Revised Plan for Addressing Abnormal Viscosity and Failure of Polyurethane Laminating Adhesive during Winter Low-Temperature Construction

During the winter and autumn seasons, dry lamination Polyurethane Adhesive is prone to experiencing seasonal quality issues such as sudden increase in viscosity, poor leveling performance, delayed cross-linking and curing, and insufficient bonding strength. Most factories maintain stable production conditions during the summer and autumn seasons, but after the onset of winter, frequent problems such as uneven coating, slight whitening of the film surface, incomplete curing, and local interlayer delamination occur. These faults are not typically due to batch quality issues of the adhesive but rather are caused by the change in the rheological properties and chemical reaction activity of the adhesive due to the low-temperature environment. This is a typical seasonal process adaptation failure and is also a key and difficult point in winter composite production management.

 

The abnormal increase in adhesive viscosity caused by environmental cooling is the most obvious process change in winter. The polyurethane adhesive resin system is highly sensitive to temperature. At low temperatures, the movement rate of resin molecules slows down, the resistance between molecules increases, and the overall viscosity of the adhesive liquid significantly rises. If production still uses the dilution ratio and coating parameters at the normal temperature, it will result in a higher working viscosity of the adhesive, large coating spreading resistance, insufficient wetting of the substrate, incomplete closure of the mesh roller dots, and ultimately lead to film surface orange peel, vertical lines, and local thin coating defects, directly reducing the flatness and uniformity of the composite film and the adhesive layer.

The low-temperature environment significantly weakens the cross-linking reaction activity of the adhesive, triggering poor curing. The temperature in winter workshop and the reference temperature in the curing room are relatively low, and the cross-linking reaction rate of polyurethane adhesive significantly decreases. It cannot complete sufficient cross-linking within the fixed curing duration and is prone to problems such as soft adhesive layer, re-adhesion after curing, and failure to meet the strength requirements. At the same time， the low-temperature weather in autumn and winter is often accompanied by high humidity， and the curing agent is easily absorbed by the air to undergo hydrolysis reactions， resulting in actual ratio imbalance， gas production and whitening of the system， not only affecting the immediate bonding effect but also significantly reducing the water resistance and bonding durability of the adhesive layer. Later， it is prone to layer separation， blistering， etc.， as delayed defects.

 

To address the drawbacks of winter low-temperature construction， seasonal process standards need to be adjusted. Before production， the polyurethane adhesive should be preheated at a constant temperature to effectively reduce the original viscosity. Combined with the adjustment of dilution ratio and coating parameters for low-temperature conditions， the working viscosity of the adhesive should be kept moderate and the coating flow should be uniform. Strictly control the temperature and humidity in the workshop， appropriately increase the curing temperature and curing time， and avoid semi-cured adhesive layers and incomplete cross-linking. At the same time， strengthen the management of adhesive sealing storage to prevent the curing agent from absorbing moisture and deteriorating. Dynamically adapt the coating speed and tension parameters of the coating vehicle. Through comprehensive winter process adaptation adjustments， various composite defects caused by low temperatures can be completely resolved， stabilizing the quality and yield of products in the autumn and winter seasons.