Our last Sign College newsletter was all about how to choose the right vinyl based on its adhesive properties. Actually, it wasn’t all about choosing the right adhesive because we couldn’t put it all in one post. There’s more to tell. Having discussed the differences between acrylic and solvent adhesives, and the applications for permanent, removable, and repositionable adhesive backed films, it’s time for part two.
Let’s look at some of the adhesive options that are relevant to achieving “trouble free stickage” with vinyl window graphics and outdoor printed signs on discolored surfaces and low energy plastics.
Clear vs. Pigmented Vinyl Adhesives
If you’ve been reading the fine print on your vinyl spec charts, you may have noticed that some films have clear adhesive and some pigmented. Generally speaking, you’ll find the clear glue on plotter films and the pigmented variety on vinyl designed for inkjet printing. Why the difference? When should you prefer one over the other? The reason plotter films are generally engineered with transparent adhesive compounds is because they are often applied on glass. Generally, vinyl letters are installed on outdoor surfaces, be they sign blanks or store windows. But occasionally, someone decides that’s too risky. An ornate graphic in gold chrome or 22 kt SignGold for instance, may be too tempting a target for vandals. Such graphics are often installed inside to protect them from idle hands. But then, how does the vinyl project the correct message to the outside world? Simply by being cut in a mirror image and adhered to the inner plane of the window. Viewers from outside are actually looking at the back—or bottom—of the vinyl, but since the adhesive is clear, all they see is your beautiful craftsmanship. (FIG.1)
So if you’re looking for a vinyl that needs to be installed indoors but viewed outdoors, always select one with a clear adhesive. An indoor mirrored installation can also help durability when using a vinyl with an acrylic adhesive. You may recall from our previous newsletter that acrylic adhesives aren’t quite as weatherproof as solvents. If you want to use a less expensive vinyl for a window graphic, you can give it more outdoor life by flipping it and applying it to the inner window pane which protects it from the moisture and environmental pollutants outdoors.
Where clear adhesives allow you to view the vinyl through the substrate, pigmented adhesives do the opposite. These formulas are designed for application over a substrate that really needs to be covered up. Think urban bus shelter. (FIG 2) The pigmented adhesive makes the vinyl more opaque so that it hides any imperfections on the substrate such as graffiti or residue from older signage. ORAJET 3651 is a good example. It has a grey, pigmented adhesive that makes it a good choice for use on a dark or discolored substrates. You may have a lower white point with such a vinyl, and that can impact image quality. But if you have to apply a print on discolored surface, the lower white point will not be as big a problem as the shadows and distractions visible through the vinyl. A variant of this is the blue backing found on some ink jet printable poster papers such as Sihl 3687 TriSolv Photo Paper
High Tack Adhesives For Low Energy Surfaces
We’ve touched on this in a previous blog post, but since we’re talking about adhesives, we should mention that some surfaces are not compatible with anything we’ve covered so far. Porous surfaces and certain plastics are very difficult, even for high quality solvent adhesives. There is a long technical explanation for this, but the basic reason is that the adhesive is unable to ‘wet out” or cure completely. Adhesive compounds are designed to be low tack initially to aid placement and positioning. Then they wet out or cure over the next few days and form a permanent bond. If they’re applied to porous surfaces or low energy plastics, the second stage never occurs and they don’t form a good seal. The result is immediate or ultimate failure of the applied graphic. Plastics that fall into this category include HDPE (high density polyethylene) and polypropylene. Some low energy plastics are unsuitable because of oil residue. These are petroleum products in which case the refining process leaves enough residue to make them unsuitable for vinyl.
Other low energy plastics cause problems because of static charges that interfere with the adhesive. These are commonly used on some really inviting vinyl substrates: motocross body parts. (FIG. 3) The fairings, gas tank covers and various trim pieces used on dirt bikes and ATVs are made from polypropylene. Conventional vinyls will not stick to these surfaces because of the inherent static charge, but there are new adhesives on the market that will. These two stage acrylic adhesives wet out and adhere well on dirt bikes, ATVs, asphalt, even garbage cans. We’re not sure how many of you want to put vinyl graphics on garbage cans, but it’s good to know that you can, if you use the right vinyl. One such vinyl is PrismJET 203HT, a high-tack version of our popular glossy printable vinyl. This is your best option for spring motocross graphics. If you prefer a two mil cast option, ask for ORAJET 3951HT. You’ll have to apply a stout overlaminate film to provide sufficient abrasion resistance. They don’t call the dirt bikes for nothing. For more details on this nifty product and motocross graphics, please visit our blog post entitled “Vinyl Sign Graphics and Low Energy Plastics”. That about covers the whys and wherefores of choosing the right adhesive-backed films for your plotter and printer vinyl graphics. Hopefully you’re now more capable of producing trouble free stickage.
