When building, assembling, or simply handling electrostatic-sensitive devices, you probably bathe yourself and your workplace in anti-static materials. It’s critical to provide a completely controlled environment to avoid causing premature device failure. What you might not know is that some of that anti-static material may not be as ESD-safe as you thought. Here’s what you need to know about purportedly ESD safe materials commonly used in 3D printing, and what you can do to best protect your electrostatic-sensitive devices.
Traditionally, ESD-safe materials are formed one of two ways: Either by spraying a conductive polymer solution onto a product during finishing, or by using a plastic that has conductive material compounded into it. We’ll be focusing on the latter.
Plastics reinforced with conductive material typically use either carbon black, milled graphite, or high levels of graphitized carbon fiber.
Most commercially available ESD-safe materials used in 3D printing rely on loading between 15-30 percent carbon black into a thermoplastic – such as ABS or polycarbonates – to qualify for an ESD rating.
When these fillers are added to thermoplastics they can achieve a surface resistance of 1.0 x 1011 Ohms, which meets ANSI/ESD standards for insulating or packaging materials. However, to meet those standards, thermoplastics are loaded with carbon black or graphite at such high levels by volume that the amount of filler can lead to a degradation in the properties of the thermoplastic itself.
To meet ANSI/ESD standards for ESD-safe materials, 3D printed thermoplastics are loaded with carbon black and graphite fillers. We’ve found that these fillers cause the thermoplastic to become more brittle.
In fact, we don’t even need to test tensile strength yet to prove how far the material degrades due to these fillers: just take a piece of ESD-safe 3D printed material and rub it on a piece of paper. The material inevitably leaves a chalk or crayon-like mark behind.
This is extremely dangerous for electronic assemblies because it means the material eventually wears down, leaving bits of plastic behind. Imagine what those miniscule bits of plastic will do to, say, a circuit board being assembled on a fixture 3D printed with this kind of material. Talk about worst case cradle failure.
It’s probably time to throw out any “ESD-safe” materials you’ve been using with your 3D printer – but don’t throw the baby out with the bathwater. There is a safer material to use when 3D printing critical electrostatic-sensitive fixtures, enclosures, and parts.
The key issue with those old ESD materials is that they required such a high level of additive or filler to qualify as ESD-safe – and, ironically, those high levels degrade the materials quickly over time to make them not only unsafe but dangerous for electrostatic-sensitive products. To counteract that, you need a thermoplastic additive that can achieve those standards at much, much lower levels--such as nanotech low levels.
Alright, we know nanotech is a term that gets overused. We can’t really help that. It’s become a buzzword in pop culture recently, mainly to justify whatever a detective or superhero might be up to in a blockbuster movie or late night television show. And it’s been misused closer to home in engineering and manufacturing marketing to promise, well, some big promises. We’re not apologizing for what other folks do with the term. We’re simply using it because we’re doing it.
One of the true, tangible and useful properties of carbon nanotubes is being able to have a highly conductive material with a very low loading level of that carbon in the plastic. Carbon nanotubes are highly anisotropic tubes with an aspect ratio on the order of 1,000 or more. 30-70 nanometers can be several tens of microns long which allows us to set up a conductive network in a plastic tube at very low levels. How low?
Essentium’s carbon nanotube ESD material sees conductivity at 1-3 percent of the active material. A continuous network in our host polymer matrix only requires 1-3 percent level of percolation of active carbon nanotube material.
That’s nearly 10X less than the amount of carbon black or graphite required in traditional ESD thermoplastics.
What makes our carbon nanotube ESD-safe material so unique is our multilayer extrusion process. We developed high quality, multi-layer structures into our filament to create the strongest bond between our thermoplastics and carbon. Our carbon nanotubes are embedded into our thermoplastics like rebar in concrete; they don’t leave particulates behind.
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