Challenges in Developing a Premask for Air-Egress Liners

Vinyl films with air-egress release liners have almost eliminated bubbles and wrinkles from applied graphics. Here’s how the product works...these release liners are comprised of multiple layers of paper, a polyethylene coating and a silicone layer. The polyethylene coating of the release liner is embossed with a textured pattern. The textured structure of the release liner imparts tiny air channels in the adhesive of the vinyl film. Think of these as escape routes for air. As the installer squeegees the facestock, the air between the film and the substrate is directed through the air channels to the edge of the graphic.

Air-egress films are great for application of vehicle wraps and other large format graphics. Typically, these very large graphics are laminated. Many graphics for wrap applications are not masked. But some are. If the graphics are comprised of rectangular panels, you can use a standard heavyweight paper premask, such as RTape Conform® 4750RLA, a heavyweight paper tape with a medium tack adhesive. Plotter cut and die cut graphics, on the other hand, will always require a pre-spacing tape to hold all of the individual pieces in place as you install the reading.

The preferred pre-spacing tape will feature an additive in the adhesive which allows the tape to adhere to the exposed areas of the release liner. RTape Conform® with RLA® Release Liner Adhesion® is acknowledged as the leading brand in the graphics marketplace. The standard RTape Conform® tapes will adhere to most release liners.

Air-egress release liners with their highly textured surface structure can be problematic. Not much will stick to these liners other than the vinyl film. The most salient issue in adhering to any texture is that the tape only sticks to the peaks of the texture and never makes contact with the valleys. This provides the tape with less surface area to adhere to.

Liner adhesion is important to the graphics provider and the installer. If the graphics are rolled and shipped and the premask tunnels on the liner, the tunnel generally travels over the vinyl film. Then, when installer receives his graphics and tries to re-adhere the premask, the paper tape invariably wrinkles. If you get a wrinkle in your premask, I can almost guarantee that you will get a wrinkle in the applied graphics.

Another hurdle in developing a tape for air-egress release liners is that the chemistry of their silicone coatings is quite different than the chemistry of a standard liner. The release values of air-egress liners are also much lower than standard liners. Release value is a measurement of how much force is required to remove a facestock from the liner.

There is good reason that air-egress liners have lower release values. In manufacturing vinyls for the sign, screen and digital markets, the release liner, not the vinyl film, is coated with liquid adhesive. After the adhesive is cured, it is laminated to the vinyl facestock. This process is called transfer coating, because the adhesive transfer from the liner to the film in the lamination process. (By comparison, coating adhesive directly onto a facestock, as is done in manufacturing application tapes and premasks, is called direct coating).

In coating the air-egress release liner, the liquid adhesive readily flows into the nooks and crannies of the textured surface. The liquid adhesive coating actually has more surface area to grab onto. If the air-egress liner used the same silicone chemistry with a higher release value that a standard vinyl uses, removing the liner from the film would be very difficult. From an installer’s perspective, a film with a low release value is highly desirable, because when you are on a scaffold or a ladder, you do not want to struggle to separate the film from the liner.

Low release values, however, present challenges for the premask manufacturer. At Nekoosa our best solution for air egress liners is a special RTape Conform® tape called 4761RLA adheres to many of the popular air egress liners used by vinyl manufacturers. Keep in mind though, that each liner manufacturer utilizes different silicone chemistries. That means that 4761RLA will adhere differently to each liner. As a word of caution, do not use 4761RLA for standard liners. The adhesion to the liner is far too great. For a sample of 4761RLA, contact your local Nekoosa distributor or order a sample directly on our website.

Conclusion

Don't Forget the Basics of Vinyl Application

Using proper application techniques, you can easily apply air egress vinyl films to surfaces with complex curves with no troubles and no bubbles.

When working with air-egress films, even a novice installer can look like a pro. Is it idiot proof? Of course not! Someone will always manage to mess things up. I actually saw a sales manager trap a humongous air bubble in his company’s film, while performing a vehicle wrap demonstration. I have no idea how he did it. This feat was no easy task, because the film used was one of the best on the market and arguably the easiest one to work with. My point is that even when you use a great product, you must employ proper application procedures, or the product will not work as intended. In working with these films, here are some recommendations:

• Only apply air-egress films dry. No wet application. The tiny air channels will trap the application fluid under the film, compromising the film’s adhesion.
• Before beginning your application, run you thumb across the edge of the squeegee to check for any nicks and rough spots. Sharpen the edge of the squeegee, rubbing the edge of one squeegee against the bead of another. Altering the angle of the squeegee in this sharpening process will ensure a good smooth edge.
• Use a hard squeegee, such as the 3M gold nylon squeegee and good pressure when applying the film onto the application substrate. By using a low squeegee angle in relation to the application surface you are less likely to entrap air. Slightly angle the squeegee away from the vinyl already applied. Always overlap your strokes.
• Remove the premask pulling it at a 180⁰ angle against itself. Pulling the premasking tape perpendicularly from the applied graphic will pull the film from the substrate.
• After removing the premask, re-squeegee the entire graphic and post heat the film.
• If you trap an air bubble under the film, puncture the vinyl with a pin or an air release tool and press down on the bubble with your thumb or a squeegee, forcing entrapped air out to escape through the hole in the film. Never use a knife to puncture bubbles. Knives cause a slash in the film, which can open up as the film shrinks. By comparison, when you puncture the film with a pinprick, the hole in the film will close around itself.
• Small bubbles under the film are nothing to worry about. After a few hot days, the air will breathe through the film and the bubbles will magically disappear.
• Inspect your work carefully, before leaving the job site. And don’t forget to pick up your area when you're finished!