carbide

1. Polyvinyl chloride resin (PVC for short) is one of the 5 general-purpose plastics, and its output is second only to
polyethylene. PVC production processes mainly include ethylene method and calcium carbide method.
Production process and raw materials
The production process of polyvinyl chloride resin is divided into petroleum route (ethylene method) and calcium carbide
route (calcium carbide method). The former uses petroleum and chlorine as raw materials, and the latter uses coal and
crude salt as raw materials. The commonality of the two processes is the final production of chlorine. Vinyl monomer (VCM)
is then polymerized to form polyvinyl chloride (PVC).
At present, the PVC industry in Western Europe, North America, the Middle East and other regions widely uses the ethylene
method, while the domestic calcium carbide method has developed rapidly, and the production capacity of the calcium
carbide method PVC assembly accounts for about 75% of the total domestic production capacity. Compared with the
ethylene method, the calcium carbide method has the advantages of less production input, simple process and lower cost.
At the same time, China’ "poor oil and rich coal" energy structure and relatively mature calcium carbide production
technology provide low-cost raw materials for the calcium carbide route.
According to the difference of polymerization degree, PVC can be divided into general-purpose resin (divided into eight
types of SG-1~SG-8) and special resin. Among them, the scope of application of special resins is closely related to customer
needs, and general-purpose resin products can be divided into soft and rigid products.
Among the various types of PVC (the following are the grades of calcium carbide process), the most common in our country
is SG-5, and then SG-3, SG-7, SG-8, etc.
The industry commonly used viscosity or K value represents the average molecular weight (or average degree of
polymerization) of PVC, that is, the length of the PVC molecular chain, to determine and distinguish the resin grades 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 larger the relative molecular mass, the higher the viscosity, the higher
the molecular weight, the higher the product's tensile strength, impact strength, and elastic modulus, but the fluidity of the
resin melt And plasticity declines. The viscosity number is usually used to express the molecular weight of the polymer and
divide the polymer model.
Comparison of production requirements
PVC has a wide range of applications, and different models are used due to different needs.
SG5 is used in pipes, profiles, plates, etc.

4. SG3 is mostly soft products and is mostly used in the manufacture of hoses, wires and cables, films, shoe materials, toys,
auto parts, conveyor belts, daily plastic products, etc.
SG7 and SG8 are mostly used in the manufacture of pipe fittings, sheets, containers and so on. In principle, the higher the
model, the greater the hardness of the product.

6. Compared with SG5, the production of SG3 requires long reaction time, high polymerization temperature, high
requirements for the addition of auxiliary materials, and higher production costs than SG5. SG3 type PVC should have high
purity, less fish eyes, easy to blister, and has the characteristics of high temperature resistance, insulation, and soft texture.
SG-7/SG-8 is compared with SG-5. The three resin production processes are basically the same, and the production
equipment is exactly the same. The main difference lies in the formulation of additives, polymerization temperature,
reaction pressure and so on.
In terms of reaction temperature and reaction pressure. The SG-8 resin has basically reached the working pressure limit of
the polymerizer, and the reaction requirements are relatively strict. The requirements on operation, safety, technology, and
personnel quality are more stringent, and the resin quality is more difficult to control.