Latex-Pigment Dispersion Coatings as Water Vapor Barrier Material on Special Paper

Most packaging solutions require adequate protection from water and water vapor. Concerns over current thermoplastic barrier materials due to lack of biodegradability, recyclability and repulpability have sparked interest in more environmentally friendly and economical alternatives such as water-based barrier coatings (WBBC). With WBBCs the barrier to water vapor still remains most challenging task, owing to hydrophilicity of available materials and required thin coating. In this thesis, the performance of latex-pigment dispersion coatings on a special paper was studied. The fundamentals of moisture transportation and emulsion polymerization are presented. The effects of amount of pigment, drying temperature, coat weight and temperature-humidity environment to water vapor transmission rate (WVTR) were studied using styrene-acrylate latex and clay pigment coating colour blends. Filler-binder compatibility and possible tortuous effect studies on diffusion were made by using a range of pigment grades, such as carbonates and clay blends, along with a range of latices of different composition. Coatings were made using laboratory scale coater, and the WVTR was determined with gravimetrical cup method. Experimental emulsion polymerizations were also carried out to study the role of latex hardness and functional monomers with different crosslinking ability. Great improvement in suppressing both WVTR and water absorption in paper is possible using styrene-acrylate based dispersion coatings. Water vapor barrier can be improved with higher coat weigh with optimized clay filler amount and drying conditions. It was evident that hydrophobic latex structure provides the main barrier component to the film structure. Functionalizing or internally crosslinking the styrene-acrylate latex can have minor impact on the barrier performance. Tropical environment WVTR tests proved to be challenging to acrylate based coatings, resulting in multiplication in WVTR values compared to standard 23 °C and 50 % relative humidity conditions