Method for making a magnetic recording disk having a corrosion-protective layer of a perfluorinated polyether acid
View Patent ↗A process is provided for synthesizing metal salts of perfluorinated polyethers containing at least one carboxylic acid group. The polymeric salts so provided are effective as anti-wetting and corrosion-protective agents. The metal salts of perfluorinated polyether acids may be used to prepare corrosion-protected substrates, including magnetic recording disks and magnetic recording heads.
1. A method for making a magnetic recording disk comprising:
(a) forming an underlayer on a disk substrate;
(b) sputter-depositing a magnetic layer onto the underlayer;
(c) sputter-depositing a carbon overcoat onto the magnetic layer, said carbon overcoat having pinholes therein exposing the magnetic layer; and
(d) applying to the carbon overcoat a corrosion-protective composition containing a corrosion-protective agent comprised of a metal salt of a perfluorinated polyether having at least one carboxylic acid group, a metal salt of a partially hydrogenated perfluorinated polyether having at least one carboxylic acid group, or a mixture thereof, thereby filling any pinholes in the carbon overcoat with the corrosion-protective composition.
2. The method of claim 1 , wherein the magnetic layer is comprised of a metal, a metal alloy, or a metal oxide.
3. The method of claim 2 , wherein the magnetic layer is comprised of a metal alloy.
4. The method of claim 3 , wherein the metal alloy is a cobalt-based alloy.
5. The method of claim 4 , wherein the corrosion-protective agent comprises a metal salt of a perfluorinated polyether having two carboxylic acid groups.
6. The method of claim 1 , wherein the underlayer comprises a chromium-containing material.
7. The method of claim 1 , further comprising coating the carbon overcoat with a lubricating film of a perfluoropolyether prior to deposition of the carbon overcoat.
8. The method of claim 1 , wherein the perfluorinated polyether is comprised of monomer units having the structure —CF 2 —O—, —CF 2 —CF 2 —O—, —CF(CF 3 )—O—, —CF(CF 3 )—CF 2 —O—, or a combination thereof.
9. The method of claim 1 , wherein the corrosion-protective agent comprises a partially hydrogenated perfluorinated polyether comprised of monomer units of the structure —CF 2 —O—, —CF 2 —CF 2 —O—, —CF(CF 3 )—O—, —CF(CF 3 )—CF 2 —O—, or a combination thereof before hydrogenation.
10. The method of claim 9 , wherein based upon the corresponding perfluorinated polyether up to about 50% of the fluorine atoms are substituted with a hydrogen atom in the partially hydrogenated perfluorinated polyether.
11. The method of claim 1 , wherein the perfluorinated polyether is a linear polymer.
12. The method of claim 1 , wherein the metal salt is an alkali metal salt.
13. The method of claim 12 , wherein the alkali metal salt is a sodium salt.
14. The method of claim 1 , wherein the perfluorinated polyether has a number average molecular weight in the range of approximately 500 to 10,000.
15. The method of claim 14 , wherein the perfluorinated polyether has a number average molecular weight in the range of approximately 1000 to 5000.
16. The method of claim 15 , wherein the perfluorinated polyether has a number average molecular weight in the range of approximately 2500 to 3500.