Antistatic additives conductive fillers

An external antistat is applied via a carrier medium to the surface of the plastic part. The same considerations and limitations apply as with nonmigrating slip additives. Conductive filler is incorporated into the organic substrates and builds up a conductive network on a molecular level. While both approaches are used in organic substrates, they are not the most common. 

Conductive fillers, intrinsically conductive polymers, and organic additives are used as antistatics. There is no common product available which has a combination of the above. The only known combinations are particulate and fibrous conductive fillers, which are claimed to produce a better effect. 

An alternative to the use of antistatic additives is the incorporation of electrically conductive fillers or reinforcements into the polymer to make the whole structure conductive. Typical additives that are used for this purpose include aluminum, steel, or carbon powders, and metal-coated glass fibers or carbon fibers. Powdered fillers are generally less expensive than fibers. Maintaining the desired fiber distribution during processing is also problematic. 

Most antistatic additives are polar waxes the alkane chain part of the molecule is attracted to the polymer, while the hydrophilic end attracts water. This moisture forms a thin conductive film on the surface of the plastic. A charge decay half time of 0.1 s or less provides adequate protection against static electrification. To achieve this, the surface resistivity must be less than 3 x 10 fl/square. Although surface films are worn away by abrasion, they are replenished by the additive slowly diffusing to the polymer surface. They will not function adequately when the relative humidity is less than 15% (not a problem in the UK ), and cannot be used for specialised polymers with melt processing temperatures exceeding 300 °C. The use of conducting fillers (see the next section) is a more permanent solution to static electrification. 

High-resistivity materials such as certain plastics are specifically susceptible to the generation of ESD. This problematic property of certain plastics is often improved by incorporating certain conductive additives and fillers called antistats to the plastic to reduce the resistivity of the plastic material. 

Carbon black filled antistatic and conducting composites usually contain 10-30 wt.% filler. (Addition of 1-2 wt.% carbon black for improving the weatherability essentially does not change the conductivity, although it somewhat increases the dielectric loss). The addition of conducting carbon black to thermoplastics increases not only the electrical conductivity, but also the modulus, tensile strength, hardness, melt viscosity and the heat distortion temperature of the compound. It reduces, however, the elongation to break and impact properties. 

Semi-conductive materials may be produced by addition of conventional carbon blacks. Resistivity is lowest for those grades with the highest structure and highest surface areas. Non-black products generally rely on the use of antistatic additives, which reduce the surface resistivity of the product, since most non-black fillers are insulating in nature. 

Examples of only a few additives are carbon black, carnauba wax, coconut shell, coke dust, macerated filler, shell flour, vermiculite, and wax. Many additives, especially those that are conductive may affect electrical properties. Most plastics, which are poor conductors of current, build up a charge of static electricity. Antistatic agents can be used to attract moisture, reducing the likelihood of a spark or discharge. 

Various approaches have been suggested to reduce the number of fires at petrol filling stations caused by static electricity. One suggestion is metal door handles. Conducting additives are used to provide static dissipation in fuel systems, but there are difficulties in achieving adequate mechanical properties in polyethylene fuel tanks when carbon black is used as a filler. Doubts have also been raised in some quarters about whether some plastic fuel tanks will be able to meet the requirements for PZEVs , or partial zero emissions vehicles, required by California s new emission standards. Inergy Automotive recommends capless filler systems with locking mechanisms. Carbon nanotubes are likely to find a role in antistatic protection. 

Additives used in final products Fillers barium titanate, calcium carbonate, carbon black, carbon black coated with conductive polymer, copper powder, hafnium powder, lead zirconium titanate, silica, tantalum powder, titanium dioxide, zeolite, zinc sulfide plasticizers adipic polyester, dibutyl phthalate, dibutyl sebacate, glyceryl tributyl-ate, tricresyl phosphate Antistatics carbon black, glycerol monooleate ... 

High-surface-area fillers, such as fine-particle grades of silica or clay, should also be surface-treated when used with antistats to avoid surface adsorption of the latter. Conductive carbon black and magnetic iron oxide typically provide adequate charge dissipation. Addition of antistatic agents should be avoided with these so as not to interfere with their function. 

---