Resin Decomposition
1. Continuous High-Temperature Heating: As plastic is heated above its melting point, it gradually degrades. The higher the temperature and the longer the duration, the faster the degradation. The degraded plastic may form carbonization, which can then lead to black spots in the plastic lining equipment production.
Resin Retention: There are parts within the extruder, such as check rings and threaded grooves, which are prone to resin retention. If resin remains in these areas for an extended period, it can easily lead to caramelization or carbonization, resulting in black spots.
Part Two: Contamination or Foreign Matter Mixed In

1. Material Issue: If particles with a lower decomposition temperature than the main resin are mixed into the hopper, these resins tend to decompose, resulting in black spots.

Recycled Plastic: The recycled plastic from film-laminating equipment becomes easier to decompose after multiple heatings, and it may also be contaminated by metal during the recycling process, leading to the formation of black spots.
3. Molding Contamination: Residual lubricants, metal powders, and resin additives may remain in the mold, which could seep out and adhere to the surface of the molded product during the molding process, forming black spots.
Insufficient Cleaning
Incomplete cleaning: If the equipment is not properly cleaned, black spots may remain in the reverse rings and thread grooves within the extruder. During subsequent production, these black spots may mix into the plastic melt, forming black spots on the plastic-coated equipment.
2. Shutdown Impact: During shutdown, plastic melt may adhere to the inner walls of the extruder barrel and head, as well as the screw. Following shutdown and as the equipment naturally cools and then reheats for the next cycle, the plastic melt on the plastic-coating equipment may undergo thermal degradation, turning yellow and becoming carbonized, ultimately forming black spots.
IV. Environmental Factors
If there is dust or oil污 in the production environment of the plastic molding equipment, these impurities may adhere to the plastic melt, eventually forming black spots.
In summary, the reasons for black spots on plastic-coating equipment may involve resin decomposition, contamination or foreign matter, insufficient cleaning, and environmental factors. To effectively prevent the occurrence of black spots, it's necessary to regularly inspect and maintain the equipment, ensure raw material quality, enhance cleaning efforts, and maintain a clean working environment.