While the sensory appeal of coatings has always been an important driver of consumer acceptance of devices and appliances, positive tactile interaction properties of coatings are gaining increased attention in an industry that has focused primarily on their optical characteristics. Understanding both the aesthetic and functional significance of these tactile characteristics is therefore an area of opportunity. Physical human contact with a surface can have positive and negative attributes; positive attributes are often associated with terms such as “good-feel” “soft touch,” “lubricious,” “warm,” “cushion,” and “slick,” but are only meaningful in the context of a specific application. For example, “slip” may be a positive attribute in one application, but negative in another. Direct contact with metal, cellulosic or polymeric substrates that are generally experienced as dull, or even unpleasant, can be transformed into an interaction that is functionally pleasant, or even luxurious, when mediated by a coating that stimulates the mechanical and thermal receptors of the skin differently. Applications that rely on positive tactile interaction with coatings include healthcare appliances, mobile devices, automotive interiors, synthetic leather, and, in a broad sense, textile finishes as well as color and hair-care cosmetics. Negative tactile interactions may simply result in touch-wear failure of a coating; in textile coatings, they may be associated with friction and modulus properties that cause decubitus ulcers. Finally, the issue of tactile properties has become critical in the market acceptance of interactive devices ranging from hand-held devices to human interfaces with robotics.
Figure 1 shows a variety of applications where tactile interactions combine with functional properties. Synthetic leather finishes require control of modulus and coefficient of friction. Capacitive arrays for fingerprint recognition require a combination of tactile interaction, dielectric properties, and permeability of gases and moisture. Oxygen permeability, hydrophilicity and mechanical properties in siloxane-urethane copolymers utilized in contact lenses demonstrate extreme control in the medical arena that can be translated from bulk molding to thick films.