Fold Cracking in Coated Woodfree Papers

摘要

This paper presents a comprehensive overview of the phenomenon of cracking when a paper or board is folded, and of the factors which influence it. The focus is on coated woodfree papers for sheet-fed offset printing with grammages higher than 170 g/m~2. Investigations carried out at MODO Hallein have paid special attention to the base paper properties and especially to the role of surface starch and of ways in which it can be softened and made less brittle. The driving force for this investigation was an increasing number of complaints relating to fold cracking, especially with respect to a 170 g/m~2 double-coated woodfree printing paper (MoDo EuroArt 170). Fold cracking of coated paper during printing and converting is influenced by nearly all steps in the papermaking process, such as fibre preparation, sheet forming, drying and coating. Each of these steps has to be considered separately and carefully if a suitable printing paper is to be created that is amenable to folding processes. It is not in fact possible to give a generally accepted recommendation for the production of paper with excellent folding proptrties. This paper tries to give advice to papermakers and converters on how to work within the realms of what is possible (fibre raw materials, costs, available equipment etc.).