A new test method to measure dynamic contact in a printing nip for rotogravure papers

In rotogravure printing a common problem is the non-transfer of ink from cells to the paper, resulting in "missing dots". This is often because of rough incompressible papers, which do not make good enough Contact with the printing cylinder. A novel method for studying dynamic contact between the paper and the print cylinder whilst in the printing nip was developed. In the method. a blue carbon paper is contacted with the lest papers and passed through a printing nip at different pressures. The resultant setoff pattern oil the test paper was captured Using a scanner and then analysed Using image analysis software. A Fast Fourier Transform (FFT) was applied to the set-off pattern to quantify the degree of variation occurring at different length scales. A range of different common coating pigments were assessed, which had been coated onto a ULWC basepaper at three different solids concentrations. When compared to the percent missing dots on the laboratory printed coatings a significant correlation between degree of contact variation and the missing clots was found.