- October 01, 2001, Richard M. Podhajny, Ph.D., Contributing Editor
Two issues that have remained in the forefront of our industry for at least two decades are environmental regulations and flexography.
As the quality of flexo continues to improve, alternative ink technologies are making their mark in the push to reduce volatile organic compounds.
We are all aware of the strides that flexo has made over the years. But just how does it stack up today against its main competitors? The Foundation of the Flexographic Technical Assn. attempted to answer that question recently with Project Fog (flexo, offset, gravure).
The FFTA presented the project at its Annual Forum, held in Nashville, TN, May 6-9. “Project FOG” used six challenging jobs printed flexographically and compared it to the same jobs printed by lithography or rotogravure. A comparison kit was made available to judges as well as the FFTA audience, and the samples were rated based on the “visual appearance of print quality.” Although this comparison was subjective, the relative ratings clearly showed that flexography's quality was on par with conventional high quality printing processes. Flexographically printed samples used in Project FOG were difficult to distinguish from traditional lithographic or rotogravure jobs.
The most dramatic visual improvement demonstrated by Project FOG was the reduction of the characteristic “flexo halo” that has been associated with flexography since its early days as the “aniline printing process.” Among the factors that have made the quality competitive are advances in press design, anilox rolls, ink metering, printing inks, and photopolymer plates.
Perhaps for the first time, the case for flexographic quality as an equal to lithography and rotogravure was made convincingly. (For more on Project FOG, see PFFC, July 2001, p. 50.)
Solvents Still Entrenched in Film Sector
Water-based inks have a solid hold on the flexographic printing industry, representing about 65% of flexo inks in use, but they are more common in some areas than in others.
While use of water-based flexographic inks today is commonplace on paper, paperboard, and corrugated, solvent-based technology continues to be well entrenched in the film printing segment of flexible packaging.
While you can get a job printed with water-based inks without having to compromise on quality, running that job water-based may require a lower press speed and more careful attention.
Thus, in wide web applications where quality and high productivity are required, solvent-based inks still provide the best alternative.
In the narrow web sector, water-based inks can be more competitive as far as productivity is concerned, because print speeds are lower. However, UV flexo technology is proving to be tough competition for water-based inks in narrow web printing.
UV, EB, and Wide Webs
Although UV technology is being used widely in narrow web flexo applications, its penetration into the wide web sector has proved to be very difficult.
Wide web converting is used in food packaging predominantly, and there is a major effort underway by UV ink and equipment suppliers to penetrate this printing segment.
Radtech Intl. has worked closely with UV and electron beam suppliers and testing laboratories to see if they can alter the stalemate currently in effect regarding the use of this technology in the wide web food sector.
Two key interpretations relative to Food and Drug Administration status have been put forward that may help change the stalemate (see “Radtech Report,” September/October 1999, pp. 44-54).
One interpretation: If there is an adequate barrier, then noncompliant materials can be used since FDA status is not required. The second perspective: If the radiation-curable material in direct contact with food has extractables less than 50 ppb, then such materials are not food additives.
Whether the food and flexible packaging industry will embrace these interpretations is still to be determined.
Products and Trends to Watch
About a year ago, UV cationic technology was set back as analytical tests showed trace levels of benzene. Some printers switched to the more traditional free radical UV technology, but it would appear that interest remains in UV cationic technology, and cationic UV materials do offer advantages in film printing applications.
One of the most important recent events has been the announcement by Sun Chemical of an FDA-compliant EB coating for direct food contact. Unlike UV, EB-cured materials do not use photoinitiators and have extremely low residuals. Sun's product, SunBeam LE, is said to provide an EB-curable coating that meets compliance of 21 CFR chapter 176.170 by meeting less than 50 ppb under certain specified conditions. These conditions are an EB dosage of 2.5-3.5 Mrads with an acceleration voltage between 100 and 150 kV. Oxygen in the chamber has to be less than 200 ppm, and the coating thickness should not exceed 8 microns.
In addition to Sun's EB coating, Rhodia has developed a UV/EB epoxy-silicone release coating under the trade name Silocolease, which the company says is FDA-compliant by extractability data [“Radtech Report,” March/April 2001, pp. 26-32.] This is a cationic-based, radiation-curable release coating that can be cured by either UV or EB.
For some time, printers have been waiting to use UV-curable jet inks. Wait no more. Chromas has mounted an Argio 75 SC digital printer that uses UV jet inks on a narrow web flexo press.
Among the trends affecting UV and water-based ink technologies are the use of presses that utilize flexo, gravure, screen, and/or digital printing stations. UV technology is well suited as an add-on station to narrow web combination presses. This can be used to apply an overprint or to print digital information using UV jet ink technology.
Environmental concerns continue to reduce the number of raw materials that we can use. Chlorinated resin use is being reduced as concern grows about its degradation to toxic chemicals in the waste stream.
Use of chlorinated solvents as well as aromatics has been reduced greatly. This trend is likely to continue and may affect some of the pigments we are using currently.
One more trend worth noting: Due to the number of international mergers, consolidations, and strategic alliances in the ink industry, today there are fewer ink companies and fewer raw materials suppliers than there were a few years ago.
Sorting it Out
Quality, productivity, environmental concerns, economic considerations: What is most important to you in an ink technology? What are you willing to sacrifice? Do you need to sacrifice anything, or can one technology do it all? The answer to this last question is: Not at the present time.
Water-based inks dry more slowly than solvent-based or UV inks. This difficulty becomes particularly acute when printing on nonabsorbent substrates. Because of this problem, press productivity favors solvents and UV technologies.
Printers that have made the switch to water-based inks will continue to run with them, but I don't think solvent-based ink users are going to turn to water-based inks anytime soon. New technology in water-based products that would improve the press speeds or printability of films is needed to jumpstart water-based technology applications.
Quality demands are driving flexo gains. Use of high-viscosity UV flexographic inks has provided quality unmatched by either water-based or solvent-based flexo inks. Using UV technology, flexo not only can compete with rotogravure and lithography but also, in most cases, shows higher print quality characteristics.
VOC reduction in water-based ink formulation is continuing — whereas 5% was the target a few years ago, 2% or lower is the current target. The desire for lower VOC emissions favors UV, since this technology has the capability for very low VOC emissions.
With the door opening for the use of some UV/EB-cured products for direct food applications, with continued improvements in the flexographic process, and with UV technology making greater inroads, the flexo picture continues to change. And all of the changes point to a greater role in the converting industry.
Dr. Richard M. Podhajny has been in the packaging and printing industries for more than 30 years. He is the author of the monthly “Material Science” column. Contact him at 215/616-6314, e-mail: email@example.com.