Paints and Coatings
Coatings syn. coating solutions are liquid, liquefiable, or mastic compositions which harden to a film to decorate or protect a variety of materials against corrosion or oxidation. Coatings, including paints (pigmented coatings), varnishes, lacquers, enam
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ble, or mastic compositions which harden to a film to decorate or protect a variety of materials against corrosion or oxidation. Coatings, including paints (pigmented coatings), varnishes, lacquers, enamels, stains, polishes, fillers, and shellacs have one or more of the following components: o
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Binders that hold the ingredients of the coating together and form tough, solid, elastic films on drying. Binders include natural or synthetic resins (e.g., rosin and balsam) which harden on evaporation of a solvent; drying oils (e.g., linseed, tung, soybean, fish, castor, perilla), organic liquids that polymerize to hard films through air oxidation; or other film-forming agents. Hardening is accelerated by the addition of paint driers or varnish driers, metals, and other compounds that speed oxidation, evaporation, or polymerization. Heat or other radiation sources may increase the rate of hardening. Pigments and dyes, including titanium dioxide, lead chromate, and aluminium flakes (which are used in aluminium paint syn. aluminium liquid to give a highly reflective metallic fmish). Dispersants, preservatives, flame retardants, fillers, and other additives. Solvents or paint thinners which carry the binder, pigments, and additives and facilitate application. These evaporate on application and are also known as reducing compounds (compounds used to reduce viscosity).
COATING TYPES
Traditionally, the taxonomy of paints was straightforward: o
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Paints were based on drying oils, water or organic solvents, and pigments. Varnishes were resin-based without pigment. Enamels were pigmented varnishes known for their hard and glossy characteristics.
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M. A. Fox, Glossary for the Worldwide Transportation of Dangerous Goods and Hazardous Materials © Springer-Verlag Berlin Heidelberg 1999
Paints and Coatings o
Lacquers were based on cellulose without pigment which dried through solvent evaporation.
Today, coatings technology has advanced to the point where these distinctions are no longer meaningful: paints can contain resins, varnishes may be pigmented, enamels can contain oils, and lacquers can contain resins: o
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Paints may contain all typical coatings components, although the use of organic solvents is being reduced to rely more heavily on water or high-solids paints. Varnishes contain gums, resins (spirit varnishes), or drying oils (oil varnishes) and solvents, but generally no pigments. Shellac derives from a resin secreted from the insect Kerria lacca collected from trees native to certain Asian countries. Dissolved in alcohol or other organic solvent, shellac becomes a spirit varnish, although it has many uses dry. Stains are often transparent varnishes with very low pigment or dye concentrations that penetrate the surface leaving little film. Enamels are characterized by their smooth and glossy appearance and hard nature. They are primarily pigmented varnishes or varnish-paint mixtures. Lacquers are clear, synthetic coatings, most often cellulose-based (such as nitrocellulose often modified wit
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