ENGEL has developed a new coinjection process which enables high and completely encapsulated recycled material content in the production of pails and is thus superior to conventional processes for sandwich injection molding. The new process is fully advantageous in the production of 5-gallon pails and is developed in cooperation with Top Grade Molds. Very short cycle times are achieved in combination with the new ENGEL duo speed injection molding machine.

Brands do not want the dark colored recycled core material to be visible at the injection point. This has driven the development of the new coinjection process. With a of more than 30 percent, the 5-gallon pails produced during the ENGEL live e-symposium easily comply with the US specifications, which are very challenging as compared with other international standards.

Combining Productivity and Efficiency
ENGEL's development partner is Top Grade Molds from Mississauga, Canada, a mold manufacturer specializing in packaging applications. The pail mold is provided by US pail manufacturer M&M Industries from Chattanooga, Tennessee. It is being deployed on an ENGEL duo speed injection molding machine, which ENGEL developed specifically to meet the requirements of producers of pails and storage and transport containers. This new large machine type combines productivity and efficiency with short cycle times. The coinjection process provides similar cycle times as producing pails in conventional single-component injection molding.

Coinjection makes it possible to concentrate the recycled material in the component's core and encapsulate it by a layer of virgin skin material. The virgin and recycled material are of the same type to ensure that the sandwich-molded parts can also be recycled at the end of their useful life. HDPE is being used for the 5-gallon pails; the recycled material here originates from post-consumer collection.

Highest Quality Product
The greatest challenge in sandwich injection molding is to achieve high recycled content without compromising product quality or performance. One focus of the development was therefore on combining the two molten plastics in the pail mold without mixing them beforehand in the melt stream. As a result, the system switches between recycled and virgin material at the cavity injection point by way of a coinjection valve gate.

5-gallon pails are universally used in North America for a wide variety of end use markets. Since the core and skin material fractions are strictly isolated from each other in the production process, and the core is encapsulated by the skin, including the injection point, the new coinjection process also can be considered for the food industry.

» Publication Date: 07/07/2021

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