We recently published a series of posts aimed at explaining the different types of industrial coatings and the strengths and weaknesses of each type. Here we’d like to go a little deeper in order to explain some of the smaller components that make up an effective protective coating in an industrial setting.
Once again, we’ll stay away from the advanced chemistry in favor of a more top-level explanation of the four components that typically make up an industrial coating.
The “binder” portion of a coating, along with the other liquid components making up the product, are known as the “vehicle.” NACE explains a binder as the “non-volatile portion of the vehicle of a formulated material.”
The primary purpose of the binder is to convert from a liquid to a solid after being applied. In order for a binder to be considered successful, it needs to make this transition from a liquid to a solid in a timely manner, while not allowing for the transmission of water, oxygen or chemicals across the barrier it forms. It also must bond well while exhibiting desired properties of strength, hardness and flex. For some application settings, it will also be important that the binder can resist a range of environmental conditions.
Coatings very often take the name of their primary binder. Alkyds, epoxies and urethanes, for example, are all named for their binding component. While the vehicle may perform the bulk of the work we expect from a protective coating, it wouldn’t be very effective without the rest of the components of a product. If a binder helps a coating get the job done, the other components help it to get the job done right.
Pigments are often described as “discreet particulate solid” components of a protective coating. All this means is that they do not dissolve into the coating’s vehicle. These are commonly added to give a coating color but can also help protect against weathering or more actively assist in the fight against corrosion by acting as cathodic protection or as a corrosion inhibitor.
Unlike pigments, additives are most commonly liquid additions to a protective coating. Together with binders and pigments, additives are present to affect the performance of the coating in some way. The additives present in a given coating were usually put there to perform a specific function or to respond to a specific challenge. These functions could include defoaming, drying, wetting, UV-resistance and more.
In many protective coatings, the exact formula of additives is treated as a closely guarded secret, responsible for making a product unique and setting it apart from its competition.
Solvents are chemicals added to a binder so that it may be applied effectively to a substrate. Many binders exist as solids at room temperature, which would make them impractical to apply without some liquefying agent. So while solvents are incredibly important in getting a protective coating onto a substrate, they serve virtually no role after the coating has been applied. In fact, the failure of a solvent to evaporate properly could result in performance problems for a protective coating down the line.
Solvents are typically judged based on two factors. “Solvency power” measures a solvent’s ability to dissolve a given binder. “Volatility” is a measure of the rate at which a solvent evaporates. It’s important that a solvent evaporates quickly enough so that more coatings can be applied as necessary or so that an asset can be put back into service, but slowly enough that the coating adheres properly to the substrate.
Solvents have come under stricter regulation over the past decades as the EPA seeks to limit the amount of volatile organic compounds (VOCs) that are released into the atmosphere. In response, more products are being manufactured that either make use of water as a solvent, use solvents that are not considered VOCs, or contain no solvents at all.