Engel processes allow packaging makers to enclose recycled material in virgin-resin layer

By Karen Hanna 

Two Engel approaches to incorporating recycled content could help molders strike a balance between sustainability and product performance.  

The approaches — co-injection and Engel’s proprietary skinmelt technique — both involve burying recycled materials in the center of outside layers of more attractive, better-performing virgin resin, according to Jim Overbeeke, business development manager for packaging for Engel North America. 

A speaker at the Plastics Industry Association’s Plastics Packaging Summit, Overbeeke said he believes industry professionals recognize the urgency to find more-sustainable alternatives to some plastic products. 

“I think that's the attitude of everybody I run into, the equipment suppliers, the partners, the molders, everybody gets that we're in a bit of hot water,” Overbeeke said. 

One obvious solution — using more recycled material — presents its own problems. 

“Everybody's accustomed to the performance of a virgin material ... how strong is it, the aesthetics of it and all the functionality, like the fit of a closure to a bottle, the tamper-evidence, how hard or easy is it to open and so on,” Overbeeke said, in explaining the need to cocoon recycled material inside virgin. “The question is, ‘Can you achieve all those performance factors and aesthetic factors that the brands want for their image?’ Because the consumer choice is still driven to a large degree by how the brand portrays itself with packaging.” 

One strategy is co-injection, a process that Engel has recently honed in partnership with Top Grade Molds, of Mississauga, Canada, and Chattanooga, Tenn., manufacturer M&M Industries. In a recent demonstration, Engel used its duo speed injection molding machine — an IMM specially developed for the production of pails and storage and transport containers — to produce 5-gallon buckets with recycled material content of more than 30 percent.  

To facilitate future recycling, the buckets were made from HDPE, with recycled post-consumer HDPE. 

Overbeeke said M&M industries still is studying just how much recyclate can be used, but a couple advantages to the process already are obvious.  

“You don't see the recycled material as the gate. It completely encapsulates the recycled [material], so that makes a cleaner package that more brands, we’re hoping, will accept,” he said.  

Large containers, like pails, are an ideal fit for the process, because they have relatively thick walls; if the walls are too thin, the inner, recyclate layer can break through the external layers, Overbeeke said. 

“We've done 30 percent and over, and we're working on sort of optimizing the process to see how far we can push that, but the original goal we were given was 25 percent,” Overbeeke said. 

In addition to its co-injection process, Engel continues to tout its skinmelt technique.  

Unlike co-injection, the skinmelt process involves fusing the melt for the skin and inner layers prior to injection. The skin – the virgin material – is the first to reach the cavity. It is pushed forward by the inflowing recyclate melt and pressed against the cavity walls, while the core is filled with recycled material. 

Both the co-injection and skinmelt approaches require two injection units, but  skinmelt “could achieve 5-10 percent more recycled core than co-injection, providing the end user allows most of the part bottom to show core material,” Overbeeke said.  

Skinmelt has its disadvantages, though. 

“That has a high recycled content at the core, but it also shows the core or the recycled material they're trying to bury, it shows that at the gate,” he said. 

Overbeeke said Engel works with molders to help them develop prototypes and specify the equipment they’ll need to perform recyclate-core molding. Together, Engel and its customers can trial new molds or processes, before the molders make significant machinery investments.