JP5577290B2 - Method for manufacturing glass substrate for magnetic information recording medium - Google Patents

Description

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

  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, with the advent of low-priced personal computers, a glass substrate for a magnetic information recording medium used therefor has been desired to be even cheaper. On the other hand, it is also desired to improve the recording density of the hard disk. It has been difficult to achieve both low cost and high density with chemically strengthened glass and crystallized glass that have been used until recently. In addition, when manufacturing these substrates with glass, if high-precision grinding and polishing processes are performed to increase the density, further costs are required. ing.

  In response to the above problem, for example, in Patent Document 1, a glass substrate whose main surface is a mirror surface is roughened by hydrofluoric acid treatment, and then grinding is performed to improve the grinding rate, thereby shortening the processing time of the grinding process. Technology is disclosed. However, when the surface is roughened by simply performing hydrofluoric acid treatment as in the above technique, the entire surface of the substrate is etched and a certain amount of material is removed over the entire surface until the desired roughness is obtained. The cutting margin in the grinding process and polishing process is reduced. Therefore, there is a dilemma that the material cost increases because it is necessary to make the glass blanks (also referred to as glass base plates) ground in advance with a sufficient thickness. In addition, since hydrofluoric acid treatment is required for a long time, it is difficult to control the roughness, and accompanying the hydrofluoric acid treatment, undulation occurs in the glass blanks, and in order to eliminate the undulation, If the processing time in the polishing process is increased and the total is considered, the manufacturing time may become longer, which may increase the cost and reduce the yield rate.

  In Patent Document 2, Young's modulus is improved by crystallizing glass after phase separation. However, by increasing the Young's modulus, the processing rate is greatly reduced, resulting in higher costs, and unevenness derived from crystal particles occurs on the glass surface due to precision polishing and cleaning processes, resulting in reduced surface quality. There was a case.

JP 2010-205382 A JP 2005-119963 A

  The present invention has been made in view of the prior art, and the problems to be solved are smoothness and undulation while enabling the processing time to be shortened by improving the processing rate in the grinding process and the polishing process. It is an object of the present invention to provide a method for producing a glass substrate for a magnetic information recording medium, which can suppress the occurrence of the above and secure the necessary characteristics as a glass substrate for a magnetic information recording medium.

In order to solve the above-mentioned problems, the present inventors have conducted intensive studies by paying attention to the composition of the glass substrate used in the manufacturing process of the glass substrate for magnetic information recording medium. As a result, glass blanks that have compositional fluctuations are intentionally created by processing at a specific heat treatment temperature into a glass composition that can partially have compositional fluctuations, and a phase with a thin SiO ₂ concentration is removed. By roughening the surface, the processing rate in the grinding process and polishing process can be improved without reducing the grinding and polishing margins, and the deterioration of high surface smoothness and waviness quality can be suppressed. It has been found that a glass substrate for an optical magnetic information recording medium having excellent surface quality can be produced without increasing the load in the grinding process or polishing process.

The method for producing a glass substrate for a magnetic information recording medium according to the present invention promotes composition fluctuation in a glass composition that can impart composition fluctuation (local compositional nonuniformity of less than 100 nm) to glass. A step of performing a heat treatment of the glass substrate at the heat treatment temperature, and a step of improving the workability of the surface by removing at least a part of the SiO ₂ concentration thin phase separated by the heat treatment, the glass transition temperature of the glass substrate And Tg (° C.), the heat treatment temperature is in the range of Tg to Tg + 100 (° C.). This is a method for producing a glass substrate for a magnetic information recording medium. The composition fluctuations may be non-uniform as long as the composition is partially non-uniform, and may be amorphous, or minute crystals may be unevenly distributed.

In the manufacturing method of the magnetic recording medium glass substrate, a step of improving the workability of the surface by removing at least a portion of the SiO ₂ concentration thin phases different reactive by SiO ₂ concentration in the glass It is preferred to include treatment with a polar solution. As the solution having different reactivity depending on the SiO ₂ concentration in the glass, for example, an alkaline polar solution having a pH of 9 or more and an acidic polar solution having a pH of 5 or less are preferably used, and particularly a solution mainly composed of hydrofluoric acid (hydrofluoric acid). Is more effective and more preferable. With such a configuration, it is possible to selectively etch a thin phase having a low SiO ₂ concentration using the relatively low concentration hydrofluoric acid used, and the glass on the entire substrate surface is removed. The surface roughness can be controlled without even reducing the grinding margin and polishing margin, and as a result, the workability such as grinding and polishing can be improved.

In the method for producing a glass substrate for a magnetic information recording medium, as a step of improving the surface workability by removing at least a part of the thin phase having a low SiO ₂ concentration, a grinding treatment with an acidic grinding fluid or an acidic treatment is performed. It is preferable to include a polishing treatment with an abrasive. With such a configuration, it is possible to perform processing while selectively removing a phase having a low SiO ₂ concentration, and the processing rate can be greatly improved.

In the method for manufacturing a glass substrate for a magnetic information recording medium, in the polishing step, the polishing is performed when a step of improving the workability of the surface by removing at least a part of the phase having a low SiO ₂ concentration is performed. It is also possible to adjust the surface roughness of the glass substrate for magnetic information recording medium after the polishing process to an appropriate range by using a polishing process (also referred to as a final polishing process or a precision polishing process) performed last. The Ra after the final polishing treatment is preferably 0.1 to 5 mm. With such a configuration, the entire substrate can be uniformly and precisely controlled to a desired surface roughness by controlling the heat treatment temperature and glass composition. Therefore, it is possible to suppress the head adsorption generated on the smooth magnetic disk, and the head can stably fly when configured as a hard disk drive device.

  In the method for manufacturing a glass substrate for a magnetic information recording medium, it is preferable that the heat treatment temperature is in a range of Tg to Tg + 70 (° C.). If it is such a structure, shape correction of glass blanks can also be performed, generating a composition fluctuation.

In the method for manufacturing a glass substrate for a magnetic information recording medium, the glass substrate is, by weight, SiO ₂ : 45 to 70%, Al ₂ O ₃ : 5 to 20%, B ₂ O ₃ : 1 to 15%, _{li 2 O: 0.1~7%, Na} 2 O: 2~10%, K 2 O: 0.5~10%, MgO: 1~20%, CaO: 0.1~7%, BaO: 0 _{~3%, SrO: 0~3%,} ZnO: 0~8%, Y 2 O 3: 0~5%, La 2 O 3: 0~5%, Gd 2 O 3: 0~5%, CeO 2 _{: 0~3%, TiO 2: 1~15} %, HfO 2: 0~3%, ZrO 2: 0~3%, Nb 2 O 5: 0~5%, Ta 2 O 5: 0~5%, sb ₂ O _3: 0~2%, it is preferred to have the respective glass component. In the present invention, the composition is not limited, but typically, if the composition is as described above, it is possible to generate composition fluctuation by performing the heating step in the temperature range of the present invention.

  According to the present invention, it is possible to improve the processing rate in the grinding process and the polishing process without reducing the grinding margin and polishing margin, and it is possible to suppress the deterioration of high surface smoothness and waviness quality. It is possible to provide a method for producing a glass substrate for a magnetic information recording medium having an excellent surface quality without increasing the load in the grinding process or polishing process.

It is a figure which shows the example of the metal mold | die for shaping | molding glass substrate blanks. It is a schematic diagram for demonstrating the molten glass supply process which supplies a molten glass to the lower mold | type of the glass substrate blanks shaping | molding metal mold | die. It is a schematic diagram which shows the pressurization process which pressurizes molten glass with the metal mold | die for glass substrate blanks shaping | molding. It is a figure which shows an example of the glass substrate for information recording media manufactured with the manufacturing method of the glass substrate for information recording media of this invention. 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 includes a step of performing a heat treatment of the glass substrate at a heat treatment temperature that promotes the composition fluctuation in a glass composition capable of giving the composition fluctuation to the glass, and Including a step of improving the workability of the surface by removing at least a part of the thin SiO ₂ concentration phase separated by the heat treatment, and the heat treatment temperature when the glass transition temperature of the glass substrate is Tg (° C.) Is in the range of Tg to Tg + 100 (° C.).

  In addition, the method for producing a glass substrate for a magnetic information recording medium according to the present embodiment can have composition fluctuation in the glass composition, and is not particularly limited except that the treatment is performed at the heat treatment temperature. Any known manufacturing method may be used.

  As a manufacturing method of the glass substrate for magnetic information recording media, for example, a glass blank manufacturing process, a 2 lapping process, a rough polishing process (primary polishing process), a precision polishing process (secondary polishing process), a cleaning process, and the like are provided. Methods 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.

<Glass substrate blanks manufacturing process>
The glass substrate blanks manufacturing process is a process of manufacturing a glass substrate including a molten glass supplying process for supplying molten glass and a pressurizing process for press molding. The glass blanks can be manufactured as follows, for example.

  FIG. 1 is a schematic view of a mold for producing the glass substrate blanks of the present invention by press molding. The glass substrate blank molding die 1 is supplied with molten glass, and includes a lower mold 5 having a first molding surface 3 for pressurizing the supplied molten glass, and a first molding surface 3 of the lower mold 5. And an upper die 2 having a second molding surface 4 for pressurizing the molten glass therebetween.

  The manufacturing method of the glass substrate blanks in the present invention is a method of manufacturing a glass substrate by press-molding molten glass, and a molten glass supply step of supplying the molten glass to the first molding surface 3 formed on the lower mold 5. Then, the first molding surface 3 and the second molding surface 4 formed on the upper mold 2 are cooled while pressing the molten glass supplied to the first molding surface 3 to obtain glass substrate blanks. Pressure process.

(Molten glass supply process)
A molten glass supply process is a process of supplying molten glass to the 1st shaping | molding surface formed in the lower mold | type. FIG. 2 is a schematic diagram showing the lower mold 5 and the molten glass 23 in the molten glass supply process. First, the molten glass 23 flows out from the outflow nozzle 21 and is supplied to the lower mold 5 (FIG. 2A). Thereafter, when the molten glass reaches a predetermined amount, the molten glass 23 is cut by the blade 22 and the molten glass 23 is separated (FIG. 2B). The molten glass 23 supplied in the molten glass supply step comes into contact with the center portion of the first molding surface 3, and cooling is started mainly by heat radiation therefrom.

  The lower mold 5 is previously heated to a predetermined temperature. As for the temperature of the lower mold 5, when the glass transition temperature is Tg (° C.), the glass forming needs to be performed in a temperature range of Tg to Tg ± 100 (° C.). When the temperature is lower than Tg-100 (° C.), the flatness of the glass substrate deteriorates, wrinkles are generated on the transfer surface, and damage due to thermal shock occurs. Moreover, when the temperature is higher than Tg + 100 (° C.), it is not preferable because fusion with the glass occurs or the mold deteriorates remarkably.

  There is no restriction | limiting in particular also in the heating means of the lower mold | type 5, It can select suitably from well-known heating means and can be used. For example, a cartridge heater that is used by being embedded in the lower mold 5 or a sheet heater that is used while being in contact with the outer side of the lower mold 5 can be used. Moreover, it can also heat using an infrared heating apparatus or a high frequency induction heating apparatus.

(Pressure process)
In the pressing step, the glass substrate blanks are cooled by pressurizing the molten glass supplied to the first molding surface 3 on the first molding surface 3 and the second molding surface 4 formed on the upper mold 2. 10 is a step of obtaining 10.

  FIG. 3 is a schematic view showing the glass substrate blanks molding die 10 and the glass substrate blanks 10 in the pressurizing step. The lower mold 5 to which the molten glass 23 is supplied in the molten glass supply process moves horizontally to a position facing the upper mold 2. Thereafter, the molten glass is pressurized with the first molding surface 3 of the lower mold 5 and the second molding surface 4 of the upper mold 2. The molten glass spreads by pressurization and contacts the periphery of the first molding surface 3. The molten glass is cooled and solidified by dissipating heat from the contact surface with the first molding surface 3 and the second molding surface 4, thereby forming a glass substrate blank 10.

  The upper mold 2 is heated to a predetermined temperature similarly to the lower mold 5. The heating temperature and heating means are the same as in the case of the lower mold 5 described above. The heating temperature may be the same as or different from the lower mold 5.

  As a pressurizing means for applying a load to the lower mold 5 and the upper mold 2 to pressurize the molten glass, a known pressurizing means can be appropriately selected and used. For example, an air cylinder, a hydraulic cylinder, an electric cylinder using a servo motor, and the like can be given.

  Next, the upper mold 2 is separated from the glass substrate blanks 10, and the glass substrate is taken out from the lower mold 5 with an adsorbing member or the like.

(Heat treatment process)
Heat treatment is performed for the purpose of promoting the composition fluctuation of the glass. At this time, the flatness correction and distortion removal of the glass blanks can be performed together. The heat treatment is performed by using a setter (alumina, zirconia, etc.), and alternately stacking with glass blanks and putting them in a heat treatment furnace. The heat treatment of the glass blank needs to be performed in a temperature range of Tg to Tg + 100 (° C.). When the temperature is lower than Tg (° C.), the glass composition fluctuation cannot be promoted, and when the temperature is higher than Tg + 100 (° C.), the shape of the glass blanks is deteriorated, and between the setters. This is not preferable because the possibility of occurrence of fusion is increased. Therefore, a particularly preferable temperature range for promoting the composition fluctuation of the glass blanks and correcting the flatness and removing the distortion is Tg to Tg + 70 ° C.

Moreover, when the said glass substrate blank is obtained by the above manufacturing methods, it has a composition fluctuation in a glass substrate blank. That is, when heat-treating the glass substrate blank after melting molding at a specific temperature, the glass composition is separated into two phases with a thin phase dark phase and SiO ₂ concentrations SiO ₂ concentration. Further, the composition fluctuation depends on the glass composition, and is obtained from the fact that when the glass in which the composition fluctuation occurs is heat-treated at a predetermined temperature, the glass shifts in an energetically stable direction and phase separation occurs.

The glass composition that can have a composition fluctuation, for example, in _{mass%, SiO 2: 45~70%,} Al 2 O 3: 5~20%, B 2 O 3: 1~15%, Li 2 O: _{0.1~7%, Na 2 O: 2~10} %, K 2 O: 0.5~10%, MgO: 1~20%, CaO: 0.1~7%, BaO: 0~3%, _{SrO: 0~3%, ZnO: 0~8} %, Y 2 O 3: 0~5%, La 2 O 3: 0~5%, Gd 2 O 3: 0~5%, CeO 2: 0~3 _{%, TiO 2: 1~15%,} HfO 2: 0~3%, ZrO 2: 0~3%, Nb 2 O 5: 0~5%, Ta 2 O 5: 0~5%, Sb 2 O 3 : 0 to 2% is preferable.

(Method for producing glass substrate for magnetic information recording medium)
A glass substrate for a magnetic information recording medium can be manufactured by adding a grinding step and a polishing step to be described later to the glass substrate blanks manufactured by the above-described manufacturing method. FIG. 4 is a diagram showing an example of a glass substrate for magnetic information recording medium manufactured by the method for manufacturing a glass substrate for magnetic information recording medium of the present invention. 4A is a perspective view, and FIG. 4B is a cross-sectional view. The glass substrate 30 for a magnetic information recording medium is a disk-shaped glass substrate in which a central hole 33 is formed, and has a main surface 31, an outer peripheral end surface 34, and an inner peripheral end surface 35. Chamfered portions 36 and 37 are formed on the outer peripheral end surface 34 and the inner peripheral end surface 35, respectively.

  By using the glass substrate blank with high flatness of the present invention, it is possible to suppress polishing variation when polishing the surface of the glass substrate blank.

<Wrapping process>
The lapping step is a step of processing the glass substrate into a predetermined plate thickness. Specifically, the process etc. which grind | polish (lapping) the both surfaces of the said glass substrate blank using an acidic grinding liquid are mentioned. By processing in this way, the parallelism, flatness and thickness of the glass substrate 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 substrate are preliminarily adjusted in the first lapping step (first lapping step), and the glass substrate is determined in the second lapping step (second lapping step). It is possible to finely adjust the parallelism, flatness and thickness of the film.

  More specifically, examples of the first lapping step include a step of making the glass substrate have a substantially uniform flatness.

  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. In addition, the surface roughness Ra of the glass substrate used in the polishing process performed by the second lapping process is preferably 0.10 μm or less, and more preferably 0.05 μm or less.

In addition, as a process of improving the workability of the surface by removing at least a part of the thin SiO ₂ concentration phase with respect to the glass substrate blanks before the grinding process, for example, SiO _{2 in} glass such as hydrofluoric acid treatment It is preferable to perform treatment with a polar solution having different reactivity depending on the concentration. Specifically, it is a process that greatly improves the processing rate by utilizing the fact that the surface of the glass blanks is appropriately roughened in advance to improve the catching of pads or pellets used during processing. The surface roughness Ra after the hydrofluoric acid treatment is preferably in the range of 0.5 to 10 μm. If it is less than 0.5 μm, the effect of improving the processing rate cannot be sufficiently obtained. On the other hand, if the thickness is larger than 10 μm, the surface is excessively roughened and cannot be completely removed by the grinding process up to the roughened depth, which may affect the subsequent polishing process. Therefore, the time and concentration of the hydrofluoric acid treatment may be appropriately adjusted so that the surface roughness is within the range.

As described above, the glass substrate blanks partially have composition fluctuations. By treating the glass substrate having this fluctuation with a polar solution having different reactivity depending on the SiO ₂ concentration in the glass such as hydrofluoric acid, or by grinding with an acidic grinding liquid, the glass substrate is uniformly applied as described above. Surface roughness can be imparted, and as a result, the processing rate in the grinding step can be improved.

<Rough polishing process>
The rough polishing step (primary polishing step) is a step of rough polishing the surface of the glass substrate 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 and / or an end surface. The main end surface is a surface parallel to the surface direction of the glass substrate. 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 the inner peripheral side perpendicular to the surface direction of the glass substrate and the surface direction of the glass substrate. Further, the outer peripheral end surface is a surface that is inclined on the outer peripheral side, the surface perpendicular to the surface direction of the glass substrate and the surface direction of the glass substrate.

  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. 5 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 this embodiment.

  A polishing apparatus 11 as shown in FIG. 5 is an apparatus capable of simultaneous grinding 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 substrate blank 10 is attached to each of 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 substrate blanks 10 can be fitted into the base plate holding holes 51 and disposed. For example, the carrier 14 may include 100 base plate holding holes 51 so that 100 glass substrate blanks 10 can be fitted and arranged. Then, 100 glass substrate blanks 10 can be processed by one process (1 batch).

  The carrier 14 sandwiched between the surface plates 12 and 13 via 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 substrate blanks 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 substrate blanks 10 and between the lower surface plate 13 and the glass substrate blanks 10, respectively. The blank 10 can be roughly polished.

  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 a solvent such as water, that is, a slurry liquid. By using a polar solution having different reactivity depending on the SiO ₂ concentration in the glass as the solvent, the polishing step is a step of improving the workability of the surface by removing at least a part of the phase having a low SiO ₂ concentration. It can also be combined.

  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 having a high CeO ₂ content and a small amount of alkaline earth metal, thereby increasing the polishing rate and polishing the glass substrate. It is considered that the smoothness of can be sufficiently improved. Also for the polishing pad, as in the case of the above-mentioned abrasive, by using a material containing a large amount of CeO ₂ and a small amount of alkaline earth metal, the polishing rate is increased and the smoothness of the glass substrate after polishing is improved. It is thought that it can be sufficiently increased.

The use of an abrasive having a high CeO ₂ content is considered to be due to the following reasons that the polishing rate can be increased and the smoothness of the polished glass substrate can be sufficiently enhanced. First, when the glass substrate and CeO ₂ come into contact with each other in a state where pressure is applied to the surface of the glass substrate during polishing, Si—O bonds, which are the main compositions on the surface of the glass substrate, are bonded to Ce—O. It is thought that it will be replaced. 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 polished glass substrate 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 a glass substrate after polishing. It is considered that the adhesion of alkaline earth metal to is suppressed. It is considered that uniform chemical strengthening is performed by performing a chemical strengthening step on such a glass substrate in which adhesion of alkaline earth metal is suppressed.

  When polishing with a polishing liquid in which the abrasive is dispersed in water, the alkaline earth metal is dissolved even when the alkaline earth metal is contained in the water. It is considered that the alkaline earth metal contained in the abrasive is less likely to adhere to the surface and is likely to adhere to the surface of the glass substrate. Therefore, it is considered that the adhesion of alkaline earth metal to the glass substrate after polishing can be sufficiently suppressed by using an abrasive with less 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 substrate. 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, the glass substrate for information recording media excellent in impact resistance can be manufactured, the polishing rate can be further increased, and the glass substrate for information recording media having higher smoothness can be manufactured. 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.

Further, the polishing liquid is in a state where the acidic abrasive is dispersed in a solvent such as water, and the content of CeO ₂ is 3 to 15% by mass with respect to the total amount of the polishing liquid. Is preferred. By doing so, the glass substrate for information recording media excellent in impact resistance can be manufactured, the polishing rate can be further increased, and the glass substrate for information recording media having higher smoothness can be manufactured. Further, in the case of the 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, the glass substrate It is considered that the alkaline earth metal contained in the abrasive is likely to adhere to the surface of the glass substrate. 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 substrate.

  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 substrate by 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.

  Further, 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, and among these, zirconium silicate is contained. 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.

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

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

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

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

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

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

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

In addition, as described above, by using a polar solution having different reactivity depending on the SiO ₂ concentration in the glass as the polishing liquid in the precision polishing step, the surface processing is performed by removing at least a part of the phase having a low SiO ₂ concentration. It is also one of the preferable forms to make it the process of improving property.

  The surface roughness Ra of the glass substrate for a magnetic information recording medium after the precision polishing treatment is preferably 0.1 to 5 mm. If it is in such a range, while having the smoothness required as a glass substrate for magnetic information recording media, while suppressing the adsorption of the head generated on an excessively smooth magnetic disk, when configured as a hard disk drive device The head can stably fly.

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

The glass substrate after the rough polishing by the rough polishing step is preferably cleaned by a cleaning step. The cleaning step after the rough polishing step is not particularly limited, and the surface is removed by cleaning with a polar solution having different reactivity depending on the SiO ₂ concentration in the glass to remove at least a part of the phase having a low SiO ₂ concentration. It is also possible to improve the workability.

For example, the glass substrate is washed with an alkaline detergent having a pH of 13 or more, and the glass substrate is rinsed. Next, the glass substrate is washed with an acid detergent having a pH of 1 or less, and the glass substrate is rinsed. Finally, the glass substrate is cleaned using a hydrofluoric acid (HF) solution. For polishing using cerium oxide, it is most efficient to perform cleaning in the order of alkali cleaning, acid cleaning, and HF cleaning. This is because the abrasive is first dispersed and removed with an alkaline detergent, then the abrasive is dissolved and removed with an acid detergent, and finally the glass substrate is etched with HF to remove the abrasive deeply stuck in the glass substrate. is there. Furthermore, in such a process, as a process for improving the workability of the surface by removing at least a part of the phase having a low SiO ₂ concentration, the polishing rate of the subsequent precision polishing process can be improved.

  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 substrate 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 substrate is taken out. And the taken-out glass substrate is immersed in a neutral detergent liquid. At that time, 120 kHz ultrasonic vibration is applied to the neutral detergent solution. Finally, the glass substrate is taken out, rinsed with pure water, and dried IPA.

The glass substrate after the cleaning 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 substrate 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 substrate, and a glass substrate for hard disk that is superior in impact resistance can be obtained. That is, when there is too much alkaline earth metal remaining on the surface of the glass substrate 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.

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

The glass substrate after the rough polishing is washed 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 substrate is too large, there is a tendency that the flatness of the glass substrate cannot be improved.

(Film formation process)
FIG. 6 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.

  Glass substrate blanks having a glass composition as shown in Table 1 were prepared and heat-treated in a temperature range of Tg to Tg + 100 ° C. (Examples 1 to 10, Comparative Example 1).

Moreover, it was confirmed whether the composition fluctuation existed in the glass substrate blank of each Example and a comparative example. As a method for confirming the composition fluctuation, a glass substrate blank is subjected to a heat treatment at a predetermined temperature, then polished until the surface becomes a mirror surface, immersed in hydrofluoric acid having a concentration of 0.1% by mass, and then the surface morphology is changed to an electron. It can be performed by observing with a microscope (SEM or TEM) whether or not the phase having a low SiO ₂ concentration is removed. The surface roughness after the hydrofluoric acid treatment was measured using AFM (manufactured by Veeco). The hydrofluoric acid treatment time was all 5 minutes.

  Further, the grinding rate was measured by processing the glass substrate after phase separation confirmation using diamond pellets and measuring the processing time when processing to a desired plate thickness. The glass transition temperature (Tg) was measured using SII TMA (thermomechanical analysis).

  From the results shown in Table 1, when Examples 1 to 10 using glass compositions capable of providing composition fluctuations are used, when the heat treatment temperature is Tg + 100 (° C.) or less, It was revealed that the surface roughness was obtained and the grinding rate was improved.

  Next, using the same glass composition as in Example 1, the heat treatment temperatures were changed to obtain glass substrates in Examples 11 to 13 and Comparative Examples 2 to 4, respectively.

  From the results in Table 2, when the heat treatment temperature is lower than Tg (° C.) (Comparative Examples 2 and 3), composition fluctuation does not occur in the glass substrate, and sufficient surface roughness can be obtained even with hydrofluoric acid treatment. The grinding rate was not improved. Further, when the temperature is higher than Tg + 100 (° C.) (Comparative Example 4), the composition fluctuation occurs, but the processing temperature is too high, the shape of the glass substrate deteriorates, the fusion with the setter occurs, and grinding occurs. I couldn't. On the other hand, when the heat treatment temperature was processed in a temperature range of Tg to Tg + 100 (° C.) (Examples 1 and 11 to 13), composition fluctuations could be generated in the glass substrate, and the grinding rate could be improved. .

DESCRIPTION OF SYMBOLS 1 Mold for shaping | molding 2 Upper mold | type 3 1st shaping | molding surface 4 2nd shaping | molding surface 5 Lower mold | type 10 Glass substrate blanks 11 Polishing apparatus 12 Upper surface plate 13 Lower surface plate 16 Pump 101 Glass substrate for magnetic information recording media

Claims (5)

In a glass composition in which composition fluctuations can be imparted to glass, a step of heat-treating the glass substrate at a heat treatment temperature that promotes composition fluctuations, and removing at least a part of the SiO ₂ concentration thin phase separated by the heat treatment Including a step of improving the workability of the surface by
When the glass transition temperature of the glass substrate is Tg (° C.), the heat treatment temperature is in the range of Tg to Tg + 100 (° C.) , and
As a step to improve the workability of the surface by removing at least a portion of the SiO ₂ concentration thin phases, magnetic information recording which comprises treatment with reactive different solutions by SiO ₂ concentration in the glass A method for producing a glass substrate for a medium. In a glass composition in which composition fluctuations can be imparted to glass, a step of heat-treating the glass substrate at a heat treatment temperature that promotes composition fluctuations, and removing at least a part of the SiO ₂ concentration thin phase separated by the heat treatment Including a step of improving the workability of the surface by
When the glass transition temperature of the glass substrate is Tg (° C.), the heat treatment temperature is in the range of Tg to Tg + 100 (° C.) , and
SiO said as the step to improve the workability of the surface by removing at least a portion of the SiO ₂ concentrations of thin phase, grinding or glass by grinding fluid with solutions of different reactivity by SiO ₂ concentration in the glass _A method for producing a glass substrate for a magnetic information recording medium , comprising a polishing treatment with a polishing agent having a solution having different reactivity depending on _two concentrations . 3. The method for producing a glass substrate for a magnetic information recording medium according to claim 2 , wherein a surface roughness Ra of the glass substrate for a magnetic information recording medium after the polishing treatment is 0.1 to 5 mm. A method for producing a glass substrate for a recording medium. The method for manufacturing a glass substrate for a magnetic information recording medium according to any one of claims 1 to 3 , wherein the heat treatment temperature is in a range of Tg to Tg + 70 (° C). A method for manufacturing a substrate. In the manufacturing method of the glass substrate for magnetic information recording media of any one of Claims 1-4 ,
The glass substrate is in weight percent,
SiO _2: 45~70%,
Al ₂ O _3: 5~20%,
B ₂ O ₃ : 1 to 15%,
Li ₂ O: 0.1 to 7%,
Na ₂ O: 2 to 10%
K ₂ O: 0.5 to 10%,
MgO: 1 to 20%,
CaO: 0.1 to 7%,
BaO: 0 to 3%,
SrO: 0 to 3%,
ZnO: 0 to 8%,
Y ₂ O _3: 0~5%,
La ₂ O _3: 0~5%,
Gd ₂ O _3: 0~5%,
CeO ₂ : 0 to 3%,
TiO _2: 1~15%,
HfO ₂ : 0 to 3%,
ZrO ₂ : 0 to 3%,
Nb ₂ O _5: 0~5%,
Ta ₂ O ₅ : 0 to 5%,
Sb ₂ O _3: 0~2%,
A method for producing a glass substrate for a magnetic information recording medium, comprising:

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