Paint Binders
The different classifications of paint such as oils, acrylics, and latex refer to the ‘binder,’ the component that sticks the colors to the wall or to a canvas and protects the finished product from damage.
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With paint, the actual color is provided by pigment; another substance binds the pigment particles to each other and allows the mixture to adhere to the wall, ceiling, or canvas. Ideally, the binder also forms a protective film over the colors to make the finished product tougher and more durable. Paints are often classified according to their binders such as oils, acrylics, or latex.
After paint is applied, it must dry and cure; two processes that are somewhat different from each other. Drying refers to the evaporation of solvents. Curing involves chemical reactions between the molecules of the binder, known as polymerization, which effectively creates a stable web or network. Some paints merely dry, some cure, and some do both.
Lacquers are paints that contain a solid binder and dry by simple solvent evaporation to form a solid film, which typically has excellent resistance to ultraviolet light. By contrast, latex paints cure through a process called coalescence, in which the evaporating solvent fuses the latex molecules into a network that prevents the redissolution of the paint upon exposure to water. That is why although you can effectively use water to clean your hands and equipment after painting the kitchen walls with latex paint, a month later, you can use water or a mild solvent to remove fingerprints from the same wall without also dissolving the paint.
Alkyd enamels cure through oxidative crosslinking of the binder, and the amount of oil present influences the drying/curing time. Products with a medium cure time are used for high gloss coatings and wood finishes. By contrast, a higher proportion of oil results in a finish that must be heated to cure, which is optimal for use in enamel paints used on metal objects. A smaller amount of oil in the mix produces “oil” paints that dry more rapidly than traditional, slow-drying paints made with linseed or poppy oils.
The widely ranging properties of various binders provide numerous different ways for us to color our world.
More information about binders may be found at http://www.paintmaking.com/binders.htm
This topic was suggested by Alexandra Watton of Oconomowoc, Wis.