The viscous flow temperature of ptfe FEP is 265 ~ 278℃, and the forming temperature range is narrow. Polytetrafluoroethylene used in wire and cable has various excellent performance, wide range of frequency, wide range of high and low temperature use, excellent chemical stability, high electrical insulation strength, good resistance to atmospheric aging, so the insulated wires with polytetrafluoroethylene have the above excellent performance. Teflon insulated wires are widely used in various kinds of wiring in aerospace. Most of the wires used in the mil-w-22759, the U.S. military standard, are of this type. Its outstanding advantage is the temperature level up to 250℃, in this temperature for a long time its mechanical strength and electrical performance will not be affected, and at the same time excellent low temperature performance, this wire can be used at a low temperature of 60℃ for a long time.
1. The melt viscosity of FEP is lower than that of PTFE. The melt viscosity at 343 ~ 393℃ is 103 ~ 104Pa·s, higher than polyethylene with the same melting index.
2.FEP is a translucent polymer with strong electrostatic adsorption. It is easy to absorb dust and impurities, which will affect the properties of processed products. Antistatic agent should be added during molding.
3. Ptfe has small thermal conductivity, and the heating rate should be paid attention to during processing. Considering the corrosion effect under the forming temperature, the processing equipment should choose chromium steel or nitriding high alloy steel as the anticorrosion layer.
3.2 forming and processing method of polyperfluoroethylene propylene
1. The temperature of injection molding cylinder and nozzle is 320 ~ 400℃, the mold temperature is 200 ~ 230℃, and the injection pressure is 29.4 ~ 137.2mpa.
2. Molding molding can produce a variety of board, bar, laminate and filling products. Heat FEP to 290 ~ 370℃ to melt it, and then cool it to 150 ~ 200℃ to 7MPa to make the melt fill the mold, compact and release the product.
3. The length to diameter ratio of the extruder is greater than 15, the compression ratio is 3:1, the die temperature is 315 ~ 400℃, the pressure is different according to the product, ptfe is generally 0.98 ~ 17.64MPa. The quenching temperature of extrusion products is 10 ~ 20℃
4. Apply FEP concentrated water dispersion solution. In the dispersion solution of FEP, add the concentrator polyoxyethylene octylphenol ether. In recent years, FEP's powder flow bed and electrostatic spraying technology have also been developed.
For the manufacturer of wires and cables, choosing suitable ptfe resin is very important to improve productivity and product quality. Generally speaking, ptfe is easy to absorb the resin of extruder and has short curing time; Compression ratio wide resin, can be suitable for various structures of the wire; In addition, ptfe insulation resin must meet the insulation performance requirements of finished wires and cables, such as voltage test, aging test and a series of routine tests.
1.2 as its name suggests, booster extrusion is to reduce the adhesive force during pushing and pressing. It should be made of petroleum products that are easy to diffuse, easy to be wetted and absorbed by resin, and easy to volatilize and leave no traces after pushing and pressing. The volatilization temperature should be lower than the sintering temperature. The adding amount of booster should be determined according to the actual use and molding conditions, generally 15% ~ 25% weight. Generally choose gasoline, petroleum ether, paraffin oil and so on.
1.3 the requirements of colorants for raw materials for coloring should have good heat resistance and stability, no decomposition and no fading at the sintering temperature of ptfe and the maximum allowable working temperature of wires and cables. Not seriously affect the insulation properties, especially the insulation of the wire to small impact; And it should have the characteristics of good coloring, bright color, good dispersion in ptfe powder, small migration and no pollution of the mold. Colorants and their dosage are usually used in the table. Teflon has good moisture and water resistance. Teflon itself has extremely low moisture permeability and water absorption. After being soaked in water for 24H, the water absorption actually equals to zero
1.4 excellent climate resistance. In atmospheric environment, because there is no photosensitive group in ptfe molecules, ozone cannot act on it, so ptfe can be used for a long time without protection under hot and hot tropical and humid climate conditions, and its performance remains unchanged.
In atmospheric environment, when the absorbed dose was up to 200Gy(2× 104rad), the elongation rate would change. At 104 Gy(106 rad), the tensile strength will be 50% of the original value, and the elongation has been reduced
1.6 other performance polytetrafluoroethylene has many advantages, but as a wire and cable insulation material, there are some disadvantages, for example: polytetrafluoroethylene processing is difficult, the process performance is poor, can not be extruded continuously, the production efficiency is low; Cold flow phenomenon under continuous load, poor cutting resistance; Due to its poor resistance to electric dissociation and radiation, the application of ptfe is limited.
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