Analysis of weather resistance of PVC profiles and pipes
Resin: PVC resin has a number of double bonds and unstable structure, which is easy to break under the damage of light and oxygen, which causes discoloration of the product. The unstable structure of different resins is not the same, that is, the stability is not the same, so choose A resin excellent in stability and weather resistance is a prerequisite for maintaining the weather resistance of the product.
Titanium Dioxide: In addition to imparting brightness and whiteness to the product, titanium dioxide can also absorb solar ultraviolet rays to avoid and reduce the influence of ultraviolet rays on the surface of PVC profiles and pipes. There are two methods for the production of titanium dioxide in the world: sulfuric acid method and oxidation. The titanium dioxide produced by the sulfuric acid method contains residual SO42-, which easily reacts with the lead in the product, and has an influence on the color of the surface of the product. In addition, the tetravalent titanium in the titanium white powder becomes trivalent titanium (the surface of the product becomes black). Titanium dioxide can be classified into anatase type and rutile type depending on the crystal form. Rutile titanium dioxide has strong ultraviolet shielding effect and excellent weather resistance; anatase titanium dioxide has the effect of promoting PVC photoaging, so gold red titanium dioxide is selected among PVC pipe and profile products.
Stabilizer: In the PVC extrusion process, the stabilizer acts to prevent the molecular chain of the PVC resin from causing damage and degradation under heat and shear, and also prevents the action of photo-oxidation and thermal oxygen during storage and use. It causes degradation. The stabilizers currently used in profiles and pipes mainly include composite lead salts, organotin and calcium-zinc stabilizers. The composite lead salts have good thermal stability, but residual SO42- and Cl3+ remain in the process. Ions, if these ions are too high, interact with Pb2+ under the direct action of visible light, producing gray spots on the surface, sometimes yellow mixed with gray, and Pb2+ remaining in the product easily reacts with S in the air to generate Black PbS, these areas on the surface of the product are easy to blacken, the organotin stabilizer has good thermal stability and transparency, but the transmittance of organotin is close to that of PVC, which cannot effectively protect the UV from destroying PVC ions, so Weather resistance is worse than lead salt and calcium-zinc stabilizer. Only a large amount of shielding titanium dioxide can be added to meet the weather resistance requirements. The main components of calcium-zinc stabilizers are calcium-zinc soap salts, auxiliary stabilizers, antioxidants, and lubricants; it acts as a stabilizing agent while absorbing UV light, and calcium-zinc stabilizers are added to a large number of different types. Antioxidants, such as 1010, 1076, can alleviate the degradation of PVC under the action of photo-oxidation and thermal oxygen, especially the initial weather resistance of PVC profiles and pipes has a greater effect.
Calcium carbonate: The content of calcium carbonate has an effect on the weatherability of the product. The higher the content of calcium carbonate, the actual reduction of the content of titanium dioxide and stabilizer, the shielding effect of titanium dioxide and the anti-oxidation and stability of the stabilizer.
Toughener: The most widely used in pipes and profiles are CPE and impact-resistant ACR. HCl is produced during the production of CPE. It is coated in CPE particles and mixed with PVC. Sex molecules, which catalyze the decomposition of PVC under the action of light, heat and oxygen, will cause discoloration of the surface of the product. The impact ACR is an acrylate core-shell copolymer, which improves the impact resistance of the product while improving the weather resistance of the product. Absorbent ACR is basically used all over the country as an impact modifier.
1. Calcium-zinc stabilizer can produce hard products with better weather resistance, and is more suitable for outdoor products.
2. The weather resistance of the product is related to the quantity of resin, titanium dioxide, stabilizer, impact modifier and calcium carbonate. To produce products that meet the requirements of weather resistance, it is necessary to select raw materials with good performance and stable quality, and design to meet the requirements of production. Formulations, calcium zinc stabilizers produced under the same conditions have better weatherability than organotin and lead salt stabilizers.
3. The weathering resistance of calcium-zinc stabilizers of different systems is quite different, which is related to the formulation composition and antioxidant content. Therefore, users are advised to use calcium-zinc stabilizers with caution.