Improvement in Heat Resistance of Perfluoropolyether Lubricant Films on Magnetic Disks by UV Irradiation with a Bias Voltage on the Disk Surface

Abstract

Our previous study confirmed that the photoelectron-assisted ultraviolet (UV) irradiation with a bias voltage between the magnetic disk and the counter electrode above the disk surface increased the bonded ratio of a perfluoropolyether lubricant film on the disk surface. In this study, two types of lubricant materials (Fomblin Z-tetraol and Moresco ADOH) were prepared and coated on disks. After coating the lubricant films, UV irradiation of the lubricated disk surface was performed using the normal process and the photoelectron-assisted process, and the depletions of these lubricant films were compared using the pin-on-disk test with the laser heating function. The results showed that the lubricant film treated with normal UV irradiation without the bias voltage showed a deeper depletion of the lubricant film than that treated with photoelectron-assisted UV irradiation, and the ADOH film showed a shallower depletion than the Z-tetraol film. However, the molecular weight distributions of the ADOH films on DLC surfaces treated by UV irradiation were compared using time-of-flight secondary ion mass spectroscopy, and the film treated with photoelectron-assisted UV irradiation did not change owing to dissociation after photoelectron capture. Photoelectron-assisted UV irradiation led to the decomposition of the cyclo-triphosphazene end groups. Therefore, it is assumed that the depletion of lubricant films treated with photoelectron-assisted UV irradiation was reduced, since the bonding strength to the DLC surface increased because of the greater decomposition of end groups.