Polytetrafluoroethylene (PTFE), commonly known as the ‘king of plastics’, has excellent chemical resistance, high temperature resistance, low dielectric constant, non-flammability, weather resistance, low coefficient of friction, non-stick and self-lubricating properties, but PTFE is difficult to flow after melting, can only be used in sintering mode of moulding, limiting the means of processing and flexibility of product design. However, PTFE is difficult to flow after melting and can only be moulded by sintering, which limits the flexibility of processing and product design. Using a small amount of perfluoroalkyl vinyl ether (PAVE) and TFE copolymer generated PFA, almost completely retained the excellent physical properties of PTFE, and PTFE similar chemical resistance and long-term operating temperature, etc., at the same time has a good melt processing performance, so that the products have a very low surface roughness and other advantages, expanding the potential for the application of PTFE.

PFA resin products are mainly in the form of emulsion, powder, granule, etc. At present, the products in China are mainly in the form of granule.The melting point of PFA is in the range of 290~312℃, the melting index is in the range of 0.8-30g/10min, and the moulding temperature is in the range of 350~410℃, and the conventional processes such as moulding, extruding, and injecting moulding can be used for the processing of PFA resin.

Compression moulding

When the melting index of PFA products is in the range of 0.8~3.0g/10min, the molecular weight is relatively high, the viscosity is large, and it is not easy to flow, so it is generally suitable for processing by moulding. The moulding temperature is 330~380℃, the pressure is 5.0~14.0MPa, and it is kept at the moulding temperature for 20~30min, then the melt is slowly cooled to 200~240℃ under pressure before it can be demoulded. The high viscosity of PFA melt, low critical shear rate and high moulding temperature should be taken into consideration when designing the mould.

Extrusion moulding

When the melting index of PFA products is greater than 3.0g/10min, it can be processed by extrusion moulding, which mainly produces pipes, cable insulation and films, etc. The screw L/D ratio of PFA is generally 20:1, and the rotational speed is set at 3~50r/min. The screw L/D ratio for PFA extrusion moulding is generally 20:1, the extrusion temperature is usually controlled at 330~425°C, and the rotational speed is set at 3~50 r/min. Due to the high melt viscosity of PFA products, there is a high tensile ratio when extruding moulding, and smooth extrudates can be obtained quickly.

The process and equipment of PFA extrusion moulding can be common with that of polyperfluoroethylene propylene (FEP), but the moulding temperature needs to be further increased. there is also a critical shear rate for melt rupture of PFA, the critical shear rate of high-speed extrusion type PFA is 50s-1, and the critical shear rate of low-speed extrusion or moulding type PFA is 3s-1. PFA's melt strength is large, and its melt elongation is large, and its melt strength is higher than that of FEP. The melt strength of PFA is large, and the melt elongation is larger than that of FEP, and a larger tensile ratio can be used in the moulding of thin tubes and monofilaments.

Injection moulding

When the melting index of PFA products in the range of 16~30g/10min, and the need to produce a variety of complex shapes of aviation, aerospace industry, electrical and electronic industry parts, medical, chemical test apparatus, etc., can be used to PFA with an ordinary screw injection moulding machine for processing. Commonly used plasticising capacity of the screw extruder, the mixing material is uniform, less stagnant material, fast transfer of stress to the mould, but with the PFA molten resin in contact with the screw, barrel and moulds, etc. need to use corrosion-resistant stainless steel production, and the use of large-diameter injection ports, runners and sprues, and runners to be as short as possible, without any obstacles and sharp corners, preferably with the spout mixed with the integration of the circular runners, the best way. All corners and intersections in the mould cavity are also round or streamlined, so that the molten resin flows in a streamlined manner. Take these measures, and control the temperature of the melt, can be avoided on the surface of the moulded material or inside the phenomenon of melt rupture.

Other moulding methods for PFA include transfer moulding, powder coating, dispersion impregnation moulding, blow moulding and vacuum moulding, which are similar to those for FEP.