Foiled by Foil

Foil is a popular addition to packaging, but it has a few converting/printing quirks. To help solve common foil woes, pP recently went to foil suppliers seeking solutions.

FOIL STAMPING HAS become a necessary capability for printers and converters to have. The substrate graces packaging in every market, and more and more consumer product companies are redesigning their packaging to include foil.

Nowadays, if printers and converters don't have foil stamping equipment, they are positioning themselves to lose new and old customers.

"With more and more customers using foils for their labels it is more important than ever that a printer is able to apply foil," said J. Michael Rivera, vice president of sales, AMAGIC Foils. "Foil application is now such a standard in the industry that a printer can no longer compete unless they have this capability."

Many printers already know this and have been proactive in adding foil stamping to their operations. But even with the prevalent use of foil decorating throughout the package-printing industry, foil has become easier but, under certain conditions, more complex, said Sam McElree, product manager - Graphics, KURZ Transfer Products.

On simplification, he said, "Foil decorating has become more of an everyday job rather than a special, less frequent run job. This allows converters and foil suppliers more opportunities for better communications to improve the efficiencies of their operations."

However, with the rising demand for quick turnarounds, printers and converters can create some potential pitfalls to the foil stamping process. McElree added, "Increasingly shorter lead times from printers and converters can lead to foil stamping over inks or coatings that are not fully cured or dried. Also, new coatings are being used on substrates before evaluation has been completed to determine the proper surface tension required for foil stamping. An ideal surface tension for foil stamping would be a dynes level of between 36 and 42."

Both of these issues can be troubling for printers and converters, on top of the normal problems they face. Luckily, there are easy fixes for these blunders and, to simplify the rectification process, packagePRINTING recently asked foil suppliers to help provide solutions to the most common foil stamping woes.

Adhesion, or lack of

In order for foil to enhance a package as it should, it needs to stick to the substrate, and the inks and coatings need to stick to the foil. But the make up of most foil and printing materials can make it hard for them to adhere to each other.

Waxes and silicones are used in the formulation of foil release liners and printing inks and coatings, and create adhesion problems. Poor adhesion means foil blistering, pickouts, and voids in the stamped impression—none of these impress customers.

Overprinting: With overprinting foil, Rivera said, "A lot of labels today require the use of silver or holographic foils with inks printed on top. The main examples are the Colgate Simply White and the Listerine mouthwash. Due to this new trend, today's foils must be over-printable with either water-based or UV-curable inks."

Many problems stemming from overprinting foil lies in the wax and silicones used with the foil release liner, which makes it hard for water-based or UV-curable inks to adhere well. One solution is to apply a primer before hot stamping foil or to forget hot stamping altogether and use cold foil printing, Rivera said.

"Problems with printability can either be resolved by applying a primer before the hot stamp foil or by the use of the cold foil printing process. The foil formula used in the cold foil printing process uses a minimal amount of wax and silicone, which makes the foil more printable as compared to hot stamping foils," he said.

If hot stamping is the process of choice, Richard Zeller, of ITW Foilmark, recommended a few other options. First of all, he said, printers and converters can lay a primer coat over the foil, which increases the surface energy of the foil, allowing for greater adhesion of the UV inks and coatings.

Secondly, using foils specifically designed for overprinting will help, too. These foils "provide a high surface energy that will provide a print-receptive surface," he said.

This also goes for the inks. Using inks formulated to adhere to hot stamping foils will have the appropriate properties needed to adhere to such a substrate, Zeller said.

Foil over print: The key is to make sure the inks and coatings are completely dried prior to foil stamping, McElree said. In addition, he suggests using inks and coatings that are wax-free.

Another way to combat the problem of foil blistering associated with laying foil over UV-cured inks and UV flood coatings is to use hybrid inks or try blind stamping, Zeller said.

If adhesion turns out not to be the root of the problem, voids and untransferred foil can also be the result of dirty or damaged dies, McElree said.

If all else fails, check the dies and keep the press up to manufacturer's specifications, he said.

Get the logistics right

Customers want their jobs turned around as quickly as possible. It'd be a simple solution if printers and converters only had to run the press faster in order to meet their customers' requirements.

But press speeds have a direct effect on how well a foil stamping unit functions, and if operators are only concentrating on speed and not paying attention to other logistics like the temperature at the surface of the die and web tension, the job will most likely end up in the scrap heap.

Speed and heat: Speed is a tricky issue, Rivera explained. "As always, speed has been a big issue especially when foil is applied on-line on a flexographic press. Since flexographic presses have a tendency for erratic registration tolerances at speeds lower than 125 fpm, a rotary hot stamp foil must be able to transfer at speeds higher than 125 fpm.

Low running speed on a rotary hot stamp machine is typically a result of the inability of the rotary hot stamp die to be able to regain enough heat after each rotation," he said.

Managing the temperature and pressure are issues that relate to speed. According to McElree, "Too much heat tends to dull the metallic finish [of the foil]; too little will cause incomplete foil transfer. Too much pressure will cause a distorted or debossed image and too little pressure will also cause incomplete foil transfer.

It is always better to check the temperatures at the stamping die surface as the indicated machine temperatures may vary from press to press. Temperature and press speeds are interrelated. If you increase your speeds significantly you will have to also increase your temperature to insure that the proper foil transfer temperatures are maintained at the higher speeds."

Web tension is another area where, if appropriate logistics aren't used, it creates problems for printers and converters. Improper web tension causes wrinkles and creases in the image area, McElree said.

This problem is easily fixed. McElree suggests increasing the rewind tension or brake tension on unwind to straighten the web path.

Looking forward

Despite the wide range of problems associated with foil stamping, many of these issues can be headed off before they occur through more testing, communicating, and development systems between suppliers of foils and inks and coatings, Zeller said.

In addition, recent advancements in foils are helping eliminate many of these common foiling woes. McElree points to better quality foils that can be run at optimal processing speeds on today's high-speed foil presses.

"This follows the trend to more inline operations where printing and foil stamping, both hot and cold, are done inline," he said.

There's also been progress in cold foil stamping systems, which helps make it a viable option to hot stamping and helps eliminate the problems associated with hot stamping.

"Although cold foil printing has been around for many years, in the past, only few printers have been successful. With the advent of the wet lamination (cure-through) cold foil process, cold foil is now commercially available. It has enabled many printers to enter the foil market with minimal investment. It has also enabled printers to apply foils on applications that are otherwise impossible with a conventional hot stamp process. One example is the foil application on a shrink sleeve label. It is by far the most significant advancement in the foil decorating industry," he said.

by Kate Sharon

Associate Editor