What began in the early 1990s as a highly specialized niche – pressure-sensitive PVC which is calendered, perforated, printed and attached to the windows of transit buses – has evolved into a huge industry that every printer should consider. Popular applications of what’s now called “window perf” include building wraps, corporate identity campaigns, retail signage and vehicle graphics. If you plan to enter this lucrative market, be forewarned that print quality and proper application will make you or break you.
Keep colours vibrant
Graphics printed on window perf tend to look washed out (compared to solid vinyl printing) because up to 50% of the film’s surface has been punched away. Several solutions are available to obtain more vibrant graphics. The first is to increase the image contrast by 10% to 20% during the design stage to compensate for the reduced image reflectivity caused by the “missing” film. Another option is to select a product featuring more print surface, such as a 65/35 perf pattern (65% print surface, 35% holes) as well as smaller holes. Third, you can even run a second pass to lay down more ink.
Bright colours are best for perforated vinyl films. Dark colours are not recommended for backgrounds or other large areas because, depending on the lighting conditions, they increase “see-through.” They also require more ink coverage which could magnify banding or other imperfections. Finally, they absorb more light and may increase heat build-up on the glass.
Intricate designs, fine detail or small text are not suitable for films with a 50/50 perforation pattern simply because half of the film has been perforated. Films with a 65/35 or 70/30 perf pattern are better suited for graphics-intensive designs. When including text, use a point size of 30 or larger for 65/35 or 70/30 films, and 50 or larger for those with a 60/40 or 50/50 perf pattern.
The role of lighting
Lighting plays a key role in the visual impact of perforated window graphics. Lighting should always be brighter on the graphics side than on the black (or see-through) side, especially at night. In some cases, such as store windows in a shopping mall, auxiliary flood lighting may be needed to illuminate the graphics. Some manufacturers now offer a perforated retro-reflective window film that allows visibility of the graphic during the day as well as under retro-reflected light at night.
Wide array of window films available
In 1995, the first window perf to enter the market was an 8 mil, premium grade, white/black composite PVC with a clear pressure-sensitive adhesive and a release liner consisting of clear PET film laminated to perforated paper. The product featured a 50/50 perf pattern and 1.5 mm holes. Today, there is a host of perforated vinyl films offered for every conceivable application. They include retro-reflective window film on emergency vehicles, 50/50 films with larger holes for building wraps, clear pressure-sensitive or non-adhesive window perf for interior mounted POP posters, and non-printable window perf for security, privacy and heat/light control. Printer/ink compatibility runs the gamut as well, from wide-format digital imaging using solvent, eco-solvent, mild solvent, UV-curable and latex inks, to aqueous inkjet, screen printing, thermal transfer, airbrushing and (now largely obsolete) electrostatic transfer.
A look at liners
The layflat release liner on perforated vinyl film is designed to catch overspray and help facilitate smooth, even transport of the film through the printer. Most release liners perform well with the wide array of printers on the market today. An exception is unperforated solid siliconized paper liners, which are not recommended for use with UV-curable printers because the UV-cured inks tend to clog (aka bridge) the film’s holes. For these printers there are several options available. To check available options, one extremely helpful site you should visit is www.clearfocus.com.
The lowdown on lamination
The use of an optically clear overlaminate provides UV protection, moisture resistance, increased image life and an attractive finish. An overlaminate also prevents the holes in perforated window film from filling with water when it rains or when the graphics are washed. Many of the same steps apply when laminating window perf as they do with solid vinyl. Allow the inks sufficient time to dry and outgas before applying an overlaminate. Use proper, even tension on the laminator to prevent wrinkles and tunneling. After lamination, wait at least 12 hours for the overlaminate’s adhesive to bond to the window perf before installing the graphics.
Confirm that the overlaminate is fully compatible with the window perf film and will not obscure visibility. If in doubt, conduct a test prior to use during production. Also, ensure that the product is rated to last the desired life of the job. Be sure to match the overlaminate to the installation surface. For curved surfaces, this means a conformable, cast PVC overlaminate. For flat glass, a less expensive polyester overlaminate may do the job. In some cases a liquid laminate may be a better alternative, especially on surfaces with extreme compound curves. To keep moisture and dirt out and to help prevent the window film edges from lifting (especially with vehicle window graphics), seal the edges with a liquid edge sealer or encapsulate them using a half inch strip of clear, pressure-sensitive overlaminating film.
Proper installation – the finishing touch
A common error made by inexperienced installers is prepping the glass with a solvent-based window cleaner such as Windex. The solvent in the glass cleaner breaks down the adhesive on the window film, causing it to lift. For best results use mild soap and water to clean the glass and dry it with lint-free towels. Use 85% isopropyl alcohol, if desired, to remove any residue – but allow it to completely evaporate before installing the film. Always follow the manufacturer’s instructions regarding installation temperature range and other guidelines.
Adding perforated window graphics to your shop’s product mix could open the door to entirely new markets and added revenue. For most printers, the learning curve with this product isn’t all that steep, and the potential rewards are high.