Imagine a label that has no release liner and requires no application equipment after it is converted. Imagine that the label is part of the container itself, sealed right in there, ready for filling. Procter & Gamble imagined such a label back in the 1970s and set out to create just such a product.
The giant consumer products company teamed up with Owens Illinois, the packaging and container company, and with Multi-Color Corporation, a Cincinnati label converter, to develop a blow-molded container with the label incorporated into the bottle during the blow molding. Thus was born the in-mold label, or IML.
Though the IML process has been around for the past quarter century, production of the labels has remained in the hands of relatively few printers and converters. Multi-Color, still a leader in the field, devotes about half of its production to in-mold labels (See the Narrow Web Profile on Multi-Color on page 32 of this issue). NorthStar Print Group, based in Watertown, WI, is also a prominent IML producer. These two companies utilize mainly the gravure printing process for their IML work, though both print the labels on flexographic presses as well.
In-mold labeling was introduced during the era of the long press run. Consumption was high, brand awareness was ever more important, and the marketplace has not yet embarked on brand diversity and micro-marketing that gave birth to multiple SKUs and the short runs that emerged during the 1990s. A product marketer with, say, a household laundry detergent was going to buy millions of labels that were all the same, so why not skip the pressure sensitive labeling application process and go with in-mold?
Today the IML market is in the process of change. Demand remains, though the customer environment is shifting somewhat.
"Some things have happened — what I call recisions — in the IML market," says Ron Schultz, president of RBS Technologies (Scottsdale, AZ) and a consultant in the IML industry. "A couple of well known in-mold label users have reverted to pressure sensitive for a variety of reasons. About two years ago, SC Johnson went back to pressure sensitive, claiming that IML was not as flexible as they wanted it to be. So they are now applying their labels in-house. One of the blow molders built a plant near Johnson's property and supplies them with a library of blank bottles, so they do their labeling themselves to control and cut off runs any time they want to.
"The other is Procter & Gamble's Pantene shampoo line, which had used IML and is now pressure sensitive. The main reason that we see is that they have increased the number of SKUs to such an extent that no single SKU has a run long enough to justify IML."
|NorthStar also won a PLGA award for this paper label.|
"The market is not less in terms of size, though it's certainly not a growing segment," says Richard Gasper, president of NorthStar Print Group. "In gravure, as we see shorter and shorter runs we continue to look for ways to try to bring the long set-up times and costs associated with cylinders more in line with shorter run volumes. As that occurs, it does open up opportunities for people to consider in-mold for run lengths that in the past have been viewed as too short for IML.
"As we see it, the market is probably growing in the 3 to 5 percent range, fueled by the continuing introduction to market of new products. In supermarkets, where detergents and other household chemicals are sold, it's unbelievable the types of products that are coming out. When Procter & Gamble and Unilever introduce something new, they tend to gravitate to the IML arena."
Blow molding vs. injection molding
In-mold labels must be constructed to withstand a beating, perhaps several, during the bottle formation process and the filling and packaging that follow. Most pressure sensitive labels are applied to packages after the bottles have been filled, so that they usually go right into the box for shipment. The IML, however, joins its container at the beginning of the process, then moves on to the filling stage, then to clean-up, boxing and shipping.
There are two types of molding: blow molding and injection molding. In North America, blow molding predominates at about 95 percent of all IML production. Most of the IML products in Europe — about 80 percent — are formed through the injection molding process.
"Blow molding is bottles — packages that hold liquid products," says Schultz. These include laundry products, juices and personal care products. Injection molding is for open-top tubs.
In Europe, the bulk of products sold in injection molded IML containers are dairy foods in one form or another, Schultz adds, such as cheeses, margarines, sauces, and so forth. "In Europe these are considered highly upscale and can command the slightly higher cost of IML. In the United States, on the other hand, dairy products are commodities. The consumer expects to get the largest quantity for the best price, and the decorating is at the lowest cost that will do the job."
Europe, with many small countries and a host of languages, is known for its short runs. "And Europeans are pickier about their products," Schultz says. "They don't like blow molded IML. Things are tolerated here that they won't put up with there. Orange peel on a label is a no-no there, but here people will put up with it. Also, you can often see the imprint of the vacuum port, which holds the label during the process, through the label. Europeans are extremely fussy about that. The end users, the manufacturers, in the US will say 'OK, a little orange peel and vacuum port isn't a problem'. Over there it is." The Europeans utilize an electrostatic process to hold the labels in place during the molding process.
|A high diecutter, such as this one at Multi-Color Corporation's plant in Batavia, OH, is the most popular cutting method for in-mold labels.|
IML labels are complex products. Most these days utilize film substrates. On press, inks are applied in the customary fashion, and protected on the surface with a top coat that can be UV or EB curable, or solvent or water based. On the back of the label is a chemistry that acts as an adhesive that is triggered during the molding process. "In blow molding, the label requires a heat seal layer on the back, whether it is a converter-applied liquid type heat seal or a co-extruded seal applied or incorporated into the film during the extrusion process," Schultz explains. "It must be a layer that can fuse to the bottle during the blow molding process. That's true of polyester bottles as well as of varieties of polyethylene and polypropylene.
"Injection molding utilizes polypropylene film, and the containers are also polypropylene. Because of the high temperature and pressure involved in the process, the label fuses to the container without the aid of a heat seal."
"The adhesive can be either water based or solvent based," says Gasper. "Some materials come with the adhesive already applied. We apply a lot of it right in line ourselves."
During the molding process, a label is removed mechanically from a magazine and inserted into the mold, held in place by vacuum. The plastic is then injected into the mold to form the bottle. The heat seal is activated and the label then becomes a part of the container.
"The plastic that becomes the bottle is first extruded and comes out in what is called a parison, a tube, at about 400° F," says Schultz. "The mold comes along and pinches off a piece of the parison. High pressure air is blown into it, and it is almost instantaneously configured into the shape of the mold. The hot plastic activates the adhesive on the back of the label.
"The difference between glue-on labels — and that includes pressure sensitive — and IML is that the in-mold label is in the wall of the bottle."
"Because of the technicalities involved, in-mold labeling is a minefield for printers," says Ken Pizzuco, plant manager at Multi-Color's Batavia, OH, production facility. One of the challenges printers face is blocking. After printing the labels are diecut in one of two ways and stacked.
"If the chemistries of the adhesive on the back and the varnish on the front are not right, the stack can turn into a brick," Pizzuco says. Multi-Color runs a battery of tests on its in-mold labels in the laboratory, sampling labels from every part of the run and recording the results in the event of a question by the customer in the future. Among tests are ink rub, color measurement, substrate thickness testing, gloss metering, and heat seal testing. "That test simulates what happens in the blow molding process," he adds.
Multi-Color also has optical brightness sensors wired into its two Comco presses at the Batavia plant. The molding process is triggered by an optical brightness sensor, so if the brightness is below spec the container will not form. "We have it configured so that the press stops if the brightness is not high enough," says Pizzuco.
Inks are critical to the IML process. "In order for ink to perform well for IML applications, the ink must accomplish several tasks," says Tom Hammer, director of product portfolio for Akzo Nobel Inks, Plymouth, MN. "The inks must provide acceptable on-press performance, time after time; they must provide desired end-use characteristics for its application of use; they must satisfy the customer (from the printer to the molder to the end user), and they must be cost effective in their use — robust, in other words."
"Inks are a challenge, in that they need to have exceptionally good abrasion resistance, and better than average heat resistance," says Schultz. "UV inks and coatings are better for IML because they are much tougher."
Diecutting is one of the most critical areas in the IML process. Labels that are printed on roll-fed flexo presses are diecut inline with a rotary die. These are then stacked and prepared for the molding process. Labels printed in sheets are stacked and run through a unit called a high diecutter. In this process, stacks of rough-cut labels are rammed through a tunnel in a specially crafted machine and emerge cut to size. Converters acknowledge that the method is not the most accurate, but it is the most popular.
Edge welding is a consequence of high diecutting to be avoided. This occurs when the coatings on the back or the surface are too sensitive and can stick together at the edges of the stack.
"Another challenge is print-to-cut registration," says Schultz. "That is important because the magazines have little fingers that hold the labels in place during the feeding process, and if the labels are slightly too large the pick-and-place device won't be able to do so one at a time. "If they are too small, they can slip out of place and fall onto the floor.
"Blocking can be death to in-mold labels. Static is another serious problem. Polyolefin labels have a tremendous static problem: Any time a label slides over something on the press it will pick up static again. We're talking about unsupported film that might be three to four mils thick."
Innovations in IML
Converters of in-mold labels are hard at work on innovations. One of these has emerged at NorthStar. "We recently introduced a clear in-mold label for polyethylene containers, focused primarily on the health and beauty product market," says Gasper. "We worked in concert with Avery Dennison to develop this product, and it has generated real interest. Customers want to see the liquid in the bottles. In the past, clear pressure sensitive was the only alternative available, but we've come up with an in-mold product that allows that clarity."
Several attempts have been made to produce a clear polyester film label to go into a clear polyester bottle, says Schultz, with no luck yet. "The big challenge is the adhesive; it has too high a melting point."
NorthStar also has developed a second-surface-printed in-mold product. "We print on clear film, reverse the graphics, and now we have ink encapsulated under two or three mils of film," Gasper says. "We also brought to market a peelable in-mold product, perfect for couponing, where the customer can pick off the top layer."