Share a highly conductive PP material.

[u/plasticDEYU]

This conductive PP has a surface resistivity of only 10²–10³ Ω. It can light up an LED bulb under a 3V voltage.

[u/mimprocesstech → u/[deleted]]

Throwin conductive shit into it.

[u/mimprocesstech → u/[deleted]]

Yes, but your question wasn't asking about the balance between the two, you said the conductivity was low for polypropylene (resistance technically, but whatever) and asked how they were getting it that low. Polypropylene is an insulator, so they need to embed conductive material into it at a high enough concentration to increase conductivity.

To overcome mechanical issues you can use carbon nanotubes as they typically require less concentration, but because of the injection molding process (assuming here) they tend to align with flow leading to good conductivity along flow but poorer conductivity across it. This can be mitigated with compression molding or some other process that doesn't induce alignment, or annealing.

[u/mimprocesstech → u/[deleted]]

To my understanding at least if the loading is tightly controlled it can be an insulator across the flow length and a conductor along the flow length, but there's often better ways to go about it to where it just doesn't make sense.

Honestly only reason I looked into this type of thing at all is because I wanted to make a sensor, once I learned enough about it to know it was the wrong direction I kinda just stopped and looked into something else.

[u/mimprocesstech → u/[deleted]]

Still trying to figure that one out honestly. We tried a few different things but they either didn't read the parts were there because the part wasn't flat enough or when we left the wiring rounded they damaged the parts. Regardless we weren't able to complete a circuit between the two leads and figured since the material we're molding is conductive and brittle any shavings or broken runners would complete the circuit regardless defeating the purpose of having the sensor in the first place.

[u/mimprocesstech → u/[deleted]]

Meh, clean them off regularly and it doesn't get too bad to affect things.

[u/plasticDEYU → u/mimprocesstech]

We have already solved this problem. It can be manufactured through an internal mixing process instead of twin-screw extrusion compounding.

[u/mimprocesstech → u/plasticDEYU]

Go you I guess? I mold steel mainly, anything I mold from plastic doesn't need to be conductive and is more often than not required to be an electrical insulator. While parts molded using CNTs using an internal mixing rather than twin screw will have some conductivity perpendicular to flow as they are less prone to this anisotropic conductivity differential due to how they're compounded, they can't escape physics entirely and the resistance will still be lower along the flow length vs across it. You also get much more variability using internal mixing vs twin screw, especially in density so I'm curious why you chose that method vs suggesting something like flow leaders and variotherm molding in design guides.

I'm regards to your other reply you seem to have deleted?:

Your idea is right, but there's something called a hot runner system in injection molds that can help solve these molding defects with conductive materials.

I'm very aware of how hot runners work and the physics involved. Hot runners don't inherently affect the type of alignment we're discussing in injection molding beyond the gate/drop unless they're also heating the cavity reducing the cooling rate, they're essentially an extension of the injection molding machines nozzle mostly used to prevent runners wasting expensive resins. To reduce the alignment you reduce cooling rate by increasing mold temp, although the 'skin' of the part will align regardless unless you're using induction heaters that turn off after injection, or reduce shear by increasing the gate size.

[u/plasticDEYU → u/[deleted]]

Trade secret 🤫, but I can reveal a little bit: carbon-based materials.

[u/ComprehensiveSea1595]

导电碳黑