Knife over roll system

The most common coating application method is the knife over roll system (Fig. 2.16). The shape and angle of the coating blade, the gap between the blade and the fabric and the viscosity of the coating all affect the amount of coating applied and the penetration into the fabric. 

Recently, hot melt PSA systems have been introduced and radiation curable PSA systems are at the commercial development stage. High solids (50%-70% by wt.) nonaqueous dispersion acrylic PSA systems have also been reported(1). Unlike the hot melt and radiation cured systems which require new capital outlay in coating head and/or curing (drying) equipment, BFG has developed PSA systems, based on Hycar 2100R reactive acrylic liquid polymers and isocyanate terminated prepolymer, which can be processed at 80% solids (by wt.) with equipment presently used in the PSA industry, namely, the reverse roll and knife-over-roll coater. 

Figures VI and VII illustrate the initial viscosity of both the Hycar 2103 and Hycar 2106 systems as well as the viscosity increase with time due to the reactive nature of the 2-component system. These figures will help in determining the percent solids necessary for processing on a given piece of equipment depending upon its viscosity handling capability. Since the 100% solids PSA systems have high initial viscosities of over 100 Pa s (100,000 cps), the conventional knife-over-roll and reverse roll coaters can not process them.

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