Laser-imageable flexographic printing precursors and methods of imaging
A laser-engravable composition comprises one or more elastomeric rubbers including at least 10 parts of one or more CLCB EPDM elastomeric rubbers, based on parts per hundred of the total weight of elastomeric rubbers (phr). The laser-engravable composition further comprises 2-30 phr of a near-infrared radiation absorber and either 1-80 phr of an inorganic, non-infrared radiation absorber filler, or a vulcanizing composition that comprises a mixture of at least two peroxides. One first peroxide has a t 90 value of 1-6 minutes as measured at 160° C., and a second peroxide has a t 90 value of 8-20 minutes as measured at 160° C. This laser-engravable composition can be used to form a laser-engravable layer on a compressible layer that is disposed on a substrate, and to form various flexographic printing precursors. The compressible layer can also be laser-engravable.
1. A flexographic printing precursor that is laser-engravable to provide a relief image, the flexographic printing precursor comprising a substrate, and having disposed over the substrate:
a compressible layer comprising microvoids or microspheres dispersed within an elastomeric rubber, and
a laser-engraveable layer disposed over the compressible layer, the laser-engraveable layer being prepared from a laser-engraveable composition comprising one or more elastomeric rubbers in an amount of at least 30 weight % and up to and including 80 weight %, based on the total laser-engraveable composition weight, the laser-engraveable composition comprising at least 10 parts and up to and including 100 parts of one or more controlled long chain branching ethylene-propylene-diene (CLCB EPDM) elastomeric rubbers, based on parts per hundred of the total weight of elastomeric rubbers (phr) in the laser-engraveable composition,
the laser-engraveable composition further comprising both of the following components a) and b), or only the following component b):
a) at least 2 phr and up to and including 30 phr of a near-infrared radiation absorber and at least 1 phr and up to and including 80 phr of an inorganic, non-infrared radiation absorber filler, wherein the weight ratio of the near-infrared radiation absorber to the inorganic, non-infrared radiation absorber filler is from 1:40 to 30:1, and
b) at least 2 phr and up to and including 30 phr of a near-infrared radiation absorber, and at least 3 phr and up to and including 20 phr of a vulcanizing composition that comprises a mixture of at least first and second peroxides,
wherein the first peroxide has a t 90 value of at least 1 minute and up to and including 6 minutes as measured at 160° C., and the second peroxide has a t 90 value of at least 8 minutes and up to and including 20 minutes as measured at 160° C., and
wherein the weight ratio of the near-infrared radiation absorber to the vulcanizing composition is from 1:10 to 10:1.
2. The flexographic printing precursor of claim 1 , wherein the compressible layer comprises microspheres, each microsphere comprising a thermoplastic polymeric outer shell.
3. The flexographic printing precursor of claim 1 , wherein the compressible layer comprises microspheres in an amount of at least 2 and up to and including 30 phr.
4. The flexographic printing precursor of claim 1 , wherein the microvoids or microspheres occupy at least 1% and up to and including 15% of the dry volume of the compressible layer.
5. The flexographic printing precursor of claim 1 , wherein the compressible layer is laser-engraveable.
6. The flexographic printing precursor of claim 1 , wherein the compressible layer comprises one or more controlled long chain branching ethylene-propylene-diene (CLCB EPDM) elastomeric rubbers.
7. The flexographic printing precursor of claim 1 , wherein the laser-engraveable layer is directly disposed on the compressible layer.
8. The flexographic printing precursor of claim 1 , wherein the compressible layer has a dry thickness of at least 50 μm and up to and including 4,000 μm.
9. The flexographic printing precursor of claim 1 , wherein the dry thickness ratio of the compressible layer to the laser-engraveable layer is from 1:80 to 80:1.
10. The flexographic printing precursor of claim 1 , wherein the laser-engraveable layer has a Δ torque (M Δ =M H −M L ) of at least 10 and up to and including 25.
11. The flexographic printing precursor of claim 1 , wherein the laser-engraveable composition comprises both components a) and b) and the weight ratio of the near-infrared radiation absorber to the inorganic, non-infrared radiation absorber filler in component a) is from 1:30 to 20:1.
12. The flexographic printing precursor of claim 1 , wherein the laser-engraveable composition comprises a conductive or non-conductive carbon black, graphene, graphite, carbon fibers, or carbon nanotubes as the near-infrared radiation absorber in an amount of at least 5 phr and up to and including 30 phr.
13. The flexographic printing precursor of claim 1 , wherein the substrate comprises one or more layers of a metal, fabric, or polymeric film, or a combination thereof.
14. The flexographic printing precursor of claim 1 , wherein the substrate comprises a fabric web disposed over a polyester support.
15. The flexographic printing precursor of claim 1 , wherein the laser-engraveable layer has a dry thickness of at least 50 μm and up to and including 4,000 μm.
16. The flexographic printing precursor of claim 1 , wherein the laser-engraveable layer further comprises carbon nanotubes, carbon fibers, or a conductive carbon black having a dibutyl phthalate (DBP) absorption value of less than 110 ml/100 g, wherein the carbon nanotubes, carbon fibers, or conductive carbon black is present in an amount of at least 3 phr and up to and including 30 phr.
17. The flexographic printing precursor of claim 1 , comprising a carbon black and wherein the weight ratio of the carbon black to the mixture of at least first and second peroxides is from 1:5 to 5:1.
18. The flexographic printing precursor of claim 1 that exhibits a t 90 value of at least 1 minute and up to and including 17 minutes at 160° C.
19. The flexographic printing precursor of claim 1 , comprising a conductive or non-conductive carbon black, carbon fibers, or carbon nanotubes as the infrared radiation absorber, and component b) but not component a).
20. The flexographic printing precursor of claim 1 , comprising a conductive or non-conductive carbon black, carbon fibers, or carbon nanotubes as the infrared radiation absorber, and both components a) and b),
wherein component a) comprises silica particles, calcium carbonate particles, or both silica and calcium carbonate particles as the non-infrared radiation absorber filler.
21. A method for providing a flexographic printing member, comprising:
imaging the laser-engraveable layer of the flexographic printing precursor of claim 1 using near-infrared radiation to provide a flexographic printing member with a relief image in the resulting laser-engraved layer.
22. The method of claim 21 , comprising imaging to provide a minimum dry relief image depth of at least 50 μm.