NL1031771C2 - Connecting thermoplastic sandwich panels. - Google Patents

Description

Short indication: The connection of thermoplastic sandwich panels

This invention relates in the first place to a method for joining thermoplastic sandwich panels, wherein a thermoplastic sandwich panel comprises a thermoplastic core layer between two fiber-reinforced thermoplastic cover layers.

For joining sandwich structures such as Nomex honeycomb with thermosetting or thermoplastic coatings, metal profiles are generally used in the art. When used in the transport sector, in particular the aerospace and aerospace industry, these metal profiles make a not insignificant contribution to the total weight, which is undesirable.

The invention has for its object to provide a coupling method in which such profiles can be dispensed with, or to provide a usable alternative to the known method.

A further object of the invention is to provide a method for manufacturing sandwich panels which are suitable for use in this coupling method according to the invention.

Yet another object of the invention is to provide an assembly of such sandwich panels that can be easily coupled to each other.

To this end, the method for joining thermoplastic sandwich panels comprises the steps of: 1) providing a first thermoplastic sandwich panel with a knife connector; 2) providing a second thermoplastic sandwich panel with a groove connector; and 3) positioning the knife connector of the first sandwich panel in the groove connector of the second sandwich panel.

In the coupling method according to the invention, a knife and groove connection is used. Knife and groove joints are generally known in the wood (processing) industry, but not for structures consisting of thermoplastic sandwich panels. The first thermoplastic sandwich panel comprises at least one peripheral edge 1031771 2 thereof a knife connector that fits into a groove connector with a complementary shape of the second thermoplastic sandwich panel. In order to facilitate positioning in step 3, the knife and groove connecting piece preferably have a conical shape in cross-section. If desired, the thermoplastic sandwich panels can be firmly connected to each other with the aid of an adhesive. A thermoplastic or thermosetting glue can be used as the adhesive, for example. The joining of the knife and groove connecting pieces via heating of the thermoplastic present in the relevant cover layers will generally not be used because of the problems in the heat transfer of a stamp used for this purpose. Resistance and induction phases are examples of other possible connection techniques. A panel will generally be flat, but also (slightly) curved or curved panels can be used with the invention.

In the context of this description, the term "composite panel" means an object with a thickness that is small compared to its length and width, and which is composed of a thermoplastic core layer and a fiber-reinforced thermoplastic cover layer.

Furthermore, the term "sandwich panel" is used in this description for a particular embodiment of a composite panel, namely an object with a thickness that is small compared to the length and width of the object, composed of a thermoplastic core layer that is between two cover layers has been prepared. The second cover layer does not necessarily have to comprise a fiber-reinforced thermoplastic, but can also comprise a fiber-reinforced or non-fiber-reinforced cover layer of another material, such as a metal plate or a fiber-reinforced thermosetting material.

A "thermoplastic sandwich panel" is understood to mean a sandwich panel with a thermoplastic core layer, wherein both cover layers of the sandwich panel comprise a fiber-reinforced thermoplastic plastic.

An "in-situ sandwich panel" designates such a thermoplastic sandwich panel which is produced by the in-situ foaming technique, in other words a thermoplastic foam layer arranged between two fiber-reinforced thermoplastic cover layers.

The core layer comprises a non-solid structure, e.g. a thermoplastic foam or a thermoplastic honeycomb. This honeycomb structure comprises substantially parallel, open tubular elements of a thermoplastic plastic that are perpendicular to the main surface of the fiber-reinforced thermoplastic layer. A thermosetting or thermoplastic glue can be used to connect the core layer to the cover layers. If possible, the thermoplastic plastic present in the core, reinforcement layers and / or cover layers itself acts as an adhesive.

A method for the manufacture of a thermoplastic sandwich panel with a thermoplastic foam core by means of in-situ foams is known, for example, from EP-A1-0636463. Such a known sandwich panel consists of a core layer which is covered with two cover layers. A cover layer comprises one or more (fiber-reinforced) thermoplastic materials. The in situ foaming process consists of various steps. The first step is an assembly step, wherein a core web comprising at least one film of a thermoplastic material, which material contains a certain amount of a suitable physical blowing agent, is positioned between, for example, two (fiber-reinforced) coatings, which are usually made from the same thermoplastic material. plastic material 25 as the core web. The core web and cover assembly is then arranged between two pressing plates in a press. In this state, a foaming step is carried out, heat and pressure being first added to the assembly via the press, so that a connection between the core web and the cover layer or cover layers is achieved. After this, during a foaming step, when the temperature has become high enough, the press is slowly opened, whereby the distance between the two pressing plates increases. This allows the physical blowing agent (swelling agent, solvent) to expand, causing the material of the core web to foam. This expansion 35 is usually carried out under controlled conditions. In this way the core web is foamed, and the connection between the core web and the cover layer or layers is effected in one production step 4 without the need to use a separate or additional glue. When a predetermined thickness of the foamed core web is obtained, the assembly is allowed to cool during a cooling step. The sandwich product thus obtained comprises the foamed core web which is covered by and connected to two cover layers. In addition, a drying step is usually carried out. The in situ foaming method can also be used with a composite panel.

Examples of swelling agents for a thermoplastic foam comprising core layer include acetone, methyl ethyl ketone, methyl acetate, methyl propionate, nitroethane, cyclohexane, ether, ethanol, methanol and pentane, as well as mixtures such as ethanol / acetone and methanol / methyl acetate. Acetone is a preferred swelling agent. Examples of suitable thermoplastic plastics for both the core layer and the fiber-reinforced cover matrix (s) include polyetherimide (PEI), polyether sulfone (PES), polysulfone, polyphenyl sulfone (PPSU), polyketone such as polyether ether ketone (PEEK), liquid crystal polymers, polycarbonate (PC), propylene (PP), etc., and combinations thereof. A preferred thermoplastic is polyetherimide. This is available from General Electric under the trade name ültem in various qualities. Glass fibers are preferred as reinforcement. Other inorganic fibers such as metal fibers, carbon fibers and organic fibers such as aramid fibers can be used in the same way, provided that they are deformable to form the groove and knife connectors. In addition to the above synthetic fibers, natural fibers can also be used, provided that they are resistant to the thermoplastic sandwich panels to be produced by deformation at fairly high temperatures with a knife and / or groove connector. The fibers can be used in the form of mats, fabrics and the like. Targeted fibers, in particular unidirectional fibers where the fiber direction is adapted to the intended application, can also be used advantageously. The core layer, e.g.

Thermoplastic honeycomb and / or thermoplastic foam may, if desired, be reinforced with fibers of the aforementioned types or with nanoparticles. Preferably, the thermoplastic material of the core layer is the same as the thermoplastic material in the cover layers. However, combinations of different thermoplastic plastics can also be used. Suitable examples thereof include PEI foam covered with coatings made from PPSU, PS, PEEK or PC, PES or PPSU foam covered with PSü or PC coatings, and PP foam covered with polyamide such as nylon coatings.

The examples mentioned apply in a similar way to the additional reinforcement layers. These can be used as a consolidated layer 10 or as a prepreg, which themselves can consist of several layers (slats) stacked on top of each other.

If desired, the core can also be composed of several layers, which are separated by an intermediate layer, such as a fiber-reinforced (thermoplastic) layer, ceramic or metal layer.

Other methods for manufacturing an assembly of a thermoplastic core layer and at least one fiber-reinforced thermoplastic cover layer include extruding a thermoplastic foam on a fiber-reinforced thermoplastic cover layer, preferably between two such cover layers and gluing a thermoplastic foam with a fiber-reinforced thermoplastic cover layer. The adhesive used must be resistant to the temperatures required for deformation into a knife or groove connection piece.

The coupling method according to the invention lends itself in particular to the modular construction of the interior of aircraft and the like, but can also be used for the layout of commercial and office buildings. Thermoplastic sandwich panels, in particular sandwich panels manufactured in situ based on e.g. PEI and PPSU have excellent fire resistance, high mechanical properties, insulating properties and are thermoplastic deformable.

The invention also provides manufacturing techniques for manufacturing the sandwich panels with either a knife connector, or a groove connector, or a combination thereof along different peripheral edges. A preferred method for providing a thermoplastic sandwich panel with a knife connector, wherein the thermoplastic sandwich panel comprises a thermoplastic core layer between two fiber-reinforced thermoplastic cover layers, comprises the steps of 5 Δ) rejuvenating a peripheral edge of a thermoplastic sandwich panel.

In this method according to the invention, a peripheral edge is deformed under the influence of heat and pressure over a predetermined width with the aid of one or more hot deformation stamps. This deformation step can if desired be subdivided into several sub-steps. As a result, the distance between the cover layers locally, i.e. at the treated peripheral edge, becomes smaller with respect to the mutual distance in the main body, the core layer present between the cover layers being somewhat compacted locally. Preferably, this peripheral edge is or is later finished, i.e. the end face where normally the foam core is exposed, is covered with a fiber-reinforced thermoplastic layer, preferably by folding one or both cover layers so that they overlap or abut each other. If desired, an additional fiber-reinforced thermoplastic layer can be utilized thereby.

A preferred method for providing a thermoplastic sandwich panel with a groove connector, wherein the thermoplastic sandwich panel comprises a thermoplastic core layer between two fiber-reinforced thermoplastic cover layers, comprises the steps of B) locally densifying the core layer between the cover layers at a head edge of a sandwich panel .

To make the groove in the sandwich panel, a mold stamp is inserted between the cover layers to a desired depth under heat and pressure. The core material such as foam is locally compacted, so that a depression or groove is formed, bounded by longitudinal edges of compacted foam.

The walls of the groove are preferably reinforced with an (additional) fiber-reinforced thermoplastic layer. In a first variant therefor, a fiber-reinforced thermoplastic reinforcement layer is applied over the head edge prior to step B).

7

During the deformation step, this is pressed into the end face by means of heat and pressure and thus forms the walls and / or bottom of the groove. A part of the core layer between the reinforcement layer and the cover layer and / or cover layers will generally be pressed into a (substantially) solid material. The stiffening can also be obtained from the cover layers themselves by finishing the peripheral edge therewith before step B). Advantageously, the end edge is clamped during step B) so that the cover layers on the main surfaces of the sandwich panel cannot deform. Depending on, among other things, the thickness of a panel, the dimensions of the groove and the thickness of the reinforcement layer, it may be necessary first to locally densify the core layer with a heated mold and then to apply a reinforcement layer in the first formed groove with a heated forming stamp. > press and record the final shape of the groove with the aid of a consolidation stamp. A glue can also be used for attaching a preformed reinforcement layer in an already formed groove.

Because of the small thickness of the thermoplastic sandwich panels, a shaping stamp is preferably used for providing the groove which is in heat-exchanging contact. with a relatively large heat reservoir to prevent the forming stamp from cooling down too much during the forming step. An additional heating step can - if desired - be carried out because the dimensions of the desired shape and thus the shape stamp are such that the flow of heat cannot take place sufficiently. In order to allow the required heat to be supplied in a short time, the fiber-reinforced thermoplastic layer to be inserted and possibly a similar layer is obtained by edge finishing of one or more of the cover layers, heated on the ends of the thermoplastic sandwich panel in order to obtain the required to be able to perform desirable deformations within a short period of time (in the order of seconds), without the temperature of the stamp or the temperature during preheating becoming so high that the foam between the groove and the coatings is too compacted, which is not desirable, and sufficient heat has nevertheless been applied such that the reinforcement layer is deformable. To retain the shape and reduce residual stresses, a consolidation stamp 8 can be used, preferably with a temperature lower than the Tg of the thermoplastic from the coatings but preferably higher than half of the relevant Tg (° C).

If desired, the thickness of the panel can be increased locally by arranging the groove in the end edge of a thermoplastic sandwich panel by choosing a suitable forming stamp (s), so that a groove having a width corresponding to the thickness of the original sandwich panel is obtained. This makes it possible to accommodate a sandwich panel with this thickness, i.e. without knife connector 10, in this groove.

The invention also relates to a thermoplastic sandwich panel with a knife connection piece, or with a groove connection piece, as well as to an assembly thereof. The invention is explained below with reference to the appended drawing, in which:

FIG. 1 shows a first embodiment of a method for making a sandwich panel with groove connector according to the invention;

FIG. 2 shows a rejuvenation that fits into the groove of figure 1. FIG. 3 shows an example of a method for manufacturing a sandwich panel with a knife connector.

FIG. 4 shows an embodiment of a method for making a sandwich panel with a groove connector;

FIG. 5 shows a method for joining two sandwich panels.

Fig. 1 shows a thermoplastic sandwich panel 10, which shows a thermoplastic foam core layer 12 between two fiber-reinforced thermoplastic cover layers 14 and 16. The end face 150 is clamped between metal or plastic clamping blocks 152. A fiber-reinforced thermoplastic reinforcement layer 70 is overlapped on the head edge 150. This reinforcement layer 70 can be preheated with a heating stamp 154. An (elongated) forming stamp 18 with a forming shoe with a temperature of the melting temperature ± 20% of the thermoplastic defining the shape of the groove to be made is positioned on the reinforcement layer 70 at the location of the foam core layer 12. Under pressure and by addition the forming die 18 then sinks into the foam core layer 12, which is thus compacted. After consolidation with the aid of a consolidation stamp (not shown), a groove 156 in an end edge of the thermoplastic sandwich panel 10 is obtained, the walls 158 and bottom 160 being formed by the co-formed reinforcement layer.

Figure 2 shows a sandwich panel 10 with a rejuvenation 100a as a knife connector that fits into the groove 156 of the sandwich panel of Figure 1.

Figure 3 shows a possible method for the manufacture 10 of knife connector 100a in a sandwich panel. Here, a hot deformation stamp 18 sinks into the sandwich panel 10, thereby forming half 104 of the required deformation for the knife connector 100a. The desired shape is consolidated using a consolidation stamp (not shown). The sandwich panel is turned over to produce the complementary portion 106 of the blade connector 100a in an identical manner. Another possibility is to perform the above process simultaneously with two form stamps, wherein it is desirable to also consolidate the shape of the knife 100a simultaneously with one or more consolidation stamps.

FIG. 4 shows an alternative method for the manufacture of a sandwich panel 10 with a groove connecting piece 156, wherein the peripheral edge 100 of the sandwich panel 10 to be worked is finished. In the case shown, the ends of both cover layers 14, 16 are folded towards each other and partially overlap each other. A mold punch 18 is then pressed into the foam core layer 12, as described above, with the cover ends co-forming and forming the walls 158 and bottom 160 of the groove 156. It will be clear that with the usual thicknesses of panels for the aerospace industry, the folded portions of the cover layers are not sufficient to cover an entire groove 156, so that here too an additional reinforcement layer is generally applied as used for the ones shown in Figure 1. method.

FIG. 5 shows the method for coupling two sandwich panels 10a, b, wherein a tapered peripheral edge 100a of a first panel 10a is positioned in a groove 156 of a second panel 10b.

1031771

Claims (16)

A method for joining thermoplastic sandwich panels, wherein a thermoplastic sandwich panel (10) comprises a thermoplastic core layer (12) between two fiber-reinforced thermoplastic cover layers (14, 16), which method comprises the steps of: 1. providing a first thermoplastic sandwich panel (10a) with a knife connector (100a); 2. providing a second thermoplastic sandwich panel (10b) with a groove connector (156); and 3) positioning the knife connector (100a) of the first sandwich panel (10a) in the groove connector (156) of the second sandwich panel (10b); The method of claim 1, wherein the blade connector 15 (100a) and the groove connector (156) are connected to each other. Method according to claim 2, wherein the knife and groove connecting piece (100a, 156) have a conical shape in cross-section. Method for providing a thermoplastic sandwich panel (10a) with a knife connector (100a), wherein the thermoplastic sandwich panel (10) comprises a thermoplastic core layer (12) between two fiber-reinforced thermoplastic cover layers (14, 16), in particular as step 1) of claim 1, the method comprising the steps of A) rejuvenating a peripheral edge (100) of a thermoplastic sandwich panel (10). 30 The method of claim 4, wherein both cover layers (14, 16) are deformed near the peripheral edge (100) while simultaneously localizing the intermediate core layer (12). 1031771 Method according to any of the preceding claims 4-5, wherein the peripheral edge (100) is finished. 7. Method for providing a thermoplastic sandwich panel (10b) with a groove connector (156), wherein the thermoplastic sandwich panel (10) comprises a thermoplastic core layer (12) between two fiber-reinforced thermoplastic cover layers (14, 16), in particular as step 2) of claim 1, which method comprises the steps of A method according to claim 7, wherein prior to step 15 B) a fiber-reinforced thermoplastic reinforcement layer (70) is applied over the head edge (150). A method according to claim 7 or 8, wherein the peripheral edge (100) is finished prior to step B). 20 A method according to any one of the preceding claims 7-9, wherein during step B) the head edge (150) is clamped. B) locally compacting the core layer (12) between the cover layers (14, 16) at an end face (150) of a thermoplastic sandwich panel (10). 11. Method according to claim 8, wherein the fiber-reinforced thermoplastic reinforcement layer (70) is preheated. 12. Thermoplastic sandwich panel, comprising a thermoplastic core layer (12) between two fiber-reinforced thermoplastic cover layers (14, 16), wherein at least one peripheral edge of the sandwich panel is provided with a knife connector (100a). The thermoplastic sandwich panel of claim 12, wherein the knife connector (100a) has a fiber-reinforced edge. 35 A thermoplastic sandwich panel comprising a thermoplastic core layer (12) between two fiber-reinforced thermoplastic cover layers (14, 16), wherein at least one peripheral edge of the sandwich panel is provided with a groove connector (156). The thermoplastic sandwich panel of claim 11, wherein the groove connector (156) has a fiber-reinforced edge. 16. Assembly of a thermoplastic sandwich panel according to claim 12 or 13 and a thermoplastic sandwich panel according to claim 14 or 15. 1 0 3 1 7 7 1