Plastic foam molding process is divided into three: the formation of bubble nucleation, nuclear expansion and foam curing. To add a chemical blowing agent PVC foam board, the bubbles the expansion of the foam sheet quality of decisive effect. PVC is a straight chain molecule, molecular chain is short, low melt strength, bubbles in the nuclear expansion into bubble process, melt is not sufficient to cover the bubble, gas is easy to overflow into bullae, reduced foam sheet product quality.
Improvement of PVC foam board quality is the key factor to improve the melt strength of PVC. From the polymer processing characteristics of PVC, improve the melt strength method has many kinds, but the most effective way is added to improve melt strength additives and reducing the processing temperature. PVC belongs to the amorphous material, with the melt temperature improve the melt strength decreased, whereas with the melt temperature lower melt strength increase, but the role of cooling limited only play a supporting role. Class ACR processing agent has improved melt strength effect, which is the most effective foam control agent. The melt strength with foam modifier content increases. Generally speaking, as long as the screw rod has enough dispersive mixing ability, add the high viscosity of the foaming regulators to improve melt strength effect is more obvious.