Metered Size Press Coating • What to expect from Specialty Starches?, PaperCon 2010 Conference

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After a short introduction to starch chemistry it is explained which qualities a starch should possess to be useful as co-binder for high performance coating colors. For good performance in terms of machine runnability and final printability of the coated papers, a lot of optimization is necessary. Based on 20 years of experience with metered size press coating, it is outlined which rheological properties are key during the different stages of this coating process. For an optimal behavior during film pre-metering, transport, transfer and solidification the high-shear viscosity and visco-elasticity combined have to be balanced and the water retention adjusted to the absorptivity of the base paper and the machine speed. These properties are influenced by the type and intensity of the starch modification and the coating solids. From a technical point of view (misting), maximized solids are desirable whereas the economics demand the maximum use of starch. The application of modern technologies enabled us to develop starches that allowed us to solve the apparent conflict of achieving the two aforementioned goals at the same time: we can run coatings in the MSP at high solids which still contain significant proportions of an intelligent bio-binder. Case studies show in detail at which stage which properties are decisive to obtain the desired result in terms of add-on, misting-free application and a regular, smooth coating layer. Modern starch technology is so flexible that the most diverse requirements of metered size press coating can be covered.

Starch-based biopolymers have developed into an absolutely essential co-binder that enables an ecological and economic coating process.