When two polymeric surfaces are rubbed together static electrical charges are generated on the surfaces. Party tricks involving picking up pieces of paper with a comb are amusing. However, static electricity can be a nuisance in the plastics industry with dust attraction during storage or in service. More serious problems occur when the static electricity discharges as a high voltage spark. This can cause damage to electronic components and igniting volatiles in fuel systems and printing lines.
Visitors to plastics processing plants are amused by tinsel decorating production lines. However, the problem can also be tackled using additives. They turn the inherently insulating thermoplastics into slightly more conductive materials to allow the static charges to leak away to earth and avoid hazardous build up.
‘Migrating Antistats’ are additives which, at levels less than 1%, migrate to the surface and form a surface conducting layer by attracting moisture from the atmosphere. Obviously they function less well at low relative humidity.
‘Permanent Antistats’ are conductive additives, such as carbon black, carbon fibre, carbon nanotubes, metal fibres and certain mineral fillers. At levels of 5 – 15 %, they function by sufficiently reducing the electrical resistance to encourage static charges to leak away harmlessly.
In selecting the appropriate additive for electrostatic dissipation, due attention has to be given to how it affects other properties. Some of the carbon additives, which now include the wonder material, graphene, will affect colour — unless you go for the Henry Ford option — and mould shrinkage can also be affected. For some there will be an increase in stiffness but one type of permanent antistat, polyether block amides, at 10 % level may give a decrease in stiffness.
This electrostatic dissipation article was written by Dr. Charlie Geddes for Hardie Polymers
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