Laser-imageable printing members and methods for wet lithographic printing

A positive working, wet lithographic printing member imageable by laser radiation, said member comprising:

• (a) an ink-accepting, hydrophobic surface layer comprising one or more polymers and being characterized by the absence of ablative absorption of said laser radiation and further characterized by being compatible with but not soluble in a cleaning solution;
• (b) an ablative layer underlying said surface layer, said ablative layer being characterized by ablative absorption of said laser radiation and by being compatible with but not excessively soluble in the cleaning solution;
• (c) a hydrophilic layer underlying said ablative layer, said hydrophilic layer comprising one or more polymers and being characterized by the absence of ablative absorption of said laser radiation;
• and
• (d) a hydrophilic metal substrate characterized by being insoluble in the cleaning solution;
• wherein said hydrophilic layer is further characterized by (i) being compatible with but not excessively soluble in water and by being at least partially removed by said laser radiation and a subsequent cleaning treatment with water or with the cleaning solution, and (ii) providing a thermal barrier between the ablative layer and the substrate.

A method of preparing a positive working, wet lithographic printing member imageable by laser radiation, said method comprising the steps of:

• (a) providing a hydrophilic metal substrate;
• (b) forming a hydrophilic layer on said substrate, said hydrophilic layer comprising one or more polymers and being characterized by the absence of ablative absorption of said laser radiation;
• (c) forming an intermediate layer overlying said hydrophilic layer, said intermediate layer comprising one or more polymers and a sensitizer, said sensitizer being characterized by absorption of said laser radiation and said intermediate layer being characterized by ablative absorption of said laser radiation;
• and
• (d) forming an ink-accepting layer overlying said intermediate layer, said ink-accepting layer comprising one or more polymers and being characterized by the absence of ablative absorption of said laser radiation;
• wherein said hydrophilic layer is further characterized by (i) being compatible with but not excessively soluble in water and by being at least partially removed by said laser radiation and subsequent cleaning treatment with water, and (ii) providing a thermal barrier between the intermediate layer and the substrate.

A method of preparing a positive working, wet lithographic printing member imageable by laser radiation, said method comprising the steps of:

• (a) providing a hydrophilic metal substrate;
• (b) forming a hydrophilic layer on said substrate, said hydrophilic layer comprising one or more polymers and being characterized by the absence of ablative absorption of said laser radiation and by being compatible with but not excessively soluble in a cleaning solution;
• (c) forming an ablative layer overlying said hydrophilic layer, said ablative layer being characterized by ablative absorption of said laser radiation and by being compatible with but not excessively soluble in the cleaning solution;
• and
• (d) forming an ink-accepting, hydrophobic layer overlying said ablative layer, said ink-accepting layer comprising one or more polymers and being characterized by the absence of ablative absorption of said laser radiation and by being compatible with but not soluble in the cleaning solution;
• wherein said hydrophilic layer is further characterized by (i) being slightly soluble but not excessively soluble in water and by being at least partially removed by said laser radiation and subsequent cleaning treatment with water, and (ii) providing a thermal barrier between the ablative layer and the substrate.