Lubrication of the razor cartridge/skin contact

Abstract

The razor cartridge/skin contact is complex due to cartridge materials and geometry, and the mechanical properties of skin. It is thought that the ideal shaving lubricant is able to flow through the guard without being wiped away (so that a sufficient amount of lubricant can reach the blades) and resist starvation under multiple, successive razor cartridge components. The objectives of the research were to: understand the friction properties of shaving fluids in a model cartridge/skin contact, measure lubricant flow through the razor cartridge contact, and assess the suitability of PEO as a shaving lubricant. Friction tests for a hard/compliant contact were carried out in conditions representative of shaving. These included improvements to surface chemistry with artificial sebum. Pure sliding tests produced variable results with poor repeatability. For a sliding/rolling contact, trends between lubricants were identified. Load, sliding speed, lubricant chemistry and surface chemistry were found to affect friction. A fluorescence technique was developed to measure razor cartridge film thickness and excellent image clarity was shown, with film thickness measurable for hard and compliant counterfaces. The lower measurable limit was 2 ± 0.4 µm (hard counterface) and 2 +3.1/-2 µm (compliant counterface). It was found that the guard and Lubrastrip maintain relatively thick and consistent lubricant films across the speed range, with minimum films formed at the blade cutting edges. Presence of the guard improved cartridge lubrication by stabilising film thickness across the blade cutting edges. Razor cartridge lubrication was found to operate in partially starved conditions, and replenishment mechanisms are discussed as well as the impact of contact conditions on cartridge film thickness. Evidence for viscoelastic effects were shown, and viscous and elastic effects were separated. Results have provided guidance on identifying a potential shaving lubricants, and recommendations have been made for further investigation and development of experimental methods.