Technology Interchange: Powder Coating Summit: A Review

By: Kevin Biller

The 2016 Powder Coating Summit provided a cornucopia of advancements in powder coating technology. Topics ranged from twocoat systems to smart in-line powder application to fluoropolymer chemistry. Allow me to give you a synopsis of some of the topics presented.

Optimal Process When Layering Powder Coatings

Rodger Talbert, noted powder coating expert and director of business development at Col-Met presented a tutorial on multi-layer powder coating technology. He explained how single coats of powder can meet indoor specifications but typically have limited corrosion resistance. Double coats with the same powder provide improved edge coverage and better corrosion resistance than a single coat. The combination of a primer plus a topcoat powder offers substantial corrosion protection. Primer options include standard epoxy, Mil-Spec (military specification) primer and zinc rich epoxy. Zinc rich powder primers provide superior corrosion resistance over blasted steel. Talbert cautioned that fully curing a primer followed by a topcoat could risk intercoat adhesion and recommended either partially curing the primer prior to topcoat application or applying a dry-ondry primer/topcoat layered system. The latter could present application challenges.

Selecting the Right Oven – Convection or Infrared

Returning speaker, Marty Sawyer, presented an excellent treatise on the pros and cons of various curing technologies for powder coatings. She began her presentation by distinguishing between the various types of heat transfer, namely convection (movement of a fluid – gas or liquid), conduction (direct contact) and radiation (electromagnetic waves). With infrared (radiation) heating absorption is key as black absorbs more than white and matte absorbs more than shiny. Convection can be either through gas combustion or electric resistance. Infrared on the other hand can be generated with gas-catalytic or electric techniques.

Sawyer didn’t promote a onesize- fits all approach to curing powder coatings. She identified the advantages of ease of operation, flexibility and tradition of using convection, but also pointed out the slow cure, cost and environmental impact inherent to this technique. Gas catalytic is low coat to operate, uses a small footprint and is very environmentally sound. Drawbacks include high initial capital cost, unsuitability for a diversity of parts and the learning curve necessary to master operation. Electric Infrared provides the fastest cure, highest gloss finish and is also environmentally friendly. On the other hand, electric IR has the highest operating cost, requires a learning curve and is the most unforgiving for diverse part geometries.

Sawyer provided an excellent video depiction of surface temperature profiles of parts passing through a gas catalytic IR tunnel. This demonstrated the speed of heat-up and the relatively good heat distribution on the coated part. The part required only 6:45 minutes gas catalytic infrared compared to 30:00 minutes of gas convection to complete the powder coating cure. Sawyer concluded with, “there are no bad technologies, just bad applications"...of technologies.

Lab Demo – Twin Screw Extrusion Technology

Randy Kincer and Paul Young of Baker Perkins were first time laboratory demo contributors and regaled attendees with a video simulation of the inner workings of a twin screw extruder. The video depicted how the materials fed into the extruder transition from a dry blend of disparate components to a homogeneous mixture. Baker Perkins has perfected the screw design of these complex machines to maintain a consistent introduction of raw materials having differing particle size, shape, bulk density and specific gravity. The video and accompanying commentary underscored the criticality of feed zone screw configuration, extrusion RPM and kneading zone design for optimal dispersion of pigments and distribution of resinous components.

Smart In-Line Powder Application

Chris Merritt, general manager for Gema USA, updated the conference delegates on the advantages of improved design powder pump technology. Gema’s patented technology utilizes a dual chamber powder pumping system which is actuated by opening and closing pinch valves. This enables the powder to be transported in a much denser phase (powder to air ratio) which translates to more constant powder output, less wear and higher transfer efficiency. These attributes are beneficial to the powder applicator challenged with a variety of powder types including thin film products, bonded metallics and unbonded metallic/special effect powders. These systems dubbed SIT include internal performance monitoring and process feedback to ensure consistent atomization of the powder as it exits the gun. The reduced air velocity required with this design ensures lower overall maintenance costs as internal parts experience reduced wear.

Fluoropolymer and Super-durable Polyster Blends

Shun Saitoh from AGC Chemicals, Japan, spoke about his interesting findings with FEVE (fluoroethylene vinyl ether) based powder coatings. Coatings based on this copolymer technology offer the ultimate in UV durability, typically enduring 20 or more years in a South Florida environment without exhibiting significant chalking or coating degradation. Saitoh recommends introducing superdurable hydroxyl functional polyester resin to FEVE based formulas for improved economics while still exceeding all common architectural specifications. In addition, he explained how this approach can be advantageous in metallic containing formulations as the polyester component stratifies below the fluoropolymer leaving the metallic portion intertwined between the FEVE and polyester. This phenomenon protects aluminum flake from the hydrolysis commonly seen with exposure to outdoor environments. Saitoh presented EDX (energy dispersive x-ray spectroscopy) cross sectional analysis to verify this stratification. Not only does this formulation system exhibit exceptional UV durability but also excellent corrosion resistance as evidenced with AGC’s 4000 hrs. Salt Fog test results.

A unique formulating approach for environmental dirt repellency was presented as well. Saitoh’s theory is predicated on lowering the Water Contact Angle (low surface energy) of the surface by the incorporation of 3 percent by weight of sodium dodecyl benzene sulfonate. This allows rain to rinse and effectively remove deposited dust and dirt particles. Performance was verified by vertically orienting coated test panels for one year in the industrial area of Chiba (east of Tokyo).

Saitoh also offered formulation tips on achieving matte finishes with FEVE based powder coatings. The incorporation of 8 percent by weight of 4 micron particle size Tospearl (Momentive) produced a 60 gloss of 30 GU. Impact resistance, adhesion and UV durability were not compromised by this matting technique.

Surface Appearance Characterization

Jeralyn Camp, end-user manager from BYK-Gardner, formerly a coatings chemist, displayed her expertise in coating characterization with her discussion on Orange Peel and Distinctness of Image (DOI). She deftly dissected the aspects of surface appearance explaining how waviness and brilliance (DOI) influence one’s perception of appearance. Real world examples were presented of how observation distance impact human eye resolution of a surface. The measurement principle that BYK-Gardner has mastered involves analyzing the reflection of concentrated light beams at a number of incident angles then using mathematical filters to discern long, medium and short wavelength patterns. This technology utilizes a total of five wavelength ranges to define surface topography. Jeralyn concluded with an offer to assist the powder coating industry in further defining and assigning hard numbers to smoothness standards.

Conductive Primer for Non-Traditional Substrates

Our efforts to inspire students to pursue careers in the powder coating industry was evident as PCI’s 2015 Scholarship awardee, Atman Fozdar of Eastern Michigan University delivered a talk on his work on the powder coating of nontraditional substrates. Fozdar, under the tutelage of Dr. Vijay Mannari, has been investigating techniques to make wood and plastic substrates conductive. By making these substrates conductive electrostatic deposition of powder can be accomplished. Fozdar identified 106 to 1012 ohms/sq. surface resistivity as a suitably conductive surface (static dissipative). The technique used to measure this is ASTM D257.

Conductive liquid primers based on various acrylic based binders were prepared using varying concentrations of conductive agents. These primers were applied to MDF (medium density fiberboard), polycarbonate and glass then cured conventionally. UV curable powder was then applied to surfaces coated with these primers. The deposited powders were melted then cured with medium pressure UV lamps. Adhesion was tested per ASTM D4541. Primers containing Deuteron™ conductive agent were found to provide the best deposition and adhesion.

To Conclude

All in all, this was the best attended and supported PC Summit. In addition to the fine technical presentations, Bob Cregg of DSM Resins gave a sparkling keynote exploring Powder Coatings—10 Years from Now and a group of industry experts conducted a lively and informative panel discussion exploring Penetrating New Markets. In addition, we continued to support students expressing an interest in powder coating technology. PCI Scholarships were awarded to Youcheng Du and Diana Marcela Rodriguez, both students from Eastern Michigan University. And the Nordson Builds—PCI Scholarship was awarded to Jakob Waffen from Ohio University.

We look forward to bringing more new technology to market in 2017.

Kevin Biller is technical editor of Powder Coated Tough magazine and president of The Powder Coating Research Group. He can be reached via email at kevinbiller@yahoo.com.