Surface Resistance
Gram weight mass per unit area quantifies the capacity of a paper or board substrate to resist liquid penetration under a fixed hydrostatic head during a duration of sixty seconds. When applying cobb 60 water absorption, technicians clamp a circular metal ring onto the sample surface and pour one hundred milliliters of distilled water inside to initiate the contact. The test relies on the pressure exerted by the column of water against the fibers.
Absorbency correlates directly to the internal sizing level of the material, which dictates how chemical additives restrict fluid flow through the interstitial gaps between cellulose chains. Heavier sizing treatments lower the numerical result because chemicals occupy the void spaces that water would otherwise inhabit. Variations in this test value signal potential failure points in downstream processes such as flexographic printing or barrier coating application where wet ink or adhesive chemistry interacts with the porous matrix.
Processing Requirement
Machine settings depend on this measurement to prevent ink bleeding or uneven substrate swelling during high speed production. Paper mills maintain precise control over sizing agents like alkyl ketene dimer or rosin soap to ensure the final product meets the specifications of the converter. Operators adjust the concentration of these internal agents to stabilize the sheet against the aqueous phase of fountain solutions found in lithography.
If the value drops too low, the sheet risks losing structural integrity when exposed to water based adhesives in lamination. High values indicate an porous surface that consumes excessive ink, driving up costs while lowering print density. Accurate monitoring allows for tighter tolerances on the filling line where moisture protection is a necessity for food contact packaging.
Barrier Performance
Converting workflows verify the integrity of wax or polymer layers by checking that the substrate beneath maintains a stable cobb 60 water absorption value before the application of final coatings. Base stock uniformity ensures the protective chemistry remains on the outer face instead of soaking into the depth of the sheet. Consistent sizing acts as a foundation for the performance of the entire multi layered package design.
Results stay within a narrow range to guarantee uniform adhesion across the entire width of the web during the converting cycle. Each mill batch carries a specific resistance profile that predicts the success of the secondary sealing process.
