Releasable flexographic printing mask with laser thermal imaging film containing lecithin

A method of forming a relief image, comprising:

• providing a relief-forming assembly comprising a mask and a relief-forming precursor in complete optical contact with the mask, wherein the mask includes:
• a transparent polymeric carrier sheet;
• a base layer on the transparent polymeric carrier sheet, wherein the base layer comprises a polymeric binder and lecithin;
• and
• an imaging layer on the base layer, wherein the imaging layer includes a non-silver halide thermally-ablatable material comprising an ablatable polymer and a colorant;
• imaged regions in the imaging layer, wherein the imaged regions have optical apertures that are substantially devoid of the ablatable polymer and colorant;
• and
• non-imaged regions in the imaging layer, wherein the non-imaged regions have the ablatable polymer and colorant;
• exposing a relief-forming layer of the relief-forming precursor to curing ultraviolet radiation through the mask to form an imaged relief-forming layer with ultraviolet-exposed regions forming polymerized regions and non-exposed regions forming non-polymerized regions in the imaged relief-forming layer;
• removing the mask from the imaged relief-forming layer;
• and
• developing the imaged relief-forming layer by removing the non-polymerized regions in the imaged relief-forming layer, thereby forming a relief image element having a relief image.