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

Abstract

The invention relates to glass, a magnetic recording medium substrate, a magnetic recording medium, a glass spacer for a magnetic recording / reproducing device, and a magnetic recording / reproducing device. The invention provides a glass for a glass spacer for a magnetic recording medium substrate or a magnetic recording / reproducing device. The present invention relates to a glass which has a SiO2 content of 56 mol% or more, a MgO content of 15 mol% to 28 mol% (inclusive), a Li2O content of 0.2 mol% or more, a Na2O content of 5 mol% or less, a total content of Al2O3, MgO and CaO of 29.0 mol% to 36.50 mol% (inclusive), a total content of SiO2, MgO, Li2O, Al2O3 and CaO of 95 mol% or more, and a molar ratio of the total content of SiO2 and MgO to the content of Li2O of 13 or more. And an amorphous glass in which the molar ratio of the CaO content to the total content of Al2O3 and MgO is 0.10 or less.

Description

[0001] This application is a divisional application. The Chinese national application number of the original application is 202080052827.0, the application date is July 22, 2020, and the name of the invention is "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". Technical Field

[0002] 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

[0003] As substrates (magnetic recording medium substrates) used for magnetic recording media such as hard disks, substrates made of aluminum alloys have been used in the past. However, aluminum alloy substrates have been pointed out to have disadvantages such as being easily deformed. Therefore, magnetic recording medium substrates made of glass are now widely used (for example, referring to patent documentation 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-814134 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] Magnetic recording medium substrates are typically cleaned with acids, alkalis, or the like to remove foreign matter adhering to the substrate surface during the manufacturing process. However, if the glass constituting the substrate has insufficient chemical resistance, even if the substrate surface is smoothed during the manufacturing process, surface roughness may result from cleaning. Therefore, it is desirable that the glass used for magnetic recording medium substrates have excellent chemical resistance.

[0009] Furthermore, it is also desired that the glass for a magnetic recording medium substrate has excellent impact resistance. This is for the following reasons.

[0010] Magnetic recording media are usually installed inside hard disk drives (HDDs) that are assembled into machines such as personal computers. Inside the HDD, two or more magnetic recording media (disks) are mounted on the rotating shaft of the shaft motor. Data is written to or read from the magnetic recording layer of the high-speed rotating magnetic recording media inside the HDD through an actuator assembled into the HDD. When the magnetic recording medium rotates at high speed for such data writing or reading, if a large impact (such as a drop or other impact) is applied to the HDD, the impact causes the magnetic recording medium inside the HDD to temporarily deform. When rotating at high speed, it collides with a component called a ramp, which may cause the magnetic recording medium to break. In order to prevent such damage, it is desired that the magnetic recording medium is not easily deformed even when subjected to an impact, that is, it has excellent impact resistance. For HDDs, although the recording capacity can be increased by reducing the thickness of each magnetic recording medium and by mounting more magnetic recording media on the HDD, generally speaking, if the thickness of the glass is reduced, it is easy to deform, and there is a tendency for the above-mentioned damage to occur. 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 an HDD and suppression of the above-mentioned breakage.

[0011] About above content, put down in writing in patent documentation 1 (Japanese Patent Laid-Open 2002-814134 communique): according to the glass put down in writing in patent documentation 1, by cleaning glass surface with acidic liquid, can make its surface clean and not make its deterioration (the 0068th paragraph of patent documentation 1 etc.).But according to the research of the inventor, from the viewpoint of previously described breakage that prevents, the impact resistance of the glass put down in writing in patent documentation 1 is insufficient.On the other hand, as the material that impact resistance is high, known sintered glass is arranged, but the manufacturing process of sintered glass is complicated.In addition, realizing the desired high smoothness of magnetic recording medium substrate by sintered glass is not easy.

[0012] 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.

[0013] Means for solving problems

[0014] 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%.

[0015] The glass for a magnetic recording medium substrate has the above-mentioned glass composition and can have excellent chemical resistance and excellent impact resistance.

[0016] Effects of the Invention

[0017] 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 including 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

[0018] [Glass for magnetic recording medium substrates]

[0019] The above-mentioned glass is amorphous glass having the composition described above. Unlike crystallized glass, amorphous glass does not substantially contain a crystalline phase and exhibits a glass transition phenomenon when the temperature is increased.

[0020] Furthermore, the glass may be an amorphous oxide glass. Oxide glass refers to glass whose main network-forming component is an oxide.

[0021] Hereinafter, the above-mentioned glass will be described in more detail.

[0022] <Glass Composition>

[0023] In the present invention and this specification, glass composition is expressed as an oxide-based glass composition. Here, "oxide-based glass composition" refers to the glass composition calculated based on the substances that completely decompose during melting of the glass raw materials and exist as oxides in the glass. Unless otherwise specified, glass composition is expressed on a molar basis (mol %, molar ratio).

[0024] The glass composition of the present invention and this specification can be determined using methods such as ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Quantitative analysis is performed on each element individually using ICP-AES. The analyzed values are then converted to oxide values. The ICP-AES analyzed values may contain a measurement error of, for example, approximately ±5% of the analyzed value. Therefore, the values expressed as oxides converted from the analyzed values may also contain an error of approximately ±5%.

[0025] In the present invention and this specification, "0% content of a component" or "not contained" or "not introduced" means that the component is substantially not contained and the content of the component is at an impurity level. For example, "less than an impurity level" means less than 0.01%.

[0026] 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%.

[0027] Hereinafter, the glass composition of the above-mentioned glass will be described in more detail.

[0028] SiO2 is a network-forming component of glass and has the effect of improving the stability of glass. In addition, SiO2 is also a component that helps to improve chemical resistance. From the perspective 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 substrate surface is usually polished. From the perspective of improving the smoothness of the polished magnetic recording medium substrate surface, it is also preferred that the SiO2 content is 54% or more. From the above perspectives, 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, particularly preferably 59% or more, and particularly further preferably 60% or more. In addition, from the perspective of the solubility of the glass, the SiO2 content is 62% or less, preferably 61% or less.

[0029] MgO has the effects of increasing the Young's modulus of glass, increasing the coefficient of thermal expansion, and optimizing the meltability and formability of glass. From the perspective of improving impact resistance, the MgO content is 15% or more. From the perspective of increasing Young's modulus and increasing the specific elastic modulus, the MgO content is also preferably 15% or more. From the above perspectives, the MgO content is preferably 16% or more, and more preferably 17% or more. Furthermore, from the perspective 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, even more preferably 24.5% or less, even more preferably 24% or less, even more preferably 23.5% or less, particularly preferably 23% or less, even more preferably 22.5% or less, even more preferably 22% or less, still more preferably 20% or less, and particularly preferably 19% or less.

[0030] Even 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, it also plays a role in ion exchange during chemical strengthening. From the perspective 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, even more preferably 2.5% or more, even more preferably 3% or more, even more preferably 3.5% or more, and even more preferably 4% or more. Furthermore, from the perspective of further improving chemical resistance and impact resistance, as well as improving the smoothness of the surface of the magnetic recording medium substrate after polishing, the Li2O content is preferably 6% or less, more preferably 5% or less.

[0031] 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, even more preferably 14 or more, and even more preferably 15 or more. From the viewpoint of devitrification resistance and solubility, the molar ratio [(SiO2 + MgO) / Li2O] is preferably 100 or less, more preferably 50 or less, even more preferably 30 or less, even more preferably 25 or less, and even more preferably 20 or less.

[0032] Na2O is a component that has the following functions: improving the solubility of glass, increasing the thermal expansion coefficient, 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 performs ion exchange during chemical strengthening. From the perspective of improving impact resistance, the Na2O content is 5% or less. From the perspective of increasing Young's modulus and increasing specific elastic modulus, the Na2O content is also preferably 5% or less. From the above perspectives, the Na2O content is preferably 4% or less, more preferably 3% or less, further preferably 2% or less, and even 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.

[0033] B2O3 is a network-forming component of glass, reducing the specific gravity of glass and improving its meltability. To further enhance impact resistance, specific elastic modulus, and 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 greater, or greater than 0%, or 0.5% or greater.

[0034] Al2O3 is a network-forming component of glass, improving heat resistance. To improve the meltability of glass, the Al2O3 content is preferably 19% or less, more preferably 18% or less, even more preferably 17% or less, still more preferably 16% or less, and even more preferably 15% or less. Furthermore, to further enhance impact resistance, Young's modulus, and specific elastic modulus, the Al2O3 content is preferably 9% or more, more preferably 10% or more, even more preferably 11% or more, and even more preferably 12% or more.

[0035] BaO improves the meltability, formability, and stability of glass, and increases the thermal expansion coefficient. To reduce the specific gravity of the glass, increase Young's modulus, improve the specific elastic modulus, and further enhance 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 greater, or greater than 0%, or 0.5% or greater.

[0036] CaO has the effects of increasing the Young's modulus and specific elastic modulus of glass, increasing the coefficient of thermal expansion, and optimizing the meltability and formability of glass. In one embodiment, the CaO content can be 0%, or 0% or more, or greater than 0%. In another embodiment, to achieve the above-mentioned effects, the CaO content is preferably 0.5% or more, more preferably 1% or more, and even more preferably 1.5% or more. In addition, to further improve 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.

[0037] 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.

[0038] From the perspective 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 greater, more preferably 0.57 or greater. Furthermore, the lower limit is preferably 0.58 or greater, 0.59 or greater, 0.60 or greater, 0.61 or greater, 0.62 or greater, 0.625 or greater, 0.63 or greater, 0.65 or greater, 0.70 or greater, 0.75 or greater, and 0.80 or greater. Furthermore, from the perspective 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.

[0039] 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, further preferably 0.30 or less, further preferably 0.24 or less, and even more preferably 0.20 or less. Furthermore, the molar ratio (CaO / Al2O3) may be, for example, 0 or greater, greater than 0, or 0.1 or greater.

[0040] From the perspective of increasing Young's modulus, increasing specific elastic modulus, and further improving impact resistance, 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. Furthermore, the molar ratio may be, for example, 0 or greater, greater than 0, 0.01 or greater, or 0.03 or greater.

[0041] From the perspective of further improving impact resistance, the molar ratio of MgO content to Li2O content (MgO / Li2O) is preferably 2.3 or greater, more preferably 2.5 or greater, even more preferably 2.7 or greater, and even more preferably 3.0 or greater. From the perspective of improving the meltability of the glass, the molar ratio (MgO / Li2O) is preferably 28 or less, more preferably 26 or less, even more preferably 24 or less, and even more preferably 22 or less.

[0042] From the perspective 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 greater, more preferably 30% or greater, even more preferably 31% or greater, still more preferably 32% or greater, and even more preferably 33% or greater. Furthermore, 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.

[0043] 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-mentioned total content is also preferably 93% or more. From the above-mentioned 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-mentioned total content (SiO2 + MgO + Li2O + Al2O3 + CaO) can be less than 100% or less than 99%.

[0044] SrO improves the meltability, formability, and stability of glass, and increases the thermal expansion coefficient. To reduce 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 greater, or 0.5% or greater.

[0045] K₂O is a component that improves the meltability and formability of glass and increases the coefficient of thermal expansion. From the perspectives 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 even more preferably 0.5% or less. In one embodiment, the K₂O content may be 0%, or may be 0% or greater, or greater than 0%.

[0046] TiO2 is a component that improves glass stability. From the perspective 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 greater than 0%, or 0.5% or more.

[0047] ZnO improves meltability. From the perspectives of reducing specific gravity, increasing Young's modulus, increasing specific elastic modulus, and further improving impact resistance, the ZnO content is preferably 2% or less, more preferably 1% or less. In one embodiment, the ZnO content may be 0%, 0% or greater, or 0.5% or greater.

[0048] From the perspective of reducing 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, still more preferably less than 3%, still more preferably 2% or less, and still more preferably 1% or less. In one embodiment, the ZrO2 content may be 0%, 0% or more, or greater than 0%, or 0.5% or more.

[0049] From the perspective of reducing 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 may be 0%, 0% or more, or greater than 0%, or 0.5% or more.

[0050] As the content expressed as a percentage other than Fe2O3, the Fe2O3 content of the above-mentioned glass may 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 percentage other than Fe2O3 is 0 mol%). The Fe2O3 content expressed as a percentage other than Fe2O3 refers to the value of the amount of Fe2O3 contained in the glass expressed as a mole percentage when the total content of the glass components other than Fe2O3 is set to 100 mol%.

[0051] The glass may contain one or more elements selected from the group consisting of Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er.

[0052] F is a component that is volatile during melting and causes striae, so the glass preferably does not contain F. Containing F is also preferred from the viewpoint of suppressing corrosion of the melting furnace, suppressing a decrease in Young's modulus, and suppressing a decrease in specific elastic modulus.

[0053] Pb, Cd, and As are substances that adversely affect the environment, and therefore, their introduction is preferably avoided.

[0054] From the perspective of achieving 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 setting the total content of SnO2 and CeO2 to 0.05% or more, a sufficient clarification effect can be achieved and the presence of bubbles can be reduced. In addition, by setting the total content (SnO2 + CeO2) to 2% or less, it is possible to prevent molten glass from being ejected during glass melting, thereby 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 preferably 0.50% or less.

[0055] SnO2 promotes clarification of glass at relatively high melting temperatures (temperatures in the range of approximately 1400-1600°C). In one embodiment, SnO2 is preferably introduced into the glass to remove bubbles from high-melting-temperature glass, as the use of environmentally friendly clarifiers such as Sb2O3 and arsenic acid is restricted. To achieve a clarification effect, the SnO2 content is preferably 0.01% or greater, more preferably 0.05% or greater, even more preferably 0.10% or greater, even more preferably 0.15% or greater, and even more preferably 0.20% or greater. 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.

[0056] CeO2, like SnO2, exhibits a glass-clarifying effect. Because CeO2 absorbs oxygen at relatively low glass melting temperatures (a temperature range of approximately 1200-1400°C) and binds it as a glass component, in one embodiment, CeO2 is preferably introduced into the glass as a clarifier. To achieve a clarification effect, the CeO2 content is preferably 0.01% or greater, more preferably 0.05% or greater, even more preferably 0.08% or greater, and even more preferably 0.10% or greater. 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 enables a clarification effect over a wide temperature range. Therefore, in one embodiment, the glass preferably contains both SnO2 and CeO2.

[0057] From the perspective of reducing environmental impact, it is desirable to control the use of Sb2O3. The Sb2O3 content in the glass is preferably within a range of 0 to 0.5%. The Sb2O3 content is more preferably 0.3% or less, further preferably 0.1% or less, even more preferably 0.05% or less, and even more preferably 0.02% or less. It is particularly preferred that no Sb2O3 be present.

[0058] To obtain a predetermined glass composition, the glass can be produced by weighing and blending glass raw materials such as oxides, carbonates, nitrates, sulfates, and hydroxides, thoroughly mixing them, heating and melting them in a melting vessel, for example, within a temperature range of 1400°C to 1600°C, and then clarifying and stirring them to fully eliminate bubbles and homogenize them, and then molding the resulting molten glass. For example, it is preferred that the glass raw materials be heated and melted in a melting tank at 1400°C to 1550°C, the resulting molten glass be heated and maintained at 1450°C to 1600°C in a clarifier, then cooled and allowed to flow out at 1200°C to 1400°C for molding.

[0059] <Glass Properties>

[0060] The glass can have the various glass properties described below by adjusting the composition as described above.

[0061] (Chemical resistance)

[0062] As an indicator of the chemical resistance of glass, the etching rate can be cited. This is the amount of etching per unit time (unit: nm / minute) when the glass is immersed in a 0.5% by mass potassium hydroxide aqueous solution maintained at a temperature of 50°C for a predetermined period of time. The etching rate of the glass can be 0.5 nm / minute or less. For the method of measuring the etching rate, refer to the description of the Examples described below. The etching rate is preferably 0 nm / minute or more and 0.5 nm / minute or less.

[0063] (Young's modulus)

[0064] 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, deformation of the substrate during the rotation of the shaft motor can be suppressed, and thus warping or bending of the magnetic recording medium accompanying 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.

[0065] (proportion)

[0066] The specific gravity of the above-mentioned glass is preferably 2.75 or less. The specific gravity of the above-mentioned glass is more preferably 2.73 or less, further preferably 2.70 or less, more preferably 2.68 or less, further preferably 2.64 or less, further preferably 2.62 or less, and particularly preferably 2.60 or less. By lowering the specific gravity of the glass used 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.

[0067] (Specific elastic modulus)

[0068] 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 expressed in g / cm 3 From the perspective of providing a substrate that is less susceptible to deformation, the glass preferably has a specific elastic modulus of 30 MNm / kg or greater, more preferably 32 MNm / kg or greater, even more preferably 33 MNm / kg or greater, even more preferably 34 MNm / kg or greater, and even more preferably 35 MNm / kg or greater. The upper limit of the specific elastic modulus is, for example, approximately 40 MNm / kg, but a higher specific elastic modulus is preferred, so there is no particular limitation.

[0069] (Coefficient of thermal expansion)

[0070] An HDD incorporating a magnetic recording medium generally has a structure in which the central portion is pressed by the shaft and chuck of a shaft motor 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 above, more preferably 43×10 -7 / ℃ or more, more preferably 44×10 -7 / ℃ or more, and more preferably 45×10 -7 / °C or more. In addition, the average linear expansion coefficient (α) of the glass at 100°C to 300°C is preferably 70×10 -7 / ℃ or less, more preferably 68×10 -7 / ℃ 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 / ℃ or less, and more preferably 53×10 -7 / ℃ or less, and more preferably 50×10 -7 / ℃ below.

[0071] (Glass transition temperature)

[0072] 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. It is preferred that the magnetic recording medium substrate has heat resistance that can withstand such high-temperature treatment, so that the flatness of the substrate can be maintained even when exposed to high temperature during high-temperature treatment. Regarding the above-mentioned glass, the glass transition temperature (hereinafter also referred to as "Tg") as an indicator of heat resistance is preferably 640°C or above, more preferably 650°C or above, further preferably 660°C or above, further preferably 670°C or above, further preferably 675°C or above, further preferably 680°C or above, particularly preferably 685°C or above, and particularly further preferably 687°C or above. The upper limit of the glass transition temperature is, for example, about 770°C or about 750°C. However, a higher glass transition temperature is more preferable from the perspective of heat resistance, so there is no particular limitation. However, the glass is not limited to substrate glass for magnetic recording media (the substrate glass for magnetic recording media having a magnetic recording layer containing a magnetic material requiring high temperature treatment), but can be used to produce magnetic recording media containing various magnetic materials.

[0073] (Glass stability)

[0074] The glass preferably exhibits high glass stability. Glass stability can be evaluated by a 16-hour hold test at 1350°C, 1300°C, or 1250°C, as detailed below. Preferably, the evaluation result is A or B, more preferably A, in at least one of the 16-hour hold test at 1350°C, 1300°C, and 1250°C, with the result being A. In a hold test at a lower temperature, a better result indicates higher glass stability.

[0075] [Magnetic recording medium substrate]

[0076] A magnetic recording medium substrate according to one embodiment of the present invention is composed of the above-mentioned glass.

[0077] Magnetic recording medium substrates can be manufactured through the following steps: preparing molten glass by heating glass raw materials, forming the molten glass into a plate using any of the following methods: press molding, down-drawing, or float glass processes, and processing the resulting plate-shaped glass. For example, in the press molding method, the molten glass flowing from a glass outflow tube is cut into a predetermined volume to obtain a desired molten glass block. This block is then press-molded using a press molding die to produce a thin-walled, disc-shaped substrate blank. Next, a center hole is provided in the resulting substrate blank, and the inner and outer circumferences are machined, with both main surfaces ground and polished. Subsequently, a cleaning process, including acid and alkaline cleaning, is performed to obtain the disc-shaped substrate.

[0078] In one embodiment, the surface and interior compositions of the magnetic recording medium substrate are homogeneous. Here, the surface and interior compositions being homogeneous means that ion exchange has not been performed (i.e., no ion exchange layer is present). Magnetic recording media without ion exchange layers are manufactured without ion exchange treatment, and thus can significantly reduce manufacturing costs.

[0079] In addition, in one embodiment, a portion 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 perpendicularly relative to the main surface and confirming the stress profile obtained in the fracture surface according to the Babinet method. "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 and is therefore called the main surface. In the case of a disc-shaped magnetic recording medium, it is equivalent to the circular surface of the disc (excluding the center hole in the case of a center hole). In addition, the presence or absence of the 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.

[0080] The ion exchange layer can be formed by contacting the substrate surface with an alkali metal salt at high temperature and exchanging the alkali metal ions in the alkali metal salt with the alkali metal ions in the substrate. Ion exchange (also known as "enhancement treatment" or "chemical enhancement") can be performed using known techniques. For example, see paragraphs 0068 to 0069 of WO2011 / 019010A1.

[0081] Above-mentioned magnetic recording medium substrate is for example below 1.5mm in thickness, preferably below 1.2mm, more preferably below 1.0mm, further preferably below 0.8mm, more preferably less than 0.8mm, further preferably below 0.7mm, further more preferably below 0.6mm. In addition, the thickness of above-mentioned magnetic recording medium substrate is for example more than 0.3mm. From the viewpoint of improving the recording capacity of HDD, it is preferred that the thickness of magnetic recording medium substrate can be made thin. In addition, above-mentioned magnetic recording medium substrate is preferably in the shape of a disk with a center hole.

[0082] The magnetic recording medium substrate is made of amorphous glass. Compared to crystallized glass, amorphous glass can achieve superior surface smoothness when processed into a substrate.

[0083] [Magnetic recording media]

[0084] One embodiment of the present invention relates to a magnetic recording medium including a magnetic recording layer on the magnetic recording medium substrate.

[0085] Magnetic recording media, also known as magnetic disks and hard disks, are suitable for various magnetic recording and reproducing devices, such as internal storage devices (local hard disks, etc.) of desktop computers, server computers, laptop computers, and mobile personal computers, 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. In the present invention and this specification, a "magnetic recording and reproducing device" refers to a device that can perform either or both of magnetic recording and reproducing information.

[0086] The magnetic recording medium is configured such that, for example, at least an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer are stacked in order from closest to the main surface on the main surface of a magnetic recording medium substrate.

[0087] For example, a magnetic recording medium substrate is introduced into a film forming device that has been evacuated, 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.

[0088] 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 formation method thereof, reference can be made to paragraph 0074 of WO2011 / 019010A1 and the description of the embodiments of the publication. 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, etc. is called a thermally assisted recording method, and the recording method assisted by microwaves is called a microwave-assisted recording method. For details thereof, 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.

[0089] Incidentally, in recent years, a DFH (Dynamic Flying Height) mechanism has been installed on the magnetic head to significantly narrow the gap between the recording and reproducing element of the magnetic head and the surface of the magnetic recording medium (low suspension quantization), thereby achieving higher recording density. The DFH mechanism refers to a function in which a very small heating unit such as a heater is provided near the recording and reproducing element of the magnetic head, so that only the periphery of the element 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 that signals of smaller magnetic particles can be detected, and higher recording density can be achieved. However, on the other hand, the gap (flying height) between the element of the magnetic head and the surface of the medium becomes extremely small. If there is surface roughness on the surface of the magnetic recording medium substrate caused by cleaning, 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 a magnetic recording medium with poor surface smoothness, the magnetic head may contact the surface of the magnetic recording medium and damage the magnetic head. Therefore, in order to prevent contact, a certain degree of flying height must be ensured. From the above perspectives, in order to produce a magnetic recording medium with high surface smoothness, it is desirable that the magnetic recording medium substrate can suppress surface roughness caused by cleaning, that is, have excellent chemical resistance. The magnetic recording medium substrate preferably has excellent chemical resistance, and thus the magnetic recording medium having the substrate is also suitable for a magnetic recording device equipped with a DFH mechanism with an extremely narrow flying height.

[0090] The dimensions of the magnetic recording medium substrate (e.g., a glass substrate for a magnetic disk) and the magnetic recording medium (e.g., a magnetic disk) are not particularly limited. For example, since a high recording density can be achieved, the medium and substrate can be miniaturized. For example, the nominal diameter can be 2.5 inches, but smaller diameters (e.g., 1 inch, 1.8 inches), 3 inches, 3.5 inches, and the like can also be used.

[0091] The magnetic recording medium is composed of the glass for a magnetic recording medium substrate according to one embodiment of the present invention and can therefore have the glass properties described above. Furthermore, the magnetic recording medium can preferably exhibit excellent impact resistance.

[0092] [Glass spacers for magnetic recording and reproduction devices]

[0093] 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,

[0094] MgO content is 15 mol% or more and 28 mol% or less,

[0095] The Li2O content is 0.2 mol% or more, and

[0096] The Na2O content is 5 mol% or less.

[0097] 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 generally provided with spacers because they fix the magnetic recording medium to the shaft of a shaft motor and / or in order to maintain a distance between two or more magnetic recording media. In recent years, a solution has been proposed to use glass spacers as the above-mentioned spacers. For reasons similar to those previously described in detail regarding glass for magnetic recording medium substrates, it is also desired that the glass spacers have excellent chemical resistance and impact resistance. In this regard, the glass having the above-mentioned composition is suitable as a glass spacer for magnetic recording and reproducing devices because it can have excellent chemical resistance and impact resistance.

[0098] The spacer for a magnetic recording / reproducing device is an annular component. Details such as the composition and manufacturing method of the glass spacer are well known. Furthermore, regarding the manufacturing method of the glass spacer, reference may be made to the aforementioned descriptions regarding the manufacturing method of the glass for a magnetic recording medium substrate and the manufacturing method of the magnetic recording medium substrate. Furthermore, regarding other details such as the glass composition and glass physical properties of the glass spacer for a magnetic recording / reproducing device according to one embodiment of the present invention, reference may be made to the aforementioned descriptions regarding the glass for a magnetic recording medium substrate, the magnetic recording medium substrate, and the magnetic recording medium according to one embodiment of the present invention.

[0099] It should be noted that the glass spacer for a magnetic recording and reproducing device can be composed of the above-mentioned glass, or can also be composed of a layer of a conductive film or other film provided on the surface of the above-mentioned glass. For example, in order to remove static electricity generated when the magnetic recording medium rotates, a conductive film such as a NiP alloy can be formed on the surface of the glass spacer by plating, dipping, evaporation, sputtering, etc. In addition, the surface smoothness of the glass spacer can be improved by grinding (for example, to an average surface roughness of less than 1 μm), thereby enhancing the close fit between the magnetic recording medium and the spacer and suppressing the occurrence of positional deviation.

[0100] [Magnetic recording and reproduction device]

[0101] One embodiment of the present invention relates to a magnetic recording and reproducing device comprising

[0102] A magnetic recording medium according to one embodiment of the present invention; and

[0103] Glass spacer according to one embodiment of the present invention

[0104] At least one of .

[0105] A 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.

[0106] 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 perspective 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, the positional deviation of the magnetic recording medium, etc.), 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 perspective, 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, the magnetic recording and reproducing device according to one embodiment of the present invention may be a device in which the glass constituting the magnetic recording medium substrate and the glass constituting the glass spacer included in the magnetic recording medium have the same glass composition.

[0107] A magnetic recording and reproducing device according to one embodiment of the present invention only needs to include at least one of a magnetic recording medium according to one embodiment of the present invention and a glass spacer according to one embodiment of the present invention. For other contents, known techniques for magnetic recording and reproducing devices can be applied. In one embodiment, as a magnetic head, an energy-assisted magnetic recording head having an energy source (e.g., a heat source such as a laser source, microwaves, etc.) for assisting magnetization reversal (assisting the writing of magnetic signals), a recording element portion, and a reproducing element portion can be used. A magnetic recording and reproducing device using an energy-assisted recording method including such an energy-assisted magnetic recording head is useful as a magnetic recording and reproducing device having high recording density and high reliability. In addition, when manufacturing a magnetic recording medium for use in a magnetic recording and reproducing device using an energy-assisted recording method such as a thermally assisted recording method including a thermally assisted magnetic recording head (the thermally assisted magnetic recording head having a laser source, etc.), a magnetic recording layer containing a magnetic material with high magnetic anisotropy energy is sometimes formed on a magnetic recording medium substrate. To form such a magnetic recording layer, film formation is generally 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.

[0108] Example

[0109] Hereinafter, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the embodiments shown in the following examples.

[0110] [Examples No. 1 to No. 139]

[0111] To obtain the glass having the composition shown in Table 1 (Table 1-1 to Table 1-7) below, raw materials such as oxides, carbonates, nitrates, sulfates, and hydroxides were weighed and mixed to obtain a blended raw material. This blended raw material was placed in a melting tank and heated and melted at a temperature within the range of 1400°C to 1600°C. The resulting molten glass was then held in a clarifier at 1400°C to 1550°C for 6 hours. The temperature was then lowered (cooled) to a temperature within the range of 1200°C to 1400°C for 1 hour, and the molten glass was then formed into a glass (amorphous oxide glass) used for the following evaluation.

[0112] <Evaluation of Glass Properties>

[0113] (1) Glass transition temperature (Tg), average linear expansion coefficient (α)

[0114] 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).

[0115] (2) Young's modulus

[0116] The Young's modulus of each glass was measured by an ultrasonic method.

[0117] (3) Specific gravity

[0118] The specific gravity of each glass was measured by the Archimedean method.

[0119] (4) Specific elastic modulus

[0120] The specific elastic modulus was calculated from the Young's modulus obtained in (2) and the specific gravity obtained in (3).

[0121] (5) Glass stability

[0122] 100g of each glass was placed in a platinum crucible, and each crucible was placed in a heating furnace set at a furnace temperature of 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 removed 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 using an optical microscope (magnification 40x to 100x), and the evaluation was performed according to the following criteria.

[0123] A: There is no crystallization on the glass surface, inside and at the interface of the bottom of the platinum crucible.

[0124] 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

[0125] 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

[0126] D: There are crystals inside the glass

[0127] E: There are crystals on the glass surface, inside and at the interface with the bottom of the platinum crucible

[0128] F: The glass has a lot of crystals and is a bit cloudy

[0129] G: Glass is cloudy

[0130] <Fabrication of Magnetic Recording Medium Substrate>

[0131] (1) Production of substrate blanks

[0132] Next, a disk-shaped substrate blank is produced according to the following method A or B. In addition, a glass blank for producing a glass spacer for a magnetic recording and reproducing device can be obtained according to the same method.

[0133] (Method A)

[0134] About the glass of composition shown in the following table, the molten glass of clarification, homogenization is received by the lower die used for compression molding while flowing out from the outflowing tube blank at a constant flow rate, and the molten glass flowing out is cut off with a cutting blade, so that a prescribed amount of molten glass block can be obtained on the lower die. Then the lower die carrying the molten glass block is immediately moved out from below the tube blank, and the upper die and the body die relative to the lower die are used to compression mold the thin-walled disc-shaped product 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, the lower die used more than two is molded into a disc-shaped substrate blank in succession by the molten glass flowing out.

[0135] (Method B)

[0136] Clarified, homogenized molten glass of the composition shown in the table below was continuously poured from above into a heat-resistant mold with a cylindrical through-hole. Molten glass was then formed into a circular shape and removed from the bottom of the through-hole. After annealing, the removed glass was sliced at regular intervals perpendicular to the cylindrical axis using a multi-wire cutter to produce disc-shaped substrate blanks.

[0137] It should be noted that, in this embodiment, the above-mentioned methods A and B are adopted, 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.

[0138] (Method C)

[0139] Alternatively, the molten glass may be poured onto a float bath and formed into a sheet of glass (float forming), and then, after annealing, a disc-shaped glass may be cut out from the sheet of glass to obtain a substrate blank.

[0140] (Method D)

[0141] 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.

[0142] (2) Preparation of glass substrate

[0143] 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 polished (mirror finish polishing) to produce a glass substrate for a magnetic disk having a diameter of 97 mm and a thickness of 0.5 mm. In addition, the glass blank used to manufacture glass spacers for magnetic recording and reproducing devices can be processed into glass spacers for magnetic recording and reproducing devices by the same method.

[0144] The glass substrate obtained above was cleaned using 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 the surface was smooth.

[0145] Four glass substrates were prepared for each glass composition, and each was used for the following evaluation (1), (2), or (3) or for the production of a magnetic recording medium described later.

[0146] <Evaluation of Magnetic Recording Medium Substrate>

[0147] (1) Etching rate (chemical resistance)

[0148] In order to produce an unetched portion on a portion of the main surface of each magnetic disk glass substrate produced above, a masking process is performed, and the glass substrate in this state is immersed in a potassium hydroxide aqueous solution with a concentration of 0.5% by mass and a liquid temperature maintained at 50°C for a predetermined time. Afterwards, the glass substrate is lifted from the aqueous solution, the mask is removed, and the depth of the drop between the portion not in contact with the aqueous solution due to the mask and the portion in contact with the aqueous solution without the mask is measured. The depth of the drop is equivalent to the amount of etching of the glass in the predetermined time (etching depth). The etching amount is divided by the immersion time to calculate the etching amount per unit time, that is, the etching rate (chemical resistance).

[0149] The etching rate (chemical resistance) obtained for each magnetic disk glass substrate in Examples was 0.5 nm / min or less.

[0150] (2) Substrate deformation at 70G impact

[0151] As an evaluation of impact resistance, the amount of substrate deformation during a 70G (G is the acceleration due to gravity) impact was determined for each of the above-produced glass substrates for magnetic disks using the following evaluation method. In an HDD, the distance between the magnetic disk and the ramp is usually about 0.25mm. Therefore, as an evaluation of impact resistance, when a large impact (e.g., an impact 70 times the acceleration due to gravity (70G)) is applied, the amount of deformation of the outer peripheral end of the magnetic disk glass substrate is preferably less than 0.25mm, and more preferably less than 0.25mm. That is, the amount of substrate deformation during a 70G impact determined by the following method is preferably less than 0.25mm, and more preferably less than 0.25mm. The amount of substrate deformation during a 70G impact can be, for example, more than 0.20mm, but is preferably less than this value.

[0152] (Evaluation method)

[0153] 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 apparatus, and end caps were attached. Each end cap was fastened and fixed with screws.

[0154] 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 to achieve the specified impact force. The cushioning material is adjusted in a micro-adjustment manner. The impact force or impact duration is measured by amplifying the output power signals of the accelerometer and the accelerometer installed on the test bench with an amplifier, and processing the output power signals of the amplifier with a personal computer to obtain the respective values. Change the test bench height or the conditions of the cushioning material, make the test bench fall several times, calculate the impact force and impact duration at this time, and determine the test bench height or the conditions of the cushioning material to obtain the specified impact force.

[0155] After determining the test bench height and cushioning material conditions, a high-speed camera is used to determine the amount of vibration (displacement) of the outer edge of the disk glass substrate during impact. Specifically, a high-intensity lighting device is used to capture high-resolution images, and the instantaneous movement of the outer edge of the disk glass substrate during impact is captured from the captured images (1 frame: 1 / 10,000 second, capture time: 30 milliseconds). The resulting images capture the behavior of the outer edge of the disk glass substrate and quantify it to determine the maximum vibration (displacement). A graph is plotted with the elapsed time after the impact as the horizontal axis and the displacement of the outer edge of the disk glass substrate as the vertical axis. On the vertical axis, negative values represent downward displacement, and positive values represent upward displacement. Due to the impact of the drop, the outer edge of the disk glass substrate displaces downward by a negative value (Y0) immediately after the drop. Immediately after the drop, the outer edge of the disk glass substrate displaces upward by a positive value (Y1), repeating this process while gradually attenuating. Therefore, the maximum downward displacement is the displacement Y0 immediately after falling, and the maximum upward displacement is the upward displacement Y1 immediately after the downward displacement Y0. The displacement when the impact force is applied is calculated as "Y1-Y0". Since the displacement "Y1-Y0" at the time of a 70G impact is a relatively small value, it is difficult to calculate the displacement with high precision. 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 linear equation of the approximate straight line is used to calculate the displacement "Y1-Y0" at 70G.

[0156] 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, with the impact force set to four different values: 120G, 140G, 170G, and 190G.

[0157] [Comparative Example 1]

[0158] A magnetic disk glass substrate was prepared using the same method as in the previous example using the glass having the composition shown in Table 3 of Patent Document 1 (Japanese Patent Application Publication No. 2002-348141). The deformation of the prepared magnetic disk glass substrate was determined using the same method as above when subjected to a 70G impact.

[0159] The above results are shown in Table 2 (Tables 2-1 to 2-7).

[0160]

[0161]

[0162]

[0163]

[0164]

[0165]

[0166]

[0167]

[0168]

[0169]

[0170]

[0171]

[0172]

[0173]

[0174] [Manufacturing of magnetic recording media (disks)]

[0175] An adhesion layer, an underlayer, 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 above by the following method to obtain a magnetic disk.

[0176] First, using a film forming apparatus that had been evacuated, an adhesion layer, a base layer, and a magnetic recording layer were sequentially formed by DC magnetron sputtering in an Ar atmosphere.

[0177] At this time, a CrTi target was used to form a 20nm thick amorphous CrTi layer as the adhesion layer. Next, a 10nm thick layer of MgO was formed as the underlayer. Separately, a FePtC or CoPtC target was used to form a 10nm thick granular FePt or CoPt layer as the magnetic recording layer at a temperature of 200°C to 400°C.

[0178] 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. 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.

[0179] Next, a protective layer of hydrogenated carbon was formed to a thickness of 3 nm by CVD using ethylene as the material gas. A lubricating layer made of PFPE (perfluoropolyether) was then formed by dip coating. The lubricating layer had a thickness of 1 nm.

[0180] By the above manufacturing process, a magnetic disk was obtained. The obtained magnetic disk was 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 1000Gbit per square inch, no collision (collision failure) between the magnetic head and the magnetic disk surface was confirmed.

[0181] 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 was obtained by the above manufacturing process using the glass of the embodiment) was mounted on a hard disk drive having a DFH mechanism. When magnetic signals were 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 made of a material different from that of the glass of one embodiment of the present invention, no collision between the magnetic head and the magnetic disk surface (collision failure) was confirmed.

[0182] Furthermore, when the magnetic disk and the glass spacer with the NiP alloy film manufactured above were mounted on a hard disk drive equipped with a DFH mechanism using the same glass material as one embodiment of the present invention, no collision between the magnetic head and the disk surface (collision failure) was observed 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 Gbits per square inch. Since the glass substrate included in the magnetic disk and the glass spacer are made of the same glass material, the phenomenon caused by the difference in thermal expansion coefficient does not occur.

[0183] According to one embodiment of the present invention, a magnetic recording medium suitable for high-density recording can be provided.

[0184] Finally, summarize the above methods.

[0185] 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%.

[0186] The glass may have excellent chemical resistance and excellent impact resistance.

[0187] In one embodiment, in the glass, the molar ratio of the total content of SiO2 and MgO to the content of Li2O [(SiO2+MgO) / Li2O] may be 13 or more.

[0188] In one embodiment, in the glass, the total content of SiO2, MgO, Li2O, Al2O3 and CaO (SiO2+MgO+Li2O+Al2O3+CaO) can be 93 mol% or more.

[0189] 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] can be 0.55 or more.

[0190] In one embodiment, in the glass, the molar ratio of the MgO content to the CaO content (MgO / CaO) may be 6 or more.

[0191] In one embodiment, when the glass is immersed in a 0.5 mass % hydrosilicic 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.

[0192] According to one embodiment, a magnetic recording medium substrate comprising the above-mentioned glass for a magnetic recording medium substrate is provided.

[0193] 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.

[0194] According to one embodiment, a magnetic recording medium including the magnetic recording medium substrate and a magnetic recording layer is provided.

[0195] According to one embodiment, 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%.

[0196] 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.

[0197] The embodiments disclosed herein are to 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 encompass all modifications within the meaning and scope equivalent to the claims.

[0198] 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.

[0199] 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 glass has an SiO2 content of 56 mol% or more, MgO content is 15 mol% or more and 28 mol% or less, Li2O content is 0.2 mol% or more, Na2O content is less than 5 mol%, The total content of Al2O3, MgO and CaO, i.e. Al2O3+MgO+CaO is 29.0 mol% or more and 36.50 mol% or less, The total content of SiO2, MgO, Li2O, Al2O3 and CaO, i.e. SiO2+MgO+Li2O+Al2O3+CaO is 95 mol% or more, The molar ratio of the total content of SiO2 and MgO to the content of Li2O, i.e. (SiO2 + MgO) / Li2O is 13 or more, and Amorphous glass in which the molar ratio of CaO content to the total content of Al2O3 and MgO, that is, CaO / (Al2O3+MgO), is 0.10 or less.

2. The glass according to claim 1, wherein The molar ratio of the total content of Al2O3 and CaO to the content of MgO, that is, (Al2O3+CaO) / MgO is 0.55 or more.

3. The glass according to claim 1, wherein The molar ratio of the MgO content to the CaO content, that is, MgO / CaO, is 6 or more. 4 . A magnetic recording medium substrate comprising the glass according to claim 1 . 5 . A magnetic recording medium comprising the magnetic recording medium substrate according to claim 4 and a magnetic recording layer.

6. A glass spacer for a magnetic recording and reproducing device, wherein: The glass spacer comprises the glass according to claim 1 .

7. A magnetic recording and reproducing device comprising the magnetic recording medium according to claim 5.

8. A magnetic recording and reproducing device comprising the glass spacer according to claim 6.

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