June 07th, 2019
Polymer shields and coatings have been used for electrical insulation of wires and cables for decades. The simplest forms involve an inner core of conductive copper wiring encapsulated in an external plastic sheath. While this form of wiring has proven enough for an enormous range of markets, higher frequency electrical signals require a more robust solution.
Coaxial cables are designed more intricately than standard copper wiring with a polymeric coat. They comprise a conductive wire rod core within a cylindrical insulating layer, which is wrapped in a shield of woven copper and covered with a rigid plastic jacket. The shared geometric axis of the rod and the shield improve signal propagation, while the electrical insulation reduces interference from signals outside the cable. This design is ideal for relatively weak signals which cannot tolerate interference, or for higher frequency voltages that should not be allowed to radiate outwards. The performance of the electrical insulation is instrumental in the success of these interlinked properties.
Outlining FLUOROWRAP® Electrical Insulation
FLUOROWRAP® wire and cable films are a series of high-performance fluoropolymer composites based on polytetrafluoroethylene (PTFE). This underlying polymer group is widely utilized as an electrical insulator due to the high electronegativity of fluorine within the linear chain, contributing to an average dielectric constant of 2.1 at 1 megahertz (MHz). It also offers excellent thermomechanical properties, primarily comprising high-strength carbon-fluorine bonds which impart high toughness and good ductility characteristics – essential properties for electrical wire insulation. These characteristics can be manipulated to optimize the polymer’s performance for distinct operating conditions.
Low density extruded PTFE, for example, is widely used in the manufacture of high-frequency coaxial cables. It provides outstanding insulating properties with low signal loss and extremely tight thickness tolerances. Extruding the polymer ensures physical uniformity across the entire length of the product which can be manufactured with long joint-free lengths, mitigating the risk of signal loss or external interference at wiring intersections.
Saint Gobain offers our E – series product line, ideal for use as electrical insulation in high-frequency cables. Each film is manufactured using a proprietary process and ASTM D4895 compliant resins. The E5 product offers a low density of 0.5g/cm3 while our E7 product is slightly higher at 0.7g/cm3. Each product offers high tensile strength in the MD and TD direction, with E5 at MD 3,500 psi and TD 80 psi while E7 is 4,00 psi in the MD and 100 ps in the TD direction.
These mechanical properties are coupled with an exceptional dielectric strength of up to 7,000 volts per mil (V/mil). FLUOROWRAP® electrical insulation is subsequently ideal for manufacturing wiring and cables for high-frequency signals in demanding markets. Satellite communications, transmission lines, cabling in aviation and aerospace applications, and many more markets are successfully serviced using FLUOROWRAP® films.