Developer regenerators
The present invention provides an aqueous regenerator for addition to an aqueous developer that contains an organic solvent, a dispersing agent and a weak base, and has a pH of between about 8 and less than about 13. The aqueous regenerator includes an organic solvent, dispersing agent, and an effective amount of a strong base such that the regenerator has a greater pH than the developer into which the regenerator is to be added.
1. A method for developing a plurality of imaged positive-working printing plate precursors each having a single radiation-sensitive coating, the method comprising:
contacting a portion of at least one of said imaged printing plate precursors with an aqueous developer comprising an organic solvent, a dispersing agent and a weak base, and having a pH between about 8 and less than about 13;
adding to the aqueous developer an effective amount of an aqueous regenerator to maintain the activity of the aqueous developer, the aqueous regenerator comprising an organic solvent, a dispersing agent, and an effective amount of at least one strong base such that the pH of the aqueous regenerator is greater than the pH of the aqueous developer by at least 0.5 pH unit, wherein the K b of the strong base is greater than the K b of the weak base; and
after adding the aqueous regenerator, contacting a portion of at least one additional imaged positive-working printing plate precursor with the aqueous developer.
2. The method of claim 1 wherein each printing plate precursor comprises a radiation-sensitive coating applied onto an aluminum-containing substrate.
3. The method of claim 2 wherein the radiation-sensitive coating is laser imageable.
4. The method of claim 2 wherein the radiation-sensitive coating comprises a polymeric material that comprises an acidic or weakly basic functionality.
5. The method of claim 4 wherein the polymeric material comprises a carboxylic acid moiety.
6. The method of claim 4 wherein the polymeric material comprises a phenolic resin.
7. The method of claim 3 wherein the radiation-sensitive coating comprises an infrared absorbing component.
8. The method of claim 1 wherein the at least one imaged printing plate precursor changes the activity of the aqueous developer upon contacting the aqueous developer.
9. The method of claim 1 comprising repeating the contacting and adding steps a plurality of times.
10. A method of forming a plurality of printing plates comprising
providing a plurality of positive-working printing plate precursors, each precursor comprising a single radiation-sensitive coating applied onto a substrate;
imagewise exposing the precursors to radiation to form a plurality of imaged printing plate precursors;
contacting a portion of at least one of the imaged printing plate precursors with an aqueous developer to form a printing plate, wherein the aqueous developer comprises an organic solvent, a dispersing agent, and a weak base, and has a pH between about 8 and less than about 13;
adding to the aqueous developer an effective amount of an aqueous regenerator to maintain the activity of the aqueous developer, the aqueous regenerator comprising an organic solvent, a dispersing agent, and an effective amount of at least one strong base such that the pH of the aqueous regenerator is greater than the pH of the aqueous developer by at least 0.5 pH unit, wherein the K b of the strong base is greater than the K b of the weak base; and
after adding the aqueous regenerator, contacting a portion of at least one additional imaged printing plate precursor with the aqueous developer to form a printing plate.
11. The method of claim 10 wherein the imagewise exposing step comprises imagewise exposing the radiation-sensitive coating with a laser.
12. The method of claim 1 wherein the weak base has a K b of between about 1×10 −2 to about 1×10 −5 and the strong base has a K b of about 1 or greater.
13. The method of claim 1 wherein the aqueous regenerator has a pH at least 0.7 higher than the pH of the aqueous developer.
14. The method of claim 1 wherein the weak base comprises an amine, sodium carbonate, potassium carbonate, sodium bicarbonate, trisodium phosphate, tripotassium phosphate, or a combination thereof, and the strong base comprises a hydroxide.
15. The method of claim 1 wherein the difference in pH between said aqueous developer and aqueous regenerator is at least 1.0 pH unit, and the pH of said aqueous developer is from about 9 to about 11.
16. The method of claim 15 wherein the pH of said aqueous developer is from about 9.5 to about 10.5.
17. The method of claim 1 wherein said radiation-sensitive coating comprises a polymeric material having an acidic moiety or a phenolic resin.