Uneven coating, inconsistent thickness, and the formation of opposite surfaces in polyurethane laminating adhesive - causes and corrective measures

In the dry lamination production process, uneven coating, inconsistent thickness on the left and right sides, and opposite surfaces are typical defects in the coating process. The problem manifests externally as inconsistent glossiness on the membrane surface, large differences in light transmittance and brightness, local higher strength and local softness after curing, and subsequent chain problems such as local excessive residual, non-drying, and delamination, which are important hazards affecting the consistency of the entire roll quality.

 

The imbalance of the coating system of the equipment is the core cause. Local blockage on the surface of the mesh roller, dried glue adhering to the mesh, will result in inconsistent glue amount on the roller surface, and long-term thin coating at corresponding positions; imbalance in the pressure of the scraper, tilting of the knife holder, and deformation of the knife edge, causing significant differences in the amount of glue scraped from both sides, directly forming opposite surfaces on the left and right sides. Accumulated glue and impurities over a long period of production will also continuously interfere with the uniformity of coating.

Improper glue conditions and process parameters will aggravate the deviation. High viscosity and poor fluidity of the glue, uneven leveling after coating, accumulation of glue in low-lying areas and thinning at high areas; uneven mixing of the glue liquid, stratification of solid content, fluctuations in coating amount before and after machine operation. Rapid changes in machine speed, uneven air force in the drying tunnel, and fluctuations in substrate tension will disrupt the uniform spread of the glue layer, causing inconsistent thickness and uneven brightness.

 

To completely improve the situation, standardized control of coating must be established. Regularly thoroughly clean the mesh roller to prevent clogging and blockage; calibrate the level and pressure of the scraper to ensure uniform scraping of the glue. Mix the glue thoroughly and ensure uniform viscosity to avoid stratified glue liquid before machine operation. Stabilize the production speed and tension, adjust the uniformity of the air force in the drying tunnel, allow the glue layer to spread uniformly and cure consistently, completely eliminate the defects of opposite surfaces and inconsistent thickness, and ensure the stable and uniform quality of the entire roll composite.