Annals of Warsaw University of Life Sciences – SGGW Forestry and Wood Technology № 11 3, 2021: 5-12 (Ann. WULS - SGGW, For. and Wood Technol. 113, 2021: 5-12)
ALEKSANDRA NISKA 1 , EDYTA MAŁACHOWSKA 2
Influence of coating grammage on the utility properties of coated papers
1 Faculty of Wood Technology, Warsaw University of Life Sciences - SGGW, Warsaw, Poland 2 Institute of Wood Sciences and Furniture, Warsaw University of Life Sciences – SGGW, Warsaw, Poland Abstract: Influence of coating grammage on the utility properties of coated papers. The paper coating offers the opportunity to create a product with high added value, the potential of which has been recognized by both paper mills and polygraphs.Indeed, paraffin coatings have excellent barrier, sliding and strength properties, and also increase the quality and durability of the print. This paper presents the results of the research on the influence of the coating weight on the functional properties of the coated paper. To this end, a commercially available paper was coated with a paraffin emulsion using various Mayer rods and then tested using standard mechanical, surface, and water absorption tests. It was found that the coating of the base paper, regardless of the amount of the applied mixture, significantly influences its hydrophobic, surface, and strength properties. Papers with the highest coating weight allowed to obtain a paper with increased strength and high surface smoothing. The completed coatings significantly increased the water barrier, regardless of their thickness Keywords : paper coating; paper hydrophobic; paper utility properties; Mayer rod; papermaking technology INTRODUCTION The coating process consists of applying a coating mixture to the surface of the paper product to improve the functional properties of the paper or for other specialized applications, depending upon the type of mixture. The coating mixture on the surface of paper leads to improvement in the printability of the paper, it also enables the temporary exposure of packaging papers to the weather conditions or reduces the penetration of liquids and fats into packages intended for contact with food. The composition of coating mixtures may differ for various applications it depends mainly on the printing technique for which the coated paper products are intended and the coating technique, and in particular the blend concentration, that can be used in a given coating technique.Depending on the intended use of the paper, it can be coated single or both sides. In the paper industry, for the coating of cartons, ready-made packages, and cardboard, emulsions based on high-melting polyethylene waxes or ethylene homopolymers and copolymers are used.These emulsions show excellent stability, a high degree of fragmentation of the wax particles to a size below 0.5 μm [1], as well as appropriate utility parameters, consisting in the production of wax coatings with an excellent barrier, sliding, and strength properties.The produced coatings are transparent, which increases the quality and durability of the print [2,3,4]. The paraffin emulsion coatingis a certain barrier to water, as it has a much lower porosity than the substrate. In the case of printing papers, excessive liquid absorption is most often associated with poor image reproduction. Such a layer, therefore, enables a clear and defect-free print to be obtained with a much lower ink requirement than in the case of paper without such a coating. Paper-based materials produced without hydrophobising agents exhibit natural hydrophilicity, i.e. the ability to absorb water, both in liquid form and from water vapor. The rate of absorption and the amount of water that the paper can absorb in a given time depends, among others, on the ingredients of the paper and its structure, the moisture content of the paper, the degree of water purity, or its temperature [5]. Most often, this is a disadvantageous phenomenon, because the absorption of liquid by the paper causes changes in
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