Coating Systems

Advances in slot die coating technology for hot melt adhesives

By Mark Miller, Coating Tech Slot Dies, LLC*

Introduction. When it comes to fluid coating onto substrates, the equipment required falls into three areas:
1. Extrusion coating
2. Hot melt coating
3. Liquid coating
What makes these three coating methods the same and what makes them different?

Extrusion coating is typically non-tacky molten polymers being cast onto substrates with a nipped roll and a large air gap. In extrusion coating, the coating head is directly fed from an extruder. Hot melt coatings are typically tackified polymer adhesives that be­have similar to molten polymers, but engage with the substrate in a proximity arrangement. Hot melt coating heads are fed by a precision metering pump being fed by an adhesive melter. Liquid coating resembles the proximity arrangement of hot melt coating, but the fluid is flowing at room temperature. Unlike extrusion and hot melt coating, liquid coating requires some form of curing to solidify the liquid on the substrate. Extrusion coating utilizes cooling to develop a solid film coating, while hot melt adhesive coatings solidify from cooling or curing.

Coating Tech Slot Dies, LLC, Eau Claire, WI 54703 USA