The size and uniformity of the cell are the key factors to affect the quality of the sheet. For the low foam sheet, the cell is small and even and the toughness of foam sheet is excellent, strength is high and the surface quality is good. From the aspect of reducing the density of the foam boards, only the small and even cell can further reduce the possibility of density.
Key points to control PVC foaming process
The plastic foam molding is divided into three processes: the formation of the bubble nucleus, the expansion of the cell nuclei, and the curing of the foam. For PVC foam sheet, adding a chemical foaming agent, the expansion of the bubble nucleus has a decisive influence on the quality of the expanded sheet. PVC belongs to the straight-chain molecules, the molecular chain is short, and melt strength is low. In the process of cell nuclei inflating into a bubble, the melt is insufficient to coat the bubbles, and the gas easily overflows into large bubbles, and to reduce the foam sheet of product quality. The key factor in improving the quality of PVC foam sheet is to improve the melt strength of the pvc mouldings. From the processing characteristics of polymer materials, there are a variety of ways to improve PVC melt strength, but the most effective way is to added the melt strength additives and lower processing temperatures. In general, as long as the screw has the enough dispersive mixing, adding the high viscosity of the foam regulator can improve the melt strength.
Processing aids in PVC foam sheet
The processing aids, such as ACR can promote PVC melt, improve surface finish, to improve the elasticity of the melt, and enhance the role of the melt elongation and strength. In addition, it is conducive to coat bubbles to prevent the collapse of the cell. The molecular weight and amount of the foam control agent have a great influence for the density of the foam sheet. With the increase in molecular weight and the PVC melt strength, the density of the foam sheet can be done less, having the same effect with enhancing the amount of the adjusting agent. There is important relationship existing between the foam regulator and foaming agent, there is an equilibrium point in the density of the foam sheet and a foam regulator. And outside this equilibrium point, the density of the foam sheet is not affected by the foaming agent content and can be maintained constantly. Increasing the foaming agent does not reduce the density, and the reasons leading to this phenomenon is in the amount of a certain amount of foaming regulator, the melt strength of PVC is limited, the excess gases that cause cell collapse or merger.
www.potentech.com
Potentech adheres to provide customers with the best pvc foam boards and service. Potentech set up 4 sales teams (Domestic sales center, International sales center, E-business center and Modified engineering plastic Department) to provide professional services, quality products and making contribution to the community.