Standard Laboratory Rub Testing for Matte Overprint Varnishes
Laboratory rub testing evaluates matte overprint varnish durability by measuring specular gloss shifts and receptor color transfer under standardized shear loads.
Delta E Color Transfer
Numerical Deviation
Mathematical calculation of the distance between two color points in a three-dimensional color space quantifies the visual change resulting from surface contact. This delta e color transfer identifies the amount of pigment that migrates from a printed surface to a secondary material during rubbing or pressure. It provides an objective metric for evaluating the rub-off characteristics of ink on newsprint and corrugated board.
Migration Evaluation
Spectrophotometers capture the lab values of the recipient material before and after a standardized rubbing test. The delta e color transfer value represents the total difference between the initial and final states of lightness and chroma. Small values indicate high resistance to smearing, while higher values suggest that the ink has not fully cured or lacks sufficient binder.
If the transfer occurs under dry conditions, it points to mechanical failure of the ink film. Wet conditions might indicate poor chemical resistance of the vehicle or the resin system.
Acceptance Threshold
Industry standards for high-speed finishing often set a maximum allowable limit for this value to prevent marking on downstream equipment. Values above a specific limit are easily detected by the human eye and signal a risk of garment staining or product contamination.