Adhesive printing forme attaching device

Abstract

The aim of the invention is to provide a device for attaching a printing plate to a printing cylinder, which device offers a uniform and optimized holding force during printing and easy removability after printing. This aim is achieved by using a device of this kind, which comprises a support (3, 4) and a layer of pressure-sensitive adhesive which is located on the support (3, 4) and has a surface (2, 5) facing the printing plate, with the surface (2, 5) of the layer of pressure-sensitive adhesive facing the printing plate comprising at least two regions (2, 5) having different adhesive forces on the printing plate.

Description

[0001] Adhesive die-casting mounting device

[0002] The present invention relates to the technical field of flexographic printing. More precisely, the invention proposes a printing plate mounting device (often simply referred to as a sleeve) for mounting a printing plate, wherein the printing plate mounting device is equipped with an adhesive layer having two or more areas with different adhesive strengths on the printing plate.

[0003] In a typical flexographic printing process, one or more flexible printing plates made of a photopolymer or rubber are attached to a printing cylinder. The printing plates have a relief that corresponds to the information to be transferred by printing. During the actual printing process, the printing plates are passed through an ink reservoir, where the relief absorbs the ink. The printing cylinder then rotates the printing plate to a transfer station, where the ink-containing surface comes into contact with the substrate to be printed. When the printing plate is removed from the substrate, the ink film splits, leaving an imprint that corresponds to the relief present on the printing plate surface. This ink transfer requires precise pressure of the printing plate on the substrate, which is essential for the uniformity of the printed image.

[0004] There are several known methods for attaching a printing plate to a printing cylinder. The most common method involves using double-sided adhesive tape. A second method involves using a sleeve or similar device permanently equipped with an adhesive surface for attaching the printing plate.

[0005] The use of double-sided tape is problematic because removing the tape from the printing cylinder and / or the printing plate can be difficult. Double-sided tape often leaves residue that can later impair the reuse of the printing plate or degrade print quality in subsequent print runs. Achieving a uniform application of the double-sided tape without creating surface irregularities that affect the printed image often requires manual work and is time-consuming. Furthermore, the use of multiple sections of double-sided tape, generally necessary due to the size of a printing plate, complicates plate alignment on the printing cylinder, especially since removing and repositioning the tape sections is challenging.

[0006] WO 95 / 19267 A1 discloses a fastening device for attaching a flexographic printing form to a plate cylinder, characterized by a flexible carrier layer and an adhesive photopolymer layer supported by the carrier layer, which is completely exposed. Thus, WO 95 / 19267 A1 describes the use of an adhesively equipped plate cylinder as a replacement for double-sided adhesive tapes. The general term "adhesive" is used here in the sense of "permanently sticky" or "permanently adhesive." The document mentions that the adhesively equipped plate cylinder can retain its adhesive properties even during continuous use and reuse, and that residues are easily removed, leaving no residual photopolymer material on the printing form.Apart from the fact that it is a photopolymer, there is no teaching on the chemistry and process for producing the adhesive-equipped plate cylinder.

[0007] WO 2010 090685 A1 describes a method for releasably attaching a printing plate to a printing cylinder, the method comprising: a) attaching a photopolymer film to the printing cylinder, wherein the photopolymer film comprises a first and a second principal surface opposite each other, the first principal surface being in contact with and attached to the printing cylinder, and wherein the first and second principal surfaces have a surface tackiness of at least 600 g, as measured by ASTM Standard D-2979-95; b) bringing the printing plate into contact with and attaching it to the second principal surface; wherein the photopolymer film comprises: a) binder; b) at least one monomer; c) photoinitiator; and d) microspheres with a diameter of less than 90 pm.

[0008] Thus, the stickiness of the photopolymer itself is used to adhere it to the printing cylinder and to attach the printing plate. Microspheres are incorporated into the photopolymer film to provide a damping effect when used in the printing press. The photopolymer layer referred to in this document is produced by mixing the photopolymer components and curing the composition after it has been cast or extruded into a film, followed by UV irradiation. The document states that the required amount of radiation varies based on the composition and thickness of the photopolymer, and that the amount of radiation used, and therefore the degree of curing, can be used to control the stiffness of the photopolymer. However, the curing must be sufficient to achieve adequate consistency and strength.This is particularly necessary because the photopolymer layer of this document does not contain a substrate on which the photopolymer layer is provided; instead, the extruded photopolymer layer is attached directly to the printing cylinder.

[0009] Due to the adhesive bond of the photopolymer layer to both the printing cylinder and the printing plate on opposite sides of the photopolymer film, such a layer can detach when the printing plate is removed from the printing cylinder, as the adhesion can be equally strong on both sides. Furthermore, if the adhesion is strong, removing or replacing the printing plate will likely damage the surface supporting the printing plate, thus reducing the lifespan of the photopolymer film. If the adhesion is insufficient, the printing plate can detach from the printing cylinder during operation. Additionally, the presence of microspheres can impair the adhesive properties of the layer and result in surface irregularities that are transferred through the printing plate, potentially reducing print quality and / or causing misalignment.US patent 2021 / 0214589 A1 discloses an adhesive printing form mounting layer comprising a carrier and a permanently sticky layer arranged on the carrier, wherein the permanently sticky layer comprises a material based on a cross-linked polyurethane.

[0010] The use of printing plate mounting devices, such as sleeves with an adhesive layer for permanently attaching a printing plate to a printing cylinder, is therefore generally known in the field. In the flexographic printing industry, campaigns of varying lengths are printed. Because the requirements for print quality and printing plates differ depending on the material being printed, foamed adhesive tapes typically ensure a secure connection 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 because the printing plates can be removed after printing and replaced with another one. Nevertheless, some basic requirements still need to be met.

[0011] The mounting of the printing plates must be simple and safe. Furthermore, it is often observed that printing plates peel away from the printing cylinder starting at their edges, a phenomenon known as "edge peeling." Such behavior of the printing plates must not occur, as it could compromise the correct printing process.

[0012] Furthermore, the printing plates must be easily removable from the sleeve without damage. A low removal force allows the operator to remove them comfortably and reduces the risk of irreversible damage to the printing plate.

[0013] However, high holding power during the printing process and easy removal afterwards represent conflicting requirements that cannot all be fully met.

[0014] One object of the present invention was 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 removal after printing. A further object of the invention was to provide a device that reduces the tendency for the edges of the printing plate to detach.

[0015] An additional objective of the invention was to enable improved print quality over many prints with one printing form and / or after reuse with many printing forms.

[0016] The solution to these problems is based on the basic idea of ​​the present invention, according to which the printing form fastening device is equipped with at least two areas of an adhesive layer which have different adhesive properties.

[0017] The problems listed above are solved by the subject matter of the invention according to the definitions in the claims. Preferred embodiments are described in the dependent claims and the following descriptions.

[0018] Embodiments subsequently designated as preferred are combined in particularly preferred embodiments with features of other embodiments designated as preferred. Combinations of two or more of the embodiments subsequently designated as particularly preferred are therefore especially preferred. Embodiments in which a feature of an embodiment designated as preferred to any extent is combined with one or more further features of other embodiments designated as preferred are also preferred.

[0019] Insofar as specific quantities or proportions of an element as well as preferred embodiments of the element are disclosed below, the specific quantities or proportions of the preferably configured elements are also disclosed. Furthermore, it is disclosed that, among the corresponding specific total quantities or proportions of the elements, at least some of the elements may be preferably configured, and in particular, that preferably configured elements may, in turn, be present in specific quantities or proportions within the specific total quantities or proportions.A first and general object of the present invention is a printing form fastening device for fastening a printing plate to a printing cylinder, wherein the printing form fastening device comprises a carrier and an adhesive layer arranged on the carrier and having a surface facing the printing plate, wherein the surface of the adhesive layer facing the printing plate comprises at least two areas with different adhesive forces on the printing plate.

[0020] The invention thus solves the aforementioned problems by segmenting the adhesive layer of the printing plate mounting device into at least two zones with different adhesive strengths on the printing plate. These zones are to be understood as corresponding to geometrically defined areas on the surface of the adhesive layer facing the printing plate. By adjusting the geometry of these zones, the invention enables the provision of one or more predefined "assembly" and "separation" or "disassembly" areas within the sleeve. The "assembly areas" exhibit a higher adhesive strength and thus support a firm adhesion of the printing plate to the printing cylinder, while the "separation zones" exhibit a lower adhesive strength and thus facilitate the removal of the printing plate after the printing process.

[0021] In other words, the first object of the invention is thus a sleeve for attaching a printing plate to a printing cylinder, which comprises an external adhesive and is characterized in that this external adhesive comprises a stronger and a weaker adhesive segment, wherein "stronger adhesive" and "weaker adhesive" refer to the adhesive performance towards the printing plate.

[0022] The printing plate mounting device typically has a cylindrical shape and an inner diameter that is matched to the diameter of the printing cylinder so that it closely surrounds it. The printing plate mounting device comprises a carrier and an adhesive layer. In many embodiments, the printing plate mounting device according to the invention is commonly referred to as a "sleeve"; therefore, the printing plate mounting device is preferably a sleeve for mounting a printing plate onto a printing cylinder.

[0023] The support, alternatively referred to as the substrate, can generally be single-layered, but preferably comprises two or more layers, each providing specific functionalities.

[0024] Preferably, the support comprises a base. The base is preferably a cylindrical support made of metals such as aluminum, polymers, or, more preferably, a combination of different materials. For example, the base can consist of fiberglass or carbon fiber fabrics encapsulated with epoxy resins and additionally coated with polyurethane. Thus, the base very preferably consists of a composite material. Functionally, the base serves as the connecting element between the printing press and other functional layers of the printing plate mounting device; furthermore, the base preferably provides the device with stability and dimensional stability.

[0025] Preferably, the carrier comprises a foam layer. The foam layer has a defined hardness and density and can thus dampen forces occurring during the printing process, ensuring the desired compressibility of the printing plate and therefore print quality. Particularly preferably, the foam layer is an open-cell polyurethane foam with a thickness of 1,200 µm to 1,800 µm. Preferably, the foam layer is provided with an adhesive layer on one or both of its main surfaces to create a firm contact with the carrier and / or another functional layer that follows the upward direction of the printing plate mounting device. Particularly preferably, the foam layer is provided with a pressure-sensitive adhesive layer on one or both of its main surfaces.Therefore, the foam layer can preferably be considered the middle layer of a single-sided or double-sided adhesive tape, and the carrier of the printing form mounting device preferably comprises a double-sided foam adhesive tape. The adhesive layers can establish firm contact between the foam layer at the base on its underside and with other parts of the device, e.g., a reinforcing film, on its upper side.

[0026] Preferably, the carrier comprises one or more films. The films preferably have a thickness of 20–150 µm. Polyester films are preferred, but polyethylene terephthalate (PET) films are even more preferred. A film can enhance the stability of the multilayer laminate and further protect the foam layer from damage when the printing plate is removed from the sleeve.

[0027] The carrier preferably comprises one or more of the functionalities listed above and thus particularly preferably includes a base, a foam layer, and one or more films. More preferably, the carrier comprises a base, a double-sided foam adhesive tape, and one or more films. Those skilled in the art understand that the carrier may comprise more functional layers than those mentioned above; for example, the carrier may include one or more additional adhesive layers arranged between the listed functional layers.

[0028] The printing form fastening device according to the invention further comprises an adhesive layer which is arranged on the carrier and has a surface facing the printing plate.

[0029] In technical terms, an adhesive is an adhesive with pressure-sensitive properties, meaning the ability to create a permanent bond to a substrate even under relatively low pressure. While not strictly adhering to this theory, it is often assumed that an adhesive can be understood as a liquid with extremely high viscosity and an elastic component, consequently exhibiting characteristic viscoelastic properties that result in the permanent self-adhesive and pressure-sensitive bonding described above. It is assumed that mechanical deformation of such adhesives leads to both viscous flow processes and the generation of elastic restoring forces. The viscous flow is necessary for adhesion, while the elastic restoring forces are necessary for cohesion.The relationship between rheology and pressure-sensitive adhesive properties is well-established in the field and described, for example, in SATA's "Handbook of Pressure Sensitive Adhesive Technology", 3rd edition (1999), pp. 153 to 203. The storage module (G. 1 The elastic and viscous components (G), which can be determined using dynamic mechanical analysis (DMA), for example with a rheometer, are typically used for a more precise description and quantification of the elastic and viscous components. In connection with the present invention, an adhesive is preferably considered to be tacky and thus a pressure-sensitive adhesive if, at a temperature of 23 °C in the deformation frequency range of 10 °C to 10 °C, it exhibits the following properties: 1 rad / s G' and G" at least partially in the range of 10 3 up to 10 7 Pa lie.

[0030] In general, the adhesive layer applied to the substrate of the device according to the invention enables the mounting of the printing plate and allows for easy attachment and removal of the printing plate without the need for additional adhesives or tapes. Furthermore, the adhesive layer can provide additional damping, which can further improve print quality.

[0031] According to the invention, the surface of the adhesive layer facing the printing plate comprises at least two areas with different adhesive strengths on the printing plate. In other words, a sleeve according to the invention does not comprise a single continuous adhesive layer, but instead a segmented adhesive layer with at least two different zones that provide different adhesive properties. This concept advantageously enables an embodiment of the device that provides at least one zone, which can be considered a "mounting zone" and has a higher adhesive strength, thus enabling good holding power and easy mounting of the printing plate, and at least one further zone, which can be considered a "dismounting zone" and has a lower adhesive strength, thus enabling easier removal of the printing plate after the printing process.

[0032] A "region" is understood as a part of the surface of the pressure-sensitive adhesive layer facing the printing plate that is geometrically separated or distinguishable from the other parts of this surface. Although the adhesive strength is described here in relation to the surface of the pressure-sensitive adhesive layer, it is understood by those skilled in the art that the adhesive strength results from the properties of the entire pressure-sensitive adhesive layer that comprises the surface region in question.

[0033] Generally, two or more areas can be present, each exhibiting a different adhesive strength on the printing plate. Furthermore, the surface of the adhesive layer facing the printing plate can comprise a first area with a specific adhesive strength on the printing plate and several separate areas, each exhibiting the same adhesive strength on the printing plate but differing from the adhesive strength of the first area.

[0034] Preferably, one or more areas with a lower adhesive strength on the printing plate than one or more other areas occupy at least 70% of the total surface area of ​​the pressure-sensitive adhesive layer facing the printing plate. This means that there are preferably more areas with relatively low adhesive strength than areas with relatively high adhesive strength, or, in other words, that the "removal zone" is larger than the "assembly zone." More preferably, one or more areas with a lower adhesive strength on the printing plate than one or more other areas occupy at least 75%, and particularly preferably at least 80%, e.g., at least 85%, of the total surface area of ​​the pressure-sensitive adhesive layer facing the printing plate.

[0035] Preferably, one or more areas with a higher adhesive strength on the printing plate than one or more other areas occupy at least 2%, more preferably at least 5%, of the total surface area of ​​the adhesive layer facing the printing plate. Preferably, each of the areas with different adhesive strengths on the printing plate occupies 5 to 95% of the total surface area of ​​the adhesive layer facing the printing plate. This means that an area with a specific adhesive strength on the printing plate preferably represents a significant portion of the sleeve's adhesive surface.

[0036] In one embodiment, a region with a higher adhesive strength than all other regions of the surface of the adhesive layer facing the printing plate extends along the ends of the printing plate, i.e., along both edges of the printing plate that run parallel to the axis of rotation of the printing cylinder or the printing form mounting device. These regions preferably each form a strip with a width of 1 to 5 cm, more preferably 1.3 to 4.5 cm, more preferably 1.5 to 4 cm, 1.7 to 3.5 cm, and most preferably 2 to 3 cm, with the strip extending from each of the two printing plate ends towards the other printing plate end.This advantageously allows the higher adhesion to be located at the end edges of the printing plate to prevent the edges from lifting, while the larger part of the contact area of ​​the pressure-sensitive adhesive layer with the printing plate is covered with pressure-sensitive adhesive with a lower adhesive strength, which promotes easier disassembly.

[0037] Preferably, the surface of the adhesive layer facing the printing plate has at least two areas with a difference in their adhesive strength on the printing plate of 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 most preferably 0.9 to 2.1 N / cm. Particularly preferably, the difference in adhesive strength on the printing plate between all areas of the surface of the adhesive layer facing the printing plate with different adhesive strengths on the printing plate is 0.5 to 2.5 N / cm, more preferably 0.7 to 2.3 N / cm, and most preferably 0.9 to 2.1 N / cm.

[0038] The different adhesive forces of the two respective areas within the surface of the pressure-sensitive adhesive layer facing the printing plate can be achieved in various ways. In one embodiment, the different adhesive forces on the printing plate are achieved by using chemically different pressure-sensitive adhesives. The term "chemically different pressure-sensitive adhesives" is understood to refer to pressure-sensitive adhesives with different chemical properties, which, for example,

[0039] Base polymers may include those belonging to different polymer classes, or base polymers belonging to the same polymer class but based on different monomer compositions; or different additives which accordingly impart different adhesive properties, e.g., different adhesive resins or the same adhesive resins but in different concentrations; or which differ in terms of the nature and / or quantity of a chemical crosslinking agent used.

[0040] Likewise, any combination of the chemically different adhesive compounds listed above, or of the methods leading to their application, can be used.

[0041] Accordingly, layers of chemically different pressure-sensitive adhesives can be applied to the substrate. This can be achieved, for example, by laminating layers of chemically different pressure-sensitive adhesives onto temporary substrate materials, laminating the layers onto the substrate in the desired geometry, and filling the seams with uncured pressure-sensitive adhesive, which is then cured, thus bonding the layers.

[0042] In another embodiment, the different adhesive forces on the printing plate are achieved through different surface structures of the otherwise identical pressure-sensitive adhesive. For example, a smooth surface can generate a comparatively high adhesive force, while a rough, structured surface of the otherwise identical pressure-sensitive adhesive layer can result in reduced adhesive force. A structured surface of the pressure-sensitive adhesive layer can be achieved by bringing a micro-embossed pattern into contact with the adhesive layer and forming a micro-replicated surface within it. This can be accomplished by casting using a tool with a micro-embossed pattern, by applying the pressure-sensitive adhesive to a release layer with the micro-embossed pattern, and / or by passing it through a press roller to press the pressure-sensitive adhesive layer against a release layer with the micro-embossed pattern.The desired embossed topography can be created in tools using any generally known techniques, selected according to the tool material and the characteristics of the desired topography. Examples of such techniques include etching (e.g., chemical etching, mechanical etching, or other ablation methods such as laser ablation or reactive ion etching), photolithography, stereolithography, micromechanical machining, knurling (e.g., cutting knurling or acid-strengthened knurling), scoring, or cutting.

[0043] Structuring the surface can be achieved by embossing grooves, thereby reducing the contact area between the adhesive and the printing plate.

[0044] Different surface textures can be created, for example, by applying different release layers to the not yet fully cured adhesive. One of these release layers can have a smooth surface, while the other can have a textured surface comprising multiple grooves that form the micro-replicated surface of the adhesive layer.

[0045] In a further embodiment, different adhesive strengths on the printing plate are achieved by different physical and / or chemical treatments, such as radiation crosslinking of the adhesive using UV radiation or an electron beam, of different segments of the otherwise identical adhesive compound. Preferably, the different adhesive strengths on the printing plate are achieved by different UV irradiation of the otherwise identical adhesive compound. Thus, in this embodiment, it may be necessary for the adhesive compound to be radiation-crosslinkable, particularly preferably UV-crosslinkable. Different adhesive strengths can then be achieved using different radiation profiles for different segments of the adhesive layer. This, in turn, can be achieved by selectively activating the radiation sources.This method advantageously allows the entire sleeve surface to be covered with the same uncrosslinked adhesive composition and requires only different treatment of the segments.

[0046] Alternatively, and particularly preferably, different adhesive strengths on the printing plate are achieved by exposing at least one area of ​​the surface of the pressure-sensitive adhesive layer facing the printing plate to a UV radiation dose that causes a loss of adhesive strength exceeding the loss of adhesive strength caused by crosslinking of the pressure-sensitive adhesive, while avoiding such exposure in at least one other area. This makes the treated area less adhesive, while one or more other areas are protected from such harsh treatment, for example, by masking them with a UV-absorbing film. Alternatively, the above-described differential treatment of different areas can be achieved by selectively activating or shielding the radiation source.

[0047] The pressure-sensitive adhesive layer of the device according to the invention can be based on one or more poly(meth)acrylates, vinyl aromatic 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 comprise one or more additives, such as adhesive resins, plasticizers, fillers, antioxidants, etc., as are generally known in the field.

[0048] Regardless of the various methods listed above for achieving different adhesive strengths, the adhesive layer of the pressure-mold fastening device according to the invention preferably comprises, and more preferably is based on, one or more polyurethanes. In their uncrosslinked state, the polyurethanes preferably each have two or more crosslinkable groups, which are more preferably ethylene unsaturated groups. Polyurethanes generally comprise two or more -NHC(O)O- bonds (urethane bonds) that are obtainable by reacting a hydroxyl group with an isocyanate group. Polyurethanes are usually formed by reacting a polyol with a polyisocyanate, e.g., by reacting a diol with a diisocyanate.The reaction between a hydroxyl group and an isocyanate group forms an -NHC(O)O- bond, and at least two -NHC(O)O- bonds are formed when a polyol reacts with a polyisocyanate.

[0049] The monomer composition on which a polyurethane of the pressure-sensitive adhesive of a sleeve according to the invention is based can additionally comprise one or more (meth)acrylate monomers, a portion of which can form additional crosslinking compounds. Furthermore, the precursor composition on which the pressure-sensitive adhesive layer, i.e., the uncrosslinked composition for the formation of the pressure-sensitive adhesive layer by crosslinking (hereinafter also referred to as the "PSA precursor composition"), is based, can also contain a thermal or photosensitive polymerization initiator for initiating a crosslinking reaction. In addition, the PSA precursor composition can also contain a solvent, a polymerization inhibitor to prevent premature crosslinking, a plasticizer, a rheology regulator, a desiccant, or similar additives generally known to those skilled in the art.

[0050] Preferably, the adhesive layer comprises one or more polyurethanes totaling at least 50 wt.%, more preferably at least 60 wt.%, most preferably at least 70 wt.%, in particular at least 80 wt.%, e.g. at least 85 wt.% and most preferably at least 90 wt.%, based on the total weight of the adhesive layer.

[0051] A polyurethane of the PSA precursor composition, i.e., a polyurethane of the pressure-sensitive adhesive layer in its uncrosslinked state, preferably comprises at least two crosslinkable groups, more preferably at least two ethylene unsaturated groups. These groups can be introduced into the polyurethane by first forming the polyurethane and then modifying it by reacting the polyurethane with a modifying compound capable of introducing the crosslinkable groups. Such a reaction can be carried out by reacting the modifying compound with unconsumed hydroxyl and / or isocyanate groups present at the chain ends of the polyurethane.If the polyurethane is derived from the reaction of a diol with a diisocyanate and is therefore linear, the introduction of crosslinkable groups, for example, ethylene-unsaturated groups, can be achieved by reacting the polyurethane polymer with a modifying compound containing a crosslinkable group and either an isocyanate group, a hydroxyl group, or both. For example, a terminal isocyanate group can be reacted with a hydroxyl-containing (meth)acrylate compound to introduce an ethylene-unsaturated group. Such a modification is preferably carried out in such a way that at least two crosslinkable groups are introduced.This can be achieved by using the same type of reaction with the same modifying compound in the case of a polyurethane with at least two groups in a molecule that are reactive towards the modifying compound; in this case, at least two equivalents of the modifying compound are used relative to one equivalent of the unmodified polymer. Of course, it is also possible to use two or more different modifying compounds that are reactive towards two or more different groups present in the unmodified polymer.

[0052] Alternatively, the crosslinkable groups can be introduced into the polyurethane by using a suitable starting compound for the synthesis of the polyurethane polymer, such as a polyol (e.g., a diol or triol) and / or a polyisocyanate (such as a diisocyanate or triisocyanate) with one or more crosslinkable groups. These groups then remain unreacted during the formation of the polyurethane polymer and can subsequently undergo a crosslinking reaction after appropriate initiation, for example, by radicals. Preferably, the monomer composition on which a polyurethane pressure-sensitive adhesive is based comprises a (meth)acrylate diol, more preferably a dihydroxyalkyl(meth)acrylate, e.g., 2,3-dihydroxypropyl methacrylate.

[0053] In general, the crosslinkable groups can be freely chosen, but are neither hydroxyl groups nor isocyanate groups, and of course not -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 radical or ionic, more preferably a radical, crosslinking reaction. While the crosslinking groups can thus be selected from those capable of reacting with the same or another crosslinking group in a different molecule of the PSA precursor composition, such as epoxide groups or alcohol / carboxylic acid ester combinations to form an ester bond, the crosslinkable groups are preferably ethylene unsaturated groups.The reason for this is that, with proper initiation, the ethylene-unsaturated groups react via a radical mechanism and, to a certain extent, are also capable of reacting with the polyurethane polymer backbone via a radical chain reaction. This is considered preferable because it eliminates the need for precise alignment of reactive groups, as the radical reaction, if properly initiated, can form a wide variety of cross-links.

[0054] The polyols and polyisocyanates used for the polyurethane backbone are generally not particularly restricted. In one embodiment, the polyurethane is linear and thus consists of one or more diols and one or more diisocyanates. The polyurethane backbone can be derived from just one diol or a mixture of two or more diols, and from just 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.

[0055] Diols include diols composed of small molecules with a molar mass of 500 or less, such as ethylene glycol and propylene glycol, but also large diols with a molar mass greater than 500, 600, 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 the characteristics of a polyurethane. Here, in the case of polymeric compounds with a molar mass distribution, the molar masses refer to the weight-average molar mass.Examples include homopolymers and copolymers of two or more ethylene-unsaturated compounds, preferably selected from the group consisting of styrenes, alkenes, and polyenes with 2 to 12 carbon atoms and cycloalkenes with 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 copolymers thereof, functionalized with two (usually terminal) hydroxyl groups. An example is a homopolymer of ethylene, propylene, 1-butene, isobutylene, or 1,3-butadiene, or a copolymer of two or more thereof, functionalized with two terminal hydroxyl groups.A polymer derived from a polyene, such as polybutadiene, is typically hydrogenated prior to its functionalization to obtain, for example, two terminal hydroxy groups, making it less susceptible to degradation. However, in connection with the present invention, a non-hydrogenated polybutadiene can also be used and subsequently functionalized to obtain, for example, two terminal hydroxy groups, because it already contains reactive groups for a subsequent crosslinking reaction.

[0056] Other examples of large diols are polyether polyols and polyester polyols, with polyether polyols being preferred because polyester polyols are generally more prone to hydrolysis and polyether polyols exhibit improved stickiness. Specific examples include poly(tetramethylene)glycol (PTMO), poly(propylene oxide)-glycol (PPO-), and poly(ethylene)glycol (PEG). For both polyester 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.

[0057] Similarly, diisocyanates can be selected from known diisocyanates used to produce polyurethanes, for example, aromatic diisocyanates such as methylenediphenyl diisocyanate (MDI) and hydrogenated MDI in all stereoisomeric forms, such as 2,2'-, 2,4'-, and 4,4'-; and toluene diisocyanate (TDI), whose stereoisomers, such as 2,4'- and 2,6'-, can also all be used. Alternatively, and preferably, aliphatic diisocyanates are used because they have a lower environmental impact and are less likely to cause health hazards. 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.Similar to diols, diisocyanates can also be compounds with a low (500 or less) or high molar mass, such as a molar mass greater than 500, 600 or more, or 1000 or more, but generally 10000 or less, such as 8000 or less, or 6000 or less. For example, 5000 or less, in the case of a polymeric compound with a molar mass distribution, is given as the weight-average molar mass to maintain the characteristics of a polyurethane. In principle, these compounds can be prepared by functionalizing a suitable compound with two isocyanate groups or by introducing a group carrying an isocyanate function at two positions.

[0058] While both the diols and the diisocyanates can thus be selected from the small molecules and large molecules defined above, in one embodiment one of the diols and the isocyanates is a small molecule (M w 500 or less), and the other is a large molecule (M w (more than 500, preferably 1000 or more). Regarding availability, the polyol is preferably a large molecule. As mentioned above, it is also possible to use more than one diol and / or more than one diisocyanate. In this case as well, preferably at least one of the two or more diols or at least one of the two or more diisocyanates is a large compound with a molecular weight of M. w of 500 or more, like 1000 or more.

[0059] 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, hydrogenated castor oil, and a palm oil-based polyester polyol.

[0060] The PSA precursor composition preferably comprises a crosslinking initiator. The term "crosslinking initiator" refers to a compound capable of initiating a crosslinking reaction by forming an ion or radical upon heating or irradiation. In a preferred embodiment, the crosslinking initiator is a UV initiator. The UV initiator may be selected from known UV initiators such as benzyl dimethyl ketal (IRGACURE® 651), benzoin isobutyl ether (BIBE), benzophenone and related derivatives, 2,2-diethoxyacetophenone, cyclohexyl phenyl ketone and such derivatives (IRGACURE® 184), mono- and diacylphosphine oxide derivatives (IRGACURE® 819), and similar substances. The more preferred UV initiators are BIBE, IRGACURE® 184, and IRGACURE® 651, of which BIBE is the most preferred. The concentration of the UV initiator can range from 0.1 to 3 wt.%, but is preferably 1 to 2 wt.%.-%, based on the total weight of the PSA precursor composition excluding the optional solvent. The UV initiator can be a single compound, but a combination of UV initiators, e.g., with sensitivities to different wavelengths, can also be used.

[0061] The PSA precursor composition optionally includes a solvent. Preferably, the PSA precursor composition is solvent-free because solvent evaporation reduces the volume of the layer formed from the PSA precursor composition and makes it difficult to adjust the thickness. Solvent evaporation can also result in a porous structure, which is undesirable. If solvent is present, its amount is typically 50 wt% or less, preferably 25 wt% or less, such as 15 wt% or less, or 10 wt% or less. The solvent may be selected from known organic solvents, such as protic and aprotic solvents and mixtures thereof. The solvent has a hydration level of 10 5Pa preferably has a boiling point of 75 °C or less. In one embodiment, the solvent is selected from ethers; alcohols; ketones and esters, such as acetone, methyl ethyl ketone, ethyl acetate and methyl acetate; ethanol; methanol; isopropanol; tetrahydrofuran and diethyl ether.

[0062] The pressure-sensitive adhesive layer preferably comprises one or more crosslinked polyurethanes, which are typically obtained by initiation of the crosslinking reaction of the PSA precursor composition described above, either by heat or radiation. Although the pressure-sensitive adhesive layer may contain other components besides the crosslinked polyurethane(s), the one or more crosslinked polyurethanes preferably constitute 80 wt.% or more, 90 wt.% or more, or 95 wt.% or more of the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer may also consist entirely of the crosslinked polyurethane(s). The pressure-sensitive adhesive layer is preferably formed by placing the PSA precursor composition on a substrate and then initiating the crosslinking reaction. The formation may, if required, also include heating the PSA precursor composition to evaporate solvent and / or unreacted monomer.

[0063] The thickness of the adhesive layer is not particularly limited as long as the object of the present invention is solved, but is typically 1.00 mm or less, 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 particularly limited, but may be 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.

[0064] The adhesive layer preferably does not contain microspheres.

[0065] In one embodiment, at least one of the areas with different adhesive strength on the printing plate is optically identifiable. Thus, the printing plate mounting device according to the invention preferably includes an identification mark that enables the differentiation of at least two areas of the surface of the adhesive layer facing the printing plate, each with different adhesive strengths. Such identification marks allow for easy identification of segments with higher or lower adhesive strength and can therefore assist the operator or the machine performing the mounting or dismounting of the printing plate in identifying "mounting" and "dismounting" zones. An identification mark can be provided, for example, by a color code.Preferably, optical identification according to the present embodiment is provided by a color marking and / or by a label. For example, the reinforcing film of the carrier can be printed with specific colors, shapes, or a label. The print can be visible through the semi-permeable outer adhesive layer. Thus, an area with high or low adhesive strength can be visually highlighted by a color code or a label that corresponds to the contour of the respective area.

[0066] The invention can be further explained using Figures 1-3.

[0067] Figure 1 shows a printing plate mounting device 1, which is generally known in the field and comprises a base 4 and a foam layer 3, together forming the support of the device. The entire surface facing the printing plate is covered with the adhesive compound 2.

[0068] Figure 2 shows an exemplary printing form fastening device 1 according to the invention, wherein the surface of the adhesive compound facing the printing plate comprises: the area 2, which is an area with a lower adhesive strength on the printing plate, and the area 5, which is an area with a higher adhesive strength on the printing plate, wherein the area 5 extends over the entire length of the printing form fastening device.

[0069] Figure 3 also shows an exemplary printing form fastening device 1 according to the invention, in which the surface of the adhesive compound facing the printing plate comprises: the area 2, which is an area with a lower adhesive strength on the printing plate, and the areas 5, which are areas with a higher adhesive strength on the printing plate, wherein the areas 5 are arranged in a geometric arrangement that differs from that of Figure 2.

[0070] Thus, Figure 3 represents an arrangement in which the surface of the adhesive layer facing the printing plate comprises a first area 2 with a specific adhesive force on the printing plate and several separate areas 5, each of which has the same adhesive force on the printing plate, but which differs from the adhesive force of the first area 2 towards the printing plate.

[0071] Experimental section

[0072] Test procedure

[0073] Method A - Adhesive strength

[0074] To determine the adhesive strength, adhesive layers with a thickness of 250 pm were subjected to an indirect measurement.

[0075] A reinforcing plate was fitted with double-sided adhesive tape. The layer of pressure-sensitive adhesive to be tested was applied to an etched PET film and covered with a release liner. The resulting sample was then applied, PET film side down, to the double-sided adhesive tape. The release liner was removed, exposing the second surface of the pressure-sensitive adhesive, and a standard, unetched PET test strip, 20 mm wide, was applied and secured by rolling back and forth five times with a 4 kg roller. The test assembly was then directly attached, and the PET test strip was peeled from the pressure-sensitive adhesive at a 90° angle and a speed of 300 mm / min using a Zwick Roell Z2.5 machine. The required tensile force was determined using a tensile tester. The results were calculated as the mean of three samples, standardized to the width of the strip, and are given in N / cm.

[0076] To measure the adhesive strength directly on the sleeve, the sleeve was first secured in a jig to hold it in position during the measurement. The PET test film was then applied directly to the sleeve and firmly attached using a plastic applicator. Afterward, it was removed, and the required force was measured as described above.

[0077] Procedure B - Edge peel test

[0078] A pressure plate (Cyrel type, DuPont, 1.7 mm thick, dimensions 200 mm x 150 mm) was applied to the self-adhesive sleeve under test (500 mm repeat) and firmly pressed down with a plastic applicator to remove any trapped air between the pressure plate and the adhesive. It was ensured that the edges of the pressure plate were completely flush with the adhesive.

[0079] The resulting assembly was stored in a climate chamber for 3 days under the conditions specified in Table 3. Afterwards, the assembly was reconditioned to normal climate (23 °C, 50% RH). Finally, the degree of lifting of the printing plate edges was measured with a ruler. The results are given in mm.

[0080] Production of pressure-sensitive adhesives

[0081] Polyurethane prepolymers were produced using a solvent-based process, starting with the components listed in Table 1.

[0082] Table 1: Chemicals used

[0083] PSA precursor composition 1 with strong adhesion

[0084] 124.79 g of Krasol® LBH 2000, 60.00 g of 2-butanone, and 1.30 g of GMMA are placed in a 500 mL glass reaction vessel. The resulting mixture is stirred until a homogeneous solution is obtained. Then, 13.70 g of IPDI is added, and the mixture is stirred until it again becomes a homogeneous solution. Next, 0.21 g of the catalyst is added, and the mixture is stirred for 24 h while it cools to room temperature. Afterward, the reaction mixture is transferred to another container and stored at 40 °C for 48 h to allow the reaction to complete.

[0085] PSA precursor composition 2 with low adhesion

[0086] 123.16 g of Krasol® LBH 2000, 60.00 g of 2-butanone, and 2.10 g of GMMA are placed in a 500 mL glass reaction vessel. The resulting mixture is stirred until a homogeneous solution is obtained. Then, 14.54 g of IPDI are added, and the mixture is stirred until it again becomes a homogeneous solution. Next, 0.21 g of the catalyst is added, and the mixture is stirred for 24 h while it cools to room temperature. Afterward, the reaction mixture is transferred to another container and stored at 40 °C for 48 h to allow the reaction to complete.

[0087] Network

[0088] A photoinitiator (0.2 wt%, based on the solid precursor composition) was added to the PSA precursor composition prepared as described above. The resulting mixture was homogenized for 5 minutes and then applied to an etched PET substrate. The solvent was evaporated for 10 minutes in a convection oven at 80 °C. The dried layers were covered with a siliconized PET film and exposed to UV radiation from a source with a dose of 2000 mJ / cm². 2 The setting was adjusted to the initiator. Adhesive layers 1 and 2, each with a thickness of 250 pm, were obtained.

[0089] Manufacturing of sleeves

[0090] Method 1: Provision of zones with different adhesive strengths by means of UV post-treatment

[0091] A strip of UV-impermeable film, 100 mm wide, was applied along the entire length of a tesa® Twinlock 74201 sleeve with a 500 mm repeat and a length of 1,400 mm. This covered 20% of the adhesive surface, leaving 80% uncovered. The surface of the prepared sleeve was then exposed to UV radiation at a dose of 5,000 mJ / cm². 2 The product was exposed to a UV curing chamber. Afterwards, the protective film was removed and the adhesive strength was measured; the test results are listed in Table 3.

[0092] As a comparison example, the entire adhesive surface of a tesa® Twinlock 74201 sleeve was treated in the same way, i.e., without any covering.

[0093] Method 2: Production of a sleeve with areas of different adhesive strength due to the use of different adhesives

[0094] A base cylinder with a 500 mm repeat was provided, fitted with double-sided polyurethane foam adhesive tape. A 250 µm thick layer of pressure-sensitive adhesive layer 1, prepared as described above, was laminated to the surface of the sleeve along its entire length in a width of 100 mm; and a 250 µm thick layer of pressure-sensitive adhesive layer 2, prepared as described above, was laminated to the remaining surface of the sleeve along its entire length in a width of 400 mm. Uncured PSA precursor composition 1 was added by syringe to cover the seam between the different adhesive layers. The photosensitive composition was cured by local irradiation with UV light to form a continuous seal.

[0095] To produce comparative examples, the base cylinder was covered with adhesive layers 1 and 2 over its entire surface.

[0096] In the examples, the ease of panel removal was individually assessed by 5 independent individuals, each experienced in panel assembly. The results are given on a scale of 1 to 4:

[0097] 1 - easy disassembly

[0098] 2 - average disassembly

[0099] 3 - difficult disassembly

[0100] 4 - Disassembly impossible without causing serious damage to the pressure plate. The test results are listed in Table 3.

[0101] Table 3: Test results See example - comparison example

[0102] List of reference symbols

[0103] 1 - Die mounting device

[0104] 2 - Adhesive compound

[0105] 3 - Foam layer 4 - Base

[0106] 5 - Adhesive compound

Claims

Patent claims 1. Printing form fastening device (1) for fastening a printing plate to a printing cylinder, wherein the printing form fastening device (1) comprises a carrier (3, 4) and an adhesive layer arranged on the carrier (3, 4) and having a surface (2, 5) facing the printing plate, wherein the surface (2, 5) of the adhesive layer facing the printing plate comprises at least two areas (2, 5) with different adhesive forces on the printing plate.

2. Printing form fastening device (1) according to claim 1 , characterized in that one or more areas (2) with a lower adhesive strength on the printing plate than one or more further areas (5) occupy at least 70% of the total surface (2, 5) of the adhesive layer facing the printing plate.

3. Printing form fastening device (1) according to claim 1 or 2, characterized in that one or more areas (5) with a higher adhesive strength on the printing plate than one or more further areas (2) occupy at least 2% of the total surface (2, 5) of the adhesive layer facing the printing plate.

4. Printing form fastening device (1) according to one of the preceding claims, characterized in that the different adhesive forces on the printing plate are achieved by using chemically different adhesive compounds.

5. Printing form fastening device (1) according to one of claims 1 to 3, characterized in that the different adhesive forces on the printing plate are achieved by different surface structures of the otherwise identical adhesive compounds.

6. Printing form fastening device (1) according to one of claims 1 to 3, characterized in that the different adhesive forces on the printing plate are achieved by different physical and / or chemical treatment of the otherwise identical adhesive compounds.

7. Printing form fastening device (1) according to claim 6, characterized in that the different adhesive forces on the printing plate are achieved by different UV irradiation of the otherwise identical adhesive compounds.

8. Printing form fastening device (1) according to one of the preceding claims, characterized in that at least one of the areas (2, 5) with different adhesive forces is optically identifiable on the printing plate.

9. Printing form fastening device (1) according to one of the preceding claims, characterized in that the surface (2, 5) of the adhesive layer facing the printing plate has at least two areas (2, 5) with a difference in their adhesive forces on the printing plate of at least 0.5 N / cm.

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