Avoiding Powder Failure

Steve Houston, TCI Powder Coatings

Powder coatings have been around and used in the industrial market space since the 1960s. The first patents were in Germany in 1966 and the United States in 1969. The idea of powder coatings was to create a coating that eliminated the use of solvents and/or hazardous chemicals that require disposal, offering the applicator a safer work environment. Powder coating grew at an enormous rate in the 1970s and 1980s with moderate growth even in the 1990s but has seen a maturity over the last decade, driven mainly by optimizing the utilization of powder coatings as well as economic slowdown in the manufacturing sectors that typically use powder coating technology.

Another reason powder has not seen the growth in some viable segments is due to its inability to gain traction and/or market pull. The Architectural market space is a good example of this. This is due primarily to the early adoption of powder technology when powder had not been proven, creating some failures that caused the market to question its viability.

Powder is not only a very environmentally friendly coating with an easy application but it can offer some exceptional aesthetics as well as very high performance if done properly. Powder can be used in almost any application where liquid is used today, as long as the part can be cured.

To highlight the optimal performance that powder coatings can deliver, let’s work backward and talk about what can cause powder coatings to fail in any given application. Here are five reasons that powder coatings may fail and what to do about them.

1. Undercured Powder Coating

2. Improper Preparation of Substrate

3. Selecting the Wrong Powder for the Application

4. Application of Powder Coatings

5. Substrate or Substrate Composition

Undercured Powder Coating

The cure of powder coating is critical and so often overlooked when it comes to getting the optimal performance a powder coating has to offer. In these times of microwaving, fast food, overnight services, and “Google me this,” speed is the name of the game. When it comes to powder coating, though, the time it takes to completely cure at a given temperature “is what it is.” Undercured powder may still look smooth and glossy, but will not achieve optimal performance. The complete crosslinking of the powder, through proper curing time, will provide the highest physical properties achievable. To add insult to injury, the method used for evaluating cure in the field is typically misunderstood. While using DCS is the best and most effective way, the cost is prohibitive and not used as a field evaluation method. So, chemical resistance is typically used in its place. Fifty double rubs of a solvent is in most cases the field method used, but how much lift is acceptable; how much softening is ok; what if the product contains a high degree of chemical resistance or is very little chemical resistant? The fact is this method can work well, but only if compared to a known cured panel of the same product.

Improper Preparation of Substrate

Improper Preparation of Substrate Part or substrate preparation is extremely important and again overlooked in many cases. The reason for this may be because it typically is not detectable immediately. It takes time to see the poor corrosion resistance or unacceptable creep in a cut or scribed area. Of course, after the product is coated, you can’t see the pretreatment. Chemical pretreatment is a very good tool for preparing the part for powder. Mechanical pretreatment is a very good tool for preparing the part for powder. But once the process is proven and acceptable, how is it maintained and policed? Even when nothing changes about the substrate, this area must be maintained with periodic evaluations. But in many cases the substrate does change—or at least the soils do. When checking pretreatment, accelerated corrosion tests are typically the order of the day, which is fine and good. You take a panel, typically 3 x 5 inches, scribe the middle of the panel with an X or a single vertical cut to the substrate and put it in a chamber that contains a salt solution. The corrosion starts at the cut and you evaluate the “creep” from the scribe. The problem is the corrosion typically does not start in the middle of a flat part or panel. It typically starts on the edge or in a deep recess where the coverage of the powder coating is thinner and the pretreatment has a more difficult time penetrating. When testing a part for proper pre- treatment, keep the part configuration/shape as a part of the evaluation method.

Selecting the Wrong Powder for the Application

Selecting an improper powder coating is a very common mistake. To understand the atmospheric conditions the powder will be subjected to is critical. Then, to understand the expectation of coating life in any given environment is paramount. Powder will not last forever—no coating will—but if selected correctly with coating life understood, it can be a very good tool for aesthetics and protection of any given asset. This is much more an issue with outdoor products. Take this exchange, for instance: Applicator: I make fencing and I have been make fencing for 20 years but never had an issue until now. Powder Supplier: What is the problem? Applicator: The powder started peeling off the part and corrosion started in less than a year. Powder Supplier: Where is this fence installed? Applicator: A brand new customer on the coast of Florida. Coastal environments are the most difficult to deal with because it is the most harsh environment for any coating. Areas of Florida have the highest UV index in the United States and a salty wet environment 24 hours a day, seven days a week. Parts will corrode faster there than in Tulsa, Phoenix, Chicago or Salt Lake City. Planning for the worst atmospheric condition is important, and in some cases a separate coating for these environments is appropriate. But, in every case, understanding the end use as well as the conditions it will be subjected to is critical to the powder coating selection process and performance success.

Application of Powder Coating

How the powder is applied can and will cause failures as well. Powders applied too thickly or too thinly each can negatively impact a powder’s optimal performance. Using thicker films than recommended cause poor appearance and will reduce flexibility and impact resistance. Using too thin a film will also cause appearance issues as well as corrosion problems, not giving the substrate the proper protection. Managing film build and understanding what it takes to give your part the proper performance in any given atmospheric condition is the best and most effective way to get the highest powder coating performance. Maintaining electrostatics is not just for good attraction but can also be an important factor in consistent film control and Faraday penetration. Good ground will affect the ability to apply the powder coating. Fluidization, clean compressed air and virgin-to-reclaim ratios are just a few areas that are typically not managed well and can cause a powder to offer less than optimal performance.

Substrate or Substrate Composition

The substrate or composition of the substrate can change and cause an ill effect on the adhesion and or corrosionresistant properties of the powder coatings. Utilizing a different source for the metal being used can bring in a variable in the coating process that can show a significant difference in performance. Remember, you are creating a layering system where each layer can and will affect the final outcome. Substrate, pretreatment and then powder—and in some cases multiple layers of powder. Do not underestimate the effect of the composition of the substrate.

The Bottom Line

If you want a coating to last decades on gas transmission lines being buried and requiring cathodic protection, powder will do it. If you want a coating to put on a high rise building that can exceed AAMA 2605 10-year exterior requirement, powder will do it. If you need a coating to be used on wire for corrosion protection, powder will do it. Looking for an FDA, NSF or antimicrobial coating? Yep, powder will do it. Need a coating for MDF, plastic or vinyl? Again, powder can do it. Do not rule out powder for anything. If done correctly, powder can be an extremely high performance coating.

Steve Houston is the vice president of sales and marketing and business expansion at TCI Powder and can be reached at 713-851- 7735 or via email at shouston@tcipowder.com.