Method of formulating ink having minimal visible coloration

1. A method of formulating an aqueous ink having minimal visible coloration, said method comprising the steps of:

providing an aqueous ink formulation comprising a sulfonated water-soluble IR-absorbing naphthalocyanine dye having a central metal atom moiety; and

adjusting a pH of said formulation to a pH value in the range of 4 to 6.5 so as to minimize visible coloration of the formulation.

2. The method of claim 1 , wherein said pH is adjusted by utilizing a buffer formulation.

3. The method of claim 1 wherein said pH is adjusted using 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 method of claim 3 , wherein the conjugate acid BH + of said at least one base B has a pK a of between 4.5 and 8.

5. The method of claim 3 , wherein said pH is adjusted using a nitrogen base, an oxyanion base or mixtures thereof.

6. The method of claim 5 , wherein said nitrogen base is a nitrogen-containing C 5-12 heteroaryl base.

7. The method of claim 6 , said nitrogen base is imidazole or pyridine.

8. The method of claim 1 , wherein said dye has a λ max of 800 nm or more.

9. The method of claim 1 , wherein said dye is of formula (II):

or a salt form thereof, wherein:

M is Ga(A 1 );

A 1 is an axial ligand selected from the group consisting of —OH, halogen, —OR 3 , —OC(O)R 4 and —O(CH 2 CH 2 O) e R e wherein e is an integer from 2 to 10 and R e is H, C 1-8 alkyl or C(O)C 1-8 alkyl;

R 1 and R 2 may be the same or different and are selected from the group consisting of hydrogen and C 1-12 alkoxy;

R 3 is selected from the group consisting of C 1-12 alkyl, C 5-12 aryl, C 5-12 arylalkyl and Si(R x )(R y )(R z );

R 4 is selected from the group consisting of C 1-12 alkyl, C 5-12 aryl and C 5-12 arylalkyl; and

R x , R y and R z may be the same or different and are selected from the group consisting of C 1-12 alkyl, C 5-12 aryl, C 5-12 arylalkyl, C 1-12 alkoxy, C 5-12 aryloxy and C 5-12 arylalkoxy.

10. The method of claim 9 , wherein A 1 is selected from the group consisting of: —OH and —Cl.

11. The method of claim 9 , wherein R 1 and R 2 are both hydrogen.