Curing of flexo printing elements using UV LED systems

A method of manufacturing a flexographic printing plate comprising the steps of:

• a) optionally, securing a negative to a first glass platen, wherein the negative has opaque areas corresponding to a reverse of a desired relief image;
• b) covering the negative or the first glass platen with a transparent cover sheet;
• c) casting at least one layer of liquid photopolymer resin on the transparent cover sheet;
• d) covering the at least one layer of liquid photopolymer resin with a backing sheet;
• e) positioning a second glass platen above the backing sheet;
• f) exposing the at least one layer of liquid photopolymer resin to actinic radiation to selectively crosslink and cure the at least one layer of liquid photopolymer resin and form the desired relief image therein;
• wherein the step of exposing the at least one layer of liquid photopolymer resin to actinic radiation comprises:
• (i) selectively exposing the at least one layer of liquid photopolymer resin to actinic radiation from a first source of actinic radiation positioned below the first glass platen to form the desired relief image in the at least one layer of liquid photopolymer resin;
• and
• (ii) exposing the at least one layer of liquid photopolymer resin to actinic radiation from a second source of actinic radiation positioned above the second glass platen to cure a portion of the least one layer of liquid photopolymer resin to create a cured floor in the least one layer of liquid photopolymer resin;
• and
• g) washing away uncured portions of the at least one layer of liquid photopolymer resin to reveal the desired relief image;
• wherein at least one of the first source of actinic radiation and the second source of actinic radiation comprises a plurality of UV LED light tubes;
• and
• wherein each of the UV LED light tubes has an output intensity of about 10 to about 40 mW/cm2 when arranged at a distance of about 1 to about 2 inches from the surface of the glass platen.