Method of making laser-ablatable elements

1. A method of preparing a laser-ablatable element comprising applying to a substrate, multiple formulations each comprising a coating solvent, a laser-ablatable polymeric binder, and an infrared radiation absorbing compound, to provide multiple sub-layers on the substrate, such that the infrared radiation absorbing compound concentration is different in each adjacent pair of sub-layers so that the concentration is always greater in each sub-layer that is closer to the substrate, and the concentration is progressively greater in the sub-layers as they are closer to the substrate after the coating solvent is removed, wherein the multiple sub-layers provide a relief-forming layer so that the sub-layer farthest from the substrate provides a relief-image forming surface,

wherein the infrared radiation-absorbing compound is present in the relief-forming layer in a concentration profile throughout depth x from the relief-image forming surface so that the absorption coefficient profile α(x) is substantially in accordance with the following equation:

α

⁡

(

x

)

=

1

β

-

x

⁢

⁢

wherein

⁢

⁢

β

≤

F

ρ

⁢

⁢

C

p

⁡

(

T

c

-

T

0

)

wherein F is the fluence (energy per unit area) of an infrared radiation source when it is used to irradiate the relief-forming layer surface, ρ is the density of the relief-forming layer, C p is the heat capacity of the relief-forming layer, T O is the initial temperature of the relief-forming layer and T c is critical ablation temperature of the relief-forming layer.

2. The method of claim 1 that provides a relief-forming layer having a dry thickness of from about 100 μm to about 4000 μm.

3. The method of claim 1 wherein the relief-forming layer has a dry thickness of from 200 to 2000 μm.

4. The method of claim 1 that provides a flexographic printing plate precursor or flexographic printing sleeve precursor.

5. The method of claim 1 further comprising forming an elastomeric rubber layer on the substrate before applying the multiple formulations.

6. The method of claim 1 wherein the substrate has an imaging side and a non-imaging side, and the method comprises applying the multiple formulations to the imaging side of the substrate to form the relief-forming layer, and forming at least one non-ablatable layer on the non-imaging side the substrate.

7. The method of claim 1 wherein the laser-ablatable polymeric binder is a crosslinked elastomer or rubbery resin.

8. The method of claim 7 wherein the crosslinked elastomer is derived by the reaction of a polyol with a polyisocyanate or the reaction of a polyamine with a polyisocyanate.

9. The method of claim 1 wherein the polymeric binder consists of a thermoplastic elastomer and a thermally initiated reaction product of a multifunctional monomer or oligomer.

10. The method of claim 1 wherein the infrared radiation absorbing compound is a carbon black, an organic or inorganic pigment, an organic dye that has a λ max of from about 800 to about 1200 nm, or any combination of these.

11. The method of claim 1 wherein the infrared radiation absorbing compound is present in the relief-forming layer in a total amount of from about 1 to about 20 weight % based on the dry weight of the relief-forming layer.

12. The method of claim 1 wherein the relief-forming layer further comprises micropores, microcapsules, or inorganic particles, or any combination thereof.

13. The method of claim 1 further comprising forming a laser-ablatable layer on the substrate before or after applying the multiple formulations.