WO2017045912A1

WO2017045912A1 - Asymmetric adhesive film having a force decoupling function

Info

Publication number: WO2017045912A1
Application number: PCT/EP2016/070401
Authority: WO
Inventors: Cornelia Sundrum; Patrik Kopf; Daniel Heinitz
Original assignee: Lohmann Gmbh & Co. Kg
Priority date: 2015-09-17
Filing date: 2016-08-30
Publication date: 2017-03-23
Also published as: DE102015115717A1; DE102015115717B4

Abstract

The present invention relates to an asymmetric double-sided adhesive film having a first adhesive layer and a reactive, structurally adhesive second adhesive layer which is different from the first adhesive layer. Owing to the structural adhesion between the adhesive film and, for example, an object consisting of an elastomer via the reactive adhesive layer, the adhesive film according to the invention brings about a force decoupling function.

Description

Asymmetrical adhesive film with a force decoupling function

Technical area

The present invention relates to an asymmetric double-sided adhesive film with Kraftentkoppelnder function.

State of the art

Asymmetric adhesive films (and in particular adhesive tapes) are generally understood as meaning double-sided adhesive films and tapes, the adhesive present on one side of the film / tape being different from that on the other side. Such asymmetric adhesive films and tapes are particularly useful where a single adhesive system is unable to satisfactorily bond two surfaces of differing nature. Asymmetrically constructed adhesive tapes are known from practice and also from the patent literature. Thus, EP 0284564 B1 already describes a multilayer heat-curable adhesive film based on epoxy resins and dicyandiamide as a curing agent, comprising a tacky curable layer and a dry curable layer for bonding structural parts, in particular of metal, optionally with nonwoven backing material between these two layers. DE 102008054031 A1 claims an adhesive multilayer composite in which two identical or different aqueous polymer dispersions are applied on each side of a carrier material. The purpose of such an adhesive tape is to achieve a certain thickness of the composite for leveling uneven ground, especially in masonry.

The aim of EP 0019451 B1 was to decouple working processes from each other already insofar as it was made possible by the multilayer adhesive system according to the invention to apply pressure-activatable adhesive layers to two different layers to be bonded to one another and subsequently to join together the layers attached to the two objects and thereby form the pressure-activatable composite adhesive material. As an aid in this case, for example, a middle release layer is provided, which is introduced between the first and second adhesive layer activatable by pressure and releasably secured thereto. After removing this middle release layer is then made by pressure a permanent connection between see the objects.

An asymmetric adhesive film is the subject of EP 0397177 A2, comprising a substrate with an adhesive layer on both sides, wherein the adhesive layers are chemically and / or geometrically and / or physically asymmetric, in particular for bonding multilayer semiconductor systems. EP 0688845 A1 describes a double-sided adhesive tape with a moisture-curing adhesive on one side and a pressure-sensitive adhesive on the other side of the support for bonding surfaces which would not be satisfactorily bondable with a single system.

Finally, US 20090317610 A1 claims a system of 2 or more, if appropriate with the aid of a primer, adhesives of different nature and / or composition applied directly to one another, for example again for bonding surfaces which are not or only insufficiently bondable with a single adhesive, or also where larger interspaces must be filled and bridged, in which a thick adhesive film of only a single adhesive due to its thickness under certain circumstances melt under pressure and so from the glue joint zT could be squeezed out. Such undesirable sticking behavior could, for example, avoid a combination of adhesives having different rheological properties.

Structural bonding or structural bonding is understood below as meaning those compounds in which the adhesive and the surfaces to be bonded are bonded to one another after curing of the adhesive in such a way that they form a homogeneous structure, so that when this structure changes due to, for example, pulling or pushing movements So the glueing connection is no longer necessarily the point at which these movements attack and weaken the bond or possibly even break it up. Structural adhesives are usually liquid adhesives, but more and more these adhesives are now also found in tape form, which has significant advantages over the liquid form. Such structural compounds are generated, for example, already by mixing and then reacting with each other different components (as in 2-component epoxy systems) or under certain Climatic conditions (minimum temperature or humidity), which cause the adhesive to harden and its structural connection with the surface to be bonded.

Ribbon structural adhesives exist as both hybrid adhesive systems, i. consisting of an adhesive based on two different, a structural adhesive effect inducing polymer bases as well as on the basis of an adhesive consisting of a single polymer backbone. The latter is discussed, for example, in tape form in DE 102010013145 A1, relating to a heat-activatable, latently reactive adhesive based on a polyurethane dispersion or also based on an epoxy-functional acrylate as described in WO 2014/044242 A1. An adhesive tape based on a plurality of different polymers which effects a structural connection is claimed, for example, in WO 2013/144776 A1, namely the combination of a specific cyanoacrylate with an ethylvinyl acetate as a film-forming copolymer and the use of this adhesive system in a single-sided or double-sided adhesive system.

Also known are double-sided adhesive tapes in which a pressure-sensitive adhesive is present on one side and a structurally bonding adhesive on the other side, e.g. described in WO 2012/152713 A1, in which the structurally binding adhesive is a thermoplastic.

Presentation of the invention

Starting from the known prior art, it is an object of the present invention to provide an improved adhesive film which allows an improved adhesive connection between two surfaces and in particular has a structure adapted to the particularities of the surfaces to be joined. In particular, in cases where one of the surfaces is subjected to lifting, pushing, pushing, turning or pulling operations, the present invention is intended to solve the problem of providing a permanently reliable adhesive bond.

This object is achieved by a double-sided adhesive film having the features of claim 1. Claim 1 1 describes an inventive use of the double-sided adhesive film. Advantageous developments emerge from the subclaims.

Brief description of the figures

The invention and preferred embodiments are explained in more detail by the following description with reference to the figures. Showing: Figure 1 is a bond between a profile and a substrate with a conventional pressure-sensitive adhesive;

Figure 2 shows a bond between a profile and a substrate with an adhesive film according to the invention; and FIG. 3 shows the schematic structure of a preferred embodiment of the adhesive film according to the invention.

In the description of the figures, the same, similar or equivalent elements in the different figures are given identical reference numerals, and a repeated description of these elements is partly omitted in order to avoid redundancies. Detailed Description of the Invention

In a first aspect, the present invention relates to an asymmetrical double-sided adhesive film, preferably in the form of an adhesive tape or a stamped part, with a carrier layer. Under double-sided adhesive film, the present invention, adhesive tapes, adhesive strips, and stamped / punched parts with a carrier layer and one adhesive layer on each side of the carrier layer. On one side of the carrier layer, the adhesive film has a first adhesive layer (for example a pressure-sensitive adhesive or a reactive adhesive), while on the other side it has an adhesive layer which is different from the first adhesive layer and has a reactive adhesive. Incidentally, "different from the first adhesive layer" means that the composition of the adhesive of the second adhesive layer is different from the composition of the adhesive of the first adhesive layer, not that only parameters independent of the composition of the adhesive layers such as the thickness of the adhesive layers are different.

Preferably, the carrier layer and the second adhesive layer act together as a force decoupling layer, as described below. Also preferably, the reactive adhesive of the second adhesive layer hardens when using the adhesive film, ie after bonding the second adhesive layer to an article, and creates a structural bond with the article. The curing of the reactive adhesive layer may take place as a consequence of a chemical reaction and / or under certain climatic conditions (temperature and / or humidity). Particularly preferred is a reactive adhesive of the second adhesive layer, which produces a structural bond with elastomers. Elastomers are understood as meaning, for example, natural rubber (NR), polybutadiene (BR), polyisoprene (IR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), ethylene-propylene rubber (EPM, EPDM), butyl rubber (NR), chloroprene rubber (CR), silicone rubber, thermoplastic elastomers (TPE), polyolefin rubbers (from Röthemeyer, Sommer, Kautschuk Technologie, Munich 2013).

In a preferred embodiment, the reactive adhesive of the second adhesive layer comprises at least one cyanoacrylate, preferably a solid cyanoacrylate, particularly preferably phenylethyl cyanoacrylate. The cyanoacrylate monomers react upon polymerization by polymerization, thereby forming a structural compound. In addition to the cyanoacrylate monomers, the adhesive, as known from the prior art, also contain one or more film formers, preferably at least one ethylene-vinyl acetate copolymer (EVA copolymer). For this purpose, the adhesive may contain suitable stabilizers to prevent the premature polymerization, as known from the prior art. The handling and coating of the reactive adhesive of the second adhesive layer preferably takes place from solvent, for example from an approximately 50% strength solution in ethyl acetate.

Depending on the intended use of the adhesive film, the reactive adhesive may contain further additives known from the prior art, such as plasticizers, defoamers, fillers, accelerators, resins, hardeners, etc. The carrier layer preferably has a film, a textile (for example woven or nonwoven) and / or a foamed material. As a material for the film can be used in addition to other plastics, for example, polyester, polycarbonate, polylactide or more preferably polymethyl methacrylate (PMMA).

The first adhesive layer of the adhesive film according to the invention may be both a pressure-sensitive adhesive layer which comprises a pressure-sensitive adhesive based on acrylate, rubber, silicone, polyurethane and / or mixtures thereof, and a reactive adhesive layer which has a second reactive adhesive which (of the composition ) is different from the above-described reactive adhesive of the second adhesive layer. Preferably, a reactive adhesive of the first adhesive layer hardens when using the adhesive film, ie, after bonding this first adhesive layer to an article, and creates a structural bond with the article. The curing of the reactive adhesive layer may take place as a consequence of a chemical reaction and / or under certain climatic conditions (temperature and / or humidity).

The advantage of a pressure-sensitive adhesive layer as a first adhesive layer is that the adhesive film (and with it the object adhesively bonded by means of the reactive second adhesive layer to the adhesive tape) can be removed again from the substrate to which the adhesive film has been bonded by means of the pressure-sensitive adhesive layer. This is particularly advantageous if the object must be replaced due to wear or if the object is to be repositioned / moved on the ground. For example, such a double-sided adhesive sheet of the invention may be used for the attachment of rubber seals, e.g. in windows and doors or in household appliances (so-called white goods), decorative moldings, e.g. in the automotive field, of rubber printing plates and blankets on printing cylinders, creasing, punching or punching tool parts, table tennis rackets, tool handles, door stoppers, etc. are used.

Surprisingly, it has been found that the as yet unspecified use of a structural reactive adhesive system in at least one adhesive layer together with another different adhesive in a second layer in an asymmetric, carrier-based, double-sided adhesive material in the form of an adhesive film, an adhesive tape, an adhesive strip or an adhesive Not only is punched parts ideally suited to durably and structurally bond different and otherwise unsatisfactorily bondable surfaces, but that such a system simultaneously produces a force decoupling layer in addition to this bonding during lifting, pushing, pushing, turning or pulling operations forms, which would be expected by their nature, that a permanent and under the influence of such lifting, pushing, pushing, turning or pulling over a long period or after numerous repetitions still exact position existing Bonding is hardly possible. Such processes are, for example, punching or printing operations. Force in the physical sense means an action on a mass that causes a change of motion. The force is a directed, ie vectorial size. If a force acts on a fixed body, it can cause it to deform, and if it acts on a moving body, it can accelerate it. Forces have different causes according to which they can be named, for example, as frictional force, impact force, tensile force, centrifugal force or weight force. If a deformation under force is proportional to the acting force and the body returns to the initial state after the end of the force action, then one speaks of an elastic deformation, the restoring force of the body is responsible lent for this return to its original state. Power decoupling in the present context means that the force acting on a body is permanently present in the dimensions required for an intended application, but the effects of this force are modified to such an extent that unwanted behaviors of the body on which the force acts are eliminated. For example, many repetitions of a force on an elastic body often cause its restoring force is negatively affected by the number of repetitions and then the body is no longer completely proportional to the number of repetitions of the force returns to its initial state, such as in operations in which a return to the initial state necessary to maintain the full functioning of the body has negative effects. Another example is when the repeated application of force eventually causes an undesirable change in the position of the body on which the force acts. This may in both cases, for example, relate to elastic sealing systems, which finally no longer develop their complete restoring force with the number of force actions or change their position under the pressure of the repeated force effects and in both cases become leaky.

Power decoupling is understood in the present case that the force is used to the full extent in which it is necessary to achieve the desired effect on a body, but negative state changes of the body due to the repeated use of this force is omitted or a clear higher levels of force can be achieved than with conventional systems until negative and undesirable effects of this force are evident - in other words, the desired failure-free operation of a system under regular or irregular repetitive force is maintained much longer than this with conventionally known systems. The cause of the force-decoupling effect of the system according to the invention given in the present case lies in the interaction of the two sides provided with adhesive as well as the carrier material of the adhesive system, such as e.g. an adhesive tape, an adhesive tape or a stamped part.

The effect of the force decoupling according to the invention over conventional bonding will be explained using the example of FIGS. 1 and 2. Fig. 1 shows the bonding of a profile (2) with a substrate (1) by means of a simple pressure-sensitive adhesive layer (3), which is suitable for bonding the materials of profile and ground together. For example, the profile (2) a Door seal made of an elastomer and the substrate (1) be a door frame made of wood. When the door is now closed, it pushes against the profile (2) and exerts a force F in the direction of the arrow on the profile (2) (Figure 1, right). This results both in a compression of the profile (2) in the direction of the force F and in an expansion of the profile (2) in the plane perpendicular to the force F. The pressure-sensitive adhesive (3) can increase the extent of the profile (2). not completely follow, causing it to stress the pressure-sensitive adhesive bond between pressure-sensitive adhesive layer (3) and substrate (1) comes. If such a load occurs with a high number of repetitions and / or over a longer period of time, a break occurs between pressure-sensitive adhesive layer (3) and substrate (1) or profile (2) or both. The bond is released and the profile starts to float. In Fig. 1, the pressure-sensitive adhesive is represented by means of a transfer adhesive layer, ie without the use of a carrier material. However, a carrier-based pressure-sensitive adhesive film also shows that, irrespective of the type or the thickness of the material, these negative consequences follow repeated use and / or after prolonged use.

An adhesive bond between profile (2) and substrate (1) with an adhesive film according to the invention is shown in FIG. 2. In this case, the adhesive film of the invention has a carrier layer (1 1), as well as on one side a first adhesive layer (12) which is suitable for the intended use sufficiently strong adhesive bond between the carrier layer (1 1) and the substrate (1) on the other hand, a second, reactive adhesive layer (10), which leads to a structural bonding of the carrier layer (1 1) with the profile (2). The structural bonding results in a reinforcement of the profile (eg of an elastomer profile) so that it acts in the direction of the arrow when a force F acts (FIG. 2, right) - for example as above a door which in the closed state against a door seal - can not spread F at the bonding point in the plane perpendicular to the force F. As a result, the bond between the carrier layer (1 1) and substrate (1), i. the first adhesive layer (12) is not stressed and remains stable even with repeated and / or prolonged exposure.

In particular, when a pressure-sensitive adhesive is used as the first adhesive layer, such a power decoupling is advantageous because in this case an unnecessary burden of the pressure-sensitive adhesive connection is avoided and therefore the pressure-sensitive adhesive material can be chosen for example so that after an age-related embrittlement of the profile or even if the profile is to be offset, the pressure-sensitive adhesive material can be removed again preferably without residue from the substrate. In principle, adhesive systems which can be used here as reactive structural structuring systems on one side or both sides of the support can be both systems based on a single polymer backbone and hybrid systems, ie mixtures of different polymer frameworks. It is advantageous if these systems are in a solid, band-shaped form. Although the use of liquid adhesive systems is certainly also conceivable from a variety of applications, however, the associated disadvantages such as the possible inaccurate order and unspeakableness and the inability to decouple the actual bonding process in terms of time and space clearly from the adhesive application process and thus also speak to rationalize the manufacturing process, for a solid, band-shaped form of application.

Such tape-shaped applications may be permanent, i. as an application period, ideally covers the entire life cycle of an application or a product in which the application has been processed, covering or even limited in time, for example, where parts of the application or product wear in use and need to be replaced at intervals to get the full functionality. Significant characteristics of products or applications in which systems according to the invention are used are, on the one hand, the adhesive force which is completely satisfactory for the respective application and, on the other hand, the decoupling of a force acting on or acting on the product to the extent that that the bond thereof is not or only to a much lesser extent adversely affected, as is the case with previously known systems.

Permanent applications in the sense of the present invention are i.a. many types of gaskets, which are repeatedly exposed to a certain force acting on them, for example in doors or windows or in machines with repeated lifting, pushing, pushing, turning or pulling operations, but at the same time on the perfect tightness of the system arrives. In such cases, it is expedient to use double-sided adhesive asymmetric adhesive systems according to the invention in which different reactive, structurally adhesive adhesives are present on the two sides.

For example, automated stamp imprints at exactly the same place in a production process or also punching or embossing processes are exposed to parts of a product or an application that are exposed to regular or permanent force effects and therefore time-limited due to wear and tear in which it insists on the permanent and perfect accuracy of the standard cens or embossing arrives in one plane. Also suitable are applications in which it depends on a rapid as possible, uncomplicated change of this part as a result of a certain wear of a part involved in the particular application. Such operations always involve a basic, unmodified and durable device which performs lifting, pushing, pulling, turning or pushing operations and a part placed on this device which is either subject to some wear and therefore residue-free at certain intervals must be removed and exchanged for a similar new part or quickly and easily interchangeable for a new application against a different type of part and thus in a way also at the same time be replaced and repositioned. FIG. 3 schematically shows a section through a preferred embodiment of an adhesive film according to the invention. The adhesive film shown has a carrier layer (1 1), which may for example consist of a film, a textile (eg fabric or nonwoven) or a foamed material. The thickness of the carrier layer can be between about 5 μιτι and about 500 μιτι. Particular preference is given to using a PMMA film with a thickness of about 90 μm as the carrier layer.

On one side of the carrier layer (11), the adhesive film has an adhesive layer (10) with a reactive adhesive based on a cyanoacrylate, in particular a solid cyanoacrylate. For example, the reactive adhesive comprises phenylethyl cyanoacrylate, especially in admixture with an EVA copolymer. In a preferred embodiment, the reactive adhesive composition consists of 50% phenylethyl cyanoacrylate, 49.5% Levamelt 900 (an EVA copolymer available from Lanxess AG, Leverkusen, Germany) and 0.5% stabilizer.

On the other side of the carrier layer (11), the adhesive film has an adhesive layer (12) with a pressure-sensitive adhesive. With its properties (viscoelasticity, adhesion to the substrate, cohesion, repositionability, residue-free detachment, long-term behavior), the PSA can be adapted to the intended use of the adhesive film. In a preferred embodiment, the PSA consists of a rubber solvent adhesive, particularly preferably based on styrene block copolymers. The construction and the adaptation of a pressure-sensitive adhesive are known to the person skilled in the art (Donata Satas: Handbook of Pressure-Sensitive Adhesive Technology, June 1982). Formulations of rubber-solvent pressure-sensitive adhesives are described, for example, in Müller, Rath: Formulation of adhesives and sealants, Hannover 2004, from page 225, in particular solvent-based adhesives based on styrene block copolymers, from page 230. At least one of the adhesive layers is covered with a covering layer (13) (also called a release liner or liner) in order, for example, to prevent adhesion of the pressure-sensitive adhesive layer to an undesired location or premature curing of the reactive adhesive layer. However, it is also quite possible to use two identical or different liners in order to cover both adhesive layers. The cover layer (13) is, for example, siliconized and is compatible with the adhesive / adhesives covering the cover layer. In this case, "compatible" means that the covering layer in the application state, ie, in the case of a covering layer for a reactive adhesive layer before curing of the reactive adhesive, can be easily detached from the respective adhesive layer and that the covering layer does not induce premature curing of the reactive adhesive In a preferred embodiment, the cover layer consists of graded siliconized PET film. "Graduated" means that the release values (ie the force to be applied in order to release the cover layer from the respective adhesive layer) may be different on both sides respective adhesive system.

If the double-sided adhesive film is in strip form and should be rolled (eg for storage, transport, etc.), it can be provided that only - as shown in Fig. 3 - a single cover layer (13) is used, which then in the rolled state the adhesive tape (not shown) covers both adhesive layers (10, 12). In this case, the covering layer is preferably compatible with both adhesives. If the double-sided adhesive film is present for example in the form of adhesive strips or diecuts and therefore can not be stored rolled or for other reasons should not be rolled, a separate cover layer is used for both adhesive layers.

In a second aspect, the present invention relates to a manufacturing method for a component using an adhesive film according to the invention. Thus, on the one hand, the two surfaces to be bonded in a single bonding operation at the same time or at a short time interval and then at the same place are connected to each other, on the other hand, the bonding process of the two surfaces both temporally and spatially separated from each other. Thus, for example, an embossing stamp can already be structurally and thus permanently connected to a corresponding adhesive film, before the adhesive-bonding connection of the embossing stamp with the latter moving this stamp at a later time and / or at another location (immediately before use / at the actual place of use) Embossing device takes place. At least in the event that an asymmetrical adhesive film according to the invention has a pressure-sensitive adhesive and a structurally adhesive layer, this becomes temporal and / or spatial decoupling The two bonding operations on the one hand for reasons of flexibility in the vast majority of possible applications sought, since the curing of the structural compound on one side of the film with simultaneous pressure-sensitive adhesive bond of the other side depending on the nature of the curing mechanism may only with great effort ( For example, under elevated temperatures or by the addition of moisture) could be accomplished.

A third aspect of the present invention relates to the use of a double-sided adhesive film according to the invention. As described above, an adhesive film according to the invention can be used to effect a force decoupling between two joining partners bonded together, e.g. a component and the surface adhered to the component (via the adhesive film). Preferably, at least one of the joining partners is elastic and more preferably at least partially consists of an elastomer.

Depending on the configuration of the first adhesive layer (eg pressure-sensitive adhesive layer, reactive adhesive layer, etc.), one of the joining partners can be redetachably or structurally connected to the other joining partner. For example, when using a pressure-sensitive adhesive layer as the first adhesive layer, the component can be repositionably fixed to the substrate, whereby a preferably residue-free detachment from the substrate and re-adhering is made possible, or at least preferably be removed without residue from the substrate. If a reactive adhesive layer is used as the first adhesive layer, the component can also be structurally connected to the substrate. Where applicable, all individual features illustrated in the above description of the invention and the embodiments may be combined and / or interchanged without departing from the scope of the invention.

LIST OF REFERENCES

1 underground

2 profile

3 pressure-sensitive adhesive layer

10 second adhesive layer (reactive adhesive)

1 1 carrier layer

12 first adhesive layer (pressure-sensitive adhesive or reactive adhesive)

13 covering layer

Claims

claims

1. Double-sided adhesive film for bonding two surfaces, comprising a first adhesive layer, a carrier layer and a second adhesive layer different from the first adhesive layer, wherein at least the second adhesive layer comprises a reactive adhesive.

The adhesive sheet of claim 1, wherein the backing layer and the second adhesive layer act together as a force decoupling layer.

3. Adhesive film according to one of the preceding claims, wherein the reactive adhesive of the second adhesive layer hardens when using the adhesive tape as a result of a chemical reaction or under certain climatic conditions (temperature and / or humidity) and produces a structural bond.

4. Adhesive film according to one of the preceding claims, wherein the reactive adhesive of the second adhesive layer, in particular on elastomers produces a structural bond.

5. Adhesive film according to one of the preceding claims, wherein the reactive adhesive comprises at least one cyanoacrylate, preferably a solid cyanoacrylate, particularly preferably phenylethyl cyanoacrylate.

6. Adhesive film according to claim 5, wherein the reactive adhesive further comprises one or more film formers, preferably at least one ethylene vinyl acetate copolymer.

7. Adhesive film according to one of the preceding claims, wherein the carrier layer comprises a film, a textile or a foam.

8. Adhesive sheet according to claim 7, wherein the film is a polyester, polycarbonate, polymethylmethacrylate or polylactide film.

9. Adhesive film according to one of the preceding claims, wherein the first adhesive layer is a pressure-sensitive adhesive layer which comprises a pressure-sensitive adhesive based on acrylate, rubber, silicone, polyurethane or mixtures thereof.

The adhesive sheet of any of claims 1-8, wherein the first adhesive layer comprises a second reactive adhesive which is different than the reactive adhesive of the second adhesive layer.

1 1. Adhesive sheet according to claim 10, wherein the second reactive adhesive of the first adhesive layer cures when using the adhesive tape as a result of a chemical reaction or under certain climatic conditions (temperature and / or humidity) and produces a structural bond.

12. Use of an adhesive film according to one of claims 1-1 1 for force decoupling between two joining partners.

13. Use according to claim 12, wherein at least one of the two joining partners is elastic and preferably at least partially consists of an elastomer.

14. Use according to one of claims 12 and 13 as far as dependent on claim 9, wherein the joining partner is releasably connected to the other joining partner.

15. Use according to one of claims 12 and 13 as far as referring back to one of claims 10 and 1 1, wherein the one joining partner is structurally connected to the other joining partner.