example.

  Next, as shown in FIG. 2, the main surfaces 7a and 7b of the glass formed into a disk shape are ground (first lapping) in order to adjust the plate thickness (step 102). Grinding is performed, for example, using a double-sided lapping machine and abrasive grains such as alumina.

Next, as shown in FIG. 2, an inner hole 5 (see FIG. 1) is formed in the center of the glass (step 103).
The inner hole 5 is formed using, for example, a core drill.

  Next, as shown in FIG. 2, the inner peripheral end face 11 and the outer peripheral end face 9 are chamfered in order to remove cracks on the end face of the glass (step 104). The chamfering is performed using, for example, a grindstone to which diamond abrasive grains are attached.

  In addition, you may add the process of grinding (2nd lapping) main surface 7a, 7b after chamfering. Thereby, the unevenness | corrugation produced by formation and chamfering of the inner hole 5 can be ground, and the burden at the time of grinding | polishing can be reduced.

Next, as shown in FIG. 2, the inner peripheral end face 11 and the outer peripheral end face 9 of the glass are polished, that is, end face polishing is performed (step 105).
The end surface polishing is performed using, for example, a rotating brush. At the time of end face polishing, the inner peripheral chamfered portions 13a and 13b and the outer peripheral chamfered portions 15a and 15b are also polished.

  Next, as shown in FIG. 2, the glass is chemically strengthened to form a chemically strengthened layer 17 (step 106).

  Specifically, a glass is immersed in a chemical strengthening solution, and ions having a larger ion radius than ions contained in the glass are included in the chemical strengthening solution. The chemical strengthening layer 17 is formed by ion exchange.

  Next, after the chemical strengthening is completed, the glass is washed to remove the surface chemical strengthening solution, and then the flatness and surface roughness of the main surfaces 7a and 7b of the glass are adjusted as shown in FIG. The main surfaces 7a and 7b are polished (step 107).

  Polishing can be performed, for example, using a double-side polishing apparatus and a hard resin polisher and using a planetary gear mechanism. As the abrasive, abrasive grains such as cerium oxide are used.

  When polishing is completed, the glass is washed to remove abrasives and impurities adhering to the surface during manufacture (step 108).

  Specific examples include physical cleaning such as scrub cleaning and ultrasonic cleaning, and chemical cleaning using a fluoride, organic acid, hydrogen peroxide, surfactant, and the like.

  Finally, the track information loss characteristic of the manufactured glass substrate 1 is evaluated (determined) (evaluation process) (step 109).

  Then, a non-defective product or a defective product is determined based on the evaluation result of the evaluation step, and the magnetic disk glass substrate is determined as a non-defective product.

Here, step 109 will be described.
First, an outline of step 109 will be described with reference to FIG.

  First, as shown in FIG. 3, the symmetry (in the thickness direction) of the glass substrate 1 is measured. Next, from the symmetry, it is determined whether or not the glass substrate 1 is a non-defective product, that is, whether or not the manufactured glass substrate 1 is one in which Track information is not lost.

  Next, step 109 will be described more specifically with reference to FIGS. 4 to 9C.

  First, as shown in FIG. 4, FIG. 5A, and FIG. 5B, what is used for the measurement of symmetry is selected from the manufactured glass substrates 1, and the selected glass substrate 1 is cut (step 201). At this time, cutting is performed so that the normal direction of the cut surface is orthogonal to the central axis of the glass substrate 1. In addition, here, it cut | disconnects along the radial direction of a glass substrate so that a cut surface may include a central axis.

  The glass substrate used for the measurement, that is, the glass substrate to be cut is extracted, for example, one for each same lot or one for every several to several tens of batches. Of course, a plurality of sheets may be extracted.

  5A and 5B, first, the glass substrate 1 is cut at a position not in contact with the inner hole 5 (FIG. 5A), and the portion of the cut glass substrate 1 that does not include the inner hole 5 is further cut along a cutting line. Although what was cut | disconnected again in the direction perpendicular | vertical with respect to a cutting line from the middle point (FIG. 5B) is utilized for the measurement, a cutting method is not limited to this.

  Next, as shown in FIG. 4 and FIG. 6A, a cross-sectional shape in the vicinity of the outer peripheral chamfered portions 15 a and 15 b of the cut glass substrate 1 (cross sections of the main surfaces 7 a and 7 b, the outer peripheral end surface 9, and the outer peripheral chamfered portions 15 a and 15 b. Shape). Specifically, the cross section is observed with a microscope, the observed image is captured by a CCD (Charge Coupled Device) camera or the like, and the external profile is converted into a digital image (step 202). The magnification of the microscope is preferably 500 to 1000 times in the case of a 1.8 inch or 2.5 inch glass substrate.

  Next, as shown in FIGS. 4 and 6B, least square lines 70a and 70b are obtained for the digitally imaged main surfaces 7a and 7b (outer profile thereof), respectively (step 203).

  Next, as shown in FIGS. 4 and 6C, a midline 90a with respect to the least squares 70a and 70b is obtained (step 204).

  Next, as shown in FIG. 4 and FIG. 6D, the outline profile digitalized based on the middle line 90a is folded, and the main surface 7a and the main surface 7b are overlapped. At that time, the following parameters are measured for the non-overlapping portions (symmetric profiles) of the outer peripheral chamfered portions 15a and 15b.

(I) With respect to the outer peripheral chamfered portions 15a and 15b, several parallel lines of the outer peripheral end surface 9 are drawn, and the parallel line distance d1 of the portion where the outer peripheral chamfered portions 15a and 15b do not overlap (FIG. 7A).
Although a plurality of d1 can be obtained, the longest distance may be used as the representative value.

(Ii) The distance d2 (FIG. 7B) of the portion where the boundary between the main surfaces 7a, 7b and the outer peripheral chamfered portions 15a, 15b does not overlap.

(Iii) Area (cross-sectional area) S (FIG. 7C) of the non-overlapping portions of the outer peripheral chamfered portions 15a and 15b.

  It can be evaluated that the closer the parameter is to 0, the higher the symmetry (that is, the track information is less likely to be lost).

  As the symmetry profile, specifically, the following patterns can be considered.

Pattern 1:
The outer peripheral chamfers 15a and 15b overlap (FIG. 8A).
Pattern 1 is an ideal pattern in which parameters (i), (ii), and (iii) are all zero.

Pattern 2:
The outer peripheral chamfered portions 15a and 15b do not overlap at the boundary with the outer peripheral end surface 9, but the outer peripheral chamfered portions 15a and 15b overlap at the boundary with the main surfaces 7a and 7b (FIG. 8B).

The reason for the profile like pattern 2 is as follows.
Reason a: When the chamfering in step 104 is misaligned between the rotation center of the glass substrate 1a and the grindstone rotating shaft for chamfering.
Reason b: A case where a branch and leaf processing method (a method of polishing one glass substrate 1a at a time) is adopted in the end surface polishing in Step 105, and a polishing brush or the like is in contact with the outer peripheral end surface 9.
In pattern 2, only parameter (ii) is zero.

Pattern 3:
The outer peripheral chamfered portions 15a and 15b do not overlap at the boundary with the main surfaces 7a and 7b, but the outer peripheral chamfered portions 15a and 15b overlap at the boundary with the outer peripheral end surface 9 (FIG. 8C).

The reason why the profile is as in pattern 3 is as follows.
Reason c: When chamfering in step 104, the center position of the glass substrate 1a in the plate thickness direction is not aligned with the center of the chamfering grindstone in the thickness direction.
Reason d: When chamfering in step 104, there is a difference in angle with respect to the main surfaces 7a and 7b of the grindstone for chamfering
Reason e: The end surface polishing in Step 105 employs a work stacking method (a method in which a plurality of glass substrates 1a are laminated and polished together), and there is a difference in the penetration of the brushes on the main surfaces 7a and 7b. If the chamfered part is polished differently.
Reason f: The case where the single-wafer processing method is adopted in the end surface polishing in Step 105 and the contact of the polishing brush with the chamfered portion differs between the main surfaces 7a and 7b.
Reason g: When there is a difference between the main surfaces 7a and 7b in the polishing process.

Pattern 4:
The outer peripheral chamfered portions 15a and 15b do not overlap and intersect at both the boundary with the outer peripheral end surface 9 and the boundary with the main surfaces 7a and 7b (FIG. 9A).

Pattern 5:
The outer peripheral chamfers 15a and 15b intersect (part 1) (FIG. 9B).

Pattern 6:
The outer peripheral chamfers 15a and 15b intersect (No. 2) (FIG. 9C).

  The cause of the profile such as the patterns 4, 5, 6 is the case where both the cause of the pattern 2 profile and the cause of the pattern 3 profile are present.

  As described above, the symmetry profile has six patterns. As in pattern 2, a specific parameter is 0, but other parameters may not be 0.

  Therefore, the accuracy of evaluation can be further improved by measuring three parameters.

  Next, it is determined whether or not the measured parameter is within a certain value. If it is within the certain value, it is determined as a non-defective product, and if it exceeds a certain value, it is determined as a defective product.

  Thus, in step 109, when evaluating the shapes of the two outer peripheral chamfered portions 15a and 15b, not only measuring and evaluating the shapes of the individual outer peripheral chamfered portions 15a and 15b, but two outer peripheral surfaces. The symmetry of the capturing parts 15a and 15b is measured and evaluated.

  In other words, as described above, glass substrates are usually mass-produced, and variations in shape occur, so that the variations are manufactured within a predetermined dimensional tolerance. Symmetry is used as a measure of.

  Therefore, compared with the case where only the shape of each of the outer peripheral chamfered portions 15a and 15b is measured / evaluated, it is possible to cope with the narrower track width by improving the recording density and the mechanical vibration of the disc by high-speed rotation, and higher accuracy. Non-defective product judgment is possible.

If it is determined in step 109 that the product is defective, the glass substrate of the population (for example, the same lot) used for measurement is determined to be defective. At this time, if regeneration is possible, chamfering or end face polishing is performed again, and if regeneration is impossible, discarding is performed.
The details of step 109 have been described above.

  Thus, the manufacturing method of the glass substrate 1 which concerns on this embodiment has the process of evaluating the track information loss characteristic of the said glass substrate from the symmetry of the shape of a glass substrate.

  Therefore, a glass substrate for a magnetic recording medium in which Track information is not lost can be manufactured.

  The glass substrate for a magnetic recording medium and the manufacturing method thereof according to the present invention are particularly important when manufacturing a patterned medium including a discrete track medium and a bit patterned medium. In the case of a patterned medium, a non-magnetic guard band part is provided between recording parts on which signals are recorded, and servo information including Track information becomes more important than conventional magnetic recording media. The ratio of losing sight of servo information increases. For this reason, by manufacturing a patterned medium using a glass substrate manufactured by the method for manufacturing a glass substrate for a magnetic recording medium according to the present invention, a magnetic recording medium capable of stable magnetic recording and reproduction can be realized.

  Further, the glass substrate for magnetic recording medium and the method for producing the same according to the present invention are particularly important when producing a heat-assisted recording medium (HAMR or TAMR).

  The present invention is particularly effective when a magnetic recording medium is manufactured using a glass substrate for a magnetic recording medium having a main surface with a surface roughness (Ra) of 0.3 nm or less.

  The present invention is particularly effective when a magnetic recording medium is manufactured using a glass substrate for a magnetic recording medium whose end face shape is a semicircular shape (including an ellipse) or a convex shape. When the end face shape is a semicircular shape (including an ellipse) or a convex shape, it is difficult to hold (hold) the glass substrate when forming a film using this glass substrate, particularly when performing sputter film formation. In addition, when the sputter target and the substrate are not parallel to each other, film formation cannot be performed uniformly in the plane. In this case, the magnetic characteristic distribution varies in the plane, and a magnetic disk with an improved S / N ratio cannot be manufactured. In addition, when a bias is applied during sputtering film formation, it is necessary to change the glass substrate in order to apply the bias. In such a case, the symmetry in the present invention is important.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Is done.

  For example, in this embodiment, the track information loss characteristic is evaluated at the end of the manufacturing process. However, the present invention is not limited to this, for example, after end face polishing (step 105 in FIG. 2). The same effect can be obtained by evaluating the track information loss characteristic after (2).

  In the present embodiment, three parameters are exemplified as symmetry parameters. However, the parameters are not necessarily limited to these three as long as the symmetry can be evaluated.

  Hereinafter, based on an Example, this invention is demonstrated in detail.

Example 1
A disk having a thickness of 0.635 mm and a radius of 65 mm was manufactured by the following procedure, and the relationship between the profile of the pattern 2 and the in-plane variation of the magnetic recording signal was obtained.

  The specific procedure is as follows.

(1) Shape processing step and first lapping step In the method of manufacturing a magnetic disk glass substrate according to this example, first, the surface of the plate glass is lapped (ground) to obtain a glass base material. Cut the material and cut out the glass disc. Various plate glasses can be used as the plate glass. This plate-like glass can be manufactured by using a known manufacturing method such as a press method, a float method, a downdraw method, a redraw method, or a fusion method using a molten glass as a material. Of these, plate glass can be produced at low cost by using the pressing method.

In this example, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper mold, a lower mold, and a barrel mold to obtain an amorphous plate glass. As the aluminosilicate _{glass, SiO} 2: 58 wt% to 75 _wt%, Al _{2 O} 3: 5 wt% to 23 wt%, _Li 2 O: 3% to 10% by weight, _Na 2 O: 4 by weight Glass containing from 13 to 13% by weight as a main component was used.

  Next, both main surfaces of the plate glass were lapped to form a disk-shaped glass base material. This lapping process was performed using alumina free abrasive grains with a double-sided lapping apparatus using a planetary gear mechanism. Specifically, the lapping platen is pressed on both sides of the plate glass from above and below, the grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relative to each other for lapping. went. By this lapping process, a glass base material having a flat main surface was obtained.

(2) Cutting process (coring, chamfering)
Next, using a cylindrical diamond drill, an inner hole was formed in the center of the glass substrate to obtain an annular glass substrate (coring). Then, the inner peripheral end face and the outer peripheral end face were ground with a diamond grindstone and subjected to predetermined chamfering (chambering).

(3) Second Lapping Step Next, a second lapping process was performed on both main surfaces of the obtained glass substrate in the same manner as in the first lapping step. By performing this second lapping step, it is possible to remove in advance the fine unevenness formed on the main surface in the cutting step and end surface polishing step, which are the previous steps, and shorten the subsequent polishing step on the main surface. Will be able to be completed in time.

(4) End surface polishing step Next, the outer peripheral end surface and the inner peripheral end surface of the glass substrate were mirror-polished by a brush polishing method. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used. And the glass substrate which finished the end surface grinding | polishing process was washed with water. By this end face polishing step, the end face of the glass substrate was processed into a mirror state that can prevent the precipitation of sodium and potassium.

(5) Main surface polishing step (first polishing step)
As a main surface polishing step, first, a first polishing step was performed. This first polishing step is mainly intended to remove scratches and distortions remaining on the main surface in the lapping step described above.

In the first polishing step, the main surface was polished using a hard resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains were used.

(6) Chemical strengthening process Next, the glass substrate which finished the above-mentioned lapping process and polishing process was chemically strengthened. For chemical strengthening, a chemical strengthening solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and the chemically strengthened solution is heated to 400 ° C., and the cleaned glass substrate is preheated to 300 ° C. And was immersed in the chemical strengthening solution for about 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, it was performed in a state of being housed in a holder so that a plurality of glass substrates were held at the end surfaces.

  Thus, by immersing in the chemical strengthening solution, the lithium ions and sodium ions in the surface layer of the glass substrate are replaced with sodium ions and potassium ions in the chemical strengthening solution, respectively, and the glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 μm.

  The glass substrate that had been subjected to the chemical strengthening treatment was immersed in a 20 ° C. water bath and rapidly cooled, and maintained for about 10 minutes. And the glass substrate which finished quenching was immersed in 10 weight% sulfuric acid heated at about 40 degreeC, and was wash | cleaned. Further, the glass substrate after the sulfuric acid cleaning was cleaned by immersing in a cleaning bath of pure water and IPA (isopropyl alcohol) sequentially.

(7) Main surface polishing process (final polishing process)
Next, a second polishing step was performed as a final polishing step. The purpose of this second polishing step is to finish the main surface into a mirror surface. In the second polishing step, mirror polishing of the main surface was performed using a soft foamed resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains (average particle diameter 0.8 μm) finer than the cerium oxide abrasive grains used in the first polishing step were used. The glass substrate which finished this 2nd grinding | polishing process was immersed in each washing | cleaning tank of neutral detergent, a pure water, and IPA sequentially, and was wash | cleaned. Note that ultrasonic waves were applied to each cleaning tank.

  As described above, by applying the first lapping step, the cutting step, the second lapping step, the end surface polishing step, the first polishing step, the chemical strengthening step, and the second polishing step, a flat and smooth, high rigidity A magnetic disk substrate was obtained.

  When the polishing was completed, the glass substrate 1a was washed to remove abrasives and impurities adhering to the surface during production, and 100 (one lot) glass substrates 1 were completed.

  Of the glass substrates 1 completed by such a procedure, one glass substrate 1 was selected per lot, a symmetry profile was obtained, and the one on which the profile of pattern 2 appeared was selected.

  Specifically, as shown in FIGS. 5A and 5B, the glass substrate 1 is cut along the radial direction so that the normal direction of the cut surface is a plane perpendicular to the central axis, as shown in FIG. Using a simple measurement system, the cut surface was observed with a CCD camera (CV-H500, manufactured by Keyence Corporation), and an image profile of the cut surface captured from the CCD camera was captured on a computer and imaged to obtain an external profile. .

  Referring briefly to FIG. 10, the measurement system includes a pedestal 31 on which the glass substrate 1 is placed, a clamp-like fixing jig 33 that fixes the glass substrate 1, a CCD camera 35 provided above the pedestal 31, and a CCD camera. A computer 37 connected to 35.

  Next, the acquired outer profile was deformed so that the outer profiles of the main surfaces 7a and 7b overlap each other, a symmetry profile was acquired, and the pattern 2 was selected.

  In the profile of the selected pattern 2, the length of the longest portion of the non-overlapping portions of the outer peripheral chamfered portions 15a and 15b was 0 to 250 μm.

  Next, the base layer 18a, the magnetic layer 18b, the protective layer 18c, and the lubricating layer 18d are provided on the main surfaces 7a and 7b of the glass substrate 1 of the same lot as the profile of the selected pattern 2, and the magnetic recording medium 100 is manufactured. The S / N ratio (under 1,500 kBPI (Bit Per Square Inch) condition) of the magnetic recording signal was determined at a rotational speed of 7,200 rpm and a measurement position r = 30 mm.

The measurement results of the S / N ratio are shown in Table 1.
In Table 1, “double circle” in the column of S / N ratio indicates a case where the S / N ratio is 16 dB or more, and “circle” indicates a case where the S / N ratio is 15.9 to 15.0 dB. X indicates that the S / N ratio is less than 15.0 dB and is regarded as a defective product.

  As is apparent from Table 1, the profile of the pattern 2 is a magnetic recording medium in which the S / N ratio increases as the length of the non-overlapping portions of the outer peripheral chamfered portions 15a and 15b decreases, and the track information is not lost. I understood.

(Example 2)
The glass substrate 1 was manufactured under the same conditions as in Example 1 except that the pattern 3 having the profile appeared was selected, and the relationship between the in-plane variations of the magnetic recording signal was obtained.

The results are shown in Table 2.
In Table 2, the meanings of “double circle”, “circle”, and “×” in the S / N ratio column are the same as those in Table 1.

  As apparent from Table 2, the profile of the pattern 3 is a magnetic recording medium in which the S / N ratio increases as the length of the non-overlapping portions of the main surfaces 7a and 7b decreases, and the track information is not lost. It was.

(Example 3)
The area of the non-overlapping portion of the profile of the samples of Examples 1 and 2 was determined, and the relationship of in-plane variation of the magnetic recording signal was determined.

The results are shown in Table 3.
In Table 3, the meanings of “double circle”, “circle”, and “×” in the S / N ratio column are the same as those in Table 1.

  As is apparent from Table 3, it was found that the smaller the area of the portion where the profiles do not overlap, the larger the S / N ratio, and the magnetic recording medium in which the Track information is not lost.

  From the above results, it was found that a strong correlation was observed between the symmetry profile and the S / N ratio of the magnetic recording signal, and the track information loss characteristic could be evaluated based on the symmetry profile.

  In the above-described embodiment, the case where the present invention is applied to the glass substrate 1 for a magnetic recording medium has been described. However, the present invention is not limited to this, and it is all necessary to define the shape of the end face. It can be applied to disc-shaped recording media.

  In the embodiment described above, the profile of the main surfaces 7a and 7b, the outer peripheral end surface 9, and the outer peripheral chamfered portions 15a and 15b is obtained by cutting the glass substrate 1 and observing the cross-sectional shape. If the external profile required in the present invention can be obtained without cutting, it is not always necessary to cut.

  That is, the profile required in the present invention is the profile of the main surfaces 7a and 7b, the outer peripheral end surface 9, and the outer peripheral chamfered portions 15a and 15b viewed from the side surface of the glass substrate 1, that is, from the direction orthogonal to the central axis. Since it is the external profile of the glass substrate 1 as seen, if such a profile can be obtained without cutting the glass substrate 1, it is not necessary to cut it.

1 ......... Glass substrate 3 ......... Main body 5 ......... Inner hole 7a ............ Main surface 17 ............ Chemical strengthening layer 18b ......... Magnetic layer

Claims (7)

An end face processing step for processing the outer peripheral end face of the doughnut-shaped glass substrate;
An evaluation step of evaluating the symmetry in the thickness direction of the end face portion of the outer periphery of the glass substrate,
Based on the evaluation step, including a determination step of determining a non-defective product / defective product,
The evaluation step includes
(A) In the outer peripheral end face part, obtain the profile of the two main surfaces of the glass substrate and the cross section in the thickness direction of the chamfered part,
(B) superimposing the external profiles of the two main surfaces at the end face of the outer periphery ;
(C) measuring symmetry from the superposition and evaluating the symmetry;
A method for manufacturing a glass substrate for a magnetic recording medium, wherein the glass substrate for a magnetic recording medium is determined as a non-defective product by the determining step. (B)
Find the least squares of the profile of the main surface of the glass substrate, find the center line for the least squares,
The method for manufacturing a glass substrate for a magnetic recording medium according to claim 1, wherein the profile of the main surface is superposed along the middle line. 3. The method of manufacturing a glass substrate for a magnetic recording medium according to claim 2, wherein (c) evaluates symmetry based on at least one of the following values.
(I) The distance between the parallel lines of the non-overlapping portions of the chamfered portion when the parallel lines of the end face of the glass substrate are drawn.
(Ii) the distance non-overlapping portion of the chamfered portions in the main surface.
(Iii) The area of the non-overlapping portion of the chamfered portion. (A) is to cut the glass substrate so that the normal direction of the cross section is perpendicular to the central axis of the glass substrate, and obtain the profile by measuring the cross-sectional shape of the glass substrate, The acquired outline profile is imaged,
(B) superimposes the imaged main surface;
Have
In the determination step, when it is determined that the glass substrate used for measurement is defective, the glass substrate of the population used for measurement is also determined to be defective.
The manufacturing method of the glass substrate for magnetic recording media of Claim 3. Has two major surfaces, a body is a disc in which the bore is formed, an inner peripheral edge surface is an end of the bore, and the outer peripheral end surface is an end of an outer periphery of the disc, and the outer peripheral end face and a chamfered portion provided between the main surface,
When the outer profile of the cross section in the thickness direction at the end face of the outer periphery is acquired, the outer profile of the two main surfaces and the chamfered portion along the middle line with respect to the least square line of the outer profile of the two main surfaces is obtained. A glass substrate for a magnetic recording medium, wherein a distance between the parallel lines of the non-overlapping portions of the chamfered portion is 140 μm or less when the parallel lines of the end surfaces of the glass substrate are drawn in a superposed state. Has two major surfaces, a body is a disc in which the bore is formed, an inner peripheral edge surface is an end of the bore, and the outer peripheral end surface is an end of an outer periphery of the disc, and the outer peripheral end face and a chamfered portion provided between the main surface,
When the outer profile of the cross section in the thickness direction at the end face of the outer periphery is acquired, the outer profile of the two main surfaces and the chamfered portion along the middle line with respect to the least square line of the outer profile of the two main surfaces is obtained. in the stacked state, in the main surface, the distance of the non-overlapping part of the chamfered portion is not more than 140 .mu.m, a glass substrate for a magnetic recording medium. Has two major surfaces, a body is a disc in which the bore is formed, an inner peripheral edge surface is an end of the bore, and the outer peripheral end surface is an end of an outer periphery of the disc, and the outer peripheral end face and a chamfered portion provided between the main surface,
When the outer profile of the cross section in the thickness direction at the end face of the outer periphery is acquired, the outer profile of the two main surfaces and the chamfered portion along the middle line with respect to the least square line of the outer profile of the two main surfaces is obtained. A glass substrate for a magnetic recording medium, wherein an area of a non-overlapping portion of the chamfered portion is 21000 μm ² or less in a superposed state.

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