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

Abstract

To provide a glass for a magnetic recording medium substrate having excellent chemical resistance and impact resistance.SOLUTION: A glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device which is an amorphous glass, in which an SiO2 content is 56 mol% or more, an MgO content is 15 mol% or more and 28 mol% or less, an Li2O content is 0.2 mol% or more, an Na2O content is 5 mol% or less, a total content (Al2O3+MgO+CaO) of Al2O3, MgO and CaO is 29 mol% or more and 36.50 mol% or less, a total content (SiO2+MgO+Li2O+Al2O3+CaO) of SiO2, MgO, Li2O, Al2O3 and CaO is 95.0 mol% or more, a molar ratio [(SiO2+MgO) / Li2O] of a total content of SiO2 and MgO to the Li2O content is 13 or more, and a molar ratio [CaO / (Al2O3+MgO)] of a CaO content to a total content of Al2O3 and MgO is 0.10 or less.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Aluminum alloy substrates have been used as substrates for magnetic recording media such as hard disks (magnetic recording medium substrates). However, it has been pointed out that aluminum alloy substrates are prone to deformation. For this reason, glass magnetic recording medium substrates are now widely used (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-814134 A Summary of the Invention [Problem to be solved by the invention]

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

[0005] Furthermore, glass for magnetic recording medium substrates is also desired to have excellent impact resistance for the following reasons. Magnetic recording media are usually mounted inside hard disk drives (HDDs) that are built into devices such as personal computers. Inside the HDD, multiple magnetic recording media (magnetic disks) are attached to the rotating shaft of a spindle motor, and an actuator built into the HDD writes and reads data to and from the magnetic recording layer of the magnetic recording media that rotates at high speed inside the HDD. If a large impact (for example, an impact due to a fall, etc.) is applied to the HDD while the magnetic recording media is rotating at high speed for such data writing and reading, the magnetic recording media inside the HDD may be temporarily deformed by the impact and collide with a part called a ramp while rotating at high speed, and this collision may damage the magnetic recording media. In order to prevent such damage, it is desirable for the magnetic recording media to be resistant to deformation even when subjected to an impact, that is, to have excellent impact resistance. For HDDs, the recording capacity can be increased by reducing the thickness of each magnetic recording medium and mounting more magnetic recording media on the HDD, but generally, glass tends to be more easily deformed when its thickness is reduced, making the above-mentioned damage more likely to occur. Therefore, in order to achieve both an increase in the recording capacity of HDDs and the prevention of the above-mentioned damage, a glass for a magnetic recording medium substrate having excellent impact resistance is desirable.

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

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

[0008] One aspect of the present invention relates to a glass for magnetic recording medium substrates (hereinafter also simply referred to as "glass") which is amorphous glass having a SiO2 content of 54 mol% or more and 62 mol% or less, an MgO content of 15 mol% or more and 28 mol% or less, a Li2O content of 0.2 mol% or more, and a Na2O content of 5 mol% or less.

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

[0010] According to one aspect of the present invention, it is possible to provide a glass for a magnetic recording medium substrate having excellent chemical resistance and impact resistance. According to another aspect, it is also possible to provide a magnetic recording medium substrate made of the above-mentioned glass for a magnetic recording medium substrate, and a magnetic recording medium including this substrate. According to yet another aspect, it is possible to provide a glass spacer for a magnetic recording device. According to yet another aspect, it is possible to provide a magnetic recording and reproducing device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0012] <Glass composition> In the present invention and this specification, the glass composition is expressed as a glass composition based on oxides. Here, "glass composition based on oxides" refers to a glass composition obtained by converting the glass raw materials into oxides that are present in the glass after being completely decomposed during melting. Furthermore, unless otherwise specified, the glass composition is expressed on a molar basis (mol %, molar ratio). The glass composition of the present invention and this specification can be determined by a method such as ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Quantitative analysis is performed for each element using ICP-AES. The analytical values ​​are then converted into oxide notation. The analytical values ​​obtained by ICP-AES may contain a measurement error of, for example, about ±5% of the analytical value. Therefore, the oxide notation values ​​converted from the analytical values ​​may also contain an error of about ±5%. In the present invention and this specification, the content of a component being 0% or not being contained or not being introduced means that the component is substantially not contained, and the content of the component is at or below the impurity level. At or below the impurity level means, for example, less than 0.01%.

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

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

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

[0016] Li2O is a component that has a strong effect of improving the meltability of glass among alkali metal oxides. In addition, when the above glass is used as a glass for chemical strengthening, it is also a component that is responsible for ion exchange during chemical strengthening. From the viewpoint of improving the meltability of 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. In addition, from the viewpoint of further improving chemical resistance and impact resistance, and improving the smoothness of the magnetic recording medium substrate surface after polishing, the Li2O content is preferably 6% or less, and more preferably 5% or less.

[0017] From the viewpoint of further improving impact resistance, the molar ratio of the total content of SiO2 and MgO to the Li2O content [(SiO2+MgO) / Li2O] is preferably 13 or more, more preferably more than 13, even more preferably 14 or more, and even more preferably 15 or more. Moreover, from the viewpoint of devitrification resistance and melting property, 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.

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

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

[0020] Al2O3 is a glass network forming component and has the function of improving heat resistance. From the viewpoint of improving the meltability of glass, the Al2O3 content is preferably 19% or less, more preferably 18% or less, even more preferably 17% or less, even more preferably 16% or less, and even more preferably 15% or less. 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, even more preferably 11% or more, and even more preferably 12% or more.

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

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

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

[0024] The molar ratio of the total content of Al2O3 and CaO to the MgO content [(Al2O3+CaO) / MgO] is preferably 0.55 or more, more preferably 0.57 or more, from the viewpoint of improving devitrification resistance and further improving chemical resistance. Furthermore, the lower limit is preferably 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 in that order. Moreover, from the viewpoint of impact resistance, the molar ratio [(Al2O3+CaO) / MgO] is preferably 1.8 or less, more preferably 1.5 or less, even more preferably 1.3 or less, even more preferably 1.2 or less, and even more preferably 1.1 or less.

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

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

[0027] From the viewpoint of further improving impact resistance, the molar ratio of the MgO content to the Li2O content (MgO / Li2O) is preferably 2.3 or more, more preferably 2.5 or more, even more preferably 2.7 or more, and even 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, even more preferably 24 or less, and even more preferably 22 or less.

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

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

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

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

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

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

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

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

[0036] The Fe2O3 content of the glass, expressed as an exclusive percentage, can be 1 mol% or less, 0.7 mol% or less, 0.5 mol% or less, 0.4 mol% or less, 0.3 mol% or less, 0.1 mol% or less, 0.07 mol% or less, 0.05 mol% or less, 0.04 mol% or less, 0.03 mol% or less, or 0.02 mol% or less. In one embodiment, the glass can be free of Fe (the Fe2O3 content expressed as an exclusive percentage is 0 mol%). The Fe2O3 content expressed as an exclusive percentage is the amount of Fe2O3 contained in the glass expressed as a molar percentage when the total content of glass components other than Fe2O3 is 100 mol%.

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

[0038] Since F is a component that is easily volatilized during melting and is also a component that causes striae, it is preferable that the above glass does not contain F. Not containing F is also preferable from the viewpoints of suppressing erosion of the melting furnace, suppressing a decrease in Young's modulus, and suppressing a decrease in the specific elastic modulus.

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

[0040] From the viewpoint of obtaining a clarification effect, the above glass may contain one or more selected from the group consisting of SnO2, CeO2, and Sb2O3. In one embodiment, the total content of SnO2 and CeO2 may be 0%. In another embodiment, the above glass may contain SnO2 and / or CeO2, and the total content of SnO2 and CeO2 (SnO2+CeO2) is preferably 0.05 to 2%. By making the total content of SnO2 and CeO2 0.05% or more, a sufficient clarification effect can be obtained and the remaining bubbles can be reduced. In addition, by making the total content (SnO2+CeO2) 2% or less, it is possible to prevent the molten glass from blowing up during glass melting, which causes a decrease in productivity. The lower limit of the total content (SnO2+CeO2) is preferably 0.10% or more, more preferably 0.20% or more, even more preferably 0.25% or more, even more preferably 0.30% or more, even more preferably 0.35% or more, and even more preferably 0.40% or more. The upper limit of the total content (SnO2+CeO2) is preferably 1.5% or less, more preferably 1.2% or less, even more preferably 1.0% or less, even more preferably 0.70% or less, even more preferably 0.65% or less, even more preferably 0.60% or less, even more preferably 0.55% or less, and even more preferably 0.50% or less.

[0041] SnO2 has the function of promoting fining when the melting temperature of the glass is relatively high (temperature range of about 1400 to 1600 ° C). In the midst of restrictions on the use of fining agents such as Sb2O3 and arsenous acid, which have a negative effect on the environment, in one embodiment, it is preferable to introduce SnO2 into the above glass in order to remove bubbles in the glass with a high melting temperature. From the viewpoint of obtaining a fining effect, the content of SnO2 is preferably 0.01% or more, more preferably 0.05% or more, even more preferably 0.10% or more, even more preferably 0.15% or more, and even more preferably 0.20% or more. In addition, the content of SnO2 is preferably 2% or less, more preferably 1.5% or less, even more preferably 1.0% or less, even more preferably 0.8% or less, and even more preferably 0.5% or less.

[0042] CeO2 is a component that exhibits a fining effect on glass, similar to SnO2. CeO2 has the function of taking in oxygen and fixing it as a glass component when the melting temperature of glass is relatively low (temperature range of about 1200 to 1400 ° C.), so in one embodiment, it is preferable to introduce CeO2 into the glass as a fining agent. From the viewpoint of obtaining a fining effect, the content of CeO2 is preferably 0.01% or more, more preferably 0.05% or more, even more preferably 0.08% or more, and even more preferably 0.10% or more. In addition, the content of CeO2 is preferably 2% or less, more preferably 1.5% or less, even more preferably 1.0% or less, even more preferably 0.8% or less, even more preferably 0.5% or less, and even more preferably 0.3% or less. By allowing SnO2 and CeO2 to coexist, a fining effect can be obtained in a wide temperature range, so in one embodiment, it is preferable that the glass contains both SnO2 and CeO2.

[0043] From the viewpoint of reducing the environmental load, it is desirable to refrain from using Sb2O3. The content of Sb2O3 in the above glass is preferably in the range of 0 to 0.5%. The content of Sb2O3 is more preferably 0.3% or less, further preferably 0.1% or less, even more preferably 0.05% or less, and still more preferably 0.02% or less, and it is particularly preferable that the glass does not contain Sb2O3.

[0044] The above glass can be produced by weighing, preparing and thoroughly mixing glass raw materials such as oxides, carbonates, nitrates, sulfates and hydroxides so as to obtain a desired glass composition, heating and melting the mixture in a melting vessel at, for example, a temperature range of 1400 to 1600°C, fining and stirring, and forming a homogenized molten glass that has been sufficiently bubble-free. For example, it is preferred that the glass raw materials are heated and melted at 1400 to 1550°C in a melting tank, the obtained molten glass is heated in a fining tank and held at 1450 to 1600°C, and then cooled to 1200 to 1400°C, at which point the glass flows out and is shaped.

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

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

[0047] (Young's Modulus) The Young's modulus of the glass is preferably 90 GPa or more. The glass for magnetic recording medium substrate having high rigidity and showing a Young's modulus of 90 GPa or more can suppress the deformation of the substrate during the rotation of the spindle motor, and therefore the warping and bending of the magnetic recording medium caused by the deformation of the substrate can be suppressed. The Young's modulus of the glass is preferably 91 GPa or more, more preferably 92 GPa or more, even more preferably 93 GPa or more, even more preferably 94 GPa or more, and even more preferably 95 GPa or more. The upper limit of the Young's modulus is, for example, about 120 GPa, but is not particularly limited because the higher the Young's modulus, the higher the rigidity and the more preferable it is.

[0048] (specific gravity) The specific gravity of the glass is preferably 2.75 or less. The specific gravity of the glass is more preferably 2.73 or less, even more preferably 2.70 or less, even more preferably 2.68 or less, even more preferably 2.64 or less, even more preferably 2.62 or less, and even more preferably 2.60 or less. By reducing the specific gravity of the glass for magnetic recording medium substrate, the magnetic recording medium substrate can be made lighter, and further the magnetic recording medium can be made lighter, which makes it possible to reduce the power consumption of the magnetic recording and reproducing device (commonly called HDD). The lower limit of the specific gravity is, for example, about 2.40, but is not particularly limited since the lower the specific gravity, the more preferable it is.

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

[0050] (Thermal expansion coefficient) HDDs incorporating magnetic recording media are usually structured so that the center part is held down by the spindle and clamp of a spindle motor to rotate the magnetic recording medium itself. Therefore, if there is a large difference in the thermal expansion coefficients of the magnetic recording medium substrate and the spindle material that constitutes the spindle part, there will be a mismatch between the thermal expansion and contraction of the spindle and the magnetic recording medium substrate in response to changes in the ambient temperature during use, resulting in deformation of the magnetic recording medium. If this phenomenon occurs, the head will not be able to read the written information, which will cause a decrease in the reliability of recording and playback. Therefore, it is desirable for the glass for magnetic recording medium substrates to have a moderate thermal expansion coefficient similar to that of the spindle material (e.g., stainless steel, etc.). In general, the spindle material for HDDs has a thermal expansion coefficient of 70×10 -7 / °C or more, and the average linear expansion coefficient (thermal expansion coefficient) of the glass for magnetic recording medium substrates at 100 to 300°C is 40×10 -7 / °C or more, the difference in thermal expansion coefficient with the spindle material is small, which can contribute to improving the reliability of the magnetic recording medium. The average linear expansion coefficient (hereinafter also referred to as "α") of the above glass at 100 to 300°C is 40×10 -7 / °C or more, and 41×10 -7 / °C or more, and more preferably 42×10 -7 / °C or more, and more preferably 43×10 -7 / °C or more, and more preferably 44×10 -7 / °C or more, and more preferably 45×10 -7 / °C or more. The average linear expansion coefficient (α) of the above glass at 100 to 300°C is 70×10 -7 / ℃ or less, and 68×10 -7 / °C or less, and more preferably 65×10 -7 / °C or less, more preferably 63×10 -7 / °C or less, and more preferably 60×10-7 / °C or less, and more preferably 57×10 -7 / °C or less, and even more preferably 55×10 -7 / °C or less, and more preferably 53×10 -7 It is even more preferable that the temperature is 50×10 -7 It is even more preferred that the temperature is equal to or lower than 1 / °C.

[0051] (glass transition temperature) A 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 anisotropic energy, which has been developed in recent years for high-density recording of magnetic recording media, a film is generally formed at a high temperature, or a heat treatment is performed at a high temperature after film formation. It is preferable that the magnetic recording medium substrate has heat resistance capable of withstanding such high-temperature treatment, because the flatness of the substrate can be maintained even when exposed to high temperatures in the high-temperature treatment. The glass has a glass transition temperature (hereinafter also referred to as "Tg"), which is an index of heat resistance, of preferably 640°C or higher, more preferably 650°C or higher, even more preferably 660°C or higher, even more preferably 670°C or higher, even more preferably 675°C or higher, even more preferably 680°C or higher, even more preferably 685°C or higher, and even more preferably 687°C or higher. The upper limit of the glass transition temperature is, for example, about 770°C or about 750°C, but is not particularly limited because the higher the glass transition temperature, the more preferable it is from the viewpoint of heat resistance. However, the above glass is not limited to glass for a substrate of a magnetic recording medium having a magnetic recording layer containing a magnetic material that requires high-temperature treatment, and can be used to produce magnetic recording media having various magnetic materials.

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

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

[0054] The magnetic recording medium substrate can be manufactured by heating glass raw materials to prepare a molten glass, forming the molten glass into a plate shape by any of the press molding, down-draw, and float methods, and processing the obtained plate-shaped glass. For example, in the press molding method, the molten glass flowing out of a glass flow pipe is cut into a predetermined volume to obtain a required molten glass lump, which is press molded in a press mold to produce a thin disk-shaped substrate blank. Next, a center hole is provided in the obtained substrate blank, and inner and outer periphery processing is performed, and both main surfaces are lapped and polished. Next, a cleaning process including acid cleaning and alkali cleaning is performed to obtain a disk-shaped substrate.

[0055] In one embodiment, the magnetic recording medium substrate has a homogeneous surface and internal composition. Here, the homogeneous surface and internal composition means that ion exchange has not been performed (i.e., the substrate does not have an ion exchange layer). The magnetic recording medium substrate without an ion exchange layer is manufactured without ion exchange processing, and therefore the manufacturing cost can be significantly reduced.

[0056] In one embodiment, the magnetic recording medium substrate has an ion exchange layer on a part or the whole of the surface. Since the ion exchange layer exhibits compressive stress, the presence or absence of the ion exchange layer can be confirmed by breaking the substrate perpendicularly to the main surface and obtaining a stress profile on the fracture surface by the Babinet method. The "main surface" is the surface on which the magnetic recording layer of the substrate is provided or is provided. This surface is called the main surface because it is the surface with the largest area among the surfaces of the magnetic recording medium substrate, and in the case of a disk-shaped magnetic recording medium, it corresponds to the circular surface of the disk (excluding the central hole if there is one). 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 in the depth direction from the substrate surface, etc.

[0057] The ion exchange layer can be formed by contacting an alkali salt with the substrate surface at high temperature and exchanging the alkali metal ions in the alkali salt with the alkali metal ions in the substrate. For ion exchange (also called "strengthening treatment" or "chemical strengthening"), known techniques can be applied, and for example, see paragraphs 0068 to 0069 of WO2011 / 019010A1.

[0058] The magnetic recording medium substrate has a thickness of, for example, 1.5 mm or less, preferably 1.2 mm or less, more preferably 1.0 mm or less, even more preferably 0.8 mm or less, even more preferably less than 0.8 mm, even more preferably 0.7 mm or less, and even more preferably 0.6 mm or less. The thickness of the magnetic recording medium substrate is, for example, 0.3 mm or more. It is preferable to be able to reduce the thickness of the magnetic recording medium substrate from the viewpoint of improving the recording capacity of HDDs. The magnetic recording medium substrate is preferably in the shape of a disk having a central hole.

[0059] The magnetic recording medium substrate is made of amorphous glass, which can achieve superior surface smoothness when processed into a substrate compared to crystallized glass.

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

[0061] Magnetic recording media are called magnetic disks, hard disks, etc., and are suitable for use in various magnetic recording and reproducing devices, such as internal storage devices (fixed disks, etc.) of desktop personal computers, server computers, notebook personal computers, mobile personal computers, etc., internal storage devices of portable recording and reproducing devices that record and replay images and / or sounds, recording and replay devices for car audio, etc. In the present invention and this specification, the term "magnetic recording and replay device" refers to a device that is capable of either or both of magnetically recording information and magnetically replaying information.

[0062] A magnetic recording medium has a configuration in which, for example, on the main surface of a magnetic recording medium substrate, at least an adhesive layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricant layer are laminated in that order from closest to the main surface. For example, the magnetic recording medium substrate is introduced into a film-forming apparatus that has been evacuated, and an adhesion layer to a magnetic layer are sequentially formed on the main surface of the magnetic recording medium substrate in an Ar atmosphere by DC (Direct Current) magnetron sputtering. For example, CrTi can be used as the adhesion layer, and for example, a material containing Ru or MgO can be used as the underlayer. In addition, a soft magnetic layer and a heat sink layer may be added as appropriate. After the above film formation, for example, a protective layer is formed using C2H4 by CVD (Chemical Vapor Deposition), and a nitriding process is performed in the same chamber to introduce nitrogen into the surface, thereby forming a magnetic recording medium. After that, for example, PFPE (polyfluoropolyether) can be applied to the protective layer by dip coating to form a lubricating layer.

[0063] For higher density recording of the magnetic recording medium, it is preferable that the magnetic recording layer contains a magnetic material with high magnetic anisotropy energy. From this point of view, a preferable magnetic material is an Fe-Pt magnetic material or a Co-Pt magnetic material. Here, "based" means containing. That is, the magnetic recording medium preferably has a magnetic recording layer containing Fe and Pt, or Co and Pt as the magnetic recording layer. For the magnetic recording layer containing such a magnetic material and the film formation method thereof, reference can be made to paragraph 0074 of WO2011 / 019010A1 and the description of the examples in the same publication. In addition, it is preferable that the magnetic recording medium having such a magnetic recording layer is applied to a magnetic recording device using a recording method called an energy-assisted recording method. Among the energy-assisted recording methods, a recording method in which magnetization reversal is assisted by irradiation of near-field light or the like is called a thermally assisted recording method, and a recording method in which magnetization reversal is assisted by microwaves is called a microwave-assisted recording method. For details of these, reference can be made to paragraph 0075 of WO2011 / 019010A1. As the magnetic material for forming the magnetic recording layer, a conventional CoPtCr-based material may be used.

[0064] In recent years, a DFH (Dynamic Flying Height) mechanism has been installed on the magnetic head to achieve a significant narrowing of the gap between the read / write element of the magnetic head and the surface of the magnetic recording medium (reducing the flying height), thereby achieving even higher recording density. The DFH mechanism is a function in which a heating unit such as a very small heater is provided near the read / write element of the magnetic head, and only the periphery of the element is protruded toward the surface of the medium. This reduces the distance (flying height) between the magnetic head and the magnetic recording layer of the medium, making it possible to pick up signals from smaller magnetic particles, thereby achieving even higher recording density. 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 the surface of the magnetic recording medium substrate is roughened by cleaning, the surface roughness of the substrate is reflected on the surface of the magnetic recording medium, and the surface smoothness of the magnetic recording medium decreases. If a magnetic head is brought close to the surface of a magnetic recording medium with poor surface smoothness, the magnetic head may come into contact with the surface of the magnetic recording medium and be damaged, so a certain flying height must be ensured to prevent the contact. From the above points, it is desirable for the magnetic recording medium substrate to be capable of suppressing surface roughening due to cleaning, that is, to have excellent chemical resistance, in order to produce a magnetic recording medium with high surface smoothness. Since the magnetic recording medium substrate preferably has excellent chemical resistance, the magnetic recording medium equipped with such a substrate is also suitable for a magnetic recording device equipped with a DFH mechanism with an extremely narrow flying height.

[0065] There is no particular limit to the dimensions of the magnetic recording medium substrate (e.g., glass substrate for magnetic disk) and the magnetic recording medium (e.g., magnetic disk), but since high recording density is possible, it is also possible to miniaturize the medium and substrate. For example, the nominal diameter can be 2.5 inches, of course, but it can also be smaller (e.g., 1 inch, 1.8 inches), or 3 inches, 3.5 inches, etc.

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

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

[0068] The magnetic recording medium can be used in a magnetic recording and reproducing device to magnetically record and / or reproduce information. The magnetic recording and reproducing device is usually provided with a spacer to fix the magnetic recording medium to the spindle of a spindle motor and / or to maintain a distance between a plurality of magnetic recording media. In recent years, it has been proposed to use a glass spacer as such a spacer. For reasons similar to those detailed above regarding the glass for the magnetic recording medium substrate, it is desired that the glass spacer also has excellent chemical resistance and impact resistance. In contrast, the glass having the above composition can have excellent chemical resistance and impact resistance, and is therefore suitable as a glass spacer for a magnetic recording and reproducing device.

[0069] The spacer for the magnetic recording and reproducing device is a ring-shaped member, and the details of the configuration, manufacturing method, etc. of the glass spacer are publicly known. For the manufacturing method of the glass spacer, the above description of the manufacturing method of the glass for a magnetic recording medium substrate and the manufacturing method of the magnetic recording medium substrate can be referred to. For other details such as the glass composition and glass physical properties of the glass spacer for the magnetic recording and reproducing device according to one aspect of the present invention, the above description of the glass for a magnetic recording medium substrate, the magnetic recording medium substrate, and the magnetic recording medium according to one aspect of the present invention can be referred to. The glass spacer for magnetic recording and reproducing devices may be made of the above-mentioned glass, or may have one or more films such as a conductive 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 may be formed on the surface of the glass spacer by plating, immersion, vapor deposition, sputtering, or other methods. The glass spacer may also be polished to increase its surface smoothness (for example, to an average surface roughness of 1 μm or less), which may increase the degree of adhesion between the magnetic recording medium and the spacer and suppress the occurrence of misalignment.

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

[0071] A magnetic recording and reproducing device includes at least one magnetic recording medium and at least one spacer, and typically further includes a spindle motor for rotating the magnetic recording medium, and at least one magnetic head for recording and / or reproducing information on the magnetic recording medium. The magnetic recording and reproducing device according to an embodiment of the present invention may include the magnetic recording medium according to an embodiment of the present invention as at least one magnetic recording medium, or may include a plurality of the magnetic recording media according to an embodiment of the present invention. The magnetic recording and reproducing device according to an embodiment of the present invention may include the glass spacer according to an embodiment of the present invention as at least one spacer, or may include a plurality of the glass spacers according to an embodiment of the present invention. A small difference between the thermal expansion coefficient of the magnetic recording medium and the thermal expansion coefficient of the spacer is preferable from the viewpoint of suppressing the occurrence of phenomena that may occur due to the difference in the thermal expansion coefficients of the two, such as distortion of the magnetic recording medium and a decrease in stability during rotation due to misalignment of the magnetic recording medium. From this viewpoint, the magnetic recording and reproducing device according to an embodiment of the present invention preferably includes the magnetic recording medium according to an embodiment of the present invention as at least one magnetic recording medium, or as more magnetic recording media when multiple magnetic recording media are included, and includes the glass spacer according to an embodiment of the present invention as at least one spacer, or as more spacers when multiple spacers are included. For example, the magnetic recording and reproducing device according to an embodiment of the present invention may be one in which 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.

[0072] The magnetic recording and reproducing device according to an embodiment of the present invention may include at least one of the magnetic recording medium according to an embodiment of the present invention and the glass spacer according to an embodiment of the present invention, and other aspects may be applied to known techniques related to magnetic recording and reproducing devices. In one embodiment, an energy-assisted magnetic recording head having an energy source (e.g., a heat source such as a laser light source, microwaves, etc.) for assisting magnetization reversal (assisting writing of a magnetic signal), a recording element portion, and a reproducing element portion can be used as the magnetic head. Such an energy-assisted recording magnetic recording and reproducing device including an energy-assisted 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 used in an energy-assisted recording magnetic recording and reproducing device including a heat-assisted recording method including a heat-assisted magnetic recording head having a laser light source or the like, a magnetic recording layer including a magnetic material with high magnetic anisotropic energy may be formed on a magnetic recording medium substrate. To form such a magnetic recording layer, a film is usually formed at a high temperature, or a heat treatment is performed at a high temperature after the film is formed. As a magnetic recording medium substrate that can have high heat resistance to such high temperature treatment, the magnetic recording medium substrate according to an embodiment of the present invention is preferable. However, the magnetic recording and reproducing device according to one aspect of the present invention is not limited to the energy-assisted magnetic recording and reproducing device. EXAMPLES

[0073] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the embodiments shown in the examples.

[0074] [Examples No. 1 to No. 139] Raw materials such as oxides, carbonates, nitrates, sulfates, and hydroxides were weighed and mixed to prepare a raw material blend so as to obtain glass having the composition shown in Table 1 (Table 1-1 to Table 1-7) below. The raw materials blend were charged into a melting vat and heated and melted in the range of 1400 to 1600°C. The obtained molten glass was held in a refining vat at 1400 to 1550°C for 6 hours, and then the temperature was lowered (cooled down) and held in the range of 1200 to 1400°C for 1 hour. The molten glass was then formed to obtain glasses (amorphous oxide glasses) for the following evaluations.

[0075] <Evaluation of glass properties> (1) Glass transition temperature (Tg), average linear expansion coefficient (α) The glass transition temperature Tg and the average linear expansion coefficient α at 100 to 300° C. of each glass were measured using a thermomechanical analysis (TMA) device.

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

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

[0078] (4) Specific elastic modulus The specific elastic modulus was calculated from the Young's modulus obtained in (2) above and the specific gravity obtained in (3).

[0079] (5) Glass stability 100g of each glass was placed in a platinum crucible, and each crucible was placed in a heating furnace with the furnace temperature set to 1250°C, 1300°C, or 1350°C, and left for 16 hours while maintaining the furnace temperature (retention test). After 16 hours, the crucible was removed from the heating furnace, and the glass in the crucible was transferred onto a refractory material and cooled to room temperature. The presence or absence of crystals in each glass was observed with an optical microscope (magnification 40 to 100 times) and evaluated according to the following criteria. A: No crystals on the glass surface, inside, or at the interface with the platinum crucible bottom B: There are less than 10 crystals with a diameter of several tens of μm on the glass surface and on the interface with the bottom of the platinum crucible per 100 g. C: More than 10 crystals with a diameter of several tens of μm on the glass surface and on the interface with the bottom of the platinum crucible per 100 g D: Crystals inside the glass E: Crystals are present on the glass surface, inside, and at the interface with the platinum crucible bottom. F: The glass is cloudy with many crystals. G: The glass is cloudy

[0080] <Preparation of magnetic recording medium substrate> (1) Preparation of the substrate blank Next, a disk-shaped substrate blank was produced by the following method A or B. Moreover, a glass blank for producing a glass spacer for a magnetic recording / reproducing device can be obtained by the same method. (Method A) For glass having the composition shown in the table below, clarified and homogenized molten glass was flowed out of the flow pipe at a constant flow rate and received by a lower mold for press molding, and the flowed molten glass was cut with a cutting blade so that a predetermined amount of molten glass gob was obtained on the lower mold. The lower mold with the molten glass gob placed thereon was immediately removed from the bottom of the pipe, and the molten glass was press-molded into a thin disk shape with a diameter of 99 mm and a thickness of 0.7 mm using an upper mold and a body mold opposed to the lower mold. The press-molded product was cooled to a temperature at which it would not deform, and then removed from the mold and annealed to obtain a substrate blank. In the above molding, the flowing molten glass was successively molded into disk-shaped substrate blanks using multiple lower molds. (Method B) For glass having the composition shown in the table below, clarified and homogenized molten glass was continuously poured from above into a heat-resistant mold having a cylindrical through-hole, formed into a cylindrical shape, and removed from the bottom of the through-hole. After annealing the removed glass, the glass was sliced ​​at regular intervals in a direction perpendicular to the cylindrical axis using a multi-wire saw to produce disk-shaped substrate blanks. Although the above-mentioned methods A and B were adopted in this embodiment, the following methods C and D are also suitable as methods for manufacturing a disk-shaped substrate blank. The following methods C and D are also suitable as methods for manufacturing a glass blank for producing a glass spacer for a magnetic recording / reproducing device. (Method C) Molten glass can be poured onto a float bath and formed into a sheet of glass (forming by the float method), and then annealed, after which a disk of glass can be hollowed out from the sheet of glass to obtain a substrate blank. (Method D) Molten glass can also be formed into a sheet of glass by the overflow downdraw method (fusion method), annealed, and then a disk of glass can be hollowed out from the sheet of glass to obtain a substrate blank.

[0081] (2) Preparation of glass substrate A through hole was drilled in the center of the substrate blank obtained by each of the above methods, the outer and inner circumferences were ground, and the main surfaces of the disks were lapped and polished (mirror polished) to finish them into glass substrates for magnetic disks with a diameter of 97 mm and a thickness of 0.5 mm. Also, by using the same method, glass blanks for producing glass spacers for magnetic recording and reproducing devices can be finished into glass spacers for magnetic recording and reproducing devices. The glass substrate obtained above was washed with a 1.7% by mass aqueous solution of hydrofluoric acid (H2SiF) and then with a 1% by mass aqueous solution of potassium hydroxide, and then rinsed with pure water and dried. When the surface of the substrate made from the glass of the example was observed under magnification, no surface roughness was observed, and the surface was smooth. For each glass composition, four glass substrates were prepared and used for the following evaluation (1), (2), or (3) or for producing a magnetic recording medium described later.

[0082] <Evaluation of magnetic recording medium substrate> (1) Etching rate (chemical resistance) A masking process was performed on a part of the main surface of each of the magnetic disk glass substrates prepared above to make a portion that was not etched, and the glass substrate in this state was immersed in a potassium hydroxide aqueous solution with a concentration of 0.5 mass % and the liquid temperature was maintained at 50°C for a predetermined time. After that, the glass substrate was pulled out of the aqueous solution, the mask was removed, and the depth of the step between the part that was not exposed to the aqueous solution due to the mask and the part that was exposed to the aqueous solution without the mask was measured. This step depth corresponds to the amount of etching (etching depth) of the glass in a predetermined time. The amount of etching per unit time, i.e., the etching rate (chemical resistance), was calculated by dividing this amount of etching by the immersion time. The etching rate (chemical resistance) determined for each of the magnetic disk glass substrates of the Examples was 0.5 nm / min or less.

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

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

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

[0086] [Table 1-1]

[0087] [Table 1-2]

[0088] [Table 1-3]

[0089] [Table 1-4]

[0090] [Table 1-5]

[0091] [Table 1-6]

[0092] [Table 1-7]

[0093] [Table 2-1]

[0094] [Table 2-2]

[0095] [Table 2-3]

[0096] [Table 2-4]

[0097] [Table 2-5]

[0098] [Table 2-6]

[0099] [Table 2-7]

[0100] [Magnetic recording medium (magnetic disk) production] By the following method, an adhesive layer, an underlayer, a magnetic recording layer, a protective layer, and a lubricant layer were formed in this order on the main surface of the magnetic disk glass substrate prepared above, to obtain a magnetic disk.

[0101] First, using a deposition apparatus that had been evacuated, an adhesive layer, an underlayer, and a magnetic recording layer were successively deposited in an Ar atmosphere by DC magnetron sputtering.

[0102] At this time, the adhesion layer was formed using a CrTi target so as to be an amorphous CrTi layer with a thickness of 20 nm. Then, a 10 nm thick layer made of MgO was formed as an underlayer. The magnetic recording layer was formed at a deposition temperature of 200 to 400°C using an FePtC or CoPtC target so as to be a 10 nm thick granular layer of FePt or CoPt.

[0103] After the magnetic recording layer was formed, the magnetic disk was transferred from the deposition device to a heating furnace and annealed. The temperature in the heating furnace during annealing was set to a range of 500 to 700°C. 10 Magnetic particles of CoPt-based alloy or FePt-based alloy with an ordered structure are formed. 10 Heating may be applied so as to produce an ordered structure.

[0104] Next, a protective layer made of hydrogenated carbon was formed to a thickness of 3 nm by CVD using ethylene as the material gas. After this, a lubricating layer made of PFPE (perfluoropolyether) was formed by dip coating. The thickness of the lubricating layer was 1 nm. A magnetic disk was obtained through the above manufacturing process. The obtained magnetic disk was mounted in a hard disk drive equipped with a DFH mechanism, and magnetic signals were recorded and reproduced in the recording area on the main surface of the magnetic disk at a recording density of 1000 gigabits per square inch. No collision between the magnetic head and the magnetic disk surface (crash failure) was observed.

[0105] In addition, a glass spacer obtained by the above manufacturing process using the glass of the embodiment and having a conductive NiP alloy film formed on its surface (glass spacer with NiP alloy film) was mounted in a hard disk drive equipped with a DFH mechanism, and magnetic signals were recorded and reproduced at a recording density of 1,000 gigabits per square inch in a recording area on the main surface of a magnetic disk separately prepared using a substrate made of a material different from the glass of one embodiment of the present invention.No collision between the magnetic head and the magnetic disk surface (crash failure) was observed.

[0106] Furthermore, when the magnetic disk and the glass spacer with NiP alloy film manufactured above using the same glass material according to one embodiment of the present invention were mounted on a hard disk drive equipped with a DFH mechanism, and magnetic signals were recorded and reproduced in the recording area on the main surface of the magnetic disk at a recording density of 1000 gigabits per square inch, no phenomenon (crash failure) was observed in which the magnetic head collided with the magnetic disk surface. Here, since the glass substrate and the glass spacer included in the magnetic disk are made of the same glass material, the phenomenon that may occur due to the difference in thermal expansion coefficient described above does not occur.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0121] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. For example, by adjusting the composition as described in the specification to the glass compositions exemplified above, it is possible to produce a glass for a magnetic recording medium substrate and a glass spacer for a magnetic recording / reproducing device according to one embodiment of the present invention. Furthermore, it is of course possible to arbitrarily combine two or more of the items described in the specification as examples or preferred ranges.

Claims

1. SiO ２ The content is 56 mol% or more, The MgO content is 15 mol % or more and 28 mol % or less, Li ２ O content is 0.2 mol% or more, Na ２ O content is 5 mol% or less, A ２ O ３ , the total content of MgO and CaO (Al ２ O ３ + MgO + CaO) is 29 mol% or more and 36.50 mol% or less, SiO ２ , MgO, Li ２ O, Al ２ O ３ and the total content of CaO (SiO ２ + MgO + Li ２ O+Al ２ O ３ + CaO) is 95.0 mol% or more, Li ２ SiO vs. O content ２ and MgO total content molar ratio [(SiO ２ + MgO) / Li ２ O] is 13 or more, A ２ O ３ The molar ratio of the CaO content to the total content of Al and MgO [CaO / (Al ２ O ３ + MgO)] is 0.10 or less, The glass for use as a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device is an amorphous glass of the above-mentioned formula (1).

2. Al vs. MgO content ２ O ３ The molar ratio of the total content of Al and CaO [(Al ２ O ３ + CaO) / MgO] is 0.55 or greater.

3. 3. The glass according to claim 1, wherein the molar ratio of the MgO content to the CaO content (MgO / CaO) is 6 or more.

4. A magnetic recording medium substrate made of the glass according to any one of claims 1 to 3.

5. 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 / reproducing device, comprising the glass according to any one of claims 1 to 3.

7. 7. A magnetic recording and reproducing apparatus comprising at least one of the magnetic recording medium according to claim 5 and the glass spacer for a magnetic recording and reproducing apparatus according to claim 6.

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