Barrier Integrity Evaluation
Integrity checks for surface coatings provide a visual verification of the continuity of a protective layer. Dye penetration testing identifies failures in the moisture or grease barriers of paperboard and flexible packaging. The liquid travels through any pinholes or cracks, leaving a visible mark on the reverse side or within the substrate.
This method provides a clear visual map of where the protection has failed.
Procedural Step
A technician applies a specific chemical solution, such as a turpentine-based dye or an aqueous ink, to the coated side of the sample. During dye penetration testing, the time taken for the liquid to appear on the other side is carefully recorded. Rapid appearance suggests a major flaw in the extrusion or coating process.
If the dye stays on the surface for the full duration of the test, the barrier is considered continuous and effective. This test is often performed on creases and folds to check if the converting process has damaged the protective layer.
Quality Assessment
Observations from the test inform the mill about the uniformity of the coating application. Because dye penetration testing is a destructive method, it is typically used on random samples from a production lot to verify consistency.
