[Solmu]

Soy and other vegetable based inks are common in the paper printing business. I've not seen any such inks for screen printing.

I'd say the same thing.

Screen printing generally either prints on textile where plastisol rules

I'd wager tuppence there's more waterbased textile printing than plastisol - it's just not happening (much) on t-shirts.

Where soy inks rule is the safe enough to eat, but since people don't eat t-shirts or political signs, no great demand exists for good enough to eat screen printing ink.

That creates a very disquieting image. The idea of being able to take a swig of the ink if I get thirsty while printing is... odd.