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I previously worked on Virtual Reality and other hardware at Valve.  I currently work at Google[x].

Prior to starting at Valve, I built computer peripherals such as keyboards, mice, and joysticks that were designed to be used inside MRI machines.  My company, Mag Design and Engineering, sold these devices directly to researchers at academic institutions who used them to publish scientific papers in peer-reviewed journals.

After work, I spend time on many different types of projects that usually involve circuit design, machining, material selection, and general fabrication/hacking.  My favorite place to be is my home workshop.

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Saturday, August 20, 2011

Effect of acetone vapor on thermal printer paper


I am not sure of the chemistry involved, but I have found that acetone and isopropanol vapor will darken the ink in thermal printer paper. There is also a strange reversible blanking effect, where continued vapor application will cause the dye to temporarily become colorless. Do you know the chemistry involved?

9 comments:

  1. Hi Ben.

    I think it is all about temperatures.

    The acetone vapor is condensing in contact with the paper and then immediately evaporating again cooling the paper and producing the darkening effect. In contrast, isopropanol doesnt achieve that same effect because acetone cools things easier because of the lower boiling point and lower specific heat.

    When you poured the acetone, I think that what happened was that the message was erased in the semi-solubilization proccess. After that the change of color is a matter of the evaporation of acetone and therefore the sinking of temperature.

    I might be wrong about this, however. I'm just a peruvian chemistry student.

    Cheers

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  2. Hmm, yeah but thermal paper is supposed to react that way to higher temperatures, not lower ones. I would guess that the acetone is acting as a catalyst...or maybe it's just an effect from one of the compounds dissolving in a solvent.

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  3. No, it's something chemical- GermX (funny story)/isopropyl does the same thing, while R134 does not.

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  4. The two major chemicals in the thermal paper - the colorless dye and the "acid" doner coreactant - will either solublize in the liquid solvent and will react to develop the black form of the dye OR the acidity of the solvent vapor will react with the colorless dye precurser to develop the colored form. Images already present on the paper will temporarily dissassociated in the presence of solvent to create the colorless structure. This will turn black again once the color molecule recrystalizes.

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  5. I agree with [Appleton]'s 2nd idea. The IPA or Acetone is slightly acidic, so when it comes into contact with the Lueco dye in the paper it protonates it, causing the dye to change from colourless to black. When the IPA is poured on the receipt it is simply dissolving the ink.
    BUT
    I did an experiment with various acids lying around the house and couldn't reproduce the effect. Then I tried vodka and noticed a little bit of discolouration. My guess is that you need a nonpolar solvent (or a something which can act as a nonpolar solvent) to dissolve the dye first. I'd suggest more experiments!

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  6. The IPA or other solvent will dissolve the Dye/acid matrix. The printer dissolves the Dye/Acid matrix allowing the two to react, darkening the paper. When cooled, the matix solidifies dark. The solvent does the same, dissolves the Dye/acid matrix allowing the two to react.

    The reversing effect is just that. The solvent seems to favor the colorless form of the dye while in solution.

    The vapor is most likely an aerosol of solvent rather than just all vapor. So there is some liquid acetone/IPA coming out of the tip the closer the tip is to the paper. Causing the Dye/Acid to slightly dissolve and shift to the colorless state, then changing back when dry.

    Rich

    BTW: Love your Blog.

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  7. It would be interesting to see what happens with thermal paper that has no printing on it. Most of the thermal papers are a lactone dye with a suitable developer such as Bisphenol A in a solvent that keeps the two apart. The thermal print head "melts" the solvent, allowing the dye and developer to come into contact. THe resultant protonation of the Dye changes allows it to undergo a ring opening, the net effect being a conjugated state that is colored. An example is the molecule "crystal violet lactone", which is a closed ring system and colorless in this state (leuco state).

    One of the solvents for this process is said to be alcohols. For the color to disappear "temporarily", the vapor (acetone or isopropyl alcohol) must temporarily allow for closure of the lactone ring. This would create a deconjucated system and, at room temperature, the leuco state.

    I think that the reasonable explanation for the chromatography effect seen with liquid solvent is that the ring closure still occurs but because it is in a liquid phase, it moves to the periphery of the liquid.

    Doug

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