Carbon specs in polyethylene LDPE film are inevitable. I had to explain this to yet another prospective customer who has a zero tolerance for carbon in film.
When simple hydrocarbons are exposed to prolonged heat, they become carbon when overcooked. PE resin which gets hung up in the extruder eventually becomes carbon. From time to time, these specs break loose and end up in the PE film. It is impossible to see all of them without 100% manual inspection which is not practical at linespeeds of hundreds of feet per minute.
Carbon will break loose more often in a "job shop" because the viscosity of the resins changes frequently.
These carbon specs are inert, they are not impurities and much less harmful than any PVC.
Just the same, perception trumps reality especially in clean room and medical where every square inch of film is inspected stiing still. Rather than set one roll of film aside, the tendency is to throw the baby out with the bathwater and reject the entire run.
In 50 years, we haven't figured out how to prevent carbon in LDPE film. The most practical solution is to just set the rolls with carbon aside.
Over the last few weeks I noticed my car's gas mileage dropped. Less than an hour after the discussion about carbon, the idiot light came on. Turns out my car needed a serious accumulated carbon buildup purge.