Defect Causes and Rectification Plan for Low Temperature Resistance of Flexible Packaging Composite Film

The packaging of frozen and refrigerated foods has extremely high requirements for the low-temperature tolerance of composite films. Ordinary polyurethane laminating adhesives tend to harden and become brittle in low-temperature environments, leading to problems such as bag bursting, cracking, layer separation, and a sharp drop in peel strength during storage in cold storage and transportation by cold chain. This is the most typical quality issue in frozen packaging and requires simultaneous optimization of adhesive selection and process.

 

The core cause of low-temperature failure lies in the overly rigid molecular structure of the adhesive layer. The conventional general-purpose polyurethane laminating adhesives have a high crosslinking density and few flexible chain segments, which are stable at room temperature. However, at low temperatures, molecular movement stops, and the adhesive layer quickly hardens and becomes brittle. It is prone to cracking and delamination under external bending and compression. In addition, improper substrate selection and low-temperature toughness of the film material will amplify the adhesive's low-temperature defect.

Process issues can also exacerbate low-temperature problems. Excessive curing leads to a sharp increase in adhesive layer rigidity and loss of toughness. Low coating amount results in insufficient buffering and extensibility of the adhesive layer, unable to counteract the stress contraction of the film material at low temperatures. Imbalanced ratios and uneven crosslinking cause local weak bonding, and cracking and delamination occur first under the concentrated low-temperature stress.

 

A thorough rectification requires the targeted selection of low-temperature-resistant modified polyurethane laminating adhesives, which are rich in flexible molecular chains and maintain excellent elasticity and bonding toughness at low temperatures. During production, excessive curing should be avoided, and the coating dry amount should be controlled moderately to ensure a flexible and full adhesive layer. Reasonable selection of low-temperature-resistant film materials and optimization of the composite tension can significantly improve the low-temperature resistance of the composite film, eliminating cracking, layer separation failures, and other brittle and layering faults in cold chain packaging.