Audit Procedures for Converter Food Contact Declarations
Auditing converter food contact declarations requires cross-referencing batch test reports, simulant conditions, dual-use additives, and NIAS screening data.
Polyolefin Set Off
Meaning
Migration of ink or additive materials from a printed surface to the rear side of an adjacent film layer occurs when polyolefin set off creates unintended physical bonds during winding or storage. This phenomenon appears during the cooling phase of high-speed extrusion where thermal energy within the roll traps volatile species between contacting sheets. Residual surface energy dictates the adhesion strength between the film faces.
High levels of slip agent or low molecular weight wax components increase the probability of unwanted transfer.
Thermal Migration
Heat accumulation inside large mill rolls drives the molecular movement across the gap between wound layers. Pressure from the tension of the winding process forces intimate contact between the outer surface of one wrap and the inner surface of the next. Cooling protocols determine the amount of time the roll remains above the threshold where mass transfer stays active.
Proper cooling prevents the film from retaining enough internal energy to sustain the attraction forces. Moulders find that managing roll hardness and ambient humidity reduces the risk of blocking or image transfer on finished products.
Economic Consequence
Excessive material transfer leads to the rejection of entire master rolls due to surface degradation or print quality loss. Production schedules face disruption when quality control detects damage upon unwinding for secondary conversion. Manufacturers measure the financial loss by calculating the weight of compromised film against the total volume of the processed lot.
Scrap rates remain high if operators fail to adjust chill roll temperatures or cooling capacity to match the output rate of the extrusion line.
Process Variable
Maintaining optimal film surface tension through corona treatment limits the propensity for chemical migration. Precise application of anti-blocking agents provides a mechanical buffer between film layers to minimize contact area. Extruders hold these parameters within narrow limits to prevent the surface from becoming too smooth or excessively tacky.
Consistent control of these variables ensures the integrity of the print during the shelf life of the package.