Engel Pairs With Top Grade Molds on Coinjection Technology

Austrian injection molding machine and automation supplier Engel (Schwertberg) teamed with Canadian tool maker Top Grade Molds (Mississaugua) to boost recycled material content in sandwich structures, molding 5-gal buckets with encapsulated recycled content of more than 30% during Engel’s recent e-symposium.

The technology offering comes as governments, brandowners and OEMs seek to boost recycled plastic content in many everyday items. Sandwiching this scrap plastic within virgin material is one means to meet these new guidelines, but many brands do not want darker recycled core material to be visible at the injection point. To satisfy this demand, new coinjection processes are being developed.

Engel partnered with Top Grade Molds—a packaging specialist—on the concept, with the mold provided by U.S. pail manufacturer M&M Industries (Chattanooga, Tenn.). That mold was run on an Engel duo speed injection molding machine developed specifically to meet the needs of pail, storage and transport container suppliers. Short cycle times were emphasized, and Engel said the coinjection process ultimately provided similar cycle times as making pails in conventional single-component injection molding. Engel says its compact dual-platen press provides a smaller footprint that saves shop floor space. HDPE was used in the virgin skin and post-consumer core, to ensure easier recycling at end of life.

To boost the bucket’s quality, the system was designed in such a way that the two materials are combined without mixing them together beforehand in the melt stream. The system switches between recycled material and virgin resin at the gate using a coinjection valve gate. Engel noted that this development furthers the company’s efforts in sandwich products with recycled cores, including its skinmelt process presented at K 2019.

A company spokesperson told Plastics Technology that the machine is equipped with two injection units, as you might find in standard 2-component molding. In this setup, a ring nozzle ensures that the two materials remain separated until the melt merging. The ratio between the two materials ultimately depends on the part design, with the injection unit sized to accommodate the amount of material required and the capabilities of the plasticizing unit.

The spokesperson said the new coinjection process was a joint development, with the mold and hot runner technology know how supplied by Top Grade. Engel developed the coinjection head, flow calculations and application technology.