The technical risks and improvement measures caused by the imbalance of the mixing ratio of the main agent and curing agent in the flexible packaging polyurethane laminating adhesive

In the dry lamination production of flexible packaging, the mixing ratio of the main agent and curing agent of the two-component Polyurethane Adhesive is a key control point that determines the final quality of the composite film. Many factories rely solely on experience to mix the adhesive, ignoring the fluctuations in the mixing ratio caused by environmental temperature and humidity, as well as batch differences of the adhesive. This can easily lead to a series of concealed quality defects, which are only exposed after the adhesive has matured, resulting in large-scale scrap.

 

When the curing agent is insufficiently added, the cross-linking reaction is incomplete, and the cross-linking density of the adhesive layer is low. The internal cohesion of the adhesive film is insufficient, resulting in a lack of bonding strength, poor drying after maturation, sticky film surface, and easy delamination during storage. At the same time, the medium resistance and boiling resistance of the composite film will significantly decline, unable to meet the requirements of medium and high-end packaging.

Excessive addition of the curing agent also poses risks. Excess curing agent cannot participate in the cross-linking reaction and remains in the adhesive layer, easily undergoing side reactions with water vapor, causing the surface of the composite film to turn white, bubble, and also increasing the odor of the finished product, increasing the pressure for controlling solvent residues, and easily causing brittle cracking at the heat seal edge during bag making and heat sealing.

 

In actual production, the mixing ratio should be strictly followed according to the product technical parameters, and random addition or reduction of the curing agent should be avoided. Under low-temperature and high-humidity working conditions, the mixing ratio should be appropriately adjusted to compensate for the consumption of curing agent by water vapor; the mixing should be thoroughly and evenly carried out, and the mixing record should be made. At the same time, the activation time of the adhesive should be controlled, and expired adhesive should not be used beyond the expiration date. This can prevent various composite defects caused by the imbalance of the mixing ratio from the source.