Method of printing an IR-absorbing dye onto a substrate

1. A method of printing an IR-absorbing dye onto a substrate whilst minimizing visible coloration of the substrate, said method comprising:

(i) preselecting said dye from a metal-cyanine of formula (I):

wherein:

Q 1 , Q 2 , Q 3 and Q 4 are the same or different and are independently selected from a C 3-20 arylene group or a C 3-20 heteroarylene group;

M is selected from Si(A 1 )(A 2 ), Ge(A 1 )(A 2 ), Ga(A 1 ), Al(A 1 ), Mn(A 1 ), Fe(A 1 ), Sn(A 1 )(A 2 ), Pb(A 1 )(A 2 );

A 1 and/or A 2 is a pentaerythritol derivative (A), a triethanolamine derivative (B), a phloroglucinol derivative (C), or a 3,5-dihydroxybenzyl alcohol derivative (D):

P 1 is selected from the group consisting of:

(CH 2 CH 2 O) y R 6 , wherein v is an integer from 2 to 5000 and R 6 is H, C 1-6 alkyl or C(O)C 1-8 alkyl;

SO 3 Z, PO 3 Z 2 , C 1-12 alkyl-CO 2 Z, C 1-12 alkyl-SO 3 Z, C 1-12 -alkyl-PO 3 Z 2 , C 1-12 alkyl-OSO 3 Z or C 1-12 -alkyl-OPO 3 Z 2 , wherein Z is H or a water-soluble cation; and

C 1-12 -alkyl-N + (R a )(R b )(R c ) or C 1-12 alkyl-U, wherein R a , R b , R c may be the same or different and are independently selected from H, C 1-8 alkyl, C 6-12 arylalkyl or C 6-12 aryl, and U is pyridinium, imidazolinium or pyrrolinium; and

(ii) printing said dye onto said substrate.

2. The method of claim 1 , wherein Q 1 , Q 2 , Q 3 and Q 4 are the same.

3. The method of claim 1 , wherein Q 1 , Q 2 , Q 3 and Q 4 are selected from an arylene or heteroarylene group of the formula:

wherein R 1 and R 2 may be the same or different and are selected from hydrogen, hydroxyl, C 1-12 alkyl, C 1-12 alkoxy, amino, C 1-12 alkylamino, di(C 1-12 alkyl)amino, halogen, cyano, thiol, C 1-12 alkylthio, nitro, carboxy, C 1-12 alkylcarbonyl, C 1-12 alkoxycarbonyl, C 1-12 alkylcarbonyloxy or C 1-12 alkylcarbonylamino;

T is C 1-30 hydrocarbyl;

W is —SO 3 H or a water-soluble salt thereof;

E is selected from —OH, O—, C 1-6 alkyl, carboxy-C 1-6 alkyl, sulfo-C 1-6 alkyl, C 1-6 alkoxy, C 5-12 arylalkyl, C 1-6 alkylcarbonyl, C 5-12 arylalkylcarbonyl, C 1-6 alkoxycarbonyl or C 5-12 arylalkoxycarbonyl;

m is 0, 1 or 2;

n is 0, 1 or 2; and

p is 0, 1 or 2.

4. The method of 3 , wherein R 1 and R 2 are selected from hydrogen or C 1-8 alkoxy.

5. The method of claim 1 , wherein said dye is printed in the form of coded data.

6. The method of claim 5 , wherein said substrate comprises an interface surface and wherein the coded data is printed over a substantial portion of said interface surface.

7. The method claim 1 , wherein said substrate is a paper sheet, a label, a tag, a packaging material or a product item.