Lithographic printing plate precursor

1. A lithographic printing plate precursor comprising a coating provided on a support having a hydrophilic surface, the coating containing thermoplastic polymer particles and an IR-dye, wherein the IR-dye contains a structural element according to Formula I,

wherein

A represents a hydrogen, an optionally substituted alkyl, aralkyl or aryl group, halogen, —OR c , —SR d , —NR f R g , —NR h (SO 2 R i ) or —NR j (CO 2 R k ) wherein R c represents an optionally substituted aryl group, R d represents an optionally substituted alkyl, aralkyl, aryl or heteroaryl group, R f represents an optionally substituted alkyl, aralkyl or aryl group, R g represents an optionally substituted aryl group, R h represents an optionally substituted alkyl or aryl group, R i represents an optionally substituted alkyl or aryl group or —NR i1 R i2 wherein R i1 and R i2 represent hydrogen, an optionally substituted alkyl or aryl group, R j represents an optionally substituted alkyl or aryl group and R k represents an optionally substituted alkyl group;

Y and Y′ independently represent —CH— or —N—;

R 1 and R 2 independently represent hydrogen, an optionally substituted alkyl or aryl group or represent the necessary atoms to form a ring; and

* represent the linking positions to the rest of the molecule.

2. The lithographic printing plate precursor according to claim 1 , wherein the IR-dye has a structure according to Formula II,

wherein

A, Y, Y′, R 1 and R 2 have the same meaning as in Formula I; T and T′ independently represent hydrogen, alkyl, halogen, alkoxy, cyano, —CO 2 R k , —CONR l R m , —SO 2 R n , —SO 2 NR o R p ) or an optionally substituted annulated benzo ring wherein R l , R m represent hydrogen, an optionally substituted alkyl or aryl group, R n represents an optionally substituted alkyl or aryl group and R o and R p represent hydrogen, an optionally substituted alkyl or aryl group;

R k , R and R′ independently represent an optionally substituted alkyl group;

Z and Z′ independently represent —S—, —CH═CH— or —CR a R b —; and

R a and R h represent an optionally substituted alkyl, aralkyl or aryl group.

3. The lithographic printing plate precursor according to claim 2 , wherein the IR-dye has a structure according to Formula III,

wherein

A, T, T′, Y, Y′, R 1 , R 2 , R a and R b have the same meaning as in Formula II;

X and X′ independently represent O, S or —CH 2 —;

n and n′ are integers ranging from 0 to 3;

M + represents a monovalent cation.

4. The lithographic printing plate precursor according to claim 1 , wherein the IR-dye has a structure according to Formula IV,

wherein

A, Y, Y′, R 1 and R 2 have the same meaning as in Formula I,

X and X′ independently represent O, S or —CH 2 —;

n and n′ are integers ranging from 0 to 3;

R 7 represents hydrogen, halogen, alkyl or alkoxy group; and

M + represents a monovalent cation.

5. The lithographic printing plate precursor according to claim 3 , wherein the IR-dye has a structure according to Formula V,

wherein

X, n, A and M + have the same meaning as in Formula III; and

R 8 represents hydrogen or Br.

6. The lithographic printing plate precursor according to claim 5 , wherein the IR-dye has a structure according to Formula VI,

wherein

R 8 , A and M + have the same meaning as in Formula V.

7. The lithographic printing plate precursor according to claim 4 , wherein the IR-dye has a structure according to Formula VII,

wherein

A, X, R 7 and n have the same meaning as in Formula IV.

8. The lithographic printing plate precursor according to claim 7 , wherein the IR-dye has a structure according to Formula VIII,

wherein

R 7 , A and M + have the same meaning as in Formula IV.

9. The lithographic printing plate precursor according claim 1 , wherein A represents H, Cl, —SR d , —NR f R g , —NR h (SO 2 R i ) or —NR j (CO 2 R k ), and R d represents an optionally substituted alkyl, aralkyl, aryl or heteroaryl group, R f represents an optionally substituted alkyl, aralkyl or aryl group, R g represents an optionally substituted aryl group, R h represents an optionally substituted alkyl or aryl group, R i represents an optionally substituted alkyl or aryl group or —NR i1 R i2 wherein R i1 and R i2 represent hydrogen, an optionally substituted alkyl or aryl group, R j represents an optionally substituted alkyl or aryl group and R k represents an optionally substituted alkyl group.

10. The lithographic printing plate precursor according to claim 1 , wherein A represents —NR h (SO 2 R i ) or —NR j (CO 2 R k ) and R h represents an optionally substituted alkyl or aryl group, R i represents an optionally substituted alkyl or aryl group or —NR i1 R i2 wherein R i1 and R i2 represent hydrogen, an optionally substituted alkyl or aryl group, R j represents an optionally substituted alkyl or aryl group and R k represents an optionally substituted alkyl group.

11. The lithographic printing plate according to claim 1 , wherein A is selected from:

wherein

Z″ represents —S—, —CH═CH— or —CR a R b —;

R a and R b represent an optionally substituted alkyl, aralkyl or aryl group;

Z′″ represents O or S;

R″ represents an optionally substituted alkyl group;

T″ represents hydrogen, alkyl, halogen, alkoxy, cyano, —CO 2 R k , —CONR l R m , —SO 2 R n , —SO 2 NR o R p or an optionally substituted annulated benzo ring wherein R l , R m represent hydrogen, an optionally substituted alkyl or aryl group, R n represents an optionally substituted alkyl or aryl group and R o and R p represent hydrogen, an optionally substituted alkyl or aryl group;

R 3 , R 4 , R 5 and R 6 independently represent an optionally substituted alkyl, aralkyl or aryl group;

M + represent a monovalent cation; and

* represents the linking position to the rest of the molecule.

12. The lithographic printing plate precursor according to claim 1 , wherein the thermoplastic particles have an average particle diameter of from 25 to 50 nm.

13. A method of preparing a lithographic printing plate comprising the steps of:

exposing a lithographic printing plate precursor as defined in claim 1 to IR radiation; and

developing the exposed precursor.

14. The method according to claim 13 , wherein the developing step is carried out off press in an automated processing unit comprising rotating brushes.

15. The method according to claim 13 , wherein the developing step is carried out on press.