Photosensitive element having reinforcing particles and method for preparing a printing form from the element
View Patent ↗The invention provides a photosensitive element and a method for preparing a printing form from the element. The photosensitive element includes a layer of a photosensitive composition containing a binder, a monomer, and a Norrish type II photoinitiator, wherein the photosensitive layer has a transmittance to actinic radiation of less than 20% and contains reinforcing particles of graphene and/or carbon nanotubes.
1. A method for preparing a printing form from a photosensitive element comprising:
a) providing the photosensitive element comprising a layer of a photosensitive composition comprising an elastomeric binder, a monomer, and a Norrish type II photoinitiator, wherein the photosensitive layer contains reinforcing particles that provide the layer with a transmittance to actinic radiation of less than 20%, wherein the reinforcing particles are selected from the group consisting of graphene, carbon nanotubes, and combinations thereof, and wherein the elastomeric binder includes pendant alkyl groups of 1 to 6 carbon atoms;
b) exposing the photosensitive element to actinic radiation; and
c) treating the exposed photosensitive element to form a relief surface suitable for printing,
wherein the exposing step is an overall exposure to cure the layer, and the treating step engraves the photosensitive element with laser radiation to selectively remove portions of the cured layer.
2. The method 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 method 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 method 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 method 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, benzl ketals, phenylglyoxylates, mono-acylphosphine, and bis-acylphosphine.
6. The method of claim 1 wherein the photoinitiator is a ketosulphone.
7. The method of claim 1 wherein the photosensitive composition further comprises a coinitiator with the photoinitiator.
8. The method 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 method of claim 7 wherein the photoinitiator is a ketosulphone and the coinitiator is an amine.
10. The method of claim 1 wherein the layer has a transmittance to actinic radiation of less than 5%.
11. The method of claim 1 wherein the binder includes pendant alkyl groups of 1 to 6 carbon atoms for donating hydrogen upon reaction with the Norrish type II photoinitiator.
12. The method of claim 1 wherein the layer has a thickness from 2 to 250 mils.
13. The method of claim 1 wherein the photosensitive layer has a transmittance to actinic radiation of less than 15%.
14. The method of claim 1 wherein the photosensitive layer has a transmittance to actinic radiation of less than 10%.