Method for permanently sealing holes with overpressure protection, adhesive element for the method, overpressure-protected substrate and use of an adhesive element

Abstract

Method for closing a continuous recess (10) in a substrate (12), comprising the method steps: a) producing or providing an adhesive element (14) comprising: i) an adhesive layer (16) comprising an adhesive, ii) a carrier layer (18) arranged on the adhesive layer (16), comprising a first carrier layer (19), iii) additionally a cover element (28) which is attached to the side of the adhesive layer (16) facing away from the carrier layer (18) in the pressure opening area (20), and b) bonding the adhesive element (14) to the substrate (12) by means of the adhesive layer (16) so that the adhesive element (14) completely covers the continuous recess (10) and the continuous recess (10) is sealed fluid-tight by the adhesive element (14), wherein the adhesive element (14) comprises a pressure opening region (20) which is at least partially surrounded by a weakened region (22) formed in the carrier layer (18), wherein the average thickness of the carrier layer (18) in the weakened region (22) is smaller than the average thickness of the carrier layer (18) in the pressure opening region (20), wherein the adhesive element (14) is designed such that the action of a predetermined opening pressure on the pressure opening region (20) at least partially irreversibly destroys the adhesive element (14) in the weakened region (22) and forms a through hole (24) in the adhesive element (14), and wherein the adhesive element (14) is bonded in such a way that the pressure opening region (20) at least partially covers the continuous recess (10) in the substrate (12).

Description

[0001] The invention relates to a method for closing a continuous recess in a substrate, a corresponding overpressure-protected substrate, an adhesive element for permanently closing holes with overpressure protection, and a use of corresponding adhesive elements for permanently closing a hole in a substrate and for creating an overpressure protection.

[0002] When manufacturing complex products, it is often necessary to provide holes in the processed components and substrates for manufacturing reasons. These holes allow further processing steps to be carried out during the manufacturing process, for example, by providing access to an interior space where additional components are to be arranged. However, at the end of the manufacturing process, these holes are often no longer required and are even detrimental for numerous end applications, for example, because they allow the ingress of moisture or contaminants.For this purpose, it is known in the prior art to permanently close corresponding through-holes in substrates during production, wherein in particular the use of adhesive elements, for example so-called die-cuts, represents an efficient possibility for permanently closing holes, as disclosed for example in EP 3569406 A1, EP 3943283 A1 or EP 3992259 A1.

[0003] In many cases, however, continuous recesses in the substrate serve more than just manufacturing purposes. Rather, it may be necessary to be able to influence the pressure inside substrates, such as battery housings. Suitable pressure regulation devices, such as valves, must be provided for the necessary pressure management in the area of ​​the continuous recesses.

[0004] So-called overpressure relief devices, sometimes also referred to as "burst systems," are particularly important in the area of ​​pressure management inside substrates. These overpressure relief devices, which are usually more complex in design, serve to protect the installed components in electronic devices, for example, and allow pressure equalization with the environment when a certain internal pressure is reached by releasing the excess pressure through venting.

[0005] Corresponding overpressure protection devices are particularly relevant for battery housings, such as those currently used in electromobility, for example. These battery housings contain the components of the electrochemical cells, which serve to electrochemically store and generate energy and are available, for example, in the form of so-called pouch cells. Such electrochemical cells, such as lithium-ion batteries, represent complex and, in some cases, failure-prone systems, particularly since they often contain flammable substances, especially electrolytes, and high temperatures can occur during operation.

[0006] As a result, in the worst case, batteries can experience what is known as thermal runaway. In the course of such a thermal runaway, the released gases or the evaporation of liquid components often lead to a strong pressure buildup inside the battery casing, which can lead to uncontrolled destruction of the battery casing, which in turn can damage surrounding battery casings, resulting in an undesirable chain reaction in the worst case.

[0007] For this reason, high-performance pressure relief devices for battery housings are particularly important for safety. The increasing relevance of electromobility in the automotive industry and the growing use of electrochemical energy storage systems are leading to a constant interest in improving pressure relief devices that are particularly suitable for use with battery housings.

[0008] A prior art overpressure relief device is disclosed, for example, in CN 107178638 A. The prior art overpressure relief devices are often technically complex components that must be fitted into the continuous recesses of the substrates with considerable manufacturing effort. They also have a comparatively high weight and a certain volume. Furthermore, corresponding prior art bursting systems often have to be specifically designed for certain hole geometries and, in many cases, cannot be flexibly adapted to different dimensions of the holes to be sealed.

[0009] US 2016 / 0 250 439 A1 discloses an arrangement for dispensing a fluid, comprising a fluid cartridge having a housing for receiving the fluid and a fluid dispensing unit configured to generate particles when the fluid is supplied to the housing with a pressurized medium.

[0010] DE 10 2020 130 440 A1 describes an overpressure protection device for limiting the pressure of a fluid, preferably air, within a fluid system. The device comprises a valve means that can be arranged on a hollow body provided for conducting the fluid and / or for filling it with the fluid. The valve means is designed to allow at least a portion of the fluid to escape from the fluid system when a maximum pressure is exceeded. The valve means is formed by a cut arranged in the hollow body.

[0011] WO 2014 / 209 218 A1 relates to a system and a packaging for food comprising a tray and a cover film having an opening for venting gas in case of overpressure.

[0012] DE 295 02 504 U1 relates to a sealable plastic container, in particular a container with a lid or a bag. Such plastic containers are used in particular for the storage and transport of waste, which must first be subjected to steam treatment for disinfection or sterilization.

[0013] WO 2021 / 115 834 A1 relates to a cartridge for a dispensing device and a method for producing a cartridge.

[0014] EP 4 213 288 A1 describes a cooling device for minimizing the spread of gas and flames escaping from at least one battery cell to adjacent other battery cells.

[0015] WO 2016 / 111762 A1 discloses a battery module having a vent path with an exit opening.

[0016] GB 2 334 812 A relates to a battery housing having a waterproof housing wall surrounding the battery, at least part of the housing wall being made of an elastic material.

[0017] The primary object of the present invention was to eliminate or at least reduce the disadvantages of the prior art.

[0018] In particular, it was the object of the present invention to provide a method for closing a continuous recess in a substrate, which method enables a reliable and fluid-tight closure of the continuous recesses, but which, as a result of an overpressure, enables a reliable pressure reduction by venting.

[0019] It was an object of the present invention that the method to be specified should be feasible using components that require the smallest possible installation space and have a low dead weight.

[0020] In addition, it was an object of the present invention that the closing of the through-holes should be particularly easy in the method to be specified, wherein easy automation should desirably be ensured.

[0021] It was a further object of the present invention that the method to be specified should be particularly time- and cost-efficient to carry out, in particular with high throughput rates, wherein the storage costs associated with the storage of the components to be used in the method should also be as low as possible.

[0022] It was a supplementary object of the present invention that the method to be specified should be particularly flexible for closing through-holes with different hole geometries due to the components to be used and ideally should not require any specific adaptation of the components used for different hole geometries.

[0023] A further object of the present invention was that the method to be specified should enable a particularly reliable and durable hole closure until the overpressure protection device is inserted. In this respect, a supplementary object of the present invention was that the overpressure protection device produced by the method to be specified should enable a pronounced directional dependence of the overpressure protection device, so that an overpressure acting on the closure from the outside should not lead to pressure equalization, even at high overpressures.

[0024] In light of the above, it was an object of the present invention to provide an overpressure-protected substrate produced by the method to be specified.

[0025] Furthermore, it was an object of the present invention to provide a component for permanently closing holes with overpressure protection, which can be used in the method to be specified and also to provide a use based thereon.

[0026] The inventors of the present invention have now found that the objects described above can surprisingly be achieved if, instead of complex, constructive bursting systems for closing through-holes in substrates, specific adhesive elements are used with which the through-hole can be glued over in a fluid-tight manner, but which, due to a weakening in the carrier layer, comprise a pressure opening area which breaks open largely irreversibly as a result of a predetermined opening pressure, so that pressure equalization can take place through the resulting through-hole in the adhesive element, as defined in the claims.

[0027] Surprisingly, this design of adhesive elements and their use in corresponding processes not only enables a reliable and fluid-tight closure of continuous recesses in substrates, but also allows for reliable opening behavior due to overpressure, which can be precisely adjusted by varying the extent of the weakening of the carrier layer. The inventors have found that the comparatively simple design of the adhesive element and its simple application result in a particularly advantageous process.

[0028] The corresponding adhesive elements are not only particularly easy to automate and cost-effective to produce, but also have a particularly low weight and volume. Advantageously, the corresponding adhesive elements and thus the corresponding process have a high tolerance for deviations in the hole geometry, allowing manufacturing tolerances to be reduced and the adhesive elements used to seal continuous recesses of different dimensions.

[0029] The above-mentioned objects are thus achieved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention emerge from the subclaims and the following statements.

[0030] Such embodiments, which are designated as preferred below, are combined in particularly preferred embodiments with features of other embodiments designated as preferred. Combinations of two or more of the embodiments designated as particularly preferred below are therefore very particularly preferred. Likewise preferred are 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 to any extent. Features of preferred adhesive elements, overpressure-protected substrates, and uses emerge from the features of preferred methods.

[0031] The invention relates to a method for closing a continuous recess in a substrate, comprising the method steps: a) producing or providing an adhesive element comprising: i) an adhesive layer comprising an adhesive, ii) a carrier layer arranged on the adhesive layer, comprising a first carrier layer, iii) additionally a cover element which is attached to the side of the adhesive layer facing away from the carrier layer in the print opening area, and b) Adhering the adhesive element to the substrate by means of the adhesive layer such that the adhesive element completely covers the continuous recess and the continuous recess is sealed fluid-tight by the adhesive element, wherein the adhesive element comprises a pressure opening region which is at least partially surrounded by a weakened region formed in the carrier layer, wherein the average thickness of the carrier layer in the weakened region is smaller than the average thickness of the carrier layer in the pressure opening region, wherein the adhesive element is designed such that the action of a predetermined opening pressure on the pressure opening region at least partially irreversibly destroys the adhesive element in the weakened region and forms a through-hole in the adhesive element, and wherein the adhesive element is adhered such that the pressure opening region at least partially covers the continuous recess in the substrate.

[0032] The method according to the invention serves for sealing, in particular the fluid-tight sealing of through-holes in substrates, in particular holes, and is particularly relevant in practice for sealing such holes through which an interior space in the substrate is fluidly connected to the environment. Accordingly, a method according to the invention is preferred, wherein the substrate comprises an interior space, which is fluid-tightly sealed by adhering the adhesive element to the through-hole.

[0033] Advantageously, the method according to the invention is essentially not limited with regard to the type of substrate. However, in the opinion of the inventors, the method according to the invention is particularly suitable for use in the closure of battery housings, since in many cases, due to the high number of individual elements, these benefit particularly strongly from the low weight and low manufacturing costs of the solution found within the scope of the present invention. Therefore, a method according to the invention is particularly preferred, wherein the substrate is a housing, preferably a housing of an electronic device or a battery, particularly preferably a battery.Additionally or alternatively, a method according to the invention is also preferred, wherein the substrate comprises one or more materials selected from the group consisting of metals, composite materials, for example comprising glass or carbon fibers, and plastics, preferably plastics and metals, particularly preferably metals, in particular coated metals.

[0034] Those skilled in the art will understand that a corresponding substrate may also comprise more than one continuous recess, but that in this case it is preferred if all of the recesses are closed using the method according to the invention. Alternatively, however, the continuous recesses present in the substrate could also be closed partially using the method according to the invention and partially using other methods, for example, using conventional adhesive elements without overpressure protection. Accordingly, a method according to the invention is preferred, wherein the substrate comprises two or more continuous recesses, wherein preferably all of the continuous recesses are closed using the method.

[0035] The adhesive element to be used in the method according to the invention is, in accordance with the understanding of a person skilled in the art, a flat adhesive element, i.e. it has a significantly greater extent in the two spatial directions of a plane than in the direction orthogonal to the plane. Corresponding adhesive elements can be produced, for example, using methods that are well known to those skilled in the art and are also used, for example, in the production of other adhesive elements. Typically, corresponding flat adhesive elements are separated from a larger adhesive composite that was previously produced using a suitable cutting process, so that the adhesive elements are available in large quantities. The separation can be carried out, for example, by punching out the adhesive elements, in which cases the term is usually used.Thus, a method according to the invention is preferred, wherein the adhesive element is produced by punching the adhesive element out of an adhesive composite comprising an adhesive layer and a carrier layer arranged on the adhesive layer, wherein the weakened region is preferably created before punching. A method according to the invention is particularly preferred in this respect, wherein the adhesive element is a die-cut product.

[0036] As an alternative to the production of the adhesive elements in the process, for example by punching, these can also be simply provided in the process according to the invention, for example by purchasing them from a supplier.

[0037] The adhesive elements used comprise an adhesive layer and a carrier layer, which are bonded together, as is familiar to those skilled in the field of adhesive technology from many adhesive tapes and similar adhesive products. The adhesive layer serves to adhere the adhesive element to the substrate and ensures the necessary adhesion of the adhesive element to the substrate to prevent unwanted, premature detachment under relatively low pressure differences between the two sides of the substrate or under other mechanical stress.

[0038] With a view to achieving the most efficient process possible, which in particular enables particularly easy application of the adhesive elements, but also allows for easy correction of imperfect application if necessary, the inventors propose embodying the adhesive as a pressure-sensitive adhesive. Accordingly, a process according to the invention is preferred, wherein the adhesive is a pressure-sensitive adhesive.

[0039] According to expert understanding, a pressure-sensitive adhesive is an adhesive that has pressure-sensitive adhesive properties, i.e., the ability to form a permanent bond to a substrate even under relatively light pressure. Such pressure-sensitive adhesive tapes are generally permanently tacky even at room temperature, meaning they exhibit a certain viscosity and tackiness, allowing them to wet the surface of a substrate even under light pressure. Without wishing to be bound by this theory, it is often assumed that a pressure-sensitive adhesive can be viewed as an extremely viscous liquid with an elastic component, which consequently has characteristic viscoelastic properties that lead to the permanent tackiness and pressure-sensitive adhesive capacity described above.It is assumed that, with corresponding pressure-sensitive adhesives, mechanical deformation results in both viscous flow processes and the buildup of elastic restoring forces. The partial viscous flow serves to achieve adhesion, while the partial elastic restoring forces are particularly necessary to achieve cohesion. The relationships between rheology and pressure-sensitive tack are known in the 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. These can be determined by means of dynamic mechanical analysis (DMA), for example using a rheometer, as disclosed, for example, in WO 2015 / 189323.In the context of the present invention, an adhesive is preferably understood as pressure-sensitive adhesive and thus as a pressure-sensitive adhesive if, at a temperature of 23 °C in the deformation frequency range of 10. 0 up to 10 1 rad / sec G' and G'' each at least partly in the range of 10 3 up to 10 7 Pa lie.

[0040] As a possible alternative embodiment to the preferred embodiment as a pressure-sensitive adhesive described above, it is conceivable to design the adhesive as a reactive adhesive, i.e., as an adhesive that only cures as a result of a curing step. The resulting curing of the adhesive and its effect as a structural adhesive make this embodiment particularly interesting for applications in which comparatively high predetermined opening pressures are to be set. Thus, a method according to the invention is preferred for certain applications, wherein the adhesive is a curable adhesive, preferably a radiation-curing and / or thermally curing adhesive, wherein the method preferably additionally comprises the following method step after method step b): c) At least partial curing of the curable adhesive.

[0041] In the inventors' estimation, a major advantage of the process according to the invention can be seen in its high flexibility with regard to the chemical nature of the adhesive used in the adhesive element. According to the inventors' estimation, the fundamental functionality of the process according to the invention arises primarily from the interaction of a specifically weakened carrier layer with a generic adhesive, and is accordingly not limited to chemically specific adhesives. This advantageously enables the selection of suitable adhesives in light of the other application requirements, in particular with regard to adhesion to the respective substrate and / or temperature resistance for the intended areas of application. However, the inventors have succeeded in identifying adhesives with which, in their estimation, particularly high-performance adhesive elements can be obtained.A method according to the invention is preferred, wherein the adhesive comprises one or more polymers selected from the group consisting of polyurethanes, poly(meth)acrylates and synthetic rubbers, preferably poly(meth)acrylates and synthetic rubbers, particularly preferably poly(meth)acrylates.

[0042] In the context of the present invention, the term "poly(meth)acrylates" encompasses, in accordance with the understanding of one skilled in the art, polyacrylates and polymethacrylates as well as copolymers of these polymers. Poly(meth)acrylates may contain minor amounts of monomer units that are not derived from (meth)acrylates. In the context of the present invention, a "poly(meth)acrylate" is accordingly understood to mean a (co)polymer whose monomer base consists of a mass fraction of 70% or more, preferably 90% or more, particularly preferably 98% or more, of monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic esters, and methacrylic esters, based on the mass of the monomer base. The mass fraction of acrylic ester and / or methacrylic ester is preferably 50% or more, particularly preferably 70% or more.Poly(meth)acrylates are generally accessible by radical polymerization of acrylic and / or methacrylic-based monomers and, if appropriate, other copolymerizable monomers.

[0043] In the inventors' estimation, it is advantageous for certain applications to embody the adhesive as a foamed adhesive, for example, as a syntactically foamed adhesive, which utilizes expanded microballoons, as are generally known from the prior art, or as a physically foamed adhesive, which can be produced, for example, using a propellant gas. Such foamed adhesives often have advantages, particularly with regard to shock resistance. In this respect, it can be seen as an advantage of the process according to the invention that, in the inventors' estimation, foaming of the adhesive does not impede the fundamental functionality of the adhesive elements according to the invention.Accordingly, for certain applications, a process according to the invention is preferred, wherein the adhesive is a foamed adhesive, wherein the adhesive is preferably a physically foamed adhesive and / or comprises one or more components selected from the group consisting of hollow spheres and at least partially expanded microballoons.

[0044] With a view to achieving the greatest possible material-saving production and good handling properties, the inventors propose that the dimensions of the adhesive layer and the carrier layer should be as similar as possible. Even if it may be preferable for some applications to allow the carrier layer to protrude beyond the adhesive layer, it is preferred, particularly with regard to manufacturing efficiency, if the carrier layer is completely covered by the adhesive layer. Thus, a method according to the invention is preferred, wherein the carrier layer is covered on one side by 50% or more, preferably by 70% or more, particularly preferably by 90% or more, very particularly preferably by 95% or more, and especially preferably essentially completely, by the adhesive layer.

[0045] According to the invention, the carrier layer comprises a first carrier layer, wherein in practice the carrier layer will in many cases consist essentially of this carrier layer. Also relevant for most embodiments is a method according to the invention wherein the adhesive layer is arranged on the first carrier layer.

[0046] It can be seen as an advantage that the method according to the invention is fundamentally very flexible with regard to the material selection of the first carrier layer and that the person skilled in the art can use typical materials that are already known as carrier materials in the field of adhesive technology. In this respect, however, the inventors have succeeded in identifying suitable materials with which very reliable and high-performance adhesive elements can be obtained for use in the method according to the invention. Preference is given to a method according to the invention in which the first carrier layer comprises a film selected from the group consisting of plastic films, for example polyester films, PEEK films, PAEK films, polyimide films or polyamide films, in particular polyester films, and metal films, preferably metal foils. Preference is additionally or alternatively given to a method according to the invention.

[0047] Particularly for more demanding applications, for example, where the adhesive closure is expected to be subjected to significant thermal and / or chemical and / or mechanical stress during use, it is possible for the carrier layer to comprise, in addition to the first carrier layer, further carrier layers that serve, for example, to optimize the physicochemical properties, in particular the surface properties. A method according to the invention is preferred, wherein the carrier layer comprises one or more, preferably two or more, particularly preferably three or more, further carrier layers, wherein the carrier layers of the carrier layer are preferably bonded to one another by intermediate adhesive layers.

[0048] In the inventors' opinion, a particularly preferred embodiment is one in which the carrier layer comprises a protective film as an additional layer, which shields the underlying carrier layers, in particular the first carrier layer, from environmental influences and is particularly advantageous when the first carrier layer is made of metal, since this can prevent unwanted corrosion and any resulting damage to the first carrier layer in the long term. A method according to the invention is preferred, wherein the carrier layer comprises a protective film as a further carrier layer on the side of the first carrier layer facing away from the adhesive layer, wherein the protective film is preferably selected from the group consisting of plastic films, wherein the protective film particularly preferably essentially completely covers the surface of the carrier layer.

[0049] According to the invention, the through-hole is completely covered with the corresponding adhesive elements and thus sealed in a fluid-tight manner. Those skilled in the art will understand that this type of overpressure protection, which is explained in more detail below, means that this fluid-tight seal can be broken open as a result of an acting pressure. For this purpose, a weakened area is provided in the adhesive element according to the invention, in which the average thickness of the carrier layer is reduced compared to the rest of the adhesive element, so that the carrier layer has a reduced mechanical load-bearing capacity in the weakened area and thus represents a type of predetermined breaking point in the carrier layer. Advantageously, the predetermined opening pressure, i.e. the pressure as a result of which the overpressure protection is intended to take effect, can be adjusted by the extent to which the weakened area is reduced.A method according to the invention is preferred, wherein the carrier layer in the weakened region has an average thickness in the range from 5 to 150 µm, preferably in the range from 10 to 100 µm, particularly preferably in the range from 15 to 60 µm, and / or wherein the average thickness of the carrier layer in the weakened region is 5 to 95%, preferably 10 to 80%, particularly preferably 20 to 60% smaller than the average thickness of the carrier layer in the pressure opening region.

[0050] The skilled person will thus understand that the adhesive element is designed to form a through-hole as a result of the action of a predetermined opening pressure on the pressure opening region. In accordance with the skilled person's understanding, this action of a predetermined opening pressure refers to a pressure difference between the two sides of the adhesive element, as occurs, for example, when the adhesive element covers a recess in an otherwise closed vessel and an increase in pressure occurs inside the vessel. It is clear to the skilled person that the predetermined opening pressure does not refer to the ambient pressure, which is experienced equally by all sides and regions of the adhesive element, so that no force is exerted on the pressure opening region relative to the rest of the adhesive element. In other words, the predetermined opening pressure thus refers to an opening pressure difference.

[0051] The term "at least partially irreversibly destroyed" used in the context of the present invention means, in accordance with the expert understanding, that complete destruction of the weakened region is not necessary, provided the destruction is sufficient to form a through-hole in the adhesive element. For example, a circular weakened region that completely surrounds a pressure opening region could be destroyed only over part of its circumference as a result of the predetermined opening pressure, so that the pressure opening region is only partially released from the adhesive element. Likewise, the destruction does not have to be completely irreversible.Due to the physico-chemical properties of typical adhesives, in particular their flow behavior, it would be at least theoretically conceivable that a pressure opening area pressed back into the adhesive element could, despite the irreversibly destroyed carrier layer, be at least temporarily closed via the interaction of the adhesive in such a way that the raised pressure opening area is held in position by the adhesive layer.

[0052] Even though it is theoretically conceivable to provide larger, flatter areas of reduced thickness, and such more complex weakened areas may be useful for specific applications, the inventors believe that, with a view to precisely opening the weakened area while simultaneously simplifying production, it is preferable to form it essentially as a groove-shaped recess, i.e., as an elongated depression, in the carrier layer. Accordingly, a method according to the invention is preferred, wherein the weakened area is formed as a groove-shaped recess in the carrier layer.

[0053] Those skilled in the art will understand that the resistance that the adhesive element can offer to an applied pressure difference after the hole has been closed is significantly influenced by the mechanical strength of the carrier layer or the first carrier layer, whereas the contribution of the adhesive layer is less, particularly since in many cases it will be flowable to a certain extent. Accordingly, unless the predetermined opening pressure is to be effective even at very low pressures, it is expedient to form the carrier layer without completely continuous perforations in order to prevent premature fluid passage at low pressures. A method according to the invention is preferred, wherein the weakened region does not comprise a recess that completely penetrates the carrier layer, in particular not the first carrier layer.

[0054] Due to the above-described significant influence of the carrier layer on the predetermined opening pressure and the generally existing flow behavior of the adhesive, it is advantageously not necessary to provide a corresponding reduction in the average thickness in the adhesive layer that complements the weakened region, which can simplify production. Against this background, a method according to the invention is preferred, wherein the average thickness of the adhesive layer in the weakened region is 20% or less, preferably 10% or less, particularly preferably 5% or less, very particularly preferably 1% or less, and especially preferably 0.1% or less, smaller than the average thickness of the adhesive layer in the pressure-opening region.

[0055] Those skilled in the art will understand that the dimensions of the pressure opening area depend on the shape of the weakened area. The pressure opening area, which is at least partially detached from the adhesive element in the event of overpressure, is thus defined in its shape and dimensions by the predetermined breaking point that causes this, i.e. the weakened area. In this respect, the inventors believe that a variety of basic shapes can be provided for the pressure opening area. With a view to simple application and secure hold of the adhesive element on the substrate, it is expedient in many cases to orient the shape of the pressure opening area to the shape of the recess to be covered and to arrange the pressure opening area relatively centrally in the adhesive element.Consequently, a method according to the invention is preferred, wherein the pressure opening region has a basic shape selected from the group consisting of circles, partial circles, in particular semicircles, ovals, or polygons, preferably selected from the group consisting of circles, semicircles, and ovals. Additionally or alternatively, a method according to the invention is preferred, wherein the pressure opening region has a basic shape that essentially corresponds to the cross-section of the continuous recess. Particularly preferred in all embodiments is a method according to the invention, wherein the center point of the adhesive element lies in the pressure opening region.

[0056] The inventors have recognized that the method according to the invention and the adhesive element used therein advantageously make it possible, with comparatively minor changes in the manufacturing process of the adhesive element, to influence how far the adhesive element opens when the overpressure protection device engages, and thus to influence the fluid flow. A very wide-opening through-hole is achieved in particular when the pressure opening area is surrounded as largely as possible by the weakened area. In one embodiment, it is particularly interesting to surround the pressure opening area essentially completely with the weakened area, so that it is particularly easy to completely remove from the adhesive element a pressure opening area that has been lifted out of the adhesive element as a result of an applied overpressure.Accordingly, a method according to the invention is preferred, wherein the pressure opening area is surrounded by the weakened area to 50% or more, preferably to 70% or more, particularly preferably to 90% or more, very particularly preferably to 95% or more, particularly preferably to substantially 100%, of the circumference of the pressure opening area.

[0057] As an alternative embodiment, the inventors propose that a partial section of the circumference of the pressure opening area deliberately not provide a weakened area, so that an unweakened twist remains between the raised pressure opening area and the remaining adhesive element, which advantageously prevents the raised pressure opening area from being torn off too easily as a result of mechanical stress and, for example, remaining as a foreign body in the housing. Thus, a method according to the invention is preferred, wherein the pressure opening area, based on the circumference of the pressure opening area, is not surrounded by the weakened area to the extent of 0.1 to 10%, preferably 0.2 to 5%, particularly preferably 0.5 to 2%, of the circumference.

[0058] The weakened area in the adhesive element, i.e., the local reduction in the average thickness in the carrier layer, can, according to the inventors' assessment, be advantageously produced using a wide range of possible methods. Punching is particularly suitable for producing adhesive elements in large quantities, whereas the use of laser structuring is particularly suitable for setting particularly precise weakened areas. In this respect, a method according to the invention is preferred, wherein the weakened area in the adhesive element is produced by means of material-removing or cutting processing methods, preferably by means of laser structuring or punching.

[0059] In the course of developing the present invention, the inventors experimented with various directions from which the material processing of the adhesive elements could take place. Initially, an attempt was made to process the material from the direction of the carrier layer, i.e., from the side facing away from the adhesive layer. Although this resulted in satisfactory weakened areas, it was partly made more difficult, particularly in mechanical processing methods, by the fact that the force acting on the carrier layer also influences the underlying adhesive layer and can, for example, press it against the substrate, which can lead to unwanted adhesion and / or deformation of the adhesive layer. The inventors have recognized that, surprisingly, it is easier to create the weakened area if the carrier layer is processed from the side covered with the adhesive layer, i.e.,when the processing takes place virtually through the adhesive layer. This is surprisingly possible because the adhesive layer is somewhat flowable due to the adhesive mass and any local material displacement generated during processing of the carrier layer can be compensated for relatively easily over time. For some applications, a method according to the invention is preferred, wherein the weakened area in the adhesive element is produced by processing the side of the carrier layer facing away from the adhesive layer. Alternatively, however, a method according to the invention is particularly preferred, wherein the weakened area in the adhesive element is produced by processing the side of the carrier layer covered with the adhesive layer, wherein the processing preferably takes place through the adhesive layer.

[0060] Those skilled in the art will understand that the predetermined opening pressure is significantly influenced by the design of the adhesive element used, and in particular by the dimensions and configuration of the weakened region, so that the structural configuration of the adhesive elements makes it possible to precisely adjust the desired opening behavior. According to the inventors' assessment, in cases where the predetermined opening pressures are very low, an inherently reduced structural integrity of the entire adhesive elements is often achieved, whereby production-related deviations in the weakened region and the resulting absolute fluctuations in the predetermined opening pressure can manifest themselves as relatively large relative uncertainties. Accordingly, the inventors propose not choosing an excessively low predetermined opening pressure.At the same time, particularly high predetermined opening pressures place, at least indirectly, higher demands on the adhesives used and their adhesive strength to the substrate, as the aim is to prevent adhesive failure of the entire adhesive element and thus premature venting before the pressure opening area opens. Accordingly, in addition to targeted lower limits for the opening pressure, the inventors also propose ranges and associated upper limits that, in their opinion, are appropriate for numerous applications and can be easily adjusted using typical adhesives and carrier materials.A method according to the invention is preferred, wherein the predetermined opening pressure is 10 kPa or more, preferably 15 kPa or more, particularly preferably 20 kPa or more, very particularly preferably 25 kPa or more, and / or wherein the predetermined opening pressure is in the range from 5 to 200 kPa, preferably in the range from 10 to 150 kPa, particularly preferably in the range from 15 to 100 kPa, very particularly preferably in the range from 2 to 50 kPa.

[0061] An advantage of the method according to the invention can be seen in the fact that the necessary bonding of the adhesive elements is particularly simple, especially compared to bursting systems known from the prior art, and can therefore also be easily automated. Accordingly, a method according to the invention is also preferred in which the bonding of the adhesive element is automated, preferably using a robot arm.

[0062] For optimal opening in the event of overpressure, the inventors propose arranging the pressure opening area essentially concentrically over the continuous recess. A method according to the invention is preferred, wherein the pressure opening area is arranged concentrically over the continuous recess.

[0063] A particularly simple design, which in particular offers great flexibility with regard to the hole geometry to be closed, is achieved when the pressure opening area is smaller than the through-hole to be closed, so that the through-hole lies completely above the pressure opening area in plan view. In these cases, a method according to the invention is preferred, wherein the pressure opening area has a smaller area than the cross-section of the through-hole, and the adhesive element is preferably bonded such that the pressure opening area is arranged completely above the through-hole.

[0064] However, in the above-described embodiment, in which the pressure opening region is completely surrounded by the edge of the continuous recess, the inventors' own experiments have shown that it is disadvantageous that it makes it difficult to achieve an anisotopic opening behavior. In other words, a corresponding embodiment is more susceptible to opening as a result of an overpressure acting on the carrier layer, i.e., in most applications, an overpressure acting on the substrate from the outside, for example, into the interior of a sealed housing. Even if this may be desirable for certain embodiments, such an opening behavior is perceived as disadvantageous for most applications, particularly in the field of battery housings.During the development process, the inventors realized that in order to adjust the directional dependence of the opening behavior, the adhesive element should be bonded in such a way that the pressure opening area protrudes at least partially beyond the edge of the continuous recess. This advantageously ensures that the overlap between the edge of the continuous recess and the pressure opening area, together with the rigidity of the carrier layer, counteracts the unintentional opening of the pressure opening area toward the closed recess.A method according to the invention is therefore particularly preferred, wherein the adhesive element is bonded on in such a way that the pressure opening area, based on the circumference of the continuous recess, projects beyond the edge of the continuous recess at least in sections, preferably by 50% or more, particularly preferably by 70% or more, very particularly preferably by 90% or more, extremely preferably by 95% or more, particularly preferably by substantially 100%, of the circumference, and / or wherein the pressure opening area has a larger area than the cross section of the continuous recess.

[0065] Based on this finding, the inventors have recognized that the degree of overlap can also advantageously be used to adjust the load pressure up to which the pressure opening area is not released from the adhesive element when pressure is applied from the outside, i.e. from the direction of the carrier layer, so that not only an advantageous anisotropy of the opening behavior can be achieved, but this can also be precisely adjusted in both directions.Accordingly, a method according to the invention is also particularly preferred, wherein the adhesive element is bonded by the pressure opening region projecting at least partially beyond the edge of the continuous recess in such a way that the bonded adhesive element withstands the action of a predetermined load pressure on the carrier layer in the pressure opening region, so that the adhesive element is not irreversibly destroyed in the weakened region and no through hole is formed in the adhesive element. A method according to the invention is very particularly preferred, wherein the predetermined load pressure is 100 kPa or more, preferably 200 kPa or more, particularly preferably 300 kPa or more, very particularly preferably 400 kPa or more.

[0066] In the advantageous embodiment described above, with an at least partial overlap of the pressure opening area with the edge of the recess, the inventors observed an effect that can limit the freest possible adjustment of the predetermined opening pressure while simultaneously setting a predetermined loading pressure. Particularly with high degrees of overlap, which may be necessary to set high loading pressures, it can happen - at least with the preferred, quite extensive coating of the carrier layer with an adhesive layer - that the adhesive interaction of the adhesive layer in the overlap area makes a noticeable contribution to the necessary opening pressure, since in this case, the adhesion between the adhesive layer and the edge of the recess must also be overcome to raise the pressure opening area.In this case, the predetermined opening pressure is no longer essentially determined by the weakening of the carrier layer; rather, the pressure required for opening must also overcome the adhesive interaction between the adhesive layer and the substrate. In order to be able to achieve small predetermined opening pressures despite large predetermined loading pressures, i.e., for example, high resistance to external stress factors, the inventors propose providing an additional cover element that can be applied to the adhesive layer and whose dimensions expediently correspond as closely as possible to the dimensions of the pressure opening area.In this case, the cover element reduces or prevents adhesive interaction between the adhesive layer in the area of ​​the print opening and the substrate, so that the adhesive element is fixed to the substrate, for example, exclusively via the adhesive interaction of the adhesive layer outside the print opening area. When pressure is applied from the outside, i.e., from the side facing away from the adhesive layer, the adhesive element, due to the overlap, offers resistance to unwanted opening. This resistance can advantageously be further increased by the additional structural integrity of the cover element, since this too would first have to be deformed to break open.Viewed from the other direction, however, the cover element prevents an adhesive interaction between the relevant part of the adhesive layer and the edge of the substrate in the area to be lifted out during overpressure opening and thus allows the setting of even low predetermined opening pressures.According to the invention, therefore, there is a method wherein the adhesive element additionally comprises a cover element which is attached to the side of the adhesive layer facing away from the carrier layer in the print opening area, wherein the cover element preferably substantially does not protrude beyond the print opening area and / or wherein the dimensions of the cover element preferably substantially correspond to the dimensions of the print opening area, or wherein the continuous recess is at least partially, preferably completely, covered with a cover element before the adhesive element is stuck on, wherein the dimensions of the cover element preferably substantially correspond to the dimensions of the print opening area, wherein the adhesive element is stuck on in such a way that the print opening area covers the cover element at least partially, preferably completely.Those skilled in the art will understand that a method according to the invention is expedient wherein the cover element does not comprise an adhesive. Rather, a method according to the invention is preferred wherein the cover element comprises a film selected from the group consisting of plastic films and metal foils.

[0067] The inventors have thus succeeded in specifying suitable dimensions for the adhesive layer, the carrier layer, and the cover element. A method according to the invention is preferred, wherein the adhesive layer has an average thickness in the range of 5 to 1500 µm, preferably in the range of 10 to 500 µm, particularly preferably in the range of 35 to 100 µm, and / or wherein the carrier layer has an average thickness in the range of 30 to 2000 µm, preferably in the range of 40 to 1000 µm, particularly preferably in the range of 50 to 500 µm, and / or wherein the cover element has an average thickness in the range of 5 to 340 µm, preferably in the range of 10 to 200 µm, particularly preferably in the range of 12 to 100 µm.

[0068] Those skilled in the art will understand that the invention also relates to an adhesive element that can be used in the method according to the invention and with which the advantages described above can be achieved. The invention thus also relates to an adhesive element for permanently sealing holes with overpressure protection, preferably in a method according to the invention, comprising: i) an adhesive layer comprising an adhesive, ii) a carrier layer arranged on the adhesive layer, comprising a first carrier layer, and iii) additionally a cover element which is attached to the side of the adhesive layer facing away from the carrier layer in the pressure opening region, wherein the adhesive element comprises a pressure opening region which is at least partially surrounded by a weakened region formed in the carrier layer, wherein the average thickness of the carrier layer in the weakened region is smaller than the average thickness of the carrier layer in the pressure opening region, wherein the adhesive element is designed such that the action of a predetermined opening pressure on the pressure opening region at least partially irreversibly destroys the adhesive element in the weakened region and forms a through-hole in the adhesive element.

[0069] According to the inventors, not only the method according to the invention and the adhesive element according to the invention used therein are advantageous, but the advantages are also transferred directly to the correspondingly produced substrates, which have an advantageous overpressure protection, wherein in particular the low inherent weight and the low inherent volume of the adhesive elements according to the invention as well as the reliable opening at predetermined opening pressures result in overpressure-protected substrates, which are particularly suitable for many applications, in particular in the field of electromobility, for example in the form of battery housings.The invention accordingly also relates to an overpressure-protected substrate, preferably producible by the method according to the invention, comprising a fluid-tightly sealed interior space with at least one fluid-tightly sealed opening, wherein the sealed opening is fluid-tightly sealed with an adhesive element according to the invention, wherein the pressure opening region of the adhesive element at least partially covers the sealed opening, wherein the overpressure-protected substrate is designed such that the adhesive element is at least partially irreversibly destroyed in the weakened region as a result of a predetermined overpressure in the interior space, so that pressure can be reduced in the interior space through the through-hole formed in the adhesive element.

[0070] Finally, the invention also relates to the use of an adhesive element according to the invention for permanently closing a hole in a substrate and for creating an overpressure protection, wherein the hole is closed with the adhesive element in such a way that the pressure opening area at least partially covers the hole in the substrate.

[0071] Preferred embodiments of the invention are explained and described in more detail below with reference to the accompanying figures. Fig. 1 a first schematic exploded view of the structure of an adhesive element according to the invention before application to the substrate in a preferred embodiment; Fig. 2 a second schematic exploded view of the structure of an adhesive element according to the invention before application to the substrate in a preferred embodiment; Fig. 3 a schematic cross-sectional view through an adhesive element according to the invention in a preferred embodiment; Fig. 4 a schematic representation of an overpressure-protected substrate according to the invention with closed overpressure protection; and Fig. 5 a schematic representation of an overpressure protected substrate according to the invention with open overpressure protection.

[0072] Fig. 1 shows a first schematic exploded view of the structure of an adhesive element 14 according to the invention before application to the substrate 12, as is done in a method according to the invention.

[0073] The adhesive element 14 according to the invention comprises an adhesive layer 16, via which the adhesive element can be attached to the substrate 12 in such a way that the continuous recess 10 in the substrate 12 is sealed in a fluid-tight, in particular gas-tight, manner. In the example shown, the Fig. 1, the substrate 12 is a metallic battery housing, wherein only one wall of the battery housing is shown, which delimits its interior.

[0074] In the example shown, the adhesive layer 16 comprises a pressure-sensitive adhesive based on poly(meth)acrylates, which can also be syntactically foamed, for example, by using expanded microballoons.

[0075] The adhesive layer 16 is arranged on the first carrier layer 19 of a multi-layer carrier layer 18 and is bonded to it via the adhesion of the adhesive. In the example shown, the Fig. 1 it can be seen from the exploded view that the first carrier layer 19 is essentially completely covered on one side by the adhesive layer 16, which is evident from the illustration of the Fig. 2 becomes clearer, in which the exploded view of the Fig. 1 is partially brought together so that the connection of the first carrier layer 19 and the adhesive layer 16 becomes clear.

[0076] In the Fig. 1 and Fig. 2, the first carrier layer 19 is a metal foil with an average thickness of approximately 80 µm. Beyond the first carrier layer 19, the carrier layer 18 comprises a protective film 26 made of polyethylene terephthalate as a further layer, which is bonded to the first carrier layer 19 via an intermediate adhesive layer 30, which is also applied over the entire surface.

[0077] In the Fig. 1 and Fig. 2, it can be clearly seen that the adhesive element 14 in the carrier layer 18 comprises a pressure opening region 20 formed by a weakened region 22. The pressure opening region 20 is located centrally in the adhesive element 14 and, in the example shown, is essentially circular, so that its basic shape essentially corresponds to the continuous recess 10 in the substrate 12, which is to be closed in the method according to the invention.

[0078] Due to this construction, the adhesive element 14 according to the invention is designed such that the action of a predetermined opening pressure on the pressure opening region 20, for example as a result of an overpressure prevailing in the interior of the substrate 12, can cause at least partially irreversible destruction in the weakened region 22, by means of which a through hole 24 is formed in the adhesive element 14.

[0079] In the example shown, the weakened region 22 is formed as a groove-shaped recess in the carrier layer 18, which extends through the protective film 26 into the first carrier layer 19 and essentially completely surrounds the pressure opening region 20, wherein the average thickness of the carrier layer 18 in the region of the weakened region 22 is reduced by approximately 20 to 60% compared to the original thickness of the carrier layer 18 and thus also compared to its average thickness in the pressure opening region 20, depending on the desired opening pressure.

[0080] In Fig. 1 that the adhesive layer 16 in the example shown has a substantially constant average thickness, which is due to a mechanical formation of the weakened region 22 by punching, in this case from the direction of the carrier layer 18, which does not affect the adhesive layer 16.

[0081] In the examples of Fig. 1 and Fig. 2, the adhesive element 14 according to the invention is bonded in the method according to the invention, for example, automatically using a robot arm, with the pressure opening region 20 and the continuous recess 10 being arranged concentrically in the example shown. To achieve advantageous anisotropy of the opening behavior, the bonding is carried out such that the pressure opening region 20 protrudes beyond the edge of the continuous recess 10 over the entire circumference of the continuous recess 10, so that the overlap can resist an externally acting load pressure.

[0082] In order to enable a precise adjustment of the desired opening pressure despite the overlap of the adhesive element 14 according to the invention with the edge of the continuous recess 10, the adhesive element 14 according to the invention comprises a cover element 28 formed from plastic film, the dimensions of which essentially correspond to those of the pressure opening area 20 and which essentially completely covers the adhesive layer 16 in the pressure opening area 20.

[0083] Fig. 3 visualizes the structure of an adhesive element 14 according to the invention in a cross-sectional view, wherein the schematically illustrated adhesive element 14 is similar in many aspects to the adhesive element 14 of the Fig. 1 and Fig. 2. In Fig. 3, however, it is indicated that the processing of the carrier layer 18 to produce the weakened region 22 can also be carried out at least partially through the adhesive layer 16, wherein advantageously, due to the flow behavior of the adhesive layer 16, no processing traces, for example in the form of a reduced thickness, remain in it even after a short time.

[0084] Fig. 4 now shows an overpressure-protected substrate 12 according to the invention, the continuous recess 10 of which is sealed fluid-tight by the adhesive element 14, as is shown, for example, in the Fig. 1 and Fig. 2 can be obtained. Due to the previously described structure of the adhesive element 14 and its arrangement over the continuous recess 10, the pressure-protected substrate 12 can be designed such that it can withstand a load pressure of 400 kPa or more acting from the direction of the carrier layer 18 without causing destruction of the adhesive element 14 in the weakened region 22. In fact, in the inventors' experiments, a corresponding structure was even able to withstand irradiation of the pressure-protected substrate 12 with a high-pressure water jet cleaner (IPX9K, ISO 20653:2013) without causing the closure to fail.

[0085] At the same time, it is possible to specifically set a predetermined opening pressure, for example in the range of 5 to 200 kPa, which, when applied in the desired opening direction, e.g. from the inside of the battery housing to the outside, causes the pressure opening area 20 to be lifted out of the adhesive element 14 as a result of at least partial destruction of the weakened area 22, thereby forming a through-hole 24 through which the overpressure can be relieved. The final state resulting from the engagement of the overpressure protection is shown in Fig. 5 schematically visualized, wherein in advantageous embodiments the complete detachment of the pressure opening area 20 from the adhesive element 14 is additionally avoided by the fact that the weakened area 22 is not guided over the entire circumference, so that an unweakened connection remains between the pressure opening area 20 and the legal adhesive element 14. List of reference symbols 10 Continuous recess 12 Substrat 14 Adhesive element 16 adhesive layer 18 Carrier layer 19 First support layer 20 Pressure opening area 22 weakening area 24 through holes 26 protective film 28 Cover element 30 intermediate adhesive layer

Claims

[1] Method for closing a continuous recess (10) in a substrate (12), comprising the method steps: a) producing or providing an adhesive element (14) comprising: i) an adhesive layer (16) comprising an adhesive, ii) a carrier layer (18) arranged on the adhesive layer (16), comprising a first carrier layer (19), iii) additionally a cover element (28) which is attached to the side of the adhesive layer (16) facing away from the carrier layer (18) in the pressure opening area (20), and b) bonding the adhesive element (14) to the substrate (12) by means of the adhesive layer (16) so that the adhesive element (14) completely covers the continuous recess (10) and the continuous recess (10) is sealed fluid-tight by the adhesive element (14), wherein the adhesive element (14) comprises a pressure opening region (20) which is at least partially surrounded by a weakened region (22) formed in the carrier layer (18), wherein the average thickness of the carrier layer (18) in the weakened region (22) is smaller than the average thickness of the carrier layer (18) in the pressure opening region (20), wherein the adhesive element (14) is designed such that the action of a predetermined opening pressure on the pressure opening region (20) at least partially irreversibly destroys the adhesive element (14) in the weakened region (22) and forms a through hole (24) in the adhesive element (14), and wherein the adhesive element (14) is bonded in such a way that the pressure opening region (20) at least partially covers the continuous recess (10) in the substrate (12). [2] Method according to claim 1, wherein the weakened region (22) is formed as a groove-shaped recess in the carrier layer (18). [3] A method according to any one of claims 1 or 2, wherein the predetermined opening pressure is 10 kPa or more. [4] Method according to one of claims 1 to 3, wherein the carrier layer (18) comprises a protective film (26) as a further carrier layer on the side of the first carrier layer (19) facing away from the adhesive layer (16). [5] Method according to one of claims 1 to 4, wherein the adhesive element (14) is bonded by the pressure opening region (20) projecting at least partially beyond the edge of the continuous recess (10) in such a way that the bonded adhesive element (14) withstands the action of a predetermined load pressure on the carrier layer (18) in the pressure opening region (20), so that the adhesive element (14) is not irreversibly destroyed in the weakened region (22) and no through hole (24) is formed in the adhesive element (14). [6] The method according to claim 5, wherein the predetermined loading pressure is 100 kPa or more. [7] Adhesive element (14) for permanently closing a continuous recess (10) in a substrate (12) by a method according to one of claims 1 to 6, comprising: i) an adhesive layer (16) comprising an adhesive, and ii) a carrier layer (18) arranged on the adhesive layer (16), comprising a first carrier layer (19), iii) additionally a cover element (28) which is attached to the side of the adhesive layer (16) facing away from the carrier layer (18) in the pressure opening area (20), wherein the adhesive element (14) comprises a pressure opening region (20) which is at least partially surrounded by a weakened region (22) formed in the carrier layer (18), wherein the average thickness of the carrier layer (18) in the weakened region (22) is smaller than the average thickness of the carrier layer (18) in the pressure opening region (20), wherein the adhesive element (14) is designed such that the action of a predetermined opening pressure on the pressure opening region (20) at least partially irreversibly destroys the adhesive element (14) in the weakened region (22) and forms a through hole (24) in the adhesive element (14). [8] Overpressure-protected substrate (12), comprising a fluid-tightly sealed interior space with at least one fluid-tightly sealed opening, wherein the sealed opening is fluid-tightly sealed with an adhesive element (14) according to claim 7, wherein the pressure opening region (20) of the adhesive element (14) at least partially covers the sealed opening, wherein the overpressure-protected substrate (12) is designed such that the adhesive element (14) is at least partially irreversibly destroyed in the weakened region (22) as a result of a predetermined overpressure in the interior space, so that a pressure reduction in the interior space can take place through the through-hole (24) formed in the adhesive element (14). [9] Use of an adhesive element (14) according to claim 7 for permanently closing a continuous recess (10) in a substrate (12) and for creating an overpressure protection, wherein the continuous recess (10) is closed with the adhesive element (14) in such a way that the pressure opening region (20) at least partially covers the continuous recess (10) in the substrate (12).

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