The procedure has long offered single-face molds a range of options for inside and outside gated packaging geometries. In the case of stack molds, however, the situation is somewhat different: IML labels, until now, could only be inserted in the outer platen of the tool. This meant that containers, for example, always had to be injected from the inside. The problems with inside gating for containers are twofold: Plastic threads can occur in the material due to unavoidable wear on the tools, and productivity is often reduced because of lower cooling of tool cores. While some moldmakers use complicated sprue bar systems in an attempt to avoid these problems by distributing the hot plastic to the outer plate, this technique is expensive and susceptible to wear.
Building on IML technologies long developed and applied within the company, Waldorf Technik (Engen, Germany) has succeeded in significantly simplifying stack IML processes. It has brought a standard automation solution for IML stack molds on stream, which was shown for the first time at NPE2015. The new system allows up to 8+8 labels to be inserted into the inner plates of stack molds as efficiently, precisely and safely as for single-face tools.
"The danger of threads forming when using efficient stack molds is lessened by injecting containers from the outside," explained Holger Kast, Sales Manager at Waldorf Technik. "Manufacturers who have hitherto been producing on single-face tools for reasons of quality can in future achieve almost double the output in the same space and with the same injection molding machine.
"By comparison with IML containers already made with stack molds, the outside gating to be used in future can be expected to result in shorter cooling times for many products and therefore to higher output", he added.
The development brings other benefits, as well. Injection molders already using a regular stack mold to produce outside gated containers and who wish to convert from offset printing or labeling to IML decoration can switch with relative ease to the new technology. In general, existing stack molds can be easily modified and adapted, at no great cost, for the IML process, now also including the new, automated option to insert the labels in the middle plates. This makes the conversion to the IML technique a relatively hassle-free procedure for injection molders.