Highly reflective substrates for the digital processing of photopolymer printing plates
View Patent ↗An improved digitally imageable relief printing element having an increased direct-cure imaging speed upon exposure to lasers and other digital sources of actinic radiation. The printing elements of the invention comprise a reflective layer beneath a photosensitive resin layer so that instead of being absorbed by the reflective layer, photons of actinic radiation are reflected back up into the photosensitive layer, thereby speeding up the curing rate of the printing element.
1. A method of direct curing a relief printing element with a source of actinic radiation, comprising the steps of:
a. providing a photocurable relief printing element comprising:
i. a reflective layer which reflective layer has a reflectivity of at least 40 percent at the wavelength(s) emitted by the source of actinic radiation;
ii. at least one photocurable layer on top of said reflective layer, and
iii. optionally, a removable coversheet on top of said at least one photocurable layer; and
b. exposing said photocurable relief printing element to the source of actinic radiation to directly cure the photocurable relief printing element;
where the source of actinic radiation comprises a laser such that at least 40 percent of the actinic radiation hitting the reflective layer is reflected back into the photocurable layer, thereby curing the photocurable layer.
2. A method according to claim 1 , wherein the photocurable layer comprises a photopolymer and a photoinitiator.
3. A method according to claim 1 , wherein the reflective layer has a reflectivity of at least 60 percent at the wavelength emitted by the actinic source and at least 60 percent of the actinic radiation hitting the reflective layer is reflected back into the photocurable layer thereby curing the photocurable layer.
4. A method according to claim 1 , wherein the source of actinic radiation is a laser selected from the group consisting of ion gas lasers, solid state lasers, semiconductor diode lasers, molecular gas lasers, and combinations of the foregoing.
5. A method according to claim 1 , wherein the source of actinic radiation has a wavelength between about 250 nanometers and about 500 nanometers.
6. A method according to claim 1 , wherein the source of actinic radiation has a wavelength between about 320 nanometers and about 420 nanometers.
7. A method according to claim 1 , wherein the reflective layer is selected from the group consisting of a reflective support and reflective coating on a support.
8. A method according to claim 7 , wherein the reflective layer is a reflective support selected from the group consisting of aluminum, zinc, tin and mixtures of the foregoing.
9. A method according to claim 7 , wherein the reflective layer is a reflective coating on a support and the reflective coating is selected from the group consisting of aluminum, tin, zinc, silver, and mixtures of the foregoing, deposited onto the support by means of vacuum deposition.
10. A method according to claim 9 , wherein the support is selected from the group consisting of metal and plastic supports.
11. A method according to claim 1 , wherein said printing element is selected from the group consisting of flexographic printing elemonts and offset printing elements.