Nozzle drool is usually a sign of a substantial reduction in the viscosity of the material. A primary cause of the reduction in viscosity is material degradation. Nozzle drool can also be caused by built up pressure in the barrel and excessive heat in the front zone or nozzle.
Material Degradation
Material degradation can cause a drop in melt viscosity which, under pressure, will leak from the nozzle. Be sure that material is sufficiently dried. Since most of our TPVs are slightly hygroscopic, drying the material at 82°C (180°F) for at least 3 hours (at least 4 hours for blends with regrind) is recommended. Reduce residence time or melt temperature to ensure that material is not being degraded in the barrel. If the machine is left idle at processing temperatures for more than 20 minutes, it is good practice to purge the material inside the barrel.
Pressure Build Up
Using decompression to deliver a short burst or pull back of the screw after it stops turning so the material is pulled under vacuum may eliminate the drool. Use caution when using decompression to eliminate drool. Excessive decompression can cause too much air to be sucked in through the nozzle.
Barrel And Nozzle Temperature
Check our Injection Molding Guide for correct processing temperatures. Another cause of drool may be improper gate selection when using hot runners (see the hot runner section of our Injection Molding Guide).
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