The Gap between a Tested Sample and the Shipped Pallet
Verify mill test certificates against ISO 2859 sampling on arrival; static swatches omit deckle variance, transit moisture creep, and food migration risks.
Cobb 60 Test
Liquid Absorption
Measured mass transference defines the Cobb 60 Test during a precise sixty second water contact window. The evaluation quantifies surface water resistance for paper and board grades by recording grammage gains per square meter under a standardized hydrostatic head. Laboratory technicians clamp circular test pieces beneath a metal ring, pour distilled liquid into the cavity, and remove the excess moisture with blotting sheets after the duration expires.
Results dictate sizing efficiency across containerboard manufacturing lines, establishing how well corrugated outer liners tolerate ambient humidity during cold storage cycles. High absorption values signal under-sized cellulose matrices prone to softening, whereas low figures restrict glue penetration during box assembly. Production tolerances demand tight variance control because excessive sizing prevents aqueous adhesive bonding on high speed folding carton machinery.
Gravimetric Mechanics
Saturated weighing scales determine final absorption metrics following controlled liquid exposure. Technicians position dry specimens on rubber mats before applying the retaining cylinder and locking the assembly with mechanical clamps. Pouring exactly one hundred milliliters of water establishes a uniform one centimeter head pressure across the upper substrate face.
Timing begins immediately upon contact and operator dexterity governs the decisive moment when absorption halts. Blotting heavy rollers press the damp surface immediately after ring removal, extracting unabsorbed droplets without disturbing swollen surface fibers. Scale measurements record the wet mass relative to initial conditioned weights, yielding grams per square meter values that mills use to adjust sizing chemical additions at wet end formers.
Surface Sizing
Sizing chemical additions dictate the boundary where liquid penetration slows inside dense paper structures. Rosin emulsions and alkyl ketene dimer dispersions coat individual cellulose fibrils, raising contact angles to repel polar liquids effectively. Starch size presses alter porosity profiles on top sheets, shifting absorption characteristics away from raw pulp defaults.
Converting operations rely upon stable sizing metrics to prevent moisture distortion during multi color offset printing runs. Variations in drying cylinder temperatures alter internal sizing efficiency, shifting test outcomes across machine direction reels. Controlled surface chemistry balances liquid resistance against printability demands, ensuring boards accept water based inks without feathering while maintaining edge wick barriers.