Be Bold

In-mold labeling (IML) is a product decoration method that has grown in popularity over the past 10 to 20 years. Why? Because it can provide lots of apple-pie type of stuff—improved quality and shelf appeal, reduced waste, reduced cost, and better durability. Who can argue with that?

The IML process gets its name from how the label is applied to the plastic packaging container. The label is placed “in the mold” as the container itself is being formed.

Plastic containers are produced using several different forming methods, including thermoforming, injection molding, and blow molding. To a large degree, the forming method used is dictated by the shape of the container.

IML is used in both injection molding and blow molding forming methods. In injection molding, molten plastic material is injected, under pressure, into a cavity (mold) that forms the shape of the container. For IML, a label is properly positioned in the cavity prior to the injection of the plastic. After the material is injected into the mold, it is allowed to cool, with the label becoming an integral part of the container.

Blow molding is similar to blowing up a balloon. The heated plastic material is extruded in the form of a tube. A mold is clamped around this tube and air is blown into the plastic tube to force it out against the cavity walls to take the shape of the bottle or container. With IML, the label is again, properly positioned against the cavity wall and adheres to the formed container as it cools to its final dimensional shape.

Benefits abound

Since the labels become an integral part of the container, Shelley Cooper, product sales manager for Valéron® Strength Films, an ITW Company, says, “IML offers more durability, with a longer lasting and better looking appearance. IML labels are basically melted to the carrier and become one unit.”

This label/container “oneness” allows the bottle to flex and be squeezed without peeling as a pressure-sensitive or glue-on label potentially can, adds John Giblin, VP of marketing for Granwell Products.

Besides the durability and potential for higher quality graphics, Ron Schultz, with the consulting firm RBS Technologies and speaking on behalf of the In-Mold Decorating Association (www.imdassociation.com), says that injection molded IML allows all five surfaces of a cube-shaped container to be labeled at the same time. “This is impossible to do with glue applied, heat transfer, or pressure-sensitive labeling,” he states.

IML films are available in both white opaque and clear (or contact clear) configurations, reports Schultz. With the clear films, consumer product companies (CPCs) can create the popular “no-label” look on personal care products such as shampoo bottles.

One of the really significant benefits for CPCs, says David Hoag, national converting sales manager for Arjobex, is that IML provides them with pre-decorated containers, which eliminates the labeling process on their manufacturing lines. With everything taken into account, this eliminates post-mold labeling equipment, labor, space, and related costs, expands Schultz.

Why synthetics?

IML got its start in the early days using traditional paper labels. Although effective as a new, innovative product decorating technique, paper’s relative incompatibility with plastic contributed to a number of problems.

“Paper labels used in early IML applications would cause quality problems (such as paneling, panel bulge, and retention blisters) due to differences in shrinkage dynamics,” says Hoag. The waste generated by these quality issues would cause further cost and handling problems as the paper labels needed to be removed from the plastic containers to allow recycling.

Synthetic papers have shrinkages that more closely match that of the container materials, helping to minimize or eliminate some of the quality issues. In addition, synthetic materials can be recycled with the container. “Since they possess the same chemical characteristics as the polypropylene [PP] and high-density polyethylene [HDPE] bottles they decorate, they enable 100 percent recyclability,” notes Giblin.

In fact, says Hoag, “One of the primary drivers for the use of synthetic papers in IML applications was recycling issues—not just post-consumer, but the generation, handling, and recycling of waste at the blow molder.”

Materials that are sometimes categorized as “synthetic papers” have changed and broadened out over the 30 to 40 years since their development. “The term ‘synthetic papers’ is actually a misnomer because these are plastic films rather than a product formed from fibers on a papermaking machine,” says Schultz. “However, they are used in many applications as a replacement for paper and have many of the printability properties of paper.

“These films have multiple advantages over paper for in-mold labeling,” continues Schultz, “including better moisture and product resistance, superior tear and abrasion resistance, recycleability with the container, and most important, the ability to conform to the plastic container without distortion as the container shrinks or expands. Film in-mold labels develop far fewer defects on the container than do paper in-mold labels. The overriding advantage is that these films are chemically very similar to the container materials and are thus more compatible with them than paper.”

As far as the type of resin being used for the labels, most of the in-mold label substrates for packaging applications are polyolefins, such as HDPE, PP, or proprietary hybrids specially engineered for IML, reports Schultz. “Each substrate has its advantages, but there is no single, universal IML substrate.”

According to Giblin, most of the substrates for blow molding are HDPE, cast PP, or other co-polymers, which all are very heat sensitive. “For injection molding, the primary material used is oriented polypropylene (OPP), which has better heat resistance features,” he says.

Hoag says the Arjobex Polyart synthetic paper is HDPE-based and is manufactured in such a way to provide stretch/shrinkage ratios that are balanced in the machine and cross directions. “Because of the way it’s manufactured, it can better match the shrinkage of the container,” he notes.

Injection vs. blow molding

As mentioned, IML can be used in both injection and blow molding container forming processes. It is interesting to note the geographical differences in the use of each.

“Compared to the other label markets, the IML market varies worldwide,” says Giblin. “The bulk of the U.S. market is blow mold labeling rather than injection in-mold labeling. However, injection IML is growing faster in the U.S. than blow molding IML. On the other hand, the European IML market is almost all injection molding IML, with the minor share being blow mold IML.”

Schultz further substantiates this observation. “In North America, 90 percent of IML is blow mold and about 10 percent injection. In Europe, its more than 95 percent injection IML and less than 5 percent blow mold.

There are technical differences required for the labels used in for these forming processes.

“Labels for blow mold IML (EB-IML)—both paper and film—must have a heat-activated adhesive layer on the back, either co-extruded during the film manufacturing process or applied during the label converting process,” says Schultz. The adhesive is activated by the expanding hot bottle plastic during blow molding.

“Labels for injection IML (IM-IML) do not need an adhesive because the injected plastic, at high temperature and pressure, fuses with the plastic film label during the molding process,” he explains. “For this to work properly, the label film and the container plastic must be the same chemical type, usually polypropylene. Also, labels for IM-IML are usually thinner than labels for EB-IML.”

Hoag notes another technical factor that contributes to the geographical differences in IML applications. “Injection molding puts more demands on the diecutting of the label,” he notes. “Labels for injection molding are almost exclusively produced using counter pressure dies, and these are not in common use in the U.S.”

Bright future

The IML market is a good one for synthetic papers (films) and will continue to grow. “The transition from paper IML to film IML has been happening for several years and is projected to continue into the future,” says Schultz. “In U.S. dollars, film is 80 percent of the IML market. The most significant growth for IML is expected in the injection arena in North America over the next few years.”

Part of the growth in IML can be attributed to its aesthetics. “IML will continue to grow as the demand for better looking and more impressive labeling is demanded in order to ensure the message reaches the consumer,” predicts Cooper. pP

Not just for IML

IML is a prime market segment for synthetic materials, but it is far from the only one. Tara Starck, product manager for Protect-all Print Media, says that her company is working closely with Xeikon on digital printing applications. While many people perceive synthetics to be mainly a white/opaque substrate, there is lots happening with clear or translucent materials. Xeikon has developed the capability for digital printing of menu boards and signs, with two-sided printing, in register.

Another market noted by Starck is the card market. Protect-all Print Media supplies Artisyn as the core stock for loyalty, ID, and credit cards. Its sister company, Protect-all, Inc., manufactures thermal laminating films. The combination of the two provides a 100 percent synthetic card that has destruct-bond properties and moisture resistance without an edge-seal lamination, she reports.

Shawn Easter, marketing manager for Acucote, says the company offers its Syntherm® synthetic material for applications requiring UV, chemical, grease, or oil resistance. It’s used in durable goods applications such as automotive and machinery applications, shipping container and drum labels, and outdoor agricultural labels.

For brand protection applications, Easter reports that Acucote’s Syntherm TE provides a durable face sheet that destructs and shows tamper-evidence when removed from a substrate. Syntherm TE is used within the health and beauty industry, on packaging containers, and for pharmaceutical closure seals.