Water Based Coatings That Keep a Pack inside the Fibre Stream
Water-based dispersion coatings achieve food barrier requirements while maintaining full fiber repulpability and standard mill recovery yields.
Alkali-Soluble Resins
Polymeric Binder
Polymeric binders containing acid-functional groups provide pigment wetting and resolubility in water-based packaging inks. Formulators rely on alkali-soluble resins to stabilize aqueous acrylic dispersions and maintain clean printing plates during long production runs. These materials are neutralized with volatile bases such as ammonia to become soluble in water.
Once the base evaporates during the drying phase, the dried film becomes resistant to water.
Dissolution Mechanism
Neutralization of the carboxyl groups along the polymer backbone creates electrostatic repulsion that forces the coiled chains to expand. Solubilizing alkali-soluble resins requires a careful balance of pH, typically maintaining a value between eight and nine to prevent precipitation. If the pH drops during printing, the resin can coagulate on the gravure cylinders or flexographic plates, leading to print defects.
Conversely, an excess of volatile amine delays the dry time of the coating and slows down the converting line. Insufficient amine leads to ink drying on the plate, whereas too much amine causes block resistance issues in the finished rolls.
Rheological Influence
Low viscosity under high shear conditions ensures that inks transfer smoothly. Including alkali-soluble resins improves the Newtonian behavior of the liquid, which prevents misting. Newtonian flow behavior helps in achieving consistent ink film thickness.