Formation of Lubricant “Sierra” at Boundary Between PFPE Solution Dipped and Un-Dipped Zones Over DLC Coated Magnetic Disks

An unstable phenomenon arising at the boundary between PFPE solution dipped and un-dipped zones over DLC coated magnetic disks has been studied. The formation conditions of a ridge of lubricant, or “sierra,” at this boundary and the structure of the “sierra” were clarified. Lubricant film having a step-shaped boundary was first formed by the halfway dip-coating method, and film thickness distribution was then measured around the boundary area. It was found that the film thickness was uniform over the entire lubricated area for a higher speed of withdrawing the disk from the lubricant solution and decreased linearly when the withdrawing speed was lowered. However, the “sierra” structure of the lubricant suddenly formed along the boundary line when the withdrawing speed was further decreased to less than a specified value of around 1 mm/s. The “sierra” was less likely to form for a lower dilution and a longer elapsed time after making the lubricant solution. It was also revealed that, along the ridgeline of the “sierra,” peaks formed periodically and the peak feet propagated in the direction perpendicular to the boundary, forming convex fronts and leaving multiplex bead chains of lubricant accumulations inside the convex.