A Coating Change That Invalidates a Food Contact Declaration
A raw material shift in barrier coatings alters chemical migration profiles, instantly invalidating food contact declarations and risking complete job quarantine.
Set off Contamination
Ink Migration
Offset contamination describes the unintended transfer of wet ink from the front of a printed sheet to the back of the subsequent sheet in a delivery pile. Printers monitor this phenomenon to prevent image ghosting or physical blocking when high tack or slow setting formulations are used on non-porous substrates. The process relies on heavy pigment loading or insufficient drying time before the mechanical pressure of the stack forces the binder into the adjacent surface.
Substrate Interaction
Surface tension between the coating and the ink vehicle governs the risk of this condition during high speed production. Paper mills supply sheets with specific absorption rates to mitigate the likelihood of transfer, as excess moisture or poor porosity forces the ink to stay on the surface rather than penetrating the fibers. Moisture control in the press room remains the most effective method for managing these variables because environmental humidity influences the drying rate of standard oxidative inks.
Technical Tolerance
Press operators establish a physical boundary for pile height based on the drying capacity of the sheet and the thickness of the ink film. Thin films exhibit lower rates of occurrence, whereas heavy solids or excessive varnish layers increase the potential for sheets to stick together under their own weight. Proper mechanical ventilation at the delivery end of the press ensures that the volatile organic compounds leave the ink film before the next sheet makes contact.
Final stacking weight dictates the permanence of the transfer once the chemical bonds form between the sheets.