Board Coating with Constant Tip Angle Control, 1998 Coating Conference Proceedings

A coating method used in board and fine paper coating is studied, where coatweight is controlled with the blade load, while maintaining the tip angle constant. The theoretical basis for two alternative coatweight control modes are compared, i.e., the traditional variable tip angle mode and the new constant tip angle mode. The influence of tip angle on coatweight and surface characteristics is studied at three different speeds and with three different coating color compositions. The results were treated with a nonlinear regression analysis to identify the parameters in a coatweight model based on theoretical and empirical work by other authors.

The results indicate that the optimum tip angle to achieve a given coatweight increases with speed. A low tip angle is recommended for high coatweights, while a higher tip angle is necessary to achieve low coatweights. The results verify that coatweight is proportional to machine speed to a power of 1.5; as shown by other authors. Viscosity has a nearly linear influence on the coatweight, while the tip angle shows an inverse quadratic proportionality to coatweight, which is explained by the equation for hydrodynamic force.

The tip angle did not significantly influence the measured surface characteristics.