The ABCs of UV-LED Printers

Several factors have propelled the growth of the UV-LED printers in the sign market. The latest generation of the print system design have dramatically increased production output and reduced scrap rates. The energy efficiency of UV-LED systems, compared to other print technologies, has also helped lower printer operating costs.

Unlike solvent and ecosolvent printers, UV inks do not emit VOCs (Volatile Organic Compounds) that pollute our environment and your workplace. Just because you can’t smell some inks doesn’t mean that these vapors aren’t in your shop’s air and are good for your health.

Because UV-LED inks do not cure by evaporation, there is no need for ventilation and they should satisfy any governmental standards for air quality. What’s more, UV inks provide the durability, chemical and abrasion resistance, as well as the print quality and color consistency needed for a broad range of interior and exterior signage applications.

Advances in machine design and ink technology have arguably made UV-LED printers more versatile than other print systems, providing sign makers with opportunities to expand into a variety of market segments from exhibit and display to vehicle graphics. What’s more, UV-LED print systems are faster, safer and more affordable.

Wider Range of Applications

Compared to solvent and ecosolvent printers, UV curable inkjet inks adhere to a wider range of substrates. In fact, you may have heard that you can print on virtually any type of substrate with UV inks. That sweeping generality definitely needs some qualification.

It is true that with UV-curable inks you can print on a wide range of flexible and rigid substrates, including pressure-sensitive vinyl, rigid vinyl, expanded PVC, polycarbonate, acrylic, polystyrene, polyester, polyethylene, polypropylene, metal and glass. “With advances in ink chemistry,” says Mark Rugen, Mutoh Director of Product Marketing & Education, “one ink system fits all print applications.” Rugen explains that some substrates may require an adhesion promoter.  

The versatility and flexibility of today’s inks allows printers to print on a vast array of both porous and non-porous substrates. “This opens the door for printers to venture into new markets including labels, advertising specialties, backlit signage, custom wall covering and POP displays” Rugen says. 

Most small sign shops do not specialize in a specific segment of the graphics market, such as wall graphics, vehicle wraps or museum graphics. Instead, these shops provide a range of products and services. “When a shop owner invests in a printer”, Rugen explains, “he needs one system, which will print on a variety of substrates for a wide range of indoor and outdoor applications.”

Technological Advancements

Faster printing speeds. Speed of the UV-LED printers have increased greatly. The latest generation of UV-LED systems have attained output speeds between 1100 square feet per hour to 3900 square feet per hour.

● More Flexible Inks. Early generations of UV curable inks were somewhat brittle and prone to cracking. However, the once brittle inks have improved significantly. Later generations of UV inks are flexible and durable enough for fleet graphics applied to vehicle surfaces with compound curves, rivets and corrugations.

● Lower Costs. At a purchase price of approximately $25,000, a 64” Roll to Roll UV-LED printer is comparably priced with ecosolvent, solvent and latex printers. At this price, shop owners can lease a new printer for $500 to $600 per month.

● Improved Curing. One of the criticisms of UV LED systems is that the spectrum of light emitted is much narrower than that of Mercury vapor UV curing systems. In recent years, this issue has been diminished with the development of new UV LED systems and new ink formulations.
The latest generation of LED curing systems, which feature a more dense arrangement of the LEDs, produces a more energy to more fully cure the ink. The higher output of these newer systems also allows for higher production speeds.

Differences in Adhesion.

Solvent inks and UV inks adhere to a substrate in different ways. Solvent inks are designed to partially solvate or dissolve the outer surface of a pressure-sensitive vinyl film in order to chemically bite into it. Printed on board stock or other porous materials, solvent inks adhere to the substrate through absorption.

While UV inks are 100% solids, solvent inks are comprised of as much as 80% solvent. Not only is solvent evaporation an environmental problem, but can be a problem when printing on some media. On some substrates, such as vinyl films, the solvent solvates the surface. As well as causing the media to soften and swell, strong solvent inks can cause some plastic films to shrink, warp or crack. What’s more, when the printed image is a bleed, in which the ink is printed edge-to-edge, the effect of solvents on plastic films can results in edge lifting.  

Free radical UV inks adhere in a very different way. They don’t solvate the substrate and don’t bond by being absorbed.  Instead, these UV inks anchor to a material mechanically, in much the same way as a pressure sensitive adhesive does.  After the ink is printed, it wets out and fills in the microscopic pores on surface of the substrate, holding on for dear life as the ink cures and becomes a solid sheet.

Another major factor in adhesion is the surface tension difference between the ink and the substrate. The ink should always be lower in surface tension than the substrate.  Some substrates, Coroplast in particular, change dramatically in surface tension over relatively short periods of time. As the surface tension or dyne level of the substrate drops, ink adhesion can become problematic.

White Ink Option.

Many of the new UV-LED printers feature white ink capability. Because UV curable inks are 100% solids, they typically provide better opacity than solvent-based inks.  This is a big advantage, when you print on colored or metalized films, because the ink has more hiding power, which helps prevent the background from overpowering the printed image. 

The ability to print CMYK plus white is also an advantage when you are printing subsurface on clear films. In these cases, you can print a wrong-reading image on the second surface and then back it up with white, before printing the background.   This is ideal for printing backlit signage.

Higher Quality Printing

Because UV inks dry immediately following exposure to the curing lamps, inks do not bleed and there is no dot gain. “UV systems can print a finer dot,” Mark Rugen explains. “That results in sharper images and finer detail as well as a wider color gamut compared to other print technologies.”

How UV-Curable Inks Work

Unlike solvent, eco-solvent or water-based inks, UV-curable inks do not evaporate into the air. Instead these inks dry or “cure” instantly through a polymerization process.  This process is initiated by exposing the inks to a certain spectrum and intensity of UV light.

UV inkjet inks are classified as 100% solids. The term “100% solids” may be confusing to many.  You might wonder how an ink could be a liquid and be classified as 100% solids. 

Here’s what they mean: 100% of what is printed on the media, stays on the media – it’s kind of like the way Vegas works. By comparison, solvent inkjet inks are less than 20% solids.  Everything that isn’t a solid evaporates into thin air, which is neither good for the health of your employees or the environment.

Here are the nuts and bolts of how UV-curable inks are formulated and how they cure. Two of the key ingredients in UV curable ink formulations are monomers and oligomers.  Monomers are very small molecules that can combine, through a chemical process called polymerization, to form much larger molecules called polymers. 

Monomers are classified as “reactive diluents”.  Reactive diluents are materials that ink manufacturers can use to replace organic solvents. In an ink formulation, the monomers perform the same purpose as a solvent, by reducing or thinning the viscosity of the ink. 

But here’s the difference, and it’s an important one. Monomers don’t evaporate; solvents do.  As the solvent in a conventional ink dries, it evaporates and these volatile organic chemicals or VOCs   get into the air, which contributes to air pollution.  Solvents in the air also pose a health risk to your employees, which are breathing this contaminated air.

What are Oligomers? Now that we covered monomers, what are oligomers?  Just like monomers, these molecules combine with monomers to form polymers.  One difference between the two is that monomers are very small particles with a low molecular weight, whereas oligomers are larger molecules with a high molecular weight.

The function of an oligomer in the ink formulation is different, too.  Whereas monomers are “reactive diluents” and perform the function of a thinner, oligomers are “reactive resins”.  Just as a resin binds a paint or ink or vinyl film together, the larger reactive resins or oligomers of a UV curable ink form the backbone of the molecular chain to which the monomers bond in the polymerization process.

Of course, monomer and oligomers aren’t the only components that comprise a UV curable ink. The other components include photo initiators, pigments, and additives. 

Photo initiators are the components that get the ball rolling in the polymerization process. When the ink is exposed to UV light, the photo initiators absorb the UV energy and break down into reactive components that initiate the polymerization process.  Polymerization is the chemical process in which the smaller monomers and oligomers bond together to form the much larger polymer molecules.  As the smaller molecules polymerize, they entrap the pigments, which give the ink its color and the additives in the cured solid inks.

Instant Cure.

One of the major benefits of UV inkjet systems is that the inks dry almost instantly, after being exposed to intense UV light.  Exposure to certain wavelengths of intense UV light initiates a chemical reaction, which cures or hardens the ink.

You will note that I hedged my bet by saying that the inks dried “almost” instantly. After exposure to UV light, prints are dry to the touch and can be handled.  Not all prints, however, are totally dry. When printing with some UV inks, you should wait an hour or two before rolling up a print, just to play it safe.  Some UV inks can continue to chemically crosslink and cure for as long as three days after the initial exposure.    As this crosslinking process continues, the inks will become harder and harder. 

By comparison, solvent and ecosolvent inks take time to dry. To fully cure, solvent an ecosolvent inks can require at least 24 hours. Often longer. This slows production time, especially when you need to laminate a print.

How UV-LED Printers Differ from Traditional UV Print Systems

There are two basic curing units used for curing UV inkjet prints: Mercury vapor UV lamps and UV LED curing systems. Mercury vapor lighting is an old technology, which has been around for at least a century.  UV inks were originally developed for this type of lighting, which emits a broad spectrum of UV light.

Compared to traditional metal halide and mercury vapor arc type UV curing systems, LED UV curing systems feature significant advantages. LED curing systems feature greater service life; require less maintenance; are easier to maintain; provide lower operating costs; and are safer to operate in your shop as well as being safer for the environment.

LED lamps generate a very narrow band of UV light, compared to the broader light band that mercury lamps produce. On the surface, this may seem a limitation. In fact, the UV-A light from LED lamps is very focused, capable of penetrating heavy ink deposits.  The results are ink is more thoroughly cured and adhesion to the print media is improved.

As UV LED technology has improved and more printer manufacturers have entered this market space, competitive pressures have driven prices lower, making these systems a more economically feasible option for sign makers.

As UV-LED printers have grown in popularity, traditional UV print systems have lost market share, especially in the sign shop universe. What accounts in part for the emergence of UV-LED is its affordability. Printers, such as Mutoh’s ValueJet 1638UR roll to roll printer, are affordably priced to compete with solvent, ecosolvent and latex printers. Mutoh’s 64” 1638UR costs a little less than $25,000. A 4-foot by 8-foot flatbed UV printers, which allow you to print on rigid substrates, can cost as little as $80,000. That’s significantly less than most traditional UV flatbed printers.

If You Can’t Stand the Heat

Mercury vapor UV lamps also generate significant heat-producing infrared light. As much as 40% of the energy consumed is converted to heat, which serves no function in the curing process.

Heat was the “Achilles Heel” of conventional UV inkjet printers, which has helped propel the growth of UV-LED curing. Conventional UV arc lamps can generate temperatures higher than 600°F. Many of these thin plastic films cannot withstand sustained temperatures greater than 150°F to 190°F.  The operating temperature of UV-LED units, by comparison, is typically about 140°F.  

High curing temperatures not only damage some thinner media, but when these substrates warp and buckle, the result is a potential head strike. Since much of the media used in wide format digital printing is plastic, that heat can cause problems including shrinking, warping and discoloration.

Longer Service Life

UV-LED lamps last 10 times longer and provide lower operational and maintenance costs than UV lamps. Whereas UV-LED lamps operate effectively for 10,000 to 20,000 hours, the lifetime of conventional UV lamps averages about 1,000 hours. Regular maintenance also includes cleaning the lamps, reflectors, light shield and air filters.

The output of LED bulbs also remains relatively constant for much of its service life, while the efficiency of mercury arc lamps begins to degrade within months of operation.  

Compared to mercury vapor lamps, UV-LED bulbs have very few service issues, which reduces maintenance costs.  Component replacement costs are also significantly lower.

Faster Start Up

Unlike UV systems utilizing mercury vapor lamps, UV-LED units are ready for printing with the flip of a switch. What’s more, if you are concerned about the environment, you will be happy to know that UV-LED lamps consume about one-quarter to one-half the energy that mercury vapor lamps consume.

Lower Operating Costs

Traditional UV curing lamps consume a tremendous amount of electricity. LED curing lamps are much more cost effective to operate. Shops may realize savings of 60% to 80% in their utility expenses.

Safer Operation

UV-LED systems are not only a much safer to operate than solvent or ecosolvent, but also much safer than conventional UV print systems in the following ways:

● No Ozone. Traditional UV lamps produce ozone, which require ventilation. LED curing lamps don’t generate significant amounts of ozone, if any, and require no ventilation. 

● No Mercury. Mercury vapor lamps contain toxic mercury requiring special handling in disposal. On the other hand, LED curing lamps are mercury free.

● No Harmful Light. Conventional UV curing lamps emit a spectrum of light, which is as damaging to a person’s eyesight as the lights used in tanning salons. By comparison, operating LED curing lamps are nearly as safe as the LED lights on your holiday decorations.   


Inkjet printers utilizing LED UV curing systems have grown in popularity as the technology has advanced. Improvements in these systems ensure reliable and faster curing of inks, and provide for high quality printing as well as improved production output.

In deciding whether to purchase any print system for your shop, make sure that it is best suited for your intended applications. Is the printer compatible with all of the media that you plan to print on?

You also need to evaluate it the new printer provides your shop with any efficiencies in production or any reduction in direct material costs. In making a decision to buy a flatbed printer, you should determine what you will save printing directly onto a substrate instead of applying pressure sensitive graphics to a substrate. You also need to calculate any reduction in direct labor costs.

If the equipment is a good fit with your shop, determine if you have the base of business which will support the expense of a new printer. A new UV-LED printer will provide your shop with new capabilities and new business opportunities as well as additional revenue. Based on the new revenue that you anticipate to generate with the printer, you should calculate how long it will take for you to pay off the equipment.