Analysis and Countermeasures of Defects in Polyethylene Blown Films

Polyethylene (PE) blown films are widely used in food packaging, agricultural mulching films, industrial protection and other fields due to their excellent flexibility, high cost performance and good processability. In actual film blowing production, affected by raw material properties, equipment precision, process parameters, operating specifications and other factors, the films are prone to quality defects such as fish eyes, uneven thickness, bubble oscillation, wrinkles and adhesion, which directly reduce the product qualification rate and service performance. To standardize production control and reduce defective products, this paper conducts a systematic analysis on common defects and corresponding optimization countermeasures based on the principles of film blowing technology and practical production experience.

The major common defects of the films include fish eyes and crystal spots, thickness deviation, unstable film bubbles, as well as surface adhesion and wrinkles. Fish eyes and crystal spots are mostly caused by poor resin plasticization resulting from impurities in raw materials, insufficient mesh count of filter screens and low extrusion temperature. These defects impair the flatness and light transmittance of films, and will adversely affect printing and lamination effects in severe cases. Uneven film thickness mainly stems from inconsistent die gap, fluctuating melt pressure and unbalanced air output of the air ring. Excessive longitudinal and transverse thickness deviation will lead to irregular rolling and uneven stress on finished products. The oscillation and snaking vibration of film bubbles are primarily attributed to uneven air volume of the air ring, misaligned bubble stabilizers, and mismatched blow-up ratio and draw ratio, which tend to produce large quantities of defective products. In addition, insufficient cooling, uneven pressure of traction rollers and lack of slip additives in raw materials will cause film wrinkles, surface adhesion and poor opening performance.

Targeted rectification countermeasures are formulated in accordance with actual production conditions to address the above defects. In terms of raw material control, qualified film-grade PE resin shall be adopted. Mixing of different materials and impurity contamination shall be eliminated, and the moisture content of raw materials shall be strictly controlled. For process regulation, the temperature shall be accurately controlled according to different materials including LDPE, LLDPE and HDPE to ensure full plasticization of resin. The blow-up ratio and draw ratio shall be properly matched, and the extrusion speed and melt pressure shall be stabilized. In terms of equipment operation and maintenance, carbonized impurities on screws and dies shall be cleaned regularly, and suitable filter screens shall be replaced. Calibration shall be performed on the die gap, flatness of the air ring and parallelism of traction rollers, and the standard angle of the herringbone board shall be adjusted. During the production and shaping stage, the cooling effect of film bubbles shall be enhanced and the height of the cooling line shall be optimized to realize uniform shaping of films.

In conclusion, most defects of PE blown films arise from the uncoordinated operation of raw materials, processes and equipment. In production, standardized raw material selection, refined process regulation and regular equipment calibration can effectively eliminate various quality problems, stabilize film quality, reduce production losses and improve production efficiency.