Method for producing a multilayer adhesive element

Abstract

The invention relates to a method for producing a multilayer adhesive element (10), comprising the method steps of: a) producing or providing a multilayer starting material (12) comprising: i) a base layer (14), wherein the base layer (14) consists at least in part of a fibrous material, ii) a cover layer (16) arranged on the base layer (14), wherein the cover layer (16) consists at least in part of a plastic, iii) a first adhesive layer (18) arranged on the side of the base layer (14) facing away from the cover layer (16), wherein the first adhesive layer (18) comprises a liquid solvent, iv) an intermediate layer (20) connected to the first adhesive layer (18), v) a second adhesive layer (22) arranged on the intermediate layer (20), and vi) a separating layer (24) arranged on the second adhesive layer (22); b) producing a large number of degassing cutouts which extend at least through the separating layer (24) and the second adhesive layer (22); and c) drying the multilayer starting material (12) provided with the degassing cutouts at a drying temperature of 130°C or more in order to remove the liquid solvent at least in part.

Description

[0001] Method for producing a multi-layer adhesive element

[0002] The invention relates to a method for producing a multi-layer adhesive element and a corresponding multi-layer adhesive element.

[0003] Multilayer adhesive elements represent high-performance materials in many areas of technology, allowing for the targeted adjustment of the surface properties of the substrates to be bonded. Due to their advantageous handling characteristics, these multilayer adhesive elements are now used in many new application areas, for example in the form of self-adhesive wallpapers or other self-adhesive decorative products.

[0004] Due to their multilayered structure, multilayer adhesive elements advantageously allow not only for optimizing the manufacturing process but also for tailoring the overall properties of the multilayer adhesive bond to the specific application requirements. A variety of adhesive and non-adhesive layers can be combined to achieve the desired property profile.

[0005] Especially in light of a growing awareness of the need for a more sustainable use of fossil resources, fibrous materials such as paper or other cellulose-based materials are of particular importance in the production of multilayer adhesive elements, particularly those intended for use as self-adhesive decorative elements. The use of such fibrous materials in the layers of multilayer adhesive elements allows for a reduction in dependence on fossil raw materials, and these fibrous materials are also generally relatively inexpensive and available with a high degree of supply security. Furthermore, the look and / or feel of such fiber-based layers is desirable for many applications, especially in the area of ​​self-adhesive decorative products.

[0006] Despite the significant advantages associated with the use of fiber-based layers in multilayer adhesive elements, their use is also perceived as disadvantageous from certain perspectives. In many cases, the application of such fiber-based layers necessitates the application of the required adhesive layers in the multilayer adhesive elements using a solvent-based adhesive, as hot extrusion processes, for example, are often unsuitable or generally not economically viable. Adhesive layers applied from aqueous solutions or aqueous dispersions are of particular economic importance in this context.Although the solvent-based application of adhesive layers to fiber-containing layers is regularly considered advantageous with regard to the properties of the adhesive layers produced and the required manufacturing effort, the presence of the solvent presents major challenges, especially when the multilayer adhesive elements are intended for high-performance applications where high dimensional accuracy is required.

[0007] Fiber-based materials, such as those made from cellulose, are often not dimensionally stable when exposed to moisture or fluctuations in humidity. Increased humidity causes the fiber-based layers to swell, altering the width and / or length of the material. A significant decrease in relative humidity can also lead to shrinkage. Consequently, the otherwise advantageous use of fiber-based layers in multilayer adhesive elements intended for dimensionally stable applications is often considered a disadvantage. Furthermore, the swelling and shrinkage behavior of such fiber-based layers can also lead to mechanical damage within the multilayer adhesive element, such as deformation and cracking.Particularly in applications in the field of decorative adhesives, for example for use as self-adhesive wallpapers, the dimensional stability of corresponding fiber-based multilayer adhesive elements is often perceived as insufficient, while the risk of deformations and cracks also conflicts with the high aesthetic requirements of the adhesive.

[0008] In the past, the problem that the solvent required for applying the adhesive layer could cause the fiber-based material to swell was solved by relatively simple drying processes. However, this approach was only practical for very simple multilayer adhesive elements with few layers, as sufficient drying could only be guaranteed for these. While conventional drying methods are sufficient for simple multilayer adhesive elements, which, for example, consist of only a paper-based layer and a solvent-based adhesive layer, it has become apparent that for many modern high-performance multilayer adhesive products, the measures known from the prior art are insufficient to guarantee the required dimensional stability of the multilayer adhesive elements produced in this way.The challenges described above are particularly pronounced for multilayer adhesive elements that have a top layer with low permeability to water or the solvent used on one side of the fiber-based layer, for example, due to a plastic coating. Such top layers, which protect the underlying fiber-based layers after application to the substrate and, in particular, shield them from unwanted contact with moisture, are desirable for numerous high-performance applications today. However, they make it difficult to remove the solvent through the essentially impermeable side of the multilayer adhesive element caused by the top layer.

[0009] In addition to such top layers, high-performance multilayer adhesive elements typically also employ intermediate layers, which are bonded to the fiber-based material using a solvent-based adhesive. At least one further adhesive layer is applied to this intermediate layer, which, from a handling perspective, must be additionally covered with a release liner. The intermediate layer and the further adhesive layer, but especially the release liner, which, due to an anti-adhesive coating, usually exhibits poor permeability to the evaporating solvent, thus also block the unimpeded escape of the solvent on the side facing away from the top layer. The poor permeability of the release liner is particularly problematic for liners coated with polyolefins, especially those coated with polyethylene.This is particularly disadvantageous, since the use of appropriate PE-coated liners generally contributes advantageously to dimensional accuracy.

[0010] Due to these poorly permeable layers on both sides, sufficient drying using state-of-the-art methods is practically impossible for many modern multi-layer adhesive elements, meaning that it cannot be carried out in a time- and / or cost-efficient manner.

[0011] The primary objective of the present invention was to eliminate or at least reduce the disadvantages of the prior art.

[0012] In particular, the object of the present invention was to provide a method for producing a multi-layer adhesive element which allows the production of multi-layer adhesive elements with complex multi-layer structures, which enable a targeted adaptation of the performance characteristics to the application requirements of the respective application case, and which, despite the use of fiber-based materials, exhibit excellent dimensional stability and are therefore also suitable for demanding and precise adhesive applications, in particular as a dimensionally stable decorative product, for example as self-adhesive wallpaper.

[0013] It was an object of the present invention that the specified method should enable the production of multilayer adhesive elements of high quality and with great reliability. It was also desirable that the specified method should be implementable in a particularly time- and cost-efficient manner.

[0014] A further objective of the present invention was to ensure that the specified method would guarantee a high level of process reliability and pose the lowest possible health risks to the workers involved in the process. It was also desirable that the specified method be feasible, as far as possible, using materials that are already employed in corresponding multilayer adhesive elements, thus minimizing the complexity of the necessary raw material logistics.

[0015] A further objective of the present invention was that the specified method should also enable the production of thick adhesive layers via the solvent-based route, while still allowing multilayer adhesive elements to be obtained with a low residual moisture content.

[0016] The inventors of the present invention have now found that the problems described above can be solved if, starting from a multilayer starting material comprising a fiber-based base layer and a top layer arranged thereon, which is connected via a solvent-based first adhesive layer to an intermediate layer and a second adhesive layer arranged thereon, which is covered by a separating liner, a plurality of degassing recesses are created in the starting material which extend at least through the separating layer and the second adhesive layer, if the composite thus provided with degassing recesses is subsequently dried at particularly high drying temperatures, as defined in the claims.

[0017] The inclusion of degassing vents advantageously allows solvent vapors, particularly water vapor, generated during drying to escape from the inner adhesive layer of the multilayer adhesive element. These vents advantageously do not impair, or only minimally impair, the performance of the remaining bond. Since the degassing vents ensure the escape of water vapor, drying can be carried out synergistically at significantly higher temperatures, allowing the solvent vapors to escape largely without pressure and without disrupting the multilayer adhesive bond.This advantageously results in the multilayer adhesive elements produced using the specified method having significantly better dimensional stability than comparable composites produced without degassing recesses and consequently with lower drying temperatures, or in the production of corresponding composites with a specific desired level of residual moisture in a significantly shorter time, thereby considerably increasing time and cost efficiency.

[0018] The aforementioned problems are thus solved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention are described in the dependent claims and the following descriptions.

[0019] Such embodiments, which are hereinafter referred to as preferred, are combined in particularly preferred embodiments with features of other embodiments referred to as preferred. Combinations of two or more of the embodiments referred to below as particularly preferred are therefore especially preferred. Also preferred are embodiments in which a feature of one embodiment, referred to as preferred to any degree, is combined with one or more further features of other embodiments, which are referred to as preferred to any degree. Features of preferred multilayer adhesive elements result from the features of preferred methods.

[0020] Particularly preferred embodiments of the invention are disclosed in the exemplary embodiments. Particularly preferred embodiments of the invention, building upon these, have two or more, preferably three or more, and most preferably four or more, of the subsequently disclosed preferred features of the invention, which are also implemented in the exemplary embodiments.

[0021] The invention relates to a method for producing a multilayer adhesive element, comprising the process steps of: a) producing or providing a multilayer starting material, comprising: i) a base layer, wherein the base layer consists at least partially of a fibrous material, ii) a cover layer arranged on the base layer, wherein the cover layer consists at least partially of a plastic, iii) a first adhesive layer arranged on the side of the base layer facing away from the cover layer, wherein the first adhesive layer comprises a liquid solvent, iv) an intermediate layer connected to the first adhesive layer, v) a second adhesive layer arranged on the intermediate layer, and vi) a release layer arranged on the second adhesive layer, b) creating a plurality of degassing recesses which extend at least through the release layer and the second adhesive layer.and c) drying the multilayer starting material provided with the degassing holes at a drying temperature of 130 °C or more to at least partially remove the liquid solvent.

[0022] The method according to the invention serves to produce a multilayer adhesive element. A major advantage of the method according to the invention is that it can, in principle, be advantageously applied to all conceivable multilayer adhesive elements that can be produced from the multilayer starting materials defined above. According to the inventors, the method according to the invention is particularly suitable for producing multilayer adhesive elements that place particularly high demands on dimensional accuracy in subsequent use, for example, self-adhesive wallpapers. A preferred method according to the invention is one in which the multilayer adhesive element is a self-adhesive decorative product, preferably a self-adhesive wallpaper. An additionally or alternatively preferred method according to the invention is one in which the base layer is a decorative layer.A preferred method is, in addition or alternatively, a method according to the invention wherein the base layer and / or the top layer, preferably the top layer, has a printed surface on the side facing away from the first adhesive layer, and / or wherein the base layer and / or the top layer, preferably the top layer, has a macroscopically structured surface on the side facing away from the first adhesive layer.

[0023] Although it would potentially be conceivable to use the inventive method for producing comparatively small, discrete, multilayer adhesive elements, for example in the form of adhesive labels, those skilled in the art understand that the advantages of the inventive method with regard to time and cost efficiency arise primarily when elongated web materials are processed, for example in a continuous or semi-continuous process. A preferred method according to the invention is therefore one in which the multilayer adhesive element is a web-shaped adhesive element, preferably with a web length of 2 m or more, more preferably 5 m or more, and / or in which the multilayer starting material is a web-shaped starting material, preferably with a web length of 2 m or more, more preferably 5 m or more.A method according to the invention is also preferred, either additionally or alternatively, wherein the method is operated as a continuous or semi-continuous process, preferably as a continuous process.

[0024] The starting point of the inventive method is a multilayer starting material, which is produced or provided in process step a) and which already largely corresponds to the multilayer adhesive element to be produced with regard to the desired layer structure.

[0025] A key component of the multilayer adhesive element to be produced, which is also present in the multilayer starting material, is the fiber-based layer, which is referred to as the "base layer" within the scope of the present invention. According to the above definition, the base layer consists at least partially of a fiber material.

[0026] In accordance with the skilled person's understanding, the term "fibers" within the scope of the present invention refers to all fibers of natural origin used in the manufacture of paper and cardboard, in particular wood pulp and cellulose, especially cellulose-based materials, i.e., in addition to primary fibers obtained from wood, also secondary fibers such as fiber obtained from recycled paper. A preferred method according to the invention is one in which the fiber is selected from the group consisting of cellulose, hemicellulose, lignin, and mixtures of these fibers, wherein the fiber preferably comprises or consists of cellulose.

[0027] The fact that the base layer comprises fibrous material means that the multilayer adhesive element to be produced is susceptible to swelling and shrinkage behavior that could compromise its dimensional stability. Therefore, this definition ensures that the desired results of the inventive method are achieved and the problems addressed are solved. In principle, it is conceivable that the base layer could comprise other components besides the fibrous material, for example, because the base layer itself is designed as a multilayer base layer. However, in accordance with the skilled person's understanding, the inventive method offers particularly significant advantages when the base layer is especially prone to adverse swelling behavior due to a very high proportion of fibrous material. Therefore, it is preferred for essentially all embodiments to provide a very high fibrous content for the base layer.A method according to the invention is therefore conceivable, wherein the base layer is a multi-layered base layer comprising two or more partial layers. However, a method according to the invention is preferred, irrespective of this, wherein the mass fraction of the fiber material in the base layer is 50% or more, preferably 70% or more, particularly preferably 80% or more, and most preferably 85% or more, based on the mass of the base layer.

[0028] In particularly preferred embodiments, paper materials can be used for the base layer, and in particular, the use of woodchip layers is conceivable, which intrinsically achieve a macroscopic structure and are well known to those skilled in the art in the field of wallpaper. A preferred method according to the invention is thus one in which the base layer consists at least partially, preferably predominantly, and particularly preferably essentially entirely of paper or cardboard, preferably paper. For some applications, a method according to the invention in which the base layer is a woodchip layer is particularly preferred.

[0029] A preferred method for dimensioning the base layer is one according to the invention, wherein the base layer has a mean thickness in the range of 70 to 500 pm, preferably in the range of 100 to 300 pm, particularly preferably in the range of 150 to 275 pm.

[0030] According to the invention, a cover layer is arranged on one side of the base layer. This cover layer serves to selectively influence the surface properties of the multilayer adhesive element on the side that faces upwards after subsequent bonding to substrates. It is preferred that the corresponding cover layer is materially bonded to the base layer, which can be achieved not only by bonding via a further adhesive layer, but also, in particular, by coating the base layer. A method according to the invention is relevant for essentially all embodiments, wherein the cover layer is materially bonded to the base layer. A further or alternative preferred method according to the invention is one in which the cover layer covers 80% or more, preferably 90% or more, particularly preferably 95% or more, most preferably 98% or more, and most preferably essentially 100% of the surface of the base layer facing away from the first adhesive layer.According to the invention, the top layer consists at least partially of a plastic, wherein this plastic hinders the drying of the multilayer adhesive element. The top layer can, for example, consist of a layer material coated with plastic, but alternatively, it can also be made essentially entirely of plastic. A preferred method according to the invention is one in which the mass fraction of the plastic in the top layer is 30% or more, preferably 50% or more, particularly preferably 70% or more, and most preferably 75% or more, based on the mass of the top layer.

[0031] A preferred method with regard to the thickness of the top layer is one according to the invention, wherein the top layer has a mean thickness in the range of 50 to 500 pm, preferably in the range of 100 to 400 pm, particularly preferably in the range of 250 to 350 pm.

[0032] For practical application, embodiments in which the plastic used is a thermoplastic are particularly relevant, as this ensures advantageous manufacturability of the top layer. A preferred method according to the invention is one in which the plastic is selected from the group consisting of thermoplastic materials, preferably polyvinyl chloride.

[0033] According to the inventors, the multilayer starting materials defined above offer advantages for all conceivable cover layers. However, the advantages of the inventive method are particularly pronounced when the cover layer offers exceptionally high resistance to the passage of the solvent that has evaporated into the gas phase. This can be assessed using the established standard ASTM E 398 "Standard Test Method for Water Vapor Transmission Rate of Sheet Materials Using Dynamic Relative Humidity Measurement," published in July 2020. A preferred method according to the invention is one in which the cover layer is at least partially impermeable to fluids, preferably impermeable to the solvent, and particularly preferably impermeable to water vapor, and / or in which the cover layer has a volume flux density for water vapor of 3 L / (m²) according to ASTM E 398. 2 s) or less, preferably 1.5 L / (m³) 2s) or less, particularly preferably 0.5 L / (m³) 2 s) or less.

[0034] On the other side of the base layer is the first adhesive layer, which serves to create a metallurgical bond with the intermediate layer, which is described in more detail below. In accordance with the skilled person's understanding, the multilayer starting material is not yet, or only minimally, dry, so that the first adhesive layer still comprises a liquid solvent. This implies that the first adhesive layer was applied by application from solution or as a dispersion. The adjective "liquid" denotes the state of matter of the solvent and is readily determinable in practice for those skilled in the art. In case of doubt, a solvent is considered liquid within the scope of the present invention if, at a temperature of 23 °C, it has a dynamic viscosity according to DIN 53019-1:2008 of 40 Pa s or less (shear rate of 1 s). -1In principle, the liquid solvent used for applying the first adhesive layer can be any solvent known to those skilled in the art, who can select the solvent for the specific adhesive layer to be applied based on their expertise or any manufacturing recommendations. However, from an ecological and economic perspective, the inventors believe that first adhesive layers in which the liquid solvent consists as much as possible of water are particularly suitable. A preferred method in this respect is one in which the solvent is selected from the group consisting of water, alcohols, esters, ketones, and mixtures of these solvents, preferably water, alcohols, and mixtures of these solvents. A preferred method in which the solvent comprises or consists of water is also preferred.A method according to the invention is particularly preferred in which the solvent consists of water to a mass fraction of 50% or more, preferably 70% or more, particularly preferably 90% or more, based on the mass of the solvent.

[0035] An exemplary method according to the invention is wherein the first adhesive layer is formed by a dispersion adhesive.

[0036] According to the inventors, adhesives with a medium solids content are particularly suitable for forming the first adhesive layer, such that the mass fraction of the liquid solvent is also preferably in a medium range. Those skilled in the art understand that the advantages of the inventive method are especially evident when the first adhesive layer contains a particularly high proportion of solvent, thus making the efficiency gains during drying particularly noticeable.A preferred method according to the invention is one in which the mass fraction of the solvent in the first adhesive layer is 20% or more, preferably 30% or more, and particularly preferably 40% or more, based on the mass of the first adhesive layer, and / or in which the mass fraction of the solvent in the first adhesive layer is in the range of 30% to 70%, preferably in the range of 35% to 65%, and particularly preferably in the range of 40% to 60%, based on the mass of the first adhesive layer. A preferred method according to the invention is analogous in which the first adhesive layer has a solids content in the range of 30% to 70%, preferably in the range of 35% to 65%, and particularly preferably in the range of 40% to 60%, based on the mass of the first adhesive layer.

[0037] From a chemical perspective, the inventors believe that poly(meth)acrylate-based adhesives are particularly suitable for forming the first adhesive layer. A preferred method according to the invention is one in which the first adhesive layer comprises one or more adhesive polymers selected from the group consisting of polyvinyl esters and poly(meth)acrylates, preferably poly(meth)acrylates, and particularly preferably polyacrylates. An additionally or alternatively preferred method according to the invention is one in which the first adhesive layer is a (meth)acrylate-based adhesive layer, preferably an aqueous (meth)acrylate-based adhesive layer.

[0038] A preferred method for dimensioning the first adhesive layer is according to the invention, wherein the basis weight of the first adhesive layer is in the range of 20 to 140 g / m². 2 , preferably in the range of 30 to 120 g / m² 2 , particularly preferably in the range of 40 to 100 g / m³ 2, lies, and / or wherein the first adhesive layer in the production of the multilayer starting material has a basis weight in the range of 20 to 140 g / m² 2 , preferably in the range of 30 to 120 g / m² 2 , particularly preferably in the range of 40 to 100 g / m³ 2 , is applied. Preferably, or alternatively, a method according to the invention is used, wherein the first adhesive layer has an average thickness in the range of 20 to 140 pm, preferably in the range of 30 to 120 pm, and particularly preferably in the range of 40 to 100 pm.

[0039] In the multilayer structure of the multilayer adhesive element, the first adhesive layer is followed by the so-called "intermediate layer," which is named according to its position in the assembly and which itself can be multilayered. A corresponding method according to the invention is conceivable in which the intermediate layer is a multilayered intermediate layer comprising two or more partial layers.

[0040] It can be seen as an advantage of the invention that the inventive method is, in principle, very flexible with regard to the design of the intermediate layer. However, the inventors suggest that intermediate layers with relatively high permeability to the solvent to be evaporated should be used advantageously. In the case of low permeability, it is expedient to create the degassing openings described below also through the intermediate layer. Suitable, highly permeable intermediate layers can be formed, for example, by using textile fabrics, in particular so-called "non-wovens." However, it is particularly preferred to use a fibrous material in the intermediate layer as well, for example, in the form of paper or cardboard, which themselves generally exhibit good permeability.In particularly preferred embodiments, these can also be combined with one another, for example by using textile fabrics whose fibers consist of a fibrous material, such as nonwoven paper. A preferred method according to the invention is therefore, wherein the intermediate layer comprises or consists of a textile fabric, the textile fabric preferably being selected from the group consisting of nonwovens. Particularly when using textile fabrics, a method according to the invention is conceivable in which the intermediate layer consists at least partially of a plastic, wherein the mass fraction of the plastic is 80% or more, preferably 90% or more, based on the mass of the intermediate layer.However, a method according to the invention is generally preferred in which the intermediate layer consists at least partially of a fibrous material, wherein the mass fraction of the fibrous material is 80% or more, preferably 90% or more, based on the mass of the intermediate layer. A method according to the invention in which the intermediate layer consists at least partially of paper or cardboard, preferably paper, is particularly preferred.

[0041] With regard to the dimensions of the intermediate layer, a method according to the invention is preferred, wherein the intermediate layer has a mean thickness in the range of 10 to 60 pm, preferably in the range of 20 to 50 pm, particularly preferably in the range of 35 to 45 pm.

[0042] The intermediate layer is followed by the second adhesive layer, which is bonded to the intermediate layer in a material-bonded manner. In subsequent use, the second adhesive layer serves to bond the multilayer adhesive element to the substrate to be bonded in a material-bonded manner. An advantage of the method according to the invention is that, in principle, a wide range of possible adhesive layers can be used, allowing the person skilled in the art to adapt the multilayer adhesive element to the specific application requirements, particularly with regard to the compatibility of the adhesive layer with the substrate to be bonded. For this purpose, the person skilled in the art adjusts, in particular, the adhesive strength that the second adhesive layer exerts on the substrate.With regard to the most practically relevant cases, the inventors believe that the second adhesive layer is also produced by applying a solvent in the vast majority of cases, so that the starting material of the second adhesive layer can potentially also comprise a liquid solvent, with the preceding statements regarding the preferred solid or solvent content of the first adhesive layer applying analogously. Particularly in the preferred production process using two or more sub-composites, however, it is advantageously possible and preferred to dry the second adhesive layer in a prior drying step, so that it has only a very low solvent content, wherein the mass fraction of liquid solvent in the second adhesive layer is 1% or less, preferably 0.5% or less, and particularly preferably 0.1% or less, based on the mass of the second adhesive layer.

[0043] The inventors generally consider it advantageous to implement the second adhesive layer with a similar adhesive chemistry to the first adhesive layer. A preferred method according to the invention is one in which the second adhesive layer comprises one or more adhesive polymers selected from the group consisting of polyvinyl esters and poly(meth)acrylates, preferably poly(meth)acrylates, and particularly preferably polyacrylates. A further or alternative preferred method according to the invention is one in which the second adhesive layer is a (meth)acrylate-based adhesive layer, preferably an aqueous (meth)acrylate-based adhesive layer.

[0044] While the dimensions of a second adhesive layer that has not yet dried are based on those of the first adhesive layer, a method according to the invention is preferred with regard to the design of the largely pre-dried second adhesive layer, wherein the second adhesive layer has an average thickness in the range of 20 to 80 pm, preferably in the range of 30 to 60 pm, particularly preferably in the range of 35 to 45 pm.

[0045] To improve handling properties, a further layer is arranged on the second adhesive layer, which, within the scope of the present invention, is referred to as a "release layer." Such materials are also known as "release liners" by those skilled in the art and are well-established in the field for covering the adhesive layers. These release layers are typically equipped on the side facing the adhesive layer with a "release layer" that reduces adhesion, with the inventors considering a single-sided application of the release layer to be preferable. Therefore, a preferred method according to the invention is one in which the release layer comprises a release layer, preferably a silicone release layer, on one or both sides, preferably on only one side.

[0046] According to the inventors, the use of a plastic-coated paper is particularly preferred for the separation layer, with a coating of polyethylene being considered especially advantageous. A preferred method according to the invention is therefore one in which the separation layer comprises a flat substrate coated with a plastic, preferably a plastic-coated paper, wherein the flat substrate is preferably coated with the plastic only on one side. An additionally or alternatively preferred method according to the invention is one in which the separation layer consists of a plastic, preferably a polyolefin, and most preferably polyethylene, to a mass fraction of 10% or more, preferably 15% or more, and particularly preferably 20% or more.

[0047] A preferred method with regard to the thickness of the separating layer is one according to the invention, wherein the separating layer has a mean thickness in the range of 100 to 200 pm, preferably in the range of 120 to 170 pm, particularly preferably in the range of 135 to 155 pm.

[0048] Analogous to the preceding descriptions regarding the top layer, the process according to the invention offers particularly significant advantages when the separation layer also offers the greatest possible resistance to the passage of solvent vapor during drying and accordingly has only a low permeability to the gaseous solvent. A preferred method according to the invention is therefore also one in which the separation layer is at least partially fluid-impermeable, preferably fluid-impermeable to the solvent, particularly preferably water vapor-impermeable, and / or in which the separation layer has a volume flux density for water vapor according to TAPPI T 215 of 3 L / (m³). 2s) or less, preferably 1.5 L / (m³) 2 s) or less, particularly preferably 0.5 L / (m³) 2 s) or less.

[0049] In principle, it is possible to produce the multilayer starting material used in process step a) in a separate, upstream manufacturing process and simply use it in the process according to the invention. However, the inventors consider it particularly preferable to integrate the drying process into the manufacturing process in such a way that the multilayer starting material is produced in process step a). In this case, the inventors believe that particularly efficient process flows can be achieved by first producing two partial composites, each comprising components of the multilayer starting material, and then bonding the partial composites together via the first adhesive layer. Therefore, a process according to the invention in which the multilayer starting material is produced is preferred.A particularly preferred method according to the invention is one in which, in process step a), a first partial composite comprising the base layer and the top layer is produced or provided as an intermediate product in the production of the multilayer starting material. A particularly preferred method according to the invention is one in which, in process step a), a second partial composite comprising the release layer, the second adhesive layer, and the intermediate layer is produced or provided as an intermediate product in the production of the multilayer starting material. A particularly preferred method according to the invention is one in which the first partial composite and the second partial composite are joined together via the first adhesive layer, the first adhesive layer preferably being coated onto the second partial composite before joining.

[0050] In process step b), recesses are created in the previously presented multilayer starting material, which, within the scope of the present invention, are referred to as "degassing recesses" in reference to their purpose. This is done with the proviso that the created degassing recesses must extend at least through the separating layer and the second adhesive layer. The inventors have found that, particularly with a sufficiently permeable design of the intermediate layer, for example, due to its construction from a fibrous material and / or its design as a textile sheet, piercing the two outermost layers is sufficient so that the degassing recesses extend to the intermediate layer. However, particularly good results were achieved with deeper degassing recesses that also extend through the intermediate layer and reach to or into the first adhesive layer.A preferred method according to the invention is therefore one in which the degassing recesses extend at least through the separating layer, the second adhesive layer, and into the intermediate layer, preferably through the intermediate layer. A further or alternative preferred method according to the invention is one in which the tool(s) used to create the degassing recesses penetrate the multilayer starting material to such an extent that the tool(s) contact the first adhesive layer.

[0051] In a process involving the production of the multilayer starting material from partial composites, it is generally possible to create the degassing recesses before or after the partial composites are joined together. However, the inventors consider it preferable to first produce the entire multilayer starting material. Thus, a process according to the invention is conceivable in which the creation of the multitude of degassing recesses takes place either on the multilayer starting material or, during its production, on a portion of the multilayer starting material, particularly the second partial composite. Preferably, the creation of the multitude of degassing recesses takes place on the multilayer starting material.

[0052] At least theoretically, it would be conceivable, and considering the goal to be achieved...

[0053] While it would be advantageous to create the degassing vents from the direction of the top layer, this would require, in light of the above definition, that the multi-layered adhesive element be essentially completely pierced. Due to the resulting damage to the top and bottom layers, this is not preferred in the vast majority of cases, especially not for decorative products such as self-adhesive wallpaper. Accordingly, in the vast majority of cases, the degassing vents are created from the direction of the release liner.A preferred method according to the invention is therefore one in which the production of the plurality of degassing recesses on the multilayer starting material is carried out from the direction of the separation layer, and / or in which the top layer, preferably the top layer and the base layer, does not include degassing recesses, and / or in which no degassing recesses are produced in the top layer, preferably in the top layer and the base layer.

[0054] The person skilled in the art understands that the objective of process step b) is to create degassing vents that extend partially into the composite of the multilayer starting material. In light of these instructions, the person skilled in the art can select a suitable tool for this purpose. The inventors have succeeded in identifying particularly advantageous methods for creating the degassing vents. A preferred method according to the invention is one in which the creation of the plurality of degassing vents is carried out by a method selected from the group consisting of needles and slots, preferably needles.

[0055] A method according to the invention is preferred for good degassing during drying, wherein in process step b) 100 or more, preferably 200 or more, particularly preferably 500 or more, degassing recesses are produced.

[0056] In the inventors' experiments, the use of a needle roller proved particularly effective for continuous or semi-continuous processes. This roller can be rolled over the multilayered starting material, or the multilayered starting material can be guided over it, in order to create degassing holes with the needles arranged on the roller. The inventors succeeded in identifying particularly advantageous designs for the dimensioning of the needles.A preferred method according to the invention is one in which the production of the plurality of degassing recesses is carried out with a needle roller or a needle plate, preferably a needle roller, wherein the needles preferably have a height of 0.7 mm or more, preferably 1.0 mm or more, particularly preferably 1.3 mm or more, and / or wherein the needles preferably have a mean diameter in the range of 1 to 3 mm, preferably in the range of 1.5 to 2.5 mm, and / or wherein the needles preferably have a mean distance to the next needles in the range of 0.5 to 1.5 cm, preferably in the range of 0.7 to 1.3 cm.A preferred method according to the invention is additionally or alternatively wherein the degassing recesses have a mean depth of 0.7 mm or more, preferably 1.0 mm or more, particularly preferably 1.3 mm or more, and / or wherein the degassing recesses have a mean diameter in the range of 1 to 3 mm, preferably in the range of 1.5 to 2.5 mm, and / or wherein the degassing recesses have a mean distance to the nearest degassing recesses in the range of 0.5 to 1.5 cm, preferably in the range of 0.7 to 1.3 cm.

[0057] In addition to determining the dimensions of the corresponding needles, the inventors have also identified suitable number densities for covering the surface with degassing pores. Excellent drying results were achieved with these densities in their own tests, and the corresponding number density can be applied analogously to the multilayer adhesive element to be produced. A preferred method according to the invention involves creating the degassing pores in process step b) with a pore density in the range of 2000 to 20000 1 / m². 2 , preferably in the range of 5000 to 15000 1 / m 2 , are produced, and / or wherein the degassing recesses in process step b) have an areal density of the degassing recesses of 1000 1 / m² 2 or more, preferably 2000 1 / m 2 or more, especially preferably 5000 1 / m 2 or more, are generated.

[0058] In process step c), the multilayered starting material, which is provided with degassing holes, is dried. This drying step can, in principle, be completely separated from the needling process, so that only those sections of the multilayered starting material that are already fully equipped with degassing holes are subjected to drying. However, the inventors believe it is also conceivable to at least partially overlap process steps b) and c) by having the needling take place in those production areas where an elevated temperature is already present. In the inventors' opinion, it is preferable to avoid generating too large an overlap between the needling and drying processes and to create the degassing holes before a significant increase in temperature.A preferred method according to the invention is one in which the drying of the multilayer starting material provided with degassing vents is carried out using a drying device, preferably a heating channel. A special feature of the method according to the invention is that the drying is carried out at a comparatively high drying temperature, which is only made possible by the presence of the degassing vents without risking damage to the composite. According to the inventors, particularly efficient drying results can be achieved at such high temperatures, especially with short production times. A preferred method according to the invention is one in which the drying of the multilayer starting material provided with the degassing vents takes place at a drying temperature of 135 °C or more, preferably 140 °C or more.

[0059] According to the inventors, it is particularly advantageous to utilize the high efficiency of the inventive method in the drying step to limit the drying time as much as possible, while also ensuring that the drying time is not too short. In a continuous or semi-continuous process, this can be influenced, for example, by the length of the drying tunnel and / or the feed rate of the web through the drying device.A preferred method according to the invention is wherein the drying of the multilayer starting material provided with the degassing recesses takes place at the drying temperature for a time of 10 s or more, preferably 30 s or more, particularly preferably 60 s or more, and / or wherein the drying of the multilayer starting material provided with the degassing recesses takes place at the drying temperature for a time in the range of 10 to 240 s, preferably in the range of 30 to 180 s.

[0060] Through their own experiments, the inventors discovered that the optimal solution to the existing conflicting objectives of low moisture content and excellent dimensional stability on the one hand, and the required drying time and associated energy costs on the other, is achieved by setting a specific reduction in the solvent content, which is referred to as adjusting the "residual moisture." Additionally or alternatively, specific absolute mass fractions of the solvent in the multilayer adhesive element can also be adjusted.In this context, a method according to the invention is preferred, wherein the drying of the multilayer starting material provided with the degassing recesses is carried out in such a way that the residual moisture of the multilayer adhesive element is 6% or less, preferably 5.5% or less, particularly preferably 5% or less, most preferably 4.5% or less, corresponding to the mass fraction of the solvent in the multilayer starting material after drying divided by the mass fraction of the solvent before drying.A preferred or alternative method according to the invention is wherein the drying of the multilayer starting material provided with the degassing recesses is carried out such that the mass fraction of the solvent in the multilayer adhesive element is 6% or less, preferably 5.5% or less, particularly preferably 5% or less, most preferably 4.5% or less, corresponding to the mass fraction of the solvent in the multilayer starting material after drying divided by the mass fraction of the solvent before drying.

[0061] The invention also relates to a multi-layer adhesive element, preferably manufactured or manufacturable using the inventive method, comprising:

[0062] I) a base layer, wherein the base layer consists at least partially of a fibrous material,

[0063] II) a top layer arranged on the base layer, wherein the top layer consists at least partially of a plastic,

[0064] III) a first adhesive layer arranged on the side of the base layer facing away from the top layer,

[0065] IV) an intermediate layer bonded to the first adhesive layer,

[0066] V) a second adhesive layer arranged on the intermediate layer, and

[0067] VI) a separating layer arranged on the second adhesive layer, wherein the multilayer adhesive element comprises a plurality of degassing recesses in the separating layer, preferably the separating layer and the second adhesive layer, particularly preferably the separating layer, the second adhesive layer and the intermediate layer.

[0068] The above definition, that the multilayer adhesive element comprises a multitude of degassing recesses in the separation layer, takes into account the fact that the degassing recesses created in the adhesive layers can close over time due to the viscosity of the adhesive.

[0069] A multi-layer adhesive element according to the invention is generally preferred, wherein the basis weight of the first adhesive layer and / or the second adhesive layer, preferably of the first adhesive layer and the second adhesive layer, is in the range of 20 to 70 g / m². 2 , preferably in the range of 25 to 60 g / m³ 2 , particularly preferably in the range of 30 to 50 g / m³ 2, lies. Preferably, or alternatively, a multi-layer adhesive element according to the invention is used, wherein the second adhesive layer comprises an adhesive compound. An adhesive compound, in accordance with the skilled person's understanding, is an adhesive compound that possesses tacky properties, i.e., the property of forming a permanent bond to a substrate even under relatively light pressure. Such adhesive elements are typically removable from the substrate after use with virtually no residue and are generally permanently tacky even at room temperature, meaning that they exhibit a certain viscosity and tackiness, allowing them to wet the surface of a substrate even with minimal pressure. The tackiness of an adhesive element results from the use of an adhesive compound.Without being bound to this theory, it is often assumed that an adhesive compound can be considered an extremely highly viscous liquid with an elastic component, which consequently exhibits characteristic viscoelastic properties that lead to the permanent inherent tackiness and pressure-sensitive adhesion described above. It is assumed that, in such adhesive compounds, mechanical deformation results in both viscous flow processes and the generation of elastic restoring forces. The viscous flow serves to achieve adhesion, while the elastic restoring forces are particularly necessary for achieving cohesion. The relationships between rheology and pressure sensitivity are known in the prior art and are described, for example, in "Satas, Handbook of Pressure Sensitive Adhesives Technology", Third Edition, (1999), pages 153 to 203.To characterize 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, as disclosed, for example, in WO 2015 / 189323 A1. Within the scope of the present invention, an adhesive compound 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, the following properties are observed: 1 rad / sec G' and G" each at least partially in the range of 10 3 up to 10 7 Pa lie.

[0070] With regard to the design of the adhesive strength of the second adhesive layer, a multi-layer adhesive element according to the invention is preferred, wherein the second adhesive layer has an adhesive strength analogous to ISO 29862:2019 (Method 1, steel, 23 °C, 50% relative humidity, peel speed: 300 mm / min, peel angle: 180°, coated on 23 pm PET film with a mass deposition of 50 g / m²). 2 ) in the range of 1.5 to 8 N / cm, preferably in the range of 2 to 6 N / cm, particularly preferably in the range of 3 to 5 N / cm. The invention and preferred embodiments of the invention are explained and described in more detail below with reference to the accompanying figures. These figures show:

[0071] Fig. 1 A schematic cross-sectional view through a multilayer starting material for use in a method according to the invention in a preferred embodiment;

[0072] Fig. 2 is a schematic visualization of the processing of the multilayer starting material of Fig. 1 in process step b) of the process according to the invention;

[0073] Fig. 3 is a schematic visualization of the processing of the multilayer starting material produced in Fig. 2, which is provided with degassing recesses, in process step c) of the process according to the invention; and

[0074] Fig. 4 is a schematic visualization of the multilayer adhesive element produced in Fig. 3.

[0075] Fig. 1 shows a schematic cross-sectional view through a multilayer starting material 12, which can be used in the production of a multilayer adhesive element 10 using the method according to the invention.

[0076] The multilayer starting material 12 comprises a cellulose layer as the base layer 14, which in the example shown consists essentially entirely of paper and has an average thickness of approximately 250 pm. The cellulose layer serving as the base layer 14 is provided on its outer surface with a printable cover layer 16, which is largely impermeable to water vapor and essentially completely covers one side of the surface of the base layer 14. In the example shown, the cover layer 16 has an average thickness of approximately 100 pm. The cover layer 16 comprises polyvinyl chloride as a thermoplastic polymer, which forms the surface of the cover layer 16. The base layer 14 and the cover layer 16 are produced as a first partial composite in process step a) of the process according to the invention during the production of the multilayer starting material 12.

[0077] As a second partial composite, the second adhesive layer 22 with a solvent-based coating is applied to the intermediate layer 20, with the application being approximately 80 g / m². 2The second adhesive layer 22 is a (meth)acrylate-based adhesive layer with a solids content of approximately 50% at the moment of application, so that the mass fraction of the liquid solvent, which in this example is water, is also approximately 50%. The second adhesive layer 22 thus produced is pre-dried to achieve a low solvent content. To cover the second adhesive layer 22 and to improve its handling properties, it is completely covered with a release liner 24, which is designed as a paper release liner coated on one side with polyethylene. The intermediate layer 18, like the pre-dried second adhesive layer 22, has an average thickness of approximately 40 µm, whereas the release liner 24 has an average thickness of approximately 145 µm.

[0078] The first and second sub-composites are laminated together in process step a) using a (meth)acrylate-based aqueous adhesive, which also has a solids content of 50% and additionally consists of water, thereby forming the first adhesive layer 18. The application is carried out at a basis weight of approximately 80 g / m². 2 .

[0079] In process step b) of the inventive process, the multilayer starting material 12 shown in Fig. 1 is provided with a plurality of degassing recesses 26. This is shown schematically in Fig. 2. The degassing recesses 26 are created using a tool 28, which in the preferred embodiment shown is a (highly simplified) needle roller. The needle roller pierces the multilayer starting material 12 from the side of the separating layer 24, thus creating the degassing recesses 26. The needles of the tool 28 are designed such that they penetrate through the separating layer 24, the second adhesive layer 22, and the intermediate layer 20, reaching into the first adhesive layer 18.The corresponding needling is carried out in such a way that 26 channels are created as degassing recesses, through which the solvent vapor produced during drying can escape, advantageously without impairing the performance of the composite thus obtained.

[0080] The needle roller used by the inventors in their own experiments had 1.5 mm high steel needles arranged at intervals of one centimeter. The average diameter of the needles was 2 mm, so that the solvent vapor produced during drying at higher temperatures could escape without pressure through the resulting degassing pores 26, without bursting the composite apart.

[0081] Starting from the schematic representation in Fig. 2, Fig. 3 shows how the tool 28 was removed to leave the degassing recess 26. Fig. 3 schematically indicates that in process step c), the drying of the multilayer starting material 12, which has degassing recesses 26, is carried out by means of a drying device 30. In the illustrated example, this is a drying tunnel through which the multilayer starting material 12, with degassing recess 26, is conveyed at a speed of approximately 50 m / min, resulting in a residence time of approximately 30 seconds in the example shown. The drying process is carried out in the example shown in Fig.3 at a temperature of 140 °C, whereby in the example shown a residual moisture of about 4.2% is achieved, which represents a significant improvement compared to an otherwise identical process in which a residual moisture of 5% was achieved with a drying temperature of only 100 °C on the same multilayer starting material 12.

[0082] Finally, Fig. 4 shows a schematic visualization of the multilayer adhesive element 10 produced by the preceding method, which can be used as self-adhesive wallpaper. The layers obtained by drying from the first adhesive layer 18 and the second adhesive layer 22 are designated as the first adhesive layer 32 and the second adhesive layer 34, respectively, to account for the change in water content during drying. Only because the escape of water vapor through the degassing opening 26 is it possible to dry at significantly higher temperatures and thus significantly improve the dimensional stability of the multilayer adhesive element 10.

[0083] List of reference signs

[0084] 10 multi-layer adhesive element

[0085] 12 multi-layered starting material

[0086] 14 Base layer 16 Top layer

[0087] 18 first adhesive layer

[0088] 20 Intermediate layer

[0089] 22 second adhesive layer

[0090] 24 Separation layer 26 Degassing recesses

[0091] 28 tools

[0092] 30 T drying device

[0093] 32 first adhesive layer

[0094] 34 second adhesive layer

Claims

Claims 1. A method for producing a multilayer adhesive element (10), comprising the process steps of: a) producing or providing a multilayer starting material (12), comprising: i) a base layer (14), wherein the base layer (14) consists at least partially of a fibrous material, ii) a cover layer (16) arranged on the base layer (14), wherein the cover layer (16) consists at least partially of a plastic, iii) a first adhesive layer (18) arranged on the side of the base layer (14) facing away from the cover layer (16), wherein the first adhesive layer (18) comprises a liquid solvent, iv) an intermediate layer (20) connected to the first adhesive layer (18), v) a second adhesive layer (22) arranged on the intermediate layer (20), and vi) a separating layer (24) arranged on the second adhesive layer (22), b) producing a plurality of degassing recesses extending at least through the separating layer (24) and the second adhesive layer (22) extend,and c) drying the multilayer starting material (12) provided with the degassing holes at a drying temperature of 130 °C or more to at least partially remove the liquid solvent.

2. The method of claim 1, wherein the multilayer adhesive element (10) is a self-adhesive decorative product.

3. Method according to one of claims 1 or 2, wherein the mass fraction of the fibrous material in the base layer (14) is 50% or more, based on the mass of the base layer (14).

4. Method according to any one of claims 1 to 3, wherein the top layer (16) has a volume flux density for water vapor according to TAPPI T 215 of 3 L / (m³). 2 s) or less.

5. A method according to any one of claims 1 to 4, wherein the solvent consists of water to a mass fraction of 50% or more, based on the mass of the solvent.

6. Method according to any one of claims 1 to 5, wherein the mass fraction of the solvent in the first adhesive layer (18) is in the range of 30 to 70%, based on the mass of the first adhesive layer (18).

7. Method according to any one of claims 1 to 6, wherein the basis weight of the first adhesive layer (18) is in the range of 30 to 140 g / m² 2 lies.

8. Method according to any one of claims 1 to 7, wherein the intermediate layer (20) comprises or consists of a textile fabric, and / or wherein the intermediate layer (20) consists at least partially of a fibrous material.

9. Method according to any one of claims 1 to 8, wherein the separating layer (24) comprises a planar substrate coated with a plastic.

10. Method according to any one of claims 1 to 9, wherein the separating layer (24) has a volume flux density for water vapor according to TAPPI T 215 of 3 L / (m³). 2 s) or less.

11. Method according to any one of claims 1 to 10, wherein in process step a) a first partial composite is produced or provided as an intermediate product in the production of the multilayer starting material (12), comprising the base layer (14) and the top layer (16), wherein in process step a) a second partial composite is produced or provided as an intermediate product in the production of the multilayer starting material (12), comprising the separating layer (24), the second adhesive layer (22) and the intermediate layer (20), wherein the first partial composite and the second partial composite are joined together via the first adhesive layer (18).

12. Method according to any one of claims 1 to 11, wherein the degassing recesses extend at least through the separating layer (24), the second adhesive layer (22) and into the intermediate layer (20).

13. Method according to any one of claims 1 to 12, wherein the degassing recesses in process step b) have an areal density of the degassing recesses in the range of 2000 to 20000 1 / m² 2 be generated.

14. Method according to any one of claims 1 to 13, wherein the drying of the multilayer starting material (12) provided with the degassing recesses takes place at a drying temperature of 135 °C or more.

15. Multilayer adhesive element (10), comprising: I) a base layer (14), wherein the base layer (14) consists at least partially of a fibrous material, II) a top layer (16) arranged on the base layer (14), wherein the top layer (16) consists at least partially of a plastic, III) a first adhesive layer (32) arranged on the side of the base layer (14) facing away from the top layer (16), IV) an intermediate layer (20) connected to the first adhesive layer (32), V) a second adhesive layer (34) arranged on the intermediate layer (20), and VI) a separating layer (24) arranged on the second adhesive layer (34), wherein the multilayer adhesive element (10) comprises a plurality of degassing recesses in the separating layer (24).

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