In-mold Labeling Is Still A Challenge In Packaging

In-mold labeling produces durable, high-impact graphics faster than post-molding labeling or printing, which is the reason why its adoption among injection molders has been so dramatic. Current growth estimates for iml range from 6 to 10%/yr into the next decade.

In-mold labeling (iml) has been used since the 1970s. European injection molders were the trailblazers, as were U.S. processors in blow molding later that decade.

With thermoforming and injection molding jousting in many packaging applications, iml would be as useful for thermoformers as for molders. But though many have attempted it, it remains “a dream unfulfilled,” says Marku Pietinen, communications vp. of Espoo, Finland-based thermoformer Huhtamaki. For high-quality containers, Huhtamaki, the global leader in rigid thinwalled packaging, has turned to off-mold pressure-sensitive labels; it stopped iml development last year.

Pietinen and other experts agree that iml thermoformed packaging remains feasible. But thermoformers may continue to lose high-end applications to injection molders using iml. Autobar and RPC, two large packaging processors supplying margarine tubs to Unilever, both dropped thermoforming in favor of iml molding at the oem’s request. Dave Edwards, managing director of Autobar Germany, in Ravensberg, explains that with iml thermoforming, “the effects and the process itself were not as good” as the results from iml moldings, alluding to off-center graphics.

iml is done by placing pre-printed labels via a robot into a mold before polymer enters the mold. The labels are held in place by vacuum, electrostatic attraction, or other means. During injection molding or blow molding, when the mold closes and molten plastic enters, a heat and pressure bond between the label and plastic is created as the plastic cools.

Thermoforming differs in that the sheet or film used is heated but not to a point that it becomes fluid. Ron Schutz, president of RBS Technologies Inc., Scottsdale, az, a consultant for the flexible packaging, converting, and labeling industries, explains that for this reason, iml thermforming labels require an adhesive, which makes them more difficult to handle and costlier.

Most leading thermoforming machine manufacturers say they have developed systems capable of iml, but price has been a prohibitive factor. Only one builder, ZMD International Inc., Long Beach, ca, actively markets a machine specifically for iml. That machine is for processing sheet for cellular phone or automotive parts, not roll-fed packaging.

Huhtamaki’s Pietinen notes that thermoforming’s efficiency is largely based on the number of cavities employed per cycle. Despite the speed and accuracy of current robots, the close proximity of the cavities dictates that for iml, processing speed must be slowed down to accommodate the insertion of labels into the cavities before each cycle. Placing labels on top of the cavities would be faster, but it requires more space to be allotted between cavities. In either case, productivity is lost, as proven in tests at the processor.

Brian Sullivan, president of Flex-Pak Consulting, Amelia, oh, has extensive iml injection molding and blow molding experience, but his efforts in drawing thermoformers to iml in the late 1990s did not fare well. He says that since thermoformed parts use less material per part, processors could not charge as much per part as injection or blow moldings. Additionally, feasibility centered on efficiency, as highlighted by Pietinen. Could robots insert labels fast enough to not negatively affect cycle times? Processors decided they could not.

Sullivan concludes that thermoformers competing against iml moldings in premium packaging applications might do better using pre-printed films that are heat-bonded to the base thermoforming material. Thermoforming of pre-printed films has increased significantly in the last two years.