Field of invention

The field of the invention relates to printing plates, printing plate precursors and methods for manufacturing thereof.

Background

Today, flexographic printing is predominantly used for packaging printing because it is the most versatile printing process with respect to printable substrates and ink systems. For example, no other industrial printing technology than flexographic printing - with the exception of screen printing and contactless digital printing, such as ink-jet - is able to print directly on corrugated board. In the Flexible Packaging segment only gravure printing successfully rivals the flexographic printing process due to the wide variety of synthetic substrates that is best coped with by using solvent based ink systems.

However, the versatility of flexographic printing also comes with a large amount of challenges where other printing processes might have advantages. A flexographic printing plate is provided with relief structures which can be made by transfer of image information onto an imageable layer of the printing plate precursor and removing parts of the imageable layer. The formed relief may then be used to transfer the information in a printing step onto a substrate. Digitally imageable flexible printing plate precursors typically comprise at least a dimensionally stable support layer, a photosensitive layer and a digitally imageable mask layer. The digitally imageable mask layer may be e.g. a laser- ablatable layer. In case of conventional printing plate precursors, the digitally imageable mask layer is replaced by a separate mask which is attached to a photosensitive layer. Being a relief printing process, flexographic printing is prone to the following challenges: bouncing caused by the plate motives; trail edge voids visible in the print; difficulty to create a 1:1 copy of the image file, caused by e.g. dot reduction due to oxygen effect and required bump up correction by which highlight information is lost or dot widening due to reactivity of the plate precursor or UV light scattering; even bigger difficulty to get a 1 : 1 copy from file to print due to dot gain during printing which requires a correction in the file, wherein the dot gain may vary depending on machine parameters (impression) and run length (due to abrasion); solvent processing takes a long time and both solvent and thermal processing produce substantial amounts of waste, such as polymer and solvent or non-woven waste; In contrast, nowadays offset printing (lithographic printing) is much less flexible with respect to substrates - it is used predominantly for printing on paper and carton board - but does not come with the disadvantages that relief structures may cause. Offset printing has less problems with dot gain (although it is an issue in offset printing as well, offset plates are not elastic and therefore do not exhibit dot gain due to mechanical compression/deformation of the printing plate), has no bouncing, no trail edge voids, and no issues with a three-dimensional dot shape as the plate is flat. Also, the plate processing is faster and simpler and causes less waste.

To produce a digital flexographic printing plate from a printing plate relief precursor, according to existing methods, first a mask is written into the digitally imageable layer, typically a laser-ablatable mask layer, based on image data to be printed. Following the writing of the mask, the plate is exposed through the mask with radiation such that the photosensitive layer undergoes polymerization or crosslinking or a reaction changing the solubility or fluidity of the photosensitive layer in the regions which are not covered by the mask. Following the exposure, the residues of the mask and of the non- exposed portions of the photosensitive layer are removed. This may be done with one or more liquids in a washer apparatus or by thermal development wherein non-exposed material of the photosensitive layer is liquefied by temperature increase and removed. To produce conventional flexographic plates, either a photographic film is used as mask or a imaged mask film is laminated on top of the plate after it has been imaged. The film or mask may be removed mechanically before the plate is processed with solvents or may be removed thermally.

Summary

The object of embodiments of the invention is to provide a printing plate capable of printing on different types of substrates, preferably including printing on corrugated board that can be easily damaged when too much pressure is applied during the printing process. It is another objet of embodiments of the invention to generate printing plates that may be used with printing equipment already available on the market. In order to do so especially the thickness of the plates should fit to the equipment. More in particular it is desirable to have a printing plate which is more flexible with respect to substrates than traditional offset printing plates. Also, the object of embodiments of the invention is to provide a method for manufacturing a printing plate which is simpler and faster than methods for producing traditional flexographic printing plates and/or creates less waste.

According to a first aspect of the invention, there is provided a printing plate or sleeve having a thickness higher than 200 pm and comprising an elastic layer having a tensile modulus lower than 500 Mpa. The tensile modulus may be determined in accordance with ISO 527-1. The printing plate or sleeve is provided at a surface thereof with first areas with a first ink repelling/attracting property and second areas with a second ink repelling/attracting property, said second ink repelling/attracting property being different from said first ink repelling/attracting property. Stated differently, a surface of the printing plate or sleeve exhibits first areas with a first ink repelling/attracting property and second areas with a second ink repelling/attracting property.

The elastic layer of the printing plate makes it possible to use the plates on flexographic printing and/or letterpress/“dry offset” printing machines as direct replacements for today’s relief printing plates. However, the printing plates of the invention may also be used in other suitable printing machines, e.g. machines specifically adapted to printing plates of the invention.

The elastic layer of the printing plate or sleeve allows printing on pressure sensitive substrates e.g. corrugated board. In addition, the first and second areas with the first and second ink repelling/attracting property can be achieved without any significant relief structures, reducing or eliminating bouncing effects and trail edge voids. Also, the significantly reduced deformation of printing features (dots) results in less dot gain problems compared to traditional flexographic printing, and hence improves the copying characteristics. In embodiments of printing plates of the invention the advantages of lithographic printing are combined with those of flexographic printing.

Embodiments of the invention will bring particular advantages to the corrugated post-print segment where, in accordance with existing printing plate methods, solvent-based plate processing takes a long time due to long drying times for the thicker plate material and where due to the thick plate material a lot of solvent is required to process the plates. Thermal processing on the other hand often cannot achieve the desired relief depths when using thick plate material and also creates a lot of non- woven waste during plate processing. Further, due to being less prone to bouncing/creation of vibrations, embodiments of printing plates of the invention may also achieve higher printing speeds in all flexographic application segments.

Preferably, the first areas correspond with imaged areas and the second areas with non-imaged areas. Imaging is a convenient means to provide the difference in ink repelling/ attracting properties between the imaged and non-imaged areas. In some embodiments the imaged areas may be ink repelling areas and the non-imaged areas may be ink attracting areas. However, in other embodiments the imaged areas may be ink attracting areas and the non-imaged areas may be ink repelling areas.

As will be explained below imaging can be used in different ways to achieve the difference in ink repelling/attracting properties. In the context of the present application, the terms “imaging” or “image-wise treatment” refer to any kind of treatment based on image data, such as radiation and/or chemical treatment and or mechanical treatment, applied through a mask layer as well as direct imaging without a mask layer, e.g. imaging by laser ablation or imaging with a scanning beam of electromagnetic radiation which is able to change surface properties.

In preferred embodiments, the creation of the first and second areas does not require the removal of any material. In some embodiments, already in the imaging step the final structure is obtained and the time-consuming step of development, i.e. removal of imaged or non-imaged material, can be omitted.

Preferably, the tensile modulus of the elastic layer is lower than 200 MPa, more preferably lower than 100 MPa, even more preferably lower than 50 MPa, e.g. lower than 20 MPa or lower than 10 MPa. Optionally, the tensile modulus may be chosen in function of the substrate to be printed. For example, the more irregular and/or pressure sensitive the surface of the substrate to be printed upon, the lower the tensile modulus.

In order to measure the tensile modulus of the elastic layer, this layer may be isolated (e.g. by peeling of the other layers) and measured as specified in the ISO 527-1 standard. The tensile modulus may then be determined as specified in section 10.3.2 of the ISO 527-1 standard, i.e. the chord slope formula may be used to calculate the tensile modulus E _t . The measurements are done for a test specimen size 5A (According to ISO 527-2:1996) with a test speed of 0.2 mm/min.

Preferably, a height difference between the first areas and the second areas is smaller than 140 pm, preferably smaller than 90 pm, more preferable smaller than 70 pm, even more preferably smaller than 50 pm. For example, the height difference may be between 1 and 20 pm, or between 1 and 10 pm. Thus, it is preferred to limit any height difference between the printing areas and the non printing areas. In that way any negative dot feature effects such as dot gain can be negligible.

Preferably, the elastic layer has a thickness higher than 200 pm, even more preferably higher than 300 pm or even higher than 400 pm. In some cases, it may be in the range of 0.7 to 7 mm. In that way, a sufficient degree of elasticity can be achieved for printing on irregular substrate surfaces.

The first and second different ink repelling/attracting property may correspond with a first and second different static water contact angle. Preferably the difference between the first and second water contact angle is higher than 10°, preferably higher than 20°, more preferably higher than 30°, and in some cases, it may be higher than 40°. In another exemplary embodiment, the first and second different ink repelling/attracting property is a first and second different static contact angle for hexadecane, wherein preferably the difference between the first and second contact angle for hexadecane is higher than 10°, preferably higher than 20°, more preferably higher than 30°.

In an exemplary embodiment, one of the first and second static water contact angle is lower than a threshold value, preferably at least 5° lower than the threshold value, more preferably at least 10° lower than the threshold value, and the other one of the first and second static water contact angle is higher than the threshold value, preferably at least 5° higher than the threshold value, more preferably at least 10° higher than the threshold value. Preferably, the threshold value is in a range between 70 to 115°. In this way, one of the first and second areas may be hydrophilic or omniphilic and the other one of the first and second areas may be hydrophobic or omniphobic. In a preferred embodiment the printing plate comprises an imageable layer in which the first and second areas are arranged as imaged and non-imaged areas. Preferably, the imaging (e.g. exposure to electromagnetic radiation, a particle beam, a gas, a liquid or mechanical treatment through a mask) is used to generate the difference in ink acceptance without removal of material. For example, an oxidation reaction may cause the imaged areas to become hydrophilic. Application of a gas for example may render the imaged area hydrophobic. It is also possible to image-wise remove the imageable layer (e.g. by means of ablation or gravure) whereby recesses are generated. Preferably, the imageable layer has a thickness below 100 pm, preferably below 50 pm, more preferably below 25 pm, even more preferably below 15 pm, most preferably below 10 pm. The imageable layer may be made of a single layer of the same material or may consist of multiple layers of different materials, e.g. a traditional mask layer on which a coating is applied. In the latter case the imaged areas may extend through the multiple layers, e.g. with the coating being removed during imaging also.

In a preferred embodiment, the first areas define recesses extending over the entire thickness of the imageable layer, and the imageable layer is in contact with the elastic layer. A surface of the elastic layer and the imageable layer may then have an opposite ink repelling/attracting property. For example, one of the surface of the elastic layer and the imageable layer is hydrophobic or omniphobic and the other one hydrophilic or omniphilic. In that manner an elastic printing plate suitable for printing on different kinds of substrates can be obtained in a simple manner. The hydrophobic material may comprise e.g. a polymer, a wax, a fluorinating or fluorinated compound, a silane, a siliconating or siliconized compound or combinations thereof. For example, the hydrophobic material may be a fluorinated polymer or copolymer, a silicone polymer or copolymer, or combinations thereof or mixtures with other compounds.

In an exemplary embodiment, the imageable layer comprises a hydrophilic or superhydrophilic material. The hydrophilic or superhydrophilic material may comprise a hydrophilic polymer, a metal oxide (e.g. SiOx, A1203,), a glass, or combinations thereof. Examples are a natural rubber, an EPDM rubber, a silicone rubber, a SIS copolymer, a SBS copolymer, a polyurethane, such as a polyurethane foam, a polyamide, a polyvinylalcohol, a polyvinyl acetate, a partially hydrolyzed polyvinyl acetate, a polyethylene vinyl acetate copolymer, a partially hydrolyzed polyethylene vinyl acetate copolymer, a functionalized polyvinyl acetate, a partially hydrolyzed polyvinyl acetate. In exemplary embodiments with a non-imageable layer below an imageable layer with recessed imaged areas extending over the entire thickness, the hydrophilicity of the imageable layer does not have to be very high but it should be higher than that of the non-imageable layer or the elastic layer.

In another exemplary embodiment, a non-imageable layer is arranged between the elastic layer and the imageable layer. In an exemplary embodiment, a thickness of the non-imageable layer is lower than 100 pm, or lower than 50 pm, or lower than 10 pm. In some cases, the thickness of the non- imageable layer may be lower than 1 pm. In that manner the non-imageable layer will not hinder the elasticity of the printing plate.

In such an embodiment, preferably the first areas define recesses extending over the entire thickness of the imageable layer, and a surface of the imageable layer and the non-imageable layer have an opposite ink repelling/attracting property, wherein preferably one of the surface of the imageable layer and the non-imageable layer is hydrophobic and the other one hydrophilic. For example, the imageable layer may be hydrophilic as described above, and the non-imageable layer may be hydrophobic.

In yet another exemplary embodiment, a non-imageable layer is arranged above the imageable layer, e.g. one side of the imageable layer may face the elastic layer and the other side the non-imageable layer. Preferably, a thickness of the non-imageable layer is lower than 10 pm, more preferably lower than 5 pm. In some cases, the thickness of the non-imageable layer may be lower than 1 pm. In such an embodiment the material of the non-imageable layer may be removed in the first or second areas together with the material of the imageable material. In such an embodiment, preferably a surface of the elastic layer and the non-imageable layer have an opposite ink repelling/attracting property, wherein preferably one of the surface of the elastic layer and the non-imageable layer is hydrophobic and the other one hydrophilic. In another exemplary embodiment, the first and second areas do not define recesses in the imageable layer; or the first or second areas define recesses which extend only partially in the imageable layer. For example, the image-wise treatment may cause a chemical reaction in the first and/or second areas which does not cause recesses. Also, the image-wise treatment may be performed so that recesses are created which do not extend all the way through the imageable layer.

In yet another exemplary embodiment, no separate imageable layer is present, and the elastic layer comprises the first and second areas. In such an embodiment, the elastic layer may be made of a material which is elastic and imageable.

In a preferred embodiment, the printing plate or sleeve further comprises a substrate layer. The substrate layer may have a tensile modulus higher than the tensile modulus of the elastic layer. The tensile modulus of the substrate is typically higher than 1 GPa, preferably higher than 1,5 GPa, more preferably higher than 2 GPa. The substrate layer may be a dimensionally stable layer (more stable than the elastic layer in an x-y direction within the layer) resulting in a more rigid, dimensionally stable printing plate with respect to deformation within the layer parallel to the surface of the layer(s). The elastic layer is arranged at a printing side of the substrate layer, e.g. the elastic layer may extend between the substrate layer and the imageable layer or between the substrate layer and the non- imageable layer. Note that also other layers may extend between the substrate layer and the imageable layer or between the substrate layer and the non-imageable layer, in addition to the elastic layer.

The substrate layer may have a shrinkage according to ASTM D1204-78 at 100°C of less than 1%, preferably less than 0,9% more preferably less than 0,8% and more preferably less than 0,6%.

Preferably, the substrate layer is made of a natural or artificial polymer, a polymer blend, a polymer film, a metal (e.g. steel, aluminum, copper or nickel), or any combination thereof. For example, the substrate layer may be made of polymers e.g. polyesters such as polyethylenterephthalate, polybutylenterephthalate, polyamide, or polycarbonate. The substrate layer may also comprise woven or nonwoven fabrics made of glass, carbon and or polymer fibers or compounds of such fibers with polymers such as fiber reinforced polymers.

Preferably, the elastic layer comprises a natural or artificial elastomeric polymer which may be crosslinked or not, an elastomeric foam or combinations thereof. For example, the polymer of the elastic layer may be selected form the group comprising a natural rubber, an EPDM rubber, a silicone rubber, a SIS copolymer, a SBS copolymer, a polyurethane, such as a polyurethane foam, a polyamide, a polyvinylalcohol, a polyvinyl acetate, a partially hydrolyzed polyvinyl acetate, a poly ethylene vinyl acetate copolymer, a partially hydrolyzed poly ethylene vinyl acetate copolymer, a functionalized polyvinyl acetate, a partially hydrolyzed polyvinyl acetate, a polyolefin, such a polyethylene or polypropylene or foams thereof, and combinations thereof. The elastic layer may be crosslinked and crosslinking may be obtained by addition or condensation reactions. The crosslinking reactions may be initiated either thermally or photochemically and/or may employ catalysts. In addition to the polymers mentioned above the elastic layer may comprise further ingredients e.g. polymerizable or crosslinkable compounds (e.g. monomers comprising ethylenically unsaturated groups, isocyanides, epoxides), fillers (organic or inorganic particles), binders (natural or artificial polymers), colorants (e.g. dyes and/or pigments), softeners (e.g. oils), initiators (e.g. thermally or photo-chemically initiating compounds), stabilizers (e.g. thermal stabilizers or photo stabilizers), surfactants (e.g. ionic or non-ionic surfactants, partially or fully fluorinated or silicon containing surfactants), adhesion promotors or combinations thereof.

In an exemplary embodiment, a surface of the first and or second areas has an ordered or non-ordered microscopic three-dimensional structure. For example, the surface may have a certain surface roughness to influence the ink repelling/attracting property. Preferably, the microscopic surface structure has relief structures having lateral dimensions smaller than 100 pm, e.g. smaller than 50 pm or smaller than 10 pm, e.g. in the range of 0.1 to 50 pm or 0.1 to 10 pm or in the range of 0.1 to 5 pm. Preferably, the microscopic surface structure has relief structures having a height smaller than 100 pm or smaller than 50 pm, e.g. smaller than 10 pm or smaller than 5 pm, or smaller than 3 pm. When there is an imageable layer present, the height is preferably smaller than the thickness of the imageable layer. It is noted that such microscopic structures may be covered with even finer relief structures, such as nano-structures. For example, the relief structures may comprise first relief features having dimensions in a range between 10 and 100 pm and second relief features in a range between 10 nm and 10 pm. Combining two scales of roughness may contribute to the quality of the (super-)hydrophobicity.

In another exemplary embodiment a surface of the first and/or second areas has an ordered or non- ordered microscopic three-dimensional structure, for example a porous material, that is filled with a lubricant where the slippery liquid-infused microscopic three-dimensional structure is designed to create a fluid/fluid interface between the lubricant and an immiscible liquid that is to be repelled like the printing ink. In an exemplary embodiment, the printing plate further comprises at least one adhesion layer arranged between adjacent layers of the printing plate, e.g. between the elastic layer and the substrate and/or between the elastic layer and the non-imageable layer and/or between the elastic layer and the imageable layer and/or between the non-imageable layer and the imageable layer. Preferably a thickness of each adhesion layer is lower than 10 pm, more preferably lower than 5 pm. In some cases, the thickness of the non-adhesion layer may be lower than 1 pm.

In such an embodiment, if an imageable layer is present, the at least one adhesion layer may comprise an adhesion layer below the imageable layer, and the first areas may define recesses extending over the entire thickness of the imageable layer. A surface of the adhesion layer and the imageable layer may then have an opposite ink repelling/attracting property, wherein preferably one of the surface of the adhesion layer and the imageable layer is hydrophobic and the other one hydrophilic.

Preferably, the printing plate or sleeve has a thickness higher than 300 pm, preferably higher than 350 pm, more preferably higher than 400 pm, most preferably higher than 600 pm and in some cases up to 7 mm, e.g. between 700 pm and 7 mm.

According to another aspect there is provided a printing precursor configured for manufacturing a printing plate of any one of the previous claims, said printing precursor having a thickness higher than 200 pm and comprising an elastic layer having a tensile modulus lower than 500 MPa, determined in accordance with ISO 527-1, said printing precursor being provided at a surface thereof with imageable areas, optionally further comprising a removable protection layer covering the imageable areas. The tensile modulus of the elastic layer is preferably lower than 200 MPa, more preferably lower than 100 MPa or even more preferably below 50 MPa, e.g. lower than 20 MPa or lower than 10 MPa.

According to another aspect there is provided a method for the manufacturing of a printing plate or sleeve. The method comprises a step a) of providing a printing precursor having a thickness higher than 200 pm and comprising a elastic layer having a tensile modulus lower than 500 MPa, and a step b) of image-wise treating the printing precursor so as to form imaged areas with a first ink repelling/attracting property and non-imaged areas with a second ink repelling/ attracting property, said second ink repelling/attracting property being different from said first ink repelling/attracting property. In that manner ink accepting and ink repelling areas may be formed during imaging and further processing or most preferably already during imaging so that other processing steps become redundant.

Preferably, the image-wise treatment comprises a treatment with a scanning beam of electromagnetic radiation, a scanning beam of a plasma, a scanning beam of particles (e.g. ions, oxides) an areal exposure to electromagnetic radiation or a plasma through a mask in-between the printing precursor and the source of electromagnetic radiation or plasma.

In an exemplary embodiment the method further comprises a step c) of treating the precursor to further change the first and/or second ink repelling/accepting property. For example, step c) may comprise a treatment with a vapor, a gas, a fluid, a solution, a particle beam or combinations thereof. In another example, step c) may be a mechanical treatment. For example, step c) may modify the surface roughness of the first or second areas. Step c) may comprise a treatment with a compound which interacts with the imaged and or non-imaged areas of the precursor to alter the first and/or second ink repelling/attracting property.

In an exemplary embodiment step a) comprises:

- optionally provision of a dimensionally stable substrate,

- optionally arranging at least one adhesion layer or non-imageable layer to the substrate,

- arranging at least an elastic layer, optionally on the substrate if present or on an adhesion layer, if present, or on a non-imageable layer, if present; also, in some cases the elastic layer may be arranged below the substrate layer, if present;

- optionally arranging at least one adhesion layer on the elastic layer,

- optionally arranging at least one non-imageable layer over the elastic layer,

- arranging an imageable layer over the elastic layer, with optionally the at least one adhesion layer and or the at least one non-imageable layer in between the imageable layer and the elastic layer,

- optionally arranging one or more additional layers on the imageable layer, such as a removable layer which is removed before performing step b).

It is noted that the list of steps above is non-exhaustive and that there could be even more layers than the ones mentioned, anywhere between the mentioned mandatory/optional layers, as long as the functionality of the elastic layer, the imageable layer and optional substrate and or adhesion and or non-imageable layers are not affected. For example, one or more further adhesion and/or foam layers or other layers may be present below the imageable layer and or the substrate layer. In a preferred embodiment, step b) comprises imaging the imageable layer over the entire thickness of the imageable layer. In that manner, when the layer below, e.g. the elastic layer or the non- imageable layer, is made of a different material, different ink repelling/attracting properties can be obtained in an easy manner.

Preferably, the imageable layer comprises or consists of a coating applied by spraying, casting, printing, curtain coating, vacuum coating, vapor deposition, lamination, roller coating or combinations thereof.

In an exemplary embodiment, during step b) the imageable layer is crosslinked in the imaged areas e.g. to the elastic layer and not in the non-imaged areas.

In an exemplary embodiment, step b) comprises providing an imaged mask layer on the elastic layer, providing a coating on the imaged mask layer, and exposing the coating such that the coating is crosslinked to the elastic layer in the imaged areas of the mask layer, and removing the coating material and optionally the mask layer material in the non-imaged areas.

In another exemplary embodiment, step b) comprises providing an imaged mask layer on the elastic layer, providing a coating on the imaged mask layer, and exposing the coating such that the coating is crosslinked to the mask layer in the non-imaged areas of the mask layer, and removing the coating material in the imaged areas.

In yet another exemplary embodiment, step b) comprises providing an imaged mask layer on the elastic layer, providing a coating on the imaged mask layer, and removing of (e.g. peeling-off) the mask layer such that the coating remains in the areas which do not contain imaged mask layer material.

In an exemplary embodiment, the image-wise treatment is done by an ablation process.

In another embodiment, step b) comprises imaging the elastic layer.

Preferably, step b) is performed such that a height difference between the imaged areas and the non- imaged areas is smaller than 140 pm, preferably smaller than 100 pm, more preferable smaller than 50 pm, even more preferably between 1 and 20 pm, most preferably between 1 and 10 pm. Preferred features for the different layers of the printing plate or sleeve and for the ink repelling/attracting properties disclosed above for the printing plate or sleeve may apply mutatis mutandis for the embodiments of the method.

According to yet another aspect of the invention there is provided a printing plate or sleeve obtained using the method of any one of the embodiments disclosed above.

The plates or sleeves according to embodiments of the invention can be used to print on both absorbent and non-absorbent substrate materials, for example, corrugated board, cardboard, cellophane, foil, fabric, plastic (metallized), metal etc. They may be used on materials with rough or smooth surfaces, and also on flexible materials like polymer films, sheets, and/or tubes or containers. Very often plastics are used as substrate due to their higher stability and/or barrier properties. Plastics used as printing substrates are for example polyethylenes, polypropylenes, polystyrenes, polyesters (e.g. polyethylene terephthalate PET, polybutylene terephthalates, polyethylene naphthalates, polylactic acid), poly carbonates, polyetheretherketone, polyvinyl chloride, acrylonitrile-butadiene- styrenes, polyvinyl alcohols, poly acrylates poly methacrylates, poly urethanes, poly amides, and their combinations (e.g. in form of co-extrudates or blends). The polymers may be used in form of homo- and or copolymers. Such substrates are mostly used for packaging; envelopes, retail bags, wallpaper, paper, newspapers, sweet wrappers, labelstock and so on.

According to another aspect, there is provided a method for printing with a printing plate or sleeve according to any one of the embodiments described above, on any one of the possible substrates mentioned above, and in particular on a pressure sensitive substrate such as corrugated board. A corrugated board typically comprises a corrugated sheet, e.g. a fluted corrugated sheet, and one or more flat linerboards. For such pressure sensitive substrates, preferably the thickness of the elastic layer is higher than 350 pm, more preferably higher than 400 pm, most preferably higher than 600 pm, and e.g. between 700 pm and 7 mm.

Brief description of the figures

The accompanying drawings are used to illustrate presently preferred non limiting exemplary embodiments of the apparatus and method of the present invention. The above and other advantages of the features and objects of the invention will become more apparent, and the invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which: Figures 1A, IB, 1C and ID are schematic sectional views of different exemplary embodiments of a printing plate.

Figure 2 illustrates schematically a first exemplary embodiment for manufacturing a printing plate. Figure 3 illustrates schematically a second exemplary embodiment for manufacturing a printing plate.

Figure 4 illustrates schematically a third and a fourth exemplary embodiment for manufacturing a printing plate.

Detailed description of embodiments

Figure 1 A illustrates an exemplary embodiment of a printing plate. The printing plate has a thickness tp higher than 200 pm. The printing plate comprises an elastic and imageable layer LEI having a tensile modulus lower than 500 MPa and a substrate layer S arranged below the elastic and imageable layer LEI. The elastic and imageable layer LEI is provided at an upper surface thereof with first areas corresponding with imaged areas AI with a first ink repelling/attracting property and with second areas corresponding with non-imaged areas AN with a second ink repelling/attracting property. The second ink repelling/attracting property is different from said first ink repelling/attracting property. The imaged areas AI may be arranged by any image-wise treatment. The image-wise treatment may be any treatment based on image data and may involve a treatment through a mask layer or a direct treatment such as a laser treatment or imaging with a scanning beam of electromagnetic radiation or particles which is able to change surface properties. The difference between the first and second ink repelling/attracting property may be due to a difference in chemical composition between the first and the second area and/or due to a difference in physical properties, such as surface roughness, between the first and the second areas.

Figure IB illustrates an exemplary embodiment of a printing plate. The printing plate has a thickness tp higher than 200 pm. The printing plate comprises a substrate layer S, an elastic layer LE having a tensile modulus lower than 500 MPa, and an imageable layer LI. The imageable layer LI is imaged and is provided at a surface thereof with first areas corresponding with imaged areas AI with a first ink repelling/attracting property and with second areas corresponding with non-imaged areas AN with a second ink repelling/attracting property. Preferably, a height difference Ah between the first areas AI and the second areas AN is smaller than 10 pm, e.g. between 1 and 10 pm. The imaged areas AI define recesses extending over the entire thickness of the imageable layer. A surface of the elastic layer LE and the imageable layer LI have an opposite ink repelling/attracting property, wherein preferably one of the surface of the elastic layer LE and the imageable layer LI is hydrophobic and the other one hydrophilic. The imaged areas AI may be arranged by any image- wise treatment. The image -wise treatment may involve a treatment through a mask layer or a direct treatment such as a laser ablation treatment or imaging with a scanning beam of electromagnetic radiation or particles which is able to change surface properties.

Figure 1C illustrates another exemplary embodiment of a printing plate. The printing plate has a thickness tp higher than 200 pm. The printing plate comprises a substrate layer S, an elastic layer LE having a tensile modulus lower than 500 MPa, a non-imageable layer LN and an imageable layer LI. The imageable layer LI is imaged and is provided at a surface thereof with first areas corresponding with imaged areas AI with a first ink repelling/attracting property and with second areas corresponding with non-imaged areas AN with a second ink repelling/attracting property. The imaged areas AI define recesses extending over the entire thickness of the imageable layer. Preferably, the thickness of the imageable layer LI is smaller than 10 pm, e.g. between 1 and 10 pm. A surface of the non-imageable layer LN and the imageable layer LI have an opposite ink repelling/attracting property, wherein preferably one of the surface of the non-imageable layer LN and the imageable layer LI is hydrophobic and the other one hydrophilic. The imaged areas AI may be arranged by any image-wise treatment. The image-wise treatment may involve a treatment through a mask layer or a direct treatment such as a laser ablation treatment or imaging with a scanning beam of electromagnetic radiation or particles which is able to change surface properties.

Ligure ID illustrates another exemplary embodiment of a printing plate. The printing plate has a thickness tp higher than 200 pm. The printing plate comprises a substrate layer S, a first adhesive layer LAI, an elastic layer LE having a tensile modulus lower than 500 MPa, a second adhesive layer LA2, a non-imageable layer LN, a third adhesive layer LA3, and an imageable layer LI. The imageable layer LI is imaged and is provided at a surface thereof with first areas corresponding with imaged areas AI with a first ink repelling/attracting property and with second areas corresponding with non-imaged areas AN with a second ink repelling/attracting property. The imaged areas AI define recesses extending over the entire thickness of the imageable layer LI. Preferably, the thickness of the imageable layer LI is smaller than 10 pm, e.g. between 1 and 10 pm. A surface of the third adhesive layer LA3 on the non-imageable layer LN and of the imageable layer LI has an opposite inkrepelling/attracting property, wherein preferably one of the surface of the third adhesive layer LA3 and the imageable layer LI is hydrophobic and the other one hydrophilic. The imaged areas AI may be arranged by any image-wise treatment. The image-wise treatment may involve a treatment through a mask layer or a direct treatment such as a laser ablation treatment or imaging with a scanning beam of electromagnetic radiation or particles which is able to change surface properties. In the embodiments of figures 1A-1D, the first and second different inkrepelling/attracting property may be a first and second different static water contact angle. Preferably the difference between the first and second water contact angle is higher than 10°, preferably higher than 20°, more preferably higher than 30°, and in some cases, it may be higher than 40°.

Figure 2 illustrates a first exemplary embodiment of a method for manufacturing a printing plate, e.g. a printing as illustrated in figure 1 A. In a first step, a printing precursor having a thickness higher than 200 pm is provided. The printing precursor comprising a elastic and imageable layer LEI having a tensile modulus lower than 500 MPa. Optionally, the printing precursor further comprises a substrate layer (not illustrated in figure 2). In a second step the printing precursor is subjected to an image-wise treatment so as to form imaged areas AI with a first ink repelling/attracting property and non-imaged areas AN with a second different ink repelling/attracting property. The image-wise treatment may involve a treatment through a mask layer or a direct treatment such as a laser ablation treatment or imaging with a scanning beam of electromagnetic radiation or particles which is able to change surface properties. In this case substantially no recess is formed at the surface.

Figure 3 illustrates a second exemplary embodiment of a method for manufacturing a printing plate, e.g. a printing as illustrated in figure IB. In a first step, a printing precursor having a thickness higher than 200 pm is provided. The printing precursor comprising a elastic layer LE having a tensile modulus lower than 500 MPa, and imageable layer LI arranged on the elastic layer LE. Optionally, the printing precursor further comprises a substrate layer (not illustrated in figure 3). In a second step the printing precursor is subjected to an image-wise treatment so as to form imaged areas AI with a first ink repelling/attracting property and non-imaged areas AN with a second different ink repelling/attracting property. The image- wise treatment may involve a treatment through a mask layer or a direct treatment such as a laser ablation treatment. Preferably, the imaged areas AI define recesses extending over the entire thickness of the imageable layer LI. Preferably, the thickness of the imageable layer LI is smaller than 10 pm, e.g. between 1 and 10 pm. Preferably, a surface of the elastic layer LE and the imageable layer LI have an opposite ink repelling/attracting property, e.g. one of the surface of the elastic layer LE and the imageable layer LI is hydrophobic and the other one hydrophilic.

Figure 4 illustrates a third and a fourth exemplary embodiment of a method for manufacturing a printing plate. In a first step, a printing precursor having a thickness higher than 200 pm is provided. The printing precursor comprising an elastic layer LE having a tensile modulus lower than 500 MPa, and imageable layer LI arranged on the elastic layer LE. Optionally, the printing precursor further comprises a substrate layer (not illustrated in figure 4). In a second step the printing precursor is subjected to an image-wise treatment so as to form imaged areas AI and non- imaged areas AN. The image-wise treatment may involve a treatment through a mask layer. The imaged areas AI may extend over the entire thickness of the imageable layer LI as illustrated in figure 4 but may also extend over less than the entire thickness. Preferably, the thickness of the imageable layer LI is smaller than 10 pm, e.g. between 1 and 10 pm.

According to the third exemplary embodiment illustrated on the left side of figure 4, the imaged areas AI of the imageable layer LI are removed and the elastic layer is treated through the mask formed by the imageable layer LI in order to treat the surface of the elastic layer LE in the imaged areas.

According to the fourth exemplary embodiment illustrated on the right side of figure 4, the non- imaged areas AN of the imageable layer LI are removed and the elastic layer is treated through the mask formed by the imageable layer LI in order to treat the surface of the elastic layer LE in the non-imaged areas.

Both for the third and the fourth exemplary embodiment, the treated surface of the elastic layer LE and the top surface of the imageable layer LI have an opposite ink repelling/attracting property, e.g. one of the treated surface of the elastic layer LE and the top surface of the imageable layer LI is hydrophobic and the other one hydrophilic.

Examples Example 1

A solution of a paraffin wax (10 w% in toluene, congealing point of the wax: 62 °C) was coated on top of the laser-ablatable mask of an ACE114D printing plate precursor (with an elastic layer based on SBS rubber, 965 pm thickness, 7.1 MPa tensile modulus, on a 175 pm PET-based support layer and a laser ablatable mask layer) and distributed evenly by a doctoral blade (100pm gap). Thus, the imageable layer here comprises the laser-ablatable mask layer (3 pm thickness) and the coating. After 30 minutes of drying at room temperature, the mask was selectively removed by laser ablation (machine: Xeikon TfxX 20, 35W, 8U/s), whereby also the wax coating was removed. The wax coating has a layer thickness of 7 pm.

The plate was irradiated for 20 minutes with UVA light (machine: Combi Fill, 17,6 mW/cm ² ) from the backside and afterwards 10 minutes simultaneously with UVA and UVC light from the front side (machine: Combi Fill, UVA 11 mW/cm ² , UVC 13 mW/cm ² ). Example 2

An image pattern was obtained by selectively covering an elastic layer based on SBS rubber with a 965 pm thickness, a tensile modulus of about 7.1 MPa, on a 175 pm PET-based support with a patterned adhesive film (Office Depot universal tape, supplier: Office Depot Europe B.V., Columbusweg 33, 5928 LA Venlo, the Netherlands, total thickness film and adhesive: 46 pm, thickness of adhesive layer: 14 pm) functioning as mask. A solution of a paraffin wax (10 w% in toluene, congealing point of the wax: 62 °C) was coated on top of mask and distributed evenly by a doctoral blade (100pm gap). After 30 minutes of drying at room temperature, the mask was manually removed, whereby also the wax coating was removed in the areas where the patterned adhesive film was present. The wax coating has a layer thickness of 3 pm.

The plate was irradiated for 20 minutes with UVA light (machine: Combi Fill, 17,6 mW/cm ² ) from the backside and afterwards for 10 minutes simultaneously with UVA and UVC light from the front side (machine: Combi Fill, UVA 11 mW/cm ² , UVC 13 mW/cm ² ).

Example 3

Example 3 was performed in the same way as example 1, but a siloxane containing impregnation spray was used instead of the paraffin wax. The siloxane coating has a layer thickness of 1 pm. Example 4

Example 4 was performed in the same way as example 2, but a siloxane containing impregnation spray was used instead of the paraffin wax. The siloxane coating has a layer thickness of 2 pm.

Example 5 Example 5 was performed in the same way as example 1, but an Ultra Ever Dry coating (UltraTech International Inc.) bottom and top coat, application according to instruction manual) was used instead of the paraffin wax. The coating has a layer thickness of 34 pm.

Example 6 Example 6 was performed in the same way as example 2, but an Ultra Ever Dry coating (UltraTech International Inc.) bottom and top-coat, application according to instruction manual) was used instead of the paraffin wax. The coating has a layer thickness of 16 pm.

Determination of static water and hexadecane contact angle: The contact-angle measurements were performed with a Keyence VHX-500F (zoom lens VH-Z20R, 50x magnification) at 21 °C with 33% relative humidity. To measure the static contact angle, a sessile drop (5 pL) of the respective liquid (distilled water, n-hexadecane: n-Hexadecan zur Sythese, supplier: VWR, article number 8.20633.0250) was dispensed on the surface with a pipette and sideview image of the macroscopic droplet profile was captured. The contact angle was determined with the integrated software (VHX500 Communication Software 1.02) of the Keyence microscope. The respective measurement was repeated for 3 times and the average value reported.

Evaluation examples 1-6

To assess the ink accepting and ink repelling properties, an ink pad (STANGER Stempelkissen 01801905 11x7 cm) was filled with a water-based ink (4 g LAMY T10 Tintenpatrone schwarz diluted with 12 g water), the respective patterned plate was pressed on the ink pad and afterwards on a sheet of paper.

The print quality was rated as follows: when the difference in the ink density between the treated and untreated area on the paper was strong and the two areas were separated by a clear border line it was denoted “+”. Results where there was a difference in the ink density between the treated and untreated area on the paper but where the difference was less strong were denoted “0”.

These experiments illustrate that coatings can be found which provide good results. The skilled person understands that further suitable coating materials can be found by trial and error methods.

Exemplary methods to generate imaged and non-imaged areas

In the exemplary methods set out below, when mentioning that a layer is ink accepting, preferably the static water contact angle is at least 5° lower than a threshold value, and when mentioning that a layer is ink repelling, preferably the static water contact angle is at least 5° higher than the threshold value. The threshold value may be e.g. between 70° and 110° or between 80° and 100°. This will be a good indication for water-based inks. However, the skilled person understands that when the ink is not water-based, contact angles measured for another liquid representative for the ink may be used, and the threshold value may be different.

Method 1 A laser-ablatable mask layer is attached, e.g. by lamination, to an elastic layer, e.g. a layer made of a rubber formulation obtaining at least a two-layer system comprising an elastic layer and a laser- ablatable imageable layer. One or more additional layers, e.g. an adhesive layer, may be added in- between the elastic layer and the imageable layer as has been explained above. The laser-ablatable mask layer is selectively removed by laser-ablation obtaining a pattern or an image on the layer below, e.g. the elastic layer.

According to a possible embodiment, the laser-ablatable mask is ink repelling and the elastic layer is ink accepting. According to another possible embodiment, the laser-ablatable mask is ink accepting and the elastic layer is ink repelling.

Method 2

A coating is applied, e.g. casted or sprayed, on a laser-ablatable mask layer of a two-layer system according to method 1. The coating is selectively removed by laser- ablation of the laser-ablatable mask layer beneath obtaining a pattern or an image. Thus the imageable layer here consist of the mask layer and the coating.

According to a possible embodiment, the coating is ink repelling and the elastic layer is ink accepting. According to another possible embodiment, the coating is ink accepting and the elastic layer is ink repelling.

Method 3

A coating is applied on an elastic layer, e.g. casted or sprayed. A laser-ablatable mask layer is attached to the dried coating on the elastic layer, e.g. by lamination. The laser-ablatable mask layer is selectively removed by laser-ablation without removing the coating beneath obtaining a pattern or an image. In such an embodiment, the coating corresponds with a non-imageable layer and the laser- ablatable mask layer corresponds with the imageable layer.

According to a possible embodiment, the coating according is ink repelling and the laser-ablatable mask is ink accepting. According to another possible embodiment, the coating is ink accepting and the laser-ablatable mask is ink repelling. Method 4

A coating is applied on a system, prepared and already imaged according to method 1. The elastic layer and the coating contain functional groups, which can be used for crosslinking. The coating is crosslinked, e.g. by UV exposure, to the elastic layer, but not to the laser-ablatable mask layer. The non-crosslinked coating and laser-ablatable mask are removed by washout with a solvent, thermal development or during print by dissolving in the ink, while the crosslinked coating remains on the elastic layer. In such a printing plate the imaged layer which remains present is the patterned coating layer. The laser-ablatable mask layer is only present in the printing precursor but not in the resulting printing plate.

According to a possible embodiment, the coating is ink repelling and the elastic layer is ink accepting. According to another possible embodiment, the coating is ink accepting, the elastic layer is ink repelling. Method 5

A coating is applied on a system, prepared and already imaged according to method 1. The elastic layer and the coating contain functional groups, which can be used for crosslinking. The coating is crosslinked, e.g. by UV exposure, to the elastic layer, but not to the laser-ablatable mask layer. The non-crosslinked coating is removed by washout with a solvent, thermal development or during print by dissolving in the ink, while the crosslinked coating and the laser-ablatable mask remain on the elastic layer. In such a printing plate the imaged layer which remains present is the patterned coating layer in the laser-ablated areas and the patterned mask layer in the non-laser-ablated areas.

According to a possible embodiment, the coating is ink repelling and the laser-ablatable mask is ink accepting. According to another possible embodiment, the coating is ink accepting and the laser- ablatable mask is ink repelling.

Method 6

A coating is applied on a system, prepared and already imaged according to method 1. The laser- ablatable mask and the coating contain functional groups, which can be used for crosslinking. The coating is crosslinked, e.g. by UV exposure, to the laser-ablatable mask layer, but not to the elastic layer. The non-crosslinked coating on top is removed by washout with a solvent, thermal development or during print by dissolving in the ink, while the crosslinked coating remains on the laser-ablatable mask layer. In such an embodiment, the imageable layer is formed by the mask layer and the coating, and the printing plate comprises a patterned coating on top of a patterned mask layer. According to a possible embodiment, the coating is ink repelling and the elastic layer is ink accepting. According to another possible embodiment, the coating is ink accepting and the elastic layer is ink repelling. Method 7

A non-ablatable mask is selectively applied to an elastic layer, e.g. a layer made of a rubber formulation, in image-forming pattern. One or more additional layers, e.g. an adhesive layer, may be present in-between the non-ablatable mask and the elastic layer. Here the non-ablatable mask corresponds with the imageable layer.

According to a possible embodiment, the mask is ink repelling and the elastic layer is ink accepting. According to another possible embodiment, the mask is ink accepting and the elastic layer is ink repelling. Method 8

A coating is applied on a system, prepared according to method 7. The non-abatable mask is removed, e.g. peeled off. Here only a patterned coating layer remains present in the resulting printing plate. The mask is only present in the printing precursor. According to a possible embodiment, the coating is ink repelling and the elastic layer is ink accepting. According to another possible embodiment, the coating is ink accepting and the elastic layer is ink repelling.

Method 9 A coating is applied on a system, prepared and already imaged according to method 7. The elastic layer and the coating contain functional groups, which can be used for crosslinking. The coating is crosslinked, e.g. by UV exposure, to the elastic layer, but not to the mask layer. The non-crosslinked coating and mask are removed by washout with a solvent, thermal development or during print by dissolving in the ink, while the crosslinked coating remains on the elastic layer. In such a printing plate the imaged layer which remains present is the patterned coating layer. The mask layer is only present in the printing precursor but not in the resulting printing plate.

According to a possible embodiment, the coating is ink repelling and the elastic layer is ink accepting. According to another possible embodiment, the coating is ink accepting and the elastic layer is ink repelling. Method 10

A coating is applied on a system, prepared and already imaged according to method 7. The elastic layer and the coating contain functional groups, which can be used for crosslinking. The coating is crosslinked, e.g. by UV exposure, to the elastic layer, but not to the mask layer. The non-crosslinked coating is removed by washout with a solvent, thermal development or during print by dissolving in the ink, while the crosslinked coating and the mask remain on the elastic layer. In such a printing plate the imaged layer which remains present is the patterned coating layer areas not covered by the mask and the patterned mask layer. According to a possible embodiment, the coating is ink repelling and the mask is ink accepting. According to another possible embodiment, the coating is ink accepting and the mask is ink repelling.

Method 11

A coating is applied on a system, prepared and already imaged according to method 7. The mask and the coating contain functional groups, which can be used for crosslinking. The coating is crosslinked, e.g. by UV exposure, to the mask layer, but not to the elastic layer. The non-crosslinked coating on top is removed by washout with a solvent, thermal development or during print by dissolving in the ink, while the crosslinked coating remains on the mask layer. In such an embodiment, the imageable layer is formed by the mask layer and the coating, and the printing plate comprises a patterned coating on top of a patterned mask layer.

According to a possible embodiment, the coating is ink repelling and the elastic layer is ink accepting. According to another possible embodiment, the coating is ink accepting and the elastic layer is ink repelling.

Support layer

In the embodiments disclosed above the elastic layer may be arranged on a support layer. The support layer may be a flexible metal, a natural or artificial polymer, paper or combinations thereof. Preferably the support layer is a flexible metal or polymer film or sheet. In case of a flexible metal, the support layer could comprise a thin film, a sieve like structure, a mesh like structure, a woven or non-woven structure or a combination thereof. Steel, copper, nickel or aluminium sheets are preferred and may be about 50 to 1000 pm thick. In case of a polymer film, the film is dimensionally stable but bendable and may be made for example from polyalkylenes, polyesters, polyethylene terephthalate, polybutylene terephthalate, polyamides und polycarbonates, polymers reinforced with woven, nonwoven or layered fibres (e.g. glass fibres, Carbon fibres, polymer fibres) or combinations thereof. Preferably polyethylene and polyester foils are used and their thickness may be in the range of about 100 to 300 pm, preferably in the range of 100 to 200 pm.

Imageable layer

The imageable layer may comprise at least one photosensitive layer and/or at least one directly engravable layer and/or one or more further additional layers. Typically, at least one of those additional layers will function as a mask layer. Between the different layers described above one or more adhesion layers may be located which ensure proper adhesion of the different layers. The directly engravable layer may be made of a resin material. The mask layer may be ablated or changed in with respect to its surface property during the image-wise treatment and forms a mask with imaged and non-imaged areas.

Optionally one of the layers undergoes a change in solubility and or fluidity upon irradiation. The change in solubility and/or fluidity may be achieved by photo-induced polymerization and or crosslinking, rendering the irradiated areas less soluble, whereupon the non-irradiated areas may be removed. In other cases, the electromagnetic radiation may cause breaking of bonds or cleavage of protective groups rendering the irradiated areas more soluble. Liquids which may be used to remove material from the exposed precursor include amongst others: water, aqueous solutions, solvents and combinations thereof. The nature of the liquid used is guided by the nature of the precursor employed. If the layer to be removed is soluble, emulsifiable or dispersible in water or aqueous solutions, water or aqueous solutions might be used. If the layer is soluble, emulsifiable or dispersible in organic solvents or mixtures, organic solvents or mixtures may be used. In the case of organically developable precursors different organic solvents or their mixtures may be used.

Whilst the principles of the invention have been set out above in connection with specific embodiments, it is to be understood that this description is merely made by way of example and not as a limitation of the scope of protection which is determined by the appended claims.