Flexographic Barrier Coating Viscosity Measurements for Aqueous Latex Formulations
Aqueous latex barrier performance depends on controlling dynamic high-shear viscosity to ensure complete anilox cell release and eliminate film pinholing.
Aqueous Latex Barrier
Barrier Dispersion
Dispersed polymer particles suspended in water form an aqueous latex barrier on paper substrates during online coating applications. Coaters apply this colloidal suspension via air knife or blade metering systems to achieve a continuous film weight target of ten grams per square meter. The coating halts moisture vapour transmission and grease migration across the substrate matrix.
Production lines set drying oven temperatures above the polymer coalescence threshold to fuse the latex particles into a pinhole free film. Mill operators measure performance using Cobb sizing tests to verify water absorption resistance before converting operations begin. Board converters utilize this treated stock for folding cartons requiring mineral oil migration resistance.
Coating Physics
Thermal energy removes the aqueous carrier phase during the drying phase, forcing individual polymer spheres into intimate contact. Capillary forces draw the remaining water toward the surface as the wet film shrinks under infrared dryer banks. High molecular weight styrene butadiene copolymers or acrylic emulsions form the continuous polymer matrix once the water vanishes entirely.
Coater speed and solids concentration govern the viscosity profile of the liquid dispersion prior to film formation. Shear forces inside the metering nip align the latex particles parallel to the cellulose fibre network.
Substrate Interaction
Cellulose fibres present an irregular topography that demands adequate latex penetration to prevent localized pinholes in the dried film. Penetration depth depends on the Gurley porosity of the underlying kraft linerboard and the surface sizing degree. Excessive binder migration leaves the paper surface starved of polymer, resulting in localized grease penetration failures during end use testing.
Converters adjust calendering pressure to smooth the micro roughness of the paper before the dispersion touches the web. Final barrier integrity relies entirely on maintaining uniform film thickness across the cross direction profile of the paper machine.