Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/62—Record carriers characterised by the selection of the material
  • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
  • G11B5/739—Magnetic recording media substrates
  • G11B5/73911—Inorganic substrates
  • G11B5/73921—Glass or ceramic substrates
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/095—Glass compositions containing silica with 40% to 90% silica, by weight containing rare earths
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/083—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound
  • C03C3/085—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal
  • C03C3/087—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal containing calcium oxide, e.g. common sheet or container glass
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B17/00—Guiding record carriers not specifically of filamentary or web form, or of supports therefor
  • G11B17/02—Details
  • G11B17/038—Centering or locking of a plurality of discs in a single cartridge
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B23/00—Record carriers not specific to the method of recording or reproducing; Accessories, e.g. containers, specially adapted for co-operation with the recording or reproducing apparatus ; Intermediate mediums; Apparatus or processes specially adapted for their manufacture
  • G11B23/02—Containers; Storing means both adapted to cooperate with the recording or reproducing means
  • G11B23/03—Containers for flat record carriers
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/127—Structure or manufacture of heads, e.g. inductive
  • G11B5/187—Structure or manufacture of the surface of the head in physical contact with, or immediately adjacent to the recording medium; Pole pieces; Gap features
  • G11B5/23—Gap features
  • G11B5/235—Selection of material for gap filler
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/62—Record carriers characterised by the selection of the material
  • G11B5/72—Protective coatings, e.g. anti-static or antifriction
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B41/00—Component parts such as frames, beds, carriages, headstocks
  • B24B41/04—Headstocks; Working-spindles; Features relating thereto
  • B24B41/047—Grinding heads for working on plane surfaces
  • B24B41/053—Grinding heads for working on plane surfaces for grinding or polishing glass

Definitions

• 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.
• a substrate made of an aluminum alloy has been used as a substrate for a magnetic recording medium such as a hard disk (magnetic recording medium substrate).
• a magnetic recording medium substrate such as a hard disk (magnetic recording medium substrate).
• the aluminum alloy substrate is easily deformed. Therefore, at present, a magnetic recording medium substrate made of glass is widely used.
• Patent Document 1 discloses non-alkali glass.
• the document states that the glass described in this document can also be used as a glass substrate for a magnetic disk (see paragraph 0014 of Patent Document 1).
• the glass for the magnetic recording medium substrate is required to have high heat resistance that can withstand high temperature treatment, specifically, to have a high glass transition temperature.
• glass for a magnetic recording medium substrate is also required to be easy to produce, that is, to have excellent productivity.
• Patent Document 1 discloses glass having a high glass transition temperature, improvement in productivity is desired.
• One aspect of the present invention is to provide a glass for a magnetic recording medium substrate having excellent heat resistance and productivity.
• One aspect of the present invention is The total content of Li 2 O, Na 2 O, K 2 O, B 2 O 3 and Zn O (Li 2 O + Na 2 O + K 2 O + B 2 O 3 + ZnO) is 0 mol% or more and 3 mol% or less.
• the molar ratio of the total content of Al 2 O 3 and Mg O to the total content of SiO 2 and CaO [(Al 2 O 3 + MgO) / (SiO 2 + CaO)] is 0.30 or more and 0.6 or less.
• the total content of SiO 2 and Al 2 O 3 (SiO 2 + Al 2 O 3 ) is 64 mol% or more and 85 mol% or less, and the total content of SiO 2 , Al 2 O 3 , MgO and CaO (SiO 2 + Al). 2 O 3 + MgO + CaO) is 87 mol% or more and 98 mol% or less, Glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device (hereinafter, also referred to as "glass A”), Regarding.
• Another aspect of the present invention is The molar ratio of the total content of Al 2 O 3 and Mg O to the total content of SiO 2 and CaO [(Al 2 O 3 + MgO) / (SiO 2 + CaO)] is 0.30 or more and 0.6 or less.
• the total content of SiO 2 and Al 2 O 3 (SiO 2 + Al 2 O 3 ) is 64 mol% or more and 85 mol% or less.
• the total content of SiO 2 , Al 2 O 3 , MgO and CaO (SiO 2 + Al 2 O 3 + MgO + CaO) is 87 mol% or more and 98 mol% or less, and the glass transition temperature is 740 ° C. or more.
• Glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device hereinafter, also referred to as "glass B"
• Glass A and glass B have the above-mentioned glass composition, and can have excellent heat resistance and excellent productivity.
• Excellent productivity means, for example, excellent meltability in one form. Further, excellent productivity means that, for example, in one form, the same polishing pad can be continuously used for a longer period of time in a polishing step usually performed for processing a magnetic recording medium substrate.
• a glass having excellent heat resistance and excellent productivity is suitable as a glass for a magnetic recording medium substrate, and is also suitable as a glass for a glass spacer for a magnetic recording / reproducing device.
• the present invention it is possible to provide glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device, which is excellent in both heat resistance and productivity. Further, according to one aspect, it is also possible to provide a magnetic recording medium substrate made of the above glass and a magnetic recording medium including the substrate. Further according to one aspect, it is possible to provide a glass spacer for a magnetic recording device made of the above glass. Further, according to one aspect, it is possible to provide a magnetic recording / reproducing device.
• the glass A and the glass B are glass for a magnetic recording medium substrate or glass for a glass spacer for a magnetic recording / reproducing device, and can be amorphous glass.
• Amorphous glass is glass that does not substantially contain a crystal phase and exhibits a glass transition phenomenon due to temperature rise, unlike crystallized glass.
• the glass can be an amorphous oxide glass.
• Oxide glass is glass in which the main network-forming component of glass is oxide. Hereinafter, the glass will be described in more detail.
• glass A and glass B will be described in more detail. Unless otherwise specified, the description of glass A can also be applied to glass B, and the description of glass B can also be applied to glass A.
• the glass composition is represented by an oxide-based glass composition.
• the "oxide-based glass composition” refers to a glass composition obtained by converting all glass raw materials into those that are decomposed at the time of melting and exist as oxides in glass. Unless otherwise specified, the glass composition shall be indicated on a molar basis (molar%, molar ratio).
• the glass composition of the present invention and the present specification can be determined by, for example, ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) or the like. Quantitative analysis is performed for each element using ICP-AES. The analytical values are then converted to oxide notation.
• the analysis value by ICP-AES may include, for example, a measurement error of about ⁇ 5% of the analysis value. Therefore, the oxide notation value converted from the analysis value may also contain an error of about ⁇ 5%.
• the content of the constituent component when the content of the constituent component is 0% or not contained or introduced, it means that the constituent component is substantially not contained, and the content of the constituent component is at the impurity level. It means that it is less than or equal to the degree.
• the impurity level or less means, for example, less than 0.01%.
• Glass composition The total content of Li 2 O, Na 2 O, K 2 O, B 2 O 3 and Zn O (Li 2 O + Na 2 O + K 2 O + B 2 O 3 + ZnO) is 3% or less from the viewpoint of improving heat resistance. It is preferably 2.8 or less, more preferably 2.6 or less, further preferably 2.4 or less, further preferably 2.0 or less, and 1.5 or less. Is even more preferably 1.0 or less, even more preferably 0.8 or less, and even more preferably 0.5 or less.
• the total content of Li 2 O, Na 2 O, K 2 O, B 2 O 3 and Zn O is 0% or more and can be 0%. , 0% or more, 0.1% or more, 0.2% or more, or 0.3% or more.
• the molar ratio of the total content of Al 2 O 3 and Mg O to the total content of SiO 2 and CaO [(Al 2 O 3 + MgO) / (SiO 2 + CaO)] is particularly high from the viewpoint of improving productivity. From the viewpoint of enabling the same polishing pad to be used for a longer period of time, it is 0.30 or more, preferably 0.32 or more, more preferably 0.34 or more, and 0. It is more preferably 36 or more, and even more preferably 0.38 or more. Further, the molar ratio [(Al 2 O 3 + MgO) / (SiO 2 + CaO)] is 0.6 or less, preferably 0.60 or less, and 0.58 or less, from the viewpoint of improving glass stability. It is more preferably 0.56 or less, further preferably 0.54 or less, further preferably 0.52 or less, further preferably 0.50 or less. More preferred.
• the total content of SiO 2 and Al 2 O 3 is 85% or less, and 83% or less, from the viewpoint of improving productivity, especially from the viewpoint of improving the meltability of glass. Is preferable. Further, from the viewpoint that the glass can exhibit a viscosity suitable for molding at a molding temperature suitable for molding glass with high productivity, the total content of SiO 2 and Al 2 O 3 (SiO 2 + Al 2 O) 3 ) is preferably 82% or less, and more preferably 81% or less. From the viewpoint of improving chemical durability, the total content of SiO 2 and Al 2 O 3 (SiO 2 + Al 2 O 3 ) is 64% or more, preferably 66% or more, preferably 68%. The above is more preferable, and 70% or more is further preferable.
• the total content of SiO 2 , Al 2 O 3 , MgO and CaO is 87% or more from the viewpoint of improving heat resistance. It is preferable that the total content (SiO 2 + Al 2 O 3 + MgO + CaO) is 87% or more from the viewpoint of improving the glass stability and lowering the specific density of the glass. From the above viewpoint, the total content (SiO 2 + Al 2 O 3 + MgO + CaO) is preferably 89% or more, more preferably 91% or more, and further preferably 93% or more. From the viewpoint of improving glass stability, the total content (SiO 2 + Al 2 O 3 + MgO + CaO) is 98% or less, preferably 97% or less, and more preferably 96% or less.
• SiO 2 is a network-forming component of glass. From the viewpoint of further improving the glass stability, the SiO 2 content is preferably 55% or more, more preferably 57% or more, and further preferably 59% or more. Further, the SiO 2 content is preferably 66% or less, more preferably 64% or less, from the viewpoint of further improving the productivity, particularly from the viewpoint of further improving the meltability of the glass. , 63% or less is more preferable.
• B 2 O 3 is also a network-forming component of glass.
• the B 2 O 3 content can be 0% or more, can be 0%, or can be greater than 0%.
• B 2 O 3 tends to volatilize during melting and tends to make the glass component ratio unstable. In addition, over-introduction tends to reduce chemical durability. From the above viewpoint, the B 2 O 3 content can be, for example, 3% or less, preferably 2% or less, more preferably 1% or less, and further preferably 0%.
• the Al 2 O 3 content is preferably 10% or more, more preferably 11% or more, and further preferably 12% or more. Further, the Al 2 O 3 content is preferably 18% or less, more preferably 17% or less, still more preferably 16% or less, from the viewpoint of further improving the glass stability. ..
• the P 2 O 5 content can be 0% or more, can be 0%, or can be greater than 0%. From the viewpoint of further improving the glass stability, the P 2 O 5 content is preferably 1% or less, more preferably 0.5% or less, and preferably 0.3% or less. More preferred.
• the MgO content is preferably 8% or more, more preferably 9% or more, still more preferably 10% or more, from the viewpoint of improving the rigidity of the glass, for example, from the viewpoint of increasing Young's modulus. It is more preferably 12% or more. From the viewpoint of further improving the glass stability, the MgO content is preferably 20% or less, more preferably 19% or less, and further preferably 18% or less.
• the CaO content can be 0% or more, 0%, or more than 0%. From the viewpoint of further improving the glass stability, the CaO content is preferably more than 0%, more preferably 0.5% or more, still more preferably 1% or more. It is more preferably 5% or more, and even more preferably 2% or more. Further, from the viewpoint of further improving productivity, particularly from the viewpoint of enabling the same polishing pad to be used for a longer period of time, the CaO content is preferably 7% or less, preferably 6%. It is more preferably less than or equal to, and even more preferably 5% or less.
• the total content of Al 2 O 3 , MgO and CaO is preferably 38% or less, more preferably 35% or less, from the viewpoint of further improving the glass stability. It is preferably 34% or less, and more preferably 34% or less. From the viewpoint of improving the rigidity of the glass, for example, from the viewpoint of improving the Young's modulus, the total content (Al 2 O 3 + MgO + CaO) is preferably 26% or more, more preferably 28% or more, and more preferably 30% or more. Is more preferable.
• the BaO content can be 0% or more, 0%, more than 0%, 0.5% or more, or 1% or more. From the viewpoint of lowering the specific density of the glass, the BaO content is preferably 3% or less, more preferably 2.5% or less, and further preferably 2% or less.
• the SrO content can be 0% or more, can be 0%, can be more than 0%, and can be more than 0% from the viewpoint of further improving the glass stability. It is preferably 0.5% or more, more preferably 1% or more. From the viewpoint of lowering the specific density of the glass, the SrO content is preferably 5% or less, more preferably 4.5% or less, further preferably 4% or less, and 3.5%. It is more preferably less than or equal to, and even more preferably 3% or less.
• the molar ratio of the CaO content to the total content of MgO, CaO, SrO and BaO [CaO / (MgO + CaO + SrO + BaO)] can be 0 and can be greater than 0.
• the molar ratio [CaO / (MgO + CaO + SrO + BaO)] is preferably more than 0.
• the molar ratio [CaO / (MgO + CaO + SrO + BaO)] is 0.36 or less. It is preferably 0.34 or less, more preferably 0.32 or less, further preferably 0.30 or less, and even more preferably 0.28 or less.
• the ZnO content can be 0% or more, 0%, more than 0%, 0.5% or more, or 1% or more. From the viewpoint of further improving the glass stability, the ZnO content is preferably 2% or less, more preferably 1.5% or less, and further preferably 1% or less.
• the total content of ZnO and BaO can be 0%, more than 0%, 0.5% or more, or 1% or more. From the viewpoint of lowering the specific density of the glass, the total content (ZnO + BaO) is preferably 2.5% or less, more preferably 2.3% or less, and preferably 2.0% or less. More preferred.
• the ZrO 2 content can be 0% or higher, 0%, greater than 0%, 0.5% or higher, or 1% or higher. From the viewpoint of further improving the glass stability, the ZrO 2 content is preferably 4% or less, more preferably 3.5% or less, further preferably 3% or less, 2 It is more preferably 5.5% or less, and even more preferably 2% or less.
• the Li 2 O content can be 0% or more, 0%, or more than 0%. From the viewpoint of further improving the heat resistance, the Li 2 O content is preferably 3% or less, more preferably 2% or less, further preferably 1% or less, and 0.5. It is more preferably% or less, and even more preferably 0.3% or less.
• the Na 2 O content can be 0% or more, 0%, or more than 0%. Further, the Na 2 O content can be, for example, 3% or less, 2.5% or less, or 2% or less.
• K 2 O may also be not less than 0%, can also be 0%, may be 0 percent. Further, K 2 O content, for example, can be 3% or less, can also be less than 2.5%, may be 2% or less.
• the molar ratio of the total content of MgO, CaO, Li 2 O, Na 2 O and K 2 O to the Al 2 O 3 content [(MgO + CaO + Li 2 O + Na 2 O + K 2 O) / Al 2 O 3 ] is heat resistant. From the viewpoint of further improvement, it is preferably 2 or less, more preferably 1.7 or less, and further preferably 1.5 or less. From the viewpoint of further improving the productivity, especially from the viewpoint of further improving the meltability of the glass, the molar ratio [(MgO + CaO + Li 2 O + Na 2 O + K 2 O) / Al 2 O 3 ] is preferably 0.8 or more. , 1.0 or more, more preferably 1.2 or more.
• the TiO 2 content can be 0% or more, 0%, more than 0%, 0.5% or more, or 1% or more. From the viewpoint of further improving the glass stability, the TiO 2 content is preferably 5% or less, more preferably 4.5% or less, further preferably 4% or less, and 3 It is more preferably 5.5% or less, further preferably 3% or less, further preferably 2.5% or less, and even more preferably 2% or less.
• the total content of TiO 2 and ZrO 2 can be 0% or more than 0%, from the viewpoint of improving the rigidity of the glass, for example, from the viewpoint of increasing Young's modulus. , 0% or more, more preferably 0.5% or more, further preferably 1% or more, still more preferably 2% or more. From the viewpoint of lowering the specific density of the glass, the total content (TiO 2 + ZrO 2 ) is preferably 6% or less, more preferably 5% or less, still more preferably 4% or less. It is more preferably 3% or less.
• the molar ratio of TiO 2 content to the total content of Al 2 O 3 , ZrO 2 and SrO is 0.15 or less from the viewpoint of improving glass stability. It is preferably 0.1 or less, more preferably 0.5 or less, further preferably 0.1 or less, and even more preferably 0.08 or less.
• the molar ratio [TiO 2 / (Al 2 O 3 + ZrO 2 + SrO)] can be 0 or more, 0 or more, from the viewpoint of further improving productivity. Above all, from the viewpoint of further improving the meltability of the glass, it is preferably more than 0, more preferably 0.01 or more, and further preferably 0.03 or more.
• the total content of B 2 O 3 , SrO, TiO 2 and ZrO 2 can be 0%, more than 0%, 0.5% or more. Alternatively, it can be 1% or more. From the viewpoint of further improving the glass stability, the total content (B 2 O 3 + SrO + TiO 2 + ZrO 2 ) is preferably 7% or less, more preferably 6.5% or less, and 6%. It is more preferably less than or equal to 5.5% or less.
• the PbO content is preferably 0.5% or less, more preferably 0.3% or less, still more preferably 0.1% or less, from the viewpoint of lowering the specific density of the glass.
• the PbO content can be 0% or higher, and can be 0%. Since PbO is a substance having an adverse effect on the environment, it is preferable to reduce its content or avoid its introduction (that is, set the content to 0%). Since Cd and As are also substances that adversely affect the environment, it is preferable to avoid their introduction.
• the glass may contain one or more selected from the group consisting of SnO 2 , CeO 2 and Sb 2 O 3.
• SnO 2 has a function of promoting clarification in a state where the melting temperature of glass is relatively high (temperature range of about 1400 to 1600 ° C.).
• the SnO 2 content can be 0% or more, 0%, or more than 0%.
• SnO 2 is introduced into glass A. Is preferable.
• the content of SnO 2 is preferably 0.01% or more, more preferably 0.05% or more, still more preferably 0.10% or more, from the viewpoint of obtaining a clarification effect. It is more preferably 0.15% or more, and even more preferably 0.20% or more. Further, the SnO 2 content is preferably 2% or less, more preferably 1.5% or less, still more preferably 1% or less, from the viewpoint of lowering the specific density of the glass. It is more preferably 0.8% or less, and even more preferably 0.5% or less.
• CeO 2 is also a component that exhibits a clarifying effect on glass.
• the CeO 2 content can be 0% or higher, 0%, or greater than 0%. Since CeO 2 has a function of taking in oxygen and fixing it as a glass component in a state where the melting temperature of the glass is relatively low (temperature range of about 1200 to 1400 ° C.), in one form, CeO 2 is used as a fining agent on the glass. It is preferable to introduce.
• the content of CeO 2 is preferably 0.01% or more, more preferably 0.05% or more, further preferably 0.08% or more, and 0. .10% or more is more preferable.
• the content of CeO 2 is preferably 2% or less, more preferably 1.5% or less, still more preferably 1% or less, from the viewpoint of lowering the specific density of the glass. It is more preferably 0.8% or less, further preferably 0.5% or less, and even more preferably 0.3% or less.
• the glass preferably contains both SnO 2 and CeO 2.
• the Sb 2 O 3 content is preferably in the range of 0 to 0.5%.
• the Sb 2 O 3 content is more preferably 0.3% or less, further preferably 0.1% or less, further preferably 0.05% or less, and 0.02% or less. It is even more preferable that Sb 2 O 3 is not contained (the content is 0%).
• the Fe 2 O 3 content can be 0% or more, 0%, or more than 0%. It is preferable to include Fe 2 O 3 in the glass from the viewpoint of improving the heat absorption efficiency during heating.
• a magnetic recording medium substrate made of glass having high heat absorption efficiency during heating can contribute to improvement in heating efficiency when forming a magnetic layer in the process of manufacturing a magnetic recording medium and / or in heating after the formation. It is preferable from the viewpoint of improving productivity.
• the Fe 2 O 3 content is preferably 1% or less, more preferably 0.5% or less, and preferably 0.1% or less. It is more preferably 0.05% or less, and even more preferably 0.05% or less.
• the Fe 2 O 3 content is indicated by an external split.
• the Fe 2 O 3 content is indicated by the molar percentage of the Fe 2 O 3 content relative to.
• the magnetic recording medium substrate is usually subjected to a high temperature treatment in the step of forming the magnetic recording layer on the substrate.
• a film is usually formed at a high temperature.
• heat treatment is performed at a high temperature after film formation. If the magnetic recording medium substrate does not have heat resistance that can withstand such a high temperature treatment, it is exposed to a high temperature in the high temperature treatment and the flatness of the substrate is impaired.
• the glass A can exhibit high heat resistance by having the above-mentioned glass composition.
• the Tg of glass A is preferably 740 ° C. or higher, more preferably 750 ° C. or higher, and 760 ° C. or higher. It is more preferable that the temperature is 770 ° C. or higher. Further, the Tg of the glass A can be, for example, 850 ° C. or lower, 830 ° C. or lower, or 810 ° C. or lower, but the higher the Tg, the more preferable it is from the viewpoint of heat resistance, so the Tg is limited to the above-exemplified value. is not it.
• the glass for the magnetic recording medium substrate has high rigidity, specifically, a high Young's modulus.
• the Young's modulus of glass A is preferably 86 GPa or more.
• the glass for a magnetic recording medium substrate having a high rigidity showing a Young's modulus of 86 GPa or more deformation of the substrate during rotation of the spindle motor can be suppressed, so that warpage and deflection of the magnetic recording medium due to the deformation of the substrate can be suppressed. can do.
• the Young's modulus of glass A is more preferably 88 GPa or more, more preferably 90 GPa or more, further preferably 92 GPa or more, and even more preferably 94 GPa or more.
• the Young's modulus of the glass A can be, for example, 120 GPa or less, 110 GPa or less, or 100 GPa or less, but the higher the Young's modulus, the higher the rigidity, which is preferable, and thus the glass A is not limited to the above-exemplified values.
• the specific gravity of the glass A is preferably 2.8 or less.
• the specific gravity of the glass A is more preferably 2.80 or less, further preferably 2.78 or less, further preferably 2.76 or less, and even more preferably 2.74 or less. It is even more preferably 2.72 or less, and even more preferably 2.70 or less.
• the specific gravity of the glass A can be, for example, 2.40 or more, but it is not limited to the above-exemplified values because the lower the specific density is, the more preferable it is.
• the specific elastic modulus is the Young's modulus of glass divided by the density.
• the density can be considered as a value obtained by adding a unit of g / cm 3 to the specific gravity of glass.
• the specific elastic modulus of the glass A is preferably 30 MNm / kg or more, more preferably 32 MN m / kg or more, and further preferably 33 MN m / kg or more. It is more preferably 34 MNm / kg or more, and even more preferably 35 MN m / kg or more.
• the specific elastic modulus can be, for example, 40 MN m / kg or less, but the higher the specific elastic modulus is, the more preferable it is, so that the specific elastic modulus is not limited to the above-exemplified value.
• An HDD incorporating a magnetic recording medium usually has a structure in which the central portion is pressed by a spindle and a clamp of a spindle motor to rotate the magnetic recording medium itself. Therefore, if there is a large difference in the coefficient of thermal expansion between the magnetic recording medium substrate and the spindle material constituting the spindle portion, the thermal expansion / contraction of the spindle and the heat of the magnetic recording medium substrate with respect to the ambient temperature change during use The expansion and thermal contraction are deviated, and as a result, the magnetic recording medium is deformed. When such a phenomenon occurs, the head cannot read the written information, which causes a decrease in the reliability of recording / playback.
• the spindle material of an HDD has an average linear expansion coefficient (coefficient of thermal expansion) of 70 ⁇ 10-7 / ° C. or higher in a temperature range of 100 to 300 ° C., and is 100 to 300 ° C. of glass for a magnetic recording medium substrate.
• coefficient of thermal expansion in the above is 30 ⁇ 10 -7 / ° C. or higher, the difference in the coefficient of thermal expansion from the spindle material is small, and it is possible to contribute to the improvement of the reliability of the magnetic recording medium.
• the average coefficient of linear expansion of glass A at 100 to 300 ° C. is preferably 34 ⁇ 10 -7 / ° C. or higher, and preferably 35 ⁇ 10 -7 / ° C. or higher. More preferably, it is 36 ⁇ 10 -7 / ° C. or higher, further preferably 37 ⁇ 10 -7 / ° C. or higher, and even more preferably 38 ⁇ 10 -7 / ° C. or higher, 39. Even more preferably, it is ⁇ 10-7 / ° C. or higher.
• the average coefficient of linear expansion ( ⁇ ) of glass A at 100 to 300 ° C. is preferably 70 ⁇ 10-7 / ° C.
• the temperature is below ° C.
• Glass stability Glass A can preferably exhibit high glass stability.
• a holding test at 1300 ° C., 1270 ° C. or 1250 ° C. for 16 hours which will be described in detail later, can be mentioned.
• 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 the lower holding temperature, the higher the glass stability.
• Glass composition In glass B, the molar ratio of the total content of Al 2 O 3 and Mg O to the total content of SiO 2 and CaO [(Al 2 O 3 + MgO) / (SiO 2 + CaO)] is 0.30 or more and 0. It is less than 6.6.
• the above description regarding glass A can be referred to.
• the total content of SiO 2 and Al 2 O 3 (SiO 2 + Al 2 O 3 ) is 64 mol% or more and 85 mol% or less.
• the above description regarding glass A can be referred to.
• the total content of SiO 2 , Al 2 O 3 , MgO and CaO is 87 mol% or more and 98 mol% or less.
• the above description regarding glass A can be referred to.
• the total content of Li 2 O, Na 2 O, K 2 O, B 2 O 3 and Zn O shall be 0 mol% or more and 3 mol% or less. Is preferable.
• the above description regarding glass A can be referred to.
• glass composition of glass B For other details of the glass composition of glass B, the previous description regarding glass A can be referred to.
• the glass transition temperature of glass B is 740 ° C. or higher.
• the above description regarding glass A can be referred to.
• the above-mentioned description regarding the glass A can be referred to.
• Glass A and glass B are prepared by weighing, blending, and sufficiently mixing glass raw materials such as oxides, carbonates, nitrates, sulfates, and hydroxides in a melting vessel so that a predetermined glass composition can be obtained.
• a predetermined glass composition can be obtained.
• it can be produced by heating, melting, clarifying, and stirring in the range of 1400 to 1600 ° C. to form a homogenized molten glass in which bubbles are sufficiently broken.
• the glass raw material is melted by heating in a melting tank at 1400 to 1550 ° C., the obtained molten glass is heated in a clarification tank to hold it at 1450 to 1600 ° C., and then lowered to 1200 to 1400 ° C. It is preferable to flow out and mold.
• meltability of glass it can be said that the smaller the amount of undissolved raw material is when melting at a certain melting temperature, the better the meltability. Glass having excellent meltability is preferable from the viewpoint of productivity because it can be uniformly melted at a lower temperature or in a shorter time.
• Magnetic recording medium board The magnetic recording medium substrate (hereinafter, also referred to as “magnetic recording medium substrate a”) according to one aspect of the present invention is made of glass A. Further, the magnetic recording medium substrate (hereinafter, also referred to as “magnetic recording medium substrate b”) according to another aspect of the present invention is made of glass B.
• molten glass is prepared by heating a glass raw material, and the molten glass is formed into a plate shape by any of a press molding method, a downdraw method, or a float method, and the obtained plate shape is obtained. It can be manufactured through the process of processing glass.
• the press molding method the molten glass flowing out from the glass outflow pipe is cut into a predetermined volume to obtain a required molten glass ingot, which is press-molded by a press molding die to produce a thin-walled disk-shaped substrate blank. ..
• the obtained substrate blank is provided with a center hole, inner and outer circumferences are processed, and both main surfaces are subjected to polishing such as lapping and polishing.
• a disk-shaped substrate can be obtained through a cleaning step including acid cleaning and alkaline cleaning.
• Known techniques for manufacturing a magnetic recording medium substrate can be applied to various steps performed to obtain the magnetic recording medium substrate.
• the glass is usually polished by supplying a polishing agent (slurry) between the glass to be polished and the polishing pad.
• a polishing agent slurry
• the polishing efficiency polishing rate
• the polishing pad cannot achieve a predetermined polishing efficiency, it is usual to replace the polishing pad. From the viewpoint of productivity, it can be said that the longer the same polishing pad can be used, the more productive it is.
• the magnetic recording medium substrate has a homogeneous surface and internal composition.
• the homogeneous surface and internal composition means that ion exchange has not been performed (that is, there is no ion exchange layer). Since the magnetic recording medium substrate having no ion exchange layer is manufactured without performing the ion exchange treatment, the manufacturing cost can be significantly reduced.
• the magnetic recording medium substrate has an ion exchange layer on a part or all 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 perpendicular to the main surface and obtaining a stress profile by the Babine method on the fracture surface.
• the "main surface” is a surface on which the magnetic recording layer of the substrate is provided or a surface on which the magnetic recording layer is provided. Since such a surface is the surface having the largest area among the surfaces of the magnetic recording medium substrate, it is called a main surface, and in the case of a disk-shaped magnetic recording medium, the circular surface of the disk (when there is a center hole). Is equivalent to (excluding the central hole).
• 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 surface of the substrate.
• the ion exchange layer can be formed by bringing an alkali salt into contact with the surface of the substrate at a high temperature and exchanging the alkali metal ions in the alkali salt with the alkali metal ions in the substrate.
• Known techniques can be applied to ion exchange (also referred to as “strengthening treatment” or "chemical strengthening"), and paragraphs 0068 to 0069 of WO2011 / 019010A1 can be referred to as an example.
• the magnetic recording medium substrate has, for example, a thickness of 1.5 mm or less, preferably 1.2 mm or less, more preferably 1.0 mm or less, still more preferably 0.8 mm or less, still more preferably less than 0.8 mm. It is 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 that the thickness of the magnetic recording medium substrate can be reduced from the viewpoint of improving the recording capacity of the HDD.
• the magnetic recording medium substrate preferably has a disk shape having a central hole.
• the magnetic recording medium substrate can be made of amorphous glass. According to the amorphous glass, excellent surface smoothness can be realized when the substrate is processed as compared with the crystallized glass.
• the magnetic recording medium substrate is made of the glass for the magnetic recording medium substrate according to one aspect of the present invention, it can have the glass physical characteristics described above for the glass.
• Magnetic recording medium One aspect of the present invention relates to a magnetic recording medium having a magnetic recording layer on the magnetic recording medium substrate.
• Magnetic recording media are called magnetic disks, hard disks, etc., and various magnetic recording / playback devices, such as internal storage devices (fixed disks, etc.) such as desktop computers, server computers, laptop computers, and mobile computers, images and / Alternatively, it is suitable for an internal storage device of a portable recording / playback device that records / reproduces audio, a recording / playback device for in-vehicle audio, and the like.
• the "magnetic recording / reproducing device” means a device capable of magnetically recording information and magnetically reproducing information, or both. ..
• the magnetic recording medium has, for example, a configuration in which at least an adhesive layer, a base layer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer are laminated on the main surface of a magnetic recording medium substrate in order from the one closest to the main surface. It has become.
• a magnetic recording medium substrate is introduced into a film forming apparatus that has been evacuated, and a magnetic layer is formed on the main surface of the magnetic recording medium substrate in an Ar atmosphere by a DC (Direct Current) magnetron sputtering method.
• the film is formed sequentially up to.
• the adhesion layer for example, CrTi can be used
• the base layer a material containing, for example, Ru or MgO can be used.
• a soft magnetic layer or a heat sink layer may be added as appropriate.
• CVD chemical Vapor Deposition
• a lubricating layer can be formed by applying PFPE (polyfluoropolyether) on the protective layer by a dip coating method.
• the magnetic recording layer preferably contains a magnetic material having high magnetic anisotropy energy.
• preferred magnetic materials include Fe-Pt-based magnetic materials and Co-Pt-based magnetic materials.
• the term "system" means that it is contained. 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.
• the magnetic recording medium having such a magnetic recording layer is preferably applied to a magnetic recording device by a recording method called an energy assist recording method.
• a recording method that assists magnetization reversal by irradiation with near-field light or the like is called a heat-assisted recording method
• a recording method that assists with microwaves is called a microwave-assisted recording method.
• a conventional CoPtCr-based material may be used as the magnetic material for forming the magnetic recording layer.
• the magnetic recording medium substrate can be used as a substrate of a magnetic recording medium applied to a magnetic recording / reproducing device provided with a magnetic head equipped with a DFH mechanism.
• both the magnetic recording medium substrate (for example, a glass substrate for a magnetic disk) and the magnetic recording medium (for example, a magnetic disk) are not particularly limited, but for example, the medium and the substrate can be miniaturized because high recording density can be achieved. It is also possible to do. It is also possible to increase the size of the medium and the substrate in order to increase the recording capacity per magnetic recording medium. For example, the nominal diameter of 2.5 inches can, of course, be smaller (eg, 1 inch, 1.8 inches), or 3 inches, 3.5 inches, or even larger.
• Glass spacer for magnetic recording / playback device The glass spacer for a magnetic recording / reproducing device (hereinafter, also referred to as “glass spacer a”) according to one aspect of the present invention is made of glass A. Further, another aspect of the present invention (hereinafter, also referred to as “glass spacer b”) is made of glass B.
• the magnetic recording medium can be used to magnetically record and / or reproduce information in a magnetic recording / playback device.
• Magnetic recording / playback devices typically include spacers to secure the magnetic recording medium to the spindle of a spindle motor and / or to maintain a distance between the plurality of magnetic recording media.
• a glass spacer as such a spacer. It is desired that this glass spacer also has excellent heat resistance and productivity for a reason similar to the reason described in detail above for glass for a magnetic recording medium substrate.
• glass having the above composition is suitable as a glass spacer for a magnetic recording / reproducing device because it can have excellent heat resistance and productivity.
• the spacer for the magnetic recording / reproducing device is a ring-shaped member, and details such as the configuration of the glass spacer and the manufacturing method are known. Further, as for the method for manufacturing the glass spacer, the above description regarding the method for manufacturing the glass for the magnetic recording medium substrate and the method for manufacturing the magnetic recording medium substrate can also be referred to. Further, for other details such as the glass composition of the glass spacer a and the physical properties of the glass, the above description regarding the magnetic recording medium substrate made of glass A and glass A and the magnetic recording medium having such a magnetic recording medium substrate can be referred to.
• the spacer for the magnetic recording / reproducing device may be made of a glass spacer a or a glass spacer b, or has a configuration in which one or more films such as a conductive film are provided on the surface of the glass spacer a or the glass spacer b. You can also.
• a conductive film such as a NiP alloy can be formed on the surface of the glass spacer by a plating method, a dipping method, a vapor deposition method, a sputtering method, or the like.
• the surface smoothness of the glass spacer can be improved by polishing (for example, the average surface roughness Ra is 1 ⁇ m or less), thereby strengthening the adhesion between the magnetic recording medium and the spacer and causing misalignment. It can be suppressed.
• Magnetic recording / playback device One aspect of the present invention is Magnetic recording medium a, Magnetic recording medium b, Glass spacer a and glass spacer b, Magnetic recording / playback device, including one or more selected from the group consisting of Regarding.
• the magnetic recording / playback device includes at least one magnetic recording medium and at least one spacer, and usually includes a spindle motor for rotationally driving the magnetic recording medium, and recording and / or information recording on the magnetic recording medium. Includes at least one magnetic head for performing reproduction.
• the magnetic recording / reproducing device may include the magnetic recording medium (magnetic recording medium a and / or magnetic recording medium b) according to one aspect of the present invention as at least one magnetic recording medium. , A plurality of magnetic recording media according to one aspect of the present invention may be included.
• the magnetic recording / reproducing device may include a glass spacer (glass spacer a and / or glass spacer b) according to one aspect of the present invention as at least one spacer, and is one of the present inventions.
• a plurality of glass spacers according to the embodiment may be included.
• the small difference between the coefficient of thermal expansion of the magnetic recording medium and the coefficient of thermal expansion of the spacer is a phenomenon that can occur due to the difference in the coefficient of thermal expansion of the two, for example, distortion of the magnetic recording medium, misalignment of the magnetic recording medium. This is preferable from the viewpoint of suppressing the occurrence of a decrease in stability during rotation due to the above.
• the magnetic recording / reproducing device is one aspect of the present invention as at least one magnetic recording medium and, when a plurality of magnetic recording media are included, as more magnetic recording media. It is preferable to include the glass spacer according to one aspect of the present invention as at least one spacer, and more spacers when a plurality of spacers are included. Further, for example, in the magnetic recording / reproducing device according to one aspect of the present invention, the glass constituting the magnetic recording medium substrate included in the magnetic recording medium and the glass constituting the glass spacer have the same glass composition. There can be.
• the magnetic recording / reproducing device may include at least one of the magnetic recording medium according to one aspect of the present invention and the glass spacer according to one aspect of the present invention, and is magnetic in other respects.
• a known technique relating to a recording / reproducing device can be applied.
• the magnetic head has an energy source (for example, a heat source such as a laser light source, a microwave, etc.) for assisting magnetization reversal (assisting writing of a magnetic signal), a recording element unit, and a reproducing element unit.
• An energy-assisted magnetic recording head can be used.
• Such an energy-assisted recording type magnetic recording / reproducing device including an energy-assisted magnetic recording head is useful as a magnetic recording / reproducing device having high recording density and high reliability. Further, when manufacturing a magnetic recording medium used in an energy-assisted recording type magnetic recording / reproducing device such as a heat-assisted recording method equipped with a heat-assisted magnetic recording head having a laser light source or the like, a magnetic material having a high magnetic anisotropic energy is used. A magnetic recording layer containing the magnetic recording layer may be formed on the magnetic recording medium substrate. In order 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.
• the magnetic recording medium substrate according to one aspect of the present invention is preferable.
• the magnetic recording / reproducing device according to one aspect of the present invention is not limited to the energy-assisted magnetic recording / reproducing device.
• Example No. 1 to No. 71 Raw materials such as oxides, carbonates, nitrates, sulfates, and hydroxides were weighed and mixed to prepare a mixed raw material so that glasses having the compositions shown in Tables 1 to 4 below could be obtained.
• A No crystals on the glass surface, inside and at the interface with the bottom of the platinum crucible
• B Within 10 crystals with a diameter of several tens of ⁇ m at the interface between the glass surface and the bottom of the platinum crucible / 100g
• C 10 or more crystals with a diameter of several tens of ⁇ m / 100 g at the interface between the glass surface and the bottom of the platinum crucible.
• D Crystals inside the glass
• E Crystals on the glass surface, inside and at the interface with the bottom of the platinum crucible
• a disk-shaped substrate blank was prepared by the following method A or B. Further, by the same method, a glass blank for manufacturing a glass spacer for a magnetic recording / reproducing device can be obtained.
• Method A For the glass with the composition shown in the table below, the clarified and homogenized molten glass flows out from the outflow pipe at a constant flow rate and is received by the lower mold for press molding, and flows out so that a predetermined amount of molten glass ingot is obtained on the lower mold. The molten glass was cut with a cutting blade.
• the lower mold on which the molten glass ingot was placed was immediately carried out from below the pipe, and was press-molded into a thin disk shape having a diameter of 99 mm and a thickness of 0.7 mm using the upper mold and the body mold facing the lower mold. After cooling the press-molded product to a temperature at which it would not be deformed, it was taken out of the mold and annealed to obtain a substrate blank. In the above-mentioned molding, the molten glass flowing out was molded one after another into a disk-shaped substrate blank using a plurality of lower dies.
• Method B For the glass having the composition shown in the table below, clarified and homogenized molten glass is continuously cast from the upper part into the through hole of a heat-resistant mold provided with a cylindrical through hole, and formed into a cylindrical shape under the through hole. I took it out from the side. After annealing the taken-out glass, the glass was sliced at regular intervals in the direction perpendicular to the cylindrical axis using a multi-wire saw to prepare a disk-shaped substrate blank. Although the above-mentioned methods A and B are adopted in this embodiment, the following methods C and D are also suitable as a method for manufacturing a disk-shaped substrate blank.
• Method C It is also possible to pour the molten glass onto a float bath, mold it into a sheet-shaped glass (molding by the float method), then anneal it, and then hollow out the disk-shaped glass from the sheet glass to obtain a substrate blank.
• Method D It is also possible to form a molten glass into a sheet-shaped glass by an overflow down draw method (fusion method), anneal it, and then hollow out a disk-shaped glass from the sheet glass to obtain a substrate blank.
• a through hole is made in the center of the substrate blank obtained by each of the above methods, and the outer and inner circumferences are ground, and the main surface of the disk is wrapped and polished (mirror polishing).
• the glass substrate for a magnetic disk having a diameter of 97 mm and a thickness of 0.5 mm was finished. Further, by the same method, the glass blank for producing the glass spacer for the magnetic recording / reproducing device can be finished into the glass spacer for the magnetic recording / reproducing device.
• the glass substrate obtained above is washed with a 1.7% by mass aqueous solution of silicic acid (H 2 SiF) and then with a 1% by mass aqueous solution of potassium hydroxide, then rinsed with pure water and then dried.
• meltability (meltability at 1500 ° C)
• Raw materials such as oxides, carbonates, nitrates, sulfates, and hydroxides were weighed and mixed to prepare a mixed raw material so that a glass having the composition shown in Table 1 below could be obtained.
• This compounding raw material was put into a melting tank and stirred several times while being heated at 1500 ° C., and then the melt in the melting tank was magnified and observed with a microscope to confirm the presence or absence of unmelted raw material. The case where there was no unmelted residue was evaluated as "A”, and the case where there was unmelted residue was evaluated as "B".
• the total amount of glass polished by the time the polishing pad is replaced is preferably 300 ⁇ m or more, more preferably 500 ⁇ m or more, and further preferably 700 ⁇ m or more.
• Magnetic disk [Making a magnetic recording medium (magnetic disk)] An adhesive layer, a base layer, a magnetic recording layer, a protective layer, and a lubricating layer were formed in this order on the main surface of the glass substrate for a magnetic disk produced above by the following method to obtain a magnetic disk.
• the adhesion layer, the base layer, and the magnetic recording layer were sequentially formed in an Ar atmosphere by a DC magnetron sputtering method using a vacuum-drawn film forming apparatus.
• the adhesion layer was formed with a CrTi target so as to be a -amorphous CrTi layer having a thickness of 20 nm. Subsequently, a 10 nm-thick layer made of MgO was formed as a base layer. Further, the magnetic recording layer was formed at a film forming temperature of 200 to 400 ° C. using a FePtC or CoPtC target so as to be a granular layer of FePt or CoPt having a thickness of 10 nm.
• the magnetic disk after the film formation up to the magnetic recording layer was transferred from the film forming apparatus into the heating furnace and annealed.
• the temperature in the heating furnace at the time of annealing was in the range of 500 to 700 ° C. This annealing process, the magnetic particles of the CoPt-based alloy and FePt based alloy L 10 ordered structure is formed.
• the invention is not limited to the above, it may be heated as L 10 regular structure results.
• a protective layer made of carbon hydride was formed at 3 nm by a CVD method using ethylene as a material gas.
• a lubricating layer made of PFPE perfluoropolyether
• the film thickness of the lubricating layer was 1 nm.
• a magnetic disk was obtained by the above manufacturing process. The obtained magnetic disk was mounted on a hard disk drive equipped with a DFH mechanism, and a magnetic signal was recorded and reproduced in a recording area on the main surface of the magnetic disk at a recording density of 1000 gigabits per square inch. No phenomenon of collision between the head and the surface of the magnetic disk (crash failure) was confirmed.
• a hard disk drive equipped with a DFH mechanism is obtained by forming a conductive film of NiP alloy on the surface of a glass spacer obtained by the above manufacturing process using the glass of the example (glass spacer with NiP alloy film).
• a magnetic signal is recorded at a recording density of 1000 gigabits per square inch in a recording area on the main surface of a magnetic disk mounted and separately prepared using a substrate of a material different from the glass according to one aspect of the present invention. Upon reproduction, the phenomenon of collision between the magnetic head and the surface of the magnetic disk (crash failure) was not confirmed.
• the magnetic disk manufactured above and the glass spacer with NiP alloy film manufactured above are mounted on a hard disk drive provided with a DFH mechanism.
• a magnetic signal was recorded and played back in a recording area on the main surface of a magnetic disk at a recording density of 1000 gigabits per square inch, the phenomenon of collision between the magnetic head and the surface of the magnetic disk (crash failure) was not confirmed. It was.
• 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 the coefficient of thermal expansion described above does not occur.
• the total content of Li 2 O, Na 2 O, K 2 O, B 2 O 3 and Zn O is 0 mol% or more and 3 mol% or less, SiO.
• the molar ratio of the total content of Al 2 O 3 and Mg O to the total content of 2 and CaO [(Al 2 O 3 + MgO) / (SiO 2 + CaO)] is 0.30 or more and 0.6 or less, SiO 2
• the total content of and Al 2 O 3 (SiO 2 + Al 2 O 3 ) is 64 mol% or more and 85 mol% or less, and the total content of SiO 2 , Al 2 O 3 , MgO and CaO (SiO 2 + Al 2 O).
• 3 + MgO + CaO) is 87 mol% or more and 98 mol% or less, and glass (glass A) for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device is provided.
• the molar ratio [(Al 2 O 3 + MgO) / (SiO 2 + CaO)] of the total content of Al 2 O 3 and Mg O to the total content of SiO 2 and Ca O is 0. 30 or more and 0.6 or less
• total content of SiO 2 and Al 2 O 3 (SiO 2 + Al 2 O 3 ) is 64 mol% or more and 85 mol% or less
• total of SiO 2 , Al 2 O 3 , MgO and CaO Glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device (glass B) having a content (SiO 2 + Al 2 O 3 + MgO + CaO) of 87 mol% or more and 98 mol% or less and a glass transition temperature of 740 ° C. or more. ) Is provided.
• Glass A and glass B can be glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing device, which is excellent in both heat resistance and productivity.
• the SiO 2 content in glass A and glass B can be 55 mol% or more and 66 mol% or less.
• the Al 2 O 3 content in glass A and glass B can be 10 mol% or more and 18 mol% or less.
• the MgO content in glass A and glass B can be 8 mol% or more and 20 mol% or less.
• the CaO content in glass A and glass B can be 0 mol% or more and 7 mol% or less.
• the molar ratio of the CaO content to the total content of MgO, CaO, SrO and BaO can be 0.4 or less.
• the Young's modulus of glass A and glass B can be 86 GPa or more.
• the specific densities of glass A and glass B can be 2.8 or less.
• the specific elastic moduli of glass A and glass B can be 30 MNm / kg or more.
• a magnetic recording medium substrate (magnetic recording medium substrate a) made of glass A is provided.
• a magnetic recording medium substrate (magnetic recording medium substrate b) made of glass B is provided.
• a magnetic recording medium having the magnetic recording medium substrate and the magnetic recording layer is provided.
• a glass spacer (glass spacer a) for a magnetic recording / reproducing device made of glass A is provided.
• a glass spacer (glass spacer b) for a magnetic recording / reproducing device made of glass B is provided.
• a magnetic recording / reproducing device including one or more selected from the group consisting of a magnetic recording medium a, a magnetic recording medium b, a glass spacer a, and a glass spacer b is provided.
• the glass for a magnetic recording medium substrate and the glass spacer for a magnetic recording / reproducing device according to one aspect of the present invention can be produced by adjusting the composition described in the specification with respect to the glass composition exemplified above. it can.

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