Coating and its functions

A coating is a covering applied to a surface,usually called a substrate.The purpose of applying a coating may be decorative, functional or both.Coatings can be applied in liquid,gaseous or solid form,such as powder coatings.Paints and lacquers are coatings that mostly serve the dual purpose of protecting the substrate and decorating,although some artist's paints are purely decorative,and paints on large industrial pipes are for corrosion protection and identification.Blue is used for process water,red for fire control etc. Functional coatings can be used to modify the surface properties of a substrate,such as adhesion,wetting,corrosion resistance or wear resistance.In other cases,such as semiconductor device manufacturing (where the substrate is a wafer),the coating adds entirely new properties,such as magnetic response or conductivity,and forms an important part of the finished product.A major consideration in most coating processes is that the coating is to be applied at a controlled thickness,and many different processes are being used to achieve this control,from simple brushes used to paint walls to some very expensive mechanically applied electronics industry coatings.A further consideration with "non-comprehensive" coatings is the need to control where the coating is applied.Many of these non-full coating processes are printing processes.Many industrial coating processes involve applying thin films of functional materials to substrates such as paper, fabric, film, foil or sheet. If the substrate starts and ends the process as a roll, the process may be referred to as "roll-to-roll" or "web-based" coating.A roll of substrate wound by a coater is commonly referred to as a roll.

Functions of coatings 

Paints are designed not only for aesthetic and decorative purposes,but also for other functions.Coatings are sometimes both decorative and specific functions.An example is the coating of pipes that carry water for fire suppression systems,which are painted with a red (for identification) anti-corrosion paint to reduce degradation.In fact,most surface coatings or paints protect the substrate to some extent,such as general maintenance paints/paints for metal and concrete.The decorative nature of coatings goes beyond imparting a specific color,but also to creating special reflective properties such as high-gloss, satin or flat/matt appearance.However, some coatings are specially designed to be highly chemical resistant.The main purpose of coatings is to protect metals and these are often referred to as anti-corrosion coatings.Such uses include protection of machinery,equipment and structures.Over the years,the design of automobiles has improved.Most are still made of metal for impact resistance.Both the exterior coating and the underbody are coated.New anti-corrosion coating can combine graphene with water-based epoxy resin.Coatings are also used to seal concrete surfaces.This will include seamless polymer/resin flooring,bund wall/containment lining,waterproofing and moisture protection of concrete walls,and concrete bridge decks.Roof coatings have been developed and improved over the years.They are primarily designed to be waterproof and reflect sunlight to help keep buildings cool.They tend to be elastic to allow the roof to move without cracking the coating membrane.Coating,sealing and waterproofing of wood has been done since biblical times and God commanded Noah to build the ark and then coat it.Wood has been a key material in construction since ancient times,so protecting it through coatings has received a lot of attention.Efforts to improve the performance of wood coatings continue.Coatings are used to modify the tribological and wear characteristics.

Other functions of the coating include:

• Antifouling coatings.

• Anti-friction, anti-wear and anti-scratch coatings for rolling bearings.

• Antimicrobial coating.

• Anti-reflective coatings, such as those found on eyeglasses.

• Coatings that alter or have magnetic, electrical or electronic properties.

• Flame retardant coatings.Phosphorous and bio-based flame retardant materials and coatings are being developed.These include coatings with swelling functionality.

• Non-stick teflon coated cooking pans.

• Optical coatings change the optical properties of a material or object.

• UV coatings.