JPH01500757A - Ambient Temperature Curable Structural Membrane Adhesive Element and Method of Use thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Structural membrane adhesive element curable at ambient temperature and its use [Background technology] The present invention relates generally to composite membrane adhesive elements for joining two structures, particularly for joining two structures. .

One of the most important aspects of many manufacturing operations is that There are joints of structures that are joined to each other in larger structures. This may be caused by other structures or They may be joined together in the final assembly. Joining structures is an important task. Ru. Damage often occurs at joints in structures.

Or, it may be necessary to satisfy specific requirements between two structures.

The joint surface of two structures is strong and can be affected by many different mechanisms such as fatigue and corrosion. Must be resistant to breakage and meet other requirements to act as an electrical insulator. This is because it is sometimes recommended to do so.

Structures used in aircraft and spacecraft are often subject to the greatest demands. This is because it must have both excellent physical properties and low weight. past In , most of this structure uses mechanisms such as rivets, bolts or screws. They were joined by mechanical fasteners or metallurgical joining techniques such as welding or soldering. recently Now that the properties of adhesives have improved, many aerospace structures can now be joined with adhesives. Wear. Adhesively bonded structures have more important structural features than fastener bonded structures. It has the following advantages. Because the bonded structure has one surface load distributed over a wide area, This is because it is actually stronger than one using a fastener. Since the load is distributed, the Significantly reduced instances of structural failure such as fatigue cracking initiated by stress concentration around fittings be done.

When bonding, the bond line must be strong and at the same time form an electrically insulating barrier. Sometimes it is necessary. As an example.

Spacecraft Electric Storage Battery Nickel Alloy Pressure Vessel With Aluminum Thermal Flange It helps dissipate the heat that accumulates in the battery when bonded. Joining line between battery and flange It is important that the parts are electrically isolated. The charge on the battery is transferred to other parts of the spacecraft. It will be. Furthermore, the adhesive has extremely low particle outgassing in the space environment [parti cle outgaslng].

In other words, the presence of the adhesive may cause it to enter the atmosphere and adversely affect other aerospace systems. must not produce any small particles.

Silicone-based adhesives [e.g. RTV5H adhesive] can be used to attach battery pressure vessels to thermal flanges. Used to join vessels. This adhesive cures and solidifies at ambient temperature and bonds to each bonding surface. Available as a paste that can be applied, the curing potential at 0 ambient temperature is applications and many other applications in joining aircraft and aerospace structures. be. There is no need to heat the entire structure being joined to elevated temperatures to cure the adhesive It is from. Silicone-based adhesives are themselves virtually electrically non-conductive However, if only adhesive is placed between the pressure vessel and the flange, both will be physically separated at individual points. The bond wire produced in contact with the wire does not meet the electrical insulation requirements.

Therefore, between the pressure vessel and the flange there is a layer of insulation, such as Mylar plastic. It is standard practice to place the insulator layer with adhesive on one side. In other words, the coupling structure The construction consists of coating the pressure vessel and flange with silicone adhesive, and applying a layer of silicone on one side of the adhesive layer. Formed by placing a layer of Mylar and then tightening the parts together for hardening.9 This method is operable but high enough to move one assembly. It takes about 148 hours to cure the silicone adhesive to a high strength, so it is slow. this The method is also not effective from a weight point of view, the adhesive is heavy and the adhesive cannot be used as a paste. This is because the thickness cannot be accurately controlled when used. All intermediate layers between bonding structures The thickness is typically about 0.030 inches, but depending on the skill of the operator applying the adhesive. The degree-dependent excess thickness adds considerably to the weight of the aerospace vehicle. this adhesive The bonding technology is also slow and expensive. 8 Workers try to make the layers as even as possible to cover the entire area. This is because the adhesive must be carefully applied to each surface so as to cover it. most Later, the most important point is that the resulting bonded structure is not due to the weakness of the adhesive itself. This is because the Mylar film inserted between the adhesive layers is weak, making the structure The structures are not connected directly to each other, but through Mylar film.

There is therefore a need for improved adhesive bonding techniques to bond structures at ambient temperatures. Existing. This technique produces a strong bond and eliminates the need for the use of adhesives. both sides of the labor, and the bonding work is completed before the bonded structure can be moved. This method of joining must be economical in terms of the time required to Must have low levels of particulate gas emissions, this technology requires battery pressure vessels and hot flan. An electrically insulated bond wire such as a wire bond must be provided, but this The technique has wide applicability to join other structures; the present invention meets these needs. meets the requirements and provides further related benefits; [Summary of the invention] The present invention is. Pre-manufactured to the exact size that corresponds to the size of the bonding surface before use. 4. Concerning the structural membrane adhesive element that can be used and its use. This pancreatic fluid adhesive element can be Can be manufactured precisely to the desired adhesive thickness to ensure electrical isolation and insulation of structures .

The bond formed is of uniform and controllable thickness and can be obtained by conventional techniques. Stronger than a bond. This pancreatic fluid adhesive element should be Manufactured in large quantities for economical production and for later use without loss of effectiveness. It can be stored for a long time.

According to the present invention, a method for bonding two structures to each other includes manufacturing a pancreatic fluid adhesive element. The pancreatic fluid adhesion agent element has a porous carrier layer and two uncured layers, one on each side of the porous carrier layer. Includes adhesive layer.

Adhesive: 5゛C adhesive to bond with sufficient strength so that the structure can be handled without separating. forming an adhesive structure (7. forming an adhesive layer by curing the adhesive material at ambient temperature; 2; forming an adhesive layer; Cool the element to a temperature low enough that the adhesive layer cannot cure; a structure for storing; and bonding adhesive elements under pressure at a temperature that allows the adhesive substance to cure; This involves placing the adhesive between the objects and curing the adhesive. mylar plastic A release film [release f'i1m] layer of such material is brought into contact with a porous carrier material. Bonding to each of the uncured adhesive layers on the non-cured side preserves and preserves the pancreatic fluid adhesive elements. Preferred for ease of handling during application.

The porous carrier layer is preferably a glass fiber mat and has a thickness of about 0.004 inches. Particularly preferred adhesive materials include preferably epoxy resins, particularly preferred having a polyamide hardener, the thickness of each adhesive layer is preferably about 0. ．． It is 0.003 inches.

In particular, the method for joining two structures to each other includes manufacturing a pancreatic fluid adhesive element, The elements consist of a fiberglass mat and two uncured elements, one on each side of the fiberglass mat. comprising an adhesive layer, wherein the adhesive material of the adhesive layer is a glass fiber mat. glass fibers with sufficient strength to flow and handle the pancreatic fluid adhesive elements without separation. An adhesive layer is bonded to the mat, and the adhesive layer is made of epoxy resin and epoxy resin that can be cured at ambient temperature. Formed with an adhesive mixture of polyamide hardener, the adhesive mixture is Fluid at ambient temperature to flow out of the fiberglass mat when handled at ambient temperature and the pancreatic fluid adhesive element is further removed from the free surface of the adhesive layer which does not come into contact with the glass fiber mat. It includes a pair of release membranes that can be peeled off to the surface; the pancreatic fluid adhesive immediately Glue by cooling the element to a temperature low enough that the adhesive mixture does not flow and harden. 17: the mixture is in a substantially solid uncured state; the adhesive mixture is solid and cannot be cured; Store the pancreatic fluid adhesive element at temperature; add a peelable release membrane layer to the structure of the two Remove under pressure between the two structures joining the pancreatic fluid adhesive elements in a suitable order. and raising the temperature of the pancreatic fluid adhesive element to a temperature at which the adhesive mixture can harden. includes. Also.

Preferably, the thickness of the glass fiber is 0.1004 inches.

Preferably, each adhesive layer has a thickness of 0.003 inches.

The composite membrane adhesive element is a porous glass fiber mat; one on each side of the fiberglass mat. a pair of adhesive layers in contact with one fiberglass mat, each adhesive layer being at ambient temperature. Adhesives that are sufficiently fluid at ambient temperatures to cure at temperatures and flow out of the fiberglass mat and a pair of Mylar release layers, each release layer comprising glass; Includes those in contact with one adhesive layer on the side of the adhesive layer remote from the fiber mat. . The adhesive mixture may be a mixture of an epoxy resin and a polyamide hardener. preferable.

The composite membrane adhesive elements of the present invention are typically manufactured in bulk and refrigerated.

It can be cut to size, packaged and stored until needed. join structures When the peeling film of 1 is to be peeled off, the pancreatic fluid adhesive layer is pressed onto the surface of 1 to be bonded, and the other Peel off the release film.

Press another surface into place. This operation is accurate, easily repeatable, and Achieve a stronger bond using much less adhesive than the method. Another 2 minutes It takes less than an hour and can be done much more times than conventional methods. preferred epoxy wood With the use of fats and hardeners, the bond structure is strong enough to move without separating the bond lines. can be obtained after about 16 hours.

Complete curing occurs after about 7 days. The strength achieved after 7 days is the same as with conventional silicone adhesive. Much larger than what you get.

The adhesive elements and methods of the present invention provide adhesive bonding structures, particularly structures that are electrically connected to one another. It is clear that this provides an important improvement when the The adhesive element can be manufactured easily and economically in a highly controllable and reproducible manner. It can then be stored indefinitely without losing its effectiveness at the time of use.

Workers can join two structures together in minutes instead of hours.

The curing operation proceeds quickly so that the bonded structure can be handled within a day. child The bonded structures of the present invention are stronger and lighter than those obtained with conventional bonding techniques. What are the features and effects?

Reference is made to the description in conjunction with the drawings, which provides a detailed explanation of the invention by way of example. So it should be clear.

[Brief explanation of the drawing] FIG. 1 is a side cross-sectional view of a pancreatic fluid adhesive element according to the present invention.

FIG. 2 is a side cross-sectional view of two structures joined using the pancreatic fluid adhesive element of FIG. 1;

FIG. 3 is an enlarged detail of FIG. 2 illustrating the porous carrier layer.

[Description of preferred embodiments] The invention can be used to join two structures together.

This is embodied in the pancreatic fluid adhesive element designated lO in FIG. Pancreatic fluid adhesive element lO is manufactured Articles that can be stored and handled prior to joining structures. Pancreatic juice adhesive element 10 includes a porous carrier layer 12, with an uncured adhesive layer 14 on each side of the carrier layer 12; Adhesive layer 14 absorbs the entire pancreatic fluid without causing separation of adhesive layer 14 from carrier layer 12. bonded to carrier layer 12 with sufficient strength to allow handling of adhesive element 10; . Because the carrier layer 12 is porous, a small amount of the material in the adhesive layer 14 is absorbed into the pancreatic fluid adhesive element 10. during the manufacture of the carrier layer 12a, thereby allowing the adhesive layer 14 and to create the necessary bond with the carrier layer 12 and retain the pancreatic fluid adhesive element 10 even before curing. Provides sufficient strength. Preferably, the side of the adhesive layer 14 not in contact with the carrier layer 12 A peeling layer 16 that can be separated into two is prepared. The pancreatic fluid adhesive element 10 is in the correct location. After manufacturing with release film layer 16.

Remove immediately before using pancreatic fluid adhesive element IO in the binding operation.

The use of a pancreatic fluid adhesive element lO for joining two constructs 18 is shown in FIG. A bond line 19 between 1B and 1B is shown. Peeling @ layer 16 removed and remaining pancreatic fluid glue required The element IO is in the correct place between the two structures 18. Each structure 18 has two layers of adhesive 14 and the other by a bonding line 19 by the porous carrier layer 12.

A preferred material for carrier layer 12 is a glass fiber mat, such as a woven fiberglass material. Ru. Fine glass fibers are woven, compressed and co-extruded to make them available on the market in various thicknesses as required. You can form a hand-made mat. The thickness of the fiberglass mat is approximately 0.004 inches. 1 layer 12, which has been found to be satisfactory with other materials, as in all mats and fabrics. porous in the sense that there is some space between the fibers that allows access to the porosity It is. This porosity is useful in the practice of this invention for the reasons illustrated in FIG. pancreatic fluid adhesive After manufacturing the element 10, the material of the adhesive layer is bonded between the fibers 20 as an intrafiber adhesive material 22. There is a continuous passageway of 9 intrafiber adhesive material 22 through the thickness of the carrier layer 12 that enters the carrier layer 12. Therefore, the carrier layer 12 becomes a fiber composite material. Fiber 20 has an intrafiber adhesive material 22 The intrafiber adhesive material 22 supports the tensile loads perpendicular to the fibers 20 withstand In contrast, non-porous layers do not allow the ingress of such adhesive substances, so The tensile and shear loads carried by the adhesive line are relatively weak between the non-porous layer and the adhesive layer. It is necessary to provide complete support at a narrow interface.

The material of adhesive layer 14 is an adhesive mixture, preferably an epoxy that cures at ambient temperature. It is a mixture of xy resin and its curing agent.

A satisfactory epoxy resin is bisphenol-A type 828 Epon epoxy. It is. Such epoxy resins are manufactured by 3M as type EC2216 epoxy resins. Available from the company. Preferred hardeners are polyamide hardeners derived from nylon structures. It is a chemical agent. Preferred epoxy resins and hardeners include 7 parts by weight of epoxy and 5 parts by weight of epoxy. of hardener, but this ratio depends on the epoxy and hardener selected. It can change. The use of polyamide hardeners is important. Glass transition at about 125°F This is because temperature is imparted to the epoxy resin and curing agent mixture. The mixture is 1.25 The pancreatic fluid adhesive element lO is flexible over a range of at least 150°F to Maintain open channel flexibility in manufacturing and storage. 1 grain if this mixture hardens in the adhesive layer Does not produce undesirable particles called child outgassing, the resulting film adhesive layer is strong after curing and which adhere well to metal surfaces such as those typically present in structure 18. No special penetration of the surface of structure 18 is required beyond normal cleaning operations. promotes bonding Wire brushing was found to be effective for this purpose. The thickness of the adhesive layer is explained However, it can vary depending on the manufacturing method.

It has been found satisfactory that the thickness of each adhesive layer 14 is approximately 0.003 inches. Ta.

The material of release membrane layer 1B is preferably a plastic film such as mylar plastic film. It's a tic. This membrane is readily available in various thicknesses, approximately o, ooos thick. It was found that the thickness of the inch was satisfactory.

The pancreatic fluid adhesive element 10 is prepared by placing a sheet of release membrane layer 16 on a smooth surface. can be manufactured. The mixture of materials of the adhesive layer 14 includes an epoxy resin and a hardener. obtained by mixing in appropriate proportions. This mixture cures at ambient temperature, but initially is slow enough that there is time to manufacture the adhesive element 10. This mixture is made from cold sugar. It has a lop-like structure and can be spread out in a slowly flowing layer. Ru. A layer of adhesive material having the desired thickness is placed on the release membrane.The thickness of the six layers is as shown in the table below. By smoothing the top surface of the layer with a roller or smoothing rod at a distance from the surface. It can be made extremely uniform.

A piece of the porous carrier layer material is gently placed on top of the adhesive layer 8 and then the rest of the adhesive material is placed on top of the adhesive layer. Spread the surface over the porous carrier layer material.

Finally, place another sheet of release membrane material on top of the top layer of adhesive.

Complete the stacking of the porous glass mat, two adhesive layers, and two release membrane layers. this During the operation, some adhesive mixture flows into the porous spaces between the fibers of the fiberglass mat. This stack is then vertically compressed to further introduce adhesive material between the fibers 20. to form an intrafiber adhesive material 22. Vertical compression causes the desired amount of pancreatic fluid adhesive element 10 to Pass the stacked material between a pair of rollers set in the gap between the thick rollers. It is convenient to do so.

The compression uniformly adjusts the thickness of the membrane 10 to the desired standard value and also applies the adhesive to the fibers of the mat. Some of the adhesive penetrates into the porous carrier layer 12, so spread it out first. The thickness of the adhesive applied should be slightly greater than the desired final thickness of the adhesive layer 14. do not have.

Approximately 0.003 inches using a fiberglass carrier layer 12 that is 0.004 inches thick. Approximately 0.004 inch of adhesive material is initially applied to obtain a final thickness of each adhesive layer 14 of It turned out that we had to expand to

The pancreatic fluid adhesive element 10 is then immediately lowered and lowered so that the adhesive mixture hardens. Cool to a temperature below which the compound solidifies.

2. At ambient temperature, the uncured adhesive mixture is sufficiently fluid to form a porous solid. The pancreatic fluid adherent element separates as it flows away from the layer.

Only by cooling to such a low temperature can the structure of the pancreatic fluid adhesive element 10 be preserved. be done. Further cooling stops the curing process so uncured film adhesive elements are preserved indefinitely can. The temperature at which the pancreatic fluid adhesive element is cooled varies depending on the nature of the adhesive mixture, but is approximately Temperatures of -40°F to about 0'F are preferred, achieving the necessary cessation of curing and commercially available. This is because the adhesive mixture is solid and can be easily achieved in the freezer. After cooling, the pancreatic fluid adhesive element is attached to the desired maximum surface area to be bonded, if known. It can be cut into the final shape with scissors or a mold. The pre-cut pieces or large sheets are then Store at low temperature until later use. Larger pancreatic fluid adhesive element lO for immediate use can be preformed.

Given the advantages of manufacturing scale economies, preformed membrane adhesive elements are often desirable. Store it in an airtight container, such as an aluminum bag, at a temperature that stops the curing process. It can be saved by A storage temperature of -40″F is effective for later use. It has been found that pancreatic fluid adhesive elements can be preserved for up to one year without loss of sex.

When a frozen piece of pancreatic fluid adhesive element 10 is used for a bonding operation, it is removed from cold storage and Immediately peel off the release film and align the adhesive surface so that the shape of the exposed element 18 matches the shape of the surface. Press the sea urchin. Epoxy resin and polyamide hardener that is flexible at cold storage temperatures The use of an adhesive mixture with will aid this stage of the bonding operation. Do not crack the adhesive element. This is because it can be bent. When the pancreatic fluid adhesive element 10 is pressed against the surface, it passes. It has been found that the pancreatic fluid adhesive element 10 usually produces sufficient adhesion to stick to the surface. Second The release membrane layer is then peeled off to expose the second adhesive surface. of other structures to be joined The surface is then pressed down and moved slightly as necessary to conform and tighten tightly.

This part of the bonding process is performed quickly, preferably with the pancreatic fluid adhesive element being heated to ambient temperature. At zero ambient temperature, the adhesive mixture will gradually flow out of the element and the pancreatic fluid adhesive element will To separate. A short time at ambient temperature is acceptable before completing the bond. The viscosity of the adhesive mixture This is because the temperature is typically high enough that it does not flow quickly enough.

As shown in Figure 2, the resulting bonded structure is strong with bonding lines, and the structure 18 conducts charge. Do not make physical contact that would cause the adhesive to thin the areas where the carrier layer is not present. There is a possibility that the two structures will come into contact.

The method of the invention is particularly applicable to nickel alloy storage batteries as well as other types of aluminum alloy storage batteries. Useful for forming. Conventionally, such a bond is made using RTV 566 type silicon. It was done using adhesive.゛ Dirt has low particulate gas emissions and is rubbery, but .

Quite weak, this substance is quite difficult to obtain in the desired small quantities between ordering and distribution. Typically it took about 4 months. A mylar plastic layer is placed between the parts to be joined. A layer of silicone adhesive was used between the layers. Silicone adhesive is as uniform as possible Applied to the surface in layers, the Mylar film is placed there, then the other adhesive layer applied. This technique is messy and slow, and requires a skilled worker to obtain a satisfactory bond line. It took more than an hour.

Even the slightest disturbance during production could interrupt the production of the bonding wire and greatly lengthen the turnaround time. success In this case, this method produces a bond line approximately 0.030 inches thick and is suitable for use in accordance with the present invention. It is three times or more the thickness of the bonding line when Even experienced workers will always be able to It is not possible to obtain a good bond.

In contrast, using the present invention, a semi-skilled person can consistently reverse the bond within about 2 minutes. Can be formed repeatedly. The bond line thickness is thin <, 0.008-0.010 inch It is. Saves thickness of bond wire material and reduces mixing of epoxy resin and hardener. This one is suitable because the composite has a slightly lower density than the silicone adhesive. Approximately 41 pounds of total weight is saved on each spacecraft when using pancreatic fluid adhesive elements. can. The value of a pound saved in orbit is currently $12,000-20,000. Therefore, the economic value of the present invention will be very clear.

A mylar interlayer was used (bonding strength with silicone adhesive was approximately 10 psi). Ru. In the present invention, the epoxy membrane adhesive using a porous intermediate layer has a lap shear test. It was determined to have a bond strength of approximately 1700-2 LOOpsi.

As is clear from the above, the present invention represents an important combination in the field of adhesive bonded structures. be. Prefabricated adhesive elements can be manufactured in large quantities and then stored until needed. Ru. Adhesive elements can be placed between structures to be quickly bonded and are much faster than traditional bonding. This invention is characterized by its ability to cure to a strong bond, exhibit low particulate outgassing, and set quickly. Although specific examples have been described, this is for illustrative purposes only; many variations may be contemplated by the present invention. is possible without departing from the spirit and scope of Therefore, the present invention is beyond the scope of the claims. It is not limited to the outside.

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Claims (1)

[Claims] 1. Strong enough to handle the porous carrier layer and adhesive structure without separating. 2 uncured adhesives, one on each side of the porous carrier layer that combine to form the adhesive structure. a membrane adhesive comprising an adhesive layer, the adhesive layer being formed of an ambient temperature curing adhesive material; manufacture the elements; cooling the adhesive element to a sufficiently low temperature that the adhesive layer does not harden; storing the adhesive element at low temperature; at a temperature and under pressure that allows the adhesive substance to cure between the structures joining said adhesive elements. A method of joining two structures comprising placing them together and curing the adhesive. 2. The membrane adhesive further contacts one of the uncured adhesive layers on the side not in contact with the porous carrier material. 2. The method of claim 1, including a combined release membrane layer. 3. Claims in which the carrier layer of the membrane adhesive element is comprised of a glass fiber mat. The method described in paragraph 1. 4. Claim 1, wherein the carrier layer of the membrane adhesive element is about 0.004 inches thick. The method described in section. 5. Claim No. 5, wherein at least one of the adhesive layers of the adhesive element comprises an epoxy resin. The method described in Section 1. 6. Claim 5, wherein the epoxy resin can be sufficiently cured at ambient temperature. Method described. 7. The method according to claim 5, wherein the adhesive layer further includes a polyamide curing agent. Law. 8. At least one of the adhesive layers of the adhesive element is about 0.003 inches thick. The method according to claim 1. 9. The method according to claim 2, wherein the release film layer is a Mylar film. 10. A porous mat of glass fiber, and one on each side of the glass fiber mat. In producing a membrane adhesive element containing two uncured adhesive layers, the adhesion of the adhesive layers The adhesive material flows into the fiberglass mat and the adhesive film elements are removed without separation. The adhesive layer is bonded to the glass fiber mat with sufficient strength to be handled, and the adhesive layer is kept at ambient temperature. Formed from a mixture of epoxy resin and polyamide curing agent that hardens at The substance is a fluid at ambient temperature and will flow out of the fiberglass mat when handled at ambient temperature. The adhesive membrane element further includes an adhesive layer that does not come into contact with the glass fiber mat. shall include a pair of separable release membrane layers on the free surface; Each adhesive element is connected at a temperature sufficiently low that the adhesive mixture is not fluid and does not harden. Immediately cooling the adhesive mixture to a temperature at which it is in a substantially solid uncured state; storing the membrane adhesive element at a temperature at which the adhesive mixture is solid and does not harden; Except for the peelable membrane that can be separated to suit the assembly of the structure in 2. The membrane adhesive element is placed under pressure between two structures to be joined, and the temperature of the adhesive element is increased. to a temperature that allows the adhesive mixture to harden. A method of joining two structures including. 11. Claim 10, wherein the fiberglass mat is approximately 0.004 inches thick. The method described in section. 12. Claim 10, wherein each of said adhesive layers is approximately 0.003 inches thick. Method described. 13 Glass fiber porous mat, a pair of adhesive layers in contact with the glass fiber mat, each of the adhesive layers having a The adhesive mixture is placed on each side of the fiberglass mat and cures at ambient temperature. containing an adhesive mixture that is fluid at ambient temperatures sufficient to flow from the unit; a pair of mylar release layers, each release layer being remote from the fiberglass mat; What is in contact with the adhesive layer on the side of the adhesive layer, A composite membrane adhesive element containing. 14. Claim 13, wherein said fiberglass mat is approximately 0.004 inches thick. Membrane adhesive elements as described in Section. 15. Claim 13, wherein each of said adhesive layers is approximately 0.003 inches thick. Membrane adhesive element as described. 16. The adhesive mixture includes a mixture of an epoxy resin and a polyamide hardener. A membrane adhesive element according to claim 13.