Control of the shelf life of flexible packaging polyurethane laminating adhesives and optimization of waste reduction

The two-component flexible packaging polyurethane laminating adhesives have a fixed shelf life, also known as the operable time, which is a key process parameter that is easily overlooked in lamination production. After the main agent and curing agent are mixed, a continuous cross-linking reaction occurs, and the viscosity of the adhesive solution will continuously increase over time. Once the applicable period is exceeded, the adhesive performance will significantly deteriorate, directly affecting the quality of the lamination.

 

The use of adhesive beyond its expiration date is extremely harmful. In the early stage, it is manifested as the adhesive solution becoming thicker, reduced fluidity, uneven coating, and appearance defects such as orange peel, thick edges, and missed coating. As the reaction continues, the adhesive solution gradually gels and fails, and the adhesive bonding activity is completely lost, resulting in poor adhesion of the composite film, local delamination, a sudden drop in medium resistance performance, and triggering batch defects.

The ambient temperature is the core factor affecting the shelf life. The higher the ambient temperature, the faster the polyurethane cross-linking reaction, and the applicable period of the adhesive is significantly shortened. In a low-temperature environment, the operation time can be appropriately extended, but it will reduce the coating leveling. At the same time, if the workshop humidity is high, water vapor participates in the reaction, which will accelerate the deterioration of the adhesive solution and shorten the usable duration.

 

During production control, it is necessary to mix the adhesive in small quantities and multiple times as needed, and avoid accumulating large amounts of mixed adhesive at once. In hot seasons, the adhesive can be stored at a lower temperature and supplied in batches. Strictly control the interval time from mixing the adhesive to coating, and resolutely prevent the reuse of adhesive that has exceeded the time limit. Standardized control of the applicable period can not only stabilize product quality but also effectively reduce adhesive waste and lower production costs.