Glass for magnetic recording medium substrate or for glass spacer to be used in magnetic recording / reproducing device, magnetic recording medium substrate, magnetic recording medium, glass spacer to be used in magnetic recording / reproducing device, and magnetic recording / reproducing device

Abstract

To provide a glass for a magnetic recording medium substrate having high rigidity.SOLUTION: Provided is a glass for a magnetic recording medium substrate or for a glass spacer for a magnetic recording / reproducing device, the glass being an amorphous glass, wherein a B2O3 content is 0.10 mol% or more and 2.00 mol% or less, a Na2O content is 1.00 mol% or more and 6.00 mol% or less, a CaO content is 0 mol% or more and 1.00 mol% or less, and a MgO content is 14.00 mol% or more.SELECTED DRAWING: None

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to PCT / JP2022 / 033744, filed September 8, 2022, the entire disclosure of which is hereby expressly incorporated by reference. [Technical Field]

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

[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, Japanese Patent Laid-Open Publication No. 2002-358626 (the entire disclosure of which is expressly incorporated herein by reference)). Summary of the Invention

[0004] Glass for magnetic recording medium substrates is desired to have high rigidity for the following reasons. Magnetic recording media are typically installed inside hard disk drives (HDDs) built into devices such as personal computers. Inside an HDD, multiple magnetic recording media (magnetic disks) are attached to the rotating shaft of a spindle motor, and an actuator built into the HDD writes and reads data to and from the magnetic recording layer of the magnetic recording media, which are rotating at high speed inside the HDD. The large vibrations of the magnetic recording media during high-speed rotation due to such data writing and reading can lead to collisions between the magnetic head and the magnetic recording media surface, resulting in head crashes. HDDs can increase their storage capacity by reducing the thickness of each magnetic recording media and incorporating more magnetic recording media. However, generally, the thinner the substrate used to make the magnetic recording media thinner, the more susceptible the magnetic recording media is to vibration during high-speed rotation. To suppress such vibrations, it is desirable to use a glass substrate for magnetic recording media that is highly rigid and less likely to vibrate during high-speed rotation, even when thinned. An example of such rigidity is the specific elastic modulus.

[0005] In view of the above, one 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.

[0006] One aspect of the present invention is as follows. [1] B2O3 content is 0.10 mol% or more and 2.00 mol% or less; Na2O content is 1.00 mol% or more and 6.00 mol% or less, CaO content is 0 mol% or more and 1.00 mol% or less, MgO content is 14.00 mol% or more, The amorphous glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device (hereinafter referred to as "glass A"). [2] B2O3 content is 0.10 mol% or more and 2.00 mol% or less; Na2O content is 1.00 mol% or more and 6.00 mol% or less, CaO content is 0 mol% or more and 1.00 mol% or less, The total content of MgO, SrO, CaO and BaO (MgO + SrO + CaO + BaO) is 14.00 mol% or more, The amorphous glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device (hereinafter referred to as "glass B"). [3] The glass according to [1] or [2], wherein the molar ratio of the Na2O content to the total content of Li2O, Na2O and K2O (Na2O / (Li2O+Na2O+K2O)) is 0.950 or more. [4] The glass according to any one of [1] to [3], which is free of Li2O and K2O. [5] The glass according to any one of [1] to [4], wherein the total content of SiO2, B2O3 and Al2O3 (SiO2+B2O3+Al2O3) is 70 mol% or more. [6] The glass according to any one of [1] to [5], wherein the total content of SiO2 and B2O3 (SiO2 + B2O3) is 58 mol% or more. [7] The glass according to any one of [1] to [6], wherein the total content of SiO2 and Al2O3 (SiO2 + Al2O3) is 70 mol% or more. [8] The glass according to [1] or [2], wherein the molar ratio of the Na2O content to the total content of Li2O, Na2O and K2O (Na2O / (Li2O+Na2O+K2O)) is 0.350 or more. [9] The glass according to [1], [2] or [8], which contains Li2O.

[10] The glass according to [1], [2], [8] or [9], wherein the molar ratio of the Li2O content to the total content of Li2O, Na2O and K2O (Li2O / (Li2O+Na2O+K2O)) is 0.600 or less.

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

[10] , wherein the molar ratio of the SiO2 content to the Na2O content (SiO2 / Na2O) is 50.0 or less.

[12] The glass according to any one of [1] to [7], wherein the molar ratio of the Na2O content to the MgO content (Na2O / MgO) exceeds 0.080.

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

[12] , having a TiO2 content of 4.00 mol % or less.

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

[13] , wherein the ZnO content is 10.00 mol % or less.

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

[14] , which has a specific modulus of elasticity of 35.0 MNm / kg or more.

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

[15] , which has a glass transition temperature of 700°C or higher.

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

[16] .

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

[17] and a magnetic recording layer.

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

[16] .

[20]

[18] The magnetic recording medium according to

[18] ,

[19] A glass spacer for a magnetic recording / reproducing device according to

[19] . A magnetic recording and reproducing device including one or more selected from the group consisting of:

[0007] According to one aspect of the present invention, a highly rigid glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device can be provided. According to another aspect, a magnetic recording medium substrate made of the above glass and a magnetic recording medium including the substrate can also be provided. According to yet another aspect, a glass spacer for a magnetic recording device made of the above glass can be provided. According to yet another aspect, a magnetic recording / reproducing device can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Glass] Hereinafter, glass A and glass B will be collectively referred to simply as "glass." Furthermore, in the following description, unless otherwise specified, the description of glass A can also be applied to glass B, and the description of glass B can also be applied to glass A. Glass A and glass B are glasses for magnetic recording medium substrates or glass spacers for magnetic recording / reproducing devices, and are amorphous glasses. Unlike crystallized glass, amorphous glass is glass that does not substantially contain a crystalline phase and exhibits a glass transition phenomenon upon heating. On the other hand, the manufacturing process of crystallized glass is complicated. Furthermore, it is not easy to achieve the high smoothness required for magnetic recording medium substrates using crystallized glass. Glass A and Glass B can also be amorphous oxide glasses, which are glasses in which the main network-forming component of the glass is an oxide. The above glass will be described in more detail below.

[0009] In the present invention and this specification, the glass composition is expressed as a glass composition based on oxides. Here, "glass composition based on oxides" refers to a glass composition obtained by converting the glass raw materials into oxides that are present in the glass after they are all decomposed during melting. Furthermore, unless otherwise specified, the glass composition is expressed on a molar basis (mol %, molar ratio). The glass composition of the present invention and the present specification can be determined by a method 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%. In the present invention and this specification, the content of a component is 0%, 0.0%, 0.00%, or not contained or not incorporated means that the component is substantially not contained, and the content of the component is at or below the impurity level. At or below the impurity level means, for example, less than 0.01%.

[0010] <Glass composition> From the viewpoint of improving chemical durability and rigidity, the B2O3 content of the glass is 2.00% or less, preferably 1.80% or less, with 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 being more preferred in this order. Glass with high chemical durability is preferred because it has high acid and / or alkali resistance, making it less likely to cause surface roughening during polishing, cleaning, etc., and therefore easier to achieve low glass surface roughness. The ability to easily achieve low roughness through polishing is hereinafter referred to as low-roughness polishing performance. From the viewpoint of improving impact resistance, meltability, and thermal stability, the B2O3 content of the glass is 0.10% or more, preferably 0.20% or more. Glass with high impact resistance is preferred because it is less likely to crack and / or chip during processing such as cutting and grinding. Glass with high thermal stability is also preferred because it is less likely to devitrify.

[0011] In one form, the glass can include one or both of SiO2 and Al2O3.

[0012] From the viewpoint of improving chemical durability, the SiO content of the glass 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, the SiO 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.

[0013] From the viewpoint of improving thermal stability, the Al2O3 content of the above glass 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. Furthermore, from the viewpoint of maintaining the temperature required for melting the glass within an appropriate range, the Al2O3 content within the above range is also preferred. On the other hand, from the viewpoint of further improving rigidity, the Al2O3 content is preferably 10.00% or more, and more preferably 11.00% or more, 12.00% or more, and 13.00% or more in that order.

[0014] In the above-mentioned glass, the total content of SiO2, B2O3, and Al2O3 (SiO2+B2O3+Al2O3) 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, from the viewpoint of enhancing the thermal stability of the glass. From the viewpoint of further improving the meltability, the total content of SiO2, B2O3, and Al2O3 (SiO2 + B2O3 + Al2O3) in the above glass is preferably 85.00% or less, and is 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.

[0015] From the viewpoint of enhancing the thermal stability of the glass, the total content of SiO2 and B2O3 (SiO2 + B2O3) 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. From the viewpoint of further improving rigidity, the total content of SiO2 and B2O3 (SiO2 + B2O3) in the above glass 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.

[0016] In the above-mentioned glass, from the viewpoint of chemical durability such as acid resistance and alkali resistance, the total content of SiO2 and Al2O3 (SiO2 + Al2O3) is preferably 70.00% or more, and more preferably in the following order: 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. Furthermore, from the viewpoint of the meltability of the glass, the total content of SiO2 and Al2O3 (SiO2 + Al2O3) of the above glass is preferably 85.00% or less, and is 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.

[0017] The glass contains Na2O as an essential component. Na2O is a component that has various functions, such as increasing the specific elastic modulus of the glass, improving meltability, increasing the thermal expansion coefficient, and reducing the viscosity of the glass during fining to promote bubble removal. Furthermore, among alkali metal oxides, the inclusion of Na2O in the glass can contribute to increasing the glass transition temperature compared to the addition of the same amount of Li2O. The Na2O content of the glass is 1.00% or more, preferably 1.50% or more, with 2.00% or more, 2.50% or more, and 3.00% or more being more preferred in that order. Furthermore, from the viewpoint of increasing the glass transition temperature, the Na2O content of the glass is 6.00% or less, preferably 5.50% or less, with 5.00% or less, 4.50% or less, and 4.00% or less being more preferred in that order.

[0018] From the viewpoint of improving the water resistance of the glass, the molar ratio of the SiO content to the NaO content (SiO / NaO) in the above glass 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, for example, 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 / NaO) is preferably 50.0 or less, more preferably 40.0 or less, and even more preferably 30.0 or less.

[0019] The glass may also contain alkali metal oxides other than Na2O. Li2O is a component that functions similarly to Na2O, but as described above, it is more likely to lower the glass transition temperature compared to adding the same amount of Na2O. The Li2O content of the glass can 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. The Li2O content of the glass can be 0%, 0% or more, or more than 0%, more than 0.10%, 0.20% or more, 0.30% or more, or 0.40% or more. The Li2O content of the glass can be more than 0.10% and less than 2.00%, 0.20% or more and 1.5% or less, or 0.30% or more and 1.3% or less. In one embodiment, the glass can be Li2O-free.

[0020] K2O is a component that functions similarly to Na2O, but because it has a larger specific gravity than Na2O, it is easier to lower the specific elastic modulus compared to adding the same amount of Na2O. The K2O content of the glass can 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. The K2O content of the glass can be 0%, 0% or more, or more than 0%. In one embodiment, the glass can be a glass that does not contain K2O. In another embodiment, the glass can be a glass that contains K2O, for example, a glass that contains 0.10% or more of K2O.

[0021] From the viewpoint of increasing the glass transition temperature and specific modulus, the molar ratio of the NaO content to the total content of LiO, NaO, and KO in the above glass (NaO / (LiO+NaO+KO)) 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. The molar ratio (NaO / (LiO+NaO+KO)) of the above glass can be 1.000, or can be 1.000 or less or less than 1.000. In one embodiment, the glass can be glass that does not contain LiO or KO. Furthermore, from the viewpoint of improving the water resistance and reducing the roughness of the glass, the molar ratio (NaO / (LiO+NaO+KO)) is preferably less than 1.000, and more preferably 0.950 or less, and more preferably 0.900 or less.

[0022] From the viewpoint of improving the water resistance of the glass, the molar ratio of the LiO content to the total content of LiO, NaO, and KO in the above glass (LiO / (LiO+NaO+KO)) is preferably 0.050 or more, and more preferably 0.100 or more. On the other hand, from the viewpoint of suppressing a decrease in the glass transition temperature, the molar ratio (LiO / (LiO+NaO+KO)) is preferably 0.600 or less, and more preferably 0.500 or less, 0.400 or less, and 0.300 or less, in that order.

[0023] The CaO content of the glass 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 can 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 the glass can be 0%, 0% or more, or more than 0%. In one embodiment, the glass preferably does not contain CaO.

[0024] Regarding alkaline earth metal oxides, the CaO content of the glass is as described above. In one embodiment, the glass may contain one or more alkaline earth metal oxides. Specific examples of alkaline earth metal oxides that may be contained in the glass include MgO, SrO, and BaO. Glass A contains MgO. From the viewpoint of improving rigidity, the MgO content of Glass 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 A 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. Glass B may contain MgO. For the MgO content of glass B, see the description of the MgO content of glass A.

[0025] In glass 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 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. For the total content of MgO, SrO, CaO, and BaO (MgO+SrO+CaO+BaO) in glass A, reference can be made to the description of the total content of MgO, SrO, CaO, and BaO (MgO+SrO+CaO+BaO) in glass B.

[0026] From the viewpoint of lowering the specific gravity and reducing raw material costs, the SrO content of the glass is preferably 4.00% or less, and 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 the glass can be 0%, or can be 0% or more or exceed 0%.

[0027] From the viewpoints of reducing the specific gravity of the glass, improving Young's modulus, and improving the specific elastic modulus, the BaO content of the glass 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 the glass can be 0%, or can be 0% or more or exceed 0%.

[0028] 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, the inventors' studies have shown that the glass 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 glass, 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.

[0029] From the viewpoints of reducing melt viscosity, lowering liquidus temperature, and improving glass roughness reduction polishing performance, the molar ratio of NaO content to MgO content (NaO / MgO) is preferably greater than 0.080. A low melt viscosity of glass is preferable from the viewpoint of moldability using various molding methods. Glass with a low liquidus temperature is preferred because it has high thermal stability. In addition, a molar ratio (NaO / MgO) of greater than 0.080 can contribute to reducing the resistivity of the molten glass. When electrical heating is performed during glass melting, 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 viewpoints, the molar ratio (NaO / MgO) is more preferably 0.090 or greater, and further preferably 0.100 or greater, 0.110 or greater, 0.120 or greater, 0.130 or greater, 0.140 or greater, 0.150 or greater, and 0.160 or greater in this order. On the other hand, from the viewpoint of increasing the glass transition temperature and specific modulus, the molar ratio (Na2O / 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.

[0030] Regarding TiO2, from the viewpoint of reducing the specific gravity and improving devitrification resistance, the TiO2 content of the glass 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. The TiO2 content of the glass can be 0%, or can be 0% or more or exceed 0%.

[0031] Regarding ZnO, from the viewpoints of reducing the specific gravity, improving 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 the above glass can be 0%, or can be 0% or more or exceed 0%.

[0032] The Fe2O3 content of the glass, 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. The Fe2O3 content is expressed as an exclusive percentage. That is, when the total content of components other than Fe2O3 contained in the glass (the total content of the glass components and additives when additives are included in addition to the glass components) is taken as 100%, the Fe2O3 content is expressed as a molar percentage of the Fe2O3 content relative to 100%. In one embodiment, the glass can be free of Fe (the Fe2O3 content expressed as an exclusive percentage is 0 mol%).

[0033] The above glass 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 enhance the thermal stability of the glass. In one embodiment, the content of one or more metal oxides 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 multiple metals are included) 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, the YO 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.

[0034] F is a component that easily volatilizes during melting and is also a component that causes striae, so the above glass preferably 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 the specific elastic modulus.

[0035] Since Pb, Cd and As are substances that have a negative impact on the environment, it is preferable to avoid introducing them.

[0036] From the viewpoint of obtaining a fining effect, the glass may contain one or more selected from the group consisting of SnO2, CeO2, and Sb2O3. In one embodiment, the total content of SnO2 and CeO2 may be 0%. In another embodiment, the glass may contain SnO2 and / or CeO2, and the total content of SnO2 and CeO2 (SnO2 + CeO2) is preferably 0.05 to 2%. When the total content of SnO2 and CeO2 is 0.05% or more, a sufficient fining effect can be obtained and residual bubbles can be reduced. Furthermore, when the total content (SnO2 + CeO2) is 2% or less, it is possible to prevent the molten glass from blowing up during glass melting, which can reduce productivity. The lower limit of the total content (SnO2 + CeO2) is preferably 0.10% or more, more preferably 0.20% or more, even more preferably 0.25% or more, still more preferably 0.30% or more, even more preferably 0.35% or more, and even more preferably 0.40% or more. The upper limit of the total content (SnO2 + CeO2) is preferably 1.5% or less, more preferably 1.2% or less, even more preferably 1.0% or less, even more preferably 0.70% or less, even more preferably 0.65% or less, even more preferably 0.60% or less, even more preferably 0.55% or less, and even more preferably 0.50% or less.

[0037] SnO2 promotes fining when the glass melting temperature is relatively high (approximately 1400 to 1600°C). With the use of environmentally harmful fining agents such as Sb2O3 and arsenous acid being restricted, in one embodiment, it is preferable to incorporate SnO2 into the glass to remove bubbles in glasses with high melting temperatures. From the viewpoint of obtaining a fining effect, the SnO2 content 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. Furthermore, the SnO2 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.

[0038] CeO2, like SnO2, is a component that exhibits a fining effect on glass. CeO2 functions to capture oxygen and fix it as a glass component when the glass melting temperature is relatively low (a temperature range of approximately 1200 to 1400°C). Therefore, in one embodiment, it is preferable to incorporate CeO2 into the above-mentioned glass as a fining agent. From the viewpoint of obtaining a fining effect, the content of CeO2 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. Furthermore, the content of CeO2 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, even more preferably 0.5% or less, and even more preferably 0.3% or less. The coexistence of SnO2 and CeO2 can obtain a fining effect over a wide temperature range. Therefore, in one embodiment, the above-mentioned glass preferably contains both SnO2 and CeO2.

[0039] From the viewpoint of reducing the environmental impact, it is desirable to refrain from using Sb2O3. The content of Sb2O3 in the above glass is preferably in the range of 0 to 0.5%. The content of Sb2O3 is more preferably 0.3% or less, even more preferably 0.1% or less, even more preferably 0.05% or less, and even more preferably 0.02% or less, and it is particularly preferable that no Sb2O3 is contained.

[0040] The above-mentioned glasses 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, for example, at a temperature in the range of 1400 to 1600°C, refining, stirring, and molding the homogenized glass melt that has been thoroughly defoamed. For example, it is preferable to heat and melt the glass raw materials in a melting vessel at 1400 to 1550°C, and then heat and hold the resulting glass melt in a refining vessel at 1450 to 1600°C, and then cool it to 1200 to 1400°C, at which point the glass is poured out and molded.

[0041] According to another aspect of the present invention, B2O3 content is 0.1 mol% or more and 2.0 mol% or less, The Na2O content is 1.0 mol% or more and 6.0 mol% or less, and CaO content is 0 mol% or more and 1.0 mol% or less, and a glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device, which is an amorphous glass and further satisfies any one or more of the following (1) to (10): can be provided.

[0042] (1) The molar ratio (Na2O / (Li2O+Na2O+K2O)) is 0.950 or more, and the total content (SiO2+B2O3+Al2O3) is 70.00% or more.

[0043] (2) Does not contain Li2O and K2O, and the total content (SiO2 + B2O3 + Al2O3) is 70.00% or more.

[0044] (3) The molar ratio (Na2O / (Li2O+Na2O+K2O)) is 0.950 or more, and the total content (SiO2+B2O3) is 58.00% or more.

[0045] (4) Does not contain Li2O and K2O, and the total content (SiO2 + B2O3) is 58.00% or more.

[0046] (5) The molar ratio (Na2O / (Li2O+Na2O+K2O)) is 0.950 or more, and the total content (SiO2+Al2O3) is 70.00% or more.

[0047] (6) Does not contain Li2O and K2O, and the total content (SiO2 + Al2O3) is 70.00% or more.

[0048] (7) The molar ratio (Na2O / (Li2O+Na2O+K2O)) is 0.950 or more, and the TiO2 content is 4.00 mol% or less.

[0049] (8) Contains no Li2O and no K2O, and has a TiO2 content of 4.00 mol% or less.

[0050] (9) The molar ratio (Na2O / (Li2O+Na2O+K2O)) is 0.950 or more, and the ZnO content is 10.00% or less.

[0051] (10) Contains no Li2O and no K2O, and has a ZnO content of 10.00% or less.

[0052] For each of the above glasses, reference can be made to the above description regarding the compositions of Glass A and Glass B and the below description regarding the physical properties of Glass A and Glass B.

[0053] According to another aspect of the present invention, B2O3 content is 0.10 mol% or more and 2.00 mol% or less, a total content of Na2O and K2O of 1.00 mol% or more and 6.00 mol% or less; CaO content is 0 mol% or more and 1.00 mol% or less, MgO content is 14.00 mol% or more, a glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device (hereinafter referred to as "glass a"), which is an amorphous glass of the above formula: B2O3 content is 0.10 mol% or more and 2.00 mol% or less, a total content of Na2O and K2O of 1.00 mol% or more and 6.00 mol% or less; CaO content is 0 mol% or more and 1.00 mol% or less, The total content of MgO, SrO, CaO and BaO (MgO + SrO + CaO + BaO) is 14.00 mol% or more, a glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device (hereinafter referred to as "glass b"), which is an amorphous glass of the above formula: can be provided.

[0054] For glass a and glass b, reference can be made to the above description regarding the compositions of glass A and glass B and the below description regarding the physical properties of glass A and glass B.

[0055] <Glass properties> By adjusting the composition as described above, the above glass can have the various glass properties described below.

[0056] (specific elastic modulus) The glass can have high rigidity due to the composition described above. The specific modulus can be used as an index of the rigidity of glass. The specific modulus is calculated by dividing the Young's modulus of the glass by its density. Here, density refers to the specific gravity of the glass multiplied by the density in g / cm. 3The specific elastic modulus of the glass is preferably 35.0 MNm / kg or more, 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 that 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 the glass may be 37.0 MNm / kg or less, taking into account the balance with the glass transition temperature.

[0057] (Young's modulus E) Young's modulus can also be used as an index of the rigidity of glass. The Young's modulus of the glass 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, and 93.0 GPa or more in this order. The Young's modulus of the glass can be, for example, 120.0 GPa or less, 110.0 GPa or less, 100 GPa or less, or 95.0 GPa or less, but since a higher Young's modulus is preferable as it increases rigidity, it is not limited to the above-mentioned values. Note that the Young's modulus of the glass 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.

[0058] (specific gravity d) By reducing the specific gravity of the glass for magnetic recording medium substrates, it is possible to reduce the weight of the magnetic recording medium substrate, and further reduce the weight of the magnetic recording medium, thereby enabling the reduction of power consumption of HDDs. The specific gravity of the glass 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 can be, for example, 2.40 or more, but is not limited to the above-mentioned exemplary values, as the lower the specific gravity, the better.

[0059] (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 substrate's flatness from decreasing due to exposure to high temperatures. In this regard, the above-mentioned glass 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 the above glass 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 the above glass 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, as a higher Tg is more preferable from the viewpoint of heat resistance.

[0060] (thermal stability) The above glass 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.

[0061] (Liquidus temperature LT) An index of the thermal stability of glass can be the liquidus temperature (LT). The LT of the above glass 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.

[0062] (coefficient of thermal expansion) HDDs incorporating magnetic recording media are typically designed to rotate the magnetic recording medium itself by holding its center 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 medium substrate and the spindle material that makes up the spindle, a mismatch will occur between the thermal expansion and contraction of the spindle and the magnetic recording medium substrate in response to ambient temperature changes during use, resulting in deformation of the magnetic recording medium. 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 used for the magnetic recording medium 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 100–300°C. -7 / °C or more, and the average linear expansion coefficient (thermal expansion coefficient) of the glass for magnetic recording medium substrates 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 35.0 × 10 -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.

[0063] The various physical properties described above can be determined by the methods described below in the examples.

[0064] [Magnetic recording medium substrate] A magnetic recording medium substrate according to one aspect of the present invention is made of the above-mentioned glass.

[0065] 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.

[0066] 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.

[0067] 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 or on which the magnetic recording layer 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.

[0068] 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; see, for example, paragraphs 0068-0069 of WO2011 / 019010A1.

[0069] 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. 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. The magnetic recording medium substrate is preferably in the shape of a disk with a center hole.

[0070] 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.

[0071] The magnetic recording medium substrate is made of the glass according to one aspect of the present invention, and therefore can have the glass properties described above for the glass.

[0072] [Magnetic recording media] One aspect of the present invention relates to a magnetic recording medium having the above magnetic recording medium substrate and a magnetic recording layer.

[0073] 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.

[0074] A magnetic recording medium is configured, for example, by stacking at least an adhesive layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer on the main surface of a magnetic recording medium substrate, in that order from the side closest to the main surface. For example, a magnetic recording medium substrate is placed in a vacuum-evacuated film-forming apparatus, and films from an adhesive layer to a 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. The adhesive layer can be made of, for example, CrTi, and the underlayer can be made of, for example, a material containing Ru or MgO. A soft magnetic layer and a heat sink layer may also be added as appropriate. After the above film formation, a protective layer can be formed using, for example, C2H4 by a CVD (Chemical Vapor Deposition) method, and a nitriding process to introduce nitrogen into the surface can be performed in the same chamber to form the magnetic recording medium. A lubricating layer can then be formed by applying, for example, PFPE (polyfluoropolyether) to the protective layer by a dip coating method.

[0075] 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 WO2011 / 019010A1 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 thermally assisted recording, and a recording method that assisted magnetization reversal by microwaves is called microwave-assisted recording. For details, see paragraph 0075 of WO2011 / 019010A1. As the magnetic material for forming the magnetic recording layer, a conventional CoPtCr-based material may be used.

[0076] Recently, 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 can be significantly narrowed (reduced flying height), thereby achieving even higher recording densities. The DFH mechanism is a function in which a heating element such as a tiny heater is provided near the read / write element of the magnetic head, causing only the periphery of the element to protrude 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.

[0077] There are no particular limitations on the dimensions of the magnetic recording medium substrate (e.g., glass substrate for magnetic disk) or the magnetic recording medium (e.g., magnetic disk). For example, since high recording density is possible, it is possible to miniaturize the medium and substrate. It is also possible to enlarge the medium and substrate in order to increase the recording capacity per magnetic recording medium. For example, the nominal diameter can be 2.5 inches, of course, but they can also be made smaller (e.g., 1 inch, 1.8 inches), or 3 inches, 3.5 inches, or even larger.

[0078] [Glass spacer for magnetic recording / reproducing devices] A glass spacer for a magnetic recording / reproducing device according to one aspect of the present invention (hereinafter also simply referred to as a "glass spacer") is made of the above glass.

[0079] 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 used 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.

[0080] The spacer for a magnetic recording / reproducing device is a ring-shaped member, and details such as the configuration and manufacturing method of the glass spacer are publicly known. For the manufacturing method of the glass spacer, reference can be made to 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. For other details such as the glass composition and physical properties of the glass spacer, reference can be made to 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. The spacer for the magnetic recording / reproducing device may be made of the glass spacer described above, or may have one or more films, such as a conductive film, formed 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, may be formed on the surface of the glass spacer by plating, immersion, vapor deposition, sputtering, or other methods. Furthermore, the glass spacer can be polished to enhance its surface smoothness (for example, to 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.

[0081] [Magnetic recording and playback device] One aspect of the present invention relates to a magnetic recording and reproducing device including one or more members selected from the group consisting of the magnetic recording medium and the glass spacer.

[0082] 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 an embodiment of the present invention may include a magnetic recording medium according to an embodiment of the present invention as at least one magnetic recording medium, or may include multiple magnetic recording media according to an embodiment of the present invention. The magnetic recording and reproducing device according to an embodiment of the present invention may include a glass spacer according to an embodiment of the present invention as at least one spacer, or may include multiple glass spacers according to an embodiment of the present invention. A small difference between the thermal expansion coefficient of the magnetic recording medium and the thermal expansion coefficient of the spacer is preferable from the viewpoint of suppressing the occurrence of phenomena that may arise due to the difference in 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 an embodiment of the present invention preferably includes a magnetic recording medium according to an embodiment 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 an embodiment of the present invention as at least one spacer, or as more spacers if multiple spacers are included. Furthermore, for example, in the magnetic recording and reproducing device according to an embodiment 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 may have the same glass composition.

[0083] A magnetic recording / reproducing device according to one embodiment of the present invention may include at least one of a magnetic recording medium according to one embodiment of the present invention and a glass spacer according to one embodiment of the present invention; otherwise, known techniques related to magnetic recording / reproducing devices can be applied. In one embodiment, the magnetic head may 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 embodiment of the present invention may be a magnetic recording medium substrate with high heat resistance capable of withstanding 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. [Example]

[0084] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the embodiments shown in the examples.

[0085] [Examples 1 to 19] 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 Table 1. This raw material blend was charged into a melting vessel and heated and melted in the range of 1400 to 1600°C. The resulting glass melt was then held in a refining vessel at 1400 to 1550°C for 6 hours, after which the temperature was lowered (cooled down) and held in the range of 1200 to 1400°C for 1 hour, after which the glass melt was formed to obtain glasses (amorphous oxide glasses) for the following evaluations.

[0086] <Evaluation of glass properties> (1) Glass transition temperature Tg, 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).

[0087] (2) Young's modulus E The Young's modulus of each glass was measured by an ultrasonic method.

[0088] (3) Specific gravity d The specific gravity of each glass was measured by Archimedes' method.

[0089] (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).

[0090] (5) 1300℃ 16h retention test 100 g of each glass was placed in a platinum crucible, which was then placed in a heating furnace with the furnace temperature set to 1300°C, and left for 16 hours (holding test) while maintaining the furnace temperature. After 16 hours, 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 under an optical microscope (magnification 40 to 100 times) 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: Less than 10 crystals with a diameter of several tens of μm on the glass surface and at the interface with the bottom of the platinum crucible per 100 g C: More than 10 crystals with a diameter of several tens of micrometers on the glass surface and at the interface with the bottom of the platinum crucible / 100g D: Crystals present inside the glass E: Crystals are present on the glass surface, inside, and at the interface with the platinum crucible bottom. F: The glass is cloudy with many crystals G: The glass is cloudy

[0091] (6) 1320℃ 16h retention test Except for the fact that the temperature inside the furnace was set to 1320°C, the retention test and the evaluation of the glass after the retention test were carried out in accordance with the method described in (5) above.

[0092] (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. After the glass in the crucible was completely molten, the internal atmosphere temperature was lowered to a predetermined temperature and maintained at that temperature for 16 hours. After maintaining the temperature for 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). After cooling, the glass was visually inspected for the presence or absence of crystal precipitation. The above operation was carried out 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.

[0093] (8) Roughness evaluation Using the method described below, magnetic disk glass substrates having the respective glass compositions shown in the table below were fabricated. Here, basic processing conditions such as polishing conditions and cleaning conditions were the same. The arithmetic mean roughness Ra (JIS B0601:2001) of the main surfaces of the magnetic disk glass substrates 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 4 is set to 1.00. The degree of roughness was ranked according to the following criteria. Note that even rank C does not pose a practical problem. Rank A: Less than 0.80 Rank B: 0.80 or more and less than 0.90 Rank C: 0.90 or higher and 1.00 or lower

[0094] The results are shown in the table below.

[0095] [Table 1]

[0096] [Table 2]

[0097] [Table 3]

[0098] [Table 4]

[0099] [Table 5]

[0100] <Preparation of magnetic recording medium substrate> (1) Preparation of substrate blank A disk-shaped substrate blank was prepared by the following method A or B. Also, a glass blank for preparing a glass spacer for a magnetic recording / reproducing device can be obtained by the same method. (Method A) For glass having the composition shown in Table 1, a clarified 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 flowing glass melt was cut with a cutting blade so that a predetermined amount of glass melt gob was obtained on the lower die. The lower die with the glass melt gob placed on it was then immediately removed from the bottom of the pipe, and using an upper die and a barrel die opposing the lower die, the glass melt was press-molded into a thin disk with a diameter of 99 mm and a thickness of 0.7 mm. 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-mentioned molding, multiple lower dies were used to successively form the flowing glass melt into disk-shaped substrate blanks. (Method B) For glass of the composition shown in Table 1, a refined and homogenized molten glass was continuously poured from above into a cylindrical through-hole of a heat-resistant mold, formed into a cylindrical shape, and removed from the bottom of the hole. After annealing the removed glass, the glass was 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). Although the present example employs the above-described methods A and B, the following methods C and D are also suitable for manufacturing a disk-shaped substrate blank. Furthermore, the following methods C and D are also suitable for manufacturing a glass blank for producing a glass spacer for a magnetic recording / reproducing device. (Method C) Molten glass can be poured onto a float bath and formed into a sheet of glass (forming by the float method), and then annealed, after which a disk of glass can be cut from the sheet of 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).

[0101] (2) Preparation of glass substrate 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 (to simultaneously form chamfered surfaces), the edges were polished, and the main surfaces of the disk were lapped and polished (mirror polished) to produce a glass substrate for a magnetic disk with an outer diameter of 97 mm, an inner circular hole diameter of 25 mm, and a thickness of 0.5 mm. Furthermore, by using a similar method, a glass blank for producing a glass spacer for a magnetic recording / reproducing device can be finished into a glass spacer for a magnetic recording / reproducing device. 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 made 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).

[0102] <Magnetic recording medium (magnetic disk) production> 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 magnetic disk glass substrate prepared above by the following method, to obtain a magnetic disk.

[0103] 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.

[0104] The adhesive layer was formed using a CrTi target to be 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 be a 10 nm thick FePt or CoPt granular layer.

[0105] 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.10 The magnetic recording layer may be heated to generate an ordered structure. For example, the temperature of the substrate during the deposition of the FePt or CoPt magnetic recording layer may be set to 500 to 700°C. 10 An ordered structure may be formed.

[0106] Next, a protective layer made of hydrogenated carbon was formed to a thickness of 3 nm 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 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.

[0107] Furthermore, a glass spacer obtained by the above manufacturing process using glass of the composition shown in Table 1 and having a NiP alloy conductive film formed on its surface (glass spacer with NiP alloy film) was installed 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.

[0108] 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.

[0109] According to one aspect of the present invention, it is possible to provide a magnetic recording medium suitable for high-density recording.

[0110] 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 a glass for a magnetic recording medium substrate and a glass spacer for a magnetic recording / reproducing device according to one embodiment 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. B ２ O ３ The content is 0.10 mol% or more and 2.00 mol% or less, Na ２ 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; MgO content is 14.00 mol% or more, The glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device is an amorphous glass of the above formula.

2. B ２ O ３ The content is 0.10 mol% or more and 2.00 mol% or less, Na ２ 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; the total content of MgO, SrO, CaO and BaO (MgO + SrO + CaO + BaO) is 14.00 mol% or more; The glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device is an amorphous glass of the above formula.

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 3. The glass of claim 1, wherein .DELTA.O) is 0.350 or greater.

4. Li ２ The glass according to any one of claims 1 to 3, which contains O.

5. 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 5. The glass according to claim 1, wherein .DELTA.O) is 0.600 or less.

6. Na ２ SiO relative to O content ２ Molar ratio of content (SiO ２ / Na ２ 6. The glass according to claim 1, wherein the value of .O) is 50.0 or less.

7. Na content relative to MgO content ２ Molar ratio of O content (Na ２ 7. The glass of claim 1, wherein the SiO2 / MgO ratio is greater than 0.

080.

8. The glass according to any one of claims 1 to 7, having a specific elastic modulus of at least 35.0 MNm / kg.

9. The glass according to any one of claims 1 to 8, which has a glass transition temperature of 700°C or higher.

10. A magnetic recording medium substrate made of the glass according to any one of claims 1 to 9.

11. A magnetic recording medium comprising the magnetic recording medium substrate according to claim 10 and a magnetic recording layer.

12. A glass spacer for a magnetic recording / reproducing device, comprising the glass according to any one of claims 1 to 9.

13. The magnetic recording medium according to claim 10, and The glass spacer for a magnetic recording / reproducing device according to claim 12 . A magnetic recording and reproducing device including one or more selected from the group consisting of:

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