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

Abstract

Provided is a glass for a magnetic recording medium substrate, which is an amorphous glass having a SiO2 content of 54 mol% to 62 mol%, a MgO content of 15 mol% to 28 mol%, a Li2O content of 0.2 mol% to 0.5 mol%, and a Na2O content of 5 mol% to 5 mol%.

Description

Technical Field

[0001] The present invention relates to glass for a magnetic recording medium substrate, a magnetic recording medium substrate, a magnetic recording medium, a glass spacer for a magnetic recording and reproducing device, and a magnetic recording and reproducing device. Background Art

[0002] As a substrate (magnetic recording medium substrate) for magnetic recording media such as hard disks, a substrate made of aluminum alloy was used in the past. However, aluminum alloy substrates are pointed out to have disadvantages such as easy deformation. Therefore, magnetic recording medium substrates made of glass are widely used now (for example, see patent document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2002-814134 Summary of the invention

[0006] Problems to be solved by the invention

[0007] In order to remove foreign matter attached to the substrate surface during the manufacturing process, the magnetic recording medium substrate is usually cleaned with acid, alkali, etc. However, when the chemical resistance of the glass constituting the substrate is insufficient, even if the substrate surface is smoothed during the manufacturing process, the surface roughness will be generated due to cleaning. Therefore, it is desired that the glass for magnetic recording medium substrates has excellent chemical resistance.

[0008] Furthermore, it is also desired that the glass for a magnetic recording medium substrate has excellent impact resistance. This is for the following reasons.

[0009] Magnetic recording media are usually installed inside hard disk drives (HDDs) that are assembled into machines such as personal computers. Inside the HDD, more than two magnetic recording media (disks) are installed on the rotating shaft of the shaft motor. Through the actuator assembled into the HDD, data is written or read from the magnetic recording layer of the magnetic recording medium that rotates at high speed inside the HDD. When the magnetic recording medium rotates at high speed for such data writing or reading, if a large impact (such as a fall or other impact) is applied to the HDD, the impact causes the magnetic recording medium inside the HDD to be temporarily deformed, and collides with a component called a ramp in a high-speed rotating state, which may cause the magnetic recording medium to be damaged. In order to prevent such damage, it is expected that it is difficult to deform even if it is impacted, that is, it has excellent impact resistance. For HDD, although the recording capacity can be increased by making the thickness of each magnetic recording medium thinner and making more magnetic recording media mounted on the HDD, generally speaking, if the thickness of the glass is made thinner, it is easy to deform and there is a tendency for the above-mentioned damage to occur easily. Therefore, a glass for a magnetic recording medium substrate having excellent impact resistance is desired while achieving both an increase in the recording capacity of the HDD and suppression of the above-mentioned damage.

[0010] About the above, put down in writing in patent documentation 1 (Japanese Patent Laid-Open 2002-814134 Gazette): according to the glass put down in writing in patent documentation 1, by cleaning the glass surface with an acidic liquid, it is possible to make its surface clean and not make it deteriorate (the 0068th paragraph of patent documentation 1 etc.). But according to the research of the inventor, from the viewpoint of preventing the previously described breakage, the impact resistance of the glass put down in writing in patent documentation 1 is insufficient. On the other hand, as the material with high impact resistance, it is known that sintered glass is arranged, but the manufacturing process of sintered glass is complicated. In addition, it is not easy to realize the required high smoothness of magnetic recording medium substrate by sintered glass.

[0011] An object of one embodiment of the present invention is to provide a glass for a magnetic recording medium substrate having excellent chemical resistance and impact resistance.

[0012] Means for solving problems

[0013] One embodiment of the present invention relates to glass for a magnetic recording medium substrate (hereinafter also referred to as "glass"), which is an amorphous glass having a SiO2 content of not less than 54 mol% and not more than 62 mol%, a MgO content of not less than 15 mol% and not more than 28 mol%, a Li2O content of not less than 0.2 mol%, and a Na2O content of not more than 5 mol%.

[0014] The glass for a magnetic recording medium substrate has the glass composition described above and can have excellent chemical resistance and excellent impact resistance.

[0015] Effects of the Invention

[0016] According to one embodiment of the present invention, a glass for a magnetic recording medium substrate having excellent chemical resistance and impact resistance can be provided. According to another embodiment, a magnetic recording medium substrate composed of the glass for a magnetic recording medium substrate and a magnetic recording medium containing the substrate can be provided. According to yet another embodiment, a glass spacer for a magnetic recording device can be provided. According to yet another embodiment, a magnetic recording and reproducing device can be provided. DETAILED DESCRIPTION

[0017] [Glass for magnetic recording medium substrates]

[0018] The above-mentioned glass is an amorphous glass having the above-mentioned composition. Unlike crystallized glass, amorphous glass does not substantially contain a crystal phase and is a glass that shows a glass transition phenomenon when the temperature rises.

[0019] In addition, the glass may be an amorphous oxide glass. Oxide glass refers to glass whose main network-forming component is an oxide.

[0020] Hereinafter, the above-mentioned glass will be described in more detail.

[0021] <Glass Composition>

[0022] In the present invention and this specification, the glass composition is expressed as the glass composition based on oxides. Here, the "glass composition based on oxides" refers to the glass composition converted to the substances that are completely decomposed when the glass raw materials are melted and exist in the form of oxides in the glass. In addition, unless otherwise stated, the glass composition is expressed on a molar basis (molar %, molar ratio).

[0023] The glass composition in the present invention and this specification can be obtained by methods such as ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Quantitative analysis is performed on each element separately using ICP-AES. Afterwards, the analysis value is converted to oxide expression. The analysis value of ICP-AES sometimes contains a measurement error of about ±5% of the analysis value, for example. Therefore, the value expressed in the oxide converted from the analysis value sometimes also contains an error of about ±5%.

[0024] In the present invention and this specification, "0% content of a constituent component" or "not included" or "not introduced" means that the constituent component is not substantially included and the content of the constituent component is at an impurity level. "Below the impurity level" means, for example, less than 0.01%.

[0025] In the glass composition of the above-mentioned glass, the SiO2 content is greater than 54 mol% and less than 62 mol%, the MgO content is greater than 15 mol% and less than 28 mol%, the Li2O content is greater than 0.2 mol%, and the Na2O content is less than 5 mol%.

[0026] Hereinafter, the glass composition of the above-mentioned glass will be described in more detail.

[0027] SiO2 is a network-forming component of glass, which has the effect of improving the stability of glass. In addition, SiO2 is also a component that helps to improve chemical resistance. From the viewpoint of improving chemical resistance and impact resistance, the SiO2 content is 54% or more. In addition, in the manufacturing process of the magnetic recording medium substrate, the surface of the substrate is usually polished. From the viewpoint of improving the smoothness of the surface of the magnetic recording medium substrate after polishing, it is also preferred that the SiO2 content is 54% or more. From the above viewpoints, the SiO2 content is preferably 55% or more, more preferably 56% or more, further preferably 57% or more, more preferably 57.5% or more, further preferably 58% or more, further preferably 58.5% or more, especially more preferably 59% or more, and especially more preferably 60% or more. In addition, from the viewpoint of the solubility of the glass, the SiO2 content is 62% or less, preferably 61% or less.

[0028] MgO has the effect of increasing the Young's modulus of the glass, increasing the thermal expansion coefficient, and optimizing the meltability or formability of the glass. From the viewpoint of improving impact resistance, the MgO content is 15% or more. From the viewpoint of improving Young's modulus and improving specific elastic modulus, the MgO content is also preferably 15% or more. From the above viewpoints, the MgO content is preferably 16% or more, and more preferably 17% or more. In addition, from the viewpoint of improving devitrification resistance, the MgO content of the above-mentioned glass is 28% or less, preferably 27% or less, more preferably 26% or less, further preferably 25% or less, more preferably 24.5% or less, further preferably 24% or less, further preferably 23.5% or less, particularly preferably 23% or less, particularly further preferably 22.5% or less, particularly further preferably 22% or less, still further more preferably 20% or less, and particularly preferably 19% or less.

[0029] Even among alkali metal oxides, Li2O is a component that has a strong effect on improving the solubility of glass. In addition, when the above-mentioned glass is used as glass for chemical strengthening, it is also a component that is responsible for ion exchange during chemical strengthening. From the viewpoint of improving the solubility of glass, the Li2O content is 0.2% or more, preferably 0.5% or more, more preferably 1% or more, further preferably 2% or more, further preferably 2.5% or more, further preferably 3% or more, further preferably 3.5% or more, and further preferably 4% or more. In addition, from the viewpoint of further improving chemical resistance and impact resistance, and improving the smoothness of the surface of the magnetic recording medium substrate after grinding, the Li2O content is preferably 6% or less, more preferably 5% or less.

[0030] From the viewpoint of further improving impact resistance, the molar ratio of the total content of SiO2 and MgO to the content of Li2O [(SiO2+MgO) / Li2O] is preferably 13 or more, more preferably greater than 13, further preferably 14 or more, and further preferably 15 or more. In addition, from the viewpoint of devitrification resistance and solubility, the molar ratio [(SiO2+MgO) / Li2O] is preferably 100 or less, more preferably 50 or less, further preferably 30 or less, further preferably 25 or less, and further preferably 20 or less.

[0031] Na2O is a component that has the following effects: improving the solubility of glass, increasing the coefficient of thermal expansion, reducing the viscosity of glass during clarification and promoting the elimination of bubbles. In addition, when the above-mentioned glass is used as glass for chemical strengthening, it is also a component that undertakes ion exchange during chemical strengthening. From the viewpoint of improving impact resistance, the Na2O content is 5% or less. From the viewpoint of increasing Young's modulus and increasing specific elastic modulus, the Na2O content is also preferably 5% or less. From the above viewpoints, the Na2O content is preferably 4% or less, more preferably 3% or less, further preferably 2% or less, and more preferably 1% or less. In one embodiment, the Na2O content can be 0%, 0% or more, or greater than 0%, or 0.5% or more.

[0032] B2O3 is a network-forming component of glass, a component that reduces the specific gravity of glass, and a component that improves melting properties. From the viewpoint of further improving impact resistance, increasing specific elastic modulus, and increasing Young's modulus, the B2O3 content is preferably 3% or less, more preferably 2% or less, and further preferably 1% or less. In one embodiment, the B2O3 content can be 0%, 0% or more, or greater than 0%, or 0.5% or more.

[0033] Al2O3 is a network-forming component of glass and has the effect of improving heat resistance. From the viewpoint of improving the solubility of glass, the Al2O3 content is preferably 19% or less, more preferably 18% or less, further preferably 17% or less, further preferably 16% or less, and further preferably 15% or less. In addition, from the viewpoint of further improving impact resistance, improving Young's modulus and improving specific elastic modulus, Al2O3 is preferably 9% or more, more preferably 10% or more, further preferably 11% or more, and further preferably 12% or more.

[0034] BaO has the effect of optimizing the melting property, formability and stability of glass and increasing the thermal expansion coefficient. From the viewpoint of reducing the specific gravity of glass, increasing Young's modulus, increasing specific elastic modulus and further improving impact resistance, the BaO content is preferably 3% or less, more preferably 2% or less, and further preferably 1% or less. In one embodiment, the BaO content can be 0%, 0% or more, or greater than 0%, or 0.5% or more.

[0035] CaO has the effect of increasing the Young's modulus and specific elastic modulus of glass, increasing the thermal expansion coefficient, and optimizing the solubility and formability of glass. In one embodiment, the CaO content can be 0%, or 0% or more, or greater than 0%. In another embodiment, from the viewpoint of obtaining the above-mentioned good effects, the CaO content is preferably 0.5% or more, more preferably 1% or more, and further preferably 1.5% or more. In addition, from the viewpoint of further improving chemical resistance, the CaO content is preferably 10% or less, more preferably 9% or less, further preferably 8% or less, further preferably 7% or less, further preferably 6% or less, further preferably 5% or less, further preferably 4% or less, and particularly preferably 3% or less.

[0036] From the viewpoint of further improving impact resistance, the molar ratio of the MgO content to the CaO content (MgO / CaO) is preferably 6 or more, more preferably 7 or more, and even more preferably 8 or more. From the viewpoint of devitrification resistance, the molar ratio (MgO / CaO) is preferably 30 or less, more preferably 25 or less, even more preferably 20 or less, further preferably 18 or less, and even more preferably 15 or less.

[0037] From the viewpoint of improving devitrification resistance and further improving chemical resistance, the molar ratio of the total content of Al2O3 and CaO to the content of MgO [(Al2O3+CaO) / MgO] is preferably 0.55 or more, and more preferably 0.57 or more. Furthermore, 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, the larger the lower limit, the more preferred. In addition, from the viewpoint of impact resistance, the above molar ratio [(Al2O3+CaO) / MgO] is preferably 1.8 or less, more preferably 1.5 or less, further preferably 1.3 or less, further preferably 1.2 or less, and further preferably 1.1 or less.

[0038] 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, further preferably 0.40 or less, further preferably 0.30 or less, further preferably 0.24 or less, and further preferably 0.20 or less. In addition, the above-mentioned molar ratio (CaO / Al2O3) may be, for example, 0 or more, greater than 0, or 0.1 or more.

[0039] From the viewpoint of improving Young's modulus, improving specific elastic modulus and further improving impact resistance, the molar ratio of 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 further preferably 0.10 or less. In addition, the above molar ratio may be, for example, 0 or more, greater than 0, 0.01 or more, or 0.03 or more.

[0040] From the viewpoint of further improving impact resistance, the molar ratio of MgO content to Li2O content (MgO / Li2O) is preferably 2.3 or more, more preferably 2.5 or more, more preferably 2.7 or more, and more preferably 3.0 or more. From the viewpoint of improving the meltability of the glass, the molar ratio (MgO / Li2O) is preferably 28 or less, more preferably 26 or less, more preferably 24 or less, and more preferably 22 or less.

[0041] From the viewpoint of increasing Young's modulus, increasing 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, further preferably 31% or more, further preferably 32% or more, and further preferably 33% or more. In addition, the above-mentioned 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.

[0042] From the viewpoint of improving solubility and improving resistance to devitrification, the total content of SiO2, MgO, Li2O, Al2O3 and CaO (SiO2+MgO+Li2O+Al2O3+CaO) is preferably 93 mol% or more. From the viewpoint of improving the smoothness of the surface of the magnetic recording medium substrate after grinding and improving the vibration and impact resistance of the magnetic recording medium having the magnetic recording medium substrate, the above total content is also preferably 93% or more. From the above viewpoints, the total content (SiO2+MgO+Li2O+Al2O3+CaO) is more preferably 94% or more, further preferably 95% or more, further preferably 96% or more, further preferably 97% or more, and further preferably 98% or more. In addition, the above total content (SiO2+MgO+Li2O+Al2O3+CaO) can be less than 100% or less than 99%.

[0043] SrO has the effect of optimizing the meltability, formability and stability of glass and increasing the thermal expansion coefficient. From the viewpoint of low specific gravity and reduction of raw material costs, the SrO content is preferably 4% or less, preferably 3% or less, more preferably 2% or less, and further preferably 1% or less. In one embodiment, the SrO content can be 0%, can be 0% or more or greater than 0%, or can be 0.5% or more.

[0044] K2O is a component that improves the meltability and formability of glass and increases the thermal expansion coefficient. From the viewpoint of reducing specific gravity, increasing Young's modulus, increasing specific elastic modulus, and further improving impact resistance, the K2O content is preferably 2% or less, more preferably 1% or less, and further preferably 0.5% or less. In one embodiment, the K2O content may be 0%, or may be 0% or more, or greater than 0%.

[0045] TiO2 is a component that improves the stability of glass. From the viewpoint of reducing specific gravity and improving resistance to devitrification, the TiO2 content is preferably 4% or less, more preferably 3% or less, further preferably 2% or less, and further preferably 1% or less. In one embodiment, the TiO2 content may be 0%, may be 0% or more, or may be greater than 0%, or may be 0.5% or more.

[0046] ZnO has the effect of improving meltability. From the viewpoint of reducing specific gravity, improving Young's modulus, improving 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%, can be 0% or more or greater than 0%, or can be 0.5% or more.

[0047] From the viewpoint of reducing specific gravity and improving resistance to devitrification, the ZrO2 content is preferably 5% or less, more preferably 4% or less, further preferably 3% or less, further preferably less than 3%, further preferably 2% or less, and further preferably 1% or less. In one embodiment, the ZrO2 content may be 0%, may be 0% or more or greater than 0%, or may be 0.5% or more.

[0048] From the viewpoint of reducing specific gravity and improving devitrification resistance, the Y2O3 content is preferably 2% or less, more preferably 1.5% or less, and further preferably 1% or less. In one embodiment, the Y2O3 content may be 0%, 0% or more or greater than 0%, or 0.5% or more.

[0049] As the content expressed as a ratio other than Fe2O3, the Fe2O3 content of the above-mentioned glass 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 above-mentioned glass may not contain Fe (the Fe2O3 content expressed as a ratio other than Fe2O3 is 0 mol%). The Fe2O3 content expressed as a ratio other than Fe2O3 refers to the value of 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 set to 100 mol%.

[0050] The glass may include one or more selected from the group consisting of Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er.

[0051] F is a component that is volatile when melted and causes striae, so the glass preferably does not contain F. Not containing F is also preferred from the viewpoint of suppressing corrosion of a melting furnace, suppressing a decrease in Young's modulus, and suppressing a decrease in specific elastic modulus.

[0052] Pb, Cd, and As are substances that adversely affect the environment, and therefore, it is preferred to avoid introducing them.

[0053] From the viewpoint of obtaining a clarification 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%. By making the total content of SnO2 and CeO2 more than 0.05%, a sufficient clarification effect can be obtained and the remaining bubbles can be reduced. In addition, by making the total content (SnO2+CeO2) less than 2%, it is possible to prevent the molten glass from being ejected during glass melting and thus reducing productivity. The lower limit of the total content (SnO2+CeO2) is preferably 0.10% or more, more preferably 0.20% or more, further preferably 0.25% or more, further preferably 0.30% or more, further preferably 0.35% or more, and further preferably 0.40% or more. In addition, the upper limit of the total content (SnO2+CeO2) is preferably 1.5% or less, more preferably 1.2% or less, further preferably 1.0% or less, further preferably 0.70% or less, further preferably 0.65% or less, further preferably 0.60% or less, particularly preferably 0.55% or less, and particularly further preferably 0.50% or less.

[0054] SnO2 has the effect of promoting the clarification of glass in a state of relatively high melting temperature (temperature range of about 1400-1600°C). In the case where the use of clarifiers such as Sb2O3 or arsenic acid that have adverse effects on the environment is restricted, in order to remove bubbles in glass with a high melting temperature, in one embodiment, SnO2 is preferably introduced into the above-mentioned glass. From the viewpoint of obtaining a clarification effect, the content of SnO2 is preferably 0.01% or more, more preferably 0.05% or more, further preferably 0.10% or more, further preferably 0.15% or more, and further preferably 0.20% or more. In addition, the content of SnO2 is preferably 2% or less, more preferably 1.5% or less, further preferably 1.0% or less, further preferably 0.8% or less, and further preferably 0.5% or less.

[0055] CeO2 is a component that shows a clarifying effect on glass like SnO2. Since CeO2 has the effect of absorbing oxygen and fixing it as a glass component when the melting temperature of the glass is relatively low (temperature range of about 1200 to 1400°C), in one embodiment, CeO2 is preferably introduced into the above-mentioned glass as a clarifying agent. From the viewpoint of obtaining a clarifying effect, the content of CeO2 is preferably 0.01% or more, more preferably 0.05% or more, further preferably 0.08% or more, and further preferably 0.10% or more. In addition, the content of CeO2 is preferably 2% or less, more preferably 1.5% or less, further preferably 1.0% or less, further preferably 0.8% or less, further preferably 0.5% or less, and further preferably 0.3% or less. By allowing SnO2 and CeO2 to coexist, a clarifying effect can be obtained in a wide temperature range. Therefore, in one embodiment, the above-mentioned glass preferably contains both SnO2 and CeO2.

[0056] From the viewpoint of reducing the environmental load, it is desirable to control the use of Sb2O3. The content of Sb2O3 in the above-mentioned glass is preferably in the range of 0 to 0.5%. The content of Sb2O3 is more preferably 0.3% or less, further preferably 0.1% or less, further preferably 0.05% or less, further preferably 0.02% or less, and particularly preferably no Sb2O3 is contained.

[0057] In order to obtain a predetermined glass composition, the glass can be produced by weighing and blending glass raw materials such as oxides, carbonates, nitrates, sulfates, hydroxides, etc., mixing them thoroughly, heating and melting them in a melting vessel, for example, in a range of 1400°C to 1600°C, clarifying and stirring them to fully eliminate bubbles and homogenize them, and molding the molten glass obtained in this way. For example, it is preferred that the glass raw materials are heated and melted in a melting tank at 1400°C to 1550°C, the obtained molten glass is heated and maintained at 1450°C to 1600°C in a clarification tank, and then the temperature is lowered and the glass is made to flow out at 1200°C to 1400°C for molding.

[0058] <Glass Properties>

[0059] The glass can have the various glass properties described below by adjusting the composition as described above.

[0060] (Chemical resistance)

[0061] As an indicator of the chemical resistance of glass, the etching rate can be cited, which is the etching amount per unit time (unit: nm / minute) when the glass is immersed in a potassium hydroxide aqueous solution with a concentration of 0.5 mass % and a liquid temperature of 50°C for a specified time. The etching rate of the above-mentioned glass can be 0.5 nm / minute or less. For the determination method of the etching rate, reference can be made to the description of the embodiments described below. The above-mentioned etching rate is preferably 0 nm / minute or more and 0.5 nm / minute or less.

[0062] (Young's modulus)

[0063] The Young's modulus of the above-mentioned glass is preferably 90 GPa or more. According to the glass for magnetic recording medium substrate with high rigidity showing a Young's modulus of 90 GPa or more, the deformation of the substrate during the rotation of the shaft motor can be suppressed, and thus the warping or bending of the magnetic recording medium with the deformation of the substrate can be suppressed. The Young's modulus of the above-mentioned glass is preferably 91 GPa or more, more preferably 92 GPa or more, further preferably 93 GPa or more, more preferably 94 GPa or more, and further preferably 95 GPa or more. The upper limit of the Young's modulus is, for example, about 120 GPa, but since the higher the Young's modulus, the higher the rigidity and the more preferred it is, there is no particular limitation.

[0064] (proportion)

[0065] The specific gravity of the above-mentioned glass is preferably below 2.75. The specific gravity of the above-mentioned glass is more preferably below 2.73, further preferably below 2.70, more preferably below 2.68, further preferably below 2.64, further preferably below 2.62, and particularly preferably below 2.60. By reducing the specific gravity of the glass for the magnetic recording medium substrate, the magnetic recording medium substrate can be lightweight, and the magnetic recording medium can be further lightweight, thereby suppressing the power consumption of the magnetic recording and reproducing device (commonly referred to as HDD). The lower limit of the specific gravity is, for example, about 2.40, but the lower the specific gravity, the more preferred it is, so there is no special limitation.

[0066] (Specific elastic modulus)

[0067] The specific elastic modulus is the Young's modulus of the glass divided by its density. Here, density can be considered to refer to the specific gravity of the glass in g / cm 3 The value of this unit. From the viewpoint of providing a substrate that is more difficult to deform, the specific elastic modulus of the glass is preferably 30MNm / kg or more, more preferably 32MNm / kg or more, further preferably 33MNm / kg or more, further preferably 34MNm / kg or more, and further preferably 35MNm / kg or more. The upper limit of the specific elastic modulus is, for example, about 40MNm / kg, but the higher the specific elastic modulus, the more preferred it is, so there is no particular limitation.

[0068] (Coefficient of thermal expansion)

[0069] An HDD in which a magnetic recording medium is assembled usually has a structure in which the central portion is pressed by the shaft of a shaft motor and a chuck to rotate the magnetic recording medium itself. Therefore, when there is a large difference in the thermal expansion coefficients of the magnetic recording medium substrate and the shaft material constituting the shaft portion, the thermal expansion / contraction of the shaft deviates from the thermal expansion / contraction of the magnetic recording medium substrate relative to the ambient temperature changes during use, resulting in deformation of the magnetic recording medium. When such a phenomenon occurs, the magnetic head will not be able to read the written information, which will cause a decrease in the reliability of recording and reproducing. Therefore, it is desired that the glass used for the magnetic recording medium substrate has a moderate thermal expansion coefficient of the same degree as that of the shaft material (such as stainless steel, etc.). Usually, the shaft material of the HDD has a thermal expansion coefficient of 70×10 -7 / ℃ or above, if the average linear expansion coefficient of the glass used for the magnetic recording medium substrate is 40×10 -7 / ℃ or more, the difference in thermal expansion coefficient with the shaft material is small, which can help improve the reliability of the magnetic recording medium. The average linear expansion coefficient of the glass at 100℃ to 300℃ (hereinafter also referred to as "α") is preferably 40×10 -7 / ℃ or more, more preferably 41×10 -7 / ℃ or more, more preferably 42×10 -7 / ℃ or more, more preferably 43×10 -7 / ℃ or more, more preferably 44×10 -7 / ℃ or more, and more preferably 45×10 -7 In addition, the average linear expansion coefficient (α) of the glass at 100°C to 300°C is preferably 70×10 -7 / °C or less, more preferably 68×10 -7 / °C or less, more preferably 65×10 -7 / ℃ or less, more preferably 63×10 -7 / ℃ or less, more preferably 60×10 -7 / ℃ or less, and more preferably 57×10 -7 / ℃ or less, and more preferably 55×10 -7 / °C or less, and more preferably 53×10 -7 / °C or less, and more preferably 50×10 -7 / ℃ below.

[0070] (Glass transition temperature)

[0071] The magnetic recording medium substrate is usually subjected to high temperature treatment in the process of forming a magnetic recording layer on the substrate. For example, in order to form a magnetic recording layer containing a magnetic material with high magnetic anisotropy energy (which has been developed in recent years for high-density recording of magnetic recording media), film formation is usually performed at a high temperature, or heat treatment is performed at a high temperature after film formation. The magnetic recording medium substrate has heat resistance that can withstand such high-temperature treatment, and the flatness of the substrate can be maintained even when exposed to high temperatures during high-temperature treatment, so it is preferred. Regarding the above-mentioned glass, the glass transition temperature (hereinafter also recorded as "Tg") as an indicator of heat resistance is preferably above 640°C, more preferably above 650°C, further preferably above 660°C, more preferably above 670°C, further preferably above 675°C, further preferably above 680°C, particularly preferably above 685°C, and particularly further preferably above 687°C. In addition, the upper limit of the glass transition temperature is, for example, about 770°C or about 750°C, but the higher the glass transition temperature, the more preferred it is from the viewpoint of heat resistance, so it is not particularly limited. However, the above-mentioned glass is not limited to substrate glass for magnetic recording media (the substrate glass for magnetic recording media has a magnetic recording layer containing a magnetic material that requires high temperature treatment), but can be used to produce magnetic recording media having various magnetic materials.

[0072] (Glass stability)

[0073] The above-mentioned glass preferably exhibits high glass stability. As an evaluation method for glass stability, a 16-hour holding test at 1350°C, 1300°C or 1250°C, which will be described in detail later, can be cited. Preferably, the evaluation result in at least one of the holding tests of 1350°C for 16 hours, 1300°C for 16 hours and 1250°C for 16 hours is A or B, more preferably A. In the holding test at a lower holding temperature, the better the result, the higher the glass stability.

[0074] [Magnetic recording medium substrate]

[0075] A magnetic recording medium substrate according to one aspect of the present invention is made of the above-mentioned glass.

[0076] The magnetic recording medium substrate can be manufactured by the following steps: preparing molten glass by heating glass raw materials, forming the molten glass into a plate by any method of a compression molding method, a down-draw method or a float method, and processing the obtained plate-shaped glass. For example, in the compression molding method, the molten glass flowing out of the glass outflow tube is cut into a specified volume to obtain a desired molten glass block, and the block is compression molded by a compression molding mold to produce a thin-walled disc-shaped substrate blank. Next, a center hole is set in the obtained substrate blank, and inner and outer circumference processing is applied, and grinding and polishing are applied to the two main surfaces. Next, a cleaning process including acid cleaning and alkali cleaning can be performed to obtain a disc-shaped substrate.

[0077] In one embodiment, the surface and internal composition of the magnetic recording medium substrate are homogeneous. Here, the surface and internal composition are homogeneous, which means that ion exchange is not performed (i.e., there is no ion exchange layer). The magnetic recording medium base without an ion exchange layer is manufactured without ion exchange treatment, so the manufacturing cost can be greatly reduced.

[0078] In addition, in one embodiment, a part or all of the surface of the magnetic recording medium substrate has an ion exchange layer. Since the ion exchange layer shows compressive stress, the presence or absence of the ion exchange layer can be confirmed by cutting the substrate vertically relative to the main surface and obtaining a stress profile according to the Babinet method in the fracture surface. "Main surface" refers to the surface of the substrate on which the magnetic recording layer is set or the surface on which the magnetic recording layer is set. This surface is the surface with the largest area among the surfaces of the magnetic recording medium substrate, so it is called the main surface. In the case of a disc-shaped magnetic recording medium, it is equivalent to the circular surface of the disc (without the center hole). In addition, the presence or absence of an ion exchange layer can also be confirmed by a method of measuring the concentration distribution of alkali metal ions from the substrate surface to the depth direction.

[0079] The ion exchange layer can be formed by contacting the substrate surface with an alkali metal salt at a high temperature and exchanging the alkali metal ions in the alkali metal salt with the alkali metal ions in the substrate. Regarding ion exchange (also called "enhancement treatment" or "chemical enhancement"), known techniques can be applied, and as an example, reference can be made to paragraphs 0068 to 0069 of WO2011 / 019010A1.

[0080] The above-mentioned magnetic recording medium substrate has a thickness of, for example, less than 1.5 mm, preferably less than 1.2 mm, more preferably less than 1.0 mm, further preferably less than 0.8 mm, more preferably less than 0.8 mm, further preferably less than 0.7 mm, and further preferably less than 0.6 mm. In addition, the thickness of the above-mentioned magnetic recording medium substrate is, for example, more than 0.3 mm. From the viewpoint of improving the recording capacity of the HDD, it is preferred that the thickness of the magnetic recording medium substrate can be made thin. In addition, the above-mentioned magnetic recording medium substrate is preferably a disk shape with a center hole.

[0081] The magnetic recording medium substrate is made of amorphous glass. Amorphous glass can achieve excellent surface smoothness when processed into a substrate compared to crystallized glass.

[0082] [Magnetic recording media]

[0083] One aspect of the present invention relates to a magnetic recording medium having a magnetic recording layer on the magnetic recording medium substrate.

[0084] Magnetic recording media are called magnetic disks, hard disks, etc., and are suitable for various magnetic recording and reproducing devices, such as internal storage devices (local hard disks, etc.) of desktop computers, server computers, notebook computers, mobile personal computers, etc., internal storage devices of portable recording and reproducing devices that record and reproduce images and / or sounds, and recording and reproducing devices for car audio systems, etc. In the present invention and this specification, a "magnetic recording and reproducing device" refers to a device that can perform one or both of magnetic recording and magnetic reproducing of information.

[0085] The magnetic recording medium is configured, for example, by laminating at least an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer on a main surface of a magnetic recording medium substrate in order of proximity to the main surface.

[0086] For example, the magnetic recording medium substrate is introduced into a vacuum film forming device, and a DC (Direct Current) magnetron sputtering method is used in an Ar atmosphere to form films on the main surface of the magnetic recording medium substrate from an adhesion layer to a magnetic layer. As the adhesion layer, for example, CrTi can be used; as the base layer, for example, a material containing Ru or MgO can be used. It should be noted that a soft magnetic layer or a heat dissipation layer can also be appropriately added. After the above-mentioned film formation, for example, a protective layer is formed using C2H4 by a CVD (Chemical Vapor Deposition) method, and a magnetic recording medium can be formed by introducing nitrogen into the surface for nitriding treatment in the same chamber. Thereafter, a lubricating layer can be formed by, for example, applying PFPE (perfluoropolyether) to the protective layer by a dip coating method.

[0087] In order to achieve higher density recording of magnetic recording media, the magnetic recording layer preferably contains a magnetic material with high magnetic anisotropy energy. As preferred magnetic materials from this point of view, Fe-Pt-based magnetic materials or Co-Pt-based magnetic materials can be cited. It should be noted that "based" here means containing. That is, the above-mentioned magnetic recording medium preferably has a magnetic recording layer containing Fe and Pt, or Co and Pt as a magnetic recording layer. Regarding the magnetic recording layer containing the above-mentioned magnetic materials and the film forming method thereof, reference can be made to paragraph 0074 of WO2011 / 019010A1 and the description of the embodiments of the gazette. In addition, the magnetic recording medium having such a magnetic recording layer is preferably suitable for a magnetic recording device using a recording method using the so-called energy-assisted recording method. Among the energy-assisted recording methods, the recording method that assists magnetization reversal by irradiation with near-field light or the like is called a thermally assisted recording method, and the recording method assisted by microwaves is called a microwave-assisted recording method. For their details, reference can be made to paragraph 0075 of WO2011 / 019010A1. It should be noted that as the magnetic material for forming the magnetic recording layer, a conventional CoPtCr-based material can be used.

[0088] By the way, in recent years, the gap between the recording and reproducing element part of the magnetic head and the surface of the magnetic recording medium has been greatly narrowed (low suspension quantization) by installing a DFH (Dynamic Flying Height) mechanism on the magnetic head, thereby achieving a higher recording density. The DFH mechanism refers to a function in which a very small heating part such as a heater is set near the recording and reproducing element part of the magnetic head, and only the periphery of the element part protrudes toward the surface of the medium. In this way, the distance (flying height) between the magnetic head and the magnetic recording layer of the medium is close, so it becomes possible to find signals of smaller magnetic particles, and a higher recording density can be achieved. However, on the other hand, the gap (flying height) between the element part of the magnetic head and the surface of the medium becomes extremely small. If there is a surface roughness caused by cleaning on the surface of the magnetic recording medium substrate, the surface roughness of the substrate is reflected on the surface of the magnetic recording medium, which will reduce the surface smoothness of the magnetic recording medium. When the magnetic head is close to the surface of the magnetic recording medium with poor surface smoothness, the magnetic head may contact the surface of the magnetic recording medium and damage the magnetic head, so in order to prevent contact, a certain degree of flying height has to be ensured. From the above viewpoints, in order to produce a magnetic recording medium with high surface smoothness, it is desirable that the magnetic recording medium substrate can suppress the surface roughness caused by cleaning, that is, has excellent chemical resistance. The above-mentioned magnetic recording medium substrate can preferably have excellent chemical resistance, so the above-mentioned magnetic recording medium with the above-mentioned substrate is also suitable for a magnetic recording device equipped with a DFH mechanism after the flying height is extremely narrowed.

[0089] The size of the magnetic recording medium substrate (e.g., glass substrate for magnetic disk) and the magnetic recording medium (e.g., magnetic disk) is not particularly limited. For example, since the recording density can be high, the medium and the substrate can be miniaturized. For example, the nominal diameter can certainly be 2.5 inches, and further can be set to a small diameter (e.g., 1 inch, 1.8 inches), or 3 inches, 3.5 inches, etc.

[0090] The magnetic recording medium is composed of the glass for a magnetic recording medium substrate according to one embodiment of the present invention, and thus can have the glass properties described above for the glass. In addition, the magnetic recording medium can preferably exhibit excellent impact resistance.

[0091] [Glass spacer for magnetic recording and reproducing device]

[0092] One embodiment of the present invention relates to a glass spacer for a magnetic recording and reproducing device comprising amorphous glass, wherein the SiO2 content of the amorphous glass is 54 mol% or more and 62 mol% or less,

[0093] The MgO content is 15 mol% to 28 mol%,

[0094] The Li2O content is 0.2 mol% or more, and

[0095] The Na2O content is 5 mol% or less.

[0096] Magnetic recording media can be used in magnetic recording and reproducing devices to magnetically record and / or reproduce information. Magnetic recording and reproducing devices are usually equipped with spacers because the magnetic recording medium is fixed to the shaft of a shaft motor and / or in order to maintain the distance between two or more magnetic recording media. In recent years, a solution using a glass spacer has been proposed as the above-mentioned spacer. For reasons similar to those previously described in detail about the glass for magnetic recording medium substrates, it is also expected that the glass spacer has excellent chemical resistance and impact resistance. In this regard, the glass having the above-mentioned composition is suitable as a glass spacer for a magnetic recording and reproducing device because it can have excellent chemical resistance and impact resistance.

[0097] The spacer for magnetic recording and reproducing device is an annular component, and the composition and manufacturing method of the glass spacer are well known. In addition, regarding the manufacturing method of the glass spacer, reference can also be made to the above-mentioned description of the manufacturing method of the glass for magnetic recording medium substrate and the manufacturing method of the magnetic recording medium substrate. In addition, regarding the glass composition, glass properties and other details of the glass spacer for magnetic recording and reproducing device of one embodiment of the present invention, reference can also be made to the above-mentioned description of the glass for magnetic recording medium substrate, magnetic recording medium substrate and magnetic recording medium of one embodiment of the present invention.

[0098] It should be noted that the glass spacer for magnetic recording and reproducing device can be composed of the above-mentioned glass, or can also be composed of a film such as a conductive film provided on the surface of the above-mentioned glass. For example, in order to remove the static electricity generated when the magnetic recording medium rotates, a conductive film such as NiP alloy can be formed on the surface of the glass spacer by plating, dipping, evaporation, sputtering, etc. In addition, the glass spacer can be polished to improve the surface smoothness (for example, the average surface roughness is less than 1 μm), thereby enhancing the closeness between the magnetic recording medium and the spacer, and suppressing the occurrence of position deviation.

[0099] [Magnetic recording and reproducing device]

[0100] One aspect of the present invention relates to a magnetic recording and reproducing device comprising

[0101] A magnetic recording medium according to one embodiment of the present invention; and

[0102] Glass spacer according to one embodiment of the present invention

[0103] At least one of .

[0104] The magnetic recording and reproducing device includes at least one magnetic recording medium and at least one spacer, and further generally includes a spindle motor for rotationally driving the magnetic recording medium and at least one magnetic head for recording and / or reproducing information on the magnetic recording medium.

[0105] The magnetic recording and reproducing device of one embodiment of the present invention may include a magnetic recording medium of one embodiment of the present invention as at least one magnetic recording medium, or may include two or more magnetic recording media of one embodiment of the present invention. The magnetic recording and reproducing device of one embodiment of the present invention may include a glass spacer of one embodiment of the present invention as at least one spacer, or may include two or more glass spacers of one embodiment of the present invention. From the viewpoint of suppressing the phenomenon caused by the difference in thermal expansion coefficients of the two (for example, the reduction in stability during rotation caused by the strain of the magnetic recording medium and the positional deviation of the magnetic recording medium), it is preferred that the difference between the thermal expansion coefficient of the magnetic recording medium and the thermal expansion coefficient of the spacer is small. From this viewpoint, the magnetic recording and reproducing device of one embodiment of the present invention preferably includes a magnetic recording medium of one embodiment of the present invention as at least one magnetic recording medium, and further includes a magnetic recording medium of one embodiment of the present invention as more magnetic recording media when including two or more magnetic recording media, and preferably includes a glass spacer of one embodiment of the present invention as at least one spacer, and further includes a glass spacer of one embodiment of the present invention as more spacers when including two or more spacers. Furthermore, for example, in the magnetic recording and reproducing device according to one aspect of the present invention, the glass constituting the magnetic recording medium substrate included in the magnetic recording medium and the glass constituting the glass spacer have the same glass composition.

[0106] The magnetic recording and reproducing device of one embodiment of the present invention only needs to include at least one of the magnetic recording medium of one embodiment of the present invention and the glass spacer of one embodiment of the present invention, and the known technology of the magnetic recording and reproducing device can be applied to the other contents. In one embodiment, as a magnetic head, an energy-assisted magnetic recording head having an energy source (such as a heat source such as a laser source, microwave, etc.) for assisting magnetization reversal (assisting the writing of magnetic signals), a recording element part and a reproducing element part can be used. A magnetic recording and reproducing device of an energy-assisted recording method including such an energy-assisted magnetic recording head is useful as a magnetic recording and reproducing device with high recording density and high reliability. In addition, when manufacturing a magnetic recording medium used in a magnetic recording and reproducing device of an energy-assisted recording method such as a thermally assisted recording method having a thermally assisted magnetic recording head (the thermally assisted magnetic recording head has a laser source, etc.), sometimes a magnetic recording layer containing a magnetic material with high magnetic anisotropy energy is formed on a magnetic recording medium substrate. In order to form such a magnetic recording layer, film formation is usually performed at a high temperature, or heat treatment is performed at a high temperature after film formation. As a magnetic recording medium substrate that can withstand such high temperature processing and has high heat resistance, the magnetic recording medium substrate of one embodiment of the present invention is preferred. However, the magnetic recording and reproducing device of one embodiment of the present invention is not limited to an energy-assisted magnetic recording and reproducing device.

[0107] Example

[0108] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the embodiments shown in the examples.

[0109] [Examples No. 1 to No. 139]

[0110] In order to obtain glass of the composition shown in Table 1 (Table 1-1 to Table 1-7) below, raw materials such as oxides, carbonates, nitrates, sulfates, hydroxides, etc. are weighed and mixed to obtain a blended raw material. The blended raw material is put into a melting tank and heated and melted in the range of 1400°C to 1600°C. After the obtained molten glass is kept at 1400°C to 1550°C for 6 hours in a clarification tank, the temperature is lowered (cooled) in the range of 1200°C to 1400°C and kept for 1 hour, the molten glass is molded to obtain glass (amorphous oxide glass) used for the following evaluation.

[0111] <Evaluation of Glass Properties>

[0112] (1) Glass transition temperature (Tg), average linear expansion coefficient (α)

[0113] The glass transition temperature Tg and the average linear expansion coefficient α at 100° C. to 300° C. of each glass were measured using a thermomechanical analyzer (TMA).

[0114] (2) Young's modulus

[0115] The Young's modulus of each glass was measured by an ultrasonic method.

[0116] (3) Specific gravity

[0117] The specific gravity of each glass was measured by the Archimedean method.

[0118] (4) Specific elastic modulus

[0119] The specific elastic modulus was calculated from the Young's modulus obtained in (2) and the specific gravity obtained in (3).

[0120] (5) Glass stability

[0121] 100g of each glass was placed in a platinum crucible, and each crucible was placed in a heating furnace with the furnace temperature set at 1250°C, 1300°C or 1350°C, and placed for 16 hours while maintaining the furnace temperature (holding test). After 16 hours, the crucible was taken out from the heating furnace, and the glass in the crucible was transferred to a refractory and cooled to room temperature. The presence or absence of crystallization of each glass was observed with an optical microscope (magnification 40 to 100 times), and evaluated according to the following criteria.

[0122] A: There is no crystallization on the glass surface, inside and at the interface of the bottom of the platinum crucible.

[0123] B: The number of crystals with a diameter of tens of microns at the interface between the glass surface and the bottom of the platinum crucible is less than 10 / 100g

[0124] C: There are more than 10 crystals with a diameter of tens of microns / 100g at the interface between the glass surface and the bottom of the platinum crucible.

[0125] D: There are crystals inside the glass

[0126] E: There are crystals on the glass surface, inside and at the interface of the bottom of the platinum crucible.

[0127] F: The glass has a lot of crystals and is a bit turbid

[0128] G: Glass is cloudy

[0129] <Fabrication of Magnetic Recording Medium Substrate>

[0130] (1) Preparation of substrate blanks

[0131] Next, a disk-shaped substrate blank is produced according to the following method A or B. In addition, according to the same method, a glass blank for producing a glass spacer for a magnetic recording and reproducing device can be obtained.

[0132] (Method A)

[0133] About the glass of the composition shown in the following table, the clarified, homogenized molten glass is received by the lower mold for compression molding while flowing out from the outflowing tube blank at a constant flow rate, and the outflowing molten glass is cut off with a cutting blade, so that a predetermined amount of molten glass block can be obtained on the lower mold. Then the lower mold carrying the molten glass block is immediately moved out from the bottom of the tube blank, and the upper mold and the body mold relative to the lower mold are used to compression mold into a thin-walled disc with a diameter of 99mm and a thickness of 0.7mm. After the compression molded product is cooled to a temperature that does not deform, it is taken out from the mold and annealed to obtain a substrate blank. It should be noted that in the above-mentioned molding, more than two lower molds are used to successively mold the outflowing molten glass into a disc-shaped substrate blank.

[0134] (Method B)

[0135] Regarding the glass of the composition shown in the table below, the clarified and homogenized molten glass was continuously cast from the top into the through hole of a heat-resistant casting mold provided with a cylindrical through hole, formed into a circle and taken out from the bottom of the through hole. After annealing the taken out glass, the glass was sliced ​​at regular intervals in a direction perpendicular to the cylindrical axis using a multi-wire cutter to produce a disc-shaped substrate blank.

[0136] It should be noted that, in this embodiment, the above-mentioned methods A and B are used, but as a method for manufacturing a disk-shaped substrate blank, the following methods C and D are also suitable. In addition, the following methods C and D are also suitable as a method for manufacturing a glass blank for manufacturing a glass spacer for a magnetic recording and reproducing device.

[0137] (Method C)

[0138] The substrate blank may be obtained by pouring the molten glass onto a float bath and forming it into a sheet of glass (float forming), and then annealing the sheet of glass and then digging out a disk of glass from the sheet of glass.

[0139] (Method D)

[0140] Alternatively, the substrate blank may be obtained by forming molten glass into a sheet of glass by an overflow down-draw method (fusion method), annealing the sheet of glass, and then digging out a disk of glass from the sheet of glass.

[0141] (2) Preparation of glass substrate

[0142] A through hole is drilled in the center of the substrate blank obtained by the above methods, and the outer and inner circumferences are ground, and the main surface of the disk is polished and polished (mirror surface grinding) to make a magnetic disk glass substrate with a diameter of 97mm and a thickness of 0.5mm. In addition, by the same method, the glass blank used to make a glass spacer for a magnetic recording and reproducing device can be processed into a glass spacer for a magnetic recording and reproducing device.

[0143] The glass substrate obtained above was cleaned with a 1.7% by mass silicic acid (H2SiF) aqueous solution and then a 1% by mass potassium hydroxide aqueous solution, and then rinsed with pure water and dried. When the surface of the substrate made of the glass of the embodiment was magnified and observed, no surface roughness was found, and it was a smooth surface.

[0144] Four glass substrates were prepared for each glass composition, and each was used for the following evaluation (1), (2) or (3) or for the preparation of a magnetic recording medium described later.

[0145] <Evaluation of Magnetic Recording Medium Substrate>

[0146] (1) Etching rate (chemical resistance)

[0147] In order to make an unetched portion on a part of the main surface of each disk glass substrate produced above, a mask treatment is performed, and the glass substrate in this state is immersed in a potassium hydroxide aqueous solution with a concentration of 0.5 mass % and a liquid temperature maintained at 50°C for a specified time. After that, the glass substrate is lifted from the aqueous solution, the mask is removed, and the depth of the drop between the portion that is not in contact with the aqueous solution due to the mask and the portion that is in contact with the aqueous solution without the mask is measured. The depth of the drop is equivalent to the etching amount (etching depth) of the glass in a specified time. The etching amount is divided by the immersion time to calculate the etching amount per unit time, that is, the etching rate (chemical resistance).

[0148] The etching rate (chemical resistance) obtained for each magnetic disk glass substrate of the example was 0.5 nm / min or less.

[0149] (2) Substrate deformation at 70G impact

[0150] As an evaluation of impact resistance, the deformation of the substrate when subjected to a 70G (G is the acceleration of gravity) impact is determined for each of the above-produced glass substrates for magnetic disks by the following evaluation method. In HDDs, the interval between the magnetic disk and the ramp is usually about 0.25 mm. Therefore, as an evaluation of impact resistance, when a large impact (e.g., an impact of 70 times the acceleration of gravity (70G)) is applied, the deformation of the outer peripheral end of the magnetic disk glass substrate is preferably less than 0.25 mm, and more preferably less than 0.25 mm. That is, the deformation of the substrate when subjected to a 70G impact determined by the following method is preferably less than 0.25 mm, and more preferably less than 0.25 mm. The deformation of the substrate when subjected to a 70G impact can be, for example, more than 0.20 mm, but is also preferably less than this value.

[0151] (Evaluation method)

[0152] The inner diameter hole of the magnetic disk glass substrate was inserted into a fixed shaft fastened to a test table of an impact test device, and end caps were attached, and each end cap was fastened and fixed with a screw.

[0153] Adjust the height of the test bench of the impact test device (the drop distance of the test bench) and the cushioning material installed on the base when the test bench falls, and adjust to the specified impact force. The cushioning material is adjusted in a micro-adjustment. The impact force or impact action time is measured by amplifying the output power signal of the acceleration sensor and the acceleration sensor installed on the test bench with an amplifier, and processing the output power signal of the amplifier with a personal computer to obtain the respective values. Change the test bench height or the cushioning material conditions, make the test bench fall several times, calculate the impact force and impact action time at this time, and determine the test bench height or the cushioning material conditions to obtain the specified impact force.

[0154] After determining the height of the test bench or the conditions of the buffer material, the amount of vibration (displacement) of the outer peripheral end of the disk glass substrate during impact is confirmed using a high-speed camera. Specifically, a high-brightness lighting device is used for high-resolution photography, and the instantaneous action of the outer peripheral end of the disk glass substrate when the impact force is applied is photographed from the read image (1 frame: 1 / 10,000 second, shooting time: 30 milliseconds). The behavior of the outer peripheral end of the disk glass substrate is captured and digitized from the results of the photography, and the maximum vibration (displacement) is calculated. The elapsed time after the impact force is applied is taken as the horizontal axis, and the displacement of the outer peripheral end of the disk glass substrate is taken as the vertical axis and a graph is drawn. On the vertical axis, negative values ​​are displacements downward, and positive values ​​are displacements upward. Due to the impact during the fall, the outer peripheral end of the disk glass substrate is displaced downward by a displacement of Y0 (negative value) just after falling, and is displaced upward by a displacement of Y1 (positive value) immediately thereafter due to the recoil, and this is repeated while gradually attenuating. Therefore, the maximum value of the downward displacement is the displacement Y0 just after falling, and the maximum value of the upward displacement is the upward displacement Y1 immediately after the displacement Y0 downward. The displacement when the impact force is applied is calculated as "Y1-Y0". Since the displacement "Y1-Y0" at the time of 70G impact is a relatively small value, it is difficult to calculate the displacement with high accuracy. Here, the magnitude of the impact force and the displacement "Y1-Y0" are proportional, so the magnitude of the impact force is changed within a range greater than 70G, and the displacement "Y1-Y0" at each impact force is calculated. A graph is drawn with the displacement "Y1-Y0" as the vertical axis and the magnitude of the impact force as the horizontal axis. An approximate straight line is drawn using the least squares method, and the displacement "Y1-Y0" of 70G is calculated using the linear equation of the approximate straight line.

[0155] The displacement "Y1-Y0" shown in Table 2 is the substrate deformation amount during a 70G impact obtained from the displacement "Y1-Y0" value under each impact force when the impact force is set to four different values ​​of 120G, 140G, 170G, and 190G.

[0156] [Comparative Example 1]

[0157] A magnetic disk glass substrate was prepared using the same method as in the above-mentioned embodiment for the glass of the composition of Example 3 shown in Table 3 of Patent Document 1 (Japanese Patent Publication No. 2002-348141). The deformation of the substrate under a 70G impact was determined using the same method as in the above-mentioned embodiment for the prepared magnetic disk glass substrate.

[0158] The above results are shown in Table 2 (Tables 2-1 to 2-7).

[0159]

[0160]

[0161]

[0162]

[0163]

[0164]

[0165]

[0166]

[0167]

[0168]

[0169]

[0170]

[0171]

[0172]

[0173] [Manufacturing of magnetic recording media (disks)]

[0174] An adhesion layer, a base layer, a magnetic recording layer, a protective layer, and a lubricating layer were sequentially formed on the main surface of the magnetic disk glass substrate produced as described above according to the following method to obtain a magnetic disk.

[0175] First, using a film forming apparatus that has been evacuated, an adhesion layer, a base layer, and a magnetic recording layer are sequentially formed in an Ar atmosphere by a DC magnetron sputtering method.

[0176] At this time, a CrTi target was used to form a film so that the adhesion layer became an amorphous CrTi layer with a thickness of 20 nm. Next, a 10 nm thick layer composed of MgO was formed as a base layer. In addition, a FePtC or CoPtC target was used to form a film at a film forming temperature of 200°C to 400°C so that the magnetic recording layer became a granular layer of FePt or CoPt with a thickness of 10 nm.

[0177] After the magnetic recording layer is formed, the magnetic disk is transferred from the film forming device to a heating furnace for annealing. The temperature in the heating furnace during annealing is set in the range of 500°C to 700°C. Through this annealing process, L 10 It should be noted that the magnetic particles of CoPt alloy or FePt alloy with regular structure are not limited to the above. 10Just heat it in a regular structure.

[0178] Next, a protective layer of 3 nm made of hydrogenated carbon was formed by CVD using ethylene as a material gas. Thereafter, a lubricating layer made of PFPE (perfluoropolyether) was formed by dip coating. The film thickness of the lubricating layer was 1 nm.

[0179] By the above manufacturing process, a magnetic disk is obtained. The obtained magnetic disk is mounted on a hard disk drive having a DFH mechanism, and when magnetic signals are recorded and reproduced in the recording area on the main surface of the magnetic disk at a recording density of 1000Gbit per 1 square inch, no phenomenon (collision failure) of magnetic head colliding with the magnetic disk surface is confirmed.

[0180] In addition, a spacer (a glass spacer with a NiP alloy film) having a NiP alloy conductive film formed on the surface of a glass spacer (the glass spacer is obtained by the above manufacturing process using the glass of the embodiment) is mounted on a hard disk drive having a DFH mechanism. When magnetic signals are recorded and reproduced at a recording density of 1000 Gbit per square inch in a recording area on the main surface of a magnetic disk prepared separately using a substrate 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 (collision failure) is confirmed.

[0181] In addition, using the same glass material as one embodiment of the present invention, the above-made magnetic disk and the above-made glass spacer with NiP alloy film were mounted on a hard disk drive having a DFH mechanism, and when magnetic signals were recorded and reproduced in the recording area on the main surface of the magnetic disk at a recording density of 1000 Gbit per square inch, no phenomenon (collision failure) of collision between the magnetic head and the magnetic disk surface was confirmed. Here, since the glass substrate included in the above-mentioned magnetic disk and the above-mentioned glass spacer are made of the same glass material, the phenomenon caused by the difference in the above-mentioned thermal expansion coefficient will not occur.

[0182] According to one aspect of the present invention, a magnetic recording medium suitable for high-density recording can be provided.

[0183] Finally, summarize the above methods.

[0184] According to one embodiment, a glass for a magnetic recording medium substrate is provided, which is an amorphous glass having a SiO2 content of not less than 54 mol% and not more than 62 mol%, a MgO content of not less than 15 mol% and not more than 28 mol%, a Li2O content of not less than 0.2 mol% and a Na2O content of not more than 5 mol%.

[0185] The above-mentioned glass can have excellent chemical resistance and excellent impact resistance.

[0186] In one embodiment, in the above-mentioned glass, the molar ratio of the total content of SiO2 and MgO to the content of Li2O [(SiO2+MgO) / Li2O] can be 13 or more.

[0187] In one embodiment, in the above-mentioned glass, the total content of SiO2, MgO, Li2O, Al2O3 and CaO (SiO2+MgO+Li2O+Al2O3+CaO) can be 93 mol% or more.

[0188] In one embodiment, in the glass, the molar ratio of the total content of Al2O3 and CaO to the content of MgO [(Al2O3+CaO) / MgO] may be 0.55 or more.

[0189] In one embodiment, in the glass, a molar ratio of MgO content to CaO content (MgO / CaO) may be 6 or more.

[0190] In one embodiment, when the glass is immersed in a 0.5 mass % fluorosilicic acid aqueous solution maintained at 50° C. for a predetermined time, the etching amount per unit time (etching rate (chemical resistance)) can be 0.5 nm / min or less.

[0191] According to one embodiment, a magnetic recording medium substrate comprising the above-mentioned glass for a magnetic recording medium substrate is provided.

[0192] In one embodiment, the magnetic recording medium substrate may have a substrate deformation amount of 0.25 mm or less when subjected to a 70G impact.

[0193] According to one embodiment, a magnetic recording medium including the magnetic recording medium substrate and a magnetic recording layer is provided.

[0194] According to one method, a glass spacer for a magnetic recording and reproducing device is provided, wherein the glass spacer comprises amorphous glass having a SiO2 content of not less than 54 mol% and not more than 62 mol%, a MgO content of not less than 15 mol% and not more than 28 mol%, a Li2O content of not less than 0.2 mol% and a Na2O content of not more than 5 mol%.

[0195] According to one embodiment, there is provided a magnetic recording and reproducing device including at least one of the magnetic recording medium and the glass spacer for a magnetic recording and reproducing device.

[0196] The embodiments disclosed this time should be understood in all respects as illustrative rather than restrictive. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0197] For example, the glass for a magnetic recording medium substrate and the glass spacer for a magnetic recording and reproducing device according to one embodiment of the present invention can be produced by adjusting the composition described in the specification with respect to the glass composition exemplified above.

[0198] Furthermore, it is of course possible to arbitrarily combine two or more of the items exemplified or described as preferred ranges in the specification.

Claims

1. A glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing device, wherein the SiO2 content is 54 mol% or more and 62 mol% or less, The MgO content is 15 mol% to 28 mol%, Li2O content is 0.2 mol% or more, Na2O content is less than 5 mol%, CaO content is 0 mol%, The TiO2 content is 0 mol% or more and 1 mol% or less, and The molar ratio of the total content of SiO2 and MgO to the content of Li2O, i.e. (SiO2+MgO) / Li2O, is 15 or more. The molar ratio of CaO content to Al2O3 content, i.e. CaO / Al2O3, is 0. The molar ratio of MgO content to Li2O content, i.e., MgO / Li2O, is 10.50 or more, In the glass composition based on oxides, the total of all oxides constituting the glass is 100 mol %. Amorphous glass that satisfies the following (1), (1) The molar ratio of the total content of Al2O3 and CaO to the content of MgO, that is, (Al2O3+CaO) / MgO, is 0.60 or more.

2. The glass according to claim 1, wherein: The total content of SiO2, MgO, Li2O, Al2O3 and CaO, that is, SiO2+MgO+Li2O+Al2O3+CaO is more than 93 mol%.

3. A magnetic recording medium substrate, comprising the glass according to claim 1 or 2. 4 . A magnetic recording medium comprising the magnetic recording medium substrate according to claim 3 and a magnetic recording layer.

5. A glass spacer for a magnetic recording and reproducing device, wherein: The glass spacer comprises the glass according to claim 1 or 2. 6 . A magnetic recording and reproducing device comprising at least one of the magnetic recording medium according to claim 4 and the glass spacer for a magnetic recording and reproducing device according to claim 5 .

Images