A coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance. In other cases, in particular in printing processes and semiconductor device fabrication (where the substrate is a wafer), the coating forms an essential part of the finished product.
Coating and printing processes involve the application of a thin film of functional material to a substrate, such as paper, fabric, film, foil, or sheet stock. This article discusses what is frequently termed "roll-to-roll" or "web-based" coating. A roll of substrate, when wound through the coating machine, is typically called a web.
Coatings may be applied as liquids, gases or solids. Coatings can be measured and tested for proper opacity and film thickness by using a drawdown card.
Famous quotes containing the word coating:
“The world is eaten up by boredom.... You can’t see it all at once. It is like dust. You go about and never notice, you breathe it in, you eat and drink it. It is sifted so fine, it doesn’t even grit on your teeth. But stand still for an instant and there it is, coating your face and hands. To shake off this drizzle of ashes you must be for ever on the go. And so people are always “on the go.””
—Georges Bernanos (1888–1948)