Wire insulation properties

Electrical Properties. CeUular polymers have two important electrical appHcations (22). One takes advantage of the combination of inherent toughness and moisture resistance of polymers along with the decreased dielectric constant and dissipation factor of the foamed state to use ceUular polymers as electrical-wire insulation (97). The other combines the low dissipation factor and the rigidity of plastic foams in the constmction of radar domes. Polyurethane foams have been used as high voltage electrical insulation (213). 

Phosphazene polymers are inherently good electrical insulators unless side-group stmctures allow ionic conduction in the presence of salts. This insulating property forms the basis for appHcations as wire and cable jackets and coatings. Polyphosphazenes also exhibit excellent visible and uv radiation transparency when chromophoric substituents are absent. 

Power factor, like the dielectric constant, is a property that represents a power loss that takes place when a wire insulation becomes the dielectric of a condenser because of a surrounding sheath or other conducting medium. 

The excellent electrical insulation properties of polyethylene have led to extensive use in cable and other wire-covering applications. Spectacular early uses included undersea cables and airborne radar and the materials continue to be used in substantial quantities. One particular trend is the increasing use of cross-linked polyethylene for this area of use. Such materials have improved heat resistance and in addition have given generally better resistance to stress cracking. Cellular polyethylene is used as the insulator for television downlead aerials. 

Its excellent electrical insulation properties lead to its use in wire insulation, in valve holders, in insulated transformers, in hermetic seals for condensers, in laminates for printed ciruitry and for many other miscellaneous electrical applications. 

Our principal concern is often the polymer s mechanical properties. For instance, the requirements of the handle of an electrician s screwdriver are very different from those of wire insulation. In the former application, we are free to choose stiff polymers of many types, including glassy amorphous polymers. In contrast, wire insulation must be flexible, which limits our choice to ductile polymers. 

Polyesters exhibit excellent electrical properties. They resist breakdown when exposed to continual electrical loads and have a high electrical resistance. For this reason, they are often used in electrical housings, as insulating films in electrical components, and as wire insulation where high temperatures are likely to be encountered. 

The polarity of EVAs leads to an increase in loss factors and dielectric constants but the insulating properties allow their use for wire coating. For example, between 10% and 30% VA ... 

Perfluoroalkyl-l,3,5-triazines are very stable to oxidation and heat. They have potential as lubricating fluids for use in aerospace work (B-74MI22003). Their polymeric products are stable elastomers with excellent rubber-like properties for use as electrical wire insulation and seals for hydraulic, lubricating and fuel systems of aircraft (B-80MI22001). Perfluoro-2,4,6-tri-n-heptyl-l,3,5-triazine is a valuable reference standard for precise mass... 

Because of increased production and the lower cost of raw material, thermoplastic elastomeric materials are a significant and growing part of the total polymers market. World consumption in 1995 is estimated to approach 1,000,000 metric tons (3). However, because the melt to solid transition is reversible, some properties of thermoplastic elastomers, eg, compression set, solvent resistance, and resistance to deformation at high temperatures, are usually not as good as those of the conventional vulcanized mbbers. Applications of thermoplastic elastomers are, therefore, in areas where these properties are less important, eg, footwear, wire insulation, adhesives, polymer blending, and not in areas such as automobile tires. 

Many of the applications in which polymers are used are based on the fact that they tend not to conduct an electrical current very well. For example, one reason for the enormous popular success of the first entirely synthetic polymer, Bakelite, in the early 1900s was its outstanding electrical insulation properties, just the characteristic needed for a host of applications in the new and growing held of electrical appliances. Within a decade after its discovery, Bakelite was being used for housing and casings for industrial and household electrical equipment and for insulation on electrical wires and structures. For the past century, the applications of many different kinds of polymers in electrical insulation have become legendary. 

EP 323142 (European) 1989 Ternary polyether ketone blend wire insulations Pirelli General PLC, UK CK Alesbury, RJ Murphy Formulation shows excellent stress craze resistance, flexibility and flame resistance Blends of polyarylene ether ketones, polyether imides and polyfimide siloxanes) were coated onto wire for solvent resistance, O index and abrasion resistance. Blends without siloxane-imide copolymer did not meet these properties... 

Kim, O.Y., Yoon, S.H., Nam, G.J., and Lim, H.J., The effect of compatibilizers on the mechanical and flame retardant properties in HFFR compounds for automotive wire insulation, in Proceedings of the 52nd IWCS/Focus International Wire Cable Symposium, Philadelphia, PA, 2003, pp. 352-356. 

---