Description

In extrusion coating a thin molten polymer film is coated on some kind of substrate. At highextrusion coating speed, even a minor disturbance on the melt web causes major quality problems, which veryrapidly lead to large quantities of waste. Therefore, higher coating speeds require polymers with high and evenquality in order to avoid waste due to polymer edge instability and web break.

The rheology-related phenomena that may cause problems in extrusion coating are neck-in (NI) anddraw-down (DD). The neck-in is the reduction of the film width and may cause uncoated areas on the substrate. Theneck-in is less if the melt elasticity is high. The draw-down is the ability of the melt to be drawn to thin filmswithout breaking. Draw-down is favored by a melt that is more viscous than elastic.

In optimizing the extrusion coating processing performance it is of utmost importance to balance the rheology of the polymer. This method describes how rheological measurements can be used to characterize LDPE. The storage modulus and zero shear viscosity have been found to be useful parameters to predict the extrusion coating performance of LDPE.