UV/EB (also called radiation cure or energy cure) inks have been in the graphic arts industry for more than 30 years in a wide array of market segments, including heavy penetration into the flexo, litho, letterpress, screen and letterset areas. However, one of the most interesting new developments is in the area of UV curable ink jet inks.
This is a rapidly growing application. Some studies show that the overall ink jet ink market has grown more than 400 percent in the last 10 years, and UV curable ink is just starting to become of a serious interest with some forecasts predicting 35 percent to 40 percent growth. Most market studies show that ink jet inks, in general, will grow an additional 300 percent over the next 10 years, as well.
Much of this growth is in the desktop area, but a substantial amount is in more specialty areas. Do not confuse UV curable inks with so-called UV ink jet inks. These inks are simply conventional resin based ink-jet inks that have resistance to UV exposure (weathering), which is an issue since most ink jet inks are based on non-colorfast dyes, not pigments.
The current market for UV curable ink jet is basically split into two main groups, industrial and wide format, with some longer term potential for the textile area as well. Industrial is basically product marking, with UV curable inks already somewhat established into the wire and cable marking area. The drivers for UV curable industrial ink jet inks are better chemical resistance and longer term durability for these applications. Another minor driver is faster curing, but most UV curable inks are still solvent-based, albeit based on fast drying solvents like acetone. These machines can use a large amount of ink but with far fewer equipment installations in the market compared to something like desktop.
An even greater area for growth is the flatbed or web wide format (also termed grand format depending on size) UV curable ink jet market. The development of UV curable ink jet here is expected to compete very favorably with screen-printing, particularly for short run applications (meaning fewer copies of each print). This area is being increasingly utilized for banners and other signage applications like truck wraps and billboards, where the durability of UV cured inks are a major driver. They also are no VOC and have better adhesion to plastics than water-based inks. Fast cure rate is also an issue as machine speeds increase. Water-based inks on non-porous substrates dry very slowly and typically have poor chemical resistance for exterior applications.
Some of the factors driving UV have been through the various equipment manufacturers. They have developed new piezo heads that can print the higher viscosity UV curable inks more effectively. UV curable inks can actually run better than conventional inks because they do not clog the ink jet orifice since they remain liquid unless they have been exposed to UV light.
Viscosity: The biggest formulating issue with ink jet inks is low viscosity. Typically the usual required range is 10-20 cPs, but this is at the elevated temperatures that ink-jet runs, typically around 40 to 45° C.
Pigment Wetting: Another aspect for UV curable ink jet is pigment wetting, since the major growth is for exterior durability applications. Therefore, the difficult aspect here is to get reasonable pigment wetting combined with low viscosity.
Exterior Durability: Wide and grand format applications are often used for banners and signs. The durability requirements are rarely for multiple years, but months are needed. Aliphatic backbones are still usually required.
Cure Rate: Cure rate can be very important for industrial marking applications. These systems can run 300 to 600 fpm easily, and UV can be an advantage when formulated correctly. This does predicate the use of more highly functional materials. Cure is less of an issue with wide format, which typically runs less than 50 fpm (and often quite a bit slower than that). However, the low viscosity requirements mean that high concentrations of low viscosity, low functionality materials are utilized, which can adversely impact cure rate.
Flexibility: Flexibility can be an issue since most of the wide format banners are printed on plastic film substrates. Use of monofunctional products can help here.
Adhesion: Again, adhesion to films used in wide format is a potential issue.
In conclusion, UV curable ink jet applications are rapidly growing and this means opportunities are available. It is rare that the printing industry has a market segment growing at these rates, and I hope all parties involved can work together to make this a technological success.
About the Author
John K. Braddock is technical service manager at Akzo Nobel Resins, and is involved in RadTech’s Graphic Arts Focus Group. For more information on RadTech, please contact Gary M. Cohen, RadTech International North America at (242) 497-1242 or visit www.radtech.org.