The Hazards and Precise Control of Mixing Ratio Deviation in Solvent-Free Polyurethane Laminating Adhesive

The solvent-free two-component polyurethane laminating adhesive is extremely sensitive to the accuracy of the mixing ratio. Even a slight deviation in the ratio of the main agent and the curing agent can seemingly have no impact on the appearance of the coating, but it will lay down a large number of latent quality risks. Compared to solvent-based laminating adhesives, the solvent-free system has 100% solid content and no solvent dilution buffer. Deviation in the mixing ratio will directly change the cross-linking structure, causing abnormal curing, adhesive failure, and post-processing re-adhesion, which are batch-related accidents that are the core hidden quality risks of solvent-free composites.

 

The problem of insufficient curing agent is the most common. Insufficient curing agent will lead to incomplete cross-linking reaction, and the adhesive layer cannot form a dense network structure. After curing, the adhesive becomes soft and has a large amount of residual viscosity, which is prone to problems such as re-adhesion, adhesion, and low peel strength. During the storage process, the unreacted main agent groups continue to precipitate, which will also cause ink migration, fogging on the plate surface, and a significant drop in water boiling resistance performance.

Excessive curing agent is also very harmful. Excess curing agent cannot participate in the cross-linking reaction and continuously generates carbon dioxide by absorbing water vapor in the air, resulting in bubbles in the composite film, white spots, interlayer voids. At the same time, the adhesive layer undergoes excessive cross-linking, becomes more rigid, and loses its toughness, making the finished product prone to cracking, brittleness, and aging performance degradation. Transparent films may also develop yellowing, haze increase, and other appearance defects.

 

Production control requires regular calibration of the mixing ratio of the adhesive mixing machine's metering pump and flow parameters to eliminate dynamic deviations caused by pressure fluctuations and pump blockages. Before starting the machine, remove the glue for calibration of the ratio to prevent imbalance caused by residual pipelines. It is strictly prohibited to adjust the ratio randomly by hand or based on experience when mixing the adhesive. Precisely lock the standard ratio and stabilize the cross-linking system to avoid various quality risks caused by poor mixing ratios from the source.