Method for providing lithographic printing plates
View Patent ↗A method of making a lithographic printing plate includes the steps of a) image-wise exposing a lithographic printing plate precursor including a hydrophilic support and a coating containing a colorant precursor to form a lithographic image consisting of printing areas and non-printing areas, b) developing the plate precursor to remove the coating in the non-printing areas from the support, and c) drying the plate precursor, and d) subjecting the plate precursor to heat or radiation to induce a colour change of the coating in the printing areas, wherein before step b) the coating in the non-printing areas and the support are characterised by a CIE 1976 colour difference ΔE 1 which is 5.0 or less, and after step d) the CIE 1976 colour difference ΔE 2 between the coating in the printing areas and the non-printing areas is more than 6.8.
1. A method of making a lithographic printing plate comprising the steps of:
a) image-wise exposing a plate precursor including a hydrophilic support and a coating containing a colorant precursor to form a lithographic image consisting of printing areas and non-printing areas; and
b) developing the plate precursor to remove the coating in the non-printing areas from the support; and
c) drying the plate precursor; and
d) subjecting the plate precursor to heat or radiation to induce a color change in the coating in the printing areas; wherein
before step b), the coating in the non-printing areas and the support have a CIE 1976 color difference ΔE 1 which is 5.0 or less; and
after step d), the CIE 1976 color difference ΔE 2 between the coating in the printing areas and the support revealed by the step of developing is more than 6.8.
2. The method of making a lithographic printing plate according to claim 1 , wherein after step d), ΔE 2 between the coating in the printing areas and the support in the non-printing areas is more than 13.6.
3. The method of making a lithographic printing plate according to claim 1 , wherein after step d), ΔE 2 between the coating in the printing areas and the support in the non-printing areas is more than 20.4.
4. The method of making a lithographic printing plate according to claim 1 , wherein the step of developing the plate precursor is performed with a solution having a pH from 3.0 to 10.0 and including a surfactant.
5. The method of making a lithographic printing plate according to claim 4 , wherein the solution has a pH from 4.0 to 9.0.
6. The method of making a lithographic printing plate according to claim 4 , wherein the solution is a gum developer.
7. The method of making a lithographic printing plate according to claim 1 , wherein the radiation is UV radiation.
8. The method of making a lithographic printing plate according to claim 4 , wherein the radiation is UV radiation.
9. The method of making a lithographic printing plate according to claim 5 , wherein the radiation is UV radiation.
10. The method of making a lithographic printing plate according to claim 7 , wherein the UV radiation is emitted by one or more LEDs.
11. The method of making a lithographic printing plate according to claim 8 , wherein the UV radiation is emitted by one or more LEDs.
12. The method of making a lithographic printing plate according to claim 1 , wherein the radiation is IR radiation.
13. The method of making a lithographic printing plate according to claim 4 , wherein the radiation is IR radiation.
14. The method of making a lithographic printing plate according to claim 5 , wherein the radiation is IR radiation.
15. The method of making a lithographic printing plate according to claim 1 , wherein the plate precursor includes a sensitizing dye having an absorption maximum in a wavelength range from 350nm to 450nm.
16. The method of making a lithographic printing plate according to claim 4 , wherein the plate precursor includes a sensitizing dye having an absorption maximum in a wavelength range from 350nm to 450nm.
17. The method of making a lithographic printing plate according to claim 1 , wherein the plate precursor includes a sensitizing dye having an absorption maximum in a wavelength range from 700nm to 1200nm.
18. The method of making a lithographic printing plate according to claim 4 , wherein the plate precursor includes a sensitizing dye having an absorption maximum in a wavelength range from 700nm to 1200nm.
19. The method of making a lithographic printing plate according to claim 1 , wherein the plate precursor is negative working.
20. The method of making a lithographic printing plate according to claim 4 , wherein the plate precursor is negative working.
21. The method of making a lithographic printing plate according to claim 19 , wherein the coating includes a sensitizing dye, a radical polymerization initiator, a radically polymerizable compound, and a binder polymer.
22. The method of making a lithographic printing plate according to claim 1 , wherein the plate precursor is positive working.
23. The method of making a lithographic printing plate according to claim 4 , wherein the plate precursor is positive working.