In the daily PVC processing application, PVC molecular chain contains strong polarity of chlorine atoms, intermolecular force is large, it determines the rigidity of PVC products, hardness and flame retardant characteristics. However, PVC is easy to produce degradation reaction under the action of heating and shear force, which causes the change of color and performance of PVC products. PVC heat stabilizer retards or inhibits the degradation of PVC resin, which plays an extremely important role in PVC molding. PVC formulation mainly for environmental protection, performance, transparency and other requirements to screen PVC heat stabilizer system.
Lead salt compound stabilizer is commonly used for PVC stabilization system, monomer including three salt, two salt, lead stearate, lead cyanourate and so on. On the basis of monomer, the compound lead stabilizer is derived, which mainly includes monomer lead stabilizer, filler and lubricant. Disadvantages of lead salt stabilizer: initial coloring, it is difficult to get transparent products, it is difficult to get bright color products, easy to produce vulcanization pollution. And the production of stabilizer manufacturers quality and level is uneven, yellow Dan in the production process is often incomplete reaction, resulting in its residual in the product, so such lead salt stabilizer with yellow or light yellow. This kind of stabilizer brings many problems in use.
Calcium and zinc stabilizer is synthesized by special composite process with calcium salt, zinc salt, lubricant, antioxidant and auxiliary stabilizer as main components. It can not only replace toxic stabilizers such as lead, cadmium salts and organotin, but also have good thermal stability, light stability, transparency and coloring power. Practice has proved that in PVC products, the processing performance is good, the heat stabilization effect is equivalent to the lead salt stabilizer, is a good stabilizer. However, the use of calcium and zinc stabilizers in special industries needs to be cautious, such as resistance, moisture absorption has strict requirements or molding time is very long and high temperature field.
Organotin stabilizer is one of the heat stabilizers. The main characteristics are high transparency, excellent heat resistance, and resistance to vulcanization pollution. Commonly used in industry are laurate esters, maleate esters and thiol organotin stabilizers. Commonly used metal salt stabilizers are: zinc stearate, cadmium stearate, calcium stearate, barium stearate, lead stearate, etc.