Glass for magnetic recording medium substrate, magnetic recording medium substrate, magnetic recording medium, glass spacer for magnetic recording / reproducing device, and magnetic recording / reproducing device

Abstract

To provide a glass for a magnetic recording medium substrate, a magnetic recording medium substrate, a magnetic recording medium, a glass spacer for a magnetic recording / reproducing device, and a magnetic recording / reproducing device, each of which has excellent chemical resistance and impact resistance.SOLUTION: A glass for a magnetic recording medium substrate is an amorphous glass with a SiO2 content of 54 mol% or more and 62 mol% or less, a MgO content of 15 mol% or more and 28 mol% or less, a Li2O content of 0.2 mol% or more, and a Na2O content of 5 mol% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a glass for a magnetic recording medium substrate, 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]

[0002] 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). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-814134 Summary of the Invention [Problem to be solved by the invention]

[0004] Magnetic recording medium substrates are usually cleaned with acids, alkalis, etc. to remove foreign matter that has adhered to the substrate surface during the manufacturing process. However, if the glass constituting the substrate does not have sufficient chemical resistance, the cleaning process will cause the surface to become rough, even if the substrate surface is finished to be smooth during the manufacturing process. Therefore, glass for magnetic recording medium substrates is desired to have excellent chemical resistance.

[0005] Furthermore, glass for magnetic recording medium substrates is also desired to have excellent impact resistance 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 layers of the magnetic recording media, which are rotating at high speed inside the HDD. If the HDD is subjected to a large impact (e.g., an impact from a drop) while the magnetic recording media is rotating at high speed for such data writing and reading, the impact can temporarily deform the magnetic recording media inside the HDD, causing it to collide with a component called a ramp while rotating at high speed, potentially resulting in damage to the magnetic recording media. To prevent such damage, it is desirable for the magnetic recording media to be resistant to deformation even when subjected to impact, i.e., have excellent impact resistance. For HDDs, reducing the thickness of each magnetic recording media disk and installing more magnetic recording media on the HDD can increase the recording capacity, but thinner glass generally tends to deform more easily, making the above-mentioned damage more likely to occur. Therefore, in order to achieve both an increase in the recording capacity of HDDs and the prevention of the above-mentioned damage, a glass for a magnetic recording medium substrate that has excellent impact resistance is desirable.

[0006] Regarding the above points, Patent Document 1 (JP 2002-814134 A) describes that the glass described therein can be cleaned by washing the glass surface with an acidic solution without deteriorating the surface (paragraph 0068 of Patent Document 1, etc.). However, according to the inventors' investigations, the impact resistance of the glass described in Patent Document 1 is not sufficient from the viewpoint of preventing breakage as described above. On the other hand, crystallized glass is known as a material with high impact resistance, but the manufacturing process for crystallized glass is complicated. Furthermore, it is not easy to achieve the high smoothness required for magnetic recording medium substrates using crystallized glass.

[0007] An object of one aspect of the present invention is to provide a glass for a magnetic recording medium substrate that is excellent in chemical resistance and impact resistance. [Means for solving the problem]

[0008] One aspect of the present invention relates to a glass for magnetic recording medium substrates (hereinafter also simply referred to as "glass"), which is amorphous glass having an SiO content of 54 mol % or more and 62 mol % or less, an MgO content of 15 mol % or more and 28 mol % or less, a LiO content of 0.2 mol % or more, and a NaO content of 5 mol % or less.

[0009] The glass for a magnetic recording medium substrate has the above glass composition and can have excellent chemical resistance and excellent impact resistance. [Effects of the Invention]

[0010] According to one aspect of the present invention, a glass for a magnetic recording medium substrate having excellent chemical resistance and impact resistance can be provided. Also, according to another aspect, a magnetic recording medium substrate made of the glass for a magnetic recording medium substrate, and a magnetic recording medium including this substrate can be provided. Furthermore, according to another aspect, a glass spacer for a magnetic recording device can be provided. Still further, according to another aspect, a magnetic recording / reproducing device can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Glass for magnetic recording media substrates] The glass is an amorphous glass having the composition described above. Unlike crystallized glass, amorphous glass is glass that does not substantially contain a crystalline phase and exhibits a glass transition phenomenon upon heating. The glass may be an amorphous oxide glass, which is a glass in which the main network-forming component is an oxide. The above glass will be described in more detail below.

[0012] <Glass composition> 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 being 0%, not containing, or not incorporating a component means that the component is substantially not contained, and the content of the component is at or below the impurity level, for example, less than 0.01%.

[0013] In the glass composition of the above glass, the SiO2 content is 54 mol% or more and 62 mol% or less, the MgO content is 15 mol% or more and 28 mol% or less, the Li2O content is 0.2 mol% or more, and the Na2O content is 5 mol% or less. The glass composition of the above glass will be described in more detail below.

[0014] SiO2 is a glass network-forming component and has the function of improving glass stability. SiO2 is also a component that contributes to improving chemical resistance. The SiO2 content is 54% or more from the viewpoints of improving chemical resistance and impact resistance. Furthermore, in the manufacturing process of a magnetic recording medium substrate, the substrate surface is usually polished. From the viewpoint of improving the smoothness of the magnetic recording medium substrate surface after polishing, an SiO2 content of 54% or more is also preferable. From the above viewpoints, the SiO2 content is preferably 55% or more, more preferably 56% or more, even more preferably 57% or more, even more preferably 57.5% or more, even more preferably 58% or more, even more preferably 58.5% or more, even more preferably 59% or more, and even more preferably 60% or more. From the viewpoint of the meltability of the glass, the SiO2 content is preferably 62% or less, and preferably 61% or less.

[0015] MgO has the functions of increasing the Young's modulus of glass, increasing the thermal expansion coefficient, and improving the meltability and formability of glass. The MgO content is 15% or more from the viewpoint of improving impact resistance. A MgO content of 15% or more is also preferable from the viewpoint of improving Young's modulus and specific modulus. From the above viewpoints, the MgO content is preferably 16% or more, and more preferably 17% or more. Furthermore, from the viewpoint of improving devitrification resistance, the MgO content of the above glass is 28% or less, preferably 27% or less, more preferably 26% or less, even more preferably 25% or less, even more preferably 24.5% or less, even more preferably 24% or less, even more preferably 23.5% or less, even more preferably 23% or less, even more preferably 22.5% or less, even more preferably 22% or less, even more preferably 20% or less, and particularly preferably 19% or less.

[0016] Among alkali metal oxides, Li2O is a component that has a strong effect on improving the meltability of glass. Furthermore, when the glass is used for chemical strengthening, Li2O is also a component responsible for ion exchange during chemical strengthening. From the viewpoint of improving the meltability of the glass, the Li2O content is 0.2% or more, preferably 0.5% or more, more preferably 1% or more, even more preferably 2% or more, still more preferably 2.5% or more, even more preferably 3% or more, still more preferably 3.5% or more, and even more preferably 4% or more. Furthermore, from the viewpoint of further improving chemical resistance and impact resistance, and improving the smoothness of the magnetic recording medium substrate surface after polishing, the Li2O content is preferably 6% or less, more preferably 5% or less.

[0017] From the viewpoint of further improving impact resistance, the molar ratio of the total content of SiO and MgO to the content of LiO [(SiO + MgO) / LiO] is preferably 13 or more, more preferably more than 13, even more preferably 14 or more, and still more preferably 15 or more. Moreover, from the viewpoint of devitrification resistance and melting property, the molar ratio [(SiO + MgO) / LiO] is preferably 100 or less, more preferably 50 or less, even more preferably 30 or less, even more preferably 25 or less, and still more preferably 20 or less.

[0018] Na2O is a component that improves the meltability of glass, increases the thermal expansion coefficient, and reduces the viscosity of the glass during fining, promoting bubble removal. Furthermore, when the above glass is used as a glass for chemical strengthening, it is also a component responsible for ion exchange during chemical strengthening. The Na2O content is 5% or less from the viewpoint of improving impact resistance. A Na2O content of 5% or less is also preferable from the viewpoint of improving Young's modulus and specific modulus of elasticity. From the above viewpoints, the Na2O content is preferably 4% or less, more preferably 3% or less, even more preferably 2% or less, and even more preferably 1% or less. In one embodiment, the Na2O content can be 0%, 0% or more, or more than 0%, or 0.5% or more.

[0019] B2O3 is a component that forms a glass network, reduces the specific gravity of the glass, and improves meltability. From the viewpoint of further improving impact resistance, improving the specific modulus of elasticity, and improving Young's modulus, the B2O3 content is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. In one embodiment, the B2O3 content can be 0%, 0% or more, or more than 0%, or 0.5% or more.

[0020] Al2O3 is a glass network-forming component and has the function of improving heat resistance. From the viewpoint of improving the meltability of the glass, the Al2O3 content is preferably 19% or less, more preferably 18% or less, even more preferably 17% or less, even more preferably 16% or less, and even more preferably 15% or less. Furthermore, from the viewpoint of further improving impact resistance, Young's modulus, and specific elastic modulus, Al2O3 is preferably 9% or more, more preferably 10% or more, even more preferably 11% or more, and even more preferably 12% or more.

[0021] BaO improves the meltability, moldability, and glass stability of the glass, and increases the thermal expansion coefficient. From the viewpoint of reducing the specific gravity of the glass, improving Young's modulus, improving the specific elastic modulus, and further improving impact resistance, the BaO content is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. In one embodiment, the BaO content can be 0%, 0% or more, or more than 0%, or 0.5% or more.

[0022] CaO functions to increase the Young's modulus and specific elastic modulus of glass, to increase the thermal expansion coefficient, and to improve the meltability and formability of glass. In one embodiment, the CaO content can be 0%, or can be 0% or more or greater than 0%. In another embodiment, from the viewpoint of obtaining the above functions well, the CaO content is preferably 0.5% or more, more preferably 1% or more, and even more preferably 1.5% or more. Furthermore, from the viewpoint of further improving chemical resistance, the CaO content is preferably 10% or less, more preferably 9% or less, even more preferably 8% or less, even more preferably 7% or less, even more preferably 6% or less, even more preferably 5% or less, even more preferably 4% or less, and even more preferably 3% or less.

[0023] From the viewpoint of further improving impact resistance, the molar ratio of the MgO content to the CaO content (MgO / CaO) is preferably at least 6, more preferably at least 7, and even more preferably at least 8. From the viewpoint of devitrification resistance, the molar ratio (MgO / CaO) is preferably at most 30, more preferably at most 25, even more preferably at most 20, even more preferably at most 18, and even more preferably at most 15.

[0024] The molar ratio of the total content of Al2O3 and CaO to the MgO content [(Al2O3 + CaO) / MgO] is preferably 0.55 or more, and more preferably 0.57 or more, from the viewpoint of improving devitrification resistance and further improving chemical resistance. Furthermore, the lower limit increases in the order of 0.58 or more, 0.59 or more, 0.60 or more, 0.61 or more, 0.62 or more, 0.625 or more, 0.63 or more, 0.65 or more, 0.70 or more, 0.75 or more, and 0.80 or more. Furthermore, from the viewpoint of impact resistance, the molar ratio [(Al2O3 + CaO) / MgO] is preferably 1.8 or less, more preferably 1.5 or less, even more preferably 1.3 or less, even more preferably 1.2 or less, and even more preferably 1.1 or less.

[0025] From the viewpoint of increasing the glass transition temperature, the molar ratio of the CaO content to the Al2O3 content (CaO / Al2O3) is preferably 0.60 or less, more preferably 0.50 or less, even more preferably 0.40 or less, even more preferably 0.30 or less, even more preferably 0.24 or less, and still more preferably 0.20 or less. Moreover, the molar ratio (CaO / Al2O3) can be, for example, 0 or more, can exceed 0, or can be 0.10 or more.

[0026] The molar ratio of the CaO content to the total content of Al2O3 and MgO [CaO / (Al2O3 + MgO)] is preferably 0.30 or less, more preferably 0.20 or less, and even more preferably 0.10 or less, from the viewpoint of improving Young's modulus, improving specific elastic modulus, and further improving impact resistance. Moreover, the molar ratio can be, for example, 0 or more, can exceed 0, can be 0.01 or more, or can be 0.03 or more.

[0027] From the viewpoint of further improving impact resistance, the molar ratio of the MgO content to the LiO content (MgO / LiO) is preferably 2.3 or more, more preferably 2.5 or more, even more preferably 2.7 or more, and still more preferably 3.0 or more. From the viewpoint of improving the meltability of the glass, the molar ratio (MgO / LiO) is preferably 28 or less, more preferably 26 or less, even more preferably 24 or less, and still more preferably 22 or less.

[0028] From the viewpoint of improving Young's modulus, improving specific elastic modulus, and further improving impact resistance, the total content of Al2O3, MgO, and CaO (Al2O3 + MgO + CaO) is preferably 29% or more, more preferably 30% or more, even more preferably 31% or more, even more preferably 32% or more, and still more preferably 33% or more. Moreover, the total content (Al2O3 + MgO + CaO) can be, for example, 50% or less, 48% or less, 46% or less, 44% or less, 43% or less, 42% or less, or 41% or less.

[0029] The total content of SiO2, MgO, Li2O, Al2O3, and CaO (SiO2 + MgO + Li2O + Al2O3 + CaO) is preferably 93 mol% or more from the viewpoints of improving meltability and devitrification resistance. A total content of 93% or more is also preferable from the viewpoints of improving the smoothness of the magnetic recording medium substrate surface after polishing and improving the vibration and impact resistance of a magnetic recording medium equipped with the magnetic recording medium substrate. From these viewpoints, the total content (SiO2 + MgO + Li2O + Al2O3 + CaO) is more preferably 94% or more, even more preferably 95% or more, even more preferably 96% or more, even more preferably 97% or more, and even more preferably 98% or more. Furthermore, the total content (SiO2 + MgO + Li2O + Al2O3 + CaO) can be 100% or less, or can be 99% or less.

[0030] SrO improves the meltability, formability, and glass stability of the glass, and increases the thermal expansion coefficient. From the viewpoint of reducing the specific gravity and raw material costs, the SrO content is preferably 4% or less, more preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. In one embodiment, the SrO content can be 0%, 0% or more, or more than 0%, or 0.5% or more.

[0031] K2O is a component that functions to improve the meltability and formability of glass and also increases the thermal expansion coefficient. From the viewpoints of reducing the specific gravity, improving Young's modulus, improving the specific elastic modulus, and further improving impact resistance, the K2O content is preferably 2% or less, more preferably 1% or less, and even more preferably 0.5% or less. In one embodiment, the K2O content can be 0%, or can be 0% or more or greater than 0%.

[0032] TiO2 is a component that improves glass stability. From the viewpoint of reducing specific gravity and improving devitrification resistance, the TiO2 content is preferably 4% or less, more preferably 3% or less, even more preferably 2% or less, and even more preferably 1% or less. In one embodiment, the TiO2 content can be 0%, 0% or more, or more than 0%, or 0.5% or more.

[0033] ZnO has the function of improving meltability. From the viewpoint of reducing the specific gravity, improving Young's modulus, improving the specific elastic modulus, and further improving impact resistance, the ZnO content is preferably 2% or less, and more preferably 1% or less. In one embodiment, the ZnO content can be 0%, 0% or more, or more than 0%, or 0.5% or more.

[0034] From the viewpoint of reducing the specific gravity and improving devitrification resistance, the ZrO2 content is preferably 5% or less, more preferably 4% or less, even more preferably 3% or less, even more preferably less than 3%, even more preferably 2% or less, and even more preferably 1% or less. In one embodiment, the ZrO2 content can be 0%, 0% or more or more than 0%, or 0.5% or more.

[0035] From the viewpoint of reducing the specific gravity and improving devitrification resistance, the Y2O3 content is preferably 2% or less, more preferably 1.5% or less, and even more preferably 1% or less. In one embodiment, the Y2O3 content can be 0%, 0% or more, or more than 0%, or 0.5% or more.

[0036] 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. In one embodiment, the glass can be free of Fe (the Fe2O3 content expressed as an exclusive percentage is 0 mol%). The Fe2O3 content expressed as an exclusive percentage is the amount of Fe2O3 contained in the glass, expressed as a molar percentage, when the total content of the glass components other than Fe2O3 is 100 mol%.

[0037] The glass may also contain one or more elements selected from the group consisting of Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er.

[0038] 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.

[0039] Since Pb, Cd and As are substances that have a negative impact on the environment, it is preferable to avoid introducing them.

[0040] From the viewpoint of obtaining a fining effect, the above 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 above 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.

[0041] 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 glass with a high melting temperature. 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.

[0042] Like SnO2, CeO2 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 CeO2 content 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 CeO2 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, 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.

[0043] 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.

[0044] 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.

[0045] <Glass properties> By adjusting the composition as described above, the above glass can have the various glass properties described below.

[0046] (chemical resistance) An example of the chemical resistance of glass is the etching rate, which is the amount of etching per unit time (unit: nm / min) when glass is immersed for a predetermined time in a 0.5 mass % potassium hydroxide aqueous solution maintained at a liquid temperature of 50°C. The etching rate of the glass can be 0.5 nm / min or less. For the method of measuring the etching rate, see the description in the Examples below. The etching rate is preferably 0 nm / min or more and 0.5 nm / min or less.

[0047] (Young's modulus) The Young's modulus of the glass is preferably 90 GPa or more. Glass for magnetic recording medium substrates, which has a high rigidity and exhibits a Young's modulus of 90 GPa or more, can suppress substrate deformation during rotation of a spindle motor, thereby suppressing warpage and deflection of the magnetic recording medium due to substrate deformation. The Young's modulus of the glass is preferably 91 GPa or more, more preferably 92 GPa or more, even more preferably 93 GPa or more, even more preferably 94 GPa or more, and even more preferably 95 GPa or more. The upper limit of the Young's modulus is, for example, about 120 GPa, but is not particularly limited, as a higher Young's modulus is preferable as it increases rigidity.

[0048] (specific gravity) The specific gravity of the glass is preferably 2.75 or less. The specific gravity of the glass is more preferably 2.73 or less, even more preferably 2.70 or less, even more preferably 2.68 or less, even more preferably 2.64 or less, even more preferably 2.62 or less, and even more preferably 2.60 or less. Reducing the specific gravity of the glass for magnetic recording medium substrates enables the weight of the magnetic recording medium substrate to be reduced, and further reduces the weight of the magnetic recording medium, thereby enabling the power consumption of magnetic recording and reproducing devices (commonly called HDDs) to be reduced. The lower limit of the specific gravity is, for example, about 2.40, but is not particularly limited as the lower the specific gravity, the better.

[0049] (specific elastic modulus) The specific elastic modulus is the Young's modulus of the glass divided by its density, where density is the specific gravity of the glass multiplied by the ratio of g / cm 3 This can be thought of as a value with the unit "modulus of elasticity." From the viewpoint of providing a substrate that is less susceptible to deformation, the specific elastic modulus of the glass is preferably 30 MNm / kg or more, more preferably 32 MNm / kg or more, even more preferably 33 MNm / kg or more, even more preferably 34 MNm / kg or more, and even more preferably 35 MNm / kg or more. The upper limit of the specific elastic modulus is, for example, about 40 MNm / kg, but is not particularly limited as a higher specific elastic modulus is preferable.

[0050] (coefficient of thermal expansion) HDDs incorporating magnetic recording media are typically designed to rotate the magnetic recording medium itself by holding down the center 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 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 for the glass used for the magnetic recording medium substrate to have a moderate thermal expansion coefficient similar to that of the spindle material (e.g., stainless steel). Generally, HDD spindle materials have a thermal expansion coefficient of 70×10°C 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 40 × 10 -7 / °C or more, the difference in thermal expansion coefficient between the glass and the spindle material is small, which can contribute to improving the reliability of the magnetic recording medium. The average linear expansion coefficient (hereinafter also referred to as "α") of the glass at 100 to 300°C is 40×10 -7 / °C or more, and -7 / °C or more, and 42 × 10 -7 / °C or more, and more preferably 43 × 10 -7 / °C or more, and more preferably 44 × 10 -7 / °C or more, and more preferably 45 × 10 -7 / °C or more. The average linear expansion coefficient (α) of the glass at 100 to 300°C is 70×10 -7 / °C or less, and -7 / °C or less, and more preferably 65 × 10 -7 / °C or less, and more preferably 63 × 10 -7 / °C or less, and more preferably 60 × 10-7 / °C or less, and more preferably 57 × 10 -7 / °C or less, and even more preferably 55 x 10 -7 / °C or less, and more preferably 53 x 10 -7 / °C or less, and even more preferably 50 × 10 -7 It is even more preferred that the temperature is 1000 K / °C or less.

[0051] (glass transition temperature) Magnetic recording medium substrates are typically 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 in magnetic recording media, film formation is typically performed at high temperatures, or a heat treatment is performed at high temperatures after film formation. It is preferable for magnetic recording medium substrates to have heat resistance capable of withstanding such high-temperature treatment, since the substrate can maintain its flatness even when exposed to high temperatures during high-temperature treatment. The glass described above preferably has a glass transition temperature (hereinafter also referred to as "Tg"), an indicator of heat resistance, of 640°C or higher, more preferably 650°C or higher, even more preferably 660°C or higher, even more preferably 670°C or higher, even more preferably 675°C or higher, even more preferably 680°C or higher, even more preferably 685°C or higher, and even more preferably 687°C or higher. The upper limit of the glass transition temperature is, for example, about 770°C or 750°C, but is not particularly limited, as a higher glass transition temperature is preferable from the standpoint of heat resistance. However, the above glass is not limited to glass for a substrate of a magnetic recording medium having a magnetic recording layer containing a magnetic material that requires high-temperature treatment, and can be used to produce magnetic recording media containing various magnetic materials.

[0052] (glass stability) The above glass preferably exhibits high glass stability. Examples of a method for evaluating glass stability include a 16-hour holding test at 1350°C, 1300°C, or 1250°C, which will be described in detail below. In at least one of the 1350°C 16-hour holding test, 1300°C 16-hour holding test, and 1250°C 16-hour holding test, the evaluation result is preferably A or B, and more preferably A. It can be said that the better the result in the holding test at a lower holding temperature, the higher the glass stability.

[0053] [Magnetic recording medium substrate] A magnetic recording medium substrate according to one aspect of the present invention is made of the above-mentioned glass.

[0054] 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 any of the press molding, down-draw, and float processes, and then processing the resulting glass melt. For example, in the press molding process, 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. Next, a center hole is formed in the resulting substrate blank, and the inner and outer peripheries are processed, and both main surfaces are lapped and polished. Next, a cleaning process including acid washing and alkali washing is performed to obtain a disk-shaped substrate.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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, 0.3 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.

[0059] 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.

[0060] [Magnetic recording media] One aspect of the present invention relates to a magnetic recording medium having a magnetic recording layer on the above magnetic recording medium substrate.

[0061] Magnetic recording media are called magnetic disks, hard disks, etc., and are suitable for use as internal storage devices (such as fixed disks) in various magnetic recording and playback devices, such as desktop personal computers, server computers, notebook personal computers, and mobile personal computers, internal storage devices in portable recording and playback devices that record and play back images and / or audio, and recording and playback devices for in-car audio. 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.

[0062] A magnetic recording medium is configured, for example, by laminating 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 this 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.

[0063] 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 preferably has 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.

[0064] In recent years, magnetic heads have been equipped with a dynamic flying height (DFH) mechanism, which significantly reduces the gap between the read / write element of the magnetic head and the surface of the magnetic recording medium (reducing the flying height), thereby achieving even higher recording densities. The DFH mechanism involves installing a heating element, such as a tiny heater, near the read / write element of the magnetic head, protruding only the area around the element toward the surface of the medium. This reduces the distance (flying height) between the magnetic head and the magnetic recording layer of the medium, enabling signals from smaller magnetic particles to be picked up, thereby achieving even higher recording densities. However, this also results in an extremely small gap (flying height) between the element of the magnetic head and the surface of the medium. If the surface of the magnetic recording medium substrate is roughened by cleaning, this surface roughness is reflected in the surface of the magnetic recording medium, reducing the surface smoothness of the magnetic recording medium. If a magnetic head is placed close to the surface of a magnetic recording medium with poor surface smoothness, the magnetic head may come into contact with the surface of the magnetic recording medium and be damaged, so a certain flying height must be maintained to prevent contact. For these reasons, in order to produce a magnetic recording medium with high surface smoothness, it is desirable for the magnetic recording medium substrate to be able to suppress surface roughening due to cleaning, i.e., to have excellent chemical resistance. Since the magnetic recording medium substrate preferably has excellent chemical resistance, the magnetic recording medium equipped with such a substrate is also suitable for a magnetic recording device equipped with a DFH mechanism that has an extremely narrow flying height.

[0065] 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), but since high recording density is possible, it is also possible to miniaturize the medium and substrate. For example, they can have a nominal diameter of 2.5 inches, as well as smaller diameters (e.g., 1 inch or 1.8 inches), or even 3 inches or 3.5 inches.

[0066] The magnetic recording medium is made of the glass for a magnetic recording medium substrate according to one aspect of the present invention, and therefore can have the glass properties described above for the glass. In addition, the magnetic recording medium preferably exhibits excellent impact resistance.

[0067] [Glass spacer for magnetic recording / reproducing devices] One aspect of the present invention is SiO2 content is 54 mol% or more and 62 mol% or less, MgO content is 15 mol% or more and 28 mol% or less, A LiO content of 0.2 mol% or more, and Na2O content is 5 mol% or less, a glass spacer for a magnetic recording / reproducing device, comprising the amorphous glass of Regarding.

[0068] 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, these glass spacers are also desired to have excellent chemical resistance and impact resistance. In contrast, glass having the above composition can have excellent chemical resistance and impact resistance, making it suitable as a glass spacer for magnetic recording and reproducing devices.

[0069] 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 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 for a magnetic recording / reproducing device according to one aspect of the present invention, reference can be made to the above descriptions regarding the glass for a magnetic recording medium substrate, the magnetic recording medium substrate, and the magnetic recording medium according to one aspect of the present invention. The glass spacer for a magnetic recording / reproducing device can be made of the above-mentioned glass, or can be configured with one or more films, such as a conductive film, provided on the surface of the above-mentioned glass. 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 other methods. Furthermore, the glass spacer can be polished to increase its surface smoothness (for example, to an average surface roughness of 1 μm or less), which strengthens the adhesion between the magnetic recording medium and the spacer and suppresses misalignment.

[0070] [Magnetic recording and playback device] One aspect of the present invention is A magnetic recording medium according to one embodiment of the present invention; and A glass spacer according to one aspect of the present invention; a magnetic recording and reproducing device including at least one of the above; Regarding.

[0071] 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.

[0072] A magnetic recording / reproducing device according to an embodiment of the present invention may include at least one of a magnetic recording medium according to an embodiment of the present invention and a glass spacer according to an embodiment of the present invention. Other aspects of the magnetic recording / reproducing device may be achieved by applying known techniques related to magnetic recording / reproducing devices. 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, a film is typically deposited at a high temperature, or a heat treatment is performed at a high temperature after deposition. A magnetic recording medium substrate according to an embodiment of the present invention is preferred as 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. [Example]

[0073] 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.

[0074] [Examples No. 1 to No. 139] Raw materials such as oxides, carbonates, nitrates, sulfates, and hydroxides were weighed and mixed to prepare blended raw materials so as to obtain glasses having the compositions shown in Table 1 below (Tables 1-1 to 1-7). These blended raw materials were charged into a melting vat and heated and melted in the range of 1400 to 1600°C. The resulting molten glass was held in a refining vat at 1400 to 1550°C for 6 hours, then 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.

[0075] <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).

[0076] (2) Young's modulus The Young's modulus of each glass was measured by an ultrasonic method.

[0077] (3) Specific gravity The specific gravity of each glass was measured by Archimedes' method.

[0078] (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).

[0079] (5) Glass stability 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 1250°C, 1300°C, or 1350°C, and left for 16 hours while maintaining the furnace temperature (holding test). 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. 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: There are less 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 per 100g. 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 per 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

[0080] <Preparation of magnetic recording medium substrate> (1) Preparation of substrate blank Next, a disk-shaped substrate blank was produced by the following method A or B. Furthermore, a glass blank for producing a glass spacer for a magnetic recording / reproducing device can be obtained by the same method. (Method A) A clarified, homogenized glass melt having the composition shown in the table below was flowed out of an outflow pipe at a constant flow rate and received by a press-molding lower mold. The flowed-out glass melt was cut with a cutting blade so as to obtain a predetermined amount of glass melt gob on the lower mold. The lower mold with the glass melt gob placed thereon was then immediately removed from the bottom of the pipe, and press-molded into a thin disk having a diameter of 99 mm and a thickness of 0.7 mm using an upper mold and a barrel mold opposed to the lower mold. The press-molded product was cooled to a temperature at which it would not deform, then removed from the mold and annealed to obtain a substrate blank. Note that in the above-described molding, multiple lower molds were used to successively form the flowing glass melt into disk-shaped substrate blanks. (Method B) A refined and homogenized glass melt having the composition shown in the table below was continuously poured from above into a cylindrical heat-resistant mold having a through-hole, formed into a cylindrical shape, and removed from the bottom of the 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. 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 bored out of the sheet of glass to obtain a substrate blank. (Method D) Alternatively, a substrate blank can be obtained by forming molten glass into a sheet of glass by the overflow downdraw method (fusion method), annealing the glass, and then boring a disk of glass from the sheet of glass.

[0081] (2) Preparation of glass substrate A through hole was drilled in the center of the substrate blank obtained by each of the above methods, the outer and inner circumferences were ground, and the main surfaces of the disk were lapped and polished (mirror polished) to finish it into a glass substrate for a magnetic disk with a diameter of 97 mm and a thickness of 0.5 mm. In addition, 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 by the same method. The glass substrate obtained above was washed with a 1.7% by mass aqueous solution of hydrofluorosilicic acid (HSiF) and then with a 1% by mass aqueous solution of potassium hydroxide, and then rinsed with pure water and dried. When the surface of the substrate made from the glass of the example was observed under magnification, no surface roughness was observed and the surface was smooth. Four glass substrates were prepared for each glass composition and used for the following evaluation (1), (2), or (3) or for preparing magnetic recording media, which will be described later.

[0082] <Evaluation of magnetic recording medium substrates> (1) Etching rate (chemical resistance) A mask treatment was applied to a portion of the main surface of each magnetic disk glass substrate prepared above to create a non-etched portion, and the glass substrate in this state was immersed for a predetermined time in a 0.5% by mass potassium hydroxide aqueous solution maintained at a liquid temperature of 50°C. The glass substrate was then removed from the aqueous solution, and the mask was removed to measure the depth of the step between the masked portion that was not exposed to the aqueous solution and the unmasked portion that was exposed to the aqueous solution. This step depth corresponds to the amount of etching of the glass in the predetermined time (etching depth). The amount of etching per unit time, i.e., the etching rate (chemical resistance), was calculated by dividing this amount of etching by the immersion time. The etching rate (chemical resistance) determined for each of the magnetic disk glass substrates of the Examples was 0.5 nm / min or less.

[0083] (2) Amount of board deformation at 70G impact To evaluate impact resistance, the substrate deformation amount upon impact of 70 G (G is gravitational acceleration) was determined for each magnetic disk glass substrate prepared above using the following evaluation method. In HDDs, the distance between the magnetic disk and the ramp is usually about 0.25 mm. Therefore, in terms of impact resistance, when a large impact, for example, an impact 70 times the gravitational acceleration (70 G), is applied, the deformation amount of the outer peripheral edge of the magnetic disk glass substrate is preferably 0.25 mm or less, more preferably less than 0.25 mm. That is, the substrate deformation amount upon impact of 70 G determined by the following method is preferably 0.25 mm or less, more preferably less than 0.25 mm. The substrate deformation amount upon impact of 70 G can be, for example, 0.20 mm or more, but is also preferably less than this value. (Evaluation method) The inner diameter hole of the glass substrate for magnetic disks is inserted into a fixed shaft fastened to the test stand of the impact test device, and the cap is placed on top, and the entire cap is screwed in place to secure it in place. The height of the test table of the impact test equipment (the distance the test table falls) and the buffer material placed on the support base when the test table falls are adjusted to achieve the specified impact force. The adjustment using the buffer material is a fine adjustment. The impact force and impact duration are measured by using an acceleration sensor attached to the test table and an amplifier to amplify the acceleration sensor's output signal, and a personal computer processes the amplifier's output signal to determine the respective values. The test table height and buffer material conditions are changed and the test table is dropped several times to determine the impact force and impact duration at each time, and the height of the test table and buffer material conditions are then determined to achieve the specified impact force. After determining the height of the test table and the conditions for the cushioning material, a high-speed camera was used to confirm the deflection (displacement) of the outer edge of the magnetic disk glass substrate upon impact. Specifically, a high-brightness lighting device was used to capture high-resolution images, and the captured images were used to capture the instantaneous movement of the outer edge of the magnetic disk glass substrate upon impact (1 frame: 1 / 10,000th of a second, shooting time: 30 ms). The behavior of the outer edge of the magnetic disk glass substrate was captured and quantified from the captured images to determine the maximum deflection (displacement). A graph was created with the elapsed time after impact on the horizontal axis and the displacement of the outer edge of the magnetic disk glass substrate on the vertical axis. Negative values ​​on the vertical axis represent downward displacement, and positive values ​​represent upward displacement. Due to the impact of the drop, the outer edge of the magnetic disk glass substrate was displaced downward by a displacement Y0 (negative value) immediately after the drop, followed by an upward displacement Y1 (positive value) immediately afterward as a reaction, and this process was repeated until the displacement decayed. Therefore, the maximum downward displacement is Y0 immediately after the drop, and the maximum upward displacement is Y1 immediately after the downward displacement Y0. The displacement when a certain impact force is applied is calculated as "Y1 - Y0." Because the displacement "Y1 - Y0" at an impact of 70G is relatively small, it is difficult to calculate the displacement with high accuracy. Therefore, since there is a proportional relationship between the magnitude of the impact force and the displacement "Y1 - Y0," the magnitude of the impact force is changed within a range greater than 70G, the displacement "Y1 - Y0" is calculated for each impact force, and this is plotted on a graph with the displacement "Y1 - Y0" on the vertical axis and the magnitude of the impact force on the horizontal axis. An approximate line is created using the least squares method, and the linear equation of this approximate line is used to calculate the displacement "Y1 - Y0" at 70G. The displacement "Y1-Y0" shown in Table 2 is the amount of substrate deformation at a 70G impact, calculated from the value of the displacement "Y1-Y0" at each impact force, with the impact force set to four different values: 120G, 140G, 170G, and 190G.

[0084] [Comparative Example 1] A magnetic disk glass substrate was produced using a glass having the composition of Example 3 shown in Table 3 of Patent Document 1 (JP 2002-348141 A) in the same manner as in the above-described Example. The substrate deformation amount of the produced magnetic disk glass substrate when subjected to a 70 G impact was determined in the same manner as above.

[0085] The above results are shown in Table 2 (Tables 2-1 to 2-7).

[0086] [Table 1-1]

[0087] [Table 1-2]

[0088] [Table 1-3]

[0089] [Table 1-4]

[0090] [Table 1-5]

[0091] [Table 1-6]

[0092] [Table 1-7]

[0093] [Table 2-1]

[0094] [Table 2-2]

[0095] [Table 2-3]

[0096] [Table 2-4]

[0097] [Table 2-5]

[0098] [Table 2-6]

[0099] [Table 2-7]

[0100] [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.

[0101] 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.

[0102] The adhesive layer was formed using a CrTi target to be a 20 nm thick amorphous CrTi layer. 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.

[0103] 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 Heating may be performed to create an ordered structure.

[0104] 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.

[0105] Furthermore, a glass spacer obtained by the above manufacturing process using the glass of the example 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 of one embodiment of the present invention. No collision between the magnetic head and the magnetic disk surface (crash failure) was observed.

[0106] 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.

[0107] According to one aspect of the present invention, it is possible to provide a magnetic recording medium suitable for high-density recording.

[0108] Finally, the above-mentioned aspects will be summarized.

[0109] According to one embodiment, there is provided a glass for a magnetic recording medium substrate, which is amorphous glass having an SiO2 content of 54 mol% or more and 62 mol% or less, an MgO content of 15 mol% or more and 28 mol% or less, a Li2O content of 0.2 mol% or more, and a Na2O content of 5 mol% or less.

[0110] The glass can have excellent chemical resistance and excellent impact resistance.

[0111] In one embodiment, in the above glass, the molar ratio of the total content of SiO2 and MgO to the content of Li2O [(SiO2+MgO) / Li2O] can be 13 or greater.

[0112] In one embodiment, in the above glass, the total content of SiO2, MgO, Li2O, Al2O3, and CaO (SiO2+MgO+Li2O+Al2O3+CaO) can be 93 mol% or more.

[0113] In one embodiment, in the above glass, the molar ratio of the total content of Al2O3 and CaO to the content of MgO [(Al2O3+CaO) / MgO] can be 0.55 or more.

[0114] In one embodiment, the molar ratio of the MgO content to the CaO content (MgO / CaO) in the above glass can be 6 or greater.

[0115] In one embodiment, the glass can have an etching amount per unit time (etching rate (chemical resistance)) of 0.5 nm / min or less when immersed for a predetermined time in an aqueous solution of hydrosilicofluoric acid with a concentration of 0.5 mass % and maintained at a liquid temperature of 50°C.

[0116] According to one embodiment, there is provided a magnetic recording medium substrate made of the above-mentioned glass for magnetic recording medium substrates.

[0117] In one embodiment, the amount of deformation of the magnetic recording medium substrate when subjected to a 70 G impact can be 0.25 mm or less.

[0118] According to one embodiment, there is provided a magnetic recording medium having the above magnetic recording medium substrate and a magnetic recording layer.

[0119] According to one embodiment, there is provided a glass spacer for a magnetic recording / reproducing device, comprising amorphous glass having an SiO2 content of 54 mol% or more and 62 mol% or less, an MgO content of 15 mol% or more and 28 mol% or less, a Li2O content of 0.2 mol% or more, and a Na2O content of 5 mol% or less.

[0120] According to one aspect, there is provided a magnetic recording and reproducing device including at least one of the above magnetic recording medium and the above glass spacer for a magnetic recording and reproducing device.

[0121] 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. SiO ２ The content is 54 mol% or more and 62 mol% or less, an MgO content of 15 mol% or more and 28 mol% or less; Li ２ The O content is 0.2 mol% or more, and Na ２ O content is 5 mol% or less, The amorphous glass for magnetic recording medium substrates is

2. Li ２ SiO relative to O content ２ and MgO total content molar ratio [(SiO ２ + MgO) / Li ２ 2. The glass for a magnetic recording medium substrate according to claim 1, wherein [O] is 13 or more.

3. SiO ２ , MgO, Li ２ O, Al ２ O ３ and the total content of CaO (SiO ２ + MgO + Li ２ O+Al ２ O ３ 3. The glass for a magnetic recording medium substrate according to claim 1, wherein the content of CaO is 93 mol % or more.

4. Al relative to MgO content ２ O ３ The molar ratio of the total content of Al and CaO [(Al ２ O ３ 4. The glass for a magnetic recording medium substrate according to claim 1, wherein the ratio of [CaO + CaO / MgO] to [MgO + CaO] is 0.55 or more.

5. 5. The glass for a magnetic recording medium substrate according to claim 1, wherein the molar ratio of the MgO content to the CaO content (MgO / CaO) is 6 or more.

6. A magnetic recording medium substrate comprising the glass for magnetic recording medium substrates according to any one of claims 1 to 5.

7. 7. A magnetic recording medium comprising the magnetic recording medium substrate according to claim 6 and a magnetic recording layer.

8. SiO ２ The content is 54 mol% or more and 62 mol% or less, an MgO content of 15 mol% or more and 28 mol% or less; Li ２ The O content is 0.2 mol% or more, and Na ２ O content is 5 mol% or less, A glass spacer for a magnetic recording / reproducing device, comprising the amorphous glass of the above-mentioned formula (1).

9. 9. A magnetic recording and reproducing device comprising at least one of the magnetic recording medium according to claim 7 and the glass spacer for a magnetic recording and reproducing device according to claim 8.

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