How to reduce air bubble during Acrylic Extrusion

During Acrylic extrusion process, one common defect is air bubble contained in products. Let us have one quick review the causes and how to reduce methods.
Causes:
1. The raw material or resin contains some moisture;
2. Some air is not exhausted between machine break and re-start;
3. The environment is too moisture;
4. Some areas of processing temperature is too high,

How to reduce?
1. Have the resin oven heated and check the water content% to meet processing requirements;
2. Adding one additional device to pre-heat the material to reduce the water content%;
3. Environment humidity check;
4. Monitoring different process points temperature, if it's over-heated, some relevant action should be in place.