Method and apparatus for applying surface treatments to photosensitive printing elements during thermal development
View Patent ↗The present invention is directed to a method and an apparatus for applying a surface treatment composition to a photosensitive printing element during thermal processing. A photosensitive printing element is contacted with a web of absorbent material that is capable of absorbing material that is melted or softened from an imaged and exposed surface of a photosensitive printing element. The web of absorbent material is coated with a surface treatment composition to transfer the surface treatment composition from the web of absorbent material to the imaged and exposed surface of the photosensitive printing element. Applying the surface treatment composition during thermal processing provides for more complete and more uniform coverage of the surface treatment composition on the photosensitive printing element.
1. A method of applying a surface treating composition to an imaged and exposed surface of a photosensitive printing element during thermal processing, the method comprising the steps of:
supporting the photosensitive printing element on a supporting means;
melting or softening non-crosslinked photopolymer on the imaged and exposed surface of the photosensitive printing element;
causing contact between the imaged and exposed surface of the photosensitive printing element and a web of absorbent material that is supported by at least a portion of at least one roll at the point of contact and is capable of absorbing non-crosslinked photopolymer that is melted or softened from the imaged and exposed surface of the photosensitive printing element wherein the web of absorbent material is coated with a surface treating composition that is transferable from the web of absorbent material to the imaged and exposed surface of the photosensitive printing element; and
maintaining contact between the web of absorbent material on the at least one roll and the imaged and exposed surface of the photosensitive printing element;
wherein the non-crosslinked photopolymer on the imaged and exposed surface of the photosensitive printing element is softened by heating the at least one roll that supports the web at the point of contact between the web and the imaged and exposed surface of the photosensitive printing element, wherein the at least one roll is heated to and operated at a temperature of between about 150 and about 250° C.;
wherein when the web of absorbent material contacts at least a portion of the imaged and exposed surface of the photosensitive printing element, the web of absorbent material absorbs the melted or softened non-crosslinked photopolymer from the imaged and exposed surface of the photosensitive printing element and the surface treating composition is transferred from the web of absorbent material to at least the portion of the imaged and exposed surface of the photosensitive printing element.
2. The method according to claim 1 , wherein the web of absorbent material is continuously supplied to at least one roll from a supply roll of the web of absorbent material.
3. The method according to claim 2 , further comprising the step of rewinding the web of absorbent material that contains melted or softened non-crosslinked photopolymer that is removed from the imaged and exposed surface of the photosensitive printing element onto a take-up roller.
4. The method according to claim 2 , wherein the photosensitive printing element is supported on a conveyor comprising a continuous loop supported by at least a first roller and a second roller.
5. The method according to claim 4 , wherein at least the first roller and the second roller rotate in a direction towards the at least one roll to move the photosensitive printing element on the continuous loop towards the at least one roll.
6. The method according to claim 4 , wherein the photosensitive printing element is held in place on the continuous loop of the conveyor by a clamp or vacuum.
7. The method according to claim 1 , wherein the photosensitive printing element is substantially planar.
8. The method according to claim 1 , wherein the photosensitive printing element is a cylindrical printing sleeve and the cylindrical printing sleeve is mounted on a sleeve mandrel.
9. The method according to claim 8 , wherein the sleeve mandrel with the photosensitive printing element mounted thereon rotates towards the at least one roll.
10. The method according to claim 1 , wherein the web of absorbent material is selected from the group consisting of paper, woven fabrics, and non-woven fabrics.
11. The method according to claim 1 , wherein the surface treating composition is selected from the group consisting of silicone emulsions, liquid polyethers, and desensitizing gums.
12. The method according to claim 1 , wherein the web of absorbent material is pre-coated with the surface treatment composition.
13. The method according to claim 1 , wherein the surface treatment composition is coated onto the web of absorbent material before the web of absorbent material is supplied to at least one roll.
14. The method according to claim 13 , comprising the step of applying the surface treatment composition to the web of absorbent material using an applicator.
15. The method according to claim 14 , wherein the surface treatment composition is supplied to the applicator from a reservoir that contains the surface treatment composition.
16. The method according to claim 1 , further composing the step of applying heat to the at least one layer of photosensitive material by positioning a heater adjacent to a point where the web of absorbent material contacts at least the portion of the imaged and exposed surface of the photosensitive printing element.