Googling the two words Flexography and Growth generates a string of search results with short descriptions that claim flexography to be the fastest growing printing process on the planet. Clicking through, one website suggests flexography is forecasted to outpace their country’s (not China) Gross National Product, while another site shows the process to now represent around 25 percent of all printing volume in North America. Whatever analogy might be used to explain the relationship between flexography and growth, it is hard to argue against the perpetual potential of this printing sector.

Much of the success in flexography can be tied to the increasing use of Ultra Violet (UV) inks and more inline converting capabilities that are moving work away from traditional offset and gravure presses. And this is just a prelude to change, as another accelerator in the form of inkjet technology is about to be tipped into the flexographic mix. Interestingly, the accelerator can relatively easily become UV-curable inkjet. The printing industry is on the doorstep of a very powerful partnership between three of its hottest trends, which have been discussed for the past few years: flexography, inkjet and UV.

Breaking this trend down to be packaging specific, the hot topics of technology are Radio Frequency Identification (RFID, explained further in Joanna Liu’s Packaging Line column, Understanding RFID, page 22) and the global transition of converters and consumer packaging goods companies toward Ultra Violet and Electron Beam (EB) curing. This trend stretches across flexible and paperboard packaging to tag and label printing.

Inkjet stands as a great technology promise for packaging, but the speed is just not there yet for most major industry applications – it is close. Technology providers still need to firm up incredible advances in their inks and printheads, made all the more interesting by their decisions between an EB or UV curing platform.

Remember the electron beam

In the midst of this flexography and packaging excitement, which today even reaches the once dirty business of standard cardboard printing because of new wide-format, hybrid presses pumping out work, it is very easy to lose sight of a technological process that is 30 or 40 years old. This is the legacy of Electron Beam technology.

It was developed in a very scientific world, as electrons are generated at very high speeds and passed through accelerators and vacuums – creating a beam that can do many things like cure ink. E-beam first appeared as an extravagance of researchers (in a sort of 1970s mainframe versus desktop computer kind of way).  Equipped with vacuums, protective shielding and an enormous power supply, e-beam systems have traditionally been very large and, therefore stagnated commercially despite many advantages.

It was very hard – or would have initially cost too much in R&D – to compress all of this technology for use in other, specific-minded manufacturing equipment. But with advances in today’s technology, this has all changed. E-beam is not saved for high-voltage, power-company work. This 1970s technology is now a glint in the eyes of many inkjet technology providers who need to build curing processes into their inkjet packaging engines.

In this sector, EB presents a tremendous platform choice for the vendors, potentially even a better option than the marketing-driven UV-curable alternatives. The lure of UV is strong because of its near-instantaneous drying power (particularly important when dealing with fussy packaging substrates) and relatively low maintenance when run through inkjet.

There is also an upswell of goodwill to be found through UV’s environmental benefits in reducing Volatile Organic Compounds (VOCs). This is evident in the marketing material of any well-tuned UV supplier – from commercial printing to sign making. But, just like in the commercial printing marketplace, the benefits of particular curing in flexography technology are only as good as the clients it needs to produce work for. UV curing, for example, has some potentially troubling implications in the food-packaging sector, one of the best growing client bases for flexography.

While UV is a very good route forward to improve the reduction of particular volatile materials, the process does face real problems of migration before it becomes truly effective and universal in food packaging. The same concerns hold true for any type of packaging material that comes in contact with the human body or other types of living ecosystems that a client, public or standards committee might deem valuable enough to protect from chemical harm.

Because of the very nature of the UV inks, there have been recorded instances of chemicals migrating from a host product’s package into another product that it touches on the shelf (or wherever it might be stored in intimate proximity). So as advancing UV technology is purposely built to reduce VOCs or Hazardous Air Pollutants, this migration problem is an unacceptable risk in the product environment for many brand owners.

The problem of migration for Ultra Violet curing arises because the process requires some form of photoinitiator. All inks, regardless of their purpose, are created as a polymer (more directly called a monomer or ligomer, depending on type). With UV inks, the photoinitiator is part of this polymer mix because it is needed, basically, to catch the photons of UV light distributed by the curing unit. As the photoinitiators in the ink catch the photon light, it creates a chemical reaction within the polymer. Put more simply, UV light shines on the ink, the photoinitiators capture energy and convert it into a chemical reaction.

Although this is somewhat technical (and at the same time a very basic explanation), the concept of how UV ink captures energy is very important for any printing company to understand if they plan significant capital investments to be made around UV inkjet with the purpose of capturing more clients in food packaging (or any other non-migration preferred application). This is because the photoinitiators – the energy catchers and, therefore, also the energy seekers – are the very chemcials that tend to migrate into other packaging.

In a food environment, the photoinitiators can also migrate out toward and be attracted by fatty material because they are sources of energy. It is a very difficult process to permanently stick these UV-enabling photoinitiators into the ink of a printed package. The level of migration really depends on the degree of reaction completion during the UV curing process. This is because the UV source, assuming it is generated from above the passing substrate during production, would cure the ink from the top, downwards. Accordingly, the more cured areas of a package are found on the outside of the ink (the portion that is readily visible), while the inside might not yet be cured.

Technology vendors in the UV inkjet marketplace are working to formulate inks that cure all the way through. In fact, UV ink only needs to attain a certain level of reaction to ensure no chemicals will migrate out. Again, these UV inks are not easy to formulate (See Toxin Guard sidebar for an interesting Canadian solution to UV ink migration). Another problem facing ink reaction relates to the power supply from the UV lamps, which can fade over time without the operator becoming aware. Of course, measurement systems can be put into place to carefully monitor a fadeout effect, but, put together, these potential UV problems present a very viable window for EB-curable inkjet in several packaging markets.

Back to EB

As the name suggests, this technology basically fires electrons into ink as opposed to the photons fired through a UV curing process. Because there are no photons being fired into the ink to cause the reaction, the use of photoinitiators is unnecessary. Just like that, E-beam has solved what many would describe as the largest concern today around chemical migration.

Secondly, the slower way in which EB works is seen as a more sound process for applications like food packaging. This may seem counterintuitive when so much of UV’s benefit is expressed through its ability to dry even the toughest substrates so quickly. In other words, the photons are absorbed so quickly by the UV ink. Because electrons are not absorbed as fast, it also means that they are able to travel much further into the ink formulation. This allows the EB to more evenly cure the ink, from top to bottom, before being absorbed, giving brand owners more confidence that enough ink has reacted so that chemicals will not be moved.

EB-curable inkjet also brings another major advantage to food packaging, in terms of gaining chemical reaction confidence, in that the technology does not vary as much as UV energy sources. EB gives out a constant level of power output. Often EB machines – at least the good ones – will shut down if the power level falls off by a predetermined level. The same safety measure can surely fit a UV machine.

While UV is certainly a very sound technology, it must be applied properly and perhaps with extra precaution than other processes. It is, after all, Ultra Violet – a tough combination of words to associate with bettering the environment. It certainly has the ability to do just that in the printing environment, and, of course, it is a very safe technology when built and used with enough knowledge. And there is certainly enough wisdom out in the world wide web to indicate UV-curable is as viable an inkjet avenue as EB-curable in the packaging world.