Phthalocyanine dyes suitable for use in offset inks

1. An IR-absorbing phthalocyanine dye suitable for formulation in a solvent-based or oil-based ink vehicle, said phthalocyanine comprising one or more sulfonate groups, wherein a counterion of at least one sulfonate group is a phosphonium cation, wherein:

each phosphonium cation is of formula: P + (R m )(R n )(R s )(R t );

each of R m , R n , R s and R t is independently selected from the group consisting of: C 1-30 alkyl,

C 5-12 aryl and C 5-30 arylalkyl; and

at least one of R m , R n , R s and R t comprises more than 4 carbon atoms.

2. The dye of claim 1 comprising a plurality of sulfonate groups.

3. The dye of claim 2 comprising a corresponding plurality of phosphonium counterions.

4. The dye of claim 1 , which is a naphthalocyanine.

5. The dye of claim 1 , which is of formula (I):

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;

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; and

Z + is the phosphonium cation of formula: P + (R m )(R n )(R s )(R t ).

6. The dye of claim 5 , wherein at least three of R m , R n , R s and R t comprise more than 4 carbon atoms.

7. The dye of claim 5 , wherein at least three of R m , R n , R s and R t are independently selected from a C 6-30 alkyl group.

8. The dye of claim 5 , wherein R 1 and R 2 are both hydrogen.

9. The dye of claim 5 , wherein M is Ga(OH).

10. A solvent-based or oil-based ink comprising a dye according to claim 1 .

11. A substrate having a dye according to claim 1 disposed thereon or therein.

12. The substrate of claim 11 , which is a label, packaging or surface of a product item.