Applying adhesive to the web in stripes, patterns or spots can open up new markets to converters.
By Jack Kenny
Running pressure sensitive label stock through an inline press requires a fair amount of skill. It’s a task that thousands of operators around the world do every day with ease and precision. They know the sound of the press when it’s running well, they watch ink delivery to plate and from plate to paper or film, and they check registration constantly. They monitor the diecutting and the rewind, flag the occasional flaw, and keep and eye on the unwind as it heads toward roll replacement. A more advanced operator will work a moveable rotary screen head or any number of press add-ons.
Now add something that makes the inline press a bit more complicated: adhesive. That brings in a new set of skills for any operator.
“It’s an entirely different technology,” says Tom Spina, president of Luminer Converting, Lakewood, NJ, USA. Luminer specializes in custom converted products, many of which make use of multiple webs with pattern and spot adhesives.
“A good press operator has experience in high quality printing, ink control, laminating, and many other aspects of printing. Add adhesive application to that mix, and now you’re putting in an entirely foreign operation that he or she now has to watch over. It is physically quite temperamental. There are stresses on both the operator and on the press; register control is one example. The entire production philosophy of the press operator changes by throwing in adhesive application,” Spina says.
“It’s likely that you want to sandwich the adhesive between two webs, so you have created a multiweb press, and that requires expert handling,” he adds. “The bottom line is that you need a mechancially talented person, a high level person.
When a label printer buys stock with adhesive on it from a supplier, Spina says, he relies on that product to meet specifications. “Though we all do QC tests on material when we buy it, we are counting on the supplier to give us a product that will physically perform.
“But when you are applying your own adhesive, now you have to worry about creating a functional label and whether it will apply properly. Is it the right adhesive? Is it the right quantity? All of those issues questions, and more, have to be answered. This is an area that requires operator complexity as well as scientific complexity.”
Once the practice of applying adhesive to a web, or webs, is mastered, advantages can be found. “It’s a way to open markets, and market segments,” Spina notes. “A lot of jobs require adhesive application, and if you can’t pattern coat or adhesive coat in line, you can’t take the job.”
One method of creating a form of pattern adhesive is called “adhesive deadening,” which involves separating the pressure sensitive web from the liner, applying a varnish over parts of the adhesive to create a dead area, and putting the web back together. “It’s not the best way to create a non-adhesive area,” says Spina. “You’re really just hiding the adhesive. When you get into putting the glue onto the substrate, you are creating a true pattern coating. That is definitely a niche.”
Adhesives are ranked in various degrees of performance, of course, such as permanent, removable, freezer grade, and so forth. Each of these can be had in various physical forms, such as hot melt, which is a solid; UV curable, also a solid; and water and solvent based adhesives, which are liquids.
The liquid adhesives require drying before they move to the next station in the press, whether for printing or diecutting or any other treatment. This can involve a major investment in hot air drying systems, which can require many feet of space for the web to travel to ensure that the glue is completely dry.
Hot melt, on the other hand, is melted in a unit on the press and cools on its own. This glue, which will dry on its own at room temperature, is customarily passed over chill rolls so that the heat generated during the adhesive application process is not transferred forward through the press to cause other problems.
Form Flo offers a slot die applicator, right, and a hot melt supply unit, left.
In slot die adhesive application, the melted adhesive is forced out from a reservoir through a slot by pressure, and transferred to the moving web. The slot is generally oriented perpendicular to the direction of web movement. The die itself is close to the substrate but separated from it by a cushion of the coating material. Slot die coating can be a fairly clean process, because the entire liquid flow path is sealed against the environment until the adhesive meets the web.
Edward D. Cohen, a web coating specialist and author of the Web Coating Blog (www.webcoatingblog.com), gives five reasons that slot dies are advantageous.
“First, it offers a closed delivery path. Unlike many coating processes that are open to atmosphere, the slot die process provides a more sterile environment, minimizes evaporation, reduces solvent discharge and prevents contamination from air borne particles.
“Second, a pre-metered application in the slot die process affords uniform, consistent coatings, unlike processes that wipe, spray or blade to spread coatings on the substrate.
“Third, it is fairly easy to change the width of coatings with the slot die process, as well as apply machine directional stripes of coated and noncoated areas. Today, this process can even apply patches of coated areas in the cross web of the substrate.
“Fourth, multiple cavity slot dies are used to apply different layers of different fluids to the substrate in a single coating station.
“Fifth, a slot die, in many cases, can be designed to process a broad range of viscosities and percent solids. These can typically handle a fairly wide range of coating speeds and fluid delivery flow rates.”
ITW Dynatec, based in Henderson, TN, USA, is one of the major suppliers of adhesive applicators to the narrow web industry (among many others). Ken Faulkner, the company’s label market specialist, says that most labels produced using applied adhesive are custom designed.
ITW Dynatec’s Apex high speed intermittent slot die
“If I’m working with a label manufacturer whose sales force wants to make specialty labels, I will talk with them about everything, such as where the applicator goes on the press, what the various ranges of slot dies are, installing, maintenance, and so on. This type of production is not beyond the small label house’s capabilities. It started out in the small label houses.”
Faulkner said that Dynatec’s first customers in the label business were buying butt stock, “and they had a small press and would coat inline and make label stock; they would buy liner, buy hot melts, and devise their own melters. We have expanded on that by offering bracketry and coating stations with chill rolls and various things that make it easier to fit.”
ITW Dynatec’s Dynamelt uses less energy than conventional equipment by heating only the adhesive in the lower portion of the hopper, thereby reducing energy consumption.
Faulkner is directly involved with press operator education. “Normally what I do is quote them two days of startup assistance. Some press operators really don’t desire this, but others are willing. They look at it as something unique, as a skill that offers them some job insurance.”
Adhesive can be added to printed or converted material at the end of the run as well. Form Flo Equipment Manufacturers, based in Phoenix, AZ, USA, makes a variety of folders, sheeters, collators and other equipment that treats printed materials on the way out of the press. Sales Manager Jeff Johnson says that the company also supplies adhesive applicators.
“On our collators and special transport systems there’s a lot of label application, so the converter wants to put glue down for those labels. We can set it up so that it uses either hot or cold glue systems,” says Johnson. “These can go cross web, with the web, in a constant solid line, a dot or a dash, circles or squares.”