JP6131187B2 - Manufacturing method of glass substrate for HDD - Google Patents

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 recent years, with the increase in the density of information stored in magnetic recording media for HDD (hard disk drive), the flying height of the magnetic head has become smaller and even a deposit of several hundred nm has caused a head crash. And cause thermal asperity. In particular, in the case of a head equipped with a DFH (dynamic flying height) mechanism, the flying height of the head is as small as several nanometers, and the cleanliness of the magnetic recording medium for HDD is strongly demanded. As the recording area is enlarged, the recording area is extended to the outer peripheral edge of the recording medium. Therefore, high cleanliness is required up to the outermost periphery of the recording medium.

  The glass substrate for HDD used for the substrate of the magnetic recording medium for HDD is cleaned with a cleaning liquid before the inspection process in the manufacturing process. In this cleaning step, the glass substrate is placed in a cleaning tank in a state of being accommodated in a dedicated container called a cleaning carrier, for example, and the cleaning liquid is poured in the cleaning tank to be cleaned.

  As described in Patent Document 1, the cleaning carrier has a structure in which a plurality of holding rods are installed in parallel with each other at a predetermined interval between a pair of opposing walls. A concave groove is formed in the circumferential direction on the peripheral surface of each holding rod. The glass substrate is held at its both end portions and lower end portions by three holding rods, fits into the groove, and is housed in the cleaning carrier in a standing state. After the cleaning, the glass substrate is dried while being accommodated in the cleaning carrier.

JP 2009-87472 A

  By the way, if a defect remains at the outer peripheral edge of the glass substrate after cleaning and drying, the recording area is disturbed when a recording layer is formed on the main surface of the glass substrate to form a magnetic recording medium. There's a problem.

  Accordingly, an object of the present invention is to provide a method for producing a glass substrate for HDD in which no defects remain on the outer peripheral edge of the glass substrate after cleaning and drying, a glass substrate for HDD produced by the production method, and the glass substrate for HDD. It is providing the magnetic recording medium for HDDs using this.

  That is, one aspect of the present invention is a method for manufacturing a glass substrate for HDD including a cleaning step of cleaning a glass substrate with a cleaning liquid. In the cleaning step, the cleaning liquid is parallel to the main surface of the glass substrate with respect to the glass substrate. A method of manufacturing a glass substrate for HDD, wherein the cleaning is performed by sequentially flowing in a plurality of different directions.

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

  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.

  The above and other objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

FIG. 1 is a perspective view of a glass substrate for HDD according to an embodiment of the present invention. FIG. 2 is a manufacturing process diagram of the glass substrate for HDD according to the embodiment of the present invention. FIG. 3 is a schematic side view showing the configuration of the main part of a double-side polishing machine used in the secondary polishing process. FIG. 4 is a drawing-substituting photograph showing an example of defects found at the outer peripheral edge of the glass substrate after the final cleaning step. FIG. 5 is a perspective view of a cleaning carrier used in the final cleaning step. FIG. 6 is a side view of the cleaning carrier. FIG. 7 is a front view of the cleaning carrier. FIG. 8 is an explanatory diagram showing an example of the direction in which the cleaning liquid is passed through the glass substrate in the final cleaning step. FIG. 9 is an explanatory view showing another example of the direction in which the cleaning liquid flows through the glass substrate in the final cleaning step.

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

  Conventionally, a defect remains in the outer peripheral edge of the glass substrate after cleaning and drying, and therefore, there is a problem that a recording area is obstructed when a recording layer is formed on the main surface of the glass substrate to form a magnetic recording medium. there were.

  Since the present inventors conventionally flowed the cleaning liquid only in one direction in the cleaning tank, a portion hidden behind the holding rod (back to the flow of the cleaning liquid) occurs at the outer peripheral end of the glass substrate, The present invention was completed by finding that a cleaning residue was generated in this portion, and that this cleaning residue was left as a defect at the outer peripheral edge of the glass substrate.

  In this embodiment, in the glass substrate cleaning process and the like, when referring to directions such as up, down, left, right, front, back, side, etc., the main surface of the glass substrate is in the direction of gravity unless otherwise specified. This refers to the main surface when the glass substrate is erected so as to be in parallel.

<Method for producing glass substrate for HDD>
The manufacturing method of the glass substrate for HDD is demonstrated with reference to the glass substrate 50 shown in FIG. 1, and the manufacturing-process figure shown in FIG.

  In the present embodiment, the HDD glass substrate 50 includes a disk processing step, a lapping step, a primary polishing (rough polishing) step, a secondary polishing (precision polishing) step, a chemical strengthening step, a final cleaning step, an inspection step, and the like. It is manufactured after.

Glass material used for the glass substrate 50 is composed of a glass composition whose main component is silicon dioxide (SiO _2). The glass composition may or may not contain magnesium, calcium and / or cerium. Typical glass compositions include, for example, SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, BaO, SrO, ZnO and the like. is there.

[Disc machining process]
In the disk processing step, a molten glass material is poured into a mold and press-molded to produce a disk-shaped glass substrate (referred to as a blank). As the size of the glass substrate at this time, for example, the outer diameter is 2.5 inches, 1.8 inches, 1.0 inches, 0.8 inches, etc., and the plate thickness is 2 mm, 1 mm, 0.8 mm, 0 .63 mm or the like. A circular hole is formed in the center part of the obtained glass substrate, for example using a diamond core drill etc., and it is set as a cyclic | annular glass substrate.

[Lapping process]
The lapping process includes a first lapping process and a second lapping process. In the first lapping step, both the front and back surfaces of the glass substrate are ground, and the overall shape of the glass substrate, that is, the parallelism, flatness, thickness and the like of the glass substrate are preliminarily adjusted. In the second lapping step, following the first lapping step, both the front and back surfaces of the glass substrate are ground again to further finely adjust the overall shape of the glass substrate, that is, the parallelism, flatness, thickness and the like of the glass substrate. In the lapping process, for example, a double-side grinding machine including an upper and lower surface plate on which diamond pellets are attached is used.

[Primary polishing process]
In the primary polishing step, both the front and back surfaces of the glass substrate are roughly polished so that the surface roughness finally obtained in the next secondary polishing step can be efficiently obtained. In this primary polishing step, for example, a double-side polishing machine having a pair of upper and lower surface plates with a foamed urethane pad attached as a polishing pad is used, and a slurry-like polishing liquid containing, for example, cerium oxide as abrasive grains as the polishing liquid Is used. However, it is not limited to this.

[Secondary polishing process]
In the secondary polishing step, following the primary polishing step, both the front and back surfaces of the glass substrate are precisely polished so that the finally obtained surface roughness can be obtained. In the secondary polishing step, as shown in FIG. 3, a double-side polishing machine 10 capable of simultaneously polishing both the front and back surfaces of the glass substrate 50 is used.

  The double-side polishing machine 10 includes a disk-shaped upper surface plate 11 and a lower surface plate 12 which are arranged at intervals in the vertical direction so as to be parallel to each other and are rotatable in opposite directions. A polishing pad (a polyurethane suede pad in this embodiment) P for polishing the front and back surfaces of the glass substrate 50 is attached to the opposing surfaces of the pair of upper and lower surface plates 11 and 12. A plurality of rotatable carriers 13 are arranged between the surface plates 11 and 12, and a plurality of glass substrates 50 are fitted and set in each carrier 13. The carrier 13 revolves around the rotation center of the surface plates 11 and 12 while rotating while holding the glass substrate 50. A slurry-like polishing liquid containing abrasive grains (colloidal silica in the present embodiment) is applied to the upper and lower surface plates 11 and 12 and the carrier 13 that are operating in this manner. 50, and between the polishing pad P of the lower surface plate 12 and the glass substrate 50, respectively, thereby performing precise polishing on both the front and back surfaces of the glass substrate 50.

  In FIG. 3, reference numeral 14 denotes a polishing liquid recovery device, reference numeral 15 denotes a polishing liquid storage tank, reference numeral 16 denotes a polishing liquid supply pipe, reference numeral 17 denotes a lubricating liquid storage tank, and reference numeral 18 denotes a lubricating liquid supply pipe.

[Chemical strengthening process]
In the chemical strengthening step, a chemical strengthening layer is formed on the surface of the glass substrate. For example, by immersing a glass substrate in a chemical strengthening treatment solution containing sodium ions or potassium ions, lithium ions existing on the surface layer of the glass substrate are replaced with sodium ions in the chemical strengthening treatment solution, or sodium ions are potassium. By replacing the ions, the surface layer of the glass substrate becomes a chemically strengthened layer. A compressive stress is applied to the chemically strengthened layer. By forming such a chemically strengthened layer, the impact resistance, vibration resistance, heat resistance, and the like of the finally obtained glass substrate 50 are improved.

[Final cleaning process]
(General)
In the final cleaning step, foreign substances adhering to the glass substrate include, for example, filtered pure water, ion-exchanged water, ultrapure water, acidic detergent, neutral detergent, alkaline detergent, organic solvent, surfactant and the like. Wash and remove using various cleaning solutions. Thereafter, the glass substrate is dried.

(Conventional final cleaning process)
Conventionally, a glass substrate is housed in a cleaning carrier, put in this state in a cleaning tank, and cleaning is performed by flowing a cleaning solution over the glass substrate in the cleaning tank. At this time, since the cleaning liquid was flowed only in one direction (for example, one direction from the bottom to the top in the vertical direction) in the cleaning tank, the back of the cleaning carrier holding rod ( A portion hidden behind the flow of the cleaning liquid is generated, and a cleaning residue is generated in this portion, and this cleaning residue becomes a defect at the outer peripheral edge of the glass substrate 50 as illustrated in FIG. There was a problem of remaining.

(Final cleaning process of this embodiment)
In the present embodiment, the glass substrate 50 is cleaned by flowing a cleaning liquid in a direction parallel to the main surface of the glass substrate 50 in a plurality of directions different from each other.

  As shown in FIGS. 5 to 7, in the cleaning carrier 20, a plurality of (five in the illustrated example) holding rods 23 are installed in parallel with each other at a predetermined interval between a pair of front and rear opposing walls 21 and 22. Structure. A concave groove is formed in the circumferential direction on the peripheral surface of each holding rod 23. The glass substrate 50 is held at its both ends and lower ends by three holding rods 23, fits into the groove, and is housed in the cleaning carrier 20 in a standing state. The cleaning carrier 20 can accommodate many glass substrates 50 at a time.

  In this embodiment, in this final cleaning step, the glass substrate 50 is held and cleaned by a plurality of holding rods 23, and after cleaning, the glass substrate 50 is held in that state, that is, held by the plurality of holding rods 23. Dry as it is. The three holding rods 23 that hold the glass substrate 50 are separated from each other by about 90 ° with respect to the center of the glass substrate 50 to be held. The glass substrate 50 is dried in a state where the holding rods 23 are separated from each other by 90 °, so that the cleaning liquid remains between the holding rod 23 that holds the outer peripheral edge of the glass substrate 50 and the glass substrate 50. Thus, it is possible to reduce the adhesion to the outer peripheral edge of the glass substrate 50.

  As shown in FIGS. 8 and 9, the glass substrate 50 is put in the cleaning tank 30 in a state where it is accommodated in the cleaning carrier 20, and the glass substrate 50 is cleaned by flowing the cleaning liquid 31 in the cleaning tank 30. At this time, the glass substrate 50 is disposed in the cleaning tank 30 so that the main surface thereof is parallel to the flow direction of the cleaning liquid 31.

  8 is provided with cleaning liquid supply / discharge devices (referred to as apparatuses for supplying or discharging the cleaning liquid 31 to or from the cleaning tank 30) 32 and 33 above and below the cleaning tank 30, and the cleaning liquid 31 is disposed inside the cleaning tank 30. The case where the main surface of the glass substrate 50 flows in two directions is shown. As a result, the cleaning liquid 31 is sequentially switched with respect to the glass substrate 50 in one direction from the bottom to the top in the vertical direction (referred to as jet) and one direction from the top to the bottom (referred to as flowing). It can flow (up and down 2 directions). Either the jet flow or the hanging flow may be performed first, and the jet flow and the flowing flow may be repeated any number of times. Moreover, you may transfer the glass substrate 50 to the washing tank only for a jet, and the washing tank only for a pouring.

  FIG. 9 shows a case where cleaning liquid supply / discharge devices 34 and 35 are provided on the left and right of the cleaning tank 30, and the cleaning liquid 31 flows in the left and right directions with respect to the main surface of the glass substrate 50 in the cleaning tank 30. As a result, with respect to the glass substrate 50, the cleaning liquid 31 is divided into one direction from left to right (referred to as a left laminar flow) and one direction from right to left (referred to as a right laminar flow) in the left and right lateral directions. In addition, the flow can be switched in order (two left and right directions). Either the left laminar flow or the right laminar flow may be performed first, and the left laminar flow and the right laminar flow may be repeated any number of times. Further, the glass substrate 50 may be transferred to a cleaning tank dedicated to the left laminar flow and a cleaning tank dedicated to the right laminar flow.

  Although not shown, the cleaning liquid supply / discharge devices 32 to 35 are provided on the top, bottom, left, and right of the cleaning tank 30, and the cleaning liquid 31 is sprayed from the bottom to the top or the top to the bottom with respect to the glass substrate 50. It may be possible to flow in a left laminar flow from left to right or a right laminar flow from right to left. Then, two or more of these directions can be arbitrarily combined and sequentially switched to allow the cleaning liquid 31 to flow over the glass substrate 50.

(Operation of this embodiment)
In the present embodiment, the cleaning liquid 31 flows in a direction parallel to the main surface of the glass substrate 50 and in a plurality of different directions in order with respect to the glass substrate 50, so that the cleaning liquid 31 flows in a certain direction. Even if it becomes a portion hidden behind the holding rod 23, that portion is not a portion hidden behind the holding rod 23 with respect to the flow of the cleaning liquid 31 in another direction. Therefore, the cleaning residue at the outer peripheral edge of the glass substrate 50 is eliminated, and it is suppressed that defects remain at the outer peripheral edge of the glass substrate 50 after cleaning and drying.

  In the present embodiment, the glass substrate 50 is cleaned while being held at three points on both side edges and a lower edge. That is, one of the three holding rods 23 holds the left end of the glass substrate 50, one holds the right end, and one holds the lower end. Thereby, the glass substrate 50 can be stably held during cleaning. Further, since the three holding portions are separated by 90 ° with respect to the center of the glass substrate 50, the cleaning liquid 31 remains between the holding rod 23 and the glass substrate 50 and adheres to the outer peripheral end portion of the glass substrate 50. That will be reduced.

  In the present embodiment, the glass substrate 50 and the holding rod 23 are in contact with each other at all the holding portions of the glass substrate 50. Thereby, it is possible to prevent the adhesion of particles to the glass substrate 50 and the generation of the dry stain of the cleaning liquid 31 when the glass substrate 50 is dried. That is, since each of the three holding rods 23 is always in contact with the glass substrate 50, it is possible to avoid the cleaning liquid 31 from being accumulated between the glass substrate 50 and the holding rod 23. If the glass substrate 50 and the holding rod 23 are separated, the cleaning liquid 31 accumulates between the glass substrate 50 and the holding rod 23 due to surface tension, and particles contained in the accumulated cleaning liquid 31 during drying. Moves to the glass substrate 50 side and remains attached to the glass substrate 50, or the cleaning liquid 31 itself moves to the glass substrate 50 side and remains on the glass substrate 50 as a dry stain. The adhesion of these particles and the dry stain of the cleaning liquid 31 also become defects. On the other hand, in this embodiment, since the glass substrate 50 and the holding rod 23 are always in contact with each other in all the holding portions of the glass substrate 50 and are not separated from each other, the above-described problems are suppressed. That is, the film of the cleaning liquid 31 between the outer peripheral end of the glass substrate 50 and the holding rod 23 that can be generated when the outer peripheral end of the glass substrate 50 and the holding rod 23 are separated can be avoided. After the substrate 50 is dried, it is possible to prevent defects such as deposits resulting from the drying of the film of the cleaning liquid 31 from remaining on the outer peripheral edge of the glass substrate 50.

  In the present embodiment, the cleaning liquid 31 is preferably flowed in the vertical direction and the horizontal direction with respect to the main surface of the glass substrate 50. Thereby, in particular, when the glass substrate 50 is held and cleaned at three points on both side ends and the lower end thereof, the cleaning liquid 31 does not remain in the holding portion during drying, and the cleaning liquid 31 on the glass substrate 50 is removed. Dry stains and particle adhesion can be prevented. In addition, the portion hidden behind the holding rod 23 is surely lost, and it is reliably suppressed that a defect remains in the outer peripheral end of the glass substrate 50 after cleaning and drying.

  In the present embodiment, the cleaning liquid 31 is flowed in two opposite directions (jet flow and flowing) in the vertical direction with respect to the main surface of the glass substrate 50 and in two opposite directions (left laminar flow and right laminar flow) in the lateral direction. It is preferable. That is, the cleaning liquid 31 is sequentially switched in the four directions of up, down, left, and right. Thereby, in particular, when the glass substrate 50 is held and cleaned at three points on both side ends and the lower end thereof, the remaining liquid of the cleaning liquid 31 on the holding portion is surely eliminated during drying, and the cleaning liquid for the glass substrate 50 is removed. Thus, it is possible to reliably prevent the 31 dry stain and particles from adhering. Further, the portion hidden behind the holding rod 23 is more reliably eliminated, and it is further reliably suppressed that a defect remains on the outer peripheral end of the glass substrate 50 after cleaning and drying.

  The flow rate (L / min) or flow rate (m / min) of the cleaning liquid 31 supplied to the cleaning tank 30 and discharged from the cleaning tank 30 (that is, passing through the cleaning tank 30) is the same as that of the cleaning liquid 31 in the cleaning tank 30. It is necessary to study from the viewpoint of increasing the substitution rate and the like, and from the viewpoint of the stability of holding the glass substrate 50 by the holding rod 23.

[Inspection process]
In the inspection process, the flatness and thickness of the glass substrate, the surface roughness, the presence or absence of defects, etc. are inspected. Only the glass substrate that has passed the inspection is stored in a dedicated storage cassette and vacuum packed in a clean environment so that foreign matter or the like does not adhere to the surface, and then shipped as a glass substrate for HDD.

<Glass substrate for HDD>
Next, the glass substrate for HDD manufactured as described above will be described. As shown in FIG. 1, the HDD glass substrate 50 according to the present embodiment suppresses remaining defects at the outer peripheral edge because the cleaning residue at the outer peripheral edge is eliminated in the cleaning process in the manufacturing process. This is a high-quality glass substrate for HDD.

<Magnetic recording medium for HDD>
Next, an HDD magnetic recording medium manufactured using the HDD glass substrate 50 will be described. The HDD magnetic recording medium according to this embodiment is manufactured by providing a magnetic film as a recording layer on the main surface of the HDD glass substrate 50. The magnetic film may be formed directly or indirectly on the main surface. 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 0.01 μm to 0.08 μm, and the film thickness by electroless plating is 0.01 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.

  In addition, since the HDD magnetic recording medium according to the present embodiment uses the HDD glass substrate 50 in which defects are suppressed from remaining at the outer peripheral end, the high-quality HDD having high cleanliness up to the outermost peripheral portion. Magnetic recording medium. For this reason, even if the recording area extends to the outer peripheral edge of the recording medium, it is possible to prevent the recording area from being damaged.

  In the present embodiment, the polishing step is performed twice. However, the polishing step is not limited to this and may be performed only once. Moreover, although the chemical strengthening process was performed after the polishing process, it may be performed before the 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 the magnetic recording medium for HDD, and can be used for the manufacture of a magneto-optical disk, an optical disk, and the like.

  The technical features of this embodiment are summarized as follows.

  The method for manufacturing a glass substrate for HDD according to the present embodiment is a method for manufacturing a glass substrate for HDD including a cleaning step of cleaning the glass substrate 50 with the cleaning liquid 31, and the cleaning liquid 31 is applied to the glass substrate 50 in the cleaning step. The substrate is washed by flowing it in a plurality of directions that are parallel to the main surface of the glass substrate 50 and different from each other.

  According to the present embodiment, the cleaning liquid 31 flows in a direction parallel to the main surface of the glass substrate 50 and in a plurality of different directions in order with respect to the glass substrate 50, so that the cleaning liquid 31 flows in a certain direction. On the other hand, even if the portion is hidden behind the holding rod 23, the portion is not hidden behind the holding rod 23 with respect to the flow of the cleaning liquid 31 in another direction. Therefore, the cleaning residue at the outer peripheral edge of the glass substrate 50 is eliminated, and it is suppressed that defects remain at the outer peripheral edge of the glass substrate 50 after cleaning and drying.

  In the present embodiment, in the cleaning step, the glass substrate 50 is cleaned by holding the glass substrate 50 at three points on both side ends and the lower end, and after cleaning, the glass substrate 50 is dried as it is, and the holding unit is made of glass. The center of the substrate 50 is separated by 90 °.

  According to this embodiment, the glass substrate 50 can be stably held during cleaning. Further, since the three holding portions are separated by 90 ° with respect to the center of the glass substrate 50, the cleaning liquid 31 remains between the holding rod 23 and the glass substrate 50 and adheres to the outer peripheral end portion of the glass substrate 50. That will be reduced.

  In the present embodiment, in the cleaning process, the glass substrate 50 is held and cleaned by the plurality of holding rods 23, and after the cleaning, the glass substrate 50 is dried as it is, and is held in all the holding portions of the glass substrate 50. The glass substrate 50 and the holding rod 23 are always in contact with each other.

  According to the present embodiment, the film of the cleaning liquid 31 between the outer peripheral end of the glass substrate 50 and the holding rod 23 that may occur when the outer peripheral end of the glass substrate 50 and the holding rod 23 are separated from each other. It is possible to prevent defects such as deposits resulting from the drying of the film of the cleaning liquid 31 from being left on the outer peripheral edge of the glass substrate 50 after the glass substrate 50 is dried.

  In the present embodiment, the cleaning liquid 31 is flowed in the vertical direction and the horizontal direction with respect to the main surface of the glass substrate 50.

  According to the present embodiment, in particular, when the glass substrate 50 is cleaned while being held at the three ends of the both side ends and the lower end thereof, the liquid remaining of the cleaning liquid 31 on the holding portion is eliminated during drying, and the glass substrate 50 is thus removed. The dry stain of the cleaning liquid 31 and the adhesion of particles can be prevented. In addition, the portion hidden behind the holding rod 23 is surely lost, and it is reliably suppressed that a defect remains in the outer peripheral end of the glass substrate 50 after cleaning and drying.

  In the present embodiment, the cleaning liquid 31 is caused to flow in two opposite directions in the vertical direction and two opposite directions in the horizontal direction with respect to the main surface of the glass substrate 50.

  According to the present embodiment, in particular, when the glass substrate 50 is cleaned while being held at three points on both side ends and the lower end thereof, the liquid residue of the cleaning liquid 31 on the holding portion is surely eliminated during drying, and the glass substrate Thus, it is possible to reliably prevent the dry stain and particles from adhering to the cleaning liquid 31. Further, the portion hidden behind the holding rod 23 is more reliably eliminated, and it is further reliably suppressed that a defect remains on the outer peripheral end of the glass substrate 50 after cleaning and drying.

  The HDD glass substrate 50 according to this embodiment is manufactured by the method for manufacturing an HDD glass substrate.

  According to the present embodiment, the cleaning residue in the manufacturing process eliminates the remaining cleaning at the outer peripheral edge, so that a high-quality HDD glass substrate 50 for HDD with suppressed defects remaining at the outer peripheral edge is obtained. It is done.

  The HDD magnetic recording medium according to the present embodiment is manufactured by providing a recording layer on the main surface of the HDD glass substrate 50.

  According to the present embodiment, since the HDD glass substrate 50 in which defects are suppressed from remaining at the outer peripheral end portion is used, a high-quality HDD magnetic recording medium with high cleanliness up to the outermost peripheral portion can be obtained. . For this reason, even if the recording area extends to the outer peripheral edge of the recording medium, it is possible to prevent the recording area from being damaged.

  According to the present embodiment, it is possible to prevent defects from remaining on the outer peripheral edge of the HDD glass substrate 50 after cleaning and drying. It can cope with miniaturization of flying height.

  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>
According to the manufacturing process shown in FIG. 2, using a glass material having the following composition (mass%), the outer diameter is about 65 mm (2.5 inches), the inner diameter (diameter of the circular hole) is about 20 mm, and the plate thickness is 1 mm. A ring-shaped aluminosilicate glass substrate was prepared.

(Composition of glass material)
・ SiO ₂ : 50 to 70%
· _Al 2 _O 3: 0.1~20%
・ B ₂ O ₃ : 0 to 5%
_However, a _{SiO 2 + Al 2 O 3 +} B 2 O 3 = 60~85%, _also a _{2 O = 0.1~20% Li 2 O} + Na 2 O + K, also a MgO + CaO + BaO + SrO + ZnO = 2~20%.

  In the final cleaning step, as shown in Table 1, in Example 1, the flow direction of the cleaning liquid was set to two directions (up and down), and the flow of the cleaning liquid was changed in the order of jet flow and flowing. The direction is set to two directions (left and right laminar flows are sequentially switched), and in Example 3, the flow direction of the cleaning liquid is four directions (up and down, left and right) (jet flow, entrainment, left laminar flow, and right layer) In Example 4, the flow direction of the cleaning liquid was set to one direction in the vertical direction and one direction in the left and right direction (the jet flow or the flowing flow and the left laminar flow or the right laminar flow were switched in order). . In Comparative Example 1, the flow direction of the cleaning liquid is only in one vertical direction (only jet or flowing), and in Example 2, the flow direction of the cleaning liquid is only in one horizontal direction (only the left laminar flow or right laminar flow). ).

  In Examples 1 to 4 and Comparative Examples 1 and 2, the cleaning carrier, the number of glass substrates accommodated in the cleaning carrier, the size of the cleaning tank, the type of cleaning liquid, the flow rate or flow rate of the cleaning liquid, and other cleaning conditions were all the same. .

<Evaluation of glass substrate for HDD>
[Presence of defects]
Whether or not there is a defect as illustrated in FIG. 4 at the outer peripheral edge of the obtained glass substrate is commercially available from Nihon Kikai Co., Ltd., using a defect visualization and appearance inspection device “Micro-MAX” And inspected. The number of samples was 100 in each of Examples 1 to 4 and Comparative Examples 1 and 2. The results are shown in Table 1.

<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.

<Evaluation of HDD magnetic recording media>
[Read / write test]
The obtained magnetic recording medium was subjected to a read / write test with a magnetic head equipped with a DFH mechanism, and the number of error occurrences was recorded. The number of samples was 50 in each of Examples 1 to 4 and Comparative Examples 1 and 2. The results are shown in Table 1.

<Consideration of results>
Compared with Comparative Examples 1 and 2 in which the cleaning liquid was allowed to flow only in one direction in the cleaning tank, Examples 1 to 4 in which the cleaning liquid was switched in a plurality of directions in the cleaning tank were used for the number of defects in the glass substrate and the magnetic recording medium. The number of read / write errors was excellent in the evaluation results.

  Among Examples 1 to 4, Example 3 in which the cleaning liquid was switched in the cleaning tank in four directions, up and down, left and right, particularly had zero glass substrate defects.

  This application is based on Japanese Patent Application No. 2011-146230 filed on June 30, 2011, the contents of which are included in the present application.

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized as gaining. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not limited to the scope of the claims. To be construed as inclusive.

  The present invention has wide industrial applicability in the technical fields of a method for manufacturing a glass substrate for HDD, a glass substrate for HDD, and a magnetic recording medium for HDD.

Claims (4)

A method for manufacturing a glass substrate for HDD comprising a cleaning step of cleaning a glass substrate with a cleaning liquid,
In the cleaning process, the glass substrate is held at three points on both side ends and the lower end with a holding rod, and the holding portion held by the holding rod is separated by 90 ° with respect to the center of the glass substrate, the cleaning fluid in a direction parallel to the main surface of the glass substrate to the glass substrate, two directions opposed to a direction parallel to any one of the connecting direction of the center and the holding portion of the glass substrate A method of manufacturing a glass substrate for HDD, wherein the substrate is washed by flowing in a plurality of mutually different directions in order. Method of manufacturing a glass substrate for an HDD according to claim 1, characterized in that flowing the cleaning liquid in the vertical and lateral directions with respect to the main surface of the glass substrate. The process for producing a glass substrate for HDD of claim 2, wherein the flowing the washing liquid in two directions facing each other in two directions and laterally opposed vertical with respect to the main surface of the glass substrate. Wherein in the washing step, after washing by passing the washing solution, the glass substrate was dried remain in that state, in all of the holding portion of the glass substrate, the said glass substrate and said holding rod is always in contact The method for producing a glass substrate for HDD according to any one of claims 1 to 3 .

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