Q: What is meant by the term “coating technology” or “coating technologies”? A: A coating technology is the chemistry of a particular type of paint or coating. In this article I will use the words “paint” and “coating” synonymously. For instance, an epoxy is one coating technology, whereas a polyurethane is another. An epoxy is a chemical compound that has a very specific chemical makeup. An epoxy “molecule1” comprises carbon, hydrogen and oxygen atoms that are arranged in a very particular way. Similarly, a polyurethane “molecule” contains carbon, hydrogen and oxygen atoms, but in addition also contains a small amount of nitrogen. What makes this molecule unique is the manner in which some groups of carbon, oxygen and nitrogen are linked together. A vast amount of science has gone and continues to proceed into researching polyurethanes. Some polyurethane coatings are formulated so that the paint can be packaged into a single can. Others are formulated in two components, A and B, and you need to mix the two components in a specified ratio, such as 2 parts Component A to 1 part Component B. Those that are packed as a single component require ambient moisture to cure the coating. The two-component technologies cure only when the two chemical mixtures come into contact with each other. A coating technology that started in the 1950s or earlier, has become one of the most popular methods for painting small and even large objects. This is powder coating2 technology. These are paints that do not contain any solvents or water but comprise a mixture of powdered resins, pigments, fillers and additives. The powdered ingredients are mixed, molten into an awful looking sludge, extruded into a solid, thick, brittle film, and then pulverized into extremely small particles. Each powder particle is between 5-20 microns in diameter. The final mixture is an extremely fine powder that resembles talc. Initially, when the powder coating is applied to a piece of metal the powder particles adhere to the metal by electrostatic forces. The panel is then placed into a high temperature oven, usually above 325oF for approximately 10-15 minutes where the powder melts, flows like hot lava, gels and then cures into a beautiful solid film. Currently, we use powder coatings for patio furniture, tubular steel, exercise equipment, hand tools, lighting fixtures, aluminum extrusions, aluminum wheels, and thousands of other uses. We can break up the topic of powder coating technology further. For instance, the resins used to make powders include epoxies, polyesters, acrylics, polyurethanes, triglycidyl Isocyanurate (TGIC) and more. For each resin, extensive scientific research has been undertaken, and hence we can refer to a “coating technology” for acrylic powder coatings, nylon powders and more. ____________________ 1 The word “molecule” does not really apply to organic resins, but for purposes of this non-scientific article and for simplicity I will use it.
2 Sometimes referred to as “powder paint” Historically, paint was solvent-based, (or solvent-borne). In other words, the ingredients that made up paint; resins, pigments, extender pigments and additives, were mixed in an organic solvent, such as mineral spirits, lacquer thinners, etc. In the early part of the 20th century a new coating technology was developed; namely waterborne coatings, such as acrylic latex, polyvinyl alcohols (PVAs), and a host of other water based systems that were almost exclusively used for painting architectural surfaces. During the past 30 years, especially on account of environmental regulations to control smog in our cities, waterborne coatings have also extended into the industrial market. Therefore, we can now purchase sophisticated waterborne coatings to paint military tanks, personnel carriers, aircraft, and other products that require outstanding chemical and physical performance. Even within the large category of waterborne coating technologies, we can break it up further into waterborne epoxy technologies, waterborne polyurethane technologies, latex technologies, and many more. Ron Joseph is a paint and coating consultant employed by Exponent Failure Analysis, Menlo Park, CA. (408) 507-7927. |
