Liquid vs. Powder for Architectural Aluminum
Q. We currently perform both liquid and powder coating on various parts and have been considering using more powder coatings on our architectural aluminum extrusions to reduce our VOCs (volatile organic compounds). We hear conflicting stories about the UV resistance of powder when compared to high-performance liquid coatings. Can powder coatings meet AAMA 2604 and 2605 standards? What other pros and cons of powder versus liquid should we consider?
A. Yes, there are powder formulas that can meet the American Architectural Manufacturers Association's standards (AAMA 2604-13 and 2605-13). The technology for the 2604 standard is typically a TGIC polyester or super-durable powder. These products are formulated with resin systems and pigmentation to meet 2604's five-year standard for gloss retention and color loss. These powder materials are comparable to two-component liquid polyester coatings and can be applied in a single coat of 1.5 to 3.0 mils. Typical uses would be window and door frames, railing and fencing, outdoor displays and light fixtures.
The 2605 standard typically calls for a fluoropolymer. Usually PVDF- or FEVE-type resins, fluoropolymers are capable of meeting 2605's more demanding 10-year gloss and color retention standards. These products are used for monumental building products and cladding. They are very effective and compare favorably to Kynar and other fluoropolymer liquid coatings.
With respect to ease of application, the powder option is a clear winner. In addition to longer filter life, powder coating requires no primer, mixing or viscosity control, as does liquid coating. Powder compliant with AAMA 2604 has no appreciable VOCs, enables overspray reclamation/reuse and provides lower disposal cost. Powder also has superior mechanical properties than most liquid coatings and better stain resistance. While is critical that the part be absolutely clean for good bonding with powder, AAMA specifications make that necessary for any coating. A poorly prepared substrate will lead to adhesion failure or early corrosion. Solvent-based liquid coatings may tolerate some surface contamination and provide initial adhesion but long-term performance is still compromised. On balance, I think that powder offers a better and cheaper coating for architectural aluminum than many of the liquid options.
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