Process for producing glass substrate for magnetic disks

Abstract

In the production of a glass substrate for magnetic disks, in a step of polishing a main surface of a circular glass plate, roll-off is reduced without reducing the polishing rate. The process comprises a step of polishing a main surface of a circular glass plate by using an acidic polishing fluid containing colloidal silica or fumed silica, and a water-soluble polymer having at least one member selected from a group consisting of a carboxylic acid group, a carboxylate group, a sulfonic acid group and a sulfonate group, bonded to its main chain, or an acidic polishing fluid containing 100 parts by mass of colloidal silica or fumed silica, and from 0.02 to 0.1 part by mass of a surfactant having a sulfonic acid group.

1 . A process for producing a glass substrate for magnetic disks, which comprises a step of polishing a main surface of a circular glass plate by using an acidic polishing fluid containing colloidal silica or fumed silica, and a water-soluble polymer having at least one member selected from a group consisting of a carboxylic acid group, a carboxylate group, a sulfonic acid group and a sulfonate group, bonded to its main chain. 
   
   
       2 . The process for producing a glass substrate for magnetic disks according to  claim 1 , wherein in the water-soluble polymer, its main chain is linear. 
   
   
       3 . The process for producing a glass substrate for magnetic disks according to  claim 1 , wherein the weight average molecular weight of the water-soluble polymer is at least 5,300. 
   
   
       4 . The process for producing a glass substrate for magnetic disks according to  claim 1 , wherein the weight average molecular weight of the water-soluble polymer is at least 6,000. 
   
   
       5 . The process for producing a glass substrate for magnetic disks according to  claim 1 , wherein the content of the water-soluble polymer in the polishing fluid is from 0.001 to 10 parts by mass per 100 parts by mass of the colloidal silica or fumed silica. 
   
   
       6 . A process for producing a glass substrate for magnetic disks, which comprises a step of polishing a main surface of a circular glass plate by using an acidic polishing fluid containing 100 parts by mass of colloidal silica or fumed silica, and from 0.02 to 0.1 part by mass of a surfactant having a sulfonic acid group. 
   
   
       7 . The process for producing a glass substrate for magnetic disks according to  claim 6 , wherein the surfactant having a sulfonic acid group is an alkyl sulfonic acid, an alkylbenzene sulfonic acid or an alkylnaphthalene sulfonic acid. 
   
   
       8 . The process for producing a glass substrate for magnetic disks according to  claim 1 , wherein the content of colloidal silica or fumed silica in the above polishing fluid is from 5 to 40 mass %. 
   
   
       9 . The process for producing a glass substrate for is magnetic disks according to  claim 6 , wherein the content of colloidal silica or fumed silica in the above polishing fluid is from 5 to 40 mass %. 
   
   
       10 . The process for producing a glass substrate for magnetic disks according to  claim 1 , wherein the average particle size of primary particles of the colloidal silica or fumed silica is from 1 to 100 nm. 
   
   
       11 . The process for producing a glass substrate for magnetic disks according to  claim 6 , wherein the average particle size of primary particles of the colloidal silica or fumed silica is from 1 to 100 nm. 
   
   
       12 . The process for producing a glass substrate for magnetic disks according to  claim 1 , wherein the acidic polishing fluid has a pH of from 1 to 7. 
   
   
       13 . The process for producing a glass substrate for magnetic disks according to  claim 6 , wherein the acidic polishing fluid has a pH of from 1 to 7.