Paints or coatings are liquid, paste, or powder products which are applied to surfaces by various methods and equipment in layers of given thickness. These form adherent films on the surface of the substrate. Film formation can occur physically or chemically. Physical film formation from liquid coatings is known as drying, whereas for powder coatings, it is melting process. Drying is always associated with evaporation of organic solvents or water. Physical film formation is only possible if the coating components remaining on the substrate are solid and nontacky. Chemical film formation is necessary if the coating components are liquid, tacky, or pasty; conversion to a solid nontacky film takes place by chemical reaction between the components. The reactive components can be constituents of the coating, and the reaction can be initiated by energy (heat or radiation) after application of the coating. However, it is also possible to add a reaction partner while applying the coating (multipack paints). A special case of chemical film formation is the oxidation of coating component(s) by atmospheric oxygen (air drying). Physical and chemical film formation are often combined, e.g., in solvent-containing stoving paints, where the first stage is solvent evaporation, after which the film is cured by stoving. The properties of a paint are determined by its qualitative and quantitative composition, suitable choice of which enables the viscosity, electrical conductivity, and drying behavior to be matched to the application conditions. Also,the properties of the coating film (luster, elasticity, scratch resistance, hardness, adhesion, and surface structure) are determined by the paint properties. However, the condition of the substrate surface (cleanliness and freedom from dust and grease) is also important.
Coatings must fulfill many requirements. They protect the substrate against corrosion, weathering, and mechanical damage; have a decorative function (automotive coatings, household appliances, furniture); provide information (traffic signs, information signs, advertising); or have other specific properties.
“Coating” is a general term denoting a material that is applied to a surface. “Paint” indicates a pigmented material, while “varnish” refers to a clear lacquer. Considering the above mentioned concept, we may conclude that paint is such a liquid, or liquid type material, which when applied in a thin layer to a surface, forms an adhering film on that surface. Paint implies the presence of a solid portion which we may refer to as the pigment, and a more or less liquid portion to which the term medium may conveniently be applied.
Now, we are much familiar with the basics of Paints or coatings and their history. we will move to Major Constituents of Paints