JP2011210311A - Glass substrate for magnetic disk and evaluation method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass substrate for a magnetic recording medium, which achieves stable reading of servo information including Track information recorded on a magnetic disk, in an HDD.SOLUTION: In the glass substrate, a parameter M which can be obtained by a formula (3) from the radial position from the center and a plate thickness is within a predetermined range.

Description

  The present invention relates to a glass substrate for a magnetic disk and a method for evaluating the same.

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

  HDD (Hard Disk Drive), one of such magnetic recording technologies, rotates a magnetic disk (magnetic recording medium) having a magnetic recording layer made of a magnetic thin film on the surface of a disk-shaped substrate and a magnetic disk at high speed. The main components are a spindle motor to be driven, a magnetic head attached to the tip of a swing arm, for reading and writing magnetic data to and from a magnetic recording layer of the magnetic disk, and a positioning device for moving the magnetic head in the radial direction on the magnetic disk. (Patent Document 1).

  Since the magnetic heads are respectively disposed opposite to the magnetic recording layers formed on both main surfaces of the magnetic disk, it is a general configuration that two magnetic heads are provided for each magnetic disk. Here, as a magnetic recording medium substrate, an aluminum substrate has been widely used in the past.

  However, with the downsizing, thinning, and high-density recording of magnetic disks, in recent years, there has been an increasing demand for glass substrates that have superior substrate surface flatness and substrate strength compared to aluminum substrates.

  Conventionally, for example, as shown in paragraph [0004] of Patent Document 2, glass substrates are chamfered by forming glass into a disk shape, and end faces and main surfaces are polished, and then impact resistance and vibration resistance are obtained. It has been manufactured by applying a chemical strengthening treatment for improving (Patent Document 2).

  The glass substrate thus produced has been used as a magnetic recording medium by providing recording layers such as a magnetic layer on both sides.

  Here, the glass substrate for the magnetic disk is formed so as to have a predetermined thickness according to the thickness required for the magnetic disk, but prevents blurring during rotation and the accompanying TMR (Track Mis Resistration). Therefore, the plate thickness of the glass substrate is preferably a constant value.

  The definition of the thickness of the glass substrate has conventionally been indicated by the distance between both main surfaces measured at one point or a plurality of points on the glass substrate (Patent Document 3).

  The glass substrate for a magnetic disk is usually mass-produced, and the thickness of the glass plate varies. Therefore, the glass substrate is manufactured so that the variation falls within a predetermined numerical range (dimensional tolerance).

JP 2001-243735 A Japanese Unexamined Patent Publication No. 2000-076652 Japanese Patent Laid-Open No. 8-147691

  Here, with the recent increase in recording density and acceleration of high-speed rotation in HDDs, the influence of TMR more than before, that is, the magnetic head flying above the magnetic disk due to disk fluttering records the radius / track position information. There is a tendency for the phenomenon of losing sight of servo information including track information.

  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 glass substrate for the magnetic disk is designed so that the magnetic head can be rotated stably so that the servo information including the track information is not lost by narrowing the track width of the magnetic disk and rotating the HDD at high speed. Thickness is also required to be more accurate than in the past, and this requirement is generally prominent in HDDs having performances of 80 GB or more / 5,400 rpm or more.

  However, even when a dimensional tolerance is managed by the conventional definition of the plate thickness and a glass substrate for a magnetic disk is manufactured, when this HDD is manufactured using the glass substrate as a magnetic disk, the servo information is lost. In some cases, it could not be completely prevented.

  In other words, even if a glass substrate for a magnetic disk having the same plate thickness, there are a mixture of those that can eliminate the influence of TMR as described above and those that cannot be done, so far only one point on the glass substrate, Alternatively, there are cases where it is not possible to clearly distinguish between good and bad only by the parameter of the distance between both main surfaces measured at a plurality of points, and the causal relationship between TMR and the planar shape cannot be clarified.

  The present invention has been made to remedy such problems. The purpose of the present invention is to realize stable reading of servo information including track information recorded on a magnetic disk when an HDD is used. An object of the present invention is to provide a glass substrate for a magnetic disk.

  As a result of intensive studies to solve the above problems, the present inventor has found that the conventional definition of the plate thickness is merely an index indicating the distance between specific points (one point or several points) on both main surfaces, and the entire surface of both main surfaces is We paid attention to the fact that it did not reflect the distribution of plate thickness.

  That is, in the conventional definition of plate thickness, even if the plate thickness varies or varies depending on the position of the main surface, the plate thickness is evaluated as the same if the plate thickness at the measurement point is the same. did.

  Therefore, as a result of further studies, the present inventor uses the index considering the distribution of the plate thickness, particularly the plate thickness information with respect to the disk radial position, as the index for evaluating the plate thickness, thereby causing the causal effect of the TMR and the plate thickness. The inventors have found that the relationship can be grasped, and have come to the present invention.

  Specifically, in order to solve the above problems, the present invention has the following configuration.

(Configuration 1) A magnetic disk glass substrate characterized in that a parameter obtained from a relationship between a radial position from the center and a plate thickness is within a predetermined range.

(Configuration 2) The glass substrate for a magnetic disk according to Configuration 1, wherein the parameter has a value obtained by multiplying a radial position from the center and a plate thickness difference or a plate thickness for one circumference of the disk.

(Configuration 3) An internal hole is provided, and the parameter has a value obtained by obtaining a relationship between a radial position from the center and a plate thickness spirally from the inner hole toward the outer periphery. Glass substrate for magnetic disk.

(Configuration 4) The magnetic disk glass substrate according to any one of Configurations 2 and 3, wherein the parameter is an M value represented by the following formulas (1) and (2).

(Configuration 5) The glass substrate for a magnetic disk according to any one of configurations 2 and 3, wherein the parameter is an M value represented by the following formula (3).

(Configuration 6) The predetermined range is a range defined by a correlation between the M value and disk balance or TMR (Track Mis Resistration) characteristics. Glass substrate for magnetic disk.

(Structure 7) The glass substrate for a magnetic disk according to structure 6, wherein the TMR (Track Mis Resistration) characteristic is Axial Displacement 3s.

(Configuration 8) The predetermined range is a range within the upper limit of the M value in a flat portion where the Axial Displacement 3s is a constant value in the correlation diagram of the M value and the Axial Displacement 3s. 8. A glass substrate for a magnetic disk according to 7.

(Arrangement 9) The magnetic disk glass substrate according to any one of Arrangements 1 to 8, and an underlayer, a magnetic layer, a protective layer, and a lubricating layer provided on the main surface of the glass substrate. A characteristic magnetic recording medium.

(Configuration 10) A method for evaluating a glass substrate for a magnetic disk, characterized in that it is determined whether or not a parameter obtained from a relationship between a radial position from the center and a plate thickness is within a predetermined range.

(Structure 11) Evaluation of the glass substrate for a magnetic disk according to Structure 10, wherein the parameter has a value obtained by multiplying a radial position from the center and a difference in plate thickness for one circumference of the disk, or a plate thickness. Method.

(Configuration 12) The magnetic disk glass according to Configuration 11, wherein the parameter has a value obtained by determining a radial position and a plate thickness from the center spirally from the inner hole to the outer periphery of the glass substrate. Evaluation method of substrate.

(Configuration 13) The method for evaluating a glass substrate for a magnetic disk according to any one of Configurations 11 and 12, wherein the parameter is an M value represented by the following formulas (1) and (2): .

(Configuration 14) The method for evaluating a glass substrate for a magnetic disk according to any one of Configurations 11 and 12, wherein the parameter is an M value represented by the following formula (3).

(Structure 15) The predetermined range is a range defined by a correlation between the M value and a disk balance or TMR (Track Mis Resistration) characteristic, according to any one of the structures 13 and 14, Evaluation method of glass substrate for magnetic disk.

(Structure 16) A method for evaluating a glass substrate for a magnetic disk according to Structure 15, wherein the TMR (Track Mis Resistration) characteristic is Axial Displacement 3s.

(Configuration 17) The predetermined range is a range within an upper limit of the M value in a flat portion where the Axial Displacement 3s is a constant value in the correlation diagram of the M value and the Axial Displacement 3s. The evaluation method of the glass substrate for magnetic discs of 16.

(Structure 18) A method for producing a glass substrate for a magnetic disk, comprising the method for evaluating a glass substrate for a magnetic disk according to any one of structures 10 to 17 in a process.

  ADVANTAGE OF THE INVENTION According to this invention, when it is set as HDD, the glass substrate for magnetic discs which can implement | achieve stably reading the servo information containing the Track information currently recorded on the magnetic disc can be provided.

1A is a plan view of the glass substrate 1, FIG. 1B is a cross-sectional view taken along the line AA of FIG. 1A, and FIG. 1C is a cross-sectional view showing the magnetic recording medium 100. 4 is a flowchart showing details of a method for manufacturing the glass substrate 1. It is a flowchart which shows the detail of step 109 of FIG. It is a figure for demonstrating step 109 of FIG. It is a figure for demonstrating step 109 of FIG. It is a conceptual diagram which shows the measurement system 51 of a TMR characteristic (Axial Displacement3s). It is a correlation diagram of M value and Axial Displacement3s.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
First, with reference to FIG. 1, the structure of the glass substrate 1 which concerns on this embodiment is demonstrated easily.

  As shown in FIG. 1A, the glass substrate 1 has a main body 3 having a disc 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 / 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 and magnetic layers. By providing the layer 18b, the protective layer 18c, and the lubricating layer 18d, the glass substrate 1 becomes the magnetic recording medium 100 (magnetic disk) (at least the magnetic layer 18b is necessary as a recording layer).

  Moreover, as shown in FIG.1 (b), the main body 3 has the inner peripheral end surface 11 and the outer peripheral end surface 9 which 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 an inner peripheral chamfered face 13 and an outer peripheral chamfered face 15 are provided, respectively.

  Furthermore, the chemical strengthening layer 17 is formed on the surface of the main body 3.

  Although details of the chemical strengthening layer 17 will be described later, for example, a part of the glass ions used as the raw material of the glass substrate 1 is replaced with ions having a larger ion radius to form a compressive stress layer.

  The glass substrate 1 has such a shape that a parameter obtained from a radial position from the center and a plate thickness (a distance between the main surface 7a and the main surface 7b) falls within a predetermined range. It will be described later.

  Next, with reference to FIGS. 1-7, the manufacturing method of the glass substrate 1 is demonstrated.

  In the following description, the glass in the manufacturing process is referred to as “glass substrate 1a”, and the finished product is referred to as “glass substrate 1”.

  First, as shown in FIG. 2, the glass used as a raw material is shape | molded in disk shape, and the glass base material 1a is manufactured (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, in order to adjust the plate thickness of the glass substrate 1a, the main surfaces 7a and 7b are ground (first lapping) using the grinding device 21 (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 substrate 1a (step 103).
The inner hole 5 is formed using, for example, a core drill.

  When sheet glass is used, steps 101 to 103 are not performed. Instead, a process of cutting the glass from the sheet shape into a disk shape using a cutter and further cutting the inner hole 5 (cutting process) is performed.

  Next, as shown in FIG. 2, the inner peripheral end face 11 and the outer peripheral end face 9 are chamfered to remove cracks on the end face of the glass substrate 1a (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 surface 11 and the outer peripheral end surface 9 of the glass substrate 1a are polished, that is, end surface polishing is performed (step 105).
The end surface polishing is performed using, for example, a rotating brush.

  Next, as shown in FIG. 2, the glass substrate 1a is chemically strengthened to form the 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 finished, the glass substrate 1a 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 substrate 1a are removed as shown in FIG. In order to adjust the thickness (substantially smooth), 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 polishing liquid, for example, a slurry obtained by dispersing abrasive grains such as cerium oxide or lanthanum oxide in water is used.

  When polishing is completed, the glass substrate 1a 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.

  Here, among steps 101 to 108, (2) second lapping that may be performed after (1) step 102 (first lapping) and chamfering (step 104), and (3) step 107 (polishing process). ) Is a process that is likely to generate a variation in the plate thickness that affects the disc balance / TMR characteristics of interest in the present application. For example, in step 102 of (1), the plate thickness difference of the material to be input is set to <100 μm, In addition, it is possible to suppress the processing pressure from changing every batch processing by increasing the number of sheets in the carrier holder that holds the material to a predetermined number (> 90% filling rate) and grinding the processing load. By varying it according to (for example, initial / middle / end), it is possible to suppress variations in the plate thickness as much as possible in the first machining stage in all machining steps. Is required. In particular, the process with the largest machining (or grinding) allowance relative to the original thickness of the material is the step 102 in many cases. Therefore, the step 102 is the process that requires the most attention in order to suppress variations in the plate thickness.

  Also, (2) in the second lapping, the same consideration as in the above (1) needs to be made, but it is desirable that the thickness difference of the workpiece (first lapping processed) to be input is <10 μm.

 Further, in the (3) polishing step, the same consideration as in the above (2) needs to be made, but it is desirable that the difference in the plate thickness of the workpiece (step 106 chemically strengthened) to be input is <5 μm.

  Finally, product inspection (inspection of plate thickness) is performed (step 109).

  Here, details of step 109 will be described with reference to FIGS.

  As described above, the glass substrate 1 has such a shape that the parameters obtained from the relationship between the radial position from the center and the plate thickness (distance between the main surface 7a and the main surface 7b) fall within a predetermined range. However, in order to evaluate it, the plate thickness is measured to obtain a parameter, and it is determined whether or not the parameter is within a predetermined range.

Specifically, the inspection is performed according to the following procedure.
First, as shown in FIG. 3, using a known thickness measuring device or the like, the thickness of the glass substrate 1 (distance between the main surface 7a and the main surface 7b) is determined for each radial position from the center. A predetermined number is measured over the entire main surface of the glass substrate 1 (step 201).

  At this time, as shown in FIG. 4, it is desirable to measure the plate thickness so as to draw a shape in which the measurement point 22 goes around spirally from a predetermined position on the inner peripheral end to a predetermined position on the outer peripheral end.

  By measuring in this way, plate thickness data can be obtained evenly for every position in the radial direction from the center over the entire main surface of the glass substrate 1.

  Next, as shown in FIG. 3, an M value, which is a parameter obtained from the relationship between the measured radial position and the plate thickness, is calculated. (Step 202).

  The M value means the total sum of the plate thickness difference at the first measurement position, the plate thickness difference at each measurement position, and the radius of the measurement position (value corresponding to the moment at the measurement position). ) (2).

  FIG. 5 shows an example of the relationship between the measured radial position and the plate thickness and Equation (1).

  Here, the “sampling number” means that the horizontal size or horizontal resolution of the measurement probe in the plate thickness measurement system to be used is one sampling unit. For example, in a non-contact measurement device, the laser spot diameter or The lateral resolution determined thereby is one sampling unit.

  In addition, as is clear from its shape, the expressions (1) and (2) are affected by the difference in the plate thickness near the outer periphery (the portion where r is large), that is, the influence of the variation in the plate thickness near the outer periphery. It is an expression that appears larger than the variation of the plate thickness.

  That is, in the disc fluttering, the displacement amount on the outer peripheral side is larger than that on the inner peripheral side (because the inner peripheral side is held by the spindle and the rigidity is larger than that on the outer peripheral side), and the M value becomes larger. This is because the variation in the plate thickness near the outer periphery has a greater influence on the disk balance / TMR characteristics than the variation in the plate thickness near the inner periphery.

  Further, in the above formulas (1) and (2), as the plate thickness difference Δt, the plate thickness at the first measurement position and the plate thickness difference at each measurement position are used, but instead of Δt, the plate at each measurement position is simply used. Thickness may be used, and specifically, an equation shown in equation (3) may be used.

  Next, it is determined from the measured M value whether or not the disk balance / TMR characteristic of the glass substrate 1 is within a predetermined range. If it is within the range, it is treated as a non-defective product, and if it is out of the range, it is treated as a defective product. Handle (step 203).

  Specifically, it is determined whether or not the M value is within a certain range from the relationship between the M value and the Axial Displacement 3s as shown in FIG. If outside, treat as defective.

Note that the Axial Displacement3s, are those which determine the substrate vibration measurement data track positioning error of integrating the average value + 3s per frequency and for each rotational speed (vibration waveform), 3s and s ² the following example It calculates | requires by Formula (4) (5).

Here, a method for obtaining the relationship between the M value and the Axial Displacement 3s as shown in FIG. 7 will be briefly described.
First, a predetermined number of glass substrates 1 to be inspected are manufactured, and an M value is obtained.

  Next, the magnetic recording medium 100 is manufactured by providing the magnetic layer 18b, the protective layer 18c, and the lubricating layer 18d on the surface of the glass substrate 1, and using the measurement system 51 shown in FIG. Axial Displacement 3s is obtained at the measurement position.

  The measurement system 51 will be briefly described. The measurement system 51 includes a laser Doppler velocimeter (LDV) 55 having a head 53 and a conversion unit 57 that performs fast Fourier transform (FFT) on data measured by the laser Doppler velocimeter 55. is doing.

Next, a correlation diagram as shown in FIG. 7 is created by plotting the relationship between the M value and the Axial Displacement 3s indicating the disk balance / TMR characteristics.
The details of step 109 have been described above.

  As described above, according to the present embodiment, the glass substrate 1 has a predetermined range in which the parameter (M value) obtained from the relationship between the radial position from the center and the plate thickness satisfies the requirements of the disk balance / TMR characteristics. Is in.

  Therefore, when the glass substrate 1 is an HDD, it can stably read servo information including Track information recorded on the magnetic disk.

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

(Example)
A glass substrate for a magnetic disk having an outer diameter of 65 mm, an inner diameter of 20 mm, and a thickness of 0.635 mm was manufactured by the following procedure, and the plate thickness was measured. The correlation between the M value and the disk balance / TMR characteristics was obtained.

  First, 100 glass substrates 1 were manufactured according to the following steps.

(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.

  When lapping, in order to prevent variation in the plate thickness, the difference in the plate thickness of the material to be input should be <100 μm, and the number of sheets entering the carrier holder holding the material should be a predetermined number or more (> 90% The filling pressure of the sheet was controlled to prevent the processing pressure from changing every time the batch processing was performed. Further, by varying the processing load according to the stage of grinding (initial stage / middle stage / end stage), the plate thickness is prevented from varying as much as possible in the lapping process stage.

(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.

In the second lapping process, as in the first lapping process, the thickness difference of the workpiece (first lapping processed) to be input is set to <10 μm so as not to cause variations in the plate thickness.

(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.

  In the main surface polishing step, as in the first lapping step, the thickness difference of the workpiece (first lapping processed) to be input was set to <5 μm so as not to cause variations in the plate thickness.

(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 glass substrates 1 were completed.

  Next, a non-contact type laser displacement meter (spot size: 20 μm) composed of LK-G15 (measuring head) / LK-G3001 (measuring controller) manufactured by Keyence Corporation is used for the thickness of 100 glass substrates 1. Then, as shown in FIG. 4, the measurement was performed in a spiral shape from the inner periphery toward the outer periphery. The spiral shape was Archimedes spiral (uniform spiral), and the sampling points were a total of 8,550,000 points every 20 μm (measured in the range of radial position r = 13.0 to 32.0 mm). The number of measurement points of 8,550,000 points is determined from the following equation.

Number of measurement points N: N = {π (32 ² −13 ² )} / π (0.01 ² ) = 8,550,000
That is, in the above formula, 32 and 13 indicate both ends of the radial position (mm), and 0.01 indicates the radius (mm) of the spot size.

  Next, M value was calculated | required from Formula (1) (2) based on the measured board thickness and position information.

  Next, the magnetic recording medium 100 is manufactured by providing the magnetic layer 18b, the protective layer 18c, and the lubricating layer 18d on the surface of the glass substrate 1, and the number of rotations is 5,400 rpm / measurement using the measurement system shown in FIG. Axial Displacement 3s was determined under the condition of position r: 30 mm.

  Next, the relationship between the M value and Axial Displacement 3s indicating the disk balance / TMR characteristics was plotted.

  As is clear from FIG. 7, a strong correlation was observed between the M value and Axial Displacement 3s.

Specifically, in FIG. 7, the Axial Displacement 3s is constant at 0.005 μm when the M value (× 10 ⁶ ) mm ³ is 20 or less, and when the M value (× 10 ⁶ ) mm ³ exceeds 20, the Axial Displacement 3 Was getting bigger.

That is, in FIG. 7, if the M value (× 10 ⁶ ) mm ³ is within 20, the Axial Displacement 3s is kept low to a constant value. Therefore, the upper limit of the M value in a glass substrate with good disk balance / TMR characteristics is 20 become.

  From the above results, it has been found that the thickness of the glass substrate 1 can be formed into a shape satisfying the requirements of the disk balance / TMR characteristics (Axial Displacement 3s) based on the parameter (M value) of the present invention.

  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 all disk shapes that require a plate thickness to be defined. It can be applied to any recording medium.

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

Claims (18)

  A magnetic disk glass substrate characterized in that a parameter obtained from a relationship between a radial position from the center and a plate thickness is within a predetermined range. The parameter is
2. A glass substrate for a magnetic disk according to claim 1, wherein the glass substrate for a magnetic disk has a value obtained by multiplying a position in a radial direction from the center and a plate thickness difference or a plate thickness in one round of the disk. Has an inner hole,
The parameter is
3. The glass substrate for a magnetic disk according to claim 2, wherein the glass substrate for a magnetic disk has a value obtained by obtaining a relation between a radial position from the center and a plate thickness spirally from the inner hole toward the outer periphery. The parameter is
4. The glass substrate for a magnetic disk according to claim 2, which has an M value represented by the following formulas (1) and (2): 5.

The parameter is
4. The glass substrate for a magnetic disk according to claim 2, which has an M value represented by the following formula (3): 5.

  6. The magnetic disk according to claim 4, wherein the predetermined range is a range defined by a correlation between the M value and a disk balance or TMR (Track Mis Resistration) characteristic. Glass substrate.   The glass substrate for a magnetic disk according to claim 6, wherein the TMR (Track Mis Resistration) characteristic is Axial Displacement 3 s.   8. The predetermined range is a range within an upper limit of the M value in a flat portion where Axial Displacement 3s is a constant value in the correlation diagram of the M value and Axial Displacement 3s. Glass substrate for magnetic disk. A glass substrate for a magnetic disk according to any one of claims 1 to 8,
An underlayer, a magnetic layer, a protective layer, a lubricating layer provided on the main surface of the glass substrate;
A magnetic recording medium comprising:   A method for evaluating a glass substrate for a magnetic disk, comprising: determining whether a parameter obtained from a relationship between a radial position from the center and a plate thickness is within a predetermined range. The parameter is
11. The method for evaluating a glass substrate for a magnetic disk according to claim 10, wherein a value obtained by multiplying a radial position from the center by a plate thickness difference or a plate thickness for one round of the disk. The parameter is
12. The method for evaluating a glass substrate for a magnetic disk according to claim 11, comprising a value obtained by obtaining a radial position and a plate thickness from the center spirally from the inner hole to the outer periphery of the glass substrate. The parameter is
The method for evaluating a glass substrate for a magnetic disk according to claim 11, wherein the M value is represented by the following formulas (1) and (2).

The parameter is
The method for evaluating a glass substrate for a magnetic disk according to claim 11, wherein the M value is represented by the following formula (3).

  15. The magnetic disk according to claim 13, wherein the predetermined range is a range defined by a correlation between the M value and disk balance or TMR (Track Mis Resistration) characteristics. Evaluation method of glass substrate.   The method for evaluating a glass substrate for a magnetic disk according to claim 15, wherein the TMR (Track Mis Resistration) characteristic is Axial Displacement 3 s.   The predetermined range is a range within an upper limit of the M value in a flat portion where the Axial Displacement 3s is a constant value in the correlation diagram of the M value and the Axial Displacement 3s. Evaluation method for glass substrates for magnetic disks.   A method for producing a glass substrate for a magnetic disk, comprising the method of evaluating a glass substrate for a magnetic disk according to any one of claims 10 to 17 in a process.

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