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Static Dissipation

Every winter we receive calls asking for help with static buildup in pneumatic systems. With lower humidity comes an increase in static electricity. One can decrease static charge through increased humidity, additives, ionization, proper grounding and surface coatings. And future blogs will address all of these options.

In pneumatic conveying a static electrical charge is usually generated by friction on the exterior or interior of the tubing. In steel tubing the charge is quickly dissipated. But in plastics tubing, the charge is usually localized; it may exist on one part of the tube, and not another part. A shock is usually rare if one were to touch the tube, but touching a non-grounded metal coupling can give a jolt.

Busada has extruded clear-rigid transparent tubing for over 60 years and we firmly recommend cellulose acetate tubing for pneumatic conveyance. Still, we also extrude ABS, PC, PETG and PVC resins. But, unless one has a specific need tor these resins, we recommend Eastman Tenite Butyrate 576E UV stabilized, and 264E FDA approved resins.

The axiom was, and still is today, “CAB provides the best transparent tubing for pneumatics due to its clarity, cellulosic base, superior impact strength, easy fabrication, and low acoustic resonance.”

However, without additives, no clear, rigid transparent tube meets the criteria for “static dissipative.”

All transparent plastics resins require additives (such as activated carbon, or quaternary amines) to become dissipative. But, additives can alter the transparency as you can see from the picture on the right.

Transparent Butyrate falls into the “insulative” category: but do to its plasticizer and moderate water absorption, it is more dissipative than acrylics, polycarbonates, PETG, and PVC as shown below.

 

Static Dissipation
Ohms Per Square Material Description
> 1013 Insulative Insulators and Base Polymers. Not and ESD material
109to 1012 Anti-Static Initial charges are surpressed. INsulates against moderate to high leakage currents.
105 to 109 Dissipative No or low initial charge. Prevents discharge to or from human contact
103 to 105 Conductive; No initial charge. Provides path for charge to bleed-off.
1 to 102 Shielding  

Most usual measurement standards are ASTM D257 and IEC 60093.

Comparison of various materials (mostly transparent) on volume resistivity.
The table below was compiled from Omnexus

Polymer Explicit name of the polymer Min Value(1015 Ohm.cm) Max Value (1015 Ohm.cm)
ABS Acrylonitrile-Butadiene Styrene 14.000 16.000
ABS/PC Acrylonitrile-Butadiene Styrene/Polycarbonat e 14.000 17.000
CAB CAB - Cellulose Acetate Butyrate 13.000 13.000
COC Cyclic Olefin Copolymer 14.000 15.000
EVA Ethylene Vinyl Acetate 15.000 15.000
PC Polycarbonate high heat 15.000 16.000
PET Polyethylene Terephtalate 16.000 16.000
PMMA Polymethylmethacrylate (Acrylic) impact modified 14.000 16.000
PS crystal Polystyrene crystal 16.000 17.000
PVC Polyvinyl Chloride rigid 15,000 16.000

 


Charles Busada - 08-Sep-2016
 

 

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