JP6196976B2 - Manufacturing method of glass substrate for information recording medium, manufacturing method of information recording medium, and glass substrate for information recording medium - Google Patents

Description

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

  Conventionally, an aluminum substrate or a glass substrate is used as an information recording medium (magnetic disk recording medium) used in a computer or the like. A magnetic thin film layer is formed on these substrates, and information is recorded on the magnetic thin film layer by magnetizing the magnetic thin film layer with a magnetic head.

  In recent years, in a hard disk drive (HDD) device, the recording density has been increased. As the recording density is increased, the gap (flying height) between the information recording medium (medium) and the head that reads and writes the recording while floating on the information recording medium is reduced to about several nanometers.

  As the flying height becomes smaller, when an information recording medium is used in a hard disk drive device, a read error and / or a write error when accessing data recorded on the medium, a head crash where the magnetic head collides with the medium surface, etc. The problem is more likely to occur.

  Therefore, the cleanliness required for the glass substrate for information recording media is very high. For example, in order to reliably remove abrasives and foreign matters, after the polishing process, it is contacted with liquid to facilitate removal of deposits and then scrub cleaning. I have responded by doing.

Patent No. 4623210

However, in the information recording medium glass substrate corresponding to the next-generation surface recording density of 630 Gbit / inch ² or more, a magnetic thin film layer is formed and the information recording medium is formed even though there is no problem in smoothness and cleanliness. In such a case, there has been a problem that the electromagnetic conversion characteristic (SNR) is lowered and the reading accuracy is lowered.

  After scrutinizing such problems, the glass substrate for information recording media is washed with an alkaline solution before the magnetic film is formed to further increase the cleanliness, which is performed by a media manufacturer, and the slight particles on the substrate are also removed. In this process, the glass component elutes slightly and the surface state changes, so that the conditions when forming the magnetic thin film layer by sputtering or the like are subsequently varied, and the above problem has occurred. I understood.

The present invention has been made in view of the above problems, and its purpose is to clean the information recording medium glass substrate with an alkaline solution before forming the magnetic film in order to improve cleanliness. An object of the present invention is to provide a method for manufacturing a glass substrate for an information recording medium, a method for manufacturing an information recording medium, and a glass substrate for an information recording medium that can suppress changes in the surface state.

One aspect of the information recording method of manufacturing a glass substrate for a medium according to the present invention is a method of manufacturing a glass substrate for an information recording medium used in the information recording medium. The process for producing a glass substrate for the information recording medium includes a precision polishing step of precision polishing a main surface of the glass member in a polishing solution containing an acid of the colloidal silica, after the precision polishing step, the dipping solution over 5 minutes 1 An immersion process and an ultrasonic cleaning process for ultrasonically cleaning the glass member after the first immersion process are provided. The surface roughness Ra of the glass member precisely polished in the precision polishing step is 3.0 mm or less in a measurement range of 1 μm 2. The pH of the solution in the first immersion process is 6.5 or more and 8.5 or less.
Another aspect of the method for producing a glass substrate for information recording medium according to the present invention is a method for producing a glass substrate for information recording medium used for an information recording medium. A precision polishing step in which the main surface of the glass member is precisely polished with a polishing liquid containing acidic colloidal silica, a first immersion step in which the main surface of the glass member is immersed in a solution after the precision polishing step, and the glass member in excess after the first immersion step. An ultrasonic cleaning process for performing sonic cleaning. The surface roughness Ra of the glass member precisely polished in the precision polishing step is 3.0 mm or less in a measurement range of 1 μm 2, and the first immersion step is performed in a sodium hydroxide solution at 40 ° C. and pH 11 to 30%. This is a step of immersing so that the change in Ra before and after the alkali treatment is 0.45 mm or less when the Ra of the main surface is measured by AFM before and after the alkali treatment for partial immersion.

  Preferably, the method further includes a second dipping step of dipping the glass member in a solution having a pH of 6.5 or more and 8.5 or less for 5 minutes or more after the ultrasonic cleaning step. Preferably, a scrub cleaning step of scrubbing the glass member after the ultrasonic cleaning step, and a third immersion step of immersing in a solution having a pH of 6.5 or more and 8.5 or less for 5 minutes or more after the scrub cleaning step are further provided.

Preferably, the method further includes a step of adding a conditioner to the solution so that the pH becomes 6.5 or more and 8.5 or less when the pH of the solution is lower than 6.5. Preferably, the pH of the solution in the first immersion step is 7 or more and 8 or less. Preferably, the immersion time in the first immersion step is 120 minutes or less.
In the method for producing an information recording medium according to the present invention, at least a magnetic film is formed on the main surface of the glass substrate for information recording medium obtained by the method for producing a glass substrate for information recording medium described above. Process.
The glass substrate for an information recording medium according to the present invention has a Ra before and after the alkali treatment when the Ra of the main surface is measured by AFM before and after the alkali treatment immersed in a sodium hydroxide solution at 40 ° C. and pH 11 for 30 minutes. Is less than 0.45 mm.

By the present invention lever, even when washing the glass substrate for information recording medium before the magnetic film formed in an alkaline solution to raise the Kiyoshisei, for an information recording medium capable of suppressing the surface state changes A glass substrate , a method for producing an information recording medium, and a glass substrate for an information recording medium can be provided .

It is a perspective view of glass substrate 1G for information recording media. It is a perspective view of an information recording medium. It is a flowchart which shows the manufacturing method of the glass substrate 1G and the information recording medium 1.

Embodiments and examples of the present invention will be described below. The same or corresponding parts are denoted by the same reference symbols, and the description thereof may not be repeated. In the embodiments and examples described below, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified. In the following embodiments, each component is not necessarily essential to the present invention unless otherwise specified.
(Configuration of information recording medium 1)
With reference to FIG. 1 and FIG. 2, the structure of the glass substrate 1G for information recording media and the information recording medium 1 is demonstrated. FIG. 1 is a perspective view of a glass substrate 1G for an information recording medium, and FIG. 2 is a perspective view of the information recording medium.

  As shown in FIG. 1, an information recording medium glass substrate 1G used for the information recording medium 1 (hereinafter referred to as “glass substrate 1G”) has an annular disk shape with a hole 11 formed in the center. ing. The glass substrate 1G has an outer peripheral end face 12, an inner peripheral end face 13, a front main surface 14, and a back main surface 15. As the glass substrate 1G, amorphous glass or the like is used. For example, the outer diameter is about 65 mm, the inner diameter is about 20 mm, the thickness is about 0.8 mm, and the surface roughness is about 2.0 mm or less.

  The inch size of the glass substrate 1G is not particularly limited, and various glass substrates 1G of 0.8 inch, 1.0 inch, 1.8 inch, 2.5 inch, and 3.5 inch are manufactured as disks for information recording media. May be.

  The thickness of the glass substrate 1G is preferably 0.30 mm to 2.2 mm because it is effective against cracking of the glass substrate 1G due to drop impact. The thickness of the glass substrate 1 </ b> G here means an average value of values measured at some arbitrary points to be pointed on the substrate.

  As shown in FIG. 2, in the information recording medium 1, a magnetic thin film layer 23 is formed on the front main surface 14 of the glass substrate 1G. In the drawing, the magnetic thin film layer 23 is formed only on the front main surface 14, but it is also possible to provide the magnetic thin film layer 23 on the back main surface 15.

  As a method of forming the magnetic thin film layer 23, a conventionally known method can be used. For example, a method of spin-coating a thermosetting resin in which magnetic particles are dispersed on the glass substrate 1G, a method of forming by sputtering. The method of forming by electroless plating is mentioned.

  The film thickness by spin coating is about 0.3 to 1.2 μm, the film thickness by sputtering is about 0.04 to 0.08 μm, and the film thickness by electroless plating is 0.05 to 0.1 μm. From the viewpoint of thinning and high density, film formation by sputtering and electroless plating is preferable.

  The magnetic material used for the magnetic thin film layer 23 is not particularly limited, and a conventionally known material can be used. However, in order to obtain a high coercive force, Co having a high crystal anisotropy is basically used to adjust the residual magnetic flux density. Co-based alloys to which Ni and Cr are added are suitable. In recent years, FePt-based materials have been used as magnetic layer materials suitable for heat-assisted recording.

  In order to improve the sliding of the magnetic head, the surface of the magnetic thin film layer 23 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.

  If necessary, an underlayer and a protective layer may be provided. The underlayer in the information recording medium 1 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.

  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 for preventing wear and corrosion of the magnetic thin film layer 23 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. The protective layer can be formed continuously with an in-line sputtering apparatus, such as an underlayer and a magnetic film. The protective layer may be a single layer, or may have a multilayer structure composed of 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 on a Cr layer diluted with an alcohol-based solvent, and then fired to form a silicon oxide (SiO2) layer. May be.

  As described above, the glass substrate 1G for information recording medium is sealed and packaged in a packaging material after manufacture and then taken out from the packaging material and provided with the magnetic thin film layer 23 and the like. Immediately prior to providing, a cleaning process is performed with an alkaline solution or the like in order to remove minute particles adhering during packaging and transportation, or to eliminate surface state non-uniformity due to different conditions.

  Even when such alkali treatment is performed, when the alkali treatment is performed in which the glass substrate for information recording medium is immersed in a sodium hydroxide solution at 40 ° C. and pH 11 for 30 minutes, the main surface of the glass substrate If the glass substrate for the information recording medium has an average value of SiOH / Si of 14 and 15 of 0.20 or more and 0.50 or less, the recording density on the magnetic recording surface is 630 Gbit / square inch or more. Even when used for an information recording medium having a very high density, it is possible to sufficiently suppress a decrease in the signal-to-noise ratio (S / N ratio).

  Next, a method of manufacturing a glass substrate that can suppress a decrease in the S / N ratio even when an alkali treatment is performed before the formation of the magnetic thin film layer will be described.

(Manufacturing process of glass substrate 1G)
Next, a method for manufacturing the glass substrate 1G and the information recording medium 1 according to the present embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing a method for manufacturing the glass substrate 1G and the information recording medium 1.

  First, in the “glass melting step” of step 10 (hereinafter abbreviated as “S10”, the same applies to step 11 and subsequent steps), the glass material constituting the glass substrate is melted.

  In the “press molding step” of S11, a glass substrate was produced by pressing the molten glass material using an upper mold and a lower mold. The glass composition used was a general aluminosilicate glass. The method for producing the glass substrate is not limited to molding, and may be cut out from plate glass, which is a known technique, and the glass composition is not limited thereto.

  In the “first lapping step (first grinding step)” of S12, both main surfaces of the glass substrate were lapped. This first lapping step was performed using a double-sided lapping device using a planetary gear mechanism. Specifically, the lapping platen was pressed on both surfaces of the glass substrate from above and below, the grinding liquid was supplied onto the main surface of the glass substrate, and these were moved relatively to perform lapping. By this lapping process, a glass substrate having a substantially flat main surface was obtained.

  In the “coring step” of S13, a cylindrical diamond drill was used to form a hole in the center of the glass substrate to produce an annular glass substrate. The inner peripheral end surface and the outer peripheral end surface of the glass substrate were ground with a diamond grindstone, and a predetermined chamfering process was performed.

  In the “second lapping step (second grinding step)” of S14, lapping was performed on both main surfaces of the glass substrate in the same manner as in the first lapping step (S12). By performing the second lapping step, the fine uneven shape formed on the main surface in the coring and end face processing in the previous step can be removed in advance. As a result, the polishing time of the main surface in the subsequent process can be shortened.

  In the “inner and outer periphery polishing step” of S15, the outer peripheral end surface of the glass substrate was subjected to mirror polishing by brush polishing. At this time, as the abrasive grains, a slurry containing general cerium oxide abrasive grains was used.

  In the “first polishing step (rough polishing step)” of S16, main surface polishing was performed. This first polishing step is mainly intended to correct scratches and / or warpage remaining on the main surface in the first and second lapping steps (S12, S14) described above. In the first polishing step, the main surface was polished by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, general cerium oxide abrasive grains were used.

  In the “chemical strengthening step” of S17, a surface reinforcing layer was formed on the main surface of the glass substrate 1G. Specifically, chemical strengthening was performed by bringing the glass substrate 1G into contact with a mixed solution of potassium nitrate (70%) and sodium nitrate (30%) heated to 300 ° C. for about 30 minutes. As a result, the lithium ion and sodium ion on the inner peripheral end surface and outer peripheral end surface of the glass substrate are respectively replaced with sodium ions and potassium ions in the chemical strengthening solution, and a compressive stress layer is formed, thereby forming the main surface of the glass substrate and The end face was strengthened.

In the “second polishing step (precise polishing step)” of S18, the main surface was subjected to precision polishing. This second polishing step aims to eliminate the fine defects on the main surface that have been generated and remain in the above-described steps and finish it in a mirror shape, to eliminate warpage and finish it to a desired flatness. In the second polishing step, polishing was performed by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, a polishing liquid containing acidic colloidal silica having a pH of 4 or less was used in order to obtain a smooth surface. When the main surface of the polished glass substrate 1G is measured with an atomic force microscope (AFM), the measurement range is 1 μm square (1 μm ² ) and the surface roughness Ra (measurement range: 1 μm square) is 3. 0 or less.

  If the glass substrate 1G is brought into contact with the acidic solution, the alkali component is eluted from the glass substrate 1G, and the skeleton is distorted and the bond is very easily broken. In the glass substrate 1G in such a state, the surface state changes due to the alkali cleaning performed before the formation of the magnetic thin film layer. Immediately after polishing, the glass substrate 1G is very activated, and the bonds are also stretched and easily broken. When contacted with an acidic solution in this state, the alkali cleaning resistance before the formation of the magnetic film becomes very low.

  In the manufacturing method according to the present embodiment, in precision polishing using colloidal silica, the particle diameter of colloidal silica is used in an acidic manner in order to agglomerate to a size suitable for use in polishing. On the other hand, since the old surface portion is always scraped by polishing and the new surface is always exposed, the old surface layer portion from which the alkali component has flowed out is removed by polishing, and the new surface layer portion is sequentially exposed. For this reason, in the manufacturing method which concerns on this Embodiment, there is no problem that the alkaline component of a surface layer flows out and a bond strength becomes weak.

  In the “first dipping step” of S19, the glass substrate 1G subjected to precision polishing is dipped in a solution having a pH of 6.5 or more and 8.5 or less for 5 minutes or more. The pH of the solution is preferably 7 or more and 8 or less. The immersion time for immersing the glass substrate 1G in the solution is 120 minutes or less. The pH of the solution used in the first immersion step is measured, and when the pH of the solution is below 6.5, an adjusting agent is added to the solution so that the pH is 6.5 or more and 8.5 or less. . As the adjusting agent, an alkaline adjusting agent is supplied to the solution.

  In the “ultrasonic cleaning process” of S20, the glass substrate 1G after the first immersion process is subjected to ultrasonic cleaning using a high frequency.

  In the “second immersion step” of S21, the glass substrate 1G that has been subjected to ultrasonic cleaning is immersed in a solution having a pH of 6.5 or more and 8.5 or less for 5 minutes or more. The pH of the solution is preferably 7 or more and 8 or less. The immersion time for immersing the glass substrate 1G in the solution is 120 minutes or less. The pH of the solution used in the second immersing step is measured, and when the pH of the solution is below 6.5, an adjusting agent is added to the solution so that the pH is 6.5 or more and 8.5 or less. . As the adjusting agent, an alkaline adjusting agent is supplied to the solution.

  In the “scrub cleaning step” of S22, scrub cleaning is performed on the glass substrate 1G subjected to the second immersion step using a scrub cleaning device.

  In the “third immersion step” of S23, the glass substrate 1G that has been scrubbed is immersed in a solution having a pH of 6.5 or more and 8.5 or less for 5 minutes or more. The pH of the solution is preferably 7 or more and 8 or less. The immersion time for immersing the glass substrate 1G in the solution is 120 minutes or less. The pH of the solution used in the third immersing step is measured, and when the pH of the solution is below 6.5, an adjusting agent is added to the solution so that the pH is 6.5 or more and 8.5 or less. . As the adjusting agent, an alkaline adjusting agent is supplied to the solution.

  In the “Final Cleaning” of S24, final cleaning of the main surface and the end surface of the glass substrate is performed. Thereby, the deposits remaining on the glass substrate are removed. The final cleaning process is a process performed at the end of the glass substrate manufacturing process, and includes a drying process as appropriate.

  The manufacturing method of the glass substrate in this Embodiment is comprised as mentioned above. The glass substrate 1G shown in FIG. 1 is obtained by using this glass substrate manufacturing method. Thereafter, the glass substrate 1G thus obtained is subjected to alkali cleaning, and then a magnetic thin film layer is formed.

  Next, according to the glass substrate 1G configured as described above, the glass substrate for an information recording medium in which the decrease in the signal-to-noise ratio (S / N ratio) is sufficiently suppressed even when the alkali treatment is performed. Can be obtained.

Examples of the present application, and SiO ₂ of 60 to 65 (mol%), and _Al 2 _{O 3} of 8 to 12 (mol%), and Na ₂ O of 5~12 (mol%), 0~3 ( (mol%) K ₂ O, 6 to 10 (mol%) MgO, and verification was performed using a glass composition containing 0 to 5 (mol%) CaO. However, the glass composition is not limited to this and can be applied to all compositions used for the glass substrate for information recording media.

  When the “first dipping step” is performed on the glass substrate subjected to the “second polishing step (precision polishing step)” of S18 shown in FIG. 3, the glass substrate is dipped for 10 minutes in various solutions having different pH values, and then “ By passing through the “ultrasonic cleaning process”, the “scrub cleaning process” in S22, and the “final cleaning process” in S24, the glass substrates according to Examples 1 to 3 and Comparative Examples 1 to 3 shown in Table 1 below are obtained. Produced.

  Table 1 below shows 10 glass substrates prepared according to each of Examples 1 to 3 and Comparative Examples 1 to 3, and 10 samples were extracted and measured with an atomic force microscope (AFM). Range: 1 μm × 1 μm). Then, it processed for 30 minutes by NaOH solution (40 degreeC) of pH11, Ra measurement (measurement range: 1 micrometer x 1 micrometer) was performed again by AFM, and the result of having evaluated the Ra change before and behind a process is shown.

  Table 1 below shows that a magnetic thin film layer is formed on 20 out of the remaining 90 glass substrates produced in each of Examples 1 to 3 and Comparative Examples 1 to 3, and electromagnetic conversion characteristics are evaluated. The result of comparing the change values is shown.

  The glass substrate was manufactured in units of 100 sheets (100 sheets / 1 batch), and since the variation in the same batch was small, the above evaluation was made.

  When evaluating electromagnetic conversion characteristics, first, the glass substrate is washed with an alkaline solution on the obtained glass substrate, and then an information recording medium is produced by forming a magnetic film. The produced information recording medium was examined by examining the recording / reproducing characteristics of the magnetic head using a spin stand. Specifically, the recording was performed by changing the recording frequency to change the recording density, recording the signal, and reading the reproduction output of this signal. As the magnetic head, a perpendicular recording merge type head in which a single pole head for recording (for recording) and a GMR head (for reproduction) were integrated was used.

  The following “A”, “B”, “C”, and “D” were adopted as judgment criteria in Table 1 above. “A” indicates that the SNR change is −0.1 db or less. “B” indicates that the SNR change is −0.11 to −0.20 db. “C” indicates that the SNR change is −0.21 to −0.30 db. “D” indicates that the SNR change is −0.31 db or less.

  As for Comparative Example 1, although the Ra change was small, Ra after the dipping process was increased, and non-standard products were generated. Similarly, in Comparative Example 3, Ra after the dipping process was deteriorated. It can be seen from Table 1 that the solution in the first immersion step preferably has a pH of 6.5 or more and 8.5 or less. It can be seen that the solution in the first immersion step preferably has a pH of 7 or more and 8 or less.

  Next, the relationship between the pH of the solution used in the “second soaking step” of S21 and the SNR change and Ra change was examined. Specifically, in the “first soaking step” of S19, the glass substrate immersed in a solution of pH 7 for 10 minutes is subjected to ultrasonic cleaning of S20, and then the glass substrate is immersed in solutions of various pHs. (S21 "second dipping process"), and then through the "scrub cleaning process" in S22 and the "final cleaning process" in S24, glass substrates according to the following Examples A, B, and C were produced. .

  Table 2 above shows the results of measuring the SNR change (db) and the Ra change for the glass substrates according to Examples A, B, and C in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 3. The following “AA”, “BB”, “CC”, “DD” were adopted as judgment criteria. “AA” indicates that the SNR change is −0.1 db or less. “BB” indicates that the SNR change is −0.11 to −0.20 db. “CC” indicates that the SNR change is −0.21 to −0.30 db. “DD” indicates that the SNR change is −0.31 db or less.

  As apparent from Table 2 above, in the “first soaking step” of S19, the glass substrate immersed in the solution having a pH of 7 for 10 minutes was subjected to ultrasonic cleaning of S20, and then the pH was 6.5 or more. According to the glass substrate obtained by immersing in a solution of 8.5 or less for 10 minutes and passing through the “scrub cleaning process” in S22 and the “final cleaning process” in S24, an information recording medium with good electromagnetic characteristics can be obtained. It can be seen that it can be obtained.

  Next, the relationship between the pH of the solution used in the third immersing step, NR change, and Ra change was examined. Specifically, “first soaking step (S19)” soaking in a solution with pH 7 for 10 minutes, “ultrasonic cleaning step (S20)”, and “second soaking in a solution with pH 7 for 10 minutes” After the “immersion step (S21)” and the “scrub cleaning step (S22)”, the glass substrate is immersed in various pH solutions (“third immersion step (S23)”). By passing (S24) ", the glass substrate which concerns on the following Example a, b, c was produced. Table 3 below shows the results of measuring the SNR change (db) and the Ra change for Examples a, b, and c as in Examples 1 to 3 and Comparative Examples 1 to 3.

  “AAA”, “BBB”, “CCC”, “DDD”, “EEE” were adopted as judgment criteria. “AAA” indicates that the SNR change is +. “BBB” indicates that the SNR change is 0 to −0.1 db. “CCC” indicates that the SNR change is −0.1 to −0.20 db. “DDD” indicates that the SNR change is −0.21 to −0.30 db. “EEE” indicates that the SNR change is −0.31 db or less. “+” Indicates that the S / N ratio is improved as compared with the standard.

  As is clear from Table 3 above, it can be seen that in any of Examples a, b, and c, a glass substrate serving as an information recording medium having good electromagnetic conversion characteristics can be obtained.

  As shown in Tables 1 to 3 above, improvement in SNR reduction is recognized by providing an immersion step using a solution having a predetermined pH. In particular, when an immersion process is provided after a process of applying physical stimulation such as a polishing process and / or a scrub cleaning process, a high effect can be seen.

  Next, the relationship between the immersion time of the solution and the Ra change (Å) and SNR change (db) was examined.

  Specifically, the immersion time is changed variously in a glass substrate subjected to the “second polishing step (precision polishing step)” in S18 shown in FIG. 3 (“first immersion step”). Then, the glass substrate according to Examples i to iv shown in Table 4 below was manufactured through the “ultrasonic cleaning process” in S20, the “scrub cleaning process” in S22, and the “final cleaning process” in S24. .

  “A1”, “A2”, “A3”, “A4”, and “A5” were adopted as judgment criteria. “A1” indicates that the SNR change is +. “A2” indicates that the SNR change is 0 to −0.1 db. “A3” indicates that the SNR change is −0.11 to −0.20 db. “A4” indicates that the SNR change is −0.21 to −0.30 db. “A5” indicates that the SNR change is −0.31 db or less.

  As is apparent from Table 4, it is understood that the immersion time in the first immersion process is preferably 120 minutes or less.

  Although the embodiments and examples of the present invention have been described above, the embodiments and examples disclosed this time should be considered as illustrative in all points and not restrictive. The 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.

The present invention can be applied to a method for producing a glass substrate for information recording medium, a method for producing an information recording medium, and a glass substrate for information recording medium .

  DESCRIPTION OF SYMBOLS 1 Information recording medium, 1G Glass substrate for information recording media, 12 Outer peripheral end surface, 13 Inner peripheral end surface, 14, 15 Main surface, 23 Magnetic thin film layer.

Claims (10)

A method for producing a glass substrate for an information recording medium used for an information recording medium,
A precision polishing step of precisely polishing the main surface of the glass member with a polishing liquid containing acidic colloidal silica;
A first immersion step of immersing in the solution for 5 minutes or more after the precision polishing step;
An ultrasonic cleaning step of performing ultrasonic cleaning on the glass member after the first immersion step;
With
The surface roughness Ra of the glass member precisely polished in the precision polishing step is 3.0 mm or less in a measurement range of 1 μm2,
PH of the solution of the first immersion step state, and are 6.5 to 8.5,
A method for producing a glass substrate for an information recording medium , comprising a step of adding a conditioner to the solution so that the pH becomes 6.5 or more and 8.5 or less when the pH of the solution is lower than 6.5 . A method for producing a glass substrate for an information recording medium used for an information recording medium,
A precision polishing step of precisely polishing the main surface of the glass member with a polishing liquid containing acidic colloidal silica;
A first dipping step of dipping in the solution after the precision polishing step;
An ultrasonic cleaning step of performing ultrasonic cleaning on the glass member after the first immersion step;
With
The surface roughness Ra of the glass member precisely polished in the precision polishing step is 3.0 mm or less in a measurement range of 1 μm2,
The first immersion step includes
Immersion so that the change in Ra before and after the alkali treatment is 0.45 mm or less when the Ra of the main surface is measured by AFM before and after the alkali treatment immersed in a sodium hydroxide solution at 40 ° C. and pH 11 for 30 minutes. Is the process of
A method for producing a glass substrate for an information recording medium.   The glass substrate for information recording media according to claim 1 or 2, further comprising a second immersing step of immersing the glass member in a solution having a pH of 6.5 or more and 8.5 or less after the ultrasonic cleaning step for 5 minutes or more. Manufacturing method. A scrub cleaning step of scrubbing the glass member after the ultrasonic cleaning step;
A third immersing step of immersing in a solution having a pH of 6.5 or more and 8.5 or less for 5 minutes or more after the scrub cleaning step;
The manufacturing method of the glass substrate for information recording media of Claim 1 or 2 further provided. The information recording medium according to claim 2 , further comprising a step of adding a conditioner to the solution such that when the pH of the solution falls below 6.5, the pH becomes 6.5 or more and 8.5 or less. Method for manufacturing glass substrate.   The manufacturing method of the glass substrate for information recording media of Claim 1 or 2 whose pH of the said solution of a said 1st immersion process is 7-8.   The method for producing a glass substrate for an information recording medium according to claim 1 or 2, wherein the immersion time in the first immersion step is 120 minutes or less.   It has the process of forming at least a magnetic film on the main surface of the glass substrate for information recording media obtained by the manufacturing method of the glass substrate for information recording media in any one of Claim 1 to 7 characterized by the above-mentioned. A method for manufacturing an information recording medium.   When the Ra of the main surface is measured by AFM before and after the alkali treatment immersed in a sodium hydroxide solution at 40 ° C. and pH 11 for 30 minutes, the change in Ra before and after the alkali treatment is 0.45 mm or less. A glass substrate for an information recording medium. The glass substrate for information recording media according to claim 9, wherein the glass substrate for information recording media is amorphous glass and has a surface roughness of 2.0 mm or less.

Images