Kao Corporation’s Skin Care Research Laboratory and Material Science Research Laboratory discover that adhesion of airborne particulates, such as dust and pollen to skin can be inhibited by use of a surface covering film with an irregular convexo-concave microstructure.
Fine Particles Cause Skin Problems
Fine particles can easily attach to skin, causing problems, such as irritation and dullness. Long-term exposure to such particulates has been reported to accelerate skin aging factors like flecks and wrinkles. A survey conducted by Kao showed that some respondents in Japan were concerned about adhesion of these particles during the pollen season, while more than 80 percent of respondents in China, Thailand, and Vietnam, where air pollution levels are high, answered that skin condition deterioration was caused by fine pollutant particulates. For fine particles ranging from 2.5-30 μm, Van der Waals force is the most important type of force. Thus, Kao has focused attention on understanding how to reduce Van der Waals force between fine particulates and skin in order to develop a technology that controls fine particle adhesion.
Van der Waals Force Contributes to Adhesion The strength of Van der Waals force is characterized as, “the closer the distance between interacting substances, the stronger the force becomes”. Thus, Kao examined the effect of extending the distance between the spherical object (particle) and adhesion surface (skin). In order to, simulate this force, convexo-concave irregularities with varied roughness on the surface were prepared. This led to identification of areas where fine particles sized 2.5-30 μm showed lower levels of adhesion. Results of the simulation revealed that formation of fine convexo-concave irregularities on a flat surface clearly inhibited adhesion of fine particles. Based on these findings, Kao investigated how to form a film with a fine irregular convexo-concave microstructure on the surface of skin. Utilizing UV scattering agents, such as titanium oxide and zinc oxide, it was possible to form film on the skin surface with a fine irregular convexo-concave microstructure, which demonstrated significantly reduced adhesion of fine particulates, like pollen and dust.
Convexo-concave Film with UV Scattering Agents The researchers discovered that when UV scattering agents are blended under practical conditions, the ability to reduce adhesion is generally lost because the surface of the film is submerged under compounding oil. Kao overcame this problem by making the UV scattering agents difficult to wet with an oil agent. This led to successful formation of a fine convexo-concave film with UV scattering agents on the surface. Experiments conducted with an artificial leather surface to which a sunscreen with the new technology had been applied clearly confirmed the ability to inhibit adhesion of model pollen, as the level of adhesion was significantly reduced as compared to untreated leather. Additional experiments were conducted with the novel sunscreen applied to one side of the face of subjects and sunscreen without this technology applied to the other side. After five hours of exposure, dirt containing fine particulates was wiped from the skin with a nonwoven cloth and quantified. The results confirmed that the quantity of particulate dirt was significantly less on skin applied with sunscreen that included a fine convexo-concave film coated with UV scattering agents as compared to the conventional sunscreen film. Development of technology based on this discovery paves the way for unique products, such as sun care applications that effectively protect skin from particulate irritants and pollutants.
cosmestics.specialchem.com, 11 August 2020
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