Is Butyrate an Antistat?
Is butyrate an antistat? We get this question often, and the answer is 'yes' and 'no.'
Every winter we receive calls asking for help with static buildup in pneumatic systems. Lower humidity brings an increase in static electricity. In pneumatic systems, one can decrease static charge through increased humidity and ionization in the airflow, additives to the resin, coating the outside surface of the tubing, and proper grounding. 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.
Burada has extruded clear-rigid transparent tubing for nearly 70 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. And the concentration of carbon needed to achieve static dissipation would make the tube black opaque.
Transparent Butyrate falls into the lower echelon category of “insulative;" but due to its plasticizer and moderate water absorption, it is less insulative than acrylics, polycarbonates, PETG, and PVC as shown below. And as humidity increases butyrate enters the category of "antistat" due to butyrate's water absorption.
Activated carbon aids the conductivity of the tubing, but at a price. The tubing will no longer be clear.
|Ohms Per Square||Material||Description|
|> 1013||Insulative||Insulators and Base Polymers.|
|109 to1012||Anti-Static||Initial charges are suppressed. Insulates against moderate to high leakage currents.|
|105 to10 9||Dissipative||No or low initial charge. Prevents discharge to or from human contact|
||Conductive||No initial charge. It provides a path for the 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)|
|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|
|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|