Recently, I came across a type of paper-like material which, when heated, puffs up. It is used, in specialist printers, to make tactile graphics for the blind: the special printer applies heat in the pattern to be printed, which then becomes raised.
However, these specialist printers are very expensive, as is the heat-sensitive "paper".
So, how about an intumescent ink? The ink could be used in a standard inkjet printer with regular paper. After the page is heated (using a hot-air gun, for instance) it would puff up to make the printed matter tactile. This would be far cheaper, I think.-- MaxwellBuchanan, Jan 10 2016 +
although, I don't see your point.-- pashute, Jan 13 2016 Doesn't an inkjet print head work by boiling some of the ink to force each drop of the ink out of the nozzle? I'm not sure if that would be a problem resulting in clogged nozzles or if you can take advantage of that so that the ink expands automatically without using a heat gun.-- scad mientist, Jan 14 2016 I think most inkjet heads these days are piezoelectric.
<some time later>
I stand corrected - it seems that most current inkject printheads do indeed use thermal vaporization to eject the droplets.
Hmmm.-- MaxwellBuchanan, Jan 14 2016 A two part explosive, like in Die Hard, could be the solution. Store them in separate colour compartments, where they can safely be boiled for ejection from the print head. Then, later, your message is exploded into the paper. Tactile.-- mitxela, Jan 14 2016 There are a number of primary explosives that are quite safe when moist, but become extremely sensitive when dry. If the design were printed with ink made from such a compound, the text would literally explode out of the paper.
It might be wise to check that the printhead return isn't too ... energetic.-- 8th of 7, Jan 14 2016 Thermographic ink (we used to call it)-- xenzag, Jan 14 2016 I had not heard of thermographic ink. However, it doesn't seem ideal. Thermography (according to Wikipedia) involves using a slow-drying ink to capture polymer particles which are then melted - so it's a bit like writing in glue and then adding glitter.-- MaxwellBuchanan, Jan 14 2016 So, not explosive, then ?-- 8th of 7, Jan 15 2016 Not as such.-- MaxwellBuchanan, Jan 17 2016 I suppose blind readers wouldn't notice the category choice.-- pocmloc, Jan 18 2016 Ooops. Fixed!-- MaxwellBuchanan, Jan 18 2016 random, halfbakery