Inkjet Printing Inks
In 2005 I wrote a PIE Quick Tips article about the ink choices you have for large-format signage printed on inkjet presses. Since then, there have been a number of developments in this area, so you now have more options than ever. Let's start with the more common inkjet printing inks and how they've evolved.
Water-Based Dyes and Water-Based Pigmented Inks
In dye-based inkjet inks the coloration has been chemically bonded to the liquid portion of the ink, forming a “solution.” In contrast, pigmented inks are “suspensions.” That is, particles of coloration are suspended within a liquid and held between water molecules. Dyes seep into the paper substrate more easily than pigments, which primarily sit up on the surface of the paper.
Although this has been changing over time as ink manufacturers have improved their ink chemistry, dye based inks are brighter and have a wider color range than pigmented inks. In contrast, pigmented inks have a longer life span and are more color-fast than dyes. (Dye-based inks fade more quickly than pigmented inks, particularly if unprotected by lamination, exposed to sunlight, or printed on substrates that chemically interact with the dyes.)
A good rule of thumb is that for short-term indoor use, both water-based dye and pigmented inks are fine. However, for protection of the large-format prints against the elements (water, wind, and sunlight), you should laminate both dye-based and pigmented inkjet prints if you plan to use them outdoors.
Solvent-based inks allow you to print on a much wider range of substrates than water-based dye or pigment inks. They are also more durable and light-fast when used for exterior signage. Since these inks are composed of pigments held within a liquid base of solvents, they are more difficult to work with and require more care than water-based inks. In addition, there are now eco-solvent inks that are more eco-friendly. However, they cannot be printed on as wide a range of surfaces as traditional solvent based inks.
Ink manufacturers have also developed non-petroleum-based inks. These are still solvent inks and therefore can be used for the same kinds of inkjet printing (more varied substrates, and exterior use involving exposure to the elements). One thing to keep in mind, though, is that even though they are based primarily on corn (a renewable resource, unlike petroleum), they are still solvent-based inks and need to be handled as such.
UV inks can be inkjet printed onto a wide variety of substrates (both porous and non-porous). You can print on paper or even metal or glass. These inks are durable and light-fast, so you can use them for exterior signage without needing to laminate the prints.
The ink works as follows:
- The ink is composed of colored pigments mixed into a synthetic resin.
- The inkjet press prints the large-format graphic.
- Ultraviolet light then cures the inks (polymerizes them, changing their chemical composition) and bonds them to the substrate (paper, glass, metal, or textile).
UV inks are not new. They have been used in offset printing for decades. For inkjet printing, they are ideal due to their instantaneous drying (curing), their printability on almost anything, and their stability.
Latex inks are water-based, pigmented inks (pigments suspended in water rather than chemically bonded to the water, as are dyes). They are durable for both interior and exterior use, and they do not need to be laminated (although lamination will increase their lifespan).
This is how they work: After the print heads apply the ink to the substrate, radiant heat and forced air within the inkjet printer cure the ink, evaporating the water-based elements and allowing the latex particles to become a durable film, adhering the pigmented particles to each other and to the substrate.
In terms of their color qualities (color gamut and color stability), as well as their durability, latex inks are comparable to low-solvent inks.
Latex inks are also flexible and stretchable, which makes them good for vehicle wraps and other applications over a base that is not absolutely flat. (For instance, latex inks are good for fabric signage.)
In addition, they can also be used for back-lit signage or even paper-based point-of-purchase displays (on either coated or uncoated stock), or for any other application that would be appropriate for low-solvent inks.
[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]