Fluorescent imaging of razor cartridge/skin lubrication

Abstract

Shaving comfort is linked to friction, and thus lubrication, in the razor cartridge/skin interface. It is a distinguishing factor when a user evaluates the perceived quality of a shave. A novel Laser Induced Fluorescence (LIF) technique was developed to study lubrication in a razor cartridge/skin mimic contact under simulated shaving conditions. The experiments were conducted with a 5-blade cartridge, loaded and sliding against a transparent silicone elastomer. The lubricant was distilled water marked with fluorescent dye. The LIF technique measured in-contact film thickness at different sliding speeds (50, 150 mm s−1) and showed differences in lubricant distribution for each component (lubricant strip, blades, guard) interface. The measured calibration film thickness range was 2–135 μm. The guard and lubricant strip maintain relatively thick and consistent lubricant films across the speed range. Minimum films were measured at the blade cutting edges, although at sliding speeds of 150 mm s−1 the blade cutting edge film thickness increases towards the back of the cartridge; and film thickness under blades 1 and 2 decreases at high speeds, suggesting starvation of fluid flow. The new technique allows study of lubrication behaviour in complex geometries, multiphase fluids and hard/soft material combinations for example oral processing, contact lens/eyelid and personal care product application. These systems are not easily studied by conventional test methods or classical lubrication analysis.