Selection of stabilizer system for PVC blown film
selection of PVC blown film stabilizer system
after the blown film material is added to the barrel by the feeding Hopper, it is subjected to shear force in the screw to generate friction heat, to raise the material temperature, it usually takes about 5 ~ for the plastic to enter the exit of the die from the Hopper ~ 6 minutes, so the heating time is longer than the calendering film. At the same time, due to the inevitable existence of dead corners in the equipment, the materials are easy to decompose. Therefore, the PVC blown film requires sufficient stability to adapt to the blow molding process.
Lead-based stabilizers are generally not used for agricultural films, because the transparency of the films made by them is poor, and more importantly, the lead-based stabilizers have sulfide pollution effects, on the farmland, PbS and lead stabilizers released by decomposition due to fertilization produce black PbS, which is not welcomed by poor and lower-middle peasants. Opaque packaging film products can use lead-based lead sulfate, lead stearate and other lead-based concealing agents, because of its low cost and good stability, but due to their large specific gravity, particles are easy to agglomerate, it is not easy to disperse, so it is easy to cause the bubble and the abnormal phenomenon of white stripes on the film during the blow molding process. At this time, the kneading process and the blow molding process must be properly adjusted to form the ideal product.
Generally, the stabilization system of agricultural film adopts solid barium stearate and cadmium stearate. These two metal soaps are rarely used alone, but the synergistic mixture of the two has multiplication effect, however, the appropriate combination can show good results. Cadmium stearate cannot be added too much. If there is more than one part, the film will be frosted during exposure, and a layer of white powdery particles will be separated out from the surface of the film. At the same time, plasticization is also difficult, and the thermal decomposition temperature and stability have a downward trend. Generally, within a certain range, the amount of barium stearate is greater than cadmium stearate, which can improve the light resistance of the film. When Ba: Cd = 4:1, the thermal stability is the highest. When Ba: Cd = 3:1, can show good thermo-optic stability.
mix a small amount of Ba and Cd soap (0. 1 ~ 0. 4 copies) Zinc stearate not only has good processing performance, but also has certain effect on aging resistance and stain resistance. When combined with epoxy ester, the decomposition temperature and thermal stability can be improved, however, when production control is not in place, it will lead to catalytic degradation during processing and black spots.
adding a certain amount of organotin stabilizer to the formula is beneficial to the blow molding process. It can make bubble normal, thickness stable, and increase surface finish and transparency. However, after it is added, it will increase the viscosity of the film, especially in the summer production, the cooling degree is not enough, so the lubricant must be added accordingly, and its cost is relatively high, therefore, it is generally only used in the packaging film formula with higher requirements.Related articles: Formulation Design of PVC blown film