JP5177328B2 - Method for manufacturing glass substrate for magnetic information recording medium - Google Patents

Description

  The present invention relates to a method for producing a glass substrate for a magnetic information recording medium.

  Among information recording media having a recording layer for recording information using properties such as magnetism, light, and magnetomagnetism, there is a magnetic disk as a representative one. As a substrate for this magnetic disk, an aluminum alloy substrate or glass substrate plated with nickel phosphorus is known. However, since the surface is hard and defects are not easily generated, a glass substrate is often used particularly in notebook computers. It has become like this. The magnetic disk substrate is mounted on a hard disk drive, and the magnetic head is levitated at a constant height relative to the substrate surface while rotating the disk at a high speed to record and reproduce magnetic information. For this purpose, it is necessary to further reduce the flying height of the magnetic head. In this case, if waviness or micro waviness is present on the magnetic disk, the magnetic head will become unstable and the head and the disk will collide. In other words, a phenomenon called head crash occurs and the hard disk may become unusable. Even when the head does not crash, the flying stability of the head is affected, so that the glide characteristics (an index of how stably the head floats on the magnetic disk) may be deteriorated.

  For example, Patent Document 1 discloses a technique for stabilizing the glide characteristics by suppressing the smoothness of the surface of the glass substrate within a specified value.

  However, when a glass substrate manufactured by this method is mounted on a hard disk, the glide characteristics deteriorate, and heat is generated due to contact between the recording / reproducing element part of the head and the magnetic disk, so that recording / reproduction is temporarily performed. There was a phenomenon called thermal aspirity that made it impossible.

  In particular, in recent years, the above phenomenon occurs due to minute surface defects, surface irregularities, waviness, etc., which have not been a problem in the past, in a hard disk in which the distance between the head recording / reproducing element having the DFH mechanism and the disk surface is about 2 nm or less The trend is becoming a habit. Furthermore, when the machining allowance of the glass substrate is reduced, the tendency for the phenomenon to occur appears more remarkably.

  Here, the DFH mechanism is a so-called ABS (Air Bearing Surface) by bringing only a head element that performs a recording / reproducing operation in a magnetic head close to the information recording medium when reading / writing information on the information recording medium. ) And the information recording medium, a dynamic flying height control technology (Dynamic Flying Height control technology, DFH control technology).

JP 2009-76167 A

  The object of the present invention has been made in view of the above prior art, and the problem to be solved is that of a glass substrate for a magnetic information recording medium with less surface waviness of the glass base plate and less waviness difference between the front and back surfaces. It is to provide a manufacturing method.

  That is, the method for producing a glass substrate for a magnetic information recording medium according to the present invention comprises a lapping step of grinding the surface of a glass base plate using an upper and lower surface plate in which fixed abrasive grains containing diamond particles are arranged on the grinding surface. A method of manufacturing a glass substrate for a magnetic information recording medium provided, wherein in the lapping step, a surface with a large swell is disposed on the upper surface plate side and a surface with a small swell is disposed on the lower surface plate side. It is characterized by.

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

It is a top view which shows the glass substrate for magnetic information recording media manufactured by the manufacturing method of the glass substrate for magnetic information recording media concerning this embodiment. It is the schematic which shows the process of the direct press method in the lapping process which concerns on this embodiment. It is a schematic sectional drawing which shows the process of the float method in the lapping process which concerns on this embodiment. It is a schematic sectional drawing which shows an example of the grinding device used at the lapping process in the manufacturing method of the glass substrate for magnetic information recording media concerning this embodiment. 1 is a partial cross-sectional perspective view showing a magnetic disk as an example of a magnetic recording medium using a glass substrate for magnetic information recording medium manufactured by the method for manufacturing a glass substrate for magnetic information recording medium according to the present embodiment.

  The method for manufacturing a glass substrate for a magnetic information recording medium according to the present embodiment includes a lapping step of grinding the surface of the glass base plate using an upper and lower surface plate in which fixed abrasive grains including diamond particles are arranged on the grinding surface. A method for producing a glass substrate for a magnetic information recording medium, wherein in the lapping step, a surface having a large undulation is disposed on the upper surface plate side and a surface having a small undulation surface is disposed on the lower surface plate side. Features.

  Moreover, the manufacturing method of the glass substrate for magnetic information recording media which concerns on this embodiment will not be specifically limited if the said lapping process is provided. Specifically, the glass material manufactured by the direct press method or the float method is arranged on the upper surface plate of the grinding machine with the large surface of the glass material being aligned, while the surface of the glass material with the small surface of the glass is disposed on the lower surface plate. Except for grinding the substrate, there is no particular limitation, and any conventional manufacturing method may be used.

  Examples of the method for producing a glass substrate for a magnetic information recording medium include a disk processing step, a lapping step, a rough polishing step (primary polishing step), a cleaning step, a chemical strengthening step, a precision polishing step (secondary polishing step), and Examples include a method including a final cleaning step. The steps may be performed in this order, or the order of the chemical strengthening step and the precision polishing step (secondary polishing step) may be switched. Furthermore, a method including steps other than these may be used. For example, an end surface polishing step may be performed between the lapping step and the rough polishing step (primary polishing step).

  Here, the disk processing step in the manufacturing method of the present invention will be described in detail.

<Disk processing process>
In the disk processing step, a through-hole 10a is formed in the center portion of a glass base plate formed from a glass material having a predetermined composition so that the inner periphery and the outer periphery are concentric circles as shown in FIG. This is a process of processing into a disk-shaped glass base plate 10. Specifically, processing is performed using a direct press method, a float method, or the like.

(Direct press method)
FIG. 2 is a schematic view showing a processing step of the glass base plate by the direct press method.

  FIG. 2A shows a lower mold 3 and an upper mold 4 constituting the mold. The upper die 4 is in contact with the lower die 3 so as to surround the molding surface when the mold is clamped, and is provided with a stopper for regulating the interval between the molding surfaces. FIG. 2B shows a casting process, and the molten glass flow 6 flowing out from the outflow pipe 5 is supplied to the center of the lower mold forming surface. In addition, as shown to Fig.2 (a) etc., the upper surface in which the shaping | molding surface of the lower mold | type 3 is formed is flat (except the part which shape | molds the thick part of a glass blank). In the next cutting step in FIG. 2C, the molten glass is cut with the cutting blade 7 to obtain the gob 2 on the lower mold surface. Subsequently, in FIG. 2 (d), the gob is pressed by the upper die 4 and the lower die 3, but the interval between the upper and lower die forming surfaces is regulated by the stopper at the time of clamping. The gob 2 is pressurized by the upper and lower molds, and is spread out in the cavity formed by the upper and lower molds, and is molded into the glass base plate 10 that is a press-formed product. The peripheral edge of the molded product does not contact either the upper mold 4 or the lower mold 3 and remains on the glass base plate 10 as a free surface. After press molding, the upper die 4 is separated from the glass base plate 10 on the lower die 3 and retracts upward. The outer diameter of the press-formed product 1 is measured using optical means by a non-contact measurement method, for example, when the molded product is released from the upper die 4 and is on the lower die 3. After the outer diameter measurement, as shown in FIG. 2 (e), after the glass base plate 10 is cooled to a temperature that does not deform even when a force for taking out is applied, a step of taking out the glass base plate 10 from the lower mold 3 is performed. .

  The surface roughness Ra of the glass base plate taken out as described above is preferably 10 μm or less and Rmax is 50 μm or less. If the surface roughness Ra or the maximum height roughness Rz of the glass base plate after the cutting process is too high, grinding damage is large, and if it is too low, the grinding process cannot be performed.

  Further, in the glass base plate taken out as described above, the surface undulation of the surface that comes into contact with the mold first, that is, the surface that comes into contact with the lower mold, is larger than the surface that comes into contact with the mold later, that is, the surface that comes into contact with the upper mold. I know that. This is because the coefficient of thermal expansion of the glass is different between the surface that comes into contact with the mold first and the surface that comes into contact with the mold later, so that the stress balance is lost and different undulations occur on each surface. That is, the ratio of the surface undulation Wa1 of the surface with a large undulation to the surface undulation Wa2 of the surface with a small undulation is 1: 1.5 to 1: 2.5.

(Float method)
FIG. 3 is a cross-sectional view showing a processing step by the float method.

  The float process step includes a cutting step in which a cut line is made on one side of a glass material formed in a plate shape on a molten metal and cut along the cut line. In the cutting step, after forming a cut line on the surface of the glass base plate that is in contact with the molten metal of the glass material, the cutting line is advanced in the thickness direction of the glass base plate to form a disk-shaped glass base plate. To cut out.

  FIG. 3A is a cross-sectional view of the plate-like glass material 1.

  As the glass material, a plate-shaped glass material manufactured by a float process is used. The float method is, for example, a method in which a molten liquid obtained by melting a glass material is poured onto molten tin and solidified as it is. In the obtained glass base plate, one surface is a free surface of glass (hereinafter referred to as a free surface) and the other surface (hereinafter referred to as a contact surface) is an interface between glass and tin. High smoothness. And as the thickness, a 0.95 mm thing is mentioned, for example. In addition, the surface roughness, for example Ra, of a glass base plate or a glass substrate can be measured using a general surface roughness measuring machine.

  For this reason, the glass material has a surface in contact with the molten metal and the other surface. In the case of the glass material 1 shown in FIG. 3A, the upper surface is the contact surface 1A, and the lower surface is the free surface 1B.

  A cut line is formed on the contact surface 1A of the glass material 1 to draw a curve that forms a substantially peripheral edge of a region to be a glass substrate for a magnetic disk. In the present embodiment, as shown in FIG. 3 (b), circular cutting lines 8 and 9 are formed on the contact surface 1A of the glass material 1 by the glass cutter 15 to draw the disc-shaped outer peripheral side and inner peripheral side, respectively. To do.

  In this case, the outer peripheral side and inner peripheral cut lines 8 and 9 are formed obliquely with respect to the thickness direction of the glass plate. Further, in the present embodiment, the cut lines 8 and 9 are formed obliquely outward from the contact surface 1A of the glass material 1 toward the free surface 1B, and when viewed in the cross-sectional view of FIG. The incisors 8 and 8 and the incisors 9 and 9 are formed in a C-shape. Further, in the present embodiment, the cut lines 8 and 9 are formed obliquely outward from the contact surface 1A of the glass material 1 toward the free surface 1B, but the present invention is not limited thereto, and for example, the contact surface 1A of the glass material 1 As shown in FIG. 3 (b), the left and right incisors 8 and 8 and the incisors 9 and 9 are formed in an inverted C shape. It is also possible to advance the cutting line so that the inner part surrounded by the cutting line is extracted upward.

  Next, as shown in FIG.3 (c), the said cut lines 8 and 9 formed in the contact surface 1A of the glass raw material 1 are advanced toward the free surface 1B side. Thereby, the inner region 10 a surrounded by the cut line 8 is separated from the glass material 1. The inner portion 10b surrounded by the cut line 9 is separated from the region 10a surrounded by the cut line 8.

  As means for advancing the cut lines 8 and 9 formed on the contact surface 1A of the glass material 1 in this way toward the free surface 1B side, means for causing a difference in thermal expansion in the glass material 1, for example, the glass material 1 A method of heating one side is preferred. By heating the glass material 1, a difference in thermal expansion occurs in the thickness direction of the glass material 1, and the glass material can be easily cut into a target disk shape.

  Subsequently, as shown in FIG. 3 (d), the inner regions 10a and 10b surrounded by the cut line 8 are pushed downward, and further, the region 10b surrounded by the cut line 9 is pushed out, so that a circle is formed at the center. A disk-shaped glass base plate 10 having holes is obtained.

  Moreover, it is preferable that the surface roughness Ra of the glass base plate after the cutting step is 5 nm to 50 nm and the maximum height roughness Rz is 20 nm to 100 nm. If the surface roughness Ra or the maximum height roughness Rz of the glass base plate after the cutting process is too high, grinding damage is large, and if it is too low, the grinding process cannot be performed.

  Moreover, in the glass base plate after the said cutting process, it turns out that the surface waviness of a free surface is large compared with a molten metal contact surface. This is thought to be because, in the float process, the occurrence of waviness can be suppressed because the interface in contact with the molten metal is more stable than the interface with air. That is, the ratio of the surface undulation Wa1 of the surface with a large undulation to the surface undulation Wa2 of the surface with a small undulation is 1: 1.2 to 1: 3.0. The free surface waviness Wa is 1 to 5 nm, and the molten metal contact surface waviness Wa is 0.6 to 3 nm.

  Further, the disk processing step of the present invention may include a step of polishing the corner (end surface) of each cut line after the cutting step. By this end surface polishing step, cracks on the glass substrate caused by the cut lines can be reduced.

  In this disk processing step, for example, the outer diameter r1 is 2.5 inches (about 64 mm), 1.8 inches (about 46 mm), 1 inch (about 25 mm), 0.8 inches (about 20 mm), etc., and the thickness is It is processed into a disk-shaped glass base plate having a thickness obtained by adding about 0.3 mm to the thickness of the finally produced glass substrate. If the thickness is exceeded, the machining allowance increases and the production efficiency deteriorates. Since the thickness of the finally manufactured glass substrate is determined, the thickness to be processed in the disk processing step is determined by calculating backward from the thickness.

<Wrapping process>
The lapping step is a step of processing the glass base plate to a predetermined plate thickness. Specifically, the process etc. which grind | polish (lapping) the both surfaces of a glass base plate are mentioned. By processing in this way, the parallelism, flatness and thickness of the glass base plate can be adjusted, and a desired surface undulation can be obtained.

  Surface waviness is a three-dimensional surface shape formed on the surface of a glass material, and can be a surface shape configured by selecting a wavelength band shape having a shape wavelength of 0.1 mm to 10 mm. . The surface waviness can be grasped by observing a predetermined region of the glass material with a microscope or the like.

  As an apparatus for observing surface waviness, Optiflat manufactured by Phase Shift Technology can be preferably used.

  In the present invention, the average height of the surface waviness is represented by Wa. The average height (Wa) of the surface waviness represents the arithmetic average roughness of the surface waviness shape. In the present embodiment, the maximum height of surface waviness may be referred to as PV. The maximum surface undulation height (PV) is the average surface of the surface undulation shape, the absolute value of the highest peak height for this average surface, and the lowest valley depth for this average surface. This is the sum of the absolute value of the height.

  The grinding apparatus used in the lapping process is not particularly limited as long as it is a grinding apparatus used for manufacturing a glass substrate. Specifically, there is a grinding apparatus 11 as shown in FIG. FIG. 4 is a schematic cross-sectional view showing an example of a grinding apparatus used in the lapping step in the method for manufacturing a glass substrate for magnetic information recording media according to the embodiment of the present invention.

  A grinding apparatus 11 as shown in FIG. 4 is an apparatus capable of simultaneous grinding on both sides. The grinding apparatus 11 includes an apparatus main body 11a and a coolant supply unit 11b that supplies coolant, which is a coolant, to the apparatus main body 11a.

  The apparatus main body 11a includes a disk-shaped upper surface plate 12 and a disk-shaped lower surface plate 13, and they are arranged vertically spaced apart so that they are parallel to each other. Then, the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 rotate in directions opposite to each other.

  In order to grind both the front and back surfaces of the glass base plate 10 on the opposing surfaces of the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13, fixed abrasive grains 14 containing diamond particles are provided. Yes. The fixed abrasive grains 14 containing diamond particles used in the lapping step may be in the form of pellets obtained by bonding a plurality of diamond particles with a resin, or by bonding or electrodeposition using a resin. You may use the sheet-like thing which adhered the diamond particle to the board | substrate 13 planarly.

  A carrier may be sandwiched between the fixed abrasive 8 and the surface plates 12 and 13. The carrier revolves in the same direction as the lower surface plate 13 with respect to the center of rotation of the surface plates 12 and 13 while rotating while holding the plurality of glass base plates 10. The disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 can be operated by separate driving. In the grinding apparatus 11 operating in this manner, the coolant 17 is supplied between the fixed abrasive grains 14 and the glass base plate 10 and between the fixed abrasive grains 14 and the glass base plate 10, whereby the glass base material is supplied. The plate 10 can be ground.

  The coolant supply unit 11 b includes a container in which a coolant 17 is placed and a pon 16. That is, the coolant 17 in the container is supplied into the surface plates 12 and 13 by the pump 16 and circulated. The facets from which the ground surfaces of the upper and lower surface plates 12 and 13 are cut off, which are generated during the circulation, are removed from the respective ground surfaces. Specifically, when the coolant 17 is circulated, the coolant is filtered with a filter provided in the lower surface plate 13, and the facet is retained in the filter.

  More specifically, the lapping process should be a process in which the entire surface of the glass base plate has a substantially uniform surface undulation. However, as a result of intensive studies by the present inventors, it has been found that a general glass base plate grinding machine having upper and lower surface plates differs in grinding ability between the upper and lower surface plates. That is, since the execution pressure varies depending on factors due to gravity, the grinding performance of the upper surface plate 12 is slightly superior to the grinding performance of the lower surface plate 13.

  Specifically, the ratio between the processing rate of the upper surface plate and the processing rate of the lower surface plate is 1: 0.9 to 1: 0.95.

  Specifically, the ratio between the processing rate of the upper surface plate and the processing rate of the lower surface plate is preferably 1: 0.8 to 1: 0.98, more preferably 1: 0.9 to 1: 0. .95.

  The processing rate is a value obtained by dividing the machining allowance by the processing time. Deviating from the processing rate ratio may result in a glass substrate having a poor processing balance.

  Moreover, the present inventors discovered that the glass base plate after the above-mentioned disk processing process has a surface with a large surface waviness and a surface with a small surface waviness. That is, in the direct press method, since the thermal expansion coefficient of the glass is different between the surface that comes into contact with the mold first and the surface that comes into contact with the mold later, the stress balance is lost, and different undulations occur on each surface. Because. Moreover, in the float process, since the interface in contact with the molten metal is more stable than the interface with air, the occurrence of undulation can be suppressed. From the above, it was found that the glass base plate that has undergone the normal disk processing step has undulations on the front and back surfaces.

  Therefore, like the lapping process in the conventional method for manufacturing a glass substrate for magnetic information recording media, a plurality of glass base plates produced by the disk machining process are randomly arranged regardless of the front and back, and the execution pressure of the grinding machine is different as it is. If lapping is performed on the upper and lower surface plates, a large number of glass substrates having different surface waviness will be generated in each glass base plate. Therefore, by grinding only the surface with a large surface waviness with an upper surface plate having a high execution pressure, that is, a high processing rate, the undulations on the front and back surfaces are inevitably small even when a plurality of glass base plates are ground. A uniform glass substrate can be reliably manufactured. In the case of the upper platen, the effective pressure applied to the substrate is constant compared to the lower platen (therefore, the effective pressure is large), so that swell can be efficiently removed. This is because the grinding process is performed together with the grinding liquid, but the grinding liquid is concentrated on the lower surface plate side by gravity. Since the grinding fluid is constantly circulated and processing is performed while removing glass sludge (glass waste) with a filter, the sludge-removed grinding fluid always flows on the upper platen side, while sludge is on the lower platen side. It tends to accumulate and the processing rate deteriorates. As a result, there is a difference in processing between the upper and lower surfaces.

  As described above, in the glass base plate after the disk processing (before the lapping step), the value of the surface waviness is different between one surface and the other surface. The ratio of the surface waviness Wa1 of the surface with large waviness to the surface waviness Wa2 of the surface with small waviness is 1: 1.2 to 1: 5.

  Further, when the arithmetic average roughness Ra of the glass base plate is measured at a plurality of locations, the difference between the minimum value and the maximum value of Ra obtained is preferably about 0.01 to 0.4 μm.

  When the lapping process is performed, polishing performed in the rough polishing process described later can be performed efficiently. Further, the surface roughness Ra of the glass base plate used in the polishing process performed by the lapping process is preferably 0.5 μm or less, and more preferably 0.3 μm or less. When the surface roughness Ra is larger than 0.5 μm, a large undulation may remain even after the subsequent polishing step. Further, the maximum height roughness Rz is preferably 3 μm or less. This is to facilitate the polishing process.

  Moreover, it is preferable that the removal allowance of the glass base plate in the said lapping process is 50 micrometers or more and 200 micrometers or less. In some cases, the advance allowance cannot sufficiently remove the undulation from 50 μm. When the advance allowance is larger than 200 μm, the processing time becomes long, and the efficiency of the manufacturing method is deteriorated as a result.

  Furthermore, in the lapping step of the present invention, the number of glass base plates to be ground must be plural, specifically 80 or more, and more preferably 100 or more. When the number of glass substrates to be ground is less than 80, undulation removal cannot be performed efficiently. This is because a further change in internal stress occurs due to a further worsening of the upper and lower processing balance, resulting in a deterioration in flatness. When the flatness deteriorates, the processing rate is affected and processing cannot be performed.

  Further, this lapping step may be performed once or twice or more. For example, when it is performed twice, the parallelism, flatness and thickness of the glass base plate are preliminarily adjusted in the first lapping process (first lapping process), and glass is used in the second lapping process (second lapping process). It becomes possible to finely adjust the parallelism, flatness and thickness of the base plate.

<Rough polishing process>
The rough polishing step (primary polishing step) is intended to remove the scratches and distortions remaining in the lapping step described above by polishing the main surface of the glass base plate with a polishing slurry containing cerium oxide. The following polishing method is used.

  The polishing apparatus used in the rough polishing step is not particularly limited as long as it is a polishing apparatus used for manufacturing a glass substrate.

  The surface to be polished in the rough polishing step is a main surface and / or an end surface. The main end surface is a surface parallel to the surface direction of the glass base plate. The end surface is a surface composed of an inner peripheral end surface and an outer peripheral end surface. Moreover, an inner peripheral end surface is a surface which has an inclination with respect to the surface of an inner peripheral side perpendicular | vertical to the surface direction of a glass base plate, and the surface direction of a glass base plate. Moreover, an outer peripheral end surface is a surface which has an inclination with respect to the surface direction of the outer peripheral side perpendicular | vertical to the surface direction of a glass base plate, and the surface direction of a glass base plate.

  Next, the abrasive | polishing agent used in the grinding | polishing process of this invention contains a cerium oxide as a main component. The content of cerium oxide is preferably 3 to 15% by mass with respect to the total amount of the polishing slurry. By setting it as such a range, the glass substrate for magnetic information recording media with higher smoothness can be manufactured.

  The polishing slurry is a liquid in which the abrasive, dispersant, etc. are dispersed in water, that is, a slurry liquid. In the state where the abrasive is dispersed in water, even if the alkaline earth metal is contained in the water, the alkaline earth metal is dissolved, so that it hardly adheres to the surface of the glass base plate and is included in the abrasive. Alkaline earth metal tends to adhere to the surface of the glass base plate. For this reason, the use of an abrasive containing a small amount of alkaline earth metal can sufficiently suppress the adhesion of alkaline earth metal to the polished glass base plate.

<Chemical strengthening process>
If the chemical strengthening process in the manufacturing method of this invention is a well-known method, it will not specifically limit. Specifically, for example, a step of immersing a glass base plate in a chemical strengthening treatment liquid and the like can be mentioned. By doing so, a chemical strengthening layer can be formed in the surface of a glass base plate, for example, a 5 micrometer area | region from the glass base plate surface. And by forming a chemical strengthening layer, impact resistance, vibration resistance, heat resistance, etc. can be improved.

  More specifically, in the chemical strengthening step, by immersing the glass base plate in a heated chemical strengthening treatment liquid, alkali metal ions such as lithium ions and sodium ions contained in the glass base plate are potassium having a larger ion radius. It is carried out by an ion exchange method for substituting alkali metal ions such as ions. Due to the strain caused by the difference in ion radius, compressive stress is generated in the ion-exchanged region, and the surface of the glass base plate is strengthened.

In this embodiment, it is thought that a strengthening layer is suitably formed by this chemical strengthening process by using the glass composition as described above as a glass base plate that is a raw material of the glass substrate. Specifically, among Li ₂ O, Na ₂ O, and K ₂ O, which are alkali components of the glass base plate, the content of Na ₂ O is large, and the sodium ions of Na ₂ O are chemically strengthened. This is thought to be because it is easily exchanged for potassium ions contained in. Further, since the polishing agent used in the polishing step before the chemical strengthening step, here the rough polishing step, is an abrasive having the above composition, the alkaline earth metal adhering to the surface of the glass base plate is used. The amount is small and the chemical strengthening is considered to be uniform. Therefore, a glass substrate excellent in impact resistance can be produced by performing a precision polishing step on a glass base plate that has been subjected to suitable chemical strengthening as in this embodiment.

  The chemical strengthening treatment liquid is not particularly limited as long as it is a chemical strengthening treatment liquid used in the chemical strengthening step in the method for producing a glass substrate for a magnetic information recording medium. Specifically, for example, a melt containing potassium ions, a melt containing potassium ions and sodium ions, and the like can be given.

  Examples of these melts include melts obtained by melting potassium nitrate, sodium nitrate, potassium carbonate, sodium carbonate, and the like. Among these, it is preferable to use a combination of a melt obtained by melting potassium nitrate and a melt obtained by melting sodium nitrate from the viewpoint of low melting point and preventing deformation of the glass base plate. At that time, a melt obtained by melting potassium nitrate and a melt obtained by melting sodium nitrate are preferably mixed in approximately the same amount.

<Precision polishing process (secondary polishing process)>
The precision polishing process is a mirror polishing process that finishes a smooth mirror surface having a surface roughness (Rmax) of about 6 nm or less, for example, while maintaining the flat and smooth main surface obtained in the rough polishing process. The precision polishing step is performed, for example, by using a polishing apparatus similar to that used in the rough polishing step and replacing the polishing pad from a hard polishing pad to a soft polishing pad. The surface to be polished in the precision polishing step is the main surface, similar to the surface to be polished in the rough polishing step.

  Further, as the abrasive used in the precision polishing step, an abrasive that causes fewer scratches even if the abrasiveness is lower than the abrasive used in the rough polishing step is used. Specifically, for example, a polishing agent containing silica-based abrasive grains (colloidal silica) having a particle diameter lower than that of the polishing agent used in the rough polishing step. The average particle diameter of the silica-based abrasive is preferably about 20 nm. And the polishing slurry liquid containing the said abrasive | polishing agent is supplied to a glass base plate, a polishing pad and a glass base plate are slid relatively, and the surface of a glass base plate is mirror-polished.

<Glass base plate composition>
First, each component of a glass base plate is further explained in full detail.

_{First, SiO 2, Al 2 O 3} , and _B 2 _{O 3} is a framework component of the glass workpiece. Li ₂ O, Na ₂ O, and K ₂ O are alkali components of the glass base plate. MgO, CaO, BaO, SrO, and ZnO are alkaline earth components of the glass base plate.

  Next, the skeleton component of the glass base plate will be described.

As the skeleton component of the glass workpiece to be used in the present embodiment, as described above, SiO ₂ is 58 to 70 wt%, _Al 2 _{O 3} is 12 to 18 _wt%, B 2 _{O 3} is 0-3 wt% (However, 0 is included), and the total thereof, that is, the total of SiO ₂ , Al ₂ O _3, and B ₂ O ₃ is 72 to 85 mass%.

SiO ₂ is a component that forms a glass skeleton (matrix). If the content of SiO ₂ is too small, the glass structure becomes unstable and the chemical durability is deteriorated, and the viscosity characteristics at the time of melting are deteriorated, which may impair the moldability. If the content of SiO ₂ is too large, with the productivity becomes poor meltability decreases, sufficient rigidity may become impossible to obtain. Therefore, the content of SiO ₂ is preferably 58 to 70% by mass.

Al ₂ O _{3 is} also a component that forms a skeleton of glass, and contributes to improvement of durability and strength and surface hardness of glass. If the content of Al ₂ O ₃ is too small, the durability and strength may not be sufficient as a glass substrate for a magnetic information recording medium. Further, when the content of Al ₂ O ₃ is too large, intensified devitrification tendency of the glass, it may stable glass formation is difficult. Therefore, the content of Al ₂ O ₃ is preferably 12 to 18% by mass.

B ₂ O ₃ has the effect of improving the chemical durability by improving the meltability and improving the productivity and stabilizing the glass structure by entering the glass skeleton. However, B ₂ O ₃ tends to volatilize when melted, and the glass component ratio tends to become unstable. Further, since the strength is lowered, the hardness is lowered, the glass substrate is easily damaged, the fracture toughness value is reduced, and the substrate tends to be damaged. For these reasons, the content of B ₂ O ₃ is preferably 3% by mass or less. _Further, it is possible to a composition that does not contain B 2 _{O 3.} In the _above, the 0 wt% in the content of 0-3 wt% B 2 _{O 3,} which means that may include aspects that do not contain B 2 _{O 3.} In addition, the notation of “0 mass%” in the glass composition of the present application document is in agreement with this, and means that it may include an embodiment not containing the component (hereinafter, the same notation is agreed).

Then, the total amount of SiO ₂ and _Al 2 _{O 3} and _B 2 _{O 3} w (FMO) is preferably 70 to 85 wt%. This is to stabilize the glass structure. If the total amount is too small, the glass structure tends to become unstable. Moreover, when there is too much this total amount, the viscosity characteristic at the time of a fusion | melting will deteriorate, and there exists a tendency for productivity to fall.

  Next, the alkali component of the glass base plate will be described.

As an alkaline component of the glass base plate used in the present embodiment, as described above, Li ₂ O is 1 to 8% by mass, Na ₂ O is ₂ to 13% by mass, and K ₂ O is 0.2 to ₂ % by mass. And the sum thereof, that is, the sum of Li ₂ O, Na ₂ O and K ₂ O is 3.2 to 23% by mass.

Li ₂ O has a unique property among alkali metal elements, and has a function of improving the solubility of the glass, while greatly improving the Young's modulus by improving the ion filling rate in the glass structure. Has an effect. Li 2 _O content is too small, there is a tendency that it is impossible to exhibit sufficient effect on improvement of the improvement and the Young's modulus of solubility. Further, the content of Li 2 _O, is too large, as described above, there are cases where the surface of the recording layer of the information recording medium serving as a trigger of a very small and thin reaction precipitates. Therefore, the content of Li ₂ O, is preferably 1 to 8 wt%.

Na 2 _O has an effect of lowering the melting temperature of the glass, the effect of increasing the coefficient of linear expansion. Further, it is considered to be a component that greatly affects the effect of chemical strengthening in the chemical strengthening process. That is, when the content of Na ₂ O is too small, not only does the melting temperature tend not to be sufficiently lowered, but the strength cannot be sufficiently increased by the chemical strengthening step. On the other hand, if the content of Na ₂ O is too large, the amount of elution increases and the recording layer may be adversely affected. Therefore, the content of Na ₂ O is preferably _{2 to} 13% by mass. In addition, this content is more than the content in a general glass substrate.

K 2 _O is, have the effect of lowering the melting temperature of the glass, the effect of increasing the coefficient of linear expansion. When the content of K ₂ O is too small, there is a tendency that the melting temperature cannot be lowered sufficiently. On the other hand, when the content of K ₂ O is too large, not only does the amount of elution increase and the recording layer may be adversely affected, but there is a tendency that the strength cannot be sufficiently increased by the chemical strengthening step. This is thought to be due to the fact that the chemical strengthening process replaces potassium ions instead of sodium ions of Na ₂ O to form a strengthened layer and inhibits this exchange. Therefore, the content of K ₂ O is preferably 0.2 to 2% by mass.

Then, Li ₂ O, Na ₂ O and _{K 2} O to the total amount w of _(R 2 O) is preferably a 3.2 to 23 wt%. If the total amount is too small, there is a tendency that the melting temperature cannot be lowered sufficiently. If the total amount is small, the content of Na ₂ O is also small, and chemical strengthening is sufficiently exerted. It tends to be difficult. On the other hand, if the total amount is too large, the amount of elution increases and the recording layer may be adversely affected.

  In addition, MgO, CaO, BaO, SrO, and ZnO, which are alkaline earth components of the glass base plate, have the effect of improving the meltability as well as increasing the thermal expansion coefficient and rigidity. The total amount w (MgO + CaO + BaO + SrO + ZnO) of MgO, CaO, BaO, SrO and ZnO is preferably 1 to 10% by mass. If the total amount is too small, the effect of improving rigidity and improving meltability tends to be insufficient. Moreover, when there is too much this total amount, there exists a tendency for a chemical structure to fall while glass structure becomes unstable and melt productivity falls.

Moreover, as a glass base plate, you may contain components other than the above. Specifically, for example, ZrO ₂ or cerium oxide may be contained. Then, the content of ZrO _2, is preferably from 0 to 5 wt%. Moreover, as content of a cerium oxide, 0-2 mass% is preferable. In addition, cerium oxide has an effect which suppresses generation | occurrence | production of a fine unevenness | corrugation when grind | polishing a glass base plate using the abrasive | polishing agent containing a cerium oxide.

  And the magnetic recording medium using the glass substrate for magnetic information recording media manufactured by the manufacturing method of the glass substrate for magnetic information recording media concerning the above-mentioned embodiment is explained.

  FIG. 5 is a partial cross-sectional perspective view showing a magnetic disk as an example of a magnetic recording medium using the glass substrate for magnetic information recording medium manufactured by the method for manufacturing a glass substrate for magnetic information recording medium according to the present embodiment. is there. The magnetic disk D includes a magnetic film 102 formed on the main surface of a circular glass substrate 101 for a magnetic information recording medium. For the formation of the magnetic film 102, a known method is used. For example, a formation method (spin coating method) for forming a magnetic film 102 by spin-coating a thermosetting resin in which magnetic particles are dispersed on a glass substrate 101 for a magnetic information recording medium, or a glass substrate for a magnetic information recording medium Examples include a formation method (sputtering method) for forming the magnetic film 102 on the substrate 101 by sputtering, a formation method (electroless plating method) for forming the magnetic film 102 on the glass substrate 101 for magnetic information recording medium by electroless plating, and the like. It is done.

  The thickness of the magnetic film 102 is about 0.3 to 1.2 μm when the spin coating method is used, and is about 0.04 to 0.08 μm when the sputtering method is used. In some cases, the thickness is about 0.05 to 0.1 μm. From the viewpoint of thinning and densification, film formation by sputtering is preferable, and film formation by electroless plating is preferable.

  The magnetic material used for the magnetic film 102 can be any known material and is not particularly limited. The magnetic material is preferably, for example, a Co-based alloy based on Co having high crystal anisotropy in order to obtain a high coercive force, and Ni or Cr added for the purpose of adjusting the residual magnetic flux density. More specifically, CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, CoCrPtSiO, and the like whose main component is Co can be given.

The magnetic film 102 has a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.) divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) in order to reduce noise. May be. Magnetic material used for the magnetic layer 102, in addition to the magnetic material, ferrite or iron - may be a rare earth, also, Fe in a non-magnetic film made of _SiO 2, BN, etc., Co, FeCo, CoNiPt and the like A granular material having a structure in which the magnetic particles are dispersed may be used. In addition, for recording on the magnetic film 102, either an inner surface type or a vertical type recording format may be used.

  In order to improve the sliding of the magnetic head, the surface of the magnetic film 102 may be thinly coated with a lubricant. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

  Furthermore, an underlayer or a protective layer may be provided on the magnetic film 102 as necessary. The underlayer in the magnetic disk D is appropriately selected according to the magnetic film 102. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. For example, in the case of the magnetic film 102 containing Co as a main component, the material of the underlayer is preferably Cr alone or a Cr alloy from the viewpoint of improving magnetic characteristics.

  Further, the underlayer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. Examples of such an underlayer having a multilayer structure include multilayer underlayers such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, and NiAl / CrV. Examples of the protective layer that prevents wear and corrosion of the magnetic film 102 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 with the underlayer and the magnetic film 102 by an in-line sputtering apparatus. These protective layers may be a single layer, or may be a multi-layer structure composed of the same or different layers.

Note that another protective layer may be formed on the protective layer or instead of the protective layer. For example, instead of the protective layer, a SiO ₂ layer may be formed on the Cr layer. Such a SiO ₂ layer is formed by dispersing and applying colloidal silica fine particles in a tetraalkoxysilane diluted with an alcohol-based solvent on the Cr layer and further baking.

  In such a magnetic recording medium based on the glass substrate 101 for magnetic information recording medium according to this embodiment, the glass substrate 101 for magnetic information recording medium is formed with the above-described composition. It can be done with high reliability.

  In addition, although the case where the glass substrate 101 for magnetic information recording media in this embodiment was used for a magnetic recording medium was demonstrated above, it is not limited to this, The glass substrate for magnetic information recording media in this embodiment 101 can also be used for magneto-optical disks, optical disks, and the like.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

  First, a general glass substrate, an abrasive, and a polishing pad used for manufacturing a glass substrate for an information recording medium were prepared. The composition of the polishing agent and the polishing pad includes those contained in general polishing agents and polishing pads used in the production of a glass substrate for information recording media.

Example 1
Using a glass substrate, a glass substrate is prepared using a float method, and by a known method, a disk processing step, a lapping step, a rough polishing step (primary polishing step), a chemical strengthening step, a precision polishing step (secondary polishing step) ) And a final washing step.

  However, in the lapping step, the surface of the glass base plate with a score line was disposed on the upper surface plate side, and the surface without a score line was disposed on the lower surface plate side. Furthermore, the lapping process was ground so that the machining allowance was 150 μm.

  At this time, in the lapping process, processing was performed using a sheet-like diamond tile (concentration: 200, particle size: 2 μm) in which diamond particles were planarly bonded to the upper surface plate 12 and the lower surface plate 13. The surface roughness of the substrate after the lapping process was 0.21 μm. The surface roughness measuring machine was measured with a contact-type roughness measuring machine (manufactured by KLA tencol).

  Thereafter, the main surface roughness of the glass substrate after the rough polishing step, the precision polishing step, and the cleaning / drying step was 0.9 mm. By smoothing the roughness of the main surface to the limit, elution of ionic components from the surface portion can be prevented. The surface roughness Ra was measured with an atomic force microscope (AFM). Measurement was performed using AFM Dimension V manufactured by Veeco. A 10 μm × 10 μm scan line was performed at 256.

(Example 2)
In the lapping step, the same procedure as in Example 1 was performed except that the grinding allowance was 50 μm. The surface roughness Ra after the lapping process was 0.41 μm. Further, the finally manufactured substrate had a surface roughness Ra of 1.0 mm.

(Comparative Example 1)
In the lapping process, it is the same as that of Example 1 except that the glass base plate obtained by the disk processing process was randomly placed on the upper and lower surfaces and ground. The machining allowance in the lapping process was 100 μm. Further, the surface roughness Ra after the lapping step was 0.31 μm, and the surface roughness Ra of the final substrate was 1.1 mm.

(Swell evaluation test)
Surface waviness after precision polishing (after cleaning / drying process) of each substrate is a three-dimensional surface shape formed on the surface of a glass material, and a wavelength band shape having a shape wavelength of 0.1 mm to 10 mm. It can be set as the surface shape comprised by selecting. The surface waviness can be grasped by observing a predetermined region of the glass material with a microscope or the like.

As the predetermined area, an area of 1837 mm ² is selected in a donut-shaped observation range in which the radius of the inner circumference is 16 mm and the radius of the outer circumference is 29 mm.

  As an apparatus for observing surface waviness, Optiflat manufactured by Phase Shift Technology can be preferably used.

  In the present invention, the average height of the surface waviness is represented by Wa. The average height Wa of the surface waviness represents the arithmetic average roughness of the surface waviness shape.

  100 surface waviness Wa of each of the surface waviness (W1) and the surface waviness (W2) having a large surface waviness is measured, and the average value is shown. Moreover, the fluctuation of these undulations is shown by measuring the standard deviation (σ).

(Glide characteristic test)
After forming the glass substrate, it was confirmed whether or not the glide stably floated when mounted on a hard disk. In the glide characteristic test, the hard disk is heat-treated, the flying height between the inspection head (head slider) and the surface of the magnetic recording medium is set to 4 nm, and the signal resulting from the collision between the inspection head and the projection on the surface of the magnetic recording medium. Is output, it is determined that the magnetic recording medium is defective.

  100 substrates manufactured by each manufacturing method were evaluated. The evaluation criteria are as follows.

◎… Defect rate is less than 5% ○… 5% or more and less than 10%

  The results are shown in Table 1.

  As is clear from the results in Table 1, it was found that Comparative Example 1 in which a plurality of glass base plates used in the grinding process were arranged at random on the front and back sides and subjected to grinding had a large variation in waviness. Also, satisfactory results were not obtained with respect to glide characteristics. On the other hand, in Examples 1 and 2, the variation of the undulation was small, and good results were obtained for the glide characteristics.

  The present specification discloses various aspects of the technology as described above, and the main technologies are summarized below.

  The method for producing a glass substrate for a magnetic information recording medium according to the present invention includes a lapping step of grinding the surface of a glass base plate using an upper and lower surface plate in which fixed abrasive grains including diamond particles are arranged on a grinding surface. A method of manufacturing a glass substrate for a magnetic information recording medium, wherein in the lapping step, a surface with a large undulation is disposed on the upper surface plate side, and a surface with a small undulation is disposed on the lower surface plate side. And

  In the method for manufacturing a glass substrate for a magnetic information recording medium, it is preferable that 80 or more glass base plates are ground in the lapping step.

  In the method for manufacturing a glass substrate for a magnetic information recording medium, in the glass base plate before the lapping step, the ratio of the surface waviness Wa1 of the surface with a large waviness to the surface waviness Wa2 of the surface with a small waviness is 1: 1. 2 to 1: 3.0 is preferred.

  In the method for manufacturing a glass substrate for a magnetic information recording medium, in the lapping step, a ratio between a processing rate of the upper surface plate and a processing rate of the lower surface plate is 1: 0.9 to 1: 0.95. Preferably it is.

  In the method for manufacturing a glass substrate for a magnetic information recording medium, it is preferable that the glass substrate after the lapping step has a surface roughness Ra of 0.5 μm or less and a surface height roughness Rz of 3 μm or less.

  In the method for manufacturing a glass substrate for a magnetic information recording medium, it is preferable that the allowance for both surfaces of the glass base plate in the lapping step is 50 μm or more and 200 μm or less.

  This application is based on Japanese Patent Application No. 2010-291207 filed on Dec. 27, 2010, 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 that this is possible. 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 covered by the claims. To be construed as inclusive.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the glass substrate for magnetic information recording media with a small wave | undulation of the whole glass base plate surface and a small difference of the wave | undulation of front and back can be provided.

Claims (6)

A method for producing a glass substrate for a magnetic information recording medium comprising a lapping process for grinding the surface of a glass base plate using an upper and lower surface plate provided with fixed abrasive grains containing diamond particles on a grinding surface,
A method for producing a glass substrate for a magnetic information recording medium, wherein in the lapping step, a surface with a large waviness is disposed on the upper surface plate side and a surface with a small waviness is disposed on the lower surface plate side.   2. The method of manufacturing a glass substrate for a magnetic information recording medium according to claim 1, wherein in the lapping step, 80 or more glass base plates are ground.   In the glass base plate before the lapping step, the ratio of the surface waviness Wa1 of the surface with large waviness to the surface waviness Wa2 of the surface with small waviness is 1: 1.2 to 1: 3.0. Item 3. A method for producing a glass substrate for a magnetic information recording medium according to Item 1 or 2. In the lapping process, the ratio of the processing rate of the processing rate and the lower plate of the upper surface plate 1: 0.9 to 1: any one of claims 1 to 3, characterized in that 0.95 the method of manufacturing a magnetic recording medium glass substrate according to claim. 5. The magnetic information recording according to claim 1 , wherein the glass substrate after the lapping step has a surface roughness Ra of 0.5 μm or less and a surface height roughness Rz of 3 μm or less. A method for producing a glass substrate for a medium. The method for producing a glass substrate for a magnetic information recording medium according to any one of claims 1 to 5 , wherein an allowance for both surfaces of the glass base plate in the lapping step is 50 µm or more and 200 µm or less.

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