Meaning
Electrostatic dissipation rate of a polymer surface after being subjected to a high-voltage corona discharge is measured by this physical property. Static charge decay governs how quickly a moulded plastic part or polymer film sheds accumulated electrical energy. If the decay rate is too slow, parts will cling to one another in the collection bins or attract airborne dust.
This property is evaluated under specific relative humidity conditions because moisture levels alter the conductivity of the polymer.
Material Formulation
Polymer resins often require the addition of migratory or permanent anti-static additives to accelerate the dissipation process. The mechanism of charge decay in these formulations relies on the migration of hydrophilic molecules to the surface where they attract ambient moisture. Virgin resins generally possess low intrinsic conductivity and require higher additive loads than recycled materials that contain conductive impurities.
Formulators must adjust these concentrations carefully to avoid affecting the tensile strength or surface gloss of the final product. In addition, excessive loading can lead to oily surface deposits that interfere with printing or adhesive bonding of the finished components.
Processing Influence
Injection moulding parameters can alter the distribution of anti-static agents and thus shift the dissipation performance. High shear rates during the injection phase can degrade these additives or force them to remain locked within the frozen core layer. When the melt temperature is set too low, the additives fail to migrate efficiently to the outer boundary.
The resulting part will exhibit slow charge decay despite having the correct raw material specification.
Static Discharge
Excess static accumulation poses safety risks and secondary processing challenges in automated assembly lines. A slow charge decay causes parts to stick to conveyor belts and transfer stations, which disrupts downstream packaging. In electronics packaging applications, a sudden discharge can ruin sensitive components.
The use of specialized test meters ensures that the dissipation time remains within the millisecond range required by handling equipment.
