Dust, fibers, hair, and plastic chips become permanent impressions when trapped between a hot sheet and the tool. Clear, glossy, and finely textured parts reveal contamination that may be invisible on the cold sheet.
Static charge attracts airborne particles to many thermoplastic sheets. Dry air, protective-film removal, conveyor motion, and wiping with unsuitable cloths can increase the charge. Contamination can also come from wood tools, trimming operations, insulation, clothing, or dirty cooling air.
Control the source
The sheet and tool should be cleaned with methods that remove particles without scratching or leaving residue. Ionized air can reduce static where it is properly installed and maintained. Vacuum extraction is preferable to blowing debris around the forming area.
Housekeeping must include racks, clamps, heaters, fans, and overhead surfaces. Cleaning the tool immediately before forming will not solve contamination that is released from the oven or cooling system during the cycle.