FR2918597A1 - METHOD FOR MANUFACTURING A PANEL OF THE BEES NID TYPE, INSTALLATION FOR CARRYING OUT THE METHOD AND THE PANEL OBTAINED - Google Patents

Abstract

The method of manufacturing a panel (1) of the honeycomb type comprising two outer skins (6) glued on both faces (3, 4) facing a central core (2) with a honeycomb structure consisting of a juxtaposition of cells (8) delimited by side walls (9) is characterized in that it consists: - in preparing the central core (2) with cells (8) by providing openings (10) in at least some of the walls (9) of said cells (8), - to position on each of the faces (3, 4) of said cell core (2) a hot melt adhesive film (5) and one of said outer skins (6). ), to seal the periphery of the multilayer assembly (1) obtained, to subject the multilayer assembly (1) obtained by the action of a hot press (14) to ensure the melting adhesive films (5), - to depressurize at least a portion of the cells (8) of the central core (2), thanks to the peripheral sealing made in the and placing in communication at least some of said cells (8) through the openings (10) formed in their walls (9), this vacuum being performed at least before the end of the hot-pressing operation and- to cool the panel obtained, while maintaining its internal depression, at least until the glue of the bonding films (5) performs its function of joining between the central cellular core (2) and the two outer skins (6).

Description

The present invention relates to the general field of sandwich panels of

  honeycomb type, consisting of a central cellular alveolar core whose two faces are covered by outer skins; it relates more particularly to a method of manufacturing such a panel, an installation for carrying out this method, and the sandwich panel obtained.

  Honeycomb panels are widely used in many industries, especially for the construction of walls, partitions, floors, ceilings, doors, tables, etc.

  These panels comprise a central core (metal or other, for example aluminum) very generally formed of a juxtaposition of tubular cells with polygonal (especially hexagonal), circular or ovoid, delimited by side walls which extend over a constant height.

  The two main faces facing this central core receive cover plates, called outer skins, secured by gluing, the nature (aluminum, steel, composite, high pressure decorative laminate) is suitable for the intended application.

  Conventionally, this outer core / skin bonding is carried out by means of thermosetting glue of the two-component type (base + hardener), based on polyurethane, epoxy or methacrylate, in combination with a pressing operation at temperatures ranging from ambient temperature up to 130 C. However, this technique has many disadvantages:

  - the adhesives used require precautions of supply and entail storage constraints (hazardous products, expiry date, storage in a protected environment), - because of the open times required by the process, the polymerization cycle times are relatively long (30 to 90 minutes),

  - The application of the glue is performed manually or with a robot, this with relatively wide grammage tolerances (eg 400 g / m2 set to guarantee 300 g / m2 minimum), - the application must be done in a air-conditioned room to guarantee a constant environment and homogeneous open times according to the seasons,

  - Paste adhesives used cause fluings that must be mastered with temporary protections expensive to implement. They require solvents for cleaning tools, pumps, etc. and they lead to harsh working conditions (wearing gloves, masks, emanating solvents, high staining power ...), - the control of collages can only be done afterwards, by taking specimens (destructive tests ) or by taping survey (tedious and subjective test).

  Other known manufacturing techniques use thermoplastic adhesives, substantially less restrictive than the aforementioned thermosetting glues.

  However, these thermoplastic adhesives require keeping the panel in press at high temperature (of the order of 180 C), for about 20 minutes, and then allowing it to cool while maintaining it under pressure between the press plates. 10 We use for this:

  - A hot plate press with heat exchanger, which itself ensures both the heating and cooling of the panel. However, the heating / cooling cycle of this type of equipment is very long and expensive in energy; or

  15 - hot / cold tandem presses, associated with appropriate transfer tooling. But it is then necessary to have two presses, which take up a lot of space, and also specific tools; or

  - Continuous pressing systems Flatbed type Calender, very expensive, bulky and lacking flexibility.

  The present invention proposes a new process and a new installation for manufacturing honeycomb sandwich panels which, while implementing relatively simple means, allow gains in particular in terms of productivity and improve the quality of the panels obtained. .

  For this, the method according to the present invention consists of:

  Preparing the cellular central core by providing openings in at least some of the walls of said cells,

  positioning on each of the faces of said cell core a hot-melt adhesive film and an outer skin,

  to make airtight the periphery of the multilayer assembly obtained,

  Subjecting the multilayer assembly obtained to the action of a hot press to ensure the fusion of the adhesive films,

  - To depressurize at least a portion, and preferably most of the cells of the central core, thanks to the peripheral sealing made beforehand and the placing in communication of at least some of said cells by the openings 35 formed in their walls, this depression being performed at least before the end of the hot pressing operation, and - to cool the panel obtained, while maintaining its setting internal vacuum, this at least until that the glue of the bonding films ensures its function of joining between the central alveolar core and the two outer skins.

  The draining properties of the honeycomb core material are therefore used to maintain the pressure on the panel during the cooling phase. Preferably, and this is the main interest of the present invention, once the hot pressing operation is completed, the panel obtained from the press is removed to achieve cooling, while maintaining its depression. internal.

  According to a particularly interesting procedure, during the hot pressing operation, the panel is applied to a temperature of between 160 and 200 ° C., for a time of between 10 and 30 minutes (preferably a temperature in the region of 180 ° C. is applied). , for 20 minutes).

  On the other hand, the vacuum operation is carried out at a value between -0.3 and -1 bar (more preferably between -0.5 and -0.8 bar).

  The installation for the implementation of this method comprises: - a heating press,

  means for effecting the peripheral sealing of the panel, and

  means enabling the internal volume of the central core of the panel to be depressed.

  On the other hand, the invention also relates to the honeycomb panel obtained by the process defined above, this panel comprising a central alveolar core on both sides facing which are glued outer skin, at least some of the cells of this central core (and preferably all or substantially all) having orifices in their side walls.

  These orifices are arranged, in number, in size and in location, so as to effect an effective communication of the internal volume of the different cells, to allow optimum drainage of the air within the central core and obtain a internal depression pushed.

  The drainage of the central core honeycomb structure can be achieved by orifices formed within the walls of the cells, substantially in the middle part. According to an alternative embodiment, these orifices are formed at one end of the walls of said cells.

  The invention will be further illustrated, without being limited in any way, by the following description, in relation to the accompanying drawings, in which: FIG. 1 is a schematic view which illustrates the initial step of the method according to the invention, corresponding to the preparation of the sandwich panel; - Figure 2 is always a schematic view showing the prepared sandwich panel ready to be in press;

  - Figure 3 shows, still schematically, the following operation of pressing the panel, associated with its setting in internal depression; - Figure 4 is a diagrammatic view which illustrates the sandwich panel out of the press, to achieve its cooling with maintenance of its setting internal vacuum;

  FIG. 5 illustrates an alveolar core variant that can be used in the context of the process according to the present invention.

  Figures 1 to 4 schematically illustrate the four main steps of the method according to the present invention, for manufacturing a honeycomb core sandwich panel coated with externally bonded skins.

  As illustrated in Figure 1 in an exploded manner, the initial step of the method

  consists in preparing a multilayer assembly or panel 1 comprising a cellular core 15 2 on the two main faces 3 and 4 of which are arranged: - a hot melt glue film 5, then - an outer skin 6. The central core 2, very generally flat and of constant thickness e, is illustrated here in cross section; its two faces 3 and 4, said main 20 correspond to its large faces whose contours define the general shape of the panel, in comparison with its small faces 7 periphery (which correspond to the edges of the panel).

  This central core 2 may have any general shape, for example square, rectangular, circular or other, and its thickness e is generally between 5 and 50 mm.

  It is formed of a juxtaposition of tubular cells 8 which open at the level of said main faces 3 and 4 and which are delimited by side walls 9 giving them a circular polygonal constant cross section or ovoid. This type of central core 2 can be obtained from metal, especially aluminum, by a conventional technique of expanding laminated strips.

  In FIG. 1, the presence of orifices 10 formed in the walls 9 of the cells 8 is noted. These orifices 10 put in communication at least some of the cells 8 juxtaposed. Preferably, the vast majority of the cells 8 of the core 2 (and preferably all the cells 8) are thus placed in communication. In the embodiment illustrated in FIG. 1, the orifices 10 have a generally circular shape with a diameter of a few millimeters (for example 3 mm), and they are formed in the median part of the walls 9. If the technique is used mentioned above for forming the core 2 (expansion of laminated strips), they can be obtained by perforation or drilling strips before expansion. The corresponding drainage can also be obtained by means of a plurality of very small perforations formed in the walls of each cell 8, made in number and in suitable dimensions. It may for example be micro-perforations made in a conventional manner during the manufacture of the core 2 to obtain a pressure equalization within the final panel, possibly associated with complementary orifices of larger diameter, regularly distributed and in number adapted. The hot-melt adhesive films 5 have a general shape which corresponds to that of the contour of the cellular core 2 to cover all of its main faces 3 and 4. These films 5 are advantageously made of thermoplastic material, for example thermoplastic copolymer based on modified low density polyethylene (type LLBPE). Their thickness (for example between 200 μm and 300 μm) is adapted in particular according to the nature of the core 2 and the two outer skins 6 that are to be secured. These outer skins 6 also have a general shape that corresponds to that of the contour of the alveolar core 2 to cover all of its faces.

  3 and 4 and thus close the apertures of the ends of the cells 8. They generally have a thickness between 0.4 and 3 mm; they can be made of metal (steel, aluminum), plastic, composite or material

high pressure decorative laminate.

  Once the multilayer assembly 1 thus constituted, sealing is effected at

  the air of its peripheral edge by any appropriate means 11 positioned against the small peripheral faces 7 of the central core 2 and interposed between the two borders

  6. These sealing means 11 may for example consist of a high performance adhesive tape structure, a foam seal structure, suitable folds.

  extending outer skins 6, reported profiles, or any combination of

  these sealing solutions. In addition, the alveolar interior volume of the multilayer assembly 1 is

  connected to a vacuum network via at least one vacuum tap 12.

  It is understood that this alveolar interior volume sealed by the two outer skins 6 and the peripheral means 11, and drained by the various orifices 10, can thus be depressed with respect to the surrounding atmospheric pressure.

  The multilayer assembly 1 thus prepared (FIG. 2) is then ready to undergo a

  hot pressing operation by means of a conventional heating press 14.

  At the time of printing, the interior volume of the multilayer assembly 1 does not need to be depressed.

  The pressing operation (FIG. 3) is performed in such a way as to compress the outer skins 6 against the main faces 3 and 4 of the central core 2 and this under high temperature, so as to effect the fusion of the adhesive films 5.

  When this fusion is obtained (or a little before), the interior volume of the multilayer assembly 1 is depressed. This depressurization generates a plating force of the outer skins 6 against the central core 2 which makes it possible to dispense with the action of the press 14. Thus, the multilayer assembly 1 can be removed from the press 14 (FIG. ) and be stored for its cooling phase, said press 14 then being released and ready to be used for a new cycle.

  The internal volume of the multilayer assembly 1 is kept under vacuum throughout the cooling phase, as long as the glue is not able to fulfill its role properly.

  At the end of the cooling phase, the depression is stopped and the peripheral sealing means 11 can be removed (in certain cases and for certain applications, depending on their nature, these sealing means 11 may be retained) .

  Depending on the thermoplastic glue used and the nature of the central core and the outer skins, the pressing operation is carried out for a period of between 10 and 30 minutes, at a temperature of between 160 and 200 ° C. (preferably for a time of about 20 minutes, at a temperature of about 180 C).

  The applied pressing force, conventional, is between 0.2 and 0.5 bar.

  On the other hand, attractive tensile / plating forces are obtained by an internal vacuum of between -0.5 bar and -0.8 bar.

  It has been experimentally demonstrated that a honeycomb panel without adhesive, subjected to a high vacuum (between -0.5 and -0.8 bar) and drained by the orifice cells, provides a rigidity comparable to that of a glued panel. Thus, the panel released at high temperature (when the bonding film is still very flexible) can no longer be deformed from the moment when it comes to apply a level of vacuum to guarantee without movement the integrity of the sandwich during the cooling phase.

  Compared to the thermosetting glue manufacturing techniques, the following advantages are obtained: improved performance of the panel, especially in peeling-drum coatings, better calibrated panel performance (low standard deviation in the values),

  - better rheological behavior of the panel (symmetry of the meniscus on the honeycomb foil),

  - weight gain of the panel: about 400 g / m2, - no glue creep,

- no open time,

  - no need for air-conditioned gluing room

  - no need for primer (good performance on sanded sheet),

  - immediate use of panels for machining (100% properties are obtained after cooling),

  use of the hot-melt film with a width of width corresponding to the width of the panel (saving time on cutting, limiting material losses, no waste to be eliminated, etc.),

- clean workstations,

  20 - the thermoplastic bonding facilitates the recycling of the product at the end of life, - possibility of bending the flat panels after pressing.

  On the other hand, compared to other pressing methods using thermoplastic adhesives, the following advantages are obtained: use of conventional production tools,

  25 - very great flexibility of use in particular at the preparation station upstream of the panels,

  - optimization of the pressing times and maximum productivity of the tool (the press cycle time is very short and it allows an optimum performance of the tool), - in the cooling phase, the panels can be stored directly in the

  Press release on mobile walkways that accompany the panel to the next station (machining, finishing),

  - The vacuum maintenance of the internal volume of the panel ensures a perfect control of gluing and flatness during the cooling phase which is naturally in the open air (the area must nevertheless be ventilated), 35 - the panels are sealed by the necessity of the specific process, - the resulting seal can be used to perform a test pressure on the finished panel to reliably guarantee non-destructive bonding performance,

  - The recyclability conditions of the panels are improved.

  In Figure 5 there is shown a central core variant 2 'may be used in the context of the method according to the present invention.

  Here, the drainage of the honeycomb is carried out by grooves 10 'made on one side of the cells 8, in particular on the side of the least exposed face (for example, in the case of a floor, the grooves are positioned on the underside).

  These end grooves 10 'can be made very easily by sawing or milling before the expansion of the strip assembly, during the manufacture of the core 2. It will be noted that all the honeycomb networks can be used to form the core. core 2, from the moment they allow to withstand the pressure, the temperature and from the moment they allow to drain the vacuum. This technique can also be used for the manufacture of curved panels on conformers. Conventionally, the panel is left on the shaper for the duration of the cycle which immobilizes the tool and brakes production rates. The present technique makes it possible to remove the curved panel from

  20 shaper before the end of the cycle, due to the preservation of the curve of the panel by maintaining its evacuation. The corresponding principle, using an internal depression of the panel, can also be implemented with paste thermosetting glues, in association with a heating press or not.

Claims (10)

  - 1.- A method of manufacturing a honeycomb type panel comprising two outer skins (6) glued on the two opposite faces (3, 4) of a central core (2, 2 ') with nest structure honeycomb consisting of a juxtaposition of cells (8) delimited by 5 side walls (9), characterized in that it consists: - in preparing the central core (2, 2 ') with cells (8) by providing openings (10, 10 ') in at least some of the walls (9) of said cells (8), - to position on each of the faces (3, 4) of said core (2, 2') a bonding film thermofusible (5) and one of said outer skins (6), 10 - to seal the periphery of the multilayer assembly (1) obtained by suitable means (11), to subject the multilayer assembly ( 1) obtained by the action of a heat press (14) to ensure the fusion of the bonding films (5), - to depressurize at least a portion of the cells (8) of the central core (2, 2 '), 15 thanks at the circumferential sealing (11) previously carried out and at the placing in communication of at least some of said cells (8) by the openings (10, 10 ') formed in their walls (9), this depression being achieved at least before the end of the hot-pressing operation, and - to cool the panel (1) obtained, while maintaining its internal depression, at least until the glue of the adhesive films ( 5) ensures its function of joining between the central alveolar core (2, 2 ') and the two outer skins (6).   2. A method according to claim 1, characterized in that it consists, once the hot pressing operation is completed, to remove the panel (1) obtained from the press (14) to achieve its cooling, while maintaining its setting in internal depression.   3. A process according to any one of claims 1 or 2, characterized in that it consists, during the hot pressing operation, to apply to the panel (1) a temperature between 160 and 200 C, this for a time between 10 and 30 minutes. 30   4. A process according to any one of claims 1 to 3, characterized in that the vacuum operation is performed at a value between -0.3 and -1 bar and preferably between - 0.5 and -0.8 bar.   5. Honeycomb-type panel obtained by the method according to any one of claims 1 to 4, comprising a central core alveolar (2, 2 ') on both sides (3, 4) facing which outer skins (6) are bonded, at least some of the cells (8) of said central core (2, 2 ') having orifices (10, 10') formed in their side walls (9).   6.- Panel according to claim 5, characterized in that it comprises a central core (2), at least some of the cells (8) have orifices (10) formed within their walls (9), substantially in part median.   7. Panel according to claim 5, characterized in that it comprises a central core (2 '), some of which at least cells (8) have orifices (10') provided at one of the ends of their walls (9)   8. Panel according to any one of claims 5 to 7, characterized in that all or substantially all the cells (8) of the central core (2, 2 ') comprise orifices (10, 10') formed in their side walls (9).   9.- Panel according to any one of claims 5 to 8, characterized in that the two outer skins (6) are secured to the central core (2, 2 ') by means of a thermoplastic type adhesive.   10.- Installation for carrying out the method according to any one of claims 1 to 4, characterized in that it comprises a heating press (14), means (11) for sealing the peripheral panel ( 1), and means (12) for the depression of the internal volume of the central core (2, 2 ') of said panel (1).