JP2012216251A - Method for manufacturing glass substrate for magnetic information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a glass substrate for a magnetic information recording medium which is capable of improving a processing rate in a grinding step and/or a polishing step and effectively removing a processing damage layer remaining on a substrate surface with a low load and has excellent impact resistance and high strength reliability by suppressing the occurrence of damage caused by polishing of a surface.SOLUTION: A method for manufacturing a glass substrate for a magnetic information recording medium comprises a tensile stress layer forming step for forming a tensile stress layer on a glass substrate surface, in which the tensile stress layer forming step is provided before a precision polishing step. The tensile stress layer forming step includes an ion exchange treatment method for exchanging alkali metal ions contained in a glass substrate. In the ion exchange treatment method, the tensile stress layer is preferably formed on the glass substrate surface by immersing the glass substrate in a processing liquid containing ions having an ion radius smaller than that of the alkali metal ions contained in the glass substrate.

Description

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

  A magnetic information recording apparatus records information on an information recording medium by using magnetism, light, magneto-optical, and the like. A typical example is a hard disk drive device. A hard disk drive device is a device that magnetically records information on a magnetic disk as an information recording medium having a recording layer formed on a substrate by a magnetic head. As a base material of such an information recording medium, a so-called substrate, a glass substrate is preferably used.

  In recent years, a low-priced personal computer has appeared, and thus a low-cost glass substrate for a magnetic information recording medium used for this is desired. On the other hand, with the rapid digitization of home appliances and the like, the amount of information handled is increasing rapidly, and it is increasingly desired to improve the recording density for hard disks as a large-capacity information recording medium. In the process of grinding or polishing, it was necessary to improve the rate, to significantly suppress the smoothness and microwaviness of the glass substrate surface, or to reduce microscopic defects.

  In particular, in order to achieve ultra-high density in recent years, ultrafine abrasive particles that can precisely and finely control the final polishing process are used for the purpose of further improving the smoothness and fine waviness quality of the substrate surface. As a result, the problem that the workability is increasingly reduced has become more prominent. For such a problem, for example, Patent Document 1 discloses a technique for improving a processing rate of a grinding process by roughening a glass substrate whose main surface is a mirror surface by hydrofluoric acid treatment and then performing grinding. Yes. However, if hydrofluoric acid treatment is performed as in the above technique, the entire substrate surface is etched, making it difficult to control the thickness. Further, quality such as smoothness and waviness may be excessively deteriorated, and it may be necessary to process excessively in order to improve and improve the characteristics, thereby reducing productivity. Further, it is necessary to newly introduce a hydrofluoric acid treatment process, which increases the cost and at the same time causes a decrease in the yield rate.

JP 2010-205382 A

  The present invention has been made in view of the prior art, and the problem to be solved is to improve the processing rate in the grinding step and / or polishing step and to reduce the processing damage layer remaining on the substrate surface with a low load. An object of the present invention is to provide a method for producing a glass substrate for a magnetic information recording medium that can be effectively removed, suppresses the occurrence of damage due to polishing of the surface, has excellent impact resistance, and has high strength and reliability. To do.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies by paying attention to the surface state before the substrate is polished in the manufacturing process of the glass substrate for magnetic information recording medium. As a result, it was found that by forming a tensile stress layer on the substrate surface before the polishing step, a glass substrate for a magnetic information recording medium capable of greatly improving the polishing rate even under the same polishing conditions can be produced. Furthermore, it was found that a glass substrate for a magnetic information recording medium obtained by such a manufacturing method can maintain excellent substrate surface quality suitable for high density and can have high strength reliability. .

  The method for manufacturing a glass substrate for a magnetic information recording medium according to the present invention includes a tensile stress layer forming step of forming a tensile stress layer on the surface of the glass substrate, and the tensile stress layer forming step is provided before the precision polishing step. It is a manufacturing method of the glass substrate for magnetic information recording media characterized.

  The tensile stress layer forming step includes an ion exchange treatment method for exchanging alkali metal ions contained in a glass substrate, and the ion exchange treatment method has an ion radius smaller than the ion radius of the alkali metal ions contained in the glass substrate. It is preferable to immerse the glass substrate in a treatment solution containing ions to form a tensile stress layer on the surface of the glass substrate. According to such a configuration, a uniform tensile stress layer can be formed on the substrate surface in a short time.

  In the ion exchange treatment method, before the tensile stress layer forming treatment, the glass substrate is immersed in a treatment liquid containing ions having an ion radius larger than the ion radius of alkali metal ions contained in the glass substrate, It is preferable to further include a compressive stress forming process for forming a compressive stress on the surface of the glass substrate. With such a configuration, by forming the compressive stress layer sufficiently deeper than the tensile stress layer, it becomes possible to generate a stronger tensile stress on the extreme outermost surface to be polished, and at a higher processing rate. A glass substrate with high strength and reliability can be obtained by allowing the polishing process to be performed and the compression stress layer appearing on the surface of the substrate.

  It is preferable that the thickness of the tensile stress layer is smaller than a machining allowance ground by the grinding process and a machining allowance polished by the polishing process. With such a configuration, tensile stress does not exist on the processed substrate surface, so that strength reliability is not impaired.

The stress of the tensile stress layer formed in the tensile stress layer forming step is preferably 0.1 to 15 kg / mm ² . With such a configuration, the processing rate in the grinding process and the polishing process can be improved, and the shape of the glass substrate can be easily controlled.

  According to the present invention, it is possible to improve the processing rate in the grinding process and / or the polishing process, and to effectively remove the processing damage layer remaining on the substrate surface with a low load, and to generate damage due to the polishing process on the surface. It is possible to provide a method for producing a glass substrate for a magnetic information recording medium, which has excellent impact resistance and high strength reliability.

It is a manufacturing process figure explaining the process in manufacture of the glass substrate for magnetic information recording media concerning this embodiment. 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 a schematic sectional drawing which shows an example of the grinding | polishing apparatus used at the rough grinding | polishing process and the precision grinding | polishing process in the manufacturing method of the glass substrate for magnetic information recording media which concerns on 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.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

  The method for manufacturing a glass substrate for a magnetic information recording medium according to the present embodiment is the method for manufacturing a glass substrate for a magnetic information recording medium including a tensile stress layer forming step of forming a tensile stress layer on the surface of the glass substrate. The forming step is provided before the precision polishing step.

  Further, the method for producing the glass substrate for magnetic information recording medium according to the present embodiment is not particularly limited except that the tensile stress layer forming step is provided before the precision polishing step, and may be a conventionally known production method. That's fine.

  As a method for producing a glass substrate for a magnetic information recording medium, in addition to the tensile stress layer forming step, for example, a disk processing step, a lapping step, a rough polishing step (primary polishing step), a precision polishing step (secondary polishing step) ), A method including a washing step and the like. The steps may be performed in this order, or the order of the precision polishing step (secondary polishing step) and the cleaning step may be switched. Furthermore, a method including steps other than these may be used. For example, you may provide what performs an end surface grinding | polishing process between a lapping process and a rough grinding | polishing process (primary grinding | polishing process).

  In particular, the cleaning process may be performed after the rough polishing process or after the precision polishing process, and may be performed once after each of the rough polishing process and the precision polishing process.

  Here, the tensile stress layer formation process in the manufacturing method of this invention is explained in full detail.

<Tensile stress layer formation process>
The tensile stress layer forming step is a step of forming a tensile stress layer on the glass substrate surface. For example, as shown in FIG. 1 (a), the tensile stress layer forming step according to the embodiment of the present invention may be provided before the precision polishing step described later, and before the grinding step. May be. By performing the tensile stress layer forming step before the polishing step, it is possible to reduce the processing time of the expensive polishing step, and to reduce the amount of abrasive such as cerium oxide. Further, the micro-waviness appearing after the tensile stress layer forming step can be easily removed by performing a polishing process thereafter.

As a method for forming the tensile stress layer, specifically, an ion exchange treatment method for exchanging alkali metal ions contained in the glass substrate and alkali metal ions contained in the treatment liquid, heating the glass surface uniformly, Due to the difference in thermal shrinkage that occurs when a temperature difference is forcibly generated between the surface and the interior, heat treatment methods that form tensile stress in the surface layer and compressive stress in the interior, and the sputtering phenomenon, make glass surface components more A sputtering utilization method for substituting with small ions and the like can be mentioned. Further, the ion exchange treatment method includes a dealkalization treatment method in which alkali ions on the surface of the substrate are extracted by being immersed in warm water or an acidic aqueous solution and exchanged with smaller H ⁺ ions.

  Hereinafter, each processing method used in the tensile stress layer forming step will be described in detail.

(Ion exchange treatment method)
The ion exchange treatment method is mainly a step of immersing the glass substrate in a treatment liquid containing ions having an ion radius smaller than that of alkali metal ions contained in the glass substrate. The ions may be ions having the same ion radius as that of the smallest alkali metal ion contained in the glass substrate. This ionic radius is a physical constant specific to each element uniquely determined by ions, as described in publications such as chemical handbooks.

  For the tensile stress layer forming step included in this ion exchange treatment method, a known ion exchange treatment method can be used. A heated molten salt can be used as the treatment liquid. The molten salt is preferably a nitrate containing an alkali metal element, such as a nitrate containing lithium nitrate. The lithium element contained in the nitrate is preferably 50 atomic% or more, more preferably 70 atomic% or more, and still more preferably 95 atomic% or more with respect to the total amount of alkali elements contained in the nitrate.

  As the ion exchange treatment method, a low temperature type ion exchange treatment method, a high temperature type ion exchange treatment method, a surface crystallization method, a dealkalization method on the glass surface, etc. can be used, but a temperature range not exceeding the annealing point of the glass. It is preferable to use a low-temperature type ion exchange treatment method from the viewpoint that ion exchange can be carried out by using this method.

  The low-temperature ion exchange treatment referred to here is a method in which the alkali metal ions in the glass are replaced with alkali metal ions having an ion radius smaller than that of the alkali metal ions in the temperature region below the annealing point of the glass. This is a method of generating tensile stress in

  In the ion exchange treatment method, the time for immersing the glass substrate in the treatment liquid is not particularly limited, but is preferably 1 hour to several tens of hours.

  In addition, before making a glass substrate contact molten salt, it is preferable to heat a glass substrate to 100 to 450 degreeC as preheating.

  The heating temperature of the molten salt when the chemical strengthening treatment is performed is preferably 280 ° C. to 660 ° C., particularly 300 ° C. to 450 ° C. from the viewpoint of good ion exchange.

  The material of the ion exchange tank for performing the ion exchange treatment method is not particularly limited as long as it is excellent in corrosion resistance and has a low dust generation property. In addition, since the molten salt is oxidizing and the processing temperature is high, by selecting a material with excellent corrosion resistance, damage and dust generation can be suppressed, thereby preventing thermal asperity failure and head crash. It is necessary to suppress it. Accordingly, a quartz material is particularly preferable as a material for the ion exchange tank, but a stainless material or a martensitic or austenitic stainless material particularly excellent in corrosion resistance can be used.

  The dealkalization treatment method, which is a kind of the ion exchange treatment method described above, will be described in detail below.

<Dealkali treatment method>
Formation of the tensile stress layer of the glass substrate by dealkalization treatment is performed by immersing the glass substrate in warm water or an acidic aqueous solution (for example, hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, or a mixed acid of hydrochloric acid and nitric acid). Specifically, it is immersed in warm water of 50 to 99 ° C. for about 5 minutes to 10 hours, or is immersed in an acidic aqueous solution at 25 ° C. to 99 ° C. and having a pH smaller than 7 for about 5 seconds to 3 hours. Is done. By this dealkalization treatment, alkali ions on the surface of the glass substrate can be extracted, and H ⁺ ions having an ion radius smaller than that of the alkali ions enter the glass substrate surface from which the alkali ions have been extracted. A stress layer will be formed.

(Heat treatment)
Formation of the tensile stress layer by heat treatment is performed by heating the glass surface layer uniformly with an electric furnace, laser pulse, or the like so that the glass surface layer has a higher temperature than the inside. Due to the difference in thermal shrinkage generated when a temperature difference is forcibly generated in the surface layer and inside of the glass substrate, tensile stress can be formed in the glass substrate surface layer and compressive stress can be formed in the inside. The tensile stress layer on the surface of the glass substrate can be obtained by heating the surface layer of the glass substrate to a temperature range above the strain point.

  By passing through the tensile stress formation process as described above, a tensile stress layer having a tensile stress can be provided on the glass substrate surface. The thickness of the tensile stress layer is not particularly limited, but is preferably smaller than a machining allowance ground by a grinding process described later and a machining allowance polished by a polishing process. When the thickness of the tensile stress layer is smaller than the allowance, the surface hardness of the substrate can be improved by allowing the inside of the glass substrate to appear on the surface after removing the tensile stress layer. This is presumably because compressive stress is formed inside the glass substrate to maintain a balanced stress state when the tensile stress layer is formed, and the compressive stress layer portion appears on the substrate surface. .

Further, the stress of the tensile stress layer forming step tensile stress layer formed in is preferably 0.1~15kg / mm ^2, more preferably 0.5 to 10 / mm ^2. If the stress is less than 0.1 kg / m ² , the effect of improving the processing rate in the subsequent grinding process or polishing process may not be sufficiently obtained. On the other hand, if it is greater than 15 kg / mm ² , the glass substrate is frequently cracked during processing, and the yield of the glass substrate may be reduced.

<Compressive stress layer formation process>
Regarding the compressive stress layer forming step included in the ion exchange processing method, as described above, in the compressive stress layer forming step in which the glass substrate and the chemical strengthening treatment liquid are first brought into contact, the ion radius of ions included in the glass substrate is determined. The treatment liquid containing ions having an ion radius larger than that of the glass substrate is brought into contact with the glass substrate for ion exchange. For this compressive stress layer forming step, the same ion exchange treatment method as the tensile stress layer forming step described above is used except that a treatment liquid containing ions larger than the ion radius of ions contained in the glass substrate is used. Can do.

  As the treatment liquid, it is preferable to use a nitrate containing an alkali metal element, for example, a nitrate containing potassium nitrate, sodium nitrate or the like.

As described above, by providing the compressive stress layer forming step before the tensile stress layer forming step,
Since the compressive stress layer is formed deeper than the tensile stress layer, the tensile stress layer can be subsequently removed at a high processing rate, and a glass substrate with high surface hardness is obtained by the appearance of the compressive stress layer on the substrate surface. be able to.

  Further, for example, as shown in FIG. 1B, the tensile stress layer forming process and the compressive stress layer forming process may be provided before the polishing process, and if the process is before the polishing process, grinding is performed. It may be before the process. Moreover, after performing a tensile stress layer formation process, a rough polishing process may be performed, and then a compression stress layer formation process may be performed.

<Disk processing process>
In the disk processing step, a through-hole 10a is formed at the center from a glass base plate formed from a glass material of a predetermined composition so that the inner periphery and the outer periphery are concentric circles as shown in FIG. This is a step of processing into a disk-shaped glass base plate 10. Specifically, for example, processing is performed as follows. First, a glass base plate that is formed into a plate shape and has a glass composition that will be described later and has a thickness of 0.95 mm is cut into a square having a predetermined size.

  Then, a circular cut line is formed on one surface of the cut glass base plate so as to form the inner circumference and the outer circumference described above with a glass cutter. And the glass base plate in which this cut line was formed is heated from the surface of the side in which the cut line was formed. By doing so, the said cut line becomes deep toward the other surface of a glass base plate. And it processes into the disk shaped glass base plate 10 in which the through-hole 10a was formed in the center part so that an inner periphery and an outer periphery may become a concentric circle.

  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 of 2 mm, 1 mm, 0.63 mm or the like. Further, when the outer diameter r1 is 2.5 inches (about 64 mm), the inner diameter r2 is processed to 0.8 inches (about 20 mm) or the like. FIG. 2 is a top view showing the glass substrate for magnetic information recording medium manufactured by the method for manufacturing the glass substrate for magnetic information recording medium according to the present embodiment.

  Moreover, the manufacturing method of the glass base plate shape | molded in plate shape is not specifically limited, For example, what was manufactured by the float glass process etc. is mentioned. 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. Since the obtained glass base plate is a free surface of glass and the other surface is an interface between glass and tin, the smoothness is high, for example, the arithmetic average roughness Ra is 0.001 μm. The following mirror surface is provided. 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.

<Lapping 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. 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.

  More specifically, examples of the first lapping step include a step of making the entire surface of the glass base plate have a substantially uniform surface roughness. At that time, for example, 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.

  The second lapping step may include a process of grinding the main surface of the roughened glass substrate using a fixed abrasive polishing pad. In this second wrapping step, for example, a roughened glass substrate is set in a wrapping apparatus, and a three-dimensional fixed abrasive with a surface pattern such as diamond tile is used. The surface can be wrapped.

  When the second lapping step is performed, polishing performed in a rough polishing step described later can be performed efficiently. Further, the surface roughness Ra of the glass base plate used in the polishing step performed by the second lapping step is preferably 0.10 μm or less, and more preferably 0.05 μm or less.

<Rough polishing process>
The rough polishing step (primary polishing step) is a step of rough polishing the surface of the glass base plate that has been subjected to the lapping step. This rough polishing is intended to remove scratches and distortions remaining in the lapping step described above, and is performed using the following polishing method.

  The surface to be polished in the rough polishing step is a main surface. The main surface is a surface parallel to the surface direction of the glass base plate.

  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. Specifically, there is a polishing apparatus 1 as shown in FIG. FIG. 3 is a schematic cross-sectional view showing an example of the polishing apparatus 1 used in the rough polishing process and the precision polishing process in the method for manufacturing a glass substrate for a magnetic information recording medium according to the present embodiment.

  A polishing apparatus 11 as shown in FIG. 3 is an apparatus capable of simultaneous polishing on both sides. The polishing apparatus 11 includes an apparatus main body 11a and a polishing liquid supply unit 11b that supplies a polishing liquid 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.

  A polishing pad 15 for polishing both the front and back surfaces of the glass base plate 10 is attached to the opposing surfaces of the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13. The polishing pad 15 used in the rough polishing step is not particularly limited as long as it is a polishing pad used in the rough polishing step. Specifically, for example, a hard polishing pad made of polyurethane or the like can be used.

  A plurality of rotatable carriers 14 are provided between the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13. The carrier 14 is provided with a plurality of base plate holding holes 51, and the glass base plate 10 can be fitted into the base plate holding holes 51. For example, the carrier 14 may include 100 base plate holding holes 51 so that 100 glass base plates 10 can be fitted and arranged. Then, 100 glass base plates 10 can be processed by one processing (1 batch).

  The carrier 14 sandwiched between the surface plates 12 and 13 through the polishing pad is the same as the lower surface plate 13 with respect to the rotation center of the surface plates 12 and 13 while rotating while holding the plurality of glass base plates 10. Revolve in the direction. The disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 can be operated by separate driving. In the polishing apparatus 11 operating as described above, the polishing slurry 16 is supplied between the upper surface plate 12 and the glass base plate 10 and between the lower surface plate 13 and the glass base plate 10, so that the glass base material is supplied. Rough polishing of the plate 10 can be performed.

  The polishing slurry supply unit 11b includes a liquid storage unit 110 and a liquid recovery unit 120. The liquid reservoir 110 includes a liquid reservoir main body 110a and a liquid supply pipe 110b having a discharge port 110e extending from the liquid reservoir main body 110a to the apparatus main body 11a. The liquid recovery part 120 was extended to the liquid recovery part main body 120a, the liquid recovery pipe 120b extended from the liquid recovery part main body 120a to the apparatus main body part 11a, and the polishing slurry supply part 11b from the liquid recovery part main body 120a. And a liquid return pipe 120c.

  Then, the polishing slurry 7 put in the liquid storage unit main body 110a is supplied from the discharge port 110e of the liquid supply pipe 110b to the apparatus main body part 11a, and from the apparatus main body part 11a through the liquid recovery pipe 120b, the liquid recovery part main body 120a. To be recovered. The recovered polishing slurry 16 is returned to the liquid storage part 110 via the liquid return pipe 120c and can be supplied again to the apparatus main body part 11a.

  The polishing liquid 16 used here is a liquid in which an abrasive is dispersed in water, that is, a slurry liquid.

  Further, the polishing pad 15 used here is a foam of synthetic resin such as urethane or polyester containing a cerium oxide abrasive.

Next, the polishing agent used in the polishing step performed before the chemical strengthening step uses a material containing a large amount of CeO ₂ and a small amount of alkaline earth metal, thereby increasing the polishing rate and increasing the glass element after polishing. It is considered that the smoothness of the plate can be sufficiently enhanced. As for the polishing pad, as in the case of the above-described polishing agent, the polishing rate is increased by using a material containing a large amount of CeO ₂ and a small amount of alkaline earth metal, and the smoothness of the glass base plate after polishing. Is considered to be sufficiently increased.

It is considered that the reason why the polishing agent having a high CeO ₂ content can increase the polishing rate and sufficiently increase the smoothness of the polished glass base plate is as follows. First, when the glass base plate and CeO ₂ come into contact with each other in the state where pressure is applied to the surface of the glass base plate during polishing, Si—O bonds, which are the main composition on the surface of the glass base plate, are Ce— It is thought to replace the bond of O. This bond is easily decomposed, but it is considered that the bond with Si is difficult to form again. Therefore, it is considered that when an abrasive having a high CeO ₂ content is used, the polishing rate can be increased and the smoothness of the glass base plate after polishing can be sufficiently increased.

Further, by using an abrasive and a polishing pad having a high CeO ₂ content and a low alkaline earth metal content, not only the smoothness can be sufficiently improved, but also the glass substrate after polishing is used. It is thought that adhesion of alkaline earth metal to the plate is suppressed. It is considered that uniform chemical strengthening is achieved by applying a chemical strengthening step to such a glass base plate in which adhesion of alkaline earth metal is suppressed.

  Note that when polishing with a polishing liquid in which the abrasive is dispersed in water, the alkaline earth metal is dissolved even if the alkaline earth metal is contained in the water. It is considered that the alkaline earth metal contained in the abrasive is likely to adhere to the surface of the glass base plate. Therefore, it is considered that adhesion of alkaline earth metal to the glass base plate after polishing can be sufficiently suppressed by using a polishing agent with little alkaline earth metal.

The CeO ₂ content is preferably as high as possible. Namely, rare earth oxide contained in the abrasive, it is preferred that all are CeO _2. This is considered to be because CeO ₂ has the most influence on the polishing properties of the glass base plate. Further, the lower the alkaline earth metal content, the better. If the alkaline earth metal contained in the abrasive is small, it is considered that the inhibition of the chemical strengthening process by the alkaline earth metal is suppressed.

Further, the content of CeO ₂ is, to the abrasive total amount is preferably 90 mass% or more. By doing so, it is possible to produce a glass substrate for a magnetic information recording medium excellent in impact resistance, further increase the polishing rate, and produce a glass substrate for a magnetic information recording medium with higher smoothness. it can. This means that the content of the alkaline earth metal that can hinder the chemical strengthening process is small, and the content of CeO ₂ that enhances the polishing property is merely large relative to the rare earth oxide contained in the abrasive. It is thought that this is also due to the large amount of the abrasive.

The polishing liquid is in a state where the abrasive is dispersed in water, and the content of CeO ₂ is preferably 3 to 15% by mass with respect to the total amount of the polishing liquid. By doing so, it is possible to produce a glass substrate for a magnetic information recording medium excellent in impact resistance, further increase the polishing rate, and produce a glass substrate for a magnetic information recording medium with higher smoothness. it can. Further, in the case of a polishing liquid in which the abrasive is dispersed in water, as described above, since the alkaline earth metal is dissolved even if the alkaline earth metal is contained in the water, It is difficult to adhere to the surface of the plate, and it is considered that the alkaline earth metal contained in the abrasive is likely to adhere to the surface of the glass base plate. Therefore, it is considered that the use of an abrasive having a small amount of alkaline earth metal can sufficiently suppress the adhesion of alkaline earth metal to the polished glass base plate.

  The abrasive has a maximum particle size distribution of 3.5 μm or less measured by the laser diffraction scattering method, and a cumulative 50 volume% diameter D50 in the particle size distribution measured by the laser diffraction scattering method is 0.4 to 0.4. It is preferable that it is 1.6 μm.

  When the particle size of the abrasive is too small, the polishing rate tends to decrease. When the particle size of the abrasive is too large, scratches that can be formed on the glass base plate due to polishing tend to occur.

  The maximum value in the particle size distribution measured by the laser diffraction scattering method is a cumulative curve obtained by setting the total volume of the powder population obtained by measurement with a laser diffraction particle size distribution measuring apparatus as 100%. It means the particle diameter of the point that is the maximum value of the curve. D50 means the particle diameter at which the cumulative curve is 50% when the total volume of the powder population obtained by measurement with a laser diffraction particle size distribution measuring device is 100%, and the cumulative curve is 50%. To do.

  The polishing liquid 16 preferably has a fluorine content of 5% by mass or less in the rough polishing step.

  The polishing pad 15 can contain zirconium silicate, zirconium oxide, manganese oxide, iron oxide, aluminum oxide, silicon carbide, or silicon dioxide in addition to cerium oxide. Among these, zirconium silicate is used. It is more preferable to make it contain.

  The blending amount of cerium oxide in the polishing pad is preferably 10 to 30% by mass and more preferably 15 to 25% by mass with respect to the total amount of the polishing pad.

  The polishing pad according to the present embodiment is manufactured, for example, by the following method.

  First, a resin solution and abrasive grains are mixed to produce an abrasive dispersion. Next, the abrasive dispersion is cured using a molding die to form a plate-like block in which the abrasive grains are fixed inside and on the surface. Subsequently, after the block is taken out of the mold, both sides of the block are ground and processed to a predetermined thickness.

  More preferably, first, the resin solution and the abrasive grains are mixed, and the mixed liquid is depressurized and defoamed to produce a foam-free abrasive dispersion. Next, the foam-free abrasive dispersion is cured using a mold to form a plate-like block in which the abrasive grains are fixed inside and on the surface of the non-foamed body. Subsequently, after the block is taken out from the mold, both sides of the block are ground and processed to a predetermined thickness.

<End face polishing process>
In the present embodiment, the polishing of the main surface is described in detail. However, it is preferable that the end surface is also polished using a conventionally used method. As a polishing method of the end face, for example, a polishing method using a polishing brush and an abrasive (particle) is generally used.

  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.

<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.

<Washing process>
The cleaning step is a step of cleaning the glass base plate that has been subjected to the rough polishing step.

  The glass base plate after the rough polishing by the rough polishing step is preferably cleaned by a cleaning step. The washing process is not particularly limited. Specifically, for example, the following washing steps are mentioned.

  First, the glass base plate is washed with an alkaline detergent having a pH of 13 or more, and the glass base plate is rinsed. Next, the glass base plate is washed with an acid detergent having a pH of 1 or less, and the glass base plate is rinsed. Finally, the glass base plate is cleaned using a hydrofluoric acid (HF) solution. Regarding cerium oxide, it is most efficient to perform cleaning in the order of alkali cleaning, acid cleaning, and HF cleaning. This is done by first dispersing and removing the abrasive with an alkaline detergent, then dissolving and removing the abrasive with an acid detergent, and finally etching the glass substrate with HF to remove the abrasive that is deeply stuck in the glass substrate. To do.

  The cleaning step is preferably performed in separate tanks for alkali cleaning, acid cleaning, and HF cleaning. This is because when these washings are performed in a single tank, efficient washing may not be possible. In particular, when the acid detergent and HF are put in the same tank, the etching rate of HF decreases at a place where there is a large amount of abrasive, and therefore there is a tendency that the inside of the substrate cannot be uniformly etched. Moreover, it is preferable to use a rinse tank after each washing. In some cases, a surfactant, a dispersing agent, a chelating agent, a reducing material, and the like may be added to these detergents. Moreover, it is preferable to apply an ultrasonic wave to each washing tank and to use deaerated water for each detergent.

  As another method, first, the glass base plate is immersed in a cleaning solution containing 1% by mass of HF and 3% by mass of sulfuric acid. At that time, an ultrasonic vibration of 80 kHz is applied to the cleaning liquid. Thereafter, the glass base plate is taken out. And the taken-out glass base plate is immersed in a neutral detergent liquid. At that time, 120 kHz ultrasonic vibration is applied to the neutral detergent solution. Finally, the glass base plate is taken out, rinsed with pure water, and IPA dried.

Further, the glass workpiece after the washing step, the alkaline earth metal remaining on the surface thereof, is preferably 10 ng / cm ² or less, more preferably 5 ng / cm ² or less. By doing so, the glass substrate for hard disks excellent in impact resistance can be obtained. This is considered to be due to the small amount of alkaline earth metal adhering to the surface of the glass base plate subjected to the chemical strengthening step, which can inhibit the chemical strengthening step. Therefore, it is considered that chemical strengthening occurs uniformly on the entire surface of the glass base plate, and a glass substrate for hard disk that is superior in impact resistance can be obtained. That is, if there is too much alkaline earth metal remaining on the surface of the glass base plate after the cleaning step, the chemical strengthening step is not suitably performed, and the impact resistance of the obtained glass substrate cannot be sufficiently increased. There is a case.

Further, the smaller the amount of alkaline earth metal remaining on the surface of the glass base plate after the washing step, the more preferable. This is because the alkaline earth metal remaining on the surface of the glass base plate polished in the polishing step before the chemical strengthening step inhibits the chemical strengthening step and inhibits uniform chemical strengthening. It is. In the present embodiment, the smaller the amount of alkaline earth metal remaining on the surface of the glass base plate after the cleaning step, the better. The amount is 10 ng / cm ² or less, and the impact resistance is excellent. It has been found that a glass substrate for a hard disk can be produced.

The glass substrate after the rough polishing is cleaned so that the amount of cerium oxide on the surface of the glass substrate is 0.125 ng / cm ² or less. When the amount of cerium oxide on the surface of the glass base plate is too large, the flatness of the glass base plate tends not to be good.

<Film formation process>
FIG. 4 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 manufacturing method according to the present embodiment. 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 used for manufacturing a glass substrate for a magnetic information recording medium was prepared. And by a known method, a disk processing step, a lapping step, a rough polishing step (primary polishing step), a compressive stress layer forming step (optional), a tensile stress layer forming step, a precision polishing step (secondary polishing step), and a cleaning The process was applied.

  In Tables 1 to 3, a process is selected from the process order I to process order VII described below, and the thickness (μm) of the compressive stress layer and / or the tensile stress layer is changed to be formed, and the grinding process and / or polishing is performed. A glass substrate for a magnetic information recording medium was manufactured by adjusting the machining allowance and the processing time when processed in the process. In addition, (-) in the following table | surface shows that the compressive-stress layer formation process or the tensile-stress layer formation process was not performed.

  In Examples 1 to 11 and Comparative Examples 1 to 10 in Tables 1 to 4, an ion exchange treatment method was used as the tensile stress layer forming step. Also, Example 12 in Table 3 used dealkalization treatment as the tensile stress layer forming step, and Example 13 used heat treatment.

  In Tables 1, 4 and 5, as described in the table, the machining allowance is based on the rough polishing step, and the processing time is the time taken for the rough polishing step. Similarly, the machining allowance and processing time in Table 2 are those obtained by the precision polishing process, and the machining allowance and machining time in Table 3 are those obtained by the grinding process.

<Process order>
(Process order I): disk processing process → lapping process → compressive stress layer forming process (optional) → tensile stress layer forming process → rough polishing process → precision polishing process → cleaning process (process order II): disk processing process → lapping process → Rough polishing process → Compression stress layer formation process (optional) → Tensile stress layer formation process → Precision polishing process → Cleaning process (process order III): Disk processing process → Compression stress layer formation process (optional) → Tensile stress layer formation process → Lapping process → Rough polishing process → Precision polishing process → Cleaning process (Sequence IV): Disk processing process → Lapping process → Tensile stress layer forming process → Rough polishing process → Compressive stress layer forming process → Precision polishing process → Cleaning process ( Process sequence V): disk machining process → tensile stress layer forming process → lapping process → rough polishing process → compressive stress layer forming process → precision polishing process → cleaning process (process sequence VI): disk machining process → drawing Stress layer formation process-> lapping process-> compression stress layer formation process-> rough polishing process-> precision polishing process-> cleaning process (process order VII): disk processing process-> lapping process-> rough polishing process-> precise polishing process-> tensile stress layer formation process → Compressive stress layer formation process (optional) → Cleaning process

(Measurement of thickness of tensile stress layer and compressive stress layer)
The cross section of the glass substrate was confirmed by observing the change in the alkali amount in the depth direction from the substrate surface with SEM-EDX. SEM was FE (field emission) type S-4800, and EDX was HORIBA EX-250.

(hardness)
The surface hardness (kg / mm ² ) was confirmed using a Vickers hardness meter (manufactured by Mitutoyo Corporation).

(Slight swell)
The microwaviness μWa was measured using a non-contact surface shape measuring instrument (New View 5000) of “Zygo Corporation”. The microwaviness μWa is measured by optical interference (Newton ring), and the amount of deviation between the reference plane and the actual plane is measured as interference fringes. The measurement principle is a method of measuring a subtle shape change of the surface by irradiating the surface of the substrate with white light and measuring an intensity change of interference between the reference light and the measurement light having different phases. The average value of the surface waviness height obtained by extracting irregularities with a period of 30 to 200 μm from the obtained measurement data is defined as micro waviness μWa.

  As is clear from Table 1, Examples 1 to 6 in which the tensile stress layer was formed had a shorter rough polishing processing time than Comparative Examples 1 and 2 in which the tensile stress layer was not formed. That is, it was found that the polishing rate was improved when the tensile stress layer was formed. Further, for Examples 1 to 4, when the polishing allowance is made larger than the thickness of the tensile stress layer, it becomes clear that the allowance is higher than those of Examples 5 and 6 smaller than those of the tensile stress layer. It has been clarified that when the compressive stress layer is formed before the tensile stress layer is formed, the hardness is further increased.

  In addition, it was found that when the tensile stress layer forming step was performed after the tensile stress layer forming step, the processing rate was lowered and a large amount of microwaviness remained.

  As is clear from Example 7 and Comparative Example 6 in Table 2, when the tensile stress layer forming step was performed between the rough polishing step and the precision polishing step, the processing rate was improved and the hardness was increased.

  From Table 3, it was found that even if the tensile stress layer forming process was performed before the lapping process, the grinding process time could be shortened. Also in Examples 9 and 10 in Table 3, as described above, it was revealed that the hardness was further increased when the compressive stress layer was formed before the tensile stress layer was formed.

  As is apparent from Table 4, the rough polishing processing time could be shortened by forming a tensile stress layer after the lapping step, that is, before the rough polishing step.

  Example 12 in Table 5 uses the dealkalization treatment method as the tensile stress layer formation step, and Example 13 uses the heat treatment method as the tensile stress layer formation step. It became clear that the processing rate and hardness which are not changed can be obtained.

DESCRIPTION OF SYMBOLS 10 Glass substrate 11 Polishing apparatus 12 Upper surface plate 13 Lower surface plate 16 Pump 101 Glass substrate for magnetic information recording media

Claims (5)

In the method for producing a glass substrate for a magnetic information recording medium, the method includes a tensile stress layer forming step of forming a tensile stress layer on the glass substrate surface
The method for producing a glass substrate for a magnetic information recording medium, wherein the tensile stress layer forming step is provided before a precision polishing step. The tensile stress layer forming step includes an ion exchange treatment method for exchanging alkali metal ions contained in the glass substrate,
The ion exchange treatment method is characterized in that the glass substrate is immersed in a treatment solution containing ions having an ion radius smaller than the ion radius of alkali metal ions contained in the glass substrate to form a tensile stress layer on the glass substrate surface. The manufacturing method of the glass substrate for magnetic information recording media of Claim 1.   The method for producing a glass substrate for a magnetic information recording medium includes the step of forming the glass in a treatment solution containing ions having an ion radius larger than the ion radius of alkali metal ions contained in the glass substrate before the tensile stress layer forming step. The method for producing a glass substrate for a magnetic information recording medium according to claim 2, further comprising a compressive stress layer forming step of immersing the substrate to form a compressive stress layer on the surface of the glass substrate.   The magnetic information recording medium according to claim 1, wherein a thickness of the tensile stress layer is smaller than a machining allowance ground by the grinding process and a machining allowance polished by the polishing process. Method for manufacturing glass substrate. 5. The magnetic information recording medium according to claim 1, wherein the tensile stress layer formed in the tensile stress layer forming step has a stress of 0.1 to 15 kg / mm ² . A method for producing a glass substrate.

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