Barrier properties and heat sealability/failure mechanisms of dispersion coated paperboard

• Plate-like fillers are often added to improve barrier properties and to prevent blocking of dispersion coatings on paper and board. We have studied the effects of clay addition, neutralizing agent and drying conditions on water vapour permeability, water absorption, oxygen permeability and heat sealability of carboxylated styrene/butyl acrylate dispersion coatings on a pilot scale. The barrier dispersions were applied on a pre-coated side of a three-ply board, using a pre-metering roll coater. Coated strips were sealed under specified conditions of temperature, time and pressure and the sealability was assessed by measuring the peak load necessary to break the joints. The surface composition of the barrier-coated board was analysed and the mode of failure was characterized by ESCA. The occurrence of pinholes in the barrier coatings was assessed by both staining tests and ESEM/EDX analysis of the surface topography. The resulting barrier properties were satisfactory as far as resistance to water transport in both liquid and vapour form is concerned. The oxygen permeability was similar to that of similar amorphous polymers. Heat-sealing tests showed that the mode of failure was mainly cohesive in nature, as fibre tear occurred when sealed strips were separated. Neutralization with sodium hydroxide gave poor adhesion and had a negative effect on the seal strength. Barrier measurements and ESEM/EDX analysis both showed that the pinholes present extended only through the barrier coating

Nyckelord

Barrier coating

carboxylated styrene/butyl acrylate latex

clay

WVTR

Cobb

heat sealability

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