GLASS FOR MAGNETIC RECORDING MEDIA SUBSTRATES, MAGNETIC RECORDING MEDIA SUBSTRATES, MAGNETIC RECORDING MEDIA AND METHOD FOR PREPARATION THEREOF

摘要

Abstract Glass for Magnetic Recording Media Substrates, Magnetic Recording Media Substrates, Magnetic Recording Media and Method for Preparation thereof The present invention relates to a glass for a magnetic recording medium substrate permitting the realization of a magnetic recording medium substrate affording good chemical durability and having an extremely flat surface, magnetic recording medium substrate a comprised of this glass, magnetic a recording medium equipped with this substrate, and methods of manufacturing the same. The glasses comprise an oxide of a first glass, comprising, as mass percentages: Si 20 to 40 percent, A! 0.1 to 10 percent, Li 0.1 to 5 percent, Na 0.1 to 10 percent, K 0 to 5 percent (where the total content of Li, Na, and is K 15 percent or less) Sn 0.005 to 0.6 percent, and Ce 0 to 1.2 percent; the Sb content is 0 to 0.1 percent; and not comprising As or F; and by having a A (Lambda) 80 of 320 or greater; an oxide of a second glass, comprising, as molar percentages: Si0 2 60 to 75 percent, Al 0 2 3 1 to 15 percent, Li 0 2 0.1 to 20 percent, Na 0 2 0.1 to 15 percent, and K 0 2 0 to 5 percent (where the total content of Li 0, 2 Na 0, 2 and K 0 2 is 25 percent or lower); based on the total amount of the glass components, 0.01 to 0.7 mass percent of Sn oxide and 0 to 1.4 mass percent of Ce oxide are added; the content of Sb oxide is 0 to 0.1 mass percent; and not comprising As or F; and an oxide of a third glass, comprising, as molar percentages: Si0 2 60 to 75 percent, AI2O3 1 to 15 percent, 229 Li 0 2 0.1 to 20 percent, Na 0 2 0.1 to 15 percent, K 0 2 0 to 5 percent (where the total content of Li 0, 2 Na 0, 2 and K 0 2 is 25 percent or less); by comprising a 0.1 to 3.5 mass percent of total content of Sn oxide and Ce oxide, based on the total amount of the glass components; the ratio of the Sn oxide content to the total content of Sn oxide and Ce oxide (Sn oxide content/(Sn oxide content + Ce oxide content)) is 0.01 to 0.99; the Sb oxide content is 0 to 0.1 percent; and comprising no As or and optionally F having a A (Lambda) 80 of 320 or greater. Figure 1. 230