| 主权项 |
1. A method for producing a protective film for a magnetic recording medium having a substrate, a magnetic layer formed on the substrate, a protective film formed on the magnetic layer, and a lubricating layer formed on the protective film, the method comprising the steps of:
(a) providing a substrate with a magnetic layer thereon; and (b) forming the protective film on the magnetic layer by means of a plasma CVD method using a mixed gas of a lower saturated hydrocarbon gas and a lower unsaturated hydrocarbon gas as a source gas, wherein the lower saturated hydrocarbon gas is selected from the group consisting of methane, ethane, propane, butane, and a mixture of two or more thereof, the lower unsaturated hydrocarbon gas is selected from the group consisting of ethylene, propylene, butylene, butadiene, and a mixture of two or more thereof, and the step (b) includes a step (b-1) of forming a first protective film on the magnetic layer and a step (b-2) of forming a second protective film on the first protective film, the step (b-1) being performed by the plasma CVD method using a source gas in which a mixture ratio between the lower saturated hydrocarbon gas and the lower unsaturated hydrocarbon gas is adjusted such that the average number of hydrogen atoms per carbon atom in the source gas becomes greater than 2.5 but less than 3.0, and the step (b-2) being performed by the plasma CVD method using a source gas in which a mixture ratio between the lower saturated hydrocarbon gas and the lower unsaturated hydrocarbon gas is adjusted such that the average number of hydrogen atoms per carbon atom in the source gas becomes greater than 2.0 but less than 2.5. |
