Paper Electronics: Conductive Paints, Inks, and More

     This Instructable is all about the amazing technology of paper electronics and conductive materials. Instead of using stubborn wires and your rusty soldering skills to painstakingly connect components, why not use paint and glue? This tutorial will share various recipes to create your very own conductive paint, tape, glue, and ink. Using a maximum of 3 easy to find ingredients, these simple materials are easy to make. All of the conductive materials explained in this Instructable are based around the conductive paint (step 1). Using increments of different chemicals, the consistency of the paint can be changed from thick to thin (glue to ink). At the end of the Instructable a simple project will be shown using conductive materials (step 5). There is also a step that is dedicated interfacing conductive materials with kits and teaching classes and workshops.
Even though commercially available conductive materials work great, they are a wee pricey and often need to be ordered online. Another disadvantage of commercial products is that they are usually only available in conductive paint form.
To start off, I would like to share some of the science behind the main ingredient used in the conductive materials; graphite. Graphite is a mineral and a form of pure carbon. Graphite is very conductive and is sometimes used in arc-lamp electrodes. Because of its conductivity, graphite is the primary candidate for making conductive materials. Its other bonuses include being easy to obtain, mixing well with paint, and coming in a very fine powdered form. 

     Here are the supplies needed to make the conductive materials in this Instructable:

- powdered graphite lubricant- from from Ace Hardware or other hardware store
- black poster paint- from local craft store or from Amazon
- paint thinner- from local hardware store or from Amazon   
- popsicle/mixing sticks- from local craft store or Walmart 
- mixing cups- I used styrofoam cups from grocery store
- measuring spoon- baking spoons will work 

     To complete the ink and stamping steps and the project, you will need these additional supplies:
- light emitting diode (led) available at local Radioshack
- 3-volt coin cell battery- available at grocery store
- sponge- some type of sponge, I got mine out of an old printer ink cartridge
- airtight vial- any type of airtight container will work
- airtight plastic container- possibly tupperware or old food container  
- paper

     Now that the materials have been gathered, it is time to begin making conductive materials!

Warnings: Some of the projects and instructions in this Instructable use paint thinner. This chemical produces nasty fumes that probably aren't very healthy for you. Perform all projects using paint thinner in a well-ventilated room. I am not responsible for any accidents that may occur while using this Instructable. 

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This Instructable is submitted for Powell Cubs for the Instructables Sponsorship Program.

     The first part of this tutorial features conductive paint. The paint will be the base of all of the other materials that are explained in this Instructable. The paint makes an ideal base because of its consistency. To make glue you add slightly more graphite powder, and to make ink a few drops of paint thinner is added... but onto that in later steps.
Conductive paint sticks well to most materials, especially paper and cardboard. Anything that the poster paint will bond to, the conductive paint will as well. I have found that this mixture of conductive paint flexes well on paper. However, sharp creases and folds will lead to a crack, usually causing a shaky connection. The conductive paint will turn out to have the same flexibility as the paint that is mixed in. 
As a general rule of thumb, use this paint in low-medium areas of stress to ensure a reliable connection. For higher stress applications resort to one of the conductive inks mentioned later in the Instructable.
The two materials used in conductive paint are powdered graphite and the poster paint. After much experimentation, I found that a mixture of 2 parts powdered graphite to 1 part black paint worked exceptionally well. 
Instructions: Using the measuring spoon, measure out two spoonfuls of powdered graphite and pour it into a mixing cup. Add 1 spoonful of the poster paint. Mix well, making sure all of the graphite is added. 

Application: Slather heavily onto the material (i.e- paper, cardboard) in the desired pattern using a paintbrush. Make sure that all lines are coated evenly. Allow a few hours to dry before using. Store remaining paint in an airtight container.
When dry, the conductive paint has a very low amount of resistance. After several tests, I calculated the resistance to be around  
115 ohms per centimeter. Even though 1 centimeter of standard 22 gauge hookup wire has a resistance of about 2 ohms, the 113 ohms difference will barely make a difference in the circuit. If the circuit schematic calls for a small resistor  (<115 ohms), it would be alright to omit it. I found that when you connect a new 9-volt battery to a painted line (of conductive paint) and attach a digital multimeter on the other side, the voltage detected is 9.27-9.28 volts out of 9.29-9.30 volts. In sum, there is a very minimal amount of voltage lost when using conductive paint. 

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