Glass substrate for magnetic disk and method for producing the same

Abstract

A method for producing a glass substrate for a magnetic disk involving the use of a polishing pad having: a first resin foam layer which forms the polishing surface, includes a resin foam having pores with a pore diameter of more than 20 μm and has a thickness of 400 μm or less; and a second resin foam layer which is provided between a platen for fixing the polishing pad and the first resin foam layer, includes a resin foam having pores with a pore diameter of 20 μm or less and has a thickness of 50 to 250 μm, and in which a total thickness of the first resin foam layer and the second resin foam layer is 550 μm or less, and a international rubber hardness degree of the polishing pad measured by the M method according to JIS K6253 is 40 IRHD or more.

1 . A method for producing a glass substrate for a magnetic disk, said method comprising a step of polishing a main surface of a circular glass plate while supplying a polishing slurry containing a polishing material,
 wherein polishing is performed, after a polishing surface is subjected to dressing treatment, by using a polishing pad having: a first resin foam layer which forms the polishing surface, comprises a resin foam having pores with a pore diameter of more than 20 μm and has a thickness of 400 μm or less; and a second resin foam layer which is provided between a platen for fixing the polishing pad and the first resin foam layer, comprises a resin foam having pores with a pore diameter of 20 μm or less and has a thickness of 50 to 250 μm,   and wherein a total thickness of the first resin foam layer and the second resin foam layer is 550 μm or less, and a international rubber hardness degree of the polishing pad measured by the M method according to JIS K6253 is 40 IRHD or more.   
     
     
         2 . The method for producing a glass substrate for a magnetic disk according to  claim 1 , wherein the second resin foam layer has a compressibility at 200 μm of 3% or less. 
     
     
         3 . The method for producing a glass substrate for a magnetic disk according to  claim 1 , wherein an open pore area ratio of the polishing surface is adjusted to 8% or more, and an average circle equivalent diameter of open pores of the polishing surface is adjusted to 10 μm or more, by the dressing treatment. 
     
     
         4 . The method for producing a glass substrate for a magnetic disk according to  claim 1 , wherein after a surface layer of the polishing pad is cut off by the dressing treatment, brush cleaning is performed while supplying pure water. 
     
     
         5 . A glass substrate for a magnetic disk produced by the method for producing a glass substrate for a magnetic disk according to  claim 1 . 
     
     
         6 . The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the first resin foam layer and the second resin foam layer are joined through a joining solution. 
     
     
         7 . The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the polishing material is a colloidal silica or a fumed silica. 
     
     
         8 . The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the first resin foam layer comprises polyurethane. 
     
     
         9 . The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the international rubber hardness degree of the polishing pad measured by the M method according to JIS K6253 is 50 IRHD or less. 
     
     
         10 . The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the first resin foam layer has a thickness of 100 to 400 μm. 
     
     
         11 . The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the second resin foam layer comprises polyethylene terephthalate. 
     
     
         12 . The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the total thickness of the first resin foam layer and the second resin foam layer is 500 μm or less. 
     
     
         13 . The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the first resin foam layer has a thickness of 350 μm or less. 
     
     
         14 . The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the second resin foam layer has a thickness of 100 to 250 μm. 
     
     
         15 . The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the international rubber hardness degree of the polishing pad measured by the M method according to JIS K6253 is 42 IRHD or more. 
     
     
         16 . The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the international rubber hardness degree of the polishing pad measured by the M method according to JIS K6253 is 46-49 IRHD.