Flexographic printing mask employing laser thermal imaging film

Abstract

The present application provides a mask element for flexographic printing. The mask element can be used to prepare a mask having a mask image. The mask element may include: a transparent polymeric carrier sheet; a barrier layer on the transparent polymeric carrier sheet, wherein the barrier layer comprises non-crosslinked nitrocellulose; and an imaging layer on the barrier layer, where the imaging layer includes a non-silver halide thermally ablatable material comprising non-crosslinked nitrocellulose, carbon black, and an infrared (IR) dye. In some aspects, the mask element also includes a transparent overcoat layer on the imaging layer. The mask may include: an imaging region in an imaging layer, wherein the imaging region has an optical aperture substantially free of carbon black thereof and non-crosslinked nitrocellulose; and a non-imaged region in the imaged layer, wherein the non-imaged region has non-crosslinked nitrocellulose, carbon black, and an infrared dye.

Description

background Technical field:

[0002] The present invention relates to a thermal imaging film for flexographic printing masks and methods of making and using the same. More particularly, the present invention relates to a thermal imaging film before or after a mask element is formed therein. Background technology:

[0003] Previously, photosensitive materials have been combined with masks that can be used to form relief images in flexographic printing plate precursors. However, the materials used for the masks may have optical properties that may alter the formation of a relief image from a photosensitive relief-forming layer, which may not be optimal. Often, the masks may have less efficient optical properties and thus require longer time in the processing of the relief-forming layer. The longer the processing time, the less economical the mask element is for the application in which the relief image is formed. Therefore, optimizing the optical properties of the mask may improve the curing of the irradiated layer in the relief-forming layer of the flexographic printing plate.

[0004] Photosensitive relief-forming materials having relief-forming materials or photosensitive layers are known in the art. U.S. Pat. No. 8,142,987 (Ali et al., hereinafter referred to as US'987) describes important advances in the art and useful materials for making flexographic relief images. US'987 describes suitable mask element precursors, photosensitive materials for the relief-forming layer, and processes and apparatus for forming mask elements from mask precursors and forming final relief images from photosensitive relief-forming precursor materials.

[0005] Typically, the mask can be brought into close contact with the photosensitive relief-forming precursor material using a laminator device or by vacuum drawdown or both, and the entirety is exposed to actinic radiation (e.g., UV radiation) to cure the photosensitive composition in the unshielded areas of the relief-forming precursor material, thereby forming a negative image of the mask in the photosensitive relief-forming precursor. The mask can then be removed, and the uncured areas on the relief-forming material are removed using a developing process. After drying and post-UV curing, the resulting imaged relief-forming precursor has a relief image that can be used for flexographic printing or letterpress printing operations.

[0006] U.S. Patent No. 7,799,504 (Zwadlo et al.) describes advances in mask element precursors. U.S. Patent No. 8,198,012 (Zwadlo et al.), U.S. Patent No. 8,945,813 (Kidnie), and U.S. Patent No. 9,250,527 (Kidnie) describe other useful mask element precursors and methods of using them. U.S. Patent No. 2019 / 0258154 (Kidnie) describes advances in photosensitive materials.

[0007] Previously, laser imaging materials included carbon black in the outer cover layer, as described in US 4,588, 674. Here, carbon black is used in the outer cover layer, and the ratio of carbon black to binder is preferably selected to obtain a hard wear resistant coating with an optical density greater than 2.0.

[0008] The claimed subject matter is not limited to implementations that solve any disadvantages described in the above-described environments or that operate only in, for example, the above-described environments.This background is provided merely to illustrate examples where the present disclosure may be applied. Summary of the invention

[0009] In some embodiments, a mask element for flexographic printing may include: a substrate; a polymer layer on the substrate; a non-silver halide thermo-ablatable imaging layer on the polymer layer, the non-silver halide thermo-ablatable imaging layer having carbon black and at least one other infrared absorbing material in a thermo-ablatable polymer binder. The substrate may be a transparent polymer carrier sheet. The polymer layer may be a barrier layer having non-cross-linked nitrocellulose. The non-silver halide thermo-ablatable imaging layer may be an imaging layer having non-cross-linked nitrocellulose, carbon black, and an infrared (IR) dye (e.g., selective for IR light absorption) (e.g., without the presence of silver halide).

[0010] In some embodiments, a mask element for flexographic printing is provided. The mask element may be a mask precursor for preparing 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, wherein the barrier layer comprises non-crosslinked nitrocellulose; and an imaging layer on the barrier layer, wherein the imaging layer comprises a heat-ablatable material, the heat-ablatable material comprising non-crosslinked nitrocellulose, carbon black, and an IR dye. In some aspects, the mask element further comprises a transparent overcoat on the imaging layer.

[0011] In some embodiments, the polymer barrier layer may be free of IR dyes. That is, the barrier layer may be free of IR dyes that selectively absorb UV light, such IR dyes can preferentially absorb IR light over visible light or UV light.

[0012] In some embodiments, the imaging layer may be free of ultraviolet (UV) dyes. That is, the imaging layer may be free of UV dyes that selectively absorb UV light, which preferentially absorbs UV light over visible light or IR light.

[0013] In some embodiments, the imaging layer is free of particles, such as thermally ablatable particles or non-thermally ablatable particles (non-thermally ablatable).

[0014] Some embodiments of the mask element may have different configurations. In some aspects, the barrier layer does not contain UV dyes. In some aspects, the barrier layer optionally contains 0-10% IR dyes. In some aspects, at least one plasticizer may be present in the barrier layer. The plasticizer in the barrier layer may be present in an amount of about 10% to about 40%. In some aspects, carbon black may be present in an amount of about 30% to about 70%. Carbon black may be pre-dispersed in nitrocellulose. In some aspects, the infrared dye in the imaging layer may be present in an amount of about 0.1% to about 15%. In addition, at least one plasticizer may be present in the imaging layer. The plasticizer in the imaging layer may be present in an amount of about 10% to about 40%. In some aspects, the plasticizer in the barrier layer may be selected from ATBC, Alchemix, PEG-1000 and combinations thereof. In some aspects, the plasticizer in the imaging layer is selected from ATBC, PEG-1000 and combinations thereof. In some aspects, the plasticizer may be a non-phthalate plasticizer.

[0015] In some embodiments, a mask may include a mask element of any embodiment, wherein at least one mask image is formed in the mask element. The mask may include an imaging region in the imaging layer, wherein the imaging region has an optical aperture, and the optical aperture is substantially free of carbon black and non-crosslinked nitrocellulose. The mask may include a non-imaging region in the imaging layer, wherein the non-imaging region has non-crosslinked nitrocellulose, carbon black, and an infrared dye, and optionally a plasticizer. The optical density of the mask in the non-imaging region may be greater than 3.0, and the optical density in the fully ablated imaging region may be less than about 0.20.

[0016] In some embodiments, a method of making a mask element may include: forming a transparent polymer carrier sheet; forming a barrier layer on the transparent polymer carrier sheet; and forming an imaging layer on the barrier layer. The method may include forming a transparent overcoat layer on the imaging layer. The method may include forming the barrier layer to include at least one plasticizer. The method may include forming the imaging layer to include at least one plasticizer.

[0017] In some embodiments, a method of making a mask may include: providing a mask element as described in one of the embodiments, wherein the imaging layer is free of any imaging regions; and imaging the mask element with infrared light to form imaging regions in the imaging layer. In some aspects, imaging ablates carbon black, non-crosslinked nitrocellulose, and other materials in the imaging layer to form an optical aperture that presents a mask image. In some embodiments, a method of making a mask for flexographic printing may include exposing a thermally ablatable imaging layer to infrared radiation to selectively ablate regions in the thermally ablatable imaging layer. A mask image is formed in the thermally ablatable imaging layer, wherein the mask image includes regions of the thermally ablatable imaging layer and regions that have been thermally ablated and in which the thermally ablatable imaging layer is omitted.

[0018] In some embodiments, a mask image is formed in the imaging layer, and the mask image includes regions of the thermally ablatable imaging layer and regions that have been thermally ablated and in which the thermally ablatable imaging layer is omitted.

[0019] In some embodiments, a relief-forming assembly may include a relief-forming precursor and a mask element for flexographic printing. The mask may include: a transparent carrier sheet substrate; a polymer barrier layer on the substrate, and the layer optionally has a plasticizer and / or at least one first infrared absorbing material; a thermally ablatable imaging layer on the polymer barrier layer, and the layer has at least one second infrared absorbing material (e.g., not carbon black), carbon black in a thermally ablatable polymer binder (e.g., non-crosslinked nitrocellulose), and optionally a plasticizer. The thermally ablatable imaging layer has a mask image formed therein. The mask image includes areas of the thermally ablatable imaging layer and areas that have been thermally ablated where the thermally ablatable imaging layer is omitted.

[0020] In some embodiments, a method of manufacturing a relief-forming assembly may include placing a mask element on a relief-forming surface of a relief-forming layer; and forming full optical contact between the mask element and the relief-forming surface. In some aspects, the method may include at least one of the following operations: laminating the mask element to the relief-forming surface; or coupling the mask element to the relief-forming surface by vacuum adsorption.

[0021] In some embodiments, a method for making a relief image in a relief-forming component may include: providing the relief-forming component described in one of the embodiments; exposing a relief-forming layer of a relief-forming precursor to curing UV light radiation through a mask element to form an imaged relief-forming layer, wherein the UV-exposed areas in the imaged relief-forming layer are formed as polymerized areas, and the unexposed areas are formed as non-polymerized areas; removing the mask element from the imaged relief-forming layer; and developing the imaged relief-forming layer by removing the non-polymerized areas in the imaged relief-forming layer to form a relief image element having a relief image.

[0022] 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; placing a top surface of the mask element on a relief-forming surface of the relief-forming layer; and forming full optical contact between the mask element and the relief-forming surface. In some aspects, the method may include laminating the mask element to the relief-forming surface. In some aspects, the method may include coupling the mask element to the relief-forming surface by vacuum suction.

[0023] In some embodiments, a method of making a relief image in a relief-forming component may include: providing a relief-forming component according to one embodiment; exposing the relief-forming layer to curing UV radiation through a mask element to form an imaged relief-forming layer, wherein UV-exposed areas are formed as polymerized areas and unexposed areas are formed as non-polymerized areas in the imaged relief-forming layer; removing the mask element from the imaged relief-forming layer; and developing the imaged relief-forming layer by removing the non-polymerized areas in the imaged relief-forming layer to form a relief image element having a relief image (e.g., without non-polymerized areas). In some aspects, the method may include polymerizing at least one photopolymerizable monomer on a relief surface of a relief image of the relief image element.

[0024] The above summary is for illustrative purposes only and is not intended to limit the present invention in any way. In addition to the above illustrative aspects, embodiments, and features, further aspects, embodiments, and features will be disclosed by reference to the drawings and the following detailed description.

[0025] BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and following information and other features of the present disclosure will become more apparent from the following description and the appended claims in conjunction with the accompanying drawings. It should be understood that these drawings depict only several embodiments consistent with the present disclosure and are therefore not to be considered limiting of its scope, and the present disclosure will be described with additional specificity and detail through the use of the accompanying drawings.

[0027] Figure 1A is a schematic cross-sectional view of a mask precursor according to one embodiment of the present invention, illustrating incident infrared radiation used to make a mask element.

[0028] Figure 1B Is Figure 1A Schematic cross-sectional view of a mask element formed from a mask precursor according to the illustrated embodiment.

[0029] Figure 1C is a schematic cross-sectional view of a relief image forming assembly according to one embodiment of the present invention, which includes Figure 1B The mask element is shown in full optical contact with the relief-forming precursor.

[0030] Figure 1D According to one embodiment of the present invention, the Figure 1B Schematic diagram of a cross-section of a relief-forming precursor formed by incident UV radiation on the mask element shown in FIG.

[0031] Figure 1E is a cross-sectional diagram showing the Figure 1DOne embodiment of a relief image element resulting from an imaging process and an appropriate development process for removing unexposed areas of a UV-sensitive layer in an imaged relief-forming precursor is shown.

[0032] Figure 2 Contains data comparing transmission optical density (TOD) and drum speed for a comparative example and two inventive examples.

[0033] The elements and components in the drawings may be arranged according to at least one embodiment described herein, and those skilled in the art may modify the arrangement based on the disclosure provided herein.

[0034] DETAILED DESCRIPTION OF THE INVENTION

[0035] In the following detailed description, reference is made to the drawings that are a part of this document. In these drawings, similar symbols generally identify similar components unless the context dictates otherwise. The exemplary embodiments, drawings, and claims described in the detailed description are not intended to be limiting. Other embodiments may be used, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It is readily understood that aspects of the present disclosure (as generally described herein and shown in the drawings) may be arranged, substituted, combined, separated, and designed in a variety of different configurations, all of which are expressly contemplated herein.

[0036] In general, the present technology provides an improved mask that can be used to UV-expose a curable material in a relief-forming plate with less time and / or energy. The improved mask in the present technology has improved optical density parameters at the optical aperture of the mask compared to other masks, which results in shorter UV exposure time or less UV energy. Therefore, shortening the UV exposure time or reducing the UV energy can provide significant economic advantages.

[0037] In some embodiments, a mask element for flexographic printing is provided. The mask element can be used to prepare a mask having a mask image. The mask element can include: a transparent polymer carrier sheet; a barrier layer on the transparent polymer carrier sheet, wherein the barrier layer includes non-crosslinked nitrocellulose and an optional plasticizer; an imaging layer on the barrier layer, wherein the imaging layer includes a heat-ablatable material, the heat-ablatable material includes non-crosslinked nitrocellulose, carbon black and infrared (IR) dye, and an optional plasticizer. In some aspects, the mask element further includes a transparent overcoat on the imaging layer.

[0038] Flexcel NX TIL-R thermal imaging film (US 8,945,813) is used in the Kodak Flexcel NX system to make flexographic printing plates. However, the use of TIL-R requires a longer main UV exposure time (e.g., 14 minutes using a 30mW UV light source, or 22 minutes using a 20mW light source) to produce high-resolution printing plates (e.g., retaining small highlights). TIL thermal imaging film (US 10,768,520) can also be used, which has a longer main UV exposure time (e.g., 14 minutes using a 30mW UV light source, or 22 minutes using a 20mW light source) to produce high-resolution printing plates (e.g., retaining small highlights). 2 ), the UV exposure time is 12 minutes. Long main UV exposure time is detrimental to the productivity of the platemaking process. Therefore, the shorter main UV exposure time (e.g., 10 to 12 minutes when using a 30mW UV light source) obtained using the improved mask described herein is therefore very helpful in improving platemaking productivity.

[0039] The composition of the improved mask allows for more efficient ablation of the mask precursor than the TIL-R mask precursor, as evidenced by the improved mask of the present invention having a lower optical density (OD) than the mask made using the TIL-R precursor. For example, when both imaging films (TIL-R and the improved mask of the present invention) were laser ablated on a laser imaging device operating at 830 nm with the same laser power and drum speed settings, the ablation time for the improved mask was significantly shorter than that for the TIL-R mask, at only 10 minutes, while the ablation time for the TIL-R mask was 13 minutes.

[0040] The lower OD value of the improved mask allows more UV light to pass through the imaging area (e.g., optical aperture) of the mask, thereby allowing faster photopolymerization of the relief-forming layer, thereby shortening the UV exposure time required to achieve the same high-resolution printing plate quality (e.g., small dots maintained on the printing plate). Masks made from the improved thermal imaging film of the present invention require significantly reduced UV main exposure times to produce high-resolution printing plates.

[0041] OD is measured by an X-Rite transmission densitometer and is defined by the following formula:

[0042] OD=-log T λ = -log[(%T λ ) / 100]

[0043] For example, OD 0.10 corresponds to 79.3% light transmission, and OD 2.0 corresponds to 1% light transmission. Values ​​may be interpolated between or extrapolated from these points.

[0044] In some embodiments, the improved mask has an optical density greater than or about 3.0 in the non-imaging area and an optical density less than or about 0.20 in the fully ablated imaging area. For example, the OD of the fully ablated imaging area of ​​the mask can be less than or about 0.18, more preferably less than or about 0.15, more preferably less than or about 0.13, and more preferably less than or about 0.12. Specific examples can include an OD range of about 0.11 to about 0.13 for the improved mask. The UV light transmittance can be about 70%-80%, or about 74%-77%, or about 75%. The OD of the non-imaging area can be greater than 3.5. The higher optical OD of the non-imaging area of ​​the mask prevents the formation of images in unintended areas. For example, an OD of 3.0 corresponds to a light transmittance of only 0.1%.

[0045] Improved masks can also have shorter exposure times, such as lower energy exposure, such as reduced joules per square centimeter. Conventional masks can have UV exposures of 24 J / cm 2 , while the UV exposure of the improved mask can be 17J / cm 2 Up to 19J / cm 2 , and up to 21J / cm 2 .

[0046] The improved mask of the present invention also provides excellent stability of the imaging film under low to high humidity conditions. This is very beneficial for the transportation, storage, and loading and unloading of the imaging film into the imaging device for mask manufacturing. Therefore, the improved mask can exhibit excellent resistance to edge curling under both low and high humidity conditions.

[0047] In addition, the improved mask can also be used to produce a printing plate suitable for flexographic printing, which can fully achieve a 100% printing effect with 0.8% dots under the condition of 150lpi.

[0048] Masks and mask precursors

[0049] The present technology provides an improved thermal imaging film, also known as a mask precursor or mask element before imaging and a mask after imaging. That is, the thermal imaging film (TIF) includes an imaging layer that forms an image when exposed to infrared light. The imaging layer can be called a non-silver halide thermally ablatable imaging layer because it has no silver halide and can be thermally ablated by infrared light. The imaging layer is provided in the mask precursor together with a barrier layer and optionally with a protective topcoat, with the imaging layer sandwiched between them. A transparent polymer carrier sheet can be used as a substrate, on which the barrier layer can be retained so that the optional protective topcoat is located on top of the imaging layer. The optional protective topcoat can be treated with small 0.3 micron to 3 micron inorganic or organic particles.

[0050] The mask can be configured for use with a relief-forming precursor having a photosensitive layer, wherein the top surface is in contact with the photosensitive layer of the relief-forming precursor. The mask is obtained by imaging the mask precursor (e.g., mask element) with IR light. Thus, the mask precursor can be prepared and treated by illumination (e.g., infrared, IR) to form the mask. The mask can then be combined with the relief-forming precursor (e.g., by lamination) and treated with light (e.g., UV), and the light-treated mask and relief-forming precursor are then separated from each other.

[0051] The mask precursor can be considered an imageable material because it has an imageable layer that forms a mask. In some embodiments, the mask precursor can include three or four layers or films as described below, in order: (a) a transparent polymer support sheet (film); (b) a barrier layer; (c) a thermally ablatable imaging layer; and (d) an optional protective top coating of a particle treatment. The thermally ablatable imaging layer can be ablated by thermal imaging with light (e.g., IR light), but the thermally ablatable imaging layer does not contain silver halide and is therefore a thermally ablatable "non-silver halide" imaging layer. Therefore, the imaging layer includes a thermally ablatable substance, such as non-crosslinked nitrocellulose, and has carbon black, IR dye (e.g., broadband light that is specific to IR light, not black body absorption).

[0052] Although the protective top coating is ablatable, it may include particles that are ablatable or non-ablatable. Although the protective top coating may include particles that are non-ablatable, the protective top coating is still ablatable. In part, the matrix of the protective top coating may be a non-crosslinked polymer, so it is ablatable.

[0053] A mask precursor for forming a mask element that is ultimately used to form a relief image can be prepared as described herein and then processed into a mask. Figure 1A As shown, it has (a) a transparent polymer carrier sheet 150, on which (b) a barrier layer 120 is directly disposed, (c) an ablatable imaging layer 130, which is directly disposed on the barrier layer 120 and is positioned to receive light 35 indicated by the arrow shown in the figure, and (d) an optional protective top coating 138 that is optionally treated with particles, which is disposed on the ablatable imaging layer 130.

[0054] Transparent polymer carrier sheet

[0055] The transparent polymer carrier sheet can be any suitable transparent substrate or film. Useful transparent polymer carrier sheets can be (but are not limited to) transparent polymer films and sheets composed of one or more polymers, such as polyesters, including polyethylene terephthalate, polyethylene naphthalate (poly (ethylene naphthalate, PEN) and fluorine polyester polymers (fluorine polyester polymers); polyethylene-polypropylene copolymers; polybutadiene; polycarbonate; polyacrylate (polymer formed at least in part from one or more (meth) acrylate ethylenically unsaturated monomers); vinyl chloride polymers, such as polyvinyl chloride and copolymers at least partially derived from vinyl chloride; hydrolyzed or unhydrolyzed cellulose acetate; and other materials that are obvious to those skilled in the art. As long as the desired transparency and protective properties are achieved, the transparent polymer carrier sheet can be composed of two or more polymer materials as a mixture or composite material. They can be formed into a single layer polymer film, or a laminate of multiple layers of polymer films. Generally speaking, the transparent polymer carrier sheet has an average dry thickness of at least 25 μm and up to and including 250 μm, or typically at least 75 μm and up to and including 175 μm.

[0056] For example, clear polyethylene terephthalate sheets available from various commercial sources are suitable as the clear polymeric carrier sheet.

[0057] If desired, the surface of the transparent polymer carrier sheet may be treated to modify its wettability and adhesion to an applied coating (e.g., a barrier coating). Such surface treatments include, but are not limited to, corona discharge treatment and application of subbing layers, as long as the desired transparency (as described above) is achieved.

[0058] If desired, the transparent polymer carrier sheet may also optionally include one or more "first" ultraviolet radiation absorbing compounds (e.g., UV dyes), but may also be free of any ultraviolet radiation absorbing compounds. One or more compounds of this type may be the same as or different from the ultraviolet radiation absorbing compounds in the imaging layer (see below). Each useful ultraviolet radiation absorbing compound typically absorbs electromagnetic radiation of at least 150 nm and up to and including 450 nm. These compounds may be present in the transparent polymer carrier sheet in an amount of at least 0.01 wt. % and up to and including 0.1 wt. %, based on the total dry weight of the transparent polymer carrier sheet. However, the transparent polymer carrier sheet may be free of any IR dyes and / or UV dyes.

[0059] In addition, the transparent polymer carrier sheet may contain one or more "adhesion promoters" to improve its adhesion to the adjacent barrier layer. Useful adhesion promoters include, but are not limited to, gelatin, polyvinylidene chloride, poly(acrylonitrile-co-vinylidene chloride-co-acrylic acid), and polyethyleneimine.

[0060] Barrier layer

[0061] In some embodiments, the mask precursor further comprises a barrier layer disposed on the transparent polymer carrier sheet and directly between the transparent polymer carrier sheet and the imaging layer. The barrier layer can be prepared according to a previous method for preparing a barrier layer (e.g., see US 9,250,527), or according to an embodiment described in more detail below. The barrier layer can be a non-crosslinked nitrocellulose, which can optionally include an IR dye (absorbing IR light) and / or a plasticizer. In some aspects, the barrier layer can be free of UV dyes (e.g., absorbing ultraviolet light). The barrier layer is typically configured as a relatively uniform coating (i.e., substantially continuous and having a fairly uniform wet thickness) on the transparent polymer carrier sheet, followed by drying if any solvent is present in the composition formulation.

[0062] The barrier layer is typically transparent, as defined above. In particular, the barrier layer is transparent to the UV radiation used to image the relief-forming precursor, as defined below. Thus, the barrier layer may be free of UV dyes or materials that selectively absorb UV light.

[0063] The barrier layer may include non-crosslinked nitrocellulose, with or without additional non-crosslinked polymers. The nitrocellulose may be non-crosslinked as described herein. The molecular weight of the nitrocellulose group unit ranges from 459.28 to 594.28 Da, and the molecular formula is [C 6 H 7 O 2 (ONO 2 ) 3 ] n , where n can be 0 to a larger number. The barrier layer can be ablated by IR radiation, as described herein. The barrier layer can provide a buffer between the imaging layer and the carrier sheet, which facilitates mask formation.

[0064] The barrier layer may include at least one plasticizer. The content of the plasticizer in the barrier layer is about 10% to about 50% by weight, about 10% to about 40% by weight, or about 20% to about 30% by weight. The plasticizer may be represented by acetyl tributyl citrate (ATBC), Alchemix and PEG-1000 or a combination thereof. The plasticizer Alchemix may be Alchemix2340, which may be called NQ Solve 1086, which may be a mixture of a polyester resin with ethyl acetate and ethanol, wherein the weight percentage of ethyl acetate is 10%-30%, ethanol is 5%-10%, and the rest is a polyester resin. The polyester resin may be a low molecular weight polyester with hydroxyl functional groups. In one example, the number average molecular weight Mn of the polyester composition may be between about 500 and about 10,000 Da or up to 1000 Da, the polydispersity is less than about 2, preferably less than about 1.8, the hydroxyl functionality is between 2 and 3, the hydroxyl value is between about 160 and about 260, and the acid value is less than about 10. PEG-1000 may be polyethylene glycol having a molecular weight of about 1000 Da.

[0065] In some embodiments, plasticizer can comprise multiple ester groups, for example, polymer or multiple ester moieties with ester, which can include alkyl. For example, ATBC comprises four alkyl esters coupled together, and Alchemix is ​​a polyester. In addition, polyethers, for example PEG, polypropylene glycol and their combinations can be used. Therefore, compounds or polymers with multiple ether groups or multiple ester groups, wherein each ether group or ester group has an alkyl component associated with each ether or ester. Therefore, alkyl ethers and alkyl esters, for example, those with multiple alkyl ether moieties or alkyl ester moieties.

[0066] The barrier layer may be free of IR dyes, but may optionally include IR dyes, for example from 0% to 10%, or up to 8%, or up to 5%, or up to 3%, or up to 2% or up to 1%. One or more IR absorbing materials, collectively referred to herein as "first" infrared radiation absorbing materials, to distinguish them from the second infrared radiation absorbing materials (described below) in the imaging layer when necessary. The first and second infrared radiation absorbing materials may be one or more dyes or pigments, or mixtures thereof, which will provide the desired spectral absorption characteristics and are independently sensitive to electromagnetic radiation in the infrared electromagnetic wavelength range of at least 700nm and up to 1,500nm, typically at least 750nm and up to 1,200nm and including 1,200nm. For example, the IR dye in the barrier layer may be free of black dyes or pigments, such as carbon black, metal oxides, and other materials such as described in US'987 (as described above). Therefore, the barrier layer may be deliberately free of carbon black, such as carbon black chips (e.g., predispersions). While IR dyes may be included, such IR dyes should be specific to IR light and exclude broadband light absorbers (such as carbon black) in the barrier layer.

[0067] Useful first IR radiation absorbing materials also include IR dyes, including but not limited to cationic infrared absorbing dyes and photothermally bleachable dyes. Examples of suitable IR dyes include, but are not limited to, azo dyes, squarilium dyes, cretonate dyes, triarylamine dyes, thiazolium dyes, indolium dyes, oxonolium dyes, oxazolium dyes, cyanine dyes, mercaptocyanine dyes, phthalocyanine dyes, indocyanine dyes, indoletricarbocyanine dyes, oxatricarbocyanine pigments, thiocyanine dyes, thiotricarbocyanine dyes, mercaptocyanine dyes, cryptocyanine dyes, naphthalocyanine dyes, polyaniline dyes, polypyrrole dyes, polythiophene dyes, chalcogenoperylenyl and di(chalcogenperylenyl)polymethine dyes, oxindolizine dyes, pyrylium dyes, pyrazoline azo dyes, oxazine dyes, naphthoquinone dyes, anthraquinone dyes, quinoneimine dyes, methine dyes, arylmethylene dyes, squalane dyes, oxazole dyes, cronine dyes, porphyrin dyes, and any substituted or ionic forms of the above dye classes. Suitable dyes are also described in US Pat. No. 5,208,135 (Patel et al.), US Pat. No. 6,569,603 (Furukawa), and US Pat. No. 6,787,281 (Tao et al.), and EP Publication No. 1,182,033 (Fijimaki et al.).

[0068] Near infrared absorbing cyanine dyes are also useful, such as described in U.S. Pat. No. 6,309,792 (Hauck et al.), U.S. Pat. No. 6,264,920 (Achilefu et al.), U.S. Pat. No. 6,153,356 (Urano et al.), U.S. Pat. No. 5,496,903 (Watanate et al.), the disclosures of all of which are incorporated herein by reference. Suitable dyes can be formed using conventional methods and starting materials, and can also be obtained from various commercial sources, including American Dye Source (Baie D'Urfe, Quebec, Canada) and FEW Chemicals (Germany).

[0069] The first infrared radiation absorbing material is typically present in a sufficient amount to provide a transmission optical density of at least 0.025 (and typically at least 0.05) at the wavelength of the electromagnetic radiation (e.g., IR) being exposed. Typically, this is achieved by including at least 0.1 wt % and up to and including 5 wt % or typically at least 0.3 wt % and up to and including 3 wt % of such material based on the total dry weight of the barrier layer.

[0070] The first infrared radiation absorbing material in the barrier layer can be the same or different chemical material as the second infrared radiation absorbing compound incorporated into the imaging layer described below. The infrared radiation absorbing material in the barrier layer can also be different from the infrared radiation absorbing material in the transparent polymer carrier. In most embodiments, the first and second infrared radiation absorbing materials are the same chemical material, but do not include black materials, such as carbon black. The infrared radiation absorbing materials can selectively absorb infrared light, so they are not broadband absorbers that absorb UV light, visible light or other non-IR light. The amounts of the first and second infrared radiation absorbing materials in the imageable material can be the same or different. In most embodiments, they are present in different amounts in the imageable material.

[0071] In some embodiments, the barrier layer may include an ablatable non-crosslinked binder material formed from an organic polymer, such as non-crosslinked nitrocellulose, present in the barrier layer in an amount of at least 30 wt % and up to and including 100 wt %, or more likely at least 50 wt % and up to and including 80 wt %, all based on the total dry weight of the layer. In some aspects, a plasticizer may be included in the above amounts, whether or not an IR dye is present, and the balance of the material may be non-crosslinked nitrocellulose.

[0072] The barrier layer typically has an average dry thickness of at least 0.5 μm and up to and including 5 μm or typically at least 0.8 μm and up to and including 3 μm.

[0073] In some embodiments, the barrier layer may be free of cross-linked nitrocellulose. In addition, the barrier layer may be free of a cross-linking agent capable of cross-linking nitrocellulose. In addition, the barrier layer may be free of a cross-linked polymer.

[0074] In some embodiments, the barrier layer may be free of particles, such as ablatable particles or non-ablatable particles. The barrier layer may be free of metal oxides.

[0075] In some embodiments, the barrier layer may be free of metallization layer materials or metals therein.

[0076] In some embodiments,

[0077] Thermally ablatable imaging layer (IL)

[0078] The imaging layer incorporated into the mask precursor is typically disposed directly on the barrier layer as a relatively uniform coating (i.e., substantially continuous and having a fairly uniform wet thickness) followed by drying if any solvent is present in the formulation. In most embodiments, the imaging layer is a single coating or application layer, but in other embodiments, there may be multiple sub-layers or sub-coatings constituting the imaging layer disposed directly on the barrier layer described above.

[0079] According to the term, the imaging layer is substantially free of silver halide. In other words, no silver halide is intentionally added or produced in the imaging layer.

[0080] In some embodiments, the imaging layer includes non-crosslinked nitrocellulose, carbon black, and an infrared dye, and optionally a plasticizer.

[0081] The nitrocellulose may be non-cross-linked, as described herein.

[0082] The imaging layer may include carbon black, and there are many types of carbon black available on the market with different particle sizes. For example, they include RAVEN 450, 760ULTRA, 890, 1020, 1250 and other carbon blacks provided by Columbian Chemicals Co. (Atlanta, Ga), and BLACK PEARLS 170, BLACK PEARLS 480, VULCAN XC72, BLACK PEARLS 1100 and other carbon blacks available from Cabot Corporation. The carbon black can be received as a dispersion or fragment. Sun Chemical's carbon black fragment "Predisol C" Black 7 is favored for its high pigment to binder ratio. Other useful carbon blacks are surface functionalized with solubility promoting groups. Carbon blacks grafted to hydrophilic nonionic polymers, such as FX-GE-003 (manufactured by Nippon Shokubai), or carbon blacks surface functionalized with anionic groups, such as 200 or Also useful is ATTACH 300 (manufactured by Cabot Corporation). For example, carbon black chips may include a carbon black material, such as a pigment, dispersed in a binder and provided in the form of small pieces or chips (e.g., not provided in a solution or in a solvent), wherein the chips are used to prepare a layer containing carbon black.

[0083] The imaging layer may contain at least one plasticizer, the plasticizer content in the imaging layer is about 10 wt % to about 50 wt %, about 10 wt % to about 40 wt %, or about 20 wt % to about 30 wt %, and the plasticizer may be the above-mentioned acetyl ATBC, Alchemix, PEG-1000 or a combination thereof.

[0084] In some embodiments, plasticizer can comprise multiple ester groups, for example, polymer or multiple ester moieties with ester, which can include alkyl. For example, ATBC comprises four alkyl esters coupled together, and Alchemix is ​​a polyester. In addition, polyethers, for example PEG, polypropylene glycol and their combinations can be used. Therefore, compounds or polymers with multiple ether groups or multiple ester groups, each ether group or ester group has an alkyl component associated with each ether or ester. Therefore, alkyl ethers and alkyl esters, for example, those with multiple alkyl ether moieties or alkyl ester moieties.

[0085] In some embodiments, the plasticizer does not include Alchemix or polyester polymers. Thus, in some embodiments, the plasticizer in the imaging layer may include a compound having multiple alkyl ester moieties coupled together in a branched form, or a polymer having multiple alkyl ester moieties linked together in a chain form.

[0086] In some embodiments, the imaging layer includes one or more ultraviolet radiation absorbing materials (UV light absorbing materials) as components. These compounds generally have an absorbance of at least 1.5 and up to and including 5 in the range of electromagnetic radiation wavelengths of at least 300 nm and up to and including 450 nm. Generally, useful ultraviolet radiation absorbing materials include, but are not limited to, benzotriazoles, halogenated benzotriazoles, triazines, benzophenones, benzoates, salicylates, substituted acrylonitriles, cyanoacrylates, benzylidene malonates, oxalanilides, and mixtures thereof. Examples of useful ultraviolet radiation absorbing materials include, but are not limited to, those named (BASF), (Keystone Aniline Corporation), (SandozChemicals Corp.), Hostavin (Clariant) and UV absorbing dyes or UV stabilizers sold by ATTACH (BASF or Ciba). Examples of useful materials are described in U.S. Patent No. 5,496,685 (Farber et al.). However, embodiments of the imaging layer also omit any UV dyes.

[0087] The imaging layer also includes one or more second infrared radiation absorbing materials as a second essential component, which are defined similarly to the first infrared radiation absorbing materials for the barrier layer described above, and they can be the same as or different from the first infrared radiation absorbing material. The one or more second infrared radiation absorbing materials can be present in the imaging layer in an amount sufficient to provide a transmission optical density of at least 0.5 and typically at least 0.75 at the exposure wavelength. Typically, this is achieved by including at least 3 weight percent and up to and including 20 weight percent of one or more second infrared radiation sensitive compounds based on the total dry weight of the imaging layer. The IR dye in the imaging layer can specifically absorb IR light in visible light and UV light, so the IR dye is not a black body material that absorbs broadband light.

[0088] The imaging layer may optionally include one or more fluorocarbon additives for improving the production of halftone dots (i.e., pixels) with sharp, generally continuous, and relatively sharp edges. Examples of useful fluorocarbon additives and amounts thereof are provided in

[0087] to

[0089] of US '987 (as described above).

[0089] Other optional components of the imaging layer include, but are not limited to, other plasticizers, coating aids or surfactants, dispersing aids, fillers, and colorants, all of which are well known in the art, such as described in

[0094] to

[0096] of US '987 (as described above). For example, the imaging layer may also contain one or more fluorocarbon additives or one or more non-heat-ablatable colorants. Examples of some other suitable plasticizers (e.g., secondary plasticizers) may include aliphatic hydrocarbon oils, such as cycloparaffinic oils and paraffinic oils, liquid polydienes, such as liquid polybutadiene, liquid polyisoprene. Typically, secondary plasticizers are liquids having a molecular weight of less than about 5,000 Da, but their molecular weight can be as high as about 30,000 Da. Low molecular weight plasticizers will include plasticizers having a molecular weight of less than about 30,000 Da. These other secondary plasticizers may also be used in barrier layers.

[0090] All essential and optional components for the imaging layer described above are dispersed in one or more ablatable polymeric binder materials, including non-crosslinked nitrocellulose, and optionally other synthetic and natural polymeric materials, which are ablatable when exposed to light radiation (e.g., IR radiation, visible radiation, or UV radiation). In certain aspects, the ablatable polymeric binder in the imaging layer is non-crosslinked, and is therefore a non-crosslinked binder. In addition, the imaging layer may be free of a crosslinking agent that crosslinks the nitrocellulose. Such materials are capable of dissolving or dispersing the essential and optional components throughout the imaging layer in a uniform manner. The one or more ablatable polymeric binder materials may be present in an amount of at least 25 weight percent and up to and including 75 weight percent, or typically at least 35 weight percent and up to and including 65 weight percent, based on the total dry weight of the imaging layer.

[0091] In addition to nitrocellulose, useful ablatable polymer binder materials include, but are not limited to, materials described, for example, in

[0081] to

[0085] of US '987. These materials may also be referred to as "adhesive binders," such as those described in

[0081] of US '987. Examples of such materials include, but are not limited to, acetyl polymers such as poly(vinyl butyral) provided by Solution, Inc. (St. Louis, Mo.), in the form of, for example, B-76, and acrylamide polymers supplied by Henkel Corp. (Gulph Mills, Pa.) in the form of MACROMELT 6900. Pressure sensitive adhesive polymers may also be used for this purpose. These materials may optionally be used with non-crosslinked nitrocellulose.

[0092] In some embodiments, it is advantageous to use thermally-combustible or thermally ablatable binder materials in the imaging layer that generate gases and 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. Pat. No. 5,171,650 to Ellis et al., at column 9, lines 41-50, the disclosure of which is incorporated herein by reference), which materials may be non-crosslinked.

[0093] Other useful ablatable materials for the imaging layer have hydroxyl groups (or hydroxyl polymers) as described in

[0082] to

[0084] of US '987 (as described above), such as polyvinyl alcohol and cellulosic polymers (e.g., nitrocellulose is included). Other useful polymers include non-crosslinked polyesters, polyamides, polycarbamates, polyolefins, polystyrenes, polyethers, polyvinyl ethers, polyvinyl esters, and polyacrylates and polymethacrylates having 1 and 2 carbon atom alkyl groups.

[0094] In addition to nitrocellulose, particularly useful ablatable materials for the imaging layer include, but are not limited to, polyurethanes, polyvinyl butyrals, (meth)acrylamide polymers, polyacetals, poly(cyanoacrylates), polymers derived at least in part from methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate, or combinations of two or more of these materials.

[0095] The imaging layer may have an average dry thickness of at least 0.5 μm and up to and including 5 μm or typically at least 0.8 μm and up to and including 2.5 μm.

[0096] Protective top coating

[0097] The mask precursor may optionally include a transparent polymer overcoat layer disposed directly on the imaging layer opposite the barrier layer. The transparent polymer overcoat layer may optionally be a particle treated protective topcoat. Adding particles to such a particle treated protective topcoat may provide the present invention with the advantages of improved resolution and increased hilite dot retention.

[0098] The protective top coating typically includes one or more transparent film-forming polymers or resins, including but not limited to methacrylic acid copolymers (e.g., copolymers of ethyl methacrylate and methacrylic acid). The body of the protective top coating may include small particles as described herein. The particles may be inorganic particles, which may be silica or metal oxide particles, less than 1 micron in size. The metal oxide particles may be ablative, such as iron oxide particles. Alternatively, the metal oxide particles may be non-ablative, such as titanium dioxide or zinc oxide. Non-ablative silica particles may also be used. These inorganic particles may be 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 range between any of the values.

[0099] The inorganic particles may be non-ablative particles as described herein. However, the protective topcoat treated with the particles is ablatable, so the polymeric host is not crosslinked. The host may be made ablatable, which may be similar to the host composition of the imaging layer.

[0100] The protective top coat may be directly attached to the imaging layer and may have an average dry thickness of at least 0.05 μm and up to and including 1 μm. The thickness may vary depending on the specific embodiment.

[0101] In some embodiments, it is advantageous to use heat-burnable or heat-ablable binder materials in the protective topcoat that generate gases and volatile fragments at temperatures below 200° C. Examples of such materials are heat-ablable nitrocellulose, polycarbonates, poly(cyanoacrylates), poly(methacrylates), poly(ethyl acrylates), polyurethanes, polyesters, polyorthoesters, polyacetals, and copolymers thereof (e.g., see U.S. Pat. No. 5,171,650 to Ellis et al., col. 9, lines 41-50, the disclosure of which is incorporated herein by reference), which materials may be non-crosslinked. 1:1 methacrylic aid-ethyl acrylate copolymers, such as The MAE30 DP is one example.

[0102] Other ablatable materials useful for protective topcoats have hydroxyl groups (or hydroxyl polymers), such as those described in

[0082] to

[0084] of U.S. Pat. No. '987 (as described above), such as polyvinyl alcohol and cellulosic polymers (e.g., nitrocellulose), which may be non-crosslinked. An exemplary group of useful polymers are non-crosslinked polyesters, polyamides, polyurethanes, polyolefins, polystyrenes, polyethers, polyvinyl ethers, polyvinyl esters, and polyacrylates and polymethacrylates having 1 and 2 carbon atom alkyl groups, and copolymers thereof. Particularly useful ablatable materials for protective topcoats include, but are not limited to, polyurethanes, polyvinyl butyrals, (meth)acrylamide polymers, nitrocellulose, polyacetals, polycyanoacrylates, polymers derived at least in part from methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate, or combinations of two or more of these materials, such as copolymers, all of which may be non-crosslinked.

[0103] In addition, the protective top coating may include fluorine particles of one or more fluorine-containing polymers dispersed therein as described above, for example, as described in U.S. Pat. No. 6,259,465 (Tutt et al.), the disclosure of which is incorporated herein by reference. An example may include polytetrafluoroethylene (PTFE). The content of fluorine particles may be from about 1% to about 40%. Preferably about 33%.

[0104] In addition, the protective top coating may include a surfactant, such as a fluorosurfactant. The fluorosurfactant may be Capstone FS-3100. The content of the fluorosurfactant may be significantly less than the content of the fluorine particles.

[0105] In some embodiments, a siloxane-containing surface additive may be included in the protective top coating. The siloxane-containing surface additive may be a polyether-modified polydimethylsiloxane, such as BYK 333. The siloxane may be present in a significantly less amount than the fluorosurfactant.

[0106] Mask

[0107] The mask precursor can be considered as an imageable material because it has an imageable layer that forms a mask. In some embodiments, the mask precursor can include four layers or films as described herein, in order: (a) a transparent polymer carrier sheet (film), optionally with a first ultraviolet light absorbing compound; (b) a barrier layer, also optionally with a first infrared radiation absorbing compound and / or a plasticizer; (c) a thermally ablatable imaging layer (IL) having carbon black, a second infrared radiation absorbing compound and an optional ultraviolet light absorbing compound, and an optional plasticizer; and (d) an optional protective top coating optionally treated with particles.

[0108] A mask precursor for forming a mask element that is ultimately used to form a relief image can be prepared as described herein and then processed into a mask. Figure 1A A mask precursor 110 is shown having (a) a transparent polymer carrier sheet 115 having (b) a barrier layer 120 disposed directly thereon, optionally comprising an ablatable adhesive material, (c) an ablatable imaging layer 130 disposed directly on the barrier layer 120 and positioned to receive light 35 indicated by arrow 35 shown in the figure, and (d) a protective top coating 138 disposed on the ablatable imaging layer 130.

[0109] Figure 1A , the exposure step of some embodiments is shown, wherein the mask precursor material 110 is image-wise exposed to infrared radiation 35 to provide exposed areas 140 and unexposed areas 142, such as Figure 1B, and corresponds to the mask image. As shown, the exposed area 140 is ablated and removed from the unexposed area 142. Therefore, the exposed area 140 forms the mask image.

[0110] Reference Figures 1A to 1E The order of providing a general description, so that some embodiments according to the present invention can be understood. As described above, Figure 1A A mask precursor 110 is shown which is exposed to exposure infrared radiation 35 to form a mask element ( Figure 1B ).

[0111] exist Figure 1C 1, mask element 136 includes imaging layer 115 overlying barrier layer 120, which in turn overlies ablated imaging layer 130 having a mask image formed therein and having ablated protective top coating 138. Mask element 136 is in intimate or complete optical contact with relief-forming precursor 155 to provide relief image-forming assembly 150 by contact with optional protective top coating 138. Relief-forming precursor 155 includes UV-sensitive layer 160 typically carried on substrate 165.

[0112] Figure 1D The step of exposing relief image forming assembly 150 to UV radiation 170 indicated by arrows is shown. UV radiation 170 passes through the transparent polymer carrier sheet 115, barrier layer 120, and exposed areas of imaging layer 130 in mask element 136 (e.g., element 140 - the portion of the imaging layer that was removed), and then through the exposed portions of particle treated protective top coating 138, thereby causing photocuring in UV sensitive layer 160 of relief forming precursor 155.

[0113] After UV exposure, the mask element 136 can be removed from the UV-sensitive layer 160 of the relief-forming precursor 155, and a development process can provide a pattern in the UV-sensitive layer 160. Figure 1E The relief image shown. Figure 1E As shown, the relief image includes relief image peaks 75 and relief image valleys 80 in the UV sensitive layer 60 .

[0114] Forming a mask

[0115] In some embodiments, a mask can be formed by creating exposed and unexposed regions in an imaging layer of a mask precursor as described herein. The choice of imaging mechanism will determine the possible variations in the image formed for the mask, as described below.

[0116] The process of exposing the mask precursor to ablative light energy to ablate the imaging layer and protective top coating in selected areas is called "imagewise exposure". In some embodiments, imagewise exposure can be achieved by thermal radiation from a thermal or infrared laser scanned or rastered under computer control. Any known scanning device can be used, including flatbed scanners, external drum scanners, and internal drum scanners. In these devices, the mask precursor material is fixed to a drum or bed, and the laser beam is focused to a point that can illuminate the imaging layer of the mask precursor material. Two or more lasers can scan different areas of the imaging layer simultaneously.

[0117] For example, the mask precursor material can be exposed to infrared radiation, for example, in the electromagnetic wavelength range of at least 700 to up to and including 1500 nm. Such mask precursor materials include one or more of the above-described second infrared radiation absorbing materials in the imaging layer to provide sensitivity to infrared radiation. In these embodiments, the mask precursor material can be suitably mounted on an infrared imager and scanned under computer control using an infrared laser (e.g., a diode laser or an Nd:YAG laser) to expose to infrared radiation. Suitable infrared imagers include, but are not limited to, the TRENDSETTER imagesetters and ThermoFlexFlexographic CTP imagers provided by Eastman Kodak Company for CTP lithographic applications and imaging flexographic printing elements, the DIMENSION imagesetters provided by Presstek (Hudson, NH) for CTP lithographic applications, the TENSOR imagesetters provided by Esko-Graphics (Kennesaw, Ga.), and the TENSOR imagesetters provided by Esko-Graphics (Kennesaw, Ga.). A digital imager (CDI SPARK) and an OMNISETTER imager for imaging flexographic printing elements were provided by Misomex International (Hudson, NH).

[0118] Figure 1A , where the mask precursor material 10 is image-wise exposed to infrared radiation 35 to provide exposed areas 40 and unexposed areas 42, such as Figure 1B 36 and corresponds to the mask image. As shown, the exposed areas 40 are ablated and removed from the unexposed areas 42. Thus, the exposed areas form the mask image.

[0119] If desired, the step of forming the mask image may also include the step of removing exposed or unexposed areas from the imaging layer. In some embodiments, the exposed areas of the imaging layer are removed, for example, by ablating the exposed material in the imaging layer. In this mechanism, the exposed areas of the imaging layer are removed from the mask element to leave the mask image by generating gases during the ablation process. Specific binders (e.g., non-cross-linked) may be present in the imaging layer that decompose to rapidly generate gases when exposed to heat (e.g., heat generated by IR laser radiation). This action is distinguished from other mass transfer techniques in that a chemical change rather than a physical change results in almost complete transfer of the imaging layer, rather than a partial transfer.

[0120] In other embodiments not shown, a mask image can be formed on the carrier sheet by creating exposed and unexposed areas in the imaging layer and selectively removing the unexposed areas.

[0121] In some embodiments, the mask image in the imaging layer of the mask element can be cured by heat treating the mask image in the imaging layer of the mask element, provided that the properties of the mask element are not adversely affected. The heat treatment can be performed in a variety of ways, including but not limited to, storage in an oven, hot air treatment, contact with a heated platen, or through a heated roller device. Heat treatment is not necessary for curing.

[0122] In other embodiments, a mask image may be formed in an imaging layer as described above, and the exposed areas may be transferred to a receiver sheet and then removed from the mask element prior to contacting the receiver sheet with a relief-forming precursor. Such procedures are well known in the art.

[0123] In a peel-off imaging mechanism, the exposed areas of the imaging layer can be removed from the carrier sheet using a suitable receiver sheet based on the differential adhesion properties in the imaging layer. After the mask precursor is image-wise exposed, the receiver sheet is separated from the carrier sheet, and the exposed or unexposed areas are retained in the mask element.

[0124] Relief Forming Precursor

[0125] In some embodiments, the photosensitive relief-forming material can be used in a relief-forming photopolymer plate precursor, the photosensitive relief-forming layer can be processed to form a relief image, and the photosensitive relief-forming layer can also be used in a solvent-washable plate or a water-washable plate.

[0126] US '987 (as described above) provides a great deal of detail of useful relief-forming precursors (e.g., flexographic printing plate precursors, relief printing plate precursors, and printed circuit boards). Such relief-forming precursors may include a suitable dimensionally stable substrate and a relief-forming layer that is sensitive to UV light (UV), and an optional coversheet and / or 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 that can produce a relief image using a masking element is useful in the practice of the present invention when a low surface energy additive is included.

[0127] In some embodiments, the relief-forming precursor generally comprises a suitable dimensionally stable substrate, a radiation-curable layer in which a flexographic relief image can be formed, and an optional cover layer on the radiation-curable layer and / or a metal layer between the substrate and the radiation-curable layer. Suitable substrates include flexible, dimensionally stable transparent polymer films and metal substrates, such as aluminum plates. Polyester films are particularly suitable for use as flexible, dimensionally stable transparent substrates. The relief-forming precursor may optionally include a metal layer disposed between the substrate and the radiation-curable layer. The metal layer may include copper or another metal or metal alloy.

[0128] Some embodiments further include a removable cover layer that protects the radiation curable layer from fingerprints and other damage and is disposed on the radiation curable layer. In some embodiments, the flexographic printing plate precursor further includes a metal layer located between the substrate and the radiation curable layer, or a cover layer and a metal layer sandwiching the radiation curable layer.

[0129] In some embodiments, the radiation-curable layer can be a UV-sensitive layer that is cured by UV light. In some aspects, the UV-sensitive layer can be at least one layer of a relief-forming precursor that is formed of a relief-forming material that is sensitive to UV. Therefore, when referring to a relief-forming material or layer, it refers to a UV-sensitive material or layer that can be irradiated by UV light and developed into a relief image.

[0130] In some embodiments, the relief-forming precursor includes: a backing or base film (e.g., as a substrate), a relief-forming layer (e.g., a UV-sensitive material); and an optional removable cover film to protect the photosensitive layer. In another option, a metal layer can be located between the substrate and the relief-forming layer.

[0131] In some embodiments, the backing or base film can be configured to provide support for the relief-forming layer of the relief-forming precursor. The backing layer can be formed by transparent or opaque materials, such as paper, cellulose film, plastic or metal. The backing layer is preferably formed by a flexible transparent material. Examples of such materials are cellulose films or plastics, such as PET (polyethylene terephthalate), PEN (polyethylene naphthalate), polyether, polyethylene, polyamide (Kevlar) or nylon. Preferably, the support layer is formed by polyethylene terephthalate (PET). It is also found that the relief-forming layer with a low surface energy additive can adhere to the support layer. The thickness of the support layer can be about 0.001 to about 0.010 inches. Optionally, various layers, such as an antihalation layer and / or an adhesive layer, can be located between the backing layer and the relief-forming layer. In some aspects, the adhesive layer can include an antihalation material (e.g., a light-absorbing substance to prevent refraction of light) or such an antihalation material can be excluded.

[0132] In some embodiments, the relief-forming layer can be a UV light-sensitive material that forms a relief image when imaged and developed using UV light, wherein the relief image has a reduced surface energy. Adding low surface energy additives to the UV light-sensitive material can provide many desirable properties for the relief image forming scheme, such as easier vacuum adsorption and better lamination to reduce bubble formation. In addition, the reduced peel force allows for easier removal of the imaging mask from the relief-forming layer after the primary UV exposure to form the relief image.

[0133] In some embodiments, by adding a low surface energy additive to the composition of the photosensitive material, a reduced surface energy and a reduced peeling force can be obtained. The low surface energy additive may be contained in the matrix of the photosensitive material so as to be present in the body and surface of the photosensitive material and distributed therein. Typically, the low surface energy additive is uniformly mixed in the photosensitive material. However, the additive may be provided randomly or non-uniformly (e.g., non-uniformly), or in the form of a concentration gradient (wherein the concentration is preferentially gradually increased to one side or the other side).

[0134] In some embodiments, the low surface energy additive may include a silicone material, such as a siloxane-based monomer having a reactive functional group. The reactive functional group may be selected to be polymerizable with other polymerizable monomers of the photosensitive material. This allows the siloxane to be incorporated into the polymeric material so that it remains in the portion of the photosensitive material remaining after the relief formation process. Thus, the reactive functional groups may be tailored based on known functional groups that may participate in polymerization reactions with other monomers of a particular type having the same functional group or a different but appropriately reactive functional group.

[0135] In some embodiments, the photosensitive material can be a UV-sensitive layer comprising: an elastic binder; at least one polymerizable or photocurable monomer; and a photopolymerization photoinitiator sensitive to UV radiation. Suitable photoinitiator compositions include, but are not limited to, those described in U.S. Pat. No. 4,323,637 (Chen et al.), U.S. Pat. No. 4,427,749 (Graetzel et al.), and U.S. Pat. No. 4,894,315 (Feinberg et al.).

[0136] The elastic binder may include more polymers or resins that are soluble, swellable or dispersible in aqueous, semi-aqueous or organic solvent developers (described below), and may include, but are not limited to, natural or synthetic polymers of conjugated dienes, block copolymers, core-shell microgels, and mixtures of microgels with preformed macromolecular polymers. The elastic binder may comprise at least 65 wt % and up to and including 90 wt % based on the total dry UV-sensitive layer weight.

[0137] In some embodiments, the elastic binder can be a single polymer or a polymer mixture (e.g., a homopolymer, a copolymer, a random copolymer, a block copolymer, any polymer having any number of different types of monomers) that is soluble, swellable, or dispersible in an aqueous, semi-aqueous, or organic solvent developer. Suitable binders include those described in U.S. Pat. No. 3,458,311 (Alles), U.S. Pat. No. 4,442,302 (Pohl), U.S. Pat. No. 4,361,640 (Pine), U.S. Pat. No. 3,794,494 (Inoue), U.S. Pat. No. 4,177,074 (Proskow), U.S. Pat. No. 4,431,723 (Proskow), and U.S. Pat. No. 4,517,279 (Worns). Binders that are soluble, swellable or dispersible in organic solvent developers include natural or synthetic polymers of conjugated dienes, including polyisoprene, 1,2-polybutadiene, 1,4-polybutadiene, butadiene / acrylonitrile, butadiene / styrene thermoplastic elastomer block copolymers and other copolymers. Block copolymers discussed in U.S. Pat. No. 4,323,636 (Chen), U.S. Pat. No. 4,430,417 (Heinz) and U.S. Pat. No. 4,045,231 (Toda) can be used. The elastomeric binder is present in an amount of at least about 65% by weight of the photosensitive material. The term "binder" as used herein includes core-shell microgels and mixtures of microgels with preformed macromolecular polymers, such as those described in U.S. Pat. No. 4,956,252 (Fryd).

[0138] At least one polymerizable monomer can be configured to be compatible with the elastic adhesive to produce a clear, non-turbid UV-sensitive imageable layer. Polymerizable monomers for this purpose are well known in the art and include ethylenically unsaturated polymerizable compounds with relatively low molecular weights (generally less than 30,000 Daltons). Suitable monomers have relatively low molecular weights, less than about 5000 Da. Unless otherwise indicated, molecular weights throughout the specification are weight average molecular weights. Examples of suitable polymerizable monomers include various monoacrylates and acrylate derivatives of polyacrylates, isocyanates, esters, and epoxides. In addition, examples of suitable monomers include tert-butyl acrylate, lauryl acrylate, monoesters and polyesters of acrylates and methacrylates of alcohols and polyols (such as alkanols), 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, butanediol dimethacrylate, hexamethylene glycol diacrylate, and hexamethylene glycol dimethacrylate), trimethylolpropane, ethoxylated trimethylolpropane; pentaerythritol, such as pentaerythritol triacrylate, dipentaerythritol, and the like. Examples of other suitable monomers include acrylate and methacrylate derivatives of isocyanates, esters, epoxides, and the like, such as decanediol 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. Examples of other monomers can be found in U.S. Pat. No. 4,323,636 (Chen), U.S. Pat. No. 4,753,865 (Fryd), U.S. Pat. No. 4,726,877 (Fryd), and U.S. Pat. No. 4,894,315 (Feinberg). The monomer may comprise at least 5% to about 25% by weight of the photosensitive material, which may be based on the total dry weight of the photosensitive material.

[0139] The photoinitiator can be any single compound or combination of compounds that is sensitive to UV radiation, generates free radicals, and initiates polymerization of a monomer or monomers without premature termination. The photoinitiator can be sensitive to visible light or UV radiation. The photoinitiator can also be insensitive to IR and / or visible radiation and thermally inactive at temperatures of 185°C and below. Examples of suitable photoinitiators include substituted and unsubstituted polynuclear quinones. Examples of suitable systems have been disclosed in U.S. Pat. No. 4,460,675 (Gruetzmacher) and U.S. Pat. No. 4,894,315 (Feinberg). The photoinitiator is typically present in an amount of 0.001% to 10.0% by weight of the photosensitive material.

[0140] In some embodiments, the photosensitive layer may include: a diblock or triblock copolymer (e.g., an elastomer); at least one photopolymerizable monomer; a photopolymerization initiator; a plasticizer; additives (e.g., stabilizers, inhibitors, colorants, solvents); and a low surface energy monomer (e.g., silicone acrylate or silicone methacrylate).

[0141] In some embodiments, the plasticizer can be any plasticizer suitable for the purposes described herein known in the photosensitive layer field. Examples of suitable plasticizers include aliphatic hydrocarbon oils, such as naphthenic oils and paraffinic oils, liquid polydienes, such as liquid polybutadiene, liquid polyisoprene. Typically, plasticizers are liquids with a molecular weight less than about 5,000Da, but the molecular weight can be up to about 30,000Da. Low molecular weight plasticizers will include plasticizers with a molecular weight less than about 30,000Da.

[0142] In some embodiments, the additives may include rheology modifiers, thermal polymerization inhibitors, stabilizers, inhibitors, tackifiers, colorants, antioxidants, antiozonants, solvents, or fillers. These materials are commonly used in photosensitive layers, and examples are provided in the cited references.

[0143] The thickness of the photosensitive layer may vary depending on the type of printing plate desired. In one embodiment, the thickness of the photosensitive layer may be, for example, about 20-250 mils (500-6,400 microns) or greater, more specifically about 20-100 mils (500-2,500 microns).

[0144] 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, when exposed through a mask element and developed, provides a relief image in the flexographic printing plate. Such relief-forming precursors typically include a suitable substrate with a photosensitive material. Examples of commercially available flexographic printing plate precursors include, but are not limited to, FLEXCELNX flexographic plate elements provided by Miraclon Corporation, FLEXCELNX flexographic plate elements provided by DuPont (Wilmington, Del.), ... Flexographic version, NYLOFLEX°FAR 284 version provided by BASF (Germany), FLEXILIGHT CBU version provided by Macdermid (Denver, Co.), and ASAHIAFP XDI provided by Asahi Kasei (Japan).

[0145] In some embodiments, the relief-forming precursor can also be used to form a printed circuit board, wherein a conductive layer (also referred to as a "printed circuit") is formed on a substrate according to a pattern determined by exposure to a mask element. Precursors suitable for printed circuit boards typically include a substrate, a metal layer, and a UV-sensitive imageable layer (e.g., a photosensitive material). Suitable substrates include, but are not limited to, polyimide films, glass-fiber reinforced epoxy or phenolic resins, or any other insulating material known in the art. The metal layer covering the substrate is typically a conductive metal, such as copper or an alloy or metal. The UV-sensitive imageable layer may include a UV-curable resin, a polymerizable monomer or oligomer, a photoinitiator, and a polymer binder. More details of printed circuit boards are provided in US '987 (described above).

[0146] Forming a relief image

[0147] After forming the mask and relief-forming precursor as described above, the mask, when it includes a protective top coating (or an imaging layer when it does not include a protective top coating), is brought into full optical contact with the relief-forming precursor including a photosensitive layer sensitive to curing UV radiation. This approach can be achieved by placing the protective top coating or imaging layer of the mask on the relief-forming precursor, or vice versa, as described in more detail below. For example, contact and coupling of the top surface of the mask to the relief-forming precursor can be achieved by using laminating equipment and processes. The top surface of the mask can also be vacuum-adsorbed onto the relief-forming precursor with or without lamination to achieve the desired full optical contact.

[0148] By referring to Figures 1A to 1E The general description provided in this order may be understood in accordance with some embodiments of the present invention. When a mask precursor 110 is used, the ablation process may also ablate away portions of the barrier layer 120.

[0149] exist Figure 1C 1, mask element 136 includes imaging layer 115 overlying barrier layer 120, which in turn overlies ablated imaging layer 130 having a mask image formed therein and having ablated protective top coating 138. Mask element 136 is in intimate or complete optical contact with relief-forming precursor 155 to provide relief image-forming assembly 150 by contacting protective top coating 138. Relief-forming precursor 155 includes UV-sensitive layer 160, typically carried on substrate 165.

[0150] Figure 1DThe step of exposing relief image forming assembly 150 to UV radiation 170 indicated by arrows is shown. UV radiation 170 passes through the transparent polymer carrier sheet 115 in mask element 136, barrier layer 120, and exposed areas of imaging layer 130 (e.g., element 140 - the portion of the imaging layer that was removed) and subsequently the exposed portions of protective top coating 138, thereby causing photocuring in UV sensitive layer 160 of relief forming precursor 155.

[0151] After UV light exposure, the masking element 136 can be removed from the UV-sensitive layer 160 of the relief-forming precursor 155, and a development process can provide a relief image in the UV-sensitive layer 160 ( Figure 1E ). As shown, the relief image includes relief image peaks 175 and relief image valleys 180 in the UV sensitive layer 160.

[0152] In some embodiments, a method of forming a relief image is provided. The method may include providing a relief-forming assembly including a mask and a relief-forming precursor in full optical contact with the mask. The method may then include exposing a relief-forming layer of the relief-forming precursor to curing UV light radiation through the mask to form an imaged relief-forming layer, wherein UV-exposed regions are formed as polymerized regions in the imaged relief-forming layer, and unexposed regions are formed as non-polymerized regions. The method may then include removing the mask from the imaged relief-forming layer. The imaged relief-forming layer may be developed by removing the non-polymerized regions in the imaged relief-forming layer, thereby forming a relief image element having a relief image.

[0153] In some aspects, the mask used during exposure has an optical density of greater than 3.0 in the non-imaged areas and an optical density of less than about 0.20 in the fully ablated imaged areas. In some aspects, the exposure is less than about 24 J / cm 2 , less than or about 22 joules / cm 2 , less than or about 21 joules / cm 2 , less than or about 20 joules / cm 2 , less than or about 19 joules / cm 2 , less than or about 18 joules / cm 2 , or less than or about 17 J / cm 2 Next proceed.

[0154] In some embodiments, the exposure is performed using a mask without a DigiCap pattern and has an optical density of less than or about 0.18, less than or about 0.16, less than or about 0.12, or less than or about 0.11.

[0155] laminated

[0156] As described above, the mask element and the relief-forming precursor can be placed in full optical contact to provide an air-free interface at the common interface between the top surface of the mask and the UV-sensitive layer. Typically, this is achieved by applying appropriate pressure or heat, or both, to press the mask layer onto the UV-sensitive layer of the relief-forming precursor prior to UV exposure to form an air-free or gap-free interface. As described above, the mask element can then be vacuum-adsorbed onto the relief-forming precursor.

[0157] Commercially available laminators that provide both heat and uniform pressure may be used, including but not limited to: KODAK Model 800XL APPROVAL LAMINATOR from Eastman Kodak Company (Rochester, NY). CODOR LPP650 LAMINATOR from CODOR (Amsterdam, Holland) and LEDCO HD laminator from Filmsource (Casselbury, FL) may also be used.

[0158] In some embodiments, the optional protective topcoat may be removed prior to lamination or other operations that form full optical contact between the mask and relief-forming precursor.The relief image-forming assembly formed by coupling the mask and relief-forming precursor may be fed into a laminator at a desired speed, temperature, and pressure.

[0159] Useful laminating (laminator) apparatus and methods of using the same are described, for example, in U.S. Pat. No. 7,802,598 (Zwadlo et al.), the disclosure of which is incorporated herein by reference. As described therein, a prepress flexographic laminator can be used to laminate a masking element ("masking film") to a relief-forming precursor ("prepress flexographic printing plate") by applying a balanced, non-distorting, optimized lamination force to achieve full optical contact while minimizing lateral distortion.

[0160] In some embodiments, the relief-forming precursor has a separation layer, a spacing layer, or a release layer on the UV-sensitive relief-forming layer.

[0161] UV exposure

[0162] After achieving complete optical contact between the mask and the relief-forming precursor as described above, the relief-forming precursor can be exposed to curing UV radiation through the mask to form an imaged relief-forming precursor having exposed areas and unexposed areas in the UV-sensitive layer. The exposed areas are cured and solidified by polymerization of the monomers in the UV-sensitive layer. The unexposed areas remain uncured and the monomers are not polymerized. Therefore, uniformly emitted curing UV radiation is projected onto the relief-forming precursor through the mask image, which preferentially blocks part of the UV radiation through the remaining portion of the imaging layer. In the unmasked (exposed) area, the curing UV radiation will cause the hardening or curing of the UV-sensitive component in the imaging layer. Therefore, the mask image is substantially opaque to the exposure or curing UV radiation, which means that the transmitted optical density of the mask image in the unexposed area should be 2 or higher, and typically 3 or higher. The remaining portion of the imaging layer still includes UV-sensitive materials to absorb UV light and block it. The unmasked (exposed) areas of the UV-sensitive component can be substantially transparent, which means that they should have a transmitted optical density of 0.5 or less, 0.2 or less, or even 0.1 or less. The masked (unexposed areas) areas in the mask may have an optical density of at least about 3 and above. Transmission optical density can be measured on a densitometer (eg, a MACBETH TR 927 densitometer) using appropriate filters.

[0163] Typically, exposure of the relief-forming precursor through the mask element is achieved by flood exposure to a suitable source of UV radiation. The exposure can be carried out in the presence of atmospheric oxygen. Exposure under vacuum is not necessary, as full optical contact has been achieved.

[0164] In making a relief imaging element (e.g., a flexographic printing plate), one side of the relief-forming precursor is typically first exposed through its transparent substrate to curing UV radiation (referred to as "back exposure") to produce a thin, uniform cured layer (e.g., relief image valleys 80) on the substrate side of the UV-sensitive layer. The relief-forming precursor is then exposed to curing UV radiation through a mask containing a mask image, thereby causing the UV-sensitive material in the unmasked (exposed) areas to harden or cure. The unexposed and uncured areas of the UV-sensitive layer can then be removed by a development process (described below), leaving the cured or hardened areas (e.g., relief image peaks 75) that define a relief image printing surface having peaks 75 and valleys 80 of the shape and size of the predetermined desired pattern. The back exposure can be performed before or after full optical contact is established between the mask element and the relief-forming layer.

[0165] The wavelength or wavelength range suitable for curing UV radiation will be determined by the electromagnetic sensitivity of the relief-forming layer. In some embodiments, the UV curing radiation may have one or more wavelengths in the range of at least 150 nm and up to and including 450 nm, or more typically at least 300 nm and up to and including 450 nm. Sources of UV radiation for flood or bulk exposure include, but are not limited to, carbon arcs, mercury vapor arcs, fluorescent lamps, electronic flash devices, and photographic flood lamps. UV radiation from mercury vapor lamps and sun lamps is particularly useful. Representative UV radiation sources include SYLVANIA 350 BLACKLIGHT fluorescent lamps (FR 48T12 / 350VL / VHO / 180, 115 watts) with a central emission wavelength of about 354 nm supplied by Topbulb (East Chicago, Ind.), and BURGESS EXPOSURE FRAME with ADDALUX 754-18017 lamps supplied by Burgess Industries, Inc. (Plymouth, Mass.), Model 5K-3343V511.

[0166] Other suitable UV radiation sources include platemakers that can be used to expose relief-forming precursors to radiation and develop imaged relief-forming materials after radiation exposure. Examples of suitable platemakers include, but are not limited to, the KELLEIGH MODEL 310 platemaker provided by Kelleigh Corporation (Trenton, NJ) and the GPP500F platemaker provided by Global Asia Ltd. (Hong Kong).

[0167] The exposure time through the mask element will depend on the nature and thickness of the UV-sensitive layer of the relief-forming precursor and the source and intensity of the UV radiation. For example, in one embodiment, a FLEXCEL-SRH plate precursor provided by Eastman Kodak Company can be mounted on a KELLEIGH MODEL 310 platemaker and back-exposed to UV-A radiation through a transparent support for about 20 seconds to prepare a thin, uniform cured layer on the support side of the relief-forming precursor. The relief image-forming assembly of the mask element and the relief-forming precursor can then be exposed to UV radiation through the mask element for about 14 minutes. The mask image information is thus transferred to the relief-forming precursor (e.g., a flexographic plate precursor).

[0168] Separating the mask from the UV-sensitive layer

[0169] Typically, the methods described herein may also include removing the mask from full optical contact with the imaged relief-forming precursor after UV exposure and before development. This removal may be accomplished by separating the top surface of the mask from the relief image. This may be accomplished using any suitable means, such as peeling the two elements apart. For example, this may be accomplished by pulling the mask away from the imaged relief-forming precursor.

[0170] In some embodiments, after UV exposure, the mask can be removed from the relief-forming layer by peeling the top surface of the mask from the relief-forming layer. This can be achieved by providing support to one of the mask or the relief-forming precursor and then applying a pulling force to the edge or end of the other of the mask or the relief-forming precursor (e.g., the relief-forming layer).

[0171] In some embodiments, the mask can be delaminated from the relief-forming precursor, for example by delaminating a protective top coating from the relief-forming layer. In these embodiments, the mask is laminated to the relief-forming layer. Then, after UV curing, the mask is delaminated from the relief-forming layer. However, this delamination does not mean that the mask itself undergoes interlayer separation, so that different layers of the mask element are separated from each other. Here, the mask as a whole is delaminated from the relief-forming layer. Therefore, although the mask is delaminated from the relief-forming layer, the mask itself does not undergo interlayer separation and damage. Similarly, the relief-forming layer is not delaminated from the relief-forming precursor.

[0172] In some embodiments, the relief-forming precursor may include or omit a transparent release layer on the UV-sensitive layer. Thus, the UV-sensitive relief-forming layer may be in direct contact with the top surface of the mask, so that separation may directly separate the mask from the relief-forming layer.

[0173] In some embodiments, the relief-forming layer may allow for less force to be applied during stripping of the mask and imaging relief image precursor (e.g., flexographic printing plate precursor). The mask may be stripped more quickly and completely from the relief-forming precursor, leaving little or no residue. This effect allows for faster development of the imaged relief image precursor, as little or no residue would inhibit the development process. Since stripping is easier, very little handling and compaction pressure is required during handling of the flexographic imaging assembly, and the process can be easily performed at room temperature. Therefore, heating may not be required during curing.

[0174] The flexographic printing plate assembly with UV-sensitive layer includes a unique combination of materials so that the mask can be quickly and completely peeled off. "Completely" means that at least 95%, preferably at least 98%, at least 99% or 100% of the mask is peeled off, leaving little or no residue. The composition of the UV-sensitive layer provides a peel force of less than about 73 grams per inch, preferably less than about 60 grams per inch, and more preferably less than about 55 grams per inch) associated with the mask including the mask image.

[0175] In some embodiments, a mask containing a mask image is removed from a UV-exposed UV-sensitive relief-forming layer of a flexographic printing plate precursor by peeling at the interface between the mask and the relief-forming layer. This peeling process can be performed as described in U.S. Pat. No. 7,802,598 using vacuum for fixation. The mask element is then pulled away from the printing plate at a corner at a rate of 2 to 10 cm / sec at a peeling angle of 150-180°, thereby substantially pulling the imaging film back on itself, and maintaining continuous motion of the imaging film near the surface of the vacuum table until the entire mask element is removed from the UV-sensitive layer of the printing plate. In the practice of the present invention, at least 95% and preferably 100% by weight of the dry mask element is removed in this operation, so that it can be roughly said that the mask element has been "completely" or substantially completely removed from the exposed radiation-curable layer precursor. "Completely" means that at least 95%, preferably at least 98%, at least 99% or 100% of the mask is peeled off, leaving little or no residue.

[0176] development

[0177] After the mask is removed from the relief-forming layer, the imaged relief-forming precursor is then typically developed with a suitable developer (or processing solution or "washout") to form a relief image. Development serves to remove the unexposed (uncured) areas of the UV-sensitive layer, leaving behind the exposed (cured) areas that define the relief image, such as Figure 1E shown.

[0178] Development can be carried out under known conditions, such as at least 1 minute up to and including 20 minutes, at a temperature of at least 20° C. up to and including 32° C. The type of development equipment and the specific developer used will determine the specific development conditions, and these conditions can be adjusted by those skilled in the art.

[0179] In some cases, post-development treatment of the relief image in the imaging relief-forming precursor may be suitable. Typical post-development treatments include drying the relief image to remove any excess solvent, and post-curing by exposing the relief image to curing radiation to cause further hardening or cross-linking. The conditions of these processes are well known to those skilled in the art. For example, the relief image can be blotted or wiped dry, or dried in a forced air or infrared oven. Drying times and temperatures are apparent to those skilled in the art. Post-curing can be performed using the same type of UV radiation as previously used to expose the relief-forming precursor through the imaging mask material.

[0180] If the relief image surface is still tacky, detackification (or "light polishing") may be used, for example, by treatment with bromide or chloride solutions or exposure to UV or visible radiation, such treatments being well known to those skilled in the art.

[0181] The generated relief image may have a depth of at least 2% and up to and including 100% of the original thickness of the UV-sensitive layer (e.g., if the layer is disposed on a substrate). For flexographic printing plates, the maximum dry depth of the relief image may be at least 150 μm to up to and including 1,000 μm, or typically at least 200 μm to up to and including 500 μm. For printed circuit boards, the UV-sensitive layer may be completely removed in either the exposed or unexposed areas to reveal the underlying metal layer. In these elements, the maximum depth of the relief image depends on the dry thickness of the UV-sensitive layer. Advantageously, in any embodiment, the relief image may have shoulder angles greater than 50°.

[0182] Those skilled in the art can readily see a variety of uses for such inked elements in a variety of industries including flexographic printing of various packaging materials.

[0183] The imaging materials of the present invention for producing mask images can be used to prepare relief printing plates, such as flexographic printing plates and relief printing plates. The masks can also be used as photomasks. "A photomask is an opaque plate or film having holes or transparent areas that allow light to pass through in a predetermined pattern. They are commonly used in photolithography and particularly in the production of integrated circuits (ICs or "chips"). Example

[0184] The commercially available Kodak Flexcel NX TIL-R was imaged by a Kodak Flexcel NX Wide Imager using a test target at a drum speed of 95 RPM and a laser power setting of 25 W. This produced an optical density of 0.80 (15.84% transmittance) for the Flexcel NX DigiCap pattern. The optical density was measured by a transmission optical densitometer from X-Rite. When a "No DC NX" (No DigiCap) pattern was applied to the test target and imaged using the No DC Imager settings of the imager equipment, the OD or Dmin was shown to be 0.18 (66.07% transmittance).

[0185] The imaged TIL-R was then laminated to a 1.14mm Flexcel NXH photopolymer plate precursor using a Kodak Flexcel NX laminator. The laminated mask and photopolymer plate sandwich / assembly was then UV exposed through a mask using an “EVO 5” exposure unit with a total exposure of 27 J / cm 2 , to form an imaged relief forming material. The image-wise exposed photopolymer is then processed using flexographic plate processing equipment, dried and post-exposed using normal procedures to produce a finished flexographic printing plate ready for flexographic printing. This plate is capable of reproducing all highlights down to 0.8% at 150 lpi.

[0186] A flexographic printing plate was produced following the general procedure described above for Comparative Example 1. The following table shows the composition of the improved mask element.

[0187]

[0188]

[0189] PCA is a mixture of 70 wt% poly(methyl cyanoacrylate) and 30 wt% poly(ethyl cyanoacrylate).Alchemix, ATBC, and PEG-1000 plasticizers are described herein.

[0190] Nitrocellulose (NC) was Scholle's E150 and Alchemix's 5 / 6SS. Carbon black flakes were Sun Chemical's "Predisol C" Blk 7, containing carbon black pigment and nitrocellulose. Prior to use, the carbon black flakes were dispersed in a solvent. To obtain higher OD, it is preferred to use flakes or dispersions with a higher ratio of carbon black pigment to binder.

[0191] The IR dye is Dye A, which has the following structure:

[0192]

[0193] 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 about 1.5 microns. It is worth noting that in the embodiments, there is no crosslinking agent in the barrier layer or imaging layer, which can be applied to all embodiments of the mask elements described herein.

[0194] The Emax adhesive of the top layer is a 60:40 copolymer of ethyl methacrylate and methacrylic acid.

[0195] The following table provides the imaging conditions, UV exposure energy, plate quality, and other physical properties of the imageable films of Comparative Example 1 and Examples 1-6.

[0196]

[0197]

[0198] In addition, Dmin together with DC provides the relationship between transmission optical density (TOD) and drum speed. Figure 2 As shown, the TOD of C2 example is lower than that of C1 example, and both are lower than the TIL-R of Comparative Example 1. C2 and C1 refer to Example 2 and Example 1 in the table. (For the procedures and comments on DC imaging and OD, see

[0183] ).

[0199] Apply standard DigiCap NX(DC) patterns to Figure 2 Image file under the conditions shown. After imaging, UV exposure and plate processing and drying steps, the DC pattern is replicated on the relief printing plate surface. The DC pattern provides a higher and more uniform solid ink density (SID). See U.S. Patent No. 8,399,177.

[0200] Summarize

[0201] The data show that the improved mask can be used to speed up the UV processing of relief-forming plates or reduce energy usage. Therefore, faster processing or less energy usage is an economic improvement, which brings benefits to the improved mask. The improved mask provides faster UV exposure time for plate making. This will improve the overall production efficiency of plate making, because UV exposure time is a rate-limiting step in the multiple plate making required by most practitioners.

[0202] The present invention reduces manufacturing costs by using a simple design and using low cost raw materials and / or reducing high cost raw materials. The improved mask also improves the moisture / temperature sensitivity of the mask by reducing edge lift of the coating film compared to TIL-R. This will help reduce problems when loading the imaging film into the imaging equipment, as high edge lift can prevent the loading of the imaging film.

[0203] definition

[0204] As used herein, to define various components of barrier layers, non-silver halide thermally ablatable imaging layers, and other materials, layers and compositions (e.g., developers or processing solutions) used in the practice of the present invention, the singular forms "a," "an," and "the" are intended to include one or more of such components (i.e., include plural references) unless otherwise indicated.

[0205] Each term not expressly defined in this application should be understood to have a meaning generally accepted by those skilled in the art. If the construction of a term would make it meaningless or essentially meaningless in context, the term should be interpreted as having a standard dictionary meaning.

[0206] Unless expressly stated otherwise, the use of numerical values ​​within the various ranges specified herein is to be considered approximate, as if the minimum and maximum values ​​within the ranges were preceded by the word "about". In this manner, slight variations slightly above and below the ranges may contribute to achieving substantially the same results as the values ​​within the ranges. In addition, the disclosure of these ranges is intended as a continuous range, including every value between the minimum and maximum values ​​and the range endpoints.

[0207] Non-silver halide thermally ablatable imaging layers are also identified herein as imaging layers.

[0208] Unless otherwise indicated herein, the term "imageable material" is used to refer to embodiment articles prepared and used in accordance with the present invention. Such imageable materials may also be referred to as "mask films," "mask precursors," or "mask elements." Imageable materials may be converted by appropriate thermal (IR) imaging into "mask elements" that contain a mask image that can be used to form a relief image in accordance with the present invention.

[0209] Unless otherwise stated, percentages are by weight.

[0210] As used herein, the term "relief-forming precursor" refers to any imageable element or imageable material that can be exposed to light by a masking element to produce a relief image. Examples of such relief-forming precursors are described in detail below, but some relief-forming precursors include flexographic printing plate precursors, relief printing plate precursors, and printed circuit boards. Details of useful relief-forming materials are described in U.S. Patent Application Publication 2005 / 0227182 (described above), the disclosure of which is incorporated herein by reference. In this disclosure, relief-forming precursors are generally identified as "radiation-sensitive elements."

[0211] Unless otherwise specified, the term "ablative" or "ablation" refers to thermal imaging by laser, which results in rapid localized changes in an imaging layer of imageable material, resulting in the ejection of material from the imaging layer. This is in contrast to other material transfer or imaging techniques such as melting, evaporation or sublimation.

[0212] The terms "optical contact" and "complete optical contact" have the same meaning and refer to two layers or two elements (such as the case of a mask element and a relief-forming precursor) that share an interface and are in physical close contact such that there are substantially no air gaps or voids between the contacting surfaces, thereby providing an "air-free interface". More precisely, two surfaces are defined to be in optical contact when the reflection and transmission properties of their interface are substantially fully described by Fresnel's laws for the reflection and transmission of light at the refractive index boundary.

[0213] Unless otherwise specified, the term "transparent" as used herein refers to the ability of a material or layer to transmit at least 95% of impinging (or incident) electromagnetic radiation, such as electromagnetic radiation having a wavelength of at least 200nm to 750nm (i.e., UV and visible radiation commonly referred to in the art).

[0214] The "average dry thickness" for a given dry layer is typically the average of 10 different measurements taken on dry cross-sectional images of that layer.

[0215] Those skilled in the art will appreciate that for the processes and methods disclosed herein, the functions performed in the processes and methods may be implemented in different orders. In addition, the steps and operations outlined are provided only as examples, and certain steps and operations may be optional, may be combined into fewer steps and operations, or may be expanded into more steps and operations without departing from the essence of the disclosed embodiments.

[0216] The present disclosure is not intended to be limited to the specific embodiments described in this application, and these implementations are intended to serve as illustrations of various aspects. Without departing from its spirit and scope, many modifications and changes may be made, which will be apparent to those skilled in the art. In addition to those listed herein, within the scope of the present disclosure, functionally equivalent methods and devices will be apparent to those skilled in the art from the above description. These modifications and changes are intended to fall within the scope of the appended claims. The present disclosure is limited only by the terms of the appended claims and the full range of equivalents granted by these claims. It should be understood that the present disclosure is not limited to specific methods, reagents, compound compositions, or biological systems, which may of course vary. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not intended to be limiting.

[0217] Regarding the use of substantially any plural and / or singular terms herein, those skilled in the art may convert the plural to the singular and / or the singular to the plural according to the context and / or application. For the sake of clarity, various singular / plural permutations and combinations may be explicitly listed herein.

[0218] Those skilled in the art will understand that, in general, the terms used herein, and particularly in the appended claims (e.g., the bodies of the appended claims), are generally intended to be "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "comprising" should be interpreted as "including but not limited to," etc.). Those skilled in the art will further understand that if a specific numerical recitation introduced into a claim is intended, such intent will be explicitly recited in the claim, and in the absence of such recitation, no such intent is present. For example, to aid understanding, the appended claims may include the use of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that a claim recitation introduced by the indefinite article "a" or "an" limits any particular claim containing such introduced claim recitation to only embodiments containing only one such recitation, even if the same claim includes the introductory phrases "one or more" or "at least one" and an indefinite article, such as "a" or "an" (e.g., "a" and / or "an" should be construed to mean "at least one" or "one or more"); this is also true for claim recitations introduced using definite articles. Furthermore, even if a specific number of an introduced claim recitation is explicitly recited, one skilled in the art will recognize that such recitation should be construed to mean at least the number of recitations (e.g., the simple recitation of "two recitations" without other modifiers means at least two recitations, or two or more recitations). Furthermore, such constructions are generally used in those cases where the convention is similar to “at least one of A, B, and C, etc.”, and it is intended that those skilled in the art will understand the convention in the sense that such constructions are used (e.g., “a system having at least one of A, B, and C” will include, but is not limited to, those 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.). Such constructions are generally used in those cases where the convention is similar to “at least one of A, B, or C, etc.”, and it is intended that those skilled in the art will understand the convention in the sense that such constructions are used (e.g., “a system having at least one of A, B, or C” will include, but is not limited to, those 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.). Those skilled in the art will further understand that, in practice, any disjunctive word and / or phrase presenting two or more alternative terms, whether in the specification, claims, or drawings, should be understood to contemplate the possibility of including one of the terms, either of the two terms, or both of the terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

[0219] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subcombination of members of the Markush group.

[0220] As will be understood by those skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof. Any listed range can be easily identified as a full description, and the same range can be decomposed into at least equal halves, one-third, one-quarter, one-fifth, a few tenths, etc. As a non-limiting example, each range discussed herein can be easily decomposed into a lower third, a middle third, and an upper third. As will be understood by those skilled in the art, all languages, such as "up to", "at least", etc. include the numbers listed, and refer to the ranges that can be subsequently decomposed into sub-ranges as discussed above. Finally, as will be understood by those skilled in the art, the range includes each individual member. Therefore, for example, a group with 1-3 grids refers to a group with 1, 2, or 3 grids. Similarly, a group with 1-5 grids refers to a group with 1, 2, 3, 4, or 5 grids, etc.

[0221] From the foregoing, it will be understood that various embodiments of the present disclosure have been described herein for illustrative purposes, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Therefore, the various embodiments disclosed herein are not intended to be limiting, and the true scope and inventive concept are indicated by the appended claims.

[0222] All references cited herein are incorporated by specific reference in their entirety.

Claims

1. A mask element for flexographic printing, the mask comprising: A transparent polymer carrier sheet; a barrier layer on a transparent polymer carrier sheet, wherein the barrier layer comprises non-cross-linked nitrocellulose; as well as An imaging layer on the barrier layer, wherein the imaging layer comprises a non-silver halide thermally ablatable material comprising non-crosslinked nitrocellulose, carbon black, and an infrared dye.

2. The mask element of claim 1 further comprising a transparent overcoat layer on the imaging layer.

3. The mask element of claim 1, wherein the barrier layer is free of UV dye and optionally contains 0-10% of IR dye.

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

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

7. The mask element of claim 6 wherein the carbon black is pre-dispersed in the nitrocellulose of the imaging layer.

8. The mask element of claim 1 wherein the infrared dye in the imaging layer is present in an amount from about 0.1% to about 15%.

9. The mask element of claim 1 further comprising at least one plasticizer in the imaging layer.

10. The mask element of claim 9 wherein the at least one plasticizer in the imaging layer is present in an amount from about 10% to about 40%.

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

12. The mask element of claim 9 wherein the at least one plasticizer in the imaging layer is selected from acetyl tributyl citrate, a polyether, or a combination thereof.

13. A mask comprising: The mask element of claim 1, wherein the mask comprises: an imaging region in the imaging layer, wherein the imaging region has an optical aperture that is substantially free of carbon black and non-crosslinked nitrocellulose; and The non-imaging area in the imaging layer, wherein the non-imaging area has non-crosslinked nitrocellulose, carbon black and infrared dye.

14. The mask of claim 13, wherein the mask has an optical density of greater than or about 3.0 in non-imaging areas and an optical density of less than or about 0.20 in imaging areas.

15. A relief forming assembly comprising: The mask according to claim 13; as well as A relief-forming precursor is in full optical contact with the mask.

16. A method of manufacturing the mask element of claim 1, comprising: forming a transparent polymer carrier sheet; forming a barrier layer on a transparent polymer carrier sheet; as well as An imaging layer is formed on the barrier layer.

17. The method of claim 16, further comprising forming a transparent overcoat layer on the imaging layer.

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

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

20. A method of manufacturing the mask of claim 14, comprising: providing a mask element without any imaging areas in the imaging layer; as well as The mask element is imaged with infrared light to form imaged areas in the imaging layer.

21. The method of claim 20, wherein imaging of the mask element results in imaged areas of the mask having an optical density of less than about 0.

20.

22. The method of claim 20, wherein the imagewise ablating of carbon black, non-crosslinked nitrocellulose and other materials in the imaging layer forms an optical aperture for the UV light.

23. A method of forming a relief image, comprising: A relief-forming assembly is provided, the assembly comprising a mask and a relief-forming precursor in full optical contact with the mask, wherein the mask comprises: A transparent polymer carrier sheet; a barrier layer on a transparent polymer carrier sheet, wherein the barrier layer comprises non-cross-linked nitrocellulose; and an imaging layer on the barrier layer, wherein the imaging layer comprises a non-silver halide heat-ablatable material comprising non-cross-linked nitrocellulose, carbon black, and an infrared dye; an imaging region in the imaging layer, wherein the imaging region has an optical aperture that is substantially free of carbon black and non-crosslinked nitrocellulose; and a non-imaging region in the imaging layer, wherein the non-imaging region has non-cross-linked nitrocellulose, carbon black, and infrared dye; exposing the relief-forming layer of the relief-forming precursor to curing ultraviolet radiation through a mask to form an imaged relief-forming layer, wherein the ultraviolet-exposed areas are formed as polymerized areas and the unexposed areas are formed as non-polymerized areas in the imaged relief-forming layer; removing the mask from the imaged relief-forming layer; and The imaged relief-forming layer is developed by removing non-polymerized regions in the imaged relief-forming layer to form a relief image element having a relief image.

24. The method of claim 23, wherein the exposing is performed using a mask having an optical density greater than 3.0 in non-imaged areas and less than about 0.20 in imaged areas.

25. The method of claim 23, wherein the exposure is less than about 24 joules / cm 2 , less than or about 22 joules / cm 2 , less than or about 21 joules / cm 2, less than or about 20 joules / cm 2 , less than or about 19 joules / cm 2 , less than or about 18 joules / cm 2 , or less than or about 17 J / cm 2 conduct.

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