In PVC foaming products, the purpose of adding ultra-high molecular weight polymers is: firstly, to promote the plasticization of PVC; secondly, to improve the melt strength of PVC foaming materials, to prevent the merging of bubbles, in order to get uniform foaming products; thirdly, to ensure that the melt has good fluidity,get good appearance of the products. Since different foam products manufacturers have different products, the equipment, process, raw materials and lubrication system used are different, so we have developed foam conditioners with different properties to meet the different needs of users.

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 bubble body. For the addition of chemical blowing agent PVC foam sheet, the expansion of the bubble core of the quality of the foam sheet plays a decisive role in the impact of PVC belongs to the straight-chain molecules, molecular chain is shorter, the melt strength is low, in the expansion of the bubble core into a bubble process, the melt is not enough to cover the bubble, the gas is easy to overflow and merge into a large bubble, reducing the quality of the foamed sheet product.

1.Stability problem;

2. Melt strength problem;

3. Lubrication problem;

4. Dispersion problem.

These four types of problems, especially the first three types of problems will be mutual constraints, cross-influence, from the surface phenomenon is sometimes difficult to immediately distinguish, to say party observation and analysis, to find the root cause of the problem in order to fundamentally solve it.

• Stability problems: lack of stability will affect the entire board, the board surface yellowing, foam sheet brittle.Melt strength problem: insufficient melt strength will lead to foam sheet bubble holes, longitudinal section of the bubble is very long. To determine whether the melt strength is insufficient, the most direct way is to go to back of the three rollers and press the sheet wrapped in the center roller with your finger, the melt strength is good when pressed to feel the elasticity. If it is difficult to spring up after pressing, it means that the melt strength is poor. Because of the screw structure and cooling methods differ greatly, it is difficult to judge whether the temperature is reasonable, in general, within the load allowed by the extrude, the 3-5 zone temperature to low for good. In the foamed pipe to get foaming uniform products, also need to ensure that the PVC material has good melt strength.
• Lubrication problems: lubricant is divided into external lubricant and internal lubricant, external slip is conducive to demold, the surface of the plate has the benefit of smoothness, external slip is too little, the extrude is not easy to control the temperature of the 5-zone, easy to heat up, which will lead to the merging core temperature is high, the middle of the plate out of the large bubbles, string of bubbles, yellowing, and other issues, the surface of the plate is also not smooth; external slip is more, the precipitation will become serious, manifested in the structure of the die inside the mold and the surface of the plate outside the slip of precipitation.which will also be manifested in some individual phenomena on the surface of the plate moving back and forth irregularly. Inside slip is conducive to plasticization and melt fluidity, inside slip is not enough plate surface is difficult to control the thickness, manifested in the middle of the plate thick and thin; inside slip more, easy to merge the phenomenon of high core temperature. Poor dispersion will bring the phenomenon of plate surface is not smooth.
• Process temperature control problems: the four problems mentioned above belong to the fundamental problem, is the foundation, is a deep-seated problem. Relative to the above four problems, process temperature control is much more intuitive, is a surface problem, but the temperature control is not good, will induce the emergence of fundamental problems. Increase the processing temperature, material stabilization time will be reduced, stability problems; the original lubrication balance will be broken, generally manifested as insufficient external lubrication, especially late external lubrication, the need to increase the amount of external lubrication additive; temperature will also lead to a reduction in the melt strength, foaming sheet vesicle increase, the number of vesicles decreased, sheet brittle and easy to fracture; temperature increase to reduce the melt strength will reduce the viscosity of the melt, the viscosity of the melt to reduce shear dispersion ability to reduce the viscosity, the viscosity of the melt. Reduced shear dispersing ability to reduce the dispersing ability of the screw is not strong, sometimes uneven dispersion.