Paints consist of a blend of components, each with their specific function. Commonly, these include the binder (or medium), solvent, base, extenders, pigments and driers, although other additives may be incorporated
into specialist paints.
The binder solidifies to produce the paint film. Traditionally, the binder was natural linseed oil, which set by gradual oxidation upon exposure to air. How ever, linseed oil has now been largely replaced by alkyd resins which oxidise in air, or vinyl and acrylic resins which solidify by drying. To ensure adequate fluidity of the paint during application by brushing or spraying,
either water or organic solvents (hydro carbons, ketones or esters) are incorporated; paint thinners have the same effect. The base material, usually white titanium dioxide, produces the required opacity, although the
body of the paint may be increased by the incorporation of inert extenders such as silica, calcium carbonate, china clay or barytes. Colouring materials are frequently a mixture of organic and inorganic dyes and pigments. Driers which induce the polymerisation of the binder ensure a rapid drying process.
Changes in legislation and environmental concerns have led to the development of paints with reduced levels of volatile organic compounds (VOCs). Mainly this has been through the increased use of water-borne rather than solvent-borne paints. In some respects water-borne paints have the advantage. They have low odour emissions, brushes can be cleaned in water and they will tolerate damp surfaces. However, they are not ideal for external use in cold and wet conditions. Other developments have been towards high-solids paints, which have low solvent content and therefore very low VOC emissions.
A further trend is towards the use of natural paints based on plant oils, casein, cellulose and mineral compositions. These are free from the high embodied energy materials such as petrochemical products and titanium dioxide. Natural paints consume considerably less energy in manufacture, are environmentally friendly in application and less problematic in waste management; however, they are not suitable for all applications. Some casein emulsions, available in a range of colours, are suitable for internal application only. However, newer eco-paints including water-based gloss paints are suitable for exterior use. Many products now carry eco-labels – some indicating the VOC content.