Isothiazolinone.

Water-based pigment ink, pretreatment and their cleaning fluids are warm, wet and full of polymer, which makes them a place for bacteria and fungi to live, so they carry a preservative, and the class the trade reaches for is the isothiazolinones. Kornit's safety data sheet for NeoPigment Eco-Rapid White puts weights on it: methylisothiazolinone at 0.0015% to under 0.02%, the chloromethyl and methyl isothiazolinone reaction mass below 0.0015%, both classified Skin Sens. 1A with H317, with the finished ink itself labelled Acute Tox. 4 with H302 and Skin Sens. 1 with H317 under 29 CFR 1910.1200. Those fractions of a per cent are all it takes to stop the ink souring in storage, and they are also all it takes to sensitise a pair of hands that meets them daily. It is a trade a shop cannot buy its way out of, because an unpreserved water-based ink is a spoilage and nozzle problem rather than a safety win. The exposure is not at the print, it is at the bottle change, the maintenance flush and the wipe-down, which are the jobs people do bare-handed at the end of a shift.