Evaluating in-mold labeling

How does this method of decoration stack up as an option?

Sterling Anthony, CPP
Sterling Anthony, CPP
An analogy would be that of a person born already clothed, because with in-mold labeling (IML), the package exits the mold already labeled.  IML, therefore, is a different category from downstream labeling, such as glued-on, pressure-sensitive, and shrink-sleeve.

Whereas downstream labeling is applied on the surface of the package, IML labels are integrated into the package's surface. The labels used in IML can be printed with any method used with downstream labels—from flexography to hot stamping—depending on the desired shelf-impact.  And since IML labels are molded into the package's surface, they resist peel, abrasion, water, chemicals, and other forces and elements that can mar downstream labels.

Furthermore, it would seem that IML offers some built-in economies, given that it eliminates the machinery and labor required of downstream labels. In this sustainability era, with its emphasis on a smaller carbon footprint, that's a winning argument, right? But hold on. As with anything associated with packaging, there are trade-offs to be managed within a systems approach.

The requirements are challenging

The labels have to endure the conditions imposed by the molding/forming process. That means that substrates, adhesives, inks, and lacquers should be chosen for their ability to withstand direct contact with molten resin/softened plastic and the temperatures inside the mold/cavity.
Temperature-compatible substrates and coatings are specialty items typically not available from the same supplier; therefore, sourcing and coordinating can be complex.  But to whatever degree that might have been a disincentive in the past, it's less so today, as more brand-owners have gained experience in those activities through supply-chain management.
One type of IML substrate is paper, but since the labeling becomes an inseparable part of the package, it has drawbacks relative to recycling.  Film substrates, by contrast, can be chosen to be compatible with recycling, that is to say, they don't contaminate the recycling regrind.  Additionally, clear film becomes "invisible" against the package's surface, presenting the printing without borders—the so-called no-label look.
Examples of IML abound in blow-molded bottles, in categories such as beverages, liquid detergents, personal-care, and car-care.  Such products provide the long production runs that make IML for blow-molding economically feasible.  In fact, IML was invented decades ago specifically for high-volume blow-molding applications, and in the U.S., the overwhelming use of IML is in blow-molding.  High volume, however, doesn't automatically justify IML, like when communication requirements call for a fold-out or pamphlet label.

Growth of IML for injection molding slow in U.S.

Often, the reason that a particular packaging technology sees less usage in the U.S. versus Europe comes down to volume, but on two levels.  One relates to market size, the other to market segmentation.  The smaller, more segmented (along language lines) European market is suited to labeling technologies that are based on lower volumes and shorter runs.   Throughout Europe, injection-molded packages (i.e. tubs and trays) decorated with IML are not only commonplace but dominate the food category.
U.S. volumes are tailored to high-cavitation stack molds, not the low-cavitation single (or dual)-face molds used for IML injection-molding in Europe.  The major holdup is investment.  IML injection-molding installations of the type required in the U.S. are a pricy proposition. Brand-owners don't want to loosen the purse strings, unsure whether the shelf-impact of IML will produce sales and profits for an adequate ROI.  So why not turn to contract packagers?  Those that are injection-molders aren't clamoring to retool for IML without assurances of long-term business from brand-owners.  Currently, IML injection-molding capacity in the U.S. is paltry, both on the supplier and end-user sides.

An associated limitation is that many injection-mold designers in the U.S. are not experienced with IML; as such, the modest U.S. demand for high-cavitation stack molds, in large part, is being met by foreign designers.  And even they are on a learning curve that's anything but steep, relying, as they do, on their experience with designing low-cavitation injection molds.

Mention has been made of the brand-owner, the molder, and the mold designer, but there is another essential member of the supply-chain and that's the automation supplier.  The short cycle-times necessary for operations in the U.S. require high automation, particularly robots.  The mold opens, the label is inserted (formed into a shape, in the case of wraparound labels), the mold closes, the plastic is injected, the part is molded, the mold opens, and the labeled part is removed.   That sequence must be done with the speed and precision that only automation can impart.

Unfortunately, automation can be a temperamental thing, intolerant of imprecise inputs.  A robot, for example, that feeds labels into the mold, must do so not only speedily, but with precise registration; however, both requirements can be compromised by die-cut labels that have been manufactured with loose tolerances.
Reintroducing sustainability into the discussion, the tactic of light-weighting can work for and against IML injection-molding.  Since the label is incorporated into the package, the wall is thickened, adding to overall structural integrity. On the other hand, labels are becoming thinner, and below a certain gauge can cause problems in automation, if the robots have difficulty manipulating the flimsy structures.

Thermoforming poses the most hurdles for IML

Even in Europe, growth has been as slow as a snail on crutches.  To begin understanding why, one starts with the fundamental difference between thermoforming and the other two technologies (blow and injection): the former is sheet-fed and the latter two are molten resin-fed. Now, consider that thermoforming is a form/fill/seal operation that includes a secondary trim operation.  Introducing IML into the equation, without a serious drop in output rates, has proven to be a stubborn challenge.

Productivity considerations aside, there's the problem of inadequate adhesion of the label to the package.   The temperature of the softened plastic sheet that is vacuum-drawn into the cavity is quite a bit lower than the temperature of molten plastic.  Whereas that stands to reason, the consequence is that the adhesive or bonding layer on the back of the label must be formulated to activate at that lower temperature; otherwise, the result is poor adhesion.
Additionally, with IML thermoforming, there can be problems with aesthetics, such as blisters and bubbles caused by air trapped between label and package wall and wrinkles caused by uneven shrinkage rates.
The importance of staying abreast of developments

Rigid plastic packaging is constantly battling encroachments from flexible packaging—and vice-versa, for that matter.  A major weapon in the battle is labeling because of its critical contributions to shelf-impact.  IML certainly can give rigid packaging eye-catching appeal, whether the involved technology is blow-molding, injection-molding, or thermoforming; but, at what overall systems cost?  The answer is fluid, such that even if IML currently doesn't recommend itself for a specific application, it behooves the brand-owner to monitor the horizon, so as not to miss advancements in machinery, materials, and technology that can tip the scales.

Sterling Anthony is a consultant, specializing in the strategic use of marketing, logistics, and packaging.  His contact information is: 100 Renaissance Center-176, Detroit, MI 48243; 313-531-1875 office; 313-531-1972 fax; sterlinganthony1@sbcglobal.net.
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