Lithographic printing plates for use with laser imaging apparatus

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

• (a) an ink-accepting surface layer characterized by the absence of ablative absorption of said laser radiation;
• (b) a second layer underlying the surface layer, said second layer comprising one or more polymers and being characterized by the ablative absorption of said laser radiation;
• (c) a hydrophilic third layer underlying the second layer, said third layer characterized by the absence of ablative absorption of said laser radiation;
• and,
• (d) a substrate;
• wherein interposed between said second layer and said third layer is a primer layer comprising a zirconium compound, said primer layer characterized by being hydrophilic, by the absence of ablative absorption of said laser radiation, by being not ablated by said ablative absorption of said second layer, and by being not soluble in water.

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

• (a) an ink-accepting surface layer characterized by the absence of ablative absorption of said laser radiation;
• (b) a second layer underlying the surface layer, said second layer comprising one or more polymers and being characterized by the ablative absorption of said laser radiation;
• and,
• (c) a hydrophilic substrate;
• wherein interposed between said second layer and said substrate is a primer layer, which primer layer is an inorganic gel layer and is characterized by being hydrophilic, by the absence of ablative absorption of said laser radiation, by being not ablated by said ablative absorption of said second layer, and by being not soluble in water.

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

• (a) an ink-accepting surface layer characterized by the absence of ablative absorption of said laser radiation;
• (b) a second layer underlying the surface layer, said second layer comprising one or more polymers and being characterized by the ablative absorption of said laser radiation;
• (c) a hydrophilic third layer underlying the second layer, said third layer characterized by the absence of ablative absorption of said laser radiation;
• and,
• (d) a substrate;
• wherein interposed between said second layer and said third layer is a primer layer, which primer layer is an inorganic gel layer and is characterized by being hydrophilic, by the absence of ablative absorption of said laser radiation, by being not ablated by said ablative absorption of said second layer, and by being not soluble in water.

A method of preparing an imaged wet lithographic printing plate, said method comprising the steps of:

• (a) providing a wet lithographic printing member comprising (i) an ink-accepting surface layer characterized by the absence of ablative absorption of laser radiation, (ii) a second layer underlying the surface layer, said second layer comprising one or more polymers and being characterized by the ablative absorption of said laser radiation, (iii) a hydrophilic substrate, and (iv) a primer layer interposed between said second layer and said substrate, said primer layer comprising an adhesion-promoting agent and being characterized by being hydrophilic, by the absence of ablative absorption of said laser radiation, by being not ablated by said ablative absorption of said second Savers and by being not soluble in water;
• (b) exposing said member to a desired imagewise exposure of said laser radiation to ablate no more than a part of the surface layer of said member and to ablate no more than a part of the second layer of said member to form a residual composite layer comprising non-ablated materials of said surface layer and non-ablated materials of said second layer, said residual composite layer being in contact with the primer layer of said member;
• and
• (c) cleaning the residual composite layer from said primer layer with water or a cleaning solution, wherein the ink-accepting surface layer of said member is not soluble in water or said cleaning solution.

A method of preparing an imaged wet lithographic printing plate, said method comprising the steps of:

• (a) providing a wet lithographic printing member comprising (i) an ink-accepting surface layer characterized by the absence of ablative absorption of said laser radiation, (i) a second layer underlying the surface layer, said second layer comprising one or more polymers and being characterized by the ablative absorption of said laser radiation (iii) a hydrophilic third layer underlying the second layer, said third layer characterized by the absence of ablative absorption of said laser radiation, (iv) a substrate, and (v) a primer layer interposed between said second layer and said third layer, said primer layer comprising an adhesion-promoting agent and being characterized by being hydrophilic, by the absence of ablative absorption of said laser radiation, by being not ablated be said ablative absorption of said second layer, and by being not soluble in water;
• (b) exposing said member to a desired imagewise exposure of laser radiation to ablate no more than a part of the surface layer of said member and to ablate no more than a part of the second layer of said member to form a residual composite layer comprising non-ablated materials of said surface layer and non-ablated materials of said second layer, said residual composite layer being in contact with the primer layer of said member;
• and
• (c) cleaning the residual composite layer from said primer layer with water or a cleaning solution, wherein the ink-accepting surface layer of said member is not soluble in water or said cleaning solution.