JPWO2013183569A1 - Manufacturing method of magnetic disk and glass substrate for information recording medium - Google Patents

Abstract

The present invention provides a method of manufacturing a magnetic disk capable of forming a magnetic recording layer at a high temperature. The present invention is a method of manufacturing a magnetic disk including a step of forming a magnetic recording layer on a glass substrate having a temperature of 550 ° C. or higher, wherein the glass substrate is expressed in mole percentage, and SiO 2 is 60 to 75%. Al2O3 is 7 to 17%, B2O3 is less than 0 to less than 2%, and one or more of MgO, CaO, SrO and BaO is contained in total and more than 18% and 26% or less, and the total content of the seven components is 95% The present invention relates to a method of manufacturing a magnetic disk that contains one or more of Li2O, Na2O, and K2O in a total of less than 1%, or that does not contain any of these three components.

Description

  The present invention relates to a method for manufacturing a magnetic disk and a glass substrate for an information recording medium, and more particularly to a method for manufacturing a magnetic disk for forming a magnetic recording layer at a high temperature and a glass substrate suitable for such a manufacturing method.

  In recent years, with the increase in recording capacity of hard disk drives, higher recording density is progressing at a high pace. However, with the increase in recording density, miniaturization of magnetic particles impairs thermal stability, and there is a problem of crosstalk or a decrease in the S / N ratio of a reproduction signal.

  Therefore, heat-assisted magnetic recording technology has attracted attention as a fusion technology of light and magnetism. This is a technique in which a magnetic recording layer is irradiated with a laser beam or near-field light and recorded by applying an external magnetic field in a state where the coercive force is lowered in a locally heated portion, and the recorded magnetization is read by a GMR element or the like. In addition, since recording can be performed on a medium having a high holding force, the magnetic particles can be miniaturized while maintaining thermal stability.

  However, in order to form a high coercive force medium as a multilayer film, it is necessary to sufficiently heat the substrate, and a high heat resistant substrate is required.

  Also in the perpendicular magnetic recording system, a magnetic recording layer different from the conventional one has been proposed to meet the demand for higher recording density, but such a magnetic recording layer needs to be formed at a high temperature. There are often.

  By the way, a silicon substrate has been proposed as a substrate that can cope with the heat-assisted magnetic recording technique described above (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2009-199633

  However, silicon substrates are generally a concern in terms of strength compared to glass substrates. Therefore, it is preferable to use a glass substrate also in the manufacture of a magnetic disk in which the magnetic recording layer is formed at a high temperature.

  Accordingly, it is an object of the present invention to provide a method for manufacturing such a magnetic disk and a method for manufacturing a glass substrate for an information recording medium suitable for such a manufacturing method.

  The present invention is a method of manufacturing a magnetic disk including a step of forming a magnetic recording layer on a glass substrate having a temperature of 550 ° C. or higher,

The glass substrate is expressed in mole percentage, and SiO ₂ is 60 to 75%, Al ₂ O ₃ is 7 to 17%, B ₂ O ₃ is less than 0 to less than 2%, and any one component of MgO, CaO, SrO and BaO More than 18% in total and 26% or less in total, the total content of the above 7 components is 95% or more, and any one or more of Li ₂ O, Na ₂ O and K ₂ O is less than 1% in total Provided is a method for manufacturing a magnetic disk which contains or does not contain any of these three components.

  In addition, the present invention provides a method for manufacturing the magnetic disk, wherein the glass substrate contains 10.5-20% in total of any one component of MgO and CaO in terms of mole percentage.

  Further, the present invention provides a method for producing the magnetic disk, wherein the glass substrate contains a molar percentage and contains 6% or more of MgO.

Further, the present invention provides a method for producing the magnetic disk, wherein the glass substrate contains Al ₂ O ₃ in excess of 18% in terms of mass percentage.

The magnetic disk having a value obtained by dividing the content (molar percentage) of SiO _{2 by} the total amount RO of the contents (molar percentage) of MgO, CaO, SrO and BaO is 4.3 or less. A manufacturing method is provided.

Further, the present invention provides a method for manufacturing the magnetic disk, wherein a temperature T _{2 at} which the viscosity of the glass substrate is 10 ² dPa · s is 1710 ° C. or lower.

  Further, the present invention provides a method for producing the magnetic disk, wherein the glass substrate has an annealing point of 650 ° C. or higher.

  Also provided is a method of manufacturing the magnetic disk, wherein the glass substrate has a specific elastic modulus of 32 MNm · kg or more.

  Further, the present invention provides a method for producing the magnetic disk, wherein the acid resistance index A of the glass substrate is 0.025 nm / h or less.

  Further, the present invention provides a method for producing the magnetic disk, wherein the glass substrate has an alkali resistance index B of 0.28 nm / h or less.

In addition, in terms of mole percentage, SiO ₂ is 60 to 75%, Al ₂ O ₃ is 7 to 17%, B ₂ O ₃ is less than 0 to less than 2%, and one or more components of MgO, CaO, SrO and BaO are contained. The total content is more than 18% and 26% or less, the total content of the above seven components is 95% or more, and any one or more of Li ₂ O, Na ₂ O and K ₂ O is contained in less than 1% in total. Or a glass substrate for an information recording medium which does not contain any of these three components.

  Moreover, the glass substrate for information recording media containing 10.5 to 20% in total of any one component of MgO and CaO in terms of mole percentage is provided.

  Moreover, the glass substrate for information recording media containing 6% or more of MgO in terms of mole percentage is provided.

Further, to provide a glass substrate for the information recording medium to 18% ultra containing Al ₂ O ₃ in mass percentage.

The glass substrate for an information recording medium, wherein a value obtained by dividing the content (molar percentage) of SiO _{2 by} the total amount RO of the contents (molar percentage) of MgO, CaO, SrO, and BaO is 4.3 or less. provide.

  Also provided is the glass substrate for information recording medium, wherein the information recording medium is a magnetic disk.

  Among the present inventions, the inventions related to these glass substrates not only enable the substrate to be heated at a high temperature in the production of the magnetic disk for forming the magnetic recording layer, but also facilitate the production as described below. Is.

International Publication No. 2011/136027 discloses a glass composition having excellent heat resistance. However, the glass viscosity of the composition indicated in the Example 14 for temperature T ₂ is high as a 10 2 ^dPa · s, solubility becomes poor and clearly can be difficult to remove the drawbacks of such bubbles.

  Further, the glass having the composition shown in Example 14 of International Publication No. 2011/136027 has a low specific elastic modulus of 31.2 MNm · kg, and fluttering phenomenon easily occurs at the time of high-speed rotation of the disk and cannot cope with a high recording density. It became clear. Furthermore, it has been clarified that the glass having the above composition has insufficient acid resistance, and a phenomenon such as surface roughness is likely to occur after a polishing process or the like, and cannot cope with a high recording density. Further, it has also been clarified that the glass having the composition has insufficient alkali resistance, and a phenomenon such as surface roughness is likely to occur after a cleaning process or the like, and cannot cope with a high recording density.

  The present inventors have found the facts as described above, have heat resistance applicable to the heat-assisted magnetic recording technology, have excellent mechanical properties, have excellent chemical durability, and have excellent solubility. The present invention has led to the invention of the glass substrate of the present invention for the purpose of providing a glass substrate.

The present invention also includes a disk processing step for processing a glass plate into a glass disc, a wrapping step for wrapping the main surface of the glass disc, a main surface polishing step for polishing the main surface wrapped with the glass disc, and these A method for producing a glass substrate for an information recording medium comprising a washing step of washing a glass disc between or after these steps, wherein the glass plate is expressed in mole percentage, and SiO ₂ is 60 to 75%. 7 to 17% of Al ₂ O ₃ , 0 to less than 2% of B ₂ O ₃ , MgO, CaO, SrO and BaO containing one or more components in total, more than 18% and 26% or less, The total content is 95% or more, and any one or more of Li ₂ O, Na ₂ O and K ₂ O is contained in total less than 1%, or none of these three components is contained. A method for producing a glass substrate for an information recording medium is provided.

  In the method for manufacturing a glass substrate for an information recording medium, the glass disk may have a so-called donut shape having a hole in the center or may have no hole. Further, the end face is usually subjected to chamfering, and may be subjected to etching treatment or mirror polishing.

  Moreover, the manufacturing method of the glass substrate for information recording media whose annealing point of the said glass substrate is 650 degreeC or more is provided.

  Moreover, the manufacturing method of the said glass substrate for information recording media which manufactures the said glass substrate using a float process or a down draw method is provided. Examples of the downdraw method include a fusion method and a slit downdraw method.

  Further, the present invention provides a method for manufacturing the glass substrate for information recording medium, wherein the information recording medium is a magnetic disk.

  According to the method of manufacturing a magnetic disk of the present invention, a magnetic recording layer can be formed on a glass substrate at a high temperature, so that the recording density of the magnetic disk can be increased. In addition, according to the method of manufacturing a magnetic disk of the present invention, the glass substrate on which the magnetic recording layer is formed has a high specific elastic modulus and is less likely to cause surface roughness in a polishing process or a cleaning process. Can be obtained.

  The glass substrate for an information recording medium of the present invention is a glass substrate that can form a magnetic recording layer at a high temperature and can increase the density of the magnetic disk.

  In addition, the glass substrate for information recording medium of the present invention is less likely to cause surface roughness with respect to an acidic polishing slurry liquid (hereinafter referred to as acid solution) in the glass substrate polishing step or the like, and the glass substrate for information recording medium of the present invention. It becomes possible to manufacture a high recording density information recording medium with high productivity. If the glass substrate is prone to surface roughness with respect to the acid solution, an alternative to an acid solution having a high pH is required. In the polishing of a glass substrate using an acid solution having a high pH, the polishing rate decreases, and it takes time for a predetermined polishing amount, resulting in a decrease in productivity. Alternatively, the polishing time until surface roughness occurs is shortened and the predetermined surface roughness is not reached.

  In addition, the glass substrate for information recording medium of the present invention is less likely to cause surface roughness with respect to an alkaline liquid in a glass substrate cleaning process or the like, and a high recording density information recording medium is obtained by using the glass substrate for information recording medium of the present invention. Can be manufactured with high productivity. If the glass substrate is prone to surface roughness with respect to the alkaline solution, an alternative to an alkaline solution having a low pH is required. Cleaning of a glass substrate using an alkaline solution having a low pH reduces the cleaning power, and takes a long time to obtain a predetermined cleanliness, resulting in a decrease in productivity. Or time until surface roughening will become short, and it will not reach predetermined cleanliness.

  The glass substrate for information recording medium of the present invention is not only capable of forming a magnetic recording layer at a high temperature but also an information recording medium glass substrate excellent in solubility, that is, mass productivity.

As the material of the magnetic recording layer for use in the production method of the magnetic disk of the present invention is a FePt or SmCo ₅ is typical.

  The magnetic recording layer is formed on a glass substrate whose temperature is typically 550 ° C. or higher. The temperature of the glass substrate is preferably 600 ° C. or higher or 650 ° C. or higher, as necessary. In addition, the temperature of this glass substrate shall be 800 degrees C or less normally.

  In the method for producing a magnetic disk of the present invention, if necessary, a layer such as an underlayer is formed between the glass substrate and the magnetic recording layer, and if necessary, a protective film or the like is formed on the magnetic recording layer. Layers are formed.

Glass constituting the glass substrate used in the manufacturing method of the magnetic disk of the present invention (hereinafter sometimes referred to as a glass substrate glass or the present invention.) And annealing point T _A of the glass substrate of the present invention, a magnetic recording layer It is preferable that the temperature is 650 ° C. or higher so that deformation of the glass during formation is suppressed and the magnetic disk can be read and written normally. More preferably, it is 700 ° C. or higher, particularly preferably 750 ° C. or higher, and typically 800 ° C. or lower.

In order for the viscosity of the substrate glass to have good solubility, the temperature T _{2 at} which 10 ² dPa · s is obtained is preferably 1710 ° C. or lower. More preferably, it is 1700 degrees C or less, More preferably, it is 1680 degrees C or less.

The density of the glass of the present invention stabilizes the disk rotation, reduces the load on the rotary motor, reduces the power consumption, reduces the exhaust heat load due to the heat generated by the motor, and makes the glass less susceptible to damage. since preferably 2.7 g / cm ³ or less, typically is 2.62 g / cm ³ or less.

  The specific elastic modulus of the substrate glass is preferably 32 MNm / kg or more in order to prevent a fluttering phenomenon during high-speed rotation and to cope with a high recording density. More preferably, it is 32.5 MNm / kg or more, More preferably, it is 33 MNm / kg or more.

  The acid resistance index A of the substrate glass is preferably 0.025 nm / h or less in order to cope with a high recording density without causing a phenomenon such as surface roughness in a polishing process or the like. More preferably, it is 0.02 nm / h or less.

  The alkali resistance index B of the substrate glass is preferably 0.28 nm / h or less in order to correspond to a high recording density without causing a phenomenon such as surface roughness in a cleaning process or the like. More preferably, it is 0.27 nm / h or less.

The acid resistance index A is determined by the following measurement method.
A glass sample having a thickness of 1 to 2 mm and a size of 4 cm square is mirror-polished on both sides with colloidal silica and the end surface is mirror-polished with cerium oxide abrasive grains. This is immersed in an aqueous HNO ₃ solution having a pH of 2 (0.01 mol / liter) kept at room temperature for 3 hours. The amount of Si eluted in the aqueous solution is analyzed by ICP mass spectrometry to obtain a measured value. The etching rate of the glass is calculated from the following formula from the amount of eluted Si, the content of SiO _{2 in the} glass and the density of the glass.
Acid resistance index A = 1000 × L1 / [d × P × (Si atomic weight = 28) / (SiO ₂ molecular weight = 60)] / 3
The unit of the acid resistance index A is nm / h, L1 is the amount of the eluted Si per unit area of the glass plate, the unit is μg / cm ² , d is the density of the glass, the unit is g / cm ³ , and P is SiO in the glass. _The unit of the mass percentage display content is 2.

The alkali resistance index B is determined by the following measurement method.
A glass sample having a thickness of 1 to 2 mm and a size of 4 cm square is mirror-polished on both sides with colloidal silica and the end surface is mirror-polished with cerium oxide abrasive grains. This is immersed in an aqueous NaOH solution having a pH of 12 (0.01 mol / liter) kept at room temperature for 3 hours while applying an ultrasonic wave of 100 kHz. The amount of Si eluted in the aqueous solution is analyzed by ICP mass spectrometry to obtain a measured value. The etching rate of the glass is calculated from the following formula from the amount of eluted Si, the content of SiO _{2 in the} glass and the density of the glass.
Acid resistance index B = 1000 × L2 / [d × P × (Si atomic weight = 28) / (SiO ₂ molecular weight = 60)] / 3
The acid resistance index B is in units of nm / h, L2 is the amount of eluted Si per unit area of the glass plate, the unit is μg / cm ² , d is the density of the glass, the unit is g / cm ³ , and P is the SiO in the glass. _The unit of the mass percentage display content is 2.

  Next, unless otherwise specified, the composition of the glass of the present invention will be described using the mole percentage display content.

SiO ₂ is an essential component. SiO ₂ is 60% or more in order to keep basic chemical durability in order to reduce the weight of the substrate and make it difficult to be damaged. Preferably it is 63% or more, More preferably, it is 65% or more, More preferably, it is 66% or more. On the other hand, the viscosity of the glass is lowered, the solubility is made good, and it is made 75% or less in order to improve the chemical durability in the composition near the present invention. Preferably it is 71% or less, More preferably, it is 70% or less, More preferably, it is 69% or less.

Al ₂ O ₃ is an essential component. Al ₂ O ₃ improves heat resistance, suppresses phase separation, maintains 7% or more to maintain the smoothness of the substrate surface after polishing and cleaning the substrate, and maintains resistance to scratches. Preferably it is 9% or more, more preferably 11% or more, more preferably more than 12%, more preferably more than 12.5%. On the other hand, Al ₂ O ₃ is made 17% or less in order to improve the glass solubility. Preferably it is 16% or less, More preferably, it is 15% or less, More preferably, it is 14% or less. Incidentally, the content of _Al 2 _{O 3} is preferably greater than 18 wt%.

B ₂ O ₃ is not an essential component, but may be contained because it has an effect of improving the solubility and fragility of glass. Maintenance of acid-resistant, and less than 2% for the improvement of T _A. Preferably it is 1.5% or less, More preferably, it is 1.0% or less, More preferably, it is 0.5% or less.

  MgO, CaO, SrO and BaO are components that improve the solubility of the glass and improve the acid resistance and alkali resistance, and any one or more components must be contained in a total (RO) amount of more than 18%. Preferably it is 18.5% or more, more preferably 19% or more. On the other hand, the RO amount is set to 26% or less in order to improve devitrification characteristics and make it difficult to be damaged. Preferably it is 24% or less, more preferably 22% or less.

Among these four components, it is preferable to contain 10.5% or more of any one of MgO and CaO. In order to improve the solubility, it is preferable that the total MgO + CaO content of MgO and CaO is 10.5% or more in order to reduce T ₂ and to prevent damage. More preferably, it is 11% or more, More preferably, it is 12% or more. In order to lower the devitrification temperature and facilitate molding, MgO + CaO is preferably 20% or less. More preferably, it is 18% or less.

The value obtained by dividing the content of SiO ₂ (mole percentage) by the total amount RO of the contents of MgO, CaO, SrO and BaO (mole percentage) increases the specific elastic modulus and improves acid resistance and alkali resistance. In order to lower the temperature T _{2 at} which the viscosity becomes 10 ² dPa · s, it is preferably 4.3 or less. More preferably, it is 4.1 or less, More preferably, it is 3.9 or less.

  MgO is a component that increases the Young's modulus, and since it has the effect of increasing the rigidity of the glass, it is preferably contained in an amount of 6% or more. More preferably, it is 7% or more.

  The glass of the present invention consists essentially of the above seven components, but may contain other components as long as the object of the present invention is not impaired. However, even in that case, the total content of these components is less than 5% for maintaining resistance to scratches, maintaining acid resistance, alkali resistance, and maintaining specific elasticity. Hereinafter, components other than the above seven components will be exemplarily described.

  ZnO is a component having the same effects as MgO, CaO, SrO and BaO, and may be contained in a range of less than 5%. The total content of ZnO and RO is preferably more than 18% and 26% or less.

Li ₂ O, since Na ₂ O and _{K 2} O decreases the _{T A,} it is preferable that the total content of these three components do not contain less than 1%, or substantially.

  Since an oxide having an atomic number larger than Ti such as V may easily damage the glass, when these oxides are contained, the total content thereof is preferably 3% or less. More preferably, it is 2% or less, particularly preferably 1% or less, and most preferably 0.3% or less.

SO ₃ , F, Cl, As ₂ O ₃ , Sb ₂ O _3, SnO _{2 and the} like are typical components as fining agents.

Seven types of glasses having compositions represented by mole percentages in the column of SiO _{2 to} BaO in Table 1 were prepared. In Table 1, MgCa is the total content of MgO and CaO, and RO is the total content of MgO, CaO, SrO and BaO. For these glasses, density d (unit: g / cm ³ ), annealing point T _A (unit: ° C), Young's modulus E (unit: GPa), specific modulus E / d (unit: MNm / kg), viscosity temperature _{T 4} but which becomes ¹⁰ 4 dPa · s (unit: ° C.), temperature _{T 2} at which the viscosity becomes ¹⁰ 2 dPa · s (unit: ° C.), devitrification temperature (unit: ° C.), acid resistance index a, resistance The alkaline index B was measured.

The above measurement was performed as follows.
Density: Measured by Archimedes method for 20 to 50 g of glass without bubbles.
Annealing point: Measured according to JIS R3103 (2001).
Young's modulus: A glass plate having a thickness of 5 to 10 mm and a size of 3 cm × 3 cm was measured by an ultrasonic pulse method.
Specific modulus: obtained by dividing the Young's modulus obtained above by the density.
T ₄ , T ₂ : Measured with a rotational viscometer.
Devitrification temperature: The glass was crushed into glass particles of about 2 mm in a mortar, and these glass particles were placed in a platinum boat and heat-treated in a temperature gradient furnace for 24 hours. The maximum value of the temperature of the glass grains on which the crystals were precipitated was defined as the devitrification temperature.

The acid resistance index A was determined by the following measurement method.
A measurement sample was obtained by mirror-polishing both surfaces of a glass plate having a thickness of 1 to 2 mm and a size of 4 cm square with colloidal silica and mirror-polishing the end surfaces with cerium oxide abrasive grains. This was immersed in an aqueous HNO ₃ solution having a pH of 2 (0.01 mol / liter) kept at room temperature for 3 hours. The amount of Si eluted in the aqueous solution was analyzed by ICP mass spectrometry to obtain a measured value. The etching rate of the glass was calculated by the following formula from the amount of dissolved Si, the content of SiO _{2 in the} glass, and the density of the glass.
Acid resistance index A = 1000 × L1 / [d × P × (Si atomic weight = 28) / (SiO ₂ molecular weight = 60)] / 3
The unit of the acid resistance index A is nm / h, L1 is the amount of the eluted Si per unit area of the glass plate, the unit is μg / cm ² , d is the density of the glass, the unit is g / cm ³ , and P is SiO in the glass. _The unit of the mass percentage display content is 2.

The alkali resistance index B was determined by the following measurement method.
A measurement sample was obtained by mirror-polishing both surfaces of a glass plate having a thickness of 1 to 2 mm and a size of 4 cm square with colloidal silica and mirror-polishing the end surfaces with cerium oxide abrasive grains. This was immersed in an aqueous NaOH solution having a pH of 12 (0.01 mol / liter) kept at room temperature for 3 hours while applying an ultrasonic wave of 100 kHz. The amount of Si eluted in the aqueous solution was analyzed by ICP mass spectrometry to obtain a measured value. The etching rate of the glass was calculated by the following formula from the amount of dissolved Si, the content of SiO _{2 in the} glass, and the density of the glass.
Alkali resistance index B = 1000 × L2 / [d × P × (Si atomic weight = 28) / (SiO ₂ molecular weight = 60)] / 3
The unit of the alkali resistance index B is nm / h, L2 is the amount of the eluted Si per unit area of the glass plate, the unit is μg / cm ² , d is the density of the glass, the unit is g / cm ³ , and P is the SiO in the glass. _The unit of the mass percentage display content is 2.

  Examples 1 to 6 are examples of the substrate glass used in the present invention. Example 7 is a substrate glass for comparison.

  Although the invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application (Japanese Patent Application No. 2012-127872) filed on June 5, 2012, and is incorporated by reference in its entirety.

  The present invention can be used for manufacturing a magnetic disk and a glass substrate for an information recording medium.

In the glass substrate mole percentage display, the SiO ₂ 6 3 ~75%, the _{Al 2 O 3 11 ~1 4%} , B 2 O 3 less than 0 to 2%, MgO, CaO, or SrO and BaO 1 component or more is contained in total, more than 18% and 26% or less, the total content of the above 7 components is 95% or more, and any one or more components of Li ₂ O, Na ₂ O and K ₂ O are 1 in total Provided is a method for manufacturing a magnetic disk that contains less than 1% or contains none of these three components.

Further, in mole percentage display, the _{SiO 2 6 3 ~75%, Al} 2 O 3 of _{11 ~1 4%, B 2 O} 3 less than 0 to 2%, MgO, CaO, any one component of SrO and BaO More than 18% in total and 26% or less in total, the total content of the above 7 components is 95% or more, and any one or more of Li ₂ O, Na ₂ O and K ₂ O is less than 1% in total Provided is a glass substrate for an information recording medium that contains or does not contain any of these three components.

Claims (12)

A method for manufacturing a magnetic disk comprising a step of forming a magnetic recording layer on a glass substrate having a temperature of 550 ° C. or higher,
The glass substrate is expressed in mole percentage, and SiO ₂ is 60 to 75%, Al ₂ O ₃ is 7 to 17%, B ₂ O ₃ is less than 0 to less than 2%, and any one component of MgO, CaO, SrO and BaO More than 18% in total and 26% or less in total, the total content of the above 7 components is 95% or more, and any one or more of Li ₂ O, Na ₂ O and K ₂ O is less than 1% in total A method of manufacturing a magnetic disk that contains or does not contain any of these three components.   2. The method of manufacturing a magnetic disk according to claim 1, wherein the glass substrate contains 10.5 to 20% of one or more components of MgO and CaO in total in terms of mole percentage.   The method of manufacturing a magnetic disk according to claim 1, wherein the glass substrate contains 6% or more of MgO in terms of mole percentage. The glass substrate, method of manufacturing a magnetic disk according to any one of claims 1 to 3, 18% ultra containing Al ₂ O ₃ in mass percentage. The value obtained by dividing the content (molar percentage) of SiO _{2 by} the total amount RO of the contents (molar percentage) of MgO, CaO, SrO and BaO is 4.3 or less. The method for manufacturing a magnetic disk according to any one of the above.   The method for manufacturing a magnetic disk according to claim 1, wherein the glass substrate has a specific modulus of elasticity of 32 MNm · kg or more.   The method for producing a magnetic disk according to claim 1, wherein the acid resistance index A of the glass substrate is 0.025 nm / h or less.   The method of manufacturing a magnetic disk according to claim 1, wherein the glass substrate has an alkali resistance index B of 0.28 nm / h or less. The method for manufacturing a magnetic disk according to claim 1, wherein a temperature T _{2 at} which the viscosity of the glass substrate becomes 10 ² dPa · s is 1710 ° C. or lower.   The method for manufacturing a magnetic disk according to claim 1, wherein the glass substrate has an annealing point of 650 ° C. or higher. In terms of mole percentage, SiO ₂ is 60 to 75%, Al ₂ O ₃ is 7 to 17%, B ₂ O ₃ is less than 0 to less than 2%, and any one or more of MgO, CaO, SrO and BaO in total More than 18% and not more than 26%, the total content of the seven components is 95% or more, and any one or more of Li ₂ O, Na ₂ O and K ₂ O is contained in total less than 1%, or A glass substrate for information recording media that does not contain any of these three components.   The glass substrate for an information recording medium according to claim 11, wherein the information recording medium is a magnetic disk.