Sign & Digital Graphics

February '19

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S I G N & D I G I T A L G R A P H I C S • February 2019 • 57 or competing technologies improve. All these inks described below either are current proven technologies used in vehicle wrapping, or are new entries looking to make a mark. True Solvent Inks True solvent inks were the first inks that were able to print directly on uncoated vinyls and films. When looking at the ink formula, it typically has a combination of solvents, pigments, and resins. The strong VOCs (volatile organic compounds) of these inks (like cyclohexanone, or 2-butoxethanol acetate) are very flammable, require venting from the printer plat- form, and need long periods between printing and lamination, or even baking. These inks are very durable and have been used for vehicle wraps in the past. They adhere well to most vinyl-based print media without issue. However, because of their volatility, VOC issues and related venting requirements, and the sometimes-high investment in the physical printer, the technology has been on the decline—especially as better solutions have become available. Eco/Light Solvent Inks The advent of eco/light solvent inks revolutionized the digital commercial wide-format printing world for wraps. Changes to the types of less-intense VOCs (like some glycol ethers, and lactone solvents) in these inks has eliminated the need for venting, and the need of baking to cure the inks. Typically many of these inks still require 12–24 hours of drying before lamination, but this could be achieved by loosely unwinding rolls, and allowing proper air flow to evacuate the solvents and cure the inks. However, some ink and equipment manufacturers have reformulated newer generations of these inks, changing the solvent packages. These newer developments in the inks now require significantly less time to cure/dry, from 1/2 to 1/4 of previously recommended times before lamination. These and other improvements have made the eco-solvent and light- solvent inks very popular in the commercial vehicle wrap markets. Latex ink technology, such as that used in this HP Latex 335 printer, has made steady inroads into wraps markets. (Image courtesy of HP Inc.) UV-Cure Inks The technology behind UV-cure inks is complex. Rather than a solvent-based carrier that needs time to dry, UV-cure inks com- bine a variety of photo-initiators, oligomers, and monomers (and pigment-based colorants) in a suspension that instantly cures into a solid polymer when exposed to UV light. Basically, the UV light excites the photo-initiators, which causes the monomers to chemically bond with the oligomers to form a polymer. Very different from solvent or eco-solvent ink chemistry. Original UV inks required the UV source to come from high- powered arc lamps that created an intense wide-spectrum of UV light and extreme heat outputs. These features made it difficult to print onto many heat-sensitive substrates as the media could be distorted by the heat. In addition, the inks were very thick, and created a "texture" as the ink piles do not flatten out like many other technologies. Also, the ink of a UV-cured image tends to be too brittle for vehicle wrapping requirements— though it has proved a perfect solution for rigid-board printing.

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