Calcium and zinc stabilizers are mainly composed of calcium stearate and zinc stearate. Because calcium stearate, zinc stearate and stearic acid structure similar, more charged calcium ions and zinc ions. How to understand an ion with a charge, the polarity is basically the attraction of the charge. The charge of calcium and zinc ions greatly enhances its polarity, to know that the polarity of calcium stearate and zinc is strong in the commonly used PVC lubricant. This gives it a stronger affinity with PVC resin, thus weakening the attraction of each layer of dissociation bond inside the PVC resin particles, promoting the PVC winding chain segment easy diffusion, the formation of a sliding layer of high viscosity, friction heat generation, high transfer efficiency of mechanical force, accelerate the material temperature rise, causing the resin transition plasticization. Lead salts on their own had no such effect.
Problems that should be noted when using calcium and zinc stabilizer in PVC processing and production:
1, confirm the green environmental protection of the 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 product and meet the requirements of the new national standards.
2, calcium zinc stabilizer internal lubrication effect is strong, need to add more external lubricant. This is described below.
3, the thermal stability of calcium zinc stabilizer is weaker than that of lead salt, the processing window is narrower, and the control requirements are higher.
4. Pay attention to the cleaning cycle in the operation process. The addition of calcium and zinc stabilizer lubricant is large, which is easy to lead to the increase of precipitation, thus affecting the cleaning cycle. For large - scale production impact is greater, to strictly select stabilizer varieties. If it is its own stabilizer, need to cooperate with the middle and late lubrication effect of PE wax (such as Qingdao Bonny 108, etc.) or oxidized wax. Also strictly control the vacuum degree, can reduce precipitation, prolong the cleaning mold time.
5, a good stabilizer formula and appropriate dosage on the appearance of the product, material properties, aging resistance and so on. In the process of replacing lead salt stabilizer with calcium and zinc stabilizer, the process parameters should be properly adjusted, in the final analysis, to achieve the material properties and plasticization degree we need. Of course, it should be noted that the amount of calcium and zinc stabilizer used in the lubricant is more than the amount of lead salt.