Substrate members for recording disks and process for producing same

Claim 2

A substrate member for recording disks comprising a sputtered film formed of at least one member selected from the group consisting of Al 2 O 3 , SiO 2 , and Si 3 N 4 on the surface of an alumina base ceramic material having therein micropores of no more than 5 microns and a relative theoretical density of no less than 96%, said sputtered film having a surface roughness of no more than 80 angstroms, being substantially pore-free and strain-free on the surface, and having a thickness of 0.3 to 30 microns.

Claim 3

A process for producing substrate members for recording disks comprising the steps: providing a film having a thickness of 0.5 to 35 microns by sputtering at least one member selected from the group consisting of Al 2 O 3 , SiO 2 , and Si 3 N 4 on the surface of an alumina base ceramic material having therein micropores of no more than 5 microns and a relative theoretical density of no less than 96%, and polishing the surface of said film under a load of 0.05 to 2 kg/cm 2 with a suspension of 0.1 to 20% by weight of a fine powder of no larger than 0.1 micron of at least one of SiO 2 , MgO, Al 2 O 3 , CeO 2 and Fe 2 O 3 , each of 99% purity or more in pure water, until a substantially pore-free and strain-free surface layer having a thickness of 0.3 to 30 microns and a surface roughness of no more than 80 angstroms is obtained.

Claim 4

A process for producing substrate members for recording disks comprising the steps: providing a film having a thickness of 0.5 to 35 microns by sputtering at least one member selected from the group consisting of Al 2 O 3 , SiO 2 , and Si 3 N 4 on the surface of an alumina base ceramic material having therein micropores of no more than 5 microns and a relative theoretical density of no less than 96%, and polishing the surface of said film under a load of 0.05 to 2 kg/cm 2 with a suspension of 0.1 to 20% by weight of a fine powder of no larger than 0.1 micron of at least one of SiO 2 , MgO, Al 2 O 3 , CeO 2 and Fe 2 O 3 , each of 99% purity or more in pure water, until a substantially pore-free and strain-free surface layer having a thickness of 0.3 to 30 microns and a surface roughness of no more than 80 angstroms is obtained.

Claim 5

A substrate member as defined in claim 1, wherein said alumina base ceramic material includes at 50% by weight of Al 2 O 3 .

Claim 6

A substrate member as defined in claim 3, wherein said alumina base ceramic material includes at least 65% by weight of Al 2 O 3 .

Claim 7

A substrate member as defined in claim 4, wherein said alumina base ceramic material includes at least 96% by weight of Al 2 O 3 .

Claim 8

A substrate member as defined in claim 1, wherein said alumina base ceramic material includes micropores of no larger than 3 microns on the surface thereof.

Claim 9

A substrate member as defined in claim 1, wherein said film has a surface roughness of 50 angstroms or less.

Claim 10

A substrate member as defined in claim 7, wherein said film has a surface roughness of 20 angstroms or less.

Claim 11

A substrate member as defined in claim 1, wherein said film is 10-20 microns thick.

Claim 12

A substrate member as defined in claim 1, which has said film on both sides of the substrate member.

Claim 13

A substrate member as defined in claim 1, wherein said film has compression stress therein.

Claim 14

A process as defined in claim 2, wherein said polishing is effected through the mechano-chemical polishing.

Claim 15

A process as defined in claim 12, wherein said mechano-chemical polishing is effected by lapping.

Claim 16

A process as defined in claim 2, wherein said film is provided on both sides of the alumina base ceramic material and said polishing is conducted simultaneously to both films.

Claim 17

A recording disk comprising the substrate member as defined in claim 1.

Claim 18

A recording disk comprising the substrate member produced by the process as defined in claim 2.

Claim 19

A recording disk as defined in claim 15 or 16, which has a magnetic recording film directly or indirectly provided on the surface of said substrate member.