Common delamination problems of flexible packaging polyurethane laminating adhesives and their solutions

Peeling and insufficient peeling force are the most common quality problems in the production of flexibe packaging lamination. Most of these issues are closely related to the selection of polyurethane laminating adhesives, coating processes, and substrate conditions. The polyurethane laminating adhesives used in flexible packaging rely on cross-linking bonding to achieve the composite of multiple layers of films. Any improper control at any stage will lead to defects such as delamination, blistering, and peeling during the storage or use of the finished products. 

 

The failure of the substrate surface treatment is the primary cause. The surface tension of polyolefin substrates such as PE and PP is relatively low. If the corona treatment fails or there are residual oil stains and dust on the surface, the Polyurethane Adhesive cannot form an effective anchoring bond, and the substrate is prone to overall delamination in the later stage. Secondly, the imbalance in the adhesive ratio and uneven mixing of the adhesive will result in incomplete reaction between the resin and the curing agent, insufficient internal cohesion of the adhesive layer, and the occurrence of pseudo-adhesion. 

Environmental and process factors are equally crucial. If the humidity in the production workshop is too high, the moisture will consume the curing agent and damage the cross-linking structure. If the curing temperature is too low or the time is insufficient, the adhesive layer cannot form a dense network structure, and the resistance to media and aging performance will significantly decrease. In addition, if the coating thickness is too thin, it will result in insufficient bonding points; if it is too thick, it is prone to internal curing lag, causing local delamination. 

 

To solve this problem, it is necessary to implement control from the source. Regularly test the surface tension of the substrate, strictly follow the standard for glue ratio, control the coating amount and curing parameters, maintain a constant temperature and humidity production environment in the workshop, which can effectively prevent the occurrence of composite delamination defects and stabilize the quality of product lamination.