Saturday, July 07, 2007


I'm gettin' places!

Okay, today has been an excellent day, and not just because it was so fine to go down to the beach riding my motorcycle.
Today I opened the boxes that arrived this week, with new products for me to go *Frankenstein* with my resins (meet my resin bottles to the right).

1st box: N-methyldiethanolamine, the stuff that stops oxygen scavenging in it's tracks.
Remember how that effect was slowing down the setting and hardening of my resins, specially for polyesters? If not, you can read about it on the post below. Well adding a little N-methyldiethanolamine has reduced the curing and hardening time from something around 40 minutes to.... UNDER 5 minutes!
Here is my big rig with the stronger fluorescent tubes, the one that's on here is the germicidal UV one.
With this setup I will nos start fine tuning the mixes so as to get something that will work perfectly well in a syringe and will be fast curing!

It's really close now! Really, this thing hardened so fast that I literally didn't see it happen. In fact it was so fast that it wrinkled the surface of the resin because it hardened before the inside got time to do so.
Just a minor problem that will be tackled in my next experiments.

2nd box: Titanium Oxide powder, a common white pigment that should act as both a filler and a co-initiator, improving depth cure. Well that hasn't worked so well. It has such a diffusion power that the UV radiation gets swamped before it can make its effect. This pigment has some serious covering properties. I will need to use a lot less to see the desired effects. To be continued...

3rd box: Copper powder. This one is straight forward: I wanted to fill my air-drying acrylic i bought the other day with a fat load of copper powder to see if i could get a conducting thread.
On this picture yous see a number of threads i spread over a Polystyrene board with my copper filled acrylic resin, after 1 hour drying. The shiny part that looks like copper I achieved by polishing the hardened thread a little, with a rounded metal object. Isn't that just the most amazingly unexpected thing? I was not hoping this good a result! And I didn't even load the resin to the maximum ability! It's loaded with about 50 volume % copper, i could probably go up to 70v%! And you know what? you could probably use any regular glue to get this stuff, it's so damn easy I tell you!

Now, not everything is perfect. The threads still have a quite high resistance.
Here I made a measure of the polished track's resistance. those are 10 kOhms by the way... And the non polished, quite porous thread has a resistance through the roof! :$ Anyway, the thread varies in resistance and sometimes it's a lot lower. This thing needs to be copper plated still, and that should get us where we want. By the way, the thread sticks pretty nicely on the board, but maybe using strong glues (epoxy?) would give us a better result, specially at very high copper loads.

Anyway, I'm very happy with my results today, I feel like I made a big leap! Cheers to you all RepRappers, and thanx for all your ideas and inspiration! I'll have some drinks on us all to celebrate this :)

Hmm... I wonder if it would work to lay down a path of plain glue/tacky polymer then blow a thick coat of conductive powder (say, graphite) onto it before it hardened?

Afterward, you could copper plate it if you needed lower resistance.

You might be able to recycle some old laser printer guts to disperse the powder.

I believe something very similar to this method is used to electroplate non-conductive objects (like tree leaves).
Yup, that's the basic idea. Mix it before or spread it over later, copper or graphite, both work. I wonder how the thread reacts to being welded though. I would imagine that the one with heavy copper load in the mix would dissipate the heat better and resist best.

Man, idon't have a reprap machine, because if I had, I would be printing circuit boards right now!
i'm really excited for the day when all you guys doing research into materials will have an easy to setup, simple reprap machine at your disposal. we're getting close... i'd say within the next year it will be very easy to setup and have a working reprap machine. in the meantime, there is some fortitude required to build one =)
I regularly use >95% filler levels with acrylic and polyurathane in my work. So you might try adding just enough polymer to hold the grains of copper together and then compress the result into a track created by two or more tracks of pure polymer. The result will be very brittle but with the support of the two tracks should hold together. I have tried it with aluminum but at nowhere near the fineness of powder that you are using.

Once we get to the point that I can build a coreblower I am intending to create vented cavities and experiment with air-fluidized powders with extremely high filler loads (+99%) to take that idea to its extreme.

Zach: my brother and me might just start building a Repstrap anytime soon. I'm just so impatient to start building a cartesian robot. Also my bro is a professional system architect with a potent knowledge of Java. So who knows, maybe i'll be printing these things sooner than expected :)

Mike: You have more knowledge than me on fillers, and I'm sure you are right with the extremely large loads of metal powder. the stuff i use is so fine that the bonus effect of being able to compress it and improve conductivity is really providential! I will try what you suggest and who knows, maybe we don't even will need to plate these threads. printing and compressing them would be enough to get a circuit board. I was also thinking about a heat system that would melt the grains together. Aluminum would be the metal of choice then as copper has a way to high melting temp. keep me in the loop with the test you make with that. With these three research lines I think we are very close to making conductive materials work, one way or the other.
By the way Mike: using furfural resins as a binder for the conductive mix would be a very smart move as these resins stick really nice to circuit-board plastics as well as many hard to adhere plastics like PVC or Melamine. Just thought I should mention this as you told you had easy access to furfural and furfuryl alcohol.
One of my next projects will be with caustic solubilzed Phenol Formaldehyde systems since they are water based and compatiable with furfural systems. The major advantage is that the polymer is a organic salt that holds onto a reasonable amount of water even when fully cured. That should make the resin an ion carrior rather than a barrior which will hopefully allow for the use of cheaper metals (aluminum) as well as coarser powders. They are also thermoset so can be used to make castable cavitites, or in this case for the end result to be flash heated with the intention of sintering the metal powder.

I think that removing a little oxidation is one thing but having abraded the entire surface, you might have increased the conductivity. You can get good connections by pressing firmly with the probes or just abrading in the areas where the probes touch allowing for true resistance to be measured. Great work, keep it up!
Nice progress. It might be worth checking out the conductive glue instructable for similar ideas
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