| A relationship exists between jacket shrinkage and the variables: draw down ratio (DDR), draw index (DI), melt temperature (Tm), molecular weight (MW) and percent HFP co-monomer for a PVDF-HFP copolymer tube-on wire extrusion process. Jacket shrinkage for this system is due to a combination of effects, the most prevalent being relaxation of polymer orientation after the drawing process. Polymer orientation was created primarily during the drawing process outside the die. It was shown that jacket shrinkage varied primarily as the draw down ratio and draw index varied. Changes in melt temperature, molecular weight, and/or comonomer composition were also shown to affect jacket shrinkage. The crystalline nature of PVDF was shown to be only a minor contributor to jacket shrinkage. Polymer orientation due to shear effects through the die was also shown to be only a minor contributor to jacket shrinkage. To produce the minimum amount of jacket shrinkage for a PVDF-HFP jacket tube-on process, it was shown that the process needed to have a draw down ratio ranging between 4 and 7, a melt temperature between 230 and 250°C, and a draw index of 1.0, coupled with a PVDF-HFP co-polymer having a relatively low molecular weight and low comonomer addition. |
