Focus: Packaging:Getting up to speed on IML

Hot, and getting hotter. That’s the forecast for IML in North America. Curious about this new technology? Find out what Europeans have known for two decades.

Thin-walled packaging suppliers in the U.S. and Canada are latching onto inmold labeling (IML) in growing numbers these days, and with good reason. The technology produces higher-quality graphics than printing, can improve barrier properties of the container, and handles five-sided shapes with ease.

So why is it that a technology practiced in Europe for the past 20 years is just now getting the green light in North America? IMM asked Rick Shaffer, president of Netstal Machinery Inc., to provide some feedback on this and other IML considerations, given the company’s extensive experience with IML molding installations.

Compelling Reasons

Shaffer believes the time for IML in the Americas has arrived. “Until relatively recently, there was a perception that this technology was too expensive to implement, and that it was also too difficult to do on a high-volume basis,” he says. “But changes in market demands and IML technology are causing packaging suppliers here to question those perceptions.”

Demands for innovation and quality graphics in packaging are two such changes, brought on by customers’ needs to differentiate products on store shelves. “More often now, packages are being designed in rectangular shapes that may require graphics on five sides,” Shaffer explains, “a category where IML is the hands-down winner. Also, the true cost of IML for traditional round containers is typically less than estimated by earlier perceptions.”Technical developments in IML labels play a role as well. For instance, using traditional PP labels can improve barrier properties of a container. Preformed EVOH labels can further enhance these characteristics.

According to Shaffer, though, the most prevalent reason to consider IML is the added design freedom and creativity it allows. “Two-part containers for products such as yogurt and fruit or salsa and chips are a big draw, for example, and IML meets the challenge of decorating these unusual shapes with high-impact graphics.”

For packaging suppliers, the IML promise of simplified manufacturing flow lines up well with lean practices. Molded parts leave the press ready to ship, eliminating work-in-process inventory, handling, and secondary printing operations. Changeover times are also simpler than with printing. The IML process can be designed for graphics changes on the fly, enabling customization for regional, recycling, or language considerations. “If you compare the total cost of ownership of this production method, you may be positively surprised,” he says.

Before You Begin

While there is a cycle time penalty to be paid using the IML process, it can be kept to a minimum with a near-zero scrap rate, according to Shaffer, provided the system is constructed correctly and a label supplier is selected carefully.

Label quality remains one of the keys to success in IML, in which high-quality graphics are printed on labels usually made of the same material as the finished container; average film thickness is about 45 to 75 µm. Quality applies to both graphics and cutting accuracy; poor cuts adversely affect label position in the mold and the ability to handle labels efficiently.Individually cut labels are optimum. “While there are applications where inline cutting systems make sense, trade-offs include reduced flexibility and increased complexity, so most manufacturers shy away from this method. And stack cutting is definitely more challenging. Labels that are cut individually provide better output and significantly lower scrap rates.” Manufacturers that currently supply labels for IML include the following:

The second half of IML involves inserting the precut label into the mold and molding the substrate material over the label. Accomplishing this with the most efficiency and the least impact on cycle time becomes the difference between success and failure. Says Shaffer, “Designing a high-quality injection molding cell with few or no compromises becomes very important.”

Difficulty Levels

Formerly reticent packaging suppliers cited the complexity of molding IML containers as a reason for avoiding the process, but the reality is that there are varying degrees of difficulty. “The possibilities are endless, and packages being produced in Europe are proof that it isn’t rocket science,” Shaffer says, “but make no mistake, it isn’t child’s play, either.”

The degree of difficulty tends to coincide with the shape of the part, starting with flat parts such as lids, progressing to rectangular parts with three-sided or five-sided labels, and peaking with round conical parts (see table below). Some of the toughest applications include four-sided rectangular parts (with no label on the bottom) and round parts with zero or little draft such as cartridges for silicone caulking tubes.

Shaffer cautions molders to keep an open mind. “Don’t automatically rule out the IML process even for complex parts. One such part incorporates two different labels per cavity with completely different shapes, and is being produced in a multicavity mold at a relatively high volume with a scrap rate of less than 1%.”

It is possible to combine technologies to achieve the most cost-effective production. For example, molding lids using the IML process in combination with multicomponent molding can improve their appearance and increase their value to customers.

Details of Mold Design

To minimize cycle time and optimize part removal, it makes sense to pay attention to mold design for IML parts. “While there is a strong economic desire to utilize existing tooling,” explains Shaffer, “this will seldom produce the best results.” To achieve the highest productivity, he recommends designing tools with the IML process in mind.

For example, gates should be placed away from the label, allowing material to make contact with the inside of the label as it enters the mold. For a rectangular part with a five-sided label, this means gating on the inside of the container rather than on the bottom. Benefits include reduced scrap rates and wider processing windows.

Other considerations are unique to IML. For one, typical ultrahigh-cavitation tools may not be the best answer. Also, the location of components such as stack mold drives, water connections, and hot runner wiring may also lead to compromises that will decrease productivity and increase the degree of difficulty.

“Be sure that you take a long look before making short-sighted decisions that will put you in a less-than-competitive position,” Shaffer says. “The bottom line is that every compromise you make in the mold design will reduce the process window and impair the ability of the injection molding machine and handling equipment to compensate, and will affect their overall efficiency.”

If a mold will not be produced in-house, Netstal suggests finding a moldmaking supplier with knowledge and experience in both packaging molds and the IML process. When creating an IML system for its customers, Netstal chooses moldmaking partners based on the shape and style of the container, type of mold (stack mold, single face, or multicomponent), cavitation, and experience level.

Handling IML

Selecting the right handling equipment for your IML application is also critical. Unlike traditional packaging applications, cycle time depends on the efficiency of the molding machine and the handling unit. Simultaneous label placement and part removal minimizes cycle time and optimizes the process.

Guidelines for selecting this equipment include ensuring that it has the necessary frame and guidance to maintain alignment and accuracy, both essential for reliability. “At the same time, the system needs to have the speed and acceleration characteristics required for a fast cycle. Often, those two requirements work against each other, but the best systems deal with this very well,” says Shaffer.

Handling equipment must also pick up very thin labels from a magazine and prepare them for the next mold-open event during the normal injection process. Several techniques can be used, depending on the style and shape of the product. Thin-walled packages are inherently fast-cycling, so the reload time for the label is quite short. For wraparound labels, suppliers often elect to prewrap the labels to save time and to keep up with high output rates.