Introduction of PVC foam sheet technology

Foaming mechanism: The purpose of adding ultra-high molecular weight polymer in PVC foam board products:

one is to promote the plasticization of PVC; Products with uniform foaming; the third is to ensure that the melt has good fluidity to obtain products with good appearance. Due to the different products of different foaming product manufacturers, the equipment, process, raw materials and lubrication systems used are different, so we have developed foaming regulators with different properties to meet the different needs of users.

1. Definition of foam material
Foamed plastics are also called foamed plastics, which are based on plastics and contain a large number of air bubbles. It can be said that they are composite materials filled with gas.

2. Classification of foam sheets
According to the different foaming ratios, it can be divided into high foaming and low foaming, and according to the softness and hardness of the foam texture, it can be divided into rigid, semi-rigid, and flexible foams. According to the cell structure, it can be divided into closed cell foam and open cell foam. The common PVC foam sheet is a rigid closed-cell low-foaming sheet.

3. Application of PVC foam board
PVC foam sheet has the advantages of chemical resistance, weather resistance, flame retardancy, etc., and is widely used in many aspects, including display panels, signs, billboards, partitions, construction panels, furniture panels, etc.

4. Key factors for evaluating the quality of foamed sheets
For foamed materials, the size and uniformity of the cells are the key factors affecting the quality of the sheet. For low-expansion foamed sheets, the cells are small and uniform, and the foamed sheets have good toughness, high strength and good surface quality. In terms of reducing the density of the foamed sheet, only small and uniform cells can further reduce the density, and it is difficult to further reduce the density if the cells are large and scattered.

5. The 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 curing of the foam. For PVC foamed sheets with chemical foaming agents added, the expansion of the bubble core has a decisive influence on the quality of the foamed sheets. PVC is a straight-chain molecule with short molecular chains and low melt strength. During 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, reducing the product quality of the foamed sheet. .
The key factor to improve the quality of PVC foam sheet is to improve 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 that improve the melt strength and reduce the processing temperature. PVC is an amorphous material, and the melt strength decreases with the increase of the melt temperature. On the contrary, the melt strength increases with the decrease of the melt temperature, but the cooling effect is limited and only plays an auxiliary role. ACR processing agents all have the effect of improving melt strength, among which foaming regulators are the most effective. Melt strength increases with increasing foam regulator content. Generally speaking, as long as the screw has sufficient dispersing and mixing ability, adding a high-viscosity foaming regulator has a more obvious effect on improving the melt strength.

6. The role of processing aids in PVC foam sheet
ACR processing aids can promote the melting of PVC, improve the surface finish, improve the elasticity of the melt, and enhance the elongation and strength of the melt. It is beneficial to encapsulate the bubbles and prevent the collapse of the bubbles. The molecular weight and dosage of the  pvc foaming regulator have a great influence on the density of the foamed sheet: with the increase of the molecular weight, the melt strength of the PVC increases, the density of the foamed sheet can be made lower, and the dosage of the regulator is increased. have the same effect. However, this effect does not have a linear relationship. Continuing to increase the molecular weight or increase the dosage will not have a very obvious effect on reducing the density, and the density will tend to be constant.
There is an important relationship between the foaming regulator and the foaming agent. There is an equilibrium point between the density of the foamed sheet and the foaming regulator. Outside this equilibrium point, the density of the foamed sheet is not affected by the content of the foaming agent. , to maintain a constant, that is, increasing the amount of foaming agent can not reduce the density, the reason for this phenomenon is that under a certain amount of foaming regulator, the melt strength of PVC is limited, and excess gas causes cells to collapse or collapse. merge.