The Influence Of Roughness And Elastic Modulus On Gravure Print Quality: A New Test Method And Model, 2004 Coating and Graphic Arts Conference

Roughness and compressibility of paper surfaces are known to be important factors for minimizing the occurrence of missing dots during gravure printing. However, in most cases, only smoothness is measured for these grades. In this research, an ultra low load indenter is used to evaluate the near surface modulus of small contact points on the sample surface. The indenter is able to measure the modulus of the paper surface at different loading rates and loading forces with a contact dimension less than 0.1 mm. Coating layers with a range of binder types and pigments are applied to a woodfree base, a wood containing base, and sized basepapers. The samples are characterized in terms of compressibility and roughness. Roughness is measured with both air leak methods and a mechanical stylus. A supercalendered (SC) grade is also tested. Samples are printed with the Heliotest in the laboratory to evaluate missing dots. A model is proposed, that describes both roughness and compression and may be able to predict rotogravure print quality.

The results show some correlation between roughness and missing dots, but compressibility of the surface can be just as important. The rough but compressible SC paper had the best performance in terms of missing dots. Air-leak roughness tests tend to group samples according to the base, but the mechanical stylus tends to give a good result for a range of bases. A large reduced modulus of the surface is found to promote missing dots. This result shows that poor compressibility is a factor in the missing dot issue. Model parameters are correlated with the indenter tests. The model predicts the occurrence of contact between the paper and the inside plane of a gravure cell in the printing event.