- November 01, 2002, Dr. Richard M. Podhajny, Ph.D., Contributing Editor
Ultraviolet-curable inks and coatings have been used in packaging for 30 years. From their humble beginnings in the early 1970s, they now hold significant market share in major printing processes, including lithography, flexography, letterpress, and of course, screen printing. The only major printing process missing is rotogravure. The primary reason for this is the low viscosity required by the rotogravure process, which has limited the use of UV inks in this application.
The primary driving force for UV technology has been the reduction of VOC emissions compared to conventional printing processes, energy savings, high print quality, and most importantly, excellent resistance characteristics. When it's done right, UV quality becomes the “gold standard.”
Various digital printing technologies are nipping on the heels of conventional printing processes. Among these, ink jet has been the most promising digital process for packaging products. Although ink jet technology has been here since the 1970s, it still is considered to be in its infancy. Recent developments in combining UV technology with ink jet holds promise for more competitive products in packaging applications.
In the last five years, development of UV-curable jet inks has become a commercial reality, although current sales are estimated to be well under a million pounds. The growth of this technology probably will be slow, but long-term prospects are good.
UV technology offers some interesting advantages to ink jet applications. UV materials do not dry on the printhead and can eliminate some of the aggravating problems associated with drying in the nozzles. The ink drying is done after printing and uses UV light. This eliminates cleaning or purging the head to remove insoluble material, as is the case with other ink jet technologies. Excellent lightfast and product resistance can be realized. The drying is fast, and the UV jet inks can be formulated with no VOC emissions.
The most promising UV jet ink technologies are based on one of three approaches below:
UV jet inks based on water-based formulations
UV jet inks based on “hot melt” application
UV jet inks based on low-viscosity versions of conventional UV formulations.
Water-based UV jet ink technology is particularly attractive since it uses water as the diluent to produce low viscosity. In this approach the ink is formulated with resin emulsions that are UV-curable. However, there are still technical challenges in dispersing the photoinitiator.
Hot melt jet inks depend on the large viscosity drop that can occur with some specialty jet ink formulations. The “hot inks” are applied by jet printer and UV-cured. Formulation challenges lie in figuring how to balance the ink stability and maintain the desired low viscosity at high ink temperature.
What about UV jet inks using conventional UV ink formulation approaches? The problem here is trying to achieve the perfect UV ink with no VOCs, excellent cure, low viscosity, etc. The biggest obstacle is to try to attain 100% solids and low viscosity. New UV-curable resins with low-viscosity characteristics are providing ink formulators with new options, but the task is a difficult one.
UV jet inks will grow in many applications, but especially in drop-on-demand (DOD). DOD applications can tolerate higher viscosities than continuous ink jet (CIJ) and are less demanding from an ink jet formulation perspective.
You can expect the use of UV jet inks to grow as a digital printing alternative that can provide excellent product resistance in many packaging applications; but its commercial applications are still to be defined.
UV jet inks are here. If you're interested, suppliers include Avecia, Coates, and Sericol.
Dr. Richard M. Podhajny has been in the packaging and printing industry for more than 30 years. Contact him at 215/616-6314; email@example.com.