For less demanding applications expanded PVC (EPVC) board is a good alternative for short-term outdoor signage, indoor retail signage, P.O.P displays, tradeshow and museum exhibits and for mounting photographs and digital prints. Some of the popular brands that are stocked by sign supply distributors are Sintra®, Celtec, Komatex and Veracel.
Available in different densities and finishes and in thickness ranging from 1mm to 30mm, rigid expanded PVC sheeting also comes in a variety of colors. That color selection is great, but the colors aren’t that durable when used outdoors. Prolonged exposed to sunlight results in fading. And what do you do if you want a custom color?
Akzo Nobel Grip Flex. One part, thermoplastic acrylic. Provides good outdoor durability. No primer typically is required, but should be top coated for optimal performance.
Matthews Acrylic Polyurethanes® (MAP). Two part polyurethane for spray application. Provides excellent outdoor durability. Spraying the substrate with Tie Bond 74 777SP adhesion promoter can ensure good adhesion to slick plastics, such as expanded PVC.
Spraylat Series 20. One part, high gloss acrylic lacquer. Fast drying, weather resistant paint with good adhesion to expanded PVC. Finish is not as hard as a two-part polyurethane.
Nazdar Solvent Screen Print Inks: 9700 Series; GV Series; System 2.
There are several reasons that these paint adhesion problems occur. Expanded PVC can have a release agent or other additives that could inhibit adhesion. The surface may be contaminated with oils or dirt. Or the surface energy of the PVC sheet may be lower than the surface energy of the paint.
Substrate Preparation. Regardless of how you intend to decorate PVC sheet, the surface must be clean. Even if you have just received new material from your sign supply or plastics distributor, a good rule of thumb to follow is to assume that all surfaces are contaminated and must be prepped. Here are some of the steps that you should take before painting:
PVC foam has a natural static charge that attracts dust, dirt, hair and plastic chips like a magnet. Briskly wiping down the sheet with a dry rag only creates more static. Instead, wash the surface with water and a mild detergent or dishwashing liquid, such as Joy.
An integral component of expanded PVC is a release agent, which can hamper paint adhesion. To remove any waxy additives on the surface of the sheet or body oils from your hands, at the very least you should wipe the surface with 70% isopropyl alcohol (IPA). You can also quick wipe the surface with a rag dampened with toluene or acetone. Don’t overdo it with these chemicals. These solvents will not only dissolve the contaminants, but will also soften up the surface of the sheet slightly allowing for improved paint adhesion. NOTE: Inhalation of toluene and other solvents can be hazardous to your health. Follow manufacturer recommendations; work in a ventilated area and wear safety glasses, air respirators and protective latex or nitrile gloves, when required. If you clean with a solvent, perform a second cleaning with IPA to remove any residue.
If the surface of the sheet is scratched or dented, you can eliminate some of these defects with a heat gun. Failure to treat the affected area usually results in the scratches showing through the paint. Carefully warm the scratched or dented area, moving the heat gun so you do not overheat and distort the substrate. Magically, the scratches will disappear. Be careful not to overheat the sheet or you will distort it. The damage that you cause will be irreparable.
One factor that makes PVC difficult to paint successfully is its dyne level, which is typically about 41. To improve adhesion painters have tried to overcome the low surface energy by lightly sanding the surface with either 220-grit or 320-grit sandpaper or by scuffing up the surface with a grey Scothchbrite® pad. Some contend that the sanding actually increase the dyne level. If you choose to scuff up the surface, wipe the surface down with 70% IPA to remove any dust created and to kill any static build up.
One brand of paint that is popular among sign makers is Krylon Fusion Paint. This paint is designed specifically for plastics. Not only will it stick to PVC, it is also available in a variety of colors. Best of all, it comes in an aerosol can.
When painting on an expanded PVC sheet, such as Sintra or Komacel, you should test the paint system on a scrap piece of material for good adhesion and compatibility. Many paints, such as latex and enamels, do not adhere well to expanded PVC. In some cases, you can improve the adhesion to the substrate by first priming it. Some of the paint systems that stick well to expanded PVC are polyurethanes and lacquers. Vinyl screen print inks, such as the Nazdar inks listed above, also adhere well.
The second test commonly used to check for good paint adhesion is the Cross Hatch Test. This is a test that screen printers use to check for ink adhesion. In performing this test, lightly score the painted area with an X-ACTO® razor knife, making eleven parallel cuts about 1/16” apart. The make another eleven cuts in the paint perpendicular to the first eleven cuts, spaced the same amount apart as the first set of cuts. The cuts in the paint will produce one hundred squares. After scoring the paint with the razor blade, apply an aggressive tape to the cut area. Screen printers typically use 3M Brand #610 Scotch Tape in performing this test. In removing the tape, pull it quickly at a 180° angle against itself. If the paint is well-adhered to the substrate, none of the tiny squares paint will come off with the tape. Some paints can embrittle or warp expanded PVC sheet. As part of your testing, be sure to evaluate any paint before using it in production.
Color Selection. As important as selecting a paint system that is compatible with the expanded PVC, color selection is also critical for exterior applications. Manufacturers will caution against painting the PVC with dark colors. The reason is that dark colors absorb heat when exposed to direct sunlight. As the PVC heats up, it expands greatly. Firmly affixed to the side of a building the expanding sign board can buckle. What’s worse is that the hot plastic can permanently warp.
Edge Treatment. During manufacturing of the expanded PVC, tiny closed cells are created. Using standard woodworking tools, expanded PVC can be cut using a utility knife or a table, band or panel saw. In fabrication, the cells are cut producing a rough edge. To smooth the rough spots, you should fill the edges with plastic wood filler or 3M’s Bondo® and then sand the area smooth.
Priming. To improve adhesion of paint to the PVC board, some, but not all, paints require a primer or adhesion promoter. Some painters have used Bulldog®, which is available in an aerosol can. Bulldog® is an adhesion promoter, which is formulated to bind to a variety of other materials such as aluminum, fiberglass and other rigid plastics. The job of the adhesion promoter is to anchor or bond the finish coat the substrate.
You can also use a primer, such as Rust-Oleum® Specialty Plastic Primer Spray, which prepares the substrate for a wide range of paints. Some painters also use satin finish Fusion as their primer. Or you can spray the sheet with Butch Anton’s Frog Juice as an adhesion promoter.
Conclusion. Before going into production, read the manufacturer’s literature thoroughly. Their user guides are quite thorough and will provide you with paint recommendations, as well as fabricating tips covering cleaning and surface preparation, blade and bit types, cutting speeds and edge-finishing suggestions. Then, after reading the recommendations, test the paint prior to production. As the primary manufacturer, you are ultimately responsible for selecting the materials for the job. Once you find a paint system that works for you, stick with it.