The causes of gelation, blockage and sedimentation of polyurethane laminating adhesive, as well as on-site prevention and control measures

Gelation, blockage and sedimentation of Polyurethane Glue are common abnormal problems in the production of flexible packaging lamination. Once gel particles appear in the glue solution, they will directly cause problems such as coating particles, sand spots, scratches on the mesh roller, and network blockage, resulting in poor appearance of the composite film, local lack of glue and delamination, and seriously affecting the continuity of production and the qualified rate of finished products.

 

Water vapor intrusion is the primary cause of gelation and blockage of the glue. The isocyanate groups in the curing agent are extremely active. Contact with moisture in the air, water-containing diluted solvents, damp glue tanks and pipelines will quickly undergo a polymerization reaction, generating insoluble gel hard masses. High humidity environments in summer, opening the storage tank, storing glue, and having unsealed equipment pipelines are the main scenarios where gelation occurs frequently in the workshop.

Glue ratio imbalance and storage exceeding the expiration date will also accelerate the blockage. When the two-component glue is mixed and exceeds the applicable period without being used in time, the glue solution will continue to cross-link and thicken, gradually forming gel clusters. The curing agent stored separately getting damp, the main agent mixed with impurities, and the mixing of new and old glue will all disrupt the stability of the system and cause local blockage and flocculent particles. The high-temperature environment will accelerate this reaction process exponentially.

 

Prevention and control measures should include sealed storage of glue tanks, preventing moisture and water ingress, testing the moisture content of solvents before use. Adhere to small amounts and multiple times of glue mixing, strictly prohibit the reuse of expired glue solutions, regularly clean and seal the glue supply pipelines and glue trays. At the same time, do a good job in dehumidification and temperature control in the workshop, filter the glue solution impurities in time, and prevent gelation blockage problems from the source to ensure the stable operation of coating production.