Laboratory Measurement of Blade Coating Runnability, 1998 Coating Conference Proceedings

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In the production of coated papers, the occurrence of bleeding hampers improvement of production efficiency. A lab-scale method for evaluating the susceptibility of coating colors to bleeding without the use of base paper was developed and investigated. The relative susceptibilities of coating colors to bleeding, as found by this method, showed a close correspondence with those obtained by pilot coater tests .

The results indicate that it would be possible to estimate the critical coating speed, defined as the speed at which bleeding will occur during coating, in a pilot or commercial coater by adjusting the data obtained by this laboratory method for the increase in the solids content of colors just under the blade due to the water absorption by the base paper as determined by separate dynamic water retention testing. The results also indicate that there is a third color property, in addition to high-shear viscosity and water retention, that determines its tendency for bleeding. This factor, though not yet identified, is most likely related to changes in the viscoelastic behavior of the color under shear application and release. The laboratory method, in any event, provides a reliable means of evaluating color runnability which includes the influence of this factor.