The Latest Advances in UV Inks, Part II
This discussion centers on cost comparisons, challenges with UV inks, and how photoinitiators work.
In Part I of this article (Screen Printing, June/July 2010, p. 26) suppliers and industry experts were asked about improvements, comparisons, and problems with UV inks. In Part II, these same professionals were asked specifics on cost comparisons, challenges with UV inks, and how photoinitiators work.
What are cost comparisons between UV inks and solvent-based ones?
Larry Hettinger While ink cost per gallon is slightly higher for UV inks, cost in-use is less due to increased space utilization, faster turn rates, lower ink consumption, and less energy required.
UV inks are more expensive than solvent inks because of the individual ink components cost. However, the higher mileage of UV inks helps to offset their higher per-gallon cost, and is one of the reasons why UV inks can deliver cost savings in use when compared with solvent inks. Further savings are achieved by the increased productivity and reduced down time associated with UV inks. Because UV ink experiences no loss during printing or curing and all of the ink printed on the substrate is incorporated into the cured ink film, UV inks permit the use of much finer mesh counts than would be used for solvent-based inks. The difference results in significantly higher area coverage per unit of ink.
Continuous UV curing units are energy efficient, using only 10-50% of the energy consumed by a hot air dryer. Flash curing units are even more energy and cost efficient. Unlike solvent inks, there is no need to install expensive pollution-control measures when using UV inks. Not only does this provide a considerable savings in terms of capital outlay, but it also further reduces energy and waste-disposal costs.
Robin McMillan UV inks may typically cost more than solvent-based inks, but they can ultimately save customers by as much as 30%, depending on the market and printers they use.
Johnny Shell, Ray Greenwood, and Jeff Burton While the waste and maintenance costs are less for UV systems, start-up and operating costs are higher. In particular, ink costs are two to four times more expensive due to higher raw material costs. However, with solvent systems, a large percent evaporates into the air, so more (by volume) is used when compared to UV.
Scott Schinlever Solvent inks are cheaper on a per-liter basis. UV inks offer higher coverage per square foot, and that evens out the cost. Printing directly on rigid substrates makes it a one-step process. It eliminates one step: mounting the flexible laminate on a substrate. Laminate can be as high as $0.30/sq ft plus production costs, and production is slow.
Steve Mitchell You really do not have energy-consumption costs that are associated with gas driers.
Michael J. Plier From the outside looking in, at first glance, solvent systems appear to have a clear cost advantage, but look closer. Speed, efficiencies, and performance rule. Along with the environmental considerations—VOCs, gas dryers, waste—UV wins all the way.
Grant Shouldice Market prices for UV inks are roughly four to five times that of solvent-based inks, but in general, solvent-based inks used to print packaging applications do not get sold into the same market segments, so it’s not a comparison that happens often.
Bruce Ridge If you compare inks that are made for similar substrates and applications, UV inks cost almost twice as much as solvent-based inks on a per-gallon basis. Then again, UV inks will yield almost twice the mileage per gallon as a comparable solvent-based ink.
Does it take longer to use UV?
Michael J. Plier No Way.
Curt Baskin No, actually it is quicker to use UV inks. Printing with UV inks is typically quicker than conventional inks as no or fewer screen-cleaning stops are required, and curing units can be run at higher speeds than conventional dryers.
Bruce Ridge UV inks speed up the printing process because they cure immediately once exposed to UV light and therefore can be printed, handled, stacked, and finished almost immediately after printing. So printing UV inks takes less time.
Larry Hettinger No. The UV curing process is completed rapidly. There is also less delay when printing multiple colors, and a reduced requirement for secondary operations, such as the stacking and cooling of substrates between colors. Fast curing cuts the time between finishing printing and beginning post-production processes, such as trimming, embossing, or diecutting. It is estimated that printing with UV inks delivers an increase up to 200% in production capacity compared to solvent inks.
Grant Shouldice There is definitely a learning curve associated with running UV inks. However, over the years the art has become fairly easy for those well versed in conventional printing processes.
Steve Mitchell The main advancement in inks is the speed that they cure. When you talk screen printing, usually the inks are thick, multilayered. UV exposure for a short period of time can quickly cure at one or perhaps two passes.
Scott Schinlever It's shorter because UV instantly cures to a substrate, and using UV saves labor steps.
Johnny Shell, Ray Greenwood, and Jeff Burton The production time associated with using UV is less given the ink’s ability to cure instantly. However, there is a period of time after the immediate cure where the cross-linking process continues to occur. So event though ink may be dry to the touch, some post-processing actions (bending , cutting, routing) should only occur after a set time period (usually around one hour for digital). Cutting some rigid materials right off the printer could result in chipping of the ink at the cut/route lines.
What applications fit UV particularly well?
Michael J. Plier With the artesian supply of new UV components, it appears that digital printing is well on its way to being one of the most versatile printing methods we have ever seen.
Grant Shouldice A substantial number of applications fit well. A wide range of adhesion, excellent aesthetic and mechanical properties, and the use on inline down-stream processes lend themselves to many applications form printing commercial, publication, and package applications.
Larry Hettinger With UV technology advancements, most applications can be printed with UV ink. The primary applications with a good fit include short-, medium-, and long-term graphics, industrial such as graphic overlay, and automotive media. Four-color-process work benefits significantly from the press/color stability of UV inks and low-dot-gain UV-ink formulations that allow for increased press speeds and reduced waste.
Bruce Ridge With a 30-year history of product development, UV screen inks perform just as well as solvent-based inks in most applications. There are only a few applications where solvent-based inks still out perform UV inks. Examples of this would include uncoated substrates, unusual 3D substrates, adhesion to extremely hard substrates like melamine, long-term exterior durable applications of seven or more years, and of course applications requiring high opacity. In the inkjet market, UV is the fastest growing segment of the printing types of inkjet printing for the reasons listed above, as well as the odor issue associated with solvent-based printers.
Robin McMillan Applications that combine multiple print disciplines, such as offset and screen printing, as used in narrow-web labels, optical disk, and some plastic-container markets all fit particularly well with the UV print process. In fact, any screen-print process that requires printing inline will benefit form UV curing due to the much smaller footprint of a UV curing unit when compared to conventional hot air or oven drying systems.
Johnny Shell, Ray Greenwood, and Jeff Burton Outdoor UV screen inks have not quite surpassed clear-coated solvent-based inks with regard to weathering (the combination of light fading, water, and temperature); however, they are nearly equal and have surpassed many solvent-based inks in pure fade resistance.
Scott Schinlever Any kind of P-O-P, banners, out-of-home signage, and any print that demands durability. Outdoor applications work well on UV prints. Printing with UV on a digital press requires no setup time. Indoor printed projects work well on UV too.
Steve Mitchell All types of packaging and labels fit UV printing.
Do you see LED low-temperature curing as a challenge to UV?
Steve Mitchell Not really a challenge, but rather LED curing would be a branch of UV curing. LED has a narrower range as far as the wavelength of the effectiveness of the photoinitiators.
Scott Schinlever The ability to cure UV inks with lower energy and lower temperature, especially at the higher speeds, is certainly a challenge and the next step in digital UV inks.
Johnny Shell, Ray Greenwood, and Jeff Burton Moderately. LED is a new technology that has been recently incorporated into the industry. The cure parameters of the ink are more tuned to the light energy emitted with LED, so there is a smaller curing window. With traditional mercury-vapor systems, the cure window is wider that accommodates a wider range of UV raw materials in the formulation. The slow adoption rate for digital LED UV is due to issues with insufficient power output and problems achieving surface cure at production speeds. LED units are also expensive for integrating in wide-array applications.
Peter Saunders At Sun Chemical we have UV inks designed specifically for LED curing units in a variety of market industries, but the majority of LED lamps used today are in inkjet applications. SunJet, the inkjet ink division, is a leader in the development of UV curing inks and has supported the industry developments for several years. It was one of the first ink companies to recognize the potential benefits to customers of inks that have the ability to part cure or pin with UV LED lamp exposure in scanning head systems. SunJet has discovered a route in formulation that allows the increased response to LED UV output to be applied to a full range of SunJet ink families. This means that popular inksets can be used with the new LED lamp technology if correctly integrated. While inkjet is currently leading the way in LED usage right now, we expect increased usage of LED UV lamps as they are developed in screen printing.
What are photoinitiators and how do they work?
Bruce Ridge Photoinitiators are chemicals that are added to the inks that are sensitive to specific wavelengths in the electromagnetic spectrum. When these chemicals are exposed to that particular wavelength of energy, they will facilitate the cross linking of the molecules in the oligomers and monomers (the resin of the system) in the ink, which results in a polymer or cured ink film.
Larry Hettinger Photoinitiators are compounds that absorb light to generate free radicals. These free radicals then react with monomers and oligomers to initiate the polymerization chain reaction. The photoinitiator package of an ink can be specifically designed to optimize the cure of the ink vehicle and UV curing equipment.
Curt Baskin Photoinitiators are compounds that absorb the UV energy from the light source on a lamp head, causing a chemical reaction that converts the liquid ink in to a solid film.
Scott Schinlever Photoinitiators have the unique capability of initiating a chain polymerization reaction. This reaction is initiated by the absorption of UV radiation and has the result of linking/cross linking all of the polymer chains within the ink, transforming the ink from a liquid to a solid.
Steve Mitchell Once UV light hits an energy curable ink or coating film, photoinitiators are the items in the ink that get the reaction started to turn a wet ink film in to a dry, cured ink film.
Johnny Shell, Ray Greenwood, and Jeff Burton Photoinitiators are the magic components of UV ink. After absorbing UV energy from the curing lamps, the photo initiators fragment in to reactive materials that start the chemical reaction known as polymerization. The process converts the liquid ink into a solid film. The types of photoinitiators most commonly used in inkjet inks free-radical in nature. Ink formulators work with photoinitiator suppliers to develop inks that are compatible with the UV output of medium-pressure mercury-vapor bulbs found in most curing systems. Unfortunately, light sources often emit excessive IR energy, have high power consumption, and need routine lamp replacement.