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In the world of powder coatings, the term “functional coatings” has historically been used to describe fusion-bonded epoxies used in pipeline and rebar applications. However, today’s powder coatings offer specialized functionalities that would fit in with the broader definition of that term. That is, they are specifically designed to provide a function beyond aesthetics and substrate protection. Among these functionalities, three stand out for their relevance in today’s environment: antimicrobial, electrostatic dissipative (ESD), and anti-graffiti powder coatings.
Antimicrobial Powder Coatings
Antimicrobial powder coatings are designed to inhibit the growth of microbes such as fungi, mold, and bacteria on coated surfaces. While these coatings have been traditionally used in environments where hygiene is critical, such as hospitals and food processing plants, the COVID-19 pandemic has expanded their usage into many high-traffic areas such as fitness centers, public transit centers, and even playground equipment.
The most common method of creating the antimicrobial properties in powder coatings is through the incorporation of silver-ion additives. These additives release Ag+ ions when exposed to moisture or humidity, acting as the active antimicrobial agents by disrupting the microbes’ cell membranes and enzymatic systems. While other materials (e.g., copper, zinc, or quaternary ammonium compounds) may be used in antimicrobial coatings, silver is more common due to its broad-spectrum efficacy, long-lasting activity, and proven effectiveness against a wide range of microorganisms. Additionally, silver is compatible with various types of coatings and has a long history of safe use in medical and industrial applications.
Antimicrobial coatings are important not only for reducing the spread of pathogens but also for preventing discoloration, unpleasant odors, and material degradation, all of which can be caused by microbial growth. Their passive, long-term functionality makes these coatings ideal for high-touch surfaces, and integration with the coating means the antimicrobial function does not require the frequent reapplication required for surface disinfectants, making it a reliable, low-maintenance solution.
ESD Powder Coatings
Electrostatic dissipative powder coatings are designed to safely dissipate static electricity from coated surfaces. These coatings are often used on components or in areas where an electrostatic discharge could damage sensitive electronic components, ignite flammable materials, or disrupt operations. Common applications include electronic enclosures, electronic assembly areas, server casings, or robotic components.
ESD functionality is achieved by incorporating conductive or semi-conductive pigments into the powder coating formulation. The most common materials used in powder coatings are conductive carbon black and carbon nanotubes. Since they are most often interior coatings, the binder is typically an epoxy or hybrid powder coating, although other types of resins can be used if an exterior-durable coating is required. In any case, the binder provides the main coating properties (e.g., adhesion), and the conductive filler provides the pathway for the electrical current. The surface resistivity requirement for ESD coatings typically falls with the range of 105 and 109 ohms per square, although the specific range may vary by application.
Properly formulated ESD coatings balance electrical performance with mechanical properties, durability, and aesthetics. Achieving this balance is dependent on the ability to properly disperse the conductive pigment into the powder coating during the extrusion step, as poor dispersion can have a negative impact on both conductivity and coating properties. Coating manufacturers who offer these ESD powder coatings have invested significant resources into understanding how the conductive materials and processing conditions affect the coatings’ performance in the field.
Anti-Graffiti Powder Coatings
Anti-graffiti powder coatings are designed to reduce the ability of spray paint, markers, and inks to absorb into the coating, thus enabling easy removal of these substances with common solvents. These coatings are often used in high-traffic areas such as public transit stations, schools, and building facades where vandalism is a concern.
To achieve the anti-graffiti properties, these coatings are developed to have a combination of low surface energy and high chemical resistance. The low surface energy is achieved using additives, such as waxes or silicone-containing materials, which migrate to the surface of the coating and prevent graffiti materials from wetting out and adhering to the coating. The high chemical resistance is gained through the use of high-crosslink-density binders, such as urethanes, which are inherently resistant to chemicals attack and prevents the degradation of the coating upon exposure to graffiti materials and cleaning solvents.
Anti-graffiti powder coatings can be formulated to offer excellent UV resistance and a variety of colors, making them suitable for both indoor and outdoor use. In addition to aesthetic preservation, these coatings reduce the maintenance costs and downtime associated with graffiti removal and repainting.
Evolving Functionalities
As performance demands on coated surfaces continue to rise, powder coatings continue to evolve. Functional coatings, such as antimicrobial, ESD, and anti-graffiti coatings, are becoming increasingly common and new functionalities are being developed as market needs continue to change. By incorporating specialized functionalities into their powder coatings, manufacturers offer end users an environmentally friendly solution that doesn’t sacrifice coating performance.
To learn more, reach out to the author at ecasebolt@chemquest.com.
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