Heat-sensitive lithographic printing plate precursor

1. A heat-sensitive lithographic printing plate precursor comprising a support having a hydrophilic surface and a coating provided on the hydrophilic surface, said coating comprising in the order given a first layer containing an oleophilic resin soluble in an aqueous alkaline developer and a second layer capable of preventing the developer from penetrating into the first layer at unexposed areas, said second layer comprising a water-repellent compound selected from the group consisting of

a polymer comprising siloxane and/or perfluoroalkyl monomeric units, and

a block- or graft-copolymer comprising a poly- or oligo(alkylene oxide) and a block of poly- or oligosiloxane and/or perfluoroalkyl units and

wherein the alkali-solubility of said coating increases on heating and said coating comprises an infrared light absorbing dye comprising at least one perfluoroalkyl group, wherein the infrared light absorbing dye carries a charge and at least one perfluoroalkyl group is included in a counter ion and contains at least 6 fluorine atoms.

2. The heat-sensitive lithographic printing plate precursor according to claim 1 wherein the infrared light absorbing dye further comprises at least one covalently bonded perfluoroalkyl group.

3. The heat sensitive lithographic printing plate precursor according to claim 2 wherein the amount of the water-repellent compound in the coating is between 0.5 and 15 mg/m 2 .

4. The heat sensitive lithographic printing plate precursor according to claim 2 wherein the second layer consists essentially of the water-repellent compound and the infrared light absorbing dye.

5. The heat sensitive lithographic printing plate precursor according to claim 2 wherein the infrared light absorbing dye corresponds to the following formula:

wherein

-L 1 - and -L 2 -independently represent a divalent linking;

-E 1 and -E 2 independently represent a neutral, anionic or cationic terminal group selected from

alkyl, —OH, —H, —Cl, —Br, —F (neutral groups);

—SO 3 − , —SO 4 − , —PO 3 2− , —COO − (anionic groups);

—[NR a R b R c ] + (cationic group);

R a , R b and R c independently represent a hydrogen atom or an alkyl group;

-A 1 - and —A 2 -independently represent —C v F 2v —, —[(CF 2 ) 2 ] w —,

a long chain alkylene group containing at least four carbon atoms, or an optionally substituted alkylene, alkenylene, arylene or aralkylene group;

with p 1 and p 2 are 0 or 1;

with v and w are 2 or an integer greater than 2;

—Y 1 — and —Y 2 — independently represent —CR 9 R 10 —, —S—, —Se—, —NR 11 —, —CH═CH— or —O—;

R 1 to R 11 each independently represent a hydrogen atom, an optionally substituted alkyl, alkenyl, aryl or aralkyl group or a group selected from a halogen atom, —NO 2 , —O—R d , —CO—R d , —CO—O—R d , —O—CO—R d , —CO—NR d R e , —NR d R e , —NR d —CO—R e , —NR d —CO—O—R e , —NR d —CO—NR e R f , —SR d , —SO—R d , —SO 2 —R d , —SO 2 —O—R d , —SO 2 NR d R c or a perfloroalkyl group, each of said groups may optionally comprise a terminal group E defined above as -E 1 and -E 2 and/or wherein two adjacent groups selected from R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , Y 1 and Y 2 together form an optionally substituted 5- or 6-membered ring;

R d , R e and R f independently represent a hydrogen or an optionally substituted alkyl, alkenyl, aryl or aralkyl group;

Z 1 and Z 3 each independently represent a hydrogen atom, an alkyl group or Z 1 and Z 3 together represent the necessary atoms to complete an optionally substituted 5- or 6-membered ring;

Z 2 represents a substituent selected from a hydrogen atom, an alkyl group, a halogen atom, an amino group, an arylthio group, an alkylthio group, an aryloxy group, an alkoxy group, a barbituric group or a thiobarbituric group, each of said groups being optionally substituted;

X represents one or more counter ions having a total charge so as to make the dye electrically neutral and wherein X comprises a perfluoroalkyl group containing at least 6 fluorine atoms;

with the proviso that at least one of R 1 to R 11 contains a perfluoroalkyl group or at least one of -A 1 - and -A 2 -contains a —C v F 2v — group or a —[(CF 2 ) 2 —O] w — group.

6. The heat sensitive lithographic printing plate precursor according to claim 5 wherein,

Z 1 and Z 3 together represent the necessary atoms to complete an optionally substituted 5- or 6-membered ring.

7. The heat sensitive lithographic printing plate precursor according to claim 6 , wherein -Z 1 and -Z 3 together represent —(CH 2 ) 2 — or —(CH 2 ) 3 —.

8. The heat sensitive lithographic printing plate precursor according to claim 7 wherein the IR light absorbing dye corresponds to one of the following formulae:

R 9 to R 10 each independently represent a hydrogen atom, an optionally substituted alkyl, alkenyl, aryl or aralkyl group or a group selected from a halogen atom, —NO 2 , —O—R d , —CO—R d , —CO—O—R d , —O—CO—R d , —CO—NR d R e , —NR d R e , —NR d —CO—R e , —NR d —CO—O—R e , —NR d —CO—NR e R f , —SR d , —SO—R d , —SO 2 —R d , —SO 2 —O—R d , —SO 2 NR d R c or a perfloroalkyl group, each of said groups may optionally comprise a terminal group E defined above as -E 1 and -E 2 , R d , R e and R f independently represent a hydrogen or an optionally substituted alkyl, alkenyl, aryl or aralkyl group.

9. The heat-sensitive lithographic printing plate precursor according to claim 1 wherein the amount of the water-repellent compound in the coating is between 0.5 and 15 mg/m 2 .

10. The heat sensitive lithographic printing plate precursor according to claim 9 wherein the second layer consists essentially of the water-repellent compound and the infrared light absorbing dye.

11. The heat-sensitive lithographic printing plate precursor according to claim 1 wherein the second layer consists essentially of the water-repellent compound and the infrared light absorbing dye.

12. The heat-sensitive lithographic printing plate precursor according to claim 1 wherein the infrared light absorbing dye corresponds to the following formula:

wherein

-L 1 - and -L 2 - independently represent a divalent linking;

-E 1 and -E 2 independently represent a neutral, anionic or cationic terminal group selected from

alkyl, —OH, —H, —Cl, —Br, —F (neutral groups);

—SO 3 − ; —SO 4 − , —PO 3 2− , —PO 4 2− , —COO − (anionic groups);

—[NR a R b R c ] + (cationic group);

R a , R b and R c independently represent a hydrogen atom or an alkyl group;

-A 1 - and -A 2 - independently represent -C v F 2v —, —[(CF 2 ) 2 —O] w —,

a long chain alkylene group containing at least four carbon atoms, or an optionally substituted alkylene, alkenylene, arylene or aralkylene group;

with p 1 and p 2 are 0 or 1;

with v and w are 2 or an integer greater than 2;

—Y 1 — and —Y 2 — independently represent —CR 9 R 10 —, —S—, —Se—, —NR 11 —,

—CH═CH— or —O—;

R 1 to R 11 each independently represent a hydrogen atom, an optionally substituted alkyl, alkenyl, aryl or aralkyl group or a group selected from a halogen atom, NO 2 , —O—R d , —CO—R d , —CO—O—R d , —O—CO—R d , —CO—NR d R e , NR d R e , —NR d —CO—R e , —NR d —CO—O—R e , —NR d —CO—NR e R r , —SR d , —SO—R d , —SO 2 —R d , —SO 2 —O—R d , —SO 2 NR d R e or a perfluoroalkyl group, each of said groups may optionally comprise a terminal group E defined above as -E 1 and -E 2 and/or wherein two adjacent groups selected from R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , Y 1 and Y 2 together form an optionally substituted 5- or 6-membered ring;

R d , R e and R f independently represent a hydrogen or an optionally substituted alkyl, alkenyl, aryl or aralkyl group;

Z 1 and Z 3 each independently represent a hydrogen atom, an alkyl group or Z 1 and Z 3 together represent the necessary atoms to complete an optionally substituted 5- or 6-membered ring;

Z 2 represents a substituent selected from a hydrogen atom, an alkyl group, a halogen atom, an amino group, an arylthio group, an alkylthio group, an aryloxy group, an alkoxy group, a barbituric group or a thiobarbituric group, each of said groups being optionally substituted;

X represents one or more counter ions having a total charge so as to make the dye electrically neutral and wherein X comprises a perfluoroalkyl group containing at least 6 fluorine atoms.

13. The heat-sensitive lithographic printing plate precursor according to claim 12 wherein —Z 1 and —Z 3 together represent the necessary atoms to complete an optionally substituted 5- or 6-membered ring.

14. The heat-sensitive lithographic printing plate precursor according to claim 13 wherein -Z 1 and -Z 3 together represent —(CH 2 ) 2 — or —(CH 2 ) 3 —.

15. The heat-sensitive lithographic printing plate precursor according to claim 14 wherein the IR light absorbing dye corresponds to one of the following formulae:

16. The heat-sensitive lithographic printing plate precursor according to claim 14 wherein the IR light absorbing dye corresponds to one of the following formulae:

wherein

m is 2 or an integer greater than 2;

R 14 represents —(CH 2 ) 2 —OCO—(CH 2 ) 2 —(CF 2 ) k —CF 3 ;

with k is 2 or an integer greater than 2; and

G represents SO 3 − , SO 4 − or COO − .