Photosensitive element having reinforcing particles and method for preparing a printing form from the element

1. A photosensitive printing form element comprising:

a solid layer of a photosensitive composition comprising an elastomeric binder, a monomer, and a Norrish type II photoinitiator;

wherein the solid photosensitive layer contains reinforcing particles that provide the layer with a transmittance to actinic radiation of less than 20%, and wherein the reinforcing particles are selected from the group consisting of graphene, carbon nanotubes, and combinations thereof.

2. The photosensitive element of claim 1 wherein the reinforcing particles are in an amount from about 0.4 to 30% by weight, based on the weight of the photosensitive composition.

3. The photosensitive element of claim 1 wherein the photosensitive composition further comprises additional reinforcing particles selected from the group consisting of carbon black, graphite, furnace black, dark pigments, and dark toners.

4. The photosensitive element of claim 1 wherein the photosensitive composition further comprises additional reinforcing particles selected from the group consisting of TiO 2 , calcium carbonate, calcium silicate, barium sulfate, mica, zinc oxide, magnesium oxide, titanium oxide, aluminum, and alumina, materials having silica-oxygen (Si—O bond) functionality, materials having phosphorus-oxygen (P—O bond) functionality, pigment particles, toner particles, and combinations thereof.

5. The photosensitive element of claim 1 wherein the Norrish type II photoinitiator is selected from the group consisting of benzophenones, ketosulphones, thioxanthones, 1,2-diketones, anthraquinone, fluorenones, xanthones, acetophenone derivatives, benzoin ethers, benzyl ketals, phenylglyoxylates, mono-acylphosphine, and bis-acylphosphine.

6. The photosensitive element of claim 1 wherein the photoinitiator is a ketosulphone.

7. The photosensitive element of claim 1 further comprising a coinitiator with the photoinitiator.

8. The photosensitive element of claim 7 wherein the coinitiator is selected from the group consisting of thiols, aldehydes, secondary alcohols, primary amines, secondary amines, and tertiary amines.

9. The photosensitive element of claim 7 wherein the photoinitiator is a ketosulphone and the coinitiator is an amine.

10. The photosensitive element of claim 1 wherein the layer has a transmittance to actinic radiation of less than 5%.

11. The photosensitive element of claim 1 wherein the binder includes sufficient pendant alkyl groups of 1 to 6 carbon atoms for donating hydrogen upon reaction with the Norrish type II photoinitiator.

12. The photosensitive element of claim 1 wherein the layer has a thickness from 2 to 250 mils.

13. The photosensitive element of claim 1 wherein the photosensitive layer has a transmittance to actinic radiation of less than 15%.

14. The photosensitive element of claim 1 wherein the photosensitive layer has a transmittance to actinic radiation of less than 10%.

15. A method for preparing a printing form from a photosensitive printing form element comprising:

a) providing the photosensitive printing form element comprising a solid layer of a photosensitive composition comprising an elastomeric binder, a monomer, and a Norrish type II photoinitiator, wherein the solid photosensitive layer contains reinforcing particles that provide the layer with a transmittance to actinic radiation of less than 20%, and wherein the reinforcing particles are selected from the group consisting of graphene, carbon nanotubes, and combinations thereof;

b) exposing the photosensitive element to actinic radiation; and

c) treating the exposed photosensitive element to form a relief surface suitable for printing.

16. The method of claim 15 wherein the exposing step is an imagewise exposure through a mask to form polymerized portions and unpolymerized portions, and the treating step is selected from the group consisting of

(a) processing with at least one washout solution selected from the group consisting of solvent solution, aqueous solution, semi-aqueous solution, and water; and

(b) heating the element to a temperature sufficient to cause unpolymerized portions to melt, flow, or soften, and removing the unpolymerized portions.