Relief-forming plate precursor

Abstract

Disclosed is a method comprising the steps of: imagewise exposing an imageable film, the imageable film comprising a carrier sheet and an imageable layer, laminating the imageable film to an imageable article, exposing the imageable article to curing radiation, thereby forming an imaged article; the imaged film is removed from the imaged article and the imaged article is developed to form a relief image. The method has a particular feature in that the imageable film comprises a carrier sheet, which is an untreated plastic film or sheet, and the imaging film can be reused several times.

Description

Technical Field

[0001] This invention relates to a method for preparing relief printing elements using a removable film. In particular, this invention relates to a mask-forming film suitable for preparing flexographic printing plates. Background Technology

[0002] A relief printing plate is a plate with an image area raised above the open area. Typically, this plate is slightly flexible, yet flexible enough to wrap around the printing cylinder and durable enough to print multiple copies. Flexography is commonly used for high-volume runs and for printing on a variety of substrates, such as paper, cardboard, corrugated board, film, foil, and laminates. Flexography is particularly interesting for printing on rough surfaces and stretched films.

[0003] Many methods for creating embossed images are known in the field of graphics. Photosensitive materials containing an ablationable layer or mask layer (so-called "integral mask" or "in-situ mask") on the surface of a photosensitive layer can be used to prepare embossed images without using photographic negatives or separate masking elements. Embossed images are formed by the following steps: first, the photosensitive material is image-wise exposed with laser radiation to selectively remove the layer in the exposed areas (i.e., forming the mask); then, it is globally exposed with photochemical radiation to cure the photosensitive layer in the unmasked areas. The remaining areas of the mask layer and the uncured portions of the photosensitive layer are then removed by one or more liquid development processes. Examples of flexographic materials with integrated masks are described, for example, in EP 3047336 and EP3304203.

[0004] The resulting surface, after development, has an embossed pattern that reproduces the image to be printed and typically includes solid areas and patterned areas containing multiple relief dots. After developing the embossed image, the embossed image printing element can be mounted on a printing press and printing can begin.

[0005] Flexographic printing plates with in-situ laser-ablable mask layers allow for direct, image-like exposure using a laser without the need for a separate masking device. However, they exhibit relatively low sensitivity to imaging radiation and often require imaging equipment equipped with a high-power laser. In practice, a sensitivity typically of at least approximately 1 J / cm² is required. 2 And typically about 3J / cm 2Used for laser ablation. Numerous attempts have been made in industry to overcome this problem by increasing the infrared sensitivity of the mask layer. However, achieving high sensitivity remains challenging due to the various quality standards that must be met simultaneously. Furthermore, because flexographic printing plates of varying thicknesses are required depending on the specific intended use, more than one imaging device may be needed for in-situ integrated mask methods.

[0006] Alternative methods include manufacturing articles with embossed images by first forming a mask image on a base material, such as by thermally imaging a suitable mask film or masking element to provide the desired pattern (typically using an infrared radiation laser under computer control), then transferring the mask image to a photosensitive material, and exposing the photosensitive material to curing radiation, typically ultraviolet radiation.

[0007] In the latter method, the mask can be formed by exposing a mask layer provided on a base material to laser radiation (typically infrared radiation). During imaging, the exposed areas are removed by, for example, laser ablation. Ablation of the mask layer can be performed using various lasers. Preferably, lasers emitting light in the near-IR wavelength range are used. These include, for example, IR laser diodes (830 nm), Nd-YAG solid-state lasers, or fiber lasers (1064 or 1100 nm, respectively). Effective absorption of the laser beam is crucial for effective ablation of the mask layer. Therefore, infrared absorbers (such as finely dispersed carbon black or IR-absorbing dyes) are typically used in the mask layer. The base material of the mask film is preferably transparent to UV light, such as a transparent polyester film. The imaged mask film is then placed on a photosensitive material (also known as a photosensitive relief forming precursor) for overall exposure with photochemical radiation (e.g., UV radiation) to solidify the photosensitive material in the unmasked areas, thereby forming a negative image of the mask element in the photosensitive relief forming precursor.

[0008] The mask film and photosensitive material are brought into close contact, for example, using a laminating machine or vacuum drawdown, or both, and subjected to overall exposure to photochemical radiation (e.g., UV radiation) to cure the photosensitive composition in the relief-forming precursor in the unmasked area.

[0009] To achieve optical contact bonding between the two, air and / or voids should be avoided between the mask film and the photosensitive material. Without optical contact bonding, the light used in the exposure step may be scattered due to the space and / or the remaining air, resulting in an embossed image that is not an accurate representation of the intended image on the mask.

[0010] Alternative methods for providing optical contact bonding between a mask film and a photosensitive material have been proposed in the art. For example, by using an imaging film adhered to the photosensitive material during a curing step, a vacuum suction step is eliminated. Furthermore, vacuum has been successfully substituted in the art by applying pressure or increasing temperature to laminate the mask film onto the photosensitive material.

[0011] The imaged mask and photosensitive material components are then imaged using UVA. The exposed areas of the photosensitive material harden or cure, becoming insoluble in the developer while remaining soluble in the unexposed areas. The cured portions define the printing area and remain on the printing plate. The mask elements can then be removed, and the remaining areas of the mask layer and the uncured portions of the photosensitive material are washed away by one or more liquid developing processes (e.g., aqueous or solvent treatment). After drying, the resulting imaged relief-forming precursor has an relief image that can be used for operations such as flexographic or letterpress printing.

[0012] EP 1146392 discloses a method for creating an embossed image by laminating an ablationable mask layer onto a UV-sensitive material using an adhesive layer to form an integral mask on the UV-sensitive material prior to the imaging / curing step.

[0013] EP 1735664 discloses a method comprising the steps of: forming a transferable mask on a carrier sheet including an imageable layer; and transferring a mask image to a photosensitive material sensitive to UV-curable radiation, such that the imageable material adheres more to the photosensitive material than to the carrier sheet.

[0014] EP 1883858 discloses a method for preparing an embossed image, the method comprising the steps of: laminating an imaging film onto a heated imageable article, the heated imageable article comprising a release layer disposed on a photosensitive material, and subsequently exposing the imageable article to curing radiation passing through the imaging film without vacuum suction. The imaging film subsequently removed from the imageable article is reusable.

[0015] EP 2987030 discloses an imageable material substantially composed of: a transparent polymer carrier sheet, a blocking layer containing a first infrared radiation absorbing compound ( wherein the carrier sheet and / or the blocking layer contains a first ultraviolet radiation absorbing compound), and a non-halide silver thermosensitive imageable layer containing a second infrared radiation absorbing compound and a second ultraviolet radiation absorbing compound.

[0016] EP 2153278 discloses a method for manufacturing an embossed image, the method comprising the steps of: laminating onto a thermal element; and a mask comprising a film containing an imageable layer on a transparent carrier sheet, the transparent carrier sheet including a transparent layer having a refractive index lower than that of the carrier sheet or lower than any optional layer between the carrier sheet and the transparent layer.

[0017] EP 3323017 discloses a laser ablation mask for exposing embossed printing plates, comprising (i) a dimensionally stable substrate sheet, (ii) a UV-transparent adhesive layer, and (iii) a laser ablation mask layer comprising cross-linked polyvinyl alcohol and materials that absorb UV / VIS light and IR light, such as carbon black.

[0018] EP 3752885 discloses an imageable material comprising: a transparent carrier sheet; a non-ablable photothermal conversion layer comprising an infrared absorber, a crosslinked adhesive and non-ablable particles; and a thermally ablable imaging layer comprising a second infrared absorber and a UV light absorber dispersed in a thermally ablable polymer adhesive.

[0019] Although valuable solutions have been provided in this field, there is still a need to further improve the quality of mask elements in an effective manner, and to improve the interlayer adhesion and tight contact between the mask elements and the relief forming precursor during imaging in the process of lamination. Invention Summary

[0020] The object of the present invention is to provide an improved imageable film characterized by both high IR sensitivity and high UV density; and a method for using the film to create embossed images.

[0021] These objectives are achieved by a method for manufacturing embossed printed elements as defined in independent claim 1, wherein preferred embodiments are defined in the dependent claims. The method of the invention comprises the following steps: a) Expos an image-capable film in an image-based manner, the image-capable film comprising: -Carrier sheet, and -Imagerable layer, This forms an imaging film that includes the mask image; b) Laminating the imaging film including the mask image onto an imageable article comprising a substrate and a photosensitive material; c) Expose an imageable article containing the imaging film including the mask image to curing radiation, thereby forming an imaging article; d) Remove the imaging film including the mask image from the imaging article; e) Develop the imaging article to form a relief image; Furthermore, a specific feature of the method is that the imageable film comprises a carrier sheet, which is an untreated plastic film or sheet, and that the imaging film can be reused multiple times. In practice, the mask image adheres more to the carrier sheet during lamination than to the imageable article, thereby not only avoiding undesirable adhesion failures that could lead to reduced sensitivity, but also removing the entire imaging film—i.e., the carrier sheet and the layers(s) thereon—before the development step. Therefore, the imaging film is reusable (i.e., the film can be reused to create embossed images), and the development of the imaged article to obtain embossed printed elements is significantly improved. These advantages are believed to be provided by the untreated carrier sheet.

[0022] Furthermore, when the carrier sheet, including the layers coated thereon, is no longer present on the embossed printing element during processing, the amount of accumulation, precipitation, or salting out of the treated components in the processing apparatus is reduced.

[0023] Other features, elements, steps, characteristics, and advantages of the invention will become more apparent from the following detailed description of preferred embodiments. Specific embodiments of the invention are also defined in the dependent claims.

[0024] Description of the implementation plan definition: The term "(imageable) film" as used herein refers to a "mask element," "mask (masking) film," or "masking element." During imaging, this film contains a "mask image" and may be referred to as a "mask," "imaging film," or "imaging masking film."

[0025] As used herein, the terms "embossing precursor" or "photosensitive material" refer to any imageable element or imageable material in which an embossed image can be produced by exposure through an imaging mask film. Examples of such embossing precursors include, for example, flexographic printing plate precursors, letterpress printing plate precursors, and printed circuit boards.

[0026] The term "embossed printing element" or "embossed printing plate" refers to an element that includes an embossed image, such as a flexographic printing plate, a letterpress printing plate, and a printed circuit board.

[0027] The term "ablation" refers to the imagerable layer of a film being imaged using thermal ablation techniques (such as laser radiation), which induce rapid localized changes within the imagerable layer, resulting in the ejection of one or more materials from the layer. This distinguishes it from other material transfer or imaging techniques where chemical changes (such as melting, evaporation, or sublimation) rather than physical changes are the primary imaging mechanism.

[0028] The term "hardening" refers to the coating becoming insoluble or non-dispersible in a developing solution, and can be achieved through polymerization and / or crosslinking of the photosensitive coating.

[0029] "Optical contact" refers to the close contact between two layers or two elements (such as an imaging masking film and a photosensitive material) such that there are essentially no air gaps or voids between the contact surfaces, thus providing an "airless interface".

[0030] The use of numerical values ​​within the various ranges specified herein is considered as approximations, as if the minimum and maximum values ​​within the range were preceded by the word "approximately". In this way, slight variations above and below the range can be used to achieve substantially the same result as values ​​within the range. Furthermore, these ranges are intended to be disclosed as continuous ranges, including every value between the minimum and maximum values, as well as the endpoints of the range.

[0031] Field preparation refers to the end user performing the entire process: i.e., image exposure, delamination, flood exposing, and development.

[0032] Unless otherwise stated, the term “transparent” as used herein means the ability of a material or layer to transmit at least 95% of incident electromagnetic radiation, such as electromagnetic radiation with wavelengths of at least 200 nm to, including, 750 nm (often referred to as UV and visible radiation, respectively).

[0033] According to the present invention, a method for on-site preparation of an embossed printing plate is provided. The method for manufacturing an embossed printing plate includes the following steps: (i) exposing an imageable film in an image manner to form a mask image; (ii) laminating the mask image onto an embossing precursor; (iii) exposing the precursor including the mask image to curing radiation; (iv) removing the mask image from the embossing precursor; and (iv) developing the embossing precursor to form an embossed printing plate. The specific steps of the method of the present invention and the components used in the method are described below.

[0034] Precursor to relief formation The embossing precursor typically contains a UV-sensitive layer on a dimensionally stable support. Preferably, the embossing precursor is a flexographic printing plate precursor, a letterpress printing plate precursor, or a printed circuit board. Most preferably, the embossing precursor is a flexographic printing plate precursor.

[0035] Suitable supports include dimensionally stable polymer films and aluminum sheets. Polyester films are particularly useful. Optionally, the support may be coated with additional layers, such as an adhesion-improving layer.

[0036] The support is typically about 20-200 micrometers thick. Optionally, the support may be pretreated to alter its wettability and / or adhesion behavior to subsequently applied coatings. Such surface treatments include corona discharge treatment, application of a subbing layer, a release layer, and / or an adhesive layer, such as an acrylic or vinyl acetate adhesive.

[0037] The embossing precursor can operate in either a positive or negative manner, but is typically negative, and preferably includes a photopolymerizable layer (a photocurable layer or embossed image forming layer). The photopolymerizable layer preferably comprises an elastomeric binder and a UV-curable composition that can be cured or hardened by primarily polymerization and / or crosslinking upon exposure to UV radiation. The UV-curable composition preferably comprises one or more polymerizable or photocurable monomers and at least one photoinitiator.

[0038] Suitable polymerizable monomers include olefinically unsaturated polymerizable compounds with relatively low molecular weights (typically less than 30,000 Daltons), such as polymerizable monomers including various monoacrylates and polyacrylates, acrylate derivatives of isocyanates, esters, and epoxides. Specific suitable monomers include, but are not limited to, tert-butyl acrylate, lauryl acrylate, monoacrylates and polyesters of acrylic acid and methacrylates of alcohols and polyols (e.g., 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, hexamethylenediol diacrylate and hexamethylenediol dimethacrylate, trimethylolpropane, ethoxylated trimethylolpropane, pentaerythritol, such as pentaerythritol triacrylate, dipentaerythritol, etc. Other examples of suitable monomers include acrylate and methacrylate derivatives of isocyanates, esters, epoxides, etc., such as decamethyl glycol diacrylate, 2,2-di(p-hydroxyphenyl)propane diacrylate, 2,2-di(p-hydroxyphenyl)propane dimethacrylate, polyoxyethyl-2,2-di(p-hydroxyphenyl)propane dimethacrylate, and 1-phenylethylidene-1,2-dimethacrylate. The typical amount of one or more polymerizable monomers in the UV-sensitive layer is at least 5% by weight and at most, including, 25% by weight, based on the total dry weight of the UV-sensitive layer.

[0039] Photoinitiators can be single compounds or combinations of compounds that are sensitive to UV radiation and generate free radicals, which initiate the polymerization of (one or more) polymerizable monomers without excessive termination. They are preferably present in an amount of about 0.001% by weight and at most, including 10% by weight, based on the total dry weight of the UV-sensitive layer. Examples of suitable photoinitiators include, but are not limited to, optionally substituted polynuclear quinones, vicinal ketaldonyl alcohols, α-hydrocarbon-substituted aromatic azoins, phenazines, oxazines, and quinone dyes and cyclohexadienone compounds.

[0040] The elastomeric adhesive preferably comprises a polymer or resin that is preferably soluble, swellable, or dispersible in aqueous, semi-aqueous, or organic solvent developers. Suitable examples include, but are not limited to, natural or synthetic polymers of conjugated diene hydrocarbons, including polyisoprene, 1,2-polybutadiene, 1,4-polybutadiene, butadiene / acrylonitrile, block copolymers such as butadiene / styrene thermoplastic elastomer block copolymers, core-shell microgels, and blends of microgels and pre-formed macromolecular polymers. The elastomeric adhesive may constitute at least 65% by weight and at most, including 90% by weight, of the total UV-sensitive layer.

[0041] The UV-sensitive layer may include other compounds providing a variety of properties, including but not limited to sensitizers, plasticizers, rheology modifiers, thermal polymerization inhibitors, tackifiers, colorants, antioxidants, anti-ozone agents, and fillers; the amounts of which are known in the art. Examples of suitable plasticizers include aliphatic hydrocarbon oils, such as naphthenic and paraffinic oils, and liquid polydienes, such as liquid polybutadiene and liquid polyisoprene. Typically, plasticizers are liquids having a molecular weight of less than about 5,000 Daltons, but can have molecular weights up to about 30,000 Daltons.

[0042] The thickness of the UV-sensitive layer is preferably at least 500 μm and at most, including, an average dry thickness of 6400 μm.

[0043] The embossing precursor can be protected from mechanical damage by, for example, a removable protective or cover sheet located on the top layer. The cover sheet should be removed before placing the mask image near the embossing precursor. Available cover sheets include flexible polymer films such as polystyrene, polyethylene, polypropylene, polycarbonate, fluoropolymers, polyamides, or polyesters. Polyesters, particularly polyethylene terephthalate (PET), are preferred.

[0044] membrane In the method of this invention, a film is used to form a mask image. The film comprises at least one imageable layer and a carrier sheet. Optionally, the film may further comprise one or more additional layers, such as a barrier layer.

[0045] Carrier sheet The carrier sheet for the membrane can be any suitable substrate. Suitable substrates include, for example, plastic sheets and films, such as polyethylene terephthalate or polyethylene naphthalate, fluorene polyester polymers, polyethylene, polypropylene, polybutadiene, polyacrylate, polycarbonate, polyvinyl chloride and its copolymers, as well as hydrolyzed and unhydrolyzed cellulose acetate. The carrier sheet should preferably be sufficiently transparent to imaging radiation, and is preferably a transparent polymer film. A preferred carrier sheet is a polyethylene terephthalate sheet, and is about 20 μm to about 200 μm thick.

[0046] The carrier sheet used in this invention is an untreated or unsubbed plastic film or sheet, that is, a plastic film or sheet that has not been treated with any (transparent) coating layer, such as an adhesion promoter layer, release layer, subbing layer, scratch-resistant (hard coating) layer, or hardened gelatin layer. Films are typically measured to be less than 0.25 mm in thickness, while sheets are typically more than 0.25 mm in thickness.

[0047] Imageable layer The imageable layer is preferably provided as a continuous, uniform coating on the carrier sheet. Preferably, one imageable layer is present on the carrier sheet, but optionally more than one imageable layer may be present on the carrier sheet. Optionally, other opaque layers, such as a barrier layer, may be present between the carrier sheet and the imageable layer. The barrier layer may include, for example, metal oxide particles, such as iron oxide particles.

[0048] The components of one or more imageable layers are preferably soluble or swellable in a suitable developer (which includes both chlorinated and non-chlorinated organic solvents), as described below.

[0049] The imageable layer may optionally comprise a polysiloxane compound. The polysiloxane compound preferably comprises siloxane units, which may be linear, branched, cyclic, or complex crosslinked polymers or copolymers. The term polysiloxane compound includes any compound containing more than one siloxane group -Si(R,R')-O-, wherein R and R' are optionally substituted alkyl or aryl groups. Preferred siloxanes are phenylalkylsiloxanes and dialkylsiloxanes, such as phenylmethylsiloxane and dimethylsiloxane. The number of siloxane groups -Si(R,R')-O- in the (co)polymer is at least 2, preferably at least 10, more preferably at least 20. It may be less than 100, preferably less than 60. The optional polysiloxane compound further preferably comprises an alkylene oxide block, said alkylene oxide block preferably comprising the formula -CnH 2n -O- units, where n is preferably an integer in the range of 2 to 5. -CnH 2n - The portion may include straight-chain or branched chains. The alkylene oxide block portion may also contain optional substituents. Suitable optional polysiloxane compounds are preferably random or block copolymers comprising siloxane and alkylene oxide groups, suitably comprising about 15 to 25 siloxane units and 50 to 70 alkylene oxide groups. Preferred optional polysiloxanes include copolymers of dimethyldichlorosilane, ethylene oxide, and propylene oxide. Specific examples of these optional compounds are as follows: Formula I Formula II Where o, p, q, r, and s are integers greater than 1.

[0050] In Formula I, a poly(alkylene oxide) block composed of ethylene oxide and propylene oxide units is grafted onto a polysiloxane block. In Formula II, a long-chain alcohol composed of ethylene oxide and propylene oxide units is grafted onto a trisiloxane group.

[0051] The polysiloxane compound may optionally be present in the imageable layer in an amount of 0.01 to 1.5% by weight, more preferably 0.04 to 1.0% by weight, and most preferably 0.1% to 0.5% by weight.

[0052] The imageable layer is preferably a laser-ablable layer and preferably comprises a thermally combustible polymer binder and an IR light-absorbing compound to make the imageable layer(s) sensitive to imaging IR radiation. The thermally combustible polymer binder may optionally be present in other optional layers. This thermally combustible polymer binder can be thermally decomposed, depolymerized, or evaporated by the IR light-absorbing compound during laser exposure without a prior melting step. Adhesives that are readily thermally combustible and produce gases and volatile debris at temperatures below about 200°C are preferred. The thermally combustible polymer binder preferably contains nitro groups or nitrate groups. In particular, nitrates of cellulose or cellulose derivatives, such as cellulose ethers, methylcellulose, ethylcellulose, nitrocellulose, 2-hydroxyethylcellulose, 2-hydroxypropylcellulose, carboxymethylcellulose, cellulose ethers, polycarbonate, polyurethane, polyester, polyorthoester, polyacetal, and copolymers thereof, are preferred binders. Other examples of heat-flammable adhesives include poly(glycidyl azide), poly(glycidyl nitrate) or poly(vinyl nitrate), nitro derivatives of polystyrene, such as polymers containing nitro-, dinitro- or trinitro-styrene groups; polyacrylates or polymethacrylates, such as polymers containing 2,4-dinitrophenyl acrylate or p-nitrophenyl acrylate as monomers; and / or combinations thereof.

[0053] Typically, the total amount of thermally combustible polymer binder in the imageable layer is about 5-80% by weight, preferably 8-60% by weight, and more preferably 10-40% by weight.

[0054] Preferred IR light-absorbing compounds convert infrared radiation (e.g., in the 750-1500 nm range) into heat. The generation of heat in the imageable layer(s) can then lead to physical or chemical changes in other components of the imageable layer, most preferably causing ablation. Preferred IR light-absorbing compounds include IR light-absorbing dyes, such as phthalocyanine dyes, cyanine dyes, terpinen dyes, and polyacetylenic dyes and / or their derivatives; metals, such as aluminum; or inorganic pigments, such as carbon black, graphite, iron oxide, or chromium oxide. In addition to IR light, carbon black (e.g., fine-grained carbon black with an average particle size of less than 30 nm) also makes the ablationable layer opaque to UV radiation.

[0055] The IR light-absorbing compound is preferably sensitive to radiation in the range of about 700 nm to 1500 nm, more preferably in the range of about 750 nm to 1200 nm. A mixture of IR light-absorbing dyes that can absorb at different wavelengths (e.g., about 830 nm and about 1064 nm) can be used. The IR light-absorbing compound is preferably present in an amount of about 1 to 30% by weight, more preferably 10 to 26% by weight, and most preferably 15 to 25% by weight, based on the dry content of the imageable layer. Alternatively, the infrared light-absorbing compound is present in an amount of less than 28% by weight, more preferably less than 26% by weight, and most preferably less than 25% by weight, based on the dry content of the imageable layer.

[0056] One or more imageable layers preferably comprise one or more UV absorbers capable of strongly absorbing and / or blocking curing radiation, for example, by reflection. The UV absorber essentially prevents curing radiation from transmitting through the mask image. Suitable examples of UV absorbers for the one or more imageable layers include mixtures of dyes and / or pigments dispersed within one or more polymer binders, with or without the aid of a dispersant. Pigments may be preferred because they do not tend to migrate. The use of pigment dispersions in imaging is well known in the art, and any conventional pigments suitable for this purpose may be used in the present invention. Particularly preferred are pigments or dyes that are non-IR absorbers, so that the imaging of the imageable film is not adversely affected.

[0057] UV absorbers preferably absorb radiation from about 150 to 400 nm. UV absorbers may also absorb visible light radiation, for example, from 350 to 750 nm.

[0058] One or more UV absorbers may be present in the imageable layer in an amount of about 10 to 50% by weight based on the dry content of the imageable layer, and preferably in an amount of about 10 to 40% by weight.

[0059] Suitable examples of UV absorbers include black dyes and / or pigments, such as carbon black, metallic particles, and metal oxides. It may be desirable to use carbon black with small particles for maximum color intensity. Fine-grained carbon black brands with an average particle size of less than 30 nm are particularly suitable. Carbon black can constitute, for example, about 10-50% by weight, more particularly about 10-40% by weight, and even more particularly about 10-30% by weight of the total weight of the imageable layer.

[0060] Specific preferred UV absorbers include benzotriazoles, halogenated benzotriazoles, high molecular weight benzotriazoles, triazines, curcumin, benzophenone, benzoate esters, titanium dioxide or zinc oxide, camphor, avobenzone, imidazoles, p-aminobenzoic acid, salicylates, substituted acrylonitriles, cyanoacrylates, benzyl malonates, oxaloaniline, and UV absorbers commercially available from ADEKA, such as ADK STABLA-24, LA-29, LA-31R(G), LA-32, LA 36(RG), LA-46, 1413, and mixtures thereof.

[0061] One or more imageable layers preferably comprise at least one polymeric binder or resin. Binding agents or resins having hydroxyl groups (e.g., poly(vinyl alcohol) and cellulose polymers, non-crosslinkable polyesters, polyamides, polyurethanes, polyolefins, polystyrene, polyethers, polyvinyl ethers, polyvinyl esters and polyacrylates and poly(meth)acrylates, terpene resins, phenolic resins, aromatic hydrocarbon resins, polyurethanes, long-chain acrylates and methacrylates, adhesive binders such as poly(vinyl butyral) and phenolic resins) are available. Preferably, these polymeric binders are soluble in suitable coating solvents, such as lower alcohols, ketones, ethers, hydrocarbons and haloalkanes, and are also preferably soluble or swellable in developer solutions.

[0062] Adhesive binders (such as thermoplastic adhesives with a glass transition temperature (Tg) of less than about 65°C, such as acetyl polymers and acrylamide polymers or pressure-sensitive adhesives) are of particular interest.

[0063] (One or more) polymeric adhesives are preferably present in an amount of 25 to 75% by weight, and more preferably 35 to 65% by weight, based on the total dry weight of the imageable layer.

[0064] Optional other components of the imageable layer (one or more) include, but are not limited to, plasticizers, coating aids, surfactants, adhesion promoters, colorants, dispersants such as polyester / polyamine copolymers, alkyl aryl polyether alcohols and acrylic adhesives, contrast agents, wetting agents and fillers. These components are preferably dispersed in one or more polymeric adhesives capable of dissolving or dispersing the components in the imageable layer.

[0065] Optional other layers The imageable layer may optionally include other layers, such as a protective layer on top of the imageable layer, i.e., a thin, UV-transparent layer that restricts oxygen diffusion, such as polyvinyl alcohol or polyamide; a non-transparent barrier layer disposed between the carrier sheet and the imageable layer; and a cover sheet comprising methacrylic acid copolymers (e.g., copolymers of ethyl methacrylate and methacrylic acid) and particles (e.g., particles of a fluoropolymer dispersed therein, which provide abrasion resistance due to the presence of, for example, the particles). An overcoat layer may also serve as a dye-blocking layer to prevent dye migration from the masking film to the photopolymer after lamination. These optional layers preferably do not significantly absorb or scatter curing radiation; for example, they preferably do not include matting agents or other light-scattering materials. The overcoat layer may be relatively thin and preferably has a dry thickness of about 0.05 to 1 μm.

[0066] Exposure in image mode The film described above is preferably irradiated in an image-like manner. Preferred devices for image-like exposure are Nd / YAG lasers (1064 nm) or diode lasers (e.g., 830 nm). After exposure to radiation and removal of the exposed portion of the imageable layer, the remaining imageable layer is referred to as the mask image.

[0067] The heat generated in the imageable layer can then cause physical or chemical changes in the components of the imageable layer, or most preferably, ablation. In the ablation mode of imaging, energy provided by a laser expels the imageable layer at the location where the laser beam strikes the film. A debris collector (e.g., a vacuum or a suitable receiver sheet) can be placed near the imageable layer to retrieve the exposed imageable layer after it has been propeled from the carrier sheet.

[0068] Preferably, the exposed area of ​​the imageable layer is removed by ablation. The imageable layer, comprising the combustible adhesive as described above, can be expelled from the carrier sheet by generating gas. The accumulation of gas below or within the exposed area of ​​the imageable layer generates pressure that expels the imageable layer from the carrier sheet in the exposed area. This action distinguishes it from other mass transfer techniques because chemical changes (e.g., bond breaking) rather than physical changes (e.g., melting, evaporation, or sublimation) result in the near-complete transfer of the imageable layer.

[0069] Lamination According to the method of the present invention, after image exposure, the exposed film (mask element) is laminated onto a UV-sensitive layer or protective layer of a suitable embossing precursor as discussed above to produce a UV-sensitive material providing an integrated masking layer. Preferably, a lamination apparatus is used to ensure complete optical contact between the exposed film and the suitable embossing precursor. The UV-sensitive layer of the embossing precursor may be adhesive, or, due to the presence of specific monomers, may be pressure-sensitive adhesive.

[0070] Preferably, the mask element and the relief forming precursor are placed in full optical contact to provide an airless interface at the shared interface. This is typically achieved in the art by laminating the mask element to the UV-sensitive layer of the relief forming precursor, which is achieved by applying appropriate pressure or heat, or both, prior to UV exposure to form an airless or gapless interface. Optionally, an anti-adhesion layer (or a release or spacer layer) may be used.

[0071] Preferably, the optional cover sheet is removed before lamination. The mask element and the embossing image forming assembly of the embossing precursor can be fed into the laminator at the desired speed, temperature, and pressure. In the art, a vacuum stage is often used to apply balanced, non-distorting, optimized lamination forces to the embossing precursor and the masking film to achieve optical contact while minimizing lateral deformation.

[0072] Available laminating (laminating) apparatuses and methods for using them are known in the art.

[0073] UV Exposure Subsequently, the relief-forming precursor is subjected to full UV light flood exposure through a mask using a suitable UV radiation source. This causes the areas of the UV-sensitive layer not covered by the mask (i.e., the imageable layer) to become insoluble in the developer (for negative working UV-sensitive materials) or soluble in the developer (for positive working UV-sensitive materials), for example, through photopolymerization or photocrosslinking. The mask image information is thus transferred to the relief-forming precursor.

[0074] Exposure can be performed in the presence of atmospheric oxygen because the relief-forming precursor and the mask are preferably in complete optical contact.

[0075] In the fabrication of the relief-forming precursor, one side of the precursor is preferably exposed to curing UV radiation through its transparent substrate (referred to as "back exposure") to prepare a thin, uniformly cured layer material (i.e., floor) on the substrate side of the UV-sensitive layer. This floor provides improved adhesion between the photopolymerizable layer and the support, contributing to increased resolution and determination of the plate relief depth. Back exposure can be performed before, during, or after the imaging step. Preferably, back exposure is performed before the UV exposure step discussed above.

[0076] The mask image is substantially opaque to UV radiation exposure or curing, meaning that the mask image should preferably have a transmitted light density of 2 or greater, and typically 3 or greater. Unmasked areas should be substantially transparent, meaning they should preferably have a UV transmitted light density of 0.5 or less, or even 0.2 or less. Transmitted light density can be measured using a suitable filter on a densitometer.

[0077] In a preferred negative working embodiment, the unexposed and therefore uncured areas of the UV-sensitive layer can then be removed by a development process (described below), leaving cured or hardened areas that define the relief image, which includes the shape and size of a predetermined pattern, including peaks and valleys.

[0078] The suitable wavelength or wavelength range for curing UV radiation is related to the electromagnetic susceptibility of the embossing precursor. Preferably, the UV curing radiation may have one or more wavelengths in the range of at least 150 nm and at most and including 450 nm, or more typically at least 300 nm and at most and including 450 nm.

[0079] Suitable sources of UV radiation for floodwise or overall exposure include, but are not limited to, carbon arcs, mercury vapor arcs, fluorescent lamps, electron flash units, and photographic flood lamps. UV radiation from mercury vapor lamps and fluorescent lamps is particularly useful.

[0080] The exposure time through the mask element will depend on the nature and thickness of the UV-sensitive layer of the embossing precursor, as well as the source and intensity of the UV radiation. For example, it may take several seconds to several minutes to prepare a thin, uniformly cured layer on the support side of the embossing precursor. The mask element and the embossing image forming assembly of the embossing precursor can then be exposed to UV radiation through the mask element, for example, for about 10 to 20 minutes.

[0081] Delamination After the exposure step and before development (see below), it is preferable to delaminate the components of the imaged relief forming precursor and the mask. This can be done in various ways, such as manually peeling the two elements apart by pulling the carrier sheet including the mask from the imaged relief forming precursor and / or in an automated manner. The entire imaging film—i.e., the carrier sheet and the layers(s) provided thereon—is removed and can be reused.

[0082] development The embossing precursor is then preferably developed with a suitable developer (or treatment solution or rinsing solution) to form an embossed image. During development, in a preferred negative working embodiment, the unexposed (uncured) areas of the UV-sensitive layer are preferably removed, leaving the exposed (cured) areas that define the embossed image.

[0083] As a developer, aqueous liquids, organic solvents, and / or solvent mixtures can be used; most preferably, aqueous developers are used. Any known solvent-based or water-based developer can be used, including non-chlorinated and / or chlorinated developers. For example, developers containing organic solvents, such mixtures of aliphatic hydrocarbons and long-chain alcohols (e.g., alcohols having at least 7 carbon atoms), perchloroethylene solvents, diethylene glycol dialkyl ethers, acetates or alcohols, carboxylic acid esters and alkoxy-substituted carboxylic acid esters, diisopropylbenzene (DIPB), methyl esters, dipropylene glycol dimethyl ether (DME), aliphatic dibasic acid ethers, alkali metal salts of (un)saturated fatty acids having 12 to 18 carbon atoms and comprising monounsaturated or polyunsaturated fatty acids or their alkali metal salts, aminopolycarboxylic acids or their alkali metal salts, and / or combinations thereof.

[0084] Development can be performed under known conditions, such as at least 1 minute and up to 20 minutes, and at a temperature of up to 50°C. The specific development conditions will be determined by the developing apparatus used and the type of particular developer, and can be adjusted by those skilled in the art.

[0085] Post-development processing After development, the resulting embossed image can be dried to remove any excess solvent. For example, the embossed image can be blotted or wiped dry, or dried in a forced air or infrared oven, for example, at 45°C-65°C for 1-4 hours for solvent-developed plates, and for example, for 10 minutes for water-developed plates. The optimal drying time and temperature can be defined by those skilled in the art.

[0086] The imaged relief-forming precursor can be post-cured by exposing the relief image to curing radiation to induce further hardening or cross-linking. Post-curing can be performed using the same type of UV radiation (previously used to expose the relief-forming precursor through an imaging mask material) or, for example, exposure to radiation with a wavelength not exceeding 300 nm.

[0087] If the surface of the embossed image is adhesive, detackification, also known as light finishing, can be used. This process, for example, by treatment with a bromide or chlorine solution or exposure to UV or visible light radiation, is well known to those skilled in the art.

[0088] The resulting relief image may have a maximum drying depth of at least 150 μm and up to and including 1000 μm, or typically at least 200 μm and up to and including 500 μm.

[0089] The embossed image obtained according to the invention can be suitably "inked" with any desirable composition, and can then be printed onto a suitable substrate or receiving material. The obtained embossed image, such as a flexographic printing plate, can be suitably used for flexographic printing on various packaging materials, for example. Example

[0090] 1. Components Carrier sheet A: Poly(ethylene terephthalate), 175μm thick, untreated; Carrier sheet B: Silphan S 100M, a 100μm thick siliconized polyethylene terephthalate, commercially available from Siliconature Spa (Italy); Carrier sheet C: A transparent layer containing the formulation of Mowiol 4-88 was coated from water onto carrier sheet A using a wire rod; after drying at 110°C for 2 minutes, a dry coverage of 500 mg / m² was obtained. 2 The transparent layer; IR Dye A: An IR absorbing dye commercially available from FEW Chemicals and having the following structure. Curcumin: a yellow dye, commercially available from Matrix Fine Chemicals; Ethyl Violet: A dye commercially available from Glenham (GLS); Neorez R650; polyurethane resin, commercially available from Covestro; DISP A: A 50 / 50 pigment dispersion of Hostaperm Blue P-BFS™ purchased from Clariant and Disperbyk 182 purchased from BYK Chemie GmbH; Dynoadd F-100: Wetting agent, available commercially from Dynea; Mowiol 4-88: Partially hydrolyzed polyvinyl alcohol, commercially available from Kuraray; MEK: Methyl ethyl ketone, which can be obtained from, for example, Sigma-Aldrich; Dowanol PM: 1-Methoxy-2-propanol, available from sources such as Sigma-Aldrich.

[0091] 2. Fabrication of imageable thin films Invention embodiments: Inv-01 and Inv-02 On carrier sheet A, an imageable layer comprising the components shown in Table 1 below is coated using a wire-wound coating bar. The resulting coating is dried at room temperature to form an imageable layer with a coating coverage of 1.5 g / m².

[0092] Table 1: Membranes Inv-01 and Inv-02 of the present invention, including untreated carrier sheet A.

[0093] Comparative Examples Comp-01 and Comp-02 Imageable layers comprising the components shown in Table 2 were coated onto carrier sheets B and C using a wire-wound coating bar. The resulting coatings were dried at room temperature to form imageable layers with a coating coverage of 1.5 g / m².

[0094] Table 2: Comparison of films Comp-01 and Comp-02 including treated carrier sheets B or C

[0095] 3. result 3.1 Evaluation of the adhesion of the imageable coating of the film to the flexographic printing plate precursor The obtained films Inv-01, Inv-02, Comp-01, and Comp-02 are laminated onto a simulated flexographic printing plate available from Toyobo without a release layer.

[0096] Subsequently, the film was manually delaminated within the time range shown in Table 3. The delaminated film and flexographic printing plate were visually inspected. The results are summarized in Table 3 below.

[0097] Table 3: Results of Adhesion Test *Adhesion level of the imageable coating of the film to the flexographic printing plate precursor after delamination: 0: No adhesion 1: Basically non-adhesive 2: Slight adhesion 3: Some may occasionally adhere. 4: Excessive adhesion 5: Overall adhesion.

[0098] 3.2 Imaging of the delaminated film and the corresponding flexographic printing plate precursor The obtained delaminated film was imaged on a CtP (PlateRite FX1200N, commercially available from Screen) and compared with a reference film (i.e., the unlaminated film). Additionally, the corresponding flexographic printing plate precursor was imaged after delamination. The results of the imaging tests are summarized in Table 4 below.

[0099] Table 4: Results of Imaging Tests *Evaluation of imaging results: 1: The image is visible after imaging; 0: The image is not visible after imaging.

[0100] The results in Table 4 show: - The imageable film is imageable and therefore reusable after delamination; and - The flexographic printing plate precursor is not image-enabled, and therefore no image-enabled coating is transferred (adhered) to the flexographic printing plate precursor.

Claims

1. A method for making a relief image comprising the steps of: a) imagewise exposing an imageable film, said imageable film comprising - a carrier sheet, and - an imageable layer, thereby forming an imaged film comprising a mask image; b) laminating said imaged film comprising a mask image to an imageable article comprising a substrate and a photosensitive material; c) exposing the imageable article comprising said imaged film comprising a mask image to curing radiation, thereby forming an imaged article; d) removing said imaged film comprising a mask image from said imaged article; e) developing said imaged article to form a relief image; characterized in that the carrier sheet is an untreated plastic film or sheet and the mask image adheres more to the carrier sheet than to the imageable article upon lamination.

2. The method according to claim 1, wherein the carrier sheet is an untreated polyethylene terephthalate, polyethylene naphthalate, fluorene polyester polymer, polyethylene, polypropylene, polybutadiene, polyacrylate, polycarbonate, polyvinyl chloride and copolymers thereof, and hydrolyzed and unhydrolyzed cellulose acetate.

3. The method according to any one of the preceding claims, wherein the imageable article consists of a substrate and a photosensitive material.

4. The method according to any one of the preceding claims, wherein the removed imaged film is reusable.

5. The method according to any one of the preceding claims, wherein the imageable layer is contiguous with the carrier sheet.

6. The method according to any one of the preceding claims, wherein the photosensitive material is not provided with a release layer.

7. The method according to any one of the preceding claims, wherein the imageable layer is an ablatable layer comprising an IR absorbing compound, a UV absorbing compound and a thermally combustible binder.

8. The method according to claim 7, wherein the thermally combustible binder is present in an amount of 10-40 wt% based on the total amount of ingredients in the imageable layer.

9. The method according to claim 7 or 8, wherein the IR light absorbing compound is a light absorbing dye selected from phthalocyanine dyes, cyanine dyes, merocyanine dyes and polymethine dyes and / or derivatives thereof.

10. The method according to claims 7 to 9, wherein the imageable layer comprises IR absorbing compound in a range between 1 wt% to 30 wt% based on the dry content of the imageable layer.

11. The method according to any one of the preceding claims, wherein the imageable film further comprises a layer comprising PVOH as the outermost layer.

12. The method according to any one of the preceding claims, wherein the imageable film consists of a carrier sheet and an imageable layer.

13. The method according to any one of the preceding claims, wherein the exposed areas of the imageable layer are removed by ablation.

14. The method according to any one of the preceding claims, wherein the imageable article is a flexographic printing plate precursor, a letterpress printing plate precursor or a printed circuit board.

15. The method according to any one of the preceding claims, wherein the imageable article is a flexographic printing plate precursor.

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