Abstract
Aqueous dispersions of styrene–butadiene (SB) copolymers were used for coating paperboard in order to improve its surface characteristics and barrier performance with regard to water vapour. The SB-grades, which were chosen from a wider range of latices evaluated in an earlier study, differed in their degrees of cross-linking and carboxylation. An important result was that the performance (including a reduction in water vapour transmission rate) of the coated products was significantly enhanced by a pretreatment (precoating or high-temperature calendering) of the board. This was interpreted as being the result of a more homogeneous polymer layer on the substrate. In most cases, the paperboard was coated on a pilot scale and a higher drying temperature improved the film formation up to a certain limit. Too high a drying intensity resulted in the appearance of defects in the polymer layer. The differences in properties between the coated specimens that could be associated with the polymer characteristics were not marked, but a higher degree of cross-linking and a lower degree of carboxylation gave the best results. The water vapour transmission rate of the coated board was substantially reduced by the addition to the coating of a small amount of paraffin wax. Contact angle measurements and electron spectroscopy for chemical analysis (ESCA) indicated that this was due to a migration of the wax to the surface of the polymer film during drying. The wax addition also reduced the tendency for the polymer layer to stick (block) at elevated temperatures.
Published Version
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