Device for attaching a printing plate to a printing cylinder

Abstract

Device (1) for attaching a printing plate to a printing cylinder, wherein the device comprises a cylindrical support with a surface oriented towards the printing plate and a pressure-sensitive adhesive layer arranged on this surface, wherein the pressure-sensitive adhesive layer has a surface oriented towards the printing plate and this surface comprises at least one more strongly adhesive region (3) and at least one less strongly adhesive region (2), in each case based on the adhesive strength to PET, determined as described herein; characterized in that the more strongly adhesive region (3) has a ratio of its maximum extent parallel to the axis of rotation of the carrier to its maximum extent perpendicular to the axis of rotation of the carrier of at least 3:1.

Description

[0001] The present invention relates to the technical field of flexographic printing. More specifically, the invention proposes a device for attaching a printing plate to a printing cylinder, said device comprising a cylindrical support and a pressure-sensitive adhesive layer, which in turn comprises at least one more strongly adhesive and at least one less strongly adhesive region. The more strongly adhesive region has a specific ratio of its maximum extent parallel to the support's axis of rotation to its maximum extent perpendicular to the support's axis of rotation.

[0002] In a typical flexographic printing process, one or more flexible printing plates made of photopolymer or rubber are attached to a printing cylinder. The printing plates have a relief that corresponds to the information to be applied. During the actual printing process, the printing plates pass through an ink reservoir, where the relief absorbs the printing ink. The printing cylinder then transports the printing plate to a transfer unit, where the ink-wetted surface comes into contact with the substrate to be printed. When the printing plate is removed from the substrate, the ink film splits and leaves an imprint corresponding to the relief on the printing plate surface. This ink transfer requires precise application of pressure when applying the printing plate to the substrate, as this pressure largely determines the uniformity of the printed image.

[0003] There are several known methods for attaching a printing plate to a printing cylinder. The most common method is the use of double-sided adhesive tape. A second method involves the use of a sleeve or similar device permanently equipped with an adhesive surface to secure the printing plate.

[0004] The use of double-sided adhesive tape is problematic in that it can be difficult to remove the tape from the printing cylinder and / or the printing plate. Furthermore, the double-sided adhesive tape often leaves residue that impairs the later reuse of the printing plate or impairs print performance in subsequent printing runs. It is often difficult to achieve a uniform application of the double-sided adhesive tape without surface irregularities that affect the printed image. Furthermore, the use of multiple double-sided adhesive tapes—which is usually necessary—complicates the alignment of the printing plate on the printing cylinder, particularly since removal and repositioning are difficult.

[0005] WO 95 / 19267 A1 discloses a fastening means for attaching a flexographic printing plate to a plate cylinder, characterized by a flexible carrier layer and an adhesive photopolymer layer supported by the carrier layer and fully exposed. Thus, WO 95 / 19267 A1 describes the use of an adhesive-coated plate cylinder as a replacement for double-sided adhesive tapes. The general term "adhesive" is used here in the sense of "permanently sticky." The document mentions that the adhesive-coated plate cylinder can retain its adhesive properties even with continued use and reuse, and that residues can be easily removed, leaving no residual photopolymer material on the printing plate. However, there is no specific teaching on the chemistry and manufacturing process of the adhesive-coated plate cylinder, except that it is photopolymeric.

[0006] WO 2010 / 090685 A1 describes a method for releasably attaching a printing plate to a printing cylinder, wherein the method a) attaching a photopolymer plate to the printing cylinder, the photopolymer plate having first and second major surfaces opposite each other, the first major surface being in contact with and attached to the printing cylinder, the first and second major surfaces having a surface adhesion of at least 600 g according to ASTM Standard D-2979-95; b) bringing the printing plate into contact with and securing it to the second main side; where the photopolymer plate a) a binder; b) at least one monomer; c) photoinitiator; and d) microspheres with a diameter of less than 90 micrometers.

[0007] Thus, the tackiness of the photopolymer is used to attach itself to the printing cylinder and to secure the printing plate to it. Microspheres are incorporated into the photopolymer plate to provide a cushioning effect when used in the printing press. The photopolymer layer described in this document is produced by mixing the components of the photopolymer and curing the composition after casting or extruding it into a plate, followed by UV irradiation. The document states that the amount of radiation required varies depending on the composition and thickness of the photopolymer and that the amount of radiation used, and thus the degree of curing, can be used to control the tackiness of the photopolymer. However, the curing must be sufficient to achieve adequate strength and rigidity.This is particularly necessary because the photopolymer layer of this document does not contain a supporting substrate; instead, the extruded photopolymer layer is attached directly to the printing cylinder.

[0008] With such a layer, due to the adhesive attachment of the printing cylinder on the one hand and the printing plate on the other hand to the opposite sides of the photopolymer plate, the photopolymer layer may detach from the printing cylinder when the printing forme is removed, as the adhesion may be equally strong on both sides. In addition, if the adhesion is strong, damage to the surface supporting the printing plate may occur when the printing plate is removed or replaced, reducing the lifespan of the photopolymer plate. If the adhesion is not strong enough, the printing plate may detach from the printing cylinder during operation. In addition, the presence of microspheres may impair the adhesive properties of the layer and lead to irregularities on the surface that are transmitted through the printing forme, potentially reducing print quality and / or causing offset.

[0009] US 2021 / 0214589 A1 discloses an adhesive printing plate mounting layer comprising a carrier and a permanently tacky layer disposed on the carrier, wherein the permanently tacky layer comprises a crosslinked polyurethane-based material.

[0010] The use of printing plate attachment devices, such as sleeves permanently coated with a pressure-sensitive adhesive layer to secure a printing plate to a printing cylinder, is therefore well known. In the flexographic printing industry, campaigns of varying lengths are printed. Since the printing plates and print quality requirements vary depending on the material to be printed, foamed adhesive tapes typically provide a secure bond between the printing plate and the printing cylinder. However, adhesive tapes only offer a one-time solution. In contrast, permanently adhesive devices can offer significant advantages in terms of cost and sustainability, as the printing plate can be removed and replaced with another printing plate after printing. However, some basic requirements must be met.

[0011] The mounting of the printing plates must be simple and safe. Furthermore, the frequently observed detachment of the edges of the printing plates from the printing cylinder must be prevented, as this compromises a clean print image.

[0012] Furthermore, the printing plates should be easy to remove from the mounting fixture without causing damage. The minimal force required for this allows for a comfortable removal process for the operator and reduces the risk of irreversibly damaging the printing plate.

[0013] However, high holding force during the printing process and easy removal afterwards represent contradictory requirements, neither of which can be fully met.

[0014] It was an object of the present invention to provide a device for attaching a printing plate to a printing cylinder that offers a well-balanced and optimized holding force during printing and easy, damage-free removal after printing. The improved removal of the printing plate should be simple and reproducible for the respective operator.

[0015] Another object of the invention was to provide a device for attaching a printing plate to a printing cylinder which reduces the tendency for edge lifting of the printing plate.

[0016] An additional aim of the invention was to enable improved print quality over many prints with one printing plate and / or after reuse with many printing plates.

[0017] The solution to these problems is based on the basic idea of ​​the present invention, according to which the printing plate fastening device should be equipped with at least two regions of a pressure-sensitive adhesive layer which have different adhesive strengths, and the region with the stronger adhesive strength should have a specific geometry with a larger extension parallel to the axis of rotation of the carrier.

[0018] The above objects are achieved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention emerge from the dependent claims and the following statements.

[0019] Embodiments that are referred to as preferred below are combined in particularly preferred embodiments with features of other embodiments that are referred to as preferred. Therefore, combinations of two or more of the embodiments referred to as particularly preferred below are very particularly preferred. Also preferred are embodiments in which a feature of one embodiment that is referred to as preferred to any extent is combined with one or more further features of other embodiments that are referred to as preferred.

[0020] To the extent that both specific amounts or proportions of an element and preferred embodiments of the element for this element are disclosed below, in particular the specific amounts or proportions of the preferably configured elements are also disclosed. Furthermore, it is disclosed that, in the corresponding specific total amounts or total proportions of the elements, at least some of the elements can be preferably configured, and in particular also that preferably configured elements can in turn be present in the specific amounts or proportions within the specific total amounts or total proportions.

[0021] A first and general object of the present invention is a device for fixing a printing plate to a printing cylinder, wherein the device comprises a cylindrical support with a surface oriented towards the printing plate and a pressure-sensitive adhesive layer arranged on this surface, wherein the pressure-sensitive adhesive layer has a surface oriented towards the printing plate and this surface comprises at least one more strongly adhesive region and at least one less strongly adhesive region, in each case based on the adhesive strength to PET, determined as described herein; which is characterized by the more strongly adhesive area has a ratio of its maximum extent parallel to the axis of rotation of the carrier to its maximum extent perpendicular to the axis of rotation of the carrier of at least 3:1.

[0022] The surface of the pressure-sensitive adhesive layer oriented toward the printing plate therefore comprises at least two areas with different adhesive strengths to PET. Since the printing plates used in flexographic printing are generally made of PET, adhesive strengths determined on PET films, for example, are representative of the adhesive strengths achieved with printing plates. In particular, the differences in adhesive strength determined on PET films are representative of the differences in adhesive strength compared to a printing plate.

[0023] The area with the stronger adhesive strength to PET or to the printing plate also has an extension parallel to the axis of rotation of the carrier that is at least three times greater than that perpendicular to it; it is therefore present as a strip that extends primarily in the direction of the axis of rotation. Since the printing plates are usually attached circumferentially to the cylindrical carrier so that their ends abut one another or at least come very close, they can be mounted so that their ends rest on the strip of the more strongly adhesive area and are held in place by it. This counteracts the tendency, which is most pronounced at the ends of the printing plates, to stand up and then detach from the carrier again. The remaining bonded area can be designed with a weaker adhesive, thus enabling easy and non-destructive removal of the printing plate after the printing process.The stronger adhesive force is therefore only effective where it is really needed, namely in the area of ​​the printing plate ends, while the weaker adhesive area is located where it would be more of a hindrance when removing the plate.

[0024] The device according to the invention comprises a cylindrical carrier with a pressure-sensitive adhesive layer applied thereto. Such devices for attaching a printing plate to a printing cylinder are generally known to those skilled in the art as "sleeves." A device according to the invention is therefore preferably a sleeve for attaching a printing plate to a printing cylinder. The inner diameter of such a sleeve is generally adapted to the diameter of the printing cylinder in order to tightly enclose it.

[0025] The cylindrical support - also referred to as "substrate" - can generally be a single layer, but preferably comprises two or more layers, each of which performs specific functions.

[0026] The cylindrical support preferably comprises a base. The base is preferably a cylindrical body made of metals such as aluminum, polymers, or preferably a combination of different materials. For example, the base can consist of fiberglass or carbon fiber fabrics encapsulated with epoxy resins and further coated with a polyurethane coating. Thus, the base is preferably made of a composite material. In terms of its function, the base is the connecting element between the printing press and all other functional layers of the device according to the invention; moreover, the base preferably provides the device with stability and dimensional accuracy.

[0027] The carrier preferably comprises a foam layer. The foam layer has a defined hardness and density and can thus cushion the forces occurring during the printing process, thereby ensuring the desired compressibility of the printing plate and thus the print quality. The foam layer is particularly preferably an open-cell polyurethane foam with a thickness of 1,200 µm - 1,800 µm. The foam layer is preferably provided with an adhesive layer on one or both main surfaces to ensure firm contact with the base and / or another functional layer. The foam layer is particularly preferably provided with a pressure-sensitive adhesive layer on one or both main surfaces. Therefore, the foam layer can be regarded as the central layer of a single-sided or double-sided adhesive tape, and the carrier of the device according to the invention preferably comprises a double-sided foamed adhesive tape.The pressure-sensitive adhesive layers can ensure firm contact of the foam layer with the base on its underside and with other parts of the device or carrier, e.g. a reinforcing film, on its upper side.

[0028] The support preferably comprises one or more reinforcing films. More preferably, the reinforcing films have a thickness of 20-150 µm. More preferably, the reinforcing films are polyester films, preferably poly(ethylene terephthalate) (PET) films. A reinforcing film can increase the stability of a multilayer support laminate and also protect the foam layer from damage when the printing plate is removed from the device.

[0029] Very preferably, the cylindrical carrier comprises one or more of the functions listed above and thus very preferably comprises a base, a foam layer, and one or more reinforcing films. More preferably, the carrier comprises a base, a double-sided foamed adhesive tape, and one or more reinforcing films. It will be understood by those skilled in the art that the carrier may comprise even more functional layers than those mentioned above; for example, the carrier may comprise multiple intermediate layers.

[0030] A device according to the invention further comprises a pressure-sensitive adhesive layer arranged on the surface of the carrier oriented towards the printing plate, which layer has a surface oriented towards the printing plate.

[0031] According to the general technical understanding, a pressure-sensitive adhesive is an adhesive that exhibits pressure-sensitive properties, i.e. can form a permanent bond to a substrate even under relatively low contact pressure. Without wishing to be bound by this theory, it is often assumed that a pressure-sensitive adhesive can be regarded as an extremely viscous liquid with an elastic component, which consequently exhibits characteristic viscoelastic properties that lead to the permanent inherent tack and pressure-sensitive adhesive capacity described above. It is assumed that with pressure-sensitive adhesives, mechanical deformation results in both viscous flow processes and the build-up of elastic restoring forces. The partial viscous flow serves to achieve adhesion, while the partial elastic restoring forces are particularly necessary to achieve cohesion.The relationships between rheology and pressure-sensitive adhesive strength are known in the art and are described, for example, in Satas, "Handbook of Pressure Sensitive Adhesive Technology", 3rd edition (1999), pages 153 to 203. To characterise the degree of elastic and viscous components, the storage modulus (G') and the loss modulus (G'') are usually used, which can be determined by means of dynamic mechanical analysis (DMA), for example using a rheometer. In the context of the present invention, a pressure-sensitive adhesive is preferably understood to be pressure-sensitively adhesive and thus a pressure-sensitive adhesive if, at a temperature of 23°C in the deformation frequency range of 10 0 up to 10 1 rad / sec G' and G'' each at least partly in the range of 10 3 up to 10 7 Pa lie.

[0032] In addition to its function as an adhesive for bonding the printing plate, the pressure-sensitive adhesive layer can also provide additional cushioning, which can further improve print quality.

[0033] According to the invention, the surface of the pressure-sensitive adhesive layer oriented toward the printing plate comprises at least one stronger and at least one weaker adhesive region, each based on the adhesive strength to PET. Thus, a device according to the invention does not fundamentally comprise a single continuous pressure-sensitive adhesive layer, but rather a segmented pressure-sensitive adhesive layer with at least two different zones that have different adhesive properties. This concept advantageously enables the design of the device with - at least one zone that can be considered as a “mounting zone” with higher adhesive strength, which enables the holding force and easy attachment of the printing plate, and - at least one further zone which can be considered as a “disassembly zone” with lower adhesive strength, which allows easy removal of the printing plate after the printing process.

[0034] The specific geometry of the more strongly adhesive area now makes it possible to concentrate the “assembly zone” on the area of ​​the joint between the two printing plate ends, which is particularly susceptible to bonding disruptions, and to designate the remaining bonding area as the “disassembly zone”.

[0035] A "region" is considered a portion of the pressure-sensitive adhesive layer's surface facing the printing plate that is geometrically separated from other portions of that surface. Although the bond strength is described herein with respect to the surface of the pressure-sensitive adhesive layer, one skilled in the art will understand that the bond strength results from the nature of the entire pressure-sensitive adhesive layer on which the respective surface region is based.

[0036] In principle, there can be two or more areas, each of which has a different adhesive strength to PET and thus to the printing plate. Thus, in principle, there can be several stronger adhesive and / or several weaker adhesive areas. In particular, the surface of the pressure-sensitive adhesive layer oriented toward the printing plate—depending on the number of printing plates to be bonded to the device—can comprise several stronger adhesive areas distributed over the remaining surface, which is designed as a weaker adhesive area.

[0037] Preferably, the weaker adhesive region or the totality of the weaker adhesive regions forms at least 70%, more preferably at least 75%, particularly preferably at least 80%, in particular at least 85% of the surface of the pressure-sensitive adhesive layer oriented toward the printing plate. The more strongly adhesive region(s) can thus be concentrated only in the area around the end edge joint of the printing plates. This significantly facilitates the removal of the printing plates after the printing process because the bond can be designed such that higher adhesive forces only have to be overcome in the area of ​​the joint, while the printing plate can otherwise be removed comparatively easily.

[0038] Accordingly, the more strongly adhesive region preferably has a maximum extent perpendicular to the axis of rotation of the carrier of 25%, more preferably of 20%, in particular of 15% of the total circumference of the carrier.

[0039] In one embodiment of the invention a) the more strongly adhesive area has different dimensions perpendicular to the axis of rotation of the support, the smallest dimension being at least 30% smaller than the largest dimension and the less strongly adhesive area being adjacent to the more strongly adhesive area where the boundary line of the more strongly adhesive area runs below its largest dimension, and / or b) the more strongly adhesive area has at least one recess with a less strongly adhesive design, and / or c) several more strongly adhesive areas are arranged in a row parallel to the axis of rotation of the carrier in such a way that there is at least one weaker adhesive area between them.

[0040] All three variants a) - c) of this embodiment offer the possibility of arranging the weaker adhesive areas in such a way that the user of the device according to the invention has a "grip" for detaching the printing plate after the printing process has been completed. The weaker adhesive areas can, for example, be arranged in these variants in such a way that the user has the option of reaching the edge or under the edge of the printing plate with a finger or a tool and slightly lifting it, since it is only weakly adhesively fixed in that area. This makes it easy to set a starting point for the further detachment process by allowing the user to exert a controlled peel force on the more strongly adhesive areas and, moreover, to benefit from the fact that larger areas of the bond are designed with weaker adhesive.

[0041] Regardless of other embodiments, the entirety of the weaker and stronger adhesive regions preferably completely covers the surface of the carrier oriented toward the printing plate. This means that the pressure-sensitive adhesive layer is not interrupted in its surface oriented toward the printing plate, but rather lies as a continuous layer on the surface of the carrier oriented toward the printing plate. Accordingly, the surface of the carrier oriented toward the printing plate is preferably not exposed at any point.

[0042] Preferably, the difference in adhesive strength between a more strongly adhesive and a less strongly adhesive region is at least 0.5 N / cm, more preferably 0.5 to 2.5 N / cm, particularly preferably 0.7 to 2.3 N / cm and in particular 0.9 to 2.1 N / cm.

[0043] The different adhesive strengths of the stronger and weaker adhesive areas within the surface of the pressure-sensitive adhesive layer oriented towards the printing plate can be realized in different ways.

[0044] In one embodiment, the different adhesive strength of a stronger and a weaker adhesive area is achieved by using different pressure-sensitive adhesives. "Different pressure-sensitive adhesives" are understood to mean pressure-sensitive adhesives of different chemical nature, e.g., pressure-sensitive adhesives, • which comprise base polymers belonging to different polymer classes; or which comprise base polymers belonging to the same polymer class but based on different monomer compositions; or • which comprise different additives that impart different adhesive properties, e.g. different adhesive resins or the same adhesive resins but in different concentrations; or • which differ in the type and / or amount of a chemical crosslinker used.

[0045] Likewise, any combination of the aforementioned methods can be used. Accordingly, layers of different pressure-sensitive adhesives can be applied side by side to the carrier. This can be achieved, for example, by a process comprising the steps - Laminating layers of different pressure-sensitive adhesives onto temporary carrier materials, - Laminating the layers onto the carrier in the desired geometry and - Filling the seams with non-crosslinked pressure-sensitive adhesive, which is then crosslinked to bond the layers.

[0046] In a further embodiment, the different adhesive strength of a stronger and a weaker adhesive region is achieved by different surface structures of the otherwise identical pressure-sensitive adhesive. For example, a smooth surface can have a comparatively high adhesive strength, while a rough, structured surface of the otherwise identical pressure-sensitive adhesive can have a reduced adhesive strength. A structured surface of the pressure-sensitive adhesive can be achieved by applying an auxiliary agent, which has a microstructure in its surface, to the pressure-sensitive adhesive layer, thus forming the replication of this structure in its surface. This can be achieved by a method selected from the group consisting of - Coating the pressure-sensitive adhesive onto a tool with an embossed microstructure, - Coating the pressure-sensitive adhesive onto a release liner having the microstructure, and - Passing through a roller, whereby the pressure-sensitive adhesive is pressed against a release liner which has the microstructure. The desired topography can be formed in tools using one of the generally known techniques, which depend on the tool material and the characteristics of the desired topography. Example techniques include etching, e.g. chemical etching, mechanical etching or other abrasive processes such as laser ablation or reactive ion etching; photolithography; stereolithography; micromachining; knurling, e.g. cutting knurling or acid-assisted knurling; scribing and cutting. The structuring of the surface can be achieved by introducing grooves, which reduces the contact area between the pressure-sensitive adhesive and the printing plate. Different surface structures can be created, for example, using differently structured release liners with which the not yet fully cured pressure-sensitive adhesive is covered.One of these release liners may have a smooth surface, while the other has a textured surface with a multitude of elevations, which are then replicated in the surface of the pressure-sensitive adhesive layer.

[0047] In a further embodiment, the different adhesive strengths of a stronger and a weaker adhesive region are achieved by different physical and / or chemical treatment, such as radiation crosslinking by means of UV radiation or electron irradiation, of different segments of the otherwise identical pressure-sensitive adhesive. Preferably, the different adhesive strengths of a stronger and a weaker adhesive region are achieved by different UV irradiation of the otherwise identical pressure-sensitive adhesive. This embodiment may therefore require that the pressure-sensitive adhesive be radiation-crosslinkable, more preferably UV-crosslinkable. Different adhesive strengths can then be achieved by using different irradiation profiles for different segments of the pressure-sensitive adhesive layer. This, in turn, can be achieved by selective activation of the radiation sources.This method advantageously allows the entire carrier surface to be coated with the same non-crosslinked pressure-sensitive adhesive; only the different treatment of the segments is then required.

[0048] Alternatively, and particularly preferably, the different adhesive strength of a stronger and a weaker adhesive area is achieved by selectively exposing at least one area of ​​the surface of the pressure-sensitive adhesive oriented towards the printing plate to treatment with UV-C radiation. UV radiation, as usually used to crosslink pressure-sensitive adhesives, is UV-A radiation. Compared to UV-A radiation, UV-C radiation penetrates the adhesive to a much lower depth. Irradiation with UV-C therefore leads to strong crosslinking in the adhesive surface, which consequently loses a significant amount of flowability and is therefore only tacky to a very low degree. The treated area thus becomes less adhesive, while one or more other areas are protected from exposure, for example by covering with a UV-absorbing film, and can remain as more adhesive areas.Alternatively, the above-mentioned different treatment of the different areas can be achieved by selective activation or shielding of the radiation source.

[0049] The pressure-sensitive adhesive layer of the device according to the invention can be based on one or more polymers selected from the group consisting of poly(meth)acrylates, vinylaromatic block copolymers, natural rubbers, polyolefins, hydrogenated polyolefins, polyurethanes, and mixtures of two or more of the aforementioned polymers. Furthermore, the pressure-sensitive adhesive layer can contain one or more additives such as tackifier resins, plasticizers, fillers, antioxidants, etc., as are generally known in the art.

[0050] Regardless of the various methods for achieving different adhesive strengths as described above, the pressure-sensitive adhesive layer of the device according to the invention preferably comprises one or more polyurethanes. In their uncrosslinked state, the polyurethanes preferably each have two or more crosslinkable groups, which are particularly preferably ethylenically unsaturated groups. Polyurethanes generally contain two or more -NHC(O)O- bonds (urethane bonds) obtained by the reaction of a hydroxy group and an isocyanate group. Polyurethanes are usually formed by the reaction of a polyol and a polyisocyanate, e.g., by the reaction of a diol and a diisocyanate. The reaction between a hydroxy group and an isocyanate group results in an -NHC(O)O- bond, and at least two NHC(O)O- bonds are formed when a polyol reacts with a polyisocyanate.This reaction is generally known in the art for the production of polyurethanes (PU).

[0051] The monomer composition on which a polyurethane of the pressure-sensitive adhesive layer of the device according to the invention is based may additionally comprise one or more (meth)acrylate monomers that can introduce additional crosslinking sites into the polyurethane. Furthermore, the precursor composition on which the pressure-sensitive adhesive layer is based, i.e., the uncrosslinked composition for forming the pressure-sensitive adhesive layer (hereinafter also referred to as "PSA precursor composition"), may also contain a thermal or photosensitive polymerization initiator for initiating a crosslinking reaction. Furthermore, the PSA precursor composition may also contain a solvent, a polymerization inhibitor to prevent premature crosslinking, a plasticizer, a rheology modifier, a desiccant, and / or other additives, as are generally known to those skilled in the art.

[0052] The pressure-sensitive adhesive layer preferably comprises one or more polyurethanes in a total amount of at least 50% by weight, preferably at least 60% by weight, particularly preferably at least 70% by weight, in particular at least 80% by weight, e.g. at least 85% by weight, and most preferably at least 90% by weight, based on the total weight of the pressure-sensitive adhesive layer.

[0053] A polyurethane of the PSA precursor composition, i.e. a polyurethane of the pressure-sensitive adhesive in its uncrosslinked state, preferably comprises at least two crosslinkable groups, more preferably at least two ethylenically unsaturated groups. These groups can be introduced into the polyurethane by first forming the polyurethane and then modifying it by reaction with a compound (modifier compound) capable of introducing the crosslinkable groups into the polyurethane. Such introduction can be effected by the reaction of the modifier compound with unconsumed hydroxyl and / or isocyanate groups present at the chain ends of the polyurethane. For example, if the polyurethane is derived from the reaction of a diol and a diisocyanate and is thus linear, the introduction of the crosslinkable groups, such asethylenically unsaturated groups, by reacting the polyurethane polymer with a modifier compound having a crosslinkable group and either an isocyanate group or a hydroxy group, or both. For example, a terminal isocyanate group can react with a hydroxy-containing (meth)acrylate compound to introduce an ethylenically unsaturated group. Such modification is preferably carried out to introduce at least two crosslinkable groups. This can be achieved by using the same type of reaction with the same modifier compound if a polyurethane has at least two groups per molecule that can react with the modifier compound. In this case, at least two equivalents of the modifier compound are used relative to one equivalent of the unmodified polymer.Of course, it is also possible to use two or more different modifier compounds that react with two or more different groups on the unmodified polymer.

[0054] Alternatively, the crosslinkable groups can be introduced into the polyurethane polymer by using a suitable starting compound for polyurethane synthesis, such as a polyol (e.g., a diol or triol) and / or a polyisocyanate (e.g., a diisocyanate or triisocyanate) having one or more crosslinkable groups. These groups can then remain unchanged during the formation of the polyurethane polymer and later undergo a crosslinking reaction after suitable initiation, e.g., radically. Preferably, the monomer composition on which a polyurethane of the pressure-sensitive adhesive layer of the device according to the invention is based comprises a (meth)acrylate diol, particularly preferably a dihydroxyalkyl (meth)acrylate, e.g., 2,3-dihydroxypropyl methacrylate.

[0055] In general, the crosslinkable groups can be freely chosen, but must not be hydroxyl groups, isocyanate groups, and of course, -NHC(O)O groups. Preferably, a polyurethane of the PSA precursor composition, i.e., a polyurethane of the pressure-sensitive adhesive in its uncrosslinked state, comprises at least two crosslinkable groups capable of undergoing a radically or ionically initiated crosslinking reaction, more preferably a radically initiated crosslinking reaction. Thus, while the crosslinking groups can be selected, for example, from those capable of reacting with the same or another crosslinking group in another molecule of the PSA precursor composition, such as epoxy groups or alcohol / carboxylic acid combinations to form an ester bond, the crosslinkable groups are preferably ethylenically unsaturated groups.The reason for this is that, with appropriate initiation, the ethylenically unsaturated groups react via a radical mechanism and can also react to some extent with the polymer backbone of the polyurethane in a radical chain reaction. This is considered preferable because it eliminates the need to achieve precise alignment of the reactive groups, as the radical reaction allows for the formation of a variety of crosslinks with appropriate initiation.

[0056] The polyols and polyisocyanates used for the polyurethane backbone are generally not further limited. In one embodiment, the polyurethane is linear and thus made from one or more diols and one or more diisocyanates. The polyurethane backbone can be obtained from only one diol, or a mixture of two or more diols and only one diisocyanate, or a mixture of two or more diisocyanates. Thus, the polyurethane backbone can be obtained from a diol and a diisocyanate, from a combination of two or more diols with a diisocyanate, from a combination of two or more diisocyanates with a diol, and from a combination of two or more diisocyanates with two or more diols.

[0057] Useful diols include smaller diols with a molecular weight of 500 or less, such as ethylene glycol and propylene glycol, but also larger diols with a molecular weight greater than 500 or more, or 600 or more, or 1000 or more, but generally 10,000 or less, such as 8,000 or less or 6,000 or less, e.g., 5,000 or less, to maintain polyurethane properties. "Molecular weight," in the case of polymeric compounds with a molecular weight distribution, is understood here to mean the weight-average molecular weight.

[0058] Examples include homopolymers and copolymers of two or more ethylenically unsaturated compounds, preferably selected from the group consisting of styrenes, alkenes, and polyenes having 2 to 12 carbon atoms and cycloalkenes having 3 to 12 carbon atoms, such as ethylene, propylene, n-butene, isobutene, 1-pentene, 2-pentene, 2-methylbut-1-ene, 1,3-butadiene, 1,3-, 1,4-, and 1,5-hexadiene, styrene, and α-methylstyrene, and their copolymers functionalized by modification with two (usually terminal) hydroxy groups. An example is a homopolymer of ethylene, propylene, 1-butene, isobutylene, or 1,3-butadiene, or a copolymer of two or more of these compounds into which two hydroxy groups have been inserted terminally. A polymer derived from a polyene, such as polybutadiene, is typically hydrogenated before being treated with, for example,two terminal hydroxy groups to make it less susceptible to degradation processes; however, in the context of the present invention, a non-hydrogenated polybutadiene can also be used and subsequently functionalized with, for example, two terminal hydroxy groups, since it already provides reactive groups for a subsequent crosslinking reaction.

[0059] Other examples of large diols include polyether polyols and polyester polyols, with polyether polyols being preferred because polyester polyols are generally more susceptible to hydrolysis and polyether polyols provide better adhesive properties. Specific examples include polytetramethylene glycol (PTMO), polypropylene oxide (PPO) glycol, and polyethylene glycol (PEG). For both polyester polyols and polyether polyols, the number of repeating units is typically 50 or more, such as 100 or more or 200 or more, but generally 1000 or less, such as 800 or less.

[0060] The diisocyanates can also be selected from diisocyanates known for the production of polyurethanes, for example, aromatic diisocyanates, e.g., methylene diphenyl diisocyanate (MDI) and hydrogenated MDI in all stereoisomeric forms such as 2,2'-, 2,4'-, and 4,4'-; and toluene diisocyanate (TDI), of which all stereoisomers such as 2,4'- and 2,6'- can be used. Alternatively, and preferably, aliphatic diisocyanates are used because they can reduce environmental impact and are less likely to cause health risks. Examples include 1,4-butane diisocyanate (BDI), 1,6-hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate (TMDI), ethyl 2,6-diisocyanatohexanoate (ELDI), methyl 2,6-diisocyanatohexanoate (MLDI), isophorone diisocyanate (IPDI), 1,4-cyclohexane diisocyanate and lysine diisocyanate.

[0061] Similar to diols, diisocyanates can be compounds with a small (500 or less) or large molecular weight, e.g., with a molecular weight of more than 500, 600 or more, or 1,000 or more, but generally 10,000 or less, such as 8,000 or less, or 6,000 or less, e.g., 5,000 or less, determined as the weight-average molecular weight in the case of a polymeric compound with a molecular weight distribution. These molecular weights allow the polyurethane properties to be well maintained.

[0062] Thus, while both the diols and the diisocyanates can each be selected from small molecules and large molecules as defined above, in one embodiment one of the diols or one of the isocyanates has a weight-average molecular weight Mw of 500 g / mol or less, and the other has a weight-average molecular weight Mw of more than 500 g / mol, preferably of 1,000 g / mol or more. In view of availability, preferably the polyol has a weight-average molecular weight Mw of more than 500 g / mol. As already mentioned, it is also possible to use more than one diol and / or more than one diisocyanate. Also in this case, preferably at least one of the two or more diols or at least one of the two or more diisocyanates has a weight-average molecular weight Mw of 500 g / mol or more, such as 1,000 g / mol or more.

[0063] In any case, the polyols and polyisocyanates can be of synthetic or natural origin. Examples of polyols of natural origin include sugars and other carbohydrates with two or more hydroxyl groups, or hydrogenated castor oil or a palm oil-based polyester polyol.

[0064] The PSA precursor composition preferably comprises a crosslinking initiator. "Crosslinking initiator" refers to a compound capable of initiating a crosslinking reaction by generating an ion or a radical upon heating or irradiation. Preferably, the crosslinking initiator is a UV initiator. The UV initiator can be selected from known UV initiators, e.g., from the group consisting of benzyl dimethyl ketal (IRGACURE® 651), benzoin isobutyl ether (BIBE), benzophenone and related derivatives, 2,2-diethoxyacetophenone, cyclohexyl phenyl ketone and derivatives thereof (IRGACURE® 184), and mono- and diacylphosphine oxide derivatives (IRGACURE® 819). The most preferred UV initiators are BIBE, IRGACURE® 184, and IRGACURE® 651, with BIBE being the most preferred. The concentration of the UV initiator can be between 0.1 and 3 wt.%, but is preferably between 1 and 2 wt.-%, based on the total weight of the PSA precursor composition, excluding the optional solvent. The UV initiator can be a compound, but a combination of UV initiators can also be used, e.g., with sensitivity to different wavelengths.

[0065] The PSA precursor composition optionally comprises a solvent. Preferably, the PSA precursor composition is solvent-free, since solvent evaporation reduces the volume of the layer formed from the PSA precursor composition and makes targeted thickness adjustment difficult. Solvent evaporation can also lead to a porous structure, which is undesirable. If present, the amount of solvent is typically 50 wt.% or less, preferably 25 wt.% or less, such as 15 wt.% or 10 wt.% or less. The solvent can be selected from known organic solvents, such as protic and aprotic solvents and mixtures thereof. The solvent preferably has a boiling point of 75°C or less at 10 5Pa. The solvent is preferably selected from ethers; alcohols; ketones and esters; e.g. from acetone, methyl ethyl ketone, ethyl acetate and methyl acetate; ethanol; methanol; isopropanol; tetrahydrofuran or diethyl ether.

[0066] The pressure-sensitive adhesive layer preferably comprises one or more crosslinked polyurethanes obtained from the crosslinking of a PSA precursor composition as described above, typically by initiation using heat or radiation. The pressure-sensitive adhesive layer preferably contains one or more crosslinked polyurethanes in a total amount of 80 wt.% or more, such as 90 wt.% or more or 95 wt.% or more, based on the total weight of the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer may also consist of the crosslinked polyurethanes.

[0067] The pressure-sensitive adhesive layer is preferably formed by applying the PSA precursor composition to a substrate and subsequently initiating the crosslinking reaction. Forming the pressure-sensitive adhesive layer may also include heating the PSA precursor composition to evaporate any solvent and / or unreacted monomer.

[0068] The thickness of the pressure-sensitive adhesive layer is not further limited as long as the object of the present invention is achieved, but is preferably 1.00 mm or less, more preferably 0.90 mm or less, 0.80 mm or less, 0.70 mm or less, 0.60 mm or less, 0.50 mm or less, or 0.45 mm or less. The lower limit is not fundamentally specified, but is preferably 0.05 mm or more, such as 0.10 mm or more, 0.15 mm or more, or 0.20 mm or more, such as 0.25 mm or more.

[0069] The pressure-sensitive adhesive layer is preferably free of microspheres.

[0070] In one embodiment, the stronger adhesive area is identifiable to the human eye without further aids. This can be achieved by appropriately marking the stronger and / or weaker adhesive area. Such an identification mark enables easy identification of the stronger and weaker adhesive areas and can therefore assist the operator or the machine that mounts or dismounts the printing plate in identifying "mounting" and "dismounting" zones. The identification mark can be created, for example, by color coding. Preferably, identifiability according to the present embodiment is achieved by color marking and / or writing. For example, the reinforcing film of the carrier can be printed with specific colors, shapes, or writing that are visible through the translucent pressure-sensitive adhesive layer.Thus, the stronger and / or weaker adhesive area can be visibly highlighted by color coding or writing that corresponds to the outline of the respective area.

[0071] Another subject of the invention is a composite comprising a printing cylinder, a device according to the invention mounted thereon and a printing plate mounted on the device.

[0072] In one embodiment, this composite is designed so that i) the printing plate is mounted on the device in the direction of rotation about the axis of rotation of the support in such a way that i1) their two ends are positioned butt-to-butt, i2) the more adhesive area of ​​the pressure-sensitive adhesive layer underlies at least the contact area of ​​the two ends of the printing plate; j) in the device according to the invention j1) the more strongly adhesive area has different dimensions perpendicular to the axis of rotation of the carrier, the smallest dimension being at least 30% smaller than the largest dimension and the less strongly adhesive area being adjacent to the more strongly adhesive area where the boundary line of the more strongly adhesive area runs below its largest dimension, and / or j2) the more strongly adhesive area has at least one recess with a less strongly adhesive design, and / or j3) several more strongly adhesive areas are arranged in a row parallel to the axis of rotation of the carrier in such a way that at least one weaker adhesive area is located between them; and k) all - weaker adhesive areas between two stronger adhesive areas arranged in series parallel to the axis of rotation of the carrier and / or - less adhesive recesses in the more adhesive area and / or - boundary lines between the weaker adhesive area and the more adhesive area in the course below its greatest extent, at least where they border on or intersect the contact area of ​​the two ends of the printing plate, are marked so as to be perceptible to the human eye without further aids.

[0073] This makes it very easy for the printing machine operator to identify the weaker adhesive areas as “handles” in order to be able to gently remove the printing plate from the carrier in the manner already described here.

[0074] The invention is described below with reference to Fig. 1 to 5 are explained in more detail.

[0075] Fig. Figure 1 shows a device 1 according to the invention, which has a pressure-sensitive adhesive layer on the surface of the cylindrical support oriented toward the printing plate, the surface of which is divided into a weaker adhesive region 2 and a stronger adhesive region 3. A printing plate can be bonded circumferentially around the device in such a way that its edges bordering the printing plate in the circumferential direction abut one another in the stronger adhesive region. Thus, the stronger adhesive force is localized in the area of ​​the edges, where the greatest tendency to detach exists, while the remaining area is designed to be weaker adhesive, thus facilitating the detachment of the printing plate.

[0076] The Fig. 2 and Fig. 3 show embodiments of a device 1 according to the invention, in each of which the more strongly adhesive region 3 has different dimensions perpendicular to the axis of rotation of the carrier, the smallest dimension being at least 30% smaller than the largest dimension and the less strongly adhesive region 2 adjoins the more strongly adhesive region 3 where the boundary line 4 of the more strongly adhesive region runs below its largest dimension.

[0077] In the embodiment according to Fig. 2, the different extent of the more strongly adhesive area 3 perpendicular to the axis of rotation of the carrier is realized by the course of the boundary lines 4 between the more strongly and less strongly adhesive areas 3 and 2, which tapers towards the edges of the device 1.

[0078] In the embodiment according to Fig. 3, the more strongly adhesive region 3 has depressions 5 along its course parallel to the rotation axis of the carrier, in which depressions the less strongly adhesive region 2 protrudes into the more strongly adhesive region 3 and borders it along the boundary line 4. For the more strongly adhesive region 3, a minimum extension b can be determined perpendicular to the rotation axis of the carrier as the distance between two depression bottoms and a maximum extension a in the regions without depressions 5.

[0079] The area of ​​the recesses 5 can serve as a handle for the operator when removing the glued printing plate.

[0080] The Fig. 4 shows an embodiment of a device 1 according to the invention, in which the more strongly adhesive region 3 has recesses 6 designed to be less adhesive, which may or may not be identical to the less strongly adhesive region 2 with regard to the underlying pressure-sensitive adhesive layer.

[0081] The recesses 6 can also serve as handles for the operator when removing the glued printing plate.

[0082] Fig. Figure 5 shows an embodiment of a device 1 according to the invention, in which several more strongly adhesive regions 3 are arranged in series parallel to the axis of rotation of the carrier such that at least one weaker adhesive region 7 is located between them. The weaker adhesive regions 7 may or may not be identical to the weaker adhesive region 2 with respect to the underlying pressure-sensitive adhesive layer.

[0083] The weaker adhesive areas 7 can serve as handles for the operator when removing the bonded printing plate. Measurement method - Determination of adhesive strength on PET

[0084] To determine the adhesive strength (peel strength), a reinforcing steel plate is first fitted with a double-sided adhesive tape. The pressure-sensitive adhesive layer to be tested is applied to an etched PET film (23 µm) and provided with a release liner. The resulting laminate is applied with the PET film side facing the double-sided adhesive tape. The release liner is removed to expose the free surface of the pressure-sensitive adhesive layer; a non-etched standard PET test film with a width of 20 mm is applied and secured by rolling back and forth five times with a 4 kg roller. The test assembly is secured, and the PET test film is peeled from the pressure-sensitive adhesive layer using a Zwick machine (Zwick Roell Z2.5) at an angle of 90° and a speed of 300 mm / min. The force required for this is determined using a tensile tester.The results are determined as an average of 3 samples, standardized to the width of the strips and expressed in N / cm. List of reference symbols 1 Device for attaching a printing plate to a printing cylinder 2 weaker adhesive area 3 stronger adhesive area 4 Boundary line 5 trough 6 recess with weaker adhesive 7 weaker adhesive area a largest extent of the more strongly adhesive area perpendicular to the rotation axis b smallest extent of the more strongly adhesive area perpendicular to the rotation axis QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 95 / 19267 A1

[0005] WO 2010 / 090685 A1

[0006] US 2021 / 0214589 A1

[0009] Cited non-patent literature

[0000] Handbook of Pressure Sensitive Adhesive Technology“, 3rd edition (1999), pages 153 to 203

[0031]

Claims

[1] Device (1) for attaching a printing plate to a printing cylinder, wherein the device comprises a cylindrical support with a surface oriented towards the printing plate and a pressure-sensitive adhesive layer arranged on this surface, wherein the pressure-sensitive adhesive layer has a surface oriented towards the printing plate and this surface comprises at least one more strongly adhesive region (3) and at least one less strongly adhesive region (2), in each case based on the adhesive strength to PET, determined as described herein; characterized by , that the more strongly adhesive region (3) has a ratio of its maximum extent parallel to the axis of rotation of the carrier to its maximum extent perpendicular to the axis of rotation of the carrier of at least 3:

1. [2] Device (1) according to claim 1, characterized bythat the weaker adhesive area (2) or the totality of the weaker adhesive areas (2) form at least 80% of the surface of the pressure-sensitive adhesive layer oriented towards the printing plate. [3] Device (1) according to one of claims 1 and 2, characterized by , that a) the more strongly adhesive region (3) has different dimensions (a), (b) perpendicular to the axis of rotation of the carrier, wherein the smallest dimension (b) is at least 30% smaller than the largest dimension (a) and the less strongly adhesive region (2) borders on the more strongly adhesive region (3) where the boundary line (4) of the more strongly adhesive region (3) runs below its largest dimension, and / or b) the more strongly adhesive area (3) has at least one recess (6) designed to be less adhesive, and / or c) several more strongly adhesive areas (3) are arranged in a row parallel to the axis of rotation of the carrier in such a way that at least one less strongly adhesive area (7) is located between them. [4] Device (1) according to one of the preceding claims, characterized by that the more strongly adhesive area (3) has a maximum extent (a) perpendicular to the axis of rotation of the carrier of 25% of the total circumference of the carrier. [5] Device (1) according to one of the preceding claims, characterized by that the totality of the weaker and stronger adhesive areas (2), (3) completely covers the surface of the carrier oriented towards the printing plate. [6] Device (1) according to one of the preceding claims, characterized by that the more adhesive area (3) is identifiable to the human eye without any further aids. [7] A composite comprising a printing cylinder, a device (1) mounted thereon according to any one of the preceding claims, and a printing plate mounted on the device (1). [8] Composite according to claim 7, characterized by , that i) the printing plate is mounted on the device in the direction of rotation about the axis of rotation of the support in such a way that i1) their two ends are positioned butt-to-butt, i2) the more strongly adhesive region (3) of the pressure-sensitive adhesive layer underlies at least the contact area of ​​the two ends of the printing plate; j) the device (1) is a device according to claim 3, and k) all - weaker adhesive areas (7) between two stronger adhesive areas (3) arranged in series parallel to the axis of rotation of the carrier and / or - recesses (6) of the more adhesive area (3) designed to be less adhesive and / or - boundary lines (4) of the weaker adhesive area (2) with the more strongly adhesive area (3) in the course below its greatest extent (a) are marked so as to be perceptible to the human eye without further aids, at least where they border on or intersect the contact area of ​​the two ends of the printing plate.

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