Sheet die start up
Vol.19 #3, Nov. 1992
To keep die lips clean during start up and initial sheet casting when molten plastic can stick to the face of the die lips, rub the lips with a silicone grease made for high temperature applications, or a high viscosity silicone oil.
Keep the layer very thin. You don't need to see it for it to be working. Indeed, if you can see the silicone, it is probably hurting your process.
See also
Die lip buildup
Sheet pinning
Silicone grease