The combination of spray and blade coating: Method development and validation on Cylindrical Laboratory Coater

Pigment coating is an essential unit operation for most high quality papers and boards that are intended to undergo printing. The currently dominating coating techniques are metered size press (MSP) and blade coating with jet, flooded nip, or short dwell-time application, which all have their distinct advantages and drawbacks. A new coating method comprising a spray application and a doctor blade is being developed to overcome some of the shortcomings, while preserving the desired features of blade coating. The main focus was on coating layer quality and on the runnability of the spray blade coater. A laboratory scale spray blade coater was constructed by modifying the coating color applicator pond of Cylindrical Laboratory Coater to house the airless high pressure spray nozzle and the hose delivering the coating color. Lightweight coated (LWC) and folding box board (FBB) bases were coated with various blade pressures and coater speeds yielding different coat weights. Judging by Parker Print-Surf roughness, gloss, and visual appearance in scanned images of coated samples, the new spray blade coating method was capable of producing high quality coating layers. The results were repeatable and the method was found suitable for studying the phenomena involved in spray blade coating process.