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. Industrial paints are specially formulated to meet the needs of various industries including aerospace, over-the-road equipment, civil projects, canning, heavy machinery, marine, etc. Sometimes paints are categorized as coatings but, generally speaking, paints dry while coatings cure. This article expands the definition some to include coatings that go on in liquid form and cure, such as the various epoxy resins, but preclude coatings that are generally applied dry, such as powder coatings.
Main Elements in Making Paint
Typically, there are four main components in paint: pigment, binder, liquid, and additives. Application methods depend on the particular paint but can include spray application, brush methods, and electrostatic spraying. Other methods include dip coating, where the product is sunk into a paint vat and electrocoating, where a charge is placed on the object as it is dipped in a tank, sometimes called e-coating.
Pigment
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 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.
Pigments must resist dissolving in the medium in which they are contained to ensure the color and opacity of the paint application. Pigments absorb all light but their own color which they reflect. A blue car under a sodium lamp will appear black because the sodium light contains no blue component. Black pigments absorb almost all visible light striking their surfaces while white pigments reflect practically all the light hitting them. Fluorescent pigments reflect light at their particular wavelengths in the visible spectrum while also absorbing ultraviolet light and re-emitting it as visible light.
Binder
In a paint mixture, the binder is responsible for providing adhesion, binding the pigment, and giving the paint resistance properties to 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.
Polyurethane paints use water or oil-based solvents as binders too, but the paints cure even as the binders evaporate.
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 binders include acrylic and vinyl acrylic.
Liquid
In the most basic sense, the liquid component of 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 basic paint thinner as the primary liquid. Typical industrial paint solvents include ketones, esters, and xylenes. These can dissolve pigments that have poor solvent resistance.
Latex-based paints, on the other hand, tend to use water as their solvent. A common solvent in alkyd paints is mineral spirits in which many pigments are insoluble, making these coatings desirable for high-gloss, decorative applications.
Additives
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 paint is exposed to freezing temperatures. Co-solvents also make application easier by lengthening the amount of time the paint can be open before beginning to set. Additives are available for improving color strength, brightness, haze, gloss, opacity, etc. often without affecting viscosity. Additives are also used to make paints self-leveling or to improve a coating’s slip resistance, for instance.
Paint Types
Paints come in mainly five forms: polyurethane, epoxy, alkyd, high zinc, and acrylic. Polyurethane paints, sometimes called simply “urethane“ paints, cure by chemical reaction or by exposure to air, heat, or UV light and are available as one- and two-part coatings. These are particularly useful as color coats where a tough, highly aesthetic finish is desired, as for automobiles.
Epoxy coatings are usually two- or three-part formulations and impart good abrasion and weathering characteristics and high heat resistance. They bond well to many materials. Epoxy resins are used in food and beverage can coatings to prevent oxidation of the container and contamination of the product. High abrasion resistance makes them popular for flooring applications. They are used extensively in the oil/gas industry for pipeline protection.
Alkyd enamel coatings provide environmental protection in interior, exterior, underwater, and underground applications, and are also used for road markings, but tend to be slower drying than other paints. Although alkyd paints behave similarly to other oil-based paints, they have fewer petroleum-based ingredients, instead using fatty acids and triglyceride oils as their major components. Typical oils used in alkyd coatings include tung oil, linseed oil, sunflower oil, etc.
High zinc coatings are particularly useful on steel as they provide both galvanic and barrier protection. They are available as organic (using epoxy or polyurethane binders) and inorganic coatings (using silicate binders) and are durable and abrasion-resistant.
Acrylic paints are useful as primers to promote adhesion. Acrylics paints tend to use fewer additives than other paints (such as surfactants and pigment dispersants). Acrylic resin is more expensive than vinyl resin and both are used in the making of latex paints–with better quality paints having a higher acrylic content. Acrylic paints are sometimes used as temporary coatings for shipping and long-term storage of equipment with additives added to make them easily stripped or peeled off.
SOURCE: https://www.thomasnet.com/articles/chemicals/paint-components-general-industrial/
