Analyzing the Influence of Color Masterbatch on the Injection Molding of Post-Industrial Plastic Waste

In injection molding, achieving a uniform color is essential to product quality. Achieving this is challenging when using virgin polymers, but becomes even more difficult when processing recycled plastic waste, which typically contains contaminants that can affect the optical properties of an injection- molded part. One approach to keeping product color constant despite inhomogeneous input materials is to add color masterbatch. For quality assurance purposes, we experimentally investigated the minimum amount of masterbatch to be added to achieve a defined color of an injection-molded part made from recycled material. To this end, we fabricated discs using mixtures of color masterbatch with virgin and recycled (shredded post-industrial waste) materials. Using a single-stage injection molding process, plastic flakes were directly processed without the intermediate step of regranulation. The process involved a robotic arm removing the part from the mold and transferring it to a photobox that guaranteed constant lighting conditions during measurement with integrated inline color and temperature sensors. The masterbatch concentration in the input material was systematically varied to determine the minimum content required for achieving a defined reference color derived from discs made from virgin material and the recommended 2 wt% of masterbatch. Our experiments demonstrate the potential for more economical use of masterbatch when processing recycled material. The color sensor further allowed us to adjust the masterbatch content during the process, as the color of each injection-molded part was measured inline in real time. This provides the basis for an automated control of masterbatch dosing.