Paint is used to decorate, protect and prolong the life of natural and synthetic materials, and acts as a barrier against environmental conditions.
Paints may be broadly classified into decorative paints, applied on site to decorate and protect buildings and other objects, and industrial coatings which are applied in factories to finish manufactured goods such as cars.
The constituents of paint
Paints contain:
pigment(s) - prime pigments to impart colour and opacity.
binder (resin) - a polymer, often referred to as resin, forming a matrix to hold the pigment in place.
extender - larger pigment particles added to improve adhesion, strengthen the film and save binder.
solvent (sometimes called a thinner) - either an organic solvent or water is used to reduce the viscosity of the paint for better application. Water-borne paints are replacing some paints that use volatile organic compounds such as the hydrocarbons which are harmful to the atmosphere.
additives are used to modify the properties of the liquid paint or dry film.
The binder (resin) and solvent together are sometimes known as the vehicle. The binder may be dissolved as a solution or carried as a dispersion of microscopically small particles in a liquid.
Depending on the type of paint and intended use, additives may include:
dispersants - to separate and stabilise pigment particles
silicones - to improve weather resistance
thixotropic agents - to give paints a jelly-like consistency that breaks down to a liquid when stirred or when a brush is dipped into it
driers - to accelerate drying time
anti-settling agents - to prevent pigment settling
bactericides - to preserve water based paints in the can
fungicides and algaecides - to protect exterior paint films against disfigurement from moulds, algae and lichen
Formulated for use
Paints are formulated according to their proposed use - primer, undercoat, special finishes (matt, gloss, heat resistance, anti-corrosion, abrasion resistance). The pigment powder is broken down into individual particles which are coated by and dispersed in the binder (resin) - known as 'wetting out'. Solvent is then added to give the required consistency. Each batch of ingredients is thoroughly mixed in large, stirred containers with the required additives.
Binders in paints
The three most important binders (resins) used in modern paints are:
acrylic polymers (resins)
alkyd polymers (resins)
epoxy polymers (resins)
Pigments used in paints
Pigments give colour and opacity to paints. Amongst the organic pigments, particularly important are azo-, phthalocyanine and anthraquinone derivatives.
The most common inorganic pigment is white titanium dioxide (titanium (IV) oxide) which provides over 70% of total pigments used. It has a high refractive index and gives a 'gloss' to the paint. Another widely used inorganic pigment is finely divided calcium carbonate. This has a low refractive index and is used, together with titanium dioxide, to produce 'matte' paints. Other pigments include iron oxides (black, yellow and red), zinc oxide and carbon black.
Powdered metals such as zinc and some metal compounds, for example zinc phosphate, have corrosion inhibiting properties.
Chemgrit Coatings supplies a variety of constituents used for both he manufacture of decorative paints and industrial coatings. These are sourced from leading suppliers around the world. For more information contact Chemgrit Coatings on www.chemgrit.co.za or athol@chemgritsa.co.za.
[Information sourced: www.essentialchemicalindustry.org]