Method for laser engraving flexographic printing articles based on millable polyurethanes

Abstract

A flexographic printing sleeve or plate is made by a method that includes providing a millable polyurethane, crosslinking the millable polyurethane, and forming a relief by at least laser engraving the crosslinked millable polyurethane. For example, crosslinking may be accomplished by a peroxide-based process or by a vulcanization process using sulfur. A relief in one example is formed by extruding the millable polyurethane, thermally crosslinking the polyurethane after the extrusion step and laser engraving the crosslinked millable polyurethane. A printing article is formed into the shape of a flat printing plate or a continuous in-the-round printing sleeve.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims the benefit of priority and is a Divisional of U.S. Non-Provisional Application Patent Application Ser. No. 12 / 356,330, filed Jan. 20, 2009, by Kanga and entitled “Laser Engravable Flexographic Printing Articles Based on Millable Polyurethanes, and Method”. The Non-Provisional Patent Application Ser. No. 12 / 356,330 is a Continuation-in-Part (CIP) of U.S. Non-Provisional Patent Application Ser. No. 11 / 813,612, filed Jul. 10, 2007, by Kanga and entitled “Laser Engravable Flexographic Printing Article.” The Non-Provisional Patent Application Ser. No. 11 / 813,612 is a U.S. national stage application of International Application No. PCT / US07 / 72246, filed Jun. 27, 2007, by Kanga and entitled “Laser Engraveable Flexographic Printing Article.” The International Application No. PCT / US2007 / 072246 claims the benefit of priority of U.S. Provisional Patent Application No. 60 / 816,786, filed Jul. 27, 2006, by Kanga. This applicatio...

AI Technical Summary

Benefits of technology

This approach enables the creation of high-resolution, laser-engravable flexographic printing plates and sleeves with improved image fidelity and productivity, overcoming the limitations of existing TPU and CPU systems by providing clean engraving without melting artifacts and achieving better ink transfer and print quality.

Problems solved by technology

This is typically a very lengthy and involved process.

A problem associated with elastomeric elements that are reinforced both mechanically and photochemically is that laser engraving does not efficiently remove the elastomeric material to provide desired relief quality, and ultimately, printing quality.

However, the presence of the additive as particulate or other absorbing material tends to reduce the penetration of the ultraviolet radiation required to photo-chemically reinforce the element.

If the elastomeric layer is insufficiently crosslinked during photochemical reinforcement, the laser radiation cannot effectively remove the material and poor relief quality of the engraved area results.

Further, the debris resulting from laser engraving tends to be tacky and difficult to completely remove from the engraved element.

Additionally, if the element is not sufficiently photo-chemically reinforced, the required end-use properties as a printing plate are not properly achieved.

These problems tend to be exacerbated with increasing concentration of the additive that enhances engraving efficacy.

One problem associated with these non-polar TPEs is that they have limited sensitivity to laser engraving because of their hydrocarbon backbone nature.

However, most of the above polar TPEs on the market would not be effective either as laser engravable systems, or as printing plates because they are not crosslinked.

Hence, the difficulty in UV crosslinking these for flexo applications.

This does not allow UV crosslinking as a viable option to crosslink such elastomers.

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