In-mold decorating (IMD) and in-mold labeling (IML) have become important techniques for both injection and blow molding. In both cases, a label or decorative film—either flat or preformed—is placed robotically in the mold and then backed up by molten plastic as the part is formed. IML now dominates in blow molding, eliminating secondary operations and improving bottle aesthetics by making the label an integral part of the container. IML is very big in Europe also for injection molded rigid packaging, but is just starting to break through in this country. There also has been more limited activity for IML in thermoformed packaging. Adolf Illig in Germany built IML thermoforming systems in 1994.
Meanwhile, in-mold film decorating is making big strides in auto parts and other durable goods as a cost-effective and environmentally benign alternative to painting, plating, printing, and hot stamping. In the last few years, IMD has started to take off in injection molding and industrial thermoforming, and there are also a few applications in polyurethane RIM and thermoplastic long-fiber composites.
IML started in bottles
IML in North America started in the 1970s with Procter & Gamble and Owens-Illinois Packaging (now part of Graham Packaging). The first applications were blow molded HDPE bottles with paper labels coated with a heat-activated adhesive.
IML and IMD first crossed paths with injection molding in the area of structural-foam molding during the mid-1970s. Placing a preformed film in the mold was a way to cover up the surface swirl on foam parts and eliminate the trouble and expense of painting.
IMD found a warmer welcome in standard injection molding. It got its start in the late 1970s with woodgrain auto interior trim, according to sources at Avery Dennison, which supplied the printed films. Since then, auto companies have taken enthusiastically to preprinted foils and dry-paint films for interior parts with woodgrain and brushed-metal appearance and exterior parts that imitate paint or bright chrome. In the 1980s, GE Plastics helped introduce IMD to cell-phone covers. Although it was not a big hit in cell phones, IMD has since moved into PDAs and other handheld electronics, as well as major appliances.
Injection molding IML began in Europe in the 1970s with paper labels on PS substrates. An estimated 85% to 95% of rigid food packaging there now uses IML, as do some durable goods such as returnable beer crates.
IML reportedly started in the U.S. in the early 1980s. Shape Inc. in Biddeford, Me., was one of the first to get into IML injection, taking a license in 1982 from Cerbo in Sweden, which held patents on a technique to inject the melt through the label. In 1983, Shape applied the process, using Cerbo’s automation, to production of video cassette sleeves in a two-cavity mold.
Problems with label quality, feeding, and handling kept IML activity low-key in the U.S. until the mid-1990s, when it was rekindled by molders’ attempts to eliminate secondary operations, reduce the scrap rate from post-mold labeling, and to produce a “no-label” look similar to that of blow molded articles. Adding a label in-mold also could permit a reduction in wall thickness while maintaining the part’s strength—a benefit not available with any other labeling technique. And the permanence of an IML label also appealed to safety issues, as a way to be sure the listing of product ingredients, health warnings, or UPC codes stayed with the package through its life cycle. Injection molders of durable goods also acquired a taste for IML, applying it to toys, lawn and garden products, all-terrain vehicles, trash containers, and even tractor body panels.