Dispersion coating with carboxylated and cross-linked styrene–butadiene latices. 1. Effect of some polymer characteristics on film properties

Abstract

Polymer dispersions can be used for coating paper products in order to e.g. enhance their barrier properties. The influence of characteristics such as the degree of cross-linking (the gel content), glass transition temperature and degree of carboxylation of styrene–butadiene (SB) latex polymers on the mechanical properties and water vapour permeability of the corresponding polymer coating films at room temperature has been investigated. The storage modulus in the rubbery region increased markedly with increasing degree of cross-linking and the blocking (sticking tendency) towards adjacent paper substrates was in general somewhat lower at higher cross-link densities. There was also a tendency for the water vapour permeability to decrease somewhat with higher degrees of cross-linking. The degrees of carboxylation were quite low for the studied SB-dispersions and it had only a minor influence on the mechanical performance and barrier properties of the films. Reducing the glass transition temperature significantly below room temperature had a negative effect with regard to the blocking/sticking tendency of the polymer and on the water vapour permeability. On the other hand, a glass transition temperature significantly above room temperature resulted in a coating film with microcracks that caused a marked deterioration in the physical properties. These films were rather brittle with a low elongation at break. All the polymer films were also characterised using scanning electron microscopy, contact angle measurements and ESCA (electron spectroscopy for chemical analysis).