JP2013016216A - Manufacturing method of glass substrate for hdd, glass substrate for hdd, and magnetic recording medium for hdd - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of glass substrate for an HDD having an improved antishock property, a glass substrate for an HDD, and a magnetic recording medium for an HDD.SOLUTION: A manufacturing method of a glass substrate for an HDD includes a molding step for molding a molten glass material into a plate-like blank and a lapping step for grinding the surface of the blank. When t represents the thickness of a final glass substrate, grinding of t×0.15 or more is performed in the lapping step. Because foreign matters and bubbles mixed near the surface of the blank during the molding step or defects such as flaws are removed during the lapping step, a possibility of the defects remaining in the final glass substrate is reduced, it is difficult for the glass substrate to be broken, and the antishock property of the glass substrate improves.

Description

  The present invention relates to a method for manufacturing a glass substrate for HDD, a glass substrate for HDD, and a magnetic recording medium for HDD.

  In general, a magnetic recording medium for HDD (Hard Disk Drive) is known as a representative information recording medium having a recording layer utilizing properties such as magnetism, light, and magnetomagnetism. Conventionally, an aluminum substrate has been widely used as an HDD substrate for manufacturing an HDD magnetic recording medium. However, in recent years, with the demand for reduction of the flying height of the magnetic head for improving the recording density, the surface smoothness is superior to that of the aluminum substrate and the surface defects are few, so that the flying height of the magnetic head can be reduced. The proportion of using glass substrates as HDD substrates is increasing.

  Magnetic recording media for HDDs mounted on mobile devices such as notebook personal computers require a substrate that is resistant to impacts. For example, as disclosed in Patent Document 1, it is subjected to chemical strengthening treatment to provide impact resistance. A glass substrate with improved resistance is often used.

  However, with the recent diversification of mobile applications, a glass substrate with further excellent impact resistance is required. For example, a glass substrate that can withstand a drop impact test exceeding 1000 G is required, but conventional glass substrates often cannot withstand this test and are often cracked.

JP 2001-167427 A

  The objective of this invention is providing the manufacturing method of the glass substrate for HDDs with which the impact resistance was further improved, the glass substrate for HDDs, and the magnetic recording medium for HDDs.

  The inventor paid attention to a molding process performed at an initial stage of the glass substrate manufacturing process. In this molding process, the molten glass material is molded into plate-shaped blanks (a work in the manufacturing process until it becomes a final glass substrate. Also simply referred to as blanks). In the vicinity of the surface of the blank, there are defects such as foreign matter, bubbles or scratches mixed in the molding process. The present inventor has found that if these defects remain in the final glass substrate, it becomes one of the causes that the final glass substrate is easily broken, and the present invention has been completed.

  That is, one aspect of the present invention is a method for manufacturing a glass substrate for HDD, which includes a molding step of molding a molten glass material into plate-shaped blanks, and a lapping step of grinding the surface of the blanks. In the lapping process, when the thickness of the substrate is t, grinding of t × 0.15 or more is performed.

  According to the method for manufacturing a glass substrate for HDD having such a configuration, there is a high possibility that defects such as foreign matters, bubbles or scratches mixed near the surface of the blank in the molding process are removed in the lapping process. Therefore, the possibility that these defects remain in the final glass substrate is reduced, the glass substrate is hardly broken, and the impact resistance of the glass substrate is improved.

  In the manufacturing method of the glass substrate for HDD of this invention, it is preferable to perform grinding below tx0.25 in a lapping process.

  According to the manufacturing method of the glass substrate for HDD of such a structure, it is not necessary to mold an excessively thick blank and it is not necessary to perform an excessive amount of grinding. This is advantageous in terms of time and economy.

  In the manufacturing method of the glass substrate for HDD of this invention, it is preferable to include the chemical strengthening process of forming the stress layer whose thickness is less than 30 micrometers on the surface of a glass substrate after a lapping process.

  According to the method for manufacturing a glass substrate for HDD having such a configuration, the surface of the glass substrate is strengthened by the stress layer, and the impact resistance of the glass substrate is further improved. Note that when the thickness of the stress layer is 30 μm or more, the flatness and surface roughness of the surface of the glass substrate decrease, which is not preferable.

  Another aspect of the present invention is a glass substrate for HDD manufactured by the method for manufacturing a glass substrate for HDD.

  According to the glass substrate for HDD of such a configuration, since defects such as foreign matters, bubbles or scratches mixed in the vicinity of the blank surface in the molding process are removed in the lapping process, it becomes difficult to break, and impact resistance is improved. It has been improved.

  Yet another aspect of the present invention is an HDD magnetic recording medium manufactured by providing a recording layer on a main surface of the HDD glass substrate.

  According to the magnetic recording medium for HDD of such a configuration, since the glass substrate for HDD which is hard to break and has improved impact resistance is used, the magnetic recording medium for HDD is also hard to break and has impact resistance. It will be improved.

  According to the present invention, an HDD glass substrate manufacturing method, an HDD glass substrate, and an HDD magnetic recording medium, which are superior in impact resistance to conventional products, are provided. The obtained glass substrate for HDD and magnetic recording medium for HDD can be obtained, and can sufficiently cope with diversification of mobile devices such as notebook personal computers.

It is a manufacturing-process figure of the glass substrate for HDD which concerns on embodiment of this invention. It is a partial side view which shows the structure of the principal part of the double-sided grinding machine used by a 1st and 2nd lapping process. FIG. 3 is an arrow view taken along line III-III in FIG. 2 and is a plan view of a lower surface plate and a carrier. It is a perspective view of the glass substrate for HDD which concerns on embodiment of this invention. It is the schematic of the apparatus for performing a drop impact test.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to this embodiment.

<Method for producing glass substrate for HDD>
With reference to the process drawing shown in FIG. 1, the manufacturing method of the glass substrate for HDD is demonstrated.

[Glass melting process]
First, a glass material is melted as a glass melting step. As a material of the glass substrate, for example, soda lime glass mainly composed of SiO ₂ , Na ₂ O, CaO; mainly composed of SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li) Aluminosilicate glass; borosilicate glass; Li ₂ O—SiO ₂ glass; Li ₂ O—Al ₂ O ₃ —SiO ₂ glass; R′O—Al ₂ O ₃ —SiO ₂ glass (R ′ = Mg) , Ca, Sr, Ba) and the like can be used. Among these, aluminosilicate glass and borosilicate glass are particularly preferable because they are excellent in impact resistance and vibration resistance.

[Molding process]
Next, as a molding step, a molten glass material is poured into a lower mold and press-molded with an upper mold to obtain a disk-shaped glass substrate (blanks). In addition, blanks are not restricted to press molding, For example, you may cut and produce the sheet glass formed by the down draw method, the float method, etc. with the grinding stone. In this molding process, foreign matter and bubbles are mixed in the vicinity of the surface of the blank, or scratches are generated, resulting in defects.

  There is no limitation on the size of the glass substrate, that is, the blanks. For example, there are glass substrates of various sizes such as an outer diameter of 2.5 inches, 1.8 inches, 1 inch, and 0.8 inches. There is no limitation on the thickness of the glass substrate. For example, there are glass substrates having various thicknesses such as 2 mm, 1 mm, 0.8 mm, and 0.63 mm.

  In the present embodiment, the blanks are formed slightly thicker than the conventional one in consideration of the grinding amount in the lapping step and the polishing amount in the polishing step, which will be described later. That is, in this embodiment, the thickness of the blank is set to, for example, 1.03 mm. On the other hand, conventionally, the thickness of blanks was set to, for example, 0.93 mm.

[Heat treatment process]
Next, as a heat treatment process, glass substrates produced by press molding or cutting are alternately stacked with heat-stable member setters and passed through a high-temperature electric furnace to reduce glass substrate warpage and glass crystallization. Promote.

[First wrapping step]
Next, as the first lapping step, both surfaces of the glass substrate are ground and the parallelism, flatness and thickness of the glass substrate are preliminarily adjusted.

[Coring process]
Next, as a coring process, a circular hole is made in the center of the glass substrate after the first lapping process. The drilling is performed by, for example, grinding with a core drill or the like provided with a diamond grindstone or the like in the cutter portion.

[Inner / outer diameter machining process]
Next, as the inner / outer diameter processing step, the inner / outer diameter processing is performed by grinding the outer peripheral end surface and the inner peripheral end surface of the glass substrate with a drum-shaped grinding wheel using, for example, diamond.

[Second wrapping step]
Next, as a second lapping step, both surfaces of the glass substrate are ground again to finely adjust the parallelism, flatness and thickness of the glass substrate.

  In the first and second lapping steps, as shown in FIGS. 2 and 3, a known grinding machine 10 called a double-side grinding machine using a planetary gear mechanism can be used. The double-sided grinding machine 10 includes a disk-shaped upper surface plate 11 and a lower surface plate 12 that are arranged vertically so as to be parallel to each other, and rotate in opposite directions. Diamond pellets 13 and 14 for grinding the main surface of the glass substrate are attached to the opposing surfaces of the upper and lower surface plates 11 and 12, respectively. Between the upper and lower surface plates 11, 12, a plurality of rotating gears are coupled to a sun gear 15 provided around the rotation axis of the lower surface plate 12 and an internal gear 16 provided in an annular shape on the outer periphery of the lower surface plate 12. The carrier 17 is disposed. A plurality of holes 18 are formed in the carrier 17, and a glass substrate (not shown) is loosely fitted and held in the holes 18. The upper and lower surface plates 11, 12, the sun gear 15 and the internal gear 16 operate by separate driving.

  The grinding operation of the grinding machine 10 is performed as follows. That is, when the upper and lower surface plates 11 and 12 rotate in opposite directions, the carrier 17 sandwiched between the upper and lower surface plates 11 and 12 via the diamond pellets 13 and 14 holds a plurality of glass substrates. Thus, while rotating, it revolves in the same direction as the lower surface plate 12 with respect to the rotation center of the surface plates 11 and 12. Grinding liquid is supplied between the diamond pellet 13 of the upper surface plate 11 and the glass substrate and between the diamond pellet 14 of the lower surface plate 12 and the glass substrate to the grinding machine 10 operating in this way. Thus, the glass substrate is ground.

When this double-side grinding machine 10 is used, the weight of the surface plates 11 and 12 applied to the glass substrate and the rotational speed of the surface plates 11 and 12 are appropriately adjusted according to the desired grinding state. The weight in the first and second lapping steps is preferably 60 g / cm ² to 120 g / cm ² . The rotation speed of the surface plates 11 and 12 is preferably about 10 to 30 rpm, and the rotation speed of the upper surface plate 11 is preferably about 30 to 40% slower than the rotation speed of the lower surface plate 12. If the weight by the surface plates 11 and 12 is increased and the rotational speed of the surface plates 11 and 12 is increased, the grinding amount increases. However, if the weight is too large, the surface roughness is not good, and if the rotational speed is too high. Flatness is not good. Further, if the weights of the surface plates 11 and 12 are reduced and the rotational speed of the surface plates 11 and 12 is decreased, the amount of grinding is reduced and the production efficiency is lowered.

  At the end of the second lapping step, defects such as large undulations, chips and cracks in the glass substrate are almost removed. The surface roughness of the main surface of the glass substrate is preferably about Ra to 0.2 μm, and the flatness of the main surface is preferably 7 to 10 μm. By maintaining such a surface state, it is possible to efficiently perform polishing in the next first polishing step.

  In the first lapping step, large waviness, chips, cracks, etc. of the glass substrate are roughly removed so that the second lapping step can be performed efficiently. Therefore, it is preferable to use diamond pellets 13 and 14 having a coarseness of # 800 mesh to # 1200 mesh, which are coarser than # 1300 mesh to # 1700 mesh used in the second lapping step. As for the surface roughness of the main surface of the glass substrate when the first lapping step is completed, Ra is preferably about 0.4 μm to 0.8 μm, and the flatness of the main surface is preferably 10 to 15 μm.

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

  In addition, the surface roughness used by this embodiment is the value which measured the range of 1 micrometer x 1 micrometer using atomic force microscope (Digital Instruments company nanoscope). Further, the flatness used in the present embodiment is a value measured by a flatness measuring device, and a difference in height (P-V value) between the highest position (P) and the lowest position (V) on the surface of the glass substrate. It is.

  In the present embodiment, the total grinding amount Q in the first and second lapping steps is t × 0.15 or more, where t is the final glass substrate thickness. Here, the final glass substrate refers to the glass substrate at the time when the second polishing process or the cleaning process is completed in the process diagram of FIG.

  For example, if the final glass substrate thickness t is 0.8 mm, the grinding amount Q in the first and second lapping steps is set to 0.12 mm or more. This increases the possibility that defects such as foreign matter, bubbles or scratches mixed near the surface of the blank in the molding process are removed in the first and second lapping processes. Therefore, the possibility that these defects remain in the final glass substrate is reduced, the glass substrate is hardly broken, and the impact resistance of the glass substrate is improved.

  The final thickness t of the glass substrate is a value specified in advance from the shipping destination of the manufactured HDD glass substrate, that is, from the customer side, and is a value known in advance before manufacturing the HDD glass substrate. .

  The upper limit value of the grinding amount Q in the first and second lapping steps is not particularly limited, but t × 0.25 is preferable. For example, assuming that the final glass substrate thickness t is 0.8 mm, the grinding amount Q in the first and second lapping steps is set to 0.2 mm or less. Thereby, it is not necessary to form an excessively thick blank and it is not necessary to perform an excessive amount of grinding. This is advantageous in terms of time and economy.

  In other words, it can be expressed as (grinding amount Q in the lapping step / final glass substrate thickness t) ≧ 15%. Further, it can be expressed as (grinding amount Q in the lapping step / final glass substrate thickness t) ≦ 25%.

[End face polishing process]
Next, as the end face polishing process, the outer peripheral end face and the inner peripheral end face of the glass substrate after the second lapping process are polished using an end face polishing machine.

[First polishing step]
Next, as a first polishing step, both surfaces of the glass substrate are polished. In the first polishing step, the surface roughness of the surface of the glass substrate is improved so that the surface roughness finally required in the second polishing step performed after the next chemical strengthening step can be efficiently obtained. Polishing is performed so that the shape of the glass substrate can be obtained efficiently.

  The polishing method is used in the first and second lapping processes shown in FIGS. 2 and 3 except that a polishing pad and a polishing liquid are used instead of the diamond pellets 13 and 14 and the grinding liquid used in the lapping process. A double-side polishing machine having a configuration similar to that of the double-side grinding machine 10 is used.

  The polishing pad is preferably a hard pad having a hardness A of about 80 to 90. For example, urethane foam is preferably used. When the hardness of the polishing pad becomes soft due to the heat generated by polishing, the shape change of the polishing surface increases, so it is preferable to use a hard pad.

  The polishing liquid preferably uses cerium oxide having an average particle diameter of 0.6 μm to 2.5 μm as abrasive grains (polishing material), and the abrasive grains are dispersed in water to form a slurry. The mixing ratio of water and abrasive grains is preferably about 1: 9 to 3: 7.

The weight applied to the glass substrate by the upper and lower surface plates is preferably 90 g / cm ² to 110 g / cm ² . The weight applied by the surface plate greatly affects the shape of the outer peripheral edge of the glass substrate. As the weight is increased, the inner side of the outer peripheral edge of the glass substrate tends to fall and rise toward the outside ("warp" shape). On the other hand, as the weight is reduced, the outer peripheral edge of the glass substrate becomes closer to a flat surface and the surface sagging tends to increase (“droop” shape). In the polishing process, generally, the weight can be determined while observing such a tendency.

  In order to improve the surface roughness of the main surface of the glass substrate, the rotational speed of the upper and lower surface plates is set to 25 rpm to 50 rpm, and the rotational speed of the upper surface plate is about 30% to 40% slower than the rotational speed of the lower surface plate. It is preferable to do this.

  The polishing amount in the first polishing step is preferably 25 μm to 40 μm. If it is less than 25 μm, scratches and defects may not be sufficiently removed. If it exceeds 40 μm, the surface roughness can be in the range of Rmax from 20 nm to 60 nm and Ra from 2 nm to 4 nm, but the polishing may be performed more than necessary, which may reduce the production efficiency.

[Chemical strengthening process]
Next, as a chemical strengthening step, a chemical strengthening layer (stress layer) is formed on the main surface, outer peripheral end face, and inner peripheral end face of the glass substrate by immersing the glass substrate in a chemical strengthening treatment solution. By forming the chemical strengthening layer on the main surface of the glass substrate, warpage of the glass substrate and roughening of the main surface can be prevented. By forming the chemically strengthened layer on the outer peripheral end surface and the inner peripheral end surface of the glass substrate, the impact resistance, vibration resistance, heat resistance, and the like of the glass substrate can be improved.

  In the chemical strengthening step, by immersing the glass substrate in a heated chemical strengthening solution, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are converted into alkali metal ions such as potassium ions having a larger ion radius. This is carried out by a replacement ion exchange method. Compressive stress is generated in the ion-exchanged region due to the distortion caused by the difference in ion radius, and the main surface, outer peripheral end surface, and inner peripheral end surface of the glass substrate are strengthened by the stress layer. As a result of strengthening the surface of the glass substrate with the stress layer, the impact resistance of the glass substrate is further improved.

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

  The thickness of the stress layer is not particularly limited, but is preferably less than 30 μm. This is because if the thickness of the stress layer is 30 μm or more, it becomes difficult to finish the flatness and surface roughness of the surface of the glass substrate to a desired standard in subsequent processing.

[Second polishing step]
Next, as a second polishing step, both surfaces of the glass substrate after the chemical strengthening step are polished more precisely. In the second polishing process, a double-side polishing machine having a configuration similar to that of the double-side polishing machine used in the first polishing process is used.

  The polishing pad used in the second polishing step is preferably a soft pad having a hardness of about 65 to 80 (Asker-C), which is softer than the polishing pad used in the first polishing step, and for example, urethane foam or suede is preferably used.

  As the polishing liquid, a slurry containing cerium oxide or the like similar to that in the first polishing step as abrasive grains (polishing material) can be used. However, in order to make the surface of the glass substrate smoother, it is preferable to use a polishing liquid having a finer grain size and less variation. For example, colloidal silica having an average particle size of 40 nm to 70 nm is preferably used as a polishing liquid in which slurry is dispersed in water as abrasive grains (abrasive). The mixing ratio of water and abrasive grains is preferably about 1: 9 to 3: 7.

The weight applied to the glass substrate by the upper and lower surface plates is preferably 90 g / cm ² to 110 g / cm ² . Further, the rotational speed of the upper and lower surface plates is preferably 15 rpm to 35 rpm, and the rotational speed of the upper surface plate is preferably about 30% to 40% slower than the rotational speed of the lower surface plate.

  By appropriately adjusting the polishing conditions in the second polishing step, the flatness of the main surface of the glass substrate can be reduced to 3 μm or less, and the surface roughness Ra of the main surface of the glass substrate can be reduced to 0.1 nm.

  The polishing amount in the second polishing step is preferably 2 μm to 5 μm. By setting the polishing amount within this range, it is possible to satisfactorily remove minute defects such as minute roughness and undulation generated on the surface of the glass substrate, or minute scratch marks generated in the previous steps.

  The glass substrate at the time when the second polishing step is completed is the final glass substrate, and the thickness is the final thickness t of the glass substrate.

[Washing process]
Next, as a cleaning process, the glass substrate after the second polishing process is scrubbed. However, the cleaning method is not limited to scrub cleaning, and any cleaning method may be used as long as it can clean the surface of the glass substrate after the polishing process.

  If necessary, the glass substrate subjected to scrub cleaning is subjected to ultrasonic cleaning and drying. The drying process is a process of drying the surface of the glass substrate after removing the cleaning liquid remaining on the surface of the glass substrate using IPA (isopropyl alcohol) or the like. For example, a water rinse cleaning process is performed on the glass substrate after scrub cleaning for 2 minutes to remove the cleaning liquid residue. Next, an IPA cleaning process is performed for 2 minutes, and water remaining on the surface of the glass substrate is removed by IPA. Finally, the IPA vapor drying step is performed for 2 minutes, and the liquid IPA adhering to the surface of the glass substrate is dried while being removed by the IPA vapor.

  The glass substrate drying process is not limited to this, and any drying method generally known as a glass substrate drying method such as spin drying or air knife drying may be used.

[Inspection process]
Next, as an inspection process, the glass substrate is visually inspected for scratches, cracks, foreign matter adhesion, and the like. If it cannot be determined visually, an inspection is performed using an optical surface analyzer (for example, “OSA6100” manufactured by KLA-TENCOL).

  Glass substrates that are determined to be non-defective in the inspection process are stored in a dedicated storage cassette in a clean environment and vacuum packed, and then shipped as a glass substrate for HDDs, so that foreign substances do not adhere to the surface. .

<Glass substrate for HDD>
Next, the glass substrate for HDD manufactured as described above will be described. As shown in FIG. 4, the HDD glass substrate 50 according to the present embodiment is difficult to break because defects such as foreign matter, bubbles or scratches mixed in the vicinity of the blank surface in the molding process are removed in the lapping process. The impact resistance is improved.

  Further, since a stress layer (chemical strengthening layer) having a thickness of less than 30 μm is formed on the surface of the glass substrate 50 in the chemical strengthening step, the surface of the glass substrate 50 is strengthened with the stress layer, and the impact resistance of the glass substrate 50 is increased. Is further improved.

<Magnetic recording medium for HDD>
Next, an HDD magnetic recording medium manufactured using the HDD glass substrate 50 will be described. The magnetic recording medium for HDD according to the present embodiment is manufactured by providing a magnetic film as a recording layer on the main surface 51 of the glass substrate 50 for HDD. The magnetic film may be formed directly or indirectly on the main surface 51. The magnetic film may be formed on one side or both sides of the glass substrate 50.

  As a method for forming the magnetic film, a conventionally known method can be used. For example, a method in which a thermosetting resin in which magnetic particles are dispersed is spin-coated on the glass substrate 50, or a method in which sputtering or electroless plating is used. And the like. The film thickness by spin coating is about 0.3 μm to 1.2 μm, the film thickness by sputtering is about 0.04 μm to 0.08 μm, and the film thickness by electroless plating is 0.05 μm to 0.1 μm. From the viewpoint of thinning and high density, film formation by sputtering or electroless plating is preferable.

  The magnetic material used for the magnetic film is not particularly limited, and conventionally known materials can be used. Among them, a Co-based alloy or the like containing Ni and Cr as the basic material for adjusting the residual magnetic flux density is preferable in order to obtain high coercive force. Specifically, CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, CoCrPtSiO, and the like whose main component is Co are preferable.

  The magnetic film may be divided into a non-magnetic film (for example, Cr, CrMo, CrV, etc.) to have a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.) in which noise is reduced.

The other magnetic material, ferrite or iron - and that of the rare earth, in a non-magnetic film made of _SiO 2, BN, etc., Fe, Co, FeCo, in granular or the like of the structure obtained by dispersing magnetic particles such CoNiPt Good.

  The magnetic film may be either an inner surface type or a vertical type recording format.

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

  In the present embodiment, if necessary, an underlayer or a protective layer may be provided in addition to the magnetic film as the recording layer. The underlayer in the HDD magnetic recording medium is selected according to the magnetic film. Examples of the material for the underlayer include at least one material selected from the group consisting of nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. In the case of a magnetic film containing Co as a main component, it is preferable to use Cr alone or a Cr alloy from the viewpoint of improving magnetic characteristics. The underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV can be used.

  The protective layer is provided to prevent wear and corrosion of the magnetic film. Examples of the protective layer include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be continuously formed by an in-line sputtering apparatus together with the underlayer and the magnetic film. Further, these protective layers may be a single layer, or may have a multilayer structure composed of the same or different layers.

Another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, colloidal silica fine particles are dispersed and applied in a tetraalkoxysilane diluted with an alcohol solvent on the Cr layer, and further baked to obtain silicon dioxide (SiO ₂ ). A layer may be formed.

  As described above, by using the HDD magnetic recording medium manufactured using the HDD glass substrate 50 according to the present embodiment as the substrate, the operation of the magnetic head at the time of high-speed rotation of the HDD can be stabilized. Can do.

  Further, according to the HDD magnetic recording medium manufactured using the HDD glass substrate 50 according to the present embodiment, the HDD glass substrate 50 which is hard to break and has improved impact resistance is used. The magnetic recording medium for use is also hard to break and has improved impact resistance.

  In the present embodiment, the lapping process and the polishing process are performed twice. However, the present invention is not limited to this, and the lapping process and the polishing process may be performed only once. Moreover, although the chemical strengthening process was performed before the second polishing process, it may be performed after the second polishing process depending on the situation. Further, the chemical strengthening step can be omitted depending on the situation.

  Furthermore, as measures against drop strength, the outer peripheral end face and the inner peripheral end face other than the main surface of the glass substrate may be strengthened, or the glass substrate is subjected to HF immersion treatment as an edge mitigation treatment for scratches generated on the glass substrate. Also good.

  The glass substrate for HDD according to the present embodiment is not limited to the use for manufacturing a magnetic recording medium for HDD, and can be used for the manufacture of, for example, a magneto-optical disk or an optical disk.

  Hereinafter, the present invention will be described in more detail through examples and comparative examples. However, the present invention is not limited to this embodiment.

<Manufacture of glass substrates for HDD>
The glass substrate for HDD was manufactured according to the manufacturing process of FIG.

[1. Glass melting process, molding process]
An aluminosilicate glass having a Tg of 480 ° C. was used as the glass material, and the molten glass material was press-molded to produce disc-shaped blanks having an outer diameter of 68 mm. The thickness of the blanks was 1.05 mm in Example 1, 1.03 mm in Example 2, 0.95 mm in Example 3, and 0.93 mm in Comparative Example 1 (see Table 1).

[2. Heat treatment process]
By alternately laminating setters and blanks made of 70 mm in outer diameter and 2 mm in thickness and made of alumina and passing through a high-temperature electric furnace set at about 430 ° C. over 2 hours, the warp and internal stress of the blanks can be reduced. Reduced.

[3. First wrapping step]
Both surfaces of the blanks were ground using a double-side grinding machine (manufactured by HAMAI). As grinding conditions, diamond pellets of # 1200 mesh were used, the load was 100 g / cm ² , the upper platen was rotated at 20 rpm, and the lower platen was rotated at 30 rpm. The blanks obtained had a flatness of 15 μm and a surface roughness Ra of 0.5 μm.

[4. Coring process]
Using a core drill equipped with a cylindrical diamond grindstone, a circular hole having a diameter of 18 mm was formed in the center of the blank.

[5. Inner / outer diameter machining process]
Using a drum-shaped diamond grindstone, the outer peripheral end surface and the inner peripheral end surface of the blanks were processed to have an inner diameter and an outer diameter of 65 mm in outer diameter and 20 mm in inner diameter.

[6. Second wrapping step]
Both surfaces of the blanks were ground again using a double-side grinding machine (manufactured by HAMAI). As grinding conditions, diamond pellets of # 1700 mesh were used, the load was 100 g / cm ² , the upper platen was rotated at 20 rpm, and the lower platen was rotated at 30 rpm. The resulting blank had a flatness of 10 μm and a surface roughness Ra of 0.25 μm.

  The total grinding amount Q in the first and second lapping steps was 0.22 mm in Example 1, 0.2 mm in Example 2, 0.12 mm in Example 3, and 0.1 mm in Comparative Example 1 (Table) 1). As a result, all the blanks had a thickness of 0.83 mm.

[7. End polishing process]
100 blanks were piled up, and in this state, the outer peripheral end face and the inner peripheral end face of the blank were polished using an end face polishing machine. Nylon fiber having a diameter of 0.2 mm was used as the brush hair of the polishing machine. As the polishing liquid, a slurry containing cerium oxide having an average particle diameter of 3 μm as abrasive grains (abrasive material) was used. As for the surface roughness of the inner peripheral end face of the obtained blank, Ra was 0.03 μm.

[8. First polishing step]
Both surfaces of the blanks were polished using a double-side polishing machine (manufactured by HAMAI). As polishing conditions, a polishing pad made of urethane foam having a hardness of 80 degrees is used, and the polishing liquid is a slurry in which cerium oxide having an average particle diameter of 1.5 μm is dispersed in water as abrasive grains (polishing material). The mixing ratio of water and abrasive grains was 2: 8. The weight was 100 g / cm ² , the upper platen was 30 rpm, and the lower platen was 50 rpm. The blanks obtained had a flatness of 4 μm and a surface roughness Ra of 0.7 nm.

  The polishing amount in the first polishing step was 25 μm in all of Examples 1 to 3 and Comparative Example 1.

[9. Chemical strengthening process]
The blank was immersed in a chemical strengthening treatment solution to form a chemical strengthening layer (stress layer) on the surface of the blank. An aqueous solution of a mixed molten salt of potassium nitrate (KNO ₃ ) and sodium nitrate (NaNO ₃ ) was used as the chemical strengthening treatment liquid. The mixing ratio was 1: 1 by mass ratio. The temperature of the chemical strengthening treatment liquid was 380 ° C., and the immersion time was 25 minutes. The thickness of the obtained stress layer was about 10 μm.

[10. Second polishing step]
Both surfaces of the blanks were further precisely polished using a double-side polishing machine (manufactured by HAMAI). As polishing conditions, the polishing pad is made of urethane foam having a hardness of Asker-C and 70 degrees, and the polishing liquid is made by dispersing colloidal silica having an average particle diameter of 60 nm in water as abrasive grains (polishing material). A slurry was used, and the mixing ratio of water and abrasive grains was 2: 8. The load was 90 g / cm ² , the rotation speed of the upper surface plate was 20 rpm, and the rotation speed of the lower surface plate was 30 rpm. The obtained glass substrate had a flatness of 2 μm and a surface roughness Ra of 0.1 nm.

  The polishing amount in the second polishing step was 5 μm in each of Examples 1 to 3 and Comparative Example 1. As a result, the final thickness t of the glass substrate was 0.8 mm (see Table 1).

[11. Cleaning process]
The glass substrate was scrubbed. A nonionic surfactant is used to increase the cleaning ability by diluting a mixture of potassium hydroxide (KOH) and sodium hydroxide (NaOH) at a mass ratio of 1: 1 as ultra-pure water (DI water). The liquid obtained by adding the agent was used. The cleaning liquid was supplied by spraying. After scrub cleaning, in order to remove the cleaning liquid remaining on the surface of the glass substrate, a water rinse cleaning process is performed in an ultrasonic bath for 2 minutes, an IPA cleaning process is performed in an ultrasonic bath for 2 minutes, and finally the glass substrate is cleaned with IPA vapor. The surface of was dried.

<Manufacture of HDD magnetic recording media>
A magnetic film (recording layer) was provided on the main surface of the obtained glass substrate to obtain a magnetic recording medium. That is, from the glass substrate side, a base layer made of Ni—Al (thickness of about 100 nm), a recording layer made of Co—Cr—Pt (thickness 20 nm), and a protective film made of DLC (Diamond Like Carbon) (thickness 5 nm) are sequentially formed. Laminated. 100 magnetic recording media were prepared for each of Examples 1 to 3 and Comparative Example 1.

<Evaluation of HDD magnetic recording media>
In order to evaluate the impact resistance of the produced magnetic recording medium, the magnetic recording medium was loaded into an HDD (hard disk drive), and a drop impact test was performed using the test apparatus shown in FIG. In FIG. 5, reference numeral 21 is a support, reference numeral 22 is a collision table, reference numeral 23 is a mounting base for a test object, reference numeral 24 is an impact G value measuring device, and reference numeral X is an HDD loaded with a magnetic recording medium.

  Two magnetic recording media are incorporated in the hard disk drive X, and fixed to the test object mounting table 23 together with the impact G value measuring device 24. The entire mounting table 23 is dropped from a height of 1 m to collide with the collision table 22. The hard disk drive X was disassembled, and it was visually confirmed whether or not the magnetic recording medium was cracked. If even one of the two sheets was broken, it was determined that there was a crack, and it was determined that there was no crack when both sheets were not broken.

  The test was performed in the order of 900G, 1000G, 1100G, 1200G, and 1300G. Five hard disk drives X were mounted on the mounting table 23 at a time. The broken hard disk drive X was replaced with a hard disk drive X incorporating two new magnetic recording media. The hard disk drive X that was not cracked was directly subjected to the next high G test.

  For each of Examples 1 to 3 and Comparative Example 1, in each G, it was recorded how many of the five hard disk drives X were not cracked. The results are shown in Table 1.

<Consideration of results>
The comparative example 1 was inferior to the result in that the grinding amount Q in the lapping step was relatively small, (grinding amount Q in the lapping step / final glass substrate thickness t) <15% (12.5 %), It is considered that defects such as foreign matter, bubbles or scratches mixed in the molding process remained on the final glass substrate. On the other hand, Examples 1 to 3 were excellent in the result because the grinding amount Q in the lapping process was relatively large, and (grinding amount Q in the lapping process / final glass substrate thickness t) ≧ 15%. (15%, 25%, 27.5%), it is considered that defects such as foreign matter, bubbles or scratches mixed in the molding process were removed in the lapping process. In particular, the example in which (grinding amount Q in the lapping step / thickness t in the final glass substrate) is 25% than in Example 3 in which the grinding amount Q in the lapping step / final glass substrate thickness t) is 15%. 2 was more excellent in impact resistance, but Example 1 with 27.5% (grinding amount Q in the lapping step / final glass substrate thickness t) was evaluated in the same manner as Example 2. . From this, it can be said that it is not always necessary to increase the thickness of the blanks up to Example 1.

10 Double-side grinding machine 22 Collision table 24 Impact G value measuring device 50 Glass substrate 51 Main surface X Hard disk drive

Claims (5)

A method for producing a glass substrate for HDD, comprising a molding step of molding a molten glass material into plate-shaped blanks, and a lapping step of grinding the surface of the blanks,
A method for producing a glass substrate for HDD, wherein t × 0.15 or more is ground in the lapping step, where t is the final thickness of the glass substrate.   2. The method for manufacturing a glass substrate for HDD according to claim 1, wherein grinding is performed at t * 0.25 or less in the lapping step.   The method for producing a glass substrate for HDD according to claim 1, further comprising a chemical strengthening step of forming a stress layer having a thickness of less than 30 μm on the surface of the glass substrate after the lapping step.   A glass substrate for HDD, which is produced by the method for producing a glass substrate for HDD according to any one of claims 1 to 3.   5. A magnetic recording medium for HDD, which is manufactured by providing a recording layer on the main surface of the glass substrate for HDD according to claim 4.

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