Polymer Dispersion
Aqueous synthetic emulsions formed by the free radical polymerisation of acrylic and methacrylic esters act as binders in pigment formulations for high brightness coated board. Formulators introduce acrylic latex to anchor pigment particles within the coating matrix, securing them against picking during lithographic offset separation. Glass transition temperatures dictate the flexibility of the resultant dry film, which avoids yellowing under ultraviolet radiation exposure because the polymer backbone lacks aromatic rings.
The system ceases to act as an unreacted dispersion once drying temperatures drive coalescing particles beyond their minimum film forming threshold.
Coating Rheology
Formulations containing these synthetic binders exhibit shear thinning behaviour across trailing blade and rod coater assemblies. Viscosity drops predictably under elevated blade pressures, which prevents streaks across high speed webs and preserves an even coat weight. Pigment binding strength derives from the carboxyl functional groups grafted onto the acrylic polymer chains, creating ionic crosslinks with chalk or kaolin particles.
Thermal stability throughout infrared drying tunnels limits binder migration toward the surface, leaving pore capillaries open for controlled ink reception.
Print Cracking Performance
Flexographic and offset carton converters evaluate the polymer specifically for score durability along package corners. High glass transition formulations generate brittle crease lines, causing catastrophic top coat flaking under ninety degree folder gluer tooling. Softer modifications absorb the tension developed on folding scores without rupturing the white mineral layer over unbleached solid bleached sulphate base stocks.
Elastic elongation in the binder prevents microscopic checking on reverse scores, preserving pristine bar code scan rates on the outer retail face.
