The influence of coating colour composition on the crack area after creasing

Clay- and GCC-based coatings with different binder systems and different binder contents on a copy paper substrate were printed and creased. The samples were then scanned using a flatbed scanner and the crack area was characterised by the area of the white regions. Cross sections of the creased samples were then prepared and studied with SEM. Replacing some of the latex with starch increased the crack area, but the crack area decreased with increasing binder level. GCC-based coatings showed a much smaller crack area than clay-based coatings. This was probably due to different cracking mechanisms. Whereas the GCC-based coatings showed small cracks perpendicular to the plane, the clay-based coatings showed cracks parallel to the plane resulting in delamination and the disruption of large sections from the surface. These large sections resulted in visible cracks.