Extrusion Metric
Pressure differential measured across the screen pack of a plastic extruder used to apply polymer coatings to paperboard. In the extrusion lamination and coating process, melt filtration pressure indicates the resistance to polymer flow through the filtration system as molten plastic is forced towards the die. This measurement shows the resistance to polymer flow through the filtration system as molten plastic is forced towards the die.
Contamination Detection
Organic residues, un-melted gel particles, and metal fragments gradually build up on the surface of the screen pack during continuous operation. This accumulation restricts the available flow area, which causes the melt filtration pressure to rise. When recycled resins are used for the polymer layer, the rate of pressure increase is typically much higher due to the presence of residual paper fibres or cross-linked polymers.
Monitoring this rate of change allows operators to assess the quality of the incoming plastic pellets.
Process Interruption
When the pressure reaches a preset limit, the screen pack must be changed to prevent screen rupture or degradation of the coated surface. Modern co-extruders use continuous screen changers to swap filters without stopping the production line, which minimizes downtime and reduces waste. Regular screen replacement prevents the occurrence of pinholes and ensures a uniform barrier layer.
