Flexographic printing precursors and methods of making

Abstract

A mixture of a high molecular weight EPDM rubber with a low molecular weight (liquid) EPDM rubber provides a highly useful laser-ablatable flexographic printing plate precursor formulation. This formulation is sensitive to infrared radiation by the incorporation of an IR absorbing compound such as a carbon black. The inclusion of the liquid EPDM rubber avoids the need for plasticizers such as process oils during manufacturing, and provides improved image sensitivity, print quality, and run length. Both flexographic printing plates and printing sleeves can be made using the mixture of EPDM rubbers.

1 . An infrared radiation ablatable flexographic printing precursor that comprises an infrared radiation ablatable layer comprising a mixture of a high molecular weight ethylene-propylene-diene terpolymer (EPDM) rubber and a low molecular weight EPDM rubber. 
     
     
         2 . The precursor of  claim 1  wherein the weight ratio of the high molecular weight EPDM to the low molecular weight EPDM rubber is from about 2:1 to about 10:1. 
     
     
         3 . The precursor of  claim 1  wherein the weight ratio of the high molecular weight EPDM to the low molecular weight EPDM rubber is from about 3:1 to about 5:1. 
     
     
         4 . The precursor of  claim 1  wherein the molecular weight of the high molecular weight EPDM is from about 200,000 to about 800,000, and the molecular weight of the low molecular weight EPDM is from about 2,000 to about 10,000. 
     
     
         5 . The precursor of  claim 1  wherein the molecular weight of the high molecular weight EPDM is from about 250,000 to about 500,000, and the molecular weight of the low molecular weight EPDM is from about 2,000 to about 8,000. 
     
     
         6 . The precursor of  claim 1  wherein the infrared radiation ablatable layer further comprises a carbon black. 
     
     
         7 . The precursor of  claim 1  wherein the infrared radiation ablatable layer further comprises a conductive carbon black. 
     
     
         8 . The precursor of  claim 1  wherein the infrared radiation ablatable layer further comprises a conductive carbon black having a dibutyl phthalate (DBP) absorption of less than 110. 
     
     
         9 . The precursor of  claim 1  wherein the infrared radiation ablatable layer further comprises a non-conductive carbon black. 
     
     
         10 . An infrared radiation ablatable flexographic printing precursor comprises an infrared radiation ablatable layer comprising from about 1 to about 20 weight % of a conductive carbon black having a dibutyl phthalate (DBP) adsorption of less than 110, and a mixture of a high molecular weight ethylene-propylene-diene terpolymer (EPDM) rubber and a low molecular weight EPDM rubber, wherein the weight ratio of the high molecular weight EPDM to the low molecular weight EPDM rubber is from about 3:1 to about 5:1. 
     
     
         11 . The precursor of  claim 10  wherein the infrared radiation ablatable layer comprises from about 2 to about 10 weight % of the conductive carbon black. 
     
     
         12 . The precursor of  claim 1  wherein the infrared radiation ablatable layer further comprises a vulcanizer. 
     
     
         13 . The precursor of  claim 12  wherein the infrared radiation ablatable layer further comprises sulfur or a peroxide as a vulcanizer and an azo crosslinking agent, or a mixture of sulfur and a peroxide, or a mixture of sulfur, an azo crosslinking agent, and a peroxide. 
     
     
         14 . The precursor of  claim 1  further comprising a polyester support upon which the infrared radiation ablatable layer is disposed. 
     
     
         15 . The precursor of  claim 1  further comprising a fabric support upon which the infrared radiation ablatable layer is disposed. 
     
     
         16 . The precursor of  claim 15  wherein the fabric support is disposed on a polyester support. 
     
     
         17 . An infrared radiation ablatable flexographic printing precursor comprises an infrared radiation ablatable layer comprising one or more inorganic fillers, a carbon black, and a mixture of a high molecular weight ethylene-propylene-diene terpolymer (EPDM) rubber and a low molecular weight EPDM rubber, wherein the weight ratio of the high molecular weight EPDM to the low molecular weight EPDM rubber is from about 2:1 to about 10:1. 
     
     
         18 . The precursor of  claim 17  wherein the infrared radiation ablatable layer further comprises one or more inorganic fillers that are chosen from silica, calcium carbonate, barium sulfate, kaolin, bentonite, zinc oxide, mica, and titanium dioxide. 
     
     
         19 . An infrared radiation ablatable flexographic printing precursor comprises an infrared radiation ablatable layer comprising:
 from about 10 to about 35 weight % of one or more inorganic fillers and from about 1 to about 20 weight % of a carbon black, wherein the weight ratio of the carbon black to the inorganic filler(s) is from about 1:50 to about 1:1.5, and a mixture of a high molecular weight ethylene-propylene-diene terpolymer (EPDM) rubber and a low molecular weight EPDM rubber, wherein the weight ratio of the high molecular weight EPDM to the low molecular weight EPDM rubber is from about 2:1 to about 10:1.   
     
     
         20 .- 26 . (canceled) 
     
     
         27 . A method of providing flexographic printing plate or sleeve comprising:
 imaging the flexographic printing precursor of  claim 1  using infrared radiation to provide a relief image in the infrared radiation ablatable layer.   
     
     
         28 . The method of  claim 27  wherein imaging is carried out using a laser at a power of at least 20 J/cm 2 . 
     
     
         29 . The method of  claim 27  further comprising removal of debris after imaging. 
     
     
         30 . The method of  claim 29  wherein debris is removed by vacuum, compressed air, brushes, rinsing with water, ultrasound, or any combination of these. 
     
     
         31 . The method of  claim 27  wherein imaging is carried out using a high power laser ablating imager. 
     
     
         32 . The method of  claim 27  wherein imaging is carried out at the same or different depths relative to the surface of the infrared radiation ablatable layer using two or more laser diodes each emitting radiation in one or more wavelengths. 
     
     
         33 . A system for providing a flexographic printing plate or printing sleeve, comprising:
 the flexographic printing precursor of  claim 1 ,   a group of one or more sources of imaging infrared radiation, each source capable of emitting infrared radiation,   a set of optical elements coupled to the sources of imaging infrared radiation to direct imaging infrared radiation from the sources onto the flexographic printing precursor.   
     
     
         34 . The system of  claim 33  wherein the sources of imaging infrared radiation are laser diodes, multi-emitter laser diodes, laser bars, laser stacks, fiber lasers, or a combination thereof. 
     
     
         35 . An infrared radiation ablatable flexographic printing precursor comprises an infrared radiation ablatable layer comprising a carbon black, one or more inorganic fillers, and one or more elastomers, wherein the weight ratio of the carbon black to the inorganic filler(s) is from about 1:50 to about 1:1.5. 
     
     
         36 . The precursor of  claim 35  wherein the elastomers includes a mixture of a high molecular weight ethylene-propylene-diene terpolymer (EPDM) rubber and a low molecular weight EPDM rubber. 
     
     
         37 . The precursor of  claim 35  wherein the weight ratio of the carbon black to the inorganic filler(s) is from about 1:20 to about 1:5