Processing and Forming Technology of Perfluoroethylene Propylene FEP (F46) and Application Fields of FEP
FEP is a copolymer of tetrafluoroethylene and hexafluoropropylene, with a hexafluoropropylene content of about 15%. It is a modified material of polytetrafluoroethylene. Full name: Fluorinated ethylene propylene copolymer (perfluoroethylene propylene copolymer), abbreviated as perfluoroethylene propylene, also known as F46.
FEP has a melting point of 580 ° F and a density of 2.15g/CC (grams per cubic centimeter). It is a soft plastic with lower tensile strength, wear resistance, and creep resistance than many engineering plastics. It is chemically inert and has a low dielectric constant of approximately 2.1 over a wide range of temperatures and frequencies. This material does not ignite and can prevent the spread of flames. It has excellent weather resistance, low friction coefficient, and can be used from low temperature to 392 ° F. This material can be made into granular products for extrusion and molding, used as powder for fluidized bed and electrostatic coating, and can also be made into aqueous dispersions. Semi finished products include film and board. Stick and single fiber.
1. FEP processing and molding technology:
FEP, like other meltable fluoroplastics, is hot pressed, die cast, and extruded using common methods (vacuum and air pressure molding). In standard equipment, all molded parts of Dankai that come into contact with molten fluoroplastics should be made of corrosion-resistant alloys. When processing meltable fluoroplastics, they should be heated to 400 ℃, and a plasticizing section should be specified in the processing unit to obtain true melt and homogenization. During FEP processing, highly toxic volatile compounds are released at high temperatures. Therefore, the exhaust fan should be turned on when performing all high-temperature (>200 ℃) operations.
1. Compression molding
Pressing thin plates with a thickness of 1-2mm can be achieved by using flat plate molds or limiters of the required thickness, consisting of two (upper and lower) nickel or chromium coated metal plates. To prevent adhesion to the metal surface, aluminum foil pads with a thickness of 0.05-0.2mm can be added between the metal and polymer. Place the compression mold or limiter containing polymer on the flat plate of the press heated to 290-310 ℃ and maintain it at this temperature for 25-30 minutes. Then press it under a pressure of 20MPa and maintain it at this pressure for about 2 minutes. Stop heating and cool it to 240-250 ℃ (cold water can be used to cool the press plate). Release the pressure, remove the compression mold or limiter with polymer and metal plate from the press, cool it to room temperature in air, and open the mold.
2. Extrusion molding
The extrusion method can prepare thin films with a thickness of 0.01-0.2mm for wire and cable insulation, thin-walled tubes, plates, container products, and fibers. In order to obtain a uniform melt and create a large surface heat transfer for the extruder structure, the aspect ratio of the barrel should be ensured to be 25-30:1. The Dankai barrel should have three or four independent heating sections, each of which should be equipped with a thermocouple and temperature regulator. The temperature inside the barrel can be increased from 270-320 ℃ to 370-400 ℃ by section, throughput, and material. It is best to use a metering screw with rapid compression (compression ratio of 3:1). Dankai extruded film (tube type and flat seam type) is used for wire insulation and fiber preparation by stretching the melt. At this point, the determination of the temperature and stretching (orientation) amount of the melt depends on the type of product. When preparing thin-walled products, the screw speed is about 10r/min, and the plate speed can reach about 70r/min.
3. Die casting molding
The die-casting method is used for processing at a temperature of 250-370 ℃, injection pressure of 50-150MPa, and fine tuning of injection rate. The flow velocity of polymer melt must be stable. The Dankai mold should be preheated to 200-250 ℃, and the shrinkage rate of the polymer melt in the mold varies from 0.9% to 1.5% depending on the wall thickness and molding conditions. When the melt flows through nozzles of any size, the shear rate is proportional to the movement rate of the polymer melt and also related to the movement rate of the piston. When the shear rate of the melt exceeds the critical value, the melt fractures and delaminates on the surface. To prevent the fracture of the melt, the flow rate of the melt should be reduced and a large-diameter casting mouth should be used.
2. FEP application areas:
The application scope of FEP is the same as PTFE, and it is used in the electrical, wireless, electronic, chemical, mechanical manufacturing, refrigeration, pharmaceutical, and other industrial sectors.
FEP is used for thin film printed boards, wire and cable insulation, generator wire windings, electrical insulation components (sheets, rods, tubes, frames, and insulators), corrosion-resistant structural products (oil-free mechanical components), coatings, and glass tarpaulins. Excellent corrosion resistance makes it applicable to chemical work equipment, heat exchangers, fractionation towers, pumps, valves, pipes, seals, pipe linings, laboratory transparent vessels, etc. FEP extruded thin-walled tubes are used for heat exchangers, suitable for heating and cooling highly corrosive liquids within the range of -200 to 200 ℃.
The use of FEP components in the refrigeration industry can withstand low temperature tests well, and FEP sheets are used to prepare pressure and vacuum products.
FEP is used for insulation of wires and cables for various purposes, especially for wires and micro electronic components in electronic assembly circuits.
FEP film is used as a seal for capacitors, separators, and chemical equipment, and is used in the printing industry to produce printed boards and flexible cables.
Thin films can be welded, vacuum formed, coated with metal, and do not require surface activation. They can bond with metal and glass cloth under heating and pressure.
FEP film has particularly high gas permeability resistance and is therefore used as a sensitive component in gas analyzers to isolate the analyzed gas from the membrane.
Summary: Although FEP and PTFE have the same application scope, FEP is easier to process and has less loss compared to PTFE. However, some of FEP's performance is inferior to PTFE.
