Flexographic printing mask having a laser thermal imaging film

Abstract

A mask element for flexographic printing is provided. The mask element can be used to manufacture a mask having a mask image. The mask element includes: a transparent polymer carrier sheet; a barrier layer on the transparent polymer carrier sheet, the barrier layer including uncrosslinked nitrocellulose; and an image forming layer on the barrier layer, the image forming layer including a non-halogenated silver thermally ablatable material including uncrosslinked nitrocellulose, carbon black, and an infrared (IR) dye. In some embodiments, the mask element further includes a transparent overcoat layer on the image forming layer. The mask can include: an imaged region in the image forming layer, the imaged region having an optical aperture substantially free of carbon black and uncrosslinked nitrocellulose therein; and a non-imaged region in the image forming layer, the non-imaged region having uncrosslinked nitrocellulose, carbon black, and an infrared dye.

Description

Technical Field

[0001] The present disclosure relates to a thermal image forming film for a flexographic printing mask, and a method for manufacturing and using the same. In particular, the present disclosure relates to a thermal image forming film before or after mask elements are formed therein.

Background Art

[0002] Previously, a mask and a photosensitive material that can be used to form a relief image in a flexographic printing plate precursor were used in combination. However, the material used for the mask may have optical properties that can change the formation of the relief image from the photosensitive relief forming layer, and may not be optimal. In many cases, it is not very effective, and thus the mask may have optical properties that require a long time for the treatment of the relief forming layer. When the treatment time is longer, in applications for forming a relief image, the mask elements become less economical. Therefore, by optimizing the optical properties of the mask, the curing of the irradiated layer of the relief forming layer of the flexographic printing plate can be improved.

[0003] A photosensitive relief forming material having a relief forming material or a photosensitive layer is well known in the art. Important advancements in the art, and useful materials for forming a flexographic relief image, are described in U.S. Patent No. 8,142,987 (Ali et al., hereinafter referred to as U.S. '987). U.S. '987 describes suitable mask element precursors, photosensitive materials for the relief forming layer, and methods and apparatuses for forming mask elements from the mask precursors and for forming a final relief image from the photosensitive relief forming precursor materials.

[0004] Typically, a laminator device or a vacuum drawdown, or both, are used to dispose a mask in intimate contact with a photosensitive relief-forming precursor material, and the chemical radiation (e.g., UV radiation) is exposed overall to cure the photosensitive composition in the relief-forming precursor material in the non-mask areas, thereby forming a negative image of the mask in the photosensitive relief-forming precursor. Next, the mask can be removed, and the uncured areas on the relief-forming material can be removed using a developing process. After drying and post-UV curing, the resulting image-formed relief-forming precursor has a relief image that can be used in flexographic or letterpress printing operations.

[0005] Advances in mask element precursors are described in U.S. Patent No. 7,799,504 (Zwadlo et al.). Another useful mask element precursors and methods of using them are described in 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). Advances in photosensitive materials are described in U.S. Patent Application Publication No. 2019 / 0258154 (Kidnie).

[0006] Previously, laser imaging materials included carbon black in a coating layer as described, for example, in U.S. Patent No. 4,588,674. Here, the carbon black is used in the upper layer such that the carbon black-to-binder ratio is preferably selected such that a hard abrasion-resistant coating having an optical density greater than 2.0 is obtained.

[0007] The claimed subject matter is not limited to embodiments that solve any disadvantages or operate only in the environments as described above. This background is provided only to illustrate examples of where the present disclosure can be utilized. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0008] In some embodiments, a mask element for flexographic printing may include: a substrate; a polymer layer on the substrate; and an image-forming layer on the polymer layer, the image-forming layer being thermally ablatable and including carbon black and at least one other infrared-absorbing material in a thermally-abatable polymer binder. The substrate may be a transparent polymer carrier sheet. The polymer layer may be a barrier layer having uncrosslinked nitrocellulose. The thermally ablatable image-forming layer of non-halogenated silver may be an image-forming layer having uncrosslinked nitrocellulose, carbon black, and an infrared (IR) dye (e.g., selective for IR light absorption) (e.g., no silver halide is present).

[0009] In some embodiments, a mask element for flexographic printing is provided. The mask element may be a mask precursor used to produce a mask having a mask image. The mask element may include: a transparent polymer carrier sheet; a barrier layer on the transparent polymer carrier sheet, the barrier layer including uncrosslinked nitrocellulose; and an image-forming layer on the barrier layer, the image-forming layer including a thermally ablatable material including uncrosslinked nitrocellulose, carbon black, and an IR dye. In some aspects, the mask element may further include a transparent overcoat layer on the image-forming layer.

[0010] In some embodiments, the polymer barrier layer may not include an IR dye. That is, the barrier layer may be selective for absorption of UV light and may not include an IR dye that can absorb IR light more than visible or UV light.

[0011] In some embodiments, the image-forming layer may not include an ultraviolet (UV) dye. That is, the image-forming layer may be selective for absorption of UV light and may not include a UV dye that can absorb UV light more than visible or IR light.

[0012] In some embodiments, the image forming layer does not include particles such as thermally ablatable particles or non-thermally-ablatable particles (not thermally ablatable).

[0013] Some embodiments of the mask element can have different configurations. In some aspects, the barrier layer does not contain a UV dye. In some aspects, the barrier layer optionally contains 0 to 10% IR dye. In some aspects, at least one plasticizer can be present in the barrier layer. The plasticizer in the barrier layer can be present in an amount of about 10% to about 40%. In some aspects, carbon black can be present in an amount of about 30% to about 70%. Carbon black can be pre-dispersed in nitrocellulose. In some aspects, the infrared dye in the image forming layer can be present in an amount of about 0.1% to about 15%. Also, at least one plasticizer can be present in the image forming layer. The plasticizer in the image forming layer can be present in an amount of about 10% to about 40%. In some aspects, the plasticizer in the barrier layer can be selected from the group consisting of ATBC, Alchemix, PEG-1000, and combinations thereof. In some aspects, the plasticizer in the image forming layer is selected from the group consisting of ATBC, PEG-1000, and combinations thereof. In some aspects, the plasticizer can be a non-phthalate plasticizer.

[0014] In some embodiments, the mask can include a mask element of any embodiment having at least one mask image formed therein. The mask can include an image-formed region in the image forming layer, and the image-formed region has an optical opening that substantially does not contain its carbon black and uncrosslinked nitrocellulose. The mask can include a non-image-forming region in the image forming layer, and the non-image-forming region has uncrosslinked nitrocellulose, carbon black, and infrared dye, and optionally a plasticizer. The mask can have an optical density greater than 3.0 in the non-image-forming region and less than about 0.20 in the completely ablated image-formed region.

[0015] In some embodiments, the method of forming a mask element can include forming a transparent polymer carrier sheet; forming a barrier layer on the transparent polymer carrier sheet; and forming an image-forming layer on the barrier layer. The method can include forming a transparent overcoat layer on the image-forming layer. The method can include forming the barrier layer to include at least one plasticizer. The method can include forming the image-forming layer to include at least one plasticizer.

[0016] In some embodiments, the method of manufacturing a mask can include providing a mask element of an embodiment that has no image-formed regions in the image-forming layer; and image-forming on the mask element using infrared light to form image-formed regions in the image-forming layer. In some aspects, by the image-forming, carbon black, uncrosslinked nitrocellulose, and another material in the image-forming layer are removed to form optical apertures that become mask images. In some embodiments, the method of manufacturing a mask for flexographic printing can include exposing a thermally ablatable image-forming layer to infrared rays and performing selective ablation of regions in the thermally ablatable image-forming layer. The thermally ablatable image-forming layer has a mask image formed therein, and the mask image includes a region of the thermally ablatable image-forming layer and a region where the thermally ablatable image-forming layer has been ablated and removed.

[0017] In some embodiments, the image-forming layer has a mask image formed therein. The mask image includes a region of the thermally ablatable image-forming layer and a region where the thermally ablatable image-forming layer has been ablated and removed.

[0018] In some embodiments, the relief forming assembly can include a relief forming precursor for flexographic printing and a mask element. The mask can include: a transparent carrier sheet substrate; a polymer barrier layer on the substrate, optionally having a plasticizer and / or at least one first infrared absorbing material; on the polymer barrier layer, at least one second infrared absorbing material (e.g., not carbon black), carbon black in a thermally ablatable ablatable polymer binder (e.g., uncrosslinked nitrocellulose), and optionally a plasticizer, and can include a thermally ablatable image forming layer. The thermally ablatable image forming layer has a mask image formed therein. The mask image includes regions of the thermally ablatable image forming layer and regions that are thermally ablated to remove the thermally ablatable image forming layer.

[0019] In some embodiments, a method of manufacturing a relief forming assembly can include: disposing a mask element on a relief forming surface of a relief forming layer; and forming a complete optical contact between the mask element and the relief forming surface. In some aspects, the method can include at least one of laminating the mask element onto the relief forming surface or bonding by vacuum draw-down of the mask element onto the relief forming surface.

[0020] In some embodiments, a method of forming a relief image in a relief forming assembly can include: providing a relief forming assembly of one of the embodiments; exposing a relief forming layer of the relief forming precursor through the mask element to curing UV light to form an image-formed relief forming layer having a polymerized region and a non-exposed region forming a non-polymerized region in the image-formed relief forming layer; removing the mask element from the image-formed relief forming layer; and developing the image-formed relief forming layer by removing the non-polymerized regions in the image-formed relief forming layer, thereby forming a relief image element having a relief image.

[0021] In some embodiments, a method of manufacturing a relief forming assembly may include: providing a mask element according to one embodiment; providing a relief forming layer according to one embodiment; disposing an upper surface of the mask element on a relief forming surface of the relief forming layer; and forming a complete optical contact between the mask element and the relief forming surface. In some aspects, the method may include laminating the mask element onto the relief forming surface. In some aspects, the method may include coupling the mask element to the relief forming surface by vacuum drawdown.

[0022] In some embodiments, a method of forming a relief image in a relief forming assembly may include: providing a relief forming assembly according to one embodiment; exposing the relief forming layer through the mask element to curing UV light to form a UV-exposed region having a polymerized region and a non-exposed region having a non-polymerized region in the image-formed relief forming layer; removing the mask element from the image-formed relief forming layer; and developing the image-formed relief forming layer by removing the non-polymerized region in the image-formed relief forming layer, thereby forming a relief image element having a relief image (e.g., not including the non-polymerized region). In some aspects, the method may include polymerizing at least one photopolymerizable monomer at a relief surface of the relief image of the relief image element.

[0023] The above summary is merely illustrative and is not intended to be limiting in any way. In addition to the foregoing illustrative aspects, embodiments, and features, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

[0024] Brief Description of the Drawings The above and following information of the present disclosure, as well as other features, will become more fully apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings. It is to be understood that these drawings represent only some embodiments according to the present disclosure and thus should not be regarded as limiting the scope. The present disclosure will be described with further particularity and detail by using the accompanying drawings.

Brief Description of the Drawings

[0025]

Figure 1A

Figure 1B

Figure 1C

Figure 1D

Figure 1E

Figure 2

Embodiments for Carrying Out the Invention

[0026] The elements and components in the figures can be arranged according to at least one embodiment described herein, and their arrangements can be changed by those skilled in the art according to the disclosure provided herein.

[0027] Detailed Description In the following detailed description, reference is made to the accompanying drawings that form a part hereof. Unless the context indicates otherwise, like reference numerals typically refer to like elements throughout the drawings. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized and other changes may be made without departing from the spirit or scope of the subject matter presented herein. As will be readily understood, the aspects of the present disclosure generally described herein and illustrated in the figures can be arranged, replaced, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.

[0028] Generally, the present technology provides an improved mask that can be used for UV exposure of curable materials in relief-forming plates in a short time and / or with less energy. Compared to other masks, the improved mask of the present technology has improved optical density parameters at the optical apertures of the mask, resulting in a shorter UV exposure time or less UV energy. Therefore, significant economic advantages can be obtained by reducing the UV exposure time or reducing the UV energy.

[0029] In some embodiments, mask elements for flexographic printing are provided. The mask elements can be used in the manufacture of masks having mask images. The mask elements can include: a transparent polymer carrier sheet; a barrier layer on the transparent polymer carrier sheet, the barrier layer including uncrosslinked nitrocellulose and optionally a plasticizer; and an image-forming layer on the barrier layer, the image-forming layer including a thermally ablatable material including uncrosslinked nitrocellulose, carbon black, and an infrared (IR) dye, and optionally a plasticizer. In some aspects, the mask elements further include a transparent overcoat layer on the image-forming layer.

[0030] To manufacture a flexographic printing plate, a Flexcel NX TIL-R thermal imaging film (U.S. Patent No. 8,945,813) is used in the Kodak Flexcel NX system. However, the use of TIL-R requires long primary UV exposure times (e.g., 14 minutes using a 30 mW UV light source or 22 minutes using a 20 mW light source) to produce high-resolution printing plates (e.g., maintaining small highlight dots). TIL thermal imaging film can also be used (U.S. Patent No. 10,768,520), which has a UV exposure time of 12 minutes using a 30 mW light source (e.g., 21 J / cm 2 ). Long primary UV exposure times are detrimental to the productivity of the plate manufacturing process. Thus, the shorter primary UV exposure times (e.g., 10 - 12 minutes using a 30 mW UV light source) obtained using the improved masks described herein are highly desirable to improve plate manufacturing productivity.

[0031] As is evident from the fact that the optical density (OD) of the improved mask of the present invention is lower than the OD of the mask from the TIL-R precursor, the composition of the improved mask enables very efficient ablation of the mask precursor as compared to ablation of the TIL-R mask precursor. For example, when both imaging films (TIL-R and the improved mask of the present invention) are laser ablated at the same laser output and drum speed settings of a laser imager operating at 830 nm, the improved mask has a much shorter ablation time of 10 minutes compared to an ablation time of 13 minutes for the TIL-R mask.

[0032] The improved mask, with a smaller OD value, allows more UV light to pass through the imaged area of the mask (e.g., the optical aperture), thus enabling faster photopolymerization formation of the relief-forming layer, and thereby shortening the required exposure time of UV light to achieve the same high-resolution plate quality such as maintaining small dots on the plate. In the mask manufactured from the improved thermal imaging film of the present invention, the required main UV exposure time for manufacturing a high-resolution printing plate is significantly shortened.

[0033] OD is defined by the following formula: OD = -logT λ = -log[(%T λ ) / 100] and is measured by an X-Rite Transmission Densitometer as so defined.

[0034] For example, an OD of 0.10 corresponds to a light transmittance of 79.3%, and an OD of 2.0 corresponds to a light transmittance of 1%. The values can be interpolated between or extrapolated from these points.

[0035] In some embodiments, the improved mask has an optical density of about 3.0 or more in the non-image forming area and about 0.20 or less in the fully ablated imaged area. For example, the OD of the fully ablated imaged area in the mask can be about 0.18 or less, more preferably about 0.15 or less, more preferably about 0.13 or less, more preferably about 0.12 or less. As a specific example, an OD in the range of about 0.11 to about 0.13 can be cited using the improved mask. The percentage of UV light transmittance can be about 70% - 80%, or about 74% - 77%, or about 75%. The OD of the non-image forming area can exceed 3.5. The larger optical OD of the non-image forming area of the mask prevents image formation in unwanted areas. For example, an OD of 3.0 corresponds to a light transmittance of only 0.1%.

[0036] The improved mask described above can also have shorter exposure, for example, shorter energy exposure, for example, fewer joules per square centimeter. Conventional masks can have 24 J / cm 2 of UV exposure, while the improved mask can have 17 J / cm 2 ~19 J / cm 2 and up to 21 J / cm 2 of UV exposure.

[0037] In the improved mask of the present invention, excellent stability of the imaging film under low to high humidity conditions can be obtained. This is highly desirable for the transportation, storage of the imaging film, and loading and unloading into the imaging device for manufacturing the mask. Therefore, the improved mask can have excellent resistance to edge curl under low humidity and high humidity conditions.

[0038] Furthermore, with the above-described improved mask, a suitable flexographic printing plate with a plate of 0.8% dots at 150 lpi reaching 100% can be obtained.

[0039] Mask and Mask Precursor The present technology provides an improved thermal imaging film, also referred to as a mask precursor, or a mask element before imaging, and a mask after mask imaging. That is, the thermal imaging film (TIF) includes an imaging layer that forms an image when exposed to infrared light. The imaging layer does not have silver halide and can be thermally ablated by infrared light, so it can be called a silver halide-free thermally ablatable imaging layer. The imaging layer is formed in a mask precursor having a barrier layer and optionally a protective topcoat, and the imaging layer is sandwiched between them. A transparent polymer carrier sheet can be used as a substrate for holding the barrier layer on top, so that an optional protective topcoat is present on the imaging layer. The optional protective topcoat can be treated with small inorganic particulate matter or organic particles in the range of 0.3 microns to 3 microns.

[0040] The mask can be configured to be used with a relief-forming precursor having a photosensitive layer, and the upper surface is brought into contact with the photosensitive layer of the relief-forming precursor. The mask is obtained by forming an image on a mask precursor (e.g., a mask element) using IR light. Therefore, the mask can be formed by fabricating a mask precursor and processing it with light (e.g., infrared, IR). Next, the mask can be combined with the relief-forming precursor (e.g., by lamination) and processed with light (e.g., UV), and then the mask and the relief-forming precursor processed with light are separated from each other.

[0041] Since the mask precursor has an imageable layer for forming a mask, it can be regarded as an imageable material. In some embodiments, the mask precursor can include, in order as described above: (a) a transparent polymer carrier sheet (film); (b) a barrier layer; (c) a thermally ablatable image-forming layer; and (d) an optional protective topcoat treated with particulate matter, three or four layers or films. The thermally ablatable image-forming layer is ablatable by thermal image formation using light, e.g., IR light, and this thermally ablatable image-forming layer does not contain silver halide, so it is a thermally ablatable "non-silver halide" image-forming layer. Thus, the image-forming layer includes a thermally ablatable substance such as carbon black, non-crosslinked nitrocellulose having an IR dye (e.g., specific to IR light and not broadband light absorption of a blackbody).

[0042] The protective topcoat can be ablatable and can include particulate matter that can be ablatable or non-ablatable. The protective topcoat can include non-ablatable particles, but the protective topcoat is still ablatable. In part, the matrix of the protective topcoat can be a non-crosslinked polymer, so it is ablatable.

[0043] The mask precursor used to form the mask element that is ultimately used to form the relief image can be fabricated as described above and then processed into a mask. In some embodiments, the mask precursor 110 is shown in FIG. 1A, which has (a) a transparent polymer carrier sheet 150, (b) a barrier layer 120 disposed directly thereon, (c) an ablatable image-forming layer 130 disposed directly on the barrier layer 120 and arranged to receive light 35 indicated by the arrow, and (d) an optional protective topcoat 138, optionally treated with particulate matter, provided over the ablatable image-forming layer 130.

[0044] transparent polymer carrier sheet The transparent polymer carrier sheet can be any suitable transparent substrate or film. Useful transparent polymer carrier sheets include, but are not limited to, transparent polymer films and sheets of one or more polymers such as polyesters such as poly(ethylene terephthalate), poly(ethylene naphthalate), and fluorinated polyester 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 unhydrolyzed cellulose acetate; and transparent polymer films and sheets composed of other materials that will be readily apparent to those skilled in the art. The transparent polymer carrier sheet can be composed of two or more polymer materials as a blend or composite material if the required transparency and protective properties are achieved. These can be formed as a single polymer film or a laminate of multiple polymer films. Generally, the transparent polymer carrier sheet has an average dry thickness of at least 25 μm and up to 250 μm, or typically at least 75 μm and up to 175 μm.

[0045] For example, transparent poly(ethylene terephthalate) sheets available from various commercial sources are suitable as the transparent polymer carrier sheet.

[0046] If necessary, the surface of the transparent polymer carrier sheet can be treated to change its wettability and adhesiveness to the coating (e.g., barrier layer coating) to be attached. Such surface treatments include, but are not limited to, corona discharge treatment and application of a sizing layer if the desired transparency (as described above) is to be achieved.

[0047] If desired, the transparent polymer carrier sheet can optionally also contain one or more "first" ultraviolet absorbing compounds (e.g., UV dyes), but it may also contain no ultraviolet absorbing compounds at all. One or more compounds of this type may be the same as or different from the ultraviolet absorbing compounds in the imaging layer (see below). Each useful ultraviolet absorbing compound generally absorbs electromagnetic radiation of at least 150 nm and 450 nm or less. These compounds can be present in the transparent polymer carrier sheet in an amount of at least 0.01% by weight and 0.1% by weight or less, based on the total dry weight of the transparent polymer carrier sheet. However, the transparent polymer carrier sheet may contain no IR dyes and / or UV dyes at all.

[0048] Furthermore, the transparent polymer carrier sheet can contain one or more "adhesion promoters" that improve the adhesiveness between it and the adjacent barrier layer. Useful adhesion promoters include, but are not limited to, gelatin, poly(vinylidene chloride), poly(acrylonitrile-co-vinylidene chloride-co-acrylic acid), and polyethyleneimine.

[0049] Barrier layer In some embodiments, the mask precursor includes a barrier layer disposed on a transparent polymer carrier sheet and directly disposed between the transparent polymer carrier sheet and the image forming layer. The barrier layer can be made like a conventional barrier layer (see, e.g., U.S. Patent No. 9,250,527), or can be made like the embodiments described in more detail below. The barrier layer can optionally be non-crosslinked nitrocellulose that includes an IR dye (which absorbs IR light) and / or a plasticizer. In some aspects, the barrier layer may not include a UV dye (e.g., which absorbs UV light). The barrier layer is generally disposed as a relatively uniform coating (i.e., substantially continuous and having a reasonably uniform wet thickness) on the transparent polymer carrier sheet and then dried if a solvent is present during the formulation of the composition.

[0050] The barrier layer is generally transparent (as defined above). In particular, the barrier layer is transparent to the UV rays used for image formation of the relief-forming precursor, as defined below. Thus, the barrier layer may not include a UV dye or material that selectively absorbs UV light.

[0051] The barrier layer can include non-crosslinked nitrocellulose with or without an additional non-crosslinked polymer. The nitrocellulose can be non-crosslinked as described herein. The molecular weight of the unit of the nitrocellulose group ranges from 459.28 to 594.28 Da, and its molecular formula is [C6H7O2(ONO2)3] n where n can be a number greater than or equal to 0. The barrier layer can be ablatable by IR irradiation as described herein. The barrier layer can serve as a buffer between the image forming layer and the carrier sheet, which is useful for mask formation.

[0052] The barrier layer can include at least one plasticizer. The plasticizer in the barrier layer is present in an amount of about 10 wt% to about 50 wt%, about 10 wt% to about 40 wt%, or about 20 wt% to about 30 wt%. Representative examples of the plasticizer can be acetyl tributyl citrate (ATBC), Alchemix, and PEG-1000, or combinations thereof. Alchemix of the plasticizer can be Alchemix 2340, which may also be called NQ Solve 1086, and can be a polyester resin in a mixture of ethyl acetate and ethyl alcohol, where ethyl acetate is 10 wt% to 30 wt% and ethyl alcohol is 5 to 10 wt%, and the balance can be the polyester resin. The polyester resin can be a low molecular weight polyester having a hydroxyl functional group. In one example, the polyester composition can have a number average molecular weight Mn between about 500 and about 10,000 Da, or up to 1000 Da, a polydispersity of less than about 2, preferably less than about 1.8, a hydroxyl functionality of 2 to 3, a hydroxyl value of about 160 to about 260, and an acid value of less than about 10. PEG-1000 can be polyethylene glycol having a molecular weight of about 1000 Da.

[0053] In some embodiments, the plasticizer can include a plurality of ester groups, for example, a polymer of esters that can include an alkyl group or can have a plurality of ester moieties. For example, ATBC includes four alkyl esters bonded to each other, and Alchemix is a polyester. Also, polyethers such as PEG, polypropylene glycol, and combinations thereof can be used. For example, a compound or polymer having a plurality of ether groups or a plurality of ester groups, each having an alkyl component associated with each ether or ester. Thus, alkyl ethers and alkyl esters such as those having a plurality of alkyl ether moieties or alkyl ester moieties.

[0054] The barrier layer may not contain an IR dye, but may optionally contain an IR dye, for example, from 0% to a maximum of 10%, or a maximum of 8%, or a maximum of 5%, or a maximum of 3%, or a maximum of 2%, or a maximum of 1%. If necessary, in order to distinguish from the second infrared absorbing material (described later) in the image forming layer, one or more infrared absorbing materials collectively identified herein as the "first" infrared absorbing material. The first and second infrared absorbing materials may be one or more dyes or pigments, or mixtures thereof, that provide the desired spectral absorption characteristics and are independently sensitive to electromagnetic radiation within the infrared electromagnetic wavelength range of at least 700 nm and 1,500 nm or less, typically at least 750 nm and 1,200 nm or less. For example, the IR dye in the barrier layer may not contain a black dye or pigment, such as carbon black, metal oxides, and another material described, for example, in U.S. '987 (described above). Thus, the barrier layer may not contain carbon black, in particular, carbon black chips (e.g., pre-dispersed). An IR dye may be included, but such an IR dye can be specific to IR light and can exclude broadband absorbers such as carbon black in the barrier layer.

[0055] Useful first infrared absorption materials include, but are not limited to, IR dyes such as cationic infrared absorption dyes and photothermally bleachable dyes. Examples of suitable IR 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, chalcogenopyrroarylidene and bis(chalcogenopyrro)polymethine dyes, oxyindolizine 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 above dye types. Suitable dyes are also described in U.S. Patent No. 5,208,135 (Patel et al.), U.S. Patent No. 6,569,603 (Furukawa), and U.S. Patent No. 6,787,281 (Tao et al.), and European Patent Application Publication No. 1,182,033 (Fijimaki et al.).

[0056] 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.), all of which disclosures are incorporated herein by reference. Suitable dyes can be formed using conventional methods and starting materials or can be obtained from various commercial sources such as American Dye Source (Baie D’Urfe, Quebec, Canada) and FEW Chemicals (Germany).

[0057] The first infrared absorbing material is generally present in an amount sufficient to obtain a transmission optical density of at least 0.025, typically at least 0.05, at the exposure electromagnetic radiation wavelength (e.g., IR). Generally, this is achieved at, for example, at least 0.1 wt% and up to 5 wt%, or typically at least 0.3 wt% and up to 3 wt%, based on the total dry weight of the barrier layer.

[0058] The first infrared absorbing material in the barrier layer may be the same or a different chemical substance from the second infrared absorbing compound contained in the image forming layer as described below. The infrared absorbing material in the barrier layer may be different from the infrared absorbing material in the transparent polymer carrier. In most embodiments, the first and second infrared absorbing materials are the same chemical substance, but blacks such as carbon black are excluded. The infrared absorbing material can be selective to selectively absorb infrared light, and thus is not a broadband absorber that absorbs UV light, visible light, or another non-IR light. The amounts of the first and second infrared absorbing materials in the image formable material may be the same or different. In most embodiments, they are present in different amounts in the image formable material.

[0059] In some embodiments, the barrier layer can include an ablatable uncrosslinked binder material formed from an organic polymer, such as uncrosslinked nitrocellulose, and can be present in the barrier layer in an amount of at least 30 wt% and up to 100 wt%, or with a higher likelihood at least 50 wt% and up to 80 wt%, based on the total dry weight of all layers. In some aspects, the plasticizer may be included in the above amounts with or without the IR dye, and the uncrosslinked nitrocellulose may be the remainder of the material.

[0060] The barrier layer generally has an average dry thickness of at least 0.5 μm and up to 5 μm, or typically at least 0.8 μm and up to 3 μm.

[0061] In some embodiments, the barrier layer may not include cross-linked nitrocellulose. Also, the barrier layer may not include a cross-linking agent capable of cross-linking nitrocellulose. Further, the barrier layer may not include a cross-linked polymer.

[0062] In some embodiments, the barrier layer may not include particles such as ablatable particles or non-ablatable particles. The barrier layer may not include a metal oxide.

[0063] In some embodiments, the barrier layer may not include a metallization layer material or metal therein.

[0064] In some embodiments, a thermally ablatable imaging layer (IL) The imaging layer incorporated into the mask precursor is generally placed directly on the barrier layer as a relatively uniform coating (i.e., substantially continuous and having a reasonably uniform wet thickness) and then dried if a solvent is present in the formulation. In most embodiments, the imaging layer is a single coating or applied layer, but in other embodiments, there can be multiple sub-layers or sub-coatings placed directly on the aforementioned barrier layer to form the imaging layer.

[0065] As described in the terminology, silver halide is substantially absent in the imaging layer. In other words, silver halide is not intentionally added or generated in the imaging layer.

[0066] In some embodiments, the imaging layer includes uncross-linked nitrocellulose, carbon black, and an infrared dye, and optionally a plasticizer.

[0067] The nitrocellulose may be uncross-linked as described herein.

[0068] The image forming layer can include carbon black, of which there are many types having various commercially available particle sizes. Examples include RAVEN 450, 760 ULTRA, 890, 1020, 1250, and others available from Columbian Chemicals Co. (Atlanta, Ga), as well as BLACK PEARLS 170, BLACK PEARLS 480, VULCAN XC72, BLACK PEARLS 1100, and others available from Cabot Corporation. Carbon black can be obtained as a dispersion or chips. Due to the large pigment-to-binder ratio, "Predisol C" Black 7 of Sun Chemical's carbon black chips is preferred. Another useful carbon black is surface-functionalized with solubilizing groups. Carbon black grafted to a hydrophilic nonionic polymer such as FX-GE-003 (manufactured by Nippon Shokubai), or carbon black surface-functionalized with anionic groups such as CAB-0-JET® 200 or CAB-O-JET® 300 (manufactured by Cabot Corporation) is also useful. For example, carbon black chips can include carbon black materials such as pigments dispersed in a binder and supplied as small pieces or chips (e.g., not provided as a solution or in a solvent), where the chips are used to form a layer having carbon black.

[0069] The image forming layer can include at least one plasticizer. The plasticizer in the image forming layer is present in an amount of about 10 wt% to about 50 wt%, about 10 wt% to about 40 wt%, or about 20 wt% to about 30 wt%. Representative examples of the plasticizer can be the aforementioned acetyl ATBC, Alchemix, and PEG-1000, or combinations thereof.

[0070] In some embodiments, the plasticizer can include a plurality of ester groups, for example, a polymer of esters that can include an alkyl group or can have a plurality of ester moieties. For example, ATBC includes four alkyl esters bonded to each other, and Alchemix is a polyester. Also, polyethers such as PEG, polypropylene glycol, and combinations thereof can be used. For example, a compound or polymer having a plurality of ether groups or a plurality of ester groups, each having an alkyl component associated with each ether or ester. Thus, alkyl ethers and alkyl esters, such as those having a plurality of alkyl ether moieties or alkyl ester moieties.

[0071] In some embodiments, the plasticizer does not include Alchemix or a polyester polymer. Thus, in some embodiments, the plasticizer in the image forming layer can include a compound that is a polymer having a plurality of alkyl ester moieties that bond to each other during branching formation or having a plurality of alkyl ester moieties that bond to each other in the chain.

[0072] In some embodiments, the image forming layer includes, as a component, one or more ultraviolet absorbing materials (UV light absorbing materials). These compounds generally have an absorbance of at least 1.5 and at most 5 within the electromagnetic radiation wavelength range of at least 300 nm and at most 450 nm. Generally, useful ultraviolet absorbing materials include, but are not limited to, benzotriazole, halogenated benzotriazole, triazine, benzophenone, benzoate, salicylate, substituted acrylonitrile, cyanoacrylate, benzylidene malonate, oxalanilide, and mixtures thereof. Examples of useful ultraviolet absorbing materials include, but are not limited to, UV absorbing dyes or UV 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 U.S. Patent No. 5,496,685 (Farber et al.). However, in embodiments of the image forming layer, any UV dyes are also excluded.

[0073] The image forming layer also includes, as a second important component, one or more second infrared absorbing materials, which are defined in the same manner as the first infrared absorbing materials described above with respect to the barrier layer, and these may be the same as or different from the first infrared absorbing materials. One or more second infrared absorbing materials can be present in the image forming layer in an amount sufficient to obtain a transmission optical density of at least 0.5, typically at least 0.75, at the exposure wavelength. Generally, this is achieved by including at least 3 wt% and at most 20 wt% of one or more second infrared sensitive compounds based on the total dry weight of the image forming layer. The IR dyes in the image forming layer can be specific to the absorption of IR light rather than visible and UV light, and thus, the IR dyes are not blackbody materials that absorb broadband light.

[0074] The image forming layer can optionally include one or more fluorocarbon additives to improve the formation of dots (i.e., pixels) having distinct, overall continuous and relatively sharp edges. Examples of useful fluorocarbon additives and amounts are shown in

[0087] -

[0089] of U.S. ‘987 (described above).

[0075] Additional optional components of the image forming layer include, but are not limited to, another plasticizer, a coating aid or surfactant, a dispersion aid, a filler, and a colorant, all of which are well known in the art as described, for example, in

[0094] -

[0096] of U.S. ‘987 (described above). For example, the image forming layer can further include one or more fluorocarbon additives or one or more thermally ablatable colorants. Some examples of other suitable plasticizers (e.g., secondary plasticizers) include aliphatic hydrocarbon oils such as naphthenic oils and paraffin oils, and liquid poly-dienes such as liquid polybutadiene and liquid polyisoprene. Generally, secondary plasticizers are liquids having a molecular weight of less than about 5,000 Da, but can have a molecular weight of up to about 30,000 Da. Low molecular weight plasticizers include a molecular weight of less than about 30,000 Da. These other secondary plasticizers can also be used in the barrier layer.

[0076] All of the essential and optional components described above with respect to the image forming layer are dispersed in one or more ablatable polymer binder materials that include uncrosslinked nitrocellulose that is ablatable when exposed to light radiation such as IR rays, visible rays, or UV rays, and optionally other synthetic and natural polymer materials. In some embodiments, the ablatable polymer binder in the image forming layer does not crosslink and is thus an uncrosslinked binder. Also, the image forming layer may not include a crosslinking agent capable of crosslinking the nitrocellulose. Such materials allow for the dissolution or dispersion of the essential and optional components in a uniform manner throughout the image forming layer. The one or more ablatable polymer binder materials can be present in an amount of at least 25 wt% and up to 75 wt%, or typically at least 35 wt% and up to 65 wt%, based on the total dry weight of the image forming layer.

[0077] In addition to nitrocellulose, useful ablatable polymer binder materials include, but are not limited to, for example, the materials described in US '987 at

[0081] -

[0085] . These materials may also be known as "adhesive binders" as described, for example, in US '987 at

[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, Mo.), and acrylamide polymers available as MACROMELT 6900 from Henkel Corp. (Gulph Mills, Pa.). For this purpose, pressure sensitive adhesive polymers can also be used. These materials can be used, optionally, with uncrosslinked nitrocellulose.

[0078] In some embodiments, it is advantageous to use in the imaging layer a binder material that is readily thermally combustible or thermally ablatable and generates gas and forms volatile fragments at temperatures below 200° C. Examples of such materials are thermally ablatable polycarbonates, poly(cyanoacrylates), polyurethanes, polyesters, polyorthoesters, polyacetals, and copolymers thereof (see, e.g., U.S. Patent No. 5,171,650 to Ellis, column 9, lines 41-50, which disclosure is incorporated herein by reference), and may be uncrosslinked.

[0079] Another useful ablatable material for the imaging layer has hydroxyl groups (or hydroxyl polymers), such as poly(vinyl alcohol) and cellulose (such as nitrocellulose already included), as described in

[0082] -

[0084] of U.S. ‘987 (aforementioned). Yet another useful polymer is an uncrosslinkable polyester, polyamide, polycarbamate, polyolefin, polystyrene, polyether, polyvinyl ether, polyvinyl ester, and polyacrylate and polymethacrylate having alkyl groups having 1 and 2 carbon atoms.

[0080] In addition to nitrocellulose, particularly useful abatable materials for the imaging layer include, but are not limited to, polyurethanes, poly(vinyl butyral), (meth)acrylamide polymers, polyacetals, poly(cyanoacrylates), polymers that are at least partially derived from any of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate, or combinations of two or more of these materials.

[0081] The imaging layer can have an average dry thickness of at least 0.5 μm and 5 μm or less, or typically at least 0.8 μm and 2.5 μm or less.

[0082] Protective topcoat The mask precursor can optionally include a transparent polymer overcoat layer disposed directly on the imaging layer opposite the barrier layer. This transparent polymer overcoat layer can optionally be a protective topcoat treated with particulate matter. By adding particulate matter into such a protective topcoat treated with particulate matter, the advantages of improved resolution and increased maintenance of highlighted dots of the present invention are obtained.

[0083] The protective topcoat generally includes, but is not limited to, one or more transparent film-forming polymers or resins such as methacrylic acid copolymers (such as copolymers of ethyl methacrylate and methacrylic acid). The body of the protective topcoat can include the small particles described herein. These particles can be inorganic particles that can be silica or metal oxide particles with a size less than 1 micron. The metal oxide particles can be ablative such as iron oxide particles. Alternatively, the metal oxide particles can be non-ablative such as titanium dioxide or zinc oxide. Non-ablative silica particles can also be used. These inorganic particles can be in any range between 0.001 micron to about 0.99 micron, or about 0.01 micron to about 0.75 micron, or about 0.05 micron to about 0.5 micron, or about 0.1 micron to about 0.25 micron, or any of the recited values.

[0084] The inorganic particles can be non-ablative particles as described herein. However, the protective topcoat treated with particulate matter is ablatable, and thus the polymer body is not cross-linked. This body can be prepared to be ablatable, which can be similar to the composition of the body of the imaging layer.

[0085] The protective topcoat can be attached directly to the imaging layer and can have an average dry thickness of at least 0.05 μm and 1 μm or less. This thickness can vary depending on the embodiment.

[0086] In some embodiments, it is advantageous to use in the protective topcoat a binder material that is readily thermally combustible or thermally ablatable and that generates gas and forms volatile fragments at a temperature of less than 200° C. Examples of such materials are thermally ablatable nitrocellulose, polycarbonate, poly(cyanoacrylate), poly(methacrylate), poly(ethyl acrylate), polyurethane, polyester, polyorthoester, polyacetal, and copolymers thereof (see, e.g., U.S. Patent No. 5,171,650 to Ellis, column 9, lines 41-50, which disclosure is incorporated herein by reference), which may be uncrosslinked. A 1:1 methacrylic aid-ethyl acrylate copolymer such as Kolicoat® MAE30 DP is one example.

[0087] Another useful ablatable material for the protective topcoat has hydroxyl groups (or hydroxyl polymers), such as poly(vinyl alcohol) and cellulose polymers (such as nitrocellulose), as described in

[0082] -

[0084] of U.S. ‘987 (supra), which may be uncrosslinked. One example of a classification of useful polymers is uncrosslinked polyesters, polyamides, polycarbamates, polyolefins, polystyrenes, polyethers, polyvinyl ethers, polyvinyl esters, and polyacrylates and polymethacrylates having alkyl groups with 1 and 2 carbon atoms, and copolymers thereof. Particularly useful abatable materials for the protective topcoat include, but are not limited to, polyurethanes, poly(vinyl butyral), (meth)acrylamide polymers, nitrocellulose, polyacetal, poly(cyanoacrylate), polymers at least partially derived from any of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate, or combinations of two or more of these materials, such as copolymers, which may be uncrosslinked.

[0088] Furthermore, the protective topcoat can include fluorine particles of one or more fluoropolymers dispersed therein, such as described in U.S. Patent No. 6,259,465 (Tutt et al.), the disclosure of which is incorporated herein by reference. As an example, polytetrafluorethylene (PTFE) can be mentioned. The fluorine particles can be present in an amount of about 1% to about 40%. Preferably about 33%.

[0089] Furthermore, the protective topcoat can include a surfactant such as a fluorosurfactant. The fluorosurfactant can be Capstone FS-3100. The fluorosurfactant can be present in an amount much less than that of the fluro-particle.

[0090] In some embodiments, a silicone-containing surface additive can be included in the protective topcoat. The silicone-containing surface additive can be a polyether-modified polydimethylsiloxane such as BYK 333. The silicone can be present in an amount much less than that of the fluro-surfactant.

[0091] Mask Since the mask precursor has an image-formable layer that forms a mask, it can be regarded as an image-forming material. In some embodiments, the mask precursor can include, in order, as described herein: (a) a transparent polymer carrier sheet (film) optionally having a first ultraviolet-absorbing compound; (b) a barrier layer optionally having a first infrared-absorbing compound and / or a plasticizer; (c) a thermally ablatable image-forming layer (IL) having carbon black, a second infrared-absorbing compound, and optionally an ultraviolet-absorbing compound, and optionally a plasticizer; and (d) an optional protective topcoat optionally treated with particulate matter.

[0092] The mask precursor used to form the mask elements that are ultimately used to form the relief image can be fabricated as described herein and then processed into a mask. In some embodiments, mask precursor 110 is shown in FIG. 1A, which includes (a) a transparent polymer carrier sheet 115, (b) a barrier layer 120 that optionally includes an ablatable binder material disposed directly thereon, (c) an ablatable imaging layer 130 disposed directly on barrier layer 120 and arranged to receive light 35 as indicated by arrow 35, and (d) a protective topcoat 138 provided on ablatable imaging layer 130.

[0093] FIG. 1A shows the exposure step for some embodiments, where mask precursor material 110 is exposed to exposure infrared light 35 in an image-like pattern to form exposed regions 140 and non-exposed regions 142 corresponding to the mask image shown in the mask elements shown in FIG. 1B. As shown, the exposed regions 140 are ablated and removed from the non-exposed regions 142. Thus, the exposed regions 140 form the mask image.

[0094] Some embodiments according to the present invention can be understood by referring to the overall description presented in the order of FIGS. 1A through 1E. As described above, FIG. 1A shows mask precursor 110 being exposed to exposure infrared light 35 to form mask elements (FIG. 1B).

[0095] In FIG. 1C, mask element 136 includes imaging layer 115 on barrier layer 120 over ablated imaging layer 130 having a mask image formed therein, together with ablated protective topcoat 138. Mask element 136 is shown in intimate or complete optical contact with relief-forming precursor 155 to obtain relief image forming assembly 150 by contacting optional protective topcoat 138. Relief-forming precursor 155 typically includes a UV-sensitive layer 160 maintained on a substrate 165.

[0096] FIG. 1D shows the step of exposing the relief image forming assembly 150 to UV light 170 indicated by the arrow. The UV light 170 passes through the transparent polymer carrier sheet 115 in the mask element 136, the barrier layer 120, and the exposed region of the image forming layer 130 (e.g., the element 140 - the removed portion of the image forming layer), and then passes through the exposed portion in the protective topcoat 138 treated with particulate matter, causing photocuring in the UV - sensitive layer 160 of the relief forming precursor 155.

[0097] After UV exposure, the mask element 136 can be removed from the UV - sensitive layer 160 of the relief forming precursor 155, and a relief image as shown in FIG. 1E can be formed in the UV - sensitive layer 160 according to a development protocol. As shown in FIG. 1E, the relief image includes ridges 75 of the relief image and valleys 80 of the relief image in the UV - sensitive layer 60.

[0098] Mask Formation In some embodiments, a mask can be formed by generating exposed and unexposed regions in the image forming layer of the mask precursor embodiments described herein. By selecting the image forming mechanism, the possible types in the formation of the mask image as described below are determined.

[0099] Exposure of the mask precursor to ablation - type light energy for ablation of the image forming layer and the protective topcoat can be performed in selected regions and is otherwise known as "image - like exposure". In some embodiments, image - like exposure can be performed using thermal radiation from a thermal laser or an infrared laser with scanning or rasterization under computer control. Any well - known scanning device such as a flat - bed scanner, an external drum scanner, and an internal drum scanner can be used. In these devices, the mask precursor material is fixed to a drum or a bed, and the laser beam can be focused into a spot and made to impinge on the image forming layer of the mask precursor material. Two or more lasers can be scanned simultaneously in different regions of the image forming layer.

[0100] For example, the mask precursor material can be exposed to infrared light within an electromagnetic wavelength range of, for example, at least 700 and 1500 nm or less. Such a mask precursor material includes one or more second infrared absorbing materials in the image forming layer as described above to make it sensitive to infrared light. In these embodiments, the mask precursor material can be appropriately mounted on an infrared imager and exposed to infrared light using an infrared laser such as a diode laser or an Nd:YAG laser that can be scanned under computer control. Suitable infrared imagers include, but are not limited to, the TRENDSETTER imagesetter and the ThermoFlex Flexographic CTP imager available from Eastman Kodak Company used for CTP lithographic plate applications and image formation of flexographic elements, the DIMENSION imagesetter available from Presstek (Hudson, N.H.) useful for CTP lithographic plate applications, the CYREL® Digital imager (CDI SPARK) available from Esko-Graphics (Kennesaw, Ga.), and the OMNISETTER imager available from Misomex International (Hudson, N.H.) useful for image formation of flexographic elements.

[0101] This exposure step for several embodiments is shown in FIG. 1A, where the mask precursor material 10 is exposed in an image-like pattern to exposure infrared light 35 to form a light region 40 and a non-exposed region 42 corresponding to the exposed mask image shown in the mask element 36 shown in FIG. 1B. As shown, the exposed region 40 is ablated and removed from the non-exposed region 42. Thus, the exposed region forms the mask image.

[0102] The step of forming the mask image can, if desired, also include the step of removing either the exposed area or the unexposed area from the image forming layer. In some embodiments, for example, the exposed area of the image forming layer is removed by ablating the exposed material in the image forming layer. In this mechanism, the exposed area of the image forming layer is removed from the mask element by gas generated during ablation leaving the mask image. A special binder (e.g., non-crosslinked) that decomposes upon exposure to heat (such as that generated by IR laser irradiation) to rapidly generate gas can be present in the image forming layer. This action should be distinguished from other mass transfer techniques in that it results in a nearly complete transfer of the image forming layer rather than a partial transfer due to a chemical change rather than a physical change.

[0103] In another embodiment not shown, an exposed area and an unexposed area are formed in the image forming layer, and a mask image can be formed on the carrier sheet by selectively removing the unexposed area.

[0104] In some embodiments, if it does not adversely affect the properties of the mask element, the mask image in the image forming layer of the mask element can be cured by heat treatment. The heat treatment can be carried out by various means including, but not limited to, storage in an oven, hot air treatment, or contact with a heated platen, or passage through a heated roller device. Curing by heat treatment is not necessary.

[0105] In yet another embodiment, the mask image can be formed in the image forming layer as described above, the exposed area can be transferred to the receptor sheet, which is then removed from the mask element and subsequently contacted with the relief forming precursor. Such procedures are well known in the art.

[0106] In the peeling image forming mechanism, the exposed area of the image forming layer can be removed from the carrier sheet using a suitable receptor sheet based on different adhesion characteristics in the image forming layer. After imagewise exposure of the mask precursor, the receptor sheet is separated from the carrier sheet, and either the exposed area or the unexposed area remains in the mask element.

[0107] Relief forming precursor In some embodiments, a photosensitive relief forming material can be used in the relief forming photopolymer plate precursor. This photosensitive relief forming layer can be processed to form a relief image. The photosensitive relief forming layer can also be used in a solvent washable plate or a water washable plate.

[0108] Many details of useful relief forming precursors such as flexographic printing plate precursors, letterpress printing plate precursors, and printed circuit boards are shown in U.S. ‘987 (described above). Such relief forming precursors can include a suitable dimensionally stable substrate, and a UV (ultraviolet) sensitive relief forming layer, and optionally a cover sheet and / or a metal layer between the substrate and the relief forming layer. Suitable substrates include dimensionally stable polymer films and aluminum sheets. Polyester films are particularly useful. Any UV sensitive material or element in which a relief image can be formed using a mask element is useful in the practice of the present invention when it includes a low surface energy additive.

[0109] In some embodiments, the relief forming precursor generally includes a suitable dimensionally stable substrate, a radiation curable layer in which a flexographic relief image can be formed, and optionally a cover sheet over the radiation curable layer, and / or a metal layer between the substrate and the radiation curable layer. Suitable substrates include flexible and dimensionally stable transparent polymer films, and metal substrates such as aluminum sheets. Polyester films are particularly useful as flexible and dimensionally stable transparent substrates. The relief forming precursor can optionally include a metal layer disposed between the substrate and the radiation curable layer. This layer can include copper or another metal or metal alloy.

[0110] Some embodiments include a radiation curable layer that protects against fingerprints and their attendant damage, and a removable cover sheet disposed over the radiation curable layer. In some embodiments, the flexographic printing plate precursor further includes a metal layer between the substrate and the radiation curable layer, or further includes both a cover sheet sandwiching the radiation curable layer and a metal layer.

[0111] In some embodiments, the radiation curable layer may be a UV-sensitive layer that cures upon exposure to UV light. In some aspects, the UV-sensitive layer may be at least one layer of a relief-forming precursor formed of a UV-sensitive relief-forming material. Thus, reference to a relief-forming material or layer means a UV-sensitive material or layer that can be irradiated with UV light and developed to obtain a relief image.

[0112] In some embodiments, the relief-forming precursor includes a backing or base film (e.g., as the substrate), a relief-forming layer (e.g., a UV-sensitive material), and optionally a removable cover sheet film for protecting the photosensitive layer. In one alternative, a metal layer can be disposed between the substrate and the relief-forming layer.

[0113] In some embodiments, the backing or base can be configured to support the relief-forming layer of the relief-forming precursor. The backing layer can 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 are cellulose film or plastic, 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 a relief-forming layer having a low surface energy additive can adhere to the support layer. The support layer can be from about 0.001 to about 0.010 inches thick. Optionally, various layers, such as an anti-halation layer and / or an adhesive layer, can be disposed between the backing layer and the relief-forming layer. In some aspects, the adhesive layer can include an anti-halation material (e.g., a light-absorbing substance for preventing refraction of light), or can exclude such an anti-halation material.

[0114] In some embodiments, the relief-forming layer can be a UV light-sensitive material that forms an image using UV light and forms a relief image after development of the image, where the relief image has a low surface energy. Adding a low surface energy additive to the UV light-sensitive material can provide a number of properties desirable for relief image formation protocols, such as easier vacuum drawdown and better lamination to reduce bubble formation. Further, the low peel force can make it easier to remove the image-formed mask from the relief-forming layer after the main UV exposure to form the relief image.

[0115] In some embodiments, low surface energy and low peel force are obtained 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 such that it is present and distributed within and on the surface of the body of the photosensitive material. In many cases, the low surface energy additive is uniformly mixed within the photosensitive material. However, this additive can be provided irregularly or non-uniformly (e.g., not uniformly), or can be provided with a gradient in which the concentration preferentially increases on one side or the other.

[0116] In some embodiments, examples of low surface energy additives can include silicone materials such as silicone-based monomers having reactive functional groups. The reactive functional groups can be selected to be polymerizable with another polymerizable monomer of the photosensitive material. Thereby, silicone can be incorporated into the polymerized material, and thus it is maintained as part of the photosensitive material that is maintained after the relief formation process. As a result, the reactive functional groups can be tailored from well-known functional groups that can participate in polymerization reactions with another monomer of a particular type having the same functional groups or different but suitable reactive functional groups.

[0117] In some embodiments, the photosensitive material may be a UV-sensitive layer comprising an elastomeric binder; at least one polymerizable or photocurable monomer; and a photoinitiator that is sensitive to UV light. Suitable photoinitiator compositions include, but are not limited to, those described in U.S. Patent No. 4,323,637 (Chen et al.), U.S. Patent No. 4,427,749 (Graetzel et al.), and U.S. Patent No. 4,894,315 (Feinberg et al.).

[0118] Examples of the elastomeric binder include, but are not limited to, additional polymers or resins that may be soluble, swellable, or dispersible in aqueous, semi-aqueous, or organic solvent developers (described below). Examples include natural or synthetic polymers of conjugated diolefins, block copolymers, core-shell microgels, and blends of microgels with preformed high molecular weight polymers. The elastomeric binder can comprise at least 65% by weight and up to 90% by weight, based on the total dry weight of the UV-sensitive layer.

[0119] In some embodiments, the elastomeric binder may be a single polymer or a mixture of polymers (e.g., homopolymers, copolymers, random copolymers, block copolymers, any one having any different types of monomers) that may be soluble, swellable, or dispersible in aqueous, semi-aqueous, or organic solvent developers. Suitable binders include those described in U.S. Patent No. 3,458,311 (Alles), U.S. Patent No. 4,442,302 (Pohl), U.S. Patent No. 4,361,640 (Pine), U.S. Patent No. 3,794,494 (Inoue), U.S. Patent No. 4,177,074 (Proskow), U.S. Patent No. 4,431,723 (Proskow), and U.S. Patent 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, such as polyisoprene, 1,2-polybutadiene, 1,4-polybutadiene, butadiene / acrylonitrile, butadiene / styrene thermoplastic elastomeric block copolymers, and other copolymers. Block copolymers discussed in U.S. Patent No. 4,323,636 (Chen), U.S. Patent No. 4,430,417 (Heinz), and U.S. Patent No. 4,045,231 (Toda) can be used. The elastomeric binder can be present in an amount of at least about 65 weight percent of the photosensitive material. As used herein, the term binder includes core-shell microgels and blends of microgels with preformed polymeric polymers, such as those described in U.S. Patent No. 4,956,252 (Fryd).

[0120] At least one polymerizable monomer can be configured to be compatible with the elastomeric binder to such an extent that a transparent and non-turbid UV-sensitive image-forming layer can be obtained. Polymerizable monomers for this purpose are well-known in the art and include ethylenically unsaturated polymerizable compounds having a relatively low molecular weight (generally less than 30,000 Daltons). Suitable monomers have a relatively low molecular weight of less than about 5000 Da. Unless otherwise specified, throughout this specification, the molecular weight is the weight-average molecular weight. Examples of suitable polymerizable monomers include various monoacrylates and polyacrylates, acrylate derivatives of isocyanates, esters, and epoxides. Further, examples of suitable monomers include t-butyl acrylate, lauryl acrylate, alcohols and polyols, such as acrylates and methacrylates of alkanols and polyesters, such as 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, such as pentaerythritol triacrylate, dipentaerythritol, etc. Another example of suitable monomers includes acrylate and methacrylate derivatives of isocyanates, esters, epoxides, etc., 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. Patent No. 4,323,636 (Chen), U.S. Patent No. 4,753,865 (Fryd), U.S. Patent No. 4,726,877 (Fryd), and U.S. Patent No. 4,894,315 (Feinberg).The monomer can constitute at least 5 wt% to about 25 wt% of the photosensitive material, which can be based on the total dry weight of the photosensitive material.

[0121] The photoinitiator is sensitive to ultraviolet light and can be any single type of compound or combination of compounds that generates free radicals to initiate the polymerization of one or more monomers without causing excessive termination reactions. The photoinitiator can be sensitive to visible light or ultraviolet light. The photoinitiator may not be sensitive to infrared and / or visible light and may be thermally inert below 185 °C. Examples of suitable photoinitiators include substituted and unsubstituted polynuclear quinones. Examples of suitable systems are disclosed in U.S. Patent No. 4,460,675 (Gruetzmacher) and U.S. Patent No. 4,894,315 (Feinberg). The photoinitiator is generally present in an amount of 0.001 wt% to 10.0 wt% based on the weight of the photosensitive material.

[0122] In some embodiments, the photosensitive layer can include: a di- or triblock copolymer (e.g., an elastomer); at least one photopolymerizable monomer; a photoinitiator; a plasticizer; additives such as stabilizers, inhibitors, colorants, solvents; and a low surface energy monomer such as a silicone acrylate or a silicone methacrylate.

[0123] In some embodiments, the plasticizer can be any suitable plasticizer well-known in the art of photosensitive layers for use as described herein. Examples of suitable plasticizers include aliphatic hydrocarbon oils such as naphthenic oils and paraffin oils, and liquid polybutadienes such as liquid polybutadiene and liquid polyisoprene. Generally, the plasticizer is a liquid having a molecular weight of less than about 5,000 Da, but can have a molecular weight of up to about 30,000 Da. A low molecular weight plasticizer includes a molecular weight of less than about 30,000 Da.

[0124] In some embodiments, additives can include rheology modifiers, thermal polymerization inhibitors, stabilizers, inhibitors, tackifiers, colorants, antioxidants, ozone degradation inhibitors, solvents, or fillers. These materials are commonly used in the photosensitive layer and examples may be shown in the incorporated references.

[0125] The thickness of the photosensitive layer can vary depending on the type of printing plate desired. In one embodiment, the photosensitive layer can be, for example, about 20 to 250 mils (500 to 6,400 microns) or more in thickness, particularly about 20 to 100 mils (500 to 2,500 microns) in thickness.

[0126] In some embodiments, the relief-forming precursor is a flexographic printing plate precursor that includes a suitable UV curable composition (e.g., photosensitive material) in a UV-sensitive layer (e.g., photosensitive layer) that forms a relief image when exposed and developed through a mask element. Such relief-forming precursors generally include a suitable substrate having a photosensitive material. Examples of commercially available flexographic printing plate precursors include, but are not limited to, the FLEXCEL NX flexo element available from Miraclon Corporation, the CYREL® flexographic plate available from DuPont (Wilmington, Del.), the NYLOFLEX° FAR 284 plate available from BASF (Germany), the FLEXILIGHT CBU plate available from Macdermid (Denver, Co.), and the ASAHI AFP XDI available from Asahi Kasei (Japan).

[0127] In some embodiments, a relief-forming precursor can also be used in the formation of a printed circuit board in which a conductive layer (also known as a “printed circuit”) is formed on a substrate in a pattern determined by exposure through a mask element. Suitable precursors for printed circuit boards generally include a substrate, a metal layer, and a UV-sensitive image-formable layer (e.g., a photosensitive material). Suitable substrates include, but are not limited to, polyimide films, glass-filled epoxies or phenol-formaldehyde, or any other insulating material well known in the art. The metal layer covering the substrate is generally a conductive metal or alloy or metal such as copper. The UV-sensitive image-formable layer can include a UV-curable resin, a polymerizable monomer, or an oligomer, a photoinitiator, and a polymer binder. Further details of the printed circuit board are shown in U.S. ‘987 (described above).

[0128] Formation of the Relief Image After both the mask and the relief-forming precursor are formed as described above, complete optical contact is formed between the protective top coat of the mask (if included) (or the image-forming layer if the protective top coat is excluded) and the relief-forming precursor including a photosensitive layer that is sensitive to curing UV light. This protocol can be achieved by placing the protective top coat or the image-forming layer of the mask on top of the relief-forming precursor, or vice versa, as will be described in more detail later. For example, the contact and bonding of the top surface of the mask to the relief-forming precursor can be done by the use and processing of a laminating device. With or without using lamination, vacuum drawdown onto the relief-forming precursor on the top surface of the mask can also be done to form the desired complete optical contact.

[0129] Some embodiments according to the present invention can be understood by referring to the overall description presented in the order of FIGS. 1A through 1E. When a mask precursor 110 is used, a part of the barrier layer 120 can also be ablated by ablation.

[0130] In FIG. 1C, the mask element 136 includes an image forming layer 115 on a barrier layer 120 over an ablated image forming layer 130 having an ablated mask image formed therein together with an ablated protective top coat 138. To obtain the relief image forming assembly 150 by contacting the protective top coat 138), the mask element 136 is shown in intimate contact with, or in complete optical contact with, a relief forming precursor 155. The relief forming precursor 155 typically includes a UV sensitive layer 160 maintained on a substrate 165.

[0131] FIG. 1D shows the step of exposing the relief image forming assembly 150 to UV rays 170 indicated by the arrows. The UV rays 170 pass through the transparent polymer carrier sheet 115 in the mask element 136, the barrier layer 120, and the exposed regions of the image forming layer 130 (e.g., the element 140 - removed portions of the image forming layer), and then through the exposed portions in the protective top coat 138 treated with particulate matter, causing photocuring in the UV sensitive layer 160 of the relief forming precursor 155.

[0132] After UV exposure, the mask element 136 can be removed from the UV sensitive layer 160 of the relief forming precursor 155, and a relief image (FIG. 1E) as shown in FIG. 1E can be formed in the UV sensitive layer 160 by a development protocol. As shown, the relief image includes relief image ridges 175 and relief image valleys 180 in the UV sensitive layer 160.

[0133] In some embodiments, a method of forming a relief image is provided. The method can include providing a relief forming assembly including a mask and a relief forming precursor that is in complete optical contact with the mask. Next, the method can include exposing a relief forming layer of the relief forming precursor through the mask to curing ultraviolet light to form an image-formed relief forming layer having an ultraviolet exposure region forming a polymerization region and a non-exposure region forming a non-polymerization region. Next, the method can include removing the mask from the image-formed relief forming layer. The image-formed relief forming layer can be developed by removing the non-polymerization region in the image-formed relief forming layer, thereby forming a relief image element having a relief image.

[0134] In some aspects, the exposure is performed using a mask having an optical density greater than 3.0 in a non-image forming area and less than about 0.20 in a completely ablated and image-formed area. In some aspects, the exposure is less than about 24 joules / cm 2 less than, about 22 joules / cm 2 or less, about 21 joules / cm 2 or less, about 20 joules / cm 2 or less, about 19 joules / cm 2 or less, about 18 joules / cm 2 or less, or about 17 joules / cm 2 or less.

[0135] In some embodiments, the exposure is performed using a mask having an optical density of about 0.18 or less, about 0.16 or less, or about 0.12 or less, or about 0.11 or less without using a DigiCap pattern.

[0136] Lamination As described above, the mask element and the relief-forming precursor can be arranged in complete optical contact such that an airless interface is formed at the shared interface between the top surface of the mask and the UV-sensitive layer. Generally, this is accomplished by applying appropriate pressure and / or heat, or both pressure and heat, to laminate the mask onto the UV-sensitive layer of the relief-forming precursor to form an air-free or gap-free interface prior to UV exposure. Next, as described above, vacuum drawdown of the masking element onto the relief-forming precursor can also be useful.

[0137] Without limitation, commercially available laminators that apply both heat and uniform pressure, such as the KODAK Model 800XL APPROVAL LAMINATOR available from Eastman Kodak Company (Rochester, NY), can be used. The CODOR LPP650 LAMINATOR available from CODOR (Amsterdam, Holland), and the LEDCO HD laminator available from Filmsource (Casselbury, FL) can also be useful.

[0138] In some embodiments, an optional protective topcoat can be removed prior to the lamination or other operation that forms a complete optical contact between the mask and the relief-forming precursor. The relief image-forming assembly formed by bonding the mask and the relief-forming precursor can be fed into a laminator at a desired speed, temperature, and pressure.

[0139] Useful lamination (laminator) apparatuses and methods of using them are described in U.S. Patent No. 7,802,598 (Zwadlo et al.), the disclosure of which is incorporated herein by reference. As described therein, a prepress flexographic plate laminator can be used to laminate a mask element (“masking film”) onto a relief-forming precursor (“prepress flexographic printing plate”) by applying a balanced, non-distorting, and optimized lamination force to achieve complete optical contact while minimizing lateral distortion.

[0140] In some embodiments, the relief forming precursor has a release layer, a spacer layer, or an anti-sticking layer on top of the UV-sensitive relief forming layer.

[0141] UV exposure As described above, after achieving complete optical contact between the mask and the relief forming precursor, the relief forming precursor is exposed to curing UV light through the mask to form an image-formed relief forming precursor having exposed and unexposed regions in the UV-sensitive layer. By polymerization of the monomers in the UV-sensitive layer, the exposed regions are cured and solidified. The unexposed regions remain uncured and the monomers do not polymerize. Thus, the curing UV light that is uniformly emitted is projected onto the relief forming precursor through a mask image that preferentially blocks a portion of the ultraviolet light by the remaining portion of the image forming layer. In the unmasked (exposed) regions, solidification or curing of the UV-sensitive composition in the image forming layer occurs by the curing UV light. Thus, the mask image is substantially opaque to the exposure UV light or the curing UV light, which means that the mask image should have a transmission optical density of 2 or more, typically 3 or more, in the unexposed regions. The remaining portion of the image forming layer still contains a UV-sensitive material for absorbing and blocking the UV light. The unmasked (exposed) regions of the UV-sensitive composition may be substantially transparent, which means that they should have a transmission optical density of 0.5 or less, 0.2 or less, or even 0.1 or less. The masked (unexposed) regions in the mask can have an optical density of at least about 3 or more. The transmission optical density can be measured using a densitometer, for example, a MACBETH TR 927 densitometer with an appropriate filter.

[0142] Generally, the exposure of the relief forming precursor through the mask element is performed by flood exposure from a suitable irradiation source of UV light. The exposure can be performed in the presence of atmospheric oxygen. Since complete optical contact has already been formed, exposure under reduced pressure is not necessary.

[0143] In the manufacture of relief image forming elements such as flexographic printing plates, one side of the relief forming precursor is generally first exposed to curing UV radiation through its transparent substrate (known as "backside exposure") to form a thin, uniform cured layer (e.g., valleys 80 of the relief image) on the substrate side of the UV - sensitive layer. Next, the relief forming precursor is exposed to curing UV radiation through a mask containing a mask image, thereby solidifying or curing in the regions not masked (exposed) to UV sensitivity. Next, by a development process (described below), the unexposed and uncured regions of the UV - sensitive layer can be removed, leaving the cured or solidified regions (e.g., peaks 75 of the relief image), thereby defining a relief image printing surface of a desired pattern with a pre - determined shape and size of peaks 75 and valleys 80. Backside exposure can be performed either before or after a complete optical contact is formed between the mask element and the relief forming layer.

[0144] The appropriate wavelength or wavelength range for the curing UV radiation is determined by the electromagnetic sensitivity of the relief forming layer. In some embodiments, the UV - curing radiation can have one or more wavelengths within a range of at least 150 nm and 450 nm or less, or more typically at least 300 nm and 450 nm or less. Examples of UV - light sources for flood exposure or overall exposure include, but are not limited to, carbon arcs, mercury vapor arcs, fluorescent lamps, electronic flash units, and photographic flood lamps. UV rays from mercury vapor lamps and sunlamps are particularly useful. Representative UV - light sources include the SYLVANIA 350 BLACKLIGHT fluorescent lamp (FR 48T12 / 350 VL / VHO / 180, 115 watts) having a central emission wavelength of about 354 nm available from Topbulb (East Chicago, Ind.), and the BURGESS EXPOSURE FRAME, Model 5K - 3343V511 having the ADDALUX 754 - 18017 lamp available from Burgess Industries, Inc. (Plymouth, Mass.).

[0145] As another suitable UV light source, a plate-making machine that can be used for both the exposure of the relief-forming precursor to radiation and the development of the imaged relief-forming material after radiation exposure can be mentioned. Examples of suitable plate-making machines include, but are not limited to, the KELLEIGH MODEL 310 PLATEMAKER available from Kelleigh Corporation (Trenton, N.J.), and the GPP500F PLATE PROCESSOR available from Global Asia Ltd. (Hong Kong).

[0146] The exposure time through the mask is determined by the nature and thickness of the UV-sensitive layer of the relief-forming precursor, as well as 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 plate-making machine and back-exposed to UV-A light through a transparent support for about 20 seconds to form a thin and uniform cured layer on the support side of the relief-forming precursor. The relief image-forming assembly of the mask and the relief-forming precursor can then be exposed to UV light through the mask for about 14 minutes. Thus, the information of the mask image is transferred to the relief-forming precursor (such as a flexographic plate precursor).

[0147] Separation of the mask from the UV-sensitive layer Generally, the method described herein can also include removing the mask from complete optical contact with the imaged relief-forming precursor after UV exposure and before development. Such removal can be performed by separating the upper surface of the mask from the relief image. This can be done using any suitable method such as peeling the two elements from each other. For example, this can be done by pulling the mask away from the imaged relief-forming precursor.

[0148] In some embodiments, after UV exposure, the mask can be removed from the relief-forming layer by peeling the upper surface of the mask from the relief-forming layer. This can be done by attaching a support to one of the mask or the relief-forming precursor, and then applying a peeling force to the other end or tip of the mask or the relief-forming precursor (e.g., the relief-forming layer).

[0149] In some embodiments, the mask can be delaminated from the relief-forming precursor, such as by delaminating a protective top coat from the relief-forming layer. In these embodiments, the mask is laminated to the relief-forming layer. Next, after UV curing, the mask is delaminated from the relief-forming layer. However, such delamination is not intended to indicate that the mask itself delaminates such that different layers of the mask delaminate from each other. In this case, the entire mask delaminates from the relief-forming layer. Thus, the mask delaminates from the relief-forming layer, but delamination and damage of the mask itself do not occur. Similarly, the relief-forming layer does not delaminate from the relief-forming precursor.

[0150] In some embodiments, the relief-forming precursor can include or exclude a transparent release layer on the UV-sensitive layer. For example, the UV-sensitive relief-forming layer can be in direct contact with the upper surface of the mask, such that upon separation, the mask is separated directly from the relief-forming layer.

[0151] In some embodiments, the force applied to the relief-forming layer can be reduced while the mask and the imaged relief image precursor (e.g., flexographic printing plate precursor) are peeled from each other. The mask can be peeled more quickly and completely from the relief-forming precursor, leaving little residual material. This effect results in less or no residual material interfering with the development process, so that the development of the imaged relief image precursor is faster. Since peeling is easier, the handling and holding pressure required for the flexographic imaging assembly is minimal, and the process can be easily performed at room temperature. Thus, heating during the curing process may not be required.

[0152] A flexographic printing plate assembly having a UV-sensitive layer includes a unique combination of materials such that mask peeling can be rapid and complete. "Complete" means that at least 95%, preferably at least 98%, at least 99%, or 100% of the mask is peeled, with very little or no residual material remaining. The composition of the UV-sensitive layer provides a peel force of less than about 73 g / inch, preferably less than about 60 g / inch, more preferably less than about 55 g / inch) for the mask including the mask image.

[0153] In some embodiments, the mask including the mask image is removed from the UV-exposed UV-sensitive relief-forming layer of the flexographic printing plate precursor by being peeled off at the interface between the mask and the relief-forming layer. This peeling process can be carried out using a vacuum to maintain it in a predetermined position as described in U.S. Patent No. 7,802,598. Next, the edge of the mask element is pulled away at a speed of 2 to 10 cm / second at a peeling angle of 150 to 180° from the printing plate, whereby, in a continuous operation until the entire mask element is removed from the UV-sensitive layer of the printing plate, the imaged film is substantially pulled back and the imaged film is maintained near the surface of the vacuum table. In the practice of the present invention, at least 95% by weight and preferably 100% of the dry mask element is removed by this operation, so that it can generally be said that the mask element is "completely" or substantially completely removed from the exposed radiation-curable layer of the precursor. "Completely" means that at least 95%, preferably at least 98%, at least 99%, or 100% of the mask is peeled off and the residual material is very little or does not exist.

[0154] Development After removing the mask from the relief-forming layer, the imaged relief-forming precursor is then generally developed using a suitable developer (or processing solution, or "washout solution") to form a relief image. Development serves to remove the unexposed (uncured) regions of the UV-sensitive layer and leave the exposed (cured) regions, defining a relief image as shown in FIG. 1E.

[0155] Development can be carried out under well-known conditions such as at least 1 minute and 20 minutes or less and at least 20°C and 32°C or less. Depending on the developing apparatus used and the type of specific developer, specific developing conditions are determined and can be adapted by those skilled in the art.

[0156] In some situations, post-development processing of the relief image in the imaged relief-forming precursor can be appropriate. Typical post-development processing includes drying the relief image to remove any excess solvent, and post-curing by exposing the relief image to curing radiation to cause further solidification or crosslinking. The conditions for these processes are well known to those skilled in the art. For example, the relief image can be dried by blotting or wiping, or by drying in a forced air oven or an infrared oven. The drying time and temperature will be apparent to those skilled in the art. Post-curing can be carried out using the same type of UV light previously used to expose the relief-forming precursor through the imaged mask material.

[0157] If the surface of the relief image remains sticky, delamination (or "optical finishing") can be used. For example, treatment with a bromide or chloride solution, or such treatment by exposure to UV or visible light, is well known to those skilled in the art.

[0158] The resulting relief image can have a depth of at least 2% and up to 100% of the original thickness of the UV-sensitive layer (for example, if this layer is disposed on a substrate). In the case of a flexographic printing plate, the maximum dry depth of the relief image can be from at least 150 μm to 1,000 μm or less, or typically from at least 200 μm to 500 μm or less. In the case of a printed circuit board, the UV-sensitive layer can completely remove either the exposed or unexposed area until the underlying metal layer appears. In such elements, the maximum depth of the relief image is determined by the dry thickness of the UV-sensitive layer. Advantageously, in any embodiment, the relief image can have a shoulder angle greater than 50°.

[0159] One skilled in the art can readily find various utilities for such inked elements in various industries such as flexographic printing of various packaging materials.

[0160] Using the image forming material of the present invention for forming a mask image, relief printing plates such as flexographic printing plates and letterpress printing plates can be manufactured. The mask can also be used as a photomask. "A photomask is an opaque plate or film having holes or transparency through which light can pass to illuminate a defined pattern. These are generally used in photolithography, particularly in the manufacture of integrated circuits (ICs or "chips")."

Example

[0161] Using a test target at a drum speed of 95 RPM and a laser output setting of 25 W, image formation of a commercially available Kodak Flexcel NX TIL-R was performed by a Kodak Flexcel NX Wide Imager. As a result, an optical density of 0.80 (transmittance of 15.84%) was obtained for the Flexcel NX DigiCap pattern. The optical density was measured by an X-Rite transmission densitometer. When a "DC NX-free" (DigiCap-free) pattern was attached to the test target and image formation was performed on the imager device using the No-DC imager setting conditions, it was shown that OD or Dmin was 0.18 (transmittance of 66.07%).

[0162] Next, using a Kodak Flexcel NX laminator, the image-formed TIL-R was laminated onto a 1.14 mm Flexcel NXH photopolymer plate precursor. The laminated mask and photopolymer plate sandwich / assembly were subjected to UV exposure through the mask using an "EVO 5" exposure device at a total amount of 27 joules / cm 2 to form an image-formed relief forming material. This imagewise exposed photopolymer was then processed by a flexographic plate processor, dried, and exposed using normal procedures to form a finished flexographic printing plate in a state usable for flexographic printing. With this plate, all of the low highlight dots at 0.8% at 150 lpi were reproduced.

[0163] A flexographic printing plate was produced according to the general procedure described above for Comparative Example 1. The following table shows the composition of the improved mask elements.

[0164]

Table 1

[0165] PCA is a mixture of 70 wt% poly(methyl cyanoacrylate) and 30 wt% poly(ethyl cyanoacrylate). The plasticizers for Alchemix, ATBC, and PEG-1000 are described herein.

[0166] Nitrocellulose (NC) is Scholle's E150 and Alchemix's 5 / 6 SS. The carbon black chip is Sun Chemical's "Predisol C" Blk 7, which contains a carbon black pigment and nitrocellulose. Before use, the carbon black chip is dispersed in a solvent. Chips or dispersions with a higher carbon black pigment to binder ratio are preferred for higher OD.

[0167] The IR dye has the following structure:

Chemical formula

[0168] CW represents the dry coating weight, where the solvent is removed during the coating process. For example, 150 mg / ft2 corresponds to a thickness of approximately 1.5 microns. In particular, in the examples, no crosslinking agent is present in the barrier layer or the imaging layer, and this applies to all embodiments of the mask elements described herein.

[0169] The Emax binder in the top layer is a 60:40 copolymer from ethyl methacrylate and methacrylic acid.

[0170] The following table shows the image formation conditions, UV exposure energy, plate quality, and further physical properties of the image-formable films of Comparative Example 1 and Examples 1 to 6.

[0171]

Table 2

[0172]

Table 3

[0173] Furthermore, Dmin with DC for showing the transmission optical density (TOD) versus the drum speed. As shown in FIG. 2, the example of C2 has a lower TOD than the example of C1, and both are lower than the TIL-R of Comparative Example 1. C2 and C1 mean Example 2 and Example 1 in the table (see

[0183] for the process and description of DC image formation and OD).

[0174] The standard DigiCap NX (DC) pattern was applied to the image file of the conditions shown in FIG. 2. This DC pattern is reproduced on the relief printing plate surface after the steps of image formation, UV exposure, plate processing, and drying. The DC pattern provides a higher and more uniform solid ink density (SID). See U.S. Patent No. 8,399,177.

[0175] Summary The data indicate that the improved mask can be used for more rapid UV processing of the relief-forming plate or for using less energy. Therefore, more rapid processing or less energy is an economic improvement, which is an advantage of the improved mask. The improved mask allows for a faster UV exposure time for plate manufacturing. Since the UV exposure time is the rate-limiting step when manufacturing multiple plates required by most practitioners, this improves the overall productivity of plate manufacturing.

[0176] In the present invention, the manufacturing cost is reduced by using a simple design and by using lower-cost raw materials and / or reducing high-cost raw materials. In the improved mask, the humidity / temperature sensitivity of the mask is also improved compared to TIL-R by reducing the edge lift of the coating film. Since high edge lift hinders the loading of the imaging film, this helps to reduce problems related to the loading of the imaging film into the image forming apparatus.

[0177] Definitions As used herein to define the various components of the barrier layer, the thermally ablatable imaging layer of non-halogenated silver, and other materials, layers, and compositions (e.g., developer or processing solution) 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 components (i.e., plural referents).

[0178] Each term not explicitly defined in this application should be understood to have the meaning generally accepted by those skilled in the art. By the construction of a term, if the term would be meaningless or essentially meaningless in its context, it should be construed to have the meaning in a standard dictionary.

[0179] The use of numerical values within the various ranges specified herein is considered to be approximate, as if the word “about” were prefixed to both the minimum and maximum values within the stated range, unless otherwise indicated to the contrary. Thus, minor variations above and below the stated range can be effective to obtain substantially the same results as the values within the range. In addition to this, the disclosure of these ranges is intended to include all values between the minimum and maximum values of the range, as well as the continuous range including the endpoints.

[0180] The thermally ablatable imaging layer of non-halogenated silver is also referred to herein as the imaging layer.

[0181] Unless otherwise stated in this specification, the term "imageable material" is used to mean an article of an embodiment made and used from the present invention. Such imageable materials may sometimes be known as "mask films", "mask precursors", or "masking elements". This imageable material can be made into a "mask element" using appropriate thermal (IR) imaging, and this mask element includes a mask image that can be used in forming a relief image according to the present invention.

[0182] Unless otherwise specified, percent values are by weight.

[0183] As used herein, the term "relief-forming precursor" means any imageable element or imageable material capable of forming a relief image by exposure through a mask element. Examples of such relief-forming precursors are described in detail below, and some relief-forming precursors include flexographic printing plate precursors, letterpress printing plate precursors, and printed circuit boards. Details of useful relief-forming materials are described in U.S. Patent Application Publication No. 2005 / 0227182 (supra), the disclosure of which is incorporated herein by reference. In this publication, relief-forming precursors are generally described as "radiation-sensitive elements".

[0184] Unless otherwise stated, the term "ablative" or "ablation" means laser thermal imaging that causes rapid local changes in the image-forming layer of an imageable material, thereby releasing the material in the image-forming layer from the image-forming layer. This can be distinguished from other mass transfer or imaging techniques such as melting, evaporation, or sublimation.

[0185] The terms "optical contact" and "perfect optical contact" have the same meaning and mean that two layers or two elements (such as in the case of a mask and a relief-forming precursor) share one interface, are in close physical contact, and thus there are essentially no voids or gaps between the contact surfaces, resulting in an "airless interface". More precisely, two surfaces are defined to be in a state of optical contact when the reflection and transmission characteristics of those interfaces are substantially completely represented by Fresnel's laws with respect to the reflection and transmission of light at the refractive index boundary.

[0186] Unless otherwise specified, the term "transparent" as used herein means the property of a material or layer that can transmit at least 95% of the impinging (or incident) electromagnetic radiation, for example, electromagnetic radiation having wavelengths of at least 200 nm and up to 750 nm (i.e., what is generally known in the art as UV and visible light).

[0187] The "average dry thickness" of a particular dried layer is generally the average of 10 different measurements of the dry cross-sectional image of that layer.

[0188] Regarding the processes and methods disclosed herein, those skilled in the art will recognize that the functions performed in those processes and methods can be carried out in a different order. Further, the steps and operations outlined are provided merely as examples, and some of these steps and operations can, without departing from the essence of the disclosed embodiments, be combined, in some cases, into fewer steps and operations or extended into additional steps and operations.

[0189] The present disclosure is not limited to the specific embodiments described in this application, which are intended to be examples of various aspects. As will be apparent to those skilled in the art, many modifications and variations can be made without departing from the spirit and scope thereof. In addition to those listed herein, functionally equivalent methods and apparatuses within the scope of the present disclosure will be apparent to those skilled in the art from the foregoing description. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure should be limited only by the appended claims and the full scope of equivalents to such claims. It should be understood that the present disclosure is not limited to a particular method, reagent, compound, composition, or biological system, which may of course vary. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0190] Regarding substantially any use of plural and / or singular terms herein, those skilled in the art can read the plural as the singular and / or the singular as the plural as appropriate to the context and / or application. Various singular / plural permutations may be specifically set forth herein for clarity.

[0191] Generally, the terms used herein, and in particular the terms used in the appended claims (e.g., the main body of the appended claims), will be understood by those skilled in the art to be generally intended as "open" terms (e.g., the term "including" should be construed to mean "including but not limited to", the term "having" should be construed to mean "having at least", the term "includes" should be construed to mean "includes but not limited to", etc.). It will further be understood by those skilled in the art that where a specific number is intended in the introduced claim, such intent will be expressly recited in that claim, and where no such recitation is present, no such intent exists. For example, by way of illustration, the following appended claims may include introducing the claim recitation with introductory phrases such as "at least one" and "one or more". However, the use of such phrases should not be construed as suggesting that the use of the indefinite article "a" or "an" to introduce the claim recitation in the same claim, even where the same claim includes an introductory phrase such as "one or more" or "at least one" and the indefinite article "a" or "an", limits any particular claim so introduced to only those embodiments including only one such recitation (e.g., "a" and / or "an" should be construed to mean "at least one" or "one or more"), and the same applies to the use of the definite article used to introduce the claim recitation. Further, even where a specific number is expressly recited in the introduced claim recitation, such recitation should be construed to mean at least the recited number (e.g., a mere recitation of "two" without other modifiers means at least two, or two or more), as will be recognized by those skilled in the art.Furthermore, when conventional expressions similar to "at least one of A, B, and C" are used, generally, such a configuration is intended in the sense that one of ordinary skill in the art would understand such conventional expressions (e.g., "a system having at least one of A, B, and C" includes, without limitation, a system 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.). When conventional expressions similar to "at least one of A, B, or C" are used, generally, such a configuration is intended in the sense that one of ordinary skill in the art would understand such conventional expressions (e.g., "a system having at least one of A, B, or C" includes, without limitation, a system 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.). It will be further understood by one of ordinary skill in the art that virtually any disjunctive word and / or phrase presenting two or more alternative terms should be understood to contemplate the possibility of including one of those terms, any of those terms, or both terms thereof, in any of the specification, claims, or drawings. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B".

[0192] Furthermore, when a feature or aspect of the present disclosure is described as a Markush group, one of ordinary skill in the art will recognize that thereby the present disclosure is also described as any individual component or subgroup of components of the Markush group.

[0193] As will be understood by those skilled in the art, for all purposes, for example with respect to the submission of specifications, all ranges disclosed herein include all possible sub-ranges and combinations of those sub-ranges. Every recited range is sufficiently described and can be readily understood as being divisible, for example, at least into halves, thirds, quarters, fifths, tenths, etc. of the same range. By way of non-limiting example, each range discussed herein can be readily divided into lower one-third, middle one-third, and upper one-third, etc. Also, as will be understood by those skilled in the art, all language such as "up to," "at least," etc. means the recited number and continues to mean ranges that can be divided into sub-ranges as described above. Finally, as will be understood by those skilled in the art, one range includes each individual element thereof. Thus, for example, a group having 1 to 3 cells means a group having 1, 2, or 3 cells. Similarly, a group having 1 to 5 cells means a group having 1, 2, 3, 4, or 5 cells, and so on.

[0194] From the above, it will be recognized that the various embodiments of the present disclosure are described herein for purposes of illustration and that various changes can be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, and the true scope and spirit thereof are indicated by the following claims.

[0195] All references cited herein are hereby incorporated by reference in their entirety.

Claims

1. A mask element for flexographic printing, wherein the mask comprises: A transparent polymer carrier sheet; and A barrier layer on the transparent polymer carrier sheet, the barrier layer comprising uncrosslinked nitrocellulose; An image-forming layer on the barrier layer, the image-forming layer comprising a non-halogenated silver thermally ablatable material comprising uncrosslinked nitrocellulose, carbon black, and an infrared dye; A mask element comprising the above.

2. The mask element according to claim 1, further comprising a transparent overcoat layer on the image-forming layer.

3. The mask element according to claim 1, wherein the barrier layer does not contain a UV dye and optionally contains 0 to 10% of an IR dye.

4. The mask element according to claim 1, further comprising at least one plasticizer in the barrier layer.

5. The mask element according to claim 4, wherein the at least one plasticizer in the barrier layer is present in an amount of about 10% to about 40%.

6. The mask element according to claim 1, wherein the carbon black is present in an amount of about 30% to about 70%.

7. The mask element according to claim 6, wherein the carbon black is pre-dispersed in the nitrocellulose of the image-forming layer.

8. The mask element according to claim 1, wherein the infrared dye in the image-forming layer is present in an amount of about 0.1% to about 15%.

9. The mask element according to claim 1, further comprising at least one plasticizer in the image-forming layer.

10. The mask element according to claim 9, wherein the at least one plasticizer in the image-forming layer is present in an amount of about 10% to about 40%.

11. The mask element according to claim 4, wherein the at least one plasticizer in the barrier layer is selected from the group consisting of acetyl tributyl citrate, polyester, polyether, or combinations thereof.

12. The mask element according to claim 9, wherein the at least one plasticizer in the image-forming layer is selected from the group consisting of acetyl tributyl citrate, polyether, or combinations thereof.

13. A mask comprising: Comprising the mask element according to claim 1, wherein the mask has: An image-formed area in the image-forming layer, the image-formed area having an optical opening substantially free of the carbon black and the uncrosslinked nitrocellulose thereof; A non-image forming region in the image forming layer, the non-image forming region having the non-crosslinked nitrocellulose, carbon black, and infrared dye; A mask comprising the same.

14. The mask according to claim 13, wherein the mask has an optical density of about 3.0 or more in the non-image forming region and about 0.20 or less in the image-formed region.

15. The mask according to claim 13; A relief-forming precursor in complete optical contact with the mask; A relief-forming assembly comprising the same.

16. A method for manufacturing a mask element according to claim 1, comprising: Forming the transparent polymer carrier sheet; Forming the barrier layer on the transparent polymer carrier sheet; Forming the image forming layer on the barrier layer; A method comprising the same.

17. The method according to claim 16, further comprising forming a transparent overcoat layer on the image forming layer.

18. The method according to claim 16, further comprising forming the barrier layer to include at least one plasticizer.

19. The method according to claim 16, further comprising forming the image forming layer to include at least one plasticizer.

20. A method for manufacturing a mask according to claim 14, comprising: Providing the mask element having no image-formed region in the image forming layer; Image-forming the mask element using infrared light to form the image-formed region in the image forming layer; A method comprising the same.

21. The method according to claim 20, wherein the mask having an optical density of less than about 0.20 in the image-formed region is obtained by the image-forming of the mask element.

22. The method according to claim 20, wherein by the image-forming, the carbon black, non-crosslinked nitrocellulose, and another material in the image forming layer are removed to form an optical aperture for UV light.

23. A method for forming a relief image, comprising: Providing a relief-forming assembly including a mask and a relief-forming precursor in complete optical contact with the mask, wherein the mask comprises: A transparent polymer carrier sheet; A barrier layer on the transparent polymer carrier sheet, the barrier layer including non-crosslinked nitrocellulose; An image forming layer on the barrier layer, the image forming layer comprising a thermally ablatable material of non-halogenated silver containing uncrosslinked nitrocellulose having carbon black and an infrared dye; An image-formed area in the image forming layer, the image-formed area having an optical opening substantially free of the carbon black and uncrosslinked nitrocellulose; A non-image forming area in the image forming layer, the non-image forming area having the uncrosslinked nitrocellulose, carbon black, and infrared dye; Comprising; Exposing the relief forming layer of the relief forming precursor through the mask to curing ultraviolet light to form a polymerized area and a non-polymerized area in the image-formed relief forming layer, thereby forming the image-formed relief forming layer; Removing the mask from the image-formed relief forming layer; Developing the image-formed relief forming layer by removing the non-polymerized area in the image-formed relief forming layer, thereby forming a relief image element having a relief image; A method comprising.

24. The method according to claim 23, wherein the exposure is performed using the mask having an optical density greater than 3.0 in the non-image forming area and less than about 0.20 in the image-formed area.

25. The exposure is less than about 24 joules / cm ２ less than about 22 joules / cm ２ or less, about 21 joules / cm ２ or less, about 20 joules / cm ２ or less, about 19 joules / cm ２ or less, about 18 joules / cm ２ or less, or about 17 joules / cm ２ The method according to claim 23, which is carried out at or less.

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