Aqueous formulation comprising low visibility naphthalocyanine dye
An aqueous formulation comprises a sulfonated water-soluble IR-absorbing naphthalocyanine dye having a central metal atom moiety. A pH of the formulation is in the range of 4 to 6.5, which minimizes visibility of the formulation.
1. An aqueous formulation comprising a sulfonated water-soluble IR-absorbing naphthalocyanine dye having a central metal atom moiety, wherein a pH of said formulation is in the range of 4 to 6.5 so as to minimize visible coloration of the formulation.
2. The formulation of claim 1 , wherein said formulation is buffered.
3. The formulation of claim 1 further comprising at least one base B, wherein a conjugate acid BH + of said at least one base B has a pK a of between 4 and 9.
4. The formulation of claim 3 , wherein a conjugate acid BH + of said at least one base B has a pK a of between 4.5 and 8.
5. The formulation of claim 3 comprising a nitrogen base, an oxyanion base or mixtures thereof.
6. The formulation of claim 5 , wherein said nitrogen base is a nitrogen-containing C 5-12 heteroaryl base.
7. The formulation of claim 6 , said nitrogen base is imidazole or pyridine.
8. An inkjet ink comprising a formulation according to claim 1 .
9. An inkjet ink comprising a dye according to claim 1 , wherein said ink has a λ max of 800 nm or more.
10. A method of minimizing visible coloration of a sulfonated water-soluble IR-absorbing naphthalocyanine dye, said naphthalocyanine dye comprising a central metal atom moiety, said method comprising formulating said naphthalocyanine dye at a pH in the range of 4 to 6.5.