Laser imaging
An ink formulation comprises a marking component and a metal salt that absorbs laser irradiation at 700-2000 mn and thereby causes the marking component to change colour. A copper salt in particular allows effective marking with a diode or CO 2 laser.
1. A method for forming an image on a substrate, which comprises applying onto the substrate an ink formulation comprising a copper salt that absorbs laser irradiation at 700-2000 nm and a marking component that can undergo a colour-forming reaction, wherein the marking component is a compound including an oxymetal anion; wherein said method further comprises irradiating the ink formulation with a laser at 700-2000 nm, thereby causing the marking component to change colour.
2. The method according to claim 1 , wherein the marking component is ammonium octamolybdate.
3. The method according to claim 1 , wherein the copper salt is a poly-metal salt.
4. The method according to claim 1 , wherein the copper salt is copper (II) hydroxyl phosphate.
5. The method according to claim 1 , wherein the ink formulation further comprises a binder.
6. The method according to claim 1 , wherein the ink formulation is water-based.
7. The method according to claim 1 , wherein the ink formulation further comprises an organic solvent.