Grease Resistance
Crease resistance testing under ASTM F119 establishes the barrier performance of flexible packaging materials against oil and grease penetration. Packagers of butter, baked goods, and pet food apply this standard to evaluate whether coated papers and laminates prevent unsightly stains and structural degradation during extended shelf life. The method exposes creased and flat substrate samples to a standard reference fluid at elevated temperatures under a constant load for specific time intervals.
Operators visually inspect the underlying creped kraft paper for dark spots that signal oil migration through pinholes or microfissures in the barrier layer. Substrates failing the threshold risk consumer rejection and package delamination upon contact with fatty contents.
Thermal Stress
Temperature acceleration alters polymer mobility within extruded coatings and wax layers during the test cycle. Fluid viscosity drops sharply at sixty degrees Celsius, forcing liquid migration through microscopic defects that remain impassable at ambient storage conditions. Creasing introduces mechanical trauma along fold lines, creating localized thinning where extrusion polyethylene or aqueous barrier coatings crack under bending stresses.
Paperboard stiffness dictates the severity of these crease fractures, because rigid folding boxboard creates sharper radii than flexible paper grades. Barrier integrity depends entirely on maintaining polymer continuity across those high-strain folding axes without sacrificing heat sealability or converting speed on packaging lines.
Migration Boundary
Endpoint determination relies on standardized staining criteria rather than chemical quantification of migrated mass. Evaluators measure the percentage of total creased surface area showing grease contact after a set exposure period, typically four hours for standard food contact laminates. High-density polyethylene extrusion coatings typically withstand prolonged exposure without failure, whereas wax-impregnated papers exhibit rapid breakthrough once temperature softens the crystalline wax structure.
Specifications derived from these results protect secondary corrugated shippers from grease staining during palletized transport and retail display.
