By Melissa Donovan
There is a lot of discussion about wanting graphics to standout, but there is also something to said for blending in. Optically clear media used in window graphic applications is one of those examples. When printed correctly, messaging of any sort pops while the media is virtually invisible.
“Optically clear media is meant to disappear on the window surface, so special handling should be used to prevent scratching or marring of the surface during printing or processing, so those imperfections aren’t left behind after the install,” explains Matt Edwards, product manager – digital print media, General Formulations.
That means choosing the correct printer and ink combination. And while we focus primarily on the print portion of the process here, it goes without saying that part of a successful disappearing act involves a good installation technique. So, be sure to check out our sidebar on page 14 for application tips.
Above: Roland’s TrueVIS VF2-640 printer offers both vivid and natural color reproduction for window graphics.
Before discussing the printing component of the application, let’s first define optically clear media.
There are different media nuances to be aware of. “In my experience clear polyester has the highest degree of clarity but does not conform. Clear cast does a great job conforming but that comes at a high cost. There are times where a near clear for short-term applications will make more sense to clients for graphic exchange versus long-term applications that will require optical clarity,” suggests Dennis Leblanc, territory manager, Drytac.
“Polyester has better optical clarity than vinyl. Polyester is a smooth and ridged product that has high clarity. Vinyl is typically not as smooth face as polyester,” explains Nate Goodman, product manager, Mactac.
Wayne Colbath, national sales manager, Continental Grafix USA, Inc., says it is important to be aware of the various media options out there and prior to choosing one, a print service provider (PSP) needs to make sure the film in question is truly optically clear. But, in his experience, polyethylene terephthalate (PET) films are the clearest.
“Manufacturing equipment and formulations can be different based on each companies’ capability. For instance, one optically clear PET that we use is a blue clear and another can be a yellow clear. Looking at them side by side there is a slight difference, but once you roll each product in a 150 feet or more roll they look very different,” shares Jim Halloran, VP sales and marketing, Lintec of America, Inc.
René Bourgeois, VP sales North America, ASLAN, agrees that PET films by their chemical structure tend to be clearer.
It is important to remember when using pressure-sensitive adhesive media that the clarity of the adhesive and smoothness/type of liner play a role in the overall clarity.
“Film liners are smoother than paper liners. A smooth film liner minimizes any adhesive distortion when the graphic is applied to the window, allowing for excellent adhesive flow out onto the window surfaces,” adds Jodi Sawyer, strategic business unit manager – retail, FLEXcon.
The lack of opaqueness in optically clear media presents difficulties in terms of the media loading into the printer.
Some substrates have a liner, and it may be clear. “Printers that have sheet/roll detection can struggle on clear medias. Lean on manufacturers and partners in the industry; often times, someone has already had to deal with the headache of troubleshooting and might be able to lend you a hand and more importantly, save time,” advises Becky McConnell, segment marketing manager – wide format inkjet, Fujifilm North America Corporation -Graphic Systems Division.
Edwards seconds paying attention to media loading technique, specifically citing that certain printers require a few special steps for loading optically clear media. Companies like General Formulations often provide helpful tutorial videos outlining the process.
“Depending on the printer it may be necessary to bypass some of the automatic media measuring and alignment components as the sensors will not be able to read optically clear media,” shares Tony Simmering, product manager, Mutoh America, Inc.
Optically clear media used for window graphics can be printed to using solvent, latex, or UV ink. Each ink set offers its own range of durability, longevity, flexibility, and color gamut. Durability is of particular importance here, as a window placement generally is in the middle of all the action.
If the optically clear media in question is, for example, a polyester film, Edwards recommends UV ink. “In general UV inks will have better durability to resist scratching.”
“UV ink tends to provide the most durability and is usually the ‘go-to’ for long-term applications, however due to its rigid nature, does not work as well in cold application—outside—and can have cracking issues. It also does not have the color gamut of the other options but that gap is narrowing,” agrees Leblanc.
Ink durability is important because optically clear materials are generally applied using wet application, according to Colbath. “The PSP needs to make sure that the ink won’t come off when the installer applies the film with the application solution and squeegee.”
After UV, the next ink type with a high level of durability is latex. “Latex inks do tend to run in the middle of the road in terms of flexibility and image quality, however do not have the durability of UV. For longer term applications a protective laminate should be considered,” explains Leblanc.
Solvent inks, in Leblanc’s opinion offer the least amount of durability. “Solvent inks tend to provide the best image quality, however offer the least durability of the ink sets. This is not necessarily a drawback but a protective laminate should be considered for longer term applications. The amount of optically clear media for solvent output can be limited as well.”
Simmering argues that eco-solvent ink provides excellent outdoor durability and longevity. “This is especially in situations like outside facing signage in windows where using optically clear media may be popular.”
Eco-solvent ink is more durable in the outdoor scenario because, according to Jim Maffeo, application specialist, Roland DGA Corporation, “eco-solvent inks penetrate the media” versus say UV inks that “sit on the top of media.”
“As it relates to ink set, just like any investment or business change, it’s important to consider the clients you need to satisfy or the prospects you plan to target and put the ink through its paces to ensure that you achieve what you set out to accomplish,” suggests McConnell.
This also means factoring in geographical considerations, says Mark Ellingsworth, applications manager, Durst Image Technology US, LLC. “For example, Southwestern regions in the U.S. are more prone to burning out of magenta and yellow colors faster due to sun intensity.” To combat this, there are options like laminate and UV liquid coating.
“Printing on optically clear films is a combination of good media with good inks, either of the two not being right can lead to issues like media coming off the windows after a few months, and inks fading too soon. So close attention needs to be paid to these aspects especially when it comes to applications for window graphics,” warns Sohil Singh, VP, StratoJet USA.
White ink can be daunting to use when printing on an opaque material, nevermind an optically clear medium. However, it really allows designers and PSPs to unleash on design possibilities.
“Adding white ink underneath colored prints completely overhauls the vibrancy and pop on optically clear media. Traditional color printing relies heavily on the color of the surface the media is being applied to and can sometimes minimize the effect of the design—very much so when applied to clear glass—whereas adding white ink resets the white point of the surface and gives the full effect of the design file,” advises Simmering.
Edwards says white ink not only provides opacity for what would otherwise be translucent inks, but can also be used as a print layer behind the full graphic or select areas to make elements stand out. Another imaginative way to use white ink involves printing gradients and patterns in white to simulate etched glass vinyl.
“The ability to print white ink even allows PSPs to provide a double-sided graphic by using their white and black inks to print a blockout layer,” adds Leblanc.
For PSPs considering using white ink in the design of a graphic, they should be aware of the nuances, like print speed or mode in relation to the type of ink and the sacrifices associated with that. “UV inks offer much faster printing of W+CMYK images. Solvent ink must dry completely before the next pass or there will be problems like chromatic banding or white ink mixing with the CMYK producing a milky looking print. UV inks cure instantly making this process more efficient,” shares Simmering.
“When printing on optically clear material with white or color ink, for most purposes it is very similar to the way we print on everything else. The one big difference is that every imperfection seems to get visibly magnified with light being transmitted through the ink and substrate. So, more often than not, most customers use one of the higher print quality modes to achieve that perfect print quality,” explains Bill Brouhle, solutions architect, Agfa.
Also consider the ink’s opacity. “If you can plan to back graphics with white ink or print two-sided window graphics, the flexibility and opacity of the white ink is critical. A print provider wants to lay down as little ink as possible to achieve opacity, and it’s important to test at different levels to achieve the opacity needed for the job,” says McConnell.
“CMYK inks are basically transparent when printed on clear media, therefore a white ink underlay is necessary to reflect the vibrancy of color inks. The big question is, how opaque does the white ink need to be to reflect the color? I find UV white ink to be the best when it comes to opacity,” notes Maffeo.
Physical characteristics of the ink are important. “The ink needs to be dense enough to hold an adequate white point. Also, because quite a bit of ink is layered—W+CMYK—the white ink in particular must have good adhesion to the film,” notes Colbath.
Leblanc notes that white ink isn’t a necessity. “Some colors offer good opacity in their own right and not all applications require the need for opacity. Optically clear medias can offer quite a lot of different effects without the need for white ink like translucent output or soft imaging while still allowing for view through.”
In addition to white ink, another favorable spot color to have on hand in relation to optically clear film is light black, notes Singh. “It allows for printing true grey tones, complimenting the black saturation, and improving the print quality.”
Other specialty options include varnishes and gloss, which Maffeo says can be incorporated into window graphics to create special dimensional and textured effects.
Automated workflow software and even RIP solutions can assist in removing a lot of the guesswork out of the design process of any graphic. In terms of optically clear media used for window graphics, these systems are especially helpful when working with white layers.
Ellingsworth admits that most RIP systems are capable of creating the white layer(s) required in a particular print job, as well as any required trapping. Sometimes even the software on the printer is capable of “imaging white floods without the need of prepress interaction.”
“RIPs can make it very easy to break apart your design file and gain a greater understanding of how white and color interact,” adds Simmering.
McConnell cautions that each process depends on the printer and the capabilities of the software included or purchased with a printer. “For example, some printers require the files to be built in a certain manner, where others can easily lay out where white ink is needed to be laid down.”
“A lot of software technologies now work in conjunction with the hardware that did not exist a few years ago. These software options of screening, wave forms, gradient masks, etc. all give us look up tables that we can rely on to achieve the results we are searching for in each application. It is just a matter of selecting the options that are made to enhance the output of the smoothness of a gradient with white ink for example when being printed on a clear substrate,” says Brouhle.
While optically clear print media is not new, Leblanc notices a rise in demand. “So it’s important to work with media manufacturers to determine product offerings and compatibilities. Creating a menu of optically clear substrates that are already tested on an individual print platform ensures seamless applications for your clients.”
It’s an excellent message to end with. Printing to optically clear media isn’t challenging, but its nuances are apparent, so understanding the printer, media, and ink and how they work in tandem is all par for the course. If you are interested in learning more, visit digitaloutput.net/webinars for an archived webinar on the topic.
Feb2022, Digital Output