DE102011076608A1 - Joint connection i.e. T-joint, for sandwich plate for e.g. structural work, has core layer, and adhesive layer applied on core layer, where connection has form of fillet weld or double-hollow fillet weld in cross-section - Google Patents

Abstract

The connection has a core layer comprising an inhomogeneous, structured support e.g. rod (5), and connected with a covering layer (2). A contact area is 3 to 30 times larger than a narrow surface of parts of the core layer. A connection surface establishes a planar connection to edge areas of the parts of the core layer. An adhesive layer is applied on the core layer, where the connection has the form of a fillet weld or double-hollow fillet weld in a cross-section. Adhesives with same or different physical and/or chemical characteristics are used for forming the adhesive layer. The core layer is made from paper or plastic layer, wire or textile core, hollow or box profile, folding metal sheets, corrugated sheets, honeycomb core or tubular core. An independent claim is also included for a method for manufacturing a joint connection.

Description

The invention relates to a joint connection for a sandwich element, which is characterized by high strength and low production costs and a method for its preparation.

Sandwich elements are characterized by a high load capacity at low weight and are used in construction, especially in shell, prefabricated, interior, as sound and heat protection elements, for the manufacture of furniture, doors or door panels, in vehicle, especially in automotive, in the Caravan production, used in ship and boat building as well as in aircraft construction and packaging technology.

Sandwich elements are known from the prior art, which usually has a core of foamed materials or a structured core, z. B. with honeycomb, web-shaped or corrugated sheet-like structure, have. In known multilayer sandwich constructions, the plate-shaped core layer is connected on one or both sides to a cover layer in a form-fitting, material or non-positive manner. For reasons of lightweight construction and environmental aspects, wood, engineered wood or natural fibers of small thickness are often used for the thin-walled cover layers. In addition, plastic or metal sheets are used as cover layers.

In order to increase the stiffness of the sandwich element, honeycomb or web structures are often used for the core layer, in which the generally vertically extending webs allow at their outer ends only a linear connection to the respective adjacent cover layer. When bonding the cover layers to the edge zone of the webs, the bonding surface between core layer and cover layer is only a fraction of the projected area of the cover layer. According to the prior art, on the one hand, the cover layer is coated over its entire surface with adhesive in order to ensure that during the joining, the narrow surfaces of the webs of the core layer are uniformly and sufficiently wetted with adhesive. The disadvantage is the significantly higher adhesive consumption, the resulting higher manufacturing costs and an undesirable increase in the weight of the sandwich element.

So is out of the EP 1 992 759 A2 a lightweight board with two cover layers and a central layer known in which the middle layer is connected to the cover layers at least in sections by adhesive. In this case, both a mounting adhesive and a final adhesive is used, wherein the curing time of the final adhesive is longer than the curing time of the assembly adhesive. In order to prevent a mutual influence of the two different adhesives, preferably adjacent areas of the middle layer or the cover layers are wetted in sections and over the entire surface with mounting adhesive or end adhesive. As a result, as shown in the figures, the entire surface of both cover layers is coated with adhesive. This results in a significantly higher adhesive consumption and higher manufacturing costs.

Alternatively, the assembly adhesive is applied to the previously applied final adhesive. Does this only partially, z. B. strip-shaped, so arise between cavities that allow no power transmission and introduction into the honeycomb structure of the middle layer. In contrast, when the assembly adhesive is applied over the entire surface of the also previously applied over the entire surface final adhesive, a relatively large amount of adhesive is required, which also leads to an undesirable increase in weight and higher manufacturing costs.

In a further alternative, the adhesive is applied to the narrow surfaces of the webs of the core layer. The narrow surfaces are wetted with adhesive in a substantially linear manner. After bonding, the strength of the sandwich element is significantly reduced, since it does not come to a complete, continuous connection between the cover layer and the narrow surfaces of the webs due to manufacturing and assembly tolerances.

Object of the present invention is to provide a joint connection for a sandwich element and a method for its production, which has a significantly reduced adhesive entry at the same or higher strength compared to the full-surface coating of the cover layer.

According to the invention the object is achieved by the features of the main claim and by a method having the features of claims 8, 9 and 10th

The joint connection between the cover layer and the web of the core layer has for this purpose an enlarged contact surface in relation to the known solutions according to the prior art.

For the purposes of this application, web means the elements or parts of the core layer which touch and support the adjacent cover layer. The inhomogeneous, structured core layer consists in particular of erected webs or honeycombs whose narrow surface is connected in a point-like or strip-like manner to the adjacent cover layer.

Under contact surface of the joint connection is understood in the context of this application, the area over which a power transmission from the top layer to the core. The contact area A _CONTACT comprises the contact area to the cover layer A _DECK and the connection surface to the core A _KERN .

For targeted enlargement of the contact surface A _CONTACT , the upper edges of the narrow surfaces of the web on one or both sides uprising and connection surfaces.

Preferably, the contact surfaces extend on both sides on the edge of the narrow surface of the web. In another, likewise preferred embodiment, the contact surfaces arranged on one or both sides of the web are arranged at points and at a distance.

The contact surfaces are formed according to the invention by a repeated adhesive application to the narrow surfaces and / or the adjacent broad surfaces of the webs.

As an adhesive, identical but also different adhesives can be used with each application of adhesive. Preferably, reactivatable adhesives are used. Alternatively, the use of non-reactivatable adhesives is possible.

According to the invention, the width in the contact area A _{AUF is} 3 to 30 times greater than the projected surface (narrow surface) of the webs of the core layer contacting the cover layer.

When using foam-forming polyurethane adhesives, a ratio of the width of the contact surface to the width of the narrow surface which makes contact with the cover layer is preferably selected to be from 5: 1 to 30: 1. Due to the loosened foam structure of the PU adhesives, the mass of the adhesive is low in comparison to the significantly increased footprint and bonding surface, so that the joined sandwich element with the same or improved strength a reduced mass compared to the prior art (full-surface adhesive coating of the entire Surface of the adjacent cover layer).

Also preferred is a ratio of the width of the footprint to the width of the narrow face of 10: 1 to 15: 1. This relationship represents an optimum relationship between the gain in strength and at the same time reduced adhesive costs in comparison to the full-surface coating of the cover layer.

Particularly preferred is a ratio of the width of the footprint to the width of the narrow surface of 4: 1 to 10: 1. As a result, an increased strength of the joint connection, in particular under dynamic stress, realized. In addition, this embodiment of the joint connection causes a favorable ratio between the gain in strength at significantly lower production costs compared to the full-surface adhesive application to the cover layer.

When using adhesives made of PVAC or hot melt adhesives (hot melt adhesives, hot melt adhesive, hot glue, hot melt), a joint connection with a ratio of the width of the footprint to the width of the narrow face of 3: 1 to 5: 1 is preferably realized. Due to the larger adhesive forces of these preferred adhesives, the size of the footprint and attachment surface can be minimized, thus reducing the applied adhesive mass and the corresponding manufacturing costs.

The production of the joint connection by enlarging the contact area and attachment surface essentially takes place in two steps:
In a first step, the enlargement of the narrow surface of the web of the core structure is carried out by the application of a first adhesive. In this case, an adhesive layer forms according to the geometry of the web structure. Due to the viscosity and the running of the adhesive, the first adhesive layer encloses the narrow or end surface of the web and / or the adjacent regions of both broad surfaces of the web and forms a substantially U-shaped structure after setting or curing. In a second step, the adhesive is applied to the narrow surface of the web, which has an enlarged surface due to the applied first adhesive layer. This second adhesive layer is the final bonding. After application of the second adhesive layer, bonding to the cover layer takes place under pressure and / or temperature.

If a larger contact area is required due to the forces and moments which the sandwich element has to absorb, the second partial step can be repeated one or more times. The adhesive is applied by known methods, such as roller application or by dipping.

The application of two or more adhesive layers to the narrow sides and the adjoining areas of the webs creates a significantly enlarged footprint and bonding surface which allows a better bond between the core layer and the cover layer. In addition to saving high-quality and expensive adhesives, the mechanical strength of the sandwich element is significantly increased compared to conventional bonding technologies and constructions.

For the bonding of wood or wood-based materials or cellulose-containing materials PVAC adhesives, PU adhesives or hotmelt adhesives are preferably used as adhesives. For the connection of plastic cover layers and honeycomb cores made of plastics epoxy resin adhesives are preferably used as adhesives.

To illustrate the essence of the invention shows 1 in a vertical sectional view of a conventional sandwich element, consisting of a central core layer with a honeycomb-shaped cavity structure and two cover layers adjacent on both sides. The middle core layer 3 consists of a honeycomb core. The two cover layers 2 each consist of a high-density fiberboard.

2 shows a horizontal section AA of the sandwich element after 1 , It becomes clear that the narrow surfaces 8th of all the bridges 5 of the core 3 less than 5% of the projected area of the adjacent surface layer 2 turn off.

3a shows in an exploded view, the joining of a sandwich element according to the prior art: The two outer layers 2 be at the, the end faces of the honeycomb of the core 3 touching wide surfaces over the entire surface with adhesive 4 coated. Subsequently, the core 3 and the two cover layers 2 assembled under pressure and / or temperature.

A disadvantage of this solution is the high adhesive requirement, since the entire surface of both outer layers 2 with glue 4 is coated. In addition to the high material costs, this also results in a higher weight of the lightweight component.

3b shows in contrast in an exploded view, the innovative joint connection before the joining of the joining partners. The order of the glue 4 takes place by rolling both on the narrow surfaces 8th the webs of the core 3 , as well as on the two adjacent broad surfaces of the webs.

3c shows an example in a Kavaliersperspektive an extracted honeycomb of a honeycomb core 3 , Each honeycomb consists of six symmetrically arranged cell walls. The cell height is h _z 19 mm. The distance between opposite cell walls (cell width w _z ) is 15 mm.

The connection of the honeycomb core 3 with the cover layers, not shown 2 takes place over the narrow surfaces 8th of the bridges 5 that as a single bridge 5.1 or as a double bridge 5.2 may be formed, as well as the two adjacent broad surfaces of the webs 5 , The wall thickness s of the individual cell walls of the honeycomb core 3 is in the range of the narrow surface 8th of the footbridge 5 0.2 mm. This makes it clear that when applying an adhesive on the circumferential narrow surfaces 8th the webs is limited, only to a very limited extent forces and moments can be transferred to the cover layers not shown. Only by the innovative design of the joint connection in the form of a one-sided or two-sided, optionally interrupted fillet weld, the contact surfaces which are decisive for the force transmission and the bonding surfaces of the adhesive bond are significantly enlarged compared with the known solutions of the prior art.

4 shows a vertical section through the joint connection. To clarify the shape of the innovative joint connection, the web of the honeycomb core and the cover layer were not shown. The adhesive layer 4 has substantially the shape of a continuous double fillet, including the narrow surface of the web of the honeycomb core, not shown. The footprint 4-1 provides the connection to the adjacent cover layer, not shown 2 ago. The footprint 4-1 is significantly increased compared to conventional adhesive joints and thus allows the transmission of greater forces and moments.

The connection area 4-2 provides the connection to the (not shown) narrow surface of the webs of the core and to the two (also not shown), adjacent wide surfaces of the webs ago.

By stress-appropriate, arcuate design of the edge zones of the adhesive layer occurring stresses can be better transferred from the top layer to the core.

To further clarify the structure of the joint connection shows 5a in an enlarged view of the bridge 5 with narrow surface 8th and the two adjacent broad surfaces 9 of the core 3 and the top cover layer 2 before joining.

5b shows in an enlarged view the bridge 5 of the core 3 and the top layer 2 after joining. The enlarged footprint and attachment surface 4-1 . 4-2 The joint connection consists of a two-ply adhesive layer 10 . 11 PVAC, which has the shape of a continuous double fillet.

After application of the first adhesive layer 10 on the narrow surface 8th and the two adjacent fringes 9 the wide surfaces 8th of the footbridge 5 is the footprint 7-1 already significantly increased compared to conventional adhesive joints according to the prior art. On this enlarged footprint 7-1 is one or more times another layer of adhesive 11 applied.

Characteristic of the innovative joint connection is the increased footprint and connection surface 4-1 . 4-2 . 7-1 . 9-1 that better transfer of forces and moments from the top layer 2 in the footbridge 5 allows. Due to the, in the section arcuate course of the two continuous adhesive layers 10 In particular, bending moments better in the webs 5 of the honeycomb core 3 be initiated. This results in a significantly higher resistance to shear and torsional stresses while reducing the weight of the sandwich panel.

8a shows in a Kavaliersperspektive the cut bridge 5 of the core 3 and the, on the narrow surface 8th and the upper edges of both broad surfaces 9 of the footbridge 5 running, continuous adhesive joint 10a in the form of a double fillet. For better representation, the top layer was 2 not shown.

8b also shows in a Kavaliersperspektive an alternative form of innovative joint connection.

The enlarged footprint consists of a multilayer adhesive layer of PVAC, the full surface on the narrow surface 8th of the bridge is applied. In addition, on the two wide surfaces 9 at the top of the bridge 5 spaced apart and staggered adhesive dots 10b applied. Thereby, the footprint for the connection with the cover layer in comparison to solutions of the prior art, in which only the narrow surface 8th of the footbridge 5 wetted with adhesive, significantly increased.

Another advantage of this joint connection is that simple dynamic stresses to which the sandwich element is exposed, by the punctiform connection - can be better absorbed - in contrast to a continuous adhesive joint.

The invention will be described in more detail below with reference to two variants and illustrated in drawings. The variants differ primarily in the form of the formation of the first adhesive layer. This first adhesive layer has the state "unformed" or "formed" after setting.

Variant 1 (adhesive layer in unformed state):

6a shows the first adhesive layer 10-1a from a reactivatable adhesive after application to the narrow surface 8th and the adjacent areas 9 both broad surfaces of the bridge 5 ,

6b shows the second adhesive layer 11-1a from a reactivatable or non-reactivatable adhesive after application to the footprint 4-1 the first adhesive layer 10-1a ,

6c shows the phase of contacting the applied with the two adhesive layers 10-1a . 11-1b provided footbridge 5 with the top layer 2 , By the contact pressure of the cover layer 2 becomes the adhesive layer 11-1b deformed.

6d shows the structure of the joint connection with increased contact patch and surface by the two adhesive layers 10-1a . 11-1c after the final bonding of the core with the top layer 2 ,

Variant 2 (adhesive layer in the formed state):

7a shows the first adhesive layer 10-2a consisting of a reactivatable or non-reactive adhesive, after application to the narrow surface and the adjacent regions of both broad surfaces of the web 5 ,

7b shows the first adhesive layer 10-2b after their formation by a temporary fixation on a non-adhesive surface with simultaneous setting.

7c shows the application of the second adhesive layer 11-2a a reactivatable or non-reactivatable adhesive on the enlarged footprint 4-1 the first adhesive layer 10-2b ,

7d shows the structure of the joining zone after the final bonding with the cover layer 2 , By the contact pressure is not yet set second adhesive layer 11-2b deformed and thus created a further enlarged footprint.

The invention will be described in more detail below with reference to several embodiments:

Embodiment 1

Sandwich element with a honeycomb core made of corrugated paper and cover layers made of thin, high-density fibreboard for use as a furniture component:
The schematic structure of a single, greatly enlarged honeycomb of the core is in a Kavaliersperspektive in 3c shown.

The honeycomb is made of corrugated material. Ripple is a type of waste paper commonly used to make the center of corrugated board ( Blechschmidt, J. [ed.] (2010): Taschenbuch der Papiertechnik. Munich: Hanser ).

The web of the honeycomb, through which the forces are transferred to the adjacent top layer, has a width s of 0.2 mm.

The cell width w _{z of} the honeycomb is 15 mm, the height h _{z of} the core is 19 mm.

The 6a to 6d show in four figures the gradual application of a hot melt adhesive to the web 5 of the honeycomb core 3 and the subsequent joining with the cover layer 2 ,

6a shows the application of the first adhesive layer of a hot melt adhesive of ethylene vinyl acetate (EVA) on the narrow surface 8th and the adjacent areas of both broad surfaces 9 of the bridges 5 of the core 3 , A hot melt adhesive with a high reaction temperature and low viscosity is used. The order of the hot melt adhesive to the core structure in a known manner by an applicator roll. The core structure dips into the hotmelt adhesive, but does not touch the roller. The gap between applicator roll and core structure is advantageously 0.1 mm to 3.0 mm. Subsequently, the first adhesive layer 10-1a cooled.

In a further step ( 6b ) becomes a second adhesive layer 11-1a a hot melt adhesive of ethylene vinyl acetate (EVA) of the same product family with the already enlarged footprint of the cured first adhesive layer 10-1a applied. This hot melt adhesive has a lower melting temperature and higher viscosity than the hot melt adhesive of the layer 10-1a , This prevents the flow of hot melt adhesive out of the joint area.

This is followed by renewed cooling of the adhesive layer 11-1a to a temperature below the melting point.

This technological step (adhesive application and cooling) can be repeated one or more times if necessary to bring a larger amount of adhesive into the joint area and thereby create a further increased footprint.

Subsequently, the actual joining process takes place. This is the top layer 2 under pressure and at a temperature at least above the melting range of the adhesive layer 10-1a lies with the honeycomb core 3 together. This creates the final bond in the form of a double fillet. During the subsequent cooling process, the cover layers become 2 and the core 3 fixed under pressure in its final position.

The ratio of the width of the footprint to the width of the narrow surface of the web after bonding is 3.2: 1.

Embodiment 2:

Sandwich element with a not explicitly shown tubular core (tube core) made of polypropylene (PP) and cover layers made of glass-fiber reinforced polypropylene (PP) for use as a component in ship interior fitting:

7 shows in an alternative embodiment in four figures the gradual application of an epoxy resin adhesive and the subsequent joining of the web 5 a Tubuskerns with a flat cover layer 2 ,

7a shows the application of the first adhesive layer 10-2a an epoxy resin adhesive on the narrow surface 8th and the adjacent upper portions of the broad surfaces 9 of the footbridge 5 of the Tubuskernes. The adhesive is applied in a manner known per se by means of a roller, wherein the core structure is immersed directly in the adhesive. During this process, the adhesive settles in the area of the connection surface 4-2 at.

In a subsequent process, the first adhesive layer binds 10-2a from. To the desired double fillet structure in the upper area of the bridge 5 To create the Tubuskern is preferably performed by a fixing device with bands. The surfaces of the bands have a non-stick coating. The adhesive initially deposits on the surface. The application of pressure in the fixing device deforms the section (cf. 7a ) drop-shaped adhesive layer 10-2a and takes the shape of one, the bridge in the area of the connection surface 4-2 Double-sided double-seamed seam 10-2b on (cf. 7b ). When leaving the fixing device with tapes, the adhesive layer dissolves 10-2b fully formed from the surface of the tape. After the first adhesive layer 10-2b is completely tied and a significantly enlarged footprint 4-1 was created, the order of a further adhesive layer takes place 11-2a made of epoxy resin on the enlarged footprint ( 7c ).

This is followed by the adhesive layer during the open time 11-2a the joining process ( 7d ), in which the top layer 2 with the enlarged footprint 4-1 at the top of the bridge 5 of the Tubuskerns is connected.

Embodiment 3 (adhesive layer unformed):

9 shows a method for applying at least two adhesive layers 10-1a and 11-1a on a core 3 , The material flow takes place from left to right.

The core 3 gets on its top and bottom with glue 22a , a high melting temperature ethylene vinylacetate hot melt adhesive, by an adhesive applicator consisting of an adhesive applicator roll 20 and a squeegee basin 21 coated. This creates the first adhesive layer 10-1a (not shown). For faster setting of the adhesive layer 10-1a Cooling is used. The air cooling 23 generates an airflow 24 that after flowing through the core 3 via a suction 25 is dissipated. Following is the core 3 with the adhesive layer 10-1a on its top and bottom by an adhesive applicator, consisting of an adhesive applicator roll 20 and a squeegee basin 21 , with glue 22b , a lower melting temperature ethylene vinyl acetate hot melt adhesive than 22a coated. This results in the adhesive layer 10-1a the second, not shown, adhesive layer 11-1a , Subsequently, the top layer 2 from the roll store 26 over the close to the core 3 spaced pulley 27 supplied on both sides.

The two-sided connection of the cover layer 2 with the core 3 done by means of a double belt press 28 (shown shortened). This is composed of drive rollers 29 , the heating zone 30 and the cooling zone 31 , After joining the core 3 with the cover layers 2 become the superposed adhesive layers 10-1a and 11-1a in the heating zone 30 heated and thus flowable, which forms on both sides of the final form of Doppelkehlnahtverklebung core and top layer.

In the cooling zone 31 the adhesive binds in its final form, creating the sandwich panel 1 arises.

Alternatively, when using adhesives 22a which require external heat input instead of cooling (eg PVAC dispersion adhesive) instead of air cooling for quick setting 23 a heater used.

Embodiment 4 (adhesive layer formed):

10 shows a method for applying at least two (not shown for illustrative reasons) adhesive layers 10-2a and 11-2a ,

adhesive layer 10-2a consisting of an adhesive 22a (Polyurethane adhesive), we will exactly in 9 applied. Unlike the procedure according to 9 is used instead of air cooling 23 a fixing device with bands 32 used in the adhesive layer 10-2a is formed, wherein the adhesive sets and reacts out. The adhesive layer takes the form of a, the web in the region of the connection surface 4-2 Double-sided fillet weld on both sides with a large footprint 4-1 at. Analogous to 9 becomes the adhesive layer 10-2a in a second application with an adhesive layer 11-2a Mistake. As an adhesive 22b For example, a higher viscosity polyurethane adhesive is used. The coated core 3 comes with the topcoat 2 in the double-belt press 28 together. This is the setting of the adhesive layer 11-2a , accelerated by heat in the heating zone 30 , The sandwich plate 1 will be in the cooling zone 31 conditioned and then from the double belt press 28 from-given.

LIST OF REFERENCE NUMBERS

1

sandwich panel

2

topsheet

3

core

4

adhesive

4-1

footprint

4-2

bonding surface

5

web

5.1

Single bridge

5.2

double bridge

6

outer broad surface of the cover layer, outside

7

Inner broad surface of the cover layer, inside

7-1

bonding-effective inner broad surface of the cover layer

8th

Narrow surface of the bridge

9

Wide surface of the bridge

9-1

Bonding effective wide surface of the bridge

10

adhesive layer 1

10a

adhesive layer 1 continuous order

10b

adhesive layer 1 selective / local order

10-1a

adhesive layer 1 after the order

10-1b

adhesive layer 1 in the final state after forming

10-2a

adhesive layer 1 after the order

10-2b

adhesive layer 1 in the final state after molding

11

adhesive layer 2

11-1a

adhesive layer 2 after the order

11-1b

adhesive layer 2 after joining with joining part (cover layer)

11-1c

adhesive layer 2 in the final state

11-2a

adhesive layer 2 after the order

11-2b

adhesive layer 2 in the final state

20

Adhesive applicator roll

21

squeegee pools

22a

Adhesive a

22b

Adhesive b

23

air cooling

24

airflow

25

suction

26

Roll storage for cover layer ( 2 )

27

Pulley (tightly spaced)

28

Double belt press (shown shortened)

29

drive roller

30

heating zone

31

cooling zone

32

Fixing device with bands

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1992759 A2 [0005]

Cited non-patent literature

• Blechschmidt, J. [ed.] (2010): Taschenbuch der Papiertechnik. Munich: Hanser [0055]

Claims (10)

Joining connection for a sandwich element with at least one core layer and at least one cover layer, wherein the core layer has an inhomogeneous, structured support against the cover layer, in particular in the form of webs and / or honeycomb and is only selectively or strip-shaped connected to the cover layer, characterized in that the joining connection in the form of a T-joint is designed as a localized adhesive bond with enlarged contact area A _{CONTACT, wherein} the contact area A _AUF 3 to 30 times greater than the narrow surface of the cover layer contacting parts of the core layer and the connection surface A _{AN is} a planar connection to the edge regions of the, the cover layer contacting parts of the core layer produces that the joint connection consists of an at least two-layer adhesive layer and the joint connection in the sectional image substantially the shape of a fillet weld or a double fillet, in particular a double fillet weld , having. Joining connection according to claim 1, characterized in that the width of the footprint A _AUF to the width b _{S of} the narrow surface of the web ( 8th ) has a ratio of 3: 1 to 30: 1. Joining connection according to claim 2, characterized in that the width of the footprint A _AUF to the width b _{S of} the narrow surface of the web ( 8th ) has a ratio of 5: 1 to 30: 1, preferably from 10: 1 to 15: 1. Joining connection according to claim 2, characterized in that the width of the footprint A _AUF to the width b _{S of} the narrow surface of the web ( 8th ) has a ratio of 10: 1 to 15: 1. Joining connection according to claim 1, characterized in that the core layer consists of paper or plastic layers, wire or textile cores, hollow or box profiles, folding plates, corrugated sheets, honeycomb cores or tubus cores. Joining compound according to claim 1, characterized in that for the formation of the individual adhesive layers adhesives having the same or different physical and / or chemical properties, preferably PVAC adhesives, hot melt adhesives or polyurethane adhesives are used. Joining connection according to claim 1 or 6, characterized in that reactive adhesives are used for the formation of the adhesive layers. Method for producing a joint connection for a sandwich element, characterized in that the surface of the core layer 3 wetted on the top and bottom by repeated dipping with at least one adhesive and then on the core layer 3 a cover layer on both sides 2 applied and under pressure with the core layer 3 is connected. Method for producing a joint connection for a sandwich element, characterized in that the surface of the core layer 3 on the top and bottom by repeated roller application wetted with at least one adhesive and subsequent to the core layer 3 a cover layer on both sides 2 applied and under pressure with the core layer 3 is connected. Method for producing a joint connection for a sandwich element, characterized in that the surface of the core layer 3 is coated on the top and bottom with a high melting temperature adhesive by means of an adhesive applicator, that subsequently this first adhesive layer is cooled, that on the core layer 3 at least one further adhesive layer is applied, wherein the adhesive has a lower melting temperature than the previously applied adhesive that subsequent to the core layer 3 a cover layer on both sides 2 applied and connected by means of a double belt press.

Images