JPWO2014002693A1 - GLASS SUBSTRATE FOR INFORMATION RECORDING MEDIUM AND METHOD FOR PRODUCING GLASS SUBSTRATE FOR INFORMATION RECORDING MEDIUM - Google Patents

Abstract

This method of manufacturing a glass substrate for an information recording medium is for an information recording medium used for an information recording medium in which a magnetic thin film layer is formed on the main surface of the glass substrate and the recording density on the magnetic recording surface is 600 Gbit / in 2 or more. The glass substrate for an information recording medium is a main surface of the glass substrate when an 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 average value of SiOH / Si is 0.20 or more and 0.50 or less.

Description

  The present invention relates to a glass substrate for information recording media and a method for producing a glass substrate for information recording media.

  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. In order to suppress these problems, since the size of defects on the substrate surface allowed as an information recording medium is also smaller, even as a glass substrate for information recording media, higher surface smoothness has been pursued, In order to suppress foreign matter adhering to the glass substrate surface and undulation of the glass substrate surface, various devices have been devised in the manufacturing method.

  On the other hand, in recent years, the storage capacity of HDDs has been further improved. At present, one 2.5-inch recording medium has a recording capacity of 500 GB (single-sided 250 GB) and a surface recording density of 600 Gbit / square inch or more. Things are being developed. In such a high recording density recording medium, even when a very smooth glass substrate is used, it can be seen that read errors and / or write errors may occur during data access, and the cause is analyzed. As a result, it turned out that the error was not caused by a conventional head crash.

  Regarding the above-mentioned problems, the glass substrate after manufacturing was examined in detail including the surface state, but no defects that would cause read errors and / or write errors were found, and specific solutions were found. However, as a result of careful examination, after the magnetic layer was provided on the manufactured glass substrate, the signal-to-noise ratio of the magnetic signal varied, which could cause read errors and / or write errors. Sex was found. In the present invention, such a variation in the signal-to-noise ratio of the magnetic signal is also referred to as a decrease in electromagnetic conversion characteristics (SNR).

  As a result of further investigation on the cause of the variation in the signal-to-noise ratio of the magnetic signal, the following has been found. Generally, a glass substrate for a recording medium is once sealed and packaged after being manufactured and then transported, and then taken out and subjected to a step of coating a magnetic layer. At that time, the surface condition of the glass substrate may become non-uniform or a small amount of particles may adhere due to differences in conditions during packaging, transportation, and removal. The cleaning is relatively high, and in some cases, the surface is cleaned using a detergent having a characteristic of slightly dissolving the surface (see JP-A-2006-127624 (Patent Document 1)). The above-mentioned variation in the signal-to-noise ratio of the magnetic signal is caused by the glass surface itself being inspected after manufacturing because the glass surface itself is damaged in the cleaning performed immediately before the coating of the magnetic layer. It became clear that the factor could not be found.

JP 2006-127624 A

  As described above, a glass substrate used in a hard disk drive device having a recording density of 600 Gbit / inch 2 or more has no problem in smoothness and cleanliness of the glass substrate itself, but as an information recording medium, electromagnetic conversion is possible. There arises a problem that the characteristic (SNR) is lowered.

  As a result of repeated verification by the inventors, a time-of-flight secondary ion mass spectrometer (ToF-SIMS) was used for the glass substrate subjected to the above-described alkali treatment step. In addition, when the value of SiOH / Si was measured, it was found that a decrease in electromagnetic conversion characteristics (SNR) occurred remarkably in a glass substrate having a very low value of SiOH / Si.

  When the value of SiOH / Si decreases on the surface of the glass substrate before the formation of the magnetic thin film layer, the polar groups on the surface of the glass substrate decrease, so that the adsorption of the magnetic thin film layer (magnetic layer) deteriorates. .

  As a result, it was found that the signal-to-noise ratio (S / N ratio: SNR) is lowered in an information recording medium in which a magnetic thin film layer is formed on a glass substrate having a reduced SiOH / Si value.

  The present invention has been made in view of the above circumstances, and even when used for an information recording medium having a very high recording density such that the recording density on the magnetic recording surface is 600 Gbit / in 2 or more, An object of the present invention is to provide a glass substrate for an information recording medium and a method for producing the glass substrate for an information recording medium that do not cause a decrease in the noise-to-noise ratio (S / N ratio).

  The glass substrate for an information recording medium based on the present invention is an information recording medium used for an information recording medium in which a magnetic thin film layer is formed on the main surface of the glass substrate and the recording density on the magnetic recording surface is 600 Gbit / square inch or more. When the glass substrate for information recording medium is subjected to an alkali treatment 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 average value of SiOH / Si on the main surface is 0.20 or more and 0.50 or less.

  In another form, the average value of SiOH / Si on the main surface of the glass substrate when the alkali treatment is performed is 0.20 or more and 0.45 or less.

  In another form, with respect to the average value of SiOH / Si on the main surface of the glass substrate before the alkali treatment, the rate of change of the average value of SiOH / Si on the main surface of the glass substrate after the alkali treatment Is 20% or less.

  A method for manufacturing a glass substrate for information recording medium according to the present invention is a method for manufacturing a glass substrate for information recording medium according to any one of the above, wherein the polishing step is performed on the main surface of the disk-shaped glass member. After the polishing step, the disk-shaped glass member after polishing is contacted with 0.1 ppm to 1.4 ppm of hydrogen water for 1 to 10 minutes, and then the disk-shaped glass member is pH 10.0 to 11.0. After the contact with the alkaline solution of 5 to 20 minutes, the disc-shaped glass member is subjected to a treatment for contacting with 0.05 to 0.5% organic acid for 5 to 20 minutes, and then the final cleaning step is performed. The

  Another method for producing a glass substrate for an information recording medium according to the present invention is a method for producing a glass substrate for an information recording medium according to any one of the above, and a polishing step for the main surface of a disk-shaped glass member After the polishing step, the disk-shaped glass member after polishing is brought into contact with an alkaline solution having a pH of 10.0 to 11.0 for 5 to 20 minutes, and then the disk-shaped glass member is 0.05 to 0. A treatment of contacting 5% organic acid for 5-20 minutes is applied, followed by a final washing step.

  Another method for producing a glass substrate for an information recording medium according to the present invention is a method for producing a glass substrate for an information recording medium according to any one of the above, and a polishing step for the main surface of a disk-shaped glass member After the polishing step, the polished disc-shaped glass member is contacted with 1.5 ppm hydrogen water for 3 minutes, and then the polished disc-shaped glass member is alkalinized with a pH of 10.0 to 11.0. The process which contacts a solution for 5 to 20 minutes is given, and the said last washing | cleaning process is given after that.

  According to the present invention, the signal-to-noise ratio (S / N ratio) is lowered even when the recording density on the magnetic recording surface is 600 Gbit / square inch or more and the recording density is very high. It is possible to provide a glass substrate for an information recording medium and a method for producing the glass substrate for an information recording medium that do not cause the problem.

It is a perspective view of the glass substrate for information recording media in an embodiment. It is a perspective view of the information recording medium in an embodiment. It is a flowchart which shows the manufacturing method of the information recording medium in embodiment. It is a figure which shows the evaluation result of the glass substrate for information recording media which concerns on Examples 1-3 and Comparative Examples 1-2.

  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 figure, 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 before the provision of, a cleaning process is performed with an alkaline solution or the like in order to remove minute particles adhering during packaging and / or transportation, or to eliminate unevenness of the surface state due to different conditions.

  Even when such an alkali treatment is performed, when the alkali treatment 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 is performed, the main substrate of the glass substrate is used. In the case of a glass substrate for information recording media in which the average value of SiOH / Si on the surfaces 14 and 15 is 0.20 or more and 0.50 or less, the recording density on the magnetic recording surface seems to be 600 Gbit / square inch or more. Even when used in an information recording medium having a very high recording density, it is possible to sufficiently suppress a decrease in the signal-to-noise ratio (S / N ratio).

(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” 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” 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 “peripheral polishing step” of S15, the outer peripheral end face 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” of S16, main surface polishing was performed. The first polishing step is mainly intended to correct scratches and 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” of S18, a main surface polishing step was performed. 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, colloidal silica having an average particle diameter of about 20 nm was used to obtain a smooth surface.

  After performing the “second polishing step”, the stability of the glass substrate is increased and the magnetic thin film layer is applied to the alkali treatment performed immediately before the magnetic thin film layer is provided on the information recording medium glass substrate. In order to suppress a decrease in electromagnetic conversion characteristics (SNR) in the information recording medium, a pretreatment step of S19 is performed to suppress the activity of the surface of the glass substrate against the alkali treatment. Specifically, when an alkali treatment 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 is performed, the average SiOH / Si of the main surfaces 14 and 15 of the glass substrate The pretreatment step is performed so that the value is 0.20 or more and 0.50 or less.

  In the step of contacting with the alkali solution, the average value of SiOH / Si after the alkali treatment can be lowered by removing in advance the components eluted by the alkali solution present on the glass substrate surface. As a result, the magnetic thin film layer Even when the alkali treatment is performed immediately before the provision of the signal, an effect of suppressing a decrease in the signal-to-noise ratio (S / N ratio) can be obtained.

  However, if the pH of the alkaline solution is increased or the contact time is increased, elution from the glass substrate surface becomes excessive and Ra of the glass substrate increases, and the smoothness necessary as a glass substrate for information recording media. Since it is difficult to sufficiently reduce the average value of SiOH / Si after alkali treatment by a single step of contacting with an alkali solution, it is necessary to carry out a combination of other steps. . As the alkaline solution, a sodium hydroxide solution or the like is preferably used.

  Here, the step of contacting the hydrogen water has a function of reducing the surface charge of the glass substrate. Therefore, deterioration of Ra of the glass substrate in the alkali treatment can be suppressed, and stability of the glass substrate surface with respect to the subsequent alkali treatment can be enhanced.

  In the step of contacting with an organic acid, the effect of smoothing the Ra of the glass substrate deteriorated by contacting with the alkali solution can be obtained without impairing the stability to the alkali treatment. On the other hand, if the concentration of the organic acid is excessively increased or contacted for a long time, Ra is deteriorated. As the organic acid, for example, ascorbic acid, sulfamic acid and the like are preferably used. Of these, ascorbic acid is preferred.

  In the present invention, “contact” with the solution means that the solution may be showered on the surface of the glass substrate, the glass substrate may be immersed in the solution, and the state in contact with the liquid is defined. If it continues for time, it will not specifically limit.

  Next, in the “Final Cleaning” of S20, 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.

  In this embodiment, the magnetic recording medium after the magnetic thin film layer is provided by the alkali treatment performed immediately before the magnetic thin film layer is provided on the glass substrate for the information recording medium. As an index that can sufficiently suppress the decrease in the signal-to-noise ratio (S / N ratio), the average value of SiOH / Si when a specific alkali treatment is applied to the glass substrate is used.

  Specifically, the pretreatment step described above is adjusted so as to satisfy the range of the average SiOH / Si value after alkali treatment in the present invention, thereby determining the glass substrate production conditions. Thereby, variation in the orientation of the magnetic thin film layer (magnetic layer), which occurs as a result of an increase in the activity of the surface of the glass substrate by the alkali treatment step performed before the application of the magnetic thin film layer, can be reduced. Even when the information recording medium is manufactured by providing a magnetic thin film layer after applying the above, a glass substrate for an information recording medium capable of sufficiently suppressing a decrease in signal-to-noise ratio (S / N ratio) is provided. Can be provided.

  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 information recording medium 1 shown in FIG. 2 is obtained using the glass substrate 1G thus obtained.

  As a magnetic thin film layer film forming step in the manufacture of an information recording medium, after cleaning the glass substrate 1G obtained through the above-described steps, both main surfaces of the glass substrate 1G are formed of an adhesion layer made of a Cr alloy and a CoFeZr alloy. An information recording medium of a perpendicular magnetic recording system is formed by sequentially forming a soft magnetic layer, an orientation control underlayer made of Ru, a perpendicular magnetic recording layer made of a CoCrPt alloy, a C-based protective layer, and an F-based lubricating layer. To manufacture. This configuration is an example of a configuration of a perpendicular magnetic recording system, and a magnetic layer or the like may be configured as an in-plane information recording medium. Thereafter, the information recording medium 1 is completed by performing a heat treatment step and the like.

(Example)
In the method for manufacturing a glass substrate shown in the above embodiment, after performing the “second polishing step”, as a pretreatment step (S19) for suppressing the activity of the surface of the glass substrate 1, Examples 1 to 3 are performed. The glass substrate 1G was manufactured by performing the process shown in FIG. The manufactured glass substrate 1G was subjected to an alkali treatment and then subjected to a magnetic thin film layer forming step to manufacture an information recording medium. Similarly, the processing shown in Comparative Example 1 to Comparative Example 2 was also performed.

Example 1
In Example 1, after performing the “second polishing step”, the glass substrate was rinsed by showering with 1.5 ppm of hydrogen water for 3 minutes. Thereafter, the glass substrate was brought into contact with a sodium hydroxide solution having a pH of 10.5 for 5 minutes, and then the glass substrate was brought into contact with 0.1% ascorbic acid for 15 minutes. Thereafter, the glass substrate was finally cleaned with pure water.

(Example 2)
In Example 2, after performing the “second polishing step”, the glass substrate 1G was rinsed by showering using pure water. Thereafter, the glass substrate 1G was brought into contact with a sodium hydroxide solution having a pH of 10.5 for 5 minutes, and then the glass substrate was brought into contact with 0.1% ascorbic acid for 15 minutes. Thereafter, the glass substrate was washed with pure water.

(Example 3)
In Example 3, after performing the “second polishing step”, the glass substrate was rinsed by showering with 1.5 ppm of hydrogen water for 3 minutes. Thereafter, the glass substrate was brought into contact with a sodium hydroxide solution having a pH of 10.5 for 5 minutes. Thereafter, the glass substrate was washed with pure water.

(Comparative Example 1)
In Comparative Example 1, after performing the “second polishing step”, the glass substrate was brought into contact with 0.1% ascorbic acid for 15 minutes. Thereafter, the glass substrate was washed with pure water.

(Comparative Example 2)
In Comparative Example 2, after the “second polishing step”, the glass substrate 1G was cleaned with pure water.

<Measurement of SiOH / Si value after alkali treatment>
Ten glass substrates 1G are extracted from 100 glass substrates 1G obtained by carrying out the above-mentioned Examples 1 to 3 and Comparative Examples 1 to 2, and a time-of-flight secondary ion mass spectrometer is obtained. Using (ToF-SIMS), the SiOH / Si values were measured at three locations on the main surface of each glass substrate 1G before the alkali treatment.

  Then, it processes for 30 minutes with pH 11 sodium hydroxide solution (40 degreeC), and again uses the time-of-flight type secondary ion mass spectrometer (ToF-SIMS), and the main surface of each glass substrate 1G after an alkali treatment is used. The SiOH / Si value was measured at three locations at the same position as the measurement of the SiOH / Si value before the alkali treatment.

  The average value of the SiOH / Si value after the alkali treatment at each evaluation point was determined, and the average value of 10 samples was taken as the SiOH / Si value in each example.

  Further, the rate of change of the value of SiOH / Si is obtained by calculating the rate of change in the value of SiOH / Si after alkali treatment with respect to the value of SiOH / Si before alkali treatment at each measurement point, and then the SiOH / Si at each measurement point. The average value of the rate of change of the values was obtained, and the average value of 10 samples was taken as the rate of change of the SiOH / Si value in each example.

  Since the glass substrate 1G is manufactured with 100 sheets per batch and the variation in evaluation within the same batch is small, the above evaluation was adopted.

<Electromagnetic conversion characteristics evaluation in information recording media>
In the electromagnetic conversion characteristic evaluation, arbitrary 20 glass substrates 1G were taken out from 90 samples that were not used in the alkali treatment test in Example 1 and Comparative Example 2. At this time, in order to adjust to a normal distribution state, the glass substrate after production was once sealed with a packing material, stored for one day, and then taken out and used.

  Before performing the magnetic thin film layer forming step, as an alkali treatment, an immersion treatment in a running water washing tank was performed for 60 minutes with a sodium hydroxide solution having a pH of 11.5 at 30 ° C.

  In the electromagnetic conversion characteristic evaluation, the magnetic thin film layer was formed on the 20 glass substrates 1G by the above-described magnetic thin film layer film forming process to obtain an information recording medium, and then the electromagnetic conversion characteristic was evaluated. Specifically, the difference in SNR with respect to the reference information recording medium was obtained.

  Evaluation of electromagnetic conversion characteristics for an information recording medium was performed by examining recording / reproducing characteristics of a magnetic head. 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. The recording density of the information recording medium was 650 Gbit / inch2.

  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. If the SNR value is ˜−0.1 db, the evaluation is “A”, if it is −0.11 db to −0.20 db, the evaluation is “B”, if it is −0.21 to −0.30 db, the evaluation is “C”, and if it is −0.31 db The evaluation was “D”. The SNR value here represents a difference with respect to a predetermined reference value.

  In order to confirm that the error is due to electromagnetic conversion characteristics, an optical system surface analyzer represented by OSA (Optical Surface Analyzer) in which the cleanliness of the glass substrate 1G before the alkali treatment is set to a predetermined detection sensitivity is used. Confirmed by defect inspection. The larger the number of defects such as deposits and / or dents per information recording medium, the better the surface cleanliness, as the defect count value by the optical system surface analyzer is larger.

  FIG. 4 shows the evaluation results in Examples 1 to 3 and Comparative Examples 1 to 2. Specifically, FIG. 4 shows (i) the value of SiOH / Si of the glass substrate after alkali treatment, and (ii) the reference in Examples 1 to 3 and Comparative Examples 1 to 2. The SNR value (db) of the information recording medium produced in Examples 1-3 and Comparative Examples 1-2, expressed as a difference with respect to the information recording medium, (iii) in Examples 1-3, and Comparative Examples 1-2 , Change rate of SiOH / Si of glass substrate before and after alkali treatment, (iv) OSA count value in Examples 1-3 and Comparative Examples 1-2, (v) Examples 1-3, and Comparative Examples 1-2 The evaluation of is shown.

  In Example 1, (i) the SiOH / Si value of the glass substrate after the alkali treatment is “0.20”, and (ii) manufactured using the glass substrate manufactured under the conditions of Example 1. The SNR value (db) of the information recording medium expressed as a difference from the reference information recording medium in the glass substrate is “0.12 (db)”, (iii) SiOH / Si of the glass substrate before and after the alkali treatment. The rate of change was “13%” (iv) and the OSA count value was “6”. As a result, the evaluation was “A”.

  In Example 2, (i) the SiOH / Si value of the glass substrate after the alkali treatment was “0.46”, and (ii) glass manufactured using the glass substrate manufactured under the conditions of Example 2. The SNR value (db) of the information recording medium expressed as the difference from the reference information recording medium in the substrate is “−0.11 (db)”, (iii) SiOH / Si of the glass substrate before and after the alkali treatment. The rate of change was “17%” (iv) and the OSA count value was “12”. As a result, although it was inferior to Example 1, evaluation "B" was obtained.

  In Example 3, (i) the value of SiOH / Si of the glass substrate after the alkali treatment is “0.50”, and (ii) glass manufactured using the glass substrate manufactured under the conditions of Example 3. The SNR value (db) of the information recording medium expressed as a difference with respect to the reference information recording medium in the substrate is “−0.21 (db)”, (iii) SiOH / Si of the glass substrate before and after the alkali treatment. The rate of change was “21%” (iv) and the OSA count value was “9”. As a result, the evaluation was “C” although it was inferior to Example 2.

  In Comparative Example 1, (i) the SiOH / Si value of the glass substrate after the alkali treatment is “0.55”, and (ii) glass manufactured using the glass substrate manufactured under the conditions of Comparative Example 1. The SNR value change (db) of the information recording medium expressed as a difference from the reference information recording medium in the substrate is “−0.35 (db)”, (iii) SiOH / Si of the glass substrate before and after the alkali treatment. The rate of change was “21%” (iv) and the OSA count value was “10”. As a result, the evaluation was “D”.

  In Comparative Example 2, (i) the SiOH / Si value of the glass substrate after the alkali treatment is “0.14”, and (ii) manufactured using the glass substrate manufactured under the conditions of Comparative Example 2. The SNR value change (db) of the information recording medium expressed as a difference from the reference information recording medium in the glass substrate is “−0.48 (db)”, (iii) SiOH of the glass substrate before and after the alkali treatment. The change rate of / Si was “28%” (iv) The OSA count value was “8”. As a result, the evaluation was “D”.

  If the evaluation is “A” to “C”, it is possible to ensure the credibility of the information recording medium. Therefore, based on the results of Examples 1 to 3 and Comparative Examples 1 to 2. The glass substrate was manufactured under the condition that the average value of SiOH / Si on the main surface measured using a time-of-flight secondary ion mass spectrometer after alkali treatment was 0.20 or more and 0.46 or less. A substrate is preferably used, and from the viewpoint of evaluation “A” and evaluation “B”, it is more preferable to use a glass substrate manufactured under conditions of 0.20 or more and 0.30 or less. In the examples and comparative examples, it was confirmed that the measured value of OSA representing the cleanliness of the glass substrate surface did not change greatly, and the Ra change value affected the SNR characteristics.

  According to the information recording medium using the glass substrate 1G within the above range, the signal-to-noise ratio (S / N ratio) is lowered even when used in a hard disk drive device with a recording density of 600 Gbit / inch 2 or more. It is possible to provide a glass substrate for an information recording medium without any problems.

  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.

  DESCRIPTION OF SYMBOLS 1 Information recording medium, 1G Glass substrate for information recording media, 11 hole, 12 outer peripheral end surface, 13 inner peripheral end surface, 14 front main surface, 15 back main surface, 23 magnetic thin film layer.

Claims (6)

A glass substrate for an information recording medium used for an information recording medium, wherein a magnetic thin film layer is formed on a main surface of a glass substrate, and a recording density on a magnetic recording surface is 600 Gbit / in 2 or more,
The information recording medium glass substrate is:
When an alkali treatment 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 average value of SiOH / Si on the main surface of the glass substrate is 0.20 or more and 0 A glass substrate for an information recording medium, which is 50 or less.   The glass substrate for an information recording medium according to claim 1, wherein an average value of SiOH / Si on the main surface of the glass substrate when the alkali treatment is performed is 0.20 or more and 0.45 or less.   The change rate of the average value of SiOH / Si on the main surface of the glass substrate after the alkali treatment is 20% or less with respect to the average value of SiOH / Si on the main surface of the glass substrate before the alkali treatment. The glass substrate for information recording media according to claim 1. It is a manufacturing method of the glass substrate for information recording media given in any 1 paragraph of Claims 1-3,
A polishing step is performed on the main surface of the disk-shaped glass member,
After the polishing step, the disk-shaped glass member after polishing is contacted with 0.1 ppm to 1.4 ppm of hydrogen water for 1 to 10 minutes, and then the disk-shaped glass member is alkali having a pH of 10.0 to 11.0. After contact with the solution for 5 to 20 minutes, the disc-shaped glass member is subjected to a treatment for contacting the organic acid of 0.05 to 0.5% for 5 to 20 minutes, and then a final cleaning step is performed. A method for producing a glass substrate for an information recording medium. It is a manufacturing method of the glass substrate for information recording media given in any 1 paragraph of Claims 1-3,
A polishing step is performed on the main surface of the disk-shaped glass member,
After the polishing step, the disk-shaped glass member after polishing is brought into contact with an alkaline solution having a pH of 10.0 to 11.0 for 5 to 20 minutes, and then the disk-shaped glass member is 0.05 to 0.5%. The manufacturing method of the glass substrate for information recording media with which the process which contacts an organic acid for 5 to 20 minutes is given, and the last washing | cleaning process is given after that. It is a manufacturing method of the glass substrate for information recording media given in any 1 paragraph of Claims 1-3,
A polishing step is performed on the main surface of the disk-shaped glass member,
After the polishing step, the polished disc-shaped glass member is contacted with 1.5 ppm of hydrogen water for 3 minutes, and then the polished disc-shaped glass member is mixed with an alkaline solution having a pH of 10.0 to 11.0 and 5 to 5. The manufacturing method of the glass substrate for information recording media with which the process which contacts for 20 minutes is given, and the said last washing | cleaning process is given after that.

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