Glass for magnetic recording medium substrate, magnetic recording medium substrate, and magnetic recording / reproducing apparatus

Abstract

Provided is a glass for a magnetic recording medium substrate, the glass being amorphous glass having a temperature T1 of 1600℃ or lower at a viscosity of 102.0 dPa·s and also having a specific elastic modulus of 34.0 MNm / kg or higher.

Description

Glass for magnetic recording medium substrate, magnetic recording medium substrate and magnetic recording / reproducing device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2022-143093, filed September 8, 2022, the entire disclosure of which is expressly incorporated herein by reference.

[0002] The present invention relates to a glass for a magnetic recording medium substrate, a magnetic recording medium substrate, and a magnetic recording / reproducing device.

[0003] Aluminum alloy substrates have traditionally been used as substrates for magnetic recording media such as hard disks (magnetic recording medium substrates). However, it has been pointed out that aluminum alloy substrates are prone to deformation. For this reason, glass magnetic recording medium substrates are now widely used (see, for example, Patent Document 1, the entire disclosure of which is expressly incorporated herein by reference).

[0004] Patent Document 1: JP 2021-86643 A

[0005] A glass magnetic recording medium substrate is produced through a process of molding molten glass.

[0006] An object of one aspect of the present invention is to provide a glass magnetic recording medium substrate suitable for molding by various molding methods.

[0007] In Patent Document 1 (JP 2021-86643 A), specifically, viscosity characteristics suitable for molding by the overflow downdraw method (see paragraph 0063 of Patent Document 1) include a high-temperature viscosity of 10 ２．５ A glass substrate for a magnetic recording medium having a temperature of 1590° C. or more and 1640° C. or less at a viscosity of 10 dPa·s has been disclosed (see Tables 1 to 3 of Patent Document 1). However, the inventors have found that a glass substrate having a viscosity of 10 dPa·s is required for molding by various molding methods such as press molding. ２．０ Glass having viscosity characteristics of 1600°C or less at a temperature of 10 dPa·s and / or ２．５ It has been newly found that a glass having a temperature of 1500° C. or less at a viscosity of 100 dPa·s is suitable.

[0008] One aspect of the present invention is as follows: [1] Viscosity 10 ２．０ A glass for a magnetic recording medium substrate (hereinafter also referred to as "glass 1-A") is an amorphous glass having a temperature T1 at a viscosity of 100 dPa·s of 1600°C or less and a specific elastic modulus of 34.0 MNm / kg or more. [2] Li ２ O and Na ２ The total content of Li and O (Li ２ O + Na ２ [3] The glass for a magnetic recording medium substrate according to [1], wherein the content of 10% by weight of the glass is 10.0 mol % or more. ２．５ A glass for a magnetic recording medium substrate (hereinafter referred to as "glass 1-B") is an amorphous glass having a temperature T2 at a viscosity of 1000 dPa·s of 1500°C or less and a specific elastic modulus of 34.0 MNm / kg or more. [4] Li ２ O and Na ２ The total content of Li and O (Li ２ O + Na ２ [5] The glass for a magnetic recording medium substrate according to [3], wherein the content of 100% by weight of the glass is 0.50 mol % or more. ２．０ The temperature T1 at dPa s is 1600 ° C. or less, and Li ２ O and Na ２ The total content of Li and O (Li ２ O + Na ２ A glass for a magnetic recording medium substrate (hereinafter referred to as "Glass 1-C"), which is an amorphous glass having 0.50 mol % or more of O. [6] A magnetic recording medium substrate made of the glass for a magnetic recording medium substrate according to any one of [1] to [5]. [7] A magnetic recording medium having the magnetic recording medium substrate according to [6] and a magnetic recording layer. [8] A magnetic recording and reproducing device including the magnetic recording medium according to [7].

[0009] Another aspect of the present invention is as follows: [1] Viscosity 10 ２．０ A glass for a magnetic recording medium substrate (hereinafter also referred to as "glass 4-A") is an amorphous glass having a temperature T1 at a viscosity of 100 dPa·s of 1700°C or less and a specific elastic modulus of 34.0 MNm / kg or more. [2] Li ２ O and Na ２ The total content of Li and O (Li ２ O + Na ２[3] The glass for a magnetic recording medium substrate according to [1], wherein the content of 10% by weight of the glass is 10.0 mol % or more. ２．５ A glass for a magnetic recording medium substrate (hereinafter referred to as "glass 4-B") is an amorphous glass having a temperature T2 at a viscosity of 1000 dPa·s of 1560°C or less and a specific elastic modulus of 34.0 MNm / kg or more. [4] Li ２ O and Na ２ The total content of Li and O (Li ２ O + Na ２ [5] The glass for a magnetic recording medium substrate according to [3], wherein the content of 100% by weight of the glass is 0.50 mol % or more. ２．０ The temperature T1 at dPa s is 1700 ° C. or less, and Li ２ O and Na ２ The total content of Li and O (Li ２ O + Na ２ A glass for a magnetic recording medium substrate (hereinafter referred to as "Glass 4-C"), which is an amorphous glass having 0.50 mol % or more of O. [6] A magnetic recording medium substrate made of the glass for a magnetic recording medium substrate according to any one of [1] to [5]. [7] A magnetic recording medium having the magnetic recording medium substrate according to [6] and a magnetic recording layer. [8] A magnetic recording and reproducing device including the magnetic recording medium according to [7].

[0010] Furthermore, glass for magnetic recording medium substrates is desired to have high rigidity. This is for the following reasons. Magnetic recording media are typically mounted inside hard disk drives (HDDs) incorporated into devices such as personal computers. Inside the HDD, multiple magnetic recording media (magnetic disks) are attached to the rotating shaft of a spindle motor, and an actuator incorporated in the HDD writes and reads data to and from the magnetic recording layer of the magnetic recording media rotating at high speed inside the HDD. If the magnetic recording media vibrates significantly while rotating at high speed for such data writing and reading, it can cause a collision between the magnetic head and the surface of the magnetic recording media, resulting in a head crash. For HDDs, the recording capacity can be increased by reducing the thickness of each magnetic recording medium and installing more magnetic recording media in the HDD. However, generally, the thinner the substrate is to make the magnetic recording media thinner, the more likely the magnetic recording media is to vibrate during high-speed rotation. To suppress such vibration, it is desirable to use a glass substrate for the magnetic recording media that is highly rigid and less likely to vibrate during high-speed rotation even when thinned. An example of such an index of rigidity is the specific elastic modulus.

[0011] In view of the above, another aspect of the present invention aims to provide a glass for a magnetic recording medium substrate having high rigidity, and in one embodiment, an object of the present invention is to provide a glass for a magnetic recording medium substrate having a high specific elastic modulus.

[0012] Another aspect of the present invention is as follows: [1] At least Li ２ Contains O, Na ２ O and K ２ The total content of B and O is 0 mol % or more and 6.00 mol % or less, ２ O ３A glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device, which is an amorphous glass having a CaO content of 0 mol % or more and 10.00 mol % or less, and a CaO content of 0 mol % or more and 1.00 mol % or less (hereinafter referred to as "glass 2"). [2] The glass according to [1], in which the CaO content is 0 mol % or more and 0.50 mol % or less. [3] The glass according to [1] or [2], in which the CaO content is 0 mol % or more and 0.10 mol % or less. [4] The glass according to any one of [1] to [3], which does not contain CaO. [5] B ２ O ３ The glass according to any one of [1] to [4], wherein the content is 0.1 mol % or more and 10.00 mol % or less. [6] SiO ２ The glass according to any one of [1] to [5], wherein the content is 50.00 mol% or more and 70.00 mol% or less. [7] SiO ２ The glass according to any one of [1] to [6], wherein the content is 55.00 mol% or more and 68.00 mol% or less. [8] Li ２ The glass according to any one of [1] to [7], wherein the O content is 1.00 mol% or more and 10.00 mol% or less. [9] Li ２ The glass according to any one of [1] to [8], wherein the O content is 3.00 mol% or more and 6.00 mol% or less.

[10] Li ２ The glass according to any one of [1] to [9], which does not contain any alkali metal oxide other than O.

[11] Al ２ O ３ The glass according to any one of [1] to

[10] , wherein the content is 10.00 mol % or more and 20.00 mol % or less.

[12] Al ２ O ３

[13] The glass according to any one of [1] to

[12] , wherein the MgO content is 10.00 mol% or more and 25.00 mol% or less.

[14] The glass according to any one of [1] to

[13] , wherein the MgO content is 10.00 mol% or more and 25.00 mol% or less.

[15] The glass according to any one of [1] to

[13] , further containing an oxide of one or more metals selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er.

[16] The glass according to any one of [1] to

[13] , wherein the ratio of Li to the MgO content is 10.00 mol% or more and 17.00 mol% or less.

[17] The glass according to any one of [1] to

[16] , wherein the ratio of Li to the MgO content is 10.00 mol% or more and 25.00 mol% or less.

[18] The glass according to any one of [1] to

[17] , further containing an oxide of one or more metals selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er.

[19] The glass according to any one of [1] to

[18] , wherein the ratio of Li to the MgO content is 10.00 mol% or more and 25.00 mol% or less. ２Molar ratio of O content (Li ２

[16] The glass according to any one of [1] to

[14] , wherein Li ２ Li relative to the total content of O and MgO ２ Molar ratio of O content (Li ２ O / (Li ２ The glass according to any one of [1] to

[15] , wherein SiO + MgO) is greater than 0.080.

[17] SiO ２ Al content ２ O ３ Molar ratio of content (Al ２ O ３ / SiO ２ The glass according to any one of [1] to

[16] , wherein SiO ２ B relative to content ２ O ３ Molar ratio of content (B ２ O ３ / SiO ２ The glass according to any one of [1] to

[17] , wherein B is greater than 0 and less than 0.020. ２ O ３ and SiO ２ B relative to the total content of ２ O ３ Molar ratio of content (B ２ O ３ / (B ２ O ３ +SiO ２ The glass according to any one of [1] to

[18] , wherein B is greater than 0 and less than 0.020. ２ O ３ , SiO ２ and Al ２ O ３ B relative to the total content of ２ O ３ Molar ratio of content (B ２ O ３ / (B ２ O ３ +SiO ２ +Al ２ O ３

[21] The glass according to any one of [1] to

[20] , wherein the molar ratio of the MgO content to the total content of MgO, CaO, SrO, and BaO (MgO / (MgO+CaO+SrO+BaO)) is 0.970 or more and 1.000 or less.

[22] Li ２ O, Na ２ O and K ２ Li relative to the total content of O ２ Molar ratio of O content (Li ２ O / (Li ２ O + Na ２ O+K ２

[23] The glass according to any one of [1] to

[21] , wherein Li ２ B relative to O content ２ O ３ Molar ratio of content (B ２ O ３ / Li ２

[0022] The glass according to any one of [1] to

[22] , wherein the specific elastic modulus is greater than 0 and less than 0.250.

[24] The glass according to any one of [1] to

[23] , wherein the specific elastic modulus is 35.0 MNm / kg or more.

[25] The glass according to any one of [1] to

[24] , wherein the glass has a glass transition temperature of 700°C or more.

[26] A magnetic recording medium substrate comprising the glass according to any one of [1] to

[25] .

[27] A magnetic recording medium having the magnetic recording medium substrate according to

[26] and a magnetic recording layer.

[28] A glass spacer for a magnetic recording / reproducing device comprising the glass according to any one of [1] to

[25] .

[29] A magnetic recording medium comprising one or more selected from the group consisting of the magnetic recording medium according to

[27] , and the glass spacer for a magnetic recording / reproducing device according to

[28] .

[0013] Another aspect of the present invention is as follows. [1] B ２ O ３ a content of 0.10 mol% or more and 2.00 mol% or less, Na ２A glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device (hereinafter referred to as "glass 3-A"), which is an amorphous glass having an O content of 1.00 mol % or more and 6.00 mol % or less, a CaO content of 0 mol % or more and 1.00 mol % or less, and an MgO content of 14.00 mol % or more. [2] B ２ O ３ a content of 0.10 mol% or more and 2.00 mol% or less, Na ２ A glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device (hereinafter referred to as "Glass 3-B") is an amorphous glass having an O content of 1.00 mol % or more and 6.00 mol % or less, a CaO content of 0 mol % or more and 1.00 mol % or less, and a total content of MgO, SrO, CaO, and BaO (MgO + SrO + CaO + BaO) of 14.00 mol % or more. [3] Li ２ O, Na ２ O and K ２ Na content relative to total O content ２ Molar ratio of O content (Na ２ O / (Li ２ O + Na ２ O+K ２ [4] The glass according to [1] or [2], wherein Li ２ O and K ２ The glass according to any one of [1] to [3], which does not contain O. [5] SiO ２ , B ２ O ３ and Al ２ O ３ The total content (SiO ２ +B ２ O ３ +Al ２ O ３ The glass according to any one of [1] to [4], wherein SiO 2 is 70 mol % or more. ２ and B ２ O ３ and the total content (SiO ２ +B ２ O ３ The glass according to any one of [1] to [5], wherein SiO 2 is 58 mol % or more. ２ and Al ２ O ３and the total content (SiO ２ +Al ２ O ３ The glass according to any one of [1] to [6], wherein Li is 70 mol % or more. ２ O, Na ２ O and K ２ Na content relative to total O content ２ Molar ratio of O content (Na ２ O / (Li ２ O + Na ２ O+K ２ The glass according to [1] or [2], wherein Li ２ The glass according to [1], [2] or [8], containing O.

[10] Li ２ O, Na ２ O and K ２ Li relative to the total content of O ２ Molar ratio of O content (Li ２ O / (Li ２ O + Na ２ O+K ２ The glass according to [1], [2], [8] or [9], wherein Na ２ SiO relative to O content ２ Molar ratio of content (SiO ２ / Na ２

[12] The glass according to any one of [1], [2] and [8] to

[10] , wherein the ratio of Na to MgO content is 50.0 or less. ２ Molar ratio of O content (Na ２

[13] The glass according to any one of [1] to [7], wherein TiO ２

[14] The glass according to any one of [1] to

[13] , having a ZnO content of 10.00 mol % or less.

[15] The glass according to any one of [1] to

[14] , having a specific elastic modulus of 35.0 MNm / kg or more.

[16] The glass according to any one of [1] to

[15] , having a glass transition temperature of 700°C or more.

[17] A magnetic recording medium substrate comprising the glass according to any one of [1] to

[16] .

[18] A magnetic recording medium having the magnetic recording medium substrate according to

[17] and a magnetic recording layer.

[19] A glass spacer for a magnetic recording / reproducing device comprising the glass according to any one of [1] to

[16] .

[20] A magnetic recording medium according to

[18] , and a glass spacer for a magnetic recording / reproducing device according to

[19] .

[0014] According to one aspect of the present invention, it is possible to provide a glass magnetic recording medium substrate that is suitable for molding by various molding methods.

[0015] Hereinafter, Glass 1-A, Glass 1-B, and Glass 1-C will also be collectively referred to as "Glass 1." Glass 3-A and Glass 3-B will also be collectively referred to as "Glass 3." Glass 4-A, Glass 4-B, and Glass 4-C will also be collectively referred to as "Glass 4." In the following description, unless otherwise specified, a description of Glass 1 can also be applied to Glass 2, Glass 3, and Glass 4, a description of Glass 2 can also be applied to Glass 1, Glass 3, and Glass 4, and a description of Glass 3 can also be applied to Glass 1, Glass 2, and Glass 4. Glass 1, Glass 2, Glass 3, and Glass 4 will also be collectively referred to simply as "glass." The glass corresponding to Glass 1 may also be a glass that corresponds to any one, two, or all of Glass 2, Glass 3, and Glass 4.

[0016] Glasses 1, 2, and 3 are amorphous glasses. Unlike glass-ceramics, amorphous glasses are glasses that do not substantially contain a crystalline phase and exhibit a glass transition phenomenon upon heating. On the other hand, the manufacturing process for glass-ceramics is complicated. Furthermore, it is not easy to achieve the high smoothness required for magnetic recording medium substrates with glass-ceramics. Furthermore, Glasses 1, 2, and 3 can be amorphous oxide glasses. Oxide glasses are glasses in which the main network-forming component of the glass is an oxide.

[0017] Glasses 1 to 4 will be described in more detail below.

[0018] In the present invention and this specification, glass compositions are expressed as oxide-based glass compositions. Here, "oxide-based glass composition" refers to a glass composition obtained by converting the glass raw materials into oxides present in the glass after they are all decomposed during melting. Furthermore, unless otherwise specified, glass compositions are expressed on a molar basis (mol %, molar ratio). The glass compositions in the present invention and this specification can be determined by methods such as ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Quantitative analysis is performed for each element using ICP-AES. The analytical values ​​are then converted into oxide notation. The analytical values ​​obtained by ICP-AES may contain a measurement error of, for example, about ±5% of the analytical value. Therefore, the oxide notation values ​​converted from the analytical values ​​may also contain an error of about ±5%. Furthermore, in the present invention and this specification, the content of a constituent component may be 0%. 0.0%, 0.00%, or "not contained" or "not incorporated" means that the component is substantially not contained, and indicates that the content of the component is at or below the impurity level. At or below the impurity level, for example, means less than 0.01%.

[0019] [Glasses 1 and 4] In the following description, unless otherwise specified, the description regarding Glass 1-A can also be applied to Glass 1-B, Glass 1-C, and Glass 4, the description regarding Glass 1-B can also be applied to Glass 1-A, Glass 1-C, and Glass 4, and the description regarding Glass 1-C can also be applied to Glass 1-A, Glass 1-B, and Glass 4.

[0020] Viscosity of Glass 1-A and Glass 1-B: 10 ２．０ The temperature T1 at dPa·s is 1600°C or less. ２．５ The temperature T2 at viscosity 10 dPa·s is 1500°C or less. ２．０ Temperature T1 and viscosity 10 in dPa s ２．５ The temperature T2 at a viscosity of dPa s can be measured by the platinum ball pulling method or the rotation method. Glasses having a temperature T1 of 1600°C or less and glasses having a temperature T2 of 1500°C or less are suitable for forming by various forming methods and are therefore preferred. Examples of methods for forming glass melt include methods A to D described in the Examples section below. Glasses having a temperature T1 of 1600°C or less and glasses having a temperature T2 of 1500°C or less can be formed by any of methods A to D, and of these, method A or method B is preferred for forming.

[0021] The temperature T1 of Glass 1-A and Glass 1-B is 1600°C or less, preferably 1550°C or less, and more preferably 1500°C or less. The lower limit of the temperature T1 is not particularly limited and can be, for example, 1300°C or more, 1350°C or more, 1400°C or more, or 1450°C or more, but may be lower than the temperatures exemplified here. In one embodiment, the temperature T1 of Glass 1-C can be in the above range.

[0022] The temperature T2 of glass 1-C is 1500°C or less, preferably 1450°C or less, and more preferably 1400°C or less. The lower limit of the temperature T2 is not particularly limited and can be, for example, 1200°C or more, 1250°C or more, 1300°C or more, or 1350°C or more, but may be lower than the temperatures exemplified here. In one embodiment, the temperature T2 of glass 1-A and the temperature T2 of glass 1-B can be within the above ranges.

[0023] Viscosity of Glass 4-A and Glass 4-B: 10 ２．０ The temperature T1 at dPa·s is 1700°C or less. ２．５ The temperature T2 at a viscosity of 1000 dPa s is 1560°C or lower. Glass having a temperature T1 of 17000°C or lower and glass having a temperature T2 of 1560°C or lower are preferred because they are suitable for forming by various forming methods. Examples of methods for forming the glass melt include methods A to D described in the Examples section below. Glass having a temperature T1 of 1700°C or lower and glass having a temperature T2 of 1560°C or lower can be formed by any of methods A to D, and of these, method A or method B is preferred for forming.

[0024] The temperature T1 of glass 4-A and glass 4-B is 1700°C or less, preferably 1690°C or less, and more preferably 1680°C or less, 1670°C or less, 1660°C or less, 1650°C or less, and 1640°C or less in that order. The lower limit of the temperature T1 is not particularly limited and can be, for example, 1300°C or more, 1350°C or more, 1400°C or more, or 1450°C or more, but may be lower than the temperatures exemplified here. In one embodiment, the temperature T1 of glass 4-C can be in the above range.

[0025] The temperature T2 of glass 4-C is 1560°C or less, preferably 1550°C or less, and more preferably 1540°C or less, 1530°C or less, 1520°C or less, and 1510°C or less in that order. The lower limit of the temperature T2 is not particularly limited and can be, for example, 1200°C or more, 1250°C or more, 1300°C or more, or 1350°C or more, but may be lower than the temperatures exemplified here. In one embodiment, the temperature T2 of glass 4-A and the temperature T2 of glass 4-B can be within the above-mentioned ranges.

[0026] In Glass 1-C and Glass 4-C, Li ２ O and Na ２ The total content of Li and O (Li ２ O + Na ２ O) is 0.50% or more. ２ O + Na ２ O) of 0.50% or more is preferable in terms of reducing the melt viscosity of the glass. Reducing the melt viscosity can contribute to making the glass temperature T1 1670°C or less or 1600°C or less. From the above viewpoint, the total content (Li ２ O + Na ２ O) is preferably 1.00% or more, and more preferably 1.50% or more, 2.00% or more, 3.00% or more, and 3.50% or more in that order. Furthermore, reducing the melt viscosity of the glass can contribute to making the glass temperature T2 1560°C or less or 1500°C or less. Therefore, the total content (Li ２ O + Na ２ O) in the above range is also preferable in terms of keeping the glass temperature T2 at 1500°C or less. ２ O + Na ２ O) can be, for example, 8.00% or less, 7.00% or less, or 6.00% or less. In one embodiment, the total content (Li ２ O + Na ２ O) can be in the ranges described above.

[0027] In one embodiment, in glasses 1-A, 1-B, 1-C, 4-A, 4-B, and 4-C, Li２ O, Na ２ O and K ２ The total content of O (Li ２ O + Na ２ O+K ２ O) can be more than 0.50%, and can be 1.00% or more, 1.50% or more, 2.00% or more, 3.00% or more, or 3.50% or more. In glasses 1-A, 1-B, 1-C, 4-A, 4-B, and 4-C, the total content (Li ２ O + Na ２ O+K ２ O) can be, for example, 10.00% or less, 9.00% or less, 8.00% or less, 7.00% or less, or 6.00% or less.

[0028] In one embodiment, in glasses 1-A, 1-B, 1-C, 4-A, 4-B, and 4-C, the Li content relative to the MgO content ２ Molar ratio of O content (Li ２ In another embodiment, in glasses 1-A, 1-B, 1-C, 4-A, 4-B, and 4-C, the ratio of Na to MgO is preferably in the range described below for glass 2. ２ Molar ratio of O content (Na ２ O / MgO) is preferably in the range described later for glass 3.

[0029] The specific elastic modulus of Glasses 1-A, 1-B, 4-A, and 4-B is 34.0 MNm / kg or more. Glasses with a specific elastic modulus of 34.0 MNm / kg or more have high rigidity and are preferred as glasses for magnetic recording medium substrates for the reasons described above. The specific elastic modulus of Glasses 1-A, 1-B, 4-A, and 4-B is preferably 34.5 MNm / kg or more, and is even more preferably 35.0 MNm / kg or more, 35.5 MNm / kg or more, 36.0 MNm / kg or more, 36.5 MNm / kg or more, 37.0 MNm / kg or more, 37.5 MNm / kg or more, and 38.0 MNm / kg or more in this order. The specific elastic moduli of Glass 1-A, Glass 1-B, 4-A, and 4-B can be, for example, 45.0 MNm / kg or less, 44.0 MNm / kg or less, 43.0 MNm / kg or less, 42.0 MNm / kg or less, 41.0 MNm / kg or less, or 40.0 MNm / kg or less. However, since a higher specific elastic modulus is preferable because it results in higher rigidity, the specific elastic moduli are not limited to the above-mentioned exemplary values. In one embodiment, the specific elastic moduli of Glasses 1-C and 4-C can be within the above-mentioned range. For glass compositions for increasing rigidity, please refer to the descriptions below regarding Glass 2 and Glass 3.

[0030] [Glass 2] <Glass composition> Glass 2 has a CaO content of 0% or more and 1.00% or less, and Li ２ It contains O as an essential component and other alkali metal oxides such as Na ２ O and K ２ The total content of B and O is 0% or more and 6.00% or less, and B ２ O ３ The content is 0% or more and 10.00% or less. Having such a composition can contribute to the ability of glass 2 to exhibit high rigidity.

[0031] The CaO content of glass 2 is 1.00% or less. A CaO content of 1.00% or less contributes to improving the rigidity of the glass and can also contribute to improving the thermal stability of the glass. From these viewpoints, the CaO content is preferably 0.9% or less, and more preferably 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less, 0.4% or less, 0.3% or less, 0.2% or less, and 0.1% or less in that order, and can also be 0%. It is more preferable that glass 2 does not contain CaO.

[0032] Glass 2 is Li ２ It contains O as an essential component and also contains other alkali metal oxides such as Na ２ O and K ２ The total content of Na ２ O+K ２ O) is 0% or more and 6.00% or less. This can also contribute to improving the rigidity of the glass. From the viewpoint of further increasing the rigidity of the glass, Na ２ O and K ２ The total content of Na ２ O+K ２ O) is preferably 5.00% or less, more preferably 4.00% or less, 3.00% or less, 2.00% or less, 1.00% or less, 0.5% or less, and 0.1% or less in that order, and can be 0%. ２ O and K ２ It is more preferable that the compound does not contain O. ２ It is more preferable that the glass 2 does not contain any alkali metal oxide other than O. In another embodiment, the glass 2 does not contain any alkali metal oxide other than Na ２ O and K ２ O, and the total content (Na ２ O+K ２ O) can be 1.00% or more, 2.00% or more, or 3.00% or more.

[0033] Li from Glass 2 ２ The O content is more than 0%, and from the viewpoint of improving thermal stability, it is preferably 0.50% or more, and more preferably 1.00% or more, 2.00% or more, and 3.00% or more in that order. Also, from the viewpoint of maintaining the temperature required for melting the glass within an appropriate range, Li ２It is preferable that the O content is in the above range. It is also preferable that the temperature required for melting the glass can be maintained within an appropriate range from the viewpoints of extending the life of the melting furnace and reducing costs by reducing the input energy. On the other hand, from the viewpoints of further improving the rigidity of the glass, further improving the devitrification resistance and / or increasing the glass transition temperature, it is preferable that the Li content be in the above range. ２ The O content is preferably 10.00% or less, and more preferably 9.00% or less, 8.00% or less, 7.00% or less, 6.00% or less, 5.00% or less, and 4.00% or less in that order.

[0034] Glass 2 B ２ O ３ From the viewpoint of improving chemical durability and rigidity, the content is 10.00% or less, preferably 9.00% or less, and more preferably 8.00% or less, 7.00% or less, 6.00% or less, 5.00% or less, 4.00% or less, 3.00% or less, 2.00% or less, 1.00% or less, 0.70% or less, and 0.50% or less in that order. Glass with high chemical durability is preferred because it has high acid and / or alkali resistance, making it difficult for surface roughening to occur during polishing, cleaning, etc., and making it easy to achieve low roughness on the glass surface. The ability to easily achieve low roughness by polishing will be referred to below as low-roughness polishing performance. Glass 2 B ２ O ３ The content can be 0% or more, and is preferably more than 0%. ２ O ３ A content of more than 0% can contribute to improving impact resistance. Glass with high impact resistance is preferred because it is less likely to crack and / or chip during processing such as cutting and grinding. From the viewpoint of improving impact resistance, meltability, and thermal stability, B of glass 2 is ２ O ３ The content is more preferably 0.10% or more, and further preferably 0.20% or more. Glass having high thermal stability is preferred because it is less likely to devitrify.

[0035] In one embodiment, glass 2 is SiO ２ and Al ２ O ３ may include one or both of the following:

[0036] Glass 2 SiO ２ From the viewpoint of improving chemical durability, the content is preferably 50.00% or more, and more preferably 51.00% or more, 52.00% or more, 53.00% or more, 54.00% or more, 55.00% or more, 56.00% or more, 57.00% or more, 58.00% or more, and 59.00% or more in that order. On the other hand, from the viewpoint of further improving rigidity, SiO ２ The content is preferably 70.00% or less, more preferably 69.00% or less, 68.00% or less, 67.00% or less, 66.00% or less, 65.00% or less, 64.00% or less, and 63.00% or less in that order.

[0037] Glass 2 Al ２ O ３ From the viewpoint of improving thermal stability, the Al content is preferably 20.00% or less, and more preferably 19.00% or less, 18.00% or less, 17.00% or less, 16.00% or less, 15.00% or less, and 14.00% or less in that order. Also, from the viewpoint of maintaining the temperature required for melting the glass within an appropriate range, Al content is preferably 20.00% or less, and more preferably 19.00% or less, 18.00% or less, 17.00% or less, 16.00% or less, 15.00% or less, and 14.00% or less in that order. ２ O ３ On the other hand, from the viewpoint of further improving rigidity, it is preferable that the content of Al is in the above range. ２ O ３ The content is preferably 10.00% or more, and more preferably 11.00% or more.

[0038] Regarding alkaline earth metal oxides, the CaO content of glass 2 is as described above. In one embodiment, glass 2 may contain one or more alkaline earth metal oxides. Specific examples of alkaline earth metal oxides that may be contained in glass 2 include MgO, SrO, and BaO. In one embodiment, glass 2 may contain MgO. From the viewpoint of further improving rigidity, the MgO content of glass 2 is preferably 10.00% or more, and is more preferably 11.00% or more, 12.00% or more, 13.00% or more, 14.00% or more, 15.00% or more, 16.00% or more, 17.00% or more, 18.00% or more, 19.00% or more, and 20.00% or more in that order. Furthermore, from the viewpoint of improving the devitrification resistance of the glass, the MgO content is preferably 28.00% or less, and more preferably 27.00% or less, 26.00% or less, 25.00% or less, 24.00% or less, 23.00% or less, 22.00% or less, 21.00% or less, 20.00% or less, 19.00% or less, and 18.00% or less in that order.

[0039] From the viewpoint of reducing the melt viscosity, lowering the liquidus temperature, and improving the glass roughness and polishing performance, the Li content relative to the MgO content is ２ Molar ratio of O content (Li ２ The molar ratio (LiO / MgO) is preferably 0.020 or more, and more preferably 0.030 or more, 0.040 or more, 0.050 or more, 0.060 or more, 0.070 or more, 0.080 or more, and more preferably more than 0.080 in that order. Glasses with low liquidus temperatures are preferred because they have high thermal stability. ２ A molar ratio (LiO / MgO) of more than 0.080 can contribute to reducing the resistivity of the molten glass. When electrical heating is performed during glass melting, a glass with a low resistivity is preferred because it can be melted by lowering the temperature in the furnace during electrical heating. From the above viewpoint, ２ The molar ratio (LiO / MgO) is more preferably 0.090 or more, and more preferably 0.100 or more, 0.110 or more, 0.120 or more, 0.130 or more, 0.140 or more, 0.150 or more, and 0.160 or more in this order. On the other hand, from the viewpoint of increasing the glass transition temperature and the specific elastic modulus, the molar ratio (Li ２O / MgO) is preferably less than 0.240, and more preferably 0.230 or less, 0.220 or less, 0.210 or less, 0.200 or less, 0.190 or less, or 0.180 or less in that order.

[0040] From the viewpoint of reducing the melt viscosity, lowering the liquidus temperature, improving the polishing performance by reducing the roughness of the glass, and reducing the specific resistance of the glass melt, Li ２ Li relative to the total content of O and MgO ２ Molar ratio of O content (Li ２ O / (Li ２ The molar ratio (Li+MgO) is preferably 0.020 or more, and more preferably 0.030 or more, 0.040 or more, 0.050 or more, 0.060 or more, 0.070 or more, 0.080 or more, more than 0.080, 0.090 or more, 0.100 or more, 0.110 or more, 0.120 or more, 0.130 or more, and 0.140 or more in that order. On the other hand, from the viewpoint of increasing the glass transition temperature and the specific elastic modulus, the molar ratio (Li+MgO) is preferably 0.020 or more, and more preferably 0.030 or more, 0.040 or more, 0.050 or more, 0.060 or more, 0.070 or more, 0.080 or more, more preferably 0.090 or more, 0.100 or more, 0.110 or more, 0.120 or more, 0.130 or more, and more preferably 0.140 or more. ２ O / (Li ２ The (MgO+MgO)) is, for example, preferably less than 0.190, and more preferably 0.180 or less, 0.170 or less, or 0.160 or less in that order.

[0041] SiO ２ Al content ２ O ３ Molar ratio of content (Al ２ O ３ / SiO ２ From the viewpoint of improving the thermal stability, the molar ratio (Al) is preferably less than 0.270, and more preferably 0.260 or less, 0.250 or less, 0.240 or less, 0.230 or less, and 0.220 or less in that order. ２ O ３ / SiO ２ ) is preferably 0.100 or more, and more preferably 0.120 or more, 0.130 or more, 0.140 or more, 0.150 or more, 0.160 or more, 0.170 or more, or 0.190 or more in that order.

[0042] SiO ２ B relative to content ２ O ３ Molar ratio of content (B ２O ３ / SiO ２ From the viewpoint of improving impact resistance, the molar ratio (B) is preferably greater than 0, and more preferably 0.001 or more, 0.002 or more, 0.003 or more, and 0.004 or more in that order. On the other hand, from the viewpoint of improving chemical durability and further suppressing volatilization of glass components during glass melting, the molar ratio (B ２ O ３ / SiO ２ ) is preferably less than 0.020, and more preferably 0.015 or less, 0.010 or less, 0.009 or less, 0.008 or less, and 0.007 or less in that order.

[0043] B ２ O ３ and SiO ２ B relative to the total content of ２ O ３ Molar ratio of content (B ２ O ３ / (B ２ O ３ +SiO ２ From the viewpoint of improving impact resistance, the molar ratio (B ) is preferably greater than 0, and more preferably 0.001 or more, 0.002 or more, 0.003 or more, and 0.004 or more in that order. On the other hand, from the viewpoint of improving chemical durability and further suppressing volatilization of glass components during glass melting, the molar ratio (B ２ O ３ / (B ２ O ３ +SiO ２ )) is preferably less than 0.020, and more preferably 0.015 or less, 0.010 or less, 0.009 or less, 0.008 or less, and 0.007 or less in that order.

[0044] B ２ O ３ , SiO ２ and Al ２ O ３ B relative to the total content of ２ O ３ Molar ratio of content (B ２ O ３ / (B ２ O ３ +SiO ２ +Al ２ O ３From the viewpoint of improving impact resistance, the molar ratio (B ) is preferably greater than 0, and more preferably 0.001 or greater, 0.002 or greater, and 0.003 or greater in that order. On the other hand, from the viewpoint of improving chemical durability and further suppressing volatilization of glass components during glass melting, the molar ratio (B ２ O ３ / (B ２ O ３ +SiO ２ +Al ２ O ３ )) is preferably less than 0.010, and more preferably 0.009 or less, 0.008 or less, 0.007 or less, and 0.006 or less in that order.

[0045] The molar ratio of the MgO content to the total content of MgO, CaO, SrO, and BaO (MgO / (MgO+CaO+SrO+BaO)) can be 1.000, 1.000 or less, or less than 1.000. MgO has a lower specific gravity than other alkaline earth metal oxides, and therefore can contribute to increasing the specific modulus of elasticity. Furthermore, in general glasses, the glass transition temperature tends to increase when alkaline earth metal oxides with a higher specific gravity are added. In contrast, according to the inventors' investigations, in Glass 2, the glass transition temperature tends to decrease when alkaline earth metal oxides with a higher specific gravity than MgO are added. From the viewpoint of increasing the specific modulus and glass transition temperature of the above-mentioned glasses, the molar ratio (MgO / (MgO+CaO+SrO+BaO)) is preferably 0.970 or more, and more preferably 0.980 or more, 0.990 or more, and 1.000, in that order.

[0046] Li ２ O, Na ２ O and K ２ Li relative to the total content of O ２ Molar ratio of O content (Li ２ O / (Li ２ O + Na ２ O+K ２ In one embodiment, from the viewpoint of increasing the specific elastic modulus, the molar ratio (Li ２ O / (Li ２ O + Na ２ O+K ２O)) is preferably 0.760 or more, and more preferably 0.800 or more, 0.850 or more, 0.900 or more, 0.950 or more, and 1.000 in that order. ２ O / (Li ２ O + Na ２ O+K ２ O)) can be less than 0.760, 0.700 or less, 0.600 or less, 0.500 or less, or 0.300 or less, and can be 0.050 or more, or 0.100 or more.

[0047] Li ２ B relative to O content ２ O ３ Molar ratio of content (B ２ O ３ / Li ２ From the viewpoint of improving impact resistance, the molar ratio (B is preferably more than 0, and more preferably 0.010 or more, 0.015 or more, 0.020 or more, 0.025 or more, 0.030 or more, 0.035 or more, 0.040 or more, 0.045 or more, 0.050 or more, 0.055 or more, 0.060 or more, 0.065 or more, and 0.070 or more in that order. On the other hand, from the viewpoint of improving chemical durability, suppressing devitrification, and suppressing deterioration of homogeneity due to composition fluctuation, the molar ratio (B ２ O ３ / Li ２ O) is preferably 0.700 or less, and more preferably 0.600 or less, 0.500 or less, 0.400 or less, 0.300 or less, 0.250 or less, less than 0.250, 0.245 or less, 0.240 or less, 0.235 or less, 0.230 or less, 0.225 or less, 0.220 or less, 0.215 or less, 0.210 or less, 0.205 or less, and 0.200 or less in that order.

[0048] Glass 2 Fe ２ O ３ The content, expressed as an exclusive percentage, can be 1 mol% or less, 0.7 mol% or less, 0.5 mol% or less, 0.4 mol% or less, 0.3 mol% or less, 0.1 mol% or less, 0.07 mol% or less, 0.05 mol% or less, 0.04 mol% or less, 0.03 mol% or less, or 0.02 mol% or less. ２ O ３The content is expressed as an exclusive percentage. That is, the Fe contained in the glass ２ O ３ When the total content of components other than (when additives are included in addition to glass components, the total content of glass components and additives) is taken as 100%, the amount of Fe relative to 100% ２ O ３ Fe content in mole percentage ２ O ３ In one embodiment, the glass 2 does not contain Fe (the Fe content in the above-mentioned external percentage is ２ O ３ The content can be 0 mol %.

[0049] Glass 2 may or may not contain one or more metals or oxides thereof selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er. Inclusion of an oxide of one or more metals selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er in a glass composition based on oxides tends to increase the thermal stability of the glass. In one embodiment, the content of oxides of one or more metals selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er (the total content when a plurality of metals are contained) can be 0%, 0% or more, or more than 0%, and can be 5.00% or less, 4.00% or less, 3.00% or less, 2.00% or less, 1.00% or less, 0.5% or less, or 0.1% or less. For example, Y ２ O ３ The content may be 0% or more, or more than 0%, and may be 3.00% or less, 2.00% or less, or 1.00% or less. ２ The content can be 0% or more, or more than 0%, and can be 3.00% or less, 2.00% or less, or 1.00% or less. ２ O ３ and TiO ２ may include one or both of the following:

[0050] F is a component that easily volatilizes during melting and is also a component that causes striae, so it is preferable that Glass 2 does not contain F. Not containing F is also preferable from the viewpoints of suppressing erosion of the melting furnace, suppressing a decrease in Young's modulus, and suppressing a decrease in specific elastic modulus.

[0051] Since Pb, Cd and As are substances that have a negative impact on the environment, it is preferable to avoid introducing them.

[0052] Glass 2 contains SnO ２ , CeO ２ and Sb ２ O ３ In one embodiment, the composition may include one or more selected from the group consisting of SnO ２ and CeO ２ In another embodiment, the total content of glass 2 can be 0%. ２ and / or CeO ２ and SnO ２ and CeO ２ The total content (SnO ２ + CeO ２ ) is preferably 0.05 to 2%. ２ and CeO ２ When the total content of SnO is 0.05% or more, a sufficient fining effect can be obtained and residual bubbles can be reduced. ２ + CeO ２ By making the total content (SnO ) 2% or less, it is possible to prevent the molten glass from blowing up during glass melting, thereby preventing a decrease in productivity. ２ + CeO ２ The lower limit of the total content (SnO ２ + CeO ２The upper limit of ) is preferably 1.5% or less, more preferably 1.2% or less, even more preferably 1.0% or less, still more preferably 0.70% or less, even more preferably 0.65% or less, still more preferably 0.60% or less, still more preferably 0.55% or less, and even more preferably 0.50% or less.

[0053] SnO ２ has the function of promoting fining when the melting temperature of the glass is relatively high (temperature range of about 1400 to 1600°C). ２ O ３ In order to remove bubbles from glass having a high melting temperature, in one embodiment, SnO is added to glass 2. ２ It is preferable to incorporate SnO. ２ From the viewpoint of obtaining a fining effect, the content of SnO is preferably 0.01% or more, more preferably 0.05% or more, even more preferably 0.10% or more, even more preferably 0.15% or more, and even more preferably 0.20% or more. ２ The content is preferably 2% or less, more preferably 1.5% or less, even more preferably 1.0% or less, even more preferably 0.8% or less, and even more preferably 0.5% or less.

[0054] CeO ２ is SnO ２ It is a component that has a fining effect on glass, similar to CeO ２ has the function of absorbing oxygen and fixing it as a glass component when the melting temperature of the glass is relatively low (temperature range of about 1200 to 1400°C). Therefore, in one embodiment, CeO is added to the glass 2 as a fining agent. ２ It is preferable to incorporate CeO ２ From the viewpoint of obtaining a fining effect, the content of CeO is preferably 0.01% or more, more preferably 0.05% or more, even more preferably 0.08% or more, and even more preferably 0.10% or more. ２The content of SnO is preferably 2% or less, more preferably 1.5% or less, even more preferably 1.0% or less, still more preferably 0.8% or less, even more preferably 0.5% or less, and still more preferably 0.3% or less. ２ and CeO ２ By coexisting with SnO, a fining effect can be obtained in a wide temperature range. ２ and CeO ２ It is preferable to include both of the above.

[0055] Sb ２ O ３ It is desirable to refrain from using Sb in glass 2 from the viewpoint of reducing the environmental load. ２ O ３ The content of Sb is preferably in the range of 0 to 0.5%. ２ O ３ The content of Sb is more preferably 0.3% or less, further preferably 0.1% or less, even more preferably 0.05% or less, and even more preferably 0.02% or less. ２ O ３ It is particularly preferred that it does not contain

[0056] Glass 2 can be produced by weighing, blending, and thoroughly mixing glass raw materials such as oxides, carbonates, nitrates, sulfates, and hydroxides so as to obtain a predetermined glass composition, heating and melting the mixture in a melting vessel at a temperature in the range of 1400 to 1600°C, for example, and then fining and stirring the mixture to form a homogenized glass melt that has been sufficiently bubble-depleted. For example, it is preferable to heat and melt the glass raw materials in a melting tank at 1400 to 1550°C, and then heat the resulting glass melt in a refining tank and hold it at 1450 to 1600°C, and then lower the temperature to 1200 to 1400°C, at which point the glass is allowed to flow and be shaped.

[0057] <Glass Physical Properties> By adjusting the composition as described above, Glass 2 can have the various glass physical properties described below.

[0058] (Specific Elastic Modulus) Glass 2 can have high rigidity due to the composition described above. The specific elastic modulus can be used as an index of the rigidity of glass. The specific elastic modulus is calculated by dividing the Young's modulus of the glass by its density. Here, density refers to the ratio of the specific gravity of the glass to the density in g / cm. ３ The specific elastic modulus of glass 2 is preferably 35.0 MNm / kg or more, and is even more preferably 35.5 MNm / kg or more, 36.0 MNm / kg or more, 36.5 MNm / kg or more, 37.0 MNm / kg or more, 37.5 MNm / kg or more, and 38.0 MNm / kg or more in this order. The specific elastic modulus can be, for example, 45.0 MNm / kg or less, 44.0 MNm / kg or less, 43.0 MNm / kg or less, 42.0 MNm / kg or less, 41.0 MNm / kg or less, or 40.0 MNm / kg or less, but is not limited to the above-exemplified values ​​because a higher specific elastic modulus is preferable because it results in higher rigidity.

[0059] (Young's Modulus E) Young's modulus can be used as an index of the rigidity of glass. The Young's modulus of glass 2 is preferably 86.0 GPa or more, more preferably 87.0 GPa or more, and more preferably 88.0 GPa or more, 89.0 GPa or more, 90.0 GPa or more, 91.0 GPa or more, 92.0 GPa or more, 93.0 GPa or more, 94.0 GPa or more, and 95.0 GPa or more in this order. The Young's modulus of glass 2 can be, for example, 120.0 GPa or less or 110.0 GPa or less, but is not limited to the above-mentioned values, since the higher the Young's modulus, the higher the rigidity and the more preferable it is.

[0060] (Specific gravity d) By reducing the specific gravity of the glass for magnetic recording medium substrate, the weight of the magnetic recording medium substrate can be reduced, and further the weight of the magnetic recording medium can be reduced, thereby reducing the power consumption of the HDD. The specific gravity of the glass 2 is preferably 2.80 or less, more preferably 2.75 or less, even more preferably 2.70 or less, still more preferably 2.65 or less, and even more preferably 2.60 or less. The specific gravity of the glass 2 can be, for example, 2.40 or more, but is not limited to the above-mentioned values, as the lower the specific gravity, the better.

[0061] (Glass Transition Temperature Tg) Magnetic recording medium substrates are usually subjected to high-temperature treatment during the process of forming a magnetic recording layer on the substrate. For example, to form a magnetic recording layer containing a magnetic material with high magnetic anisotropy energy, which has been developed in recent years for higher density recording of magnetic recording media, film formation is usually carried out at high temperatures, or a heat treatment is carried out at high temperatures after film formation. It is preferable for the magnetic recording medium substrate to have heat resistance that can withstand such high-temperature treatment in order to prevent the flatness of the substrate from decreasing due to exposure to high temperatures. In this regard, glass 2 can also exhibit high heat resistance by having the above-mentioned glass composition. Regarding the glass transition temperature Tg, which is an index of heat resistance, the Tg of glass 2 can be, for example, 550°C or higher, preferably 600°C or higher, and more preferably 610°C or higher, 620°C or higher, 630°C or higher, 640°C or higher, 650°C or higher, 660°C or higher, 670°C or higher, 680°C or higher, 690°C or higher, 700°C or higher, 710°C or higher, 720°C or higher, 730°C or higher, 740°C or higher, and 750°C or higher. Furthermore, the Tg of glass 2 can be, for example, 850°C or lower, 830°C or lower, 810°C or lower, 790°C or lower, 770°C or lower, or 750°C or lower, but is not limited to the above-mentioned exemplary values ​​because a higher Tg is preferable from the viewpoint of heat resistance.

[0062] (Thermal Expansion Coefficient) HDDs incorporating magnetic recording media are typically designed to rotate the magnetic recording media itself by holding down the central portion with the spindle and clamp of a spindle motor. Therefore, if there is a large difference in the thermal expansion coefficients of the magnetic recording media substrate and the spindle material that constitutes the spindle, a mismatch will occur between the thermal expansion and contraction of the spindle and the thermal expansion and contraction of the magnetic recording media substrate in response to ambient temperature changes during use, resulting in deformation of the magnetic recording media. This phenomenon can cause the head to be unable to read written information, resulting in reduced reliability of recording and playback. Therefore, it is desirable to avoid too large a difference between the thermal expansion coefficient of the glass for the magnetic recording media substrate and that of the spindle material (e.g., stainless steel). Generally, HDD spindle materials have a thermal expansion coefficient of 70×10 in the temperature range of 100 to 300°C.－７ / °C or more, and the average linear expansion coefficient (thermal expansion coefficient) of the glass for a magnetic recording medium substrate at 100 to 300°C is 30.0 × 10 －７ / °C or more, the difference in thermal expansion coefficient with the spindle material is small, which can contribute to improving the reliability of the magnetic recording medium. On the other hand, if the thermal expansion coefficient of the glass substrate is too large, the substrate may crack due to heating during film formation. The average linear expansion coefficient α of Glass 2 at 100 to 300°C is 34.0 × 10 －７ / °C or more, and －７ / ℃ or more, 36.0 × 10 －７ / ℃ or more, 37.0 × 10 －７ / ℃ or more, 38.0 × 10 －７ / ℃ or more, 39.0 × 10 －７ / ℃ or more, 40.0 × 10 －７ / °C or more. The average linear expansion coefficient α of glass 2 at 100 to 300°C is 70.0 × 10 －７ / °C or less, and －７ / ℃ or less, 65.0 × 10 －７ / ℃ or less, 63.0 × 10 －７ / ℃ or less, 60.0 × 10 －７ / ℃ or less, 57.0 × 10 －７ / ℃ or less, 55.0 × 10 －７ / ℃ or less, 50.0 × 10 －７ / °C or less is more preferable in this order.

[0063] (Liquidus Temperature LT) An index of the thermal stability of glass can be the liquidus temperature (LT). The LT of glass 2 is preferably 1330°C or less, more preferably 1320°C or less, and further preferably 1310°C or less, 1300°C or less, 1290°C or less, 1280°C or less, 1270°C or less, 1260°C or less, 1250°C or less, and 1240°C or less in this order. Glass with a low liquidus temperature LT is preferred because it is less likely to cause devitrification. The lower limit of LT can be, for example, 800°C or more, but is not particularly limited.

[0064] The various physical properties described above and the various physical properties described below can be determined by the methods described later in the examples.

[0065] [Glass 3] <Glass composition> Glass 3 B ２ O ３ From the viewpoint of improving chemical durability and rigidity, the content is 2.00% or less, preferably 1.80% or less, and more preferably 1.50% or less, 1.20% or less, 1.00% or less, 0.80% or less, 0.70% or less, 0.60% or less, 0.50% or less, and 0.40% or less in that order. Glasses with high chemical durability are preferred for the reasons described above. Glass 3 B ２ O ３ The content is 0.10% or more, preferably 0.20% or more, from the viewpoint of improving impact resistance, meltability, and thermal stability. As described above, glass with high impact resistance is preferred because it is less likely to crack and / or chip during processing such as cutting and grinding. Furthermore, glass with high thermal stability is preferred because it is less likely to cause devitrification.

[0066] In one embodiment, the glass 3 is SiO ２ and Al ２ O ３ may include one or both of the following:

[0067] Glass 3 SiO ２ From the viewpoint of improving chemical durability, the content is preferably 50.00% or more, and more preferably 51.00% or more, 52.00% or more, 53.00% or more, 54.00% or more, 55.00% or more, 56.00% or more, 57.00% or more, 58.00% or more, 59.00% or more, 60.00% or more, 61.00% or more, 62.00% or more, 63.00% or more, and 64.00% or more in that order. Glass with high chemical durability is preferred because it is less likely to cause surface roughening during polishing or cleaning. On the other hand, from the viewpoint of further improving rigidity, SiO ２The content is preferably 75.00% or less, and more preferably 74.00% or less, 73.0% or less, 72.0% or less, 71.0% or less, 70.0% or less, 69.0% or less, 68.0% or less, 67.0% or less, 66.0% or less, 65.00% or less, 64.00% or less, 63.00% or less, 62.00% or less, and 61.00% or less in that order.

[0068] Glass 3 Al ２ O ３ From the viewpoint of improving thermal stability, the Al content is preferably 20.00% or less, and more preferably 19.00% or less, 18.00% or less, 17.00% or less, and 16.00% or less in that order. Also, from the viewpoint of maintaining the temperature required for melting the glass within an appropriate range, Al ２ O ３ On the other hand, from the viewpoint of further improving rigidity, it is preferable that the content of Al is in the above range. ２ O ３ The content is preferably 10.00% or more, more preferably 11.00% or more, 12.00% or more, and 13.00% or more in that order.

[0069] In glass 3, SiO ２ , B ２ O ３ and Al ２ O ３ The total content (SiO ２ +B ２ O ３ +Al ２ O ３ From the viewpoint of enhancing the thermal stability of the glass, the SiO content of glass 3 is preferably 70.00% or more, and more preferably 71.00% or more, 72.00% or more, 73.00% or more, 74.00% or more, 75.00% or more, 76.00% or more, 77.00% or more, 78.00% or more, and 79.00% or more in that order. ２ , B ２ O ３ and Al ２ O ３ The total content (SiO ２ +B ２ O ３ +Al ２ O ３) is preferably 85.00% or less, and more preferably 84.00% or less, 83.00% or less, 82.00% or less, 81.00% or less, 80.00% or less, 79.00% or less, 78.00% or less, 77.00% or less, 76.00% or less, 75.00% or less, and 74.00% or less in that order.

[0070] SiO ２ and B ２ O ３ and the total content (SiO ２ +B ２ O ３ From the viewpoint of enhancing the thermal stability of the glass, the SiO content of glass 3 is preferably 58.00% or more, and more preferably 59.00% or more, 60.00% or more, 61.00% or more, 62.00% or more, 63.00% or more, and 64.00% or more in that order. ２ and B ２ O ３ and the total content (SiO ２ +B ２ O ３ ) is preferably 77.00% or less, and more preferably in order of 76.00% or less, 75.00% or less, 74.00% or less, 73.00% or less, 72.00% or less, 71.00% or less, 70.00% or less, 69.00% or less, 68.00% or less, 67.00% or less, 66.00% or less, 65.00% or less, 64.00% or less, 63.00% or less, and 62.00% or less.

[0071] In the glass 3, from the viewpoint of chemical durability such as acid resistance and alkali resistance, SiO ２ and Al ２ O ３ and the total content (SiO ２ +Al ２ O ３ ) is preferably 70.00% or more, and more preferably 71.00% or more, 72.00% or more, 73.00% or more, 74.00% or more, 75.00% or more, 76.00% or more, 77.00% or more, 78.00% or more, and 79.00% or more in that order. ２ and Al ２ O ３ and the total content (SiO２ +Al ２ O ３ ) is preferably 85.00% or less, and more preferably 84.00% or less, 83.00% or less, 82.00% or less, 81.00% or less, 80.00% or less, 79.00% or less, 78.00% or less, 77.00% or less, 76.00% or less, 75.00% or less, and 74.00% or less in that order.

[0072] Glass 3 contains Na as an essential component. ２ Contains O. Na ２ O is a component that has various functions, such as increasing the specific elastic modulus of glass, improving meltability, increasing the thermal expansion coefficient, and reducing the viscosity of glass during fining to promote bubble removal. ２ The inclusion of O in the glass is equivalent to the inclusion of the same amount of Li ２ The addition of Na in Glass 3 can contribute to increasing the glass transition temperature compared to the addition of O. ２ The O content is 1.00% or more, preferably 1.50% or more, and more preferably 2.00% or more, 2.50% or more, and 3.00% or more in that order. ２ The O content is 6.00% or less, preferably 5.50% or less, and more preferably 5.00% or less, 4.50% or less, and 4.00% or less in that order.

[0073] From the viewpoint of improving the water resistance of the glass, in Glass 3, Na ２ SiO relative to O content ２ Molar ratio of content (SiO ２ / Na ２O) is preferably 12.0 or more, and more preferably 15.0 or more, 16.0 or more, 17.0 or more, and 18.0 or more in that order. Excellent water resistance of glass is preferable in order to prevent the glass surface from becoming rough and losing its smoothness (i.e., increasing surface roughness) when an ultra-smoothly polished glass surface comes into contact with water during cleaning or the like. The lower the surface roughness of the glass, the more easily the orientation of the magnetic particles improves, and the easier it is to reduce the gap between the magnetic head and the magnetic recording medium (the flying height of the magnetic head), which is preferable. On the other hand, from the viewpoint of improving the meltability of the glass, the molar ratio (SiO ２ / Na ２ O) is preferably 50.0 or less, more preferably 40.0 or less, and even more preferably 30.0 or less.

[0074] Glass 3 is Na ２ It may also contain an alkali metal oxide other than O. ２ O is the above Na ２ It is a component that has the same function as O, but as mentioned above, the same amount of Na ２ The glass transition temperature can be lowered more easily than when O is added. ２ The O content may be, for example, 6.00% or less, 5.00% or less, 4.00% or less, 3.00% or less, 2.00% or less, 1.50% or less, 1.00% or less, 0.50% or less, or 0.10% or less. ２ The O content can be 0%, 0% or more, or greater than 0%. ２ It may be an O-free glass.

[0075] K ２ O is the above Na ２ It is a component that has the same function as O, but Na ２ Since it has a higher specific gravity than O, the same amount of Na ２ The specific elastic modulus can be easily reduced compared to when O is added. ２ The O content may be, for example, 6.00% or less, 5.00% or less, 4.00% or less, 3.00% or less, 2.00% or less, 1.50% or less, 1.00% or less, 0.50% or less, or 0.10% or less.２ The O content can be 0%, 0% or more, or greater than 0%. ２ In another embodiment, the glass 3 may be a glass that does not contain K. ２ It can be a glass containing O, for example, K ２ The glass may contain 0.10% or more of O.

[0076] From the viewpoint of increasing the glass transition temperature and the specific elastic modulus, in Glass 3, Li ２ O, Na ２ O and K ２ Na content relative to total O content ２ Molar ratio of O content (Na ２ O / (Li ２ O + Na ２ O+K ２ The molar ratio (NaO)) of glass 3 is preferably 0.350 or more, and more preferably 0.400 or more, 0.450 or more, 0.500 or more, 0.550 or more, 0.600 or more, 0.650 or more, 0.700 or more, 0.750 or more, 0.800 or more, 0.850 or more, 0.900 or more, 0.950 or more, 0.960 or more, 0.970 or more, 0.980 or more, and 0.990 or more in this order. ２ O / (Li ２ O + Na ２ O+K ２ O)) can be 1.000, or can be less than or equal to 1.000. In one embodiment, glass 3 contains Li ２ O and K ２ The glass may be one that does not contain O. In addition, the above molar ratio (Na ２ O / (Li ２ O + Na ２ O+K ２ From the viewpoint of improving the water resistance and reducing the roughness of the glass, O)) is preferably less than 1.000, and more preferably 0.950 or less, and more preferably 0.900 or less.

[0077] From the viewpoint of improving the water resistance of the glass, the glass contains Li ２ O, Na ２ O and K ２ Li relative to the total content of O ２Molar ratio of O content (Li ２ O / (Li ２ O + Na ２ O+K ２ On the other hand, from the viewpoint of suppressing a decrease in the glass transition temperature, the molar ratio (Li ２ O / (Li ２ O + Na ２ O+K ２ O)) is preferably 0.600 or less, more preferably 0.500 or less, 0.400 or less, and 0.300 or less in that order.

[0078] The CaO content of Glass 3 is 1.00% or less. A CaO content of 1.00% or less contributes to increasing the specific elastic modulus and glass transition temperature of the glass, and may also contribute to improving the thermal stability of the glass. From these viewpoints, the CaO content is preferably 0.90% or less, and more preferably 0.80% or less, 0.70% or less, 0.60% or less, 0.50% or less, 0.40% or less, 0.30% or less, 0.20% or less, and 0.10% or less in this order. The CaO content of Glass 3 can be 0%, 0% or more, or more than 0%. In one embodiment, Glass 3 preferably does not contain CaO.

[0079] Regarding alkaline earth metal oxides, the CaO content of Glass 3 is as described above. In one embodiment, Glass 3 may contain one or more alkaline earth metal oxides. Specific examples of alkaline earth metal oxides that may be contained in Glass 3 include MgO, SrO, and BaO. Glass 3-A contains MgO. From the viewpoint of improving rigidity, the MgO content of Glass 3-A is 14.00% or more, preferably 14.50% or more, and more preferably 15.00% or more, 15.50% or more, and 16.00% or more in that order. Furthermore, from the viewpoint of improving the devitrification resistance of the glass, the MgO content of Glass 3-A is preferably 28.00% or less, and is more preferably 27.00% or less, 26.00% or less, 25.00% or less, 24.00% or less, 23.00% or less, 22.00% or less, 21.00% or less, 20.00% or less, 19.00% or less, and 18.00% or less in that order. Glass 3-B may contain MgO. For the MgO content of Glass 3-B, see the description regarding the MgO content of Glass 3-A.

[0080] In glass 3-B, the total content of MgO, SrO, CaO, and BaO (MgO + SrO + CaO + BaO) is, from the viewpoint of improving rigidity, 14.00 mol% or more, preferably 14.50% or more, and more preferably 15.00% or more, 15.50% or more, and 16.00% or more in that order. Furthermore, from the viewpoint of improving devitrification resistance of the glass, the total content of MgO, SrO, CaO, and BaO (MgO + SrO + CaO + BaO) in glass 3-B is preferably 28.00% or less, and more preferably 27.00% or less, 26.00% or less, 25.00% or less, 24.00% or less, 23.00% or less, 22.00% or less, 21.00% or less, 20.00% or less, 19.00% or less, and 18.00% or less in that order. With regard to the total content of MgO, SrO, CaO, and BaO (MgO+SrO+CaO+BaO) in Glass 3-A, reference can be made to the description regarding the total content of MgO, SrO, CaO, and BaO (MgO+SrO+CaO+BaO) in Glass 3-B.

[0081] From the viewpoint of reducing the specific gravity and the raw material cost, the SrO content of glass 3 is preferably 4.00% or less, and is more preferably 3.00% or less, 2.00% or less, 1.00% or less, and 0.50% or less in that order. In one embodiment, the SrO content of glass 3 can be 0%, 0% or more, or more than 0%.

[0082] From the viewpoints of reducing the specific gravity of the glass, improving the Young's modulus, and improving the specific elastic modulus, the BaO content of glass 3 is preferably 3.00% or less, and more preferably 2.00% or less, 1.00% or less, and 0.50% or less in that order. In one embodiment, the BaO content of glass 3 can be 0%, 0% or more, or more than 0%.

[0083] The molar ratio of the MgO content to the total content of MgO, CaO, SrO, and BaO (MgO / (MgO+CaO+SrO+BaO)) can be 1.000, 1.000 or less, or less than 1.000. MgO has a lower specific gravity than other alkaline earth metal oxides, and therefore can contribute to increasing the specific modulus of elasticity. Furthermore, in general glasses, the glass transition temperature tends to increase when alkaline earth metal oxides with a higher specific gravity are added. In contrast, according to the inventors' investigations, in Glass 3, the glass transition temperature tends to decrease when alkaline earth metal oxides with a higher specific gravity than MgO are added. From the viewpoint of increasing the specific modulus and glass transition temperature of Glass 3, the molar ratio (MgO / (MgO+CaO+SrO+BaO)) is preferably 0.800 or more, and more preferably 0.850 or more, 0.900 or more, 0.950 or more, and 1.000, in that order.

[0084] In glass 3, the ratio of Na to MgO content was determined from the viewpoints of reducing the melt viscosity, lowering the liquidus temperature, and improving the polishing performance of the glass by reducing the roughness. ２ Molar ratio of O content (Na ２ The molar ratio (Na O / MgO) of glass 3 is preferably greater than 0.080. ２ From the above viewpoint, the molar ratio (Na O / MgO) of glass 3 can contribute to reducing the specific resistance of the glass melt. ２On the other hand, from the viewpoint of increasing the glass transition temperature and the specific elastic modulus, the molar ratio (NaO / MgO) of glass 3 is more preferably 0.090 or more, and further preferably 0.100 or more, 0.110 or more, 0.120 or more, 0.130 or more, 0.140 or more, 0.150 or more, and 0.160 or more in that order. ２ O / MgO) is preferably less than 0.240, and more preferably 0.230 or less, 0.220 or less, 0.210 or less, 0.200 or less, 0.190 or less, or 0.180 or less in that order.

[0085] TiO ２ Regarding the TiO of Glass 3, from the viewpoint of reducing the specific gravity and improving the devitrification resistance, ２ The content is preferably 4.00% or less, and more preferably 3.00% or less, 2.00% or less, and 1.00% or less in that order. ２ The content can be 0%, or can be equal to or greater than 0%.

[0086] Regarding ZnO, from the viewpoints of reducing the specific gravity, improving the Young's modulus, and improving the specific elastic modulus, the ZnO content is preferably 10.00% or less, and more preferably 8.00% or less, 6.00% or less, 4.00% or less, 2.00% or less, and 1.00% or less in that order. The ZnO content of glass 3 can be 0%, 0% or more, or more than 0%.

[0087] Glass 3 Fe ２ O ３ The content, expressed as an exclusive percentage, can be 1 mol% or less, 0.7 mol% or less, 0.5 mol% or less, 0.4 mol% or less, 0.3 mol% or less, 0.1 mol% or less, 0.07 mol% or less, 0.05 mol% or less, 0.04 mol% or less, 0.03 mol% or less, or 0.02 mol% or less. ２ O ３ The content is expressed as an exclusive percentage. That is, the Fe contained in the glass ２ O ３ When the total content of components other than (when additives are included in addition to glass components, the total content of glass components and additives) is taken as 100%, the amount of Fe relative to 100% ２ O ３Fe content in mole percentage ２ O ３ In one embodiment, the glass 3 does not contain Fe (the Fe content in the above-mentioned external percentage is ２ O ３ The content can be 0 mol %.

[0088] Glass 3 may or may not contain one or more metals or oxides thereof selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er. Inclusion of an oxide of one or more metals selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er in a glass composition based on oxides tends to increase the thermal stability of the glass. In one embodiment, the content of oxides of one or more metals selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er (the total content when a plurality of metals are contained) can be 0%, 0% or more, or more than 0%, and can be 5.00% or less, 4.00% or less, 3.00% or less, 2.00% or less, 1.00% or less, 0.50% or less, or 0.10% or less. For example, Y ２ O ３ The content can be 0% or more or more than 0%, and can be 3.00% or less, 2.00% or less, or 1.00% or less.

[0089] F is a component that easily volatilizes during melting and is also a component that causes striae, so it is preferable that glass 3 does not contain F. Not containing F is also preferable from the viewpoints of suppressing erosion of the melting furnace, suppressing a decrease in Young's modulus, and suppressing a decrease in specific elastic modulus.

[0090] Since Pb, Cd and As are substances that have a negative impact on the environment, it is preferable to avoid introducing them.

[0091] Glass 3 contains SnO ２ , CeO ２ and Sb ２ O ３In one embodiment, the composition may include one or more selected from the group consisting of SnO ２ and CeO ２ In another embodiment, the total content of SnO ２ and / or CeO ２ and SnO ２ and CeO ２ The total content (SnO ２ + CeO ２ ) is preferably 0.05 to 2%. ２ and CeO ２ When the total content of SnO is 0.05% or more, a sufficient fining effect can be obtained and residual bubbles can be reduced. ２ + CeO ２ By making the total content (SnO ) 2% or less, it is possible to prevent the molten glass from blowing up during glass melting, thereby preventing a decrease in productivity. ２ + CeO ２ The lower limit of the total content (SnO ２ + CeO ２ The upper limit of ) is preferably 1.5% or less, more preferably 1.2% or less, even more preferably 1.0% or less, still more preferably 0.70% or less, even more preferably 0.65% or less, still more preferably 0.60% or less, still more preferably 0.55% or less, and even more preferably 0.50% or less.

[0092] SnO ２ has the function of promoting fining when the melting temperature of the glass is relatively high (temperature range of about 1400 to 1600°C). ２ O ３ In order to remove bubbles from glass with a high melting temperature, in one embodiment, SnO is added to the glass 3.２ It is preferable to incorporate SnO. ２ From the viewpoint of obtaining a fining effect, the content of SnO is preferably 0.01% or more, more preferably 0.05% or more, even more preferably 0.10% or more, even more preferably 0.15% or more, and even more preferably 0.20% or more. ２ The content is preferably 2% or less, more preferably 1.5% or less, even more preferably 1.0% or less, even more preferably 0.8% or less, and even more preferably 0.5% or less.

[0093] CeO ２ is SnO ２ It is a component that has a fining effect on glass, similar to CeO ２ has the function of taking in oxygen and fixing it as a glass component when the melting temperature of the glass is relatively low (temperature range of about 1200 to 1400°C). Therefore, in one embodiment, CeO is added to the glass 3 as a fining agent. ２ It is preferable to incorporate CeO ２ From the viewpoint of obtaining a fining effect, the content of CeO is preferably 0.01% or more, more preferably 0.05% or more, even more preferably 0.08% or more, and even more preferably 0.10% or more. ２ The content of SnO is preferably 2% or less, more preferably 1.5% or less, even more preferably 1.0% or less, still more preferably 0.8% or less, even more preferably 0.5% or less, and still more preferably 0.3% or less. ２ and CeO ２ By coexisting with SnO, a fining effect can be obtained in a wide temperature range. ２ and CeO ２ It is preferable to include both of the above.

[0094] Sb ２ O ３ It is desirable to refrain from using Sb in glass 3 from the viewpoint of reducing the environmental load. ２ O ３The content of Sb is preferably in the range of 0 to 0.5%. ２ O ３ The content of Sb is more preferably 0.3% or less, further preferably 0.1% or less, even more preferably 0.05% or less, and even more preferably 0.02% or less. ２ O ３ It is particularly preferred that it does not contain

[0095] Glass 3 can be produced by weighing, blending, and thoroughly mixing glass raw materials such as oxides, carbonates, nitrates, sulfates, and hydroxides so as to obtain a predetermined glass composition, heating and melting the mixture in a melting vessel at, for example, a temperature range of 1400 to 1600°C, refining, stirring, and molding the homogenized molten glass that has been sufficiently defoamed. For example, it is preferable to heat and melt the glass raw materials in a melting tank at 1400 to 1550°C, and then heat and hold the resulting molten glass in a refining tank at 1450 to 1600°C, and then lower the temperature to 1200 to 1400°C, at which point the glass is allowed to flow and be molded.

[0096] According to another aspect of the present invention, ２ O ３ The content is 0.1 mol% or more and 2.0 mol% or less, Na ２ The present invention can provide an amorphous glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device, which has an O content of 1.0 mol % or more and 6.0 mol % or less, and a CaO content of 0 mol % or more and 1.0 mol % or less, and further satisfies any one or more of the following (1) to (10):

[0097] (1) Molar ratio (Na ２ O / (Li ２ O + Na ２ O+K ２ O)) is 0.950 or more, and the total content (SiO ２ +B ２ O ３ +Al ２ O ３ ) is over 70.00%.

[0098] (2) Li ２ O and K ２O is not contained, and the total content (SiO ２ +B ２ O ３ +Al ２ O ３ ) is over 70.00%.

[0099] (3) Molar ratio (Na ２ O / (Li ２ O + Na ２ O+K ２ O)) is 0.950 or more, and the total content (SiO ２ +B ２ O ３ ) is over 58.00%.

[0100] (4) Li ２ O and K ２ O is not contained, and the total content (SiO ２ +B ２ O ３ ) is over 58.00%.

[0101] (5) Molar ratio (Na ２ O / (Li ２ O + Na ２ O+K ２ O)) is 0.950 or more, and the total content (SiO ２ +Al ２ O ３ ) is over 70.00%.

[0102] (6) Li ２ O and K ２ O is not contained, and the total content (SiO ２ +Al ２ O ３ ) is over 70.00%.

[0103] (7) Molar ratio (Na ２ O / (Li ２ O + Na ２ O+K ２ O)) is 0.950 or more, and TiO ２ The content is 4.00 mol% or less.

[0104] (8) Li ２ O and K ２ Does not contain O and TiO ２ The content is 4.00 mol% or less.

[0105] (9) Molar ratio (Na ２ O / (Li ２ O + Na ２ O+K ２ O)) is 0.950 or more, and the ZnO content is 10.00% or less.

[0106] (10) Li ２ O and K ２ Contains no O and has a ZnO content of 10.00% or less.

[0107] For each of the above glasses, reference can be made to the above description regarding the compositions of Glass 3-A and Glass 3-B and the below description regarding the physical properties of Glass 3-A and Glass 3-B.

[0108] According to another aspect of the present invention, ２ O ３ a content of 0.10 mol% or more and 2.00 mol% or less, Na ２ O and K ２ A glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device (hereinafter referred to as "glass 3-a"), which is an amorphous glass having a total content of 1.00 mol % or more and 6.00 mol % or less with O, a CaO content of 0 mol % or more and 1.00 mol % or less, and an MgO content of 14.00 mol % or more. ２ O ３ a content of 0.10 mol% or more and 2.00 mol% or less, Na ２ O and K ２ a glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device (hereinafter referred to as "glass 3-b"), which is an amorphous glass having a total content of MgO and SrO of 1.00 mol % or more and 6.00 mol % or less, a CaO content of 0 mol % or more and 1.00 mol % or less, and a total content of MgO, SrO, CaO, and BaO (MgO + SrO + CaO + BaO) of 14.00 mol % or more.

[0109] For Glass 3-a and Glass 3-b, reference can be made to the above description regarding the compositions of Glass 3-A and Glass 3-B and the below description regarding the physical properties of Glass 3-A and Glass 3-B.

[0110] <Glass Physical Properties> By adjusting the composition as described above, Glass 3 can have the various glass physical properties described below.

[0111] (Specific Elastic Modulus) Glass 3 can have high rigidity by having the composition described above. The specific elastic modulus of glass 3 is preferably 35.0 MNm / kg or more, and is even more preferably 35.5 MNm / kg or more, 36.0 MNm / kg or more, 36.5 MNm / kg or more, and 37.0 MNm / kg or more in this order. The specific elastic modulus can be, for example, 45.0 MNm / kg or less, 44.0 MNm / kg or less, 43.0 MNm / kg or less, 42.0 MNm / kg or less, 41.0 MNm / kg or less, 40.0 MNm / kg or less, 39.0 MNm / kg or less, or 38.0 MNm / kg or less. However, since a higher specific elastic modulus is preferable because it increases rigidity, the specific elastic modulus is not limited to the above-mentioned exemplary values. Note that the specific elastic modulus of glass 3 may be 37.0 MNm / kg or less, taking into account the balance with the glass transition temperature.

[0112] (Young's Modulus E) The Young's modulus of glass 3 is preferably 86.0 GPa or more, more preferably 87.0 GPa or more, and even more preferably 88.0 GPa or more, 89.0 GPa or more, 90.0 GPa or more, 91.0 GPa or more, 92.0 GPa or more, and 93.0 GPa or more in this order. The Young's modulus of glass 3 can be, for example, 120.0 GPa or less, 110.0 GPa or less, 100 GPa or less, or 95.0 GPa or less. However, since a higher Young's modulus is preferable because it increases rigidity, the Young's modulus is not limited to the above-mentioned values. Note that the Young's modulus of glass 3 may be 94.0 GPa or less, 93.0 GPa or less, or 92.0 GPa or less, taking into account the balance with the glass transition temperature.

[0113] (Specific Gravity d) The specific gravity of the glass 3 is preferably 2.80 or less, more preferably 2.75 or less, even more preferably 2.70 or less, still more preferably 2.65 or less, and still more preferably 2.60 or less. The specific gravity of the glass 3 can be, for example, 2.40 or more, but since a lower specific gravity is more preferable, the specific gravity is not limited to the above-mentioned example values.

[0114] (Glass Transition Temperature Tg) By having the above glass composition, glass 3 can also exhibit high heat resistance. With regard to the glass transition temperature Tg, which is an index of heat resistance, the Tg of glass 3 can be, for example, 550°C or higher, preferably 600°C or higher, and is more preferably 610°C or higher, 620°C or higher, 630°C or higher, 640°C or higher, 650°C or higher, 660°C or higher, 670°C or higher, 680°C or higher, 690°C or higher, 700°C or higher, 710°C or higher, 720°C or higher, 730°C or higher, 740°C or higher, and 750°C or higher. Furthermore, the Tg of glass 3 can be, for example, 850°C or lower, 830°C or lower, 810°C or lower, 790°C or lower, 770°C or lower, or 750°C or lower, but is not limited to the above-exemplified values ​​because a higher Tg is preferable from the viewpoint of heat resistance.

[0115] (Thermal Stability) Glass 3 preferably exhibits high thermal stability. Methods for evaluating thermal stability include a 1300°C 16-hour holding test and a 1320°C 16-hour holding test, which will be described in detail below. In the 1300°C 16-hour holding test, the evaluation result is preferably A or B, and more preferably A. In the 1320°C 16-hour holding test, the evaluation result is preferably A or B, and more preferably A.

[0116] [Magnetic Recording Medium Substrate] A magnetic recording medium substrate according to one aspect of the present invention is made of any of the glasses described above.

[0117] A magnetic recording medium substrate can be manufactured by heating glass raw materials to prepare a glass melt, forming the glass melt into a plate by, for example, a press molding method, a down-draw method, or a float method, and then processing the resulting glass melt. For example, in a press molding method, the glass melt flowing out of a glass flow pipe is cut to a predetermined volume to obtain a desired glass melt lump, which is then press-molded in a press mold to produce a thin, disk-shaped substrate blank. The resulting substrate blank is then provided with a central hole, and the inner and outer peripheries are processed, and both main surfaces are polished by lapping, polishing, or the like. A disk-shaped substrate can then be obtained by a cleaning process that includes acid cleaning and alkali cleaning. Known techniques related to the manufacture of magnetic recording medium substrates can be applied to the various steps performed to obtain the magnetic recording medium substrate.

[0118] In one embodiment, the magnetic recording medium substrate has a homogeneous surface and internal composition. Here, "homogeneous surface and internal composition" means that ion exchange has not been performed (i.e., the substrate does not have an ion exchange layer). Magnetic recording medium substrates without an ion exchange layer can be manufactured without ion exchange treatment, thereby significantly reducing manufacturing costs.

[0119] In one embodiment, the magnetic recording medium substrate has an ion-exchange layer on part or all of its surface. Because the ion-exchange layer exhibits compressive stress, the presence or absence of the ion-exchange layer can be confirmed by breaking the substrate perpendicular to the main surface and obtaining a stress profile on the fracture surface using the Babinet method. The "main surface" refers to the surface of the substrate on which the magnetic recording layer is provided or is provided. This surface is called the main surface because it has the largest area among the surfaces of the magnetic recording medium substrate. In the case of a disk-shaped magnetic recording medium, this corresponds to the circular surface of the disk (excluding the center hole, if any). The presence or absence of the ion-exchange layer can also be confirmed by measuring the concentration distribution of alkali metal ions in the depth direction from the substrate surface.

[0120] The ion exchange layer can be formed by contacting an alkali salt with the substrate surface at high temperature and exchanging the alkali metal ions in the alkali salt with the alkali metal ions in the substrate. Ion exchange (also called "strengthening treatment" or "chemical strengthening") can be performed using known techniques. For example, see paragraphs 0068 to 0069 of WO2011 / 019010A1.

[0121] The magnetic recording medium substrate has a thickness of, for example, 1.5 mm or less, preferably 1.2 mm or less, more preferably 1.0 mm or less, even more preferably 0.8 mm or less, even more preferably less than 0.8 mm, even more preferably 0.7 mm or less, and even more preferably 0.6 mm or less. Furthermore, the thickness of the magnetic recording medium substrate is, for example, 0.2 mm or more. Reducing the thickness of the magnetic recording medium substrate is preferable from the viewpoint of improving the recording capacity of HDDs. Furthermore, the magnetic recording medium substrate is preferably in the shape of a disk having a center hole.

[0122] The magnetic recording medium substrate is made of amorphous glass, which can achieve superior surface smoothness when processed into a substrate compared to glass-ceramics.

[0123] The magnetic recording medium substrate is made of any of the above glasses, and therefore can have the glass properties described above for the above glasses.

[0124] [Magnetic Recording Medium] One aspect of the present invention relates to a magnetic recording medium having the above-described magnetic recording medium substrate and a magnetic recording layer.

[0125] Magnetic recording media are called magnetic disks, hard disks, etc., and are suitable for various magnetic recording and playback devices, such as internal storage devices (fixed disks, etc.) of desktop personal computers, server computers, notebook personal computers, mobile personal computers, etc., internal storage devices of portable recording and playback devices that record and play back images and / or audio, recording and playback devices for in-car audio, etc. In this invention and this specification, the term "magnetic recording and playback device" refers to a device that is capable of either or both of magnetically recording information and magnetically playing back information.

[0126] The magnetic recording medium has a structure in which, for example, at least an adhesive layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer are laminated on the main surface of a magnetic recording medium substrate in order from the side closest to the main surface. For example, the magnetic recording medium substrate is introduced into a vacuum-drawn film-forming device, and films from the adhesive layer to the magnetic layer are sequentially formed on the main surface of the magnetic recording medium substrate using a DC (Direct Current) magnetron sputtering method in an Ar atmosphere. For example, CrTi can be used as the adhesive layer, and a material containing Ru or MgO can be used as the underlayer. Note that a soft magnetic layer and a heat sink layer may be added as appropriate. After the above-mentioned film formation, a C layer is formed by, for example, a CVD (Chemical Vapor Deposition) method. ２ H ４ A magnetic recording medium can be formed by forming a protective layer using a nitriding agent and then performing a nitriding process to introduce nitrogen into the surface in the same chamber. Thereafter, a lubricating layer can be formed by applying, for example, PFPE (polyfluoropolyether) onto the protective layer by a dip coating method.

[0127] To achieve even higher recording densities in magnetic recording media, the magnetic recording layer preferably contains a magnetic material with high magnetic anisotropy energy. From this perspective, preferred magnetic materials include Fe—Pt-based magnetic materials or Co—Pt-based magnetic materials. Here, "based" means "contained." That is, the magnetic recording medium can have a magnetic recording layer containing Fe and Pt, or Co and Pt. For magnetic recording layers containing such magnetic materials and methods for forming them, see paragraph 0074 of WO 2011 / 019010 A1 and the examples therein. Furthermore, magnetic recording media having such magnetic recording layers are preferably applied to magnetic recording devices using a recording method known as energy-assisted recording. Among energy-assisted recording methods, a recording method that assisted magnetization reversal by irradiation with near-field light or the like is called a thermally assisted recording method, and a recording method that assisted magnetization reversal by microwaves is called a microwave-assisted recording method. For details, see paragraph 0075 of WO 2011 / 019010 A1. As the magnetic material for forming the magnetic recording layer, a conventional CoPtCr-based material may be used.

[0128] In recent years, by incorporating a DFH (Dynamic Flying Height) mechanism into a magnetic head, the gap between the read / write element of the magnetic head and the surface of the magnetic recording medium has been significantly narrowed (reduced flying height), thereby achieving even higher recording densities. The DFH mechanism is a function in which a heating unit such as a very small heater is provided near the read / write element of the magnetic head, and only the periphery of the element protrudes toward the surface of the medium. This reduces the distance (flying height) between the magnetic head and the magnetic recording layer of the medium, making it possible to pick up signals from smaller magnetic particles and achieving even higher recording densities. In one embodiment, the magnetic recording medium substrate can be used as a substrate for a magnetic recording medium applied to a magnetic recording / reproducing device equipped with a magnetic head equipped with a DFH mechanism.

[0129] There are no particular limitations on the dimensions of the magnetic recording medium substrate (e.g., a glass substrate for a magnetic disk) or the magnetic recording medium (e.g., a magnetic disk). For example, since high recording density is possible, the medium and substrate can be made smaller. Furthermore, in order to increase the recording capacity per magnetic recording medium, the medium and substrate can be made larger. For example, the nominal diameter can be 2.5 inches, of course, but they can also be made smaller (e.g., 1 inch or 1.8 inches), or 3 inches, 3.5 inches, or even larger.

[0130] [Glass Spacer for Magnetic Recording / Reproducing Device] A glass spacer for a magnetic recording / reproducing device (hereinafter also simply referred to as "glass spacer") according to one aspect of the present invention is made of the above-mentioned glass.

[0131] Magnetic recording media can be used in magnetic recording and / or reproducing devices to magnetically record and / or reproduce information. Magnetic recording and reproducing devices typically include spacers for fixing the magnetic recording media to the spindle of a spindle motor and / or for maintaining a distance between multiple magnetic recording media. In recent years, the use of glass spacers as such spacers has been proposed. For reasons similar to those detailed above for the glass for magnetic recording medium substrates, it is desirable for these glass spacers to have high rigidity. In contrast, glass having the above composition can have high rigidity, making it suitable as a glass spacer for magnetic recording and reproducing devices.

[0132] The spacer for a magnetic recording / reproducing device is a ring-shaped member, and details such as the structure and manufacturing method of the glass spacer are publicly known. Regarding the manufacturing method of the glass spacer, the above-mentioned descriptions regarding the manufacturing method of glass for a magnetic recording medium substrate and the manufacturing method of a magnetic recording medium substrate can be referenced. Regarding other details such as the glass composition and physical properties of the glass spacer, the above-mentioned descriptions regarding the glass, the magnetic recording medium substrate made of the glass, and the magnetic recording medium having such a magnetic recording medium substrate can be referenced. The spacer for a magnetic recording / reproducing device can be composed of the above-mentioned glass spacer, or can be configured with one or more layers such as a conductive film provided on the surface of the glass spacer. For example, to remove static electricity generated during rotation of the magnetic recording medium, a conductive film such as a NiP alloy can be formed on the surface of the glass spacer by plating, immersion, vapor deposition, sputtering, or the like. Furthermore, the glass spacer can be polished to increase its surface smoothness (e.g., an average surface roughness Ra of 1 μm or less), thereby strengthening the adhesion between the magnetic recording medium and the spacer and suppressing misalignment.

[0133] [Magnetic Recording and Reproducing Apparatus] One aspect of the present invention relates to a magnetic recording and reproducing apparatus including one or more members selected from the group consisting of the magnetic recording medium and the glass spacer.

[0134] A magnetic recording and reproducing device includes at least one magnetic recording medium and at least one spacer, and typically further includes a spindle motor for rotating the magnetic recording medium and at least one magnetic head for recording and / or reproducing information on the magnetic recording medium. The magnetic recording and reproducing device according to one aspect of the present invention may include a magnetic recording medium according to one aspect of the present invention as at least one magnetic recording medium, or may include multiple magnetic recording media according to one aspect of the present invention. The magnetic recording and reproducing device according to one aspect of the present invention may include a glass spacer according to one aspect of the present invention as at least one spacer, or may include multiple glass spacers according to one aspect of the present invention. A small difference between the thermal expansion coefficients of the magnetic recording medium and the spacer is preferable from the viewpoint of suppressing the occurrence of phenomena that may arise due to the difference between the thermal expansion coefficients, such as distortion of the magnetic recording medium and reduced stability during rotation due to misalignment of the magnetic recording medium. From this viewpoint, the magnetic recording and reproducing device according to one aspect of the present invention preferably includes a magnetic recording medium according to one aspect of the present invention as at least one magnetic recording medium, or as more magnetic recording media if multiple magnetic recording media are included, and preferably includes a glass spacer according to one aspect of the present invention as at least one spacer, or as more spacers if multiple spacers are included. Furthermore, for example, in a magnetic recording and reproducing device according to one aspect of the present invention, the glass constituting the magnetic recording medium substrate included in the magnetic recording medium and the glass constituting the glass spacer can have the same glass composition.

[0135] A magnetic recording / reproducing device according to one aspect of the present invention may include at least one of a magnetic recording medium according to one aspect of the present invention and a glass spacer according to one aspect of the present invention; otherwise, known techniques related to magnetic recording / reproducing devices can be applied. In one aspect, the magnetic head can be an energy-assisted magnetic recording head having an energy source (e.g., a heat source such as a laser light source, microwaves, etc.) for assisting magnetization reversal (assisting the writing of magnetic signals), a recording element, and a reproducing element. Such an energy-assisted magnetic recording head-equipped magnetic recording / reproducing device is useful as a magnetic recording / reproducing device with high recording density and high reliability. Furthermore, during the manufacture of magnetic recording media used in energy-assisted recording magnetic recording / reproducing devices, such as thermally assisted recording magnetic recording devices equipped with a thermally assisted magnetic recording head having a laser light source, a magnetic recording layer containing a magnetic material with high magnetic anisotropy energy may be formed on a magnetic recording medium substrate. To form such a magnetic recording layer, typically, film deposition is performed at high temperature, or a heat treatment is performed at high temperature after film deposition. In one embodiment, the magnetic recording medium substrate according to one aspect of the present invention can be a magnetic recording medium substrate with high heat resistance that can withstand such high-temperature treatment. However, the magnetic recording and reproducing device according to one aspect of the present invention is not limited to an energy-assisted magnetic recording and reproducing device.

[0136] The present invention will be described in more detail below using examples. However, the present invention is not limited to the embodiments shown in the examples. [Examples 1 to 81] Raw materials such as oxides, carbonates, nitrates, sulfates, and hydroxides were weighed and mixed to prepare a raw material blend so as to obtain glass having the composition shown in the table below. This raw material blend was charged into a melting tank and heated and melted in the range of 1400 to 1600°C. The resulting glass melt was then held in a refining tank at 1400 to 1550°C for 6 hours, and then the temperature was lowered (cooled down) to a range of 1200 to 1400°C for 1 hour. The glass melt was then formed to obtain glasses (amorphous oxide glasses) for the following evaluations. The glasses of Examples 1 to 62 correspond to at least Glass 2. The glasses of Examples 63 to 81 correspond to at least Glass 3. Among the glasses of Examples 1 to 81, some also correspond to Glass 1 and / or Glass 4, as described in the table below and with regard to T1 and T2.

[0137] <Evaluation of Glass Physical Properties> (1) Glass Transition Temperature Tg and Average Linear Expansion Coefficient α The glass transition temperature Tg and the average linear expansion coefficient α at 100 to 300° C. of each glass were measured using a thermomechanical analyzer (TMA).

[0138] (2) Young's Modulus E The Young's modulus of each glass was measured by an ultrasonic method.

[0139] (3) Specific Gravity d The specific gravity of each glass was measured by Archimedes' method.

[0140] (4) Specific Elastic Modulus The specific elastic modulus was calculated from the Young's modulus obtained in (2) above and the specific gravity obtained in (3) above.

[0141] (5) 1300°C 16h Holding Test 100g of each glass was placed in a platinum crucible, and each crucible was placed in a heating furnace with the furnace temperature set to 1300°C, and left for 16 hours while maintaining the furnace temperature (holding test). After 16 hours had passed, the crucible was removed from the heating furnace, and the glass in the crucible was transferred onto a refractory material and cooled to room temperature (20°C to 25°C). The presence or absence of crystals in each glass was observed with an optical microscope (magnification 40 to 100x), and evaluated according to the following criteria. A: No crystals on the glass surface, inside, or at the interface with the platinum crucible bottom. B: Up to 10 crystals with a diameter of several tens of microns per 100g at the interface with the glass surface and the platinum crucible bottom. C: More than 10 crystals with a diameter of several tens of microns per 100g at the interface with the glass surface and the platinum crucible bottom. D: Crystals present inside the glass. E: Crystals present on the glass surface, inside, and at the interface with the platinum crucible bottom. F: Numerous crystals throughout the glass, slightly cloudy. G: The glass is cloudy.

[0142] (6) 1320°C 16-Hour Holding Test A holding test and evaluation of the glass after the holding test were carried out by the method described in (5) above, except that the furnace temperature was set to 1320°C.

[0143] (7) Liquidus Temperature LT The liquidus temperatures of the glasses shown in the table below were determined by the following method. 50 g of glass was weighed into a platinum crucible. This platinum crucible, with a platinum lid attached, was placed in a heating furnace with an internal atmosphere temperature of 1350°C. The glass in the crucible was then completely molten, and the internal atmosphere temperature was lowered to a predetermined temperature and maintained at that temperature for 16 hours. After 16 hours, the platinum crucible was removed from the furnace and left to cool the glass to room temperature (approximately 20°C to 25°C). The cooled glass was visually observed to check for the presence or absence of crystal precipitation. The above procedure was performed from 1330°C to 1200°C in 10°C increments, and the lowest temperature at which no crystal precipitation was observed was taken as the liquidus temperature LT.

[0144] The liquidus temperature LT of the glasses of Examples 17, 18, 22, 29, 32, and 33 was confirmed to be 1300°C or lower by the following method. 50 g of glass was weighed into a platinum crucible. This platinum crucible was placed in a heating furnace with an internal atmosphere temperature of 1350°C with a platinum lid attached, and the glass in the crucible was completely molten. The internal atmosphere temperature was then lowered to 1300°C and maintained at that temperature for 16 hours. After 16 hours, the platinum crucible was removed from the furnace and left to cool the glass to room temperature (approximately 20°C to 25°C). The cooled glass was visually observed to check for the presence or absence of crystal precipitation, and no crystal precipitation was observed.

[0145] (8) Roughness Evaluation Magnetic disk glass substrates having each glass composition shown in the table below were produced using the method described below. The basic processing conditions, such as polishing and cleaning conditions, were the same for all substrates. The arithmetic mean roughness Ra (JIS B0601:2001) of the main surface of the magnetic disk glass substrate after final cleaning was measured using an AFM (atomic force microscope). The Ra measured for each glass is shown as a relative value (ratio) when the Ra measured for Example 66 is set to 1.00. The degree of roughness was ranked according to the following criteria. Even Rank C does not pose any practical problems. Rank A: Less than 0.80 Rank B: 0.80 or more but less than 0.90 Rank C: 0.90 or more but 1.00 or less

[0146] The results are shown in the table below.

[0147]

[0148]

[0149]

[0150]

[0151]

[0152]

[0153]

[0154]

[0155]

[0156]

[0157]

[0158]

[0159]

[0160]

[0161] The results shown in the above table confirm that the glasses of Examples 1 to 81 have high rigidity. For example, the glass of Example 27 shown in Table 5 of JP-A No. 2002-358626 (hereinafter referred to as "comparison glass") has a glass composition expressed in mol % of SiO ２ : 65.0%, Al ２ O ３ :7.0%. MgO: 1.0%, CaO: 1.0%, Li ２ O: 10.0%, Na ２ O: 10.5%, K ２ The glass composition of this comparative glass was different from that of the glass according to one embodiment of the present invention described above in detail, with an O content of 2.5%. The Young's modulus of this comparative glass, calculated by dividing the Young's modulus by the density shown in Table 5 of JP 2002-358626 A, was approximately 32.45, which was lower than the specific modulus values ​​of Examples 1 to 81 shown in the table above.

[0162] (7) Viscosity 10 ２．０ Temperature T1 and viscosity 10 at dPa·s ２．５Temperature T2 at dPa s For the glasses of Examples 1 to 81, the temperatures T1 and T2 were measured by the platinum sphere pulling method. The temperatures T1 of the glasses of Examples 1 to 62 were 1600°C or less. For example, the temperature T1 was 1468°C for Example 4 and 1593°C for Example 21. The temperatures T1 of the glasses of Examples 63 to 79 were 1670°C or less. For example, the temperature T1 was 1635°C for Example 71 and 1662°C for Example 72. The temperatures T1 of the glasses of Examples 80 and 81 were 1700°C or less. The temperatures T2 of the glasses of Examples 1 to 62 were 1500°C or less. For example, the temperature T2 was 1364°C for Example 4 and 1481°C for Example 21. The temperatures T2 of the glasses of Examples 63 to 79 were 1530°C or less. For example, the temperature T1 was 1510° C. in Example 71 and 1520° C. in Example 72. The temperature T2 of the glasses of Examples 80 and 81 was 1560° C. or lower.

[0163] <Preparation of Magnetic Recording Media Substrates> (1) Preparation of Substrate Blanks Disk-shaped substrate blanks were prepared by Method A or B below. Glass blanks for preparing glass spacers for magnetic recording / reproducing devices can also be obtained by a similar method. (Method A) For glass having the composition shown in the above table, a refined and homogenized glass melt was flowed out of an outflow pipe at a constant flow rate and received by a press-molding lower die. The flowed-out glass melt was cut with a cutting blade to obtain a predetermined amount of glass melt gob on the lower die. The lower die with the glass melt gob loaded thereon was then immediately removed from the bottom of the pipe, and press-molded into a thin disk with a diameter of 99 mm and a thickness of 0.7 mm using an upper die and a barrel die facing the lower die. The press-molded product was cooled to a temperature at which it would not deform, then removed from the die and annealed to obtain a substrate blank (amorphous oxide glass). In the above-described molding process, multiple lower dies were used to successively mold the flowing glass melt into disk-shaped substrate blanks. (Method B) Fined and homogenized molten glass of the composition shown in the table above was continuously poured from above into a heat-resistant mold with a cylindrical through-hole, formed into a cylindrical shape, and removed from below the through-hole. The removed glass was annealed and then sliced ​​at regular intervals in a direction perpendicular to the cylindrical axis using a multi-wire saw to produce disk-shaped substrate blanks (amorphous oxide glass). While the above-described methods A and B were employed in this example, the following methods C and D are also suitable for producing disk-shaped substrate blanks. Furthermore, the following methods C and D are also suitable for producing glass blanks for producing glass spacers for magnetic recording / reproducing devices. (Method C) The molten glass can also be poured onto a float bath, formed into a glass sheet (by the float method), annealed, and then cut into disk-shaped glass from the sheet glass to obtain a substrate blank (amorphous oxide glass). (Method D) Molten glass can also be formed into a glass sheet by the overflow downdraw method (fusion method), annealed, and then a disk-shaped glass can be cut from the glass sheet to obtain a substrate blank (amorphous oxide glass).

[0164] (2) Preparation of Glass Substrates. A through-hole was drilled in the center of the substrate blank (amorphous oxide glass) obtained by each of the above methods, and the outer and inner peripheries were ground (simultaneously forming chamfered surfaces). The edges were polished, and the main surfaces of the disk were lapped and polished (mirror polished) to produce a magnetic disk glass substrate with an outer diameter of 97 mm, an inner circular hole diameter of 25 mm, and a thickness of 0.5 mm. Using a similar method, a glass blank for producing glass spacers for magnetic recording / reproducing devices can also be finished into a glass spacer for magnetic recording / reproducing devices. The glass substrate obtained above was scrubbed, washed with an aqueous potassium hydroxide solution, rinsed with pure water, and then dried. When the surface of the substrate prepared from the glass of the example was observed with an atomic force microscope (AFM), no surface roughness was observed, and the surface was smooth (low roughness).

[0165] <Preparation of magnetic recording medium (magnetic disk)> An adhesive layer, an underlayer, a magnetic recording layer, a protective layer, and a lubricating layer were formed in this order on the main surface of the glass substrate for magnetic disk prepared above by the following method, thereby obtaining a magnetic disk.

[0166] First, using a vacuum-drawn film-forming apparatus, an adhesive layer, an underlayer, and a magnetic recording layer were successively formed in an Ar atmosphere by DC magnetron sputtering.

[0167] The adhesive layer was formed using a CrTi target to form an amorphous CrTi layer with a thickness of 20 nm. A 10 nm thick MgO layer was then formed as an underlayer. The magnetic recording layer was formed using an FePtC or CoPtC target at a deposition temperature of 200 to 400°C to form a 10 nm thick granular layer of FePt or CoPt.

[0168] After the magnetic recording layer was formed, the magnetic disk was transferred from the film forming apparatus to a heating furnace and annealed. The temperature in the heating furnace during annealing was set to a range of 500 to 700°C. １０ Magnetic particles of CoPt-based alloy or FePt-based alloy with an ordered structure are formed. １０The magnetic recording layer may be heated to generate an ordered structure. For example, the temperature of the substrate when depositing a magnetic recording layer of FePt or CoPt is set to 500 to 700° C., thereby forming an L １０ An ordered structure may be formed.

[0169] Next, a 3 nm protective layer made of hydrogenated carbon was formed by CVD using ethylene as the source gas. After this, a lubricating layer made of PFPE (perfluoropolyether) was formed by dip coating. The lubricating layer had a thickness of 1 nm. A magnetic disk was obtained through the above manufacturing process. The obtained magnetic disk was installed in a hard disk drive equipped with a DFH mechanism, and magnetic signals were recorded and reproduced in the recording area on the main surface of the magnetic disk at a recording density of 1000 gigabits per square inch. No collision between the magnetic head and the magnetic disk surface (crash failure) was observed.

[0170] Furthermore, a glass spacer obtained by the above manufacturing process using glass having the composition shown in the above table and having a NiP alloy conductive film formed on its surface (a glass spacer with a NiP alloy film) was mounted in a hard disk drive equipped with a DFH mechanism, and magnetic signals were recorded and reproduced at a recording density of 1000 gigabits per square inch in a recording area on the main surface of a magnetic disk separately prepared using a substrate made of a material different from the glass according to one embodiment of the present invention. No collision between the magnetic head and the magnetic disk surface (crash failure) was observed.

[0171] Furthermore, when the magnetic disk and the glass spacer with NiP alloy film manufactured as described above using the same glass material according to one embodiment of the present invention were mounted in a hard disk drive equipped with a DFH mechanism, and magnetic signals were recorded and reproduced in the recording area on the main surface of the magnetic disk at a recording density of 1000 gigabits per square inch, no collision between the magnetic head and the magnetic disk surface (crash failure) was observed. Here, since the glass substrate and the glass spacer included in the magnetic disk are made of the same glass material, the phenomenon that can occur due to the difference in thermal expansion coefficient described above does not occur.

[0172] According to one aspect of the present invention, it is possible to provide a magnetic recording medium suitable for high-density recording.

[0173] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. For example, by adjusting the composition as described in the specification to the glass compositions exemplified above, it is possible to produce glass for magnetic recording medium substrates and glass spacers for magnetic recording / reproducing devices according to one aspect of the present invention. Furthermore, it is of course possible to arbitrarily combine two or more of the items described in the specification as examples or preferred ranges.

Claims

1. A molar ratio of the Na 2 O content to the MgO content (Na 2 O / MgO) of 0.120 or more and less than 0.240, CaO content is 1.00 mol% or less, The MgO content is 14.00 mol% or more and 22.00 mol% or less, The Li 2 O content is 3.00 mol % or less; Viscosity 10 ２．０ The temperature T1 at dPa·s is 1600° C. or less, and A glass for a magnetic recording medium substrate, which is an amorphous glass having a specific elastic modulus of 34.0 MNm / kg or more.

2. A molar ratio of the Na 2 O content to the MgO content (Na 2 O / MgO) of 0.120 or more and less than 0.240; CaO content is 1.00 mol% or less, The MgO content is 14.00 mol% or more and 22.00 mol% or less, The Li 2 O content is 3.00 mol % or less; Viscosity 10 ２．５ The temperature T2 at dPa·s is 1500° C. or less, and A glass for a magnetic recording medium substrate, which is an amorphous glass having a specific elastic modulus of 34.0 MNm / kg or more.

3. A molar ratio of the Na 2 O content to the MgO content (Na 2 O / MgO) of 0.120 or more and less than 0.240; CaO content is 1.00 mol% or less, The MgO content is 14.00 mol% or more and 22.00 mol% or less, The Li 2 O content is 3.00 mol% or less, and Viscosity 10 ２．０ A glass for a magnetic recording medium substrate, which is an amorphous glass having a temperature T1 at dPa·s of 1600° C. or less.

4. The glass for a magnetic recording medium substrate according to claim 1, wherein the total content of SiO 2 and B 2 O 3 (SiO 2 +B 2 O 3 ) is 63.00 mol % or more.

5. The glass for a magnetic recording medium substrate according to claim 2, wherein the total content of SiO 2 and B 2 O 3 (SiO 2 +B 2 O 3 ) is 63.00 mol % or more.

6. The glass for a magnetic recording medium substrate according to claim 3, wherein the total content of SiO 2 and B 2 O 3 (SiO 2 +B 2 O 3 ) is 63.00 mol % or more.

7. A magnetic recording medium substrate comprising the glass for magnetic recording medium substrates according to any one of claims 1 to 6.

8. A magnetic recording medium comprising the magnetic recording medium substrate according to claim 7 and a magnetic recording layer.

9. 9. A magnetic recording and reproducing device comprising the magnetic recording medium according to claim 8 and a magnetic head.