Conductive thermoplastic compounds conductivity

Conductive Thermoplastic Compounds. Conductive thermoplastic compounds were prepared using Eeonomers. Volume resistivity as a fimction of Eeonomer content is shown in Figure 4 for nylon-6 and ABS compounds. The volume resistivity is observed to fall several orders of magnitude between 5 and 10 wt % of composite concentration. This indicates that the resistivity is very responsive to Eeonomer loading level and that percolation is occurring within this range. 

For EMI shielding applications, numerous processes are used, some require conductive fillers. These applications include parts molded with conductive filler and conductive paints. Conductive fillers used in commercial applications include aluminum, silver, nickel, and copper flakes and powders, stainless steel fibers, and fibers and flakes coated by nickel and silver. Thermoplastic compounds can provide up to 65-70 dB of electromagnetic noise attenuation but obtaining values over 45 dB is difficult. Static dissipative compounds (ESD) are mostly produced with carbon black which accounts for approximately 90% of the market but many other fillers are also used. 

The principal fillers used for molding compounds and other thermoset and thermoplastic compounds can be classified as (1) agricultural and plant products, (2) conductive fillers, (3) fibrous fillers, (4) mineral fillers, and (5) reclaimed material. 

The properties of some thermoplastic compounds that were prepared with Eeonomer additives are given in Table I. Also, listed as a control for comparison is a nylon-6 compound with uncoated carbon black. The mechanical properties of the Eeonomer - nylon compounds are observed to be similar or better than the control. Note that in the nylon-6 case, the polypyrrole - Eeonomer compound offers improved mechanical properties over the polyaniline composite while still retaining the same conductivity level. 

Power Cables. The materials mosdy used to produce power cables are ethylene copolymers loaded with conductive carbon black for semiconductive shielding layers, polyethylene or ethylene—propylene mbber-based compounds as insulations, and either thermoplastic materials (eg, polyethylene, PVC) or thermosetting (based on chlorinated polyethylene (CPE), chlorosulfonated polyethylene (CSPE), chloroprene, etc) for jackets. 

Suspensions of polyacetylene were prepared as burrs or fibers (46) by using a vanadium catalyst. When the solvent was removed, films of polyacetylene were formed with densities greater than that prepared by the Shirakawa method. These suspensions were mixed with various fillers to yield composite materials. Coatings were prepared by similar techniques. Blends of polypyrrole, polyacetylene, and phthalocyanines with thermoplastics were prepared (47) by using the compounding techniques typically used to disperse colorants and stabilizers in conventional thermoplastics. Materials with useful antistatic properties were obtained with conductivities from 10" to 10" S/cm. The blends were transparent and had colors characteristic of the conducting polymer. For example, plaques containing frans-polyacetylene had the characteristic violet color exhibited by thin films of solid trans-polyacetylene. 

Polyurethane pre-polymer or thermoplastic polyurethanes are prepared by the reaction of polyester or polyether diols with diisocyanates. The reaction can be conducted in bulk, in a solvent, or in an aqueous solution or dispersion. Unless the reaction is carried out at an elevated temperature a catalyst is required. Organotin compounds are the prime catalyst for this reaction. 

Carbon-black-filled rubber compounds are usually produced on Banbury-type mixers, while conductive thermoplastics are preferably produced on twin-screw extruders. Unlike other filled compounds or polymer blends it is essential to adhere very precisely to the carbon-black concentration and the production parameters, since a very delicate balancing act is usually required to stay on the tight-rope of optimum composition and avoid falling into the pits of insufficient conductivity, inadequate mechanical properties or sharply increased viscosity. 

Polymeric compounds are specific sealing materials intended to line or impregnate conducting hardware as well as electric radio circuits for electric insulation. They are based on epoxy and unsaturated polyester resins, liquid organosilicon rubbers and monomers (initial products for S3mthesizing pol3Tnethacrylates and polyurethanes). Compounds based on thermoplastic materials (tar, rosin, cerezin) in the form of solid or wax-like masses, heated for transformation into the liquid state, are confined to this application. 

The developments at Fraunhofer ICT focus on the combination of graphites and carbon black with different particle geometry and size distribution, to obtain as many contacts as possible between the conductive fillers, and thus produce conductive paths. The polymer serves in the material mixture as a binder to achieve a mechanically stable gas-tight system and to make a thermoplastic processing of the material compounds possible (Fig. 10). 

By combination of electrically conductive fillers of different particle sizes and size distributions, thermoplastic processable polymer compounds with 80 mass... 

---