The causes and improvement solutions for the insufficient initial adhesion of solvent-free polyurethane laminating adhesive

The weak initial adhesion is a typical problem in solvent-free lamination production. The viscosity of solvent-free adhesives is high at room temperature, and the process of solvent-free wetting and penetration occurs. The bonding strength of the film material immediately after the lamination is completed is extremely low, which easily leads to shifting, warping, wrinkling during winding, misalignment of the film layer, etc., seriously affecting the stability of subsequent cutting and bag-making processing. This is a key control pain point of the solvent-free process.

 

The insufficient initial adhesion mainly stems from product characteristics and process deviations. After the solvent-free two-component adhesive is mixed, the initial cross-linking reaction is slow, and a high-strength bond cannot be formed within a short period of time. It mainly relies on mechanical bonding to fix the film layer. At the same time, when the coating temperature is too low, the fluidity and wetting property of the adhesive deteriorate, and it cannot fully adhere to the microscopic surface of the substrate, resulting in poor anchoring effect and further reducing the initial adhesion force.

In addition, deviation in the ratio and uneven mixing of the adhesive can cause local lag in the reaction of the adhesive layer, resulting in weak initial adhesion in some areas. Low room temperature, insufficient composite pressure, and improper tension matching during winding can all lead to loose adhesion between the film surface, resulting in whole or local slippage and loose winding defects, and an increase in the defective rate of semi-finished products before finalization.

 

Improvement in production can be achieved by increasing temperature control for adhesion, optimizing coating temperature, and enhancing the smoothness and wetting effect of the adhesive flow. Precise calibration of the ratio, uniform mixing of the adhesive, and ensuring consistency of the adhesive layer reaction. At the same time, reasonably increasing the composite pressure and matching the gradient winding tension, and when necessary, using high initial adhesion-modifying solvent-free adhesives. Multiple measures can completely solve the problem of insufficient initial adhesion and ensure the flat and stable semi-finished product rolls.