Electron Beam Curing in Graphic Arts.
Initial acceptance was held back by the standard reluctance to jump into a new technology and several other justified reasons as hindsight shows. Initial beams had many flaws that are now, for the most part, addressed with current technology. The reliability of the initial beams was poor. Downtime was significant due to this. The overall size of the initial units was also a consideration.
Certainly one of the largest problems with early beams was the cost of the units. For a printer to put down a million dollars for an unproven drying technology was a daunting task in the mid-'70s and perhaps just a bit foolhardy.
None the less, at least one gambler anted up and the birth of EB curing took place. It was not until Tetra Pak installed EB curing units on web offset presses around the world that EB curing really was accepted as a way to convert packaging. This endeavor also assisted in getting energy curing accepted in the food packaging market.
Today, with newer systems, reliability is no longer an issue, the cost of the system is significantly reduced, the size of the unit is a fraction of what it once was and the overused phrase "user friendly" can truly be applied.
EB and Graphic Arts
Although many other applications have accepted EB curing and have contributed to the growth, one of the mainstays of the technology has been in the graphic arts industry, where the use of EB curing to convert inks and coatings continues to grow and find new applications.
EB curing started in the web offset area and continues to have a strong following, with several new installations going in yearly. This has been a natural in many ways since the press design and general appearance does not significantly change. In conventional web offset printing where a drying oven is used, the oven sits at the end of the press and removes the solvent from the ink.
EB curing offers the same general configuration with some significant advantages. Evaporation of solvent from a heatset ink requires a thermal oven to "cook" the solvent out of the ink film. The typical thermal input required is a web temperature of 250[degrees]F to 260[degrees]F. This temperature limits some of the substrates that can be used. The drying oven must also be long enough to allow sufficient dwell time for the solvent to move through the ink film to be driven off. After the web is heated to drive off the solvent, the web must be cooled so that it can be handled. This requires a series of cooled rollers called chill rollers.
Both the drying oven and the chill rolls require significant amounts of energy to run correctly. With EB curing, there isn't any need for this. More importantly, the solvent is eliminated since EB inks and coatings do not contain solvents. This leads to the elimination of the required "end of pipe" pollution control equipment which is required in heatset printing.
The EB unit also provides a smaller footprint than does the chill roll and oven. This leads to a shorter web path and provides for a significantly lower waste of paper, a simpler web path and faster re-webs.
Paper shrinks in an oven due to the heat. The lack of heat in an EB unit can result in a 0.6 to 0.8 percent savings on paper cost since a narrower paper can be purchased.
This may not sound like much, but when you are purchasing millions of dollars in paper, the resulting savings can be sizeable. Let's take a typical M-1000 web heatset press. In a typical 12-hour period the press will consume 24 rolls of paper or about 48,000 pounds. This is equivalent to 48 tons of paper per day or around 17,000 tons of paper per year. (So much for the paperless age!) If this paper is coated paper, it is currently selling for around $900 per ton, and if it is uncoated, it is selling for around $750 per ton. Doing the simple math, this works out to $15.3 million for coated paper and $12.8 million for uncoated. At 0.8 percent savings, this is $122,000 for coated paper use and $102,000 for uncoated paper use.
EB curing also offers some unique possibilities in food packaging applications.
EB cured inks and coatings provide very high performance with very low odors and extractables. It is not that other technologies can not deliver similar results, but EB curing offers the ability to do this with a wider process window and good economics. Fugitive solvents do not exist since solvents are not a part of the formulations. The ER curing reaction is an addition polymerization. This means that the molecules link together as opposed to being "spit out," as happens in some other reactive processes.
Areas for Growth
In sheetfed offset printing, EB technology has not found a niche. Part of this is due to the cost of the units and part of this is size. The inerting of the curing chamber also presents a challenge to the use of EB curing in sheetfed printing. It would not appear to be an easy task to convey a sheet into and out of an inerted chamber. How do you handle the sheet without losing considerable amounts of nitrogen? It is much simpler to accomplish this with a web but that is a challenge for the engineers to figure out.
Even with UV curing, which currently fits well into sheetfed printing, the market has not totally embraced the technology. This is despite the advantages that UV curing offers: instant drying, interstation curing, dry trapping and high resistance to scuff and abrasion. As in other printing processes, ER would provide curing which is independent of color and film thickness, unlike UV curing. This would certainly be of benefit if ER curing could be economically adapted to sheetfed printing.
Although flexographic printing is a web process, ER curing has not been able to penetrate this market since the very fluid inks are currently dried between the print units. There are some applications where the coatings applied over the inks are cured with ER curing. These applications have often moved to ER curing once that it was found the UV cured product was not sufficient. New applications combining both UV and EB curing are being implemented in flexography. In some flexo applications, UV is used to set the inks and EB is used to cure the coating and finish curing the inks. This provides finished properties which UV alone can not duplicate.
Gravure printing has also not readily embraced EB curing. Several units have been installed on gravure presses over the years for curing coatings but the technology has not moved much beyond a few tentative forays. Again, since the inks are dried between units, the use of EB has not penetrated the ink curing market. Another difficulty has been that ink technology has previously not been available to offer the low viscosity needed for this printing technique. This situation with ink technology may change as advances in vehicles and monomers continue to increase formulation flexibility. Whether this will present opportunities for EB cured gravure inks remains to be seen.
Typical screen and letterpress printing have not seen EB curing in the market due to the size and nature of the presses. Although it would appear unlikely for ER to find a niche in these applications, market needs may change and afford an opportunity.
The use of EB curing to crosslink coatings is applicable for any web application. This would include offset, gravure, flexography, letterpress and even screen applications. It all depends on the end product requirements and the economics of the application. As pollution abatement issues continue to pressure industry; applications for energy curing will continue to grow. EB coating technology offers many unique properties compared to solvent-, water-based and UV curing materials. In some cases, EB coatings can actually replace laminated structures to not only offer better economics but also provide for more readily recycled products. As the cost of EB units decreases and the formulations become more cost-effective and technically robust, the use of electron beam curing will continue to grow.
Currently, EB is a viable and growing technology in many markets. Further applications will continue to be found as printers seek methods of improving their products or processes. The EB unit is being miniaturized and the cost of the equipment is being reduced. Ink and coatings technology is improving relative to existing deficiencies. Newer technologies are approaching such applications as food packaging, which were thought to be impossible just a few years ago due to the FDA issues. Extractables are approaching the deminimus level and may actually comply with FDA regulations in a few years.
One major area that would certainly help market penetration would be improvement in the economics of the chemistry. Lower costs always seem to sell better. There have been improvements over the years but further improvements are needed. With all the positive attributes relative to performance and environmental issues, better economics would make the change over decision very simple and would accelerate the acceptance and application of EB technology.
Current barriers are only challenges to be conquered by future thinking innovative scientists. If a market need is truly out there, I have no doubt that someone will find a way to meet it.
Anthony J. Beans manager of energy curable inks at Sun Chemical Corporation. He holds three patents in energy curing and has published several books and articles on energy curing. He is also a member of the RadTech International Board of Directors and is a National Association of Printing Ink Manufacturers' Printing Ink Pioneer Award recipient. Mr. Bean presented this article at RadTech 2000 in Baltimore, MD in April.
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|Author:||Bean, Anthony J.|
|Date:||Jun 1, 2000|
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