Greetings everybody,

I have a returning problem during TPE processing (2K overmold), what I couldn’t solve yet.
TPE-SEBS overmolded on PP with talcum additive.

The tool is an index rotary plate mold. The tool is a valve gated 4 cavity tool. The valves controlled by hydraulic.

The production is runs well, the parameters are stable, the part quality is fine. But after a few weeks of production, contamination appears on the TPE material. The injection pressure increasing and also the fill time. The cavity balance starts to became wrong. One cavity starts to overfill, while other cavities are underfilled.

In the past, after this issue, the toolshop disassemled the tool and we see the TPE material burned on the valve pins, and inside the manifold (which we can’t check.)
We checked the hydraulic valve pins and there is no oil leakage. The pins moves at the same time and same speed. They open at the beginning of the injection phase with a delay. (-0,5 s)
At the end of the production we use a purging compound to clean the barrel and the hot-runner system. We also ue it when there is a longer stillstand of the machine.

In the material datasheet the range of the melt temperature is given beetween 160 – 240°C. We use 200 °C.
I checked the residence time of the material, and it’s 1,7 minute. The maximum residence time is 5 minute for this material.
We use 50% of the barrel capacity.

I’m new to this TPE processing and I don’t have any ideas how to solve this issue.

Thanks for the advice!