There is, in some ways, a fundamental paradox when it comes to wide-format inks. There are more ink choices than ever, and yet for any given piece of equipment, you are generally stuck in a “one-cartridge-fits-all” situation. If you purchase a latex ink printer, you’re not going to be able to swap out the ink and run UV-curable ink, for example. For commercial printers who hail from the days of offset, when you could often just grab a new can of ink for each job if you had to, this can seem like one of those “I’d better back the right horse” kinds of decisions.
However, this doesn’t need to be as limiting as it sounds, and many of today’s inks are improving in terms of flexibility. Still, ink technology is an important consideration when choosing wide-format printing equipment. After all, it affects what you can print on and, therefore, what potential applications you can print. And not only that, ink can be a substantial cost center for a print operation.
As substrates have proliferated and the number of applications for wide-format graphics has grown exponentially, inks have kept pace, and equipment manufacturers and print providers have kept the pressure on ink manufacturers to devise new formulations that boost quality, durability, performance, and price.
In part one of this two-part feature, we will look at the basics of wide-format ink and the choices available. In part two, we will look at some of the more practical considerations of ink selection as it applies to choosing specific types of equipment and producing specific applications.
To Dye For
In very basic terms, ink—be it for wide-format or any other purpose—comprises two elements: a colorant and a vehicle. The colorant is the material that, as you would expect, imparts a specific color to the ink, while the vehicle is the medium—such as a fluid—by which the colorant is transported to the substrate. (We associate “vehicle” with a car, but the word comes from the Latin vehiculum or “means of transport.”) The colorant can either be a pigment (solid particles) or a dye (liquids), and the vehicle can be based on any of a variety of liquids, from water to volatile solvents.
Let’s have a look at the primary categories of wide-format inks.
Solvent Inks
As you may remember from high school chemistry, a solvent is any material that can dissolve another substance, which is called a solute, to form a solution. Solvents are usually liquids, but gases and even solids can be solvents. When we talk about inks, the term “solvent” is used to refer to a class of chemicals called volatile organic compounds (VOCs). Although we all know people with volatile personalities, in chemistry, volatility is a measure of how readily a liquid evaporates; the more volatile it is, the faster it evaporates. We tend not to know too many people like this. Volatility is important because printers usually need inks to dry as quickly as possible, and while absorption into the substrate is one part of the drying equation, evaporation is another.
Solvent inks are pigment- rather than dye-based, which makes them long-lasting and fade-resistant. Solvent inks are generally inexpensive, comparatively speaking, and are waterproof and UV-resistant, traits which make them good for outdoor applications. They can also be printed on a wide variety of substrates, but work best on uncoated or non-absorbent materials.
The drawback to solvent inks—which is why they are quickly being replaced with alternative ink formulations—is that the vapors can be toxic, making them a workplace hazard necessitating special ventilation systems. At the same time, discarding the used solvent becomes an environmental issue, subject to regulation. In response to these drawbacks, there have emerged...
Eco-Solvent Inks
These inks comprise a “milder” type of solvent. “Aggressive” solvents evaporate quickly and readily. However, they tend to be the most hazardous, just like aggressive drivers. On the other hand, mild solvents take longer to evaporate, often requiring extra help such as heat, but are less hazardous. So these so-called eco-solvent inks have emerged to try to mitigate some of the problems and hazards associated with solvent inks. The term “eco” is a bit of a misnomer, as they are not 100% environmentally friendly and still possess some of the hazards of more aggressive solvents, although they do require less ventilation; “mild solvent inks” is perhaps a better term. (We will look at some other environmental concerns in part two of this feature.) Still, eco-solvent inks have become a popular option as the color quality, durability, performance, and cost have all improved.
In terms of workplace safety and the environment, perhaps the safest inks are...
Aqueous Inks
Water of course is a solvent (if you make a pitcher of lemonade, the water is the solvent, the lemonade powder is the solute, and the resulting solution is perfect on a hot summer day), but inks that use a predominantly water-based vehicle are considered distinct from solvent inks. Aqueous inks can be either dye- or pigment-based, and often include other liquids than pure water, such as glycol, to help improve performance and volatility. As it is, aqueous inks often require special coated substrates to adhere properly, and are not always well-suited to non-paper substrates, such as plastics or vinyls, although some newer formulations are conquering these limitations.
Then we have..
UV Inks
Ultraviolet-curing, or UV, inks have started to penetrate (as it were) into conventional offset printing, but have also found a comfortable home in wide-format printing. UV inks comprise a cocktail of chemicals (such as acrylic monomers and an initiator) that, when exposed to ultraviolet light, dry more or less instantly. The benefits of UV inks include not only rapid drying time, but also more vibrant colors (UV inks do not have time to penetrate into the substrate, which is what can cause fading), greater choice in substrates (including plastics, vinyl, foil, paperboard, and other specialty substrates), and increased health and safety for press operators and the environment (the UV printing process does not use solvents and therefore does not emit volatile organic compounds). Some of the drawbacks of UV inks include heat and energy use to power the UV lamps, as well as the fact that ultraviolet light can be hazardous without adequate precautions and protection, as anyone who has ever had a sunburn (or melanoma) can tell you. However, new printers that use much cooler and faster LED lamps are starting to appear on the market and it’s not difficult to forecast increased market share for these devices as the cost comes down.
UV inks are being used in some of the most exciting applications in wide-format today, as are...
Latex Inks
In general terms, the word “latex” refers to a “stable dispersion (emulsion) of polymer microparticles in an aqueous medium” (the word originates from the Latin latex, meaning “liquid, fluid,” which is pretty unspecific), and in the case of inks is not related to the natural latex exuded by plants or the synthetic latex used to make gloves or other faux rubber items. “Latex” is a generic chemical term and anyone with latex allergies can work with latex inks without incident. (HP tells me they get this question a lot.)
Latex inks are water-based, using an “aqueous-dispersed polymer.” The first latex ink printers were introduced by HP in 2008, and other manufacturers such as Ricoh and Mimaki have since released latex devices. It has been said that latex inks are better environmentally than aggressive solvent inks, and generally this is true (latex inks are odorless and require no special ventilation or other handling requirements), although their environmental friendliness may be a tad overstated. Latex inks have traditionally (to the extent that anything about them can be said to be “traditional”) been thought of as an upgrade to aqueous inks. What has driven the market for latex inks and their corresponding devices has been their flexibility, their ability to print on a wide variety of coated and uncoated substrates for both indoor and outdoor use on the same machine. They also dry quickly, which speeds the workflow as finishing operations can be applied immediately after printing.
We’ll talk more about latex inks—and, indeed, all inks—in part two of this feature.
Flowing Forward
Part one had covered the basics of wide-format ink. In part two, we will take a closer look at how inks handle different applications (or, perhaps, vice versa) and, more importantly, how to think about ink in the context of choosing wide-format equipment, and how to measure and evaluate estimates of things like “cost per square foot.”
