Coating structure with calcium carbonate pigments and its influence on paper and print gloss

graph 5100, Micromeritics) and the specific surface area was measured by nitrogen adsorption, the BET-method (ASAP 2000, Micromeritics). The particle size distribution (PSD), a narrow or broad distribution, was determined by using the equation: PSD slope=[75% (ESD)-25% (ESD)]/2.APS, where ESD means equivalent spherical diameter and APS means average particle size. Oil absorption, packing index, colour and abrasivity determinations followed standardised methods. Both pigments and coated paper porosity were evaluated using the mercury intrusion porosimeter technique (Poresizer 5320, Micromeritics). An offset base paper (reference base) having a grammage of 100g/m2 has been used and was coated on both sides. Coating weight on each side was 15 g/m2. All coating formulations were prepared using the same additives and keeping the same processing conditions during coating and calendering. Methodology being used can be found in [1]. Several paper properties were assessed, such as: structural properties (bulk, thickness, Bendtsen air permeability, Bendtsen roughness and profilometry), optical properties (opacity, gloss and light scattering) and, finally, printing property (print gloss). Paper coating machine was an Endupap Universal Coating Machine developed by CTP (Centre Technique de l’Industrie des Papiers, Cartons et Celluloses de Grenoble). The main operative conditions were as follows: velocity 5 m/min; drying temperature 170oC; drying time 1 minute and roll coater number 0.05 graduation. Calendering conditions were: temperature 60oC; linear pressure 70 N/mm; velocity 22.9 m/min. and 1 nip calender.