METHOD OF FLEXOGRAPHIC PATTERNING USING PHOTOCURABLE COMPOSITION
Photocured patterns can be provided using relief printing members such as flexographic printing plates. A photocurable composition has at least one N-oxyazinium salt photoinitiator, a photosensitizer for the N-oxyazinium salt, an N-oxyazinium salt efficiency amplifier, and one or more photocurable acrylates. After the photocurable composition is applied using the relief printing member, it is then exposed to suitable radiation to form a photocured pattern on the substrate.
1 . A method for providing a photocured pattern, comprising:
applying a photocurable composition to a substrate in a patternwise fashion using a relief printing member to form a pattern of the photocurable composition, and
exposing the pattern of the photocurable composition to photocuring radiation to form a photocured pattern on the substrate,
wherein the photocurable composition comprising an N-oxyazinium salt photoinitiator, a photosensitizer for the N-oxyazinium salt, an N-oxyazinium salt efficiency amplifier, and one or more photocurable acrylates.
2 . The method of claim 1 , wherein the relief printing member is a flexographic printing member.
3 . The method of claim 1 , wherein the photocurable composition further comprises an inert organic solvent.
4 . The method of claim 1 , wherein at least one of the one or more acrylates is a solvent for the photocurable composition.
5 . The method of claim 1 , wherein the exposing is carried out in the presence of oxygen.
6 . The method of claim 1 , wherein the exposing is carried out using radiation having a wavelength of at least 300 nm and up to and including 1250 nm.
7 . The method of claim 1 , wherein the photocurable composition comprises at least one photocurable acrylate acting as the solvent.
8 . The method of claim 1 wherein the N-oxyazinium salt efficiency amplifier is an organic phosphite.
9 . The method of claim 1 wherein the N-oxyazinium salt efficiency amplifier is an organic phosphite having the formula:
(R′O) 3 P
wherein the multiple R′ groups are the same or different alkyl groups wherein the multiple R groups are the same or different hydrogen atoms or alkyl groups, or two R′ groups can form a cyclic aliphatic ring or fused ring system, x is a number at least 2 and up to and including 20, and y is at least 1 and up to and including 20.
10 . The method of claim 1 , wherein the N-oxyazinium salt efficiency amplifier is a phosphite that is present in the photocurable composition at a molar ratio to the N-oxyazinium salt photoinitiator is at least 0.001:1 and up to and including 10:1.
11 . The method of claim 1 , wherein the N-oxyazinium salt photoinitiator is represented by either of the following Structures (I) and (II):
wherein A and B in Structure (I) independently represent a carbon, C—R 5 , C—R 6 or nitrogen, X is O, R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 are independently hydrogen, or alkyl or aryl groups, any of the A, B, and R groups where chemically feasible can be joined to form a ring, and Y is a charge balancing anion that can be a separate moiety or part of an A, B, or R,
wherein A in Structure (II) represents a carbon, C—R 5 , nitrogen, sulfur or oxygen atom with sufficient bonds and substituents to form a heteroaromatic ring, X is O, R 1 , R 2 , R 3 , R 1 , and R 5 are independently hydrogen, or alkyl or aryl groups, or any two R groups may form a ring, and Y is a charge balancing anion that can be a separate moiety or part of an R group.
12 . The method of claim 1 , wherein the N-oxyazinium salt photoinitiator has a cation represented by one of the following formulae:
wherein R 1 represents a substituted or unsubstituted alkyl group, substituted or unsubstituted aryl group, or an acyl group, wherein R 1 can also include a charge balancing anion, the R 2 groups independently represent hydrogen, or a substituted or unsubstituted alkyl, aryl, or heteroaryl group, X is a divalent linking group, and Z is an alkylidene group.
13 . The method of claim 1 , wherein the N-oxyazinium salt photoinitiator has a reduction potential less negative than −1.4 V and comprises an N-oxy group that is capable of releasing an oxy radical during irradiation of the photocurable composition.
14 . The method of claim 1 , wherein the photocurable composition comprises the N-oxyazinium salt photoinitiator in an amount of at least 6×10 −7 and up to and including 6×10 −2 moles per gram of one or more photocurable acrylates.
15 . The method of claim 1 , wherein the photosensitizer is present in the photocurable composition in an amount of at least 5×10 −7 and up to and including 1×10 −4 moles per gram of one or more photocurable acrylates.
16 . The method of claim 1 , wherein the photosensitizer for the N-oxyazinium salt photoinitiator has a triplet energy of at least 20 kcal/mole of N-oxyazinium salt.
17 . The method of claim 1 , wherein the one or more photocurable acrylates comprises an acrylate that comprises the photosensitizer for the N-oxyazinium salt photoinitiator.