Occurrence of reverse side effects in corona treatment of dispersion-coated paperboard and its influence on grease barrier properties

Abstract

The uncoated side of dispersion-barrier-coated paperboards was exposed to positive and negative direct current corona treatments in order to confirm the occurrence of backside treatment and clarify its effects on the usability of the paperboard. The main component of the coating dispersions was hydroxypropylated potato starch and the effects of talc and styrene-butadiene latex additions on backside treatment were evaluated. Coatings with a high talc proportion showed excellent initial grease resistance, but corona-induced strikethroughs caused a drastic decrease in grease penetration time. The root-mean-square roughness measurements revealed moderate surface roughening at the backside, indicating thus backside treatment. The alterations in surface free energies and rapeseed oil contact angles confirmed the occurrence of backside treatment. The high polarization potential of latex played a key role in these observations. At the same time, the inertity of talc had a stabilizing effect but it did not prevent backside treatment completely. X-ray photoelectron spectroscopy results verified that backside treatment occurs also when the barrier-coated side of the substrate is treated with corona, indicating that a dispersion coating layer does not prevent this undesired phenomenon. Bearing in mind that expressing customized information or including personalized elements in food food packages or disposable cups and plates is under great interest, it can be assumed the exposure of packaging materials to corona will become more common in the near future, and the need for optimizing bio-based packaging materials for such purposes is obvious.