Standard Bench Viscometry Methods for Aqueous Paper Coating Emulsions
Bench viscometry of paper coating emulsions requires standardized temperature control, verified spindle geometry, and multi-shear profiling to ensure runnability.
Latex Emulsion
Liquid Binder
Synthetic polymers suspended in water allow for the formation of a durable film upon evaporation in diverse coating applications. Latex emulsion provides the cohesive force that holds pigments and fillers together on a substrate surface after the carrier liquid disappears. High solid content determines the dry film thickness left behind on paper or board, while the glass transition temperature of the polymer controls the flexibility and hardness of the final surface.
Manufacturers formulate these dispersions to achieve specific adhesion levels and water resistance on porous or nonporous printing stocks.
Adhesion Dynamics
Shear forces inside a coating head influence how effectively the droplets pack together during the drying process. Latex emulsion requires a specific temperature window to ensure that the individual particles coalesce into a continuous layer without cracking. If the environment stays below the minimum film forming temperature, the particles remain separate and result in a chalky surface with low rub resistance.
Additives such as surfactants adjust the surface tension to maintain a uniform distribution across the web.
Production Constraints
Compatibility with existing mill equipment dictates the choice of chemistry for any given converting line. Stability remains a requirement during high speed pumping and application because mechanical agitation can prematurely trigger the coagulation of the binder. Filtration removes any gel particles that form during storage or handling before the material reaches the applicator roll.
Controlled pH levels keep the dispersion from destabilizing during the addition of other formulation components. Successful coating depends on maintaining the viscosity within a tight range to prevent streaks or uneven pick strength during the transfer to the substrate.