Polyvinyl chloride (PVC) is a widely used polymer. The range of additives used with this polymer can alter its physical properties. It can become a tough rigid polymer used for water pipes to a pliable material used for fabric applications.
Not necessary as PVC absorbs little water.
160 C 220 C [320 F 428 F]
20 C 70 C [68 F 158 F]
Up to 150 MPa
Up to 100 MPa
Relatively slow to avoid material degradation
All conventional gate types can be used. Pin-point and circular tapered gates are used for molding small components and fan gates are typically used for thick sections. Keep the minimum diameter of pin-point or circular tapered gates at 1 mm, and the thickness of fan gates at not be less than 1 mm.
Make sprues as short as possible; typical runner sizes are 6 - 10 mm and have a full round cross-section. You can use insulated hot runners and certain types of hot sprue bushings with PVC.
Rigid (unplasticized) PVC, which is produced from sodium chloride and natural gas, is one of the most widely used plastic materials. The repeat chemical structure is vinyl chloride. Additives are mixed with PVC to make it processible. PVC grades produced by suspension or mass polymerization techniques are the major types used for melt processing. PVC is substantially an amorphous material.
The additives used include stabilizers, lubricants, processing aids, pigments, impact modifiers, and fillers. The features of PVC include low combustibility, toughness (designed to be unbreakable), good weatherability (color and impact retention and no loss in stiffness), and excellent dimensional stability. PVC is highly resistant to oxidizing and reducing agents, and strong acids. However, unplasticized PVC is not recommended for environmental and continuous use above 60 C [140 F]. It is not resistant to concentrated oxidizing acids such as sulfuric or nitric acid, and is unsuitable for use with aromatic and chlorinated hydrocarbons.
Process the material at the correct melt temperature. Otherwise, severe problems from decomposition (which produces hydrochloric acid which in turn accelerates decomposition) can occur.
PVC is a relatively stiff flow material and has a narrow processing range. The molecular weight determines the flow characteristics. Materials with a higher molecular weight are more difficult to process. To modify this condition, add lubricants. Typically, however, relatively low molecular weight grades are used in molding.
Shrinkage is fairly low (0.002 0.006 mm/mm [0.2 0.6%]).