JP5327608B2 - Disc material polishing method and polishing apparatus - Google Patents

Description

The present invention relates to a disk material polishing method and a polishing apparatus .

  A glass substrate mounted on various magnetic recording devices and corresponding to a magnetoresistive head or a large magnetoresistive head or the like, that is, a substrate for a magnetic disk (for example, hard disk) is produced by, for example, the following steps Is done. First, a glass material is press-molded in a semi-molten state to form a disk-shaped plate material (melt press material), or a sheet-shaped material is cut into a specified size to obtain a square plate-shaped plate material. . Then, by making a circular hole in the central part of the disk-shaped plate material or by cutting out the central part and the outer peripheral part, a circular plate having a circular hole in the central part, that is, a donut-shaped glass disk material can be obtained. Next, chamfering (chamfer processing) is performed on the ridge corner portions of the peripheral portion such as the outer peripheral portion and the inner peripheral portion of the doughnut-shaped glass disk material. Through these steps, a donut-shaped glass disk material having a substantially predetermined dimension is obtained. Further, lapping is performed on the main surface of the donut-shaped glass disk material having a substantially predetermined dimension. Then, the glass disk material thus obtained is subjected to polishing including finish polishing so that the end surfaces (outer peripheral end surface and inner peripheral end surface) and the main surface are mirror surfaces. In this manner, a glass disk material as a glass substrate used for manufacturing a magnetic disk is obtained.

  In addition, examples of the magnetic disk substrate include an aluminum substrate and a ceramic substrate as a nonmagnetic substrate. However, these are all subjected to a polishing process including finish polishing so as to have a surface having a certain level of smoothness.

For example, Patent Document 1 discloses a manufacturing method that has been devised to obtain a substrate having a smooth surface free from protrusions due to residual abrasive or the like on the surface. According to the description relating to this method, in the final polishing process using the polishing liquid and the polishing pad to obtain such a substrate, the polishing agent concentration of the polishing liquid is gradually or stepwise reduced, and finally the polishing agent concentration Is made substantially zero. Specifically, first, polishing is performed using a polishing solution in which cerium oxide is dissolved in water to a concentration of 2% by weight under conditions of a polishing processing pressure of 30 to 100 g / cm ² , and then the polishing agent is added. Polishing is performed by shutting off the supply of the polishing liquid, and supplying only water as a polishing liquid.

  On the other hand, Patent Document 2 discloses that polishing is performed in two steps in order to obtain a high-smooth substrate necessary for a magnetic disk having a high recording density, particularly 50 Gbit / in 2 or more. . According to the description in Patent Document 2, polishing using a polishing liquid containing alumina abrasive grains having an average particle size of 0.05 to 0.5 μm and an oxidizing agent is performed, and thereafter, an average particle size of 0.005 to 0 is performed. A final polishing process using a polishing liquid containing 1 μm silica particles is performed.

JP 2000-53450 A JP 2005-63530 A

  A magnetic disk is generally used in an information processing apparatus such as a computer, but its usage environment is diverse. For example, magnetic disks are used in stationary type storage devices and mobile type storage devices. When a magnetic disk is used as a large-capacity hard disk in a stationary type storage device, the surface of a substrate used for manufacturing the magnetic disk is required to have a substantially smooth surface. On the other hand, when a magnetic disk is used in a small drive of a mobile type storage device, the diameter of the magnetic disk is small. It is required to form minute irregularities on the surface of the substrate to be formed.

  Thus, it is necessary to change the surface roughness of the magnetic disk substrate depending on the type of hard disk and medium. Therefore, conventionally, it has been necessary to appropriately change the size of the abrasive contained in the polishing polishing liquid in the process of producing the substrate disk material in accordance with the respective required surface roughness.

  In general, a polishing apparatus that can simultaneously polish both sides of a disk material, that is, a double-side polishing apparatus, is used for polishing in the process of manufacturing a disk material for a substrate. This double-side polishing apparatus includes a disk-shaped horizontal upper surface plate and a lower surface plate to which a polishing medium such as a polishing cloth is attached. Then, while holding and rotating the substrate disk material between both surface plates, polishing is performed while flowing a polishing liquid containing an abrasive such as free abrasive grains, such as alumina-based slurry, colloidal silica-based slurry, etc. A polishing medium is brought into contact with the surface of the target disc material, and the surface is polished (a mixture of an abrasive such as abrasive grains and a solvent is referred to as slurry).

  In such a polishing apparatus, the polishing liquid used for polishing the disk material is changed from a certain polishing liquid to the polishing agent contained in the polishing liquid according to the predetermined surface roughness required for the surface of the disk material. When replacing with a polishing liquid containing an abrasive having a different size from the above, it is necessary to replace the polishing medium. This is because it becomes difficult to make the surface roughness of the disk material a predetermined surface roughness when an abrasive having a characteristic different from that of the contained abrasive is mixed in the polishing liquid to be used. However, for example, the existence of such a work process complicates the polishing process of the disk material and can therefore be a cost obstacle.

  Accordingly, the present invention has been made in view of such a point, and an object thereof is to obtain a disk material having surfaces with different surface roughnesses by a simple method.

In order to achieve the above object, the present invention provides a polishing liquid containing an abrasive having a concentration set based on a required surface roughness for a disk material (a surface roughness of the surface required for the disk material). The disc material is polished using Preferably, according to the present invention, the first polishing is performed based on a correlation between a polishing agent concentration and a finished surface roughness , and a first polishing step of polishing the disk material using a polishing liquid containing a first concentration of polishing agent. The disk material polished in the first polishing step is polished by using a polishing liquid containing a second concentration of the second concentration lower than the first concentration and having a finished surface roughness larger than the finished surface roughness of the step. A second polishing step. However, the second concentration may be set based on the required surface roughness for the disk material. The first concentration may be set based on the required polishing rate for the disk material. However, the present invention allows a polishing method having one or a plurality of polishing steps other than the first polishing step and the second polishing step before, during, and after these two polishing steps. The second polishing step is preferably a final polishing step, that is, a final polishing step.

By having such a configuration, at least the concentration of the disk material, particularly the main surface of the disk material, is changed without changing the characteristics (size, shape, hardness, etc.) of the abrasive contained in the polishing liquid. By simply polishing, the surface can be substantially mirror-finished or have a desired roughness. Therefore, it is not necessary to change the polishing liquid to a polishing liquid containing a different polishing agent in the polishing step, and thereby, a plurality of polishing media can be replaced depending on the type of polishing agent in the polishing liquid. It becomes possible to eliminate the use of a polishing apparatus of the table.

  The first polishing step corresponds to, for example, a polishing step in the previous stage of final polishing of the disk material. Therefore, in the first polishing step, it is desired to achieve a high polishing rate while considering the required surface roughness for the disk material in the second polishing step. Considering this point, the first concentration of the polishing agent used in the first polishing step may be set based on the required polishing rate for the disk material. Here, the required polishing rate can be a required polishing rate.

  On the other hand, the second polishing step corresponds to, for example, a polishing step in the finishing stage, which is performed on the disk material polished in the first polishing step. Therefore, in the second polishing process, it is required that the accuracy of the surface of the disk material be a desired roughness, that is, a required surface roughness. Considering this point, the second concentration of the polishing agent used in the second polishing step may be set based on the required surface roughness of the disk material.

  In this way, the concentration of the abrasive contained in the polishing liquid for polishing the disk material is decreased step by step while keeping the same abrasive, and set based on the required surface roughness for the disk material in the second polishing step. By using the polishing liquid containing the second concentration abrasive, the surface roughness of the disk material can be made appropriate. Therefore, from the disk material polishing operation, the use of multiple types of abrasives, the replacement work of the polishing medium during the disk material polishing process, and the multiple devices according to the difference in the abrasive contained in the polishing liquid Use can be eliminated. That is, it is possible to obtain a disk material having surfaces with different surface roughnesses by a simple method. The disk material manufactured through such a process is used as a magnetic disk substrate, for example. That is, a magnetic disk substrate having surfaces with different surface roughnesses can be produced by a simple method as described above.

  The present invention also resides in a magnetic disk including the magnetic disk substrate thus manufactured.

  According to the present invention, by changing the concentration of the abrasive in the polishing liquid stepwise to a concentration set based on the required surface roughness for the disk material, and polishing the disk material, various surface roughnesses are obtained. Thus, it is possible to easily provide a disk material having a surface with good productivity, and for example, it is possible to provide a magnetic disk substrate or a magnetic disk at low cost.

It is a mimetic diagram of a disc material polisher of an embodiment concerning the present invention. It is a flowchart showing the flow of grinding | polishing of a disk material. It is a graph showing the example of relationship between the abrasive | polishing agent density | concentration of polishing liquid, and the finishing surface roughness of the surface of a disk material. It is a graph showing the example of a relationship between the abrasive | polishing agent density | concentration of polishing liquid, and the polishing process speed of a disk material.

  In general, in the disk material polishing using the conventional apparatus and method, the disk material is polished such that the locus of the abrasive such as abrasive grains is transferred to the disk material. Therefore, a sufficient amount of abrasive concentration such as 20% by weight is required for the polishing liquid. In general, it has been considered that the finished surface roughness of the disk material varies greatly depending on the size of the abrasive such as abrasive grains used for polishing the disk material. For example, when increasing the finished surface roughness of the surface of the disk material, that is, when obtaining a rough finished surface, a polishing liquid containing a relatively large abrasive has been used. Therefore, when different finish surface roughness is required among a plurality of disk materials, the optimum size is selected from among a plurality of polishing liquids mainly containing different abrasives depending on the disk material to be polished. A polishing liquid containing an abrasive was selected and used for the polishing. This is because a plurality of polishing liquids having different sizes of abrasives are used, so that a polishing medium such as a dedicated polishing pad is prepared every time the polishing liquid used is changed, or each time the polishing liquid is changed. It was necessary to change the polishing apparatus. This is expensive in terms of cost because it is necessary to prepare a plurality of members and the like, and is complicated in terms of workability.

  In consideration of these, the present inventors have made various studies on the polishing of the disk material through various experiments and the like, and the concentration of the abrasive in the polishing liquid used for polishing the disk material is determined by the surface of the polished disk material. It was found that it greatly affects the roughness. Specifically, if the polishing agent concentration in the polishing liquid is reduced under a certain processing pressure, the surface roughness of the disk material increases or decreases so as to have a certain concentration at the peak, so the concentration of the polishing agent in the polishing liquid is set appropriately. It was found that the surface of the disk material can be changed to a surface having a desired surface roughness by polishing the disk material while adjusting to. Further, in connection with this, the inventors have found that the disk material can be polished at high speed using various abrasives by appropriately adjusting the concentration of the abrasive in the polishing liquid and polishing the disk material. Based on these findings, the present inventors have completed the present invention that makes it possible to obtain disk materials having surfaces with various surface roughnesses at low cost.

  In short, the present invention may comprise a configuration in which the disk material is polished using a polishing liquid containing an abrasive having a concentration set based on the required surface roughness of the disk material. Preferably, it includes a first polishing step of polishing the disk material with a polishing liquid containing a first concentration of abrasive, and a polishing containing the same concentration of the second concentration lower than the first concentration. And a second polishing step of polishing the disk material polished in the first polishing step using the liquid. However, preferably, the second concentration is set based on the required surface roughness for the disk material.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. However, the embodiment described below is an example applied to the glass disk material D in the process of manufacturing the magnetic disk glass substrate. However, the disk material that is the subject of the present invention may include various disk materials other than the glass disk material, such as those made of aluminum or ceramics. In this specification, in order to distinguish a semi-processed product from a raw material to a product that is, for example, a magnetic disk substrate (substrate) from a finished product that can be used as such a product, in principle, a disc It is called a material. However, this does not exclude that such a disk material is referred to as a substrate, nor does it exclude that all processed materials (for example, products) are referred to as disk materials. .

  First, a disk material polishing apparatus 10 will be described with reference to the schematic view of FIG. The polishing apparatus 10 includes a lower surface plate 14 on which a polishing cloth 12 as a polishing medium is mounted, an upper surface plate 18 on which a polishing cloth 16 as a polishing medium is mounted so as to face the polishing cloth 12, and both A holding means 20 for holding the disk material D between the surface plates 14 and 18 so as to be capable of relative movement, and a polishing liquid supply means 22 for supplying a polishing liquid so as to flow to the contact portion between the polishing cloths 12 and 16 and the disk material D. And is configured.

  The lower surface plate 14 is installed so as to be horizontally rotatable by a rotating means including a motor or the like, and can rotate the polishing cloth 12 positioned on the upper surface thereof in the horizontal direction. The upper surface plate 18 is disposed on the upper position of the lower surface plate 14 so as to face the lower surface plate 14 in a coaxial manner. Further, the upper surface plate 18 can be rotated in the horizontal direction by rotating means including a motor or the like and can be moved up and down in the vertical direction by lifting means. The polishing cloths 12 and 16 each have a donut shape.

  The holding unit 20 includes a relative movement unit 24 and a holding member 26. The relative movement means 24 is an internal gear 30 disposed concentrically at a radially outward position of the sun gear 28 disposed substantially at the axial center position of the polishing cloths 12, 16 between the both polishing cloths 12, 16. Have The holding member 26 is formed to hold the disk material D, and is placed on the polishing cloth 12 of the lower surface plate 14 in mesh with both the internal gear 30 and the sun gear 28. In this state, it is formed by an external gear disposed between the two gears 28 and 30.

The polishing liquid supply means 22 includes a first valve 34 for supplying a reference polishing liquid 32 containing a predetermined concentration of abrasive, a second valve 38 for supplying water or pure water 36, and a reference polishing liquid 32. It has a liquid reservoir 40 that constitutes a part of a common passage of two flow paths for flowing water 36 and a pipe 42 that forms a part of the common passage so as to communicate with the liquid reservoir 40. The reference polishing liquid 32 stored in the tank can flow into the liquid reservoir 40 by opening the first valve 34. Further, the water 36 stored in the tank can flow into the liquid reservoir 40 by opening the second valve 38. Then, the fluid from the liquid reservoir 40 is supplied from the upper surface plate 18 to the upper surface of the disk material D via the pipe 42. The reference polishing liquid 32 and / or the water 36 may be circulated in the polishing apparatus 10, and a circulator for that purpose may be provided in the polishing apparatus 10 as necessary. However, when a circulation device is provided, the circulation device may include a separation member such as a filter so that the reference polishing liquid 32 and the water 36 can be appropriately separated. However, here, the solvent of the reference polishing liquid 32 is water.

  The operation of the polishing apparatus 10 for the disk material D having such a configuration will be described. However, the control of the above various means and the control of the actuators for driving both valves 34 and 38 are performed based on electric signals from the control means such as an electronic control unit. However, all or some of the driving may be performed manually or by a mechanical mechanism.

  In the polishing apparatus 10 configured as described above, the disk material D is disposed in the disk material mounting hole of the holding member 26 as shown in FIG. Then, the elevating means is driven so that the upper and lower polishing cloths 12 and 16 are pressed against the upper and lower surfaces of the disk material D. On the other hand, the valves 34 and 38 are controlled so as to supply the reference polishing liquid 32, the water 36, or a mixture thereof toward the disc material D. For example, when only the reference polishing liquid 32 is supplied, only the first valve 34 is opened, and when only the water 36 is supplied, only the second valve 38 is opened. When supplying the polishing liquid M composed of the mixed liquid of the reference polishing liquid 32 and the water 36, both valves 34 and 38 are opened. On the other hand, it is adjusted based on the polishing agent concentration required for the polishing liquid M supplied. Note that the opening degree of both the valves 34 and 38 is adjusted based on data related to the abrasive concentration of the liquid mixture previously determined based on experiments. Preferably, the data is stored in the storage unit of the control means so as to be usable.

  The upper and lower polishing cloths 12 and 16 are pressed against the upper and lower surfaces of the disk material D and the polishing liquid 32 and the like are supplied, while the sun gear 28 is rotated and the upper and lower surface plates 14 and 18 are rotated. Are driven to rotate in the same direction or in opposite directions. Thereby, the holding member 26 is rotated around the sun gear 28 while rotating, and both surfaces of the disk material D are polished.

  In particular, here, the polishing of the disk material D by the polishing apparatus 10 is performed while changing the polishing agent concentration of the polishing liquid stepwise. The flow of this polishing will be described based on the flowchart of FIG.

  First, in step S201, the disc material D is set in the polishing apparatus 10 as described above. The pre-finish polishing in the first stage, that is, the first polishing process is performed on the installed disk material D in step S203. As the first polishing process, the disk material D is polished using the reference polishing liquid 32 itself as the polishing liquid. In this first stage, the first valve 34 is opened while the second valve 38 is kept closed. As a result, the polishing liquid containing a predetermined concentration of abrasive, which is the reference polishing liquid 32 itself, is supplied to the disk material D, and the disk material D is polished. Since this first polishing process is intended for pre-finish polishing of the disk material D, various polishing conditions are set by paying attention to the polishing speed of the disk material D. The size or average particle size of the abrasive, such as abrasive grains, is 1 nm to 10 μm in diameter, preferably 5 nm to 1 μm, and more preferably 5 nm to 100 nm. However, the size of the abrasive is a polishing liquid (solvent is, for example, water or alcohol) containing a normal abrasive concentration, for example, 8 to 20% by weight (wt%), and the disc is subjected to a predetermined pressure. The material D is selected so that it can be polished to a predetermined thickness at a certain high speed. The size of the abrasive is selected so that the required surface roughness can be appropriately realized in the finish polishing of the disk material D described later.

  The disc material D subjected to the first polishing process in step S203 is subjected to the second stage polishing, that is, the second polishing process, in step S205. However, the polishing in the second stage corresponds to finish polishing here. In the second polishing process, the second valve 38 is opened while the first valve 34 is opened. As a result, a polishing liquid M that is a mixed liquid of the reference polishing liquid 32 and the water 36 is formed, and the polishing liquid M is supplied to the disk material D, and the disk material D is polished. In this second polishing process, the disk material D is finish-polished, so that the polishing liquid M used in the second polishing process contains the same size and type of abrasive as the abrasive in the reference polishing liquid 32. In addition, an abrasive having an abrasive concentration different from the abrasive concentration in the reference polishing liquid 32 is included. However, the polishing agent concentration of the polishing liquid M used in the second stage is lower than the polishing agent concentration with respect to the reference polishing liquid 32 in the first stage. It is set so that the required surface roughness can be realized. For example, the abrasive concentration in the second stage is included in the concentration range of 0.2 to 5 wt%. It should be noted that the adjustment of the abrasive concentration in the second stage can be performed by supplying a polishing solution having a low concentration separately instead of supplying water.

  In this case, the disk material that has been subjected to the second polishing process in step S205 is removed from the polishing apparatus 10 in step S207, and in some cases, a magnetic disk substrate is obtained through a separate cleaning process or the like. However, between steps S205 and S207, the first cloth 34 is closed and the second valve 38 is opened, and the polishing cloths 12 and 16 are moved with respect to the disk material D as in the polishing in the second polishing process. Thus, a cleaning process may be provided to remove the abrasive and the like from the surface of the disk material D.

  Thus, here, the disk material D is polished in a substantially two-step polishing process (steps S203 and S205). Since the difference in the polishing conditions in these two polishing steps is only the concentration of the abrasive with respect to the polishing liquid (and the pressure may be changed), the same polishing is performed during the polishing operation of the disk material D. The device 10 can be used continuously. Therefore, the disk material D can be easily polished at low cost. Moreover, since it is sufficient to change only the polishing agent concentration of the polishing liquid in this way, the number of polishing liquids to be prepared is substantially one. Therefore, also in this respect, the polishing operation can be simplified at low cost.

  Next, this polishing will be described based on experimental results. However, below, the experimental result with respect to the disk material made from an amorphous glass is demonstrated. In the following description, the lapping disk material D is polished through three polishing steps. Among these, the polishing in the last two polishing steps corresponds to the first and second polishing processes. In the description, the disk material is indicated by reference numerals “D1, D2, D3,...” In order to clarify appropriately which manufacturing stage the disk material D is from.

  First, the production of the disk material before the polishing process will be specifically described. The amorphous glass material was subjected to inner / outer shape processing or the like, and a disk material D1 having a hole around the central axis and having a disk shape with a predetermined dimension of about 1 mm was produced. The disk material D1 was lapped under the following conditions to obtain a disk material D2. However, the thickness of the disk material D2 was about 0.53 mm, and the finished surface roughness was Ra 0.3 μm. Here, the disc material D2 was subjected to washing and drying after lapping. A lapping process uses a lapping machine (both sides 9B polishing machine) manufactured by Speed Fam Co., Ltd. having a cast iron surface plate, and a working fluid in which GC # 1500 is dispersed at a concentration of 10 wt% (pure water dilution); It was performed under processing conditions such as a processing pressure of 8 kPa.

The disk material D2 thus lapped was subjected to rough polishing. Rough polishing was performed using a double-sided 9B polishing machine polishing apparatus manufactured by Speed Fam Co., Ltd. having the same configuration as the polishing apparatus 10 described above, in which a foamed urethane polishing pad manufactured by Ehime Fujibo Co., Ltd. was used as the polishing cloth. As the polishing liquid 32, a polishing liquid in which Millek (registered trademark) (average particle diameter: about 1.5 μm) manufactured by Mitsui Kinzoku Co., Ltd. was dispersed at a concentration of 10 wt% (pure water dilution) was used under a processing pressure of 9.8 kPa. Rough polishing was performed. Here, with respect to the disk material D3 after the rough polishing, the first valve 34 is closed and the second valve 38 is opened, and only the water 36 is supplied to clean the disk material D3.
The rough polishing process was performed under such processing conditions, and the finished surface roughness of the surface of the disk material D3 after the rough polishing process was Ra 0.6 nm.

  The disk material D3 thus subjected to the rough polishing process is subjected to a pre-finish polishing process (corresponding to the first polishing process) and a final polishing process (described above) under various conditions so that the thickness is 0.5 mm. Equivalent to the second polishing process). Note that the pre-finish polishing and the finish polishing are performed substantially continuously.

  In the pre-finish polishing process and the final polishing process, the same type of polishing cloth and polishing apparatus as those used in the rough polishing process were used as the polishing cloths 12 and 16 and the polishing apparatus 10. As the polishing liquid 32, a polishing liquid obtained by diluting ST-ZL2 (average particle diameter: 80 nm) manufactured by Nissan Chemical Industries with pure water was used. However, the abrasive concentration of the polishing liquid 32 was 15 wt%. Then, the disk material D3 is installed in the polishing apparatus 10 (see step S201), and the pre-finishing polishing process (see step S203) and the final polishing process (step S203) are performed on the disk material D3 under a processing pressure of 9.8 kPa. (See S205).

In the pre-finish polishing step, only the first valve 34 is opened with the second valve 38 closed, that is, the polishing liquid 32 containing ST-ZL2 as an abrasive and having an abrasive concentration of 15 wt% is applied to the disk material D3. While supplying, the disk material D3 was polished for 10 minutes. Then, preferably after that, the second valve 38 is opened to a predetermined opening while the first valve 34 is opened, and the disc material D4 subjected to the pre-finish polishing process is finished for 5 minutes. Processing was performed. However, an experiment was conducted with respect to the case where the predetermined opening of the second valve 38 was set to four openings so that the abrasive concentration of the polishing liquid M was 1, 3, 4, or 15 wt%, and the results were compared. did. Note that the disc material D5 that had been subjected to the final polishing process was cleaned so as to remove the polishing agent such as abrasive grains on the surface and polishing debris, and to make the disc material D5 into a clean state. This cleaning may be performed by closing the first valve 34 and keeping the second valve 38 open. Table 1 shows the finished surface roughness Ra of the four types of disc materials produced with different abrasive concentrations. The finished surface roughness Ra is obtained by measuring an area of 10 μm ² with an AFM (atomic force microscope).

  From the results of Table 1, it is clear that disk materials having different surface roughnesses can be obtained by variously changing the abrasive concentration of the polishing liquid used for performing the finish polishing process (see step S205). is there. Therefore, in order to examine in more detail what kind of polishing condition the disk material D5 having the finished surface can be obtained when the disk material D4 is subjected to finish polishing under various polishing conditions, experiments were performed with various concentrations of the abrasive. It was. The experimental results are shown in the graph of FIG. FIG. 3 shows the results for four cases where the polishing pressure was variously changed to 2 kPa, 3 kPa, 9 kPa, and 15 kPa. The polishing conditions are the same as those of the final polishing process in the above experimental example except that the polishing agent concentration, the polishing pressure, and the use of colloidal silica (average particle size: 80 nm) as the polishing agent. However, the polishing conditions for the disk material D3 in the pre-finish polishing process (see step S203) are the same as those in the experiment described above, except for the type of abrasive.

  From the graph of FIG. 3, it can be understood that the finished surface roughness Ra of the disk material D5 shows the roughest peak when the abrasive concentration is about 1 wt%. It can also be seen that when the abrasive concentration is in the range of 0.2 to 5 wt%, the finished surface roughness Ra greatly increases and decreases with the peak value as a boundary. That is, the disc material D5 having a surface with a predetermined surface roughness is obtained by performing the above-described finish polishing on the disc material D4 while appropriately adjusting the abrasive concentration of the polishing liquid to a concentration within this concentration range. It is understood that can be obtained. However, here, the concentration range of 0.2 to 5 wt% of the abrasive concentration is referred to as a polishing region that can be used for finish polishing. 3 that the increase / decrease width of the finished surface roughness Ra increases as the polishing pressure is increased.

  On the other hand, in the region where the abrasive concentration exceeds 5 wt%, preferably in the region of 8 wt% or more (in FIG. 3, the results regarding the region up to 15 wt% are shown), there is a large difference in the finished surface roughness. Is no longer allowed. This means that in polishing with a polishing liquid having an abrasive concentration belonging to such a region, roughness corresponding to the size of the abrasive can be realized on the surface of the disk material D5.

  On the other hand, an experiment was conducted to examine what processing speed can be realized under what polishing conditions. The experimental results are shown in the graph of FIG. FIG. 4 shows the results for three cases where the polishing pressure was variously changed to 3 kPa, 9 kPa, and 15 kPa. In this experiment, colloidal silica (average particle diameter: 50 nm) was used as an abrasive, and a liquid in which it was dispersed in an aqueous NaOH solution having a pH of 9.8 was used as an abrasive. The polishing conditions here are the same as those in the pre-finish polishing step (see step S203 above) in the above experimental example, except that the concentration of the abrasive is variously changed and the polishing pressure is changed.

  From the graph of FIG. 4, it is understood that the processing speed can be increased when the abrasive concentration is about 5 wt% concentration or more, preferably 6 to 15 wt% concentration region, more preferably 8 to 15 wt% concentration region. it can. It can be seen that the higher the polishing pressure, the faster the processing speed. Here, this abrasive concentration region is referred to as a high-speed region where the polishing rate is high. From this experimental result referring to the experimental result of FIG. 3 above, by adjusting the abrasive concentration so as to belong to the high speed region, a polishing liquid containing a fine polishing agent for final polishing can be used. It can be understood that high-speed polishing can be performed.

  As described above, the polishing agent concentration of the polishing liquid containing a small amount, preferably one kind of polishing agent, is changed variously, and preferably, polishing is performed using the polishing liquid having the polishing agent concentration in the high-speed region, and then the polishing agent in the polishing region. It has been clarified that it is possible to obtain a disk material D having a high-precision finished surface at high speed by polishing the disk material D using a polishing liquid diluted to a concentration. In this way, the polishing rate and the finished surface roughness can be adjusted to desired values by simply changing the polishing agent concentration of the polishing liquid containing the polishing agent for finish polishing. Can be used in the finish polishing process for a long time. Therefore, since the types of polishing media and polishing apparatuses to be used can be reduced, the polishing process can be simplified and the cost for the polishing process can be reduced.

  Note that, as described above, when the polishing agent concentration of the polishing liquid is decreased under a certain polishing pressure, the surface roughness of the finished surface increases or decreases to have a certain concentration at the peak. Concentration control is effective for controlling the surface roughness of the disk material. This is thought to be because the density of the abrasive affects the surface roughness because the movement behavior of the abrasive during polishing creates the geometrical surface of the disk material.

  Therefore, it has been found that the above-described polishing method described using the polishing apparatus 10 for the disk material D can provide a good disk material, thereby obtaining a good glass substrate for a magnetic disk. Then, an adhesion layer, an underlayer magnetic layer, a carbon protective layer, and the like are formed on the substrate thus obtained by various means and methods such as sputtering or CVD, and a liquid lubricant is applied thereon. Thus, a magnetic disk can be obtained. However, in the process, texture processing, polishing processing, or the like can be arbitrarily performed. The magnetic disk manufactured in this way may be a longitudinal magnetic recording magnetic disk or a perpendicular magnetic recording magnetic disk.

  In addition, the abrasive | polishing agent used for grinding | polishing of disk material is not limited to the said abrasive | polishing agent, Colloidal silica, an alumina, a diamond, a zirconia oxide, a cerium oxide etc. may be sufficient. Moreover, the solvent of polishing liquid is not limited to water, NaOH aqueous solution, etc., It can be various liquids, for example, an alkaline liquid, an acidic liquid, etc. The polishing pressure is not limited to the above description, and is set to, for example, a pressure of 4.9 kPa to 14.7 kPa, preferably a pressure of 7.84 kPa to 11.8 kPa. Further, the size of the abrasive contained in the polishing liquid used substantially in common in the first polishing process and the second polishing process is required for the required surface roughness, that is, the surface of the disk material D after the finish polishing process. Various finishes can be selected so that the finished surface roughness can be realized.

  Although the present invention has been described with a certain degree of specificity in the above-described embodiments and modifications thereof, various modifications can be made to the present invention without departing from the spirit and scope of the invention described in the claims. It should be understood that modifications and changes are possible. That is, the present invention includes modifications and changes that fall within the scope and spirit of the appended claims and their equivalents.

DESCRIPTION OF SYMBOLS 10 Polishing apparatus 12, 16 Polishing cloth 14 Lower surface plate 18 Upper surface plate 20 Holding means 22 Polishing liquid supply means 32 Standard polishing liquid 34 1st valve 36 Water 38 2nd valve D Disc material

Claims (2)

A first polishing step of polishing the disk material using a polishing liquid containing a first concentration of abrasive;
Based on the correlation between the polishing agent concentration and the finished surface roughness, the polishing agent contains a second concentration lower than the first concentration and having a finished surface roughness larger than the finished surface roughness of the first polishing step. Using a polishing liquid, and a second polishing step for polishing the disk material polished in the first polishing step,
The first concentration is set based on a required polishing rate for the disk material,
The disk material polishing method, wherein the second concentration is set based on a required surface roughness of the disk material. First polishing means for polishing the disk material using a polishing liquid containing a first concentration of abrasive;
Based on the correlation between the abrasive concentration and the finished surface roughness, the polishing liquid corresponding to the second concentration lower than the first concentration has a finished surface roughness larger than the finished surface roughness by the polishing of the first polishing means. Second polishing means for polishing the disk material polished by the first polishing means using a polishing liquid containing
Including
The first concentration is set based on a required polishing rate for the disk material,
The disk material polishing apparatus, wherein the second concentration is set based on a required surface roughness of the disk material.

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