Method for producing a honeycomb plate

Abstract

The invention relates to a method for producing a honeycomb plate, wherein the honeycomb plate comprises a first cover layer (1) and a second cover layer (2) and a core element (3) arranged between the first cover layer (1) and the second cover layer (2), wherein the core element (3) has a honeycomb structure with cells (5) delimited by connection pieces (4) and wherein the core element (3) has a first surface (6) which rests against the first cover layer (1) and a second surface (7) which rests against the second cover layer (2), said method comprising the following steps: i) providing the core element (3) and the first and the second cover layers (1, 2); ii) spraying a hot-melt adhesive (8) onto at least one surface (6, 7) of the core element (3), wherein the hot-melt adhesive (8) is stretched during spraying such that a net-like adhesive structure (9) is formed on the at least one surface (6, 7) of the core element (3); iii) heating the at least one surface (6, 7) of the core element (3) provided with hot-melt adhesive (8) and thereby reactivating the hot-melt adhesive (8); iv) pressing a cover layer (1, 2) onto the at least one surface (6, 7) of the core element (3) provided with hot-melt adhesive (8); v) optionally carrying out method steps ii) to iv) for the second surface (7) of the core element (3) and the second cover layer (2) such that the core element (3) is arranged between the two cover layers (1, 2).

Description

[0001] .Method for producing a honeycomb panel'

[0002] Description

[0003] The invention relates to a method for producing a honeycomb panel.

[0004] A honeycomb sandwich panel, or honeycomb panel for short, is a mostly three-layer composite construction in which a core element is arranged between two outer cover layers. This core element has a honeycomb structure formed by a multitude of webs, usually with hexagonal cells. Such honeycomb panels can, for example, be made entirely of paper-based materials, but they can also include plastics or aluminum. In particular, the cover layers can also be made of a different material than the core element. For example, the cover layers can be designed as thin wooden panels, while the core element is made of paper or cardboard.

[0005] Due to their special structure, honeycomb panels exhibit high mechanical rigidity while remaining lightweight. They are therefore particularly suitable for use in the furniture industry, but they are also used in aircraft, ship, and automotive construction, as well as for facade elements.

[0006] Such honeycomb panels are typically manufactured by bonding the core element to the cover layers. A suitable adhesive, such as a liquid polyurethane or dispersion adhesive or a meltable film, is applied over the entire surface of the cover layers, and the core element is inserted between the cover layers. To achieve good adhesion between the core element and the cover layers, it is necessary to press the composite together for an extended period during the drying process.

[0007] A disadvantage of the uniform and full-surface adhesive application is that a large portion of the adhesive remains unused on the cover layers in the opening areas of the cells, since the bond between the cover layers and the core element only occurs in the area of ​​the webs forming the honeycomb structure. At the same time, the webs form only very narrow contact areas.

[0008] DE 10 2006 060 940 B4 describes a further development of such a method for producing a lightweight construction panel. In this process, an adhesive is first applied to the surface of a cover layer over the entire surface or in the form of droplets and / or stripes, and the core element is then placed on the adhesive-coated cover layer. In order to distribute the applied adhesive so that it is concentrated less in the opening areas of the cells and more in the area of ​​the webs of the core element, DE 10 2006 060 940 B4 proposes implementing a relative movement between the adhesive-coated cover layer and the applied core element. The relative movement can be, for example, a translational movement or a rotational movement, or a combination of a translational and a rotational movement.In any case, the frictional relative movement redistributes a certain proportion of the liquid adhesive so that it concentrates primarily in the area of ​​the webs of the core element, thereby improving adhesion between the core element and the cover layer.

[0009] However, this process is comparatively complex. Furthermore, adhesive components remain in areas of the cover layer where no core element webs are located, meaning that these adhesive components do not contribute to the bond. In the interest of resource-efficient use of materials, this is considered worthy of improvement.

[0010] The present invention therefore has the object of providing an efficient method for producing a honeycomb panel, which is associated with a lower consumption of adhesive and at the same time creates a particularly good bond between the core element and the two cover layers.

[0011] This object is achieved by a method having the features of patent claim 1 .

[0012] Advantageous embodiments and further developments of the invention are the subject of the dependent claims.

[0013] According to claim 1, the invention relates to a method for producing a honeycomb panel, wherein the honeycomb panel comprises a first cover layer and a second cover layer and a core element arranged between the first cover layer and the second cover layer, wherein the core element has a honeycomb structure with cells delimited by webs and wherein the core element has a first surface which bears against the first cover layer and a second surface which bears against the second cover layer, comprising the following steps: i) providing the core element and the first and second cover layers; ii) spraying a hot-melt adhesive onto at least one surface of the core element, wherein the hot-melt adhesive is stretched during spraying so that a net-like adhesive structure is formed on the at least one surface of the core element;iii) heating the at least one surface of the core element provided with hot-melt adhesive and thereby reactivating the hot-melt adhesive; iv) pressing a cover layer onto the at least one surface of the core element provided with hot-melt adhesive; v) optionally carrying out process steps ii) to iv) for the second surface of the core element and the second cover layer, so that the core element is arranged between the two cover layers.

[0014] In other words, the invention provides that the adhesive is not applied to the cover layers, as is known from the prior art, but that the surfaces of the core element are provided with adhesive. For this purpose, the method according to the invention proposes spraying a hot melt adhesive onto at least one surface of the core element, wherein the hot melt adhesive is stretched during spraying so that a net-like adhesive structure is formed on the at least one surface of the core element. The stretching of the adhesive can be achieved by using a special nozzle through which the adhesive is sprayed onto the surface of the core element without contact and under pressure. The adhesive threads formed in this way form a net-like structure on the surface of the core element, i.e. they lie on the webs and span the opening areas of the cells.

[0015] The heating of at least one surface of the core element provided with hot melt adhesive in a subsequent process step provided according to the invention reactivates the pre-stretched hot melt adhesive. The invention makes use of the knowledge that the network structure created by the adhesive dissolves during the reactivation and the adhesive retreats towards the webs of the honeycomb structure. As a result, there is no longer any adhesive in the opening areas of the cells; instead, the adhesive is concentrated exclusively in the area of ​​the webs of the honeycomb structure. The adhesive also adheres to the lateral areas of the webs, so that when a cover layer is subsequently applied or pressed onto the core element, a particularly good bond can be created between the cover layer and the core element due to the particularly high adhesive concentration in the area of ​​the webs.The cover layer must be pressed on within the open time of the hot-melt adhesive. Open time is the period of time within which an adhesive can form an adhesive bond before it subsequently solidifies again. The method according to the invention thus makes it easy to provide a local adhesive concentration precisely in those areas of the honeycomb structure that actually contribute to the bond. Investigations on honeycomb panels produced using the method according to the invention show that the adhesive remains in the area of ​​the webs even after the core element and cover layers have been joined, effectively enclosing them, so that larger contact areas are formed between the core element and cover layers compared to conventional joining methods.Since no adhesive remains unused in the opening areas of the cells, the amount of adhesive applied can be reduced overall compared to prior art processes. This makes the process according to the invention particularly resource-efficient. At the same time, the hot-melt adhesive has the advantage over liquid-applied, water-based adhesives of developing handling strength within a few seconds, as the heat is dissipated very quickly via the cover layer. This eliminates the need for energy- and time-consuming drying processes that would otherwise be required, and the formed component can be processed immediately.

[0016] In principle, with the method according to the invention, initially only the first surface of the core element can be provided with hot-melt adhesive in the manner described above. This can then be heated, and the first cover layer can be pressed on. The aforementioned method steps can then be carried out analogously for the second surface of the core element and the second cover layer. Alternatively, the first and second surfaces of the core element can also be provided with hot-melt adhesive simultaneously or immediately one after the other. Subsequently, both surfaces can be heated simultaneously or immediately one after the other, and the first cover layer can be pressed onto the first surface and the second cover layer onto the second surface of the core element.Between the process step of spraying the adhesive and the step of reactivating the adhesive by heating, there can generally be a certain period of time during which the solidified adhesive network structure remains on the honeycomb panel. This period can range from a few seconds to several hours.

[0017] According to a preferred embodiment of the invention, the hot-melt adhesive can be sprayed onto the surfaces of the core element by spin spraying using a compressed-air-operated spiral nozzle. In this case, the adhesive is expelled through a central nozzle, with additional compressed-air channels arranged spirally around the nozzle. By blowing in air, the adhesive is stretched, and the emerging adhesive threads are set in rotation. The adhesive threads catch on the webs and spread like a spider's web over the entire honeycomb structure of the core element. In principle, other nozzles can also be used, allowing the hot-melt adhesive to be applied to the core element in a contactless and stretched manner.

[0018] It can be provided that the hot melt adhesive is sprayed at an angle a of 30° to 60° with respect to the surface of the core element. For example, the hot melt adhesive can be sprayed at an angle of approximately 45° with respect to the surface of the core element. A thermoplastic hot melt adhesive, for example, can be used as the hot melt adhesive. Alternatively, a reactive hot melt adhesive can also be used. When using a reactive hot melt adhesive, the solidified adhesive can be reactivated using hot steam. This can further accelerate the subsequent crosslinking. Reactive polyurethane-based hot melt adhesives react with ambient air humidity after application, which means that such bonds have greater heat resistance because they do not remelt.This can be accelerated by introducing moisture during the reactivation of the adhesive.

[0019] Depending on the hot-melt adhesive used, the application temperature of the adhesive can range between approximately 120°C and 210°C. Hot-melt adhesives generally have the property of solidifying immediately upon cooling after application. This creates a solidified adhesive network on the surface of the core element, which can generally remain there for an extended period of time, for example, several hours, before subsequent processing steps are carried out.

[0020] One embodiment of the invention provides that the heating of the at least one adhesive-coated surface of the core element is carried out by hot air and / or hot steam and / or infrared radiation. Generally, it is necessary to heat the pre-stretched hot-melt adhesive above its softening point to initiate the desired reactivation. This can be achieved excellently through the use of hot air and / or hot steam and / or infrared radiation. The use of infrared radiation is particularly advantageous when the hot-melt adhesive contains an admixture of an infrared-reactive additive. This can further shorten reaction times.

[0021] An embodiment of the invention provides that the hot-melt adhesive has a basis weight of 30 to 90 g / m 2sprayed onto the core element. For example, the hot melt adhesive with a basis weight of 60 g / m 2 sprayed onto the core element. It has been shown that such an amount of adhesive is sufficient to achieve the desired strength of the bond when using the method according to the invention. In contrast, in methods known from the prior art, in which a dispersion adhesive is applied to the entire surface or at least in strips to the cover layers, adhesive quantities of 120 g / m 2 and more is required to achieve a reliable bond. For aluminum honeycomb panels, the adhesive consumption is even higher using state-of-the-art processes; these typically use liquid polyurethane adhesives with a surface weight of approximately 250 g / m 2applied to the cover layers. Since the process according to the invention can provide a local adhesive concentration precisely in those areas of the honeycomb structure that actually contribute to the bond, the amount of adhesive applied can be significantly reduced.

[0022] According to one embodiment, the core element comprises a paper-based material. For example, the core element can be made of thin cardboard. The cover layers can also be made of a paper-based material. However, they can also be made of wood, such as MDF. Such honeycomb panels are particularly suitable for use in furniture construction and interior design.

[0023] Alternatively, the core element can comprise an aluminum-based material. The cover layers can also be made of aluminum sheets. Preferred applications for aluminum honeycomb panels include construction, transportation, and shipbuilding.

[0024] In principle, a variety of material combinations are possible in the formation of honeycomb panels and the method according to the invention is suitable for efficient and resource-saving production of such honeycomb panels, regardless of the specific materials.

[0025] The invention will be explained in more detail below using an exemplary embodiment and with reference to the accompanying drawings. They show:

[0026] Figure 1 : the process step of spraying a hot melt adhesive onto a

[0027] Surface of the core element;

[0028] Figure 2: a net-like adhesive structure formed on the surface of the core element;

[0029] Figure 3: the process step of heating the adhesive-coated surface of the core element;

[0030] Figure 4: the process step of pressing the cover layer onto the adhesive-coated surface of the core element;

[0031] Figure 5: a honeycomb panel produced by the method according to the invention in a

[0032] Sectional view.

[0033] In a first method step, a core element 3 as well as a first cover layer 1 and a second cover layer 2 are provided. Figure 1 shows a core element 3 made of a paper-based material; the two cover layers 1, 2 are not shown in Figure 1. The core element 3 has a honeycomb structure with hexagonal cells 5 delimited by webs 4. In the illustration in Figure 1, a first surface 6 of the core element 3 is oriented upwards, while a second surface 7 of the core element is oriented downwards.

[0034] Figure 1 shows the process step of spraying a hot-melt adhesive 8 onto the first surface 6 of the core element 3. The hot-melt adhesive 8 is a reactive hot-melt adhesive. The hot-melt adhesive 8 is sprayed at an angle a of approximately 45° relative to the surface 6 of the core element 3 using a compressed-air-operated spiral nozzle 10, shown only schematically. The hot-melt adhesive is expelled through a central nozzle, with compressed-air channels arranged spirally around the nozzle. By blowing in air, the adhesive is stretched, and the emerging adhesive threads are set in rotation. The adhesive threads catch on the webs 4 of the honeycomb structure and settle over the opening areas of the cells 5.The nozzle 10 is guided over the surface 6 of the core element 3 such that a dense, net-like adhesive structure 9 forms on the first surface 6 of the core element 3. This state is illustrated in Figure 2. The hot-melt adhesive 8 is applied with a basis weight of approximately 60 g / m. 2 applied.

[0035] In a subsequent process step, schematically illustrated in Figure 3, the first surface 6 of the core element 3, which is provided with hot-melt adhesive 8, is heated. The heating is carried out using hot air 11 from a hot air source 12. The heating reactivates the stretched hot-melt adhesive 8. The net-like adhesive structure 9 created in the preceding process step dissolves, and the hot-melt adhesive 8 retracts toward the webs 4 of the honeycomb structure. Consequently, there is no longer any hot-melt adhesive 8 in the opening areas of the cells 5; rather, the hot-melt adhesive 8 is concentrated exclusively in the area of ​​the webs 4 of the honeycomb structure. This state is illustrated in Figure 3.

[0036] In a subsequent process step, as shown in Figure 4, the first cover layer 1, which here is designed as a thin MDF board, is placed in a direction indicated by the arrow 13 onto the first surface 6 of the core element 3 provided with hot melt adhesive 8 and lightly pressed on. Since the reactivated hot melt adhesive 8, as will be explained in more detail below in connection with Figure 5, also adheres to the lateral areas of the webs 4, the locally particularly high adhesive concentration in the area of ​​the webs 4 creates a particularly good bond between the cover layer 1 and the core element 3. The pressing on of the cover layer 1 must take place within the open time of the hot melt adhesive 8.Since the introduced heat is dissipated very quickly via the first cover layer 1, the hot melt adhesive 8 solidifies immediately and further time- and energy-consuming drying processes can be dispensed with.

[0037] In an analogous manner, by repeating the described method steps, the second cover layer 2 (not shown here) is also connected to the second surface 7 of the core element 3, which here faces downwards. For this purpose, hot-melt adhesive 8 is sprayed onto the second surface 7 of the core element 3 in the manner described above, so that a net-like adhesive structure is formed. The second surface 7 is then heated with the aid of hot steam 11, so that the hot-melt adhesive 8 is reactivated and retracts towards the webs 4 in the manner described above. The second cover layer 2 can then be pressed onto the second surface 7 of the core element 3 in a direction indicated by the arrow 14, so that the core element 3 is finally arranged between the two cover layers 1, 2.

[0038] Figure 5 shows a sectional view of a section of a honeycomb panel produced using the method according to the invention. It can be clearly seen here that the hot-melt adhesive 8 retracts toward the webs 4 of the core element 3 and, in particular, also adheres to the lateral areas of the webs 4, effectively enclosing them, so that overall enlarged contact areas 15 are formed in the area of ​​the webs 4.

[0039] The method according to the invention thus makes it possible to easily provide a local adhesive concentration precisely in those areas of the honeycomb structure that actually contribute to the bond. Compared to conventional joining methods, larger contact areas are formed between the core element 3 and the cover layers 1, 2, so that a better bond between the core element 3 and the cover layers 1, 2 can be achieved with an overall reduced use of adhesive.

[0040] Furthermore, the method according to the invention is characterized by the fact that a honeycomb panel produced using this method can be immediately further processed, since the short reaction times of the hot-melt adhesive 8 eliminate the need for time-consuming and energy-consuming drying processes. The method according to the invention is particularly suitable for the production of honeycomb panels for the furniture industry and for the production of lightweight aluminum panels.

Claims

1 . A method for producing a honeycomb panel, wherein the honeycomb panel comprises a first cover layer (1) and a second cover layer (2) and a core element (3) arranged between the first cover layer (1) and the second cover layer (2), wherein the core element (3) has a honeycomb structure with cells (5) delimited by webs (4) and wherein the core element (3) has a first surface (6) which bears against the first cover layer (1) and a second surface (7) which bears against the second cover layer (2), comprising the following steps: i) providing the core element (3) and the first and second cover layers (1, 2); ii) spraying a hot-melt adhesive (8) onto at least one surface (6, 7) of the core element (3), wherein the hot-melt adhesive (8) is stretched during spraying so that a net-like adhesive structure (9) is formed on the at least one surface (6, 7) of the core element (3);iii) heating the at least one surface (6, 7) of the core element (3) provided with hot-melt adhesive (8) and thereby reactivating the hot-melt adhesive (8); iv) pressing a cover layer (1, 2) onto the at least one surface (6, 7) of the core element (3) provided with hot-melt adhesive (8); v) optionally carrying out method steps ii) to iv) for the second surface (7) of the core element (3) and the second cover layer (2), so that the core element (3) is arranged between the two cover layers (1, 2); 2. Method according to claim 1, characterized in that the hot-melt adhesive (8) is applied to the surfaces (6, 7) of the core element (3) by spin spraying with the aid of a compressed air-operated spiral nozzle (10).

3. Method according to claim 1 or 2, characterized in that the hot-melt adhesive (8) is sprayed at an angle a of 30° to 60°, preferably of approximately 45°, with respect to the surfaces (6, 7) of the core element (3).

4. Method according to one of claims 1 to 3, characterized in that a reactive hot-melt adhesive (8) is used.

5. Method according to one of claims 1 to 4, characterized in that the heating of the at least one surface (6, 7) of the core element (3) provided with hot-melt adhesive (8) is carried out by hot air and / or by hot steam (11) and / or by infrared radiation.

6. Method according to one of claims 1 to 5, characterized in that the hot-melt adhesive (8) with a basis weight of 30 to 90 g / m 2 is sprayed onto the surfaces (6, 7) of the core element (3).

7. Method according to one of claims 1 to 6, characterized in that the core element (3) comprises a paper-based material.

8. Method according to one of claims 1 to 6, characterized in that the core element (3) comprises an aluminum-based material.

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