The hypothesis of the present study is that thin multiple layer coatings on paperboard from the aqueous solutions of poly(vinyl alcohol) (PVOH) at high machine speeds is more effective in terms of barrier properties than one or two thick layers. The objectives included attempts to use surface roughness parameters to understand the coating process and mechanisms behind coating defects. The present study is focused on pilot-scaled PVOH coating onto uncoated paperboard at machine speeds of 400 m/min. The multiple coating operation was carried out in six passes with a dry coat weight of about 1 g/m² in each layer. The concept of thin multiple coatings resulted in coated surfaces without detected pinholes and with Kit rating 12 after only two thin layers. However, the oxygen transmission rates were still fairly high (100 ± 89 cm³/m² day atm) after six layers, and some coating defects (such as craters and cracks) could be identified. The analyses of surface structure indicated that the surface properties are affected by water uptake during the coating processes. The compression of paperboard beneath the metering element seemed to be required to achieve homogeneous thin layers. However, an analysis of defects revealed flaws and inhomogeneities near objects protruding from the surface, such as surface fibers and craters, caused by blistering. For rough paperboard substrates, the desired barrier properties may require a careful balance between sufficient compression for fiber coverage and gentle compression in order to avoid defects near craters and surface fibers.

This study investigates the impact of multilayer structures and drying strategies on the barrier properties of high-speed starch/bentonite-coated paperboard. The study examines the impact of drying at a high machine speed of 400 m min⁻¹, addressing a key knowledge gap. The hypotheses were that thin multilayer coatings reduce oxygen permeability more effectively than thick single or double coatings and that gentle infrared (IR) drying would be required to achieve this effect. The experiments comprised up to six consecutive coating applications, each providing a dry coat weight between 0.5 and 1.5 g m⁻². The IR dryer power ranged from 207 kW to 829 kW, and different IR frame positions were tested. The results indicated that thin multilayer coatings resulted in fewer pinholes, lower oxygen transmission rates, and improved grease resistance compared with one or two thick layers. However, the effectiveness of the multilayer-coated paperboard was influenced by the employed drying strategy. Specifically, gentle IR drying reduced pinholes, lowered oxygen transmission rates and enhanced grease resistance.

This study investigates the impact of multilayers and drying strategies on the barrier properties of high-speed starch/bentonite-coated paperboard. The machine speed was 400 m/min. The hypotheses were that thin multilayer coatings reduce oxygen permea-bility more effectively than thick single or double coatings and that gentle infrared (IR) drying is required to engender this effect. The experiments involved coating paperboard up to six times with dry coat weights between 0.5 and 1.5 g/m² in each layer. The IR dryer power ranged from 207 kW to 829 kW, and different IR element positions were tested. The results indicated that thin multilayer coatings resulted in fewer pinholes, lower oxygen transmission rates and improved grease resistance compared with one or two thick layers. However, the effectiveness of the multilayer-coated paperboard was in-fluenced by the employed drying strategy. Specifically, gentle IR drying reduced pin-holes, lowered oxygen transmission rates and enhanced grease resistance.