Causes and Improvement Solutions for Vertical Lines, Texturing, and Linear Scratch Defects in Polyurethane Laminating Adhesive Coating

In the dry lamination coating process, vertical lines, texturing, and longitudinal line scratches are very common surface defects, often occurring in high-speed production and high-viscosity coating conditions. This problem manifests as regular or irregular longitudinal lines on the film surface, significant light transmission after coating, and uneven plate surface. It not only affects the appearance grade but also causes local uneven thickness of the adhesive layer, resulting in deviation in peel strength and local adhesion failure, etc., which are quality hazards.

 

Poor viscosity and leveling performance of the adhesive are the core reasons for the appearance of vertical lines. Excessive viscosity of the Polyurethane Adhesive and insufficient dilution lead to poor fluidity and extensibility of the adhesive solution, and the dots cannot be quickly closed and leveled after being coated by the mesh roller. The higher the machine speed, the shorter the leveling time of the adhesive solution, and the longer the dot traces are stretched and solidified, forming continuous longitudinal scratch lines. This defect will further aggravate in low-temperature environments.

Abnormal equipment conditions are the key factor for the high incidence of line scratches. Blockage of the mesh roller, accumulation of adhesive, and local wear cause uneven coating of adhesive. After coating, fixed vertical lines are formed. Uneven scraper pressure, worn knife edge, and residual adhesive debris will continuously scrape out strip-shaped adhesive traces. In addition, impurities in the adhesive solution, crust particles, and those stuck between the scraper and the mesh roller will also cause continuous line defects.

 

On-site rectification requires comprehensive optimization of process and equipment management. Precisely control the working viscosity of the adhesive to ensure excellent leveling performance. Reasonably match the dilution parameters according to the machine speed and reserve sufficient leveling time. Regularly clean and maintain the mesh roller, grind the knife edge, remove adhesive debris, and ensure a clean and smooth coating system. Stabilizing process parameters and equipment status can completely eliminate vertical lines and texturing defects, ensuring uniform and flat adhesive layers.