Thermal initiator system using leuco dyes and polyhalogene compounds

1. Initiator system comprising:

(a) at least one compound capable of absorbing IR radiation selected from the group consisting of triarylamine dyes, thiazolium dyes, indolium dyes, oxazolium dyes, cyanine dyes, polyaniline dyes, polypyrrole dyes, polythiophene dyes and phthalocyanine pigments,

(b) at least one polyhaloalkyl-substituted compound capable of producing radicals

(c) at least one polycarboxylic acid represented by the following formula I

R 4 —(CR 5 R 6 ) r —Y—CH 2 COOH   (I)

wherein Y is selected from the group consisting of O, S and NR 7 ,

each of R 4 , R 5 and R 6 is independently selected from the group consisting of hydrogen, C 1 -C 4 alkyl, aryl which is optionally substituted, —COOH and NR 8 CH 2 COOH,

R 7 is selected from the group consisting of hydrogen, C 1 -C 6 alkyl,

—CH 2 CH 2 OH, and C 1 -C 5 alkyl substituted with —COOH,

R 8 is selected from the group consisting of —CH 2 COOH, —CH 2 OH and —(CH 2 ) 2 N(CH 2 COOH) 2

and r is 0, 1, 2 or 3

and wherein at least one of R 4 , R 5 , R 6 , R 7 and R 8 includes a —COOH group, or a salt thereof, and

(d) at least one leuco dye, wherein:

ox a <red b +1.6 eV

where ox a =oxidation potential of component (a) in eV

red b =reduction potential of component (b) in eV.

2. Initiator system according to claim 1 wherein the compound capable of absorbing IR-radiation is a cyanine dye.

3. Initiator system according to claim 2 wherein the compound capable of absorbing IR-radiation is a cyanine dye of the formula (A)

wherein:

each X independently represents S, O, NR or C(alkyl) 2 ;

each R 1 independently is an alkyl group, an alkylsulfonate or an alkylammonium group;

R 2 represents hydrogen, halogen, SR, SO 2 R, OR or NR 2 ;

each R 3 independently represents a hydrogen atom, an alkyl group, COOR, OR, SR, NR 2 , a halogen atom or an optionally substituted benzofused ring;

A − represents an anion;

- - Q - - represents an optional carbocyclic five- or six-membered ring;

each R independently represents hydrogen, an alkyl or aryl group;

each n independently is 0, 1, 2 or 3.

4. Initiator system according to claim 1 , wherein the compound capable of absorbing IR-radiation is selected from the group consisting of

2-[2-[2-thiophenyl-3-[2-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-ethylidene]- 1-cyclopenten-1 -yl ]-ethenyl]- 1,3,3-trimethyl-3H-indoliumtosylate

2-[2-[2-phenylsulfonyl-3-[2-(1,3-dihydro- 1,3,3-trimethyl-2H-indol-2-ylidene)-ethylidene ]-1 -cyclohexen- 1 -yl]-ethenyl]- 1,3,3-trimethyl-3H-indoliumchloride,

2-[2-[2-thiophenyl-3-[2-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-ethylidene ]-1-cyclohexen-1 -yl]-ethenyl]-1,3,3-trimethyl-3H-indoliumchloride,

2-[2-[2-chloro-3 -[2-(1,3-dihydro- 1,3,3-trimethyl-2H-indol-2-ylidene ]-ethylidene]-1-cyclohexen-1 -yl]-ethenyl]-1,3,3-trimethyl-3H-indolium-tosylate and

2-[2-[2-chloro-3-[2-ethyl-(3H-benzthiazol-2-ylidene)-ethylidene]1-cyclohexen-1 -yl ]-ethenyl]-3-ethyl-benzthiazolium-tosylate.

5. Initatior system according to claim 1 , wherein the compound capable of producing radicals is selected from the group consisting of

2-phenyl-4,6-bis-(trichloromethyl)-s-triazine,

2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-s-triazine, tribromomethylphenylsulfone,

2,4,6-tri(trichloromethyl)-s-triazine and

1,2,3,4-tetrabromo-n-butane.

6. Initiator system according to claim 1 , wherein the polycarboxylic acid is a compound selected from the group consisting of

wherein Ar represents a mono-, poly- or unsubstituted aryl group, p is an integer from 1 to 5, R 9 and R 10 are independently selected from the group consisting of hydrogen and C 1 -C 4 alkyl and q is 0 or an integer from 1 to 3, R 11 represents a hydrogen atom or a C 1 -C 6 alkyl group and k and m each are an integer from 1 to 5.

7. Initiator system according to claim 6 , wherein the polycarboxylic acid is selected from the group consisting of anilino diacetic acid and N-(carboxymethyl)-N-benzyl-glycine.

8. Initiator system according to claim 1 , wherein the polycarboxylic acid is an aliphatic polyacetic acid with all —CH 2 COOH groups being bonded to at least one nitrogen atom.

9. Initiator system according to claim 8 , wherein the polycarboxylic acid is selected from the group consisting of ethylene diamine tetra-acetic acid, nitrilo tri-acetic acid, diethylene triamine penta-acetic acid and N-hydroxyethyl ethylene diamine tri-acetic acid.

10. Initator system according to claim 1 , wherein the leuco dye is selected from the group consisting of triarylmethanes, thioxanthenes, 9,10-dihydro-acridines and phenoxazines.

11. IR-sensitive composition comprising:

(i) an initiator system comprising

(a) at least one compound capable of absorbing IR radiation selected from the group consisting of triarylamine dyes, thiazolium dyes, indolium dyes, oxazolium dyes, cyanine dyes, polyaniline dyes, polypyrrole dyes, polythiophene dyes and phthalocyanine pigments,

(b) at least one polyhaloalkyl-substituted compound capable of producing radicals

(c) at least one polycarboxylic acid represented by the following formula I

R 4 —(CR 5 R 6 ) r —Y—CH 2 COOH  (I)

wherein Y is selected from the group consisting of O, S and NR 7 ,

each of R 4 , R 5 and R 6 is independently selected from the group consisting of hydrogen, C 1 -C 4 alkyl, aryl which is optionally substituted, —COOH and NR 8 CH 2 COOH,

R 7 is selected from the group consisting of hydrogen, C 1 -C 6 alkyl, —CH 2 CH 2 OH, and C 1 -C 5 alkyl substituted with —COOH,

R 8 is selected from the group consisting of —CH 2 COOH, —CH 2 OH and —(CH 2 ) 2 N(CH 2 COOH) 2

and r is 0, 1, 2 or 3

wherein at least one of R 4 , R 5 , R 6 , R 7 and R 8 includes a —COOH group, or a salt thereof, and

(d) at least one leuco dye,

wherein:

ox a <red b +1.6 eV

where ox a oxidation potential of component (a) in eV

red b reduction potential of component (b) in eV

(ii) at least one component selected from the group consisting of unsaturated free radical polymerizable monomers, oligomers which are free radical polymerizable and polymers containing C═C bonds wherein the C═C bonds are located in at least one selected from the group consisting of the back bone of the polymers and the side chain groups of the polymers, and

(iii) at least one polymeric binder.

12. Composition according to claim 11 , wherein the compound capable of absorbing IR-radiation is a cyanine dye of the formula (A)

wherein:

each X independently represents S, O, NR or C(alkyl) 2 ;

each R 1 independently is an alkyl group, an alkylsulfonate or an alkylammonium group;

R 2 represents hydrogen, halogen, SR, SO 2 R, OR or NR 2 ;

each R 3 independently represents a hydrogen atom, an alkyl group, COOR, OR, SR, NR 2 , a halogen atom or an optionally substituted benzofused ring;

A−represents an anion; - - Q - - represents an optional bridge completing a carbocyclic five- or six- membered ring;

each R independently represents hydrogen, an alkyl or aryl group;

each n independently is 0, 1, 2 or 3.

13. Composition according to claim 11 , wherein the compound capable of producing radicals is selected from the group consisting of

2-phenyl-4,6-bis-(trichloromethyl)-s-triazine,

2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-s-triazine, tribromomethylphenylsulfone,

2,4,6-tri(trichloromethyl)-s-triazine and

1,2,3,4-tetrabromo-n-butane.

14. Composition according to claim 11 , wherein the polyearboxylic acid is selected from the group consisting of

wherein Ar represents a mono-, poly- or unsubstituted aryl group, p is an integer from 1 to 5, R 5 and R 6 are independently selected from the group consisting of hydrogen and C 1 -C 4 alkyl, q is 0 or an integer from 1 to 3, R 11 represents a hydrogen atom or a C 1 -C 6 alkyl group and k and m each are an integer from 1 to 5.

15. Composition according to claim 11 wherein the polycarboxylic acid is an aliphatic polyacetic acid with all —CH 2 COOH being bonded to at least one nitrogen atom.

16. Composition according to claim 11 , wherein the leuco dye is selected from the group consisting of triarylmethanes, thioxanthenes, 9,10-dihydro-acridines and phenoxazines.

17. Composition according to claim 11 , wherein the polymeric binders have an acid number of >70 mg KOH/g.

18. Printing plate precursor, comprising a coating with an IR-sensitive composition, the IR-sensitive composition including

(i) an initiator system comprising

(a) at least one compound capable of absorbing IR radiation selected from the group consisting of triarylamine dyes, thiazolium dyes, indolium dyes, oxazolium dyes, cyanine dyes, polyaniline dyes, polypyrrole dyes, polythiophene dyes and phthalocyanine pigments

(b) at least one polyhaloalkyl-substituted compound capable of producing radicals,

(c) at least one polycarboxylic acid represented by the following formula I

R 4 —(CR 5 R 6 ) r —Y—CH 2 COOH   (I)

wherein Y is selected from the group consisting of O, S and NR 7 ,

each of R 4 , R 5 and R 6 is independently selected from the group consisting of hydrogen, C 1 -C 4 alkyl, aryl which is optionally substituted, —COOH and NR 8 CH 2 COOH,

R 7 is selected from the group consisting of hydrogen, C 1 -C 6 alkyl,

—CH 2 CH 2 OH, and C 1 -C 5 alkyl substituted with —COOH,

R 8 is selected from the group consisting of —CH 2 COOH, —CH 2 OH and —(CH 2 ) 2 N(CH 2 COOH) 2

and r is 0, 1, 2 or 3

wherein at least one of R 4 , R 5 , R 6 , R 7 and R 8 includes a —COOH group, or a salt thereof, and

(d) at least one leuco dye,

wherein:

ox a <red b +1.6 eV

where ox a =oxidation potential of component (a) in eV

red b =reduction potential of component (b) in eV

(ii) at least one component selected from the group consisting of unsaturated free radical polymerizable monomers, oligomers which are free radical polymerizable and polymers containing C═C bonds wherein the C═C bonds are located in at least one selected from the group consisting of the back bone of the polymers and the side chain groups of the polymers, and

(iii) at least one polymeric binder.

19. Printing plate precursor according to claim 18 , wherein the compound of absorbing IR-radiation is a cyanine dye of the formula (A)

wherein

each X independently represents S, O, NR or C(alkyl) 2 ;

each R 1 independently is an alkyl group, an alkylsulfonate or an alkylammonium group;

R 2 represents hydrogen, halogen, SR, SO 2 R, OR or NR 2 ;

each R 3 independently represents a hydrogen atom, an alkyl group, COOR, OR, SR, NR 2 , a halogen atom or an optionally substituted benzofused ring;

A−represents an anion;

- - Q - - represents an optional bridge completing a carbocyclic five- or six- membered ring;

each R independently represents hydrogen, an alkyl or aryl group;

each n independently is 0, 1, 2 or 3.

20. Printing plate precursor according to claim 18 , wherein the compound capable of producing radicals is selected from the group consisting of

2-phenyl-4,6-bis-(trichloromethyl)-s-triazine,

2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-s-triazine, tribromomethylphenylsulfone,

2,4,6-tri(trichloromethyl)-s-triazine and

1,2,3,4-tetrabromo-n-butane.

21. Printing plate precursor according to claim 18 , wherein the polycarboxylic acid is a compound selected from the group consisting of

wherein Ar represents a mono-, poly- or unsubstituted aryl group, p is an integer from 1 to 5, R 9 and R 10 are independently selected from the group consisting of hydrogen and C 1 -C 4 alkyl, q is 0 or an integer from 1 to 3, R 11 represents a hydrogen atom or a C 1 -C 6 alkyl group and k and m each are an integer from 1 to 5.

22. Printing plate precursor according to claim 18 wherein the polycarboxylic acid is an aliphatic polyacetic acid with all —CH 2 COOH groups being bonded to at least one nitrogen atom.

23. Printing plate precursor according to claim 18 , wherein the leuco dye is selected from the group consisting of triarylmethanes, thioxanthenes, 9,10-dihydroacridines and phenoxazines.

24. Composition according to claim 11 , further comprising a contrast-enhancing colorant.

25. Composition according to claim 11 , wherein the IR-sensitive composition comprises 0.5 to 8 wt.-% of the leuco dye, based on the total solids content of the composition.

26. Composition according to claim 11 , wherein the IR-sensitive composition comprises 1 to 5 wt.-% of the leuco dye, based on the total solids content of the composition.

27. Composition according to claim 11 , wherein the IR-sensitive composition comprises 1.5 to 4 wt.-% of the leuco dye, based on the total solids content of the composition.

28. Printing plate precursor according to claim 18 , wherein the IR-sensitive composition further comprises a contrast-enhancing colorant.

29. Printing plate precursor according to claim 18 , wherein the IR-sensitive composition comprises 0.5 to 8 wt.-% of the leuco dye, based on the total solids content of the composition.

30. Printing plate precursor according to claim 18 , wherein the IR-sensitive composition comprises 1 to 5 wt.-% of the leuco dye, based on the total solids content of the composition.

31. Printing plate precursor according to claim 18 , wherein the IR-sensitive composition comprises 1.5 to 4 wt.-% of the leuco dye, based on the total solids content of the composition.

32. Printing plate precursor according to claim 18 , further comprising an oxygen-impermeable overcoat.