Thin Is In

Driven by brand owner desires for lower costs, thinner substrates—some just 23 microns or thinner—have become increasingly common on the presses of many converters. On one hand, thinner stocks can reduce material costs, require fewer reel changes, and can decrease waste and reel weight. But thin materials can also pose difficulties for converters when it comes to diecutting and trimming.

"As stocks become thinner, the operating window for diecutting becomes smaller, especially as you consider the separation of the waste matrix," says David Morris, president of Kocher & Beck. "But a lot depends on the nature of the facestock and the adhesive. Typically with papers you require a bursting action and the blade doesn't need to penetrate fully though the material to allow clean matrix removal, while synthetics require a full clean cut without damaging the liner."

Many customers don't want to see any evidence of marking in the liner, fearing that a weakened liner can cause problems when the label and liner are separated as the label is applied to the product. "To address this, label converters are seeking to make the absolute minimum impact on the liner," affirms Morris. He notes that the application—separating the labels from the supporting liners—must work as well as possible, so the cut must be clean and accurate.

"Waste is another concern," adds Wade Fouts, vice president of sales at Wilson Manufacturing. "Being able to set up and run a thinner stock with accurate cuts and minimal waste of time and materials is important for a converter."

Another factor that can make diecutting challenging is drying lamps, which can soften substrates and adhesives, resulting in matrix separation issues. Familiarity with substrate characteristics is critical here, as is operator skill in optimizing the press for a particular application.

Speed presents another challenge because thinner stocks can be harder to cut if run at the same speed used for thicker materials. While a press cannot be significantly slowed and still maintain adequate throughput for a given job, an increase in the repeat and a modest speed reduction may help thinner stocks cut and strip more easily and reliably.

Where the die meets the anvil

Yet whether the substrates are thick or thin, standard or customized, and whether the job is difficult or simple, much of the success in diecutting challenging substrates still comes down to some basics: the condition of the anvils and dies. "Whether the die is solid or flexible, the cylinders, anvils and dies all have to be well maintained and in excellent condition," affirms Morris. "Otherwise the operators will be fighting a losing battle of control and be struggling to achieve an accurate cut."

Fouts agrees. "Diecutting depends on very exact pressures and that means a sharp die and an anvil that offers a good surface beneath the liner stock," he says. "And anvil wear results in an accumulated error over time. Anvil condition is especially important for thinner stocks, and problems will show up much sooner if the anvil is worn."

Converters all know this, but these components are not always as well-maintained as they should be. Dies, both solid and flexible, are a highly visible part of the process, right out in plain sight, and can be different for every job. What converters often underestimate is just how often they need to be sharpened or even replaced. Although a die can usually be sharpened four times before it is worn out, there is no clear rule of thumb. How long a given die can go before needing sharpening varies due to run lengths, repeat length, substrates used, anvil condition, and overall press maintenance. "Still," notes Fouts, "we have more dies come in for repair due to damage than for sharpening due to wear. These are delicate pieces of machinery. You can't just throw one around like it's a Craftsman wrench."

Because anvils are less noticeable it's easy to assume they will continue to perform well. But they do wear, resulting in difficulties, especially on challenging substrates. Fouts relates how one converter was always sending in dies for resharpening, even though Fouts told him the anvils were really the problem. When the customer finally ordered new anvils, he found he was spending far less money on die resharpening. The moral of the story is that if you harbor any doubts about your dies or anvils, have a technical rep from your supplier of choice inspect them and alert you to any weak points so they can be addressed before a difficult job goes on press.

The bearers of success

Another key factor—and one often overlooked—is lubrication. You wouldn't run your car or truck without proper lubrication and a flexo press is no different. Even though the bearer bars (also called bearers) on both rotary dies and anvils are under constant pressure, it is not uncommon for flexo presses to be run without sufficient lubricants on these critical surfaces. The resulting heat and pressure puts enormous stress on the bearer surfaces causing excessive wear, unpredictable cutting, waste of unacceptable finished product, and costly replacement of both die and anvil rollers (and possibly servo motors). It happens like this: when a die is not cutting correctly an inadequately trained press operator may increase the pressure on the die. The cut may improve—temporarily—but the added pressure increases the dynamic load and heats up the bearing surfaces. This can bring the rollers to the point at which they no longer function properly. Then, when they are sent out for servicing, the converter gets the sad news that the costly parts are worn beyond repair due to a simple lack of lubrication.

Ask questions

Both Fouts and Morris encourage converters to take advantage of the expertise offered by the various suppliers, from press vendors to die suppliers to ink companies and more. "Have a good line of communication with your suppliers," encourages Fouts. "If a converter knows they are going to be taking on a difficult job they should paint a real clear picture of the work with their die and press manufacturers who can then advise them how to get the best results." Tapping this external knowledge resource will be increasingly important as even thinner substrates come to market such as those in the 10 to 13 micron range.

When asked, suppliers are eager to share their knowledge to help a converter run a challenging job successfully. "If converters are unfamiliar with a substrate or will have to make a difficult cut, we encourage them to send us samples of the materials," says Morris. "Then we can test it and make recommendations." Die makers can also recommend the right type of die for a given job or substrate to help ensure optimal results.

Still, some converters won't take advantage of this readily available resource, perhaps in part because of the added time required for off-site testing. Yet, there are shops that won't send a die supplier 25 feet of material to test but are willing to waste several times that much doing their own testing. To be fair, some shops may possess the necessary expertise, but there's also no shame in drawing on a supplier's knowledge to help ensure a job will run correctly. Moreover, suppliers want to see converters succeed. They understand the pressures of tight turnaround times, the demand for less downtime, and that smart converters want to be educated on the nuances of converting and be better equipped to educate customers.

Press makers are working to ensure their systems are solid platforms for the ever more demanding needs of brand owners. Similarly, die manufacturers are making extremely accurate dies that can work with thinner substrates. Materials that seemed all but impossible to run just a few years ago are now business as usual. As converters work with suppliers and pay attention to all the details, runs requiring diecutting on even the most demanding substrates will just be another job to finish and ship out. pP