Laser Imaged Printing Plates
Laser-imageable flexographic printing plates and a method of making same are disclosed. A thin masking layer comprising insoluble particles is laminated to a photopolymer layer. The insoluble particles in the masking layer roughen the photopolymer surface when the masking layer is laminated to the photopolymer surface. The masking layer is selectively ablated from the photopolymer using a laser operating at a selected wavelength to create an in situ negative. The resulting negative can be subjected to typical UV flood exposure and development.
1 . A laser imagable printing element comprising:
a) a substrate;
b) at least one photpolymer layer upon the substrate which cures upon exposure to UV light; and
c) a masking layer upon the surface of the photopolymer layer which is furthest from the substrate, which masking layer comprises (i) a polymer matrix, (ii) material which strongly absorbs both UV and IR light, and (iii) particles with a size in the range of 0.25 microns to 35 microns.
2 . The element of claim 1 wherein said substrate is translucent to UV light.
3 . The element of claim I wherein said at least one photopolymer layer comprises a binder, a monomer and a photoinitiator.
4 . The element of claim 3 wherein said binder comprises a material selected from the group consisting of polyurethane, acrylonitrile rubber, a diblock or triblock copolymer made from styrene-isoprene or styrene-butadiene, and combinations thereof.
5 . The element of claim 1 wherein the polymer matrix comprises a polyamide.
6 . The element of claim 1 wherein the polymer matrix comprises a cellulosic polymer.
7 . The element of claim 6 wherein the polymer matrix comprises hydroxypropyl cellulose.
8 . The element of claim 1 wherein the particles are insoluble in the polymer matrix.
9 . The element of claim 1 wherein the particles comprise a material selected from the group consisting of polyamide and polyacrylic.
10 . A method of preparing a laser imagable printing element comprising:
a. providing a substrate;
b. coating at least one photpolymer layer upon the substrate which at least one photpolymer layer cures upon exposure to UV light; and
c. laminating a masking layer upon the surface of the photopolymer layer which is furthest from the substrate, which masking layer comprises (i) a polymer matrix, (ii) material which strongly absorbs both UV and IR light, and (iii) particles with a size in the range of 0.25 microns to 35 microns.
11 . The method of claim 10 wherein said substrate is translucent to UV light.
12 . The method of claim 10 wherein said at least one photopolymer layer comprises a binder, a monomer and a photoinitiator.
13 . The element of claim 12 wherein said binder comprises a material selected from the group consisting of polyurethane, acrylonitrile rubber, a diblock or triblock copolymer made from styrene-isoprene or styrene-butadiene, and combinations thereof.
14 . The method of claim 10 wherein the polymer matrix comprises a polyamide.
15 . The method of claim 10 wherein the polymer matrix comprises a cellulosic polymer.
16 . The method of claim 15 wherein the polymer matrix comprises hydroxypropyl cellulose.
17 . The method of claim 10 wherein after step (c) the masking layer of the printing element is selectively ablated by a laser driven by a digital file containing the desired image stored in a digital manner.
18 . The method according to claim 17 wherein after ablation the printing element is exposed to UV light which cures the photopolymer layer in areas exposed by ablation but leaves the unablated areas uncured.
19 . The method according to claim 18 wherein the uncured areas of the photpolymer are developed away creating the relief image.
20 . The element of claim 10 wherein the particles are insoluble in the polymer matrix.
21 . The element of claim 10 wherein the particles comprise a material selected from the group consisting of polyamide and polyacrylic.