Varnishing of Fiber-based Closures

Abstract: This research aims to investigate water-based varnishes and technologies to coat fiber-based closures to attain water barrier properties. To ensure recyclability the repulpability of coated and uncoated lids is tested. The research approach is exploratory. The investigation begins with the application of varnishes using a spray gun, brush, and dip coating followed by spraying equipment from Spraying Systems. Nine varnishes are tested in the research. Based on the chosen minimum criteria to select the varnish, the primary objective is to analyze which of the varnishes show the following results 1) lower amount of dry coat weight(g/m2) (2) long penetration time (min) (3) high contact angle (°). The appearance (color, texture, and homogenous coating) of the coated lid is evaluated through visual observation. Hydrophobicity is evaluated through water contact angle measurements using a goniometer, penetration time and visual observation. The repulpability trials of the uncoated lid and coated (selected varnish) material is tested using the lab equipment at Karlstad University. The results show that closures coated with varnish 6 and 8 meet the minimum requirement; have a good visual appearance in terms of color and texture, high contact angle and relatively long penetration time. Repulpability results show that lids coated with varnish 6 are recyclable. Spray coating technology appears to be a potential process for implementation, although up-scaling is yet to be evaluated.