Powder Coating Clinic: Powder in Layers

 

Q. We are in the process of designing a new powder system for aluminum extrusions and building panels. Our current system uses a six-stage dip pretreatment process and a three-layer liquid paint process (prime, color coat, clear coat) that meets AAMA 2605 standards (American Architectural Manufacturers Association). What layers of coating should we use and can we can meet the AAMA 2605 standards with powder? 

A. The layers you will want to consider may vary depending on what you are doing and what powder you use for the color. If you use a chrome pretreatment, there may be some jobs that can be done with one coat of powder. This would not meet AAMA 2605 for performance but it would meet AAMA 2603 and may meet AAMA 2604 standards. Addition of primer will enhance performance significantly. It will increase the film thickness and improve the resistance to moisture penetration. The primer coat is gelled to a partial cure and then the color coat is added. The two layers can then be co-cured for an outstanding finish with excellent mechanical properties, good edge coverage and very good corrosion resistance. The color and gloss retention can meet AAMA 2604 if the proper color coat is used. 

In some cases, there are so-called super-durable resins that can approach the performance for AAMA 2605. Most coating professionals agree that a fluoro-polymer powder is required to meet that level of color and gloss retention and compete with similar liquid systems. 

A clear coat may be required if the color coat is lower in UV resistance or if it contains metallic content. The metallic powder often has lower resistance to mar or abrasion and to sunlight. Plan your system for all three layers of flexibility for different types of jobs and different performance standards. Also, be sure to plan a pretreatment system for outdoor-durable performance.

 

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Originally published in the December 2016 issue.