E32 - Characterisation of paper surfaces for improved printing paper grades

The main objective of the Action was to develop and improve methods for analysis of printing paper surfaces in order to improve print quality.

A novel method suitable for detailed studies of the compressed paper structure has been developed. This method may be used to study both printed and unprinted paper samples under load, and offers the possibility to compress the paper with realistic backing materials and pressures for the printing situation. Furthermore, a method has been elaborated to measure the local stress distribution obtained in a paper surface when it is exposed for a certain pressure. Data obtained with this technique correlates with missing dots in rotogravure prints. A modification of the Bentsen roughness characterisation method has also been developed.

Further, the Action made efforts to develop methods that can measure ink distribution on printed surfaces and correlate this to the local topography and chemistry. It has been demonstrated that clay particles in yellow ink may be used as a tracer when studying ink pigment distribution with a scanning electron microscope. Clay may also be used when examining both the printing paper surface and paper cross-sections. It has also been shown that ink pigment penetration increased with increasing surface roughness and increased printing pressure. Data presented revealed that the oil component in the ink may contribute to as much as 70 % of the print-through. Another new technique measures absorption rate of coatings and is useful for understanding print quality in inkjet printing. A method to study fines in cross-sectional Scanning Electron Microscope images has also been presented. This method provides a useful tool to quantify digital-fines, and may be used in further studies to increase the knowledge of paper-ink interactions. Knowledge gaps and relevant research have been widely discussed.

The Action provided a platform for interaction between scientists and papermakers in Europe which has been able to ensure a comprehensive transfer of knowledge, to achieve progress regarding the influence of paper structure and chemistry on the obtainable print quality for different printing processes as well as to identify knowledge gaps and to suggest relevant research. The Action has created a valuable network of scientists and persons from the industry comprising not only the paper making industry, but also the entire printing industry as well as suppliers of chemicals and equipment to both of these industries.
The generated knowledge has been compiled on the Action web-site (http://www.pfi.no/gary/COSTE32.htm), which will be maintained further on.

The Action organised two conferences. The first was held in Autumn 2005 in Madrid, focusing on paper and ink properties and their relation to offset printability. The final conference was arranged in Autumn 2007 in Grenoble, with a broader discussion on paper in printing processes.