Causes and Control Measures for Coagulation of Polyurethane Adhesive Sheets and Premature Gelation of Adhesive Liquid in Flexible Packaging Dry Lamination Production

In the field of flexible packaging dry lamination production, coagulation of Polyurethane Adhesive sheets and premature gelation of adhesive liquid are relatively common on-site faults. The formation of a hard layer on the surface of the adhesive liquid and its premature gelation can mix with the adhesive liquid in the adhesive tank, causing blockage of the screen roller, uneven coating, and crystal points and other defects on the composite film. Premature gelation of the adhesive liquid directly leads to the waste of adhesive and disrupts the normal production rhythm.

 

Environmental moisture intrusion is the primary cause of coagulation of the adhesive sheet. The components of two-component polyurethane curing agent are highly prone to react with moisture in the air. High humidity in the workshop, open placement of the adhesive sheet, and inadequate sealing of the supply system allow moisture to continuously contact the surface of the adhesive liquid. The surface layer undergoes cross-linking first, resulting in a layer of elastic rubber sheet.

Secondly, if the adhesive is stored for an excessive period after activation, it will also accelerate the overall gelation. The mixed adhesive liquid after mixing has an effective usage period. After exceeding the activation period, the molecules continue to react, the viscosity rises rapidly, and the fluidity is lost, no longer suitable for machine coating. During high-speed production interruptions and machine shutdowns, the adhesive liquid remains in the adhesive sheet and pipeline, which will also accelerate coagulation and gelation.

 

In terms of production control, after mixing the adhesive, it must strictly follow the activation time and be used immediately. The adhesive sheet should be sealed with a cover plate to reduce contact with air; in high-humidity weather, the workshop should be dehumidified. During shutdown intervals, the surface coagulation of the adhesive sheet should be cleaned promptly. For long-term shutdowns, the adhesive liquid in the supply pipeline should be drained. Adhesive liquid that has already gelled and formed lumps must not be diluted and reused to avoid hidden quality risks for the composite products.