JP5778165B2 - Method for manufacturing glass substrate for information recording medium and method for manufacturing information recording medium - Google Patents

Description

The present invention relates to a method for manufacturing a glass substrate for an information recording medium and an information recording medium, and more particularly to a method for manufacturing a glass substrate for an information recording medium used for manufacturing an information recording medium and a method for manufacturing an information recording medium.

  In recent information recording media such as memory hard disk drives, there is an increasing demand for cleanliness and smoothness of the glass substrate in order to increase the recording density. In recent years, it has been demanded that the outermost end of the glass substrate be finished with high cleanliness.

  Japanese Patent Laying-Open No. 2006-306924 (Patent Document 1) discloses a step of suppressing the adhesion of colloidal silica to a substrate in a polishing step in the process of manufacturing a glass substrate.

JP 2006-306924 A

However, as a result of the diligent research by the inventors, the zeta potential on the particle surface of the colloidal silica and the zeta potential on the surface of the glass substrate are controlled, and the colloidal silica is repelled against the glass substrate by the respective zeta potential relationship. Even in this case, it was found that the adhesion of colloidal silica to the substrate was not sufficiently suppressed. In particular, in the polishing process, it has been found that the adhesion of colloidal silica from the carrier holding the glass substrate to the edge of the glass substrate is not suppressed.

The present invention has been made in view of the above circumstances, and is a glass substrate for an information recording medium capable of sufficiently suppressing re-adhesion of colloidal silica to a glass substrate in the glass substrate production process. It is an object to provide a manufacturing method and a manufacturing method of an information recording medium .

In the manufacturing method of the glass substrate for information recording media based on this invention, it is a manufacturing method of the glass substrate for information recording media in which a magnetic recording layer is formed in the main surface of a glass substrate, Comprising: During the manufacturing process of the said glass substrate And a step of polishing using colloidal silica in a state where the glass substrate is held by the carrier of the polishing apparatus using a polishing apparatus, and the step of polishing the glass substrate is performed on the particle surface of the colloidal silica . the potential relationship between the zeta potential and the zeta potential of the surface of the carrier, the colloidal silica with repel against the carrier, the potential of the zeta potential of the zeta potential and the surface of the glass substrate of the particle surface of the colloidal silica the relationship with the colloidal silica is repelled from the above glass substrate, a step of polishing the glass substrate When including, a zeta potential of the particle surface of the colloidal silica expressed as ζsi [mV], the zeta potential of the surface of the carrier expressed as ζc [mV], represents the zeta potential of the surface of the glass substrate and ζs [mV], The glass substrate is polished at each zeta potential that satisfies the conditions of ζsi [mV] <0 [mV] , ζc [mV] <0 [mV] , and ζs [mV] <0 [mV] . A water-soluble polymer or a surfactant is used as each zeta potential adjusting agent, and the zeta potential ζc [mV] on the surface of the carrier is adjusted before polishing the glass substrate.

The zeta potential ζsi the particle surface of the upper Symbol colloidal silica [mV], the zeta potential ζc of the surface of the carrier [mV], and zeta potential ζs of the surface of the glass substrate [mV] is the formula 3 formula 1 below Satisfy the relationship. | Ζsi−ζc | ≦ 20 [mV] Equation 1, | ζsi−ζs | ≦ 20 [mV] Equation 2, | ζc−ζs | ≦ 20 [mV] Equation 3.

  In another embodiment, the pH in the polishing step is 3-13. Further preferred pH is 10-13.

  In another embodiment, the method includes a step of subjecting the glass substrate to a chemical strengthening treatment, and the step of polishing the glass substrate is performed on the glass substrate subjected to the chemical strengthening treatment.

In the method for manufacturing an information recording medium based on the present invention, a step of manufacturing a glass substrate for information recording medium by the method for manufacturing a glass substrate for information recording medium according to any one of the above, and the glass substrate for information recording medium Forming a magnetic thin film layer on the main surface of the glass substrate for an information recording medium obtained by the manufacturing process.

ADVANTAGE OF THE INVENTION According to this invention, in the manufacturing process of a glass substrate, the manufacturing method of the glass substrate for information recording media which can fully suppress the reattachment of colloidal silica to the glass substrate, and the manufacturing method of an information recording medium are provided. It becomes possible.

It is a perspective view which shows the glass substrate obtained by the manufacturing method of the glass substrate in embodiment. It is a perspective view which shows the magnetic disc provided with the glass substrate obtained by the manufacturing method of the glass substrate in embodiment. It is a flowchart figure which shows the manufacturing method of the glass substrate in embodiment. It is a fragmentary sectional view of the double-side polish apparatus used for a grinding | polishing process. FIG. 5 is a cross-sectional view taken along line VV in FIG. 4. It is a figure which shows the evaluation result which manufactured the glass substrate by "the process I." It is a figure which shows the evaluation result which manufactured the glass substrate at "the process II." It is a figure which shows the evaluation result which manufactured the glass substrate at "the process III."

  Embodiments based on the present invention will be described below with reference to the drawings. In the description of the embodiments, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, amount, or the like unless otherwise specified. In the description of the embodiments, the same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated.

[Glass substrate 1 and magnetic disk 10]
With reference to FIG. 1 and FIG. 2, the glass substrate 1 obtained by the manufacturing method of the glass substrate for information recording media based on this Embodiment and the magnetic disc 10 provided with the glass substrate 1 are demonstrated first. FIG. 1 is a perspective view showing a glass substrate 1 used for a magnetic disk 10 (see FIG. 2). FIG. 2 is a perspective view showing a magnetic disk 10 provided with a glass substrate 1 as an information recording medium.

  As shown in FIG. 1, a glass substrate 1 (glass substrate for information recording medium) used for a magnetic disk 10 has an annular disk shape with a hole 1H formed in the center. The glass substrate 1 has a front main surface 1A, a back main surface 1B, an inner peripheral end surface 1C, and an outer peripheral end surface 1D.

  The size of the glass substrate 1 is, for example, 0.8 inch, 1.0 inch, 1.8 inch, 2.5 inch, or 3.5 inch. The thickness of the glass substrate is, for example, 0.30 to 2.2 mm from the viewpoint of preventing breakage. In the present embodiment, the glass substrate has an outer diameter of about 64 mm, an inner diameter of about 20 mm, and a thickness of about 0.8 mm. The thickness of the glass substrate is a value calculated by averaging the values measured at a plurality of arbitrary points to be pointed on the glass substrate.

  As shown in FIG. 2, the magnetic disk 10 is formed by forming a magnetic thin film layer 2 on the front main surface 1A of the glass substrate 1 described above. In FIG. 2, the magnetic thin film layer 2 is formed only on the front main surface 1A, but the magnetic thin film layer 2 may also be formed on the back main surface 1B.

  The magnetic thin film layer 2 is formed by spin-coating a thermosetting resin in which magnetic particles are dispersed on the front main surface 1A of the glass substrate 1 (spin coating method). The magnetic thin film layer 2 may be formed on the front main surface 1A of the glass substrate 1 by a sputtering method, an electroless plating method, or the like.

  The film thickness of the magnetic thin film layer 2 formed on the front main surface 1A of the glass substrate 1 is about 0.3 μm to 1.2 μm in the case of the spin coating method, about 0.04 μm to 0.08 μm in the case of the sputtering method, In the case of the electroless plating method, the thickness is about 0.05 μm to 0.1 μm. From the viewpoint of thinning and high density, the magnetic thin film layer 2 is preferably formed by sputtering or electroless plating.

  The magnetic material used for the magnetic thin film layer 2 is not particularly limited, and a conventionally known material can be used. However, in order to obtain a high coercive force, Co having high crystal anisotropy is basically used for the purpose of adjusting the residual magnetic flux density. A Co-based alloy to which Ni or Cr is added is suitable. Further, as a magnetic layer material suitable for heat-assisted recording, an FePt-based material may be used.

  In addition, a lubricant may be thinly coated on the surface of the magnetic thin film layer 2 in order to improve the sliding of the magnetic recording head. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon.

  Furthermore, you may provide a base layer and a protective layer as needed. The underlayer in the magnetic disk 10 is selected according to the magnetic film. 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.

  Further, the underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

  Examples of the protective layer that prevents wear and corrosion of the magnetic thin film layer 2 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 formed continuously with an in-line type sputtering apparatus, such as an underlayer and a magnetic film. In addition, these protective layers may be a single layer, or may have a multilayer structure including the same or different layers.

  Another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, colloidal silica fine particles are dispersed and coated in a tetraalkoxylane diluted with an alcohol-based solvent on the Cr layer, and then fired to form a silicon oxide (SiO2) layer. May be.

[Glass substrate manufacturing method]
Next, the manufacturing method of the glass substrate (glass substrate for information recording media) in this Embodiment is demonstrated using the flowchart figure shown in FIG.

  The glass substrate manufacturing method in the present embodiment includes a glass blank material preparation step (step S10), a glass substrate formation step (step S20), a polishing step (step S30), a chemical strengthening step (step S40), and a cleaning step ( Step S50). The magnetic thin film forming step (step S60) may be performed on the glass substrate (corresponding to the glass substrate 1 in FIG. 1) obtained through the chemical strengthening treatment step (step S40). The magnetic disk 10 is obtained by the magnetic thin film forming step (step S60).

  Hereinafter, details of each of these steps S10 to S60 will be described in order. In the following, simple cleaning appropriately performed between steps S10 to S60 is not described.

(Glass blank material preparation process)
In the glass blank material preparation step (step S10), the glass material constituting the glass substrate is melted (step S11). The glass material is, for example, aluminosilicate glass. The molten glass material is poured onto the lower mold and then press-molded with the upper mold and the lower mold (step S12). A disk-shaped glass blank (glass base material) is formed by press molding. The glass blank material may be formed by cutting out a sheet glass (sheet glass) formed by a downdraw method or a float method with a grinding wheel.

(Glass substrate forming process)
Next, in the glass substrate forming step (step S20), a lapping process is performed on both main surfaces of the press-molded glass blank (step S21). Both main surfaces of a glass blank material are the main surfaces used as the front main surface 1A and the main surface used as the back main surface 1B in FIG. 1 through each process mentioned later (henceforth, both main surfaces) Also called). The lapping polishing process is performed by pressing a lapping platen such as a double-sided lapping device using a planetary gear mechanism against both main surfaces. The approximate parallelism, flatness, thickness, and the like of the glass substrate are preliminarily adjusted by the lapping process.

  After the lapping process, a coring (inner peripheral cut) process is performed on the center portion of the glass blank using a cylindrical diamond drill or the like (step S22). By the coring process, an annular glass substrate having a hole in the center is obtained. A predetermined chamfering process may be performed on the hole in the center.

(Polishing process)
Next, in the polishing step (step S30), similarly to step S21 described above, lap polishing is performed on both main surfaces of the glass substrate (step S31). In the coring step (step S22), fine scratches and protrusions formed on both main surfaces of the glass substrate are removed. After the lapping process, the outer peripheral end surface of the glass substrate is polished into a mirror surface by a brush (step S32). As the abrasive grains, a slurry containing cerium oxide abrasive grains is used.

  Next, as a first polishing polishing step (rough polishing), the warp of the glass substrate is corrected while removing scratches remaining on both main surfaces of the glass substrate in the lapping polishing step (step S31) (step S32). In the first polishing step, a double-side polishing device using a planetary gear mechanism is used.

  In the second polish polishing step (precision polishing), the glass substrate is subjected to polishing again, and fine defects remaining on both main surfaces of the glass substrate are eliminated (step S34). Both main surfaces of the glass substrate are finished to have a mirror-like surface, thereby forming a desired flatness and eliminating the warpage of the glass substrate. In the second polishing step, a double-side polishing device using a planetary gear mechanism is used. Colloidal silica is used as the abrasive.

  Here, with reference to FIG. 4 and FIG. 5, the structure of the double-side polish apparatus 1000 is demonstrated easily. 4 is a partial cross-sectional view of a double-side polishing apparatus 1000 used in the polishing process, and FIG. 5 is a cross-sectional view taken along line VV in FIG.

  Referring to FIG. 4, double-side polishing apparatus 1000 has an upper surface plate (upper whetstone holding surface plate) 300 and lower surface plate (lower whetstone holding) to which pellet holding plates 300a and 400a holding a number of grinding pellets 100 are attached. A disk-shaped glass substrate 1 held by a carrier 500 is disposed between a surface plate 400. The upper surface plate 300 and the lower surface plate 400 rotate in opposite directions.

  Also, as shown in FIG. 5, a sun gear 600 and an internal gear 700 are provided between the upper surface plate 300 and the lower surface plate 400, and the carrier 500 is disposed between them. A gear that meshes with the sun gear 600 and the internal gear 700 is formed on the outer periphery of the carrier 500. Accordingly, the sun gear 600 and the internal gear 700 are rotated with the rotation of the upper and lower surface plates, so that the carrier 500 rotates and revolves.

  Regarding the rotation direction of the carrier 500, it is possible to select either clockwise or counterclockwise by changing the rotation speed of the sun gear 600 and the rotation speed of the internal gear 700. In this processing apparatus, the carrier 500 rotates and revolves around the sun gear 600, and the upper and lower surface plates 300 and 400 rotate in opposite directions. When viewed from above the processing apparatus, the upper surface plate 300 rotates in the clockwise direction, and the sun gear 600, the internal gear 700, and the lower surface plate 400 all rotate in the counterclockwise direction.

In this polishing step, the colloidal silica is repelled with respect to the carrier 500 by the potential relationship between the zeta potential on the particle surface of the colloidal silica and the zeta potential on the surface of the carrier 500 on which the glass substrate 1 is placed. The colloidal silica is repelled from the glass substrate 1 by the potential relationship between the zeta potential on the surface of the silica particles and the zeta potential on the surface of the glass substrate 1 .

When the zeta potential of the colloidal silica particle surface is expressed as ζsi [mV] , the zeta potential of the surface of the carrier 500 is expressed as ζc [mV], and the zeta potential of the surface of the glass substrate 1 is expressed as ζs [mV] , ζsi [ The glass substrate 1 is polished at each zeta potential satisfying the conditions of mV] <0 [mV] , ζc [mV] <0 [mV] , and ζs [mV] <0 [mV] .

More preferably, the zeta potential ζsi the particle surface of the colloidal silica [mV], the zeta potential ζc of the surface of the carrier 500 [mV], and zeta potential ζs surface of the glass substrate 1 [mV] is, from the equation 1 below It is preferable to satisfy the relationship of Equation 3.

| Ζsi−ζc | ≦ 20 [mV] Equation 1
| Ζsi−ζs | ≦ 20 [mV] Equation 2
| Ζc−ζs | ≦ 20 [mV] Equation 3
Also, the zeta potential ζsi the particle surface of the colloidal silica [mV], the zeta potential ζc of the surface of the carrier 500 [mV], and, as a modifier of the zeta potential of the zeta potential ζs surface of the glass substrate 1 [mV], Water soluble polymers or surfactants can be used. Examples of the water-soluble polymer include polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl pyrrolidone, (meth) acrylic acid (co) polymer, poly (meth) acrylamide (co) polymer, or ethylene glycol. Examples of the surfactant include phosphoric acid surfactants, sulfonic acid surfactants, and nonionic surfactants.

When adjusting the zeta potential on the surface of the carrier 500, in addition to changing the pH of the polishing liquid, the water-soluble polymer or surfactant used in the treatment is treated with the water-soluble polymer or surfactant. It is possible to increase or decrease the value of the zeta potential by adjusting. For example, when the contact time with the water-soluble polymer is increased and the introduction amount of OH groups or COOH groups on the glass substrate or carrier surface is increased, the value of zeta potential decreases, and the OH group or COOH group When the introduction amount is decreased, the zeta potential value tends to increase.

The zeta potential on the surface of the colloidal silica can be adjusted by adjusting the pH of the polishing liquid. If the polishing liquid is increased in pH, that is, adjusted to the alkaline side, the zeta potential decreases (adjustable to the negative side) and polishing is performed. When the pH of the liquid is reduced, that is, adjusted to the acidic side, the zeta potential increases (adjustable to the positive side). Furthermore, it can be similarly adjusted by the above water-soluble polymer or surfactant.

  Also preferably, the pH of the colloidal silica in the polishing step is 3-13. More preferably, the pH is 10-13.

(Chemical strengthening process)
Referring again to FIG. 3, after the glass substrate is cleaned, the chemically strengthened layers are formed on both main surfaces of the glass substrate by immersing the glass substrate in the chemically strengthened treatment liquid (step S <b> 40).

  Alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are replaced by alkali metal ions such as potassium ions having a larger ion radius than these ions (ion exchange method). Compressive stress is generated in the ion-exchanged region due to the strain caused by the difference in ion radius, and both main surfaces of the glass substrate are strengthened. As described above, a glass substrate corresponding to the glass substrate 1 shown in FIG. 1 is obtained.

  The glass substrate 1 may be further subjected to a polishing polishing process with a machining allowance on both main surfaces of 0.1 μm or more and 0.5 μm or less. By removing the deposits remaining on the main surface of the glass substrate after the chemical strengthening step, the occurrence of head crashes in the magnetic disk manufactured using the glass substrate 1 is reduced. Further, by setting the machining allowance on both main surfaces in the polishing process to be 0.1 μm or more and 0.5 μm or less, the unevenness of stress generated by the chemical strengthening process does not appear on the surface. The manufacturing method of the glass substrate in the present embodiment is configured as described above.

  Note that a chemical strengthening step may be performed between the first polishing step (rough polishing) and the second polishing step (precision polishing).

(Washing process)
Next, the glass substrate is cleaned (step S50). By cleaning the two main surfaces of the glass substrate with detergent, pure water, ozone, IPA (isopropyl alcohol), UV (ultraviolet) ozone, or the like, the deposits attached to the two main surfaces of the glass substrate are removed.

  Thereafter, the number of deposits on the surface of the glass substrate is inspected using an optical defect inspection apparatus or the like.

(Magnetic thin film formation process)
Magnetic thin film layers are formed on both main surfaces (or one of the main surfaces) of the glass substrate (corresponding to the glass substrate 1 shown in FIG. 1) on which the chemical strengthening treatment has been completed. The magnetic thin film layer includes an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoFeZr alloy, an orientation control underlayer made of Ru, a perpendicular magnetic recording layer made of a CoCrPt alloy, a protective layer made of a C system, and a lubrication made of an F system. It is formed by sequentially depositing layers. By forming the magnetic thin film layer, a perpendicular magnetic recording disk corresponding to the magnetic disk 10 shown in FIG. 2 can be obtained.

  The magnetic disk in the present embodiment is an example of a perpendicular magnetic disk composed of a magnetic thin film layer. The magnetic disk may be composed of a magnetic layer or the like as a so-called in-plane magnetic disk.

(Action / Effect)
As described above, in the present embodiment, in the polishing step, not only the colloidal silica is repelled from the glass substrate 1 by the potential relationship between the zeta potential on the particle surface of the colloidal silica and the zeta potential on the surface of the glass substrate 1. The colloidal silica is repelled against the carrier 500 by the potential relationship between the zeta potential on the particle surface of the colloidal silica and the zeta potential on the surface of the carrier 500 on which the glass substrate 1 is placed. Thereby, the adhesion of the colloidal silica to the carrier 500 is suppressed, so that the reattachment of the colloidal silica from the carrier 500 to the glass substrate 1 can be prevented.

[Examples and Comparative Examples]
Next, with reference to FIGS. 6 to 8, Examples 1 to 3 , Examples A to C , Examples a to c , Comparative Examples 1 to 5 , Comparative Examples A to E , and Comparative Examples a to e explain. In addition, the manufacturing process demonstrated in FIG. 3 is called "process I", and the manufacturing process which employ | adopted the chemical strengthening process between the 1st polish grinding | polishing process (rough grinding | polishing) and the 2nd polish grinding | polishing process (precision grinding | polishing). The manufacturing process that does not employ the chemical strengthening process is referred to as “process II” and is referred to as “process III”.

Examples 1 to 3 and Comparative Examples 1 to 5 shown in FIG. 6 are glass substrates manufactured by “Step I”, and Examples A to C and Comparative Examples A to E shown in FIG. II ”is a glass substrate manufactured by“ Step III ”. Examples a to c and comparative examples a to e illustrated in FIG. 8 are glass substrates manufactured by“ Step III ”.

  Moreover, the composition of a glass substrate is the mass%, and is SiO2: 50% -70%, Al2O3: 0% -20%, B2O3: 0% -5%.

However, SiO2 + Al2O3 + B2O3 = 50% -80%
Li2 + Na2 + K2O = 0% to 20%
MgO + CaO + BaO + SrO + ZnO = 2% -20%
It is.

(Examples 1 to 3 and Comparative Examples 1 to 5 )
With reference to FIG. 6, the evaluation result which manufactured the glass substrate by "the process I" is shown as Examples 1-3 and Comparative Examples 1-5 . Examples 1 to 3 and Comparative Examples 1 to 5 show the results of polishing at each pH shown in FIG.

  For colloidal silica, Compol 20 manufactured by Fujimi Incorporated was used, and a polishing process was performed using a suede polishing pad.

The Zeda potential was measured using ELSZ-2 manufactured by Otsuka Electronics. For the carrier and the glass substrate, a sample of a predetermined size (37 mm × 16 mm × 5 mm) was prepared, and the zeta potential [mV] of each surface was measured using a flat cell of the carrier and the glass substrate. For colloidal silica, the zeta potential [mV] of the particle surface of colloidal silica was measured using a flow cell unit. The applied voltage is 60 mV / cm. As the number of defects, the number of defects on the end face of the glass substrate was evaluated.

Further, in this example, the zeta potential [mV] of the particle surface of colloidal silica, the surface of the carrier and the surface of the glass substrate was adjusted by adjusting the pH of the polishing liquid as shown in FIG. It adjusted by adjusting the time made to contact phosphoric acid type surfactant solution as surfactant before. Specifically, it was adjusted by changing the concentration of the phosphoric acid surfactant (monoalkyl phosphate solution) (usually 1% solution). When the concentration is increased, the zeta potential decreases, and when the concentration is decreased, the zeta potential tends to increase (or remain unchanged with no treatment).

The number of defects in Example 1 was “6”, the number of defects in Example 2 was “8”, the number of defects in Example 3 was “9”, and the evaluation results were all excellent (A). The number of defects in Comparative Example 5 was “17”, and the evaluation result was good (B). In each of Examples 1 to 3 and Comparative Example 5 , the zeta potential of the colloidal silica particle surface is expressed as ζsi [mV] , the zeta potential of the carrier surface is expressed as ζc [mV], and the surface of the glass substrate when representing the zeta potential and ζs [mV], ζsi [mV ] <0 [mV], ζc [mV] <0 [mV], met the conditions of ζs [mV] <0 [mV ].

  Moreover, Example 1-Example 3 whose evaluation result is excellent (A) has the conditional expressions of the following formulas 1 to 3.

| Ζsi−ζc | ≦ 20 [mV] Equation 1
| Ζsi−ζs | ≦ 20 [mV] Equation 2
| Ζc−ζs | ≦ 20 [mV] Equation 3
On the other hand, in Comparative Example 1, ζsi = 0 [mV] , ζc = −20 (<0) [mV] , ζs = −45 (<0) [mV] , Since the conditional expression was not provided, the number of defects was “25” and the evaluation was possible (C). In Comparative Example 2, ζsi = 5 (> 0) [mV] , ζc = −10 (<0) [mV] , ζs = −15 (<0) [mV] , and the above formula 1 From the fact that the conditional expression of Formula 3 is not satisfied, the number of defects was “28” and the evaluation was possible (C). In Comparative Example 3, ζsi = 5 (> 0) [mV] , ζc = 3 (> 0) [mV] , and ζs = −20 (<0) [mV]. Since the conditional expression of Expression 3 was not satisfied, the number of defects was “60” and the evaluation was not (D). Moreover, since the comparative example 4 is because pH is 14 and Formula 3 is not satisfy | filled, the number of defects is "55" and evaluation was unsatisfactory (D).

(Examples A to C and Comparative examples A to E )
Referring to FIG. 7, the evaluation result of the production of glass substrates in the "Step II", shown as Examples A to C and Comparative Examples A to E. Examples A to C and Comparative Examples A to E show the results of polishing at each pH shown in FIG.

  For colloidal silica, Compol 20 manufactured by Fujimi Incorporated was used, and a polishing process was performed using a suede polishing pad.

  The Zeda potential was measured using ELSZ-2 manufactured by Otsuka Electronics. For the carrier and the glass substrate, a sample having a predetermined size (37 mm × 16 mm × 5 mm) was prepared, and the zeta potential was measured using a flat cell of the carrier and the glass substrate. For colloidal silica, the zeta potential was measured using a flow cell unit. The applied voltage is 60 mV / cm. As the number of defects, the number of defects on the end face of the glass substrate was evaluated.

The number of defects in Example A was “7”, the number of defects in Example B was “6”, the number of defects in Example C was “10”, and the evaluation results were all excellent (A). The number of defects in Comparative Example E was “18”, and the evaluation result was good (B). In all of Examples A to C and Comparative Example E , the zeta potential of colloidal silica is expressed as ζsi [mV] , the zeta potential of the carrier is expressed as ζc [mV], and the zeta potential of the glass substrate is expressed as ζs [mV]. The following conditions were satisfied : ζsi <0 [mV] , ζc <0 [mV] , ζs <0 [mV] .

  In addition, Example A to Example C, whose evaluation results are excellent (A), include conditional expressions of Expressions 1 to 3 below.

| Ζsi−ζc | ≦ 20 [mV] Equation 1
| Ζsi−ζs | ≦ 20 [mV] Equation 2
| Ζc−ζs | ≦ 20 [mV] Equation 3
On the other hand, in Comparative Example A, ζsi = 0 [mV] , ζc = −20 (<0) [mV] , ζs = −45 (<0) [mV] , Since the conditional expression was not provided, the number of defects was “27” and the evaluation was possible (C). Further, Comparative Example B has the following conditions: ζsi = 5 (> 0) [mV] , ζc = −10 (<0) [mV] , ζs = −13 (<0) [mV] From the fact that the conditional expression of Formula 3 is not satisfied, the number of defects was “29” and the evaluation was possible (C). Further, Comparative Example C has the following conditions: ζsi = 5 (> 0) [mV] , ζc = 3 (> 0) [mV] , ζs = −20 (<0) [mV] Since the conditional expression of Expression 3 was not satisfied, the number of defects was “57” and the evaluation was not (D). Moreover, since the comparative example D had pH 14 and did not satisfy | fill Formula 3, the number of defects was "57" and evaluation was unsatisfactory (D).

(Examples a to c and comparative examples a to e )
Referring to FIG. 8, the evaluation result of the production of glass substrates in the "Step III", shown as Examples a to c and Comparative Examples a to e. Examples a to c and comparative examples a to e show the results of polishing at each pH shown in FIG.

  For colloidal silica, Compol 20 manufactured by Fujimi Incorporated was used, and a polishing process was performed using a suede polishing pad.

  The Zeda potential was measured using ELSZ-2 manufactured by Otsuka Electronics. For the carrier and the glass substrate, a sample having a predetermined size (37 mm × 16 mm × 5 mm) was prepared, and the zeta potential was measured using a flat cell of the carrier and the glass substrate. For colloidal silica, the zeta potential was measured using a flow cell unit. The applied voltage is 60 mV / cm. As the number of defects, the number of defects on the end face of the glass substrate was evaluated.

The number of defects in Example a was “14”, the number of defects in Example b was “16”, the number of defects in Example c was “18”, and the evaluation results were all good (B). The number of defects in Comparative Example e was “23”, and the evaluation result was “C”. In each of Examples a to c , when the zeta potential of colloidal silica is expressed as ζsi [mV] , the zeta potential of carriers is expressed as ζc [mV], and the zeta potential of the glass substrate is expressed as ζs [mV] , ζsi < The conditions of 0 [mV] , ζc <0 [mV] , and ζs <0 [mV] were satisfied. However, the comparative example e does not have the conditional expressions of the following expressions 1 to 3.

In addition, Example a to Example c having a good evaluation result (B) include conditional expressions of the following Expressions 1 to 3.

| Ζsi−ζc | ≦ 20 [mV] Equation 1
| Ζsi−ζs | ≦ 20 [mV] Equation 2
| Ζc−ζs | ≦ 20 [mV] Equation 3
The evaluation results of Examples a to c are inferior to those of Examples 1 to 3 and Examples A to C. In “Step III”, the evaluation results are “Step I” and “Step II”. This is because the "chemical strengthening process" is not adopted.

In Comparative Example a, ζsi = 0 [mV] , ζc = −20 (<0) [mV] , ζs = −45 (<0) [mV] , and the conditional expressions of Formulas 1 to 3 above. The number of defects was “30” and the evaluation was acceptable (C). The comparative example b has the following conditions: ζsi = 5 (> 0) [mV] , ζc = −10 (<0) [mV] , ζs = −15 (<0) [mV] From the fact that the conditional expression of Formula 3 is not satisfied, the number of defects was “38” and the evaluation was not (D). Further, Comparative Example c has the following conditions: ζsi = 5 (> 0) [mV] , ζc = 3 (> 0) [mV] , ζs = −20 (<0) [mV] Since the conditional expression of Expression 3 was not satisfied, the number of defects was “70” and the evaluation was not (D). Moreover, since the comparative example d was pH 14 and did not satisfy | fill Formula 3, the number of defects was "68" and evaluation was unsatisfactory (D).

The evaluation results of Comparative Examples a to e are inferior to those of Comparative Examples 1 to 5 and Comparative Examples A to E in “Step III” in “Step I” and “Step II”. This is because the "chemical strengthening process" is not adopted.

  The embodiment and each example based on the present invention have been described above, but the embodiment and each example disclosed this time are illustrative in all points and are not restrictive. The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 glass substrate, 1A front main surface, 1B back main surface, 1C inner peripheral end surface, 1D outer peripheral end surface, 1H hole, 2 magnetic thin film layer, 10 magnetic disk, 100 grinding pellet, 300a, 400a pellet holding plate, 300 upper surface Panel (upper whetstone holding surface plate), 400 lower surface plate (lower whetstone holding surface plate), 500 carrier, 600 sun gear, 700 internal gear, 1000 double-side polishing machine.

Claims (4)

A method for producing a glass substrate for an information recording medium in which a magnetic thin film layer (2) is formed on a main surface of a glass substrate (1),
During the manufacturing process of the glass substrate (1), a colloidal silica is used in a state where the glass substrate (1) is held by the carrier (500) of the polishing apparatus (1000) using a polishing apparatus (1000). Including a polishing step,
The step of polishing the glass substrate (1) includes:
The colloidal silica is repelled from the carrier (500) by the potential relationship between the zeta potential on the particle surface of the colloidal silica and the zeta potential on the surface of the carrier (500), and the zeta on the particle surface of the colloidal silica. A step of polishing the glass substrate (1) by repelling the colloidal silica with respect to the glass substrate (1) according to a potential relationship between a potential and a zeta potential of the surface of the glass substrate (1);
The zeta potential of the particle surface of the colloidal silica expressed as ζsi [mV], the zeta potential of the surface of said carrier (500) represents a ζc [mV], the ζs the zeta potential of the surface of the glass substrate (1) [mV ] , The glass substrate (1) is polished at each zeta potential satisfying the conditions of ζsi [mV] <0 [mV] , ζc [mV] <0 [mV] , and ζs [mV] <0 [mV]. the line stomach,
As a regulator of each zeta potential, a water-soluble polymer or a surfactant is used,
Before polishing the glass substrate (1), the zeta potential ζc [mV] of the surface of the carrier (500) is adjusted,
The zeta potential ζsi [mV] on the surface of the colloidal silica particles, the zeta potential ζc [mV] on the surface of the carrier (500), and the zeta potential ζs [mV] on the surface of the glass substrate (1) are as follows: A method for producing a glass substrate for an information recording medium, which satisfies the relationship of Expressions 1 to 3 .
| Ζsi−ζc | ≦ 20 [mV] Equation 1
| Ζsi−ζs | ≦ 20 [mV] Equation 2
| Ζc−ζs | ≦ 20 [mV] Equation 3 The method for producing a glass substrate for an information recording medium according to claim 1 , wherein the pH in the polishing step is 3 to 13. Including a step of subjecting the glass substrate (1) to chemical strengthening treatment,
The method for producing a glass substrate for an information recording medium according to claim 1 or 2 , wherein the step of polishing the glass substrate (1) is performed on the glass substrate (1) subjected to the chemical strengthening treatment. . A step of producing a glass substrate for information recording medium by the method for producing a glass substrate for information recording medium according to any one of claims 1 to 3,
Forming a magnetic thin film layer on the main surface of the glass substrate for information recording medium obtained by the manufacturing process of the glass substrate for information recording medium;
An information recording medium manufacturing method comprising:

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