Method and apparatus for exposure of flexographic printing plates using light emitting diode (LED) radiation sources

A process for exposing a printing plate comprising a photosensitive polymer activated by exposure to radiation, the printing plate having a non-printing back side and a printing front side with a mask for defining an image to be printed, the method comprising:

• controlling one or more radiation sources collectively arranged to expose the front side and the back side of the printing plate to radiation, the front side radiation source and the back side radiation source each comprising a respective set of LED point sources each configured to emit UV light, the plurality of LED point sources in at least one of the front side set or back side set controllable in a plurality of LED point source subsets smaller than an entirety of the collective irradiation field corresponding to the respective set, wherein the plurality of LED point source subsets are controllable together, individually controllable, or controllable in one or more groups;
• measuring radiation output from the plurality of subsets of LED point sources with a sensor configured to measure incident radiation at a predetermined distance from each of the plurality of subsets of LED sources, and varying intensity of at least one subset of LED sources by a factor relative to another subset of LED sources, based upon the incident radiation measured by the sensor, to give the radiation emitted by the respective set an intended degree of homogeneity.

A system for preparing a printing plate, the printing plate comprising a photosensitive polymer activated by exposure to actinic radiation and having a non-printing back side and a printing front side with a mask for defining an image to be printed, the printing plate having a lateral width and a lateral length and disposed in a stationary position, the system comprising:

• an apparatus comprising:
• a plurality of radiation sources configured to emit the actinic radiation toward the printing plate with the printing plate in the stationary position, each of the radiation sources comprises a light emitting diode (LED) configured to emit actinic ultraviolet (UV) radiation, the plurality of radiation sources including:
• a set of front LED sources positioned to emit radiation toward the front side of the plate, the set of front LED sources together defining a collective irradiation field covering an area at least coextensive with at least one of the lateral length and lateral width of the plate;
• a set of back LED sources positioned to emit radiation toward the back side of the plate, the set of back LED sources together defining a collective irradiation field covering an area at least coextensive with at least one of the lateral length and lateral width of the plate;
• at least one controller connected to the plurality of radiation sources and configured to activate the plurality of radiation sources to emit the actinic radiation in a predetermined pattern, the plurality of radiation sources in at least one of the set of back LED sources or the set of front LED sources controllable in subsets smaller than an entirety of the collective irradiation field corresponding to the respective set, such that the plurality of LED point source subsets are controllable together, individually controllable, or controllable in one or more groups, and wherein at least a first LED point source subset is configured to be controlled by the at least one controller at a first intensity differing by a factor relative to a second intensity of a second LED point source subset to give the radiation emitted by the respective set an intended degree of homogeneity;
• and
• a holder for disposing the printing plate in the stationary position, the holder comprising a material that is transmissive of the actinic radiation and that defines a horizontal surface relative to a ground on which the apparatus is disposed.