Patent ID: 8402790

Claim:
A process for producing a magnetic disk, comprising forming a magnetic recording layer on a glass substrate for an information recording medium, wherein the glass substrate for an information recording medium is produced by a process comprising processing a glass formed into a plate by a float process, a down-draw method or a press method, wherein, in cooling of the glass in a last step, a time during which the glass temperature is at most a temperature where a glass viscosity becomes 10 10 dPa·s (T 10 ) and is at least its strain point (T Str ) is at least 13 minutes, wherein the alminosilicate glass comprises from 64 to 67% of SiO 2 , from 8 to 10% of Al 2 O 3 , from 10 to 13% of Li 2 O, from 9 to 12% of Na 2 O, from 0 to 2% of K 2 O and from 2 to 4% of ZrO 2 , provided that the total content of Li 2 O, Na 2 O and K 2 O, Li 2 O+Na 2 O+K 2 O, is from 21 to 25% and wherein the glass substrate has an A Total of at most 20.5 nmol/cm 2 , wherein A Total is the sum of acid resistances A Si , A Al , A Li , A Na and A Zr , wherein A Si , A Al , A Li , A Na and A Zr are measured by immersing a glass plate having a thickness of 1 mm and a size of 4 cm square and having both surfaces mirror polished with cerium oxide in 0.01 N nitric acid at 25° C. for 3 hours, followed by eluting the nitric acid to measure the eluted amounts of Si, Al, Li, Na and Zr, and dividing the elution amounts by the surface area of the glass plate to obtain A Si , A Al , A Li , A Na and A Zr .