Glass for glass spacer for magnetic recording medium substrate or magnetic recording regeneration device, magnetic recording medium substrate, magnetic recording medium, glass spacer for magnetic recording regeneration device, and magnetic recording regeneration device

Abstract

To provide glass for a magnetic recording medium substrate having high stiffness.SOLUTION: Glass for a glass spacer for a magnetic recording medium substrate or magnetic recording regeneration device which is an amorphous glass containing at least Li2O, in which a total content of Na2O and K2O is 0-6.0 mol%, a B2O3 content is 0-10.0 mol%, and a CaO content is 0-1.0 mol%.SELECTED DRAWING: None

Description

[Technical field]

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

[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 2002-358626 A Summary of the Invention [Problem to be solved by the invention]

[0004] Glass for magnetic recording medium substrates is desired to have high rigidity 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 data to the magnetic recording layer of the magnetic recording media rotating at high speed inside the HDD and reads data from the magnetic recording layer. If the magnetic recording media vibrates significantly while rotating at high speed for such data writing and reading, it may cause a head crash due to a collision between the magnetic head and the surface of the magnetic recording media. 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. However, in general, the thinner the substrate is to make the magnetic recording media thinner, the more likely the magnetic recording media will vibrate when rotating at high speed. In order to suppress such vibration, it is desirable to use a glass substrate for the magnetic recording media, which has high rigidity and is less likely to vibrate when rotating at high speed even when made thin.

[0005] In view of the above, an object of one aspect of the present invention is to provide a glass for a magnetic recording medium substrate having high rigidity. [Means for solving the problem]

[0006] One aspect of the present invention is Contains at least LiO, The total content of Na2O and K2O is 0 mol% or more and 6.0 mol% or less, The B2O3 content is 0 mol% or more and 10.0 mol% or less, and CaO content is 0 mol% or more and 1.0 mol% or less, a glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device, the glass being an amorphous glass of Regarding. Effect of the Invention

[0007] According to one aspect of the present invention, it is possible to provide a glass having high rigidity for use in a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing device. According to another aspect, it is also possible to provide a magnetic recording medium substrate made of the above glass, 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 made of the above glass. According to yet another aspect, it is possible to provide a magnetic recording and reproducing device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Glass] The above glass is a glass for magnetic recording medium substrate or a glass spacer for magnetic recording / reproducing device, and is amorphous glass. Unlike crystallized glass, amorphous glass is a glass that does not substantially contain a crystalline phase and shows a glass transition phenomenon by heating. On the other hand, crystallized glass has a complicated manufacturing process. In addition, it is not easy to achieve the high smoothness required for magnetic recording medium substrate by using crystallized glass. 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.

[0009] In the present invention and this specification, the glass composition is expressed as a glass composition based on oxides. Here, "glass composition based on oxides" refers to a glass composition obtained by converting the glass raw materials into oxides that are present in the glass after 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%.

[0010] <Glass composition> The glass contains a small amount of CaO of 0% or more and 1.0% or less, Li2O as an essential component, the total content of other alkali metal oxides Na2O and K2O of 0% or more and 6.0% or less, and the B2O3 content of 0% or more and 10.0% or less. Having such a composition can contribute to the glass being able to exhibit high rigidity.

[0011] The CaO content of the glass is 1.0% or less. A CaO content of 1.0% or less contributes to improving the rigidity of the glass and can also contribute to improving the thermal stability of the glass. From these viewpoints, the CaO content is preferably 0.9% or less, more preferably 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less, 0.4% or less, 0.3% or less, 0.2% or less, and 0.1% or less in that order, and can also be 0%. It is more preferable that the glass does not contain CaO.

[0012] The above glass contains Li2O as an essential component, and the total content (Na2O+K2O) of other alkali metal oxides Na2O and K2O is 0% or more and 6.0% or less. This can also contribute to improving the rigidity of the glass. From the viewpoint of further increasing the rigidity of the glass, the total content (Na2O+K2O) of Na2O and K2O is preferably 5.0% or less, more preferably 4.0% or less, 3.0% or less, 2.0% or less, 1.0% or less, 0.5% or less, and 0.1% or less, and can be 0%. It is more preferable that the above glass does not contain Na2O and K2O, and even more preferable that the glass does not contain alkali metal oxides other than Li2O.

[0013] The Li2O content of the above glass is more than 0%, and from the viewpoint of improving thermal stability, it is preferably 1.0% or more, more preferably 2.0% or more, and even more preferably 3.0% or more. Also, from the viewpoint of maintaining the temperature required for melting the glass within an appropriate range, it is preferable that the Li2O content is in the above range. Being able to maintain the temperature required for melting the glass within an appropriate range is also preferable from the viewpoint of extending the life of the melting furnace and reducing costs by reducing the input energy. On the other hand, from the viewpoint of further improving the rigidity of the glass, furthermore, from the viewpoint of improving the devitrification resistance and / or from the viewpoint of increasing the glass transition temperature, the Li2O content is preferably 10.0% or less, and more preferably in the order of 9.0% or less, 8.0% or less, 7.0% or less, 6.0% or less, 5.0% or less, and 4.0% or less.

[0014] The B2O3 content of the glass is 10.0% or less, preferably 9.0% or less, in order of 8.0% or less, 7.0% or less, 6.0% or less, 5.0% or less, 4.0% or less, 3.0% or less, 2.0% or less, 1.0% or less, and 0.5% or less, in that order. The B2O3 content of the glass is 0% or more, and from the viewpoint of improving impact resistance and thermal stability, it is preferably 0.1% or more, and more preferably 0.2% or more. Glass with high impact resistance is preferable because cracking and chipping are unlikely to occur during processing such as cutting and grinding. Glass with high thermal stability is also preferable because it is unlikely to cause devitrification.

[0015] In one form, the glass may include one or both of SiO2 and Al2O3.

[0016] From the viewpoint of improving chemical durability, the SiO2 content of the glass is preferably 50.0% or more, more preferably 51.0% or more, 52.0% or more, 53.0% or more, 54.0% or more, and 55.0% or more in that order. Glass with high chemical durability is preferable because it is less likely to cause surface roughness during polishing or cleaning. On the other hand, from the viewpoint of further improving rigidity, the SiO2 content is preferably 70.0% or less, more preferably 69.0% or less, 68.0% or less, 67.0% or less, 66.0% or less, 65.0% or less, 64.0% or less, and 63.0% or less in that order.

[0017] From the viewpoint of improving thermal stability, the Al2O3 content of the above glass is preferably 20.0% or less, and more preferably 19.0% or less, 18.0% or less, 17.0% or less, 16.0% or less, 15.0% or less, and 14.0% or less in that order. Also, from the viewpoint of maintaining the temperature required for melting the glass within an appropriate range, it is preferable that the Al2O3 content is within the above range. On the other hand, from the viewpoint of further improving rigidity, the Al2O3 content is preferably 10.0% or more, and more preferably 11.0% or more.

[0018] Concerning the alkaline earth metal oxide, the CaO content of the glass is as described above. In one embodiment, the glass may contain one or more alkaline earth metal oxides. Specific examples of the alkaline earth metal oxides that may be contained in the glass include MgO, SrO, and BaO. In one embodiment, the glass may contain MgO. From the viewpoint of further improving the rigidity, the MgO content of the glass is preferably 10.0% or more, more preferably 11.0% or more, and more preferably 12.0% or more in this order. In addition, from the viewpoint of improving the devitrification resistance of the glass, the MgO content is preferably 28.0% or less, and more preferably 27.0% or less, 26.0% or less, 25.0% or less, 24.0% or less, 23.0% or less, 22.0% or less, 21.0% or less, 20.0% or less, 19.0% or less, and 18.0% or less in this order.

[0019] The Fe2O3 content of the glass can be 1 mol% or less, 0.7 mol% or less, 0.5 mol% or less, 0.4 mol% or less, 0.3 mol% or less, 0.1 mol% or less, 0.07 mol% or less, 0.05 mol% or less, 0.04 mol% or less, 0.03 mol% or less, or 0.02 mol% or less, as a content expressed by an exclusive percentage. The Fe2O3 content is expressed by an exclusive percentage. That is, when the total content of components other than Fe2O3 contained in the glass (the total content of the glass components and additives when additives are included in addition to the glass components) is taken as 100%, the Fe2O3 content is expressed as a molar percentage of the Fe2O3 content relative to 100%. In one embodiment, the glass can be free of Fe (the Fe2O3 content expressed by the exclusive percentage can be 0 mol%).

[0020] The above glass may or may not contain one or more metals or oxides thereof selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er. In the glass composition based on oxides, the inclusion of one or more oxides of metals selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er tends to increase the thermal stability of the glass. In one embodiment, the content of one or more metal oxides selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er (the total content when a plurality of metal oxides are included) can be 0%, 0% or more, or more than 0%, and can be 5.0% or less, 4.0% or less, 3.0% or less, 2.0% or less, 1.0% or less, 0.5% or less, or 0.1% or less. For example, the Y2O3 content can be 0% or more, or more than 0%, and can be 3.0% or less, 2.0% or less, or 1.0% or less. The TiO2 content can be 0% or more, or more than 0%, and can be 3.0% or less, 2.0% or less, or 1.0% or less. In one embodiment, the glass can include one or both of Y2O3 and TiO2.

[0021] 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.

[0022] Since Pb, Cd and As are substances that have a negative impact on the environment, it is preferable to avoid introducing these.

[0023] 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.

[0024] 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 that have a negative effect on the environment, such as Sb2O3 and arsenous acid, in one embodiment, it is preferable to introduce SnO2 into the 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.

[0025] 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 above 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 above glass contains both SnO2 and CeO2.

[0026] 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.

[0027] 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.

[0028] <Glass properties> By adjusting the composition as described above, the above glass can have various glass properties as described below.

[0029] (Specific elastic modulus) The glass has the above-mentioned composition and thus has high rigidity. The specific elastic modulus can be used as an index of the rigidity of the glass. The specific elastic modulus is calculated by dividing the Young's modulus of the glass by the density. Here, density refers to the specific gravity of the glass divided by the density in g / cm. 3The specific elastic modulus of the glass is preferably 35.0MNm / kg or more, more preferably 35.5MNm / kg or more, 36.0MNm / kg or more, 36.5MNm / kg or more, 37.0MNm / kg or more, 37.5MNm / kg or more, and 38.0MNm / kg or more in that order. The specific elastic modulus can be, for example, 45.0MNm / kg or less, 44.0MNm / kg or less, 43.0MNm / kg or less, 42.0MNm / kg or less, 41.0MNm / kg or less, or 40.0MNm / kg or less, but is not limited to the above exemplified values ​​because the higher the specific elastic modulus, the higher the rigidity and the more preferable it is.

[0030] (Young's modulus E) The Young's modulus can also be mentioned as an index of the rigidity of glass. The Young's modulus of the above glass is preferably 86.0GPa or more, more preferably 87.0GPa or more, more preferably 88.0GPa or more, 89.0GPa or more, 90.0GPa or more, 91.0GPa or more, 92.0GPa or more, 93.0GPa or more, 94.0GPa or more, and 95.0GPa or more in this order. The Young's modulus of the above glass can be, for example, 120.0GPa or less or 110.0GPa or less, but is not limited to the above exemplified values, since the higher the Young's modulus, the higher the rigidity and the more preferable it is.

[0031] (specific gravity d) The low specific gravity of the glass for magnetic recording medium substrate can reduce the weight of the magnetic recording medium substrate, and further reduce the weight of the magnetic recording medium, which can reduce the power consumption of the HDD. The specific gravity of the glass is preferably 2.80 or less, more preferably 2.75 or less, even more preferably 2.70 or less, even more preferably 2.65 or less, and even more preferably 2.60 or less. The specific gravity of the glass can be, for example, 2.40 or more, but is not limited to the above-mentioned values, since the lower the specific gravity, the more preferable it is.

[0032] (glass transition temperature Tg) 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 usually 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 in order to prevent the flatness of the substrate from being reduced by exposure to high temperatures. In this regard, the above glass can also exhibit high heat resistance by having the above glass composition. Regarding the glass transition temperature Tg, which is an index of heat resistance, the Tg of the above glass can be, for example, 550° C. or more, preferably 600° C. or more, more preferably 610° C. or more, 620° C. or more, 630° C. or more, 640° C. or more, 650° C. or more, 660° C. or more, 670° C. or more, 680° C. or more, 690° C. or more, 700° C. or more, 710° C. or more, 720° C. or more, 730° C. or more, 740° C. or more, and 750° C. or more in that order. In addition, the Tg of the above glass can be, for example, 850° C. or less, 830° C. or less, 810° C. or less, 790° C. or less, 770° C. or less, or 750° C. or less, but is not limited to the above exemplified values, since a higher Tg is more preferable from the viewpoint of heat resistance.

[0033] (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 to prevent the difference between the thermal expansion coefficient of the glass for the magnetic recording medium substrate and that of the spindle material (such as stainless steel) from becoming too large. In general, the thermal expansion coefficient of the spindle material for HDDs is 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 30.0 × 10 -7 / °C or more, the difference in thermal expansion coefficient between the spindle material and the glass is small, which contributes to improving the reliability of the magnetic recording medium. -7 / °C or more, and 35.0 x 10 -7 / °C or more, and more preferably 36.0×10 -7 / °C or more, more preferably 37.0 x 10 -7 / °C or more, more preferably 38.0 x 10 -7 / °C or more, and more preferably 39.0 x 10 -7 It is even more preferable that the temperature is 40.0×10 -7 / °C or more. The average linear expansion coefficient α of the above glass at 100 to 300°C is 70.0 × 10 -7 / ℃ or less, and 68.0×10 -7 / °C or less, and more preferably 65.0×10 -7 / °C or less, more preferably 63.0×10 -7 / °C or less, and more preferably 60.0×10 -7 / °C or less, and more preferably 57.0×10 -7 / °C or less, and even more preferably 55.0×10 -7 It is even more preferable that the temperature is 0.15 to 1.5°C.

[0034] (Liquidus temperature LT) An index of the thermal stability of glass can be the liquidus temperature (LT). The LT of the above glass is preferably 1320°C or less, more preferably 1310°C or less, and further preferably 1300°C or less, 1290°C or less, 1280°C or less, 1270°C or less, 1260°C or less, 1250°C or less, and 1240°C or less in this order. Glass with a low liquidus temperature LT is preferable because it is less likely to cause devitrification. The lower limit of LT can be, for example, 800°C or more, but is not particularly limited.

[0035] The various physical properties mentioned above can be determined by the methods described below in the Examples.

[0036] [Magnetic recording medium substrate] A magnetic recording medium substrate according to one aspect of the present invention is made of the above-mentioned glass.

[0037] 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 outflow 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, the obtained substrate blank is provided with a center hole, and is subjected to inner and outer periphery processing, and polishing processing such as lapping and polishing is performed on both main surfaces. Next, a cleaning process including acid cleaning and alkali cleaning is performed to obtain a disk-shaped substrate. For the various steps performed to obtain the above magnetic recording medium substrate, known techniques related to the manufacture of magnetic recording medium substrates can be applied.

[0038] 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.

[0039] 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, or the like.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Since the magnetic recording medium substrate is made of the glass according to one aspect of the present invention, it can have the glass properties described above for the glass.

[0044] [Magnetic recording media] One aspect of the present invention relates to a magnetic recording medium having the above magnetic recording medium substrate and a magnetic recording layer.

[0045] Magnetic recording media are called magnetic disks, hard disks, etc., and are suitable for various magnetic recording and reproducing devices, for example, 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 reproduce images and / or sounds, recording and reproducing devices of in-car audio, etc. In this invention and this specification, the term "magnetic recording and reproducing device" refers to a device that is capable of either or both of magnetically recording information and magnetically reproducing information.

[0046] 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.

[0047] 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 can be an Fe-Pt magnetic material or a Co-Pt magnetic material. Here, "based" means containing. That is, the magnetic recording medium can have 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.

[0048] In recent years, a DFH (Dynamic Flying Height) mechanism has been installed on a magnetic head to significantly narrow 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 of providing a heating unit such as a very small heater near the read / write element of the magnetic head and protruding only the periphery of the element toward the surface of the medium. This reduces the distance (flying height) between the magnetic head and the magnetic recording layer of the medium, making it possible to pick up signals from smaller magnetic particles and achieve even higher recording density. In one embodiment, the magnetic recording medium substrate can be used as a substrate for a magnetic recording medium applied to a magnetic recording and reproducing device equipped with a magnetic head equipped with a DFH mechanism.

[0049] There are no particular limitations on the dimensions of the magnetic recording medium substrate (e.g., glass substrate for magnetic disk) and the magnetic recording medium (e.g., magnetic disk). For example, it is possible to miniaturize the medium and substrate since high recording density is possible. It is also possible to enlarge the medium and substrate in order to increase the recording capacity per magnetic recording medium. For example, the nominal diameter can of course be 2.5 inches, but it can also be smaller (e.g., 1 inch, 1.8 inches), or 3 inches, 3.5 inches, or even larger.

[0050] [Glass spacer for magnetic recording / reproducing devices] A glass spacer for a magnetic recording / reproducing device according to one embodiment of the present invention (hereinafter, also simply referred to as a "glass spacer") is made of the above glass.

[0051] 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 desirable for this glass spacer to have high rigidity. In contrast, the glass having the above composition can have high rigidity, and is therefore suitable as a glass spacer for a magnetic recording and reproducing device.

[0052] 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 descriptions on the manufacturing method of glass for magnetic recording medium substrate and the manufacturing method of magnetic recording medium substrate can be referred to. For other details such as the glass composition and glass physical properties of the glass spacer, the above descriptions on the glass, the magnetic recording medium substrate made of the glass, and the magnetic recording medium having such a magnetic recording medium substrate can be referred to. The spacer for the magnetic recording and reproducing device may be made of the above-mentioned glass spacer, or may have one or more layers of a conductive film or the like provided on the surface of the above-mentioned glass spacer. For example, in order to remove static electricity generated during rotation of the magnetic recording medium, a conductive film of a NiP alloy or the like may be formed on the surface of the glass spacer by plating, immersion, deposition, sputtering, or the like. In addition, the glass spacer may be polished to increase the surface smoothness (for example, the average surface roughness Ra is 1 μm or less), which may increase the degree of adhesion between the magnetic recording medium and the spacer and suppress the occurrence of positional deviation.

[0053] [Magnetic recording and playback device] One aspect of the present invention relates to a magnetic recording and reproducing device including one or more members selected from the group consisting of the magnetic recording medium and the glass spacer.

[0054] 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.

[0055] 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. In one embodiment, the magnetic recording medium substrate according to an embodiment of the present invention may be a magnetic recording medium substrate having high heat resistance that can withstand such high-temperature treatment. However, the magnetic recording and reproducing device according to one aspect of the present invention is not limited to the energy-assisted magnetic recording and reproducing device. EXAMPLES

[0056] 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.

[0057] [Examples 1 to 62] Raw materials such as oxides, carbonates, nitrates, sulfates, and hydroxides were weighed and mixed to prepare a raw material blend so as to obtain glass having the composition shown in Table 1. This raw material blend was charged into a melting vat and heated and melted in the range of 1400-1600°C to obtain a molten glass. The molten glass was then held in a refining vat at 1400-1550°C for six hours, after which the temperature was lowered (cooled down) and held in the range of 1200-1400°C for one hour, after which the molten glass was formed to obtain glasses (amorphous oxide glasses) for the following evaluations.

[0058] <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.

[0059] (2) Young's modulus E The Young's modulus of each glass was measured by an ultrasonic method.

[0060] (3) Specific gravity d The specific gravity of each glass was measured by Archimedes' method.

[0061] (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).

[0062] The above results are shown in Table 1 (Table 1-1 to Table 1-5).

[0063] [Table 1-1]

[0064] [Table 1-2]

[0065] [Table 1-3]

[0066] [Table 1-4]

[0067] [Table 1-5]

[0068] From the results shown in Table 1, it can be confirmed that the glasses of Examples 1 to 62 have high rigidity. For example, the glass of Example 27 shown in Table 5 of JP-A-2002-358626 (hereinafter referred to as "comparative glass") has a glass composition in mol% of SiO2: 65.0%, Al2O3: 7.0%, MgO: 1.0%, CaO: 1.0%, Li2O: 10.0%, Na2O: 10.5%, and K2O: 2.5%, which is different from the glass according to one embodiment of the present invention described above in detail. The value calculated by dividing the Young's modulus value shown in Table 5 of JP-A-2002-358626 by the density value for this comparative glass is about 32.45, which is lower than the specific elastic modulus value of Examples 1 to 62 shown in Table 1.

[0069] (5) Liquidus temperature LT The liquidus temperatures of the glasses shown in Table 2 were determined by the following method. 50 g of glass was weighed into a platinum crucible. This platinum crucible was placed in a heating furnace with a platinum lid and the glass in the crucible was completely molten, and then the furnace atmosphere temperature was lowered to a predetermined temperature and maintained at that temperature for 16 hours. After maintaining for 16 hours, the platinum crucible was taken out of the furnace and left to cool the glass to room temperature (about 20°C to 25°C). The glass after cooling was visually observed to check for the presence or absence of crystal precipitation. The above operation was carried out from 1280°C to 1200°C in 10°C increments, and the lowest temperature at which no crystal precipitation was observed was taken as the liquidus temperature LT.

[0070] [Table 2]

[0071] For the glasses of Examples 17, 18, 22, 29, and 33, it was confirmed that the liquidus temperature LT was 1300° C. or lower by the following method. 50 g of glass was weighed into a platinum crucible. This platinum crucible was placed in a heating furnace with a platinum lid and the glass in the crucible was completely molten, and then the furnace atmosphere temperature was lowered to 1300°C and held at that temperature for 16 hours. After holding for 16 hours, the platinum crucible was taken out of the furnace and left to cool the glass to room temperature (about 20°C to 25°C). The glass after cooling was visually observed to check for the presence or absence of crystal precipitation, and no crystal precipitation was observed.

[0072] <Preparation of magnetic recording medium substrate> (1) Preparation of the substrate blank A disk-shaped substrate blank was prepared by the following method A or B. Also, 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 Table 1, 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-out molten glass was cut with a cutting blade so as to obtain a predetermined amount of molten glass gob 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 (amorphous oxide glass). In the above-mentioned molding, the flowing molten glass was successively formed into disk-shaped substrate blanks using multiple lower molds. (Method B) For glass with the composition shown in Table 1, clarified and homogenized molten glass was continuously poured from above into a cylindrical through-hole of a heat-resistant mold, formed into a cylindrical shape, and removed from the bottom of the hole. After annealing the removed glass, a multi-wire saw was used to slice the glass at regular intervals in a direction perpendicular to the cylindrical axis to produce disk-shaped substrate blanks (amorphous oxide glass). 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 that, a disk of glass can be hollowed out from the sheet glass to obtain a substrate blank (amorphous oxide glass). (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 (amorphous oxide glass).

[0073] (2) Preparation of glass substrate A through hole was drilled in the center of the substrate blank (amorphous oxide glass) obtained by each of the above methods, the outer and inner circumferences were ground, and the main surface of the disk was lapped and polished (mirror polished) to finish it into a glass substrate for a magnetic disk with a diameter of 97 mm and a thickness of 0.5 mm. Also, by using the same method, a glass blank for producing a glass spacer for a magnetic recording and reproducing device can be finished into a glass spacer for a magnetic recording and reproducing device. 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.

[0074] <Making magnetic recording media (magnetic disks)> 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] In addition, a glass spacer obtained by the above manufacturing process using glass of the composition shown in Table 1 and having a conductive NiP alloy film formed on its surface (glass spacer with NiP alloy film) was installed in a hard disk drive equipped with a DFH mechanism, and magnetic signals were recorded and reproduced at a recording density of 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, and no collision between the magnetic head and the magnetic disk surface (crash failure) was observed.

[0080] 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.

[0081] According to one aspect of the present invention, it is possible to provide a magnetic recording medium suitable for high density recording.

[0082] Finally, the above-mentioned aspects will be summarized.

[0083] According to one embodiment, there is provided a glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing device, which is an amorphous glass containing at least Li2O, with a total content of Na2O and K2O of 0 mol % or more and 6.0 mol % or less, a B2O3 content of 0 mol % or more and 10.0 mol % or less, and a CaO content of 0 mol % or more and 1.0 mol % or less.

[0084] The glass can have high rigidity.

[0085] In one embodiment, the CaO content of the glass can be 0 mol % or more and 0.5 mol % or less.

[0086] In one embodiment, the CaO content of the glass can be 0 mol % or more and 0.1 mol % or less.

[0087] In one form, the glass can be a CaO-free glass.

[0088] In one embodiment, the B2O3 content of the glass can be from 0.1 mol % to 10.0 mol %.

[0089] In one embodiment, the SiO2 content of the glass can be 50.0 mol % or more and 70.0 mol % or less.

[0090] In one embodiment, the SiO2 content of the glass can be 55.0 mol % or more and 68.0 mol % or less.

[0091] In one embodiment, the Li2O content of the glass can be 1.0 mol % or more and 10.0 mol % or less.

[0092] In one embodiment, the Li2O content of the glass can be equal to or greater than 3.0 mol % and equal to or less than 6.0 mol %.

[0093] In one embodiment, the glass can be a glass that does not contain any alkali metal oxides other than Li2O.

[0094] In one embodiment, the Al2O3 content of the glass can be equal to or greater than 10.0 mol % and equal to or less than 20.0 mol %.

[0095] In one embodiment, the Al2O3 content of the glass can be equal to or greater than 10.0 mol % and equal to or less than 17.0 mol %.

[0096] In one embodiment, the MgO content of the glass can be 10.0 mol % or more and 25.0 mol % or less.

[0097] In one embodiment, the glass can further comprise an oxide of one or more metals selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er.

[0098] In one embodiment, the specific elastic modulus of the glass can be 35.0 MNm / kg or more.

[0099] According to one embodiment, there is provided a magnetic recording medium substrate made of the above glass.

[0100] According to one embodiment, there is provided a magnetic recording medium having the above magnetic recording medium substrate and a magnetic recording layer.

[0101] According to one embodiment, there is provided a glass spacer for a magnetic recording / reproducing device, which is made of the above glass.

[0102] According to one embodiment, the magnetic recording medium and the glass spacer for the magnetic recording / reproducing device are provided. There is provided a magnetic recording and reproducing device including one or more selected from the group consisting of:

[0103] 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. Li ２ The O content is 2.0 mol% or more and 6.0 mol% or less, Na ２ O and K ２ The total content of O is 0 mol% or more and 0.5 mol% or less, B ２ O ３ The content is 0 mol% or more and 0.5 mol% or less, SiO ２ The content is 54.0 mol% or more and 70.0 mol% or less, A ２ O ３ The content is 10.0 mol% or more and 19.0 mol% or less, The CaO content is 0 mol% or more and 0.1 mol% or less, The MgO content is 12.0 mol% or more and 26.0 mol% or less, TiO ２ The content is 0 mol% or more and 0.5 mol% or less, Young's modulus is 94.0 GPa or more, and A glass transition temperature Tg of 697° C. or higher; 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. B ２ O ３ The glass according to claim 1 , wherein the content is from 0.1 mol % to 0.5 mol %.

3. Li ２ 3. The glass of claim 1, which is free of alkali metal oxides other than O.

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. 6. A magnetic recording and reproducing apparatus comprising the magnetic recording medium and a magnetic head according to claim 5.