Plasma Treatment Replaces Release Agent
In many cases, damage-free release and ejection of molded parts from the mold requires a chemical release agent. This is especially true of injection molded parts with PU elements, since the PU adheres strongly to the steel surface of the mold cavity.
Until now, wet chemical release agents were sprayed into the mold to achieve this release action. The drawbacks of this approach include contamination of other areas of the mold as well as increased maintenance, as molds require regular cleaning. In addition, traces of the release agent usually remain on the ejected parts, which can cause considerable difficulties during subsequent post-molding operations.
A different approach to facilitating release and ejection of PU foam is based on the application of a long-lasting coating to the surface of the mold. It must be kept in mind, however, that such coatings must be “refreshed sooner or later. To prevent extended interruptions of production requires several mold inserts that can be interchanged as necessary.
The so-called open-air plasma technique now offers a new approach to applying release coatings to the cavity’s surface by means of plasma-induced polymerization. Depending on the geometry of area being treated, the process of applying the coating takes only a few seconds and can be incorporated into the injection molding cycle. The coating is refreshed automatically and directly in the mold at specific time intervals that depend on the material and processing conditions. The plasma system is located next to the injection molding machine, with the nozzles mounted to a robot arm. The release coating created is only a few nanometers thick, so that the dimensional accuracy of the molded part is not affected.