Abstract: A method for simultaneously coating multiple thin layers of relatively viscous fluids comprises the relative adjustment of the viscosity of the fluids in order to achieve a viscosity ratio in the optimum range without adversely affecting the adhesive properties of the fluids. In the preferrred method, viscosity is adjusted by varying the temperature of one or both fluids prior to coating and/or by reformulating the liquids to vary their relative viscosities.

Abstract: A method for simultaneously coating multiple thin layers of relatively viscous fluids comprises the adjustment of the pressure gradients in the interface region between two confluent flows. In particular, the pressure gradient along the middle lip is regulated so as to not be excessively positive, in order to position the separating line of the top flow at a particular point on the die lips, thus enhancing stable flow. In one aspect of the method, a step configuration is designed into the die lips so that the downstream lip steps away from the web in the direction of web travel. In another aspect of the method, the pressure gradient at various locations in the bead is controlled by beveling the upstream and downstream lips. In yet a further aspect of the present method, the viscosities of the two liquids being coated are matched at the relevant shear rates to promote good coating quality.