Flexographic printing plate precursor, imaging assembly and use

Abstract

SOLUTION: A relief-forming precursor includes a substrate and a relief-forming layer having: a polymer; at least one photopolymerizable monomer; a photopolymerization initiator; and a low surface energy monomer. A relief-forming assembly includes a relief-forming precursor having a low surface energy monomer and a mask element that is in complete optical contact with the relief-forming surface. A method of making a relief image includes: exposing the relief-forming layer to curing UV radiation through the mask element to form an imaged relief-forming layer with polymerized regions and non-polymerized regions; removing the mask element from the imaged relief-forming layer; and developing the imaged relief-forming layer by removing the non-polymerized regions, thereby forming a relief image. A relief image layer has an elastomer and copolymer that includes at least one photopolymerized monomer and a low surface energy monomer that has a silicone moiety with a relief surface having the silicone moiety.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present disclosure relates to flexographic printing plate precursors, imaging assemblies, and methods of making and using the same. More particularly, the disclosure relates to a photosensitive layer of a relief-forming precursor configured to have reduced release forces so that the resulting relief image has reduced surface energy. [Background technology]

[0002] [Description of Related Art]

[0003] Traditionally, in flexographic printing plate precursors, a mask has been combined with a photosensitive material. However, it can be difficult to remove the mask from the photosensitive relief-forming layer without damaging the mask or the photosensitive relief-forming layer. In many cases, the photosensitive relief-forming layer can be damaged during the mask removal process. A damaged photosensitive relief-forming layer is not useful for flexographic printing plates because it has artifacts caused by the damage. As a result, research continues to develop techniques to improve the ability to remove the mask from the photosensitive relief-forming layer without causing damage.

[0003] Photosensitive relief-forming materials having a relief-forming substance or photosensitive layer are known in the art. U.S. Patent Application Publication No. 2005 / 0227182 (Ali et al., hereinafter referred to as U.S. '182) describes significant advances in the art and materials useful for producing flexographic relief images. U.S. '182 describes suitable mask element precursors, photosensitive materials for the relief-forming layer, and processes and apparatus for forming mask elements from the mask precursor and for forming a final relief image from the photosensitive relief-forming precursor material.

[0004] Typically, the mask element is placed in intimate contact with the photosensitive relief-forming precursor material using a laminator apparatus or vacuum drawdown, or both, and then exposed overall to actinic radiation (e.g., ultraviolet radiation) to harden the photosensitive composition in the relief-forming precursor material in the unmasked areas, thereby forming a negative image of the mask element in the photosensitive relief-forming precursor. The mask element may then be removed, and the unhardened areas on the relief-forming material may be removed by a development process. After drying, the resulting imaged relief-forming precursor has a relief image that can be used for flexographic or letterpress printing operations.

[0005] U.S. Patent No. 7,799,504 (Zwadlo et al.) describes improvements to mask element precursors. U.S. Patent No. 8,198,012 (Zwadlo et al.), U.S. Patent No. 8,945,813 (Kidnie), and U.S. Patent No. 9,250,527 (Kidnie) describe other useful mask element precursors and processes for using them. U.S. Patent Application Publication No. 2019 / 0258154 (Kidnie) describes improvements to photosensitive materials. U.S. Patent No. 8,530,142 (Zwadlo) describes a photopolymer plate precursor that includes a low surface energy release layer over the photosensitive layer to facilitate release. U.S. Patent No. 10,207,491 (Ali et al.) describes a method for making a flexographic printing plate, including laminating a mask image to a flexographic printing plate precursor, exposing to ultraviolet light to form a relief pattern, and peeling the mask from the photosensitive layer. U.S. Pat. No. 9,114,601 (Baldwin et al.) describes a flexographic printing plate precursor consisting of two photosensitive layers, with low surface energy silicone monomers only in the lower photosensitive layer in contact with the backing layer and no silicone monomers in the upper photosensitive layer in contact with the mask layer and which is taught to have a higher surface energy (e.g., 5 dynes / cm or greater) than the lower layer.

[0006] While the mask element precursors described in the above publications have found great value in the flexographic printing industry, it is desirable to further improve the process for efficiently making mask elements, as well as improve interlayer adhesion during imaging when using lamination processes, adhesion between the mask element and the relief-forming precursor, and better drawdown of the mask element onto the relief-forming precursor when using vacuum drawdown.

[0007] Therefore, there is a need for techniques that can be used to provide photosensitive layers with reduced surface energy and peel forces upon mask removal. Summary of the Invention

[0008] In some embodiments, the relief-forming precursor may comprise a substrate and a relief-forming layer. The relief-forming layer may be provided with a bottom surface facing the substrate and a relief-forming surface facing away from the substrate. In some aspects, the relief-forming layer may comprise a polymer, such as an elastomer, at least one photopolymerizable monomer, a photopolymerization initiator, and a low-surface energy monomer. In some aspects, the low-surface energy monomer has a silicone moiety attached (e.g., via a linker) to at least one polymerizable functional group. In some aspects, the at least one polymerizable functional group comprises at least one acrylate moiety. In some aspects, the at least one acrylate moiety comprises an acrylate or methacrylate. In some aspects, the low-surface energy monomer comprises multiple polymerizable functional groups attached to silicone moieties (e.g., silicone polymer, PDMS).

[0009] In some embodiments, the relief-forming precursor may comprise an adhesive layer on the substrate opposite the relief-forming layer, and in some aspects, an antihalation material may be included in or omitted from the adhesive layer.

[0010] In some embodiments, the relief-forming precursor may consist essentially of, in order, a substrate, an optional metal layer on the substrate, a single layer of a relief-forming layer on the substrate or the metal layer, and an optional cover sheet on the relief-forming layer.

[0011] In some embodiments, the relief-forming assembly may include a relief-forming precursor and a mask element. In some aspects, the relief-forming precursor may be comprised of any of the embodiments having a low surface energy monomer described herein. In some aspects, the mask element may include an imaged layer having a mask image. In some aspects, the mask element may be in full optical contact with the relief-forming surface of the relief-forming layer.

[0012] In some embodiments, the relief-forming assembly may consist essentially of, in order, a substrate, an optional metal layer on the substrate, and a single layer of a relief-forming layer on the substrate or metal layer, in complete optical contact with the relief-forming surface of the relief-forming layer.

[0013] In some embodiments, a method of making a relief-forming assembly may include providing a mask element according to an embodiment, providing a relief-forming layer having a low surface energy monomer according to an embodiment, disposing the imaged layer of the mask element on a relief-forming surface of the relief-forming layer, and forming intimate optical contact between the mask element and the relief-forming surface. In some aspects, the method may include laminating the mask element to the relief-forming surface. In some aspects, the method may include bonding the mask element to the relief-forming surface by vacuum drawdown.

[0014] In some embodiments, a method for producing a relief image in a relief-forming assembly may include providing a relief-forming assembly according to an embodiment; exposing the relief-forming layer to curing ultraviolet light through a mask element to form an imaged relief-forming layer in the imaged relief-forming layer having ultraviolet-exposed areas that form polymerized regions and unexposed areas that form unpolymerized regions; removing the mask element from the imaged relief-forming layer; and developing the imaged relief-forming layer by removing the unpolymerized areas in the imaged relief-forming layer, thereby forming a relief image element having a relief image (e.g., free of unpolymerized regions). In some aspects, the method may include polymerizing at least one photopolymerizable monomer and a low-surface-energy monomer with a photoinitiator such that low-surface-energy portions are present in the body and relief surface of the relief image of the relief image element. In some aspects, the method may include polymerizing a plurality of polymerizable functional groups of the low-surface-energy monomer with the at least one photopolymerizable monomer to form a crosslinked polymeric relief image element. In some embodiments, the low surface energy monomer has a silicone moiety attached to at least one polymerizable functional group, hi some embodiments, the at least one polymerizable functional group comprises at least one acrylate moiety.

[0015] In some embodiments, the relief image element may comprise a substrate and a relief image layer. The relief image layer may comprise an elastomer and a copolymer. The copolymer may comprise at least one photopolymerizable monomer and a low surface energy monomer having a silicone moiety. The relief surface of the relief image layer may comprise relief image ridges and valleys, with a portion of the silicone moiety present in the relief surface. In some embodiments, the copolymer comprises crosslinks between the photopolymerizable monomer and the low surface energy monomer.

[0016] The foregoing summary is illustrative only and is not intended to be limiting in any way. In addition to the exemplary aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. [Brief explanation of the drawings]

[0017] The foregoing and following information, as well as other features of the present disclosure, will become more fully apparent from the following specification and appended claims, taken in conjunction with the accompanying drawings, which illustrate only some embodiments of the present disclosure and, therefore, are understood not to be intended to limit its scope, and which will be used to describe the present disclosure with further specificity and detail.

[0018] [Figure 1A] 1 is a schematic cross-sectional view of one embodiment of a mask precursor according to the present invention, showing incident infrared radiation useful for fabricating mask elements. [Figure 1B] 1B is a schematic cross-sectional view illustrating one embodiment of a mask element formed from the mask precursor of FIG. 1A. [Figure 1C] FIG. 1C is a schematic cross-sectional view of one embodiment of a relief imaging assembly according to the present invention, comprising the mask element of FIG. 1B in intimate optical contact with a relief-forming precursor. [Figure 1D] 1C is a schematic cross-sectional view illustrating one embodiment of forming an imaged relief-forming precursor using ultraviolet light incident through the mask element of FIG. 1B. [Figure 1E] FIG. 1E is a schematic cross-sectional view of one embodiment of a relief image element provided after the imaging of FIG. 1D and a suitable development process to remove unexposed areas of the UV-sensitive layer of the imaged relief-forming precursor.

[0019] The elements and components in the above figures may be arranged in accordance with at least one of the embodiments described herein, and such arrangements may be modified by one skilled in the art in accordance with the disclosure provided herein. DETAILED DESCRIPTION OF THE INVENTION

[0020] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, like numerals generally refer to like elements unless the context requires otherwise. The exemplary embodiments described in the detailed description, drawings, and claims are not intended to be limiting. Other embodiments may be utilized, and other modifications may be made without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are expressly contemplated herein.

[0021] Relief-forming precursor Generally, the present technology includes a photosensitive relief-forming material usable in a relief-forming photopolymer plate precursor, the precursor comprising a low-surface energy additive that provides reduced surface energy and reduced peel force so that other layers, films, or objects can be removed from the photosensitive relief-forming material without damaging any of these components. The resulting relief image element, which still has the low-surface energy additive, for example, by being integrated (e.g., polymerized and / or crosslinked) with the matrix, has reduced surface energy due to the presence of the integrated low-surface energy additive on the surface of the relief image. In particular, the reduced peel force and reduced surface energy of the photosensitive relief-forming layer can improve bonding with the mask and separation of the mask from the imaged relief-forming layer, thereby improving the properties of the photosensitive relief-forming layer and allowing for improved use, imaging, and development. For example, the reduced surface energy from the low-surface energy additive can reduce the surface energy of the material, thereby allowing for better and more complete optical bonding of the mask layer to the material and thus improving separation. The subsequent reduction in surface energy also improves the use of the resulting photopolymer plate having relief image elements. The improved photosensitive relief-forming layer can also be used in solvent- or water-developable plates.

[0022] U.S. '182 (cited above) provides details of useful relief-forming precursors, such as flexographic printing plate precursors, letterpress printing plate precursors, and printed circuit boards. Such relief-forming precursors may comprise a suitable dimensionally stable substrate, a UV-sensitive relief-forming layer, and, optionally, a cover sheet and / or metal layer between the substrate and the relief-forming layer. Suitable substrates include dimensionally stable polymeric films and aluminum sheets. Polyester films are particularly useful. Any UV-sensitive material or element in which a relief image can be generated using a mask element is useful in the practice of the present invention, provided it contains a low surface energy additive.

[0023] In some embodiments, the relief-forming precursor generally comprises a suitable dimensionally stable substrate, a radiation-curable layer containing a low surface energy additive and capable of forming a flexographic relief image therein, and, optionally, a cover sheet on the radiation-curable layer and / or a metal layer between the substrate and the radiation-curable layer. Suitable substrates include flexible, dimensionally stable, transparent polymeric films and metal substrates such as aluminum sheets. Polyester films are particularly useful as flexible, dimensionally stable, transparent substrates. The relief-forming precursor may optionally comprise a metal layer disposed between the substrate and the radiation-curable layer. The metal layer may comprise copper or other metals or metal alloys.

[0024] In some embodiments, a removable cover sheet is also provided that is disposed over the radiation-curable layer to protect the radiation-curable layer from fingerprints and other damage. The lithographic printing plate precursor further comprises a metal layer between the substrate and the radiation-curable layer, or both the cover sheet and the metal layer sandwiching the radiation-curable layer.

[0025] In some embodiments, the radiation-curable layer can be a UV-sensitive layer that is cured by UV light. In some aspects, the UV-sensitive layer can be at least one layer of a relief-forming precursor formed by a UV-sensitive relief-forming material. Thus, references to a relief-forming material or a relief-forming layer refer to a UV-sensitive material or layer that can be irradiated with UV light and developed into a relief image.

[0026] In some embodiments, the relief-forming precursor comprises a backing or base film (e.g., as a substrate), a relief-forming layer (e.g., a UV-sensitive material), and, optionally, a removable cover sheet film to protect the photosensitive layer. Alternatively, a metal layer may be located between the substrate and the relief-forming layer.

[0027] In some embodiments, a backing film or base film may be configured to provide support for the relief-forming layer of the relief-forming precursor. The backing layer may be formed from a transparent or opaque material, such as paper, cellulose film, plastic, or metal. The backing layer is preferably formed from a flexible, transparent material. Examples of such materials include cellulose film or plastics such as PET (polyethylene terephthalate), PEN (polyethylene naphthalate), polyether, polyethylene, polyamide (Kevlar), or nylon. Preferably, the support layer is formed from polyethylene terephthalate (PET). It has also been found that the relief-forming layer having a low surface energy additive can be adhered to the support layer. The support layer may have a thickness of about 0.001 to about 0.010 inches. Various layers, such as an antihalation layer and / or an adhesive layer, may be disposed between the backing layer and the relief-forming layer, as needed. In some embodiments, the adhesive layer may include an antihalation material (e.g., a light-absorbing material to prevent light refraction), or may be free of such an antihalation material.

[0028] In some embodiments, the relief-forming layer with reduced release force can be an ultraviolet-light-sensitive material that, when imaged with ultraviolet light and developed, forms a relief image with reduced surface energy. Adding a low-surface-energy additive to the ultraviolet-light-sensitive material provides many desirable properties to the relief-image-forming protocol, such as easier vacuum drawdown and improved lamination to reduce bubble formation. Additionally, reduced release force allows for easier removal of the imaged mask from the relief-forming layer after the primary ultraviolet exposure to form the relief image. The protocol can then be performed by peeling the mask from the imaged relief-forming layer. The improved separation due to reduced surface energy and reduced release force is applicable to larger plate sizes required for commercial applications. Thus, photosensitive relief-forming materials with reduced surface energy and release force facilitate separation of the assembly of mask elements and photopolymer plate precursors.

[0029] In some embodiments, the reduction in surface energy and the reduction in peel force are achieved by incorporating a low surface energy additive into the composition of the photosensitive material. The low surface energy additive may be included within the matrix of the photosensitive material so that it is present and distributed within the body and on the surface of the photosensitive material. In many cases, the low surface energy additive is homogeneously mixed within the photosensitive material. However, the additive may also be provided randomly or heterogeneously (e.g., non-homogeneously), or in a gradient where the concentration preferentially increases on one side or the other.

[0030] In some embodiments, the low surface energy additive is a silicone having reactive functional groups. The reactive functional groups may include silicone materials such as silicone-based monomers. The reactive functional groups may be selected to be polymerizable with other polymerizable monomers of the photosensitive material. This allows the silicone to be incorporated into the polymer so that it is retained in the portions of the photosensitive material that remain after the relief formation process. As a result, the reactive functional groups can be made from known functional groups that participate in polymerization reactions with other monomers of a particular type that have the same or different but suitable reactive functional groups.

[0031] The low surface energy additive allows for easier separation of the mask from the relief-forming precursor and also reduces the surface energy for the relief image layer of the flexographic printing plate, which provides additional benefits for printing.

[0032] In some embodiments, the silicone material of the low surface energy additive may include an acrylate functional group that may be reactive upon polymerization. While acrylates (e.g., with a hydrogen on the alpha carbon) may be used, other acrylates with a substituent on the alpha carbon may also be used. Other acrylates may be substituted acrylates with a substituent on the alpha carbon. Common examples include methacrylates with a methyl group on the alpha carbon. The silicone moiety may be attached to an ester oxygen of the acrylate moiety. The silicone moiety may include a linker to the oxygen.

[0033] In some embodiments, the silicone material may include a polydimethylsiloxane (PDMS) backbone with alkyl or alkoxy side chains and acrylate groups, such as acrylate or methacrylate. Such silicone acrylate additives are commercially available from various suppliers and may be referred to as TEGO RAD (silicone polyether acrylates), such as TEGO RAD 2250, TEGO RAD 2300, TEGO RAD 2500, TEGO RAD 2700, CN9800 (difunctional aliphatic silicone acrylate oligomer), EBECRYL 350 (silicone diacrylate), etc.

[0034] In some embodiments, the silicone material may comprise the structure of Formula 1 or Formula 2 or Formula 3 or Formula 4 or Formula 5 below.

[0035] [ka] formula 1

[0036] [ka] formula 2

[0037] [ka] formula 3

[0038] [ka] formula 4

[0039] [ka] formula 5

[0040] Formula 1 may have m and n as defined below, and each X may independently be a substituent or a polymerizable functional group, with at least one X in monomer "m" being a polymerizable functional group. In each of the above formulas, n is in the range of 1 to 50 (or 10 to 20 or 14 to 16), and m is in the range of 0.1 to 10 (or 0.5 to 5 or 0.9 to 3 or 1 to 3), e.g., m is 1 for each monomer. The molecular weight may be in the range of 1,000 g / mol to 2,500 g / mol. Y may be any linker, such as those described herein or known in the art. For example, Y may be a linker shown in Formula 4 or Formula 5. The linker Y may also include a C1-C10 alkyl. R may be a substituent such as an alkyl (e.g., methyl, ethyl, propyl, etc.).

[0041] In some embodiments, the linker Y can be a hydrocarbon chain with or without one or more heteroatoms such as O, N, or S, with or without one or more substituents on the atoms of the chain. The linker Y can include straight chain aliphatic compounds, branched chain aliphatic compounds, cyclic aliphatic compounds, substituted aliphatic compounds, unsubstituted aliphatic compounds, saturated aliphatic compounds, unsaturated aliphatic compounds, aromatic compounds, polyaromatic compounds, substituted aromatic compounds, heteroaromatic compounds, ethers, amines, primary amines, secondary amines, tertiary amines, aliphatic amines, carbonyls, carboxyls, amides, esters, amino acids, peptides, polypeptides, and derivatives thereof, substituted or unsubstituted, with or without heteroatoms or combinations thereof. In some embodiments, linker Y may include C1-C24 alkyl, C2-C24 alkenyl, C2-C24 alkynyl, C1-C24 alkyl ester, C6-C20 aryl, C7-C24 alkaryl, C7-C24 aralkyl, amino, mono- and di-(alkyl) substituted amino, mono- and di-(aryl) substituted amino, alkylamido, arylamido, imino, alkylimino, arylimino, nitro, nitroso, sulfo, sulfonate, alkylsulfanyl, arylsulfanyl, alkylsulfinyl, arylsulfinyl, alkylsulfonyl, arylsulfonyl, phosphono, phosphonate, phosphinate, phospho, phosphino, all with or without heteroatoms, all with or without substituents, derivatives, and combinations thereof.

[0042] In some embodiments, the substituent X or the substituents on the linker are selected from hydrogen, alkyl, alkenyl, alkynyl, alkyl ester, aryl, alkaryl, aralkyl, halo, hydroxyl, sulfhydryl, any of which may or may not contain heteroatoms, any of which may contain straight chains, any of which may contain branched chains, any of which may contain rings, derivatives thereof, and combinations thereof. alkoxy, alkenyloxy, alkynyloxy, aryloxy, acyl, alkylcarbonyl, arylcarbonyl, acyloxy, alkoxycarbonyl, aryloxycarbonyl, halocarbonyl, alkylcarbonate, arylcarbonate, carboxy, carboxylate, carbamoyl, mono(alkyl)-substituted carbamoyl, di(alkyl)-substituted carbamoyl, mono-substituted arylcarbamoyl, thiocarbamoyl, carbamide, cyano, isocyano, cyanate, isocyanate, iso Common substituents may include thiocyanato, azide, formyl, thioformyl, amino, mono- and di(alkyl)-substituted amino, mono- and di(aryl)-substituted amino, alkylamido, arylamido, imino, alkylimino, arylimino, nitro, nitroso, sulfo, sulfonate, alkylsulfanyl, arylsulfanyl, alkylsulfinyl, arylsulfinyl, alkylsulfonyl, arylsulfonyl, phosphono, phosphonate, phosphinate, phospho, phosphino, etc. For example, Formula 4 and Formula 5 show alkyl ester linkers substituted with hydroxyl.

[0043] Regarding Formulas 2 to 5: when m is 1 the silicone monomer is monofunctional, when m is 2 the silicone monomer is difunctional, when m is 3 the monomer is trifunctional, etc. Thus, the monomer may be polyfunctional, thereby enabling crosslinking during polymerization, for example when m is 2 or greater. Formula 1 may be monofunctional when only one X is a polymerizable functional group and m is 1, but may be polyfunctional in other cases.

[0044] In some embodiments, the silicone moiety may be a monoacrylate, diacrylate, triacrylate, or other multiacrylate. Diacrylates and higher acrylates can participate in crosslinking with polymerizable monomers. As a result, polymerization can result in crosslinking using silicone multiacrylate monomers as low surface energy additives. Thus, forming an imaged UV-sensitive material may involve crosslinking monomers with silicone multiacrylate monomers.

[0045] In some embodiments, the low surface energy additive is not a silicone oil. That is, the low surface energy additive is not a silicone not contained within the material. Instead, in some embodiments, a low surface energy additive is included that has a reactive functional group capable of participating in polymerization so that the silicone is covalently bonded to the polymer. In some aspects, the low surface energy additive polymerizes upon exposure to curing UV light. For example, silicone acrylate or silicone methacrylate may be used. Thus, the low surface energy additive includes a silicone that contains functional groups for polymerization and crosslinking to the polymer matrix and reduces the surface energy and release force of the UV-sensitive layer. By incorporating it into the binder, migration of the silicone, which can be a problem with silicone oil, is suppressed. Thus, in some embodiments, silicone oil or other silicones that do not contain polymerizable functional groups are excluded from the present invention.

[0046] In some embodiments, the relief-forming precursor may comprise only a single layer or UV-sensitive material. That is, the substrate of the relief-forming precursor may comprise only a single layer of UV-sensitive material with a low surface energy additive. Thus, the UV-sensitive material is the top layer in a state where it can be combined with a mask, and this UV-sensitive material is the only UV-sensitive material in the relief-forming precursor. Another UV-sensitive layer, whether adjacent or spaced apart, is omitted from the relief-forming precursors described herein. Thus, the UV-sensitive layer as a whole includes the low surface energy additive.

[0047] In some embodiments, the low surface energy additive, such as a silicone acrylate, is present in an amount ranging from about 0.1% to about 5% by weight of the material, or from about 0.2% to about 4% by weight, from about 0.3% to about 3% by weight, from about 0.4% to about 2% by weight, from about 0.5% to about 1%, or It may be included in the UV-sensitive material in an amount ranging from any of the above endpoints, such as from 0.5% to about 2%.

[0048] In some embodiments, the low surface energy additive may be distributed throughout the matrix. In some aspects, the low surface energy additive may be added to the top surface of the UV-sensitive material.

[0049] The photosensitive layer having the low surface energy additive may be present in a relief-forming precursor, which may be a positive- or negative-acting relief-forming precursor, but is typically negative-acting, and includes a UV-sensitive layer (alternatively a photohardenable or relief-image-forming layer or photosensitive layer) that generally includes a UV-curable composition that hardens by polymerization or crosslinking upon exposure to curing UV light. Details of various compositions of UV-sensitive, relief-forming precursors are disclosed in U.S. '182 (supra) and the references cited therein.

[0050] Some embodiments of the relief-forming precursor may include a removable cover sheet over the photosensitive layer that has reduced surface energy and reduced release force, which facilitates removal of the cover sheet.

[0051] In some embodiments, the photosensitive material with reduced surface energy and peel force may be a UV-sensitive layer comprising an elastomeric binder, at least one polymerizable or photocurable monomer, a UV-sensitive photopolymerization photoinitiator, and a low surface energy monomer, such as the polymerizable silicone material described herein. Suitable photoinitiator compositions include, but are not limited to, those described in U.S. Pat. No. 4,323,637 (Chen et al.), U.S. Pat. No. 4,427,749 (Graetzel et al.), and U.S. Pat. No. 4,894,315 (Feinberg et al.). The low surface energy monomer may be added to the photoinitiator composition to form a photosensitive material with reduced surface energy and peel force.

[0052] The elastomeric binder may comprise one or more polymers or resins that are soluble, swellable, or dispersible in aqueous, semi-aqueous, or organic solvent developers (described below), and may include, but are not limited to, natural or synthetic polymers of conjugated diolefins, block copolymers, core-shell microgels, and mixtures of microgels with preformed polymeric polymers. The elastomeric binder may comprise 65% to 90% by weight of the total dry weight of the UV-sensitive layer.

[0053] In some embodiments, the elastomeric binder may be a single polymer or a mixture of polymers (e.g., homopolymers, copolymers, random copolymers, or block copolymers, any of which may have any number of different types of monomers), and the polymer or mixture may be soluble, swellable, or dispersible in aqueous, semi-aqueous, or organic solvent developers. Suitable binders include those described in U.S. Pat. No. 3,458,311 (Alles), U.S. Pat. No. 4,442,302 (Pohl), U.S. Pat. No. 4,361,640 (Pine), U.S. Pat. No. 3,794,494 (Inoue), U.S. Pat. No. 4,177,074 (Proskow), U.S. Pat. No. 4,431,723 (Proskow), and U.S. Pat. No. 4,517,279 (Worns). Binders that are soluble, swellable, or dispersible in organic solvent developers include natural or synthetic polymers of conjugated diolefin hydrocarbons, including polyisoprene, 1,2-polybutadiene, 1,4-polybutadiene, thermoplastic elastomeric block copolymers of butadiene / acrylonitrile, butadiene / styrene, and other copolymers. U.S. Pat. No. 4,323,636 (Chen); U.S. Pat. No. 4,430,411 (Franklin); Block copolymers such as those disclosed in U.S. Patent No. 7 (Heinz) and U.S. Patent No. 4,045,231 (Toda) may also be used. The elastomeric binder may be present in an amount of about 65% or more by weight of the photosensitive material. As used herein, the term binder includes core-shell microgels and mixtures of microgels and preformed polymeric polymers, such as those described in U.S. Patent No. 4,956,252 (Fryd).

[0054] The at least one polymerizable monomer may be configured to have compatibility with the elastomeric binder to the extent that a clear, non-cloudy, UV-sensitive imaging layer is produced. Polymerizable monomers for this application are well known in the art and include ethylenically unsaturated polymerizable compounds having relatively low molecular weights (generally less than 30,000 daltons). Suitable monomers have relatively low molecular weights of less than about 5,000 daltons. Unless otherwise specified, molecular weights throughout the specification are weight average molecular weights. Examples of suitable polymerizable monomers include various mono- and polyacrylates, acrylate derivatives of isocyanates, esters, and epoxides. Further examples of suitable monomers include t-butyl acrylate, lauryl acrylate, acrylate and methacrylate monoesters and polyesters of alcohols and polyols, such as alkanols, for example, 1,4-butanediol diacrylate, 2,2,4-trimethyl-1,3-pentanediol dimethacrylate, and 2,2-dimethylolpropane diacrylate, alkylene glycols, such as tripropylene glycol diacrylate, butylene glycol dimethacrylate, hexamethylene glycol diacrylate, and hexamethylene glycol dimethacrylate, trimethylolpropane, ethoxylated trimethylolpropane, pentaerythritol, for example, pentaerythritol triacrylate, and dipentaerythritol. Other examples of suitable monomers include acrylate and methacrylate derivatives of isocyanates, esters, and epoxides, such as decamethylene glycol diacrylate, 2,2-di(p-hydroxyphenyl)propane diacrylate, 2,2-di(p-hydroxyphenyl)propane dimethacrylate, polyoxyethyl-2,2-di(p-hydroxyphenyl)propane dimethacrylate, and 1-phenylethylene-1,2-dimethacrylate. Further examples of monomers can be found in U.S. Pat. No. 4,323,636 (Chen), U.S. Pat. No. 4,753,865 (Fryd), U.S. Pat. No. 4,726,877 (Fryd), and U.S. Pat. No. 4,894,315 (Feinberg).The monomer may comprise from 5% to about 25% by weight of the photosensitive material, which may be based on the total dry weight of the photosensitive material.

[0055] The photoinitiator may be any single compound or combination of compounds sensitive to ultraviolet light that generates free radicals that initiate the polymerization of one or more monomers without undue termination. The photoinitiator may be sensitive to visible light or ultraviolet light. The photoinitiator may also be insensitive to ultraviolet and / or visible light and thermally inactive below 185°C. Examples of suitable photoinitiators include substituted and unsubstituted polynuclear quinones. Examples of suitable systems are disclosed in U.S. Pat. No. 4,460,675 (Gruetzmacher) and U.S. Pat. No. 4,894,315 (Feinberg). The photoinitiator is generally present in an amount of 0.001% to 10.0% by weight, based on the weight of the photosensitive material.

[0056] In some embodiments, the photosensitive layer may include a diblock or triblock copolymer (e.g., an elastomer), at least one photopolymerizable monomer, a photoinitiator, a plasticizer, additives such as stabilizers, inhibitors, colorants, solvents, and the like, and a low surface energy monomer such as a silicone acrylate or silicone methacrylate.

[0057] In embodiments, the plasticizer may be any suitable plasticizer known in the art for photosensitive layers used in the applications described herein. Examples of suitable plasticizers include naphtha, ... Examples of suitable plasticizers include aliphatic hydrocarbon oils such as tartaric acid oil, paraffin oil, and liquid polydiene (e.g., liquid polybutadiene, liquid polyisoprene). Generally, plasticizers are liquids with a molecular weight of less than about 5,000 daltons, but can have a molecular weight of up to about 30,000 daltons. Plasticizers with low molecular weights include those with a molecular weight of less than about 30,000 daltons.

[0058] In some embodiments, additives may include rheology modifiers, thermal polymerization inhibitors, stabilizers, retarders, tackifiers, colorants, antioxidants, antiozonants, solvents, or fillers, which are commonly used in photosensitive layers and examples of which may be found in the incorporated references.

[0059] The thickness of the photosensitive layer may vary depending on the type of printing plate intended. In one embodiment, the photosensitive layer may have a thickness of, for example, about 20 to 250 mils (500 to 6,400 microns) or more, more specifically, a thickness of about 20 to 100 mils (500 to 2,500 microns).

[0060] In some embodiments, the relief-forming precursor is a flexographic printing plate precursor comprising a suitable UV-curable composition (e.g., a photosensitive material) in a UV-sensitive layer (e.g., a photosensitive layer) that provides a relief image in a flexographic printing plate when exposed through a mask element and developed. Such a relief-forming precursor generally comprises a suitable substrate containing a photosensitive material. Examples of commercially available flexographic printing plate precursors include, but are not limited to, FLEXCEL NX flexographic elements available from Miraclone Corporation, CYREL® flexographic plates available from DuPont (Wilmington, Delaware), NYLOFLEX FAR 284 plates available from BASF (Germany), FLEXILIGHT CBU plates available from Macdermid (Denver, Colorado), and ASAHI AFP XDI available from Asahi Kasei (Japan). These flexographic printing plate precursors may be modified to include the low surface energy monomers described herein.

[0061] In some embodiments, the relief-forming precursor may be used to form a printed circuit board, in which a conductive layer (also known as a "printed circuit") is formed on a substrate in a pattern defined by exposure through a mask element. A suitable precursor for a printed circuit board generally comprises a substrate, a metal layer, and a UV-sensitive imaging layer (e.g., a photosensitive material). Suitable substrates include, but are not limited to, polyimide film, glass-filled epoxy or phenol formaldehyde, or any other insulating material known in the art. The metal layer covering the substrate is generally a conductive metal, such as copper, or an alloy or metal. The UV-sensitive imaging layer may include a UV-curable resin, a polymerizable monomer or oligomer, a photoinitiator, and a polymeric binder. Printed circuit boards are discussed in more detail in U.S. '182 (ibid.).

[0062] Masks and mask precursors A mask to be used with a relief-forming precursor having a photosensitive layer with a low surface energy additive can be prepared from a mask precursor. The mask precursor can be prepared and treated with light (e.g., infrared light) to form a mask. The mask can then be combined with the relief-forming precursor (e.g., by lamination) and treated, after which the light-treated mask and the relief-forming precursor are separated from each other. During the separation process, it is important not to damage the relief-forming layer. Therefore, the low surface energy additive in the relief-forming layer of the relief-forming precursor can facilitate separation (e.g., peeling) of the mask from the imaged relief-forming layer of the relief-forming precursor.

[0063] A mask precursor is considered an imaging material because it has an imaging layer that forms a mask. The mask precursor may comprise three essential layers or films, as described below: (a) a transparent polymeric carrier sheet, (b) a light-to-heat conversion (LTHC) layer, and (c) a non-silver halide thermally ablatable imaging layer (IL). The LTHC layer cannot be ablatable by thermal imaging with light, such as infrared light. While a non-silver halide thermally ablatable imaging layer can be ablatable by thermal imaging with light, such as infrared light, such a thermally ablatable imaging layer does not contain silver halide and is therefore a thermally ablatable "non-silver halide" imaging layer. Thus, the LTHC layer contains a material that cannot be ablatable by thermal energy during imaging with infrared light in the IL layer. Meanwhile, the IL layer contains a thermally ablatable material. Only these three layers or films are essential to form a mask element (e.g., referred to as a mask) having a mask image in the IL layer. However, as described below, in some embodiments, a (d) transparent polymeric overcoat layer may be disposed directly on the IL, although this optional feature is not required for the formation of the mask or the use of the mask image; rather, it may be useful for providing abrasion resistance in some applications.

[0064] A mask precursor used to form mask elements that will ultimately be used to form the relief image may be prepared and then processed into a mask as described herein. In some embodiments, a mask precursor 10 is illustrated in FIG. 1A. Mask precursor 10 includes (a) a transparent polymeric carrier sheet 15, upon which is disposed directly (b) an LTHC layer 20, which includes a non-ablatable binder material with non-ablatable particles 25 (described in more detail below), and (c) an ablatable IL 30, which is disposed directly on LTHC layer 20 and is positioned to receive light 35, as indicated by the arrows.

[0065] Transparent polymer carrier sheet The transparent polymeric carrier sheet may be any suitable transparent substrate or film. Useful transparent polymeric carrier sheets may be, for example, but are not limited to, transparent polymeric films and sheets composed of one or more polymers such as polyesters, including poly(ethylene terephthalate), poly(ethylene naphthalate), and fluoropolyester polymers; polyethylene-polypropylene copolymers; polybutadiene; polycarbonate; polyacrylates (polymers formed at least in part from one or more (meth)acrylate ethylenically unsaturated monomers); vinyl chloride polymers such as polyvinyl chloride and copolymers derived at least in part from vinyl chloride; hydrolyzed or non-hydrolyzed cellulose acetate; and other materials apparent to those skilled in the art. The transparent polymeric carrier sheet may also be composed of a mixture or composite of two or more polymeric materials, so long as the required transparency and protective properties are obtained. The transparent polymeric carrier sheet may be formed as a single layer polymeric film or as a laminate of multiple polymeric films. Generally, the average dry thickness of the transparent polymeric carrier sheet is 25 μm to 250 μm, typically 75 μm to 175 μm.

[0066] For example, transparent poly(ethylene terephthalate) sheets available from a variety of commercial sources are suitable as transparent polymeric carrier sheets.

[0067] If desired, the surface of the transparent polymeric carrier sheet may be treated to modify its wetting or adhesion to the applied coating (e.g., LTHC layer coating). Such surface treatments include, but are not limited to, corona discharge treatment and application of a primer layer, so long as the desired transparency (as described above) is achieved.

[0068] Optionally, the transparent polymeric carrier sheet may also include one or more "first" ultraviolet absorbing compounds (discussed below with respect to the LTHC layer and IL). One or more such compounds may be the same as or different from the ultraviolet absorbing compounds in the IL (see below). Useful ultraviolet absorbing compounds generally each absorb radiation between 150 nm and 450 nm. These compounds may be present in the transparent polymeric carrier sheet in an amount of 0.01 wt % to 0.1 wt %, based on the total dry weight of the transparent polymeric carrier sheet.

[0069] Additionally, the transparent polymeric carrier sheet may contain one or more "adhesion promoters" that enhance adhesion to the adjacent LTHC layer. Useful adhesion promoters include, but are not limited to, gelatin, polyvinylidene chloride, poly(acrylonitrile-co-vinylidene chloride-co-acrylic acid), and polyethyleneimine.

[0070] Non-ablatable light-to-heat conversion (LTHC) layer The mask precursor also includes a non-ablatable LTHC layer disposed on the transparent polymeric carrier sheet and directly between the transparent polymeric carrier sheet and the IL. A suitable LTHC layer configuration has three essential components: (i) a first infrared-absorbing material; (ii) a non-ablatable cross-linked binder material that is a thermally cross-linked organic polymer that is non-ablatable by radiation, such as infrared, visible, or ultraviolet radiation; and (iii) non-ablatable particles that are non-ablatable by radiation, such as infrared, visible, or ultraviolet radiation. The LTHC layer is generally disposed as a relatively uniform (i.e., substantially continuous and fairly uniform in wet thickness) coating on the transparent polymeric carrier sheet, and then dried if a solvent is present in the composition formulation.

[0071] The LTHC layer is generally transparent as that term is defined above, and in particular, the LTHC layer is transparent to the ultraviolet light used to image the relief-forming precursor, as described below.

[0072] Herein, one or more infrared-absorbing materials are collectively referred to as a "first" infrared-absorbing material, to distinguish it from a second infrared-absorbing material (described below) in the IL, if necessary. The first infrared-absorbing material may also be present in a transparent polymeric carrier sheet. The first and second infrared-absorbing materials may be one or more dyes or pigments, or mixtures thereof, that provide desired spectral absorption characteristics and independent radiation sensitivity in the infrared radiation wavelength range of 700 nm to 1500 nm, typically 750 nm to 1200 nm. Such materials may be particulate in nature and dispersed in a non-ablatable crosslinked binder material (ii) described below. For example, they may be black dyes or black pigments, such as carbon black, metal oxides, and other materials described, for example, in U.S. '182 (ibid.).

[0073] One suitable infrared-absorbing pigment is carbon black, and many types of carbon black with different particle sizes are commercially available. Examples include RAVEN 450, 760, ULTRA 890, 1020, 1250, and others available from Columbian Chemicals Co. (Atlanta, Georgia), and BLACK PEARLS 170, BLACK PEARLS 480, VULCAN XC72, BLACK PEARLS 1100, and others available from Cabot Corporation. Other useful carbon blacks are surface-functionalized with solubilizing groups. Carbon blacks grafted to hydrophilic nonionic polymers such as FX-GE-003 (manufactured by Nippon Shokubai) or surface-functionalized with anionic groups such as CAB-O-JET® 200 or CAB-O-JET® 300 (manufactured by Cabot Corporation) are also useful.

[0074] Useful first infrared-absorbing materials also include, but are not limited to, infrared dyes, including cationic infrared-absorbing dyes and photothermally bleachable dyes. Examples of suitable infrared dyes include, but are not limited to, azo dyes, squarylium dyes, croconate dyes, triarylamine dyes, thiazolium dyes, indolium dyes, oxonol dyes, oxazolium dyes, cyanine dyes, merocyanine dyes, phthalocyanine dyes, indocyanine dyes, indotricarbocyanine dyes, oxatricarbocyanine dyes, thiocyanine dyes, thiatricarbocyanine dyes, merocyanine dyes, cryptocyanine dyes, naphthalocyanine dyes, polyaniline dyes, polypyrrole dyes, polythiophene dyes, chalcogenopyrilarylidene and bi(chalcogenopyril)polymethine dyes, oxiindolizine dyes, pyrylium dyes, pyrazoline azo dyes, oxazine dyes, naphthoquinone dyes, anthraquinone dyes, quinoneimine dyes, methine dyes, arylmethine dyes, squarine dyes, oxazole dyes, croconine dyes, porphyrin dyes, and any substituted or ionic form of the dye classes previously described. Suitable dyes are also described in U.S. Pat. No. 5,208,135 (Patel et al.), U.S. Pat. No. 6,569,603 (Furukawa), U.S. Pat. No. 6,787,281 (Tao et al.), and European Patent Application Publication No. 1,182,033 (Fijimaki et al.). One class of suitable cyanine dyes is outlined by the formula in paragraph

[0026] of WO 2004 / 101280.

[0075] Near-infrared absorbing cyanine dyes are also useful, and are described, for example, in U.S. Patent No. 6,309,792 (Hauck et al.), U.S. Patent No. 6,264,920 (Achilefu et al.), U.S. Patent No. 6,153,356 (Urano et al.), and U.S. Patent No. 5,496,903 (Watanate et al.), the entire disclosures of which are incorporated herein by reference. Suitable dyes may be produced using conventional methods and starting materials, or may be obtained from a variety of commercial sources, including American Dye Source (Baie-d'Urfé, Quebec, Canada) and FEW Chemicals (Germany).

[0076] The first infrared absorber is generally present in an amount sufficient to provide a transmission optical density at the exposure radiation wavelength (e.g., infrared) of 0.025 or greater, typically 0.05 or greater, which is generally achieved by including 0.1% to 5% by weight, typically 0.3% to 3% by weight, based on the total dry weight of the LTHC layer.

[0077] The first infrared-absorbing material in the LTHC layer can be the same or a different chemical entity as the second infrared-absorbing compound introduced into the IL, as described below. The infrared-absorbing material in the LTHC layer can also be different from the infrared-absorbing material in the transparent polymeric carrier. In many embodiments, the first and second infrared-absorbing materials are the same chemical entity. The amounts of the first and second infrared-absorbing materials in the imaging material can be the same or different. In many embodiments, they are present in amounts that are

[0078] As previously mentioned, the LTHC layer comprises a non-ablatable crosslinked binder formed from one or more thermally crosslinkable organic polymeric binders derived from crosslinked thermally crosslinkable organic polymeric binders. The term "thermally crosslinkable" means that crosslinkable groups are present and include, for example, hydroxy-containing polymers. Particularly useful thermally crosslinkable organic polymers include, but are not limited to, crosslinkable nitrocellulose, crosslinkable polyesters such as polyesters containing hydroxy groups, polyvinyl alcohol, polyvinyl acetals such as polyvinyl butyral, or combinations of two or more such crosslinkable organic polymeric materials. Corresponding non-ablatable crosslinked binder materials may be obtained by crosslinking the above-mentioned thermally crosslinkable organic polymeric materials.

[0079] The non-ablatable cross-linked binder material formed from thermally cross-linked organic polymers is It may be present in an amount of 40% to 90% by weight, more preferably 50% to 80% by weight, based on the total dry weight of the LTHC layer.

[0080] The third essential component of the LTHC layer is non-ablatable particles that cannot be ablated by light or heat from light; therefore, non-ablatable particles are considered to be thermally non-ablatable particles. Thermally non-ablatable particles are defined as those that are not thermally ablated under exposure to light during mask formation or relief image formation. The non-ablatable particles may have an average particle size of 0.1 μm to 20 μm, or 5 μm to 15 μm. Here, the term "average" is used to refer to the measured particle size of the dispersed particles, which may be determined from manufacturer specifications or by measuring and averaging at least 10 different particles.

[0081] The term "non-ablatable" in reference to non-ablatable particles is used herein to mean that the particles have a lower sensitivity to the laser imaging wavelength and intensity than materials that are highly susceptible to the laser imaging ablation process that forms the mask. The particles also have a lower sensitivity to ultraviolet light when forming a relief image from the mask and relief-forming precursor. Materials that are sensitive to the laser thermal imaging ablation process are ablatable because they strongly absorb the laser wavelength of the imaging laser and have a low thermal decomposition temperature; such materials are not used for non-ablatable particles. In contrast, the non-ablatable particles used in the present invention do not strongly absorb the laser imaging wavelength and do not have a sufficiently low thermal decomposition temperature. Some of the non-ablatable particles may protrude from the LTHC layer, e.g., into the IL, but are retained within the LTHC layer or at least partially embedded within the LTHC layer.

[0082] Non-ablatable particles useful in the LTHC layer include, but are not limited to, silica, titanium dioxide, zinc oxide particles, or combinations of two or more such particles. Silica particles are particularly useful in the practice of the present invention. Furthermore, such non-ablatable particles may be present in the LTHC layer in an amount of 0.2 wt. % to 10 wt. %, or 1 wt. % to 7 wt. %, based on the total dry weight of the LTHC layer.

[0083] Optionally, upon formation, the LTHC layer may include one or more thermal crosslinkers to facilitate processing of the mask element. Such optional thermal crosslinkers facilitate crosslinking of the thermally crosslinkable organic binder polymer during application and drying of the LTHC layer to form a non-ablatable crosslinked binder. Heat may be utilized for drying during formation of the mask element. The thermal crosslinker may be present in an amount of 5% to 25% by weight, based on the total dry weight of the crosslinkable polymers crosslinked within the non-ablatable LTHC layer. Examples of such materials include, but are not limited to, melamine-formaldehyde resins, dialdehydes, phenolic resins, polyfunctional aziridines, isocyanates, including polyisocyanates, and urea-formaldehyde epoxies. However, because the resulting LTHC layer is a crosslinked binder, the crosslinker may be present entirely, absent, or in only small amounts in the resulting non-ablatable crosslinked material.

[0084] The LTHC layer generally has an average dry thickness of from 1 μm to 5 μm, typically from 1 μm to 3 μm.

[0085] Non-silver halide thermally ablatable imaging layers (ILs) The IL incorporated into the mask precursor is generally disposed directly on the LTHC layer as a relatively uniform (i.e., substantially continuous and fairly uniform wet thickness) coating, and then If a solvent is present in the formulation, it is dried. In many embodiments, the IL is a single coated or applied layer, but in other embodiments, there may be multiple sublayers or subcoatings comprising the IL that are disposed directly on the LTHC layer described above.

[0086] As noted in the terminology section, there is substantially no silver halide present in the IL, in other words, no silver halide is intentionally added or created within the IL.

[0087] ILs generally contain one or more ultraviolet absorbers (ultraviolet light absorbers) as an essential component. These compounds generally have an absorbance of 1.5 to 5 in the radiation wavelength range of 300 nm to 450 nm. In general, useful ultraviolet absorbers include, but are not limited to, benzotriazoles, halogenated benzotriazoles, triazines, benzophenones, benzoates, salicylates, substituted acrylonitriles, cyanoacrylates, benzylidene malonates, oxalanilides, and mixtures thereof. Examples of useful ultraviolet absorbers include, but are not limited to, ultraviolet absorbing dyes or ultraviolet stabilizers sold under the names Uvinul® (BASF), Keyplast® (Keystone Aniline Corporation), Sanduvor® (Sandoz Chemicals Corp.), Hostavin (Clariant), and Tinuvin® (BASF or Ciba). Examples of useful materials are described in US Pat. No. 5,496,685 (Farber et al.).

[0088] The one or more UV absorbing compounds may be present in the IL in an amount of 10% to 40% by weight, typically 15% to 30% by weight, based on the total dry weight of the IL.

[0089] The IL also includes one or more second infrared-absorbing materials as a second essential component, which are defined similarly to the first infrared-absorbing materials described above for the LTHC layer and may be the same as or different from the first infrared-absorbing materials. The one or more second infrared-absorbing materials may be present in the IL in an amount sufficient to provide a transmission optical density of 0.5 or greater, typically 0.75 or greater, at the exposure wavelength. Generally, this is achieved by including 3% to 20% by weight of the one or more second infrared-sensitive compounds, based on the total dry weight of the IL.

[0090] The IL may optionally contain one or more fluorocarbon additives to improve the production of clear, generally continuous, and relatively sharp-edged halftone dots (i.e., pixels). Examples of useful fluorocarbon additives and the amounts thereof are set forth in paragraphs

[0087] -

[0089] of US '182 (ibid.).

[0091] Further optional components of the IL include, but are not limited to, plasticizers, coating aids or surfactants, dispersing aids, fillers, and colorants, all of which are well known in the art, as described, for example, in paragraphs

[0094] -

[0096] of U.S. '182 (ibid.). For example, the IL may further include one or more fluorocarbon additives or one or more non-thermally ablatable colorants.

[0092] All of the essential and optional components described above with respect to the IL are dispersed in one or more ablatable polymeric binder materials, including both synthetic and natural polymeric materials that are ablatable upon exposure to light, such as infrared, visible, or ultraviolet light. In some embodiments, the ablatable polymeric binder in the IL is not crosslinked and is therefore a non-crosslinked binder. Such materials allow the essential and optional components to be dissolved or dispersed uniformly throughout the IL. The one or more ablatable polymeric binder materials may comprise 25% to 75% by weight, typically 25% to 75% by weight, based on the total dry weight of the IL. may be present in an amount of 35% to 65% by weight.

[0093] Useful ablatable polymeric binder materials include, but are not limited to, those described in U.S. '182, paragraphs

[0081] through

[0085] . These materials are also known as "adhesive binders," as described in U.S. '182, paragraph

[0081] . Examples of such materials include, but are not limited to, acetyl polymers, such as poly(vinyl butyral), available as BUTVAR® B-76 from Solution, Inc. (St. Louis, Missouri), and acrylamide polymers, such as MACROMELT 6900 from Henkel Corp. (Gulf Mills, Pennsylvania). Pressure-sensitive adhesive polymers can also be used for this purpose.

[0094] In some embodiments, it is advantageous to use materials in the IL that are readily thermally combustible or ablatable and produce gases and volatile fragments at temperatures below 200° C. Examples of these materials are thermally ablatable nitrocellulose, polycarbonates, poly(cyanoacrylates), polyurethanes, polyesters, polyorthoesters, polyacetals, and copolymers thereof, which may be non-crosslinked (see, e.g., U.S. Pat. No. 5,171,650 to Ellis et al., column 9, lines 41-50, the disclosure of which is incorporated herein by reference).

[0095] Other useful ablatable materials for the IL have hydroxy groups (or hydroxy polymers) such as those described in U.S. '182 (ibid.), paragraphs

[0082] -

[0084] , such as poly(vinyl alcohol) and cellulosic polymers (e.g., nitrocellulose). Still other useful polymers are non-crosslinkable polyesters, polyamides, polycarbamates, polyolefins, polystyrenes, polyethers, polyvinyl ethers, polyvinyl esters, and polyacrylates and polymethacrylates having alkyl groups containing 1 to 2 carbon atoms.

[0096] Particularly useful ablatable materials for the IL include, but are not limited to, polyurethane, poly(vinyl butyral), (meth)acrylamide polymers, nitrocellulose, polyacetal, poly(cyanoacrylate), and polymers derived at least in part from any of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate, or combinations of two or more of these materials.

[0097] The IL has an average dry thickness of 0.5 μm to 5 μm, typically 0.8 μm to 2.5 μm.

[0098] Transparent polymer overcoat layer In some embodiments, the mask precursor optionally includes a transparent polymeric overcoat layer disposed directly on the IL opposite the LTHC layer. However, such a transparent polymeric overcoat layer is not required for the benefits of the present invention. The transparent polymeric overcoat layer generally includes one or more transparent film-forming polymers or resins, including, but not limited to, methacrylic acid copolymers (e.g., copolymers of ethyl methacrylate and methacrylic acid) with one or more fluoropolymer particles dispersed therein, as described, for example, in U.S. Pat. No. 6,259,465 (Tutt et al.), the disclosure of which is incorporated herein by reference. The transparent polymeric overcoat layer can provide abrasion resistance during processing due to the presence of the fluoropolymer particles. The transparent polymeric overcoat layer also provides a high degree of abrasion resistance when the mask element and the relief-forming precursor are in perfect optical contact. It can also act as a barrier to chemical migration from the mask elements to the relief-forming precursor.

[0099] When present, the transparent polymeric overcoat layer may be applied directly to the IL and may have an average dry thickness of from 0.05 μm to 1 μm.

[0100] Formation of mask elements In some embodiments, a mask may be formed by generating exposed and unexposed regions in the IL of a mask precursor described herein. The choice of imaging mechanism determines the possible variations in the formation of the mask image, as described below.

[0101] The exposure of the mask precursor to ablative light energy may be performed in selected areas, also known as "imagewise exposure." In some embodiments, imagewise exposure may be achieved using thermal radiation from a thermal or radiant laser that is scanned or rastered under computer control. Any of the known scanning devices may be used, including flatbed scanners, external drum scanners, and internal drum scanners. In these devices, the mask precursor material is fixed to a drum or bed, and a laser beam is focused to a spot that can impinge on the IL of the mask precursor material. Two or more lasers may simultaneously scan different areas of the IL.

[0102] For example, the mask precursor material may be exposed to infrared radiation, e.g., infrared radiation in the 700-1500 nm radiation wavelength range. Such mask precursor materials include one or more second infrared-absorbing materials in the IL that provide sensitivity to infrared radiation, as described above. In these embodiments, the mask precursor material may be exposed to infrared radiation using an infrared laser, such as a diode laser or Nd:YAG laser, that may be suitably attached to an infrared imager and scanned under computer control. Suitable infrared imagers include, but are not limited to, the TRENDSETTER imagesetter and ThermoFlex flexo CTP imager available from Eastman Kodak Company for use in CTP plate applications and imaging flexographic elements, the DIMENSION imagesetter available from Presstek (Hudson, NH) useful for CTP plate applications, the CYREL® Digital Imager (CDI SPARK) available from Esko-Graphics (Kennesaw, GA), and the OMNISETTER imager available from Misomex International (Hudson, NH) useful for imaging flexographic elements.

[0103] This exposure step is illustrated, for some embodiments, in Figure 1A, where a mask precursor material 10 is exposed to exposing infrared radiation 35 in an imagewise pattern to provide exposed regions 40 and unexposed regions 42, which are illustrated in mask element 36 shown in Figure 1B. These regions correspond to the mask image. As shown, exposed regions 40 are ablated and removed from unexposed regions 42. Thus, these exposed regions form the mask image.

[0104] The mask image formation step may also include removing the exposed or unexposed regions from the IL, as needed. In some embodiments, the exposed regions of the IL are removed, for example, by ablation of the exposed material in the IL. In this mechanism, the exposed regions of the IL are removed from the mask element by gas generation during ablation, leaving behind the mask image. The IL may also contain specific binders (e.g., non-crosslinked) that decompose when exposed to heat (e.g., generated by irradiation with an infrared laser) to rapidly generate gas. This effect allows for a chemical, rather than physical, change to occur, resulting in near-complete, rather than partial, migration of the IL. This distinguishes it from other mass transfer techniques.

[0105] In another embodiment, not shown, a mask image may be formed on the carrier sheet (and the LTHC layer disposed thereon) by creating exposed and unexposed areas in the IL and selectively removing the unexposed areas.

[0106] In some embodiments, the mask image in the IL of the mask element may be hardened by heat treatment, provided that the properties of the mask element are not adversely affected. Heat treatment may be accomplished by a variety of means, including, but not limited to, exposure to an oven, hot air treatment, contact with a heated platen, or passage through a heated roller device. Heat treatment is not necessary to effect hardening.

[0107] In yet another embodiment, the mask image may be formed in the IL as described above, and the exposed areas may then be transferred to a receptor sheet that is removed from the mask element prior to contact with the relief-forming precursor. Such processes are well known in the art.

[0108] In a peel-apart imaging mechanism, the exposed areas of the IL may be removed from the carrier sheet (and the LTHC layer disposed thereon) using a suitable receptor sheet based on unique adhesion properties within the IL. After image-wise exposure of the mask precursor, the receptor sheet is separated from the carrier sheet, leaving either the exposed or unexposed areas as mask elements.

[0109] Relief image formation After both the mask element and the relief-forming precursor are formed as described above, the mask element is brought into intimate optical contact with the relief-forming precursor, which includes a photosensitive layer with a low surface energy additive and is sensitive to UV curing light. This protocol may be performed by placing the mask element on the relief-forming precursor or the relief-forming precursor on the mask element, as described in more detail below. For example, contacting and bonding the mask element to the relief-forming precursor may be performed using a lamination device and lamination process. Vacuum drawdown of the mask element onto the relief-forming precursor may also be performed, with or without lamination, to achieve the desired intimate optical contact.

[0110] Some embodiments of the present invention can be understood with reference to the schematic diagrams shown in the series of Figures 1A-1E. As noted above, Figure 1A shows an imaging material 10 being exposed to infrared exposure radiation 35 to form mask elements 36 (Figure 1B).

[0111] 1C, mask element 36 comprises IL layer 15 over LTHC layer 20 (e.g., containing non-ablatable particles) overlying ablated IL layer 30 with a mask image formed therein. Mask element 36 is shown in intimate or full optical contact with relief-forming precursor 55, providing relief image-forming assembly 50. Relief-forming precursor 55 typically comprises UV-sensitive layer 60 (e.g., a photosensitive relief-forming layer having a low surface energy additive and sensitive to UV curing light) carried on substrate 65.

[0112] 1D illustrates the step of exposing relief imaging assembly 50 to ultraviolet light 70, indicated by arrows. UV light 70 passes through transparent polymeric carrier sheet 15 of mask element 36, LTHC layer 20, and exposed areas of IL 30 (e.g., portions of the IL layer where element 40 has been removed), causing photocuring in UV-sensitive layer 60 of relief-forming precursor 55.

[0113] After UV exposure, mask elements 36 may be removed from UV-sensitive layer 60 of relief-forming precursor 55, and a development protocol may provide a relief image (FIG. 1E) in UV-sensitive layer 60. As shown, this relief image has relief image peaks 75 and relief image valleys 80 in UV-sensitive layer 60.

[0114] Lamination As discussed above, the mask element and the relief-forming precursor may be in complete optical contact so as to provide an air-free interface at their shared interface. Typically, this is accomplished by laminating the mask element to the UV-sensitive layer of the relief-forming precursor by applying appropriate pressure or heat, or both, to form an air-free or void-free interface prior to UV exposure. However, if the relief-forming precursor comprises a UV-sensitive layer 60 having a low surface energy additive, as discussed above, the lamination step may not be necessary. As discussed above, vacuum drawdown of the mask element onto the relief-forming precursor may then be useful.

[0115] Commercially available laminators that provide both heat and uniform pressure may be used. Examples of such laminators include, but are not limited to, the KODAK model 800XL APPROVAL LAMINATOR available from Eastman Kodak Company (Rochester, NY). The CODOR LPP650 LAMINATOR available from CODOR (Amsterdam, The Netherlands) and the LEDCO HD Laminator available from Filmsource (Casselberry, FL) may also be useful. If a transparent polymeric overcoat layer is applied directly to the IL of the mask element material, this layer may be removed before lamination or other operations that form intimate optical contact between the mask element and the relief-forming precursor. The relief-image-forming assembly formed by combining the mask element and the relief-forming precursor may be fed into the laminator at the desired speed, temperature, and pressure.

[0116] Useful laminator apparatus and methods for their use are described, for example, in U.S. Patent No. 7,802,598 (Zwadlo et al.), the disclosure of which is incorporated herein by reference. As described therein, a pre-press flexographic plate laminator may be used to laminate a mask element ("masking film") onto a relief-forming precursor ("pre-press flexographic printing plate") by applying a balanced, distortion-free, optimized lamination force to minimize lateral distortion while achieving perfect optical contact.

[0117] In some embodiments, the relief-forming precursor does not have a separating layer, spacer layer, or anti-stick layer on the UV-sensitive relief-forming layer, and therefore pressure alone may be sufficient to achieve an air-free interface, since the relief-forming layer with the low surface energy additive therein may remain tacky or function as a pressure-sensitive adhesive due to the presence of the polymerizable monomer. The amount of low surface energy additive may be adjusted within the parameters defined herein to obtain the desired or optimal amount of adhesion. Too much low surface energy monomer may result in a surface with low adhesion, in which case thermal lamination may be used to provide optical contact with the mask.

[0118] UV exposure After achieving full optical contact between the mask element and the relief-forming precursor as described above, the relief-forming precursor may be exposed to curing UV light through the mask element to form an imaged relief-forming precursor having exposed and unexposed areas in the UV-sensitive layer. The exposed areas are cured and solidified by polymerizing the monomers in the UV-sensitive layer. The unexposed areas remain uncured, and the monomers are not polymerized. Thus, the uniformly emitted curing UV light Lines are projected onto the relief-forming precursor through a mask image that preferentially blocks a portion of the UV light through the remainder of the IL layer. In the unmasked (exposed) areas, the UV curing light hardens the UV-sensitive composition in the IL. The mask image is therefore substantially opaque to the exposing or curing UV light. This means that the mask image has a transmission density of 2 or greater, typically 3 or greater, in the unexposed areas. The remainder of the IL layer still contains the UV-sensitive material to absorb and block UV light. The unmasked (exposed) areas of the UV-sensitive composition may be substantially transparent. This means that the exposed areas have a transmission density of 0.5 or less, or 0.1 or less, more typically 0.5 to 0.1, or 0.1 to 0.3. The transmission density may be measured using an appropriate filter on a densitometer, such as a MACBETH TR 927 densitometer.

[0119] Generally, exposure of the relief-forming precursor through the mask element is achieved by flood exposure from a suitable ultraviolet radiation source. Exposure may be carried out in the presence of atmospheric oxygen. Exposure in a vacuum is not necessary if perfect optical contact is already made.

[0120] In the manufacture of relief image-forming elements, such as flexographic printing plates, generally, one side of a relief-forming precursor may first be exposed to UV curing light through a transparent substrate (known as a "back exposure") to prepare a thin, uniformly hardened layer (e.g., relief image valleys 80) on the substrate side of the UV-sensitive layer. The relief-forming precursor is then exposed to UV curing light through a mask element containing a mask image, thereby hardening the UV-sensitive layer in the unmasked (exposed) areas. The unexposed and unhardened areas of the UV-sensitive layer may then be removed by a development process (described below), leaving hardened areas (e.g., relief image peaks 75) that define a relief image printing surface having a predetermined, desired pattern of the shape and size of peaks 75 and valleys 80. The back exposure may occur either before or after full optical contact is made between the mask element and the relief-forming layer.

[0121] The wavelength or wavelength range suitable for the curing UV light is determined by the sensitivity of the relief-forming layer to electromagnetic radiation. In some embodiments, the curing UV light may have one or more wavelengths in the range of 150 nm to 450 nm, more typically 300 nm to 450 nm. UV light sources for flood or overall exposure include, but are not limited to, carbon arcs, mercury vapor arcs, fluorescent lamps, electronic flash units, and photographic flood lamps. UV light from mercury vapor lamps and sunlamps is particularly useful. Exemplary UV light sources include the SYLVANIA 350 BLACKLIGHT fluorescent lamp (FR 48T12 / 350 VL / VHO / 180, 115 watts) with a central emission wavelength of approximately 354 nm, available from Topbulb (East Chicago, Indiana), and the BURGESS EXPOSURE FRAME, Model 5K-3343V511, equipped with an ADDALUX 754-18017 lamp, available from Burgess Industries, Inc. (Plymouth, Massachusetts).

[0122] Other suitable sources of ultraviolet radiation include platemakers that can be used both to expose the relief-forming precursor and to develop the imaged relief-forming material after exposure. Examples of suitable platemakers include the KELLEIGH MODEL 310 PLATEMAKER available from Kelleigh Corporation (Trenton, NJ) and the GPP500F PLATE available from Global Asia Ltd. (Hong Kong). Examples of processors include, but are not limited to, processors.

[0123] The duration of exposure through the mask element is determined by the nature and thickness of the UV-sensitive layer of the relief-forming precursor, and the source and intensity of the UV light. For example, in one embodiment, a FLEXCEL-SRH plate precursor available from Eastman Kodak Company is mounted on a KELLEIGH MODEL 310 PLATEMAKER, A thin, uniform, cured layer may be prepared on the support side of the relief-forming precursor by back-exposing it to UV-A radiation through the transparent support for approximately 20 seconds. The relief-image-forming assembly of the mask element and the relief-forming precursor may then be exposed to UV radiation through the mask element for approximately 14 minutes. In this manner, the mask image information is transferred to the relief-forming precursor (e.g., a flexographic plate precursor).

[0124] Separation of the mask from the UV-sensitive layer Generally, the methods described herein may include removing the mask element from full optical contact with the imaged relief-forming precursor after UV exposure and before development. This may be done in any suitable manner, such as by peeling the elements apart. For example, it may be achieved by pulling the mask element away from the imaged relief-forming precursor.

[0125] In some embodiments, after UV exposure, the mask elements may be removed from the relief-forming layer by peeling them off. This may be done by providing support for one of the mask elements or the relief-forming precursor and then applying a pulling force to the edge or end of the other of the mask elements or the relief-forming precursor (e.g., the relief-forming layer). The low surface energy additive can reduce the surface energy and peel force, allowing the mask elements of the relief-forming layer to be more easily separated without damage. Thus, the ease of peeling or separation due to the reduced surface energy and peel force reduces peeling of the mask elements, thereby allowing the mask elements to be reused. Additionally, the reduced surface energy and peel force can reduce degradation and undesired breakage of the peaks of the relief-forming layer.

[0126] In some embodiments, the mask elements may be released from the relief-forming precursor, for example, by peeling them from the relief-forming layer. In these embodiments, the mask elements are laminated to the relief-forming layer. The mask is then peeled from the relief-forming layer after UV curing. However, such peeling is not intended to indicate that the mask itself undergoes delamination, such that different layers of the mask element are peeled from each other. Here, due to the presence of the low surface energy additive, the mask elements are peeled in their entirety from the relief-forming layer. Thus, while the mask is peeled from the relief-forming layer, the mask itself does not delaminate or break. Similarly, the relief-forming layer is not peeled from the relief-forming precursor.

[0127] In some embodiments, the relief-forming precursor may not include a transparent release layer on the UV-sensitive layer. In that case, the low surface energy additive allows the mask to be more easily peeled from the relief-forming precursor. Thus, the UV-sensitive relief-forming layer can be in direct contact with the mask elements, so that separation directly separates the mask from the relief-forming layer. The low surface energy additive can reduce surface energy and adhesion, so separation occurs cleanly without damaging either the mask elements or the relief-forming precursor.

[0128] In some embodiments, the relief-forming layer allows for a reduction in the force applied during peeling of the mask from the imaged relief image precursor (e.g., flexographic printing plate precursor). This comparison of force reduction for the present invention is relative to a relief-forming layer that does not contain a low surface energy additive. Thus, the low surface energy additive reduces the surface energy and peel force compared to the same composition without the low surface energy additive. The mask can be peeled more quickly and completely from the relief-forming precursor, leaving little or no residue. This effect allows for faster development of the imaged relief image precursor because there is little or no residue that inhibits the development process. The easier peeling minimizes handling and holding pressure of the flexographic imaging assembly, and the process can be easily carried out at room temperature, so no heat is required during the curing process.

[0129] The flexographic printing plate assembly with a UV-sensitive layer has a unique combination of materials that allows for rapid and complete mask peeling. "Complete" means that 95% or more, preferably 98% or more, 99% or more, or 100% of the mask is peeled away, leaving little or no residue. The composition of the UV-sensitive layer provides a peel force to the mask element bearing the mask image of less than about 73 g / inch, preferably less than about 60 g / inch, and more preferably less than about 55 g / inch. The relief-forming layer may have a measurable peel force to the mask of about 1 g / inch or more, about 5 g / inch or more, or about 10 g / inch or more.

[0130] In some embodiments, the relief-forming layer is a solvent-developable plate precursor and has a peel force from a mask element bearing a mask image of less than about 73 g / in, preferably less than about 60 g / in, and more preferably less than about 55 g / in. The solvent-developable relief-forming layer may have a measurable peel force from a mask of about 1 g / in or more, about 5 g / in or more, or about 10 g / in or more.

[0131] In some embodiments, the relief-forming layer is a water-developable plate precursor and has a peel force from a mask element bearing a mask image of less than about 40 g / in, preferably less than about 30 g / in, and more preferably less than about 20 g / in. The water-developable relief-forming layer may have a measurable peel force from a mask of about 1 g / in or more, about 5 g / in or more, or about 10 g / in or more.

[0132] The peel force value can be measured by attaching a 2.54 cm wide, 25.4 cm long mask strip laminated to the UV-sensitive layer with a low surface energy additive of a UV-exposed flexographic printing plate, plate-side down, with double-sided tape to an IMASS SP-2000 Slip / Peel Tester (IMASS Inc., Accord, Massachusetts). The leading edge of the mask is pulled away from the printing plate and mounted in a force gauge. The maximum peel force per g / linear inch (2.54 cm) width of film is measured at a peel angle of 180° and a peel speed of 2 cm / sec.

[0133] In some embodiments, the mask element containing the mask image is removed from the UV-exposed, UV-sensitive, relief-forming layer of the flexographic printing plate precursor by peeling the mask element at the interface between the mask element and the relief-forming layer. This peeling process may be performed as described in U.S. Pat. No. 7,802,598, using a vacuum for retention. The corners of the mask element are then pulled away from the printing plate at a speed of 2-10 cm / sec and a peel angle of 150-180°, thereby pulling the imaged film substantially back onto the mask element and holding the imaged film in continuous motion near the surface of the vacuum table until the entire mask element is removed from the UV-sensitive layer of the printing plate. In the practice of the present invention, the mask element can generally be said to be "completely" or substantially completely removed from the exposed, radiation-curable layer of the precursor because 95% or more by weight of the dried mask element is removed in this operation. "Completely" means that 95% or more, preferably 98% or more, 99% or more, or 100% of the mask is peeled away, leaving little or no residue.

[0134] developing After the mask elements are removed from the relief-forming layer, the imaged relief-forming precursor is then typically developed with a suitable developer (or processing solution or "washout solution") to form a relief image. Development causes the unexposed (uncured) areas of the UV-sensitive layer to It is removed, leaving exposed (hardened) areas that define a relief image, as shown in Figure IE.

[0135] Any known organic solvent-based or aqueous developer can be used in this process, including known developers containing predominantly chlorinated organic solvents. However, other useful developers are predominantly non-chlorinated organic solvents. By "predominantly," we mean that more than 50% (by weight) of the developer contains one or more non-chlorinated organic solvents, such as aliphatic hydrocarbons or long-chain alcohols (i.e., alcohols having at least 7 carbon atoms). The remainder of the developer may be chlorinated organic solvents known in the art for this application.

[0136] Certain useful developers are primarily known as "perchloroethylene alternative solvents" (PAS). These PAS are generally volatile organic compounds typically composed of a mixture of aliphatic hydrocarbons and long-chain alcohols. Examples of such commercially available solvents include, but are not limited to, PLATESOLV available from Hydrite Chemical Co. (Brookfield, Wisconsin), NYLOSOLV® available from BASF (Germany), FLEXOSOL® available from DuPont (Wilmington, Delaware), OptiSol® available from DuPont (Wilmington, Delaware), and SOLVIT® QD available from MacDermid (Denver, Colorado).

[0137] Other useful developers are described in U.S. Pat. No. 5,354,645 (Schober et al.), the disclosure of which is incorporated herein by reference. These developers include one or more of diethylene glycol dialkyl ethers, acetate esters or alcohols, carboxylic acid esters, and esters of alkoxy-substituted carboxylic acids. Still other useful developers are described in U.S. Pat. No. 6,162,593 (Wyatt et al.), which describes developers containing diisopropylbenzene (DIPB), and U.S. Pat. No. 6,248,502 (Eklund).

[0138] Further useful developers are described in U.S. Pat. No. 6,582,886 (Hendrickson et al.), which contain methyl esters alone or in mixtures with cosolvents, such as various alcohols, that are soluble in the methyl esters. U.S. Patent Application Publication No. 2010 / 0068651 (Bradford) describes useful developers containing dipropylene glycol dimethyl ether (DME), alone or in combination with various cosolvents, such as alcohols and aliphatic dibasic ethers. Still other useful developers are described in U.S. Patent Application Publication No. 2011 / 0183260 (Fohrenkamm et al.). Other useful developers are described in U.S. Pat. No. 8,771,925 (Fohrenkamm et al.). These developers contain diisopropylbenzene and one or more organic cosolvents, one of which is an aliphatic dibasic ester. Still other useful developers are disclosed in U.S. Pat. No. 9,005,884 (Yawata et al.). These treatment solutions may contain an alkali metal salt of a saturated fatty acid having 12 to 18 carbon atoms and an alkali metal salt of an unsaturated fatty acid having 12 to 18 carbon atoms, with the weight ratio of the first fatty acid salt to the second fatty acid salt being 20:80 to 80:20.

[0139] Still other useful developers are described in commonly assigned, co-pending U.S. Patent No. 10,248,025 (Ollmann et al.). Such flexographic developers comprise: a) a fatty acid composition consisting of one or more saturated or unsaturated fatty acids or alkali metal salts thereof, each individually having from 12 to 20 carbon atoms, present in an amount of from 0.25% to 2.0% by weight, and at least 85% by weight of the fatty acid composition being made up of one or more C18 mono- or polyunsaturated fatty acids or alkali metal salts thereof; b) an aminopolycarboxylic acid or alkali metal salt thereof in an amount of from 0.05% to 0.30% by weight; c) an aminopolycarboxylic acid or alkali metal salt thereof in an amount of from 0.05% to 0.30% by weight; ) a buffer compound in an amount of 0.5% to 0.60% by weight, and d) water.

[0140] Development may be carried out under known conditions, for example, for 1 minute to 20 minutes at a temperature of 20° C. to 32° C. The type of development equipment and the particular developer used will dictate the specific development conditions, which may also be adapted by one skilled in the art.

[0141] In some circumstances, it may be appropriate to perform a post-development treatment of the relief image in the imaged relief-forming precursor. Typical post-development treatments include drying the relief image to remove excess solvent and post-curing the relief image by exposing it to curing radiation to cause further hardening or crosslinking. The conditions for these processes are well known to those skilled in the art. For example, the relief image may be dried by blotting or wiping, or may be dried in a forced air or infrared oven. Drying times and temperatures will be apparent to those skilled in the art. The post-curing may be performed using the same type of ultraviolet light previously used to expose the relief-forming precursor through the imaged masking material.

[0142] If the relief image surface still remains tacky, detackification (or "light finishing") may be used. Such treatments, for example, by treatment with bromide or chloride solutions or exposure to ultraviolet or visible light, are well known to those skilled in the art.

[0143] The resulting relief image may have a depth of 2% to 100% of the original thickness of the UV-sensitive layer (e.g., when the UV-sensitive layer is disposed on a substrate). In the case of a flexographic printing plate, the maximum dry depth of the relief image may be 150 μm to 1000 μm, typically 200 μm to 500 μm. In the case of a printed circuit board, the UV-sensitive layer may be completely removed in the exposed or unexposed areas to expose the underlying metal layer. In such elements, the maximum depth of the relief image depends on the dry thickness of the UV-sensitive layer. Advantageously, in any embodiment, the relief image may have a shoulder angle greater than 50°.

[0144] Thus, in some embodiments, the method is carried out where the relief-forming precursor is a UV-sensitive flexographic printing plate precursor, and the precursor is imaged and developed to provide a flexographic printing plate having a relief image layer formed from the relief-forming layer of the relief-forming precursor. Similarly, letterpress printing plates may be prepared from suitable precursor elements.

[0145] After exposure, the relief image layer may continue to include a low surface energy additive that is integrated into or adhered (e.g., polymerized) to the polymer of the relief image layer. Thus, the ready-to-use relief image layer may have low surface energy portions present at the exposed surface. As a result, the relief image layer has an exposed surface where the silicone is exposed, which results in a relatively low surface energy, as described below.

[0146] In some embodiments, the relief image layer may receive ink during the process of creating the relief image with ink. The ink may be applied to the relief image layer in an appropriate amount to help reduce printing dot gain. Therefore, the relief image having polymerized low surface energy portions can easily reduce printing dot gain. This eliminates the problem of excessive printing dot gain in flexographic printing plates.

[0147] In some embodiments, the ink-bearing relief image layer may be washed to remove the ink for various reasons, such as changing the color or cleaning the surface to allow for the application of new ink. In addition, replacing the ink may help remove particles from the relief image layer that may be generated during the process. In addition to facilitating ink washing, the relief image layer may also be washed to remove low surface energy areas to facilitate ink removal from surface features (e.g., ridges, valleys, etc.) after printing. This provides a clean relief surface, allowing the plate to be stored and subsequently used again for printing.

[0148] Those skilled in the art will readily recognize the various uses that such inked elements have in a variety of industries, including flexographic printing of various packaging materials.

[0149] Example Preparation of relief-forming precursor The polymer / binder is introduced into a double-arm sigma mixer heated to 120°C along with the plasticizer. Once the plasticizer is absorbed into the binder and the mixture reaches a homogeneous "semi-molten" state, the remainder of the premix formulation, including the monomer, stabilizer, photoinitiator, inhibitor, colorant, and solvent, is gradually added as a solution in Comparative Example 1. Additionally, a silicone acrylate monomer, such as a silicone polyether acrylate (e.g., Evonik's TEGO RAD 2250, herein referred to as TR2250), is further introduced as a cyclopentanone solution in the examples described herein. Thus, TR2250 is omitted in the comparative examples and included in the examples. The composition continues to be mixed for 1 to 1.5 hours until no binder particles are visible and the melt is homogeneous. Once the melt reaches the mixing temperature, the mixer temperature can be turned off. The material is then allowed to "cool" in the mixer for a period of time (to approximately 75°C) without mixing before being removed.

[0150] Once the materials are removed from the mixer, the required amount of photosensitive photopolymer mixture is measured out and placed between the base film and cover sheet. A suitable feeler gauge is used to determine the exact thickness of the plate, and the feeler gauge is placed between the base film and cover film. This sandwich (base film, photosensitive photopolymer, and cover film) is then placed in a hot metal press set to ∼240°F and pressed at approximately 20 tons of pressure for 2-3 minutes to produce a photosensitive printing plate precursor.

[0151] Comparative Example 1 The formulation is prepared without the low surface energy monomer TR2250. Following the procedure described above, a solvent-processable photosensitive flexographic printing plate precursor was prepared using a photopolymer composition similar to that described in U.S. Pat. No. 6,897,006. The composition consisted of 60 parts by weight of a triblock copolymer (trade name Kraton 405), 30.17 parts by weight of a polybutadiene plasticizer (trade name Nisso PB2000 manufactured by Nippon Soda Co., Ltd. and Polyvest 110 manufactured by Evonik), a total of 0.91 parts by weight of stabilizers and inhibitors (BHT Swanox, Nonflex EBP, Q-1301), 0.13 parts by weight of a solvent (THF), 0.92 parts by weight of colorants (Diaresin Blue and NBT-1150 Green), 1.34 parts by weight of a benzyl dimethyl ketal photoinitiator (Omnirad 651), and a total of 7.69 parts by weight of crosslinking monomers (HDDA and TMPTA).

[0152] Example 1 A formulation was prepared using low surface energy silicone polyether acrylate, TEGO RAD 2250. A flexographic printing plate photopolymer was obtained as described in Comparative Example 1, except that 0.5% of low surface energy silicone polyether acrylate (TR2250) was added and cyclopentanone was used as the solvent instead of THF.

[0153] Comparative Example 2 As Comparative Example 2 for Example 2, Flexcel NX Ultra photopolymer plate precursor, commercially available from Miraclon Corporation, was used.

[0154] Example 2 To test the effectiveness of low-surface-energy monomers (e.g., silicone acrylates) in reducing / enhancing the release of mask elements from water-developable flexographic printing plate precursors, TR2250 was introduced into Flexcel NX Ultra photopolymer plate precursors (e.g., UV-sensitive materials) by scraping a photosensitive photopolymer mixture from the Flexcel NX Ultra photopolymer plate precursor and placing the photopolymer mixture in a Sigma mixer set at 120°C. The mixture quickly reached a semi-molten state, at which point 1 part by weight of TR2250 was slowly added. The composition was then mixed for an additional hour, allowed to cool, and finally removed from the mixer. The mixture, now containing TR2250, was then used in an appropriate amount to prepare a UV-curable photosensitive flexographic printing plate precursor material using the procedure detailed above.

[0155] Comparative Example 3 As a comparative / test example, bis(3-aminopropyl)-terminated poly(dimethylsiloxane) (Sigma Aldrich), an amino-functionalized silicone oil similar to the amino-functionalized silicone oil described in U.S. Pat. No. 8,114,566, was incorporated into the photosensitive polymer composition of Comparative Example 1 in an amount of 0.5 parts by weight.

[0156] After removing the cover sheet from the photopolymer plate precursor, the imaged mask was laminated to the imaging surface (relief-forming layer) of the flexographic printing plate precursor. Lamination was performed using a commercially available Flexcel NX Wide 5080 Laminator with standard settings, placing the mask element in direct and intimate contact with the imaging surface of the UV-sensitive layer of the relief-forming precursor. Following lamination, the mask element and relief-forming precursor were uniformly exposed through the backside, followed by an imagewise exposure through the mask element on the frontside. Numerous air bubbles were observed at the interface between the mask and the relief-forming layer. Air bubble formation is known to adversely affect image reproduction from the mask onto the UV-sensitive material because it creates gaps between the mask image and the relief-forming material, disrupting intimate contact between the mask and the relief-forming layer. In contrast, the examples containing silicone monomers did not form air bubbles.

[0157] Peel force measurement Peel force measurements were performed according to the process described in U.S. Patent No. 10,207,491. After removing the cover sheet from the relief-forming layer of the relief-forming precursor, the imaged mask was laminated to the imaging surface of the UV-sensitive layer. Lamination was performed using a commercially available Flexcel NX Wide 5080 Laminator with standard settings, with the mask element in direct and intimate contact with the imaging surface of the relief-forming layer. Following lamination, the mask element and relief-forming precursor were uniformly exposed through the backside, followed by an imagewise frontside exposure through the mask element. Two-inch-wide samples for use in peel testing were cut for each combination of laminated and exposed sample pieces. For this test, the relief-forming precursor was adhered to a stainless steel plate using 3M® double-sided clear adhesive tape E1120H. Peel force (in grams) was measured using an IMASS Adhesion Tester SP-2100 (available from Imass, Inc., Hingham, Massachusetts) with a 5 kg load, a 180° peel angle, and a peel rate of 12 inches / minute. Measurements were averaged over 5 seconds and with a 1 second delay.

[0158] Forming a flexographic printing plate having a relief image After removing the cover film from the relief-forming layer of the relief-forming precursor, followed by laminating the mask and UV curing as described above, the mask is removed from the photosensitive layer manually or by a mechanical process. is treated with a solvent or aqueous plate treating agent depending on the nature of the photopolymer plate precursor, dried and finished (post-exposed to UV light) to obtain a relief printing plate.

[0159] Surface energy measurement To determine the surface energy value of the relief flexographic printing plate, first, contact angles were measured using a polar (water) liquid drop and a dispersive (diiodomethane) liquid drop.

[0160] The surface energy components for each liquid used are as follows: water:

[0161]

number

[0162]

number

[0163]

number

[0164]

number

[0165]

number

[0166]

number

[0167]

number

[0168]

number

[0169]

number

[0170]

number

[0171]

number

[0172]

number

[0173]

number

[0174]

number

[0175] An Overview of Surface Energy and Peel Force The peel force to peel the mask element from the imaged relief-forming layer of the relief-forming precursor was measured as described herein. Additionally, the relief-forming layer was developed into a relief image layer for a relief printing plate, and the surface energy of the relief image layer was then measured as described herein.

[0176] As shown in Table 1, the examples are compared with the comparative examples. The peel force for removing the mask element from the imaged relief-forming layer of the relief-forming precursor is significantly reduced. The leaf printing plate has a reduced surface energy compared to the high surface energy of the relief image layer that does not contain the low surface energy additive.

[0177] As can be seen from Table 1, for the solvent-developable relief-forming precursor, Example 1, which contains a low surface energy monomer, shows a 30% reduction in the amount of force required to peel a mask TIL-R (e.g., a mask described in U.S. Pat. No. 8,945,813 (Kidnie)) from the plate compared to Comparative Example 1. Also, when a mask such as that described in U.S. Patent Application Publication No. 2019 / 0258154 (Kidnie) is used, the peel force is reduced by 65% ​​compared to Comparative Example 1. This significant reduction in peel force allows the imaged mask to be easily peeled and removed from the plate, which may enable peeling to be performed by simple mechanical devices for automated removal of the mask from the relief-forming layer.

[0178] Additionally, as shown in Table 1, the peel force of Example 2 (water-developable Ultra NX plate with low surface energy monomer) was reduced by 52% compared to Comparative Example 2, which allows the mask to be more easily peeled from the water-developable relief-forming layer of the flexographic plate precursor, which may help prevent accidental damage to the relief-forming layer of the mask or relief flexographic printing plate during separation.

[0179] [Table 1]

[0180] It should be noted that different types of plates may have different surface energies with respect to the low surface energy additive. That is, the type of matrix material of the relief-forming layer is the basis for the surface energy. In some cases, the surface energy can be significantly reduced by adding a low surface energy additive. Therefore, the reduction in surface energy is compared to the same type of material that does not contain the low surface energy additive silicone acrylate. Therefore, when a low surface energy additive is added to a material such as Comparative Example 2, as in Example 2, the surface energy is further reduced.

[0181] In view of the above, the low surface energy additive can reduce the peel force for UV-curable relief-forming materials for various types of matrix materials. This allows the use of certain types of polymerizable monomers in the matrix, and as a result, the addition of the low surface energy additive reduces the peel force for those specific types of monomers. It is understood that different types of monomers and the resulting polymers may have different peel forces without the low surface energy additive, and the addition of the low surface energy additive reduces the peel force for each of those different types of monomers and resulting polymers. Similarly, the surface energy for one type of polymer may be higher than that of another type of polymer. However, the low surface energy additive can reduce the surface energy of those polymers in the resulting relief image layer. Thus, the low surface energy additive reduces the peel force for peeling the mask from the UV-sensitive layer and reduces the surface energy of the resulting relief image layer compared to a composition without the low surface energy additive.

[0182] In some embodiments, the peel force may be less than about 73.41 g / inch for either type of mask. For solvent-developable plate precursors, the peel force may be less than about 70 g / inch, more preferably less than about 60 g / inch, more preferably less than about 55 g / inch, more preferably less than about 50 g / inch. For water-developable plate precursors, the peel force may be less than about 30 g / inch, more preferably less than about 25 g / inch, more preferably less than about 20 g / inch, more preferably less than about 15 g / inch.

[0183] In some embodiments, the surface energy of the solvent-developable relief image layer can be less than about 60 mj / m2, more preferably less than about 58 mj / m2, less than about 57 mj / m2, or less than about 56 mj / m2, and the surface energy of the water-developable relief image layer can be less than about 46 mj / m2, more preferably less than about 45 mj / m2, less than about 44 mj / m2, or less than about 43 mj / m2.

[0184] definition As used herein to define various components of the non-ablatable light-to-heat conversion (LTHC) layer, the non-silver halide thermally ablatable imaging layer (IL), and other materials, layers, and ingredients (e.g., developers and processing solutions) used in the practice of the present invention, unless otherwise indicated, the singular forms "a," "an," and "the" are intended to include one or more of those components (i.e., include plural referents).

[0185] Each term not expressly defined in this application is understood to have the meaning generally accepted by those skilled in the art. If the construction of a term renders the term meaningless or substantially meaningless in the context, it should be construed as having its standard dictionary meaning.

[0186] The various ranges of numerical values ​​specified herein, unless otherwise expressly stated, are intended to be approximations, as if both the minimum and maximum values ​​within the stated range were preceded by the word "about." In this manner, slight variations above or below the stated ranges may be effective to achieve substantially similar results as values ​​within the range. The disclosure of these ranges also includes continuous ranges, including all values ​​between the minimum and maximum values. as well as the endpoints of the ranges are intended.

[0187] In this specification, the non-ablatable light-to-heat conversion layer is also referred to as the LTHC layer.

[0188] Non-silver halide thermally ablatable imaging layers are also referred to herein as ILs.

[0189] As used herein, unless otherwise specified, the term "imaging material" is used to refer to embodiments prepared and used in accordance with the present invention. Such imaging materials may also be known as "mask films," "mask precursors," or "masking elements." The imaging material may be converted by suitable thermal (infrared) imaging into a "mask element," which contains a mask image that can be used to form a relief image in accordance with the present invention.

[0190] Unless otherwise indicated, percentages are by weight.

[0191] The term "relief-forming precursor" is used herein to refer to any imaging element or imaging material in which a relief image can be generated by exposure through a mask element. Examples of such relief-forming precursors are described in more detail below, but some relief-forming precursors include flexographic printing plate precursors, letterpress printing plate precursors, and printed circuit boards. Further details about relief-forming materials are described in U.S. Patent Application Publication No. 2005 / 0227182 (cited above), the disclosure of which is incorporated herein by reference. In this document, relief-forming precursors are generally referred to as "radiation-sensitive elements."

[0192] Unless otherwise indicated, the term "ablative" or "ablation" refers to thermal imaging with a laser that produces rapid localized changes in a non-silver halide thermally ablatable imaging layer (IL) of an imaging material, thereby removing material within the IL from the IL. This is distinguishable from other mass transfer or imaging techniques such as melting, evaporation, or sublimation.

[0193] The terms "optical contact" and "perfect optical contact" are synonymous and mean that two layers or elements (such as a mask element and a relief-forming precursor) share an interface and are in intimate physical contact such that there is substantially no air gap or void between the contacting surfaces, thereby providing an "air-free interface." More precisely, two surfaces are defined to be in optical contact when the reflective and transmissive properties of their interface are substantially completely described by Fresnel's laws for the reflection and transmission of light at refractive index boundaries.

[0194] Unless otherwise specified, the term "transparent," as used herein, refers to the ability of a material or layer to transmit at least 95% of impinging (or incident) radiation, such as radiation having wavelengths between 200 nm and 750 nm (i.e., radiation commonly known in the art as ultraviolet and visible light). The transparent polymeric carrier sheets and LTHC layers described below specifically possess this characteristic.

[0195] The "average dry thickness" of a given dry layer is generally the average of 10 different measurements on a dry cross-sectional image of that layer.

[0196] Those skilled in the art will appreciate that, for the processes and methods disclosed herein, the functions performed in the processes and methods may be performed in differing order. Additionally, the outlined steps and operations are presented by way of example only, and some of the steps and operations may be optional, combined into fewer steps and operations, or expanded into additional steps and operations without detracting from the essence of the disclosed embodiments.

[0197] The present disclosure is not limited to the specific embodiments described in this application, which are intended as illustrations of various aspects. As will be apparent to those skilled in the art, numerous modifications and variations are possible without departing from the spirit and scope of the present disclosure. Functionally equivalent methods and devices within the scope of the present disclosure, in addition to the methods and devices recited herein, will be apparent to those skilled in the art from the foregoing description. Such modifications and variations are intended to be included within the scope of the appended claims. The present disclosure is limited only by the language of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that the present disclosure is not limited to particular methods, reagents, compounds, compositions, or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0198] With respect to the use of substantially all plural and / or singular terms herein, those skilled in the art can convert from plural to singular and / or from singular to plural as appropriate to the context and / or application. For ease of understanding, various singular / plural permutations may be expressly explained herein.

[0199] Those skilled in the art will understand that, in general, the terminology used herein, and particularly in the appended claims (e.g., the body of the appended claims), is generally intended as "open" language (e.g., the term "comprising" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "including" should be interpreted as "including but not limited to," etc.). Those skilled in the art will further understand that where a specific number recitation is intended in an introduced claim, such intention will be expressly recited in the claim, and that, in the absence of such recitation, no such intention exists. For example, as an aid to understanding, the appended claims may include introducing claim recitations using the introductory phrases "at least one" and "one or more." However, the use of such phrases should not be construed as suggesting that introducing a claim recitation with the indefinite article "a" or "an" limits any particular claim that includes the claim recitation so introduced to embodiments that include only one such recitation, even if the same claim also includes the introductory phrase "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should be construed to mean "at least one" or "one or more"). The same applies to the use of definite articles used to introduce claim recitations. Those skilled in the art will also understand that even if a specific number is explicitly recited in an introduced claim recitation, such a recitation should be construed to mean at least the recited number (e.g., the mere recitation of "two recitations" without any other modifier means at least two recitations, or more than two recitations).Furthermore, in instances where conventional language similar to "at least one of A, B, and C, etc." is used, such syntax is typically intended in the sense that one of ordinary skill in the art would understand the conventional language (e.g., "a system having at least one of A, B, and C" includes, but is not limited to, systems having A only, B only, C only, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). In instances where conventional language similar to "at least one of A, B, or C, etc." is used, it is typically intended that Such syntax is intended in the sense that one of ordinary skill in the art would understand the conventional expression (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). One of ordinary skill in the art will further understand that virtually any disjunctive word and / or phrase presenting two or more alternative terms, whether in the specification, claims, or drawings, should be understood to contemplate the possibility of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

[0200] Additionally, when features or aspects of the present disclosure are described as a Markush group, one skilled in the art will recognize that the present disclosure also is described as any individual component or subgroup of the members of the Markush group.

[0201] Those skilled in the art will appreciate that, for all purposes, e.g., upon filing of a specification, all ranges disclosed herein encompass all possible subranges and combinations of subranges. Recited ranges will be readily understood as fully descriptive and enabling that range to be divided into at least two, three, four, five, ten, etc. As a non-limiting example, each range described herein can be readily divided into a lower third, a middle third, and an upper third, etc. Those skilled in the art will also appreciate that all terms such as "up to," "at least," etc., refer to ranges that are inclusive of the recited number and can subsequently be divided into subranges as described above. Finally, those skilled in the art will appreciate that ranges include each individual element. Thus, for example, a group having 1 to 3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1 to 5 cells refers to groups having 1, 2, 3, 4, or 5 cells, etc.

[0202] From the foregoing, it will be understood that various embodiments of the present disclosure have been described herein for purposes of illustration and that various modifications and variations are possible without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the appended claims.

[0203] All references cited herein are hereby incorporated by reference in their entirety.

Claims

1. A relief-forming precursor comprising: A substrate; a relief-forming layer having a bottom surface facing the substrate and a relief-forming surface facing away from the substrate, polymer, at least one photopolymerizable monomer; a photoinitiator, and a relief-forming layer containing a low surface energy monomer; a relief-forming precursor comprising:

2. The relief-forming precursor of claim 1 , wherein the low surface energy monomer has a silicone moiety attached to at least one polymerizable functional group.

3. The relief-forming precursor of claim 2 , wherein the at least one polymerizable functional group comprises at least one acrylate moiety.

4. The relief-forming precursor of claim 3 , wherein the at least one acrylate moiety comprises an acrylate or a methacrylate.

5. The relief-forming precursor of claim 2 , wherein the low surface energy monomer further comprises a plurality of polymerizable functional groups attached to the silicone moiety.

6. In order, The substrate; an optional metal layer on the substrate; a single layer of said relief-forming layer on said substrate or metal layer; 10. The relief-forming precursor of claim 1, consisting essentially of said relief-forming layer and an optional cover sheet over said relief-forming layer.

7. 1. A relief forming assembly comprising: A relief-forming precursor according to claim 1; a mask element having an imaged layer having a mask image, the mask element being in complete optical contact with the relief-forming surface of the relief-forming layer; A relief forming assembly comprising:

8. The relief forming assembly of claim 7 , wherein the low surface energy monomer comprises a silicone moiety bonded to at least one polymerizable functional group.

9. The relief-forming assembly of claim 8 , wherein the at least one polymerizable functional group comprises at least one acrylate moiety.

10. The relief forming assembly of claim 9 , wherein the at least one acrylate moiety comprises an acrylate or a methacrylate.

11. The relief-forming assembly of claim 7 , further comprising an adhesive layer on the substrate opposite the relief-forming layer.

12. The relief formation according to claim 11 , further comprising an antihalation material in the adhesive layer. assembly.

13. In order, The substrate; an optional metal layer on the substrate; a single layer of said relief-forming layer on said substrate or metal layer; 8. The relief forming assembly of claim 7, consisting essentially of said mask element.

14. 10. A method of making the relief forming assembly of claim 7, comprising: disposing the imaged layer of the mask element on the relief-forming surface of the relief-forming layer; forming said complete optical contact between said mask element and said relief-forming surface; A method comprising:

15. laminating the mask element to the relief-forming surface; and 15. The method of claim 14, including at least one of bonding the mask elements to the relief-forming surface by vacuum drawdown.

16. 1. A method of producing a relief image in a relief forming assembly, comprising: Providing a relief forming assembly according to claim 7; exposing the relief-forming layer through the mask element to curing ultraviolet light to form an imaged relief-forming layer having ultraviolet-exposed areas forming polymerized regions and unexposed areas forming non-polymerized regions within the imaged relief-forming layer; removing the mask elements from the imaged relief-forming layer; developing the imaged relief-forming layer by removing the unpolymerized areas in the imaged relief-forming layer, thereby forming a relief image element having a relief image; A method comprising:

17. 17. The method of claim 16, further comprising polymerizing the at least one photopolymerizable monomer and the low surface energy monomer with the photoinitiator such that low surface energy portions are present on the relief surface of the relief image of the relief image element.

18. 20. The method of claim 17, further comprising polymerizing a plurality of polymerizable functional groups of the low surface energy monomer with the at least one photopolymerizable monomer to form a crosslinked polymeric relief image element.

19. 20. The method of claim 17, wherein the low surface energy monomer has a silicone moiety attached to at least one polymerizable functional group.

20. 20. The method of claim 19, wherein the at least one polymerizable functional group comprises at least one acrylate moiety.

21. A relief image element comprising: A substrate; a relief image layer having an elastomer and a copolymer, the copolymer comprising at least one photopolymerizable monomer and a low surface energy monomer having a silicone moiety, the relief surface of the relief image layer having relief image ridges and valleys, and a portion of the silicone moiety present in the relief surface; A relief image element comprising:

22. 22. The relief image element of claim 21, wherein said copolymer comprises crosslinking said photopolymerizable monomer with a low surface energy monomer.

Images