PTFE has excellent electrical insulation properties. The dielectric loss tangent tga and relative permittivity Er change very little from the power frequency to 109 Hz. From room temperature to 300°C, the dielectric loss tangent tga of PTFE changes very little.
The relative permittivity Er decreases with increasing temperature. The insulation resistivity of PTFE is relatively high, its volume resistivity Pv is generally greater than 1015Ω·m, and the surface resistivity Ps is generally greater than 1016Ω. Even if it is immersed in water for a long time, the change is not significant, and the temperature change is not large.
Impedance of PTFE raw material tape insulated radio frequency cable
Attenuation is one of the most important parameters of radio frequency cables. It reflects the loss of electromagnetic energy transmitted along the cable. The greater the attenuation of the cable, the more serious the loss of the transmission signal and the worse the transmission efficiency of the cable. In order to improve The transmission efficiency of radio frequency cables should be as low as possible. The attenuation of coaxial radio frequency cables is mainly caused by conductor attenuation and medium attenuation.
After PTFE raw tape replaces solid PTFE insulation, it can greatly reduce the attenuation of radio frequency cables, which can be reduced by 15~30%. However, due to the high price of PTFE raw tape, its price is about 3 to 4 times that of PTFE.
Increasing the manufacturing cost of the cable, it can only be used in a special environment where the outer diameter of the cable is small, the attenuation is relatively low, and the temperature resistance level is high. With the continuous development of fluoroplastic production and processing technology, the price of PTFE raw tape will gradually decrease, and it will be more widely used in the wire and cable industry.
Application of PTFE in Batteries
The application of PTFE in batteries is a 60% solid PTFE emulsion. Mainly used in power batteries such as nickel-metal hydride, nickel-cadmium, lead acid, and fuel cells. The network formed by the fibrillation of PTFE emulsion can contain active substances well, but if the single addition amount is too large, it will produce a large impedance and affect the charge and discharge performance.
Experiments have proved that the compounding of PTFE emulsion and sodium carboxymethyl cellulose can make up for this shortcoming. The carboxymethyl cellulose solution produces water evaporation during the forming process of the pole piece, which increases the porosity of the pole piece, increases the true specific surface area of the electrode, and effectively reduces the electrochemical polarization of the electrode, thereby increasing the electrode’s Discharge capacity. Experiments show that the dosage of 60% PTFE emulsion is 1.5~2.5 parts. The CMC concentration ratio is stable at 2%.
Application of PTFE in Capacitors
The application of PTFE in capacitors is a 60% solid PTFE emulsion. Mainly used for super capacitors. Electrochemical capacitor (referred to as electrochemical capacitor) is a new type of energy storage device between traditional capacitors and batteries. It has the advantages of high specific power, good reversibility, and long cycle life. It is usually used to meet instantaneous high-power requirements to compensate for the lack of high-current discharge of the battery. ).
Now supercapacitors are generally multi-water systems, one is environmental protection, the other is large capacity, one is low cost, and the process control is relatively simple. After mixing the active material, conductive agent, binder, thickener (CMC) and 60% PTFE emulsion, it is directly applied to the nickel foam. It is better to add 60% PTFE emulsion to the two components. PTFE emulsion is a dispersion of PTFE, polymerized into an aqueous dispersion, its solid content is about 60% of PTFE, and it is stabilized by a nonionic surfactant. It has excellent heat resistance, cold resistance and abrasion resistance, as well as excellent electrical insulation properties, and is not affected by temperature and frequency.
In addition, it also has the characteristics of non-stickiness, non-absorption, non-burning, etc., and fibrosis occurs after high temperature. The formed network structure can be uniformly coated with active materials, and the effect is very good. In the state of repeated oxygen release from the positive electrode, the anti-oxidation effect is good.
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