Online-Concepts for the production of coated papers are today widely used within the paper industry. Thernintroduction of the Metered Size Press as an applicator with low mechanical impact on the paper webrncertainly had an influence on this and the consequential further development of alternative non impactrntechnology, i.e. practically non contact coating systems.rnThe Curtain Coater is already a successfully introduced technique for the production of special papers withrnmore than 20 applications world wide. This system because of its good coverage makes it interesting forrnthe field of graphical papers.rnThe use of conventional offset colours in curtain coating leads to runnability problems and surface defectsrnespecially at high speeds. The disturbances are caused primarily as a result of the insufficient stretchabilityrnof the coating colour. Therefore, it was essential to optimise the recipe to meet the special demands of therncurtain coater.rnRheological measurements were used in a precise investigation which made it possible to evaluate suitablernmodifications under laboratory conditions.rnIn particular the extensional rheology, a totally new technique in assessing coating colours, showedrnexcellent correlation between the laboratory assessment and behaviour on the Curtain Coater.rnWith the correct choice of a suitable co-binder it was possible to control the coating defects associated withrnconventional coating mixes. Particularly the use of a special water soluble thickener with high molecularrnweight made it possible to achieve a problem free runnabilty at high speeds and excellent coating quality.
展开▼
