Imaging element comprising a thermally activated crosslinking agent

A positive-working imageable element comprising, in order:

• (a) a substrate comprising a hydrophilic surface;
• (b) an underlayer over the hydrophilic surface;
• and
• (c) an imageable layer;
• in which:
• the element comprises a photothermal conversion material;
• the imageable layer is ink receptive;
• the imageable layer is insoluble in an aqueous alkaline developer;
• the imageable layer comprises a first polymeric material;
• the underlayer is soluble in the aqueous alkaline developer;
• the underlayer comprises a thermally activated crosslinking agent and a second polymeric material;
• and
• the second polymeric material comprises one or more functional groups selected from the group consisting of carboxyl, carboxylic acid anhydride, phenolic hydroxyl, and sulphonamide.

A method for forming an image, the method comprising the steps of:

• (a) imaging an imageable element and forming an imaged element comprising imaged and unimaged regions in the element, in which the imageable element comprises, in order:
• a substrate comprising a hydrophilic surface;
• and
• an imageable layer over the hydrophilic surface;
• in which:
• the imageable layer is ink receptive;
• the element comprises a compound that comprises a multiplicity of oxazoline groups;
• the element comprises a polymeric material that comprises one or more functional groups selected from the group consisting of carboxyl, carboxylic acid anhydride, phenolic hydroxyl, and sulphonamide;
• and
• the compound that comprises the multiplicity of oxazoline groups and the polymeric material that comprises one or more functional groups selected from the group consisting of carboxyl, carboxylic acid anhydride, phenolic hydroxyl, and sulphonamide are in the same layer;
• (b) forming a developed element by developing the imaged element with an aqueous alkaline developer and removing one of the imaged regions and the unimaged regions;
• and
• (c) forming the lithographic printing plate by baking the developed element and crosslinking the polymeric material with the oxazoline groups, in which the oxazoline groups do not substantially crosslink the polymeric material prior to step (c).

A method for forming an image, the method comprising the steps of:

• (a) imaging a positive-working imageable element and forming an imaged element comprising imaged and unimaged regions in the element, in which the positive-working imageable element comprises, in order:
• a substrate comprising a hydrophilic surface;
• an underlayer over the hydrophilic surface;
• and
• an imageable layer;
• in which:
• the element comprises a photothermal conversion material;
• the imageable layer is ink receptive;
• the imageable layer is insoluble in an aqueous alkaline developer;
• the imageable layer comprises a first polymeric material;
• the underlayer is soluble in the aqueous alkaline developer;
• the underlayer comprises a thermally activated crosslinking agent and a second polymeric material;
• and
• the second polymeric material comprises one or more functional groups selected from the group consisting of carboxyl, carboxylic acid anhydride, phenolic hydroxyl, and sulphonamide;
• (b) forming a developed element by developing the imaged element with an aqueous alkaline developer and removing the imaged regions;
• and
• (c) forming the lithographic printing plate by baking the developed element and crosslinking the second polymeric material, in which the thermally activated crosslinking agent does not substantially crosslink the second polymeric material prior to step (c).