The Influence of PCL-ZNO Coating Composition on Coated Offset Cardboard Prints

The most significant printing branch in these days is packaging printing. Packaging must primarily preserve the product from damaging, but atthe same time must attract the consumersto be picked up from the shelf in the store. To ensure protective and aesthetic role of the packaging the prints are commonly coated with varnishes which will improve visual, mechanical, surface, and optical properties. In this paper a coating composed of polycaprolactone (PCL) and nanoscale ZnOwas used to coat the offset prints on the cardboard. The coatingswereprepared by adding various weight amounts of the ZnO nanoparticles (weight ratios of 0.1, 0.5 and 1%) into the mixture of PCL and ethyl-acetate. The coatingswereapplied onto prepared offset prints. The prints wereevaluated before and after coating process by determining colour coordinates, print gloss, watervapour permeability and by calculating colour difference.The results showed that on the uncoated paper coating with prepared OVPs did not affect the colour reproduction outside acceptable tolerance levels, except formagenta coated with w(ZnO) = 0.5 and 1%.The coating with prepared coatings caused almost none change of print gloss on uncoated paper, but increased the print gloss on coated paper. The water-vapor permeability was lowered on both investigated paper types but on the uncoated paper the addition of ZnO nanoparticles decreased barrier properties in comparison to the coating composed of only PCL. Increasing the mass of added ZnO increases barrier properties of the print on both investigated cardboards.To conclude, this research has proved applicability of the PCL-ZnO coatings as a OVP on cardboard offset prints as it did not highly influenced colour reproduction but had decreased water vapour transmission rate. On the coated paper/cardboard one must take into account the increased colour difference ofmagenta and chose the ink to be closerto the target values at the beginning. In addition, to further investigate applicability in the packaging printing, further research should include investigation of resistance to ink fading in the ageing process, bending tests, adhesion etc.
Offset printing, coating, PCL, surface free energy, colour difference, nano ZnO