Industrial paint, as used to protect metal, wood, and a wide range of other materials, possesses a variety of traits that can be manipulated to provide application-specific coverage. Of course, these characteristics depend in a large part upon the ingredients of the paint and the performance specifications of the selected application. Application methods, too, can influence the quality of the paint coverage and determine how well paint adheres to the substrate. Typically, there are four main components in a paint: pigment, binder, liquid, and additives. Application methods depend on the particular paint, but can include spray application, brush methods, and electrostatic spraying.
A paint’s pigment plays a large role in determining color and appearance. Some pigments also provide added bulk, helping to thicken a paint when needed. In its unmixed form, a pigment is simply a powder. There are two general categories of pigments: prime and extender.
Prime pigments are mainly responsible for color or whiteness in a paint, as well as the paint’s ability to hide undesirable surface flaws. In paints that exhibit a white hue, titanium dioxide is the main ingredient. In paints the express other colors, the pigments are selected to absorb only certain kinds of light, thus yielding a given color. Organic pigments yield the brightest colors, while inorganic pigments yield less bright but more durable colors.
Extender pigments are designed to add bulk, but are not as well-suited to hiding surface flaws as prime pigments. They do, however, influence the paint’s overall sheen, color retention, and abrasion resistance. Silica and silicates, for example, are extender pigments that increase the paint’s durability. Zinc oxide helps prevent mildew and corrosion, and is especially useful in outdoor applications.
In a paint mixture, the binder is responsible for providing adhesion, binding the pigment, and also gives the paint resistance properties which make the final coating tough and durable. The binder itself is clear and glossy, but the presence of pigment interferes with this quality. Depending on the ratio of pigment to binder, or the PVC (pigment volume concentration) the paint can assume varying levels of glossy finish. Paints with the glossiest finish often have a typical PVC of 15 percent, while the most matte paints have a PVC anywhere from 40 to 80 percent. Paints with less gloss have more binder per unit of pigment, and tend to be more durable. There are two specific types of binder: oil-based and latex-based.
Oil-based paint requires a binder that has similar properties to the paint—in this case, the binder oxidizes or dries when exposed to air, hardening along with the rest of the paint. Once applied, the liquid factor of an oil-based paint evaporates, and the binder then reacts with the air to harden into place with the pigment. However, sometimes this process can result in over-dry, brittle paint, and chipping can occur. Additionally, the oxidation makes the paint prone to yellowing.
Latex-based paints actually do not possess latex—rather, the binder that is used (plastic-like in nature) creates a film in the paint that resembles natural latex rubber. Almost all water-based paints have a latex-based binder. When the coating is applied, water evaporates from the paint, leaving behind a film of pigment and latex-based binder, which bind together into one continuous coating. The process by which the binder and pigment are fused is called coalescence. However, because the binding agent is thermoplastic, it cannot be applied at too low a temperature or the binder will be too hard and difficulty will arise during fusing. Common types of latex-based binder include acrylic and vinyl acrylic.
In the most basic sense, the liquid component of a paint is simply responsible for transporting the binder and pigment to the substrate surface. The type of liquid depends upon the other components of the given paint. Oil-based paints, for example, can use a basic paint thinner as the primary liquid. Latex-based paints, on the other hand, tend to use water as their liquid.
When certain properties need to be manipulated or enhanced, additives are often the solution. Thickeners, for example, are additives that help thicken the paint to make application easier. Surfactants help disperse pigments within the paint, ensuring the coat is even and stays in place. Co-solvents help the binder film formation and help prevent paint damage from occurring if the pain is frozen. Co-solvents also make application easier by lengthening the amount of time the paint can be open before beginning to set.