On-press developable lithographic printing plate

1. An imageable element comprising:

a substrate; and

a layer of an imageable composition over the substrate;

in which:

the imageable composition comprises:

a photothermal conversion material, and

particles of a polyurethane polymer;

the polyurethane polymer comprises urethane linkages in the main chain;

the polyurethane polymer does not comprise side chain urethane groups;

the polyurethane polymer is prepared by reaction of a diisocyanate and a dihydroxy compound, and

the dihydroxy compound comprises about 1-25% of a carboxy functional diol or a mixture of carboxy functional diols.

2. The element of claim 1 in which the dihydroxy compound comprises about 3-15% of the carboxy functional diol or mixture of carboxy functional diols, about 0-50% of an aromatic diol or mixture of aromatic diols, and about 35-97% of an aliphatic diol or mixture of aliphatic diols.

3. The element of claim 1 in which the polyurethane polymer comprises blocking groups.

4. The element of claim 1 in which the polyurethane polymer does not comprise blocking groups.

5. The element of claim 1 in which the imageable layer comprises, based on the dry weight of the imageable layer: about 80% to about 99% of the polyurethane particles, based on the dry weight of the particles; about 0.01% to about 5% of a surfactant or mixture of surfactants; and about 0.5% to about 20% of the infrared absorber or mixture of infrared absorbers.

6. The element of claim 5 which the dihydroxy compound comprises about 3-15% of the carbaxy functional diol or mixture of carboxy functional diols, about 0-50% of an aromatic diol or mixture of aromatic diols, and about 35-97% of an aliphatic dial or mixture of aliphatic diols.

7. The element of claim 6 in which the imageable layer comprises: about 85% to about 95% of the polyurethane particles, based on the dry weight of the particles; about 0.1% to about 1% of the surfactant or mixture of surfactants; and about 1% to about 15% of the infrared absorber or mixture of infrared absorbers; and the polyurethane particles have a diameter of 0.01-0.5 micrometers.

8. The element of claim 6 in which the carboxyl functional diol or mixture of carboxyl functional diols is selected from the group consisting of 2,2-bis(hydroxymethyl) propionic acid, 2,2-dimethylol propanoic acid), 2,2-bis(2-hydroxyethyl) propionic acid, 2,2-bis(3-hydroxypropyl) propionic acid, bis(hydroxymethyl)acetic acid, bis(4-hydroxyphenyl)acetic acid, 2,2-bis(hydroxymethyl) butyric acid, 2,2-bis(hydroxymethyl) pentanoic acid, tartaric acid, and mixtures thereof.

9. The element of claim 1 in which the imageable layer additionally comprises a water soluble polymer or a mixture of water soluble polymers.

10. The element of claim 9 in which the imageable layer comprises: about 60% to about 95% of the polyurethane particles, based an the dry weight of the particles; about 0.01% to about 5% of a surfactant or mixture of surfactants; about 0.5% to 20% of the infrared absorber or mixture of infrared absorbers; and about 3% to 30% of the water soluble polymer or mixture of water soluble polymers.

11. The element of claim 10 in which the dihydroxy compound comprises about 3-15% of the carboxy functional diol or mixture of carboxy functional diols, about 0-50% of an aromatic diol or mixture of aromatic diols, and about 35-97% of an aliphatic diol or mixture of aliphatic diols.

12. The element of claim 11 in which the imageable layer comprises, based on the dry weight of the imageable layer: about 70% to about 90% of the polyurethane particles, based on the dry weight of the particles; about 0.1% to about 1% of the surfactant or mixture of surfactants; about 1% to about 15% of the infrared absorber or mixture of infrared absorbers; and about 5% to about 20% of the water soluble polymer or mixture of water soluble polymers; and the polyurethane particles have a diameter of 0.01-0.5 micrometers.

13. The element of claim 1 in which at least one end of the polyurethane polymer is either a blocking group or an amine group.

14. The element of claim 1 in which both ends of the polyurethane polymer are each either a blocking group or an amine group.

15. The element of claim 14 in which the dihydroxy compound comprises about 3-15% of a carboxy functional diol or mixture of carboxy functional diols, about 0-50% of an aromatic diol or mixture of aromatic diols, and about 35-97% of an aliphatic diol or mixture of aliphatic diols.

16. The element of claim 15 in which the imageable layer additionally comprises a water soluble polymer or a mixture of water soluble polymers.

17. The element of claim 1 in which the polyurethane polymer is not crosslinked.

18. The element of claim 17 in which the imageable layer additionally comprises a water soluble polymer or a mixture of water soluble polymers.

19. A method for forming an image, the method comprising the steps of:

(a) thermally imaging an imageable element to produce an imaged imageable element comprising imaged regions and unimaged regions in the layer of imageable composition, the imageabie element comprising:

a substrate; and

a layer of an imageable composition over the substrate;

in which:

the imageabie composition comprises:

a photothermal conversion material, and

particles of a polyurethane polymer;

the polyurethane polymer comprises urethane linkages in the main chain;

the polyurethane polymer does not comprise side chain urethane groups;

the polyurethane polymer is prepared by reaction of a diisocyanate and a dihydroxy compound, and

the dihydroxy compound comprises about 1-25% of a carboxy functional diol or a mixture of carboxy functional diols;

(b) developing the imaged imageable element by applying fountain solution and lithographic ink to the layer of imageable composition, removing the unimaged regions, and forming the image.

20. The method of claim 19 in which the imageabie layer comprises, based on the dry weight of the imageable layer: about 80% to about 99% of the polyurethane particles, based on the dry weight of the particles; about 0.01% to about 5% of a surfactant or mixture of surfactants; and about 0.5% to about 20% of the infrared absorber or mixture of infrared absorbers.

21. The method of claim 20 in which the dihydroxy compound comprises about 3-15% of the carboxy functional diol or mixture of carboxy functional diols, about 0-50% of an aromatic diol or mixture of aromatic diols, and about 35-97% of an aliphatic diol or a mixture of aliphatic diols.

22. The method of claim 21 in which the imageable layer comprises: about 85% to about 95% of the polyurethane particles, based on the dry weight of the particles; about 0.1% to about 1% of the surfactant or mixture of surfactants; and about 1% to about 15% of the infrared absorber or mixture of infrared absorbers; and the polyurethane particles have a diameter of 0.01-0.5 micrometers.

23. The method of claim 19 in which the imageable layer additionally comprises a water soluble polymer or a mixture of water soluble polymers.

24. The method of claim 23 in which the imageable layer comprises: about 60% to about 95% of the polyurethane particles, based on the dry weight of the particles; about 0.01% to about 5% of a surfactant or mixture of surfactants; about 0.5% to 20% of the infrared absorber or mixture of infrared absorbers; and about 3% to 30% of the water soluble polymer or mixture of water soluble polymers.

25. The method of claim 24 in which the dihydroxy compound comprises about 3-15% of the carboxy functional diol or mixture of carboxy functional diols, about 0-50% of an aromatic diol or mixture of aromatic diols, and about 35-97% of an aliphatic diol or mixture of aliphatic diols.

26. The method of claim 25 in which the imageable layer comprises, based on the dry weight of the imageable layer: about 70% to about 90% of the polyurethane particles, based on the dry weight of the particles; about 0.1% to about 1% of the surfactant or mixture of surfactants; about 1% to about 15% of the infrared absorber or mixture of infrared absorbers; and about 5% to about 20% of the water soluble polymer or mixture of water soluble polymers; and the polyurethane particles have a diameter of 0.01-0.5 micrometers.

27. The method of claim 26 additionally comprising, after step (b),

(c) applying a fountain solution and then a lithographic ink to the image, forming an ink image, and transferring the ink image to a receiver.

28. The method of claim 19 in which the polyurethane polymer is not crosslinked.

29. The method of claim 28 in which the imageable layer additionally comprises a water soluble polymer or a mixture of water soluble polymers.

30. An imageable element comprising:

a substrate; and

a layer of an imageable composition over the substrate;

in which:

the imageable composition comprises:

a photothermal conversion material, and

particles of a polyurethane polymer;

the polyurethane polymer comprises urethane linkages in the main chain;

the polyurethane polymer does not comprise side chain urethane groups;

the particles consist essentially of the polyurethane polymer;

the polyurethane polymer is prepared by reaction of a diisocyanate and a dihydroxy compound; and

the dihydroxy compound comprises about 1-25% of a carboxy functional diol or a mixture of carboxy functional diols.

31. The element of claim 30 in which the imageable layer comprises, based on the dry weight of the imageable layer: about 80% to about 99% of the polyurethane particles, based on the dry weight of the particles; about 0.01% to about 5% of a surfactant or mixture of surfactants; and about 0.5% to about 20% of the infrared absorber or mixture of infrared absorbers.

32. The element of claim 31 in which the imageable layer comprises: about 85% to about 95% of the polyurethane particles, based on the dry weight of the particles; about 0.1% to about 1% of the surfactant or mixture of surfactants; and about 1% to about 15% of the infrared absorber or mixture of infrared absorbers; and the polyurethane particles have a diameter of 0.01-0.5 micrometers.

33. The element of claim 30 in which the imageable layer additionally comprises a water soluble polymer or a mixture of water soluble polymers.

34. The element of claim 33 in which the imageable layer comprises: about 60% to about 95% of the polyurethane particles, based on the dry weight of the particles; about 0.01% to about 5% of a surfactant or mixture of surfactants; about 0.5% to 20% of the infrared absorber or mixture of infrared absorbers; and about 3% to 30% of the water soluble polymer or mixture of water soluble polymers.

35. The element of claim 34 in which the imageable layer comprises, based on the dry weight of the imageable layer: about 70% to about 90% of the polyurethane particles, based on the dry weight of the particles; about 0.1% to about 1% of the surfactant or mixture of surfactants; about 1% to about 15% of the infrared absorber or mixture of infrared absorbers; and about 5% to about 20% of the water soluble polymer or mixture of water soluble polymers; and the polyurethane particles have a diameter of 0.01-0.5 micrometers.

36. The element of claim 30 in which the polyurethane polymer is not crosslinked.

37. A method for forming an image, the method comprising the steps of:

(a) thermally imaging an imageable element to produce an imaged imageable element comprising imaged regions and unimaged regions in the layer of imageable composition, the imageable element comprising:

a substrate; and

a layer of an imageable composition over the substrate;

in which:

the imageable composition comprises:

a photothermal conversion material, and

particles of a polyurethane polymer;

the polyurethane polymer comprises urethane linkages in the main chain;

the polyurethane polymer does not comprise side chain urethane groups;

the particles consist essentially of the polyurethane polymer;

the polyurethane polymer is prepared by reaction of a diisocyanate and a dihydroxy compound; and

the dihydroxy compound comprises about 1-25% of a carboxy functional diol or a mixture of carboxy functional diols;

(b) developing the imaged imageabie element by applying fountain solution and lithographic ink to the layer of imageable composition, removing the unimaged regions, and forming the image.

38. The method of claim 37 in which the imageable layer comprises, based on the dry weight of the imageable layer: about 80% to about 99% of the polyurethane particles, based on the dry weight of the particles; about 0.01% to about 5% of a surfactant or mixture of surfactants; and about 0.5% to about 20% of the infrared absorber or mixture of infrared absorbers.

39. The method of claim 37 in which the imageable layer additionally comprises a water soluble polymer or a mixture of water soluble polymers.

40. The method of claim 39 in which the imageable layer comprises: about 60% to about 95% of the polyurethane particles, based on the dry weight of the particles; about 0.01% to about 5% of a surfactant or mixture of surfactants; about 0.5% to 20% of the infrared absorber or mixture of infrared absorbers; and about 3% to 30% of the water soluble polymer or mixture of water soluble polymers.