Key points of pvc foaming process control
Plastic foam molding is divided into three processes: the formation of the bubble core, the expansion of the bubble core and the solidification of the bubble. For the pvc foamed sheet with chemical foaming agent, the expansion of the bubble core has a decisive influence on the quality of the foamed sheet. PVC is a linear molecule with short molecular chain and low melt strength. In the process of bubble core expansion into bubbles, the melt is not enough to cover the bubbles, and the gas is easy to overflow and merge into large bubbles, which reduces the product quality of the foamed sheet. .
The key factor to improve the quality of PVC foam sheet is to increase the melt strength of PVC. From the analysis of the processing characteristics of polymer materials, there are many ways to improve the melt strength of PVC, but the most effective way is to add additives to improve the melt strength and reduce the processing temperature. PVC is an amorphous material. As the melt temperature increases, the melt strength decreases. On the contrary, as the melt temperature decreases, the melt strength increases, but the cooling effect is limited and only plays an auxiliary role. ACR processing agents have the effect of improving the melt strength, and the foaming regulator is the most effective. The melt strength increases with the increase of the foaming regulator content. Generally speaking, as long as the screw has sufficient dispersing and mixing ability, the addition of a high-viscosity foaming regulator has a more obvious effect on improving the melt strength.