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.

What is claimed is: 
     
         1 . A method of making a flexographic printing article comprising:
 (a) providing a millable polyurethane;   (b) thermally crosslinking the millable polyurethane to provide a laser-engravable element; and   (c) forming a relief in the element by at least laser engraving the crosslinked millable polyurethane.   
     
     
         2 . A method according to  claim 1 , wherein crosslinking the millable polyurethane includes the step of crosslinking by a process selected from the group consisting of a peroxide-based process and a vulcanization process using sulfur. 
     
     
         3 . A method according to  claim 1 , further comprising the step of adding a binder selected from the group consisting of a polyester-based polyurethane processed as a millable polyurethane, and a polyether-based polyurethane processed as a millable polyurethane. 
     
     
         4 . A method according to  claim 1 , wherein the step of forming a relief in the element includes the step of engraving the element using laser radiation having a wavelength between approximately 830 nanometers and approximately 1100 nanometers. 
     
     
         5 . A method according to  claim 1 , wherein the step of forming a relief in the element includes the step of engraving the element using laser radiation having a wavelength between approximately 830 nanometers and approximately 10,600 nanometers. 
     
     
         6 . A method according to  claim 1 , wherein the step of forming a relief includes the step of extruding the millable polyurethane into an article selected from the group consisting of a flat printing plate and a continuous in-the-round printing sleeve. 
     
     
         7 . A method according to  claim 1 , further comprising the step of adding an additive for increasing laser absorptivity of the element, wherein the additive is selected from the group consisting of nanomaterials, mica, carbon black, kaolin clay, antimony tin oxide, and copper oxide. 
     
     
         8 . A method according to  claim 1 , further comprising the step of adding an additive for increasing heat dissipation in the element, wherein the additive is selected from the group consisting of metal-based nanoparticles, metal-oxide based nanoparticles, carbotherm boron nitride platelets, carbon black, and graphite. 
     
     
         9 . A method according to  claim 1 , further comprising the step of adding an additive for reducing the density of the element, wherein the additive is selected from the group consisting of microspheres, boroscilicate glass bubbles, spherical porous silica, crosslinked microspheres, and unexpanded microspheres containing liquid hydrocarbon. 
     
     
         10 . A method according to  claim 1 , further comprising the step of adding a burn-rate modifier for decreasing the pyrolysis temperature of the element, wherein the additive is selected from the group consisting of ammonium perchlorate, ammonium nitrate, potassium nitrate, iron oxide, copper oxide, copper chromate, chrome oxide, manganese oxide, ferrocene, aluminum, boron, magnesium powder, oxetane group energetic thermoplastic elastomers, and azide group energetic thermoplastic elastomers.