Injection compression molding on stack molds

Injection compression molding… Netstal presented at Fakuma 2015 a world first injection compression molding on a stack mold. This new innovation was demonstrated using a 15 oz (425 g) margarine tub made from PP that is manufactured with 4+4 cavities on an ELION 2800-2000 and weighs only 10.7 g.

World first: injection compression molding on stack molds

Following close collaboration between the mold manufacturer Plastisud, the automation specialist Machines Pagès and the Swiss injection molding manufacturer Netstal, the injection compression molding process and the stack mold technology were brought under the same roof. It appears almost trivial at first sight: a slightly modified injection molding machine from the Netstal ELION Hybrid series molding margarine tubs in standard format 15oz (425 grams) with IML decoration in a cycle time of five seconds. On closer inspection, it turns out that the process is performed in a stack mold with 4+4 cavities. "The really revolutionary thing about the whole process is hidden from view: the polypropylene packaging is not injection molded but manufactured in an injection compression molding process," explains Markus Dal Pian, Vice President, Sales & Marketing at Netstal. "This combination of injection compression molding and stack mold is a complete novelty in the industrial production of packaging," emphasizes Dal Pian. The cavities are partially filled in only 100 ms with extremely even results and the process is performed at a low pressure to prevent tension in the material. The high quality of the platen parallelism guarantees a synchronicity of 99.98 % between the mold, machine and automation system.

A partnership for success

In just a few months, Plastisud developed a stack mold specially adapted to the requirements of the new production process. "The unique injection compression molding technology guarantees perfectly balanced parting planes with an extremely low dispersion rate" explains Laurent Buzzo, CEO of Plastisud. Thomas Iten, PAC application engineer at Netstal emphasizes: "The special design of the stack mold developed by Plastisud plays a key role in this application." The automation specialist Machines Pagès provides specific know-how in the area of handling systems for in-mold labeling (IML) to ensure that the automation process has been adapted perfectly to the machine and mold.

A genuine innovative leap

Iten is convinced that "the combination of the injection compression molding process with a specially balanced stack mold is a genuine innovative leap" because "this configuration uncompromisingly combines the advantages of the two technologies." The fundamental benefits of injection compression molding include narrow wall thicknesses and a lighter product resulting in lower unit costs. Furthermore, the end product (lids in particular) shows fewer signs of distortion and has a greater dimensional accuracy due to the lower stresses placed on the material. These properties make the end product much more attractive for packers such as margarine manufacturers compared to other processes. The financial benefits are equally as important for the packaging manufacturer: a significant increase in productivity through the use of a stack mold and drastic reduction in material costs by up to 20% as well as total flexibility in terms of shape, appearance and decoration of the manufactured part.