Powder coating is a great alternative to paint, offering excellent resistance to corrosion, chemical, heat, impact, abrasion, UV and salt spray. The coating process is environmentally safe, emitting zero to near zero volatile organic compounds (VOC) and does not produce hazardous waste or use solvents.
Commonly Used Coatings by POWDERgroup
Polyester TGIC Powder coatings
Polyester TGIC coatings utilize the epoxy functional cross-linker TGIC (triglycidyl isocyanurate). Use of this low molecular weight, multifunctional cross-linker enables polyester TGIC formulations to contain 90% or greater resin within the binder system. Weathering of polyester TGIC powders is comparable to polyester urethane coatings.
Polyester TGIC coatings typically offer faster or lower temperature, curing than do polyester urethanes. Unlike urethane coatings, polyester/TGIC coatings maintain excellent mechanical properties at film builds above 3 mils (75) with no out gassing (TGIC is non-blocked). Additionally, polyester TGIC coatings will provide good edge cover when sharp edges are present, due to the inherent higher melt viscosities of TGIC-based coatings, which may also increase surface roughness (orange peel). Over-bake color stability of TGIC-based coatings is excellent. Although adhesion and corrosion resistance properties are similar to polyester urethane coatings, chemical and solvent resistance may be somewhat reduced.
Typical applications for polyester TGIC coatings are aluminum extrusions, automotive wheels, pole-and pad-mounted transformers, air conditioners, fencing, gas cylinders and lawn furniture.
Polyester Urethane Powder Coatings
Urethane-cured polyester powder coatings combine very smooth, exceptional thin film capability, with excellent mar and chip resistance, and good weathering properties. Adhesion to properly prepared (pretreated) substrates will provide very durable coatings with long-term resistance to humidity and corrosion. They are typically resistant to many dilute aqueous acids, salts, aromatic and aliphatic hydrocarbons, grease and oils.
Polyester urethanes exhibit a wide range of chemical a physical properties depending on the resin and cross-linker chosen. Typical IPDI-based cross-linkers used in polyester urethanes are blocked with e-caprolactam, but occasionally other agents, primarily oximes, are also employed. It is necessary for the cross-linker to unblock before the powder can cure. For this reason, cure temperatures must be above the unblocking temperature. With standard e-caprolactam containing powder a coating, unblocking occurs at approximately 340 degrees F (172 degrees C); therefore, cure temperatures must be in excess if 340 degrees F. Normally polyester urethanes are applied in 1-3mil (25-75u) thicknesses because higher film builds may exhibit a decrease in mechanical properties and outgassing effects due to e-caprolactam evolution.
Typical applications utilizing polyester urethane coatings are fluorescent light fixtures, lawn and garden equipment, electrical enclosures, playground equipment, range panels, air conditioners, automotive trim and patio furniture.
Epoxy Powder Coatings
Epoxy-based powder coatings were the first thermosetting systems to become commercially available and are still widely used today. Although epoxy powders can be used in decorative applications where they are not subject to UV radiation, they are used primarily as functional coatings for substrate protection where inherent toughness, corrosion resistance, flexibility and adhesion are required.
Because of the large number of available epoxy resins each resin’s ability to react with a wide variety of curing agents, nearly and combination of desired physical properties can be obtained. With proper selection of components (raw materials), epoxy-based (pure epoxies and hybrids) coating powders can be formulated to be FDA compliant for food contact applications. The primary limitations of epoxy-based coatings are their poor weather ability.
Functional Epoxy-Based Powder Coatings
As stated above, the terms functional and decorative, as applied to epoxy powders, may be miss-leading. However, with functional epoxy-based powder coatings, appearance is less of a consideration.
The two major uses of functional epoxies are electrical insulations and corrosion protection. They offer many designs, cost and production advantages over conventional insulating coatings such a tape wrapping, phenolic sleeving, and polyester sheeting. Powder coatings conform exactly to each contour of the electrical parts, bonding to the surface to become permanent, integral insulation that is void-free and low of bulk. It is the nature of epoxies to provide outstanding properties and to retain these properties after long term heat aging.
UV Cure Coatings
UV cure powders are fast reacting, non-polluting systems that have opened new markets for powder coatings. Currently available resins, photo initiators and additives melt easily in the 200 degree F to 250 degree F range, making this technology a good fit for applications on wood, MDF, temperature sensitive metals, plastics, and high-speed metal substrate applications.
Antimicrobial Powder Coatings
Consumer products that prevent the spread and growth of microbes continue to be a growing trend in the marketplace. Powder coatings are now available that are formulated to prevent the spread and migration of bacteria on products finished with these new coatings.
Antimicrobials are organic materials, which are drug-based, or inorganic, which are usually based on precious metal such as silver. The major difference is that microbe resistance to drug-based antimicrobials can build up to the point where they are no longer effective.
Biocides must be mobile in order to migrate to the coating-microorganism interface where they can kill the microbe and to provide long lasting efficacy. Antimicrobial powder coatings can be applied by the same methods as other thermoset powders. These new antimicrobial powder coatings are being used on hardware such as door handles, school lockers, appliances, and HVAC systems.