Coating
A coating is a covering that is applied to the surface of an object, usually referred to as the substrate. The purpose of applying the coating may be decorative, functional, or both. Paints and lacquers are coatings that mostly have dual uses of protecting the substrate and being decorative, although some artists paints are only for decoration, and the paint on large industrial pipes is for preventing corrosion and identification e.g. blue for process water, red for fire-fighting control etc. Functional coatings may be applied to change the surface properties of the substrate, such as adhesion, wettability, corrosion  resistance, or wear resistance. In other cases, e.g. semiconductor device fabrication (where the substrate is a wafer), the coating adds a completely new property, such as a magnetic response or electrical conductivity, and forms an essential part of the finished product. A major consideration for most coating processes is that the coating is to be applied at a controlled thickness, and a number of different processes are in use to achieve this control, ranging from a simple brush for painting a wall, to some very expensive machinery applying coatings in the electronics industry. A further consideration for 'non-all-over ' coatings is that control is needed as to where the coating is to be applied. A number of these non-all-over coating processes are printing processes. Many industrial coating processes involve the application of a thin film of functional material to a substrate, such as paper, fabric, film, foil, or sheet stock. If the substrate starts and ends the process wound up in a roll, the process may be 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 e.g. Powder coatings. Coating Analysis. Numerous methods exist for evaluating coatings, including both destructive and non-destructive methods. The most common destructive method is microscopy of a mounted cross-section of the coating and substrate. The most common non-destructive techniques include ultrasonic thickness measurement, XRF (X-ray fluorescence) coatings thickness measurement, and ultra-micro hardness testing. Coating formulation. The formulation of the coating depends primarily on the function of the coating and also on aesthetics required such as color and gloss. The four primary ingredients are the resin (or binder), solvent which maybe water (or solventless), pigment(s ) and additives. Coating processes. Coating processes may be classified as follows: Roll-to-roll coating processes. Common roll-to-roll coating processes include: