Method of making laser-ablatable elements

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, Cp is the heat capacity of the relief-forming layer, TO is the initial temperature of the relief-forming layer and Tc is critical ablation temperature of the relief-forming layer.