When protecting metal through coating solutions, the most common approach is to coat the metal with a two-coat system—a primer and then a finishing coat. Alternatively, direct-to-metal (DTM) coatings provide the protection of a primer with the aesthetics of a top coat (a two-in-one solution). DTM coatings are applied directly to a metal surface and can adhere without the need for a primer. In addition, most DTM coatings (but not all) are expected to be applied in only one application. This one-coat process makes DTM coatings more efficient, requiring fewer production steps and less labor, resulting in opportunities to reduce costs.
DTM coatings have been more commonly used in lighter duty service, such as industrial applications for touching up machinery/equipment or for DIY applications. Two-coating systems are still more common where the protection requirements of an application increase or the service environment is particularly harsh such as in marine, petrochemical, infrastructure and energy related applications. However, as DTM coatings continue to evolve and improve, they can be used in a wider variety of applications and are getting closer in performance desired for heavy-duty applications.
What Sets DTM Coatings Apart?
Labor and time—those are two of the primary advantages of DTM coatings. Because they do not require a prime coat, DTM coatings can be less labor intensive to apply and they cost less. In many cases, 80 percent of the cost of a coating job involves labor and 20 percent is the actual materials used. With DTM, it’s the same protection, but with one less coat. Less coats brings improved efficiency and additional time savings.
From a sustainability perspective, DTM coatings offer additional advantages. Multi-coat systems require two or more layers, which means more materials. They might also have more solvent or hazardous chemicals, whereas DTM coatings are typically water-based.
Considerations When Using DTM Coatings
Because there is often only one layer, it’s important to ensure there are no film defects when applying a DTM coating. If a spot is missed or coated too thin, metal can be exposed. It’s also important to ensure the same level of performance and durability, even though there is only half as much material as a two-coat system.
Adhesion can be another challenge. Typically, primers are based on strong epoxies which offer exceptional adhesion. While epoxies are great for adhesion in primers, they lack the weatherability and UV resistance required for use as a top coat. That’s why DTM coatings are most often acrylics or polyurethanes. They have the aesthetic properties required of a top coat, and while they don’t have the same innate adhesion, with a little effort in formulating, the adhesion properties in acrylics or polyurethanes can be greatly improved.
Lubrizol Addresses DTM Challenges
Lubrizol has developed a couple of different acrylic emulsions and polyurethane dispersions for DTM coatings. Our most recent innovation, based on our proprietary polyamide technology, is Aptalon™ M8120. This polyurethane is designed for superior adhesion and corrosion resistance for metal, while also providing excellent protection from weather, chemicals and water.
Aptalon M8120 is different from other DTM dispersions on the market that are based in acrylics or alkyds. Aptalon M8120 is a urethane with higher hardness than acrylics and alkyds; higher chemical resistance; and, better impact resistance and flexibility. Flexibility in a coating is important because it offers more durability. That’s evident in a piece of coated equipment with a brittle coating, which can chip and flake off if hit with a rock, leaving the metal exposed.
Coatings can usually be either hard or flexible, but usually not both. Aptalon M8120 can deliver both, which is unique. It is harder than the normal acrylic, but also very flexible. This combination means outstanding toughness and durability opportunities for coatings.
For more information about Aptalon M8120 or for other DTM challenges, contact a Lubrizol expert.