Recorded February 17th, 2011
Presented by RTP Company
Would you like to know how plastics are made conductive? Then join Dr. Joel Bell, senior product development engineer at custom compounder RTP Company, as he explores the world of conductive compounds from concept to commercial applications.
During an informative hour presentation, Joel will explain; How levels of conductivity are defined; how conductive plastics are measured, current additive technologies, and advantages and benefits of each additive. Whether the topic of conductive compounds is new to you, or you have been covered head-to-toe in carbon black for years, this webinar is a great opportunity to broaden your knowledge about conductive plastic compounds.
Questions and Answers
Q: What is LPC?
A: LPC refers to Liquid Particle Count. This is where a sample of the material is subjected to ultrasonic agitation in a liquid and then that liquid is analyzed to see what size and quantity of particles are removed from the sample.
Q: When the anti static charge decays, does it decay to the air, to surounding surfaces…?
A: Typically you need to ground the part/device in some manner, whether it be through a metal contact, human contact, etc.
Q: Can I simply improved the conductivity of an injected molded part by putting a mirror finish on the mold rather than adding a conductive filler (assuming I only need static dissipative level of conductivity)?
A: Surface appearance can affect the conductivity performance in a material, but you still need to have an additive present in the material that gives the conductive performance needed.
Q: First question for after the presentation. When you injection mold using carbon fibers say in an Acetal is a dedicated press needed, or is there any effects to the tool or press. For instance you might see some effect to the tool when using glass fibers would you see something similar with carbon fibers?
A: Carbon fiber will not be as abrasive as glass fiber, but will behave differently than an unfilled resin.
Q: Are products like polyaniline (still ?) used for improved conductivity ?
A: This type of product falls under the additives of inherently conductive polymers (ICP). At this time there is not a commercially available source of ICP suitable for polymer compounding.
Q: Could CNT technologies be used in continuous extrusion process for cable jacketing/insulating? Is it available? In use? Applications?
A: CNT technologies can be used in any typical polymer processing method including extrusion, injection molding, compression molding, etc. We would have to have more specific information to offer something further.
Q: What is the effect of 10% carbon balck on tensile properties on PS and HDPE
A: There won’t be a large increase in strength or modulus and typically elongation and impact decrease.
Q: Can you speak generally oh the processing and materials for mfging molded magnets?
A: This is not related to conductivity. Please contact RTP directly to discuss.
Q: How does cost of EMi conductive plastic compare to Vacuum metallizing
A: There is not a simple answer for this question. You have to look at all of the variables and processes needed in the metallization process along with the improved design flexibility offered by the plastic compound when considering the price. The price per pound of an EMI compound will be higher than the base resin.
Q: Is there any way to relate ohms and ohms/sq, even roughly?
A: In general the surface resistance (ohms) would be a decade lower than surface resistivity (ohm/sq).
Q: Is it safe to say that there would not be much difference in surface resistivity between a 15% versus 30% carbon fiber filled PC?
A: There is a diminishing return or ability to lower surface resistivity when you start to approach high levels of carbon fiber. The point where this occurs in PC is proprietary, but in general 30% would be considered a high loading level.
Q: Is RTP has supplied conductive plastic (EMI shield) in auto industry?
A: Yes we have supplied EMI materials into the auto industry and I strongly encourage you to directly contact RTP for further information.
Q: Does Carbon Black Absorb water. Does it matter the Shrinkage?
A: Yes carbon black will absorb moisture and this can have an effect on all physical properties. We suggest drying all conductive compounds per datasheet recommendations.
Q: Do you have a Office In India?
A: We have sales contacts in India, please see our website.
Q: What is tribrocharging?
A: Tribocharging is where a charge is transferred from one material to another during contact and the excess charge that builds up on one of the surfaces can be discharged in an ESD event. An example of this is when you walk across carpet and then shock yourself on a door knob.
Q: What effect does exposure to high heat and humidity have on base resin conductivity?
A: This is dependent on the actual conductive technology, but typically the more important concern is how the base resin is affected by these conditions. If the base resin is degraded, this will reduce conductive performance.
Q: What are recommended conductive materials for direct water immersion at 250F?
A: We would need more information on the conductivity target and actual application. However, it can be assumed at this temperature that a carbon based additive would most likely be used.
Q: please explain Anistropy and Tribocharging
A: Anisotropy refers to properties being different in different directions on a part. In the case of carbon fiber, conductive properties will be affected by how the fiber orientates in the part. Tribocharging is defined above.
Q: Can thermal and electrical conductive additives be added to extrusion grade polymers to achieve conductivity through the cross section of the extrudate?
A: Answered above.
Q: We use a custom made structural foam hopper in a powder handling system.
A number of metal parts are attached to the hopper. All the metal parts
need to be grounded to avoid sparks. We now paint the outside of the hopper
with conductive paint to provide the ground paths to the metal parts.
Could we make the hopper material conductive enough to do the grounding?
MATERIAL: POLYMER RESOURCES PPO-SF1, GRAY
DENSITY: 0.032 LBS/CU.IN
FLAME RATED UL 94-V0 OR BETTER
PAINT ALL EXTERIOR SURFACES WITH ACHESON ELECTRODAG 550.
MASK ALL THREADS, AND MASK THE INDICATED SURFACES ON SHEET 3.
SLIGHT OVERSPRAY PERMITTED
A: This is a specific application that is best handled with direct communication.
Q: what type of measurement technique for surface resistivity is appropriate for small contoured parts?
A: It is probably best to use a small probe type instrument like that described in the presentation. Pro-Stat is one manufacturer.
Q: Is pre-conditioning of samples required for measurement of resistivity? if so, what type of conditioning?
A: Typical conditioning is 24 hrs. at 50% RH and RT (72 F). Some specifications may also call out lower RH.
Q: is there a mathematical correlation between resistivity and resistance?
A: For volume, this can be calculated by the equation given in the presentation. For surface it is a bit more complicated, because the measurement type will affect the resistance. I would recommend referring to ASTM D257 or ESD STM11.11.
Q: WHat is the best way to eliminate swirls in either black or yellow PC/ABS RTP #2599 X 113333?
A: Please contact RTP for more information about this topic.
Q: Typically what product int the automotive industry are currently using the EMI & the thermal conductivity material?
A: Please contact RTP for more information about this topic.
Q: Do you measure EMI shielding using other methods?
A: We typically target certain levels of volume resistivity for the materials and then have the customer validate in their part. Remember that part design will also greatly affect performance.
Q: When doing a shielding effectiveness test, can the test sample be compression molded instead of injection molded?
A: Yes compression molding could work, but there must not be measurable voids in the part or performance will be significantly lowered.
Q: Can we add Aluminum particles to increase the conductivity?
A: Typically very high loading level of metal powders is needed to reach percolation and this becomes disadvantageous from a specific gravity, cost, and processing standpoint.
Q: can this material withstand the high temperature of the vehicle ecoat and paint processes, ie. 205°C for an hour minimum?
A: Performance would be dictated by the base resin.
Q: Could a PC/ABS blend with additives be electrically conductive enough to conduct charge from a AA battery? If so, which type of additive would be best? Would multiple colors still be available? What material properties would be impacted?
A: Please contact RTP for more information about this topic.
Q: which is good instrument for measuring surface resistivity of wires type structure
A: It is probably best to use a small probe type instrument like that described in the presentation. Pro-Stat is one manufacturer.
Q: what is effect of carbon fibers on elongation of polymer
A: There will be a reduction in elongation due to the reinforcing qualities of the carbon fiber
Q: how CNT affect ductility of the high perfromance polymers such as PEEK
A: In general ductility will be reduced, but this is dictated by the dispersion of the CNT.
Q: Can we use steel fibers in extruder with polymer
A: Yes, this is possible but some process modifications may be needed.
Q: do you have some experience with CNT composite for gas sensor apllications
A: Please contact RTP for more information about this topic.
Q: why doesn’t the stainless steel additive affect strength
A: The stainless steel fiber is flexible and fluffy and in general doesn’t create a good bond with the polymer. Therefore, you do not get any reinforcing effect like with carbon fiber or glass fiber.
Q: you showed a photo of a polyemr with CNT’s added. In the photo there were some balc clumps. Were these clumps of nanotubes?
A: I believe you are referring the first picture in the CNT section which shows the CNTs in a medium (not polymer) and there are individual CNTs along with clumps of the CNTs.
Q: Can you quantify what level of surface roughness is achievable with CNT?
A: This will depend on the resin type and molding surface.
Q: What maximum thermal conductivity one can expect with ceramic filler?
A: One might expect to achieve an increase from standard 0.2 W/mK to 1-5 W/mK.
Q: How difficult is the control of conductivity in a carbon black vinyl? How can it be controlled?
A: RTP does not compound with PVC, so we have limited experience. However, I would expect it to have a sharp percolation threshold just like in other polymers.
Q: Loresta tester – is this a good or bad measurement device for surface and volume resistivity compared to other devices?
A: I have never come in contact with the brand of equipment.
Q: Does conductive filler affect radio frequency attenuation.
A: It may have some effect, but this is additive type and quantity dependent.
Q: is it always necessary to use dispersing agents to achieve sufficient levels of dispersion in engineered polymers/nanotubes blends?
A: The methods to achieve proper dispersion of CNTs are proprietary.
Q: Is there hope that CNT technology will improve to where they become more conductive than they currently are in polyolefins?
A: Work is ongoing with CNTs in polyolefins, but there a seriously compatibility issues that need to be addressed. It is possible that in the future performance will be improved.
Q: What would you recommend for a conductive overmolding on a polycarbonate part? Need an insulating outer surface with a conductive inner surface.
A: Please contact RTP for more information about this topic.
Q: What is the minimum dosage that carbon black in polymer matrix to get conductivity?
A: Actual additive quantities used in formulas is proprietary.
Q: If comparing with carbon nanotube and carbon black for conductivity, how much difference in composites with same loading?
A: CNTs are able to achieve similar conductive performance to carbon black at significantly lower loading levels. For a rough idea refer to the percolation graph in the presentation and see the comparison between SS and carbon black.
Q: Where is you R&D developments with graphene as additive?
A: Graphene is a fairly new carbon based additive and development is ongoing. At this time there is not a commercially viable supply of this additive.
Q: Can you please explain the tribocharge effect?
A: Answered above.
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