Generation of radial striations on particulate coated magnetic disks

In the manufacture of particulate magnetic disks using an air barrier coater to prevent solvent evaporation, and which allows thin (less than 750nm) films to be obtained, radial striations occur in the coating during the high velocity spin-off step. The radial striations are a function of the shear modulus of the coating, the spin-off velocity and the fluid (gas) turbulence at the coating/fluid interface. Experiments showed that this phenomenon corresponds in mechanism to the phenomenon observed by Hansen and Hunston in their studies on the interaction of turbulent boundary layers with compliant surfaces. Hansen and Hunston derived an expression to describe the onset of the radial striation formation. This expression can approximately describe the phenomenon which occurs on particulate magnetic disks.