JP4198607B2 - Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk - Google Patents

Description

  The present invention relates to a magnetic disk mounted on a magnetic disk device such as an HDD (hard disk drive) and a method for manufacturing a glass substrate for the magnetic disk.

In recent years, with the advancement of the information society, the progress of information recording technology is remarkable. One of the devices that can realize the highest recording density as an information recording device is an HDD. In the HDD, a recording density of about 40 gigabits per square inch has been achieved, and a recording density particularly high among information recording devices can be realized. If a recording density of 40 gigabits per square inch can be realized, for example, it is possible to store about 20 gigabytes of information on a 2.5 inch type (65 mm diameter) magnetic disk.
One of the reasons why such a high recording density can be realized in the HDD is that the mounted parts are manufactured with extremely high machining accuracy. The surface of the magnetic disk is precisely smoothed with a surface accuracy of about 10 nm, and this high degree of smoothness enables the magnetic head to safely record and reproduce even when flying with a low flying height of about 20 nm. Yes.

A glass substrate for a magnetic disk is known as a substrate capable of realizing such high smoothness. The glass substrate has an advantage that the surface can be finished with high smoothness by mirror polishing and has high rigidity so that it can withstand high-speed disk rotation.
In manufacturing a glass substrate for a magnetic disk, first, a glass disk is molded from molten glass by direct pressing. Next, lapping for improving dimensional accuracy and shape accuracy is performed on the molded glass disk. In this lapping process, a glass disk main surface is ground using a hard abrasive such as diamond, usually using a double-side lapping apparatus. By lapping the main surface of the glass disk in this way, a predetermined plate thickness and flatness are processed, and a predetermined surface roughness is obtained.
After the lapping process, mirror polishing is performed to obtain a highly accurate plane.
As a conventional technique, Patent Document 1 below discloses a manufacturing method capable of manufacturing a glass substrate having high flatness and smoothness with a high yield. Patent Document 2 below discloses a method for processing a glass substrate that improves the substrate surface characteristics and is suitable for an information recording medium. Further, Patent Document 3 below discloses a recycling system for a supply liquid for a glass grinding machine that can improve the operating rate of the glass grinding machine.

JP 2001-191247 A JP 2000-339672 A Japanese Patent Laid-Open No. 11-169849

In the lapping process described above, in a double-sided lapping machine, a glass disk held by a carrier is closely attached between upper and lower surface plates to which pellets to which hard abrasive grains such as diamond abrasive grains are fixed are attached, and the glass disk is further moved up and down. In general, both surfaces of the glass disk are ground simultaneously by relatively moving the glass disk and the upper and lower surface plates while pressing with a predetermined pressure by the surface plate. At this time, the grinding liquid is supplied to cool the working surface or to promote the processing. This grinding liquid is supplied again to the lapping apparatus after use and is recycled.
However, in the lapping process, a large amount of grinding debris (hereinafter referred to as “sludge”) is generated, and when the sludge is circulated and used in the grinding fluid, the abrasive grains on the surface of the surface plate act on the main surface of the glass disk. This hinders grinding and significantly reduces grinding efficiency. Therefore, conventionally, the sludge in the grinding fluid is removed as much as possible by using a filtering means. Specifically, in Patent Document 3, for example, the liquid discharged from the grinding machine is stored in a storage tank, and the liquid discharged in the storage tank is sucked up and filtered by a pump through a microporous hollow fiber membrane of 0.5 μm or less. A recycling system for supplying the grinding fluid to the grinding machine is described. According to this method, relatively large-diameter sludge settles in the storage tank, and small-diameter sludge is filtered by the hollow fiber membrane when sucked up by a pump. The liquid is again supplied to the grinding machine and recycled.

  As described above, conventionally, it has been said that it is better to remove sludge mixed in the grinding liquid as much as possible with the grinding process and keep the grinding liquid clean, but according to the study of the present inventors, it is included in the grinding liquid. When almost all of the sludge has been removed, the reduction in the grinding speed can be prevented, but the abrasive grains on the surface of the surface plate may be deeply cut into the main surface of the glass disk, leading to deterioration of the surface roughness. It has been found. In this case, even if a finishing process such as mirror polishing is performed after the grinding process, the grinding marks cannot be completely removed and remain as a concave defect on the glass disk main surface. Therefore, when a magnetic disk is used, thermal asperity (TA), Prone to errors such as missing and short time modulation. In particular, as the information recording density increases and the recording bits become smaller, it cannot be used as a glass substrate for a magnetic disk that requires high-precision smoothness.

  In the present invention, grinding marks generated in the grinding process of the main surface of the glass disk cannot be completely removed in the subsequent polishing process and remain as concave defects, or if the concave defects are to be removed more precisely. For example, it has been made in view of the conventional problem of requiring a longer polishing time and consequently reducing the manufacturing cost. Accordingly, it is an object of the present invention to provide a method for manufacturing a glass substrate for a magnetic disk that improves surface quality, and secondly, reduces manufacturing time by reducing processing time and improving product yield. The third object is to provide a method for producing a glass substrate for a magnetic disk that enables the above-mentioned, and third, to provide a method for producing a magnetic disk suitable for increasing the information recording density.

  The present inventor conducted research to solve the above problems, and in the grinding process of the main surface of the glass disk, it is preferable that particles in a predetermined range are positively mixed in the grinding liquid. I found out that it was effective. Then, it was found that there is a correlation between the particle size of the particles mixed in the grinding liquid, the grinding efficiency, and the surface roughness of the glass disk main surface. In other words, if particles larger than the specified range (for example, sludge) are mixed in the grinding fluid, the particles obstruct cutting of abrasive grains on the surface of the surface plate into the main surface of the glass disk, greatly reducing the grinding speed. Therefore, in order to obtain a predetermined surface roughness, the grinding time becomes long. On the other hand, if the size of the particles mixed in the grinding liquid is smaller than a predetermined range, the particles do not function as a buffer material between the abrasive grains and the glass disk, and the abrasive grains are made of glass. Since the main surface of the disk is deeply cut to cause defects such as cracks, the surface roughness of the main surface of the glass disk is deteriorated, and even if polishing is performed thereafter, the defects remain and the product yield decreases. If it is attempted to remove this defect by polishing, the polishing process takes a long time and presses the manufacturing cost. That is, according to the present inventors' earnest research, grinding is not performed while removing particles contained in the grinding fluid, for example, sludge generated during grinding, and cleaning the grinding fluid as much as possible. High yield can be maintained without lowering the grinding efficiency by actively interposing such particles in the fluid and managing the particle size of the particles mixed in the grinding fluid within a specified range. There was found.

Accordingly, the present invention has the following configuration.
(Configuration 1) Magnetic having a step of grinding a glass disk main surface by pressing a grinding platen fixed with a grindstone against a glass disc and relatively moving the platen and the glass disc while supplying a grinding liquid. A method for producing a glass substrate for a disk, characterized in that grinding is performed while supplying a grinding liquid containing particles having a particle size smaller than the arithmetic average surface roughness of the glass disk main surface before grinding. Method for manufacturing glass substrate.
(Configuration 2) Magnetic having a step of grinding a glass disk main surface by pressing a grinding platen fixed with a grindstone against a glass disc and relatively moving the platen and the glass disc while supplying a grinding liquid. A method for producing a glass substrate for a disk, wherein the grinding is performed while supplying a grinding liquid containing particles having a particle size smaller than the arithmetic average surface roughness of the grindstone. .
(Configuration 3) The configuration 1 is characterized in that the average particle size of the particles contained in the grinding liquid is adjusted to be larger than a desired value of the arithmetic average surface roughness of the main surface of the glass disk obtained by grinding. Or the manufacturing method of the glass substrate for magnetic discs of 2.
(Configuration 4) The average particle size of the particles contained in the grinding liquid is smaller than the arithmetic average surface roughness of the main surface of the glass disk before grinding, and a desired value of the arithmetic average surface roughness of the main surface of the glass disk obtained by grinding. The method for producing a glass substrate for a magnetic disk according to Configuration 1 or 2, wherein the glass substrate is adjusted so as to be larger.
(Structure 5) The method for producing a glass substrate for a magnetic disk according to any one of Structures 1 to 4, wherein the particles contained in the grinding liquid are glass particles.
(Structure 6) The method for producing a glass substrate for a magnetic disk according to any one of structures 1 to 5, wherein the grinding liquid is alkaline.
(Structure 7) The method for producing a glass substrate for a magnetic disk according to any one of structures 1 to 6, wherein the glass disk is a glass disk containing amorphous glass.
(Structure 8) The method for manufacturing a glass substrate for a magnetic disk according to any one of structures 1 to 7, wherein the grindstone includes diamond abrasive grains.
(Structure 9) The main surface of a glass disk whose end face is polished to a mirror surface is ground by the grinding step, and then the main surface is polished to a mirror surface. Manufacturing method of glass substrate for magnetic disk.
(Configuration 10) A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on a glass substrate for a magnetic disk obtained by the manufacturing method according to any one of configurations 1 to 9.

  In the present invention, the parameter used as the surface roughness is an arithmetic average surface roughness (also referred to as centerline average height) Ra calculated in accordance with Japanese Industrial Standard (JIS) B0601. As the surface roughness in the present invention, for example, the surface area roughness measured with an atomic force microscope (AFM) can be used. Hereinafter, in this specification, surface roughness shall mean arithmetic mean surface roughness (Ra).

The method for manufacturing a glass substrate for a magnetic disk according to the present invention includes a step of grinding the main surface of the glass disk as in Configuration 1, and in this grinding step, the surface roughness before grinding of the main surface of the glass disk is increased. Grinding is performed while supplying a grinding liquid containing small-diameter particles.
In general, a lapping process for improving dimensional accuracy and shape accuracy is performed on a glass disk molded to a predetermined size from molten glass. In this lapping process, the glass disk main surface is first ground to a predetermined surface roughness. The grinding process of the main surface of the glass disk is performed by, for example, using a double-sided simultaneous processing machine (grinding machine), pressing the upper and lower surface plates to which the grindstone is fixed against the glass disk, and supplying the grinding liquid. The main surface of the glass disk is ground by moving the disk relatively. In this configuration, in the grinding process of the glass disk main surface, grinding is performed while supplying a grinding liquid containing particles having a particle diameter smaller than the surface roughness of the glass disk main surface before grinding.

Thus, by grinding while supplying a grinding liquid containing particles having a particle size smaller than the surface roughness before grinding of the glass disk main surface, the particles are transferred to the glass disk main surface of the grindstone on the surface of the surface plate. Therefore, the cutting efficiency can be prevented from being lowered. Therefore, it is possible to prevent an increase in processing time for obtaining a predetermined surface roughness by grinding.
In addition, as long as it is in the range which does not impair the effect of this invention, the particle | grains larger than the surface roughness before grinding of the glass disk main surface may be contained in the grinding liquid.

Moreover, the manufacturing method of the glass substrate for magnetic disks of this invention performs grinding, supplying the grinding fluid containing the particle | grains of a particle size smaller than the surface roughness of a grindstone in the said grinding process as it exists in the structure 2. It is characterized by that.
As described above, in the grinding process of the main surface of the glass disk, it is also possible to perform grinding while supplying a grinding liquid containing particles having a particle size smaller than the surface roughness of the grindstone on the surface of the surface plate. Since the cutting of the grindstone on the surface is not hindered, it is possible to prevent a reduction in grinding efficiency, and it is also possible to prevent an increase in processing time for obtaining a predetermined surface roughness by grinding. In the configuration 2, as long as the effects of the present invention are not impaired, particles having a particle size larger than the surface roughness of the grindstone may be contained in the grinding fluid.

Further, in the method for producing a glass substrate for a magnetic disk of the present invention, the lower limit value of the particle size of the particles contained in the grinding fluid is obtained by grinding so that the average particle size of the particles is as in Configuration 3. It is preferable to adjust so that it may become larger than the desired value of the surface roughness of the glass disk main surface.
Thus, in the grinding process of the glass disk main surface, the average particle diameter of the particles contained in the grinding liquid is adjusted to be larger than the desired value of the surface roughness of the glass disk main surface obtained by grinding. Therefore, the particles serve as a cushioning material between the grinding wheel on the surface of the platen and the glass disk during grinding, so that the grinding stone is not deeply cut into the main surface of the glass disk to prevent defects such as cracks. it can. Therefore, it is possible to prevent an increase in the processing time for precisely removing defects generated in the grinding process in the subsequent polishing process, and it is possible to secure a high product yield and to reduce the manufacturing cost.
In addition, the value of the average particle diameter of the particles contained in the grinding fluid increases greatly when, for example, coarse particles are mixed, and does not represent a typical particle size in the particle size distribution of the particles contained in the grinding fluid. In some cases, instead of the value of the average particle size, for example, the value of the particle size corresponding to the peak (mode) of the particle size distribution may be used for adjustment.

Further, in the method for producing a glass substrate for a magnetic disk of the present invention, as in Configuration 4, the average particle size of the particles contained in the grinding liquid is greater than the arithmetic average surface roughness of the glass disk main surface before grinding. It is also a preferable aspect that the adjustment is made so that it is larger than the desired value of the arithmetic average surface roughness of the main surface of the glass disk obtained by grinding. As a result, the particles contained in the grinding fluid do not interfere with the cutting of the grindstone into the main surface of the glass disk, so that the reduction in grinding efficiency can be prevented, and the particles act as a cushioning material between the grindstone and the glass disk. Therefore, it is possible to prevent the grindstone from being deeply cut into the main surface of the glass disk and causing defects such as cracks.
The particles contained in the grinding fluid are preferably glass particles as in the constitution 5. This is because grinding waste, which is glass particles, is always generated with the grinding of the glass disk, so that it is not necessary to supply other particles to the grinding fluid, and the management of the grinding fluid in the present invention is easy. Moreover, it is preferable also from a viewpoint of improving the effect | action of this invention because the particle | grains contained in a grinding fluid and a to-be-processed object (glass disk) are the same materials.
Moreover, as the said grinding fluid is in the structure 6, it is suitable that it is alkaline. It is because the grinding speed can be improved by the etching action of glass because the grinding liquid is prepared to be alkaline. In order to adjust the grinding liquid to be alkaline, it is preferable to add an alkaline agent such as sodium hydroxide or potassium hydroxide to the grinding liquid to adjust the pH to about 8 to 12.

The glass disk used in the present invention is preferably a glass disk containing amorphous glass as in the structure 7. If the glass disk contains amorphous glass, since the distribution of crystal grains on the surface is small, it is easy to perform processing with high grinding efficiency, and distortion due to grinding processing does not easily remain, so the effect of the present invention is preferably obtained. It is. In the present invention, a glass disk made of amorphous glass is more preferable.
Further, as the glass composition of the glass disk in the present invention, aluminosilicate glass, soda lime glass, quartz glass, cristobalite or glass containing lithium disilicate can be used. Among them, when aluminosilicate glass is used, workability, rigidity From the viewpoint of, it is excellent in practicality.
As such an aluminosilicate glass, for example, an aluminosilicate glass containing at least an alkali metal oxide and an alkaline earth metal oxide is preferably used. Examples of such glass, such as SiO ₂ from 58 to 75 wt%, the Al ₂ O ₃ 5 to 23 wt%, the Li ₂ O 3 to 10 wt%, a Na ₂ O 4 to 13 wt%, the main component An aluminosilicate glass contained as can be preferably mentioned.

Here, the double-sided processing machine used for the grinding process of the said glass disk main surface is demonstrated. FIG. 1 is a partial cross-sectional view showing an example of a double-sided processing machine (planetary gear motion system), and FIG. 2 is a cross-sectional view taken along line II-II in FIG.
A glass disk 2 held by a carrier 5 is arranged between an upper surface plate 3 and a lower surface plate 4 to which pellet holding plates 3a and 4a holding a large number of grinding pellets 1 are attached. The upper surface plate 3 and the lower surface plate 4 rotate in opposite directions. A sun gear 6 and an internal gear 7 are provided between the upper surface plate 3 and the lower surface plate 4, and the carrier 5 Is placed between them. A gear meshing with the sun gear 6 and the internal gear 7 is formed on the outer periphery of the carrier 5. As a result, the sun gear 6 and the internal gear 7 rotate with the rotation of the upper and lower surface plates 3 and 4, and the carrier 5 rotates and revolves (planetary gear motion).
The grinding pellet 1 as a grindstone is obtained by solidifying abrasive grains with a resin or the like. The shape of each pellet 1 depends on the material and grain size of the abrasive grain, the type of material of the glass disk that is the workpiece, and the like. In addition, a circle, a rectangle, or the like is selected as appropriate. Further, the size is appropriately selected. A typical example of such a pellet to which abrasive grains are fixed is a diamond pellet. In the present invention, this diamond pellet can be preferably used (Configuration 8). Diamond pellets are diamond abrasive grains of a predetermined particle size fixed using a support material such as resin (for example, acrylic resin). Mechanical properties can be changed by changing the mixing ratio of diamond abrasive grains and support material. Different diamond pellets can be made. The surface roughness of the grindstone in the above-described configuration 2 is a surface acting in contact with the glass disk, that is, the surface roughness of the diamond pellet when using such diamond pellets to which diamond abrasive grains are fixed.

  As in the above-described configurations 1 to 4, as a specific method for managing the particle size or average particle size of the particles contained in the grinding liquid within a predetermined range, a grinding machine (for example, the above-described double-sided processing machine) is used. A preferred example is a method in which a particle removing means such as a centrifugal separator or a filtering means such as a filter is installed in the middle of a circulation path for supplying the used grinding liquid discharged again to the grinding machine. Among these, the centrifuge can mainly control the average particle size of particles contained in the grinding fluid. When a centrifuge is used, the cut point can be adjusted by the number of rotations thereof, the grinding fluid supply flow rate per unit time, and the like. For example, the cut point can be adjusted to be shifted to the larger particle size as the rotational speed is higher or the grinding fluid supply flow rate is higher. On the other hand, the filter can manage the maximum diameter of particles contained in the grinding fluid. Examples of such a filter include a hollow fiber filter, a ceramic filter, and a diatomaceous earth filter. In the case of a hollow fiber filter, the cut point of the particles can be adjusted depending on the size of the fine pore diameter.

In the present invention, particle removing means such as the above centrifugal separator and filtering means such as a filter may be used alone or in combination. When using a centrifuge and a filter together, it is better to place a centrifuge at the front stage in the middle of the circulation path where the used grinding fluid discharged from the grinding machine is supplied again to the grinding machine, and a filter at the rear stage. It is desirable from the viewpoint of preventing clogging of the filter. Further, a plurality of centrifuges having different cut points may be used in combination.
Here, as an example of the case where the centrifuge is used alone, for example, the main surface of the glass disk with respect to the surface roughness of the main surface of the glass disk before grinding or the surface roughness of the grindstone of the grinding surface plate. When the desired value of the surface roughness after surface grinding differs by about two orders of magnitude, the particle size or average particle size of the particles contained in the grinding liquid is managed within a predetermined range as in the above-described configurations 1 to 4. Therefore, the operating conditions of the centrifuge can be set as follows, for example.

Ra / 100 <r <Ra (1)
r = (4.5 ηv) ^1/2 · {x (ρ−ρ ₀ )} ⁻¹ / ² · ω ⁻¹ (2)
η: Viscosity of grinding fluid
v: Velocity of particles in the direction perpendicular to the rotation axis of the centrifuge (the length of the perpendicular dropped from the grinding fluid supply point of the rotating chamber to the outer wall / the value of the average residence time of the grinding fluid in the rotating chamber can be substituted)
x: Average length of the vertical line from the outer peripheral wall to the rotation axis and the vertical line from the inner peripheral wall to the rotation axis ρ: Density of particles ρ ₀ : Density of grinding fluid not containing particles ω: Centrifuge angular velocity

R in the above equation (1) is a cut point (particle size of particles to be removed) of the centrifuge, and is represented by the above equation (2). Further, Ra in the above formula (1) is the surface roughness Ra of the grindstone of the grinding machine (Ra of the surface acting on the work piece), and r is within the range of the above formula (1). Various operating conditions can be set.
The above equation (2) can be derived by applying the parameters in the centrifuge based on the following equation (3), which is well known as the Stokes equation.
D (resistance) = 6πηrv (3)
Of course, the operating conditions of the centrifuge set in this way are merely examples.

Further, in the method for producing a glass substrate for a magnetic disk of the present invention, as in the configuration 9, after grinding the main surface of the glass disk whose end face is polished into a mirror surface by the grinding step as in the processing order, It is also preferable to polish the main surface to a mirror surface.
In the conventional processing sequence, the main surface of the glass disk is ground to flatten the main surface, and then the polishing process is started. First, the end surface (outer periphery and inner periphery) of the glass disk is polished, and then the main surface is polished. The end face and the main surface were mirrored. Here, the grinding of the main surface of the glass disk is performed using fixed abrasive grains such as diamond pellets as described above, and the subsequent end face polishing and main surface polishing of the glass disk are performed by, for example, free abrasive grains such as cerium oxide and a polishing pad. It is done using.
In the case of such a conventional processing sequence, in the end face polishing after the glass disk main surface grinding, each glass is processed because a large number of glass disks are processed with their main surfaces being laminated directly or via a spacer. Concave defects such as scratches and scratches are easily formed on the main surface of the disk. Therefore, since it is necessary to precisely remove the concave defects in the main surface polishing in the next process, a lot of machining allowance is required. Since the removal rate of polishing is slower than that of grinding, a long processing time is required to remove a predetermined machining allowance. In addition, when this polishing allowance is insufficient, it remains as a concave defect, and therefore, when used as a magnetic disk, it tends to cause errors such as TA and missing.

Then, this inventor examined changing a process order like the structure 9, ie, processing a glass disk in the order of following (1)-(3).
(1) Glass disk end surface polishing (2) Glass disk main surface grinding (3) Glass disk main surface polishing The main surface formed during end surface polishing by performing main surface grinding in this way after end polishing of the glass disk. Although it is necessary to remove concave defects such as scratches and scratches at the time of main surface grinding, the removal rate of grinding is fast so that the processing can be completed in a short processing time and the main surface can be flattened. According to the study of the present inventor, the processing time can be shortened by about 20 minutes in one batch (100 sheets) processing, for example, as compared with the conventional processing order. Therefore, if 10,000 discs are processed, the time can be reduced by about 30 hours. In addition to this processing sequence, the glass disk main surface grinding is preferably fixed abrasive grinding. When the main surface grinding of the glass disk with the fixed abrasive is performed, the end surface quality is not deteriorated during the main surface grinding, and the mirror surface state by the end surface polishing in the previous step can be maintained. On the other hand, when main surface grinding is performed with loose abrasive grains, loose abrasive grains generally containing high-hardness abrasive grains (such as alumina abrasive grains) are generally required because of the need to secure a removal rate and shorten the grinding time. Use. However, such a high-abrasive abrasive grain has a problem that the loose abrasive grains that wrap around the end face during main surface grinding tend to damage the end face. In addition, since the carrier for holding the disk and the disk end face come into contact with each other during main surface grinding, there is a problem in that loose abrasive grains are interposed between the carrier and the disk end face and the end face is further damaged. In short, when the main surface is ground with loose abrasive grains, the mirror surface state by end face polishing in the previous step is deteriorated, and if scratches remain on the end face of the glass disk, a failure such as TA tends to occur when the magnetic disk is formed.

  As described above, according to the processing sequence as in the configuration 9 of the present invention, the manufacturing cost can be reduced by shortening the processing time, so that it is possible to provide a low-cost glass substrate for a magnetic disk and a magnetic disk. Further, since both the main surface quality and the end surface quality of the glass disk can be mirror-finished, it is possible to contribute to an increase in recording density of the magnetic disk.

Examples of the magnetic disk in the present invention include a magnetic disk in which a magnetic layer, a protective layer, and a lubricating layer are sequentially formed on the glass substrate for a magnetic disk obtained by the above production method. As the magnetic layer, a Co-based magnetic layer suitable for increasing the recording density is preferable. Examples of such a magnetic layer include a CoPt magnetic layer and a CoCrPt magnetic layer. A preferred method for forming the magnetic layer is DC magnetron sputtering.
Preferred examples of the protective layer include carbon-based protective layers. Among the carbon-based protective layers, the hydrogenated carbon protective layer and the nitrogenated carbon protective layer are particularly preferable because they have high adhesion to the lubricating layer. The hydrogen concentration in carbon is 10 at% to 30 at% when measured by HFS (hydrogen forward scattering method), and the nitrogen concentration in carbon is 4 at% to 12 at% when measured by XPS (X-ray photoelectron spectroscopy). It is preferable that In forming the protective layer, a DC magnetron sputtering method, a plasma CVD method, or the like can be preferably exemplified.

  As the lubricating layer, perfluoropolyether (PFPE) can be preferably used. Since PFPE has a flexible main chain structure, moderate lubricity can be realized. It is more preferable to use a PFPE derivative in which a polar group is introduced into the terminal functional group of PFPE. Examples of such derivatives include alcohol-modified PFPE. An alcohol-modified product having a polar group, particularly a hydroxyl group, is preferable because it has high adhesion to the carbon-based protective layer, and thus can suppress the transfer of the lubricant to the magnetic head. An example of the method for forming the lubricating layer is a dipping method.

  As described above, according to the present invention, it is possible to provide a method for manufacturing a glass substrate for a magnetic disk that can reduce processing time and manufacturing cost by improving product yield. Moreover, according to this invention, the manufacturing method of the glass substrate for magnetic discs which can aim at the improvement of the main surface quality and end surface quality of a glass substrate can be provided. Furthermore, according to the present invention, a magnetic disk suitable for increasing the information recording density can be provided.

Hereinafter, embodiments of the present invention will be described in detail with specific examples, but the present invention is not limited to these embodiments.
(Example 1)
Hereinafter, the manufacturing method of the glass substrate for magnetic disks of a present Example is demonstrated.
(1) Lapping process (grinding process)
An amorphous glass disk made of aluminosilicate glass having a diameter of 66 mmφ was obtained from the molten glass by direct pressing. Aluminosilicate glass is _SiO 2: 63.6 _{weight%, Al} 2 O 3: 14.2 _wt%, Na 2 O: 10.4 _wt%, Li 2 O: 5.4 _wt%, ZrO 2: 6.0 An aluminosilicate glass having a composition of wt%, Sb ₂ O ₃ : 0.4 wt% was used.

Next, a lapping process was performed on the glass disk in order to improve dimensional accuracy and shape accuracy. This lapping process was performed using the double-sided processing machine shown in FIGS. Specifically, first, alumina loose abrasive grains having a particle size of # 400 were used, and the sun gear and the internal gear were rotated to wrap both surfaces of the glass disk housed in the carrier. Next, a hole was made in the center portion of the glass disk using a cylindrical grindstone, and the outer peripheral end face was ground to a diameter of 65 mmφ, and then a predetermined chamfering process was performed on the outer peripheral end face and the inner peripheral end face. The surface roughness of the main surface of the glass disk was 1.1 μm in Ra.
Next, the grinding wheel was changed to diamond pellets in which # 280 diamond aggregated abrasive grains were hardened with an acrylic resin, and the main surface of the glass disk was ground. In addition, when the surface roughness of the said diamond pellet was measured, it was 1.0 micrometer in Ra. The processing pressure at this time was 100 g / cm ² , the rotation speed of the upper and lower surface plates was 20 rotations / second, and the removal thickness by grinding was 200 μm.

In addition, this grinding process is performed while supplying the grinding fluid, and a circulation path is provided in which the used grinding fluid is discharged from the double-sided processing machine and supplied again. A bobbin filter with a 90% removal diameter of 3 μm was installed. Furthermore, a 400-liter storage tank was installed between the path from the processing machine to the centrifuge and between the path from the centrifuge to the filter. As the grinding liquid, a water-soluble grinding liquid diluted with pure water was supplied to the processing machine. The centrifuge has a rotating chamber capacity of 10 liters, an outer diameter of 32 cm, an average length of 13 cm perpendicular to the rotating shaft from the outer peripheral wall to the rotating shaft, and a vertical line extending from the inner peripheral wall to the rotating shaft. The one with a length of 6 cm perpendicular to the outer peripheral wall from the point was used. The centrifuge was operated under the following conditions.
Number of revolutions: 1700 revolutions / second, that is, ω = 178 seconds− ¹
Grinding fluid supply speed: 10 liters / min. That is, the average residence time of the grinding fluid in the rotating chamber = 60 seconds. The viscosity of the grinding fluid measured with a rotary viscometer is 1.1 × 10 ⁻² poise, the density of the grinding fluid. Was 1.0 g / cm ² , and the density of the sludge of the glass particles mixed in the grinding liquid during grinding was 2.5 g / cm ² .

When the above parameters are substituted into the above-described equation (2), the cut point of the centrifuge is r = 0.90 μm.
Using such operating conditions, the particle size distribution of the sludge contained in the grinding fluid supplied to the double-sided processing machine through the centrifuge and the filter is the maximum particle size Dmax = 0.9 μm, the average particle size Da = 0. It adjusted so that it might be set to 48 micrometers. The peak size of the particle size distribution was adjusted to 0.28 μm.
As described above, even when the glass disk was processed in 7 batches (700 sheets), the processing rate did not decrease and was stable at about 5 μm / min. When the surface roughness of the main surface of the glass disk thus obtained by grinding was measured with an AFM (atomic force microscope), Ra was a smooth surface of 0.09 μm, and the desired value of the surface roughness by grinding ( It was confirmed that Ra was about 0.1 μm). The surface roughness is calculated from the surface area measurement result by AFM (atomic force microscope) according to Japanese Industrial Standard (JIS) B0601.

(2) Mirror Polishing Step Next, the surface roughness of the end surface (inner circumference, outer circumference) of the glass disk was polished to about 0.04 μm by Ra while rotating the glass disk by brush polishing.
Thereafter, the first mirror polishing process on the main surface of the glass disk was performed using a double-side polishing machine similar to the planetary gear motion type double-side machine using the lapping process. In a double-side polishing machine, a glass disk held by a carrier is closely attached between an upper and lower surface plate on which a polishing pad is affixed as a polisher, and the carrier is meshed with a sun gear and an internal gear so that the glass substrate is vertically fixed. It is clamped by the board. After that, by supplying a polishing liquid between the polishing pad and the polishing surface of the glass disk and rotating it, the glass disk revolves (planetary gear motion) while rotating on the surface plate, and both surfaces are mirror-polished simultaneously. Is.
Specifically, a polishing process was performed using a hard urethane foam polishing pad as the polisher. As the polishing liquid, free abrasive grains containing cerium oxide abrasive grains and pure water were used.
In the above-described end surface polishing step, a concave defect such as scratches or scratches due to laminating processing was formed on the main surface of the glass disk. Therefore, a lot of machining allowance was required to remove the concave defect, and the polishing time was lengthened. It cost.

Next, using the double-side polishing machine of the same type as that used in the first mirror polishing process, the polisher was changed to a soft polishing pad (suede pad), and the second mirror polishing process was performed. The purpose of the second mirror polishing step is to reduce the surface roughness to, for example, Rmax 5 nm or less and Ra 0.5 nm or less while maintaining the flat surface obtained in the first mirror polishing step described above. To do. By this mirror polishing process, the main surface of the glass disk is finished in a mirror state.
As the polishing liquid, cerium oxide-based abrasive grains and free abrasive grains containing pure water were used.
The glass disk after mirror polishing was cleaned with a cleaning solution containing sulfuric acid to remove residues such as abrasive grains and clean.
When the glass disk thus polished was visually inspected under a condensing lamp, only 300 of the inspected glass disks were found to be defective, with a high yield of 99.3%. there were.
Moreover, when the surface roughness of the obtained glass disk was measured with AFM (atomic force microscope), it was confirmed that Rmax was 4.0 nm and Ra was a smooth mirror surface with 0.4 nm.

(3) Chemical strengthening process Next, the chemical strengthening process by a low temperature type ion exchange method was performed on condition of the following.
For chemical strengthening, a chemically strengthened molten salt in which potassium nitrate (60%) and sodium nitrate (40%) were mixed was prepared, and a glass disk was immersed in the chemically strengthened molten salt for chemical strengthening treatment. A high compressive stress is formed on the surface of the glass disk by this chemical strengthening step, so that a glass substrate having excellent impact resistance can be obtained.
The glass disk after chemical strengthening was washed and dried.
Next, a visual inspection of the glass disk surface after the cleaning and a precise inspection using light reflection / scattering / transmission were performed. As a result, no defects such as protrusions or flaws due to deposits were found on the glass disk surface.
As described above, the glass substrate for magnetic disk of this example was obtained.

(Example 2)
Next, the magnetic disk of this example was manufactured as follows.
The magnetic disk in this example is a magnetic disk in which an underlayer, a magnetic layer, a protective layer, and a lubricating layer are sequentially formed on the magnetic disk glass substrate obtained in Example 1.
An underlayer and a magnetic layer were sequentially formed on the glass substrate in an argon atmosphere using a DC magnetron sputtering method.
The underlayer has a function of orienting the magnetic particles of the magnetic layer in the plane of the disk. CrW alloy metal was used.
Next, a magnetic layer was formed. A ferromagnetic magnetic layer of CoCrPtB alloy was used as the material of the magnetic layer.
A protective layer was formed by the plasma CVD method on the magnetic disk thus formed up to the magnetic layer. Specifically, a hydrogenated carbon protective layer was formed using acetylene gas. The film thickness is 5 nm. When the hydrogen content was measured by HFS (hydrogen forward scattering method), it was found to be 20 at%.
A lubricating layer was formed on the protective layer by a dip method. Specifically, a lubricant composed of a perfluoropolyether compound having hydroxyl groups at both ends of the main chain was applied. The film thickness is 1 nm. After forming this lubricating layer, heat treatment was performed at 100 ° C., and the lubricating layer was adhered onto the protective layer.

The magnetic disk of this example was obtained as described above.
When the obtained magnetic disk was evaluated for glide characteristics, the touchdown height was 4.5 nm. The touchdown height decreases the flying height of the flying head in order (for example, lowering the rotational speed of the magnetic disk), finds the flying height that starts to contact the magnetic disk, and determines the flying height of the magnetic disk. In order to measure the capability, normally, an HDD that requires a recording density of 40 Gbit / inch ² or more is required to have a touchdown height of 5 nm or less.
In addition, when the head flying height was set to 12 nm and the head was loaded and unloaded repeatedly in an environment of 70 ° C and 80% RH, LUL durability was tested. After 600,000 consecutive LUL tests No head crash failure occurred. Normally used HDDs require about 10 years of use in order to exceed 600,000 LUL times. Further, when a thermal asperity (TA) test was conducted using a flying height 12 nm GMR head, no thermal asperity failure occurred.

(Example 3)
In the manufacturing process of the glass substrate for magnetic disk of Example 1, the processing order of Example 1 is changed, the end surface of the molded glass disk is ground, and then the end surface mirror polishing is performed. The surface was ground and the main surface was further mirror polished. That is, the first embodiment differs from the first embodiment in that the main surface of the glass disk is ground after the end surface of the glass disk is polished to a mirror surface. Other than that, for example, the processing conditions of each step were the same as in Example 1.
In this example, since the main surface grinding was performed after the end surface mirror polishing of the glass disk, scratches on the main surface formed during the end surface mirror polishing, and concave defects such as scratches were shortened by grinding processing with a fast removal rate. Since the main surface mirror polishing process time thereafter did not have to be particularly long, it was possible to reduce the time by about 20 minutes with one batch (100 sheets) compared to Example 1.
On the magnetic disk glass substrate obtained in this example, a magnetic layer and the like were formed in the same manner as in Example 2 to produce a magnetic disk. When the obtained magnetic disk was evaluated in the same manner as in Example 2, no head crash failure or thermal asperity failure occurred, and a good evaluation was obtained.

(Comparative example)
In this comparative example, in the (1) lapping process of the first embodiment, as in the first embodiment, the grinding is performed while supplying the grinding fluid, and the used grinding fluid is discharged from the double-sided processing machine and supplied again. A centrifuge was installed at the front stage in the middle of the path, and a bobbin filter with a 90% removal diameter of 3 μm was installed at the rear stage. The centrifuge was operated under the following conditions.
Rotational speed: 7000 revolutions / second Grinding fluid supply speed: 0.3 liter / minute The grinding fluid supplied to the double-sided processing machine through the centrifugal separator and the filter under such operating conditions contained no sludge. That is, sludge generated by grinding is removed through a centrifugal separator and a filter, and a grinding liquid not containing sludge is supplied to the double-sided processing machine.
When 7 batches (700 sheets) of glass disks were processed as described above, the initial processing rate was about 5 μm / min, but gradually decreased to about 4 μm / min. The surface roughness of the main surface of the glass disk thus obtained by grinding was measured with an AFM (Atomic Force Microscope). As a result, Rmax was 2.5 μm, Ra was 0.18 μm, and Rmax was particularly large. . Grinding marks were formed by the abrasive grains being deeply cut into the glass disk, and the surface roughness deteriorated.
In addition, when grinding was performed in the same manner while supplying only a new grinding fluid without circulating the grinding fluid, grinding marks were confirmed on the glass disk as in this comparative example.

After the grinding step, the polishing step and the chemical strengthening step were performed in the same manner as in Example 1 to obtain a glass substrate for magnetic disk of this comparative example. When the glass disk that had been polished was visually inspected under a condenser lamp, 61 of the 300 glass disks that were inspected were found to be defective, with a low yield of 79.7%. Met. This defect is because grinding marks could not be removed even if polishing was performed after grinding, and if this defect was to be removed precisely, the polishing process took a long time and the manufacturing cost increased. End up.
A magnetic layer or the like was formed on the glass substrate for a magnetic disk of this comparative example in the same manner as in Example 2 to produce a magnetic disk. The obtained magnetic disk was evaluated in the same manner as in Example 2. As a result, a head crash failure and a thermal asperity failure occurred and the HDD failed.

It is a fragmentary sectional view which shows an example of the double-sided processing machine used for grinding. It is the II-II sectional view taken on the line of FIG.

Explanation of symbols

1 Pellet for grinding 2 Glass disk 3 Upper surface plate 4 Lower surface plate 3a, 4a Pellet holding plate 5 Carrier 6 Sun gear 7 Internal gear

Claims (7)

A glass substrate for a magnetic disk having a step of grinding a main surface of a glass disk by pressing a grinding surface plate with a grindstone pressed against the glass disk and moving the surface plate and the glass disk relatively while supplying a grinding liquid. A manufacturing method of
Particles having a particle size smaller than the arithmetic average surface roughness before grinding of the glass disk main surface by adjusting the particle size distribution of grinding scraps contained in the grinding fluid and contained in the grinding fluid The average particle size of the magnetic disk glass substrate is characterized in that grinding is performed while supplying a grinding liquid adjusted to be larger than the arithmetic average surface roughness value of the main surface of the glass disk obtained by grinding. Production method. A glass substrate for a magnetic disk having a step of grinding a main surface of a glass disk by pressing a grinding surface plate with a grindstone pressed against the glass disk and moving the surface plate and the glass disk relatively while supplying a grinding liquid. A manufacturing method of
Adjusting the particle size distribution of the grinding scraps contained in the grinding fluid, containing particles having a particle size smaller than the arithmetic average surface roughness of the grindstone , and the average particle size of the particles contained in the grinding fluid, A method for producing a glass substrate for a magnetic disk, comprising performing grinding while supplying a grinding liquid adjusted to be larger than an arithmetic average surface roughness value of a main surface of a glass disk obtained by grinding . The average particle size of the particles contained in the grinding liquid is smaller than the arithmetic average surface roughness of the glass disk main surface before grinding, and larger than the arithmetic average surface roughness value of the glass disk main surface obtained by grinding. The method for producing a glass substrate for a magnetic disk according to claim 1 or 2, wherein Method of manufacturing a glass substrate according to any one of claims 1 to 3, wherein the particles contained in the grinding fluid is glass particles. Method of manufacturing a glass substrate according to any one of claims 1 to 4 in the grinding wheel, characterized in that contains diamond abrasive grains. After grinding in the step of performing a main surface of a glass disk which end face is polished to a mirror surface of the grinding, for a magnetic disk according to any one of claims 1 to 5, characterized in that polishing the main surface mirror A method for producing a glass substrate. In claim 1 to a glass substrate for a magnetic disk obtained by the production method according to any one of 6, a manufacturing method of a magnetic disk, which comprises forming at least a magnetic layer.

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