How do you make scratch off tickets?

What is the material used to make the silver scratch-off area on prepaid cards and lottery tickets?

• Is it something best not inhaled? Just something I'm working on, I hate that stuff though.

• Answer:

  The material is known as a UV ink [1]. Not the ink that becomes visible under UV light as is referred to on Wikipedia [2], but an ink that 'dries' under UV radiation. UV inks are essentially a mixture of colored monomers [3] and oligomers [4] (the individual chemical units that eventually form 'polymers' [5]) and reaction 'photo-initiators' that become active when exposed to UV radiation. The monomers and oligomers form a viscous liquid, thus serving simultaneously as the 'pigment' and 'solvent' of a conventional ink; they do not need an organic solvent as a fluid base, and do not 'dry' in air like typical solvent-based inks. On exposure to UV light, the initiators set off the polymerization reaction, rapidly cross-linking [6] the monomers and oligomers into a solid 'plastic' polymer, in a process known as 'curing'. This polymerization process also inspired the alternative naming of UV inks as 'latex inks'. Source: http://www.signindustry.com/flatbed_UV/articles/images/2008-11-UV_Ink_Reaction_to_.gif These inks are favored in the printing industry for their lack of harmful organic solvent evaporation during drying, ability to dry-on-demand, and high pigment-to-ink volume ratio [7]. Typically an ink would be composed up to 40% by solvent [1]. UV inks, made up almost entirely by the pigment molecules, can achieve equivalent color density as conventional inks with far less liquid. The production of scratch-off tickets is a two-step process [8] - a substrate is covered by a thick, smooth layer of UV ink coating, and then printed with a special 'scratch-off' black/silver UV ink [9] (scratch-off inks can sometimes be solvent-based [10]). An optional third step could involve printing text or images over the scratch-off area, with yet another type of UV ink [9]. These UV inks are essentially liquid/solid plastic, being made up of organic chemicals and non-natural polymeric materials. So they probably shouldn't be inhaled or ingested. [1] http://www.flexoexchange.com/gorilla/uvink1.html [2] http://en.wikipedia.org/wiki/UV_tattoo [3] http://en.wikipedia.org/wiki/Monomer [4] http://en.wikipedia.org/wiki/Oligomer [5] http://en.wikipedia.org/wiki/Polymerization [6] http://en.wikipedia.org/wiki/Cross-link [7] http://www.signindustry.com/flatbed_UV/articles/2008-11-17-SGIA_Primer_on_UV-Curable_Inkjet_Inks.php3 [8] http://www.pulserl.com/assets/pdfs/WB%20Flexo%20Scratch%20Off%20Inks%20Xsys.pdf [9] http://www.hwsands.com/files/print-color/English/900%20Series/995-20050-xxx_UV%20Scratch%20Off%20Inks%20for%20Flexo%20Printing.pdf [10] http://www.nazdar.com/pdf/Scratch_Off_Solvent_Inks_TDS_Rev_2.pdf