Hot melt extrusion coating machine
A hot melt extrusion coating machine is a specialized type of hot melt coating equipment that uses an extruder screw or gear pump to force molten polymer (usually polyethylene, polypropylene, EVA, or hot melt adhesive with very high viscosity) through a flat die onto a moving substrate. Unlike roll or spray coating, extrusion coating produces a thick, uniform layer with excellent edge definition. The machine comprises an extruder barrel with heating zones, a screw drive, a die assembly, a chill roll, and a nip roll. It operates typically at temperatures between 150°C and 320°C.
The extrusion process starts with solid thermoplastic resin or adhesive pellets being fed into the hopper. They are conveyed forward by the rotating screw while being heated to a molten state. The molten material then passes through a screen pack and into a coat-hanger style die, which distributes it evenly across the width. The molten curtain exits the die lip and is drawn down onto the substrate (e.g., paper, cardboard, aluminum foil) which is moving over a chill roll. The nip roll applies pressure to bond the extrudate to the substrate, and the chill roll rapidly solidifies the coating.
Hot Melt Coating Machine - Hot Melt Adhesive Coating Machine
Primary applications of hot melt extrusion coating machines include: 1) Liquid packaging board (e.g., milk cartons) where a layer of polyethylene is extruded onto paperboard to provide moisture and grease resistance. 2) Release liners for labels, where a silicone coating is extruded or laminated. 3) Industrial tapes requiring high-tack hot melt layers. 4) Coated fabrics for tarpaulins or tents. 5) Asphalt-based membranes. The extrusion coating can achieve coat weights from 10 to over 100 gsm with thickness uniformity of ±2%.
Key benefits of extrusion coating include the ability to handle very high melt viscosities (up to 100,000 cP or more), which cannot be pumped by standard gear pumps. The process also allows co-extrusion, where two or more layers of different polymers are extruded simultaneously through a multi-manifold die, creating composite coatings with enhanced properties (e.g., sealability + adhesion). Additionally, extrusion coating eliminates the need for a separate adhesive application step because the molten polymer itself acts as the adhesive and coating layer.
When choosing a hot melt extrusion coating machine, factors such as screw diameter (typically 45mm to 150mm), L/D ratio (24:1 to 32:1), die width, and line speed (50–500 m/min) must be matched to the substrate and coating thickness. The chill roll surface finish and cooling capacity determine the gloss and crystallization rate of the coating. Safety features include melt pressure transducers, burst discs, and emergency brake systems. Regular maintenance involves screw pull-out cleaning, die lip adjustment, and roll grinding. Extrusion coating is a mature technology, widely used in packaging converting, and offers excellent barrier properties compared to solvent-based coatings.
