Efficient injection compression molding of IML thin-walled cups

An electric Allrounder 720 A in the "Ultimate" performance variant demonstrates at NPE 2024 that high-quality injection molding technology can be an alternative to thermoforming. The exhibit uses injection compression molding to produce thin-walled IML cups that can be easily recycled after use.

The directly driven high-performance machine with a clamping force of 320 tons (2,900 kN) is equipped with a 29.8-ounce (size 1300) injection unit that is specifically optimized for high performance. Thanks to high-precision servo motors from Arburg's sister company AMKmotion, very high injection volume flows and injection speeds of up to 15.7 inches (400 mm) per second can be achieved.

IML cups only 0.015 inch (0.37 mm) thick

The exhibit uses a 4-cavity mold from Brink to produce thin-walled IML round cups from polypropylene (PP) using injection compression molding at an injection pressure of just 23,000 psi (1,600 bar). For process monitoring, the mold is equipped with six high-resolution inductive position measuring and embossing sensors. Four molded parts, each weighing 0.37 ounces (10.4 g) and with a wall thickness of only 0.015 inch (0.37 mm), are pro­duced in a cycle time of 3.95 seconds. The plastic has a biomass footprint and ISCC-certified. Also integrated into the production cell is a side-entry robot from Brink that inserts the labels, removes the finished cups and stacks them on a conveyor belt.

Resource-saving and recyclable

In this particularly resource-saving application for the packaging industry, special emphasis was placed on energy efficiency and on a part design that saves materials. Thanks to the all-electric packaging machine in combination with injection compression molding, the energy footprint is improved by 20 per cent with a significant reduction in part weight from 0.45 to 0.37 ounces (13 to 10.4 g). The flowpath/wall thickness ratio is 380:1. Normally, this would require a very high level of injection pressure – at the expense of energy requirements and mold wear. This is why injection compression molding is used for this application. Compared to classic injection molding, this process requires significantly less injection pressure and it is possible to work with mold temperatures of 68 instead of 54 degrees Fahrenheit (20 respectively 12 °C). The special "Next Cycle IML" label can be separated from the PP of the cup during recycling, so that the product can be recycled by type after use. In contrast to thermo­forming, there are no pre-produced foils and stamping waste.