I have been experimenting with a number of inks and methods of application.
The inks: 1. Silver ink: on Ebay $19 for 15g bottle https://www.ebay.pl/itm/Silver-Conductive-Paste-Paint-Ink-PCB-Membrane-Screenable-60-Silver-15-grams/264195847562?hash=item3d834cb58a:g:RRcAAOSwsClbkP2m Material: It is composed of 60% silver. It is not waterbased, I am not sure exactly with this one it can not be thinned with terps, however I have not tried white spirit.
Application: I have been painting with it, I attempted to put it inside a refillable paint marker with little success. It claims it is screenable- but it is really messy and sticky, with such a small quantity I have been reluctant to try. I am keen to find a way to insert it into a rollerball pen.
Conductivity: Very good, even without curing the conductivity is 0.14Ω for a 2mm width, 8cm line. Heat curing seems to make little difference to the conductivity.
2. Working Ink: £5.85 for a 10ml applicator bottle. http://workingink.co.uk/ Material: I think it is a mix of Carbon, Graphite and other things. Though it comes with little documentation and little to be found on their website. It is waterbased. Application: It comes in a useful squeezy bottle. It is runny, so not suitable for delicate circuit work. I think it could be screenprinted with, but yet to try. Conductivity: Compared to the silver ink and circuit scribe this has a high resistance. I imagine it could be good for heat pads, when screenprinted. Not only did I test the resistance of various line widths, but I also tested applying different layers of ink, which I applied pressure to (rubbing with a spoon) after. The resistance is measure at 8cm
Working Ink, single application, various line widths.
Working ink, Same Line width, number of layers applied.
3. Homemade variations 1: Carbon Nanotubes, Glue and Water. Material: As you can imagine, this was a pretty gluey mixture, it did not spread evenly, nor was it very fine. Conductivity: The same tests were conducted for this as for the Working Ink, Of line width and number of applications. Measured at 8cm. It has a very high resistance. Wouldn't recommend it for much, really. However, one interesting thing was that it’s resistance decreased (from 41k to 16k) with heat curing.
3. Homemade ink 2: Graphene Glue and Water. Material:This was a lot finer than the nanotubes, Im not sure I put muc effort into this ink after the previous one not working so well. Application:The same as other homemade inks. Conductivity: Even worse.
Graphene Line width tests.
Graphene Thickness Test.
3.Homemade Ink 3: Graphite, Glue and Water. Material: Smooth, and easy to mix, plus when dried and rubbed for pressure (annealed) it gives off a great sheen. The pictures look black, but actually it is the same colour as pencil lead.
Application:Very smooth once again. Also, it stuck pretty well and did not smudge too much afterwards. Obviously, if you put a piece of paper to cover it when you annealed it, this would probably give a clean line. It could do delicate work as well as it was quite fine.
Conductivity: I would say about as good as the working ink. Annealing after application really helps with the conductivity – I just took a spoon and rubbed hard. TBH got similar results to the working ink.
Graphite Width Thickness test
4. CuPro Coat: $29.95/4 ounce tin. http://www.lessemf.com/292.html Material: Copper based, so prone to oxidising if left out. Has a pungent smell, but it claims to be water based.
Application: It is water based, so can be thinned with water, it is pretty liquidy, with large particles. I attempted screen printing it, with a low mesh count screen, however it still was only able to pass a few runs before clogging the screen. Conductivity: According to the website this is <<5 Ohm/square at 1 mil dry film thickness; <0.10 Ohm/square at 2 mil dry film thickness However I am yet to test it as I did earlier. There is good documentation of it here: http://highlowtech.org/wiki/pmwiki.php?n=Main.PaperCircuits
5. Circuitscribe: about $11 for a 10ml pen. https://www.ceneo.pl/784773 Material: It claims it is silver, however I think there is something else in these. After a small amount of time, the lines change from silver to a brass colour with oxidation. Application: I have to give it to these guys, the rollerball pen works really well. I have been able to put this into my cricut cutter no problem and is one of the best features. Conductivity: This is ok – it is said to be 1ohm per cm, it vastly depends on the surface which you apply this to. However, I found that if you cure it (I stuck it in an oven for about 10 minutes – until the paper almost turned brown!) It vastly reduced the resistance – to match the 60% silver ink. I will be doing a future piece about all of this, but it seems to prevent the oxidation as well. Their paperduino instructables has some gaps but is an exciting project which I hope to take further. https://www.instructables.com/id/Paperduino-20-with-Circuit-Scribe/
Paperduino initial try
6. Mg Chemicals Silver pen and nickel pen (discontinued)
I completely failed to get either of these to work. I am unsure if the ones I purchased off Allegro were faulty. I watched a number of videos and read instructions, but without success.
Future tests : To examine how much the current the inks could take, for example on the circuit scribe website it states: The ink can support a maximum current of ~175 mA on standard copy paper. Higher currents cause joule heating, which creates a drop in resistance due to sintering the particles. Current exceeding 400 mA might break the trace in a thin spot.
Applications for the inks – heat pads and other forms.
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