Method for making a lithographic printing plate precursor

1. A method for making a lithographic printing plate precursor comprising the steps of:

coating an aqueous composition having a pH≦5 on a support having a hydrophilic surface or which is provided with a hydrophilic layer, the aqueous composition including a hydrophilic binder, colloidal silica, and hydrophobic thermoplastic polymer particles stabilized with an anionic dispersant, wherein the silica carries a negative charge; and

drying the composition thereby obtaining a coating on the support.

2. A method for making a lithographic printing plate precursor comprising the steps of:

coating a first composition on a support having a hydrophilic surface or a hydrophilic layer, the first composition including a hydrophilic binder, an optional cross-inking agent, and hydrophobic thermoplastic polymer particles stabilized with an anionic dispersant thereby obtaining an image-recording layer;

coating a second composition on the image-recording layer, the second composition having a pH≦5 and including negatively charged colloidal silica; and

drying the first and second compositions thereby obtaining a coating on the support.

3. The method according to claim 1 , wherein the pH≦4.5.

4. The method according to claim 2 , wherein the pH <4.5.

5. The method according to claim 4 , wherein the optional crosslinking agent is tetra-alkyl orthosilicate.

6. The method according to claim 1 , wherein the colloidal silica is present in the coating in an amount ranging from 0.005 g/m 2 to 1 g/m 2 .

7. The method according to claim 2 , wherein the colloidal silica is present in the coating in an amount ranging from 0.005 g/m 2 to 1 g/m 2 .

8. The method according to claim 1 , wherein the colloidal silica is present in the coating in an amount ranging from 0.01 g/m 2 to 0.8 g/m 2 .

9. The method according to claim 2 , wherein the colloidal silica is present in the coating in an amount ranging from 0.01 g/m 2 to 0.8 g/m 2 .

10. The method according to claim 1 , wherein the hydrophobic thermoplastic polymer particles have an average particle size in the range from 40 nm to 70 nm.

11. The method according to claim 2 , wherein the hydrophobic thermoplastic polymer particles have an average particle size in the range from 40 nm to 70 nm.

12. The method according to claim 1 , wherein the amount of the hydrophobic thermoplastic polymer particles in the coating is at least 70% by weight.

13. The method according to claim 2 , wherein the amount of the hydrophobic thermoplastic polymer particles in the coating is at least 70% by weight.

14. The method according to claim 1 , wherein the hydrophobic thermoplastic polymer particles include at least 5% wt of nitrogen containing units.

15. The method according to claim 2 , wherein the hydrophobic thermoplastic polymer particles include at least 5% wt of nitrogen containing units.

16. A method for making a lithographic printing plate comprising the steps of:

providing a heat-sensitive, negative-working printing plate precursor obtained by the method according to claim 1 ;

exposing the coating to heat, thereby inducing coalescence of the thermoplastic polymer particles at exposed areas of the coating; and

optionally developing the exposed coating with a processing liquid.

17. A method for making a lithographic printing plate comprising the steps of:

providing a heat-sensitive, negative-working printing plate precursor obtained by the method according to claim 2 ;

exposing the coating to heat, thereby inducing coalescence of the thermoplastic polymer particles at exposed areas of the coating; and

optionally developing the exposed coating with a processing liquid.

18. A method for making a lithographic printing plate comprising the steps of

providing a heat-sensitive, negative-working printing plate precursor obtained by the method according to claim 1 ;

exposing the coating to heat, thereby inducing coalescence of the thermoplastic polymer particles at exposed areas of the coating;

mounting the exposed precursor on a printing press whereby the precursor is developed by supplying ink and/or fountain solution to the precursor.

19. A method for making a lithographic printing plate comprising the steps of

providing a heat-sensitive, negative-working printing plate precursor obtained by the method according to claim 2 ;

exposing the coating to heat, thereby inducing coalescence of the thermoplastic polymer particles at exposed areas of the coating;

mounting the exposed precursor on a printing press whereby the precursor is developed by supplying ink and/or fountain solution to the precursor.