Marrying Ink and Vinyl

So, you’ve taken the step — leap may be the better word — and invested in a new wide- or grand-format, digital inkjet printer. Great – now, what are you going to print on? Quite likely, one of the first things that goes on your printer will be a roll of digital, pressure-sensitive, adhesive vinyl (DPSA). Whether you opted for eco-solvent, mild-solvent, full-solvent or UV-curable inks, each type will interact with your media differently and produce different results.

You’ll need to learn which DPSA will provide the most consistent return. This column explains how different ink technologies interact with different vinyl types, and the anticipated outcomes. Printer manufacturers’ data also explains inks’ effects on media, and how that relates to your specific application.

Think ink

Before we talk about ink’s effects on DPSA, let’s briefly discuss how each ink technology "sticks" to the media’s surface. All media discussed here are uncoated, and the ink must find a way to bind to the film. For this explanation, we’ll group eco-solvents, mild solvents and true solvents together, and discuss how these inks bind differently than UV-curable consumables. Later, I’ll discuss how the solvent-ink types differ.

"Solvent" inks are called this for a very good reason – they contain solvents. The solvent and pigment are pre-mixed for two very important reasons — to prevent clogging those very expensive printheads, and to carry the pigment to the vinyl’s surface.

Once the ink hits the surface, the solvent "bites" into the media and carries the pigment with it (if you’re a fisherman, think of tag-and-release). Once the solvent has done its job, it evaporates, or "outgases," with the aid of heat and ventilation, and the pigment is left buried in the media.

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UV-curable inks implement a completely different approach. Instead of a solvent carrier, these ink pigments mix with a polymer-based chemical carrier that, when exposed to UV light, instantly binds and, thus, leaves the pigment in place.

So, in this case, when the ink hits the media surface, it’s exposed to UV light and "cures" onto the media surface. The big difference is that the ink doesn’t penetrate the vinyl; it sits right on top. Besides being a very cool process, it offers the added benefit of sticking to just about anything, However, I would strongly discourage trying to change the color of the family dog.

Solvent solutions

With this basic understanding of solvent-based and UV-curable ink interaction with the media, let’s examine different types of inks and their compatibility with various types of DPSA. The solvent side of the street offers different flavors – full, mild and eco. I’m not a chemical engineer, and I don’t know each ink type’s chemical composition, so I’ll keep this basic for both our sakes.

Let’s start with true solvent inks, the hard stuff. They’ll penetrate virtually any uncoated surface that can fit under the printhead, and they’re typically shipped in bulk containers that allow uninterrupted printing. And, they’re more economical than any lower-solvent brethren. Their primary drawback is having cyclohexane as an ingredient, which means that you may start hallucinating or, in severe cases, convulsing, if locked in a closed, improperly ventilated room with one of these printers.

I asked Kurt Hixon, marketing manager for Gandinnovations (San Antonio), which manufactures the Jet-i line of solvent and UV-curable, grand-format printers, what results users could expect when printing on DPSA. He said, "Solvent inks need to release vapors and dry. The release may affect the adhesive backing because the gases are released through the material into the backing."

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This depends heavily upon your particular media choices. If the facestock and adhesive aren’t sufficiently structurally stable, the ink penetration can lead to premature failures.

However, when you have a sturdy film, the reaction may make the adhesive have more aggressive properties during installation. To combat this effect, make sure your printer is adjusted so the inks cure as quickly as possible.

According to Hixon, "The proper color profile is key in regulating proper ink saturation. This will ensure that you aren’t putting down too much ink, but just enough to ensure a good image."

When inks cure, the faster they can outgas, the less likely they’ll penetrate the adhesive. So, use as much post-heat as possible. And, on smaller jobs, if you’re using a take-up reel, remove the printer roll as soon as possible.

Now, let’s look at the other solvent varieties, mild and eco. They differ because mild solvents still contain some of the same characteristics as true solvents, but they’re less harsh and in a different form. Conversely, eco-solvents have been completely stripped of hazardous chemicals.

I asked Randy Anderson, Mutoh America’s (Phoenix) program manager, for recommended applications. He replied, "Mild solvent inks are a bit more aggressive, so they offer better scratch resistance and a more attractive price. Eco-solvent inks are for those customers who don’t want a solvent ink or to ventilate their printers."

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I also asked Randy if thickness would affect print quality, ink saturation or drying times. He said, "In our testing, we’ve observed no differences based on the film thickness."

Again, we can attribute this to proper profiling. Correct ink saturation and proper post-print heat enable maximum production efficiency.

Unmistakable UV

We’ve looked at some predictable outcomes when printing with any derivative of solvent-based inks. Remember, the image is actually buried into the DPSA’s initial layer. What results can we expect if the ink just sits on top? Let’s examine how UV-curable inks may create different reactions.

Earlier, I said UV inks could basically print on just about anything. However, this wasn’t always the case. Some early ink versions were brittle, so, once the ink cured onto the media’s surface, it would actually "pop" off if it were even slightly moved. With dramatic improvements, this ink technology is more flexible and, thus, prints on an even wider variety of materials. However, our focus is its ability to print on DPSA.

Different UV-ink varieties remain on the market today, so, before printing on DPSA with your UV machine, make sure the inks are highly flexible. Hixon said, "Current inks allow applications that they simply couldn’t use two years ago."

An ink’s ability to adhere to the film’s surface during manipulating and stretching critically impacts UV-curable printing. For vehicle wraps, for instance, only solvent-based printing was once feasible.

However, UV inks still have a breaking point, and, if they’re stretched beyond that point, they’ll still "pop" off the film’s surface and ruin the image. Further, because the ink sits atop the media, the adhesive never suffers any adverse effects. This is key for long-term, outdoor graphics.

As with any new technology, cutting-edge equipment offers advantages and disadvantages. With UV printing, the biggest disadvantage (depending on your financial stature) may be cost. UV flatbeds and roll-to-roll printers will launch later this year. They’ll be impressive, but I advise extensive research before committing to such a large investment.

Summary

Whether printing with solvent-based or UV-curable inks, the graphics market has changed considerably just over the last two years, and (as if you had any doubt) it will continue to do so. You and your clients must understand what can and can’t be achieved with currently available technology. Continued ink and media evolutions will allow users to push the envelope with their applications. These advancements will push the industry into new markets that once were thought impossible. Welcome aboard, and enjoy the ride.