THE EFFECT OF SURFACE BINDER CONTENT ON PRINT DENSITY AND INK RECEPTIVITY OF COATED PAPER

The effect of binder content in the coating surface on print density a nd ink receptivity of model coated papers has been investigated in ord er to better understand the relations between uneven binder migration and print-density variations in offset printing. For model coated pape rs with a similar surface finish, the print density was solely determi ned by the amount of ink transferred, suggesting that print density va riations are caused by uneven ink transfer in the printing nips, and n ot uneven ink pigment penetration. For coatings prepared with an ident ical formulation, more ink was transferred to the coatings with a lowe r surface binder content, providing further evidence that uneven binde r migration causes uneven ink transfer, leading to print-density varia tions. In addition, we have found, as expected, that binder content in the coating surface depends on both binder addition level in the coat ing colour formulation and on base stock absorbency. This further indi cates the importance of controlling uniformity of base sheet absorbenc y in preventing print mottle on coated papers.