Through the Looking Glass:Advanced UV Technologies Inside Every Day Products

By Dr. Gilles Catherin, Siegwerk, Siegwerk | 11.27.13

While we are drinking a glass of juice from a carton pack, a cup of tea from a metal tin or paying with a credit card, few of us would recognize the enormous R&D effort that has been invested in the associated ink and printing technologies

Alice in the Wonderland

Very few people, except of course Alice herself, can see all the “magic” hidden in every day life. Even less people might perceive the sophisticated technologies “inside” the numerous packages we use in our daily life.

Indeed, while we are drinking a glass of juice from a carton pack, a cup of tea from a metal tin or paying with a credit card, few of us would recognize the enormous R&D effort that has been invested in the associated ink and printing technologies. The result brings us these common, convenient, safe and attractive printed products.

Among the different available technologies, UV cured inks are more and more the system of choice. This is mostly due to their great formulation flexibility and hence, suitability for all printing techniques, substrates and end-uses.

Global travel and communication has developed a “global culture.” One sign of this global culture is that today, many people around the world start their day with a glass of fruit juice. That juice is likely to be packed in a carton made by one of the large international packaging groups.

However, only a small percentage of these “breakfast” consumers would understand the technology behind these attractive looking packs. The printing processes have evolved and developed tremendously over the years and now deliver high quality, multi-color images.

Flexography is often the preferred print technology. It provides high productivity while maintaining high print quality. UV curing is a frequently used technology, providing printers with high speed drying, excellent print sharpness and perfect adhesion on this type of PE coated carton.

However, the flexographic process requires inks with both high pigment concentration and low viscosity, creating challenges for the ink formulators.

For UV printed packages, these challenges have increased recently due to stricter regulatory requirements for food packaging, in particular relating to potential migration of raw materials and impurities into the food.

Studies have shown that chemicals from the print can migrate through the pack and into the food. To avoid any risk for human health, the threshold of migration for substances without an adequate toxicological evaluation cannot be higher than 10 ppb. This level is now easily detectable with new hi-tech analytical equipment such as GC/MS.

After a complex development, including the synthesis of new raw materials, Siegwerk is now one of the few ink manufacturers that has been able to meet the challenge of developing appropriate UV inks. These have low viscosity, high strength, low migration and are based on novel materials including “non migrating” polymeric photoinitiators and highly functional monomers.

But only few consumers would realize that its taken years of chemical research to develop these patented technologies. And thus, right across the world, people can enjoy a fresh and healthy morning juice from an attractively printed pack!

Toast and Butter for Breakfast

Whether it’s on a “baguette” in France, a bagel in America or simple toast in London, most of us enjoy having butter with our breakfast.

Due to the demands of globalization and distribution through supermarkets, the packaging structure of our butter (and similar products) has been transformed from its original paper/aluminum wrapping to the brightly printed plastic containers being utilized today.

Again, while casually spreading their butter on their toast, it wouldn’t spring to the consumers mind that, besides looking fresh and attractive in its pack, the butter label is not simply wrapped around the plastic, but somehow “integrated” into the packaging and hence non-removable.

Without knowing it, we are in fact using a sophisticated packaging technology, known as “In Mould Labelling” (because the plastic OPP material is injected into a mould, which already contains the printed label).

Naturally, due to printing onto a plastic substrate that has well known adhesion issues, UV technology is more and more the preferred choice, be it on a high-speed narrow web, offset or flexo press.

Similar to our previous “juice pack “application, the challenge for the ink formulator has been to balance adhesion on a difficult substrate vs. printability in offset and the risk of migration and/or odor contamination into the butter.

It is also noteworthy that due to the high temperatures reached during the moulding process and the ”greasy” nature of butter itself, the challenge, to minimize the risk of migration, is significant.

UV overprint varnish is often used to help protect the printed colors, although it adds another level of complexity. However, thanks to new technologies, our ink scientists have come up with a perfect “fit to purpose” ink that is robust enough to work without OPV. It combines the latest generation of “inert” resins for adhesion, together with highly reactive monomers and low migration photoinitiators.

Drinking Water Stays Healthy

It is widely accepted that drinking enough water through the day contributes to staying healthy. The adoption of this idea has been such that men and women, young or old, from all walks of life, can be seen drinking from their favorite bottle of mineral water throughout the world!

However, when taking a break to drink from our light and handy bottle, the effort taken to prevent off taste or odor being transferred to a sensitive product such as water is often forgotten.

Global brands packed in PET bottles are frequently transported over long distances. Naturally, to be compatible with the recycling of the bottle, the label has also to be a polyolefinic material, preferably mono-oriented polypropylene (OPP).

For relatively short runs, high-speed reel-to-reel printing presses have been developed and are commonly used. Formulators were faced with the challenge of creating an ink with perfect adhesion on OPP as well as fast drying speeds. Hence, the ink needs to be very reactive and not only compatible with the offset process with its attendant ink-water balance constraints, but also presenting no risk of migration of any of its components through the substrate into the water.

Unfortunately, real cases have indeed proven that inadequate formulations were prone to release some of their components, such as low molecular weight photoinitiators, through the bottle into the liquid inside.

To acknowledge the difficulties, we also need to consider that for water labels, other issues such as high opacity of the white in either gravure or offset printing is desired. This is not so easy to achieve without the potential problem that the highly pigmented white will be brittle and can crack during labeling. Anyway, it has been overcome and we can enjoy our preferred brand of water anywhere in the world these days!

Lunch Break – nything You Like... With a Simple Piece of Plastic!

A highlight of the day for people in many countries is the lunch break. Time to relax, socialize and enjoy good food. It’s made easy these days without even using cash from your wallet. The whole menu is available using the magic piece of plastic known as credit card.

Over the last 20 years, the use of credit cards has become so common that even in the most remote places of the world, few would realize that this has been one of the major technical developments of the 1990s, and continues to undergo constant evolution.

The first difficulty is related to the printing process itself when, as is very often the case, waterless offset is used. As any printer knows, water is certainly difficult to control on an offset press, but no water at all is even more of a challenge. Changes in the viscosity of the ink, related in particular to a change in press temperature, lead to a variety of printing issues such as smearing, greasing, dot enlargement, etc.

From a formulator’s viewpoint, this calls for particular attention to the polarity of the ink system and of its components. The high polarity of UV curable materials adds an additional obstacle.

The second major difficulty is related to the substrate. Normally PVC (or ABS) is used, which is known as one of the most challenging substrates for ink adhesion, in particular because of its very smooth and “closed” surface. Also, the card manufacturing process involves OPP film lamination on top of the ink. Consequently, the ink should be compatible with this process to avoid issues such as poor adhesion of the OPP film.

Fortunately, resin chemists have been able to build new structures combining both the right polarity and the functional groups needed to achieve adhesion and also lamination ability.

Thanks to them, we can pay easily for our lunch, everywhere in the world, and afterwards, do some shopping as well, with our magic cards.

Four O’Clock! Time for a Nice Cup of Tea!

The English habit to relax with a nice cup of tea at four o’clock sharp is now widespread throughout the world. Of course, real connoisseurs would never use tea bags but take fresh tea, often from a decorative metal tin reflecting the quality of the brand.

Of these connoisseurs, only a few would know that this tea tin is today more and more often printed by dry offset using UV inks instead of conventional oil-based inks.

One of the main reasons for this change is the economical benefits offered by a UV printed process, the printed sheets being instantly dried under UV lamps, rather than dried in hot air ovens. Using such a process not only lowers the investment cost of the equipment, but also reduces lead time through improved quicker production.

UV technology also makes the hexachromic printing process simpler, further improving process efficiency and allowing faster design changes.

For the ink manufacturer, the initial target was to develop an ink with fast drying, excellent adhesion to metal and good heat resistance. However, due to the diversity of shapes of the metal tins, including post print embossing, the ink film also needs to have higher flexibility to avoid cracking.

Of course, the dry offset process itself imparts specific demands on the formulator. Viscosity stability versus temperature and correct ink tack sequences when hexachromy is used are important factors to be controlled.

More of a surprise though for non-experts is the very demanding specification on low odor/low migration ink for metal tins. Although there is no risk of migration and little possibilities of odor contamination to the product inside, the tins should not produce an odor on the shelves of the retailer, which could taint other products.

Formulators have been able to capitalize on the developments in UV systems for food packaging; in order to meet these multiple challenges, developing inks adequate for metal printing: performing well in dry offset, suitable for post processing of the metal sheets and without residual odor.

Home Sweet Home!

No matter how enjoyable the work day, for most people, arriving home at night is a time to relax and enjoy. There are, of course, many ways to relax. Listening to good music whilst having a drink “on the rocks” must be one of the favorites.

When selecting the music, the music buff doesn’t reflect on the complex process that has created the attractive surface of a CD or DVD. These are made from polycarbonate, and then screenprinted with an opaque UV white ink and waterless UV offset colors.

Nor would they consider, when taking a luxury liquor box from the cabinet, that this pack is the result of very sophisticated print techniques and ink technologies. Indeed, in order to achieve the “luxury” appearance demanded by such products, metallic effects together with combinations of matte and gloss inks and varnishes often need to be printed on metalized polyester/carton printed in up to five layers.

The stringent demands of such liquor boxes, and similarly cosmetics boxes, usually means that sheetfed offset printing techniques together with UV inks and varnishes are chosen.

Again, after extensive research and development work, UV has been proven to be a perfect system for this demanding application, providing adhesion to the polyester (with a primer), and the excellent flexibility and scratch resistance needed to avoid any cracking in the folds of the box.

Needless to say, most of these products are shipped across the world. The appearance must remain perfect during this journey, demanding that the print withstands the mechanical strains and climate changes which occur during transportation.

Brand consistency is very important for these luxury items, the sophistication of the box being mirrored by the bottle label itself, calling for metallic and a wide range of other “special effect” prints. Printing metallic effects, opaque white inks, special effect inks, effect overprint varnishes, very fine texts and process prints on the same label and in optimum quality, has required the development of very specific presses, which combine several processes in-line such as screen, flexo, offset or gravure.

For the inks to overprint well on top of each other, achieving good lay, dot sharpness and color strength, the surface tension of each layer has to be fine-tuned.

It is well known to the ink specialist that the surface tension of any ink has to be significantly lower that the surface tension of the ink it is overprinting in order to achieve a good “wetting,” and hence good adhesion and print quality. At the “end of the day,” a lot of effort from formulators was needed to provide solutions for these high quality brands; their reward, bringing a touch of luxury to the daily life of the consumer!

Time for Bed!

The daily routine of showering, using liquid soap in a PE bottle printed with letterpress UV, followed by application of skin care products from embossed UV offset metal containers, before brushing one’s teeth with toothpaste from a metallo-plastic tube printed with flexo UV inks, are some of the final ways in which our daily life is made more colorful and convenient.

A fitting end to a day, during which each of us has been close to the “magic” provided by technology experts who have made all these “simple” products possible: a journey through the fantastic UV technology, thanks, in particular, to Siegwerk’s passion to make great inks with our “Heart & Soul”:

• “Ink” providing the know-how for optimum packing performances and quality at competitive costs.

• “Heart” developing safer products for the consumer, causing no deterioration to the packed food.

• “Soul” creating safer products for the environment, eliminating solvent and waste water emissions.

UV: a dream technology!

Dr. Gilles Catherin, engineer in chemistry and PhD in macromolecular chemistry obtained in 1979, is a real “Inky.” His career in printing inks started in 1982 with Sicpa. Within this group, he has been successively technical director in France, operational director in Asia-Pacific region, and general director for South East Asia. With Sicpa first and with Siegwerk as of 2005, he has organized the research activities and became vice president of innovation. His innovative ideas have made him the co-inventor of more than 12 patents covering different ink technologies as well as manufacturing processes. Since 2010, he works as a consultant to transfer his recognized expertise and knowledge.

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