The main components of calcium and zinc stabilizer are calcium stearate and zinc stearate. Due to the structure similarity of calcium stearate and zinc stearate, there are more charged calcium ions and zinc ions. How to understand charged ions, in plain English, the polarity is the attraction of the charge. The charge of calcium and zinc ions greatly enhances its polarity. It is necessary to know that the polarity of calcium and zinc stearate in the commonly used lubricant of PVC is strong. This gives it a stronger affinity with PVC resin, thus weakening the attraction of the PVC resin particles inside each layer from the sub-bond, promote PVC winding chain segment easy to spread, the formation of a sliding layer of high viscosity, friction heat, high transfer efficiency of mechanical force, accelerate the material heating, causing resin transition plasticization. The lead salt itself had no such effect.
Problems that should be paid attention to when using calcium and zinc stabilizer in PVC processing and production:
1, confirm the green environmental protection of stabilizer formula; It is necessary to pay attention to whether the content of heavy metals (lead, cadmium, tin, barium) can meet the requirements of the new national standards.
2, calcium zinc stabilizer lubrication is strong, to add more external lubricant. This is described below.
3. The thermal stability of calcium and zinc stabilizer is weaker than that of lead salt, and the processing window is narrower and the control requirements are higher.
4, the operation process pay attention to the mold cleaning cycle, calcium and zinc stabilizer lubricant added more, easy to lead to the increase of precipitation, thus affecting the film cleaning cycle. For large-scale production has a greater impact, we should strictly select the stabilizer variety. If it is its own stabilizer, it is necessary to cooperate with PE wax with good lubrication effect in the middle and late period (such as 108 Qingdao Bonny, etc.) or oxidized wax. Also strictly control the vacuum degree, can reduce precipitation, prolong the time of cleaning mold.
5, good stabilizer formula and appropriate dosage of the product appearance, material properties, aging resistance and so on have little influence. In the process of replacing lead salt stabilizer with calcium and zinc stabilizer, the technological parameters should be adjusted appropriately to achieve the material properties and plasticization degree we need in the final analysis. Of course, it should be noted that calcium and zinc stabilizers use more lubricant than lead salts.