Dual-wavelength positive-working radiation-sensitive elements

A radiation-sensitive composition comprising:

• a. at least one polyvinyl acetal comprising at least one acetal group, with at least one acetal group having a directly attached phenolic group and
• b. a radiation-sensitive substance that comprises at least one of:
• i. a quinonediazide group and
• ii. an onium salt,
• said composition further comprising a developability-enhancing substance.

A radiation-sensitive printing precursor comprising:

• a. a base, and
• b. a radiation-sensitive composition on a surface of the base, the composition comprising:
• iii. an acetal polymer substance comprising at least an acetal group with a directly attached phenolic group and
• iv. a radiation-sensitive substance that comprises at least one of:
• (1) a quinonediazide group and
• (2) an onium salt,
• the radiation-sensitive printing precursor further comprising an infrared light-to-heat converting substance.

A method for making a radiation-sensitive precursor, the method comprising the steps of coating on a surface of a base a layer of a radiation-sensitive composition and drying the layer, wherein the composition comprises:

• a. a polyvinyl acetal derived from polyvinyl alcohol by condensation with aldehydes and comprising at least an acetal group with a directly attached phenolic group and
• b. a radiation-sensitive substance that comprises at least one of:
• v. a quinonediazide group and
• vi. an onium salt,
• wherein the radiation-sensitive composition further comprises an infrared light-to-heat converting substance with a λmax within 10 nm of the wavelength of maximum output of the radiation source.

A method for making a lithographic master, the method comprising the steps of:

• a. providing a radiation-sensitive precursor, the precursor comprising
• vii. a lithographic base and
• viii. a coated and dried layer of a radiation-sensitive composition, the composition comprising
• (1) a polyvinyl acetal derived from polyvinyl alcohol by condensation with aldehydes and comprising at least an acetal group with a directly attached phenolic group and
• (2) a radiation-sensitive substance that comprises at least one of a quinonediazide group and an onium salt,
• b. imagewise irradiating areas of the layer with imaging radiation to render the layer more eluable in an aqueous alkaline solution in the areas irradiated and
• c. treating the resulting imaged precursor with alkaline aqueous solution to remove eluable parts of the radiation-sensitive coating, wherein the composition further comprises an infrared light-to-heat converting substance with a λmax within 10 nm of the wavelength of maximum output of the radiation source.