Method of making relief image printing elements

1. A method of flood exposing a photocurable printing blank to actinic radiation from a UV LED light source, the photocurable printing blank comprising a support, at least one photocurable layer upon the support, wherein the at least one photocurable layer is capable of being selectively crosslinked and cured upon exposure to actinic radiation and wherein the at least one photocurable layer comprises (a) at least one elastomeric binder, (b) at least one ethylenically unsaturated monomer, (c) a photoinitiator having a favorable absorption profile in a wavelength region used for exposing the at least one photocurable layer to actinic radiation, wherein the wavelength region is between 300 and 475 nm, and a photographic negative or digitally imaged mask layer disposed on the at least one photocurable layer; the method comprising the steps of:

a) positioning the photocurable printing blank in an exposure unit, wherein the exposure unit comprises one or more high intensity UV LED light sources, wherein the one or more high intensity UV LED light sources have an intensity of at least 200 mW/cm 2 ;

b) modulating intensity of the one or more high intensity UV LED light sources to a lower intensity, wherein the modulated intensity is less than 100 mW/cm 2 at the surface of the photocurable printing blank; and

c) flood exposing the photocurable printing blank through the photographic negative or the digitally imaged mask layer to actinic radiation from the one or more modulated UV LED light sources;

wherein portions of the at least one photocurable layer not covered by the photographic negative or digitally imaged mask layer crosslink and cure to create a relief image therein;

wherein the one or more high intensity UV LED light sources are modulated by mounting a light bar comprising a plurality of high intensity UV LEDs within a series of reflective mirrors;

wherein the light bar is mounted at a top of a mirrored box and wherein the mirrored box and the photocurable printing blank do not move relative to each other during the flood exposure step.

2. The method according to claim 1 , wherein the one or more high intensity UV LED light sources each have an output intensity of at least 500 mW/cm 2 .

3. The method according to claim 1 , wherein the modulated intensity is less than 20 mW/cm 2 at the surface of the photocurable printing blank.

4. A method of flood exposing a photocurable printing blank to actinic radiation from a UV LED light source, the photocurable printing blank comprising a support, at least one photocurable layer upon the support, wherein the at least one photocurable layer is capable of being selectively crosslinked and cured upon exposure to actinic radiation and wherein the at least one photocurable layer comprises (a) at least one elastomeric binder, (b) at least one ethylenically unsaturated monomer, (c) a photoinitiator having a favorable absorption profile in a wavelength region used for exposing the at least one photocurable layer to actinic radiation, wherein the wavelength region is between 300 and 475 nm, and a photographic negative or digitally imaged mask layer disposed on the at least one photocurable layer; the method comprising the steps of:

a) positioning the photocurable printing blank in an exposure unit, wherein the exposure unit comprises one or more high intensity UV LED light sources, wherein the one or more high intensity UV LED light sources have an intensity of at least 200 mW/cm 2 ;

b) modulating intensity of the one or more high intensity UV LED light sources to a lower intensity, wherein the modulated intensity is less than 100 mW/cm 2 at the surface of the photocurable printing blank; and

c) flood exposing the photocurable printing blank through the photographic negative or the digitally imaged mask layer to actinic radiation from the one or more modulated UV LED light sources;

wherein portions of the at least one photocurable layer not covered by the photographic negative or digitally imaged mask layer crosslink and cure to create a relief image therein;

wherein the one or more high intensity UV LED light sources are modulated by arranging the one or more high intensity UV LED light sources at a distance at a distance of from 2 inches to 20 inches from the surface of the photocurable printing blank.

5. The method according to claim 1 , wherein the photocurable printing blank is exposed to a static exposure of actinic radiation from the UV LED light sources mounted in the light bar through the mirrored box.

6. The method according to claim 1 , wherein the series of reflective mirrors direct light equally down onto an entirety of the surface of the photocurable printing blanks.

7. The method according to claim 1 , wherein the mirrors in the mirrored box are angled, wherein a shape of relief printing dots is controlled.

8. The method according to claim 7 , wherein the angle of the mirrors in the mirrored box is between 60 degrees and 110 degrees, as measured from vertical.

9. The method according to claim 8 , wherein the angle of the mirrors in the mirrored box is between 70 degrees and 90 degrees, as measured from vertical.

10. The method according to claim 1 , wherein the mirrored box is operatively connected to a controller, wherein the controller controls the angle of the mirrors in the mirrored box.

11. The method according to claim 4 , wherein the one or more high intensity UV LED light sources are arranged at a distance of from 2 inches to 12 inches from the surface of the photocurable printing blank.

12. The method according to claim 4 , wherein the one or more high intensity UV LED light sources each have an output intensity of at least 500 mW/cm 2 .

13. The method according to claim 4 , wherein the modulated intensity is less than 20 mW/cm 2 at the surface of the photocurable printing blank.