Innovative and Conventional Antistatic Solutions
Usual plastics are insulating materials subjected to electrostatic build-up and discharge depending on the surface resistivity of the part.
In general, dissipative or ESD polymers have:
- A surface resistivity in a range from 105 or 106 up to 1012 ohms.
- A static discharge half-life generally inferior to 60 seconds.
According to the targeted application, beware of too low resistivity leading to conductive polymers and inherent risks. Problems are of very various seriousness, from minor to very serious and even dreadful ones:
- Dust and other pollutants attraction with marketing, use and processing problems
- Electrostatic build-up or discharges when touching the plastic parts: synthetic carpets, knobs, car handles
- Painting and printing defects
- Fire or explosion of inflammable or explosive environment, organic powders
- TV, radio, electronic interferences
Electrostatic build-up and discharges are widespread in:
- Continuous processing of plastics such as films
- Electronic manufacturing, handling and repairing
- Electronic applications
- Packaging of dusty organic materials
- Aeronautics: lightning and interferences
- Automotive: Electrostatic discharge of fuel lines leading to fires
- Inflammable and explosive environments: healthcare, operating theatre, painting shops
- Use in cleaning of roo
It is a difficult problem and there is not any universal strategy but multiple ways are used, sometimes in combination. Among several routes used to minimize the static build-up let us quote:
- Choice of antistatic grades
- Addition of antistatic agents to conventional plastic grades:
- Organic non-black additives
- Conductive fillers: carbon blacks, fibers, graphites, carbon nanotubes
- Alloying with inherently conductive plastics
- Coating with a permanent conductive surface layer
- Use of temporary external antistatic agents
To end, if polymer modification is not desired, use antistatic equipment neutralizing electric charges to proceed to a processing phase for example.
Organic Non-black Additives
The non-black antistatics have been used for a long time but their action depends on the hygrometry. New generations such as H2Stat (by Teknor Apex) are marketed without this drawback and are efficient with an hygrometry as low as 15 %. They migrate to the surface and interact with atmospheric moisture reducing surface resistivity and hence dissipating high electric charge densities, to give a long-lasting anti-static effect to the plastic part.
The principle of the action of an amphiphilic antistatic additive, for example an ester of fatty acid, follows this theoretical way:
- A lipophilic segment made of a long chain of -CH2- loves the polymer
- A hydrophilic end-chain, the ester function in that example attracts the water or the moisture of the environment.
- The moisture trapped by the hydrophilic end of molecules forms a thin conductive film at the surface of the plastic if the atmospheric moisture is sufficient. If the moisture level is too low, the antistatic becomes inefficient.
- The antistatic agent migrates slowly to the surface at a controlled rate to maintain long-lasting conductivity.
The used additive levels in the polymer are typically in a range of less than 1 % to few percents.
The antistatic additives often are:
- Alkanes sulfanates
- Fatty alcohols
- Quaternary ammonium salts
- Soaps of fatty acids
Several chemical functions can be combined in the same molecule.
Numerous proprietary antistatic additives are marketed and Table 2 shows some examples without claiming to be exhaustive.
Ready-to-use Solutions: Special Versions of Plastics and Antistatic Masterbatches
Producers or compounders market antistatic versions or masterbatches usable for almost all polymer families, for example:
Commodity plastics such as PS, PP
Engineering plastics such as ABS, PA 6/6, PA 6, PC, POM, PBT, PPO, PPS
Specialty plastics such as PEI, PEEK
Alloys such as PC/PMMA, PC/ABS
For ESD grades, properties and rheology can be slightly different from standard grades as we can do it