Method of imaging and developing positive-working imageable elements
View Patent ↗A method of making imaged elements such as lithographic printing plates is achieved by imagewise exposing an infrared radiation-sensitive positive-working imageable element to provide exposed and non-exposed regions. The imaged element is developed using a single processing solution having a pH of from about 9 to about 11.5 and containing carbonate ion and at least 1 weight % of one or more anionic surfactants, to remove predominantly only the exposed regions to provide an image and to provide a protective coating on the imaged surface. The imageable element comprises a substrate and a radiation absorbing compound, and has an imageable layer on the substrate that comprises a developability-enhancing compound and a poly(vinyl acetal) in which at least 25 mol % of its recurring units comprise pendant nitro-substituted phenolic groups.
1. A method of making an imaged element comprising:
A) imagewise exposing an infrared radiation-sensitive positive-working imageable element comprising a substrate and an infrared radiation-sensitive compound, and having on said substrate an imageable layer that comprises a developability-enhancing compound and a poly(vinyl acetal) in which at least 25 mol % of its recurring units comprise pendant nitro-substituted phenolic groups, to imaging radiation at a wavelength of from about 700 to about 1400 nm to provide exposed and non-exposed regions, and
B) applying a single processing solution having a pH of from about 9 to about 11.5 to said imagewise exposed element both: (1) to remove predominantly only said exposed regions, and (2) to provide a protective coating over all of said non-exposed and exposed regions of the resulting lithographic printing plate, said single processing solution comprising a carbonate and at least 1 weight % of one or more anionic surfactants.
2. The method of claim 1 wherein said single processing solution has a pH of from about 9 to about 11 and comprises at least 0.5 and up to 10 weight % carbonate ion.
3. The method of claim 1 wherein said single processing solution further comprises at least 0.001 weight % of an organic phosphonic acid or polycarboxylic acid, or a salt of either acid that is different than said one or more anionic surfactants.
4. The method of claim 1 wherein said single processing solution is essentially free of silicates, metasilicates, and has less than 8 weight % of organic solvents.
5. The method of claim 1 wherein at least one of said one or more anionic surfactants has a sulfonic acid group or salt thereof and is present in said single processing solution in an amount of from about 1 to about 45 weight %.
6. The method of claim 1 wherein at least one of said one or more anionic surfactants is an alkyldiphenyloxide disulfonate that is present in said single processing solution in an amount of from about 1 to about 20 weight %.
7. The method of claim 6 wherein said single processing solution comprises two or more different anionic surfactants one of which is an alkali alkyl naphthalene sulfonate that is present in an amount of from about 5 to about 20 weight %.
8. The method of claim 1 wherein said imagewise exposing is carried out at an energy of from about 100 to about 300 mJ/cm 2 .
9. The method of claim 1 wherein said developing is carried out at up to 35° C. for up to and including 3 minutes and said single processing solution comprises carbonate ion in an amount of from about 1 to about 7 weight %.
10. The method of claim 1 wherein said poly(vinyl acetal) comprises at least 25 and up to 80 mol % of recurring units represented by the following Structure (Ic):
wherein R and R′ are independently hydrogen or a substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, or halo group, and R 3 is a nitro-substituted phenol, nitro-substituted naphthol, or nitro-substituted anthracenol group.
11. The method of claim 10 wherein said poly(vinyl acetal) is represented by the following Structure (I):
-(A) k -(B) l -(C) m -(D) n - (I)
wherein:
A represents recurring units represented by the following Structure (Ia):
B represents recurring units represented by the following Structure (Ib):
C represents recurring units represented by the Structure (Ic) as defined above,
D represents recurring units represented by the following Structure (Id):
k is from about 1 to about 20 mol %, l is from about 5 to about 50 mol %, m is from about 25 to about 80 mol %, and n is from 0 to about 40 mol %,
R and R′ are independently hydrogen or a substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, or halo group,
R 1 is a substituted or unsubstituted alkyl or aryl carboxylic acid ester,
R 2 is hydroxy group, and
R 4 is a substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, or substituted or unsubstituted aryl group.
12. The method of claim 11 wherein k is from about 2 to about 12 mol %, l is from about 20 to about 35 mol %, m is from about 35 to about 70 mol %, and n is from 10 to about 30 mol %.
13. The method of claim 1 wherein said infrared radiation absorbing compound is present in said imageable layer.
14. The method of claim 1 wherein said substrate contains aluminum and has a hydrophilic surface upon which said imageable layer is disposed.
15. The method of claim 1 wherein said imageable layer comprises said infrared radiation absorbing compound and further comprises a colorant.
16. The method of claim 15 wherein one or both of said infrared radiation absorbing compound and said colorant are pigments.
17. The method of claim 1 further comprising mechanically removing excess single processing solution from said imaged element, with optional drying.
18. The method of claim 17 wherein said excess single processing solution is removed using a squeegee or nip rollers.
19. A lithographic printing plate obtained by the method of claim 1 .
20. A method of lithographic printing comprising, in order:
A) using infrared radiation, imagewise exposing an infrared radiation-sensitive positive-working imageable element comprising a substrate and an infrared radiation-sensitive compound, and having on said substrate an imageable layer that comprises a developability-enhancing compound and a poly(vinyl acetal) in which at least 25 mol % of its recurring units comprise pendant nitro-substituted phenolic groups, to provide exposed and non-exposed regions,
B) applying a single processing solution having a pH of from about 9 to about 11.5 to said imagewise exposed element both: (1) to remove predominantly only said exposed regions, and (2) to provide a protective coating over all of said non-exposed and exposed regions of the resulting lithographic printing plate, said single processing solution comprising a carbonate and at least 1 weight % of one or more anionic surfactants,
C) removing excess single processing solution from said imaged element followed by optional drying, and
D) contacting said imaged element with a lithographic printing ink, fountain solution, or both, and printing on a receiving material.