NL2012710C2 - IMPACT RESISTANT THERMOPLASTIC SANDWICH MATERIAL. - Google Patents

Description

IMPACT RESISTANT THERMOPLASTIC SANDWICH MATERIAL

The present invention relates to a shock-absorbing element for a feed or aircraft, in particular an automobile or an aircraft. The invention also relates to a floor panel or bottom plate of a flying or vehicle made of such an element. The invention further relates to methods for manufacturing a reinforcement structure for such a shock-absorbing element and to methods for manufacturing a shock-absorbing element provided with one or more of such reinforcement structures. The present invention furthermore relates to a panel for enclosures or the entire enclosure with such panels, wherein the panel can have an electromagnetic screen (ings) function (EMS).

A development has been initiated in the aircraft industry in recent years in which more and more metal parts are being replaced by parts made entirely or partly from plastic. The use of plastic has several advantages. In many cases, plastic parts are relatively lightweight and can be produced with fewer tools than metal parts. In addition, the possibility of glue connections is prominent and not to mention the possibility of function integration.

Characteristic of a large group of these plastic parts is the possibility to reinforce them with the help of fibers. Commonly used reinforcing materials include glass and carbon. This can be added in various forms depending on the production process. For example, there are fibers with a discrete length, endless fibers and knitwear or fabrics.

For example, aircraft panels with a sandwich structure are known consisting of two thermosetting, (fiber) reinforced, skins with a PU (polyurethane) foam layer in between. However, these known panels have the drawback that they consist of three glued layers and can only be machined "mechanically" by means of sawing, drilling, gluing, etc. This does not benefit the structural integrity and may, for example in the event of breakage, pose a risk to the passengers.

A production method is also known in which a thermoplastic sandwich can be made which is foamed in-situ, whereby a homogeneous sandwich is formed, which can be formed into a 3D panel by means of (local) heating. A method is also known in which a sandwich can be produced using injection molding technology. Propellant gases from introduced materials can thereby be expanded to create foam.

In contrast to the panels consisting of a thermoset, the thermoplastic sandwich is easy to recycle. Given the high material prices, this is an additional advantage.

Although this thermoplastic sandwich has many advantages over the thermosetting variants, the fiber reinforcements that are used are naturally based on contributing to the weight reduction over existing panels.

However, a disadvantage of these reinforcements is the lack of integrity in the event of a high or strong energy impact ("impact"). Especially with carbon, this leads to a strong fragmentation of the material and a high risk of injury.

It is an object of the invention to provide a preferably thermoplastic sandwich material in which at least one of the abovementioned drawbacks according to the state of the art is obviated.

It is also an object of the invention to provide a method for manufacturing a thermoplastic sandwich material provided with such a reinforcing structure.

It is a further object of the invention to provide a method for manufacturing an impact-resistant panel provided with such a reinforcing structure.

In addition, it may be an object of the invention to provide a method for manufacturing a housing panel or even a housing from almost or entirely exclusively such panels, preferably with an electromagnetic shielding function, also called "Electro-Magnetic Shielding" (EMS). mentioned. The panels and / or resulting housings may also be part or object of the present invention, or merely an appearance thereof.

The pursuit of weight saving in the aircraft and automobile industry has led to the increasing use of plastics.

Fiber reinforcements are used to meet the high mechanical strength and stiffness requirements. These fibers can be distinguished from each other by the type of fiber, the length and the appearance, i.e. as a discrete length, as a unidirectional fiber or in fabric form of any kind.

A common disadvantage of these fiber reinforcements is the fact that the strength and stiffness have increased, but also the brittleness. In other words, the integrity (the staying together of the taxed parts) of the whole has declined.

It is known from previous patents that this integrity can be improved by means of metal weave requirement, cords and the like.

The processes used for this include compression and injection molding. A handicap with these processes is the occurrence of shear stresses while the material flows. This requires relatively expensive weft threads in the fabrication of the fabric. BACKGROUND ART: EP 1996388 relates to thermoplastic material with an embedded reinforcement layer of, for example, metal knit or fabric, which reinforcement layer is embedded in a thermoplastic polymer material.

From the published patent application EP-0636463 it is known to apply in an intermediate product an impregnated foam film 4 between two or more tissue skins 2, 3, to heat the assembly and, after reaching the desired temperature, the impregnated foam film 4 in allow the whole to foam up by slowly opening a press, with the intermediate 1 in it. This yields sandwich panels 6 with a foamed layer 5 and on at least one side thereof a skin layer 2 or 3. This state of the art is shown in Figure IA.

THE INVENTION

According to the invention, at least one reinforcement layer is added to the package. This creates a sheet material with an increased impact resistance to load on one or both sides. This is shown in the attached sectional views in Figs. IB - 1D, in which properties, elements, aspects and components can be indicated with the same reference numbers as those in Fig. IA. Specific preferred embodiments are defined in dependent claims, and are described below.

In the drawing:

Figure 1A an example of the known art; and

Figures IB - 1D show various embodiments of the present invention;

Figures 2A and 2B schematically show views of possible production processes;

Figures 3A and 3B show various views of mutually different embodiments of products resulting from the production processes; and

Figures 4A - 4D show an embodiment with a local (in the middle, for example) force passage.

Figure 1B shows an embodiment of an intermediate product 7 of two skin layers 2, 3 and an intermediate foamable layer 4, and with a reinforcement layer 8 close to one of the skin layers 2 or 3, and a resulting product 9 with foamed material in the intermediate layer 5, after applying the method according to the invention and foaming the material in the foamable layer 4.

Fig. 1C shows a variant of an intermediate product 10 with the reinforcement layer 8 centrally between the skin layers 2, 3 and in the foamable layer 4 resp. foamed layer 5 in end product 11.

Figure 1D shows an embodiment of an intermediate product 13 with two reinforcement layers 8, 12, each against a skin layer 2, 3, both in the intermediate product 13 and in a final product 14. It is noted that in addition in this embodiment a foam layer may be provided between the skin layers 2, 3 and the reinforcement layer 8 immediately below or behind it (seen from the outside), in particular, but not exclusively, in case there is doubt about an adequate adhesion of the skin layers 2, 3 directly on or to the reinforcement layer, which could be improved, in particular but not exclusively, when the reinforcement layers 8 are formed by bare steel cords or comprise these bare steel cords. This may also be the case in the embodiment of Fig. 1B, where also a reinforcement layer 8 is provided behind or directly against the skin layer 2 and between which, optionally, a foamable or foamed layer can be provided for the purpose of bonding the reinforcement layer with possibly steel cords. therein and the relevant skin layer 2.

An additionally obtained, other property of the new resulting often plate-shaped material with metal in the material of the reinforcement layer is an electromagnetic shielding (EM shielding).

The basis of the invention lies in an in situ foaming based system, as known from EP 0636463, which may be referred to herein as the FITS system. This is a thermoplastic foam.

Matrix material is thermoplastic PEI (polyetherimide), but amorphous or crystalline thermoplastics such as PA, PP or any other thermoplastic may also be used instead. Under the influence of a physical or chemical foaming agent or blowing agent in the relevant film, the matrix material can foam according to the in-situ foaming technique, reference being made for reference to EP-0636463 to illustrate known foaming agents, which (and other) foam agents are incorporated herein by reference herein to EP 0636463.

Examples of materials in the reinforcement layer 8 are: steel cords; aramid; polyester; and metal fabrics / knits from steel, copper, etc. It is important here that the cords have a minimum distance from each other, which is determined by, among other things, the thickness of the foam layer, the ability of material to be foamed to adhere well to the reinforcement layer to penetrate well through this during foaming, et cetera. Decisive for, among other things, further strength of a resulting product is namely a sufficient adhesion surface of the foam to the outer skins 2, 3.

It is possible that in practice a total thickness of foamable foil must have the same thickness as the thickness of the reinforcement layer 8, for example because otherwise a sufficient pressure cannot be exerted on the foil and in such a case foil can start to foam. if this is a slight difference, I do not know what is happening, but if it is larger then it is very likely that the formation of the foam can strongly influence the mechanical properties of the foam.

In an application with cords, these can vary in length, thickness (number of monofilaments), number, structure, and other properties, partly or entirely dependent on intended applications. Such applications can be: impact-sensitive panels in aircraft impact-sensitive parts in cars structural basic material for the automotive industry. Electromagnetic construction material.

Figure 2A shows a mold 15 with a package 10 therein, such as that of Figure 1C. The mold 15 comprises upper mold half 17, 18 and lower mold half 16, 19. Each mold half 17, 18 and 16, 19 comprises a central part 16, 17 and at least one or more than one edge part 18, 19. is shown with double arrows that central mold parts 16, 17 and wheel parts 18, 19 can be moved separately.

From the situation with the mold 15 in an open condition, the package 10 is laid or assembled in the mold 15. For the sake of completeness, it is noted here that such a package 10 preferably comprises at least one skin layer 2 or 3 and a reinforcement layer 8, with also foamable material up to the edges of the package 10, as also represented by the reference numbers for the foamed layer or layers 5 in figures 3A and 3B.

Subsequently, heating of the package takes place, in particular to heat the foamable material of the layers 4. This can be done via direct or indirect heating of the mold parts, 16, 17, 18, 19 and in a closed state of the mold 15.

Subsequently, the central parts 16, 17 of the mold 15 are gradually opened to foam the foamable layers 4 and to form the foamed layers 5 in Figure 1C. The edge parts 18, 19 of the mold remain closed or closed, so that the foamable layer in an edge strip 20 of the package 10 and the final product 11 in Figure 1C has no chance of foaming. In such a way, the edge strip 20 (not shown in Figure 1C) acquires a compact and dense shape, which is extremely suitable for inserting holes (not shown), for example by drilling, which holes can serve for mounting and / or assembly of products 11.

In an embodiment of the products 21 in Figure 3A, an edge strip 22 on the underside of the product 21 is flush with more centrally located parts thereof. This can be achieved by making the central mold part 16 a unit with the edge part 19 or the edge parts 19, or by keeping the central mold part 16 still with respect to the edge parts 18, 19, when the opposite central mold part 17 is moved away of the package to give the foamable layer room to foam.

In another embodiment of a product 23, an edge strip 24 is centrally located with respect to the thickness of the product 23. This can be achieved by having the opposing central mold parts 16, 17 move through opposite movements after the mold 15 has been closed and the package 10 is heated so that the foamable layers 4 in Figure 1C can foam in both directions relative to the centrally located reinforcement layer 8. The edge strip 24 is also dense and compact here, because the edge parts 18, 19 of the mold remain closed during the foaming of the foamable layers 4.

It is possible that some skin materials of skins 2, 3 may retract laterally during foaming of the foamable material from a clamping action of the edge parts 18, 19, if these materials do not stretch in a process such as that in conjunction with Figures 2A and 2B described, despite clamping force thereon between clamping edge parts 18, 19. In such cases it may be possible first to form a complete plate element 11, as in figure 1B, and then to compress edges of the formed plate 9, 11 or 14, while being foamed. material between the reinforcement layer 8 and the skin layers 2 is compressed again. For this purpose, the mold of figures 2A and 2B can be used such that the edge parts first move with the central parts 16, 17 during foaming and then are moved back on each other if the central parts remain spaced apart. Another device can also be used for this purpose.

Figures 4A - 4D indicate how a local (in the middle, for example) force passage 31 could be made. For this purpose, first a clamp or press 25 must be used to locally compress plate 11 of a particularly foamed material 5 therein. To this end, a kind of cross 30 may be provided in the clamp or press 25, as shown in Figure 4E on the side of Figure 4A, to make a local weakening in addition to the compression of the foamed material 5, and around the skins 2, 3 to be given (for which heating could be applied). When a hole 28 is formed, a heated mandrel 26 can first be inserted through the layers of the plate 11, with which it is possible to cause the steel wires or other elements or components of the reinforcement layer 8 to deviate slightly from each other. In order to obtain an improved safety against corrosion, in particular in the case of steel wires, if used in the reinforcement layer 8, a layer of PEI 27 - shown schematically in Figure 4C as a drop 27 to be applied - could be arranged around the hole. arranged by means of, for example, injection molding or in any other way, to form an edge 29 around and in hole 28, and thereby also realize the force passage 31 with corrosion protection.

Weft threads of the reinforcement layer 8 can consist of any plastic that can be woven, such as polyester, PA, PP, PEI, Aramid, etc. In contrast to a GMT variant, there is no question here of transverse forces.

An advantage of the application as EMS is the fact that by converting the plate at right angles, a "seamless" shield can be formed.

In an embodiment not shown, a single of the skin layers 2, 3 can be applied, with the reinforcement layer 8 - centrally in the foamed layer 4 as in Figure 1C, and / or - against the single skin layer 2 or 3, as shown in Figure 1B. and / or - in place of at least one of the skin layers 2, 3, wherein the reinforcement layer 8 can simultaneously serve as reinforcement layer 8 and skin layer 2, 3. Also a layer with traditional skin material 2, 3 and a reinforcement layer 8 integrated therein is possible within the scope of the present invention.

Claims (15)

An intermediate, comprising at least one skin layer, and a foamable layer, further comprising a reinforcement layer, which is embedded in the foamable layer or between the foamable layer and the skin layer. A product comprising of at least one skin layer, and a foamed layer, further comprising a reinforcing layer, which is embedded in the foamed layer or between the foamed layer and the skin layer. A product according to claim 2, comprising an edge strip where foamable material is compressed. A method for manufacturing a product according to claim 2 from an intermediate product according to claim 1, comprising foaming the foamable layer in the intermediate product, for example by heating it. The method of claim 4, wherein the intermediate comprises at least one edge, and the method comprises clamping the edge. The method of claim 5, wherein the clamping of the edge comprises: engaging an assembly of at least the foamable or foamed layer, the reinforcement layer and the at least one skin layer. A vehicle, such as a car or an aircraft, comprising at least one product according to claim 2 or 3. An intermediate or a product or a vehicle or a method according to any of the preceding claims, wherein the reinforcement layer comprises metal. The intermediate or product or vehicle or the method of claim 8, wherein the reinforcement layer comprises a set of cords or a fabric / knit of metal threads. The intermediate or product or vehicle or the method according to claim 8 or 9, wherein the fabric / knit comprises a metal from the group, which comprises at least: steel, copper and stainless steel. The intermediate or product or vehicle or the method according to claim 5, 6 or 7, wherein at least one of the at least one skin layer and the foamable or foamed layer is thermoplastic. The intermediate or product or vehicle or the method according to at least one of the preceding claims 8 to 11, wherein an electromagnetic protective layer is applied. The intermediate or product or vehicle or the method of claim 12, wherein the screen layer is formed by the reinforcement layer. The intermediate or product or vehicle or method according to at least one of the preceding claims 8-13, wherein the foamable or foamed material comprises at least: a physical or chemical foaming agent or blowing agent and one or more than one of the materials from the group comprising amorphous and crystalline materials, thermoplastic materials, polyether imide, polyurethane, polypropylene and polyamide, et cetera. The intermediate or product or vehicle or method according to at least one of the preceding claims 8-14, wherein the foamed layer is locally compressed along at least one of: an edge; and includes an angle, and optionally a passage or other force guide.