Method for producing structural adhesive connection and method for separating structural adhesive connection

Abstract

The invention relates to a method for producing a structural adhesive connection between a first metal connection part (10) and a second connection part (20), each having at least one adhesive surface (F1, F2) provided for an adhesive process, the method comprises the following steps: applying an electrically insulating adhesion promoter (H1) to the adhesive surface (F1) of the first metal connection (10); -cathodically dip-painting the first metal connection (10), the adhesion surface (F1) coated with the adhesion promoter (H1) remaining unpainted; bonding the connecting parts (10, 20), for which purpose the bonding surface (F1) of the first metal connecting part (10), which is coated with the adhesion promoter (H1), is bonded to the bonding surface (F2) of the second connecting part (20) by introducing an adhesive (K). The invention also relates to a method for separating a structural adhesive connection produced according to the invention, for which purpose the connection part (10, 20) is heated or cooled in the region of the adhesive connection and thus the adhesion promoter (H1, H2) is decomposed or embrittled.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for producing a structural adhesive connection between a first metal connection and a second connection. The invention also relates to a method for separating a structural adhesive connection produced according to the invention. BACKGROUND

[0002] A method for producing a structural adhesive connection between two components is known from DE 10 2010 033 113 A1. SUMMARY

[0003] The invention addresses the technical problem of providing an additional method for producing a structural adhesive connection between two connections, wherein at least one of the two connections is to be metallic and is additionally to have a cathodic dip coating.

[0004] This technical problem is solved by the method according to the invention of claim 1. By way of the dependent claims, the invention also extends to a method for separating a structural adhesive connection produced according to the invention. Further features of the invention are analogously derived for both inventive solutions from the dependent claims, the following description of the invention, which also explicitly includes the features described by way of example and optionally, and the figures.

[0005] The method according to the invention for producing a structural adhesive connection between a first metal connection and a second connection, the first metal connection and the second connection each having at least one adhesive surface provided for the adhesive process, comprises the following steps, which are preferably carried out automatically or at least partially automatically:

[0006] - applying an electrically insulating adhesion promoter to the adhesive surface(s) of the first metal connection, such that the adhesive surface is coated with the adhesion promoter; and thereafter

[0007] - cathodically dip coating the first metal connection, wherein the adhesive surface coated with the adhesion promoter or provided with the adhesion promoter layer is not coated with the coating, i.e. the previously applied adhesion promoter remains uncoated or paint-free; and thereafter

[0008] - adhesive bonding the connections, for which purpose the adhesive-bonded adhesive surface of the first metal connection is adhesive-bonded to the adhesive surface of the second connection by introducing an adhesive.

[0009] For the description of the invention, the terms "adhesive" and "adhesive process" are used, which are to be regarded as synonyms for the terms "adhesive bond" and "adhesive bonding process".

[0010] A structural adhesive connection (hereinafter also only adhesive connection) is understood to mean a connection of high strength by means of an adhesive, i.e. based on the adhesive's adhesive force and cohesive force, which is also resistant to temperature changes, for example in the range from -40°C to +80°C. The structural adhesive connection in question is preferably used in vehicle construction and can in particular also withstand dynamic and highly dynamic loads, for example in the event of a crash.

[0011] The connecting piece is a component which is provided as a single component or which is integrated into a component group (module). The metal connecting piece is a component which consists of metal, for example aluminium or steel, or has at least a metal surface, wherein the metal connecting piece is in particular a sheet metal part or a cast part. According to the application, at least the first connecting piece is a metal component. The second connecting piece can be a non-metal component, for example a plastic component or a plastic composite component, but also a metal component. Preferably, the first and second connecting pieces are vehicle components, for example bodywork components or battery components.

[0012] According to the application, an adhesion promoter is applied or laid onto the adhesive surface of the first metal connecting piece. The adhesion promoter (also referred to as primer) is an adhesive primer which is applied directly to the bare metal surface, wherein the application should only take place locally in the region of the adhesive surface. Preferably, an adhesion promoter based on epoxy resin or acrylic resin (acrylate) is used. The adhesion promoter can have supplementary components, for example a modifier for increasing the crash resistance and / or an agent or element for a debonding function (see below). As an adhesion promoter, it is also possible to use a specially adapted or modified adhesive, in particular a structural adhesive. The adhesive surface can be cleaned before the adhesion promoter is applied, in particular in order to remove oil residues, wherein it is also possible to use an oil-resistant adhesion promoter. The adhesion promoter can have a liquid, gel-like or paste-like consistency, or can also be film-like. The application can take place, for example, by means of a nozzle, a brush, a press roller or the like. The application can also take place by printing or lamination. Before further processing, it is also provided that drying takes place if necessary.

[0013] According to the application, an electrically insulating adhesion promoter is used, which forms an electrically insulating coating or adhesion promoter layer after application to the adhesive surface. The adhesion promoter is preferably applied with a layer thickness of at least 25 pm, in particular at least 50 pm, in order to achieve a sufficiently good electrical insulation, wherein it is preferably provided that the maximum layer thickness does not exceed 100 pm. It is of course also possible to apply or lay a suitable adhesion promoter on the adhesive surface of the second connecting piece. The second connecting piece can likewise be metallic, so that the previous explanations likewise apply analogously to the second connecting piece.

[0014] According to the application, the first metal connecting piece is cathodically dip-coated after application of the adhesion promoter. Here, the connecting piece is, if necessary, pre-treated, negatively polarized electrically and immersed in a paint bath with positively charged paint particles (so-called KTL process, i.e. cathodic dip coating process, see corresponding specialist literature) in order to lay or apply a paint layer, in particular a so-called primer layer. This paint layer or primer layer applied by cathodic dip coating can have a layer thickness or paint layer thickness of 10 to 50 μιη and more. Due to the electrically insulating effect, the adhesion promoter or the adhesion promoter layer on the adhesive surface is not coated with paint or at least not stably coated with paint during cathodic dip coating and therefore does not need to be covered.

[0015] After laying the paint layer or primer layer in the paint bath, the paint layer or primer layer is preferably also dried (also referred to as baked) in a so-called KTL oven, in particular at a KTL oven temperature in the range of approximately 180 to 220 °C. During this drying process, the adhesion promoter can also be cured, in particular by cross-linking reactions, and obtain its full functionality. Paint deposits possibly present on the adhesion promoter can be removed relatively easily before or, if necessary, after drying, for example by blowing off, wiping or peeling off.

[0016] It is preferably provided that the thickness of the adhesion promoter or the layer thickness of the adhesion promoter layer is coordinated with the thickness or layer thickness of the paint layer or primer layer applied by cathodic dip coating, wherein the minimum layer thickness of the adhesion promoter is derived, in particular, from the electrical insulation to be achieved (see above). It is preferably provided that the paint layer or primer layer applied during cathodic dip coating is substantially the same thickness as the previously applied adhesion promoter. In other words, the paint layer or primer layer applied during cathodic dip coating and the previously applied adhesion promoter layer have substantially the same layer thickness, so that in some cases interfering step transitions are avoided. It can also be provided, however, that the adhesion promoter layer and the paint layer or primer layer have different layer thicknesses.

[0017] Optionally, at least one further paint layer, for example a color paint layer and / or a clear coat layer, can also be applied on the connecting piece after cathodic dip coating and before adhesion, without the adhesion promoter being coated in the process, for which the adhesion promoter can be covered, for example.

[0018] To bond the connecting parts, an adhesive is used, preferably a so-called structural adhesive, in particular a two-component structural adhesive, such as a polyurethane or epoxy (resin) adhesive. The bonding process can include the following sub-steps: applying the adhesive to the bonding surface coated with an adhesion promoter or to the adhesion promoter of the first metal component and / or to the bonding surface of the second component (which may also be coated with an adhesion promoter), aligning the connecting parts, optionally including a pressing process, and curing the adhesive under ambient conditions or under pressure and / or heat (the temperature reached during this process is typically below or at least not above the KTL oven temperature). Alternatively, after the connecting parts have been aligned, the adhesive can also be injected into the bonding gap or bond seam.

[0019] The adhesion promoter applied to at least the first metal connecting part improves the adhesion between the adhesive and the connecting part and also improves the durability of the adhesive joint. Furthermore, during cathodic dip painting, the adhesion promoter prevents paint from being applied to the bonding surface. Consequently, the structural adhesive joint produced according to the present invention is formed without cathodic dip painting (i.e., almost directly without an intermediate layer of paint) and is therefore significantly more stable or more load-resistant and robust (due to the lack of strength or durability limitations due to the paint layer) than conventional adhesive joints that include cathodic dip painting. This results in advantages in terms of static, vibration, and dynamic load-bearing capacity, and particularly crash stability, for the structural adhesive joint in vehicle construction. To enable separation of this relatively robust or stable adhesive joint and thus re-disassembly of the connecting parts, a method for separating the connecting parts, also according to the present invention, is described below.

[0020] A further advantage of the present invention is that bonding can be performed at a much later point in complex manufacturing sequences, which facilitates the implementation of modular construction. For example, in vehicle construction, the joining process, which previously took place in body-in-white production before cathodic dip painting, can be transferred to vehicle assembly after cathodic dip painting, thus facilitating modularization.

[0021] The adhesion promoter for the first metal connection can comprise at least one component which enables targeted separation or loosening of the structural adhesive connection at a later point in time, which can also be referred to as debonding function. The same preferably applies to the adhesion promoter for the second connection as well. This component is in particular a reagent integrated into the composition, such as an intumescent, or other elements mixed in, which for example constitute a chemical intended breaking point, so that the internal cohesion or cohesion of the adhesion promoter is cancelled or released, for example by breaking the polymer chains contained in the thermoset polymer matrix, in the case of thermal action, in particular above the KTL oven temperature, or other suitable energy action. Likewise, it can also be a component, in particular a reagent integrated into the composition or other elements mixed in, which leads to targeted or particularly severe embrittlement of the adhesion promoter or the adhesion promoter layer in the case of very cold action, for example temperatures below -40°. Thus, the adhesive connection can be separated or loosened again at the adhesion promoter or within the adhesion promoter layer at a later point in time, for example for maintenance or recycling purposes, relatively easily (see below), without having to have a special adhesive with debonding function for this purpose.

[0022] As already explained, the second connection can also be metallic. In this case, the method according to the application for producing a structural adhesive connection preferably comprises the following additional method steps, which are carried out before the bonding:

[0023] - applying an electrically insulating adhesion promoter to the bonding surface of the second metal connection, wherein the adhesion promoter is in particular the same adhesion promoter as is also used for the first metal connection;

[0024] - cathodically dip-coating the second metal connection, wherein the adhesion promoter-coated bonding surface remains unpainted.

[0025] The previous explanations similarly apply for these additional method steps.

[0026] The method for separating or loosening a structural adhesive connection manufactured according to the application using at least one adhesion promoter having a debonding function (see above) according to the application provides that the connection or connection assembly adhesively connected according to the application is heated or cooled at least in the region of the adhesive connection, in particular only locally in the region of the adhesive connection (this can be achieved, for example, by means of a hot air blower or so-called hot air gun or cold spray), so that the adhesion promoter is decomposed or embrittled, almost ready for separation, as described above, so that a simple separation can be achieved (without great outlay). Here, the structural adhesive connection is thus separated within the adhesion promoter or adhesion promoter layer, to some extent between one connection or both connections and the adhesive or adhesive layer. That is, the separation or loosening of the adhesive connection does not take place at or within the adhesive, so that an adhesive without a corresponding debonding additive or the like can be used for the adhesive process. This method is also advantageous for possible reuse of the connections.

[0027] The two methods according to the application can be summarized or combined into one method for manufacturing a structural adhesive connection (between a first metal connection and a second connection) and later separating the structural adhesive connection, which has the respective steps described herein.

[0028] The application is explained in more detail below by way of example and in a non-limiting manner with reference to the accompanying drawings. The features shown in the schematic drawings and / or explained below can also be general features of the application independently of the specific feature combinations. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The steps of the method for manufacturing a structural adhesive connection according to the application are shown.

[0030] Figure 2 With Figure 1 Different implementation possibilities are shown analogously to the lower part of the figure. DETAILED DESCRIPTION

[0031] Figure 1 A first metal connection 10 is shown, which is adhesively connected with a second connection 20. The first metal connection 10 is, for example, a sheet metal part. The second connection 20 can be a plastic component or a plastic composite component or likewise a metal component, in particular a sheet metal part.

[0032] An electrically insulating adhesion promoter H1 is applied to the bonding surface F1 of the first metal connector 10, which is provided for bonding, so that a corresponding adhesion promoter layer is present on the bonding surface F1. Subsequently, a lacquer layer L1 is applied to the first metal connector 10 by cathodic dip painting, without applying an adhesion promoter or adhesion promoter layer H1 during this process. The connectors 10 and 20 are then bonded together. To this end, the bonding surface F1 of the first metal connector 10, which has been coated with the adhesion promoter H1, is bonded to the bonding surface F2 of the second connector 20, which is provided for this purpose, by introducing an adhesive K. Further details and implementation variants are described above.

[0033] exist Figure 2 In the embodiment shown, the (lower) second connecting part 20 is also provided with an adhesion promoter or an adhesion promoter layer H2 and a cathodically applied lacquer layer L2, which is similar to Figure 1 The embodiment shown is applied before bonding. The adhesion promoters H1, H2 can be identical or different. The same applies to the lacquer layers L1, L2.

[0034] As mentioned above, the adhesion promoter H1 and / or the adhesion promoter H2 can be provided with a so-called debonding function, which enables separation or release of the adhesive connection by heat and / or cold action, thereby enabling disassembly of the connection parts 10 , 20 , as indicated by arrows T.

[0035] Reference Signs List

[0036] 10 First connecting piece

[0037] 20 Second connecting piece

[0038] F1 bonding surface

[0039] F2 bonding surface

[0040] H1 Adhesion Promoter

[0041] H2 Adhesion Promoter

[0042] K Adhesive

[0043] L1 paint layer

[0044] L2 paint layer

[0045] T separation

Claims

1. A method for producing a structural adhesive connection between a first metal connecting part (10) and a second connecting part (20), the first metal connecting part and the second connecting part each having at least one adhesive surface (F1, F2) provided for the adhesive bonding process, the method comprising the following steps: - applying an electrically insulating adhesion promoter (H1) to the bonding surface (F1) of the first metal connector (10); - cathodic dip painting of the first metal connecting part (10), wherein the bonding surface (F1) coated with the adhesion promoter (H1) remains unpainted; The connecting parts (10, 20) are bonded together, for which purpose the bonding surface (F1) of the first metal connecting part (10) coated with the adhesion promoter (H1) is bonded to the bonding surface (F2) of the second connecting part (20) by introducing an adhesive (K).

2. The method according to claim 1, characterized in that The adhesion promoter (H1) comprises components which enable the structural adhesive bond to be separated at a later point in time (T).

3. The method according to any one of the preceding claims, characterized in that The adhesion promoter (H1) is applied in a layer thickness of at least 25 μm, preferably at least 50 μm.

4. The method according to any one of the preceding claims, characterized in that The paint layer ( L1 ) applied during cathodic dip painting is as thick as the previously applied adhesion promoter ( H1 ).

5. The method according to any one of the preceding claims, characterized in that The second connecting part (20) is also made of metal and for this purpose the following additional steps are provided before bonding: - applying an electrically insulating adhesion promoter (H2) to the bonding surface (F2) of the second metal connector (20); The second metal connecting part (20) is subjected to cathodic dip painting, wherein the bonding surface (F2) coated with the adhesion promoter (H2) remains unpainted.

6. A method for separating (T) a structural adhesive connection produced according to any one of the preceding claims 2 to 5, characterized in that The connecting parts (10, 20) are heated or cooled in the region of the adhesive connection and thereby decompose the adhesion promoter (H1, H2) or embrittle it.

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