The customer reported that sealing failures were occurring randomly in 500g coffee bags

The customer reported that sealing failures were occurring randomly in 500g coffee bags; some cartons were completely fine, while others had side or bottom seals opening even though the sealing temperature, machine, and operator remained the same. Upon inspection, it was identified that the inner PE layer was too thin and had a narrow sealing temperature window. Normal machine temperature fluctuations of approximately 5°C, combined with the heavy coffee weight and uneven thickness in the gusset area, resulted in occasional under-sealing and over-melting. This is why the defect appeared random rather than continuous. After increasing the PE thickness to 80–100 microns, using a wider sealing-range PE grade, and slightly extending the sealing time at the gusset and bottom seal areas, sealing stability was restored, and the leakage issue was fully resolved.