The mechanical properties of 3D printed thermoplastic materials have been fairly well explored at this point. Sure there is always room for improvement… gradually, over time, researchers will create new polymer blends, or new filled plastics, and there will be incremental gains in strength.
Eventually, the engineering polymer materials will be comparable to certain metals in terms of weight and strength. All good.
But there is more to 3D printed polymers than mere specific strength.
Several companies have been playing around with the electrical properties of the feedstocks, for a while, with the intention of making them conductive and static-dissipative.
In this post, we will take a look at static-dissipative, or so-called ESD safe materials.
ESD, or electrostatic discharge, is the discharge of electricity between a statically charged object (such as your hand), and another object of a different potential, such as a metal doorknob.
You know what happens next: you touch the doorknob, you get a shock.
If that happens every single day for a year in a classroom, then it can leave a Pavlovian fear of metal doorknobs (speaking from experience).
Human beings can begin to feel ESD on the skin at around 2000-3000 volts. Obviously the current is negligible, otherwise it would kill you.
Small electronics components such as the transistors on an IC, however, can be utterly destroyed by ESD with voltages lower than just 10 volts of static electricity.
That’s not to mention the arcs caused as a statically charged object tries to ground itself across an air gap. You don’t really want these sparks flying around as you fill your fuel tank with petrol.
Both of these reasons and more are why product designers and engineers need ESD safe plastics. The protect ESD sensitive electronic components during manufacture and stop gas stations from exploding.
In terms of ESD safe materials, they can be divided into two main groups.
These are conductive, and static-dissipative materials.
Conductors have low electrical resistance and can transfer electric charge via the bulk material or over the surface. In ESD application, they are used in those ESD bracelets that you wear on your wrist and connect to ground. They are also used on those plates that you stand on when entering an ESD controlled area, such as in an electronics factory.
Conductive vs. Static-Dissipative Materials
Conductive materials have a very low electrical resistance, allowing electrons to flow easily across their surface or through the bulk of the material. Charge flows quickly from one conductor to the next.
With static-dissipative materials, the charge flows more slowly. When an arc occurs, it does so at a slower velocity, and with lower energy as it tries to reach ground.
Plastics are insulators. They hold charge, and have a high electrical resistance. To have a path to ground, conductive fillers must be added to the material in order to be dissipative.
In order to be classed as an ESD safe material, the surface resistance of that material must fall within the range of 105 Ω and 1011 Ω. If it is less than that range, it is conductive. If it is more, then it is an insulator.
Here are a few different materials which are designed for ESD applications covering the main plastic printing methods.
If filament deposition is your thing, then you have a lot of options for ESD safe filaments.
Most of them modify the surface resistance by addition of some form of carbon.
ESD safe materials are available in a wide variety of different polymer flavors including high-temperature nylon, TPU and polycarbonate. Ultimaker has a great overview of ESD safe materials which are also tested on their machines, right here.
The ESD friendly sintered plastic feedstocks are less numerous than their extruded filament counterparts. But they are still commercially available for anyone who owns an SLS machine capable of printing plastics.
Plastic company Igus has a sintered material named iglidur I8-ESD, for example. It has a high abrasion resistance and is electrostatically dissipative. According to the website, it is compatible with most SLS Machines.
There seems to be a distinct shortage of options where it comes to ESD safe photopolymeric resins for some reason. Even Carbon doesn’t have anything listed.
There is a company named 3DResyns who advertise a variety of conductive resins, and they state on the website that by adding various conductive and semi-conductive particles to their blend, they can custom manufacture ESD safe photopolymeric resins to your requirements.
Additionally, there is a company named Fortify who makes a hybrid DLP / composite printer, who have a couple of options regarding ESD safe materials.
Their printing process involves normal layerwise deposition, as found in a typical photopolymer printing process, but with the addition of a mixing tank that injects the additives into the base resin. They call this process Digital Composite Manufacturing.
Additionally the system has something called “Fluxprint”, which uses magnets to align the particles in the resin as it is curing. This apparently enhances the strength of the parts.
Interestingly, the Fortify site says that the functional additives must be uniformly distributed to achieve consistent material properties. Their so-called Continuous Kinetic Mixing process addresses this issue by blending resin and additives constantly, alleviating settling of additive particles.
Asides from these two companies, no further resin manufacturers were found selling ESD resins.
Why is this?
We conclude it may be a couple of reasons.
Firstly, it may simply be as Fortify has stated. Maybe the resins and additives must be constantly mixed to print properly, hence why nobody is doing it.
Or, we may simply have the search term wrong on Google.
If anyone knows the answer as to why there are so few ESD safe photopolymer resins available, let us know in the comments.
And in the meantime, if you need anything printed that is ESD safe, then you will have a lot more luck with filament extrusion printers or powderbed fusion plastics.
Next article, we will take a look at the conductive feedstock options. That is the materials with surface resistance of less than 105 Ω.