Heat-sensitive lithographic printing plate precursor

1. A positive-working lithographic printing plate precursor comprising on a support having a hydrophilic surface or which is provided with a hydrophilic layer, an oleophilic coating comprising an infrared absorbing agent, an alkali-soluble polymeric binder and a polysiloxane comprising a plurality of recurring units represented by —Si(RR′)—O— wherein R and R′ independently represent an alkyl, an aryl or a polyalkylene-oxide group, the polysiloxane further comprising at least one carboxylic acid group or a salt thereof and at least one linker group, wherein the at least one linker group is bonded to an end of the polysiloxane, and wherein at least one carboxylic acid group or a salt thereof is bonded to the linker group.

2. A positive-working lithographic printing plate precursor according to claim 1 , wherein the polysiloxane comprises at least two carboxylic acid groups or salts thereof and two linker groups, wherein a linker group is bonded to each end of the polysiloxane, and wherein a carboxylic acid group or a salt thereof is bonded to each linker group.

3. A positive-working lithographic printing plate precursor according to claim 2 , wherein the alkali-soluble polymeric binder is a phenolic resin.

4. A positive-working lithographic printing plate precursor according to claim 2 , wherein the coating further comprises a dissolution inhibitor comprising an organic compound comprising an aromatic group and a hydrogen bonding site.

5. A positive-working lithographic printing plate precursor according to claim 1 , wherein the coating further comprises a dissolution inhibitor comprising an organic compound comprising an aromatic group and a hydrogen bonding site.

6. A positive-working lithographic printing plate precursor according to claim 1 , wherein the alkali-soluble polymeric binder is a phenolic resin.

7. A positive-working lithographic printing plate precursor according to claim 1 , wherein the polysiloxane is present in the coating in an amount ranging from 0.5 to 25 mg/m 2 .

8. The positive-working lithographic printing plate precursor according to claim 1 , wherein the linker group is alkylene, arylene, heteroarylene, ——O—, —O—(CH 2 ) k —, —O—CO—(CH 2 ) k —, —(CH 2 ) k —O—CO—(CH 2 ) l —, —(CH 2 ) k —CO—(CH 2 ) l —, —CO—O—(CH 2 ) k —, —(CH 2 ) k —COO—(CH 2 ) l —, —CO—(CH 2 ) k — or combinations thereof, wherein k and 1 independently represent an integer ≧1.

9. The positive-working lithographic printing plate precursor according to claim 8 , wherein the linker group is alkylene, —O—(CH 2 ) k —, —(CH 2 ) k —CO—(CH 2 ) l — or —CO—(CH 2 ) k —.

10. The positive-working lithographic printing plate precursor according to claim 9 , wherein the recurring units are diphenyl-siloxanes, dimethyl-siloxanes and/or phenylmethyl-siloxanes.

11. A positive-working lithographic printing plate precursor comprising, on a support having a hydrophilic surface or which is provided with a hydrophilic layer, an oleophilic coating comprising an infrared absorbing agent, an alkali-soluble polymeric binder and a polysiloxane, wherein the polysiloxane comprises a plurality of recurring units represented by —Si(RR′)—O— wherein R and R′ independently represent an alkyl, an aryl or a polyalkylene-oxide group, the polysiloxane further comprising at least one carboxylic acid group or a salt thereof and at least one linker group, wherein a linker group is bonded to an end of the polysiloxane, wherein at least one carboxylic acid group or a salt thereof is bonded to the linker group, wherein the alkali-soluble polymeric binder is a phenolic resin, and wherein the phenolic resin is a novolac resin, a resol resin or a polyvinylphenol and the phenyl group or the hydroxy group of the phenolic monomeric unit of the phenolic resin is chemically modified with an organic substituent.

12. A positive-working lithographic printing plate precursor according to claim 11 , wherein the polysiloxane is present in the coating in an amount ranging from 0.5 to 25 mg/m 2 .

13. A positive-working lithographic printing plate precursor according to claim 12 , wherein the coating further comprises a dissolution inhibitor comprising an organic compound comprising an aromatic group and a hydrogen bonding site.

14. A positive-working lithographic printing plate precursor according to claim 11 , wherein the polysiloxane comprises at least two carboxylic acid groups or salts thereof and two linker groups, wherein a linker group is bonded to each end of the polysiloxane, and wherein a carboxylic acid group or a salt thereof is bonded to each linker group.

15. A positive-working lithographic printing plate precursor according to claim 14 , wherein the coating further comprises a dissolution inhibitor comprising an organic compound comprising an aromatic group and a hydrogen bonding site.

16. A positive-working lithographic printing plate precursor according to claim 11 , wherein the coating further comprises a dissolution inhibitor comprising an organic compound comprising an aromatic group and a hydrogen bonding site.

17. The positive-working lithographic printing plate precursor according to claim 11 , wherein the linker group is alkylene, arylene, heteroarylene, —O—, —O—(CH 2 ) k —, —O—CO—(CH 2 ) k —, —(CH 2 ) k —O—CO—(CH 2 ) l —, —(CH 2 ) k —CO—(CH 2 ) l —, —CO—O—(CH 2 ) k —, —(CH 2 ) k —COO—(CH 2 ) l —, —CO—(CH 2 ) k — or combinations thereof, wherein k and 1 independently represent an integer ≧1.

18. A method for making a positive-working lithographic printing plate precursor comprising the steps of: (a) providing a support having a hydrophilic surface or which is provided with a hydrophilic layer, and (b) applying onto the hydrophilic surface or hydrophilic layer an oleophilic coating comprising an infrared absorbing agent, an alkali-soluble polymeric binder and a polysiloxane, the polysiloxane comprising a plurality of recurring units represented by —Si(RR′)—O— wherein R and R′ independently represent an alkyl, an aryl or a polyalkylene-oxide group, the polysiloxane further comprising at least one carboxylic acid group or a salt thereof and at least one linker group, wherein a linker group is bonded to an end of the polysiloxane, and wherein at least one carboxylic acid group or a salt thereof is bonded to the linker group.

19. A method according to claim 18 , wherein the coating further comprises a dissolution inhibitor comprising an organic compound comprising an aromatic group and a hydrogen bonding site.

20. A method for making a positive-working lithographic printing plate precursor according to claim 18 , wherein the polysiloxane is present in the coating in an amount ranging from 0.5 to 25 mg/m 2 .

21. A method for making a positive-working lithographic printing plate precursor according to claim 18 , wherein the linker group is alkylene, arylene, heteroarylene, —O—, —O—(CH 2 ) k —, —O—CO—(CH 2 ) k —, —(CH 2 ) k —O—CO—(CH 2 ) l —, —(CH 2 ) k —CO—(CH 2 ) l —, —CO—O—(CH 2 ) k —, —(CH 2 ) k —COO—(CH 2 ) l —, —CO—(CH 2 ) k — or combinations thereof, wherein k and 1 independently represent an integer ≧1.

22. A method for making a positive-working lithographic printing plate comprising the steps of:

(a) exposing imagewise a heat-sensitive lithographic printing plate precursor to infrared light, the printing plate precursor comprising, on a support having a hydrophilic surface or which is provided with a hydrophilic layer, an oleophilic coating comprising an infrared absorbing agent, an alkali-soluble polymeric binder and a polysiloxane, wherein the polysiloxane comprises a plurality of recurring units represented by —Si(RR′)—O— wherein R and R′ independently represent an alkyl, an aryl or a polyalkylene-oxide group, the polysiloxane further comprising at least one carboxylic acid group or a salt thereof and at least one linker group, wherein a linker group is bonded to an end of the polysiloxane, and wherein at least one carboxylic acid group or a salt thereof is bonded to the linker group, and

(b) developing the imagewise exposed printing plate precursor with an aqueous alkaline developer so that the imagewise exposed areas are dissolved.

23. A method according to claim 22 , wherein the polysiloxane comprises at least two carboxylic acid groups or salts thereof and two linker groups, wherein a linker group is bonded to each end of the polysiloxane and wherein a carboxylic acid group or a salt thereof is bonded to each linker group.

24. A method according to claim 23 , wherein the alkali-soluble polymeric binder is a phenolic resin.

25. A method according to claim 22 , wherein the coating further comprises a dissolution inhibitor comprising an organic compound comprising an aromatic group and a hydrogen bonding site.

26. A method for making a positive-working lithographic printing plate precursor according to claim 22 , wherein the polysiloxane is present in the coating in an amount ranging from 0.5 to 25 mg/m 2 .

27. A method for making a positive-working lithographic printing plate comprising the steps of:

(a) exposing imagewise a heat-sensitive lithographic printing plate precursor to infrared light, the printing plate precursor comprising, on a support having a hydrophilic surface or which is provided with a hydrophilic layer, an oleophilic coating comprising an infrared absorbing agent, an alkali-soluble polymeric binder and a polysiloxane, wherein the polysiloxane, wherein the polysiloxane comprises a plurality of recurring units represented by —Si(RR′)—O— wherein R and R′ independently represent an alkyl, an aryl or a polyalkylene-oxide group, the polysiloxane further comprising at least one carboxylic acid group or a salt thereof and at least one linker group, wherein a linker group is bonded to an end of the polysiloxane, and wherein at least one carboxylic acid group or a salt thereof is bonded to the linker group, and

(b) developing the imagewise exposed printing plate precursor with an aqueous alkaline developer so that the exposed areas are dissolved,

wherein the alkali-soluble polymeric binder is a phenolic resin, and wherein the phenolic resin is a novolac resin, a resol resin or a polyvinylphenol and the phenyl group or the hydroxy group of the phenolic monomeric unit of the phenolic resin is chemically modified with an organic substituent.

28. A method according to claim 27 , wherein the coating further comprises a dissolution inhibitor comprising an organic compound comprising an aromatic group and a hydrogen bonding site.

29. A method for making a positive-working lithographic printing plate precursor according to claim 27 , wherein the polysiloxane is present in the coating in an amount ranging from 0.5 to 25 mg/m 2 .

30. A positive-working lithographic printing plate precursor comprising on a support having a hydrophilic surface or which is provided with a hydrophilic layer, an oleophilic coating comprising an infrared absorbing agent, an alkali-soluble polymeric binder and a polysiloxane comprising a plurality of recurring units, the polysiloxane further comprising at least one carboxylic acid group or a salt thereof and at least one linker group, wherein the at least one linker group is bonded to an end of the polysiloxane, and wherein at least one carboxylic acid group or a salt thereof is bonded to the linker group.