Ecosolvent Printing

Editor’s Note: Jan Van Hemelen of Avosi (Ruiselede, Belgium) and Jo Vanneste of Industrial Consultants (Aalter, Belgium) helped Jim prepare this month’s article.

Ecosolvent printers have been a real godsend for the sign industry. The printers’ low price tags are a major reason why they’re so popular. Not suprisingly, an estimated 60% of signshops anticipate purchasing ecosolvent printers.

Printer setup is rather straightforward. Approximately two hours after unpacking the equipment, you’re ready to print. Plus, there are no dangerous fumes or odors, and no ventilation system is required. And, if you follow a few basic rules, you should have few, if any, problems.

If problems occur, they typically involve poor ink adhesion, shrinkage, vinyl curling, color shift and/or dot gain. For trouble-free results, use the right material, operate the equipment in a suitable environment and use the proper print settings. This month’s column offers suggestions for printing onto vinyl using an ecosolvent printer.

The right stuff

The latest generation of ecosolvent inks allows you to print onto various uncoated, monomeric and polymeric calendered vinyls and cast-vinyl films. However, this doesn’t mean you’ll get great results with every vinyl.

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You can’t print onto every type of vinyl. Actually, you can only print onto a limited range of uncoated vinyl films. With some vinyls, ink adhesion is a problem. For this reason, prior to production, you must test and evaluate your vinyl choice with your printer and inks.

To choose the right material, consult the printer manufacturer and distributor. Because many printer companies have performed extensive vinyl tests, they can tell you which films work best with their systems. Plus, they have profiles for the recommended films. As a rule of thumb, vinyl films with a matte finish print better than high-gloss films. Furthermore, films with polyethylene-coated liners are generally less prone to curling than films with clay-coated liners.

Prior to printing, wipe down the vinyl using a towel moistened with Rapidtac or isopropyl alcohol to remove dust and other contaminants, such as oils and plasticizer. A dry, clean and dust-free surface is thus ready for printing

Control your shop environment

Although ecosolvent printers are designed to function in an office or signshop, you’ll achieve the best printing results if you operate in a clean, temperature- and humidity-controlled environment.

Ink adhesion largely depends on ink and film chemistry, but other variables exist. Two different printers using the same equipment, ink and vinyl film can produce different results. Humidity, temperature and cleanliness also affect printing results.

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For consistent results, you must control your shop’s humidity and temperature. Manufacturers recommend their optimal humidity and temperature conditions. When printing onto vinyl, shop temperatures should be between 65 and 85°F (18 and 30°C); relative humidity should be between 30 and 70%.

The lack of environmental control can contribute to color shift, which explains why some shops can print a file on different days and achieve different results. Companies that specialize in digital printing often invest in an environmental-control system, which maintains consistent temperature and humidity year round.

Shop conditions can vary from one season to another, especially when you change from air conditioning to a heating cycle. If your shop’s temperature is too low, and/or the humidity is too high, the ink won’t wet out the surface and sufficiently bind the vinyl for good ink adhesion.

Instead, the ink will pool on the surface and form little islands. This condition occurs more frequently with heavier ink deposits. Extremely cold or hot shop environments can contribute to ink-adhesion problems. Humidity control is also important. If relative humidity is too high, you could experience dot gain. If the humidity is too low, it could contribute to clogged nozzles.

Machine settings

Ecosolvent printers can produce high-quality prints for such durable signage applications as fleet graphics. Their resolutions range from 180 to 1,440 dpi.

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Because machine settings for printing onto vinyl will vary, you must establish a profile for each film. The profile defines the ink, material, printer speed and resolution. The best profile will yield the optimal print quality based on a given set of variables. Remember, if you change one of these variables, you must change the profile. Printing variables account for color shift as much as fading is caused by the sun’s bleaching effects.

Any setting recommendations should be regarded as guidelines, not hard and fast rules. When printing onto any vinyl, "test, don’t guess" before you go into production. When establishing a profile, print a test swatch with ink lay down from 0 to 100%, generally at increments of 10%.

The newest generations of ecosolvent inks are designed to work with the printers’ multiple heating phases. In the preheating phase, the vinyl is heated to prepare the film’s surface to accept the ink. With ecosolvent printers, you can adjust the printer temperatures from 40 to 122°F (35 to 50°C). Preheating opens up the micropores on the vinyl’s surface, which gives the film more "tooth" for the ink to bite into. The heating also helps prevent dot gain and prohibits the ink droplet from contracting to maintain dot integrity.

To achieve acceptable adhesion, the ink must flow into the pores. During printing, the ink is heated, which helps it wet out on the film’s surface. After printing, the curing phase fixes, or locks, the ink into place to bond the ink to the vinyl. For the ink to cure, the solvent must evaporate. The process is time and temperature dependent. In colder shop temperatures, the ink doesn’t flow as well onto the vinyl’s surface, and often, the ink doesn’t cure properly.

Inadequate ink curing can affect some vinyl films’ adhesion. Remember, the ecosolvent ink comprises a solvent. If the solvent doesn’t evaporate from the ink, it can penetrate the vinyl and attack the film’s adhesive layer. High heat can cause the ink to dry too fast and clog the nozzles.

Ink primarily comprises the carrier or vehicle, which is typically either water or solvent. As the ink cures, the carrier evaporates — it shrinks. By removing the large volume of solvent, mechanical tension is created. In this curing process, the ink contracts, which contributes to the vinyl’s contraction.

The heat used in ecosolvent printers contributes to the vinyl’s contraction or shrinkage. Heat affects any material — this is especially true of vinyl. During the printing process, the vinyl is subjected to several temperature changes. On the roll, the vinyl is at room temperature. Then the film is pre-heated. Under the printheads, the film is subjected to even higher heat. After printing, the vinyl is heated again to cure the ink. Finally, the vinyl cools back down.

As the vinyl is heated in the printer, it expands. As the vinyl cools down, it contracts. If the film expands and contracts at a much greater rate than the liner, tunneling could occur. Because elevated temperatures can contribute to shrinkage and curling, some signmakers prefer to lower the heat settings.

Heavy ink concentration, which occurs when you print a solid color or drop shadows, also contributes to shrinking and curling. Drop shadows create great contrast between lettering and a sign’s background, and produce a 3-D look. But when the shadow bleeds to the edge of a cutline, the vinyl can curl. Thus, to minimize curling, try to provide a 1/4-in., or 6mm, outline around the printed image.

Heavy ink concentrations can cause other problems; they can take forever to dry. The ink can also bleed or puddle into ink islands. A slower printing speed also reduces the likelihood of vinyl contraction, because the ink has extra time to start drying before another ink layer is printed. The downside is less printing efficiency.

During heating, the expanding vinyl can tunnel on the release liner. Tunnels between the vinyl and release liner can form as the heated film under the dryer expands and pushes against a cooler, rigid, film mass.

When printing onto vinyl, use lower-resolution settings. On glossier films, this will help prevent the dots of higher-resolution prints from running together. When printing higher resolutions, adjust the density curve in your profile to control the amount of ink that you print. Also, slow down your print speed. You’ll experience less bleeding, especially when printing onto glossier vinyls. You also give the ink more time to dry before the printheads make another pass. Generally, you get better results with matte-finish vinyls, as opposed to glossy ones.

Vinyl graphics don’t usually need a high resolution. With such outdoor applications as fleet graphics, prints are viewed from a distance. In such cases, lower-resolution graphics provide more contrast and, consequently, are more readable.

Finishing the job

Printer manufacturers claim that overlaminates, or clearcoats, aren’t necessary for most signage applications. At the very least, digital prints should be lightly sprayed with an aerosol clearcoat. Before weeding, spray the print with a uniform coating. Then, weed the print. You can apply application tape as soon as the clearcoat is dry — usually within 15 minutes.

You can use either a water- or solvent-based clearcoat. Spraying a medium coating of clear is recommended. But don’t overdo it. Heavy coatings may cause the ink to run. However, you really have to overdo it to damage a print. Waterbased clearcoats usually dry faster than solvent-based ones. To my knowledge, a waterbased, clear, aerosol version isn’t available. You can apply clearcoat with a brush; however, in most cases, the coating is heavier than it should be.

Some solutions for preventing curling include: printing at lower resolutions, lowering the heat settings, laminating your application tape soon after printing and cutting, and applying the graphics as soon as possible.