Lily:
I wasn't sure if you were making siding, window profile or pipe.
What I'll share is related to siding.
When you talk to your compound supplier, ask them what type of impact modifier (acrylic, CPE, etc), stabilizer and process aiding are in there, in addition to the lubricant. For example, we saw that CPE processed much differently than acrylic. CPE burned around the edge of the dye and processed over a much narrower window than acrylic did.
Good luck
B. Polimera