Standard Method
Standardized laboratory test methods quantify the surface resistance of paper and paperboard to hydrocarbon liquids and synthetic grease penetrants. Referred to in technical specifications as kit tappi t 559, this procedure applies numbered mixtures of castor oil, toluene, and n-heptane to evaluate oil repellency. The method tests fluorochemical-treated paper, dispersion-coated board, and naturally dense greaseproof substrates.
It does not measure true fluid barrier performance over long storage periods or under elevated temperature conditions.
Chemical Protocol
Testing procedures rely on twelve distinct reagent mixtures possessing decreasing surface tension and increasing solvent aggressiveness. Solution Number 1 contains pure castor oil, representing the mildest exposure, while Solution Number 12 consists entirely of heptane and toluene. Technicians drop single drops of selected test solutions onto the substrate surface from a specified height.
After fifteen seconds of contact, an absorbent tissue wipes away the liquid, and visual inspection checks for surface darkening or pinhole penetration. The highest solution number that remains on the sheet surface without wetting or staining defines the numerical rating. Fluorinated surface treatments achieve high numerical ratings by lowering substrate surface energy.
Modern fluorine-free barrier formulations rely on dense polymer networks to resist low surface tension solvents. Temperature variations in the laboratory alter liquid viscosity and surface energy, requiring strict climate control during testing.
Surface Boundary
Quality assurance departments utilize numerical ratings to verify greaseproof properties during paper machine production runs. Converting operations demand specific threshold ratings prior to manufacturing food packaging cartons. Test results provide rapid benchmark data for mill quality control.
