Adhesion to Powder Coated Paints

Why Pressure Sensitive Materials Fail to Adhere to Powder Coated Surfaces?

Adhesion failures of pressure sensitive materials, such as labels, decorative films, foam tapes and graphic panels, to powder coated substrates are quite common.  Just as there are several reasons for these failures, there are several steps that the fabricator can take to avoid these problems. Most importantly, before manufacturing a pressure sensitive product, such as a label, you must have a thorough understanding of physical properties of the substrate. Equally important is selecting the right adhesive product for the application.

Thin powder coat paints generally have a highly textured “orange peel” finish. On industrial products these textures are cost-effective, durable and aesthetically pleasing. Adhesion to these finishes, however, can be problematic, and often require pressure sensitive facestocks with a high coat weight, low surface energy  adhesive. 

Powder Coating Basics

I like to describe powder coating as dried paint in a powdered state. Unlike liquid paint, it has no solvent and consequently none of those nasty VOCs.

If you were wondering how the powder was applied, the process is really quite simple. The powder, which consists of very fine plastic particles, is sprayed on the substrate using a spray gun similar to conventional spray guns used for paint.

In conventional applications, the powder sticks electrostatically. That’s the trick. A metal part, for example, is negatively charged with electrical current. As the powder is sprayed, it is positively charged. The tiny plastic particles are attracted to the oppositely charged part.  

When these plastic powders are baked at high temperatures (in the range of 400⁰F or 204⁰C), they flow out and fuse together form a tough, solid, chemically resistant coating. To top it off some of these coatings are absolutely beautiful. It’s no wonder that powder coating is growing in popularity.

Low Energy Surfaces

What’s important to remember is that powder coating is plastic. Some of these coating materials are thermoplastic and some are thermoset. Typically, these coatings are low energy surfaces.

Because surface energy affects how an adhesive wets out or spreads over the substrate, it is critical to achieving a good adhesion. If the adhesive wets out well, it will flow into the microscopic pores of the surface and create a strong mechanical bond.   For a pressure sensitive adhesive to wet out and adhere adequately, the surface energy of the adhesive should be lower than the surface energy of the substrate.

Standard adhesives used on pressure sensitive films typically do not wet out well on low surface energy materials, such as polyethylene and polypropylene.  The metaphor generally used to describe the disparity of surface energies is a beaded up droplet of rainwater on a newly waxed hood of a car. By comparison, on a high energy surface the adhesive will readily wet out. The point is that low energy surfaces, such as powder coated paints, can be very difficult to adhere to and require special adhesives.

Additives

Other factors which can inhibit adhesion of a pressure sensitive material to a powder coated surface are additives in the powder. Waxes and slip agents, in the powder coated paints can inhibit adhesion, resulting in problems, such as edge lift and tunneling.

Surface Texture

The texture of the substrate can also affect adhesion. Some powder coated jobs have a very smooth and high gloss finish. Other surfaces have a rough “orange peel” finish. Both high gloss finishes and rough surfaces can be problematic.

Highly textured surfaces are especially troublesome. On rough surfaces, a thin coating of adhesive, in the range of 1 to 2 mils, may not be adequate. Here’s why. Thinner coats of adhesive may not flow into the crevices or valleys of the surface. Instead, the adhesive merely makes contact with peaks of surface. Insufficient surface contact generally results in adhesion failure.

High gloss coatings are also prone to problems. These smooth, glossy surfaces are extremely slick, and have less tooth for a good bond.  

Conclusion

As a fabricator, prior to manufacturing, thoroughly investigate the type of surface that you are adhering to.  Then select the right product for the application. Powder coat paints typically have a low surface energy and require a low surface energy adhesive. Rough textures will require adhesives with heavier coat weights. Products with 1 and 2 mils of adhesive are generally not adequate. For rough surfaces, an adhesive coat weight of 5 mils is typically required. 

Finally, whenever you are trying something new always "Test, Don't Guess" before going into production. For example, before attempting to laminate a 5 mil LSE adhesive to a pressure sensitive label stock, test the two adhesives for chemical compatibility. 

Recommended Article
Pressure Sensitives 101 Made Easier


CLICK HERE FOR HINGST SIGN POST ARTICLES IN PDF FORMAT

Vinyl Application Videos

Squeegee Technique. Nothing is more basic in vinyl application than the squeegee. But some squeegees work better than others. And there are right ways and wrong ways to use this simple tool. This video clip reviews squeegee selection, squeegee care and squeegee technique. Click to Link

Wet Applications. Dry applications are typically recommended for most vinyl applications. For those exceptions to the rule, this instructional video explains the right way to perform a wet application. Click to Link

Application of Window Graphics. Installing vinyl graphics on glass can be challenging, because the adhesive aggressively grabs onto this high energy surface. Repositioning graphics on window is generally difficult, if not impossible. This instructional video explains how to dry apply window graphics right the first time. It also describes the necessary steps required for surface preparation. Click to Link

Transferring Frosted Window Graphics Films.  Because frosted window films are highly textured, transferring cut vinyl graphics can be problematic. This video provides direction in selection of the right application tape and how to apply these films quickly, easily and without problems. Click to Link

3-Step Surface Prep. This instructional video describes how to properly clean the surface of a vehicle before applying pressure sensitive vinyl graphics to a trailer or doing a full wrap of a car or van. This three step surface prep involves detergent washing, solvent cleaning and a final wipe down with IPA. Click to Link

Vinyl Application Over Rivets. Applying vinyl graphics on vehicle surfaces with rivets is challenging for most sign makers. Vinyl failures to these surfaces are all too common. This video demonstrates some tips and procedures, used by professional decal installers, which will make these demanding applications easier and more trouble-free.  Click to Link

Vinyl Application to Corrugations. Learn how to apply vinyl graphics to corrugations in a relaxed state. Forcing films into the valleys of corrugations puts too much mechanical stress on the film. Sooner or later, the vinyl will lift or tent in valleys. Click to Link

Applying Air Egress Vinyls. Vinyl films with air egress release liners have almost eliminated bubbles and wrinkles from applied graphics. Air egress release liners with their highly textured surface structure are problematic. Not much will stick to these liners other than the vinyl film. At RTape our best premask solution for air egress liners is a special Conform® tape called 4761RLA. Click to Link

About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.

Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer.  Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.

Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for  publications, such as  Signs Canada, SignCraft,  Signs of the Times, Screen Printing, Sign and Digital Graphics and  Sign Builder Illustrated. He also posted more than 325 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.  Vinyl Sign Techniques is available at sign supply distributors and at Amazon. 

© 2016 Jim Hingst