Overview of PVC industry
Polyvinyl Chloride Resin (PVC) is one of the five general plastics, and its output is second only to polyethylene. PVC production processes mainly include ethylene process and calcium carbide process. According to different processes, the upstream industries are ethylene industry and calcium carbide industry respectively. In downstream industries, PVC is widely used in construction, medical treatment, automobile and other fields because of its corrosion resistance, electrical insulation, flame retardancy, light weight and high strength.
Production process and raw materials
The production process of Pvc Resin is divided into petroleum process (ethylene process) and calcium carbide process (calcium carbide process). The former uses petroleum and chlorine as raw materials, and the latter uses coal and raw salt as raw materials. The commonness of the two processes is to finally produce vinyl chloride monomer (VCM) and then polymerize to produce polyvinyl chloride (PVC).
At present, ethylene method is widely used in PVC industry in Western Europe, North America, the Middle East and other regions, while calcium carbide method is developing rapidly in China. The PVC loading capacity of calcium carbide method accounts for about 75% of the total domestic capacity. Compared with the ethylene process with petroleum as raw material, calcium carbide process has the advantages of less production investment, simple process and low cost. At the same time, China's energy structure of "poor oil and rich coal" and relatively mature calcium carbide production technology provide cheap raw materials for the calcium carbide route.
Daily model and purpose
PVC is widely used in construction, medical treatment, automobile and other fields because of its advantages of corrosion resistance, electrical insulation, flame retardancy, light weight, high strength and easy processing. Among them, the consumption of the construction industry accounts for about 60%, and the profiles, pipes and sheets made of general-purpose resins SG-5, SG-7 and SG-8 are mainly used to replace the traditional wood, metal and cement.
According to the difference of polymerization degree, PVC can be divided into general Resin (SG-1 ~ SG-8) and special resin. The application scope of special resin is closely related to customer needs. General resin products can be divided into soft products and hard products
Daily model
PVC models (hereinafter referred to as carbide process brand), the most common in China is SG-5, followed by SG-3, SG-7, SG-8, etc.
Viscosity or K value is commonly used in industry to represent the average molecular weight (or average degree of polymerization) of PVC, that is, the length of PVC molecular chain to determine and distinguish the brand of resin and corresponding processing parameters. The molecular weight of the resin is related to the physical and mechanical properties of the product.
PVC is an amorphous linear polymer compound. The greater its relative molecular weight, the higher its viscosity, the higher its high molecular weight, the higher its tensile strength, impact strength and elastic modulus, but the fluidity and plasticity of the resin melt decrease. Viscosity number is usually used to represent the molecular weight of polymer and divide the model of polymer.
Comparison of production requirements
PVC has a wide range of applications, and different models are adopted due to different needs.
SG5 shall be used for pipes, profiles, plates, etc.
SG3 is mostly soft products, which are mainly used to manufacture hoses, wires and cables, films, shoe materials, toys, auto parts, conveyor belts, daily plastic products, etc.
SG7 and SG8 are mostly used to manufacture pipe fittings, sheets, containers, etc. In principle, the higher the model, the greater the hardness of the product.
Compared with SG5, the production of SG3 requires long reaction time, high polymerization temperature, high requirements for the addition of auxiliary materials, and the production cost is higher than SG5. SG3 PVC has the characteristics of high purity, less fish eyes, easy blistering, high temperature resistance, insulation, soft product texture and so on.
SG-7 / SG-8 vs. SG-5. The production processes of the three resins are basically the same, and the production devices are exactly the same. The main differences lie in the formulation of additives, polymerization temperature, reaction pressure and so on.
In terms of reaction temperature and reaction pressure. The of SG-8 resin has basically reached the working pressure limit of polymerization kettle, the reaction conditions are more stringent, the requirements for operation, safety, technology and personnel quality are more stringent, and the resin quality is more difficult to control.
