Twenty Kinds of Plastics and Their Properties—(19) PVC
19. PVC polyvinyl chloride
Typical application range:
Water supply pipeline, household pipe, house wall board, commercial machine shell, electronic product packaging, medical equipment, food packaging and so on.
Injection molding process conditions:
Drying process: dry treatment is usually not required.
Melting temperature: 185~205 °C
Mold temperature: 20~50 °C
Injection pressure: can be as large as 1500bar
Pressure protection: can be as large as 1000bar
Injection speed: in order to avoid material degradation, the injection speed is generally required.
Runner and gate: all regular gates can be used. If the smaller parts are processed, it is best to use a tip gate or a latent gate; for the thicker parts, it is best to use a fan-shaped gate. The minimum diameter of the needle tip gate or the latent gate should be 1mm; the thickness of the fan-shaped gate should not be less than 1mm.
Chemical and physical properties:
Rigid PVC is one of the most widely used plastic materials. PVC material is a kind of non crystalline material. In practical use, PVC materials are often used as stabilizers, lubricants, auxiliary processing agents, color materials, impact agents and other additives. The PVC material is non combustible, high strength, excellent resistance to climate variability and geometric stability. PVC has strong resistance to oxidants, reducers and strong acids. However, it can be corroded by concentrated oxidizing acid, such as concentrated sulfuric acid and concentrated nitric acid, and is not suitable for contact with aromatic hydrocarbons and chlorinated hydrocarbons.
The melting temperature of PVC is a very important process parameter in the process of processing. If this parameter is improper, the problem of material decomposition will be caused. The flow characteristic of PVC is rather poor, and its process range is very narrow. Especially for large molecular weight PVC materials, it is more difficult to process (usually lubricants are added to improve the flow characteristics). Therefore, PVC materials with small molecular weight are commonly used. The shrinkage rate of PVC is quite low, which is generally 0.2~0.6%.